Analytical Models of Breakdown Voltage and Specific On-Resistance for Vertical GaN Unipolar Devices

Abstract

In this paper, the analytical models of breakdown voltage design parameters and minimum specific on-resistance in vertical gallium nitride unipolar devices are proposed. Considering the discrepancy of the impact ionization coefficients (IIC) reported in previous literatures from the Monte Carlo simulations and experiments, the analytical models of avalanche breakdown of gallium nitride devices both in punch-through and non-punch-through conditions are presented, i.e., the relationship between the breakdown voltage, drift doping concentration, drift thickness and critical electric field, which shows high accuracy with the results from numerical simulations. The comparison with the reported experimental results demonstrates the comparatively higher accuracy of the IIC data from Baliga. Taking into account the incomplete ionization in dopant impurities in GaN, the tradeoff between specific on-resistance and breakdown voltage is also given, demonstrating the optimized punch-through design has minimum specific on-resistance, which can be reduced by up to 12% for breakdown voltage from 1 kV to 15 kV. Meanwhile, the corresponding drift thickness can be reduced by from 18% to 20%, which can largely reduce the fabrication cost of epitaxial growth. The proposed optimized relationship is in good accordance with the results from MEDICI simulations.