Optoelectronic component and method for producing an optoelectronic component

An optoelectronic component for mixing electromagnetic radiation having different wavelengths, more particularly in the far field. A first semiconductor chip for emitting electromagnetic radiation in a first spectral range is provided on a carrier. Furthermore, at least one a second semiconductor chip for emitting electromagnetic radiation in a second spectral range is provided on the carrier. The first and second spectral ranges differ from one another. The first semiconductor chip and the second semiconductor chip are arranged in a single package. The first semiconductor chip is optically isolated from the second semiconductor chip by a barrier. The first semiconductor chip and the second semiconductor chip are arranged centosymmetrically about a common center o(Z) of symmetry.

RELATED APPLICATIONS

This is a U.S. National Phase Application under 35 USC 371 of International Application PCT/EP2011/054106 filed on Mar. 18, 2011.

This application claims the priority of German application no. 10 2010 027 875.0 filed Apr. 16, 2010, the entire content of which is hereby incorporated by reference.

FIELD OF THE INVENTION

The present invention relates to an optoelectronic component for mixing electromagnetic radiation of different wavelengths. A method for producing an optoelectronic component is also proposed.

BACKGROUND OF THE INVENTION

To produce mixed light, semiconductor chips which emit electromagnetic radiation of different wavelengths can be combined directly adjacent to one another in an optoelectronic component. In this situation, one semiconductor chip may partially absorb the electromagnetic radiation of another semiconductor chip, which impairs the light output of the optoelectronic component.

For example, to produce warm white light, blue emitting InGaN semiconductor chips can be combined with red emitting AlGaInP semiconductor chips. High absorption losses may occur here, as the AlGaInP semiconductor chips are strongly absorbent of the electromagnetic radiation with wavelengths below about 600 nm emitted by the InGaN semiconductor chips, i.e. particularly in the blue region of the spectrum.

SUMMARY OF THE INVENTION

One object of the invention is to provide an optoelectronic component that minimizes the absorption losses.

Various embodiments have an optoelectronic component for mixing electromagnetic radiation of different wavelengths, particularly in the far field. On a carrier there is provided at least one first semiconductor chip for emitting electromagnetic radiation in a first spectral range. Also provided on the carrier is at least one second semiconductor chip for emitting electromagnetic radiation in a second spectral range. The first and second spectral ranges are different from one another. The at least one first semiconductor chip and the at least one second semiconductor chip are disposed in a single package. The at least one first semiconductor chip is optically isolated from the at least one second semiconductor chip by a barrier. In addition, the at least one first semiconductor chip and the at least one second semiconductor chip are each disposed centrosymmetrically about a common center of symmetry.

The barrier prevents the electromagnetic radiation emitted by the second semiconductor chips from being absorbed by the first semiconductor chips. Centrosymmetric means that the first semiconductor chips and the second semiconductor chips are each disposed about a common center of symmetry. In other words, the optoelectronic component has a common center of gravity for the first and the second semiconductor chips. Consequently, the mixed light emanating from the optoelectronic component exhibits a very good mix of the electromagnetic radiations from the first and the second spectral range. The mix is good particularly in the far field.

In a preferred embodiment, the first semiconductor chips can be disposed in an inner region of the optoelectronic component. The second semiconductor chips can be disposed in an outer region. In particular, the second semiconductor chips can be disposed in a ring pattern around the first semiconductor chips. This is advantageous, as it ensures a uniform luminance, particularly in the far field.

In a preferred embodiment, an additional barrier is disposed around the second semiconductor chips. This is advantageous, as it enables unwanted discharge of encapsulating material to the outside to be prevented.

In a preferred embodiment, the barrier between the first and the second semiconductor chips is ring-shaped. This is advantageous, as it ensures mixing of the electromagnetic radiation not just in the far field but even after a few centimeters. This can take place, for example, on a matt surface.

The additional barrier can also be ring-shaped.

In a preferred embodiment, the barriers can have a height of between about 200 μm and about 2 mm, preferably a height of about 500 μm. This is advantageous, as it prevents electromagnetic radiation of the second semiconductor chips from being absorbed by the first semiconductor chips.

The semiconductor chips have at least one active zone which emits electromagnetic radiation. The active zones can be pn-junctions, double heterostructure, multiple quantum well structure (MQW), single quantum well structure (SQW). Quantum well structure means: quantum wells (3-dim), quantum wires (2-dim) and quantum dots (1-dim).

In a preferred embodiment, the first semiconductor chip can be an AlGaInP semiconductor chip which is designed to emit electromagnetic radiation particularly in the red region of the spectrum.

The second semiconductor chip can be grown on a III-V compound semiconductor material, in particular a nitride compound semiconductor material such as gallium nitride (GaN). The second semiconductor chip can be, for example, an InGaN semiconductor chip which is designed to emit electromagnetic radiation particularly in the blue region of the spectrum.

In a preferred embodiment, some of the electromagnetic radiation from the blue spectral range emitted by the InGaN semiconductor chips can be converted into the yellow-green spectral range by a conversion means. The conversion means can have luminescent particles. The luminescent particles can contain phosphors. The phosphors can contain yttrium aluminum garnet. The partial conversion of blue light into yellow light is particularly advantageous, as white light can be produced by superimposing blue and yellow light.

Disposing the AlGaInP semiconductor chips and the InGaN semiconductor chips in one package is particularly advantageous, as it ensures good mixing of the electromagnetic radiation in the red spectral range with the blue and yellow-green radiation coming from the InGaN semiconductor chips. This mix of blue, yellow and red light is particularly suitable for producing warm white light. Due to the centrosymmetrical arrangement of the AlGaInP and InGaN semiconductor chips, it can also be ensured that the warm white light has high color homogeneity at least in the far field. As the AlGaInP semiconductor chips are strongly absorbent of electromagnetic radiation with wavelengths below about 600 nm, it is particularly advantageous for the AlGaInP and InGaN semiconductor chips to be separated by an optical barrier.

The semiconductor chips can be encapsulated. An encapsulating material serves to protect the contact wires, but above all to increase the efficiency of the coupling-out of electromagnetic radiation. With encapsulating material, the efficiency can be increased by up to 80% compared to the efficiency without encapsulating material.

The AlGaInP semiconductor chips in the center are encapsulated in a first encapsulating material. Silicone or epoxy resin can be used as encapsulants. The barrier around the AlGaInP semiconductor chips also serves as a flow-stop for the first encapsulating material. The first encapsulating material contains as few scattering centers as possible. The red light should leave the first encapsulating material as completely as possible without wavelength conversion. In particular, the first encapsulating material contains no phosphor.

In a preferred embodiment, the InGaN semiconductor chips are encapsulated in a second encapsulating material, in particular of silicone, in the form of a planar volume encapsulation. The second encapsulating material contains a conversion means, in particular a phosphor. Some of the electromagnetic radiation from the blue region of the spectrum emitted by the InGaN semiconductor chips is converted by the conversion means into electromagnetic radiation in the yellow-green spectral range.

In a preferred embodiment, a hemispherical coupling-out lens spans the AlGaInP semiconductor chips. In other words, the coupling-out lens covers the area enclosed by the barrier around the AlGaInP semiconductor chips, i.e. the inner region or more specifically the emitting area. The coupling-out lens is advantageous, as it increases the coupling-out efficiency for the electromagnetic radiation by reducing the amount of totally reflected radiation compared to an arrangement without lens.

In a preferred embodiment, the geometry of the coupling-out lens fulfills the so-called Weierstrass condition. This condition requires that the ratio of the radius of the circular area on which the AlGaInP semiconductor chips are disposed to the radius of the coupling-out lens corresponds to the ratio of the refractive index outside the coupling-out lens to the refractive index inside the coupling-out lens. This condition can be formulated thus:
radiusarea/radiuslens≦refractive indexoutside/refractive indexlens

The refractive index of air, i.e. 1, is taken as the refractive index outside the coupling-out lens. The coupling-out lens can consist of high refractive index glass having a refractive index of 1.5. This results in the following condition:
radiusarea/radiuslens≦1/1.5=⅔.

If the coupling-out lens consists of conventional silicone, the refractive index is 1.4. If the coupling-out lens consists of high refractive index silicone, the refractive index is 1.54.

Other encapsulating materials can also be used for the coupling-out lens.

For simplicity's sake, the value of 1.5 can be taken as the refractive index for the above encapsulating materials.

If the Weierstrass condition is fulfilled, the total internal reflection taking place at the transition from coupling-out lens to air is minimized. This is particularly advantageous, as it reduces the coupling-out losses.

In order to fulfill the Weierstrass condition, the AlGaInP semiconductor chips cannot be disposed in arbitrary proximity to the barrier, but must be disposed as centrally as possible.

The coupling-out lens can preferably be adhesively attached or produced by the encapsulating process itself.

If the Weierstrass condition is fulfilled, a Lambertian far field is produced for the electromagnetic radiation emitted by the AlGaInP semiconductor chips.

In a preferred embodiment, the InGaN semiconductor chips are formed as volume emitters, in particular as sapphire chips.

In another preferred embodiment, the InGaN semiconductor chips are implemented as surface emitters, in particular as thin film chips. The surface emitters are at least partially disposed in a highly reflective material, in particular a TiO2filled silicone. Alternatively, the silicone can also be filled with ZrO2, Al2O3or ZnO. The InGaN semiconductor chips are embedded in the white silicone up to the epitaxial height. This is particularly advantageous, as it enables up to 95% reflectivity to be achieved. By comparison, the carrier is highly absorbent and the InGaN semiconductor chip itself has a reflectivity of only about 85%.

Planar conversion encapsulation with the second encapsulating material takes place onto the layer of TiO2filled silicone. Such planar conversion encapsulations provide a Lambertian radiation profile of the emitted electromagnetic radiation.

In a preferred embodiment, the barriers are highly reflective. A reflectivity of greater than 90%, preferably of greater than 95%, is achievable. TiO2, ZrO2, Al2O3or ZnO filled PBT (polybutylene terephthalate) can be used as the barrier material. The high reflectivity of the barrier is particularly advantageous, as it minimizes the absorption losses in the barriers.

Different embodiments have a method for producing an optoelectronic component for mixing electromagnetic radiation of different wavelengths, particularly in the far field. This involves the following steps: first, at least one first semiconductor chip and at least one second semiconductor chip are disposed on a carrier. The at least one first semiconductor chip and the at least one second semiconductor chip are disposed in a package. The at least one first semiconductor chip and the at least one second semiconductor chip are disposed centrosymmetrically with respect to a common center of symmetry. A barrier is then disposed between the at least one first semiconductor chip and the at least one second semiconductor chip.

Alternatively, the barrier can already be present prior to the disposing of the semiconductor chips. In particular, premold packages can be used for this purpose.

The barrier serves to provide complete optical isolation of the inner region containing the first semiconductor chips from the outer region containing the second semiconductor chips.

DETAILED DESCRIPTION OF THE DRAWINGS

Elements that are identical, similar or produce an identical effect are provided with the same reference characters in the figures. The figures and the relative sizes of the elements represented in the figures are not to be considered as being to scale. Rather, individual elements may be shown exaggeratedly large for the sake of clarity and better understanding.

FIG. 1ashows a plan view of an optoelectronic component1. The optoelectronic component1is used for mixing electromagnetic radiation having different wavelengths, particularly in the far field. First semiconductor chips3for emitting electromagnetic radiation in a first spectral range are provided on a carrier2. Second semiconductor chips4for emitting electromagnetic radiation in a second spectral range are likewise provided on the carrier2. The first semiconductor chips3and the second semiconductor chips4are disposed in a single package. The first semiconductor chips3are optically isolated from the second semiconductor chips4by a barrier5. A plurality of first semiconductor chips3and a plurality of second semiconductor chips4are provided. The first semiconductor chips3and the second semiconductor chips4are in each case disposed centrosymmetrically about a common center of symmetry Z.

The first semiconductor chips3are disposed in the inner region113, in the center of the optoelectronic component1. The second semiconductor chips4are disposed in an outer region114, in a ring pattern around the first semiconductor chips3.

The barrier5between the first semiconductor chips3and the second semiconductor chips4is ring-shaped. The barrier5has a high reflectivity of more than 90%, preferably of more than 95%.

The first semiconductor chips3can be implemented as AlGaInP semiconductor chips. AlGaInP semiconductor chips emit electromagnetic radiation preferably from the red region of the spectrum.

The second semiconductor chips4can be implemented as InGaN semiconductor chips. InGaN semiconductor chips preferably emit electromagnetic radiation from the UV to the green region of the spectrum, with particular preference from the blue region of the spectrum.

FIG. 1bshows a sectional view of the optoelectronic component fromFIG. 1a. The highly reflective barrier5has a height of between about 200 μm and about 2 mm, preferably a height of about 500 μm. As inFIG. 1a, the AlGaInP semiconductor chips3and the InGaN semiconductor chips4are disposed centrosymmetrically about the common center of symmetry Z. The AlGaInP semiconductor chips3are encapsulated in a first encapsulating material7. The encapsulating material7can comprise silicone or epoxy resin. The InGaN semiconductor chips4are encapsulated in a second encapsulating material9, in particular of silicone. The second encapsulating material9has the shape of a planar volume encapsulation that is flush with the barrier5.

FIG. 1cshows another sectional view of the optoelectronic component fromFIG. 1a.FIG. 1cdiffers fromFIG. 1bonly in that, in the region of the AlGaInP semiconductor chips3, the carrier2is lined with a third encapsulating material18between the AlGaInP semiconductor chips3. A white TiO2filled compound can be used as the third encapsulating material18. The third encapsulating material18ensures that red scattered light is efficiently reflected.

FIG. 1dshows another sectional view of the optoelectronic component fromFIG. 1a.FIG. 1dshows InGaN semiconductor chips4bwhich are implemented as surface emitters, in particular as thin film chips.FIG. 1ddiffers fromFIG. 1bonly in that the InGaN semiconductor chips4bare embedded in a highly reflective material11, in particular a TiO2filled silicone. As an alternative to a TiO2filler, the silicone can also be filled with ZrO2, Al2O3or ZnO. The highly reflective material11can be flush with the surface emitters4b. A second encapsulating material9is applied to the surface emitters4band the highly reflective material11.

FIG. 2ashows a plan view of another optoelectronic component. The AlGaInP semiconductor chips3are disposed in the inner region113in a square pattern around the center Z. The AlGaInP semiconductor chips3are enclosed by the barrier5. The InGaN semiconductor chips4are disposed in the outer region114in a square pattern around the AlGaInP semiconductor chips3. The arrangement of the InGaN semiconductor chips is also symmetrical about the center Z.

FIG. 2bshows a plan view of another optoelectronic component1. InGaN semiconductor chips4are disposed in a rectangular manner inside the barrier5. AlGaInP semiconductor chips3are disposed outside the barrier5. The center Z is again the common center of symmetry for the InGaN semiconductor chips4and the AlGaInP semiconductor chips3.

FIG. 3shows a plan view of another optoelectronic component1. Disposed in the center of the optoelectronic component1is a single AlGaInP semiconductor chip3which is laterally enclosed by the highly reflective barrier5. In the outer region114, a plurality of InGaN semiconductor chips are disposed in a ring pattern around the center Z.

FIG. 4ashows a 3-dimensional view of an optoelectronic component. A hemispherical coupling-out lens6whose geometry satisfies the Weierstrass condition spans the AlGaInP semiconductor chips3. The InGaN semiconductor chips4spaced at regular intervals encircle the AlGaInP semiconductor chips3. The barrier5isolates the inner region113containing the AlGaInP semiconductor chips3from the outer region114containing the InGaN semiconductor chips4. The center Z is again the common center of symmetry for the InGaN semiconductor chips4and the AlGaInP semiconductor chips3.

FIG. 4bshows a sectional view of the optoelectronic component fromFIG. 4a. The exemplary embodiment inFIG. 4bcorresponds to the exemplary embodiment inFIG. 1bexcept that a coupling-out lens6is disposed above the inner region113in which the AlGaInP semiconductor chips3are disposed. The coupling-out lens6satisfies the Weierstrass condition.

This means that the radius13of the coupling-out lens6and the radius12of the emitting area are related as follows:
radiusarea/radiuslens≦refractive indexoutside/refractive indexlens

The refractive index outside is 1. The refractive index of the lens is assumed to be 1.5.

FIG. 5ashows a 3-dimensional view of an optoelectronic component. As an addition to the exemplary embodiment shown inFIG. 4a, the InGaN semiconductor chips4disposed in a circular pattern about the center of symmetry Z are enclosed by an additional ring-shaped barrier8. The additional barrier8has a reflectivity greater than 90%, preferably greater than 95%. The InGaN semiconductor chips4are encapsulated in a second encapsulating material9. The second encapsulating material9has a conversion means17, in particular a phosphor. Some of the electromagnetic radiation from the blue region of the spectrum emitted by the InGaN semiconductor chips4is converted by the conversion means17into the yellow-green spectral range. The semiconductor chips3,4are connected to power sources (not shown) via electrical interconnects and traces10.

FIG. 5bshows a sectional view of the optoelectronic component fromFIG. 5a. InGaN semiconductor chips4aas volume emitters, in particular as sapphire chips, are completely encapsulated in the second encapsulating material9. A conversion means17in the form of luminescent particles is incorporated in the encapsulation. The luminescent particles can comprise phosphors. As in the exemplary embodiment inFIG. 4b, a coupling-out lens6completely covers the inner region113. The outer region114is enclosed by another highly reflective barrier8. The additional barrier8has a reflectivity greater than 90%, preferably greater than

FIG. 6shows a sectional view of an optoelectronic component. The InGaN semiconductor chips4bare designed as surface emitters, in particular as thin film chips. The InGaN semiconductor chips4bare laterally encapsulated in a highly reflective material11, in particular white silicone. The second encapsulating material9is applied to said highly reflective material11. The second encapsulating material9comprises the conversion means17.FIG. 6andFIG. 5bare otherwise identical.

FIG. 7shows a sectional view of an optoelectronic component1. The AlGaInP semiconductor chips3in the inner region113of the optoelectronic component1are laterally encapsulated in a third encapsulating material18. The third encapsulating material18can be filled with TiO2particles. The third encapsulating material18ensures that scattered light coupled into the coupling-out lens6from the region of the InGaN semiconductor chips4via the region of the AlGaInP semiconductor chips3is efficiently reflected. The scattered light is preferably white mixed light. The first encapsulating material7is applied to the third encapsulating material18.

FIG. 8shows a detail fromFIG. 5a, namely the inner region113of the optoelectronic component1which is enclosed by the barrier5. The inner region113constitutes a circular emitting area14. This emitting area14has a particular radius12. The hemispherical lens6extends over the emitting area14. The hemispherical lens6has a particular radius13. The lens6has a refractive index15of about 1.5. Outside the lens6, the refractive index of air is assumed, namely 1. The two radii12and13are selected such that the Weierstrass condition is satisfied.

To illustrate the underlying concept, the optoelectronic component has been described with reference to a number of exemplary embodiments. These exemplary embodiments are not limited to particular combinations of features. Even though some features and implementations have only been described in connection with a particular exemplary embodiment or individual exemplary embodiments, they can in each case be combined with other features from other exemplary embodiments. It is likewise conceivable to omit or add individual described features or particular implementations in exemplary embodiments, provided that the general technical teaching remains realized.