Single Barrier Heterostructure Research Articles

Enhanced shot noise from tunneling and space-charge positive feedback

We propose a mechanism which can lead to shot-noise enhancement when electronic transport is controlled by tunneling. Numerical simulations performed for a single barrier heterostructure made with ${\mathrm{G}\mathrm{a}\mathrm{A}\mathrm{s}/\mathrm{A}\mathrm{l}}_{0.25}{\mathrm{Ga}}_{0.75}\mathrm{As}$ at $300\mathrm{K}$ evidence an increase of the Fano factor up to a value of $7$ at intermediate bias voltages significantly larger than the thermal value $KT/e$ in the region of positive differential resistance. The positive feedback between space charge and single electron tunneling probability is ultimately responsible for the super-Poissonian pulse distribution so found.

Dissociation of indirect excitons: Discontinuity and bistability in the tunnel current of single-barrier heterostructures

We observed a new discontinuity and bistability in the tunnel current of a 12-nm single-barrier GaAs/AlAs p-i-n heterostructure where a system of spatially separated two-dimensional electron and hole (e-h) layers of equal and tunable density is realized. Both features appear at T less than or similar to 300 mK and are substantially enhanced in a magnetic field B greater than or similar to 10 T perpendicular to the layers. They correspond to a discontinuity in the e-h density and in the phase of the current magneto-oscillations, which we suggest to arise from a transition between indirect excitons and the uncoupled e-h gases. [S0163-1829(99) 12343-9].

Capacitance engineering for InP-based heterostructure barrier varactor

We investigate new schemes of InP-based heterostructure barrier varactors with the aim of enhancing the capacitance nonlinearity of the devices. Starting from a generic step-like InGaAs/InAlAs/AlAs single barrier heterostructure, planar-doped and buried InAs quantum-well barrier heterostructures were successfully fabricated. It is shown that both solutions lead to more efficient screening of electric field near equilibrium and hence to improvement in the capacitance-voltage ratios with values as high as /spl sim/7:1. Under bias, the capacitance modulation is governed by an escaping mechanism in contrast to the conventional depletion operation mode observed for conventional varactors.

Resonant Γ–X–Γ tunneling in GaAs/AlAs/GaAs single barrier heterostructures at zero and elevated magnetic field

We report the observation of resonant tunneling and magneto-tunneling between states of different effective mass derived from zone centre (Γ) and zone edge (X) points of the Brillouin zone in single AlAs barrier diodes. The nature of the X states involved (longitudinal Xzor transverseXxy ) is deduced from the observed resonances in the conductance versus bias characteristics at zero magnetic field (B). At finite B, the σ–V curves exhibit resonant magneto-tunneling with XzLandau levels (LL), whilst no evidence of resonances withXxy LLs is found. Clear observation of both LL index (in-plane momentum) conserving and non-conserving tunneling to Xzallows the transverse effective mass in AlAs to be determined. As a consequence of the different effective masses, momentum-conserving tunneling is inhibited at B=0, but is restored when high B is applied.

Magneto-Optical Study of Correlated Electron–Hole Layers in Single-Barrier Heterostructures

We report the low-temperature photoluminescence investigation of a single-barrier GaAs/AlAs/ GaAs p-i-n heterostructure with applied magnetic fields of up to 17 T. Under conditions of forward bias, electrons and holes accumulate at opposite sides of the barrier to form two coupled 2D layers of tunable density. We observe an onset of polarized recombination peaks originating from these layers when the filling factor is immediately lower than two. From the properties of the onset and the shift of the peaks with applied voltage we conclude that we have to take into account the Coulomb interaction between the layers to describe properly the physical situation of the system and we propose the picture of a correlated ground state to explain the experimental findings.

Optical Spectroscopy and Transport Studies of Tunnelling Processes and Hot Electron Relaxation in GaAs–AlGaAs and GaAs–AlAs Single Barrier Heterostructures

Optical Spectroscopy and Transport Studies of Tunnelling Processes and Hot Electron Relaxation in GaAs–AlGaAs and GaAs–AlAs Single Barrier Heterostructures

Negative differential resistance in InGaAs/AlAsSb/InGaAs single-barrier heterostructure

We have observed negative differential resistance in InP lattice-matched InGaAs/AlAsSb/InGaAs single-barrier tunneling heterostructure. With a 10-nm-thick barrier, the diode exhibits a peak-to-valley current ratio of 4.2 (1.2) and peak current density of 54 (158) A/cm2 at 100 K (300 K).

Tunnelling resonances in a single-barrier heterostructure

Tunnelling resonances in a single-barrier heterostructure

Resonant tunneling through a pseudo-quantum well in single-barrier heterostructure

Resonant tunneling through virtual states in a wide pseudo-quantum well has been observed at liquid He temperature. This well is formed in the spacer layer region (n −-GaAs) of the single barrier heterostructure n +-GaAs/n −-GaAs/AlAs/n −-GaAs/n +-GaAs due to electron reflection from the main barrier at one side and from the smooth potential drop through the n −/n + junction in GaAs at the other side.

Scattering-matrix method for the tight-binding model of heterostructure electronic states.

Models of resonant-tunneling diodes based on the envelope-function approximation often give unsatisfactory results. In order to address some of the shortcomings of these models, we employ a tight-binding model that allows more careful treatment of heterointerfaces than is possible in the envelope-function approach. We use a scattering-matrix technique to carry out the calculation and present an improved method that allows us to calculate transfer across larger device dimensions. The method is applied to the calculation of transmission amplitudes for a single-barrier heterostructure. \textcopyright{} 1996 The American Physical Society.

Rezonansy pri tunnelirovanii v geterostrukturakh s odinochnym bar'erom

Rezonansy pri tunnelirovanii v geterostrukturakh s odinochnym bar'erom

Theoretical study on interband tunneling of holes through GaAs/AlAs/GaAs single-barrier heterostructures.

Tunneling of holes through GaAs/AlAs/GaAs single-barrier structures is studied within an elastic multichannel scattering theory. The multiband nature of valence bands requires us to take into account several paths of tunneling between bands with different effective masses, and such an effect of interband tunneling has not been studied as far as we know. Calculated transmission coefficients for GaAs/AlAs/GaAs structures indicate that tunneling current is strongly enhanced due to interband tunneling. We also point out that tunneling current is affected by the phase difference between amplitudes through different paths when in-channel states are coherent. The possibility of such an interference effect is discussed.

Electroluminescence spectroscopy in a high magnetic field of the ballistic-electron energy distribution in single-barrier heterostructures.

A high-resolution electroluminescence study of the hot-electron energy distribution, and of the nature of the tunneling processes, in GaAs/${\mathrm{Al}}_{\mathit{x}}$${\mathrm{Ga}}_{1\mathrm{\ensuremath{-}}\mathit{x}}$As single-barrier p-i-n diodes is reported. Application of quantizing magnetic fields permits electron injection from narrow, well-defined electron states into the collector region, even at high emitter density. As a result ballistic-electron peaks, accompanied by their LO-phonon cascade, are clearly resolved. Cross-barrier recombination is also observed. The energy distribution of the ballistic electrons is shown to reflect exactly that of the emitter electrons, even though the density is \ensuremath{\sim}${10}^{5}$ times lower, thus demonstrating that the two-dimensional to three-dimensional tunneling process is elastic and independent of the in-plane motion. The energy relaxation of the ballistic electrons is shown to be dominated by LO-phonon emission, with energy randomization by, e.g., carrier-carrier scattering playing no significant role.

Resonant tunneling of a Wannier exciton through a single-barrier heterostructure.

Quantum tunneling of a Wannier exciton through a heterobarrier structure is studied theoretically by applying the recursion method to the Green's function in a one-dimensional model. It is predicted that, when the barrier width is comparable with or smaller than the spatial extension of the relative motion of the exciton, the transmission spectrum will have sharp resonance structures even for single-barrier tunneling without a quantum-well region. This is due to the resonance with the quasibound state of the exciton in which the electron and the hole are trapped by the barrier with a spatially separated configuration.

Modelling of single barrier heterostructures including band bending and non-parabolicity effects of the band structure

Following the stationary-state approach a modified Thomas-Fermi-approximation (MTFA) is used for the evaluation of the propeties of type-I- and type-II-staggered-single barrier heterostructures. The presented model reflects the real physical situation, but in comparison with the self-consistent technique the numerical efforts are reduced. The non-parabolicity of the band strucutre is also included using simple, but very convenient analytical formulae. Several properties of InGaAs/InAlAs-and InAs/AlGaSb-configurations are investigated. The results of the MTFA, the semi-classical model and the model of Paasch and Übensee [ Physica status solidi (b) 113, 165 (1982)] are mutually compared.

Electron tunneling through single-barrier heterostructures in a magnetic field.

Electron tunneling through single-barrier heterostructures in a magnetic field.

Γ-X intervalley transfer in single AlAs barriers under hydrostatic pressure

We have investigated the contribution of Γ-X intervalley transfer to the tunneling current in single AlAs barrier heterostructures grown on a GaAs substrate by measuring I-V characteristics at low temperature and under hydrostatic pressure up to 9 kbar. The application of hydrostatic pressure affects the contribution of the Γ-X transfer process to the total tunneling current at a given bias voltage. Experimental results are compared with current-voltage characteristics calculated with a model taking into account the Γ-X transfer at heterointerfaces. Only transfer processes involving the longitudinal X valley in AlAs are considered in the calculations. Very good agreement is found for low bias conditions at all pressures.

Effect of a transverse magnetic field on tunneling in single- and double-barrier structures

Magneto-oscillations in the current through single-barrier heterostructures have been observed, due to electrons tunneling from a 2DEG in a lightly-doped emitter into interfacial Landau states (skipping orbits) in the collector contact. We have calculated the dependence of tunnel current on magnetic field and bias voltage using the Bardeen transfer Hamiltonian approach within a WKB approximation. A physical interpretation of the results is given in terms of the effect of the magnetic field on barrier transmission and on the amplitudes of the confined wave functions. The model is extended to double-barrier structures.

Transverse Transport in n+GaAs/AlxGa1−xAs/n−GaAs Structures

AbstractThe dc current–voltage characteristics and the real and imaginary parts of the differential conductivity of a single barrier heterostructure based on n+GaAs/AlxGa1−xAs/n−GaAs are investigated. The temperature dependence of the modulated structure related to the emission of longitudinal optical phonons is measured in the region from 1.3 to 90 K and compared with microscopic models proposed to describe it. A detailed examination of the capacitance indicates the presence of an appreciable negative charge in the barrier or at its interface, but then the current and its temperature dependence can only by explained when additionally the presence of conducting channels in the barrier is assumed.

Band structure engineering for electron tunneling in heterostructures

Summary form only given. It has been shows that inelastic tunneling via the AlGaAs X minimum is responsible for the excess valley current in GaAs/AlGaAs resonant tunneling devices. In addition, negative differential resistance has been observed in GaAs/AlAs/GaAs single-barrier heterostructures, due to the presence of a quasi-bound state associated with the X-point profile. This surprising result is due to the fact that, although the Gamma -point profile of this heterostructure is a simple single tunneling barrier, the X-point profile actually constitutes a quantum well some 0.3 eV deep lying about 0.2 eV above the Gamma -point of GaAs. Another way to realize single-barrier devices with negative differential resistance is based on tunneling below the midgap. In this case, the barrier transmission probability decreases with applied bias because the decay constant increases toward the middle of the bandgap. Room-temperature observations of this type of negative differential resistance were made. Peak-to-valley ratios of 1.6:1 are seen in InAs/AlGaSb single-barrier devices exhibiting this phenomenon. >