Abstract:
c-GaN films on GaAs (001) substrates were investigated using TEM to verify effects of buffer layer growth temperature on micro-structures. Growth temperature of the GaN buffer layer was varied in a range of 550 to 600°C and GaN film was grown at high temperature (∼900°C). For GaN buffer layer at 550°C, the plan-view TEM micrographs of c-GaN films show high density of stacking faults (SFs) and dislocations. At the GaN/GaAs interface, the electron diffraction (ED) pattern demonstrated different type of single diffraction spots which include the high intensity of streaking. This results indicated that the high density of SFs become dense into hexagonal phase single crystal. For 575°C GaN buffer layer, the wide SFs are observed that these broad lines are not expanding to the GaN surface and the dislocations are less found than the other temperature. Moreover, cross-sectional TEM micrographs and the ED pattern at interface show pyramid like structure and less intensity of the steak lines, respectively. There are no diffraction spots related to hexagonal structure. For 600°C GaN buffer layer, there are the steaking of diffraction spots which represent hexagonal phase inclusions at interface. V-shape voids defects are penetrating in the GaAs surface which were caused the thermal decomposition of As. Our results indicated that, the high quality of GaN film with cubic phase purity grown on GaAs (001) are achieved from the optimum growth temperature GaN buffer layer of 575°C.
