New contact development for Si(Li) orthogonal-strip detectors

Abstract

At present, the contacts generally used for lithium-drifted silicon detectors consist of a diffused lithium layer (n-type) and a gold surface barrier (p-type). These contacts work well for unsegmented detectors. However, they both have disadvantages if used for segmented detectors. For this reason, we are developing new types of contacts that will be more robust and easier to segment. To replace the lithium n-type contact, we are using a thin layer of amorphous silicon (α-Si) with metalization on top. The new p-type contact consists of boron implanted into the silicon and annealed at the relatively low temperature of 500°C. The implantation and annealing is carried out as the first step in the process, prior to lithium drifting. Detectors have been fabricated using the new contacts both with and without a guard ring. They performed as well as detectors with standard contacts at operating temperatures between 80 and 240K. We will present data on the leakage current vs. temperature, isolation resistance between the guard ring and the center contact versus temperature and bias voltage, electronic noise and energy resolution versus temperature, as well as 57Co spectra.