Laurens Wigbolt Molenkamp

Coulomb-Blockade Oscillations in the Thermopower of a Quantum Dot.

The thermopower of a quantum dot, defined in the two-dimensional electron gas in a GaAs-AlxGa1-xAs heterostructure, is investigated using a current heating technique. At lattice temperatures kBT much smaller than the charging energy e2/C, and at small heating currents, sawtoohlike thermopower oscillations are observed as a function of gate voltage, in agreement with a recent theory. In addition, a remarkable sign reversal of the amplitude of the thermopower oscillations is found in the non-linear regime at large heating currents.

Thermo-electric properties of quantum point contacts

The conductance, the thermal conductance, the thermopower and the Peltier coefficient of a quantum point contact all exhibit quantum size effects. The authors review and extend the theory of these effects. In addition, they review their experimental work on the quantum oscillations in the thermopower, observed using a current heating technique. New data are presented showing evidence for quantum steps in the thermal conductance, and (less unequivocally) for quantum oscillations in the Peltier coefficient. For these new experiments the authors have used a quantum point contact as a miniature thermometer.

Electron-electron scattering probed by a collimated electron beam

The authors compare the effects of current heating, hot-electron injection and lattice temperature on the attenuation of a collimated ballistic electron beam in a two-dimensional electron gas. In the electron gas heating and injection experiments, they use a quantum point contact as a local thermometer. They find that electron-electron scattering is the dominant factor determining the temperature dependence of the collimation signal.

Sawtooth-like thermopower oscillations of a quantum dot in the Coulomb blockade regime

Current heating is used to measure the thermopower of a quantum dot in the Coulomb blockade regime. We observe sawtooth-like oscillations as a function of gate voltage in the thermovoltage across the dot. These observations are compared with measured Coulomb blockade oscillations in the conductance, and with theory.

Quantum effects in thermal and thermo-electric transport in semiconductor nanostructures

Current heating is used to create a micron-scale hot electron reservoir in semiconductor nanostructures at low temperatures. This techniques enables the study of quantum effects in various thermo-electric transport coefficients.

Multiple quantum well structures and high-power lasers of gaas- algaas grown by metalorganic vapor phase epitaxy (MOVPE)1

Abstract GaAs/AlGaAs GRIN-SCH type multiple quantum well lasers with four wells of 11 nm GaAs, grown in an MOVPE chimney reactor, exhibit an output power as high as 110 mW/facet (CW, 30°C; 5 μm stripe) and 1.3 W/facet (pulsed, 30°C; 53 μm stripe) until catastrophic optical damage occurs. 2000 hours life tests conducted at 60°C and 15 mW CW show no noticeable degradation for the 5 μm stripe laser with a reflective coating on both facets. Raman spectroscopy on similar multiple quantum well structures with 65 GaAs wells is used to ascertain that the wells have minimum residual aluminum- content.

Selective backscattering and the breakdown of the quantum Hall effect

We study the breakdown of the quantum Hall effect in a narrow channel using quantum point contacts as edge channel mixers, and as voltage probes. We observe a dependence of the two-terminal and Hall resistances in the breakdown regime on the adjustment of the point contacts, in a manner which demonstrates selective backscattering in the highest occupied Landau level. An extension of Buttikers theory of the quantum Hall effect with a Hall-voltage dependent backscattering rate accounts for some of our observations.

GaAs-AlGaAs Multiple Quantum Well Structures And High-Power Lasers Grown By Metalorganic Vapor Phase Epitaxy (Movpe) In A Chimney Reactor.

GaAs/AlGaAs GRIN-SCH type multiple quantum well lasers with 4 wells of 11 nm GaAs, grown in an MOVPE chimney reactor, exhibit an output power as high as 110 mW/facet (CW, 30°C; 5 μm stripe) and 1.3 W/facet (pulsed, 30°C; 53 μm stripe) until catastrophic optical damage occurs. 2000 hours life tests conducted at 60°C and 15 mW CW show no noticeable degradation for the 5 μm stripe laser with a reflective coating on both facets. Raman spectroscopy on similar multiple quantum well structures with 65 GaAs wells is used to ascertain that the wells have minimum residual aluminum-content.