AVS 56th International Symposium & Exhibition
    Thin Film Monday Sessions
       Session TF1+PV-MoA

Paper TF1+PV-MoA1
Growth and Structure of RF Sputter-Deposited Cadmium Sulfide (CdS) Thin Films

Monday, November 9, 2009, 2:00 pm, Room A8

Session: Chalcogenide Photovoltaics
Presenter: R.S. Vemuri, University of Texas at El Paso
Authors: R.S. Vemuri, University of Texas at El Paso
D. Zubia, University of Texas at El Paso
C. McClure, University of Texas at El Paso
C.V. Ramana, University of Texas at El Paso
Correspondent: Click to Email
Cadmium sulfide (CdS) is a group II–VI semiconductor, which finds many scientific and technological applications. CdS thin films are particualrly interesting for application in large area photovotaics in addition to field-effect transistors, visible spectral range photoconductors, optical filters and nonlinear integrated optical devices. However, growth and optimization of conditions to produce high-quality CdS layers is important for enhanced photovoltaic device performances. In the present work, ordered cubic structured CdS films for application in CdTe/CdS solar cells were produced using RF magnetron sputtering. Pure CdS target was employed for sputtering. Two sets of CdS films were deposited: (1) at varying powers, in the range of 70-130 W, at constant Ar pressure of 7 mTorr, and (2) at varying Ar pressures, in the range of 5-20 mTorr at a constant power of 100 W. A detailed structural characterization was made to understand the effect of processing conditions on the morphology evolution, grain size, and crystal structure of the CdS films. High-resolution scanning electron microscopy (HRSEM) measurements revealed the smooth surface morphology of the CdS layers both as a function of sputtering power and Ar-pressure. CdS films grown at 70-130 W were found to be nanocrystalline, exhibiting grain-size (L) dependence on the sputtering-power (W). L increased with W yielding the highest average L=145 nm at 105 W. Further increase in W resulted in decreasing L. Similarly, under varying Ar pressure, the highest L (~138 nm) values were found at 5 mTorr. X-ray diffraction (XRD) analysis indicated that the entire set of deposited CdS films exhibit highly oriented cubic structure. L values evaluated from XRD are in good agreement with the HRSEM results. The optical characteristics were evaluated and a functional relationship between growth conditions and band gap, useful to tailor the CdS films for desired solar-cell application, was found. The results obtained will be presented and discussed.