Limitation of Na-H codoping in achieving device-quality p-type ZnO

Na-H in-situ codoping in single crystalline ZnO films was carried out by plasma assisted molecular beam epitaxy. It is found that Na-H codoping dramatically enhances the formation of substitutional Na (NaZn) in ZnO lattice due to the unchanged Fermi level. The annealing temperature needed to kick out H, however, is very high, which would concurrently result in a notable decrease of Na concentration to its solution limit in ZnO, namely, in the range of 1017 cm−3. Our results suggest that Na-H codoping method has a limited effect on enhancing the p-type conductivity of ZnO.