Cubic GaN Heteroepitaxy on Thin-SiC-Covered Si(001)
- PDF / 1,283,471 Bytes
- 6 Pages / 612 x 792 pts (letter) Page_size
- 20 Downloads / 203 Views
s://www.cambridge.org/core. IP address: 213.108.2.91, on 11 Jul 2020 at 12:33:45, subject to the Cambridge Core terms of use, available at https://www.cambridge.org/core/terms. https://doi.org/10.1557/S1092578300002386
order to form SiC layers. The SiC-formed Si(001) substrates were then cooled down to room temperature and immediately transferred to the MBE growth chamber . They were then annealed at 1000 °C for 1 min and cooled down to a growth temperature of 600 to 900 °C. GaN films were grown using RF-MBE under the following growth conditions: the nitrogen gas flow rate was set at 2 sccm and the RF-power was set at 300 W. Gallium molecular beam was supplied to the substrate by using a Knudsen-cell operating at 850 to 1000 °C. The surface morphology and the quality of GaN films were characterized by using in-situ reflection high energy electron diffraction (RHEED) and cross-sectional transmission electron microscopy (XTEM) as well as x-ray diffraction (XRD) measurements. Photoluminescence (PL) measurements were also carried out using a 325 nm beam from a He-Cd laser. THIN SiC LAYER FORMATION Figure 1 shows high-resolution XTEM (HRXTEM) micrographs of the substrates carbonized at 950 °C for 10 min under various C 2H2 pressures. For a C 2H2 pressure of 5 × 10-7 Torr small SiC islands were formed on the Si. A RHEED pattern of the as-grown SiC layer showed three-dimensional diffused spots, as seen in the inset of Fig. 1(a). For a C2H2 pressure of 5 × 10 -6 Torr the surface morphology of the SiC became flat (Fig. 1(b)), and a streaky RHEED pattern was observed. The film thickness of the SiC was approximately 4 nm. With a higher C2H2 pressure of 5 × 10-5 Torr an approximately 5-nm-thick SiC layer was formed. The clear spotty pattern shown in the inset of the Fig. 1(c) indicates that the surface flatness of the SiC was more degraded than that of the SiC grown at a pressure of 5 × 10 -6 Torr. As shown in Fig. 1(b), the spacing between two {111} planes of the SiC layer was approximately 0.25 nm by referring to the spacing of 0.31 nm between {111}Si and was almost the same as that of bulk β-SiC. This indicates that the misfit between SiC and Si was almost completely relaxed by the generation of misfit dislocations in the SiC layer. Figure 2 shows HRXTEM micrographs of Si substrates carbonized at 950 °C under a C2H2 pressure of 5 × 10-6 Torr for (a) 1 min and (b) 3 min. As seen in Fig. 2(a), a 1-nm-thick SiC layer was formed. The RHEED pattern of the SiC was more diffused than that of the thicker SiC layers. After carbonization for 3 min the thickness of the SiC layer was approximately 3 nm and the surface morphology was two-dimensional (Fig. 2(b)). Further growth of the SiC layer was saturated at 4 nm with the carbonization time up to 10 min as shown in Fig. 1(b). This thickness saturation of the SiC layer is known to be due to the suppression of the outdiffusion of Si atoms from the substrates during the SiC formation [9]. The GaN films grown on the substrates of Figs. 1(b), 1(c) and 2(b) became single-crystal cubic GaN f
Data Loading...
