The gallium-arsenide/aluminum-gallium - arsenide tunneling emitter bipolar transistor: Theory and experiment

The Tunneling Emitter Bipolar Transistor (TEBT) was, for the first time, successfully grown, fabricated, and tested at dc. Device structures grown by molecular beam epitaxy with two different tunneling barrier AlAs mole fractions and each for two different barrier thicknesses were characterized at several temperatures. A differential current gain of 410 was achieved at room temperature (RT) using a single 50 A AlAs tunneling barrier. Devices with either thinner barriers (20 A) or Al{dollar}sb{lcub}0.38{rcub}{dollar}Ga{dollar}sb{lcub}0.62{rcub}{dollar}As barriers had lower gains. Al{dollar}sb{lcub}0.24{rcub}{dollar}Ga{dollar}sb{lcub}0.76{rcub}{dollar}As/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 current were measured for all devices and, for the TEBT's they showed a functional dependence on the interfacial barrier AlAs mole fraction and thickness which can be attributed to the effect that the barrier exerts on the electrons and holes transport. The variable temperature measurements showed an increased dependence upon the barrier composition and thickness at low temperature.; An analytical model was developed which can take into account several carrier transport mechanisms and was compared to actual measured data. A qualitative agreement was found in some structures but not in others due the lack of knowledge of the actual dopant distribution following the Be diffusion out of the base region. The activation energies of the various current components were extracted from Arrhenius plots and compared favorably to predicted values. Judging from the temperature dependence of the collector current in devices with 50-A-thick barriers, phonon-assisted electron tunneling was inferred.; An improvement on the TEBT structure was suggested which incorporates an AlGaAs emitter and was called the Tunneling Emitter Heterojunction Bipolar Transistor (TEHBT). Several TEHBT structures, all with AlAs barriers, were grown, fabricated, and tested at various temperatures. The TEHBT showed better performance than the TEBT at all temperatures notably at high collector current levels. However, it exhibited a lesser dependence on the barrier thickness than did the TEBT. The analytical model was applied to the TEHBT and was found useful in interpreting the extracted energies of the different current components. The TEHBT can be used as a high gain, high sensitivity phototransistor detector.