Investigation of Structural, Electrical, and Optical Properties for Al-Doped ZnO Films Deposited at Different Substrate Temperatures and H2 Ratios

Abstract

Al-doped ZnO (ZnO:Al) films were deposited at different substrate temperatures and H2/(H2+Ar) flow ratios by rf magnetron sputtering. The (002) preferred orientation is observed in all the deposited films; stress is decreased and crystallinity is improved for the films deposited at RT but they have no obvious change for the films deposited at 100–300°C with increase in H2 ratio. With increasing H2 ratio, carrier concentration and mobility obviously increase for the films deposited at RT and 100°C, and they slightly increase for the films deposited at 200°C but they are almost unchanged for the films deposited at 300°C. The results imply that the hydrogen is doped into ZnO lattice to form interstitial hydrogen (Hi), which is unstable above 200°C. The average transmittance of the films in visible region is above 80%, and it can be increased due to the hydrogen doping. The energy gap (Eg) of the films is mainly controlled by the carrier concentration, but it is also related to the crystallite size and stress for ZnO:Al films deposited at RT. The carrier transport mechanism and Eg as a function of carrier concentration in ZnO:Al films are also discussed.