- Email: [email protected]
The role of antiphase domain boundary density on the surface roughness of GaSb epilayers grown on Si (001) substrates
Superlattices and Microstructures 140 (2020) 106450
Contents lists available at ScienceDirect
Superlattices and Microstructures journal homepage: www.elsevier.com/locate/superlattices
The role of antiphase domain boundary density on the surface roughness of GaSb epilayers grown on Si (001) substrates B. Arpapay *, U. Serincan Eskisehir Technical University, Faculty of Science, Department of Physics, Nanoboyut Research Laboratory, Eskisehir, Turkey
A R T I C L E I N F O
A B S T R A C T
Keywords: MBE GaSb epilayer APB SEM Lattice mismatched growth
GaSb epilayers were grown on nominal Si (001) substrates by molecular beam epitaxy, using AlSb nucleation layer (NL) as an interfacial misfit array. The effects of AlSb NL thickness, growth temperature and post annealing on the GaSb epilayers in terms of formation of antiphase boundaries (APBs) were monitored by scanning electron microscopy (SEM). APBs were identified via SEM following a defect sensitive etch solution treatment. SEM images of etched samples were used to calculate the APB densities and the results were correlated with the surface roughness of the samples. We found that the density of APBs together with the area peak-to-valley height has a role on the surface roughness of the GaSb epilayers grown on nominal Si (001) substrates.
1. Introduction During the last twenty years, GaSb based heterostructures have been very attractive choice for a wide range of applications in especially infrared detection and imaging [1]. Meanwhile, the concept of integration of group III-V compounds on Si substrates be comes an opportunity due to the availability of low cost/high quality Si wafers in large diameters. Hence, a buffer layer having smooth surface with devoid of defects is important for the growth of group III-V heterostructures on nominal Si substrates. To this purpose, achieving high quality GaSb epilayer on Si substrate is of increasing interest as it would allow the integration of photodetectors based on the 6.1 Å family of semiconductor materials [2] with the mature Si technology [3,4]. However, the success of that interest depends on overcoming crucial obstacles including large lattice mismatch between group III-V semiconductors and Si, differences in their thermal expansion coefficients and non-polar surface chemical bonding feature of Si. Thus, the generation of misfit dislocations, threading dislocations (TDs), antiphase boundaries (APBs), micro-twins (MTs) and micro cracks are a direct result of those drawbacks. Especially, the defects such as TDs and APBs acting as nonradiative recombination centers [5–7] are undesirable as leading to poor device performance and reliability [8–11]. The lattice constant difference between most group III-V semiconductors and Si promotes the Volmer-Weber growth mode [12,13]. This is due to the partial wetting condition which is attributed to the fundamental reason of the structural defects. Among those defects, antiphase domains (APDs) are the consequence of the heterophase coalescence of stable islands, following the group III-V nucleation on Si surface. Hence, the density and size of APDs strongly depend on the nature of stable islands on Si surface, which is determined by the growth kinetics such as growth temperature, group V/III ratio, group-III atoms and the vicinality of substrate surface [12]. Until now, APD-free GaAs epilayers grown on nominal Si substrates by using molecular beam epitaxy (MBE) and metalorganic chemical vapor deposition (MOCVD) were achieved [14–16]. On the other hand, considering the lattice mismatch between GaSb and Si as high
* Corresponding author. E-mail addresses: [email protected], [email protected] (B. Arpapay). https://doi.org/10.1016/j.spmi.2020.106450 Received 29 October 2019; Received in revised form 3 February 2020; Accepted 17 February 2020 Available online 20 February 2020 0749-6036/© 2020 Elsevier Ltd. All rights reserved.
Superlattices and Microstructures 140 (2020) 106450
B. Arpapay and U. Serincan
Table 1 Growth parameters of the samples. Sample Code
Sample Set
AlSb NL Thickness (ML)
GaSb Growth Temperature (oC)
Post Annealing Temperature (oC)
S#1 S#2 S#3 S#4 S#5 S#6 S#7 S#8 S#9 S#10
Set Set Set Set Set Set Set Set Set Set
5 10 20 40 80 20 20 20 20 20
530 530 530 530 530 550 570 530 530 530
– – – – – – – 550 570 590
1 1 1, 2 and 3 1 1 2 2 3 3 3
as 12% and the critical thickness of 0.67 monolayer GaSb on Si [17], very large GaSb islands tend to form on Si substrate [18,19] at the early stage of the growth. Consequently, this lessens the quality of GaSb epilayers with rougher surfaces. However, the initial growth of AlSb nucleation layer (NL) on Si has been a prevailing method that suppresses crystal imperfections in GaSb epilayers [20]. The afore-mentioned obstacles about the growth of GaSb on Si could be tailored at some level by using strain relief interfacial misfit array, post annealing treatment, low/high growth temperature combinations, strain-layer superlattices (SLs) and Si substrates with various miscut angles [9,18,21–25]. However, depending on the preferred approach and growth parameters, crystal defects still form in various combinations. Hence, it is crucial to identify and reduce the density of defects that can reach to the surface in order to grow device quality epilayers. So far, the defects that can form during the growth of GaSb on Si have been extensively studied by high-resolution transmission electron microscopy (TEM) [17,19,26–29]. In addition to those reports, Rodriguez et al. [30] observed TDs and MTs at the surface of the GaSb epilayers on highly miscut Si substrate via AlSb NLusing atomic force microscopy (AFM). They reported increasing density of the MTs with increasing AlSb NL thickness. Furthermore, in the same study, it was reported that the surface roughness of the GaSb epilayer was dominated by MTs. In another study, it was shown that two step (low followed by high growth temperature) growth of GaSb on Si by MOCVD results in an APB free surface with very low surface roughness but a TDs density of 109 cm 2 [31]. Madisetti et al. [8] introduced a more complex structure (AlSb QDs þ GaSb/AlSb SL þ InSb QDs) and the density of MTs was determined as ~2 � 104 cm 1 for 800 nm thick GaSb layer. On the other hand, to the best of our knowledge, the role of APB density on the surface morphology of GaSb epilayers grown on nominal Si (001) substrates by using MBE hasn’t been reported in the literature yet. In this study, we performed scanning electron microscopy (SEM) and AFM measurements (published in elsewhere [32]) to monitor the effects of AlSb NL thickness, growth temperature and post annealing on the surface roughness of GaSb epilayers grown on nominal Si (001) substrates by molecular beam epitaxy (MBE). Although AFM images provide 3D information about surface morphology, there are some limitations such as slow scanning speed, limited scanning area and limited surface roughness height. On the contrary, SEM is capable of scanning at relatively fast speeds while monitoring in real time, imaging an area on the order of square millimeters and identifying large features at the scale of millimeters. Hence, in this study we present SEM images collected from the surface of the as-grown and etched GaSb epilayers grown on nominal Si (001) substrates in order to study the correlation between the APB density and the surface roughness of the samples. The samples were grouped into three different sets according to AlSb NL thickness, growth temperature and post annealing treatment condition as Set 1, Set 2 and Set 3, respectively. The results reported here are crucial to improve the knowledge and understanding on the growth of device quality GaSb epilayers on nominal Si (001) substrates for the fabrication of Sb-based devices on Si. 2. Experimental details GaSb epilayers were grown on epi-ready 2-inch intrinsic (001) orientated Si substrates using Veeco GEN20MC solid-source MBE system equipped with valved antimony (Sb) cracker cell, aluminium (Al) and gallium (Ga) dual filament cells. Sb2 were used as groupV fluxes by keeping the cracker temperature at 900 � C. The beam equivalent pressure (BEP) was measured by an ionization gauge at the back of the substrate manipulator, when it was rotated into the direct beam path. The base pressure of the MBE system was 7 � 10 11 Torr at the standby temperature of the effusion cells. Substrate temperature was monitored by using an IRCON pyrometer. Si substrates were degassed at a temperature of 400 � C for 20 min in the buffer chamber before they were transferred to the growth chamber. In the growth chamber, native oxide was desorbed from the Si substrate surface at 850 � C and desorption process was verified by reflection high-energy electron diffraction (not shown here). Following oxide desorption, temperature of the substrate was reduced to 485 � C and exposed to the Sb flux (BEP: 1.6 � 10 7 Torr) for 5 min. At that temperature, AlSb NL was applied to enhance the crystal quality of GaSb epilayer. For the AlSb NL, the ratio of SbBEP/AlBEP and the Al flux BEP were kept at 50 and 6.2 � 10 9 Torr, respectively. To understand the effect of NL thickness on the surface roughness of GaSb epilayer five different thicknesses between 5 and 80 ML were used (Set 1). The thickness of the AlSb NL was determined by the 2D growth rate of AlSb which was 0.1 ML/s. For the GaSb epilayer, substrate temperature was increased to 530 � C under Sb flux and Ga shutter was opened to grow 1 μm thick non-intentionally doped GaSb epilayer. The GaSb epilayer was grown with a SbBEP/GaBEP ratio of 10 where the GaBEP was 7.0 � 10 8 Torr. For the AlSb NL thickness of 20 ML, two additional growth temperatures (at 550 and 570 � C, Set 2) and three different post annealing temperatures (at 550, 570 and 590 � C for 30 min, Set 3) were applied to investigate the influence of the growth temperature and post annealing on the 2
Superlattices and Microstructures 140 (2020) 106450
B. Arpapay and U. Serincan
Fig. 1. SEM images of as-grown GaSb epilayers grown on Si having AlSb NL thickness of (a) 5, (b) 10, (c) 20, (d) 40 and (e) 80 MLs.
formation of APBs in GaSb epilayer. The samples were exposed to Sb flux (BEP: 7.8 � 10 7 Torr) during the post annealing. The growth parameters of the samples are summarized in Table 1. The surface morphologies of the samples were investigated using ZEISS model ULTRAplus field emission scanning electron mi croscope (FE-SEM) operating at 15 kV and equipped with energy dispersive spectroscopy (EDS) (EDAX/AMETEK materials analysis division) tool for elemental analysis. All the SEM images presents the surface along [100] crystallographic direction. In order to identify the APBs, HCl:H2O2:H2O (4:2:1) at 70 � C for 15 s was used as the defect sensitive solution [33]. After etching, SEM images were obtained and the APBs densities were determined by estimating the number of boundaries that cross along APDs. To this purpose, we drew 11 lines along [110] direction at equal intervals on the image and counted the numbers of boundaries crossing the 12 μm in length and divided the number of boundaries by 12 μm [34]. In order to have better statistics, we selected three different regions (~100 μm2) on the etched sample and by taking the average of the determined values, the APB density was computed. The surface morphologies of the samples were investigated by NT-MDT NANOEDUCATOR II model AFM using aluminum coated silicon nitride tip in semi-contact mode. The scanning area was chosen as 100 μm2 and the root-mean-square roughness (RMS) and the area peak-to-valley height (PV) values of the as-grown samples were conducted. The details of the AFM measurements and the results can be found in Ref. [32]. 3. Results and discussions As summarized in Table 1, the growth parameters of all the samples in the Set 1 were kept the same except that AlSb NL thickness. The surface morphologies of the as-grown samples were analyzed by SEM and the obtained images are presented in Fig. 1(a)-(e). The APBs are seen in the SEM images of the as-grown samples as well as either isolated single segments or connected segments in L-like shapes which are attributed to MTs [30]. However, to define those segments without any doubt more powerful methods should be performed such as TEM. As can be seen in Fig. 2(a)-(e), after the etching, the APBs have become more prominent. The APB density for each sample were determined by using Fig. 2(a)–(e) and plotted as a function of AlSb NL thickness in Fig. 3. In order to present the role of the APB density on the surface of the as-grown GaSb epilayers, both RMS and PV values are given in Fig. 3, as well. As it can be perceived from the figure, the APB density changes as a function AlSb NL thickness. Namely, up to 20 ML it decreases and reaches to a minimum value of 0.55 μm 1 where above 20 ML it increases and reaches to a maximum value of 0.66 μm 1. From the AFM 3
Superlattices and Microstructures 140 (2020) 106450
B. Arpapay and U. Serincan
Fig. 2. SEM images of etched GaSb epilayers grown on Si having AlSb NL thickness of (a) 5, (b) 10, (c) 20, (d) 40 and (e) 80 MLs.
Fig. 3. APB density, RMS and PV values of the GaSb epilayers grown on Si as a function of AlSb NL thickness. The dotted lines are guide for the eyes. APB densities are obtained from etched samples where RMS and PV values are obtained from as-grown ones.
measurements, the surface characteristics can be obtained in terms of roughness, describing by RMS and PV [32]. While RMS roughness is the average deviation of mean profile height over the sampling length, PV is a measurement of the maximum height difference on a surface area. As shown in Fig. 3, the RMS and PV follow almost the same trend and the deterioration in the RMS is directly related to the APB density. Those results indicate that in this set the sample S#3 shows the best performance and the optimized AlSb NL thickness should be 20 ML. After the determination of optimized AlSb NL thickness, the effect of growth temperature on the GaSb epitaxial films in terms of APB density and RMS value was investigated. The images obtained from SEM for as-grown and etched films are presented in Fig. 4. It is observed that increasing growth temperature results in a significant improvement on etch pits: Actually, no etch pits are identified for the samples grown at 550 and 570 � C as seen in Fig. 4(e)–(f). Moreover, the sample grown at 550 � C exhibits an APB density of as low as 4
Superlattices and Microstructures 140 (2020) 106450
B. Arpapay and U. Serincan
Fig. 4. SEM images of (a–c) as-grown and (d–f) etched samples grown at different growth temperatures (Tg).
Fig. 5. APB density, RMS and PV values of the GaSb epilayers grown on Si as a function of growth temperature. The dotted lines are guide for the eyes. APB densities are obtained from etched samples where RMS and PV values are obtained from as-grown ones.
0.53 μm 1. Reduction in the APB density is an expected result and it is related to the kinking and self-annihilation of APBs during the growth at higher temperatures [35–37]. On the other hand, for the growth temperature of 570 � C, APB density increases and reaches to 0.63 μm 1 which is even higher than the ones grown at 530 � C (see Fig. 5). Although higher growth temperature leads to the APBs self-annihilation, the increase in the APB density is unclear for the sample grown at 570 � C. At this point, it is worth to note that the decrease in the APB density doesn’t lead to an improvement in the RMS value. It is believed that, this behavior of the sample S#6 can be explained by its PV value which is higher than the sample grown at 530 � C. It seems that the decrease in the APB density cannot compensate the increase in the PV value which results in a higher RMS value compared to the ones grown at 530 � C. It is known that the APDs have a role in the surface morphology depending on the growth temperature such as higher growth temperatures can trigger larger APDs and lead to lower APB density [36,38,39]. Hence, increase in the PV value might be explained by the initiation of 5
Superlattices and Microstructures 140 (2020) 106450
B. Arpapay and U. Serincan
Fig. 6. SEM images of etched GaSb epilayers on Si grown at 530 � C (a) as-grown and post annealed (Ta) at (b) 550, (c) 570 and (d) 590 � C for 30 min including elemental EDS analysis.
Fig. 7. SEM images of etched GaSb epilayers on Si grown at 530 � C (a) as-grown and post annealed (Ta) at (b) 550 and (c) 570 � C for 30 min.
self-annihilation of APBs via kinking to higher index planes and the APDsˈ self-annihilation regions under the surface which induces sharper surface undulation with an increase in the growth temperature. As can be seen from Fig. 5, this fact is supported by the PV and RMS values obtained from S#6. In general, large RMS value introduces large PV value, while the opposite is not always true. In other words, the sharper surface boundaries lead to larger PV value although the RMS roughness does not affected much. Keeping in mind that further investigation is needed to reveal the APB formation mechanism with respect to the growth temperature, the results ob tained from Set 1 demonstrate that using a relatively lower temperature (530 � C) gives rise to a smoother surface and can be accepted as a more suitable temperature to grow GaSb epilayers on nominal Si (001) substrates. It is well known that post annealing in the growth chamber helps to improve the crystal quality of the epilayer. To this purpose, 6
Superlattices and Microstructures 140 (2020) 106450
B. Arpapay and U. Serincan
Fig. 8. APB density, RMS and PV values of the GaSb epilayers grown on Si as a function of post annealing temperature. The dotted lines are guide for the eyes. APB densities are obtained from etched samples where RMS and PV values are obtained from as-grown ones.
following the growth process, three different post annealing temperatures for 30 min were applied to the samples in Set 3. The SEM images obtained from the surface of the as-grown samples in Set 3 are shown in Fig. 6. For the sample post annealed at 590 � C, Ga droplets at the surface was observed due to Sb desorption at elevated temperature. In order to define the Ga droplets, elemental analysis at two different locations on the surface were conducted and the results are presented in Fig. 6. As can be seen, elemental analysis clearly indicates that the regions marked by yellow and blue plus signs refer to Ga and Ga/Sb elements, respectively. Due to the special condition of this sample, it was not subjected to the etch process. Comparing the SEM images of etched surfaces in Fig. 7, it is observed that post annealing has a similar effect as growing GaSb epilayers at relatively higher temperatures. Namely, the post annealed samples do not exhibit etch pits in contrast to the reference sample, S#3. Etch pits are attributed to TDs which are related to the imperfections of the misfit dislocation network [40]. Hence, disappearing of etch pits may be explained by two scenarios: Higher growth temperatures or post annealing enhance the misfit dislocation array perfection at the interface that prevents propagation of defects into the GaSb epilayer [40] or TDs merge into the APBs [41,42]. It is detected that the APB density decreases significantly and reaches to a value of 0.50 μm 1 for a post annealing of 550 � C for 30 min (see Fig. 8). It is worth to note that this value is the lowest value obtained among all the samples. In addition, although the PV value increases, the RMS value improves due to a significant decrease in the APB density and reaches to a value of 0.98 nm which is crucial for the growth of a Sb-based heterostructures on Si substrates [32]. Contrary to the improvement in the sample which was post annealed at 550 � C, Fig. 8 depicts that a further increase in the post annealing temperature causes an increase in both the APB density and PV value. Although the APB density of the sample S#9 is lower than the reference sample, because of the increase in the PV value, the RMS value worsens which is undesired. Guo et al. [43]. reported that an APB-modified thermodynamic equilibrium mechanism can be used to explain the alteration of surface roughness. It was claimed that the post-growth annealing leads an enhanced migration of the surface atoms toward more stable positions, such as free crystalline sites. Thus, antiphase and main phase regions are separated and appear like crystalline mountains, giving rise to an increase in the surface roughness due to the deep trenches in the boundary lines. As can be observed in Fig. 7, the higher post annealing temperature might promote this event further. It is apparent that the post annealing process has an impact on the mobility of atoms involving APBs. Besides, the reduction of the APB density depending on the post annealing temperature can be explained by the atomic motions toward APBs’ centers of curvature, happening near the surface region [44]. Together with the previous results, it seems that the best crystal quality GaSb epilayer was achieved from the sample grown at the growth temperature of 530 � C following the post annealing treatment at 550 � C for 30 min. Although further investigation should be performed for the optimization of the post annealing process, the results are important to demonstrate the role of the APB density on the surface morphology of the GaSb epilayers grown on nominal Si (001) substrates. 4. Conclusion We have shown that APB density together with the PV value has a significant role on the RMS value of the GaSb epilayers grown on nominal Si (001) substrates. By applying a defect sensitive solution, APBs were identified clearly and their densities were determined. Considering 5–80 ML AlSb NL used in this study, it was demonstrated that the 20 ML AlSb NL offered the lowest APB density and RMS value. In addition, it was shown that growth temperature higher than 530 � C yields lower APB density. However, due to the increase in PV value, higher RMS value was found compared to the one grown at 530 � C. The post annealing process revealed that the APB density and RMS value could be significantly improved. As a result, the lowest APB density and RMS value were obtained from the sample grown at 530 � C and post annealed at 550 � C for 30 min as 0.50 μm 1 and 0.98 nm, respectively. Declaration of competing interests The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper. 7
Superlattices and Microstructures 140 (2020) 106450
B. Arpapay and U. Serincan
CRediT authorship contribution statement B. Arpapay: Conceptualization, Methodology, Validation, Investigation, Data curation, Writing - original draft, Visualization. U. Serincan: Resources, Writing - review & editing, Supervision, Project administration, Funding acquisition. Acknowledgements _ This work was supported in part by the Scientific and Technological Research Council of Turkey (TÜBITAK) under the Grant No. 116F199 and by Eskis¸ehir Technical University under the Project No. BAP-1305F092. Appendix A. Supplementary data Supplementary data to this article can be found online at https://doi.org/10.1016/j.spmi.2020.106450.
References [1] M. Razeghi, A. Haddadi, A.M. Hoang, E.K. Huang, G. Chen, S. Bogdanov, S.R. Darvish, F. Callewaert, R. McClintock, Advances in antimonide-based Type-II superlattices for infrared detection and imaging at center for quantum devices, Infrared Phys. Technol. 59 (2013) 41–52, https://doi.org/10.1016/j. infrared.2012.12.008. [2] H. Kroemer, The 6.1 Å family (InAs, GaSb, AlSb) and its heterostructures: a selective review, Physica E 20 (2004) 196–203, https://doi.org/10.1016/j. physe.2003.08.003. [3] Z. Deng, D. Guo, C.G. Burguete, Z. Xie, J. Huang, H. Liu, J. Wu, B. Chen, Demonstration of Si based InAs/GaAsb type-II superlattice p-i-n photodetector, Infrared Phys. Technol. 101 (2019) 133–137, https://doi.org/10.1016/j.infrared.2019.06.011. [4] E. Delli, V. Letka, P.D. Hodgson, E. Repiso, J.P. Hayton, A.P. Craig, Q. Lu, R. Beanland, A. Krier, A.R.J. Marshall, P.J. Carrington, Mid-infrared InAs/InAsSb superlattice nBn photodetector monolithically integrated onto silicon, ACS Photonics 6 (2019) 538–544, https://doi.org/10.1021/acsphotonics.8b01550. [5] S.N.G. Chu, S. Nakahara, S.J. Pearton, T. Boone, S.M. Vernon, Antiphase domains in GaAs grown by metalorganic chemical vapor deposition on silicon-oninsulator, J. Appl. Phys. 64 (1988) 2981–2989, https://doi.org/10.1063/1.341561. [6] S.F. Fang, K. Adomi, S. Iyer, H. Morkoç, H. Zabel, C. Choi, N. Otsuka, Gallium arsenide and other compound semiconductors on silicon, J. Appl. Phys. 68 (1990) R31–R58, https://doi.org/10.1063/1.346284. [7] G. Brammertz, Y. Mols, S. Degroote, V. Motsnyi, M. Leys, G. Borghs, M. Caymax, Low-temperature photoluminescence study of thin epitaxial GaAs films on Ge, J. Appl. Phys. 99 (2006), 093514, https://doi.org/10.1063/1.2194111. [8] S.K. Madisetti, V. Tokranov, A. Greene, S. Novak, M. Yakimov, S. Oktyabrsky, S. Bantley, A.P. Jacob, GaSb on Si: structural defects and their effects on surface morphology and electrical properties, Mater. Res. Soc. Symp. Proc. 1635 (2014) 115–120, https://doi.org/10.1557/opl.2014.219. [9] A.P. Craig, P.J. Carrington, H. Liu, A.R.J. Marshall, Characterization of 6.1 Å III-V materials grown on GaAs and Si: a comparison of GaSb/GaAs epitaxy and GaSb/AlSb/Si epitaxy, J. Cryst. Growth 435 (2016) 56–61, https://doi.org/10.1016/j.jcrysgro.2015.11.025. [10] S. Sasaki, K. Dropiewski, S. Madisetti, V. Tokranov, M. Yakimov, S. Oktyabrsky, S. Bentley, R. Galatage, A.P. Jacob, Electrical properties related to growth defects in metamorphic GaSb films on Si, J. Vacum Sci. Tech. B 35 (2017), 011203, https://doi.org/10.1116/1.4973215. [11] J. Tournet, S. Parola, A. Vauthelin, D. Montesdeoca Cardenes, S. Soresi, F. Martinez, Q. Lu, Y. Cuminal, P.J. Carrington, J. D�ecobert, A. Krier, Y. Rouillard, E. Tourni� e, GaSb-based solar cells for multi-junction integration on Si substrates, Sol. Energy Mater. Sol. Cell. 191 (2019) 444–450, https://doi.org/10.1016/j. solmat.2018.11.035. [12] I. Lucci, S. Charbonnier, L. Pedesseau, M. Vallet, L. Cerutti, J.-B. Rodriguez, E. Tourni�e, R. Bernard, A. L�etoublon, N. Bertru, A. Le Corre, S. Rennesson, F. Semond, G. Patriarche, L. Largeau, P. Turban, A. Ponchet, C. Cornet, Universal description of III-V/Si epitaxial growth processes, Phys. Rev. Mater. 2 (2018), https://doi.org/10.1103/PhysRevMaterials.2.060401, 060401(R). [13] A. Ponchet, G. Patriarche, J.-B. Rodriquez, L. Cerutti, E. Tourni�e, Interface energy analysis of III-V islands on Si (001) in the Volmer-Weber growth mode, Appl. Phys. Lett. 113 (2018), 191601, https://doi.org/10.1063/1.5055056. [14] R. Alcotte, M. Martin, J. Moeyaert, R. Cipro, S. David, F. Bassani, F. Ducroquet, Y. Bogumilowicz, E. Sanchez, Z. Ye, X.Y. Bao, J.B. Pin, T. Baron, Epitaxial growth of antiphase boundary free GaAs layer on 300 mm Si(001) substrate by metalorganic chemical vapour deposition with high mobility, APL. Mater. 4 (2016), 046101, https://doi.org/10.1063/1.4945586. [15] M.T. Huu Ha, S.H. Huynh, H.B. Do, T.A. Nguyen, Q.H. Luc, E.Y. Chang, Demonstrating antiphase domain boundary-free GaAs buffer layer on zero off-cut Si (001) substrate for interfacial misfit dislocation GaSb film by metalorganic chemical vapor deposition, Mater. Res. Express 4 (2017), 085901, https://doi.org/ 10.1088/2053-1591/aa8043. [16] J. Kwoen, J. Lee, K. Watanabe, Y. Arakawa, Elimination of anti-phase boundaries in a GaAs layer directly-grown on an on-axis Si(001) substrate by optimizing an AlGaAs nucleation layer, Jpn. J. Appl. Phys. 58 (2019), https://doi.org/10.7567/1347-4065/aaffc2. SBBE07. [17] S. Hosseini Vajargah, S. Ghanad-Tavakoli, J.S. Preston, R.N. Kleiman, G.A. Botton, Growth mechanisms of GaSb heteroepitaxial films on Si with an AlSb buffer layer, J. Appl. Phys. 114 (2013), 113101, https://doi.org/10.1063/1.4820255. [18] K. Akahane, N. Yamamoto, S. Gozu, A. Ueta, N. Ohtani, Initial growth stage of GaSb on Si (001) substrates with AlSb initiation layers, J. Cryst. Growth 283 (2005) 297–302, https://doi.org/10.1016/j.jcrysgro.2005.06.001. [19] Y.H. Kim, Y.K. Noh, M.D. Kim, J.E. Oh, K.S. Chung, Transmission electron microscopy study of the initial growth stage of GaSb grown on Si (100) substrate by molecular beam epitaxy method, Thin Solid Films 518 (2010) 2280–2284, https://doi.org/10.1016/j.tsf.2009.09.120. [20] K. Akahane, N. Yamamoto, S. Gozu, N. Ohtani, Heteroepitaxial growth of GaSb on Si(001) substrates, J. Cryst. Growth 264 (2004) 21–25, https://doi.org/ 10.1016/j.jcrysgro.2003.12.041. [21] S.H. Huang, G. Balakrishnan, A. Khoshakhlagh, L.R. Dawson, D.L. Huffaker, Simultaneous interfacial misfit array formation and antiphase domain suppression on miscut silicon substrate, Appl. Phys. Lett. 93 (2008), 071102, https://doi.org/10.1063/1.2970997. [22] Y.K. Noh, M.D. Kim, J.E. Oh, W.C. Yang, Structural and optical properties of GaSb films grown on AlSb/Si (100) by insertion of a thin GaSb interlayer grown at a low temperature, J. Kor. Phys. Soc. 57 (2010) 173–177, https://doi.org/10.3938/jkps.57.173. [23] Y.K. Noh, M.D. Kim, J.E. Oh, W.C. Yang, Y.H. Kim, Growth of low defect AlGaSb films on Si (100) using AlSb and InSb quantum dots intermediate layers, J. Cryst. Growth 323 (2011) 405–408, https://doi.org/10.1016/j.jcrysgro.2011.01.027. [24] J.B. Rodriquez, K. Madiomanana, L. Cerutti, A. Castellano, E. Tourni�e, X-ray diffraction study of GaSb grown by molecular beam epitaxy on silicon substrates, J. Cryst. Growth 439 (2016) 33–39, https://doi.org/10.1016/j.jcrysgro.2016.01.005. [25] B.W. Jia, K.H. Tan, W.K. Loke, S. Wicaksono, S.F. Yoon, Growth and characterization of InSb on (100) Si for mid-infrared application, Appl. Surf. Sci. 440 (2018) 939–945, https://doi.org/10.1016/j.apsusc.2018.01.219.
8
Superlattices and Microstructures 140 (2020) 106450
B. Arpapay and U. Serincan
[26] Y.K. Kim, J.Y. Lee, Y.G. Noh, M.D. Kim, S.M. Cho, Y.J. Kwon, J.E. Oh, Growth mode and structural characterization of GaSb on Si (001) substrate: A transmission electron microscopy study, Appl. Phys. Lett. 88 (2006), 241907, https://doi.org/10.1063/1.2209714. [27] S. Hosseini Vajargah, M. Couillard, K. Cui, S. Ghanad Tavakoli, B. Robinson, R.N. Kleiman, J.S. Preston, G.A. Botton, Strain relief and AlSb buffer layer morphology in GaSb heteroepitaxial films grown on Si as revealed by high-angle annular dark-field scanning transmission electron microscopy, Appl. Phys. Lett. 98 (2011), 082113, https://doi.org/10.1063/1.3551626. [28] S. Hosseini Vajargah, S.Y. Woo, S. Ghanad-Tavakoli, R.N. Kleiman, J.S. Preston, G.A. Botton, Atomic-resolution study of polarity reversal in GaSb grown on Si by scanning transmission electron microscopy, J. Appl. Phys. 112 (2012), 093101, https://doi.org/10.1063/1.4759160. [29] S.Y. Woo, S. Hosseini Vajargah, S. Ghanad-Tavakoli, R.N. Kleiman, G.A. Botton, Direct observation of anti-phase boundaries in heteroepitaxy of GaSb thin films grown on Si (001) by transmission electron microscopy, J. Appl. Phys. 112 (2012), 074306, https://doi.org/10.1063/1.4756957. [30] J.B. Rodriguez, L. Cerutti, G. Patriarche, L. Largeau, K. Madiomanana, E. Tourni� e, Characterization of antimonide based material grown by molecular epitaxy on vicinal silicon substrates via a low temperature AlSb nucleation layer, J. Cryst. Growth 477 (2017) 65–71, https://doi.org/10.1016/j.jcrysgro.2017.04.003. [31] T. Cerba, M. Martin, J. Moeyaert, S. David, J.L. Rouviere, L. Cerutti, R. Alcotte, J.B. Rodriquez, M. Bawedin, H. Boutry, F. Bassani, Y. Bogumilowicz, P. Gergaud, E. Tourni� e, T. Baron, Anti phase boundary free GaSb layer grown on 300 mm (001)-Si substrate by metal organic chemical vapor deposition, Thin Solid Films 645 (2018) 5–9, https://doi.org/10.1016/j.tsf.2017.10.024. [32] U. Serincan, B. Arpapay, Structural and optical characterization of GaSb on Si (001) grown by molecular beam epitaxy, Semicond. Sci. Technol. 34 (2019), 035013, https://doi.org/10.1088/1361-6641/aafcbe. [33] L. Reijnen, R. Brunton, I.R. Grant, GaSb single-crystal growth by vertical gradient freeze, J. Cryst. Growth 275 (2005) e595–e600, https://doi.org/10.1016/j. jcrysgro.2004.11.003. [34] G. Naresh-Kumar, A. Vilalta-Clemente, H. Jussila, A. Winkelmann, G. Nolze, S. Vespucci, S. Nagarajan, A.J. Wilkinson, C. Trager-Cowan, Quantitative imaging of anti-phase domains by polarity sensitive orientation mapping using electron backscatter diffraction, Sci. Rep. 7 (2017) 10916, https://doi.org/10.1038/ s41598-017-11187-z. [35] I. N� emeth, B. Kunert, W. Stolz, K. Volz, Ways to quantitatively defect antiphase disorder in GaP films grown on Si(001) by transmission electron microscopy, J. Cryst. Growth 310 (2008) 4763–4767, https://doi.org/10.1016/j.jcrysgro.2008.07.105. [36] K. Volz, A. Beyer, W. Witte, J. Ohlmann, I. N� emeth, B. Kunert, W. Stolz, GaP-nucleation on exact Si (001) substrates for III/V device integration, J. Cryst. Growth 315 (2011) 37–47, https://doi.org/10.1016/j.jcrysgro.2010.10.036. [37] C.S.C. Barrett, T.P. Martin, X.-Y. Bao, E.L. Kennon, L. Gutierrez, P. Martin, E. Sanchez, K.S. Jones, Effect of bulk growth temperature on antiphase domain boundary annihilation rate in MOCVD-grown GaAs on Si, J. Cryst. Growth 450 (2016) 39–44, https://doi.org/10.1016/j.jcrysgro.2016.06.021. [38] M.K. Hudait, S.B. Krupanidhi, Self-annihilation of antiphase boundaries in GaAs epilayers on Ge substrates grown by metal-organic vapor-phase epitaxy, J. Appl. Phys. 89 (2001) 5972, https://doi.org/10.1063/1.1368870. [39] Y. Li, G. Salviati, M.M.G. Bongers, L. Lazzarini, L. Nasi, L.J. Giling, On the formation of antiphase domains in the system of GaAs on Ge, J. Cryst. Growth 163 (1996) 195–202, https://doi.org/10.1016/0022-0248(95)00958-2. [40] A. Rocher, E. Snoeck, Misfit dislocations in (001) semiconductor heterostructures grown by epitaxy, Mater. Sci. Eng. B67 (1999) 62–69, https://doi.org/ 10.1016/S0921-5107(99)00210-X. [41] M. Niehle, A. Trampet, J.B. Rodriguez, L. Cerutti, E. Tourni� e, Electron tomography on III-Sb heterostructures on vicinal Si(001) substrates: anti-phase boundaries as a sink for threading dislocations, Scripta Mater. 132 (2017) 5–8, https://doi.org/10.1016/j.scriptamat.2017.01.018. [42] M. Niehle, J.B. Rodriguez, L. Cerutti, E. Tourni�e, A. Trampet, The interaction of extended defects as the origin of step bunching in epitaxial III-V layers on vicinal Si(001) substrates, Phys. Status Solidi Rapid Res. Lett. (2019), 1900290, https://doi.org/10.1002/pssr.201900290. [43] W. Guo, A. Bondi, C. Cornet, A. L� etoublon, O. Durand, T. Rohel, S. Boyer-Richard, N. Bertru, S. Loualiche, J. Even, A. Le Corre, Thermodynamic evolution of antiphase boundaries in GaP/Si epilayers evidenced by advanced X-ray scattering, Appl. Surf. Sci. 258 (2012) 2808–2815, https://doi.org/10.1016/j. apsusc.2011.10.139. [44] C.S.C. Barrett, A. Atassi, E.L. Kennon, Z. Weinrich, K. Haynes, X.-Y. Bao, P. Martin, K.S. Jones, Dissolution of antiphase domain boundaries in GaAs on Si(001) via post-growth annealing, J. Mater. Sci. 54 (2019) 7028–7034, https://doi.org/10.1007/s10853-019-03353-7.
9
Contents lists available at ScienceDirect
Superlattices and Microstructures journal homepage: www.elsevier.com/locate/superlattices
The role of antiphase domain boundary density on the surface roughness of GaSb epilayers grown on Si (001) substrates B. Arpapay *, U. Serincan Eskisehir Technical University, Faculty of Science, Department of Physics, Nanoboyut Research Laboratory, Eskisehir, Turkey
A R T I C L E I N F O
A B S T R A C T
Keywords: MBE GaSb epilayer APB SEM Lattice mismatched growth
GaSb epilayers were grown on nominal Si (001) substrates by molecular beam epitaxy, using AlSb nucleation layer (NL) as an interfacial misfit array. The effects of AlSb NL thickness, growth temperature and post annealing on the GaSb epilayers in terms of formation of antiphase boundaries (APBs) were monitored by scanning electron microscopy (SEM). APBs were identified via SEM following a defect sensitive etch solution treatment. SEM images of etched samples were used to calculate the APB densities and the results were correlated with the surface roughness of the samples. We found that the density of APBs together with the area peak-to-valley height has a role on the surface roughness of the GaSb epilayers grown on nominal Si (001) substrates.
1. Introduction During the last twenty years, GaSb based heterostructures have been very attractive choice for a wide range of applications in especially infrared detection and imaging [1]. Meanwhile, the concept of integration of group III-V compounds on Si substrates be comes an opportunity due to the availability of low cost/high quality Si wafers in large diameters. Hence, a buffer layer having smooth surface with devoid of defects is important for the growth of group III-V heterostructures on nominal Si substrates. To this purpose, achieving high quality GaSb epilayer on Si substrate is of increasing interest as it would allow the integration of photodetectors based on the 6.1 Å family of semiconductor materials [2] with the mature Si technology [3,4]. However, the success of that interest depends on overcoming crucial obstacles including large lattice mismatch between group III-V semiconductors and Si, differences in their thermal expansion coefficients and non-polar surface chemical bonding feature of Si. Thus, the generation of misfit dislocations, threading dislocations (TDs), antiphase boundaries (APBs), micro-twins (MTs) and micro cracks are a direct result of those drawbacks. Especially, the defects such as TDs and APBs acting as nonradiative recombination centers [5–7] are undesirable as leading to poor device performance and reliability [8–11]. The lattice constant difference between most group III-V semiconductors and Si promotes the Volmer-Weber growth mode [12,13]. This is due to the partial wetting condition which is attributed to the fundamental reason of the structural defects. Among those defects, antiphase domains (APDs) are the consequence of the heterophase coalescence of stable islands, following the group III-V nucleation on Si surface. Hence, the density and size of APDs strongly depend on the nature of stable islands on Si surface, which is determined by the growth kinetics such as growth temperature, group V/III ratio, group-III atoms and the vicinality of substrate surface [12]. Until now, APD-free GaAs epilayers grown on nominal Si substrates by using molecular beam epitaxy (MBE) and metalorganic chemical vapor deposition (MOCVD) were achieved [14–16]. On the other hand, considering the lattice mismatch between GaSb and Si as high
* Corresponding author. E-mail addresses: [email protected], [email protected] (B. Arpapay). https://doi.org/10.1016/j.spmi.2020.106450 Received 29 October 2019; Received in revised form 3 February 2020; Accepted 17 February 2020 Available online 20 February 2020 0749-6036/© 2020 Elsevier Ltd. All rights reserved.
Superlattices and Microstructures 140 (2020) 106450
B. Arpapay and U. Serincan
Table 1 Growth parameters of the samples. Sample Code
Sample Set
AlSb NL Thickness (ML)
GaSb Growth Temperature (oC)
Post Annealing Temperature (oC)
S#1 S#2 S#3 S#4 S#5 S#6 S#7 S#8 S#9 S#10
Set Set Set Set Set Set Set Set Set Set
5 10 20 40 80 20 20 20 20 20
530 530 530 530 530 550 570 530 530 530
– – – – – – – 550 570 590
1 1 1, 2 and 3 1 1 2 2 3 3 3
as 12% and the critical thickness of 0.67 monolayer GaSb on Si [17], very large GaSb islands tend to form on Si substrate [18,19] at the early stage of the growth. Consequently, this lessens the quality of GaSb epilayers with rougher surfaces. However, the initial growth of AlSb nucleation layer (NL) on Si has been a prevailing method that suppresses crystal imperfections in GaSb epilayers [20]. The afore-mentioned obstacles about the growth of GaSb on Si could be tailored at some level by using strain relief interfacial misfit array, post annealing treatment, low/high growth temperature combinations, strain-layer superlattices (SLs) and Si substrates with various miscut angles [9,18,21–25]. However, depending on the preferred approach and growth parameters, crystal defects still form in various combinations. Hence, it is crucial to identify and reduce the density of defects that can reach to the surface in order to grow device quality epilayers. So far, the defects that can form during the growth of GaSb on Si have been extensively studied by high-resolution transmission electron microscopy (TEM) [17,19,26–29]. In addition to those reports, Rodriguez et al. [30] observed TDs and MTs at the surface of the GaSb epilayers on highly miscut Si substrate via AlSb NLusing atomic force microscopy (AFM). They reported increasing density of the MTs with increasing AlSb NL thickness. Furthermore, in the same study, it was reported that the surface roughness of the GaSb epilayer was dominated by MTs. In another study, it was shown that two step (low followed by high growth temperature) growth of GaSb on Si by MOCVD results in an APB free surface with very low surface roughness but a TDs density of 109 cm 2 [31]. Madisetti et al. [8] introduced a more complex structure (AlSb QDs þ GaSb/AlSb SL þ InSb QDs) and the density of MTs was determined as ~2 � 104 cm 1 for 800 nm thick GaSb layer. On the other hand, to the best of our knowledge, the role of APB density on the surface morphology of GaSb epilayers grown on nominal Si (001) substrates by using MBE hasn’t been reported in the literature yet. In this study, we performed scanning electron microscopy (SEM) and AFM measurements (published in elsewhere [32]) to monitor the effects of AlSb NL thickness, growth temperature and post annealing on the surface roughness of GaSb epilayers grown on nominal Si (001) substrates by molecular beam epitaxy (MBE). Although AFM images provide 3D information about surface morphology, there are some limitations such as slow scanning speed, limited scanning area and limited surface roughness height. On the contrary, SEM is capable of scanning at relatively fast speeds while monitoring in real time, imaging an area on the order of square millimeters and identifying large features at the scale of millimeters. Hence, in this study we present SEM images collected from the surface of the as-grown and etched GaSb epilayers grown on nominal Si (001) substrates in order to study the correlation between the APB density and the surface roughness of the samples. The samples were grouped into three different sets according to AlSb NL thickness, growth temperature and post annealing treatment condition as Set 1, Set 2 and Set 3, respectively. The results reported here are crucial to improve the knowledge and understanding on the growth of device quality GaSb epilayers on nominal Si (001) substrates for the fabrication of Sb-based devices on Si. 2. Experimental details GaSb epilayers were grown on epi-ready 2-inch intrinsic (001) orientated Si substrates using Veeco GEN20MC solid-source MBE system equipped with valved antimony (Sb) cracker cell, aluminium (Al) and gallium (Ga) dual filament cells. Sb2 were used as groupV fluxes by keeping the cracker temperature at 900 � C. The beam equivalent pressure (BEP) was measured by an ionization gauge at the back of the substrate manipulator, when it was rotated into the direct beam path. The base pressure of the MBE system was 7 � 10 11 Torr at the standby temperature of the effusion cells. Substrate temperature was monitored by using an IRCON pyrometer. Si substrates were degassed at a temperature of 400 � C for 20 min in the buffer chamber before they were transferred to the growth chamber. In the growth chamber, native oxide was desorbed from the Si substrate surface at 850 � C and desorption process was verified by reflection high-energy electron diffraction (not shown here). Following oxide desorption, temperature of the substrate was reduced to 485 � C and exposed to the Sb flux (BEP: 1.6 � 10 7 Torr) for 5 min. At that temperature, AlSb NL was applied to enhance the crystal quality of GaSb epilayer. For the AlSb NL, the ratio of SbBEP/AlBEP and the Al flux BEP were kept at 50 and 6.2 � 10 9 Torr, respectively. To understand the effect of NL thickness on the surface roughness of GaSb epilayer five different thicknesses between 5 and 80 ML were used (Set 1). The thickness of the AlSb NL was determined by the 2D growth rate of AlSb which was 0.1 ML/s. For the GaSb epilayer, substrate temperature was increased to 530 � C under Sb flux and Ga shutter was opened to grow 1 μm thick non-intentionally doped GaSb epilayer. The GaSb epilayer was grown with a SbBEP/GaBEP ratio of 10 where the GaBEP was 7.0 � 10 8 Torr. For the AlSb NL thickness of 20 ML, two additional growth temperatures (at 550 and 570 � C, Set 2) and three different post annealing temperatures (at 550, 570 and 590 � C for 30 min, Set 3) were applied to investigate the influence of the growth temperature and post annealing on the 2
Superlattices and Microstructures 140 (2020) 106450
B. Arpapay and U. Serincan
Fig. 1. SEM images of as-grown GaSb epilayers grown on Si having AlSb NL thickness of (a) 5, (b) 10, (c) 20, (d) 40 and (e) 80 MLs.
formation of APBs in GaSb epilayer. The samples were exposed to Sb flux (BEP: 7.8 � 10 7 Torr) during the post annealing. The growth parameters of the samples are summarized in Table 1. The surface morphologies of the samples were investigated using ZEISS model ULTRAplus field emission scanning electron mi croscope (FE-SEM) operating at 15 kV and equipped with energy dispersive spectroscopy (EDS) (EDAX/AMETEK materials analysis division) tool for elemental analysis. All the SEM images presents the surface along [100] crystallographic direction. In order to identify the APBs, HCl:H2O2:H2O (4:2:1) at 70 � C for 15 s was used as the defect sensitive solution [33]. After etching, SEM images were obtained and the APBs densities were determined by estimating the number of boundaries that cross along APDs. To this purpose, we drew 11 lines along [110] direction at equal intervals on the image and counted the numbers of boundaries crossing the 12 μm in length and divided the number of boundaries by 12 μm [34]. In order to have better statistics, we selected three different regions (~100 μm2) on the etched sample and by taking the average of the determined values, the APB density was computed. The surface morphologies of the samples were investigated by NT-MDT NANOEDUCATOR II model AFM using aluminum coated silicon nitride tip in semi-contact mode. The scanning area was chosen as 100 μm2 and the root-mean-square roughness (RMS) and the area peak-to-valley height (PV) values of the as-grown samples were conducted. The details of the AFM measurements and the results can be found in Ref. [32]. 3. Results and discussions As summarized in Table 1, the growth parameters of all the samples in the Set 1 were kept the same except that AlSb NL thickness. The surface morphologies of the as-grown samples were analyzed by SEM and the obtained images are presented in Fig. 1(a)-(e). The APBs are seen in the SEM images of the as-grown samples as well as either isolated single segments or connected segments in L-like shapes which are attributed to MTs [30]. However, to define those segments without any doubt more powerful methods should be performed such as TEM. As can be seen in Fig. 2(a)-(e), after the etching, the APBs have become more prominent. The APB density for each sample were determined by using Fig. 2(a)–(e) and plotted as a function of AlSb NL thickness in Fig. 3. In order to present the role of the APB density on the surface of the as-grown GaSb epilayers, both RMS and PV values are given in Fig. 3, as well. As it can be perceived from the figure, the APB density changes as a function AlSb NL thickness. Namely, up to 20 ML it decreases and reaches to a minimum value of 0.55 μm 1 where above 20 ML it increases and reaches to a maximum value of 0.66 μm 1. From the AFM 3
Superlattices and Microstructures 140 (2020) 106450
B. Arpapay and U. Serincan
Fig. 2. SEM images of etched GaSb epilayers grown on Si having AlSb NL thickness of (a) 5, (b) 10, (c) 20, (d) 40 and (e) 80 MLs.
Fig. 3. APB density, RMS and PV values of the GaSb epilayers grown on Si as a function of AlSb NL thickness. The dotted lines are guide for the eyes. APB densities are obtained from etched samples where RMS and PV values are obtained from as-grown ones.
measurements, the surface characteristics can be obtained in terms of roughness, describing by RMS and PV [32]. While RMS roughness is the average deviation of mean profile height over the sampling length, PV is a measurement of the maximum height difference on a surface area. As shown in Fig. 3, the RMS and PV follow almost the same trend and the deterioration in the RMS is directly related to the APB density. Those results indicate that in this set the sample S#3 shows the best performance and the optimized AlSb NL thickness should be 20 ML. After the determination of optimized AlSb NL thickness, the effect of growth temperature on the GaSb epitaxial films in terms of APB density and RMS value was investigated. The images obtained from SEM for as-grown and etched films are presented in Fig. 4. It is observed that increasing growth temperature results in a significant improvement on etch pits: Actually, no etch pits are identified for the samples grown at 550 and 570 � C as seen in Fig. 4(e)–(f). Moreover, the sample grown at 550 � C exhibits an APB density of as low as 4
Superlattices and Microstructures 140 (2020) 106450
B. Arpapay and U. Serincan
Fig. 4. SEM images of (a–c) as-grown and (d–f) etched samples grown at different growth temperatures (Tg).
Fig. 5. APB density, RMS and PV values of the GaSb epilayers grown on Si as a function of growth temperature. The dotted lines are guide for the eyes. APB densities are obtained from etched samples where RMS and PV values are obtained from as-grown ones.
0.53 μm 1. Reduction in the APB density is an expected result and it is related to the kinking and self-annihilation of APBs during the growth at higher temperatures [35–37]. On the other hand, for the growth temperature of 570 � C, APB density increases and reaches to 0.63 μm 1 which is even higher than the ones grown at 530 � C (see Fig. 5). Although higher growth temperature leads to the APBs self-annihilation, the increase in the APB density is unclear for the sample grown at 570 � C. At this point, it is worth to note that the decrease in the APB density doesn’t lead to an improvement in the RMS value. It is believed that, this behavior of the sample S#6 can be explained by its PV value which is higher than the sample grown at 530 � C. It seems that the decrease in the APB density cannot compensate the increase in the PV value which results in a higher RMS value compared to the ones grown at 530 � C. It is known that the APDs have a role in the surface morphology depending on the growth temperature such as higher growth temperatures can trigger larger APDs and lead to lower APB density [36,38,39]. Hence, increase in the PV value might be explained by the initiation of 5
Superlattices and Microstructures 140 (2020) 106450
B. Arpapay and U. Serincan
Fig. 6. SEM images of etched GaSb epilayers on Si grown at 530 � C (a) as-grown and post annealed (Ta) at (b) 550, (c) 570 and (d) 590 � C for 30 min including elemental EDS analysis.
Fig. 7. SEM images of etched GaSb epilayers on Si grown at 530 � C (a) as-grown and post annealed (Ta) at (b) 550 and (c) 570 � C for 30 min.
self-annihilation of APBs via kinking to higher index planes and the APDsˈ self-annihilation regions under the surface which induces sharper surface undulation with an increase in the growth temperature. As can be seen from Fig. 5, this fact is supported by the PV and RMS values obtained from S#6. In general, large RMS value introduces large PV value, while the opposite is not always true. In other words, the sharper surface boundaries lead to larger PV value although the RMS roughness does not affected much. Keeping in mind that further investigation is needed to reveal the APB formation mechanism with respect to the growth temperature, the results ob tained from Set 1 demonstrate that using a relatively lower temperature (530 � C) gives rise to a smoother surface and can be accepted as a more suitable temperature to grow GaSb epilayers on nominal Si (001) substrates. It is well known that post annealing in the growth chamber helps to improve the crystal quality of the epilayer. To this purpose, 6
Superlattices and Microstructures 140 (2020) 106450
B. Arpapay and U. Serincan
Fig. 8. APB density, RMS and PV values of the GaSb epilayers grown on Si as a function of post annealing temperature. The dotted lines are guide for the eyes. APB densities are obtained from etched samples where RMS and PV values are obtained from as-grown ones.
following the growth process, three different post annealing temperatures for 30 min were applied to the samples in Set 3. The SEM images obtained from the surface of the as-grown samples in Set 3 are shown in Fig. 6. For the sample post annealed at 590 � C, Ga droplets at the surface was observed due to Sb desorption at elevated temperature. In order to define the Ga droplets, elemental analysis at two different locations on the surface were conducted and the results are presented in Fig. 6. As can be seen, elemental analysis clearly indicates that the regions marked by yellow and blue plus signs refer to Ga and Ga/Sb elements, respectively. Due to the special condition of this sample, it was not subjected to the etch process. Comparing the SEM images of etched surfaces in Fig. 7, it is observed that post annealing has a similar effect as growing GaSb epilayers at relatively higher temperatures. Namely, the post annealed samples do not exhibit etch pits in contrast to the reference sample, S#3. Etch pits are attributed to TDs which are related to the imperfections of the misfit dislocation network [40]. Hence, disappearing of etch pits may be explained by two scenarios: Higher growth temperatures or post annealing enhance the misfit dislocation array perfection at the interface that prevents propagation of defects into the GaSb epilayer [40] or TDs merge into the APBs [41,42]. It is detected that the APB density decreases significantly and reaches to a value of 0.50 μm 1 for a post annealing of 550 � C for 30 min (see Fig. 8). It is worth to note that this value is the lowest value obtained among all the samples. In addition, although the PV value increases, the RMS value improves due to a significant decrease in the APB density and reaches to a value of 0.98 nm which is crucial for the growth of a Sb-based heterostructures on Si substrates [32]. Contrary to the improvement in the sample which was post annealed at 550 � C, Fig. 8 depicts that a further increase in the post annealing temperature causes an increase in both the APB density and PV value. Although the APB density of the sample S#9 is lower than the reference sample, because of the increase in the PV value, the RMS value worsens which is undesired. Guo et al. [43]. reported that an APB-modified thermodynamic equilibrium mechanism can be used to explain the alteration of surface roughness. It was claimed that the post-growth annealing leads an enhanced migration of the surface atoms toward more stable positions, such as free crystalline sites. Thus, antiphase and main phase regions are separated and appear like crystalline mountains, giving rise to an increase in the surface roughness due to the deep trenches in the boundary lines. As can be observed in Fig. 7, the higher post annealing temperature might promote this event further. It is apparent that the post annealing process has an impact on the mobility of atoms involving APBs. Besides, the reduction of the APB density depending on the post annealing temperature can be explained by the atomic motions toward APBs’ centers of curvature, happening near the surface region [44]. Together with the previous results, it seems that the best crystal quality GaSb epilayer was achieved from the sample grown at the growth temperature of 530 � C following the post annealing treatment at 550 � C for 30 min. Although further investigation should be performed for the optimization of the post annealing process, the results are important to demonstrate the role of the APB density on the surface morphology of the GaSb epilayers grown on nominal Si (001) substrates. 4. Conclusion We have shown that APB density together with the PV value has a significant role on the RMS value of the GaSb epilayers grown on nominal Si (001) substrates. By applying a defect sensitive solution, APBs were identified clearly and their densities were determined. Considering 5–80 ML AlSb NL used in this study, it was demonstrated that the 20 ML AlSb NL offered the lowest APB density and RMS value. In addition, it was shown that growth temperature higher than 530 � C yields lower APB density. However, due to the increase in PV value, higher RMS value was found compared to the one grown at 530 � C. The post annealing process revealed that the APB density and RMS value could be significantly improved. As a result, the lowest APB density and RMS value were obtained from the sample grown at 530 � C and post annealed at 550 � C for 30 min as 0.50 μm 1 and 0.98 nm, respectively. Declaration of competing interests The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper. 7
Superlattices and Microstructures 140 (2020) 106450
B. Arpapay and U. Serincan
CRediT authorship contribution statement B. Arpapay: Conceptualization, Methodology, Validation, Investigation, Data curation, Writing - original draft, Visualization. U. Serincan: Resources, Writing - review & editing, Supervision, Project administration, Funding acquisition. Acknowledgements _ This work was supported in part by the Scientific and Technological Research Council of Turkey (TÜBITAK) under the Grant No. 116F199 and by Eskis¸ehir Technical University under the Project No. BAP-1305F092. Appendix A. Supplementary data Supplementary data to this article can be found online at https://doi.org/10.1016/j.spmi.2020.106450.
References [1] M. Razeghi, A. Haddadi, A.M. Hoang, E.K. Huang, G. Chen, S. Bogdanov, S.R. Darvish, F. Callewaert, R. McClintock, Advances in antimonide-based Type-II superlattices for infrared detection and imaging at center for quantum devices, Infrared Phys. Technol. 59 (2013) 41–52, https://doi.org/10.1016/j. infrared.2012.12.008. [2] H. Kroemer, The 6.1 Å family (InAs, GaSb, AlSb) and its heterostructures: a selective review, Physica E 20 (2004) 196–203, https://doi.org/10.1016/j. physe.2003.08.003. [3] Z. Deng, D. Guo, C.G. Burguete, Z. Xie, J. Huang, H. Liu, J. Wu, B. Chen, Demonstration of Si based InAs/GaAsb type-II superlattice p-i-n photodetector, Infrared Phys. Technol. 101 (2019) 133–137, https://doi.org/10.1016/j.infrared.2019.06.011. [4] E. Delli, V. Letka, P.D. Hodgson, E. Repiso, J.P. Hayton, A.P. Craig, Q. Lu, R. Beanland, A. Krier, A.R.J. Marshall, P.J. Carrington, Mid-infrared InAs/InAsSb superlattice nBn photodetector monolithically integrated onto silicon, ACS Photonics 6 (2019) 538–544, https://doi.org/10.1021/acsphotonics.8b01550. [5] S.N.G. Chu, S. Nakahara, S.J. Pearton, T. Boone, S.M. Vernon, Antiphase domains in GaAs grown by metalorganic chemical vapor deposition on silicon-oninsulator, J. Appl. Phys. 64 (1988) 2981–2989, https://doi.org/10.1063/1.341561. [6] S.F. Fang, K. Adomi, S. Iyer, H. Morkoç, H. Zabel, C. Choi, N. Otsuka, Gallium arsenide and other compound semiconductors on silicon, J. Appl. Phys. 68 (1990) R31–R58, https://doi.org/10.1063/1.346284. [7] G. Brammertz, Y. Mols, S. Degroote, V. Motsnyi, M. Leys, G. Borghs, M. Caymax, Low-temperature photoluminescence study of thin epitaxial GaAs films on Ge, J. Appl. Phys. 99 (2006), 093514, https://doi.org/10.1063/1.2194111. [8] S.K. Madisetti, V. Tokranov, A. Greene, S. Novak, M. Yakimov, S. Oktyabrsky, S. Bantley, A.P. Jacob, GaSb on Si: structural defects and their effects on surface morphology and electrical properties, Mater. Res. Soc. Symp. Proc. 1635 (2014) 115–120, https://doi.org/10.1557/opl.2014.219. [9] A.P. Craig, P.J. Carrington, H. Liu, A.R.J. Marshall, Characterization of 6.1 Å III-V materials grown on GaAs and Si: a comparison of GaSb/GaAs epitaxy and GaSb/AlSb/Si epitaxy, J. Cryst. Growth 435 (2016) 56–61, https://doi.org/10.1016/j.jcrysgro.2015.11.025. [10] S. Sasaki, K. Dropiewski, S. Madisetti, V. Tokranov, M. Yakimov, S. Oktyabrsky, S. Bentley, R. Galatage, A.P. Jacob, Electrical properties related to growth defects in metamorphic GaSb films on Si, J. Vacum Sci. Tech. B 35 (2017), 011203, https://doi.org/10.1116/1.4973215. [11] J. Tournet, S. Parola, A. Vauthelin, D. Montesdeoca Cardenes, S. Soresi, F. Martinez, Q. Lu, Y. Cuminal, P.J. Carrington, J. D�ecobert, A. Krier, Y. Rouillard, E. Tourni� e, GaSb-based solar cells for multi-junction integration on Si substrates, Sol. Energy Mater. Sol. Cell. 191 (2019) 444–450, https://doi.org/10.1016/j. solmat.2018.11.035. [12] I. Lucci, S. Charbonnier, L. Pedesseau, M. Vallet, L. Cerutti, J.-B. Rodriguez, E. Tourni�e, R. Bernard, A. L�etoublon, N. Bertru, A. Le Corre, S. Rennesson, F. Semond, G. Patriarche, L. Largeau, P. Turban, A. Ponchet, C. Cornet, Universal description of III-V/Si epitaxial growth processes, Phys. Rev. Mater. 2 (2018), https://doi.org/10.1103/PhysRevMaterials.2.060401, 060401(R). [13] A. Ponchet, G. Patriarche, J.-B. Rodriquez, L. Cerutti, E. Tourni�e, Interface energy analysis of III-V islands on Si (001) in the Volmer-Weber growth mode, Appl. Phys. Lett. 113 (2018), 191601, https://doi.org/10.1063/1.5055056. [14] R. Alcotte, M. Martin, J. Moeyaert, R. Cipro, S. David, F. Bassani, F. Ducroquet, Y. Bogumilowicz, E. Sanchez, Z. Ye, X.Y. Bao, J.B. Pin, T. Baron, Epitaxial growth of antiphase boundary free GaAs layer on 300 mm Si(001) substrate by metalorganic chemical vapour deposition with high mobility, APL. Mater. 4 (2016), 046101, https://doi.org/10.1063/1.4945586. [15] M.T. Huu Ha, S.H. Huynh, H.B. Do, T.A. Nguyen, Q.H. Luc, E.Y. Chang, Demonstrating antiphase domain boundary-free GaAs buffer layer on zero off-cut Si (001) substrate for interfacial misfit dislocation GaSb film by metalorganic chemical vapor deposition, Mater. Res. Express 4 (2017), 085901, https://doi.org/ 10.1088/2053-1591/aa8043. [16] J. Kwoen, J. Lee, K. Watanabe, Y. Arakawa, Elimination of anti-phase boundaries in a GaAs layer directly-grown on an on-axis Si(001) substrate by optimizing an AlGaAs nucleation layer, Jpn. J. Appl. Phys. 58 (2019), https://doi.org/10.7567/1347-4065/aaffc2. SBBE07. [17] S. Hosseini Vajargah, S. Ghanad-Tavakoli, J.S. Preston, R.N. Kleiman, G.A. Botton, Growth mechanisms of GaSb heteroepitaxial films on Si with an AlSb buffer layer, J. Appl. Phys. 114 (2013), 113101, https://doi.org/10.1063/1.4820255. [18] K. Akahane, N. Yamamoto, S. Gozu, A. Ueta, N. Ohtani, Initial growth stage of GaSb on Si (001) substrates with AlSb initiation layers, J. Cryst. Growth 283 (2005) 297–302, https://doi.org/10.1016/j.jcrysgro.2005.06.001. [19] Y.H. Kim, Y.K. Noh, M.D. Kim, J.E. Oh, K.S. Chung, Transmission electron microscopy study of the initial growth stage of GaSb grown on Si (100) substrate by molecular beam epitaxy method, Thin Solid Films 518 (2010) 2280–2284, https://doi.org/10.1016/j.tsf.2009.09.120. [20] K. Akahane, N. Yamamoto, S. Gozu, N. Ohtani, Heteroepitaxial growth of GaSb on Si(001) substrates, J. Cryst. Growth 264 (2004) 21–25, https://doi.org/ 10.1016/j.jcrysgro.2003.12.041. [21] S.H. Huang, G. Balakrishnan, A. Khoshakhlagh, L.R. Dawson, D.L. Huffaker, Simultaneous interfacial misfit array formation and antiphase domain suppression on miscut silicon substrate, Appl. Phys. Lett. 93 (2008), 071102, https://doi.org/10.1063/1.2970997. [22] Y.K. Noh, M.D. Kim, J.E. Oh, W.C. Yang, Structural and optical properties of GaSb films grown on AlSb/Si (100) by insertion of a thin GaSb interlayer grown at a low temperature, J. Kor. Phys. Soc. 57 (2010) 173–177, https://doi.org/10.3938/jkps.57.173. [23] Y.K. Noh, M.D. Kim, J.E. Oh, W.C. Yang, Y.H. Kim, Growth of low defect AlGaSb films on Si (100) using AlSb and InSb quantum dots intermediate layers, J. Cryst. Growth 323 (2011) 405–408, https://doi.org/10.1016/j.jcrysgro.2011.01.027. [24] J.B. Rodriquez, K. Madiomanana, L. Cerutti, A. Castellano, E. Tourni�e, X-ray diffraction study of GaSb grown by molecular beam epitaxy on silicon substrates, J. Cryst. Growth 439 (2016) 33–39, https://doi.org/10.1016/j.jcrysgro.2016.01.005. [25] B.W. Jia, K.H. Tan, W.K. Loke, S. Wicaksono, S.F. Yoon, Growth and characterization of InSb on (100) Si for mid-infrared application, Appl. Surf. Sci. 440 (2018) 939–945, https://doi.org/10.1016/j.apsusc.2018.01.219.
8
Superlattices and Microstructures 140 (2020) 106450
B. Arpapay and U. Serincan
[26] Y.K. Kim, J.Y. Lee, Y.G. Noh, M.D. Kim, S.M. Cho, Y.J. Kwon, J.E. Oh, Growth mode and structural characterization of GaSb on Si (001) substrate: A transmission electron microscopy study, Appl. Phys. Lett. 88 (2006), 241907, https://doi.org/10.1063/1.2209714. [27] S. Hosseini Vajargah, M. Couillard, K. Cui, S. Ghanad Tavakoli, B. Robinson, R.N. Kleiman, J.S. Preston, G.A. Botton, Strain relief and AlSb buffer layer morphology in GaSb heteroepitaxial films grown on Si as revealed by high-angle annular dark-field scanning transmission electron microscopy, Appl. Phys. Lett. 98 (2011), 082113, https://doi.org/10.1063/1.3551626. [28] S. Hosseini Vajargah, S.Y. Woo, S. Ghanad-Tavakoli, R.N. Kleiman, J.S. Preston, G.A. Botton, Atomic-resolution study of polarity reversal in GaSb grown on Si by scanning transmission electron microscopy, J. Appl. Phys. 112 (2012), 093101, https://doi.org/10.1063/1.4759160. [29] S.Y. Woo, S. Hosseini Vajargah, S. Ghanad-Tavakoli, R.N. Kleiman, G.A. Botton, Direct observation of anti-phase boundaries in heteroepitaxy of GaSb thin films grown on Si (001) by transmission electron microscopy, J. Appl. Phys. 112 (2012), 074306, https://doi.org/10.1063/1.4756957. [30] J.B. Rodriguez, L. Cerutti, G. Patriarche, L. Largeau, K. Madiomanana, E. Tourni� e, Characterization of antimonide based material grown by molecular epitaxy on vicinal silicon substrates via a low temperature AlSb nucleation layer, J. Cryst. Growth 477 (2017) 65–71, https://doi.org/10.1016/j.jcrysgro.2017.04.003. [31] T. Cerba, M. Martin, J. Moeyaert, S. David, J.L. Rouviere, L. Cerutti, R. Alcotte, J.B. Rodriquez, M. Bawedin, H. Boutry, F. Bassani, Y. Bogumilowicz, P. Gergaud, E. Tourni� e, T. Baron, Anti phase boundary free GaSb layer grown on 300 mm (001)-Si substrate by metal organic chemical vapor deposition, Thin Solid Films 645 (2018) 5–9, https://doi.org/10.1016/j.tsf.2017.10.024. [32] U. Serincan, B. Arpapay, Structural and optical characterization of GaSb on Si (001) grown by molecular beam epitaxy, Semicond. Sci. Technol. 34 (2019), 035013, https://doi.org/10.1088/1361-6641/aafcbe. [33] L. Reijnen, R. Brunton, I.R. Grant, GaSb single-crystal growth by vertical gradient freeze, J. Cryst. Growth 275 (2005) e595–e600, https://doi.org/10.1016/j. jcrysgro.2004.11.003. [34] G. Naresh-Kumar, A. Vilalta-Clemente, H. Jussila, A. Winkelmann, G. Nolze, S. Vespucci, S. Nagarajan, A.J. Wilkinson, C. Trager-Cowan, Quantitative imaging of anti-phase domains by polarity sensitive orientation mapping using electron backscatter diffraction, Sci. Rep. 7 (2017) 10916, https://doi.org/10.1038/ s41598-017-11187-z. [35] I. N� emeth, B. Kunert, W. Stolz, K. Volz, Ways to quantitatively defect antiphase disorder in GaP films grown on Si(001) by transmission electron microscopy, J. Cryst. Growth 310 (2008) 4763–4767, https://doi.org/10.1016/j.jcrysgro.2008.07.105. [36] K. Volz, A. Beyer, W. Witte, J. Ohlmann, I. N� emeth, B. Kunert, W. Stolz, GaP-nucleation on exact Si (001) substrates for III/V device integration, J. Cryst. Growth 315 (2011) 37–47, https://doi.org/10.1016/j.jcrysgro.2010.10.036. [37] C.S.C. Barrett, T.P. Martin, X.-Y. Bao, E.L. Kennon, L. Gutierrez, P. Martin, E. Sanchez, K.S. Jones, Effect of bulk growth temperature on antiphase domain boundary annihilation rate in MOCVD-grown GaAs on Si, J. Cryst. Growth 450 (2016) 39–44, https://doi.org/10.1016/j.jcrysgro.2016.06.021. [38] M.K. Hudait, S.B. Krupanidhi, Self-annihilation of antiphase boundaries in GaAs epilayers on Ge substrates grown by metal-organic vapor-phase epitaxy, J. Appl. Phys. 89 (2001) 5972, https://doi.org/10.1063/1.1368870. [39] Y. Li, G. Salviati, M.M.G. Bongers, L. Lazzarini, L. Nasi, L.J. Giling, On the formation of antiphase domains in the system of GaAs on Ge, J. Cryst. Growth 163 (1996) 195–202, https://doi.org/10.1016/0022-0248(95)00958-2. [40] A. Rocher, E. Snoeck, Misfit dislocations in (001) semiconductor heterostructures grown by epitaxy, Mater. Sci. Eng. B67 (1999) 62–69, https://doi.org/ 10.1016/S0921-5107(99)00210-X. [41] M. Niehle, A. Trampet, J.B. Rodriguez, L. Cerutti, E. Tourni� e, Electron tomography on III-Sb heterostructures on vicinal Si(001) substrates: anti-phase boundaries as a sink for threading dislocations, Scripta Mater. 132 (2017) 5–8, https://doi.org/10.1016/j.scriptamat.2017.01.018. [42] M. Niehle, J.B. Rodriguez, L. Cerutti, E. Tourni�e, A. Trampet, The interaction of extended defects as the origin of step bunching in epitaxial III-V layers on vicinal Si(001) substrates, Phys. Status Solidi Rapid Res. Lett. (2019), 1900290, https://doi.org/10.1002/pssr.201900290. [43] W. Guo, A. Bondi, C. Cornet, A. L� etoublon, O. Durand, T. Rohel, S. Boyer-Richard, N. Bertru, S. Loualiche, J. Even, A. Le Corre, Thermodynamic evolution of antiphase boundaries in GaP/Si epilayers evidenced by advanced X-ray scattering, Appl. Surf. Sci. 258 (2012) 2808–2815, https://doi.org/10.1016/j. apsusc.2011.10.139. [44] C.S.C. Barrett, A. Atassi, E.L. Kennon, Z. Weinrich, K. Haynes, X.-Y. Bao, P. Martin, K.S. Jones, Dissolution of antiphase domain boundaries in GaAs on Si(001) via post-growth annealing, J. Mater. Sci. 54 (2019) 7028–7034, https://doi.org/10.1007/s10853-019-03353-7.
9