Selective-area growth study of GaN micropillars for quasi-vertical Schottky diodes

Abstract

In this work, metal organic vapor phase epitaxy (MOVPE) is employed for selective-area growth (SAG) of undoped and lightly n-doped GaN micropillars on masked GaN-on-sapphire templates. In micropillar geometry, the limits of GaN drift layer thickness in hetereoepitaxial Schottky diodes are expected to be significantly pushed upwards. This is an important step towards the realization of GaN-based quasi-vertical power devices with high breakdown voltage (V br) on low-cost foreign substrates. Micropillar growth evolution and the impact of growth rate and V/III ratio on micropillar morphology and parasitic GaN deposition on AlOx hard masks are investigated. By using a combination of low growth rate and high V/III ratio, 12–22 µm high micropillars with planar pillar tops are grown in circular mask openings with radii of 35–100 µm. The threading dislocation density of the highest pillars is (1.4 ± 0.3) × 107 cm−2. Schottky diodes on micropillars with lowest net doping concentration (N D − N A) of 1.3 × 1016 cm−3 exhibit excellent forward characteristics with ideality factors , on/off-ratios up to 1010, and on-resistances R on 1 m cm−2.