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Abstract This paper presents the design, material growth and fabrication of AlGaN laser structures grown by plasma-assisted molecular beam epitaxy. Considering hole transport to be the major challenge, our ultraviolet-A diode laser structures have a compositionally graded transparent tunnel junction, resulting in superior hole injection and a low contact resistance. By optimizing active region thickness, a five-fold improvement in photoluminescence intensity is obtained compared to that of our own non-optimized test structures. The electrical and optical characteristics of processed devices demonstrate only spontaneous emission with a peak wavelength at 354 nm. The devices operate up to a continuous-wave current density of 11.1 kA cm⁻²at room temperature, which is the highest reported for laser structures grown on AlGaN templates. Additionally, they exhibit a record-low voltage drop of 8.5 V to achieve this current density. 

AlGaN-based ultra-violet light emitting diodes (UV LEDs) are promising for a range of applications, including water purification, air disinfection and medical sensing. However, widespread adoption of UV LEDs is limited by the poor device efficiency. This has been attributed to the strong internal light absorption and poor electrical injection efficiency for the conventional UV LED structures, which typically use an absorbing p-GaN layer for p-type contact. Recent development of ultra-wide banggap AlGaN tunnel junctions enabled a novel UV LED design with the absence of the absorbing p-GaN contact layer. In this presentation, we will discuss recent progress of the AlGaN tunnel junctions and the development of tunnel junction-based UV LEDs, and discuss the challenges and future perspectives for the realization of high power, high efficiency UV LEDs. 

Ultra-violet (UV) light emitting diodes operating at 339 nm using transparent interband tunnel junctions are reported. Tunneling-based ultraviolet light emitting diodes were grown by plasma-assisted molecular beam epitaxy on 30% Al-content AlGaN layers. A low tunnel junction voltage drop is obtained through the use of compositionally graded n and p-type layers in the tunnel junction, which enhance hole density and tunneling rates. The transparent tunnel junction-based UV LED reported here show a low voltage drop of 5.55 V at 20 A/cm2 and an on-wafer external quantum efficiency of 1.02% at 80 A/cm2. 

Abstract In this work, we demonstrate two-junction UV LEDs enabled by transparent tunnel junctions. Low voltage-drop tunnel junctions were realized in Al_0.3Ga_0.7N layers through a combination of high doping and compositional grading. Capacitance and current–voltage measurements confirmed the operation of two junctions in series. The voltage drop of the two-junction LED was 2.1 times that of an equivalent single-junction LED, and the two-junction LED had higher external quantum efficiency (147%) than the single junction. 

Molecular beam epitaxy-grown GaN/AlGaN-based active regions were optimized by varying quantum-well widths to yield increased photoluminescence intensity at UV-A wavelengths. The optimized gain medium was then used in electrically-pumped laser structures with transparent tunnel junctions.