Preparation And Optical/Electrical Studies Of Doped ZnS Thin Films By Vacuum Evaporation Technology

ZnS is an important Ⅱ-Ⅵ semiconductor material with a wide direct band gap ranging from 3.5eV to 3.7eV. In addition, the applications of pure ZnS film were greatly limited due to its high resistivity. To improve its electric/optic performance, the study of ZnS:In films is performed, which will lay a foundation for ZnS application in solar cell and opto-electronic devices.In this work, ZnS films were prepared by vacuum evaporation technology, and the influence of preparation parameters on In-doped ZnS thin films were detailedly studied. The main results obtained are as follows:1、ZnS:In thin films are mainly of cubic sturcture with (111) preffered orientation. By increasing In content, some other structural phases appear, and the resistivity is decreased firstly and then increased, however, the mobility is firstly increased and then decreased and the carrier concentration is continuously increased until it reaches one value. When In-doped proportion is at 6 at.%, the film obtains the best optical transmittance about 85%, the lowest resistivity of 0.045Ω·cm and the mobility about 69.6cm2·v-1·s-1.2, Only ZnS phase is observed for ZnS:In film when substrate temperature is below 100℃. With the increase of substrate temperature, the resistivity of ZnS:In film is decreased firstly and then increased, whereas thin film mobility is increased and then decreased. It is found that the film has best optical and electrical performance when substrate temperature is about 100℃.3, With the increase of annealing temperature, the resistivity of ZnS:In films is decreased firstly and then increased, whereas thin film mobility is increased and then decreased, thin film carrier concentration is increased observably, maintained at a value nearby, finally. Similar as annealing temperature, the resistivity of the ZnS:In films is decreased firstly and then increased,whereas thin film mobility is increased and then decreased with the increase of annealing time. When the annealing temperature is 470℃ and annealing time is 2.5h, the Zns:In film has a better electrical properties.4、The performance of Al-doped ZnS film and In-Al co-doped ZnS films was also studied. The optimum parameters (E.g., dopant concentration, substrate temperature, annealing temperature, annealing time, etc.) are obtained. With the resistivity of 14.3Ω·cm when Al-doped proportion is about 6at.%, substrate temperature is 150℃, annealing temperature is 470℃ and annealing time is 2.5h in the ZnS:In film. Also, with the resistivity of 3.9* 10-3Ω·cm when substrate temperature is 150℃, annealing temperature is 475℃ and annealing time is 2.5h in the In-Al co-doped ZnS film.5、Under the optimum conditions obtained above, ZnS:In/Si, ZnS:Al-In/Si PN junctions with good performance were fabricated.In conclusion, the doped ZnS thin films with different doping elements have been prepared by vacuum evaporation technology. We find that the best doping concentration is 6 at.%, substrate temperature is 100℃, annealing temperature is 470 ℃ and annealing time is 2.5h, respectively. The appropriate doped ZnS thin films show good performance. This result obtained in this thesis is beneficial to ZnS-based PN junction.