Investigation of new approaches for InGaN growth with high indium content for CPV application

Abstract

We propose to use two new approaches that may overcome the issues of phase separation and high dislocation density in InGaN-based PIN solar cells. The first approach consists in the growth of a thick multi-layered InGaN/GaN absorber. The periodical insertion of the thin GaN interlayers should absorb the In excess and relieve compressive strain. The InGaN layers need to be thin enough to remain fully strained and without phase separation. The second approach consists in the growth of InGaN nano-structures for the achievement of high In content thick InGaN layers. It allows the elimination of the preexisting dislocations in the underlying template. It also allows strain relaxation of InGaN layers without any dislocations, leading to higher In incorporation and reduced piezo-electric effect. The two approaches lead to structural, morphological, and luminescence properties that are significantly improved when compared to those of thick InGaN layers. Corresponding full PIN structures have been realized by growing a p-type GaN layer on the top the half PIN structures. External quantum efficiency, electro-luminescence, and photo-current characterizations have been carried out on the different structures and reveal an enhancement of the performances of the InGaN PIN PV cells when the thick InGaN layer is replaced by either InGaN/GaN multi-layered or InGaN nanorod layer.