On the spectrometric performance limit of radiation detectors based on semi-insulating GaAs

In this work, basic tasks related to the spectrometric performance of X- and gamma-ray radiation-imaging detectors based on semi-insulating (SI) GaAs are studied. The state of the art in this field is reported. The importance of a low-noise front-end read-out electronic chain is demonstrated. Four different charge-sensitive preamplifiers are tested and compared. The investigation of SI GaAs detectors considered for imaging applications is focused on the study of different electrode technologies. A blocking electrode is obtained by a surface Schottky barrier or an MBE-grown P+ layer. An ohmic N+ contact is fabricated using alloyed AuGeNi metallization or an advanced, quasi-ohmic non-injecting system created by a non-stoichiometric buffer grown by low-temperature MBE at the metal-semiconductor interface. This latter approach is considered as an improvement of the "non-alloyed" ohmic contact. The pulse height spectra obtained with Am-241 and Co-51 sources and corresponding detector energy resolution are evaluated. The role of detector geometry and temperature on the spectrometric performance is studied.