Optical investigations on sputtered CuCl thin films
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0891-EE03-22.1
Optical investigations on sputtered CuCl thin films
Gomathi Natarajan1,a), A. Mitra2, L. O’Reilly1, S. Daniels1, D. C. Cameron3, P. J. McNally1, O. F. Lucas1 and L. Bradley2 1
Nanomaterials Processing Laboratory (NPL), School of Electronic Engineering, Dublin City University, Dublin-9, Ireland 2 Optoelectronics Laboratory, Trinity College, Dublin-2, Ireland 3 Advanced Surface Technology Research Laboratory (ASTRaL), Mikkeli Research Centre, Lappeenranta University of Technology, PL181, 50101 Mikkeli, Finland. a) email: [email protected] ABSTRACT Copper (I) chloride (CuCl) is a potential candidate for ultra violet optoelectronics due to the fact that it is closely lattice matched with silicon, which makes it readily integrable with silicon device technology. The structural and optoelectronic properties of CuCl thin films deposited by RF magnetron sputtering are investigated. The crystallinity is studied using X-ray diffraction which confirms the growth of CuCl thin films with cubic zinc blende structure predominantly orientated in direction. Excitonic transitions in the thin films were thoroughly investigated using optical absorbance and luminescence spectroscopies. Room temperature absorption spectroscopic analysis confirms the existence of two exciton peaks namely Z12 and Z3 at 372 and 380 nm respectively. A strong UV emission is observed at room temperature in cathodoluminescence and photoluminescence spectra due to the recombination of Z3 exciton at approximately 384 nm. In the low temperature photoluminescence spectrum, a free exciton (Z3) and a bound exciton (I1) are observed. A variation of 1.3 nm to 10 nm was observed in the Z3 exciton line width from 10 K to 300 K. INTRODUCTION Ultraviolet and blue optoelectronics have been dominated by group III nitrides and their variants which are generally grown on sapphire or silicon carbide substrates [1]. A large lattice mismatch between the film and the substrate results in the formation of high dislocation densities and ultimately reduces the emission lifetime and reliability of the device. Moreover, any device that is based on silicon is more readily integrable with current Si based technology. Epitaxial
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growth of GaN layers on Si has been demonstrated by few research groups [2-4]. However, a large lattice mismatch of about 17 % between the hexagonal GaN and cubic Si is still an issue in the device fabrication. Copper (I) Chloride has a cubic zinc blende structure with a very small lattice mismatch of less than 0.4 % to Si. This close match in the crystal structures and lattice parameters opens up the possibility of using CuCl-Si as a heteroepitaxial system with low defect density. CuCl is a direct-band-gap semiconductor with band-gap energy of 3.39 eV. Due to a large band-gap energy, CuCl becomes an excellent semiconductor material for applications considered for other wide-band-gap materials like ZnO, GaN and SiC. As a potential alternative for GaN based materials, CuCl has very attractive features for optoelectron
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