J. Cibert

Carrier-induced ferromagnetism in p − Zn 1 − x Mn x Te

We present a systematic study of the ferromagnetic transition induced by the holes in nitrogen doped

STRAIN MAPPING OF ULTRATHIN EPITAXIAL ZNTE AND MNTE LAYERS EMBEDDED IN CDTE

{\mathrm{Zn}}_{1\ensuremath{-}x}{\mathrm{Mn}}_{x}\mathrm{Te}

Structure and magnetism of self-organized Ge(1-x)Mn(x) nano-columns

epitaxial layers, with particular emphasis on the values of the Curie-Weiss temperature as a function of the carrier and spin concentrations. The data are obtained from thorough analyses of the results of magnetization, magnetoresistance, and spin-dependent Hall effect measurements. The experimental findings compare favorably, without adjustable parameters, with the prediction of the Rudermann-Kittel-Kasuya-Yosida (RKKY) model or its continuous-medium limit, that is, the Zener model, provided that the presence of the competing antiferromagnetic spin-spin superexchange interaction is taken into account, and the complex structure of the valence band is properly incorporated into the calculation of the spin susceptibility of the hole liquid. In general terms, the findings demonstrate how the interplay between the ferromagnetic RKKY interaction, carrier localization, and intrinsic antiferromagnetic superexchange affects the ordering temperature and the saturation value of magnetization in magnetically and electrostatically disordered systems.

Ordered magnetic phase in Cd1-xMnxTe/Cd1-y-zMgyZnzTe : N heterostructures: magnetooptical studies

High‐resolution electron microscopy is used to investigate the morphology of ultrathin pseudomorphic (001) ZnTe and MnTe strained layers grown in CdTe. Local distortions of the crystal lattice are measured directly on high‐resolution images by use of image processing software. In the case of ZnTe/CdTe superlattices, the method yields the location of Zn within each place in the heterostructure and the total amount of Zn per period. For MnTe layers embedded in CdTe, one can deduce the atomic morphology of the interfaces which are shown to present a clear asymmetry.

Carrier-induced ferromagnetic interactions in p-doped Zn(1−x)MnxTe epilayers

We report on the structural and magnetic properties of thin Ge(1-x)Mn(x)films grown by molecular beam epitaxy (MBE) on Ge(001) substrates at temperatures (Tg) ranging from 80°C to 200°C, with average Mn contents between 1 % and 11 %. Their crystalline structure, morphology and composition have been investigated by transmission electron microscopy (TEM), electron energy loss spectroscopy and x-ray diffraction. In the whole range of growth temperatures and Mn concentrations, we observed the formation of manganese rich nanostructures embedded in a nearly pure germanium matrix. Growth temperature mostly determines the structural properties of Mn-rich nanostructures. For low growth temperatures (below 120°C), we evidenced a two-dimensional spinodal decomposition resulting in the formation of vertical one-dimensional nanostructures (nanocolumns). Moreover we show in this paper the influence of growth parameters (Tg and Mn content) on this decomposition i.e. on nanocolumns size and density. For temperatures higher than 180°C, we observed the formation of Ge3Mn5 clusters. For intermediate growth temperatures nanocolumns and nanoclusters coexist. Combining high resolution TEM and superconducting quantum interference device magnetometry, we could evidence at least four different magnetic phases in Ge(1-x)Mn(x) films: (i) paramagnetic diluted Mn atoms in the germanium matrix, (ii) superparamagnetic and ferromagnetic low-Tc nanocolumns (120 K 400 K) and (iv) Ge3Mn5 clusters.

Strong influence of Ga/N flux ratio on Mn incorporation into Ga1−xMnxN epilayers grown by plasma-assisted molecular beam epitaxy

Photoluminescence magnetospectroscopy is employed to examine the low-temperature magnetic phase that is induced by the carrier-mediated ferromagnetic exchange interaction in modulation-doped Cd1-xMnxTe quantum well. Unusual properties of the domain structure are linked to tendency towards spin-density wave formation in this low-dimensional magnetic system

RHEED, XPS, HRTEM and channeling studies of molecular beam epitaxy growth of CdTe On (001) GaAs

Abstract p-type doping of molecular-beam-epitaxy grown layers of the diluted magnetic semiconductor Zn(1−x)MnxTe is achieved by using an active nitrogen cell. The strong interaction between the localized Mn spins and the holes deeply modifies the transport properties (metal–insulator transition, spin-dependent Hall effect). In spite of the weak localization of the carriers at low temperature, the holes clearly induce a ferromagnetic interaction between the localized spins, which is discussed as a function of Mn content and hole concentration.

Structure of (111) CdTe epilayers on misoriented (001) GaAs

We report the growth of Mn-doped wurtzite GaN epilayers by nitrogen plasma-assisted molecular beam epitaxy, with a systematic attention to the dependence on the growth conditions. The addition of Mn modifies the growth diagram related to the Ga/N flux ratio. In particular, the stable Ga-bilayer coverage on the growth surface for the Ga-rich condition is destabilized in the presence of Mn. Mn incorporation in the epilayers is found to strongly depend on the Ga/N flux ratio: it varies by two orders of magnitude between the Ga-rich and the N-rich growth conditions. X-ray diffraction measurements on epilayers grown in the stoichiometric condition reveal a clear contrast between the precipitation of perovskite GaMn3N clusters at Mn compositions higher than 1.7%, and the single phase of wurtzite Ga1−xMnxN at lower Mn compositions.

p-type doping of II–VI heterostructures from surface states: Application to ferromagnetic Cd1−xMnxTe quantum wells

Abstract MBE growth of CdTe on (001) GaAs can be achieved either in the (001) or the (111) orientation. We present a study of CdTe/(001) GaAs interfaces by reflection high energy diffraction (RHEED), X-ray photo emission spectroscopy (XPS), high resolution transmission electron microscopy (HRTEM) and channeling. A detailed phase diagram of the GaAs-Te precursor surfaces is reported. The surfaces are analyzed by RHEED and XPS and CdTe growth is characterized on each of them. The (2×1) and (6×1)100 GaAs-Te superstructures allow (001) CdTe growth, while the Te poor (6×1), (6×1)111 and incommensurate (∗ × 3) ones (∗ indicating incommensurate phase in the [1 1 0] direction) induce (111) CdTe growth. XPS reveals three different Te adsorption sites (identified as TeAs, TeGa and TeTe) with concentrations depending on the Te-precursor surface. By HRTEM we observe, in the case of (001)CdTe/(001)GaAs, that the lattice mismatch is accommodated by a square array of Lomer-type edge dislocations with their 1 2 a〈110〉 Burgers vector in the interface plane. Moreover, the defect concentration within the layer is greatly reduced by use of thin ZnTe buffer layers. In the case of (111) CdTe growth, ion channeling shows that (111) CdTe grown on (001) GaAs presents a (111)B face and confirms the epitaxial relationship [11 2 ]CdTe ⫫ [110]GaAs. By HRTEM we reveal that growth proceeds by formation of flat islands. Twinning is present parallel to the interface: it can be eliminated by using GaAs substrates tilted around the [1 1 0] axis.

Ferromagnetic Ga1 − xMnxN epilayers vs. antiferromagnetic GaMn3N clusters

Results concerning [111]CdTe growth on misoriented (001) GaAs substrates are presented and discussed. Growing CdTe on GaAs substrates with Ga steps results in twin‐free layers, which is not the case for As steps. The tilt of the (111) CdTe planes with respect to the (001) GaAs planes is reported versus the GaAs substrate misorientation. We propose a model that establishes a correspondence between the measured tilt and the presence of interface dislocations as observed by high‐resolution electron microscopy. This model also takes into account the effects of the surface morphology on the suppression of twins.