B.R. Snell

The resistance of two quantum point contacts in series

The resistance of two quantum point contacts (QPCs) in series is investigated experimentally. The voltage is measured both across and in between the series pair. The normalised transmission coefficient, T, for ballistic transport is determined from the data using simple theory. T varies between 0.5 and 1.0 depending on the number of conducting 1D channels through each point contact. T is always found to be a minimum value when the number of 1D channels in each QPC is the same.

A model for the origin of the oscillatory structure in the reverse bias J(V) characteristics of n+GaAs/(AlGa)As/n-GaAs/n+GaAs tunnelling devices

The oscillatory structure in the low-temperature reverse bias characteristics of n+GaAs/(AlGa)As/n-GaAs/n+GaAs tunnelling devices is explained in terms of the modulation of the resistivity of the undepleted region of the n- layer above the substrate by means of energy relaxation of hot electrons arriving from the high-field depletion layer beyond the barrier.

GaAs/(AlGa)As tunnelling devices: Hydrostatic pressure investigation and model for the J(V) characteristics

Abstract A model of GaAs/(AlGa)As tunnelling devices in reverse bias is presented. It accounts for the form of the low-temperature J ( V ) characteristics and the occurrence of oscillatory phonon structure. Measurements of the effect of hydrostatic pressure on the J ( V ) curves and of the temperature dependence of the oscillatory amplitudes are reported and are discussed in terms of the model.

Tunneling and magneto-tunnelling effects in n+GaAs/(AlGa)As/n-GaAs/n+GaAs devices

Oscillatory stuctures recently reported by Hickmott et al. (1984) in the I-V characteristics of n+GaAs/(AlGa)As/n-GaAs/n+GaAs tunnelling devices are observed at zero magnetic field and temperatures up to 50K, demonstrating that neutralisation of donors by magnetic freeze-out in the n-GaAs layer is not required to observe the structure.

Electric field-induced quasi-elastic inter-landau level scattering in the space-charge-limited magnetoconductivity of n+n−n+ InP structures

Abstract Magnetophonon resonance and quasi-elastic inter-Landau level scattering (QUILLS) are investigated in the transverse magnetoconductivity, σ xx , of short (1 μm) n + n − n + InP structures under conditions of space-charge-limited conduction. The damping of the magnetophonon resonance amplitudes at large E is also investigated. The electric field dependence of the QUILLS process in InP is in excellent agreement with a model that we have previously proposed to describe the process in n + nn + GaAs layers. The observed form of the space-charge-limited current-voltage characteristics (I ∝ V 2 ) is discussed in terms of the behaviour of electrons in short, lightly doped semiconductor layers under the influence of large, mutually perpendicular electric and magnetic fields.

Tunnelling and hot electron effects in single barrier (AlGa)AsGaAs heterostructure devices

Abstract Experimental investigations of the effect of hydrostatic pressure (up to 15 kilobar) and magnetic field (up to 11 T) on the low temperature J(V) characteristics of single barrier n + GaAs/(AlGa)As/n − GaAs/n + GaAs tunnelling structures are reported. The pressure dependence is accurately described by the effective mass/WKB model up to 10 kilobar. At higher pressure the observed breakdown of the model indicates the onset of band structure effects associated with the higher conduction band minima. The reduction of the tunnelling current in an applied magnetic field is discussed in terms of the effect of the diamagnetic energy in increasing the effective height of the barrier. The paper reviews recent models that have been proposed to explain the origin of the oscillatory structure of period ΔV = ↔hω L /e observed in the low temperature reverse bias J(V) characteristics.

ELECTRON TUNNELLING INTO INTERFACIAL LANDAU STATES IN SINGLE BARRIER N-TYPE (InGa)As/InP/(InGa)As HETEROSTRUCTURES

Abstract A new type of tunnelling phenomenon in forward-biased single-barrier n + (InGa)As/n − (InGa)As/InP/n + (InGa)As/n + InP heterostructures has been observed when a quantizing magnetic field is applied in the plane of the InP barrier. The occurrence of two distinct series of resonances in the voltage- or field-dependence of the current is interpreted in terms of electron tunnelling from a 2DEG in the n − layer into interfacial Landau states in the n + (InGa)As. These states correspond to classical skipping orbits of an electron along the tunnel barrier interface. For devices in which the n + (InGa)As/n + InP interface at the back end of the gate is within − 0.3 μm of the barrier, the interfacial Landau states are observed to evolve into box-quantized states as the magnetic field is reduced to zero.

Quantised hall effect and magnetoresistance through a quantum point contact

The four-terminal magnetoresistance and quantised Hall effect through a quantum point contact are investigated in a two-dimensional electron gas (2DEG) based on an n-type (AlGa)As/GaAs single heterostructure. Depending on the choice of current and voltage contacts we measure three different magnetoresistances in a quantising magnetic field. The results agree with a simple model based on conduction via edge states and also with a more conventional analysis based on the properties of a bulk 2DEG.

Oscillatory structure in the reverse bias J(V) plots of n+GaAs/(AlGa)As/n−GaAs/n+GaAs structures

Abstract The J(V) characteristics of (AlGa)As/GaAs tunnelling devices are investigated over a range of magnetic fields and temperatures. Pronounced oscillatory structure with period ΔV = ħωL/e is observed in reverse bias even at zero magnetic field. A model is presented to explain the behaviour of this type of device.

Validation of magnetophonon spectroscopy as a tool for analyzing hot‐electron effects in devices

It is shown that very high precision hot‐electron magnetophonon experiments made on n+n−n+‐GaAs sandwich device structures which are customized for magnetoresistance measurements can be very accurately modeled by a new Monte Carlo technique. The latter takes account of the Landau quantization and device architecture as well as material parameters. It is proposed that this combination of experiment and modeling yields a quantitative tool for the direct analysis of spatially localized very nonequilibrium electron distributions in small devices and low dimensional structures.