Activities towards p-Type Doping of ZnO

Zinc oxide (ZnO) is an interesting and promising semiconductor material for many potential applications, e.g. in opto-electronics and for sensor devices. However, its p-type doping represents a challenging problem, and the physical reasons of its mostly n-type conductivity are not perfectly clear at present.
Firstly, efforts to achieve p-type conductivity by ion implantation are reviewed, and the creation of a p-n junction by N+ ion implantation with post-implantation annealing is discussed.
Secondly, ways to achieve p-type ZnO nanorods by various growth conditions are presented. Their characterization by electrical, optical and positron annihilation spectroscopy methods will also be included.
Third, the preparation of Schottky contacts on ZnO with the surface pre-treatments of hydrogen peroxide is mentioned in some detail as this is a demand of the device formation process.
Finally, the possible incorporation of hydrogen and nitrogen into structural defects, which can act as trapping sites for positrons, is discussed. This will be discussed in the context of positron experimental and theoretical results and estimated H and N contents in a selected variety of ZnO materials.