Hetero-junction bipolar transistor.

摘要

An object of the present invention is to suppress the surface recombination over the whole area of the external base of a hetero-junction bipolar transistor (HBT), to keep the current gain large, and to reduce the base contact resistance. The HBT of the invention has, as a surface protective film layer, a p-type semiconductor layer which has the higher portential of the energy conduction band than the base layer on an external base outside the junction between the mesa of the n-type emitter layer and the p-type base layer, and a base electrode thereon. Preferably, it has as a base contact layer a p-type semiconductor layer which shows reduced contact resistance with the base electrode on the surface protective layer comprising a p-type semiconductor layer. More preferabiy, it has a structure wherein a base electrode is formed on the base contact layer in contact with the projection part of the emitter electrode to the base contact layers A method of producing this HBT comprises at least the steps of forming an emitter mask on the portion to be an emitter on a multi-layer structure material having an n-type semiconductor layer for forming a collector, a p-type semiconductor layer or forming a base, and an n-type semiconductor layer for forming an emitter in this order from the substrate, and etching by using the emitter mask to form an emitter mesa and to expose a base layer; epitaxially forming as a surface protective film layer a p-type semiconductor layer which show the higher potential of the energy conduction band than the base layer on the external base outside the junction part between the emitter mesa and the base layer by using the emitter mask; and epitaxially forming a base electrode on the p-type surface protective film layer.