GaN homoepitaxial layers grown by metalorganic chemical vapor deposition

GaN homoepitaxial layers were grown using metalorganic chemical vapor deposition on the highly conductive GaN bulk crystals grown at high hydrostatic pressure. The epitaxial growth process was monitored by reflectivity of red laser light. The oscillations of its intensity served for the precise evaluation of the growth rate. The layers were then investigated using far-infrared reflectivity (FIR), x-ray diffraction, and photoluminescence. The FIR spectrum gave small free-electron concentration in the layers in contrast to the substrates which had about $2.5×1019 cm−3$ of free electrons. In x-ray diffraction, the peaks of the substrate and of the layer were separated due to the difference between the lattice parameters of the bulk GaN substrate (expanded by free electrons and point defects) and the layer which had a low free electron concentration. Both peaks had rocking curves with half widths of about 20 arcsec. The photoluminescence spectrum contained narrow peaks of less than 1 meV with the excitonic lines well resolved. The spectrum was dominated by the donor-bound exciton peak. All acceptor-related peaks had small intensities that indicated a very low acceptor concentration in the layers.