Stress test measurements of lattice‐matched InAlN/AlN/GaN HFET structures

Abstract

InAlN/GaN heterostructures offer some benefits over existing AlGaN/GaN heterostructures for HFET device applications. In addition to having a larger bandgap than typical AlGaN compounds used in HFET devices (with Al < 30%), which leads to better confinement and subsequent larger power carrying capacity, InAlN can be grown lattice-matched to GaN, resulting in strain-free heterostructures. As such, latticematched InAlN provides a unique system wherein the reliability of the devices may exceed that of the strained AlGaN/GaN devices as a result of being able to decouple the hot electron/hot phonon effects on the reliability from the strain related issues. In this work, we subjected lattice-matched InAlN-based HFETs to electrical stress and observed the corresponding degradation in maximum drain current. We found that the degradation rates are lower only for a narrow range of moderate gate biases, corresponding to low field average 2-dimensional electron gas (2DEG) densities of 9-10 Â 10 12 cm À2 . We propose that the degradation is attributable to the buildup of hot phonons since the degradation rates as a function of electron density generally follow the hot phonon lifetime versus electron density. This provides evidence that hot phonons have a significant role in device degradation and there exists an optimal 2DEG density to minimize hot phonon related degradation. We did not observe any correlation between the degradation rate and the gate leakage.

Signature of Hot Phonons in Reliability of Nitride Transistors and Signal Delay

“…Device reliability was investigated on a set of nominally identical InAlN/AlN/GaN HFETs prepared from the same wafer [2,13,14]. Drain current was measured as a function of time for the devices biased to the same drain voltage of 20 V and different gate voltages.…”