Electron Trapping in Neutron-Irradiated Silicon Studied by Space-Charge-Limited Current

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Abstract
The trapping and detrapping of electrons is studied through measurements of space‐charge‐limited current in the temperature range 77≤T≤293°K in high‐purity silicon after irradiaton with 14‐MeV neutrons at a dose of about 1.2×1011 neutrons/cm2. A model is developed which describes most of the results quantitatively and self‐consistently, including dc characteristics. Two distinct trap levels exist: The ``fast'' levels lie at Etf =0.14±0.005 eV below the conduction band, with a concentration of Ntf ≃1.4×1012 cm−3 and a capture cross section of σ f ≃4×10−17 cm2 at 77°K. The ``slow'' levels lie at Ets =0.47±0.01 eV below the conduction band, with a concentration of Nts ≃1.6×1012 cm−3 and a capture cross section of σ s ≃1.4×10−14 cm2 at 293°K. At 77°K, injected free electrons are initially captured by the fast 0.14‐eV traps and then sink into the deep 0.47‐eV traps, predominantly without being reemitted into the band. Above approximately 110°K, the detrapping rate from the shallow traps becomes so fast that the deep traps dominate. The results also offer a direct verification of the simple model of space‐charge‐limited current dominated by shallow and deep traps. Some pertinent unresolved questions are also formulated.