Optimization of 0.25µm GaN HEMTs through numerical simulations

0.25µm GaN HEMTs performance dependence from epitaxial and geometrical parameters has been investigated by means of numerical simulations. A single-heterojunction GaN HEMT structure with an iron doped buffer layer also including a mushroom-gate layout forming a gate-connected field-plate over the device SiN passivation layer was considered. Numerical simulations including static-IV characteristics and breakdown voltage estimation, small signal analysis and double pulse-IV characteristics have been carried out on more than 400 different structures. Simulations results showed that contact resistance, gate-source spacing, barrier thickness and AlGaN/SiN interface trap density are critical for improving device RF gain. Field-plate extension and passivation layer thickness were found to be parameters that can be used for trading off between device breakdown voltage and RF gain. Increasing iron-doping in the buffer layer leaded to larger breakdown voltage and RF gain but, due to the enhanced trapping effects, also to poorer large-signal operation.