Optical properties of cubic GaN grown on 3C-SiC (100) substrates by metalorganic vapor phase epitaxy

Cubic GaN with different low-temperature buffer layers were grown on 3C-SiC (100) substrates by metalorganic vapor phase epitaxy (MOVPE). The sample s urface morphology was affected considerably by the thickness of the buffer layer. An X-ray diffraction-peak shift was observed for these samples, indi cating the existence of residual strain inside the crystal. The origin of t he residual strain can be attributed to the different thermal expansion coe fficients of GaN and 3C-SiC, The residual strain has a strong influence on the excitonic transition energies. From the strain dependence of the shift of the exciton peaks, the value of the excitonic bandgap and the strain coe fficient (relation between strain parallel to z-axis and exciton energy) of cubic GaN were estimated.