Realization Of High Optical Output Of Vertical Ultraviolet Semiconductor Lasers! Promising Practical Applications in The Fields Of Medicine And Laser Processing

Recently, a Japanese research study team has fabricated an AlGaN-based vertical deep ultraviolet-emitting semiconductor laser device, which is expected to be applied in the fields of laser processing, biotechnology and medicine.
As we all know, ultraviolet (UV) light is an electromagnetic wave with a wavelength range of 100 to 380 nm. These wavelengths can be divided into three regions: UV-A (315-380 nm), UV-B (280-315 nm), and UV-C (100-280 nm). ), the latter two regions containing deep ultraviolet light.
Laser light sources emitting in the UV region, such as gas lasers and solid-state lasers based on harmonics of yttrium-aluminum-garnet lasers, can be used in a wide range of applications, including biotechnology, dermatological treatments, UV curing processes and laser processing. However, such lasers suffer from large size, high power consumption, limited wavelength range and low efficiency.

In recent years, the development of high-performance semiconductor lasers that generate light by injecting a current has been promoted in parallel with the continuous development of manufacturing technology. These include ultraviolet light-emitting devices based on the semiconductor material aluminum gallium nitride AlGaN. However, their maximum optical output power in the deep UV region is only about 150 mW, which is far below the power required for medical and industrial applications. Increasing the device's injection current is critical to increasing the output power. This requires an increase in device size and also needs to ensure that the current flows uniformly in the device.
In the context of this research, a Japanese research team led by Prof. Motome Iwaya of the Department of Materials Science and Engineering at Meijo University has successfully developed high-performance vertical AlGaN-type UV-B semiconductor laser diodes. The study was published in the journal Applied Physics Letters.
Prof. Motome Iwaya has stated that existing AlGaN-based deep-ultraviolet lasers utilize insulating materials such as sapphire and AlN to obtain high-quality crystals. But because current flows laterally in these devices, to improve their light output, scientists explored vertical devices, in which the p- and n-electrodes face each other in a p-n junction. But for the past few years, vertical configurations have been used to realize high-power semiconductor devices. But for semiconductor lasers, the development of such configurations has been stagnant and has not yet been realized for deep-ultraviolet light-emitting devices based on aluminum nitride. To this end, the researchers first fabricated high-quality aluminum nitride on a sapphire substrate. Periodic aluminum nitride nanopillars were then formed and deposited with aluminum nitride-based laser structures.
The team utilized an innovative laser stripping technique based on pulsed solid-state lasers to strip the device structures from the substrate. They also developed a semiconductor process to fabricate the electrodes, current-limiting structures, and insulating layers needed for laser oscillations, and a cleaving method using blades to form excellent optical resonators. The resulting AlGaN-based deep UV-B semiconductor laser diode has novel and unique properties. It operates at room temperature, emits extremely sharp light at 298.1 nm, has a well-defined threshold current and strong transverse electrical polarization. The researchers also observed a laser-specific spot-like far-field pattern, confirming the device's oscillations.
The study demonstrates that vertical devices can provide high currents for the operation of high-power devices. In the future, it will play a greater role in new cost-effective fabrication processes for electric vehicles and artificial intelligence, among others. And the researchers also hope that aluminum nitride-based vertical UV lasers will find practical applications in medical and manufacturing fields.