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Improved electrical properties of non-hydrogenated a-Si densified by IBAD

Some effects of ion bombardment on the growth of non-hydrogenated amorphous silicon films were studied using samples prepared with low-energy ion-beam-assisted deposition (IBAD). Inert gas ions were used to determine the effects of the ion beam on pure amorphous silicon without the complication of simultaneous chemical effects. The ion bombardment was found to increase the film density, improve film stability, increase the effective conductivity activation energies and to move the position of the infrared absorption peak assigned to silicon-carbon bonds to larger wavenumbers. The largest effective conductivity activation energies and the lowest conductivities were obtained from films made with Ar+ ions and bombarding energies around 100 eV. However, these 'best' films still do not have a sufficiently low defect density to be useful semiconductors. The improvements are consistent with the thesis that densification of the growing film is the primary effect of the beam. However, for the conditions used, the densification appears to saturate, leaving a relatively large number of dangling bonds in the films. These may result from the presence of Ar known to be in the films, although the results are consistent with the topological model which suggests that the best conditions for forming covalently bonded solids are obtained when the number of bonding constraints is equal to the number of degrees of freedom.