Effect of 8 MeV Si ions irradiation and thermal annealing in ZnO thin ﬁlms D.R. Herna ´ ndez-Socorro a,n , Z. Montiel-Gonza ´ lez c , S.E. Rodil-Posada c , L. Flores-Morales b , H. Cruz-Manjarrez a , J.M. Herna ´ ndez-Alca ´ ntara a , L. Rodrı ´guez-Ferna ´ ndez a a Instituto de Fı ´sica, Universidad Nacional Auto ´noma de Me´xico, Ciudad Universitaria, Me´xico, D.F. 04510, Me´xico b Facultad de Ciencias, Universidad Nacional Auto ´noma de Me ´xico, Departamento de Fı ´sica, Ciudad Universitaria, Me´xico, D.F. 04510, Me ´xico c Instituto de Investigaciones en Materiales, Universidad Nacional Auto ´noma de Me´xico, Ciudad Universitaria, Me´xico, D.F. 04510, Me´xico article info Article history: Received 20 August 2011 Received in revised form 11 May 2012 Accepted 13 May 2012 Communicated by M.S. Goorsky Available online 4 June 2012 Keywords: A1. Defects A1. Ion beam A1. Photoluminescence A1. Spectroscopic ellipsometry B1. Zinc oxide B2. Semiconducting materials abstract ZnO thin ﬁlms deposited by RF magnetron sputtering on silicon (100) wafers were irradiated by 8 MeV Si ions and thermal annealed in order to study optical properties. The presence of defects inside thin ﬁlms as well as their implications was discussed by Photoluminescence and Spectroscopic Ellipsometry. Photoluminescence conﬁrmed presence of energy states in forbidden band-gap associates with ultraviolet emission and Zn i ,O i and O Zn defects according to the treatment received. Spectroscopic Ellipsometry using the Tauc–Lorentz model plus a Lorentz oscillator was found to be the best model to describe the properties of irradiated samples that did not receive a second thermal annealing treatment. Through this model, it was possible to obtain optical band-gap in the range of 3.1–3.3 eV and excellent approximation of position in energy of the oscillator. & 2012 Elsevier B.V. All rights reserved. 1. Introduction Zinc oxide (ZnO) is a semiconductor with a band-gap greater than 3.0 eV and a large exciton binding energy of 60 meV at room temperature. There are several applications for ZnO thin ﬁlms, such as transparent electrodes in optoelectronic devices [1,2], surface acoustic wave devices [2], varistors [1,3], heat mirrors for energy saving [4], solar cells [2,4], gas sensor [2,3], and blue and ultraviolet optical devices [5]. However, there is a lack of information concerning process–properties relationships. These relationships are quite important in developing ZnO-based devices. One remarkable aspect is the inﬂuence of defects caused by processes such as thermal annealing and ion irradiation on the electric and optical properties. There is a controversy about the nature of defects generated in as-deposited material and the ones induced after irradiation and/or thermal annealing. Good quality ZnO ﬁlms were grown through different meth- ods, such as reactive thermal and electron-beam evaporation [6], sol–gel [7,8], pulse laser deposition [9], chemical vapor deposition [10], and magnetron sputtering [11]. Among all, magnetron sputtering showed several advantages, for example, low substrate temperature (down to room temperature), good adhesion between ﬁlm and substrate, scalability to large areas (upto 3  6m 2 ), great thickness uniformity with a deposition rate range (25–10,000 ˚ A/min) and high ﬁlm density [12–14]. For optical application a few microns of thickness are required to hold light wavelength for optical waveguides. Ion irradiation of thin ﬁlms is a process outside thermody- namic equilibrium which produces damage and structural changes unattainable through conventional techniques. Through high-energy-ion-trace some damage is produced mainly by elec- tronic stopping. This damage causes modiﬁcations in ﬁlms prop- erties which depend on irradiation conditions (ion type, energy and ﬂuence). Under controlled conditions this technique become promising for new materials synthesis, even more, considering that implantation and ion irradiation is widely applied in semi- conductor industry [15]. Previously Muntele et al. reported morphological changes in ZnO ﬁlms by 5 MeV Si ion irradiation [11]. The effect on optical properties of sputtered ZnO ﬁlms through irradiation of 8 MeV Si ions and thermal annealing was analyzed in this research. Si ions at this energy are implanted in substrate at several microns deep. Then, it is possible to avoid the effects caused by Si impurities in the thin ﬁlms. Photoexcitation, produc- tion and annihilation of defects and its inﬂuence in refractive index and band-gap were the properties analyzed. In order to characterize the ﬁlms several techniques were used, for example, Contents lists available at SciVerse ScienceDirect journal homepage: www.elsevier.com/locate/jcrysgro Journal of Crystal Growth 0022-0248/$ - see front matter & 2012 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.jcrysgro.2012.05.038 n Corresponding author. Tel.: þ52 55 56225160; fax: þ52 55 56225009. E-mail address: dhssocorro@yahoo.com.ar (D.R. Herna ´ ndez-Socorro). Journal of Crystal Growth 354 (2012) 169–173