PHOTODETECTOR

Abstract

A photodetector comprising an optical waveguide structure comprising at least three stripes spaced from one another such that a slot is present between each two adjacent stripes of the at least three stripes. A graphene absorption layer is provided over or underneath the at least three stripes. There is an electrode for each stripe, over or underneath the graphene absorption layer. The photodetector is configured such that two adjacent electrodes are biased using opposite polarities to create a p-n junction effect in a portion of the graphene absorption layer. In particular the portion of the graphene absorption layer is located over or underneath each respective slot between said each two adjacent stripes.

Claims

1. A photodetector comprising: an optical waveguide structure comprising at least three stripes spaced from one another such that a slot is present between each two adjacent stripes of the at least three stripes; a graphene absorption layer provided over or underneath the at least three stripes; an electrode for each stripe, over or underneath the graphene absorption layer; and wherein the photodetector is configured such that two adjacent electrodes are biased using opposite polarities to create a p-n junction effect in a portion of the graphene absorption layer, wherein the portion of the graphene absorption layer is located over or underneath each respective slot between said each two adjacent stripes.

2. A photodetector according to claim 1, wherein the optical waveguide structure comprises at least four stripes in which: a first slot is present between a first stripe and a second stripe; a second slot is present between the first stripe and a third stripe in one side of the first slot; and a third slot is present between the second stripe and a fourth stripe in an opposite side of the second slot.

3. A photodetector according to claim 2, wherein the first slot is located between the second and third slots, and wherein the width of the second and third slots is greater than the width of the first slot.

4. A photodetector according to claim 3, wherein the third and fourth stripes each are wider than the first and second stripes.

5. A photodetector according to claim 2, 3 or 4, wherein an arrangement of the first and third stripes is symmetrical to an arrangement of the second and fourth stripes.

6. A photodetector according to claim 1, wherein the photodetector is configured such that a photo-thermoelectric effect (PTE) is generated in each slot.

7. A photodetector according to claim 1, further comprising a pair of contacts operatively connected with each portion of the graphene absorption layer located over or underneath each slot to extract electrical signal out of the graphene absorption layer.

8. A photodetector according to claim 1, wherein the stripes of the optical waveguide comprise silicon nitride.

9. A photodetector according to claim 1, wherein at least some of the plurality of electrodes are metal electrodes.

10. A photodetector according to claim 1, wherein at least some of the plurality of electrodes are made of a semiconductor material.

11. A photodetector according to claim 1, wherein the graphene absorbing layer is located on top of the stripes and each electrode is formed on top of the graphene absorption layer.

12. A photodetector according to claim 1, wherein the graphene absorbing layer is located over the stripes, and wherein each electrode is formed between the graphene absorption layer and each stripe of the optical waveguide structure.

13. A photodetector according to claim 1, wherein the graphene absorbing layer is located underneath the stripes, and wherein each electrode is formed between the graphene absorption layer and each stripe of the optical waveguide structure.

14. A photodetector according to claim 1, wherein the graphene absorbing layer is located underneath the stripes, and wherein each electrode is formed underneath the graphene absorption layer.

15. A photodetector according to claim 1, wherein the graphene absorbing layer is located underneath the stripes, and wherein each electrode is formed on top of each stripe.

16. A photodetector according to claim 15, wherein the stripe of the waveguide structure comprises doped silicon.

17. A photodetector according to claim 1, wherein the electrodes cover an end portion of the stripes.

18. A photodetector according to claim 1, wherein the stripes have a lower refractive index than the slots at a wavelength of operation.

19. A graphene photodetector comprising: a wideband optical waveguide structure comprising: a first slot waveguide structure comprising a first pair of longitudinal stripes defining a first slot therebetween; a second pair of longitudinal stripes one to each side of the first slot waveguide structure defining a pair of second slots each between one of the first and second stripes, wherein the second slots are wider than the first slots; a layer of graphene bridging the first and second slots; and a set of electrodes one over or underneath each of the longitudinal stripes for biasing the electrodes to create p-n junctions in regions of the graphene over or underneath the slots.

20. A method of fabricating a photodetector as claimed in any claim 1, wherein the method uses a CMOS or CMOS-compatible process.

Description

DRAWINGS

[0027] These and other aspects of the invention will now be further described by way of example only, with reference to the accompanying Figures, in which:

[0028] FIG. 1 shows a known graphene photodetector;

[0029] FIG. 2 shows a proposed photodetector according to one example;

[0030] FIG. 3 shows high field intensity between waveguides of the photodetector of FIG. 2; and

[0031] FIG. 4 shows simulation results showing high field intensity between waveguides.

DESCRIPTION

[0032] FIG. 2 shows a proposed photodetector 200 according to one example. The photodetector includes a plurality of fingers or stripes 230a-f having a plurality of slots between the stripes 230a-f. An electrode 235a-f is provided for each stripe 230a-f. A graphene layer (no shown) is provided over the stripes 230a-f. In one example, the graphene layer can be between the electrodes and stripes. In another example, the graphene layer can be on top of the electrodes 235a-f where the electrodes are directly over the waveguide stripes 230a-f. In an alternative example, the electrodes and the graphene layer can be underneath the waveguide stripes 230a-f.

[0033] In the arrangement of FIG. 1, symmetric stripes of waveguides are formed by adding waveguide stripe 230b next to stripe 230c and by adding stripe 230e next to stripe 230d. The lateral distance between stripes 230e and 230d is the same as the lateral distance between stripes 230b and 230c. Furthermore, stripe 230a is placed in one side of 230b and stripe 230f is placed in another side of 230e. The lateral distance of between stripe 230f and stripe 230e (or the width of the slot between them) is the same as the lateral distance between stripe 230b and 230a. In one example, the width of stripes 230c, d is the same. The width of stripes 230b, e is the same. The width of the stripes 230a, f is the same. Although this type of symmetrical structure may be preferred, the invention is not restricted to such a symmetric structure. Any three waveguide stripes with two slots would be suitable for the operation of the proposed structure.

[0034] In one example, the waveguide stripes are made of silicon or silicon nitride. The electrode material may be metal or any other suitable electrode material.

[0035] FIG. 3 shows high field intensity between waveguides of the photodetector of FIG. 2. There reference numerals used in FIG. 3 are the same as those in FIG. 2. When alternative biasing is applied in the electrodes 235a-f, a high field intensity is generated in the slots between the stripes 230a-f.

[0036] FIG. 4 shows simulation results showing high field intensity between waveguides at three telecom wavelengths (e.g. 850 nm, 1300 nm, 1550 nm) and as well as 2000 nm.

[0037] No doubt many other effective alternatives will occur to the skilled person. It will be understood that the invention is not limited to the described embodiments and encompasses modifications apparent to those skilled in the art lying within the spirit and scope of the claims appended hereto.