Optoelectronic semiconductor chips

Abstract

In one embodiment, an optoelectronic semiconductor chip (1) comprises a semiconductor layer sequence (2) having an active region (23) for generating radiation of a wavelength L having a maximum intensity. A mirror (3) comprises a cover layer (31). The cover layer (31) is made of a material transmissive to radiation and has an optical thickness between 0.5L and 3L, inclusive. Following the cover layer (31) in a direction facing away from the semiconductor layer sequence (2) are between two and ten intermediate layers (32, 33, 34, 35) of the mirror (3), inclusive. The intermediate layers (32, 33, 34, 35) alternately have a high refractive index and a low refractive index. The optical thickness of at least one intermediate layer (32, 33, 34, 35) is not equal to L / 4. Following the intermediate layers (32, 33, 34, 35) in a direction facing away from the semiconductor layer sequence (2) is at least one metal layer (39) of the mirror (3) as a reflective layer.

Description

Technical Field

[0001] An optoelectronic semiconductor chip is provided. Summary of the Invention

[0002] The object to be achieved is to specify an optoelectronic semiconductor chip having a mirror with high reflectivity.

[0003] The object is also achieved by an optoelectronic semiconductor chip having the features of the invention. Preferred developments are the subject matter of the following description.

[0004] According to at least one embodiment, the optoelectronic semiconductor chip is configured to generate radiation, in particular to generate near-ultraviolet radiation, visible light, and / or near-infrared radiation. The semiconductor chip is, for example, a light-emitting diode chip or a laser diode chip. Preferably, the semiconductor chip is an LED chip for generating yellow, orange, or red light.

[0005] According to at least one embodiment, a semiconductor chip includes a semiconductor layer sequence. The semiconductor layer sequence contains at least one active region for generating radiation. The radiation has a wavelength L of maximum intensity. The active region is preferably located between the p-doped side and the n-doped side of the semiconductor layer sequence. In particular, a single quantum well structure, a multiple quantum well structure, and / or a pn junction is present in the active region. The active region extends, in particular, perpendicular to the growth direction of the semiconductor layer sequence.

[0006] The semiconductor layer sequence is preferably based on 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 m N, or phosphide compound semiconductor materials, such as Al n In 1-n-m Ga m P, or arsenide compound semiconductor materials such as Al n In 1-n-m Ga m As or Al n Ga m In 1-n-m As k P 1-k, where 0≤n≤1, 0≤m≤1 and n+m≤1, and 0≤k<1, respectively. Preferably, for at least one layer or for all layers of the semiconductor layer sequence, 0<n≤0.8, 0.4≤m<1 and n+m≤0.95, and 0<k≤0.5 apply. The semiconductor layer sequence may contain dopants and additional components. For simplicity, however, only the essential components of the crystal lattice of the semiconductor layer sequence, namely Al, As, Ga, In, N, or P, are described, even though these components may be partially replaced and / or supplemented by small amounts of other substances.

[0007] According to at least one embodiment, the semiconductor chip comprises one or more mirrors. Preferably, exactly one mirror is used for reflecting radiation. The mirror is arranged on the back side of the semiconductor layer sequence, which is opposite the light coupling-out side of the semiconductor layer sequence.

[0008] According to at least one embodiment, the mirror includes at least one, preferably exactly one, covering layer. The covering layer can be the thickest layer of the mirror, in particular the thickest layer of the mirror composed of a material that is translucent to radiation generated during operation. The covering layer is the layer of the mirror that is closest to the semiconductor layer sequence. The covering layer can contact the semiconductor layer sequence in a planar manner.

[0009] According to at least one embodiment, the cover layer consists of a material that is translucent to the radiation generated during operation, in particular a material with a low refractive index. A low refractive index can mean that the refractive index of the cover layer is at least 0.5, 1, or 1.5 less than the average refractive index of the semiconductor layer sequence. The cover layer is preferably composed of a dielectric material, but alternatively it can also be composed of a conductive material. The material of the cover layer is, for example, an oxide, a nitride, or an oxynitride.

[0010] According to at least one embodiment, the cover layer has a relatively large optical thickness. The term optical thickness refers to the product of the geometric thickness of the respective layer and its refractive index relative to the wavelength of maximum intensity. Preferably, the cover layer has an optical thickness of at least 0.5 L or 1.0 L. Alternatively or additionally, the optical thickness is at most 5 L, 3 L, 2 L, or 1.5 L.

[0011] The wavelength of maximum intensity, L, here and below, refers to the vacuum wavelength. If the vacuum wavelength is, for example, 600 nm, then a value of 0.5 L corresponds to a thickness of 300 nm. If, for example, 300 nm is used to represent the optical thickness, and the refractive index at wavelength L is, for example, 1.5, then the geometric thickness associated with the corresponding optical thickness is the value at 300 nm divided by the refractive index, or 200 nm. In other words, the so-called optical thickness refers to the wavelength of maximum intensity, L, with the refractive index of the relevant layer used as a divisor for the conversion to the geometric thickness. The refractive index refers to a temperature of 300 Kelvin, or to the appropriate operating temperature of the semiconductor chip.

[0012] According to at least one embodiment, the mirror comprises a plurality of intermediate layers. The number of intermediate layers is preferably at most fifteen, ten, or seven. In a direction facing away from the semiconductor layer sequence, the intermediate layers follow the cover layer, in particular directly following the cover layer. In particular, there are two, three, four, or five intermediate layers, particularly preferably three or four intermediate layers.

[0013] According to at least one embodiment, the intermediate layers are each composed of a material that is transparent to the radiation generated during operation, such as an oxide, nitride or oxynitride. The intermediate layers can be dielectric or, alternatively, conductive. The intermediate layers are composed of at least two different materials, wherein each intermediate layer itself is preferably composed of a single material. In a direction facing away from the cover layer, the intermediate layers alternately have a high refractive index and a low refractive index for the radiation generated during operation. The refractive index difference between adjacent intermediate layers and / or with the cover layer is preferably at least 0.5 or 1. It is possible that one intermediate layer, in particular the intermediate layer with the low refractive index, is composed of the same material as the cover layer.

[0014] According to at least one embodiment, the thickness of at least one intermediate layer is not equal to L / 4. In other words, at least one intermediate layer is not a layer as used in conventional Bragg mirrors. It is possible that no intermediate layer has a thickness of L / 4. This applies in particular with a tolerance of 0.03L, 0.02L, or 0.01L.

[0015] According to at least one embodiment, the mirror includes a metal layer. The metal layer follows the intermediate layer in a direction facing away from the semiconductor layer sequence, in particular directly following the intermediate layer. The metal layer is designed as a reflective layer and serves to reflect radiation generated during operation. Radiation that passes from the semiconductor layer sequence through the cover layer and the intermediate layer to the metal layer is reflected at the metal layer.

[0016] In at least one embodiment, the optoelectronic semiconductor chip includes a semiconductor layer sequence having an active region for generating radiation of a wavelength L with maximum intensity. A mirror for radiation is located on the back side, which is opposite to the light coupling output side. The mirror includes a cover layer, which is closest to the semiconductor layer sequence. The cover layer is composed of a material that is transparent to radiation and has an optical thickness between 0.5L and 3L (including boundary values). Following the cover layer in the direction away from the semiconductor layer sequence are two and ten intermediate layers (including boundary values) of the mirror. The intermediate layers alternately have a high refractive index and a low refractive index for radiation and are each composed of a material that is transparent to radiation. The optical thickness of at least one intermediate layer is not equal to L / 4. Following the intermediate layer in the direction away from the semiconductor layer sequence are at least one metal layer of the mirror as a reflective layer.

[0017] The mirror is thus a dielectric Bragg mirror, in particular for a broad wavelength range, for example the spectral range from yellow to infrared. The mirror is preferably used for light-emitting diode chips based on InGaAlP and / or on AlGaAs.

[0018] The mirrors described here can achieve increased reflectivity, particularly with dielectric mirrors, particularly for thin-film LEDs, where the growth substrate is remote from the semiconductor layer sequence. This applies, for example, to InGaAlP-based LED chips produced using thin-film technology, or TF technology for short.

[0019] A key element in thin-layer technology, such as InGaAlP / AlGaAs diodes, is the dielectric-metal mirror. The first part of such a mirror consists of a thick dielectric layer. The dielectric material of the first layer should have a low refractive index to maximize the refractive index difference between the adjacent semiconductor material and the first mirror layer and, in this way, the critical angle for total internal reflection. The metal behind the dielectric layer, typically Au or Ag, reflects light that is not reflected at the first boundary surface.

[0020] InGaAs / AlGaAs chips manufactured using OSRAM TF technology, such as the TF5 and TF6 configurations, use mirrors consisting of a thick SiO2 layer, for example with a thickness of 530 nm, and an Au layer behind it. Other variations of dielectric mirrors exist in InGaAlP / AlGaAs diodes from other manufacturers, but these always have only a single dielectric layer, such as MgF2 in the case of EpiStar. For GaN light-emitting diodes, it has been proposed to increase the mirror reflectivity by introducing so-called dielectric DBRs, or distributed Bragg reflectors. Such a mirror consists of a pair of, for example, SiO2 / TiO2 layers with a thickness of L / 4, see, for example, the publication by Hongjun Chen et al., “Enhanced Performance of GaN-Based Light-Emitting Diodes by Using Al Mirror and Atomic Layer Deposition—TiO2 / Al2O3 Distributed Bragg Reflector Backside Reflector with Patterned Sapphire Substrate,” Applied Physics Express, Vol. 6, No. 2, 2013, DOI: https: / / doi.org / 10.7567 / APEX.6.022101.

[0021] The basic concept of the mirror described here is to use a stack of dielectric layers, preferably with optimized thickness, instead of a single SiO2 layer. Conventional DBR mirrors consist of multiple L / 4 layers composed of two dielectric materials. The materials should have a large difference in refractive index to maximize the reflection of radiation at each boundary surface. A disadvantage of this conventional approach is that this construction results in a strong angular and spectral dependence of the reflection. This means that the L / 4 construction does not improve the mirror's reflectivity when integrated over the angle.

[0022] The Bragg mirror proposed here differs from the conventional DBR in several points:

[0023] 1) The first dielectric layer close to the semiconductor material has a low refractive index and a thickness such that a large critical angle for total reflection is achieved at the first boundary surface.

[0024] 2) The layers behind it are not L / 4 thick in order to avoid angular and spectral minima. The thickness of these layers is selected so that they ensure a high structural interference of the light reflected at each boundary surface, but at the same time exhibit very low wavelength and angular dependence.

[0025] 3) The number of layers behind it is preferably reduced to three or four to reduce the complexity of the design and minimize the adverse effect on thermal conductivity through the LED.

[0026] The above-described dielectric stack increases the reflectivity and brightness, in particular, of InGaAlP light-emitting diodes.

[0027] In particular, the following aspects should be taken into consideration:

[0028] A) Select dielectric material:

[0029] As mentioned above, the dielectric material should be selected so that it has a sufficiently high refractive index difference. The first layer should be a low-refractive-index layer. Examples of suitable material pairs are: i) SiO2 with n = 1.46 and / or Nb2O5 with n = 2.3, ii) SiO2 and TiO2 with n = 2.3 to 2.4, iii) MgF2 and Nb2O5 with n = 1.37, and iv) MgF2 and TiO2. The values mentioned apply to a temperature of 300 K and a wavelength of 616 nm. The thickness of the individual layers is preferably optimized for each material selection.

[0030] B) Number and thickness of layers:

[0031] The total number of layers can be low, for example, three or four. Advantageously, the number of layers is limited, as thicker dielectric mirrors have a negative impact on the thermal properties of the LED. To maximize reflectivity over a wide angular and spectral range, it is advantageous if the layers differ from L / 4 and if the layers with low and high refractive indices have different optical thicknesses. For example, the first layer is thick, in particular approximately 520 nm. The underlying Nb2O5 and SiO2 layers each have a thickness slightly greater or less than L / 3. These designs do not produce strong angular reflection minima.

[0032] However, there are equivalent configurations:

[0033] i) The thickness of the first layer can be chosen to be larger or smaller. However, if the first layer is too thin, for example thinner than approximately L / 2, then the reflection improvement is lost.

[0034] ii) For thinner dielectric layers, it is not necessary that layers of the same material have the same optical thickness. Equivalent designs exist where each layer has a different optical thickness. A thickness greater than L / 4, but less than L / 2, preferably L / 3 + / - 20%, is optimal.

[0035] iii) It is possible to use different numbers of dielectric layers. The total number of layers can be greater than 4. Good designs exist for both odd and even numbers of layers.

[0036] iv) When an odd number of dielectric layers is used, each layer can be L / 4 thick or thinner. However, if a thickness of L / 4 is chosen, then a minimum in reflectivity occurs at a specific angle, thereby reducing the overall integrated reflectivity of the mirror.

[0037] C) Select the metal behind the dielectric layer:

[0038] The broadband, spectrally reflective Bragg mirror described herein can be used with Au, Ag, or Al as the metal mirror layer or with any other metal mirror thereafter. For good adhesion of the dielectric layer to the metal mirror, an additional thin adhesion layer is preferably used, for example, one made of a transparent conductive oxide (TCO), such as ITO, ZnO, or the like. Other possible materials are, for example, insulating oxides such as Al2O3 or metals such as Ti.

[0039] D) Use in different chip designs, e.g. in combination with p-contacts:

[0040] i) The dielectric layer stack of the mirror is deposited directly on the semiconductor material. To contact the semiconductor, the mirror is structured, for example, photolithographically. The semiconductor material is preferably contacted via metal contacts, such as point contacts.

[0041] ii) Contact and current spreading are performed via a thin TCO layer, for example made of ITO. Subsequently, a Bragg stack is deposited on the TCO layer and structured so that the TCO is contacted via metallic contacts. Such TCO contacts, in particular on GaP, are known, for example, from publication DE 10

[0042] 2017 101 637 A1, the disclosure of which is hereby incorporated by reference. Other TCOs such as IZO or ZnO are also possible, either alone or in combination.

[0043] iii) The use of a Bragg mirror in conjunction with a TCO layer as a contact layer also offers advantages for subsequent processing. Bragg mirrors are typically structured using dry etching to avoid underetching if the two dielectric materials have different etching rates in wet etching processes. However, dry etching directly onto the semiconductor material can introduce defects and complicate the formation of low-ohmic electrical contacts.

[0044] Dry etching on the TCO does not, however, affect the contact resistance.

[0045] iv) With conventional DBR mirrors, significant changes in the light distribution are expected due to the strong angular and spectral dependence of the reflection pattern. With the broadband Bragg mirrors described here, the light distribution remains Lambertian. The light distribution was measured for an LED chip with a single SiO2 layer and the mirror design described here; no deviations in the reflection properties were observed.

[0046] According to at least one embodiment, the semiconductor chip includes one or more adhesion-promoting layers and / or one or more contact layers. The adhesion-promoting layer is preferably located between the metal layer and the last dielectric mirror layer. Preferably, the adhesion-promoting layer is layered and directly adjacent to the metal layer and the adjacent dielectric layer. The contact layer is preferably disposed directly between the cover layer and the semiconductor layer sequence.

[0047] According to at least one embodiment, the adhesion promotion layer and / or the contact layer consists of a transparent conductive oxide.

[0048] Transparent conductive oxides (TCOs) are transparent conductive materials, usually metal oxides such as zinc oxide, tin oxide, cadmium oxide, titanium oxide, indium oxide or indium tin oxide (ITO). In addition to binary metal oxides such as ZnO, SnO2 or In2O3, ternary metal oxides such as Zn2SnO4, CdSnO3, ZnSnO3, MgIn2O4, GaInO3, Zn2In2O5 or In4Sn3O 12Or mixtures of different transparent conductive oxides also belong to the TCO family. Furthermore, TCOs do not necessarily correspond to a stoichiometric composition and can also be p-doped or n-doped.

[0049] According to at least one embodiment, the adhesion and / or contact layers have a relatively low optical thickness. Due to the low thickness of the adhesion and / or contact layers, these layers may be non-functional. In particular, the adhesion and / or contact layers have an optical thickness of at most L / 5, L / 7, or L / 9. For example, the geometric thickness of the adhesion and / or contact layers is at least 0.5 nm, 2 nm, or 5 nm and / or at most 250 nm, 100 nm, 40 nm, or 30 nm.

[0050] According to at least one embodiment, at least 30%, 50%, or 80% of the intermediate layers, or all of the intermediate layers, have an optical thickness of L / 3. This optical thickness is particularly present with a tolerance of a maximum of L / 15, 0.06L, L / 20, or L / 30. It is also possible for only one or only two intermediate layers to have an optical thickness of L / 3, with the aforementioned tolerances.

[0051] According to at least one embodiment, the mirror has exactly three intermediate layers. Alternatively, the mirror has exactly four intermediate layers. That is, together with the cover layer, the mirror then comprises exactly four or exactly five layers composed of a material that preferably has a high refractive index and a low refractive index alternating in a direction facing away from the semiconductor layer sequence and is composed of a material that is translucent to radiation.

[0052] According to at least one embodiment, the mirror has at most one, at most two, or at most three intermediate layers, each of which has an optical thickness of (L / 4+N / 2)+ / -L / 20. N is a natural number greater than or equal to zero. Alternatively or additionally, the proportion of these intermediate layers, based on the total amount of intermediate layers in the mirror, is at most 60%, 40%, or 20%.

[0053] Alternatively, it is possible that none of the intermediate layers have such an optical thickness. That is, the mirror can have no L / 4 layer or essentially no L / 4 layer, which is used in conventional Bragg mirrors.

[0054] According to at least one embodiment, the optical thickness of the cover layer is at least 0.9 L or L or 1.1 L or 1.2 L. Alternatively or additionally, the optical thickness of the cover layer is at most 1.8 L or 1.6 L or 1.4 L. In particular, the optical thickness of the cover layer is between 1.15 L and 1.3 L.

[0055] According to at least one embodiment, the intermediate layer or at least one of the intermediate layers or at least half of the intermediate layers has an optical thickness of at least 0.27 L or 0.3 L or 0.32 L. Alternatively or additionally, the optical thickness of the intermediate layer in question is at most 0.43 L or 0.4 L or 0.36 L. Preferably, there are exactly two such intermediate layers.

[0056] According to at least one embodiment, the mirror has an intermediate layer with a low refractive index located therebetween, preferably arranged directly between two of the intermediate layers listed in the previous paragraph. The intermediate layer located therebetween preferably has an optical thickness of at least 0.26L or 0.28L and / or a maximum of 0.38L or 0.35L or 0.31L. Preferably, the refractive index difference between these intermediate layers with a low refractive index and the adjacent intermediate layers is at least 0.04L or 0.06L or 0.08L, respectively.

[0057] According to at least one embodiment, the optical thickness of at least three intermediate layers increases in a direction away from the cover layer. This applies in particular to intermediate layers that follow one another. The intermediate layers preferably begin at the cover layer. The difference in optical thickness between adjacent intermediate layers of this type is preferably at least 0.03L or 0.06L and / or at most 0.2L, 0.15L, or 0.1L.

[0058] According to at least one embodiment, the optical thickness of at least three intermediate layers increases in the direction away from the metal layer. This preferably applies to intermediate layers that follow one another directly, and in particular, starting directly at the metal layer. The difference in optical thickness of these adjacent intermediate layers is preferably relatively large and, for example, is at least 0.06L, 0.09L, or 0.11L and / or at most 0.18L, 0.14L, or 0.12L.

[0059] According to at least one embodiment, the optical thickness of the intermediate layer or layers is at most L / 5. In particular, there is exactly one such relatively thin intermediate layer. The intermediate layer or layers are preferably located closer to the metal layer than the cover layer. Preferably, exactly one intermediate layer of small thickness is located, for example, directly on the metal layer.

[0060] According to at least one embodiment, the total optical thickness of the cover layer together with all intermediate layers is at least 1.6 L or 1.8 L or 2.1 L. Alternatively or additionally, the total thickness is at most 3.5 L or 2.7 L or 2.3 L. In other words, the total thickness is relatively small.

[0061] For all preceding and succeeding optical thicknesses of the cover and intermediate layers, it is appropriate to add n L / 2, where n is a natural number greater than or equal to one, in particular equal to 1, i.e., n=1. Increasing the optical thickness by n L / 2 does not change the optical effect of the relevant layer, or does not change significantly. To simplify the above description of the thickness, the optional additional addend n L / 2 is generally not included. However, it is particularly preferred to omit this addend, so that n=0.

[0062] According to at least one embodiment, the intermediate layer or the last intermediate layer, i.e., the intermediate layer closest to the metal layer, has a thickness different from L / 4. Preferably, the optical thickness of these intermediate layers is between 0.28L and 0.45L, or, for n=1, between 0.78L and 0.95L. In this case, preferably at least 50% or 75% of the remaining intermediate layers, or all of the remaining intermediate layers, have an optical thickness between 0.255L and 0.45L (limiting values included), or between 0.755L and 0.95L (limiting values included). This applies in particular when the last intermediate layer closest to the metal layer is a high-refractive-index layer.

[0063] According to at least one embodiment, the last intermediate layer closest to the metal layer has an optical thickness between 0.28 L and 0.48 L (limit values included). This applies in particular when the last intermediate layer is a layer with a low refractive index.

[0064] According to at least one embodiment, the intermediate layer, optionally together with the cover layer, consists of exactly two different materials. That is, the mirror together with the metal layer preferably consists of only three different materials.

[0065] According to at least one embodiment, the mirror is made up of more than two light-transmitting materials, for example, made up of three or four such materials. It is feasible that the intermediate layer comprises at least two such materials and the cover layer is made up of another material. It is also feasible that each intermediate layer or each in the intermediate layer together with the cover layer is made up of its own material.

[0066] According to at least one embodiment, the cover layer, all intermediate layers and the metal layer follow one another directly and preferably in a planar manner. There are then no further components between the aforementioned components.

[0067] According to at least one embodiment, the cover layer, the intermediate layer, and the optional metal layer are each flat layers of constant thickness. The cover layer, the intermediate layer, and the optional metal layer can extend one above the other, overlapping one another. It is possible for the cover layer and / or the intermediate layer to extend laterally beyond the metal layer in order to provide an enclosure for the metal layer against external environmental influences.

[0068] According to at least one embodiment, the semiconductor layer sequence and / or the contact layer are structured. As a result, these layers have an uneven topography. The mirror can follow this topography, in particular remain intact. This means that the cover layer, the intermediate layer, and / or the metal layer are then unevenly shaped.

[0069] According to at least one embodiment, the cover layer and the low-refractive-index intermediate layer each comprise silicon dioxide or magnesium difluoride as a material. In particular, Nb2O5 or titanium dioxide is used as a material for the high-refractive-index intermediate layer. In particular, the cover layer and the low-refractive-index intermediate layer are composed of silicon dioxide, while the high-refractive-index intermediate layer is composed of Nb2O5. In this case, the cover layer and the intermediate layer generally preferably have alternating high and low refractive indices, starting with the low-refractive-index cover layer.

[0070] According to at least one embodiment, the metal layer is composed of gold, a gold alloy, silver, a silver alloy, or aluminum or an aluminum alloy. The thickness of the metal layer is preferably at least 50 nm, 100 nm, or 200 nm. The metal layer is preferably located directly on the intermediate layer.

[0071] Alternatively to a metal layer directly on the intermediate layer, at least one adhesion-improving layer, for example a titanium layer, a platinum layer, and / or a palladium layer, can be arranged between the intermediate layer and the metal layer, wherein such an adhesion-improving layer is preferably substantially optically inactive and has a thickness of, in particular, a maximum of 5 nm, 2 nm, or 1 nm. Furthermore, the adhesion-improving layer can consist of a dielectric oxide, such as aluminum oxide, or of a TCO.

[0072] According to at least one embodiment, the metal layer of the mirror is ohmically connected to an electrode of the semiconductor chip, or the metal layer forms part of an electrode. This means that the semiconductor layer sequence, in particular the p-doped side of the semiconductor layer sequence, is energized via the metal layer. This means that the mirror can be located on the p-doped side.

[0073] According to at least one embodiment, the semiconductor chip includes one or more electrical vias for electrical contacting, in particular, the p-doped side. Preferably, one or all of the vias extend through the mirror, i.e., in particular, through the cover layer and through all intermediate layers. This allows the metal layer of the mirror to be electrically connected to the semiconductor layer sequence or an additional contact layer via the vias.

[0074] According to at least one embodiment, the contact layer extends continuously through all through-holes. As a result, the contact layer can simultaneously serve as a current spreading layer. The adhesion promoter layer can also be structured in at least one contact region and then need not be electrically conductive.

[0075] According to at least one embodiment, the semiconductor layer sequence is based on the material system AlInGaAs and / or the material system InGaAlP. In other words, the semiconductor chip is an arsenide- or phosphide-based component. The wavelength L of maximum intensity is preferably at least 570 nm or 590 nm and / or at most 950 nm, 840 nm, or 700 nm. In particular, red light is generated by means of the semiconductor chip during normal operation. BRIEF DESCRIPTION OF THE DRAWINGS

[0076] The optoelectronic semiconductor chip described herein will be described in detail below using exemplary embodiments with reference to the accompanying drawings. Identical reference numerals identify identical elements in the various figures. However, the illustrations are not true to scale; rather, individual elements may be shown exaggeratedly for a better understanding.

[0077] The accompanying drawings show:

[0078] Figure 1 shows a schematic sectional view of an exemplary embodiment of an optoelectronic semiconductor chip described here;

[0079] Figure 2 and 3 Schematic cross-sectional views showing variations of semiconductor chips;

[0080] Figure 4 and 5 shows a schematic sectional view of an exemplary embodiment of an optoelectronic semiconductor chip described here;

[0081] Figure 6 A schematic curve showing the dependence of the reflectivity on the thickness of the cover layer for one variant and exemplary embodiment of the optoelectronic semiconductor chip described here;

[0082] Figure 7 A schematic comparison diagram showing the reflectivity of different semiconductor chips;

[0083] Figure 8 A to 8G show diagrams of the reflectivity of exemplary embodiments and variants of a semiconductor chip as a function of the angle of incidence and as a function of the wavelength;

[0084] Figure 9 a diagram showing the dependence of radiation intensity on radiation angle; and

[0085] Figures 10 to 14 A schematic sectional view of an exemplary embodiment of an optoelectronic semiconductor chip described here is shown. DETAILED DESCRIPTION

[0086] exist Figure 1An exemplary embodiment of a semiconductor chip 1 is described in FIG. The semiconductor chip 1 comprises a semiconductor layer sequence 2 . In the semiconductor chip 2 , an active layer 23 is located between a p-doped side 21 and an n-doped side 22 .

[0087] Directly above the semiconductor layer sequence 2 is a mirror 3 for reflecting radiation generated in the active region 23 during operation, which has a wavelength L of maximum intensity. The mirror 3 comprises a covering layer 31, which directly adjoins the semiconductor layer sequence 2. The covering layer 31 can be the thickest layer of the mirror 3. The covering layer 31 has a relatively low refractive index.

[0088] In a direction facing away from the cover layer 31, the mirror 3 has a plurality of intermediate layers 32, 33. The intermediate layers 32, 33, preferably together with the cover layer 31, have alternating high and low refractive indices.

[0089] A metal layer 39 as a reflective layer follows directly behind the intermediate layers 32, 33 in a direction facing away from the semiconductor layer sequence 2. The metal layer 39 preferably consists of gold, alternatively silver.

[0090] The intermediate layers 32, 33 of the mirror 3, in particular together with the cover layer 31, form a modified Bragg mirror. In this case, all intermediate layers 32, 33 have an optical thickness different from L / 4, unlike in conventional Bragg mirrors. This allows for a reduced spectral and angular dependence of the reflection properties.

[0091] The cover layer 31 is composed, for example, of silicon dioxide and has a thickness of 520 nm. The first intermediate layer 32 is composed, for example, of Nb2O5 and has a thickness of 95 nm. The second intermediate layer 33 is composed, for example, of silicon dioxide and has a thickness of 120 nm. At a wavelength L of maximum intensity of 616 nm and at room temperature, the optical thicknesses of these layers are 0.35 and 0.28 L, respectively, as shown in FIG. Figure 1 As given in . The cover layer 31 has an optical thickness of 1.23 L. The geometric thickness can be adjusted in relation to the wavelength L of maximum intensity.

[0092] The values stated apply for the optical thickness, preferably with a tolerance of a maximum of 0.03 L or 0.02 L, in particular with regard to the intermediate layers 32 , 33 .

[0093] exist Figure 2 A variant of the semiconductor chip 1 ′ is shown in FIG. As in conventional Bragg mirrors, the intermediate layers 32 , 33 are each L / 4 layers, i.e., layers with an optical thickness of L / 4. For example, there are 10.5 layer pairs, i.e., 21 layers. The first intermediate layer 32 is composed, for example, of silicon dioxide, while the second intermediate layer 33 is composed of Nb 5 O 2 . Thus, there are a relatively large number of layers. Furthermore, in Figure 2 Missing in Figure 1 In the embodiment of the present invention, a thick cover layer is present.

[0094] exist Figure 3 In the variant 1 ' there is a thick cover layer 31 and two layer pairs consisting of intermediate layers 32, 33, each of which has an optical thickness of L / 4. Figure 3 The wavelength L of the maximum intensity, which is 616 nm by way of example, indicates the material and the geometrical layer thickness.

[0095] In an embodiment of the semiconductor chip 1, as in Figure 4 As shown in FIG, there are three intermediate layers 32, 33, 34, which follow the cover layer 31. The cover layer 31 has an optical thickness of approximately 1.22 L. The optical thickness of the intermediate layers 32, 33, 34 increases starting from the cover layer 31 in the direction of the metal layer 39. In this case, the difference in optical thickness between adjacent intermediate layers 32, 33, 34 increases towards the metal layer 39.

[0096] exist Figure 5 In the embodiment of FIG. 4 , there are four intermediate layers 32, 33, 34, and 35. For three of these intermediate layers, the optical thickness increases in a direction away from the metal layer 39, starting at the metal layer 39. The intermediate layer 32 closest to the cover layer 31 has the second highest optical thickness. The intermediate layer 35 closest to the metal layer 39 is significantly thinner than L / 4.

[0097] exist Figure 4 and 5 The materials and thicknesses mentioned in are to be understood as examples only. All layers 31, 32, 33, 34, 35 each have an optical thickness not equal to L / 4. The optical thickness of the intermediate layers 32, 33, 34, 35 is as in Figure 4 and 5 As described in , it can also be applied in a slightly modified form, for example with a tolerance of maximum 0.04L or 0.02L each.

[0098] exist Figure 6 The reflectivity R in percent is recorded relative to the thickness T of the cover layer T in nm. Here, Figure 1 The embodiment of the semiconductor chip 1 in FIG. 1 is compared with the variant 1 ′. The variant 1 ′, as in FIG. Figure 6 As described in Figure 3 The variant 1 ′ of FIG. 1 , however, does not have the intermediate layers 32 , 33 .

[0099] from Figure 6 As can be seen in FIG, for the exemplary embodiment of the semiconductor chip 1 , the reflectivity R is reduced by the excessively thin cover layer 31 and a reflectivity R that is approximately 0.4 percent higher is achieved compared to variant 1 ′.

[0100] exist Figure 7 For example, Figure 6 Explained and based on Figure 3 Variant 1', and Figure 2 Variant 1' and Figure 5 . It can be seen that, by means of Figure 5 The structure of the semiconductor chip 1 in FIG. 1 can achieve a significantly improved reflectivity R. The reflectivity R, as in FIG. Figure 7 As given in , this involves the reflectivity integrated over all angles.

[0101] exist Figure 8 The reflectivity R is reported for the various embodiments and variants in A to 8F relative to the angle of incidence E in degrees and the wavelength λ in nm. The reflectivity R is coded in Figure 8 Depicted in G.

[0102] Figure 8 A relates to a variant 1 ′ having a mirror with a thick silicon dioxide layer and a gold layer directly underneath, ie without intermediate layers 32 , 33 . Figure 3 structure.

[0103] exist Figure 8 Variant 1' is described in B, in which 10 layer pairs of silicon dioxide and Nb2O5 are used, correspondingly 20 layers, of which the bottom layer is directly on the metal mirror composed of Nb2O5. Figure 8 B's device corresponds to Figure 2 The variant 1 ′ of FIG. 1 , however, does not have the intermediate layer 32 of low refractive index closest to the metal layer 39 .

[0104] In such a Figure 8 In the variant 1' described in C, there are 10.5 layer pairs, corresponding to 21 layers, as in Figure 2 According to this, a layer with a low refractive index is located directly on the metal mirror.

[0105] Figure 8 D shows the Figure 1 The reflectivity of an embodiment of the semiconductor chip 1 is shown in FIG.

[0106] exist Figure 8 Description in E Figure 5 The reflectivity R of an embodiment of the semiconductor chip 1 is shown in FIG.

[0107] Finally, in Figure 8 Description in F Figure 3 The reflectivity R of the variant 1'.

[0108] Especially from Figure 8 D and 8E show that a relatively high reflectivity R can be achieved up to a relatively small angle of incidence E, as in Figure 8 B and 8 C are different. In addition, in particular at longer wavelengths above 600 nm, a significantly lower spectral dependence of the reflectivity R can be achieved.

[0109] Due to the strong modulation of the reflectivity R, as in Figure 8 As can be seen in Figures B and 8C, a larger number of layer pairs does not result in an overall increase in reflectivity. Figure 7 Visible in.

[0110] exist Figure 9 The radiation intensity I is recorded normalized to the radiation angle A. This is a variant 1 ', as in Figure 6 As described in Figure 3 The configuration without the intermediate layers 32, 33 and Figure 1 An ideal Lambertian emission characteristic is additionally explained.

[0111] from Figure 9 As can be seen from the diagram, no deviations are visible between Example 1 and Variant 1' over a wide angular range. In particular, within the angular range of + / -70°, there are no significant deviations from the Lambertian emission characteristic. The intensity I relates in particular to the luminous flux averaged over all wavelengths.

[0112] exist Figure 10 In the embodiment of the semiconductor chip 1, a plurality of electrical vias 5 are formed through the layers 31, 32, and 33 of the mirror 3. The vias 5 are preferably metallic vias. The semiconductor layer sequence 2 is electrically connected to the metal layer 39 of the mirror 3 via the vias 5. The metal layer 39 is thus part of an electrode 6 for electrically supplying the semiconductor chip 1.

[0113] The through-hole 5 is, for example, trapezoidal when viewed in cross section and can optionally taper in the direction toward the semiconductor layer sequence 2. Alternatively, the through-hole 5 can also be rectangular in cross section.

[0114] exist Figure 11 In the exemplary embodiment of , a contact layer 4 is additionally present. The contact layer 4 extends over the semiconductor layer sequence 2 and in particular completely covers each through-hole 5. The contact layer can be removed outside the through-hole 5.

[0115] The contact layer 4 is preferably made of a transparent conductive oxide, such as ITO. The thickness of the contact layer 4 is, for example, between 15 nm and 30 nm and is therefore preferably so thin that it does not significantly affect the optical properties of the mirror 3 and / or the semiconductor chip 1. Such a contact layer 4 is preferably also Figure 1 、 4If the contact layer 4 adopts a greater thickness and becomes optically effective, the thicknesses of the cover layer 31 and the intermediate layers 31, 32, 33, 34 may be adjusted accordingly in order to induce a maximum reflectivity.

[0116] exist Figure 12 It is described in FIG that the cover layer 31 and the intermediate layers 32, 33, 34 extend over the entire surface of the metal layer 39. The layers 31, 32, 33, 34 are preferably made of a conductive material, such as a transparent conductive oxide. Figure 10 and 11 The contact layer 4 can also be omitted.

[0117] One of the electrodes 6 is located on the light coupling-out side 10 and can be connected to a current spreading structure (not shown). The metal layer 39 of the mirror 3 can be located on the electrode 6 of the carrier 7. External electrical contact can optionally be made via the region of the electrode 6 adjacent to the semiconductor layer sequence 2, for example, via bonding wires. The electrode 6 on the light coupling-out side 10 can also be contacted, for example, via bonding wires. If the carrier 7 is electrically conductive, contact can be made without bonding wires from the side having the metal layer 39.

[0118] The further electrode 6 on the light coupling-out side 10 is Figure 10 and 11 There is no explanation in Figures 10 to 12 Unlike the illustration, a flip-chip configuration is also possible.

[0119] exist Figure 13 In the exemplary embodiments A to 13C, an adhesion promoting layer 8 is additionally present, which is located between the metal layer 39 and the intermediate layer directly adjoining the metal layer 39. The adhesion promoting layer 8 is formed according to Figure 13 B extends continuously on the metal layer 39 and also completely covers the through-hole 5, so that the through-hole 5 is surrounded by the adhesion-promoting layer 8. Figure 13 In A, the adhesion promoting layer 8 is limited to the boundary between the metal layer 39 and the nearest intermediate layer 32 .

[0120] In addition, Figure 13 B shows that the contact layer 4 is present in addition to the adhesion promoting layer 8. The adhesion promoting layer 8 and the contact layer 4 can consist of the same material or of different materials.

[0121] exist Figure 13 C constitutes an adhesion layer 8, such as Figure 13 As described in A. In addition, a contact layer 4 is present.

[0122] The adhesion layer 8 is preferably made of a transparent conductive oxide such as ITO. The thickness of the adhesion layer 8 is, for example, between 1 nm and 20 nm and is preferably so thin that the adhesion layer 8 is optically ineffective and has no or no significant effect on the optical properties of the mirror 3 and / or the semiconductor chip 1.

[0123] As in Figure 13 The adhesion-promoting layer 8 shown in Figures A to 13C is preferably also present in all other exemplary embodiments.

[0124] exist Figure 14 As shown in Figures 14A and 14B, respectively, the semiconductor layer sequence 2 of the semiconductor chip 1 is structured. The through-hole 5 is preferably located in an area of the semiconductor layer sequence 2 that is thicker than the remaining areas. By structuring the semiconductor layer sequence 2 in this way, it is possible to prevent the active area 23 from being energized directly under the electrode 6. The electrode 6 directly on the semiconductor layer sequence 2 is formed, for example, by a current distribution tab. In addition, the light output efficiency can be improved by this structuring because light can be redirected on the structuring portion. The cover layer 31 and the intermediate layers 32, 33 and the metal layer 39 imitate the semiconductor layer sequence 2 in a shape-matched manner. That is, the mirror 3 extends planarly on the semiconductor layer sequence 2, but is not formed flatly, but rather draws the morphology of the semiconductor layer sequence 2.

[0125] exist Figure 14 B shows that a contact layer 4 is additionally present. The contact layer 4 is applied only locally, starting from at least one associated through-hole 5. Figure 14 In contrast to the illustration of B, due to the low lateral conductivity of the first side 21 of the semiconductor layer sequence 2 , it is possible to define where the active region 23 is energized. Structuring of the semiconductor layer sequence 2 itself is then unnecessary.

[0126] Components shown in the figures, unless otherwise specified, preferably follow one another directly in the order in which they are shown. Layers that are not in contact in the figures are preferably spaced apart from one another. Whenever lines are shown parallel to one another, the corresponding surfaces are preferably also oriented parallel to one another. Similarly, unless otherwise specified, the relative positions of the components shown in the figures are accurately depicted.

[0127] The invention described here is not restricted by the description based on the exemplary embodiments. Rather, the invention comprises any novel feature and any combination of features, which in particular includes any combination of features in the exemplary embodiments, even if the feature or the combination itself is not described in detail in the exemplary embodiments.

[0128] This application claims the priority of German patent applications 10 2018 106 001.7 and 10 2018 107 667.3, the disclosures of which are incorporated herein by reference.

[0129] Reference Signs List

[0130] 1 Optoelectronic semiconductor chips

[0131] 1' Variants of semiconductor chips

[0132] 10 Optical coupling output side

[0133] 12 Dorsal

[0134] 2 Semiconductor layer sequence

[0135] 21 p-type doping side

[0136] 22 n-type doping side

[0137] 23 Active region

[0138] 3 mirrors

[0139] 31 Covering

[0140] 32 First Intermediate Layer

[0141] 33 Second middle layer

[0142] 34 Additional middle layer

[0143] 35 Middle Layer

[0144] 39 metal layers

[0145] 4 Contact layer

[0146] 5 Electrical vias

[0147] 6 electrodes

[0148] 7 bearing parts

[0149] 8 Adhesion layer

[0150] A is the radiation angle in degrees

[0151] E is the angle of incidence in degrees

[0152] I. Intensity

[0153] L wavelength of maximum intensity

[0154] R Reflectance in %

[0155] T Thickness of the covering layer

[0156] λ wavelength in nm

Claims

1. An optoelectronic semiconductor chip (1), comprising: - a semiconductor layer sequence (2) having an active region (23) for generating radiation of a wavelength L having a maximum intensity; and a mirror (3) for radiation on the rear side (12), which is opposite the light coupling-out side (10), in - the mirror (3) comprises a cover layer (31), which is located closest to the semiconductor layer sequence (2), - the cover layer (31) consists of a material that is transmissive to the radiation and has an optical thickness between 0.5 L and 3 L, limit values included, - between 2 and 7 intermediate layers (32, 33, 34, 35), inclusive, follow directly after the cover layer (31) in a direction facing away from the semiconductor layer sequence (2), the intermediate layers (32, 33, 34, 35) alternately have a high refractive index and a low refractive index for the radiation and are each composed of a material that is transmissive to the radiation, - the thickness of at least one of the intermediate layers (32, 33, 34, 35) is not equal to L / 4, - at least one metal layer (39) as a reflective layer directly follows the intermediate layer (32, 33, 34, 35) in a direction facing away from the semiconductor layer sequence (2), or an adhesion-promoting layer (8) is located directly between the intermediate layer (32, 33, 34, 35) and the metal layer (39), and The metal layer (39) is configured to supply current to the semiconductor layer sequence (2).

2. The optoelectronic semiconductor chip (1) according to claim 1, wherein a contact layer (4) composed of a transparent conductive oxide is located directly between the cover layer (31) and the semiconductor layer sequence (2), The contact layer (4) has a thickness between 2 nm and 300 nm inclusive.

3. The optoelectronic semiconductor chip (1) according to claim 1 or 2, wherein the mirror (3) comprises exactly three or exactly four of the intermediate layers, The intermediate layers each have an optical thickness of L / 3 with a tolerance of at most 0.06L.

4. The optoelectronic semiconductor chip (1) according to claim 1 or 2, The cover layer (31) has an optical thickness between 0.9 L and 1.6 L, inclusive.

5. The optoelectronic semiconductor chip (1) according to claim 1 or 2, The high-refractive-index intermediate layers each have an optical thickness between 0.3 L and 0.4 L, inclusive, and the low-refractive-index intermediate layers located therebetween each have an optical thickness between 0.26 L and 0.35 L, inclusive.

6. The optoelectronic semiconductor chip (1) according to claim 1 or 2, wherein the total optical thickness of the cover layer (31) together with all intermediate layers (32, 33, 34, 35) is between 1.6L and 2.7L, inclusive, The cover layer (31) and the intermediate layers (32, 33, 34, 35) are composed altogether of exactly two different materials.

7. The optoelectronic semiconductor chip (1) according to claim 1 or 2, wherein the cover layer (31), the intermediate layer (32, 33, 34, 35) and the metal layer (39) follow one another directly and areally, At least the cover layer (31) and the intermediate layers (32, 33, 34, 35) are each layers of constant thickness and extend overlapping each other.

8. The optoelectronic semiconductor chip (1) according to claim 1 or 2, wherein the cover layer (31) is composed of SiO2 and the intermediate layers (32, 33, 34, 35) are alternately composed of Nb2O5 and SiO2, The metal layer (39) is made of gold or silver.

9. The optoelectronic semiconductor chip (1) according to claim 1 or 2, The metal layer (39) is ohmically electrically connected to an electrode (6) of the optoelectronic semiconductor chip (1) or is part of the electrode (6).

10. The optoelectronic semiconductor chip (1) according to claim 2, wherein the mirror (3) is located on the p-doped side (21) of the semiconductor layer sequence (2), A plurality of electrical vias (5) for electrically contacting the p-doped side (21) extend through the mirror (3).

11. The optoelectronic semiconductor chip (1) according to claim 10, The through holes (5) are each metallic and penetrate the cover layer (31) and all intermediate layers (32, 33, 34, 35).

12. The optoelectronic semiconductor chip (1) according to claim 10 or 11, The contact layer (4) and / or the adhesion-promoting layer (8) extend continuously over all through-holes (5).

13. The optoelectronic semiconductor chip (1) according to claim 10 or 11, The contact layer (4) extends only partially over the semiconductor layer sequence (2) starting from the through-hole (5), so that the contact layer (4) is completely or partially removed from the region next to the through-hole (5).

14. The optoelectronic semiconductor chip (1) according to claim 1 or 2, The semiconductor layer sequence (2) is based on AlInGaAs or on InGaAlP, and the wavelength L of the maximum intensity lies between 570 nm and 950 nm inclusive.

15. The optoelectronic semiconductor chip (1) according to claim 1 or 2, wherein at least 50% of the intermediate layers (32, 33, 34, 35) have an optical thickness of L / 3 with a tolerance of at most L / 15, The low-refractive-index cover layer (31) and all intermediate layers (32, 33, 34, 35) are each composed of an oxide, a nitride or an oxynitride and are each dielectric.

16. The optoelectronic semiconductor chip (1) according to claim 1 or 2, The mirror (3) has at most two intermediate layers (32, 33, 34, 35), each of which has an optical thickness of (L / 4+N / 2)+ / -L / 20, wherein N is a natural number greater than or equal to zero.

17. The optoelectronic semiconductor chip (1) according to claim 1 or 2, wherein the optical thickness of at least three of the intermediate layers (32, 33, 34, 35) increases in a direction away from the cover layer (31), The difference in optical thickness between adjacent intermediate layers ( 32 , 33 , 34 , 35 ) lies between 0.03 L and 0.15 L, inclusive.

18. The optoelectronic semiconductor chip (1) according to claim 1 or 2, wherein the optical thickness of at least three of the intermediate layers (32, 33, 34, 35) increases in a direction away from the metal layer (39), The difference in optical thickness between adjacent intermediate layers ( 32 , 33 , 34 , 35 ) lies between 0.09 L and 0.14 L, inclusive.

19. The optoelectronic semiconductor chip (1) according to claim 1 or 2, wherein the optical thickness of one of the intermediate layers (32, 33, 34, 35) is at most L / 5, The intermediate layers (32, 33, 34, 35) are closer to the metal layer (39) than the cover layer (31).

20. The optoelectronic semiconductor chip (1) according to claim 1 or 2, wherein the intermediate layer (32, 33, 34, 35) closest to the metal layer (39) has an optical thickness between 0.28L and 0.45L, inclusive, or an optical thickness between 0.78L and 0.95L, inclusive, wherein at least 50% of the remaining intermediate layers (32, 33, 34, 35) have an optical thickness between 0.255 L and 0.45 L, inclusive, or between 0.755 L and 0.95 L, inclusive, and The intermediate layer (32, 33, 34, 35) closest to the metal layer (39) is a layer with a high refractive index.

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