On the Temperature Coefficient of the Ionization Energy in III-V Compound Semiconductors

Abstract

The work function Φ is one of the most interesting electronic surface properties since it contains bulk as well as surface contributions. It is defined as the energy distance between the Fermi level E_F and the vacuum level E_vac′, and in metals it thus measures the energy necessary to remove an electron from the highest occupied state inside to “just outside” the solid. In semiconductors the Fermi level generally lies within the bulk band gap (Fig. 1). In the bulk and at the surface of a semiconductor the positions of the Fermi level with respect to the band edges may differ due to the presence of surface states within the bulk band gap. Cleaved InP (110) and GaAs (110) surfaces, which will be considered in the present paper, exhibit no intrinsic surface states within the bulk band /1/ and obviously show no surface band-bending. Although the temperature variations of the band gap and of the bulk position of the Fermi level with respect to the band edges are well known and may be calculated from the doping, respectively, the temperature dependence of the work function may only be predicted if the temperature coefficients of the ionization energy I or of the electron affinity x have been determined. In the present paper we will show the ionization energy of InP (110) surfaces to be insensitive to variations in temperature. The same result has been earlier reported by Mönch et al. /2, 6/ for GaAs cleaved surfaces. These data will be also analyzed.