Abstract:
A light-emitting semiconductor component includes a thin film stack having a front side and a rear side, a photon-emitting zone formed in an active layer, and contact points formed on the front side and rear side of the thin film stack to impress current into the active layer. The photon-emitting zone is separated physically from the contact points in the plane of the thin film stack. As a result, the absorption of the radiation at the contact points can be minimized.

Description:
BACKGROUND OF THE INVENTION 
     Field of the Invention 
     The invention relates to a light-emitting semiconductor component including a thin film stack having a front side, a rear side, an active layer formed with a photon-emitting zone therein, and contact points formed on the front side and rear side of the thin film stack for impressing current into the active layer. 
     Thin film light-emitting diodes are known, for example, from Published European Patent Application EP 0 905 797 A. The thin film principle is in this case based on internal multiple reflections, combined with internal scattering of the light rays. In this case, the designation “thin” relates in functional terms to the optical thickness of the light-emitting diode. Between two scattering reflections, the absorption suffered by a light ray should be as low as possible. 
     SUMMARY OF THE INVENTION 
     It is accordingly an object of the invention to further reduce the light absorption in generic light-emitting semiconductor components and in this way to increase the external efficiency of the component. 
     With the foregoing and other objects in view there is provided, in accordance with the invention, a light-emitting semiconductor component including: a thin film stack having a front side and a rear side, the film stack including an active layer formed with a photon-emitting zone; and a plurality of contact points for impressing current into the active layer, the plurality of the contact points formed on the front side and the rear side. The photon-emitting zone is separated physically from the plurality of the contact points. 
     In accordance with an added feature of the invention, the active layer is formed with interruptions physically separating the photon-emitting zone from the plurality of the contact points. 
     In accordance with an additional feature of the invention, the film stack is formed with a plurality of cutouts interrupting the active layer in regions above ones of the plurality of the contact points on the rear side. 
     In accordance with another feature of the invention, the film stack includes a plurality of regions adjoining the plurality of the cutouts; and the plurality of the regions are formed with at least partly oblique flanks for scattering light. 
     In accordance with a further feature of the invention, the film stack is formed with a cutout interrupting the active layer in a region around one of the plurality of the contact points on the front side. 
     In accordance with a further added feature of the invention, the film stack includes a region adjoining the cutout; and the region is formed with at least partly oblique flanks for scattering light. 
     In accordance with a further additional feature of the invention, a sheathing layer electrically connects the photon-emitting zone to the plurality of the contact points. 
     In accordance with another added feature of the invention, the sheathing layer has a thickness; and a ratio of the distance between the photon-emitting zone and the nearest one of the plurality of the contact points to the thickness of the sheathing layer is between 1 and 20, inclusive, and even more preferably is between 1 and 10, inclusive. 
     In accordance with another further feature of the invention, the rear side has a total area; and ones of the plurality of the contact points that are on the rear side assume an area of 2% to 25% of the total area of the rear side, and even more preferably assume an area of 5% to 15% of the total area of the rear side. 
     In accordance with an added feature of the invention, ones of the plurality of the contact points on the rear side are a plurality of mutually spaced apart contact points. 
     In accordance with an additional feature of the invention, one of the plurality of the contact points is formed on the front side and defines a central middle contact point. 
     In accordance with another feature of the invention, ones of the plurality of the contact points on the rear side are a plurality of mutually spaced apart contact points; one of the plurality of the contact points is formed on the front side and defines a central middle contact point; and the plurality of the mutually spaced apart contact points on the rear side are configured on a circumference of a circle and are concentrically configured with respect to the middle contact point on the front side. 
     In accordance with a further feature of the invention, a highly reflective mirror layer is configured on the rear side, except for locations of ones of the plurality of the contact points on the rear side. 
     In accordance with a further added feature of the invention, there is provided, a first sheathing layer having a roughened front side. The first sheathing layer is formed on the front side of the film stack, at least in the photon-emitting zone. 
     In accordance with a further additional feature of the invention, there is provided, a second sheathing layer having a roughened rear side. The second sheathing layer is formed on the rear side of the film stack, at least in the photon-emitting zone. 
     In accordance with another added feature of the invention, the film stack has a thickness between 3 μm and 50 μm. 
     In accordance with another further added feature of the invention, the film stack has a thickness between 5 μm and 25 μm. 
     In accordance with yet an added feature of the invention, the film stack has a layer sequence based on Al x Ga y In 1−x−y P, with 0≦x≦1, 0≦y≦1 and x+y≦1. 
     In accordance with yet an additional feature of the invention, the film stack includes sheathing layers with material originating from the Al x Ga (1−x) As material system, with 0≦x≦1. 
     In accordance with yet another feature of the invention, the active layer is configured between the sheathing layers; and the active layer has material that originates from a material system described by a general formula Al x Ga y In 1−x−y P, with 0≦x ≦1, 0≦y≦1 and x+y≦1. 
     In accordance with yet a further feature of the invention, the film stack has a layer sequence based on Al x Ga (1−x) As with 0≦x ≦1. 
     In accordance with yet a further added feature of the invention, the film stack has layers defining planes running through the film stack and through the plurality of the contact points. 
     With the foregoing and other objects in view there is also provided, in accordance with the invention, an infrared-emitting luminescent diode including: a thin film stack having a front side and a rear side, the film stack including an active layer formed with a photon-emitting zone; and a plurality of contact points for impressing current into the active layer. The plurality of the contact points are formed on the front side and the rear side, and the photon-emitting zone is separated physically from the plurality of the contact points. 
     According to the invention, in a light-emitting semiconductor component of the type mentioned at the beginning, the photon-emitting zone is arranged physically separated from the contact points in the plane of the thin film stack. 
     The invention is therefore based on the idea of physically separating the electric contact points and the light-producing areas to keep the light produced in the active zone away from the contact points. Since the contact points with their typical reflectivity of only about 30% contribute substantially to the absorption of the radiation propagating in the thin film stack, the intended aim of reducing the overall absorption is achieved as a result. 
     In a preferred refinement, the photon-emitting zone is separated physically from the contact points by interruptions in the active layer. 
     In particular, the thin film stack can advantageously have cutouts interrupting the active layer in a region above the rear-side contact points. 
     Likewise, the thin film stack can advantageously have cutouts interrupting the active layer in a region around the upper side contact points. 
     As a result of interrupting the active layer, the cutouts have the effect of physically separating the light-producing zone from the contact points of the upper or rear side of the film thin stack. 
     The regions of the thin film stack that adjoin the cutouts preferably have at least partly oblique flanks to scatter light. As a result, the scattering processes needed for the thin film light-emitting diode are already made possible by the etching process required to produce the cutouts. An additional process step can be dispensed with. 
     However, the scattering processes can be introduced in another way, in particular by providing a first sheathing layer with a roughened front side formed on the upper side of the thin film stack, at least in the photon-emitting zone. Alternatively or additionally, a second sheathing layer with a roughened rear side can be formed on the rear side of the thin film stack, at least in the photon-emitting zone. 
     The photon-emitting zone is expediently connected electrically to the contact points via a sheathing layer. This ensures the electrical contact for feeding current into the active layer. At the same time, the propagation of the radiation produced in the photon-emitting zone is low over the comparatively thin sheathing layer. 
     The ratio of the distance of the photon-emitting zone from the nearest contact point to the thickness of the electrically connected sheathing layer is advantageously between and including 1 and 20, and even more preferably between and including 1 and 10. 
     In a preferred refinement, the proportion of the contact points applied to the rear side of the thin film stack assumes an area of 2% to 25%, and even more preferably an area of 5% to 15%, of the total area of the rear side. 
     In this case, the contact points applied to the rear size of the thin film stack can be formed as a plurality of mutually spaced contact points. 
     The contact points applied to the front side of the thin film stack can in particular be formed by a central middle contact point. 
     In a particularly preferred refinement, the contact points of the rear side are arranged on the circumference of a circle and are concentrically arranged with respect to a middle contact point of the front side. 
     The rear side of the thin film stack, with the exception of the area of the contact points, is expediently provided with a highly reflective mirror layer, which for example, consists of a dielectric such as SiN, SiO 2  or the like and a metallization such as Au, Ag, Al or the like. 
     The thin film stack preferably has a thickness between 3 μm and 50 μm, and even more preferably between 5 μm and 25 μm. 
     In an expedient refinement, the thin film stack has a layer sequence based on Al x Ga y In 1−x−y P, where 0≦x≦1, 0≦y≦1 and x+y≦1. The material of the sheathing layers in this configuration can alternatively originate from the Al x Ga (1−x) As material system. Likewise, the inventive arrangement can also be used for thin film stacks wholly based on the Al x Ga (1−x) As material system, such as for infrared-emitting luminescent diodes. 
     Other features which are considered as characteristic for the invention are set forth in the appended claims. 
     Although the invention is illustrated and described herein as embodied in a light-emitting semiconductor component, it is nevertheless not intended to be limited to the details shown, since various modifications and structural changes may be made therein without departing from the spirit of the invention and within the scope and range of equivalents of the claims. 
     The construction and method of operation of the invention, however, together with additional objects and advantages thereof will be best understood from the following description of specific embodiments when read in connection with the accompanying drawings. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a schematic cross-sectional view of a first exemplary embodiment of a light-emitting semiconductor component; 
     FIG. 2 is a schematic plan view of the semiconductor component shown in FIG. 1, which shows rear side contact points. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Referring now to the figures of the drawing in detail and first, particularly, to FIG. 1 thereof, there is schematically shown a cross sectional view through a thin film light-emitting diode  10  including a thin film stack  12 , which is fitted to a conductive carrier substrate  2  provided with metal contacts  4 ,  6 . The electrical and mechanical connection of the thin film stack  12  to the carrier substrate  2  is produced in a manner known per se, and will therefore not be described further below. 
     The thin film stack  12  contains a p-doped first sheathing layer  20 , which for example, has AlGaInP or AlGaAs, an active layer  22 , which for example, has AlGaInP, and an n-doped second sheathing layer  24 , which for example, has AlGaInP or AlGaAs. The conductivity types of the first and second sheathing layer can also be interchanged. 
     The first and second sheathing layer  20 ,  24  and the active layer  22  can in this case be both individual layers and formed from a plurality of part layers, in particular of the same conductivity type, but of different material compositions. 
     Fitted to the front side  16  of the second sheathing layer  24  is a central middle contact  26 , which in the exemplary embodiment, represents the n contact of the light-emitting diode, and for example, can be fabricated from a conventional metallic material suitable for this purpose. Electrical contact with the p side is made via the metal layers  6  and  4  of the conductive carrier substrate  2 , which for example, can again be fabricated from conventional metallic materials suitable for the purpose. A p contact layer of the thin film stack has a continuous contact layer  30 , which is connected electrically to the metal layer  4  applied to the front side of the carrier substrate  2  and can also be fabricated from a conventional suitable metallic material. 
     However, current is not fed into the active layer over the entire area of the contact layer  30 , but only at specific alloyed contact points  32 . As can best be seen in FIG. 2, the total area of the alloyed contact points  32  occupies only a small part of the base area of the light-emitting diode. In the exemplary embodiment, the contact points  32  have, for example, a proportion of 5% of the base area. Other proportions however, in the range from about 3% to about 15% also supply good or very good results. 
     The region of the rear side  14  of the thin film stack  12  in which no contact points  32  are alloyed is occupied by a highly reflective, non-alloyed mirror  34 . This can consist, for example, of a dielectric such as SiN, SiO 2  or the like and a metallization such as Au, Ag, Al or the like. 
     The contact points  32  are arranged on the rear side  14  spaced apart from one another on the circumference of a circle concentrically with respect to the middle contact of the front side  16 . 
     In a region above the contact points  32 , in each case the second sheathing layer  24  and the active layer  22  are removed, for example by etching, so that cutouts  36  are produced in the thin film stack. As FIG. 1 shows, the first sheathing layer  20  is also thinned. However, care must be taken here that the remaining residual thickness of the sheathing layer  20  is still sufficient to permit subsequent alloying of the contact points  32 . In addition, a sufficiently high transverse conductivity must remain in order to carry the current into the adjacent zone  40  producing photons. In this case, a remaining residual thickness of the sheathing layer  20  of about 1 μm has proven to be adequate for the AlGaInP/AlGaAs material system. 
     As a result of removing the second sheathing layer  24  and the active layer  22  over the contact points  32 , the production of light over the contact points  32  is prevented. The light produced in the zones  40  producing photons can then penetrate into the areas of the contact points  32  only over the residual height of the first sheathing layer  20 , and is therefore drastically reduced. The undesired absorption at the contact points  32  of the light produced is therefore also significantly suppressed. 
     In the regions  40  of the thin film stack that adjoin the cutouts  36 , photons are produced in the active layer  22  in a conventional way and are coupled out directly or after internal scatter as useful radiation from the light-emitting diode. 
     In order also to minimize the light absorption at the front side middle contact point  26 , an annular cutout  38  is introduced into the thin film stack  12  by etching the active layer  22  and the first sheathing layer  20 . As a result, the zone  40  producing photons is also physically separated from the contact point  26 . 
     If the second sheathing layer  24  is the sheathing layer with the higher transverse conductivity, which is the case in the exemplary embodiment because of the n-doping of the second sheathing layer, and if this layer is not severed, then somewhat further physical separation, in particular a multiple of the thickness of the first sheathing layer  20 , which has a lower transverse conductivity as a p-doped layer, may be sufficient to ensure that the light is produced at a sufficient distance from the contact point  26 . In this case, the physical separation can preferably be at least 5 times to 20 times the thickness of the first sheathing layer  20 . 
     The internal scattering processes needed for the thin film light-emitting diode are provided in the exemplary embodiment by the oblique flanks  42  of the cutouts  36 . However, alternatively or additionally, they can also be produced by other methods, such as a roughened front side  16  of the second sheathing layer  24  or a roughened rear side  14  of the first sheathing layer  20 .