Properties of phosphorus-doped zinc oxide films grown by pulsed laser deposition

Electrical and chemical bonding properties of P-doped ZnO thin films grown by pulsed laser deposition on sapphire substrates were systematically characterized utilizing the Hall effect and x-ray photoelectron spectroscopy (XPS) measurements. Oxygen growth pressure and postannealing processing play a great role in the properties of these films. Increasing oxygen growth pressure from 5 to 20 Pa enhanced the resistivity of P-doped ZnO films by three orders of magnitude. P-doped ZnO films grown at 700 deg. C under 20 Pa O2 exhibited p-type conductivity with hole concentration of 5x1017 cm-3 and hole mobility of 0.3 cm2/V s. Rapid thermal annealing processing decreased the electron density in the P-doped ZnO films. XPS binding energies of P 2s and 2p peaks showed formation of P-O bonds which increased with oxygen pressure in the films. This indicates formation of defect complexes of P dopants occupying zinc sites PZn and zinc vacancies VZn in the P-doped ZnO films.