Infrared Photo-Response of Fe-Shunted Ba-122 Thin Film Microstructures

We present a study of the response to pulsed infrared radiation of Fe layer shunted pnictide thin film microstructures. The thin film multilayer consisting of 20-nm-thick Fe buffer, 50-nm-thick Ba(Fe, Co)₂As₂ film, and gold protection layer were deposited on heated MgO and MgAl₂O₄ substrates by pulsed-laser deposition. The multilayers were patterned into 5- to 8-μm-wide and 5-μm-long microbridges by electron-beam lithography and ion-milling technique. The microbridges show T_c ≈ 20 K and a critical current density up to 2.56 MA/cm² at T = 10 K. The photo-response of Fe-shunted Ba(Fe, Co)₂As₂ thin film microbridges to infrared radiation was studied in a wide range of incident optical power, operation temperature, and bias current. We have found that the electron energy relaxation in studied multilayers is dependent on substrate material and is 1.75 times faster in the case of MgAl₂O₄ characterized by lattice matching to the pnictide film in comparison to the MgO substrate.