Search Results

Now showing 1 - 3 of 3
  • Item
    Towards 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.
  • Item
    Terahertz 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.
  • Item
    Ion dynamics in Al-Stabilized Li7La3Zr2O12 single crystals – Macroscopic transport and the elementary steps of ion hopping
    (Amsterdam : Elsevier, 2020) Posch, Patrick; Lunghammer, Sarah; Berendts, Stefan; Ganschow, Steffen; Redhammer, Günther J.; Wilkening, Alexandra; Lerch, Martin; Gadermaier, Bernhard; Rettenwander, Daniel; Wilkening, H. Martin R.
    Li7La3Zr2O12 (LLZO) garnet-type ceramics are considered as very promising candidates for solid electrolytes and have been extensively studied in the past few years. Several studies report on an increase in ionic conductivity by doping with ions, such as Al3+ and Ga3+, to stabilize the cubic modification of LLZO. Unfortunately, so far ion dynamics have mainly been studied using powdered samples. Such studies may suffer from chemical heterogeneities concerning Al distribution. Here, we took advantage of Al-stabilized LLZO single crystals to throw light on the elementary steps of ion hopping. We used 7Li nuclear magnetic resonance (NMR) spin-lattice relaxation measurements and conductivity spectroscopy to probe dynamic parameters from both a microscopic and macroscopic point of view. At 293 K the total conductivity turned out to be 0.082 mS cm−1, which is remarkably good for LLZO exhibiting an Al-content of only 0.37 wt%. Most importantly, 7Li NMR spin-lock transients revealed two overlapping diffusion-induced processes. Overall, activation energies from spin-lock NMR excellently agree with that from conductivity measurements; both techniques yield values around 0.36 eV. The corresponding diffusion coefficients deduced from NMR and conductivity measurements almost coincide. The magnetic spin fluctuations sensed by NMR provide an in-depth look at the elementary jump processes, which can barely be revealed by macroscopic impedance spectroscopy providing average values. In particular, we were able to precisely measure the local hopping barrier (0.20 eV) characterizing forward-backward jumps between the sites 24d and 96h. © 2019 The Author(s)