Nanostructures and defects in silicon-hydrogen alloys prepared by argon dilution

Nanostructural heterogeneity of silicon-hydrogen (Si:H) alloy films deposit ed in a conventional radio frequency plasma-enhanced chemical vapour deposi tion unit from silane argon mixture has been studied by small-angle X-ray s cattering (SAXS). The densities of defect states of SI:H films have been es timated by dual beam photoconductivity (DBP), photothermal deflection spect roscopy (PDS) and the modulated photocurrent (MPC) method. From the structu ral and defect studies we identify two regions of Ar dilution, where the st ructure of the films are distinctly different. Up to 90% Ar dilution, the n anostructural as well as the large-scale (>30 nm) structural heterogeneitie s in the amorphous Si:H (a-Si:H) network decrease. A lowering of the bulk d efect density has also been observed in this Ar dilution region. Increasing Ar dilution to greater than 90% of the mixture, the a-Si:H films show some dense regions embedded in the amorphous matrix. The high- and low-density amorphous structures within the films can explain the experimental results obtained from SAXS, DBP and PDS, A negligible conduction band tail, as obse rved from MPC result, suggests the formation of high degree of crystallinit y in the film deposited with 99% Ar dilution and higher rf power density (8 0 mW/cm(2)). (C) 2000 Elsevier Science B.V. All rights reserved.