Converter for an optoelectronic component, optoelectronic component, method for forming a converter for an optoelectronic component and material for a reflector of an optoelectronic component

Abstract

A converter for an optoelectronic component, an optoelectronic component, a method for forming a converter for an optoelectronic component and a material for a reflector of an optoelectronic component are disclosed. In an embodiment, a converter includes a conversion element for converting a wavelength of electromagnetic radiation which passes through at least a part of the conversion element and a reflector, wherein the reflector includes a reflector material which includes MgF.sub.2 and/or an inorganic material as a matrix material in which a plurality of particles is embedded, wherein a refractive index of the matrix material amounts to at least 1 and at most 2, and wherein a refractive index of the particles amounts to at least 1.5.

Claims

1. A converter for an optoelectronic component, the converter comprising: a conversion element configured to convert a wavelength of electromagnetic radiation which passes through at least a part of the conversion element; and a reflector, wherein the reflector comprises a reflector material which comprises MgF.sub.2 and/or an inorganic material as a matrix material in which a plurality of particles is embedded, wherein a refractive index of the matrix material amounts to at least 1 and at most 2, and wherein a refractive index of the particles amounts to at least 1.5.

2. The converter according to claim 1, wherein a difference between the refractive index of the matrix material and the refractive index of a material of the particles amounts to at least 0.1 and at most 1.5.

3. The converter according to claim 1, wherein the reflector material is a ceramic.

4. The converter according to claim 1, wherein the particles embedded in the matrix material of the reflector material comprise TiO.sub.2.

5. The converter according to claim 1, wherein the reflector material is an inorganic material.

6. The converter according to claim 1, wherein the reflector material is free of alumina.

7. The converter according to claim 1, wherein the reflector is in direct contact with the conversion element.

8. The converter according to claim 1, wherein the reflector adjoins the conversion element in at least two directions.

9. The converter according to claim 1, wherein the reflector material is formed by sintering.

10. The converter according to claim 1, wherein a particle size distribution D50 of the particles embedded in the matrix material is at least 100 nm and less than 15 m.

11. The converter according to claim 1, wherein a concentration of the particles embedded in the matrix material of the reflector material amounts to at least 5% and at most 90%.

12. The converter according to claim 1, wherein a porosity of the reflector material amounts to less than 2 volume percent.

13. The converter according to claim 1, wherein conversion particles are dispersed in the matrix material of the conversion element.

14. An optoelectronic component comprising: the converter according to claim 1; and an optoelectronic semiconductor chip.

15. A method for forming a converter for an optoelectronic component, the method comprising: providing a conversion element for converting a wavelength of electromagnetic radiation which passes through at least a part of the conversion element; and forming a reflector comprising a reflector material, wherein the reflector material is formed by sintering, wherein the reflector material comprises MgF.sub.2 and/or an inorganic material as a matrix material, in which a plurality of particles is embedded, wherein a refractive index of the matrix material amounts to at least 1 and at most 2, and wherein a refractive index of the particles amounts to at least 1.5.

16. The method according to claim 15, wherein, during sintering, the materials of the reflector material are pressed together.

17. The method according to claim 15, wherein the particles embedded in the matrix material of the reflector material comprise TiO.sub.2.

18. The method according to claim 15, wherein the reflector material is formed by spark-plasma-sintering.

19. A material for a reflector of an optoelectronic component, the material comprising: MgF.sub.2 as a matrix material; and TiO.sub.2 particles incorporated in the matrix material, wherein a particle size distribution D50 of the TiO.sub.2 particles is at least 100 nm and less than 15 m.

20. The converter according to claim 1, wherein a reflectivity of the reflector is at least 90%.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) The following description of figures may further illustrate and explain exemplary embodiments. Components that are functionally identical or have an identical effect are denoted by identical references. Identical or effectively identical components might be described only with respect to the figures where they occur first. Their description is not necessarily repeated in successive figures.

(2) FIGS. 1A and 1B show schematic cross sections through converters;

(3) FIGS. 2A and 2B show cut-away views through exemplary embodiments of the converter;

(4) FIG. 3 shows a cut-away view of an exemplary embodiment of an optoelectronic component;

(5) In FIGS. 4 and 5 optical properties of two converters and an embodiment of the converter are compared; and

(6) FIGS. 6 and 7 show cutaway views of exemplary embodiments of an optoelectronic component.

DETAILED DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS

(7) In FIG. 1A a schematic cross section through a converter 20 which is no embodiment of the converter 20 described herein is shown. The converter 20 comprises a conversion element 22 and a reflector 23 which are arranged on a dichroic filter 26. The conversion element 22 comprises a matrix material in which conversion particles 24 are embedded. The conversion element 22 is arranged to convert electromagnetic radiation passing the conversion element 22. The reflector 23 surrounds the conversion element 22 in lateral directions x which extend parallel to a main plane of extension of the dichroic filter 26. The reflector 23 is arranged to reflect electromagnetic radiation hitting the reflector 23.

(8) The converter 20 is arranged in a transmissive configuration. This means, a light source is arranged at a first side 27 of the converter 20. Electromagnetic radiation emitted by the light source passes the converter 20 through the dichroic filter 26 and the conversion element 22 towards a second side 28 of the converter 20 which faces away from the first side 27. In this way, electromagnetic radiation emitted by the light source passes the conversion element 22. The opening angle of the electromagnetic radiation emitted by the light source is shown schematically. By passing the conversion element 22 the wavelength of the electromagnetic radiation is converted. The electromagnetic radiation passing the conversion element 22 is scattered at the conversion particles 24. Therefore, at least a part of the electromagnetic radiation leaves the conversion element 22 at side surfaces 29 which extend traverse to the main plane of extension of the dichroic filter 26. The electromagnetic radiation leaving the conversion element 22 at the side surfaces 29 can be reflected at the reflector 23 back towards the conversion element 22. In this way, most of the electromagnetic radiation is emitted at the second side 28 of the converter 20. Such a converter 20 can be employed in optoelectronic devices where it is desired to tune the wavelength of the emitted electromagnetic radiation.

(9) In FIG. 1B a schematic cross section through a converter 20 which is no embodiment of the converter 20 described herein is shown. In comparison to the converter 20 which is shown in FIG. 1A, here the converter 20 is arranged in a reflective configuration. This means, the conversion element 22 is arranged on a carrier 38 which is reflective. A light source is arranged in such a way, that the electromagnetic radiation emitted by the light source hits the conversion element 22 at a first side 27. Electromagnetic radiation entering the conversion element 22 passes the conversion element 22 and can be reflected by the carrier 38 or the reflector 23 which surrounds the conversion element 22. Thus, the converted electromagnetic radiation leaves the conversion element 22 at the first side 27.

(10) The converters 20 shown in FIGS. 1A and 1B are particularly suitable to be employed in laser devices.

(11) In FIG. 2A a cutaway view of an exemplary embodiment of the converter 20 is shown. Similar to FIG. 1, the converter 20 is arranged in a transmissive configuration. The converter 20 is arranged to be employed in an optoelectronic component 21. The converter 20 comprises a conversion element 22 for converting the wavelength of electromagnetic radiation which passes through at least a part of the conversion element 22. The conversion element 22 comprises a matrix material in which conversion particles 24 are dispersed. The conversion element 22 is arranged on a dichroic filter 26. A first side 27 of the conversion element 22 faces the dichroic filter 26 and a second side 28 of the conversion element 22 faces away from the first side 27. Furthermore, the conversion element 22 comprises side surfaces 29 which run traverse to the main plane of extension of the dichroic filter 26.

(12) The converter 20 further comprises a reflector 23. The reflector 23 is arranged adjacent to the conversion element 22. In lateral directions x the reflector 23 completely surrounds the conversion element 22. The first side 27 and the second side 28 of the conversion element 22 are free of the reflector 23. At the side surfaces 29 the reflector 23 is in direct contact with the conversion element 22. The reflector 23 comprises a reflector material which comprises MgF.sub.2 and/or an inorganic material as a matrix material, in which a plurality of particles is embedded. The difference between the refractive index of the matrix material and the refractive index of the material of the particles amounts to at least 0.1 and at most 1.5.

(13) The reflector material is a ceramic and the particles embedded in the matrix material of the reflector material can comprise TiO.sub.2. Therefore, the reflector material is an inorganic material and it is free of alumina. The particle size distribution D50 of the particles embedded in the matrix material is at least 100 nm and less than 15 m. Furthermore, the concentration of the particles embedded in the matrix material of the reflector material amounts to at least 5% and at most 90%. The porosity of the reflector material amounts to less than 2 volume percent.

(14) The reflector 23 is surrounded by a holder 30 in lateral directions x. The holder 30 stabilizes the converter 20.

(15) The converter 20 can be employed in an optoelectronic component 21 where electromagnetic radiation is emitted by a light source, for example, a laser, and directed towards the conversion element 22. The direction of propagation of the radiation is shown by arrows. The wavelength of electromagnetic radiation emitted by the light source is converted or at least partially converted while the electromagnetic radiation passes the conversion element 22. After the conversion and possible reflection at the reflector 23 most of the electromagnetic radiation leaves the conversion element 22 at the second side 28.

(16) The part of the electromagnetic radiation passing the conversion element 22 which is not scattered at any conversion particles 24 is not converted. Therefore, electromagnetic radiation with a converted wavelength and electromagnetic radiation with the wavelength emitted by the light source can leave the conversion element 22 at the second side 28. Thus, in this embodiment the converter 20 is employed in a transmissive configuration.

(17) The converter 20 can be formed by providing the conversion element 22 and forming the reflector 23 which comprises the reflector material. The reflector material is formed by sintering, for example, by spark-plasma-sintering. During sintering MgF.sub.2 and/or an inorganic material and a plurality of particles is pressed together.

(18) In FIG. 2B a cutaway view of a further exemplary embodiment of the converter 20 is shown. In this embodiment the converter 20 is arranged in a reflective configuration. The conversion element 22 is surrounded by the reflector 23 in lateral directions x and at the first side 27 of the conversion element 22. The reflector 23 is surrounded by the holder 30 in lateral directions x. The conversion element 22, the reflector 23 and the holder 30 are arranged on a heat sink 31. The heat sink 31 is arranged at a side of the reflector 23 which faces away from the conversion element 22.

(19) Electromagnetic radiation emitted by a light source enters the conversion element 22 at the second side 28 of the conversion element 22. The electromagnetic radiation entering the conversion element 22 can be scattered at conversion particles 24, be reflected at the reflector 23 and leave the conversion element 22 at the second side 28. As the reflector 23 surrounds the conversion element 22 from all sides except for the second side 28, electromagnetic radiation leaving the conversion element 22 at a side which is not the second side 28 is reflected back to the conversion element 22 by the reflector 23. It is possible that a part of the electromagnetic radiation entering the conversion element 22 is not converted. Therefore, electromagnetic radiation with an unmodified wavelength can leave the conversion element 22 at the second side 28.

(20) As the reflector material has a high thermal conductivity heat can efficiently be transferred from the conversion element 22 to the heat sink 31.

(21) For the embodiments of the converter 20 shown in FIGS. 2A and 2B it is advantageous that the reflector material has a high reflectivity, as losses within the converter 20 are minimized. Furthermore, since the light penetration depth of the reflector material is low, the size of the reflector 23 and thus of the converter 20 can be kept small. In addition, as the reflector material has a high thermal robustness the light source can be a laser or the electromagnetic radiation emitted by the light source can have a high luminance.

(22) In FIG. 3 a cutaway view of an exemplary embodiment of the optoelectronic component 21 is shown. A semiconductor chip 25 is surrounded by a conversion element 22. The semiconductor chip 25 can, for example, be a light-emitting diode. The conversion element 22 can completely surround the semiconductor chip 25 in lateral directions x and at a second side 28 of the semiconductor chip 25. At a first side 27 of the semiconductor chip 25 which faces away from the second side 28 the semiconductor chip 25 is partially covered by the conversion element 22. The semiconductor chip 25 and the conversion element 22 are arranged on a carrier 38. At a top side 32 of the carrier 38 electrical contacts 33 are arranged.

(23) Via interconnects 34 the electrical contacts 33 are electrically connected with the semiconductor chip 25. The interconnects 34 are arranged at the first side 27 of the semiconductor chip 25. The electrical contacts 33 are electrically connected with at least one through-contact 35 which extends through the carrier 38 from the top side 32 to a bottom side 36 which faces away from the top side 32. The through-contact 35 can comprise an electrically conductive material. The carrier 38 comprises the reflector 23 which comprises the reflector material. The reflector 23 is arranged adjacent to the conversion element 22. Therefore, electromagnetic radiation leaving the conversion element 22 in the direction of the carrier 38 is reflected at the reflector 23 back towards the conversion element 22. As the reflector material is a ceramic, the reflector 23 can act as the carrier 38.

(24) With FIGS. 4 and 5 the optical properties of two reflector materials are compared to the optical properties of an exemplary embodiment of the reflector material of the converter 20 described herein.

(25) For a first sample S1 and a second sample S2, the reflector material consists of alumina. The third sample S3 is an exemplary embodiment of the reflector material of the converter 20. In the third sample S3 the reflector material comprises MgF.sub.2 and TiO.sub.2 particles. All three samples S1, S2, S3 are provided with a thickness of approximately 100 m.

(26) For all three samples S1, S2, S3 the ratio of forward to backward scattering and an estimate of the fraction of total scattered power to the incident laser power are determined. The results are shown in the table shown in FIG. 4. Each row corresponds to one of the samples S1, S2, S3. In the first column the thickness T of each sample is given in m. In the second column the ratio R of forward to backward scattering is provided. In the third column an estimate of the fraction F of the total scattered power to the incident laser power is given. A small value of the ratio of forward to backward scattering relates to a high reflectivity. Therefore, the reflectivity of the reflector material described herein is substantially improved in comparison to the other two samples. The fraction of the total scattered power to the incident laser power gives an estimate of the power absorbed by the respective reflector material and is similar for all three samples. As the absorption is small also for the reflector material described herein, the reflector 23 can be employed as a diffuse reflector.

(27) In FIG. 5 bi-directional scattering distribution measurements (BSDF) for the three samples S1, S2, S3 are shown. On the x-axis the angle is plotted in degrees. On the y-axis the bi-directional scattering distribution is plotted. For a wide range of angles sample S3 shows the greatest back-scattering and thus the highest reflectivity.

(28) In FIG. 6 a cutaway view of an exemplary embodiment of an optoelectronic component 21 is shown. The optoelectronic component 21 comprises the converter 20 and an optoelectronic semiconductor chip 25. In this case the optoelectronic semiconductor chip 25 is an edge-emitting laser diode. The semiconductor chip 25 is arranged on a carrier 38. On a top side 32 of the carrier 38 electrical contacts 33 are arranged which are electrically connected with the semiconductor chip 25. Electromagnetic radiation emitted by the semiconductor chip 25 during operation is deflected at an optical element 37 in a direction which is perpendicular to the main plane of extension of the carrier 38. On a side of the semiconductor chip 25 facing away from the carrier 38 the converter 20 is arranged. The converter 20 is arranged in such a way that the electromagnetic radiation deflected at the optical 37 enters the conversion element 22. In lateral directions x the conversion element 22 is surrounded by the reflector 23. At a side facing away from the semiconductor chip 25 electromagnetic radiation which passes the conversion element 22 can leave the optoelectronic component 21. Thus, the converter 20 is arranged in a transmissive configuration.

(29) In FIG. 7 a cutaway view of a further exemplary embodiment of the optoelectronic component 21 is shown. The optoelectronic component 21 comprises the converter 20 and two optoelectronic semiconductor chips 25. The semiconductor chips 25 are edge-emitting laser diodes. The converter 20 is arranged between the two semiconductor chips 25 in a lateral direction x in such a way that most of the electromagnetic radiation emitted by the semiconductor chips 25 hits the conversion element 22. The converter 20 has the setup which is shown in FIG. 1B. This means it is arranged in a reflective configuration. The electromagnetic radiation entering the conversion element 22 can be reflected at the reflector 23 and leave the optoelectronic component 21 in a direction which runs traverse or perpendicular to the main plane of extension of the converter 20.

(30) The description with the aid of the exemplary embodiments does not limit the invention thereto. Rather, the invention comprises any new feature and any combination of features, which in particular includes any combination of features in the patent claims, even if this feature or this combination is not itself explicitly stated in the patent claims or exemplary embodiments.