Axially-integrated epitaxially-grown tandem wire arrays
A photoelectrode, methods of making and using, including systems for water-splitting are provided. The photoelectrode can be a semiconducting material having a photocatalyst such as nickel or nickel-molybdenum coated on the material. The photoelectrode includes an elongated axially integrated wire having at least two different wire compositions.
1. A method of making a nano- or micro-wire, comprising:
(a) fabricating a first junction structure on an Si substrate comprising
(i) forming a templated oxide layer on the Si substrate, wherein the templated oxide layer comprises an opening therein for the formation of the first junction structure; and
(ii) growing the first junction structure on the substrate, wherein the growth of the first junction structure is supported by a catalyst deposited in the opening in the templated oxide layer;
(b) encapsulating the fabricated first junction structure in a passivation layer;
(c) etching the passivation layer at an end of the first junction structure, to remove the catalyst and an end portion of the first junction structure such that a hollow tube of the passivation layer extends above the first junction structure;
(d) depositing an ohmic contact layer on the first junction structure in the hollow tube; and
(e) growing a second junction structure on the ohmic contact layer in the hollow tube to form the nano- or micro-wire comprising an axially integrated junction.
2. The method of claim 1 , wherein the passivation layer comprises SiO 2 , Si 3 N 4 , SiO x N y or amorphous Si and wherein the encapsulating of (b) comprises depositing the passivation layer on the first junction structure.
3. The method of claim 1 , wherein the second junction structure is grown by a metal-organic chemical vapor deposition (MOCVD) system or a molecular beam epitaxy (MBE) system.
4. The method of claim 1 , wherein the ohmic contact layer comprises a semiconducting material.
5. The method of claim 4 , wherein the semiconducting material comprises a material selected from the group consisting of GaAs, GaP, GaAs x P 1-x , Al x Ga 1-x , As, Al x Ga 1-x As y P 1-y , In x Ga 1-x As, In x Ga 1-x P, In x Ga 1-x As y P 1-y , As y P 1-y , Al x In 1-x As y P 1-y , Al x Ga 1-x As y N z P 1-y-z , Zn 3 P 2 , Zn 3 S 2 , and ZnP x S 1-x (0≤x≤1, 0≤y≤1, 0≤z≤1, 0≤y+z≤1).
6. The method of claim 5 , wherein the second junction structure comprise GaAs y P 1-y (0≤y≤1).
7. The method of claim 4 , wherein the ohmic contact layer comprises a tunnel junction or a tunnel junction and a graded composition segment.
8. The method of claim 1 , further comprising substantially embedding the nano- or micro-wire in a wax, glass or polymer.
9. The method of claim 8 , wherein the embedded nano- or micro-wire is mechanically removed from the Si substrate.
10. The method of claim 9 , further comprising applying a hydrogen evolving and/or oxygen evolving catalyst to the nano- or micro-wire.
11. The method according to claim 10 , wherein the hydrogen evolving and/or oxygen evolving catalyst is selected from the group consisting of Pt, Co, Cu, Fe, MoS x where x is nominally 2, or a sub or super-stoichiometric, Ni, CoMo, CoW, FeMo, NiCo, NiFe, NiFeC, NiFeS, NiMnS, NiMo, NiMoP, NiSn, NiW, NiZn, NiZnP, CoNiFe, NiCoPMo, NiMoCo, NiMoCu, NiMoFe, NiMoW, NiSiMo, NiSiW, NiWPCu, IrO x where x is nominally 2, or sub or super-stoichiometric, Pt, Co, Co/(PO 4 ) 3− , Co/(BO 3 ) 3− , CoP, Cu, Fe, Mn, Ni, Ni/(BO 3 ) 3− , NiP, Pb, CoFe, CoPSc 2 O 3 , FeMn, NiCo, NiCr, NiCu, NiFe, NiLa, NiLa, NiPSc 2 O 3 , NiSn, NiZn and NiMoFe.