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Misfit Dislocation Superlattice Production

IP.com Disclosure Number: IPCOM000062381D
Original Publication Date: 1986-Nov-01
Included in the Prior Art Database: 2005-Mar-09
Document File: 3 page(s) / 47K

Publishing Venue

IBM

Related People

Kaplan, SB: AUTHOR [+4]

Abstract

A semiconductor superlattice is produced by using lattice misfit dislocations in epitaxial layers in order to form a mask. Misfits have been formed, for example, in GaInAs/GaAs MBE (molecular beam epitaxy) layers with an average spacing as small as 40 nm. In order to form a periodic array of such dislocations, a dislocation-free single-crystal substrate is employed so that there are no pinning sites for the misfit dislocations. A second material with the same crystal structure but a different lattice constant, i.e., with a lattice mismatch, is then grown epitaxially on top of the first to a thickness great enough that the elastic stress is relieved by the generation of misfit dislocations. The array of misfit dislocations will be square and regularly spaced in both directions after moderate annealing.

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Misfit Dislocation Superlattice Production

A semiconductor superlattice is produced by using lattice misfit dislocations in epitaxial layers in order to form a mask. Misfits have been formed, for example, in GaInAs/GaAs MBE (molecular beam epitaxy) layers with an average spacing as small as 40 nm. In order to form a periodic array of such dislocations, a dislocation-free single-crystal substrate is employed so that there are no pinning sites for the misfit dislocations. A second material with the same crystal structure but a different lattice constant, i.e., with a lattice mismatch, is then grown epitaxially on top of the first to a thickness great enough that the elastic stress is relieved by the generation of misfit dislocations. The array of misfit dislocations will be square and regularly spaced in both directions after moderate annealing. The spacing between dislocations is just that required to match the effective lattice constant of the overlayer to the substrate, and thus it will be inversely proportional to the degree of lattice mismatch. A 1% mismatch will result in a period of 100 atomic spacings, which is well within the capacity of the art. Mismatches as great as 10% and less than 0.01% are obtainable. The layers thus obtained are then used as a mask to selectively pass ions, atoms or electrons. These will channel through the layer structure in the regions near the midlines between dislocations and not in the regions near the dislocations themselves. This is because the two crystal lattices are in register along the midlines and out of register around the dislocations. If a well-collimated beam of electrons, ions or atoms impinges on the dislocated layer at normal incidence, then they will pass out the bottom in a square array replicating the dislocation array. However, if the beam is tilted off normal in the direction of one of the two sets of dislocation lines, then the electrons, ions or atoms will pass only in the lines of that set. These arrays of lines of channelled particles may be used either to dope a semiconductor substrate themselves or to produce a second mask by exposing a photoresist or ablating any convenient material. In Fig. 1, the production of a reusable mask that can be used to expose photoresist is illustrated...