Influence of the GaN cap layer thickness on the two- dimensional electron gas (2-DEG) sheet charge density of GaN/AlInN/GaN HEMTs with polarization effect

In this study, GaN/AlInN/GaN high electron mobility transistor (HEMT) with various GaN cap layer thickness and with heavily n-doping GaN cap layer were presented. In order to investigate the effects of a GaN capping layer on performance of the (GaN/AlInN/GaN) heterostructures, a simple analytical model for the threshold voltage of GaN/AlInN/GaN high electron mobility transistor (HEMT) is proposed by solving one dimensional (1 D) Poisson equation, leads to find the relation between the two dimensional electron gas (2DEG) and the control voltage. Spontaneous and piezoelectric polarizations at AlInN/GaN and GaN/AlInN interfaces have been incorporated in the analysis. Our simulations indicate that the GaN cap layer reduces the sheet density of the two dimensional electron gas (2DEG), leading to a decrease of the drain current, and that n+ doped GaN cap layer provides a higher sheet density than undoped one.