Vertical cavity surface emitting laser having multiple top-side contacts
View Patent ↗A VCSEL with undoped mirrors. An essentially undoped bottom DBR mirror is formed on a substrate. A periodically doped first conduction layer region is formed on the bottom DBR mirror. The first conduction layer region is heavily doped at a location where the optical electric field is at about a minimum. An active layer, including quantum wells, is on the first conduction layer region. A periodically doped second conduction layer region is connected to the active layer. The second conduction layer region is heavily doped where the optical electric field is at a minimum. An aperture is formed in the epitaxial structure above the quantum wells. A top mirror coupled to the periodically doped second conduction layer region. The top mirror is essentially undoped and formed in a mesa structure. An oxide is formed around the mesa structure to protect the top mirror during wet oxidation processes.
1. A method of fabricating a VCSEL comprising:
forming an essentially undoped bottom mirror on a substrate wherein forming a bottom mirror comprises forming alternating layers of materials with different indices of refraction;
forming a first conduction layer region on the bottom mirror, wherein forming the first conduction layer region comprises doping portions of the first conduction layer region more heavily at a location where optoelectronic energy is at about a minimum when the VCSEL is in use;
forming an active layer that contains quantum wells on the first conduction layer region;
forming a second conduction layer region on the active layer, wherein forming a second conduction layer region comprises doping portions of the second conduction layer region more heavily at a location where the optoelectronic energy is at about a minimum when the VCSEL is in use;
forming an epitaxial structure having an aperture, the epitaxial structure being formed above the quantum wells and below the second conduction layer region;
forming a ramp layer positioned between the aperture and the second conduction layer region so as to have a ramp of aluminum in the ramp layer;
forming a top mirror on the second conduction layer region such that the top mirror is essentially undoped and such that the top mirror forms a mesa structure; and
forming an oxide layer around the mesa structure to protect the top mirror from a wet oxidation step.
2. The method of claim 1 , wherein forming a top mirror comprises forming alternating layers of AlAs and GaAs.
3. The method of claim 1 , wherein forming an oxide layer around the mesa structure comprises depositing the oxide layer using plasma enhanced chemical vapor deposition.
4. The method of claim 1 , further comprising:
implanting ions to isolate a VCSEL from other VCSELs on a wafer;
forming a second intracavity contact on the second conduction layer region.
5. The method of claim 1 comprising:
performing a first etch to form a mesa structure in the top mirror, wherein the mesa structure includes at least a portion of the top mirror;
depositing a photoresist layer to form an HF shield mask around at least a portion of the mesa structure;
performing an HF etch to expose a portion of the second conduction layer; and
forming the oxide layer around the mesa structure to protect the top mirror from a wet oxidation step.
6. The VCSEL of claim 1 , wherein the bottom mirror is a DBR mirror.
7. The VCSEL of claim 1 , wherein the doped first conduction layer region and/or doped second conduction region includes a heavily doped layer at the location the optoelectic field is a minimum.
8. The VCSEL of claim 1 , comprising defining the aperture with an oxidized layer.
9. The VCSEL of claim 8 , comprising forming the oxidized layer to define the aperture and include AlGaAs.
10. The VCSEL of claim 9 , wherein the ramp layer, second conduction layer region, and oxidized layer are within a null of the standing wave of the VCSEL.
11. The VCSEL of claim 1 , wherein the ramp layer is within a null of a standing wave of the VCSEL.
12. The VCSEL of claim 1 , wherein the ramp layer and second conduction layer region are within a null of a standing wave of the VCSEL.
13. The VCSEL of claim 1 , wherein the top mirror is essentially undoped.
14. The VCSEL of claim 1 , wherein the top mirror includes a plurality of layers of AlGaAs having an aluminum content in a range of 70% to 100%.
15. The VCSEL of claim 1 , wherein the top mirror forms a mesa structure.
16. A method of fabricating a VCSEL comprising:
forming an essentially undoped bottom mirror on a substrate wherein forming a bottom mirror comprises forming alternating layers of materials with different indices of refraction;
forming a first conduction layer region on the bottom mirror, wherein forming a first conduction layer region comprises doping portions of the first conduction layer region more heavily at a location where the optoelectronic energy is at about a minimum when the VCSEL is in use;
forming an active layer that contains quantum wells on the first conduction layer region;
forming a second conduction layer region on the active layer, wherein forming a second conduction layer region comprises doping portions of the second conduction layer region more heavily at a location where the optoelectronic energy is at about a minimum when the VCSEL is in use;
forming an epitaxial structure having an aperture, the epitaxial structure being formed above the quantum wells and below the second conduction layer region;
forming a ramp layer positioned between the aperture and the second conduction layer region so as to have a ramp of aluminum in the ramp layer;
forming a top mirror on the second conduction layer region such that the top mirror is essentially undoped and such that the top mirror forms a mesa structure; and
forming an oxide layer around the mesa structure to protect the top mirror from a wet oxidation step, wherein the oxide layer comprises a layer of silicon dioxide that surrounds the top mirror.
17. The VCSEL of claim 16 , comprising forming the VCSEL to include:
the bottom mirror is a DBR mirror;
the doped first conduction layer region and/or doped second conduction region includes a heavily doped layer at the location the optoelectic field is a minimum;
the aperture being defined with an oxidized layer having AlGaAs;
the ramp layer is within a null of a standing wave of the VCSEL; and
the top mirror is essentially undoped and includes a plurality of layers of AlGaAs having an aluminum content in a range of 70% to 100% and has a mesa structure.
18. The VCSEL of claim 17 , wherein the ramp layer and second conduction layer region are within a null of a standing wave of the VCSEL.
19. The VCSEL of claim 17 , wherein the ramp layer, second conduction layer region, and oxidized layer are within a null of the standing wave of the VCSEL.
20. A method of fabricating a VCSEL comprising:
forming an essentially undoped bottom DBR mirror on a substrate wherein forming a bottom mirror comprises forming alternating layers of materials with different indices of refraction;
forming a periodically doped first conduction layer region of a first conductivity type on the bottom mirror, wherein forming the first conduction layer region comprises doping portions of the first conduction layer region more heavily at a location where optoelectronic energy is at about a minimum when the VCSEL is in use;
forming an active layer that contains quantum wells on the periodically doped first conduction layer region;
forming a periodically doped second conduction layer region of a second conductivity type on the active layer, wherein forming a second conduction layer region comprises doping portions of the second conduction layer region more heavily at a location where the optoelectronic energy is at about a minimum when the VCSEL is in use;
forming an epitaxial structure having an aperture defined by an oxidized AlGaAs layer, the epitaxial structure being formed above the quantum wells and below the second conduction layer region;
forming a ramp layer positioned between the aperture and the second conduction layer region so as to have a ramp of aluminum in the ramp layer;
forming a top mirror on the second conduction layer region such that the top mirror is essentially undoped and such that the top mirror forms a mesa structure and includes a plurality of layers of AlGaAs having an aluminum content in a range of 70% to 100%; and
forming an oxide layer of around the mesa structure to protect the top mirror from a wet oxidation step,
wherein the ramp layer, second conduction layer, and oxidized AlGaAs layer are within a single null of a standing wave of the VCSEL.