Study of self-sensitization of wide-gap oxides to visible light by intrinsic defects: From Terenin to the present days

Abstract

We present the results of the investigation of the role of intrinsic point defects in wide-bandgap oxides photo-sensitization. This is one of numerous directions of researches pioneered by academician A.N. Terenin in the Leningrad (St. Petersburg) State University and continued by his disciples. The step-by-step experimental investigations of photo-excitation of the electronic sub-system of wide-bandgap oxides and further relaxation channels are analyzed in situ in three phases: solid – adsorbate – gas. The spectroscopy of optical activation and the spectroscopy of diffuse reflection are used for identification of initial and final excited states of the system. Photoluminescence (PL) and thermo-stimulated luminescence (TSL) are used to study radiative channels. Thermo-programmed desorption (TPD), FTIR and ESR spectroscopies are used to study the precursors and adsorbed species in the excited system. The final steps – photo-adsorption/desorption and chemical reactions in gaseous phase are analyzed using the mass-spectrometry (MS). In situ UV (8.43eV) Photoelectron spectroscopy (UPS) is used to monitor the electro-physical parameters of the sample: Fermi level EF, band bending VS, density of occupied states (DOS) and dipole potential δ. Common and specific features of wide-bandgap oxides – insulators and semiconductors – are analyzed.