Compound semiconductor heterojunction bipolar transistor

Abstract

Generally, and in one form of the invention a method for making a heterojunction bipolar transistor comprising the steps of forming a compound semiconductor material structure comprised of a plurality of layers, wherein at least one of the plurality of layers is comprised of a first material (e.g. GaAs 36) and at least one of the remaining of the plurality of layers is comprised of a second material (e.g. AlGaAs 32); and etching the layers comprised of the first material with an etchant that does not appreciably etch the layers of the second material is disclosed. A surprising aspect of this invention is that no additional etch stop layer was added in the material structure. Etchants were found that stop on the wide band gap emitter layer (e.g. AlGaAs) usually found in heterojunction bipolar transistors despite the similarity of the materials. An advantage of this method is that a reference point for timing subsequent etches is established at a point other than the top of the uppermost of the layers, thereby improving the accuracy with which the depth of the subsequent etching can be controlled. Improved etch depth accuracy directly relates to more producible and higher yield heterojunction bipolar transistor devices. Other devices, systems, and methods are also disclosed.