We report on the study of spin photocurrents in (110)-grown quantum well structures. 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 spin dependent origin.

No abstract

No abstract

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 intersubband laser.

We calculated the material gain and the threshold current density for quantum wire intersubband laser structures. In quantum cascade laser devices with active regions of lower dimensionality a reduction of the nonradiative losses and consequently an increase in the material gain and a reduction of the threshold current density is predicted. In our calculations of the material gain and the threshold current density for a realistic quantum wire intersubband laser structure fabricated by the cleaved edge overgrowth ͑CEO͒ technique, however, it turns out that excited states formed in those structures even reduce the material gain compared to conventional quantum well cascade lasers. The threshold current density also turns out to be increased due to the reduced material gain on the one hand and due to a small optical confinement factor in such structures on the other hand. The main consequence for the design of such quantum wire laser structures is to avoid the formation of excited states to be able to benefit from the reduction of the dimensionality of the electron system in terms of reduced nonradiative losses.