Engineering the properties of Czochralski silicon for infrared optics applications

Defect engineering adapted from the integrated circuit industry has been employed to reduce the bulk absorption coefficient in single-crystal Czochralski silicon samples from a large diameter boule (460 mm). A high temperature heat treatment followed by a rapid quench dissolves thermal donors and precipitates that may be initially present in the as-grown material. The engineered samples show a reduction in the bulk absorption coefficient across the 1.3 to 5 {dollar}mu{dollar}m bandwidth, with a factor of four reduction obtained over the HF laser bandwidth (2.6 to 3 {dollar}mu{dollar}m). These results were systematically obtained for samples up to 5.08 cm thick and 5.08 cm in diameter. The procedure has been corroborated by results from Hall measurements, infrared laser absorption calorimetry experiments, and infrared spectroscopy.; The thermal conductivity of the large diameter silicon was also determined. Direct measurements showed that the thermal conductivity was consistent with literature values, {dollar}{lcub}sim{rcub}{dollar}126 W/m-K. Defect engineering had no impact on this value. Several hypotheses which had been made to explain an unusually high thermal conductivity during previous HF laser calorimetry experiments were disproven. The likely cause of the observed high thermal conductivity was attributed to VLA coatings scatter, which can result in radiation impinging on the thermocouples.; Chemical etching studies detected stacking faults and a high dislocation density ({dollar}{lcub}sim{rcub}{dollar}350 cm{dollar}sp{lcub}-2{rcub}{dollar}) in the large diameter silicon. The presence of stacking faults was attributed to incomplete removal of the mechanical damage caused by lapping. It was shown that the damage was constrained to within {dollar}{lcub}sim{rcub}{dollar}10 {dollar}mu{dollar}m of the surface, and may be a concern during substrate fabrication. The presence of sub-surface damage was corroborated by high resolution x-ray diffraction measurements. The large diameter silicon is of poor quality when compared to state-of-the-art silicon used by the integrated circuit industry.; The results of these investigations have positive implications for infrared optics applications. The as-grown thermal history of the silicon can be replaced by an as-desired thermal history which reduces the absorption. Since the bulk absorption has a direct impact on substrate heating and thermal distortion, then the performance of a mirror can be improved by this procedure. Potential applications include transmissive optics such as infrared windows, diagnostic mirrors, and beam-splitters.