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. The HVPE layers were found to grow primarily with Ga-polarity. 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 an increase in layer thickness was observed for all of the 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.