INTERNAL PHOTOEMISSION ON A-SI-H SCHOTTKY-BARRIER STRUCTURES REVISITED

Direct measurements of mobility gaps in hydrogenated amorphous silicon (a-Si:H) using internal photoemission (IPE) of electrons and holes ha ve been carried out. The analysis used in the measurement of metal/a-S i:H Schottky barrier heights in the previous studies was based on the classical Fowler theory. More detailed treatment of IPE in a-Si:H Scho ttky barriers, however, shows that the IPE yields Y(hv) proportional t o(hv - E(T))(2+c) rather than (hv - E(T))(2), where E(T) is the thresh old energy. In the case of parabolic extended band states, c = 1/2 and the exponent is 5/2 in place of 2. The extrapolations of yield versus hv result in barrier heights lower than those determined by the Fowle r theory but can be fitted over a larger energy range. The effects of the new analysis of experimental results on different a-Si:H materials are presented and discussed.