Quantized current jumps in silicon photoconductors at room temperature

Abstract

We report on the observation of quantized jumps due to single-carrier trapping and detrapping at defect states in silicon photoconductors of 103 μm3 in volume. A specifically designed electrical test structure in a low-doped (2×1014 cm−3) silicon crystal was fabricated. It consists in four substrate resistances connected in a Wheatstone bridge. After the exposure to light, the bridge offset voltage recovers its equilibrium value with steps of 5–10 μV, corresponding to the emission or capture of a single carrier. Such structures also display random telegraph signals in the dark, with steps of similar amplitude. This behavior is observed with structures processed on Czochralski-grown substrates and not with those processed on float-zone substrates. Simple calculations based on quantized free carrier concentration variations corroborate the above measurements.