C. Chaubet

Behavior of the contacts of quantum Hall effect devices at high currents

We have analyzed the behavior of contacts of quantum Hall effect devices while increasing the current through the sample. Experiments have been performed in the i=2 plateau, which is used in all metrological measurements of the von Klitzing constant RK, before the onset of dissipation. Using only electrical measurements, we show that a high electric field zone appears in the vicinity of the current contact which injects the electrons in the two-dimensional electron gas, when the current is increased. This heating phenomenon develops in the region close to the source, increases the electronic temperature in the sample, and limits the precision in the measurement of RK. We have studied several samples of different width, using a well-defined configuration for the measurements. It is observed that the threshold current for the onset of the voltage drop across the contact increases with the width of the Hall bar. Consequences for high precision measurements are discussed in terms of experimental protocol and ...

Cyclotron emission study of electron masses in GaAs-GaAlAs heterostructures

We study far-infrared cyclotron emission from GaAs-GaAlAs heterostructures, induced by electric pulses in the presence of a magnetic field and hydrostatic pressure. Cyclotron masses are measured as functions of 2D electron density in the strong electron heating regime at the pressures of P=0 and P=7 kbar. The results are described by an effective two-level k.p theory, which takes consistently into account the effect of band non-parabolicity on electric and magnetic quantization. It is shown that the observed emission spectrum is due to several transitions between Landau levels, since the 2D electron gas is non-degenerate. The same theory is used to describe cyclotron absorption data of other authors, obtained at zero and non-zero pressures under the conditions of degenerate electron gas. It is shown that the cyclotron absorption can be measured in two different regimes, which explains a strong dependence of the data on photon energy. A very good theoretical description of various emission and absorption experiments is achieved with the use of bulk GaAs parameters.

Anharmonicity and asymmetry of Landau levels for a disordered two-dimensional electron gas

We calculate the density of states of a two-dimensional electron gas located at the interface of a strongly disordered

A universal law to characterize ohmic contacts of small high electron mobility transistors

\mathrm{Ga}\mathrm{Al}\mathrm{As}∕\mathrm{Ga}\mathrm{As}

Cyclotron FIR emission from hot electrons in GaAsGaAlAs heterostructures

heterojunction. The disorder potential is created by two delta doped layers. The first layer includes the parent donors which provides the well with electrons and creates a smooth disorder potential. The second layer is doped with either acceptor or donor impurities, and is located inside the well, thus creating a strongly disordered potential. We calculate the density of states in the presence of a magnetic field of arbitrary strength by taking into account all perturbative terms in the fifth Klauders approximation. We find an anharmonic spectrum, strongly asymmetric, for the Landau level density of states. At low field, the attractive potential creates the well-known band tails or impurity bands. At higher field, we show that impurity bands are also created by repulsive potentials. We discuss the consequences of the anharmonicity and asymmetry on physical properties in the quantum Hall effect regime.

Conduction electrons localized by charged magneto-acceptors A 2 in GaAs/GaAlAs quantum wells

We have processed very small high electron mobility transistor (HEMT) on the two dimensional electron gas of a GaAs/GaInAs heterostructure. The contacts (down to 2 μm wide) connect channels of different lengths and widths. We measure the saturation I(V) curves and obtain the source drain voltage at saturation. Experiments demonstrate a universal linear dependence of the saturation voltage drop with the length of the channel, whatever its width. Our experimental result is understood with basic equations of the 2D channel, taking into account the contact resistivity. The universal law Usat(L) gives a nice way to measure easily and precisely the resistivity of contacts in ultrasmall devices when their width cannot be precisely known, like in narrow two dimensional electron gas.

Admittance of multiterminal quantum Hall conductors at kilohertz frequencies

Abstract We study far infrared emission from GaAsGaAlAs heterostructures, induced by electric pulses in the presence of a magnetic field and a hydrostatic pressure. Cyclotron masses are measured as functions of 2D electron density in the strong electron heating regime at pressures P = 0 and P = 7 kbar and the detection energy of 4.43 meV. The results are described by an effective two-level k · p theory, which takes consistently into account the effect of bands nonparabolicity in GaAs on electric and magnetic quantization. It is shown that the observed emission spectrum is due to eight transitions between Landau levels (populated up to the optic phonon energy), since under the strong heating conditions the 2D electron gas is nondegenerate. This is independently confirmed by magnetotransport measurements. Very good theoretical description of emission experiments at pressures P = 0 and P = 7 is achieved with the use of bulk GaAs parameters. Theoretical estimations of the heating conditions in crossed magnetic and electric fields indicate that the electric field in our GaAsGaAlAs structures is highly inhomogeneous.

Inter and intra Landau level scatterings as a mechanism for the onset of the voltage drop across the contact at high currents in the quantum Hall effect regime

A variational theory is presented of A

Tunneling and Coulomb Blockade in narrow GaAs/InGaAs/AlGaAs Hall bars in the quantum hall regime

^{1-}

Heating process in the pre-breakdown regime of the quantum Hall effect: a size-dependent effect

and A