I have a question about the dead layer properties of HPGe gamma semiconductor detectors. I found this on Wikipedia
As of 2012 HPGe detectors commonly use lithium diffusion to make an n+ ohmic contact, and boron implantation to make a p+ contact. Coaxial detectors with a central n+ contact are referred to as n-type detectors, while p-type detectors have a p+ central contact. The thickness of these contacts represents a dead layer around the surface of the crystal within which energy depositions do not result in detector signals. The central contact in these detectors is opposite to the surface contact, making the dead layer in n-type detectors smaller than the dead layer in p-type detectors. Typical dead layer thicknesses are several hundred micrometers for an Li diffusion layer, and a few tenths of a micrometer for a B implantation layer. https://en.wikipedia.org/wiki/Semiconductor_detector
I have some problems understanding this. First of all I can't imagine how a lattice of Ge with Li doping would look like, since Li has only 1 valance electron (Does it mean that 3 holes are created?). If this is the case, why exactly Li is chosen? Moreover, I don't understand why one of the layers is thicker. My guess is that this has something to do with the lithium diffusion process, but that is just a guess.
I would appreciate your help to understand the properties of those layers.