Surface Effects on P Type High Purity Germanium Detectors at 77°K

Ellipsometry has been used to measure the thickness of the residual film on the germanium surface after etching. Residual film thicknesses of 4 Å, 20 Å and 500 Å are obtained for the 10:1, 3:1 and 1:10 etches, respectively. A single detector was processed a total of 63 times using a variety of surface treatments. This study showed high breakdown voltage could be obtained with a variety of etches, but that the time the detector remains in the quenching solution should be minimized. The edge of the depletion region was scanned with a collimated 60 kV γ source after each surface treatment. The two scan results that could reprevroducibly be obtained were the type C, obtained with a 3:1 or 10:1 etch, a water quench, a brief evacuation and a rapid cool down, and the type B obtained using the same procedure with a 1:10 etch. The type C scan can be eliminated by heating in vacuum and restored by exposure to room air suggesting that it is caused by water vapor adsorbed on the surface. The type C scan is believed to result from hole trapping at the surface of the depletion region. An external electric field has been used to increase the breakdown voltage of the detector.