Investigation on the deposition of an AlN-ZnO/ZnO/AlN-ZnO double heterojunction structure using radio frequency magnetron cosputtering technology

A symmetric AlN-ZnO/ZnO/AlN-ZnO double heterojunction structure was consecutively deposited onto silicon substrate using cosputtering technology and then annealed at 700 °C under vacuum ambient for 30 min. The crystalline quality of the ZnO film in the heterojunction structure was significantly improved as verified by X-ray diffraction (XRD) and photoluminescence (PL) measurements. Improvement on the crystalline structure was ascribed to the stress in the ZnO active film, which was effectively buffered by the underlayered AlN-ZnO layer. Native oxygen vacancies in the ZnO film also were effectively suppressed due to a little diffusion of the Al atoms from the cosputtered AlN-ZnO layer, and led to an increase in the carrier concentration. Such ZnO film deposited onto the homogeneous AlN-ZnO buffer layer emitted an intense near-band-edge emission, and the deep level emission was absent. The ultraviolet emission was further enhanced by covering an AlN-ZnO barrier laye, which was a consequence of the improvement on the carrier confinement. Accordingly, single ultraviolet emission with a quality ZnO crystalline structure, which is very promising for application in short-wavelength optoelectronic devices, was realized from the ZnO film sandwiched by the homogeneity of the cosputtered AlN-ZnO layers.