Study of temperature-dependent charge conduction in silicon-nanocrystal/SiO2 multilayers

Abstract

Silicon-nanocrystals (Si-NCs) realized by SiOx<2/SiO2 multilayer (ML) approach have shown promise for realizing tightly-controlled dimensions, thus efficiently exploiting the size-dependent quantum effects for device applications. Unfortunately, the confining insulating barriers (SiO2 sublayers), instrumental for realizing quantum size effects in Si-NC MLs, can also hinder the charge conduction which is crucial for device applications including Si-NC based tandem solar cells and multi-exciton solar cells. Owing to this, a comprehensive study of conduction mechanisms has been carried out using a thorough analysis of temperature-dependent dark I-V measurements of SiO2 thin film and Si-NC multilayer samples fabricated by Inductively Coupled Plasma CVD (ICPCVD). As the ML samples consisted of interleaved SiO2 sublayers, current in SiO2 thin film has initially been studied to understand the conduction properties of bulk ICPCVD SiO2. For 21nm thick SiO2 film, conduction is observed to be dominated by Fowler–Nordheim (FN) tunneling for higher electric fields (>8MV/cm; independent of temperature), while for lower electric fields (5–8MV/cm) at higher temperatures, the trap-related Generalized Poole–Frenkel (GPF) is dominant. This signified the role of traps in modifying the conduction in bulk ICPCVD SiO2 films. We then present the conduction in ML samples. For multilayer samples with SiO2 sublayer thickness of 1.5nm and 2.5nm, Direct Tunneling (DT) is observed to be dominant, while for SiO2 sublayer thickness of 3.5nm, Space Charge Limited Conduction (SCLC) with exponential trap distribution is found to be the dominant conduction mechanism. This signifies the role of traps in modifying the conduction in Si-NC multilayer samples and SiO2 sublayer thickness dependence.