ABSTRACT
The concept of bandgap engineering has been used for many years in compound semiconductors such as gallium arsenide (GaAs) and indium phosphide (InP) to realize a host of novel electronic devices. A bandgap-engineered transistor is compositionally altered in a manner that improves a specific device metric (e.g., speed). A transistor designer might choose, for instance, to make a bipolar transistor that has a GaAs base and collector region, but which also has a AlGaAs emitter. Such a device has electrical properties that are inherently superior to what could be achieved using a single semiconductor. In addition to simply combining two different materials (e.g., AlGaAs and GaAs), bandgap engineering often involves compositional grading of materials within a device. For instance, one might choose to vary the Al content in an AlGaAs/GaAs transistor from a mole fraction of 0.4 to 0.6 across a given distance within the emitter.
