Influence of collector design on InGaP/GaAs HBT linearity

Linearity characteristics of InGaP/GaAs heterojunction bipolar transistors with various collector profiles are examined. Output third-order intercept point is measured as a function of bias current and voltage at 5 GHz. The results from this study indicate that IP3 varies with current in a complex manner and is significantly dependent on the collector design. A dynamic trend in IP3 is observed where a peak occurs at a current just below Kirk effect and a trough occurs at the onset of Kirk effect. Although the Gummel-Poon model is not able to predict this behavior, a large signal HBT model, which accounts for collector space-charge effects such as electron velocity modulation and Kirk effect, can properly represent the measured data. For accurate linearity predictions, these effects should be included in a large signal HBT model.