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US 5,659,187 AGranted
Low defect density/arbitrary lattice constant heteroepitaxial layers
AssigneeInternational Business Machines Corporation
InventorsFrancoise Kolmer Legoues, Bernard Steele Meyerson
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Abstract
A multi-layered structure and process for forming it are described, incorporating a single crystal substrate, a plurality of epitaxial layers having graded composition wherein the layers have changing lattice spacings not exceeding about 2 percent per 1000 .ANG. of thickness whereby misfit dislocations are formed to relieve strain and then move to the edges of respective layers. The invention overcomes the problem of large numbers of misfit dislocations threading to the surface of the top layer, especially during device processing at temperatures in a range from 700 to 900 degrees Celsius. Fully relaxed, incommensurate structures having low defect densities are obtained, where arbitrary combinations of materials can be used.
Claims74
A multilayered material having a low defect top layer comprising:
- a single crystalline substrate of a first element having a first set of one or more lattice parameters corresponding to the spacing of atoms in one or more directions, and a plurality of epitaxial layers of said first element and a second element of the form A.sub.x B.sub.1-x, each said layer having substantially constant composition, each said layer having a thickness in the range from 5 atoms to less than the critical thickness of said layer, said composition of said first and second elements in a selected number of said plurality of layer selected to change from layer to layer one or more lattice parameters corresponding to the spacing of atoms in one or more directions in the range from about 0.025 to about 2 percent per 1000 Angstroms of thickness, one or more layers below said top layer of said plurality of layers having misfit dislocations to relieve strain therein, said top layer being single crystal and incommensurate with respect to layers below said one or more layers, said incommensurate single crystal top layer having less than 1.times.10.sup.5 threading defects/cm.sup.2.
A multilayered material having a low defect top layer comprising:
- a plurality of substantially single crystal layers having a plurality of respective lattice spacings, said respective lattice spacings changing less than 2 percent per 1000 Angstroms of thickness whereby misfit dislocations forming in one ore more layers below a top layer of said plurality of layers do not bunch at one crystalline plane but are spread over the thickness of said one or more layers, allowing some of the threading parts of said misfit dislocations to move to the edges of said plurality of layers, said top layer being single crystal and incommensurate with respect to layers below said one or more layers, said incommensurate single crystal top layer having less than 1.times.10.sup.5 threading defects/cm.sup.2.
A multilayered material having a low defect layer comprising:
- a single crystal substrate,
- a plurality of lattice matched layers formed on said single crystal substrate, each of said layers having an associated relaxed lattice parameter at times there is no strain in said layer, said relaxed lattice parameter mismatched with that of the adjacent layer by less than about 2 percent per 1000 Angstroms of the thickness of said plurality of layers to provide a strained commensurate layer,
- an upper layer converted into a fully relaxed incommensurate layer having a defect density less than 1.times.10.sup.5 threading defects/cm.sup.2, said fully relaxed incommensurate layer due to the generation of misfit dislocations being more or less uniformly distributed in said plurality of layers having lattice parameter mismatch with that of an adjacent layer, and wherein greater than 99 percent of said misfit dislocations move in said respective layers at times during growth or formation of subsequent layers.
A semiconductor laser medium for generating coherent radiation comprising:
- a single crystal substrate having a first set of lattice parameters corresponding to the spacing of atoms in one or more directions,
- a first plurality of layers having a respective selected composition to provide a changing lattice parameter from said first set of lattice parameters to a second set of lattice parameters on the upper surface of said first plurality of layers,
- said composition of each layer being selected to limit the change of one or more of said lattice parameters in said first plurality of layers in the range from about 0.025 to about 2 percent per 1000 Angstroms thickness,
- an upper layer of said first plurality of layers being single crystal and incommensurate with respect to said substrate, said incommensurate single crystal upper layer having less than 1.times.10.sup.5 threading defects/cm.sup.2,
- a second plurality of atomically thin layers, formed on said upper layer of said first plurality of layers, having alternating composition from a first element to a second element, said thickness of said second plurality of atomically thin layers selected to provide a combined composition of said first and second elements to generate a structure where one of its lattice constants correspond to a predetermined third lattice parameter, said third lattice parameter with 1 percent of one said second set of lattice parameters, several of said layers of said second plurality of atomically thin layers being less than 10 atoms thick whereby zone folding of the bandgap occurs to provide a direct bandgap laser medium.
2 more elements
A structure to provide a second epitaxial layer of a second material comprising:
- a single crystalline substrate of a first material having a first set of lattice parameters corresponding to the spacing of atoms in one or more directions,
- a first epitaxial layer positioned on said single crystalline substrate having a lower surface with a selected composition of the form A.sub.x B.sub.1-x, where A and B are elements, to provide a second set of lattice parameters at said lower surface, said second set of lattice parameters corresponding to the spacing of atoms in one or more directions and matching said first set of lattice parameters,
- said first epitaxial layer having a changing concentration profile as a function of height in said first epitaxial layer to provide a third set of lattice parameters corresponding to the spacing of atoms in one or more directions at the upper surface of said first epitaxial layer,
- said changing concentration profile being adjusted to limit the change of lattice parameters in the range from about 0.025 to 2 percent per 1,000 Angstroms of layer thickness,
- said upper surface of said first epitaxial layer being single crystal and incommensurate with respect to said substrate, said upper surface having less than 1.times.10.sup.5 threading defects/cm.sup.2, and
- a second epitaxial layer of said second material being formed on said upper surface and having a fourth set of lattice parameters.
3 more elements
A structure including, in combination:
- a single crystalline substrate of a first set of lattice parameters corresponding to the spacing of atoms in one or more directions,
- a first epitaxial layer of a graded composition, said composition changing such that the lattice parameters of said first epitaxial layer change from those of said single crystalline substrate to a desired second set of lattice parameters corresponding to the spacing of atoms in one or more directions,
- a second epitaxial layer of substantially constant composition on said first epitaxial layer, said second epitaxial layer having a set of equilibrium lattice parameters equivalent to said second set of lattice parameters, said second epitaxial layer being of sufficient thickness to fully relax to its equilibrium, strain-free set of lattice parameters, and
- wherein the grading of composition of said first epitaxial layer occurs at a rate sufficient to ensure that misfit dislocations will nucleate and migrate to relieve stress in said first epitaxial layer at times said second layer is formed, the upper surface of said first epitaxial layer being single crystal and incommensurate with respect to said single crystalline substrate, said upper surface of said first epitaxial layer having less than 1.times.10.sup.5 threading defects/cm.sup.2.
1 more element
A semiconductor waveguide for passing predetermined wavelengths of radiant energy comprising:
- a single crystal substrate having a first set of lattice parameters corresponding to the spacing of atoms in one or more directions,
- a first epitaxially formed layer having a graded composition to provide one or more changing lattice parameters from said first set of lattice parameters to a second set of lattice parameters on the upper surface of said layer,
- said graded composition adjusted to limit the change of one or more of said lattice parameters in said plurality of layers in the range of 0.025 to 2 percent per 1000 Angstroms thickness,
- said upper surface of said first epitaxially formed layer being single crystal and incommensurate with respect to said single crystal substrate, said upper surface of said first epitaxially formed layer having less than 1.times.10.sup.5 threading defects/cm.sup.2,
- a second layer epitaxially formed on said upper surface of said first layer,
- a third layer epitaxially formed on the upper surface of said second layer,
- said third layer includes material selected to be transmissive to said predetermined wavelengths of radiant energy and having a third set of lattice parameters,
- said second set of lattice parameters on the upper surface of said first layer corresponding to within 1 percent of said respective third set of lattice parameters.
5 more elements
A structure including
- a crystalline substrate having a first lattice parameter,
- a first epitaxial layer thereon, said epitaxial layer having a lattice parameter graded along a direction perpendicular to a plane of said substrate, said grading being at an average rate whereby misfit dislocations do not bunch at a crystalline plane in said first epitaxial layer, said misfit dislocations spreading over the thickness of said first epitaxial layer,
- wherein the surface region of said first epitaxial layer is incommensurate with respect to said crystalline substrate and has a dislocation defect density less than about 10.sup.5 /cm.sup.2.
Dependencies are inferred from the claim text.