  Semiconductor detector fabrication technologies developed decades ago are
widely employed today to produce gamma-ray detectors from large volume, single
crystals of high purity Ge (HPGe). Most all of these detectors are used
exclusively for spectroscopy measurements and are of simple designs with only
two impurity based electrical contacts produced with B implantation and Li
diffusion. Though these technologies work well for the simple spectroscopy
detectors, the Li contact in particular is thick and lacks room temperature
stability in a manner that makes it inappropriate for many of the more complex
detectors needed for gamma-ray imaging and particle tracking applications. Thin
films of amorphous semiconductors such as sputter deposited amorphous Ge (a-Ge)
are the basis for an alternative electrical contact that is easy to fabricate,
thin, and can be finely segmented. The a-Ge also functions well as a
passivation coating on the HPGe surfaces not covered by the electrical
contacts. The properties of the a-Ge affect the performance of the resultant
detectors, and these properties substantially depend on and are controllable
through the sputter deposition process parameters. The subject of this paper is
this interconnection of fabrication process parameters, a-Ge properties, and
detector performance. The properties of a-Ge thin film electrical resistance,
a-Ge contact electron injection, and room temperature storage stability were
evaluated as a function of the sputter process parameters of sputter gas
pressure and sputter gas H2 composition. Two different sputter deposition
systems were used to produce a-Ge resistors and HPGe detectors with a-Ge
electrical contacts. These samples were electrically characterized as a
function of temperature. A summary of this study and discussion of the
relevance of the findings to the optimization of detector performance are given
in this paper.
