Negative differential conductivity in AlGaN/GaN HEMTs: real space charge transfer from 2D to 3D GaN states?

摘要

We report on non-thermal negative differeential conductivity (NDC) in AlGaN/GaN HEMTs grown on sapphire substrates by low-pressure MOCVD. The sheet electron density was on the order of few times 10~(12) cm~(-2) and the Hall mobility was, 1, 000 cm~2/V.s. The HEMTs had threshold voltage close to zero and could operate at high positive gate bias up to 3 to 3.5 Volts, with a very low gate leakage current. NDC was observed at the gate bias larger than 1.5V and at the drain biases between approximately 0.5Vg and Vg. We excluded the possibility of self-heating as the cuase, since the NDC occurs at relatively small power levels where self-heating effects are neglighibe.