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Friday, 24 January 2020

New UV-C laser diode promises to disinfect your various health conditions

Structure and prototype of the UV-C laser diode. [Image: Asahi Kasei Corp / Nagoya University]


Japanese researchers made a laser diode that emits the shortest wavelength ultraviolet light ever achieved, covering an area of ​​applications that until now has not benefited from lasers.

These new devices could be used for health disinfection, treatment of skin diseases, such as psoriasis, and gas and DNA analysis.

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"Our laser diode emits the shortest wavelength in the world, at 271.8 nanometers (nm), under injection of alternating [electrical] current at room temperature," announced Professor Chiaki Sasaoka, from Nagoya University.

Previous efforts in the development of ultraviolet laser diodes have only managed to achieve emissions up to 336 nm, explains Sasaoka, not reaching the short-wavelength ultraviolet, or UV-C, which is in the range between 200 and 280 nm.


Material quality

To overcome the various problems that had been preventing the manufacture of this UV-C diode, the team used a high quality aluminum nitride (AlN) substrate as a basis to form the layers of the laser diode. The quality of the material was essential, since the lower quality AlN contains a large number of defects, which end up affecting the efficiency of the active layer of the laser diode in converting electrical energy into light energy.

In a laser diode the ‘p-type’ and ‘n-type’ layers are separated by a ‘quantum well’. When an electric current is passed through a laser diode, positively charged openings in the p-type layer and negatively charged electrons in the n-type flow flow to the center to connect, energy in the form of light particles called photons, is released.

The researchers designed quantum so well that it emitted deep UV light. P and N type layers consist of aluminum gallium nitride (AlGaN). The cladding layer, also made of AlGaN, is arranged on both sides of the p and n layers. The layer below the n-type layer contains silicon impurities, a process called doping. Doping is used as a technique to change material properties.

The layer above the p-type layer is subject to distributed polarization doping which touches the layer without adding impurity.

The aluminum content of the p-side layer is designed so that it is highest at the bottom and reduced at the top. The researchers believe that this aluminum gradient increases the flow of positively charged openings. Finally, a top contact layer was added, which consisted of p-type AlGaN magnesium alloy.



The researchers found that the doping of polarization - insertion of elements to change the behavior of the material - of the coating layer on the positive side ensured operation with a "remarkably low operating voltage" of 13.8V, and the emission "of the shortest length of wave reported so far ".

Asahi Kasei Corporation has already taken an interest in the project, and will help researchers develop deep UV lasers to come up with a commercial product.


Bibliography:

Article: A 271.8 nm deep-ultraviolet laser diode for room temperature operation

Authors: Ziyi Zhang, Maki Kushimoto, Tadayoshi Sakai, Naoharu Sugiyama, Leo J. Schowalter, Chiaki Sasaoka, Hiroshi Amano

Magazine: Applied Physics Express

DOI: 10.7567 / 1882 -0786 / ab50e0

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