The prime objective of the research was to investigate the fabrication, stability and electronic properties of a-Si:H devices deposited using electron cyclotron resonance (ECR) plasma deposition technique. Both reactive (hydrogen) and non-reactive (helium) gases were used as the primary plasma gas. The reactants generated by the ECR plasma from these gases were allowed to flow towards the substrate, where they reacted with silane to give rise to growth of a-Si:H. In general, we used a high dilution ratio of plasma gas (H2 or He) to silane, about 15:1 to 20:1; for growing a-Si:H. Very high quality a-Si:H films could be deposited using H-ECR plasma at relatively higher temperatures (325°C-375°C). The use of He in the discharge does not lead to any etching during growth (as with H-plasma), but does lead to significant ion bombardment. We found that by using a highly diluted He-ECR growth technique, we can reduce the Tauc bandgap of a-Si:H to 1.67eV, which is significantly lower than the 1.75eV obtained with H as the plasma gas. We further found that the hydrogen content in the films grown using He dilution was much lower than the H content in the films made using H-dilution. The microstructure of these films were further probed using TEM. We succeeded in making reasonable quality devices from the ECR-deposited a-Si:H materials prepared at high temperatures. The devices were deposited both on tin oxide (superstrate) and stainless steel (substrate) substrates. To deposit the superstrate type devices on tin oxide substrate we had to overcome various problems, such as reduction in tin oxide at high temperature and diffusion of B across the p-i interface at high temperature. The reduction in tin oxide was avoided by using a He-diluted p-layer deposited at low temperature. The diffusion of 'B' was avoided by using an a-Si:H buffer layer with a high C content between the p and i-layer. We found that the design of the buffer layer was critical to achieving good performance. While we had successfully solved these problems a lower temperatures (up to 360°C), it became progressively more difficult to solve the diffusion problem as the growth temperature was increased. These problems were overcome by the use of a substrate cell geometry. We could finally achieve fill factors of about 72% using such geometries. We also investigated the stability of the cells that we made using ECR plasma and compared it with the cells grown using glow discharge growth technique. We found that the solar cells made using H-ECR growth technique were more stable than those made using glow discharge technique. The hole mobility lifetime product ([mu][tau]) has not been previously measured in a-Si:H based devices grown using EGR growth technique. We measured the hole [mu][tau] product in devices, by making a systematic series of devices, all with same p and n Bayers, but with i-layers grown using hydrogen or helium dilutions and at different growth temperatures. Using quantum efficiency spectroscopy, we could deduce the hole [mu][tau] product. The quantum efficiency values were accurately modeled by adjusting just two parameters: the p-layer absorption and the hole [mu][tau] product. The results were quantified by modifying the earlier model, developed by Greg Baldwin.