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Ohmic Contact Technique for N Type GaAs, GaAsP, and GaAlAs

IP.com Disclosure Number: IPCOM000080866D
Original Publication Date: 1974-Feb-01
Included in the Prior Art Database: 2005-Feb-27
Document File: 1 page(s) / 12K

Publishing Venue

IBM

Related People

Rideout, VL: AUTHOR

Abstract

An improvement in the ohmic contact technique for N-type gallium arsenide wafers shown in U.S. Patent #3,386,867, issued June 4, 1968, in the name of J.L. Staples is described.

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Ohmic Contact Technique for N Type GaAs, GaAsP, and GaAlAs

An improvement in the ohmic contact technique for N-type gallium arsenide wafers shown in U.S. Patent #3,386,867, issued June 4, 1968, in the name of J.L. Staples is described.

When alloyed with gallium arsenide wafers, a layer of gold (88 wt. %) and germanium (12 wt. %) eutectic mixture gives a low-resistance ohmic contact. A major problem arises, however, in that the wetting action of this eutectic mixture is poor and hence it tends to coalesce or form into globules, causing a nonuniform contact surface. Staples discovered that adding nickel to the eutectic gold and germanium mixture yields a uniform contact surface.

In the patent, germenium (approx. 11 wt. %), gold (approx. 84 wt. %) and nickel (approx. 5 wt. %) are coevaporated from a resistance heated source in a vacuum chamber. The different melting points of the three materials insure that the layer sequence will be first germanium, then gold, and finally nickel. A fabrication shortcoming is that the entire charge must be evaporated to dryness to insure stoichiometry. Furthermore, the thicknesses of the layers are determined by the amounts of material used. Such an approach is not well suited to mass production, because the charge must be carefully weighed and replenished after each evaporation. Sequential evaporation of the materials by the well-controlled electron-beam evaporation technique would appear to offer a solution, but nickel is very difficult to evaporate uniformly with an electron beam.

It is disclosed here that p...