A new model for the phototransistor

We reported the fabrication, characterization and modeling of a heterojunction phototransistor. Both Gummel-plot and common-emitter configurations are employed to characterize HPT´s performances and to clearly demonstrate what difference between a voltage-biased and a current-biased HPT. The performances of the voltage- and current-source biased HPTs were also compared to the results from a newly proposed HPT model and related circuit with good agreement found. Although an independent voltage source pushes HBT´s operating point to a higher current level. where the dc current gain is larger, however, the photocurrent generated within B-C region gives very little contribution to final collector current. The optical gain obtained from high-voltage-source biased HPT is even smaller than that of a HPT with a floating base. In addition, a modified extended Ebers-Moll model was successfully used to analyze what the common-emitter characteristics and Gummel-plot differences with input base current as well as base-en-Litter voltage between the dark and illumination situation.