An analysis of the anomalous dip in scattering parameter S/sub 22/ of InGaP-GaAs heterojunction bipolar transistors (HBTs)

The kink phenomenon in scattering parameter S/sub 22/ of InGaP-GaAs heterojunction bipolar transistors (HBTs) was explained quantitatively for the first time. Our results show that the output impedance of InGaP-GaAs HBTs can be represented by a simple series resistance-capacitance (R-C) circuit at low frequencies and a simple parallel R-C circuit at high frequencies very accurately because of the high output resistance of HBTs. The behavior of S/sub 22/ of HBTs is in contrast with that of field effect transistors (FETs), where the smaller drain-source output resistance R/sub ds/ obscures the ambivalent characteristics.