Preparation and Characterization of Hydrogenated Amorphous-Silicon Films Produced by Ion Plating and Hydrogenated Amorphous-Boron Films Produced by Glow-Discharge Decomposition. Final Report, April 1, 1980-May 31, 1981

摘要

This program has had two main goals - the investigation of ion-plating as a novel means of a-Si:H film preparation and the evaluation of a-B:H as a candidate solar cell material. Substantial progress has been made in both areas. Co-evaporation doping of a-Si:H by Ga has been achieved, and it has been shown that Ga is a p-type dopant. The thermoelastic properties of a-Si:H have been determined. It has been shown to be possible to produce stress-free films of a-Si:H by the use of Invar substrates. Positron annihilation Doppler measurements of a-Si:H show a systematic decrease in line width as one proceeds from crystalline Si to a-Si to a-Si:H. Detailed studies of the optical band gap of a-B:H show that the band gap of this material may be controlled over the wide range from 0.9 to 2.2 eV. Samples of band gaps near 1.45 eV can be produced either by the use of post deposition heat-treatments (7 hours at 360 exp 0 C) or by the use of hot (350 exp 0 C) substrates during deposition. The band gap is a function of the B/H ratio, and it has also been possible to produce 1.45 eV band gap films through the use of BF sub 3 /B sub 2 /H sub 6 gas ratios of 8:1. These films can be doped n-type either by the use of C (as ethylene) or Si (as silane) additives to the BF sub 3 /B sub 2 H sub 6 glow. Electron spin resonance measurements of such optimized films give evidence of fluorine as well as hydrogen incorporation into the films. The photoconductivity of a-B:H films is found to be sensitive to impurity contamination. In the best films, however, room temperature photoconductivities two orders greater than dark photoconductivities have been observed. The use of higher purity boron (99.9995%) as a cathode material for our DC glow is expected to improve this conductivity further. (ERA citation 07:010438)