Deep-ultraviolet integrated photonic and optoelectronic devices:A prospect of the hybridization of group Ⅲ–nitrides, Ⅲ–oxides,and two-dimensional materials

Progress in the design and fabrication of ultraviolet and deep-ultraviolet groupⅢ–nitride optoelectronic devices,based on aluminum gallium nitride and boron nitride and their alloys,and the heterogeneous integration with two-dimensional and oxide-based materials is reviewed.We emphasize wide-bandgap nitride compound semiconductors(i.e.,(B,Al,Ga)N)as the deep-ultraviolet materials of interest,and two-dimensional materials,namely graphene,two-dimensional boron nitride,and two-dimensional transition metal dichalcogenides,along with gallium oxide,as the hybrid integrated materials.We examine their crystallographic properties and elaborate on the challenges that hinder the realization of efficient and reliable ultraviolet and deep-ultraviolet devices.In this article we provide an overview of aluminum nitride,sapphire,and gallium oxide as platforms for deep-ultraviolet optoelectronic devices,in which we criticize the status of sapphire as a platform for efficient deep-ultraviolet devices and detail advancements in device growth and fabrication on aluminum nitride and gallium oxide substrates.A critical review of the current status of deep-ultraviolet light emission and detection materials and devices is provided.

Large-scale and high-quality III-nitride membranes through microcavity-assisted crack propagation by engineering tensile-stressed Ni layers

Epitaxially grown III-nitride alloys are tightly bonded materials with mixed covalent-ionic bonds.This tight bonding presents tremendous challenges in developing III-nitride membranes,even though semiconductor membranes can provide numerous advantages by removing thick,inflexible,and costly substrates.Herein,cavities with various sizes were introduced by overgrowing target layers,such as undoped GaN and green LEDs,on nanoporous templates prepared by electrochemical etching of n-type GaN.The large primary interfacial toughness was effectively reduced according to the design of the cavity density,and the overgrown target layers were then conveniently exfoliated by engineering tensile-stressed Ni layers.The resulting III-nitride membranes maintained high crystal quality even after exfoliation due to the use of GaN-based nanoporous templates with the same lattice constant.The microcavity-assisted crack propagation process developed for the current III-nitride membranes forms a universal process for developing various kinds of large-scale and high-quality semiconductor membranes.

High-speed colour-converting photodetector with all-inorganic CsPbBr_(3) perovskite nanocrystals for ultraviolet light communication

Optical wireless communication(OWC)using the ultra-broad spectrum of the visible-to-ultraviolet(UV)wavelength region remains a vital field of research for mitigating the saturated bandwidth of radio-frequency(RF)communication.However,the lack of an efficient UV photodetection methodology hinders the development of UV-based communication.The key technological impediment is related to the low UV-photon absorption in existing silicon photodetectors,which offer low-cost and mature platforms.To address this technology gap,we report a hybrid Sibased photodetection scheme by incorporating CsPbBr_(3) perovskite nanocrystals(NCs)with a high photoluminescence quantum yield(PLQY)and a fast photoluminescence(PL)decay time as a UV-to-visible colourconverting layer for high-speed solar-blind UV communication.The facile formation of drop-cast CsPbBr_(3) perovskite NCs leads to a high PLQY of up to ~73% and strong absorption in the UV region.With the addition of the NC layer,a nearly threefold improvement in the responsivity and an increase of ~25% in the external quantum efficiency(EQE)of the solar-blind region compared to a commercial silicon-based photodetector were observed.Moreover,timeresolved photoluminescence measurements demonstrated a decay time of 4.5 ns under a 372-nm UV excitation source,thus elucidating the potential of this layer as a fast colour-converting layer.A high data rate of up to 34 Mbps in solar-blind communication was achieved using the hybrid CsPbBr_(3)-silicon photodetection scheme in conjunction with a 278-nm UVC light-emitting diode(LED).These findings demonstrate the feasibility of an integrated high-speed photoreceiver design of a composition-tuneable perovskite-based phosphor and a low-cost silicon-based photodetector for UV communication.

A flexible capacitive photoreceptor for the biomimetic retina

Neuromorphic vision sensors have been extremely beneficial in developing energy-efficient intelligent systems for robotics and privacy-preserving security applications.There is a dire need for devices to mimic the retina's photoreceptors that encode the light illumination into a sequence of spikes to develop such sensors.Herein,we develop a hybrid perovskite-based flexible photoreceptor whose capacitance changes proportionally to the light intensity mimicking the retina's rod cells,paving the way for developing an efficient artificial retina network.The proposed device constitutes a hybrid nanocomposite of perovskites(methyl-ammonium lead bromide)and the ferroelectric terpolymer(polyvinylidene fluoride trifluoroethylene-chlorofluoroethylene).A metal-insulator-metal type capacitor with the prepared composite exhibits the unique and photosensitive capacitive behavior at various light intensities in the visible light spectrum.The proposed photoreceptor mimics the spectral sensitivity curve of human photopic vision.The hybrid nanocomposite is stable in ambient air for 129 weeks,with no observable degradation of the composite due to the encapsulation of hybrid perovskites in the hydrophobic polymer.The functionality of the proposed photoreceptor to recognize handwritten digits(MNIST)dataset using an unsupervised trained spiking neural network with 72.05%recognition accuracy is demonstrated.This demonstration proves the potential of the proposed sensor for neuromorphic vision applications.

A tutorial on laser-based lighting and visible light communications:device and technology [Invited]

This tutorial focuses on devices and technologies that are part of laser-based visible light communication(VLC)systems. Laser-based VLC systems have advantages over their light-emitting-diode-based counterparts, including having high transmission speed and long transmission distance. We summarize terminologies related to laser-based solid-state lighting and VLC, and further review the advances in device design and performance.The high-speed modulation characteristics of laser diodes and superluminescent diodes and the on-chip integration of optoelectronic components in the visible color regime, such as the high-speed integrated photodetector,are introduced. The modulation technology for laser-based white light communication systems and the challenges for future development are then discussed.