Production of Thick Semiconductor Radiation Detectors by Lithium Drifting

The application of semiconductor junction radiation detectors1 to penetrating radiation depends on the production of devices having thick depletion layers. In this connection the lithium drift technique developed by Pell2,3,4 has been employed with considerable success5,6,7,8,9. A difficulty encountered with this method is the long time required to produce compensated regions a few millimeters or more in thickness. However it can be shown that the compensated region produced by drifting at constant temperature is proportional to the cube root of the total energy dissipated in the drifting process. This indicates the importance of operating at the highest attainable power at all times, and has led to the design of a system employing a fluorocarbon liquid as a vapor phase coolant in conjunction with a pulsed constant wattage supply. Significantly improved drift rates have been achieved with this technique, which has the added advantage of being well suited to the simultaneous drifting of a number of detectors at constant power from a single power supply.