Method of at least partially releasing an epitaxial layer
A method of at least partially releasing an epitaxial layer of a material from a substrate. The method comprises the steps of: forming a patterned sacrificial layer on the substrate such that the substrate is partially exposed and partially covered by the sacrificial layer; growing the epitaxial layer on the patterned sacrificial layer by nano-epitaxial lateral overgrowth such that the epitaxial layer is formed above an intermediate layer comprising the patterned sacrificial layer and said material; and selectively etching the patterned sacrificial layer such that the epitaxial layer is at least partially released from the substrate.
1. A method of at least partially releasing an epitaxial layer of a material from a substrate, the method comprising the steps of:
forming a patterned sacrificial layer on the substrate such that the substrate is partially exposed and partially covered by the sacrificial layer;
growing the epitaxial layer on the patterned sacrificial layer by nano-epitaxial lateral overgrowth such that the epitaxial layer is formed above an intermediate layer comprising the patterned sacrificial layer and said material; and
selectively etching the patterned sacrificial layer such that the epitaxial layer debonds from the substrate for lift-off.
2. The method as claimed in claim 1 , wherein the substrate comprises a template layer for promoting the nano-epitaxial overgrowth.
3. The method as claimed in claim 2 , wherein the patterned sacrificial layer is selectively etched such that the epitaxial layer debonds from the template layer for lift-off.
4. The method as claimed in claim 3 , wherein the epitaxial layer debonds at an interface between the template layer and nano-structures of said material formed on the template layer as part of the nano-epitaxial growth of the epitaxial layer.
5. The method as claimed in claim 2 , wherein the template layer and epitaxial layer comprises a Group III-V nitride; or a Group III-V nitride ternary or quaternary alloy.
6. The method as claimed in claim 5 , wherein the Group III-V nitride comprises one or more of a group consisting of aluminum nitride (AlN), gallium nitride (GaN), indium nitride (InN), aluminum gallium nitride (AlGaN) and indium gallium nitride (InGaN).
7. The method as claimed in claim 1 , wherein the substrate comprises one or more of a group consisting of silicon (Si), silicon carbide (SiC) and sapphire.
8. The method as claimed in claim 2 , wherein the template layer is formed by a method comprising one or more of a group consisting of metal-organic chemical vapor deposition (MOCVD), molecular beam epitaxy (MBE) or hydride vapour phase epitaxy (HVPE).
9. The method as claimed in claim 1 , wherein the patterned sacrificial layer is formed by a method comprising one or more of a group consisting of plasma enhanced chemical vapor deposition (PECVD), sputtering or spin-on glass.
10. The method as claimed in claim 1 , wherein the patterned sacrificial layer comprises one or more of a group consisting of silicon dioxide (SiO 2 ), silicon nitride (Si 3 N 4 ), and titanium oxide (TiO 2 ).
11. The method as claimed in claim 1 , wherein the patterned sacrificial layer is patterned by a method comprising one or more of a group consisting of nanoimprint lithography (NIL), use of anodized aluminum oxide (AAO) as an etch mask, electron beam lithography and interference lithography.
12. The method as claimed in claim 1 , wherein the nano-epitaxial lateral overgrowth is formed by a method comprising one or more of a group consisting of metal-organic chemical vapor deposition (MOCVD), molecular beam epitaxy (MBE) or hydride vapour phase epitaxy (HVPE).
13. The method as claimed in claim 1 , wherein the patterned sacrificial layer comprises a plurality of pores, dots or strips.
14. The method as claimed in claim 1 , further comprising, prior to etching the patterned sacrificial layer, forming trenches in the substrate to define mesa structures on the substrate, whereby etching of the patterned sacrificial layer in the regions of the mesa structures is facilitated.
15. The method as claimed in claim 1 , wherein the step of forming the patterned sacrificial layer comprises selecting a pattern based on desired optical characteristics of the lift-off epitaxial layer.
16. The method as claimed in claim 15 , wherein the pattern is selected to increase a surface roughness of the lift-off epitaxial layer.
17. The method as claimed in claim 15 , wherein the pattern is selected to provide a diffraction grating on a surface of the lift-off epitaxial layer.
18. A device comprising an epitaxial layer at least partially released using a method as claimed in claim 1 .
19. The device as claimed in claim 18 , comprising an LED structure, a Laser Diode or a High Electron Mobility Transistor.
20. A method of at least partially releasing an epitaxial layer of a material from a substrate, the method comprising the steps of:
forming a patterned sacrificial layer on the substrate such that the substrate is partially exposed and partially covered by the sacrificial layer;
growing the epitaxial layer on the patterned sacrificial layer by nano-epitaxial lateral overgrowth such that the epitaxial layer is formed above an intermediate layer comprising the patterned sacrificial layer and said material;
forming one or more holes in the epitaxial layer for entry of an etching agent to contact the patterned sacrificial layer; and
selectively etching the patterned sacrificial layer with the etching agent such that the epitaxial layer is at least partially released from the substrate.
21. The method as claimed in claim 20 , wherein the patterned sacrificial layer is selectively etched such that the epitaxial layer is undercut or such that a cavity is formed underneath the epitaxial layer.
22. The method as claimed in claim 20 , wherein the holes are formed as photonic holes for providing an optical cavity in the epitaxial layer.