Material properties and growth chemistry of nanocrystalline silicon films used for photovoltaic devices

We report on the growth chemistry and properties of nanocrystalline Si:H (nc-Si:H) films and devices grown using three different growth techniques ECR plasma, VHF plasma and hot wire. It is found that the films grown using ECR plasma deposition are predominantly <111> oriented, whereas the orientation depends upon pressure, growth rate and ion bombardment in films grown using VHF plasma. Remote hot wire grown films also show both <111> and <220> orientations. It is also found that all the films are stressed, with both compressive and tensile stress being present in the same film. The stress depends upon the grain size. Stress can explain the shift in Raman peak from its nominal value of 520 cm^-1. Devices with good minority carrier diffusion lengths can be fabricated in both <111> and <220> materials. Electron mobilities are in the range of 0.5-1.0 cm²/Vs.