Optical polarisation anisotropy in a ‐plane GaN/AlGaN multiple quantum well structures

Abstract

AbstractIn this paper we report on the optical properties of a series of a ‐plane GaN/AlGaN multiple quantum well structures of varying well width. The low temperature photoluminescence spectrum of each structure is characterised by two distinct emission bands, both of which shift to higher energy with decreasing well thickness. The origin of the lower energy emission band is attributed to the recombination of carriers trapped in regions of the quantum wells intersected by basal plane stacking faults. The higher energy feature is assigned to localised exciton recombination at well width fluctuations. We have used photoluminescence excitation spectroscopy to reveal details of the bandstructure of the quantum wells. Excitation with unpolarised light resulted in the observation of exciton transitions associated with the n = 1 and n = 2 electron sub‐bands. For linearly polarised (E⊥c and E‖c) excitation, both the transitions observed with unpolarised light were shown to consist of overlapping transitions involving heavy and light hole like valence subbands. Their observed polarisation anisotropy was attributed to anisotropic biaxial compressive strain in the GaN film. As well as the exciton transitions we were also able to resolve well defined continuum edges in some of the excitation spectra. This enabled us to estimate the exciton binding energy of the n = 1 heavy and light hole states for quantum wells of differing width. Values were found to lie in the range of 38 to 76 ±5 meV. (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)