A study of the optical and polarisation properties of InGaN/GaN multiple quantum wells grown on a-plane and m-plane GaN substrates

TL;DR

This study compares the optical and polarisation properties of InGaN/GaN quantum wells grown on a-plane and m-plane GaN substrates, revealing differences in emission spectra, polarisation degree, and valence band splitting.

Contribution

It provides a comparative analysis of polarisation and emission characteristics of quantum wells on different GaN substrate orientations, highlighting the influence of growth plane on optical properties.

Findings

Broader emission spectra with increased In content.

Lower polarisation degree in a-plane samples at 10 K.

Valence band splitting between 23-54 meV.

Abstract

In this paper we report on a comparative study of the low temperature emission and polarisation properties of InGaN/GaN quantum wells (QWs) grown on nonpolar a-plane and m-plane free-standing bulk GaN substrates where the In content varied from 0.14 to 0.28 in the m-plane series and 0.08 to 0.21 for the a-plane series. The low temperature photoluminescence spectra from both sets of samples are very broad with full width at half-maximum height increasing from 81 to 330 meV as the In fraction increases. Comparative photoluminescence excitation spectroscopy indicates that the recombination mainly involves strongly localised carriers. At a temperature of 10 K the degree of linear polarisation of the a-plane samples is much smaller than of the m-plane counterparts and also varies across the spectrum. From polarisation-resolved photoluminescence excitation spectroscopy we measured the energy splitting between the lowest valence sub-band states to lie in the range of 23-54 meV for both a-and m-plane samples in which we could observe distinct exciton features in the polarised photoluminescence excitation spectroscopy. Thus, the thermal occupation of a higher valence subband cannot be responsible for the reduction of the degree of linear polarisation. Time-resolved spectroscopy indicates that in a-plane samples there is an extra emission component which at least partly responsible for the reduction in the degree of linear polarisation.