Structure, methods for producing a structure and optoelectronic device

Abstract

A structure and a method for producing a structure are disclosed. In an embodiment a structure includes at least one semiconductor structure comprising at least one semiconductor nanocrystal and a high-density element for increasing a density of the structure, wherein a density of the high-density element is greater than a density of silica, and wherein the structure is configured to emit light.

Claims

1. A structure comprising: at least one semiconductor structure comprising at least one semiconductor nanocrystal; and a high-density element configured to increase a density of the structure, wherein a density of the high-density element is greater than a density of silica, and wherein the structure is configured to emit light.

2. The structure according to claim 1, wherein an average density per semiconductor nanocrystal of the structure is higher than an average density per semiconductor nanocrystal of the semiconductor structure without the high-density element.

3. The structure according to claim 1, wherein the at least one semiconductor structure is bonded to a surface of a high-density particle.

4. The structure according to claim 3, wherein the high-density particle is a luminescent phosphor particle or a non-emissive particle.

5. The structure according to claim 3, wherein the at least one semiconductor structure is bonded to the surface of the high-density particle with inorganic linkers, organic linkers or non-covalent linking.

6. The structure according to claim 1, wherein each semiconductor nanocrystal comprises an individual first layer surrounding the semiconductor nanocrystal.

7. The structure according to claim 6, wherein the first layer comprises silica or a high-density oxide.

8. The structure according to claim 6, wherein the first layer comprises at least two regions.

9. The structure according to claim 6, wherein at least two semiconductor nanocrystals each comprising the first layer are aggregated and surrounded by a second layer.

10. The structure according to claim 9, wherein the second layer comprises silica or a high-density oxide.

11. The structure according to claim 9, wherein the second layer comprises a high-density oxide, and wherein a thickness of the second layer is greater than 0 nm and smaller than or equal to 100 nm.

12. The structure according to claim 9, wherein the second layer comprises a high-density oxide, and wherein the second layer is in direct contact to the first layers.

13. The structure according to claim 6, wherein the first layer comprises a high-density oxide, and wherein the first layer is in direct contact to the semiconductor nanocrystals.

14. An optoelectronic device comprising: a semiconductor chip configured to emit a primary radiation; and a conversion element configured to convert at least part of the primary radiation into a secondary radiation, wherein the conversion element comprises at least one structure according to claim 1.

15. The optoelectronic device according to claim 14, wherein the conversion element comprises a single layer of matrix material and at least two wavelength converting compounds with different energy emissions arranged in layers in the single layer of matrix material, wherein the wavelength converting compounds are arranged in order of their energy emission, wherein the wavelength converting compound with a lowest energy emission is arranged closest to the semiconductor chip, and wherein at least one of the wavelength converting compounds comprises the structure.

16. The optoelectronic device according to claim 14, wherein the conversion element comprises a single layer of matrix material, a plurality of structures in the single layer of matrix material, a green phosphor in the single layer of matrix material and a red phosphor in the single layer of matrix material, and wherein the plurality of structures is arranged adjacent to the semiconductor chip, the red phosphor is arranged adjacent to the plurality of structures and the green phosphor is arranged adjacent to the red phosphor.

17. The optoelectronic device according to claim 14, wherein the structure comprises semiconductor structures bonded to a surface of a high-density particle, and wherein the high-density particle is a luminescent phosphor particle.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) Advantageous embodiments and developments of the conversion layer, the light-emitting device, and the method of producing a light-emitting device will become apparent from the exemplary embodiments described below in conjunction with the figures.

(2) In the figures;

(3) FIGS. 1A-C each shows a schematic illustration of a semiconductor structure according to different embodiments of the structure;

(4) FIG. 2 shows a schematic illustration of a structure according to one embodiment;

(5) FIG. 3 shows schematic illustrations of different binding motifs according to different embodiments;

(6) FIGS. 4A-F and 5 each show different schematic illustrations of a structure according to different embodiments; and

(7) FIG. 6 shows a schematic illustration of an optoelectronic device according to one embodiment.

(8) In the exemplary embodiments and figures, similar or similarly acting constituent parts are provided with the same reference symbols. The elements illustrated in the figures and their size relationships among one another should not be regarded as true to scale. Rather, individual elements may be represented with an exaggerated size for the sake of better representability and/or for the sake of better understanding.

DETAILED DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS

(9) The FIGS. 1A-C each shows a schematic illustration of a semiconductor structure 2.

(10) The semiconductor structure 2 in FIG. 1A comprises a semiconductor nanocrystal 3. The semiconductor nanocrystal 3 comprises a core and at least one shell surrounding the core. The semiconductor nanocrystal 3 can optionally comprise further shells and layers.

(11) The semiconductor structure 2 in FIG. 1B comprises a semiconductor nanocrystal 3 surrounded with a first layer 4. The first layer 4 surrounds the semiconductor nanocrystal 3 at least partially, preferably completely. In other words, the first layer 4 encapsulates or encases the semiconductor nanocrystal 3. In particular, the first layer 4 is in direct mechanical contact to the semiconductor nanocrystal 3. The first layer 4 comprises a metal oxide, for example silica. As indicated by the dashed line in FIG. 1B, the first layer 4 may comprise at least two regions comprising the same or a different material.

(12) The semiconductor structure 2 in FIG. 1C differs from the semiconductor structure 2 in FIG. 1B in that at least two semiconductor nanocrystals 3 each individuality encapsulated in the first layer 4 are aggregated and surrounded with a second layer 5. In other words, the second layer 5 encapsulates or encases the individually encapsulated semiconductor nanocrystals 3. In particular, the second layer 5 is in direct mechanical contact to the first layers 4 of the semiconductor nanocrystals 3. In particular, the first layers 4 of the semiconductor nanocrystals 3 are not in direct mechanical contact to one another. In other words, the semiconductor nanocrystals 3 comprising first layers 4 are held together by the second layer 5 without the first layers 4 of the semiconductor nanocrystals 3 touching directly. Thus, the semiconductor nanocrystals 3 are aggregated by encapsulation in the second layer 5. The second layer 5 comprises a metal oxide, for example silica. The second layer 5 may comprise the same or a different material than the first layers 4. The second layer 5 may comprise at least two regions comprising the same or a different material (not shown here).

(13) Alternatively, the semiconductor nanocrystals 3 comprising first layers 4 are aggregated with the first layers 4 touching directly and surrounded with the second layer 5.

(14) FIG. 2 shows a schematic illustration of a structure 1. The structure 1 comprises a plurality of semiconductor structures 2 bonded to the surface of a high-density particle 6. In this instance, the semiconductor structures 2 are semiconductor structures 2 as shown in FIG. 1C. It is also possible, that the semiconductor structures 2 as shown in FIGS. 1A and 1B are bonded to the surface of a high-density particle 6. In particular, the semiconductor nanocrystals 3 are passivated with a first layer 4 and/or a second layer 5 is shown in FIGS. 1B and 1C for facilitating the bonding to the high-density particle and for protecting the semiconductor nanocrystals 3 from degradation.

(15) A structure 1 comprising semiconductor structures 2 bonded to high-density particles 6 may have a higher average density per semiconductor nanocrystal 3 than the average density per semiconductor nanocrystal 3 of the semiconductor structure 2.

(16) The high-density particle 6 is a relatively large particle compared to the semiconductor structures 2. Thus, a plurality of semiconductor structures 2 can be bonded to the surface of the high-density particle 6. The high-density particle 6 can be a luminescent phosphor particle such as activated metal nitrides, activated metal oxynitrides or activated garnets. Alternatively, the high-density particle 6 can be a non-emissive particle such as bismuth silicate particles, un-activated nitrides or un-activated garnets. For example, crystalline Bi.sub.12SiO.sub.20 can be used. Crystalline Bi.sub.12SiO.sub.20 with a bulk density of 90.2 g cm.sup.−3 is significantly denser than, for example, crystalline SiO.sub.2 with a bulk density of 2.7 g cm.sup.−3. All these materials provide a useful mean of coupling to semiconductor structures comprising an outer layer of silica through the formation of Si—O—Si or Al—O—Si or other metal-O—Si bonds.

(17) In particular, the semiconductor structure 2 can be configured or designed in such a way that it absorbs no or nearly no radiation in the green or red wavelength range. Thus, very high amounts of semiconductor structures 2 can be attached to luminescent red or green phosphor particles without resulting in excessive trivial energy transfer to the semiconductor structure 2.

(18) Semiconductor structures 2 bonded to non-emissive particles benefit from the increased density of the high-density particle 6 but are not associated with another color of the emitter. These adducts might be more flexible reagents in fine-tuning color properties.

(19) For bonding a high-density particle 6 and a semiconductor structure 2, the surfaces of the high-density particle 6 and/or the semiconductor structure 2 are functionalized. Functionalizing the surfaces can either be achieved by using coupling reagents or by modifying the surface structure.

(20) Modifying the surface structure may require an additional surface preparation step. In particular, re-hydroxylation approaches can be used, for example, to generate reactive Si—OH functionalities on the surface of the high-density particle 6 such as garnets or on the silica surface of the semiconductor structure 2.

(21) Alternatively, coupling reagents such as bifunctional chemical linkers can be used. The linker is used to bond the semiconductor structure 2 to the high-density particle 6.

(22) Semiconductor structures 2 can be bonded to high-density particles 6 using bifunctional chemical linkers as follows:

(23) A stirred solution of high-density particles 6 are chemically modified by addition of a second solution of bifunctional chemical linkers. At the completion of the reaction, a solution of linker-decorated high-density particles 6 is obtained, and only minimal amounts of linker exist freely in the solution. To this solution, a third solution of semiconductor structures 2 is added. The resulting product comprises high-density particle 6 decorated with semiconductor structures 2 as shown in FIG. 2. Importantly, the sequential method and the control of reactant and reagent amounts prevent the formation of large semiconductor structure aggregates that are not bonded to a high-density particle 6.

(24) Alternatively, it is possible to functionalize the surface of the semiconductor structures 2 and subsequently add the high-density particles 6 to obtain high-density particle 6 decorated with semiconductor structures 2 as shown in FIG. 2.

(25) Alternatively, it is possible to functionalize the surface of the semiconductor structures 2 and the surface of the high-density particles 6 separately and subsequently mix the functionalized high-density particles 6 with the functionalized semiconductor structures 2 in order to obtain high-density particle 6 decorated with semiconductor structures 2 as shown in FIG. 2.

(26) The properties of the bifunctional chemical linker affects the chemical composition and properties of the interface between the high-density particle 6 and the semiconductor structure 2. FIG. 3 shows three different binding motifs that result in different interfaces with different properties.

(27) FIGS. 3I-III each show a semiconductor structure 2 comprising semiconductor nanocrystals 3 individually encapsulated by a first layer 4 aggregated and surrounded by a second layer 5. The semiconductor structures 2 are bonded to the surface of a high-density particle 6 using different linkers. The linkers in FIGS. 3I and 3II covalently bond the high-density particle 6 and the semiconductor structure 2, while the linkers in FIG. 3III form less-than-covalent attachments like van der Waals interactions between the high-density particle 6 and the semiconductor structure 2.

(28) In FIG. 3I, inorganic linkers, for example, alkyl silicates like tetramethylorthosilicate, or aluminum nitrate Al(NO.sub.3).sub.3, or calcium nitrate Ca(NO.sub.3).sub.2 form a thin, inorganic interface comprising, for example, silicate, aluminate, or calcium silicate hydrate. Thin, inorganic interfaces are chosen to minimize inter-particle distance and provide an inorganic barrier with distinct water transport and corrosion and dissolution limiting properties.

(29) Alternatively, a thin, inorganic interface can be obtained as follows:

(30) A stirred solution of high-density particles, for example, phosphor particles or bismuth silicate particles are chemically modified by addition of a base to convert surface metal-OH to metal-O.sup.−, for example, Si—O.sup.−. A second solution of di- or trivalent ions such as Ca.sup.2+ or Al.sup.3+ is added to the first solution to decorate the high-density particle 6 with di- or trivalent ions. To this solution, the third solution of semiconductor structures 2 suspended in a basic aqueous media is added to form structures similar to that in FIG. 3I. This approach creates a tight binding of semiconductor structures 2 and high-density particle 6 using a linker with controllable hydration.

(31) In FIG. 3II, organic linkers, for example, long bifunctional alkyl chains form a thick, organic interface comprising, for example, 1,2-bis(triethoxysilyl)ethane. Thick, organic interfaces are chosen to maximize inter-particle distance and include an organic barrier that relies on different chemical principles tournament oxygen and water transport and thus corrosion and dissolution of semiconductor structures 2 and high-density particle 6.

(32) In FIG. 3III, non-covalent linking is shown. Non-covalent linking means less-than-covalent attachments between the semiconductor structure 2 and the high-density particle 6. In particular, the linkers are covalently bonded to the surface of the semiconductor structure 2 or the surface of the high-density particle 6.

(33) The linkers can be hydrophobically modified alkyl silanes, for example, organochlorosilanes such as chloro(dimethyl)octylsilane or trimethoxysilanes, that are allowed to coalesce through concentration. The binding motif is provided by van der Waals interactions between alkyl chains. Alternatively, similarly modified hydrophobic semiconductor structures 2 and high-density particle 6 can be bridged via surfactant mediated means, for example, coupling through tetrabutylammonium halides.

(34) Less-than-covalent attachments are easily reversible and serve to relax stress and strain within the composite particles and can result in a more easily controlled ratio of semiconductor structures 2 to high-density particles 6.

(35) FIGS. 4A-E show different schematic illustration of a structure 1.

(36) The structure 1 in FIG. 4A comprises a semiconductor structure 2 comprising one semiconductor nanocrystals 3. The semiconductor nanocrystals 3 and thus the semiconductor structure 2 is surrounded with a high-density oxide layer 7. The high-density oxide layer 7 surrounds the semiconductor nanocrystal 3 at least partially, preferably completely. In particular, the high-density oxide layer 7 is in direct mechanical contact to the semiconductor nanocrystal 3. The high-density oxide layer 7 comprises a high-density oxide, for example, bismuth oxide, bismuth silicate, tin oxide, barium oxide, tungsten oxide or combinations thereof.

(37) The structure 1 in FIG. 4B comprises the structure 1 from FIG. 4A with a further layer 8 surrounding at least partially, preferably completely, the high-density oxide layer 7. In particular, the further layer 8 is in direct mechanical contact to the high-density oxide layer 7. The further layer 8 comprises a metal oxide, for example, silica.

(38) The structure 1 in FIG. 4C comprises a plurality of structures 1 from FIG. 4A that are aggregated and surrounded by a further layer 8. In particular, the plurality of structures 1 from FIG. 4A are held together by the further layer 8 without the high-density oxide layers 7 touching directly. Thus, the structures 1 from FIG. 4A are aggregated by encapsulation in the further layer 8.

(39) Alternatively, the plurality of structures 1 from FIG. 4A are aggregated with the high-density oxide layers 7 touching directly and further surrounded with further layer 8.

(40) The structures 1 according to FIG. 4A-C can be produced as follows:

(41) A dispersion of pre-formed semiconductor nanocrystals 3 is combined with a bifunctional linker and with a micellar suspension of organic solvent, water, and surfactant. Addition of a high-density oxide reagent, for example, a silica and bismuth precursor such as tetraethyl orthosilicate and bismuth nitrate, and a catalyst, for example, aqueous base, initiates polymerization of the mixed metal oxide nucleated at the surface of the semiconductor nanocrystal 3. Structures 1 according to FIG. 4A can then be isolated.

(42) Following the isolation of the structure 1 according to FIG. 4A, the structures 1 can be surrounded with a further layer 8 with a similar method as for surrounding the semiconductor nanocrystals 3 with a high-density oxide layer 7. Structures 1 according to FIG. 4B can then be isolated.

(43) Alternatively, following the isolation of the structure 1 according to FIG. 4A, the structures 1 can be aggregated and re-polymerized into larger structures. In the re-polymerization step, further layer 8 is formed. During aggregation and re-polymerization, the plurality of structures 1 can be aggregated and surrounded with the further layer 8 either with the high-density oxide layers 7 of the structures 1 touching directly or without the high-density oxide layers 7 of the structures 1 touching directly. Structures 1 according to FIG. 4C can then be isolated.

(44) The structure 1 in FIG. 4D comprises a semiconductor structure 2 comprising a semiconductor nanocrystal 3 surrounded with a first layer 4. A high-density oxide layer 7 surrounds the first layer 4 at least partially, preferably completely. In particular, the high-density oxide layer 7 is in direct mechanical contact to the first layer 4.

(45) The structures 1 according to FIG. 4D can be produced as follows:

(46) A dispersion of pre-formed semiconductor structures 2 comprising a semiconductor nanocrystal 3 surrounded with the first layer 4 is combined with a bifunctional linker and with a micellar suspension of organic solvent, water, and surfactant. Addition of a high-density oxide reagent, for example, a silica and bismuth precursor such as tetraethyl orthosilicate and bismuth nitrate, and a catalyst, for example, aqueous base, initiates polymerization of the mixed metal oxide nucleated at the surface of the semiconductor structure 2. Structures 1 according to FIG. 4D can then be isolated.

(47) The structure 1 in FIG. 4E comprises a plurality of semiconductor structures 2 each comprising a semiconductor nanocrystal 3 surrounded with a first layer 4. The plurality of semiconductor structures 2 are aggregated and surrounded by a high-density oxide layer 7. In particular, the plurality of structures 1 from FIG. 4A are held together by the high-density oxide layer 7 without the first layers 4 touching directly. Thus, the structures 1 from FIG. 4A are aggregated by encapsulation in the high-density oxide layer 7.

(48) Alternatively, the plurality of structures 1 from FIG. 4A are aggregated with the first layers 4 touching directly and surrounded with the high-density oxide layer 7.

(49) The structures 1 according to FIG. 4E can be produced as follows:

(50) A plurality of preformed semiconductor structures 2 can be aggregated and re-polymerized. In the re-polymerization step, the high-density oxide layer 7 is formed comprising, for example, bismuth silicate. Structures 1 according to FIG. 4E can then be isolated.

(51) The structure 1 in FIG. 4F comprises a semiconductor structures 2 comprising a plurality of semiconductor nanocrystal 3 surrounded with a first layer 4, aggregated and surrounded with a second layer 5. A high-density oxide layer 7 surrounds the second layer 5 at least partially, preferably completely. In particular, the high-density oxide layer 7 is in direct mechanical contact to the second layer 5.

(52) FIGS. 5I-III show schematic illustrations of structures 1 according to FIG. 4A with different thicknesses of the high-density oxide layer 7. For example, the thickness of the high-density oxide layer 7 is about 10 nm, about 25 nm in FIG. 5II, and about 50 nm in FIG. 5III. The thickness of the high-density oxide layer 7 can be approximately in a range of greater than 0 nm to at most 100 nm with a delta of approximately 5 nm.

(53) A layer sizing control can be achieved as follows:

(54) An amount of high-density oxide reagent, for example, a bismuth silicate precursor, is increased at the beginning of the surrounding or shelling reaction, and additional precursors are injected one or more additional times throughout the surrounding or shelling reaction. For example, a syringe pump is used to increase the overall amount of precursors, but dispensing is performed slowly during the reaction time. Upon initiation of growth of a high-density oxide layer, the final size of the layer can be controlled by the amount of precursors and injection method. When growing layers thicker than approximately 30 nm, it can be critical to control the amount and rate of precursors entering into the reaction mixture to avoid forming free high-density oxide particles.

(55) FIG. 6 shows a schematic illustration of an optoelectronic device 10 with a semiconductor chip 11 with an active layer stack and an active region (not shown here). The semiconductor chip 11 emits a primary radiation during operation of the optoelectronic device 10. In particular, the primary radiation is electromagnetic radiation in the visible wavelength range, preferably in the wavelength range with wavelength greater than 400 nm.

(56) The optoelectronic device 10 further comprises a conversion element 12. The conversion element 12 is configured to convert at least part of the primary radiation into a secondary radiation. The secondary radiation is electromagnetic radiation with a wavelength range at least partially, preferably completely, different than the wavelength range of the primary radiation. For example, the conversion element 12 converts the primary radiation into secondary radiation in the visible wavelength range.

(57) The conversion element 12 comprises at least one structure 1, preferably a plurality of structures 1. The structures 1 are embedded in a matrix material 13 such as silicone, polysiloxane or epoxy. In particular, the structures 1 are arranged in close proximity to the semiconductor chip in the matrix material 13.

(58) The structures 1 can be semiconductor structures 2 bonded to a high-density particle 6 that is a luminescent phosphor particle. In this instance, the structures 1 can be configured to convert primary radiation into radiation of two different wavelength ranges. For example, the semiconductor nanocrystals 3 in the semiconductor structure 2 convert primary radiation into red radiation and the luminescent phosphor particle converts the primary radiation into green radiation. The optoelectronic device 10 can thus emit white light while comprising only one wavelength converting compound.

(59) Alternatively, the structures 1 can be configured to only emit radiation of one wavelength range. For example, semiconductor structures 2 bonded to a high-density particle 6 that is a non-emissive particle or semiconductor structures 2 surrounded with a high-density oxide layer 7 can be used.

(60) The conversion element 12 can comprise further wavelength converting compounds in addition to the structures 1. For example, the conversion element 12 comprises phosphor particles such as red or green phosphors. In particular, the wavelength converting compounds in the conversion element 12 have different energy emissions and thus emits electromagnetic radiation of different wavelength ranges.

(61) The wavelength converting compounds can be arranged in order of their energy emission in the single layer of matrix material 13. In particular, the wavelength converting compound with the lowest energy emission is arranged closest to the semiconductor chip 11. This can be achieved by layering. The reddest emitting wavelength converting compound is located in close vicinity to the semiconductor chip 11 and the bluest emitting wavelength converting compound is located farthest away from the semiconductor chip 11.

(62) As shown in the exemplary embodiment of FIG. 6, the conversion element 12 comprises a single layer of the matrix material 13 and three wavelength converting compounds 1, 14, 15 with different energy emissions arranged in layers in the single layer of matrix material 13. In this instance, the structures 1 are the wavelength converting compound with the reddest emission and thus arranged closest to the semiconductor chip 11. The wavelength converting compound 14 can be a red phosphor with a higher energy emission than the structures 1 and the wavelength converting compound 15 can be a green phosphor with a higher energy emission than the structures 1 and the wavelength converting compound 14. The wavelength converting compound 14 is arranged between the structures 1 and the wavelength converting compound 15.

(63) Such a layering can be achieved by synthesizing structures 1 of maximum density. Additionally, the average density of the wavelength converting compounds 14, 15 can be lowered by functionalizing their surface with alkyl and/or silane chains of different lengths and branching ratios. The three different wavelength converting compounds 1, 14, 15 are added to the same matrix material 13, for example, silicone, and subjected to either thermal or forced sedimentation ultimately leading to the spatial arrangement shown in FIG. 6.

(64) The features and exemplary embodiments described in connection with the figures can be combined with each other according to further exemplary embodiments, even if not all combinations are explicitly described. Furthermore, the exemplary embodiments described in connection with the figures may have alternative or additional features as described in the general part.

(65) The invention is not restricted to the exemplary embodiments by the description on the basis of said exemplary embodiments. Rather, the invention encompasses any new feature and also any combination of features, which in particular comprises any combination of features in the patent claims and any combination of features in the exemplary embodiments, even if this feature or this combination itself is not explicitly specified in the patent claims or exemplary embodiments.