Dependence of leakage current on the performance of Silicon Drift Detector based X-ray spectrometer

We have developed Silicon Drift Detector (SDD) based X-ray spectrometer for the future planetary/space exploration missions. This spectrometer provides the energy resolution of similar to 150 eV at 5.9 keV for the pulse peaking time of 3 mu s and the detector kept at -40 degrees C. The energy resolution of the SDD based X-ray spectrometer depends on the detector leakage current and the electronics noise associated with the signal readout and processing electronics. We have measured energy resolution and leakage current for two sets of SDDs having active area of 40 mm(2) and 109 mm(2) respectively. It is shown that the leakage current for small area (40 mm(2)) SDD detector varies from similar to 0.6 nA at 20 degrees C to similar to 0.2 pA at -40 degrees C and for large area (109 mm(2)) SDD detector, the leakage current varies from similar to 0.9 nA at 20 degrees C to similar to 1 pA at -50 degrees C. The total measured Equivalent Noise Charge (ENC) of the spectrometer system varies from -34.5 erms at -3 degrees C to 11 erms at -40 degrees C for small area detector and 42 erms at -8 degrees C to 13 erms at -50 degrees C for large area detector.