A Hybrid model for the origin of photoluminescence from Ge nanocrystals in SiO$_2$ matrix

TL;DR

This paper investigates the origin of visible photoluminescence in germanium nanocrystals within SiO$_2$ matrices, proposing a hybrid model that combines quantum confinement and defect states based on experimental and literature analysis.

Contribution

It introduces a hybrid model explaining photoluminescence in Ge nanocrystals, supported by combined photoluminescence and Raman measurements from two growth techniques.

Findings

Photoluminescence observed in Ge nanocrystals is due to a combination of quantum confinement and defect states.

Experimental data supports the hybrid model over single-mechanism explanations.

The study compares two growth methods, revealing their influence on luminescence properties.

Abstract

In spite of several articles, the origin of visible luminescence from germanium nanocrystals in SiO$_2$ matrix is controversial even today. Some authors attribute the luminescence to quantum confinement of charge carriers in these nanocrystals. On the other hand, surface or defect states formed during the growth process, have also been proposed as the source of luminescence in this system. We have addressed this long standing query by simultaneous photoluminescence and Raman measurements on germanium nanocrystals embedded in SiO$_2$ matrix, grown by two different techniques: (i) low energy ion-implantation and (ii) atom beam sputtering. Along with our own experimental observations, we have summarized relevant information available in the literature and proposed a \emph{Hybrid Model} to explain the visible photoluminescence from nanocrystalline germanium in SiO$_2$ matrix.