TABLE OF CONTENTS The plasma polymerized amorphous semiconductor, which has so far been studied in greatest detail and also appears to be of greatest applied interest, is hydrogenated silicon (a-Si:H). Initial studies of this material were done in the sixties by Sterling and co-workers [105], [106], who demonstrated the radio-frequency (r.f.) glow discharge deposition of a-Si:H from silane (SiH 4). This was followed by the very important works of Spear and LeComber [107], [108], who reported on successful n- and p-doping a-Si:H. In the same time, the first thin-film photovoltaic solar cell using a-Si:H was fabricated [109]. In 1975 and 1976, research confirmed that plasma-deposited films from silane contained hydrogen [11O], [111]. The first commercial product based on a-Si:H photovoltaic batteries for calculators was introduced in 1980. Since then a-Si:H has found increased applications as large-area, thin-film amorphous semiconductor for photovoltaic solar energy modules [112] and thin-film transistors (TFT) that are most often used in controlling active-matrix liquid crystals displays (LCD) [113].
Although the electronic structure as well as electrical and optical properties of a-Si:H films have been widely characterized and extensively reviewed [8], [114], [115], [116], its DOS distribution function has been the subject of much controversy in the last 25 years. Nevertheless, one can acknowledge undoubtedly this material to be a typical representative of the hydrogenated amorphous semiconductors. A band model of a-Si:H commonly used nowadays, resulting from a variety of experimental...
