Exciton Luminescence in Semiconductors. Surface Recombination and Space‐Charge‐Layer Effects

Abstract

AbstractThe effect of surface conditions on excitonic luminescence of wide‐band gap semiconductors like CdS in a situation when excitons are created by the binding of electron—hole pairs is considered. The surface contribution is considered by the velocity of surface exciton annihilation, the effective rate of electron and hole surface recombination, and by surface band bending. The analysis of continuity equations for electrons, holes, and excitons in line with Poisson's equation is carried out. The above set of equations is found to have analytical solutions in the following simple situations: a) at low exciton concentrations when both transfer and annihilation of the excitation energy are determined by the motion and recombination of electrons and holes; b) intermediate exciton concentrations when excitation energy transfer is realized by electron—hole diffusion while its annihilation is due mainly to the excitonic channel; c) high exciton concentrations (in respect to the minor carrier concentrations) when the diffusion as well as the annihilation of a excitation energy is realized by the excitonic channel. A new physical picture of the appearence of “dead” layer in excitonic luminescence based on the enhanced electron—hole recombination near the semiconductor surface, particularly, in conditions of a strong tunneling ionisation of excitons in surface electric fields is proposed.