Work

Fs-laser significantly enhances both above- and below-bandgap absorption in germanium

Year: 2024

Type: article

Abstract: Fs-laser irradiation is a promising fabrication method for future broadband optoelectronic applications as it creates antireflective micro- and nanoscale structures on semiconductor surfaces and introduces below-bandgap absorption; however, its application has mainly been limited to silicon. This paper demonstrates that fs-laser technology enables high optical absorption both above and below the bandgap in germanium (Ge). With optimized laser parameters, we achieve a maximum above-bandgap absorptance of 95% and over 70% below-bandgap absorptance, due to the creation of surface microstructures and structural defects, respectively. Raman spectroscopy reveals that under intense laser irradiation, Ge may undergo a phase transition to structures with a narrower bandgap extending the absorption to the mid-infrared region. Furthermore, we develop a hyperdoping process using Ti coating pre-laser processing followed by rapid thermal annealing, which results in 90% above-bandgap absorption and a 12% relative increase in below-bandgap absorption along with a high degree of crystallinity. The increased below-bandgap absorption is attributed to Ti doping and is twice as high as reported earlier. Our findings should have significant implications for the future Ge-based infrared applications.

Source: Optical Materials Express

DOI: 10.1364/ome.545692

Authors: Xiaolong Liu, Dmytro V. Gnatyuk, Julius Halmela, Ville Vähänissi, Hele Savin

Language: English

Topic: Laser Material Processing Techniques

Subfield: Computational Mechanics

Field: Engineering

Domain: Physical Sciences

Open Access status: gold

Estimated APC paid: $1,983

Funder: Academy of Finland

Awards: Super-sensitive ?/X- and NIR-radiation detectors via defect-free nanostructures: Next Imaging Revolution? (NIR), Photonics Research and Innovation, Femtosecond-Laser Hyperdoped Germanium for Broadband Infrared Photonic Applications