Optimization of p-type AlGaN/GaN and GaN/InGaN Superlattice Design for Enhanced Vertical Transport

We report on p-type AlGaN/GaN and GaN/InGaN superlattice (SL) designs with significantly improved vertical and lateral electrical conductivity (σ v and σ L ). Composition-graded p–AlGaN layers were used to produce eight fold reduction in barrier height and a ~40% increase in the sheet hole density in the p-GaN wells compared to typical SL structures. Thirteen orders of magnitude and 35 times improvement is obtained for σ v and σ L compared to typical SL and bulk p-GaN, respectively. A similar approach for p-GaN/InGaN SL resulted in seven fold reduction in barrier height and a ~30% increase in the sheet hole density in the p-InGaN wells compared to a typical SL structures. σ L is strongly dependent on hole mobility in the well and about 19 times improvement is obtained for the optimized design, SL-B, with µ p =30 cm 2 V-1s −1 compared to bulk-InGaN. More than 10 orders of magnitude improvement in σ V is obtained for SL-B compared to modulation doped SL.