150 research outputs found
Design and performance of an erbium-doped silicon waveguide detector operating at 1.5 ”m
A new concept for an infrared waveguide detector based on silicon is introduced. It is fabricated using silicon-on-insulator material, and consists of an erbium-doped p-n junction located in the core of a silicon ridge waveguide. The detection scheme relies on the optical absorption of 1.5-”m light by Er3+ ions in the waveguide core, followed by electron-hole pair generation by the excited Er and subsequent carrier separation by the electric field of the p-n junction. By performing optical mode calculations and including realistic doping profiles, we show that an external quantum efficiency of 10^-3 can be achieved in a 4-cm-long waveguide detector fabricated using standard silicon processing. It is found that the quantum efficiency of the detector is mainly limited by free carrier absorption in the waveguide core, and may be further enhanced by optimizing the electrical doping profiles. Preliminary photocurrent measurements on an erbium-doped Si waveguide detector at room temperature show a clear erbium related photocurrent at 1.5 ”m
Temperature dependence and quenching processes of the intra-4f luminescence of Er in crystalline Si
8 pågs.; 7 figs.The luminescence quenching of Er in crystalline Si at temperatures between 77 and 300 K is investigated. Samples were prepared by solid-phase epitaxy of Er-implanted amorphous Si layers with or without O codoping. After epitaxial regrowth at 620°C, thermal annealing at 900°C for 30 sec was performed in order to eliminate residual defects in the regrown layer and electrically and optically activate the Er ions. Measurements of photoluminescence intensity and time decay were performed as a function of temperature and pump power. By increasing the temperature from 77 K to room temperature the luminescence intensity decreases by ~ three orders of magnitude in the Er-doped sample without O codoping, but only by a factor of 30 in the O-doped sample. In this sample room-temperature photo-luminescence and electroluminescence have been observed. Time-decay curves show a fast initial decay (~100 ¿sec) followed by a slow decay (~1 msec), with the relative intensity of these two components depending on temperature, pump power, and O codoping. The decay curves can be fitted by a sum of two exponential functions revealing the existence, in both samples, of two different classes of optically active Er sites. The concentration of excitable sites belonging to the slow-decaying class is similar for the samples with or without O codoping and rapidly decreases when temperature is increased. At temperatures above 150 K the Er luminescence is dominated by the fast-decaying centers the concentration of which is greatly increased by the presence of O. It is found that in the absence of oxygen room-temperature luminescence is hampered by the limited amount of excitable Er ions. In contrast, in O-doped samples the nonradiative decay of excited Er is the main quenching mechanism. The main factors determining the temperature quenching of Er luminescence and the crucial role of oxygen are discussed. © 1994 The American Physical Society.This work has been partially supported by
GNSM-CNR. Work at the FOM Institute is part of the
research program of the foundation for Fundamental
Research on Matter (FOM), and was made possible by
financial support from the Dutch organization for the
Advancement of Research (NWO}, the Foundation for
Technical Research (STW}, and the IC Technology Program
(IOP Electro-optics) of the Ministry of Economic
Affairs.Peer Reviewe
Optical and electrical doping of silicon with holmium
2 MeV holmium ions were implanted into Czochralski grown Si at a fluence of 5.5*10^14 Ho/cm^2. Some samples were
co-implanted with oxygen to a concentration of (7±1)*10^19 cm^(-3). After recrystallization, strong Ho segregation to the
surface is observed, which is fully suppressed by co-doping with O. After recrystallization, photoluminescence peaks are
observed at 1.197, 1.96 and 2.06 lm, characteristic for the 5-I-6 --> 5-I-8 and 5-I-7 --> 5-I-8 transitions of Ho^(3+). The Ho^(3+) luminescence
lifetime at 1.197 lm is 14 ms at 12 K. The luminescence intensity shows temperature quenching with an
activation energy of 11 meV, both with and without O co-doping. The observed PL quenching cannot be explained by
free carrier Auger quenching, but instead must be due to energy backtransfer or electron hole pair dissociation.
Spreading resistance measurements indicate that Ho exhibits donor behavior, and that in the presence of O the free
carrier concentration is enhanced by more than two orders of magnitude. In the O co-doped sample 20% of the Ho^(3+)
was electrically active at room temperature
Poincaré on the Foundation of Geometry in the Understanding
This paper is about PoincarĂ©âs view of the foundations of geometry. According to the established view, which has been inherited from the logical positivists, PoincarĂ©, like Hilbert, held that axioms in geometry are schemata that provide implicit definitions of geometric terms, a view he expresses by stating that the axioms of geometry are âdefinitions in disguise.â I argue that this view does not accord well with PoincarĂ©âs core commitment in the philosophy of geometry: the view that geometry is the study of groups of operations. In place of the established view I offer a revised view, according to which PoincarĂ© held that axioms in geometry are in fact assertions about invariants of groups. Groups, as forms of the understanding, are prior in conception to the objects of geometry and afford the proper definition of those objects, according to PoincarĂ©. PoincarĂ©âs view therefore contrasts sharply with Kantâs foundation of geometry in a unique form of sensibility. According to my interpretation, axioms are not definitions in disguise because they themselves implicitly define their terms, but rather because they disguise the definitions which imply them
The good, the bad and the ugly
This paper discusses the neo-logicist approach to the foundations of mathematics by highlighting an issue that arises from looking at the Bad Company objection from an epistemological perspective. For the most part, our issue is independent of the details of any resolution of the Bad Company objection and, as we will show, it concerns other foundational approaches in the philosophy of mathematics. In the first two sections, we give a brief overview of the "Scottish" neo-logicist school, present a generic form of the Bad Company objection and introduce an epistemic issue connected to this general problem that will be the focus of the rest of the paper. In the third section, we present an alternative approach within philosophy of mathematics, a view that emerges from Hilbert's Grundlagen der Geometrie (1899, Leipzig: Teubner; Foundations of geometry (trans.: Townsend, E.). La Salle, Illinois: Open Court, 1959.). We will argue that Bad Company-style worries, and our concomitant epistemic issue, also affects this conception and other foundationalist approaches. In the following sections, we then offer various ways to address our epistemic concern, arguing, in the end, that none resolves the issue. The final section offers our own resolution which, however, runs against the foundationalist spirit of the Scottish neo-logicist program
Electron paramagnetic resonance and photoluminescence study of Er-impurity complexes in Si
Molecular differences between ductal carcinoma in situ and adjacent invasive breast carcinoma: a multiplex ligation-dependent probe amplification study
Ductal carcinoma in situ (DCIS) accounts for approximately 20% of mammographically detected breast cancers. Although DCIS is generally highly curable, some women with DCIS will develop life-threatening invasive breast cancer, but the determinants of progression to infiltrating ductal cancer (IDC) are largely unknown. In the current study, we used multiplex ligation-dependent probe amplification (MLPA), a multiplex PCR-based test, to compare copy numbers of 21 breast cancer related genes between laser-microdissected DCIS and adjacent IDC lesions in 39 patients. Genes included in this study were ESR1, EGFR, FGFR1, ADAM9, IKBKB, PRDM14, MTDH, MYC, CCND1, EMSY, CDH1, TRAF4, CPD, MED1, HER2, CDC6, TOP2A, MAPT, BIRC5, CCNE1 and AURKA
Electrical Control of Optical Emitter Relaxation Pathways enabled by Graphene
Controlling the energy flow processes and the associated energy relaxation
rates of a light emitter is of high fundamental interest, and has many
applications in the fields of quantum optics, photovoltaics, photodetection,
biosensing and light emission. While advanced dielectric and metallic systems
have been developed to tailor the interaction between an emitter and its
environment, active control of the energy flow has remained challenging. Here,
we demonstrate in-situ electrical control of the relaxation pathways of excited
erbium ions, which emit light at the technologically relevant telecommunication
wavelength of 1.5 m. By placing the erbium at a few nanometres distance
from graphene, we modify the relaxation rate by more than a factor of three,
and control whether the emitter decays into either electron-hole pairs, emitted
photons or graphene near-infrared plasmons, confined to 15 nm to the sheet.
These capabilities to dictate optical energy transfer processes through
electrical control of the local density of optical states constitute a new
paradigm for active (quantum) photonics.Comment: 9 pages, 4 figure
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