Abstract
In an embodiment an optoelectronic device includes an epitaxially grown functional layer stack having a first layer, an active region arranged on the first layer, a second layer arranged on the active region and a third layer arranged on the second layer, the third layer having a higher concentration of the dopant of the second conductivity type than the second layer and an electrically conductive contact layer arranged on the third layer, wherein the functional layer stack is laterally limited by side surfaces of the functional layer stack and includes a central region along a center line of the functional layer stack, wherein the central region is spaced from the side surfaces, wherein a current path from the electrically conductive contact layer through the third layer to the second layer is limited to the central region, and wherein the third layer includes at least one intersection and the at least one intersection divides the third layer into at least a first region and a second region separated from the first region, the first region being limited to the central region.
Claims
1.-20. (canceled)
21. An optoelectronic device comprising: an epitaxially grown functional layer stack comprising: a first layer with a dopant of a first conductivity type; an active region arranged on the first layer; a second layer with a dopant of a second conductivity type arranged on the active region; and a third layer with the dopant of the second conductivity type arranged on the second layer, the third layer having a higher concentration of the dopant of the second conductivity type than the second layer; and an electrically conductive contact layer arranged on the third layer, wherein the functional layer stack is laterally limited by side surfaces of the functional layer stack and comprises a central region along a center line of the functional layer stack, wherein the central region is spaced from the side surfaces, wherein a current path from the electrically conductive contact layer through the third layer to the second layer is limited to the central region, and wherein the third layer comprises at least one intersection and the at least one intersection divides the third layer into at least a first region and a second region separated from the first region, the first region being limited to the central region.
22. The optoelectronic device according to claim 21, wherein the electrically conductive contact layer electrically contacts the third layer only in the central region and/or is arranged on the third layer only in the central region.
23. The optoelectronic device according to claim 21, wherein the third layer, or the third layer and the second layer, comprises a first surface structuring on a surface facing the electrically conductive contact layer with a plurality of protrusions and trenches.
24. The optoelectronic device according to claim 23, wherein protrusions of the first surface structuring in the central region are higher than protrusions of the first surface structuring outside the central region.
25. The optoelectronic device according to claim 23, wherein protrusions of the first surface structuring at least in the central region have a planarized surface facing the electrically conductive contact layer.
26. The optoelectronic device according to claim 23, wherein protrusions of the first surface structuring electrically contact the electrically conductive contact layer in the central region.
27. The optoelectronic device according to claim 21, wherein the second layer comprises a second surface structuring on a surface facing the electrically conductive contact layer with a plurality of protrusions and trenches in an area outside the central region.
28. The optoelectronic device according to claim 21, further comprising a planarization layer arranged on the third and/or second layer, wherein the planarization layer fills the at least one intersection and/or trenches of first and/or second surface structuring.
29. The optoelectronic device according to claim 28, wherein the planarization layer is of an electrically isolating material.
30. The optoelectronic device according to claim 21, wherein the central region is limited to half of a distance between two opposing side surfaces of the functional layer stack.
31. The optoelectronic device according to claim 21, wherein the first layer and/or the second layer and/or the third layer comprises a base material selected from the group consisting of GaN, AlGaN, AlGaInP, AlGaInN and AlGaP.
32. A method for manufacturing at least one optoelectronic device, the method comprising: providing a functional layer stack comprising: a first layer with a dopant of a first conductivity type; an active region arranged on the first layer; a second layer with a dopant of a second conductivity type arranged on the active region; and a third layer with the dopant of the second conductivity type arranged on the second layer, the third layer having a higher concentration of the dopant of the second conductivity type than the second layer, wherein the functional layer stack is laterally limited by side surfaces of the functional layer stack and comprises a central region along a center line of the functional layer stack, and wherein the central region is spaced from the side surfaces; providing an electrically conductive contact layer on the third layer such that a current path from the electrically conductive contact layer through the third layer to the second layer is limited to the central region; and creating at least one intersection in the third layer such that the at least one intersection divides the third layer into at least a first region and a second region separated from the first region, the first region being limited to the central region.
33. The method according to claim 32, further comprising removing the third layer in an area outside the central region.
34. The method according to claim 32, further comprising roughening a surface of the third layer facing the electrically conductive contact layer to create a first surface structuring with a plurality of protrusions and trenches.
35. The method according to claim 34, further comprising planarizing protrusions of the first surface structuring at least in the central region.
36. The method according to claim 32, further comprising roughening a surface of the second layer facing the electrically conductive contact layer in an area outside the central region to create a second surface structuring with a plurality of protrusions and trenches.
37. The method according to claim 32, further comprising filling the at least one intersection and/or trenches of first and/or second surface structuring with an electrically isolating filling material.
Description
BRIEF DESCRIPTION OF THE DRAWINGS
[0052] In the following, embodiments of the invention will be explained in more detail with reference to the accompanying drawings.
[0053] FIG. 1 shows a cross sectional view of an optoelectronic device;
[0054] FIG. 2A and 2B show each a cross sectional view of an optoelectronic device according to some aspects of the invention; and
[0055] FIG. 3A to 7C show each a cross sectional view of a further embodiment of an optoelectronic
DETAILED DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS
[0056] The present disclosure will now be described more fully hereinafter with reference to the accompanying drawings, in which exemplary embodiments of the disclosure are shown. The disclosure may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein; rather, these embodiments are provided for thoroughness and completeness. Like reference characters refer to like elements throughout the description. The drawings are not necessarily to scale and certain features may be exaggerated in order to better illustrate and explain the exemplary embodiments of the present disclosure.
[0057] FIG. 1 shows a cross-sectional view of an optoelectronic device comprising a layer stack 2 with a first layer 3 with a dopant of a first conductivity type, an active region 4 arranged on the first layer 3, a second layer 5 with a dopant of a second conductivity type arranged on the active region 4, and a third layer 6 with the dopant of the second conductivity type arranged on the second layer 5, the third layer 6 having a higher concentration of the dopant of the second conductivity type than the second layer 5. Further to this, an electrically conductive contact layer 7 is arranged on the third layer 6. By electrically connecting the optoelectronic device, charge carriers (indicated by the tree arrows) are due to the high doping of the third layer 6 spread throughout the third layer and introduced in the active region 4 of the optoelectronic device and recombine under the emission of light. However, charge carriers recombining alongside surfaces of the functional layer stack may due to impurities of the material recombine without an emission of light leading to non-radiative losses (indicated by the two lightning bolts). These non-radiative losses reduce the internal efficiency (IQE) of the optoelectronic device and are thus unwanted, in particular for the optoelectronic device being particularly small.
[0058] The inventors however found that implementing a current confinement for the functional layer stack, such that a carrier flow within the layer stack is centered to a central region of the functional layer stack can help to reduce these non-radiative losses. By a current confinement the carrier density alongside surfaces 8 of the layer stack is reduced and impurities along the side faces have no or less significant influence on (efficiency-) losses by non-radiative recombination of the carriers. The functional layer stack and/or an electrically conductive contact layer arranged on the functional layer stack is therefore modified/configured to form a current path from the electrically conductive contact layer through the layer stack only in a central region of the layer stack as shown in several embodiment in FIGS. 2A to 7C. Some of the embodiments shown in the Figures additionally provide an improved outcoupling of light generated in the layer stack, by providing an outcoupling structure on a surface of the layer stack facing the conductive contact layer.
[0059] FIG. 2A shows an optoelectronic device 1 in a cross-sectional view. The optoelectronic device 1 comprises a layer stack 2 with a first layer 3 with a dopant of a first conductivity type, an active region 4 arranged on the first layer 3, a second layer 5 with a dopant of a second conductivity type arranged on the active region 4, and a third layer 6 with the dopant of the second conductivity type arranged on the second layer 5, the third layer 6 having a higher concentration of the dopant of the second conductivity type than the second layer 5. Further to this, an electrically conductive contact layer 7 is arranged on the third layer 6. The functional layer stack 2 is laterally limited by side surfaces 8 of the functional layer stack 2 and comprises a central region 9 along a center line 10 of the functional layer stack 2. The central region 9 is spaced from the side surfaces 8 forming a subregion of the layer stack extending throughout the layer stack along the center line 10 of the functional layer stack. To provide a current confinement the third layer 6 is modified in such that a current path from the electrically conductive contact layer 7 through the third layer 6 to the second layer 5 is limited to the central region 9. An area of the third layer 6 outside the central region has been removed or its height has been reduced in an area outside the central region for this purpose, in order to guide a current introduced into the electrically conductive contact layer 7 to the central region and not spread it throughout an entire third layer extending over the entire functional layer stack 2. The removal of an area of the third layer 6 outside the central region can in addition also lead to an at least partial removal of the second layer 5 reducing its height in an area outside the central region.
[0060] FIG. 2B shows an alternative embodiment of the optoelectronic device 1. To provide a current confinement the third layer 6 has not been removed entirely in areas outside the central region but intersections 11 have been introduced to divide the third layer 6 into a first region 6a and a second region 6b. The first region 6a is thereby limited to the central region 9 and the electrically conductive contact layer 7 contacts the third layer only in the first region/central region. A current path from the electrically conductive contact layer 7 through the third layer 6 to the second layer 5 is thus limited to the central region 9 in order to guide a current introduced to the electrically conductive contact layer 7 to the central region and not spread it throughout the entire third layer 6.
[0061] FIGS. 3A to 3C show embodiments in which the area of the third layer 6 outside the central region 9 has been removed to provide a current confinement. In addition a first surface structuring 12 is provided on the third layer 6 on a surface facing the electrically conductive contact layer 7 comprising a plurality of protrusions and trenches. The first surface structuring can be to improve the outcoupling efficiency of the optoelectronic device 1.
[0062] As shown in FIG. 3A and 3B a planarization layer 14 is arranged on the layer stack 2 replacing areas which have been removed from the third layer 6 outside the central region and to provide the first surface structuring 12. The planarization layer 14 is in particular of a transparent material, which in case of FIGS. 3A and 3B could in addition be an electrically isolating material to not counteract the current confinement generated by removing the third layer outside the central region. The electrically conductive contact layer 7 contacts the protrusions of the first surface structuring while the trenches are filled by the planarization layer. For better contacting the protrusions can be planarized to provide a good contact surface for the electrically conductive contact layer 7.
[0063] The electrically conductive contact layer 7 can extend over the entire functional layer stack (see FIG. 3A) or can be limited to the central region 9 (see FIG. 3B). In particular in case of the electrically conductive contact layer 7 extending over the entire functional layer stack it may be of a transparent conductive material to allow the light being generated in the functional layer stack to emerge from the optoelectronic device 1.
[0064] As shown in FIG. 3C, the planarization layer can also only cover the first surface structuring filling the trenches of the first structuring 12. In this case the planarization layer can also be of an electrically conductive material such as for example a TCO, to provide a good current spreading into the third layer within the central region 9.
[0065] FIGS. 4A and 4B show embodiments of the optoelectronic device 1 without a planarization layer. The optoelectronic device of FIG. 4A and in particular the third layer 6 of the optoelectronic device 1 comprises in addition to the embodiment shown in FIG. 2B a first surface structuring on the second region 6b of the third layer 6 on a surface facing the electrically conductive contact layer 7. The first surface structuring comprises a plurality of protrusions and trenches and can be to improve the outcoupling efficiency of the optoelectronic device 1.
[0066] The optoelectronic device of FIG. 4B and in particular the second layer 6 of the optoelectronic device 1 outside the central region comprises in addition to the embodiment shown in FIG. 2A a second surface structuring on a surface facing the electrically conductive contact layer 7. The second surface structuring comprises a plurality of protrusions and trenches and can be to improve the outcoupling efficiency of the optoelectronic device 1.
[0067] In a not shown embodiment, the third layer 6 of the optoelectronic device 1 comprises as for example shown in FIG. 4A a first surface structuring on the second region 6b of the third layer 6 on a surface facing the electrically conductive contact layer 7, wherein the first surface structuring extends down into the second layer 5 as well. The first surface structuring thus comprises a plurality of protrusions and trenches, wherein the trenches can at least partly be arranged in the second layer 5 and can be to improve the outcoupling efficiency of the optoelectronic device 1.
[0068] FIGS. 5A to 5C show embodiments of the optoelectronic device 1 which in addition to the embodiment shown in FIG. 4A comprise a planarization layer 14 and in which the first surface structuring 12 also extends on a surface of the third layer 6 in the central region 9. Protrusions of the first surface structuring 12 are thereby higher in the central region 9 than in an area outside the central region to provide a contacting surface for the electrically conductive contact layer 7 and to provide a current confinement to the central region 9 when arranging the third layer with an electrically conductive contact layer 7 extending over the entire functional layer stack as shown in FIG. 5A.
[0069] In addition, and to provide the current confinement the third layer may comprise at least one intersection dividing the third layer in at least a first and a second region, where the first region is in contact to the electrically conductive contact layer 7 and forms the current path from the electrically conductive contact layer 7 to the second layer.
[0070] As shown in FIG. 5A and 5B the planarization layer 14 is arranged on the layer stack 2 replacing areas which have been removed from the third layer 6 outside the central region and to provide the first surface structuring 12. The planarization layer 14 is in particular of a transparent material, which in case of FIGS. 5A and 5B should in addition be an electrically isolating material to not counteract the current confinement generated by removing the third layer outside the central region. The electrically conductive contact layer 7 contacts the protrusions of the first surface structuring while the trenches are filled by the planarization layer. For better contacting the protrusions can be planarized to provide a good contact surface for the electrically conductive contact layer 7.
[0071] The electrically conductive contact layer 7 can extend over the entire functional layer stack (see FIG. 5A) or can be limited to the central region 9 (see FIG. 5B). In particular in case of the electrically conductive contact layer 7 extending over the entire functional layer stack it may be of a transparent conductive material to allow the light being generated in the functional layer stack to emerge from the optoelectronic device 1.
[0072] As shown in FIG. 5C, the planarization layer 14 can also only cover the first surface structuring 12 filling the trenches of the first structuring 12 in the central region 9. In this case the planarization layer can also be of an electrically conductive material such as for example a TCO, to provide a good current spreading into the third layer within the central region 9.
[0073] FIGS. 6A and 6B show embodiments of the optoelectronic device 1 in which compared to the embodiment shown in FIG. 5A and 5B protrusions of the first surface structuring 12 substantially have the same height throughout the first surface structuring 12. To provide a current confinement to the central region 9, the third layer comprises intersections 11 dividing the third layer into a first region 6a and a second region 6b, where the first region is limited to the central region and contacts the electrically conductive contact layer 7 also being limited to the central region 9.
[0074] As shown in FIG. 6A, the planarization layer 14 is arranged on the layer stack 2 replacing areas which have been removed from the third layer 6 in in the intersections and in the trenches of the first surface structuring. The planarization layer 14 can, as shown in FIG. 6B, only cover the first surface structuring 12 filling the trenches of the first structuring 12 in the central region 9. In this case the planarization layer can also be of an electrically conductive material such as for example a TCO, to provide a good current spreading into the third layer within the central region 9.
[0075] FIGS. 7A to 7C show a further development of the embodiment of FIG. 4B, according to which not only the second layer comprises the second surface structuring 13, but the third layer 6 also comprises a first surface structuring provided on the third layer 6 on a surface facing the electrically conductive contact layer 7 comprising a plurality of protrusions and trenches. The first surface structuring can be to improve the outcoupling efficiency of the optoelectronic device 1.
[0076] As shown in FIG. 7A and 7B a planarization layer 14 is arranged on the layer stack 2 replacing areas which have been removed from the third layer 6 outside the central region and to provide the first surface structuring 12 as well as in the trenches of the second surface structuring 13. The planarization layer 14 is in particular of a transparent material, which in case of FIGS. 3A and 3B should in addition be an electrically isolating material to not counteract the current confinement generated by removing the third layer outside the central region. The electrically conductive contact layer 7 contacts the protrusions of the first surface structuring while the trenches are filled by the planarization layer. For better contacting the protrusions can be planarized to provide a good contact surface for the electrically conductive contact layer 7.
[0077] The electrically conductive contact layer 7 can extend over the entire functional layer stack (see FIG. 7A) or can be limited to the central region 9 (see FIG. 7B). In particular in case of the electrically conductive contact layer 7 extending over the entire functional layer stack it may be of a transparent conductive material to allow the light being generated in the functional layer stack to emerge from the optoelectronic device 1.
[0078] As shown in FIG. 7C, the planarization layer can also only cover the first surface structuring filling the trenches of the first structuring 12. In this case the planarization layer can also be of an electrically conductive material such as for example a TCO, to provide a good current spreading into the third layer within the central region 9.
