Optimum emitter grading for heterojunction bipolar transistors.

A simple procedure has been used to determine the optimum emitter grading for a heterojunction bipolar transistor (HBT). Use of this procedure allows maximum hole confinement in addition to minimum base/emitter turn-on voltage, leading to a negligible collector/emitter offset voltage, both of which are necessary for high performance devices. By using a parabolic grading function at the emitter/base junction a Np(+)n Ga(0.7)Al(0. 3)As/GaAs HBT has been fabricated, using MBE, with a negligible collector/emitter offset voltage.