A study of the deep electron traps in semiconducting CdS

Abstract

Deep‐level transient spectroscopy by means of capacitance transients has been applied to study the characteristics of deep electron traps in low‐resistivity CdS. Thermal activation of the capacitance transients for Schottky barriers formed on three different single crystals indicates the presence of nine electron traps located between 210 and 730 meV from the conduction band. Measured trap concentrations range from low 10¹¹ to high 10¹⁴ cm⁻³. Among the nine detected electron traps there is one with an activation energy of 210 meV which is found in the three crystals, while the traps located at 420, 470, and 730 meV from the conduction band are found in two crystals only, although not the same two crystals in all cases. Direct capture‐cross‐section measurements are performed for the level situated at 210 meV by studying the time‐dependent peak amplitude associated with trap refilling. It is shown that a time exponential variation of the trap filling process is only obtained under suitable biasing conditions. No significant variation of the capture cross section S∼3×10⁻¹³ cm² is obtained in the explored temperature range 100–120 °K.