Influence of Rapid Thermal Annealing on the Characteristics of InGaN/GaN MQWs

N-type InGaN/GaN multiple-quantum-wells (MQWs) were grown on sapphire substrates by metal organic chemical vapor deposition (MOCVD). The crystal quality and optical properties of samples after rapid thermal annealing (RTA) at different temperatures in a range from 400 to 800°C are investigated by X-ray diffraction (XRD) and photoluminescence (PL) spectrum. The experimental results show that the peaks of InGaN, InN and In can be observed in all samples. And the results are induced by the phase separation and In-clusters. The luminescence peak of the samples annealed showed a red shift. It is caused by strain stress relaxation during the RTA process. Furthermore, some defects can be eliminated and the best annealing temperature is from 500°C to 700°C

Influence of Rapid Thermal Annealing on the Characteristics of InGaN/GaN MQWs

N-type InGaN/GaN multiple-quantum-wells (MQWs) were grown on sapphire substrates by metal organic chemical vapor deposition (MOCVD). The crystal quality and optical properties of samples after rapid thermal annealing (RTA) at different temperatures in a range from 400 to 800°C are investigated by X-ray diffraction (XRD) and photoluminescence (PL) spectrum. The experimental results show that the peaks of InGaN, InN and In can be observed in all samples. And the results are induced by the phase separation and In-clusters. The luminescence peak of the samples annealed showed a red shift. It is caused by strain stress relaxation during the RTA process. Furthermore, some defects can be eliminated and the best annealing temperature is from 500°C to 700°C

High-Switching-Ratio Photodetectors Based on Perovskite CH3NH3PbI3 Nanowires

Hybrid organic-inorganic perovskite materials have attracted extensive attention due to their impressive performance in photovoltaic devices. One-dimensional perovskite CH3NH3PbI3 nanomaterials, possessing unique structural features such as large surface-to-volume ratio, anisotropic geometry and quantum confinement, may have excellent optoelectronic properties, which could be utilized to fabricate high-performance photodetectors. However, in comparison to CH3NH3PbI3 thin films, reports on the fabrication of CH3NH3PbI3 nanowires for optoelectrical application are rather limited. Herein, a two-step spin-coating process has been utilized to fabricate pure-phase and single-crystalline CH3NH3PbI3 nanowires on a substrate without mesoporous TiO2 or Al2O3. The size and density of CH3NH3PbI3 nanowires can be easily controlled by changing the PbI2 precursor concentration. The as-prepared CH3NH3PbI3 nanowires are utilized to fabricate photodetectors, which exhibit a fairly high switching ratio of ~600, a responsivity of 55 mA/W, and a normalized detectivity of 0.5 × 1011 jones under 532 nm light illumination (40 mW/cm2) at a very low bias voltage of 0.1 V. The as-prepared perovskite CH3NH3PbI3 nanowires with excellent optoelectronic properties are regarded to be a potential candidate for high-performance photodetector application

Numerical Simulation of Multi-Crystalline Silicon Crystal Growth Using a Macro–Micro Coupled Method during the Directional Solidification Process

In this work, the crystal growth of multi-crystalline silicon (mc-Si) during the directional solidification process was studied using the cellular automaton method. The boundary heat transfer coefficient was adjusted to get a suitable temperature field and a high-quality mc-Si ingot. Under the conditions of top adiabatic and bottom constant heat flux, the shape of the crystal-melt interface changes from concave to convex with the decrease of the heat transfer coefficient on the side boundaries. In addition, the nuclei form at the bottom boundary while columnar crystals develop into silicon melt with amzigzag-faceted interface. The higher-energy silicon grains were merged into lower energy ones. In the end, the number of silicon grains decreases with the increase of crystal length

Cellular Automaton Modeling of the Transition of Multi-Crystalline Silicon from a Planar Faceted Front to Equiaxed Growth

A modeling approach combining the lattice Boltzmann (LB) method and the cellular automaton (CA) technique are developed to simulate the faceted front to equiaxed structure transition (FET) of directional solidification of multi-crystalline silicon. The LB method is used for the coupled calculation of velocity, temperature and solute content field, while the CA method is used to compute the nucleation at the silicon-crucible interface and on SiC particles, as well as the mechanism of growth and capturing. For silicon, the interface kinetic coefficient is rather low, which means that the kinetic undercooling can be large. A strong anisotropy in the surface tension and interfacial kinetics are considered in the model. A faceted front in conjunction with a sufficiently high carbon content can lead to equiaxed growth by nucleation on SiC. The temperature gradient in Si melt at the interface is negative, which leads to the occurrence of a faceted interface. The higher the absolute value of thermal gradients, the faster the growth velocity. Due to differences in the degree of undercooling, there will be the unification of facets in front of the solid-liquid interface. Transitions from faceted front to thermal equiaxed dendrites or faceted equiaxed grains are observed with smaller or larger impurity contents, respectively

Determination of the basic optical parameters of ZnSnN2

Polycrystalline ZnSnN2 thin films were successfully prepared by DC magnetron sputtering at room temperature. Both the as-deposited and annealed films showed n-type conduction, with electron concentration varying between 1.6 x 10(18) and 2.3 x 10(17) cm(-3) and the maximummobility of 3.98 cm(2) V-1 s(-1). The basic optical parameters such as the refraction index, extinction coefficient, and absorption coefficient were precisely determined through the spectroscopic ellipsometry measurement and analysis. The optical bandgap of the ZnSnN2 films was calculated to around 1.9 eV, with the absorption coefficient greater than 104 cm(-1) at wavelengths less than 845 nm. The easy-fabricated ZnSnN2 possesses a sound absorption coefficient ranging from the ultraviolet through visible light and into the near-infrared, comparable to some typical photovoltaic materials such as GaAs, CdTe, and InP. (C) 2015 Optical Society of Americ

Mo-Doped Ni₃S₂ Nanosheet Arrays for Overall Water Splitting

Designing effective and low-cost bifunctional electrocatalysts for the alkaline hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) is essential to achieve green development of the hydrogen economy. Herein, we have developed Mo-doped Ni3S2 nanosheet array catalysts with excellent electrochemical properties. Only 85 mV (HER) and 230 mV (OER) overpotentials are required under alkaline conditions at 10 mA cm–2 and remain undegraded for 100 h. In addition, it only required 1.52 V at 10 mA cm–2 in an alkaline electrolyzer, and it remained unchanged for more than 100 h in stability tests, outperforming most reported electrocatalysts. Experiments and density functional theory (DFT) calculations confirmed that the doping of Mo could expose more active sites of Ni3S2 and optimize the adsorption free energy of the intermediate, which in turn improves its intrinsic activity. This work reveals the key role of Mo in Ni3S2 electrocatalytic performance enhancement at the atomic scale

Semiconducting ZnSnN2 thin films for Si/ZnSnN2 p-n junctions

ZnSnN2 is regarded as a promising photovoltaic absorber candidate due to earth-abundance, non-toxicity, and high absorption coefficient. However, it is still a great challenge to synthesize ZnSnN2 films with a low electron concentration, in order to promote the applications of ZnSnN2 as the core active layer in optoelectronic devices. In this work, polycrystalline and high resistance ZnSnN2 films were fabricated by magnetron sputtering technique, then semiconducting films were achieved after post-annealing, and finally Si/ZnSnN2 p-n junctions were constructed. The electron concentration and Hall mobility were enhanced from 2.77 x 10(17) to 6.78 x 10(17) cm(-3) and from 0.37 to 2.07 cm(2) V-1 s(-1), corresponding to the annealing temperature from 200 to 350 degrees C. After annealing at 300 degrees C, the p-n junction exhibited the optimum rectifying characteristics, with a forward-to-reverse ratio over 10(3). The achievement of this ZnSnN2-based p-n junction makes an opening step forward to realize the practical application of the ZnSnN2 material. In addition, the nonideal behaviors of the p-n junctions under both positive and negative voltages are discussed, in hope of suggesting some ideas to further improve the rectifying characteristics. (C) 2016 AIP Publishing LLC