Growth and Characterization of Lanthanum Germanide Thin Films by the Thermal Evaporation Technique

Abstract Lanthanum germanide (La6Ge) thin films are successfully fabricated using the thermal evaporation technique under a vacuum pressure of 10−5 mbar. The resulting films display an orthorhombic structure, characterized by lattice parameters of a = 8.725 Å, b = 8.063 Å, and c = 5.569 Å. Optical analysis of the La6Ge thin films reveal their high transparency, with an energy bandgap of 3.75±0.04 eV. The bandgap exhibits indirect allowed transitions and featured energy band tails with widths measuring (1.64±0.14) eV. In addition, dielectric dispersion analyses indicate the presence of two dominant dielectric resonance peaks centered at 3.15 and 2.08 eV. Moreover, the La6Ge films demonstrate a terahertz (THz) cutoff frequency of 1.0 THz when illuminated with infrared and visible light. This cutoff frequency increases to 45.6 THz in the ultraviolet range. Furthermore, by utilizing the Drude–Lorentz method, the investigation of optical conductivity parameters reveals that the lanthanum germanide optical filters can achieve free hole density and drift mobility values of 14.44 cm2 V−1 s−1 and 2.8×1018 cm−3, respectively, under infrared light irradiation. The outstanding optical and dielectric properties exhibited by the La6Ge thin films make them excellent candidates for highly transparent optical filters suitable for terahertz technology.