MICROSTRUCTURE OF GAN FILMS ON GAAS(1 0 0) SUBSTRATES GROWN BY HYDRIDE VAPOR-PHASE EPITAXY

We have characterized the microstructure of GaN films on GaAs(100) vic inal substrates grown by hydride vapor-phase epitaxy using transmissio n electron microscopy (TEM). For the substrates misoriented toward the [111]B direction, a single-domain GaN overlayer having a wurtzite str ucture with hexagonal symmetry was observed to be predominantly grown on a GaN buffer layer, with the c-axis parallel to the (111)B directio n of the GaAs substrate. Cross-sectional TEM unambiguously revealed a buffer-layer structure consisting of two to four kinds of cell-like do mains that had a hexagonal structure. We found that only one of the ce ll domains preferentially grew into a thick overlayer, leading to the formation of the single-domain structure. Furthermore, we observed cha racteristic defects due to this anisotropic film orientation with resp ect to the GaAs(100) substrate. The growth mechanism of the hexagonal GaN films mediated by the stacking-fault nucleation on the GaAs(100) s urface is discussed.