Electrical and Optical Properties of ZnO Irradiated with Hydrogen Plasma

Abstract

The influence of intrinsic defects and hydrogen-defect complexes on the properties of n-type ZnO crystals has been studied in terms of annealing and hydrogen plasma irradiation. Electrical and optical properties have been found to be dependent on annealing conditions and hydrogen plasma irradiation. When an as-polished sample was annealed in Ar atmosphere containing Zn vapor at 800°C for 2 h, the color of the sample changed into orange because of the formation of oxygen vacancies (V_O). In spite of the V_O formation, Hall mobility of the sample increased from 162 to 210 cm²V⁻¹s⁻¹. Carrier concentration also increased by about four orders of magnitude. The simultaneous increases in carrier concentration and Hall mobility indicate that zinc vacancy (V_Zn) concentration, which acts as a compensation acceptor, are decreased by supplying Zn vapor during the annealing. Hydrogen plasma irradiation did not affect electrical properties of the sample annealed in Ar atmosphere containing Zn vapor, but improved those of the sample annealed in pure Ar atmosphere. The carrier concentration and Hall mobility increased by hydrogen plasma irradiation decreased with increasing post-annealing temperature. The post-annealing temperature dependence suggests that V_Zn passivated by hydrogen starts to dissociate at temperatures around 400°C.