Light emitting diode and method for producing a light emitting diode

0001A light-emitting diode is specified. Furthermore, a method for producing a light-emitting diode is specified.

0002The printed matter<de-docref CY="US" DNUM="3710167" KI="A">US 3 710 167 A</de-docref>, <de-docref CY="DE" DNUM="102014100747" KI="A1">DE 10 2014 100 747 A1</de-docref>, <de-docref CY="WO" DNUM="2008130207" KI="A1">WO 2008/ 130 207 A1</de-docref>, <de-docref CY="EP" DNUM="1760798" KI="A1">EP 1 760 798 A1</de-docref>, <de-docref CY="US" DNUM="20100258833" KI="A1">US 2010 / 0 258 833 A1</de-docref>, and<de-docref CY="US" DNUM="20060220035" KI="A1">US 2006 / 0 220 035 A1</de-docref> describe light-emitting diodes and processes for producing light-emitting diodes.

0003One problem to be solved is to provide a light-emitting diode with a structured-appearing luminous surface. Another problem to be solved is to provide a method for producing such a light-emitting diode.

0004These objects are achieved by the light-emitting diode according to claim 1 and the method according to claim 14.

0005According to at least one embodiment, the light-emitting diode comprises a layer sequence with an active layer that emits radiation during operation. The light-emitting diode can be an organic or an inorganic light-emitting diode.

0006In the case of an inorganic light-emitting diode, or LED for short, the layer sequence is, for example, a semiconductor layer sequence based on a III-V compound semiconductor material. The semiconductor material is, for example, a nitride compound semiconductor material, such as Al_nIn_{1 nm}Ga_mN, or a phosphide compound semiconductor material such as Al_nIn_{1 nm}Ga_mP, or an arsenide compound semiconductor material, such as Al_nIn_{1 nm}Ga_mAs, where 0 ≤ n ≤ 1, 0 ≤ m ≤ 1, and m + n ≤ 1. The semiconductor layer sequence may contain dopants as well as additional components. For the sake of simplicity, however, only the essential components of the crystal lattice of the semiconductor layer sequence, i.e., Al, As, Ga, In, N, or P, are specified, even though these may be partially replaced and/or supplemented by small amounts of other substances. The semiconductor layer sequence is preferably based on AlInGaN.

0007The active layer has, for example, at least one pn junction and/or a quantum well structure in the form of a single quantum well, SQW for short, or in the form of a multi-quantum well structure, MQW for short.

0008In the case of an organic light-emitting diode (OLED), for example, the active layer comprises an organic emitter material. Further layers in the layer sequence can then be organic electron-transport layers, hole-transport layers, electron-injection layers, or hole-injection layers.

0009For example, the light-emitting diode and/or the active layer emits UV radiation or infrared radiation or visible light, such as blue, green, yellow, red or white light, during operation.

0010According to at least one embodiment, the light-emitting diode has at least one supply element arranged on a first main side of the layer sequence. During operation, electrical current is conducted, in particular over a large area, into or out of the layer sequence via the supply element. The supply element preferably forms a first electrode of the light-emitting diode.

0011A main side runs essentially parallel to a main extension direction of the active layer. "Planar" means, in particular, that current is conducted into or out of the layer sequence over the entire extent of a partial area of ​​the supply element running parallel to the active layer. At least the partial area completely overlaps the active layer in a plan view of the first main side. A main current flow direction in the area of ​​the partial surface is then perpendicular to the main extension direction of the active layer.

0012The supply element is preferably an electrically conductive element, which is, for example, a metal such as Al, Ag, Au, In, Ti, Pt, Zr, or an oxide, for example a transparent conductive oxide, TCO for short, such as indium tin oxide, ITO for short, or BaO_x or ThO_x The supply element can comprise multiple subregions and/or material layers made of different materials. However, the supply element can also have the same material composition along its entire lateral extent. "Lateral" here and in the following refers to a direction parallel to a main extension direction of the active layer.

0013In particular, the supply element is designed as a strip or conductor track with a width of, for example, at least 5 µm, 10 µm, or 20 µm. The supply element is preferably a continuous, in particular simply connected, element that is, for example, free of openings. For example, the supply element is rectangular, L-shaped, or U-shaped when viewed from above onto the first main side.

0014According to at least one embodiment, a contact region of the supply element protrudes laterally from the layer sequence. Thus, in a plan view of the first main side, the contact region does not overlap with the layer sequence and serves in particular for external electrical contacting of the supply element.

0015According to at least one embodiment, a tunnel layer is arranged between the active layer or the layer sequence and the supply element. The tunnel layer may comprise or consist of an electrically insulating material, such as a ceramic. In particular, the tunnel layer comprises or consists of an oxide of the material of the tunnel element. For example, the tunnel layer comprises aluminum oxide, such as Al₂O₃, or titanium oxide, such as TiO₂, or zirconium oxide, such as ZrO₂, or silicon oxide, such as SiO₂, on, or consists of. The tunnel layer preferably has a uniform material composition along its entire lateral extent.

0016The tunnel layer has, for example, a thickness of at least 0.5 nm, or at least 1 nm, or at least 2 nm. Alternatively or additionally, the thickness of the tunnel layer is at most 20 nm, or 10 nm, or 5 nm. The thickness of a layer or element is understood here and below to mean, in particular, the maximum or average thickness along the entire lateral extent of the layer or element.

0017According to at least one embodiment, the supply element is partially or completely covered by the active layer and the tunnel layer in a plan view of a second main side of the layer sequence opposite the first main side. This means that the tunnel layer, the active layer, and the supply element all overlap with each other in one region. In this region, the tunnel layer is arranged directly between the layer sequence and the supply element.

0018According to at least one embodiment, a current flow between the supply element and the layer sequence is only possible through a quantum mechanical tunneling effect. This means that the tunnel layer, if chosen to be sufficiently thick, for example, thicker than 10 nm, 100 nm, or 1 µm, would have an electrically insulating effect. At typical operating voltages for LEDs of, for example, a maximum of 10 V, no current would flow between the supply element and the layer sequence. Only the small thickness of the tunnel layer allows the quantum mechanical tunneling effect to occur through the tunnel layer during normal operation, allowing charge carriers to pass from the supply element into the layer sequence or vice versa, even at typical operating voltages. This results in such a strong current flow that the active layer emits radiation, a large amount of radiation that is perceptible to an observer, for example.

0019According to at least one embodiment, at least two subregions are formed in the region of the supply element, lying adjacent to one another in the lateral direction. In the subregions, the tunnel layer and/or the supply element are deliberately designed differently, so that the tunneling probabilities through the tunnel layer differ from one another in the different subregions. "Targeted design" specifically means that these are not merely fluctuations in the tunneling probability along the supply element due to manufacturing. Rather, the tunneling probabilities in the individual sections are intentionally and controlled to be different from one another. In particular, the sub-areas do not have arbitrary geometric shapes, but have well-defined geometric shapes within the manufacturing tolerance, such as rectangles, circles, squares, U-shapes, L-shapes.

0020The quantum mechanical tunneling probability depends on both the height of the potential barrier for charge carriers formed by the tunneling layer and the thickness of the tunneling layer. Furthermore, the tunneling probability increases with the electric field strength in the tunneling layer.

0021In at least one embodiment, the light-emitting diode comprises a layer sequence with an active layer emitting radiation during operation, at least one supply element arranged on a first main side of the layer sequence and via which electrical current is conducted into or out of the layer sequence during operation, and a tunnel layer between the active layer and the supply element. In plan view, the supply element is partially or completely covered by the active layer and the tunnel layer. Current flow between the supply element and the layer sequence is only possible through a tunneling effect. In the region of the supply element, at least two sub-regions are formed which are located next to one another in the lateral direction and in which the tunnel layer and/or the supply element are deliberately designed differently, so that the tunneling probabilities through the tunnel layer in the different sub-regions are different from one another.

0022The light-emitting diode described here utilizes, among other things, the idea of ​​exploiting the quantum mechanical tunneling effect to locally and specifically influence the strength of a current injected into a layer sequence. For example, the supply element can conduct current below the layer sequence to an injection region without injecting the current into the layer sequence outside the injection region. This is achieved, for example, by choosing a low tunneling probability through the tunnel layer outside the injection region. In contrast, the tunneling probability is high within the injection region, so that the layer sequence there is energized. The supply element can be invisible to an observer, for example, due to its thinness or transparent material.

0023The invention described here also makes it possible to easily create a brightness profile along a light-emitting surface of the LED. Areas where the tunneling probability is higher appear brighter to an observer, while areas where the tunneling probability is lower or negligible appear darker to an observer or do not glow at all. The invention thus makes it possible to display signatures such as patterns or characters in a surface light source with an unstructured active layer. It is also possible to make the illuminated surface appear pixelated or segmented without having to structure the active layer, i.e., without having to provide it with interruptions or perforations.

0024The tunnel layer between the supply element and the layer sequence preferably also serves as passivation or encapsulation and offers improved tightness of the light-emitting diode against air and/or water.

0025According to at least one embodiment, the subregions have a lateral extent along a main extension direction of the active layer of at least 10 µm, or at least 20 µm, or at least 50 µm. The area of ​​the subregions is, for example, at least 100 µm.² or 400 µm² or 1000 µm². With such a size or area in lateral direction, the subregions defined here differ from any random subregions with different tunneling probabilities caused by manufacturing tolerances.

0026According to at least one embodiment, a tunneling probability averaged over the entire area of ​​a first partial region is at most 95% or at most 80% or at most 70% or at most 50% or at most 10% of the tunneling probability averaged over an entire area of ​​the second partial region.

0027The current passing through the tunneling layer in a particular region depends on both the area of ​​the corresponding region and the tunneling probability in that region. By adjusting the area and the tunneling probability, the brightness or intensity of the active layer in a current-carrying region can be controlled. Furthermore, a difference in brightness between two regions can be varied by changing the applied voltage. This is due to the nonlinearity of the tunneling probability through the tunnel layer and the nonlinearity of the current-voltage characteristic of the layer sequence.

0028According to at least one embodiment, the light-emitting diode has a single tunnel layer and/or a single active layer. The tunnel layer and the active layer preferably overlap completely and differ, for example, in their lateral extent by at most 10% or 5%.

0029According to at least one embodiment, the active layer and/or the tunnel layer are simply formed as a continuous layer. In particular, the active layer and/or the tunnel layer have no interruptions such as perforations. The appearance of a segmented or structured luminous surface can thus be achieved without structuring the active layer or the tunnel layer. Vias for power supply are not necessary for the LED described here. According to at least one embodiment, the supply element directly borders the tunnel layer, i.e., it is in direct mechanical contact with the tunnel layer. The tunnel layer and the supply element preferably lie flat against one another.

0030According to the invention, the supply element has different materials bordering the tunnel layer in the different subregions. As a result, the height of a tunnel barrier or potential barrier between the supply element and the tunnel layer varies in the different subregions. For example, the boundary region between the tunnel layer and the supply element is formed over its entire surface with one material in the first partial region and is formed over its entire surface with another material in the second partial region.

0031The height of the tunnel barrier is determined, among other things, by the difference in the work functions of the material of the tunnel layer and the material bordering the tunnel layer. Materials with low work functions, such as Al, In, Ca, Mo, K, or alloys thereof, are suitable for the materials bordering the tunnel layer in the second sub-region. Materials with high work functions, such as Au, Pt, Pd, can border the tunnel layer in the first sub-region.

0032According to at least one embodiment, the tunnel layer has different thicknesses in the different subregions. The thickness of a subregion is, for example, the average thickness of the tunnel layer over the entire area of ​​the subregion. The difference in the thickness of the tunnel layer in the different subregions, at which a perceptible difference in brightness occurs for the observer, also depends on the material of the tunnel layer and the supply element. For example, the difference in the thickness of the tunnel layer in the different subregions is at least 0.5 nm, at least 1 nm, or at least 2 nm.

0033According to at least one embodiment, the side of the tunnel layer facing away from the active layer is planar along its entire lateral extent within the manufacturing tolerance. "Planar" here and below means that a surface or interface is free of intentionally introduced steps or dislocations. However, steps and dislocations can occur due to manufacturing tolerances.

0034According to at least one embodiment, the tunnel layer and/or the supply element have different structures with peaks and/or edges within the different subregions. During operation, different electric field strengths then develop between the supply element and the layer sequence in the different subregions. Particularly high field strengths can develop in the area of ​​tips and edges during operation, increasing the tunneling probability there. By deliberately introducing structuring, such as pyramid-like elevations, the tunneling probabilities in these areas can be specifically influenced. Structuring can be achieved, for example, using isotropic etching. The different sub-areas can, for example, be structured differently with regard to the following characteristics: density of the tips and/or edges, shape of the tips and/or edges such as differently rounded tips and/or edges, nesting of different tips.

0035According to at least one embodiment, an electrically conductive contact element is arranged between the tunnel layer and the layer sequence in the region of the supply element. In plan view, for example, onto the second main side of the layer sequence, the contact element partially or completely overlaps with the second partial region of the supply element. In particular, current which is fed through the tunnel layer in the second sub-region of the supply element first reaches the contact element at least partially or completely before it reaches the layer sequence.

0036According to at least one embodiment, the contact element is in direct mechanical and electrical contact with the tunnel layer and/or the layer sequence. Current can therefore be injected directly into the tunnel layer or the layer sequence via the contact element.

0037According to at least one embodiment, the contact element, during intended operation, effects a lateral current distribution of the tunnel current passing through the tunnel layer in the second partial region.

0038According to at least one embodiment, the contact element has a uniform material composition along its entire lateral extent. The contact element is, for example, formed as a single piece and/or simply connected. For example, the contact element comprises or consists of a metal such as Al, Ag, Au, Cu, Ti, Pt, Mg, or graphene. It is also possible for the contact element to be transparent, for example, to comprise or consist of a transparent conductive oxide.

0039According to at least one embodiment, the contact element is flat along its entire lateral extent and within the manufacturing tolerance on a side facing the active layer and/or has a constant thickness.

0040According to at least one embodiment, the light-emitting diode has a plurality of supply elements. Each supply element can be designed in accordance with the previously described supply element. In particular, the supply elements can be electrically insulated from one another in the lateral direction.

0041According to at least one embodiment, each supply element is uniquely assigned a separate contact element described above. This means, in particular, that a tunneling current only occurs between the mutually assigned elements. When viewed from above, each contact element overlaps at least partially or completely with the second subregion of the supply element assigned to it.

0042According to at least one embodiment, the different contact elements are laterally spaced from one another by electrically insulating regions. Thus, during operation, no direct current flow occurs between two adjacent contact elements. The gap between two adjacent contact elements can be formed, for example, by a cavity or by the tunnel layer.

0043According to at least one embodiment, each contact element defines the size of a pixel of a pixelated luminous area when viewed from above the light-emitting diode. If the layer sequence is energized via one of the contact elements during operation, light emission in the active layer occurs only in the immediate area directly above the contact element due to the preferably low lateral electrical conductivity within the layer sequence. The area or pixel of the luminous surface that appears luminous to an observer then corresponds in size and geometric shape predominantly to the size and geometric shape of the contact element.

0044For example, if several contact elements are arranged in a matrix on the first main side of the layer sequence, these contact elements can define a pixellated illuminated area of ​​a display. Each contact element is preferably controlled via its associated supply element.

0045According to at least one embodiment, the supply elements can be individually and independently controlled or energized to activate or deactivate the pixels. For example, the supply elements can be energized via direct current or pulse-width modulation.

0046According to at least one embodiment, in plan view, for example, viewed from the second main side of the layer sequence, a first partial region of a supply element intersects a contact element of another supply element. This means, in particular, that at least one supply element overlaps with two contact elements in plan view. However, only the contact element that overlaps with the second sub-area of ​​the supply element is uniquely assigned to the supply element. The contact element that only overlaps with the first sub-area of ​​the supply element is, for example, uniquely assigned to a different supply element.

0047According to at least one embodiment, the tunneling probability in the first subregion is at most 1%, or at most 0.5%, or at most 0.1%, or at most 0.05% of the tunneling probability in the second subregion. Thus, in the first subregion, a current flow between the supply element and the contact element(s) arranged above the first subregion is preferably negligible. The tunneling current in the first sub-region is therefore preferably insufficient to generate a visible glow in the active layer above. This is also due to the nonlinearity of the current-voltage characteristic of the layer sequence.

0048According to at least one embodiment, a uniquely assigned contact element is arranged above each sub-area of ​​a supply element. Thus, at least two contact elements are uniquely assigned to each supply element. The contact element is connected to the different sub-areas in the current flowing through the different sub-regions into the assigned contact elements can then be distributed laterally via the contact elements. The current strength in turn depends on the tunneling probability in the sub-areas as well as on the area of ​​the sub-areas.

0049According to at least one embodiment, the contact elements of the different subregions are also laterally spaced from one another by electrically insulating regions, such as the tunnel layer. Thus, no direct current flow occurs between the contact elements of the different subregions.

0050According to at least one embodiment, the light-emitting diode has a single supply element that extends completely or almost completely along the entire lateral extent of the active layer. Preferably, the supply element covers, for example, at least 90%, 95%, or 99% of the active layer of the layer sequence in plan view.

0051According to at least one embodiment, the tunnel layer directly borders the layer sequence, so that when the LED is energized, an observer perceives a structured luminous surface in the region of the supply element due to the different current densities in the different subregions. In this case, no lateral current distribution occurs using contact elements. Only the size and area of ​​the subregions of the supply element or the tunnel layer determine the size and area of ​​the different luminous intensity regions of the active layer. This, in turn, is due to the low lateral conductivity within the layer sequence. For example, the sheet resistance across the entire layer sequence is at least 100 Ω/□, 1,000 Ω/□, or 10,000 Ω/□.

0052According to at least one embodiment, the side of the supply element facing and/or facing away from the tunnel layer is formed flat along the entire lateral extent within the manufacturing tolerance.<br />For example, the supply element has a constant thickness along its entire lateral extent.

0053According to at least one embodiment, the tunnel layer is planar along its entire lateral extent on a side facing the layer sequence within the manufacturing tolerance.

0054According to at least one embodiment, the supply element comprises a plurality of electrically conductive material layers stacked one above the other. The different material layers comprise, for example, or consist of different materials or material compositions.

0055According to at least one embodiment, the number of material layers varies in the different subregions, so that the side of the supply element facing the tunnel layer has a step in the transition region from one subregion to a directly adjacent subregion. In particular, different numbers of the different material layers are removed or stacked on top of one another in the different subregions. The height of the step between two adjacent sub-areas then corresponds to the height or thickness of the additional material layers removed or deposited in one sub-area. The material layers can, for example, comprise or be formed from one or more of the following materials: Al, Ag, Au, In, ITO, Pt. In particular, mixtures of transparent and non-transparent material layers are conceivable.

0056The thickness of the supply element is, for example, at least 50 nm or 100 nm or 150 nm. Alternatively or additionally, the thickness of the supply element is at most 400 nm or at most 300 nm or at most 200 nm.

0057According to at least one embodiment, the tunnel layer has a constant thickness in the region of the entire supply element within the manufacturing tolerance. If, for example, the supply element is designed in a stepped manner on the side facing the layer sequence, the tunnel layer replicates the steps of the supply element in a conformal or form-fitting manner.<br />Furthermore, a method for producing a light-emitting diode is specified. The method is particularly suitable for producing a light-emitting diode described here. This means that all features disclosed in connection with the light-emitting diode are also disclosed for the method, and vice versa.

0058According to at least one embodiment, the method for producing a light-emitting diode comprises a step A) in which a substrate is provided. The substrate can be transparent or non-transparent, flexible or rigid, and/or formed as a film. The substrate can be, for example, a glass substrate, a plastic substrate, a ceramic substrate, a metal substrate, or a semiconductor substrate. In particular, the substrate is self-supporting and suitable for the application or growth of further layers.

0059In a subsequent step B), at least one supply element is arranged on the substrate. The supply element can be deposited, for example, by vapor deposition or sputtering. Structuring of the supply element can be achieved by etching, a shadow mask process, or ablation.

0060In a further step C), a tunnel layer is applied to the substrate. For example, the tunnel layer and the substrate then at least partially enclose the supply element. The tunnel layer can be applied, for example, using atomic layer deposition (ALD) or physical or chemical vapor deposition (PVD or CVD). It is also possible to apply the tunnel layer by vapor deposition or a screen printing stencil and a printing process. Furthermore, the tunnel layer can also be produced by oxidation, such as anodic oxidation, of the supply element.

0061In a further step D), a layer sequence with an active layer that emits radiation during operation is formed on the substrate. If the layer sequence is an organic layer sequence, for example, it can be applied in solution, with the solvent subsequently evaporated. An inorganic layer sequence with an active layer can be applied, for example, by bonding from a growth substrate to the substrate. After application of the layer sequence, the tunnel layer and the supply element are preferably arranged between the substrate and the layer sequence.

0062In steps B) and/or C), the supply element and/or the tunnel layer in the region of the supply element is specifically structured to create at least two subregions that are laterally adjacent to one another, in which the tunnel layer and/or the supply element are specifically designed differently. As a result, the tunneling probabilities through the tunnel layer differ from one another in the different subregions during operation.

0063According to at least one embodiment, steps A) to D) are performed in the specified order and in separate process steps. Alternatively, steps D), C), and B) can also be performed in this order. The supply element and the tunnel layer are then formed on a side of the layer sequence facing away from the substrate.

0064According to at least one embodiment, a contact element is applied to the tunnel layer or the layer sequence, so that the contact element is arranged between the tunnel layer and the layer sequence in the finished light-emitting diode. The contact element can be applied or structured using lithography, printing, microablation, or a mask process.

0065According to at least one embodiment, in step B), several different material layers are first stacked one above the other over the entire surface in the region of the supply element. Subsequently, different numbers of material layers are removed in the different partial regions, so that the uppermost layers of the supply element, as seen from the substrate, have different material compositions in the different partial regions. In this way, the supply element receives a side with a targeted step that faces the layer sequence. Alternatively, the different material layers can also be structured during stacking, eliminating the need for subsequent selective removal.

0066According to at least one embodiment, in step B), the partial regions are selectively coated with different material layers. The material layers preferably have the same thickness within the manufacturing tolerance. After coating in the different partial regions, the uppermost layers in the partial regions, as seen from the substrate, have different material compositions. Preferably, the supply element is flat along its entire lateral extent on a side facing away from the substrate. The material layers are thus arranged laterally next to one another and not on top of one another. This can be achieved by printing, lift-off, or structured disposition.

0067According to at least one embodiment, the tunnel layer is applied using a screen printing stencil. For this purpose, the screen printing stencil preferably has subregions in which the size and/or density of perforations in the screen printing stencil vary. If the tunnel layer material is pressed through the screen printing stencil using a squeegee, for example, the penetration rates of the tunnel layer material will vary in the different sections of the stencil. Thus, for example, with a constant squeegee pressure, the thickness of the resulting tunnel layer will vary in the different sections of the screen printing stencil. The sub-areas of the screen printing stencil then correspond to the sub-areas with the different tunneling probabilities of the supply element.

0068A light-emitting diode described herein and a method for producing a light-emitting diode described herein are explained in more detail below with reference to drawings using exemplary embodiments. Like reference numerals indicate like elements in the individual figures. However, they are not drawn to scale; rather, individual elements may be exaggerated for clarity.

0069They show:<ul id="ul_0001" list-style="none"><li id="ul_0001_0001"><figref>1A to 2C, 4A to 4D, 9A to 9F, 11A to 11E</figref> various embodiments of light-emitting diodes in side view and top view,</li><li id="ul_0001_0002"><figref>3</figref> a state-of-the-art organic light-emitting diode,</li><li id="ul_0001_0003"><figref>5A</figref> and<figref>5B</figref> various embodiments of a supply element of a light-emitting diode described here,</li><li id="ul_0001_0004"><figref>5A to 8F</figref> various positions in embodiments of methods for producing lead elements of a light-emitting diode described here,</li><li id="ul_0001_0005"><figref>10A</figref> and<figref>10B</figref> various positions in embodiments for producing a light-emitting diode,</li><li id="ul_0001_0006"><figref>12A</figref> and<figref>12B</figref> Tables with numerical examples for different tunnel layers.</li></ul>

0070In the example of<figref>1A</figref> A light-emitting diode 100 is shown in a lateral cross-sectional view. The light-emitting diode 100 comprises a substrate 7 on which a plurality of lead elements 3 are arranged laterally next to one another. The substrate 7 is, for example, a glass or plastic substrate. The lead elements 3 are spaced apart from one another in the lateral direction parallel to a main extension direction of the substrate 7. Each supply element 3 has two subregions 31, 32 arranged side by side. The thickness of the supply elements 3 is constant along the entire lateral direction. In the different subregions 31, 32 of the supply elements 3, the supply elements 3 have different material compositions. For example, the first subregion 31 is made of Au or In, while the second subregion 32 is made of Al, for example.

0071A tunnel layer 2 is applied directly to the supply elements 3. The tunnel layer 2 also fills the gaps between adjacent supply elements 3 and electrically insulates the supply elements 3 from each other. The tunnel layer 2 is applied in the area of ​​the supply elements 3 with a thickness of, for example, at least 2 nm and at most 20 nm. The tunnel layer 2 is, for example, an electrically insulating layer, such as an Al₂O₃-Layer. Tunnel layer 2 is simply connected along its entire lateral extent, thus having no vertical perforations perpendicular to the lateral direction.

0072The tunnel layer 2 is<figref>1A</figref> A plurality of contact elements 4 are directly applied. The contact elements 4 are not in direct contact with the supply elements 3, but are spaced from the supply elements 3 by the tunnel layer 2 in a vertical direction, perpendicular to the lateral direction. Current or charge carriers that want to pass from a contact element 4 to a supply element 3, or vice versa, must always cross the tunnel layer 2. The contact elements 4 are preferably electrically conductive and consist, for example, of a metal or a TCO.

0073In the example of<figref>1A</figref> Each supply element 3 is uniquely assigned a contact element 4 and arranged vertically above the corresponding supply element 3. The contact elements 4 are spaced from each other in a lateral direction, so that no direct current flow between two adjacent contact elements 4 is possible.<br />A layer sequence 1 with an active layer 10 that emits radiation during operation is applied directly to the contact elements 4 and the tunnel layer 2. Layer sequence 1 is, for example, an organic layer sequence, with the active layer comprising, for example, organic emitter molecules. However, an inorganic layer sequence is also possible. The layer sequence 1 has a first main side 11 and a second main side 12 opposite the first main side 11, wherein the contact elements 4, the tunnel layer 2 and the supply elements 3 are arranged on the first main side 11.

0074In the example of<figref>1A</figref> The tunnel layer 2, the active layer 10, the supply elements 3, and the contact elements 4 are each formed as a single, interconnected structure. In particular, the active layer 10 has no vias or perforations.

0075A second, simply connected contact layer 5 is applied to the second main side 12 of the layer sequence 1, forming an electrical counter-contact or counter-electrode to the contact elements 4 or the supply elements 3. In the present example, the second contact layer 5 is formed, for example, from a transparent material such as a TCO. The second contact layer covers the entire active layer 10 and/or all supply elements 3.

0076A thin film encapsulation 6 is applied to the second contact layer 5, which encapsulates the layer sequence 1 and protects it from external influences.<br />The LED 100 of the<figref>1A</figref> is designed as a so-called top emitter. In this case, the contact elements 4, the supply elements 3, and/or the substrate 7 can be reflective of electromagnetic radiation emitted by the active layer 10. The electromagnetic radiation is coupled out of the light-emitting diode 100 via a luminous surface 13 of the light-emitting diode 100 facing away from the substrate 7.

0077In the example of<figref>1B</figref> is the LED 100 of the<figref>1A</figref> 13 in a top view of the luminous surface 13. The substrate 7, on which the layer sequence 1 is formed, can be seen. The supply elements 3 are arranged below the layer sequence 1, each partially overlapping the layer sequence 1. A contact region of each supply element 3 protrudes laterally from the layer sequence 1. The contact regions are designed for electrically contacting the supply elements 3.

0078In addition, the contact elements 4 are shown as dashed elements in the<figref>1B</figref> made visible. Each contact element 4 partially overlaps with a supply element 3 uniquely assigned to it. In particular, each contact element 4 completely overlaps the second partial area 32 of the assigned supply element 3. In addition,<figref>1B</figref> It can be seen that some of the supply elements 3 in the first partial area 31 overlap with two contact elements 4.

0079In the examples of the<figref>1A</figref> and<figref>1B</figref> For example, the tunneling probability from the supply element 3 through the tunnel layer 2 into the associated contact element 4 in the first sub-region 31 is at most 1% of the tunneling probability in the second sub-region 32. Accordingly, in the first sub-region 31, almost no current flows from the supply element 3 into the contact element 4 during operation. Only in the second sub-region 32 does a significant current flow from the supply element 3 into the contact element 4 occur. During operation, the current can then be distributed laterally within the contact element 4 and injected into the layer sequence 1. Due to the low lateral electrical conductivity in the layer sequence 1, significant radiation generation occurs only in a region of the active layer 10 located directly above the contact element 4. During operation, the contact elements 4 can therefore define the size of a luminous image point or pixel of the light-emitting diode 100.

0080In the embodiment of the<figref>1B</figref> advantageously, internal contact elements 4 surrounded by further contact elements 4 can be energized in a simple manner. The supply element 3 assigned to the internal contact element 4 overlaps, as seen in plan view, with a contact element 4 not assigned to it. However, since this overlap only occurs in the first partial area 31, the supply element 3 does not energize this contact element 4.

0081The embodiment of the<figref>1C</figref> essentially corresponds to the embodiment of the<figref>1A</figref>In contrast to<figref>1A</figref> The contact elements 4, the supply elements 3, and the substrate 7 are now transparent. The second contact layer 5, in contrast, is made of a reflective material, such as Al or Ag. Radiation generated in the active layer 10 of the layer sequence 1 then leaves the light-emitting diode 100 via the substrate 7 during operation. The light-emitting diode 100 is a so-called bottom emitter.

0082In the example of<figref>1D</figref> In contrast to the embodiment of the<figref>1C</figref> The second contact layer 5 is now also transparent. In this case, the light-emitting diode 100 has two opposing luminous surfaces 13, through which electromagnetic radiation is coupled out during operation. The light-emitting diode 100 is a so-called top-bottom emitter.

0083In the example of<figref>1E</figref> The contact elements 4, the tunnel layer 2 and the supply elements 3 are formed on the first main side 11 of the layer sequence 1, the substrate 7 is formed on the second main side 12 of the layer sequence 1. The second contact layer 5 is in this case arranged between the substrate 7 and the layer sequence 1. The light-emitting diode 100 of the<figref>1E</figref> is again designed as a bottom emitter, i.e. the substrate 7 and the second contact layer 5 are transparent, the contact elements 4 are, for example, reflective. The functional principle of the light-emitting diode 100 of the<figref>1E</figref> corresponds to the functional principle of the LEDs in the previous embodiments.<br />In the example of<figref>1F</figref> A light-emitting diode 100 is shown in which supply elements 3, a tunnel layer 2, and contact elements 4 uniquely assigned to the supply elements 3 are applied to both the first main side 11 and the second main side 12 of the layer sequence 1. In contrast to the previous exemplary embodiments, there is therefore no simply connected second contact layer 5 extending over the entire extent of the layer sequence 1.

0084In the example of<figref>2A to 2C</figref> a light-emitting diode 100 is shown in plan view of the luminous surface 13. In<figref>2A</figref> A luminous image generated by the luminous surface 13 is shown. The luminous image comprises a circle and two concentric rings around the circle. In total, there are three different image areas or pixels. The image areas should have different brightnesses during operation. This is shown in<figref>2A</figref> outlined by the different shades of the image areas.

0085In<figref>2B</figref> This shows how the different current supply and brightness of the three image areas are realized. For demonstration purposes, layer sequence 1 has been removed. Only the supply elements 3 and the contact elements 4 are visible. The contact elements 4 have the desired shape and size of the image areas. In particular, the contact elements 4 are formed as a circle and two concentric rings, which are laterally spaced from one another and electrically insulated from one another. A uniquely assigned supply element 3 extends into each contact element 4, with the contact element 4 completely overlapping the second partial region 32 of the associated supply element 3. Only in the second subregion 32 is the tunneling probability sufficiently high to result in a significant current flow between the supply element 3 and the associated contact element 4. In this way, each contact element 4 or each associated image area can be controlled independently of the other contact elements 4 via the supply elements 3.

0086The product of the current density supplied to the supply elements 3 and the area of ​​the partial areas 32 determines how much current reaches the associated contact elements 4. The greater this current and the smaller the area of ​​the contact element 4, the brighter the associated image area illuminates during operation.

0087In the example of<figref>2B</figref> The outer illuminated area, i.e., the outer concentric ring, has the largest area, while the inner circular image area has the smallest area. Accordingly, the inner image area is the brightest during operation.

0088In the example shown below<figref>2C</figref> Only the substrate 7 and the supply elements 3 applied thereto are shown. The contact elements 4 and the tunnel layer 2 have been removed.

0089In<figref>3</figref> A prior art light-emitting diode 100 is shown. Unlike the light-emitting diode 100 described in this invention, the light-emitting diode of the<figref>3</figref> no supply elements 3 or contact elements 4. Rather, a flat first contact layer 50 is applied to the first main side 11 of the layer sequence 1, and a flat second contact layer 5 is applied to the second main side 12 of the layer sequence 1. The second contact layer 5 is guided onto the substrate 7 along side surfaces of the layer sequence 1 and is electrically connected there to a contact area. Likewise, the contact layer 50 extends laterally out of the layer sequence 1 and is electrically connected to a contact area. For electrical insulation between the first contact layer 50 and the second contact layer 5, an insulating layer 9 is applied to the side surfaces of the layer sequence 1.

0090In the example of<figref>4A</figref> a top emitter is again shown, in which the luminous surface 13 is formed on a side of the light-emitting diode 100 opposite the substrate 7. Unlike in the embodiments of<figref>1A to 2C</figref> The light-emitting diode 100 now has a single, simply connected supply element 3, which extends almost along the entire lateral extent of the layer sequence 1. The supply element 3 has laterally adjacent partial regions 31, 32, 33, 34, each with different tunneling probabilities through the tunnel layer 2. The tunnel layer 2 borders in the embodiment of the<figref>4A</figref> directly to the layer sequence 1, so an additional contact element 4 is not used.

0091The different subregions 31, 32, 33, 34 of the supply element 3 have, for example, different materials bordering the tunnel layer 2, so that the tunnel barriers and thus the tunnel probabilities are different. In this way, different amounts of current or different current densities reach the overlying layer sequence 1 via the different partial areas 31, 32, 33, 34, which is why the active layer 10 generates different amounts of radiation in the different partial areas 31, 32, 33, 34. For an observer, the luminous surface 13 of the light-emitting diode 100 then illuminates with different intensities in the different partial areas 31, 32, 33, 34 during operation, which is indicated by the arrows of different thickness in the<figref>4A</figref> is marked.

0092The embodiment of the<figref>4B</figref> essentially corresponds to the embodiment of the<figref>4A</figref>, except that the second contact layer 5 is reflective and the light-emitting diode 100 is operated as a bottom emitter.

0093In the<figref>4C</figref> The second contact layer 5 and the supply element 3 are transparent. The light-emitting diode 100 is operated as a top-bottom emitter.

0094In the example of<figref>4D</figref> are as in the example of<figref>4C</figref> The second contact layer 5 and the substrate 7 are transparent. The supply element 3 is transparent in some partial areas 31, 33 and reflective in other partial areas 32, 34. The resulting luminous image therefore depends on whether the observer is looking at the substrate 7 or the second contact layer 5.

0095In the<figref>5A</figref> and<figref>5B</figref> Two different embodiments of a supply element 3 used here are shown. In the<figref>5A</figref> The supply element 3 is formed with a thickness that is constant within the manufacturing tolerance along the entire lateral extent of the supply element 3. The partial regions 31, 32 are formed by two adjacent material layers of different materials.

0096In contrast, in the<figref>5B</figref> The supply element 3 is formed from three superimposed material layers 301, 302, 303. In some areas, the third material layer 303 is removed; in other areas, both the third material layer 303 and the second material layer 302 are removed. This creates steps within the supply element 3. The tunneling probability varies depending on which material layer is exposed and thus directly borders the tunnel layer 2. In this way, different sub-areas 31, 32, 33 with different tunneling probabilities are formed.

0097In the<figref>6A to 6F</figref> various positions in the production of an embodiment of a supply element 3 for a light-emitting diode 100 are shown.

0098In the<figref>6A</figref> A carrier is initially provided. In the following<figref>6B</figref> four material layers 301, 302, 303, 304 of different materials or material compositions are stacked on top of each other.

0099<figref>6C</figref> shows a position in which the fourth material layer 304, which is furthest away from the carrier, is partially removed and the third material layer 303 is exposed there.

0100In a further step, shown in the<figref>6D</figref>, the third material layer 303 is also partially removed, so that the second material layer 302 is partially exposed.

0101In the<figref>6E</figref> Additional trenches are introduced into the second material layer 302, creating a supply element 3 with three laterally spaced-apart subregions 31, 32, 33. In the first subregion 31, an outer side of the supply element 3 facing away from the carrier is formed by the fourth material layer 304, in the second subregion 32 by the second material layer 302, and in the third subregion 33 by the third material layer 303.

0102Afterwards,<figref>6F</figref> A simply connected tunnel layer 2 is applied over the entire surface and directly to the subregions 31, 32, 33. The tunnel layer 2 has a constant average thickness in all subregions 31, 32, 33, 34. The tunneling probability through the tunnel layer 2 is therefore determined only by the material of the material layers 302, 303, 304 bordering the tunnel layer 2.

0103In the example of<figref>7A to 7F</figref> Positions in an alternative method for producing an embodiment of a lead element 3 for a light-emitting diode 100 are indicated. In this case, again,<figref>7A</figref> a carrier is provided on which<figref>7B</figref> a first material layer 301 is applied. A structured second material layer 302 is applied to the first material layer 301 (<figref>7C</figref>). In<figref>7D</figref> a third material layer 303 is applied to some areas of the second material layer 302.

0104In<figref>7E</figref> Finally, a fourth material layer 304 is applied to a region of the third material layer 303, creating a total of three sub-regions 31, 32, 33, in which the uppermost material layer, furthest from the carrier, each comprises different materials. The material layers are thus applied additively, for example, by printing or selective disposition.

0105In<figref>7F</figref> the partial areas 31, 32, 33 are again covered with a tunnel layer 2.

0106In the<figref>8A to 8F</figref> various positions in a further alternative method for producing an embodiment of a lead element 3 for a light-emitting diode 100 are shown.

0107For this purpose,<figref>8A</figref> A carrier is provided again, onto which the<figref>8B to 8E</figref> Material layers 301, 302, 303, 304 are applied laterally next to one another. The material layers 301, 302, 303, 304 each have the same thickness within the manufacturing tolerance, so that the resulting supply element 3 has a constant thickness within the manufacturing tolerance along its entire lateral extent.

0108In the<figref>8F</figref> a position is shown in which a simply connected tunnel layer 2 is applied to the entire surface of the supply element 3.

0109In the embodiment of the<figref>9A</figref> a light-emitting diode 100 is shown which, like the light-emitting diode 100 of the<figref>4B</figref> is designed as a bottom emitter. In contrast to the<figref>4B</figref> is the tunneling probability through tunnel layer 2 in<figref>9A</figref> but not influenced by a variation of the material of the supply element 3 in the lateral direction. Rather, the supply element 3 is<figref>9A</figref> along its entire lateral extent with the same material composition.<figref>9A</figref> The thickness of tunnel layer 2 varies along its lateral extent, so that tunnel layer 2 has a different thickness in each subregion 31, 32, 33, 34. Due to the different thicknesses, different tunneling probabilities through tunnel layer 2 arise. As a result, the current flowing through tunnel layer 2 into layer sequence 1, and thus the emitted brightness, varies in the different subregions 31, 32, 33, 34.

0110In<figref>9B</figref> is essentially the same embodiment as in<figref>9A</figref> In the example of the<figref>9B</figref> However, the supply element 3 is reflective, while the second contact layer 5 is radiation-permeable.<figref>9B</figref> The light-emitting diode 100 is designed as a top emitter.

0111In<figref>9C</figref> the light-emitting diode 100 is formed as a top-bottom emitter with a transparent lead element 3 and a transparent contact layer 5.

0112In the example of<figref>9D</figref> The tunnel layer 2 and the supply element 3 are formed on a side of the layer sequence 1 facing away from the substrate 7. However, the functional principle still corresponds to that of the light-emitting diodes 100 of the<figref>9A to 9C</figref>.

0113In the example of<figref>9E</figref> is essentially the same light-emitting diode 100 as in<figref>9A</figref> shown. In addition, however, between the tunnel layer 2 and the layer sequence 1, in each sub-region 31, 32, 33, 34, a contact element 4 is arranged that is uniquely assigned to the corresponding sub-region 31, 32, 33, 34. The contact elements 4 are in direct contact with the layer sequence 1 and the tunnel layer 2. The individual contact elements 4 cover the associated sub-area 31, 32, 33, 34 in plan view, but do not extend laterally beyond the respective sub-area 31, 32, 33, 34. In particular, the contact elements 4 are electrically insulated from one another, so that no direct electrical current flow is possible between the contact elements 4. The contact elements 4 ensure a lateral current distribution within the sub-areas 31, 32, 33, 34 and thus a more homogeneous luminance within the sub-areas 31, 32, 33, 34.

0114In the example of<figref>9F</figref> An embodiment of a light-emitting diode 100 is shown in plan view. For example, the light-emitting diode 100 is a light-emitting diode with the functional principle of one of the light-emitting diodes of the<figref>9A to 9E</figref>. By means of partial areas 31, 32, 33, 34 with different tunnel probabilities, a luminous surface 13 with a lettering can be realized. In the embodiment of the<figref>9F</figref> the lettering “OLED” shines brighter than the corresponding background.

0115In the<figref>10A to 10B</figref> Positions in process steps for producing a tunnel layer 2 with different thicknesses in different sub-regions 31, 32 are shown.

0116In<figref>10A</figref> A substrate 7 with a supply element 3 applied thereto is shown. A screen printing stencil 8 with two regions 81, 82 is also arranged above the supply element 3. In the different regions 81, 82, the screen printing stencil has openings 80 of different sizes and densities. In the first region 81, the density of the openings 80 and the lateral extent of the openings 80 are smaller than in the second region 82. If the tunnel layer material 2 is now pressed through the screen printing stencil 8 using a squeegee, the<figref>10B</figref> Tunnel layer 2 shown with two subregions 31, 32, in which the thickness of tunnel layer 2 is different. The size and geometric shape of subregions 31, 32 correspond to the size and geometric shape of regions 81, 82 of screen printing stencil 8.

0117In the<figref>11A to 11E</figref> Further embodiments of a light-emitting diode 100 are shown in side view.

0118The embodiment of the<figref>11A</figref> essentially corresponds to the embodiment of the<figref>9A</figref>. Unlike in<figref>9A</figref> is in<figref>11A</figref> However, the thickness of tunnel layer 2 does not vary; rather, the tunnel layer 2 is provided with different structures in the different subregions 31, 32. In the first subregion 31, the tunnel layer 2 has no intentionally introduced structure, whereas in the second subregion 32, pyramid-like elevations are intentionally introduced into the tunnel layer 2. In the area of ​​the peaks and valleys of the pyramids, higher field strengths occur in tunnel layer 2 during operation, which increases the tunneling probability through tunnel layer 2. Therefore, during operation, there is a stronger radiation emission in the second sub-area 32 than in the first sub-area 31. In<figref>11A</figref> the first partial region 31 forms an edge region or, in the lateral direction, an outer region of the tunnel layer 2. Since the tunnel layer 2 can be chosen to be thick in the unstructured first partial region 31, additional protection of the light-emitting diode 100 against external influences can thus be provided.

0119In<figref>11A</figref> The side of the tunnel layer 2 facing away from the supply element 3 is provided with the structure, while the side of the tunnel layer 2 facing the supply element 3 is flat along its entire lateral extent within the manufacturing tolerance. Furthermore, a contact element 4 is applied to the structured side of the tunnel layer 2 in the area of ​​the structures, which replicates the structures. The contact element 4 results in a more uniform current distribution along the second partial region 32. The layer sequence 1 applied to the tunnel layer 2 forms the structures of the tunnel layer 2 or the contact elements 4 in a form-fitting manner.

0120In the example of<figref>11B</figref> is in contrast to<figref>11A</figref> the tunnel layer 2 and the supply element 3 are applied on a side of the layer sequence 1 facing away from the substrate 7. In addition, several laterally spaced supply elements 3 are applied to the tunnel layer 2. Each of these supply elements 3 is electrically controllable individually and independently of the other supply elements 3. Each supply element 3 also comprises a<figref>11A</figref> described first sub-area 31 and a second sub-area 32 with structures. Between the layer sequence 1 and the tunnel layer 2, contact elements 4 are also arranged, which are uniquely assigned to the supply elements 3. In this way, as in connection with<figref>1A</figref> and<figref>1B</figref> described a pixellated display can be realized.

0121In the example of<figref>11C</figref> are the contact elements 4, the supply elements 3 and the tunnel layer 2 of the<figref>11B</figref> again placed on the side of the layer sequence 1 facing the substrate 7. The structuring of the tunnel layer 2 is again formed on a side facing the layer sequence 1. The structuring within the tunnel layer 2 is completely filled by the contact elements 4, so that the sides of the contact elements 4 facing the layer sequence 1 are flat. Advantageously, the layer sequence 1 can then be formed with a constant thickness along the entire lateral extent.

0122The embodiment of the<figref>11D</figref> essentially corresponds to the embodiment of the<figref>11A</figref>. Only the contact elements 4 between layer sequence 1 and tunnel layer 2 are<figref>11D</figref> waived.

0123In the example of<figref>11E</figref> A light-emitting diode 100 is shown in which the tunnel layer 2 is provided with different structures. In the second 32 and third subregions 33, the pyramid-like elevations have different heights but almost identical base widths. The tips of the pyramid-like elevations are therefore of different points in the different subregions 32, 33, resulting in different electric fields of different strengths being formed at the tips. In sections 32 and 33, different tunnel currents therefore occur during operation. This is also influenced by the different density of pyramid-like elevations.

0124In the table of<figref>12A</figref> Different examples of tunneling probabilities through a tunnel layer are given. The first column lists different materials (3) for the feed element 3. The second column lists the material (2) of the tunnel layer 2, which is produced by atomic layer deposition. The third column lists different thicknesses (d) of the tunnel layer 2 in nanometers. The fourth column shows the current densities (j) measured for a specific voltage through the tunnel layer 2 in mA/cm² The fifth and sixth columns show possible areas (A) of the supply element 3 in cm² and the resulting current (I) through the tunnel layer 2 is given in mA. The seventh and eighth columns show the work function (ΔW) of the material of the supply element 3 and the potential barrier (ΔΦ) to the tunnel layer 2, each in eV.

0125As the table of<figref>12A</figref> As can be seen, the tunneling probability and thus the current density is higher for a lead element 3 made of Al than for Au or In. Furthermore, the table shows that the current density decreases as the thickness of the tunnel layer 2 increases.

0126In the table of<figref>12B</figref> A more detailed investigation of the current density or current as a function of the thickness of the tunnel layer 2 is shown. Al is chosen as the material of the supply element 3. The thickness of the tunnel layer 2 is varied by approximately 1% steps. The resulting current density and the current through an area of ​​20 cm² The flowing current decreases with increasing thickness of tunnel layer 2. The resulting current or the resulting current density changes by only 4% for a 1% deviation in layer thickness.

0127Tunnel layers 2 can be manufactured with very high precision in terms of their thickness, for example, by oxidizing the associated supply element 3. Indeed, tunnel layers 2 can be precisely tuned to the Angstrom level by oxidation. With slow oxidation, for example, a 10 nm tunnel layer can be grown in approximately 10 hours. Layer thicknesses of tunnel layer 2 can thus be kept constant to within less than 1% deviation.

0128From the table of<figref>12B</figref> It can be seen that such small variations in the thickness of the tunnel layer have only a small influence on the current density through tunnel layer 2.