Lattice-mismatched crystal structures and semiconductor device using the same
AssigneeHitachi, Ltd.
InventorsTomoyoshi Mishima, Katsuhiko Higuchi, Mitsuhiro Mori, Makoto Kudo, Chushiro Kusano
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Abstract
A semiconductor device has a lattice-mismatched crystal structure including a semiconductor film formed on a substrate with an intervening buffer layer. The buffer layer has a plurality of layers, including first sublayers, or regions, in which an element that controls the lattice constant is provided in increasing mole fraction, and second sublayers, or regions, in which the lattice constant is maintained. The first sublayers and second sublayers are provided in alternating fashion. The resulting device has an increased electron mobility as compared with the prior art.
Claims32
A lattice-mismatched crystal structure, comprising:
- a substrate crystal;
- a semiconductor buffer layer 1 .mu.m thick or less on the substrate crystal;
- and
- a semiconductor film having a lattice constant different from that of the substrate crystal in the direction parallel to a face of the substrate crystal;
- wherein the buffer layer includes a plurality of first regions and a plurality of second regions formed in multilayer, the lattice constants of the first regions in a direction parallel to the substrate crystal face increasing toward the semiconductor film in a layer stacking direction;
- wherein the first regions have a thickness sufficient to relax the lattice strain resulting from lattice mismatch with the substrate crystal;
- wherein the second regions are formed on and in contact with the semiconductor-film-side of respective ones of the first regions, the lattice constants of the second regions in the direction parallel to the substrate crystal face being constant in the layer stacking direction, and
- wherein the lattice constant of the buffer layer in the direction parallel to the substrate crystal face is continuous in the layer stacking direction.
A semiconductor wafer, comprising:
- a multilayer semiconductor layer on a substrate crystal;
- wherein the semiconductor layer includes a plurality of first regions and a plurality of second regions formed in multilayer in a layer stacking direction, the lattice constants of the first regions in the direction parallel to a face of the substrate crystal being different from that of the substrate crystal and increasing toward the semiconductor film crystal in the layer stacking direction;
- wherein the first regions have such a thickness as to relax the lattice strain resulting from the lattice mismatch with the substrate crystal;
- wherein the second regions are formed on and in contact with the opposite-to-the-substrate-crystal side of the first regions, the lattice constants of the second regions in the direction parallel to the substrate crystal face being constant in the layer stacking direction;
- and
- wherein the lattice constant of the semiconductor layer in the direction parallel to the substrate crystal face is continuous in the layer stacking direction.
A lattice-mismatched crystal structure, comprising:
- a substrate;
- a multilayered buffer layer including alternating sublayers, every other sublayer beginning with the sublayer contacting the substrate having a lattice strain-absorbing characteristic characterized by respective lattice constants that increase in a direction perpendicularly away from a plane of the substrate, and the other sublayers having a lattice-absorbing characteristic characterized by lattice constants that are each unchanging in the direction perpendicular to the plane of the substrate;
- and
- a plurality of layers formed on said buffer layer, each of said plurality of layers having a lattice constant that is different from a lattice constant of the substrate in a direction parallel to the substrate plane.
Dependencies are inferred from the claim text.