Analysis and design of CW-LD pumped stable Q-switched laser

A high power continuous wave (CW) laser diode (LD) pumped acousto-optic Q-switched Nd:YVO4 laser is presented. A short pulse at the 1064 nm is obtained. With a repetition rate of 50 kHz, the maximum average output power of 5.72 W is achieved. The optical conversion efficiency and the slope efficiency are up to 28% and 32.4% respectively. At the repetition rate of 10 kHz and the pulse width of 16.3ns, the maximum single pulse energy of 286 μJ and the peak power of 13kW are acquired. The laser can be used as a signal source in the free-space optical communication. The output signal agrees with the modulate signal well.     

Modeling and analysis of actively Q-switched Fe:ZnSe laser pumped by a 2.8 μm fiber laser

A theoretical model concerning active Q-switching of an Fe: ZnSe laser pumped by a continuous-wave(CW) 2.8 μm fiber laser is developed. Calculations are compared with the recently reported experiment results, and good agreement is achieved. Effects of principal parameters, including pump power, output reflectivity, ion concentration and temperature of crystal, on the laser output performance are investigated and analyzed. Numerical results demonstrate that similar to highly efficient CWFe: ZnSe ...     

On the thermoelectric properties and band gap of silicon–germanium alloys in the high-temperature region

For n- and p-type Si_0.85Ge_0.15 alloys, the thermoelectric properties (thermopower, resistivity, thermal conductivity, and thermoelectric efficiency) are determined in the range from room temperature to 1200°C. The measurements are carried out with an upgraded device [1] by absolute and steady-state methods with thermal screens. The device is upgraded to extend the working-temperature range to ~1500 K. On the basis of these data, the energy-related capabilities of the alloy are estimated; the thermal band-gap width is calculated in the temperature range of ~1300–1400 K.     

Effect of the Phase Composition and Local Crystal Structure on the Transport Properties of the ZrO2–Y2O3 and ZrO2–Gd2O3 Solid Solutions

Russian Microelectronics - The results of investigating the crystal structure, ionic conductivity, and local structure of the (ZrO2)1 –x(Gd2O3)x and (ZrO2)1 –x(Y2O3)x (x = 0.04, 0.08,...     

Effect of the Composition on the Dielectric Properties and Charge Transfer in 2D GaS1 –хSeх Materials

Russian Microelectronics - The effect of the composition of the GaS–GaSe layered solid solutions on their dielectric characteristics and ac conductivity in the frequency band of 5 × 104...     

Limiting parameters of high-power single-stripe laser diodes in the range of 800–808 nm in the pulsed mode

Experimental results on the study of the output parameters of high-power continuous-wave (cw) laser diodes operating in the pulsed mode and the results of numerical simulation of the total efficiency of laser diodes with cavity lengths of 3 and 4 mm in a wide range of pump currents are presented. The spectral parameters of the high-power laser diodes are studied at various pulse-repetition rates. The possible causes of the limited output power in the pulsed mode are discussed.     

Numerical Determination of Stress Fields of and Forces on Line Dislocations in Anisotropic Multilayer Structures

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Implementation of the Broad band User AccessNetwork and the Study of the Key Algorithm for Improving the Performance of Asymmetrical Networks

This thesis is based on the design and development of ADSL access networks. We h ave completed the hardware and software functions in two main ADSL equipments: A TU C and ATU R. With the system design, we carry out researches to find out ef fective methods to improved performance in the following aspects: (a) how to all ocate limited bandwith among services with different QoS requirements and (b) what is the effect of asymmetric links on TCP end to end flow control mech anism. We make detailed analyses and propose useful solutions to those problems we find. The main contents of this thesis are as follows: (1) the design and rea l ization of ADSL access system. This part includes the principles of ADSL access technology, ADSL broadband access network architecture, and ATM over ADSL protoc ol models that we use in our system. We give detailed hardware and software desi gn steps in this part, and list system testing results to show the system perfor mance. In our hardware, the CPU is a RISC microprocessor. Combined with a high speed digital signal processor, the whole system can hold high reliability. Our software design platform is a Psos multi task real time operation system. We h ave developed a series of hardware drivers besides other tasks for high level co ntrol and interruption processing. Currently, our system has reached the expecte d performance under test environment. Our next step is the development of DSLAM and in this part we give a feasible design scheme. (2) Packet scheduling policy I n ADSL system. In order to optimize ATU R performance, we need a scheduling pol icy to regulate the order and number of packet output to the uplink. For this pu rpose, we study the scheduling algorithm design methods in a single network node and their performance. After studying the existing algorithms carefully, we fir st conclude certain important design principles and criterions for scheduling po licy evaluation. And then by using service curve function, we make detailed perf ormance analysis of a typical scheduling policy — the earliest deadline first. The advantage of characterizing service by using a function is that the service curve can provide a wide spectrum of service characterization. With this method, we first develop a generalized algorithm for calculating the deadlines used in the service curve based on the earliest deadline first policy, and then design a simplified computing program for an important curve. After that, holding fair b andwidth allocation and packet deadline guarantee as policy evaluation standards , we analyze this scheduling policy performance and propose solutions to those p roblems that we find. Finally, we, in theory, prove these improving algorithms. All these solutions and algorithms we design in this part are now under developm ent in real systems and will enhance system performance. (3) Effects of asymmetr I c links on TCP performance and solutions. TCP is a widely used transmission cont rol protocol. It regulates its forward data sending through reverse ACKs. What a re the new problems to its flow control mechanism on asymmetric links and how to solve them are the two main points of this part. We first study the relationshi p between normalized bandwidth ratio, link buffer capacity and TCP link throughp ut under asymmetric link models. We find that TCP ack transportation on slow bac kward link is a key reason that causes the problems in TCP asymmetric links. Ser ving this as a start point, we present several improving solutions to TCP flow c ontrol algorithm and test them through simulation. Besides, TCP has been widely implemented in many networks. To give compatibility with current TCP end users, we use scheduling solutions to regulate data packet and ack packet transmission ratio onto uplinks. In the theoretical analysis of several typical scheduling po licies, we find a feasible algorithm to control TCP data efficiency on asymmetri c links. Finally, we prove those analyses and propose algorithm through simulati on.     

Direct calculations on the band offsets of large-lattice-mismatched and heterovalent Si and III–V semiconductors

Band offset in semiconductors is a fundamental physical quantity that determines the performance of optoelectronic devices. However, the current method of calculating band offset is difficult to apply directly to the large-lattice-mismatched and heterovalent semiconductors because of the existing electric field and large strain at the interfaces. Here, we proposed a modified method to calculate band offsets for such systems, in which the core energy level shifts caused by heterovalent effects and lattice mismatch are estimated by interface reconstruction and the insertion of unidirectional strain structures as transitions, respectively. Taking the Si and III–V systems as examples, the results have the same accuracy as what is a widely used method for small-lattice-mismatched systems, and are much closer to the experimental values for the large-lattice-mismatched and heterovalent systems. Furthermore, by systematically studying the heterojunctions of Si and III–V semiconductors along different directions, it is found that the band offsets of Si/InAs and Si/InSb systems in [100], [110] and [111] directions belong to the type I, and could be beneficial for silicon-based luminescence performance. Our study offers a more reliable and direct method for calculating band offsets of large-lattice-mismatched and heterovalent semiconductors, and could provide theoretical support for the design of the high-performance silicon-based light sources.     

Direct calculations on the band offsets of large-lattice-mismatched and heterovalent Si and Ⅲ-Ⅴ semiconductors

Band offset in semiconductors is a fundamental physical quantity that determines the performance of optoelectron-ic devices.However,the current method of calculating band offset is difficult to apply directly to the large-lattice-mismatched and heterovalent semiconductors because of the existing electric field and large strain at the interfaces.Here,we proposed a modified method to calculate band offsets for such systems,in which the core energy level shifts caused by heterovalent ef-fects and lattice mismatch are estimated by interface reconstruction and the insertion of unidirectional strain structures as trans-itions,respectively.Taking the Si and Ⅲ-Ⅴ systems as examples,the results have the same accuracy as what is a widely used method for small-lattice-mismatched systems,and are much closer to the experimental values for the large-lattice-mis-matched and heterovalent systems.Furthermore,by systematically studying the heterojunctions of Si and Ⅲ-Ⅴ semiconduct-ors along different directions,it is found that the band offsets of Si/lnAs and Si/lnSb systems in[100],[110]and[111]direc-tions belong to the type I,and could be beneficial for silicon-based luminescence performance.Our study offers a more reli-able and direct method for calculating band offsets of large-lattice-mismatched and heterovalent semiconductors,and could provide theoretical support for the design of the high-performance silicon-based light sources.     

Formation of absolute PBG of 2D square lattice by changing the shapes and orientations of rods

Since 2Dphotonic crystal has been successfullyfabri-cated[1], many researches have shownthat loweringthesymmetry of the photonic crystals can contribute to ob-taining a large Photonic band gap(PBG)[2]. More re-cently,it has been shown that reorienting the directionof square rods in square lattices can make an absolutePBG appear and even move towards the direction ofhigher frequency[2]. In this letter we mainly concerned with the absolutePBGin 2D square lattice structures , which array with…     

Propagation of short radio waves and the potential of the Earth’s ionosphere radio-sounding method for calculation of maximum usable frequencies

The influence of the ionosphere on propagation of short radio waves is considered. Data on the monthly average diurnal values of critical frequencies at midlatitudes are presented. The applicability of the radio-sounding method to investigation of the state of the Earth’s ionosphere is demonstrated. Comparison of the data obtained from the path sounding of the ionosphere and from the radio-sounding method is performed. It is shown that satellite navigation systems can be used for prediction of the propagation conditions of short radio waves.     

Unveiling the Synergy of Interfacial Contact and Defects in α-Fe2O3 for Enhanced Photo-Electrochemical Water Splitting

Photo-electrochemical (PEC) water splitting is a promising method for converting solar energy into clean energy, but the mechanism of improving PEC efficiency through the interfacial contact and defect strategy remains highly controversial. Herein, reduced graphene oxide (rGO) and oxygen vacancies are introduced into α-Fe₂O₃ nanorod (NR) arrays using a simple spin-coating method and acid treatment. The resultant oxygen vacancy–α-Fe₂O₃/rGO-integrated system exhibits a higher photocurrent, four times than the pristine α-Fe₂O₃. It is well evidenced that the electronic interface interaction between α-Fe₂O₃ and rGO is boosted with the oxygen vacancies, facilitating electron transfer from α-Fe₂O₃ to rGO. Moreover, the oxygen vacancies not only create interband states in α-Fe₂O₃ that can trap photogenerated holes and thus facilitate charge separation but significantly also strengthen the adsorption of oxidative intermediates and reduce the energy barrier of rate-determining step during oxygen evolution reaction (OER). This study demonstrates an rGO–oxygen vacancy synergistic interfacial contact and defect modification approach to design semiconducting photocatalysts for high-efficiency solar energy capture and conversion. The generated principle is expected to be extendable to another material system.     

The More,the Better–Recent Advances in Construction of 2D Multi-Heterostructures

The past few years have witnessed significant development in the controlled growth of 2D heterostructures. Among those kinds of heterostructures, vertical and lateral ones have drawn the most attention. Vertical heterostructures can be created in the mode of layer by layer. The layer number and sequence in the vertical orientation can be modulated and thus leading to customized properties. However, the fabrication of lateral heterostructures has been met with challenges. The most concerning issue is related to the consistency at the atomic scale when two layers are stitched in a lateral direction. Adhering to the concept of epitaxial growth, chemical vapor deposition (CVD) has exerted significant impact in forming 2D lateral heterostructures. In this review, recent academic breakthroughs involving controlled growth of multi-heterostructures by CVD are present. The CVD technique in terms of growth parameters, choice of catalysts, and mechanism is fully emphasized, offering guidelines for shaping novel 2D heterostructures. Several novel multi-heterostructures attained by the CVD method are exhibited. Further, the properties and devices are described to demonstrate the unique features of multi-heterostructures. The great advances in precisely constructing multi-heterostructure are expected to push forward the way for 2D materials to industrialization and commercialization.     

Ab initio studies of the band parameters of III–V and II–VI zinc-blende semiconductors

Electronic band-structure calculations are performed for zinc-blende III–V (AlP, AlAs, AlSb, GaP, GaAs, GaP, InP, InAs, and InSb) and II–VI (ZnS, ZnSe, ZnTe, CdS, CdSe, and CdTe) semiconductors using an ab initio pseudopotential method within a local-density approximation (LDA). Lattice parameters, band gaps, Luttinger parameters, momentum matrix elements and effective masses are studied in detail. It is shown that LDA calculations cannot systematically give accurate band parameters. It is found that LDA band parameters calculated using experimentally determined lattice constants are more accurate than those using LDA lattice constants. We found that inclusion of the d electrons of Group-II atoms in the core gives more accurate band parameters.     

Silane-Mediated Expansion of Domains in Si-Doped κ-Ga2O3 Epitaxy and its Impact on the In-Plane Electronic Conduction

Unintentionally doped (001)-oriented orthorhombic κ-Ga₂O₃ epitaxial films on c-plane sapphire substrates are characterized by the presence of ≈ 10 nm wide columnar rotational domains that can severely inhibit in-plane electronic conduction. Comparing the in- and out-of-plane resistance on well-defined sample geometries, it is experimentally proved that the in-plane resistivity is at least ten times higher than the out-of-plane one. The introduction of silane during metal-organic vapor phase epitaxial growth not only allows for n-type Si extrinsic doping, but also results in the increase of more than one order of magnitude in the domain size (up to ≈ 300 nm) and mobility (highest µ ≈ 10 cm²V⁻¹s⁻¹, with corresponding lowest ρ ≈ 0.2 Ωcm). To qualitatively compare the mean domain dimension in κ-Ga₂O₃ epitaxial films, non-destructive experimental procedures are provided based on X-ray diffraction and Raman spectroscopy. The results of this study pave the way to significantly improved in-plane conduction in κ-Ga₂O₃ and its possible breakthrough in new generation electronics. The set of cross-linked experimental techniques and corresponding interpretation here proposed can apply to a wide range of material systems that suffer/benefit from domain-related functional properties.     

Dielectric Spectroscopy and Features of the Mechanism of the Semiconductor–Metal Phase Transition in VO2 Films

Semiconductors - In the range of 0.1–106 Hz, the temperature-induced transformation of the frequency dependences of the dielectric-loss tangent tanδ(f) as well as the Cole–Cole...     

Formation of the superconductor-semiconductor interface between Bi2Sr2CaCu2O8−x and indium-tin oxide

Planar heterostructures consisting of semiconducting highly textured indium-tin oxide (ITO) overlayers and c-axis oriented superconducting Bi₂Sr₂CaCu₂O_8−x (2212) underlayers have been formed onto MgO(100) substrates using dc magnetron sputtering. Annealing of the structures in air at 500 °C resulted in the appearance of both the interface resistivity anomaly at superconductive transition temperature—T_c and nonlinear current vs voltage behavior characteristics for a S-N junction. Meanwhile gradual change of the electrical properties towards S-I-N type behavior have been indicated with subsequent heat treatment in air at 50–100 °C. The origin of the insulating I-interlayer we associate with reversible oxygen removal in the 2212 compound at superconductor-semiconductor interface.     

Software Simulation in GSM Environment and Hardware Implementation of Improved Multi—band Excitation Vocoder

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Decoupling the Impacts of Engineering Defects and Band Gap Alignment Mechanism on the Catalytic Performance of Holey 2D CeO2−x-Based Heterojunctions

Critical catalysis studies often lack elucidation of the mechanistic role of defect equilibria in solid solubility and charge compensation. This approach is applied to interpret the physicochemical properties and catalytic performance of a free-standing 2D–3D CeO_2−x scaffold, which is comprised of holey 2D nanosheets, and its heterojunctions with MoO_3−x and RuO₂. The band gap alignment and structural defects are engineered using density functional theory (DFT) simulations and atomic characterization. Further, the heterojunctions are used in hydrogen evolution reaction (HER) and catalytic ozonation applications, and the impacts of the metal oxide heteroatoms are analyzed. A key outcome is that the principal regulator of the ozonation performance is not oxygen vacancies but the concentration of Ce³⁺ and Ce vacancies. Cation vacancy defects are measured to be as high as 8.1 at% for Ru-CeO_2−x. The homogeneous distribution of chemisorbed, Mo-oxide, heterojunction nanoparticles on the CeO_2−x holey nanosheets facilitates intervalence charge transfer, resulting in the dominant effect and resultant ≈50% decrease in overpotential for HER. The heterojunctions are tested for aqueous-catalytic ozonation of salicylic acid, revealing excellent catalytic performance from Mo doping despite the adverse impact of Ce vacancies. The present study highlights the use of defect engineering to leverage experimental and DFT results for band alignment.