Towards sub-300 nm laser diodes on bulk AlN substrates

Optoelectronic devices such as light-emitting diodes (LEDs) and lasers emitting in the ultraviolet (UV) spectral range are of great interest for various applications. These include water purification, bioagent detection systems, medical diagnosis devices, UV curing, and material processing. However, the realization of high performance devices within the AlGaInN material system remains still challenging due to physical limitations and the complexity of synthesizing material of high crystalline quality. Typically, the performance of such devices significantly degrades as the wavelength becomes shorter with increasing Al fraction in the epitaxial layers [1]. This reduction in performance can be ascribed in part to reduced electron and hole concentrations as well as to a reduction in injection efficiency. Another major factor underlying the lower performance is the degradation in material quality, for example, when using foreign substrates like sapphire or SiC. For these reasons, the shortest emission wavelength from a laser diode reported to date is 336 nm [2].