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- ItemTerahertz stimulated emission from silicon doped by hydrogenlike acceptors(College Park : American Institute of Physics Inc., 2014) Pavlov, S.G.; Deßmann, N.; Shastin, V.N.; Zhukavin, R.K.; Redlich, B.; van der Meer, A.F.G.; Mittendorff, M.; Winnerl, S.; Abrosimov, N.V.; Riemann, H.; Hübers, H.-W.Stimulated emission in the terahertz frequency range has been realized from boron acceptor centers in silicon. Population inversion is achieved at resonant optical excitation on the 1Λ8+ → 1Λ7- , 1Λ6-, 1Λ8- intracenter transitions with a midinfrared free-electron laser. Lasing occurs on two intracenter transitions around 1.75 THz. The upper laser levels are the 1Λ7- , 1Λ6- , and 1Λ8- states, and the lower laser level for both emission lines is the 2Λ8+ state. In contrast to n-type intracenter silicon lasers, boron-doped silicon lasers do not involve the excited states with the longest lifetimes. Instead, the absorption cross section for the pump radiation is the dominating factor. The four-level lasing scheme implies that the deepest even-parity boron state is the 2Λ8+ state and not the 1Λ7+ split-off ground state, as indicated by other experiments. This is confirmed by infrared absorption spectroscopy of Si:B.
- ItemViolation of a Leggett-Garg inequality with ideal non-invasive measurements(London : Nature Publishing Group, 2012) Knee, G.C.; Simmons, S.; Gauger, E.M.; Morton, J.J.L.; Riemann, H.; Abrosimov, N.V.; Becker, P.; Pohl, H.-J.; Itoh, K.M.; Thewalt, M.L.W.; Briggs, G.A.D.; Benjamin, S.C.The quantum superposition principle states that an entity can exist in two different states simultaneously, counter to our 'classical' intuition. Is it possible to understand a given system's behaviour without such a concept? A test designed by Leggett and Garg can rule out this possibility. The test, originally intended for macroscopic objects, has been implemented in various systems. However to date no experiment has employed the 'ideal negative result' measurements that are required for the most robust test. Here we introduce a general protocol for these special measurements using an ancillary system, which acts as a local measuring device but which need not be perfectly prepared. We report an experimental realization using spin-bearing phosphorus impurities in silicon. The results demonstrate the necessity of a non-classical picture for this class of microscopic system. Our procedure can be applied to systems of any size, whether individually controlled or in a spatial ensemble.
- ItemStructural and chemical investigations of adapted Siemens feed rods for an optimized float zone process(Amsterdam [u.a.] : Elsevier, 2013) Richter, S.; Werner, M.; Schley, M.; Schaaff, F.; Riemann, H.; Rost, H.-J.; Zobel, F.; Kunert, R.; Dold, P.; Hagendorf, C.The optimization of the float zone process for industrial application is a promising way to crystallize high purity silicon for high efficiency solar cells with reduced process costs. We investigated two differently produced Siemens rods which should be used as feed material for the float zone process. The aim is to identify and to improve material properties of the feed rods which have a high impact to the float zone process. We show here microstructural and chemical analysis comparing feed rods manufactured under standard conditions and under float zone adapted conditions. To resolve the growth behavior of the grains SEM/EBSD mappings are performed at different positions. TEM analyses are used to investigate the interface region between the mono- and the multicrystalline silicon within the Siemens feed rod. Additionally, drilled cores are cut out from the feed rods containing the region of the slim rod. Afterwards, the drilled cores are crystallized with the float zone process. Finally, carbon and oxygen measurements with FT-IR spectrometry on different positions of the crystallized drilled cores of the Siemens feed rods show the influence of the slim rod material to the float zone process.
- ItemInfluence of slim rod material properties to the Siemens feed rod and the float zone process(Amsterdam [u.a.] : Elsevier, 2014) Richter, S.; Werner, M.; Schley, M.; Schaaff, F.; Riemann, H.; Rost, H.-J.; Zobel, F.; Kunert, R.; Dold, P.; Hagendorf, C.The identification and understanding of material properties influencing the float zone process is important to crystallize high purity silicon for high efficiency solar cells. Also the knowledge of minimal requirements to crystallize monocrystalline silicon with the float zone process is of interest from an economic point of view. In the present study, feed rods for the float zone process composed of a central slim rod and the deposited silicon from the Siemens process are investigated. Previous studies have shown that the slim rod has a significant impact on the purity and suitability for further crystallization processes. In particular, contaminations like substitutional carbon and the presence of precipitates as well as the formation of oxide layers play an important role and are investigated in detail. For this purpose different slim rod materials were used in deposition and float zone crystallization experiments. Samples were prepared by cross sectioning and core drilling of Siemens rods, which were recrystallized with the float zone process. Recrystallized drilled cores are analyzed with FT-IR spectrometry concerning the carbon and oxygen content. To estimate the grain growth behavior on the slim rod surface in dependence of the used slim rod material, EBSD mappings inside a SEM are performed on squared and circular slim rods. TEM analysis was used to investigate the presence of an oxide layer at the interface between slim rod and deposited polycrystalline silicon. Additionally the influence of a nitrogen-containing gas atmosphere during the slim rod pulling is investigated by IR microscopy and ToF-SIMS regarding Si3N4 precipitation.
- ItemSi:P as a laboratory analogue for hydrogen on high magnetic field white dwarf stars(London : Nature Publishing Group, 2013) Murdin, B.N.; Li, J.; Pang, M.L.Y.; Bowyer, E.T.; Litvinenko, K.L.; Clowes, S.K.; Engelkamp, H.; Pidgeon, C.R.; Galbraith, I.; Abrosimov, N.V.; Riemann, H.; Pavlov, S.G.; Hübers, H.-W.; Murdin, P.G.Laboratory spectroscopy of atomic hydrogen in a magnetic flux density of 10 5 T (1 gigagauss), the maximum observed on high-field magnetic white dwarfs, is impossible because practically available fields are about a thousand times less. In this regime, the cyclotron and binding energies become equal. Here we demonstrate Lyman series spectra for phosphorus impurities in silicon up to the equivalent field, which is scaled to 32.8 T by the effective mass and dielectric constant. The spectra reproduce the high-field theory for free hydrogen, with quadratic Zeeman splitting and strong mixing of spherical harmonics. They show the way for experiments on He and H 2 analogues, and for investigation of He 2, a bound molecule predicted under extreme field conditions.
- ItemOptical pumping and readout of bismuth hyperfine states in silicon for atomic clock applications([London] : Macmillan Publishers Limited, part of Springer Nature, 2015) Saeedi, K.; Szech, M.; Dluhy, P.; Salvail, J.Z.; Morse, K.J.; Riemann, H.; Abrosimov, N.V.; Nötzel, N.; Litvinenko, K.L.; Murdin, B.N.; Thewalt, M.L.W.The push for a semiconductor-based quantum information technology has renewed interest in the spin states and optical transitions of shallow donors in silicon, including the donor bound exciton transitions in the near-infrared and the Rydberg, or hydrogenic, transitions in the mid-infrared. The deepest group V donor in silicon, bismuth, has a large zero-field ground state hyperfine splitting, comparable to that of rubidium, upon which the now-ubiquitous rubidium atomic clock time standard is based. Here we show that the ground state hyperfine populations of bismuth can be read out using the mid-infrared Rydberg transitions, analogous to the optical readout of the rubidium ground state populations upon which rubidium clock technology is based. We further use these transitions to demonstrate strong population pumping by resonant excitation of the bound exciton transitions, suggesting several possible approaches to a solid-state atomic clock using bismuth in silicon, or eventually in enriched 28Si.