Film-thickness-dependent conduction in ordered Si quantum dot arrays

In recent years, silicon nanostructures hae been investigated extensively for their potential use in photonic and photovoltaic applications. So far, for silicon quantum dots embedded in SiO2, control over inter-dot distance and size has only been observed in multiple bilayer stacks of silicon-rich oxides and silicon dioxide. In this work, for the first time the fabrication of spatially well-ordered Si quantum dots (QDs) in SiO2 is demonstrated, without using the multilayer approach. This ordered formation, confirmed with TEM micrographs, depends on the thickness of the initially deposited sub-stoichiometric silicon oxide film. Grazing incidence x-ray diffraction confirms the crystallinity of the 5 nm QDs while photoluminescence shows augmented bandgap values. Low-temperature current-voltage measurements demonstrate film thickness and order-dependent conduction mechanisms, showing the transition from temperature-dependent conduction in randomly placed dots to temperature-independent tunnelling for geometrically ordered nanocrystals. Contrary to expectations from dielectric materials, significant conduction and photocarrier generation have been observed in our Si QDs embedded in SiO2 demonstrating the possibility of forming initial film-thickness-controlled conductive films. This conduction via the silicon quantum dots in thick single layers is a promising result for integration into photovoltaic devices.