118 research outputs found
Bandgap narrowing in Mn doped GaAs probed by room-temperature photoluminescence
The electronic band structure of the (Ga,Mn)As system has been one of the
most intriguing problems in solid state physics over the past two decades.
Determination of the band structure evolution with increasing Mn concentration
is a key issue to understand the origin of ferromagnetism. Here we present room
temperature photoluminescence and ellipsometry measurements of
Ga_{100%-x}Mn_{x}As alloy. The up-shift of the valence-band is proven by the
red shift of the room temperature near band gap emission from the
Ga_{100%-x}Mn_{x}As alloy with increasing Mn content. It is shown that even a
doping by 0.02 at.% of Mn affects the valence-band edge and it merges with the
impurity band for a Mn concentration as low as 0.6 at.%. Both X-ray diffraction
pattern and high resolution cross-sectional TEM images confirmed full
recrystallization of the implanted layer and GaMnAs alloy formation.Comment: 24 pages, 7 figures, accepted at Phys. Rev. B 201
Extended Infrared Photoresponse in Te-Hyperdoped Si at Room Temperature
Presently, silicon photonics requires photodetectors that are sensitive in a
broad infrared range, can operate at room temperature, and are suitable for
integration with the existing Si-technology process. Here, we demonstrate
strong room-temperature sub-band-gap photoresponse of photodiodes based on Si
hyperdoped with tellurium. The epitaxially recrystallized Te-hyperdoped Si
layers are developed by ion implantation combined with pulsed-laser melting and
incorporate Te-dopant concentrations several orders of magnitude above the
solid solubility limit. With increasing Te concentration, the Te-hyperdoped
layer changes from insulating to quasi-metallic behavior with a finite
conductivity as the temperature tends to zero. The optical absorptance is found
to increase monotonically with increasing Te concentration and extends well
into the mid-infrared range. Temperature-dependent optoelectronic photoresponse
unambiguously demonstrates that the extended infrared photoresponsivity from
Te-hyperdoped Si p-n photodiodes is mediated by a Te intermediate band within
the upper half of the Si band gap. This work contributes to pave the way toward
establishing a Si-based broadband infrared photonic system operating at room
temperature.Comment: 18 pages, 7 figure
Multiple Conclusion Rules in Logics with the Disjunction Property
We prove that for the intermediate logics with the disjunction property any
basis of admissible rules can be reduced to a basis of admissible m-rules
(multiple-conclusion rules), and every basis of admissible m-rules can be
reduced to a basis of admissible rules. These results can be generalized to a
broad class of logics including positive logic and its extensions, Johansson
logic, normal extensions of S4, n-transitive logics and intuitionistic modal
logics
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