Applied Surface Science 315 (2014) 116–123 Contents lists available at ScienceDirect Applied Surface Science journal h om epa ge: www.elsevier.com/locate/apsusc Spectroscopic ellipsometry characterization of amorphous and crystalline TiO 2 thin films grown by atomic layer deposition at different temperatures D. Saha a,∗ , R.S. Ajimsha a , K. Rajiv b , C. Mukherjee b , M. Gupta c , P. Misra a , L.M. Kukreja a a Laser Materials Processing Division, Raja Ramanna Centre for Advanced Technology, Indore 452013, India b Mechanical and Optical Support Section, Raja Ramanna Centre for Advanced Technology, Indore 452013, India c UGC-DAE Consortium, Indore Centre, Khandwa Road, Indore 452017, India a r t i c l e i n f o Article history: Received 9 April 2014 Received in revised form 13 June 2014 Accepted 17 July 2014 Available online 25 July 2014 Keywords: Atomic layer deposition Spectroscopic ellipsometry Large-grained anatase Columnar growth a b s t r a c t TiO 2 thin films of widely different structural and morphological characteristics were grown on Si (1 0 0) substrates using Atomic Layer Deposition (ALD) by varying the substrate temperature (T s ) in a wide range (50 ◦ C ≤ T s ≤ 400 ◦ C). Spectroscopic ellipsometry (SE) measurements were carried out to investigate the effect of growth temperature on the optical properties of the films. Measured SE data were analyzed by considering double layer optical model for the sample together with the single oscillator Tauc-Lorentz dispersion relation. Surface roughness was taken into consideration due to the columnar growths of grains in crystalline films. The refractive index was found to be increased from amorphous (T s ≤ 150 ◦ C) to the nanocrystalline films (250 0 < T s ≤ 400 ◦ C). The pronounced surface roughening for the large-grained anatase film obtained at the amorphous to crystalline phase transformation temperature of 200 ◦ C, impeded SE measurement. The dispersions of refractive indices below the interband absorption edge were found to be strongly correlated with the single oscillator Wemple–DiDomenico (WD) model. The increase in dispersion energy parameter in WD model from disordered amorphous to the more ordered nanocrys- talline films was found to be associated with the increase in the film density and coordination number. © 2014 Elsevier B.V. All rights reserved. 1. Introduction Titanium dioxide (TiO 2 ) is a versatile wide band-gap semicon- ductor with a combination of unique properties which include its high refractive index, high dielectric constant, high photocat- alytic activity, good chemical stability and biocompatibility [1–8]. However, the optical, electronic and catalytic properties of TiO 2 are strongly dependent on its crystalline phase, crystalline qual- ity and surface morphology. The high dielectric constant of TiO 2 allows it to replace conventional silicon dioxide (SiO 2 ) for fabricat- ing capacitors in dynamic random access memory (DRAM) devices and ultrathin gate dielectric layers in field effect transistors [2,3]. For efficient dielectric performance i.e., to eliminate leakage cur- rent, amorphous TiO 2 is more suitable than its polycrystalline form. Moreover, amorphous TiO 2 due to its smooth surface morphology has been successfully used for fabricating thin film and multilayer antireflective coatings, transparent conducting oxides when doped ∗ Corresponding author. Tel.: +91 731 2488374; fax: +91 731 2488330. E-mail addresses: babaisps@rrcat.gov.in, sahaphys@gmail.com (D. Saha). with Nb, F, W etc. [4–7]. On the contrary, mesoporous anatase TiO 2 (E g = 3.2 eV) due to its increased surface area and higher Fermi level compared to the rutile phase (E g = 3.0 eV) has been reported as an ideal candidate for fabricating photo anode in dye-sensitized solar cells (DSSCs) and photocatalytic cells [8,9]. So far a variety of deposition techniques including hydrothermal method, pulsed laser deposition (PLD), sol–gel method, sputtering etc. have been explored to grow TiO 2 thin films and nanostruc- tures [1,9–11]. In recent years, atomic layer deposition (ALD) which is a particularly attractive technique in microelectronics manu- facturing has received considerable interest within the scientific community to grow TiO 2 on planar and high aspect ratio substrates like aerogel template, anodic aluminium oxide (AAO), inverse opal etc. for the aforesaid applications [3,12–16]. ALD relies on two complementary and self-limiting gas-solid reactions in which two different precursors are chemisorbed on the growing film surface during their alternate pulses [17]. The idealized growth of TiO 2 in ALD using TiCl 4 and deionized H 2 O proceeds according to the following irreversible exchange reactions, n(–OH)(s) + TiCl 4 (g) → (–O–) n TiCl 4-n (s) + nHCl(g) (1) http://dx.doi.org/10.1016/j.apsusc.2014.07.098 0169-4332/© 2014 Elsevier B.V. All rights reserved.