Growth and Optical Properties of Direct Band Gap Ge/Ge_0.87Sn_0.13 Core/Shell Nanowire Arrays

Area of Science:

• Semiconductor Physics
• Materials Science
• Optoelectronics

Background:

• Group IV semiconductor optoelectronics are advancing with Germanium-Tin (GeSn) alloys.
• Achieving strain-free, direct band gap GeSn with high Tin (Sn) content (>9%) on Ge/Si virtual substrates is crucial.

Purpose of the Study:

• To demonstrate the growth of Ge/GeSn core/shell nanowire arrays with high Sn incorporation.
• To investigate the impact of nanowire geometry on strain relaxation and defect formation in GeSn alloys.
• To evaluate the optoelectronic properties of GeSn nanowires for infrared applications.

Main Methods:

• Growth of Ge/GeSn core/shell nanowire arrays using advanced deposition techniques.
• Characterization of material composition, crystal structure, and strain using techniques like Transmission Electron Microscopy (TEM) and X-ray Diffraction (XRD).
• Photoluminescence (PL) spectroscopy and optical absorption measurements at room temperature.

Main Results:

• Successful growth of Ge/GeSn core/shell nanowires with up to 13% Sn incorporation, free from Sn clusters.
• Nanowire geometry effectively relaxes strain and minimizes structural defects in the Ge_0.87Sn_0.13 shell.
• Observed room-temperature photoluminescence centered at 0.465 eV and over 98% optical absorption.

Conclusions:

• Direct band gap GeSn alloys in a nanowire geometry offer a promising pathway for Group IV optoelectronics.
• The developed GeSn nanowires are suitable for low-cost, high-efficiency photodetectors in the short-wave infrared spectrum.
• This approach paves the way for advanced thermal imaging devices and other infrared optoelectronic applications.