a-Si:H i-layers were deposited at different substrate temperatures and plasma excitation frequencies, while the other deposition parameters were kept constant. These layers were characterised by measuring the intrinsic mechanical stress and the defect density. At deposition temperatures of 200 to 250°C low stress and a low defect density were obtained for excitation frequencies between 60 and 70 MHz. A second part shows the spectral response of thick p-i-n diodes for different reverse bias voltages. The data reveal a better collection efficiency for the case where generation of carriers is uniform throughout the i-layer, as compared to non-uniform generation, where carriers concentrate near the p-i interface.