Bipolar transistor device having phosphorous

摘要

A Si_1-xGe_x layer 111 b functioning as the base composed of an i-Si_1-xGe_x layer and a p⁺ Si_1-xGe_x layer is formed on a collector layer 102 , and a Si cap layer 111 a as the emitter is formed on the p⁺ Si_1-xGe_x layer. An emitter lead electrode 129 , which is composed of an n^- polysilicon layer 129 b containing phosphorus in a concentration equal to or lower than the solid-solubility limit for single-crystal silicon and a n⁺ polysilicon layer 129 a containing phosphorus in a high concentration, is formed on the Si cap layer 111 a in a base opening 118 . The impurity concentration distribution in the base layer is properly maintained by suppressing the Si cap layer 111 a from being doped with phosphorus (P) in an excessively high concentration. The upper portion of the Si cap layer 111 a may contain a p-type impurity. The p-type impurity concentration distribution in the base layer of an NPN bipolar transistor is thus properly maintained.