Germanium crystals on silicon show their light

TL;DR

This paper demonstrates significant emission enhancement in germanium-on-silicon crystals by controlling defects and carrier diffusion, advancing the development of integrated electronic and photonic devices.

Contribution

It introduces a method to mitigate defect effects in Ge/Si crystals, enabling efficient quantum well emitters and improving luminescence for silicon-based photonics.

Findings

Defect control drastically enhances luminescence.

Band-gap-engineered reflectors regulate carrier diffusion.

Design of efficient quantum well emitters achieved.

Abstract

Germanium and silicon-germanium alloys have found entry into Si technology thanks to their compatibility with Si processing and their ability to tailor electronic properties by strain and band-gap engineering. Germanium's potential to extend Si functionalities, as exemplified by lasing action of strained-Ge on Si substrates, has brought the material back to attention. Yet despite these advances, non-radiative transitions, induced by crystal defects originating from the Ge/Si interface, continue to be a serious bottleneck. Here we demonstrate the drastic emission enhancement achieved via control and mitigation over the parasitic activity of defects in micronscale Ge/Si crystals. We unravel how defects affect interband luminescence and minimize their influence by controlling carrier diffusion with band-gap-engineered reflectors. We finally extended this approach designing efficient quantum well emitters. Our results pave the way for the large-scale implementation of advanced electronic and photonic structures unaffected by the ubiquitous presence of defects developed at epitaxial interfaces.