The patent badge is an abbreviated version of the USPTO patent document. The patent badge does contain a link to the full patent document.
The patent badge is an abbreviated version of the USPTO patent document. The patent badge covers the following: Patent number, Date patent was issued, Date patent was filed, Title of the patent, Applicant, Inventor, Assignee, Attorney firm, Primary examiner, Assistant examiner, CPCs, and Abstract. The patent badge does contain a link to the full patent document (in Adobe Acrobat format, aka pdf). To download or print any patent click here.
Patent No.:
Date of Patent:
Mar. 12, 2002
Filed:
Jul. 21, 1999
Takaki Niwa, Tokyo, JP;
NEC Corporation, Tokyo, JP;
Abstract
A heterojunction bipolar transistor having reduced parasitic emitter resistance. The bipolar transistor comprises a semi-insulating substrate, a collector contact layer formed on the semi-insulating substrate, a collector layer formed on the collector contact layer, a base layer formed on the collector layer, an emitter layer formed on the base layer, a composition graded layer formed on the emitter layer, and an emitter contact layer formed on the composition graded layer. A forbidden band width of the emitter layer is wider than that of the base layer. A forbidden band width of the emitter contact layer is narrower than that of the emitter layer and impurity concentration of the emitter contact layer is higher than that of the emitter layer. Composition of the composition graded layer is inclined so as to avoid discontinuity of conduction band or valence band at the interface between the composition graded layer and the emitter layer and at the interface between the composition graded layer and the emitter contact layer, and impurity concentration of the composition graded layer is higher than that of the emitter layer.