DE102018101089A1 - EPITACT CONVERSION ELEMENT, PROCESS FOR PREPARING AN EPITACTIC CONVERSION ELEMENT, RADIATION-EMITTING SEMICONDUCTOR CHIP AND METHOD FOR PRODUCING A RADIATION-EMITTING SEMICONDUCTOR CHIP - Google Patents

Abstract

An epitaxial conversion element (1) is specified, which converts electromagnetic radiation of an excitation spectrum (2) into electromagnetic radiation of an emission spectrum (3). The epitaxial conversion element (1) has a plurality of epitaxial conversion layers (4), wherein - each epitaxial conversion layer (4) electromagnetic radiation of the excitation spectrum (2) into electromagnetic radiation of a single spectrum (5) converts and the emission spectrum (3) from the In addition, a method for producing the epitaxial conversion element, a radiation-emitting semiconductor chip, and a method for producing the radiation-emitting Semiconductor chips specified.

Description

An epitaxial conversion element, a method for producing the epitaxial conversion element, a radiation-emitting semiconductor chip and a method for producing the radiation-emitting semiconductor chip are specified.

Epitaxial conversion elements and radiation-emitting semiconductor chips are, for example, in the document EP 2193550 B1 described.

It is intended to specify a conversion element which is suitable for converting electromagnetic radiation having a comparatively narrow excitation spectrum into a broader emission spectrum. In addition, a radiation-emitting semiconductor chip with such a conversion element and a method for its production will be given. Finally, a method for producing the radiation-emitting semiconductor chip is to be provided.

These objects are achieved by an epitaxial conversion element having the features of patent claim 1, by a method having the steps of patent claim 10, by a radiation-emitting semiconductor chip having the features of patent claim 11 and by a method having the steps of patent claim 17.

Advantageous embodiments and further developments of the epitaxial conversion element, the radiation-emitting semiconductor chip and the two methods are each the subject of the dependent claims.

According to one embodiment of the epitaxial conversion element, the epitaxial conversion element converts electromagnetic radiation of an excitation spectrum into electromagnetic radiation of an emission spectrum.

According to a further embodiment of the epitaxial conversion element, the epitaxial conversion element comprises a multiplicity of epitaxial conversion layers. The epitaxial conversion layers are preferably epitaxially grown and stacked along a stacking direction. Particularly preferably, the epitaxial conversion layers are each in direct contact with each other.

The epitaxial conversion layers preferably each comprise a semiconductor material having a bandgap between a valence band and a conduction band. In the present case, the wavelength-converting properties of the epitaxial conversion layers are based on the photoluminescent properties of the semiconductor material of the epitaxial conversion layers. The semiconductor material of the epitaxial conversion layers absorb electromagnetic radiation of a wavelength range, in this case from the excitation spectrum, so that states in the conduction band of the semiconductor material are excited, which relax with emission of electromagnetic radiation of a further wavelength range, in the present case from the emission spectrum. The further wavelength range preferably comprises larger wavelengths than the wavelength range which is absorbed.

According to one embodiment of the epitaxial conversion element, each epitaxial conversion layer converts electromagnetic radiation of the excitation spectrum into electromagnetic radiation of a single spectrum. The emission spectrum is particularly preferably composed of the individual spectra of the epitaxial conversion layers. The individual spectrum here depends on the band gap of the semiconductor material of the respective epitaxial conversion layer. Consequently, the excitation spectrum depends on the band gaps of the semiconductor materials of the epitaxial conversion layers.

According to another embodiment of the epitaxial conversion element, an FWHM width (short for English "Full Width Half Maximum Width") of the emission spectrum is wider than a FWHM width of the excitation spectrum.

The spectra described here, such as the emission spectrum, the excitation spectrum and the individual spectra, are generally in each case a diagram in which the spectral intensity or the spectral luminous flux per wavelength interval of the electromagnetic radiation emitted by an element as a function of the wavelength λ is shown. In other words, the respective spectrum represents a curve in which the wavelength is plotted on the x-axis and the spectral intensity or the spectral luminous flux is plotted on the y-axis. The spectrum preferably has a maximum at a peak wavelength. The term FWHM width refers to a curve having a maximum, such as the emission spectrum, the excitation spectrum or the individual spectra, where the FWHM width is that region on the x-axis that corresponds to the two y-values that the Half of the maximum.

Particularly preferably, the excitation spectrum has only a single maximum at the peak wavelength. For example, the excitation spectrum is symmetrical to the maximum.

Also, the emission spectrum particularly preferably has only a single maximum. The emission spectrum can also be formed symmetrically to the maximum.

Particularly preferably, the individual spectra of the epitaxial conversion layers each differ from one another. Also, each individual spectrum particularly preferably has only a single maximum at the peak wavelength. The individual spectra can also be formed symmetrically to their maximum.

According to a further embodiment of the epitaxial conversion element, the epitaxial conversion layers are each formed differently from one another. Particularly preferably, the individual spectra of the epitaxial conversion layers each differ from one another. If the epitaxial conversion layers are each formed differently from one another, their individual spectra generally also differ from one another.

For example, the epitaxial conversion layers are based on the same material system or consist of materials of the same material system, but the materials have a different composition. For example, the material system is a III-V semiconductor material system, such as a nitride compound semiconductor material system, an arsenide compound semiconductor material system, a phosphide compound semiconductor material system, or an antimonide compound semiconductor material system.

The nitride compound semiconductor material system comprises nitride compound semiconductor materials. Nitride compound semiconductor materials are compound semiconductor materials containing nitrogen, such as the materials of the system In _x Al _y Ga _1-xy N where 0≤x≤1, 0≤y≤1, and x + y≤1.

An epitaxial conversion element based on a nitride compound semiconductor material is suitable, for example, for converting electromagnetic radiation of an excitation spectrum from the ultraviolet spectral range into a broader, blue emission spectrum.

The arsenide compound semiconductor material system includes arsenide compound semiconductor materials. Arsenide compound semiconductor materials are compound semiconductor materials containing arsenic such as the materials of the system In _x Al _y Ga _1-xy As where 0 ≦ x ≦ 1, 0 ≦ y ≦ 1, and x + y ≦ 1.

An epitaxial conversion element based on an arsenide compound semiconductor material is suitable, for example, for converting electromagnetic radiation of an excitation spectrum from the red spectral region into a broader, infrared emission spectrum comprising electromagnetic radiation with wavelengths of up to 2 micrometers. The epitaxial conversion layers of such an epitaxial conversion element include, for example, InGaAs / GaAs.

The phosphide compound semiconductor material system includes phosphide compound semiconductor materials. Phosphide compound semiconductor materials are compound semiconductor materials containing phosphorus such as the materials of the system In _x Al _y Ga _1-xy P where 0≤x≤1, 0≤y≤1 and x + y≤1.

An epitaxial conversion element based on a phosphide compound semiconductor material is suitable, for example, for converting electromagnetic radiation of an excitation spectrum from the blue spectral range into a broader, green-red emission spectrum.

The antimony compound semiconductor material system comprises antimonide compound semiconductor materials. Antimonide compound semiconductor materials are compound semiconductor materials containing antimony, such as the materials of the system In _x Al _y Ga _1-xy Sb where 0 ≦ x ≦ 1, 0 ≦ y ≦ 1, and x + y ≦ 1.

An epitaxial conversion element based on an antimonide compound semiconductor material is suitable, for example, for converting electromagnetic radiation of an excitation spectrum from the red spectral region into a broader, long-wave infrared emission spectrum comprising electromagnetic radiation having wavelengths of at least 2 micrometers.

According to a further embodiment, the epitaxial conversion element comprises epitaxial conversion layers, each having different thicknesses. Even so, epitaxial conversion layers with different individual spectra can be achieved. The different thicknesses of the epitaxial conversion layers are preferably chosen such that a desired shape of the emission spectrum is achieved. For example, a single epitaxial conversion layer has a thickness of between 5 nanometers and 1000 nanometers inclusive.

The photoluminescent properties of the epitaxial conversion layers can be estimated with a simplified model. The number of photons emitted by an epitaxial conversion layer and thus the absorption of electromagnetic radiation depends on the internal quantum efficiency IQE and the absorption coefficient of the epitaxial conversion layer. The absorption of electromagnetic radiation of a single epitaxial Conversion layer is proportional to exp (-α _m d _m ), where α _m the absorption coefficient of the epitaxial conversion layer and d _m the thickness of the epitaxial conversion layer is. Further boundary conditions for the emission spectrum are its desired shape and its FWHM width. The FWHM width of the single spectrum depends on the temperature and the intensity of the excitation spectrum.

The shape of the emission spectrum can be adjusted by adjusting the thickness and the band gaps of the epitaxial conversion layers, wherein the band gaps of the epitaxial conversion layers depends in particular on their material composition.

The FWHM width of the emission spectrum is influenced in particular by the total number of epitaxial conversion layers. In the simplest case, all epitaxial conversion layers emit single spectra of the same intensity, so that a uniform emission spectrum is generated. The maximum emitted spectral power density of the emission spectrum is limited to the spectral power density of the excitation spectrum divided by the total number of conversion layers N. The thickness of the mth epitaxial conversion layer d _m in the limit IQE = 1 is given by: $${\text{d}}_{\text{m}}=\left(1/{\mathrm{\alpha }}_{\text{m}}\right)*\text{ln}\left\{\left(\text{N}-\text{m}+\text{1}\right)/\left(\text{N}-\text{m}\right)\right\},$$

Each individual spectrum also has a FWHM width AE on, by the temperature T and depends on the power density of the excitation spectrum. For example, the FWHM width is δE _m each individual spectrum is proportional to δE _m = βk _B T, where the coefficient β a measure of the broadening of the individual spectrum and k _B the Bolztmann constant is. Typically, the value of the coefficient is β between 1 and 2. The FWHM width AE For example, a single spectrum ranges from 20 nanometers to 50 nanometers inclusive.

From the FWHM width δE _m = βk _B T for the mth individual spectrum results for a total number N epitaxial conversion layers has an absolute FWHM width of the emission spectrum of ΔE = Nβk _B T.

Assuming the above-mentioned approximations, a minimum thickness of the epitaxial conversion layer results from the quantization condition, that is, when the thickness of the epitaxial conversion layer is lowered below a certain limit value, the distance between two directly adjacent individual spectra is reduced. The condition for the minimum thickness d _min of a single epitaxial conversion layer results in: d _min ≥ {h ² / m _eff δE _m } ^1/2 , where h is Planck's constant and meff is the effective electron mass of the semiconductor material of the epitaxial conversion layer. From this condition, there is an upper limit to the number of epitaxial conversion layers in the epitaxial conversion element Nmax as follows: Nmax <1 / {1-exp (-αd _min )}. Here, α is the absorption coefficient of the thinnest epitaxial conversion layer of the epitaxial conversion element.

According to a further embodiment of the epitaxial conversion element, the thicknesses of the epitaxial conversion layers increase continuously from a radiation entrance surface of the epitaxial conversion element to a radiation exit surface of the epitaxial conversion element.

The individual epitaxial conversion layers preferably have slightly different band gaps. According to one embodiment of the epitaxial conversion element, the band gaps of the epitaxial conversion layers continuously increase from the radiation entrance surface of the conversion element to the radiation exit surface of the conversion element.

Particularly preferably, the individual spectra of the epitaxial conversion layers are partially overlapping and partially formed distinct from each other. By way of example, two directly adjacent individual spectra each overlap in a certain area while they are in each case distinct from one another in a further area. For example, the distance results Δλ between two maxima of directly adjacent single spectra with a FWHM width AE about 1.24 / δE.

According to a further embodiment of the epitaxial conversion element, this comprises a multiplicity of barrier layers. Particularly preferably, a barrier layer is arranged in each case between two epitaxial conversion layers. The barrier layers are particularly preferably designed to enclose electrical charge carriers, such as electrons and holes, within the adjacent epitaxial conversion layer.

Particularly preferably, the two barrier layers are in direct contact with the adjacent epitaxial conversion layer. The barrier layers have preferably grown epitaxially. The barrier layers are preferably based on the same material system as the epitaxial conversion layers. For example, the barrier layers have a thickness that is between 5 nanometers inclusive and 2 micrometers inclusive.

According to a further embodiment of the epitaxial conversion element, this has a cover layer. For example, the radiation exit surface of the conversion element is formed by the cover layer. The cover layer is particularly preferably transparent to electromagnetic radiation of the excitation spectrum and / or of the emission spectrum. In this case, "transparent" particularly preferably means that the cover layer transmits at least 80%, preferably at least 85% and particularly preferably at least 90%, of the respective electromagnetic radiation.

According to a further embodiment of the epitaxial conversion element, the cover layer has a roughened surface. The surface of the cover layer can also be structured. The roughening or structuring of the cover layer serves for better light extraction from the epitaxial conversion element. For example, the cover layer has a thickness between 500 nanometers inclusive and 2 micrometers inclusive.

The cover layer comprises, for example, an oxide, such as silicon dioxide, or is formed from such a material. A cover layer comprising silicon dioxide may be mechanically stably connected to an epitaxial semiconductor layer sequence, for example by bonding.

The epitaxial conversion element can be produced in particular by the method described below. Features and embodiments that are described herein only in connection with the epitaxial conversion element may also be formed in the method and vice versa.

According to one embodiment of the method, a growth substrate is provided. On the growth substrate, the epitaxial conversion layers of the epitaxial conversion element are epitaxially deposited.

Particularly preferably, all epitaxial conversion layers are grown epitaxially on a common growth substrate, preferably lattice-matched.

For example, an epitaxial conversion element based on a phosphide compound semiconductor material that converts electromagnetic radiation of a blue excitation spectrum to a broader green-red emission spectrum may be grown epitaxially on a GaAs substrate.

Furthermore, an epitaxial conversion element based on an arsenide compound semiconductor material that converts red-spectrum electromagnetic radiation into a broader infrared emission spectrum of wavelengths up to 1.1 microns can be epitaxially grown on a GaAs substrate. The epitaxial conversion layers here have preferably grown pseudomorphically and have, for example, InGaAs / GaAs.

For example, to achieve an epitaxial conversion element that converts red-spectrum electromagnetic radiation into a broader infrared emission spectrum having wavelengths of between 1 micron and 2 microns inclusive, epitaxial conversion layers alternately comprising AlInGaAs / InP can be grown epitaxially on an InP substrate ,

For example, an epitaxial conversion element based on an antimonide compound semiconductor material that converts electromagnetic radiation of a red excitation spectrum into a broader infrared emission spectrum having wavelengths of at least 2 microns can be epitaxially grown on a GaSb substrate.

The epitaxial conversion element described here is particularly suitable for being used in a radiation-emitting semiconductor chip. Features and configurations that are described herein only in connection with the epitaxial conversion element can also be formed in the radiation-emitting semiconductor chip and vice versa.

According to one embodiment, the radiation-emitting semiconductor chip comprises the epitaxial conversion element described here.

Furthermore, the radiation-emitting semiconductor chip preferably comprises an epitaxial semiconductor layer sequence with an active zone. The active zone is adapted to emit electromagnetic radiation of a first spectrum at least partially coincident with the excitation spectrum. The epitaxial conversion element preferably converts electromagnetic radiation of the active zone at least partially into radiation of the emission spectrum. Particularly preferably, the epitaxial conversion element completely converts electromagnetic radiation of the active zone into radiation of the emission spectrum.

For example, the epitaxial semiconductor layer sequence and the epitaxial conversion element may be grown epitaxially together on a growth substrate. In other words, the epitaxial semiconductor layer sequence and the epitaxial conversion element be formed monolithically with each other. In this case, the radiation-emitting semiconductor chip is in particular free of a connecting layer which mechanically stably interconnects the epitaxial semiconductor layer sequence and the epitaxial conversion element.

Alternatively, it is also possible that the epitaxial semiconductor layer sequence and the epitaxial conversion element are epitaxially grown separately on different growth substrates. In this case, the radiation-emitting semiconductor chip preferably comprises a connection layer which mechanically stably interconnects the epitaxial semiconductor layer sequence and the epitaxial conversion element. The connection layer is particularly preferably transparent to the electromagnetic radiation of the epitaxial semiconductor layer sequence as well as the electromagnetic radiation of the epitaxial conversion element. By way of example, the connection layer is an adhesive layer.

According to a further embodiment, the epitaxial semiconductor layer sequence is arranged on a support. The carrier is in particular intended to mechanically stabilize the epitaxial semiconductor layer sequence. In this case, the support is particularly preferably different from the growth substrate of the epitaxial semiconductor layer sequence. Particularly preferably, a reflective layer is arranged between the carrier and the epitaxial semiconductor layer sequence, which is in particular suitable for directing radiation of the active zone to a radiation exit surface of the radiation-emitting semiconductor chip.

The epitaxial conversion element and / or the radiation-emitting semiconductor chip can serve, for example, as a light source in a miniaturized optical gas sensor.

According to a further embodiment, the epitaxial semiconductor layer sequence is based on a phosphide compound semiconductor material and the first spectrum comprises red light. The epitaxial conversion element in this embodiment of the radiation-emitting semiconductor chip is particularly preferably based on an arsenide compound semiconductor material and converts the red light of the first spectrum into infrared light, particularly preferably completely. Such a semiconductor chip can be used in particular advantageously as a light source in an optical gas sensor.

The radiation-emitting semiconductor chip can be produced, for example, by the method described below. Features and embodiments described herein only in connection with the radiation-emitting semiconductor chip may also be formed in the method and vice versa.

According to one embodiment of the method for producing a radiation-emitting semiconductor chip, a growth substrate is provided. On the growth substrate, an epitaxial conversion element is preferably grown epitaxially.

According to a further embodiment of the method for producing the radiation-emitting semiconductor chip, an epitaxial semiconductor layer sequence is applied to the epitaxial conversion element.

For example, the epitaxial semiconductor layer sequence can also be epitaxially deposited on the epitaxial conversion element. Here, the same growth substrate is used for the epitaxial conversion element and the epitaxial semiconductor layer sequence.

Alternatively, it is also possible for the epitaxial semiconductor layer sequence to be epitaxially deposited on a further growth substrate, which is different from the growth substrate of the epitaxial conversion element. In this embodiment of the method for producing the radiation-emitting semiconductor chip, the epitaxial semiconductor layer sequence is mechanically stably connected to the epitaxial conversion element, preferably through a connection layer.

The present conversion element is based on the idea of making use of the photoluminescent properties of epitaxially grown semiconductor layers for wavelength conversion. In particular, a comparatively narrow excitation spectrum, such as that produced by a light-emitting diode with an active zone, is to be converted into a broader emission spectrum. For this purpose, the epitaxial conversion element preferably comprises a multiplicity of epitaxial conversion layers stacked on top of one another, which have mutually different emission properties and conversion properties. In this way, the emission spectrum of the epitaxial conversion element can be composed specifically from the individual spectra of the different epitaxial conversion layers.

In particular, the proposed epitaxial conversion element can be produced comparatively inexpensively, scalably and reliably, so that a light source with a comparatively broad emission spectrum can be achieved. Different spectral regions of the emission spectrum can be achieved by the use of various semiconductor compound materials and respectively adapted excitation spectra are achieved. In particular, by adjusting the excitation spectrum to the epitaxial conversion element, Stokes losses can be reduced, so that more effective light conversion can be achieved.

• 1 zeigt eine schematische Schnittdarstellung eines strahlungsemittierenden Halbleiterchips gemäß einem Ausführungsbeispiel.
• 2 zeigt eine schematische Schnittdarstellung durch einen Bereich eines epitaktischen Konversionselements gemäß einem Ausführungsbeispiel.
• 3 zeigt eine schematische Darstellung der Bandstruktur eines epitaktischen Konversionselements gemäß einem weiteren Ausführungsbeispiel.
• Anhand der schematischen Schnittdarstellungen der 4 und 5 wird ein Verfahren zur Herstellung eines strahlungsemittierenden Halbleiterchips näher beschrieben.
• Anhand der schematischen Schnittdarstellungen der 6 und 7 wird ein Verfahren zur Herstellung eines epitaktischen Konversionselements näher beschrieben.
• 8 zeigt simulierte Werte der FWHM-Breite eines Emissionsspektrums gemäß einem Ausführungsbeispiel auf der rechten vertikalen Achse und simulierte Dicken der epitaktischen Konversionsschichten gemäß einem Ausführungsbeispiel auf der linken vertikalen Achse in Abhängigkeit der Gesamtanzahl N an epitaktischen Konversionsschichten.
• 9 zeigt Simulationsergebnisse eines Emissionsspektrums bei einem vorgegebenen Anregungsspektrum gemäß einem Ausführungsbeispiel.

Further advantageous embodiments and developments of the invention will become apparent from the embodiments described below in conjunction with the figures.

• 1 shows a schematic sectional view of a radiation-emitting semiconductor chip according to an embodiment.
• 2 shows a schematic sectional view through a portion of an epitaxial conversion element according to an embodiment.
• 3 shows a schematic representation of the band structure of an epitaxial conversion element according to another embodiment.
• Based on the schematic sectional views of 4 and 5 a method for producing a radiation-emitting semiconductor chip is described in more detail.
• Based on the schematic sectional views of 6 and 7 a method for producing an epitaxial conversion element will be described in more detail.
• 8th shows simulated values of the FWHM width of an emission spectrum according to an embodiment on the right vertical axis and simulated thicknesses of the epitaxial conversion layers according to an embodiment on the left vertical axis as a function of the total number N on epitaxial conversion layers.
• 9 shows simulation results of an emission spectrum at a given excitation spectrum according to an embodiment.

The same, similar or equivalent elements are provided in the figures with the same reference numerals. The figures and the proportions of the elements shown in the figures with each other are not to be considered to scale. Rather, individual elements, in particular layer thicknesses, can be shown exaggeratedly large for better representability and / or better understanding.

The radiation-emitting semiconductor chip according to the exemplary embodiment of FIG 1 has an epitaxial conversion element 1 on. The epitaxial conversion element 1 converts an electromagnetic radiation of an excitation spectrum 2 in electromagnetic radiation of an emission spectrum 3 um, preferably completely. More preferably, an FWHM width ΔE = N * δE of the emission spectrum is wider than a FWHM width AE of the excitation spectrum 2 , Here, N denotes the total number of epitaxial conversion layers 4 ,

The epitaxial conversion element 1 includes a variety of epitaxial conversion layers 4 , Every epitaxial conversion layer 4 converts electromagnetic radiation of the excitation spectrum 2 in electromagnetic radiation of a single spectrum 5 around. The single spectra 5 Here in each case differ from each other. The emission spectrum 3 consists of the individual spectra 5 the epitaxial conversion layers 4 together.

Furthermore, the epitaxial conversion element comprises 1 a cover layer 6 responsible for electromagnetic radiation of the emission spectrum 3 and optionally for electromagnetic radiation of the excitation spectrum 2 is transparent. The cover layer 6 has a structuring 7 on, the decoupling of electromagnetic radiation, in particular at least the emission spectrum 3 , from the epitaxial conversion element 1 improved with advantage.

The epitaxial conversion element 1 is with a connection layer 8th , such as an adhesive layer, with an epitaxial semiconductor layer sequence 9 mechanically stable connected.

The epitaxial semiconductor layer sequence 9 includes an active zone 10 , which emits in operation electromagnetic radiation of a first spectrum, at least partially with the excitation spectrum 2 of the epitaxial conversion element 1 matches. The epitaxial semiconductor layer sequence 9 is on a carrier 11 arranged. Between the carrier 11 and the epitaxial semiconductor layer sequence 9 is a reflective layer 12 arranged, which is adapted to electromagnetic radiation of the active zone 10 to direct to a radiation exit surface of the semiconductor chip.

An embodiment of the epitaxial conversion element 1 is determined by the 2 explained in more detail, wherein 2 for clarity only represents a section. The epitaxial conversion element 1 has several epitaxial conversion layers 4 of which three are shown in the present case. The thicknesses and band gaps of the epitaxial conversion layers 4 take at the epitaxial conversion element 1 according to the embodiment of the 2 from a radiation entrance surface 13 of the epitaxial conversion element 1 to a Radiation exit area 14 of the epitaxial conversion element 1 continuously too. Therefore, the individual spectra differ 5 that of the epitaxial conversion layers 4 emitted electromagnetic radiation from each other.

The epitaxial conversion layers 4 according to the 2 continue to have at least two barrier layers 15 on, between which one of the epitaxial conversion layers 4 is arranged. The barrier stories 15 are in direct contact with the epitaxial conversion layer 4 and concentrate electrical charge carriers, such as electrons or holes, within the epitaxial conversion layer 4 ,

An epitaxial conversion element 1 may have a band diagram as shown schematically in FIG 3 is shown. The epitaxial conversion element 1 indicates a total number N of epitaxial conversion layers 4 on. The epitaxial conversion layers 4 are consecutively numbered from m = 1 to m = N.

An emission energy of the individual spectra 5 the epitaxial conversion layers 4 takes from the radiation entrance surface 13 of the epitaxial conversion element 1 to the radiation exit surface 14 of the epitaxial conversion element 1 to. The FWHM width AE the emission spectrum 3 is proportional to Ack _B T , The constant a depends on the choice of band gaps of the epitaxial conversion layers 4 from. With k _B is the Boltzmann constant and with T the temperature indicated.

In the method for producing a radiation-emitting semiconductor chip according to the exemplary embodiment of the 4 and 5 becomes a growth substrate 16 for the epitaxial conversion layers 4 of the epitaxial conversion element 1 provided. On the growth substrate 16 becomes a transparent cover layer 6 applied, in turn, the epitaxial conversion layers 4 of the epitaxial conversion element 1 to be ordered.

On the epitaxial conversion layers 4 becomes an epitaxial semiconductor layer sequence 9 arranged. The epitaxial semiconductor layer sequence 9 comprises an epitaxially grown electrical n-contact layer 17 , which for example comprises n-InGaAlP or consists of this material. On the n-contact layer 17 is an n-type current spreading layer 18 arranged. On the n-current spreading layer 18 is still an active zone 10 arranged, which is adapted to generate electromagnetic radiation of a first spectrum. The first spectrum has present red light or consists of red light. On the active zone 10 is finally a p-type current spreading layer 19 applied ( 4 ).

The epitaxial semiconductor layer sequence 9 is based here on a Phosphidverbindungshalbleitermaterial, such as InGaAlP.

In a next step, attention is paid to the exposed main area of the epitaxial semiconductor layer sequence 9 A carrier 22 applied and the growth substrate 16 removed, for example by etching. The cover layer 6 of the epitaxial conversion element 1 serves as etch stop layer and forms in the finished radiation-emitting semiconductor chip whose radiation exit surface ( 5 ).

In the process for producing an epitaxial conversion element 1 according to the embodiment of the 6 and 7 becomes a growth substrate in a first step 16 for the epitaxial conversion layers 4 provided ( 6 ). In the growth substrate 16 it may be, for example, a GaAs substrate.

In a next step, as in 7 schematically shown, the epitaxial conversion layers 4 and the barrier stories 15 epitaxially on the growth substrate 16 deposited. The epitaxial conversion layers 4 of the epitaxial conversion element 1 For example, they can be based on a phosphide compound semiconductor material. Such an epitaxial conversion element 1 is suitable for electromagnetic radiation of an excitation spectrum 2 from the blue spectral range at least partially into a green-red emission spectrum 3 convert.

Furthermore, it is also possible that the epitaxial conversion layers 4 AlGalnAs / GaAs include. Such an epitaxial conversion element 1 is suitable for an emission spectrum 3 with wavelengths up to 1.1 microns. The epitaxial growth of the epitaxial conversion layers 4 is particularly preferably pseudomorphic or lattice-matched.

The diagram according to the 8th shows simulated values of thickness d _m the mth epitaxial conversion layer 4 in nanometers (left y Axis) depending on the total number of epitaxial conversion layers N (x-axis) according to the formula d _m = (1 / α _m ) * ln {(N-m + 1) / (Nm)}. In this approximation, a photon recycling effect is neglected. If this effect were included, the thickness of the epitaxial conversion layers would increase 4 reduce with smaller band gaps. This would result in a reduction of the possible total number of epitaxial conversion layers 4 according to N _max <1 / {1-exp (-αd _min )}.

In addition, the diagram shows the 8th simulated values of the FWHM width AE the emission spectrum 3 in milli-electron volts (right y-axis) depending on the total number N of epitaxial conversion layers 4 according to the formula ΔE = βNk _B T once for β = 1.5 and once for β = 0.5. The constant β is a measure of the distance between the maxima of two directly adjacent individual spectra 5 , The value 0.5 for β should in this case lead to a more uniform emission spectrum 3 to lead. The right y- Axis is limited to 500 milli-electron volts, the FWHM width AE the emission spectrum 3 but it can also be above that.

The minimum thickness d _min an epitaxial conversion layer 4 this results in about 15 nanometers, while the maximum value of the total Nmax of epitaxial conversion layers 4 is about 36. The thickness of the individual epitaxial conversion layers 4 is, for example, between 10 nanometers inclusive and 100 nanometers inclusive.

In the 8th simulated values apply, for example, to an AlGaAs-based epitaxial conversion element 1 , whose excitation spectrum 2 a peak wavelength λ _peak of about 650 nanometers and having a structure such as in 4 disclosed.

9 shows a diagram with a simulated emission spectrum 3 starting from a likewise illustrated excitation spectrum 2 , The total number N of epitaxial conversion layers 4 here is 10. The emission spectrum 3 consists of the individual spectra 5 the epitaxial conversion layers 4 together. The emission spectrum 3 of the epitaxial conversion element 1 has a much larger FWHM range AE on as the excitation spectrum 2 ,

The invention is not limited by the description based on the embodiments of these. Rather, the invention encompasses any novel feature as well as any combination of features, including in particular any combination of features in the claims, even if this feature or combination itself is not explicitly stated in the patent claims or exemplary embodiments.

LIST OF REFERENCE NUMBERS

1

conversion element

2

excitation spectrum

3

emission spectrum

4

conversion layer

5

Single spectrum

6

topcoat

7

structuring

8th

link layer

9

epitaxial semiconductor layer sequence

10

active zone

11

carrier

12

reflective layer

13

Radiation entrance surface of the conversion element

14

Radiation exit surface of the conversion element

15

barrier layers

16

growth substrate

17

n-contact layer

18

n-current spreading layer

19

p-current-spreading layer

ΔE, δE

FWHM width

λ _peak

Peak wavelength

QUOTES INCLUDE IN THE DESCRIPTION

This list of the documents listed by the applicant has been generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Cited patent literature

• EP 2193550 B1 [0002]

Claims (19)

Epitaxial conversion element (1), which converts electromagnetic radiation of an excitation spectrum (2) into electromagnetic radiation of an emission spectrum (3), having a plurality of epitaxial conversion layers (4), wherein - converts each epitaxial conversion layer (4) electromagnetic radiation of the excitation spectrum (2) into electromagnetic radiation of a single spectrum (5) and the emission spectrum (3) from the individual spectra (5) composed, and - a FWHM width of the emission spectrum (3) is wider than a FWHM width of the excitation spectrum (2). Epitaxial conversion element (1) according to the preceding claim, wherein the epitaxial conversion layers (4) are each formed differently from each other, so that the individual spectra (5) differ from each other. Epitaxial conversion element (1) according to one of the preceding claims, in which the epitaxial conversion layers (4) are based on the same material system but each have different compositions. Epitaxial conversion element (1) according to one of the preceding claims, in which the epitaxial conversion layers (4) have different thicknesses. An epitaxial conversion element (1) according to any one of the preceding claims, wherein the thicknesses of the epitaxial conversion layers (4) increase continuously from a radiation entrance surface (13) of the epitaxial conversion element (1) to a radiation exit surface (14) of the epitaxial conversion element (1). Epitaxial conversion element (1) according to one of the preceding claims, in which the band gaps of the epitaxial conversion layers (4) increase continuously from the radiation entrance surface (13) of the epitaxial conversion element (1) to the radiation exit surface (14) of the epitaxial conversion element (1). Epitaxial conversion element (1) according to one of the above claims, in which the individual spectra (5) are partially overlapping and partially distinct from one another. Epitaxial conversion element (1) according to one of the above claims, having a multiplicity of barrier layers (15), wherein a respective barrier layer (15) is arranged between two epitaxial conversion layers (4). Epitaxial conversion element (1) according to one of the preceding claims, in which a radiation exit surface (13) of the epitaxial conversion element (1) is formed by a roughened cover layer (6). Process for producing an epitaxial conversion element (1) according to one of the preceding claims, having the following steps: - Providing a growth substrate (16), and epitaxially depositing epitaxial conversion layers (4) on the growth substrate (16). A radiation-emitting semiconductor chip comprising: - an epitaxial conversion element (1) according to one of Claims 1 to 9 , and - an epitaxial semiconductor layer sequence (9) comprising an active region (10), the active region (10) being adapted to emit electromagnetic radiation of a first spectrum at least partially coincident with the excitation spectrum (2) epitaxial conversion element (1) at least partially converts electromagnetic radiation of the active zone (10) into radiation of the emission spectrum (3). A radiation-emitting semiconductor chip according to the preceding claim, in which the epitaxial conversion element (1) completely converts the electromagnetic radiation of the active zone (10) into radiation of the emission spectrum (3). Radiation-emitting semiconductor chip according to one of Claims 11 to 12 in which the epitaxial semiconductor layer sequence (9) and the epitaxial conversion element (1) are monolithic. Radiation-emitting semiconductor chip according to one of Claims 11 to 13 in which the epitaxial semiconductor layer sequence (9) and the epitaxial conversion element (1) are mechanically stably interconnected by a connecting layer (8). Radiation-emitting semiconductor chip according to one of Claims 11 to 14 , in which the epitaxial semiconductor layer sequence (9) is arranged on a carrier (11), wherein a reflective layer (12) is arranged between the carrier (11) and the epitaxial semiconductor layer sequence (9). Radiation-emitting semiconductor chip according to one of Claims 11 to 15 in which - the epitaxial semiconductor layer sequence (9) is based on a phosphide compound semiconductor material and the first spectrum comprises red light, and - the epitaxial conversion element (1) is based on an arsenide compound semiconductor material and converts the red light of the first spectrum into infrared light. A method for producing a radiation-emitting semiconductor chip according to one of Claims 11 to 16 with the following steps: - providing a growth substrate (16), - epitaxially growing an epitaxial conversion element (1) onto the growth substrate (16), and - applying an epitaxial semiconductor layer sequence (9) to the epitaxial conversion element (1). Method according to the preceding claim, in which the epitaxial semiconductor layer sequence (9) is deposited epitaxially on the epitaxial conversion element (1). Method according to Claim 17 in which - the epitaxial semiconductor layer sequence (9) is epitaxially deposited on a further growth substrate which is different from the growth substrate (16) of the epitaxial conversion element (1), and - the epitaxial semiconductor layer sequence (9) is connected to the epitaxial conversion element (1) mechanically stable by a connecting layer (8) is connected.

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