HALTING CHROMIUM MIGRATION IN GaAs DEVICES
Original Publication Date: 1984-Dec-01
Included in the Prior Art Database: 2005-Feb-06
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.