Photoelectron studies of the densities of states in the gallium chalcogenides

Photoelectron energy distributions for the layered semiconductors GaSe and GaS are reported using Nei, Hei, Heii, and Mg $K\alpha$ photons. The deep-lying chalcogen $s$ bands and the gallium $3d$ core levels have been located, and considerable structure resolved in the main $p$-like bonding band for both materials. The empirically determined density of states have been compared with that determined from a pseudopotential-energy-band scheme, and good agreement is seen for features in the energy distributions recorded at high photon energy (Heii or Mg $K\alpha$). In addition to this information on the occupied energy bands, the secondary electron background observed in both He and Nei energy distributions is shown to exhibit pronounced structure characteristic of the one-electron conduction-band density of states, where again, close correlations are observed with the calculated-energy-band scheme.