THE ESR STUDY OF AMORPHOUS THIN FILMS OF MIXED OXIDES In2O3–SnO2 SYSTEM DEPOSITED BY CO-EVAPORATION
Abstract
The ESR spectra of amorphous thin films of mixed oxides In2O3–SnO2 system is presented. An initial increase in the intensity of ESR signal at g=1.994, and decrease in the intensity of the signal at g=1.98 with an increase in Sn content in In2O3 lattice is caused by the Sn atom substitution of In atom, giving out one extra electron. The decrease in the intensity of ESR signal at g=1.994 and an increase in the intensity of the signals at g=1.98 above the critical Sn content (10 mol% SnO2) is caused by the defects formed by Sn atoms, which act as carrier traps rather than as electron donors. The increase in the intensity of ESR signal at g=1.89 with the increase in Sn content in mixed oxides In2O3–SnO2 system is caused by the increase in the concentration of oxygen vacancies, which are generated in the In2O3 and SnO2 lattices by thermal evaporation. The increase in the intensity of ESR signals at g=1.994, g=1.98 and g=1.89 with the increase in thickness is caused by the bulk properties of the films. The increase in the intensity of ESR signals at g=1.994, g=1.98 and g=1.89 with the increase in substrate temperatures is due to the increase in the concentration of oxygen vacancies, which are generated at higher substrate temperatures and to the diffusion of Sn atoms from interstitial locations into the In cation sites, which result in higher electron concentration. The decrease in the intensity of ESR signals at g=1.994, g=1.98 and g=1.89 with an increase in annealing temperature is attributed to the rearrangement of the atoms and to the removal of voids, which causes a decrease in the number of unsatisfied bonds and formation of indium and tin species of lower valence states. The new oxidation states, the In2+ and the Sn2+, formed due to the annealing of the samples can be attributed to the internal electron transfer from oxygen 2p to the In5s and Sn5s levels, both in In2O3 and SnO2.
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