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

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 A, b = 8.063 A, and c = 5.569 A. Optical analysis of the La6Ge thin films reveal their high transparency, with an energy bandgap of 3.75 & PLUSMN;0.04 eV. The bandgap exhibits indirect allowed transitions and featured energy band tails with widths measuring (1.64 & PLUSMN;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 cm(2) V-1 s(-1) and 2.8x10(18) 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.