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Effect of Chlorine doping on electrical and optical properties of ZnO thin films

Ekaterina Chikoidze 1Mircea Modreanu 2Micheal Nolan 2Julien Barjon 1Wojciech Pacuski 3Vincent Sallet 1Pierre Galtier 1

1. University of Versailles CNRS (GEMAC), 1, Place A. Briand, Meudon 92195, France
2. University College Cork, NMRC (NMRC), Lee Maltings, Prospect Row, Cork, Ireland
3. Warsaw University, Faculty of Physics, Hoża 69, Warszawa 00-681, Poland


ZnO is a semiconductor oxide material with low resistivity, high transmittance up to UV spectral range and with a good chemical stability under strong reducing environments. It is thus a promising Transparent Conductive Oxide (TCO) and a possible alternative to tin oxide and indium tin oxide to be used as transparent electrode for photovoltaic solar cell for example [1]. We present a study of chlorine doping of ZnO. ZnO:Cl layers have been grown by MOCVD technique, in a vertical geometry reactor. The optimal growth temperature for the quality of the layers was found T=425°C. This relatively low growth temperature is compatible with further processing of TCO based devices. The growth was performed on c-sapphire and fused silica. The theta-2theta X-ray diffraction scans present the ZnO wurtzite symmetry structure without any additional phase. Transport properties were studied for samples with different content of chlorine. Hall Effect measurements show the increase of electron carrier concentration and decreases of electron mobility while increasing the amount of chlorine incorporated in ZnO. Carrier concentration as high as 6.51020cm-3 has been achieved with resistivity of ρ=1.4x10-3 Wcm. Activation energy related with chlorine centre has been determined from temperature dependent Hall measurements. Optical transmittance is greater than 82%. Low temperature cathodoluminescence and photoluminescence show strong UV excitonic emission for all ZnO:Cl, reflecting the conservation of the optical properties of the layers. First principles calculations using density functional theory are presented for the electronic structure of models of Cl-doped ZnO. These results demonstrate that the use of Chlorine is an interesting route to achieve high level of n-type doping by MOCVD with keeping high VIS–IR transparency of the ZnO layers.

[1]A.Guillen-Santiago, M.Olivera, A.Maldonado, et al. Phys.Stat.Sol.(a) 201, (2004), 952


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Presentation: Oral at E-MRS Fall Meeting 2007, Symposium H, by Ekaterina Chikoidze
See On-line Journal of E-MRS Fall Meeting 2007

Submitted: 2007-05-09 13:46
Revised:   2009-06-07 00:44