Thomas Herrle

Spin photocurrents and the circular photon drag effect in (110)-grown quantum well structures

The study of spin photocurrents in (110)-grown quantum well structures is reported. The investigated effects comprise the circular photogalvanic effect and so far not observed circular photon drag effect. The experimental data can be described by an analytical expression derived from a phenomenological theory. A microscopic model of the circular photon drag effect is developed demonstrating that the generated current has a spin dependent origin.

Spin photocurrents in (110)-grown quantum well structures

The circular photogalvanic effect and the circular photon drag effect are observed and investigated in detail in (110)-grown quantum well structures. The experimental data are well described by phenomenological theory and microscopic models of both effects are developed being in agreement with experimental data.

Field-effect-induced midinfrared electroluminescence of a quantum-wire-cascade structure by remote δ-doping

We present a quantum-cascade emitter in the galliumarsenide/aluminum–galliumarsenide (GaAs/AlGaAs) heterosystem whose emission properties are controlled by an additional electric field perpendicular to the transport direction. In our case, the additional field is established by remote δ-silicon doping, which is also responsible for charge carrier supply. The field originating from the δ-doping gives rise to an in-plane confinement creating a quantum-wire cascade. This field-effect quantum-cascade emitter is realized using the cleaved edge overgrowth method. Radiative electronic transitions between discrete energy levels in coupled quantum wires were calculated for such a structure. Without an additional electric field, no significant transport is observed. With a field applied, midinfrared emission is observed at a peak wave number of 1200 cm−1 with a full width at half maximum of 300 cm−1 for a heat-sink temperature of 20 K. The presented sample is an experimental proposal for a unipolar quantum-wire int...

Current-induced heating in quantum well and quantum wire intersubband emitter structures

We discuss the influence of current-induced heating on the current-voltage (I-V) characteristics and the spectral behavior in quantum well and quantum wire intersubband emitter structures. A conventional quantum cascade laser structure in the AlGaAs∕GaAs material system with undoped cladding layers and an undoped active region is examined. This heterostructure serves as a first growth step for quantum wire intersubband emitters fabricated by the cleaved-edge overgrowth technique. We discuss the influence of electrons supplied by a remote δ-silicon doping. Duty-cycle dependent measurements on the quantum wire structures confirm the influence of current-induced heating on the I-V characteristics as well as on the emission spectra.

Field‐effect induced mid‐infrared intersubband electroluminescence of quantum wire cascade structures

Employing the Cleaved Edge Overgrowth technique, GaAs/AlGaAs quantum wire cascade structures have been fabricated. The quantum wire states are formed by the perpendicular overlap of two confinement potentials, one resulting from a strong potential modulation generated by quantum wells along the [001]‐crystal direction, and a second resulting from an additional in‐plane confinement generated by a silicon‐δ‐doping along the [110]‐crystal direction. Radiative electronic transitions between discrete energy levels in coupled quantum wires are predicted in these samples. Above a threshold of 200 mA, mid‐infrared electroluminescence is observed at an energy of 150 meV. The devices were temperature controlled at 20 K. The emission intensity is clearly current dependent and rises linearly with a slope efficiency of 0.1 nW/mA up to a maximum output power of 17 nW.

Probing spin-polarized currents in the quantum Hall regime

An experiment to probe spin-polarized currents in the quantum Hall regime is suggested that takes advantage of the large Zeeman-splitting in the paramagnetic diluted magnetic semiconductor zinc manganese selenide (Zn1−xMnxSe). In the proposed experiment spin-polarized electrons are injected by ZnMnSe-contacts into a gallium arsenide (GaAs) two-dimensional electron gas (2DEG) arranged in a Hall bar geometry. We calculated the resulting Hall resistance for this experimental setup within the framework of the Landauer–Buttiker formalism. These calculations predict for 100% spin injection through the ZnMnSe-contacts a Hall resistance twice as high as in the case of no spin-polarized injection of charge carriers into a 2DEG for filling factor ν=2.We also investigated the influence of the equilibration of the spin-polarized electrons within the 2DEG on the Hall resistance. In addition, in our model we expect no coupling between the contact and the 2DEG for odd filling factors of the 2DEG for 100% spin injection, because of the opposite sign of the g-factors of ZnMnSe and GaAs.