Ion Implantation of ZnO by the Group IV elements Si and Ge: Doping, defects and nanocrystallization

Abstract

Zinc Oxide (ZnO) is a promising material for future use in both solar cells as a transparent conductive oxide, in addition to a range of other electrical applications, due to its low cost, transparency, and electrical properties. Using ion implantation group IV elements Si and Ge have been implanted into a ZnO matrix, and annealed at a broad range of temperatures to monitor the lattice disorder caused by implantation, dopant characteristics, and potential for formation of nanostructures. Si implanted ZnO shows promising defect annihilation, and a crystal quality very close to that of virgin ZnO after annealing at 800C. In addition donor activation is indicated already at room temperature by SSRM and hall effect measurements, making Si a promising candidate for implantation processing in ZnO. Ge implanted material shows similar dopant properties as Si, but high amounts of implantation damage, and precipitation of new phases at higher annealing temperatures makes it less suited for implantation doping. However, interesting observations have been done using TEM imaging, EELS, and EDS on precipitates formed during annealing at 800C and 1000C. Ge precipitations with a diameter of 10 nm enclosed by Zn2GeO4 is indicated by EELS and EDS after annealing at 800C. After 1000C Ge precipitations seem to be fully oxidized into Zn2GeO4, and 100 nm long and 20 nm wide rods of the same material, as well as other particle shapes of varied sizes, are observed using TEM imaging, and is further indicated by XRD.