OPTOELECTRONIC SEMICONDUCTOR CHIP

Abstract

Optoelectronic semiconductor chip (1) with - a semiconductor layer sequence (2) with an active zone (23) for generating radiation with a wavelength of maximum intensity L, and - a mirror (3) for the radiation at a rear side (12) opposite a light output coupling side (10), wherein - the mirror (3) includes a cover layer (31) which is located closest to the semiconductor layer sequence (2), - the cover layer (31) is made of a material that is transparent to radiation and has an optical thickness between 0.5 L and 3 L inclusive, - directly following the top layer (31) in the direction away from the semiconductor layer sequence (2) between including 2 and 7 intermediate layers (32, 33, 34, 35), - the intermediate layers (32, 33, 34, 35) alternately have high and low refractive indices for radiation and are each made of a material permeable to radiation, - a thickness of at least one of the intermediate layers (32, 33, 34, 35) is not equal to L / 4, and - the intermediate layers (32, 33, 34, 35) in the direction away from the semiconductor layer sequence (2) are followed directly by a metal layer (39) as a reflection layer or an adhesion mediation layer (8) is located directly between the intermediate layers (32, 33, 34, 35) and the metal layer (39).

Description

[0001] An optoelectronic semiconductor chip is specified.

[0002] Optoelectronic semiconductor chips using dielectric and metallic mirrors are known from US 2018 / 0076362A1 and US 2016 / 0087173A1.

[0003] One task to be solved is to specify an optoelectronic semiconductor chip that has a mirror with high reflectivity.

[0004] This problem is solved, among other things, by an optoelectronic semiconductor chip with the features of the independent claim. Preferred embodiments are the subject of the remaining claims.

[0005] The optoelectronic semiconductor chip is designed for generating radiation, in particular near-ultraviolet, visible, and / or near-infrared radiation. The semiconductor chip is, for example, a light-emitting diode (LED) chip or a laser diode chip. Preferably, the semiconductor chip is an LED chip for generating yellow, orange, or red light.

[0006] The semiconductor chip comprises a sequence of semiconductor layers. The semiconductor layer sequence includes at least one active zone for generating radiation. The radiation has a wavelength of maximum intensity L. The active zone is preferably located between a p-doped face and an n-doped face of the semiconductor layer sequence. The active zone contains, in particular, a single quantum well structure, a multiple quantum well structure, and / or a pn junction. The active zone extends, in particular, perpendicular to a growth direction of the semiconductor layer sequence.

[0007] The semiconductor layer sequence is preferably based on a III-V compound semiconductor material. This semiconductor material is, for example, a nitride compound semiconductor such as Al. n In 1-n-m Ga m N or a phosphide compound semiconductor material such as Al n In 1-n-m Ga mP or also an arsenide compound semiconductor material such as Al n In 1-n-m Ga m As or like Al n Ga m In 1-n-m As k P 1-k' where 0 ≤ n ≤ 1, 0 ≤ m ≤ 1, and n + m ≤ 1, as well as 0 ≤ k < 1. 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, as well as 0 < k ≤ 0.5, apply. The semiconductor layer sequence may contain dopants and 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.

[0008] The semiconductor chip includes one or more mirrors. Preferably, exactly one mirror serves to reflect the radiation. The mirror is attached to a back side of the semiconductor layer sequence that faces a light-emitting side of the semiconductor layer sequence.

[0009] The mirror comprises at least one, preferably exactly one, cover layer. The cover layer can be the thickest layer of the mirror, in particular the thickest layer of the mirror made of a material transparent to the radiation generated during operation. The cover layer is the layer of the mirror that is closest to the semiconductor layer sequence. The cover layer can be in contact with the semiconductor layer sequence over its entire surface.

[0010] The cover layer is made of a material transparent to the radiation generated during operation, and in particular, a material with a low refractive index. Low refractive index can mean that the refractive index of the cover layer is at least 0.5, 1, or 1.5 lower than the average refractive index of the semiconductor layer sequence. Preferably, the cover layer is made of a dielectric material, but alternatively, it can also be made of an electrically conductive material. Examples of cover layer materials include oxides, nitrides, and oxynitrides.

[0011] In particular, the top layer has a comparatively large optical thickness. The term optical thickness refers to the product of the geometric thickness of the respective layer and its refractive index with respect to the wavelength of maximum intensity.

[0012] The top layer has an optical thickness of at least 0.5 L, or preferably 1.0 L. This optical thickness is at most 3 L, or for example 2 L, or for example 1.5 L.

[0013] The wavelength of maximum intensity L refers here and in the following 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 this value of, for example, 300 nm is used to denote an optical thickness, and the refractive index at wavelength L is, for example, 1.5, then the geometric thickness assigned to the corresponding optical thickness is accordingly 300 nm divided by the refractive index, i.e., 200 nm. In other words, the aforementioned optical thicknesses are referenced to the wavelengths of maximum intensity L, whereby the refractive index of the respective layer must be taken into account as a divisor for conversion to geometric thicknesses. The refractive indices refer to a temperature of 300 K or to the intended operating temperature of the semiconductor chip.

[0014] The mirror comprises several intermediate layers. The number of intermediate layers is preferably at most fifteen, ten, or seven. According to the claim, the number of intermediate layers is at most seven. The intermediate layers follow the top layer directly away from the semiconductor layer sequence. In particular, two, three, four, or five of the intermediate layers are present, most preferably three or four.

[0015] The intermediate layers are each made of a material transparent to the radiation generated during operation, such as an oxide, a nitride, or an oxynitride. The intermediate layers can be dielectric or, alternatively, electrically conductive. The intermediate layers consist of at least two different materials, with each intermediate layer preferably being made of a single material.

[0016] In the direction away from the top layer, the intermediate layers exhibit alternating high and low refractive indices for the radiation generated during operation. A refractive index difference between adjacent intermediate layers and / or towards the top layer is preferably at least 0.5 or 1. It is possible that one type of intermediate layer, particularly the low-refractive-index intermediate layers, is made of the same material as the top layer.

[0017] The thickness of at least one of the intermediate layers is not equal to L / 4. In other words, at least one of the intermediate layers is not a layer as used in conventional Bragg mirrors. It is possible that none of the intermediate layers has a thickness of L / 4. This is especially true with a tolerance of 0.03 L, 0.02 L, or 0.01 L.

[0018] The mirror comprises a metal layer. This metal layer follows the intermediate layers directly away from the semiconductor layer sequence. Alternatively, an adhesion promoter layer is located directly between the intermediate layers and the metal layer. The metal layer is designed as a reflective layer and serves to reflect the radiation generated during operation. Radiation components that travel from the semiconductor layer sequence through the top layer and the intermediate layers to the metal layer are reflected by the metal layer.

[0019] The optoelectronic semiconductor chip comprises a sequence of semiconductor layers with an active zone for generating radiation with a wavelength of maximum intensity L. A reflector for the radiation is located on a rear side opposite a light-emitting side. The reflector includes a cover layer closest to the semiconductor layer sequence. The cover layer is made of a radiation-transparent material and has an optical thickness between 0.5 L and 3 L inclusive. Between the cover layer and the semiconductor layer sequence are two and seven intermediate layers of the reflector, inclusive. The intermediate layers have alternating high and low refractive indices for the radiation and are each made of a radiation-transparent material. The optical thickness of at least one of the intermediate layers is not L / 4.Following the intermediate layers in the direction away from the semiconductor layer sequence, at least one metal layer of the mirror acts as a reflection layer directly behind it, or an adhesion-promoting layer lies directly between the intermediate layers and the metal layer.

[0020] The mirror is therefore a dielectric Bragg mirror suitable for a broad wavelength range, for example from the yellow to the infrared spectral range. It is preferably used for LED chips based on InGaAlP and / or AlGaAs.

[0021] The mirror described here enables increased reflectivity, especially for dielectric mirrors, particularly for thin-film LEDs where a growth substrate is separated from a sequence of semiconductor layers. This applies, for example, to LED chips based on InGaAlP, which are manufactured using thin-film technology (TF technology).

[0022] A key element in thin-film technology, such as that used for InGaAlP / AlGaAs diodes, is a dielectric-metal mirror. The first part of such a mirror consists of a thick layer of dielectric material. The dielectric material of this first layer should have a low refractive index to maximize the difference in refractive index between an adjacent semiconductor material and the first mirror layer, thereby maximizing the critical angle of total internal reflection. The metal, usually gold or silver, behind the dielectric layer reflects light that is not reflected at the first interface.

[0023] InGaAs / AlGaAs chips manufactured using Osram TF technology, for example TF5 and TF6 packages, utilize mirrors consisting of a thick SiO2 layer, for example, 530 nm thick, and an Au layer behind it. Other variations of the dielectric mirror are found in InGaAlP / AlGaAs diodes from other manufacturers, but always with only a single layer of dielectric material, for example, MgF2 in the case of EpiStar. For GaN LEDs, it has been proposed to increase the mirror reflectivity by incorporating a so-called dielectric DBR, or Distributed Bragg Reflector. Such mirrors consist of pairs of approximately SiO2. 2 / TiO2 layers with L / 4 thickness, see for example the publication 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” in Applied Physics Express, Volume 6, Number 2, from page 022101, from 2013, DOI: https: / / doi.org / 10.7567 / APEX.6.022101.

[0024] A key principle of the mirror described here is to use a stack of preferably dielectric layers of optimized thickness instead of a single SiO2 layer. A conventional DBR mirror consists of several L / 4 layers of two dielectric materials. These materials should have a large refractive index difference to maximize radiation reflection at each interface. A disadvantage of this conventional approach is that such a setup leads to a strong angular and spectral dependence of the reflection. Consequently, when integrating over the angle, the L / 4 setup does not result in an improvement in the mirror's reflectivity.

[0025] The Bragg mirror proposed here differs from a classic DBR in several respects: 1) The first dielectric layer near the semiconductor material has a low refractive index and is thick to achieve a large critical angle of total internal reflection at the first interface. 2) To avoid angular and spectral minima, the underlying layers are not L / 4 thick. Their thickness is chosen to ensure high constructive interference of light reflected at each interface, while simultaneously exhibiting very weak wavelength and angular dependence. 3) The number of underlying layers is preferably reduced to three or four to reduce the complexity of the design and to minimize a negative impact on thermal conductivity from the LED.

[0026] The dielectric stack described above increases the specular reflection and brightness specifically of InGaAlP LEDs. In particular, the following aspects must be taken into account: A) Choice of dielectric material:

[0027] As mentioned above, the dielectric materials should be chosen to have 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 Nb₂O₅ with n = 2.3, ii) SiO₂ and TiO₂ with n = 2.3 to 2.4, iii) MgF₂ with n = 1.37 and Nb₂O₅, iv) MgF₂ and TiO₂. The values ​​given are valid for a temperature of 300 K and a wavelength of 616 nm. For different material choices, the thicknesses of the individual layers are preferably further optimized. B) Number and thickness of layers:

[0028] The total number of layers can be low, for example, three or four. Limiting the number of layers is advantageous because a thick dielectric mirror negatively impacts the LED's thermal properties. To maximize reflectance over a wide angular and spectral range, it is beneficial for the layers to differ by L / 4 and for low- and high-refractive-index layers to have different optical thicknesses.

[0029] For example, the first layer is thick, specifically approximately 520 nm. The subsequent Nb2O5 and SiO2 layers each have thicknesses slightly greater or less than L / 3. For this configuration, no strong reflection minima occur across the angle.

[0030] However, there are equivalent designs: 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, the reflection improvement is lost. ii) For thinner dielectric layers, it is not necessary for layers of the same material to have the same optical thickness. Equivalent designs exist where each layer has a different optical thickness. Thicknesses greater than L / 4 but less than L / 2, preferably L / 3 ± 20%, are optimal. 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. iv) When using an odd number of dielectric layers, individual layers can be made L / 4 thick or thinner. However, if an L / 4 thickness is chosen, minima in the reflectance occur at certain angles. This reduces the overall integrated reflectance of the mirror. C) Selection of the metal behind the dielectric layers:

[0031] The spectrally broadband reflecting Bragg mirror described here can be used with Au, Ag, or Al as the metal mirror layer, or with any other metal mirror behind it. For good adhesion of the dielectric layers to the metal mirror, an additional thin adhesive layer is preferably used, for example, made of a transparent conductive oxide (TCO) such as ITO, ZnO, or the like. Other possible materials include insulating oxides such as Al₂O₃ or metals such as Ti. D) Use in different chip designs, for example in combination with a p-contact: i) The dielectric layer stack of the mirror is deposited directly onto the semiconductor material. The mirror is structured, for example photolithographically, to contact the semiconductor. The semiconductor material is preferably contacted by metallic contacts such as point contacts. (ii) Contacting and current expansion are achieved through a thin TCO layer, for example made of ITO. Subsequently, the Bragg stack is deposited and structured on the TCO layer to contact the TCO via metallic contact points. Such TCO contacts, particularly on GaP, are known, for example, from German patent application DE 10 2017 101 637 A1, the disclosure of which is referenced here. Other TCOs such as IZO or ZnO are also possible, either individually or in combination. iii) The use of a Bragg mirror in combination with a TCO layer as a contact layer also offers advantages for subsequent processing. Bragg mirrors are typically patterned by dry etching to avoid under-etching if the two dielectric materials have different etch rates in a wet etching process. However, dry etching directly onto a semiconductor material can introduce defects and makes it difficult to form a low-resistance electrical contact. Dry etching onto TCO, however, does not affect the contact resistance. iv) For a conventional DBR mirror, a significant variation in the light distribution would be expected due to strong angular and spectral dependencies in the reflection pattern. In the case of the broadband Bragg mirror described here, the light distribution remains Lambertian. The light distribution was measured for an LED chip with a single SiO2 layer and with a mirror design described here; no deviations in the reflection characteristics were observed.

[0032] The semiconductor chip can comprise one or more adhesion layers and / or one or more contact layers. The adhesion layer is located between the metal layer and the last dielectric mirror layer, if such an adhesion layer is provided. Preferably, the adhesion layer borders directly and over its entire area to the metal layer and the adjacent dielectric layer. The contact layer is preferably placed directly between the top layer and the semiconductor layer sequence.

[0033] According to at least one embodiment, the adhesion-promoting layer and / or the contact layer is made of a transparent conductive oxide.

[0034] Transparent conductive oxides (TCOs) are transparent, electrically conductive materials, typically metal oxides such as zinc oxide, tin oxide, cadmium oxide, titanium oxide, indium oxide, or indium tin oxide (ITO). Besides binary metal-oxygen compounds like ZnO, SnO₂, or In₂O₃, ternary metal-oxygen compounds such as Zn₂SnO₄, CdSnO₃, ZnSnO₃, MgIn₂O₄, GaInO₃, Zn₂In₂O₅, or In₄Sn₃O₄ also belong to this group. 12 or mixtures of different transparent conductive oxides belong to the group of TCOs. Furthermore, TCOs do not necessarily have a stoichiometric composition and can also be p-doped or n-doped.

[0035] According to at least one embodiment, the adhesion promoter layer and / or the contact layer has a relatively small optical thickness. Due to the small thickness of the adhesion promoter layer and / or the contact layer, it is possible for it to be optically non-functional. In particular, the optical thickness of the adhesion promoter layer and / or the contact layer is at most L / 5, L / 7, or L / 9. For example, the geometric thickness of the adhesion promoter layer and / or the contact layer is at least 0.5 nm, 2 nm, or 5 nm and / or at most 250 nm, 100 nm, 40 nm, or 30 nm.

[0036] 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 specified with a tolerance of at most L / 15, 0.06 L, L / 20, or L / 30. It is also possible that only one or only two of the intermediate layers have an optical thickness of L / 3, with the aforementioned tolerances.

[0037] 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 top layer, the mirror then comprises exactly four or exactly five layers of materials which preferably have alternating high and low refractive indices in the direction away from the semiconductor layer sequence and are made of materials transparent to radiation.

[0038] According to at least one embodiment, the mirror has at most one, at most two, or at most three intermediate layers, exhibiting 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 such intermediate layers is at most 60%, 40%, or 20%, respectively, based on the total number of intermediate layers of the mirror.

[0039] Alternatively, it is possible that none of the intermediate layers has such an optical thickness. That is, the mirror can be free or substantially free of L / 4 layers used in conventional Bragg mirrors.

[0040] According to at least one embodiment, the optical thickness of the top 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 top layer is at most 1.8 L or 1.6 L or 1.4 L. In particular, the optical thickness of the top layer is between 1.15 L and 1.3 L.

[0041] According to at least one embodiment, the intermediate layers, or at least one of the intermediate layers, or at least half of the intermediate layers, have an optical thickness of at least 0.27 L, 0.3 L, or 0.32 L. Alternatively or additionally, the optical thickness of the intermediate layers in question is at most 0.43 L, 0.4 L, or 0.36 L. Preferably, exactly two such intermediate layers are present.

[0042] According to at least one embodiment, the mirror has an intermediate, low-refractive-index layer, preferably located directly between two of the intermediate layers listed in the preceding paragraph. The intermediate layer preferably has an optical thickness of at least 0.26 L or 0.28 L and / or at most 0.38 L, 0.35 L, or 0.31 L. Preferably, the refractive index difference between this low-refractive-index intermediate layer and adjacent intermediate layers is at least 0.04 L, 0.06 L, or 0.08 L.

[0043] According to at least one embodiment, the optical thickness of at least three of the intermediate layers increases in the direction away from the top layer. This applies particularly to successive intermediate layers. The intermediate layers preferably begin at the top layer. The difference in optical thickness between adjacent intermediate layers of this type is preferably at least 0.03 L or 0.06 L and / or at most 0.2 L or 0.15 L or 0.1 L.

[0044] According to at least one embodiment, the optical thickness of at least three of the intermediate layers increases in the direction away from the metal layer. This preferably applies to immediately successive intermediate layers and, in particular, starting directly at the metal layer. The difference in the optical thicknesses of these adjacent intermediate layers is preferably relatively large and is, for example, at least 0.06 L, 0.09 L, or 0.11 L and / or at most 0.18 L, 0.14 L, or 0.12 L.

[0045] According to at least one embodiment, the optical thickness of one or more of the intermediate layers is at most L / 5. In particular, exactly one such comparatively thin intermediate layer is present. This intermediate layer or these intermediate layers are preferably located closer to the metal layer than to the top layer. The preferably exactly one intermediate layer with the small thickness is, for example, located directly adjacent to the metal layer.

[0046] According to at least one embodiment, the total optical thickness of the top layer together with all intermediate layers is at least 1.6 L, 1.8 L, or 2.1 L. Alternatively or additionally, the total thickness is at most 3.5 L, 2.7 L, or 2.3 L. In other words, the total thickness is comparatively small.

[0047] For all the aforementioned and subsequent optical thicknesses of the top layer and the intermediate layers, it can be added that n L / 2 is added in each case, where n is a natural number greater than or equal to one, in particular equal to one, i.e., n = 1. Increasing the optical thickness by n L / 2 does not change the optical effectiveness of the layer in question, or does not change it significantly. To simplify the preceding descriptions of the thicknesses, the optionally possible additional term n L / 2 is usually omitted. Preferably, however, this term is omitted, so that n = 0.

[0048] According to at least one embodiment, the last intermediate layer, i.e., the layer closest to the metal layer, has a thickness other than L / 4. Preferably, the optical thickness of this intermediate layer is between 0.28 L and 0.45 L inclusive, or, for n = 1, between 0.78 L and 0.95 L inclusive. In this embodiment, preferably at least 50% or 75% of the remaining intermediate layers, or all remaining intermediate layers, have an optical thickness between 0.255 L and 0.45 L inclusive, or between 0.755 L and 0.95 L inclusive. This is particularly true if the last intermediate layer closest to the metal layer is a high-refractive-index layer.

[0049] 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 inclusive. This is particularly true if the last intermediate layer is a low-refractive-index layer.

[0050] According to at least one embodiment, the intermediate layers, optionally together with the top layer, are made of exactly two different materials. That is to say, the mirror, together with the metal layer, is preferably made of only three different materials.

[0051] According to at least one embodiment, the mirror is composed of more than two translucent materials, for example, three or four such materials. It is possible that the intermediate layers comprise at least two such materials and that the top layer is made of a further material. Furthermore, it is possible that each intermediate layer, or each of the intermediate layers together with the top layer, is made of a separate material.

[0052] According to at least one embodiment, the top layer, all intermediate layers, and the metal layer follow each other directly and preferably over a flat surface. No further components are located between the aforementioned components.

[0053] According to at least one embodiment, the top layer, the intermediate layers, and optionally the metal layer are each flat layers of uniform thickness. The top layer, the intermediate layers, and optionally the metal layer can be perfectly aligned. It is possible for the top layer and / or the intermediate layer to extend laterally beyond the metal layer to encapsulate the metal layer against external environmental influences.

[0054] According to at least one embodiment, the semiconductor layer sequence and / or the contact layer is structured. These layers therefore have a non-planar topography. The mirror can follow this topography, particularly with respect to its shape. That is, the top layer, the intermediate layers, and / or the metal layer are not planar.

[0055] According to at least one embodiment, the top layer and low-refractive-index interlayers each comprise silicon dioxide or magnesium fluoride. The high-refractive-index interlayers are preferably made of Nb₂O₅ or titanium dioxide. In particular, the top layer and the low-refractive-index interlayers are made of silicon dioxide, and the high-refractive-index interlayers are made of Nb₂O₅. The top layer and the interlayers, taken together, preferably have alternating high and low refractive indices, starting with the low-refractive-index top layer.

[0056] According to at least one embodiment, the metal layer is made 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 adjacent to the intermediate layers.

[0057] As an alternative to a metal layer directly on the intermediate layers, at least one adhesion-enhancing layer, for example a titanium layer, a platinum layer and / or a palladium layer, can be applied between the intermediate layers and the metal layer. Such an adhesion-enhancing layer is preferably optically essentially ineffective and, in particular, has a thickness of at most 5 nm, 2 nm, or 1 nm. Furthermore, the adhesion-enhancing layer can consist of a dielectric oxide such as aluminum oxide or of a TCO.

[0058] 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 a current is applied to the semiconductor layer sequence via the metal layer, in particular to the p-doped side of the semiconductor layer sequence. Therefore, the mirror can be located on the p-doped side.

[0059] According to at least one embodiment, the semiconductor chip comprises one or more electrical vias for electrical contact, particularly of the p-doped side. One or all of the vias preferably extend through the mirror, i.e., in particular through the top layer and through all intermediate layers. This allows the metal layer of the mirror to be electrically connected to the semiconductor layer sequence or the additional contact layer via the vias.

[0060] According to at least one embodiment, the contact layer extends continuously across all vias. This allows the contact layer to simultaneously serve as a current-expansion layer. The adhesion promoter layer can also be structured in at least one contact area and therefore does not need to be electrically conductive.

[0061] According to at least one embodiment, the semiconductor layer sequence is based on the AlInGaAs material system and / or the InGaAlP material system. In other words, the semiconductor chip is a component based on an arsenide or a phosphide. The wavelength of maximum intensity L is preferably at least 570 nm or 590 nm and / or at most 950 nm, 840 nm, or 700 nm. In particular, the semiconductor chip generates red light during intended operation.

[0062] The following section provides a more detailed explanation of an optoelectronic semiconductor chip described herein, using exemplary embodiments and reference to the drawing. Identical reference symbols indicate identical elements in the individual figures. However, the figures are not to scale; rather, individual elements may be exaggerated for clarity.

[0063] They show: Fig. 1 a schematic sectional view of an embodiment of an optoelectronic semiconductor chip described herein, Fig. 2 and Fig. 3 schematic sectional views of variations of semiconductor chips, Fig. 4 and Fig. 5 schematic sectional views of exemplary embodiments of the optoelectronic semiconductor chips described here, Fig. 6 a schematic curve of a reflectivity as a function of the thickness of the cover layer of a modification and an embodiment of an optoelectronic semiconductor chip described here, Fig. 7 a schematic comparison of the reflectivity of different semiconductor chips, Fig. 8A to 8G schematic representations of reflectivity for variations and embodiments of semiconductor chips with respect to an angle of incidence and with respect to wavelength, Fig. 9 a schematic representation of the dependence of the emitted intensity on a radiation angle, and Fig. 10, Fig. 11, Fig. 12, Fig. 13 to Fig. 14 schematic sectional views of exemplary embodiments of the optoelectronic semiconductor chips described herein.

[0064] In Fig. Figure 1 illustrates an embodiment of a semiconductor chip 1. The semiconductor chip 1 comprises a sequence of semiconductor layers 2. In the sequence of semiconductor layers 2, there is an active zone 23 between a p-doped side 21 and an n-doped side 22.

[0065] Directly adjacent to the semiconductor layer sequence 2 is a mirror 3 for reflecting radiation generated during operation in the active zone 23, which has a wavelength of maximum intensity L. The mirror 3 includes a cover layer 31 that is directly adjacent to the semiconductor layer sequence 2. The cover layer 31 can be the thickest layer of the mirror 3. The cover layer 31 has a relatively low refractive index.

[0066] In the direction away from the top layer 31, the mirror 3 has several intermediate layers 32, 33. The intermediate layers 32, 33, preferably together with the top layer 31, have alternating high and low refractive indices.

[0067] Following the intermediate layers 32, 33 in the direction away from the semiconductor layer sequence 2 is a metal layer 39 serving as a reflective layer. The metal layer 39 is preferably made of gold, alternatively of silver.

[0068] The intermediate layers 32, 33 of the mirror 3, together with the top layer 31, form a modified Bragg mirror. Unlike a classical Bragg mirror, all intermediate layers 32, 33 have an optical thickness different from L / 4. This results in a reduced spectral and angular dependence of the reflection behavior.

[0069] The top layer 31, for example, is made of silicon dioxide with a thickness of 520 nm. The first intermediate layers 32 are made of Nb₂O₅, for example, with a thickness of 95 nm. The second intermediate layer 33 is made of silicon dioxide, for example, with a thickness of 120 nm. At a wavelength of maximum intensity L of 616 nm and at room temperature, the corresponding optical thicknesses of these layers are 0.35 and 0.28 L, as shown in Fig. 1 is specified. The cover layer 31 has an optical thickness of 1.23 L. The geometric thicknesses must be adjusted depending on the wavelength of maximum intensity L.

[0070] The stated values ​​for the optical thicknesses preferably apply with a tolerance of at most 0.03 L or 0.02 L, particularly with regard to the intermediate layers 32, 33.

[0071] In Fig. Figure 2 shows a modification 1' of a semiconductor chip. The intermediate layers 32 and 33 are each L / 4 layers, as in a classic Bragg mirror, i.e., layers with an optical thickness of L / 4. For example, there are 10.5 layer pairs, or 21 layers. The first intermediate layers 32 are made of silicon dioxide, for example, and the second intermediate layers 33 are made of Nb5O2. Thus, there is a comparatively large number of layers. Furthermore, [the following is missing in] Fig. 2 a thick top layer, as in the embodiment of the Fig. 1 available.

[0072] In the variation 1' in Fig. 3. A thick top layer 31 is present, as well as two pairs of intermediate layers 32, 33, each with an optical thickness of L / 4. The materials and geometric layer thicknesses are exemplary for a wavelength of maximum intensity L of 616 nm. Fig. 3 indicated.

[0073] In the embodiment of the semiconductor chip 1, as shown in Fig. As shown in Figure 4, three of the intermediate layers 32, 33, 34 are present, following the top layer 31. The top layer 31 has an optical thickness of approximately 1.22 L. The optical thicknesses of the intermediate layers 32, 33, 34 increase from the top layer 31 towards the metal layer 39. The differences in optical thickness between adjacent intermediate layers 32, 33, 34 increase towards the metal layer 39.

[0074] In the exemplary embodiment of the Fig. In the 5th part, four of the intermediate layers 32, 33, 34, 35 are present. For three of the intermediate layers 33, 34, 35, the optical thickness increases in the direction away from the metal layer 39, starting at the metal layer 39. The intermediate layer 32 closest to the top layer 31 has the second highest optical thickness. The intermediate layer 35 closest to the metal layer 39 is significantly thinner than L / 4.

[0075] The in the Fig. 4 and Fig. The materials and thicknesses mentioned in section 5 are merely examples. All layers 31, 32, 33, 34, 35 have optical thicknesses other than L / 4. The optical thicknesses of the intermediate layers 32, 33, 34, 35, as shown in the Fig. 4 and Fig. The values ​​specified in point 5 may also apply in a slightly modified form, for example with a tolerance of no more than 0.04 L or 0.02 L each.

[0076] In Fig. Figure 6 shows a reflectivity R in percent versus the thickness of the cover layer T in nm. The embodiment of the semiconductor chip 1 is shown. Fig. 1 compared with a variation 1'. This variation 1', as in Fig. 6 illustrates, corresponds to the modification 1' of the Fig. 3, but excluding the intermediate layers 32, 33.

[0077] Out of Fig. Figure 6 shows that for the embodiment of the semiconductor chip 1, the reflectivity R is reduced by a cover layer 31 that is too thin, and that compared to the modification 1', a reflectivity R is approximately 0.4 percentage points higher.

[0078] In Fig. 7 are the reflectivities R for the modification 1', as in conjunction with Fig. 6 explained and based on Fig. 3, as well as the variation 1' of the Fig. 2 and the embodiment of the semiconductor chip 1 from Fig. 5 compared. It can be seen that the structure of semiconductor chip 1 is made up of Fig. 5 allows for a significantly increased reflectivity R. The reflectivity R, as in Fig. The value given in 7 refers to the reflectivity integrated over all angles.

[0079] In the Fig. Figures 8A to 8F show the reflectivity R with respect to an angle of incidence E in degrees and the wavelength λ in nm, for various embodiments and modifications. The coding of the reflectivity R is in Fig. 8G is displayed.

[0080] Fig. 8A refers to a variation 1' with a mirror having a thick silicon dioxide layer and a gold layer directly underneath, i.e., the structure of the Fig. 3 without the intermediate layers 32, 33.

[0081] In Fig. 8B is a variation 1' illustrated, in which 10 layer pairs, corresponding to 20 layers, of silicon dioxide and Nb2O5 are used, with the bottom layer being directly on the metal mirror made of Nb2O5. The component of the Fig. 8B therefore corresponds to modification 1' of the Fig. 2, but excluding the low-refractive-index intermediate layer 32 closest to the metal layer 39.

[0082] In variation 1', as in Fig. Figure 8C illustrates that there are 10.5 layer pairs, corresponding to 21 layers, as shown in Fig. Figure 2 illustrates this. Accordingly, a low-refractive-index layer is located directly on the metal mirror.

[0083] Fig. Figure 8D shows the reflectivity for the embodiment of semiconductor chip 1 according to Fig. 1.

[0084] In Fig. 8E is the reflectivity R for the embodiment of semiconductor chip 1 of the Fig. 5 illustrated.

[0085] Finally, in Fig. 8F the reflectivity R for the modification 1' from Fig. 3 reproduced.

[0086] Especially the Fig. 8D and Fig. It can be seen from 8E that a consistently high reflectivity R can be achieved even at comparatively small angles of incidence E, unlike, for example, in the Fig. 8B and Fig. 8C. Furthermore, especially at longer wavelengths above 600 nm, a significantly lower spectral dependence of the reflectivity R can be achieved.

[0087] Due to the strong modulation of the reflectivity R, as in the Fig. 8B and Fig. To detect 8C, the larger number of layer pairs does not lead to an overall increase in reflectivity. This is also evident from Fig. 7 to recognize.

[0088] In Fig. 9 is a radiated intensity I, normalized to one, plotted against a radiation angle A. The variation 1' is as shown in Fig. 6 described, i.e. the design of the Fig. 3 without the intermediate layers 32, 33, with the embodiment of the semiconductor chip 1 made of Fig. 1 compared. Additionally, an ideal Lambert radiation pattern is illustrated.

[0089] The Fig. Figure 9 shows that no deviations between embodiment 1 and modification 1' are discernible over a large angular range. In particular, within the angular range of + / - 70°, there are no significant deviations from a Lambertian emission characteristic. The intensity I refers specifically to a luminous flux averaged over all wavelengths.

[0090] In the embodiment of semiconductor chip 1 of the Fig. Several electrical vias 5 are formed through layers 31, 32, 33 of the mirror 3. The vias 5 are preferably metallic. 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 thus forms part of an electrode 6 for supplying current to the semiconductor chip 1.

[0091] The vias 5 are, for example, trapezoidal in cross-section and can optionally narrow towards the semiconductor layer sequence 2. Alternatively, the vias 5 can also be rectangular in cross-section.

[0092] In the exemplary embodiment of the Fig. In addition, a contact layer 4 is present in 11. The contact layer 4 extends across the semiconductor layer sequence 2 and, in particular, completely covers each of the vias 5. Outside of the vias 5, the contact layer can be removed.

[0093] 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 thus preferably so thin that it has no significant influence on the optical properties of the mirror 3 and / or the semiconductor chip 1. Such a contact layer 4 is also preferably used in the examples of Fig. 1, Fig. 4 and Fig. 5. If the contact layer 4 assumes a greater thickness and becomes optically effective, the thicknesses of the top layer 31 and the intermediate layers 31, 32, 33, 34 may need to be adjusted accordingly to achieve maximum reflectivity.

[0094] In Fig. Figure 12 illustrates that the top layer 31 and the intermediate layers 32, 33, 34 extend across the entire surface of the metal layer 39. The layers 31, 32, 33, 34 are preferably made of an electrically conductive material such as a transparent conductive oxide. This allows for vias, as shown in the Fig. 10 or Fig. 11 are present, omitted. Contact layer 4 can also be omitted.

[0095] One of the electrodes 6 is located on the light-extraction side 10 and can be connected to a current-expansion structure (not shown). The metal layer 39 of the mirror 3 can be located on the electrode 6 on the support 7. External electrical contact is optionally possible via areas of the electrode 6 adjacent to the semiconductor layer sequence 2, for example, via bond wires. The electrode 6 on the light-extraction side 10 can also be contacted, for example, via a bond wire. If the support 7 is electrically conductive, a bond-wire-free connection can be achieved from the side with the metal layer 39.

[0096] The further electrode 6 on the light output coupling side 10 is in the Fig. 10 and Fig. 11 not illustrated. In contrast to the illustrations of the Fig. 10, Fig. 11 to Fig. 12 flip-chip designs are also possible.

[0097] In the exemplary embodiments of the Fig. In 13A to 13C, an additional adhesion-promoting layer 8 is present, located between the metal layer 39 and the intermediate layer, which lies directly adjacent to the metal layer 39. The adhesion-promoting layer 8 extends according to Fig. 13B extends continuously across the metal layer 39 and also completely covers the vias 5, so that the vias 5 are overmolded by the adhesion promoter layer 8. In Fig. In contrast, in 13A the adhesion mediation layer 8 is limited to the boundary between the metal layer 39 and the nearest intermediate layer 32.

[0098] Furthermore, in Fig. Figure 13B 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 be made of the same or different materials.

[0099] In Fig. 13C is the detention mediation layer 8 designed as in Fig. Figure 13A illustrates this. Additionally, contact layer 4 is present.

[0100] 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 thus preferably so thin that the adhesion layer 8 is optically ineffective and has no or no significant influence on the optical properties of the mirror 3 and / or the semiconductor chip 1.

[0101] A detention mediation layer 8, as in the Fig. The embodiment shown in 13A to 13C is preferably also present in all other embodiments.

[0102] In the Fig. 14A and Fig. Figure 14B shows that the semiconductor layer sequence 2 of the semiconductor chip 1 is structured. The vias 5 are preferentially located in regions of the semiconductor layer sequence 2 that are thicker than other regions. This structuring of the semiconductor layer sequence 2 prevents the active zone 23 directly below the electrode 6 from being energized. The electrode 6, located directly adjacent to the semiconductor layer sequence 2, is formed, for example, by current distribution bridges. Furthermore, such structuring can increase light extraction efficiency, as light deflection can occur at the structure. The top layer 31, the intermediate layers 32 and 33, and the metal layer 39 faithfully reproduce the shape of the semiconductor layer sequence 2. That is, the mirror 3 extends over the semiconductor layer sequence 2, but is not planar; rather, it replicates the topography of the semiconductor layer sequence 2.

[0103] In Fig. Figure 14B shows that the contact layer 4 is also present. The contact layer 4 is only applied locally, each originating from at least one associated via 5. This differs from the illustration of the Fig. Due to the low electrical transverse conductivity of the first side 21 of the semiconductor layer sequence 2, it is possible to adjust where the active zone 23 is energized, as described in 14B. Structuring of the semiconductor layer sequence 2 itself is then unnecessary.

[0104] Unless otherwise indicated, the components shown in the figures preferably follow one another in the specified order. Layers that do not touch each other in the figures are preferably spaced apart. Where lines are drawn parallel to each other, the corresponding surfaces are preferably also aligned parallel to each other. Likewise, unless otherwise indicated, the relative positions of the drawn components to each other are correctly represented in the figures. Reference symbol list 1 optoelectronic semiconductor chip 1' Modification of a semiconductor chip 10 Light output side 12 Back 2 Semiconductor layer sequence 21 p-dotted page 22 n-dotted page 23 active zones 3 mirrors 31 Top layer 32 first intermediate shift 33 second intermediate shift 34 more intermediate shifts 35 Intermediate shift 39 Metal layer 4 Contact layer 5 electrical vias 6 electrode 7 carriers 8 Detention mediation layer A Beam angle in ° E Angle of incidence in ° I Intensity L wavelength of maximum intensity R reflectivity in % T Thickness of the top layer λ Wavelength in nm

Claims

[1] Optoelectronic semiconductor chip (1) with - a semiconductor layer sequence (2) with an active zone (23) for generating radiation with a wavelength of maximum intensity L, and - a mirror (3) for the radiation at a rear side (12) opposite a light output coupling side (10), wherein - the mirror (3) includes a cover layer (31) which is located closest to the semiconductor layer sequence (2), - the cover layer (31) is made of a material that is transparent to radiation and has an optical thickness between 0.5 L and 3 L inclusive, - directly following the top layer (31) in the direction away from the semiconductor layer sequence (2) between including 2 and 7 intermediate layers (32, 33, 34, 35), - the intermediate layers (32, 33, 34, 35) alternately have high and low refractive indices for radiation and are each made of a material permeable to radiation, - a thickness of at least one of the intermediate layers (32, 33, 34, 35) is not equal to L / 4, and - the intermediate layers (32, 33, 34, 35) in the direction away from the semiconductor layer sequence (2) are followed directly by a metal layer (39) as a reflection layer or an adhesion mediation layer (8) is located directly between the intermediate layers (32, 33, 34, 35) and the metal layer (39). [2] Optoelectronic semiconductor chip (1) according to claim 1, in which a contact layer (4) made of a transparent conductive oxide is located directly between the cover layer (31) and the semiconductor layer sequence (2), wherein the contact layer (4) has a thickness between 2 nm and 300 nm inclusive. [3] Optoelectronic semiconductor chip (1) according to any one of the preceding claims, where 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, wherein the low refractive index cover layer (31) and all intermediate layers (32, 33, 34, 35) are each made of an oxide, a nitride or an oxynitride and are each dielectric. [4] Optoelectronic semiconductor chip (1) according to any one of the preceding claims, in which the mirror (3) contains exactly three or exactly four of the intermediate layers (31, 32), wherein the intermediate layers (32, 33) each have an optical thickness of L / 3, with a tolerance of at most 0.06 L. [5] Optoelectronic semiconductor chip (1) according to any one of claims 1 to 4, wherein the mirror (3) has at most two intermediate layers (32, 33, 34, 35) with an optical thickness of (L / 4 + N / 2) + / - L / 20, where N is a natural number greater than or equal to zero. [6] Optoelectronic semiconductor chip (1) according to any of the preceding claims, wherein the cover layer (31) has an optical thickness between 0.9 L and 1.6 L inclusive. [7] Optoelectronic semiconductor chip (1) according to one of the preceding claims, wherein high refractive index interlayers (33) each have an optical thickness between inclusive 0.3 L and 0.4 L and an intermediate low refractive index interlayer (32) has an optical thickness between inclusive 0.26 L and 0.35 L. [8] Optoelectronic semiconductor chip (1) according to any one of the preceding claims, in which the optical thickness of at least three of the intermediate layers (32, 33, 34, 35) increases in the direction away from the top layer (31), where the difference in optical thickness between adjacent of these intermediate layers (32, 33, 34, 35) is between inclusive 0.03 L and 0.15 L. [9] Optoelectronic semiconductor chip (1) according to any one of the preceding claims, in which the optical thickness of at least three of the intermediate layers (32, 33, 34, 35) increases in the direction away from the metal layer (39), where the difference in optical thickness between adjacent of these intermediate layers (32, 33, 34, 35) is between inclusive 0.09 L and 0.14 L. [10] Optoelectronic semiconductor chip (1) according to any one of the preceding claims, where the optical thickness of one of the intermediate layers (32, 33, 34, 35) is at most L / 5, wherein this intermediate layer (32, 33, 34, 35) is closer to the metal layer (39) than to the top layer (31). [11] Optoelectronic semiconductor chip (1) according to any one of the preceding claims, in which the intermediate layer (32, 33, 34, 35) nearest to the metal layer (39) has an optical thickness between inclusive 0.28 L and 0.45 L or between inclusive 0.78 L and 0.95 L, wherein at least 50% of the remaining intermediate layers (32, 33, 34, 35) have an optical thickness between and including 0.255 L and 0.45 L or between and including 0.755 L and 0.95 L, and wherein the intermediate layer (32, 33, 34, 35) which is closest to the metal layer (39) is a high refractive index layer. [12] Optoelectronic semiconductor chip (1) according to any one of the preceding claims, where the total optical thickness of the top layer (31) together with all intermediate layers (32, 33, 34, 35) is between 1.6 L and 2.7 L inclusive, wherein the top layer (31) and the intermediate layers (32, 33, 34, 35) together are made up of exactly two different materials. [13] Optoelectronic semiconductor chip (1) according to any one of the preceding claims, in which the top layer (31), the intermediate layers (32, 33, 34, 35) and the metal layer (39) follow each other directly and over a flat area, wherein at least the top layer (31) and the intermediate layers (32, 33, 34, 35) are each layers of constant thickness and run congruently with each other. [14] Optoelectronic semiconductor chip (1) according to any one of the preceding claims, in which the top layer (31) is made of SiO2 and the intermediate layers (32, 33, 34, 35) are alternately made of Nb2O5 and SiO2, wherein the metal layer (39) is made of gold or silver. [15] Optoelectronic semiconductor chip (1) according to one of the preceding claims, wherein the metal layer (39) is ohmically connected to an electrode (6) of the semiconductor chip (1) or is part of an electrode (6). [16] Optoelectronic semiconductor chip (1) according to any one of the preceding claims, in which the mirror (3) is located on a p-doped side (21) of the semiconductor layer sequence (2), wherein several electrical vias (5) pass through the mirror (3) for electrical contacting of the p-doped side (21). [17] Optoelectronic semiconductor chip (1) according to claim 16, in which the vias (5) are each metallic and penetrate the top layer (31) as well as all intermediate layers (32, 33, 34, 35), and wherein the adhesion mediation layer (8) is located directly between the metal layer (39) and the intermediate layer (32, 33, 34) nearest to the metal layer (39). [18] Optoelectronic semiconductor chip (1) according to claim 2 and according to claim 16 or 17, wherein the contact layer (4) and / or the adhesion media layer (8) extends continuously over all vias (5). [19] Optoelectronic semiconductor chip (1) according to claim 2 and according to one of claims 16 or 17, in which the contact layer (4) extends only partially over the semiconductor layer sequence (2) starting from the vias (5), such that the contact layer (4) is completely or partially removed from areas next to the vias (5). [20] Optoelectronic semiconductor chip (1) according to any of the preceding claims, wherein the semiconductor layer sequence (2) is based on AlInGaAs or on InGaAlP and the wavelength of maximum intensity L is between 570 nm and 950 nm inclusive.

Images