Direct bandgap emission from strain-doped germanium

Area of Science:

• Materials Science
• Condensed Matter Physics
• Semiconductor Physics

Background:

• Germanium (Ge) is a promising material for silicon (Si)-compatible optoelectronics.
• Ge's indirect bandgap limits its efficiency as a light emitter.
• Lithiation causes significant volume expansion in Ge, utilized in Li-ion batteries.

Purpose of the Study:

• To investigate the potential of lattice expansion via atom incorporation to achieve a direct bandgap in Ge.
• To explore the use of Lithium (Li) and noble gas atoms for bandgap engineering in Ge.
• To demonstrate tunable light emission properties in modified Ge.

Main Methods:

• First-principles calculations were employed to model the effects of atom incorporation on Ge's electronic band structure.
• Simulations analyzed the lattice expansion and strain induced by dopant atoms.
• The dipole transition matrix element was calculated to assess light-emitting efficiency.

Main Results:

• A minimal concentration of 3 atomic percent (at.%) Li was found to be sufficient to convert Ge from an indirect to a direct bandgap.
• The resulting direct bandgap in Li-doped Ge exhibits a dipole transition matrix element comparable to direct bandgap semiconductors.
• Noble gas atom implantation was proposed as an alternative for Si Complementary-Metal-Oxide-Semiconductors (CMOS) compatibility.
• Tunable emission wavelengths across the mid-infrared to far-infrared spectrum were demonstrated by manipulating dopant concentration.

Conclusions:

• Incorporating Li atoms into Ge can engineer a direct bandgap, overcoming its inherent limitations for light emission.
• This approach offers a novel pathway for developing efficient Ge-based light emitters compatible with Si technology.
• The tunability of emission wavelengths presents opportunities for various photonic applications, warranting experimental validation.