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Notes: We investigate in detail the occurrence of magnetic domains in epitaxially grown MnAs films on GaAs(001) by magnetic force microscopy (MFM). MnAs layers exhibit in their demagnetized state a very complex magnetic domain structure. High resolution MFM images reveal detailed information on the domain wall. Additionally, we imaged magnetic domains in the dependence on the applied magnetic field. This detailed investigation gives new insight into the correlation between film topography and magnetic domain structures. Systematic magnetization measurements in-plane and out-of-plane have shown high anisotropy in our films. The out-of-plane magnetization determined as a function of the applied field reveals that the direction of the magnetic moments in the domain walls are out-of-plane, thus the domain walls are determined as 180° Bloch type. © 2000 American Institute of Physics.

Notes: We have used a 90° double reflection high-energy electron diffraction (RHEED) setup to perform a comprehensive real-time study of the morphology of vicinal GaAs(001) surfaces during molecular beam epitaxy. The technique allows to record RHEED intensities simultaneously in the [1¯10] and [110] azimuths and thus enables a detailed study of anisotropy effects. Comparative measurements on surfaces with 2° misorientation towards (111)Ga (A surface) and towards (11¯1)As (B surface), respectively, show that independent on the step type and reconstruction anisotropy, recordings of the specular beam intensity in the azimuth perpendicular to the steps are clearly dominated by the evolution of the staircase order whereas intensity recordings in the azimuth parallel to the steps reveal the evolution of the step edge roughness. Measurements over a wide range of substrate temperatures give insight in the competition between kinetic processes and thermodynamic equilibrium on a length scale accessible to RHEED. For the A surface the transition between two-dimensional (2D) growth and step-flow growth occurs not only at higher temperature than on the B surface, but the disappearance of the intensity oscillations occurs also at different substrate temperatures in different azimuths. The ∼20 °C higher disappearance temperature in the [1¯10] azimuth is explained with a model based on previous scanning tunneling microscopy results which revealed an increasing elongation of the islands in [1¯10] direction with increasing substrate temperature. The B surface is more isotropic and hence no difference in the transition temperature in the two azimuths could be detected. During growth in the transition range between 2D and step-flow growth we observe increased terrace width fluctuations on the B surface, whereas the A surface becomes more uniformly stepped. This demonstrates that in the kinetically controlled regime the anisotropic barrier height for downward diffusion of adatoms over step edges plays an important role for the evolution of the surface morphology. At elevated temperature the barrier height allows downward jumps of the adatoms over B-type steps but not over A-type steps. At conditions close to the thermodynamic equilibrium a kinetic smoothing is observed on the A as well as on the B surface indicating another mechanism to be effective with a change of the energetics due to ordering of the steps in combination with a disordering of the reconstruction on the terraces. This surface is, however, metastable and recovers after growth interruption rapidly (at substrate temperatures 〉580 °C within less than 1s) to the equilibrium bunched surface. © 1997 American Institute of Physics.

Notes: Reflection high energy electron diffraction intensity oscillations are found to be shifted in phase by the predeposition of Si atoms on the (100) GaAs surface during molecular beam epitaxy. The shift is related to a change in surface reconstruction and is a linear function of the Si density. It is only observed in a narrow range of GaAs growth parameters. A different behavior is seen for (100) AlAs, which we attribute to a roughening of the growth front. The phase shift for (100) GaAs is less pronounced on the {01} streaks. This can be explained by a different surface structure near steps running along [11¯0]. © 1995 American Institute of Physics.

Notes: Hot carrier transport processes in GaAs with δ-like high Si doping have been investigated. In the high electric field region the current density decays with time by as much as 20%, an indication of electron trapping. The electron traps are metastable and the electrons can be released by light or thermal excitation. DX− centers can explain the observations, however, other types of localized electron states cannot be unambiguously excluded. © 1995 American Institute of Physics.

Notes: Using resonant Raman spectroscopy we have studied novel GaAs/AlAs superlattice (SL) structures, grown on (113) substrates, where the GaAs and AlAs layer widths vary periodically on a nanometer scale along the lateral [11¯0] direction. We observe sharp confined LO phonon lines for both (113) and simultaneously grown (001) SLs, for a range of different layer widths, whose frequencies map the bulk GaAs LO dispersion. The confined phonon lines of the (113) SLs show a side peak, which can be assigned to a mode with finite k vector parallel to the layers, induced by the lateral periodicity.

Notes: Raman scattering by collective electronic excitations from a δ-doping layer has been used to investigate the ordered incorporation of Si dopant atoms on vicinal GaAs(001) surfaces. In a series of δ-doped samples grown by molecular beam epitaxy (MBE) under specific conditions the Si dopant atoms were found to be incorporated predominantly on Ga sites, even at a doping concentration as high as 1.8×1013 cm−2. A pronounced polarization asymmetry in the Raman scattering intensity of collective intersubband plasmon-phonon modes was observed in a sample grown under conditions established by real-time high-energy electron diffraction to be favorable for wirelike Si incorporation.

Notes: On GaAs (110) substrates a distinct step structure exists on the surface during molecular beam epitaxy of GaAs/AlAs multilayer structures which is monitored in situ by reflection high-energy electron diffraction. This peculiar surface structure results in thicker GaAs (AlAs) channels associated with the step planes giving rise to pronounced redshifts of the luminescence. The observation of hot exciton luminescence indicates increased exciton stability and exciton phonon interaction due to strong lateral localization of the excitons in the GaAs channels. The measured optical anisotropy is in agreement with the lateral potential introduced by the faceting of the GaAs/AlAs interface.

Notes: We demonstrate patterning of ferromagnetic MnAs layers on GaAs substrates by optical writing with a focused laser beam. Depending on the writing conditions, stripes with ridge- and groove-shaped cross sections can be produced without damage of the GaAs substrate. Using in situ control by resistance measurements, conditions for the preparation of completely insulating stripes can be established. The formation of insulating and paramagnetic Mn3O4 during optical writing is verified by Raman scattering. © 2001 American Institute of Physics.

Notes: We investigate the atomic interface structure and the residual strain state of ferromagnetic α (hexagonal) MnAs layers on cubic GaAs(001) by means of high-resolution transmission electron microscopy and electron diffraction. Despite the different symmetries of the adjacent planes at the heterointerface and the large and orientation-dependent lattice mismatch, the hexagonal MnAs grows epitaxially on GaAs(001) with the (11¯.0) prism plane parallel to the cubic substrate. The atomic arrangement at the interface, which is defined by the accommodation of the large lattice mismatch, explains this extreme case of heteroepitaxial alignment. The anisotropic residual strain distribution is discussed with respect to the particular process of lattice misfit relaxation in the presence of the ferromagnetic phase transition. © 2001 American Institute of Physics.

Notes: The surface topography of epitaxial MnAs films on GaAs(001) is studied by scanning probe microscopy. We provide direct experimental evidence for temperature-dependent elastic domains of the coexisting ferromagnetic αMnAs and paramagnetic βMnAs phases. The results agree well with a theoretical model for the elastic equilibrium of periodic domains. © 2002 American Institute of Physics.