BALLISTIC COLLECTION TRANSISTORS AND THEIR APPLICATIONS
We describe the design, fabrication and application of ballistic collection transistors (BCTs) in which electron velocity overshoot is introduced in the collector of a GaAs-based heterojunction bipolar transistor. The guideline for the BCT design is the effective confinement of electrons to the Γ-valley, as simulated by Monte Carlo analysis, and the control of electron energy is accomplished basically with an i-p+-n+ doping profile. Microwave characterization demonstrates the existence of significant overshoot and cutoff frequencies higher than 100 GHz at collector current densities in the mid 104 A/cm 2 range for a typical BCT structure. Some high speed integrated circuits implemented with BCTs include a selector circuit that operates at bit rates up to 40 Gb/s, a dynamic frequency divider with divide-by-four function up to 50 GHz and a broadband preamplifier having an S21 bandwidth as high as 40 GHz.