Guard ring elimination in CdTe and CdZnTe detectors

CdTe and CdZnTe deliver good energy resolution and stopping power in a room temperature solid state detector. Currently, these materials are becoming more available and larger detectors are being constructed by tiling many single crystal modules together. However, CdTe and CdZnTe remain expensive and it is therefore desirable to make use of as much of the crystal as possible and to tile the individual crystals closely with little or no dead space. Reducing surface current on these crystals without the use of guard rings could allow pixel maps to be extended to the edge of the crystal, thus making more effective use of the material and allowing tiling with less dead space. We have therefore developed a method of passivating the surface current in single crystal CdTe and CdZnTe detectors. Using this passivation method we have constructed a CdTe detector with 256 pixels which extend all the way to the edge of the crystal. To validate our results, we have also constructed a testing device, based on spring loaded gold plated pins, which can non-destructively test the current in each pixel of such a detector. Using this testing device, we have compared the dark current of edge pixels before and after our passivation process and see a significant reduction in surface current after passivation. The elimination of guard rings along with our implementation of a backplane readout solution allows this detector module to be tiled with dead space close that of the pixel septa.