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Eliminating a High Concentration of Dislocations Disclosure Number: IPCOM000077962D
Original Publication Date: 1972-Oct-01
Included in the Prior Art Database: 2005-Feb-25
Document File: 2 page(s) / 31K

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Matthews, JW: AUTHOR


A. Removal of a high density of dislocations from large crystals

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Eliminating a High Concentration of Dislocations

A. Removal of a high density of dislocations from large crystals

The crystal of Fig. 1 is necked during its growth. Coincident with the neck is a change in composition that extends over a small length h. This change in composition has associated with it a change in lattice parameter of whose maximum value is approx.< 0.005. If the neck has radius R then the maximum dislocation density which can be removed is

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which is an order of magnitude larger than the value for an unnecked crystal approx. 1 cm in diameter.

The choice of growth direction or of the plane of the interface in the neck is important. It must be such as to remove all dislocations. For fee materials which slip on (111) <110>, this direction is near <210>. B. Removal of Dislocations from Doped Regions

The method can be applied to small doped regions of semiconductors.

The method is illustrated in Fig. 2 which shows a small doped region of radius R and depth h. The doped crystal is under stress, because its unstrained lattice parameter differs from that of the undoped substrate. This stress exerts a force on dislocations which happen to thread the doped portion. They move under the influence of this stress to the edges of the doped volume. If R = 10 mu m, f = 10/-5/, which is the sort of misfit generated by the addition of dopants, and b = 4 Angstroms and cos lambda = 1 over 2, then rho(max) == 10/6/ per cm/2/. The density which can be rem...