Large-area Si(Li) orthogonal-strip detectors

Segmented lithium drifted silicon detectors are being developed for use in large Compton cameras and for medical imaging. We have successfully fabricated 3.5 mm thick crossed-strip detectors with active areas of 40×40 mm² with a 2 mm strip pitch. These detectors utilize new contact technology consisting of a boron implanted p-type contact and an amorphous silicon (α-Si) n-type contact. Good energy resolution and excellent strip separation was obtained from both contacts at relatively high operating temperatures. An energy resolution of 2.1 keV FWHM at 122 keV was obtained for the α-Si strip at temperatures up to 200 K and for the boron strip at temperatures up to 240 K. Measurements of the charge sharing between the strips were also performed. When the detector was flood illuminated with 60 keV gamma-rays, a small signal deficit was observed for events in which the signal was shared between two adjacent strips. The amount of deficit depended on the contact type, strip geometry and the operating temperature.