| 1. |
- 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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| 2. |
- 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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| 3. |
- Spindlberger, L., et al.
(författare)
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Optical Properties of Vanadium in 4H Silicon Carbide for Quantum Technology
- 2019
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Ingår i: Physical Review Applied. - : AMER PHYSICAL SOC. - 2331-7019. ; 12:1
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Tidskriftsartikel (refereegranskat)abstract
- We study the optical properties of tetravalent-vanadium impurities in 4H silicon carbide. Light emission from two crystalline sites is observed at wavelengths of 1.28 and 1.33 mu m, with optical lifetimes of 163 and 43 ns, respectively, which remains stable up to 50 and 20 K, respectively. Moreover, spectrally broad photoluminescence is observed up to room temperature. Group-theory and ab initio density-functional supercell calculations enable unequivocal site assignment and shed light on the spectral features of the defects. Specifically, our numerical simulations indicate that the site assignment is reversed with respect to previous assumptions. Our calculations show that vanadium in silicon carbide has highly favorable properties for the generation of single photons in the telecommunication wavelength regime. Combined with the available electronic and nuclear degrees of freedom, vanadium presents all the ingredients required for a highly efficient spin-photon interface.
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| 4. |
- 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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