The Effect on Turn-On Voltage (VBE) of AlGaAs/GaAs HBT's due to the Structure of the Emitter-Base Heterojunction

The effects on the turn-on voltage (VBE) of collector current in AlGaAs/GaAs HBT's due to Be diffusion and discontinuity in the conduction band are investigated. It is clarified that VBE increases significantly with the decrease in saturation current due to Be diffusion into the AlGaAs emitter during MBE growth. It is also found that the VBE's of HBT's with Al compositionally abrupt and graded emitter-base junctions and homojunction GaAs bipolar transistors are the same. These results indicate that the spike-like potential barrier at the heterojunction has no influence on the electron injection from emitter to base.