Growth and Characterization of GaN Thin Films on Si(111) Substrates Using SiC Intermediate Layer
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on Si substrate have a rough SiC/Si interface, a poor single crystal quality, a high concentration of lattice defects and high level of background impurities. Also, it is not easy to solve these problems because of the differences of thermal expansion coefficient and extremely large lattice mismatch (~20%) between SiC and Si. In spite of these problems, it was tried to grow the GaN films on Si substrate using SiC as intermediate layer, because of the SiC intermediate layers act on reduce the lattice mismatch and relax thermal expansion. In the previously reports, SiC films were successfully grown on directly Si(111) substrates.[6][7] SiC(111) planes is a better lattice match to subsequent growth of hexagonal GaN films than SiC(100) planes. In this work, we grow the GaN films on Si(111) substrates using the SiC intermediate layer by low pressure metalorganic chemical vapor deposition (LPMOCVD) and investigate the structural and optical characterization of GaN films. We compare properties of the GaN films growth on SiC/Si(111) with AlN or GaN buffer layer and without buffer layer. We also compare the results of the GaN films grown with and without high temperature thermal treatment of SiC intermediate layer in H2 ambient. EXPERIMENT The SiC films on (111)-oriented Si substrates were grown by chemical vapor deposition (CVD) system using the tetramethylsilane (TMS) as the single source precursor. Before the loading into CVD system, the Si substrates were degreased in organic solvents and surface oxide was removed by etching in HF solution. The reactor
Fig. 1 Optical microscope picture of the surface morphology of a 3-C SiC grown on Si(111) substrate.
Fig. 2 Wide angular range x-ray diffraction spectra of 3-C SiC grown on Si(111) substrate.
was evacuated down to 5 torr pressure. The Si substrate was thermally cleaned at 1100 °C for 5 minute in H2 ambient. Then, the reactor temperature was increased to 1250 °C for the SiC deposition. During the SiC growth, the TMS flow rate and H2 flow rate were 1 sccm and 1000 sccm, respectively. The Si terminated SiC surface was obtained by
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immediately flow of SiH4 gas after growth of SiC film at the same temperature. After 1 hour growth, the surface morphology and structural properties of the SiC films were investigated by optical microscope and x-ray diffraction (XRD), respectively. Figure 1 shows the optical microscope image. The surface morphology of SiC films grown on Si(111) is the shape of scales which comes from the surface of Si after thermal cleaning before the SiC growth. In figure 2, wide angle x-ray diffraction spectra of SiC film on Si(111) substrate is showed. The 2 peak of SiC(111) planes at 35.65 degree reveals that the SiC film has a 3C phase crystal structure. The Si-terminated SiC/Si(111) substrate was cleaned again in organic solvents adding ultra sonic agitation. And the surface of SiC/Si(111) substrate was etched by dipping in 48% HF:H2O for 3 sec and rinsed D. I. water. GaN layer was grown on SiC/Si(111) by low pressure MOCVD system, us
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