Segmentation of the Outer Contact on P-Type Coaxial Germanium Detectors

Germanium detector arrays are needed for low-level counting facilities. The applications of such user facilities include characterization of low-level radioactive samples. In addition, the same detector arrays can perform important fundamental physics measurements including the search for rare-events like neutrinoless double-beta decay. Germanium coaxial detectors having segmented outer contacts can provide sensitivity improvement in low-background measurements. The segmented outer detector contact allows pulse-shape analysis measurements that provide additional background reduction. Currently, n-type (reverse electrode) germanium coaxial detectors are used whenever a segmented coaxial detector is needed because the outer boron (electron barrier) contact is thin and can be relatively easily segmented. Coaxial detectors fabricated from p-type germanium cost less, usually have better energy resolution, and can be larger than n-type coaxial detectors. However, it is difficult to reliably segment p-type coaxial detectors because thick (tilde 1 mm) lithium-diffused (hole barrier) contacts are the standard outside contact for p-type coaxial detectors. During this Phase II small business innovation research grant (SBIR), we are developing thinner, segmented, and stable lithium-diffused contacts. Many small planar test detectors have been fabricated with segmented lithium-diffused contacts. Center contact and guard-ring structures have been fabricated on the detectors to study the rectification and segmentation properties of lithium-diffused contacts. Fabrication techniques have been established that successfully produce repeatable rectification and segmentation. The rectification and segmentation appear to be stable with respect to modest temperature cycles. These results are fundamental steps toward developing segmented lithium-diffused contacts for p-type coaxial detectors.
Presented at the Monitoring Research Review (29th): Ground-Based Nuclear Explosion Monitoring Technologies, held in Denver, CO on 25-27 September 2007. Published in the Proceedings of the Monitoring Research Review (29th): Ground-Based Nuclear Explosion Monitoring Technologies, p764-769, 2007. Sponsored by the National Nuclear Security Administration (NNSA) and the Air Force Research Laboratory (AFRL). The original document contains color images.