Reflection high-energy electron diffraction patterns of CrSi_2 films on (111) silicon

Highly oriented films of the semiconducting transition metal silicide, CrSi2, were grown on (111) silicon substrates, with the matching crystallographic faces being CrSi_2(001)/Si(111). Reflection high‐energy electron diffraction (RHEED) yielded symmetric patterns of sharp streaks. The expected streak spacings for different incident RHEED beam directions were calculated from the reciprocal net of the CrSi_2(001) face and shown to match the observed spacings. The predominant azimuthal orientation of the films was thus determined to be CrSi_2〈210〉∥Si〈110〉. This highly desirable heteroepitaxial relationship may be described with a common unit mesh of 51 Å^2 and a mismatch of −0.3%. RHEED also revealed the presence of limited film regions of a competing azimuthal orientation, CrSi_2〈110〉∥Si〈110〉. A new common unit mesh for this competing orientation is suggested; it possesses an area of 612 Å^2 and a mismatch of −1.2%

Bringing an emphasis on technical writing to a freshman course in electrical engineering

Includes bibliographical references (page 41).We have recently added a strong writing component to one of our freshman courses in electrical engineering. The students prepared two kinds of reports—memoranda and formal engineering project reports. Our instructional objectives were to execute well these two forms: to write with a professional tone, and to make good choices about which technical material to include. To meet these objectives, model memos and engineering project reports were developed, lectures about these memos and reports were presented, a Web site for the course was developed, the technical aspects of the reports were graded by a student hourly grader, the writing aspects of the reports were evaluated by a professor, and followup debriefings were conducted at the lecture class meetings. We report on the development process and discuss student response to the course

Theoretical study of interacting hole gas in p-doped bulk III-V semiconductors

We study the homogeneous interacting hole gas in $p$-doped bulk III-V semiconductors. The structure of the valence band is modelled by Luttinger's Hamiltonian in the spherical approximation, giving rise to heavy and light hole dispersion branches, and the Coulomb repulsion is taken into account via a self-consistent Hartree-Fock treatment. As a nontrivial feature of the model, the self-consistent solutions of the Hartree-Fock equations can be found in an almost purely analytical fashion, which is not the case for other types of effective spin-orbit coupling terms. In particular, the Coulomb interaction renormalizes the Fermi wave numbers for heavy and light holes. As a consequence, the ground state energy found in the self-consistent Hartree-Fock approach and the result from lowest-order perturbation theory do not agree. We discuss the consequences of our observations for ferromagnetic semiconductors, and for the possible observation of the spin-Hall effect in bulk $p$-doped semiconductors. Finally, we also investigate elementary properties of the dielectric function in such systems.Comment: 9 pages, 5 figures, title slightly changed in the course of editorial process, a few references added, version to appear in Phys. Rev.

Channeling of MeV ions in polyatomic epitaxial films: ReSi2 on Si(100)

Channeling of a He beam in the energy range from 1.4 to 2.7 MeV in a polyatomic epitaxial ReSi2 film (∼150 nm thick) was studied by detecting backscattered He ions. The critical angles and the minimum yields of both the heavy (Re) and the light (Si) elements are obtained directly from backscattering measurements. The critical angles of both Re and Si scale as √1/E. The critical angle of Re is always about 2.3 times that of Si. The minimum yields of both Re and Si do not change over this energy range. The minimum yield of Re (2%) is about 1/7 that of Si (14%). The results are explained qualitatively and quantitatively by the continuum model suitably extended for polyatomic crystals. An important corollary is that a high value for the minimum yield of the light element in a polyatomic single crystal does not necessarily mean that the sublattice of the light element is disordered

Epitaxial ternary RexMo1-xSi2 thin films on Si(100)

Includes bibliographical references (page 3927).Reactive deposition epitaxy was used to synthesize thin layers of RexMo1-xSi2 on Si(100). In the case of x>=1, ReSi2 layers of excellent crystalline quality have been reported previously [J.E. Mahan, K. M. Geib, G. Y. Robinson, R. G. Long, Y. Xinghua, G. Bai, and M.-A. Nicolet, Appl. Phys. Lett. 56, 2439 (1990)]. In the case of x=0, however, virtually no alignment of theMoSi2 and the substrate is found, although this silicide is nearly isomorphic to ReSi2. For intermediate values of x, highly epitaxial ternary silicides are obtained, at least for a Mo fraction up to 1/3

Spin-Hall transport of heavy holes in III-V semiconductor quantum wells

We investigate spin transport of heavy holes in III-V semiconductor quantum wells in the presence of spin-orbit coupling of the Rashba type due to structure-inversion asymmetry. Similarly to the case of electrons, the longitudinal spin conductivity vanishes, whereas the off-diagonal elements of the spin-conductivity tensor are finite giving rise to an intrinsic spin-Hall effect. For a clean system we find a closed expression for the spin-Hall conductivity depending on the length scale of the Rashba coupling and the hole density. In this limit the spin-Hall conductivity is enhanced compared to its value for electron systems, and it vanishes with increasing strength of the impurity scattering. As an aside, we also derive explicit expressions for the Fermi momenta and the densities of holes in the different dispersion branches as a function of the spin-orbit coupling parameter and the total hole density. These results are of relevance for the interpretation of possible Shubnikov-de Haas measurements detecting the Rashba spin splitting.Comment: 6 pages, 2 figures included, some prefactor corrected, version to be published in Phys. Rev.

Spin susceptibilities, spin densities and their connection to spin-currents

We calculate the frequency dependent spin susceptibilities for a two-dimensional electron gas with both Rashba and Dresselhaus spin-orbit interaction. The resonances of the susceptibilities depends on the relative values of the Rashba and Dresselhaus spin-orbit constants, which could be manipulated by gate voltages. We derive exact continuity equations, with source terms, for the spin density and use those to connect the spin current to the spin density. In the free electron model the susceptibilities play a central role in the spin dynamics since both the spin density and the spin current are proportional to them.Comment: 6 pages, revtex4 styl

Van der Waals epitaxial growth of GaSe on Si(111), The

Includes bibliographical references (pages 7293-7294).GaSe, a layered semiconductor, may be grown on the Si(111) surface by molecular beam epitaxy. The crystalline quality is relatively good, in the sense that the MeV4He ion minimum channeling yield (~30%) is as low as that of state-of-the-art bulk material, and the interface is atomically abrupt. The initial film deposits are epitaxial islands, and subsequent growth is in the Frank-van der Merwe mode. With the islands already relaxed at the nucleation stage and coalescing to essentially uniform coverage with the first monolayer of deposition, GaSe on Si(111) provides an example of van der Waals epitaxy. However, it is difficult to understand how epitaxy (crystallographic alignment with the substrate) can occur in such a case, where the film is incommensurate starting from the initial nuclei. A mechanism for alignment of the islands is proposed: they are aligned with the silicon substrate through the influence of dangling bonds at their perimeter, being "quasi-commensurate" by virtue of their small lateral size. Although discommensurate regions are created as the islands grow laterally, there is simply no change in their orientation

Thin film growth of semiconducting Mg2Si by codeposition

Includes bibliographical references (page 1088).Ultrahigh vacuum evaporation of magnesium onto a hot silicon substrate (⩾200 °C), with the intention of forming a Mg2Si thin film by reaction, does not result in any accumulation of magnesium or its silicide. On the other hand, codeposition of magnesium with silicon at 200 °C, using a magnesium-rich flux ratio, gives a stoichiometric Mg2Si film which can be grown several hundreds of nm thick. The number of magnesium atoms which condense is equal to twice the number of silicon atoms which were deposited; all the silicon condenses while the excess magnesium in the flux desorbs. The Mg2Si layers thus obtained are polycrystalline with a (111) texture. From the surface roughness analysis, a self-affine growth mode with a roughness exponent equal to 1 is deduced