Deposition of thin films for sensors by pulsed laser ablation of iron and chromium silicide targets

Thin films were deposited by KrF laser ablation of CrSi2 and β-FeSi2 targets with the aim to obtain silicide thin films and layers with narrow band gap for sensor applications. The CrSi2-based films exhibit both semiconductor and metal properties, depending on the deposition conditions. Thus, the film of d ≅ 40 nm thick, deposited on Si at 740 K, presents a band gap Eg ≅ 0.18 eV, and large thermo electromotive force (e.m.f.) coefficient α ≅ 1.0–1.4 mV/K at 300 ≤ T ≤ 340 K and a coefficient of tensosensitivity (R–R0)/R0ɛ ≅ 5. The film with the same thickness, but deposited on SiO2 at 740 K, presents a metal behavior at 125 ≤ T ≤ 296 K and a semiconductor one at 77 ≤ T ≤ 125 K. Its coefficient α varies in the range 5.0–7.5 μV/K at 300 ≤ T ≤ 340 K. The 750 nm thick film deposited on SiO2 at 740 K exhibits only semiconductor behavior in the range 296–77 K with Eg ≅ 0.013 eV and α ≅ 10–15 μV/K at 293 ≤ T ≤ 340 K. The coefficient of tensosensitivity for these films is changing in the range 2–5. The β-FeSi2-based films deposited on SiO2 at 295 ≤ T ≤ 740 K show only semiconductor behavior. The thicker the film, the higher Eg: d ≅ 150 nm, Eg ≅ 0.032 eV; d ≅ 70 nm, Eg ≅ 0.027 eV; d ≅ 60 nm, Eg ≅ 0.023 eV. The higher Eg, the higher coefficient α. The coefficient of tensosensitivity for these films varies in the range 2.3–4.7. The more the semiconductor phase content in the deposited film, the higher are the values of α and (R–R0)/R0ɛ.