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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. |