In this work, we fabricated and characterized 4 × 4 parallel flip-chip AlGaN-based micro-LED arrays with varied mesa diameters of 120 µm, 100 µm, 80 µm, and 60 µm. The reported micro-LED arrays have a maximum bandwidth of 380 MHz and a peak wavelength of ∼275 nm. It is found that the electrical and optical characteristics of AlGaN-based micro-LED arrays show strong size dependence for ultraviolet communication (UVC). The differential resistance increases from 28.8 Ω to 112 Ω, the external quantum efficiency (EQE) is increased by ∼30%, and the bandwidth doubles as the diameter of individual micro-LED decreases from 120 µm to 60 µm. Our research proves that tailoring the mesa size of parallel flip-chip AlGaN-based micro-LED arrays can further enhance its bandwidth and promote its application in UVC.

The demand for effective sterilization methods, particularly in the wake of the Covid-19 pandemic, has sparked interest in the use of deep ultraviolet (DUV) radiation for disinfection. The high risk of skin/eye exposure to the high-energy DUV radiation requires the integration of DUV and visible (VIS) LED chips to sterilize and indicate its operation simultaneously in the portable sterilization devices. However, conventional double-chip integration suffers from high power consumption and fabrication complexity. This study sets out to explore the monolithic integration of DUV and VIS LEDs for the radiative sterilization application. This is accomplished by cascading AlGaN/AlGaN/AlGaN multiple quantum wells (QWs) and GaN/InGaN/GaN QWs through the compositional grading AlGaN cascade region. The inevitable overflown electrons from DUV QWs are deliberately introduced into the VIS QWs, allowing for the electron–hole recombination and the simultaneous emission of VIS light. Both experiment and simulation results confirm the feasibility of the proposed dual-wavelength LED integration. The proposed DUV&VIS LED shows an external quantum efficiency and wall-plug efficiency of 2.03% and 1.54% at 40 mA, respectively. This study establishes a quantitative framework for the monolithic integration of DUV and VIS LEDs for radiative sterilization, which has the potential to replace the current technique of using discrete DUV and VIS double-chip configurations.

It is well known that inclined sidewall scattering structures can improve the light extraction efficiency (LEE) of micro deep ultraviolet (DUV) light-emitting diodes (LEDs). However, effective inclined sidewall designs for chip-scale high-power DUV LEDs are rarely reported. In this work, we use a fluorine-based oily liquid to form a self-assembled liquid cup. It has a chip-scale inclined sidewall surrounding the DUV LED chip. Experimental and simulation results show that the LEE of DUV LED with liquid cup is significantly enhanced. It can be attributed to the enlarged light escape cone, the additional out-light areas, and the scattering effects of the inclined sidewall. Consequently, the proposed DUV LED achieves a wall-plug efficiency (WPE) of 10.7% at 350 mA. Compared to conventional DUV LEDs, the WPE is enhanced by 64.9%. Moreover, the optical field distribution shows more light from the proposed DUV LED is deflected towards the vertical direction. This method shows great potential to advance high-power DUV LED development and expedite the replacement of mercury lamps.

Hexagonal boron nitride (h-BN) is one promising material class for applications in DUV optoelectronics due to the layered structure and ultra-wide bandgap. The synthesis of h-BN with smooth surface morphology and high quality on dielectric substrates is the key to construct efficient functional devices thereon. In this study, we reported wafer-scale h-BN on c-plane sapphire substrates by metal organic chemical vapor deposition utilizing the flow modulation epitaxy (FME) with growth interruptions. The effect of the growth interruption location within FME on the surface morphology and crystalline quality of h-BN films was systematically investigated. The interruption after the TEB injection could promote the mobility of B adatoms, and the interruption after the NH₃ injection could further relieve the passivation of N terminal growth fronts and mitigate the parasitic gas-phase reaction between growth precursors. By simultaneously employing interruptions after TEB and NH₃ injections, the growth rate of h-BN increased significantly from 0.16 nm/min to 4.76 nm/min, and the surface roughness of 2-nm-thick h-BN was reduced to 0.587 nm. In addition, h-BN grown with an interruption solely after the NH₃ injection presented the best crystallinity because the relatively slow growth rate reduced the possibility of impurity incorporation.

Self-injection locking (SIL) of semiconductor lasers to on-chip microcavities enables significant laser noise purification and diverse nonlinear optical actions. Realizing nonlinear SIL in new material platforms is essential for advancing photonic integrated circuits. Here, we demonstrate nonlinear SIL in AlN microcavities that generates stimulated Raman lasers (SRLs) and microcombs. We achieve SRL emission with an output power exceeding 10 mW and a fundamental linewidth below 70 Hz in the 1750 nm band. The Kerr effect further mediates stimulated emissions at the second-Stokes and anti-Stokes frequencies. Multi-timescale thermal relaxations during turnkey SIL enable GHz-level frequency sweeps of the SRL and pump. Raman actions also render a Stokes platicon microcomb state with coemission in the pump and Stokes bands. Hybrid-integrated crystalline microresonators can be a versatile platform to investigate nonlinear photon-phonon interactions.