Growth ambient dependence of defects, structural disorder and photoluminescence in SnO 2 ﬁlms deposited by reactive magnetron sputtering Shikha Bansal a , D.K. Pandya a , Subhash C. Kashyap a,⇑ , D. Haranath b a Thin Film Laboratory, Department of Physics, Indian Institute of Technology Delhi, New Delhi 110016, India b National Physical Laboratory, Council of Scientiﬁc and Industrial Research, Dr. KS Krishnan Road, New Delhi 110012, India article info Article history: Received 25 March 2013 Received in revised form 21 August 2013 Accepted 22 August 2013 Available online 31 August 2013 Keywords: Photoluminescence Urbach tail width SnO 2 thin ﬁlms Optical band gap Electrical properties Reactive sputtering abstract The present paper deals with the study of photoluminescence (PL) and the other physical properties (structural, electrical and optical) of SnO 2 thin ﬁlms with controlled disorder and intrinsic defects induced during the reactive magnetron sputtering by changing oxygen ﬂow rate from 12 to 16 sccm. The changes in unit cell volume, near band-edge optical transparency and width of Urbach tail in the ﬁlms are correlated with the structural disorder and presence of intrinsic defects induced by growth under different oxygen partial pressures. The increased intensity of the PL near UV emission and decrease in the intensity of visible emission peaks with increase in oxygen ﬂow rate is linked with the decrease in oxygen vacancies and tin interstitials in the ﬁlms. With increasing oxygen content, whereas the electrical resistivity of the ﬁlms minimizes to a value of 4.3  10 2 ohm cm at 14 sccm, the mobility of the ﬁlms increases to a saturation value 15 cm 2 V 1 s 1 . The donor-defect concentration linked carrier density is observed to decrease monotonically from 2  10 19 to 0.6  10 19 cm 3 . Ó 2013 Elsevier B.V. All rights reserved. 1. Introduction Tin oxide has a wide and direct band gap of 3.6 eV, with high electrical conductivity, high optical transparency in the visible re- gime and a high exciton binding energy of 130 meV at room tem- perature [1]. These properties make SnO 2 a favored candidate to be used as transparent conducting electrode in opto-electronic de- vices such as UV laser diodes and UV-blue light-emitting diodes [2,3]. The study of photoluminescence (PL) properties of SnO 2 ﬁlms is of signiﬁcance for large-scale optical-electronic integration of these devices. The PL characteristics in wide band gap semiconduc- tors are controlled by transitions from/to certain allowed energy states in the forbidden energy gap. PL peaks are typically attributed to radiative recombination involving some defect states such as tin interstitials, dangling bonds, or oxygen vacancies [4–8]. Ma et al. [9] attributed the room temperature UV emission to the donor acceptor band transition resulting from Sb doping in Sb:SnO 2 thin ﬁlms. Ni et al. [10] have studied the photoluminescence properties of Sb:SnO 2 thin ﬁlms annealed at different temperatures and duration and attributed the ‘‘red-shift’’ in PL peaks to the larger crystallite size and compressive stress. Kim et al. [11] ascribed the origin of UV emission in pristine SnO 2 thin ﬁlms to the electronic transitions from the donor levels formed by oxygen vacancies to the acceptor levels formed by other defects and impu- rities. Jeong et al. [12] have reported a decrease in UV emission due to improvement in the crystallinity of SnO 2 ﬁlms. It is thus clearly seen that many researchers have reported the PL properties of the undoped and doped SnO 2 thin ﬁlms processed under different environments and have explained the origin of the luminescence in SnO 2 thin ﬁlms on the basis of defect structure. Theoretical der- ivations have predicted the presence of many new energy states in the band gap related to oxygen vacancies at surface and in bulk [13]. The oxygen vacancies exist at different depths in metal oxides with different formation energies [14], and are related to the com- plex optical transition mechanism involving states in the band gap. An understanding of their role in inducing PL and associated changes in physical properties is, therefore, of scientiﬁc and prac- tical importance. For such a study it is desirable to have samples with controlled defect states. In this paper, we have attempted to understand the effect of the change in oxygen content during growth on the defects (especially oxygen vacancies) and associated control of photoluminescence, electrical and optical properties of otherwise undoped SnO 2 ﬁlms. The observed photoluminescence and the estimated electrical transport properties of SnO 2 thin ﬁlms, deposited by varying oxygen concentration during pulsed dc mag- netron reactive sputtering, have successfully been correlated and explained in terms of defects and structural disorder. 0925-8388/$ - see front matter Ó 2013 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.jallcom.2013.08.135 ⇑ Corresponding author. Tel.: +91 11 26591346; fax: +91 11 26581114. E-mail address: skashyap@physics.iitd.ac.in (S.C. Kashyap). Journal of Alloys and Compounds 583 (2014) 186–190 Contents lists available at ScienceDirect Journal of Alloys and Compounds journal homepage: www.elsevier.com/locate/jalcom