Sub-Band Gap Photodetection from the Titanium Nitride/Germanium Heterostructure

Area of Science:

• Materials Science
• Optoelectronics
• Nanotechnology

Background:

• Harnessing longer wavelength light is crucial for advanced optoelectronic applications.
• Photoexcited hot carriers offer a pathway to utilize sub-band gap energies.
• Germanium (Ge) has limitations in absorbing light beyond its band gap.

Purpose of the Study:

• To demonstrate hot-carrier-mediated sub-band gap photodetection in germanium-based heterojunction devices.
• To investigate the performance of germanium/titanium nitride (Ge/TiN) interfaces for near-infrared (NIR) photodetection.
• To explore the potential of titanium nitride (TiN) as a cost-effective alternative to traditional metals in photodetectors.

Main Methods:

• Fabrication of planar Ge/TiN heterojunction interfaces using dc sputtering.
• Characterization of photocurrent generation under near-infrared (NIR) light illumination.
• Comparison of device performance with different metal contacts (Nickel, Gold, none).

Main Results:

• Photocurrent generation confirmed up to 2600 nm, significantly exceeding the absorption limit of Ge.
• Nickel contacts yielded photocurrent three orders of magnitude higher than other configurations.
• Achieved a specific detectivity (D*) of 6.32 × 10^5 Jones at 2000 nm without bias.

Conclusions:

• The Ge/TiN heterojunction exhibits efficient hot-carrier-mediated sub-band gap photodetection.
• Superior performance is attributed to TiN's broad absorption, plasmonic hot carrier transfer, and built-in potential.
• TiN is a promising, robust, and cost-effective material for NIR photodetection and photovoltaics when integrated with Ge.