Germanium solar cell and method for the production thereof

1. A method of passivating and contacting a surface of a germanium substrate, comprising, in sequence:

(a) providing a germanium substrate having a first surface, wherein the first surface is a surface of an emitter;

(b) forming a passivation layer of amorphous silicon or hydrogenated amorphous silicon on said first surface to passivate the surface of the emitter;

(c) forming a contact layer of metal on said passivation layer; and thereafter

(d) heating the substrate and layers at a temperature of from about 150° C. to less than 300° C., whereby particles of metal from the contact layer diffuse through the passivation layer to form a conductive path between the contact layer and the germanium emitter.

2. The method according to claim 1 , wherein said contact resistivity is less than about 10 −4 Ωcm 2 .

3. The method according to claim 1 , further comprising cleaning said first surface before forming said passivation layer, said cleaning comprising applying a H 2 containing plasma to said first surface.

4. The method according to claim 1 , wherein said forming said passivation layer is performed by plasma enhanced chemical vapor deposition (PECVD).

5. The method according to claim 4 , wherein said PECVD is performed at a temperature of from about 150° C. to about 300° C.

6. The method according to claim 1 , wherein said passivation layer has a thickness of less than about 100 nm.

7. The method according to claim 6 , wherein said passivation layer has a thickness of less than about 40 nm.

8. The method according to claim 1 , wherein said passivation layer has a thickness of from about 10 nm to about 50 nm.

9. The method according to claim 1 , wherein said contact layer comprises Ag or Au.

10. The method according to claim 1 , further comprising patterning the contact layer to form a contact grid, wherein patterning is performed after forming the contact layer of metal on said passivation layer and before heating the substrate and layers at a temperature of from about 150° C. to less than 300° C.

11. The method according to claim 1 , wherein said heating is performed at a temperature of from about 160° C. to about 220° C.

12. The method according to claim 1 , further comprising, before forming a passivation layer:

forming an emitter area in said germanium substrate;

forming a back contact on a second surface of said germanium substrate and thereby realizing a back surface field; and

etching mesa structures so as to define photo voltaic cell regions.

13. The method according to claim 12 , further comprising forming an antireflective coating on exposed parts of the passivation layer and the contact layer, wherein said forming an antireflective coating is performed after the heating.

14. A photovoltaic device comprising:

a germanium substrate having a back surface, the germanium substrate further having therein an emitter, the emitter having a surface opposite the back surface of the germanium substrate;

a back contact on said back surface of said germanium substrate providing a back surface field;

a passivation layer of plasma enhanced chemical vapor deposition (PECVD) deposited amorphous silicon material formed on said emitter surface;

a contacting layer comprising a conductive material formed on said passivation layer, wherein a conductive path is formed between the contacting layer and the emitter by particles of said conductive material having diffused into said passivation layer;

photovoltaic cell regions; and

an antireflective coating on exposed parts of said passivation layer and said contact layer.

15. The method according to claim 12 , wherein a germanium solar cell, a thermophotovoltaic cell or a photodetector comprises the emitter.