High performance GeSi avalanche photodiode operating beyond Ge bandgap limits
Avalanche photodiodes (APDs) having at least one top stressor layer disposed on a germanium (Ge)-containing absorption layer are described herein. The top stressor layer can increase the tensile strain of the Ge-containing absorption layer, thus extending the absorption of APDs to longer wavelengths beyond 1550 nm. In one embodiment, the top stressor layer has a four-layer structure, including an amorphous silicon (Si) layer disposed on the Ge-containing absorption layer; a first silicon dioxide (SiO 2 ) layer disposed on the amorphous Si layer, a silicon nitride (SiN) layer disposed on the first SiO 2 layer, and a second SiO 2 layer disposed on the SiN layer. The Ge-containing absorption layer can be further doped by p-type dopants. The doping concentration of p-type dopants is controlled such that a graded doping profile is formed within the Ge-containing absorption layer to decrease the dark currents in APDs.
1. An avalanche photodiode, comprising:
a substrate; and
a multi-layer structure disposed on a first surface of the substrate, comprising:
at least one top stressor layer including an amorphous silicon (Si) layer, the at least one top stressor layer coupled to at least one metal contact of a first electrical polarity;
a germanium (Ge)-containing absorption layer on which the at least one top stressor layer is disposed;
a charge layer on which the Ge-containing absorption layer is disposed;
a multiplication layer on which the charge layer is disposed; and
a contact layer on which the multiplication layer is disposed, the contact layer coupled to at least one metal contact of a second electrical polarity opposite to the first electrical polarity,
wherein the at least one top stressor layer is configured to increase a tensile strain in the Ge-containing absorption layer such that absorption of the Ge-containing absorption layer between 1550 nm and 1650 nm is increased.
2. The avalanche photodiode of claim 1 , wherein the at least one top stressor layer further comprises:
a first silicon dioxide (SiO 2 ) layer disposed on the amorphous Si layer;
a silicon nitride (SiN) layer disposed on the first SiO 2 layer; and
a second SiO 2 layer disposed on the SiN layer.
3. The avalanche photodiode of claim 1 , wherein the Ge-containing absorption layer comprises Ge, germanium-silicon (GeSi), or silicon-germanium-carbon (SiGeC).
4. The avalanche photodiode of claim 1 , wherein the charge layer comprises p-type Si, p-type GeSi, or p-type SiGeC.
5. The avalanche photodiode of claim 1 , wherein the multiplication layer comprises intrinsic Si or lightly doped n-type Si.
6. The avalanche photodiode of claim 1 , wherein the contact layer comprises n-type Si.
7. The avalanche photodiode of claim 1 , wherein the substrate comprises a Si substrate or a silicon-on-insulator (SOI) substrate.
8. The avalanche photodiode of claim 1 , further comprising:
at least one anti-reflection layer disposed on a second surface of the substrate opposite to the first surface,
wherein the at least one anti-reflection layer comprises a single SiO 2 layer or three layers comprising a SiN layer disposed between two SiO 2 layers.
9. The avalanche photodiode of claim 1 , wherein the Ge-containing absorption layer further comprises p-type dopants, a doping concentration of the p-type dopants is controlled such that a graded doping profile of the p-type dopants is formed within the Ge-containing absorption layer.
10. The avalanche photodiode of claim 9 , wherein the p-type dopant comprises gallium (Ga) or boron (B).
11. An avalanche photodiode, comprising:
a substrate; and
a multi-layer structure disposed on a first surface of the substrate, comprising:
at least one top stressor layer including an amorphous silicon layer, the at least one top stressor layer coupled to at least one metal contact of a first electrical polarity;
a germanium (Ge) absorption layer on which the at least one top stressor layer is disposed;
a charge layer on which the Ge absorption layer is disposed;
a multiplication layer on which the charge layer is disposed; and
a contact layer on which the multiplication layer is disposed, the contact layer coupled to at least one metal contact of a second electrical polarity opposite to the first electrical polarity,
wherein the at least one top stressor layer is configured to increase a tensile strain in the Ge absorption layer such that absorption of the Ge absorption layer between 1550 nm and 1650 nm is increased.
12. The avalanche photodiode of claim 11 , wherein the at least one top stressor layer further comprises:
a first silicon dioxide SiO 2 layer disposed on the amorphous Si layer;
a silicon nitride (SiN) layer disposed on the first SiO 2 layer; and
a second SiO 2 layer disposed on the SiN layer.
13. The avalanche photodiode of claim 11 , wherein the charge layer comprises p-type Si, p-type GeSi, or p-type SiGeC, wherein the multiplication layer comprises intrinsic Si or lightly doped n-type Si, and wherein the contact layer comprises n-type Si.
14. The avalanche photodiode of claim 11 , wherein the substrate comprises a Si substrate or a silicon-on-insulator (SOI) substrate.
15. The avalanche photodiode of claim 11 , further comprising at least one anti-reflection layer disposed on a second surface of the substrate opposite to the first surface, wherein the at least one anti-reflection layer comprises a single SiO2 layer or three layers comprising a SiN layer disposed between two SiO2 layers.
16. The avalanche photodiode of claim 11 , wherein the Ge absorption layer further comprises p-type dopants, a doping concentration of the p-type dopants is controlled such that a graded doping profile of the p-type dopants is formed within the Ge absorption layer.
17. The avalanche photodiode of claim 16 , wherein the p-type dopant comprises gallium (Ga) or boron (B).
18. An avalanche photodiode, comprising:
a substrate;
a multi-layer structure disposed on the substrate, comprising:
at least one top stressor layer including an amorphous silicon layer, the at least one top stressor layer coupled to at least one metal contact of a first electrical polarity;
a germanium (Ge)-containing absorption layer doped with p-type dopants on which the at least one top stressor layer is disposed, a doping concentration of the p-type dopants is controlled such that a graded doping profile of the p-type dopants is formed within the Ge-containing absorption layer;
a charge layer on which the Ge-containing absorption layer is disposed;
a multiplication layer on which the charge layer is disposed; and
a contact layer on which the multiplication layer is disposed, the contact layer coupled to at least one metal contact of a second electrical polarity opposite to the first electrical polarity,
wherein the at least one top stressor layer is configured to increase a tensile strain in the Ge-containing absorption layer such that absorption of the Ge-containing absorption layer between 1550 nm and 1650 nm is increased.
19. The avalanche photodiode of claim 18 , wherein the at least one top stressor layer further comprises:
a first silicon dioxide (SiO 2 ) layer disposed on the amorphous Si layer;
a silicon nitride (SiN) layer disposed on the first SiO 2 layer; and
a second SiO 2 layer disposed on the SiN layer.
20. The avalanche photodiode of claim 18 , wherein the Ge-containing absorption layer comprises Ge, germanium-silicon (GeSi), or silicon-germanium-carbon (SiGeC), and wherein the p-type dopant comprises gallium (Ga) or boron (B).