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

Silicon-nanocrystals (Si-NCs) realized by SiO_{x < 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 21 nm thick SiO₂ film, conduction is observed to be dominated by Fowler–Nordheim (FN) tunneling for higher electric fields (> 8 MV/cm; independent of temperature), while for lower electric fields (5–8 MV/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 1.5 nm and 2.5 nm, Direct Tunneling (DT) is observed to be dominant, while for SiO₂ sublayer thickness of 3.5 nm, 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. - Highlights: • Electrical conduction in SiO₂ film & Si-nanocrystal layers (Si-NCs) is reported. • SiO₂/SiO_x multilayer based Si-NCs were realized by Inductively Coupled plasma CVD. • For SiO₂ film, Fowler–Nordheim tunneling & Generalized Poole–Frenkel are observed. • For Si-NCs with thin SiO₂ sublayers (< 2.5 nm) Direct Tunneling is dominant. • For Si-NCs with 3.5 nm SiO₂ sublayers Space Charge Limited Conduction is dominant.