Phase change-regulated nonlinear optical properties of GeSb 4 Te 7 films prepared by RF magnetron sputtering

Novel passive devices such as all-optical diodes and all-optical logic gates require materials with appropriate both saturable and reverse saturable absorption properties. In this work, a series of GeSb 4 Te 7 films were prepared by radio frequency magnetron sputtering and annealed at different temperatures to induce phase changes. Open-aperture Z-Scan experiments revealed that GeSb 4 Te 7 films featured a large nonlinear absorption coefficient that varied with the extent of phase change induced by the annealing temperature. To understand the underlying reason, a three-level model was developed to explain the competition between ground-state absorption and excited-state absorption during the process. The large nonlinear absorption coefficient of GeSb 4 Te 7 films ( β_eff = - 20368.90 cm/GW) shows that ternary material demonstrates outstanding nonlinear optical absorption capability. Impressively, the annealing treatment induced microstructural changes in the GeSb 4 Te 7 films that caused a transition from reverse saturable absorption to saturable absorption, offering great potential for innovative passive nonlinear optical devices.