342 research outputs found
Observation of surface states on heavily indium doped SnTe(111), a superconducting topological crystalline insulator
The topological crystalline insulator tin telluride is known to host
superconductivity when doped with indium (SnInTe), and for low
indium contents () it is known that the topological surface states are
preserved. Here we present the growth, characterization and angle resolved
photoemission spectroscopy analysis of samples with much heavier In doping (up
to ), a regime where the superconducting temperature is increased
nearly fourfold. We demonstrate that despite strong p-type doping, Dirac-like
surface states persist
Radiation Induced Point and Cluster-Related Defects with Strong Impact to Damage Properties of Silicon Detectors
This work focuses on the investigation of radiation induced defects
responsible for the degradation of silicon detectors. Comparative studies of
the defects induced by irradiation with 60Co- rays, 6 and 15 MeV electrons, 23
GeV protons and 1 MeV equivalent reactor neutrons revealed the existence of
point defects and cluster related centers having a strong impact on damage
properties of Si diodes. The detailed relation between the microscopic reasons
as based on defect analysis and their macroscopic consequences for detector
performance are presented. In particular, it is shown that the changes in the
Si device properties after exposure to high levels of 60Co- doses can be
completely understood by the formation of two point defects, both depending
strongly on the Oxygen concentration in the silicon bulk. Specific for hadron
irradiation are the annealing effects which decrease resp. increase the
originally observed damage effects as seen by the changes of the depletion
voltage. A group of three cluster related defects, revealed as deep hole traps,
proved to be responsible specifically for the reverse annealing. Their
formation is not affected by the Oxygen content or Si growth procedure
suggesting that they are complexes of multi-vacancies located inside extended
disordered regions.Comment: 14 pages, 15 figure
Effect of Native Defects on Optical Properties of InxGa1-xN Alloys
The energy position of the optical absorption edge and the free carrier
populations in InxGa1-xN ternary alloys can be controlled using high energy
4He+ irradiation. The blue shift of the absorption edge after irradiation in
In-rich material (x > 0.34) is attributed to the band-filling effect
(Burstein-Moss shift) due to the native donors introduced by the irradiation.
In Ga-rich material, optical absorption measurements show that the
irradiation-introduced native defects are inside the bandgap, where they are
incorporated as acceptors. The observed irradiation-produced changes in the
optical absorption edge and the carrier populations in InxGa1-xN are in
excellent agreement with the predictions of the amphoteric defect model
Energetic stability and magnetic properties of Mn dimers in silicon
We present an accurate first-principles study of magnetism and energetics of single Mn impurities and Mn dimers in Si. Our results, in general agreement with available experiments, show that (i) Mn atoms tend to aggregate, the formation energy of dimers being lower than the sum of the separate constituents, (ii) ferromagnetic coupling is favored between the Mn atoms constituting the dimers in p-type Si, switching to an antiferromagnetic coupling in n-type Si, (iii) Mn atoms show donors (acceptor) properties in p-type (n-type) Si, therefore they tend to compensate doping, while dimers being neutral or acceptors allow for Si to be doped p-type. (C) 2004 American Institute of Physics
Lattice Expansion of (Ga,Mn)As: The Role of Substitutional Mn and of the Compensating Defects
We apply the density-functional technique to determine the lattice constant
of GaAs supercells containing Mn_Ga, Mn_int, and As_Ga impurities, and use a
linear interpolation to describe the dependence of the lattice constant a of
Ga_{1-x}Mn_xAs on the concentrations of these impurities. The results of the
supercell calculations confirm that Mn_Ga does not contribute to the lattice
expansion. The increase of a is due to both Mn_int and As_Ga, that are both
created in the as-grown (Ga,Mn)As in proportion to x, and that are most
probably present in a remarkable amount also in the best annealed materials.Comment: 3 pages, 2 figures, presented at XXXIV Int. School. on the Physics of
Semiconducting Compounds - Jaszowiec 2005, Ustron-Jaszowiec, Poland, June
4-10, 200
Origin of the n-type conductivity of InN: the role of positively charged dislocations
As-grown InN is known to exhibit high unintentional n-type conductivity. Hall measurements from a range of high-quality single-crystalline epitaxially grown InN films reveal a dramatic reduction in the electron density (from low 1019 to low 1017 cm–3) with increasing film thickness (from 50 to 12 000 nm). The combination of background donors from impurities and the extreme electron accumulation at InN surfaces is shown to be insufficient to reproduce the measured film thickness dependence of the free-electron density. When positively charged nitrogen vacancies (VN+) along dislocations are also included, agreement is obtained between the calculated and experimental thickness dependence of the free-electron concentration
Origin of the anomalous magnetic circular dichroism spectral shape in ferromagnetic (Ga,Mn)As: Impurity bands inside the band gap
The electronic structure of a prototype dilute magnetic semiconductor (DMS),
Ga1-xMnxAs, is studied by magnetic circular dichroism (MCD) spectroscopy. We
prove that the optical transitions originated from impurity bands cause the
strong positive MCD background. The MCD signal due to the E0 transition from
the valence band to the conduction band is negative indicating that the p-d
exchange interactions between the p-carriers and d-spin is antiferromagnetic.
The negative E0 MCD signal also indicates that the hole-doping of the valence
band is not so large as previously assumed. The impurity bands seem to play
important roles for the ferromagnetism of Ga1-xMnxAs.Comment: 13 pages, 3 figure
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