Smart, high-power ultraviolet (UV)-B light-emitting diodes (LEDs) are demanded for real world applications, including vitamin D3 production in human skin (295–304 nm), immunotherapy (310 nm) and enriching phytochemicals in plants (310 nm).

Crystal growth of eco-friendly, ultrawide bandgap aluminium gallium nitride (AlGaN) semiconductor-based ultraviolet-B (UVB) light-emitting diodes (LEDs) hold the potential to replace toxic mercury-based ultraviolet lamps. One of the major drawbacks in the utilisation of AlGaN-based UVB LEDs is their low efficiency of about 6.5%. The study investigates the influence of Al-graded p-type multi-quantum-barrier electron-blocking-layer (Al-grad p-MQB EBL) and Al-graded p-AlGaN hole source layer (HSL) on the generation and injection of 3D holes in the active region. Using the new UVB LED design, a significant improvement in the experimental efficiency and light output power of about 8.2% and 36 mW is noticed. This is accomplished by the transparent nature of Al-graded Mg-doped p-AlGaN HSL for 3D holes generation and p-MQB EBL structure for holes transport toward multi-quantum-wells via intra-band tunnelling. Based on both the numerical and experimental studies, the influence of sub-nanometre scale Ni film deposited underneath the 200 nm-thick Al-film p-electrode on the optical reflectance in UVB LED is investigated. A remarkable improvement in the efficiency of up to 9.6% and light output power of 40 mW, even in the absence of standard package, flip-chip, and resin-like lenses, is achieved on bare-wafer under continuous-wave operation at room temperature. The enhanced performance is attributed to the use of Al-graded p-MQB EBL coupled with softly polarised p-AlGaN HSL and the highly reflective 0.4 nm-thick Ni and 200 nm-thick Al p-electrode in the UVB LED. This research study provides a new avenue to improve the performance of high-power p-AlGaN-based UVB LEDs and other optoelectronic devices in III–V semiconductors.

B-doped p-BaSi₂ layer growth by molecular beam epitaxy and the influence of rapid thermal annealing (RTA) on hole concentrations were presented. The hole concentration was controlled in the range between 10¹⁷ and 10²⁰ cm⁻³ at room temperature by changing the temperature of the B Knudsen cell crucible. The acceptor level of the B atoms was estimated to be approximately 23 meV. High hole concentrations exceeding 1 × 10²⁰ cm⁻³ were achieved via dopant activation using RTA at 800 °C in Ar. The activation efficiency was increased up to 10%.

Internal quantum efficiency (IQE) and stimulated emission properties of AlGaN-based UV-C multiple quantum wells grown on c-plane sapphire substrates were assessed using photoluminescence spectroscopy. The IQEs were estimated to be 53% at room temperature and 16% at 750 K. Furthermore, optically pumped stimulated emission was clearly observed at room temperature. The threshold excitation power densities were estimated to be 13 kW/cm² at 10 K and 69 kW/cm² at room temperature. The temperature dependence of the threshold excitation power density suggested that the mechanism of optical gain formation changed from excitonic transition to degenerated electron–hole plasma between 200 and 250 K.

The highest photoresponsivity and an internal quantum efficiency exceeding 70% at 1.55 eV were achieved for 400 nm thick undoped n-type BaSi2epitaxial layers formed on a n +-BaSi2/p +-Si tunnel junction (TJ) on Si(111). The diffusion of Sb atoms was effectively suppressed by an intermediate polycrystalline Si layer grown by solid phase epitaxy, located between the TJ and undoped BaSi2 layers.