Abstract

Little attention has been paid to amorphous semiconductor surfaces since the valence band photoemission spectra of amorphous Si and Ge were first measured 15 years ago. This neglect has been due, in part, to the lack of a well-defined amorphous structure and the resulting preparation-dependent nature of amorphous semiconductor properties, which has frustrated the reproducibility of both surface and bulk measurements. Persistent efforts have minimized the impact of these materials issues, but an important stumbling block has remained to further understanding the surface electronic structure of technologically-important amorphous semiconductors such as hydrogenated amorphous silicon (a-Si:H). In such materials, measurement of the distribution of gap states (typically present in densities below 10¹⁹ eV^-1cm^-3) is of primary importance and requires sensitivities orders of magnitude higher than those available with conventional photoemission methods. The recent development of total yield, with its high dynamic range (10⁷: 1) and energy resolution (ΔE≦0.1 eV), as a surface gap state spectroscopy has opened up an exciting new window on the surface electronic structure of an entire class of increasingly important technological materials.¹

© 1989 Optical Society of America