DEFECTS AND DISORDER BROADENED BAND TAILS IN COMPENSATED HYDROGENATED AMORPHOUS-SILICON

The effect of dopant incorporation on the localized state distribution in compensated a-Si:H films is investigated via photoelectron yield spectroscopy. Results indicate that except for high phosphorus concentrations (above 100 ppm in the gas phase), compensated films possess a lower near-surface defect density than in undoped films. However, the incorporation of phosphorus is observed to lead to a considerable increase in the valence band tail characteristic energy E(ov). E(ov) increases from a value of 44 meV in singly doped p-type films (doped with 500 ppm of diborane) to about 63 meV in compensated films prepared with the addition of 10 ppm of phosphine. By contrast, typical undoped a-Si:H films possess an E(ov) of around 50 meV. Boron compensation of phosphorus doped a-Si:H films is observed to have no effect on the conduction band tail characteristic energy. Thus, while B incorporation has no effect on the conduction band tail density of states in P doped films, P incorporation leads to an increase in the valence band tail in B doped films. The data is compared with the prediction of various models forwarded to interpret the density of states in compensated a-Si:H.