Fabrication of Vertical AlGaN-based UV-B Semiconductor Lasers

In recent years, the performance of AlGaN-based ultraviolet semiconductor light-emitting devices has been rapidly improving; in LEDs, high-performance devices with external quantum efficiencies approaching 10% are being realized in the wide wavelength range from UV-A to UV-C. On the other hand, similarly in semiconductor lasers, device operation at room temperature has been realized in the wide wavelength range from UV-A to UV-C. The most important challenge for achieving even higher performance in the future is to increase optical output power. To increase the optical output of light-emitting devices, it is necessary to improve the external quantum efficiency of the device itself and to increase the operating current. To increase the operating current, it is essential to increase the device size, which requires the realization of vertical devices in which the current flows perpendicularly to the p-n junction. However, most of the current AlGaN-based ultraviolet light-emitting devices use insulating sapphire or AlN as a substrate to obtain high-quality crystals, resulting in lateral devices in which the current flows horizontally in the n-type layer. Especially in semiconductor lasers, there are no reported cases of vertical devices in UV-B and UV-C. In this report, we present the results of successful room-temperature operation of vertical AlGaN-based UV-B laser diodes by using a laser lift-off method and a substrate exfoliation technique with heated and pressurized water. We also would like to discuss the device characteristics and other related topics.