Current transport mechanisms in GaN-based metal-semiconductor-metal photodetectors

We report on the current transport mechanisms dominant at the Schottky interface of metal-semiconductor-metal photodetectors fabricated on single-crystal GaN, with active layers of 1.5 and 4.0 mu m thickness. We have modeled transport in the 1.5 mu m devices using thermionic emission theory, and in the 4.0 mu m devices using thermionic field emission theory. We have obtained a good fit to the experimental data. We hypothesize that traps in the GaN are related to a combination of surface defects (possibly threading dislocations), and deep-level bulk states that cue within a tunneling distance of the interface. A simple qualitative model is presented. (C) 1998 American Institute of Physics.