Electronic Spectra of Trigonal and Disordered Phases of Tellurium and Selenium. I. Theory

Abstract

The electronic density of states of trigonal and amorphous tellurium and selenium are calculated in the energy region of the two-highest-valence-band triplets and the two-lowest-conduction-band triplets. The calculations are performed using the pseudopotential scheme. The structural model for the amorphous phases is based on the assumption that the average short-range order is the same as in the trigonal crystals. The main results are that (i) the density of states of the amorphous phases of both materials is essentially structureless in the energy region of the second-conduction-band triplet; (ii) some fine structure is maintained in the two valence bands and the first conduction band. These can be associated with parts of the density of states contributed from a region of the Brillouin zone along the $k_z$ axis. The results are compared to those obtained by using a tight-binding approximation. The comparison with experimental data will be performed in an accompanying paper.