Structural, defect, and device behavior of hydrogenated amorphous Si near and above the onset of microcrystallinity

High-hydrogen-diluted films of hydrogenated amorphous Si (a-Si:H) 0.5 mu m in thickness and optimized for solar cell efficiency and stability, are found to be partially microcrystalline (mu c) if deposited directly on stainless steel (SS) substrates but are fully amorphous if a thin n layer of a-Si:H or mu c-Si:H is first deposited on the SS. In these latter cases, partial microcrystallinity develops as the films are grown thicker (1.5-2.5 mu m) and this is accompanied by sharp drops in solar cell open circuit voltage. For the fully amorphous films, x-ray diffraction (XRD) shows improved medium-range order compared to undiluted films and this correlates with better light stability. Capacitance profiling shows a decrease in deep defect density as growth proceeds further from the substrate, consistent with the XRD evidence of improved order for thicker films. (C) 1999 American Institute of Physics.