Transparent cosputtered ITO-ZnO electrode ohmic contact to n-type ZnO for ZnO/GaN heterojunction light-emitting diode

A transparent cosputtered ITO-ZnO film was used as an ohmic contact electrode to the n-type ZnO layer. The contact resistance of the ITO-ZnO/n-ZnO contact system was optimized by a rapid thermal annealing (RTA) treatment. Through x-ray diffraction and Auger electron spectroscopy depth profile measurements, the achievement on the ohmic contact of the ITO-ZnO/n-ZnO contact system was attributed to the outdiffusion of the oxygen atoms at the n-type ZnO layer surface, which was favourable for the increase of the electron carriers. By contrast, the mechanism responsible for the degradation of the contact resistance was due to the significant outdiffusion of the zinc atoms at the n-type ZnO layer surface, which also resulted in the marked peak shift of the Zn2In2O5 phase. The resulting n-ZnO/p-GaN heterojunction light-emitting diode fabrication, which used the transparent ITO-ZnO/n-ZnO ohmic contact system, exhibited rectifying behaviour and emitted a near-ultraviolet radiation at approximately 410 nm.