Ultrahigh-Speed Bipolar Transistors

The invention in 1949 by Bardeen, Brattain and Shockley of the bipolar transistor has had tremendous technological ramifications heralding as it did an era of semiconductor microelectronics. The physics underlying their invention involves the diffusive motion of charge carriers through a semiconductor. Apart from resistive and capacitive effects (RC time constants), low diffusion velocities (~10 sup 7 cms sup (-1)) limit the ultimate speed of this type of transistor.