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Perovskite crystals-with their exceptional nonlinear optical properties, lasing and waveguiding capabilities-offer a promising platform for integrated photonic circuitry within the strong-coupling regime at room temperature. Here we demonstrate a versatile template-assisted method to efficiently fabricate large-scale waveguiding perovskite crystals of arbitrarily predefined geometry such as microwires, couplers and splitters. We non-resonantly stimulate a condensate of waveguided exciton-polaritons resulting in bright polariton lasing from the transverse interfaces and corners of our perovskite microstructures. Large blueshifts with excitation power and high mutual coherence between the different edge and corner lasing signals are detected in the far-field photoluminescence, implying that a spatially extended condensates of coherent polaritons has formed. The condensate polaritons are found to propagate over long distances in the wires from the excitation spot and can couple to neighbouring wires through large air gaps, making our platform promising for integrated polaritonic circuitry and on-chip optical devices with strong nonlinearities., (© 2024. The Author(s), under exclusive licence to Springer Nature Limited.)

Examples are presented that application of amorphous Al x O y nucleation layer is an efficient way of controlling spatial distribution of GaN nanowires grown by plasma-assisted molecular beam epitaxy. On GaN/sapphire substrates Al x O y stripes induce formation of GaN nanowires while a compact GaN layer is formed outside the stripes. We show that the ratio of nanowire length h to the thickness of the compact layer d can be tailored by adjusting impinging gallium and nitrogen fluxes. Calculations of the h/d aspect ratio were performed taking into account dependence of nanowire incubation time on the growth parameters. In agreement with calculations we found that the value of h/d ratio can be increased by increasing the N/Ga flux ratio in the way that the N-limited growth regime determines nanowire axial growth rate while growth of compact layer remains Ga-limited. This ensures the highest value of the h/d aspect ratio. Local modification of GaN growth kinetics caused by surface diffusion of Ga adatoms through the boundary separating the Al x O y stripe and the GaN/sapphire substrate is discussed. We show that during the nanowire incubation period gallium is transported out of the Al x O y stripe, which delays nanowire nucleation onset and leads to reduced length of GaN nanowires in the vicinity of the stripe edge. Simultaneously the growth on the GaN/sapphire substrate is locally enhanced, so the planar GaN layers adopts a typical edge shape of mesa structures grown by selective area growth. Ga diffusion length on a-Al x O y surface of ∼500 nm is inferred from our results.

AlGaN/GaN high electron mobility transistors on semi-insulating bulk ammonothermal GaN have been investigated. By application of regrown ohmic contacts, the problem with obtaining low resistance ohmic contacts to low-dislocation high electron mobility transistor (HEMT) structures was solved. The maximum output current was about 1 A/mm and contact resistances was in the range of 0.3⁻0.6 Ω ·mm. Good microwave performance was obtained due to the absence of parasitic elements such as high access resistance.

The recent rapid development of transparent electronics, notably displays and control circuits, requires the development of highly transparent energy storage devices, such as supercapacitors. The devices reported to date utilize carbon-based electrodes for high performance, however at the cost of their low transparency around 50%, insufficient for real transparent devices. To overcome this obstacle, in this communication highly transparent supercapacitors were fabricated based on ZnO/MnO 2 nanostructured electrodes. ZnO served as an intrinsically transparent skeleton for increasing the electrode surface, while MnO 2 nanoparticles were applied for high capacitance. Two MnO 2 synthesis routes were followed, based on the reaction of KMnO 4 with Mn(Ac) 2 and PAH, leading to the synthesis of β-MnO 2 with minority α-MnO 2 nanoparticles and amorphous MnO 2 with embedded β-MnO 2 , respectively. The devices based on such electrodes showed high capacitances of 2.6 mF cm -2 and 1.6 mF cm -2 , respectively, at a scan rate of 1 mV s -1 and capacitances of 104 μF cm -2 and 204 μF cm -2 at a very high rate of 1 V s -1 , not studied for transparent supercapacitors previously. Additionally, the Mn(Ac) 2 devices exhibited very high transparencies of 86% vs. air, far superior to other transparent energy storage devices reported with similar charge storage properties. This high device performance was achieved with a non-acidic LiCl gel electrolyte, reducing corrosion and handling risks associated with conventional highly concentrated acidic electrolytes, enabling applications in safe, wearable, transparent devices.