Experimental determination of the density of gap states in amorphous silicon by Schottky barrier admittance

Abstract

Experimental admittance measurements are presented for an n-type doped amorphous-silicon Schottky barrier. The measurements are shown to be quite consistent with the theory described by Archibald and Abram (1983, 1986) and, using this theory, an estimate of the density of states in the upper half of the mobility gap is calculated. The average value is ∼ 10¹⁷ cm⁻³ eV⁻¹ and there is a minimum situated approximately 0˙4 eV below the conduction-band mobility edge. This result is in approximate agreement with the density of states deduced by Lang, Cohen and Harbison (1982) using deep-level transient spectroscopy. The test-fit value for the gap-state capture/emission time constant τ₀ is found to be 10⁻¹² s.