Thermal stability of cubic GaN film grown by molecular-beam epitaxy on GaAs(001)

The thermal stability of cubic-phase GaN (c-GaN) film grown by molecular-beam epitaxy was investigated by Raman scattering spectroscopy and X-ray scattering. The results of Raman scattering shows that, after annealing at 1000°C, the intensity of transverse (TO) and longitudinal (LO) optical peaks from cubic phase obviously decreases while the intensity of TOb peak from the boundary effect slightly decreases, but the transformation of the hexagonal phase (α-GaN) can not be detected due to a little of α-GaN inclusion. X-ray reflectivity measurements indicate that there is a high-electron-density layer between the substrate and the GaN film, and it becomes uniform and much thinner after high-temperature annealing, counting for the Raman results of the intensity change of the TOb peak. The results of high-angle X-ray diffraction and X-ray reciprocal space mapping revealed that the relative content of α-GaN obviously increases after annealing at 1000°C, and (101̄1) is the most stable diffraction lattice of the α-GaN hexagonal phase.