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 cm 2 squares for further processing. An Al 2 O 3 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 SiO 2 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.