Silicon-Modified rare-earth transitions - a new route to Near- and Mid-IR Photonics

Silicon underpins microelectronics but lacks the photonic capability needed for next-generation systems and currently relies on a highly undesirable hybridization of separate discrete devices using direct band gap semiconductors. Rare-earth (RE) implantation is a promising approach to bestow photonic capability to silicon but is limited to internal RE transition wavelengths. Reported here is the first observation of direct optical transitions from the silicon band edge to internal f-levels of implanted REs (Ce, Eu, and Yb); this overturns previously held assumptions about the alignment of RE levels to the silicon band gap. The photoluminescence lines are massively redshifted to several technologically useful wavelengths and modeling of their splitting indicates that they must originate from the REs. Eu-implanted silicon devices display a greatly enhanced electroluminescence efficiency of 8%. Also observed is the first crystal field splitting in Ce luminescence. Mid-IR silicon photodetectors with specific detectivities comparable to existing state-of-the-art mid-IR detectors are demonstrated

Super-enhancement of 1.54 mu m emission from erbium codoped with oxygen in silicon-on-insulator

We acknowledge the European Research Council for financial support under the FP7 for the award of the ERC Advanced Investigator Grant SILAMPS 226470 and the Royal Society UK for the award of the 2015 Brian Mercer Award for Innovation

Donor ionization in size controlled silicon nanocrystals: The transition from defect passivation to free electron generation

We studied the photoluminescence spectra of silicon and phosphorus co-implanted silica thin films on (100) silicon substrates as a function of isothermal annealing time. The rapid phase segregation, formation, and growth dynamics of intrinsic silicon nanocrystals are observed, in the first 600 s of rapid thermal processing, using dark field mode X-TEM. For short annealing times, when the nanocrystal size distribution exhibits a relatively small mean diameter, formation in the presence of phosphorus yields an increase in the luminescence intensity and a blue shift in the emission peak compared with intrinsic nanocrystals. As the mean size increases with annealing time, this enhancement rapidly diminishes and the peak energy shifts further to the red than the intrinsic nanocrystals. These results indicate the existence of competing pathways for the donor electron, which depends strongly on the nanocrystal size. In samples containing a large density of relatively small nanocrystals, the tendency of phosphorus to accumulate at the nanocrystal-oxide interface means that ionization results in a passivation of dangling bond (Pb -centre) type defects, through a charge compensation mechanism. As the size distribution evolves with isothermal annealing, the density of large nanocrystals increases at the expense of smaller nanocrystals, through an Ostwald ripening mechanism, and the majority of phosphorus atoms occupy substitutional lattice sites within the nanocrystals. As a consequence of the smaller band-gap, ionization of phosphorus donors at these sites increases the free carrier concentration and opens up an efficient, non-radiative de-excitation route for photo-generated electrons via Auger recombination. This effect is exacerbated by an enhanced diffusion in phosphorus doped glasses, which accelerates silicon nanocrystal growth

n-type chalcogenides by ion implantation.

Carrier-type reversal to enable the formation of semiconductor p-n junctions is a prerequisite for many electronic applications. Chalcogenide glasses are p-type semiconductors and their applications have been limited by the extraordinary difficulty in obtaining n-type conductivity. The ability to form chalcogenide glass p-n junctions could improve the performance of phase-change memory and thermoelectric devices and allow the direct electronic control of nonlinear optical devices. Previously, carrier-type reversal has been restricted to the GeCh (Ch=S, Se, Te) family of glasses, with very high Bi or Pb 'doping' concentrations (~5-11 at.%), incorporated during high-temperature glass melting. Here we report the first n-type doping of chalcogenide glasses by ion implantation of Bi into GeTe and GaLaSO amorphous films, demonstrating rectification and photocurrent in a Bi-implanted GaLaSO device. The electrical doping effect of Bi is observed at a 100 times lower concentration than for Bi melt-doped GeCh glasses.This work was supported by the UK EPSRC grants EP/I018417/1, EP/I019065/1 and EP/I018050/1.This is the author accepted manuscript. The final version is available from NPG via http://dx.doi.org/10.1038/ncomms634

Solid phase epitaxial re-growth of Sn ion implanted germanium thin films

Doping of Ge with Sn atoms by ion implantation and annealing by solid phase epitaxial re-growth process was investigated as a possible way to create GeSn layers. Ion implantation was carried out at liquid nitrogen to avoid nano-void formation and three implant doses were tested: 5×10, 1×10 and 5×10 at/cm, respectively. Implant energy was set to 45 keV and implants were carried out through an 11 nm SiNO film to prevent Sn out-diffusion upon annealing. This was only partially effective. Samples were then annealed in inert atmosphere either at 350°C varying anneal time or for 100 s varying temperature from 300 to 500°C. SPER was effective to anneal damage without Sn diffusion at 350° for samples implanted at medium and low fluences whereas the 5×10 at/cm samples remained with a ∼15 nm amorphous layer even when applying the highest thermal budget. © 2012 American Institute of Physics

Three-dimensional photographic analysis of the face in European adults from southern Spain with normal occlusion: reference anthropometric measurements

Background: Recent non-invasive 3D photography method has been applied to facial analysis, offering numerous advantages in orthodontic. The purpose of this study was to analyze the faces of a sample of healthy European adults from southern Spain with normal occlusion in order to establish reference facial soft tissue anthropometric parameters in this specific geographic-ethnic population, as well as to analyze sexual dimorphism. Methods: A sample of 100 healthy adult volunteers consisting of 50 women (mean age, 22.92 ± 1.56 years) and 50 men (mean age, 22.37 ± 2.12 years) were enrolled in this study. All participants had normal occlusion, skeletal Class I, mesofacial pattern, and healthy body mass index. Three-dimensional photographs of the faces were captured noninvasively using Planmeca ProMax 3D ProFace®. Thirty landmarks related to the face, eyes, nose, and orolabial and chin areas were identified. Results: Male displayed higher values in all vertical and transversal dimensions, with the exception of the lower lip height. Larger differences between sexes were observed in face, mandible, and nose. Male also had higher values in the angular measurements which referred to the nose. No sex differences were found in transverse upper lip prominence or transverse mandibular prominence. No differences were found in the ratio measurements, with the exception of intercantal width/nasal width, which was higher in women than in men. Conclusions: Reference anthropometric measurements of facial soft tissues have been established in European adults from southern Spain with normal occlusion. Significant sexual dimorphism was found, with remarkable differences in size between sexe

Measurement of the cross-section of high transverse momentum vector bosons reconstructed as single jets and studies of jet substructure in pp collisions at √s = 7 TeV with the ATLAS detector

This paper presents a measurement of the cross-section for high transverse momentum W and Z bosons produced in pp collisions and decaying to all-hadronic final states. The data used in the analysis were recorded by the ATLAS detector at the CERN Large Hadron Collider at a centre-of-mass energy of √s = 7 TeV;{\rm Te}{\rm V}$and correspond to an integrated luminosity of$4.6\;{\rm f}{{{\rm b}}^{-1}}$. The measurement is performed by reconstructing the boosted W or Z bosons in single jets. The reconstructed jet mass is used to identify the W and Z bosons, and a jet substructure method based on energy cluster information in the jet centre-of-mass frame is used to suppress the large multi-jet background. The cross-section for events with a hadronically decaying W or Z boson, with transverse momentum${{p}_{{\rm T}}}\gt 320\;{\rm Ge}{\rm V}$and pseudorapidity$|\eta |\lt 1.9$, is measured to be${{\sigma }_{W+Z}}=8.5\pm 1.7$ pb and is compared to next-to-leading-order calculations. The selected events are further used to study jet grooming techniques

Search for the neutral Higgs bosons of the minimal supersymmetric standard model in pp collisions at root s=7 TeV with the ATLAS detector

A search for neutral Higgs bosons of the Minimal Supersymmetric Standard Model (MSSM) is reported. The analysis is based on a sample of proton-proton collisions at a centre-of-mass energy of 7TeV recorded with the ATLAS detector at the Large Hadron Collider. The data were recorded in 2011 and correspond to an integrated luminosity of 4.7 fb-1 to 4.8 fb-1. Higgs boson decays into oppositely-charged muon or τ lepton pairs are considered for final states requiring either the presence or absence of b-jets. No statistically significant excess over the expected background is observed and exclusion limits at the 95% confidence level are derived. The exclusion limits are for the production cross-section of a generic neutral Higgs boson, φ, as a function of the Higgs boson mass and for h/A/H production in the MSSM as a function of the parameters mA and tan β in the mhmax scenario for mA in the range of 90GeV to 500 GeV. Copyright CERN