Based on the observation of the degradation of the base transfer factor caused by the insertion of the quantum well (QW) together with the heavy base doping, this work demonstrates the physical modeling of the quantum-well heterojunction bipolar transistor, known as the transistor laser. By revising the conventional bipolar junction transistor charge control model, this work accounts for the degraded base transfer ratio, which contrasts with the constant base transport factor close to unity in conventional bipolar junction transistor operation, and its variation with the base current. The approach of this work is to assess the concentration of base minority carrier captured in the QW and give an analytical expression for the carrier lifetime in the base, which is a key factor for device frequency performance. Expressions for the physical parameters such as capture time, base recombination lifetime and base transit time are obtained in terms of experimental values such as base current, and device design parameters such as base width, QW width and QW location. While the calculated base recombination lifetime can be of the order of a fraction of a nanosecond, the QW capture time is found to be of the order of a picosecond. These parameters retrieved from the calculation are then used to successfully reproduce the optical frequency response diagrams of the light-emitting transistor and transistor laser obtained from experiments.
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Physical modeling of base carrier lifetime and frequency response of heterojunction bipolar transistor