Investigation of amorphous germanium contact properties with planar detectors made from USD-grown germanium crystals

Abstract

A: The characterization of detectors fabricated from home-grown crystals is the most direct way to study crystal properties. We fabricated planar detectors from high-purity germanium (HPGe) crystals grown at the University of South Dakota (USD). In the fabrication process, a HPGe crystal slice cut from a USD-grown crystal was coated with a high resistivity thin film of amorphous Ge (a-Ge) followed by depositing a thin layer of aluminum on top of the a-Ge film to define the physical area of the contacts. We investigated the detector performance including the I-V characteristics, C-V characteristics and spectroscopy measurements for a few detectors. The results document the good quality of the USD-grown crystals and electrical contacts. K: amorphorous germanium contacts, planar germanium detectors, leakage current, gamma ray spectroscopy 1Corresponding author.

Characterization of high-purity germanium detectors with amorphous germanium contacts in cryogenic liquids

“…Their leakage current measurement results were shown together with those mea- The side surface leakage currents of USD-R02 were typically higher than its bulk leakage currents through the central contact around operational voltages in both environments. These results are consistent with more thorough investigations done in vacuum at USD with more sample detectors [38,39], that is, the performance of the detectors made at USD has yet to be improved to match that of the detectors made at LBNL by Mark Amman, in particular, the quality of the side surface. Nevertheless, the performance of USD-8-4-15 in both cryogenic liquid is very encouraging.…”

“…Detector USD-8-4-15 was operated in LAr once. Below 800 V, the leakage current was below 1 pA. Its significantly lower leakage current is a clear evidence that the quality of the amorphous germanium surface made at LBNL [35,46] was better than that made at USD [38,39]. The quick rise of the leakage current above 800 V was due to damage to the detector when it fell from the PTFE stage during the preparation of the fifth thermal cycle in LN 2 .…”

“…A dozen mini planar detectors have been fabricated at the University of South Dakota (USD) using the technique developed at LBNL and HPGe crystals produced at the USD crystal pulling facility [38]. They perform well in a traditional vacuum cryostat [39]. A cryostat, Gerdalinchen II [40], has been developed at the Max-Planck-Institut (MPI) für Physik in Munich to study segmented HPGe detectors directly submerged in cryogenic liquids, including liquid nitrogen (LN 2 ) and LAr.…”

The impact of the charge barrier height on Germanium (Ge) detectors with amorphous-Ge contacts for light dark matter searches

“…For the details about how to convert an HPGe crystal into a planar detector with a guardring structure shown in Fig. 3, please refer to our previous work [42,43]. Due to more uncertain handling processes involved before the a-Ge coating on the bottom contact, it is expected that the top and bottom contacts may not have the same quality.…”

“…In addition, a large number of detectors with great detector performance have been fabricated successfully at LBNL using this technology. More recently, a dozen small detectors made from USD-grown crystals have also been fabricated successfully at the University of South Dakota (USD) [42,43] using the same technology. With a-Ge contact technology, as shown in Fig.…”