REDUCTION OF THE BULK ABSORPTION-COEFFICIENT IN SILICON OPTICS FOR HIGH-ENERGY LASERS THROUGH DEFECT ENGINEERING

We engineered a factor-of-4 reduction in the bulk absorption coefficie nt over the 2.6-to-3.0-mu m bandwidth in single-crystal Czochralski si licon optics for high-energy infrared lasers with high-temperature ann ealing treatments. Defect engineering adapted from the integrated circ uit industry has been used to reduce the absorption coefficient across the 1.5-to-5-mu m bandwidth for substrates up to 5 cm thick. A high-t emperature oxygen-dispersion anneal dissolves precipitates and thermal donors that are present in the as-grown material. The process has bee n verified experimentally with Fourier transform infrared spectroscopy , infrared laser calorimetry, and Hall measurements. Reduction of the absorption coefficient results in less substrate heating and thermal d istortion of the optical surface. The process is appropriate for other silicon infrared optics applications such as thermal-imaging systems, infrared windows, and spectrophotometers.