스퍼터링법으로 증착한 CdS박막의 표면처리에 따른 전기적 특성

Abstract

CdS thin film is a well-known -typed semiconductor material. CdS is also widely used material as a window layer with some chalcogenide photovoltaic thin films in the heterostructured solar cells due to its high transmitivity, low resistivity, and excellent transmittance with a band gap of 2.42 eV, which was deposited by sputtering method in this experiment. The sputtering method was employed for a large-area preparation of CdS thin film. In this study, the sputtering-deposited CdS thin films were treated by the plasmas under the various conditions with some process parameters including under the fixed process condition including RF power and gas flow rate but the chaned treatment times and treatment time with Ar or O2 gases. Surface morphology and structure of them were analyzed by AFM and XRD. The effects of each plasma treatment on the electrical and optical properties of CdS thin film were investigated by UV-Visible spectrophotometer and Hall effect measurement. The roles of morphology and structure of plasma-treated CdS thin films were compared by the optical and electrical characteristics. In other way to enhance the optical characteristics of CdS thin film as a window layer, the patterned surface was employed on the interface with CdTe thin film. Nano sphere lithography (NSL) is one of the most useful techniques for the formation of periodic structures. Polystyrene nano spheres were used for pattern mask with good periodic structure. Ar, Cl2 and O2 gases were employed for the etchant gas in this experiment. Surface profiles of the patterned CdS thin film was examined by AFM and SEM. Optical and electrical properties of the patterned CdS thin films were analyzed with 500nm diameter polystyrene nano spheres. The improvement of optical property was obtained in the patterned CdS thin film. XRD peak values show little different value depending on process conditions. The transmittance whit the sample treated by the O2 gas plasma was 65.1% (the highest), while that with the Ar gas plasma showed the lowest. Hall mobility with Ar gas plasma sample showed the highest values. The surface roughness can be seen that a similar value. After the etching process with the Polystyrene nano sphere mask the nano-sized structures on the surface of both thin films were produced regardless of gas mixture. Ar, Cl2 gas plasma showed the relatively high transmittance after etching process. The addition of O2 gas in the etching process showed the lowest transmittance. The sheet resistance and carrier motility were in proned by the etching process with Cl2/Ar gas mixture, but they were diminished when the O2 gas was added to the gas mixture. These results confirmed that the better thin film properties can be obtained with periodic nano-structures on the surface of CdS thin film.