Effects of hydrogen implantation on the photoluminescence and carrier mobility of ZnO films

A study of the effects of H+ implantation on the photoluminescence (PL) and carrier mobility of ZnO thin films is presented. The 4.2 K PL of the as-grown films exhibits free-exciton luminescence at 3.3755 eV and strong bound-exciton luminescence between 3.33 and 3.37 eV including a peak observed at 3.3313 eV which is identified as the collapse of excitons bound to structural defects. While the implantation process results in a slight reduction of the overall PL intensity due to the introduction of nonradiative centers, the intensity of the 3.3313 eV bound-exciton peak is reduced by more than two orders of magnitude. We attribute this reduction to preferential interaction of hydrogen with structural defects, such as passivation or the formation of complex defects. Room temperature Hall measurements show that changes in the optical properties of H-implanted ZnO are also accompanied by an increased carrier concentration and decreased carrier mobility.