Direct Bandgap Emission from Hexagonal Ge and SiGe Alloys

TL;DR

This paper reports the discovery of efficient light emission from direct bandgap hexagonal Ge and SiGe alloys, enabling integration of electronic and optoelectronic functionalities on silicon-based platforms.

Contribution

It demonstrates for the first time that hexagonal Ge and SiGe alloys can emit light efficiently via a direct bandgap, with tunable emission wavelengths and excellent agreement with ab initio theory.

Findings

Efficient, temperature-insensitive light emission observed.

Emission wavelength tunable across a broad range.

Experimental results match theoretical predictions.

Abstract

Silicon crystallized in the usual cubic (diamond) lattice structure has dominated the electronics industry for more than half a century. However, cubic silicon (Si), germanium (Ge) and SiGe-alloys are all indirect bandgap semiconductors that cannot emit light efficiently. Accordingly, achieving efficient light emission from group-IV materials has been a holy grail in silicon technology for decades and, despite tremendous efforts, it has remained elusive. Here, we demonstrate efficient light emission from direct bandgap hexagonal Ge and SiGe alloys. We measure a subnanosecond, temperature-insensitive radiative recombination lifetime and observe a similar emission yield to direct bandgap III-V semiconductors. Moreover, we demonstrate how by controlling the composition of the hexagonal SiGe alloy, the emission wavelength can be continuously tuned in a broad range, while preserving a direct bandgap. Our experimental findings are shown to be in excellent quantitative agreement with the ab initio theory. Hexagonal SiGe embodies an ideal material system to fully unite electronic and optoelectronic functionalities on a single chip, opening the way towards novel device concepts and information processing technologies.