Development of Cosputtered Amorphous Ge–Bi–Se Films for Nonlinear Infrared Photonic Applications

Accepted manuscript of a journal paper published in ACS Applied Optical Materials. Abstract: RF magnetron cosputtered amorphous Ge–Bi–Se films were fabricated using polycrystalline GeSe₂ and Bi₂Se₃ targets. Their structural, linear, and nonlinear optical properties were studied to understand compositional influence for future photonic applications. A broader Ge–Bi–Se amorphous region with a noticeably high bismuth atomic percentage (up to at % Bi = 36%) is observed using this deposition method compared to ≤16 at % in the conventional Ge₂₀Se_80–xBi_x bulk glass synthesis [Ikari, T. Phys. Rev. B 1993, 47(9), 4984]. The structural characteristics of the cosputtered films were analyzed using Raman spectroscopy, where increasing bismuth concentration shifted all vibrational bands to the lower energy side with reduced intensity. A decrease in optical band gap energy values from 2.04 (±0.02) eV (Bi atom % = 0) to 0.73 (±0.02) eV (Bi atom % = 36) and the corresponding increase in refractive index value n from 2.41 (±0.01) to 4.09 (±0.01) at telecommunication wavelength indicate the strong influence of bismuth on the optical properties of the films. Third-order nonlinear optical parameters were calculated from linear parameters using semiempirical equations and Sheik-Bahae formalism in order to allow their prediction according to the film composition and taking into account the wavelength of use. Following these simulations, which enabled the selection of promising compositions in terms of optical nonlinearity applications, this work also focused on demonstrating the feasibility of manufacturing ridge waveguides from these cosputtered films by RF magnetron using dry etching with the aim of offering Ge–Bi–Se-based integrated optical circuits.