AC CONDUCTION IN MIXED OXIDESAl–In2O3–SnO2–AlSTRUCTURE DEPOSITED BY CO-EVAPORATION

Conductivity-frequency and capacitance-frequency characteristics of mixed oxidesAl–In2O3–SnO2–Alstructure are examined to elicit any correlation with the conduction mechanisms most often observed in thin film work. The existence of Schottky barriers is believed to be due to a strong donor band in the insulator established during the vacuum evaporation when a layer of mixed oxidesIn2O3–SnO2system is sandwiched between two metal electrodes. Low values of activation energy at low temperatures indicate that the transport of the carriers between localized states is mainly due to electronic hopping over the barrier separating the two nearest neighbor sites. The increase in the formation of ionized donors with increase in temperature during electrical measurements indicates that electronic part of the conductivity is higher than the ionic part. The initial increase in conductivity with increase inSncontent inIn2O3lattice is caused by theSnatom substitution ofInatom, giving out one extra electron. The decrease in electrical conductivity above the criticalSncontent (10 mol%SnO2) is caused by the defects formed bySnatoms, which act as carrier traps rather than electron donors. The increase in electrical conductivity with film thickness is caused by the increase in free carriers density, which is generated by oxygen vacancy acting as two electron donor. The increase in conductivity with substrate and annealing temperatures is due to either the severe deficiency of oxygen, which deteriorates the film properties and reduces the mobility of the carriers or to the diffusion ofSnatoms from interstitial locations into theIncation sites and formation of indium species of lower oxidation state(In2+). Calculations ofCand σacfrom tan δ measurements suggest that there is some kind of space-charge polarization in the material, caused by the storage of carriers at the electrodes. Capacitance decreases not only with the rise of frequency but also with the lowering of temperature. At low temperatures the major contribution to capacitance arises from the ionic polarization, however, with the increase of temperature the contribution from orientation polarization would considerably increase. The decrease in capacitance with the increase in frequency may be attributed to interfacial polarization.