SEMICONDUCTOR LAYERING SEQUENCE FOR GENERATING VISIBLE LIGHT AND LIGHT EMITTING DIODE

Abstract

In at least one embodiment, the semiconductor layering sequence (1) is designed for generating light and comprises semiconductor columns (2). The semiconductor columns (2) have a respective core (21) made of a semiconductor material of a first conductivity type, and a core shell (23) surrounding the core (21) made of a semiconductor material of a second conductivity type. There is an active zone (22) between the core (21) and the core shell (23) for generating a primary radiation by means of electroluminescence. A respective conversion shell (4) is placed onto the semiconductor columns (2), which conversion shell at least partially interlockingly surrounds the corresponding core shell (23), and which at least partially absorbs the primary radiation and converts same into a secondary radiation of a longer wavelength by means of photoluminescence. The conversion shells (4) which are applied to adjacent semiconductor columns (2), only incompletely fill an intermediate space between the semiconductor columns (2).

Claims

1. Semiconductor layer sequence for generating visible light with a multiplicity of semiconductor columns, wherein the semiconductor columns each comprise a core of a semiconductor material of a first conductivity type and a core shell around the core of a semiconductor material of second conductivity type, an active zone of the semiconductor columns is located between the core and the core shell for generating primary radiation by means of electroluminescence, the semiconductor material of the first conductivity type is n-doped and the semiconductor material of the second conductivity type is p-doped and the core, the active zone and the core shell are based on the same semiconductor material, a conversion shell is applied onto each of the semiconductor columns, said conversion shell surrounding the associated core shell at least partially form-fittingly and at least partially absorbing the primary radiation and converting it into secondary radiation of a longer wavelength by way of photoluminescence, the conversion shell is applied directly onto the core shell and the core shell has a constant layer thickness, the conversion shells, which are applied to adjacent semiconductor columns, only incompletely fill an interspace between these semiconductor columns, such that no continuous, rectilinear connection is produced between adjacent semiconductor columns solely by way of the conversion shells, and the conversion shells each have a constant thickness, with a tolerance of at most 20% of an average thickness of the conversion shells.

2. Semiconductor layer sequence according to claim 1, in which the semiconductor material of the first conductivity type and the semiconductor material of the second conductivity type as well as the active zone are based on AlInGaN, the semiconductor columns are grown on a contiguous base layer, which is based on AlInGaN, such that foot points of the semiconductor columns each emerge from the base layer, and the conversion shell is free of organic materials and is applied to the semiconductor columns (2) form-fittingly at least on each of tips, opposite the foot points, and on lateral surfaces which connect the tips to the foot points.

3. Semiconductor layer sequence according to claim 1, wherein the average thickness of the conversion shell is between 2 nm and 500 nm inclusive, an average column diameter of the semiconductor columns is between 0.1 μm and 5 μm inclusive, an average column height of the semiconductor columns amounts to between 0.5 μm and 50 μm inclusive, a quotient of the column height and the column diameter is at least 2.5 and at most 100, and an average distance between adjacent semiconductor columns amounts to between 0.5 μm and 10 μm inclusive.

4. Semiconductor layer sequence according to claim 1, in which the conversion shell for converting the primary radiation consists of a layer of a III-V semiconductor material or of a II-VI semiconductor material, wherein this semiconductor material is doped or is provided with defects with a dopant concentration of between 1×10.sup.18 l/cm.sup.3 and 1×10.sup.22 l/cm.sup.3 inclusive.

5. Semiconductor layer sequence according to claim 1, in which the conversion shell for converting the primary radiation comprises at least one of a layer of an organic semiconductor material, of a doped transparent conductive oxide, and of a doped dielectric material.

6. (canceled)

7. Semiconductor layer sequence according to claim 16, in which an interlayer is located between the core shell and the conversion shell, wherein the interlayer directly adjoins the core shell and the conversion shell, and wherein the interlayer is electrically conductive and transmissive to the primary radiation and is formed from a transparent conductive oxide.

8. Semiconductor layer sequence according to claim 16, in which an interlayer is located between the core shell and the conversion shell, wherein the interlayer is electrically insulating and transmissive to the primary radiation and is formed from dielectric material.

9. Semiconductor layer sequence according to claim 2, in which the conversion shell connects together the foot points of adjacent semiconductor columns and is formed as a continuous layer, wherein the foot points are in direct contact with the base layer only at openings in a mask layer and, between the semiconductor columns, the conversion shell is separated from the base layer by the mask layer.

10. Semiconductor layer sequence according to claim 1, in which all the semiconductor columns or in which groups of a plurality of semiconductor columns are electrically connected in parallel.

11. Semiconductor layer sequence according to claim 1, in which the primary radiation is blue light and exhibits a wavelength of maximum intensity of between 420 nm and 485 nm inclusive, wherein the interlayer has no wavelength-modifying characteristics with regard to the primary radiation or the secondary radiation and is formed from indium-tin oxide or from ZnO.

12. Semiconductor layer sequence according to claim 1, in which the conversion shell comprises on each of the semiconductor columns a plurality of three-dimensional conversion structures or consists of such three-dimensional conversion structures.

13. Light-emitting diode with at least one semiconductor layer sequence according to claim 1, and at least two electrical terminals to feed current to the semiconductor layer sequence, wherein the light-emitting diode can be handled as a self-contained electronic component.

14. Light-emitting diode according to claim 14, in which, when in proper use, the conversion shell is the only photoluminescent component, wherein the light-emitting diode emits white light when in proper use.

15. Light-emitting diode according to claim 13, in which at least one further luminescent material for at least partial conversion of the primary radiation and/or of the secondary radiation into longer-wavelength tertiary radiation by means of photoluminescence is arranged downstream of the semiconductor layer sequence, wherein an average distance between the further luminescent material and the semiconductor columns amounts to at least 1 μm and at least one organic bonding agent is located between the luminescent material and the semiconductor columns.

16. Semiconductor layer sequence for generating visible light with a multiplicity of semiconductor columns, wherein the semiconductor columns each comprise a core of a semiconductor material of a first conductivity type and a core shell around the core of a semiconductor material of second conductivity type, an active zone of the semiconductor columns is located between the core and the core shell for generating primary radiation by means of electroluminescence, a conversion shell is applied onto each of the semiconductor columns, said conversion shell surrounding the associated core shell at least partially form-fittingly and at least partially absorbing the primary radiation and converting it into secondary radiation of a longer wavelength by way of photoluminescence, the conversion shells, which are applied to adjacent semiconductor columns, only incompletely fill an interspace between these semiconductor columns, such that no continuous, rectilinear connection is produced between adjacent semiconductor columns solely by way of the conversion shells, and the conversion shells each have a constant thickness, with a tolerance of at most 20% of an average thickness of the conversion shells.

Description

IN THE FIGURES

[0060] FIGS. 1 to 7 are schematic sectional representations of exemplary embodiments of semiconductor layer sequences described herein, and

[0061] FIG. 8 is a schematic sectional representation of a modification of a semiconductor layer sequence.

[0062] FIG. 1 is a schematic sectional representation of an exemplary embodiment of a semiconductor layer sequence 1. The semiconductor layer sequence 1 is attached to a substrate 9, for instance a growth substrate of sapphire. A buffer layer 8, which may also be composed of a plurality of layers, is located on the substrate 9. The buffer layer 8 is formed of at least one semiconductor material such as undoped GaN.

[0063] A base layer 5, preferably formed of a doped semiconductor material such as n-GaN, is applied to the buffer layer 8. A mask layer 6, for instance of silicon dioxide, is in turn applied to the base layer 5. The mask layer 6 comprises a multiplicity of openings, from which foot points 25 of semiconductor columns 2 are grown.

[0064] The semiconductor columns 2 comprise a core 21, which is preferably based on the same semiconductor material as the base layer 5, for example on n-GaN. The core 21 grows from the foot points 25, i.e. from the openings in the mask layer 6. Electrical n-contacting of the individual cores 21 proceeds by way of the contiguous base layer 5, which is preferably electrically conductive.

[0065] An active zone 22 is grown directly on and round the cores 21 of the semiconductor columns 2. The active zone 22, which may be based on the material system InGaN, preferably comprises a multiple quantum well structure.

[0066] A core shell 23 of a semiconductor material of a different conductivity type is grown directly onto and around the active zone 22. The core shell 23 preferably comprises p-GaN. Via the cores 21 and the core shells 23, charge carriers are injected into the active zone 22, such that primary radiation, preferably from the blue region of the spectrum, is generated in the active zone 22 by way of charge carrier recombination.

[0067] A conversion shell 4 is grown directly onto the core shell 23, for example epitaxially. The conversion shell 4 is formed for example from one or more layers of a III-V semiconductor material and/or a II-VI semiconductor material. The conversion shell 4 may also be constructed with a multiplicity of layers in a manner similar to a multiple quantum well structure. Alternatively, the conversion shell 4 is formed as a single, homogeneous layer.

[0068] The conversion shell 4 is designed to absorb only part of the primary radiation generated in the active zone 22 and to convert it by photoluminescence into longer-wavelength secondary radiation. This makes it possible, without further, additional luminescent materials, to generate polychromatic light, in particular white light, directly from the semiconductor layer sequence 1. It is in this case possible for a plurality of different, secondary radiation-generating conversion shells 4 to be applied, indeed on different semiconductor columns 2.

[0069] In a direction perpendicular to the base layer 5, the semiconductor columns 2 have an approximately constant diameter, along entire lateral surfaces 26. The lateral surfaces 26 in this case connect the foot points 25 with tips 27. The tips 27 are pyramidal or conical or alternatively end with a flat plateau. The conversion shell 4 extends over the entire lateral surface 26 and over the entire tips 27. The conversion shell 4 is separated from the base layer 5 by the semiconductor columns 2 and by the mask layer 6. Each of the semiconductor columns 2 is provided with its own conversion shell 4. Adjacent conversion shells 4 are formed in multiple pieces and are not in direct contact with one another.

[0070] An average diameter of the semiconductor columns 2 in the region of the lateral surface 26 is preferably at least 0.5 μm and/or at most 3 μm. An average distance between adjacent semiconductor columns is for example at least 2 μm and/or at most 10 μm. A height of the semiconductor columns 2, from the foot points 25 up to the tips 27, is in particular at least 5 μm and/or at most 240 μm. A thickness of the core shell 23 is for example at least 30 nm and/or at most 150 nm or 500 nm. The thickness of the conversion shell 4 preferably amounts to at least 15 nm and/or at most 50 nm.

[0071] The semiconductor columns 2 may serve as a waveguide, such that primary radiation exits the active zone 22 mainly at the tips 27 and at the foot points 25. Because the conversion shell 4 lies close to the active zone 22, efficient coupling takes place between radiation guided in the semiconductor columns 2 and the conversion shell 4. For example, a distance between the active zone 22 and the conversion shell 4 is at most 200 nm or 400 nm.

[0072] Unlike in the representation in FIG. 1, as also in all the other exemplary embodiments, it is possible for the conversion shell 4 to have a greater thickness at the tips 27 than at the lateral surfaces 26. For example, the thickness of the conversion shell 4 at the tips 27 is increased at least by a factor of 1.5 or 2.5 or 4 and/or at most by a factor 10 or 5 relative to the thickness at the lateral surfaces 26. The conversion shell 4 then preferably has a first constant thickness at the tips 27 and a second, smaller constant thickness at the lateral surfaces 26.

[0073] An optical behavior of the semiconductor columns 2 is indicated for example in Kölper et al., Phys. Status Solidi A, 1-9, 2012, DOI:10.1002/PSSA.201228178 or Kölper et al., Proceedings of SPIE, paper no. 793314, 2011. The disclosure content of these documents is hereby included by reference. Possible growth conditions for the production of semiconductor columns as described above are indicated for instance in Mandl et al., Phys. Status Solidi RRL, pages 1 to 15, 2013, DOI 10.1002/pssr.201307250. The disclosure content of this document is included by reference.

[0074] The conversion shell 4 is for example a layer of electrically non-conductive GaN, in which for instance metal ions are embedded for the purpose of photoluminescence. Likewise, an electrically conductive or an electrically insulating semiconductor layer of a semiconductor material which is different from a semiconductor material of the semiconductor columns may be used. This semiconductor material may be doped with metal ions or indeed comprise defects for the purpose of photoluminescence.

[0075] In the exemplary embodiment as shown in FIG. 2, an interlayer 3 is mounted between the core shell 23 and the conversion shell 4. The interlayer 3 is preferably thin, for example with a thickness of between 15 nm and 50 nm. The interlayer 3 may be thinner than the conversion shell 4. The interlayer 3 is a dielectric layer. The conversion shell 4 is for example configured as indicated in connection with FIG. 1.

[0076] In the exemplary embodiment as shown in FIG. 3, the conversion shell 4 is formed by a dielectric material which comprises metal ions as doping for the purpose of photoluminescence. Instead of a dielectric material, it is also possible to use a transparent, conductive material such as indium-tin oxide or zinc oxide which for example comprises metal ions as doping for the purpose of photoluminescence.

[0077] FIG. 4 shows that the conversion shell 4, which is for example formed as shown in connection with FIGS. 1 and 2, is a continuous layer. This means that the conversion shell 4 also completely or substantially completely covers the mask layer 6. The conversion shell 4 is then preferably of electrically conductive construction and is electrically conductively coupled to the core shells 23. The semiconductor columns 2 may consequently have current fed on the p-side.

[0078] In the exemplary embodiment as shown in FIG. 5, the conversion shell 4 likewise takes the form of a continuous layer. The conversion shell 4 is here for instance constructed as stated in connection with FIG. 3. Preferably, however, the conversion shell 4 is an electrically conductive layer which is designed to inject current into the core shell 23.

[0079] In FIG. 6, the interlayer 3 is located between the conversion shell 4 and the core shell 23. The interlayer 3 is preferably electrically conductive and radiation-transmissive and not designed to convert the primary radiation or the secondary radiation. The interlayer 3 may be a continuous layer which, viewed in plan view, extends between adjacent semiconductor columns 2 and connects them together electrically. The interlayer 3 is then for example formed from zinc oxide or ITO.

[0080] According to FIG. 7, the conversion shell 4 covers only part of the core shell 23. The conversion shell 4 is embodied by a multiplicity of three-dimensional conversion structures. In this case, the three-dimensional conversion structures are formed by conversion columns which extend in the direction away from the semiconductor columns 2. The conversion columns 4 may here be comparatively elongate, see the left-hand semiconductor column 2 in FIG. 7. Alternatively, the conversion columns may also be relatively short or also have a pyramidal, conical, prismatic or rounded form, see the semiconductor column 2 located on the right in FIG. 7.

[0081] In all the exemplary embodiments of FIGS. 1 to 7, the conversion shell is in each case grown directly on the interlayer or the semiconductor columns 2. The conversion shell 4 therefore follows the shape of the semiconductor columns 2, lying closely against the semiconductor columns 2 and being connected intimately and in form-fittingly therewith. Contiguous growth of the conversion shell 4 on the semiconductor columns 2, optionally via the interlayer 3, may be proven for instance with the assistance of electron microscopy.

[0082] In the variant as shown in FIG. 8, no conversion shell is present. Alternatively, a further converter material 7 for wavelength conversion is present, for instance in the form of particles which may be embedded in a matrix material which is not shown. The further converter material 7 substantially fills the entire interspace between adjacent semiconductor columns 2. However, due to the small distance between the semiconductor columns 2 in FIG. 8, this interspace is only comparatively unevenly filled. In such a development, it is only possible to achieve relatively poor optical coupling of the semiconductor columns 2 to the further converter material 7.

[0083] Such a further converter material 7 may additionally be present in light-emitting diodes which comprise semiconductor layer sequences 1 described herein.

[0084] The further converter material 7 is preferably a luminescent material or a luminescent material mixture comprising at least one of the following luminescent materials: Eu.sup.2+-doped nitrides such as (Ca, Sr)AlSiN.sub.3:Eu.sup.2+, Sr(Ca, Sr)Si.sub.2Al.sub.2N.sub.6:Eu.sup.2+, (Sr,Ca)AlSiN.sub.3*Si.sub.2N.sub.2O:Eu.sup.2+, (Ca,Ba,Sr).sub.2Si.sub.5N.sub.8:Eu.sup.2+, (Sr,Ca)[LiAl.sub.3N.sub.4]:Eu.sup.2+; garnets from the general system (Gd,Lu,Tb,Y).sub.3(Al,Ga,D).sub.5(O,X).sub.12:RE with X=halide, N or divalent element, D=tri- or tetravalent element and RE=rare earth metals such as Lu.sub.3(Al.sub.1-xGa.sub.x).sub.5O.sub.12Ce.sup.3+, Y.sub.3(Al.sub.1-xGa.sub.x).sub.5O.sub.12:Ce.sup.3+; Eu.sup.2+-doped sulfides such as (Ca,Sr,Ba)S:Eu.sup.2+; Eu.sup.2+-doped SiONs such as (Ba,Sr,Ca)Si.sub.2O.sub.2N.sub.2:Eu.sup.2+; SiAlONs for instance from the system Li.sub.xM.sub.yLn.sub.zSi.sub.12-(m+n)Al.sub.(m+n)O.sub.nN.sub.16-n; beta-SiAlONs from the system Si.sub.6-xAl.sub.zO.sub.yN.sub.8-y:RE.sub.z; nitrido-orthosilicates such as AE.sub.2-x-a RE.sub.xEu.sub.aSiO.sub.4-xN.sub.x, AE.sub.2-x-aRE.sub.xEu.sub.aSi.sub.1-yO.sub.4-x-2yN.sub.x with RE=rare earth metal and AE=alkaline earth metal; orthosilicates such as (Ba,Sr,Ca,Mg).sub.2SiO.sub.4:Eu.sup.2+; chlorosilicates such as Ca.sub.8Mg(SiO.sub.4).sub.4Cl.sub.2:Eu.sup.2+; chlorophosphates such as (Sr,Ba,Ca,Mg).sub.10(PO.sub.4).sub.6Cl.sub.2:Eu.sup.2+; BAM luminescent materials from the BaO—MgO—Al.sub.2O.sub.3 system such as BaMgAl.sub.10O.sub.17:Eu.sup.2+; halophosphates such as M.sub.5(PO.sub.4).sub.3(Cl,F):(Eu.sup.2+,Sb.sup.3+,Mn.sup.2+); SCAP luminescent materials such as (Sr,Ba,Ca).sub.5(PO.sub.4).sub.3Cl:Eu.sup.2+. The luminescent materials stated in document EP 2 549 330 A1 may also be used as luminescent materials. With regard to the luminescent materials used, the disclosure content of this document is included by reference. “Quantum dots” may moreover also be introduced as converter material. Quantum dots in the form of nanocrystalline materials which contain a group II-VI compound and/or a group III-V compound and/or a group IV-VI compound and/or metal nanocrystals, are preferred in this case.

[0085] The invention described here is not restricted by the description given with reference to the exemplary embodiments. Rather, the invention encompasses any novel feature and any combination of features, including in particular any combination of features in the claims, even if this feature or this combination is not itself explicitly indicated in the claims or exemplary embodiments.

[0086] The work on which this application is based was funded by the European Union under funding code NMP3-SL-2012-280694.

[0087] This patent application claims priority from German patent application 10 2014 117 995.1, the disclosure content of which is hereby included by reference.