1,720,971 research outputs found
Strained Ge Channels with High Hole Mobility Grown on Si Substrates by Molecular Beam Epitaxy
No full textStrained modulation-doped quantum wells (QW) offer a huge potential for semiconductor device applications due to their high mobility. The material Ge is particularly interesting here, exhibiting the highest bulk hole-mobility of all known semiconductors. However, the growth for Ge QW structures is quite complex and a special virtual substrate (VS) technique is needed. The VS is commonly grown with thicknesses of over 1 μm , making it difficult for integration with other devices on a single chip. In this paper, we report on the growth of a 15 nm thick strained Ge QW on top of a Si1−xGex VS and Si0.2Ge0.8 buffer layer, using Molecular Beam Epitaxy. The Si1−xGex VS is grown by deposition of 100 nm Ge with a subsequent high-temperature annealing step, followed by a 100 nm thick Si0.2Ge0.8 buffer layer. The resulting two-dimensional hole gas reaches a hole mobility of over 8⋅104cm2V−1s−1 with a corresponding sheet carrier density of 5.7⋅1011cm−2 at 8 K. The Ge QW is further analysed, and comparing it to a sample with a higher VS thickness, a possible limitation of the mobility due to background doping is being discussed. These results show that complementary metal-oxide-semiconductor (CMOS) compatible device integration of the Ge QW is possible, thin buffer layers suffice for the mobilities achieved and background doping limits the low-temperature mobility
High mobility Ge 2DHG based MODFETs for low-temperature applications
No full textModulation-doped field-effect transistors (MODFET) that are typically based on either a two-dimensional electron gas or a two-dimensional hole gas (2DHG) are highly suitable for low-temperature applications due to the high mobilities attained by the charge carriers in the device channel. The Ge 2DHG is particularly interesting, since Ge exhibits the highest hole mobility among all semiconductors. In this paper, we report on the temperature-dependent direct current-characteristics of normally-on MODFETs based on a high mobility Ge 2DHG. Here, we specifically investigate device characteristics down to cryogenic temperatures and analyze the impact of different MOD-doping on device performance. We find that the largest On-Off ratio of I-On/I-Off = 3.2 x 10(6) and lowest sub-threshold swing (SS) of SS = 64 mV dec(-1) at a temperature of T = 7.5 K are attained for a MOD-doping of N-A = 5 x 10(17) cm(-3), while the highest effective mobility mu(eff) = 864 cm(2) V(-1)s(-1) is obtained from a device with a MOD-doping of N-A = 1.1 x 10(18) cm(-3). Furthermore, while effective mobilities in the devices are strongly reduced compared to Hall mobilities measured in the unstructured Ge 2DHGs, both quantities can be seen to follow a similar trend. Our results motivate further investigations of Ge 2DHG MODFETs for applications in cryogenic low-noise amplifiers, besides their well-established potential for spintronic applications
Sharp MIR plasmonic modes in gratings made of heavily doped pulsed laser-melted Ge1-xSnx
Get PDFPlasmonic structures made out of highly doped group-IV semiconductor materials are of large interest for the realization of fully integrated mid-infrared (MIR) devices. Utilizing highly doped Ge1-xSnx alloys grown on Si substrates is one promising route to enable device operation at near-infrared (NIR) wavelengths. Due to the lower effective mass of electrons in Sn compared to Ge, the incorporation of Sn can potentially lower the plasma wavelength of Ge1-xSnx alloys compared to that of pure Ge. However, defects introduced by the large lattice mismatch to Si substrates as well as the introduction of alloy scattering limit device applications in practice. Here, we investigate pulsed laser melting as one strategy to increase material quality in highly doped Ge1-xSnx alloys. We show that a pulsed laser melting treatment of our Ge1-xSnx films not only serves to lower the material’s plasma frequency but also leads to an increase in active dopant concentration. We demonstrate the application of this material in plasmonic gratings with sharp optical extinction peaks at MIR wavelengths
A mid-infrared laser microscope for the time-resolved study of light-induced protein conformational changes
No full textWe have developed a confocal laser microscope operating in the mid-infrared range for the study of light-sensitive proteins, such as rhodopsins. The microscope features a co-aligned infrared and visible illumination path for the selective excitation and probing of proteins located in the IR focus only. An external-cavity tunable quantum cascade laser provides a wavelength tuning range (5.80-6.35 mu m or 1570-1724 cm(-1)) suitable for studying protein conformational changes as a function of time delay after visible light excitation with a pulsed LED. Using cryogen-free detectors, the relative changes in the infrared absorption of rhodopsin thin films around 10(-4) have been observed with a time resolution down to 30 ms. The measured full-width at half maximum of the Airy disk at lambda= 6.08 mu m in transmission mode with a confocal arrangement of apertures is 6.6 mu m or 1.1.. Dark-adapted sample replacement at the beginning of each photocycle is then enabled by exchanging the illuminated thin-film location with the microscope mapping stage synchronized to data acquisition and LED excitation and by averaging hundreds of time traces acquired in different nearby locations within a homogeneous film area. We demonstrate that this instrument provides crucial advantages for time-resolved IR studies of rhodopsin thin films with a slow photocycle. Time-resolved studies of inhomogeneous samples may also be possible with the presented instrument
Titanium and Nickel as alternative materials for mid Infrared plasmonic
No full textFinding suitable materials with low Drude losses for plasmonic applications at mid-infrared wavelengths is challenging. Highly doped Germanium and Germanium Tin alloys have been investigated to that end but are difficult to utilize at wavelengths closer to the near infrared region. In this work, we present results on the fabrication and optical characterization of Titanium and Nickel comb antennas. Extinction spectra were obtained via Fourier Transform Infrared (FTIR) Spectroscopy and verified via Finite Difference Time Domain (FDTD) simulation. The measured spectra show distinct extinction peaks in the range between 4 μm and 11 μm which can be correlated to a plasmonic mode forming at the antenna substrate interface showing that it is possible to excite localized plasmonic modes at the interface between such antennas and a Silicon substrate
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe 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
Plasmonics-integrated Ge PIN-photodetectors
No full textRefractive index sensors can be designed for high sensitivities at small device foot-print. Using a complementary metal-oxide-semiconductor compatible process for fabrication paves the way to cheap devices enabling integrated biosensors. We present results on combining vertical Ge PIN photodetectors with metallic nanostructures such as Al nanohole arrays placed directly on top of the diode. The interaction of plasmonic resonances and photonic modes such as waveguide modes or optical modes in nanostructured photodetectors can potentially be exploited to design refractive index sensors with very high sensitivities. We discuss how the interplay of material properties and device geometry can be tailored for applications in integrated biosensing
Variations on the Author
Get PDF“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Get PDFWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
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