ENHANCED IONIC-CONDUCTION MECHANISMS AT LIL AL2O3 INTERFACES/

Electrical conduction in LiI thin films has been measured in situ duri ng growth as a function of film thickness and temperature. Films grown at 27 degrees C exhibited an enhancement of the ionic conduction of s imilar to 40X the bulk value in a region extending similar to 100 nm a bove the interface. The enhanced conduction was not stable and decreas ed with a log(time) dependence during annealing at the growth temperat ure. The activation energy for conduction was 0.47+/-0.03 eV, approxim ately equal to the value for extrinsic conduction in bulk LiI. Films g rown at 100 degrees C, on the other hand, showed no enhancement near t he interface, and a nearly linear increase in conductance with thickne ss after an initial nucleation stage. The conductivity of these films was stable at and above the growth temperature and exhibited an activa tion energy of 0.75+/-0.03 eV, which is comparable to the value for in trinsic LiI. X-ray diffraction measurements on the samples showed that all films were cubic LiI. Films grown near room temperature had a str ong (002) orientation while those grown at elevated temperatures were (111) with a mosaic spread of <0.4 degrees. The data show conclusively that there is no enhancement due to space-charge layer formation at t he film/substrate interface. On the other hand, the data are all consi stent with a model that assumes the conduction enhancement is caused b y the overlapping strain fields of dislocations formed during growth.