First-principles study of p-type ZnO by S–Na co-doping

Using the first-principles method based on the density functional theory, the formation energy, electronic structures of S–Na co-doping in ZnO were calculated. The calculated results show that Na_Zn–S_O have smaller formation energy than Na_in–S_O in energy ranges from –3.10 to 0 eV of ${\mu }_O$, indicating that it opens up a new opportunity for growth the p-type ZnO. The band structure shows that the Na_Zn system is a p-type direct-band-gap semiconductor material and the calculated band gap (0.84 eV) is larger than pure ZnO (0.74 eV). The Na_Zn–S_O system is also a p-type semiconductor material with a direct band gap (0.80 eV). The influence of S–Na co-doping in ZnO on p-type conductivity is also discussed. The effective masses of Na_Zn–S_O are larger than effective masses of Na_Zn and the Na_Zn–S_O have more hole carriers than Na_Zn, meaning the hole in the Na_Zn–S_O system may have a better carrier transfer character. So we inferred that Na_Zn–S_O should be a candidate of p-type conduction. (paper)