Figure of Merit for Detectors Based on Laser-Induced hermoelectric Voltages in La_1-xCa_xMnO₃ and Ba₂Cu₃O_7-σ Thin Films

A figure of merit (FOM) Z = U_p/τ_r, where U_p is the peak voltage, and τ_r is the rise time of the laser-induced thermoelectric voltage (LITV) signal, is defined for photodetector based on the LITV and the influence of the parameters on FOM is analysed based on the time dependence of LITVs in La_1-xCa_xMnO₃ (LCMO) and YBa₂Cu₃O_7-σ (YBCO) thin films grown on vicinal-cut substrates. We find that the FOM increases as the photon penetration depth decreases, and linearly increases with the thermal diffusion constant D. To achieve the highest FOM, the film thickness d has to be controlled to an optimum value. We also find that the FOM is directly proportional to the laser absorption coefficient α₀, the laser energy density per pulse E, the illuminated length of film l, sin(2α) αis the vicinal-cut angle, the Seebeck coefficient anisotropy (S_ab - S_c ), and is inversely proportional to the mass density ρ and the specific heat c₀.