Ghazali et al. Nanoscale Research Letters 2014, 9:685http://www.nanoscalereslett.com/content/9/1/685

NANO EXPRESS Open Access

Synthesis of gallium nitride nanostructures bynitridation of electrochemically deposited galliumoxide on silicon substrateNorizzawati Mohd Ghazali1, Kanji Yasui2 and Abdul Manaf Hashim1*

Abstract

Gallium nitride (GaN) nanostructures were successfully synthesized by the nitridation of the electrochemically depositedgallium oxide (Ga2O3) through the utilization of a so-called ammoniating process. Ga2O3 nanostructures were firstlydeposited on Si substrate by a simple two-terminal electrochemical technique at a constant current density of 0.15A/cm2 using a mixture of Ga2O3, HCl, NH4OH and H2O for 2 h. Then, the deposited Ga2O3 sample was ammoniated ina horizontal quartz tube single zone furnace at various ammoniating times and temperatures. The complete nitridationof Ga2O3 nanostructures at temperatures of 850°C and below was not observed even the ammoniating time was keptup to 45 min. After the ammoniating process at temperature of 900°C for 15 min, several prominent diffraction peakscorrespond to hexagonal GaN (h-GaN) planes were detected, while no diffraction peak of Ga2O3 structure was detected,suggesting a complete transformation of Ga2O3 to GaN. Thus, temperature seems to be a key parameter in a nitridationprocess where the deoxidization rate of Ga2O3 to generate gaseous Ga2O increase with temperature. The growthmechanism for the transformation of Ga2O3 to GaN was proposed and discussed. It was found that a completetransformation can not be realized without a complete deoxidization of Ga2O3. A significant change of morphologicalstructures takes place after a complete transformation of Ga2O3 to GaN where the original nanorod structures of Ga2O3

diminish, and a new nanowire-like GaN structures appear. These results show that the presented method seems to bepromising in producing high-quality h-GaN nanostructures on Si.

Keywords: Electrochemical deposition; Gallium oxide; Gallium nitride; Nanostructure; Nitridation

BackgroundGallium nitride (GaN) is a very hard, chemically and mech-anically stable wide bandgap (3.4 eV) semiconductor mater-ial with high heat capacity and thermal conductivity whichmakes it suitable to be used for sensors [1-8], high powerelectronic devices such as field-effect transistor (FET) [9]and optoelectronic devices such as light-emitting diode(LED) [10]. Up to this date, many techniques have beenexplored to synthesize GaN nanostructures including nano-wires, nanorods, nanodots and so forth since such low-dimensional nanostructures are promising for increasingthe performance optoelectronic devices and the sensitivityof sensors [11,12]. For example, GaN nanorods and nano-wires have been applied for chemical sensing application as

* Correspondence: abdmanaf@utm.my1Malaysia-Japan International Institute of Technology, Universiti TeknologiMalaysia, Jalan Semarak, 54100 Kuala Lumpur, MalaysiaFull list of author information is available at the end of the article

© 2014 Ghazali et al.; licensee Springer. This isAttribution License (http://creativecommons.orin any medium, provided the original work is p

reported by Wright et al. [13] and Huang Y et al. [14],respectively, due to a large surface to volume ratio. GaNnanodots have been used in photodetectors as reported byKumar et al. [15].Recently, GaN on silicon carbide (SiC) or sapphire sub-

strate have been widely used for several specific electronicapplications. However, these substrates are expensive andnot available in large wafer size [16]. According toKukushkin et al., Si substrate seems to be more preferablefor the heterostructure growth of GaN due to the availa-bility of Si in large wafer size, the low price of Si and thematurity of Si-based technology [17]. In addition, the inte-gration of GaN-based devices on Si platform seems to bevery attractive for the hybrid integration towards ‘Morethan Moore’ technology [18]. Several vapor-phase tech-niques have been reported for growing GaN nanostructuresdirectly on Si with high quality which include molecularbeam epitaxy (MBE) [19], metal-organic chemical vapor

an Open Access article distributed under the terms of the Creative Commonsg/licenses/by/4.0), which permits unrestricted use, distribution, and reproductionroperly credited.

Ghazali et al. Nanoscale Research Letters 2014, 9:685 Page 2 of 8http://www.nanoscalereslett.com/content/9/1/685

deposition (MOCVD) [20] and hydride vapor phase epitaxy(HVPE) [21]. However, these vapor-phase techniques aretoo expensive and their growth parameters are quite com-plicated. In recent years, a transformation of the grown gal-lium oxide (Ga2O3) structures on Si to GaN by a so-callednitridation seems to be a simple method to create a GaN/Si heterostructure [22]. Here, a nitridation is achieved byannealing the Ga2O3 structures in ammonia gas. Li et al.reported the repeatable transformation of the CVD-grownGaN structures to Ga2O3 structures by an annealing in airand back to GaN structures by an annealing in ammonia[23]. Moreover, there are several studies reporting theformation of GaN nanostructures by annealing the sput-tered Ga2O3 layer on metal-coated Si substrates in ammo-nia [24-27]. To our knowledge, the nitridation of theelectrochemically deposited Ga2O3 structures on bare Sisubstrates to form GaN nanostructures without the assist-ance of metal catalyzers does not appear in the publishedliterature.Recently, we report the growth of Ga2O3 nanostructures

directly on Si without any assistance of metal catalyzer byusing a simple electrochemical deposition [28]. This liquid-phase technique provides several advantages such as highcontrollability of thickness and morphologies of Ga2O3

nanostructures due to a less number of growth parameters.In this work, we investigate the formation of GaN nano-structures by ammoniating the electrochemically depositedβ-Ga2O3 nanostructures on Si substrate. Up to this date,no such similar work is reported where a combination ofliquid-phase and vapor-phase methods is utilized to form aGaN/Si heterostructure. The effects of the ammoniatingtimes and temperatures were studied. The mechanism forthe growth of GaN was proposed and discussed.

MethodsIn this study, the synthesis can be divided into twomajor processes; i) a formation of Ga2O3 structures asthe ‘seed’ structures and ii) an ammoniating process totransform Ga2O3 to be GaN. The deposition of Ga2O3

on Si (100) substrate (resistivity of 15 to 25 Ω · cm) wascarried out by a simple two-terminal electrochemicalprocess. In the electrochemical process, a mixture ofGa2O3 (99.99%), HCl (36%), NH4OH (25%) and DI waterwas used as an electrolyte [28]. Since Ga2O3 is insolublein water, HCl is added to dissolve Ga2O3. The prepar-ation of electrolyte was done as follows. First, Ga2O3

was dissolved in 1.5 ml HCl. Then, 6.5 ml DI water wasadded into the solution, followed by NH4OH as a pre-cipitator, so that the pH of the mixture could be easilyadjusted. The deposition was done in electrolyte withGa2O3 molarity of 1.0 M (pH 6) at a constant currentdensity of 0.15 A/cm2. The Si substrate was cleaned withmodified RCA cleaning using ethanol, acetone and DIwater prior to the deposition in order to remove a native

oxide layer. The growth time was fixed at 2 h. In thiselectrochemical process, a platinum (Pt) wire was usedas an anode and Si substrate as a cathode. The sche-matic of electrochemical setup is shown in Figure 1a.After the deposition, the sample was immersed into theDI water to remove any unwanted residue.The electrochemically deposited Ga2O3 was ammoni-

ated in a quartz tube furnace as shown in Figure 1b, atvarious times of 15, 30 and 45 min and temperatures of800°C, 850°C and 900°C under a flow of ammonia (NH3)gas of 100 sccm at atmospheric pressure. The timingchart of ammoniating process is shown in Figure 1c. Be-fore starting the ammoniating process, the sample wasput inside the quartz tube furnace and then the nitrogen(N2) gas was purged for 10 min to flush out the air inthe quartz tube. After that, the temperature was in-creased up to the setting temperatures, i.e. 800°C, 850°Cand 900°C from room temperature (RT) with a rampingrate of 28°C/min. After reaching the setting temperature,N2 gas was stopped and NH3 gas was introduced intothe furnace. The furnace was immediately switched offupon reaching the setting ammoniating time. At thesame time, NH3 gas was immediately stopped and N2

gas was purged back into the furnace for 1 h to removethe remaining NH3 gas during the cooling down process.The ammoniated structures were characterized using field-emission scanning electron microscopy (FESEM; HitachiSU8083, Hitachi, Ltd, Chiyoda-ku, Japan), energy disper-sive X-ray (EDX) spectroscopy and X-ray diffraction (XRD;Bruker D8 Advance, Bruker AXS, Inc., Yokohama-shi,Japan).

Results and discussionThe nitridation of Ga2O3 to form GaN can be describedas follows. Firstly, NH3 decomposes to N2 and H2 at hightemperatures as illustrated by Equation 1 [29]. Then,Ga2O3 structures are deoxidized by H2 to form gaseousGa2O as illustrated by Equation 2. Finally, GaN structureis synthesized through the reaction of Ga2O and NH3.

2NH3 gð Þ→N2 gð Þ þ 3H2 gð Þ ð1ÞGa2O3 sð Þ þ 2H2 gð Þ→Ga2O gð Þ þ 2H2O gð Þ ð2ÞGa2O gð Þ þ 2NH3 gð Þ→2GaN sð Þ þ 2H2 gð Þ þH2O gð Þ

ð3ÞFigure 2a shows the top view FESEM images of the

electrochemically deposited Ga2O3 nanorods on Si sub-strate before the ammoniating process was applied. Thelengths and diameters of the grown Ga2O3 nanorodswere estimated to be in the range of 1,000 to 4,200 nmand 200 to 1,000 nm, respectively. It is noted that themeasured EDX spectra confirm the elements of Ga andO, indicating the formation of Ga2O3 nanostructure.

Figure 1 Schematic of (a) electrochemical setup, (b) nitridation set up and (c) growth timing chart.

Figure 2 Top view FESEM images of samples. (a) Before nitridation, (b) after 15 min, (c) after 30 min and (d) after 45 min of nitridation at 850°C.

Ghazali et al. Nanoscale Research Letters 2014, 9:685 Page 3 of 8http://www.nanoscalereslett.com/content/9/1/685

Ghazali et al. Nanoscale Research Letters 2014, 9:685 Page 4 of 8http://www.nanoscalereslett.com/content/9/1/685

Figure 2b,c,d shows the top view FESEM images afterthe ammoniating process at 850°C for 15, 30 and45 min, respectively. In a glance, it can be seen thatthere is no significant change of morphology takingplace even at long ammoniating time of 45 min. How-ever, it can be seen that there is a slight change on thesurface of nanorods where the numbers of ‘hole’ in-crease with the ammoniating time. From the EDX ana-lysis as shown in Figure 3a, the atomic percentage of Nincreases with ammoniating time while the atomic per-centage of O decreases and the drastic changes seem totake place after ammoniating time of 30 min. Figure 3bshows the XRD spectra of samples before and after theammoniating process at 850°C for 15, 30 and 45 mintogether with the XRD spectra of bare Si. In the bare Si,five peaks were observed at 33.1°, 47.8°, 54.7°, 56.4° and61.8° corresponding to Si(112), Si(002), Si(004), Si(113)and Si(024), respectively. The as-grown Ga2O3 nanorodsshow three prominent peaks at 31.8°, 46.2° and 55.5°corresponding to β-Ga2O3(202), β-Ga2O3(112) and β-Ga2O3(002), respectively. After being ammoniated for15, 30 and 45 min, several peaks corresponding tohexagonal GaN (h-GaN) planes were observed. However,β-Ga2O3-related peaks were still detected in all grownsamples suggesting that β-Ga2O3 structures are notcompletely being transformed to GaN. From these XRDresults, it can be said that an ammoniating time is not adominant parameter since the complete transformationof Ga2O3 to GaN does not occur even at a long ammo-niating time of 45 min.Figure 4a,b,c,d shows the FESEM images for the as-

grown sample and the ammoniated samples at tempera-tures of 800°C, 850°C and 900°C for 15 min, respectively.It is noted here that β-Ga2O3 nanorods as shown inFigure 4a were also grown using the similar proceduresand conditions with the samples shown in Figure 2

Figure 3 EDX analysis and XRD spectra. (a) Atomic percentage obtainedat 850°C with various nitridation times.

where their properties are similar. After being ammoni-ated at 800°C and 850°C, the general shape of the nano-rods is still being preserved where no significant change intheir morphologies is observed, as shown in Figure 4b,c,respectively. However, the same phenomenon with thesamples shown in Figure 2 was observed where the num-bers of ‘hole’ structures in the nanorods increase with thetemperature. When the sample was further ammoniatedat 900°C, as shown in Figure 4d, the structures have chan-ged from nanorods to nanowires with the estimatedlengths of 0.4 to 1.0 μm and diameters of 0.05 to 0.08 μm.This result is consistent with the result reported byKim et al. where they claimed that the change of morph-ology could be significantly affected by the ammoniatingtemperature [30]. Figure 5a shows the EDX analysis forthe samples ammoniated at temperatures of 800°C, 850°Cand 900°C. It can be seen that the atomic percentage of Nincreases with temperature while the atomic percentage ofO decreases. As shown in Figure 5a, the drastic change inthe atomic percentage seems to take place from 800°C to850°C. Figure 5b shows the XRD spectra of the as-grownsamples and the ammoniated samples at temperatures of800°C, 850°C and 900°C for 15 min together with theXRD spectra of bare Si. After being ammoniated at 800°C,850°C and 900°C, several h-GaN-related peaks were ob-served. However, as expected, β-Ga2O3-related peaks arebeing detected for the samples ammoniated at 800°C and850°C, suggesting the incomplete transformation of β-Ga2O3 to GaN. It can be simply said that the completetransformation was achieved at ammoniating temperatureof 900°C where no β-Ga2O3-related peak was observedexcept h-GaN peaks. The peaks related to GaN structureswere detected at 32.5°, 34.6°, 36.9° and 58.0° correspondingto h-GaN(010), h-GaN(002), h-GaN(011) and h-GaN(110), respectively. The obtained results show a similartendency with the results reported by Li et al. [31] where

from the EDX analysis and (b) XRD spectra of the samples nitridated

Figure 4 Top view FESEM images of samples. (a) Before nitridation, (b) after nitridation at 800°C, (c) after nitridation at 850°C and (d) afternitridation at 900°C for 15 min.

Ghazali et al. Nanoscale Research Letters 2014, 9:685 Page 5 of 8http://www.nanoscalereslett.com/content/9/1/685

the complete transformed GaN with hexagonal wurtzitestructure was obtained at a temperature of 900°C. It isnoted that from the EDX analysis, the atomic percentageof O is not zero in the sample of 900°C. It is speculatedthat the detected O element is contributed by a nativeoxide layer in the sample after being exposed to air ambi-ent. From these XRD results, it can be said that an ammo-niating temperature is the key parameter in producing thecomplete transformation of Ga2O3 to GaN since it takesonly a short ammoniating time of 15 min.Based on the obtained morphological and structural

properties, the reaction mechanism for the transformation

Figure 5 EDX analysis and XRD spectra. (a) Atomic percentage obtainedat various temperatures for 15 min.

of Ga2O3 to GaN under a flow of ammonia with thedependence of temperatures is proposed and discussed. Inprinciple, as shown by Equation 1, with the increase oftemperature, the decomposition rate of NH3 should be in-creased, resulting to the generation of a high density of H2.Then, this leads to the higher deoxidization or vaporizationrate of Ga2O3 structures to form gaseous Ga2O, as illus-trated by Equation 2 [32]. Finally, this situation would in-crease the reaction of gaseous Ga2O and NH3 to promotethe formation of a GaN structure. This means that thetransformation of Ga2O3 to GaN does not proceed withoutthe deoxidation or vaporization of Ga2O3 or, in other

from the EDX analysis and (b) XRD spectra of the samples nitridated

Ghazali et al. Nanoscale Research Letters 2014, 9:685 Page 6 of 8http://www.nanoscalereslett.com/content/9/1/685

words, without the existence of gaseous Ga2O. Due to suchdeoxidization and reaction activities, it is speculated thatthe original morphological structure of Ga2O3 will bediminished and a new morphological structure of GaN willbe formed. As shown in Figure 4b, the SEM image of theammoniated structure at temperature of 800°C shows nosignificant change of the morphology as compared to theunammoniated structure shown in Figure 4a. This seemsto show that the temperature of 800°C is considerably lowfor the aggressive deoxidization or vaporization of Ga2O3

to take place, resulting to low reaction of gaseous Ga2Oand NH3 to form GaN. This also agrees with the XRD ana-lysis as shown in Figure 5b where the sample ammoniatedat temperature of 800°C contains a mixture of Ga2O3 andGaN structures. Figure 6a illustrates the growth mechan-ism for the temperature of 800°C. When the temperatureis increased to 850°C, the morphology of the ammoniatedstructure shows a slight change where the numbers of‘hole’ structures seem to be increased as shown in Figure 4c.It can be said that the deoxidization or vaporization rate ofGa2O3 slightly increases to form gaseous Ga2O. However,

Figure 6 Proposed growth mechanism for the transformation Ga2O3

(c) 900°C.

since the original structure of Ga2O3 does not diminishand the XRD spectra also shows a mixture of Ga2O3 andGaN, it can be said that the temperature of 850°C is stillnot favorable to drastically increase the density of gaseousGa2O to continuously react with NH3 to form a GaNstructure. Figure 6b illustrates the growth mechanism forthe temperature of 850°C. At high temperature of 900°C,as shown in Figure 4d, it can be seen that the originalnanorod structure of Ga2O3 has diminished and a newstructure in the form of nanowire-like structure has beenproduced. It can be said that temperature of 900°C seemsto be high enough to realize a complete deoxidization ofGa2O3 to generate a high density of gaseous Ga2O. Thus,the reaction of gaseous Ga2O and NH3 seems to be wellpromoted at such condition to form GaN nanowires. It isnoteworthy that during the ammoniating process attemperature of 900°C, white ‘cloudy’ ambient was observedin the furnace which seems to indicate the aggressive deox-idization of Ga2O3 to form Ga2O gaseous. After ammoni-ating process, it was found that the original white colour ofthe as-grown Ga2O3 diminished and new structures in

to GaN. At ammoniating temperatures of (a) 800°C, (b) 850°C and

Ghazali et al. Nanoscale Research Letters 2014, 9:685 Page 7 of 8http://www.nanoscalereslett.com/content/9/1/685

light yellow colour appeared. The XRD spectra as shown inFigure 5b reveals that the detected peaks belong only to thestructures of GaN. It can be said that the temperature of900°C is favorable to drastically increase the deoxidizationrate of Ga2O3 to generate gaseous Ga2O to continuouslyreact with NH3 to form GaN with new morphologicalnanostructures.

ConclusionsThe nitridation of the electrochemically grown Ga2O3

nanostructures to form GaN nanostructures on Si plat-form have been studied by varying the ammoniating timesand temperatures. The complete transformation of Ga2O3

nanorods to h-GaN nanowires was achieved at 900°C witha short ammoniating time of 15 min. The obtained resultssuggest that the effect of the ammoniating temperature inrealizing a complete transformation is more prominentthan the ammoniating time. Form the proposed growthmechanism, it was found that a complete transformationto GaN nanostructures can not be realized without acomplete deoxidization of Ga2O3. In a complete trans-formation process, it seems to show the occurence ofmorphological change. The presented method seems to bepromising for the formation of h-GaN nanostructures onSi for the applications in sensing and optoelectronics.

Competing interestsThe authors declare that they have no competing interests.

Authors’ contributionsNMG designed and performed the experiments, participated in the dataanalysis and prepared the manuscripts. KY participated in the nitridationprocess and revision of manuscript. AMH conceived the study, designed theexperiments, participated in the data analysis and revised the manuscript. Allauthors read and approved the final manuscript.

AcknowledgementsThe authors would like to thank for the supports provided by MIMOS Berhadand Universiti Sains Malaysia. N. M. Ghazali thanks Malaysia-Japan InternationalInstitute of Technology (MJIIT) for the scholarship. This work was supported byNippon Sheet Glass Corp, Hitachi Foundation, MJIIT, universiti TeknologiMalaysia, Malaysian Ministry of Education and Malaysian Ministry of Science,Technology and Innovation through various research grants.

Author details1Malaysia-Japan International Institute of Technology, Universiti TeknologiMalaysia, Jalan Semarak, 54100 Kuala Lumpur, Malaysia. 2Department ofElectrical Engineering, Nagaoka University of Technology,Kamitomioka-machi, Nagaoka, Niigata 940-2137, Japan.

Received: 24 October 2014 Accepted: 9 December 2014Published: 18 December 2014

References1. Abidin MSZ, Shahjahan, Hashim AM: Surface reaction of undoped AlGaN/

GaN HEMT based two terminal device in H+ and OH-ion-containedaqueous solution. Sains Malaysiana 2013, 2:197–203.

2. Abidin MSZ, Hashim AM, Sharifabad ME, Rahman SFA, Sadoh T: Open-gatedpH sensor fabricated on an undoped-AlGaN/GaN HEMT structure. Sensors2011, 11:3067–3077.

3. Mohamad M, Mustafa F, Rahman SFA, Abidin MSZ, Ali NK, Hashim AM,Aziz AA, Hashim MR: The sensing performance of hydrogen gas sensorutilizing undoped-AlGaN/GaN HEMT. J Appl Sci 2010, 16:1797–1801.

4. Pearton SJ, Fan R: Gallium nitride-based gas, chemical and biomedicalsensors. Instrum Meas Mag IEEE 2012, 15:16–21.

5. Chu BH, Sam Kang BS, Hung SC, Chen KH, Ren F, Sciullo A, Gila BP,Pearton SJ: Aluminum gallium nitride (GaN)/GaN high electron mobilitytransistor-based sensors for glucose detection in exhaled breathcondensate. J Diabetes Sci Technol 2010, 4:171–179.

6. Chitara B, Late DJ, Krupanidhi SB, Rao CNR: Room-temperature gas sensorsbased on gallium nitride nanoparticles. Solid State Commun 2010,150:2053–2056.

7. Schalwig J, Muller G, Ambacher O, Stutzman M: Group III-nitride based gassensing devices. Phys Stat Sol (a) 2001, 185:39–45.

8. Lee DS, Lee JH, Lee YH, Lee DD: GaN thin films as gas sensors. SensorActuat B Chem 2003, 6989:1–6.

9. Micovic M, Hashimoto P, Hu M, Milosavljevic I, Duvall J, Willadesen PJ, Wong WS,Conway AM, Kurdoghlian A, Deelman PW, Moon JS, Schmitz A, Delaney MJ:GaN double heterojunction field effect transistor for microwave andmillimeterwave power applications. IEDM Technical Digest 2004, 33:807–810.

10. Choi JH, Zoulkarneev A, Kim S, Baik CW, Yang MH, Park SS, Suh H, Kim UJ,Son HB, Lee JS, Kim M, Kim JM, Kim K: Nearly singe-crystalline GaNlight-emitting diodes on amorphous glass substrates. Nat Photonics 2011,5:763–769.

11. Kang MS, Lee CH, Park JB, Yoo H, Yi GC: Gallium nitride nanostructures forlight-emitting diode application. Nano energy 2012, 1:391–400.

12. Shur MS: GaN based transistors for high power applications. Solid State Electron1998, 42:2131–2138.

13. Wright JS, Lim W, Norton DP, Pearton SJ, Ren F, Johnson JL, Ural A: Nitrideand oxide semiconductor nanostructured hydrogen gas sensors.Semicond Sci Technol 2010, 25:1–8.

14. Huang Y, Duan X, Cui Y, Lieber CM: Gallium nitride nanowire nanodevices.Nano Lett 2012, 2:101–104.

15. Kumar M, Roul B, Bhat TN, Rajpalke MK, Krupanidhi SB: Structural characterizationand ultraviolet photoresponse of GaN nanodots grown by molecular beamepitaxy. Appl Phy Express 2012, 5:1–3.

16. Pal S, Jacob C: Silicon-a new substrate for GaN growth. Bull Mater Sci2004, 27:501–504.

17. Kukushkin SA, Osipov AV, Bessolov VN, Medvedev BK, Nevolin VK, Tcarik KA:Substrate for epitaxy of gallium nitride–new material and technique.Rev Adv Mater Sci 2008, 17:1–32.

18. Takagi S, Sugiyama M, Yasuda T, Takenaka M: Ge/III-V channel engineeringfor future CMOS. ECS Trans 2009, 5:9–20.

19. Calarco R, Meijers RJ, Debnath RK, Stoica T, Sutter E, Lu H: Nucleation andgrowth of GaN nanowires on Si (111) performed by molecular beamepitaxy. Nano Lett 2007, 7:2248–2251.

20. Haffouz S, Kirilyuk V, Hageman PR, Macht L, Weyher JL, Larsen PK:Improvement of the optical properties of metalorganic chemical vapordeposition grown on GaN on sapphire by an in situ SiN treatment.Appl Phys Lett 2001, 79:2390–2392.

21. Paskova T, Darakchieva V, Valcheva E, Paskov PP, Ivanov IG, Monemar B,Bottcher T, Roder C, Hommel D: Hydride vapor-phase epitaxial GaN thickfilms for quasi substrate applications. J Electron Matter 2004, 33:389–394.

22. Yam FK, Low LL, Oh SA, Hassan Z: Gallium nitride: an overview ofstructural defects. In Optoelectronic Materials and Technique. Edited byPredeep P. Malaysia: InTech publication; 2011:99–137.

23. Li J, An L, Lu C, Liu J: Conversion between hexagonal GaN and β-Ga2O3nanowires and their electrical transport properties. Nano Lett 2006, 6:148–152.

24. Qin LX, Xue CS, Zhuang HZ, Yang ZZ, Li H, Chen JH, Wang Y: Influence ofammoniating temperature on co-catalyzed GaN nanowires. Appl Phys A2008, 91:675–678.

25. Shi F, Wang Y, Xue C: Synthesis of GaN nanowires by CVD method: effectof reaction temperature. J Exp Nanosci 2011, 6:238–247.

26. Zhuang H, Wang J, Zhang X, Li J: Influence of ammoniating time on Nb-catalyzed GaN nanostructured materials. Int J Nanosci 2011, 10:1209–1214.

27. Xue C, Wu Y, Zhuang H, Tian D, Liu Y, He J, Al Y, Sun L, Wang F: Fabricationand photoluminescence of GaN nanowires prepared by ammoniatingGa2O3/BN films on Si substrate. Chin Sci Bull 2006, 51:1662–1665.

28. Ghazali NM, Mahmood MR, Yasui K, Hashim AM: Electrochemically depositedgallium oxide nanostructures on silicon substrates. Nanoscale Res Lett2014, 9:120.

29. Xia QL, Shan XC, Zhao ZH, Zhu YZ, Hua CJ, Hong L: Synthesis of large-scaleGaN nanowires by ammoniating Ga2O3 films on co layer deposited on Si(111) substrates. Chin Phys Soc 2008, 17:2180–2183.

Ghazali et al. Nanoscale Research Letters 2014, 9:685 Page 8 of 8http://www.nanoscalereslett.com/content/9/1/685

30. Kim HW, Myung JH, Shim SH: A study of Ga2O3 nanomaterialssynthesized by the thermal evaporation of GaN powders. Mater Sci Forum2006, 510:654–657.

31. Li D, Wang F, Zhu J, Liu D, Wang X, Xiang L: Microwave hydrothermalsynthesis of GaN nanorods. Mater Sci Forum 2011, 675:251–254.

32. Luo L, Yu K, Zhua Z, Zhang Y, Ma H, Xue C, Yang Y, Chen S: Field emissionfrom GaN nanobelts with Herringbone morphology. Mater Lett 2004,58:2893–2896.

doi:10.1186/1556-276X-9-685Cite this article as: Ghazali et al.: Synthesis of gallium nitridenanostructures by nitridation of electrochemically deposited galliumoxide on silicon substrate. Nanoscale Research Letters 2014 9:685.

Submit your manuscript to a journal and benefi t from:

7 Convenient online submission

7 Rigorous peer review

7 Immediate publication on acceptance

7 Open access: articles freely available online

7 High visibility within the fi eld

7 Retaining the copyright to your article

Submit your next manuscript at 7 springeropen.com