Carrier type- and concentration-dependent absorption and photoluminescence of ZnO films doped with different Na contents

The electrical and optical properties of zinc oxide (ZnO) films doped with different Na contents and grown by pulsed laser deposition were investigated. Hall measurements witnessed the conductivity conversion from n-type to p-type with targeted Na doping content increased up to more than 1%. The photoluminescence intensity first decreased as the targeted Na content increased to 1%, while non-degraded and even enhanced PL intensity was observed in p-type ZnO:Na_0.02 film. This photoluminescence enhancement was ascribed to enhanced radiative recombination with more acceptor (Na_Zn) introduced. The band-gap shift of ZnO:Na_x films was related to the variation of carrier type and concentration. Band-gap shrinkage was adopted to explain the carrier type- and concentration-dependent band-gap shift of ZnO:Na_x films.