Fabrication of Vertical AlGaN-Based Ultraviolet-B Laser Diodes Using a Substrate Exfoliation Method with Water

Vertical AlGaN-based ultraviolet-B laser diodes (LDs) are fabricated by exfoliating sapphire substrates using a substrate exfoliation method with water. Wafers with the device structure on a sapphire substrate are cut into 1.1 cm2 squares for further processing. An Al2O3 interlayer dielectric film is applied to the wafer, followed by the addition of a Ni/Pt/Au p-electrode. The wafer is then supported by an AlN-polycrystalline-sintered substrate using AuSn solder, and the sapphire substrate is exfoliated through the use of water. Following exfoliation, the devices undergo several steps, including chemical-mechanical polishing, device separation , application of SiO2 insulating film, and the formation of Ti/Pt/Au/Ti/Au n and pad electrodes. Finally, mirrors are formed through cleavage. The performance of the devices is assessed by injecting pulsed current into them at room temperature. In the results, a shift from spontaneous emission spectrum to a very sharp multimode laser oscillation spectrum with a wavelength of approximately 304 nm by increasing the injection current, a clear threshold current at approximately 600 mA, strong transverse field polarization characteristics, and a spotlike far-field pattern characteristic of lasers, is shown. In these results, it is confirmed that the vertical LD is operating properly. Herein, room-temperature pulse-driven operation of an AlGaN-based vertical ultraviolet B laser diode (LD) is demonstrated by exfoliating a sapphire substrate using a substrate exfoliation method with water. The device demonstrates clear characteristics such as sharp emission at 304 nm, well-defined threshold current. Namely, it is confirmed that the vertical LD is operating properly.image (c) 2024 WILEY-VCH GmbH