Optoelectronic semiconductor chip and method for producing an optoelectronic semiconductor chip

Abstract

Optoelectronic semiconductor chip (100), comprising: - a semiconductor layer sequence (1) with an active layer (10), a doped current spreading layer (11) and a coupling-out layer (12), which are arranged one above the other in this order, - a contact element (2) for injecting first charge carriers into the current spreading layer (11), wherein - the active layer (10) generates primary radiation during normal operation, - the current spreading layer (11) has a greater lateral electrical conductivity than the coupling-out layer (12), - the coupling-out layer (12) has coupling-out structures (121) for coupling out radiation on an exit side (120) facing away from the active layer (10), - the coupling-out layer (12) has a lower absorption coefficient for the primary radiation than the current spreading layer (11), - the contact element (2) has a bottom surface (20) which adjoins the semiconductor material of the semiconductor layer sequence (1), - the semiconductor layer sequence (1) has a doped contact layer (13) which is thinner than the current spreading layer (11) and has a higher doping than the current spreading layer (11), and - the contact layer (13) adjoins the bottom surface (20) of the contact element (2).

Description

[0001] An optoelectronic semiconductor chip is specified. Furthermore, a method for producing an optoelectronic semiconductor chip is specified.

[0002] Optoelectronic semiconductor chips and methods for producing an optoelectronic semiconductor chip are already known from the documents DE 10 2008 062 932 A1, DE 10 2016 104 965 A1, DE 10 2016 106 928 A1 and US 2007 / 0 018 184 A1.

[0003] One problem to be solved is to provide an optoelectronic semiconductor chip with high radiation output efficiency. Another problem to be solved is to provide a method for producing such a semiconductor chip.

[0004] These objects are achieved, among other things, by the subject matter of the independent patent claims. Advantageous embodiments and further developments are the subject matter of the dependent patent claims.

[0005] The optoelectronic semiconductor chip comprises a semiconductor layer sequence with an active layer, a doped current spreading layer, and a coupling-out layer, which are arranged one above the other in this order. Preferably, the layers are epitaxially grown one above the other in this order. These layers can be directly adjacent to one another. Alternatively, further semiconductor layers can be arranged between these layers. These layers are part of the semiconductor layer sequence and are thus semiconductor layers.

[0006] The semiconductor layer sequence is based, for example, on a III-V compound semiconductor material. In particular, the layers mentioned are based on or consist of a III-V compound semiconductor material. The semiconductor material is, for example, a nitride compound semiconductor material, such as Al n In 1-n-m Ga mN, or a phosphide compound semiconductor material, such as Al n In 1-n-m Ga m P, or an arsenide compound semiconductor material, such as Al n In 1-n-m Ga m Ace or Al n In 1-n-m Ga m AsP, 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 Al. n In 1-n-m Ga m P.

[0007] During normal operation, the active layer generates primary electromagnetic radiation. This occurs through the recombination of electrons and holes in the region of the active layer. The active layer contains, in particular, at least one pn junction and / or at least one quantum well structure and can, for example, generate primary electromagnetic radiation in the blue, green, or red spectral range, or in the UV or IR range, during normal operation. The semiconductor chip preferably comprises precisely one contiguous, in particular singly contiguous, active layer. Alternatively, the active layer can also be segmented.

[0008] A semiconductor chip is understood here and below to be a separately handleable and electrically contactable element. A semiconductor chip is created in particular by singulation from a wafer composite. In particular, side surfaces of such a semiconductor chip then have, for example, traces from the singulation process of the wafer composite. A semiconductor chip preferably comprises precisely one originally contiguous region of the semiconductor layer sequence grown in the wafer composite. The semiconductor layer sequence of the semiconductor chip is preferably contiguous. The lateral extent of the semiconductor chip is, for example, at most 1%, at most 5%, or at most 10% larger than the lateral extent of the active layer or the semiconductor layer sequence. The semiconductor chip also comprises, for example, the growth substrate on which the entire semiconductor layer sequence has grown.

[0009] Here and in the following, lateral extension is understood to mean, in particular, an extension or expansion in any lateral direction. A lateral direction is a direction parallel to the main plane of extension of the active layer.

[0010] The semiconductor chip can be a so-called volume emitter, in particular a flip chip. In this case, the semiconductor chip preferably also includes the growth substrate. Alternatively, the semiconductor chip can also be a surface emitter, in particular a so-called thin-film chip. In this case, the growth substrate is detached, for example. The growth substrate is based, for example, on GaAs.

[0011] The current spreading layer and / or the coupling-out layer can each comprise a plurality of sublayers. The sublayers then differ, for example, in terms of their stoichiometric composition and / or doping. The lateral dimensions of the current spreading layer and the coupling-out layer are preferably each at least 90% or at least 95% of the lateral dimensions of the semiconductor chip.

[0012] The current spreading layer has a greater lateral electrical conductivity than the coupling-out layer. The current spreading layer can be n- or p-doped. For example, the doping of the current spreading layer is at least 5 10 17 cm -3 or at least 1·10 18 cm -3 or at least 5·10 18 cm -3The current spreading layer, for example, has an electrical conductivity in the lateral direction that is at least ten times greater, or at least 100 times greater, or at least 1000 times greater than the coupling-out layer. Te or Si, for example, is used as a dopant. The lateral conductivity is the conductivity in a lateral direction.

[0013] The doping of a layer is understood here and in the following to mean in particular the doping averaged over the entire volume of the respective layer.

[0014] The current spreading layer has, for example, an average thickness of at least 400 nm or at least 500 nm. Alternatively or additionally, the average thickness of the current spreading layer is at most 4 µm, at most 3 µm, or at most 2 µm. The thickness is measured perpendicular to the main extension plane of the active layer.

[0015] The outcoupling layer has outcoupling structures for radiation extraction on an exit side facing away from the active layer. The outcoupling structures are elevations, for example pyramid-like, conical, truncated pyramid-like, truncated conical, or spherical segment-like elevations, of the outcoupling layer. The outcoupling structures are thus formed from the outcoupling layer or are part of the outcoupling layer.

[0016] The output coupling structures reduce the proportion of primary radiation that would otherwise be prevented from exiting through the exit side due to total internal reflection. The output coupling structures result in a redistribution of the primary radiation.

[0017] Preferably, at least 75%, or at least 80%, or at least 90%, or at least 95% of the surface of the exit side is structured. The remaining area of ​​the exit side can be unstructured, in particular planar, within the manufacturing tolerance. The structured area, i.e., the area with the coupling-out structures, serves to couple out the primary radiation. The unstructured area can serve to contact the semiconductor layer sequence.

[0018] The exit side is, for example, a cover side or a cover surface of the semiconductor layer sequence. The semiconductor layer sequence then terminates at least partially with the exit side. In this case, no semiconductor material is arranged downstream of the exit side, at least in the structured region and in a direction away from the active layer.

[0019] The coupling-out layer has, for example, an average thickness of at least 200 nm or at least 500 nm. Alternatively or additionally, the average thickness of the coupling-out layer can be at most 1.5 µm or at most 1.0 µm. A maximum thickness of the coupling-out layer is, for example, at most 2.5 µm or at most 2 µm.

[0020] The coupling-out layer has a lower absorption coefficient for the primary radiation than the current spreading layer. The absorption coefficient of the coupling-out layer is, for example, at most half, at most one-third, at most one-quarter, at most one-tenth, or at most 1 / 50 of the absorption coefficient of the current spreading layer.

[0021] The absorption coefficient is a measure of the reduction in intensity of electromagnetic radiation when it passes through a given material. Its dimension is 1 / length. A large absorption coefficient means that the material shields the radiation in question relatively effectively, while a small one means that it is more permeable to the radiation. In the term absorption coefficient, the term absorption is not only understood in the narrow sense of the transfer of radiation energy to the medium. Rather, scattering processes that merely deflect the radiation from its intended direction also contribute to the decrease in intensity (extinction).

[0022] The absorption coefficient of a layer is understood here to be the absorption coefficient averaged over the entire volume of the respective layer. Furthermore, the absorption coefficient is preferably given here for the wavelength at which the primary radiation exhibits a global intensity maximum.

[0023] The optoelectronic semiconductor chip comprises a semiconductor layer sequence with an active layer, a doped current spreading layer, and a coupling-out layer, arranged one above the other in this order. During normal operation, the active layer generates primary radiation. The current spreading layer has a greater lateral electrical conductivity than the coupling-out layer. The coupling-out layer has coupling-out structures for coupling out radiation on an exit side facing away from the active layer. The coupling-out layer has a lower absorption coefficient for the primary radiation than the current spreading layer.

[0024] The present invention is based, among other things, on the finding that for good radiation extraction from one side of the semiconductor layer sequence, namely the exit side, this side is often structured or roughened. The thickness of the roughened semiconductor layer is several hundred nm. The structured part of the semiconductor layer sequence is no longer available or is only available to a limited extent, for example, as a contact or for lateral current distribution.

[0025] One idea of ​​the present invention is therefore to design the region with the coupling-out structures to be as little absorbent as possible for the primary radiation, in particular less absorbent than the current spreading layer. To this end, an outcoupling layer different from the current spreading layer is used, which has a low absorption coefficient.

[0026] According to at least one embodiment, the exit side of the coupling-out layer has a roughness of at least 200 nm, or at least 500 nm, or at least 700 nm, or at least 1 µm. Alternatively or additionally, the roughness can be at most 1.7 µm or at most 1.5 µm.

[0027] The roughness of the exit side is determined by the outcoupling structures. Roughness is a measure of the variation in the surface height of the exit side caused by the outcoupling structures. For example, only structures that produce a small variation in surface height are considered roughened. A "small variation" is, for example, a variation that is small compared to the lateral dimension of the semiconductor chip, for example, at most 1 / 10, at most 1 / 20, or at most 1 / 100 of the lateral dimension of the semiconductor chip.

[0028] The roughness can be the mean roughness. This means that the roughness indicates the average distance between a measuring point on the exit surface and a central surface. The central surface intersects the actual surface profile within a measuring range such that the sum of the measured profile deviations relative to the central surface is minimized. Alternatively, the roughness can also be the root mean square roughness, i.e., the mean square profile deviation from the central surface, or the maximum roughness, i.e., the maximum measured profile deviation from the central surface.

[0029] According to at least one embodiment, the coupling-out layer has a lower defect density than the current spreading layer. For example, the defect density in the current spreading layer is at least twice as large, at least three times as large, at least four times as large, or at least ten times as large as in the coupling-out layer. The defect density is the defect density averaged over the entire volume of the respective layer. A low defect density generally results in lower absorption of the primary radiation.

[0030] For example, the defect density can be adjusted during layer growth. For example, the absorption layer can be grown at higher temperatures than the current spreading layer, thereby reducing the defect density. Because the current spreading layer is highly doped, and high doping often results in a lower growth temperature, the current spreading layer can generally only be grown with a relatively high defect density.

[0031] The defect density of a layer is the defect density averaged over the entire volume of the layer.

[0032] According to at least one embodiment, the band gap of the coupling-out layer is greater than the energy of the primary radiation. The energy of the primary radiation is understood to mean, in particular, the energy or wavelength at which the primary radiation has a global intensity maximum. For example, the band gap of the coupling-out layer is at least 0.03 eV, or at least 0.05 eV, or at least 0.07 eV, or at least 0.09 eV, or at least 0.1 eV, or at least 0.2 eV greater than the energy of the primary radiation. A high band gap of the coupling-out layer further reduces the proportion of absorbed primary radiation.

[0033] Here, too, the band gap of a layer is defined as the band gap averaged over the entire volume of the layer. The band gap can be adjusted, for example, by the precise stoichiometric composition within the layers.

[0034] Alternatively or additionally, the band gap of the coupling-out layer may be larger, for example by at least 0.03 eV or at least 0.05 eV or at least 0.07 eV or at least 0.09 eV or at least 0.1 eV or at least 0.2 eV larger than the band gap of the current spreading layer.

[0035] According to at least one embodiment, the semiconductor layer sequence is based on Al n In 1-n-m Ga m P with 0 ≤ n ≤ 1, 0 ≤ m ≤ 1 and m + n ≤ 1. The current spreading layer and / or the coupling-out layer can be based on Al n In 1-n P, i.e. have a negligible Ga content.

[0036] According to at least one embodiment, the current spreading layer has a higher Ga content than the coupling-out layer. For example, the Ga content in the current spreading layer is at least 200%, at least 300%, or at least 500% of the Ga content in the coupling-out layer. A higher Ga content increases the conductivity and reduces the band gap.

[0037] The optoelectronic semiconductor chip further comprises a contact element for injecting first charge carriers into the current spreading layer. The contact element comprises, for example, metal or consists thereof. In particular, the contact element is formed from a material different from the semiconductor material of the semiconductor layer sequence.

[0038] The first charge carriers are electrons or holes. The first charge carriers are injected into the semiconductor layer sequence via the contact element. The first charge carriers can be injected directly into the current spreading layer or indirectly, by first being injected into another semiconductor layer and then into the current spreading layer.

[0039] The contact element can be arranged on the exit side. In this case, the coupling-out layer is between the contact element and the current spreading layer. Alternatively, the contact element can extend from the exit side into the semiconductor layer sequence and open into the semiconductor layer sequence in the region between the active layer and the exit side. Alternatively, the contact element can also extend from the side of the semiconductor layer sequence opposite the exit side through the active layer. In this case, the contact element is a so-called through-hole plating.

[0040] If the contact element is arranged on the exit side, the exit side is preferably not structured in the region of the contact element, but rather flat within the manufacturing tolerance. If the contact element extends from the exit side through the coupling-out layer, the coupling-out layer has a recess or hole in the region of the contact element. Outside of this region, the exit side is structured. The region in which the contact element is arranged is also referred to here and below as the contact section of the semiconductor layer sequence. The region in which the coupling-out layer is structured is also referred to here and below as the coupling-out section of the semiconductor layer sequence.

[0041] At least in the contact section, the coupling-out layer can be at least lightly doped in order to enable current conduction from the contact element through the coupling-out layer to the current spreading layer.

[0042] The contact element has a bottom surface that borders the semiconductor material of the semiconductor layer sequence. The bottom surface preferably runs essentially parallel to the active layer. "Essentially" here means within the manufacturing tolerance.

[0043] The semiconductor layer sequence comprises a doped contact layer that is thinner than the current spreading layer and has a higher doping than the current spreading layer.

[0044] For example, the doping of the contact layer is at least twice as large, or at least five times as large, or at least ten times as large as the doping of the current spreading layer. For example, the doping of the contact layer is at least 5 1018 cm -3 or at least 1·10 19 cm -3 In particular, the contact layer has the same doping type as the current spreading layer. Thus, if the current spreading layer is n-doped, the contact layer is also n-doped.

[0045] The average thickness of the contact layer is, for example, at most half, at most one-third, at most one-quarter, or at most one-tenth of the average thickness of the current spreading layer. For example, the contact layer has an average thickness of at most 150 nm or at most 100 nm. Alternatively or additionally, the average thickness of the contact layer can be at least 50 nm. The contact layer is based, for example, on AlInGaP.

[0046] The contact layer can have a different stoichiometric composition than the adjacent layers. Alternatively, the contact layer can simply be a highly doped region within a layer and thus have the same stoichiometric composition as this layer.

[0047] The contact layer borders the bottom surface of the contact element. The contact layer reduces the contact resistance between the contact element and the semiconductor material of the semiconductor layer sequence.

[0048] According to at least one embodiment, the contact layer is arranged on the exit side of the coupling-out layer and borders the exit side. This means that the contact layer is arranged downstream of the exit side in the direction away from the active layer.

[0049] According to at least one embodiment, a lateral extent of the contact layer or an area of ​​the contact layer substantially corresponds to the lateral extent or the area of ​​the bottom surface of the contact element. For example, the lateral extent of the contact layer deviates by at most 30%, or at most 20%, or at most 10%, or at most 5% from the lateral extent of the bottom surface of the contact element. Viewed in plan view of the exit side, the area occupied by the contact element lies, for example, entirely within the area occupied by the contact layer. The contact layer is preferably limited to the contact section. In the region of the coupling-out section, the semiconductor layer sequence is preferably free of the contact layer.

[0050] Alternatively, it is also possible that the lateral extent of the contact layer essentially corresponds to the lateral extent of the active layer, i.e. with a deviation of at most 20%.

[0051] According to at least one embodiment, the lateral extent or the area of ​​the bottom surface is at most 25% or at most 20% or at most 10% or at most 5% of the lateral extent or the area of ​​the active layer.

[0052] Here, the lateral extension is again defined as the extension along any direction parallel to the main plane of the active layer. The area of ​​the active layer is the area of ​​the active layer viewed from the exit side.

[0053] According to at least one embodiment, the contact layer is arranged between the current spreading layer and the exit side and borders the current spreading layer. In this case, the contact element extends through the coupling-out layer.

[0054] According to at least one embodiment, the bottom surface of the contact element directly adjoins the current spreading layer. In this case, a separate contact layer is dispensed with.

[0055] According to at least one embodiment, the coupling-out layer has a lower doping than the current spreading layer. For example, the doping in the current spreading layer is at least ten times as large, at least 100 times as large, or at least 1000 times as large as in the coupling-out layer.

[0056] The coupling-out layer, for example, has a doping of at most 5·10 17 cm -3 or at most 1·10 17 cm-3 or at most 5·10 16 cm -3 Alternatively or additionally, the doping of the coupling-out layer can be at least 1 10 16 cm -3 Preferably, the coupling-out layer then has the same doping type as the current spreading layer.

[0057] According to at least one embodiment, the coupling-out layer is nominally undoped. For example, a doping concentration in the coupling-out layer is then at most 1 10 15 cm -3 or at most 1·10 14 cm -3 .

[0058] Furthermore, a method for producing an optoelectronic semiconductor chip is specified. The method is particularly suitable for producing an optoelectronic semiconductor chip described here. All features disclosed in connection with the optoelectronic semiconductor chip are therefore also disclosed for the method, and vice versa.

[0059] According to at least one embodiment, the method for producing an optoelectronic semiconductor chip comprises a step A) in which a semiconductor layer sequence is provided with a doped contact layer, a less heavily doped coupling-out layer, and an active layer, which are arranged one above the other in this order. The active layer generates primary radiation during normal operation.

[0060] The information previously provided for the semiconductor chip regarding the active layer, the contact layer, and the coupling-out layer, particularly with regard to their doping concentrations and / or thicknesses, can also apply here. The contact layer, for example, is based on AlInGaP. The less heavily doped coupling-out layer means, in this case, that it is less heavily doped than the contact layer.

[0061] The contact layer is preferably a cover layer of the semiconductor layer sequence. Thus, no further semiconductor layer is arranged downstream of the contact layer in the direction away from the active layer.

[0062] According to at least one embodiment, the method comprises a step B) in which a photoresist layer is applied to the side of the contact layer facing away from the active layer, wherein the photoresist layer completely covers the contact layer both in a coupling-out section and in a contact section of the semiconductor layer sequence.

[0063] The coupling-out section and the contact section are laterally adjacent regions or sections of the semiconductor layer sequence. For example, when viewed from above, the contact layer's area is at most 25%, at most 20%, at most 10%, or at most 5% of the area of ​​the coupling-out section.

[0064] The photoresist layer completely covers both the surface of the coupling-out section and the surface of the contact section. In particular, the photoresist layer is initially formed as a single, continuous layer. The thickness of the photoresist layer is, for example, between 1 µm and 5 µm. The photoresist layer is applied directly onto the contact layer, for example.

[0065] According to at least one embodiment, the method comprises a step C) in which the photoresist layer is structured and partially removed in the region of the coupling-out section. Preferably, islands of the photoresist layer remain. The islands are, for example, simply connected and spaced apart from one another. The contact layer can be exposed between the islands. The photoresist layer is structured, for example, by lithography, for example, using a mask.

[0066] For example, the islands each have a diameter, measured in the lateral direction, between 0.1 µm and 2.5 µm. The distance between any two adjacent islands is, for example, between 0.1 µm and 10 µm. For example, at least 100 islands are created from the photoresist layer in the area of ​​the coupling-out section.

[0067] According to at least one embodiment, the method comprises a step D) in which an etching process is performed. In the regions of the coupling-out section in which the photoresist layer was removed, etching is carried out completely through the contact layer and into the coupling-out layer, thereby creating coupling-out structures in the coupling-out layer. The contact layer is removed in the region of the coupling-out section. However, the photoresist layer is not penetrated in the region of the contact section.

[0068] Preferably, in step D) at least 90% or at least 95% or at least 99% or 100% of the contact layer in the coupling-out section is removed.

[0069] In areas of the coupling-out section where the photoresist layer has been removed, the etching agents used attack the semiconductor layer sequence, penetrating the first contact layer and penetrating into the coupling-out layer. The coupling-out layer is preferably not completely etched through. Etching away the semiconductor layer sequence in the area around the islands creates coupling-out structures in the coupling-out layer. The size of the coupling-out structures is determined by the size of the islands and the type of etching process.

[0070] The etching agents used in the etching process are preferably applied equally to the coupling-out section and the contact section. The photoresist layer and the etching agents are selected in particular so that the photoresist layer in the contact section is not completely penetrated. For example, the etching rate for the photoresist layer is lower than for the semiconductor layer sequence.

[0071] After the etching process, the photoresist layer still completely covers the contact section. The fact that the photoresist layer is not penetrated in the area of ​​the contact section means, in particular, that the etching process in step D) does not create holes in the photoresist layer, exposing the material beneath the photoresist layer and attacking it with the etching agents.

[0072] According to at least one embodiment, the method comprises a step E) in which the photoresist layer in the region of the contact section is removed. After removing the photoresist layer, for example, the contact layer in the region of the contact section is exposed.

[0073] According to at least one embodiment, the method comprises a step F) in which a contact element is applied to the contact layer in the region of the contact section. In particular, the contact element is brought into direct contact with the exposed contact layer. The contact element is deposited, for example, by vapor deposition.

[0074] According to at least one embodiment, steps A) to F) are carried out in the specified order and consecutively.

[0075] According to at least one embodiment, in step D), a first etchant is first used, which attacks the material of the photoresist layer and partially or completely removes the photoresist layer in the region of the coupling-out section.

[0076] For example, at least 90%, or at least 95%, or 100% of the photoresist layer in the coupling-out section is removed with the first etchant. If the photoresist layer in the coupling-out section is not completely removed, a stripping process, such as ashing, for example, using an oxygen plasma, can be used after the application of the first etchant to remove the remnants of the photoresist layer in the coupling-out section.

[0077] Complete or almost complete etching away of the photoresist layer in the coupling-out section generally does not result in the photoresist layer in the contact section also being completely etched away. Due to the structuring of the photoresist layer and the resulting larger attack surface, the photoresist layer in the coupling-out section is etched away more quickly than in the contact section.

[0078] For example, a dry chemical etchant is used as the first etchant. For example, the first etchant is chlorine-based. The first etchant can etch in a directional or non-directional manner.

[0079] However, the first etchant does not only attack the photoresist layer, but also etches through the contact layer, penetrates the decoupling layer and produces the decoupling structures.

[0080] According to at least one embodiment, the first etchant attacks the contact layer.

[0081] According to at least one embodiment, the first etchant is used until the contact layer in the coupling-out section is removed.

[0082] According to at least one embodiment, a second etchant is used in step D) after the first etchant has partially or completely removed the photoresist layer in the region of the coupling-out section. The second etchant attacks the contact layer. The second etchant is used until the contact layer in the coupling-out section is removed.

[0083] Even with the second etchant, the photoresist layer in the area of ​​the contact section is preferably not yet penetrated.

[0084] The second etchant, for example, is used to further develop or define the coupling-out structures. The second etchant is, in particular, a different etchant than the first etchant. For example, the second etchant is an isotropic etchant. The second etchant can, for example, etch away the contact layer more quickly than the first etchant.

[0085] According to at least one embodiment, step F) is performed before step B). In step B), the photoresist layer is then applied to the contact element in the region of the contact section. The contact element is thus covered by the photoresist layer.

[0086] An optoelectronic semiconductor chip described herein and a method for producing an optoelectronic semiconductor chip 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.

[0087] They show: Fig. 1 a modification of an optoelectronic semiconductor chip, Fig. 2 to 5 different embodiments of the optoelectronic semiconductor chip in cross-sectional view, Fig. 6A to 8D show various positions in various embodiments of the method for producing an optoelectronic semiconductor chip, Fig. 9A a photograph of an output layer as produced by the method, Fig. 9B shows an embodiment of the optoelectronic semiconductor chip in plan view.

[0088] Fig. 1 shows a modification of the optoelectronic semiconductor chip 100. The optoelectronic semiconductor chip 100 comprises a semiconductor layer sequence 1 with an active layer 10 for generating electromagnetic primary radiation, a current spreading layer 11, which in the present case is n-doped, for example, and a p-doped semiconductor layer 14. The current spreading layer 11 simultaneously serves as an output layer and is provided with output structures 121 on an exit side 120 facing away from the active layer 10. The semiconductor layer sequence 1 is based, for example, on AlInGaP. The current spreading layer 11 has, in the present case, for example, a doping concentration of at least 5 10 18 cm -3The dopant in the current spreading layer 11 is, for example, Si or Te.

[0089] The semiconductor layer sequence 1 is divided laterally into a contact section 123 and one or more coupling-out sections 122. In the contact section 123, the exit side 120 is planar within the manufacturing tolerance. The coupling-out structures 121 are provided only in the coupling-out section 122.

[0090] A contact element 2 is arranged in the contact section 123 on the exit side 120. The contact element 2 comprises a bottom surface 20, which runs essentially parallel to the active layer 10 and is in direct contact with the semiconductor material of the semiconductor layer sequence 1. For example, electrons are injected into the current spreading layer 11 via the contact element 2. The contact element 2 is formed, for example, from a metallic material.

[0091] To reduce the contact resistance between the contact element 2 and the current spreading layer 11, a contact layer 13 is provided between the contact element 2 and the current spreading layer 11. The contact layer 13 has, for example, a doping concentration at least twice as high as that of the current spreading layer 11, but is significantly thinner. The area of ​​the contact layer 13 essentially corresponds to the area of ​​the bottom surface 20 of the contact element 2.

[0092] During normal operation of the semiconductor chip 100 of the Fig. 1, primary radiation is generated in the active layer 10. The primary radiation is coupled out via the exit side 120 using the coupling-out structures 121.

[0093] In particular, due to the high doping of the current spreading layer 11 and the associated high doping in the coupling-out structures 121, the primary radiation is increasingly absorbed within the coupling-out structures 121, which reduces the efficiency of the semiconductor chip 100.

[0094] In the Fig. 2 shows a first embodiment of the optoelectronic semiconductor chip 100. The structure of the semiconductor chip 100 essentially corresponds to the structure of the semiconductor chip 100 of Fig. 1. Unlike in the Fig. 1, however, the current spreading layer 11 is not structured. Rather, an outcoupling layer 12 is provided on the side facing away from the active layer 10. The outcoupling layer 12 now comprises the exit side 120 with the outcoupling structures 121. The outcoupling layer 12 is a semiconductor layer of the semiconductor layer sequence 1. However, the outcoupling layer 12 is selected such that it has a lower absorption coefficient for the primary radiation of the active layer 10 than the current spreading layer 11. This results in fewer absorption losses in the outcoupling structures 121.

[0095] In order to ensure a lower absorption coefficient in the coupling-out layer 12, the coupling-out layer 12 can, for example, be less heavily doped than the current spreading layer 11. In the present case, a light doping, for example of at least 1 10 17 cm -3but advantageous in order to enable transport of the electrons from the contact element 2 to the current spreading layer 11 through the coupling-out layer 12.

[0096] To achieve a low absorption coefficient in the coupling-out layer 12, the coupling-out layer 12 can also be grown with a lower defect density than the current spreading layer 11. It is also possible to select a composition for the coupling-out layer 12 whose band gap is larger than the energy of the primary radiation.

[0097] In the Fig. 3 shows a second embodiment of the optoelectronic semiconductor chip 100. Unlike in the Fig. 2, the contact element 2 is now not mounted on the exit side 120, but penetrates the coupling-out layer 12 starting from the exit side 120. The contact element 2 borders with its bottom surface 20 on the contact layer 13. The contact layer 13, in turn, borders on the current spreading layer 11.

[0098] In the Fig. The third embodiment of the optoelectronic semiconductor chip 100 shown in Figure 4 is different from that in Fig. 3, the contact layer 13 is not limited to the lateral extent of the contact element 2. Rather, the contact layer 13 extends over the entire lateral extent of the semiconductor chip.

[0099] In the fourth embodiment of the Fig. 5, a contact layer 13 is omitted. The contact element 2 directly borders the current spreading layer 11.

[0100] In the Fig. 6A shows a first position in a first exemplary embodiment of the method for producing an optoelectronic semiconductor chip. A semiconductor layer sequence 1 with an active layer 10, a coupling-out layer 12, and a contact layer 13 is provided. The contact layer 13 is highly doped. The coupling-out layer 12 is less heavily doped. Contrary to what is shown, a current spreading layer can be arranged between the coupling-out layer 12 and the active layer 10. The semiconductor layer sequence 1 is based, for example, on AlInGaP.

[0101] A photoresist layer 3 is applied to the contact layer 13. The photoresist layer 3 is patterned and partially removed in an outcoupling section 122. This leaves islands 30 of photoresist. The contact layer 13 is exposed between the islands 30.

[0102] In a contact section 123 arranged laterally next to the coupling-out section 122, the photoresist layer 3 extends without interruption.

[0103] In the Fig. 6B shows a second position of the process, in which the contact layer 13 has been etched through by means of a first etchant in areas where the photoresist layer 2 was removed. The first etchant has also penetrated into the coupling-out layer 12 and etched into it. As a result, coupling-out structures 121 have been created in the coupling-out layer 12. In the present case, these coupling-out structures 121 are truncated pyramid-shaped.

[0104] For example, the first etchant is a chlorine-based dry chemical etchant. The first etchant etches anisotropically.

[0105] Contrary to what is shown in the figures, the coupling-out layer 12 is preferably not completely etched through. This means that even after the etching process, the coupling-out layer 12 is preferably simply connected.

[0106] In the Fig. Figure 6C shows a third stage of the process. The first etchant was applied until the contact layer 13 and the photoresist layer 3 in the coupling-out section 122 were completely removed. The remaining coupling-out structures 121 consist exclusively of the coupling-out layer 12.

[0107] In the contact section 123, however, the semiconductor layer sequence 1 is still completely covered by the photoresist layer 3. Accordingly, the contact layer 13 is also still present.

[0108] By removing the photoresist layer 3 in the contact section 123 and applying a contact element to the exposed contact layer 13, the semiconductor layer sequence 1 can be electrically contacted.

[0109] In the Fig. 7A shows a first position in a second embodiment of the method. The position of the Fig. 7A corresponds to the position of the Fig. 6A.

[0110] In the Fig. 7B shows a second position in which etching was carried out with a first etchant until the photoresist layer 3 in the coupling-out section 122 was removed.

[0111] Again, decoupling structures 121 have been created due to the islands in the photoresist layer 3. However, the photoresist layer 3 in the contact section 123 is not completely penetrated, which is due, among other things, to the fact that the photoresist layer 3 in the contact section 123 was not structured.

[0112] In the Fig. Figure 7C shows a third stage of the process. Using a second etchant, which differs from the first etchant, the semiconductor layer sequence 1 was further etched. In the process, the contact layer 13 in the coupling-out section 122 was removed. What remains are coupling-out structures 121, which consist exclusively of the coupling-out layer 12.

[0113] The second etchant may, for example, be an isotropic etchant.

[0114] In the Fig. A third embodiment of the method is shown in Figures 8A to 8D. The Fig. 8A and Fig. The positions shown in Figure 8B correspond to the positions of the Fig. 6A and Fig. 6B. Again, coupling-out structures 121 were created in the coupling-out section 122 by means of a first etchant. The photoresist layer 3 and the contact layer 13 in the coupling-out section 122 were not completely removed by the first etchant.

[0115] In the Fig. 8C shows a position in which the photoresist layer 3 in the coupling-out section 122 is completely removed using, for example, an oxygen plasma. In the contact section 123, however, the photoresist layer 3 is not completely removed, which is again due to the smaller contact surface in the contact section 123.

[0116] In the Fig. 8D shows a position in which the contact layer 13 in the coupling-out section 122 is then also removed, for example by means of a second etchant different from the first etchant.

[0117] In the Fig. Figure 9A shows a photograph of an outcoupling layer 12 after it has been patterned using the method described here. The resulting outcoupling structures 121 are conical. Photoresist layer 3 is still present around the patterned area. In particular, a photograph of the process between steps D) and E) is shown here.

[0118] In the Fig. Figure 9B shows the finished semiconductor chip 100 in a top view of the exit side 120. The structured coupling-out section 122 and the smaller contact section 123 with the contact element 2 can be seen. List of reference symbols 1 Semiconductor layer sequence 2 contact element 3 photoresist layer 10 active layer 11 Current spreading layer 12 Decoupling layer 13 Contact layer 14 Semiconductor layer 20 Bottom surface of contact element 2 30 island from the photoresist layer 3 100 optoelectronic semiconductor chips 120 Exit side 121 decoupling structures 122 decoupling section 123 Contact section

Claims

[1] Optoelectronic semiconductor chip (100), comprising: - a semiconductor layer sequence (1) with an active layer (10), a doped current spreading layer (11) and a coupling-out layer (12), which are arranged one above the other in this order, - a contact element (2) for injecting first charge carriers into the current spreading layer (11), wherein - the active layer (10) generates primary radiation during normal operation, - the current spreading layer (11) has a greater lateral electrical conductivity than the coupling-out layer (12), - the coupling-out layer (12) has coupling-out structures (121) for coupling out radiation on an exit side (120) facing away from the active layer (10), - the coupling-out layer (12) has a lower absorption coefficient for the primary radiation than the current spreading layer (11), - the contact element (2) has a bottom surface (20) which adjoins the semiconductor material of the semiconductor layer sequence (1), - the semiconductor layer sequence (1) has a doped contact layer (13) which is thinner than the current spreading layer (11) and has a higher doping than the current spreading layer (11), and - the contact layer (13) adjoins the bottom surface (20) of the contact element (2). [2] Optoelectronic semiconductor chip (100) according to claim 1, wherein the exit side (120) of the coupling-out layer (12) has a roughness of at least 200 nm. [3] Optoelectronic semiconductor chip (100) according to one of the preceding claims, wherein - the coupling-out layer (12) has a lower defect density than the current spreading layer (11) and / or - the band gap of the coupling-out layer (12) is larger than the energy of the primary radiation. [4] Optoelectronic semiconductor chip (100) according to one of the preceding claims, wherein - the semiconductor layer sequence (1) on Al n In 1-n-m Ga m P with 0 ≤ n ≤ 1, 0 ≤ m ≤ 1 and m + n ≤ 1, - the current spreading layer (11) has a greater Ga content than the coupling-out layer (12). [5] Optoelectronic semiconductor chip (100) according to one of the preceding claims, wherein the contact layer (13) is arranged on the exit side (120) of the coupling-out layer (12) and adjoins the exit side (120). [6] Optoelectronic semiconductor chip (100) according to one of the preceding claims, wherein - a lateral extension of the contact layer (13) essentially corresponds to the lateral extension of the bottom surface (20) of the contact element (2), - the lateral extent of the base area (20) is at most 25% of the lateral extent of the active layer (10). [7] Optoelectronic semiconductor chip (100) according to one of claims 1 to 4, wherein the contact layer (13) is arranged between the current spreading layer (11) and the exit side (120) and adjoins the current spreading layer (11). [8] Optoelectronic semiconductor chip (100) according to one of the preceding claims, wherein the bottom surface (20) of the contact element (2) directly adjoins the current spreading layer (11). [9] Optoelectronic semiconductor chip (100) according to one of the preceding claims, wherein the coupling-out layer (12) has a lower doping than the current spreading layer (11). [10] Optoelectronic semiconductor chip (100) according to one of the preceding claims, wherein the coupling-out layer (12) is nominally undoped. [11] A method for producing an optoelectronic semiconductor chip (100), comprising the steps of: A) providing a semiconductor layer sequence comprising a doped contact layer (13), a less heavily doped coupling-out layer (12) and an active layer (10) arranged one above the other in this order, the active layer (10) generating primary radiation during normal operation; B) applying a photoresist layer (3) to the side of the contact layer (13) facing away from the active layer (10), wherein the photoresist layer (3) completely covers the contact layer (13) both in a coupling-out section (122) and in a contact section (123) of the semiconductor layer sequence (1); C) Structuring and partially removing the photoresist layer (3) in the region of the coupling-out section (122); D) Carrying out an etching process with which - in the areas of the coupling-out section (122) in which the photoresist layer (3) has been removed, etching is carried out completely through the contact layer (13) and into the coupling-out layer (12), whereby coupling-out structures (121) are formed in the coupling-out layer (12), - the contact layer (13) in the coupling-out section (122) is removed, - the photoresist layer (3) is not penetrated in the region of the contact section (123); E) removing the photoresist layer (3) in the region of the contact section (123); F) Applying a contact element (2) to the contact layer (13) in the region of the contact section (123). [12] Method according to claim 11, wherein in step D) a first etchant is first used which attacks the material of the photoresist layer (3) and partially or completely removes the photoresist layer (3) in the coupling-out section (122). [13] The method of claim 12, wherein - the first etchant attacks the contact layer (13), - the first etchant is used until the contact layer (13) in the region of the coupling-out section (122) is completely removed. [14] The method of claim 12, wherein - in step D), a second etchant is used after the first etchant has partially or completely removed the photoresist layer (3) in the region of the coupling-out section (122), wherein - the second etchant attacks the contact layer (13), - the second etchant is used until the contact layer (13) in the coupling-out section (122) is removed. [15] Method according to one of the preceding claims, wherein - step F) is carried out before step B) and - in step B) the photoresist layer (3) is applied to the contact element (2) in the region of the contact section (123).

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