Interrelation of the construction of the metamorphic InAlAs/InGaAs nanoheterostructures with the InAs content in the active layer of 76–100% with their surface morphology and electrical properties

The influence of the construction of a metamorphic buffer on the surface morphology and electrical properties of InAlAs/InGaAs/InAlAs nanoheterostructures with InAs content in the active layer from 76 to 100% with the use of the GaAs and InP substrates is studied. It is shown that such parameters as the electron mobility and the concentration, as well as the root-mean-square surface roughness, substantially depend on the construction of the metamorphic buffer. It is established experimentally that these parameters largely depend on the maximal local gradient of the lattice constant of the metamorphic buffer in the growth direction of the layers rather than on its average value. It is shown that, with selection of the construction of the metamorphic buffer, it is possible to form nanostructured surfaces with a large-periodic profile.     

Thermal Analysis of InAlAs/InGaAs/InP Mid-infrared QCLs Operating in CW Mode

A simulation method for the thermal analysis of InAlAs/InGaAs/InP mid-infrared quantum cascade lasers (QCLs) based on finite-element method (FEM) is presented. The thermal distribution of the QCLs on substrate-side or epilayer-side mounting forms is simulated and the results are compared. Results show that the epilayer-side mounting form has much better heat dissipation capability than the substrate-side mounting.     

Optical properties of metamorphic GaAs/InAlGaAs/InGaAs heterostructures with InAs/InGaAs quantum wells,emitting light in the 1250–1400-nm spectral range

It is demonstrated that metamorphic GaAs/InAlGaAs/InGaAs heterostructures with InAs/InGaAs quantum wells, which emit light in the 1250–1400 nm spectral range, can be fabricated by molecular-beam epitaxy. The structural and optical properties of the heterostructures are studied by X-ray diffraction analysis, transmission electron microscopy, and the photoluminescence method. Comparative analysis of the integrated photoluminescence intensity of the heterostructures and a reference sample confirm the high efficiency of radiative recombination in the heterostructures. It is confirmed by transmission electron microscopy that dislocations do not penetrate into the active region of the metamorphic heterostructures, where the radiative recombination of carriers occurs.     

Structural Investigation of InGaAs/InP Quantum Wire Array Using Triple-Axis X-ray Diffractometry

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Study of the parameters of nanoscale layers in nanoheterostructures based on II–VI semiconductor compounds

Wide-gap ZnSe-based nanoheterostructures grown by molecular-beam epitaxy are studied by local cathodoluminescence and X-ray microanalysis. It is shown that the used methods allow nondestructive determination of the depth, elemental composition, and geometrical parameters of the nanoscale ZnCdSe layer. The accuracy of the results is verified by transmission electron microscopy. The research techniques are based on the possibility of varying the primary electron-beam energy, which results in changes in the regions of characteristic X-ray and cathodoluminescence generation.     

Determination of the electron concentration and mobility in the vicinity of a quantum well and δ-doped layer in InGaAs/GaAs heterostructures

Comparative admittance measurements in mesadiodes on an n ⁺-GaAs substrate and in ring planar diode structures on an i-GaAs substrate, which contain a Si ??-doped layer and an InGaAs quantum well in the GaAs epitaxial layer are performed. The possibility of determining the concentration profile and electron mobility in the vicinity of the ??-doped layer and the InGaAs quantum well is shown based on an analysis of the simultaneously measured capacitance-voltage and conductance-voltage characteristics of the mesadiodes. By performing such measurements for i-GaAs-based ring diode structures with the given geometry, it is possible to reliably determine only the concentration profile. The influence of the relative location of the quantum well and ??-doped layer on the concentration profile and mobility is revealed. The phenomenon of Maxwell relaxation in i-GaAs-based ring diode structures is discussed.     

Measurement of the concentration of 2D electrons in δ-doped InGaAs/GaAs pseudomorphic transistor structures using the photoluminescence spectroscopy

Concentration of 2D electrons n _s is measured in the modulation-doped PHEMT structures with the aid of two photoluminescence (PL) methods using halfwidth of the 1e-1hh band and the energy difference E _F-E _1e in the experimental PL spectra. The applicability of the methods is analyzed, and a method for the determination of energy E _F from the temperature dependence of the intensity ratio of the 2e-1hh and 1e-1hh bands is proposed. It is demonstrated that concentrations n _s are in good agreement with the results of the Hall-effect measurements at relatively low concentrations (n _s ≤ 2.5 × 10¹²) when the parallel conduction along the δ layer is absent. At stronger doping, the PL methods yield more accurate concentrations n _s .     

Characterization of a Quantum Well in an Si/Si1–xGex/Si Heterostructure by X-ray Diffractometry

Rocking curves with a pronounced pendulum-solution pattern are obtained for Si_{1 – x} Ge _x /Si specimens with a single quantum well (QW) by double-crystal x-ray diffractometry. These oscillations are typical of the rocking curves for GaAs multilayers with QWs. With Si–Ge multilayers, they are obtained for the first time. The Ge depth profiles of the QW are reconstructed from the rocking curves. As a result, the thicknesses of both QW interfacial layers are estimated.     

Bimodality in the Electroluminescence Spectra of InGaAs Quantum Well–Dot Nanostructures

Semiconductors - The polarization-resolved electroluminescence spectra of waveguide structures based on quantum well–dots are investigated in the temperature range of 60–300 K. It is...     

Features of conduction mechanisms in Si/oligo-β-naphthol/metal heterostructures

Conduction mechanisms in Si-polymer-metal heterostructures with oligo-β-naphthol as a wide band-gap polymer have been studied. The results obtained are explained within the models of hopping transport via trap levels, Schottky emission, and field tunneling emission. Different charge transport mechanisms operate in different temperature ranges and under different electric fields.     

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.     

Development of Multilayer Optics for the EUV, Soft X-ray and X-ray Regions in Tongji University

1 Introduction The EUV and X- ray optics has been regarded as one of the important fields in modern optics, having many promising applications in next generation lithography system, astronomical telescope, spectroscopy, plasma diagnostics and X- ray laser. However, in the EUV and X- ray regions, the nature of the complex optical con- stants of all materials makes the realization of the ideal optical elements like ones working in visible region im-possible. The development of EUV and X- ra…     

Effect of the Spread of the Depths of p–n Junction on the Parameters of InGaAs/InP Avalanche Photodiodes

Journal of Communications Technology and Electronics - Permissible deviations of the diffusion depth and selection of the optimal type of epitaxial structures for fabrication of the InGaAs/InP...     

A data-driven approach to diagnostics of repetitive processes in the distribution domain – Applications to gearbox diagnostics in industrial robots and rotating machines

This paper presents a data-driven approach to diagnostics of systems that operate in a repetitive manner. Considering that data batches collected from a repetitive operation will be similar unless in the presence of an abnormality, a condition change is inferred by comparing the monitored data against an available nominal batch. The method proposed considers the comparison of data in the distribution domain, which reveals information of the data amplitude. This is achieved with the use of kernel density estimates and the Kullback–Leibler distance. To decrease sensitivity to disturbances while increasing sensitivity to faults, the use of a weighting vector is suggested which is chosen based on a labeled dataset. The framework is simple to implement and can be used without process interruption, in a batch manner. The approach is demonstrated with successful experimental and simulation applications to wear diagnostics in an industrial robot gearbox and for diagnostics of gear faults in a rotating machine.     

Spectral-kinetic properties of heterostructures with GaAsSb/InGaAs/GaAs-based quantum wells emitting in the range of 1.0–1.2 μm

The spectral-kinetic properties of heterostructures with GaAs/GaAsSb-based and GaAsSb/InGaAs/GaAs-based quantum wells, emitting in the range of 1.0–1.2 μm are studied with picosecond and nanosecond temporal resolution. Intense photoluminescence in the GaAsSb/InGaAs/GaAs structure, as well as an increase in the photoluminescence wavelength by a factor of 2.5 and a shift of the location of the maximum of the peak (～100 meV) to the longer-wavelength region were observed up to room temperature. It is established that as the molar fraction of Sb and the thickness of the InGaAs layer increase, the energy of the fundamental transition decreases by a factor of 140 meV compared with the GaAsSb/InGaAs/GaAs structure with a lower Sb content and a smaller thickness of the InGaAs layer. At 300 K, the emission wavelength of such a structure was 1.18 μm. In addition, an increase in the thickness of the InGaAs layer led to an increase in the room-temperature photoluminescence intensity by a factor of 60, which is associated with a decrease in the energy of the fundamental state for electrons in the InGaAs layer and, consequently, to larger electron localization and smaller temperature quenching of photoluminescence.     

Influence of the control mode on overlapping commutation of thyristors in a series inverter†

The paper describes the effects of changes in the triggering frequency on the maximum working frequency of a series inverter. Inverters differ in the type of load and in the mutual coupling existing between two commutation inductors in the circuit. It has been shown that the transient state is a result of changes in thyristor commutation from natural or critical to overlapping, and is dependent on the mode of change of the triggering frequency. The region of overlapping commutation has been determined by using two types of frequency change: fast (by keying modulation) and slow (by frequency modulation). The results show that slow changes in thyristor commutation permit a higher maximum working frequency than do fast changes. The region of overlapping commutation of thyristors is defined by new limit curves. The results may, for example, be applied in the design of an ultrasonic generator operating with frequency modulation.     

Analysis of the Effect of Spacer Layers on Nonlinear Distortions of the Current–Voltage Characteristics of GaAlAs/InGaAs pHEMTs

Semiconductors - The paper presents the results of modeling the electrophysical parameters of AlGaAs/InGaAs/GaAs pseudomorphic high electron mobility transistor (pHEMT) structures via...     

A voltage mode buck DC–DC converter with automatic PWM/PSM mode switching by detecting the transient inductor current

This paper presents a voltage mode buck DC–DC converter that integrates pulse-width modulation (PWM) and pulse-skipping modulation (PSM) to achieve high efficiency under heavy and light load conditions, respectively. Automatic mode-switching is implemented simply by detecting the voltage drop of high-side power switch when it is on, which indicates the transient current flowing through the inductor. Unlike other methods based on average current sensing, the proposed auto-mode switching scheme is implemented based on voltage comparison and simple control logic circuit. In order to avoid unstable mode switching near the load condition boundary, the mode switching threshold voltage is set differently in PWM and PSM mode. Besides, a 16-cycle counter is also used to ensure correct detection of the change in the load condition and fast response of the converter. In addition, a dual-path error amplifier with clamp circuit is also adopted to realize loop compensation and ensure 100 % duty cycle operation. Fabricated in a 0.18-μm standard CMOS technology, the DC–DC converter is able to operate under supply voltage from 2.8 to 5.5 V with 3-MHz clock frequency. Measurement results show that the converter achieves a peak efficiency of 93 %, and an output voltage ripple of less than 40 mV, while the chip area is 1.02 mm².     

Anomalous dispersion, differential gain, and dispersion of the α-factor in InGaAs/AlGaAs/GaAs strained quantum-well semiconductor lasers

A new procedure for the experimental determination of the differential gain and dispersion of the amplitude-phase coupling coefficient in semiconductor injection lasers was proposed and implemented. The α-factor and differential gain for InGaAs/AlGaAs/GaAs single quantum well (QW) semiconductor lasers were determined using this procedure in a wide spectral range (from 957 to 996 nm) at various pumping current densities (from 280 to 850 A/cm²). The factor which characterizes the dispersion of the group velocity and restricts the minimum duration of the lasing pulse at the level of 10^?13 s was experimentally determined for InGaAs lasers for the first time.     

Specific Features of the Current–Voltage Characteristics of p–nStructures with an Interfacial Layer in the Base Region

An analytical expression for the current–voltage characteristic of a p–nstructure with an interfacial layer in the base region was derived. Conditions under which the interfacial layer leads to an increase in the saturation current and the reverse current becomes bias-dependent are considered.