Surface structures of aluminum nitride crystals

Abstract

The surface structures of (0001) and (000^-1) faces of single crystals of A1N grown by the sublimation method were observed and classified in relation to the piezoelectric effect. The piezoelectric effect bears a relation with the surface structures of blade-shaped crystals and part of tabular crystals. The surface which is charged positively by a compressive stresss in the direction parallel to the c-axis is defined as the (000^-1) face. The surface which is charged negatively by the same stress is defined as the (0001) face. On the (000^-1) face, hexagonal growth hillocks and bunched growth steps were observed and on the (0001) face, only irregular thin growth layers or flat faces without any characteristic features were observed. It can be concluded therefore that the growth rate normal to the (000^-1) face is larger than that normal to the (0001) face. Most of the tabular crystals do not show the difference in the surface structure. Some of them have the surface structure characteristic of the (0001) on both surfaces and other crystals have the surface structure characteristic of the (000^-1) on both surfaces. It is concluded that these crystals have interstice lattice stacking faults in the basal planes due to the formation of Al₂CO. In fact, no piezoelectric effect was observed on these crystals.