Modeling and Analysis of Normally-OFF p-GaN Gate AlGaN/GaN HEMT as an ON-Chip Capacitor

An accurate physics-based analytical model for the gate capacitance of p-GaN gate AlGaN/GaN high electron mobility transistor (HEMT) is presented. The Poisson's equation is formulated considering the incomplete ionization of acceptors in the p-GaN cap layer and the out-diffusion of Mg acceptors into the AlGaN barrier layer, which is solved in conjunction with the charge equation in the AlGaN/GaN quantum well. The model is validated across a wide bias range and shows a good agreement with the experimental results. The effect of individual device parameters on the capacitance-voltage (C-V) characteristics is also analyzed using this model. A simplified equivalent circuit model is also presented to intuitively explain the C-Vcharacteristics of these normally-OFF devices.