DE102006046227A1 - Semiconductor layer structure has super lattice with alternative stacked layers of connecting semiconductors of one composition and another composition, where stacked layers have doping agents in specific concentration - Google Patents

Abstract

The structure has a super lattice (9) with alternative stacked layers of connecting semiconductors with two compositions (a,b). The stacked layers have doping agents in a specific concentration (c), which is different in two layers of equal composition in the super lattice with an undoped layer. The doping agents are assigned in a vertical position (z) within the structure, where the concentration of one stacked layer (9a) of former composition, is assigned by a function and the concentration of another stacked layer (9b) of later composition, is assigned by another function. An independent claim is also included for an opto-electronic element with a semiconductor layer structure.

Description

The The invention relates to a semiconductor layer structure comprising a superlattice from alternately stacked layers of III-V compound semiconductors a first and at least one second composition. The invention further relates to an optoelectronic component, the has such a semiconductor layer structure.

Compared with a layer of equal thickness of only one material of a composition have superlattices with alternating stacked layers of different composition different electrical, optical and epitaxial properties. In particular, with suitable composition and doping, a superlattice of alternately stacked p-doped gallium nitride (GaN) and p-doped aluminum gallium nitride (AlGaN) layers have a higher conductivity have as a p-doped pure GaN or AlGaN layer of the same Thickness. Due to these properties, superlattices are often used in electronic and optoelectronic components.

task The invention is a semiconductor layer structure with superlattice of the type mentioned with improved electrical and optical To create properties. It is another object of the invention to specify an optoelectronic component having such a semiconductor layer structure.

These The object is according to claim 1 by a semiconductor layer structure of the aforementioned type solved, where the layers of the superlattice Contain dopants in predetermined concentrations and wherein the concentrations of the dopants in at least two layers of a same composition in the superlattice are different.

Basically as superlattice denotes a structure having a periodicity whose period length is larger as the lattice constants of inserted materials. As part of the Registration is as a super grid a sequence of alternating stacked layers, in which in a direction perpendicular to the interfaces between the layers, ie e.g. in the growth direction of the layers, a layer sequence, comprising at least two layers of different types, repeated. alternating is understood to mean that two or more layers alternate. Within the repetitive layer sequence can be a Type be represented by more than one layer. Examples of such superlattices are given by the following layer sequences: "ab | ab | ab | ...", "abc | abc | abc | ...", "abcb | abcb | ..." and "ababababc | ababababc | ..." where a, b and c indicate layers of each type and the repeating layer sequence by the separator "|" is clarified.

in the The scope of the application is the composition of a layer by elements contained in the layer and their nominal (i.e. Framework of accuracy of composition monitoring during or after the growth process) stoichiometry defined, wherein dopants and impurities are not taken into account become. The stoichiometry is by the content (proportion) of the individual elements in the layer given. For the number of elements of a layer is within the scope of the application no limit. The layers of the superlattice may be e.g. be elementary, i. consist of only one element, or be binary, ternary, quaternary, etc.

different Concentrations of the dopants in at least two layers of the same Composition, ie a non-constant doping level in layers same composition within the superlattice, are suitable the electrical and optical properties of the superlattice best possible to adapt given requirements. Frequently the given requirements are to the overlapping no over its entire thickness the same, for example, because physical variables, such as an electrical or optical field strength that influences the requirements have, also about the thickness of the superlattice are not constant. With an over the supergrid Not constant doping level can take this fact into account become.

According to advantageous embodiments of the semiconductor layer structure, the superlattice has alternately stacked In _x Al _y Ga _1-xy N and In _w Al _z Ga _{1 -wz} N layers with 0 ≦ x, y, w, z ≦ 1 and x + y ≤ 1 and w + z ≤ 1 or alternately stacked In _x Al _y Ga _1-xy P and In _w Al _z Ga _1-wz P layers with 0 ≤ x, y, w, z ≤ 1 and x + y ≤ 1 and w + z ≦ 1 or alternately stacked In _x Al _y Ga _1-xy As and In _w Al _z Ga _1-wz As Layers with 0 ≤ x, y, w, z ≤ 1 and x + y ≤ 1 and w + z ≤ 1. On the one hand, these material systems are of great technological importance, and on the other hand, in these systems, an advantageous conductivity increase of the hole line can be observed through the use of a superlattice.

According to a further advantageous embodiment of the semiconductor layer structure, the individual layers of the superlattice are assigned a vertical position within the semiconductor layer structure and the concentration of the dopants of a layer is dependent on their vertical position within the semiconductor layer structure in a predefined manner. In this way, the superlattice and its properties can optimally adapt to changing physical quantities within the semiconductor layer structure be adjusted.

According to others Advantageous embodiments is the dependence of the concentration the dopants from the vertical position either for all layers given by a common function or she is for layers the first composition by a first function and for layers the at least one second composition by at least one second function specified. Particularly preferred is the first and / or the at least one second and / or the common function one Step function or a monotone increasing / decreasing function or a linear function or a polynomial function or a root function or an exponential function or a logarithmic function or a periodic function or a superposition of said functions or contains Proportions of one of these functions.

According to others Advantageous embodiments, the concentration of dopants within a layer of the superlattice constant or graded.

According to others Advantageous embodiments are either all layers of the superlattice doped with the same dopant or the superlattice has layers, which are doped with different dopants. In another preferred embodiment, the superlattice has at least one layer up, which is undoped. In particular, it is preferred that the dopants Magnesium (Mg) and / or silicon (Si) are.

The Task is further solved by an optoelectronic device, the has a semiconductor layer structure of the type described above. During operation, a radiation field is formed in an optoelectronic component built with a customary within the device highly inhomogeneous field strength amplitude. A semiconductor layer structure with a superlattice, in the at least two layers of the same composition dopants contained in varying concentrations, can be in its electrical and optical properties best possible to the prevailing inhomogeneous Field strength amplitude be adapted to the optical radiation field.

According to one advantageous embodiment of the optoelectronic component has this one optically active layer, and the concentration of Dopants of layers of one or more compositions within the superlattice The semiconductor layer structure increases with increasing distance from the optically active layer. As with an optoelectronic device with optically active layer, the field strength amplitude of the radiation field usually decreases with increasing distance from the optically active layer and a high dopant concentration typically with a high optical absorption goes along in this way optical losses are reduced.

According to others Advantageous embodiments is the optoelectronic device a light emitting diode or a laser diode.

Further advantageous embodiments of the invention will become apparent from the in the following in connection with those described in the figures Embodiments.

It demonstrate:

1 a cross-sectional drawing of an opto-electronic device having a semiconductor layer structure with superlattice and the

2 - 5 schematic representations of field strength amplitude and refractive index and dopant concentration within a superlattice in various embodiments of a semiconductor layer structure with superlattice.

In 1 the layer sequence of a semiconductor layer structure of an optoelectronic component with a superlattice is shown schematically in cross section. On a substrate 1 are an adaptation layer 2 and following an n-doped contact layer 3 grew up. For ease of illustration, the doping type of layers is given below by prefixing the letter n or p, that is, z. B. n-contact layer 3 ,

On the n-contact layer 3 there is an n-cladding layer 4 and an n-waveguide layer 5 , This is an active layer 6 applied, then a barrier layer 7 and a p-waveguide layer 8th , This is followed by a p-cladding layer, which acts as a superlattice 9 is executed. The superlattice 9 indicates the alternating stacked layers 9a a first composition a and 9b a second composition b. layers 9a . 9b of the same composition a, b are summarized below using the term layer group 9a . 9b referenced.

On the supergrid 9 is a p-contact layer 10 grew up. In the right-hand area, the layer sequence is by etching down to a surface of the n-contact layer facing away from the substrate 3 removed, or was not built up in this area by masking. On the exposed surface of the n-contact layer 3 is a n-contact 11 applied. On the p-contact layer 10 there is a p-contact 12 ,

The 1 is as a schematic drawing too understand. In particular, the layer thicknesses shown are not true to scale.

The exemplary embodiment shown can be based, for example, on the basis of the In _x Al _y Ga _1-xy N, In _x Al _y Ga _1-xy As, In _x Al _y Ga _1-xy P or In _x Ga _1-x As _y N _1-y with 0 ≤ x ≤ 1, 0 ≤ y ≤ 1, 0 ≤ x + y ≤ 1 material system can be realized. Of course, the invention is not limited to these material systems, but may also be based on other material systems depending on the desired wavelength or other requirement.

This in 1 shown component represents a double heterostructure laser diode. In the following is an example of a realization in In _x Al _y Ga _1-xy N material system described in more detail. In such a case, sapphire can be used as a substrate 1 Use and n-doped GaN as n-contact layer 3 be used. For n-doping of the GaN layer preferably silicon (Si) is used. As an adjustment layer 2 is typically an aluminum nitride (AlN) layer between the sapphire substrate 1 and the GaN n contact layer 3 to adapt the different lattice constants of this layer.

Analogously, the p-contact layer 10 be realized by a magnesium (Mg) p-doped GaN layer, wherein a hole line induced by the magnesium perturbations is activated after growth of the layer in a known manner, for example by electron irradiation or thermal treatment. As n- or p-contacts 11 respectively. 12 For example, electrodes such as aluminum or nickel may be applied to the corresponding n- or p-type contact layers 3 respectively. 10 be evaporated. The necessary for the purpose of exposing the n-contact layer 3 can be done for example by a dry etching in chlorine gas or by argon ion sputtering.

Alternatively, instead of a non-conductive substrate 1 a conductive substrate such as gallium nitride (GaN) or silicon carbide (SiC) can be used. In such a case, the n-contact layer 3 and optionally, for example when using GaN, the matching layer 2 omitted. The n-contact 11 can then contact the p-contact 12 are applied on the side facing away from the semiconductor layer structure of the substrate, so that a vertically conductive semiconductor layer structure is formed.

Without limitation, in the 1 an embodiment shown in the first n-doped layers on the substrate 1 are applied. An arrangement in which p-doped layers are closer to the substrate 1 are arranged as the n-doped layers, is also possible. The two embodiments can have different properties with respect to the charge carrier injection into the semiconductor layer structure. Depending on the desired properties, each of the embodiments may prove advantageous in individual cases.

The active layer 6 may be, for example, a single or multiple quantum layer structure in which indium gallium nitride (InGaN) quantum layers are stacked alternately with AlGaN barrier layers.

When Quantum layer is to be understood in the context of the invention, a layer which is so dimensioned or structured that one for the generation of radiation significant quantization of carrier energy levels, for example by confinement. In particular, includes the term quantum layer is no indication or limitation over the dimensionality the quantization. The quantum layer can be a two-dimensional Quantum well form or structural elements with lower dimensionality such as quantum wires or Contain quantum dots or combinations of these structures.

In addition, the use of a photoluminescent active layer, for. B. an impurity-doped InGaN layer as the active layer 6 conceivable.

The the active layer 6 surrounding layers (n- and p-waveguide layers 5 respectively. 8th , n-cladding layer 4 , Super grid 9 as p-cladding layer and barrier layer 7 ) have a larger bandgap than the active layer 6 , This causes a concentration or confinement, also known as confinement, of charge carriers on the active layer 6 , The number of layers provided for this purpose is not fixed to the number of five layers shown in the figure, but in principle arbitrary.

Furthermore, they form the active layer 6 surrounding layers provide a waveguide for those in the active layer 6 generated radiation. Good waveguiding properties are achieved when the refractive index in a direction perpendicular to the active layer 6 decreases from this outwards. Since GaN has a higher refractive index than AlGaN, they are closer to the active layer 6 arranged n- and p-waveguide layers 5 respectively. 8th executed in the embodiment as GaN layers. The n-cladding layer 4 and the superlattice 9 as p-cladding layer are preferably aluminum-containing.

On the substrate 1 facing side of the active layer 6 (n-doped side) may be the waveguide layer 5 Consequently, it may be embodied as a Si-doped GaN layer and the cladding layer 4 correspondingly as an Si-doped AlGaN layer. On the substrate 1 opposite side of the active layer 6 (P-doped side) is analogous to a magnesium (Mg) -doped GaN layer as a waveguide layer 8th used. To direct recombination of electrons from the active layer 6 into the waveguide layer 8th diffuse, to prevent with the holes located there, is between the two layers in addition the barrier layer 7 intended. This can be realized by an AlGaN layer, which is typically significantly thinner than the n- and p-waveguide layers 5 respectively. 8th , the n-cladding layer 4 or the superlattice 9 is executed.

The p-side cladding layer is through the superlattice 9 realized.

In the embodiment of 1 is the superlattice 9 by alternately arranged layers 9a the first composition a and layers 9b formed of the second composition b. By way of example and for a clearer illustration, only 3 layers of the two different compositions a and b are shown in the figure. In actual implementations of the invention, the superlattice typically has a larger number of layers, for example, tens to hundreds of layers of each composition. Typical layer thicknesses for a single layer of the superlattice 9 are in the range of a few nm to several tens of nm, for example between 2 nm and 50 nm and preferably between 3 nm and 10 nm. Layers of the same composition have nominal (ie within the accuracy of the layer thickness control during or after the growth process) the same Layer thickness on. The layers 9a the first composition a and the layers 9b However, the second composition b may differ in their thickness (asymmetric superlattice) or be the same (symmetric superlattice).

The superlattice 9 can not only, as shown, consist of layers with two different compositions a, b, but also of layers having three or more different compositions, for example, by a layer sequence "abcdabcdabcd ..." or "abcbabcb ..." is formed, wherein c and d are compositions which differ from each other and from the first and second compositions a and b. As already stated, the application defines the composition of a layer by elements contained in the layer as well as its nominal (ie within the accuracy of the composition monitoring during or after the growth process) stoichiometry, whereby dopants and impurities are not taken into account. For the purposes of this definition, for example, Al _0.1 Ga _0.9 N layers and Al _0.2 Ga _0.8 N layers therefore have different compositions, while an Si n-doped GaN layer and an undoped GaN layer are to be regarded as layers of the same composition. There is no limit to the number of elements in a layer. The layers of the superlattice 9 For example, they can be elementary, that is, consist of only one element, or they can be binary, ternary, quaternary, and so on.

In the GaN-based material system, the superlattice 9 exist as a p-type cladding layer, for example, of alternating Mg-doped GaN layers and Mg-doped AlGaN layers. Due to the high activation energy of the Mg doping atoms, the electrical conductivity of p-doped layers is low. In addition, AlGaN has a larger band gap than GaN and has lower conductivity due to lower doping efficiency. The doping efficiency indicates the concentration at which dopants are actually taken up by the material and which fraction of doped atoms taken up in principle (ie irrelevant temperature-induced occupation effects) can at all contribute to the conductivity. Among other things, the doping efficiency depends on which lattice or interstitials occupy the doping atoms.

By using higher and more efficiently dopable and thus more conductive GaN layers, the superlattice can be used 9 compared with a p-doped pure AlGaN cladding layer have an increased conductivity with effectively the same refractive index. An effectively same refractive index can be due to an increased aluminum content in the superlattice 9 AlGaN layers used can be achieved compared to the AlGaN cladding layer.

Instead of a GaN / AlGaN superlattice 9 is also a superlattice 9 in which Al _x Ga _1-x N / Al _y Ga _1-y N layers with 0 ≦ x, y ≦ 1 and x ≠ y are alternately stacked. Furthermore, also for the n-doped AlGaN cladding layer 4 the use of a superlattice conceivable. Due to the generally higher conductivity of n-type doped layers, an advantage in this case is not primarily in increased vertical conductivity. Advantages, however, result from a possible reduction of tension in the active layer 6 be induced. Another advantage, which comes into play in particular with lateral current introduction, is due to the increased lateral current conductivity of a superlattice.

Superlattice, in which all layers 9a the first composition a or all layers 9b the second composition b the same doping, ie the same dopant in the same concentration, have, for example, from EP 0881666 B1 or from the publication of P. Kozodoy et al. in Applied Physics Letters 1999, Vol. 74, No. 24, p. 3681 known.

In contrast, according to the invention, the concentration of the dopants is different in at least two layers of the same composition. Thus, according to the invention, there is at least one layer of at least one group of layers 9a and or 9b which is doped differently than the remaining layers of the layer group.

The following are related to the 2 to 5 Semiconductor layer structures described in which the doping level of layers of the same composition (layer group) varies within a superlattice. The layer sequence of the exemplary embodiments shown below corresponds in principle to FIG 1 shown example, with the exception of the n-contact layer 3 , the adjustment layer 2 and the substrate 1 included in the diagrams of the 2 to 5 are not reproduced.

In the 2 to 5 For example, in each case a diagram is shown for various exemplary embodiments of a semiconductor layer structure, in which a refractive index n (right ordinate) and a field amplitude A of the optical radiation field (left ordinate) are specified as a function of the vertical position z within the semiconductor layer structure (abscissa) , Based on the same vertical position z, the respective layer sequence is shown above the diagrams, the layers being given the same reference numerals as those in FIG 1 are introduced. The vertical position z within the semiconductor layer structure is that of the active layer 6 remote interface of the p-contact layer 10 calculated against the growth direction in nm. Of course, the position reference can be chosen arbitrarily, for example, could be a side of the superlattice 9 be used as a position reference.

Since layers of different composition have different refractive indices, the layer structure of the representation of the refractive index n as a function of the vertical position z within the semiconductor layer structure can be read off. GaN layers have a refractive index n of about 2.52. The refractive index n of AlGaN layers decreases with increasing Al content from this value. In the in the 2 - 5 The embodiments shown are the p-contact layer 10 , the p-waveguide layer 8th and the n-waveguide layer 5 GaN layers. The barrier layer 7 and the n-cladding layer 4 are AlGaN layers, where the barrier layer 7 a high and the n-cladding layer 4 has an average Al content. As a dopant for p-type doping Mg and Si can be used as a dopant for n-doping.

The superlattice 9 is formed by 10 alternately stacked GaN / AlGaN layers. Again, the number of layers is only exemplary and not too large because of the clarity. Typically, the superlattice has 9 a greater number of layers, for example, tens to hundreds of layers of each composition. In analogy to 1 In the following, the GaN layers are referred to as layers of a first composition a with the reference symbol 9a and the AlGaN layers as layers of a second composition b with the reference numeral 9b , The superlattice points to its on the p-contact layer 10 adjacent side (left side in the diagrams) a GaN layer 9a on and on its to the p-waveguide layer 8th adjacent side (right side in the diagrams) an AlGaN layer 9b , The superlattice 9 acts as a p-shell layer.

The field amplitude A of the optical radiation field, the operation of the semiconductor layer structure in the active layer 6 is given in arbitrary units on the left ordinate. The field amplitude A shows in all embodiments, a bell-curve-like course with a normalized to the value of 1 maximum in the active layer 6 , The drop in field strength on both sides of the active layer 6 is determined by the course of the refractive index n.

For the layers of the superlattice 9 In addition, the dopant concentration c, also called doping level, is indicated by a bar chart superimposed on the representation. Like the field amplitude A, the doping degree c is given in arbitrary units on the left-hand abscissa. Unless otherwise described in the individual case, the illustrated dopant concentration c refers to the substance used for p-doping, eg Mg.

At the in 2a shown embodiment of a semiconductor layer structure, all GaN layers 9a of the superlattice 9 an equal dopant concentration c (constant doping within the GaN layer group). The AlGaN layers 9b have the same dopant concentration c, except that of the p-type waveguide layer 8th adjacent layer (right side of the superlattice 9 in the diagram). This layer is undoped, wherein in the context of the application under an undoped layer a nominal, ie within technically measurable and controllable limits, undoped layer is to be understood.

At the in 2 B not only the embodiment shown directly to the p-waveguide layer 8th adjacent AlGaN layer, but also the next GaN layer undoped. As in 2a are the rest of the layers 9a and 9b constantly doped with the same dopant concentration c (homogeneous doping in this area).

From the course of the field amplitude A, it can be seen that in the operation of the active layer 6 generated radiation penetrates with almost 80% of its maximum amplitude in the superlattice. A comparison of the absorption coefficients for radiation of a wavelength of 400 nm shows, for example, that Mg-doped GaN (dopant concentration 4 × 10 ¹⁹ cm ^-3 ) has a 10-fold higher absorption coefficient than undoped GaN ( Source: M. Kumerato et al., Phys. stat. sol. 2002, Vol. 192, No. 2, p. 329 ). In particular in the range of high field strengths A, absorption losses in the superlattice can thus be achieved by using undoped or only very low doped layers 9 reduce. To a decrease in the conductivity of the superlattice caused by the use of undoped or only very low doped layers 9 counteract, the dopant concentration c in the remaining layers may be slightly higher compared to a superlattice which is homogeneously doped over all layers. Due to the linearly decreasing field amplitude A, slightly higher absorption losses associated with the increased doping level of the remaining layers are smaller than the reduction of the absorption losses by the undoped layers. The superlattice 9 has thus effectively (in the sum of all layers 9a and 9b ) a lower absorption at the same conductivity than known from the prior art superlattice.

The same effect also occurs with the in 3a and 3b shown embodiments. In both cases, the dopant concentration c is constant within a layer group, except for the p-waveguide layer 8th adjacent undoped layers. In the example of 3a are each a GaN layer 9a and an AlGaN layer 9b undoped; in the example of 3b are a GaN layer 9a and two AlGaN layers 9b undoped. Unlike the ones in the 2 Illustrated embodiments here is the doping level of the constantly doped GaN layers 9a however, in one case larger ( 3a ) and in the other case smaller ( 3b ) as the doping level of the AlGaN constant-doped layers 9b , In particular, the in 3b shown case where the AlGaN layers 9b are doped higher than the GaN layers 9a , is suitable for high conductivity of the superlattice 9 to achieve low optical absorption. The absorption coefficient is for radiation of the active layer 6 , which may be between 330 nm and 480 nm, for example, because of the larger band gap for AlGaN lower than for GaN. For this reason, the doping degree of AlGaN layers 9a higher than that of the GaN layers 9b without this leading to a strong absorption in the superlattice 9 leads.

4 shows three further embodiments of a semiconductor layer structure. Common to these examples is that within one or both layer groups, the dopant concentration c for layers in a region of the superlattice 9 is constant and decreases linearly in another area.

In the example of 4a is the dopant concentration c respectively in the first 6 of the p-contact layer 10 facing AlGaN and GaN layers 9b . 9a (left side in the diagram) constant and the same for both layer types. In the next four, the active layer 6 facing layers, the dopant concentration c linearly drops to zero.

The embodiment in 4b shows a fundamentally similar course of the doping. Here, the constant range extends to 4 layers each, with the doping level for GaN layers 9a higher than for AlGaN layers 9b , In each of the 6 layers following in the direction of the active layer, the dopant concentration c within each layer group decreases linearly to a value which is different from zero.

In the example of 4c the dopant concentration c runs within the superlattice 9 for the GaN layers 9a as in the example of 4b , the degree of doping of the AlGaN layers 9b however, is constant at a low level.

In the embodiments of 4 is by moving towards the active layer 6 over several layers extending waste the doping degree, and thus the absorption coefficient of the layers, even better adapted to the course of the field amplitude A as in the embodiments of the 2 and 3 ,

A problem with devices with Mg-doped layers is that the dopant Mg can migrate by diffusion processes in the active zone during operation of the device, resulting in high optical absorption losses there. In the described superlattices 9 results in this regard as a further advantage that the undoped or lightly doped, the active layer 6 facing layers represent concentration decreases for diffusing Mg and thus a migration of Mg into the active layer 6 counteract.

Alternatively, it can also be provided in all exemplary embodiments shown to use Si n-doped layers instead of the undoped layers. The absorption coefficient of Si-doped GaN layers lies between that of an undoped layer and a layer doped with Mg (with the same dopant concentration c as in the case of Si). Possibly, a slightly lower conductivity may result than in the case of undoped layers, a formation of line inhibiting, operated in the reverse direction However, pn transitions do not occur with layers of a thickness typically provided in the superlattice.

Even with the use of Si-doped layers within the superlattice optical absorption losses are reduced and simultaneously a high conductivity of the superlattice 9 reached. In addition, Si-doped layers act as a diffusion barrier for diffusing Mg and thus act in a similar way as undoped layers migrate from Mg to the active layer 6 into it.

Generalized can the course of the dopant concentration c, also called doping profile, within the superlattice 9 by an (envelope) function indicating the dopant concentration c of a layer depending on the position of the layer. In this case, either a common function for all groups of layers can be specified, such as in the embodiments of the 2a . 2 B . 4a and 5a (see below), or it can be given for each layer group its own function, such as in the 3a . 3b . 4b . 4c and 5b (see below). The embodiments of the 2 and 3 can be described by step functions, which are the 4 by a superposition of step function and linear function. In principle, however, any arbitrary, eg non-linear, function course is possible.

Examples of semiconductor layer structures with non-linear doping profiles are in 5 shown. In the example of 5a is the course of the dopant concentration c for both layer groups (layers 9a . 9b ) equal. The course is towards the active layer 6 Overlinear monotonically decreasing and approximately mirror-image adapted to the course of the field amplitude A, so that there is a low optical absorption in areas of high field strength. In low field strengths, the absorption coefficient is high, but there is only a low absolute optical absorption. An optimum between low overlap of the optical radiation with strongly absorbing regions and nevertheless good electrical conductivity can be achieved.

In the example of 5b is the doping profile for the GaN and AlGaN layers 9a . 9b differently. For the strongly absorbing GaN layers 9a is again one towards the active layer 6 sloping course of the dopant concentration c provided. In the case of the AlGaN layers, which in principle are less strongly absorbing due to their larger band gap 9b is the course to compensate for the electrical conductivity tends to be reversed. This embodiment shows a good compromise between low optical absorption and good electrical conductivity in the event that the total Mg dopant level within the superlattice 9 should be limited. Without this restriction is also conceivable, all AlGaN layers 9b to dope with a constantly high Mg concentration.

Within a layer, the dopant concentration c in the superlattice 9 be constant or graded. Examples in which within a non-constant doping profile the doping level is not constant even within a layer are shown in FIGS 4 . 5a and 5b (here only GaN layers 9a ). In this case, the dopant concentration c within a layer follows the course of the (envelope) function. For the AlGaN layers 9b in 5b In contrast, the doping level varies within the layer groups, but is constant for each individual layer. In such a case, the value of the (envelope) function at a fixed position within each layer, eg in the middle of a layer, for example, defines the dopant concentration c for the entire layer. A graded doping level within a layer can aid the conductivity-enhancing effect of a superlattice.

The within a layer group and also within a layer of the superlattice 9 actual course of the dopant concentration c may, for example by diffusion processes, deviate from the nominally predetermined in the manufacturing process concentration curve. In practice, this deviation may manifest itself, for example, in a softening or smearing of stages or regions with a high concentration gradient, which has an effect on the basic properties of the superlattice according to the invention 9 but does not affect and its advantages over known, homogeneously doped superlattices does not diminish.

The explanation The invention with reference to the described embodiments is not as restriction to understand the invention thereto. Rather, the invention includes also the combination with all others in the embodiments and the other description, even if these Combination are not the subject of a claim.

Claims (17)

Semiconductor layered structure comprising a superlattice ( 9 ) of alternating stacked layers ( 9a . 9b ) of III-V compound semiconductors of a first composition (a) and at least one second composition (b), wherein the layers ( 9a . 9b ) Dopants in predetermined concentrations and wherein the concentrations of the dopants in at least two layers of a same composition in the superlattice ( 9 ) are different. Semiconductor layered structure according to Claim 1, in which the superlattice ( 9 ) has alternately stacked In _x Al _y Ga _1-xy N and In _w Al _z Ga _1-wz N layers with 0 ≦ x, y, w, z ≦ 1 and x + y ≦ 1 and w + z ≦ 1 , Semiconductor layered structure according to Claim 1, in which the superlattice ( 9 ) alternately stacked In _x Al _y Ga _1-xy P and In _w Al _z Ga _1-wz P layers with 0 ≤ x, y, w, z ≤ 1 or alternately stacked In _x Al _y Ga _1-xy As- and In _w Al _z Ga _1-wz As layers with 0≤x, y, w, z≤1 and x + y≤1 and w + z≤1. Semiconductor layered structure according to one of Claims 1 to 3, in which individual layers of the superlattice ( 9 ) is assigned a vertical position z within the semiconductor layer structure and the concentration of the dopants of a layer ( 9a . 9b ) in a predetermined manner depending on its vertical position z within the semiconductor layer structure. Semiconductor layer structure according to claim 4, wherein the dependence of the concentration of the dopants on the vertical position z for all layers ( 9a . 9b ) of the superlattice ( 9 ) is given by a common function. A semiconductor layered structure according to claim 4, wherein the dependence of the concentration of dopants on the vertical position z for layers ( 9a ) of the first composition (a) by a first function and for layers ( 9b ) of the at least one second composition (b) is predetermined by at least one second function. Semiconductor layer structure according to one of claims 5 or 6, in which the first and / or the at least one second and / or the common function is a step function or a monotonically increasing / decreasing one Function or a linear function or a polynomial function or a root function or an exponential function or a logarithmic function or a periodic function or superposition of said Functions is or contains portions of one of these functions. Semiconductor layered structure according to one of Claims 1 to 7, in which the concentration of the dopants within at least one layer ( 9a . 9b ) of the superlattice ( 9 ) is constant. Semiconductor layered structure according to one of Claims 1 to 8, in which the concentration of dopants within at least one layer ( 9a . 9b ) of the superlattice ( 9 ) is graded. Semiconductor layered structure according to one of Claims 1 to 9, in which all layers ( 9a . 9b ) of the superlattice ( 9 ) are doped with the same dopant. Semiconductor layered structure according to one of Claims 1 to 9, in which the superlattice ( 9 ) Has layers doped with different dopants. Semiconductor layered structure according to one of Claims 1 to 9, in which the superlattice ( 9 ) has at least one layer which is undoped. Semiconductor layer structure according to one of claims 1 to 12, in which the dopants Mg and / or Si are. Optoelectronic component, the semiconductor layer structure according to one of claims 1 to 13 has. Optoelectronic component according to Claim 14, which has an optically active layer ( 6 ) and in which the concentration of the dopants in layers of at least one of the compositions (a, b) within the superlattice (US Pat. 9 ) of the semiconductor layer structure increases with increasing distance from the optically active layer. Optoelectronic component according to one of claims 14 or 15, which is a light emitting diode. Optoelectronic component according to one of claims 14 or 15, which is a laser diode.