Imaging charge trap distributions in GaN using environmental scanning electron microscopy

We present direct experimental evidence for a field assisted component in images acquired using the gaseous secondary electron detector (GSED) employed in environmental scanning electron microscopes. Enhanced secondary electron (SE) emission was observed in GSED images of epitaxial GaN bombarded with MeV He ions. The increase in SE emission is attributed to an electric field generated by electrons trapped at defects produced by ion implantation. The presence of nonradiative recombination centers and of trapped charge in implanted GaN was established by cathodoluminescence spectroscopy and energy dispersive x-ray spectrometry. The field assisted SE component is distinguishable from the "normal" GSED signal by characteristic pressure and temperature dependencies. The presented results demonstrate the utility of the GSED for imaging charge trap distributions in semiconductors.