Zn Doped Nanocrystalline CuCl Thin Films for Optoelctronic Applications
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Zn Doped Nanocrystalline CuCl Thin Films for Optoelctronic Applications K. V. Rajani 1, F. Olabanji Lucas 2, M. M. Alam 2, S. Daniels 1 and P. J. McNally 2 1
Nanomaterials Processing Laboratory, NCPST, School of Electronic Engineering, Dublin City University, Dublin 9, Ireland 2 Nanomaterials Processing Laboratory, RINCE, School of Electronic Engineering, Dublin City University, Dublin 9, Ireland. ABSTRACT We report on the use of Zn as an n-type dopant in CuCl thin films for optoelectronic applications, wherein maximum n-type doping of the order of 1018 cm -3 has been achieved. Zn doped nanocrystalline CuCl thin films are successfully deposited on glass and Si substrates by pulsed dc magnetron sputtering. Structural and morphological properties are investigated using X-ray diffraction (XRD) studies and Scanning Electron Microscopy (SEM), respectively. The conductivity of the CuCl:Zn films is examined using the four point probe technique. An order of magnitude increase in the conductivity of CuCl, by the doping with Zn is reported herein. The doped CuCl films display strong room temperature cathodoluminescence (CL) at λ~ 385nm, which is similar to that of the undoped films. Hall Effect measurements show an n-type conductivity of the doped films. INTRODUCTION The search for wide band gap semiconductor materials has great importance in the optoelectronics industry due to their interesting applications in the development of solid state emitters [1, 2]. Zincblende γ-CuCl is a direct band gap (~3.39 eV at room temperature) compound semiconductor with much larger excitonic binding energy (~ 190 meV) [3] when compared to the III-N [4] and ZnO [5] semiconductors. This high binding energy of CuCl guarantees excitonic luminescence at room temperature and beyond. Further to this, it has a relatively small lattice mismatch with Si (< 0.4 %), which may improve the reliability of the light emitting devices made out of these based on CuCl/Si structures. All of these advantages of CuCl can be used for the development of an exciton based semiconducting optical emitter by effectively doping the material system. Numerous reports on the electrical characteristics of CuCl have been published so far. The total electrical conductivity and the electron hole conductivity in copper halides have been reported by Wagner et al. many years ago [6]. They reported p-type conductivity for the as deposited copper chloride films due to the presence of copper vacancies caused by the excess halogen. The p-type conductivity in CuBr has been demonstrated by Knauth et al. using Hall Effect experiments [7]. The first report of the n- type doping of the CuCl films was performed by the co-evaporation of ZnCl2 and CuCl by O’Reilly et al. [8]. They reported a relatively low carrier concentration of the order of 1016/ cm3 for the doped CuCl films due to the simultaneous inclusion of Zn and Cl in the CuCl film.
Here we present the first report on the pulsed dc magnetron sputtering deposition of the CuCl: Zn films on glass and Si substrate using a
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