Investigations of phonon sidebands in InGaN/GaN multi-quantum well luminescence

Abstract

Analysis of the phonon sidebands (PSB) observed in the photoluminescence (PL) spectra from a series of InGaN/GaN multi-quantum wells is described. The structures are grown by metal organic vapour phase epitaxy (MOVPE) on sapphire substrates and cover a range of emission wavelengths (390–600 nm) and number of quantum wells (from 1 to 10). Up to four phonon satellites are observed in the side-band of the quantum well luminescence, with an energy separation similar to the GaN LO-phonon energy (∼90 meV). The relative intensity and spectral properties of these satellites have been investigated as a function of the peak energy of the luminescence, sample temperature and the number of wells. Huang–Rhys parameters in the range 0.1–0.6 are observed. Analysis of the shape of the PSBs from the single quantum wells (SQWs) indicate that a significant fraction (∼40%) of the excitons are strongly localised. This fraction shows some increase for samples emitting at longer wavelengths. The relative strength of the first phonon satellite, compared with the no-phonon peak, is observed to increase with temperature and decrease with the number of periods in the multi-quantum well structures.