Sub-bandgap photonic base current method for characterization of interface states at heterointerfaces in heterojunction bipolar transistors

In this paper, we propose a novel photonic base current analysis method to characterize the interface states in heterojunction bipolar transistors (HBTs) by using the photonic I-V characteristics under sub-bandgap photonic excitation. For the photonic current-voltage characterization of HBTs, an optical source with a, photon energy less than the bandgap energy of Al0.3Ga0.7As and GaAs (E-ph = 0.95 eV < E-g,E-AlGAs = 1.79 eV & E-g,E-GaAs = 1.45 eV) is employed for the characterization of the interface states distributed in the photo-responsive energy band (E-C - 0.95 less than or equal to E-it less than or equal to E-C) in emitter-base heterojunction at HBTs. The proposed novel method, which is applied to bipolar junction transistors for the first time, is simple, and an accurate analysis of interface traps in HBTs is possible. By using the photonic base-current and the dark-base-current, we qualitatively analyze the interface trap at the Al0.3Ga0.7As/GaAs heterojunction interface in HBTs.