Optical and electrical properties of ZnO/Si heterostructures after plasma treatment and millisecond annealing

Nowadays, the transparent and conductive ZnO layer is a basic material for the front contact in thin-film photovoltaics. A highly doped n-type ZnO thin layer is an attractive candidate to replace the much more expensive indium-tin-oxide layer in the microelectronic industry. The optoelectronic properties of the ZnO are determined by the type of doping and carrier concentration. The n-type conductivity of ZnO is easily achieved by substitution of Zn by group III elements (Al, Ga, In), or by doping with halogen elements (F, Cl or I) substituting into the oxygen lattice site. Here we will present the utilisation of plasma immersion ion implantation (PIII) and millisecond range flash lamp annealing (FLA) techniques for the formation of highly p- and n-type ZnO films on silicon substrate. Whereas the n-type doping is made by incorporation of F into ZnO, the p-type ZnO films are obtained due to the PIII of N and P. Both p- and n-type dopants are activated using post-implantation millisecond range FLA process. The microstructural and opto-electrical investigations confirm the formation of a high-quality, highly-doped ZnO layer. Moreover the current-voltage characteristics show a heterojunction between ZnO and Si. It is shown that the SF6 plasma treatment efficiently passivates the surface state and bulk defects in the ZnO film significantly improving the near band gap emission from ZnO.