INFLUENCE ON THE TRANSPORT-PROPERTIES OF THE DEPOSITION TEMPERATURE OF A-SI-H FILMS DEPOSITED FROM MIXTURES OF SILANE IN HELIUM AT HIGH DEPOSITION RATES

We study the electronic properties of hydrogenated amorphous silicon ( a-Si:H) deposited at high rates (up to 11 Angstrom/s) in a silane-heli um mixture containing 60% of helium and compare them with those of ''s tandard'' a-Si:H deposited at 250 degrees C in pure silane. For the fi lms obtained under helium dilution in silane, increasing the depositio n temperature from 250 degrees C to 350 degrees C leads to improved el ectronic properties (an increase of the trap-limited mobility along wi th a decrease in the density of states (DOS) of the conduction band ta il), while the characteristic features deduced from photothermal defle ction spectroscopy absorption spectra (Urbach tail, deep defect densit y), which are mainly related to the DOS below midgap, remain unchanged . The changes in the electronic properties are correlated to changes i n the hydrogen-related structure of the material.