241 research outputs found
A Magnetic Resonance Force Microscopy Quantum Computer with Tellurium Donors in Silicon
We propose a magnetic resonance force microscopy (MRFM)-based nuclear spin
quantum computer using tellurium impurities in silicon. This approach to
quantum computing combines the well-developed silicon technology with expected
advances in MRFM.Comment: 9 pages, 1 figur
Insulator-to-metal transition in sulfur-doped silicon
We observe an insulator-to-metal (I-M) transition in crystalline silicon
doped with sulfur to non- equilibrium concentrations using ion implantation
followed by pulsed laser melting and rapid resolidification. This I-M
transition is due to a dopant known to produce only deep levels at equilibrium
concentrations. Temperature-dependent conductivity and Hall effect measurements
for temperatures T > 1.7 K both indicate that a transition from insulating to
metallic conduction occurs at a sulfur concentration between 1.8 and 4.3 x
10^20 cm-3. Conduction in insulating samples is consistent with variable range
hopping with a Coulomb gap. The capacity for deep states to effect metallic
conduction by delocalization is the only known route to bulk intermediate band
photovoltaics in silicon.Comment: Submission formatting; 4 journal pages equivalen
Single Spin Measurement using Single Electron Transistors to Probe Two Electron Systems
We present a method for measuring single spins embedded in a solid by probing
two electron systems with a single electron transistor (SET). Restrictions
imposed by the Pauli Principle on allowed two electron states mean that the
spin state of such systems has a profound impact on the orbital states
(positions) of the electrons, a parameter which SET's are extremely well suited
to measure. We focus on a particular system capable of being fabricated with
current technology: a Te double donor in Si adjacent to a Si/SiO2 interface and
lying directly beneath the SET island electrode, and we outline a measurement
strategy capable of resolving single electron and nuclear spins in this system.
We discuss the limitations of the measurement imposed by spin scattering
arising from fluctuations emanating from the SET and from lattice phonons. We
conclude that measurement of single spins, a necessary requirement for several
proposed quantum computer architectures, is feasible in Si using this strategy.Comment: 22 Pages, 8 Figures; revised version contains updated references and
small textual changes. Submitted to Phys. Rev.
Titanium trisulfide monolayer: A new direct-gap semiconductor with high and anisotropic carrier mobility
A new two-dimensional (2D) layered material, namely, titanium trisulfide
(TiS) monolayer sheet, is predicted to possess desired electronic
properties for nanoelectronic applications. On basis of the first-principles
calculations within the framework of density functional theory and deformation
theory, we show that the TiS 2D crystal is a direct gap semiconductor with
a band gap of 1.06 eV and high carrier mobility. More remarkably, the in-plane
electron mobility of the 2D TiS is highly anisotropic, amounting to
10,000 cmVs in the \emph{b} direction, which is higher
than that of the MoS monolayer. Meanwhile, the hole mobility is about two
orders of magnitude lower. We also find that bulk TiS possesses lower
cleavage energy than graphite, indicating high possibility of exfoliation for
TiS monolayers or multilayers. Both dynamical and thermal stability of the
TiS monolayer is examined via phonon-spectrum calculation and
Born-Oppenheimer molecular dynamics simulation in \emph{NPT} ensemble. The
predicted novel electronic properties render the TiS monolayer an
attractive 2D material for applications in future nanoelectronics.Comment: 4 figure
Demonstration of the operation principles of intermediate band solar cells at room temperature
In this work we report, for the first time at room temperature, experimental results that prove, simultaneously in the same device, the two main physical principles involved in the operation of intermediate band solar cells: (1) the production of sub-bandgap photocurrent by two optical transitions through the intermediate band; (2) the generation of an output voltage which is not limited by the photon energy absorption threshold. These principles, which had always required cryogenic temperatures to be evidenced all together, are now demonstrated at room temperature on an intermediate band solar cell based on InAs quantum dots with Al0.3Ga0.7As barriers
SULLE PECULIARITÀ DEL SISTEMA SEGNICO MIMICO-GESTUALE
La persona sorda non sente il mondo intorno a sé, bensì lo guarda e non può perciò rappresentarlo con la voce, organo strettamente dipendente dall’udito, ma può invece rappresentarlo con i gesti e con la mimica. Il mondo, sia quello circostante che quello interiore, si costituisce per la persona sorda mediante il canale visivo e si articola dunque in segni mimico-gestuali piuttosto che vocali. La peculiarità del sistema mimico-gestuale si misura sulla base dell’analisi dei quattro parametri manuali (il luogo dello spazio in cui avviene la configurazione manuale, la configurazione e il movimento delle mani, l’orientamento del palmo delle mani) e delle componenti non manuali di cui esso si compone. Ciascun segno si distingue da un altro per differenze oppositive tra uno o più di questi elementi che lo compongono. La struttura oppositiva che caratterizza la lingua delle persone sorde differisce in quanto la lingua dei sordi sfrutta il canale visivo anziché quello uditivo e si costituisce nella materia manuale, gestuale quindi, anziché in quella fonica. Nella costituzione del segno delle persone sorde, inoltre, le componenti non manuali non sono semplici elementi paralinguistici che accompagnano la semiosi enfatizzandola, come per le lingue vocali, bensì sono veri e propri elementi costitutivi del segno la cui carenza compromette la comprensione reciproca
Understanding of sub-band gap absorption of femtosecond-laser sulfur hyperdoped silicon using synchrotron-based techniques
[[abstract]]The correlation between sub-band gap absorption and the chemical states and electronic and atomic structures of S-hyperdoped Si have been extensively studied, using synchrotron-based x-ray photoelectron spectroscopy (XPS), x-ray absorption near-edge spectroscopy (XANES), extended x-ray absorption fine structure (EXAFS), valence-band photoemission spectroscopy (VB-PES) and first-principles calculation. S 2p XPS spectra reveal that the S-hyperdoped Si with the greatest (~87%) sub-band gap absorption contains the highest concentration of S2− (monosulfide) species. Annealing S-hyperdoped Si reduces the sub-band gap absorptance and the concentration of S2− species, but significantly increases the concentration of larger S clusters [polysulfides (Sn2−, n > 2)]. The Si K-edge XANES spectra show that S hyperdoping in Si increases (decreased) the occupied (unoccupied) electronic density of states at/above the conduction-band-minimum. VB-PES spectra evidently reveal that the S-dopants not only form an impurity band deep within the band gap, giving rise to the sub-band gap absorption, but also cause the insulator-to-metal transition in S-hyperdoped Si samples. Based on the experimental results and the calculations by density functional theory, the chemical state of the S species and the formation of the S-dopant states in the band gap of Si are critical in determining the sub-band gap absorptance of hyperdoped Si samples.[[notice]]補正完畢[[journaltype]]國外[[incitationindex]]SCI[[ispeerreviewed]]Y[[booktype]]電子版[[countrycodes]]GB
Photovoltaic properties of thermally-grown selenium-doped silicon photodiodes for infrared detection applications
Interband excitation induced absorption by deep impurities in GaP
Transient optical absorption at energies below the band gap in GaP crystals following pulsed interband excitation was observed. The additional absorption attained its maximum about 25 μsec after the excitation pulse and lasted about 100 μsec. The spectral dependence of the rise time and decay time of the absorption and that of the induced optical cross section were determined. The results suggest that the induced absorption is caused by several deep impurity levels, which are most probably due to Cu, being populated by the recombination of excited electrons
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