AVS 52nd International Symposium
    Thin Films Monday Sessions
       Session TF+EM-MoM

Paper TF+EM-MoM10
Plasma-Assisted Co-Evaporation of Thin Films for Photovoltaic Applications

Monday, October 31, 2005, 11:20 am, Room 306

Session: Thin Films for Photovoltaic and Energy Applications
Presenter: C.A. Wolden, Colorado School of Mines
Authors: S. Kosaraju, Colorado School of Mines
J.A. Harvey, Colorado School of Mines
C.A. Wolden, Colorado School of Mines
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This presentation describes the development of plasma-assisted co-evaporation (PACE) and its application to the formation of @beta@-In@sub 2@S@sub 3@ and InN thin films. The former is an alternative window layer for copper indium diselenide based devices and the latter is a potential absorber. In PACE metals are supplied by conventional thermal evaporation, while the chalcogen or nitrogen gas precursors are activated by an inductively coupled plasma (ICP) source. The performance of the ICP source to activate both H@sub 2@S and N@sub 2@ was measured and optimized using a combination of optical emission spectroscopy and mass spectrometry. Transport modeling was used to quantify the flux distributions of both the co-evaporated metal and the reactive species from ICP source impinging upon the substrate. The source geometries were positioned asymmetrically so that the influence of composition and absolute rate could be ascertained from a single deposition experiment in a combinatorial approach. Model predictions were compared and validated using measurements of film thickness, composition, and quality. Through the deposition of @beta@-In@sub 2@S@sub 3@ and InN it was demonstrated that PACE provides substantial improvements in both materials utilization and substrate temperature reduction. For the case of @beta@-In@sub 2@S@sub 3@ it was observed that film quality was highly sensitive to the S/In ratio. The buffer layer was formed as low as 100 °C, and it was found that both the morphology and optical band gap were strong functions of temperature. In the case of InN the most important parameter was the excitation of nitrogen in the ICP source. It was shown that the introduction of argon was beneficial to nitrogen activation as evidenced by measurements of crystal quality and electronic properties.