Vapor-Liquid-Solid Growth of Site-Controlled Monolayer MoS2 Films Via Pressure-Induc ed Supercritical Phase Nucleation.

In this study, a novel pressure-induced supercritical phase nucleation method is proposed to synthesize monolayer MoS2 films, which is promoter free and can avoid contamination of films derived from these heterogeneous promoters in most of the existing techniques. The low-crystallinity and size-controlled MoO2(acac)2 particles are recrystallized on the substrate via the pressure-sensitive solvent capacity of supercritical CO2 and these particles are used as growth sites. The size of single-crystal MoS2 on the substrate is found to be dependent on the wetting area of the pyrolyzed precursor droplets (MoO2) on the surface, and the formation of continuous films with high coverage is mainly controlled by the coalescence of MoO2 droplets. It is enhanced by the increase of the nucleation site density, which can be adjusted by the supersaturation of the supercritical fluid solution. Our findings pave a new way for the controllable growth of MoS2 and other two-dimensional materials and provide sufficient and valuable evidence for vapor-liquid-solid growth.

Stable and Self-Powered Solar-Blind Ultraviolet Photodetectors Based on a Cs3Cu2I5/ß-Ga2O3 Heterojunction Prepared by Dual-Source Vapor Codeposition.

Self-powered solar-blind ultraviolet (UV) photodetectors have drawn worldwide attention in recent years because of their important applications in military and civilian areas. In this study, a dual-source vapor codeposition technique was employed, for the first time, to prepare a nontoxic copper halide Cs3Cu2I5, which was integrated with the ß-Ga2O3 wafer to construct a type-II heterojunction for photodetection applications. By optimizing the annealing conditions, high-quality Cs3Cu2I5 films with dense morphology, high crystallinity, and a long carrier lifetime of 1.02 µs were acquired. Because of the high material integrity of Cs3Cu2I5 films and effective interfacial carrier transfer from Cs3Cu2I5 to ß-Ga2O3, a heterojunction device demonstrates a good solar-blind UV response property and operates at zero bias. Typically, the photodetector presents a low dark current (∼1.2 pA), a high solar-blind/UVA rejection ratio (∼1.0 × 103), a relatively fast photoresponse speed (37/45 ms), and a high photo-to-dark current ratio (∼5.1 × 104) at zero bias. Moreover, even after 12-h continuous working and 2-month storage without encapsulation in ambient air, the photodetection ability of the device can almost be maintained, demonstrating outstanding air stability. Our results suggest that nontoxic Cs3Cu2I5 is able to serve as a prospective candidate for stable solar-blind UV photodetection.

Timing Performance Simulation for 3D 4H-SiC Detector.

To meet the high radiation challenge for detectors in future high-energy physics, a novel 3D 4H-SiC detector was investigated. Three-dimensional 4H-SiC detectors could potentially operate in a harsh radiation and room-temperature environment because of its high thermal conductivity and high atomic displacement threshold energy. Its 3D structure, which decouples the thickness and the distance between electrodes, further improves the timing performance and the radiation hardness of the detector. We developed a simulation software-RASER (RAdiation SEmiconductoR)-to simulate the time resolution of planar and 3D 4H-SiC detectors with different parameters and structures, and the reliability of the software was verified by comparing the simulated and measured time-resolution results of the same detector. The rough time resolution of the 3D 4H-SiC detector was estimated, and the simulation parameters could be used as guideline to 3D 4H-SiC detector design and optimization.

An effective hydroxylation route for a highly sensitive glucose sensor using APTES/GOx functionalized AlGaN/GaN high electron mobility transistor.

A highly sensitive glucose sensor based on AlGaN/GaN high electron mobility transistor (HEMT) has been fabricated. The hydroxyl groups on the GaN surface were achieved by the decomposition of hydrogen peroxide solution (H2O2) under UV irradiation for the production of hydroxyl radicals. The self-assembled monolayers (SAMs) of 3-aminopropyltriethoxysilane (APTES) with terminal amino groups formed on the hydroxylation surface were used as substrates for glucose oxidase (GOx) immobilization. The chemical groups on the GaN surface after hydroxylation were confirmed by X-ray photoelectron spectroscopy. From the analysis of current signals, the biosensor constructed with APTES/GOx exhibited good current response to glucose over a linear range from 10 to 100 µM with a sensitivity of 3.15 × 104 µA mM-1 cm-2 and a detection limit of 10 nM. Meanwhile, the anticipated idea about the hydroxylation of GaN surface, can be an efficient approach for the design of AlGaN/GaN HEMT based biosensors in the future.

Self-powered SBD solar-blind photodetector fabricated on the single crystal of ß-Ga2O3.

A Schottky barrier diode (SBD) solar-blind photodetector was fabricated based on the single crystal ß-Ga2O3. Cu and Ti/Au were deposited on the top and bottom surface of Ga2O3 as Schottky and ohmic contacts, respectively. The SBD exhibits a higher rectification ratio of up to 5 × 107 at ±2 V. The photoresponse spectra show a maximum responsivity at 241 nm and a cutoff wavelength of 256 nm. The solar-blind/ultraviolet and solar-blind/visible rejection ratio can reach a high level of up to 200 and 1000, respectively. It is interesting that the device has a clear response to the solar-blind wavelength at zero bias, which confirms it can be used as a self-powered solar-blind photodetector.

Low Al-composition p-GaN/Mg-doped Al0.25Ga0.75N/n+-GaN polarization-induced backward tunneling junction grown by metal-organic chemical vapor deposition on sapphire substrate.

Low Al-composition p-GaN/Mg-doped Al0.25Ga0.75N/n(+)-GaN polarization-induced backward tunneling junction (PIBTJ) was grown by metal-organic chemical vapor deposition on sapphire substrate. A self-consistent solution of Poisson-Schrödinger equations combined with polarization-induced theory was used to model PIBTJ structure, energy band diagrams and free carrier concentrations distribution. The PIBTJ displays reliable and reproducible backward tunneling with a current density of 3 A/cm(2) at the reverse bias of -1 V. The absence of negative differential resistance behavior of PIBTJ at forward bias can mainly be attributed to the hole compensation centers, including C, H and O impurities, accumulated at the p-GaN/Mg-doped AlGaN heterointerface.

Electrically driven ultraviolet random lasing from an n-MgZnO/i-ZnO/SiO2/p-Si asymmetric double heterojunction.

Electrically pumped lasing action has been realized in ZnO from an n-MgZnO/i-ZnO/SiO2/p-Si asymmetric double heterostructure, an ultralow threshold of 3.9 mA was obtained. The mechanism of the laser is associated with the in-plane random resonator cavities formed in the ZnO films and the elaborate hollow-shaped SiO2 cladding pattern, which prevent the lateral diffusion of injection current and ultimately lower the threshold current of the laser diode. In addition, a waveguide mechanism due to different refractive indices of three epilayers enhances the guided optical field on the ZnO side, resulting in an improved light extraction efficiency.