Photoconductivity study of Ca2Si epitaxial film on Si(111) substrate

Semiconductor calcium semi-silicide (Ca2Si) with a complex crystal and energy band structure is theoretically characterized by a direct fundamental transition, which is difficult to identify experimentally in Ca2Si films due to high absorption at defect levels. The study of the temperature dependences of photoconductivity in Ca2Si epitaxial films is one of the methods for assessing both the nature of the fundamental transition and a number of thermodynamic parameters. In this work, photoconductivity was firstly observed in an epitaxial Ca2Si film grown on a Si(111) substrate in the temperature range from 10 K to 300 K. Based on an analysis of the parameters of three thermodynamic models, the existence of a direct fundamental transition E-g = 1.195 eV at 0 K was proved, and the effective phonon energy (< E-ph >), the Einstein (Xi) and Debye (theta(D)) temperatures, as well as the electron-phonon coupling constant, and the hole mobility were determined.