Characteristics of surface states at the insulator-semiconductor interface in the thin-film electroluminescent structures based on ZnS:Mn

Abstract

Distributions of the density of occupied surface electron states at the cathode interface between the insulator and phosphor in thin-film electroluminescent emitters are simulated in relation to the energy on the basis of experimental data. The dependences of the above distributions on the conditions of excitation of emitters are obtained. It is shown that these distributions shift to deeper levels of surface states as the frequency of excitation voltage is decreased and the pause between two neighboring switched-on states of emitters is increased, which corresponds to the cascade mechanism of relaxation of electrons captured by surface states. The coefficient of cascade capture of electrons prior to relaxation ((4−5) × 10−12 cm2/s), instantaneous lifetime of electrons prior to relaxation (0.2–0.25 s), cross section for capture of electrons to deeper levels of surface states (in excess or on the order of (6.7−8.3) × 10−21 cm2), largest values of the densities of occupied surface states at the cathode boundary from which electron tunnel (∼2.5 × 1013 cm−2), and energy density of above-specified surface states (7 × 1014 cm−2 eV−1) have been determined. The values of the quasi-equilibrium Fermi level at the surface in the course of the activity of electroluminescent emitters varies in the range from 0.9 to 1.35 eV, depending on conditions of excitation.