Method of fabricating low-dislocation-density epitaxially-grown films with textured surfaces
View Patent ↗A method for forming a surface-textured single-crystal film layer by growing the film atop a layer of microparticles on a substrate and subsequently selectively etching away the microparticles to release the surface-textured single-crystal film layer from the substrate. This method is applicable to a very wide variety of substrates and films. In some embodiments, the film is an epitaxial film that has been grown in crystallographic alignment with respect to a crystalline substrate.
1. A method for preparing a surface-textured single-crystal film layer, the method comprising:
preparing a layered structure comprising a substrate with a crystalline surface, a layer of microparticles atop the substrate; and a single-crystal film layer atop the layer of microparticles, wherein the single-crystal film layer is connected epitaxially to the crystalline surface of the substrate;
selectively etching the microparticles using an etchant that etches the microparticles sufficiently rapidly to substantially etch away the solid interface between the microparticles and at least one of the substrate and the single-crystal film layer while not substantially etching the single-crystal film layer; and
releasing the single-crystal film layer from the substrate when a sufficient amount of the microparticles have been etched away, wherein the single-crystal film layer that has been released is the surface-textured single-crystal film layer.
2. The method of claim 1 , wherein the step of preparing the layered structure further comprises
applying at least one monolayer of spheroidal particles to the substrate comprising a base substrate and a first layer of growth material, the at least one monolayer having interstices between the spheroidal particles oriented to permit access of reactant gases to the first layer of growth material;
initiating growth of a second layer of growth material at sites on the first layer of growth material that are exposed to reactant gases through the interstices;
growing the growth material through the interstices;
terminating adjacent to the spheroidal particles a plurality of threading dislocations propagating through the growth material; and
coalescing the growth material growing through adjacent interstices to form the single-crystal film layer comprising the second layer of growth material with reduced dislocation density atop the at least one monolayer of spheroidal particles.
3. The method of claim 2 , wherein the step of applying the at least one monolayer of spheroidal particles comprises the steps of
preparing the monolayer of spheroidal particles using a Langmuir Blodgett technique; and
applying the monolayer of spheroidal particles to the first layer of growth material using a Langmuir Blodgett coating technique.
4. The method of claim 2 , wherein the step of applying the at least one monolayer of spheroidal particles comprises applying a suspension of spheroidal particles to the substrate by a spin-coating technique or a drop-coating technique.
5. The method of claim 2 , wherein the monolayer consists of spheroidal particles arranged substantially in a close-packed geometry.
6. The method of claim 2 , wherein the spheroidal particles comprise a material selected from the group consisting of silicon dioxide, silicon nitride, silicon oxynitride Al 2 O 3 , TiO 2 , ZrO 2 , Fe 3 O 4 , ZrHfO 4 , ZrHfO 4 , CaCO 3 , and glass.
7. The method of claim 2 , wherein the step of growing the growth material through the interstices at least in part employs reaction conditions that form faceted structures suitable for promoting redirection of threading dislocations away from a vertical propagation direction.
8. The method of claim 7 , wherein the step of coalescing the growth material employs reaction conditions that promote lateral growth of the growth material.
9. The method of claim 2 , wherein at least one of a carrier gas and the reactant gas inhibits nucleation and growth of the growth material directly on the spheroidal particles.
10. The method of claim 2 , wherein the spheroidal particles have a diameter greater than approximately 100 nm and less than approximately 100 micrometers.
11. The method of claim 2 , wherein the growth material is a Group III nitride.
12. The method of claim 2 , wherein the steps of initiating growth, growing the growth material, terminating the plurality of threading dislocations, and coalescing the growth materials are performed in a chemical vapor deposition reactor or a hydride vapor phase reactor.
13. The method of claim 1 , wherein a texture of the surface-textured single-crystal film layer comprises an array of concavities of substantially inverse spherical profile.
14. The method of claim 1 , wherein the single-crystal film layer is a compound semiconductor material selected from the group consisting of GaN, InGaN, AlGaN, AlInGaN, ternary Group III nitrides, quaternary Group III nitrides, InP, GaAs, InAs, AlAs, ternary Group III arsenides, quaternary Group III arsenides, SiGe, ZnO, and III-VI semiconductors.
15. The method of claim 1 , wherein the layer of microparticles comprises at plurality of monolayers of microparticles.
16. The method of claim 1 , wherein the layer of microparticles comprise silica microparticles and the etchant is comprises at least one of an HF solution, a buffered oxide etching solution, a KOH solution, and SF 6 .
17. The method of claim 1 , further comprising at least one of etching and polishing the single-crystal film layer.
18. The method of claim 1 , wherein the single crystal film layer is a Group III nitride and the microparticles are silica microparticles.