Phase pure cubic (c-) GaN/AlGaN heterostructures on 3C-SiC free standing (001) substrates have successfully been developed. Almost complete (100%) phase pure c-GaN films are achieved with 2-nm surface roughness on 3C-SiC substrate and stoichiometric growth conditions. The polarization effect in c-GaN/AlGaN has been evaluated, based on measuring the transition energy of GaN/AlGaN quantum wells (QWs). It is demonstrated that the polarization electric fields are negligible small in c-GaN/AlGaN/3C-SiC compared with those of hexagonal (h-)GaN/AlGaN, 710 kV/cm for Al content x of 0.15, and 1.4 MV/cm for x of 0.25. A sheet carrier concentration of c-GaN/AlGaN heterojunction interface is estimated to 1.61012 cm-2, one order of magnitude smaller than that of h-GaN/AlGaN. The band diagrams of c-GaN/AlGaN HEMTs have been simulated to demonstrate the normally-off mode operation. The blocking voltage capability of GaN films was demonstrated with C-V measurement of Schottky diode test vehicle, and extrapolated higher than 600 V in c-GaN films at a doping level below 51015 cm-3, to show the possibility for high power electronics applications.

We studied Si and Mg doping characteristics in cubic GaN and fabricated a light emitting diode of cubic GaN on a GaAs substrate by metalorganic vapor-phase epitaxy. The diode structure consisted of undoped and Mg-doped GaN stacking layers deposited on Si-doped GaN and AlGaN layers. The electron-beam-induced-current signal and current injection characteristics of this diode structure were measured. There was a peak at the interface between the Mg-doped and undoped GaN in the electron-beam-induced-current signal. This shows successful growth of the p-n junction. Light emitting operation was achieved by currents injected through the conducting GaAs substrate of this diode at room temperature. We observed electroluminescence below the bandgap energy of cubic GaN with a peak at 2.6 eV.