Analytical Model for Schottky Barrier Height and Threshold Voltage of AlGaN/GaN HEMTs With Piezoelectric Effect

Abstract

Physics-based models for calculating the threshold voltage ( ${V}_{\text {th}}$ ) of GaN-based high electron mobility transistor (HEMT) is proposed. Assuming that the 2-D electron gas in III–V heterostructures originate from donor-like surface states, an analytical expression for $\phi _{b}$ is derived based on the condition of charge neutrality across the barrier layer and applied to develop ${V}_{\text {th}}$ model. Effects of introducing a GaN cap layer on distribution of surface donor states and strain relaxation due to high barrier layer Al composition are considered in the derivation of the models. Calculated ${V}_{\text {th}}$ values are in excellent agreement with the values extracted from static ${I}_{d}$ – ${V}_{g}$ measurement data for devices with different gate lengths. Furthermore, the ${V}_{\text {th}}$ models are implemented in the physics-based ${I}$ – ${V}$ model previously proposed by our group for AlGaN/GaN HEMTs and tested with devices of different geometries. Excellent agreement is obtained between the model and experimental data of the drain current and transconductance of the devices over a full range of bias conditions.