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AlGaAs/GaAs tunneling emitter bipolar transistors (TEBT’s), grown by molecular beam epitaxy, have been fabricated. Device structures with two different tunneling barrier Al mole fractions and each for two different barrier thicknesses were characterized at room temperature. A differential current gain of 410 was achieved using a single 50 Å AlAs tunneling barrier. Devices with either thinner barriers (20 Å) or Al0.38Ga0.62As barriers had lower gains. Al0.24Ga0.76As/GaAs heterojunction bipolar transistors and GaAs homojunction bipolar transistors without tunneling barriers were also fabricated and characterized, for comparison. The performance of the homojunction devices was improved in all cases by inserting the tunneling barrier. The variations of the base and collector currents were measured for all devices and, for the TEBT’s they showed a functional dependence on the interfacial barrier Al mole fraction and thickness, which was attributed to carrier tunneling through the barrier. Furthermore, the above characteristics exhibit a clear electron-to-hole preferential tunneling.

We report on replacing the GaAs base in the AlGaAs/GaAs heterojunction bipolar transistor with pseudomorphic GaInAs. Base regions consisting of uniform Ga0.95In0.05As and graded Ga1−yInyAs (y=0.0–0.05) are compared to base regions consisting of GaAs. The highest dc common emitter current gain is obtained with the graded Ga1−yInyAs base.