On the Conduction Mechanism of Silicate Glass Doped by Oxide Compounds of Ruthenium (Thick Film Resistors). 2. Nanocrystals in the Glass and Charge Carrier's Localization

摘要

Conduction mechanism of doped silicate glasses based on existence of nanocrystals is proposed. These nanocrystals are effective centers of localization of free charge carriers, and variable range hopping of last ones takes place. It is shown that dopant atoms generate narrow impurity subband of about 0,03 eV in width, which is slightly (less than 0.01 eV) separated from the top of the valence band of the glass or abutted on them, so thermal activation coexists with hopping conduction. Because of it the resistivity of the doped silicate glass is proportional to exp(-aT-ζ) at low temperatures (T < 50 K), 0.4 < ζ < 0.8. Structural transitions of nanocrystals take place at high temperatures (T > 800 K) and the conductivity of the doped silicate glass decreases sharply. Beyond the conductivity minimum (above 1000 K) the impurity subband and the top of the valence band of glass are separated by energy gap of 0.05 – 1.5 eV in width, so doped silicate glass behaves like a typical semiconductor.