Structural and Optical Properties of InGaN/GaN Vertical Light Emitting Diodes from Flat and Patterned Sapphire Substrates

Abstract

In this thesis, I report the structural and optical properties of InGaN/GaN VLED that were grown on two kinds of sapphire substrates in which one is a hexagonal array of hemispherical patterns and the other is flat substrate by low-pressure metal-organic chemical vapor deposition (MOCVD). The VLED structures on Cu carriers are fabricated by using electroplating and laser lift-off (LLO) processes. A photoluminescence (PL) intensity comparison of the VLED on two substrates before and after LLO process was presented. The PL properties of VLED grown on PSS have significant advantage compared with the one on FSS. After removing the substrates, defect distribution in the GaN layers lifted-off from flat sapphire substrate (FSS) and patterned sapphire substrates (PSS) has been investigated by using low temperature KOH selective wet etching and cathodoluminescence (CL) mapping. The GaN lifted-off from PSS (GaN-PSS) even though suffers from a higher laser irradiation but it still indicates a higher CL intensity and more uniform emission than the GaN lifted-off from FSS (GaN-FSS). It means that GaN-FSS has higher defect density and deeper defect distribution than the other.