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METAL-InAs CONTACT FOR VERTICAL HETEROJUNCTION TRANSISTORS

IP.com Disclosure Number: IPCOM000062161D
Original Publication Date: 1986-Oct-01
Included in the Prior Art Database: 2005-Mar-09
Document File: 2 page(s) / 43K

Publishing Venue

IBM

Related People

Jackson, TN: AUTHOR [+3]

Abstract

Unipolar transistors of the metal base type have long been of interest for high speed applications. Of particular interest recently are devices in which an epitaxial n++ semiconductor, such as InGaAs, replaces a metal for the base layer, in order to minimize base losses associated with scattering at the metal/semiconductor or base/collector interface. A contact structure is provided which makes selective low resistance contact to the thin base region. The contact structure is illustrated in Figs. 1, 2 and 3. The transistor type of interest (Fig. 1) consists of a InGaAs base sandwiched between two GaAs layers, which serve as emitter and collector. In Fig. 2, a detail of Fig. 1 is shown where a mesa, which defines the device, is etched so as to leave a sloping edge on which the various layers are exposed.

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METAL-InAs CONTACT FOR VERTICAL HETEROJUNCTION TRANSISTORS

Unipolar transistors of the metal base type have long been of interest for high speed applications. Of particular interest recently are devices in which an epitaxial n++ semiconductor, such as InGaAs, replaces a metal for the base layer, in order to minimize base losses associated with scattering at the metal/semiconductor or base/collector interface. A contact structure is provided which makes selective low resistance contact to the thin base region. The contact structure is illustrated in Figs. 1, 2 and 3. The transistor type of interest (Fig. 1) consists of a InGaAs base sandwiched between two GaAs layers, which serve as emitter and collector. In Fig. 2, a detail of Fig. 1 is shown where a mesa, which defines the device, is etched so as to leave a sloping edge on which the various layers are exposed. A metal is deposited over this edge which forms a Schottky barrier which has a typical N 0.8 electron volt barrier to GaAs. The barrier height to the InGaAs layer decreases with increasing In fraction. The In fraction in the base will be small, because the height of the emitter-base and base-collector barriers is determined by the GaAs-InGaAs composition difference, and this height should be kept relatively small. The composition of the base may be graded or stepped, to provide for differing barriers between the base and the emitter and collector. The unique feature is shown in Fig. 3 with the inclusion of...