Radiation Effects on Current Gain in BC-107 transistor

Abstract

Bipolar Junction Transistors are known to exhibit changes in their electrical characteristics when exposed to low level gamma radiation. The study examines the forward current gain factor in silicon npn BJT's due to radiation from a weak cesium-137 source. Barium K X-ray photons 32.6 keV and 662 keV gamma photons from Cesium-137 weak source bombard the p-n junction of the transistor. 32.6 keV X-ray photons interaction causes additional electron in the junction and 662 keV gamma photons interact through Compton scattering and cause secondary electrons in the p-n junction with energy of 0.2 MeV to 1.0 MeV. These secondary electrons displace the Si atoms near the p-n junction of the transistor and cause damages by forming trapping centres in the junction region altering the electrical properties of the transistor. In this work, we have investigated the current gain in BC-107 transistor operating in Common Emitter mode through its input and output characteristics to assess variation in its performance both before and after radiation exposure. Collector current shows decrement due to trapping centers formed in the collector region. The current gain of the transistor decrease with radiation exposure. Anomaly in the current gain of BC-107 transistor is accounted for the photo electrons added in the forward bias region of the emitter base junction due to radiation exposure. An uncertainty of less than 2% in the measurement of current gain and transconductance is been reported.