Arrays of high-aspect-ratio germanium nanostructures with nanoscale pitch and methods for the fabrication thereof
Methods for fabricating thin, high-aspect-ratio Ge nanostructures from high-quality, single-crystalline Ge substrates are provided. Also provided are grating structures made using the methods. The methods utilize a thin layer of graphene between a surface of a Ge substrate, and an overlying resist layer. The graphene passivates the surface, preventing the formation of water-soluble native Ge oxides that can result in the lift-off of the resist during the development of the resist.
1. A method for patterning a substrate comprising germanium, the method comprising:
providing a structure comprising:
the substrate comprising germanium; and
a passivating layer of graphene over a surface of the substrate;
applying a resist layer comprising a photoresist or an electron beam resist over the passivating layer of graphene, such that the passivating layer of graphene is disposed between the substrate and the resist layer;
forming a pattern in the resist layer;
transferring the pattern from the resist layer into the passivating layer of graphene;
transferring the pattern from the passivating layer of graphene into the substrate to form a patterned substrate; and
removing the resist layer.
2. The method of claim 1 , wherein the substrate is a doped or undoped germanium substrate.
3. The method of claim 2 further comprising removing the passivating layer of graphene from the patterned substrate.
4. The method of claim 2 , wherein the resist layer is not removed prior to transferring the pattern from the passivating layer of graphene into the doped or undoped germanium substrate.
5. The method of claim 2 , wherein the resist layer is removed prior to transferring the pattern from the passivating layer of graphene into the doped or undoped germanium substrate.
6. The method of claim 2 , wherein the pattern from the passivating layer of graphene is transferred into the doped or undoped germanium substrate by low-energy electron enhanced etching.
7. The method of claim 2 , wherein the patterned substrate comprises a plurality of germanium fins.
8. The method of claim 7 , wherein the germanium fins have widths in the range from 5 nm to 50 nm and aspect ratios in the range from 5 to 10.
9. The method of claim 2 , wherein the step of providing a structure comprising:
the substrate comprising germanium; and a passivating layer of graphene over a surface of the substrate comprises growing a passivating layer of graphene directly on the surface of the substrate at a temperature at which native germanium oxide is removed from the surface.
10. The method of claim 2 , wherein the step of providing a structure comprising:
the substrate comprising germanium; and a passivating layer of graphene over a surface of the substrate comprises removing native germanium oxide from the surface of the substrate and transferring a passivating layer of graphene onto the surface of the substrate from which the native germanium oxide has been removed.
11. The method of claim 7 , wherein the germanium fins are arranged in parallel on the surface of the substrate.
12. The method of claim 7 , wherein the germanium fins have widths of less than 40 nm and aspect ratios of at least 6.
13. The method of claim 7 , wherein the germanium fins have a pitch of 100 nm or less.
14. The method of claim 13 , wherein the germanium fins have a pitch in the range from 20 nm to 100 nm.
15. The method of claim 7 comprising at least ten germanium fins.
16. The method of claim 15 , wherein the germanium fins have widths in the range from 10 nm to 50 nm.