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- ItemFirst Terahertz-range Experiments on Pump – Probe Setup at Novosibirsk free Electron Laser(Amsterdam [u.a.] : Elsevier, 2016) Choporova, Yulia Yu.; Gerasimov, Vasily V.; Knyazev, Boris A.; Sergeev, Sergey M.; Shevchenko, Oleg A.; Zhukavin, Roman K.; Abrosimov, Nikolay V.; Kovalevsky, Konstantin A.; Ovchar, Vladimir K.; Hübers, Heinz-Wilhelm; Kulipanov, Gennady N.; Shastin, Valery N.; Schneider, Harald; Vinokurov, Nikolay A.A single-color pump-probe system has been commissioned at the Novosibirsk free electron laser. The laser emits a tunable monochromatic terahertz radiation. To prove the proper system operation, we investigated the time-resolved absorption of a sample of n-type germanium doped with antimony, which was previously investigated at the FELBE facility, in the temperature range from 5 to 40 K. The measured relaxation time amounted to about 1.7 ns, which agreed with the results obtained at the FELBE. The results of pump-probe measurements of non-equilibrium dynamics of hot electrons in the germanium crystal at cryogenic temperatures are presented for wavelengths of 105, 141 and 150 μm.
- ItemComputational Simulations of the Lateral-Photovoltage-Scanning-Method(London [u.a.] : Institute of Physics, 2018) Kayser, S.; Lüdge, A.; Böttcher, K.The major task for the Lateral-Photovoltage-Scanning-Method is to detect doping striations and the shape of the solid-liquid-interface of an indirect semiconductor crystal. This method is sensitive to the gradient of the charge carrier density. Attempting to simulate the signal generation of the LPS-Method, we are using a three dimensional Finite Volume approach for solving the van Roosbroeck equations with COMSOL Multiphysics in a silicon sample. We show that the simulated LPS-voltage is directly proportional to the gradient of a given doping distribution, which is also the case for the measured LPS-voltage.
- ItemTerahertz emission from lithium doped silicon under continuous wave interband optical excitation(Bristol : IOP Publ., 2015) Andrianov, A.V.; Zakhar'in, A.O.; Zhukavin, R.K.; Shastin, V.N.; Abrosimov, N.V.We report on experimental observation and study of terahertz emission from lithium doped silicon crystals under continuous wave band-to-band optical excitation. It is shown that radiative transitions of electrons from 2P excited states of lithium donor to the 1S(A1) donor ground state prevail in the emission spectrum. The terahertz emission occurs due to capture of nonequilibrium electrons to charged donors, which in turn are generated in the crystal as a result of impurity assisted electron-hole recombination. Besides the intracentre radiative transitions the terahertz emission spectrum exhibits also features at about 12.7 and 15.27 meV, which could be related to intraexciton transitions and transitions from the continuum to the free exciton ground state.
- ItemTowards a life-time-limited 8-octave-infrared photoconductive germanium detector(Bristol : IOP Publ., 2015) Pavlov, S.G.; Deßmann, N.; Pohl, A.; Abrosimov, N.V.; Mittendorff, M.; Winnerl, S.; Zhukavin, R.K; Tsyplenkov, V.V.; Shengurov, D.V.; Shastin, V.N.; Hübers, H.-W.Ultrafast, ultra-broad-band photoconductive detector based on heavily doped and highly compensated germanium has been demonstrated. Such a material demonstrates optical sensitivity in the more than 8 octaves, in the infrared, from about 2 mm to about 8 μm. The spectral sensitivity peaks up between 2 THz and 2.5 THz and is slowly reduced towards lower and higher frequencies. The life times of free electrons/holes measured by a pump-probe technique approach a few tenths of picoseconds and remain almost independent on the optical input intensity and on the temperature of a detector in the operation range. During operation, a detector is cooled down to liquid helium temperature but has been approved to detect, with a reduced sensitivity, up to liquid nitrogen temperature. The response time is shorter than 200 ps that is significantly faster than previously reported times.
- ItemStudy on the Properties of High Purity Germanium Crystals(Bristol : IOP Publ., 2015) Yang, G.; Mei, H.; Guan, Y.T.; Wang, G.J.; Mei, D.M.; Irmscher, K.In the crystal growth lab of South Dakota University, we are growing high purity germanium (HPGe) crystals and using the grown crystals to make radiation detectors. As the detector grade HPGe crystals, they have to meet two critical requirements: an impurity level of ∼109 to 10 atoms /cm3 and a dislocation density in the range of ∼102 to 104 / cm3. In the present work, we have used the following four characterization techniques to investigate the properties of the grown crystals. First of all, an x-ray diffraction method was used to determine crystal orientation. Secondly, the van der Pauw Hall effect measurement was used to measure the electrical properties. Thirdly, a photo-thermal ionization spectroscopy (PTIS) was used to identify what the impurity atoms are in the crystal. Lastly, an optical microscope observation was used to measure dislocation density in the crystal. All of these characterization techniques have provided great helps to our crystal activities.
- ItemThe spin-flip scattering effect in the spin transport in silicon doped with bismuth(Bristol : IOP Publ., 2017) Ezhevskii, A.A.; Detochenko, A.P.; Soukhorukov, A.V.; Guseinov, D.V.; Kudrin, A.V.; Abrosimov, N.V.; Riemann, H.Spin transport of conduction electrons in silicon samples doped with bismuth in the 1.1•1013 - 7.7•1015 cm-3 concentration range was studied by the Hall effect measurements. The dependence of the Hall voltage magnitude on the magnetic field is the sum of the normal and spin Hall effects. The electrons are partially polarized by an external magnetic field and are scattered by the bismuth spin-orbit potential. Spin-flip scattering results in the additional electromotive force which compensates the normal Hall effect in strong magnetic fields.
- ItemRelaxation of Coulomb States in semiconductors probed by FEL radiation(Les Ulis : EDP Sciences, 2018) Zhukavin, R.Kh.; Kovalevsky, K.A.; Tsyplenkov, V.V.; Pavlov, S.G.; Hübers, H-W.; Choporova, Yu.Yu.; Knyazev, B.A.; Klopf, J.M.; Redlich, B.; Abrosimov, N.V.; Astrov, Yu.A.; Shastin, V.N.; Silaev, A.A.This article has no abstract.