Injection of spin polarized electrons from a metal into a semiconductor is demonstrated for a GaAs/(In,Ga)As light emitting diode covered with Fe. The circular polarization degree of the observed electroluminescence reveals a spin injection efficiency of 2%. The underlying injection mechanism is explained in terms of a tunneling process.

The interaction between surface acoustic waves and quasi-two-dimensional inversion electron systems on GaAs/Al"Ga& As heterojunctions is investigated in high magnetic fields and at low temperatures. The interaction of the surface acoustic wave with high-mobility inversion electrons leads to strong quantum oscillations in both the transmitted surface wave intensity as well as in the sound velocity, rejecting the quantum oscillations of the magnetoconductivity as a function of an applied magnetic field. We study the dependence of thip interaction on the magnetic field and on the surface-acoustic-wave power and frequency, and discuss the results using simple models. The inhuence of slight spatial inhomogeneities in the carrier density on the line shape of the quantum oscillations is analyzed in detail and related to their inAuence on the quantum Hall effect. First experimental results on the interaction of surface acoustic waves with two-dimensional electron systems in gated heterojunctions providing an adjustable carrier density are presented.define the piezoelectric coupling coefficient 2(U -Uo) K =

No abstract

We report the observation of resonant edge excitations of a high-mobility two-dimensional electron system in the regime of the fractional quantum Hal1 effect. Narrow edge resonances are observed only on fractional or integer Hall plateaus and have a resonance frequency proportional to the quantized Hall conductivity.We interpret our results using a theory of edge magnetoplasmons in the quantum Hall regime. Resonant edge excitations of a bounded two-dimensional electron system (2D ES) in a perpendicular magnetic field 8, edge magnetoplasmons (EMP's), are modes with wavelengths defined by the sample perimeter. First studies by Allen, Stormer, and Hwang ' withGaAs/Al"Gal -"As heterojunctions and by Mast, Dahm, and Fetter on the surface of liquid helium have stimulated a large body of experimental' and theoretical work. ' ' Experimentally, systems have been investigated with sizes that differ by many orders of magnitudes.

We investigate the molecular beam epitaxy of InSb on (001) GaSb by reflection high energy electron diffraction and atomic force microscopy. The growth process is found to follow the Stransky–Krastanov growth scheme with the onset to three-dimensional growth occurring between 1.7 and 2.8 InSb monolayers depending on substrate temperature. The critical thickness is enhanced at low temperature because of a kinetically limited adatom diffusion length and, apparently, at high temperature because of the thermally activated desorption of In. On the basis of these results, the segregation of In during the growth of (Ga,In)Sb is analyzed in situ, yielding a segregation energy of 0.11 eV.