Thin films of gallium arsenide on low-cost substrates. Quarterly project report No. 2, October 3, 1976--January 1, 1977

The metallorganic chemical vapor deposition (MO-CVD) technique is being applied to the growth of thin films of GaAs and GaAlAs on inexpensive polycrystalline or amorphous substrate materials (glasses, glass-ceramics, alumina ceramics, and metals) for use in fabrication of large-area low-cost photovoltaic device structures. Trimethylgallium (TMG), arsine (AsH/sub 3/), and trimethylaluminum (TMA) are mixed in appropriate concentrations at room temperature in the gaseous state and pyrolyzed at the substrate, which is heated in a vertical reactor chamber to temperatures in the range 600 to 800/sup 0/C, to produce the desired film composition and properties. The effects of H/sub 2/ and AsH/sub 3/ atmospheres at temperatures of 625 to 725/sup 0/C and the effects of several different cleaning procedures on the surfaces of candidate substrates have been investigated. Composite substrates, consisting of deposited Mo layers on several of the other substrate materials, and deliberately textured glass surfaces have been evaluated for GaAs film growth. Efforts have continued to acquire new or improved materials from various manufacturers for evaluation as possible substrates. A new dedicated reactor system was completed during the quarter and used for growth of undoped GaAs films on single-crystal substrates, to establish and characterize reactor performance, and for growth of Se-doped GaAs films on single-crystal substrates, to establish the n-type doping capabilities of the new reactor. The majority of the MO-CVD experiments, however, have involved the reactor system in use since the program began, and include growth of GaAlAs on single-crystal substrates; growth of polycrystalline GaAs on candidate low-cost substrates; and studies of the nucleation of GaAs on low-cost substrates. Results of these experiments are discussed in detail.