223 research outputs found
Measuring dopant concentrations in compensated p-type crystalline silicon via iron-acceptor pairing
We present a method for measuring the concentrations of ionized acceptors and donors in compensated p-type silicon at room temperature.Carrier lifetimemeasurements on silicon wafers that contain minute traces of iron allow the iron-acceptor pair formation rate to be determined, which in turn allows the acceptor concentration to be calculated. Coupled with an independent measurement of the resistivity and a mobility model that accounts for majority and minority impurity scatterings of charge carriers, it is then possible to also estimate the total concentration of ionized donors. The method is valid for combinations of different acceptor and donor species.D.M. is supported by an Australian Research Council
fellowship. L.J.G. would like to acknowledge SenterNovem
for support
Recombination activity of interstitial iron and other transition metal point defects in p- and n-type crystalline silicon
Interstitial iron in crystalline silicon has a much larger capture cross section for electrons than holes. According to the ShockleyâReadâHall model, the low-injection carrier lifetime in p-type silicon should therefore be much lower that in n-type silicon, while in high injection they should be equal. In this work we confirm this modeling using purposely iron-contaminated samples. A survey of other transition metal impurities in silicon reveals that those which tend to occupy interstitial sites at room temperature also have significantly larger capture cross sections for electrons. Since these are also the most probable metal point defects to occur during high temperature processing, using n-type wafers for devices such as solar cells may offer greater immunity to the effects of metal contaminants.This work has been supported by the Australian Research
Council and The Netherlands Agency for Energy and
the Environment
Dynamics of light-induced FeB pair dissociation in crystalline silicon
The dynamics of light-induced dissociation of ironâboron (FeB) pairs in p-type crystalline silicon is investigated. The dissociation is observed to be a single-exponential process which is balanced with thermal repairing. The dissociation rate is proportional to the square of the carrier generation rate and the inverse square of the FeB concentration. This suggests that the dissociation process involves two recombination or electron capture events. A proportionality constant of 5Ă10â»Âčâ”s describes the dissociation rate well in the absence of other significant recombination channels. The dissociation rate decreases in the presence of other recombination channels. These results can be used for reliable detection of iron in silicon devices and materials, and for further elucidation of the electronically driven FeB dissociation reaction.This work was supported by NOVEM (The Netherlands
Agency for Energy and the Environment) and the Australian
Research Council
Sum rule for transport in a Luttinger liquid with long range interaction in the presence of an impurity
We show that the non-linear dc transport in a Luttinger liquid with
interaction of finite range in the presence of an impurity is governed by a sum
rule which causes the charging energy to vanish.Comment: 5 pages, RevTeX, 1 figure, to be published in Europhysics Letter
Non-Abelian phases, charge pumping, and quantum computation with Josephson junctions
Non-Abelian geometric phases can be generated and detected in certain
superconducting nanocircuits. Here we consider an example where the holonomies
are related to the adiabatic charge dynamics of the Josephson network. We
demonstrate that such a device can be applied both for adiabatic charge pumping
and as an implementation of a quantum computer.Comment: 11 pages RevTex, 3 figures in eps format, revised versio
Cooper pair cotunneling in single charge transistors with dissipative electromagnetic environment
We observed current-voltage characteristics of superconducting single charge
transistors with on-chip resistors of R about R_Q = h/4e^2 = 6.45 kOhm, which
are explained in terms of Cooper-pair cotunneling. Both the effective strength
of Josephson coupling and the cotunneling current are modulated by the
gate-induced charge on the transistor island. For increasing values of the
resistance R we found the Cooper pair current at small transport voltages to be
dramatically suppressed.Comment: 4 pages and 2 figure
Light-induced boron-oxygen defect generation in compensated p-type Czochralski silicon
The concentration of boron-oxygen defects generated in compensated p-type Czochralski silicon has been measured via carrier lifetime measurements taken before and after activating the defect with illumination. The rate of formation of these defects was also measured. Both the concentration and the rate were found to depend on the net doping rather than the total boron concentration. These results imply that the additional compensated boron exists in a form that is not able to bond with the oxygen dimers, thus prohibiting the formation of the defect. This could be explained by the presence of boron-phosphorus complexes, as proposed in previous work. Evidence for reduced carrier mobilities in compensated silicon is also presented, which has implications for photoconductance-based carrier lifetime measurements and solar cell performance.D.M. is supported by an Australian Research Council
QEII Fellowship, L.J.G. acknowledges SenterNovem for
support, and B.L. and J.S. acknowledge the support of the
German Academic Exchange Service
Arrays of Josephson junctions in an environment with vanishing impedance
The Hamiltonian operator for an unbiased array of Josephson junctions with
gate voltages is constructed when only Cooper pair tunnelling and charging
effects are taken into account. The supercurrent through the system and the
pumped current induced by changing the gate voltages periodically are discussed
with an emphasis on the inaccuracies in the Cooper pair pumping.
Renormalisation of the Hamiltonian operator is used in order to reliably
parametrise the effects due to inhomogeneity in the array and non-ideal gating
sequences. The relatively simple model yields an explicit, testable prediction
based on three experimentally motivated and determinable parameters.Comment: 13 pages, 9 figures, uses RevTeX and epsfig, Revised version, Better
readability and some new result
Mode-Locking in Quantum-Hall-Effect Point Contacts
We study the effect of an ac drive on the current-voltage (I-V)
characteristics of a tunnel junction between two fractional Quantum Hall fluids
at filling an odd integer. Within the chiral Luttinger liquid model
of edge states, the point contact dynamics is described by a driven damped
quantum mechanical pendulum. In a semi-classical limit which ignores electron
tunnelling, this model exhibits mode-locking, which corresponds to current
plateaus in the I-V curve at integer multiples of , with
the ac drive angular frequency. By analyzing the full quantum model at
non-zero using perturbative and exact methods, we study the effect of
quantum fluctuation on the mode-locked plateaus. For quantum
fluctuations smear completely the plateaus, leaving no trace of the ac drive.
For smeared plateaus remain in the I-V curve, but are not
centered at the currents . For rounded plateaus
centered around the quantized current values are found. The possibility of
using mode locking in FQHE point contacts as a current-to-frequency standard is
discussed.Comment: 12 pages, 8 figures, minor change
Quantum Phase Transitions in Josephson Junction Chains
We investigate the quantum phase transition in a one-dimensional chain of
ultra-small superconducting grains, considering both the self- and junction
capacitances. At zero temperature, the system is transformed into a
two-dimensional system of classical vortices, where the junction capacitance
introduces anisotropy in the interaction between vortices. This leads to the
superconductor-insulator transition of the Berezinskii-Kosterlitz-Thouless
type, as the ratios of the Josephson coupling energy to the charging energies
are varied. It is found that the junction capacitance plays a role similar to
that of dissipation and tends to suppress quantum fluctuations; nevertheless
the insulator region survives even for arbitrarily large values of the junction
capacitance.Comment: REVTeX+5 EPS figures, To appear in PRB Rapid
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