- Email: [email protected]
The surface morphology research of the BGaN thin films deposited by thermionic vacuum arc
Accepted Manuscript The surface morphology research of the BGaN thin films deposited by thermionic vacuum arc Soner Özen, Suat Pat, Volkan Şenay, Şadan Korkmaz PII:
S0042-207X(16)30639-X
DOI:
10.1016/j.vacuum.2016.10.033
Reference:
VAC 7180
To appear in:
Vacuum
Received Date: 1 October 2016 Accepted Date: 26 October 2016
Please cite this article as: Özen S, Pat S, Şenay V, Korkmaz Ş, The surface morphology research of the BGaN thin films deposited by thermionic vacuum arc, Vaccum (2016), doi: 10.1016/ j.vacuum.2016.10.033. This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
ACCEPTED MANUSCRIPT
The Surface Morphology Research of the BGaN Thin Films Deposited by Thermionic Vacuum Arc
1
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Soner Özen1, Suat Pat1, Volkan Şenay2, Şadan Korkmaz1 Department of Physics, Eskişehir Osmangazi University Meşelik Campus, 26480, Turkey 2
Primary Science Education Department, Bayburt University, 69000, Turkey
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Corresponding author’s email: [email protected]
Abstract
In this paper, BGaN thin films with two different thicknesses were deposited on two different substrates and their surface morphologies were investigated. The amorphous glass and semicrystalline polyethylene terephthalate substrates were selected. At the same time, two
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different deposition angles are selected with a view to the effect of deposition angle on surface morphology. The surface and optical properties were determined by using X-ray diffractometer (XRD), atomic force microscope (AFM), spectroscopic ellipsometry (SE) and
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optical interferometer. The thicknesses of thin films on substrates are about 30 nm and 40 nm. According to the atomic force microscope images, small-dimensional grains observed on
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relatively large grains. The roughness values of the thin films on the polyethylene terephthalate substrate are lower than on the glass substrate. Keywords: GaN thin film; surface properties; XRD; refractive index; thermionic vacuum arc
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1. Introduction: Gallium nitride based semiconductor thin film growth techniques have been intensely researched for the last 25 years [1-9]. Thermionic vacuum arc (TVA) technique which
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deposition mechanism for gallium nitride based solid-state applications was used for BGaN thin film deposition. The deposition and growth of III nitride compounds at high temperatures includes a number of challenges in point of substrate selection [10, 11]. TVA technique offer
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possibility thin film growth on all types of substrate [12-17].
The main aim of this study is to investigate the surface morphologies of the BGaN thin films
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deposited on two different substrates. The novelty of the study is that BGaN thin films were deposited on different substrates by using TVA technique for the first time. The BGaN materials are interesting for the wide band gap engineering [18-20]. The wide band gap engineering provides control of band gap energy by changing the composition of an alloy for
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applications such as light emitting diode (LED), laser diode (LD) and sensor etc. The band gap energy increases by the increasing boron composition of BGaN alloy [21-23]. BGaN layers can be used as semi-insulating buffer layer [24-26]. The BGaN semi-insulating layers
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are used to provide highly electrical resistivity. The electrical resistivity increases by the increasing boron composition of BGaN alloy [24]. The highly resistant BGaN layers can play
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a significant role in high electron mobility transistor (HEMT) design [27, 28]. The model HEMT structure can be formed of two distinct semiconductor layers. The band gap difference results in the formation of conduction and valence band discontinuities at the layer interface or heterojunction creating a quantum well in the conduction band.
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2. Experimental Details: In this research, the investigated BGaN thin films were coated on two amorphous glasses (G1, G2) and two semi-crystalline polyethylene terephthalate (P1, P2) substrates by using the TVA
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technique. Substrates of the G1, G2, P1, and P2 samples were located at a distance of 90 mm, 94 mm, 90 mm, and 94 mm above the anode, respectively. The angles between substrates and anode electrode were 6 degrees for G1, 20 degrees for G2, 6 degrees for P1, and 20 degrees
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for P2. The distance between the anode and the cathode electrodes was d=4 mm. The cathode was made from a tungsten wire with a diameter of 1 mm. The boron piece (Alfa Aesar,
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99.95%) and gallium nitride powder (Alfa Aesar, 99.99%) were placed on the anode electrode in tungsten crucible. Contrary to other vacuum techniques, used anode materials do not need special shapes like granule, target, rod, etc. The vacuum was obtained by a coupled pumping down system with a mechanical and a diffusion pump, ensuring an end pressure in the vessel close to 10-6 Torr. The coating process were performed in 2 × 10− 5 Torr. The filament heating
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current was 18 A. The voltage applied to the space between anode and cathode was 200 V. The applied voltage was suddenly dropped to 0 V and the discharge current increase to 600 mA from 0 A. The produced plasma was localized around the electrodes. The deposition
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Figure 1.
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process was carried out for 50 seconds. Schematic view of the production system is showed in
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Figure 1. Schematic view of the TVA electrodes arrangement for produced BGaN thin films
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3. Results and Discussion:
The refractive index (n) versus to the wavelength and thicknesses are measured by using Filmetrics F20 device and spectroscopic ellipsometry (SE). The thicknesses of the produced samples were measured as 45 nm for G1 sample, 32 nm for G2 sample, 40 nm for P1 sample,
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and 32 nm for P2 sample, respectively. The differences in the thicknesses have been formed due to the distance between anode and substrate. The values of refractive index (n) with increased wavelength are decreased in accordance with the Cauchy model. It is well known
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that the Cauchy dispersive model is used in spectral regions where thin films are transparent. According to Figure 2(a), the refractive index changed directly proportional to the thickness
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of the produced thin film and substrate. The thickness effect of BGaN thin film on the PET substrate was caused to minimum difference in the refractive index values. The refractive index of produced thin films on the glass substrate showed a pronounced variation. This variation is closely related with packing density of the thin film.
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Figure 2. (a) Refractive index plots of the produced BGaN thin films in the two different analysis methods, (b) Optical band gap energies of the produced BGaN thin films determined by Tauc method
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Figure 2(b) shows the Tauc plot of (αhν)2 vs. hν which gives direct optical band gap energy.
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Tauc method is a simple method to determine direct band gap energy of produced thin film. The optical band gap energy is determined from absorbance spectrum. The direct band gap energy of thin films on glass substrates is approximately 3.75 eV and the direct band gap energy of thin films on PET substrates is approximately 3.9 eV.
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Rigaku MiniFlex 600 XRD with SmartLab goniometer in the 2θ range of 10–80° was used to analyze the crystallographic structures of the BGaN thin films on the transparent substrates. An X-ray diffractometer with Cu-Kα1 radiation (λ=1.5406 A°) as the radiation source was
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used. The XRD spectrum of the produced samples is presented in Figure 3. The X-ray diffraction patterns of the BGaN thin films coated on the glass substrates exhibited single diffraction peak at 43.88°, corresponding to the (113) peak of the GaN structure [29]. The X-
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ray diffraction patterns of the samples coated on the polyethylene terephthalate (PET) substrates exhibited diffraction peaks at 25.82°, 46.48°, 53.1°, 64.58° corresponding to the
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peak of the PET structure [8, 30, 31], and at 44.3° corresponding to the (113) peak of the GaN structure [29, 32]. The GaN peak shifting of the coated on the PET substrate is due to background of the PET substrate. The average nano-crystalline sizes (NCS) were calculated using the Debye-Scherrer formula given below
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NCS = 0.94λ/(βcosθΒ)
(2)
where λ is the X-ray wavelength, θΒ is the Bragg diffraction angle, and β is the full width at half-maximum (FWHM) of the XRD peak appearing at the diffraction angle θΒ. The average
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about 54 nm.
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NCS of G1 and G2 samples are about 89 nm and the average NCS of P1 and P2 samples are
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Figure 3. XRD patterns of the produced BGaN thin films on the transparent substrates
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The 2 µm× 2 µm scale atomic force microscope (AFM) images of the top surface were performed in non-contact mode by using Ambios Q-Scope AFM. Surface morphology and dimensional analysis images of the all produced samples are showed in the Figure 4 and Figure 5. AFM images of produced samples were showed uniform distribution surface with spherical particles. Nano-size patterns are observed on the surfaces of all samples. As results
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of the histogram analyze, the average heights are 12.08 nm for G1 sample, 9.03 nm for G2 sample, 9.6 nm for P1 sample, and 7.3 nm for P2 sample. The mean roughness (Ra) represents the mean value of the surface height relating to a centre plane. The root mean square
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roughness (Rq) is the standard deviation of the surface height within the scanned area. The all roughness values were presented in the Figure 4. The P1 and P2 samples showed smoother
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than G1 and G2 samples. The decrease of Rq value is directly correlated to the decrease of lattice mismatch between produced thin film and substrate [26].
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and (d) P2 sample
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Figure 4. The 3D AFM images of the produced (a) G1 sample, (b) G2 sample, (c) P1 sample,
Figure 5. Dimensional analysis graphic of the produced (a) G1 sample, (b) G2 sample, (c) P1 sample, and (d) P2 sample 8
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The AFM images revealed presence of relatively small grains growth on top of the large main grains. According to dimensional analysis results, 83 nm grains observed on the 267 nm
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grains for G1 sample; 100 nm grains observed on the 210 nm grains for G2 sample; 70 nm grains observed on the 123 nm grains for P1 sample; 43 nm grains observed on the 86 nm grains for P2 sample. It is seen that the grain sizes decreased with increasing of the angle
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between substrates and anode electrode. Also, BGaN thin films on the PET substrate were smaller grain size and more smooth than on the glass substrate.
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4. Conclusion:
The BGaN thin films were deposited on amorphous and semi-crystalline substrates by means of the TVA technique in just 50 s. The crystalline structure of the produced BGaN thin films are in the (113) orientation. The AFM dimensional analysis showed the distribution of
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spherical grains over the total surface of the substrates with compact morphology and well defined grains. According to produced samples on the glass substrates, the BGaN thin films on the PET substrates were smaller nano sizes, and low roughness. The band gap values are
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suitable for thin films except G1 sample. Acknowledgement
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The authors would like to thank support by the Scientific Research Projects Commission of Eskişehir Osmangazi University (project number: 201619A218). References
[1] Denbaars S. Gallium-nitride-based materials for blue to ultraviolet optoelectronics devices. Proceedings of the IEEE. 1997;85:1740-9.
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[2] Lei T, Fanciulli M, Molnar R, Moustakas T, Graham R, Scanlon J. Epitaxial growth of zinc blende and wurtzitic gallium nitride thin films on (001) silicon. Appl Phys Lett. 1991;59:944-6.
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[3] Chen C-C, Yeh C-C, Chen C-H, Yu M-Y, Liu H-L, Wu J-J, et al. Catalytic growth and characterization of gallium nitride nanowires. J Am Chem Soc. 2001;123:2791-8.
[4] Xiao R, Liao H, Cue N, Sun X, Kwok H. Growth of c‐axis oriented gallium nitride thin
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films on an amorphous substrate by the liquid‐target pulsed laser deposition technique. J Appl Phys. 1996;80:4226-8.
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[5] Fong C, Ng S, Yam F, HASSAN H, Hassan Z. Growth of Gallium Nitride Thin Film with the Aid of Polymethyl Methacrylate. Sains Malaysiana. 2014;43:1943-9. [6] Fong CY, Ng SS, Yam FK, Abu Hassan H, Hassan Z. Spin Coating Deposition of cOriented Wurtzite Gallium Nitride Thin Film. Applied Mechanics and Materials: Trans Tech Publ; 2015. p. 70-5.
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[7] Umeda S, Kato T, Kitano T, Kondo T, Matsubara H, Kamiyama S, et al. Metal–Organic Vapor Phase Epitaxy Growth of Embedded Gallium Nitride Nanocolumn for Reduction in Dislocation Density. Jpn J Appl Phys. 2013;52:08JE23.
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[8] Pat S, Korkmaz Ş, Özen S, Şenay V. GaN thin film deposition on glass and PET substrates by thermionic vacuum arc (TVA). Mater Chem Phys. 2015;159:1-5.
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[9] Chopra KN. A Technical Note on Gallium Nitride Technology and short Qualitative Review of its Novel Applications. Lat Am J Phys Educ Vol. 2014;8:541. [10] Ponce F, Major Jr J, Plano W, Welch D. Crystalline structure of AlGaN epitaxy on sapphire using AlN buffer layers. Appl Phys Lett. 1994;65:2302-4. [11] Puchinger M, Wagner T, Rodewald D, Bill J, Aldinger F, Lange FF. Gallium nitride thin layers via a liquid precursor route. J Cryst Growth. 2000;208:153-9.
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[12] Özen S, Şenay V, Pat S, Korkmaz Ş. Investigation on the morphology and surface free energy of the AlGaN thin film. J Alloy Compd. 2015;653:162-7. [13] Özen S, Pat S, Şenay V, Korkmaz Ş, Geçici B. Some Physical Properties of the SiGe
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Thin Film Coatings by Thermionic Vacuum Arc (TVA). J Nanoelectron Optoe. 2015;10:5660.
[14] Vladoiu R, Ciupina V, Surdu-Bob C, Lungu C, Janik J, Skalny J, et al. Properties of the
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carbon thin films deposited by thermionic vacuum arc. J Optoelectron Adv M. 2007;9:862.
[15] Kuncser V, Mustata I, Lungu C, Lungu A, Zaroschi V, Keune W, et al. Fe–Cu granular
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thin films with giant magnetoresistance by thermionic vacuum arc method: preparation and structural characterization. Surface and Coatings Technology. 2005;200:980-3. [16] Şenay V, Özen S, Pat S, Geçici B, Korkmaz Ş. A new method for titania thin film production Thermionic vacuum arc method. Journal of Thermoplastic Composite Materials. 2015:0892705715614060.
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[17] Özen S, Şenay V, Pat S, Korkmaz Ş. The influence of voltage applied between the electrodes on optical and morphological properties of the InGaN thin films grown by thermionic vacuum arc. Scanning. 2015;38:14-20.
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[18] Orsal G, Maloufi N, Gautier S, Alnot M, Sirenko A, Bouchaour M, et al. Effect of boron incorporation on growth behavior of BGaN/GaN by MOVPE. J Cryst Growth.
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2008;310:5058-62.
[19] Salvestrini J, Ahaitouf A, Srour H, Gautier S, Moudakir T, Assouar B, et al. Tuning of internal gain, dark current and cutoff wavelength of UV photodetectors using quasi-alloy of BGaN-GaN and BGaN-AlN superlattices. SPIE OPTO: International Society for Optics and Photonics; 2012. p. 82682S-S-10. [20] Teles L, Scolfaro L, Leite J, Furthmüller J, Bechstedt F. Spinodal decomposition in BxGa1− xN and BxAl1− xN alloys. Appl Phys Lett. 2002;80:1177-9. 11
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[21] Honda T, Shibata M, Kurimoto M, Tsubamoto M, Yamamoto J, Kawanishi H. Band-gap energy and effective mass of BGaN. Jpn J Appl Phys. 2000;39:2389. [22] Ougazzaden A, Gautier S, Sartel C, Maloufi N, Martin J, Jomard F. BGaN materials on
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GaN/sapphire substrate by MOVPE using N 2 carrier gas. J Cryst Growth. 2007;298:316-9. [23] Sakai S, Ueta Y, Terauchi Y. Band gap energy and band lineup of III-V alloy semiconductors incorporating nitrogen and boron. Jpn J Appl Phys. 1993;32:4413.
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[24] Baghdadli T, Hamady S, Gautier S, Moudakir T, Benyoucef B, Ougazzaden A. Electrical and structural characterizations of BGaN thin films grown by metal‐organic vapor‐phase
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epitaxy. physica status solidi (c). 2009;6:S1029-S32.
[25] Akasaka T, Makimoto T. BGaN micro-islands as novel buffers for GaN hetero-epitaxy. Jpn J Appl Phys. 2005;44:L1506.
[26] Ougazzaden A, Gautier S, Aggerstam T, Martin J, Bouchaour M, Baghdadli T, et al. Progress on new wide bandgap materials BGaN, BGaAlN and their potential applications.
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Integrated Optoelectronic Devices 2007: International Society for Optics and Photonics; 2007. p. 64791G-G-7.
[27] Ravindran V, Boucherit M, Soltani A, Gautier S, Moudakir T, Dickerson J, et al. Dual-
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purpose BGaN layers on performance of nitride-based high electron mobility transistors. Appl Phys Lett. 2012;100:243503.
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[28] Dickerson JR, Ravindran V, Moudakir T, Gautier S, Voss PL, Ougazzaden A. A study of BGaN back-barriers for AlGaN/GaN HEMTs. The European Physical Journal Applied Physics. 2012;60:30101.
[29] Choi SH, King GC, Park Y. Epitaxial growth of cubic crystalline semiconductor alloys on basal plane of trigonal or hexagonal crystal. Google Patents; 2009. [30] Mark JE. Physical properties of polymers handbook: Springer; 1996.
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[31] Ong W, Low Q, Huang W, Van Kan J, Ho G. Patterned growth of vertically-aligned ZnO nanorods on a flexible platform for feasible transparent and conformable electronics applications. J Mater Chem. 2012;22:8518-24.
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[32] Özen S, Şenay V, Pat S, Korkmaz Ş. Morphological and optical comparison of the Si doped GaN thin film deposited onto the transparent substrates. Materials Research Express.
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2016;3:045012.
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Highlights Nano structured BGaN deposited,
The BGaN thin films are produced in a very short period of time,
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The BGaN layers have low roughness.
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The effect of deposition angle on surface morphology was observed,
S0042-207X(16)30639-X
DOI:
10.1016/j.vacuum.2016.10.033
Reference:
VAC 7180
To appear in:
Vacuum
Received Date: 1 October 2016 Accepted Date: 26 October 2016
Please cite this article as: Özen S, Pat S, Şenay V, Korkmaz Ş, The surface morphology research of the BGaN thin films deposited by thermionic vacuum arc, Vaccum (2016), doi: 10.1016/ j.vacuum.2016.10.033. This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
ACCEPTED MANUSCRIPT
The Surface Morphology Research of the BGaN Thin Films Deposited by Thermionic Vacuum Arc
1
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Soner Özen1, Suat Pat1, Volkan Şenay2, Şadan Korkmaz1 Department of Physics, Eskişehir Osmangazi University Meşelik Campus, 26480, Turkey 2
Primary Science Education Department, Bayburt University, 69000, Turkey
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Corresponding author’s email: [email protected]
Abstract
In this paper, BGaN thin films with two different thicknesses were deposited on two different substrates and their surface morphologies were investigated. The amorphous glass and semicrystalline polyethylene terephthalate substrates were selected. At the same time, two
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different deposition angles are selected with a view to the effect of deposition angle on surface morphology. The surface and optical properties were determined by using X-ray diffractometer (XRD), atomic force microscope (AFM), spectroscopic ellipsometry (SE) and
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optical interferometer. The thicknesses of thin films on substrates are about 30 nm and 40 nm. According to the atomic force microscope images, small-dimensional grains observed on
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relatively large grains. The roughness values of the thin films on the polyethylene terephthalate substrate are lower than on the glass substrate. Keywords: GaN thin film; surface properties; XRD; refractive index; thermionic vacuum arc
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1. Introduction: Gallium nitride based semiconductor thin film growth techniques have been intensely researched for the last 25 years [1-9]. Thermionic vacuum arc (TVA) technique which
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deposition mechanism for gallium nitride based solid-state applications was used for BGaN thin film deposition. The deposition and growth of III nitride compounds at high temperatures includes a number of challenges in point of substrate selection [10, 11]. TVA technique offer
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possibility thin film growth on all types of substrate [12-17].
The main aim of this study is to investigate the surface morphologies of the BGaN thin films
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deposited on two different substrates. The novelty of the study is that BGaN thin films were deposited on different substrates by using TVA technique for the first time. The BGaN materials are interesting for the wide band gap engineering [18-20]. The wide band gap engineering provides control of band gap energy by changing the composition of an alloy for
TE D
applications such as light emitting diode (LED), laser diode (LD) and sensor etc. The band gap energy increases by the increasing boron composition of BGaN alloy [21-23]. BGaN layers can be used as semi-insulating buffer layer [24-26]. The BGaN semi-insulating layers
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are used to provide highly electrical resistivity. The electrical resistivity increases by the increasing boron composition of BGaN alloy [24]. The highly resistant BGaN layers can play
AC C
a significant role in high electron mobility transistor (HEMT) design [27, 28]. The model HEMT structure can be formed of two distinct semiconductor layers. The band gap difference results in the formation of conduction and valence band discontinuities at the layer interface or heterojunction creating a quantum well in the conduction band.
2
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2. Experimental Details: In this research, the investigated BGaN thin films were coated on two amorphous glasses (G1, G2) and two semi-crystalline polyethylene terephthalate (P1, P2) substrates by using the TVA
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technique. Substrates of the G1, G2, P1, and P2 samples were located at a distance of 90 mm, 94 mm, 90 mm, and 94 mm above the anode, respectively. The angles between substrates and anode electrode were 6 degrees for G1, 20 degrees for G2, 6 degrees for P1, and 20 degrees
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for P2. The distance between the anode and the cathode electrodes was d=4 mm. The cathode was made from a tungsten wire with a diameter of 1 mm. The boron piece (Alfa Aesar,
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99.95%) and gallium nitride powder (Alfa Aesar, 99.99%) were placed on the anode electrode in tungsten crucible. Contrary to other vacuum techniques, used anode materials do not need special shapes like granule, target, rod, etc. The vacuum was obtained by a coupled pumping down system with a mechanical and a diffusion pump, ensuring an end pressure in the vessel close to 10-6 Torr. The coating process were performed in 2 × 10− 5 Torr. The filament heating
TE D
current was 18 A. The voltage applied to the space between anode and cathode was 200 V. The applied voltage was suddenly dropped to 0 V and the discharge current increase to 600 mA from 0 A. The produced plasma was localized around the electrodes. The deposition
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Figure 1.
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process was carried out for 50 seconds. Schematic view of the production system is showed in
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Figure 1. Schematic view of the TVA electrodes arrangement for produced BGaN thin films
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3. Results and Discussion:
The refractive index (n) versus to the wavelength and thicknesses are measured by using Filmetrics F20 device and spectroscopic ellipsometry (SE). The thicknesses of the produced samples were measured as 45 nm for G1 sample, 32 nm for G2 sample, 40 nm for P1 sample,
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and 32 nm for P2 sample, respectively. The differences in the thicknesses have been formed due to the distance between anode and substrate. The values of refractive index (n) with increased wavelength are decreased in accordance with the Cauchy model. It is well known
EP
that the Cauchy dispersive model is used in spectral regions where thin films are transparent. According to Figure 2(a), the refractive index changed directly proportional to the thickness
AC C
of the produced thin film and substrate. The thickness effect of BGaN thin film on the PET substrate was caused to minimum difference in the refractive index values. The refractive index of produced thin films on the glass substrate showed a pronounced variation. This variation is closely related with packing density of the thin film.
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Figure 2. (a) Refractive index plots of the produced BGaN thin films in the two different analysis methods, (b) Optical band gap energies of the produced BGaN thin films determined by Tauc method
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Figure 2(b) shows the Tauc plot of (αhν)2 vs. hν which gives direct optical band gap energy.
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Tauc method is a simple method to determine direct band gap energy of produced thin film. The optical band gap energy is determined from absorbance spectrum. The direct band gap energy of thin films on glass substrates is approximately 3.75 eV and the direct band gap energy of thin films on PET substrates is approximately 3.9 eV.
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Rigaku MiniFlex 600 XRD with SmartLab goniometer in the 2θ range of 10–80° was used to analyze the crystallographic structures of the BGaN thin films on the transparent substrates. An X-ray diffractometer with Cu-Kα1 radiation (λ=1.5406 A°) as the radiation source was
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used. The XRD spectrum of the produced samples is presented in Figure 3. The X-ray diffraction patterns of the BGaN thin films coated on the glass substrates exhibited single diffraction peak at 43.88°, corresponding to the (113) peak of the GaN structure [29]. The X-
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ray diffraction patterns of the samples coated on the polyethylene terephthalate (PET) substrates exhibited diffraction peaks at 25.82°, 46.48°, 53.1°, 64.58° corresponding to the
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peak of the PET structure [8, 30, 31], and at 44.3° corresponding to the (113) peak of the GaN structure [29, 32]. The GaN peak shifting of the coated on the PET substrate is due to background of the PET substrate. The average nano-crystalline sizes (NCS) were calculated using the Debye-Scherrer formula given below
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NCS = 0.94λ/(βcosθΒ)
(2)
where λ is the X-ray wavelength, θΒ is the Bragg diffraction angle, and β is the full width at half-maximum (FWHM) of the XRD peak appearing at the diffraction angle θΒ. The average
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about 54 nm.
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NCS of G1 and G2 samples are about 89 nm and the average NCS of P1 and P2 samples are
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Figure 3. XRD patterns of the produced BGaN thin films on the transparent substrates
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The 2 µm× 2 µm scale atomic force microscope (AFM) images of the top surface were performed in non-contact mode by using Ambios Q-Scope AFM. Surface morphology and dimensional analysis images of the all produced samples are showed in the Figure 4 and Figure 5. AFM images of produced samples were showed uniform distribution surface with spherical particles. Nano-size patterns are observed on the surfaces of all samples. As results
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of the histogram analyze, the average heights are 12.08 nm for G1 sample, 9.03 nm for G2 sample, 9.6 nm for P1 sample, and 7.3 nm for P2 sample. The mean roughness (Ra) represents the mean value of the surface height relating to a centre plane. The root mean square
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roughness (Rq) is the standard deviation of the surface height within the scanned area. The all roughness values were presented in the Figure 4. The P1 and P2 samples showed smoother
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than G1 and G2 samples. The decrease of Rq value is directly correlated to the decrease of lattice mismatch between produced thin film and substrate [26].
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and (d) P2 sample
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Figure 4. The 3D AFM images of the produced (a) G1 sample, (b) G2 sample, (c) P1 sample,
Figure 5. Dimensional analysis graphic of the produced (a) G1 sample, (b) G2 sample, (c) P1 sample, and (d) P2 sample 8
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The AFM images revealed presence of relatively small grains growth on top of the large main grains. According to dimensional analysis results, 83 nm grains observed on the 267 nm
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grains for G1 sample; 100 nm grains observed on the 210 nm grains for G2 sample; 70 nm grains observed on the 123 nm grains for P1 sample; 43 nm grains observed on the 86 nm grains for P2 sample. It is seen that the grain sizes decreased with increasing of the angle
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between substrates and anode electrode. Also, BGaN thin films on the PET substrate were smaller grain size and more smooth than on the glass substrate.
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4. Conclusion:
The BGaN thin films were deposited on amorphous and semi-crystalline substrates by means of the TVA technique in just 50 s. The crystalline structure of the produced BGaN thin films are in the (113) orientation. The AFM dimensional analysis showed the distribution of
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spherical grains over the total surface of the substrates with compact morphology and well defined grains. According to produced samples on the glass substrates, the BGaN thin films on the PET substrates were smaller nano sizes, and low roughness. The band gap values are
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suitable for thin films except G1 sample. Acknowledgement
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The authors would like to thank support by the Scientific Research Projects Commission of Eskişehir Osmangazi University (project number: 201619A218). References
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2016;3:045012.
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Highlights Nano structured BGaN deposited,
The BGaN thin films are produced in a very short period of time,
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The BGaN layers have low roughness.
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The effect of deposition angle on surface morphology was observed,