Well-aligned ZnO/ZnSe core/shell nanowire arrays with type-II energy alignment are synthesized via a two-step chemical vapor deposition method. Morphology and structure studies reveal a transition layer of wurtzite ZnSe between the wurtzite ZnO core and the cubic ZnSe shell. Type-II interfacial transitions are observed in the spectral region from visible to near infrared in transmission and photoluminescence. More significantly, for the first time, the interfacial transition is shown to extend the photoresponse of the prototype photovoltaic device based on the coaxial nanowire array to a threshold much below the bandgap of either component (3.3 and 2.7 eV, respectively) at 1.6 eV, with an external quantum efficiency of ∼4% at 1.9 eV and 9.5% at 3 eV. These results represent a major advance towards the realization of all-inorganic type-II heterojunction photovoltaic devices in an optimal device architecture.

We report the development of complete structural AlGaN-based deep-ultraviolet light-emitting diodes with an aluminum thin layer for increasing light extraction efficiency. A 217% enhancement in peak photoluminescence intensity at 294 nm is observed. Cathodoluminescence measurement demonstrates that the internal quantum efficiency of the deep-UV LEDs coated with Al layer is not enhanced. The emission enhancement of deep-UV LEDs is attributed to the higher LEE by the surface plasmon-transverse magnetic wave coupling. When the proportion of the TM wave to the Al layer increases with the Al content in the Al_xGa_1-xN multiple quantum wells, i.e., the band edge emission energy, the enhancement ratio of the Al-coated deep-UV LEDs increases.

Here we report a comprehensive numerical study for the operating behavior and physical mechanism of nitride micro-light-emitting-diode (micro-LED) at low current density. Analysis for the polarization effect shows that micro-LED suffers a severer quantum-confined Stark effect at low current density, which poses challenges for improving efficiency and realizing stable full-color emission. Carrier transport and matching are analyzed to determine the best operating conditions and optimize the structure design of micro-LED at low current density. It is shown that less quantum well number in the active region enhances carrier matching and radiative recombination rate, leading to higher quantum efficiency and output power. Effectiveness of the electron blocking layer (EBL) for micro-LED is discussed. By removing the EBL, the electron confinement and hole injection are found to be improved simultaneously, hence the emission of micro-LED is enhanced significantly at low current density. The recombination processes regarding Auger and Shockley–Read–Hall are investigated, and the sensitivity to defect is highlighted for micro-LED at low current density.Synopsis: The polarization-induced QCSE, the carrier transport and matching, and recombination processes of InGaN micro-LEDs operating at low current density are numerically investigated. Based on the understanding of these device behaviors and mechanisms, specifically designed epitaxial structures including two QWs, highly doped or without EBL and p-GaN with high hole concentration for the efficient micro-LED emissive display are proposed. The sensitivity to defect density is also highlighted for micro-LED.

As demonstrated during the COVID-19 pandemic, advanced deep ultraviolet (DUV) light sources (200–280 nm), such as AlGaN-based light-emitting diodes (LEDs) show excellence in preventing virus transmission, which further reveals their wide applications from biological, environmental, industrial to medical. However, the relatively low external quantum efficiencies (mostly lower than 10%) strongly restrict their wider or even potential applications, which have been known related to the intrinsic properties of high Al-content AlGaN semiconductor materials and especially their quantum structures. Here, we review recent progress in the development of novel concepts and techniques in AlGaN-based LEDs and summarize the multiple physical fields as a toolkit for effectively controlling and tailoring the crucial properties of nitride quantum structures. In addition, we describe the key challenges for further increasing the efficiency of DUV LEDs and provide an outlook for future developments.