Symmetric versus nonsymmetric structure of the phosphorus vacancy on InP(110)

The atomic and electronic structure of positively charged P vacancies on InP(110) surfaces is determined by combining scanning tunneling microscopy, photoelectron spectroscopy, and density-functional theory calculations. The vacancy exhibits a nonsymmetric rebonded atomic configuration with a charge transfer level 0.75+/-0.1 eV above the valence band maximum. The scanning tunneling microscopy (STM) images show only a time average of two degenerate geometries, due to a thermal flip motion between the mirror configurations. This leads to an apparently symmetric STM image, although the ground state atomic structure is nonsymmetric.     

Tunneling negative-U centers and photo-induced reactions in solids

A model of tunneling centers which acquire the negative-U value as a result of a dependence shown by the electron-vibration interaction constant upon the center charge state is proposed. We address the question whether the model is of a sufficiently general character to be applied to the investigation of the tunneling probabilities for centers due to the reversible rearrangements brought about in lattice defects by optical pumping, photo-induced reactions occurring in semiconductors and photochromic materials, and by adsorbate photodesorption. The tunneling systems of the type being considered have been observed in the experimentally investigated gold centers in silicon.     

A Bistable Defect in InP

Point defects in n-indium phosphide were studied by deep-level transient spectroscopy (DLTS). A radiation-induced bistable defect is found to form under irradiation of a space-charge region of n-InP Shottky-barrier diodes. The transformations of the defect configuration stimulated by heating, illumination, and current flow are studied.__________Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 4, pp. 80–84, April, 2005.     

Laser-polarization-dependent spontaneous emission of the zero phonon line from single nitrogen vacancy center in diamond

We investigate spontaneous emission properties and control of the zero phonon line （ZPL） from a diamond nitrogen- vacancy （NV） center coherently driven by a single ellipfically polarized control field. We use the Schrrdinger equation to calculate the probability amplitudes of the wave function of the coupled system and derive analytical expressions of the spontaneous emission spectra. The numerical results show that a few interesting phenomena such as enhancement, narrowing, suppression, and quenching of the ZPL spontaneous emission can be realized by modulating the polarization- dependent phase, the Zeeman shift, and the intensity of the control field in our system. In the dressed-state picture of the control field, we find that multiple spontaneously generated coherence arises due to three close-lying states decaying to the same state. These results are useful in real experiments.     

InP native oxide: A drift factor in InP-MIS

It is shown that a native oxide in a InP-MIS structure is a key parameter in the time instability of the device. This is demonstrated in experiments on Al/SiO₂/native oxide/InP structures with different native oxide thicknesses. A minimum of the flat-band voltage drift is observed for thicknesses close to 30 Å. A model which considers traps distributed as a continuum of states in the insulator and tunneling with the InP surface channel is consistent with these results.     

A negatively charged silicon vacancy in SiC: Spin polarization effects

The equilibrium geometry and hyperfine interaction constants of the nearest and next-to-nearest neighbor atoms are calculated for a negatively charged silicon vacancy in the high-spin state in cubic SiC. The calculations are performed within the cluster approach in terms of the density-functional theory (DFT). It is shown that the results of calculations with the use of a 70-atom cluster are in good agreement with experimental data. A detailed consideration is given to spin polarization in the electron subsystem and the applicability of a simple LCAO model that is commonly used in the interpretation of the electron paramagnetic resonance data for semiconductors. The spin density distribution for the defect under investigation is analyzed in terms of localized orbitals.     

Pressure-induced delocalization of negative-U centres in semiconducting glasses

Delocalization of the negative-U centres and/or their excitations, strongly localized at ambient pressure, is predicted to occur in semiconducting glasses at the accessible high critical pressure p_c ≈ 10⁵ bar. The phenomenon is shown to exist because of the increase of the centres overlap with growing pressure, which increases the centres concentration. Then, non-localized charge carriers, related to the negative-U centres, become essential at sufficiently high p > p_c, giving rise to dramatic changes in electron (e.g., transport) processes in semiconducting glasses.