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Influence of substrate and substrate temperature on the structural, optical and surface properties of InGaN thin films prepared by RFMS method
Microelectronic Engineering 207 (2019) 15–18
Contents lists available at ScienceDirect
Microelectronic Engineering journal homepage: www.elsevier.com/locate/mee
Research paper
Influence of substrate and substrate temperature on the structural, optical and surface properties of InGaN thin films prepared by RFMS method
T
⁎
Erman Erdoğana, , Mutlu Kundakçıb a b
Department of Electrical & Electronics Engineering, Muş Alparslan University, Muş 49250, Turkey Department of Physics, Atatürk University, Erzurum 25240, Turkey
A R T I C LE I N FO
A B S T R A C T
Keywords: InGaN growth Thin films Sputtering technique Substrate temperature Silicon substrate
In this work, the pure InGaN thin films were grown using n-type and p-type silicon substrates at varying substrate temperatures using the sputtering method. The effects of substrate and substrate temperature on the structural, morphological and optical properties of the thin films grown were investigated. X-ray diffraction (XRD) analyzes of the obtained films illustrates crystal structures at 500̊ C substrate temperature, the films were found to be hexagonal. Scanning electron microscopy (SEM) was used to investigate the shape, size and surface distribution of the particles formed on film surfaces. The reflection and optical band gap (Eg) of the films were investigated from the optical analyzes taken with the UV-VIS spectrophotometer. As a result of these analyzes, it has been reached that the substrate and substrate temperature have a great influence on the structural, morphological and optical properties of the films. The experimental findings obtained in the study are compared with the studies given in the literature and the similarities and differences are discussed.
1. Introduction Technology that is in a very important position in our daily life is being developed day by day and scientists are working hard to make this technology effective. In technological applications, semiconductors cannot be ignored. Progress in electronics and computer science has been achieved by researching the specific characteristics of semiconductors, and technological developments have accelerated accordingly [1]. In recent years, the use of wide band gap semiconductor materials in technology and electronics has expanded. In this context, comprehensive research is being conducted to develop cheaper materials and technology [2]. The high iconicity, direct band gap, high optical transmittance for absorption and luminescence and their wide band gaps are of great interest to the group III-V compounds formed by the association of the elements of group IIIA and VA of the periodic table. III-V semiconductor heterojunctions are used in various fields today [3,4]. Among these areas, light emitting diodes (LED), photodetectors, transistors and high efficiency solar cells can be shown as the most important ones [5]. In this research work, InGaN semiconducting heterojunction thin films were grown using sputtering method and investigated using various characterization techniques. Deposition of InGaN thin films can be obtained by using various methods such as; molecular beam epitaxy (MBE) [6,7], metal organic chemical vapor deposition (MOCVD) [8,9] and radio frequency ⁎
magnetron sputtering (RFMS) [10–13]. Sputtering thin film growth technique is basically a process in which after an inert gas (noble gas, usually argon), which is sent between two differently polarized electrodes, is converted into a positive ion, the material is accelerated towards the target material in the cathode (negative electrode) these scraped particles will grow one by one on the base placed exactly opposite the target. More importantly, RFMS produces a dense microstructure which preponderates most of other thin film growth methods [14,15]. The applied RF power, voltage difference and distance between anode and cathode, substrate temperature, distance between target material and substrate, oxygen and argon partial pressures, substrate heating and cooling times are used for magnetron sputtering technique. Among these parameters different groups determine the different properties of produced films. The process parameters used for the magnetron sputtering technique mentioned above will have different values for the different kinds of materials desired to be produced. In order to obtain different forms of different materials, it is also necessary to optimize the production parameters thoroughly; reducing a parameter can affect all other parameters. In this study, the substrate temperature used during the thin film growth process is often required so that the desired film crystallizes. Different production temperatures are required for the production of films from each material in multi-crystal or single crystal structures. We
Corresponding author. E-mail address: [email protected] (E. Erdoğan).
https://doi.org/10.1016/j.mee.2018.12.010 Received 14 July 2018; Received in revised form 18 October 2018; Accepted 11 December 2018 Available online 04 January 2019 0167-9317/ © 2019 Elsevier B.V. All rights reserved.
Microelectronic Engineering 207 (2019) 15–18
E. Erdoğan, M. Kundakçı
Table 1 InGaN thin film growth parameters on silicon substrates by RF sputtering. Substrate temperature (C°)
RF power (Watt)
Base pressure (Torr)
Working pressure (Torr)
Deposition rate (nm)
Deposition time (minute)
Argon gas flow rate (sccm)
Thickness (nm)
300 500
100 100
1.4 × 10−6 9.8 × 10−7
1.4 × 10−2 1.4 × 10−2
0.0–0.01 0.01
153 136
100 100
150 ± 3 150 ± 3
try to demystify the effect of substrate and substrate temperature on structural and optical properties of InGaN thin films deposited on two types of Si (n-type and p-type) substrates. The characterizations of the films were done and discussed in a wide area with XRD, SEM and UV–Vis Spectrometer based on the variations of substrate and substrate temperature. 2. Experimental InGaN thin films were deposited by RFMS using %99.95 InGaN target at East Anatolian High Technology Application and Research Center (DAYTAM). Silicon substrates were chemically cleaned with the chemical cleaning procedure to remove the surface contamination prior to the insertion in the vacuum chamber. Structural and optical properties of InGaN thin films have been investigated. It has been tried to determine the properties and differences of these produced films. Before the deposition, the target was pre-sputtered for a few min each time to remove any contaminants from the target surface and to reach equilibrium conditions. The experimental parameters used to obtain InGaN thin films by reactive RF sputtering are shown in Table 1. During the deposition the substrate stage maintained a constant rotation speed. The sputtering was manually terminated and the approximately 150 nm thickness of the thin film was obtained by using an Au coated quartz crystal thickness monitor controlling. In addition, the film thicknesses were confirmed after deposition with the help of a profilometer, and the thickness of all the obtained films was measured as 150 nm. Microstructures, crystal orientations and crystallographic information of InGaN thin films produced by reactive r.f. sputtering technique were obtained by using PANalytical Empyrean X-ray diffraction device. Reflection measurements were performed using doublebeam UV–vis Spectrometer with UV-3600 Plus model. SEM images were taken with Sigma 300 Model Zeiss Gemini FEG-SEM device.
Fig. 1. XRD diffraction pattern of InGaN thin film deposited at different substrates and substrate temperatures.
substrates. The lattice constants a = b = 3,33 Å, c = 5,39 Å, especially three distinct peaks were observed in deposited InGaN thin film at 500 °C. For the films prepared at 500 °C, new peaks were observed at (002) and (101) orientations compared to the films grown at 300 °C. Additionally, no changes have been observed in terms of substrate conductivity type. However, with the most severe peak (100) orientation was observed both substrate temperatures. It was found that all of the InGaN films obtained were hexagonal (wurtzite) and preferred orientations of (100). Wang et al. found (002), (100) and (101) peaks of InxGa1-xN films deposited on silicon for different In compositions. They reported that deposited films have hexagonal crystal system [16].
3. Results 3.2. Optical investigations 3.1. XRD investigations Interaction of the electromagnetic waveguide to a crystal plane with the electrical charges present in the crystal is called end-effect energy loss absorption. The most commonly used method for determining the energy band gap of semiconductors is the optical reflection method. UV–Visible spectrophotometer was used to determine the reflection spectrum of InGaN thin films in ultra-violet (UV) and visible (Vis) regions and to characterize their optical properties. The light passing through the uncoated silicon was normalized so that reflection value of the thin films was not affected by reflection value of the substrates. The measurement range is between 200 nm and 800 nm. Fig. 2 shows the reflection spectrum as a function of wavelength of the InGaN thin films on p-type and n-type silicon substrates at various substrate temperatures. As seen from reflection graph against wavelength in Fig. 2, we can see that the InGaN thin film grown on both silicon substrates at 300 °C substrate temperature has more reflection value at larger wave length and we see that it reaches a reflection value of about 55% at 200 nm. It is also seen that in the case of a films deposited at a temperature of 500 °C substrate temperature, we obtain lower reflection values for both silicon substrates. It is seen that the variation of the substrate temperature has an important influence on reflection graphs of the films.
One of the most powerful techniques for determining the structural properties of semiconductors is the x-ray diffraction method. XRD analyzes of InGaN thin films at different substrate and substrate temperatures produced on silicon substrates by sputtering technique were carried out by taking diffraction patterns at 10 < 2θ < 80 using CuKα rays with λ = 0.1540 nm wavelength. The film grown at 500 °C in the XRD analysis results of the InGaN structure by sputtering at different substrate temperatures has hexagonal crystal structure. It is seen that when the substrate temperature value is lowered, the crystal structure of InGaN films gradually deteriorates. In this case, we can say that the substrate temperature has an important influence on the crystal structures of InGaN films in particular. It is thought that the high substrate temperature reduces the stress / compression on the films and thus improves the crystallization. From these results it can be concluded that the elevated substrate temperatures are the suitable growth conditions to prepare good quality polycrystalline thin film. The effect of substrate and substrate temperature changes is shown in the Fig. 1. XRD diffraction patterns grown by the RF sputtering method on the InGaN thin film indicate that InGaN thin film seems to have greater intensity at (100) peak at both n-type and p-type silicon 16
Microelectronic Engineering 207 (2019) 15–18
E. Erdoğan, M. Kundakçı
Table 2 Energy band gap values of InGaN thin films at different substrates and substrate temperatures. Energy band gap
n-type Si 300 °C
n-type Si 500 °C
p-type Si 300 °C
p-type Si 500 °C
Eg (eV)
1.403
1.606
1.568
1.573
structural, optical and morphological properties of InGaN thin films grown by RFMS technique on p-Si (100) and n-Si (111) substrates have been investigated. Given the optical properties, it is clearly shown that the energy band gaps of InGaN films growing on silicon bases can be controlled by varying the substrate temperature in order to achieve the maximum absorption of solar energy in increasing the efficiency of a solar cell. Films with low reflection values in different regions of the electromagnetic spectrum can be used in anti-reflection coating applications, films with good surface morphology can be used in optoelectronic applications and, films with polycrystalline structure are suitable for applications such as LED and laser diode. Films with low substrate temperature values have some defects and grain boundaries. Intrinsic stress / compression are produced in these defects and at the grain boundaries, along with the narrowing of the gap between bordering upon grains due to interatomic forces along the sheet boundaries and adherence to the film substrate. Therefore, the number of grain boundaries reduces at higher substrate temperatures and the heat treatment during deposition decreases the concentration of crystal defects in the matrix. For this reason, it can be said that the high substrate temperature reduces the stress on the films and thus improves the crystallization [19]. The lower crystallite size relates to the modification of the nucleation kinetics affected by the substrate temperature. For samples grown at high temperatures, the change in diffraction peaks can be attributed to thermal stresses originating from substrate heating [20]. The increase in c-axis orientation with increasing surface temperature can be ascribed to the raise in surface diffusion of absorbed species [21]. Higher deposition rates at high substrate temperatures may possibly be related to chemical adsorption and the reorganization of certain chemical bonds in the substrate surface. The mobility of the atomic clusters, which accumulate on the substrate, increases with the increase of substrate temperature in accordance with the energies. This increase in the mobility of the atoms on the substrate will cause preferential orientation of the films [22]. More dense films can be obtained at higher substrate temperatures and ratios. If grain boundaries are not clear at RF power and grain boundaries become more apparent as the temperature increases, it can be said that the thermal energy is more effective than the kinetic energy in the crystallization nucleation process. At higher substrate temperature, there is sufficient thermal energy to combine the smaller particles and the structure is transported to a
Fig. 2. Reflection graph against wavelength of the InGaN thin films grown at different substrates and substrate temperatures.
In this study, energy band gap values of InGaN films grown on silicon substrates were calculated with Kubelka-Munk Eq. [17]. The Kubelka-Munk plot was used to determine the optical band gap of the InGaN thin film grown on the silicon substrates as the energy at which the extrapolated linear part of F(R) vs. hν plot intersects the energy axis and found to be 1.403 eV, 1.606 eV, 1.568 eV and 1.573 eV for n-type and p-type silicon for 300 °C and 500 °C, respectively as seen in Fig. 3. Wang and his friends reported the optical band gap of InGaN thin films under different working pressures in terms of pascal unit. They found that with increasing working pressure the optical band gap of films are increasing. The obtained optical band gaps are found to be 2.62 eV (0.5 Pa), 2.67 eV (0.66 Pa), 2.70 eV (0.8 Pa) and 2.78 eV (1.0 Pa) [18] (Table 2). 3.3. SEM investigations Fig. 4 illustrates the SEM images of the surface of the InGaN films grown at different substrates and substrate temperatures. It is clear that surface morphology of the films depends on the substrates temperatures. The surface morphology of the InGaN films grown at 300̊ C substrate temperature (Fig. 4(a)) displays dentritic structure over the surface. 4. Conclusion and discussion Effect of substrate conductivity type and substrate temperature on
Fig. 3. Energy band gap graph of InGaN thin films grown at different substrates and substrate temperatures. 17
Microelectronic Engineering 207 (2019) 15–18
E. Erdoğan, M. Kundakçı
Fig. 4. SEM images of InGaN thin film grown on silicon substrates at different substrate temperatures.
transition zone of tightly packed granules [23,24]. [12]
Acknowledgement
[13]
We are thankful to Dr. Emre Gür (Physics Dept., Atatürk University,) for all deposition and characterization measurements made at DAYTAM. We would like to thank Ahmet Emre Kasapoğlu (DAYTAM) for helping us working on the growth system.
[14] [15] [16]
References
[17]
[1] L.I. Berger, Semiconductor Materials, Vol. 12 CRC press, 1997, pp. 954–963. [2] S.M. Sze, K.K. Ng, Physics of Semiconductor Devices, John wiley & sons, 2006. [3] O. Ambacher, Growth and applications of group III-nitrides, J. Phys. D. Appl. Phys. 31 (20) (1998) 2653. [4] S.C. Jain, M. Willander, J. Narayan, R.V. Overstraeten, III–nitrides: growth, characterization, and properties, J. Appl. Phys. 87 (3) (2000) 965–1006. [5] C.F. Huang, W.Y. Hsieh, B.C. Hsieh, C.H. Hsieh, C.F. Lin, Characterization of InGaNbased photovoltaic devices by varying the indium contents, Thin Solid Films 529 (2013) 278–281. [6] C.A. Fabien, B.P. Gunning, W.A. Doolittle, A.M. Fischer, Y.O. Wei, H. Xie, F.A. Ponce, Low-temperature growth of InGaN films over the entire composition range by MBE, J. Cryst. Growth 425 (2015) 115–118. [7] I. Gherasoiu, K.M. Yu, L. Reichertz, W. Walukiewicz, InGaN pn-junctions grown by PA-MBE: Material characterization and fabrication of nanocolumn electroluminescent devices, J. Cryst. Growth 425 (2015) 393–397. [8] Y.S. Chen, C.H. Liao, C.T. Kuo, R.C.C. Tsiang, H.C. Wang, Indium droplet formation in InGaN thin films with single and double heterojunctions prepared by MOCVD, Nanoscale Res. Lett. 9 (1) (2014) 334. [9] P.C. Chang, C.L. Yu, Y.W. Jahn, S.J. Chang, K.H. Lee, Effect of growth temperature on the indium incorporation in InGaN epitaxial films, Advanced Materials Research, Vol. 287 Trans Tech Publications, 2011, pp. 1456–1459. [10] P. Jakkala, M.E. Kordesch, Electrical properties of InGaN thin films grown by RF sputtering at different temperatures, varying nitrogen and argon partial pressure ratios, Mater. Res. Express 3 (10) (2016) 106406. [11] B.S. Yadav, P. Mohanta, R.S. Srinivasa, S.S. Major, Electrical and optical properties
[18] [19]
[20]
[21]
[22]
[23]
[24]
18
of transparent conducting InxGa1− xN alloy films deposited by reactive co-sputtering of GaAs and indium, Thin Solid Films 555 (2014) 179–184. T. Itoh, S. Hibino, T. Sahashi, Y. Kato, S. Koiso, F. Ohashi, S. Nonomura, InXGa1-XN films deposited by reactive RF-sputtering, J. Non-Cryst. Solids 358 (17) (2012) 2362–2365. C.C. Li, D.H. Kuo, P.W. Hsieh, Y.S. Huang, Thick InxGa1− xN films prepared by reactive sputtering with single cermet targets, J. Electron. Mater. 42 (8) (2013) 2445–2449. P.J. Kelly, R.D. Arnell, Magnetron sputtering: a review of recent developments and applications, Vacuum 56 (3) (2000) 159–172. S. Swann, Magnetron sputtering, Phys. Technol. 19 (2) (1988) 67. X. Wang, L. He, X. Li, X. Su, Z. Zhang, W. Zhao, Structural and Morphological Characteristics of Inxga1-xN Films Grown on SI (111) by Reactive Magnetron Sputtering, MATEC Web of Conferences, Vol. 67 EDP Sciences, 2016, p. 04013. B. Rajamannan, S. Mugundan, G. Viruthagiri, P. Praveen, N. Shanmugam, Linear and nonlinear optical studies of bare and copper doped TiO2 nanoparticles via sol gel technique, Spectrochim. Acta A Mol. Biomol. Spectrosc. 118 (2014) 651–656. J. Wang, X.J. Shi, J. Zhu, Low-temperature growth of InxGa1− xN films by radiofrequency magnetron sputtering, Appl. Surf. Sci. 265 (2013) 399–404. S. Kaya, E. Yilmaz, H. Karacali, A.O. Cetinkaya, A. Aktag, Samarium oxide thin films deposited by reactive sputtering: effects of sputtering power and substrate temperature on microstructure, morphology and electrical properties, Mater. Sci. Semicond. Process. 33 (2015) 42–48. D. Hou, Y. Lu, F. Song, Effects of substrate temperature on properties of vanadium oxide thin films on Si substrate, Second International Conference on Photonics and Optical Engineering.International Society for Optics and Photonics, Vol. 10256 2017, p. 102560R. D.K. Pradhan, S. Kumari, D.K. Pradhan, A. Kumar, R.S. Katiyar, R.E. Cohen, Effect of Substrate Temperature on Structural and Magnetic Properties of c-axis Ori-ented Spinel Ferrite Ni0. 65Zn0. 35Fe2O4 (NZFO) Thin Films, (2018). X. Liu, J. Hao, H. Yang, X. Lin, X. Zeng, Substrate temperature effect on the microstructure and properties of (Si, Al)/aC: H films prepared through magnetron sputtering deposition, J. Nanomater. 2015 (2015) 1. H. Ahn, J. Seo, H. Shin, Y. Um, Substrate effects on the structural properties of Cd1xMnxTe thin films grown via magnetron Co-sputtering, J. Korean Phys. Soc. 67 (4) (2015) 668–671. N. Ghobadi, M. Ganji, C. Luna, A. Arman, A. Ahmadpourian, Effects of substrate temperature on the properties of sputtered TiN thin films, J. Mater. Sci. Mater. Electron. 27 (3) (2016) 2800–2808.
Contents lists available at ScienceDirect
Microelectronic Engineering journal homepage: www.elsevier.com/locate/mee
Research paper
Influence of substrate and substrate temperature on the structural, optical and surface properties of InGaN thin films prepared by RFMS method
T
⁎
Erman Erdoğana, , Mutlu Kundakçıb a b
Department of Electrical & Electronics Engineering, Muş Alparslan University, Muş 49250, Turkey Department of Physics, Atatürk University, Erzurum 25240, Turkey
A R T I C LE I N FO
A B S T R A C T
Keywords: InGaN growth Thin films Sputtering technique Substrate temperature Silicon substrate
In this work, the pure InGaN thin films were grown using n-type and p-type silicon substrates at varying substrate temperatures using the sputtering method. The effects of substrate and substrate temperature on the structural, morphological and optical properties of the thin films grown were investigated. X-ray diffraction (XRD) analyzes of the obtained films illustrates crystal structures at 500̊ C substrate temperature, the films were found to be hexagonal. Scanning electron microscopy (SEM) was used to investigate the shape, size and surface distribution of the particles formed on film surfaces. The reflection and optical band gap (Eg) of the films were investigated from the optical analyzes taken with the UV-VIS spectrophotometer. As a result of these analyzes, it has been reached that the substrate and substrate temperature have a great influence on the structural, morphological and optical properties of the films. The experimental findings obtained in the study are compared with the studies given in the literature and the similarities and differences are discussed.
1. Introduction Technology that is in a very important position in our daily life is being developed day by day and scientists are working hard to make this technology effective. In technological applications, semiconductors cannot be ignored. Progress in electronics and computer science has been achieved by researching the specific characteristics of semiconductors, and technological developments have accelerated accordingly [1]. In recent years, the use of wide band gap semiconductor materials in technology and electronics has expanded. In this context, comprehensive research is being conducted to develop cheaper materials and technology [2]. The high iconicity, direct band gap, high optical transmittance for absorption and luminescence and their wide band gaps are of great interest to the group III-V compounds formed by the association of the elements of group IIIA and VA of the periodic table. III-V semiconductor heterojunctions are used in various fields today [3,4]. Among these areas, light emitting diodes (LED), photodetectors, transistors and high efficiency solar cells can be shown as the most important ones [5]. In this research work, InGaN semiconducting heterojunction thin films were grown using sputtering method and investigated using various characterization techniques. Deposition of InGaN thin films can be obtained by using various methods such as; molecular beam epitaxy (MBE) [6,7], metal organic chemical vapor deposition (MOCVD) [8,9] and radio frequency ⁎
magnetron sputtering (RFMS) [10–13]. Sputtering thin film growth technique is basically a process in which after an inert gas (noble gas, usually argon), which is sent between two differently polarized electrodes, is converted into a positive ion, the material is accelerated towards the target material in the cathode (negative electrode) these scraped particles will grow one by one on the base placed exactly opposite the target. More importantly, RFMS produces a dense microstructure which preponderates most of other thin film growth methods [14,15]. The applied RF power, voltage difference and distance between anode and cathode, substrate temperature, distance between target material and substrate, oxygen and argon partial pressures, substrate heating and cooling times are used for magnetron sputtering technique. Among these parameters different groups determine the different properties of produced films. The process parameters used for the magnetron sputtering technique mentioned above will have different values for the different kinds of materials desired to be produced. In order to obtain different forms of different materials, it is also necessary to optimize the production parameters thoroughly; reducing a parameter can affect all other parameters. In this study, the substrate temperature used during the thin film growth process is often required so that the desired film crystallizes. Different production temperatures are required for the production of films from each material in multi-crystal or single crystal structures. We
Corresponding author. E-mail address: [email protected] (E. Erdoğan).
https://doi.org/10.1016/j.mee.2018.12.010 Received 14 July 2018; Received in revised form 18 October 2018; Accepted 11 December 2018 Available online 04 January 2019 0167-9317/ © 2019 Elsevier B.V. All rights reserved.
Microelectronic Engineering 207 (2019) 15–18
E. Erdoğan, M. Kundakçı
Table 1 InGaN thin film growth parameters on silicon substrates by RF sputtering. Substrate temperature (C°)
RF power (Watt)
Base pressure (Torr)
Working pressure (Torr)
Deposition rate (nm)
Deposition time (minute)
Argon gas flow rate (sccm)
Thickness (nm)
300 500
100 100
1.4 × 10−6 9.8 × 10−7
1.4 × 10−2 1.4 × 10−2
0.0–0.01 0.01
153 136
100 100
150 ± 3 150 ± 3
try to demystify the effect of substrate and substrate temperature on structural and optical properties of InGaN thin films deposited on two types of Si (n-type and p-type) substrates. The characterizations of the films were done and discussed in a wide area with XRD, SEM and UV–Vis Spectrometer based on the variations of substrate and substrate temperature. 2. Experimental InGaN thin films were deposited by RFMS using %99.95 InGaN target at East Anatolian High Technology Application and Research Center (DAYTAM). Silicon substrates were chemically cleaned with the chemical cleaning procedure to remove the surface contamination prior to the insertion in the vacuum chamber. Structural and optical properties of InGaN thin films have been investigated. It has been tried to determine the properties and differences of these produced films. Before the deposition, the target was pre-sputtered for a few min each time to remove any contaminants from the target surface and to reach equilibrium conditions. The experimental parameters used to obtain InGaN thin films by reactive RF sputtering are shown in Table 1. During the deposition the substrate stage maintained a constant rotation speed. The sputtering was manually terminated and the approximately 150 nm thickness of the thin film was obtained by using an Au coated quartz crystal thickness monitor controlling. In addition, the film thicknesses were confirmed after deposition with the help of a profilometer, and the thickness of all the obtained films was measured as 150 nm. Microstructures, crystal orientations and crystallographic information of InGaN thin films produced by reactive r.f. sputtering technique were obtained by using PANalytical Empyrean X-ray diffraction device. Reflection measurements were performed using doublebeam UV–vis Spectrometer with UV-3600 Plus model. SEM images were taken with Sigma 300 Model Zeiss Gemini FEG-SEM device.
Fig. 1. XRD diffraction pattern of InGaN thin film deposited at different substrates and substrate temperatures.
substrates. The lattice constants a = b = 3,33 Å, c = 5,39 Å, especially three distinct peaks were observed in deposited InGaN thin film at 500 °C. For the films prepared at 500 °C, new peaks were observed at (002) and (101) orientations compared to the films grown at 300 °C. Additionally, no changes have been observed in terms of substrate conductivity type. However, with the most severe peak (100) orientation was observed both substrate temperatures. It was found that all of the InGaN films obtained were hexagonal (wurtzite) and preferred orientations of (100). Wang et al. found (002), (100) and (101) peaks of InxGa1-xN films deposited on silicon for different In compositions. They reported that deposited films have hexagonal crystal system [16].
3. Results 3.2. Optical investigations 3.1. XRD investigations Interaction of the electromagnetic waveguide to a crystal plane with the electrical charges present in the crystal is called end-effect energy loss absorption. The most commonly used method for determining the energy band gap of semiconductors is the optical reflection method. UV–Visible spectrophotometer was used to determine the reflection spectrum of InGaN thin films in ultra-violet (UV) and visible (Vis) regions and to characterize their optical properties. The light passing through the uncoated silicon was normalized so that reflection value of the thin films was not affected by reflection value of the substrates. The measurement range is between 200 nm and 800 nm. Fig. 2 shows the reflection spectrum as a function of wavelength of the InGaN thin films on p-type and n-type silicon substrates at various substrate temperatures. As seen from reflection graph against wavelength in Fig. 2, we can see that the InGaN thin film grown on both silicon substrates at 300 °C substrate temperature has more reflection value at larger wave length and we see that it reaches a reflection value of about 55% at 200 nm. It is also seen that in the case of a films deposited at a temperature of 500 °C substrate temperature, we obtain lower reflection values for both silicon substrates. It is seen that the variation of the substrate temperature has an important influence on reflection graphs of the films.
One of the most powerful techniques for determining the structural properties of semiconductors is the x-ray diffraction method. XRD analyzes of InGaN thin films at different substrate and substrate temperatures produced on silicon substrates by sputtering technique were carried out by taking diffraction patterns at 10 < 2θ < 80 using CuKα rays with λ = 0.1540 nm wavelength. The film grown at 500 °C in the XRD analysis results of the InGaN structure by sputtering at different substrate temperatures has hexagonal crystal structure. It is seen that when the substrate temperature value is lowered, the crystal structure of InGaN films gradually deteriorates. In this case, we can say that the substrate temperature has an important influence on the crystal structures of InGaN films in particular. It is thought that the high substrate temperature reduces the stress / compression on the films and thus improves the crystallization. From these results it can be concluded that the elevated substrate temperatures are the suitable growth conditions to prepare good quality polycrystalline thin film. The effect of substrate and substrate temperature changes is shown in the Fig. 1. XRD diffraction patterns grown by the RF sputtering method on the InGaN thin film indicate that InGaN thin film seems to have greater intensity at (100) peak at both n-type and p-type silicon 16
Microelectronic Engineering 207 (2019) 15–18
E. Erdoğan, M. Kundakçı
Table 2 Energy band gap values of InGaN thin films at different substrates and substrate temperatures. Energy band gap
n-type Si 300 °C
n-type Si 500 °C
p-type Si 300 °C
p-type Si 500 °C
Eg (eV)
1.403
1.606
1.568
1.573
structural, optical and morphological properties of InGaN thin films grown by RFMS technique on p-Si (100) and n-Si (111) substrates have been investigated. Given the optical properties, it is clearly shown that the energy band gaps of InGaN films growing on silicon bases can be controlled by varying the substrate temperature in order to achieve the maximum absorption of solar energy in increasing the efficiency of a solar cell. Films with low reflection values in different regions of the electromagnetic spectrum can be used in anti-reflection coating applications, films with good surface morphology can be used in optoelectronic applications and, films with polycrystalline structure are suitable for applications such as LED and laser diode. Films with low substrate temperature values have some defects and grain boundaries. Intrinsic stress / compression are produced in these defects and at the grain boundaries, along with the narrowing of the gap between bordering upon grains due to interatomic forces along the sheet boundaries and adherence to the film substrate. Therefore, the number of grain boundaries reduces at higher substrate temperatures and the heat treatment during deposition decreases the concentration of crystal defects in the matrix. For this reason, it can be said that the high substrate temperature reduces the stress on the films and thus improves the crystallization [19]. The lower crystallite size relates to the modification of the nucleation kinetics affected by the substrate temperature. For samples grown at high temperatures, the change in diffraction peaks can be attributed to thermal stresses originating from substrate heating [20]. The increase in c-axis orientation with increasing surface temperature can be ascribed to the raise in surface diffusion of absorbed species [21]. Higher deposition rates at high substrate temperatures may possibly be related to chemical adsorption and the reorganization of certain chemical bonds in the substrate surface. The mobility of the atomic clusters, which accumulate on the substrate, increases with the increase of substrate temperature in accordance with the energies. This increase in the mobility of the atoms on the substrate will cause preferential orientation of the films [22]. More dense films can be obtained at higher substrate temperatures and ratios. If grain boundaries are not clear at RF power and grain boundaries become more apparent as the temperature increases, it can be said that the thermal energy is more effective than the kinetic energy in the crystallization nucleation process. At higher substrate temperature, there is sufficient thermal energy to combine the smaller particles and the structure is transported to a
Fig. 2. Reflection graph against wavelength of the InGaN thin films grown at different substrates and substrate temperatures.
In this study, energy band gap values of InGaN films grown on silicon substrates were calculated with Kubelka-Munk Eq. [17]. The Kubelka-Munk plot was used to determine the optical band gap of the InGaN thin film grown on the silicon substrates as the energy at which the extrapolated linear part of F(R) vs. hν plot intersects the energy axis and found to be 1.403 eV, 1.606 eV, 1.568 eV and 1.573 eV for n-type and p-type silicon for 300 °C and 500 °C, respectively as seen in Fig. 3. Wang and his friends reported the optical band gap of InGaN thin films under different working pressures in terms of pascal unit. They found that with increasing working pressure the optical band gap of films are increasing. The obtained optical band gaps are found to be 2.62 eV (0.5 Pa), 2.67 eV (0.66 Pa), 2.70 eV (0.8 Pa) and 2.78 eV (1.0 Pa) [18] (Table 2). 3.3. SEM investigations Fig. 4 illustrates the SEM images of the surface of the InGaN films grown at different substrates and substrate temperatures. It is clear that surface morphology of the films depends on the substrates temperatures. The surface morphology of the InGaN films grown at 300̊ C substrate temperature (Fig. 4(a)) displays dentritic structure over the surface. 4. Conclusion and discussion Effect of substrate conductivity type and substrate temperature on
Fig. 3. Energy band gap graph of InGaN thin films grown at different substrates and substrate temperatures. 17
Microelectronic Engineering 207 (2019) 15–18
E. Erdoğan, M. Kundakçı
Fig. 4. SEM images of InGaN thin film grown on silicon substrates at different substrate temperatures.
transition zone of tightly packed granules [23,24]. [12]
Acknowledgement
[13]
We are thankful to Dr. Emre Gür (Physics Dept., Atatürk University,) for all deposition and characterization measurements made at DAYTAM. We would like to thank Ahmet Emre Kasapoğlu (DAYTAM) for helping us working on the growth system.
[14] [15] [16]
References
[17]
[1] L.I. Berger, Semiconductor Materials, Vol. 12 CRC press, 1997, pp. 954–963. [2] S.M. Sze, K.K. Ng, Physics of Semiconductor Devices, John wiley & sons, 2006. [3] O. Ambacher, Growth and applications of group III-nitrides, J. Phys. D. Appl. Phys. 31 (20) (1998) 2653. [4] S.C. Jain, M. Willander, J. Narayan, R.V. Overstraeten, III–nitrides: growth, characterization, and properties, J. Appl. Phys. 87 (3) (2000) 965–1006. [5] C.F. Huang, W.Y. Hsieh, B.C. Hsieh, C.H. Hsieh, C.F. Lin, Characterization of InGaNbased photovoltaic devices by varying the indium contents, Thin Solid Films 529 (2013) 278–281. [6] C.A. Fabien, B.P. Gunning, W.A. Doolittle, A.M. Fischer, Y.O. Wei, H. Xie, F.A. Ponce, Low-temperature growth of InGaN films over the entire composition range by MBE, J. Cryst. Growth 425 (2015) 115–118. [7] I. Gherasoiu, K.M. Yu, L. Reichertz, W. Walukiewicz, InGaN pn-junctions grown by PA-MBE: Material characterization and fabrication of nanocolumn electroluminescent devices, J. Cryst. Growth 425 (2015) 393–397. [8] Y.S. Chen, C.H. Liao, C.T. Kuo, R.C.C. Tsiang, H.C. Wang, Indium droplet formation in InGaN thin films with single and double heterojunctions prepared by MOCVD, Nanoscale Res. Lett. 9 (1) (2014) 334. [9] P.C. Chang, C.L. Yu, Y.W. Jahn, S.J. Chang, K.H. Lee, Effect of growth temperature on the indium incorporation in InGaN epitaxial films, Advanced Materials Research, Vol. 287 Trans Tech Publications, 2011, pp. 1456–1459. [10] P. Jakkala, M.E. Kordesch, Electrical properties of InGaN thin films grown by RF sputtering at different temperatures, varying nitrogen and argon partial pressure ratios, Mater. Res. Express 3 (10) (2016) 106406. [11] B.S. Yadav, P. Mohanta, R.S. Srinivasa, S.S. Major, Electrical and optical properties
[18] [19]
[20]
[21]
[22]
[23]
[24]
18
of transparent conducting InxGa1− xN alloy films deposited by reactive co-sputtering of GaAs and indium, Thin Solid Films 555 (2014) 179–184. T. Itoh, S. Hibino, T. Sahashi, Y. Kato, S. Koiso, F. Ohashi, S. Nonomura, InXGa1-XN films deposited by reactive RF-sputtering, J. Non-Cryst. Solids 358 (17) (2012) 2362–2365. C.C. Li, D.H. Kuo, P.W. Hsieh, Y.S. Huang, Thick InxGa1− xN films prepared by reactive sputtering with single cermet targets, J. Electron. Mater. 42 (8) (2013) 2445–2449. P.J. Kelly, R.D. Arnell, Magnetron sputtering: a review of recent developments and applications, Vacuum 56 (3) (2000) 159–172. S. Swann, Magnetron sputtering, Phys. Technol. 19 (2) (1988) 67. X. Wang, L. He, X. Li, X. Su, Z. Zhang, W. Zhao, Structural and Morphological Characteristics of Inxga1-xN Films Grown on SI (111) by Reactive Magnetron Sputtering, MATEC Web of Conferences, Vol. 67 EDP Sciences, 2016, p. 04013. B. Rajamannan, S. Mugundan, G. Viruthagiri, P. Praveen, N. Shanmugam, Linear and nonlinear optical studies of bare and copper doped TiO2 nanoparticles via sol gel technique, Spectrochim. Acta A Mol. Biomol. Spectrosc. 118 (2014) 651–656. J. Wang, X.J. Shi, J. Zhu, Low-temperature growth of InxGa1− xN films by radiofrequency magnetron sputtering, Appl. Surf. Sci. 265 (2013) 399–404. S. Kaya, E. Yilmaz, H. Karacali, A.O. Cetinkaya, A. Aktag, Samarium oxide thin films deposited by reactive sputtering: effects of sputtering power and substrate temperature on microstructure, morphology and electrical properties, Mater. Sci. Semicond. Process. 33 (2015) 42–48. D. Hou, Y. Lu, F. Song, Effects of substrate temperature on properties of vanadium oxide thin films on Si substrate, Second International Conference on Photonics and Optical Engineering.International Society for Optics and Photonics, Vol. 10256 2017, p. 102560R. D.K. Pradhan, S. Kumari, D.K. Pradhan, A. Kumar, R.S. Katiyar, R.E. Cohen, Effect of Substrate Temperature on Structural and Magnetic Properties of c-axis Ori-ented Spinel Ferrite Ni0. 65Zn0. 35Fe2O4 (NZFO) Thin Films, (2018). X. Liu, J. Hao, H. Yang, X. Lin, X. Zeng, Substrate temperature effect on the microstructure and properties of (Si, Al)/aC: H films prepared through magnetron sputtering deposition, J. Nanomater. 2015 (2015) 1. H. Ahn, J. Seo, H. Shin, Y. Um, Substrate effects on the structural properties of Cd1xMnxTe thin films grown via magnetron Co-sputtering, J. Korean Phys. Soc. 67 (4) (2015) 668–671. N. Ghobadi, M. Ganji, C. Luna, A. Arman, A. Ahmadpourian, Effects of substrate temperature on the properties of sputtered TiN thin films, J. Mater. Sci. Mater. Electron. 27 (3) (2016) 2800–2808.