Study of bulk semi-insulating GaAs radiation detectors: Role of ohmic contact metallization in electrical charge transport and detection performance

Current-voltage (I-V) characteristics of radiation detector structures based on semi-insulating (SI) GaAs obtained with new types of metallizations used to form quasi-ohmic contacts are described. Three different metals (In, Gd and Mg), having lower work function in comparison with the standard AuGeNi eutectic alloy, were used. The new contacts form a blocking barrier for holes ("minority" carriers in SI GaAs). Such contacts, which could effectively replace standard alloyed N⁺ "ohmic" contact, show an unusual electrical charge transport as deduced from the measured I-V characteristics. Pulse-height spectra of²⁴¹ Am and ⁵⁷Co radionuclide sources detected by the structures demonstrating performance ofthe detectors are also reported.