ORIGIN OF THE CHANGES IN PHYSICAL-PROPERTIES OF SNO2 THIN POLYCRYSTALLINE FILMS SUBJECTED TO THERMAL-TREATMENT

Thin polycrystalline films of undoped SnO2 were deposited on substrate s of industrial devitrified glass by metalloorganic chemical vapor dep osition at 390 degrees C with a subsequent annealing in air or vacuum in the temperature range from 380 to 750 degrees C, The structure and electrical characteristics of the films before and after annealing wer e studied. Annealing above 500 degrees C in air results in a weak (1.5 - to 2-fold) rise in the conductivity that is related to an increase o f the mean crystallite size. Vacuum annealing at temperatures higher t han 500 degrees C causes a significant fall in the conductivity (by 3- 4 orders of magnitude), which can be accounted for by a decrease in th e bulk conductivity of crystallites due to the generation of defects i n the anion sublattice of the semiconductor and, probably, to the form ation of an impurity phase. The above changes in the film properties a re assumed to be associated with the well-known phase transition obser ved in SnO2 near 450 degrees C.