Nanosecond Carrier Lifetime of Hexagonal Ge

Area of Science:

• Materials Science
• Semiconductor Physics
• Nanotechnology

Background:

• Hexagonal silicon-germanium (hex-SiGe) alloys are promising for silicon-compatible direct bandgap semiconductors.
• Theoretical models predict bulk hexagonal germanium (hex-Ge) to have weak dipole activity, contrasting with alloyed hex-SiGe where disorder enables light emission.

Purpose of the Study:

• To experimentally investigate the radiative properties of hexagonal germanium (hex-Ge) nanowires.
• To determine the radiative lifetime and optical transition matrix element of hex-Ge nanowires.
• To assess the potential of hex-Ge nanostructures for optoelectronic applications.

Main Methods:

• Photoluminescence spectroscopy of hex-Ge nanowires across a range of excitation densities.
• Advanced spectral line shape analysis using the Lasher-Stern-Würfel (LSW) model.
• Analysis of photoinduced bandfilling to determine excited carrier density.

Main Results:

• Observed radiative recombination in hex-Ge nanowires is as strong as in hex-SiGe.
• Extracted a radiative lifetime of (2.1 ± 0.3) ns by equating carrier generation and recombination rates.
• Determined a high oscillator strength of 10.5 ± 0.9, comparable to III-V semiconductors.

Conclusions:

• Hexagonal germanium nanowires possess strong optical properties, challenging previous theoretical predictions for the bulk material.
• The quantified radiative lifetime and high oscillator strength indicate hex-Ge nanostructures are well-suited for optoelectronic devices.
• This research opens avenues for novel semiconductor-based optoelectronics utilizing hexagonal germanium.