Polarization interface charge model to calculate threshold voltage of AlGaN/GaN HEMTs

A model to calculate the threshold voltage and sheet carrier concentration of AlGaN/GaN high electron mobility transistors more precisely is developed using an advanced polarization charge model based on the dipole nature of polarization. In the conventional model, the polarization charges are assumed to be located exactly at the AlGaN/GaN interface. Instead, a new model assumes the positive polarization charges at the bottom of the AlGaN layer and the negative polarization charges at the top of the GaN layer are located at different positions, with a distance of about a unit-cell height in the vicinity of the AlGaN/GaN interface. The proposed model helps reproduce experimentally obtained sheet carrier concentration for as-grown samples with reasonable material parameters. Unlike the conventional model, it is not necessary to assume unrealistically high barrier height or carrier compensation by deep traps to adjust the carrier concentration to experimental data.