H. Lage

One‐dimensional lateral‐field‐effect transistor with trench gate‐channel insulation

A novel unipolar transistor device has been realized starting from two‐dimensional electron systems (2DES) in modulation‐doped AlGaAs/GaAs heterostructures. A 600‐nm‐wide 1D channel is insulated laterally from 2DES regimes by 700‐nm‐wide deep mesa etched trenches. The conductivity in the quasi‐one‐dimensional channel can be tuned via the in‐plane lateral field effect of the adjacent 2DES gates where the vacuum (or air) in the etched trenches serves as the dielectric. Room‐temperature operation is demonstrated yielding a 17 μS transconductance corresponding to 170 mS/mm 2D transconductance.

Observation and analysis of quantum wire structures by high-resolution X-ray diffraction

We report on the double-crystal X-ray diffraction analysis of AlGaAs/GaAs quantum wire structures. We show that X-ray scattering is very sensitive to the modulation of structural parameters parallel to the crystal surface under certain diffraction conditions. The experimental diffraction patterns exhibit quantum wire satellite peaks which allow us to determine the quantum wire period and the quantum wire width. Furthermore, we found that due to the finite lateral width of the quantum wires a partial asymmetric strain relaxation of the unit cell occurs resulting in an orthorhombic lattice deformation.

Triple crystal x‐ray diffractometry of periodic arrays of semiconductor quantum wires

Kinematical diffraction theory and the optical coherence formalism have been used for calculating the diffuse x‐ray scattering from periodic quantum wires. The method calculates the distribution of the diffusely scattered intensity in the reciprocal lattice plane. The simulated distributions have been compared with those measured on a InAs/GaAs quantum wire by means of triple crystal x‐ray diffractometry and a good agreement has been achieved. The method can be applied to studies of internal stress relaxation in quantum wires.

Electroluminescence spectroscopy of resonantly coupled GaAs‐AlAs superlattices

The resonant coupling of different electronic subbands between adjacent wells in GaAs‐AlAs superlattices is investigated with electroluminescence (EL) spectroscopy as a function of the applied forward bias. The EL efficiency, i.e., the EL intensity normalized to the current, exhibits a resonant behavior. An efficient occupation of the second subband by sequential resonant tunneling is observed at higher bias.

Role of broken translational invariance for the optical response of excitons in low-dimensional semiconductors

We manipulate the center-of-mass motion of excitons by introducing fractions of a monolayer of InAs in bulklike GaAs. Deposition of InAs on various terraced surfaces provides the direct experimental control of the lateral extent of the InAs insertion and thus of the exciton motion. The optical response of excitons attached to these InAs insertions is predominantly determined by the dimensionality of their translational motion.

Magneto-optics of electron-gases confined in GaAs quantum dots

Photoluminescence spectroscopy has been used to probe the occupied electron states below the Fermi energy of zero-dimensional electron systems in both zero and finite magnetic fields. The arrays of modulation-doped quantum dots investigated were fabricated by reactive-ion etching of Al0.3Ga0.7As/GaAs heterojunctions with a δ-layer of Be present in the GaAs at 200 A from the interface in order to improve luminescence efficiency. We show that the low magnetic field dispersion (B < 8 T) of the acceptor recombination line is directly related to the magnetic field dependence of the total ground state energy of interacting electrons in the quantum dots.

Temporal evolution of the electron-hole plasma recombination in quantum wires

The authors report the results of a spectroscopic investigation of the radiative recombination processes occurring in a dense electron-hole plasma confined in quasi-one-dimensional semiconductor quantum wires. Intersubband transitions involving quantum wire states with quantum number as high as ny=5 are observed in the photoluminescence spectra recorded under stationary conditions of high excitation intensity. The temporal evolution of the luminescence is characterized by a decay time of about 800 ps longer than the one measured in the two-dimensional reference heterostructure.

Electroluminescence spectroscopy of resonant tunnelling in GaAs-AlAs superlattices

Resonant tunnelling between different subbands of adjacent wells is investigated with electroluminescence spectroscopy as a function of forward bias voltage. The observed near-bandgap electroluminescence lines indicate a strong inhomogeneity in the electric field as well as in the carrier distribution. This interpretation is supported by calculations. Electroluminescence lines originating from excited conduction and valence subband states demonstrate an efficient occupation of these subbands by resonant tunnelling.

Landau versus one-dimensional quantization in GaAs

Abstract We investigate quantum wires with time-resolved magnetoluminescence spectroscopy under high excitation intensity at fields up to 14 T. A transition from one-dimensional quantization to Landau quantization takes place at 6 T for a GaAs wire with an active cross section of 60 nm x 10.6 nm. Bandgap renormalization appears to be enhanced by 30% in comparison to quantum wells.

Linear and nonlinear optical properties of GaAs quantum wires—center-of-mass, excitonic and electron-hole plasma quantization

We have studied wide quantum well structures with various spectroscopic tools. The effects originating from lateral quantization are found to be strongly dependent on the state under investigation and on the excited carrier density. While conventional low-intensity photoluminescence excitation spectroscopy reveals the quantization of the excitons center-of-mass motion, two-photon absorption spectroscopy indicates that higher excitonic states are completely quantized by the lateral confinement. The energy positions are found to be in good agreement with one-dimensional (1D) subband calculations. Additionally, transitions between 1D subbands can be found under high excitation conditions. The singularity of the 1D-density of states is reflected by distinct peaks in the time resolved spectra of a dense electron-hole plasma, which is optically excited by high power laser pulses.