A Nanomembrane-Based Bandgap-Tunable Germanium Microdisk Using Lithographically-Customizable Biaxial Strain for Silicon-Compatible Optoelectronics

TL;DR

This paper introduces a CMOS-compatible method to induce large, tunable biaxial strain in germanium nanomembranes, enabling bandgap engineering and significant performance improvements for silicon-compatible optoelectronic devices.

Contribution

A novel lithographic technique to apply and customize large biaxial strain in germanium microdisks, enhancing their optoelectronic properties.

Findings

Achieved biaxial strains up to 1.11% in germanium microdisks.

Observed redshift and enhancement in light emission due to strain.

Predicted >200x reduction in lasing threshold for strained germanium lasers.

Abstract

Strain engineering has proven to be vital for germanium-based photonics, in particular light emission. However, applying a large permanent biaxial strain to germanium has been a challenge. We present a simple, CMOS-compatible technique to conveniently induce a large, spatially homogenous strain in microdisks patterned within ultrathin germanium nanomembranes. Our technique works by concentrating and amplifying a pre-existing small strain into the microdisk region. Biaxial strains as large as 1.11% are observed by Raman spectroscopy and are further confirmed by photoluminescence measurements, which show enhanced and redshifted light emission from the strained microdisks. Our technique allows the amount of biaxial strain to be customized lithographically, allowing the bandgaps of different microdisks to be independently tuned in a single mask process. Our theoretical calculations show that this platform can deliver substantial performance improvements, including a >200x reduction in the lasing threshold, to biaxially strained germanium lasers for silicon-compatible optical interconnects.