New issue of GaN nanoparticles solar cell

Accepted Manuscript New Issue of GaN Nanoparticles Solar Cell M.A. Qaeed, K. Ibrahim, K.M.A. Saron, M.S. Mukhlif, A. Ismail, Nezar.G. Elfadill, Khaled. M. Chahrour, Q.N. Abdullah, K.S.A. Aldroobi PII:

S1567-1739(15)00024-3

DOI:

10.1016/j.cap.2015.02.001

Reference:

CAP 3857

To appear in:

Current Applied Physics

Received Date: 6 October 2014 Revised Date:

1 February 2015

Accepted Date: 2 February 2015

Please cite this article as: M.A. Qaeed, K. Ibrahim, K.M.A. Saron, M.S. Mukhlif, A. Ismail, N.G. Elfadill, K.M. Chahrour, Q.N. Abdullah, K.S.A. Aldroobi, New Issue of GaN Nanoparticles Solar Cell, Current Applied Physics (2015), doi: 10.1016/j.cap.2015.02.001. 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

New Issue of GaN Nanoparticles Solar Cell M. A. Qaeed1,2, K. Ibrahim1, K.M.A.Saron3, M. S. Mukhlif1, A.Ismail1 Nezar.G. Elfadill1, Khaled. M. Chahrour1, Q.N.Abdullah, and K.S.A. Aldroobi2 1

RI PT

Nano-Optoelectronics Research and Technology Laboratory, School of Physics, Universiti Sains Malaysia, Penang, Malaysia 2 Physics Department, Faculty of Education, Hodeidah University, Al-Hodeidah, Yemen 3

SC

AL-Ghad International Collages for Applied Medical Sciences, Riyadh 2174, Saudi Arabia

.*Corresponding author: Tel: +60 1131321908 ; fax: +60 46579150

M AN U

E-mail address: [email protected] (M. A. Qaeed) Abstract

This study involves the synthesis of gallium nitride (GaN) nanoparticles(NPs) under different low temperatures using a simple chemical method. The nanoparticles are

TE D

spin coated on Si substrate to fabricate the solar cell. The FESEM images obtained indicate the presence of cubic GaN nanoparticle with average diameter of 50nm synthesized at at 90°C. The spin coating technique deposited n-GaN NPs/Si(111)

EP

produced a heterojunction solar cell with fill factor of 0.56 and conversion efficiency of 2.06%. Based on these results, this study proposes a novel low cost technique for

AC C

the fabrication of GaN NPs solar cells. Keywords: Nanoparticles; Chemical Method; Optical properties;

Nitrides; Low

Temperature; Solar Cell 1. Introduction

Gallium nitride (GaN) nanoparticles (NPs) have been recognized as the most suitable material for optoelectronic and electronic applications [1-6]. High purity GaN nanoparticles are crucial for fabricating devices because of their applicability as active regions in the fabrication of color tunable light emitting diodes and laser diodes due to 1

ACCEPTED MANUSCRIPT their direct wide band gaps[7]. In addition, features such as high breakdown field and carrier mobility, high temperature, and chemical stability make them valuable materials for fabricating devices of short-wavelength electroluminescence due to their relative stability even under harsh environments and better chemical stability. These

RI PT

properties make it suitable for many applications such as optoelectronic and photovoltaic energy conversion solar cells [8-10]. [8-10]. Cubic GaN of a zinc blende structure is of great interest because it is predicted to possess superior electronic

SC

properties for device applications such as solar due to have high p-type conductivity in c–GaN, high electron mobility, lower phonon scattering and higher saturated

M AN U

electron drift velocity than wurtzite[11]. It is also predicted theoretically that the optical gain in c-GaN quantum wells might be higher than that in hexagonal GaN wells.

GaN NPs have been synthesized using different methods [12-21], which

TE D

include pyrolysis at high temperature, formation of colloidal GaN quantum dot technique, chemical and combustion methods [22-27]. However, most of these

EP

methods require high temperature and expensive chemicals for preparation. Therefore, there is the need for an economical method as a viable alternative to the

AC C

conventional methods for the large scale synthesis of GaN NPs at low temperature, which can be applied in solar cell fabrication. To achieve this objective, GaN NPs were synthesized at 90°C under atmospheric pressure. This method was found to be highly suitable for large scale production of nanoparticles. Furthermore, the chemicals used in this process are relatively cheaper than those currently being utilized in solar cells fabrication[28] 2. Experimental Details

2

ACCEPTED MANUSCRIPT 2.1 Synthesis of GaN Nanoparticles The materials used for the synthesis were purchased from Acros Organics, and they include Gallium (III) acetylacetonate (Ga(acac)3; 99.99%) was procured from Sigma-Aldrich, while Methanol, Oleylamine (C18-content 80–90%), Toluene,

RI PT

HNO3 (34.5%) and NH4OH (28-30%). To prepare the GaN nanoparticles, 200mg of Ga(acac)3 was mixed in 10ml of Oleylamine under ambient conditions. The mixture was poured into a rotary evaporator flask placed in water bath of 90°C. 10ml of

SC

HNO3, and 20ml of NH4OH was subsequently added to the solution. The solution was stirred for 12 hours to dissolve the mixture completely[29, 30] . Afterwards, the

M AN U

solutions were spin coated on a Silicon substrate. Fig.1(a,b) shows the GaN NPs before and after the centrifugation process. The reactions can be elucidated from the following formulas:



TE D

3() + 11   3(  ) + 3() + 2 ↑ +4 (1) 



NH4OH   +  !   +  (2) 



(  ) + 3  !  ( ) +3  ↑ +   ↑ (3) 

AC C

EP

( ) +   3 +  (4)

3

ACCEPTED MANUSCRIPT Fig.1. (a) GaN nanoparticles after stirring in the rotary evaporator.(b) GaN nanoparticles after the centrifugation process collected with acetone. The thickness of synthesized GaN nanoparticle films on Si substrate was calculated using Filmmetrics (model: Filmetrics F20) to be about 1µm. The films

RI PT

were characterized using high resolution field emission scanning electron microscopy (FESEM), energy dispersive X-ray spectroscopy (EDX: FEI, Nova Nano SEM model number 450) and X-ray diffraction (XRD) with Cu Kα1radiation (λ= 1.5406 Å)

SC

source. 2.2 Fabrication of Solar Cell

M AN U

The GaN nanoparticles solar cell designed as shown in Fig.4d were fabricated on an absorber layer p- type Si (111) using the spin coating technique. The solar cell window comprises 1µm thick GaN NPs with a carrier concentration of 2×1017cm-3 and resistivity of 0.99 (Ohm-cm). The Al coating was applied on the cell back and

TE D

through the mask on the front contact using a small size brush of 0.32mm finger length and 0.55mm finger spacing. The cell was then baked at 80°C for 20 minutes. These steps were taken to replicate an actual fabrication of solar cell at low

EP

temperature. The I-V characteristics of the cell were measured using a Keithely 2400

AC C

electrometer under simulated sunlight of 30 mW/cm2.

3. Result and discussion 3.1 XRD Analysis

The XRD patterns of GaN nanoparticles spin synthesized at 60°C, 75°C and 90˚C is shown in Fig. 2. The distinct peak observed at 2θ = 28.23 corresponds to the Si substrate[31]. Ga2O3 dominates in the sample synthesized at 60˚C, as shown by the peaks reflected from (-110), (-202), (-111), (111), (-311) and (-603) planes of 4

ACCEPTED MANUSCRIPT Ga2O3[32, 33]. This indicates that this reaction temperature is not enough to produce GaN. For the sample synthesized at 75˚C, Ga2O3 peaks were reflected from (-110), (111) and (-311) planes. However, only the peak reflected from (100) plane at 32.22 indicates GaN because at this temperature (75˚C), some peaks of Ga2O3 that appeared

RI PT

in the low temperature (60˚C) are concealed. The sample synthesized at 90˚C exhibits h-GaN nanoparticles peaks at 2θ= 32.3 and 57.9 which are reflected from (100) and (110) planes, respectively, and two peaks of c-GaN at 2θ = 39.1° and 45.48°

AC C

EP

TE D

M AN U

SC

corresponding to the cubic phase reflected from (111) and (200)[34-36].

Fig.2. XRD analysis of GaN NPs for three samples synthesized under(60, 75, and 90˚C) for 12 hours 5

ACCEPTED MANUSCRIPT In Fig.(2) the broad of the h-GaN (1000) peak can be attributed to a reduction in particle size and defect in crystal. Meanwhile, point defects introduce strain which depends on the size and type of the defect (vacancies and substitutional impurities) [11]. In addition, the present of cubic phase can also affect the peak intensity and the

RI PT

sharpness of the hexagonal phase.

The XRD measurement confirms the sample is characterized by cubic phase crystallinity. This indicates that GaN can be synthesized at 90˚C by enabling the

SC

Olaylamine solvent to dislocate the acetylacetonate group causing the Nitrogen atom

M AN U

to be detached (free) and subsequently bond with the gallium atom as shown in furmulas 1,2 and 3. The phase transformation observed at higher temperatures may be due to thermodynamic stabilization. The mechanisms responsible for the formation of the metastable nature of zinc-blende GaN phase at higher temperature is proposed, in which the impact of the ionic chemical reaction species impinging on the surface of

TE D

growing nanoparticles plays a key role in phase transition the of GaN [11, 37]. The latice parameters of a =3.18 Ao and c = 5.166A° for hexagonal phase are

EP

consistent with the standard values. The crystal grain size (Dp) of the GaN

AC C

nanoparticles was calculated from the XRD peaks using Scherrer’s formula (4)[31]. %.'(

"# = )*+,-

(4)

The average diameter of cubic and hexagonal structure of the GaN NPs are

outlined in Table(1).

Table 1: The nanoparticle size of h-GaN NPs

Phase

FWHM

hexagonal

2Theta (degree) 32.3

0.402

NP size(nm) 71.05

cubic cubic hexagonal

39.1 45.48 57.9

0.434 0.595 0.405

54.70 34.54 40.53

6

Average Size(nm) 50.20

ACCEPTED MANUSCRIPT The formation of nanoparticles which shaped cubic GaN was attributed to a sudden phase transition where the size of nanoparticles decreases. On the other hand, low growth temperature led to sufficient accumulation of Ga and atomic stacking faults in the wurtzite which has effect on the surface reconstruction of h-GaN [37, 38].

RI PT

With increasing temperatures crystal structure in GaN, NP changes from thermodynamically stable wurtzite to metastable zinc blende. The phase transformation observed at higher temperatures may be due to the surface ordering

FESEM and TEM analysis

M AN U

3.2

SC

which changed via reconstruction[39].

The FESEM images (Fig.3,90°C) depict the surface morphology of the cubic GaN nanoparticles spin coated on Si substrate of less than 500nm particle size. A closer view of the GaN nanoparticles showing distinct cubic shaped crystals of less than 200nm particle size is observed in Fig. 3(90°C,c). The EDX analysis

TE D

(Fig.3,90°C,b) shows Oxygen composition of 41% for the sample synthesized at 60˚C, which decreases in the second sample synthesized at 75°C and almost absent in

EP

the third sample produced at 90°C. Thus, it can be deduced that the oxygen composition decreases with increase in temperature while the surface morphology

AC C

becomes enhanced as shown in the FESEM micrographs. Also, this indicates that the third sample is like to be free of any impurities. Fig.3(90°C,d) shows a unimodal particle size distribution of nanoparticles on the Si surface. TEM was performed to obtain a submicroscopic image of the nanoparticles. of

less than 200nm. The cubic nature of the sample is clearly observable in the TEM images (Fig.3. 90°C,e). However, there are possible hexagonal crystals present in the sample as indicated by the hexagonal peaks in the XRD measurement. The TEM images support the FESEM images of cubic GaN. The FESEM with EDX and TEM 7

ACCEPTED MANUSCRIPT also validate the chemical purity of the GaN NPs earlier shown with the XRD data. Therefore, it can be inferred that temperature and the presence of Oleylamine are key

AC C

EP

TE D

M AN U

SC

RI PT

factors in the synthesis GaN NPs.

Fig. 3.FESEM and EDX measurements of the samples GaN NPs synthesized under (60, 90°C for 12 hours (a,b,c,d and e) are FESEM, under 500nm, EDX, FESEM under 200nm, the nanoparticles distribution, and TEM of the sample synthesized under 90°C respectively. 8

ACCEPTED MANUSCRIPT

3.3

Hetero-junction solar cell fabrication The Gan NPs were spin coated on 1 cm2 Si substrate to create the solar cell. A

hetero-junction band diagram for n-GaN/p-Si solar cell illustrated in (Fig. 4,b) was

RI PT

constructed based on the assumption that the electron affinities (χ) of Si and GaN were 4.05 eV and 4.2eV respectively[40]. The band gap energies for Si and GaN at room temperature are 1.12 and 3.4 eV, respectively. As shown in the energy band =

χ(GaN) – χ(Si) = 4.2-4.05 =

SC

diagram, the energy barrier ∆EC for an electron is ∆EC

M AN U

0.15eV, and the energy barrier ∆Ev = Eg(GaN) + ∆EC - Eg( Si) = 3.4+0.15 -1.12 = 2.43eV. Thus, there are two energy band offsets as a result of the different electron affinities and band gaps between Si and GaN.

The fabricated solar cell design is shown in (Fig.4.d). The I–V plot of solar

TE D

cell in the dark and under light is illustrated in Fig.4a and 4c, respectively. The fill factor (FF) and efficiency (η) were subsequently calculated using the formulae below

AC C

EP

(5,6)[41].

.. =

3=

/0 10 (5) /,* 1+*

/,* 1+* .. (6) 4

The I–V Characteristics of the Al/n-GaN/p-Si/Al films shown in Fig. 4a

signify that good ohmic contacts are formed on both electrodes. These results point out that the rectifying characteristics are attributable to the heterojunction of the nGaN/p-Si solar cell in the dark. The transmitting light passing through the GaN layer is absorbed in the p-Si layer while the resultant electrons and holes drift towards GaN

9

ACCEPTED MANUSCRIPT (negative) side and Si (positive) side, respectively, to produce photocurrent. The spin coating technique was used to deposit n-GaN/Si(111) heterojunction. The gap between nanostructured features, surface irregularities, and variations in thickness (such as nanostructure tapering) of the GaN all contribute to improve the use of GaN

EP

TE D

M AN U

SC

RI PT

nanoparticles as anti-reflection layers.

AC C

Fig.4. (a) I-V characteristics of the fabricated GaN/ Si solar cells in the dark. (b) the energy band diagram of hetero-junction n-GaN/P-Si solar cell the curve of the solar cell under the light, (c) the I-V curve of the solar cell under the light and (d) schematic of the GaN/Si solar cell structure. The synthesized solar cell is depicted in Fig.4(d). The rational value of series

resistance of 0.063 Ohm calculated by linearly fitting the high–voltage part of the curve of current against voltage (Fig. 4a) indicates the synthesized solar cells are of good quality. This value is either attributable to the quality of contact processes or the decrease in the deviation of the solar cell physical configuration [42]. Other values

10

ACCEPTED MANUSCRIPT obtained include: JSC of 2.2 mA/cm2, VOC of 0.50 V, FF of 0.56 and a conversion efficiency of 2.04%, which are well within the range of this report[31] . Table (2): The hetero-junction n-GaN/P-Si solar cell parameters Vmax (V) 0.39

Imax (mA) 1.6

Voc (V) 0.50

FF

η

Rs(Ω)

0.56

2.04

0.063

SC

4. Conclusion

Jsc (mA/cm2) 2.20

RI PT

The parameters Values

This study proposes a novel method for synthesizing GaN nanoparticles at low

M AN U

temperature, to upscale their suitability for industrial scale production of solar cells. To confirm the viability of this technique, Homo-junction solar cells were successfully fabricated. The c-GaN NPs were identified and evaluated using FESEM and XRD. The hetero-junction solar cell GaN NPs exhibited a conversion efficiency

TE D

of 2.04% and fill factor of 0.56. This further affirms the preferential use of GaN nanoparticles in laboratory and industrial-scale fabrication of solar cells. In addition, GaN(NPs) films can effectively be used as texturing layers to reduce the surface

AC C

EP

reflection, particularly within the long wavelength range of 450–750 nm.

5. Acknowledgement

I wish to thank the Ministry of Higher Education, Malaysia for supporting this

work under grant No: 203/PSF/6721001, and also Hodeidah University for awarding the scholarship to assist my pursuit of a PhD. References [1] Z.C. Feng, T.R. Yang, Y.T. Hou, Infrared reflectance analysis of GaN epitaxial layers grown on sapphire and silicon substrates, Mater. Sci. Semicond. Process., 4 (2001) 571-576. 11

ACCEPTED MANUSCRIPT

AC C

EP

TE D

M AN U

SC

RI PT

[2] K.M.A. Saron, M.R. Hashim, M.A. Qaeed, K. Al-heuseen, N.G. Elfadill, The excellent spontaneous ultraviolet emission of GaN nanostructures grown on silicon substrates by thermal vapor deposition, Mater. Sci. Semicond. Process., Process. 29 (2015) 106–111. [3] L. Pang, K. Kim, Improvement of Ohmic contacts to n-type GaN using a Ti/Al multi-layered contact scheme, Mater. Sci. Semicond. Process. [4] M.Z. Mohd Yusoff, Z. Hassan, N.M. Ahmed, H. Abu Hassan, M.J. Abdullah, M. Rashid, pn-Junction photodiode based on GaN grown on Si (111) by plasma-assisted molecular beam epitaxy, Mater. Sci. Semicond. Process., 16 (2013) 1859-1864. [5] A. Pérez-Tomás, A. Fontserè, M.R. Jennings, P.M. Gammon, Modeling the effect of thin gate insulators (SiO2, SiN, Al2O3 and HfO2) on AlGaN/GaN HEMT forward characteristics grown on Si, sapphire and SiC, Mater. Sci. Semicond. Process., 16 (2013) 1336-1345. [6] Q. Hu, T. Wei, R. Duan, J. Yang, Z. Huo, Y. Zeng, S. Xu, Polarity dependent structure and optical properties of freestanding GaN layers grown by hydride vapor phase epitaxy, Mater. Sci. Semicond. Process., 15 (2012) 15-19. [7] B.C. Joshi, M. Mathew, B. Joshi, D. Kumar, C. Dhanavantri, Characterization of GaN/AlGaN epitaxial layers grown by metalorganic chemical vapour deposition for high electron mobility transistor applications, Pramana, 74 (2010) 135-141. [8] Y. Tang, Z. Chen, H. Song, C. Lee, H. Cong, H. Cheng, W. Zhang, I. Bello, S. Lee, Vertically aligned p-type single-crystalline GaN nanorod arrays on n-type Si for heterojunction photovoltaic cells, Nano Lett., 8 (2008) 4191-4195. [9] D.-W. Kang, J.-Y. Kwon, J. Shim, H.-M. Lee, M.-K. Han, Highly conductive GaN anti-reflection layer at transparent conducting oxide/Si interface for silicon thin film solar cells, Sol. Energy Mater. Sol. Cells, 105 (2012) 317-321. [10] P. Kumar, S. Guha, F. Shahedipour-Sandvik, K. Narayan, Hybrid n-GaN and polymer interfaces: Model systems for tunable photodiodes, Org. Electron., 14 (2013) 2818-2825. [11] J.H. Kim, P.H. Holloway, Wurtzite to zinc-blende phase transition in gallium nitride thin films, Appl. Phys. Lett., 84 (2004) 711-713. [12] M.J. Shin, M. Kim, G.S. Lee, H.S. Ahn, S.N. Yi, D.H. Ha, A GaN nanoneedle inorganic/organic heterojunction structure for optoelectronic devices, Mater. Lett., 91 (2013) 191-194. [13] N. Kobayashi, Y. Kobayashi, In-situ optical monitoring of surface morphology and stoichiometry during GaN metal organic vapor phase epitaxy, Appl. Surf. Sci., 159 (2000) 398-404. [14] H. Grahn, Polarization properties of nonpolar GaN films and (In, Ga) N/GaN multiple quantum wells, Phys Status Solidi (b), 241 (2004) 2795-2801. [15] L. Li, L. Liu, L. Wang, D. Li, J. Song, N. Liu, W. Chen, Y. Wang, Z. Yang, X. Hu, The influence of AlN interlayers on the microstructural and electrical properties of p-type AlGaN/GaN superlattices grown on GaN/sapphire templates, Appl. Phys. A, 108 (2012) 857-862. [16] A. Yamada, K. Ho, T. Maruyama, K. Akimoto, Molecular beam epitaxy of GaN on a substrate of MoS2 layered compound, Appl. Phys. A, 69 (1999) 89-92. [17] J. Wang, S. Feng, D. Yu, High-quality GaN nanowires synthesized using a CVD approach, Appl. Phys. A, 75 (2002) 691-693. [18] X. Cai, Y. Wang, Z. Li, X. Lv, J. Zhang, L. Ying, B. Zhang, Improved photovoltaic performance of InGaN/GaN solar cells with optimized transparent current spreading layers, Appl. Phys. A, 111 (2013) 483-486.

12

ACCEPTED MANUSCRIPT

AC C

EP

TE D

M AN U

SC

RI PT

[19] L. Jiang, X. Wang, H. Xiao, Z. Wang, C. Yang, M. Zhang, Properties investigation of GaN films implanted by Sm ions under different implantation and annealing conditions, Appl. Phys. A, 104 (2011) 429-432. [20] J.B. Park, N.-J. Kim, Y.-J. Kim, S.-H. Lee, G.-C. Yi, Metal catalyst-assisted growth of GaN nanowires on graphene films for flexible photocatalyst applications, CAP, 14 (2014) 1437-1442. [21] S.K. Sharma, S. Heo, B. Lee, H. Lee, C. Kim, D.Y. Kim, Influence of growth temperature and post-annealing on an n-ZnO/p-GaN heterojunction diode, CAP. [22] S. Bak, D.-H. Mun, K. Jung, J. Park, H. Bae, I. Lee, J.-S. Ha, T. Jeong, T. Oh, Effect of Al pre-deposition on AlN buffer layer and GaN film grown on Si (111) substrate by MOCVD, Electron Mater Lett, 9 (2013) 367-370. [23] Y.S. Lee, T.H. Seo, A.H. Park, K.J. Lee, S.J. Chung, E.-K. Suh, Influence of controlled growth rate on tilt mosaic microstructures of nonpolar a-plane GaN epilayers grown on r-plane sapphire, Electron Mater Lett, 8 (2012) 335-339. [24] Y.S. Lee, S.J. Chung, E.-K. Suh, Effects of dislocations on the carrier transport and optical properties of GaN films grown with an in-situ SiN x insertion layer, Electron Mater Lett, 8 (2012) 141-146. [25] J.-H. Choi, S.-H. Jang, J.-S. Jang, Electrical, optical, and structural characteristics of ohmic contacts between p-GaN and ITO deposited by DC-and RF-magnetron sputtering, Electron Mater Lett, 9 (2013) 425-428. [26] Y. Lin, Y. Liu, C. Chang, C. Liu, Warpage and stress relaxation of the transferred GaN LED epi-layer on electroplated Cu substrates, Electron Mater Lett, 9 (2013) 441-444. [27] V. Glukhanyuk, H. Przybylińska, A. Kozanecki, W. Jantsch, Optical properties of a single Er center in GaN, Opt. Mater., 28 (2006) 746-749. [28] N. Kaur, M. Singh, D. Pathak, T. Wagner, J. Nunzi, Organic materials for photovoltaic applications: Review and mechanism, Synth. Met., 190 (2014) 20-26. [29] M.A. Qaeed, K. Ibrahim, K.M. Saron, M. Ahmed, N.K. Allam, LowTemperature Solution-Processed Flexible Solar Cells Based on (In, Ga) N Nanocubes, ACS applied materials & interfaces, 6 (2014) 9925-9931. [30] M.A. Qaeed, K. Ibrahim, K.M.A. Saron, Q.N. Abdullah, N. Elfadill, S. Abud, K. Chahrour, The effective role of time in synthesising InN by chemical method at low temperature, J Mater Sci- Mater EL, 25 (2014) 1376-1380. [31] K. Saron, M. Hashim, N.K. Allam, Heteroepitaxial growth of GaN/Si (111) junctions in ammonia-free atmosphere: Charge transport, optoelectronic, and photovoltaic properties, J. Appl. Phys., 113 (2013) 124304-124306. [32] Y. Li, T. Tokizono, M. Liao, M. Zhong, Y. Koide, I. Yamada, J.J. Delaunay, Efficient Assembly of Bridged β‐Ga2O3 Nanowires for Solar‐Blind Photodetection, Adv. Funct. Mater., 20 (2010) 3972-3978. [33] Q. Xu, S. Zhang, Fabrication and photoluminescence of bita-Ga2O3 nanorods, Superlattices Microstruct., 44 (2008) 715-720. [34] C.M. Balkas, R.F. Davis, Synthesis Routes and Characterization of High-Purity, Single‐Phase Gallium Nitride Powders, J. Am. Ceram. Soc., 79 (1996) 2309-2312. [35] A.F. Wright, J.S. Nelson, Consistent structural properties for AlN, GaN, and InN, Phys Rev B, 51 (1995) 7866-7869. [36] C. Falter, M. Klenner, Q. Chen, Role of bonding, reduced screening, and structure in the high-temperature superconductors, Phys Rev B, 48 (1993) 16690. [37] O. Zsebök, J. Thordson, J. Gunnarsson, Q. Zhao, L. Ilver, T. Andersson, The effect of the first GaN monolayer on the nitridation damage of molecular beam epitaxy grown GaN on GaAs (001), J. Appl. Phys., 89 (2001) 3662-3667. 13

ACCEPTED MANUSCRIPT

AC C

EP

TE D

M AN U

SC

RI PT

[38] Y. Wang, X. Du, Z. Mei, Z. Zeng, M. Ying, H. Yuan, J. Jia, Q. Xue, Z. Zhang, Cubic nitridation layers on sapphire substrate and their role in polarity selection of ZnO films, Appl. Phys. Lett., 87 (2005) 051901-051901-051903. [39] J. Neugebauer, T. Zywietz, M. Scheffler, J.E. Northrup, C.G. Van de Walle, Clean and As-covered zinc-blende GaN (001) surfaces: Novel surface structures and surfactant behavior, Phys. Rev. Lett., 80 (1998) 3097. [40] D.-K. Hwang, S.-H. Kang, J.-H. Lim, E.-J. Yang, J.-Y. Oh, J.-H. Yang, S.-J. Park, p-ZnO/ n-GaN heterostructure ZnO light-emitting diodes, Appl. Phys. Lett., 86 (2005) 222101-222103. [41] M.A. Qaeed, K. Ibrahim, K. Saron, A. Salhin, Optical and structural properties of indium nitride nanoparticles synthesized by chemical method at low temperature, Solar Energy, 97 (2013) 614-619. [42] M. Wolf, H. Rauschenbach, Series resistance effects on solar cell measurements, VDI BERICHT, 3 (1963) 455-479.

14