氧对于在Ar/O氛围下用近空间升华法制备的CdS薄膜的影响

Effect of oxygen on CdS polycrystalline thin films prepared in ambient of Ar and O_2 by close spaced sublimation technology

采用近空间升华法(CSS)在氩/氧气氛中制备了硫化镉(CdS)多晶薄膜.利用XRD,XPS,AFM,UV-VIS光谱和四探针技术等测试和分析手段系统研究了氧对薄膜的成分、结构、光学和电学等性质的影响.结果表明,用近空间升华法制备的CdS薄膜具有六方相结构,膜层致密、均匀,平均晶粒大小约为40 nm,富硫.氧掺入后部分与镉生成氧化镉,并随着氧含量的增加,薄膜的成分有趋于化学计量比的趋势,光学带隙加宽,光暗电导比增加.此外,还利用扫描电镜(SEM)观察了CdS/CdTe断面结合光谱响应(QE)的结果讨论了氧对CdS/CdTe界面互扩散的影响.发现,随着CdS薄膜制备气氛中氧分压的升高,CdS/CdTe界面的互扩散程度降低,有利于提高器件在500—600 nm波长范围内的光谱响应.认为,氧含量的增加不但使CdS薄膜在光伏应用方面的质量得到改善,而且CdTe太阳电池器件中的CdS/CdTe界面也得到了优化.

In this paper,CdS polycrystalline thin films were prepared with the close-spaced sublimation（CSS） technology.In the deposition process,a controlled ambient of Ar and O2 mixture was used.The effect of oxygen on the microstructure,composition,morphology as well as optical and electrical properties of CdS thin films were studied systemically by XRD,XPS,AFM,UV-VIS and four-probe array method.The results showed that the CSS-grown CdS thin film has the hexagonal structure with crystallite size about 40 nm and the composition of them were rich in S.The impurity oxygen atoms mixed into CdS thin films and partly formed CdO,and with the increase of O2 concentration the chemical composition tinds more closely to the ideal stoichiometric proportion of CdO,the optical gap of thin films broadened and the ratio of photoconductivity to darkconductivity increased.Fortunately these effects are benefitial to CdS thin films for the photovoltaic application as a window layer.Additionally,it view of CdS/CdTe interface,we investigated the influence of oxygen on the cross-section morphology of CdS/CdTe thin films and the spectral response（SR） of the device.Then the results indicated that with the increase of O2 concentration in deposition ambient,the interdiffusion between CdS and CdTe decreased,and the SR of device in the range from 500 nm to 600 nm increased.We believe that the oxygen in CSS-grown CdS thin films plays a very important role in two aspects,firstly in improving the quality of CdS thin films for photovoltaic application,secondly in optimizing the CdS/CdTe interfacial properties in the CdTe solar cells.