Electrically active centers induced by electron irradiation in n-type si detectors

Electrically active centers induced by 1 MeV electron irradiation in n-type Si detectors have been studied by Deep Level Transient Spectroscopy (DLTS). The detectors have p+-n-n+ structure where the n-layer is epitaxially grown Si with a resistivity of 20-25 Ω cm and a thickness of 25 μm. The epitaxial layer is grown on n+-Si substrate and the p+ layer is formed with boron implantation. The 1 MeV electron irradiation has been performed with doses of 4.5×1014 and 3.0×1015 cm−2. DLTS measurements reveal the formation of several dominating electron traps identified as the vacancy-oxygen pair (VO) and the two charge states of the divacancy: the singly negative (V2(−/0)) and the doubly negative (V2(=/−)). Besides, a close to mid-gap electron trap with an activation energy of 0.52 eV has been observed in the DLTS measurements. Annealing studies reveal that the mid-gap trap is stable up to 250 °C. Formation of a trap with an activation energy of 0.36 eV is observed during the annealing study. The identity of these two traps is discussed.