Laserkristallisiertes polykristallines Silizium - Wasserstoffbindungen und elektronische Eigenschaften

In dieser Arbeit wird laserkristallisiertes polykristallines Silizium (poly-Si) untersucht. Zwei Schwerpunkte stehen im Mittelpunkt der Arbeit: Die Bindungen von Wasserstoff (H), der sich nach der Kristallisation von hydrogenisiertem amorphem Silizium (a-Si:H) noch im Material be...

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Bibliographic Details
Main Author: Brendel, Karsten
Contributors: Fuhs, Walther (Prof. Dr.) (Thesis advisor)
Format: Dissertation
Language:German
Published: Philipps-Universität Marburg 2003
Physik
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Table of Contents: In this thesis polycrystalline silicon is investigated. On one hand the focus of this work is on hydrogen which is in the polycrystalline (poly-Si) sample after crystallisation of hydrogenated amorphous silicon (a-Si:H). On the other hand the electronic properties of poly-Si is investigated. In the following the main results are summarised. During the step-by-step crystallisation the hydrogen content of the film decreases. However, the hydrogen concentration in fully crystallised poly-Si can be up to 17 at.%. Hydrogen depth profiles show that the sample is dehydrogenated predominately at the surface near region. From hydrogen effusion measurements the hydrogen density of states can be calculated. A variation of the hydrogen content and the hydrogen binding energies of a-Si:H is obtained by variation of the deposition temperature. Laser crystallisation results in an increase of the H-binding energies of 0.2 - 0.3 eV. The deposition temperature of a-Si:H also influences the H-density of states in laser crystallised poly-Si. With increasing deposition temperature the hydrogen in poly-Si is bond in complexes with larger binding energies. A comparison with theoretical values of hydrogen binding energies in various complexes shows that a significant amount of hydrogen in poly-Si is bound at silicon dangling-bonds. In addition H is probably bound in complexes like platelets with different size. The hydrogen in the samples can be activated to passivate silicon dangling-bonds and thus the defect density is reduced. The process of defect passivation is thermally activated. The activation energy of 0.2 eV is independent of the position of the fermi energy. The doping efficiency of laser crystallised poly-Si is equal to unity. Electron paramagnetic resonance (EPR) measurements performed at room temperature show the resonance of the silicon dangling-bond. The spin density for undoped poly-Si amounts to 5x1018 cm-3. This value is constant for phosphorous concentrations up to 1x1019 cm-3. This shows that the dangling-bonds are predominately located at grain boundaries. For P-doped samples and at low temperatures the resonance of conducting electrons (CE) appears in the EPR-spectra with a g-value of 1.998. The g-value and the linewidth of the signal as a function of the doping concentration and the temperature is similar to single crystal silicon. The susceptibility of the CE resonance as a function of temperature can be described by a sum of Curie- and Pauli-like paramagnetism. With increasing P-concentration the Curie-part decreases and the Pauli-part increases. This is also similar to results for single crystal silicon but stays in contrast to results obtained for microcrytalline silicon. Luminescence measurements show a broad luminescene band centred at 0.98 eV which is attributed to band-tail luminescence. With increasing doping concentration the luminescence maximum shifts to higher energies. This is explained by a filling process of band-tail states. The results of the electronic properties are summarised to a schematic electronic density of states of poly-Si.