Origin of ultraviolet electroluminescence in n -ZnO/p -GaN and n -MgZnO/p -GaN heterojunction light-emitting diodes

Abstract

In this work, a series of n-ZnO/p-GaN and n-MgZnO/p-GaN heterojunctions are designed and fabricated. The carrier transport and recombination mechanism is discussed based on electroluminescence (EL) and photoluminescence (PL) spectra, current–voltage (I–V) characteristics as well as energy band diagram. For ZnO device, the near-ultraviolet (UV) emission at ∼400 nm is attributed to the spatially-indirect, interfacial transition from ZnO conduction band minimum to GaN acceptor level. While for MgZnO diodes, their UV EL is independent on Mg composition, is thought to origin from the donor–acceptor pair (DAP) recombination in GaN layer. Our experiment results suggest that pure ZnO or MgZnO emission can hardly be achieved in n-(Mg)ZnO/p-GaN heterojunctions, rational device design towards (Mg)ZnO exciton emission is more important in the further work. EL spectra of different n-MgxZn1−xO/p-GaN diodes and the schematic carrier transport and recombination process.