  High purity Ge (HPGe) is the key material for gamma ray detector production.
Its high purity level (< 2x10^(-4) ppb of doping impurity) has to be preserved
in the bulk during the processes needed to form the detector junctions. With
the goal of improving the device performance and expanding the application
fields, in this paper many alternative doping processes are evaluated, in order
to verify their effect on the purity of the material. In more detail, we
investigated the electrical activation of contaminating doping defects or
impurities inside the bulk HPGe, induced by both conventional and
non-conventional surface doping processes, such as B ion implantation, P and Ga
diffusion from Spin-On Doping (SOD) sources, Sb equilibrium diffusion from a
remote sputtered source and laser thermal annealing (LTA) of sputtered Sb.
Doping defects, thermally-activated during high temperature annealing, were
characterized through electrical measurements. A phenomenological model
describing the contamination process was developed and used to analyze the
diffusion parameters and possible process thermal windows. It resulted that
out-of-equilibrium doping processes confined to the HPGe surface have higher
possibilities to be successfully employed for the formation of thin contacts,
maintaining the pristine purity of the bulk material. Among them, laser thermal
annealing turned out to be the most promising.
