Heterojunction bipolar transistor

The heterojunction bipolar transistor (English, HBT or HJBT, dt » heterojunction bipolar transition " ) is a bipolar transistor ( BJT), the emitter material is selected to be different than that of the base. The eponymous hetero structure. It therefore corresponds to the execution of a bipolar high- Electron - Mobility - transistor ( HEMT).

Design and function

By choosing a material with a larger emitter bandgap than that of the base material, it is possible to achieve a very small hole injection from the base into the emitter (see construction of a bipolar transistor ). This is achieved in that on the basis of the embodiment of the HBT of an npn transistor through the material, only the change in valence deeper is mainly responsible for the larger band gap. The small injection of holes into the emitter, in turn, allows in the base having a high p -type doping, which has large electric mobilities in the base result. This high minority carrier mobility is crucial for very fast switching of the transistor.

This transistor architecture, switching frequencies above 600 GHz can be achieved. Wide dissemination has therefore found for example in the power amplifiers of mobile devices, this type of transistor.

Today HBTs consist mostly of carbon -doped silicon germanium (SiGe: C) or gallium arsenide (GaAs ). This material mixture influences the effective mass of the electrons in the material system. The electron is under the influence of the germanium atom is much easier and thus has a lower inertia, which allows the electron to move to a higher mobility in the material. The carbon binds the boron dopant in the base. This has a much sharper doping result, what the component can be even faster.