Ultraviolet vertical-cavity surface-emitting lasers and vertical microcavities for blue lasers
Doctoral thesis, 2021

III-nitride materials are used for ultraviolet (UV) and visible light emitters. One such light source is the vertical-cavity surface-emitting laser (VCSEL) that could find applications within areas ranging from sterilization and medical treatment to car headlights and augmented reality displays. These devices are not yet commercialized, because of challenging mirror formation and electrical injection. However, due to the recent substantial performance improvement of blue-emitting VCSELs, it might not be long before they are available. UV VCSELs, on the other hand, are far from ready. Until recently, there were no VCSELs emitting in the UVB (280-320 nm) or at shorter wavelengths.

In this thesis, the first UVB VCSELs are demonstrated. These optically pumped devices emitting at wavelengths around 310 nm were realized by removing the substrate from high Al-content AlGaN structures using electrochemical etching, which allowed for the deposition of a high-reflectivity dielectric distributed Bragg reflector (DBR) on each side of the cavity. Thresholds below 1 MW/cm^2 were achieved by optimizing the sacrificial layer to achieve smooth etched surfaces and by accurately setting the cavity length and thereby the detuning.

Furthermore, electrically conductive DBRs for blue VCSELs were investigated. Insertion of interlayers in AlN/GaN DBRs increased the vertical resistance while measurements and simulations of ZnO/GaN multilayers showed that the resistance is similar to, or lower than, the lowest reported for pure III-nitride DBRs, as a result of the partial cancellation of polarization fields.

Finally, vertical cavities based on dislocation-free GaN microprism are demonstrated. The quality factor is strongly dependent on the prism diameter and is around 500 at yellow wavelengths for prisms with a 1-μm diameter. Simulations show that the quality factor should be approximately four times larger in the targeted blue wavelength regime.

These results serve as building blocks for future dislocation-free small-footprint VCSELs grown on low-cost substrates as well as short-cavity blue VCSELs with electrically conductive DBRs. Additionally, the UV VCSEL demonstration is an important step towards a compact, energy-efficient light source with attractive beam characteristics using a technology with great potential for realizing VCSELs in almost the full UV spectrum.



electrochemical etching

vertical-cavity surface-emitting laser


electrical conductivity



distributed Bragg reflector

A423 (Kollektorn) at the Department of Microtechnology and Nanoscience (MC2), Kemivägen 9, Gothenburg, Zoom, PW: 048859
Opponent: Prof. Tetsuya Takeuchi, Meijo University, Japan


Filip Hjort

Chalmers, Microtechnology and Nanoscience (MC2), Photonics

A 310 nm Optically Pumped AlGaN Vertical-Cavity Surface-Emitting Laser

ACS Photonics,; Vol. 8(2021)p. 135-141

Journal article

Giulia Cardinali, Filip Hjort, Nando Prokop, Johannes Enslin, Munise Cobet, Michael A. Bergmann, Johan Gustavsson, Joachim Ciers, Ines Häusler, Tim Kolbe, Tim Wernicke, Åsa Haglund, and Michael Kneissl, ”Low-threshold UVB VCSELs enabled by post-growth cavity length adjustment and smooth surfaces”

Vertical Electrical Conductivity of ZnO/GaN Multilayers for Application in Distributed Bragg Reflectors

IEEE Journal of Quantum Electronics,; Vol. 54(2018)

Journal article

Optical microprism cavities based on dislocation-free GaN

Applied Physics Letters,; Vol. 117(2020)

Journal article

Miniaturized laser sources for ultraviolet and blue light emission

The vertical-cavity surface-emitting laser (VCSEL) is a miniaturized light source with a low power consumption and a well-shaped light beam that can be used to send information at high speeds. VCSELs emitting infrared light are used to transmit data in data centers and for face recognition in smartphones. These lasers could also be used in, for example, augment reality displays and car headlights. However, for this to become a reality the performance of VCSELs emitting visible light, in particular blue and green, must improve. This thesis investigates electrically conductive mirrors and nanowire-based cavities that could be used to advance the development of such VCSELs. Additionally, VCSELs with emission further into the ultraviolet spectrum than previously possible are demonstrated, which is a first step towards realizing VCSELs that could be used for treatments of skin diseases and sterilization of bacteria and viruses. Thus, this thesis provides valuable insights for extending a popular laser source to shorter wavelengths of light and enabling a wide range of new applications.

Ljusstarka ultravioletta och violetta mikrolasrar som använder nanotrådar för att möjliggöra defekt-fria material och optimala kavitetslösningar.

Swedish Research Council (VR) (2016-04686), 2017-01-01 -- 2020-12-31.

Microcavity laser breakthrough for ultraviolet light (UV-LASE)

European Commission (EC) (EC/HORIZON/865622), 2020-08-01 -- 2025-07-31.

Ett komponent-fysikaliskt perspektiv på blå mikrokavitets-lasrar och resonanta lysdiodrar i III-nitrid-material

Swedish Energy Agency (2014-006476), 2015-01-01 -- 2018-12-31.

UV-blue-green resonant light-emitters

Swedish Foundation for Strategic Research (SSF) (IB13-0004), 2014-09-01 -- 2019-08-31.

Ultravioletta och blå mikrokavitetslasrar

Swedish Research Council (VR) (2018-00295), 2019-01-01 -- 2024-12-31.

Areas of Advance

Nanoscience and Nanotechnology (SO 2010-2017, EI 2018-)

Subject Categories

Physical Sciences

Electrical Engineering, Electronic Engineering, Information Engineering

Nano Technology


Chalmers Materials Analysis Laboratory

Nanofabrication Laboratory



Doktorsavhandlingar vid Chalmers tekniska högskola. Ny serie: 4966


Chalmers University of Technology

A423 (Kollektorn) at the Department of Microtechnology and Nanoscience (MC2), Kemivägen 9, Gothenburg, Zoom, PW: 048859


Opponent: Prof. Tetsuya Takeuchi, Meijo University, Japan

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