Electrical transport and photocurrent mechanisms in silicon nanocrystal multilayers

Abstract

In this study, we investigated the lateral electrical transport and photocurrent mechanisms in multilayers of two-dimensional arrays of silicon nanocrystals (SiNCs), grown on quartz substrates by low pressure chemical vapor deposition (LPCVD) of Si and thermal oxidation. At low voltages, electrical conduction was ohmic, whereas at higher voltages, it was space charge limited in the presence of traps. At temperatures higher than 200 K both dark current and photocurrent were determined by thermal activation of carriers across the energy band gap, with an activation energy depending either on the applied voltage or on illumination. At temperatures lower than 200 K, the rate of current variation with temperature was smaller as transport was realized by carrier hopping, via phonons, between trapping states within the energy band gap, located near in energy and around the Fermi level. However, at the same temperature range, photocurrent was independent of temperature, as it was determined by carrier hopping from higher energy states to progressively lower ones. From this analysis, carrier concentration, an effective carrier mobility and trap density were extracted.