M. Eddrief

Growth of ZnSe layers on β(2×4)As, (i×3)Te, and (4×2)Ga-terminated (0 0 1)GaAs substrates

We have studied the influence of the surface stoichiometry of the (001)GaAs surface (β(2 × 4)As, (i x 3)Te, and (4 x 2)Ga) on the growth mode and defect generation in MBE-grown ZnSe. For the β(2 x 4)As and (i x 3)Te surfaces, no interfacial compounds are formed and the observed stacking faults are not related to the interface. The stacking fault densities and the critical thicknesses are comparable for both the β(2 x 4)As and (i x 3)Te. For the ZnSe layers grown onto a (4 x 2)Ga surface, a different behavior is observed. Ga-related precipitates are formed near the interface. For thicknesses below 100 nm the misfit is partially relaxed by dislocations generated to accommodate the precipitates. Few stacking faults are generated and are seen to be nucleated at the precipitates.

Growth morphology of MnAs epilayers on GaAs(1 1 1)-B substrates by molecular beam epitaxy

Abstract MnAs epilayers were grown by molecular beam epitaxy on GaAs(1xa01xa01)B substrates. The morphology of epilayers has been studied by coupling several in situ techniques. Two distinct growth regimes were distinguished as a function of the substrate temperature. For the growth at 320°C, the system shows an intriguing mechanism of relaxation that produces MnAs isolated islands (the so-called “blocks”) with constant height. The explanation for this mechanism associates the large mobility of atoms at this temperature with the strain due to the important misfit. At lower temperature (200°C) the surface mobility is greatly reduced which results in a more homogeneous film.

Fe/ZnSe(001) Schottky-barrier height evaluated by photoemission

We present the Schottky-barrier height determination for the Fe/ZnSe(001) system performed by core and valence level photoelectron emission spectroscopy. Above the thickness of 2 ML, the Fe–Fermi level position is stabilized at 1.6 eV above the valence-band maximum of the n-type undoped ZnSe. This corresponds to a Schottky-barrier height value of 1.1 eV. A bulk-like d-band electronic structure could be observed for thickness as thin as 2 ML of Fe.

Resonant tunnel magnetoresistance in epitaxial metal-semiconductor heterostructures

We report on resonant tunneling magnetoresistance via localized states (LS) through a ZnSe semiconducting barrier which can reverse the sign of the effective spin polarization of tunneling electrons. Experiments performed on Fe/ZnSe/Fe planar junctions have shown that positive, negative, or even its sign-reversible magnetoresistance can be obtained, depending on the bias voltage, the energy of LS in the ZnSe barrier, and spatial symmetry. The averaging of conduction over all LS in a junction under resonant condition is strongly detrimental to the magnetoresistance.

Tuning the period of elastic MnAs/GaAs(001) α−β pattern by Fe deposition

The alpha-beta elastic striped pattern of MnAs/GaAs(001) is shown to be perturbed by Fe overlayer growth. After nanometric Fe thin film deposition, the elastic pattern is still present in the 10-45 degrees C temperature range, but the period of the pattern increases by up to 40% for MnAs epilayers 70 to 400 nm thick. This observation can be interpreted within a simple model calculation of the pattern elastic energy, providing quantitative agreement with the experimental results

The use of thickness graded samples to investigate the elastic to plastic relaxation in ZnSe/GaAs(001)

The strain relaxation process of ZnSe grown by molecular beam epitaxy on GaAs(001) has been studied using high resolution x-ray diffraction. One single sample with a tailored thickness gradient has been used, allowing us to continuously follow the strain in a wide range of thicknesses. The relaxation starts around 1300 A with the coexistence of fully strained and partially relaxed regions of the ZnSe and continues up to 1600 A. These findings can be explained by the formation of misfit dislocations on the top surface with subsequent migration to the ZnSe/GaAs interface.

Growth and magnetic properties of MnAs epitaxied on GaAs(111)B

We have grown MnAs layers on GaAs(111)B by molecular beam epitaxy and studied their surface and epilayer morphology and its interconnection with magnetic properties. The influence of growth variables such as the As/Mn flux ratio and substrate temperature on the properties of the epilayer was studied. These parameters were found to drastically modify the epilayers characteristics, including its structural quality, and also strongly alter its magnetic properties. A more in-depth knowledge of how these parameters affect epilayers would be extremely useful in tailoring epilayers with specific desirable properties. (c) 2006 American Institute of Physics.

Surface structure and magnetic properties of MnAs epilayers grown on vicinal GaAs(001) substrates

In this study, we have investigated the influence of the vicinality on the surface morphology of MnAs/GaAs(001) epilayers at the nanoscale. The microscopic structure of the MnAs surface is strongly affected by the miscut angle of the substrate, while the characteristic MnAs alpha-beta micronic self-organized stripes pattern remains largely unaffected. Even though the surface morphology is quite different from epilayers deposited on nominal substrates (no miscut), the magnetic properties of the films grown on vicinal substrates are nearly unaltered. That is, the temperature for the onset of the beta phase, for decreasing temperature, the coercive field, and the remnant magnetization are similar to films grown on nominal substrates. These findings open interesting prospects concerning the use of MnAs/GaAs(001) epilayers as temperature-dependent striped templates for the subsequent growth of magnetic thin films and the formation of a great variety of nanostructures.

Magnetic and chemical aspects of Cr-based films grown on GaAs(001)

We have investigated the magnetic and chemical properties of very thin films of Cr, CrAs, and arsenized Cr, grown by molecular beam epitaxy on GaAs (001), using x-ray photoemission spectroscopy and SQUID magnetometry. The substrate was kept at 200 degrees C in an As-rich environment for incoming Cr atoms at the GaAs surface. Gallium segregation and the chemical reactivity between Ga and Cr have negligible contribution to the formation of different thin films. A clear ferromagnetic response, even at room temperature, suggests the formation hk of a very thin buried interfacial layer during the growth process.

Impacts of highly charged ions as seeds in a magneto-structural phase transition of magnetocaloric thin films

Investigation on modifications of structural and magnetic properties of magnetocaloric thin films induced by slow highly charged ions bombardment under well-controlled conditions is presented. The ions induce defects/constraints that facilitate nucleation of one phase with respect to the other in the first-order magnetostructural MnAs, with a consequent suppression of thermal hysteresis, but without any significant perturbation on the other structural and magnetic properties.