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Two-dimensional electron systems have been fabricated by focused ion beam implantation of Si dopant ions in undoped III/V heterostructures grown by molecular beam epitaxy. With this method, lateral patterning of two-dimensional electron gases is possible while the planarity of the sample surface is conserved. In this paper, we present a systematic study of this technique and discuss its potential for applications. In detail, different base material systems are experimentally investigated and compared. The electronic properties of the samples are characterized by low-field Hall measurements, capacitance-voltage spectroscopy, and measurements of the longitudinal magnetoresistance at low temperatures. The dependence of the electronic properties on the implantation parameters is discussed. [ABSTRACT FROM AUTHOR]

The effects of confinement on biexciton renormalization in self-assembled InAs and interfacial GaAs quantum dot (QD) ensembles are studied using two-dimensional Fourier-transform spectroscopy. We find that in thermally annealed InAs QDs, changes in the biexciton transition energy are strongly correlated with those of the exciton and that the biexciton binding energy is similar for all QDs in the ensemble. These results are in contrast to those from GaAs QDs formed from interfacial fluctuations of a narrow quantum well (QW). In both the GaAs QW and QDs, correlation is reduced and the biexciton binding exhibits a strong dependence on localization. Comparison with simulations reveals how confinement and Coulomb interactions modify biexciton renormalization. [ABSTRACT FROM AUTHOR]

A two-dimensional electron gas (2DEG) situated nearby a single layer of self-assembled quantum dots (QDs) in an inverted high electron mobility transistor (HEMT) structure is used as a detector for time-resolved tunneling measurements. We demonstrate a strong influence of charged QDs on the conductance of the 2DEG which allows us to probe the tunneling dynamics between the 2DEG and the QDs time resolved. Measurements of hysteresis curves with different sweep times and real-time conductance measurements in combination with an boxcar-like evaluation method enables us to unambiguously identify the transients as tunneling events between the s- and p-electron QD states and the 2DEG and rule out defect-related transients. [ABSTRACT FROM AUTHOR]

Injection of mode-filtered electrons into a phase-sensitive four-terminal waveguide Aharonov-Bohm (AB) ring is studied. An individually tuneable quantum point contact (QPC) in a waveguide lead of the GaAs/AlGaAs-ring allows to selectively couple to one-dimensional modes in the ring. Thus, we demonstrate single-mode transport in a multimode waveguide structure. Coherent mode-filtering by the lowest QPC subband is verified by nonlocal bend resistance and phase-sensitive AB interference measurements. [ABSTRACT FROM AUTHOR]

Nanoscale devices are fabricated from modulation-doped GaAs/AlGaAs heterostructures, where the two-dimensional electron system is initially depleted. Upon removing the p-type capping layer that compensates for the n-type supply layer, the electron system is induced. Arbitrarily shaped areal, line, and dot elements, i.e. the nanostructures and 2D leads, are simultaneously fabricated by patterning a thin resist layer with an atomic force microscope and subsequent selective wet etching. In this way a single-electron transistor (SET) with a 60 nm diameter island, a 60 nm wide electron waveguide (EWG), and an Aharonov–Bohm (AB) loop of 110 nm average diameter are prepared. Measurements at T=1.5 K reveal Coulomb-blockade, quantized conductance and AB-oscillations for the SET, EWG, and AB loop, respectively. Finally, an EWG is demonstrated in split-gate geometry where the compensating layer is used as split gate. [Copyright &y& Elsevier]