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Ultraviolet-C Vertical-Cavity Surface-Emitting Lasers with Precise Cavity Length Control

E. Torres1, J. Ciers1, N. Rebelo1, F. Hjort1, M.A. Bergmann1, S. Graupeter2, J. Enslin2,3, G. Cardinalli2, T. Wernicke2, M. Kneissl2,3, and Å. Haglund1

Published in:

Laser Photonics Rev., vol. 18, no. 13, pp. 2402203, doi:10.1002/lpor.202402203 (2025).

Abstract:

In vertical-cavity surface-emitting lasers (VCSELs), the cavity length defines the resonance wavelength, which is directly related to the laser detuning, that is, the difference between resonance wavelength and gain peak. A low detuning maximizes the modal gain leading to a reduction of the threshold. Therefore, controlling the cavity length of VCSELs is of great importance. Here optically pumped ultraviolet-C (wavelength ≤ 280 nm) VCSELs with precise cavity length control are demonstrated. The VCSEL structure is formed by an AlN cavity with 5 × Al0.40Ga0.60/Al0.70Ga0.30N quantum wells and a top HfO2 spacer layer with dielectric SiO2/HfO2 distributed Bragg reflectors on both sides of the cavity. To access the N-face side of the cavity, a new methodology referred to as photo-assisted electrochemical etching is employed for substrate removal. Across a 0.9 mm × 1.2 mm area, the lasing wavelength varies a maximum of 1.17 nm between different UVC VCSELs, exhibiting threshold pump power densities from 0.7 MW/cm2 to 3.7 MW/cm2 and detuning values between 0 to 2 nm. The results show that VCSELs with a cavity length variation lower than 1% can be obtained with this technology.

1 Department of Microtechnology and Nanosciense Chalmers University of Technology, 41296 Gothenburg, Sweden
2 Institute of Solid State Physics, Technische Universität Berlin, 10623 Berlin, Germany
3 Ferdinand-Braun-Institut (FBH), 12489 Berlin, Germany

Index Terms:

AlGaN, electrochemical etching, photo-assisted electrochemical etching, UVC, VCSEL

© 2025 The Author(s). Laser & Photonics Reviews published by Wiley-VCH GmbH. This is an open access article under the terms of the Creative Commons Attribution License, which permits use, distribution and reproduction in any medium, provided the original work is properly cited.
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