GaAs-based Heterostructures Research Articles

Lateral ambipolar drift of the excess charge carriers in the GaAs-based heterostructures with quantum wells and impurity δ-layers in the adjacent barriers

The low-temperature ambipolar photoconduction in the InGaAs/GaAs and GaAs/AlGaAs heterostructures containing the compositional quantum well (QW) tunnel-coupled with the impurity δ-well have been studied under a wide electric field range. The “stretched” bipolar drift length in the InGaAs/GaAs structure is shown to achieve a few mm at the fields of ∼70 V/cm and exceed that in the GaAs/AlGaAs structure at the comparable field strength by half an order of magnitude. The photoconductivity decay is up to several tens μs long and its behavior is fitted by the single- and “stretched-" exponent functions. The obtained results are shown to be caused by spatial separation of the non-equilibrium charge carriers in the potential profile engineered by such QW configuration and the dispersion law of holes in them.

Investigation of GaAs-based nanowire heterostructures using tomography based on STEM-HAADF tilt-series [1]

Investigation of GaAs-based nanowire heterostructures using tomography based on STEM-HAADF tilt-series [1]

A study of tunneling in triangular resonant tunnel diodes: Effect of barrier width, barrier height, pressure, temperature, and heterostructure strain

Using the transfer matrix, the transmission coefficient of electrons is examined in the triangular double-barrier semiconductor heterostructure. GaAs-based heterostructure is considered to study the role of barrier width, barrier height, pressure and temperature. The geometrical parameters of the heterostructures (barrier width and barrier height) and the external perturbation (pressure and temperature) influence the tunneling properties. The tunneling time of the electrons is also studied using Heisenberg's uncertainty principle. The account of the heterostructure strain is also discussed.

Demonstration of high sensitivity of microwave-induced resistance oscillations to circular polarization

We demonstrate that long-debated immunity of microwave-induced resistance oscillations (MIRO) to the sense of circular polarization is not a generic property of this phenomenon in solid-state two-dimensional electron systems. Using a large-area GaAs-based heterostructure we detect up to 30 times larger MIRO signal for the cyclotron resonance (CR) active helicity, fully consistent with the concurrently measured transmission and the deduced CR shape of the Drude absorption. We further elaborate conditions to avoid extrinsic factors capable of producing an apparent immunity of the photoresponse.

Near-infrared range tuneability in GaAs-based type-II nanoscale heterostructure emitter

We present the investigation of energy wavefunctions, dispersion profile, dipole momentum behavior, and optical gain for a nanoscale heterostructure formed with material layers of InAlAs/InGaAs/GaAsSb/InGaAs/InAlAs on a GaAs substrate. The designed structure is simulated with a 6 band k p formalism for the investigation. At room temperature, the 1548-nm wavelength has an optical gain of 2352/cm, making it suitable for NIR applications. The response of the designed heterostructure is also investigated with external temperature, strain, charge density, and electric field variations to report the tunability of the optical gain and wavelength. Due to its tunability in the NIR wavelength region, this structure can be used for different NIR applications without changing the material system.

Suppression of Surface-Related Loss in a Gated Semiconductor Microcavity

We present a surface passivation method that reduces surface-related losses by almost two orders of magnitude in a highly miniaturized GaAs open microcavity. The microcavity consists of a curved dielectric distributed Bragg reflector (DBR) with radius $\sim 10$ $\mu$m paired with a GaAs-based heterostructure. The heterostructure consists of a semiconductor DBR followed by an n-i-p diode with a layer of quantum dots in the intrinsic region. Free-carrier absorption in the highly doped n- and p-layers is minimized by positioning them close to a node of the vacuum electromagnetic-field. The surface, however, resides at an anti-node of the vacuum field and results in significant loss. These losses are much reduced by surface passivation. The strong dependence on wavelength implies that the main effect of the surface passivation is to eliminate the surface electric field, thereby quenching below-bandgap absorption via a Franz-Keldysh-like effect. An additional benefit is that the surface passivation reduces scattering at the GaAs surface. These results are important in other nano-photonic devices which rely on a GaAs-vacuum interface to confine the electromagnetic field.

Влияние состава зародышевого слоя AlGaAs на формирование антифазных доменов в структурах (Al)GaAs, выращенных газофазной эпитаксией на подложках Ge/Si(100)

GaAs-based heterostructures grown by metalorganic vapor-phase epitaxy on virtual Ge/Si substrates using an AlxGa1-xAs seed layer with different aluminum content x in the solid solution are investigated. The effect of solid solution composition on the density and size of antiphase domains emerging on the sample surface and on the optical properties of the GaAs layer is shown. Si(100) substrates with a small unintentional miscut of 0.7° to [110] were used for growth.

Terahertz photoresistivity of a high-mobility 3D topological insulator based on a strained HgTe film

We report on a detailed study of terahertz (THz) photoresistivity in a strained HgTe three-dimensional topological insulator (3D TI) for all Fermi level positions: inside the conduction and valence bands and in the bulk gap. In the presence of a magnetic field, we detect a resonance corresponding to the cyclotron resonance (CR) in the top surface Dirac fermions (DFs) and examine the nontrivial dependence of the surface state cyclotron mass on the Fermi level position. We also detect additional resonant features at moderate electron densities and demonstrate that they are caused by the mixing of surface DFs and bulk electrons. At high electron densities, we observe THz radiation-induced 1/B-periodic low-field magneto-oscillations coupled to harmonics of the CR and demonstrate that they have a common origin with microwave-induced resistance oscillations previously observed in high mobility GaAs-based heterostructures. This observation attests the superior quality of a 2D electron system formed by helical surface states in strained HgTe films.

Integration of electrochemical capacitance–voltage characteristics: a new procedure for obtaining free charge carrier depth distribution profiles with high resolution

A novel electrochemical profiling technique consisting in integration capacitance–voltage characteristics was proposed, developed and proven. The aim is to overcome the insufficient resolution in charge carrier concentration measurements during commonly used electrochemical capacitance–voltage profiling. This is very actual task for modern low-dimensional optoelectronics. According to the introduced “profiling window”, after each etching step the coordinate interval is selected, the concentration distribution in which is to be matched itself and by the first derivative at the edges with the concentration in adjacent intervals. To achieve these conditions the minimum dissipation factor should be maintained for each C–V characteristic at the corresponding etching depth. The method allows both to obtain general free charge carrier concentration depth distribution over unlimited structure depth and to achieve necessary resolution in key regions, even if they are lying at a high depth. Particularly, in GaAs-based heterostructure concentration profile of deep-lying quantum well and a delta layer (ultra-thin (2 nm) profile of dopant with extremely high concentration) were confidently distinguished with magnitude difference of 20% in the dip region in between. Besides, we have shown how quantum-confined objects of different origins give different concentration responses when electrochemical capacitance–voltage profiling with sequential etching. An explanation for this dissimilarity is given.

Thresholdless excitation of edge plasmons by transverse current

We theoretically demonstrate that dc electron flow across the junction of two-dimensional electron systems leads to excitation of edge magnetoplasmons. The threshold current for such plasmon excitation does not depend on contact effects and approaches zero for ballistic electron systems, which makes a strong distinction from the well-known Dyakonov-Shur and Cerenkov-type instabilities. We estimate the competing plasmon energy gain from dc current and loss due to electron scattering. We show that plasmon self excitation is feasible in GaAs-based heterostructures at $T\lesssim 200$ K and magnetic fields $B \lesssim 10$ T.

Observation of Terahertz-Induced Magnetooscillations in Graphene.

When high-frequency radiation is incident upon graphene subjected to a perpendicular magnetic field, graphene absorbs incident photons by allowing transitions between nearest Landau levels that follow strict selection rules dictated by angular momentum conservation. Here, we show a qualitative deviation from this behavior in high-quality graphene devices exposed to terahertz (THz) radiation. We demonstrate the emergence of a pronounced THz-driven photoresponse, which exhibits low-field magnetooscillations governed by the ratio of the frequency of the incoming radiation and the quasiclassical cyclotron frequency. We analyze the modifications of generated photovoltage with the radiation frequency and carrier density and demonstrate that the observed photoresponse shares a common origin with microwave-induced resistance oscillations discovered in GaAs-based heterostructures; however, in graphene it appears at much higher frequencies and persists above liquid nitrogen temperatures. Our observations expand the family of radiation-driven phenomena in graphene, paving the way for future studies of nonequilibrium electron transport.

Atomic Structure of Extended Defects in GaAs-based Heterostructures

Journal Article Atomic Structure of Extended Defects in GaAs-based Heterostructures Get access Abhinandan Gangopadhyay, Abhinandan Gangopadhyay School for Engineering of Matter, Transport and Energy, Arizona State University, Tempe, AZ Corresponding author: abhinandan.gangopadhyay@asu.edu Search for other works by this author on: Oxford Academic Google Scholar Aymeric Maros, Aymeric Maros School of Electrical, Computer and Energy Engineering, Arizona State University, Tempe, AZ Search for other works by this author on: Oxford Academic Google Scholar Nikolai Faleev, Nikolai Faleev School of Electrical, Computer and Energy Engineering, Arizona State University, Tempe, AZ Search for other works by this author on: Oxford Academic Google Scholar Richard R King, Richard R King School of Electrical, Computer and Energy Engineering, Arizona State University, Tempe, AZ Search for other works by this author on: Oxford Academic Google Scholar David J Smith David J Smith Department of Physics, Arizona State University, Tempe, AZ Search for other works by this author on: Oxford Academic Google Scholar Microscopy and Microanalysis, Volume 25, Issue S2, 1 August 2019, Pages 2022–2023, https://doi.org/10.1017/S1431927619010845 Published: 01 August 2019

Simulation of the concentration profiles of GaAs LED and HEMT heterostructures

GaAs-based LED and HEMT heterostructures were investigated using numerical simulation of the self-consistent Schrödinger and Poisson equations. The depth distributions of free charge carriers were obtained by simulation and analyzed in detail, then compared to measurements made using the ECV technique.

Effects of Magnetic Ordering in Conductivity and Magnetization of GaAs-Based Semiconductor Heterostructures upon Changing the Concentration of the Delta-Layer of Manganese Admixture

Characteristic effects of magnetic ordering and conduction in semiconductor heterostructures with a GaAs : Be/Ga0.84In0.16As/GaAs quantum well and manganese δ-layers of different thickness (from 0.4 to 2 monolayers) were studied based on analysis of magnetic field and temperature dependences, galvanomagnetic effects, and magnetization. An anomalous dependence of the conductivity on the manganese atoms concentration in the δ-layer was observed, which was due to a strong scattering of charge carriers in the structures with the low content of magnetic impurities. Magnetic properties of the heterostructures clearly indicated the magnetic ordering of the impurity system (saturation and hysteresis of the magnetization and fulfillment of the Curie–Weiss law at increasing temperature). Parameters of the magnetic subsystem allowed revealing different types of ordering in the systems with different concentrations of the magnetic impurity. Changing the concentration of the Mn admixture in the δ-layer was shown to influence significantly the conductivity and magnetism in the studied structures.

Defect Evolution in GaAs-based Low-mismatch Heterostructures

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Study of Electrophysical Characteristics of pHEMT Heterostructures by the Methods of Impedance Spectroscopy

The methods of impedance spectroscopy of (Al, In, Ga)As-based pHEMT heterostructures are developed using an LCR meter in the frequency range 0.1–2000 kHz and a vector network analyzer at higher frequencies of 0.01–3 GHz. These methods determine all the main parameters of the pHEMT heterostructures, including the threshold voltage, the channel resistance, the sheet density of electrons, and their mobility at operating biases.

Electron Holographic Study of Semiconductor Light-Emitting Diodes.

Semiconductor light-emitting diodes (LEDs), especially GaN-based heterostructures, are widely used in light illumination. The lack of inversion symmetry of wurtzite crystal structures and the lattice mismatch at heterointerfaces cause large polarization fields with contributions from both spontaneous polarization and piezoelectric polarization, which in turn results in obvious quantum confined stark effect. It is possible to alleviate this effect if the local electrostatic fields and band alignment induced charge redistribution can be quantitatively determined across the heterostructures. In this Concept, the applications of electron holography to investigate semiconductor LEDs are summarized. Following the off-axis electron holography scheme, the GaN-based LED heterostructures including InGaN/GaN-based quantum wells, other GaN-based quantum wells, and other forms of GaN-based LED materials are discussed, focusing on the local potential drops, polarization fields, and charge distributions. Moreover, GaAs-based LED heterostructures are briefly discussed. The in-line electron holography scheme emphasizes the capability of large area strain mapping across LED heterostructures with high spatial resolution and accuracy, which is combined with quantitative electrostatic measurements and other advanced transmission electron microscopy characterizations to provide an overall nanometer scale perspective of LED devices for further improvement in their electric and optical properties.

Contactless characterization of manganese and carbon delta-layers in gallium arsenide

Single manganese and carbon δ-layers in undoped GaAs are analyzed by photoreflectance spectroscopy. The strength of built-in electric fields, determined by this method, is shown to increase with increasing layer concentration of introduced impurities and well correlate with technological and Hall data. The use of phase-sensitive photoreflectance makes it possible to measure the surface field and the field induced by δ-doping separately. This fact allows one to determine without contact the fraction of electrically active Mn impurity and reveal the contribution of carbon δ-layers to the characteristics of GaAs-based heterostructures.

A peculiarity of quantum hot-electron real space transfer in dual-channel GaAs-based heterostructures

The model has been proposed for calculation of the electron transport via the double conducting channels formed in heterostructures with the tunnel-coupled quantum wells with the essentially different mobility of electrons. Experiments to test the dependences of the transport characteristics on the temperature and electric field were carried out on the heterostructures based on GaAs. The well with a high electron mobility was formed as an AlGaAs–GaAs–AlGaAs undoped quantum well. The tunnel-coupled well was formed either by a delta layer of impurity or a short-period superlattice (SPSL) fragment. Based on comparison of the experimental and calculated data, it is established that the electron temperatures in such coupled channels in the course of heating them by the electric field strongly differ from each other; their dependences in both wells on the electric field are found. This difference leads to a considerable redistribution of electrons between wells. For the structure with the SPSL fragment at fields more than 450 V cm−1 an inversion of the electron population between the two lower size-quantization energy subbands takes place.

Variational approach to the soft-Coulomb potential in low-dimensional quantum systems

The variational method is used to obtain the ground- and first-excited states for the soft-Coulomb central potential, 1/r2+d2, characterized by a bias distance d, taken into account as a fixed parameter. Applications are presented for spatially indirect excitons, i.e., photo-generated electron-hole (e-h) bound pairs, where the two charges are kept separated in two different regions of a heterostructure. We consider one- or two-dimensional systems, namely, quantum wires or wells, respectively, and compare the results with numerical calculations obtained by finite-difference diagonalization of the Hamiltonian. An explicit example is given for GaAs-based heterostructures.