Method of using a germanium layer transfer to Si for photovoltaic applications and heterostructure made thereby
Ge/Si and other nonsilicon film heterostructures are formed by hydrogen-induced exfoliation of the Ge film which is wafer bonded to a cheaper substrate, such as Si. A thin, single-crystal layer of Ge is transferred to Si substrate. The bond at the interface of the Ge/Si heterostructures is covalent to ensure good thermal contact, mechanical strength, and to enable the formation of an ohmic contact between the Si substrate and Ge layers. To accomplish this type of bond, hydrophobic wafer bonding is used, because as the invention demonstrates the hydrogen-surface-terminating species that facilitate van der Waals bonding evolves at temperatures above 600° C. into covalent bonding in hydrophobically bound Ge/Si layer transferred systems.
1. A multi-junction solar cell, comprising:
an exfoliated film of a first semiconductor material bonded to a second material different from the first semiconductor material; and
a multi-junction solar cell formed on the exfoliated film;
wherein the exfoliated thin film is formed by ion implantation into a bulk first semiconductor substrate, bonding the bulk first semiconductor substrate and the second material and annealing the bonded bulk first semiconductor substrate to exfoliate the film from the bulk first semiconductor substrate to the second material.
2. The solar cell of claim 1 , wherein the second material comprises a second semiconductor material different from the first semiconductor material.
3. The solar cell of claim 2 , wherein the first semiconductor material comprises InP or GaAs and the second semiconductor material comprises a III-V semiconductor material or silicon.
4. The solar cell of claim 2 , further comprising an anti-bubble layer located between the exfoliated film and the second semiconductor material.
5. The solar cell of claim 2 , wherein an ohmic contact is formed between the exfoliated film and the second semiconductor material.
6. The solar cell of claim 2 , wherein covalent bonds are formed between the exfoliated film and the second semiconductor material.
7. The solar cell of claim 2 , wherein the first semiconductor material comprises InP and the second semiconductor material comprises a III-V semiconductor material different from InP.
8. The solar cell of claim 7 , wherein the multi-junction solar cell comprises a multi-junction solar cell which is epitaxially grown on the exfoliated InP film.
9. A method of making a semiconductor device, comprising:
performing ion implantation into a bulk first semiconductor substrate;
hydrophobically passivating at least one of the bulk first semiconductor substrate and a second semiconductor material different from the first semiconductor material;
bonding the bulk first semiconductor substrate with the second semiconductor material;
annealing the bonded bulk first semiconductor substrate to exfoliate a film from the bulk first semiconductor substrate to the second semiconductor material; and
forming a semiconductor device on the exfoliated film bonded to a second semiconductor material;
wherein an ohmic contact exists between the exfoliated film and the second semiconductor material.
10. The method of claim 9 , further comprising smoothing an exposed surface of the exfoliated film prior to the step of forming the semiconductor device.
11. The method of claim 9 , wherein the semiconductor device comprises a laser, a light emitting diode or a multi-junction solar cell epitaxially grown the exfoliated film.
12. The method of claim 9 , wherein performing ion implantation comprises implanting H + or He + ions.
13. The method of claim 9 , wherein hydrophobically passivating at least one of the bulk first semiconductor substrate and a second semiconductor material comprises hydrophobically passivating both the bulk first semiconductor substrate and the second semiconductor material.
14. The method of claim 9 , further comprising forming an amorphous silicon layer on the bulk first semiconductor substrate prior to the step of bonding, such that the amorphous silicon layer is located between the exfoliated film and the second semiconductor material.
15. The method of claim 9 , wherein the first semiconductor material substrate comprises Ge or a III-V semiconductor material and the second semiconductor material comprises a III-V semiconductor material or silicon.
16. The method of claim 15 , wherein the first semiconductor substrate material comprises InP and the second semiconductor material comprises a III-V semiconductor material different from InP.
17. A method of making a multi-junction solar cell, comprising:
performing ion implantation into a bulk first semiconductor substrate;
bonding the bulk first semiconductor substrate with a second semiconductor material different from the first semiconductor material;
annealing the bonded bulk first semiconductor substrate to exfoliate a film from the bulk first semiconductor substrate to the second semiconductor material; and
forming a multi-junction solar cell on the exfoliated film bonded to the second semiconductor material.
18. The method of claim 17 , wherein an ohmic contact is formed between the exfoliated film and the second semiconductor material.
19. The method of claim 17 , further comprising hydrophobically passivating at least one of the bulk first semiconductor substrate and the second semiconductor material such that covalent bonds are formed between the bulk first semiconductor substrate and the second semiconductor material after the step of bonding.
20. The method of claim 17 , further comprising forming an anti-bubble layer between the bulk first semiconductor substrate and the second semiconductor material.
21. The method of claim 17 , wherein the first semiconductor substrate material comprises a III-V semiconductor material and the second semiconductor material comprises a III-V semiconductor material or silicon.
22. The method of claim 21 , wherein the first semiconductor material substrate comprises InP and the second semiconductor material comprises a III-V semiconductor material different from InP.
23. The method of claim 22 , wherein the multi-junction solar cell comprises a multi-junction solar cell which is epitaxially grown on the exfoliated InP film.