Accurate determination of dislocation density in GaN using chemical mechanical polishing

GaN based epitaxial films form active layers in UV-blue-green light emitting diodes, laser diodes and high power electronic devices. Traditionally, transmission electron microscopy, X-ray diffraction, cathodoluminescence and wet etching based techniques are used to measure dislocation density and film quality. In this article we have used chemical mechanical polishing (CMP) process to delineate dislocation sites in GaN epitaxial film and bulk substrate as shallow pits of 1-10 nm depth. In addition, a high pressure CMP process reliably delineated screw dislocations, which formed pits with depths ∼15 nm compared to shallower pits formed at edge dislocation sites. The dislocation density was found to closely correlate with that calculated from cathodoluminescence measurements and defect selective wet etching.