The effects of radiation-induced interface traps on base current in gated bipolar test structures

Ionizing radiation experiments on gated bipolar transistors used as radiation test structures show a broadening in the peak base current profile after irradiation. The primary mechanism for this effect is identified as the change in the charge state of radiation-induced interface traps in the oxide over the base. From theoretical analysis using Shockley–Reed–Hall (SRH) statistics, a mathematical formulation of effective Fermi level, Ef,eff is derived to describe the charge state of interface traps in a gated bipolar transistor under forward bipolar operation as the surface of the transistor is changed from accumulation to inversion by biasing on the gate terminal.