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We report on the growth and properties of novel amorphous Silicon (a-Si:H) p-i-n devices prepared using chemical annealing with argon gas. The i layer in the p-i-n devices was grown using a layer by layer approach, where the growth of a very thin a-Si:H layer (7-30 angstroms) grown using a silane:argon mixture was followed by chemical anneal by argon ions. Repeated cycling of such growth/anneal cycles was used to produce the desired total thickness of the i layer. The thickness of the a-Si layer, and duration of the anneal time, were varied systematically. Pressure and power of the plasma discharge were also systematically varied. It was found that a thin a-Si layer, <10 angstroms, and low pressures which led to relatively high ion flux on the surface, gave rise to a significantly smaller bandgap in the device, as indicated by a significant lateral shift in the quantum efficiency vs. photon energy curve to lower energies. The smallest Tauc gap observed was in the range of 1.62 eV. Corresponding to this smaller bandgap, the current in the solar cell increased, and the voltage decreased. The Urbach energies of the valence band tail were also measured in the device, using the quantum efficiency vs. energy curve, and found to be in the range of45 meV, indicating high quality devices. Too much ion bombardment led to an increase in Urbach energy, and an increase in defect density in the material. Raman spectra of the device i layer indicated an amorphous structure. When hydrogen was added to argon during the annealing cycle, some materials turned microcrystalline, as indicated by the Raman spectrum, and confirmed using x-ray diffraction.

Chemical annealing is a powerful technique for controlling H bonding and optical absorption in amorphous semiconductors. We have shown previously that the use of careful chemical annealing by Argon can lower the bandgap of a-Si:H while maintaining electronic properties in both films and devices. In this work, we describe new work on chemical annealing of A-(Si,Ge):H films and devices. The technique consists in growing very thin layers (1-3 nm) of A-(Si,Ge) from mixtures of hydrogen, Silane and Germane, and then subjecting this thin layer to ion bombardment by Ar. The cycle is repeated many times to achieve the desired thickness of the intrinsic layer. The resulting film and device were measured for their composition using energy dispersive spectroscopy (EDS) analysis. We discovered that the composition itself, namely the Ge:Si ratio in the film, could be varied by changing the ion bombardment conditions. Lower energy bombardment led to a higher Ge:Si ratio for the same germane/Silane ratio in the gas phase. By controlling ion bombardment during the Ar annealing cycle, we were able to reduce the H content of the film and achieve good electronic properties. It will be shown that by appropriate control over ion energies, one can obtain films and devices which are of good quality and low bandgap as well.