The wave function of a hole bound to an individual Mn acceptor in GaAs is spatially mapped by scanning tunneling microscopy at room temperature and an anisotropic, crosslike shape is observed. The spatial structure is compared with that from an envelope-function, effective mass model and from a tight-binding model. This demonstrates that anisotropy arising from the cubic symmetry of the GaAs crystal produces the crosslike shape for the hole wave function. Thus the coupling between Mn dopants in GaMnAs mediated by such holes will be highly anisotropic.

We have experimentally achieved spin polarization by a lateral current in a single nonmagnetic semiconductor heterojunction. The effect does not require an applied magnetic field. The current-induced spin orientation can be seen as the inverse of the circular photogalvanic effect (also often referred to as spin photocurrents): the nonequilibrium spin changes its sign as the current reverses.

We have studied the effect of impurity doping on the optical properties of indium phosphide (InP) nanowires. Photoluminescence measurements have been performed on individual nanowires at low temperatures (5–70 K) and at low excitation intensities (0.5–10W∕cm2). We show that the observed redshift (200 meV) and the linewidth (70 meV) of the emission of p-type InP wires are a result of a built-in electric field in the nanowires. This bandbending is induced by Fermi-level pinning at the nanowire surface. Upon increasing the excitation intensity, the typical emission from these p-InP wires blueshifts with 70meV∕decade, due to a reduction of the bandbending induced by an increase in the carrier concentration. For intrinsic and n-type nanowires, we found several impurity-related emission lines.

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The electron, hole, and exciton g factors and diamagnetic coefficients have been calculated using envelopefunction theory for cylindrical InAs/InP quantum dots in the presence of a magnetic field parallel to the dot symmetry axis. A clear connection is established between the electron g factor and the amplitude of those valence-state envelope functions that possess nonzero orbital momentum associated with the envelope function. The dependence of the exciton diamagnetic coefficients on the quantum dot height is found to correlate with the energy dependence of the effective mass. Calculated exciton g factor and diamagnetic coefficients, constructed from the values associated with the electron and hole constituents of the exciton, match experimental data well, however including the Coulomb interaction between the electron and hole states improves the agreement. Remote-band contributions to the valence-band electronic structure, included perturbatively, reduce the agreement between theory and experiment.

Transition-metal dopants such as Mn determine the ferromagnetism in dilute magnetic semiconductors such as Ga(1-x)Mn(x)As. Recently, the acceptor states of Mn dopants in GaAs were found to be highly anisotropic owing to the symmetry of the host crystal. Here, we show how the shape of such a state can be modified by local strain. The Mn acceptors near InAs quantum dots are mapped at room temperature by scanning tunnelling microscopy. Dramatic distortions and a reduction in the symmetry of the wavefunction of the hole bound to the Mn acceptor are observed originating from strain induced by quantum dots. Calculations of the acceptor-state wavefunction in the presence of strain, within a tight-binding model and within an effective-mass model, agree with the experimentally observed shape. The magnetic easy axes of strained lightly doped Ga(1-x)Mn(x)As can be explained on the basis of the observed local density of states for the single Mn spin.

Circulating orbital currents produced by the spin-orbit interaction for a single electron spin in a quantum dot are explicitly evaluated at zero magnetic field, along with their effect on the total magnetic moment (spin and orbital) of the electron spin. The currents are dominated by coherent superpositions of the conduction and valence envelope functions of the electronic state, are smoothly varying within the quantum dot, and are peaked roughly halfway between the dot center and edge. Thus the spatial structure of the spin contribution to the magnetic moment (which is peaked at the dot center) differs greatly from the spatial structure of the orbital contribution. Even when the spin and orbital magnetic moments cancel (for g = 0) the spin can interact strongly with local magnetic fields, e.g. from other spins, which has implications for spin lifetimes and spin manipulation.

Scanning tunneling spectroscopy was performed at low temperature on buried manganese ͑Mn͒ acceptors below the ͑110͒ surface of gallium arsenide. The main Mn-induced features consisted of a number of dI / dV peaks in the band gap of the host material. The peaks in the band gap are followed by negative differential conductivity, which can be understood in terms of an energy-filter mechanism. The spectroscopic features detected on the Mn atoms clearly depend on the depth of the addressed acceptor below the surface. Combining the depth dependence of the positions of the Mn-induced peaks and using the energy-filter model to explain the negative resistance qualitatively proves that the binding energy of the hole bound to the Mn atom increases for Mn acceptors closer to the surface.