TABLE OF CONTENTS Esame et al. [168] have made a comprehensive comparison of three state-of-the-art heterojunction bipolar transistors; AlGaAs/GaAs, Si/SiGe and InGaAs/InP HBTs. Direct current and bias point simulations of the devices were performed using Agilent's ADS design tool and a comparison is given for a wide range of FOM specifications. It has been concluded that GaAs based HBTs are suitable for high-power applications due to their high-breakdown voltages, SiGe-based HBTs are promising for low noise applications due to their low noise figures and InP will be the choice, if very high-data rates are of primary importance since InP-based HBT transistors have superior material properties leading to Terahertz frequency operation.
For device I V curve families V ce is swept from 0 to 5 V and I b from 10 to 100 mA. As seen from Figure 10.24, for 70 ?A base current the AlGaAs/GaAs device's collector current is 6 mA, while it is 11 mA for the Si/SiGe device and 4 mA for the InGaAs/InP HBT at their optimal V ce for class A operation. Since the breakdown voltage phenomena were not modelled for the AlGaAs/GaAs and InGaAs/InP devices, no collector-base breakdown can be seen in Figure 10.24(a) and (c). However, for the Si/SiGe device, this breakdown can be seen at around 5 V of collector-emitter voltage (Figure 10.24b). This low BV cbo is the main problem for the SiGe-based heterojunction transistors and limits their use in some application areas such as base...
