Luminescent N-polar (In,Ga)N/GaN quantum wells grown by plasma-assisted molecular beam epitaxy at high temperature

TL;DR

This study demonstrates that high-temperature plasma-assisted molecular beam epitaxy enables the growth of luminescent N-polar (In,Ga)N/GaN quantum wells with high indium content and stable green luminescence up to room temperature, unlike conventional growth temperatures.

Contribution

It reveals that increasing growth temperature to 730°C on N-polar GaN substrates produces high-quality, luminescent quantum wells with homogeneous In distribution and stable emission, contrasting with lower-temperature growth results.

Findings

Quantum wells on N-polar GaN exhibit green luminescence up to room temperature.

High growth temperature results in In incorporation and abrupt interfaces.

Thermal quenching is caused by nonradiative Shockley-Read-Hall centers.

Abstract

N-polar (In,Ga)N/GaN quantum wells prepared on freestanding GaN substrates by plasma-assisted molecular beam epitaxy at conventional growth temperatures of about 650 {\deg}C do not exhibit any detectable luminescence even at 10 K. In the present work, we investigate (In,Ga)N/GaN quantum wells grown on Ga- and N-polar GaN substrates at a constant temperature of 730 {\deg}C. This exceptionally high temperature results in a vanishing In incorporation for the Ga-polar sample. In contrast, quantum wells with an In content of 20% and abrupt interfaces are formed on N-polar GaN. Moreover, these quantum wells exhibit a spatially homogeneous green luminescence band up to room temperature, but the intensity of this band is observed to strongly quench with temperature. Temperature-dependent photoluminescence transients show that this thermal quenching is related to a high density of nonradiative Shockley-Read-Hall centers with large capture coefficients for electrons and holes.