Production of Lithium Drifted Germanium Detectors by AC Drift

Thick planar detectors have been produced by ac drifting. Lithium is diffused on two opposite surfaces of a p-germanium block, thus producing an n+ pn+ structure with two diodes back to back. Drift then proceeds from the two surfaces on alternate half cycles of the ac field. When the two compensated regions meet, one n-contact is removed and replaced by a p-contact. Any remaining uncompensated regions are then compensated by a dc drift. The p-contact is produced by diffusing gallium-indium eutectic at 400°C. By this technique it is possible to drift as deep at 2 cm and thus to produce a large volume detector with low capacitance.