We present ab initio quantum-mechanical molecular-dynamics simulations of the liquid-metal--amorphous-semiconductor transition in Ge. Our simulations are based on (a) finite-temperature density-functional theory of the one-electron states, (b) exact energy minimization and hence calculation of the exact Hellmann-Feynman forces after each molecular-dynamics step using preconditioned conjugate-gradient techniques, (c) accurate nonlocal pseudopotentials, and (d) Nos\'e dynamics for generating a canonical ensemble. This method gives perfect control of the adiabaticity of the electron-ion ensemble and allows us to perform simulations over more than 30 ps. The computer-generated ensemble describes the structural, dynamic, and electronic properties of liquid and amorphous Ge in very good agreement with experiment. The simulation allows us to study in detail the changes in the structure-property relationship through the metal-semiconductor transition. We report a detailed analysis of the local structural properties and their changes induced by an annealing process. The geometrical, bonding, and spectral properties of defects in the disordered tetrahedral network are investigated and compared with experiment.

Ab initio molecular-dynamics simulation of the liquid-metal-amorphous-semiconductor transition in germanium.

The semiconductor ZnO has gained substantial interest in the research community in part because of its large exciton binding energy (60meV) which could lead to lasing action based on exciton recombination even above room temperature. Even though research focusing on ZnO goes back many decades, the renewed interest is fueled by availability of high-quality substrates and reports of p-type conduction and ferromagnetic behavior when doped with transitions metals, both of which remain controversial. It is this renewed interest in ZnO which forms the basis of this review. As mentioned already, ZnO is not new to the semiconductor field, with studies of its lattice parameter dating back to 1935 by Bunn [Proc. Phys. Soc. London 47, 836 (1935)], studies of its vibrational properties with Raman scattering in 1966 by Damen et al. [Phys. Rev. 142, 570 (1966)], detailed optical studies in 1954 by Mollwo [Z. Angew. Phys. 6, 257 (1954)], and its growth by chemical-vapor transport in 1970 by Galli and Coker [Appl. Phys. ...

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A comprehensive review of zno materials and devices

This review provides numerical and graphical information about many (but by no means all) of the physical and electronic properties of GaAs that are useful to those engaged in experimental research and development on this material. The emphasis is on properties of GaAs itself, and the host of effects associated with the presence of specific impurities and defects is excluded from coverage. The geometry of the sphalerite lattice and of the first Brillouin zone of reciprocal space are used to pave the way for material concerning elastic moduli, speeds of sound, and phonon dispersion curves. A section on thermal properties includes material on the phase diagram and liquidus curve, thermal expansion coefficient as a function of temperature, specific heat and equivalent Debye temperature behavior, and thermal conduction. The discussion of optical properties focusses on dispersion of the dielectric constant from low frequencies [κ0(300)=12.85] through the reststrahlen range to the intrinsic edge, and on the ass...

Semiconducting and other major properties of gallium arsenide

A broad review of recent research work on the preparation and the remarkable properties of intercalation compounds of graphite, covering a wide range of topics from the basic chemistry, physics and materials science to engineering applications.

Intercalation compounds of graphite

X-ray photoelectron spectroscopic studies of iron oxides

A comprehensive survey of the total valence-band x-ray-photoemission spectra of 14 semiconductors is reported: cubic GaP, GaAs, GaSb, InP, InAs, InSb, ZnS, ZnSe, ZnTe, CdTe, and HgTe, hexagonal ZnO, CdS, and CdSe. The binding energies of the outermost d shells were determined relative both to the top of the valence bands (E;sup V;sub B;) and to the Fermi level of a thin layer of gold that was vapor deposited after each run (E;sup F;sub B;). The Fermi level fell near the center of the gap for six samples, near the top for two, and near the bottom for three. Evidence for an apparent increase in core d-level spin-orbit slitting over free-atom values was interpreted as a possible spreading of a ..gamma../sub 7/ and a ..gamma../sub 8/ level from the upper (d /sub 3///sub 2/) ..gamma../sub 8/ level by a tetrahedral crystal field. The s, p valence-band spectra showed three main peaks, wth considerable structure on the ''least-bound'' peak. Characteristic binding energies of spectral features in I'(E) are tabulated. The energies of the characteristic symmetry points L/sub 3/, X/sub 5/, W/sub 2/ ..sigma..;sup min 1;, W/sub 1/, X/sub 3/(L/sub 1/), X/sub 1/, L/sub 1/, and ..gamma../sub 1/ for the 11 cubicmore » compounds are compared with UPS and theoretical band-structure results. The energies calculated using the relativistic-orthogonalized-plane-wave approach with X;sub infinityBETA; exchange agree very well with experiment, on the whole. The desities of states calculated using the empirical-psuedopotenital method provided a useful basis for relating features in I'(E) to energies of the characteristic symmetry points. 21 tables, 16 figures« less

Total valence-band densities of states of III-V and II-VI compounds from x-ray photoemission spectroscopy

The high-resolution x-ray photoemission spectra (XPS) of the total valence bands of atomically clean diamond, graphite, and glassy carbon, obtained with monochromatized Al K ..cap alpha.. radiation, are reported and discussed. By comparing valence-band and carbon-1s photoelectron kinetic energies, the XPS valence-band spectra I'E) of diamond and graphite were rigorously affixed to the same energy scale as earlier K x-ray emission spectra i(E). The two spectra - I'(E) and i(E) - have very different energy dependencies of intensity because selection rules and cross-section ratios render i(E) sensitive only to 2p character and I'(E) far more sensitive to 2s character. Taken together, I'(E) and i(E) show that the fractional p character in the diamond valence band increases from approx. 16% at the bottom of the band to approx. 92% at the top, with an average hybridization of approx. s/sup 1/ /sup 2/p/sup 2/ /sup 8/. The spectra agree well with the density of states of Painter et al, but indicate a valence-band width of 24.2(10) eV rather than their 20.8 eV. The C(1s) binding energy of 284.68(20) eV in graphite agrees well with a recent theoretical estimate of 284.4(3) eV by Davis and Shirley. Analysis of I'(E) i(E) for graphite resolvesmore » the valence bands cleanly into sigma and ..pi.. bands, with the spectrum I'(E) of the former resembling that of diamond, but with a stronger 2s admixture (sp/sup 2/ vs sp/sup 3/). The XPS cross section of the (p/sub z/)..pi.. bands was very low, as expected by symmetry. The bandwidth of 24(1) eV somewhat exceeded Painter and Ellis's calculated value of 19.3 eV. Glassy carbon showed an I'(E) between that of diamond and graphite, consistent with an amorphous lattice containing both trigonal and tetrahedral bonds. 8 figures, 3 tables.« less

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X-ray photoemission studies of diamond, graphite, and glassy carbon valence bands

High-resolution x-ray photoelectron spectra of the total valence bands of crystalline and amorphous silicon and germanium are reported. For the crystals, the spectra yield results that are strikingly similar to current theoretical calculations of the electron density of states, $\ensuremath{\rho}(E)$. Amorphous Si and Ge exhibit definite band structures that are similar to one another but markedly different from the crystalline results. They agree very well with the theoretical model of Joannopoulos and Cohen.

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X-Ray Photoemission Spectra of Crystalline and Amorphous Si and Ge Valence Bands

The ${L}_{2}{M}_{45}{M}_{45}$ and ${L}_{3}{M}_{45}{M}_{45}$ Auger spectra of clean metallic copper and zinc were measured. A theory was developed to predict the Auger energies. The theory employs experimental electron binding energies, which were also measured, two-electron integrals, and Hartree-Fock energies. It accounts for multiplet splitting in the ${d}^{8}$ final state, predicting structure in excellent agreement with experiment in zinc and in very good agreement in copper. It also accounts for "static" atomic relaxation and for static extra-atomic relaxation (screening), which is related to the Friedel theory of alloys. The theory developed here predicts the Auger energies to within 1 eV in zinc and 2-3 eV in copper. Since atomic integrals were used, the success of the theory implies that an atomistic approach to Auger energies is valid for these metals. The magnitude of the extra-atomic relaxation energy (\ensuremath{\sim} 10 eV) suggests that it may be a crucial factor in Auger energy shifts arising from chemical environment or surface condition.

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L 2 , 3 M 45 M 45 Auger Spectra of Metallic Copper and Zinc: Theory and Experiment

X-ray-photoelectron-spectroscopy studies on clean metallic zinc are reported. A well-defined Fermi edge was observed, and the $3d$ band peak was located at ${E}_{F}\ensuremath{-}10.2$ eV. The data analysis raised the question of the extent to which valence-band photoemission spectra of metals are distorted, relative to one-electron "frozen-orbital" band-structure calculations, by differential relaxation. Atomic hole-state calculations by Lindgren and by Gelius and Siegbahn indicate that (intra-) atomic relaxation can vary by up to 5 eV between $3d$ and $4s$ shells. Thus valence-band spectra in $3d$ transition metals can be seriously distorted by atomic relaxation alone. It is argued that the $3d$ bands probably lie below the $4s$, $4p$ valence bands in zinc in the initial state, but not in the photoemission spectrum. The nickel photoemission spectrum may well be distorted by relaxation. The magnitude of the extra-atomic relaxation energy $\ensuremath{\Delta}{E}_{B}$ was estimated in several ways. Empirical estimates were based on comparisons among photoemission and optical data on several elements. Semiempirical estimates were based on theoretical atomic binding energies and experimental binding energies in metals. All estimates were in rather good agreement, showing extra-atomic relaxation energies of up to \ensuremath{\sim} 15 eV. A theoretical model was derived, based on the assumption that extra-atomic relaxation occurs through screening of the hole state by formation of a semilocalized exction. This process was described by Friedel as positive phase shifts in the conduction bands. The model predicts a slow rise in $\ensuremath{\Delta}{E}_{B}$ in the $3d$ series and a sudden drop between Ni and Cu, in excellent agreement with experiment.

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R. A. Pollak

Papers

Total valence-band densities of states of III-V and II-VI compounds from x-ray photoemission spectroscopy

X-ray photoemission studies of diamond, graphite, and glassy carbon valence bands

X-Ray Photoemission Spectra of Crystalline and Amorphous Si and Ge Valence Bands

L 2 , 3 M 45 M 45 Auger Spectra of Metallic Copper and Zinc: Theory and Experiment

X-Ray Photoemission from Zinc: Evidence for Extra-Atomic Relaxation via Semilocalized Excitons