S. Schmitt-Rink

Linear and nonlinear optical properties of semiconductor quantum wells

Abstract In this article we review the experimental and theoretical investigations of the linear and nonlinear optical properties of semiconductor quantum well structures, including the effects of electrostatic fields, extrinsic carriers and real or virtual photocarriers.

Electroabsorption of highly confined systems: Theory of the quantum‐confined Franz–Keldysh effect in semiconductor quantum wires and dots

Semiconductor quantum wells are known to show large electroabsorption (e.g., the quantum‐confined Stark effect) that results in low‐energy optical modulating and switching devices. We show theoretically that the electroabsorption and associated electrorefraction in lower dimensional structures could be much larger, suggesting very low energy devices. We illustrate the theory with specific calculations for hypothetical GaAs‐like quantum wires and dots.

How fast is excitonic electroabsorption

Many semiconductor light modulators rely on changes in excitonic absorption induced by electric fields. We study their temporal response in the framework of a one-dimensional model, for which we solve exactly the timedependent Schrödinger equation. For a homogeneously broadened system, the electroabsorption response time is found to be simply the inverse of the (field-induced) exciton linewidth, which can be as short as 50 fsec.

Femtosecond excitonic optoelectronics

The authors discuss a novel approach to femtosecond optoelectronics which uses the excitonic response to electric fields as a detector and the excitonic nonlinear response to optical fields as a generator. The sensitivity of the quantum-well exciton to applied electric fields is used to measure electrical transients with femtosecond time resolution. The authors examine several mechanisms for femtosecond electrical pulse generation, including exciton ionization and two-photon absorption, and present measurements of the propagation properties of coplanar striplines on ultrathin semiconductor substrates in the 1-100-THz frequency range. The generation and detection of an electrical pulse with a 180-fs risetime propagating on a coplanar stripline on GaAs/AlGaAs quantum wells are demonstrated. >

Large optical singularities of the one-dimensional electron gas in semiconductor quantum wires

Modulation-doped quantum wire structures have been fabricated in the extreme quantum limit in which only the lowest one-dimensional (1D) subband is occupied by electrons. A pronounced Fermi edge singularity is observed for the first time in the absorption and emission spectra of the 1D electron gas. It has a strong temperature dependence determined by the Fermi energy and is much sharper than in two dimensions. The experimental results agree qualitatively with exact diagonalization studies of finite Hubbard chains.

The excitonic optical stark effect in semiconductor quantum wells probed with femtosecond optical pulses

Abstract We review recent experimental and theoretical studies of the excitonic optical Stark effect in semiconductor quantum wells probed with femtosecond optical pulses.

Long-wavelength behavior, impurity scattering and magnetic excitations in a marginal Fermi liquid

The marginal Fermi liquid hypothesis about the excitation spectrum of the high-temperature superconductors is supplemented to specify the long-wavelength behavior; it is shown that there are no anomalous renormalizations of the compressibility and the uniform paramagnetic susceptibility. Consideration of elastic scattering from impurities leads to the conclusion that as temperature is decreased, the scattering approaches the unitarity limit. We discuss the possibility that at T → 0, a marginal Fermi liquid is either a superconductor or an insulator. Predictions for the magnetic structure factor observable in neutron scattering consistent with the nuclear relaxation rate on copper and on oxygen are also given.

On the temperature sensitivity of semiconductor lasers

The temperature dependence of below‐threshold emission from multiple quantum well semiconductor lasers is well characterized by a power law, in excellent agreement with Landau–Ginzburg theory of second‐order phase transitions. We thereby show that it is the temperature dependence of net gain and not that of nonradiative recombination which primarily determines temperature sensitivity of threshold in long‐wavelength injection lasers.

Coherent and incoherent tunneling in asymmetric double quantum wells

The authors discuss tunnelling processes in double quantum well structures in two limiting cases. Firstly, they report the coherent oscillations of a photogenerated electronic wavepacket between the wells. The THz oscillations are traced by an optical pump-probe as well as by four-wave-mixing spectroscopy. A comparison with theory shows that the two experiments give complementary information about the various relaxation processes. Secondly, they discuss hole tunnelling in weakly coupled wells as an example of resonant tunnelling in the limit of strong scattering. The experimental and theoretical results show that the resonant tunnelling process is considerably slowed down by the scattering and relaxation processes.

Inelastic scattering of electrons traversing semiconductor heterojunctions

We calculate the contribution of polar optic phonons to the inelastic scattering rate for an electron traversing semiconductor heterojunctions. In typical geometries, a dramatic reduction in scattering rate compared to the bulk value is found for a limited range of electron energies. This effect is related to spatial separation of initial and final electron wave functions either side of the heterojunction caused by quantum mechanical reflection at the interface. The influence of this phenomenon on the performance of devices, such as unipolar hot‐electron transistors, is discussed.