Combined techniques for recovery of radiation damaged detectors

Radiation defects introduced by the electrons and X-rays emitted by the linear Varian TrueBeam type commercial therapy accelerators have been examined by combining various spectral techniques. The means for recovery of radiation detector functionality by combined heat treatment and laser anneal technologies were developed. The sets of OSRAM commercial SFH-2700 PIN diodes of dimensions less than 600 μm have been examined as potential small area radiation sensors. The identification of radiation trap origin and structure was performed by using deep-level transient (DLT) spectral variations and trap activation energy values extracted from Arrhenius plots. Several DLT peaks, namely 7 majority carrier traps and 2 minority carrier traps were resolved in the small dose (≤1 kGy) electron irradiated detectors. The prevailed increase of DLT spectral peaks ascribed to deep majority carrier traps was obtained with enhancement of electron irradiation dose. The electron traps attributed to the carbon interstitial (Ci(-/0)) defects as well as carbon complexes composed of interstitial-substitutional carbon atoms (CiCs(-/0)) and vacancy oxygen (VOi(-/0)) complexes were revealed. The majority carrier traps assigned to double (V2=/-) and triple vacancy (V3=/-) prevailed in the spectral range of deep centres. The prevailing minority hole traps H1, attributed to positively charged (Ci(+/0)) carbon interstitials, and H2, associated with complexes of carbon and oxygen interstitials (CiOi(+/0)), have been clarified. The same nomenclature of the majority and minority carrier traps (E1-E7) as well as (H1, H2) has been revealed on X-ray irradiated diodes. The two-step radiation defect removal has been implemented by the initial heating (Qfurnace) of the irradiated sample using the furnace setting, to raise the material temperature to a safe level Tfurnace, with further IR laser annealing procedure, using mJ energy pulses. The intense laser beam was impinged onto the diode peripheral boundary to bypass the metallic electrode layers. The diode was thereby near-homogeneously irradiated by laser beam propagating through sensor material in light–waveguide mode. Quality of heat treatment was evaluated either by DLTS measurements of the post-annealed sensors or by control of the barrier capacitance value during laser anneal procedures using BELIV technique. The change of concentration of the photo-active and thermal emission centres, introduced by 6 MeV electron irradiation has been confir