Granted Patent B2

US 7,795,064 · App. 12/260,688 · Granted Sep 14, 2010

Abstract

Claims (49)

1. A front-illuminated avalanche photodiode (APD) comprising:

an APD body of semiconductor material, including:

a substrate; and

a layer stack, disposed on a front surface of the substrate, comprising:

an absorption layer for absorbing light at an absorption wavelength band to generate a photocurrent;

a multiplication layer, including a multiplication region, for multiplying the photocurrent through avalanche multiplication; and

a field-control layer for controlling electric fields in the absorption layer and the multiplication layer;

wherein a back surface of the APD body is mechanically and chemically polished; and

a reflector having a reflectance of greater than 90% at the absorption wavelength band, for reflecting light at the absorption wavelength band toward the absorption layer, disposed on the back surface of the APD body.

2. The front-illuminated APD of claim 1 , wherein the layer stack further comprises a buffer layer, for accommodating lattice mismatch between the substrate and the layer stack, and a grading layer, for facilitating current flow between the absorption layer and the multiplication layer; and wherein the multiplication layer further includes a diffusion region, for defining the multiplication region and for providing a p-n junction.

3. The front-illuminated APD of claim 1 , wherein the layer stack further includes a buffer layer, for accommodating lattice mismatch between the substrate and the layer stack, and a window layer, for transmitting light at the absorption wavelength band to the absorption layer; and wherein the window layer includes a diffusion region, for defining the multiplication region and for providing a p-n junction.

4. The front-illuminated APD of claim 1 , wherein the reflector is disposed on the entire back surface of the APD body.

5. The front-illuminated APD of claim 1 , further comprising an annular back contact of metallic material, for passing current to or from the front-illuminated APD, disposed on an annular contact region of the back surface of the APD body; wherein an inner circumference of the back contact defines a circular reflector region of the back surface of the APD body; and wherein the reflector is disposed on the reflector region of the back surface of the APD body.

6. The front-illuminated APD of claim 5 , wherein the reflector is disposed only on the reflector region of the back surface of the APD body.

7. The front-illuminated APD of claim 1 , wherein the APD body further includes a back trench, for shortening an optical path between the absorption layer and the reflector, disposed in the substrate and in a back portion of the layer stack not comprising the absorption layer, the multiplication layer, nor the field-control layer.

8. The front-illuminated APD of claim 1 , wherein the APD body further includes a front mesa, for allowing front contacting, including a front portion of the layer stack comprising the absorption layer, the multiplication layer, and the field-control layer.

9. The front-illuminated APD of claim 1 , wherein the layer stack further comprises an etch-stop layer, for preventing etching of a portion of the layer stack.

10. The front-illuminated APD of claim 9 , wherein the APD body further includes a back trench, for shortening an optical path between the absorption layer and the reflector, disposed in the substrate and in a back portion of the layer stack behind the etch-stop layer, such that the back surface of the APD body includes a reflector region of a back surface of the etch-stop layer.

11. The front-illuminated APD of claim 9 , wherein the APD body further includes a front mesa, for allowing front contacting, including a front portion of the layer stack in front of the etch-stop layer, such that a front surface of the APD body includes a contact region of a front surface of the etch-stop layer; further comprising a back contact of metallic material, for passing current to or from the front-illuminated APD, disposed on the contact region of the front surface of the etch-stop layer.

12. The front-illuminated APD of claim 1 , wherein the absorption layer has a thickness of less than 1 μm.

13. The front-illuminated APD of claim 1 , wherein the reflector includes a layer of a noble metal or a layer of an alloy of a noble metal.

14. The front-illuminated APD of claim 13 , wherein the reflector further includes one or more layers of dielectric compounds.

15. The front-illuminated APD of claim 1 , wherein the reflector includes one or more layers of dielectric compounds.

16. A method of fabricating a front-illuminated APD, comprising:

i) forming an APD body of semiconductor material, including:

a) providing a substrate; and

b) epitaxially growing a layer stack on a front surface of the substrate, comprising:

epitaxially growing an absorption layer, for absorbing light at an absorption wavelength band to generate a photocurrent;

epitaxially growing a multiplication layer, including a multiplication region, for multiplying the photocurrent through avalanche multiplication; and

epitaxially growing a field-control layer for controlling electric fields in the absorption layer and the multiplication layer;

ii) mechanically and chemically polishing a back surface of the APD body; and

iii) depositing a reflector having a reflectance of greater than 90% at the absorption wavelength band on the back surface of the APD body.

17. The method of claim 16 , wherein ib) further comprises:

epitaxially growing a buffer layer, for accommodating lattice mismatch between the substrate and the layer stack;

epitaxially growing a grading layer, for facilitating current flow between the absorption layer and the multiplication layer; and

diffusing a dopant into the multiplication layer to form a diffusion region, for defining the multiplication region and for providing a p-n junction, in a front portion of the multiplication layer.

18. The method of claim 16 , wherein ib) further comprises:

epitaxially growing a buffer layer, for accommodating lattice mismatch between the substrate and the layer stack;

epitaxially growing a window layer, for transmitting light at the absorption wavelength band to the absorption layer; and

diffusing a dopant into the window layer to form a diffusion region, for defining the multiplication region and for providing a p-n junction, in the window layer.

19. The method of claim 16 , wherein iii) includes depositing the reflector on the entire back surface of the APD body.

20. The method of claim 16 , further comprising:

etching the reflector to expose an annular contact region of the back surface of the APD body; and

depositing an annular back contact of metallic material, for passing current to or from the front-illuminated APD, on the contact region of the back surface of the APD body.

21. The method of claim 16 , wherein i) further includes etching the substrate and a back portion of the layer stack not comprising the absorption layer, the multiplication layer, nor the field-control layer to form a back trench, for shortening an optical path between the absorption layer and the reflector.

22. The method of claim 16 , wherein i) further includes etching a front portion of the layer stack comprising the absorption layer, the multiplication layer, and the field-control layer to form a front mesa, for allowing front contacting.

23. The method of claim 16 , wherein ib) further comprises epitaxially growing an etch-stop layer, for preventing etching of a portion of the layer stack.

24. The method of claim 23 , wherein i) further includes etching the substrate and a back portion of the layer stack behind the etch-stop layer to form a back trench, for shortening an optical path between the absorption layer and the reflector, and to expose a reflector region of a back surface of the etch-stop layer, such that the back surface of the APD body includes the reflector region of the back surface of the etch-stop layer.

25. The method of claim 23 , wherein i) further includes etching a front portion of the layer stack in front of the etch-stop layer to form a front mesa, for allowing front contacting, and to expose a contact region of a front surface the etch-stop layer, such that a front surface of the APD body includes the contact region of the front surface of the etch-stop layer; further comprising depositing an annular back contact on the contact region of the front surface of the etch-stop layer.

Assignments (7)