Direct Bandgap Light Emission from Strained Ge Nanowires Coupled with High-Q Optical Cavities

TL;DR

This paper demonstrates a germanium-based light emitter integrated with high-Q optical cavities, achieving tunable emission and enhanced photoluminescence, advancing silicon-compatible on-chip light sources.

Contribution

It introduces a strained germanium nanowire light emitter with high-Q cavities, showing tunable emission and detailed gain/loss analysis for silicon photonics.

Findings

Achieved quality factors up to 2,000 in germanium cavities.

Emission wavelength tunable over 400 nm with a single lithography step.

Free carrier absorption limits net gain despite high tensile strain.

Abstract

A silicon-compatible light source is the final missing piece for completing high-speed, low-power on-chip optical interconnects. In this paper, we present a germanium-based light emitter that encompasses all the aspects of potential low-threshold lasers: highly strained germanium gain medium, strain-induced pseudo-heterostructure, and high-Q optical cavity. Our light emitting structure presents greatly enhanced photoluminescence into cavity modes with measured quality factors of up to 2,000. The emission wavelength is tuned over more than 400 nm with a single lithography step. We find increased optical gain in optical cavities formed with germanium under high (>2.3%) tensile strain. Through quantitative analysis of gain/loss mechanisms, we find that free carrier absorption from the hole bands dominates the gain, resulting in no net gain even from highly strained, n-type doped germanium.