1,721,058 research outputs found
Excitation and nonradiative deexcitation processes of Er3+ in crystalline Si
No full textA detailed investigation on the excitation and deexcitation processes of Er3+ in Si is reported. In particular, we explored Er pumping through electron-hole pair recombination and Er deexcitation through Auger processes transferring energy to either free or bound electrons and holes. Since Er donor behavior would result in a free-carrier concentration varying along its profile, experiments have been performed by embedding the whole Er profile within previously prepared n-doped or p-doped regions. Multiple P (B) implants were performed in n-type (p-type) Czochralski Si samples in order to realize uniform dopant concentrations from 4 x 10(16) to 1.2 x 10(18)/cm(3) at depths between 0.5 and 2.5 mu m below the surface. These samples have been subsequently implanted with 4 MeV 3.3 x 10(13) Er/cm(2) and annealed at 900 degrees C for 30 min. Free electrons or holes concentrations in the region where Er sits were measured by spreading resistance profiling. It has been found that the release of electrons or holes from shallow donors and accepters, occurring at temperatures between 15 and 100 K, produces a strong reduction of both time decay and luminescence intensity at 1.54 mu m. These phenomena are produced by Auger deexcitation of the Er3+ intra-4f electrons with energy transfer to free carriers. The Auger coefficient of this process has been measured to be C-A similar to 5 x 10(-13) cm(3) s(-1) for both free electrons and free holes. Moreover, at 15 K (when the free carriers are frozen and the donor and acceptor levels occupied) the Er3+ time decay has been found to depend on the P (or B) concentrations. This is attributed to an impurity Auger deexcitation to electrons (or holes) bound to shallow donors (accepters): the efficiency of this process has been determined to be two orders of magnitude smaller with respect to the Auger deexcitation with free carriers. Furthermore, at temperatures above 100 K a nonradiative back-transfer decay process, characterized by an activation energy of 0.15 eV, is seen to set in for both p-type and n-type samples. This suggests that the back-transfer process, which severely limits the high-temperature luminescence efficiency, is always completed by a thermalization of an electron trapped at an Er-related level to the conduction band. Finally, by analysis of the pump power dependence of time decay and luminescence yield at 15 K, we have found that excitation of Er through the recombination of an electron-hole pair is a very efficient process, characterized by an effective cross section of 3 x 10(-15) cm(2) and able to provide an internal quantum efficiency as high as 10% at low temperatures (15 K) and pump powers (below 1 mW). This efficiency is significantly reduced when, at higher temperatures and/or high pump powers, strong nonradiative decay processes set in. These phenomena are investigated in detail and their impact on device operation perspectives are analyzed and discussed. [S0163-1829(98)01008-X]
Room-temperature Electroluminescence From Er-doped Crystalline Si
No full textWe have obtained room-temperature electroluminescence (EL) at approximately 1.54 mum from Er and O co-doped crystalline p-n Si diodes fabricated by ion implantation, under both forward and reverse bias conditions. Under forward bias, the EL intensity decreases by a factor of approximately 15 on going from 110 to 300 K, where a weak peak is still visible. In contrast, we report the first sharp luminescence peak obtained under reverse bias conditions in the breakdown regime. In this case the EL intensity decreases only by a factor of 4 on going from 110 to 300 K and the room-temperature yield is more than one order of magnitude higher than under forward bias. The data suggest that Er excitation occurs through electron-hole mediated processes under forward bias and through impact excitatio
Erbium implantation in silicon: from materials properties to light emitting devices
No full textErbium implantation in silicon has recently emerged as a promising method to tailor the optical properties of Si towards the achievement of a light emission at 1.54 mu m. In this paper we will review our recent work on this subject. In particular a detailed investigation of the nonradiative processes, competing with the radiative emission of Er in Si will be presented, Among these processes, an Auger de-excitation with the energy released to free carriers will be demonstrated to be extremely efficient, with an Auger coefficient C-A similar to 4.4 x 10(-13) cm(3) s(-1). Using the knowledge on the material properties, an efficient Er implanted light emitting diode has been fabricated. It will be shown that by exciting Er within the depletion region of reverse biased p(+)-n(+) Si diodes in the breakdown regime it is possible to avoid Auger quenching and to achieve high efficiency. Moreover, at the switch off of the diode, when the depletion region shrinks, the excited Er ions become suddenly embedded within the neutral heavily doped region of the device. In this region Auger de-excitation with free carriers sets in and quenches the luminescence rapidly. This allows modulation of the light emitting devices at frequencies as high as a few MHz. These data will be presented and discussed. (C) 1998 Elsevier Science S.A. All rights reserved
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Molecular Recognition of Alcohol Vapours by Novel Langmuir-Schäfer Calix[4]Pyrrole Thin Films
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