Mechanism of p-type conductivity for phosphorus-doped ZnO thin film

A p-type phosphorus-doped ZnO film (ZnO : P) was grown on a quartz substrate by sputtering a ZnO target mixed with 2 wt% P2O5 using a mixture of Ar and O-2 and then annealed rapidly at 750 degrees C for 5 min in air ambient. The lattice constant of the c-axis was 0.5176 nm, smaller than the value of 0.5211 nm of pure ZnO, implying substitutional P at a Zn antisite (P-Zn). The binding energy of P-2p1/3 is 133.5 eV, which is different from that of the P-O bond in P2O5 and of the P-Zn bond in Zn3P2, but close to that of P-O-P and P-O-Zn bonds in zinc phosphate glass mainly composed of ZnO and P2O5. The 80 K photoluminescence spectrum shows neutral acceptor bound exciton emission at 3.34 eV. Based on the above experimental results, it is suggested that P substitutes for a Zn antisite in the ZnO : P and forms an acceptor complex with two Zn vacancies, and the acceptor complex is responsible for p-type conductivity of ZnO : P.