Analysis of activation energy and conductivity in 1 MeV neutron irradiated silicon diodes

Abstract

In a highly 1 MeV neutron-irradiated silicon (Si) diode, an ohmic current-voltage (I-V) behaviour is observed, with the ohmic region increasing with radiation fluence. Reverse current (minority carrier density) increasing more drastically than forward current (majority carrier density) explains the conductivity-type inversion of material-based devices from n-to p-type after irradiation. The reverse current activation energy decreases from 0.86 eV for unirradiated Si diodes to 0.54 eV for the highest irradiated diodes, confirming the material conductivity-type inversion. The activation energy is independent of the radiation fluence just below the Si intrinsic Fermi energy, showing that when the defects near the centre of the Si band gap dominate the conduction mechanism, diode properties are independent of incident radiation. Despite its detrimental effects, radiation can improve the stability of diode properties. The stability of the properties is important for the fabrication of sensors for current and future high-energy physics experiments. The improved stability is because of radiation-induced defect levels close to the centre of the band gap that behave as generation-recombination (g-r) centres in Si.