Abstract

The permeable base transistor (PBT) was conceived in 1979¹ and the first devices were fabricated shortly thereafter². Numerical simulations predicted usable gains in the EHF frequency range³ and high speed performance in a logic circuit⁴. A three-dimensional drawing of a GaAs PBT showing a cutaway region is shown in Figure 1. The unique feature of a PBT is the thin tungsten grating of submicrometer periodicity (3200 Angstroms in the devices we have fabricated) embedded in the single-crystal GaAs. The tungsten grating separates the emitter layer from the collector layer and forms the base of the transistor. Because the tungsten forms a Schottky barrier with the GaAs, the voltage on the metal can be used to control the current flowing from the collector the emitter. The critical length of the control region is determined by the metallization thickness and the depletion width around the tungsten. Hence it can be made quite short, giving rise to the PBT's high frequency and high speed properties. In the device of Figure 1 proton bombardment is used to isolate and define the device and to provide insulating regions on which to fabricate contact pads.

© 1985 Optical Society of America