New Paramagnetic Center and High Conductivity in a-Si 1-x Ru x :H Thin Films
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New Paramagnetic Center and High Conductivity in a-Si1-xRux:H Thin Films Jian He, Wei Li*, Rui Xu, An-ran Guo,Yin Wang and Ya-dong Jiang State Key Laboratory of Electronic Thin Films and Integrated Devices, University of Electronic Science and Technology of China, Chengdu 610054, China E-mail: [email protected] ABSTRACT In this work, the metallic element Ru is introduced into a-Si:H. The structural and electrical properties of the films doped with Ru have been investigated. Raman spectra reveal that the addition of Ru disarranges further the intrinsically disordered amorphous network and generates more coordinated defects. Meanwhile, a new paramagnetic signal, associated with the holes localized in valence band tail, has been observed. Moreover, the conductivity increases by about nine orders of magnitude with the increase of doping concentration, and the temperature coefficient of resistance (TCR) results show that this material may have a potential application in the infrared detectors. INTRODUCTION Over the last few decades, the doping of crystalline semiconductor with metallic elements, such as Gd [1], Tm and Yb [2], has been of considerable interest due to its potential application in stimulated emission and infrared detection. The key scientific concerns, in particular, focus on the electronic configuration, the local coordination of impurities in the lattice and their interaction with the host. Because of the low solubility in lattice, it becomes more difficult for metal atoms to get into the covalent semiconductor like silicon and germanium. In contrast, this problem can be partially overcome in the amorphous counterpart because the disorder of the amorphous network allows it to accommodate more metal atoms with different size. Hydrogenated amorphous silicon (a-Si:H), a technologically important material, is widely used in many practical applications, such as the production of solar cells [3], infrared detectors in night vision systems [4], and thin film transistors in flat panel display devices [5]. In addition, aSi:H is also an ideal theory model in amorphous semiconductor physics. Consequently, the metal doping of a-Si:H has been an interesting area and there are many investigations on the a-Si:H doped by metallic elements, especially rare-earth elements. It is reported that the electrical properties of the doped a-Si:H with La, Nd, Er, Lu or Pr exhibit a large degree of variation [6]. Kumeda et. al [7, 8] found that in the electronic spin resonance (ESR) measurement the resonance signal of Mn, Fe and Ni impurities in a-Si:H can be observed and the paramagnetic neutral dangling bond (D0) density decreases as the impurities concentration increases. However, the effects of the incorporation of metal impurities on the microstructure and properties of disordered semiconductors are not completely known and understood. In recent years, metallic element Ru has attracted increasing attention due to its several applications: (i) the barrier layer for Cu metallization in electronic devices [9]; (ii) the capping mate
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