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Reach-Through Contact for Heterojunction Structures

IP.com Disclosure Number: IPCOM000062184D
Original Publication Date: 1986-Oct-01
Included in the Prior Art Database: 2005-Mar-09
Document File: 2 page(s) / 59K

Publishing Venue

IBM

Related People

Jackson, TN: AUTHOR [+4]

Abstract

The contact is formed using an alloy of a metal with a small percentage of an impurity ingredient that, when the alloy is fused with semiconductor material of the heterojunction structure, the metal forms an alloy with one ingredient thereof and the impurity diffuses in snowplow fashion into the heterojunction structure. As an illustration, this is accomplished using, for example, a Pd-Mg alloy in which the Mg concentration is 2% or less. When a thin film of this alloy is deposited on GaAs and heated to 500ŒC, it is converted to PdGa. The Mg diffuses/snowplows into GaAs at the interface, producing a p+ doped layer of GaAs. Since PdGa is a nearly stoichiometric compound, this reaction is very controllable.

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Reach-Through Contact for Heterojunction Structures

The contact is formed using an alloy of a metal with a small percentage of an impurity ingredient that, when the alloy is fused with semiconductor material of the heterojunction structure, the metal forms an alloy with one ingredient thereof and the impurity diffuses in snowplow fashion into the heterojunction structure. As an illustration, this is accomplished using, for example, a Pd-Mg alloy in which the Mg concentration is 2% or less. When a thin film of this alloy is deposited on GaAs and heated to 500OEC, it is converted to PdGa. The Mg diffuses/snowplows into GaAs at the interface, producing a p+ doped layer of GaAs. Since PdGa is a nearly stoichiometric compound, this reaction is very controllable. For example, 100 nanometers (nm) of Pd will react with the GaAs and be converted to 140 nm of PdGa, with a thin p+ (Mg-doped) GaAs region immediately adjacent to the PdGa caused by snowplowing of the Mg out of the PdGa compound. The use of this material in contacting thin active device layers will be illustrated for the three cases: (1) heterojunction hot electron ("metal base") transistor base contact, (2) heterojunction bipolar transistor base contact, and (3) contact to a Modulation Doped Field-Effect Transistor (MODFET) 2D electron gas. (1) Hot electron transistor: In a metal base transistor, base losses, particularly those due to scattering at the base-collector interface, are reduced if the metal is replaced by an epitaxial semiconductor having a smaller bandgap than the emitter and collector (a double heterojunction structure). A critical problem in unipolar transistors of this type is the contact to the base region. This is particularly difficult because of the chemical similarity of the constituents, which makes it hard to etch into the thin base...