Semiconductor photodiode

1. A semiconductor photodiode, comprising

a light-absorbing layer;

an optical waveguide via which light can evanescently be coupled into the light-absorbing layer; and

a doped contact layer arranged between the light-absorbing layer and the optical waveguide,

wherein the optical waveguide at least sectionally has a doping which produces a diffusion barrier counteracting a diffusion of dopant of the contact layer into the optical waveguide.

2. The semiconductor photodiode according to claim 1 , wherein the at least sectionwise doping of the optical waveguide is complementary to the doping of the contact layer.

3. The semiconductor photodiode according to claim 1 , wherein the doping of the contact layer is a p-doping.

4. The semiconductor photodiode according to claim 3 , wherein the doping of the optical waveguide for producing the diffusion barrier is an n-doping.

5. The semiconductor photodiode according to claim 1 , wherein in a first region facing the contact layer the optical waveguide has the doping acting as a diffusion barrier and a further doping in a second region.

6. The semiconductor photodiode according to claim 5 , wherein the second region is formed semi-insulating due to the further doping.

7. The semiconductor photodiode according to claim 1 , wherein between the contact layer and the optical waveguide a blocking layer is disposed, which as an additional diffusion barrier counteracts a diffusion of dopant of the contact layer into the optical waveguide.

8. The semiconductor photodiode according to claim 7 , wherein the blocking layer has a doping complementary to the doping of the contact layer.

9. The semiconductor photodiode according to claim 8 , wherein the doping of the blocking layer is an n-doping.

10. The semiconductor photodiode according to claim 1 , wherein on a side of the light-absorbing layer facing away from the contact layer a further, complementarily doped contact layer is arranged.

11. The semiconductor photodiode according to claim 10 , wherein the further contact layer is n-doped.

12. The semiconductor photodiode according claim 10 , wherein the semiconductor photodiode is formed as an avalanche photodiode, wherein a multiplier layer is arranged on a side of the light-absorbing layer facing away from the contact layer and between the light-absorbing layer and the further contact layer.

13. The semiconductor photodiode according to claim 1 , wherein the optical waveguide is formed in the form of a rib or strip waveguide.

14. The semiconductor photodiode according to claim 1 , wherein the optical waveguide is at least partly arranged on a semi-insulating substrate, and/or is at least partly formed by the semi-insulating substrate.

15. The semiconductor photodiode according to claim 14 , wherein the optical waveguide is at least partly grown on the semi-insulating substrate.

16. The semiconductor photodiode according to claim 1 , wherein the substrate is made of indium phosphide, wherein the contact layer and the optical waveguide are at least partly formed from an InGaAsP layer.

17. The semiconductor photodiode according to claim 1 , wherein the index of refraction of the contact layer is greater than the index of refraction of the optical waveguide and/or the index of refraction of the light-absorbing layer is greater than the index of refraction of the optical waveguide.

18. A method for manufacturing a semiconductor photodiode according to claim 1 , the method comprising the following steps:

producing a light-absorbing layer;

producing an optical waveguide such that via the optical waveguide light can evanescently be coupled into the light-absorbing layer;

producing a doped contact layer between the light-absorbing layer and the optical waveguide ( 12 ); and

doping of the optical waveguide such that a diffusion barrier is obtained, which counteracts a diffusion of dopant of the contact layer into the optical waveguide.