An optically enhanced crystalline silicon allotrope: hydrogen passivated type II silicon clathrate

TL;DR

This paper demonstrates that hydrogen passivation significantly improves the optoelectronic properties of type II silicon clathrates by reducing defects and doping levels, leading to enhanced photoluminescence and potential for silicon-based light-emitting devices.

Contribution

It introduces hydrogen passivation as a novel method to enhance the optoelectronic quality of silicon clathrates, enabling their application in light-emitting devices.

Findings

NaD and SiD complexes reduce donor density and dangling bonds

Photoluminescence intensity increases by 40 times after passivation

Stable improvements up to 400°C in silicon clathrates

Abstract

While Si clathrates have been explored as promising direct bandgap semiconductors, their practical optoelectronic performance has been limited by high doping levels and structural defects. Hydrogen has long been used to improve the optoelectronic quality of conventional Si, yet its role in clathrate structures remains unexplored. In this study, we demonstrate that hydrogen (deuterium) can be incorporated into type II Si clathrate framework using remote plasma treatment. This process leads to the formation of NaD and SiD complexes, which significantly reduce both the Na donor density and dangling bond defects. Electron paramagnetic resonance confirms nearly a tenfold decrease in Na-related donor states, resulting in the lowest doping level reported in Si clathrates to date. Following passivation, the integrated photoluminescence intensity increases by a factor of 40, accompanied by a blue shift of the main emission peak, consistent with a transition closer to the intrinsic band edge. A new emission peak at 930 nm, attributed to hydrogen-related recombination centers, also appears. These improvements remain stable up to 400 oC. Altogether, this work establishes hydrogen passivation as a viable strategy for enhancing light emission in Si clathrates and opens a new pathway toward their application in Si-based light-emitting diodes and other direct-bandgap optoelectronic devices.