Patent ID: 8178946

Claim:
A heterojunction bipolar transistor (HBT) having an emitter, a base, and a collector, the base comprising: a first semiconductor layer coupled to the collector, the first semiconductor layer having a first bandgap between a first conduction band and a first valence band; and at least two layer groups coupled between the emitter and the first semiconductor layer, each semiconductor layer group comprising: a second semiconductor layer having a second bandgap between a second conduction band and a second valence band, wherein the second valence band is higher than the first valence band and wherein the second bandgap is less than the first bandgap; and a third semiconductor layer coupled to the second semiconductor layer and having a third bandgap between a third conduction band and a third valence band; wherein each of the third valence bands is lower than each of the second valence bands and wherein the third bandgap is greater than the second bandgap; and wherein one of the third semiconductor layers is coupled to the emitter and one of the second semiconductor layers is coupled to the first semiconductor layer.