Scaling 'Ballistic' Heterojunction Bipolar Transistors.

Reducing length scales in n-p-n heterojunction bipolar transistors leads to unexpected changes in the fundamental limits of device performance. Very high p-type carrier concentrations in the base result in a reduced inelastic electron scattering rate. In addition, there exists a maximum base/collector bias above which ballistic collector transport is not possible and correct scaling requires the n-type collector contact to be unusually heavily doped.