WO2016015746A1

WO2016015746A1 - Dbr mirror and optoelectronic component having a dbr mirror

Info

Publication number: WO2016015746A1
Application number: PCT/EP2014/066183
Authority: WO
Inventors: Julian IKONOMOV
Original assignee: Osram Opto Semiconductors Gmbh
Priority date: 2014-07-28
Filing date: 2014-07-28
Publication date: 2016-02-04

Abstract

The invention relates to a DBR mirror, comprising a first layer stack (11), which has a plurality of layer pairs (5), wherein the layer pairs each comprise a first layer (1) composed of a first material having an index of refraction n₁ and a second layer (2) composed of a second material having an index of refraction n₂, and comprising a second layer stack (12), which has a plurality of layer pairs (6), wherein the layer pairs each comprise a third layer (3) composed of a third material having an index of refraction n₃ and a fourth layer (4) composed of a fourth material having an index of refraction n4. The first layers (1) each have a thickness di = λ1/ (4n1), the second layers (2) each have a thickness d₂ = λ₂/ (4n₂), the third layers (3) each have a thickness d₃ = λ₃/ (4n₃), and the fourth layers (4) each have a thickness d₄ = λ₄/ (4n₄), wherein λ₁, λ₂, λ₃, and λ₄ are central wavelengths that are different from each other.

Description

description

DBR mirror and optoelectronic device with a DBR mirror

The invention relates to a DBR mirror and a

Optoelectronic component with a DBR mirror.

DBR (Distributed Bragg Reflector) mirrors exhibit

Generally a periodic layer stack

alternating first layers of a first

dielectric material having a first refractive index ni and second layers comprising a second dielectric

Material with a second refractive index ri2 on. The first refractive index ni and the second refractive index ri2 advantageously have the greatest possible difference in order to achieve the highest possible reflection. The layer thicknesses of the first layers and second layers of the layer pairs are set in a DBR mirror such that the optical layer thickness n * d is equal to a quarter wavelength λ / 4 of a central wavelength λ at which the DBR mirror is

Reflection maximum should have. Under the optical

Layer thickness is understood here and below as the product of the thickness d and the refractive index n.

The maximum reflectivity at the central wavelength depends on the number of layer pairs and on the difference between the two refractive indices ni and ri2. A high reflectivity is with a DBR mirror usually only in a wavelength range Δλ to the

Central wavelength achieved around, this being

Wavelength range is also referred to as stopband. The width of the stopband depends on the difference between the two refractive indices ni and ri2. For one

given combination of material of a first material and a second material, therefore, the width of the stop band of a conventional DBR mirror can not be extended. For some applications, however, there is a wider stopband

desired than can be achieved with a conventional DBR mirror.

One solution may be to combine a DBR mirror with a metal mirror, with the metal mirror being positioned behind the DBR mirror as viewed from the direction of the incident light. In this case, light is with

Wavelengths that are not reflected by the DBR mirror are at least partially reflected at the backside metal layer. When used in an optoelectronic semiconductor chip, however, this embodiment has the disadvantage that, in the case of optoelectronic semiconductor chips, which are used in the

Waferverbund be prepared, the dicing of the

Wafer composite to individual semiconductor chips, z. B. by means of a laser beam, is difficult.

Therefore, a problem to be solved is one

indicate improved DBR mirror, which is characterized by a high reflectivity in a large spectral range

out draws.

This object is achieved by a DBR mirror according to the

independent claim 1 solved. Advantageous embodiments and further developments of the invention are the subject of

dependent claims. In accordance with at least one embodiment, the DBR mirror comprises a first layer stack comprising a plurality of layer pairs

wherein the layer pairs each have a first layer of a first material with a refractive index ni and a second layer of a second material with a refractive index ri2. The refractive indices ni of the first material and ri2 of the second material are

different from each other. For example, the first one

Material has a lower refractive index, in particular a refractive index ni -S 1.6, and the second material has a higher refractive index, in particular a refractive index ri2> 1.6. The first layer stack thus has a periodic sequence of alternating first layers having a lower refractive index and second layers having a higher refractive index.

Furthermore, the DBR mirror advantageously has a second layer stack which has a plurality of layer pairs, the layer pairs each having a third layer of a third material with a refractive index n ₃ and a fourth layer of a fourth material with a refractive index n ₄ . The refractive indices n _{3 of} the third material and n _{4 of} the fourth material are different from each other. In particular, the third material may have a lower

Refractive index 113, in particular a refractive index n ₃ <1.6, and the fourth material has a higher refractive index, in particular a refractive index n ₄ > 1.6. Like the first layer stack, the second is also advantageous

Layer stack formed by a periodic sequence of alternating third layers with lower refractive index and fourth layers with the higher refractive index. In the case of the DBR mirror, the first layers advantageously each have a thickness di = Xi / (4ni), where λι is a first central wavelength, and the second layers each have a thickness d2 = λ ₂ / (4n ₂ ), where λ _{2 is} a second central wavelength. In other words, the optical thickness ni * di of the first layers in the first layer stack is equal to a quarter wavelength λι / 4 for a first

Central wavelength λι, and the optical thickness n ₂ * d _{2 of} the second layers in the first layer stack is equal to a quarter wavelength λ _2/4 for a second

Central wavelength λ ₂ . The first central wavelength λι and the second central wavelength λ ₂ are different from each other. The layer thickness di of the first layers and the layer thickness d _{2 of} the second layers are therefore for each other

different central wavelengths optimized.

In the second layer stack, the third layers advantageously each have a thickness d ₃ = λ ₃ / (4n ₃ ), where λ _{3 is} a third central wavelength, and the fourth layers each have a thickness d ₄ = λ ₄ / (4n ₄ ) on, where λ _{4 is} a fourth central wavelength. In other words, the optical thickness n3 * d ₃ of the third layer is equal to a quarter wavelength λ ₃ / for the third central wavelength Ä _3, and the optical thickness n ₄ * d ₄ of the fourth layers is equal to a quarter wavelength λ _4/4 for the fourth

Central wavelength λ ₄ . The third and the fourth

Central wavelength are different from each other. So as in the first layer stack are also in the second

Layer stack, the layer thicknesses and the alternating third and fourth layers, which form the layer pairs optimized for mutually different central wavelengths. Advantageous in the DBR mirror are the four

Central wavelength λι, λ ₂ , λ3 and λ ₄ different from each other. Because the central wavelengths for which the

Layer thicknesses of the first and second layers in the first layer stack and third and fourth layers in the second layer stack are optimized, different from each other, can be particularly broad with the DBR mirror

Reflection maximum, so a wide stop band can be achieved.

The selection of the four central wavelengths is based on the stop band provided for the application of the DBR mirror. The four central wavelengths and the resulting layer thicknesses of the first, second, third and fourth

Layers in the layer pairs can, for. B. by a

Computer simulation are determined. In the

Computer simulation z. B. the materials and the

Fixed number of pairs of layers in the first layer stack and the second layer stack, the four

Central wavelengths λι, λ ₂ , λ3 and λ ₄ are varied as parameters in an iterative process in order to achieve the best possible match between the simulated reflection curve and the desired reflection curve. According to a preferred embodiment of the DBR mirror, the third material is the same as the first material. In particular, in the first layer stack, the first material having the lower refractive index may be the same material as the third material having the lower refractive index in the second layer stack.

According to a further advantageous embodiment, in the case of the DBR mirror, the fourth material is equal to the second material. In particular, the second material with the higher

Refractive index in the first layer stack equal to the fourth higher refractive index material in the second layer stack

Be layer stack.

According to an advantageous embodiment, both the third material is equal to the first material and the fourth

Material equal to the second material. In this case, the layer pairs in the first layer stack and the second layer stack are each formed from the same material pairing. In particular, the DBR mirror in this embodiment advantageously contains only two different

Layer materials, whereby the production is advantageously simplified. In this embodiment applies to the

Refractive indices ni = n ₃ and ri2 = n ₄ , provided that there are slight differences between the refractive indices of the same

Materials are negligibly small due to the dispersion at the different central wavelengths. According to at least one advantageous embodiment, the first material is a silicon oxide, in particular Si0 ₂ - silicon oxide has a low refractive index, which is about ni = 1.5. The second and / or the fourth material is preferably a titanium oxide, an aluminum oxide or a niobium oxide, in particular T1O ₂ , Al ₂ O ₃ or b ₂ Ü ₅ . Titanium oxide advantageously has a comparatively high refractive index, which is about n ₂ = 2.5. Due to the comparatively large

Refractive index difference between silicon oxide and

Titanium oxide is this material pairing in particular for

Achieving a high reflection in the visible spectral range suitable. The total number of layers in the DBR mirror is advantageously not more than 40, preferably not more than 24. It has been found that in the optimization of the layer thicknesses of the individual layers described herein with respect to four different central wavelengths

comparatively small total number of layers high reflection over a comparatively wide spectral range can be achieved. In particular, it has been found that a stop band with a predetermined width can be achieved with a smaller number of layers than with two stacked layer stacks in which the first and second layers of the first layer stack and the third and fourth layers of the second layer stack in terms of their Layer thickness are optimized in each case with respect to the same central wavelength.

According to an advantageous embodiment, a number of the layer pairs in the first layer stack is between

including five and ten inclusive. The first

Layer stack can z. B. have six pairs of layers with a total of twelve individual layers. Furthermore, the number of layer pairs in the second layer stack is also

preferably between five and ten inclusive. By way of example, the second layer stack can have six layer pairs with a total of twelve individual layers.

The number of layer pairs in the first layer stack and the second layer stack is preferably the same. In this way, it is advantageously achieved that the first layer stack and the second layer stack are approximately equal to

Total reflection of the DBR mirror contribute. For example, the first layer stack and the second layer stack each have six pairs of layers, so that the total number of layers in the DBR mirror is 24.

In a preferred embodiment of the DBR mirror

The central wavelengths differ in each case

at least 20 nm from each other. Especially preferred

The central wavelengths differ in each case

at least 30 nm from each other. This way you can

Advantageously, a particularly wide reflection maximum can be achieved.

Furthermore, it is advantageous if the smallest of the central wavelengths and the largest of the central wavelengths each differ by at least 150 nm, preferably by at least 200 nm. In this way, advantageously a particularly wide stop band is achieved.

In an advantageous embodiment of the DBR mirror, the central wavelengths are in the visible spectral range

between 400 nm and 800 nm. The DBR mirror described here is particularly suitable for producing a stopband that extends approximately over the entire visible

Spectral range extends. Alternatively, however, the proposed principle can also be used for DBR mirrors outside the visible spectral range, for example in the UV or IR spectral range.

It will continue to be an optoelectronic device

given a DBR mirror according to the above

Having described advantageous embodiments.

The optoelectronic component can in particular be an LED. In particular, the DBR mirror can be referred to as the back Reflector be provided in the optoelectronic device, wherein the DBR mirror on one of

Radiation exit surface opposite the back of the device is arranged. In this case, radiation that is emitted toward the rear side of the component, for example in the direction of a substrate, is advantageously provided by the DBR mirror

Radiation exit surface reflected. Due to the comparatively wide stop band, the DBR mirror is particularly well suited for optoelectronic components which have a broad emission spectrum. This is the case in particular with LEDs. Particularly suitable is the DBR mirror for LEDs, which is a converter layer

to convert at least a portion of the emitted light into light of a longer wavelength.

For example, white light can be generated in this way by means of a UV-light-emitting or blue-light emitting LED, by means of a part of the emitted radiation by means of the

Converter layer is converted into yellow light. The DBR mirror is advantageously suitable for a LED with converter layer to reflect both the light emitted by the active layer and the converted light.

Furthermore, the DBR mirror is opto-electronic

Suitable components in which a plurality of active zones having different emission wavelengths in one

Layer stack are arranged one above the other. In this case, the DBR mirror with broadband reflection has the advantage that it can preferably reflect the light of all emitted wavelengths. The invention will be described below with reference to

Embodiments in connection with the figures

explained in more detail. FIG. 1 shows a schematic illustration of a cross section through a DBR mirror according to FIG

Embodiment, a graphical representation of the reflection R in

Dependence on the wavelength λ for the DBR mirror according to the exemplary embodiment in comparison to a double DBR mirror with the same number of layers,

Figure 3 is a graphical representation of the reflection R in

Dependence on the wavelength λ for the DBR mirror according to the embodiment compared to a double DBR mirror with 40 layers, and

Figure 4 is a schematic representation of a cross section through an optoelectronic device with a DBR mirror according to an embodiment.

Identical or equivalent components are each provided with the same reference numerals in the figures. The

Components shown and the proportions of the components with each other are not to be regarded as true to scale.

The DBR mirror 10 shown schematically in cross section in FIG. 1 consists of a first layer stack 11 and a second layer stack 12 arranged thereon. The DBR mirror 10 may, for example, be applied to a substrate 7, wherein the substrate 7 may be, for example, a substrate or a layer of an optoelectronic semiconductor component.

The first layer stack 11 consists of a plurality of layer pairs 5, wherein the layer pairs 5 are each formed from a first layer 1 and a second layer 2. The first

Layers 1 are made of a first material with a

low refractive index ni and the second layers 2 are formed from a second material having a high refractive index ri2. Preferably ni -S is 1.6 and ri2> 1.6. In the exemplary embodiment, the first layers 1 are S1O ₂ layers and the second layers 2 are Ti0 ₂ layers. The number of layer pairs 5 in the first layer stack 11 is advantageously between five and ten. In which

In the exemplary embodiment, the first layer stack 11 has six pairs of layers 5.

The second layer stack 12 consists of several

Layer pairs 6, each consisting of a third layer 3 of a third material and a fourth layer 4 of a fourth material. The third layers 3 have a low refractive index n ₃ and the fourth layers 4 have a high refractive index n ₄ . Preferably n _{3 is} <1.6 and n ₄ > 1.6. The number of layer pairs 6 in the second layer stack 12 is advantageously between five and ten. In the exemplary embodiment, the second layer stack 12 has six pairs of layers 6. Thus, the layer stacks 11, 12 each have the same number of layer pairs 5, 6 in the exemplary embodiment. This has the advantage that the Reflectivity of the layer stack 11, 12 is approximately equal.

In the embodiment, the material of the third layers 3 is equal to the material of the first layers 1.

Furthermore, the material of the fourth layers 4 is equal to the material of the second layers 2. Thus, the second layer stack 12 consists of third layers 3 of SiO ₂ and fourth layers 4 of TiO ₂ . Alternatively, however, it would also be possible for the third layers 3 and / or the fourth layers 4 to be formed from materials other than the first ones

Layers 1 and the second layers 2 of the first

Layer stack 11. The use of the same material for the lower refractive index layers 1, 3 and the higher refractive index layers 2, 4 in the first layer stack 11 and the second layer stack 12 has the advantage that the DBR mirror 10 is only two various

Having materials and therefore is comparatively easy to produce.

In the DBR mirror 10, the layer thicknesses di of the first layers 1, d _{2 of} the second layers 2, d3 of the third

Layers 3 and d4 of the fourth layers 4 are each optimized for a different central wavelength. The first layers 1 have a thickness di = Xi / (4ni), where λι = 597, 6 nm is the first central wavelength. The second layers 2 have a thickness d ₂ = λ ₂ / (4n ₂ ), where λ ₂ = 627, 2 nm is the second central wavelength. In the first layer stack 11, therefore, the first layers 1 and the second layers 2 are not optimized for the same, but for different central wavelengths λι, λ ₂ . The thicknesses of the first layers 1 are di = 102.7 nm. The thicknesses of the second layers 2 are d ₂ = 68.0 nm. The third layers 3 each have a thickness d3 =

Ä3 / (4n3), where λ3 = 519.2 nm the third

Central wavelength is. The fourth layers 4 each have a thickness d4 = λ ₄ / (4n ₄ ), where λ ₄ = 425, 5 nm is the fourth central wavelength. The thicknesses of the third

Layers 3 amount to d3 = 89.1 nm. The thicknesses of the fourth layers 4 are d ₄ = 42.4 nm. Within the second layer stack 12 are thus the

Layer thicknesses of the third layers 3 and the fourth

Layers ₄ optimized for different central wavelengths λ3, λ4. In particular, in the DBR mirror all four central wavelengths λι, λ ₂ , λ3 and λ ₄ are different from each other. The central wavelengths advantageously differ in each case by at least 20 nm, preferably by at least 30 nm from each other. The four central wavelengths λι, λ ₂ , λ3 and λ ₄ are in an iterative process, in particular by

Simulation calculations, determined. Preferably, the smallest central wavelength and the largest differ

Central wavelength by at least 150 nm and more preferably by at least 200 nm from each other. In this way, a particularly broad reflection maximum of the DBR mirror 10 can be achieved. The DBR mirror 10 may in particular be provided to reflect light in the largest possible area of the visible spectral range. In this case, in particular all four central wavelengths λι, λ ₂ , λ 3 and λ ₄ in the visible spectral range between 400 nm and 800 nm are included.

Figure 2 shows the reflection curve 21 of the DBR mirror according to the embodiment of Figure 1 in comparison to

Reflection curve 22 of a double DBR not according to the invention Mirror, which has two stacked layer stack. In the non-inventive double DBR mirror, the first and second layers of the first

Layer stack optimized for the same central wavelength 485 nm and the third and fourth layers of the second layer stack to the same central wavelength 600 nm. Both DBR mirrors have a number of 24 layers. The comparison of the reflection curves 21, 22 shows that the DBR mirror according to the embodiment has a wider

Reflection maximum than the double DBR mirror has.

FIG. 3 shows the reflection curve 21 of the DBR mirror according to the exemplary embodiment of FIG. 1 in comparison to FIG

Reflection curve 23 of a non-inventive double DBR mirror, wherein the double DBR mirror is a first

Layer stack with ten layer pairs of Si0 ₂ layers and Ti0 ₂ layers whose layer thicknesses are optimized for the same central wavelength 485 nm. The double DBR mirror furthermore has a second layer stack with ten layer pairs of SiO ₂ layers and TiO ₂ layers, the layer thicknesses each being for a second layer

Central wavelength of 600 nm are optimized. Despite the lower number of layers of only 24 layers that is

Reflection maximum of the DBR mirror according to the

Embodiment wider than the reflection maximum of the comparative example not according to the invention, which has a total of 40 layers.

FIG. 4 schematically shows an exemplary embodiment of an optoelectronic component 30 which contains a DBR mirror 10 according to one exemplary embodiment. The

Optoelectronic component is an LED which, for example, has a first semiconductor region 31 of a first conductivity type, a second semiconductor region 33 of a second conductivity type and an active layer 32 arranged therebetween.

The semiconductor layer sequence 31, 32, 33 is in the

Embodiment arranged on a transparent substrate 34, which may be, for example, a sapphire substrate. The DBR mirror 10 is z. B. between the connection layer 34 and the semiconductor layer stack 31, 32, 33 are arranged. Radiation, which is emitted in the active layer 33 in the direction of the substrate 34, is advantageously reflected by the DBR mirror 10 toward a radiation exit side 35. The broad reflection maximum of the DBR mirror 10 is particularly advantageous when the active layer 32 emits radiation in a comparatively large spectral range. Unlike the one shown

Embodiment, the semiconductor layer sequence

In particular, have a plurality of active layers, the

Emit radiation of different wavelengths. The use of the DBR mirror 10 is not limited to use as a back mirror in an LED. Rather, the DBR mirror can be advantageously used in various optical or optoelectronic components in which a high reflection over a wide spectral range is desired.

The invention is not limited by the description with reference to the embodiments. Rather, the includes

Invention every new feature as well as every combination of

Features, which includes in particular any combination of features in the claims, even if this feature or this combination itself is not explicitly in the

Claims or embodiments is given.

Claims

claims

1. DBR mirror, comprising:

- A first layer stack (11), the more

Layer pairs (5), wherein the pairs of layers each have a first layer (1) of a first material having a refractive index ni and a second layer (2) of a second material having a refractive index n ₂ and

- A second layer stack (12), the more

Layer pairs (6), wherein the layer pairs each have a third layer (3) of a third material having a refractive index n ₃ and a fourth layer (4) of a fourth material having a refractive index n ₄ ,

in which

- The first layers (1) each have a thickness di =

Xi / (4ni), where λι a first

Central wavelength is,

- The second layers (2) each have a thickness d2 = λ ₂ / (4n ₂ ), wherein λ _{2 is} a second

Central wavelength is,

- The third layers (3) each have a thickness d ₃ = Ä3 / (4n ₃ ), wherein λ _{3 is} a third

Central wavelength is,

- The fourth layers (4) each have a thickness d ₄ = λ ₄ / (4n ₄ ), wherein λ _{4 is} a fourth

Central wavelength is, and

- The four central wavelengths λι, λ ₂ , λ ₃ and λ ₄

are different from each other.

2. DBR mirror according to claim 1,

wherein the third material is equal to the first material is.

3. DBR mirror according to one of the preceding claims, wherein the fourth material is equal to the second material.

4. DBR mirror according to one of the preceding claims, wherein the first material and / or the third material is silicon oxide.

5. DBR mirror according to one of the preceding claims, wherein the second and / or the fourth material is titanium oxide, alumina or niobium oxide.

6. DBR mirror according to one of the preceding claims, wherein a total number of layers (1, 2, 3, 4) is not more than 40.

7. DBR mirror according to one of the preceding claims, wherein the number of layer pairs (5) in the first

Layer stack (11) and / or the number of layer pairs (6) in the second layer stack (12) is between 5 and 10.

8. DBR mirror according to one of the preceding claims, wherein the number of layer pairs (5) in the first layer stack (11) is equal to the number of layer pairs (6) in the second layer stack (12).

9. DBR mirror according to one of the preceding claims, wherein the central wavelength λι, λ ₂ , λ ₃ and λ ₄

each differ by at least 20 nm from each other.

10. DBR mirror according to one of the preceding claims, wherein the central wavelength λι, λ ₂ , λ3 and λ ₄ each differ by at least 30 nm from each other.

11. DBR mirror according to one of the preceding claims,

wherein the smallest of the central wavelength λι, λ ₂ , λ3 and λ ₄ and the largest of the central wavelength λι, λ ₂ , λ3 and λ ₄ differ by at least 150 nm from each other.

12. DBR mirror according to one of the preceding claims,

wherein the central wavelength λι, λ ₂ , λ3 and λ ₄ im

visible spectral range between 400 nm and 800 nm are included.

13. An optoelectronic component comprising a DBR mirror according to one of the preceding claims.

14. Optoelectronic component according to claim 14,

wherein the optoelectronic component is an LED.

15. The optoelectronic component according to claim 14 or 15, wherein the DBR mirror at a rear side of the

optoelectronic component is arranged, wherein the back of a radiation exit surface

opposite.