Photogenerated carriers at defect states in polycrystalline GaN using sub-bandgap laser-excited scanning tunneling spectroscopy*

Photo-induced carriers at defect states in GaN layers dominates the performances of nitride-based compound devices. In this work, sub-bandgap laser-excited cross-sectional scanning tunneling microscopy and spectroscopy demonstrate a great potential to obtain photo-induced electronic properties at defect-rich GaN films under the illumination condition. A spectacular enhancement in the tunneling current at positive voltages is observed in the defect-rich GaN layers under illumination, resulting from the excitation of free charge carriers at defect states. Thus, sub-bandgap laser-excited scanning tunneling spectroscopy provides us an opportunity to characterize the existence of charge carriers at defect states and demonstrates the behavior of photo-induced carriers in GaN layers.