A model for calculating impact ionization transition rate in wurtzite GaN for use in breakdown voltage simulation

Abstract

A model for calculating impact ionization transition rate (IITR) in wurtzite GaN has been developed for use in breakdown voltage simulations. The characteristic feature of the model is to calculate energy-dependent IITR by taking a conduction band index into account. Depending on the band index, the IITR values calculated by the proposed model show spreading by three orders of magnitude in the electron energy range from 6.5 to 8 eV, while this spreading is totally disregarded in the conventional model. An impact ionization coefficient is calculated based on a full band Monte Carlo simulation which incorporates IITRs by the proposed model. The calculated impact ionization coefficients by the proposed model exhibit better agreements with those by the rigorous model. The proposed model is applied to the calculation of breakdown characteristics for AlGaN/GaN HEMTs and demonstrates a higher breakdown voltage by about 30% than that by the conventional model.