Investigation of AlGaAs/GaAs Superlattice-Emitter Resonant Tunneling Bipolar Transistor (SE-RTBT)

A superlattice-emitter resonant tunneling bipolar transistor (SE-RTBT) has been successfully fabricated using GaAs based materials and demonstrated at both room temperature and 77 K. In an SE-RTBT, the i-Al_{0. 5}Ga_{0. 5}As/n⁺-GaAs superlattice is used as a reflection barrier to prevent holes from being injected into the emitter region while electrons can pass to the base and then reach the collector easily. High emitter injection efficiency and hence high current gain are sustained. With a doping ratio of 0.1 between emitter and base, common-emitter current gain of up to 60 and a collector-emitter offset voltage of 55 mV were obtained at room temperature. At low temperature, where the thermionic emission current is negligible, the superiattice acts as a resonant tunneling barrier. Experimentally, at 77 K, the proposed device exhibits significant double-negative-differential-resistance (NDR) behavior with peak-to-valley current ratios of 4: 1 and 2.8: 1 due to resonance through the ground and the first-excited bands in the superiattice, respectively. From Schrodinger’s equation, there are two minibands: the ground state band E₂= 91 meV and the first-excited band E₂ = 260 meV, with band widths of ΔE₁, = 7 meV and Δ E₂ = 13.5 meV. Furthermore, three operating regimes of transistor action with maximum current gains of 67, 38, and 35 were observed in common-emitter configurations. Based on these properties, the proposed SE-RTBT can be employed as a functional device which provides good potential for frequency multipliers and multiple-valued logic circuit applications.