| 1. |
- Bruzzi, M, et al.
(författare)
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Radiation-hard semiconductor detectors for SuperLHC
- 2005
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Ingår i: Nuclear Instruments & Methods in Physics Research. Section A: Accelerators, Spectrometers, Detectors, and Associated Equipment. - : Elsevier BV. - 0167-5087 .- 0168-9002. ; 541:1-2, s. 189-201
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Tidskriftsartikel (refereegranskat)abstract
- An option of increasing the luminosity of the Large Hadron Collider (LHC) at CERN to 1035 cm-2 s-1 has been envisaged to extend the physics reach of the machine. An efficient tracking down to a few centimetres from the interaction point will be required to exploit the physics potential of the upgraded LHC. As a consequence, the semiconductor detectors close to the interaction region will receive severe doses of fast hadron irradiation and the inner tracker detectors will need to survive fast hadron fluences of up to above 1016cm-2. The CERN-RD50 project "Development of Radiation Hard Semiconductor Devices for Very High Luminosity Colliders" has been established in 2002 to explore detector materials and technologies that will allow to operate devices up to, or beyond, this limit. The strategies followed by RD50 to enhance the radiation tolerance include the development of new or defect engineered detector materials (SiC, GaN, Czochralski and epitaxial silicon, oxygen enriched Float Zone silicon), the improvement of present detector designs and the understanding of the microscopic defects causing the degradation of the irradiated detectors. The latest advancements within the RD50 collaboration on radiation hard semiconductor detectors will be reviewed and discussed in this work.
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| 2. |
- Habibpour, Omid, 1979, et al.
(författare)
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A W-band MMIC Resistive Mixer Based on Epitaxial Graphene FET
- 2017
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Ingår i: IEEE Microwave and Wireless Components Letters. - : Institute of Electrical and Electronics Engineers (IEEE). - 1558-1764 .- 1531-1309. ; 27:2, s. 168-170
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Tidskriftsartikel (refereegranskat)abstract
- This letter presents the design, fabrication and characterization of the first graphene based monolithic microwave integrated circuit (MMIC) in microstrip technology operating in W-band. The circuit is a resistive mixer in a 250 nm graphene field effect transistor (G-FET) technology on a SiC substrate. A conversion loss of 18 dB is achieved which is limited by the available local oscillator (LO) power. The mixer exhibits a flat response over radio frequency (RF) range of 90-100 GHz. The RF bandwidth is also limited by the measurement setup.
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| 3. |
- Melios, C., et al.
(författare)
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Tuning epitaxial graphene sensitivity to water by hydrogen intercalation
- 2017
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Ingår i: Nanoscale. - : Royal Society of Chemistry (RSC). - 2040-3372 .- 2040-3364. ; 9:10, s. 3440-3448
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Tidskriftsartikel (refereegranskat)abstract
- The effects of humidity on the electronic properties of quasi-free standing one layer graphene (QFS 1LG) are investigated via simultaneous magneto-transport in the van der Pauw geometry and local work function measurements in a controlled environment. QFS 1LG on 4H-SiC(0001) is obtained by hydrogen intercalation of the interfacial layer. In this system, the carrier concentration experiences a two-fold increase in sensitivity to changes in relative humidity as compared to the as-grown epitaxial graphene. This enhanced sensitivity to water is attributed to the lowering of the hydrophobicity of QFS 1LG, which results from spontaneous polarization of 4H-SiC(0001) strongly influencing the graphene. Moreover, the superior carrier mobility of the QFS 1LG system is retained even at the highest humidity. The work function maps constructed from Kelvin probe force microscopy also revealed higher sensitivity to water for 1LG compared to 2LG in both QFS 1LG and as-grown systems. These results point to a new field of applications for QFS 1LG, i.e., as humidity sensors, and the corresponding need for metrology in calibration of graphene-based sensors and devices.
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| 4. |
- Strupinski, W., et al.
(författare)
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MOVPE strain layers - growth and application
- 2000
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Ingår i: Journal of Crystal Growth. ; 221, s. 20-25
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Tidskriftsartikel (refereegranskat)abstract
- The critical thickness, characteristic for the lattice-mismatch parameter, plays a key role in the growth of strain layers. The driving force for the 2D-3D transition can be minimized by slowing the relaxation of misfit strain. As a result the relatively smooth layer is deposited at lower temperature for the optimal growth rate. The quality of the InGaAs- and AlAs-strained layers deposited on InP substrate have been examined by the XRD, AFM and SIMS methods. Atomic force microscopy allows to observe 3D growth mode even for very thin layers. Relatively strong relaxation effects are recognized by surface roughness. Two-dimensional di!raction measurement is a much more sensitive tool for the estimation of relaxation degree. The observations results were applied in the heterostructure barrier varactor (HBV) diode. In order to minimize the conduction current through HBV two materials with different design of the barriers were studied: one heterostructure with three homogeneous lattice matched barriers consisting of 20nm Al0.48In0.52As and another one with strained step-like barriers consisting of 5 nm Al0.48In0.52As, 3 nm AlAs and 5 nm Al0.48In0.52As. We found that the use of strained step-like barriers results in a much lower conduction current. For current density
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| 5. |
- Strupinski, W., et al.
(författare)
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New method for determination of the peak-velocity in epitaxial semiconductor structures by dc measurements on microbridges
- 1991
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Ingår i: Applied Physics Letters. - : AIP Publishing. - 0003-6951 .- 1077-3118. ; 59:24, s. 3151-3153
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Tidskriftsartikel (refereegranskat)abstract
- A simple current-voltage measurement technique using microbridge patterns is described as a fast method for the determination of the effective peak electron velocity in III-V semiconducting materials. The method is tested for GaAs samples. Microbridge patterns with different geometries were investigated and the influence of ''self-heating'' by power dissipation was examined. Some other potential sources of errors deteriorating the accuracy of measurements were determined.
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| 6. |
- Vasek, P., et al.
(författare)
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Magnetotransport in graphene on silicon side of SiC
- 2013
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Ingår i: Journal of Physics, Conference Series. - : Institute of Physics Publishing (IOPP). - 1742-6588 .- 1742-6596. ; 456:1, s. 012038-
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Tidskriftsartikel (refereegranskat)abstract
- We have studied the transport properties of graphene grown on silicon side of SiC. Samples under study have been prepared by two different growth methods in two different laboratories. Magnetoresistance and Hall resistance have been measured at temperatures between 4 and 100 K in resistive magnet in magnetic fields up to 22 T. In spite of differences in sample preparation, the field dependence of resistances measured on both sets of samples exhibits two periods of magneto-oscillations indicating two different parallel conducting channels with different concentrations of carriers. The semi-quantitative agreement with the model calculation allows for conclusion that channels are formed by high-density and low-density Dirac carriers. The coexistence of two different groups of carriers on the silicon side of SiC was not reported before.
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| 7. |
- Winters, Michael, 1986, et al.
(författare)
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Characterization and physical modeling of MOS capacitors in epitaxial graphene monolayers and bilayers on 6H-SiC
- 2016
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Ingår i: AIP Advances. - : AMER INST PHYSICS. - 2158-3226. ; 6:8
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Tidskriftsartikel (refereegranskat)abstract
- Capacitance voltage (CV) measurements are performed on planar MOS capacitors with an Al2O3 dielectric fabricated in hydrogen intercalated monolayer and bilayer graphene grown on 6H-SiC as a function of frequency and temperature. Quantitative models of the CV data are presented in conjunction with the measurements in order to facilitate a physical understanding of graphene MOS systems. An interface state density of order 2 . 10(12)eV(-1)cm(-2) is found in both material systems. Surface potential fluctuations of order 80-90meV are also assessed in the context of measured data. In bilayer material, a narrow bandgap of 260meV is observed consequent to the spontaneous polarization in the substrate. Supporting measurements of material anisotropy and temperature dependent hysteresis are also presented in the context of the CV data and provide valuable insight into measured and modeled data. The methods outlined in this work should be applicable to most graphene MOS systems. (C) 2016 Author(s). All article content, except where otherwise noted, is licensed under a Creative Commons Attribution (CC BY) license (http://creativecommons.org/licenses/by/4.0/).
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| 8. |
- Winters, Michael, 1986, et al.
(författare)
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High frequency electromagnetic detection by nonlinear conduction modulation in graphene nanowire diodes
- 2015
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Ingår i: Applied Physics Letters. - : AIP Publishing. - 0003-6951 .- 1077-3118. ; 107:14
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Tidskriftsartikel (refereegranskat)abstract
- We present graphene nanowires implemented as dispersion free self switched microwave diode detectors. The microwave properties of the detectors are investigated using vector corrected large signal measurements in order to determine the detector responsivity and noise equivalent power (NEP) as a function of frequency, input power, and device geometry. We identify two distinct conductance nonlinearities which generate detector responsivity: an edge effect nonlinearity near zero bias due to lateral gating of the nanowire structures, and a velocity saturation nonlinearity which generates current compression at high power levels. The scaling study shows that detector responsivity obeys an exponential scaling law with respect to nanowire width, and a peak responsivity (NEP) of 250 V/W (50 pW/ Hz) is observed in detectors of the smallest width. The results are promising as the devices exhibit responsivities which are comparable to state of the art self switched detectors in semiconductor technologies.
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