Cap layer effect in DC and RF characteristics of InP based n-p-n metamorphic δ-doped heterojunction bipolar transistor

The effect of InGaAsP and InGaAs cap layers in InP n-p-n heterojunction bipolar transistor (HBT) is presented. The common figures of merit (FOM) in each case are compared to assess their potentials for operation at high frequency. The Gummel-Poon plot of experimental reported result has been used to validate the data obtained from simulation using ATLAS module of Silvaco software tool. After models validation in TCAD tool, the DC and RF characteristics of the HBTs with different cap layers are examined and then a comparative analysis is carried out based on the characteristics such as I–V behaviour, frequency response, minimum noise figure and maximum cut-off frequency. With the change in InGaAs cap to InGaAsP cap, the DC current gain increases from 255 to 300, VCE,offset is reduced from 131 to 76 mV, Early Voltage (VA) increases from −42 to −190 V, cut-off frequency ft is increased from 24.34 MHz to 8.04 GHz, and the maximum oscillation of frequency(fmax) is improves from 13.79 to 37.11 GHz