Surface effects in Germanium           I.Abt  May 2023
===============================

Example: point contact detectors    [inverted coax is similar] 

              p-type                         n-type               
_________________________________________________________________

Li drifted   large outside contact          small central contact
==========
O(1mm)       reduces fiducial volume        irrelevant 

metalisation should be there                has to be there
             to stabilise field             for contact


signals      part might be held             irrelevant
             --> slow release
             works together with
	     impurity profile
	     
Energy loss  substantial                    substantial
             alpha penetration < 20 micron
-------------------------------------------------------------------
p-implant.   small central contact          large outside contact
==========
O(100nm)     irrelevant                     irrelevant

metalisation needed for contact             better to stabilize field
                                            over long distances

signals      irrelevant                     irrelevant

Energy loss  small                          small
                                            can only be seen for alphas

_______________________________________________________________________

amorphous germanium: no experience myself; only know about planar geometries
=========    which are not ideal for pulse shape analysis
_________________________________________________________________________

passivation  always dependent on detector geometry
===========

dangers:     dead layer and  charge up

             should not be in contact with metallisation on HV
	        --> charge up
	     should not be covered by something
	        --> charge up
	        [even though kapton seems okay -- no influence
		 observed for an n-type detector]

surface channels: The actual situation is complicated
charge up             
       ==>  charges can be drawn towards the surface and drift there
	        -- sometimes slowly
		-- sometimes get stopped
                -- maybe T dependent
		
             all depends on small changes in geometry like
	     layer thicknesses
	     n-type and p-type with otherwise identical geometry
	     act differently due to layer thicknesses

             can be helpful -- can see alphas through a surface channel
	                       with 6 micron dead layer
			       while gammas say > 100 micron dead layer
			       
             significant influence due to environment
	     ==> stay 1cm away from the detector to avoid
	         Same p-type detector responded significantly
		 different in two test-setups.