| 1. |
- Lynch, S.A., et al.
(författare)
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Toward silicon-based lasers for terahertz sources
- 2006
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Ingår i: IEEE Journal of Selected Topics in Quantum Electronics. - 1077-260X .- 1558-4542. ; 12:6, s. 1570-1577
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Tidskriftsartikel (refereegranskat)abstract
- Producing an electrically pumped silicon-based laser at terahertz frequencies is gaining increased attention these days. This paper reviews the recent advances in the search for a silicon-based terahertz laser. Topics covered include resonant tunneling in p-type Si/SiGe, terahertz intersubband electroluminescence from quantum cascade structures, intersubband lifetime measurements in Si/SiGe quantum wells, enhanced optical guiding using buried suicide layers, and the potential for exploiting common impurity dopants in silicon such as boron and phosphorus to realize a terahertz laser. © 2006 IEEE.
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| 2. |
- Zhao, Ming, et al.
(författare)
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Strain-symmetrized Si/SiGe multi-quantum well structures grown by molecular beam epitaxy for intersubband engineering
- 2006
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Ingår i: Journal of luminescence. - : Elsevier BV. - 0022-2313. ; 121:2, s. 403-408
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Tidskriftsartikel (refereegranskat)abstract
- Three strain-symmetrized Si/SiGe multi-quantum well structures, designed for probing the carrier lifetime of intrawell intersubband transitions between heavy hole 1 (HH1) and light hole 1 (LH1) states with transition energies below the optical phonon energy, were grown by molecular beam epitaxy at low temperature on fully relaxed SiGe virtual substrates. The grown structures were characterized by using various experimental techniques, showing a high crystalline quality and very precise growth control. The lifetime of the LH1 excited state was determined directly with pump-probe spectroscopy. The measurements indicated an increase of the lifetime by a factor of 2 due to the increasingly unconfined LH1 state, which agreed very well with the design. It also showed a very long lifetime of several hundred picoseconds for the holes excited out of the well to transit back to the well through a diagonal process.
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| 3. |
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| 4. |
- López-Dekker, P., et al.
(författare)
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BIOMASS end-to-end mission performance assessment
- 2012
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Ingår i: Proc. IGARSS 2012, IEEE International Geoscience and Remote Sensing Symposium, Munich, Germany, 22-27 July 2012. - 2153-6996. - 9781467311588 ; , s. 1602-1605
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Konferensbidrag (refereegranskat)abstract
- This paper provides an overview of the BIOMASS Mission End-to-End simulator (BEES) and of the mission performance analysis performed with it. The end-to-end performance, in terms of biomass estimates error, is close to the 20% error goal set for the mission. The main sources of errors are temporal decorrelation and the limited available bandwidth, while system induced errors have a negligible impact on the final performance.
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| 5. |
- López-Dekker, P., et al.
(författare)
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BIOMASS End-to-End performance Simulator
- 2011
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Ingår i: IEEE International Geoscience and Remote Sensing Symposium, IGARSS 2011. Vancouver, 24-29 July 2011. - 9781457710049 ; , s. 4249-4252
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Konferensbidrag (refereegranskat)abstract
- This paper discusses the implementation of an end-to-end simulator for the BIOMASS mission. An overview of the system architecture is provided along with a functional description of the modules that comprise the simulator.
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| 6. |
- Pidgeon, CR, et al.
(författare)
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Pump-probe measurement of lifetime engineering in SiGe quantum wells below the optical phonon energy
- 2005
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Ingår i: Semiconductor Science and Technology. - 0268-1242 .- 1361-6641. ; 20:10, s. L50-L52
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Tidskriftsartikel (refereegranskat)abstract
- We have directly determined with pump/probe spectroscopy the light hole (LH1) excited state lifetime for the lowest heavy hole to light hole intrawell subband transition (HH1-LH1) for three prototype samples of Si/SiGe strain-symmetrized multi-quantum well structures, designed to have the final LH1 state increasingly unconfined. The transition energy is below the optical phonon energy. We find that a decay time of 20 ps for sample 1 with a well width of 5.0 nm lengthens to 40 ps for sample 3 with a well width of 3.0 nm, in good agreement with the design. In addition, we have measured the lifetime for holes excited out of the well, from which we determine the lifetime for diagonal transitions (back into the well) to be of approx. several hundred picoseconds.
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| 7. |
- Rauter, P., et al.
(författare)
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Direct determination of ultrafast intersubband hole relaxation times in voltage biased SiGe quantum wells by a density matrix interpretation of femtosecond resolved photocurrent experiments
- 2007
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Ingår i: New Journal of Physics. - : Institute of Physics (IoP) and Deutsche Physikalische Gesellschaft. - 1367-2630. ; 9
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Tidskriftsartikel (refereegranskat)abstract
- We report the quantitative and direct determination of hole intersubband relaxation times in a voltage biased SiGe heterostructure using density matrix calculations applied to a four-level system in order to interpret photocurrent (PC) pump-pump experiments. One consistent set of parameters allows the simulation of two kinds of experiments, namely pump-pump photocurrent experiments at a free electron laser (wavelength 7.9 mu m) and the laser-power dependence of the PC signal. This strongly confirms the high reliability of these parameter values, of which the most interesting in respect to Si based quantum cascade laser development is the extracted heavy-hole relaxation time. The simulations show that this relaxation time directly determines the experimentally observed decay of the pump-pump photocurrent signal as a function of the delay time. For a heavy hole intersubband spacing of 160 meV, a value of 550 fs was obtained. The experimental method was further applied to determine the LH1-HH1 relaxation time of a second sample with a transition energy below the optical phonon energy. The observed relaxation time of 16 ps is consistent with the value found for the same structure by transmission pump-probe experiments.
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| 8. |
- Sjögren, T.K., et al.
(författare)
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Suppression of Clutter in Multichannel SAR GMTI
- 2014
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Ingår i: IEEE Transactions on Geoscience and Remote Sensing. - 0196-2892 .- 1558-0644. ; 52:7, s. 4005-4013
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Tidskriftsartikel (refereegranskat)abstract
- In this paper, the results of moving-target detection in multichannel UHF-band synthetic aperture radar (SAR) dataare shown. The clutter suppression is done using finite-impulse response (FIR) filtering of multichannel SAR in combination with a two-stage fast-backprojection algorithm to focus the moving target using relative speed. The FIR filter coefficients are chosen with the use of space-time adaptive processing filtering. Two parameters are used for target focusing, target speed in range and in azimuth. When the target is focused, both speed parameters of the target are found. In the experimental results, two channels wereused in order to suppress clutter. In the resulting SAR images, it is obvious that very strong scatterers and the forest areas have been suppressed in comparison to the moving target in the image scene. The gain obtained can be measured using signal-to-clutterand- noise-ratio gain, which is about 19 dB. Another way to measure the signal processing gain is the ability to suppress the strongest reflecting object in the SAR scene. The gain of the targetin relation to this object is 25 dB. This shows that using UHF-band SAR ground moving target indication (GMTI) for suppressing forest and increasing the target signal can work.
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