Patent ID: 7115918

Claim:
An indium phosphide-based semiconductor double hetero-structure bipolar transistor comprising: an emitter region having a first bandgap; a base region in electrical communication with the emitter region, the base region having a second bandgap different from the first bandgap; a collector region containing indium and phosphorous and in electrical communication with the base and the emitter regions, the collector region having a third bandgap different from the second bandgap, the collector region containing at least three layers having different carrier concentrations; and a sub-collector in electrical communication with the collector region, wherein the collector region comprises a first layer, a second layer adjacent to the first layer that has a lowest carrier concentration of the three layers, and a third layer adjacent to the second layer that has a highest carrier concentration of the three layers, and the first layer is closer to the sub-collector than either the second or third layers.