Vertical cavity surface emitting laser with undoped top mirror

• US 20060072639A1
• Filed: 09/08/2005
• Published: 04/06/2006
• Est. Priority Date: 10/01/2004
• Status: Active Grant

• Current Assignee: II-VI Delaware, Inc. (Coherent Corp.)
• Original Assignee: Finisar Corporation (II-VI Incorporated)
• Inventors: Biard, James Robert, Penner, R. Scott, Johnson, Ralph H.
• Granted Patent: US 7,860,137 B2
• Time in Patent Office: Days
• US Class Current: 372/43.10
• CPC Class Codes: H01S 5/18308 having a special structure for lateral current or light confinement
• CPC Class Codes: H01S 5/18313 by oxidizing at least one of the DBR layers
• CPC Class Codes: H01S 5/1833 with more than one structure
• CPC Class Codes: H01S 5/18341 Intra-cavity contacts
• CPC Class Codes: H01S 5/18369 based on dielectric materials
• CPC Class Codes: H01S 5/2086 lateral etch control, e.g. mask induced
• CPC Class Codes: H01S 5/3095 Tunnel junction
• CPC Class Codes: H01S 5/3211 characterised by special cladding layers, e.g. details on band-discontinuities

Abstract

A VCSEL with undoped top mirror. The VCSEL is formed from an epitaxial structure deposited on a substrate. A doped bottom mirror is formed on the substrate. An active layer that includes quantum wells is formed on the bottom mirror. A periodically doped conduction layer is formed on the active layer. The periodically doped conduction layer is heavily doped at locations where the optical energy is at a minimum when the VCSEL is in operation. A current aperture is used between the conduction layer and the active region. An undoped top mirror is formed on the heavily doped conduction layer.

Claims

1. A VCSEL comprising a substrate of a first conductivity type and an epitaxial structure, wherein the epitaxial structure comprises:

a bottom DBR mirror disposed on the substrate wherein the bottom mirror is doped to the first conductivity type;

an active layer disposed on the bottom mirror that contains quantum wells;

a periodically doped first conduction layer of a second conductivity type, the first conduction layer coupled to the active layer, the doped first conduction layer being heavily doped at a location where the optical electric field is at about a minimum;

an aperture formed in the epitaxial structure above the quantum wells; and

a top mirror coupled to the periodically doped first conduction layer, wherein the top mirror is essentially undoped.

2. The VCSEL of claim 1, wherein the top mirror comprises alternating layers of GaAs and AlGaAs.

3. The VCSEL of claim 2, wherein the AlGaAs is 87.5%.

4. The VCSEL of claim 1, wherein the top mirror comprises alternating layers of GaAs and AlAs when the VCSEL is constructed using an oxide to seal the top mirror during a fabrication process of the VCSEL.

5. The VCSEL of claim 1, wherein the first conduction layer comprises a sheet resistivity of about 500 Ohms/square.

6. The VCSEL of claim 1, wherein the first conduction layer is doped at between about 5×

10¹⁹ to 1×

10²⁰ at about the minimum of the optical electric field and less than 1×

10¹⁸ away from the minimum of the optical electric field.

7. The VCSEL of claim 1 wherein the bottom DBR mirror comprises alternating layers of AlAs and GaAs, further wherein the bottom DBR mirror comprises ramps between the AlAs and GaAs layers.

8. The VCSEL of claim 7, wherein the ramps comprise a step in composition from AlAs to AlGaAs with about 30 to 38% aluminum and an essentially linear ramp of aluminum composition from about 33% to zero (GaAs) after the step.

9. The VCSEL of claim 1, wherein the active region comprises a tunnel junction coupled to the first conductive layer and the quantum wells.

10. The VCSEL of claim 1, wherein the epitaxial structure contains a second conduction layer coupled to the first conduction layer and the active layer.

11. The VCSEL of claim 1, wherein the epitaxial structure contains a second and third conduction layer coupled to the first conduction layer and the active layer.

12. The VCSEL of claim 1, further comprising an intracavity contact coupled to the first conduction layer.

13. The VCSEL of claim 12, wherein the intracavity contact comprises TiAu.

14. The VCSEL of claim 12, wherein the top mirror forms at least a portion of a mesa and the intracavity contact metal is coupled to the sides of the mesa.

15. The VCSEL of claim 1, further comprising a wagon wheel structure formed from trenches etched into the conduction layer.

16. The VCSEL of claim 1, wherein the bottom spacer is periodically doped such that a portion where the optical power or electric field is at about a minimum when the VCSEL is in use is more heavily doped than other portions of the bottom spacer.

17. A method of fabricating a VCSEL comprising:

forming a bottom mirror on a substrate wherein forming a bottom mirror comprises forming alternating layers of materials with different indices of refraction, wherein at least a portion of the materials are doped;

forming an active layer that contains quantum wells on the bottom mirror;

forming a conduction layer region on the active layer, wherein forming a conduction layer region comprises doping portions of the conduction layer region more heavily at a location where the optoelectronic energy is at about a minimum when the VCSEL is in use; and

forming a top mirror on the conduction layer region such that the top mirror is essentially undoped.

18. The method of claim 17, wherein forming a top mirror comprises forming alternating layers of AlAs and GaAs.

19. The method of claim 17, further comprising etching to the conduction layer region.

20. The method of claim 19, wherein etching to the conduction layer region comprises:

etching using a reactive ion etch to an etch stop layer formed on the conduction layer region, and

using a dilute HF etch to etch through the etch stop layer.

21. The method of claim 19, further comprising forming an intracavity contact that is coupled to the conduction layer region.

22. The method of claim 17, further comprising:

depositing a dielectric layer on the conduction layer region;

slope etching the dielectric layer; and

depositing a metal contact on the conduction layer region and the slope etch dielectric layer.

23. The method of claim 17, further comprising:

forming a periodically doped spacer layer on the bottom mirror;

wherein forming the active layer comprises forming the active layer on the periodically doped spacer layer;

etching to the periodically doped spacer layer; and

forming a second intracavity contact on the periodically doped spacer layer.

24. A VCSEL formed on a substrate comprising:

an undoped top mirror;

a periodically doped conduction layer coupled to the undoped top mirror;

an active region coupled to the conduction layer;

a periodically doped spacer layer coupled to the active region;

an undoped bottom mirror coupled to the periodically doped spacer layer;

a first intracavity contact coupled to the periodically doped conduction layer;

a second intracavity contact coupled to the periodically doped spacer layer.