The near band-edge emission and photoconductivity response of phosphorus-doped ZnO thin films grown by pulsed laser deposition

The photo-response of phosphorus-doped ZnO thin films is reported. In particular, room temperature photoluminescence and ultraviolet photoconductivity are measured for epitaxial films grown by pulsed laser deposition. For the as-deposited films, the near band-edge emission in P-doped films is reduced in intensity and shifts to higher energy relative to the undoped materials. Annealing in 100 Torr of oxygen decreases the near band-edge photoluminescence intensity for both the undoped and P-doped material. However, an enhancement in the visible orange-red emission due to defect states in the gap is observed with oxygen annealing, which correlates with a decrease in conductivity. The visible luminescence is consistent with radiative recombination involving deep states. Ultraviolet photoconductivity is observed for the annealed films, and is most notable for the phosphorus-doped materials. These results are consistent with the phosphorus introducing a deep level in the gap that is heavily compensated by a defect-related shallow donor in the as-deposited films.