Photoelectronic Analysis of Imperfections in Grown Stannic Oxide Single Crystals

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Abstract
A study of the imperfection properties of grown stannic oxide single crystals was made using photoelectronic techniques. The primary objective has been to propose an energy level scheme for defects in these samples based on the results of measurements of spectral response, thermally stimulated currents, thermal quenching, and dark conductivity as a function of temperature. Measurements of thermally stimulated current indicated the existence of three trapping levels with average activation energies of 0.21, 0.52, and 0.60 eV. Comparison with dark conductivity data implied the 0.60‐eV trap to be associated with the compensated portion of those donor states responsible for the normal n‐type conductivity. Extrinsic thermal quenching results established that these levels were all trapping states for electrons, with the two shallow ones completely compensated and the deeper one only partially compensated. The results of intrinsic thermal quenching measurements indicated the existence of a compensated acceptor level lying 0.33 eV above the valence band and acting under certain conditions as a sensitizing center. The ratio of hole to electron capture cross sections for this level was found to be 7×102. Also found were more‐or‐less discrete levels having optical activation energies of approximately 1.0, 1.3, and 1.8 eV. These levels were determined from spectral response measurements which, in addition, show the existence of other unresolved levels lying further from the conduction band than 2.0 eV and a fundamental absorption edge at 4.0 eV.

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