Reflectance and electroreflectance of TiO2single crystals. I. Optical spectra

Abstract

Normal-incidence reflectance and electroreflectance (ER) spectra of single crystalline TiO₂ (rutile) have been measured as a function of temperature, field orientation and light polarisation. Spectra of the dielectric constant and their field dependence are obtained by Kramers-Kronig transformation. The low-temperature ER spectra are a superposition of large and broad structures with field-independent halfwidths of 100 to 300 meV and a fine structure of which the individual, field-dependent, features may be as narrow as 10 meV. Some experimental procedures are given which were found to be essential for obtaining controlled conditions in the surface region. Optimum results are obtained by using NaOH-etched samples. Some additionally observed phenomena, such as chemisorption induced reflectance changes, low-temperature electroluminescence and band population effects in electroreflectance are briefly discussed.