Silicon Nanocrystallites in SiO2 Matrix: The Role of Disorder and Size

TL;DR

This study uses first-principles calculations to analyze how disorder and size influence the structural, electronic, and optical properties of silicon nanocrystals embedded in SiO2, revealing the dominant role of amorphization.

Contribution

It provides a comparative analysis of crystalline and amorphous silicon nanoclusters in SiO2, highlighting the impact of disorder on opto-electronic properties and the importance of local field effects.

Findings

Amorphization reduces the fundamental gap and enhances visible absorption.

Increasing nanocluster size lowers the absorption threshold consistent with quantum confinement.

Local field effects are critical in crystalline but minor in amorphous systems.

Abstract

We compare, through first-principles pseudopotential calculations, the structural, electronic and optical properties of different size silicon nanoclusters embedded in a SiO2 crystalline or amorphous matrix, with that of free-standing, hydrogenated and hydroxided silicon nanoclusters of corresponding size and shape. We find that the largest effect on the opto-electronic behavior is due to the amorphization of the embedded nanocluster. In that, the amorphization reduces the fundamental gap while increasing the absorption strength in the visible range. Increasing the nanocluster size does not change substantially this picture but only leads to the reduction of the absorption threshold, following the quantum confinement rule. Finally, through the calculation of the optical absorption spectra both in a indipendent-particle and many-body approach, we show that the effect of local fields is crucial for describing properly the optical behavior of the crystalline case while it is of minor importance for amorphous systems.