Electron energy band alignment at the (100)Si/MgO interface

The electron energy band diagram at the (100)Si/MgO interface is characterized using internal photoemission of electrons and holes from Si into the oxide. For the as-deposited amorphous MgO the interface barriers correspond to a band gap width of 6.1 eV, i.e., much lower than the conventionally assumed bulk crystal value (7.83 eV). The annealing-induced crystallization of MgO mostly affects the energy of the valence band while the conduction band bottom retains its energy position at 3.37 +/- 0.05 eV above the top of the silicon valence band.(C) 2010 American Institute of Physics. (doi:10.1063/1.3294328

Diffraction and quasiclassical limit of the Aharonov--Bohm effect

Since the Aharonov-Bohm effect is the purely quantum effect that has no analogues in classical physics, its persistence in the quasiclassical limit seems to be hardly possible. Nevertheless, we show that the scattering Aharonov-Bohm effect does persist in the quasiclassical limit owing to the diffraction, i.e. the Fraunhofer diffraction in the case when space outside the enclosed magnetic flux is Euclidean, and the Fresnel diffraction in the case when the outer space is conical. Hence, the enclosed magnetic flux can serve as a gate for the propagation of short-wavelength, almost classical, particles. In the case of conical space, this quasiclassical effect which is in principle detectable depends on the particle spin.Comment: 12 pages, minor changes, references update

Intrinsic Charge Trapping in Amorphous Oxide Films: Status and Challenges

We review the current understanding of intrinsic electron and hole trapping in insulating amorphous oxide films on semiconductor and metal substrates. The experimental and theoretical evidences are provided for the existence of intrinsic deep electron and hole trap states caused by the disorder of amorphous metal oxide films. We start from presenting the results for amorphous (a) HfO<sub>2</sub>, chosen due to the availability of highest purity amorphous films, which is vital for studying their intrinsic electronic properties. Exhaustive photo-depopulation spectroscopy (EPDS) measurements and theoretical calculations using density functional theory (DFT) shed light on the atomic nature of electronic gap states responsible for deep electron trapping observed in a-HfO<sub>2</sub>. We review theoretical methods used for creating models of amorphous structures and electronic structure calculations of amorphous oxides and outline some of the challenges in modelling defects in amorphous materials. We then discuss theoretical models of electron polarons and bi-polarons in a-HfO<sub>2</sub> and demonstrate that these intrinsic states originate from low-coordinated ions and elongated metal-oxygen bonds in the amorphous oxide network. Similarly, holes can be captured at under-coordinated O sites. We then discuss electron and hole trapping in other amorphous oxides, such as a-SiO<sub>2</sub>, a-Al<sub>2</sub>O<sub>3</sub>, a-TiO<sub>2</sub>. We propose that the presence of low-coordinated ions in amorphous oxides with electron states of significant p and d character near the conduction band minimum (CBM) can lead to electron trapping and that deep hole trapping should be common to all amorphous oxides. Finally, we demonstrate that bi-electron trapping in a-HfO<sub>2</sub> and a-SiO<sub>2</sub> weakens Hf(Si)-O bonds and significantly reduces barriers for forming Frenkel defects, neutral O vacancies and O<sup>2-</sup> ions in these materials. These results should be useful for better understanding of electronic properties and structural evolution of thin amorphous films under carrier injection conditions

Low temperature spin fluctuations in geometrically frustrated Yb3Ga5O12

In the garnet structure compound Yb3Ga5O12, the Yb3+ ions (ground state effective spin S' = 1/2) are situated on two interpenetrating corner sharing triangular sublattices such that frustrated magnetic interactions are possible. Previous specific heat measurements evidenced the development of short range magnetic correlations below 0.5K and a lambda-transition at 54mK (Filippi et al. J. Phys. C: Solid State Physics 13 (1980) 1277). From 170-Yb M"ossbauer spectroscopy measurements down to 36mK, we find there is no static magnetic order at temperatures below that of the lambda-transition. Below 0.3K, the fluctuation frequency of the short range correlated Yb3+ moments progressively slows down and as the temperature tends to 0, the frequency tends to a quasi-saturated value of 3 x 10^9 s^-1. We also examined the Yb3+ paramagnetic relaxation rates up to 300K using 172-Yb perturbed angular correlation measurements: they evidence phonon driven processes.Comment: 6 pages, 5 figure

Interface barriers at the interfaces of polar GaAs(111) faces with Al2O3

Internal photoemission measurements of barriers for electrons at interfaces between GaAs(111) and atomic-layer deposited Al2O3 indicate that changing the GaAs polar crystal face orientation from the Ga-terminated (111)A to the As-terminated (111)B has no effect on the barrier height and remains the same as at the non-polar GaAs(100)/Al2O3 interface. Moreover, the presence of native oxide on GaAs(111) or passivation of this surface with sulphur also have no measurable influence on the GaAs(111)/Al2O3 barrier. These results suggest that the orientation and composition-sensitive surface dipoles conventionally observed at GaAs surfaces are effectively compensated at GaAs/oxide interfaces. (C) 2012 American Institute of Physics. (http://dx.doi.org/10.1063/1.3698461

Electron band alignment between (100)InP and atomic-layer deposited Al2O3

Energy barriers at interfaces of (100)InP with atomic-layer deposited Al2O3 are determined using internal photoemission of electrons. The barrier height between the top of the InP valence band and bottom of the alumina conduction band is found to be 4.05 +/- 0.10 eV corresponding to a conduction band offset of 2.7 eV. An interlayer associated with the oxidation of InP may result in a lower barrier for electron injection potentially leading to charge instability of the insulating stack. A wide-gap P-rich interlayer has a potential to reduce this degrading effect as compared to In-rich oxides. (C) 2010 American Institute of Physics. (doi: 10.1063/1.3496039

Six-dimensional Davidson potential as a dynamical symmetry of the symplectic Interacting Vector Boson Model

A six-dimensional Davidson potential, introduced within the framework of the Interacting Vector Boson Model (IVBM), is used to describe nuclei that exhibit transitional spectra between the purely rotational and vibrational limits of the theory. The results are shown to relate to a new dynamical symmetry that starts with the $Sp(12,R) \supset SU(1,1) \times SO(6)$ reduction. Exact solutions for the eigenstates of the model Hamiltonian in the basis defined by a convenient subgroup chain of SO(6) are obtained. A comparison of the theoretical results with experimental data for heavy nuclei with transitional spectra illustrates the applicability of the theory.Comment: 9 pages, 4 figure

Superradiance from an ultrathin film of three-level V-type atoms: Interplay between splitting, quantum coherence and local-field effects

We carry out a theoretical study of the collective spontaneous emission (superradiance) from an ultrathin film comprised of three-level atoms with $V$-configuration of the operating transitions. As the thickness of the system is small compared to the emission wavelength inside the film, the local-field correction to the averaged Maxwell field is relevant. We show that the interplay between the low-frequency quantum coherence within the subspace of the upper doublet states and the local-field correction may drastically affect the branching ratio of the operating transitions. This effect may be used for controlling the emission process by varying the doublet splitting and the amount of low-frequency coherence.Comment: 15 pages, 5 figure