Growth of Al2O3 thin film by oxidation of resistively evaporated Al on top of SnO2, and electrical properties of the heterojunction SnO2/Al2O3

Aiming for the investigation of insulating properties of aluminum oxide (Al 2 O 3 ) layers, as well as the combination of this oxide with tin dioxide (SnO 2 ) for application in transparent field effect transistors, Al thin films are deposited by resistive evaporation on top of SnO 2 thin films deposited by sol–gel dip-coating process. The oxidation of Al films to Al 2 O 3 are carried out by thermal annealing at 500 °C in room conditions or oxygen atmosphere. X-ray diffraction data indicate that tetragonal Al 2 O 3 is indeed obtained. A simple device and electric circuit is proposed to measure the insulating properties of aluminum oxide and the transport properties of SnO 2 as well. Results indicate a fair insulation when four layers or Al 2 O 3 are grown on the tin dioxide film, concomitant with thermal annealing between each layer. The current magnitude through the insulating layer is only 0.2% of the current through the semiconductor film, even though the conductivity of the SnO 2 alone is not very high (the average resistivity is 2 Ω cm), because no doping is used. The presented results are a good indication that this combination may be useful for transparent devices.