THE EFFECT OF DEPOSITION CONDITIONS ON THE STRUCTURAL, OPTOELECTRONIC AND DEVICE PROPERTIES OF HYDROGENATED AMORPHOUS SILICON AND SILICON-GERMANIUM ALLOYS (SOLAR CELL, THIN FILM TRANSISTORS).

摘要

RF glow discharge deposition conditions affect the concentration and configurations of bonded hydrogen in a-Si:H as observed by IR spectrometry. High deposition temperatures decrease hydrogen content in the film. At 5% atomic hydrogen concentration, a-Si:H is dominated by electron conduction, while at 18% atomic hydrogen concentration, the film becomes a hole dominated system. In the range of 6-15% atomic hydrogen, a-Si:H is a two-carrier system of electrons and holes. The electronic properties and density of states were investigated by using field effect transistor structures. By tuning the deposition process one can produce materials with a low density of states and high electron mobility. These materials have been used to fabricate thin film transistors with ON/OFF ratios as high as 10('7). This is a significant improvement over the best value in the literature of a-Si:H transistors.;Light exposure was found to involve an increase in the density of midgap states and in the slope of the conduction band tail of a-Si:H. The latter effect has not been observed previously.;The first a-Ge:H and a-SiGe:H transistors with appreciable field effect response were developed by reducing the deleterious dihydride content in the films. a-SiGe:H alloys are found to be overy-hydrogenated and to contain excess dihydride. Although both a-Ge:H and a-SiGe:H have a higher density of midgap states than does a-Si:H, their hole mobilities were found to be higher than a-Si:H. This is in part due to a shifting of the asymmetry in the density of states profiles.