Properties of polycrystalline GaAs films grown by the close spaced vapour transport technique on Mo substrates

This thesis is a study of the properties of thin GaAs films grown on molybdenum substrates by the close spaced vapour transport (CSVT) deposition technique with the intention that the GaAs/Mo structure would be used as the semiconductor and substrate for economic solar cells. The GaAs films were polycrystalline cubic crystals with no preferred orientation. The crystallite area increased with the temperature at which the substrate was held during growth and at 710°C grain sizes of 100 μm² were observed. The crystallites formed a columnar-like structure with crystal size comparable to the film thickness. No impurities of foreign instrus-ions existed in the films in quantities observable on the electron micro-probe. The resistivity of the GaAs films was 220 Ω cm, hence acceptable for thin film solar cells, however, the GaAs/Mo contact was mildly rectifying. Diodes were fabricated by the deposition of Au onto the GaAs films and the resulting barriers showed values of barrier height of approximately 0.8 eV, ideality factor n = 1.5 to 2, and depletion-layer majority carrier concentration of roughly 10¹⁶ cm⁻³ as measured by J-V and C-V methods. The GaAs films show promise for use in solar cells provided that the Mo/GaAs interface resistance can be reduced.Applied Science, Faculty ofElectrical and Computer Engineering, Department ofGraduat