Simulation of the Piezoelectric Effect on the Device Characteristics of AlGaN/GaN Insulated-Gate Heterostructure Field Effect Transistors

The piezoelectric effect (PE) on the device characteristics due to lattice mismatch in the heterostructure was simulated by solving Poisson and Schrodinger equations self-consistently for GaN-based field effect transistors (FET). By comparing the simulation results obtained with and without PE, we found the following. (1) PE shifts the threshold voltage (V th) of FET; this V th shift widens the flat region in transconductance–gate voltage (G m–V gs) and cutoff frequency–gate voltage (f T–V gs) characteristics. (2) G m is higher with PE than without PE, while f T values are nearly the same for both with and without PE. (3) The equilibrium two-dimensional channel electron gas (2DEG) concentration (N ch) increases considerably with PE. This 2DEG concentration greatly reduces the parasitic resistance between the gate and the source/drain. We concluded that PE improves FET performance, and we determined the optimal FET structure with PE from the viewpoint of charge control.