We propose a new method for calculating optical defect levels and thermodynamic charge-transition levels of point defects in semiconductors, which includes quasiparticle corrections to the Kohn-Sham eigenvalues of density-functional theory. Its applicability is demonstrated for anion vacancies at the (110) surfaces of III-V semiconductors. We find the (+/0) charge-transition level to be 0.49 eV above the surface valence-band maximum for GaAs(110) and 0.82 eV for InP(110). The results show a clear improvement over the local-density approximation and agree closely with an experimental analysis.

We have performed total-energy density-functional calculations using first-principles pseudopotentials to determine the atomic and electronic structure of neutral surface and subsurface vacancies at the GaP ͑110͒ surface. The cation as well as the anion surface vacancy show a pronounced inward relaxation of the three nearest-neighbor atoms towards the vacancy while the surface point-group symmetry is maintained. For both types of vacancies we find a singly occupied level at midgap. Subsurface vacancies below the second layer display essentially the same properties as bulk defects. Our results for vacancies in the second layer show features not observed for either surface or bulk vacancies: Large relaxations occur and both defects are unstable against the formation of antisite vacancy complexes. Simulating scanning tunneling microscope pictures of the different vacancies, we find excellent agreement with experimental data for the surface vacancies and predict the signatures of subsurface vacancies.

The atomic and electronic structure of positively charged P vacancies on InP(110) surfaces is determined by combining scanning tunneling microscopy, photoelectron spectroscopy, and densityfunctional 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. Copyright 2000 by the American Physical Society. 73.20.Hb, 61.16.Ch, 71.15.Mb, Although it is well known that point defects can exert a profound influence on the physical properties of semiconductors, the determination of the atomic scale geometric and electronic structure of point defects has remained a challenging task for theoretical as well as experimental research. One particularly striking example is anion vacancies on (110) surfaces of III-V semiconductors, where no agreement has been reached regarding even basic properties, such as (i) the symmetry of the atomic structure and (ii) the energy of defect levels in the band gap: Although recent density-functional theory (DFT) calculations for positively charged arsenic vacancies on the GaAs (110) surface agreed that the gallium atoms neighboring the vacancy relax into the surface layer (in contrast with an earlier tight-binding calculation [1]), one calculation found a rebonded configuration breaking the mirror symmetry of the surface [2], whereas the other predicted a fully symmetric configuration to have the lowest energy [3]. High resolution scanning tunneling microscopy (STM) images show a density of states preserving the mirror symmetry of the surface at the defect site [1,4]. Although this seems to favor a symmetric atomic structure, the experimental results could not be matched to results of any of the DFT calculations [5][6][7][8]. Furthermore, scanning tunneling spectroscopy (STS) yielded a local downward band bending of 0.1 eV [1], whereas surface photovoltage measurements found a band bending of 0.53 ± 0.3 eV [9] at the site of the positively charged As vacancy on pdoped GaAs(110) surfaces. Concerning the energy levels, the two different DFT calculations predicted the charge transfer levels (+/0) to be 0.32 eV [2] and 0.1 eV [3], and the lowest Kohn-Sham eigenvalues in the band gap to be 0.73 eV [2] and 0.06 eV [3] above the valence band maximum (VBM). In view of this puzzling situation it is obvious that the interpretation of the experimental STM images as well as the structure of the anion vacancies on (110) surfaces of III-V semiconductors are still under debate [5][6][7][8].Discrepancies such as those pointed out above can arise due to limitations of the methods used. On the theoretical side DFT calculations have proven to be powerful to determine the structure of point defects [10]. Yet differences in the size of the s...

We identify surface anion antisite defects in ͑110͒ surfaces of GaAs, GaP, and InP using scanning tunneling microscopy combined with density-functional theory calculations. In contrast to subsurface arsenic antisite defects, surface antisite defects are electrically inactive and have a very localized defect state which gives rise to a distinct feature in scanning tunneling microscopy images.

The first case of pseudohypoparathyroidism with postmortem examination is reported. Microscopic examination shows hyperplastic upper parathyroid glands (only one was found) and normal age involution in the two found lower glands. All the bones examinated offered signs of exagerated bone replacement in time before death. In the cortical bone of the femur many lacunae of Howship with spare giant cell osteoclasts were seen. Circumscript calcifications in the renal medulla and in the thyroid gland were observed.