SYNTHESIS OF NANOMETRIC IRON AND CHROMIUM OXIDE FILMS BY REACTIVE PULSED LASER DEPOSITION FOR PHOTO-THERMO SENSORS

摘要

Films based on oxides of transitional metals have semiconducting properties that make them up-to-date materials for functional electronics. The reactive pulsed laser deposition (RPLD) allows the control of thickness and stoichiometry of deposits in order to obtain semiconductor structures with accurately tailored thickness and band gap. It is very important to study electrical, structural and optical properties of these semiconducting nanometric films, as sensing characteristics strongly depend on these properties.We deposited iron oxide (Fe_2O_3_x; 0≤x≤ 1) and chromium oxide (Cr_3.xO_3-y; 0≤x≤2; 0≤y≤2) films on <100> Si substrate by RPLD using a KrF laser. The deposited nanometric films (thickness 50-200 nm) of iron and chromium oxides have large thermo electromotive force (e.m.f.) coefficient (S). The S coefficient of iron oxide films varied in the range 0.8-1.65 mV/K in the temperature range 210-322 K. The maximum value of the S coefficient (1.65mV/K) was measured in the temperature range 270-290 K. The largest photosensitivity (F) of iron oxides films was about 44 V/W for white light at power density (I) of about 6x10~(-3) W/cm~2.As regards chromium oxide films, the S coefficient varied in the range 0.30-4.5 mV/K in the temperature range 210-333 K, with the maximum of 3.5-4.5 mV/K in the temperature range 270-290 K. The largest photosensitivity of chromium oxide films was about 2.5 V_c/W at 1= 6x10~(-3) W/cm2. Our results show that RPLD is a very simple procedure to synthesize of iron and chromium oxide nanometric films with variable stoichiometry and, consequently, with different values of their band gap result in variable the S coefficient and the photosensitivity (F). The deposited films present large thermo e.m.f. coefficient and high photosensitivity that make them up-to-date materials for photo-thermo sensors.