Ge Microdisk with Lithographically-Tunable Strain using CMOS-Compatible Process

TL;DR

This paper demonstrates a CMOS-compatible process to create germanium microdisks with tunable biaxial tensile strain, enabling efficient on-chip light sources through optical resonances and strain engineering.

Contribution

It introduces a novel stress concentration technique and strain compensation method to produce strain-tunable germanium microdisks compatible with standard CMOS fabrication.

Findings

Achieved ~0.7% biaxial tensile strain in germanium microdisks.

Confirmed homogeneous strain distribution via Raman spectroscopy and simulations.

Observed optical whispering gallery modes matching FDTD simulations.

Abstract

We present germanium microdisk optical resonators under a large biaxial tensile strain using a CMOS-compatible fabrication process. Biaxial tensile strain of ~0.7% is achieved by means of a stress concentration technique that allows the strain level to be customized by carefully selecting certain lithographic dimensions. The partial strain relaxation at the edges of a patterned germanium microdisk is compensated by depositing compressively stressed silicon nitride layer. Two-dimensional Raman spectroscopy measurements along with finite-element method simulations confirm a relatively homogeneous strain distribution within the final microdisk structure. Photoluminescence results show clear optical resonances due to whispering gallery modes which are in good agreement with finite-difference time-domain optical simulations. Our bandgap-customizable microdisks present a new route towards an efficient germanium light source for on-chip optical interconnects.