Optoelectronic semiconductor device and method for manufacturing an optoelectronic semiconductor device

Abstract

Optoelectronic semiconductor device (1) comprising - comprising a sequence of semiconductor layers (2) - a first semiconductor layer (3) with a first surface (3A), - a second semiconductor layer (5) with a first surface (5A), - a first main surface (2A) and a second main surface (2B) opposite the first main surface (2A), wherein the first surfaces (3A, 5A) of the first and second semiconductor layers (3, 5) are at least partially arranged on the first main surface (2A), - a directionally reflecting layer (7) arranged on the first principal surface (2A), - a first contact structure (8) for electrically connecting the first semiconductor layer (3), comprising a first current expansion structure (9) arranged on the first surface (3A) of the first semiconductor layer (3) and partially adjacent to the at least one directionally reflective layer (7), - a second contact structure (15) for electrically connecting the second semiconductor layer (5), comprising a second current expansion structure (16) arranged on the first surface (5A) of the second semiconductor layer (5) and partially adjacent to the at least one directionally reflective layer (7), wherein the first current expansion structure (9) and the second current expansion structure (16) each consist of at least one transparent conductive oxide.

Description

[0001] The present application relates to an optoelectronic semiconductor component and a method for producing an optoelectronic semiconductor component. In particular, the optoelectronic semiconductor component is a radiation-emitting semiconductor component, for example, an LED.

[0002] There are various chip designs, which are associated, for example, with different assembly technologies. For example, documents DE 10 2012 217 533 A1, DE 10 2016 119 539 A1, and US 2014 / 0 159 091 A1 describe optoelectronic semiconductor components with various chip designs. One possible chip design is a flip-chip construction, in which the chip is mounted upside down and bond pads of different polarities for external electrical contacting are arranged on the same side of a semiconductor body of the chip.

[0003] The increasing miniaturization of optoelectronic semiconductor components requires, on the one hand, improved electrical contacting of the semiconductor component, for example, with regard to current spreading, and, on the other hand, improved outcoupling efficiency. While electrical contacting could be improved by using a metal structure, such a structure could have an adverse effect on outcoupling efficiency due to its absorption coefficient.

[0004] The objects to be achieved in the present application are to provide an improved optoelectronic semiconductor component and an improved method for producing an optoelectronic semiconductor component. These objects can be achieved, inter alia, by an optoelectronic semiconductor component having the features of the independent device claim and by a method having the features of the independent method claim.

[0005] According to at least one embodiment of an optoelectronic semiconductor component, the optoelectronic semiconductor component comprises a semiconductor layer sequence, wherein the semiconductor layer sequence comprises a first semiconductor layer having a first surface, a second semiconductor layer having a first surface, a first main surface, and a second main surface opposite the first main surface. In particular, the first surfaces of the first and second semiconductor layers are at least partially arranged on the first main surface of the semiconductor layer sequence. Furthermore, the optoelectronic semiconductor component comprises a directionally reflective layer arranged on the first main surface. In the context of the present application, "directionally reflective" refers to a reflection property characterized by the fact that a majority of the radiation is reflected in one direction or within a small angular range.

[0006] Furthermore, the optoelectronic semiconductor component comprises a first contact structure for electrically connecting the first semiconductor layer, wherein the first contact structure has a first current spreading structure arranged on the first surface of the first semiconductor layer and partially adjacent to the at least one directionally reflective layer. In the context of the present application, "arranged on (...)" means following in a non-parallel, preferably vertical direction.

[0007] Furthermore, the optoelectronic semiconductor component comprises a second contact structure for electrically connecting the second semiconductor layer, which has a second current spreading structure arranged on the first surface of the second semiconductor layer and partially adjacent to the at least one directionally reflective layer. Furthermore, the first current spreading structure and the second current spreading structure each consist of at least one transparent conductive oxide. Even if the first current spreading structure and the second current spreading structure each consist of at least one transparent conductive oxide, the structures may contain additional components that do not significantly alter the characteristic physical properties of the transparent conductive oxide(s).

[0008] Transparent conductive oxides (TCOs) are transparent conductive materials, typically metal oxides such as zinc oxide, tin oxide, cadmium oxide, titanium oxide, indium oxide, or indium tin oxide (ITO). In addition to binary metal-oxygen compounds such as ZnO, SnO2, or In2O3, ternary metal-oxygen compounds such as Zn2SnO4, CdSnO3, ZnSnO3, MgIn2O4, GaInO3, Zn2In2O5, or In4Sn3O12, or mixtures of various transparent conductive oxides, TCOs also belong to the group of transparent conductive oxides. Furthermore, TCOs do not necessarily have to conform to a stoichiometric composition and can also be p- or n-doped.

[0009] In an advantageous embodiment, the first current spreading structure has a contact layer. The contact layer is preferably a single layer, which in particular consists of a TCO, for example, ITO. Particularly preferably, the contact layer directly adjoins the first semiconductor layer. Furthermore, the first current spreading structure can have a current spreading layer, which in particular consists of at least one transparent conductive oxide. The contact layer can be thinner than the current spreading layer.

[0010] In an advantageous embodiment, the current spreading layer of the first current spreading structure is a multilayer comprising at least two sublayers. The two sublayers preferably differ in their material composition and / or thickness.

[0011] According to at least one embodiment, the second current spreading structure comprises a current spreading layer, which preferably consists of at least one transparent conductive oxide. Particularly preferably, the current spreading layer of the second current spreading structure is a multilayer comprising at least two sublayers. In particular, the two sublayers differ in their material composition and / or thickness. The second current spreading structure can consist of the current spreading layer and need not comprise any further layers. The current spreading layer can be arranged directly on the first surface of the second semiconductor layer. In other words, no further layer needs to be located between the current spreading layer and the second semiconductor layer.

[0012] During operation, charge carriers are preferably impressed directly from the current spreading structures into the semiconductor layer sequence. Particularly preferably, the first and second current spreading structures have a relatively low sheet resistance, so that current crowding hardly occurs. A preferred sheet resistance is a maximum of 45 ohms / square, although deviations of 10% are tolerable.

[0013] One advantage of the device is that the TCOs used for the current spreading structures reduce absorption losses and increase the contact area with negligible absorption losses. This allows both current spreading and outcoupling efficiency to be improved simultaneously.

[0014] In an advantageous embodiment, the first current spreading structure and the second current spreading structure are free of Au and / or Ag.

[0015] Suitable thicknesses of the current spreading layers range between 5 nm and 500 nm, preferably between 15 nm and 150 nm, particularly preferably between 60 nm and 100 nm, with deviations of 10% being tolerable. The first and second current spreading layers can be multilayers, each comprising at least two sublayers, preferably made of different TCO materials, for example, a sublayer of ZnO and a sublayer of ITO. The sublayer of ZnO can, for example, be 15 nm thick, while the sublayer of ITO can be 70 nm thick.

[0016] In addition, suitable thicknesses of the contact layer of the first current spreading structure are in a range between 15 nm and 200 nm, preferably between 20 nm and 90 nm, particularly preferably between 50 nm and 70 nm, whereby deviations of 10% are tolerable.

[0017] In a preferred embodiment of the optoelectronic semiconductor component, the first semiconductor layer has a first conductivity type and the second semiconductor layer has a second conductivity type. In particular, the first semiconductor layer is a p-doped layer, while the second semiconductor layer is an n-doped layer. Preferably, an active zone is located between the first semiconductor layer and the second semiconductor layer. Additional layers, doped or undoped, can be arranged between the first semiconductor layer and the active zone, as well as between the second semiconductor layer and the active zone.

[0018] According to at least one embodiment, the active zone is provided for generating electromagnetic radiation. In this case, the term "electromagnetic radiation" refers in particular to infrared, visible, and / or ultraviolet electromagnetic radiation. In particular, the active zone is provided for the emission of blue or green light. During operation, a major portion of the generated radiation can be emitted laterally, i.e., at side surfaces of the optoelectronic semiconductor component. A smaller portion of the radiation can be emitted on the top side of the optoelectronic semiconductor component.

[0019] Materials based on nitride compound semiconductors are suitable for the semiconductor layer sequence. In this context, "based on nitride compound semiconductors" means that at least one layer of the semiconductor layer sequence comprises a nitride III / V compound semiconductor material, preferably Al n Ga mIn 1-n-m N, where 0 ≤ n ≤ 1, 0 ≤ m ≤ 1 and n+m ≤ 1, without necessarily having a mathematically exact composition according to the above formula. Rather, it can contain one or more dopants and additional components that affect the characteristic physical properties of Al n Ga m In 1- n-m N material does not change significantly. However, for simplicity, the above formula only includes the essential components of the crystal lattice (Al, Ga, In, N), although these can be partially replaced by small amounts of other substances.

[0020] According to at least one embodiment, the optoelectronic semiconductor component comprises a carrier on which the semiconductor layer sequence is arranged. In particular, the carrier is a growth substrate on which the semiconductor layer sequence has been epitaxially deposited. In this context, "epitaxial deposition on the growth substrate" means that the growth substrate is used for the deposition and / or growth of the semiconductor layer sequence. The second semiconductor layer is, for example, in direct contact with the growth substrate.

[0021] The carrier or growth substrate preferably comprises or consists of sapphire, SiC, and / or GaN. Particularly preferably, the growth substrate consists of sapphire, and the optoelectronic semiconductor component is a miniature sapphire flip chip. "Miniature" in the context of the present application preferably refers to a size of approximately 200 x 200 µm. 2and / or a low operating current, which makes it possible to dispense with a metallic current spreading layer, especially made of Au. The directionally reflective layer allows the device to be flipped over and achieves significantly high reflection to emit radiation from the sides and top.

[0022] According to an advantageous embodiment, the carrier is structured on a first surface on which the semiconductor layer sequence is arranged. Due to its roughness, the structured first surface contributes to increasing the outcoupling efficiency. In particular, the carrier is a structured sapphire substrate, and the refractive index difference between the semiconductor layer sequence and the carrier is linearly reduced by a "transition layer" formed on the first surface of the structured carrier.

[0023] According to at least one embodiment, the directionally reflective layer comprises or consists of a dielectric material. The directionally reflective layer can be a single layer or a multiple layer comprising at least two sublayers with a higher and lower refractive index. The directionally reflective layer is preferably a DBR (Distributed Bragg Reflector) layer. Suitable materials for the directionally reflective layer or the sublayers are oxides such as SiO2, TiO2, Nb2O5, Al2O3 or nitrides such as Si3N4 or SiNx, where "x" denotes a non-stoichiometric amount of nitride, or fluorides such as MgF2.Suitable layer thicknesses of the directionally reflective layer are in the range between 500 nm and 6000 nm, preferably in the range between 1000 nm and 5000 nm, particularly preferably between 1500 nm and 4500 nm, whereby deviations of 10% are tolerable.

[0024] According to at least one embodiment, the contact layer and the current spreading layer of the first current spreading structure are spaced apart from one another, in particular in the vertical direction, and the directionally reflective layer is arranged between the contact layer and the current spreading layer. In this case, the first current spreading structure can have at least one via element that electrically connects the current spreading layer to the contact layer. Alternatively, the current spreading layer can also be arranged directly on the contact layer.

[0025] According to at least one embodiment, the first semiconductor layer has a recess, and the second semiconductor layer is arranged at a bottom of the recess. In particular, the current spreading layer of the second current spreading structure is arranged in the recess on the second semiconductor layer.

[0026] In a preferred embodiment, the current spreading layer of the first current spreading structure partially surrounds the current spreading layer of the second current spreading structure laterally in a plan view of the first main surface. For example, the current spreading layer of the second current spreading structure can be elliptical, oval, or strip-shaped, and at least a portion of the current spreading layer of the first current spreading structure that faces the other current spreading layer can be curved, in particular U-shaped.

[0027] According to at least one embodiment, the first contact structure comprises a first feedthrough element arranged on a side of the first current spreading structure facing away from the semiconductor layer sequence. Furthermore, the second contact structure comprises a second feedthrough element arranged on a side of the second current spreading structure facing away from the semiconductor layer sequence. Advantageously, the feedthrough elements are metallic elements.

[0028] According to at least one embodiment, the first contact structure has a first bond pad arranged on a side of the first feedthrough element facing away from the semiconductor layer sequence, and the second contact structure has a second bond pad arranged on a side of the second feedthrough element facing away from the semiconductor layer sequence, wherein the first and second bond pads are provided for external contacting of the optoelectronic semiconductor component. In particular, the first and second bond pads are each metallic layers. The first and second bond pads can each have multiple layers. For example, the first and second bond pads can each comprise at least one of the following layers: an adhesion layer, a reflection layer, a barrier layer, and an encapsulation layer. Suitable materials for the adhesion layer are, for example, Ti, Cr, Al, Mo, Ni, or W.Suitable materials for the reflective layer include Ag, Al, or Rh. Suitable materials for the barrier layer include Ti, Pt, Ni, Cr, Rh, or Ru. The encapsulation layer can include or consist of Au, for example. In particular, the feedthrough elements are made of the same material as the bond pads.

[0029] In a preferred embodiment, the feedthrough elements are laterally surrounded by the directionally reflective layer, an additional directionally reflective layer, or a passivation layer. In particular, the feedthrough elements are electrically insulated from one another by the directionally reflective layer, the additional directionally reflective layer, or the passivation layer. The feedthrough elements and / or bond pads can have a significant influence on the overall reflection occurring in the component.

[0030] According to at least one embodiment, the optoelectronic semiconductor component further comprises an omnidirectionally reflective layer arranged on a side of the directionally reflective layer facing away from the semiconductor layer sequence. In the context of the present application, "omnidirectionally reflective" refers to a reflection property characterized by the radiation being distributed largely uniformly across all angles.

[0031] In particular, the omnidirectionally reflective layer is a metallic layer. The omnidirectionally reflective layer preferably contains Al or Rh. The omnidirectionally reflective layer makes it possible to increase reflection even in areas not covered by metallic elements, such as the bond pads.

[0032] Preferably, the omnidirectionally reflective layer is part of the first and second contact structures. The first contact structure has a first via element that electrically connects the omnidirectionally reflective layer to the first current spreading structure, and the second contact structure has a second via element that electrically connects the omnidirectionally reflective layer to the second current spreading structure. A passivation layer can be arranged on a side of the omnidirectionally reflective layer facing away from the directionally reflective layer. The passivation layer can be a single or multiple layer of dielectrics such as SiO2, TiO2, Al2O3, SiNx, silicon oxynitride, and Nb2O5.

[0033] According to at least one embodiment, the component comprises an additional directionally reflective layer, wherein the current spreading layer of the first current spreading structure is arranged between the directionally reflective layer and the additional directionally reflective layer. In this embodiment, direct incidence of radiation onto metal elements such as feedthrough elements or bond pads can be prevented, thus reducing absorption. The additional directionally reflective layer can be designed like the aforementioned directionally reflective layer.

[0034] According to at least one embodiment of a method for producing an optoelectronic semiconductor component, a semiconductor layer sequence is provided, comprising a first semiconductor layer having a first surface, a second semiconductor layer having a first surface, a first main surface, and a second main surface opposite the first main surface. Furthermore, a directionally reflective layer is applied to the first main surface. A first contact structure for electrically connecting the first semiconductor layer is produced, which first contact structure has a first current spreading structure arranged on the first surface of the first semiconductor layer and partially adjoins the at least one directionally reflective layer.A second contact structure for electrically connecting the second semiconductor layer is created, which comprises a second current spreading structure arranged on the first surface of the second semiconductor layer and partially adjacent to the at least one directionally reflective layer. In particular, the first current spreading structure and the second current spreading structure are each made of at least one transparent conductive oxide.

[0035] According to an advantageous aspect of the method, a contact layer of the first current spreading structure is first applied to the first main surface. Subsequently, a recess is created that extends through the contact layer and the first semiconductor layer to the second semiconductor layer. The recess is preferably produced by an etching process, for example, by dry chemical etching. Third, a current spreading layer of the second current spreading structure is applied to the second semiconductor layer in the recess. In particular, the contact layer and the current spreading layer are made of at least one transparent conductive oxide.

[0036] In an advantageous variant of the method, a current spreading layer of the first current spreading structure is applied to the contact layer. Preferably, the current spreading layer of the first current spreading structure and the current spreading layer of the second current spreading structure are produced in a single process step. When producing openings for feedthrough elements in the directionally reflective layer, the current spreading layers can serve as etch stop layers for dry chemical etching. This sets a boundary condition for the layer thicknesses. Alternatively, if lift-off structuring of the directionally reflective layer is performed, the etch stop layer and thus the current spreading layers are not limited in their thickness.

[0037] According to at least one embodiment, an oxygen flow is adjusted during the application of the current spreading layer(s) such that an absorption coefficient of the current spreading layer(s) is as low as possible.

[0038] According to a preferred embodiment, a first circumferential edge can be formed in the semiconductor layer sequence such that the second semiconductor layer protrudes laterally beyond the first semiconductor layer. Furthermore, a second circumferential edge can be formed such that the carrier protrudes laterally beyond the second semiconductor layer. The lateral projections serve to electrically insulate the sidewall of the component. In detail, the second / first semiconductor layer is set back from the edge of the carrier to create a safety distance. Without this safety distance, for example, an electrically conductive adhesive could come into contact with the p-bond pad and the second semiconductor layer and thus provoke a short circuit. The edges are preferably produced by an etching process, for example by dry chemical etching.

[0039] The process described above is particularly suitable for the production of the optoelectronic semiconductor components described here. Features described in connection with the component therefore also apply to the process, and vice versa.

[0040] The described optoelectronic semiconductor component can be used as a backlight unit for an LCD (Liquid Crystal Device) panel.

[0041] Further features, embodiments and advantages will become apparent from the following description of the embodiments in conjunction with the figures.

[0042] They show: Fig. 1 a schematic cross-sectional view of a section of an optoelectronic semiconductor component according to a first embodiment, Fig. 2 a schematic cross-sectional view of a section of an optoelectronic semiconductor component according to a second embodiment, Fig. 3 a schematic cross-sectional view of a section of an optoelectronic semiconductor component according to a third embodiment, Fig. 4A to 4E show various steps of a method for producing an optoelectronic semiconductor component according to a first embodiment, Fig. 5A to 5E show various steps of a method for producing an optoelectronic semiconductor component according to a second embodiment, Fig. 6 a diagram in which a surface resistance is plotted against an oxygen flow, Fig. 7 a diagram in which an absorption coefficient is plotted against an oxygen flux, Fig. 8A to 8D each show a distribution of the sheet resistance on the first main surface of a semiconductor layer sequence, Fig. 9 a table showing relative light generation as a function of sheet resistance.

[0043] In the illustrated embodiments and figures, identical, similar, or similarly functioning elements may be provided with the same reference numerals. The illustrated elements and their relative proportions are not necessarily to scale; rather, individual elements may be exaggerated for clarity and / or clarity.

[0044] Fig. 1 shows a cross-sectional view of a section of an optoelectronic semiconductor component 1 along the Fig. Line AA' shown in Figure 4E.

[0045] The optoelectronic semiconductor component 1 comprises a semiconductor layer sequence 2 arranged on a carrier 6. In the context of the present application, "arranged on (...)" means following V in a non-parallel, preferably vertical direction.

[0046] The semiconductor layer sequence 2 comprises a first semiconductor layer 3, a second semiconductor layer 5, and an active zone 4 arranged between the first and second semiconductor layers 3, 5. The first semiconductor layer 3 has a first surface 3A facing away from the second semiconductor layer 5. The second semiconductor layer 5 has a first surface 5A facing away from the carrier 6.

[0047] The semiconductor layer sequence 2 has a first main surface 2A and a second main surface 2B opposite the first main surface 2A. The first surfaces 3A, 5A of the first and second semiconductor layers 3, 5 are at least partially arranged on the first main surface 2A of the semiconductor layer sequence 2. In particular, a portion of the first surface 5A of the second semiconductor layer 5 is covered by the active zone 4 and the first semiconductor layer 3 and is therefore not arranged on the first main surface 2A.

[0048] In addition, the optoelectronic semiconductor component 1 comprises a directionally reflective layer 7 arranged on the first main surface 2A.

[0049] Furthermore, the optoelectronic semiconductor component 1 comprises a first contact structure 8 and a second contact structure 15, wherein the first contact structure 8 has a first current spreading structure 9 and the second contact structure 15 has a second current spreading structure 16. The first current spreading structure 9 is arranged on the first surface 3A of the first semiconductor layer 3 and partially adjoins the directionally reflective layer 7. The second current spreading structure 16 is arranged on the first surface 5A of the second semiconductor layer 5 and partially adjoins the directionally reflective layer 7. In particular, the first current spreading structure 9 comprises a contact layer 10 and a current spreading layer 11, wherein the contact layer 10 is arranged directly on the first surface 3A of the first semiconductor layer 3 and the current spreading layer 11 is arranged directly on the contact layer 10.Furthermore, the second current spreading structure 16 comprises or preferably consists of a current spreading layer 17 which is arranged directly on the first surface 5A of the second semiconductor layer 5.

[0050] Furthermore, the first contact structure 8 comprises a bond pad 14 and a feedthrough element 13, wherein the feedthrough element 13 is arranged between the first current spreading structure 9 and the bond pad 14. And the second contact structure 15 comprises a bond pad 19 and a feedthrough element 18, wherein the feedthrough element 18 is arranged between the second current spreading structure 16 and the bond pad 19. The feedthrough elements 13, 18 are arranged in openings of the directionally reflective layer 7.

[0051] The contact structures 8, 15 are arranged on the same side of the optoelectronic semiconductor component 1. In particular, the optoelectronic semiconductor component 1 is designed as a flip-chip and can be mounted, for example, upside down on a printed circuit board.

[0052] The first current spreading structure 9 and the second current spreading structure 16 each consist of at least one transparent conductive oxide. The current spreading layers 11, 17 can each be a single layer or a multilayer consisting of TCO(s). Sublayers of the multilayer can differ in their material composition and / or thickness. Suitable thicknesses of the current spreading layers 11, 17 are in a range between 5 nm and 500 nm, preferably between 15 nm and 150 nm, particularly preferably between 60 nm and 100 nm, with deviations of 10% being tolerable. For example, one sublayer consists of ZnO and one sublayer of ITO. The sublayer of ZnO can, for example, be 15 nm thick, while the sublayer of ITO can be 70 nm thick. In particular, the current spreading layers 11, 17 of the current spreading structures 9, 16 are identical. Here the thickness is an extension in the vertical direction V.

[0053] The contact layer 10 is preferably a single layer of TCO, preferably ITO. In particular, the contact layer 10 differs from the current spreading layer 11 of the first current spreading structure 9 in terms of its material composition and / or thickness. The contact layer 10 can be thinner than the current spreading layer 11 of the first current spreading structure 9. Suitable thicknesses of the contact layer 10 are in a range between 15 nm and 200 nm, preferably between 20 nm and 90 nm, particularly preferably between 50 nm and 70 nm, with deviations of 10% being tolerable.

[0054] The directionally reflective layer 7 is a multilayer comprising a plurality of sublayers with different refractive indices, wherein a sublayer with a lower refractive index is arranged between two sublayers with a higher refractive index. Preferably, the directionally reflective layer 7 is a DBR (Distributed Bragg Reflector) layer. Suitable materials for the directionally reflective layer 7 or the sublayers are oxides such as SiO2, TiO2, Nb2O5, Al2O3, or nitrides such as Si3N4 or SiNx, where "x" denotes a non-stoichiometric amount of nitride, or fluorides such as MgF2. Suitable layer thicknesses of the directionally reflective layer 7 are in the range between 500 nm and 6000 nm, preferably in the range between 1000 nm and 5000 nm, particularly preferably between 1500 nm and 4500 nm, whereby deviations of 10% are tolerable.

[0055] The semiconductor layer sequence 2 preferably comprises a material based on nitride compound semiconductors, as mentioned above. And the active zone 4 is configured to emit blue or green light.

[0056] The carrier 6, which is preferably the growth substrate, is made in particular of sapphire. The carrier 6 is structured on a first surface 6A, on which the semiconductor layer sequence 2 is arranged. Due to its roughness, the structured first surface 6A contributes to increasing the outcoupling efficiency, since the refractive index difference between the semiconductor layer sequence 2 and the carrier 6 is linearly reduced by a "transition layer" formed on the first surface 6A of the carrier 6.

[0057] The feedthrough elements 13, 18 are metallic elements. Furthermore, the first and second bond pads 14, 19 are each metallic layers with a thickness of preferably 100 nm to 1500 nm. The metallic feedthrough elements 13, 18 and bond pads 14, 19 contribute to broadening the angular distribution of the reflected radiation.

[0058] The first and second bond pads 14, 19 can each have multiple layers. For example, the first and second bond pads 14, 19 can each comprise at least one of the following layers: an adhesion layer with a thickness of preferably approximately 1 to 10 nm, a reflection layer with a thickness of preferably approximately 100 to 600 nm, a barrier layer, and an encapsulation layer. Suitable materials for the adhesion layer are, for example, Ti, Cr, Al, Mo, Ni, or W. Suitable materials for the reflection layer are, for example, Ag, Al, or Rh. Suitable materials for the barrier layer are, for example, Ti, Pt, Ni, Cr, Rh, or Ru. And the encapsulation layer can, for example, contain or consist of Au.

[0059] Advantageously, the optoelectronic semiconductor component 1 is a miniature sapphire flip chip with a size of approximately 200 x 200 µm 2and / or a low operating current of approximately 10 mA, which makes it possible to dispense with a metallic current spreading layer, in particular made of Au. During operation, a major portion of the generated radiation can be emitted laterally, i.e., at side surfaces 1A of the optoelectronic semiconductor component 1. A smaller portion of the radiation can be emitted at a top side 1B of the optoelectronic semiconductor component 1. The directionally reflective layer 7 enables the component 1 to be turned over and achieves significantly high reflection to emit radiation laterally and at the top.

[0060] The first contact structure 8 is provided for electrically connecting the first semiconductor layer 3, while the second contact structure 15 is provided for electrically connecting the second semiconductor layer 5. In particular, the first and second contact structures 8, 15 are electrically insulated by the directionally reflective layer 7. The first and second bond pads 14, 19 are provided for external contacting of the optoelectronic semiconductor component 1.

[0061] An advantage of component 1 is that, due to the TCOs used for the current spreading structures 9, 16, the absorption losses at the contact structures 8, 15 can be reduced and the contact area can be increased with negligible absorption losses. This allows both the current spreading and the coupling efficiency to be improved simultaneously.

[0062] Fig. 2 shows a second embodiment of an optoelectronic semiconductor component 1. The differences from the first embodiment are explained below.

[0063] The optoelectronic semiconductor component 1 comprises an omnidirectionally reflective layer 20, which is arranged on a side of the directionally reflective layer 7 facing away from the semiconductor layer sequence 2. In particular, the omnidirectionally reflective layer 20 is a metallic layer that covers a large portion of the first main surface 2A. The omnidirectionally reflective layer 20 preferably contains Al or Rh. The omnidirectionally reflective layer 20 makes it possible to increase the reflection even in regions that are not covered by metallic elements, for example, the bond pads 14, 19.

[0064] In particular, the omnidirectionally reflective layer 20 is part of the first and second contact structures 8, 15 and is arranged between the respective current spreading structure 9, 16 and the respective feedthrough element 13, 18. To prevent a short circuit between the contact structures 8, 15, the omnidirectionally reflective layer 20 comprises a first part 20A and a second part 20B, which are separated from each other.

[0065] The first contact structure 8 comprises a plurality of via elements 21 that electrically connect the omnidirectionally reflective layer 20 to the first current spreading structure 9, and the second contact structure 15 comprises a second via element 21 that electrically connects the omnidirectionally reflective layer 20 to the second current spreading structure 16. Since the omnidirectionally reflective layer 20 ensures good current spreading, a current spreading layer is not required in the first current spreading structure 9.

[0066] A passivation layer 22 is arranged on a side of the omnidirectionally reflective layer 20 facing away from the directionally reflective layer 7. The passivation layer 22 can be a single or multiple layer of dielectrics such as SiO2, TiO2, Al2O3, SiNx, silicon oxynitride, and Nb2O5. The passivation layer 22 electrically separates the omnidirectionally reflective layer 20 from the bond pads 14, 19, which is necessary to prevent a short circuit, since, for example, the n-type bond pad 19 can lie on the part 20A of the omnidirectionally reflective layer 20 in the vertical direction V.

[0067] Fig. 3 shows a third embodiment of an optoelectronic semiconductor component 1. The differences from the first embodiment are explained below.

[0068] The current spreading layers 11, 17 are stacked locally on the directionally reflective layer 7. This prevents direct metal contact with the second semiconductor layer 5 or the contact layer 10, thus reducing absorption. In other words, the current spreading layers 11, 17 shield the metallic elements 13, 14, 18, 19 from direct radiation incidence, thus reducing absorption.

[0069] The contact layer 10 and the current spreading layer 11 of the first current spreading structure 9 are spaced apart from each other in the vertical direction V, and the directionally reflective layer 7 is arranged between the contact layer 10 and the current spreading layer 11. The first current spreading structure 9 comprises a plurality of via elements 12 that electrically connect the current spreading layer 11 to the contact layer 10.

[0070] The component 1 comprises an additional directionally reflective layer 23, wherein the current spreading layer 11 of the first current spreading structure 9 is arranged between the directionally reflective layer 7 and the additional directionally reflective layer 23. The additional directionally reflective layer 23 can be designed like the above-mentioned directionally reflective layer 7. A multilayer design of the additional directionally reflective layer 23 is advantageous for light reflection at the n-bond pad 19.

[0071] In connection with the Fig. 4A to 4E describe a method according to a first embodiment for producing an optoelectronic semiconductor component 1. The method is particularly suitable for producing an optoelectronic semiconductor component 1 according to the first embodiment.

[0072] A semiconductor layer sequence 2 is provided, and a contact layer 10 of a first current spreading structure 9 is applied to a first main surface of a first semiconductor layer (see Fig. 4A).

[0073] A depression 24 is created which extends through the contact layer 10 and the first semiconductor layer to the second semiconductor layer 5 (see Fig. 4A). The recess 24 is laterally surrounded by the first semiconductor layer. The recess 24 has, for example, an oval or elliptical cross-sectional shape.

[0074] In addition, a first peripheral edge 25 is formed in the semiconductor layer sequence 2 such that the second semiconductor layer 5 projects laterally beyond the first semiconductor layer (see Fig. 4A). In addition, a second peripheral edge 26 can be formed such that the carrier 6 projects laterally beyond the second semiconductor layer 5 (see Fig. 4B). This lateral projection serves to electrically insulate the sidewall of the component. In detail, the second semiconductor layer 5 is set back from the edge of the carrier 6 to create a safety margin. Without this safety margin, an electrically conductive adhesive could come into contact with the p-type bond pad and the second semiconductor layer 2, thus causing a short circuit. Preferably, the recess 24 and the edges 25, 26 are produced by an etching process, for example, by dry chemical etching.

[0075] In the recess 24, a current spreading layer 17 of the second current spreading structure 16 is applied on the second semiconductor layer (see Fig. 4C). The current spreading layer 17 can be strip-shaped and, like the recess 24, have an oval or elliptical shape. A current spreading layer 11 of the first current spreading structure 9 is applied to the contact layer 10. Preferably, the current spreading layers 11, 17 are produced in one process step. In particular, during the application of the current spreading layers 11, 17, an oxygen flow is adjusted such that an absorption coefficient of the current spreading layers 11, 17 is as low as possible. This is described in connection with Fig. 7 described in more detail.

[0076] The current spreading layer 11 partially surrounds the current spreading layer 17 laterally in a plan view of the first main surface. The current spreading layer 11 is formed in an arc shape, in particular U-shaped.

[0077] A directionally reflective layer is applied to the first main surface (not shown). Openings for feedthrough elements 13, 18 are created in the directionally reflective layer. Advantageously, the current spreading layers 11, 17 can serve as etch stop layers for dry chemical etching. Alternatively, the openings can also be created by lift-off structuring. The feedthrough elements 13, 18 are deposited in the openings (see Fig. 4D). In particular, the feedthrough elements 13, 18 are galvanically deposited.

[0078] A first bond pad 14 is arranged on a side of the first feedthrough element 13 facing away from the semiconductor layer sequence 2, and a second bond pad 19 is arranged on a side of the second feedthrough element 18 facing away from the semiconductor layer sequence 2. In particular, the bond pads 14, 19 are deposited by electroplating. The current spreading layer 11 laterally overlaps the bond pads 14, 19 in a plan view of the first main surface. Furthermore, the current spreading layer 17 laterally overlaps the bond pad 19 in a plan view of the first main surface.

[0079] With regard to the structural and material properties of the semiconductor layer sequence 2, the contact layer 10, the current spreading layers 11, 17, the directionally reflective layer, the feedthrough elements 13, 18 and the bond pads 14, 19, reference is made to the information in connection with the above-mentioned optoelectronic semiconductor component 1.

[0080] In connection with the Fig. 5A to 5E describe a second embodiment of a method for producing an optoelectronic semiconductor component 1. The differences from the first embodiment of a method are explained below.

[0081] The current spreading layer 11 comprises a main region 11A, which is arranged in the plan view of the first main surface between the p- and the n-bonding pad 14, 19 (see Fig. 5E). In addition, the current spreading layer 11 includes an extension 11B that laterally overlaps the bond pad 14. Since the stack of the directionally reflective layer and the respective bond pad 14, 19 creates an omnidirectionally reflective layer stack with a certain reflectivity, and the stack of the directionally reflective layer and the main region 11A creates an omnidirectionally reflective layer stack with a different reflectivity, if the main region 11A is optically active, the non-overlapping arrangement contributes to optimizing the reflectivity of the different stacks.

[0082] In the Fig. 6 and Fig. Figure 7 shows the physical properties, namely the sheet resistance R [Ω / □], where □ stands for “square”, and the absorption coefficient α [%] of a 70 nm thick current spreading layer made of ITO with 10% Sn content as a function of the oxygen flow F [sccm], which stands for standard cubic meter, during sputtering. Fig. 6, the current spreading layer is applied to a Si substrate, while in Fig. 7 the current spreading layer is applied to a glass substrate.

[0083] At an oxygen flow F of ~1.5 sccm, the sheet resistance R and the absorption coefficient α are lowest at a wavelength of 450 nm. In particular, the absorption coefficient drops to ~2%. In contrast, the reflection coefficient in air for a conventional Al expansion layer is only ~93%. Furthermore, this value decreases in the LED chip, where Al is deposited on GaN, and the reflectivity drops to ~86%.

[0084] Essentially, the n-type current spreading layer defines the n-type contact region. In conventional flip-chip technology, the n-type contact region and its ~86% reflectivity, which affects the device's brightness, are interconnected. For example, a larger n-type contact area allows for a reduction in the voltage contribution of the n-type contact, but increases the absorption loss at the Al layer.

[0085] In contrast, the transparent n-type current spreading layer made of TCO allows for an increase in the n-type contact area with negligible absorption. The voltage and brightness are no longer coupled, providing an additional degree of freedom.

[0086] The Fig. 8B to 8D show electro-optical simulations of a chip design according to the first embodiments of an optoelectronic semiconductor device and a method. The pixel density represents the current density J [A / cm 2 ] represents. Fig. Figure 8A shows the current density of a device without p- and n-type current spreading layers made of TCO and thus with massive current crowding near the p-type via. Fig. Figure 8B shows the current density J of an optoelectronic semiconductor device with a p- and n-type current spreading layer made of TCO with a sheet resistance of 43 ohms / square. Fig. Figure 8C shows the current density J of an optoelectronic semiconductor device with a p- and n-type current spreading layer made of TCO with a sheet resistance R of 21 ohms / square. Fig. Figure 8D shows the current density J of an optoelectronic semiconductor device with a p- and n-type current spreading layer made of TCO with a sheet resistance R of 8 ohms / square. The lower the sheet resistance R, the less current crowding occurs.

[0087] The table in Fig. 9 shows the voltage Uf(10 mA) [V] and the relative generated light O [%] for the different surface resistances R of the Fig. 8A to 8D. The voltage Uf decreases and the brightness O increases due to the "droop" effect of InGaN-based LEDs, which is related to the current density J. List of reference symbols 1 optoelectronic semiconductor component 1A side surface 1B Top 2 Semiconductor layer sequence 2A first main area 2B second main area 3 first semiconductor layer 3A first surface of the first semiconductor layer 4 active zones 5 second semiconductor layer 5A first surface of the second semiconductor layer 6 carriers 6A first surface 7 directionally reflective layer 8 first contact structure 9 first current widening structure 10 Contact layer of the first current spreading structure 11 Current spreading layer of the first current spreading structure 11A Main area of ​​the current spreading layer 11B Extension of the current spreading layer 12 Via element of the first current spreading structure 13 Implementation element of the first contact structure 14 Bond pad of the first contact structure 15 second contact structure 16 second current spreading structure 17 Current spreading layer of the second current spreading structure 18 Feedthrough element of the second contact structure 19 Bond pad of the second contact structure 20 omnidirectional reflective layer 20A first part of the omnidirectional reflective layer 20B second part of the omnidirectional reflective layer 21 Through-hole plating element 22 Passivation layer 23 directionally reflective layer 24 Deepening 25 first surrounding edge 26 second surrounding edge α absorption coefficient F River J current density O relative generated light R surface resistance Uf voltage V vertical direction

Claims

[1] Optoelectronic semiconductor component (1) comprising - a semiconductor layer sequence (2) comprising - a first semiconductor layer (3) having a first surface (3A), - a second semiconductor layer (5) having a first surface (5A), - a first main surface (2A) and a second main surface (2B) opposite the first main surface (2A), wherein the first surfaces (3A, 5A) of the first and second semiconductor layers (3, 5) are arranged at least partially on the first main surface (2A), - a directionally reflective layer (7) arranged on the first main surface (2A), - a first contact structure (8) for electrically connecting the first semiconductor layer (3), comprising a first current spreading structure (9) arranged on the first surface (3A) of the first semiconductor layer (3) and partially adjacent to the at least one directionally reflective layer (7), - a second contact structure (15) for electrically connecting the second semiconductor layer (5), comprising a second current spreading structure (16) which is arranged on the first surface (5A) of the second semiconductor layer (5) and partially adjoins the at least one directionally reflective layer (7), wherein the first current spreading structure (9) and the second current spreading structure (16) each consist of at least one transparent conductive oxide. [2] Optoelectronic semiconductor component (1) according to the preceding claim, wherein the first current spreading structure (9) has a contact layer (10) which is a single layer and directly adjoins the first semiconductor layer (3). [3] Optoelectronic semiconductor component (1) according to one of the preceding claims, wherein the first current spreading structure (9) has a current spreading layer (11) consisting of at least one transparent conductive oxide. [4] Optoelectronic semiconductor component (1) according to the preceding claim, wherein the current spreading layer (11) is a multilayer comprising at least two sublayers, wherein the two sublayers differ in their material composition and / or thickness. [5] Optoelectronic semiconductor component (1) according to one of claims 3 and 4 in conjunction with claim 2, wherein the contact layer (10) and the current spreading layer (11) are spaced apart from one another and the directionally reflective layer (7) is arranged between the contact layer (10) and the current spreading layer (11). [6] Optoelectronic semiconductor component (1) according to one of the preceding claims, wherein the second current spreading structure (16) has a current spreading layer (17) consisting of at least one transparent conductive oxide. [7] Optoelectronic semiconductor component (1) according to the preceding claim, wherein the current spreading layer (17) is a multilayer comprising at least two sublayers, wherein the two sublayers differ in their material composition and / or thickness. [8] Optoelectronic semiconductor component (1) according to claim 6 or 7 in conjunction with one of claims 3 to 5, wherein the current spreading layer (11) of the first current spreading structure (9) partially laterally surrounds the current spreading layer (17) of the second current spreading structure (16) in a plan view of the first main surface (2A). [9] Optoelectronic semiconductor component (1) according to one of the preceding claims, further comprising an omnidirectionally reflective layer (20) which is arranged on a side of the directionally reflective layer (7) facing away from the semiconductor layer sequence (2). [10] Optoelectronic semiconductor component (1) according to the preceding claim, wherein the omnidirectionally reflecting layer (20) is part of the first and second contact structure (8, 15). [11] Optoelectronic semiconductor component (1) according to one of the preceding claims, wherein the first semiconductor layer (3) has a recess (24) and the second semiconductor layer (5) is arranged at a bottom of the recess (24). [12] Method for producing an optoelectronic semiconductor component (1) comprising the following steps: - Providing a semiconductor layer sequence (2) comprising - a first semiconductor layer (3) having a first surface (3A), - a second semiconductor layer (5) having a first surface (5A), - a first main surface (2A) and a second main surface (2B) opposite the first main surface (2A), - applying a directionally reflective layer (7) to the first main surface (2A), - producing a first contact structure (8) for electrically connecting the first semiconductor layer (3), comprising a first current spreading structure (9) which is arranged on the first surface (3A) of the first semiconductor layer (3) and partially adjoins the at least one directionally reflective layer (7), - producing a second contact structure (15) for electrically connecting the second semiconductor layer (5), comprising a second current spreading structure (16) which is arranged on the first surface (5A) of the second semiconductor layer (5) and partially adjoins the at least one directionally reflective layer (7), wherein the first current spreading structure (9) and the second current spreading structure (16) are each made of at least one transparent conductive oxide. [13] Method according to the preceding claim, comprising the following steps: - applying a contact layer (10) of the first current spreading structure (9) to the first main surface (2A), - creating a recess (24) which extends through the contact layer (10) and the first semiconductor layer (3) to the second semiconductor layer (5), - applying a current spreading layer (17) of the second current spreading structure (16) in the recess (24) onto the second semiconductor layer (5), wherein the contact layer (10) and the current spreading layer (17) are made of at least one transparent conductive oxide. [14] Method according to the preceding claim, wherein a current spreading layer (11) of the first current spreading structure (9) is applied to the contact layer (10). [15] Method according to the preceding claim, wherein the current spreading layer (11) of the first current spreading structure (9) and the current spreading layer (17) of the second current spreading structure (16) are produced in one method step. [16] Method according to one of claims 13 to 15, wherein during the application of the current spreading layer (17) an oxygen flow is adjusted such that an absorption coefficient of the current spreading layer (17) is as low as possible.

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