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
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.
results of the electronic properties are summarised to a
schematic electronic density of states of