GaAs Heterostructures Research Articles

Dimensional resonance of intrinsic stimulated picosecond emission while it induces a photonic crystal and electron population oscillations in heterostructure Al<sub>x</sub>Ga<sub>1–x</sub>As–GaAs–Al<sub>x</sub>Ga<sub>1–x</sub>As

Powerful picosecond optical pumping of the GaAs heterostructure layer causes the generation of stimulated picosecond emission in it. Due to its high intensity, the emission induces a Bragg grating of the electron population in the active region of the layer, making the latter an active photonic crystal. In the emission field, the inverse population of electrons oscillates with time, which should lead to spatiotemporal modulation of the emission and this population. It has been discovered that if the distance Y between the end of the heterostructure and the center of the active medium and the geometric parameters of the indicated modulation and movement of emission in the photonic crystal satisfy certain conditions, then dimensional resonance occurs - a maximum of modulation of the dependence of the energy of emission emerging from the end on Y and on pump energy appears locally.

High-Q two-dimensional photonic crystal nanocavity on glass with an upper glass thin film.

We numerically analyze two-dimensional photonic crystal (PhC) nanocavities on glass with a thin glass film on top of the structure. We investigated a multistep heterostructure GaAs PhC nanocavity located on glass. We found that covering the structure even with a very thin glass film efficiently suppresses unwanted polarization mode conversion occurring due to the asymmetric refractive index environment around the PhC. We also uncovered that the glass-covered structure can exhibit a higher Q factor than that observed in the structure symmetrically cladded with thick glass. We point out that the mode mismatch between the PhC nanocavity and modes in the upper glass film largely contributed to the observed Q-factor enhancement. These observations were further analyzed through the comparison among different types of on-glass PhC nanocavities covered with thin glass films. We also discuss that the in-plane structure of the upper glass film is important for additionally enhancing the Q factor of the nanocavity.

High-quality single InGaAs/GaAs quantum dot growth on a silicon substrate for quantum photonic applications

Developing non-classical light sources for use in quantum information technology is a primary goal of quantum nanophotonics. Significant progress has been made in this area using quantum dots grown on III/V semiconductor substrates. However, it is crucial to develop quantum light sources based on silicon wafers to facilitate large-scale integration of electronic circuits and quantum photonic structures. We present a method for the direct heteroepitaxial growth of high-quality InGaAs quantum dots on silicon, which enables the fabrication of scalable and cost-effective quantum photonics devices that are compatible with silicon technology. To achieve high-quality GaAs heterostructures, we apply an intermediate GaP buffer and defect-reducing layers on a silicon substrate. The epitaxially grown quantum dots exhibit optical and quantum-optical properties similar to reference ones based on conventional GaAs substrates. The distributed Bragg reflector used as a backside mirror enables us to achieve bright emission with up to (18 ± 1)% photon extraction efficiency. Additionally, the quantum dots exhibit strong multi-photon suppression with g(2)(τ) = (3.7 ± 0.2) × 10−2 and high photon indistinguishability V = (66 ± 19)% under non-resonant excitation. These results indicate the high potential of our heteroepitaxy approach in the field of silicon-compatible quantum nanophotonics. Our approach can pave the way for future chips that combine electronic and quantum photonic functionality.

Self-consistent Analysis for Optimization of AlGaAs/GaAs Based Heterostructure

The heterostructures are suitable for developing high-performance electronic and optoelectronic devices. In this work, a significant interest in the design and analysis of compound semiconductor Aluminium Gallium Arsenide (AlGaAs) and Gallium Arsenide (GaAs) heterostructures has been realized. These structures are fabricated with alternating layers of GaAs (a direct bandgap material) and AlGaAs (an indirect bandgap material) and have been used to design a range of high-performance devices, including lasers, solar cells, and field-effect transistors. A 30 nm AlGaAs consisting of a middle layer between two GaAs layers with a GaAs substrate has been reported. This work has been carried out at 300 K utilizing a quantum transport and self-consistent method for the proposed AlGaAs/GaAs one-dimensional heterostructure with a gate length of 2 nm and a voltage varying from 0 to 0.1 V. The measured values of doping density (nd) and electron density (ne) of AlGaAs/GaAs one-dimensional heterostructure are 8.96 × 1011 cm−3 and 2 × 1026 cm−3, respectively. The system response to geometric changes in several parameters has been realized. Hence, confined restricted states were computed using wave functions and energies. The GaAs layer on top of quantum well heterostructure interfaces has been used to modulate the wave functions (eigenstates) resulting in pseudo-one dimensional or small-dimension eigenstates. In this work, a comprehensive analysis of 1D AlGaAs/GaAs heterostructure through benchmarking with several homo-structures (various thicknesses) has been performed.

Caloric Effect Due to the Aharonov-Bohm Flux in an Antidot.

In this work, we report the caloric effect for an electronic system of the antidot type, modeled by combining a repulsive and attractive potential (parabolic confinement). In this system, we consider the action of a perpendicular external magnetic field and the possibility of having an Aharonov-Bohm flux (AB-flux) generated by a current passing through a solenoid placed inside the forbidden zone for the electron. The energy levels are obtained analytically, and the model is known as the Bogachek and Landman model. We propose to control the caloric response of the system by varying only the AB-flux, finding that, in the absence of an external magnetic field, the maximization of the effect always occurs at the same AB-flux intensity, independently of the temperature, while fixing the external magnetic field at a non-zero value breaks this symmetry and changes the point where the caloric phenomenon is maximized and is different depending on the temperature to which the process is carried. Our calculations indicate that using an effective electron mass of GaAs heterostructures and a trap intensity of the order of 2.896 meV, the modification of the AB-flux achieves a variation in temperature of the order of 1 K. Our analysis suggests that increasing the parabolic confinement twofold increases the effect threefold, while increasing the antidot size generates the reverse effect, i.e., a strong decrease in the caloric phenomenon under study. Due to the great diversity in technological applications that have antidots in electronics, the possibility of controlling their thermal response simply by varying the intensity of the internal current inside the solenoid (i.e., the intensity of AB-flux) can be a platform of interest for experimental studies.

Coulomb Correlation Gap at Magnetic Tunneling between Graphene Layers

The strong suppression of equilibrium magnetic tunneling in a graphene/hBN/graphene heterostructure caused by the Coulomb correlation gap in the tunneling density of states has been found. Comparison has shown that the suppression of the equilibrium tunneling conductivity {{G}_{0}} in a high magnetic field with a decrease in the temperature and the dependence of the observed gap width Δ on the filling factor of Landau levels ν are qualitatively similar to the respective results of similar experiments in GaAs heterostructures and has confirmed our hypothesis concerning the nature of the effect. However, the determined gap width Δ is much larger than those measured in all previous works in semiconductor heterostructures probably because the cyclotron energy in graphene is much higher than that in GaAs in the region of low Landau levels.

High-Power Laser Diodes Based on InGaAs(P)/Al(In)GaAs(P)/GaAs Heterostructures with Low Internal Optical Loss

High-Power Laser Diodes Based on InGaAs(P)/Al(In)GaAs(P)/GaAs Heterostructures with Low Internal Optical Loss

Lattice Strain Relaxation and Compositional Control in As-Rich GaAsP/(100)GaAs Heterostructures Grown by MOVPE.

The fabrication of high-efficiency GaAsP-based solar cells on GaAs wafers requires addressing structural issues arising from the materials lattice mismatch. We report on tensile strain relaxation and composition control of MOVPE-grown As-rich GaAs1-xPx/(100)GaAs heterostructures studied by double-crystal X-ray diffraction and field emission scanning electron microscopy. Thin (80-150 nm) GaAs1-xPx epilayers appear partially relaxed (within 1-12% of the initial misfit) through a network of misfit dislocations along the sample [011] and [011-] in plane directions. Values of the residual lattice strain as a function of epilayer thickness were compared with predictions from the equilibrium (Matthews-Blakeslee) and energy balance models. It is shown that the epilayers relax at a slower rate than expected based on the equilibrium model, an effect ascribed to the existence of an energy barrier to the nucleation of new dislocations. The study of GaAs1-xPx composition as a function of the V-group precursors ratio in the vapor during growth allowed for the determination of the As/P anion segregation coefficient. The latter agrees with values reported in the literature for P-rich alloys grown using the same precursor combination. P-incorporation into nearly pseudomorphic heterostructures turns out to be kinetically activated, with an activation energy EA = 1.41 ± 0.04 eV over the entire alloy compositional range.

Equilibrium current distributions and W∞ gauge theory in quantum Hall systems of conventional electrons and Dirac electrons

In equilibrium planer systems of Hall electrons, such as GaAs heterostructures and graphene, support two species of current counterflowing along the system edges, as observed recently in experiment using a nanoscale magnetometer. We examine distinct origins and distinctive features of these equilibrium currents, with the Coulombic many-body effects taken into account, and derive their real-space distributions. Our basic tool of analysis is a reformulation of quantum Hall systems as a ${W}_{\ensuremath{\infty}}$ gauge theory, which allows one to diagonalize the total Hamiltonian according to the resolutions of external probes. These equilibrium currents are deeply tied to the orbital magnetization in quantum Hall systems. Special attention is drawn to the case of graphene, especially the neutral $(\ensuremath{\nu}=0)$ ground state and its intrinsic diamagnetic response that combines with the equilibrium currents to govern the orbital magnetization and its oscillations with filling.

Si‐Doping of Low‐Temperature‐Grown GaAs Heterostructures on (100) and (111)A GaAs Substrates

Utilizing the amphoteric property of silicon impurity in GaAs (111)A for acceptor doping of low‐temperature‐grown (LTG‐) GaAs films and LTG‐GaAs‐based heterostructures for THz photoconductive applications is proposed and realized. The electronic properties of superlattice structures {LTG‐GaAs/GaAs:Si} grown by molecular beam epitaxy on (100) and (111)A GaAs substrates are experimentally investigated, where GaAs:Si are silicon‐doped GaAs layers grown at standard conditions. The use of GaAs substrates with surface orientation (111)A results in spatially indirect p‐type doping of LTG‐GaAs layers. In addition, the charge redistribution at the LTG‐GaAs/GaAs:Si interfaces, due to the presence of silicon atoms in GaAs:Si layers and antisite point defects in adjacent LTG‐GaAs layers, is also analyzed by means of band structure modeling.

Improved Tunneling Property of p+Si Nanomembrane/n+GaAs Heterostructures through Ultraviolet/Ozone Interface Treatment

Here, heterostructures composed of p+Si nanomembranes (NM)/n+GaAs were fabricated by ultraviolet/ozone (UV/O3, UVO) treatment, and their tunneling properties were investigated. The hydrogen (H)-terminated Si NM was bonded to the oxygen (O)-terminated GaAs substrate, leading to Si/GaAs tunnel junctions (TJs). The atomic-scale features of the H-O-terminated Si/GaAs TJ were analyzed and compared to those of Si/GaAs heterojunctions with no UVO treatment. The electrical characteristics demonstrated the emergence of negative differential resistance, with an average peak-to-valley current ratio of 3.49, which was examined based on the band-to-band tunneling and thermionic emission theories.

Effects of a far-infrared photon cavity field on the magnetization of a square quantum dot array

The orbital and spin magnetization of a cavity-embedded quantum dot array defined in a GaAs heterostructure are calculated within quantum-electrodynamical density-functional theory. To this end, a gradient-based exchange-correlation functional recently employed for atomic systems is adapted to the hosting two-dimensional electron gas submitted to an external perpendicular homogeneous magnetic field. Numerical results reveal the polarizing effects of the cavity photon field on the electron charge distribution and nontrivial changes of the orbital magnetization. We discuss its intertwined dependence on the electron number in each dot, and on the electron-photon coupling strength. In particular, the calculated dispersion of the photon-dressed electron states around the Fermi energy as a function of the electron-photon coupling strength indicates the formation of magnetoplasmon-polaritons in the dots.

Scaling behavior of electron decoherence in a graphene Mach-Zehnder interferometer

Over the past 20 years, many efforts have been made to understand and control decoherence in 2D electron systems. In particular, several types of electronic interferometers have been considered in GaAs heterostructures, in order to protect the interfering electrons from decoherence. Nevertheless, it is now understood that several intrinsic decoherence sources fundamentally limit more advanced quantum manipulations. Here, we show that graphene offers a unique possibility to reach a regime where the decoherence is frozen and to study unexplored regimes of electron interferometry. We probe the decoherence of electron channels in a graphene quantum Hall PN junction, forming a Mach-Zehnder interferometer1,2, and unveil a scaling behavior of decay of the interference visibility with the temperature scaled by the interferometer length. It exhibits a remarkable crossover from an exponential decay at higher temperature to an algebraic decay at lower temperature where almost no decoherence occurs, a regime previously unobserved in GaAs interferometers.

Rydberg exciton-polaritons in a magnetic field

We theoretically investigate exciton-polaritons in a two-dimensional (2D) semiconductor heterostructure, where a static magnetic field is applied perpendicular to the plane. To explore the interplay between magnetic field and a strong light-matter coupling, we employ a fully microscopic theory that explicitly incorporates electrons, holes and photons in a semiconductor microcavity. Furthermore, we exploit a mapping between the 2D harmonic oscillator and the 2D hydrogen atom that allows us to efficiently solve the problem numerically for the entire Rydberg series as well as for the ground-state exciton. In contrast to previous approaches, we can readily obtain the real-space exciton wave functions and we show how they shrink in size with increasing magnetic field, which mirrors their increasing interaction energy and oscillator strength. We compare our theory with recent experiments on exciton-polaritons in GaAs heterostructures in an external magnetic field and we find excellent agreement with the measured polariton energies. Crucially, we are able to capture the observed light-induced changes to the exciton in the regime of very strong light-matter coupling where a perturbative coupled oscillator description breaks down. Our work can guide future experimental efforts to engineer and control Rydberg excitons and exciton-polaritons in a range of 2D materials.

Generation of microwave harmonics by non-ohmic surface layers in quantum wells of compound semiconductors at low lattice temperatures

It is well known that the free electron ensemble in the material of a semiconductor structure, at times, may exhibit electrical nonlinearity, when an effectively large electric field is applied. Under the condition, when a microwave field is also superimposed at the input, the efficiency of generation of second harmonic has been estimated here, using the electrical nonlinearity of the surface layers in infinite triangular quantum wells of compound semiconductors at low lattice temperatures. The nonlinear electrical characteristics are obtainable in the widely used framework of the field-dependent effective electron temperature approximation. Some of the explicit low-temperature features, like the degeneracy of the ensemble, and their interaction with the piezoelectric phonons, are taken into account. The efficiency characteristics which are thus obtained for some practically used modulation doped heterostructures of compounds, like InSb, GaAs, and GaN, seem to be interesting. Moreover, the specific low-temperature features are found to effect significant changes in the efficiency characteristics of the layers of such compounds. How the present analysis leaves much scope for further refinement is also discussed.

Study of the Crystalline State of MBE (013)HgCdTe/CdTe/ZnTe/GaAs Heterostructure Layers by the Second Harmonic Generation Method

The crystal perfection of HgCdTe layers of heterostructures grown on (013)GaAs substrates with ZnTe and CdTe buffer layers and orientation rotation in the plane(angle φ) and perpendicular to the growth direction (angle theta) were studied by the method of second harmonic generation. A change in the angle φ for CdTe layers was observed depending on the GaAs substrate orientation and its non-monotonic change throughout thickness in the MCT layer of constant composition and graded widegap layers at its boundaries. An increase in the angle theta was observed when growing the upper graded widegap MCT layer. The absolute value of the angle theta can be used for a qualitative assessment of the crystalline perfection of the HgCdTe layers. Keywords: crystals of the sphalerite class, second harmonic, azimuthal angular dependencies, crystal perfection, CdxHg1-xTe heterostructures.

Combined impact of B2H6 flow and growth temperature on morphological, structural, optical, and electrical properties of MOCVD-grown B(In)GaAs heterostructures designed for optoelectronics

BGaAs/GaAs epilayers and BInGaAs/GaAs quantum well (QW) have been prepared using metal–organic chemical vapor deposition under different growth conditions, and their physical and structural properties have been examined. SEM-EDS investigation showed a dependence of surface properties of the ternary compound on the growth conditions. High-resolution X-ray diffraction evidenced a tensile strain for the ternary alloys whatever the growth condition, while the quaternary QW always shows a compressive strain state. Room temperature optical absorption allowed to follow the variation of the bandgap with boron incorporation. Photoluminescence measurements confirmed the carrier-localization phenomenon and its dependence with the growth conditions. Deposition temperature and diborane (B2H6) flow rate are with particularly significant effects on the optical properties: lower diborane flow rate and high growth temperature enhance the radiative emission. Computer simulation using localized state ensemble model quantitatively relates the lattice inhomogeneity to the optical properties and suggests a way to engineer the localization phenomenon and avoid clustering effects. Electrical investigations by current–voltage, capacitance and conductance methods have been performed for the first time on selected BGaAs samples. The ideality factor of Schottky barriers has been determined, while their height and film doping level could only be approximately estimated. Such physical properties make boron-based alloys very promising for applications in multijunction solar cells.

Voltage-controlled long-range propagation of indirect excitons in a van der Waals heterostructure

Indirect excitons (IXs), also known as interlayer excitons, can form the medium for excitonic devices whose operation is based on controlled propagation of excitons. A proof of principle for excitonic devices was demonstrated in GaAs heterostructures where the operation of excitonic devices is limited to low temperatures. IXs in van der Waals transition-metal dichalcogenide (TMD) heterostructures are characterized by high binding energies making IXs robust at room temperature and offering an opportunity to create excitonic devices operating at high temperatures suitable for applications. However, a characteristic feature of TMD heterostructures is the presence of moir\'e superlattice potentials, which are predicted to cause modulations of IX energy reaching tens of meV. These in-plane energy landscapes can lead to IX localization, making IX propagation fundamentally different in TMD and GaAs heterostructures and making uncertain if long-range IX propagation can be realized in TMD heterostructures. In this work, we realize long-range IX propagation with the $1/e$ IX luminescence decay distances reaching 13 microns in a MoSe$_2$/WSe$_2$ heterostructure. We trace the IX luminescence along the IX propagation path. We also realize control of the long-range IX propagation: the IX luminescence signal in the drain of an excitonic transistor is controlled within 40 times by gate voltage. These data show that the long-range IX propagation is possible in TMD heterostructures with the predicted moir\'e superlattice potentials.

Role of resident electrons in the manifestation of a spin polarization memory effect in Mn delta-doped GaAs heterostructures

The spin-memory effect in the GaAs / InGaAs heterostructures with $\delta$<Mn> layer in GaAs barrier have been investigated. The effect consists in spin polarization of Mn atoms due to interaction with photogenerated spin-polarized holes. The investigation of the effect was carried out by analyzing the polarization of the probe photoluminescence pulse in the pump-probe technique. It was shown that the circular polarization degree of probe pulse generated photoluminescence is strongly affected by the interaction of hole spins with spins of Mn atoms polarized by the pump pulse. The latter leads to decrease of circular polarization degree as compared with single pulse excitation ($\delta P$ effect). The amplitude of $\delta P$-effect is most strongly affected by the concentration of resident electrons in the quantum well which is believed to be due the specific compliance with selection rules for optical transition with the participation of unpolarized resident electrons. The rest of the sample's parameters including the spatial separation between $\delta$<Mn> layer and InGaAs quantum well ($d_s$) have a minor effect on the $\delta P$ value which leads to a paradoxical situation of decreasing $\delta P$-effect with the decrease of $d_s$. The proposed experimental technique consisting in creating the significant concentration of resident electrons in the QW may serve as a reliable photoluminescence method determining the strength of this effect as well as the Mn spin relaxation time in a particular nanostructure.

(Invited) Recent Advances in the Modeling of ZnSySe1-y / GaAs (001) Heterostructures with Application to Dislocation Sidewall Gettering

In this talk we will describe state-of-the-art approaches to the modeling of strain relaxation and dislocations in ZnSySe1-y/GaAs (001) heterostructures, with applications to dislocation sidewall gettering (DSG) in devices. Current modeling approaches are based on the extension of the original Dodson and Tsao plastic flow model [B. W. Dodson and J. Y. Tsao, Appl. Phys. Lett., 51, 1325 (1987); Appl. Phys. Lett., 52, 852 (1988)] to include compositional grading and multilayers, dislocation interactions, and differential thermal expansion. Important recent breakthroughs have greatly enhanced the utility of these modeling approaches in three respects: i) pinning interactions have been included in graded and multilayered structures, providing a better description of the rate of strain relaxation as well as the limiting strain; ii) a refined model describing the interaction length for dislocation-dislocation interactions was formulated to include jogging in compositionally-graded and step-graded layers; and iii) inclusion of back-and-forth weaving of dislocations provides a more accurate description of heterostructures containing strain reversals, such as strained-layer superlattices or overshoot graded layers. We will describe these three key advances and use reasonable estimates of the kinetic parameters for ZnSySe1-y to explain and illustrate practical features of dislocation sidewall gettering in II-VI heterostructures.