P.S.S. Guimaraes

Hot-electron magnetophonon spectroscopy on micron- and sub-micron-size n+nn+ GaAs structures

Magnetophonon resonance is used to study electronic conduction processes in a series of short n+nn+ GaAs sandwich structures with active (n) layer thickness between 0.25 and 9 mu m for E up to 20 kV cm-1 and B up to 18 T. The high electric fields induce a new contribution to sigma xx, quasi-elastic inter-Landau-level scattering. The onset condition for this process can be derived from the properties of the electron eigenfunctions and eigenvalues in crossed E and B fields. A possible relation between this process and the destruction of the non-dissipative current in the quantum Hall effect is discussed. Electric-field-induced damping of the amplitudes of the magnetophonon extrema is reported and discussed in terms of the intracollisional field effect and the theory of Barker.

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.

Resonant magnetoresistance measurements in short (∼ 1 μm) n+nn+ GaAs structures: Investigation of the electric field dependence of quasi-elastic inter-Landau level scattering processes

Abstract The contribution of quasi-elastic inter-Landau level scattering (QUILLS) by acoustic phonons to the high field transverse magnetoconductivity σ xx of short (∼ 1 μm) n + nn + GaAs devices is investigated experimentally and theoretically. It is shown that the very strong electric field dependence of QUILLS can be understood in terms of the inter-Landau level acoustic phonon scattering matrix.

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.

Degenerate n-type GaAs doped with Cr: an intermediate-valence and/or Kondo system?

The Cr1+ level in GaAs (the so-called two-electron trap level) is investigated using optical absorption and de Haas-Shubnikov measurements for a series of heavily doped n-type samples with Fermi levels up to 120 meV above the conduction band edge. The level is shown to have the form of a broadened distribution of width 26 meV centred at 45 meV (4K) above the band edge. Analogues with intermediate-valence and Kondo systems are briefly discussed.

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.