In the mid to late 80's there was considerable effort directed at the hetroepitaxial growth of III-V's (GaAs, GaP and InP) on Si substrates for solar cell applications. The primary incentive for this work was the cost reduction of expensive substrate materials. This is particularly important when considering large scale production of terrestrial photovoltaic modules. In the U.S. these efforts produced cell efficiencies up to 21% and continued development of this solar cell structure is currently being pursued in Japan. Similar cost effective structures are being investigated at NREL such as the growth of polycrystalline GaAs films on inexpensive glass substrates for solar cell applications. Polycrystalline films, however, tend to contain a high density of grain boundaries which are regions for carrier recombination and enhanced dopant diffusion which can limit cell performance. In order to reduce the detrimental effects of grain boundaries, the growth of large grain (hence low boundary area) GaAs is being investigated