RADIATION-DAMAGE IN NEUTRON TRANSMUTATION DOPED SILICON - ELECTRICAL PROPERTY STUDIES

Radiation damage in neutron-transmutation-doped (NTD) silicon, irradiated to introduce 5×1013 to 6×1016 phosphorus cm-3, has been studied by electrical property measurements. The experimental results indicate that thermal-neutron-induced (n,γ) recoil-type damage can be annealed at 400 °C. The nature of any remaining lattice defects and their annealing behavior above 400 °C is a function of the fast-neutron fluence. Small defect clusters are present in Si irradiated with a light-to-moderate fast-neutron fluence (?5×1018 n cm-2), and temperature-dependent Hall coefficient measurements indicate that at least two deep acceptor levels and one deep donor level are formed during annealing. One of these acceptor levels anneals at ∼450 °C, and the other two levels anneal at ∼550 °C. A shallow acceptor level near the valence band that anneals at 750 °C is also observed. Larger defect clusters which reduce the electron mobility tremendously and distort the band structure are formed in heavily irradiated Si (5×1018 to 1020 n cm-2). Virtually all of the electrically detectable radiation damage in NTD Si irradiated with a fast-neutron fluence up to 10 20 n cm-2 can be removed by annealing at 750 °C for 1/2 h. There is some indication that a minority-carrier-recombination effect remains even after such annealing.