The goal of this project is to ascertain the influence of vacuum ultraviolet radiation (1200A) on the epitaxial crystallization of gallium arsenide (GaAs). A definitive study is planned to quantitatively assess the epitaxial growth rate and the crystalline quality of GaAs films synthesized under conditions such that the flux of ultraviolet radiation is varied over four orders of magnitude while other growth parameters are held essentially constant. The results of this study could have a significant impact on fundamental understanding of vapor phase epitaxy, and may provide a means for lowering the temperature requirements of epitaxial crystallization of technologically important electronic and photonic materials without compromising the exceedingly high crystal quality needed for advanced electronic and photonic devices.