Simulation of piezoresistivity effect in FETs

AlGaN/GaN and AlGaAs/InGaAs/GaAs HEMT structures are investigated theoretically to calculate the dependence of the 2DEG sheet resistance on strain. The inhomogeneous strain pattern induced by an external force is computed numerically using a continuous media model, assuming that the structures are grown on a thick substrate which remains unstrained. Current transport is simulated by means of a drift-diffusion model taking the spontaneous and piezoelectric polarization into account. The effect of strain onto the band structure is treated in the framework of k · p theory. The structures are simulated for different external pressures in order to study the relative change of resistance. The AlGaN/GaN structure shows an increasing resistance for increasing stress which can be related to the change of the piezoelectric polarization in the device. In the GaAs-based structure the effect depends on substrate termination and is more pronounced for B-face polarity.