Search

Two-dimensional (2D)/three-dimensional (3D) halide perovskite heterostructures have been extensively studied for their ability to combine the outstanding long-term stability of 2D perovskites with the superb optoelectronic properties of 3D perovskites. While current studies mostly focus on vertically stacked 2D/3D perovskite heterostructures, a theoretical understanding regarding the optoelectronic properties of 2D/3D perovskite lateral heterostructures is still lacking. Herein, we construct a series of 2D/3D perovskite lateral heterostructures to study their optoelectronic properties and interfacial charge transfer using density functional theory (DFT) calculations. We find that the band alignments of 2D/3D heterostructures can be regulated by varying the quantum-well thickness of 2D perovskites. Moreover, decreasing the 2D component ratio in 2D/3D heterostructures can be favorable to form type-I band alignment, whereas a large component ratio of 2D perovskites tends to form type-II band alignment. We can improve the amount of charge transfer at the 2D/3D perovskite interfaces and the light absorption of 2D perovskites by increasing quantum-well thickness. These present findings can provide a clear designing principle for achieving 3D/2D perovskite lateral heterostructures with tunable optoelectronic properties. [ABSTRACT FROM AUTHOR]

The high built-in polarization field is a fingerprint of III-nitride heterostructures. Alloy composition and doping profile significantly affect the magnitude of the electric field present in subsequent layers, but the sign of the electric field is usually defined by substrate polarity and external bias. Here, we propose to utilize acceptor and donor doping concentrations exceeding 1020 cm−3 to obtain a high junction field that can solely abolish built-in polarization for a polar (0001) InGaN/GaN quantum well (QW). We have used photoluminescence (PL), time-resolved PL (TRPL), and contactless electroreflectance in order to gain insight into the strength of the electric field present in the grown heterostructures. Good match between expected and measured electric field values was obtained. A dramatic decrease in the luminescence lifetime for a flat QW was confirmed using TRPL. The presented results open a way to realize devices that profit from the low built-in field, like photodetectors, using abundant polar substrates. [ABSTRACT FROM AUTHOR]

HgTe has been considered to be one of the most versatile topological materials. Depending on the in‐plane strain, Weyl and Dirac semi‐metal, as well as topological insulator phases, are feasible. Here, for the first time it is reported, that an InAs:S substrate promotes an initial 2D growth of a ZnTe thin layer and subsequent high crystalline quality ZnTe/CdTe superlattices serve as a smooth and continuous virtual substrate for the growth of (Cd,Hg)Te/HgTe/(Cd,Hg)Te heterostructures with unstrained quantum well HgTe (topological insulator) and compressively strained bulk HgTe (Weyl semimetal) by molecular beam epitaxy. Compared with the superlattices previously grown on GaAs substrates, the quantum well and bulk heterostructures exhibit homogeneous surfaces with root mean square roughnesses of 0.88–0.93 nm, which is three times lower than those observed for 3D islands (2.7–3.4 nm) on GaAs substrates. Additionally, magnetotransport measurements confirm high electronic quality and demonstrate that the S‐doped InAs substrate can be used as an effective back gate. These results manifest a (big) step forward toward the improvement of micro‐ and nanometer‐sized top‐ and back‐gated device fabrication on topological materials. [ABSTRACT FROM AUTHOR]

The misfit dislocation formation related to plastic strain relaxation in Si or Ge quantum well layers in SiGe heterostructures for spin qubits tends to negatively affect the qubit behaviors. Therefore, it is essential to understand and then suppress the misfit dislocation formation in the quantum well layers in order to achieve high-performance qubits. In this work, we studied the misfit dislocation propagation kinetics and interactions by annealing the strained Si or Ge layers grown by molecular beam epitaxy. The annealing temperatures are from 500 to 600 °C for Si layers and from 300 to 400 °C for Ge layers. The misfit dislocations were investigated by electron channeling contrast imaging. Our results show that the misfit dislocation propagation is a thermally activated process. Alongside, the blocking and unblocking interactions during misfit dislocations were also observed. The blocking interactions will reduce the strain relaxation according to theoretical calculation. These observations imply that it is possible to suppress the misfit dislocation formation kinetically by reducing the temperatures during the SiGe heterostructure epitaxy and post-epitaxy processes for developing well-functional SiGe-based spin qubits. [ABSTRACT FROM AUTHOR]

An isotopically enriched 28Si/SiGe undoped heterostructure is a promising platform for Si-based qubits due to the long coherence time by reducing 29Si isotopes with non-zero nuclear spins. Carriers in the buried Si quantum well (QW) of the Si/SiGe heterostructures could tunnel to the oxide/Si interface, increasing charge noise and leading to charge instability. In this work, we investigate the tunneling effects on carrier distribution and transport properties in an isotopically enriched 28Si/SiGe undoped heterostructure and its transient characteristics by controlling the hold time of gate biasing under different drain biases. By holding the gate bias for a longer time, the drain is reduced since more carriers in the buried QW tunnel to the oxide interface. Furthermore, under a larger drain bias, more carriers can move across the Si/SiGe heterojunction to the oxide interface and are trapped, resulting in a stronger current reduction, which is explained by a lucky electron model. [ABSTRACT FROM AUTHOR]

In this work, the dependence of the oscillation of the combined density of states on a strong magnetic field in heterostructures based on a rectangular quantum well is studied. The effect of a quantizing magnetic field on the temperature dependence of the combined density of states in nanoscale straight-band heterostructures is investigated. A new mathematical model has been developed for calculating the temperature dependence of the two-dimensional combined density of quantum well states in quantizing magnetic fields. The proposed model explains the experimental results in nanoscale straight-band semiconductors with a parabolic dispersion law. [ABSTRACT FROM AUTHOR]

The introduction of selective area growth (SAG) in a mature semi‐insulating buried heterostructure (SIBH) platform for the realization of photonic integrated circuits on monolithic InP has been demonstrated. A thorough determination of the relations between quantum well thickness, transition energies, and mask geometries is performed on dedicated wafers by means of extensive micro‐X‐Ray diffraction and microphotoluminescence measurements. Based on those results, SAG is used to grow, with a single epitaxy step, AlGaInAs multiple quantum wells heterostructures, to tailor the active regions of Fabry–Pérot and distributed feedback (DFB) lasers emitting in the O‐Band. SIBH DFB lasers are realized, exhibiting threshold currents < 7.2 mA (at 25 °C), and emitting over 100‐nm spectral range in the O‐Band. [ABSTRACT FROM AUTHOR]

In this work, the influence of two-dimensional state density on oscillations of transverse electrical conductivity in heterostructures with rectangular quantum wells is investigated. A new analytical expression is derived for calculating the temperature dependence of the transverse electrical conductivity oscillation and the magnetoresistance of a quantum well. For the first time, a mechanism has been developed for oscillating the transverse electrical conductivity and magnetoresistance of a quantum well from the first-order derivative of the magnetic field (differential) ∂ (ρ ⊥ 2 d (E , B , T , d)) ∂ B at low temperatures and weak magnetic fields. The oscillations of electrical conductivity and magnetoresistance of a narrow-band quantum well with a nonparabolic dispersion law are investigated. The proposed theory investigated the results of experiments of a narrow-band quantum well (InxGa 1 − x Sb). [ABSTRACT FROM AUTHOR]

Engineering conduction-band valley couplings is a key challenge for Si-based spin qubits. Recent work has shown that the most reliable method for enhancing valley couplings entails adding Ge concentration oscillations to the quantum well. However, ultrashort oscillation periods are difficult to grow, while long oscillation periods do not provide useful improvements. Here, we show that the main benefits of short-wavelength oscillations can be achieved in long-wavelength structures through a second-order coupling process involving Brillouin-zone folding induced by shear strain. We finally show that such strain can be achieved through common fabrication techniques, making this an exceptionally promising system for scalable quantum computing. [ABSTRACT FROM AUTHOR]

A parabolic potential that confines charge carriers along the growth direction of quantum wells semiconductor systems is characterized by a single resonance frequency, associated to intersubband transitions. Motivated by fascinating quantum optics applications leveraging on this property, we use the technologically relevant SiGe material system to design, grow, and characterize n-type doped parabolic quantum wells realized by continuously grading Ge-rich Si1−xGex alloys, deposited on silicon wafers. An extensive structural analysis highlights the capability of the ultra-high-vacuum chemical vapor deposition technique here used to precisely control the quadratic confining potential and the target doping profile. The absorption spectrum, measured by means of Fourier transform infrared spectroscopy, revealed a single peak with a full width at half maximum at low and room temperature of about 2 and 5 meV, respectively, associated to degenerate intersubband transitions. The energy of the absorption resonance scales with the inverse of the well width, covering the 2.5–5 THz spectral range, and is almost independent of temperature and doping, as predicted for a parabolic confining potential. On the basis of these results, we discuss the perspective observation of THz strong light–matter coupling in this silicon compatible material system, leveraging on intersubband transitions embedded in all-semiconductor microcavities. [ABSTRACT FROM AUTHOR]

The influence of AlGaAsP, GaAsP and AlGaAs/GaAsP compensating layers on the optical quality of the active area based on InGaAs/GaAs quantum wells for LEDs emitting at a wavelength of 940 nm has been studied. Heterostructures with multiple quantum wells have been grown by MOVPE technique using various approaches to compensating structural stresses. An increase in photoluminescence intensity by more than 32% was demonstrated when using AlGaAs/GaAsP compensating layers. [ABSTRACT FROM AUTHOR]

In this work, the influence of light on the temperature dependence of transverse magnetoresistance oscillations is studied. A generalized mathematical expression that calculates the temperature and light dependence of the quasi-Fermi levels of small-scale p-type semiconductor structures in a quantizing magnetic field is derived. New analytical expressions have been found to represent the temperature dependence of transverse differential magnetoresistance oscillations in dark and light situations, taking into account the effect of light on the oscillations of the Fermi energy of small-scale semiconductor structures. A mathematical model has been developed that determines the light dependence of the second-order derivative of the transverse magnetoresistance oscillations of p-type semiconductors with quantum wells by magnetic field induction. A new theory is proposed, which explains the reasons for the significant shift of the differential magnetoresistance oscillations along the vertical axis measured in the experiment for dark and light conditions. [ABSTRACT FROM AUTHOR]

In order to shift the light emission of nitride quantum structures towards the red color, the technological problem of low In incorporation in InGaN−based heterostructures has to be solved. To overcome this problem, we consider superlattices grown on InGaN buffers with different In content. Based on the comparison of the calculated ab initio superlattice band gaps with the photoluminescence emission energies obtained from the measurements on the specially designed samples grown by metal-organic vapor phase epitaxy, it is shown that by changing the superlattice parameters and the composition of the buffer structures, the light emission can be shifted to lower energies by about 167 nm (0.72 eV) in comparison to the case of a similar type of superlattices grown on GaN substrate. The importance of using superlattices to achieve red emission and the critical role of the InGaN buffer are demonstrated. [ABSTRACT FROM AUTHOR]

The importance of the phonon bottleneck effect on the optoelectronic properties of organic-inorganic hybrid perovskites (OIHPs) has been well documented. While randomly distributed multiple quantum wells (MQWs) are frequently generated in 2D/3D perovskite heterostructures, the influence of MQWs formation in 2D/3D perovskite heterostructures on the phonon bottleneck effect is poorly understood. In this study, we construct 2D/3D perovskite heterostructures using 2D OIHP (NH3(CH2)8NH3PbI4, OdAPbI4) to passivate 3D OIHP (FAPbI3) and investigate their excitons and carrier dynamics by employing photoluminescence (PL) spectroscopy and femtosecond optical-pump terahertz-probe spectroscopy (fsOPTPS). We observe the formation of MQWs and establish a structure-dynamics-property relationship among the exciton formation time (TEF), the hot carrier cooling rate (kcool) and the effective charge-carrier mobility(ϕμ). The formation of MQWs could significantly invalidate the phonon bottleneck effect and modulate the optoelectronic properties of 2D/3D perovskite heterostructures. This work provides valuable information on the importance of band alignment and the phonon bottleneck effect in the strategy of 2D/3D perovskite heterostructures. [ABSTRACT FROM AUTHOR]

The low-temperature photoluminescence (PL) and PL excitation (PLE) spectra of two systems of CdTe quantum wells (QWs) separated by CdMnTe and CdMgTe barriers 20 nm thick are studied. The experimental PL spectra are compared with calculations that take into account the exciton effect and the influence of internal strains. The scatter of our data does not exceed that expected for monolayer fluctuations of the QW width. In the PLE spectra of a thick QW, bands were found that correspond to the increase of PL from a thick QW upon excitation of a neighbor narrow QW. The mechanism of energy transfer between QWs separated by thick barriers is discussed. [ABSTRACT FROM AUTHOR]

The influence of InGaAlAs waveguide composition on the photoluminescence and electroluminescence of 1550 nm spectral range heterostructures based on thin strained In0.74Ga0.26As quantum wells has been studied. An approach is proposed that allows based on the analysis of electroluminescence to carry out a comparative analysis of the deferential gain in fabricated laser diodes. It is shown that decrease of the molar fraction of aluminum in waveguide InGaAlAs layers matched in lattice constant with InP leads to falling of integrated photoluminescence intensity, however, laser diodes with In0.53Ga0.31Al0.16As waveguide layers demonstrate a higher differential gain compared to laser diodes with In0.53Ga0.27Al0.20As waveguide. [ABSTRACT FROM AUTHOR]

The ongoing miniaturization of semiconductor devices renders charge‐carrier transport along interfaces increasingly important. The characteristic length scales in state‐of‐the‐art semiconductor technology span only a few nanometers. Consequently, charge‐carrier transport inevitably occurs directly at interfaces between adjacent layers rather than being confined to a single material. Herein, charge‐carrier diffusion is systematically studied in prototypical active layer systems, namely, in type‐I direct‐gap quantum wells and in type‐II heterostructures. The impact of internal interfaces is revealed in detail as charge‐carrier diffusion takes place much closer to or even across the internal interfaces in type‐II heterostructures. Type‐I quantum wells and type‐II heterostructures exhibit comparable diffusion rates given similar inhomogeneous exciton linewidths. Consequently, the changes in the structural quality of the interfaces are responsible for changes in diffusion and charge‐carrier transport along interfaces rather than the existence of the interfaces themselves. [ABSTRACT FROM AUTHOR]

We present detailed theoretical analysis of nonradiative Auger recombination in narrow-gap mercury-cadmium-telluride quantum wells (HgCdTe QWs). We suggest a microscopic model to calculate Auger recombination rates in the QWs with different Cd fraction as functions of non-equilibrium carrier density with account to the complex band dispersions and wavefunctions, degenerate carrier statistics, and screening effects. Our model is validated by the comparison of measured photoconductivity kinetics with the simulated curves. Furthermore, we use the developed calculation technique to evaluate different designs of HgCdTe/CdHgTe QWs for the far-IR emitters. In particular, we consider a series of QWs with the fixed bandgap of 40 meV (lasing wavelength about 30 μm) and find out that lasing may be favored in the QWs with moderate (6%–9%) cadmium content and not in the pure binary HgTe QWs, which is in contrast to intuitive expectations within threshold energy concept for Auger recombination. Though cadmium-free QWs do provide the highest possible Auger threshold energies, Cd-containing QWs feature much more efficient screening of Coulomb potential (and so Auger interaction) by free charge carriers. The latter effect contributes decisively into the suppression of Auger processes at low temperatures and high carrier concentrations. [ABSTRACT FROM AUTHOR]

Carrier localization effects in III-N heterostructures are often studied in the frame of modified continuum-based models utilizing a single-band effective mass approximation. However, there exists no comparison between the results of a modified continuum model and atomistic calculations on the same underlying disordered energy landscape. We present a theoretical framework that establishes a connection between atomistic tight-binding theory and continuum-based electronic structure models, here a single-band effective mass approximation, and provide such a comparison for the electronic structure of (In,Ga)N quantum wells. In our approach, in principle, the effective masses are the only adjustable parameters since the confinement energy landscape is directly obtained from tight-binding theory. We find that the electronic structure calculated within effective mass approximation and the tight-binding model differ noticeably. However, at least in terms of energy eigenvalues, an improved agreement between the two methods can be achieved by adjusting the band offsets in the continuum model, enabling, therefore, a recipe for constructing a modified continuum model that gives a reasonable approximation of the tight-binding energies. Carrier localization characteristics for energetically low lying, strongly localized states differ, however, significantly from those obtained using the tight-binding model. For energetically higher lying, more delocalized states, good agreement may be achieved. Therefore, the atomistically motivated continuum-based single-band effective mass model established provides a good, computationally efficient alternative to fully atomistic investigations, at least at when targeting questions related to higher temperatures and carrier densities in (In,Ga)N systems. [ABSTRACT FROM AUTHOR]

By taking advantage of the GaAs (631) corrugation self-assembled on top of multi-quantum well heterostructure interfaces, the modulation of the confined state wave functions (eigenstates) has been achieved, attaining quasi-one-dimensional or fractional dimension eigenstates. Two different theoretical approaches were used to compute the energy shift of subband optical transitions as a function of the interface corrugation geometrical configuration. For large nominal quantum well widths and small corrugation amplitude, the perturbation theory was employed, while a modified Lanczos algorithm assisted us to calculate the shifts when the corrugation amplitude was comparable to the nominal quantum well width. Experimentally, the heterostructures were grown by molecular beam epitaxy on (001) and (631) oriented substrates, where the quasi-one-dimensional ordering was reached by changing the As to Ga molecular beam fluxes ratio. It was found that the corrugated interfaces (i) break the wave function's in-plane symmetry, allowing transitions that, in principle, must be forbidden and (ii) induce blue shifts or red shifts in the order of 10 meV to the energy spectrum of the quantum wires depending on the lateral and vertical periodicities, exhibiting the presence of a lateral confinement system. The main result is the effective modulation of eigenstates through the interface corrugation control. Additionally, it was found that the interface modulation effect is greater for harmonic (n > 1) heavy (and light) hole subbands than for the ground states. [ABSTRACT FROM AUTHOR]

The intriguing potential of III-V-N-Bi materials like InSbNBi can lead to pervasive research curiosity in the long wavelength infrared (LWIR) regime. In this article, we have explored numerous prospective possibilities of utilizing InSbNBi for optoelectronic applications using a 16 band k·p Hamiltonian. Considering the lattice-matched condition of InSbNBi with host InSb, we have anticipated the bandgap, spin–orbit coupling splitting energy (Δ SO ) and the corresponding operating wavelength of InSb0.9772N0.0028Bi0.02 as 68 meV, 0.824 eV, and around ∼18.23 μm, respectively. At room temperature, a wide range of selective bandgaps and related wavelengths ranging from 160 meV (∼8 μm) to 40 meV (∼30 μm) were obtained for Bi and N concentrations up to 2.5% and 0.35%, respectively. Co-incorporation of N and Bi results in ∼1.5 times reduction in the electron effective mass (0.0091 m0) compared to the host (0.014 m0), which further improves the optical gain of the InSbNBi/InSb quantum well system. The effect of both types of strain (compressive and tensile) on the InSbNBi/InSb system generated due to the deviation from the lattice matched ratio (0.14) of N and Bi offers interesting results. Along with a red shift in optical spectra, compressive strain (∼0.1%) offers a reduction in bandgap, electron effective mass, and enhancement in Δ SO by 44.7 meV, 0.0024 m0, and 12 meV, respectively. On the contrary, tensile strain (∼1.14%) increases the bandgap and the electron effective mass by 26.7 meV and 0.0066 m0, respectively, and reduces Δ SO by 219 meV. Nevertheless, tensile strain beyond 0.25% for a N concentration of 1.3% and fixed Bi concentration (1%) convert the InSbNBi/InSb heterostructure from a type I structure to a type II broken gap structure, which enables the possibility of realizing InSbNBi/InSb material for tunnel junction devices and the intermediate band solar cell along with the LWIR detector. [ABSTRACT FROM AUTHOR]

We studied the charge scattering mechanisms present in In0.2Al0.8Sb/InAs/Al0.8Ga0.2Sb wells placed in close proximity to the surface of the heterostructures, at depths from 7 nm to 15 nm. The heterostructures were either unintentionally doped, doped from below the channel, or from above the channel. Measurements of sheet and Hall resistances were performed at T = 2 K in a variable magnetic field and under illumination with wavelengths of 400 nm up to 1300 nm. The charge density dependencies of the Hall mobility and quantum scattering time were used to infer the dominant scattering mechanisms. We found that the surface proximity induces significant band bending and an asymmetric placement of the charge distribution in the well. The result is an increase in interface roughness scattering, which reduces the mobility and the quantum scattering time values. In addition, the quantum scattering time is sensitive to scattering off charged impurities, remote or close to the well. Top doping restores the band profile symmetry and improves the transport. A symmetric profile, however, lowers the expectations for a strong spin–orbit coupling and spintronic applications. [ABSTRACT FROM AUTHOR]

Type-II quantum well (QW) heterostructures based on the InAs/GaSb/AlSb material system have important applications in interband tunneling and midinfrared optoelectronic devices. From the perspective of interband tunneling conditions in widely used type-II QWs such as N-QW, W-QW, and M-QW structures, this work studies how energy levels for electronic and light-hole states are varied with various combinations of semiconductor material layers. Using a two-band model, analytical expressions are derived for the transition well widths that correspond to the critical layer thicknesses for bound- or quasibound states to appear in the interband tunneling region in type-II heterostructures, which provide meaningful connections to semiconductor material parameters. Calculations of transition well widths are carried out for several InAs/GaSb/AlSb-based type-II QW structures. The results and understanding gained from the study may be helpful in designing and developing midinfrared optoelectronic devices such as interband cascade lasers, photodetectors, and thermophotovoltaic cells. [ABSTRACT FROM AUTHOR]

We grow strained Ge/SiGe heterostructures by reduced-pressure chemical vapor deposition on 100 mm Ge wafers. The use of Ge wafers as substrates for epitaxy enables high-quality Ge-rich SiGe strain-relaxed buffers with a threading dislocation density of (6 ± 1) × 10 5 cm − 2 , nearly an order of magnitude improvement compared to control strain-relaxed buffers on Si wafers. The associated reduction in short-range scattering allows for a drastic improvement of the disorder properties of the two-dimensional hole gas, measured in several Ge/SiGe heterostructure field-effect transistors. We measure an average low percolation density of (1.22 ± 0.03) × 10 10 cm − 2 and an average maximum mobility of (3.4 ± 0.1) × 10 6 cm 2 / Vs and quantum mobility of (8.4 ± 0.5) × 10 4 cm 2 / Vs when the hole density in the quantum well is saturated to (1.65 ± 0.02) × 10 11 cm − 2 . We anticipate immediate application of these heterostructures for next-generation, higher-performance Ge spin-qubits, and their integration into larger quantum processors. [ABSTRACT FROM AUTHOR]

Lateral ambipolar diffusion in an InGaN/GaN single quantum well (SQW) structure grown on bulk GaN is studied by microphotoluminescence (μPL) investigations. The analysis is done via pinhole scans, that is, by decoupling the excitation area from the detection area and scanning the latter one. Knowing the size of the excited region, conclusions about the carrier transport in the in‐plane layer of the QW can be drawn. In this study, a diffusion length Ld up to 12 μm is observed at room temperature. Furthermore, the energy of the spectral peak is analyzed as a function of distance, showing a pronounced blueshift at the excitation center. An increase in distance to the injection region is accompanied by a redshift. The indication of peak energy is used to relate the drop of PL intensity with increasing radius to actual diffusion of charge carriers. In addition, temperature‐dependent studies of the diffusion behavior are done, covering the range between 10 K and room temperature. No significant change of diffusion length can be seen with temperature, indicating that temperature dependencies of carrier lifetime and of mobility compensate each other. [ABSTRACT FROM AUTHOR]

The paper presents the results of studying the nature of the energy levels of an electron in a quantum well of heterostructures AlAs/InxGa1−xAs/AlAs containing a thin InAs nanolayer. The dependences of these energy levels on the thickness En(b) of the InAs layer are analysed by numerical and analytical methods. An analytical formula for the dependence En(b) is obtained in the model of an infinitely deep well. The dependence of the energy levels on the thickness b of the InAs nanolayer found in the model of parabolic bands turned out to be strong and complex. In the model of nonparabolic bands, due to the growth of the electron mass with respect to energy, the number of energy levels in the well increased, and the En(b) dependences were noticeably suppressed. The nature and causes of these regularities are analysed. [ABSTRACT FROM AUTHOR]

Solid‐state‐based quantum technologies, such as electronic spin‐qubits, constitute a leading approach to the realization of quantum computation. Electronic spin‐qubits hosted in semiconductor heterostructures demand the highest crystalline quality, specifically with respect to the structure and formation of in‐plane misfit dislocations (MDs). Here, the formation mechanisms of MD networks in such Si/SiGe heterostructures are investigated. For this purpose, strained Si layers on relaxed Si0.7Ge0.3 with thicknesses above the critical thickness are grown by molecular beam epitaxy to allow for the formation of MDs. MDs are mapped out by electron channeling contrast imaging and the experimental results are compared to MD networks calculated by Monte Carlo simulations. The simulations show that the ratio between the threading dislocation density (TDD) and the average length of MDs is a constant for a given set of parameters, here 2.9 for sufficiently large dislocation statistics and simultaneous extension of MDs. Further, the fractal dimension of the MD network determined by the box‐counting method as an alternative quantity to characterize MD networks is introduced. This allows to infer the formation mechanism of MDs in real devices and hence the quantification of resulting average relaxation within the Si‐quantum well. [ABSTRACT FROM AUTHOR]

Group IV Ge1-xSnx alloy in bulk form and heterostructures using quantum wells (QWs) GeSn/SiGeSn pairs show promise for laser sources in recent years. In this paper, we present the design of transistor laser (TL) structure with a SiGeSn emitter, GeSn QW embedded in the SiGeSn base, and a GeSn collector grown on the top of 200 nm thick strain-relaxed GeSn buffer, compatible with current CMOS technology. The GeSn layer is assumed to have composition of x > 0.08 to achieve the direct band-gap nature. The lasing is examined in terms of minimum base threshold current and optimum lasing action obtained by using Ge 0.87 Sn 0.13 / Si 0.05 Ge 0.82 Sn 0.13 MQW TL structure. The performance of proposed structure is compared with the theoretical values of already reported GeSn TL and some of the experimental values of InGaAs TL. The proposed design reduces the lasing threshold base current to some extent (~ 1.133 mA) and enhances the modulation bandwidth upto ~ 75.9 GHz. [ABSTRACT FROM AUTHOR]

This paper reports an optimization scheme of type-II GaAsSb/InAs/InGaAs quantum wells using the six bands k · p method. By calculating the optical gain, the optimal structures of the quantum wells are obtained. We observed that without an electric field, the thickness values of symmetrical quantum wells designed by the AdaGrad algorithm are 2.97, 2.81, and 6.21 nm, respectively, and the gain intensity is 6489 cm−1 that is about 1600 cm−1 higher than the original empirical design scheme. The thickness of asymmetric quantum wells designed by the Adam algorithm is 5.56, 2.72, 1.88, 3.16, and 2.46 nm under the external electric field of 75 kV/cm, respectively, and the gain intensity is 5729 cm−1 that is about 2300 cm−1 higher than the original empirical design scheme. The optimized scheme effectively suppresses the gain attenuation caused by the electric field and is helpful to improve the performance of interband cascade lasers. [ABSTRACT FROM AUTHOR]

In this work, a new model has been developed for calculating the effect of a quantizing magnetic field on the temperature dependence of the two-dimensional combined density of states in direct-gap heterostructures with quantum wells. The temperature dependence of the oscillations of the two-dimensional combined density of states of the quantum well is explained by the thermal smearing of the Gaussian distribution function in a strong magnetic field. Based on the proposed new models, the Landau levels of charge carriers in a direct-gap quantum well are determined in a wide temperature range. The experimental results were interpreted using the oscillations of the combined density of states of the quantum well in a quantizing magnetic field. [ABSTRACT FROM AUTHOR]

Bandgap engineering and quantum confinement in semiconductor heterostructures provide the means to fine‐tune material response to electromagnetic fields and light in a wide range of the spectrum. Nonetheless, forming semiconductor heterostructures on lattice‐mismatched substrates is a challenge for several decades, leading to restrictions for device integration and the lack of efficient devices in important wavelength bands. Here, it is shown that the van der Waals epitaxy of 2D GaSe and InSe heterostructures occur on substrates with substantially different lattice parameters, namely silicon and sapphire. The GaSe/InSe heteroepitaxy is applied in the growth of quantum wells and superlattices presenting photoluminescence and absorption related to interband transitions. [ABSTRACT FROM AUTHOR]

This article describes GaN/AlN heterostructures for ultraviolet-C (UVC) emitters with multiple (up to 400 periods) two-dimensional (2D)-quantum disk/quantum well structures with the same GaN nominal thicknesses of 1.5 and 16 ML-thick AlN barrier layers, which were grown by plasma-assisted molecular-beam epitaxy in a wide range of gallium and activated nitrogen flux ratios (Ga/N2*) on c-sapphire substrates. An increase in the Ga/N2* ratio from 1.1 to 2.2 made it possible to change the 2D-topography of the structures due to a transition from the mixed spiral and 2D-nucleation growth to a purely spiral growth. As a result, the emission energy (wavelength) could be varied from 5.21 eV (238 nm) to 4.68 eV (265 nm) owing to the correspondingly increased carrier localization energy. Using electron-beam pumping with a maximum pulse current of 2 A at an electron energy of 12.5 keV, a maximum output optical power of 50 W was achieved for the 265 nm structure, while the structure emitting at 238 nm demonstrated a power of 10 W. [ABSTRACT FROM AUTHOR]

We report the growth of hexagonal boron gallium nitride alloys, h-GaxB1−xN, on hexagonal boron nitride (h-BN) templates by metalorganic chemical vapor deposition and the observation of the critical thickness (LC) phenomenon in the h-GaBN/BN heterostructure system. It was observed that GaxB1−xN alloys in a pure hexagonal phase can be obtained when the film thickness is below LC. X-ray diffraction (XRD) θ–2θ measurement results revealed the formation of separate wurtzite (w)-GaN domains within the h-GaBN matrix when the film thickness is beyond LC. XRD results were supported by photoluminescence spectroscopy which revealed the absence of the band edge emission of w-GaN near 3.4 eV in very thin layers, but an increase in the w-GaN band edge emission with an increase in the h-GaxB1−xN layer thickness beyond LC. Despite the fact that layered structured materials generally possess a weak interlayer interaction, our results revealed that phase separation still occurs in layered h-GaxB1−xN alloys and the critical thickness depends on the Ga composition. The present study also provided insights into possible ways to synthesize layered GaBN/BN heterostructures and quantum wells in the pure hexagonal phase with tunable bandgaps and optical properties, which would open up many new applications. [ABSTRACT FROM AUTHOR]

The frozen internal polarization-induced electric fields due to broken inversion symmetry in all conventional blue and green nitride semiconductor light-emitting semiconductor quantum well heterostructures point in a direction opposite to what is desired for efficient flow of electrons and holes. This state of affairs has persisted because of the desire to have p-type hole injectors on top of the quantum well active region. Because of the internal polarization fields in nitride heterostructures, there exist four permutations of doping and polarization for the realization of such light emitters. Which permutation is the most desirable for efficient light emission? In this work, we answer this question by demonstrating a fundamentally new approach toward efficient light emission with "bottom-tunnel junctions." The bottom-tunnel junction design aligns the polarization fields in the desired direction in the quantum well while simultaneously eliminating the need for p-type contacts and allowing efficient current spreading. By preventing electron overshoot past quantum wells, it disables carrier recombination in undesired regions of the quantized heterostructures and opens up the possibility for new geometries of integrating and stacking multiple light emitters. [ABSTRACT FROM AUTHOR]

The second-harmonic generation susceptibility is theoretically investigated based on the compact density-matrix formalism in two- and three-level AlGaN/GaN systems. The electronic states and their related wave functions were calculated by solving self-consistently the Schrödinger–Poisson equations within the effective mass and Hartree approximations. The presence of spontaneous and piezoelectric polarizations is taken into account in the modeling part. It was revealed from the relevant results that (i) the second-order susceptibility shows a multiple peak structure due to intersubband and their corresponding virtual transitions, (ii) the use of a back doping as well as the optimization of the layer widths in delta-doped AlGaN/GaN asymmetric quantum wells improved considerably the second-harmonic susceptibility, and (iii) the three-level AlGaN/GaN system is the most efficient structure, which generates the second-harmonic with a significant intensity up to 4.36 × 10−5 mV−1. Numerical results of the present work could lay the basis for research in AlGaN-related optoelectronic device applications. [ABSTRACT FROM AUTHOR]

Spin–orbit interaction and spin-relaxation mechanisms of a shallow InAs quantum well heterostructure are investigated by magnetoconductance measurements as a function of an applied top-gate voltage. The data are fit using a Iordanskii–Lyanda-Geller–Pikus model and two distinct transport regimes are identified. The spin–orbit interaction splitting energy is extracted from the fits to the data, which also displays two distinct regimes. The different regimes exhibit different spin-scattering mechanisms, the identification of which is of relevance for device platforms of reduced dimensionality which utilize the spin–orbit interaction. [ABSTRACT FROM AUTHOR]

The effect of thermally generated equilibrium carrier distribution on the vacancy generation, recombination, and mobility in a semiconductor heterostructure with an undoped quantum well is studied. A different rate of thermally generated equilibrium carriers in layers with different band gaps at annealing temperatures forms a charge-carrier density gradient along a heterostructure. The nonuniform spatial distribution of charged vacancy concentration that appears as a result of strong dependence in the vacancy formation rate on the local charge-carrier density is revealed. A model of vacancy-mediated diffusion at high temperatures typical for post-growth annealing that takes into account this effect and dynamics of nonequilibrium vacancy concentration is developed. The change of atomic diffusivity rate in time that follows on the of spatial vacancy distribution dynamics in a model heterostructure with quantum wells during a high-temperature annealing at fixed temperatures is demonstrated by computational modeling. [ABSTRACT FROM AUTHOR]

The electronic quasi-bound state in the continuum concept is explored in an InGaAs/InAlAs heterostructure to create a voltage-tunable dual-colour quantum Bragg mirror detector. This heterostructure is based on one main quantum well embedded between two different superlattices. By bandgap engineering, each superlattice gives rise to quasi-bound states in the continuum with a preferential direction for electron extraction. Due to these states, the photovoltaic photocurrent presents a dual-colour response, one in a positive direction at 340 meV (3.6 μm), and one in a negative direction at 430 meV (2.9 μm). The simultaneous dual-colour detection can be switched to a single-colour detection (340 meV or 430 meV) by applying a bias voltage. At 77 K, the specific detectivity for simultaneous dual-colour is 2.5·108 Jones, while the single-colour detectivities are 2.6·109 Jones at +2.0 V and 7.7·108 Jones at -1.6 V for 340 meV and 430 meV, respectively. [ABSTRACT FROM AUTHOR]

The magneto-quantum and quantum interference effects in a two-dimensional gas of p-type charge carriers are studied for three quantum wells made of practically pure germanium in a Si0.6Ge0.4/Si0.2Ge0.8/Si0.6Ge0.4 heterostructure. The quantum well widths were 8 nm for sample I, 19.5 nm for sample II, and 25.6 nm for sample III. The dependences of resistance on the magnetic field for all samples exhibit Shubnikov–de Haas oscillations. Their analysis made it possible to calculate the kinetic characteristics of charge carriers for the cases of one (sample I) and two occupied subbands (samples II and III). In the region of weak magnetic fields (B < 0.1 T), the effect of weak localization of holes was revealed, which determines the negative magnetoresistance and the increase in resistance with decreasing temperature. The manifestation of the charge carriers interaction effect at various temperatures and magnetic fields is discovered and analyzed. A transition from the diffusion mode of manifestation of the quantum correction to the intermediate, and then to the ballistic mode is observed. In all regions, the behavior of the quantum correction due to the charge carriers interaction effect is in good agreement with modern theoretical predictions. The temperature dependences of the hole-phonon relaxation time are calculated. In weak magnetic fields, with an increase in the temperature of the 2D system, a transition from the "partial inelasticity" mode, characterized by the dependence τ h ph − 1 ∝ T 2 , to the small-angle scattering mode, described by the relation τ h ph − 1 ∝ T 5 , takes place. In stronger magnetic fields for samples with two occupied subbands, the dependence τ h ph − 1 ∝ T 3 was observed. Possible explanations for this dependence are presented. [ABSTRACT FROM AUTHOR]

HgCdTe-based heterostructures with quantum wells (QWs) are a promising material for semiconductor lasers in the atmospheric transparency window (3–5 μm) thanks to the possibility of suppressing Auger recombination due to the no-parabolic law of carrier dispersion. In this work, we analyze the thresholds of stimulated emission (SE) under optical pumping from heterostructures with a different number of QWs in the active region of the structure. Total losses in structures are determined from the comparison of thresholds for the different number of QWs in the active region. It is shown that, thanks to the increased modal gain, a higher number of QWs results in lower threshold pumping intensity and, consequently, higher temperature of SE. These results indicate that improvements to the modal gain can result in a moderate uplift in the temperature of SE from mid-infrared HgCdTe-based heterostructures. On the other hand, at a high enough QW count threshold, the intensity no longer depends on the number of the QWs and is determined by the transparency concentration of a single QW. [ABSTRACT FROM AUTHOR]

InGaN-ZnSnN2 based quantum wells (QWs) structure is proposed and studied as an active region for high efficiency amber (λ ∼ 600 nm) light emitting diodes (LEDs), which remains a great challenge in pure InGaN based LEDs. In the proposed InGaN-ZnSnN2 QW heterostructure, the thin ZnSnN2 layer serves as a confinement layer for the hole wavefunction utilizing the large band offset at the InGaN-ZnSnN2 interface in the valence band. The barrier layer is composed of GaN or AlGaN/GaN in which the thin AlGaN layer is used for a better confinement of the electron wavefunction in the conduction band. Utilizing the properties of band offsets between ZnSnN2 and InGaN, the design of InGaN-ZnSnN2 QW allows us to use much lower In-content (∼10%) to reach peak emission wavelength at 600 nm, which is unachievable in conventional InGaN QW LEDs. Furthermore, the electron-hole wavefunction overlap (Γe-h) for the InGaN-ZnSnN2 QW design is significantly increased to 60% vs. 8% from that of the conventional InGaN QW emitting at the same wavelength. The tremendous enhancement in electron-hole wavefunction overlap results in ∼225× increase in the spontaneous emission radiative recombination rate of the proposed QW as compared to that of the conventional one using much higher In-content. The InGaN-ZnSnN2 QW structure design provides a promising route to achieve high efficiency amber LEDs. [ABSTRACT FROM AUTHOR]

The nonradiative lifetime (τNR) of the near-band-edge emission in various quality GaN samples is compared with the results of positron annihilation measurement, in order to identify the origin and to determine the capture-cross-section of the major intrinsic nonradiative recombination centers (NRCs). The room-temperature τNR of various n-type GaN samples increased with decreasing the concentration of divacancies composed of a Ga vacancy (VGa) and a N vacancy (VN), namely, VGaVN. The τNR value also increased with increasing the diffusion length of positrons, which is almost proportional to the inverse third root of the gross concentration of all point defects. The results indicate that major intrinsic NRC in n-type GaN is VGaVN. From the relationship between its concentration and τNR, its hole capture-cross-section is estimated to be about 7 × 10−14 cm2. Different from the case of 4H-SiC, the major NRCs in p-type and n-type GaN are different: the major NRCs in Mg-doped p-type GaN epilayers are assigned to multiple vacancies containing a VGa and two (or three) VNs, namely, VGa(VN)n (n =2 or 3). The ion-implanted Mg-doped GaN films are found to contain larger size vacancy complexes such as (VGa)3(VN)3. In analogy with GaN, major NRCs in Al0.6Ga0.4N alloys are assigned to vacancy complexes containing an Al vacancy or a VGa. [ABSTRACT FROM AUTHOR]

The emissivity of a combined profile quantum well, which is a well obtained by composing several rectangular wells of different thicknesses and heights, is considered. The lower well of the smallest thickness and the greatest depth is radiating, and other wells located above it are designed to increase the rate of capture of charge carriers from the barrier layers. A technique for compiling a well with a combined profile, determining the number of combined wells, their depth and thickness, as well as the content of indium in them, is given. As an example, under the assumption of additivity of the formation of energy spectrum of a combined profile well when three wells are combined, the possibility of a multiple increase in the radiation intensity of a heterostructure with the combined profile wells in comparison with a heterostructure with rectangular wells is shown. [ABSTRACT FROM AUTHOR]

Heterostructures with thin Hg(Cd)Te/CdHgTe quantum wells (QWs) are attractive for the development of mid-infrared interband lasers. Of particular interest are room-temperature operating emitters for the short-wavelength infrared range (SWIR, typically defined as 1.7–3 μm). In this work, we report on the observation of stimulated emission (SE) in the 2.65–2.75 µm wavelength range at room temperature in an optically pumped HgCdTe QW laser heterostructure. We study a series of three samples with lengths ranging from 2.5 to 7 mm and discuss the effects related to the non-uniformity of the excitation beam profile. SE threshold intensity and the magnitude of pump-induced carrier heating are found to be effectively dependent on the chip size, which should be accounted for in possible designs of HgCdTe-based optical converters. We also pay attention to the problem of active medium engineering in order to push the SE wavelength towards the 3–5 µm atmospheric window and to lower the SE threshold. [ABSTRACT FROM AUTHOR]

The work is devoted to the theoretical study of plasmon gain in HgTe/CdHgTe multi-quantum-well heterostructures. The spectra of plasmons and plasmon gain are found in structures with 2â€"8 quantum wells (QWs) under the condition of inverse band population. A nonmonotonic increase in the plasmon gain with an increase in the number of QWs is shown. The dependence of the threshold concentration of nonequilibrium carriers for stimulated plasmon emission on the number of QWs in structures with 1â€"8 QWs has been studied. [ABSTRACT FROM AUTHOR]

Three types of GaAsP metamorphic buffer layers, including linearly graded, step graded, and metamorphic superlattices, were compared for the purposes of virtual substrates for red laser diode heterostructures. Laser diodes were fabricated on GaAs substrates and relaxed GaAsP metamorphic superlattice virtual substrates. A laser diode structure with a tensile-strained quantum well on a standard miscut GaAs substrate achieved TM-polarized emission at a 638 nm wavelength with 45% peak power conversion efficiency (PCE) at a 880 mW continuous wave (CW) output power with T0 = 77 K and T1 = 266 K. An analogous laser diode structure with a compressively strained quantum well on the metamorphic superlattice emitted TE-polarized 639 nm light with 35.5% peak PCE at 880 mW CW with T0 = 90 K and T1 = 300 K. [ABSTRACT FROM AUTHOR]

The electrical and luminescent characteristics of the heterostructure with a 20 nm-wide n -InAsSbP/ n -InAs 0.95 Sb 0.05 / p -InAsSbP single quantum well, grown on an n -InAs substrate by the MOVPE method, have been studied. An intense room temperature electroluminescence (EL) with a maximum near the photon energy of 0.34 eV and a FWHM of 32 meV was discovered. It was established that the EL in such single quantum well has been emitted due to type I radiative transitions between the ground levels of electrons and holes both at forward and reverse bias. The characteristics of heterostructures with a single quantum well and the active region based on a bulk InAsSb layer of the same composition have been compared. • Room temperature electroluminescence was found in InAsSb/InAsSbP quantum well. • Electroluminescence was emitted at both polarities of applied external bias. • Spectral position of emission band was constant for the forward and reverse bias. • Phase of electroluminescence remained unchanged when bias polarity was switched. [ABSTRACT FROM AUTHOR]

The effect of an InP cap on the photoluminescence (PL) spectrum of an InGaAsP/InAlAs quantum well (QW) is investigated using excitation power and temperature dependent PL. An as-grown sample with the InP cap layer shows an inverted interface created between InP and InAlAs that has a transition energy very close to the transition energy of the QW; consequently, there is an overlap between them. On the other hand, the QW sample with the cap layer etched away does not have a feature due to the inverted interface; even at very low power, the only observed feature is due to the QW transition. [ABSTRACT FROM AUTHOR]