Gd-doping effects on properties of amorphous silicon films prepared by electron beam evaporations
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Gd-doping effects on properties of amorphous silicon films prepared by electron beam evaporations Runjin Gan,a) Fengmin Liu, and Li Qi Department of Basic Science Courses, BIM, Beijing 100085, People’s Republic of China
Jizheng Wang Department of Physics, Lanzhou University, Lanzhou 730000, People’s Republic of China (Received 14 August 1995; accepted 18 August 1997)
Gd-doped amorphous silicon films have been prepared by the electron beam evaporation technique, employing the experimental methods of dc conductivity temperature properties, ESR (electron spin resonance) spectra, and optical band gap Eopt measurements. We have investigated the optical and electrical properties of the films. The results show that at 290 K , T , 330 K, hopping conduction in Gd impurity states near Fermi level is predominant, and at 330 K , T , 500 K extended state conduction dominates due to electrons exited from the impurity states. At a Gd concentration of about 1.0 at. % spin density Ns , peak-peak width DBpp and line-shape factor l of ESR spectra change their dependence on Gd contents. The optical gap of the films narrows with increasing Gd contents in the films from 1.68 eV to 0.42 eV. The results were explained on the basis of the partial compensation of Gd atoms for dangling bonds Si03 .
I. INTRODUCTION
Amorphous semiconductor-metal alloy films have been studied thoroughly, mainly to investigate the optical and electrical properties, and the nature of the transition from semiconductor to metal, which exhibits interesting physical properties.1–3 Because of their unusual structure and properties, the alloy films are of scientific and practical interest. Transition metals with nonfilled 3D shell easily interact with lattice imperfection in a-Si films, so amorphous silicon transition metal alloy films have been widely studied.4–6 It was shown that doping with medium levels of 3D transition metals makes it possible to reduce the localized state density of dangling bonds considerably, and transition metals have higher doping efficiency. The rare earth metals have unsaturated inner 4f shells which are shielded by the filled outer shells. The rare earth ions have been incorporated easily into semiconductors and into crystalline silicon by doping or ion implantation technique. They were doped into noncrystal hosts.7–9 Optical, mechanical, and other physical properties of host materials, such as GaAs, ZnS, CaS, and amorphous glass especially, can be improved by properly doping rare earths. In this paper, we report the experimental results of conductivity, electron spin resonance (ESR), and optical bond gap in Gd-doped a-Si films with various Gd doping levels by the electron beam evaporation technique. Our a)
Corresponding author. J. Mater. Res., Vol. 13, No. 7, Jul 1998
http://journals.cambridge.org
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results show that in the regions of Gd contents more and less than 1.0 at. %, the dependences of conductivity, spin density Ns , peak-peak width DBpp , and line-shape f
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