Defects and intermediate chemical phases at nanoscale heterointerfaces of GaN, AlGaN, and SiC can dominate their macroscopic electronic properties. We have used low energy electron-excited nanoscale luminescence spectroscopy in combination with secondary ion mass spectrometry and internal photoemission spectroscopy to correlate interface physical and electronic properties for a variety of Schottky barrier and heterointerfaces involving these semiconductors. These results demonstrate the key role of initial surface processing and subsequent chemical interaction on the heterointerface electronic states, barriers, and carrier concentrations. (c) 2004 Published by Elsevier B.V.