CdTe Thin Films: Spray Deposition Using a Nanoparticle Ink Precursor

Authors: Douglas L. Schulz, Martin Pehnt, Calvin J. Curtis, David S. Ginley

In: Mat. Res. Soc. Symp. Proc. 426 (1996), 349-354. CdTe thin film growth using nanoparticle precursors and spray deposition has been investigated. Employing a metathesis approach, cadmium iodide was reacted with sodium telluride in methanol solvent resulting in the formation of soluble Nal and insoluble CdTe nanoparticles. After appropriate chemical workup, methanol-capped CdTe colloids were isolated. CdTe colloids prepared by this method exhibit a dependence of the nanoparticle diameter upon reaction temperature as determined by transmission electron microscopy (TEM) and UV-Visible spectroscopy (UV-Vis). CdTe thin film formation was achieved by spray depositing the nanoparticle colloids (25–75 Å diameter) onto substrates at elevated temperatures (T = 280–440 °C) with no further thermal treatment. These films were characterized by XRD, x-ray photoelectron spectroscopy (XPS), and atomic force microscopy (AFM). Cubic CdTe phase formation was observed by XRD with a contaminant oxide phase also detected. XPS analysis showed that CdTe films produced by this one-step method contained no Na or C, but substantial O. AFM gave CdTe grain sizes of ˜0.1–0.3 pim for films sprayed at 400 °C. A layer-by-layer film growth mechanism proposed for the one-step spray deposition of nanoparticle precursors will be discussed.