Quantized resonant-tunneling phenomena of AlGaAs/GaAs/InGaAs heterojunction bipolar transistors

The quantized resonant-tunneling behaviors of heterojunction bipolar transistors (HBTs) with an n-AlGaAs/n-GaAs/n(-)-InGaAs heterostructure emitter and an ultra thin p(+)-GaAs base layer are demonstrated by theoretical and experimental analysis. In these devices, a thin n(-)-InGaAs pseudomorphic quantum well (QW) in the emitter region is formed between the n-GaAs emitter and the ultra thin p(+)-GaAs base layer. By solving the Poisson equation, the design of the n-GaAs emitter layer is discussed. A transfer-matrix method is developed to describe the quantum mechanism of miniband structures, in which electrons tunnel resonantly from the depleted emitter side to the collector side through the InGaAs QW and ultra thin p(+)-GaAs base layers., A device with high current gain, low offset voltage, and a pronounced N-shaped negative-differential-resistance (NDR) phenomenon at room temperature is observed experimentally.