WO2009155899A1

WO2009155899A1 - Radiation-emitting semiconductor chip

Info

Publication number: WO2009155899A1
Application number: PCT/DE2009/000856
Authority: WO
Inventors: Krister Bergenek; Ralph Wirth; Norbert Linder; Christopher Wiesmann
Original assignee: Osram Opto Semiconductors Gmbh
Priority date: 2008-06-27
Filing date: 2009-06-17
Publication date: 2009-12-30
Also published as: DE102008030751A1; TWI415296B; TW201010141A

Abstract

The invention relates to a radiation-emitting semiconductor chip having a front (7) which is provided for the coupling out of light. The radiation-emitting semiconductor chip comprises the following elements from the back (8), opposite the front (7), towards the front (7) in the indicated order: an active layer (1) which is designed for the emission of electromagnetic radiation; a mixing layer (2) which contains scattering elements (21) for scattering the electromagnetic radiation; a transition layer (3) which has a refractive index smaller than the refractive index of the active layer (1); and a first photonic crystal (4).

Description

description

Radiation-emitting semiconductor chip

This patent application claims the priority of German Patent Application 102008030751.3, the disclosure of which is hereby incorporated by reference.

The present application relates to a radiation-emitting semiconductor chip.

It is an object of the present application to specify a radiation-emitting semiconductor chip which is suitable for the directed coupling out of electromagnetic radiation with a particularly high efficiency.

This object is achieved by a radiation-emitting semiconductor chip according to claim 1. Embodiments and further developments of the semiconductor chip are specified in the dependent claims. The disclosure of the claims is hereby expressly incorporated by reference into the description.

A radiation-emitting semiconductor chip is specified. The semiconductor chip has a front side, which is provided for radiation decoupling. In the direction from a rear side opposite the front side to the front side, the semiconductor chip initially has an active layer which is provided for the emission of electromagnetic radiation.

The active layer has in particular a sequence of inorganic semiconductor layers, in particular it has a active zone between an n-type layer and a p-type layer. In one embodiment, the active layer is based on an Ill / V compound semiconductor material. Alternatively, the active layer may also contain organic material, such as a polymer or a small molecule material ("small molecules"). Then, the semiconductor chip is an organic light emitting diode (OLED, organic light emitting diode).

"Based on a III / V compound semiconductor material" in the present context means that the active layer or at least one semiconductor layer of the active layer at least one element of the third main group, such as B, Al, Ga, In, and an element of the fifth main group, such as N, P, As. In particular, the term "III / V compound semiconductor material" includes the group of binary, ternary or quaternary compounds containing at least one element from the third main group and at least one element from the fifth main group, for example nitride and phosphide compound semiconductors , Such a binary, ternary or quaternary compound may also have, for example, one or more dopants and additional constituents.

"Based on nitride compound semiconductor material" in the present context means that the active layer or at least a part thereof, particularly preferably at least the active zone, comprises or consists of a nitride compound semiconductor material, preferably Al _n Ga _m Ini_ _n _ _m N, where O ≦ n ≦ l, O ≦ m ≦ l and n + m ≦ 1. In this case, this material does not necessarily have a mathematically exact composition according to the above formula. Rather, it may, for example, one or more dopants and additional Have constituents. For the sake of simplicity, however, the above formula contains only the essential constituents of the crystal lattice (Al, Ga, In, N), even if these can be partially replaced and / or supplemented by small amounts of further substances. Correspondingly, in this context "based on phosphide compound semiconductor material" means that the active layer or at least a part thereof, more preferably at least the active zone, preferably Al _n Ga _m In _n _ _ _m P or As _n Ga _m In ^ _ _n _ _m P, where O ≤ n ≤ l, O ≤ m ≤ l and n + m ≤ 1. In this case, this material does not necessarily have to have a mathematically exact composition according to the above formula. Rather, it may have one or more dopants as well as additional ingredients. For the sake of simplicity, however, the above formula contains only the essential constituents of the crystal lattice (Al or As, Ga, In, P), even if these may be partially replaced by small amounts of other substances. Examples of phosphide and nitride semiconductor materials are GaN, InGaAlP and AlGaAs, the indices (n, m) being omitted for simplicity.

The active layer is followed in the direction from the back to the front by a mixing layer, which contains scattering elements for scattering the electromagnetic radiation. The blending layer is followed in this direction by a transition layer having a refractive index which is smaller than the refractive index of the active layer. In particular, the refractive index of the transition layer is also greater than 1, ie greater than the refractive index of air. For example, the refractive index of the transition layer is smaller than the refractive index of that semiconductor layer of the inorganic semiconductor layer sequence of the active layer, which faces the transition layer. In particular, the refractive index of the transition layer smaller than an average value of refractive indices of the inorganic semiconductor layers of the active layer.

The transition layer is followed by a first photonic crystal in the direction from the back to the front. In a preferred embodiment, the photonic crystal has a one-dimensional or two-dimensional lateral structuring. Alternatively, a photonic crystal with a three-dimensional structuring is conceivable.

A photonic crystal which has a one-dimensional or two-dimensional lateral structuring is understood here to mean a photonic crystal which has structural units which, in plan view, face the front side of the semiconductor chip in one direction (one-dimensional lateral structuring) or in two different directions (two-dimensional lateral structures) Structuring) follow each other laterally. Structural units in the present context are the basic elements which define the lateral structuring, for example individual webs, grooves, protrusions or recesses.

In the third spatial direction, ie in particular in the direction of the top view of the front side, the first photonic crystal, which has a one- or two-dimensional lateral structuring, in particular has no successive structural units. In other words, the structural units are preferably arranged in a single layer. In contrast, structural units of the photonic crystal follow one another in three different spatial directions in a three-dimensional structuring. In the case of a one-dimensional structuring, the photonic crystal has, for example, grooves and / or webs which in particular run parallel or approximately parallel. As "webs" and "grooves" in the present context, elevations and depressions are referred to, which have a dimension in plan view of the front in the direction in which they follow one another, which is less than in a direction perpendicular thereto. For example, in this last-mentioned direction, the extension of the webs is at least twice as large, preferably at least five times as large as in the direction in which the webs follow one another. In particular, the webs and / or grooves extend essentially over an entire length of the semiconductor chip.

In the case of a two-dimensional lateral structuring, the structural units can be arranged, for example, at grid points of an imaginary two-dimensional grid. For example, the grid may be a rectangular or hexagonal grid. The structural units are, for example, projections, such as columns or nubs, and / or recesses. The structural units preferably have a polygonal or round, in particular elliptical or circular, cross section in plan view of the front side.

The one- or two-dimensional lateral structuring may be periodic. Even a quasiperiodic, that is an ordered, non-periodic structuring is conceivable. As quasiperiodische structuring, for example Archimedean lattice in question. In one embodiment, the structuring is designed as a honeycomb grid.

Archimedean lattices are surface-filling arrangements of polygons in which all lattice sites are equivalent. there For example, various types of polygons may be used for a full-surface array, such as triangles, squares, hexagons, and / or octagons. In particular, the (imaginary) polygons each contain a plurality of structural units.

As an alternative to periodic or quasiperiodic structuring, disordered structurings are also suitable for the one- or two-dimensional lateral structuring of the first photonic crystal, in which each laterally adjacent structural units have characteristic spacings. That laterally adjacent structural units have characteristic distances in the present context means that the pair distribution function, which describes the lateral distances of the adjacent structural units, has a maximum at a certain distance or several specific distances.

By means of the combination of mixing layer, transition layer and photonic crystal, advantageously a directional decoupling of the electromagnetic radiation from the semiconductor chip can be achieved with a particularly high efficiency.

It is currently believed by the inventors that part of the electromagnetic radiation emitted by the active layer is emitted in so-called guided modes. The guided modes propagate in the active layer, similar to a waveguide, but do not leave the active layer. Such guided modes can be assigned a modal refractive index n _moc j. The modal refractive index of a mode is related to the propagation angle θ of the mode by the relationship: θ = aresin (n _{mo (j} / n).

n is the refractive index of the material in which the fashion propagates. For guided modes, 1 <n _{mO (} j <n.

A photonic crystal is suitable for directionally coupling out guided modes from the semiconductor chip when the modal refractive index of the guided modes is within a certain range Δnp _C. For example, this range Δn _{pc has} a width of approximately Δnp _C = 0.8. For electromagnetic radiation outside this range, a satisfactory angular distribution of the radiation intensity coupled out from the photonic crystal can generally not be achieved.

The refractive index of the active layer is usually comparatively high. For example, it is about 2.5 for GaN and about 3.4 for AlGaInP. If the photonic crystal is applied directly to a semiconductor layer of the active layer or to a layer with a comparably large refractive index, there is a risk that a comparatively large proportion of the guided modes will not be coupled out of the semiconductor chip.

Instead, according to the present application, the photonic crystal is advantageously deposited on a transition layer having a relatively low refractive index. For example, the refractive index of the transition layer is less than or equal to 2.5, preferably less than or equal to 2. In one embodiment, the refractive index of the transition layer has a value between 1.4 and 1.9, in particular between 1.4 and 1.8, for example, between 1.7 and 1.8, with the boundaries each included.

The modal refractive indices n _{mo (} j of the guided modes are reduced to be less than or equal to the refractive index of the transition layer in the transition from the active layer to the transition layer by means of the intermixing layer The range Δnp _{C of} the modal indices of refraction n _{mO (} j The range Δn _{mc of} the modal indices of refraction n _{mO (} j, which propagate in the transition _layer are then advantageously approximately equal, and it can be achieved by means of the scattering at the scattering elements of the intermixing layer that a particularly large fraction In this way, the risk of total reflection of guided modes at the transition between the active layer and the transition layer is particularly low.

The present application advantageously takes advantage of the finding that by means of the intermixing layer and the transition layer a low-loss mode compression of the guided modes can be achieved in a small range of modal refractive indices. In this way, a particularly large portion of the guided modes are coupled out of the semiconductor chip by means of the first photonic crystal.

For example, by means of the first photonic crystal, the transition layer and the intermixing layer (based on the light intensity), at least 30 percent, preferably at least 35 percent of the electromagnetic radiation coupled out from the front side is at an angle of less than or equal to 30 ° to the surface normal of a main extension plane of the semiconductor chip emitted. A Lambertian emitter emits only about 25 percent of the electromagnetic radiation in this angular range. Compared with a Lambertian emitter, the proportion of the electromagnetic radiation emitted at an angle of less than or equal to 30 ° to the surface normal of the main plane of extension is thus advantageously increased by about 20% or more, preferably by about 40% or more.

In one embodiment, the active layer adjoins the intermixing layer and / or the intermixing layer to the transition layer and / or the transition layer to the first photonic crystal. Preferably, the active layer, the intermixing layer, the transition layer and the first photonic crystal are formed by directly successive layers of the semiconductor chip.

In a further embodiment, at least a part of the scattering elements is formed by defects of the mixing layer. Preferably, the intermixing layer has a large density of defects. In a development of this embodiment, the mixing layer is a buffer layer.

The defects are, in particular, lattice defects of a crystalline material, preferably a semiconductor material, which is contained in the intermixing layer or of which the intermixing layer consists. For example, the intermixing layer contains the same semiconductor material as the active layer.

In the present context, a "large density of defects" means that the defect density, ie in particular in particular the number of lattice defects per volume, in the intermixing layer is at least twice as large, preferably at least five times as large and in particular at least ten times as large as in one of the intermixing layer facing and in particular adjacent to this semiconductor layer of the active layer. In one embodiment, the defect density was in the mixing layer has a value greater than or equal to lO -'- S cm "- preferably ^ of greater than or equal to 10 ^ 6 cm ^~ 3, for example, it has a value of 1 () 17 ^cm" 3 or more.

A buffer layer is in particular a semiconductor layer directly adjacent to a growth substrate. It is, for example, applied to the growth substrate in front of semiconductor layers of an active layer of the semiconductor chip produced epitaxially on the growth substrate. For example, it serves to adapt a lattice constant of the growth substrate to a lattice constant of a semiconductor layer of the active layer. A buffer layer advantageously has a large density of lattice defects, which can represent at least part of the scattering elements.

In another embodiment, at least a part of the scattering elements is formed by a structured interface. The interface can be structured regularly or irregularly. For example, it is an interface between the active layer and the transition layer. In one embodiment, the intermixing layer has scattering elements whose lateral extent has a value which is greater than or equal to 0.5 times a wavelength of an emission maximum of the electromagnetic radiation which is emitted by the active layer during operation of the semiconductor chip. Preferably, the lateral extent less than or equal to five times the wavelength of the emission maximum. In principle, the term "wavelength" in the context of the present application is to be understood as meaning the vacuum wavelength.

In a further embodiment, at least a part of the scattering elements is formed by a second photonic crystal. Conveniently, a characteristic feature size of the first photonic crystal is larger than a corresponding feature feature size of the second photonic crystal. The characteristic structure size may be, for example, a lattice constant or the lateral spacing of neighboring structural units of the respective photonic crystal. By way of example, the characteristic structure size of the first photonic crystal is greater by a factor of 1.5 or more, in particular by a factor of 2 or more, than the corresponding characteristic structure size of the second photonic crystal. In this way, it is advantageously possible to achieve a particularly efficient compression of the modal refractive indices of the modes conducted in the active layer into a mode range which is decoupled from the first photonic crystal.

In another embodiment, the characteristic structure size of the first photonic crystal is smaller than a wavelength of an emission maximum of the electromagnetic radiation emitted by the active layer during operation of the semiconductor chip. For example, the feature size is less than or equal to 0.75 times the wavelength.

In a further embodiment, a characteristic structure size, for example a lattice constant, of the first photonic crystal greater than the wavelength of the emission maximum of the electromagnetic radiation emitted by the active layer multiplied by the inverse of the refractive index of the transition layer. The characteristic feature size is preferably greater than or equal to 0.5 times and in particular greater than or equal to 0.65 times the wavelength.

The characteristic feature size of the second photonic crystal in one embodiment has a value that is between that of the emission maximum wavelength multiplied by the inverse of the transition layer refractive index and the emission maximum wavelength value multiplied by the inverse of the refractive index of the active layer. For example, the characteristic feature size has a value between 0.28 and 0.7 times the emission maximum wavelength, with the limits included. Investigations by the inventors have shown that with such structure sizes a particularly efficient decoupling can be achieved.

In another embodiment of the semiconductor chip, the active layer is preceded by a rear reflector layer in the direction from the rear side to the front side. With the rear reflector layer, a further increase in the efficiency can be achieved with which electromagnetic radiation is coupled out of the semiconductor chip by the first photonic crystal. In one embodiment of the semiconductor chip, a layer of a transparent, conductive oxide is arranged between the rear reflector layer and the active layer. In a further embodiment, a lateral reflector layer is applied at least on a partial region of one or more side surfaces of the semiconductor chip. In the case of a semiconductor chip with a lateral reflector layer, the proportion of the electromagnetic radiation which is coupled out by the side surfaces is particularly low. In this way, a particularly large portion of the electromagnetic radiation directed by means of the first photonic crystal is coupled out of the semiconductor chip. So a particularly well-directed radiation can be achieved.

In a further embodiment of the semiconductor chip, the transition layer is formed by a growth substrate or a thinned residue of the growth substrate. In another embodiment, the transition layer comprises a silicon oxide, a silicon nitride, titanium dioxide and / or a transparent, conductive oxide such as indium tin oxide (ITO) and / or ZnO or consists of at least one of these materials. For example, the transition layer comprises a transparent conductive oxide having a refractive index of less than or equal to 2, for example a refractive index of about 1.9.

A preferred layer thickness of the transition layer has a value between 1 μm and 10 μm, including the limits. Investigations by the inventors have shown that such a layer thickness has an advantageous effect with respect to the propagation and the absorption of the guided modes. A refractive index of the transition layer is less than or equal to 2 in one embodiment.

In a further embodiment, the semiconductor chip is free of a growth substrate. In the present context, "free of In a growth substrate, a growth substrate optionally used to grow the active layer is removed from the active layer or at least heavily thinned, in particular, it is thinned so that it is not self-supporting on its own or together with the active layer alone strongly thinned growth substrate is particularly unsuitable as such for the function of a growth substrate.

In particular, the semiconductor chip is a so-called thin-film light-emitting diode chip.

A thin-film light-emitting diode chip is characterized by at least one of the following characteristic features:

the thin-film light-emitting diode chip has a carrier element which is not the growth substrate on which the active layer has been epitaxially grown, but a separate carrier element which has subsequently been attached to the active layer;

on a major surface of the active layer facing the carrier element, a reflective layer is applied or formed which reflects back at least part of the electromagnetic radiation generated in the semiconductor layer sequence;

the active layer has a thickness in the range of 20 μm or less, in particular in the range of 10 μm or less;

the thin-film light-emitting diode chip is free of a growth substrate; and

the active layer contains at least one semiconductor layer with at least one surface which has a mixing structure which, in the ideal case, results in an approximately ergo-elastic distribution of the light in the semiconductor layers. result, that is, it has the most ergodisch stochastic scattering behavior; If desired, this semiconductor layer may optionally be contained in the mixing layer.

A basic principle of a thin-film light-emitting diode chip is described, for example, in the publication I. Schnitzer et al. , Appl. Phys. Lett. 63 (16) 18 October 1993, pages 2174 - 2176, the disclosure of which is hereby incorporated by reference. Examples of thin-film light-emitting diode chips are described in the publications EP 0905797 A2 and WO 02/13281 A1, the disclosure content of which is hereby also incorporated by reference.

While thin-film light-emitting diode chips are often Lambert's surface radiators to a good approximation, in contrast, the semiconductor chip according to the present application can represent an efficient thin-film light-emitting diode chip with a directional emission characteristic.

Further advantages and advantageous embodiments and developments will become apparent from the following, described in connection with the figures embodiments.

Show it:

FIG. 1 shows a schematic cross section through an optoelectronic semiconductor chip according to a first exemplary embodiment,

FIG. 2 shows a schematic cross section through an optoelectronic semiconductor chip according to a second exemplary embodiment, FIG. 3 shows a schematic cross section through an optoelectronic semiconductor chip according to a third exemplary embodiment,

FIG. 4A shows a schematic plan view of a front side of the semiconductor chip according to FIG. 1,

FIG. 4B shows a schematic plan view of the front side of a semiconductor chip according to a variant of the first exemplary embodiment, and FIG

FIG. 4C shows a schematic plan view of the front side of a semiconductor chip according to a second variant of the first exemplary embodiment.

In the figures and exemplary embodiments, identical or similar components as well as identical or similar components are provided with the same reference numerals. The figures and the proportions of the elements shown in the figures are not to be considered as true to scale. Rather, individual elements such as layers for better understanding and / or better representability can be exaggerated.

FIG. 1 shows a first exemplary embodiment of an optoelectronic semiconductor chip. The semiconductor chip is provided for coupling electromagnetic radiation from a front side 7. It has an active layer 1 with a sequence of semiconductor layers. The sequence of semiconductor layers includes an active region 11 between an n-type layer 13 and a p-type layer 12. In the embodiment of Figure 1, the n-type layer 13 faces the front side 7. Alternatively, the P-type layer 12 facing the front side 7 and the n-type layer 13 may be disposed on the side facing away from the front side 7 of the active zone 11.

The active zone 11 preferably contains a pn junction, a double heterostructure, a single quantum well (SQW, single quantum well) or, more preferably, a multiple quantum well structure (MQW, multi quantum well) for generating radiation. The term quantum well structure unfolds no significance with regard to the dimensionality of the quantization. It thus includes u.a. Quantum wells, quantum wires and quantum dots and any combination of these structures. Examples of MQW structures are described in the publications WO 01/39282, US 5,831,277, US 6,172,382 Bl and US 5,684,309, the disclosure content of which is hereby incorporated by reference.

Towards a rear side 8 of the semiconductor chip opposite the front side, the first active layer 1 is followed by a layer 6 made of a transparent, conductive oxide such as ITO (indium-tin oxide) and subsequently a rear-side reflector layer 5 comprising, for example, a metal such as Ag contains or consists of.

Towards the rear side 8 towards the front side 7, the active layer 1 is followed by a mixing layer 2. Subsequent to the mixing layer 2, a transition layer 3 is arranged in the direction from the rear side 8 to the front side 7. At a major surface of the transition layer 3 facing the front side 7, a first photonic crystal 4 is applied or formed. The transition layer 3 in the present case is a layer comprising sapphire. In particular, the transition layer 3 in the present case is a thinned residue of a growth substrate. The transition layer 3 has a refractive index of less than or equal to 1.8, in particular between 1.76 and 1.78. Its layer thickness is for example about 10 μm.

In the present case, the intermixing layer 2 is a gallium nitride layer which is applied to the growth substrate 3 as a buffer layer. It serves to adapt a lattice constant of the transition layer 3 to a lattice constant of the n-conductive layer 13 of the active layer 1. The active layer 1 is deposited on the buffer layer 2 by means of epitaxial growth and in particular also contains GaN and / or AlInGaN. The refractive index of the intermixing layer 2 and / or the active layer 1 has in particular a value of about 2.5.

In the present case, the intermixing layer 2 has a large density of lattice defects 21. The lattice defects 21 form scattering elements, on which electromagnetic radiation emitted by the active zone 11 in the direction of the front side 7 is scattered.

By means of the rear reflector layer 5, a portion of the radiation emitted by the active zone 11 in the direction of the rear side 8 is reflected back in the direction of the front side 7. In this way, a particularly large portion of the electromagnetic radiation on the front side 7 is coupled out through the first photonic crystal 4. The first photonic crystal 4 is formed, for example, from a front-side edge region of the transition layer 3. In particular, a structuring of the front-side main surface of the transition layer 3 represents the first photonic crystal 4. The structuring is produced, for example, by means of an etching process.

The photonic crystal 4 has a plurality of structural units 41. The structural units follow each other laterally in at least one spatial direction. The structural units 41 can be arranged periodically, quasi-periodically or not periodically. In any case, adjacent structural units 41 have a characteristic lateral distance Dl from each other. If the structural units 41 are laterally adjacent to one another in two mutually different spatial directions, it is also possible that there are two different characteristic distances, one in each of the two spatial directions, which are different from one another.

In the direction from the rear side 8 to the front side 7, the first photonic crystal in the present exemplary embodiment has an extension between 150 nm and 300 nm inclusive. In particular, the first photonic crystal 4 has exactly one layer of structural units 41 in this direction. In other words, the structural units 41 in the direction from the back 8 to the front 7 are preferably not stacked. In particular, the structural units 41 each preferably have an extent of between 150 nm and 300 nm inclusive in the direction from the rear side 8 to the front side 7.

In the present case, the first photonic crystal 4 has a two-dimensional lateral structuring. In FIG. 4A this is shown in a schematic plan view of the front side 7. In the present case, the structural units 41 periodically follow one another in plan view of the front side 7 in two mutually perpendicular directions. In the present case, adjacent structural units 41 have the same distance D1 from each other along each of these two directions. The distance D1 in the present exemplary embodiment has a value which corresponds to a wavelength of an emission maximum of the electromagnetic radiation emitted by the active zone 112, multiplied by the reciprocal of 1.4 equivalent.

In FIG. 4A, an electrical contact layer 9 omitted in FIG. 1 for the sake of clarity is shown. The electrical contact layer 9 has in particular a metallic material. By way of example, the electrical contact layer 9 may be a bonding pad.

The electrical contact layer 9 can be applied via structural units 41 of the first photonic crystal 4. Alternatively, the surface of the front side 7 covered by the bonding pad 9 may also be free of structural units 41 of the first photonic crystal.

FIG. 4B shows a variant of the first exemplary embodiment in a schematic plan view of the front side 7 of the semiconductor chip. In this variant, structural units 41 of the first photonic crystal follow one another only in one spatial direction. In the present case, this is a one-dimensional lateral structuring.

The photonic crystal in this variant, for example, webs 41 as structural units. The webs have in the direction in which they follow each other, an extension, the For example, in this direction, the extension of the webs 41 is at least twice as large, preferably at least five times as large as in the direction in which the webs 41 follow one another. In particular, the webs extend substantially over an entire edge length of the semiconductor chip.

FIG. 4C shows a further variant of the first photonic crystal 4 in a schematic plan view of the front side 7 of the radiation-emitting semiconductor chip. In the present variant, clusters 42 of structural units 41 are arranged on the front side 7 of the radiation-emitting semiconductor chip and form the first photonic crystal 4.

The clusters 42 are arranged periodically, for example. By contrast, there is no periodicity for the individual structural units 41 in the present case. In the present case, therefore, there is an ordered, non-periodic structure, ie a quasiperiodic two-dimensional lateral structuring of the first photonic crystal 4. Also other quasiperiodische structuring, such as Archimedean lattice of clusters 42 of structural units 41, in particular from different types of clusters 42, for example N-angular clusters and M-angular clusters with N ≠ M are conceivable.

By means of the mixing layer 2, the transition layer 3 and the first photonic crystal 4, a proportion of about 35% (based on the light intensity) of the electromagnetic radiation decoupled from the front side 7 during operation is present at an angle α to a surface normal 100 of a main extension plane of the semiconductor chip having a value of 0 ° ≦ α ≦ 30 °.

FIG. 2 shows a second exemplary embodiment of a radiation-emitting semiconductor chip in a schematic cross-section.

The second embodiment differs from the first embodiment initially in that the mixing layer 2 is not formed by a buffer layer. Rather, in the present exemplary embodiment, the mixing layer 2 contains a main surface of the active layer 1 facing the front side, which is provided with a structuring 20. The growth substrate on which the semiconductor layers of the active layer 1 are epitaxially grown is completely removed in the present embodiment. Alternatively, the growth substrate or, preferably, a thinned residue of the growth substrate may be contained in the active layer 1. The growth substrate or the thinned residue of the growth substrate includes, for example, the front-side major surface having the pattern 20.

The structuring 20 contains a plurality of basic units 21. The structuring 20 in the present case is an irregular structuring. By means of basic units 21 of the structuring 20, scattering elements are formed which scatter electromagnetic radiation emitted by the active zone 11. The basic units 21 have a lateral extent, which is in particular greater than or equal to a quarter of the wavelength of the emission maximum of the electromagnetic radiation emitted by the active zone 11. In an irregular structuring 20 has in particular a Average value of the lateral extents of the basic units 21 such a value. In this way, efficient scattering of the electromagnetic radiation emitted by the active zone 11 can be achieved.

In the second embodiment, a transition layer 3 which comprises or consists of silicon dioxide is applied to the structuring 20 in the second exemplary embodiment. The transition layer here has a refractive index of less than or equal to 1.5, for example about 1.47. The active layer may comprise, for example, AlInGaN having a refractive index of about 2.5 - as in the first embodiment - or AlGaInP having a refractive index of about 3.4.

The first photonic crystal 4 can be produced in the silicon dioxide layer 3 by means of an etching process, as in the first exemplary embodiment. Alternatively, it may also be applied to the silicon dioxide layer 3.

Another difference from the first exemplary embodiment is that a lateral reflector layer 10 is applied to the flanks of the transition layer 3. For example, it is formed circumferentially around the semiconductor chip. The lateral reflector layer 10 may be embodied, for example, as a dielectric mirror or as a metal layer.

FIG. 3 shows a schematic cross section through a radiation-emitting semiconductor chip according to a third exemplary embodiment.

The semiconductor chip according to the third embodiment differs from that of the second embodiment in that the scattering elements 21 of the mixing Layer 2 are formed by a second photonic crystal 20. The second photonic crystal 20 may, for example, be applied to a semiconductor layer, such as the n-type layer 13, of the active layer 1. Alternatively, it may also be formed in a front edge region of the active layer 1.

The second photonic crystal 20 has structural units 21 which - in particular analogously to the first photonic crystal 4 - can follow one another in one or two spatial directions periodically, quasi-periodically or disorderly. A characteristic structure size D2 of the second photonic crystal 20 is smaller than the corresponding characteristic structure size of the first photonic crystal 4. For example, a lateral distance D2 of the respectively adjacent structural units 21 of the second photonic crystal 20 is smaller than the lateral distance D1 of adjacent structural units 41 of the first photonic crystal Crystal 4. The lateral distance of two structural units 21 of the second photonic crystal 20 is, for example, about half the distance Dl of two adjacent structural units 41 of the first photonic crystal 4.

The side reflector layer 10 is also pulled over the side surfaces of the intermixing layer 2 and the active layer 1 in the semiconductor chip according to the third embodiment. In order to reduce the risk of an electrical short circuit of the active layer 1 through the lateral reflector layer 10, the latter in the present case is preferably designed to be electrically insulating, for example as a dielectric mirror layer or, for example, has at least one dielectric layer facing the active layer 1. The invention is not limited by the description based on the embodiments of these. Rather, it includes every new feature, as well as any combination of features, which in particular includes any combination of features in the claims, even if this feature or combination itself is not explicitly stated in the claims or exemplary embodiments.

Claims

claims

1. A radiation-emitting semiconductor chip having a front side (7), which is provided for radiation decoupling, in the direction from a front side opposite the front side (8) towards the front of the following elements in the order indicated: a) an active layer (1) b) a mixing layer (2) containing scattering elements (21) for scattering the electromagnetic radiation; c) a transition layer (3) having a refractive index smaller than the refractive index of the active layer , and d) a first photonic crystal (4).

2. The semiconductor chip according to claim 1, wherein the first photonic crystal (4) has a one- or two-dimensional lateral structuring.

A semiconductor chip according to claim 1 or 2, wherein the intermixing layer (2) is adjacent to the transition layer (3) and the transition layer is adjacent to the first photonic crystal (4).

4. The semiconductor chip according to one of the preceding claims, wherein a refractive index of the transition layer (3) is less than or equal to 2.

5. Semiconductor chip according to one of the preceding claims, wherein at least part of the scattering elements (21) of defects in the mixing layer (2) is formed.

6. Semiconductor chip according to one of the preceding claims, wherein at least part of the scattering elements (21) is formed by a regularly or irregularly structured interface (20).

7. Semiconductor chip according to one of the preceding claims, wherein at least a part of the scattering elements (21) by a second photonic crystal (20) is formed.

8. A semiconductor chip according to claim 7, wherein a characteristic feature size (Dl) of the first photonic crystal (4) is greater than a corresponding characteristic feature size (D2) of the second photonic crystal (20).

9. The semiconductor chip according to claim 1, wherein a characteristic structure size of the first photonic crystal is smaller than a wavelength of an emission maximum of the electromagnetic radiation emitted by the active layer.

10. Semiconductor chip according to one of the preceding claims, wherein a characteristic structure size (Dl) of the first photonic crystal (4) is greater than a wavelength of an emission maximum of the active layer (1) emitted electromagnetic radiation multiplied by the inverse of the refractive index of the transition layer ( 3).

11. The semiconductor chip according to one of the preceding claims, wherein the active layer (1) in the direction from the back

(8) to the front (7) precedes a rear reflector layer (5).

12. Semiconductor chip according to one of the preceding claims, wherein at least on a partial region of a side surface of the semiconductor chip, a lateral reflector layer (10) is applied.

A semiconductor chip according to any one of the preceding claims, wherein the junction layer (3) has a layer thickness of between 1 μm and 10 μm, the boundaries being included.

14. Semiconductor chip according to one of the preceding claims, in which the transition layer (3) comprises sapphire, titanium dioxide, silicon dioxide, a silicon nitride and / or a transparent conductive oxide.

15. The semiconductor chip according to claim 1, wherein at least 30% of the electromagnetic radiation coupled out from the front side is emitted at an angle (α) of less than or equal to 30 ° to a surface normal (100) of a main extension plane of the semiconductor chip.