STRUCTURE AND METHOD FOR THE FABRICATION OF A GALLIUM NITRIDE VERTICAL CAVITY SURFACE EMITTING LASER

• US 20140023102A1
• Filed: 07/22/2013
• Published: 01/23/2014
• Est. Priority Date: 07/20/2012
• Status: Active Grant

• Current Assignee: Regents of the University of California (University of California)
• Original Assignee: Regents of the University of California (University of California)
• Inventors: Holder, Casey O., Feezell, Daniel F., DenBaars, Steven P., Speck, James S., Nakamura, Shuji
• Granted Patent: US 9,136,673 B2
• Time in Patent Office: Days
• US Class Current: 372/44.01
• CPC Class Codes: B82Y 20/00 Nanooptics, e.g. quantum optics or photonic crystals
• CPC Class Codes: H01S 2301/176 Specific passivation layers on surfaces other than the emission facet
• CPC Class Codes: H01S 5/0087 for illuminating phosphorescent or fluorescent materials, e.g. using optical arrangements specifically adapted for guiding or shaping laser beams illuminating these materials
• CPC Class Codes: H01S 5/0215 Bonding to the substrate
• CPC Class Codes: H01S 5/0217 Removal of the substrate
• CPC Class Codes: H01S 5/02484 Sapphire or diamond heat spreaders
• CPC Class Codes: H01S 5/04253 having specific optical properties, e.g. transparent electrodes
• CPC Class Codes: H01S 5/04254 characterised by the shape
• CPC Class Codes: H01S 5/0654 Single longitudinal mode emission
• CPC Class Codes: H01S 5/1039 Details on the cavity length
• CPC Class Codes: H01S 5/183 having only vertical cavities, e.g. vertical cavity surface-emitting lasers [VCSEL]
• CPC Class Codes: H01S 5/18341 Intra-cavity contacts
• CPC Class Codes: H01S 5/18355 having a defined polarisation
• CPC Class Codes: H01S 5/18358 containing spacer layers to adjust the phase of the light wave in the cavity
• CPC Class Codes: H01S 5/18369 based on dielectric materials
• CPC Class Codes: H01S 5/2009 by using electron barrier layers
• CPC Class Codes: H01S 5/209 special etch stop layers
• CPC Class Codes: H01S 5/32025 non-polar orientation
• CPC Class Codes: H01S 5/320275 semi-polar orientation
• CPC Class Codes: H01S 5/34333 with a well layer based on Ga(In)N or Ga(In)P, e.g. blue laser
• CPC Class Codes: H01S 5/423 : having a vertical cavity

Abstract

A III-Nitride based Vertical Cavity Surface Emitting Laser (VCSEL), wherein a cavity length of the VCSEL is controlled by etching.

Claims

1. A III-Nitride based Vertical Cavity Surface Emitting Laser (VCSEL), comprising a cavity length controlled by etching.

2. The VCSEL of claim 1, wherein an Aluminum (Al) containing layer in the VCSEL'"'"'s epitaxial structure is used as an etch stop layer for the etching.

3. The VCSEL of claim 2, wherein the etching is carried out by photoelectrochemical etching.

4. The VCSEL of claim 1, wherein an Indium (In) containing layer in the VCSEL'"'"'s epitaxial structure is used as a sacrificial layer for the VCSEL'"'"'s substrate removal by the etching.

5. The VCSEL of claim 4, wherein the etching is carried out by photoelectrochemical etching.

6. The VCSEL of claim 1, wherein the VCSEL is a nonpolar or semipolar III-Nitride VCSEL.

7. The VCSEL of claim 1, wherein the VCSEL is grown on a nonpolar or semipolar substrate.

8. The VCSEL of claim 1, wherein a longitudinal mode of the VCSEL is a single mode.

9. The VCSEL of claim 1, wherein the cavity length is controlled after at least partially removing a substrate on which the VCSEL is grown.

10. A method of fabricating a III-Nitride based Vertical Cavity Surface Emitting Laser (VCSEL), comprising controlling or defining a cavity length of the VCSEL by etching.

11. The method of claim 10, further comprising:

providing or fabricating a III-nitride VCSEL structure grown on a III-nitride substrate and comprising an etch stop layer below an active region;

fabricating a first cavity mirror for the VCSEL on a first side of the VCSEL structure;

attaching the VCSEL structure, at the first cavity mirror, to a submount;

etching down to the etch stop layer to control or define the cavity length of the VCSEL; and

fabricating a second cavity mirror for the VCSEL on the second side of the VCSEL, wherein the first cavity mirror and the second cavity mirror define the VCSEL'"'"'s laser cavity having the cavity length.

12. The method of claim 11, wherein:

the VCSEL structure comprises one or more sacrificial layers containing indium below the active region,

laterally photoelectrochemically etching the sacrificial layers, and

the etch stop layer comprises aluminum.

13. The method of claim 10, comprising:

obtaining or growing epitaxial layers on a nonpolar or semipolar surface of a III-nitride substrate to form a VCSEL structure, the VCSEL structure comprising;

an active region;

an aluminum containing etch stop layer placed between the active region and the substrate to define the VCSEL'"'"'s cavity length;

a p-type GaN layer, wherein the active region is between the p-type GaN layer and the aluminum containing etch stop layer;

an n-type GaN layer that is part of the substrate or between the substrate and the aluminum containing etch stop layer;

etching a mesa through the active region but stopping above the etch stop layer, to form a top surface of the epitaxial layers;

coating the top surface of the wafer with dielectric material;

etching an aperture in the dielectric material;

patterning and depositing a transparent conductive layer on the dielectric material and in the aperture to contact the p-GaN layer in the aperture;

patterning and depositing metal on the transparent conductive layer, wherein the metal does not extend into the aperture;

depositing and patterning a first dielectric Distributed Bragg Reflector (DBR) on the metal;

depositing pad metal on the first dielectric DBR, wherein;

(i) the pad metal makes n-type contact in a field around the first dielectric DBR to protect the first dielectric DBR during a subsequent etch,

(ii) the pad metal coats a top of the first dielectric DBR for bonding to a submount in a subsequent flip-chip bonding process, and

(iii) the pad metal is continuous from the top of the first dielectric DBR to the transparent conductive layer to inject current from the submount to the transparent conductive layer;

flip-chip bonding the submount to the top of the first dielectric DBR using the pad metal;

patterning and depositing a metal n-contact on the n-type GaN layer;

selectively etching down to the Aluminum containing etch stop layer; and

depositing a second dielectric DBR on the aluminum containing stop etch layer and the metal n-type contact, wherein the light from the VCSEL is emitted through the second dielectric DBR.

14. The method of claim 13, wherein the epitaxial layers comprise an Indium containing sacrificial layer between the substrate and the aluminum containing etch stop layer, the method further comprising at least partially removing the substrate by laterally photoelectrochemically (PEC) etching the substrate down to the In containing sacrificial layer.

15. The method of claim 13, wherein the aluminum containing etch stop layer is positioned to define the cavity length such that the VCSEL has single mode operation or the cavity length is 3 micrometers or less.

16. The method of claim 10, wherein the controlling or defining the cavity length of the VCSEL by etching is after at least partially removing a substrate on which the VCSEL is grown.

17. A device, comprising:

a non-polar or semi-polar III-nitride Vertical Cavity Surface Emitting Laser (VCSEL) fabricated on a non-polar or semi-polar substrate.

18. The device of claim 17, wherein light emitted from the VCSEL is polarization locked, wherein the light'"'"'s polarization is locked to a certain direction in the VCSEL.

19. The device of claim 17, wherein the VCSEL is grown on a non-polar or semipolar GaN or III-nitride substrate.

20. The device of claim 19, wherein the VCSEL is grown on a non-polar m-plane substrate and light emitted by VCSEL is polarization-locked along an a-direction of the VCSEL.

21. The device of claim 19, wherein the VCSEL is grown on a semi-polar substrate and light emitted by VCSEL is polarization-locked along an a-direction of the VCSEL.

22. The device of claim 17, wherein the semipolar VCSEL emits blue to green color light.

23. The device of claim 17, wherein the nonpolar VCSEL emits Ultraviolet (UV) to blue color light.

24. The device of claim 17, wherein the VCSEL has a cavity length of less than 3 microns.

25. The device of claim 17, wherein the VCSEL comprises a cavity formed by etching of epitaxial layers during or after the substrate'"'"'s partial or total removal.

26. The device of claim 17, wherein the VCSEL comprises a cavity length such that the VCSEL has single longitudinal mode operation.

27. The device of claim 17, wherein the VCSEL emits light with an output power of no less than 19.5 microwatts or at least 19.5 microwatts, above threshold.

28. The device of claim 17, wherein the VCSEL emits light with a polarization ratio of no less than 0.72 or at least 0.72, above threshold.

29. The device of claim 17, wherein the VCSEL'"'"'s light emission has a full width at half maximum of 0.25 nm or less, or no more than 0.25 nm, above threshold.