Patent ID: 7038256
Filing Date: 2006-05-02
Classification: H01L

Abstract:
1. A heterojunction bipolar transistor structure, comprising: a substrate; a semiconductor collector layer formed over the substrate; a semiconductor base layer formed over the collector layer; and a semiconductor emitter layer formed over the base layer; wherein a base-emitter heterojunction is formed between the base layer and the emitter layer, and a base-collector heterojunction is formed between the base layer and the collector layer; wherein the structure has a bandgap profile defined by a conduction band edge and a valence band edge; wherein the bandgap profile when the base layer, emitter layer and collector layer are considered isolated makes an abrupt transition at the base-emitter heterojunction and at the base-collector heterojunction, and the abrupt transition is in each case defined by an abrupt transition in the valence band edge but not in the conduction band edge; and wherein the bandgap profile when the structure layers are considered to be joined, provides for a reduced base-emitter turn-on voltage and no electron trapping at the base-collector heterojunction.