Burying surface defects in InGaN underlayer to increase blue LED efficiency (Conference Presentation)

Abstract

Blue light emitting diodes (LEDs) currently exhibit wall plug efficiency exceeding 80%. This is the consequence of the extraordinary property of InGaN/GaN quantum wells (QWs) to emit light despite a high density of structural defects, i.e. threading dislocations. This has been ascribed to carrier localization in potential fluctuations induced by InGaN random alloy disorder. However, high efficiency LEDs commonly feature an InGaN layer, which is underneath the InGaN/GaN QW active region. This underlayer (UL) is known to dramatically increase the efficiency of blue LEDs. Several explanations have been proposed such as screening of threading dislocations due to V-pit formation, decrease of the internal electric field in the InGaN/GaN QWs due to band bending, or improved carrier injection. Another hypothesis is that defects are present at the GaN surface and lead to non-radiative recombination centers once incorporated in InGaN/GaN QWs. Thus, the role of the InGaN UL is to capture those defects resulting in a “clean” GaN surface before the growth of the InGaN/GaN QW active region. In this talk, we will present a comprehensive study of the effect of InGaN UL on the internal quantum efficiency of InGaN/GaN QWs. We will confirm that the role of this layer is to incorporate defects, which lie at the GaN surface. An origin of those defects will be proposed in view of secondary ion mass spectrometry analysis.