The influence of base bias on the collector photocurrent for InGaP ∕ GaAs heterojunction phototransistors

• Published in: Journal of applied physics Vol. 97; no. 3; pp. 034502 - 034502-7
• Main Authors: Tan, S. W., Chen, H. R., Chen, W. T., Hsu, M. K., Lin, A. H., Lour, W. S.
• Format: Journal Article
• Language: English
• Published: American Institute of Physics 01.02.2005
• ISSN: 0021-8979; 1089-7550
• DOI: 10.1063/1.1847721

Fabrication, characterization, and theoretical modeling of two-terminal and three-terminal heterojunction phototransistors ( 2 T - and 3 T - HPTs ) based on InGaP ∕ GaAs are reported. For a current-bias 3 T - HPT , an independent current flowing into or out of base electrode is employed to modulate the operating point of a heterojunction bipolar transistor (HBT). The operating point of a HBT in the presence of a positive bias current can be tuned to a higher current level where the current gain is larger. It is found that the optical gain increases from 28.4 for a 2 T - HPT to 34 for a 3 T - HPT with a bias current of 10 μ A . The achievement of tunability of the operating point of a HBT has also been attempted with an independent voltage source. Nevertheless, our work reveals that the p - i - n photocurrent generated within the B - C region contributes very little to the final collector photocurrent for a voltage-bias 3 T - HPT , resulting in a rather small optical gain in the range 0.8 - 1.6 . A simple equivalent circuit model is developed to explain the differences between a current- and a voltage-bias 3 T - HPT . Our calculated results are in good agreement with the experimental ones.