Gate Leakage Current in Nitride-Based HFETs.

摘要

Reliability issues like the gate leakage current, drain current collapse and breakdown limit the performance of the GaN based HFETs. In this work, the physics of the reliability issues in GaN HFETs is discussed. A new comprehensive physics based model of the gate leakage current in nitride-based HFETs is demonstrated and used to explain leakage currents in these devices when under high field operation. The model explains for the first time the physics of the gate leakage current in AlGaN/GaN HFETs by considering two paths of the leakage current flow: (1) surface layer conduction, and (2) conduction from the gate to the two-dimensional electron gas (2DEG) channel. The current transport mechanism through the surface of the device is modeled using space charge limited (SCL) transport in the presence of traps. Trap assisted tunneling (TAT) is considered for the evaluation of the electrons tunneling from the Schottky gate contact (on the drain side) to the 2DEG channel. The model adequately explains the measured gate leakage current and, predicts accurately the experimentally observed change in slope of the gate leakage current versus the gate to drain voltage. The trap levels extracted from the model are consistent with the reports presented in the literature. The gate leakage current in N-polar InAlN/GaN HFETs is modeled by considering space charge limited current flow in the presence of deep traps in the InAlN layer. The drain current collapse phenomenon in AlGaN/GaN HFETs is explained using circuit based simulation. TCAD simulation of GaN HFETs is performed to conceptually show the experimental observation of the gate to drain spacing dependence on the device breakdown voltage.