Low Barriers and Faster Electron/Ion Transport Rates through the Ga2O3/MnCO3 Anode with a Heterojunction Structure for Lithium-Ion Batteries.

Electrode stability can be controlled to a large extent by constructing suitable composite structures, in which the heterojunction structure can affect the transport of electrons and ions through the effect of the interface state, changed band gap width, and the electric field at the interface. As a promising electrode material, the Ga-based material has a conversion between solid and liquid phases in the electrochemical reaction process, which endows it with self-healing properties with the structure and morphology. Based on these, the Ga2O3/MnCO3 composite was successfully synthesized with a heterogeneous structure by introducing a Ga source in the hydrothermal process. Benefitting from the acceleration effect of the internal electric field and the narrower band gap at the interface, a high-capacity Ga2O3/MnCO3 composite electrode (1112 mAh·g-1 after 225 cycles at 0.1 A·g-1 and 457.1 mAh·g-1 after 400 cycles at 1 A·g-1) can be achieved for lithium-ion batteries. The results can provide a reference for the research and preparation of electrode materials with high performance.

Ga2O3 Quantum Dots with N-Doped Amorphous Carbon Fixed for Efficient Storage and Transfer of Lithium Ions by Introduction of Dopamine Hydrochloride.

The Ga2O3 anode has great potential due to its self-healing and high theoretical capacity in lithium-ion batteries. Like anodes with other transition metal oxides, the Ga2O3 anode has the problems of structural change and low electrical conductivity. The electrochemical performance of the Ga2O3 anode still needs to be improved. In this work, we synthesized a Ga2O3 quantum dots@N-doped carbon (Ga2O3-QD@NC) composite by hydrothermal reaction with a carbon source of dopamine hydrochloride, in which Ga2O3 quantum dots were dispersed in the interior of the amorphous carbon. Such a special structure is conducive to the high-speed migration of lithium ions and electrons and effectively inhibits volume expansion and agglomeration. Smaller and more uniform quantum dots facilitate efficient repair of the structure. Due to these advantages, the Ga2O3-QD@NC electrode has great electrochemical performance. The Ga2O3-QD@NC electrode has an initial discharge capacity of 1580 mAh g-1 with a high first Coulombic efficiency of 62.8% and a cycling capacity of 953 mAh g-1 under 0.1 A g-1. It even has a capacity of 460 mAh g-1 at 1 A g-1 after 300 cycles. This strategy can provide a new direction for the Ga2O3 anode in lithium-ion batteries with high capacity.

Interface Engineering Ti3 C2 MXene/Silicon Self-Powered Photodetectors with High Responsivity and Detectivity for Weak Light Applications.

Interfacial engineering and heterostructures designing are two efficient routes to improve photoelectric characteristics of a photodetector. Herein, a Ti3 C2 MXene/Si heterojunction photodetector with ultrahigh specific detectivity (2.03 × 1013 Jones) and remarkable responsivity (402 mA W-1 ) at zero external bias without decline as with increasing the light power is reported. This is achieved by chemically regrown interfacial SiOx layer and the control of Ti3 C2 MXene thickness to suppress the dark noise current and improve the photoresponse. The photodetector demonstrates a high light on/off ratio of over 106 , an outstanding peak external quantum efficiency (EQE) of 60.3%, while it maintains an ultralow dark current at 0 V bias. Moreover, the device holds high performance with EQE of over 55% even after encapsulated with silicone, trying to resolve the air stability issue of Ti3 C2 MXene. Such a photodetector with high detectivity, high responsivity, and self-powered capability is particularly applicable to detect weak light signal, which presents high potential for imaging, communication and sensing applications.

Performance enhancement of AlGaN-based 365 nm ultraviolet light-emitting diodes with a band-engineering last quantum barrier.

In this Letter, the characteristics of the AlGaN-based near-ultraviolet light-emitting diodes with a band-engineering last quantum barrier (LQB) were analyzed experimentally and numerically. The experimental results show that the peak wavelengths of UV-LEDs are around 368 nm with a full width at half-maximum of 12-14 nm, and the optical and electrical properties are improved by using an AlxGa1-xN LQB with a gradually decreasing Al content. The designed LQB can reduce the forward voltage from 4.35 to 4.29 V and markedly enhance LOP by 47.4% at an injection current of 200 mA, compared with the original structure. These improvements are mainly attributed to less electron leakage and higher hole injection efficiency, resulting from the weakened polarization field in the electron-blocking layer (EBL) and LQB, as well as the alleviation of the band bending at the EBL/LQB interface.

Simultaneously Enhancing Light Emission and Suppressing Efficiency Droop in GaN Microwire-Based Ultraviolet Light-Emitting Diode by the Piezo-Phototronic Effect.

Achievement of p-n homojuncted GaN enables the birth of III-nitride light emitters. Owing to the wurtzite-structure of GaN, piezoelectric polarization charges present at the interface can effectively control/tune the optoelectric behaviors of local charge-carriers (i.e., the piezo-phototronic effect). Here, we demonstrate the significantly enhanced light-output efficiency and suppressed efficiency droop in GaN microwire (MW)-based p-n junction ultraviolet light-emitting diode (UV LED) by the piezo-phototronic effect. By applying a -0.12% static compressive strain perpendicular to the p-n junction interface, the relative external quantum efficiency of the LED is enhanced by over 600%. Furthermore, efficiency droop is markedly reduced from 46.6% to 7.5% and corresponding droop onset current density shifts from 10 to 26.7 A cm-2. Enhanced electrons confinement and improved holes injection efficiency by the piezo-phototronic effect are revealed and theoretically confirmed as the physical mechanisms. This study offers an unconventional path to develop high efficiency, strong brightness and high power III-nitride light sources.

Efficient blue light emission from In0.16Ga0.84N/GaN multiple quantum wells excited by 2.48-µm femtosecond laser pulses.

We report on the efficient blue light emission from In0.16Ga0.84N/GaN multiple quantum wells excited by femtosecond laser pulses with long wavelengths ranging from 1.24 to 2.48 µm. It is found that the trap states in GaN barrier layers lead to an efficient cascade multiphoton absorption in which the carriers are generated through simultaneous absorption of n (n=1 and 2) photons to the trap states, followed by simultaneous absorption of m (m=3, 4, and 5) photons to the conduction band. The dependence of the upconversion luminescence on excitation intensity exhibits a slope between n and n+m, which is in good agreement with the prediction based on the rate equation model.

Epitaxial Growth of the Large-Scale, Highly-Ordered 3D GaN-Truncated Pyramid Array Toward an Ultrahigh Rejection Ratio and Responsivity Visible-Blind Ultraviolet Photodetection.

The micro- and nanostructures of III-nitride semiconductors captivate strong interest owing to their distinctive properties and myriad potential applications. Nevertheless, challenges endure in managing the damage inflicted on crystals through top-down processes or achieving extensive control over the large-area growth of these microstructures via bottom-up methods, thereby impacting their optical and electronic properties. Here, we present novel epitaxially grown 3D GaN truncated pyramid arrays (TPAs) on patterned Si substrates, devoid of any catalyst. These GaN TPAs feature highly ordered, large-scale structures, attributed to the utilization of 3D Si substrates and thin AlN interlayers to alleviate epitaxial strains and limit dislocation formation. Comprehensive characterization via scanning electron microscopy, transmission electron microscopy, Raman spectroscopy, and cathodoluminescence attests to the superior structural and optical attributes of these crystals. Furthermore, photoluminescence and ultraviolet (UV)-visible diffuse reflectance spectroscopy reveal sharp band-edge emission and significant light trapping in the UV bands. Employing these GaN TPAs, we constructed metal-semiconductor-metal visible-blind UV photodetectors (PDs) incorporating Ti3C2 MXene as Schottky electrodes. These PDs display exceptional responsivity, achieving 5.32 × 103 mA/W at 255 nm and an ultrahigh UV/visible rejection ratio (R255nm/R450nm) approaching 106, which are 1-2 orders of magnitude higher than most recently reported works. This exploration showcases novel GaN-based microstructures characterized by uniformity, ordered geometry, and exemplary crystalline integrity, paving the way for developing optoelectronic applications.

Enhanced performance of InGaN/GaN based solar cells with an In(0.05)Ga(0.95)N ultra-thin inserting layer between GaN barrier and In(0.2)Ga(0.8)N well.

The effect of ultra-thin inserting layer (UIL) on the photovoltaic performances of InGaN/GaN solar cells is investigated. With UIL implemented, the open-circuit voltage was increased from 1.4 V to 1.7 V, short-circuit current density was increased by 65% and external quantum efficiency was increased by 59%, compared to its counterparts at room temperature under 1-sun AM1.5G illumination. The improvements in electrical and photovoltaic properties are mainly attributed to the UIL which can boost the crystal quality and alleviate strain. Moreover, it can act as a transition layer for higher indium incorporation and an effective light sub-absorption layer in multiple quantum wells.

GaN/Gr (2D)/Si (3D) Combined High-Performance Hot Electron Transistors.

To overcome the problem of minority carrier storage time in bipolar transistors, a hot electron transistor (HET) has been proposed. This device has the advantage of high working speed and some complex logic functions can be completed by using one component. Here, we demonstrate a mixed-dimensional HET composed of GaN/AlN microwires, graphene (Gr), and Si. The electrons between GaN/AlN are injected into graphene by an F-N tunneling mechanism to achieve high speed hot electrons, then cross graphene by ballistic transport, and are collected in a nearly lossless manner through a low-barrier Si. Therefore, the device shows a record DC gain of 16.2, a collection efficiency close to the limit of 99.9% based on the graphene hot electron transistor (GHET), an emitter current density of about 68.7 A/cm2, and a high on/off current ratio reaching ∼107. Meanwhile, the current saturation range is wide, beyond those of most GHETs. It has potential applications as a power amplifier.

Synergistic Ion-Anchoring Passivation for Perovskite Solar Cells with Efficiency Exceeding 24% and Ultra-Ambient Stability.

The high-density defect states existing at the grain boundaries and heterojunction interfaces induce nonradiative charge recombination and ion migration processes within perovskite film, which seriously impair the device efficiency and stability. Here, we propose a novel synergistic ion-anchoring passivation (SIP) strategy for high-performance perovskite solar cells, by designing a multifunctional molecule to heal the charged defects via electrostatic interactions. The anion and cation species of the multifunctional molecule are rationally screened via high-throughput DFT simulation and experimental verification, which act as efficient surface passivation agents to heal the lead- and iodine-related defects. As a result, the defect-less perovskite films deliver encouraging device power conversion efficiency >24% with negligible hysteresis. A remarkable open-circuit voltage (Voc) of 1.17 V was obtained with a Voc deficit of 370 mV, featuring the outstanding defect-passivation capability of the SIP strategy. Moreover, the SIP-treated devices show exceptional ambient stability and maintain 70% of the initial efficiency after 150 h of high humidity exposure (relative humidity 70%-80%). Our results highlight the importance of the rational design of passivation agents to realize high-performance perovskite electronics.

Two-In-One: End-Emitting Blue LED and Self-Powered UV Photodetector based on Single Trapezoidal PIN GaN Microwire for Ambient Light UV Monitoring and Feedback.

With the continuous miniaturization and integration of the semiconductor industry, micro/nanoscale integrated photonics has received extensive attention as a key technology for optical communication, optical storage, and optical interconnection. Here, a two-in-one device is reported with both unidirectional blue light emission and UV photodetection functions based on single trapezoidal PIN GaN microwire. By constructing a Fabry-Perot resonator cavity structure, the end-emitting blue light-emitting diode with a low turn-on voltage (≈0.97 V) and high color purity (full width at half maximum ≈22 nm) is implemented. Furthermore, benefiting from the slow growth rate of the semipolar planes on both sides of the trapezoidal microwire and the high diffuse reflectivity of the patterned substrate, the trapezoidal microwire sides can be used as a high-performance UV photodetector. In self-driven mode, the device exhibits a large responsivity (0.218 A W-1 ), high external quantum efficiency (83.31%) and fast response speed (rise/decay time of 0.48/0.98 ms). Finally, the prepared two-in-one device is successfully integrated into ambient light UV monitoring and feedback system and tested. This work provides a novel strategy to combine luminescence with photodetection, demonstrating high potential for applications, such as on-chip photonic integration, energy-saving communication and ambient light monitoring and feedback system.

Improved color rendering of phosphor-converted white light-emitting diodes with dual-blue active layers and n-type AlGaN layer.

An InGaN/GaN blue light-emitting diode (LED) structure and an InGaN/GaN blue-violet LED structure were grown sequentially on the same sapphire substrate by metal-organic chemical vapor deposition. It was found that the insertion of an n-type AlGaN layer below the dual blue-emitting active layers showed better spectral stability at the different driving current relative to the traditional p-type AlGaN electron-blocking layer. In addition, color rendering index of a Y3Al5O12:Ce3+ phosphor-converted white LED based on a dual blue-emitting chip with n-type AlGaN reached 91 at 20 mA, and Commission Internationale de L'Eclairage coordinates almost remained at the same point from 5 to 60 mA.

Improvement Strategies for Stability and Efficiency of Perovskite Solar Cells.

Recently, perovskites have garnered great attention owing to their outstanding characteristics, such as tunable bandgap, rapid absorption reaction, low cost and solution-based processing, leading to the development of high-quality and low-cost photovoltaic devices. However, the key challenges, such as stability, large-area processing, and toxicity, hinder the commercialization of perovskite solar cells (PSCs). In recent years, several studies have been carried out to overcome these issues and realize the commercialization of PSCs. Herein, the stability and photovoltaic efficiency improvement strategies of perovskite solar cells are briefly summarized from several directions, such as precursor doping, selection of hole/electron transport layer, tandem solar cell structure, and graphene-based PSCs. According to reference and analysis, we present our perspective on the future research directions and challenges of PSCs.

A high-performance polarization-sensitive and stable self-powered UV photodetector based on a dendritic crystal lead-free metal-halide CsCu2I3/GaN heterostructure.

Polarization-sensitive photodetectors are the core of optics applications and have been successfully demonstrated in photodetectors based on the newly-emerging metal-halide perovskites. However, achieving high polarization sensitivity is still extremely challenging. In addition, most of the previously reported photodetectors were concentrated on 1D lead-halide perovskites and 2D asymmetric intrinsic structure materials, but suffered from being external bias driven, lead-toxicity, poor stability and complex processes, severely limiting their practical applications. Here, we demonstrate a high-performance polarization-sensitive and stable polarization-sensitive UV photodetector based on a dendritic crystal lead-free metal-halide CsCu2I3/GaN heterostructure. By combining the anisotropic morphology and asymmetric intrinsic structure of CsCu2I3 dendrites with the isotropic material GaN film, a high specific surface area and built-in electric field are achieved, exhibiting an ultra-high polarization selectivity up to 28.7 and 102.8 under self-driving mode and -3 V bias, respectively. To our knowledge, such a high polarization selectivity has exceeded those of all of the reported perovskite-based devices, and is comparable to, or even superior to, those of the conventional 2D heterostructure materials. Interestingly, the unsealed device shows outstanding stability, and can be stored for over 2 months, and effectively maintained the performance even after repeated heating (373K)-cooling (300K) for different periods of time in ambient air, indicating a remarkable temperature tolerance and desired compatibility for applications under harsh conditions. Such excellent performance and simple method strongly show that the CsCu2I3/GaN heterojunction photodetector has great potential in practical applications with high polarization-sensitivity. This work provides a new insight into designing novel high-performance polarization-sensitive optoelectronic devices.

Effect of the thickness of undoped GaN interlayers between multiple quantum wells and the p-doped layer on the performance of GaN light-emitting diodes.

InGaN based light-emitting diodes (LEDs) with undoped GaN interlayer of variant thicknesses grown by metal-organic chemical vapor deposition technique have been investigated. It was found that the thickness of undoped GaN interlayers affected LEDs' performance greatly. The LED with 50 nm undoped GaN interlayer showed higher light output power and lower reverse-leakage current compared with the others at 20 mA. Based on electrical and optical characteristics analysis and numerical simulation, these improvements are mainly attributed to the improvement of the quality of depletion region by inserting an undoped GaN layer, as well as reduction of the Shockley-Read-Hall recombination in InGaN/GaN MQWs.

Ultrathin nickel oxide film as a hole buffer layer to enhance the optoelectronic performance of a polymer light-emitting diode.

In order to promote a polymer LED (PLED), we fabricated and introduced an ultrathin nickel oxide (NiO) buffer layer (<10 nm) between the indium tin oxide (ITO) anode and the poly (3, 4-ethylenedioxythiophene) hole injection layer in the PLED. The NiO buffer layer was easily formed on the ITO anode by electron-beam deposition of a nickel (Ni) metal source and an oxygen plasma treatment process. As a result, the PLED device with the NiO buffer layer on its ITO anode had the same turn-on voltage as conventional PLED devices without the NiO buffer layer, and the luminance of the PLED device with the NiO buffer layer was doubled, compared with the conventional PLED devices without the NiO buffer layer. Improvement of the optoelectronic performance of the PLED can be attributed to the increase of the current driven into the diode, resulting from the NiO buffer layer, which can enhance the hole injection and balance the injection of the two types of carriers (holes and electrons). Thus it is an excellent choice to introduce the NiO buffer layer onto the ITO anode of the PLED devices in order to enhance the optoelectronic performance of PLED devices.

Epitaxial Lift-Off of Flexible GaN-Based HEMT Arrays with Performances Optimization by the Piezotronic Effect.

High-electron-mobility transistors (HEMTs) are a promising device in the field of radio frequency and wireless communication. However, to unlock the full potential of HEMTs, the fabrication of large-size flexible HEMTs is required. Herein, a large-sized (> 2 cm2) of AlGaN/AlN/GaN heterostructure-based HEMTs were successfully stripped from sapphire substrate to a flexible polyethylene terephthalate substrate by an electrochemical lift-off technique. The piezotronic effect was then induced to optimize the electron transport performance by modulating/tuning the physical properties of two-dimensional electron gas (2DEG) and phonons. The saturation current of the flexible HEMT is enhanced by 3.15% under the 0.547% tensile condition, and the thermal degradation of the HEMT was also obviously suppressed under compressive straining. The corresponding electrical performance changes and energy diagrams systematically illustrate the intrinsic mechanism. This work not only provides in-depth understanding of the piezotronic effect in tuning 2DEG and phonon properties in GaN HEMTs, but also demonstrates a low-cost method to optimize its electronic and thermal properties.

Surface plasmon interference on the surface of an aluminum-covered fiber core array for solgel fabrication of submicrometer gratings.

An interesting method to fabricate submicrometer gratings (SMGs) utilizing the interference of surface plasmon waves (SPWs) is presented. The stationary wave field off the aluminum (Al) layer surface of an Al-covered UV fiber core, formed by the interference of the induced SPWs, has been employed as a submicrometer photolithography tool to inscribe SMGs on the surface of a self-processing hybrid HfO(2)/SiO(2) solgel film. Using atomic force microscopy, the period of the fabricated SMGs was measured as 105 nm. The intensity distribution of the stationary wave field was measured by a near-field scanning optical microscope and anastomosed with theoretical values calculated by using FDTD simulations.

InGaN Nanorods Decorated with Au Nanoparticles for Enhanced Water Splitting Based on Surface Plasmon Resonance Effects.

Photoelectrochemical (PEC) water splitting has great application potential in converting solar energy into hydrogen energy. However, what stands in the way of the practical application of this technology is the low conversion efficiency, which can be promoted by optimizing the material structure and device design for surface functionalization. In this work, we deposited gold nanoparticles (Au NPs) with different loading densities on the surface of InGaN nanorod (NR) arrays through a chemical solvent route to obtain a composite PEC water splitting system. Enhanced photocatalytic activity, which can be demonstrated by the surface plasmon resonance (SPR) effect induced by Au NPs, occurred and was further confirmed to be associated with the different loading densities of Au NPs. These discoveries use solar water splitting as a platform and provide ideas for exploring the mechanism of SPR enhancement.

In Situ Conformal Coating of Polyaniline on GaN Microwires for Ultrafast, Self-Driven Heterojunction Ultraviolet Photodetectors.

Independent and zero-maintenance systems would be in urgent need in the near future internet of things. Here, we present high-performance, self-driven organic/inorganic heterojunction ultraviolet (UV) photodetectors (PDs) by in situ polymerization of polyaniline (PANI) on Gallium nitride microwires. The GaN microwires with a high crystalline quality are grown on patterned Si substrates by metal organic chemical vapor deposition. Using a facile in situ chemical polymerization method, PANI is conformally coated on the surface of GaN microwires. The constructed GaN/PANI hybrid microwire PD exhibits a high responsivity of 178 mA/W, a remarkable detectivity of 4.67 × 1014 jones, and an ultrafast UV photoresponse speed (rise time of 0.2 ms and fall time of 0.3 ms) under zero bias. The intimate heterojunction in the form of N-Ga-N bonds between GaN and PANI may account for the observed high performances. The presented self-driven microwire UV PDs featuring ultrahigh-speed (sub-millisecond) response to UV light may find applications in future nano/micro-photosensor networks.