940-nm VCSELs grown by molecular beam epitaxy on Ge(001)

TL;DR

This paper reports the first successful growth and demonstration of 940 nm VCSELs on Ge substrates using molecular beam epitaxy, with real-time monitoring and low-threshold lasing at room temperature.

Contribution

It introduces a novel monolithic integration of 940 nm VCSELs on Ge via MBE, combining in situ growth monitoring and demonstrating practical device operation.

Findings

First demonstration of 940 nm VCSELs on Ge by MBE.

Room-temperature lasing with threshold currents below 3 mA.

Successful real-time growth analysis using multispectral reflectometry.

Abstract

Vertical-cavity surface-emitting laser (VCSEL) structures emitting near 940 nm were grown by solid source molecular beam epitaxy (MBE) on Ge(001) substrates. The VCSEL MBE-growth was realized upon a virtual substrate composed of GaAs on Ge grown by melatorganic vapour phase epitaxy (MOVPE). In situ monitoring during MBE growth employed multispectral reflectometry and magnification-inferred curvature imaging for real-time growth analysis. Curvature measurements revealed progressive compressive stress, while optical reflectivity data confirmed uniform layer growth and accurate stopband formation. Fabricated devices with mesa diameters of 35-40 $\mu$m, corresponding to oxide apertures of approximately 11-16 $\mu$m, exhibited room-temperature lasing under continuous-wave bias with threshold currents below 3 mA. To the best of our knowledge, this is the first demonstration of monolithically integrated 940 nm VCSELs grown on Ge substrates by MBE. These results confirm the viability of MBE-grown VCSELs on Ge with in situ process control for scalable optoelectronic integration.