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Author: Kittler, M. × Type: Text ×

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    Room temperature direct band gap emission from Ge p-i-n heterojunction photodiodes
    (London : Hindawi, 2012) Kasper, E.; Oehme, M.; Arguirov, T.; Werner, J.; Kittler, M.; Schulze, J.
    Room temperature direct band gap emission is observed for Si-substrate-based Ge p-i-n heterojunction photodiode structures operated under forward bias. Comparisons of electroluminescence with photoluminescence spectra allow separating emission from intrinsic Ge (0.8 eV) and highly doped Ge (0.73 eV). Electroluminescence stems fromcarrier injection into the intrinsic layer, whereas photoluminescence originates from the highly n-doped top layer because the exciting visible laser wavelength is strongly absorbed in Ge. High doping levels led to an apparent band gap narrowing from carrier-impurity interaction. The emission shifts to higher wavelengths with increasing current level which is explained by device heating. The heterostructure layer sequence and the light emitting device are similar to earlier presented photodetectors. This is an important aspect for monolithic integration of silicon microelectronics and silicon photonics.
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    Single-electron transitions in one-dimensional native nanostructures
    (Bristol : Institute of Physics Publishing, 2014) Reiche, M.; Kittler, M.; Schmelz, M.; Stolz, R.; Pippel, E.; Uebensee, H.; Kermann, M.; Ortlepp, T.
    Low-temperature measurements proved the existence of a two-dimensional electron gas at defined dislocation arrays in silicon. As a consequence, single-electron transitions (Coulomb blockades) are observed. It is shown that the high strain at dislocation cores modifies the band structure and results in the formation of quantum wells along dislocation lines. This causes quantization of energy levels inducing the formation of Coulomb blockades.
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    On the electronic properties of a single dislocation
    (College Park : American Institute of Physics Inc., 2014) Reiche, M.; Kittler, M.; Erfurth, W.; Pippel, E.; Sklarek, K.; Blumtritt, H.; Haehnel, A.; Uebensee, H.
    A detailed knowledge of the electronic properties of individual dislocations is necessary for next generation nanodevices. Dislocations are fundamental crystal defects controlling the growth of different nanostructures (nanowires) or appear during device processing. We present a method to record electric properties of single dislocations in thin silicon layers. Results of measurements on single screw dislocations are shown for the first time. Assuming a cross-section area of the dislocation core of about 1 nm2, the current density through a single dislocation is J = 3.8 × 1012 A/cm2 corresponding to a resistivity of ρ ≅ 1 × 10-8 Ω cm. This is about eight orders of magnitude lower than the surrounding silicon matrix. The reason of the supermetallic behavior is the high strain in the cores of the dissociated dislocations modifying the local band structure resulting in high conductive carrier channels along defect cores.
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    Investigation of emitter homogeneity on laser doped emitters
    (Amsterdam [u.a.] : Elsevier, 2011) Germershausen, S.; Bartholomäus, L.; Seidel, U.; Hanisch, N.; Schieferdecker, A.; Küsters, K.H.; Kittler, M.; Ametowobla, M.; Einsele, F.; Dallmann, G.
    The selective emitter formation by laser doping is a well known process to increase the efficiency of silicon solar cells [1], [2]. For the characterization of laser doped emitters, SIMS (Secondary Ion Mass Spectroscopy) and ECV (Electrochemical Capacitance Voltage Measurement) techniques are used to analyze the emitter profile [3]. It is very difficult to get acceptable result by SIMS on a textured surface, so only ECV can be used. It has been shown, that a charge carrier depth profile can be measured on a homogeneous emitter only by ECV. The use of laser doping results in a non-homogeneous emitter. We have shown that the emitter depth is not just a function of the pulse power, but in addition of the surface structure of the wafer. The texture seems responsible for a strong variability in the doping profile. It has been shown, that the ECV measurement is not applicable to characterize the emitter depth on laser doped areas, because of the microscopic inhomogeneities in the emitter on the macroscopic measurement area. The real emitter profiles are to complex to be characterized by SIMS or ECV. We have shown that the variation in the emitter profile is resulting from the texture in the laser-doped regions.