Spreading of an active region of semi-insulating GaAs detectors after radiation degradation

The radiation hardness of GaAs detectors against high-energy electrons goes up to a few MGy. Their degradation is mainly connected to the decrease of the charge collection efficiency and the increase of the reverse current. On the other hand, an improvement in detection efficiency was observed at low degradation doses. The explanation that this could be caused by an enlargement of the detector active area due to spreading of the collecting electric field caused by radiation -induced defects is studied in this paper. We have used the alpha particles of 241Am, which interact in the GaAs surface layer, to study the enlargement of the detector active region after its degradation by 5 MeV electrons with doses ranging from 24 to 2000 kGy. The results show that the electric field spreads behind the Schottky contact metallization edges not only with increasing applied reverse bias but also with rising cumulative dose of radiation degradation in the dose range from 24 up to 100 kGy, followed by a slight reduction in area size. The electric collecting field keeps larger dimensions than before detector degradation for doses up to 600 kGy. For higher doses than 1000 kGy, the active area of the detector was reduced below its initial size before degradation. Moreover, the improvement of detection efficiency with increasing bias applied becomes weaker with increasing degradation dose. Radiation degradation affects the electric field distribution in semi -insulating GaAs detectors and the results obtained may provide useful knowledge to preparation of multi -pixel GaAs structures for imaging and particle tracking.