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HALTING CHROMIUM MIGRATION IN GaAs DEVICES

IP.com Disclosure Number: IPCOM000044640D
Original Publication Date: 1984-Dec-01
Included in the Prior Art Database: 2005-Feb-06
Document File: 2 page(s) / 30K

Publishing Venue

IBM

Related People

Chang, CA: AUTHOR [+3]

Abstract

Cr+ ions are frequently used to make GaAs substrates electrically insulating. However, Cr+ is quite mobile and will permeate any epitaxial GaAs in the device. This makes the electrical characteristics of the epitaxial GaAs layer unpredictable. In order to halt Cr+ diffusion, a metal or oxide barrier is used. However, the presence of such a barrier creates problems of lattice mismatch in the epitaxial growth. This, in turn, invariably leads to defects in the device layer. To overcome this problem, a layer of epitaxially grown GaSb is used to halt Cr+ migration. GaSb has a 7.5% lattice mismatch with GaAs, but a defect-free GaAs layer can be obtained by the step-graded growth technique. This technique has been demonstrated for the InAs/GaAs system which has a comparable mismatch (7%). Reference is made to C.A.

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HALTING CHROMIUM MIGRATION IN GaAs DEVICES

Cr+ ions are frequently used to make GaAs substrates electrically insulating. However, Cr+ is quite mobile and will permeate any epitaxial GaAs in the device. This makes the electrical characteristics of the epitaxial GaAs layer unpredictable. In order to halt Cr+ diffusion, a metal or oxide barrier is used. However, the presence of such a barrier creates problems of lattice mismatch in the epitaxial growth. This, in turn, invariably leads to defects in the device layer. To overcome this problem, a layer of epitaxially grown GaSb is used to halt Cr+ migration. GaSb has a 7.5% lattice mismatch with GaAs, but a defect-free GaAs layer can be obtained by the step-graded growth technique. This technique has been demonstrated for the InAs/GaAs system which has a comparable mismatch (7%). Reference is made to C.A. Chang, et al, Appl. Phys. Lett. 39, 808 (1981); ibid, 37, 538 (1980); and C. A. Chang et al, J. Vac. Sci . Technol . 17, 603 (1980). In the fabrication of devices as illustrated in the figure, a thin layer of approximately 0.2-0.4 micron of GaSb is grown on Cr:GaAs. After this, a graded layer of GaSbxAsl-x is grown to a thickness of approximately 1 micron, to provide the defect-free surface on which the GaAs device layer can be fabricated.

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