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Show 4.2 Advantages of HBT Technology It has already been mentioned that HBT technology nabl high r p d and frequency of circuit operation than rnost available technologi s. Th advantag of HBTs over Silicon Bipolar Transistors and Field Effect Transistors can b s n below in a more detailed manner. In cornparison with Silicon Bipolar Transistors, HBTs have the following us ful properties. • The wide-band-gap emitter in HBT enables a much higher base doping concentration and hence a lower base resistance. • The base-emitter capacitance can be reduced by lowering emitter doping and minority carriage storage in the emitter. • High electron mobility, built-in drift fields, and velocity overshoot combine to reduce electron transit time. • Semi insulating substrates help reduce parasitic substrate capacitance. • Early voltages are higher and high injection effects are negligible due to high base doping. HBTs also have many advantages over FETs, and they can be summarized as follows. • The entire emitter area conducts current, leading to high current handling capability and high transconductance. • The base-emitter junction, which is the control region of the device, is very well shielded from the output voltage, leading to low output conductance which enables obtaining enormous voltage amplifications. • Higher speeds with relaxed lithographic dimensions. • The device is well shielded from traps in the bulk and surface regions, con- |
