BACKGROUND OF THE INVENTION

Field of the Invention

[0002] The invention lies in the field of semiconductor technology. More specifically, the invention relates to a radiation-emitting semiconductor component having a multilayer structure, an active layer serving for generating radiation within the multilayer structure, electrical contacts, which are electrically conductively connected to the active layer, and a radiation-transmissive window having a first main surface and a second main surface opposite to the first main surface. The first main surface of the window adjoins the multilayer structure. The invention also pertains to a method of producing such a radiation-emitting semiconductor component.

[0003] Radiation-emitting semiconductor components of the type mentioned generally have a semiconductor multilayer system with an active layer serving for generating radiation, which system is applied to a carrier. Radiation is coupled out through the carrier, the carrier being transparent with respect to the radiation thus generated. In that configuration, however, the radiation efficiency is greatly limited by total reflection at the carrier surface. This problem surface is particularly pronounced in the case of carriers having a high refractive index, such as SiC (silicon carbide) substrates for example, and it is further aggravated if the refractive index of the carrier is greater than the refractive index of the multilayer system.

[0004] The influence of total reflection on the coupling-out of radiation is illustrated by way of an example in FIG. 9 using a prior art GaN-based multilayer system 20 on a parallelepipedal SiC substrate 19 that is rectangular in section. The SiC substrate 19 has a refractive index of about 2.7 and it represents the optically denser medium by comparison with the multilayer system 20 , which has a refractive index of about 2.5. The semiconductor structure shown is surrounded by a medium having a low refractive index, for example air.

[0005] The multilayer structure 20 has an active radiation-generating layer 21 . A small radiation-emitting volume 23 , which can be described in an approximation as an isotropic point radiator, shall be picked out of the active layer 21 . The following consideration is applicable to virtually all such partial volumes 21 of the active layer.

[0006] The radiation 22 emitted by the volume 23 in the direction of the SiC substrate 19 firstly impinges on the multilayer system/substrate interface and, upon entering the substrate, is refracted in the direction of the normal to the interface.

[0007] Direct coupling-out of the radiation at the substrate main surface 25 opposite to the interface is possible only for radiation portions whose angle of incidence is less than the angle of total reflection (in each case relative to the normal to the coupling-out surface 25 ). For a substrate of high refractive index, the angle of total reflection is comparatively small and amounts to about 22° for SiC, for example.

[0008] Therefore, only a small portion 22 c of the radiation generated is directly coupled out from the center of the beam pencil 22 a, b, c . The remainder of the radiation generated is subjected to total reflection.

[0009] The radiation portion 22 b subjected to total reflection at the coupling-out surface 25 subsequently impinges on the substrate side surface 26 at an even shallower angle and is once again subjected to total reflection.

[0010] The remaining radiation portions 22 a , which first impinge on the side surfaces 26 of the substrate 19 , are likewise subjected to total reflection firstly at the side surfaces 26 and then at the coupling-out surface 25 .

[0011] In the case of the right-angled (i.e., orthogonal) configuration of side and main surfaces shown, the angle of incidence undergoes transition after reflection into itself or the complementary angle, so that the radiation portions 22 a, b cannot be coupled out at these surfaces even after multiple reflections.

[0012] Consequently, only a very small portion 22 c of the entire radiation 22 emitted in the direction of the substrate 19 is coupled out. The remainder of the radiation 22 a, b circulates in the substrate 19 while undergoing multiple total reflection, possibly enters the multilayer structure 20 again and is finally absorbed in the course of this cyclic propagation.

[0013] U.S. Pat. No. 6,229,160 and the corresponding German patent application DE 198 07 758 A1 disclose a light-emitting semiconductor component whose semiconductor side surfaces are completely or partly beveled in order to increase the radiation efficiency, so that the substrate acquires the form of a truncated pyramid. This beveling reduces the angle of incidence for parts of the radiation generated upon impingement on the side surfaces at the angle of total reflection, so that these radiation portions can be coupled out.

[0014] Since the additional coupling-out of radiation is effected only at the edge regions of the component, the radiation efficiency is increased only slightly, particularly in the case of large-surface components with comparatively thin substrates. Moreover, many placement installations are designed for semiconductor chips with a substrate in parallelepipedal or cuboid form. Changing the basic form of the substrate may lead to functional disturbances or necessitate costly conversions in the case of such installations.

SUMMARY OF THE INVENTION

[0015] It is accordingly an object of the invention to provide a radiation-emitting semiconductor component and a corresponding production method which overcome the above-mentioned disadvantages of the heretofore-known devices and methods of this general type and which provide for a radiation-emitting semiconductor component having an improved radiation efficiency.

[0016] With the foregoing and other objects in view there is provided, in accordance with the invention, a radiation-emitting semiconductor component, comprising:

[0017] a multilayer structure including an active layer for generating radiation in the multilayer structure;

[0018] electrical contacts connected to the active layer;

[0019] a radiation-transmissive window with a first main surface adjoining the multilayer structure and a second main surface opposite the first main surface;

[0020] the second main surface having at least one void, such as a trench recess or a pit recess, formed therein for increasing a coupling-out of radiation from the window.

[0021] In other words, the invention provides for the formation of a radiation-emitting semiconductor component having a multilayer structure, an active layer serving for generating radiation within the multilayer structure, contacts electrically connected to the active layer, and a window which is transmissive for the radiation generated and has a first main surface and a second main surface opposite to the first main surface, the first main surface of the window adjoining the multilayer structure and at least one trench-like or pit-like recess being formed in the window from the second main surface for the purpose of increasing the radiation efficiency.

[0022] In this case, the recess is embodied in such a way that parts of the radiation generated are coupled out at its boundary surfaces or reflected in a manner that promotes the coupling-out from the window.

[0023] A coupling-out of radiation portions is achieved by virtue of the fact that the boundary surfaces of the recess are at least partly arranged in such a way that the angle of incidence of said radiation portions on the boundary surfaces is as small as possible and, in particular, is less than the angle of total reflection.

[0024] Reflection promoting the coupling-out is present for example if radiation portions are firstly subjected to total reflection by the boundary surfaces of the recess, the cyclic propagation being broken within the window, so that the relevant radiation portions can be coupled out at least after a few further reflections at a boundary surface of the window.

[0025] The interruption of a cyclic propagation has the effect of increasing the radiation efficiency particularly in the case of a window whose side surfaces are arranged perpendicularly to the main surfaces. As described in the introduction, cyclically propagating radiation pencils form very easily in the case of such arrangements with a cubic or parallelepipedal window, with the result that the proportion of radiation that cannot be coupled out is correspondingly high.

[0026] Increasing the radiation efficiency by means of a recess in the window advantageously requires no changes to the enveloping basic form of the window, so that production and placement installations whose function is defined for specific predetermined basic forms of the window can also be used for producing components according to the invention. The invention can achieve, in particular, a high radiation efficiency with known and established basic forms of window such as, for example, an enveloping cube or parallelepiped form.

[0027] In order to further increase the radiation efficiency, preferably a plurality of recesses are formed in the window in the case of the invention. A plurality of uniform recesses is particularly preferred with regard to the number of production steps, which is to be kept low.

[0028] In contrast to edge structuring of the window in order to increase the radiation efficiency, for example by beveling the side surfaces, the invention can achieve an improved coupling-out over a larger surface and a more uniform distribution of the coupled-out radiation on this surface. This is particularly advantageous for large-surface components since, with the component surface scaled upward, the ratio of periphery to surface decreases. Therefore, in the case of large-surface components, means for increasing the radiation efficiency that are restricted to the periphery of the components are generally far less efficient than means for increasing the radiation efficiency that are applied in the surface.

[0029] In a preferred refinement of the invention, the recess in the window has at least one planar side surface, which forms an angle that differs from 90° with the second main surface of the window. Said angle is particularly preferably between 20° and 70°. Such a recess may be realized for example in the form of a trench with side walls which are inclined with respect to the main surfaces, which trench can be produced for example by correspondingly sawing into the window. Such a trench preferably has a trapezoidal cross section tapering in the direction of the multilayer structure.

[0030] In order to further increase the radiation efficiency, it is also possible to form a plurality of trenches that cross one another or run parallel. A parallel arrangement brings about an asymmetrical directional characteristic of the radiation generated, while trenches that cross one another lead to a uniform distribution of the coupled-out radiation. One of the two embodiments may be more advantageous depending on the surface of application.

[0031] In a further preferred refinement of the invention, the recess is completely or partly bounded by curved surfaces. In an advantageous manner, reflection at curved boundary surfaces of a recess largely precludes cyclic propagations. In this case, the recesses may be formed in particular in the form of a hemisphere, a sphere segment, an ellipsoid segment, a cone or a truncated cone. Similar forms which emerge for example from the abovementioned basic forms through distortions such as stretching, compression or shearing are also suitable.

[0032] Such forms can be produced for example by laser ablation or etching. The abovementioned trench-type recesses may also be bounded by curved surfaces and be formed for example with a semicircular cross section.

[0033] In a preferred development of the invention, the multilayer structure is produced by epitaxy. The window may subsequently also be produced from the epitaxial substrate. The invention has particular advantages in the case of substrates of high refractive index such as SiC, for example, with correspondingly large total reflection ranges, particularly when the refractive index of the substrate is greater than the refractive index of the multilayer structure. In this case, the refractive index of the multilayer structure is to be understood as the refractive index of that region of the multilayer structure which adjoins the substrate, since the extent of total reflection is significantly determined by the jump in refractive index at the interface between substrate and multilayer structure. The multilayer structure is generally composed of materials which have negligible differences in refractive index with respect to one another compared with the refractive index of the substrate. Therefore, the average refractive index of the materials contained in the multilayer structure can also be used as the refractive index of said multilayer structure.

[0034] As described in the introduction, this case arises primarily with GaN-based multilayer structures. These are multilayer structures which contain GaN or a compound that is derived therefrom or related thereto. These include, in particular, GaN itself, mixed-crystal systems based thereon, such as AlGaN (Al _1-x Ga _x N, 0≦x≦1), InGaN (In _1-x Ga _x N, 0≦x≦1) and AlInGaN (Al _1-x-y In _x Ga _y N, 0≦x≦1, 0≦y≦1) and also AlN, InN and InAlN (In _1-x Al _x N, 0≦x≦1).

[0035] Such multilayer structures are usually grown by epitaxy on an SiC or sapphire substrate which is at least partly transparent to the radiation generated, principally in the blue and green spectral region. In the case of both substrates, the invention can increase the radiation efficiency by reducing the total reflection losses, the invention being particularly advantageous for SiC substrates on account of the problem surface resulting from the high refractive index as described in the introduction.

[0036] However, the invention is not restricted to GaN-based systems, but rather may likewise be applied to other semiconductor systems such as, for example, to GaAs- GaP- or ZnSe-based materials. Here, too, a considerable part of the radiation generated remains in the multi-layer structure/window arrangement on account of total reflection and is finally absorbed.

[0037] Likewise, the invention is also advantageous for window materials other than those mentioned hitherto, for example quartz glass, diamond, ITO (indium tin oxide) or materials based on ZnO, SnO, InO or GaP, since it is generally the case with all these windows that, during the coupling-out, there is a transition to an optically less dense medium at which total reflection can occur and the degree of coupling-out is correspondingly reduced.

[0038] Furthermore, the invention is also advantageous for semiconductor bodies or windows that are potted or provided with an encapsulation in some other way, since the encapsulation generally has the lower refractive index, so that the radiation efficiency is reduced by total reflection in this case as well.

[0039] A window made of the abovementioned materials may be applied to the multilayer structure after the production of the latter. During the epitaxial production, this is possible for example in that after the epitaxy the epitaxial substrate is stripped away and in place thereof the window is connected to the multilayer structure by means of a wafer bonding method. As an alternative, the window may also be applied to the semiconductor surface produced by epitaxy and afterward the epitaxial substrate may be stripped away. This procedure has the advantage that the epitaxial substrate can be reused, which leads to a significant cost advantage particularly in the case of expensive materials such as SiC substrates, for example.

[0040] A method according to the invention for producing a radiation-emitting semiconductor component of the type mentioned begins with the provision of a window layer, for example in the form of a suitable substrate or wafer, having a first main surface and a second main surface opposite to the first main surface.

[0041] In the next step, a semiconductor layer sequence corresponding to the multilayer structure to be formed is applied to the first main surface. The application is preferably by epitaxy or by means of a wafer bonding method.

[0042] Afterward, a saw blade with a shaping edge is used to saw into the window layer from the second main surface and a trench-type recess is thus formed in the substrate. In this case, the cutting depth is less than the thickness of the window layer.

[0043] The components are finally completed. This comprises, for example, contact connection and singulation of the semiconductor layer sequence. During singulation, the composite comprising window layer and semiconductor layer sequence is divided into a plurality of windows each with a multilayer structure arranged thereon.

[0044] As an alternative, the recesses can also be etched using a suitable mask technique or produced by means of laser ablation. This alternative makes it possible to form spatially isolated recesses, that is to say recesses which do not extend over the entire surface of the window layer or larger partial regions thereof.

[0045] Isolated recesses may be formed as described above, for example, in the shape of a cone, a truncated cone, a hemisphere, a sphere segment, an ellipsoid segment or a similar form.

[0046] Other features which are considered as characteristic for the invention are set forth in the appended claims.

[0047] Although the invention is illustrated and described herein as embodied in a radiation-emitting semiconductor component and method for producing it, 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.

[0048] 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.