Design and Simulation of 5–20-kV GaN Enhancement-Mode Vertical Superjunction HEMT

The systematic design process using numerical simulations of the novel gallium nitride (GaN) enhancement-mode vertical superjunction high electron mobility transistor (HEMT) with breakdown voltage (BV) in the range of 5-20 kV is presented. The GaN superjunction pillar structure in the drift region of the vertical HEMT is first optimized using a simpler GaN superjunction diode structure, and the optimum half-pillar charge dosage is obtained to be 8×10¹² cm^-2, which is consistent with the value estimated from the Gauss´s Law. The GaN vertical superjunction HEMT is then simulated and optimized, and the Ron,sp-BV tradeoff curves in the range of 5-20 kV are obtained by varying the epi thickness. The Ron,sp-BV tradeoff is found to improve with smaller pillar width as in silicon superjunction MOSFETs, and the best Ron,sp of 4.2 mΩ-cm² with BV of 12.4 kV is projected with half-pillar width of 3 μm. The robustness of the superjunction HEMT is also examined using structure with half-pillar width of 8 μm, and compared with the GaN vertical HEMT with conventional drift layer and same dimensions. The simulated on-state BV of the GaN vertical superjunction HEMT shows a 4.5% drop from the off-state BV and is only slightly higher than the 1.7% drop of the conventional GaN vertical HEMT.