Epitaxial growth of SiC on complex substrates was carried out at substrate temperature from 1200 degreesC to 1400 degreesC. Three kinds of new complex substrates, c-plane sapphire, AlN/sapphire, and GaN/AlN/sapphire, were used in this study. We obtained a growth rate in the range of 1-6 mum/h. Thick (6 mum) SIC epitaxial layers with no cracks were successfully obtained on AlN/sapphire and GaN/AlN/sapphire substrates. X-ray diffraction patterns have confirmed that single-crystal SiC was obtained on these complex substrates. Analysis of optical transmission spectra of the SIC grown on sapphire substrates shows the lowest-energy gap near 2.2 eV, which is the value for cubic SiC. The undoped SIC showed n-type electrical conductivity. (C) 2001 Elsevier Science B.V. All rights reserved

Li JM

Lin LY

Luo MC

Sun GS

Sun GS,Chinese Acad Sci,Inst Semicond,Beijing 100083,Peoples R China.

Wang L

Zhang FF

Zhu SR

Knowledge Repository of SEMI,CAS

Journal of Crystal Growth 227–228 (2001) 811–815Epitaxial growth of SiC on complex substratesG.S. Sun*, J.M. Li, M.C. Luo, S.R. Zhu, L. Wang, F.F. Zhang, L.Y. LinInstitute of Semiconductors, Chinese Academy of Sciences, Beijing 100083, People’s Republic of ChinaAbstractEpitaxial growth of SiC on complex substrates was carried out at substrate temperature from 12008C to 14008C.Three kinds of new complex substrates, c-plane sapphire, AlN/sapphire, and GaN/AlN/sapphire, were used in thisstudy. We obtained a growth rate in the range of 1–6 mm/h. Thick (6 mm) SiC epitaxial layers with no cracks weresuccessfully obtained on AlN/sapphire and GaN/AlN/sapphire substrates. X-ray diﬀraction patterns have conﬁrmedthat single-crystal SiC was obtained on these complex substrates. Analysis of optical transmission spectra of the SiCgrown on sapphire substrates shows the lowest-energy gap near 2.2 eV, which is the value for cubic SiC. The undopedSiC showed n-type electrical conductivity. # 2001 Elsevier Science B.V. All rights reserved.PACS: 81.15.H; 61.10.N; 78.66.D; 78.20.C; 68.55Keywords: A1. Optical microscopy; A1. X-ray diﬀraction; A3. Molecular beam epitaxy; B2. Semiconducting silicon compounds1. IntroductionSilicon carbide (SiC) is a rapidly developingwide-band-gap semiconductor, because it ismechanically strong, chemically inert, and suitablefor high-temperature, high-frequency, andhigh-power electronics. SiC epitaxial layers areroutinely deposited onto a silicon wafer orsublimation-grown bulk hexagonal SiC by mole-cular beam epitaxy (MBE) or chemical vapordeposition (CVD). Crystal growth of SiC onsapphire is quite interesting from the point viewof semiconductor-on-insulator (SOI) structures.For most high-power applications, an insulatingor semi-insulating substrate supporting the deviceis necessary to reduce parasitic eﬀects and toincrease the maximum power capability of thedevice. There are several reports using sapphiresubstrates [1–6]. The nucleation and adherence ofthe SiC ﬁlms on sapphire substrates were vastlyimproved with an AlN buﬀer layer and uniformand continuous SiC ﬁlms could be obtained onsapphire substrates [5]. In this paper we investi-gated the crystal growth of SiC on complexsubstrates, including c-plane sapphire, AlN/sap-phire, and GaN/AlN/sapphire. The experimentalresults of SiC epitaxy on such substrates arereported here. In order to simplify the growthprocess, the SiC layers on sapphire substrates witha thin nitridation layer obtained by adding NH3 tothe chamber at 11008C prior to the growth of SiCwere compared with those on AlN/sapphiresubstrates prepared by MBE.*Corresponding author.E-mail address: gshsun@red.semi.ac.cn (G.S. Sun).0022-0248/01/$ - see front matter # 2001 Elsevier Science B.V. All rights reserved.PII: S 0 0 2 2 - 0 2 4 8 ( 0 1 ) 0 0 8 8 9 - 22. ExperimentalThree kinds of new substrates, c-plane sapphire,AlN/sapphire, and GaN/AlN/sapphire, were usedas substrates for SiC epitaxy. Both AlN/sapphireand GaN/AlN/sapphire were grown by MBE inthis laboratory on c-plane sapphire substrates.Single crystalline AlN (0 0 0 1) and GaN (0 0 0 1)layers with thickness of 1.0–1.5 mm and 0.5–0.8 mmwere obtained in the temperature ranges of 7008C–8508C and 8008C–8508C, respectively. Immedi-ately before use the sapphire substrates wereultrasonically cleaned for 10min each in (i)trichloroethylene; (ii) acetone; (iii) ethyl alcohol,then treated with H2SO4 :H3PO3 (3 : 1) solution atabout 1608C for 15min, and ﬁnally dried inﬂowing dry nitrogen. The growth of SiC oncomplex substrates was carried out in a modiﬁedMBE system in the temperature range of 12008C–14008C using Si2H6 and C2H4 at a pressure of200Torr, which is in the CVD pressure range. Pd-cell-puriﬁed hydrogen was used as the carrier gas.The conﬁguration and description of the modiﬁedMBE setup will be published elsewhere.Before growth, the complex substrates wereannealed in hydrogen at 12008C for 10min at apressure of 200Torr in order to remove any traceof contamination and to produce a surface suitablefor epitaxy. After such thermal cleaning, Si2H6 andC2H4 were introduced until desired values werereached. SiC was grown with the following ﬂowrates: 2 sccm Si2H6, 3 sccm C2H4, and an addi-tional 2000 sccm H2. The substrate temperatureranging from 12008C to 14008C was estimated byusing an optical pyrometer through a window atside of the chamber. Under these conditions, thegrowth rate for SiC was in the range of 1–5 mm/h.Room-temperature electrical and optical prop-erties were obtained using Van der Pauw–Hallmethod and analysis of transmission spectra on anumber of SiC samples on these substrates. Theundoped SiC layers show n-type electricalconductivity with mobilities of approximately2–7 cm2/V s and (Nd–Na) in the range of3.3 10187.7 1018 cm3. The structural proper-ties were studied using Rigaku D/max-2400 X-raydiﬀractometer. Surface morphologies of the epi-layers were characterized by Nomarski diﬀerentialinterference contrast optical microscopy. Thethickness was determined by step-height proﬁler(TENCOR alpha-step 250).3. Results and discussionWe obtained the optical-absorption spectra fora few SiC epitaxial layers deposited on sapphiresubstrates by measuring the optical transmissionspectra. As the frequency increases above thatcorresponding to the lowest band gap the absorp-tion due to interband transitions becomes domi-nant. The absorption coeﬃcient of this type oftransition has the following form, neglecting thephonon energies compared to the total transitionenergy [5]aðEÞ ¼ CðE  EgÞ2n1; ð1Þwhere E ¼ hn and Eg is the energy gap. Thus, byplotting ðahnÞ1=2 as a function of E, the lowestindirect gap can be obtained from a linear ﬁt to theappropriate range of the curve. Fig. 1 shows atypical plot. The band gap is determined to be2.2 eV, showing that the epitaxial layers depositedon sapphire have a structure of cubic (3C) SiC. Wehave not measured the optical transmissionspectra for SiC on AlN/sapphire and GaN/AlN/sapphire substrates.Fig. 1. Plot of the square root of the product of the absorptioncoeﬃcient times the photon energy, as a function of the energyfor a typical SiC/sapphire sample. The thickness of SiC is1.5 mm.G.S. Sun et al. / Journal of Crystal Growth 227–228 (2001) 811–815812Optical microphotographs ( 600 magniﬁca-tion) of surface morphology of the epitaxial layersgrown at four diﬀerent growth temperatures onsapphire substrates are shown in Fig. 2. This ﬁgureillustrates the reduction in the density of surfacespot-like features by increasing the substratetemperature from 12408C to 13508C. It can beseen that the surface of the epitaxial layer grown at13508C is nearly featureless.Fig. 3 shows typical X-ray diﬀraction patternsfrom the SiC on (a) sapphire, (b) AlN deposited onsapphire, and (c) GaN deposited on AlN/sapphire.In Fig. 3(a), the X-ray diﬀraction pattern showsSiC (1 1 1) at 35.68 and (2 2 2) at 75.38 from crystalplanes parallel to the substrate. The (1 1 1) peakoriginates in the fundamental lattice spacing of2.52 A˚ along the trigonal axis of SiC, whereas the(2 2 2) peak is the corresponding second-orderdiﬀraction. The (1 1 1) peak possesses the narrow-est full width at half maximum (FWHM) of 0.168.This result indicates that the SiC epitaxial layerson sapphire substrates are crystalline with sub-stantial (1 1 1) preferential orientation. Because ofthe close lattice match of AlN and SiC, thepositions of the two SiC peaks were at 35.88 and75.88, respectively, for SiC on AlN/sapphire asshown in Fig. 3(b). The AlN (0 0 0 2) peak at2y=36.18 was buried in the strong SiC peak. TwoSiC peaks at 35.68 and at 75.28 are clearly seen inFig. 3(c) for SiC deposited on GaN/AlN/sapphiresubstrate. These results demonstrate single epitax-ial SiC crystal layers because of the absence ofother SiC peaks and the suitability of AlN andGaN as a buﬀer layer to grow epitaxial SiC onsapphire substrates. Since the diﬀraction peak ataround 2y=35.68 may come from (1 1 1) plane ofcubic SiC, the polytypes of SiC deposited on AlN/sapphire and GaN/AlN/sapphire substrates areyet to be identiﬁed.In order to simplify the growth process, thenitridation process was employed in the hetero-epitaxial growth of SiC on sapphire, instead ofgrowing AlN on sapphire substrates by MBE. Thenitridized ﬁlm was formed by supplying NH3 tothe heated sapphire substrate at temperature of11008C for 10min in this study. This procedureFig. 2. Nomarski diﬀerential interference contrast optical microphotographs ( 600 magniﬁcation) of the surface morphology of theepitaxial layers grown on sapphire substrates at four diﬀerent growth temperatures.G.S. Sun et al. / Journal of Crystal Growth 227–228 (2001) 811–815 813has as a consequence the formation of a relaxedAlN thin layer [7,8]. Fig. 4 shows a typical result ofX-ray diﬀraction measurement of a SiC samplegrown on nitridized sapphire. The presence of SiC(1 1 1) and SiC (2 2 2) peaks at 2y=35.68 and 75.48,respectively, and the absence of any other reﬂec-tions corroborates that the SiC ﬁlm is singlecrystalline.The electrical properties of SiC on these fourtypes of substrates obtained by Hall measurementsat room temperature are comparable. In the caseof SiC grown directly on sapphire we have notbeen able to grow epitaxial layers thicker than1 mm. When the substrates were cooled fromgrowth temperature down to room temperature,epitaxial layers thicker than this appear to peel oﬀfrom the edges, as described in Ref. [9]. However,because of the close lattice match of AlN and SiC,GaN and SiC, thick SiC epitaxial layers up to 6 mmwith no cracks were successfully obtained on AlN/sapphire and GaN/AlN/sapphire as well as nitri-dized sapphire. To our knowledge, there are noreports on growth of SiC on nitridized sapphiresubstrates.Fig. 3. X-ray diﬀraction patterns from the SiC on (a) sapphire, (b) AlN deposited on sapphire, and (c) GaN deposited on AlN/sapphire.Fig. 4. Typical result of X-ray diﬀraction measurement of SiCﬁlm grown on nitridized sapphire substrate. The growthtemperature was 13508C.G.S. Sun et al. / Journal of Crystal Growth 227–228 (2001) 811–8158144. ConclusionEpitaxial growth of SiC on complex substrateswas carried out at substrate temperature from12008C to 14008C. Analysis of optical transmis-sion spectra of the SiC grown on sapphiresubstrates shows the lowest energy gap near2.2 eV, which is the value for cubic SiC. X-raydiﬀraction patterns have conﬁrmed that single-crystal SiC was obtained on complex substrates.Single crystalline 3C-SiC epitaxial layers can alsobe grown on nitridized sapphire substrates. ThickSiC epitaxial layers with no cracks were success-fully obtained on AlN/sapphire, GaN/AlN/sap-phire, and nitridized sapphire substrates.AcknowledgementsWe gratefully acknowledge the support of theNational Natural Science Foundation.References[1] L. Rimai, R. Ager, J. Hangas, E.M. Logothetis, J. Appl.Phys. 73 (1993) 8242.[2] H. Nakamatsu, S. Kawai, MRS Symp. Proc. 97 (1987) 189.[3] J.C. Pazik, G. Kelner, N. Bottka, Appl. Phys. Lett. 58(1991) 1419.[4] S. Misawa, S. Yoshida, S. Gonda, Extended Abstracts, The44th Autumn Meeting, The Japan Society of AppliedPhysics, Vol. 27, 1983, pp. A-11.[5] B.S. Sywe, Z.J. Yu, S. Burckhard, J.H. Edger, J. Chaudhuri,J. Electrochem. Soc. 141 (1994) 510.[6] S. Nishino, K. Takahashi, H. Tanaka, J. Saraie, Proceed-ings of the Fifth SiC and Related Materials Conference,Washington DC, 1993, p. 63.[7] T.D. Moustakas, R.J. Molnar, T. Lei, G. Menon, C.R.Eddy, Jr., Mater. Res. Soc. Symp. Proc. 242 (1992). 427.[8] N. Grandjean, J. Massies, M. Leroux, Appl. Phys. Lett. 69(1996) 2071.[9] X. Tang, K.G. Irvine, Z. Ping, M.G. Spencer, B. Molnar,Mater. Sci. Eng. B 11 (1992) 39.G.S. Sun et al. / Journal of Crystal Growth 227–228 (2001) 811–815 815

Epitaxial growth of SiC on complex substrates

Sun GS Chinese Acad Sci Inst Semicond Beijing 100083 Peoples R China.

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Epitaxial growth of SiC on complex substrates

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