Patent ID: 7544577

Claim:
A method for enhancing carrier mobility in a heterojunction bipolar transistor that has a SiGe-containing base layer of not more than about 100 nm in thickness, while without changing quasi-static drift field of said base layer, comprising: measuring the thickness of said SiGe-containing base layer; calculating a critical germanium content based on the thickness of the SiGe-containing base layer, wherein the calculated critical germanium content of the SiGe-containing base layer is not less than about 10 atomic %; measuring germanium content in said SiGe-containing base layer to determine germanium content profile of said SiGe-containing base layer; and changing the germanium content profile of the SiGe-containing base layer, by uniformly increasing the germanium content in the SiGe-containing base layer by a sufficient amount so that the changed germanium content profile has an average germanium content of not less than about 80% of the calculated critical germanium content.