Photon synthesis of iron oxide thin films for thermo-photo-chemical sensors

Abstract

Ultraviolet photons of KrF-laser (248nm) and of photodiode (360nm) were used for the synthesis of iron oxide thin films with variable thickness, stoichiometry and electrical properties. The reactive pulsed laser deposition (RPLD) method was based on KrF-laser and photon-induced chemical vapor deposition (PCVD) was based on a photodiode. Deposited films demonstrated semiconductor properties with variable band gap (Eg). The film thickness (50–140nm) and Eg depended on the laser pulse number, oxygen and iron carbonyl vapor pressure in the deposition chamber, and exposure time to the substrate surface with ultraviolet (UV) radiation. Sensing characteristics strongly depended on electrical and structural properties of such thin films. Iron oxide films were deposited on 〈100〉 Si substrate and had large thermo electromotive force (e.m.f.) coefficient (S) and high photosensitivity (F). The largest value of the S coefficient obtained by RPLD was about 1.65mV/K in the range 270–290K and by PCVD was about 1.5mV/K in the range 280–322K. The largest value F obtained by RPLD and PCVD was about 44Vc/W and 40Vc/W, accordingly, for white light at power density (I≅0.006W/cm2). It was shown that the S coefficient and F strongly depended on Eg. Moreover, these films were tested as chemical sensors: the largest sensitivity of NO molecules was at the level of 3×1012cm−3. Our results showed that RPLD and PCVD were used to synthesize semiconductor iron oxide thin films with different sensing properties. So iron oxide thin films synthesized by UV photons are up-to-date materials for multi-parameter sensors: thermo-photo-chemical sensors operating at moderate temperature.