VCSEL with emission on substrate side
A VCSEL is described that provides for emission from the substrate side. The VCSEL comprises a substrate having first and second major surfaces, a first distributed Bragg reflector (DBR) on the first major surface of the substrate, an active region on the first DBR, and a second DBR on the active region. These elements are aligned on a longitudinal axis along which laser radiation is emitted. In an illustrative embodiment of the invention, an open region extends through the substrate along the longitudinal axis between the second major surface of the substrate and the first DBR. An anti-reflection coating and a first ohmic contact are located on the first DBR in this region. Preferably the first ohmic contact extends around all or part of the anti-reflection coating. A second ohmic contact is located on the surface of the second DBR. The two DBRs form a laser cavity; and emission takes place along the longitudinal axis through the anti-reflection coating. A method for forming the VCSEL is also described.
1. A vertical cavity surface emitting laser (VCSEL) comprising:
a substrate;
a first distributed Bragg reflector (DBR) on a first major surface of the substrate;
an open region in the substrate that exposes part of a first surface of the first DBR;
an anti-reflection coating on a first portion of the exposed first surface of the first DBR;
a first electrical contact on a second portion of the exposed first surface of the first DBR;
an active region on a second surface of the first DBR;
a second DBR adjacent the active region; and
a second electrical contact on the second DBR.
2. The VCSEL of claim 1 wherein the first electrical contact and the first DBR are a first conductivity type and the second electrical contact and the second DBR are a second conductivity type, opposite the first conductivity type.
3. The VCSEL of claim 1 wherein the substrate is n-type GaAs.
4. The VCSEL of claim 3 wherein the first and second DBRs comprise alternating first and second layers of AlGaAs and GaAs and the layers are approximately one quarter wavelength in thickness at the operating wavelength of the VCSEL.
5. The VCSEL of claim 1 further comprising an oxide aperture aligned with the anti-reflection coating for confining current flow in the VCSEL.
6. The VCSEL of claim 1 further comprising an aperture layer disposed between the active region and the second DBR, the aperture layer having an aperture therein for confining current flow along a longitudinal axis of the VCSEL.
7. The VCSEL of claim 1 further comprising an annular implanted region in the second DBR that is aligned with the anti-reflection coating.
8. The VCSEL of claim 1 wherein the first electrical contact substantially surrounds the periphery of the anti-reflection coating on the first DBR.
9. A vertical cavity surface emitting laser (VCSEL) comprising:
an active region having first and second major surfaces;
a first distributed Bragg reflector (DBR) on the first major surface of the active region;
an anti-reflection coating on a first portion of an exposed surface of the first DBR;
a first electrical contact on a second portion of the exposed surface of the first DBR, and substantially surrounding a periphery of the antireflection coating on the first DBR;
a substrate on the first DBR, wherein the substrate has an open region within which the first electrical contact and the anti-reflection coating are located;
an aperture layer on the second major surface of the active region having an aperture aligned with the anti-reflection coating;
a second DBR on the aperture layer; and
a second electrical contact on the second DBR.
10. The VCSEL of claim 9 wherein the first electrical contact and the first DBR are a first conductivity type and the second electrical contact and the second DBR are a second conductivity type, opposite the first conductivity type.
11. The VCSEL of claim 9 wherein the substrate is n-type GaAs.
12. The VCSEL of claim 11 wherein the first and second DBRs comprise alternating first and second layers of AlGaAs and GaAs and the layers are approximately one quarter wavelength in thickness at the operating wavelength of the VCSEL.
13. A vertical cavity surface emitting laser (VCSEL) comprising:
an active region having first and second major surfaces;
a first distributed Bragg reflector (DBR) on the first major surface of the active region;
an anti-reflection coating on a first portion of an exposed surface of the first DBR;
a first ohmic contact on a second portion of the exposed surface of the first DBR;
a second DBR on the second major surface of the active region; and
a second ohmic contact on the second DBR.
14. The VCSEL of claim 13 wherein the first ohmic contact and the first DBR are a first conductivity type and the second ohmic contact and the second DBR are a second conductivity type, opposite the first conductivity type.
15. The VCSEL of claim 13 further comprising an aperture layer disposed between the active region and the second DBR, the aperture layer having an aperture therein for confining current flow along a longitudinal axis of the VCSEL.
16. A method for fabricating a vertical cavity surface emitting laser comprising:
forming a first distributed Bragg reflector (DBR) on a first major surface of a substrate;
forming an active region on the first DBR;
forming a second DBR on the active region;
removing a portion of the substrate to expose a portion of the first DBR;
forming a first electrical contact on a first part of an exposed surface of the first DBR;
forming an anti-reflection coating on a second part of the exposed portion of the first DBR; and
forming a second electrical contact on the second DBR.
17. The method of claim 16 further comprising
forming an aperture layer between the active region and the second DBR; and
forming an aperture in the aperture layer, the aperture for confining current flow along a longitudinal axis of the VCSEL.
18. The method of claim 16 further comprising implanting an annular region in the second DBR that is aligned with the anti-reflection coating.
19. The VCSEL of claim 9 wherein the open region forms sidewalls in the substrate and the first electrical contact extends along at least a portion of the sidewalls.
20. The VCSEL of claim 9 wherein the aperture confines current flow along a longitudinal axis of the VCSEL.
21. The method of claim 17 wherein the aperture is formed by oxidation or ion implantation.