OPTOELECTRONIC SEMICONDUCTOR CHIP, METHOD FOR PRODUCING AN OPTOELECTRONIC SEMICONDUCTOR CHIP, CONVERSION ELEMENT AND PHOSPHOR FOR A CONVERSION ELEMENT

Abstract

An optoelectronic semiconductor chip having a semiconductor body (1) that is suitable for emitting electromagnetic radiation in a first wavelength range from a radiation exit face (3) is specified. Furthermore, the semiconductor chip comprises a ceramic or monocrystalline conversion platelet (6) that is suitable for converting electromagnetic radiation in the first wavelength range into electromagnetic radiation in a second wavelength range, which is different from the first wavelength range, and a wavelength-converting joining layer (7) that connects the conversion platelet (6) to the radiation exit face (3), wherein the wavelength-converting joining layer (7) has luminescent material particles (4) that are suitable for converting radiation in the first wavelength range into radiation in a third wavelength range, which is different from the first wavelength range and the second wavelength range. The wavelength-converting joining layer (7) furthermore has a thickness of no more than 30 micrometres. A method for fabricating an optoelectronic semiconductor chip, a further semiconductor chip, conversion element and luminescent material are specified.

Claims

1. Optoelectronic semiconductor chip comprising: a semiconductor body suitable for emitting electromagnetic radiation in a first wavelength region from a radiation exit surface; a ceramic or monocrystalline conversion plate suitable for converting electromagnetic radiation in the first wavelength region into electromagnetic radiation in a second wavelength region, which differs from the first wavelength region; a wavelength-converting joining layer that bonds the conversion plate to the radiation exit surface, wherein the wavelength-converting joining layer comprises phosphor particles which are suitable for converting radiation in the first wavelength region into radiation in a third wavelength region, which differs from the first wavelength region and from the second wavelength region; and the wavelength-converting joining layer has a maximum thickness of 30 micrometers.

2. Optoelectronic semiconductor chip as claimed in the claim 1 wherein the wavelength-converting joining layer has a maximum thickness of 10 micrometers.

3. Optoelectronic semiconductor chip as claimed in claim 1, wherein the radiation in the first wavelength region is blue light, the radiation in the second wavelength region is green or green-yellow light, and the radiation in the third wavelength region is red light.

4. Optoelectronic semiconductor chip as claimed in claim 1, wherein the phosphor particles are doped with europium as activator, where the concentration of the europium equals at least 1 mol %.

5. Optoelectronic semiconductor chip as claimed in claim 1 wherein phosphor particles are doped with europium as activator, where the concentration of the europium equals at least 1 mol %, and the wavelength-converting joining layer has a maximum thickness of 15 micrometers.

6. Optoelectronic semiconductor chip as claimed in claim 1, wherein the concentration of the phosphor particles in the wavelength-converting joining layer is between 50 wt % and 70 wt % inclusive.

7. Optoelectronic semiconductor chip as claimed in claim 1, which emits mixed-color radiation composed of radiation in the first, the second and the third wavelength region, wherein a color location of the mixed-color radiation lies in the warm-white region.

8. Method for producing an optoelectronic semiconductor chip as claimed in claim 1, comprising the following steps: providing a joining material in which phosphor particles are incorporated; applying the joining material containing the phosphor particles to a radiation exit surface of a semiconductor body or to a main face of the ceramic or monocrystalline conversion plate; placing a ceramic or monocrystalline conversion plate or the semiconductor body on the joining material; and curing the joining material.

9. Method as claimed in claim 8, wherein the joining material containing the phosphor particles is applied by spray-coating or by printing.

10. Method as claimed in claim 8, wherein a pre-cured conversion film is used as the joining material.

11. Conversion element comprising: a ceramic or monocrystalline conversion plate suitable for converting electromagnetic radiation in a first wavelength region into electromagnetic radiation in a second wavelength region, which differs from the first wavelength region; and a conversion layer, which is made of a resin in which are incorporated phosphor particles, wherein the conversion layer is applied to a main face of the conversion plate, the phosphor particles are suitable for converting radiation in the first wavelength region into radiation in a third wavelength region, which differs from the first wavelength region and from the second wavelength region; and the conversion layer has a thickness that is not greater than 30 micrometers.

12. Conversion element according to claim 11, wherein the phosphor particles are doped with europium as activator, where the concentration of the europium is at least 1 mol %.

13. Optoelectronic semiconductor chip comprising: a semiconductor body suitable for emitting electromagnetic radiation in a first wavelength region from a radiation exit surface; a conversion element as claimed in claim 1, which is applied to the radiation exit surface of the semiconductor body by a transparent joining layer.

14. Optoelectronic semiconductor chip as claimed in claim 13, wherein the transparent joining layer is not thicker than 5 micrometers.

15. Optoelectronic device as claimed claim 13, wherein the conversion element is arranged such that the conversion layer faces the radiation exit surface of the semiconductor body.

16. Optoelectronic semiconductor chip comprising: a semiconductor body suitable for emitting electromagnetic radiation in a first wavelength region from a radiation exit surface; a ceramic or monocrystalline conversion plate suitable for converting electromagnetic radiation in the first wavelength region into electromagnetic radiation in a second wavelength region, which differs from the first wavelength region; a wavelength-converting joining layer that bonds the conversion plate to the radiation exit surface, wherein the wavelength-converting joining layer comprises phosphor particles which are suitable for converting radiation in the first wavelength region into radiation in a third wavelength region, which differs from the first wavelength region and from the second wavelength region; and the wavelength-converting joining layer has a maximum thickness of 30 micrometers, wherein the phosphor particles are doped with europium as activator, where the concentration of the europium equals at least 1 mol %.

17. Conversion element according to claim 1, wherein the phosphor particles are doped with europium as activator, where the concentration of the europium is at least 3 mol %.

18. Conversion element according to claim 11, wherein the phosphor particles are doped with europium as activator, where the concentration of the europium is at least 3 mol %.

Description

[0070] In the figures, the same reference numbers are used to denote identical, similar or equivalent elements. The figures and the relative sizes of the elements illustrated in the figures shall not be considered to be to scale. Indeed individual elements, in particular layer thicknesses, may be shown exaggeratedly large in order to improve visualization and/or understanding.

[0071] In the method according to the exemplified embodiment of FIGS. 1 to 3, a semiconductor body 1 is first provided. The semiconductor body 1 comprises an active zone 2 suitable for emitting electromagnetic radiation in a first wavelength region from a radiation exit surface 3 of the semiconductor body 1 (FIG. 1). The semiconductor body 1 in this case emits blue light having a dominant wavelength of 450 nanometers. The semiconductor body 1 is here based on a nitride compound semiconductor material. Nitride compound semiconductor materials are compound semiconductor materials that contain nitrogen, for instance materials from the system In.sub.xAl.sub.yGa.sub.1−x−yN, where 0≦x≦1, 0≦y≦1 and x+y≦1.

[0072] In a next step, phosphor particles 4 are introduced into a joining material, for instance a silicone (process not shown). The phosphor particles 4 here comprise or are made of a CaAlSiN phosphor. The CaAlSiN phosphor is given by the formula (Sr,Ca)AlSiN.sub.3, for example, and is suitable for converting blue light emitted by the semiconductor body 1 into red light having a dominant wavelength of 603 nanometers. The diameter of the phosphor particles 4 does not exceed 20 micrometers.

[0073] The joining material containing the phosphor particles 4 is applied to the radiation exit surface 3 of the semiconductor body 1 as a layer 5, for instance by means of spray-coating (FIG. 2)

[0074] Then a ceramic or monocrystalline conversion plate 6 is placed on the layer 5 made of the joining material containing the phosphor particles 4. The conversion plate 6 is suitable for converting radiation in the first wavelength region, so in this case blue light from the semiconductor body 1, into green or green-yellow radiation.

[0075] Finally, the joining material is cured and a wavelength-converting joining layer 7 is produced which bonds the semiconductor body 1 to the conversion plate 6 in a mechanically robust manner (FIG. 3). The wavelength-converting joining layer 7 has a thickness of approximately 20 micrometers. The concentration of the phosphor particles 4 inside the wavelength-converting joining layer 7 in this embodiment equals approximately 54 wt %.

[0076] The conversion plate 6 comprises or is made of a phosphor that has the following formula: Lu.sub.3A;.sub.5O.sub.12:Ce.sup.3+, where the Ce content equals 1 mol %.

[0077] The optoelectronic semiconductor chip according to the exemplified embodiment in FIG. 3 emits during operation mixed-color radiation consisting of primary blue light from the semiconductor body 1, red light converted by the phosphor particles 4, and green/green-yellow light converted by the conversion plate 6. The CRI value (Color Rendering Index) of this light equals approximately 92. Particularly preferably, the mixed-color light has a color location in the warm-white region of the CIE chromaticity diagram of 2700 K, for example.

[0078] A simulation of the temperature at a main face 8 of the wavelength-converting joining layer 7, assuming an ambient temperature of 80° C. and a current density inside the semiconductor body 1 of 2 A/mm.sup.2, yields a value of approximately 155° C. This simulation is based on the conversion losses inside the wavelength-converting joining layer 7, which are converted into heat. Although a temperature of 155° C. lies close to the maximum permitted continuous operating temperature of silicone of 160° C., it does not exceed it. In addition, the semiconductor chip can be subjected to higher current densities than semiconductor chips having purely resin-based, thick conversion layers, which typically have maximum current densities of 1 A/mm.sup.2 to 1.5 A/mm.sup.2. Thus not only is the optoelectronic semiconductor chip according to the exemplified embodiment in FIG. 3 suitable for efficient emission of warm-white light of high color rendering index and high luminance, but furthermore it also has a long lifetime.

[0079] Unlike the optoelectronic semiconductor chip according to the exemplified embodiment in FIG. 3, the optoelectronic semiconductor chip according to the exemplified embodiment in FIG. 4 comprises phosphor particles 4 in the wavelength-converting joining layer 7 that comprise a 226 phosphor or are made of a 226 phosphor. The 226 phosphor, when excited with blue light from the semiconductor body 1, emits red light having a dominant wavelength of 601 nanometers. The diameter of the phosphor particles 4 does not exceed 10 micrometers in this case. The thickness of the wavelength-converting joining layer 7 is accordingly also not greater than 10 micrometers. Such a reduction in the thickness of the wavelength-converting joining layer 7 would not be possible for the exemplified embodiment shown in FIG. 3 because the CaAlSiN phosphor used there does not have a sufficient conversion rate. The concentration of the phosphor particles 4 in the wavelength-converting joining layer 7 here has a value of approximately 59 wt %. The mixed-color light, which consists of blue light from the semiconductor body 1, green/green-yellow light from the conversion plate 6 and red light from the phosphor particles 4 and is emitted by the semiconductor chip shown in FIG. 4, has a CRI value of approximately 93.

[0080] A simulation of the temperature of a main face 8 of the wavelength-converting joining layer 7 of the semiconductor chip according to exemplified embodiment in FIG. 4 yields a maximum value of 146° C. This means that the optoelectronic semiconductor chip could be operated at a 10° C. higher ambient temperature than the semiconductor chip according to the exemplified embodiment in FIG. 3. Alternatively, the current density to which the semiconductor chip is subjected could be increased by 10% to 2.2 A/mm.sup.2. Using said altered values yields in each case a simulated temperature of 155° C. as the maximum temperature of the wavelength-converting joining layer 7.

[0081] The conversion element 9 according to the exemplified embodiment in FIG. 5 comprises a ceramic or monocrystalline conversion plate 6 suitable for converting radiation in a first wavelength region, preferably blue light, into radiation in a second wavelength region, preferably green/green-yellow light. A conversion layer 11 is applied to a main face 10 of the conversion plate 6. The conversion layer 11 is made of a resin in which are incorporated phosphor particles 4. The phosphor particles 4 are suitable for converting radiation in the first wavelength region into radiation in a third wavelength region, preferably into red light. In this case, the thickness of the conversion layer 11 particularly preferably has a value that is not greater than 30 micrometers, and particularly preferably is not greater than 20 micrometers.

[0082] The optoelectronic semiconductor chip according to the exemplified embodiment in FIG. 6 comprises a semiconductor body 1 such as that already described with reference to FIG. 1. A conversion element 9, such as that already described with reference to FIG. 5, is applied to the radiation exit surface 3 of the semiconductor body 1. The conversion element 9 is affixed to the radiation exit surface 3 of the semiconductor body 1 by a transparent joining layer 12, for instance made of silicone. Said transparent joining layer 12 is in direct contact both with the radiation exit surface 3 of the semiconductor body and with the conversion layer 11 of the conversion element 9. Particularly preferably, the thickness of the transparent joining layer 12 is no greater than 5 micrometers.

[0083] FIG. 7 shows in detail main interatomic distances for a 226 phosphor Sr(Sr.sub.aCa.sub.1−a) Si.sub.2Al.sub.2N.sub.6. In direct comparison with nitrides of similar composition, e.g. SrAlSiN.sub.3 (ICSD 419410), CaAlSiN.sub.3 (ICSD 161796) or (Sr,Ca)AlSiN.sub.3 (ICSD 163203) it can be observed that there is a slightly larger and a slightly smaller environment around the alkaline earth atoms Sr and Ca. In SrAlSiN.sub.3, CaAlSiN.sub.3 and (Sr,Ca)AlSiN.sub.3, for the alkaline earth atoms there is only a 5-fold coordination with a mean Sr—N distance of 267 pm. In the structure of a 226 phosphor Sr(Sr.sub.aCa.sub.1−a)Si.sub.2Al.sub.2N.sub.6, Sr1 forms a 6-fold coordination with a mean Sr1-N distance of 272 pm, Sr2/Ca2 forms a 5-fold coordination with a mean Sr2/Ca2-N distance of 264 pm.

[0084] FIGS. 8 and 9 are used to describe in greater detail the structure of a 226 phosphor type Sr(Sr.sub.aCa.sub.1−a)Si.sub.2Al.sub.2N.sub.6. FIG. 8 shows a view towards the layers of Sr(Sr.sub.aCa.sub.1−a)Si.sub.2Al.sub.2N.sub.6. The layers are derived from AlN. The tetrahedra here symbolize (Si/Al)N.sub.4 groups. Compared with AlN there are individual tetrahedra missing that have been replaced by an alkaline earth ion (white circles for Sr alone and black circles for a mix of Sr/Ca). The tetrahedra are considerably distorted compared with AlN. All the bond lengths and angles, however, are similar to those in other nitridosilicates.

[0085] FIG. 9 shows a 226 phosphor Sr(Sr.sub.aCa.sub.1−a)Si.sub.2Al.sub.2N.sub.6 from the [010] direction. It clearly shows the 3D spatial network of the (Si/Al)N.sub.4 tetrahedra. Layers extend in the a-c plane that are linked in the b-direction (not shown) into a 3D network. Embedded therebetween are located layers containing alternately the pure Sr sites (shown as white circles) and the mixed-occupancy Sr/Ca sites (shown as black circles).

[0086] FIG. 10 shows from the [010] direction for comparison the structure of (Sr.sub.0.846Ca.sub.0.211)AlSiN.sub.3 (ICSD 163203) known form the literature. In this case, all the Sr/Ca sites (black) are mixed-occupancy. There are no pure Sr sites.

[0087] This re-arrangement for the 226 phosphor Sr(Sr.sub.aCa.sub.1−a)Si.sub.2Al.sub.2N.sub.6:Eu into sites with mixed Sr/Ca occupancy and sites fully occupied solely by Sr is advantageous e.g. compared with the structure of (Sr,Ca)AlSiN.sub.3 (cf. FIG. 10) in which there is only a mixed-occupancy site available for the activator atoms (dopant), which results in widening of emission, which of course is based on the interaction between the activator and the surrounding host lattice, and in more pronounced quenching properties. The structure of a 226 phosphor Sr(Sr.sub.aCa.sub.1−a)Si.sub.2Al.sub.2N.sub.6:Eu, on the other hand, provides the activator, in this case preferably Eu, with an excellent Sr site, without any disordering and its associated disadvantages. The improved properties of the luminescence can be explained loosely by this structure. According to this model representation, the Eu mainly occupies only the pure Sr plane and occupies the mixed plane rather less.

[0088] Based on FIG. 9, it is also possible to represent a phosphor of lower symmetry corresponding to the space groups 1 to 3 of the International Tables of Crystallography, Volume A, i.e. the space groups P1, P1, P2, by, for example, splitting the mixed layer into planes of different occupancy (in part) according to pure Sr along with mixed occupancy.

[0089] The present application claims priority from German application DE 10 2014 117 448.8, the disclosure of which is hereby included by reference.

[0090] The description based on the exemplified embodiments has no limiting effect on the invention. Instead, the invention includes every novel feature and every combination of features, which in particular includes every combination of features in the claims, even if this feature or combination is not itself explicitly mentioned in the claims or exemplified embodiments.