Seminars Archive

TEM Studies of Defects in III-V Compounds

Abstract
High quality GaN/AlN layers grown on (111) Si substrates have been used as the seeding layer for lateral epitactic overgrowth. The selective overgrowth was controlled by depositing a Si3N4 mask on the GaN layer. Growth of additional GaN resulted in the formation of GaN pyramids above the apertures in the patterned Si3N4. Transmission electron microscopy showed that the GaN pyramids, the GaN seed layer, and the AlN buffer layer in the samples have the usual epitactic relationship with respect to the Si substrate. The pyramids were found to consist of a defective core region and a more nearly defect-free outer region. In the core of the pyramid (at, or above, the aperture in the mask), numerous dislocations thread through the pyramid perpendicular to the interface plane. Some of these threading dislocations, which originated from the GaN/AlN seed layer, bend abruptly through 90* at the edge of this core region. In the outer part of the GaN pyramid, the density of vertically propagating dislocations was much lower. Most of the dislocations in this region are very closely parallel to the original (0001) substrate plane. Planar defects, usually lying parallel to the interface plane, were observed near the Si3N4 interface. The top few microns of material may then be essentially defect-free. The growth mechanism of the GaN pyramids is discussed in light of this defect structure. If time permits, some new studies on defects such as the double ribbon, antiphase boundaries and grain boundaries in GaP will also be presented. The interest in these studies is the role of antisite bonding in determining the structure and properties of defects in these cubic polar semiconductors.