Showing papers by "Peter H. Beton published in 1992"

Resonant tunneling through the bound states of a single donor atom in a quantum well.

Abstract: We have observed a series of sharp peaks in the low-temperature I(V) characteristics of a gated 1 \ensuremath{\mu}m\ifmmode\times\else\texttimes\fi{}1 \ensuremath{\mu}m GaAs/(AlGa)As resonant tunneling diode, in which the gate is used to reduce the effective cross-sectional area from 0.7 to 0.1 \ensuremath{\mu}${\mathrm{m}}^{2}$. These peaks, which occur at voltages well below the calculated resonant threshold, show a weak dependence on temperature, magnetic field, and cross-sectional area. We argue that this subthreshold structure is due to an inhomogeneity in the device, which gives rise to a localized preferential current path, and we deduce that the spatial extent of the inhomogeneity is approximately 25 nm. The likely origin of the inhomogeneity is a background donor impurity in the quantum well.

Breakdown of universal scaling of conductance fluctuations in high magnetic fields.

Abstract: We have studied universal conductance fluctuations in the nonlocal magnetoresistance of ${\mathit{n}}^{+}$-GaAs wires. The Lee-Stone correlation field \ensuremath{\Delta}${\mathit{B}}_{\mathit{c}}$ increases by a factor of 5 as the magnetic field increases from 0 to 12 T but the amplitude of the fluctuations does not change. It is possible to explain the increase of \ensuremath{\Delta}${\mathit{B}}_{\mathit{c}}$ quantitatively in terms of a variation of the size of the phase coherence length. However, this should also give rise to a large change in the fluctuation amplitude, which is not observed. This implies that the universal scaling of the conductance fluctuations is not valid in high magnetic fields.

Edge effects in a gated submicron resonant tunneling diode

Abstract: We have investigated the current‐voltage [I(V)] characteristics of a gated GaAs/(AlGa)As resonant tunneling diode. As the negative gate voltage is progressively increased I(V) becomes asymmetric. In particular the peak‐to‐valley ratio in forward bias is decreased from ≂20 to ≂1, but in reverse bias remains constant ≂20. This arises from a lateral variation of the voltage drop across the emitter tunnel barrier, which in forward bias leads to a smearing of the resonance. We discuss the relationship between our experiment and the low peak‐to‐valley ratios of two‐terminal submicron resonant tunneling diodes observed by other groups.

Asymmetry in the I(V) characteristics of a gated resonant tunnelling diode

Abstract: The authors have investigated the I(V) characteristics of a GaAs/(AlGa)As resonant tunnelling diode in which the effective cross-sectional area, A, may be varied using a gate. As A is progressively reduced I(V) becomes asymmetric. In particular the peak to valley ratio in forward bias is decreased from a value approximately=20 to approximately=1, but in reverse bias remains constant at approximately=20. They propose that this arises from a lateral variation of the voltage drop across the tunnel barriers which leads to a smearing of the resonance. As A is reduced they also observe additional maxima and minima in I(V).

Nonlinear conductance of quantum point contacts in a magnetic field

Abstract: The conductance of geometrically asymmetric quantum point contacts formed in 2D electron gas (2 DEGs) in GaAs/(AlGa)As heterojunctions has been studied as a function of the applied bias and magnetic field. The nonlinear conductance is found to be independent of bias direction in zero magnetic field in agreement with other workers but at higher magnetic fields the I(V) curves are highly asymmetric in terms of both the onset and the type of nonlinearity observed. The curves are described using simple theory. The same experimental arrangement is also used to study nonlinearity in the quantum Hall regime when the device acts as an adjustable, narrow channel. The nonlinearity is qualitatively different to the first case and there are discontinuous changes in the dissipation which the authors identify with scattering between magneto-electric subbands.

Effects of High Frequency Delocalization on the Quantum Hall Effect

Abstract: The width of the QHE plateaus ΔB is investigated in GaAs/-AlGaAs using DC and microwave (MW) techniques. ΔB is narrower at MW frequencies than at DC and saturates below 2.4K. No fractional plateaus were observed at MW frequencies where they appeared at DC.