Laser Diode Emits Deep UV Light

Asahi Kasei Corporation succeeded in designing a laser diode that emits deep-ultraviolet light. The laser diode emits the world’s shortest lasing wavelength, at 271.8 nanometers (nm), under pulsed [electric] current injection at room temperature.

Previous efforts in the development of ultraviolet laser diodes had only managed to achieve emissions down to 336 nm.

Laser diodes that emit short-wavelength ultraviolet light, which is called UV-C and is in the wavelength region of 200 to 280 nm, could be used for disinfection in healthcare, for treating skin conditions such as psoriasis, and for analyzing gases and DNA.

The Nagoya University deep-ultraviolet laser diode overcomes several issues encountered by scientists in their work towards the development of these semiconducting devices.

The team used a high quality aluminium nitride (AlN) substrate as their base for building up the layers of the laser diode.

Applied Physics Express – A 271.8 nm deep-ultraviolet laser diode for room temperature operation

Researchers present a deep-ultraviolet semiconductor laser diode that operates under current injection at room temperature and at a very short wavelength. The laser structure was grown on the (0001) face of a single-crystal aluminum nitride substrate. The measured lasing wavelength was 271.8 nm with a pulsed duration of 50 ns and a repetition frequency of 2 kHz. A polarization-induced doping cladding layer was employed to achieve hole conductivity and injection without intentional impurity doping. Even with this undoped layer, we were still able to achieve a low operation voltage of 13.8 V at a lasing threshold current of 0.4 A.

Ultraviolet (UV) laser diodes (LDs) operating at wavelengths of the UV-C region (100–280 nm) are potential enabling devices for a number of applications, such as bio-/chemical sensing, small particle detection, disinfection, medical treatment and surface monitoring. Since the breakthrough on epitaxial growth of group-III nitrides demonstrated the potential for low-cost semiconductor UV light emitting devices,1) enormous efforts have been made on developing UV light emitting diodes (LEDs).2) These UV LEDs have already demonstrated wavelengths down to 210 nm, deep into the UV-C.3) On the other hand, UV LDs have only been demonstrated in the wavelength span of UV-A (315–400 nm).4–10) New technical issues have been encountered in attempts to shorter lasing wavelengths. For instance, while UV LEDs have successfully been demonstrated on foreign substrates such as SiC or sapphire, the relatively thick layers with high Al concentration required for LDs cause high dislocation densities and even crack formation which can significantly degrade the internal quantum efficiency (IQE) of the active layer.11) This issue can be well addressed by using single-crystal aluminum nitride (AlN) as the epitaxial substrate.

SOURCES – Applied Physics Express, Asahi Kasei Corporation
Written By Brian Wang,