Optical Characterisation of Non-polar InGaN/GaN Quantum Wells

Abstract

In this thesis I present research on the optical characterisation of InGaN/GaN quantum wells (QWs) grown in the non-polar the a-plane (11-20) and m-plane (1-100) orientations. The research is performed using optical techniques such as photoluminescence (PL), photoluminescence excitation (PLE), time-resolved photoluminescence (TRPL) and photoluminescence decay time studies. Additionally comparisons are drawn to structural details provided by the University of Cambridge.In the first section I investigate and compare various defect reduction techniques that are utilised in the growth of a-plane GaN on r-plane sapphire. These are included as a way of reducing the density of basal-plane stacking faults (BSFs) and threading dislocations (TDs). I will show that a comparison between the integrated emission intensity of the donor-bound exciton against that of the BSFs and the TDs can be used as a means of comparing the relative crystal quality of different samples. I will also show that techniques which employ a physical layer to block BSFs and TDs from propagating are the most effective in reducing their densities for a-plane GaN grown on r-plane sapphire.In the second section I discuss the characterisation of m-plane InGaN/GaN QWs, focusing primarily on the presence of an extended low energy emission tail. Through the use of decay time studies and TRPL I am able to show that the extended low energy emission tail originates from semi-polar QWs which form during growth. Additionally I show that over the majority of the emission band, the PL decay time possesses a single time constant that does not vary significantly with detection energy. This observation is consistent with the recombination of localised excitons in the m-plane InGaN/GaN QWs.For the final section I compare InGaN/GaN QWs grown on the a-plane and the m-plane for the purpose of understanding why m-plane samples typically exhibit superior optical properties. In this section I identify an additional emission band that exists on the high energy side of the QW emission and is comparably stronger in the a-plane samples. This emission band is responsible for the difference in the PL decay times observed between each non-polar growth orientation, as well for as the reduction in the degree of linear polarisation measured for a-plane QW samples.

Date of Award	1 Aug 2016
Original language	English
Awarding Institution	The University of Manchester
Supervisor	Philip Dawson (Supervisor)