The growth of ZnO-on-GaN heterostructures was implemented using the vapor cooling condensation system. The technique thus developed was employed to fabricate both the p-GaN∕n-ZnO:In (p-n) and p-GaN∕i-ZnO∕n-ZnO:In (p-i-n) heterojunction light-emitting diodes (LEDs). A rectifying diodelike behavior was clearly observed from both the p-n and p-i-n heterojunction LEDs, with the forward turn-on voltage of 3V and the reverse breakdown voltage of −15V determined for the p-n heterojunction LEDs, compared to 7 and −23V, respectively, for the p-i-n heterojunction LEDs. Based on the results of photoluminescence and electroluminescence studies conducted on these LED structures, the ZnO layer responsible for the peak emission wavelength of 385nm were also verified experimentally.

Nitride-based blue light emitting diodes (LEDs) with an n + -short period superlattice (SPS) tunnel contact layer and an indium tin oxide (ITO) transparent contact were fabricated. Compared with conventional nitride-based LEDs with Ni/Au upper contacts, it was found that we could achieve a 60% increase in electroluminescence (EL) intensity by using ITO upper contacts. However, it was also found that the lifetime of ITO LEDs were much shorter. Furthermore, it was found that we could achieve a longer lifetime and a smaller reverse leakage current ( ) by the deposition of a SiO 2 layer on top of the ITO LEDs.

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