Charge transfer processes in a-WO3Si heterostructure during electro- and photochromism

Heterostructure a-WO3Si was obtained by vacuum condensation of thermally evaporated tungsten trioxide powder on n-Si substrate under conditions leading to formation of a transparent WO3 film (stoichiometric) and with color centers (partially reduced). For both types of structures, high frequency C-V characteristics have been investigated as well as an influence of color center formation in a-WO3 on charge parameters of heterojunction at the double injection of protons and electrons into the film and with UV irradiation for different exposure times. A single energy level of fast surface states was found in the structure with WO3−x film arranged by 0.06 eV below the Fermi level in Si. Density of states at this level increases in electrochromic process and decreases in photochromic one. A structural-energy model of coloring process is proposed.