205 research outputs found
Photoconductivity of Single-crystalline Selenium Nanotubes
Photoconductivity of single-crystalline selenium nanotubes (SCSNT) under a
range of illumination intensities of a 633nm laser is carried out with a novel
two terminal device arrangement at room temperature. It's found that SCSNT
forms Schottky barriers with the W and Au contacts, and the barrier height is a
function of the light intensities. In low illumination regime below 1.46x10E-4
muWmum-2, the Au-Se-W hybrid structure exhibits sharp switch on/off behavior,
and the turn-on voltages decrease with increasing illuminating intensities. In
the high illumination regime above 7x10E-4 muWmum-2, the device exhibits ohmic
conductance with a photoconductivity as high as 0.59Ohmcm-1, significantly
higher that reported values for carbon and GaN nanotubes. This finding suggests
that SCSNT is potentially a good photo-sensor material as well we a very
effective solar cell material.Comment: 12pages including 5 figures, submitted to Nanotechnolog
Resonances in Ferromagnetic Gratings Detected by Microwave Photoconductivity
We investigate the impact of microwave excited spin excitations on the DC
charge transport in a ferromagnetic (FM) grating. We observe both resonant and
nonresonant microwave photoresistance. Resonant features are identified as the
ferromagnetic resonance (FMR) and ferromagnetic antiresonance (FMAR). A
macroscopic model based on Maxwell and Landau-Lifschitz equations reveals the
macroscopic nature of the FMAR. The experimental approach and results provide
new insight in the interplay between photonic, spintronic, and charge effects
in FM microstructures.Comment: 4 pages, 4 figure
Electron spin phase relaxation of phosphorus donors in nuclear spin enriched silicon
We report a pulsed EPR study of the phase relaxation of electron spins bound
to phosphorus donors in isotopically purified 29^Si and natural abundance Si
single crystals measured at 8 K.Comment: 5 pages, 3 figure
Electrical detection of 31P spin quantum states
In recent years, a variety of solid-state qubits has been realized, including
quantum dots, superconducting tunnel junctions and point defects. Due to its
potential compatibility with existing microelectronics, the proposal by Kane
based on phosphorus donors in Si has also been pursued intensively. A key issue
of this concept is the readout of the P quantum state. While electrical
measurements of magnetic resonance have been performed on single spins, the
statistical nature of these experiments based on random telegraph noise
measurements has impeded the readout of single spin states. In this letter, we
demonstrate the measurement of the spin state of P donor electrons in silicon
and the observation of Rabi flops by purely electric means, accomplished by
coherent manipulation of spin-dependent charge carrier recombination between
the P donor and paramagnetic localized states at the Si/SiO2 interface via
pulsed electrically detected magnetic resonance. The electron spin information
is shown to be coupled through the hyperfine interaction with the P nucleus,
which demonstrates the feasibility of a recombination-based readout of nuclear
spins
Study of Staebler-Wronsky degradation effect in a Si:H based P-I-N solar cells
The objective of this study is to improve the stability and efficiency of thin solar cells with emphasis on a-Si:H devices. The research project was broken down into three main phases. The first involves designing and building a UHV glow discharge system; the second involves making good quality films and eventually efficient cells; the final phase will be analytical
Photoconductivity of biased graphene
Graphene is a promising candidate for optoelectronic applications such as
photodetectors, terahertz imagers, and plasmonic devices. The origin of
photoresponse in graphene junctions has been studied extensively and is
attributed to either thermoelectric or photovoltaic effects. In addition, hot
carrier transport and carrier multiplication are thought to play an important
role. Here we report the intrinsic photoresponse in biased but otherwise
homogeneous graphene. In this classic photoconductivity experiment, the
thermoelectric effects are insignificant. Instead, the photovoltaic and a
photo-induced bolometric effect dominate the photoresponse due to hot
photocarrier generation and subsequent lattice heating through electron-phonon
cooling channels respectively. The measured photocurrent displays polarity
reversal as it alternates between these two mechanisms in a backgate voltage
sweep. Our analysis yields elevated electron and phonon temperatures, with the
former an order higher than the latter, confirming that hot electrons drive the
photovoltaic response of homogeneous graphene near the Dirac point
Reversible Engineering of Topological Insulator Surface State Conductivity through Optical Excitation
Despite the broadband response, limited optical absorption at a particular
wavelength hinders the development of optoelectronics based on Dirac fermions.
Heterostructures of graphene and various semiconductors have been explored for
this purpose, while non-ideal interfaces often limit the performance. The
topological insulator is a natural hybrid system, with the surface states
hosting high-mobility Dirac fermions and the small-bandgap semiconducting bulk
state strongly absorbing light. In this work, we show a large photocurrent
response from a field effect transistor device based on intrinsic topological
insulator Sn-Bi1.1Sb0.9Te2S. The photocurrent response is non-volatile and
sensitively depends on the initial Fermi energy of the surface state, and it
can be erased by controlling the gate voltage. Our observations can be
explained with a remote photo-doping mechanism, in which the light excites the
defects in the bulk and frees the localized carriers to the surface state. This
photodoping modulates the surface state conductivity without compromising the
mobility, and it also significantly modify the quantum Hall effect of the
surface state. Our work thus illustrates a route to reversibly manipulate the
surface states through optical excitation, shedding light into utilizing
topological surface states for quantum optoelectronics
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