<title>Deposition of films and layers for sensors with PLD and LIFT method</title>

Abstract

Two methods were used for the deposition of thin films and layers: pulsed laser deposition (PLD) and laser-induced film transfer (LIFT). The first one was based on using KrF laser radiation. Thin films and layers were deposited by KrF laser ablation of CrSi₂ and β-FeSi₂ targets with the aim to obtain silicide layers with narrow band gap for sensor applications. The CrSi₂-based films display both semiconductor and metal properties, depending on the deposition parameters. Thus, the film d ≅ 40 nm thick, deposited on Si at 740 K, presents a band gap E_g ≅ 0.18 eV, a thermo e.m.f. coefficient α ≅ 1.0-1.4 mV/K for 300≤T≤340 K and a coefficient of tensosensitivity (R-R₀)/R_0ε) ≅ 5. The film with the same thickness, but deposited on SiO₂ at 740 K, presents a metal behavior in the range 125≤T≤296 K and a semiconductor one for 77≤T≤125 K. Its α coefficient changes in the range 5.0 - 7.5 μV/K for 300≤T≤340 K. The 750 nm thick film deposited on SiO₂ at 740 K displays only semiconductor behavior in the range 296-77 K with E_g ≅ 0.013 eV and α ≅ 10-15 μV/K for 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 E_g: d ≅ 150 nm, E_g ≅ 0.032 eV; d ≅ 70 nm, E_g ≅ 0.027 eV; d ≅ 60 nm, E_g ≅ 0.023 eV. The thermo e.m.f coefficient α ≅ 10 μV/K for the 150 nm thick film and α 8 μV/K for the 60 nm thick film at 293≤T≤340 K. The coefficient of tensosensitivity for these films varies in the range 2.3-4.7. The second one was based on LIFT of CrSi₂ and β-FeSi₂ targets, using a Q-switched Nd: YAG laser. The α coefficient for the deposited layer from β-FeSi₂ is about 2.2 μV/K with E_g ≅ 0.05 eV. While decreasing the average power density of the Q-switched Nd: YAG laser, the band gap decreases down to 0.005 eV. For this film we found α ≅ 2.0 μV/K. The α coefficient for the deposited layer from CrSi₂ is about 36 μV/K with E_g ≅ 0.09 eV. Coefficient of thermo e.m.f. for layers obtained by LIFT method was measured at 300≤T≤350 K. The coefficient of tensosensitivity for layers obtained by LIFT varied in the range 1.5-4.2. The higher the semiconductor phase content in the deposited films and layers obtained by PLD and LIFT methods, the higher are the values of α and (R-R₀)/R_0ε.