Distributed bragg reflector for optoelectronic device
View Patent ↗An oxide-confined VCSELs having a distributed Bragg reflector with a heavily doped high Al content oxide aperture forming layer disposed between a low Al content first layer and a medium Al content second layer. Between the first layer and the oxide aperture forming layer there may be a thin transition region wherein the Al content changes from a higher Al content to a lower Al content. In some embodiments, the Al concentration from the oxide aperture forming layer to the second layer may occur in a step. The oxide aperture forming layer may be disposed at or near a null or a node of the electric field produced by resonant laser light. During the oxidization of the oxide aperture forming layer, all or some of the other aluminum bearing DBR layers may also become oxidized, but to a substantially lesser degree. The junction between the oxidized portion and un-oxidized portion of these layers is believed to reduce the stability and/or reliability of the device. To alleviate this, the present invention contemplates providing an implant, etch or other suitable process to reduce or eliminate one or more electrical artifacts associated with the junction between the oxidized portion and un-oxidized portion of these layers as well as reducing the oxidation of other aluminum bearing layers of the DBR.
1. A vertical cavity surface emitting laser, comprising:
an active region for emitting light at a predetermined wavelength in response to an applied electric current;
a first distributed Bragg reflector mirror situated adjacent one side of the active region, said first distributed Bragg reflector mirror for reflecting light emitted by said active region back toward said active region;
a second distributed Bragg reflector mirror situated adjacent the opposite side of said active region, said second distributed Bragg reflector mirror for reflecting light emitted by said active region back toward said active region;
wherein said second distributed Bragg reflector mirror includes:
a first layer having an Al content below about 35%;
a second layer having an Al content between about 70% and 90%;
an oxide aperture forming layer having an Al content greater than about 95%;
wherein said oxide aperture forming layer is disposed between said first layer and said second layer; and
a transition region disposed between said oxide aperture forming layer and said first layer, wherein said transition region has an Al content that varies from a higher Al content near said oxide aperture forming layer to a lower Al content near said first layer.
2. A vertical cavity surface emitting laser according to claim 1 , wherein said oxide aperture forming layer has an Al content of about 98%.
3. A vertical cavity surface emitting laser according to claim 1 , wherein said first layer has an Al content between 12% and 18%.
4. A vertical cavity surface emitting laser according to claim 1 , wherein said second layer has an Al content near 65%.
5. A vertical cavity surface emitting laser according to claim 1 , wherein said Al content of said transition region varies substantially linearly.
6. A vertical cavity surface emitting laser according to claim 1 , wherein said Al content of said transition region varies substantially non-linearly.
7. A vertical cavity surface emitting laser according to claim 1 , wherein said transition region is doped with an acceptor concentration that varies from a higher concentration near said oxide aperture forming layer to a lower concentration near said first layer.
8. A vertical cavity surface emitting laser according to claim 1 , wherein said oxide aperture forming layer is doped with an impurity more heavily than the first layer and second layer.
9. A vertical cavity surface emitting laser according to claim 1 , wherein said oxide aperture forming layer is disposed at or near the null of an electric field produced by resonant laser light.
10. A vertical cavity surface emitting laser according to claim 1 , wherein said transition region is between about 10 and 100 nm thick.
11. A vertical cavity surface emitting laser according to claim 10 , wherein said transition region is about 20 nm thick.
12. A Vertical Cavity Surface Emitting Laser (VCSEL), comprising:
an active region for emitting light at a predetermined wavelength in response to an applied electric current;
a first distributed Bragg reflector mirror situated on one side of said active region, said first distributed Bragg reflector mirror for reflecting light emitted by said active region back toward said active region;
a second distributed Bragg reflector mirror situated on an opposite side of said active region, said second distributed Bragg reflector mirror for reflecting light emitted by said active region back toward said active region, the second distributed Bragg reflector mirror having a side edge;
wherein said second distributed Bragg reflector mirror includes:
one or more first DBR mirror layers, each of the one or more first DBR mirror layers including an oxidized region extending from the side edge of the second DBR to an oxide termination edge that is situated greater than a first distance from the side edge of the second DBR;
one or more second DBR mirror layers, each of the one or more second DBR mirror layers including an oxidized region extending from the side edge of the second DBR to an oxide termination edge that is situated less than a second distance from the side edge of the second DBR, wherein the first distance is greater than the second distance;
means for reducing or eliminating one or more electrical artifacts related to the oxide termination edge of at least some of the one or more second DBR mirror layers;
a first one of the one or more second DBR mirror layers having a first concentration of an oxidizable material;
a second one of the second DBR mirror layers having a second concentration of an oxidizable material; and
a selected one of the one or more first DBR mirror layers having a third concentration of an oxidizable material, wherein the selected one of the one or more first DBR mirror layers is disposed between said first one of the second DBR mirror layers and said second one of the second DBR mirror layers, and
wherein the first concentration of the oxidizable material is less than the second concentration of the oxidizable material, and the second concentration of the oxidizable material is below the third concentration of the oxidizable material.
13. Vertical Cavity Surface Emitting Laser (VCSEL) according to claim 12 further comprising:
a transition region disposed between said selected one of the one or more first DBR mirror layers and said first one of the second DBR mirror layers, wherein said transition region has a concentration of an oxidizable material that varies from a higher content near said selected one of the one or more first DBR mirror layers to a lower content near said first one of the second DBR mirror layers.
14. A Vertical Cavity Surface Emitting Laser according to claim 12 wherein said means for reducing or eliminating selected electrical artifacts related to the oxide termination edge of at least some of the one or more second DBR mirror layers includes an implant that crosses the oxide termination edge of at least some of the one or more second DBR mirror layers.
15. A Vertical Cavity Surface Emitting Laser according to claim 12 wherein said means for reducing or eliminating selected electrical artifacts related to the oxide termination edge of at least some of the one or more second DBR mirror layers includes an implant that extends from the edge of the DBR past the second distance.
16. A Vertical Cavity Surface Emitting Laser according to claim 12 wherein said implant does not extend all the way to the first distance.
17. A Vertical Cavity Surface Emitting Laser according to claim 12 wherein said means for reducing or eliminating selected electrical artifacts related to the oxide termination edge of at least some of the one or more second DBR mirror layers includes an implant that at least partially electrically isolates the oxide termination edge of at least some of the one or more second DBR mirror layers from a region of the one or more second DBR mirror layers that resides inside the first distance.
18. A Vertical Cavity Surface Emitting Laser according to claim 12 wherein said means for reducing or eliminating selected electrical artifacts related to the oxide termination edge of at least some of the one or more second DBR mirror layers includes an implant that extends down through the active region.
19. A Vertical Cavity Surface Emitting Laser according to claim 12 wherein said side edge of the second distributed Bragg reflector mirror does not extend down into the active region.
20. A Vertical Cavity Surface Emitting Laser according to claim 12 wherein said means for reducing or eliminating selected electrical artifacts related to the oxide termination edge of at least some of the one or more second DBR mirror layers includes a proton implant.
21. A Vertical Cavity Surface Emitting Laser according to claim 12 wherein said means for reducing or eliminating selected electrical artifacts related to the oxide termination edge of at least some of the one or more second DBR mirror layers includes an implant of an electrically active impurity.
22. A Vertical Cavity Surface Emitting Laser according to claim 12 wherein said means for reducing or eliminating selected electrical artifacts related to the oxide termination edge of at least some of the one or more second DBR mirror layers includes a helium implant.
23. A Vertical Cavity Surface Emitting Laser according to claim 12 wherein the means for reducing or eliminating selected electrical affects of the oxide termination edge of the one or more second DBR mirror layers includes removing a portion of the one or more second DBR mirror layers that includes the oxide termination edge of the one or more second DBR mirror layers.
24. A Vertical Cavity Surface Emitting Laser according to claim 12 wherein said selected one of the one or more first DBR mirror layers is disposed at or near an expected null of an electric field produced by resonant laser light of the Vertical Cavity Surface Emitting Laser.