A new structure for controlling dark current due to surface generation in drift detectors

A new approach has been developed to control dark current due to surface generation in silicon drift detectors. Instead of using a guard anode to collect current generated at the surface in the areas between the p+ rings, these areas are filled with n+ diffusion rings. This approach reduces the depleted area of the silicon/SiO2 interface, which is the source of the surface current, from about 50% of the detector area to less than 2%. Superior robustness to process and material defects make this technique preferable to a design using a guard anode to collect surface current in our experiments. The new structure has been applied to an 8 mm diameter cylindrical drift detector. X-ray test results show good signal collection from the full detector volume.