DE102014117803A1 - Method for producing a light-emitting diode - Google Patents

Abstract

The invention relates to a method for producing a light-emitting diode (1), wherein a light-emitting diode structure (1a) is provided with a radiation exit side (1b), wherein the light-emitting diode structure (1a) comprises a semiconductor layer sequence (3) and an active layer (3a) columnar structure elements (4) are formed on the radiation exit side (1b) and the structural elements (4) have a main extension direction in the direction perpendicular to the radiation exit side (1b), and a converter material (5) on the radiation exit side (1b) with the structural elements (4) is applied, wherein the converter material (5) in a first relative movement (A) relative to the light emitting diode structure (1a) and parallel to the main extension direction of the structural elements (4) is moved, and the converter material (5) in a second relative movement (B) perpendicular to the main extension direction the structural elements (4) is moved.

Description

The invention relates to a method for producing a light-emitting diode.

In the case of arranging converter materials on semiconductor layers with structural elements on the surface, in the case of small-scale structures and distances between the structures in the micrometer range, large particles of converter materials are not suitable for attaching the converter materials in the interstices between the structural elements. Also, particle size reduction processes only marginally improve the placement of small particles within the interstices, as most processes only achieve incomplete particle size reduction and still leave behind a certain number of larger particles or agglomerates. By attaching particles to the gap, which exceed the size of the gap, filling of the gap is made difficult with smaller particles of converter materials.

The invention has for its object to provide a method for producing a light-emitting diode, which is characterized by an improved and more effective arrangement of converter material.

This object is achieved by a method according to the independent claim. Advantageous embodiments and modifications of the invention are the subject of the dependent claims.

In a method for producing a light-emitting diode, a light-emitting diode structure having a radiation exit side is provided in a method step, the light-emitting diode structure comprising a semiconductor layer sequence and an active layer, and wherein columnar structure elements are formed on the radiation exit side and the structure elements have a main extension direction in the direction perpendicular to the radiation exit side ,

The provided light-emitting diode structure advantageously comprises a radiation exit side with three-dimensionally formed structural elements, wherein the structural elements improve the coupling-out of radiation of the active layer from the light-emitting diode structure. The structural elements can be arranged, for example, epitaxially or by means of other known processes on the radiation exit side of the semiconductor layer sequence. The structural elements preferably comprise semiconductor material and in one embodiment may comprise the active layer.

Due to the three-dimensional expansion, the structural elements advantageously bring about an enlargement of the surface of the radiation exit side. Due to their columnar structure, the structural elements advantageously have a greater height than lateral extent (width). The structural elements may have a round, oval or angular, for example, a hexagonal cross-sectional area.

Intermediate areas, in particular distances, are arranged between the individual structural elements. The distances may be the same size or it is also possible that the structural elements have an uneven distribution.

Furthermore, in a method step for producing a light-emitting diode, a converter material is applied to the radiation exit side with the structure elements, the converter material being moved in a first relative movement relative to the light-emitting diode structure and parallel to the main extension direction of the structure elements.

The movement of the converter material relative to the light-emitting diode structure can be achieved either by moving the light-emitting diode structure itself or by moving the converter material. In this case, the converter material is moved, for example, as a particle stream or in a suspension to the structural elements to and along this.

As a result, an accumulation and consequently arrangement or attachment of the converter material on the radiation exit side of the light-emitting diode structure, preferably on a radiating surface of the semiconductor layer sequence and the surfaces of the structural elements, can take place. Advantageously, the converter material is thus introduced into the intermediate spaces between the structural elements. The radiation exit side of the semiconductor layer sequence thus has a spatial structure, wherein due to the structuring formed recesses, depressions or trenches with the conversion layer are at least locally filled.

A connection of the converter material to side surfaces of the structural elements advantageously effects a conversion of the radiation laterally emitted by the structural elements.

Furthermore, the configuration with structural elements offers a good connection of the converter material to the surface of the light-emitting diode structure, whereby advantageously a good heat dissipation from the converter material can be achieved. For example, an increasing loss of efficiency of the converter material, which increases as a result of increasing temperature, can occur as a result of Conversion losses such as Stokes losses can strongly heat, can be reduced advantageously.

To increase the emission of light from the structural elements, it is advantageous to convert the light coupled out laterally from the structural elements into a wavelength which is not or only slightly reabsorbed by the adjacent structural elements. Thus, the proportion of light coupled out laterally from the structural elements can be increased and the overall efficiency increased. For example, in the generation of white light, a laterally emitted and converted light component can advantageously lead to light mixing with forwardly emitted light. In the case of the lateral emission of, for example, blue light, such a conversion can advantageously take place in longer-wave, approximately yellow, light. The structural elements can have nitride compound semiconductor materials, in particular InAlGaN, and, for example, emit light of blue to green wavelength in the range from 400 nm to 550 nm, depending on the content of In.

In a further method step, the converter material is moved in a second relative movement perpendicular to the main extension direction of the structural elements.

Large particles or agglomerates of converter material, which clog the interstices between the structural elements during or after the first relative movement and / or can attach to tips of the structural elements, are advantageously removed by means of a second movement component from the front side of the structural elements. By a movement perpendicular to the structural elements can advantageously be achieved at the tips of the structural elements, a flow of the converter material, which is greater than a flow in the interstices of the structural elements. Thus, it is possible to specifically remove converter material particles at the tips of the structural elements again.

The first and the second relative movement can take place sequentially in succession or in parallel. Advantageously, with the structural elements and the two relative movements, optimum filling of the interstices of the structural elements as well as filtering out of particles and agglomerates of converter material fitting into these interstices and targeted deposition of converter material can take place. The method described for removing too large particles from the tips is more effective than mere sedimentation in a suspension. Furthermore, it is also possible to carry out a sedimentation step of the converter material during or between the relative movements.

The application of converter material by both relative movements can also take place on planar components, wherein the structural elements are subsequently formed, for example by a lithographic step on a lacquer on a radiation exit side of a light-emitting component. The lacquer can also be used for structuring a material on the radiation exit side of a light-emitting component, for example for structuring a dielectric by etching or a metal applied by electroplating, which then serves as a structural element. The passive, without active (light-generating) layer formed structural elements can serve as a filter for the application of the particles of the converter material. For example, the structural elements have a ratio of their height to width of almost one. After carrying out the method with the two relative movements, the passive structural elements can advantageously be detached from the planar component or remain thereon.

The converter material may comprise particles of different sizes.

The converter material can advantageously comprise only a specific material or a mixture of several materials with agglomerates and particles of different grain sizes.

The sizes of particles and agglomerates can range from a few 100 nm to several 10 microns. Small particles can advantageously be introduced well into intermediate spaces between the structural elements. A filtering out of particles and agglomerates of converter material which fit into the interstices of the structural elements can also take place for mixtures of different large particles of converter materials by the first and second relative movement.

Advantageously, very small particles of converter material can be arranged on the side surfaces of the structural elements, which leads to a good sideways-acting scattering of coupled-out light in the intermediate spaces. In other words, due to particularly small particles of a few 100 nm to a few micrometers, the coupled-out light is scattered on side surfaces particularly well in the direction of the main extension direction of the structural elements and thus in the emission direction of the light-emitting diode.

In accordance with at least one embodiment of the method, the light-emitting diode structure with the semiconductor layer sequence and the structural elements is introduced into a bath, wherein the bath contains the converter material, and the first relative movement is effected by a flow in the bath and / or by a movement of the light-emitting diode structure.

The bath advantageously comprises a liquid with the converter material, wherein the converter material and the liquid form a suspension. In other words, particles of the converter material are not dissolved in the liquid. In the case of a suspension with particles of different sizes, an intermediate step of the process with a sedimentation of the particles, preferably a larger particle type, can also take place in the bath.

Furthermore, it is possible to carry out a process step in an intermediate step after a sequence of two relative movements, for example after the sedimentation of converter particles not applied to the light-emitting diode structure with which the particles of the converter material can be reduced, for example by grinding processes. The thus processed converter material can be re-introduced into the bathroom.

In accordance with at least one embodiment of the method, the first relative movement takes place by electrophoretic deposition.

By means of an applied electric field, electrically charged converter materials can be moved towards the structural elements according to the first relative movement and thus generate the particle flow in the bath.

In accordance with at least one embodiment of the method, the second relative movement is effected by a flow in the bath and / or by a movement of the light-emitting diode structure.

The second relative movement can advantageously be achieved in accordance with the first relative movement by moving the light-emitting diode structure itself and / or by moving the converter material, for example by a flow. The movement is advantageously possible in all directions perpendicular to the main extension direction of the structural elements.

According to at least one embodiment of the method, a mixing of the bath takes place before the converter material is moved.

In order to achieve a more homogeneous distribution of the converter material in the bath, the bath is advantageously mixed with the converter material before the relative movements. This can be achieved with particles of different sizes that even smaller particles during relative movements, especially during the first relative movement, can get into the interstices of the structural elements.

In accordance with at least one embodiment of the method, a gas flow comprising the converter material in the first relative movement impinges on the light-emitting diode structure.

In this case, the converter material is moved in the direction of the main extension direction of the structural elements. The gas stream may advantageously comprise only one type and size or a mixture of several types and particle sizes of the converter material.

In accordance with at least one embodiment of the method, the second relative movement takes place by moving the light-emitting diode structure.

In the case of a gas flow, the particles and agglomerates accumulated at the tips of the structural elements can be detached from converter materials by a second relative movement, so that the interstices of the structural elements can be further filled with smaller particles. In the case of a gas flow of converter materials can be moved as a second relative movement, the light emitting diode structure in a permanent reciprocating motion (shaking), wherein the movement can take place in any direction perpendicular to the main extension direction of the structural elements. A joint action of second relative movement and gravitational force advantageously enhances the stripping effect of the particles of the converter material which are too large for the filling of intermediate spaces.

In accordance with at least one embodiment of the method, the second relative movement takes place parallel to the gravitational force.

In this way, the second relative movement and the gravitational force act together and thus increasingly on the converter materials. Stripping large particles and agglomerates is thus possible even more effectively.

In accordance with at least one embodiment of the method, the first relative movement and the second relative movement are repeated until intermediate spaces between the structural elements are at least partially filled with the converter material.

Thus, advantageously, the first relative movement and the second relative movement can be repeated successively in a sequence or take place over a longer period of time. After each sequence of relative movements, a renewed mixing of the converter materials can take place.

For light-emitting diodes which emit white light, it is advantageous to fill up the gaps between the structural elements to a great extent or even to overfill them in order to increase the degree of conversion. This is in particular by an embodiment of the method in connection with a bath with several repetitions and any intermediate steps such as sedimentation or processes for comminuting particles advantageous. In this case, a reuse of particles in a bath or for other processes can take place and converter material can be saved in repeated coating processes.

In accordance with at least one embodiment of the method, the structural elements have different interspaces relative to one another.

By varying distances to each other converter material can be introduced with particles and agglomerates of different sizes between the respective regions of the structural elements. Thus, during the two relative movements, it is advantageous to filter out and arrange particles of different sizes correspondingly at the interspaces of different sizes. In other words, advantageously particles of a particular size can be arranged specifically at designated areas. In order to avoid an accumulation of converter material at certain areas of the radiation exit side, cover elements can be applied in these areas and removed again after the application of the converter material.

In accordance with at least one embodiment of the method, the converter material comprises different phosphors for converting the radiation emitted by the active layer into light of different wavelengths.

The converter material advantageously comprises a mixture of different phosphors which form particles and agglomerates of different sizes.

According to at least one embodiment of the method, the different phosphors are deposited on the radiation exit side as a function of the interstices of the structural elements in different regions.

By using different converter materials for conversion to different wavelengths, according to the method for the targeted arrangement of particles, depending on their size, a radiation exit side can be realized with areas which emit light in different wavelengths. With this method, areas of the radiation exit side with different converter materials are advantageously produced in a self-organized process by the two relative movements in a high precision.

This type of arrangement of different converter materials is particularly advantageous in the production of small-scale and micropixeled displays and light-emitting diodes. Elaborate adjustment steps and sequential structuring processes can be dispensed with and the accuracy of the range division is significantly improved and can be carried out particularly small-scale. The arrangement of the converter materials can advantageously be carried out with exact position accuracy at an area predefined by the spacings of the structural elements.

In accordance with at least one embodiment of the method, the structural elements comprise a columnar core of a first semiconductor material, and an active layer and another semiconductor material completely cover the core completely including the side edges of the core.

Structural elements in the embodiment with a shell around a three-dimensional core (core shell) are advantageously well suited for enlarging the active area of the semiconductor. In this case, the sequence of layers may comprise a first n- or p-doped semiconductor, an active layer and a second n- or p-doped semiconductor which is doped against the first semiconductor.

According to at least one embodiment of the method, the formation of the structure elements takes place at the radiation exit side by means of a mask layer, wherein the structure elements are each arranged in an opening of the mask layer.

The structural elements are formed, for example, by means of a growth process in the openings of the mask. The mask can be structured, for example, as a photoresist using a lithographic process. The growth can also take place for structural elements which have no active layer and are produced, for example, on planar light-emitting diodes. The mask may comprise, for example, SiNx or SiO ₂ .

According to at least one embodiment of the method, the structural elements at least partially on the shape of a cylinder, a cuboid, a prism, a pyramid or a truncated pyramid. According to at least one embodiment of the method, the structural elements and the converter material are encapsulated on the radiation exit side with a potting.

The potting advantageously comprises a matrix material that is transparent to the wavelengths emitted by the features and conversion materials. The encapsulation can advantageously be varied in shape and cured to complete the light-emitting diode.

Further advantages, advantageous embodiments and developments emerge from the embodiments described below in conjunction with the figures.

The 1 shows the semiconductor layer sequence with structural elements of the light emitting diode in a schematic side view.

The 2a and 2 B show the arrangement of structural elements on a radiation exit side in a plan view.

The 3a . 3b . 5a and 5b show a schematic sequence of process steps a) and b) in a bath.

The 4a and 4b show a schematic sequence of process steps a) and b) with a gas stream.

Identical or equivalent elements are each provided with the same reference numerals in the figures. The components shown in the figures and the size ratios of the components with each other are not to be regarded as true to scale.

The 1 shows a schematic side view of the light emitting diode 1 with the light-emitting diode structure 1a comprising a radiation exit side 1b , a semiconductor layer sequence 3 and an active layer 3a with columnar structural elements 4 at a radiation exit side 1b which is a main extension direction in the direction perpendicular to the radiation exit side 1b exhibit. Neighboring structural elements 4 have a gap 41 between each other. The arrangement of 1 shows the light-emitting diode structure 1a before carrying out the method steps a) and b).

The light-emitting diode structure 1a advantageously comprises a substrate 31 with a semiconductor layer sequence arranged thereon 3 which has several layers 32 may include.

On the radiation exit side 1b the semiconductor layer sequence 3 this has a mask layer 6 with openings 6a on, with the structural elements 4 each in the openings 6a are arranged. The structural elements are, for example, by means of a growth process in the openings of the mask layer 6 educated. The mask layer 6 For example, it can be patterned by photoresist using a lithographic process. The mask layer 6 includes, for example, SiO ₂ . The structural elements 4 are elongated and may at least partially have the shape of a cylinder, a cuboid, a prism, a pyramid or a truncated pyramid.

The structural elements 4 have a columnar core of a first semiconductor material 3b on and an active layer 3a and another semiconductor material 3c cover the core one by one completely including the side edges 4a of the core. The sequence includes, for example, a first semiconductor material 3b of an n-doped semiconductor, for example n-doped GaN, and another semiconductor material 3c from a p-doped semiconductor, for example p-doped GaN.

The 2a and 2 B show the arrangement of structural elements 4 on a radiation exit side 1b the semiconductor layer sequence in a plan view. In the 2a are the structural elements 4 shown in a cubic arrangement, wherein the structural elements 4 between each other a gap 41 which, for example, between adjacent structural elements 4 is the same size.

In the 2 B are the structural elements 4 shown in a hexagonal arrangement.

The 3a shows the light-emitting diode structure 1a , for example from the 1 during the process step a). In a bath 10 , which converter material 5 advantageously comprises in a suspension, the light-emitting diode structure 1a with the semiconductor layer sequence 3 and the structural elements 4 in a first relative movement A parallel to the main extension direction of the structural elements 4 moves, thereby accumulating and thus arranging or attaching the converter material 5 on the radiation exit side 1b the semiconductor layer sequence 3 and on the surfaces of the structural elements 4 he follows. Furthermore, it is also possible by means of an applied electric field electrically charged converter material 5 according to the first relative movement A in the direction of the structural elements 4 to move and this by electrophoretic deposition on the structural elements 4 attach. Particles and agglomerates of the converter material 5 are thus advantageously in the interstices 41 between the structural elements 4 brought in. The converter material 5 may include particles and agglomerates of different size and material composition. Before introducing the light-emitting diode structure 1a in the bathroom 10 can be beneficial even more processes in the bathroom 10 take place, for example, a mixing of the converter material 5 ,

In the 3b in a further method step b) a second relative movement B of the converter material takes place 5 perpendicular to the main extension direction of the structural elements 4 ,

Large particles or agglomerates of converter material 5 which, during or after the first relative movement, the gaps 41 between the structural elements 4 clog and / or stick to tips of the structural elements 4 attach, be beneficial from the front of the structural elements 4 away. By a movement perpendicular to the structural elements can advantageously be achieved at the tips of the structural elements, a flow of the converter material, which is greater than a flow in the interstices 41 the structural elements 4 , Thus, it is possible accumulated particles of converter material 5 at the tips and in the upper regions of the structural elements 4 to remove. The process step a) after the 3a can be done again and so an advantageous filling of the spaces 41 with particles or agglomerates of converter material 5 which take place after their expansion in these spaces 41 fit. The first and the second relative movement from the 3a and 3b can take place sequentially in succession or in parallel. Furthermore, it is also possible during or between the relative movements of the 3a and 3b to carry out a sedimentation step of the converter material. The first relative movement and the second relative movement can be repeated until interspaces 41 between the structural elements 4 at least partially with the converter material 5 are filled.

The 4a shows the light-emitting diode structure 1a from the 3a during the process step a), wherein the light-emitting diode structure 1a is not introduced in a bath but a gas stream 8th comprising the converter material 5 in the first relative movement A to the light-emitting diode structure 1a incident. The gas stream can advantageously only one type and size or a mixture of several types and particle sizes of the converter material 5 include.

In the 4b becomes the light-emitting diode structure 1a from the 4a during the impact of the gas flow 8th by a second relative movement B perpendicular to the main extension direction of the structural elements 4 and moved parallel to the gravitational force. The at the tips of the structural elements 4 accumulated particles and agglomerates of converter materials 5 are detached so that the interstices of the structural elements can be further filled with smaller particles.

The second relative movement B takes place, for example, in a permanent shaking movement of the light-emitting diode structure 1a sequentially after or in parallel with the first relative movement A out of the 4a , A joint action of second relative movement B and gravitational force g advantageously enhances the stripping effect of the filling of gaps 41 too large particles of the converter material 5 , Advantageously, the stripped particles can subsequently be sedimented and comminuted for a further process step a), or be used for other processes.

The 5a shows the light-emitting diode structure 1a , for example from the 3a , during process step a) in a bath 10 , which converter material 5 advantageously in a suspension. The light-emitting diode structure 1a with the semiconductor layer sequence 3 and the structural elements 4 is in a first relative movement A parallel to the main extension direction of the structural elements 4 moved, wherein the structural elements have different spaces 41 to each other. The converter material 5 can be different phosphors 51 for converting the radiation emitted by the active layer into light of different wavelengths. Particles and agglomerates of different phosphors 51 can only be in intermediate spaces 41 are introduced, which are sufficiently wide. Are particles and agglomerates of a phosphor too large for a gap 41 so they jam in front of it.

In the 5b will the arrangement of 5a moved in a second relative movement B after the process step b) and particles and agglomerates which are too large for a gap 41 are moved away from this. The two relative movements can be carried out first with particles of larger diameter and narrow distribution of the diameter and then in a bath with particles of smaller diameter and narrow distribution of the diameter. It is also conceivable to carry out the process simultaneously in a bath with large and small particles. In this way, it is advantageous during the two relative movements A and B to filter out and arrange particles of different sizes and different phosphors 51 according to the different sizes of spaces 41 , In other words, advantageously particles of a particular size and conversion color can be arranged specifically at designated areas.

With this method, areas of the radiation exit side with different converter materials are advantageously produced in a self-organized process by the two relative movements in a high precision. This type of arrangement of different converter materials is particularly advantageous in the production of small-scale and micropixellated displays and light-emitting diodes.

The invention is not limited by the description based on the embodiments of these. Rather, the invention encompasses any novel feature as well as any combination of features, including in particular any combination of features in the claims, even if this feature or combination itself is not explicitly stated in the patent claims or exemplary embodiments.

Claims (16)

Method for producing a light-emitting diode ( 1 ) with the steps - providing a light-emitting diode structure ( 1a ) with a radiation exit side ( 1b ), wherein the light-emitting diode structure ( 1a ) a semiconductor layer sequence ( 3 ) and an active layer ( 3a ), and wherein columnar structural elements ( 4 ) at the radiation exit side ( 1b ) are formed and the structural elements ( 4 ) a main extension direction in the direction perpendicular to the radiation exit side ( 1b ), and - applying a converter material ( 5 ) on the radiation exit side ( 1b ) with the structural elements ( 4 ), where a) the converter material ( 5 ) in a first relative movement (A) relative to the light-emitting diode structure ( 1a ) and parallel to the main extension direction of the structural elements ( 4 ), and b) the converter material ( 5 ) in a second relative movement (B) perpendicular to the main extension direction of the structural elements ( 4 ) is moved. Method according to the preceding claim, in which the light-emitting diode structure ( 1a ) with the semiconductor layer sequence ( 3 ) and the structural elements ( 4 ) in a bath ( 10 ), the bath ( 10 ) the converter material ( 5 ), and the first relative movement (A) by a flow in the bath ( 10 ) and / or by moving the light-emitting diode structure ( 1a ) he follows.  Method according to the preceding claim, in which the first relative movement (A) is effected by electrophoretic deposition. Method according to one of claims 2 or 3, wherein the second relative movement (B) by a flow in the bath ( 10 ) and / or by moving the light-emitting diode structure ( 1a ) he follows. Method according to one of claims 2 to 4, wherein prior to moving the converter material ( 5 ) a mixing (D) of the bath ( 10 ) he follows. Process according to Claim 1, in which a gas stream ( 8th ) comprising the converter material ( 5 ) in the first relative movement (A) to the light-emitting diode structure ( 1a ). Method according to the preceding claim, in which the second relative movement (B) is achieved by moving the light-emitting diode structure ( 1a ) he follows.  Method according to one of the preceding claims, in which the second relative movement (B) takes place parallel to the gravitational force (g). Method according to one of the preceding claims, in which the first relative movement (A) and the second relative movement (B) are repeated until clearances ( 41 ) between the structural elements ( 4 ) at least partially with the converter material ( 5 ) are filled. Method according to one of the preceding claims, in which the structural elements ( 4 ) different spaces ( 41 ) to each other. Method according to one of the preceding claims, in which the converter material ( 5 ) different phosphors for the conversion of the active layer ( 3a ) comprises emitted radiation in light of different wavelengths. Method according to claims 10 and 11, wherein on the radiation exit side ( 1b ) the different phosphors depending on the spaces ( 41 ) of the structural elements ( 4 ) are deposited in different areas. Method according to one of the preceding claims, in which the structural elements ( 4 ) a columnar core of a first semiconductor material ( 3b ), and an active layer ( 3a ) and another semiconductor material ( 3c ) the core in succession completely including the side edges ( 4a ) of the core. Method according to one of the preceding claims, in which the formation of the structural elements ( 4 ) at the radiation exit side ( 1b ) by means of a mask layer ( 6 ), the structural elements ( 4 ) in each case in an opening ( 6a ) of the mask layer ( 6 ) to be ordered. Method according to one of the preceding claims, in which the structural elements ( 4 ) at least partially have the shape of a cylinder, a cuboid, a prism, a pyramid or a truncated pyramid. Method according to one of the preceding claims, in which the structural elements ( 4 ) and the converter material ( 5 ) on the radiation exit side ( 1b ) with a potting ( 11 ) are encapsulated.

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