Abstract

A bipolar structure provides many potential benefits for picosecond electronic circuits: (a) current flow is vertical, through epitaxial layers whose total thickness is only a few tenths of a micron, decreasing carrier transit times; (b) large amounts of current can be carried by modest size transistors, enabling rapid charging of interconnect capacitances; and (c) threshold voltages are tied to built-in potentials of p-n junctions, which are easy to reproduce device-to-device, enabling accurate logic voltages to be established. Added advantages result from using III-V heterojunctions rather than Si: (a) high electron mobility; (b) pronounced transient electron velocity overshoot effects; (c) ability to incorporate quasi-electric fields into the devices by semiconductor composition variations; and (d) ability to insure adequate emitter efficiency with wide gap emitters. As a result of these advantages, HBTs offer prospects for switching time delays in the sub 10 pS regime, with a robust, manufacturable fabrication process.

© 1985 Optical Society of America