Effects of high-temperature gamma ray and electron irradiation on npn Si transistors

The degradation of npn Si transistors, subjected to γ and 1-and 2-MeV electrons at different irradiation temperature, is studied. For the 20°C irradiation I_B increases significantly, while I_C markedly decreases for V_BE above 0.6 V. The radiation-induced degradation becomes significantly smaller for higher exposure temperatures. For the 200°C irradiation, I_B remains of the same order as before irradiation, while I_C is nearly identical. It is also noticed that h_FE for the 200°C γ-ray irradiation amounts to 82% of the starting value. A broad distribution of hole trapping levels is observed in the base region for the 20°C exposure, while an electron trap with energy level Ec - 0.18 eV and a broad DLTS signal around 150 K was found in the collector region. The hole capture levels in the base are related to radiation damage at the Si-SiO₂ interface region. It is concluded that the radiation-induced defects in the base and collector regions correlate well with the device degradation of the npn Si transistors.