Papers by Keyword: Cubic GaN

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.

Abstract: Epitaxial lateral overgrowth (ELO) was performed to grow cubic GaN layers on stripe-patterned GaAs (001) substrates via metalorganic vapor phase epitaxy. Growth time was varied from 10 to 120 minutes to investigate an evolution of growth morphologies and crystal structures of GaN, which were respectively analyzed by scanning electron microscopy and micro-Raman scattering spectroscopy. Growth features of ELO cubic GaN for [1-10] oriented mask stripe-pattern showed the {113} side-wall facets. On the other hand, the {111} side-wall facets were observed for ELO cubic GaN grown on the [110] oriented mask stripe-pattern. In case of [100] oriented mask stripe-pattern, growth feature with top rough surface and unclear side-wall facets was obtained. Micro-Raman spectroscopy was used as a tool to identify both cubic and hexagonal GaN structures performed on surface of the top and side-wall facets of the GaN stripes. ELO cubic GaN layer with growth time of 60 min along the [1-10] oriented mask stripe-pattern exhibited the highest ratio of cubic to hexagonal GaN, which was examined from an integrated intensity of LO phonon mode at 738 cm^-1 for cubic GaN comparing with that of hexagonal GaN, appearing at A₁ (TO) 538 cm^-1, E₁ (TO) 558 cm^-1 and E₂ (high) 568 cm^-1.

Abstract: Cubic GaN, AlxGa1-xN/GaN and InyGa1-yN/GaN multiple quantum well (MQW) layers were grown by plasma assisted molecular beam epitaxy on 200 &m thick free standing 3C-SiC substrates. The influence of the surface roughness of the 3C-SiC substrates and the influence of metal coverage during growth are discussed. Optimum growth conditions of c-III nitrides exist, when a one monolayer Ga coverage is formed at the growing surface. The improvement of the structural properties of cubic III-nitride layers and multilayers grown on 3C-SiC substrates is demonstrated by 1 μm thick c-GaN layers with a minimum x-ray rocking curve width of 16 arcmin, and by c-AlGaN/GaN and c-InGaN/GaN MQWs which showed up to five satellite peaks in X-ray diffraction, respectively.