Abstract: Heterojunction bipolar transistors (130) with bases (138) including an etch stop element are disclosed. The preferred embodiment devices have Al.sub.z Ga.sub.1-z As emitters (140) and GaAs collectors (136) and bases (138) with In.sub.y Ga.sub.1-y As added to the bases (138) to stop chloride plasma etches.

Abstract: A new kind of electronic logic circuit, wherein potential wells (e.g. islands of GaAs in an AlGaAs lattice) are made small enough that the energy levels of carriers within the wells are discretely quantized. This means that, when the bias between the wells is adjusted to align energy levels of the two wells, tunneling will occur very rapidly, whereas when the energy levels are not aligned, tunneling will be greatly reduced. In particular, the wells are optimized to have sharp enough resonant tunneling peaks that the change in potential caused by the difference between the number of carriers stored between two adjacent tunnel wells is itself enough to permit or preclude resonant tunneling. Thus, a tremendous variety of logic functions, including all primitive Boolean functions can be embodied in this logic.