Growth of InGaN films on hardness-controlled bulk GaN substrates

Abstract

We carried out an evaluation of the crystalline quality of bulk GaN substrates and the properties of InGaN films grown on them. The Urbach energy estimated by photothermal deflection spectroscopy and the tail states near the valence band maximum determined by hard X-ray photoemission spectroscopy were larger for hardness-controlled bulk GaN (hard GaN) than those for conventional bulk GaN (conventional GaN). However, InGaN on hard GaN grows in a step-flow-like mode, while InGaN grown on conventional GaN exhibits spiral-like growth. The photoluminescence decay at room temperature for InGaN grown on the hard GaN was 470 ps, compared with 50 ps for that grown on the conventional GaN. This can be attributed to the suppression of spiral-like growth due to the resistance to deformation of the hard GaN. These results indicate that substrate hardness is one of the most important factors for III-V nitride growth on the bulk GaN substrate.