Physics of Gallium Nitride Quantum Wells

UoM administered thesis: Master of Philosophy

  • Authors:
  • Lydia Jim

Abstract

In this thesis, studies performed on InGaN/GaN quantum well (QW) structures using photoluminescence (PL) spectroscopy are presented. Green light-emitting InGaN/GaN QW structures with a varying number of QWs (1, 3, 5 & 10) were investigated with respect to the effect of QW number on internal quantum efficiency (IQE). 10 K transient PL measurements performed on the samples showed that the QW samples have different lifetimes. This suggests that there is a varying level of indium content amongst the samples, different average QW layer thickness between the samples and/or strain relaxation in the 10 QW sample. Comparing the 3 and 5 QW samples, which have similar lifetimes, the 300 K excitation power dependent IQE measurements performed on the samples shows that IQE increases with QW number; this can be attributed due to the increased recapture of escaped thermally excited carriers. Additionally, InGaN/GaN QWs with varying growth temperatures were studied with respect to their high energy band (HEB) and efficiency droop behaviour; the samples grown at higher growth temperatures have a lower defect density and this could affect the HEB and efficiency droop. The HEB is a recently reported feature on the high energy side of the typical emission peak in the PL spectra of InGaN/GaN QWs. 10 K excitation power dependent PL showed that the sample with the highest growth temperature exhibited efficiency droop at a higher excitation compared to the other samples; this may be because efficiency droop is influenced by defect-related recombination. 10 K time-resolved PL showed that the samples have similar HEB behaviour despite their different growth temperatures; monoexponential decay components and inflections which corresponded to the HEB were observed in the time decay measurements. 10 K excitation power varying time decay measurements performed across the PL spectra on one of the samples showed that the lifetime of the carriers at a given emission energy is constant at low carrier densities and decreases at high carrier densities; this reduction in lifetime occurred at a higher carrier density at higher PL emission energies.

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Original languageEnglish
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Award date1 Aug 2019