Defects in m-face GaN films grown by halide vapor phase epitaxy on LiAlO2

Free-standing wafers (50 mm diameter) of GaN were grown by halide vapor phase epitaxy on lattice-matched gamma-LiAlO2. We report a transmission electron microscopy study of defects and defect densities in these wafers. The growth direction is [10 (1) over bar0]. Stacking faults in the basal plane are seen when viewing the specimen in the [1 (2) over bar 10] direction with an average spacing of less than 100 nm. Convergent beam electron diffraction measurements show no switch in the polarity and thus the faults are proposed to be ABABACAC changes in the stacking. Threading dislocations are found to have a correlated arrangement with a density of 3x10(8) cm(-2) when viewing the [1 (2) over bar 10] direction and widely varying (depending upon location) when viewing in the [0001] direction. These dislocations act as "seeds" for postgrowth surface features that directly exhibit the correlated nature of these threading dislocations. (C) 2003 American Institute of Physics.