PHOTOELECTRONIC PROCESSES IN RUTILE

From a wide variety of experiments which include photoconductivity and photoluminescence excitation spectra, thermoluminescence, thermally stimulated current, electroreflectance spectra, kinetic response of photoconductivity, and optical and thermal bleaching of traps, a large number of defect energy levels were detected. A consistent interpretation of all of the data, combined with a knowledge of expected crystal field splittings, leads to the assignment of specific levels and observed transitions to Ti3+ interstitial ions. This center is also responsible for the luminescence emission at 0.85 μ. At least eight shallow-trap levels (<1 eV) were detected, and the possible assignment of one of these levels to oxygen vacancies is discussed. The thermal ionization energies of these traps, determined from the initial rise of the thermoluminescence glow, are in good agreement with those determined from Fermi-level analysis of the thermally stimulated current curves. The optical ionization energies of some of these levels were found to be 2.5 times their thermal ionization energies from the results of experiments utilizing modified optical bleaching techniques. The intensity of structures in photoconductivity excitation spectra depends on the electron population of the traps. A structure at 3.2 eV (0.39 μ) in photoluminescence excitation spectra (seen also in photocurrent excitation spectra when the traps are populated) is believed to be related to the onset of direct optical transitions. © 1969 The American Physical Society.