150 research outputs found
Comment on "Diffusion of n-type dopants in germanium"
No full textThe authors of the above paper call into question recent evidence on the properties of self-interstitials, I, in Ge [Cowern et al., Phys. Rev. Lett. 110, 155501 (2013)]. We show that this judgment stems from invalid model assumptions during analysis of data on B marker-layer diffusion during proton irradiation, and that a corrected analysis fully supports the reported evidence. As previously stated, I-mediated self-diffusion in Ge exhibits two distinct regimes of temperature, T: high-T, dominated by amorphous-like mono-interstitial clusters - i-morphs - with self-diffusion entropy30k, and low-T, where transport is dominated by simple self-interstitials. In a transitional range centered on 475°C both mechanisms contribute. The experimental I migration energy of 1.84±0.26 eV reported by the Münster group based on measurements of self-diffusion during irradiation at 550°C<T<680°C further establishes our proposed i-morph mechanism
Self-assembled germanium islands grown on (001) silicon substrates by low-pressure chemical vapor deposition
No full textThe time evolution of self-assembled Ge islands, during low-pressure chemical vapor deposition (LPCVD) of Ge on Si at 650 Deg C using high growth rates, has been investigated by atomic force microscopy, transmission electron microscopy, and Rutherford backscattering spectrometry. We have found three different island structures The smallest islands are "lens-shaped" and characterized by a rather narrow size distribution, ~4nm high and ~20nm wide. Next to form are a distinct population of multifaceted "dome shaped" islands, up to 25nm high and 80-150 nm wide. Finally, the largest islands that form are square-based truncated pyramids with a very narrow size distribution ~50nm high and ~250nm wide. The pyramidal islands normally seen in the intermediate size range (~150nm) are not observed. The small lens-shaped islands appear to be defect free, while some of the multifaceted islands as well as all the large truncated pyramids contain misfit dislocations. The existence of multifaceted islands, in the size range where multifaceted "dome shaped" islands have previously been reported, is attributed to the high growth rate used. Furthermore, under the growth conditions used, the truncated-pyramid-shaped islands are characterized by a very narrow size distribution
Estudo do motor de indução trifásico e desenvolvimento de um dispositivo de proteção efetiva de motores operando em condições anormais: rotor bloqueado e falta de fase
No full textDissertação (mestrado) - Universidade Federal de Santa Catarina, Centro Tecnológico, Programa de Pós-Graduação em Engenharia Mecânica, Florianópolis, 2007.Motores de indução são máquinas robustas, de construção relativamente simples e com vida depende quase exclusivamente da vida da isolação dos enrolamentos. Esta, por sua vez, é afetada por muitos fatores onde o mais importante é sem dúvida a temperatura de trabalho dos materiais isolantes utilizados. Devido a isso, para a proteção dos motores, eles devem ser protegidos contra aumentos de temperatura por um dispositivo integrante do motor ou um dispositivo de proteção independente em todas as condições de operação. O relé de sobrecarga térmico com sensibilidade a falta de fase, que opera pelo principio dos bimetais, é o dispositivo de proteção independente mais utilizado para proteção térmica de motores. Testes experimentais para avaliação da proteção efetiva realizada por esse dispositivo em condições de operação anormais do motor de indução, rotor bloqueado e falta de fase, foram realizados e com base nas avaliações e resultados obtidos, um novo sistema de proteção é proposto de forma a oferecer proteção efetiva as mais diversas condições de operação do motor. A validação e implementação do sistema proposto são realizadas através de simulações com auxílio do software P-Spice e testes experimentais em protótipo.The induction motors are robust machines and quite simple in their construction. In general, their lifetime depends on the life of the winding isolation. This is affected by many factors like vibrations, corrosive environments and others. Undoubtedly, among all these factors, the most important is the working temperature of the used insulating materials. Due of this, induction motors must be protected against temperature rise by a protective device, which is a part of the motor or an independent protective device, during all operation conditions. Overload relay with single phasing failure sensitivity, which achieved using the bimetal principle, is the most used independent protective device for thermal motor protection. Experimental tests were made to evaluate the effective motor protection by this device under abnormal motor operation conditions, blocked rotor and single phasing. Based on results and evaluations found, a new protective system was proposed in order to provide effective protection under several motor operation conditions: normal and abnormal conditions. The validity and implementation of proposed system were made thought simulations, assisted by P-Spice software, and experimental tests using a prototype
Effect of oxygen on the diffusion of nitrogen implanted in silicon
No full textNitrogen implants were performed in Si wafers of variable purity, i.e., epitaxial layers, float zone, and Czochralski silicon (CZ-Si). The diffusion behavior of nitrogen reported by Hockett in Appl. Phys. Lett., 54. 1793 (1989), where nitrogen diffuses for several micrometers at temperatures as low as 750°C and the profiles assume a "double-peak" structure, is peculiar of CZ-Si. In contrast, in pure epitaxial-Si, nitrogen is immobile at low temperature but, at a higher temperature (850°C), the broadening of the nitrogen profile never assumes the shape observed in CZ-Si. Our results suggest that oxygen determines the shape of the nitrogen diffusion profiles. © 2004 The Electrochemical Society. All rights reserved
Structural and electrical characterisation of ion-implanted strained silicon
No full textThe production of low resistance ultra-shallow junctions for e.g. source/drain extensions using low energy ion-implantation will be required for future CMOS devices [1]. This architecture will require implants which demonstrate high electrical activation and nm range depth profiles. We investigate the properties of Sb implants in tensile strained silicon due to their potential to satisfy these criteria, and the carrier mobility enhancements associated with tensile strained silicon. Low energy (in this case 2 keV)implants coupled with Sb’s large atomic radius are capable of providing ~ 10 nm implant depths. In addition to this, Sb, in the presence of tensile strain demonstrates higher electrical activation when compared with the more traditional n-type dopant As [2].
We now report on the initial results of an ongoing systematic study over a wide silicon tensile strain range (from 0.4 to 1.25 % strain) in order to establish clear strain-related trends. Graded Si1-xGex virtual substrates (VS) with are used as template substrates, upon which tensile strained Si layers are grown. Prior to implantation the 0.1 ≤ x ≤ 0.3 quality of the strained layer and SiGe buffer is assessed using UV micro-Raman spectroscopy (μRS), synchrotron x-ray topography (SXRT) and high resolution x-ray diffraction (HR-XRD). For measurements of strain following implantation, HR-XRD is found to be more useful than μRS due to additional carrier-concentration induced Si
Raman peak shifts in the Raman spectra , these obscure small changes in the strain state, and result from the degenerate doping levels achieved in these samples (~7x1020 cm-3).
Using x-ray techniques, we find clear evidence of tilt in the SiGe VS at Ge concentrations > 23% (i.e. ε > 0.9 %), this tilt impacts on the quality of the strained Si. In
addition to this, stacking faults have been detected non-destructively in the higher strain samples (ε = 1.25%, VS = Si0.7Ge0.3) using SXRT in transmission mode
Role of self- and boron-interstitial clusters in transient enhanced diffusion in silicon
No full textWe investigate the nucleation and evolution of boron-interstitial clusters (BIC), driven by high interstitial supersaturations, S(t), during Si implant damage annealing. The BICs are "fabricated" in a narrow band by overlapping the Si implant damage tail with a lightly doped B buried layer. The BIC band is found to be a net sink for interstitials at supersaturations S(t)>104. Our results suggest that silicon self-interstitial defects are the primary source of interstitials driving transient enhanced diffusion, and that BICs act as a secondary "buffer" for the interstitial supersaturatio
Effect of B dose and Ge preamorphization energy on the electrical and structural properties of ultrashallow junctions in silicon-on-insulator
No full textFormation of highly activated, ultra-shallow and abrupt profiles is a key requirement for the next generations of CMOS devices, particularly for source-drain extensions. For p-type dopant implants (boron), a promising method of increasing junction abruptness is to use Ge preamorphizing implants prior to ultra-low energy B implantation and solid-phase epitaxy regrowth to re-crystallize the amorphous Si. However, for future technology nodes, new issues arise when bulk silicon is supplanted by silicon-on-insulator (SOI). Previous results have shown that the buried Si/SiO2 interface can improve dopant activation, but the effect depends on the detailed preamorphization conditions and further optimization is required. In this paper a range of B doses and Ge energies have been chosen in order to situate the end-of-range (EOR) defect band at various distances from the back interface of the active silicon film (the interface with the buried oxide), in order to explore and optimize further the effect of the interface on dopant behavior. Electrical and structural properties were measured by Hall Effect and SIMS techniques. The results show that the boron deactivates less in SOI material than in bulk silicon, and crucially, that the effect increases as the distance from the EOR defect band to the back interface is decreased. For the closest distances, an increase injunction steepness is also observed, even though the B is located close to the top surface, and thus far from the back interface. The position of the EOR defect band shows the strongest influence for lower B doses.</p
Effect of buried Si SiO2 interface on dopant and defect evolution in preamorphizing implant ultrashallow junction
No full textP -type ultrashallow junctions are widely fabricated using Ge preamorphization prior to ultralow-energy boron implantation. However, for future technology nodes, issues arise when bulk silicon is supplanted by silicon-on-insulator (SOI). An understanding of the effect of the buried Si SiO2 interface on defect evolution, electrical activation, and diffusion is needed in order to optimize the preamorphization technique. In the present study, boron has been implanted in germanium preamorphized silicon and SOI wafers with different preamorphizing implant conditions. Subsequent to implantation an isothermal annealing study of the samples was carried out. Electrical and structural properties were measured by Hall-effect and secondary-ion-mass spectroscopy techniques. The results show a variety of interesting effects. For the case where the Ge preamorphization end-of-range defects are close to the buried oxide interface, there is less dopant deactivation and less transient-enhanced diffusion, due to a lower interstitial gradient towards the surface.</p
Diffusion and activation of ultrashallow B implants in silicon on insulator:End-of-range defect dissolution and the buried Si/SiO2 interface
No full textThe fabrication of preamorphized p-type ultrashallow junctions in silicon-on-insulator (SOI) has been investigated. Electrical and structural measurements after annealing show that boron deactivation and transient enhanced diffusion are reduced in SOI compared to bulk wafers. The reduction is strongest when the end-of-range defects of the preamorphizing implant are located deep within the silicon overlayer of the SOI silicon substrate. Results reveal a very substantial increase in the dissolution rate of the end-of-range defect band. A key player in this effect is the buried Si/SiO2 interface, which acts as an efficient sink for interstitials competing with the silicon surface.</p
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