الفهرس 
Chapter 1: INTRODUCTIONOnly 14 pages are availabe for public view
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Abstract
Thin films of hydrogenated amorphous SiGe (a-Si0.47Ge0.53:H) and nano-multilayers
(NML) of a-Si:H(3 nm)/a-Ge:H (1.2 – 2 nm) have been deposited by the glowdischarge
technique from SiH4 and GeH4 gases. Also B- and P-doped multilayers of
a-Si:H/a-Ge:H were deposited from SiH4 and GeH4 mixed with B2H4 and PH3
gases, respectively. The thin films of a-Si0.47Ge0.53:H were prepared at substrate
temperature 200 and 250oC while the multilayers of a-Si:H(3 nm)/a-Ge:H (1.2–2
nm) and doped a-Si:H/a-Ge:H were deposited at 200oC. The influence of annealing
on the structure and stability of the samples has been studied by X- ray diffraction,
IR spectroscopy and scanning electron microscope (SEM). The optical and
electrical measurements were carried out before and after annealing at different
temperatures.
The results reveal that the total hydrogen content calculated from the IR spectra is
decreased by rising the substrate temperature and/or submitted the samples to
annealing. With raising the substrate temperature, (Ts), of a-Si0.47Ge0.53:H films
from 200 to 250 ºC, the hydrogen related absorption lines decreased in intensity and
the bending modes that are due to dihydride groups (Si-H2 and Ge-H2) in a highly
hydrogenated materials (Ts = 200oC) disappear while the Si-H stretching mode at
2000 cm-1 increases in intensity relative to the 2100 cm-1 stretching mode and
becomes dominant. Upon annealing at 300 and 450oC, the IR spectra of a-
Si0.47Ge0.53:H and a-Si:H(3 nm)/a-Ge:H (1.2–2 nm) multilayers showed that the
integrated absorption intensity of Ge-H and Si-H stretching bonds is decreased
indicating that the hydrogen moves around in Ge network and is partially
evolved, thus causing a change in the atomic density of the SiGe network. The
hydrogen evolved from Ge leads to structural relaxation. Films annealed at 300oC
for 8 h exhibit surface and bulk degradation with formation of bubbles which give
rise to surface bumps. The hydrogen forming the bubbles comes from the rupture of
2
the weak bonds of Ge-H activated by the thermal energy of the annealing.
Remarkable structural degradation was observed in samples annealed at high
temperature 450oC because of the formation of surface bumps and eventually
craters when the bubbles blow up. The X-ray data of films annealed at 300 and
450°C for 8 h illustrated some crystallizing Ge-Ge phases.
The optical measurements showed that the optical energy gap Eg decreases as the
substrate temperate Ts increases and/or upon annealing while the Urbach energy Eu
is increased partially due to the decrease of total hydrogen content (NH) and
partially due to crystallization effects.
The electrical measurements were carried out at different annealed temperatures and
annealing time. The results illustrated that the electrical conductivity is increased
with increasing the annealing temperature and/or annealing time which is partially
due to formation of H bubbles and partially due to crystallization effects. On the
other hand it was found that the activation energy of crystallization deduced from
the annealing time dependence of the conductivity using Avrami’s equation is
structural dependent.
Concerning doping of a-Si:H/a-Ge:H multilayers with born (B) or phosphorus
(P), the results illustrated that the optical band gap is strongly decreased while the
Urbach energy and the electrical conductivity increase sharply.