Helical-type surface defects in GaN thin films epitaxially grown on GaN templates at reduced temperatures

摘要

Surface pits in the form of v-shaped defects and resulting surface roughening, previously associated solely with InGaN films, were observed and investigated using atomic force microscopy on GaN films grown at 780℃ via metalorganic vapor phase epitaxy on conventionally and pendeo-epitaxially deposited GaN thin film templates. The density of the v-shaped defects was similar to the density of threading dislocations of ～ 3 x 10~9 cm~(-2) (that originate from the heteroepitaxial interface between the GaN template layer and the SiC substrate). Moreover, the v-defect density was diminished with decreases in the dislocation density via increases in the template layer thickness or the use of pendeo-epitaxial seed layers. A concomitant reduction in the full-width half-maxima of the X-ray rocking curves was also observed. A qualitative model is presented that describes the formation of v-shaped defects as a result of interactions between the movement of surface steps, screw-type dislocation cores, and clusters of atoms on the terraces that form under conditions of high surface undercooling.