Tem Study of Interfaces and Defects in MOCVD-Grown Gan on SiC on Simox
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ABSTRACT SiC was grown on the top Si layer of SIMOX by carbonization followed by chemical vapor deposition (CVD). Subsequently, GaN was deposited on the SiC by metalorganic (MO)CVD to produce a GaN/SiC/Si/Si0 2/Si multilayer structure. This multilayer film was investigated by conventional transmission electron microscopy (TEM) and high resolution (HR)TEM using cross-sectional thin foils. The GaN layer was found to consist of predominately hexagonal gallium nitride (h-GaN), and a smaller fraction of cubic GaN (c-GaN) crystallites. The orientation relationship between most of the h-GaN grains and cubic SiC (3C-SiC) was found to
be
(0001)GavN(1I1 1)sic;
[112 O]GaN//[I
I
O]sic,
while most of the c-GaN grains had an orientation
relationship (O01)GaN//(O0l)SiC; [1 I 0]GaN/[l O]siC with respect to the 3C-SiC substrate. The hexagonal grains of GaN were found to grow as two variants. In this paper, the defects in both hGaN and c-GaN are characterized and discussed. INTRODUCTION Gallium nitride and related materials have been successfully employed in many devices such as lasers [1] and transistors [2]. Sapphire (ct-AL 20 3) is probably the most common substrate for growth of GaN films [3]. However, the large lattice mismatch between GaN and A120 3 may be the main cause for the presence of the large defect density that is observed in the GaN films; it is well-established that defects in semiconductor thin films deteriorate their electronic and/or optoelectronic properties. Consequently, alternative substrates are being studied with the aim of growing films with a lesser defect density, with the aim of achieving improved optoelectronic properties. Various other substrates, such as 6H-SiC [4-6], MgA120 4 [7], Si (1 11) [8], GaAs [9] and ZnO [10] have been employed to grow wurtzitic GaN film. Silicon carbide (SiC) has the added advantage over many other substrates in that is a wide-band-gap semiconductor with high thermal stability, excellent resistance to chemical attack, high thermal conductivity, high electron mobility, and small lattice mismatch with GaN (Ad/d=4%). Thus, SiC has been considered as a potentially ideal substrate or buffer layer for the growth of GaN thin films [11]. In this paper, we report a transmission electron microscopy study of GaN grown on SiC on SIMOX by metalorganic chemical vapor deposition (MOCVD).
471 Mat. Res. Soc. Symp. Proc. Vol. 482 ©1998 Materials Research Society
EXPERIMENTAL SiC is desirable for a number of reasons including its use in a large area wafer form for manufacturing high-power, high-temperature, electronics devices; it is also a nearly latticematched substrate for group IIl-nitrides. In addition, when SiC is epitaxially deposited on silicon-on-insulator (SOI) substrates, it may pave the way for monolithic integration of GaN photonic devices with advanced Si technology. In the present work a SPI-MOCVDTM reactor was used for growth of SiC on SO. The details of the process for growing the SIMOX substrate can be found elsewhere [121. For growing SiC, the top Si layer of SIMO
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