EXTENDED DEFECTS AND POLARITY OF HYDRIDE VAPOR PHASE EPITAXY GaN

Hydride vapor phase epitaxy (HVPE) GaN layers on sapphire substrates and so-called free-standing platelets (layers removed from the sapphire) were studied by different transmission electron microscopy (TEM) techniques. Polarity determined by convergent beam electron diffraction (CBED) and distribution of structural defects, determined by conventional TEM, are discussed. HVPE layers were found to grow primarily with Gapolarity. A few inversion domains (areas with N-polarity) were observed on the substrate side of one of the free-standing layers. The dominant structural defects in HVPE GaN layers are threading dislocations. A systematic reduction of their density with increase in layer thickness was observed for all samples. The experimental results indicate that the density of dislocations is inversely proportional to the distance from the substrate, which agrees with the theoretical model.