Analysis of the mechanisms of electron recombination in HgCdTe infrared photodiode

This paper presents an experimental study of minority carrier lifetime and recombination mechanisms in HgCdTe photodiode. The excitation light source is a wavelength-tunable pulsed infrared laser. A constant background illumination has been introduced to minimize the effect of the junction equivalent capacitor and resistance. The decay of the photo-generated voltage is recorded by a storage oscilloscope. By fitting the exponentially decay curve, the time constant has been obtained which is regarded as the photo-generated minority carrier lifetime of the HgCdTe photodiode. The experimental results show that the carrier lifetime is in the range of 18–407 ns at 77 K for the measured detectors of four Cd compositions. It was found that the Auger recombination process is more effective for low Cd composition while the radiative recombination process became more important for high composition materials. The Shockley–Read–Hall recombination processes could not be ignored for all Cd composition.     

Value of Optical Bypass in Packet Ring Networks

This paper firstly examines the value of optical bypass scheme in packet ring networks. An Integer Linear Program (ILP) formulation is presented and analytical results under different traffic patterns are given.     

Prediction of lattice constant in perovskites of GdFeO3 structure

Lattice constants in GdFeO₃-type ABO₃ perovskites are correlated to their constituent elemental properties by using linear regression (LR) and artificial neural networks (ANN) techniques and a sample set of 157 known GdFeO₃-type ABO₃ perovskites. LR models are first obtained using two elemental ionic radii only and ANN models, using five elemental properties; ionic radii, electronegativities of cation A and B, and the valence of ion A, are further developed to improve the model predictability, which reaches an error limits of less than 2%. It is shown that lattice constants of these compounds only roughly correlate to their ionic radii, and for a good prediction model 3 more elemental properties (electronegativity and valence) are necessary. In new materials research, where lattice constant is one of the key design target, the developed LR and ANN models may be used to screen and shortlist promising perovskites from a large pool of all possible candidates. These selected compounds may undergo further test using relatively more expensive experiments or quantum mechanics computations.     

TM掺杂Ⅱ-Ⅳ-Ⅴ2黄铜矿半导体的电磁性质

利用自旋局域密度泛函的第一性原理对3d过渡金属(TM=V，Cr，Mn，Fe，Co和Ni)掺杂的Ⅱ-Ⅳ-Ⅴ2(CdGeP2和ZnGeP2)黄铜矿半导体的电磁性质进行系统计算，结果发现：V和Cr掺杂的CdGeP2和ZnGeP2将出现铁磁状态(FM)，Mn，Fe以及Co掺杂的CdGeB和ZnGeP2将出现反铁磁状态(AFM)，而Ni掺杂时，稀磁半导体(DMS)的磁性比较不稳定，其中Cr掺杂的CdGeP2和ZnGeP2将可能是具有较高居里温度Tc的DMS，当TM-3d电子的t2g态部分被填充时，其掺杂的DMS将出现FM状态；而当TM-3d电子的t2g态全满或者全空时，其掺杂的DMS将出现AFM状态，在(Cd，Mn)GeP，和(Zn，Mn)(GeP2中分别掺入电子和空穴载流子，可以发现载流子是否具有TM-3d电子的巡游特性是。DMS是否出现FM状态的主要原因。     

A meshless model for transient heat conduction analyses of 3D axisymmetric functionally graded solids

A meshless numerical model is developed for analyzing transient heat conductions in three-dimensional （3D） axisymmetric continuously nonhomogeneous functionally graded materials （FGMs）. Axial symmetry of geometry and boundary conditions reduces the original 3D initial-boundary value problem into a two-dimensional （2D） problem. Local weak forms are derived for small polygonal sub-domains which surround nodal points distributed over the cross section. In order to simplify the treatment of the essential boundary conditions, spatial variations of the temperature and heat flux at discrete time instants are interpolated by the natural neighbor interpolation. Moreover, the using of three-node triangular finite element method （FEM） shape functions as test functions reduces the orders of integrands involved in domain integrals. The semi-discrete heat conduction equation is solved numerically with the traditional two-point difference technique in the time domain. Two numerical examples are investigated and excellent results are obtained, demonstrating the potential application of the proposed approach.     

Mixed multi-region design of diffractive optical element for projection exposure system

The diffractive optical element (DOE) is widely used to generate various illumination modes in the projection lithography system. The working principle and design methods of the DOE are discussed in detail in this paper. A mixed multi-region design method is proposed to calculate the phase of DOE based on the poor spatial coherence of excimer laser, using the Gerchberg–Saxton (GS) algorithm. The DOEs generating circular, dipole and quadrupole illumination modes are designed and simulated by three different methods: single region design, repeated multi-region design and mixed multi-region design. The performance of these DOEs are compared and analyzed with these three design methods. The mixed multi-region design method is used to design the DOEs generating three illumination modes, the diffraction efficiencies are greater than 85%, and the non-uniformities of illumination are less than 3%. The analysis results indicate that the DOE designed by the mixed multi-region design can achieve higher diffraction efficiency and illumination uniformity of the far-field intensity distribution without modifying the GS algorithm.     

Ranking spreaders by decomposing complex networks

Ranking the nodes? ability of spreading in networks is crucial for designing efficient strategies to hinder spreading in the case of diseases or accelerate spreading in the case of information dissemination. In the well-known k-shell method, nodes are ranked only according to the links between the remaining nodes (residual links) while the links connecting to the removed nodes (exhausted links) are entirely ignored. In this Letter, we propose a mixed degree decomposition (MDD) procedure in which both the residual degree and the exhausted degree are considered. By simulating the epidemic spreading process on real networks, we show that the MDD method can outperform the k-shell and degree methods in ranking spreaders.     

Near-infrared downconversion in Eu2＋ and Pr3＋ co-doped KSrPO4 phosphor

A novel near-infrared (NIR) downconversion (DC) phosphor KSrPO4 :Eu2+ , Pr3+ is synthesized by the conventional high temperature solid-state reaction. The Eu2+ acts as an efficient sensitizer for Pr3+ in the KSrPO4 host. With broad-band near-ultraviolet light excitation induced by the 4f→5d transition of Eu2+ , the characteristic NIR emission of Pr3+ , peaking at 974 nm and 1019 nm due to 3P0 → 1G4 and 1G4 → 3H4 transitions, is generated as a result of the energy transfer from Eu2+ to Pr3+ . The luminescence spectra in both the visible and the NIR regions and the decay lifetime curves of Eu2+ prove the energy transfer from Eu2+ to Pr3+ . This Eu2+ and Pr3+ co-doped KSrPO4 phosphor may be a promising candidate to modify the spectral mismatch behavior of crystalline solar cells and sunlight.     

Characterization of ceramic PVD thin films on AZ31 magnesium alloys

Ceramic thin films have been widely used to protect the metal substrate as coatings in the past years. In order to improve the poor corrosion resistance of AZ31 magnesium alloy, the study in this paper used the electron beam evaporation method to prepare ceramic PVD films on its surface with TiO₂ and Al₂O₃ as donors, respectively. Atomic force microscopy (AFM), scanning electron microscope (SEM), energy dispersive X-ray spectrometer (EDS), Auger electron spectroscopy (AES) and X-ray diffraction (XRD) were used to investigate the surface morphology, composition and microstructure of the thin films. Both films deposited on AZ31 took on compact top surface morphologies and grew as amorphous structures on substrate. AES test not only showed that films compositions deviated the standard stoichiometric ratios, but also found that element Mg diffused into films and existed as magnesium oxide in the TiO_x film as well as the AlO_x film. In the electrochemical corrosion test, the AlO_x coating on AZ31 exhibited the largest electrochemical impedance in a 3.5% NaCl solution. But it did not show better corrosion resistance than others for the poorer adhesion. Even if its thickness was small, the TiO_x coating on AZ31 exhibited the best corrosion resistance in this study. According to the observation and analysis, the damage of these films on AZ31 in aggressive solutions was mainly due to the existence of pores, microcracks, vacancies and poor adhesion between coating and substrate.