Two-dimensional hexagonal boron nitride (h-BN) single crystals with various shapes have been synthesized by chemical vapor deposition over the past several years. Here, we report the formation of three-leaf dart (3LD)-shaped single crystals of h-BN on a Cu foil by atmospheric-pressure chemical vapor deposition. The leaves of the 3LD-shaped h-BN are as long as 18 μm, and their edges are smooth armchair on one side and stepped armchair on the other. Careful analysis revealed that surface oxygen plays an important role in the formation of the 3LD shape. Oxygen suppressed h-BN nucleation by passivating Cu surface active sites and lowered the edge attachment energy, which caused the growth kinetics to change to a diffusion-controlled mode.

Physical vapor deposition (PVD) has been an important method to synthesize metallic nanorods during the past two decades. Based on the main physical process of crystal growth, this letter made a growth model of metallic nanorods with kinetic lattice Monte Carlo (KLMC) method and studied the effects of three-dimensional (3D) Ehrlich–Schwoebel (ES) barrier during the metallic nanorods growth. According to the simulation results, a large 3D ES barrier affects the surface morphology apparently. With analyze the simulation results, 3D ES barrier promotes the step formation and increases the step height greatly, and it is the main factor of metallic nanorods formation.

Self-assembled submicron nickel particles were successfully synthesized via the one-step surfactant-assisted solvothermal method. The impact of surfactant and reducing agent stoichiometry is investigated in this manuscript. Different morphologies and structures of Ni particles, including flower-like nanoflakes, hydrangea-like structures, chain structures, sphere-like structures, and hollow structures were prepared through different processing conditions with two parameters such as temperature and time. Based on scanning electron microscopy (SEM), X-ray diffraction (XRD), thermal gravimetric analysis (TGA) and vibrating sample magnetometry (VSM), the submicron nickel particles show good saturation magnetization and excellent thermal stabilities with a possible growth mechanism for the variety of the structure-tuned formation. Importantly, the microwave absorption properties of the submicron nickel particles were studied. The lowest reflection loss of Ni-P9/T200/H15 with a thin layer thickness of 1.7 mm can reach −42.6 dB at 17.3 GHz.

Organo-lead perovskite materials as light harvesters have represented a hot field of research on high-efficiency perovskite solar cells. In such cells, the quality of organo-lead perovskite films is most critial to device performance, essentially affected by varying halide composition. Meanwhile, the understanding of formation mechanisms and basic properties of these hybrid perovskites is still ongoing. Herein, we report a one-step solution processing strategy to investigate the role of precursor in the context of hybrid perovskites, in which the molar ratio of the methylammonium compound and lead salts is closely correlated to the characteristics of the hybrid perovskite films. We investigate the molar ratio dependence of the mixed-halides incorporation of three organolead trihalide perovskite absorbers, CH3NH3PbI3-aBra, CH3NH3PbI3-aCla and CH3NH3PbBr3-aCla, and compare them with three pure (CH3NH3PbI3, CH3NH3PbBr3, and CH3NH3PbCl3) perovskites. We find the versatility of the hybrid perovskites affected by excess organic compounds. Specifically, the synergistic effect of the mixed-halides in tuning perovskite composition demonstrated that the different perovskite compositions deserved more in-depth understanding from with the varying of the crystal transformation, morphological framework, thermal decomposition and optical performance of the hybrid perovskites. Moreover, this work provides visual evidence for the design of the mixed halide perovskites based on these hybrids, which paves a way for improvements with selective properties in lead halide perovskite-based devices.

We report a simple solution route for preparing a sGO-PEDOT composite HTL by combining solution-processable sGO with commercialized PEDOT:PSS solution. The PSCs based on these sGO-PEDOT composite HTLs were systematically investigated.

An efficient approach to engineering the Al 2 O 3 /GaN positive interface fixed charges by post-dielectric annealing in nitrogen is demonstrated. The remarkable reduction of interface fixed charges from 1.44 × 10 13 to 3 × 10 12 cm -2 was observed, which leads to a record high threshold voltage (V TH ) of 7.6 V obtained in the Al 2 O 3 /GaN MOSFETs. The significantly reduced interface fixed charges and the corresponding remote scattering effect enable respectable improvement in the electron mobility that results in a high drain current density of 355 mA/mm in the device. These competitive results reveal that the method reported in this letter is promising in pushing V TH more positive and simultaneously achieving good device performance of normally-off GaN power devices.

In this paper, we report an experimental observation of the two-stage turn-on characteristic in normally-OFF Al2O3/GaN metal-oxide-semiconductor high electron mobility transistors (MOS-HEMTs) on Si substrate. The impact of oxide/GaN interface traps with different energy levels on the switching behavior of the device was extensively examined by simulation and verified by measurements. The interface traps at 0.4 eV below the bottom of the conduction band (Eit = EC-0.4 eV) of GaN buffer with a density of Dit= 6.5×1012 cm-2 was identified responsible for the observed two-stage turn-on characteristic. The weak Fermi-level pinning (WFLP) induced by the dynamic electron filling of interface traps may hamper the electron from accumulating in the Al2O3/GaN MOS-channel and then manifests a premature turn-on during the switching-on process. (© 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Pure metallic nickel submicron spheres (Ni-SSs), flower-like nickel nanoflakes, and hollow micrometer-sized nickel spheres/tubes were controllably synthesized by a facile and efficient one-step solvothermal method with no reducing agent. The characteristics of these nickel nanostructures include morphology, structure, and purification. Possible synthesis mechanisms were discussed in detail. The resultant Ni-SSs had a wide diameter distribution of 200~800 nm through the aggregation of small nickel nanocrystals. The ferromagnetic behaviors of Ni-SSs investigated at room temperature showed high coercivity values. Furthermore, the microwave absorption properties of magnetic Ni-SSs were studied in the frequency range of 0.5–18.0 GHz. The minimum reflection loss reached −17.9 dB at 17.8 GHz with a thin absorption thickness of 1.2 mm, suggesting that the submicron spherical structures could exhibit excellent microwave absorption properties. More importantly, this one-pot synthesize route provides a universal and convenient way for preparation of larger scale pure Ni-SSs, showing excellent microwave absorption properties.

An efficient approach to engineering the AhOß/GaN positive interface fixed charges (Qit+) by post-dielectric annealing in nitrogen is demonstrated. The remarkable reduction of Qit+ from 1.44×1013 to 3×1012 cm−2 was observed, which leads to a record high threshold voltage (Vth) of +7.6 V obtained in the AhOß/GaN MOSFETs. The positive interface charges were proposed originating from the N-vacancy and O-substitution at the AhOß/GaN interface by Ab inito study. The significantly reduced Qit+ also effectively depresses the remote scattering effect that enables respectable improvement in the electron mobility, which results in a high drain current density of 355 mA/mm in the device with dimensions of Lg/Lgs/Lgd/Wg=2/1.5/5/50 μm. The device with Lgd of 20 μm delivers a high breakdown voltage of 1054 V @ 1 μA/mm. Owing to the uniquely high Vth the fabricated normally-off device features substantially improved faulty turn-on immunity compared with the device with lower Vth. These competitive results reveal that the method reported in this work is promising in pushing the Vth more positive and simultaneously achieving good device performance of normally-off GaN power devices with improved fail-safe capability.

An AlGaN/GaN-on-Si lateral power diode with recessed metal/Al2O3/III-nitride (MIS)-gated ohmic anode for improved forward conduction and reverse blocking has been realized. The low onset voltage of ~0.6 V with good uniformity for the fabricated 189 devices is obtained. In comparison with the conventional Schottky diode the specific ON-resistance (RON,SP) was reduced by 51% in a device with anode-to-cathode spacing (LAC) of 5 μm. The incorporation of high-k dielectric in the recessed gate region enabling two-order lower reverse leakage comparing with the conventional device, leading to a high breakdown voltage over 1.1 kV at leakage current as low as 10 μA/mm in device with LAC=20μm. The strong reverse blocking over 600 V was still achieved at 150°C. The proposed diode is compatible with GaN normally OFF MIS high-electron-mobility transistors, revealing its potential for highly efficient GaN-on-Si power ICs.

An AlGaN/GaN lateral power diode on Si substrate with recessed Metal/Al2O3/III-Nitride (MIS) Gated hybrid anode (MG-HAD) for improved forward conduction and reverse blocking has been realized. The low turn-on voltage of 0.6 V with good uniformity for the fabricated 189 devices is obtained. In comparison with the conventional device, the forward current at 2 V was increased by 5 times that leading to a 51% reduction in specific ON-resistance (RON, SP). The incorporation of high-k dielectric in the recessed gate region enabling 2-order lower reverse leakage comparing with the conventional device, leading to a high breakdown voltage over 1.1 kV at leakage current as low as 10 μA/mm in the MG-HAD with anode-to-cathode distance (LD) of 20 μm. The strong reverse blocking over 600 V was still achieved at 150 °C. The proposed diode is compatible with GaN normally-off MIS high-electron-mobility transistors (MISHEMTs), revealing its great potential for highly efficient GaN-on-Si power ICs.

In this paper, the partial gate recess for performance improvement of enhancement-mode (E-mode) GaN power devices is experimentally demonstrated. The gate recess with a careful control of the recess depth was performed with an optimized recessed barrier thickness of similar to 1.5 nm that is thin enough to completely deplete the 2-D electron gas channel in the gate region. Meanwhile, the remaining barrier preserves the as-grown quantum well of the heterostructure physically intact and thus, effectively mitigates the lattice damage caused by gate recess. The fabricated E-mode Al2O3/AlGaN/GaN MISFETs deliver a threshold voltage (V-TH) of +1.5 V. The maximum drain current density (I-D,I-max) and transconductance (G(m,max)) are 693 mA/mm and 166 mS/mm, respectively. The MISFETs with an L-GD of 10 mu m feature an OFF-state breakdown voltage of 860 V at a leakage current of 1 mu A/mm. The corresponding specific ON-resistance (R-ON,R-sp) is as low as 1.18 m Omega.cm(2) yielding a high-power figure of merit of 626 MW/cm(2). In comparison with the reference MOSFETs by fully gate recess, the respectably improved device performance of the MISFETs attributes to the enhanced electron mobility achieved by the partial gate recess.