Analysis Of The Optoelectronic Properties And Effect Mechanism Of The Hydrogen-Related Defects In Hydrogen Treated ZnO-Based Thin Films

ZnO-based transparent conductive thin films were prepared in two different ways by RF magnetron sputtering:（1） ZnO and ZnO:Al（AZO） films were prepared in Ar+O₂ and Ar atmosphere respectively, and then annealed in Ar+H₂ atmosphere;（2） ZnO-based films were prepared in Ar+H₂ atmosphere directly. The characterization methods of XRD, Hall effect, XPS, transmittance spetrum, PL spectrum were used to study the films’ crystal structure, optoelectronic properties, defect states and chemical states. Based on these results, the influencing mechanism of H-related defects on the optoelectronic properties in the films were analyzed in depth.It has been comparatively investigated that the effect of hydrogen annealing on the properties in ZnO films prepared in different atmosphere. All the films exhibit hexagonal wurtzite structure with a c-axis preferred orientation, and the films’ crystalline quality can be obviously improved after hydrogen annealing. The average transmittance in visible region is not affected by hydrogen annealing, and it is above 85% for all the films. ZnO thin films prepared with oxygen would result in O-face, and there are lots of acceptors in the films, such as the absorbed oxygen species at the surface and interface, Oi and V_zn etc, their compensating and scattering effects can lead to poor conductivity in the films. After hydrogen annealing, the introduced hydrogen would passivate the acceptors mentioned above by the desorption of surface oxygen species, formingV_zn -Hn complexes and escape of Oi, moreover the mobility increases due to the improvement of the films’ crystalline quality, therefore, the conductive properties in the films are significantly improved. ZnO thin films prepared without oxygen will result in Zn-face, and there are less oxygen-related acceptors in the films, as a result, better conductivity is achieved. More V_zn acceptors will be produced in the films after hydrogen annealing, therefore, the films’ conductivity decreases.It has been comparatively investigated that the effect of hydrogen annealing on the properties in AZO films prepared in different atmosphere. Hydrogen annealing has no obvious effect on the films’ crystalline quality and transmittance. After hydrogen annealing, the resistivity significantly decreases in the films prepared with oxygen, it is because hydrogen can passivate the related acceptors. This is consistent with the results of ZnO films. While the resistivity in the films prepared without oxygen keeps no change after hydrogen annealing, which is different from the results of ZnO thin films. It is because Al doping would induce the change of the films’ polarity, and the content of V_zn acceptors cannot increase in the films after hydrogen annealing. Moreover, the background carrier concentration in the films is very high. Therefore, the hydrogen passivation to V_zn cannot give significant influence on the electrical properties in the AZO films prepared without oxygen. Although the conductivity in the AZO films prepared with oxygen can be significantly improved after hydrogen annealing, it is still lower than that in the AZO films deposited without oxygen.The influence of H₂ flow ratio on the properties in ZnO and AZO thin films were also comparatively investigated. The hydrogen introduction in sputtering gas gives little influence on the crystalline quality of ZnO thin films, but it can induce the deterioration of the crystalline quality of AZO films. For all the films preparated with hydrogen, the average transmittance in visible region is above 85%. After hydrogen addition, both the resistivity in ZnO films and the resistivity in AZO films decrease dramatically. Studies exhibit that the Al content and the chemical states of Al and Zn in the films are not affected by the addition of hydrogen, and hydrogen as shallow donors cannot dramatically improve the conductivity in the films, it is still the effect of hydrogen passivation to the related acceptors which induces the improvement of the films’ conductive properties. Compared to hydrogen annealing, the hydrogen introduction in sputtering gas can more effectively reduce the films’ resistivity. We suggest that the latter is more favorable for hydrogen entering into the films’ interior to passivate the acceptors and improve the electrical properties in the films.