Fabrication of (In,Ga)N pseudo-substrates by a three-step growth protocol without ex-situ processing

TL;DR

This paper presents a three-step in-situ growth process to fabricate (In,Ga)N pseudo-substrates with improved properties, avoiding ex-situ processing and enabling scalable production for high-efficiency red LEDs.

Contribution

The study introduces a novel three-step growth protocol that enhances (In,Ga)N pseudo-substrate quality without ex-situ processing, improving In content and strain relaxation.

Findings

Higher In content (~0.3) in pseudo-substrates

Approximately 80% strain relaxation achieved

Narrower photoluminescence linewidth

Abstract

We fabricate (In,Ga)N pseudo-substrates with a total thickness of ~1 um grown on GaN templates using plasma-assisted molecular beam epitaxy. In a three-step process, we change growth conditions from N-rich to metal-rich in order to sequentially form a roughened GaN layer, relaxed (In,Ga)N nanostructures, and a coalesced, smooth (In,Ga)N layer. Samples are analyzed by scanning electron and atomic force microscopy, X-ray diffraction, as well as photo- and cathodoluminescence spectroscopy. Compared to a reference layer grown directly on GaN, the pseudo-substrate exhibits a higher In content (~0.3), strain relaxation degree (~80%), narrower photoluminescence linewidth, and larger area fraction of bright regions in cathodoluminescence maps, showing the benefits of the three-step growth protocol. This straightforward approach does not necessitate any ex-situ processing and could enable the scalable fabrication of (In,Ga)N pseudo-substrates for high-efficiency red-emitting (In,Ga)N devices.