Effect of the interface on n-ZnO/p-GaN heterojunction light emitting diodes

We report on n-ZnO/p-GaN heterojunction light-emitting diodes (LEDs) fabricated from ZnO films, for which the electrical properties and oxygen contents were controlled by post-annealing. Intense violet emission with a peak wavelength near 381 nm was observed in the electroluminescence (EL) spectra and was attributed to the near-band-edge emission of the n-ZnO layer. With increasing annealing time, however, the EL peak position broadened and showed a strong deep-level emission. The LEDs were yellowish in color due to the formation of an interface (i.e., a Ga-O mixed region) and to deep-level impurities associated with an increase in oxygen in the ZnO films and in the intermediate layer between the ZnO and the GaN layers.