Formation and characterization of Ag2La thin films designed for high k -dielectric and terahertz applications

Abstract

Herein two stacked nanosheets of lanthanum and silver coated by the thermal evaporation technique under a vacuum pressure of 10– 5 mbar are used to form Ag2La compound. Ag2La thin films exhibited crystalline orthorhombic structure with lattice parameters, crystallite sizes and defect densities of a = 6.670 Å, b = 10.386 Å, c = 7.485 Å, 29 nm and 3.99 × 1011 lines/cm2, respectively. The films showed an indirect band gap of 3.25 eV. The band gap contained energy band tails of widths of 0.75 eV. In addition, the dielectric dispersion analyses on the Ag2La film have shown their excellent performance as high k dielectric materials displaying high dielectric constant value of 9.5 at incident light energy of 2.12 eV. On the other hand the optical conductivity and terahertz cutoff frequency spectral analyses have shown that Ag2La films have potentials applications in terahertz technology. The terahertz cutoff frequency varied in the range of 2–9 THz based on the driving light signal energy. As optical resonators they showed high sensitivity to visible and ultraviolet light signals. A respective high drift mobility of ~ 1.5 cm2/ Vs and 44 cm2/ Vs are estimated for the semitransparent Ag2La terahertz optical filters. The simplicity of producing Ag2La compound, the high dielectric constant values and the semiconducting characteristics of this compound make it attractive for high k-dielectric devices and for terahertz technology applications.