FIELD OF THE INVENTION 
     The invention relates to an optoelectronic component with an adjustable property and a method for producing an optoelectronic semiconductor component. 
     BACKGROUND OF THE INVENTION 
     Optoelectronic components, e.g. with a planar optical waveguide structure, comprising buffer layer, core layer and covering or cladding layer, are fixed constituent parts of optical fiber transmission technology. 
     In this case, it is known that said components comprising different layers are constructed successively; a layer structure is produced. Typical layer production methods are e.g. PVD, CVD, PECVD, flame hydrolysis. Semiconductor layers, metal layers or SiO 2  layers are used as the layers. 
     In this case, it is in some instances necessary in a targeted manner to incorporate layers having a defined optical refractive index in said layer structure. In the layers in which the refractive index is intended to be changed in a targeted manner, it is necessary to interrupt the layer construction and to introduce a new adapted layer having a changed refractive index either over the whole area or locally by patterning methods. This interrupts the construction of the layer structure and thus costs valuable process time. Moreover, the production difficulties increase with every layer that is additionally required. 
     SUMMARY OF THE INVENTION 
     The present invention is based on the object of providing an optoelectronic component with a layer structure, in which the optical properties of at least one layer, in particular of an optical waveguide, can be changed by means of a simple method step. 
     This object is achieved according to the invention by means of an optoelectronic component having the features of claim  1 , in that at least one irradiation-sensitive structure is arranged in the layer structure, the refractive index of the irradiation-sensitive structure being able to be permanently altered in a manner dependent on an irradiation. The refractive index of the irradiation-sensitive structure can be altered by an irradiation even if the entire layer structure has already been produced, i.e. an interruption of the construction for the targeted introduction of a layer having a different refractive index is not necessary. 
     In an advantageous refinement of the invention, the layer structure (in which the irradiation-sensitive structure is embedded) comprises SiO 2 , SiO 2 —B 2 O 3  and/or SiO 2 —B 2 O 3 —P 2 O 5  or has proportions of at least one of said substances. 
     In this case, it is advantageous if the irradiation-sensitive structure has a doping made of germanium oxide. Furthermore, it is advantageous if the irradiation-sensitive structure has a doping made of hydrogen. As an alternative, it is advantageous if the irradiation-sensitive structure has
     a) germanium oxide and hydrogen,   b) tin oxide,   c) tin oxide and germanium oxide,   d) germanium oxide
 
as doping. These dopings make it possible to alter the refractive index of the structure in a targeted manner and permanently by means of an irradiation.
   

     In this case, it is advantageous if the irradiation-sensitive structure is arranged in a core layer of a waveguide structure. It is also possible to arrange the irradiation-sensitive structure in a buffer layer or a covering layer of a waveguide structure. Different components can be constructed depending on the vertical positioning of the irradiation-sensitive structure. 
     The irradiation-sensitive structure is advantageously arranged over the whole area in a layer or locally in a layer, in particular as a grating structure. A grating structure may be used e.g. for a laser diode. 
     It is an advantage if the optoelectronic component according to the invention is designed as a vertical coupler or as a laser diode. 
     The irradiation-sensitive structure is advantageously part of a layer structure comprising SiO 2  layers with different layer dopings. 
     The object is also achieved by means of a method in which
     a) an irradiation-sensitive structure is applied to a layer of a layer structure or to a substrate and afterward   b) a radiation is radiated onto the irradiation-sensitive structure in order to alter the refractive index of the irradiation-sensitive structure in a targeted manner.   

     The irradiation is advantageously an electromagnetic radiation, in particular UV light in the wavelength range of between 190 and 250 nm. It is also possible for the irradiation to have a particle radiation, in particular an ion radiation, electron radiation or neutron radiation. 
     For the further construction of the optoelectronic component, in an advantageous manner, after the irradiation, at least one layer is arranged above the irradiation-sensitive structure. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The invention is explained in more detail below using a plurality of exemplary embodiments with reference to the figures of the drawings, in which: 
         FIGS. 1A to 1C  show diagrammatic sectional views of a layer structure of an optoelectronic semiconductor component according to the prior art; 
         FIGS. 2A and 2B  show diagrammatic sectional views of one embodiment of an optoelectronic semiconductor component according to the invention; 
         FIGS. 3A to 3D  show diagrammatic sectional views of embodiments of an optoelectronic semiconductor component with a different arrangement of an irradiation-sensitive structure; 
         FIGS. 4A and 4B  shows diagrammatic sectional views of two further embodiments of optoelectronic semiconductor components according to the invention; 
         FIG. 5  shows a diagrammatic illustration of a functional relationship between refractive index and material composition with the irradiation as parameters. 
     
    
    
     DESCRIPTION OF THE INVENTION 
       FIGS. 1A to 1C  are used to illustrate how layer structures  1  of optoelectronic components according to the prior art are constructed. Optoelectronic components with layer structures, such as e.g. laser diodes, photodiodes or optocouplers, are known per se, so that only the layer structures of the optoelectronic components are represented here for illustration purposes. 
     In this case, the known construction of a waveguide structure of an optoelectronic component is illustrated here as an example. The construction begins with a buffer layer  11  and a core layer  12  on a substrate  30  ( FIG. 1A ), afterward a layer having a changed refractive index  2  is arranged on or in the core layer  12  ( FIG. 1B ). The core layer  12  is then constructed further and then terminated by the covering layer  13  ( FIG. 1C ). 
     The respective layers  2 ,  11 ,  12 ,  13  are applied by different methods: semiconductor layers are deposited epitaxially and doped SiO 2 /Si layers are deposited by means of flame hydrolysis or PECVD. 
     In the layer in which the intention is to achieve a change in the refractive index, it is necessary, in accordance with the prior art, to interrupt the growth or the deposition ( FIG. 1A ), to introduce a new adapted layer having a changed refractive index either over the whole area or locally by patterning methods, and afterward to continue the original growth or deposition (see  FIGS. 1B and 1C ). 
     In this case, what is disadvantageous, in particular, is that the deposition or growth process has to be interrupted. It is also necessary to deposit an additional layer  2  in order to influence the refractive index. Moreover, the overgrowth of this locally patterned additional layer  2  is not without problems. 
       FIGS. 2A and 2B  illustrate one embodiment of the optoelectronic component according to the invention and the production thereof, which avoids these disadvantages. 
     An optoelectronic component according to the invention has an irradiation-sensitive structure  10 ′ (the index “′” designates an irradiation-sensitive structure before an irradiation), with which the refractive index can be altered in a targeted manner, e.g. after the application of the layers. 
     Here, too, a waveguide structure is chosen as an example, it also being possible, in principle, to use an irradiation-sensitive structure  10 ′ in other optoelectronic semiconductor components, e.g. a laser diode. 
       FIG. 2A  illustrates that firstly all the layers  10 ′,  11 ,  12 ,  13  are applied or deposited successively without interruption either epitaxially or by means of flame hydrolysis or PECVD. In principle, further methods, such as PVD or CVD, are also possible. 
     At the place where the layer region having the changed refractive index is subsequently intended to be produced, an irradiation-sensitive structure  10 ′ is deposited in this case (here in the core layer  12  of the waveguide structure). This irradiation-sensitive structure  10 ′ may be arranged over the whole area in a plane or only locally. 
     The difference with respect to the adjacent layers (buffer layer  11 , covering layer  13 , core layer  12 ) is that the latter are in contrast not irradiation-sensitive. 
     This is achieved, as illustrated in  FIG. 2B , in that the irradiation-sensitive structure  10 ″ (“″” denotes irradiation-sensitive structure after the irradiation) contains at least one additional suitable dopant which reacts to a targeted irradiation. Without irradiation, said dopant has no influence on the refractive index in said structure  10  and the embedding thereof, i.e. the same refractive index as that of the surrounding medium is present. 
     In the present case, the irradiation-sensitive structure  10 ′ would have the same refractive index as the surrounding core layer  12  before the irradiation  20 . 
       FIG. 2B  illustrates that, by means of targeted irradiation  20 , the irradiation-sensitive dopant in the irradiation-sensitive structure  10 ′ is excited and the refractive index changes to the new desired value in this layer region. This relationship is described in more detail in  FIG. 5 . 
     In this case, it must be ensured that after the irradiation has been switched off, this change in the refractive index remains in the irradiation-sensitive structure  10 ″ and does not revert to the initial value. 
     This method makes it possible to realize local buried structures in a targeted manner at complete layer sequences. It is also possible to simultaneously monitor the change obtained in the refractive index by means of suitable measurement methods. 
     In this case, it is possible to alter the refractive index of an entire layer over the whole area, or a local region. 
     UV light in a wavelength range of between 190 and 250 nm is used here as the irradiation  20 . Germanium oxide and hydrogen, which, under UV light, alter their configuration in the core layer  12  and thus change the refractive index in a targeted manner, are used here as the dopant of the irradiation-sensitive structure  10 , which is part of a layer structure comprising e.g. SiO 2  layers with different layer dopings. As an alternative, germanium oxide and hydrogen alone are also possible as the dopant. Tin oxide and germanium oxide in combination or germanium oxide alone are also possible as dopants. 
     As an alternative, electromagnetic beams having a different wavelength may also be used. Particle beams, such as e.g. ions or neutrons, are also possible as an alternative or in addition. In this case, it is essential to coordinate the type of irradiation with the dopant in the irradiation-sensitive structure  10 . 
     It is thus possible for all the required layers  11 ,  12 ,  13  to be deposited completely without any interruption. The targeted change in the refractive index only takes place afterward. 
       FIGS. 3A to 3D  illustrate four embodiments of a layer structure in which locally irradiation-sensitive structures  10 ″ are arranged in different planes with a changed refractive index after the irradiation, a construction of the layer structure of substrate  30 , buffer layer  11 , core layer  12  and covering layer  13  being present. 
     In  FIGS. 3A to 3D , the irradiation-sensitive structure  10  is in each case designed as a grating structure. 
       FIG. 3A  shows an arrangement of the irradiation-sensitive structure  10 ″ in the buffer layer  11 . 
       FIG. 3D  illustrates an arrangement of the irradiation-sensitive structure  10 ″ in the covering layer  13 . The choice of the distance between the irradiation-sensitive structures  10  and the core layer  12  enables a defined overcoupling or crosstalk of light from the core layer  12  into another waveguide (or vice versa). 
     If these regions, as shown in  FIGS. 3B to 3C , are designed in the form of grating structures, then two applications result depending on the dimensioning: 
     If the grating structure (i.e. the irradiation-sensitive structure  10 ″ after the irradiation) is situated in the upper edge of the core layer  12 , then it enables light to be coupled out from the waveguide, e.g. for monitor applications (see T. Erdogan, “Fiber Gratings”, Photonics Spectra, January 1998, page 98-97). 
     If the grating structure (i.e. the irradiation-sensitive structure  10 ″ after the irradiation) extends over the entire vertical thickness d of the core layer  12 , then a waveguide selectivity is obtained in the transmission behavior (e.g. Bragg grating, see e.g. R. März: “Integrated Optics: Design and Modelling”, Artech House, Boston, 1995, Seiten page 231 et seq). 
       FIGS. 4A and 4B  illustrate two further embodiments of optoelectronic components according to the invention. The basic construction of the structure corresponds to that in  FIGS. 1 ,  2  and  3 , so that reference may be made to this description. 
       FIG. 4A  shows a planar optical waveguide structure in which part of the light guided in the core layer  12  is coupled out through the introduction of a specially dimensioned local grating structure  10 ″ in the form of an irradiation-sensitive structure. This coupled-out light may be captured e.g. by a monitor diode provided on the upper edge of the planar waveguide structure (light power measurement). 
       FIG. 4B  illustrates the principle of a vertical coupler. In this case, in the covering layer  13 , at a specific distance from the core layer  12 , by means of the targeted irradiation, a waveguide is generated in/from an irradiation-sensitive layer  10 ″, said waveguide usually having the same dimensions and the same refractive index as the core layer  12 . 
       FIG. 5  diagrammatically shows the relationship between the refractive index of an irradiation-sensitive structure and the material composition thereof. 
     As mentioned above, the irradiation-sensitive structure contains an additional suitable “dopant” which reacts to a targeted irradiation. What is important in this case is that said “dopant” has no influence on the refractive index without irradiation in said layer (material system C-D), i.e. the same refractive index as that of the surrounding medium (material A-B) is present. By means of targeted irradiation, the irradiation-sensitive dopant is excited and changes the refractive index to the new desired value in this layer region. In this case, it has to be ensured that, after the irradiation has been switched off, this change in the refractive index remains and does not revert to the initial value. 
     Appropriate material systems are, inter alia, semiconductors (e.g. Si, InGaAlAs), dielectrics (e.g. SiO 2 ) and plastics (e.g. polymers) 
     The embodiment of the invention is not restricted to the preferred exemplary embodiments specified above. Rather, a number of variants are conceivable which make use of the optoelectronic semiconductor component according to the invention and the method for producing said component also in the case of embodiments of fundamentally different configuration. 
     LIST OF REFERENCE SYMBOLS 
     
         
           1  Layer structure 
           10  Irradiation-sensitive structure (′: before the irradiation, ″ after the irradiation) 
           11  Buffer layer 
           12  Core layer 
           13  Covering layer 
           20  Irradiation 
           30  Substrate 
         d Thickness of the core layer
The invention relates to an optoelectronic component and a method for producing it, in particular a waveguide structure, featuring at least one irradiation-sensitive structure in a layer structure of the optoelectronic component, the refractive index of the irradiation-sensitive structure being able to be permanently altered in a manner dependent on an irradiation. It is thus possible to change the properties of at least one layer, in particular of an optical waveguide, in a targeted manner by means of a simple method step.