X-Ray and Far-uv Photoemission from Amorphous and Crystalline Films of Se and Te

Photoemission experiments have been performed on amorphous and crystalline films of Se and Te using photon excitation energies of 1486.6 ($\mathrm{Al}K\alpha$), 40.8, and 21.2 eV (He II and He I). From these experiments we have determined the densities of valence states, the binding energies of the core levels, the characteristic loss functions, and the plasma frequencies. Comparisons of the experimental to the theoretical densities of states are made for both the amorphous and crystalline forms. The optical properties of Te in the region of interband transitions are shown to be described well by a simple model based on the density of valence states. Evidence that the optical absorption peak from the Se $3d$ level may be of excitonic origin is presented.