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

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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 (Vth) of FET; this Vth shift widens the flat region in transconductance–gate voltage (Gm–Vgs) and cutoff frequency–gate voltage (fT–Vgs) characteristics. (2) Gm is higher with PE than without PE, while fT values are nearly the same for both with and without PE. (3) The equilibrium two-dimensional channel electron gas (2DEG) concentration (Nch) 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.
1998-11-15