Thanks to their multi-valley, anisotropic, energy band structure, two-dimensional electron systems (2DESs) in modulation-doped AlAs quantum wells (QWs) provide a unique platform to investigate electron interaction physics and ballistic transport. Indeed, a plethora of phenomena unseen in other 2DESs have been observed over the past decade. However, a foundation for sample design is still lackin...

The behavior of spin diffusion in doped semiconductors is shown to be qualitatively different than in undoped (intrinsic) ones. Whereas a spin packet in an intrinsic semiconductor must be a multiple-band disturbance, involving inhomogeneous distributions of both electrons and holes, in a doped semiconductor a single-band disturbance is possible. For n-doped nonmagnetic semiconductors the enhanc...

Ultrafast terahertz spectroscopy can be used to probe charge and spin dynamics in semiconductors. We have studied THz emission from bulk InAs and GaAs and from GaAs/AlGaAs quantum wells as a function of magnetic field. Ultrashort pulses of THz radiation were produced at semiconductor surfaces by photoexcitation with a femtosecond TiSapphire laser, and we recorded the THz emission spectrum and t...

A model that explains the unusual characteristics of the AlGaAs/GaAs modulation-doped field-effect transistor (MODFET) with InAs quantum dots incorporated in the GaAs channel is presented. It is shown that the negative charge of electrons confined in quantum dots decreases the threshold gate–drain voltage at which the channel is fully depleted. This provides an impact ionization of quantum dots...

Exchange-constants have been evaluated from first-principles in Mn-doped Ge, mainly focusing on the effects of the impurity concentration and of the arrangement of Mn-atoms in the semiconducting matrix. As expected, the Mn-concentration strongly affects the magnitude of the exchange constants (especially between Mn as first-nearest-neighbors (NNs) in the cation position). Interestingly, the arr...

The scanning tunneling microscope is used to study GaAs epitaxial structures, cleaved in ultrahigh vacuum, and viewed in cross section. Two applications are described: in the first, the net donor concentration in Si-doped GaAs is deduced by direct measurement of the depletion width at pn junctions. In the vicinity of the pn junctions, net donor concentrations of greater than 2X 10 cm3 are obser...

The development and characterization of high-performance nanocontacts to n-GaAs are reported. The nanocontacts can be made to both undoped and p-doped low-temperature-grown GaAs ~LTG:GaAs! cap layers. The geometry of the nanocontact is well characterized and requires the deposition of a 4 nm single-crystalline Au cluster onto an ohmic contact structure which features a chemically stable LTG:GaA...

We report on the molecular beam epitaxy growth of Au-assisted GaAs p-type-doped NW arrays on the n-type GaAs(111)B substrate and their photovoltaic properties. The samples are grown at different substrate temperature within the range from 520 to 580 °C. It is shown that the dependence of conversion efficiency on the substrate temperature has a maximum at the substrate temperature of 550 °C. For...

We have investigated the gate-dependent magnetoresistance of strongly asymmetric double-well structures. The structures were prepared by inserting a thin Al0.3Ga0.7As barrier into the GaAs buffer layer of standard modulation-doped GaAs/Al0.3Ga0.7As heterojunctions. The resulting double-well system consists of a nearly rectangular well and of a triangular well coupled by tunneling through the th...