Supporting Information
Visible Photocurrent in Chemically Doped TiO2-Based Schottky
Diodes
Hyungtak Seo
Department of Energy Systems Research and Department of Materials Science and
Engineering, Ajou University, Suwon 443-739, Republic of Korea
1. Spectroscopic ellipsometry analysis of TiO2/SiO2/Si stack
The conduction band edge states of the TiO2 layers were analyzed from the absorption
spectra obtained by a rotating compensator-enhanced spectroscopic ellipsometry (SE)
measurement with a spectrum resolution of 15 meV. SE determines the complex reflectance
ratio, ρ=rp/rs where rp and rs are the complex reflectance values of waves in polarized optical
light that are parallel (p) and perpendicular (s) to the plane of incidence, respectively. Visible
and UV light was used with an energy range 1.5 eV: 8267 Å–6 eV: 2066 Å from an optical light
source (a monochromatic light from Xenon lamp) to excite the electrons from the top of the
valence band to the conduction band in the overlayer (i.e., TiO2). From  , optical properties
such as the index of reflection (n), extinction coefficient (k), and dielectric function (  ) were
determined. In order to extract the dielectric function of the TiO2 overlayer from the pseudodielectric function of the entire stack of TiO2/SiO2/Si, a three-phase model (i.e., air, TiO2, and
SiO2/Si substrate) was applied to first analyze the dielectric function of bare glass and then
differentiate the dielectric functions of the a-IGZO overlayers. The generalized equation for
the optical three-phase model is expressed as follows:

4dna  s ( s   o )( o   a )   s
  sin 2  
    s 

 o ( s   a )
a

1/ 2
(S1)
where <ε> is the measured pseudo-dielectric function, εs is the substrate (SiO2/Si) dielectric
function, εa is the air dielectric function, εo is the overlayer (TiO2) dielectric function, d is the
overlayer thickness, na is the index of reflectance for air, λ is the wavelength of incident
polarized light, and φ is the angle of incidence (fixed at 67.08°). Because all parameters except
εo are already known, εo can be obtained by iterative calculations using Equation (S1).
The absorption coefficient, α, is obtained from the λ and k values by the following
conversion equation:
α=4πk/λ
where k is the extinction coefficient and λ is the wavelength of incident light.
(S2)