Grain boundary passivation in cuprous oxide thin films via nitrogen annealing

In this work, polycrystalline cuprous oxide (Cu2O) films deposited by magnetron sputtering were annealed in situ in N2 atmospheres. Room-temperature and temperature-dependent Hall-effect measurements were performed on as-deposited and N2-annealed Cu2O films to probe the electrical transport mechanisms. The results show that the hole mobility of 0.8 Pa N2-annealed Cu2O film is enhanced compared with its as-deposited counterpart. It is shown that at low temperatures, the hole mobilities of Cu2O films appear to be limited by grain boundary scattering, while acoustic-phonon scattering comes into play at elevated temperatures. Moreover, the grain boundary potential barrier height which inhibits the hole transport is found to be reduced by N2-annealing at 0.8 Pa, thereby leading to the observed improvement in the hole mobility. It is thought that N2 is mainly concentrated at the grain boundaries in polycrystalline Cu2O films, thus passivating the grain boundary defect trap states. The results reported in this work suggest that N2-annealing induced grain boundary passivation could be an effective method to improve the photoelectric properties of polycrystalline Cu2O films.