710 research outputs found
Imaging interstitial iron concentrations in boron-doped crystalline silicon using photoluminescence
Imaging the band-to-band photoluminescence of silicon wafers is known to provide rapid and high-resolution images of the carrier lifetime. Here, we show that such photoluminescence images, taken before and after dissociation of iron-boron pairs, allow an accurate image of the interstitial iron concentration across a boron-doped p-type silicon wafer to be generated. Such iron images can be obtained more rapidly than with existing point-by-point iron mapping techniques. However, because the technique is best used at moderate illumination intensities, it is important to adopt a generalized analysis that takes account of different injection levels across a wafer. The technique has been verified via measurement of a deliberately contaminated single-crystal silicon wafer with a range of known iron concentrations. It has also been applied to directionally solidified ingot-grown multicrystalline silicon wafers made for solar cell production, which contain a detectible amount of unwanted iron. The iron images on these wafers reveal internal gettering of iron to grain boundaries and dislocated regions during ingot growth.D.M. is supported by an Australian Research Council
QEII Fellowship. The Centre of Excellence for Advanced
Silicon Photovoltaics and Photonics at UNSW is funded by
the Australian Research Council
Imaging crystal orientations in multicrystalline silicon wafers via photoluminescence
We present a method for monitoring crystal orientations in chemically polished and unpassivated multicrystalline silicon wafers based on band-to-band photoluminescence imaging. The photoluminescence intensity from such wafers is dominated by surface recombination, which is crystal orientation dependent. We demonstrate that a strong correlation exists between the surface energy of different grain orientations, which are modelled based on first principles, and their corresponding photoluminescence intensity. This method may be useful in monitoring mixes of crystal orientations in multicrystalline or so-called “cast monocrystalline” wafers.H. C. Sio acknowledges scholarship support from
BT Imaging and the Australian Solar Institute, and the
Centre for Advanced Microscopy at ANU for SEM access.
This work has been supported by the Australian Research
Council
Progress in atom chips and the integration of optical microcavities
We review recent progress at the Centre for Cold Matter in developing atom
chips. An important advantage of miniaturizing atom traps on a chip is the
possibility of obtaining very tight trapping structures with the capability of
manipulating atoms on the micron length scale. We recall some of the pros and
cons of bringing atoms close to the chip surface, as is required in order to
make small static structures, and we discuss the relative merits of metallic,
dielectric and superconducting chip surfaces. We point out that the addition of
integrated optical devices on the chip can enhance its capability through
single atom detection and controlled photon production. Finally, we review the
status of integrated microcavities that have recently been demonstrated at our
Centre and discuss their prospects for future development.Comment: 12 pages, 6 figures, proceedings of the ICOLS07 conferenc
Photonics in photovoltaic systems
This paper gives an overview on photonics for photovoltaic systems. Starting from the spectral and angular distribution of the electromagnetic radiation from the sun, many important optical approaches how to improve the efficiency of solar cells are presented and discussed. Topics include antireflective coatings, various light trapping structures, refractive, reflective and fluorescent concentrators, and components for spectral management. The theoretical background is shortly described and examples of the experimental and also of the commercial realisation are given
Robust Entanglement through Macroscopic Quantum Jumps
We propose an entanglement generation scheme that requires neither the
coherent evolution of a quantum system nor the detection of single photons.
Instead, the desired state is heralded by a {\em macroscopic} quantum jump.
Macroscopic quantum jumps manifest themselves as a random telegraph signal with
long intervals of intense fluorescence (light periods) interrupted by the
complete absence of photons (dark periods). Here we show that a system of two
atoms trapped inside an optical cavity can be designed such that a dark period
prepares the atoms in a maximally entangled ground state. Achieving fidelities
above 0.9 is possible even when the single-atom cooperativity parameter C is as
low as 10 and when using a photon detector with an efficiency as low as eta =
0.2.Comment: 5 pages, 4 figures, more detailed discussion of underlying physical
effect, references update
Atom detection and photon production in a scalable, open, optical microcavity
A microfabricated Fabry-Perot optical resonator has been used for atom
detection and photon production with less than 1 atom on average in the cavity
mode. Our cavity design combines the intrinsic scalability of microfabrication
processes with direct coupling of the cavity field to single-mode optical
waveguides or fibers. The presence of the atom is seen through changes in both
the intensity and the noise characteristics of probe light reflected from the
cavity input mirror. An excitation laser passing transversely through the
cavity triggers photon emission into the cavity mode and hence into the
single-mode fiber. These are first steps towards building an optical
microcavity network on an atom chip for applications in quantum information
processing.Comment: 4 pages, 4 figures. A typographical error in the published paper has
been corrected (equation of the corrected normalized variance, page 3, 2nd
paragraph
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