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A physical model-based simulation is conducted to investigate the design of an efficient high-speed quantum-well waveguide-photodetector (WGPD). The WGPD structure is optimized in terms of photoabsorber thickness, i-region thickness, cladding doping and thickness. The carrier transit-time and device capacitance effect are reduced for a WGPD by employing a ≤ 50 nm thin-photoabsorber in a 0.66 μ m thick i-region design. A three-fold improvement in responsivity up to 0.82 A/W is obtained by using two graded-index layers. The accurately positioned TPA layer in a thick i-region can provide up to 50 % increase in bandwidth of 65 GHz for a 25 μ m long WGPD. The optimized WGPD design can achieve 3-dB bandwidth over 80 and 50 GHz for 25 and 50 μ m long WGPD, respectively. The device satisfies the requirements of high-speed, low dark current, high responsivity, and integration capabilities, which is an essential prerequisite for high-performance detectors in future optical communication systems. [ABSTRACT FROM AUTHOR]

Surface plasmon (SP)-enhanced quantum-well (QW) LEDs have proved their potential in replacing conventional lighting devices for their high-performance capabilities in ultraviolet (UV), blue and green spectral ranges. The SP-enhanced QW-LEDs have applications in light emission enhancement, light polarization, color conversion, and speed modulation. The electric field of the plasmonic mode of a metal couples with the exciton energy of QWs in resonance results in efficiency enhancement to several folds. The strength of the SP–QW coupling is mainly influenced by the type of metal used for SP enhancement, the metal nanostructure geometry, and the penetration depth of the SP fringing field in the p-GaN. The use of an appropriate dielectric interlayer between the metal and the p-GaN allows further control over SP resonance with QW emission wavelength. The penetration depth defines the p-GaN thickness and the QW period number for effective SP–QW coupling. The optimization of these parameters is key to achieve high efficiencies in SP-enhanced QW-LEDs for various applications. This review explains the SP enhancement mechanism and the key challenges facing the SP enhancement of QW-LEDs. The main factors that affect the SP–QW coupling have been explained in detail based on recent reports devoted to this field.

Abstract Opto-electronic properties of excitons under parallel and perpendicular magnetic field are investigated on various thickness of GaAs/AlGaAs quantum well. An analytical expression of diamagnetic energy under a parallel magnetic field is derived by solving the Schrödinger equation of exciton in quantum wells. The transformation underlying the solution of Schrödinger equation suggests that an in-plane separation between electron and hole may increase with an increasing parallel magnetic field, leading to a reduced coulomb interaction and slow radiative recombination rate. As a consequence of this, even in the absence of an external electrical bias, parallel magnetic field induces a chiral charge transportation across the hetero-interfaces of a quantum well, which gives rise to an increasing in-plane magneto-photovoltage signal. The present investigation provides a unique method to control the recombination and transportation of charges by the strength and orientation of a magnetic field. [ABSTRACT FROM AUTHOR]

A low threshold current density of 2 μm InGaAsSb/AlGaAsSb muti-quantum well (MQW) laser diode with carrier blocking layer (CBL) is demonstrated by simulation and fabrication. The carrier leakage is found to be theoretically suppressed for the devices with CBL. All the laser wafers are grown with a solid source Molecular Beam Epitaxy(MBE) System. Experimental results reveal the samples with CBL exhibits ultra-low threshold current densities of 142 A/cm2 and high slope efficiency of 0.158 W/A, which is better than 215 A/cm2 and 0.122 W/A achieved in the conventional InGaAsSb/AlGaAsSb LDs at room temperature. This improvement in device performance comes from meticulously designing the carrier blocking layers to increase carrier confinement and injection efficiency. [ABSTRACT FROM AUTHOR]

The on-center shallow-donor impurity binding energy in lattice matched InP/In 0.53 Ga 0.47 As square quantum well structure have been theoretically investigated using effective mass and variational techniques. The effects of hydrostatic pressure, temperature and well width has been calculated and the results are discussed. [ABSTRACT FROM AUTHOR]

The development of pixel arrays close to the interaction point in large detector systems used in high energy physics require high radiation hardness for the pixels and their readout. A pixel device based on a quantum well, called the DoTPiX uses a sensing n-channel MOS device with a control gate. A buried Ge layer acts as a current modulation gate, which localize holes generated by impinging particles. The DotPIX buried Ge gate is obtained by low temperature epitaxial growth of Ge on Si. We have started to study the different ways to achieve these prerequisites: the need for a low temperature budget to reduce the Ge and Si intermixing, which may be detrimental to the DoTPiX operation. The use of Si thermal oxide is investigated together with that of deposited oxide (Hafnium Oxide for example), which differs from the Silicon Dioxide. The possibility of a combination of thermal silicon dioxide and deposited oxides opens another possibility in this study. [ABSTRACT FROM AUTHOR]

Within the framework of the effective mass approximation, an excited electron is studied in a cadmium sulfide (CdS) quantum well with varying well widths. The envelope function approximation is employed involving a three parameter variational calculation wherein one of these parameters is the distance between the electron and the hole. The relative change in the electron's energy (relative to its energy when it is in the valence band; in the hole) is investigated as a function of the electron–hole distance. Results from numerical calculations are presented and the non-linear behavior of different sized CdS quantum wells are discussed. Comparisons between experimentally measured CdS band gap energies (as a function of well-width) and the simulation data are made. A good agreement between the current model and experimental data exists. Density functional theory (DFT) calculations are done on crystallites of extremely small sizes to compare the current model's bandgap energies to DFT-predicted bandgap values at these extremes. [ABSTRACT FROM AUTHOR]

An ion-sensitive field-effect transistor (ISFET) with improved sensing current and voltage sensitivity is realized by using a sSi/Si 0.5 Ge 0.5 /sSOI quantum-well (QW) heterostructure and an Al 2 O 3 dielectric layer as sensing membrane coupling with the back-gate. The voltage sensitivity is much higher than the reference SOI ISFET, typically at low drain current due to the high hole mobility confined in the SiGe QW. A high voltage sensitivity 360 mV/pH with a linearity of 99.89% was achieved for QW ISFET. The results of the planar QW ISFET show great potential for low cost, real-time monitoring of bio-chemicals due to its simplified process. [ABSTRACT FROM AUTHOR]

We have calculated the ground state binding energy using variational methods and the effective mass approximation for the hydrogenic impurity in square quantum well structure made up of GaAs/InGaAs/GaAs epilayers under the action of hydrostatic pressure and temperature for different well widths and barrier heights. The effects of the variation of hydrostatic pressure and temperature can be summarized as follows; impurity binding energy is a negligibly decreasing function of temperature for fixed pressure and is an increasing function of pressure for fixed temperature. [ABSTRACT FROM AUTHOR]

A high-κ/metal-gate (HKMG) last process for fabricating strained Si 0.5 Ge 0.5 quantum-well (QW) p-channel metal oxide semiconductor field effect transistors (p-MOSFETs) is presented. Because the HKMG was formed after the ion-implant doping activation process, the thermal budget issue could be mitigated. The transistor features good transfer and output characteristics with I on / I off ratio up to 10 6 and threshold voltage ( V T ) down to 0.1 V. The effective hole mobility of the SiGe QW transistor reaches 215 cm 2 /V s for strong inversion conditions, which is 2.74 times the SOI device’s hole mobility. [ABSTRACT FROM AUTHOR]

Highlights: [•] We investigated several effects on hole mobility of quantum-well p-MOSFETs. [•] The Si cap layer improves the hole mobility by suppressing the scattering. [•] High strain in SiGe reduces hole mobilities as enhancing the Ge interdiffusion. [•] Hole mobility is dominated by Coulomb scattering at low temperatures. [ABSTRACT FROM AUTHOR]

Drift-diffusion computer simulation model available in Synopsys' Sentaurus TCAD User Guide is used to study electrical and optical characteristics of a separate-confinement heterostructure laser based on AlGaAs. We investigate the role of the width and depth of quantum-well active region, below and above the lasing threshold. The device properties depend on both, the number of bound quantum-well states and on closeness of the highest bound states to conduction or valence band offset. The lasing action may not exist at certain widths or depths of quantum-well, and the threshold current is a discontinuous function of these parameters, at such values of quantum-well width or depth when the highest quantum-well bound states cross conduction or valence band energy offset. The effects are more pronounced at low temperatures. Discontinuities in characteristics are found, at certain conditions, in temperature dependences as well. The carriers scattering time on quantum-well is shown to have a crucial role for the amplitude of discontinuities of these characteristics. The current below the lasing threshold and the threshold current density itself decrease with an increase of quantum-well scattering times and the amplitude of discontinuities decreases then as well. [ABSTRACT FROM AUTHOR]

In this paper, a double quantum-well nanotube tunneling field-effect transistor is introduced. In order to provide higher scalability, we utilize the core-shell gate architecture. The dominant transport mechanism in our device is in-line tunneling of charge carriers from a germanium source region to two silicon quantum-wells, which are located at the opposite sides of the source and separately controlled by the gates. We show that the fabrication process flow of the proposed device is CMOS-technology compatible. A numerical device simulator, that is calibrated to measured data of a fabricated Ge-source NW TFET, is employed to realistically investigate the switching and analog characteristics of the device. According to the obtained results, our device exhibits an I on / I off ratio of 2.85 × 109, an on-state current of 38.73 μA/μm, a minimum subthreshold swing of 2mV/dec, and a cut-off frequency of 44.7 GHz. We also show that with a slight modification of the device structure, in exchange for a negligible reduction of on-state current, the I on / I off ratio can reach to ∼1011 and ambipolarity vanishes considerably. [ABSTRACT FROM AUTHOR]

In this paper we present a physical modeling and simulation result of an optical memory cell based on a semiconductor quantum-dot in quantum-well hybrid structure. The physical modeling and simulation were done in Crosslight Apsys software which offers advanced models for photoelectric devices. We have optimized the scan conditions, iterative algorithm and other simulation parameters in order to obtain a solution. The calculated I-V and C-V curves agree with the experimental results and demonstrate that the cell can be used for photon storage. [ABSTRACT FROM AUTHOR]

Abstract: Quantum-wells and quantum dots and related semiconductor nanostructures have been widely investigated for infrared devices. Here we propose a new general approach to make use of polar optical phonons in quantum-wells for infrared (IR) and terahertz (THz) detection. As the first example, we show the coupling of phonon and intersubband transition leading to Fano resonance in photocurrent spectra. We investigate the phenomenon experimentally in specially designed GaAs/AlGaAs quantum-well infrared photodetectors. Finally, we discuss the future research and potentials. [Copyright &y& Elsevier]

The Authors report an analytical model to investigate optoelectronic characteristics reliance of a Transistor Laser on Quantum Well Location. Using simulated base recombination lifetime, optical frequency response for different quantum-well locations extracted. Slipping the well towards the collector, improves the optical bandwidth where a maximum of ≈54 GHz is observed. No resonance peak, limiting factor in diode lasers, is occurred in this enhancement method. Analyzing current gain ( β) as a function of the quantum well location, exhibits a decrease in β when the well moved in the direction of the collector so that a trade-off between optical and electrical properties of transistor laser is evident. The trade-off is utilized in conjunction with previously reported experimental researches to find an optimum place of quantum well for desired performance. [ABSTRACT FROM AUTHOR]

Abstract: Sustaining Moore’s Law of doubling CMOS transistor density every twenty four months will require not only shrinking the transistor dimensions, but also introduction of new materials and new device architectures to achieve the highest performance per watt of power dissipation. Compound semiconductor-based quantum-well field effect transistors have recently emerged as a promising transistor option for future ultra low-power logic applications. This paper reviews the opportunities and challenges in this exciting field of research. [Copyright &y& Elsevier]

Abstract: We have modeled the effect of compositional interdiffusion on the optical properties of GaSb/AlGaSb and InGaAsSb/AlGaAsSb quantum-well structures grown on GaSb substrate. Blue shifts of emission wavelength as large as 270 nm and 700 nm are predicted from a 6 nm wide interdiffused GaSb/AlGaSb quantum-well for a diffusion length of 3 nm, and from a 10 nm wide interdiffused InGaAsSb/AlGaAsSb quantum-well for a diffusion length of 5 nm, respectively. The effects of the as-grown quantum-well width and applied electric field on the emission wavelength and their relationship to the interdiffusion are also investigated. [Copyright &y& Elsevier]

Abstract: In this study, a single, simple and an accurate computer-aided design model is developed in order to obtain the injection level dependence of the critical quantities of broad-area (with a width of 50μm or more) InGaAs deep quantum-well (QW) lasers. Each of these quantities (gain, refractive index variation, and alpha (α) parameter) requires lengthy mathematical calculations with the use of different theories, assumptions, approximations, and estimations of some parameter values. The model is based on artificial neural network (ANN) approach that the total computational time is in the order of microseconds for the whole quantities in order to get their accurate values. The results are in very good agreement with the previously obtained results from an InGaAs deep QW laser sample. [Copyright &y& Elsevier]

Abstract: Confined optical phonons are discussed for a semiconductor quantum-well based on Si/Ge by using a theory developed some years ago. In the present treatment this theory is adapted to a nonpolar material and generalized to the case when the phonon dispersion law involves both linear and quadratic terms in the wave vector. We apply a continuous medium model leading to a system of coupled differential equations describing oscillations of mixed nature. The solutions of the fundamental equations are found by taking advantage of analogous works on the subject. We are thus led to a description of long wavelength optical phonons allowing close comparisons with both experimental data and calculations along atomistic models. Dependence of the phonon frequency on the wave vector, the phonon dispersion curves, are discussed in detailed form considering two different matching approximations: the complete and the incomplete matching problems. [Copyright &y& Elsevier]

Abstract: TlGaAs/GaAs multiple-quantum-well (MQW) structures were grown on GaAs substrates at a substrate temperature of 190°C by molecular-beam epitaxy. The MQW structures were intended to consist of four identical TlGaAs wells, each of which is sandwiched by GaAs barrier layers. X-ray diffraction was used to investigate the limits to Tl content and thickness of the TlGaAs well layer for forming the MQW structures. Successful growth of TlGaAs/GaAs MQW structures having nominal Tl contents of 6, 8, and 9% was confirmed for the three different well thicknesses of about 15, 10, and 5nm, respectively, while further increase in Tl content resulted in failure in forming MQW structures. The bounds for forming the MQW structures are discussed in terms of the epitaxial thickness of TlGaAs. The effect of the MQW structures on retarding the formation of Tl droplets is pointed out. [Copyright &y& Elsevier]

We study the ferromagnetism in III-V diluted magnetic semiconductor (DMS) quantum-wells theoretically and numerically taking into account the occupation of multiple subbands by holes in quantum wells. Starting from the mean-field theory of carrier-induced ferromagnetism in III-V DMS along with the exchange-correlation interaction of holes within the local spin density approximation, we found that the ferromagnetic transition temperature Tc of DMS quantum-wells exhibits step-function-like dependence on the hole density, reflecting the quasi-two-dimensional nature of systems. Moreover, the temperature dependence of the spin polarization shows quite distinct characteristics depending on the hole density. [ABSTRACT FROM AUTHOR]

The value of the α (Alpha) parameter, which is also called Linewidth enhancement factor, is particularly important in optical communication systems. This paper presents a new approach based on artificial neural networks (ANNs) to determine the α parameter for different number of quantum-wells (QWs). ANNs are trained in different structures with the use of five learning algorithms to obtain better performance and faster error convergence. The Levenberg–Marquardt (LM) algorithm, which has a quadratic speed of convergence, gives the best result among other learning algorithms used in the analysis. Both the training and the test results are in very good agreement with the experimental results reported elsewhere. [Copyright &y& Elsevier]

Abstract: In this paper, the effects of hydrostatic stress on the density of donor impurity states and donor-related optical absorption spectra in a GaAs–Ga1− x Al x As quantum wells are obtained. We calculate the shallow-donor binding energy for different well widths and different values of hydrostatic stress. We find that for large well widths the binding energy increases slowly with hydrostatic stress, as opposed to the behavior of the binding energy for wells with small width. One of the results shows that the binding energy does not change appreciably with the impurity position when the width of the well is small and the hydrostatic stress is high. Two structures in both, the density of states and the optical absorption spectra, associated with impurities located close to the center and to the edges of the structure, are obtained. We have also observed that the density of states and the optical absorption spectra depend strongly on the applied hydrostatic stress. [Copyright &y& Elsevier]

Ferromagnetism in III–V diluted magnetic semiconductor (DMS) quantum wells is studied theoretically paying special attention to the occupation of multiple subbands by holes and the effect of static electric field perpendicular to the well plane. Our calculations show that the ferromagnetic transition temperature Tc of DMS quantum-well exhibits step-function-like dependence on the carrier concentration, reflecting the quasi-two-dimensional nature of systems. The Tc can be sensitively controlled by the application of electric field when the hole density is small so as to occupy only a few subbands. [Copyright &y& Elsevier]

A previous theory for studying the distribution of non-uniform fields in multiple-quantum-well photodetectors under an ac voltage is generalized by including non-adiabatic space-charge-field effects. Numerical calculations indicate that field-domain effects are only important at high temperatures or high voltages when both injection and sequential-tunneling currents are significant. On the other hand, it is found that the non-adiabatic effects included in this generalized theory become significant at low temperatures and low voltages when field-domain effects are negligible. In order to explain the non-adiabatic charge-density fluctuations quantum-statistically, a non-adiabatic differential equation is derived based on the self-consistent Hartree model by using a shifted Fermi–Dirac model for the local fluctuation of electron distributions. The non-adiabatic effect is found to cause an “equilibrium” state variation with time under an ac voltage. [Copyright &y& Elsevier]

A new kind of single-quantum-well electroluminescent (EL) device consists of a hole transport N,N-Bis(3-methyphenyl)-N,N-diphenylbenzidine(TPD) layer, and electron transport 8-(quinolinolate)-aluminum(Alq) layer and a light emitting layer of Alq doped with 5,6,11,12-tetraphenylnaphthacene (rubrene) has been fabricated by the multisource-type high-vaccum organic molecular deposition. The dopant rubrene is as a potential well, and the undoped Alq layer is as a barrier layer. The EL spectra shows the spectral narrowing and the emission peak energy blue-shift, and the efficiency and luminance of the device have been significantly improved. The experimental phenomena is explained as the result of recombination of carriers from the quantized energy state. [ABSTRACT FROM AUTHOR]

Surface plasmon (SP)-enhanced quantum-well (QW) LEDs have proved their potential in replacing conventional lighting devices for their high-performance capabilities in ultraviolet (UV), blue and green spectral ranges. The SP-enhanced QW-LEDs have applications in light emission enhancement, light polarization, color conversion, and speed modulation. The electric field of the plasmonic mode of a metal couples with the exciton energy of QWs in resonance results in efficiency enhancement to several folds. The strength of the SP–QW coupling is mainly influenced by the type of metal used for SP enhancement, the metal nanostructure geometry, and the penetration depth of the SP fringing field in the p-GaN. The use of an appropriate dielectric interlayer between the metal and the p-GaN allows further control over SP resonance with QW emission wavelength. The penetration depth defines the p-GaN thickness and the QW period number for effective SP–QW coupling. The optimization of these parameters is key to achieve high efficiencies in SP-enhanced QW-LEDs for various applications. This review explains the SP enhancement mechanism and the key challenges facing the SP enhancement of QW-LEDs. The main factors that affect the SP–QW coupling have been explained in detail based on recent reports devoted to this field. [ABSTRACT FROM AUTHOR]

In this paper, we present an InGaAs/GaAs strain QW laser with tilted waveguide emitting at 1054 nm that has been fabricated by Metal-Organic Chemical-Vapor Deposition (MOCVD) on a GaAs substrate. The active region consists of 6 nm QW separated by a 60-nm barrier within a two-step graded-index separated-confinement heterostructure (GRINSCH) region. The use of a Strained Buffer Layer (SBL) is shown to significantly improve the laser performance. The composition and micro-structure quality of the QW was measured by high-resolution X-ray diffraction. The strain QW laser exhibits a threshold current of 9 mA and a slope efficiency of 0.4 W/A (unused antireflection coating on the facets). Stable fundamental transverse mode operation was obtained up to 33 mW emitted power at an injection current of 100 mA. The spectral width of the strain QW laser is 1.6 nm at an injection current of 50 mA. [ABSTRACT FROM AUTHOR]

An efficient and useful method for the incorporation of colloidal quantum dots (QDs) into ionic matrices is demonstrated. We prepared three different synthesis methods, which are traditional saturated-salt water, methanol-assisted, and ethanol-assisted methods. The continuous thermal and photonic stress tests indicate that the high temperature, instead of photonic excitation stress, is more detrimental to the illumination capability of the quantum dots. While the traditional saturated-salt water synthesis and methanol-assisted method are quite effective in low temperature and low photon excitation intensity, the quantum dots sealed by the ethanol-assisted method cannot hold under all conditions. An over-1000-h aging test can provide crucial information for the longevity of these quantum dots, and more than 10,000 h of lifetime can be expected. [ABSTRACT FROM AUTHOR]

Alterations of device characteristics as a result of γ-ray irradiation of quantum well lasers are different from those of heterostructure bulk lasers with respect to optical emission properties. We propose that these irradiation effects may be caused by structural changes in the quantum layers, due to an atomic displacement and migration between layers and due to changes in the degree of strain between the layers. This affects the layers’ atomic composition, which changes the band-gap energy levels and the refraction indexes, and, as a result, the carrier and optical confinements, respectively. The changes in optical radiation characteristics brought about by γ-ray irradiation are desirable ones for utilization in most optical fiber communication systems. [Copyright &y& Elsevier]