Germanium vertically light-emitting micro-gears generating orbital angular momentum.

Area of Science:

• Optoelectronics
• Materials Science
• Nanotechnology

Background:

• Germanium (Ge) is a promising material for optical gain media on complementary metal-oxide-semiconductor (CMOS) chips.
• Tensile strain is crucial for overcoming Ge's indirect bandgap and enabling efficient light emission.
• Existing methods for strain induction in Ge are limited, necessitating novel approaches for on-chip integration.

Purpose of the Study:

• To engineer tensile strain in high-crystalline-quality germanium-on-silicon-on-insulator (Ge-on-SOI) micro-gears.
• To investigate the optical properties and light emission characteristics of strained Ge micro-gears.
• To demonstrate the generation of optical modes with orbital angular momentum (OAM) in a Ge-based light source.

Main Methods:

• Fabrication of Ge micro-gears on silicon pillars using etching techniques.
• Induction of biaxial tensile strain via thermal stresses in encapsulating SiO2 layers.
• Characterization using Raman spectroscopy, finite-element method (FEM) simulations, and photo-luminescence (PL) spectroscopy.
• Analysis of optical modes using finite-difference time-domain (FDTD) simulations.

Main Results:

• Achieved biaxial tensile strain in Ge micro-gears ranging from 0.3-0.5%.
• Observed multiple sharp-peak resonances in the direct-gap region of Ge at room temperature via PL.
• Identified vertically emitted optical modes with non-zero orbital angular momentum (OAM) using FDTD simulations.

Conclusions:

• Successfully demonstrated strain engineering in Ge micro-gears for enhanced optical properties.
• Achieved room-temperature photo-luminescence from strained Ge, indicating potential for light emission.
• First-ever demonstration of orbital angular momentum (OAM) generation from a germanium light source.