Na-doped P-type ZnO Thin Films Prepared By DC Reactive Magnetron Sputtering

Zinc oxide (ZnO) is a novel II-VI compound semiconductor with a wide direct bandgap. It is a unique material that exhibits optoelectronic, piezoelectric, thermoelectric and ferromagnetic multiple properties. In particular, it is a potential candidate for applications in optoelectronic devices, including detectors, light emitting diodes (LEDs) and laser diodes (LDs), due to its direct wide-bandgap (3.37eV) and high exciton binding energy (60meV, 25meV for GaN), which will favor efficient excitonic emission processes at room temperature.To realize these device applications, an imperative issue is to fabricate both high-quality p-type and n-type ZnO films. Intrinsic ZnO thin film shows n-type due to intrinsic defects. It can be easily prepared high-quality n-type using group-Ill elements(Al, Ga, In, etc.) doping. However, it is difficult to dope p-type. There are several possbile reasons for this dilemma: (1) lack of shallow-acceptor dopants;(2) low solubility of such dopants;and (3) compensation by increased levels of impurity and native defect donor species. N-doped ZnO thin films can not be reproduced perfectly despite N element is considered as the best candidate for p-type ZnO from theories. Codoping method by Yamamoto provides a new approach for high-quality p-type ZnO thin films. However, the mobility of the codoped thin film is low because of the acceptor with the donor dopants . And the second phase will emerge with active donors of high content. We attempted to prepared group-I elements doped ZnO thin films as they have the shallow acceptor levels in ZnO.ZnO:Na films were prepared by DC reactive Magnetron sputtering technique at different substrate temperature and different atmosphere. The structure and properties are characterized by XRD, SEM, Transmission spectra and Hall. The study shows: we can prepare p-type ZnO thin films by Na doping. When Ar:O₂ ratio is 2:1, p-ZnO thin film deposited at 550°C has the better electrical properties, resistivity p = 59.9Ω.cm, carrier concentration n_p=2.57x10¹⁷cm-3, mobility μ=0.406cm²/V·S.