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Growth of indium nitride nanopetal structures onindium oxide buffer layerVidya N. Singh1,∗, G. Partheepan2, Brijesh Kumar3, and Ankur Khare4�†

1CSIR—National Physical Laboratory, Dr. K. S. Krishnan Marg, New Delhi 110012, India2Department of Civil Engineering, Amity School of Engineering and Technology,Amity University Uttar Pradesh, Noida 201303, India3Electrical Engineering Department, Indian Institute of Technology Delhi, Hauz Khas, New Delhi 110016, India4Department of Chemical Engineering and Materials Science, University of Minnesota, Minneapolis,Minnesota 55455, USA

ABSTRACT

This paper presents a simple method for controlling crystalline quality and morphology of InN. A buffer layerof indium oxide is deposited in-situ on Si substrate before growing InN by atmospheric pressure-halide vapourphase epitaxy. Glancing angle X-ray diffraction and scanning electron microscopic studies have been carriedout. Buffer layer of indium oxide helps in the growth of indium nitride nanopetals.

Keywords: Indium Nitride, Nanopetals, Buffer Layer, Indium Oxide, Chemical Vapour Deposition.

1. INTRODUCTIONIndium nitride is an important semiconductor, whichhas potentially important applications in optoelectronicdevices. The mobility of InN is very high and is insen-sitive to variation in temperature and doping concentra-tion, which makes it a potential material for use in veryhigh frequency field-effect transistors.�1–4� Its alloy withGa (InxGa1−xN) is a potentially useful solar cell mate-rial as the variation of its band gap with concentrationcan be used to cover the complete solar spectrum andresult in developing high efficiency solar cells and light-emitting diodes.�5–8� In spite of all the benefits describedabove, InN has not received much attention as GaN orAlN because of the difficulty in preparing InN. It decom-poses at a lower temperature of about 500 �C into indiumand nitrogen and has a tendency to form oxide ratherthan nitride. Only a few studies have been reported on the

∗Author to whom correspondence should be addressed.Email: [email protected]

†Present address: Dow Solar Solutions, The Dow Chemical Company,1381 Building, Midland, MI 48667, USA

synthesis of indium nitride nanostructures. In some stud-ies, In2O3 has been used as a precursor for synthesizingInN.�9–11� Luo et al. have synthesized InN nanobelts onthe surface of the ceramic boat by the nitridation of In2O3

precursor.�9� Yin et al. have synthesized InN nanotubesusing In2O3 as the precursor.�10� Tang et al. have synthe-sized InN nanowires using the mixture of In+ In2O3 on agold deposited Si substrate.�11� In some studies, InN nano-structures have been grown on Si or sapphire substratesusing buffer layers like GaN, AlN, In2O3 etc.�12–14� Thetwo step method of depositing a buffer layer has nowbecome a standard method for the heteroepitaxial growthof InN. This method is commonly used to alleviate lat-tice mismatch and thermal expansion coefficient differencebetween the substrate and InN during thin film growth. Ithas been reported that the lattice mismatch between In2O3

and InN is 2.1% in comparison to a large (8.0%) latticemismatch between Si and InN.�15�16�

In the present study, the role of In2O3 buffer layer onthe formation of InN nanostructures has been studied bycarrying out in-situ growth of In2O3 buffer layers in atmo-spheric pressure halide chemical vapor deposition process.

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Materials ExpressGrowth of indium nitride nanopetal structures on indium oxide buffer layerSingh et al.

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n

N2InCl3 inceramiccrucible

NH3

Si substrate onceramic plate

To Rotary

Heating ZoneRubber O-ring

Fig. 1. Schematic diagram of the deposition set up.

2. EXPERIMENTAL DETAILSThe growth of indium oxide buffer layer has been carriedout in a horizontal tube furnace fitted with quartz tubeof 60 mm diameter. As shown in Figure 1, the precur-sor InCl3 ·3H2O is taken in a ceramic boat and placed inthe heating zone of the furnace. A Si (100) substrate isplaced 100 mm downstream from the boat. Si substrate iscleaned by ultrasonification for 120 s using HF and de-ionized (DI) water in the ratio 1:10, followed by rinsingwith DI water and acetone. The furnace is heated till thetemperature reaches 450 �C. In order to grow In2O3 bufferlayer, nitrogen at 80 sccm is used as the carrier gas.In2O3 buffer layer deposition is carried out for 30 min-

utes. In2O3 coated silicon substrate is then used for thedeposition of InN. For the deposition of InN, in additionto nitrogen as carrier gas, ammonia (NH3� as a source ofactive nitrogen is also passed over the substrate at a flowrate of 150 sccm.It may be noted that the ammonia supply is maintained

till the furnace temperature is lowered to room temperature.Structural characterization of the deposited layer was car-ried out using glancing angle X-ray diffraction (GAXRD)with CuK� radiation using Philips X’pert PRO system. Thediffractogram was recorded by performing slow scan witha step size of 0.01� and a counting time of 2 s at each step.Morphological characterization was done using ScanningElectron Microscope (SEM), Zeiss Evo 40 series.

3. RESULTS AND DISCUSSIONFigures 2(a)–(b) show XRD diffractogram and SEMmicrograph of In2O3 nanoparticles deposited over Si sub-strate, on which InN petals have been grown. The mostintense peak present in the XRD spectrum of In2O3 sam-ple at 2� = 30�7, d = 2�908 Å, I/I0 = 100 corresponds to(222) plane of cubic In2O3. The peaks at 35.5, 3.527 Å;45.0, 2.015 Å; 55.5, 1.655 Å, and 60.6, 1.527 Å corre-spond to the (400), (431), (611) and (622) planes of thecubic In2O3 respectively. Other small intensity peaks aremarked in the figure. Figures 2(c)–(d) show the XRD andSEM micrograph of InN deposited on bare Si substrate.The absence of any deposition shows that a buffer layeris necessary for InN growth. It has been reported that InNfilm grown on bare Si substrate is of very poor quality.Yamamoto et al. attempted the MOVPE growth of InN onSi substrate. The growth was unsuccessful because of the

formation of an amorphous SiNx layer on the substratesurface, as a result of the unintentional nitridation of thesubstrate surface during the growth.�17� The Si substratesurface becomes nitrided during the growth at low temper-ature (400 �C) resulting in the formation of SiNx at surfaceand deteriorates the growth of InN film. Therefore in orderto grow InN on Si substrate, a buffer layer is required.Figures 2(e)–(f) show the XRD and SEM image of InN

deposited on Si substrates having an In2O3 layer. TheXRD pattern shown in Figure 2(e) indicates the formationof indium nitride. The peaks in the XRD pattern corre-spond to two materials, wurtzite type indium nitride (a=0�351 nm and c = 0�5669 nm) and cubic indium oxide(a = 1�0117 nm). The most intense peak is of InN (101)and it is relatively very intense compared to other peaksof indium nitride or oxide, which shows that the growth ofthe indium nitride is highly oriented along the (101) plane.As indicated in the Figure 2(e), there are some peaks dueto In2O3 from the buffer layer.

The SEM micrograph as shown in Figure 2(f) revealsthe formation of nanopetal structures of indium nitride.The petals are very narrow at the roots and broaden out aswe move towards the edges, just like the petal of a flower.The petals are less than 100 nm in thickness and are about5 �m long from the root to the edge. The width of some ofthe nanopetals is as large as 7 �m near the edges. From themicrograph, it appears as if many different flowers havebeen placed adjacent to each of the nucleation point. Forexample, from the place where one petal originates, manyothers also originate. It is possible that a number of nucle-ation sites are formed on the In2O3 nanoparticles. This isfollowed by the growth of InN resulting in the formationof petal-like structures.In one study, Lozano et al. have grown cubic InN lay-

ers by molecular beam epitaxy on buffer layers of indiumoxide (520 nm thick) prepared onto sapphire substrates.�18�

Using TEM they have shown that the intermediate indiumoxide layer presents a body centered cubic (bcc) struc-ture, with bcc-In2O3 (001) parallel to Al2O3 (0001). In thestudy, a zinc-blende phase of InN (001) was grown with amisfit of 1.6%. In the present study, In2O3 has been grownon a bare Si substrate. The In2O3 produced are in the shapeof spherical particles. It should be noted that the growthof In2O3 spheres used in this study for the growth of InNnanopetals doesn’t depend upon the substrate and thereforethis structure can be deposited on other transparent sub-strates. Thus, the structure of In2O3 (doped for higher con-ductivity) as a transparent conducting medium; and InNover it can be directly used for device applications.In another study, Lan et al. have grown single crys-

tal indium nitride nanorods on Si substrates by catalyticchemical vapor deposition.�19� With the help of Raman andHRTEM analysis, they have suggested that the presenceof a minute amount of oxygen is necessary for the growthof InN nanorods. The residual oxygen in the growth envi-ronment and/or native oxide on the Si substrate forms

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Materials ExpressGrowth of indium nitride nanopetal structures on indium oxide buffer layer

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(b)

30 605040

Inte

nsity

(ar

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) InN

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InN

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Fig. 2. (a) XRD and (b) SEM of In2O3 nanoparticles deposited over Si substrate on which InN petals have been grown; (c) XRD and (d) SEMmicrograph of InN deposited on Si substrate. The absence of any petal type of structure proves that a buffer layer of In2O3 is necessary for petalgrowth; (e) XRD of nanopetals showing formation of mainly InN along with some indium oxide and (f) SEM micrograph showing the formation ofnano-petals of InN deposited on a buffer layer of indium oxide.

In2O3 on Au nanoparticles. In their study, they have shownthat when the reaction time was increased from 0 minto 180 min, peaks in the Raman spectrum correspondingto In2O3 decreased and the peaks corresponding to InNbecame intense. It is possible that ammonia gas would

decompose to form NH, NH2, H2, and N2 at high temper-ature, oxygen would be released and some of the In2O3

may convert to InN at the subsequent growth stage. Thus,indium oxide seems to be crucial for the growth of InNnanopetals.

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Materials ExpressGrowth of indium nitride nanopetal structures on indium oxide buffer layerSingh et al.

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Si Substrate Si Substrate Si Substrate

In2O3 nanoparticles

InCl3 + O2InCl3 + NH3

InN nanopetals

(a) (b) (c)

Fig. 3. (a) Bare Si substrate used for the growth of In2O3 buffer layer,(b) growth of In2O3 nanoparticles, (c) growth of InN petal-like structureover the In2O3 nanoparticles buffer layer.

Based on the above results and discussion, the growthmechanism of InN nanorods is proposed. Figure 3 showsa schematic diagram of the growth model. In2O3 nano-particles having spherical shape were grown in the firststep (Fig. 3(b)).InCl3 ·3H2O reacts with the oxygen present in the tube

and forms indium oxide, which gets deposited on the Sisubstrate.

4InCl3+3O2 → 2In2O3+6Cl2 (1)

The following reaction carried out at 450 �C in flow ofNH3 and N2 results in the formation of indium nitride(Fig. 3(c))

InCl3+NH3 → InN+3HCl (2)

Thus, nitrogen from the ammonia reacts with indiumfrom INCl3 and InN is formed over the In2O3 nano-particles. It is possible that a number of nucleation sites areformed on the In2O3 nanoparticles. Due to the increasedtemperature and thus due to the presence of excess amountof available indium and nitrogen, InN is grown over In2O3.The formation of petal-like structures may be due to theIn2O3 providing the initial nucleation steps and due to thestructure of InN. This is a preliminary explanation; furtherwork is needed to understand the mechanism completely.Formation of petal like nanostructures allows an infi-

nite potential barrier at the boundaries. Thus, the nanopetalstructures can be used in applications where there is a needof a truly two-dimensional structure. There is a possibil-ity that the 2-D structures can have better field emissionproperties than pseudo 2D or 1-D nanostructures.�20�21� Itis expected that 2-D structures will have ballistic transportof electrons, as scattering in one dimension is completelyabsent. It should be mentioned here that the above men-tioned properties will be visible only when the dimensionof the nanopetal falls in the quantum confinement regime.In this study, we have shown a method to grow 2D InNnanostructures using In2O3 buffer layer. The growth ofIn2O3 layers on Si substrate is recent, and further studiesare needed for understanding its nature and improving thefilm quality. The good assembly between InN and In2O3

makes them an excellent candidate to integrate high qual-ity InN layers with high electrical conductivity contactsfor devices.

4. CONCLUSIONInN nanopetals have been synthesized for the first timeusing atmospheric pressure halide vapor phase epitaxy(AP-HVPE). This was accomplished by depositing anovel buffer layer of indium oxide on silicon substrate.Formation of islands of indium oxide buffer layer is con-sidered to be the main step in the mechanism for thegrowth of nanopetals. This buffer layer also improved thecrystalline quality of indium nitride as has been demon-strated by the XRD analysis.

Acknowledgments: Authors are grateful to ProfessorBR Mehta, to allow to use his lab for the research work.

References and Notes1. Y. Saito, N. Teraguchi, A. Suzuki, T. Araki, and Y. Nanishi; Growth

of high-electron-mobility InN by RF molecular beam epitaxy; Jpn.J. Appl. Phys. 40, 91 (2001).

2. N. Khan, A. Sedhain, J. Li, J. Y. Lin, and H. X. Jiang; High mobilityInN epilayers grown on AlN epilayer templates; Appl. Phys. Lett.92, 172101 (2008).

3. C.-A. Chang, C.-F. Shih, N.-C. Chen, P.-H. Chang, and K.-S. Liu;High mobility InN films grown by metal-organic vapor phase epi-taxy; Phys. Status Solidi C 1, 2559 (2004).

4. Z. L. Xie,, R. Zhang, B. Liu, L. Li, C. X. Liu, X. Q. Xiu, H. Zhao,P. Han, S. L. Gu, Y. Shi, and Y. D. Zheng; The high mobility InNfilm grown by MOCVD with GaN buffer layer; J. Crystal Growth298, 409 (2007).

5. M. E. Neil and A. M. Barnett; The spectral p–n junction modelfor tandem solar-cell design; IEEE Trans. Electron Devices 34, 257(1987).

6. S. Nakamura, T. Mukai, M. Senoh, and N. Iwasa; Thermal annealingeffects on p-type Mg-doped GaN films; Jpn. J. App. Phys. 31, 139(1992).

7. S. Orlando, A. Santagata, G. P. Parisi, L. Medici, S. Kaciulis,A. Mezzi, A. Bellucci, E. Cappelli, and D. M. Trucchi; Struc-tural, chemical, and electrical characterization of indium nitrideproduced by pulsed laser ablation; Phys. Status Solidi C 9, 993(2012).

8. S. A. Jensen, J. Versluis, E. Cánovas, J. J. H. Pijpers, I. R. Sellers,and M. Bonn, Carrier multiplication in bulk indium nitride; Appl.Phys. Lett. 101, 222113 (2012).

9. S. Luo, W. Zhou, Z. Zhang, X. Dou, L. Lifeng, X. Zhao, D. Liu,L. Song, Y. Xiang, J. Zhou, and S. Xie; Bulk-quantity synthe-sis of single-crystalline indium nitride nanobelts; Chem. Phys. Lett.411, 361 (2005).

10. T. Tang, S. Han, W. Jin, X. Liu, C. Li, D. Zhang, C. Zhou,B. Chen, J. Han, and M. Meyyapan; Synthesis and characterizationof single crystal indium nitride nanowires; J. Mater. Res. 19, 424(2004).

11. L.-W. Yin, Y. Bando, D. Golberg, and M.-S. Li; Growth of single-crystal indium nitride nanotubes and nanowires by a controlled-carbonitridation reaction route; Adv. Mater. 16, 1833 (2004).

12. C.-H. Shen, H.-W. Lin, H.-M. Lee, C.-L. Wu, J.-T. Hsu, and S. Gwo;Self-assembled InN quantum dots grown on AlN/Si (111) andGaN/Al2O3 (0001) by plasma-assisted molecular-beam epitaxy underStranski–Krastanow mode; Thin Solid Films 494, 79 (2006).

13. A. Syrkin, A. Usikov, V. Soukhoveev, O. Kovalenkov, V. Ivantsov,V. Dmitriev, C. Collins, E. Readinger, N. Shmidt, V. Davydov,S. Nikishin, V. Kuryatkov, D. Song, D. Rosenbladt, and M. Holtz;InN-based layers grown by modified HVPE; Phys. Stat. Sol. �c�3, 1444 (2006).

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14. H. Lu, W. J. Schaff, J. Hwang, H. Wu, G. Koley, and L. Eastman;Effect of an AlN buffer layer on the epitaxial growth of InN bymolecular-beam epitaxy; Appl. Phys. Lett. 79, 1489 (2001).

15. Ch. Y. Wang, V. Lebedev, V. Cimalla, Th. Kups, K. Tonisch, andO. Ambacher; Structural studies of single crystalline In2O3 films epi-taxially grown on InN (0001); Appl. Phys. Lett. 90, 221902 (2007).

16. C.-L. Hsiao, L.-W. Tu, M. Chen, Z.-W. Jiang, N.-W. Fan, Y.-J. Tu,and K.-R. Wang; Polycrystalline to single-crystalline InN grown onSi (111) substrates by plasma-assisted molecular-beam epitaxy; Jpn.J. Appl. Phys. 44, L1076 (2005).

17. A Yamamoto, M. Tsujino, M. Ohkubo, and A. Hashimoto; Nitrida-tion effects of substrate surface on the metalorganic chemical vapordeposition growth of InN on Si and �-Al2O3 substrates; J. Cryst.Growth 137, 415 (1994).

18. J. G. Lozano, F. M. Morales, R. García, and D. González,V. Lebedev, Ch. Y. Wang, V. Cimalla, and O. Ambacher; Cubic InNgrowth on sapphire (0001) using cubic indium oxide as buffer layer;Appl. Phys. Lett. 90, 091901 (2007).

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Received: 22 May 2013. Revised/Accepted: 1 September 2013.

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Materials Express - Brijesh Kumarbrijeshkumar.com/wp-content/uploads/2014/10/2013... · Vidya N. Singh 1,, G. Partheepan 2, Brijesh Kumar 3, and Ankur Khare 4 1CSIR National Physical