Ultrathin entrance windows for silicon drift detectors

Detectors with ultrathin entrance windows have been fabricated, which show an overall improvement of the detector performance in the optical and X-ray region as well as for heavy ions. The quantum efficiency was higher than 60% within the entire wavelength range between 200 nm and 800 nm. In the soft X-ray region the spectroscopic resolution could be improved significantly. For the MnKα line a peak to valley ratio of 5700 : 1 was achieved. Measurements with 241Am α-particles revealed an effective ''dead'' layer width of less than 150 A. The compatibility of the technology to produce thin entrance windows with the planar process allows its application on various pn-junction detector designs. A new silicon drift detector with a total area of 21 mm2 was successfully tested and operated at count rates up to 3 x 107 s-1 cm-2. At room temperature, the devices have shown an energy resolution for the MnKα line of 227 eV (FWHM) with shaping times of 250-500 ns, decreasing to 152 eV at -20 C. The fast readout in combination with a large detector area, a homogeneous entrance window and an exceptionally low noise without the need of an extensive cooling system makes them especially suited for spectroscopic applications in non-laboratory environments. (orig.)