WO2025131983A1

WO2025131983A1 - Structure, method for producing a structure and optoelectronic device

Info

Publication number: WO2025131983A1
Application number: PCT/EP2024/085887
Authority: WO
Inventors: Aidan CORYELL
Original assignee: Ams Osram International GmbH
Current assignee: Ams Osram International GmbH
Priority date: 2023-12-21
Filing date: 2024-12-12
Publication date: 2025-06-26
Anticipated expiration: 2026-06-21

Abstract

A structure is specified. According to one embodiment, the structure (1) comprises a semiconductor nanocrystal (2) configured to convert a primary radiation into a secondary radiation, and a passivation layer (3) at least partially surrounding the semiconductor nanocrystal (2), wherein the passivation layer (3) comprises a single-faceted layer (31) and a multifaceted layer (32), wherein the single-faceted layer (31) is arranged between the semiconductor nanocrystal (2) and the multifaceted layer (32), and wherein the single-faceted layer (31) and the multifaceted layer (32) each comprise a semiconductor material. Furthermore, a method for producing a structure and an optoelectronic device, in particular comprising a micro-LED, are specified.

Description

STRUCTURE, METHOD FOR PRODUCING A STRUCTURE AND OPTOELECTRONIC DEVICE

A structure, a method for producing a structure, and an optoelectronic device are specified.

It is an object to provide a structure with improved efficiency. Additionally, it is an object to provide a simple method for producing a structure with improved efficiency. Furthermore, it is an object to provide an optoelectronic device with improved efficiency.

A structure is specified. In particular, the structure is a discrete nanoparticle. A nanoparticle is a small object with dimensions in the nanometer range. For example, the structure comprises an extension of the most 100 nm, in particular of at most 50 nm, along its largest dimension. The structure can be a spherical and/or an elongated structure.

According to at least one embodiment, the structure comprises a semiconductor nanocrystal configured to convert a primary radiation into a secondary radiation. The primary radiation and the secondary radiation can at least partially differ from each other. For example, the semiconductor nanocrystal absorbs the primary radiation, converts the primary radiation into secondary radiation, and emits the secondary radiation. In particular, a wavelength or wavelength range of the secondary radiation is in the visible or infrared wavelength range of the electromagnetic spectrum, for example, between and including 300 nm and 2000 nm, for instance, between and including 400 nm and 1000 nm. The semiconductor nanocrystal is , in particular, a particle having a diameter of between and including 1 nm and 100 nm, for example between and including 2 nm and 20 nm, for instance between and including 2 nm and 8 nm . Due to their small si ze , semiconductor nanocrystals have di f ferent properties than a bulk material formed from the same material . It is possible that the semiconductor nanocrystal is spherical , rod-shaped, or cuboid . For example , a surface of the semiconductor nanocrystal is uni form or uneven . The semiconductor nanocrystal is , in particular, a discrete particle . In particular, the semiconductor nanocrystal is a nanoparticle with a mostly crystalline structure , for example , a semiconductor nanoparticle or a quantum dot . In particular, the semiconductor nanocrystal is composed of atoms in a single- or polycrystalline arrangement . For example , the semiconductor nanoparticle is formed from at least one semiconductor material .

According to at least one embodiment , the structure comprises a passivation layer at least partially, in particular completely, surrounding the semiconductor nanocrystal . The passivation layer is configured for electronic passivation . The passivation layer may further improve robustness and/or confinement . In particular, a semiconductor material of the passivation layer comprises a larger band gap than the at least one semiconductor material of the semiconductor nanocrystal .

According to at least one embodiment , the passivation layer comprises a single- faceted layer and a multi faceted layer, wherein the single- faceted layer is arranged between the semiconductor nanocrystal and the multi faceted layer . Here and in the following, a single-faceted layer is a regularly shaped layer having no apparent defects. In particular, the single-faceted layer comprises or consists of monolayers that are continuously grown around the semiconductor nanocrystal. For example, the single-faceted layer is grown epitaxially. The single-faceted layer can also be referred to as a smooth layer. Here and in the following, a multifaceted layer is in irregularly shaped layer. In particular, the multifaceted layer does not comprise or consist of continuous monolayers. For example, the multifaceted layer comprises or consists of islands of growth around the single-faceted layer. For instance, the multifaceted layer is a polycrystalline layer. The multifaceted layer can also be referred to as a bumpy layer .

According to at least one embodiment, the single-faceted layer and the multifaceted layer each comprise or consist of a semiconductor material. The single-faceted layer and the multifaceted layer can comprise or consist of different semiconductor materials or the same semiconductor material. In particular, a single-faceted layer and the multifaceted layer each comprise a metal chalcogenide semiconductor material or a metal pnictide semiconductor material. A metal chalcogenide semiconductor material is a chemical compound consisting of at least one chalcogen anion of the group 16 elements of the periodic table and at least one or more metal cation. For example, the metal chalcogenide semiconductor material is zinc sulfide (ZnS) , zinc selenide (ZnSe) , zinc telluride (ZnTe) , magnesium sulfide (MgS) , magnesium selenide (MgSe) , magnesium telluride (MgTe) , cadmium sulfide (CdS) , cadmium selenide (CdSe) , cadmium telluride (CdTe) , mercury sulfide (HgS) , mercury selenide (HgSe) , mercury telluride (HgTe) , lead sulfide (PbS) , lead selenide (PbSe) , lead telluride (PbTe) , or aluminum sulfide (AIS) . For instance, the metal chalcogenide semiconductor material is ZnS, ZnSe, or MgS . A metal pnictide semiconductor material is a chemical compound consisting of at least one pnictogen anion of the group 15 elements of the periodic table and at least one or more metal cation. For example, the metal pnictide semiconductor material is aluminum phosphide (A1P) , aluminum arsenide (AlAs) , gallium phosphide (GaP) , gallium arsenide (GaAs) , indium phosphide (InP) , indium arsenide (InAs) , indium gallium phosphide (InGaP) , indium gallium arsenide (InGaAs) , or zinc phosphide (ZnP) . For instance, the metal pnictide semiconductor material is indium phosphide (InP) .

According to at least one embodiment, the structure comprises a semiconductor nanocrystal configured to convert a primary radiation into a secondary radiation and a passivation layer at least partially surrounding the semiconductor nanocrystal, wherein the passivation layer comprises a single-faceted layer and a multifaceted layer, wherein the single-faceted layer is arranged between the semiconductor nanocrystal and the multifaceted layer, and wherein the single-faceted layer and the multifaceted layer each comprise a semiconductor material .

It is an idea of the present application to provide a structure having a thick passivation layer by combining a single-faceted layer with a multifaceted layer. The multifaceted layer on top of the single-faceted layer increases the protection of the semiconductor nanocrystal while enabling a thick passivation layer.

Due to a lattice mismatch between the material of the semiconductor nanocrystal and the material of the passivation layer, a passivation layer consisting of a single- faceted layer cannot be grown beyond a speci fic number of monolayers that depends on the lattice mismatch to prevent the introduction of defects into the passivation layer that would be detrimental to the semiconductor nanocrystals performance at high flux as well as the fluorescent properties of the semiconductor nanocrystal .

Growing a multi faceted layer on the single- faceted layer further protects the surface of the semiconductor nanocrystal . The multi faceted layer, in particular the islands of the multi faceted layer, introduces less strain in the structure than a thicker single- faceted layer . As a result , a thicker passivation layer can be grown on the semiconductor nanocrystal .

Furthermore , a passivation layer comprising a single- faceted layer and a multi faceted layer improves the photoluminescence quantum yield maintenance , in particular at increasing flux of a semiconductor chip used to excite the structure , of semiconductor nanocrystals over that of the same semiconductor nanocrystals with only a single- faceted layer as the passivation layer . Semiconductor nanocrystals surrounded with a single- faceted layer and a multi faceted layer have a fluorescence that decreases less with increasing semiconductor chip flux than semiconductor nanocrystals surrounded only with a single- faceted layer, enabling them to also have higher fluorescence at high flux .

According to at least one embodiment , the single- faceted layer and the multi faceted layer each comprise the same semiconductor material . In particular, the semiconductor material is ZnS . A single- faceted layer and a multi faceted layer of the same semiconductor material can advantageously be provided simply and cost-ef f iciently .

According to at least one embodiment , the semiconductor material is ZnS . In particular, ZnS has a higher bandgap than the at least one semiconductor material of the semiconductor nanocrystal . ZnS can advantageously be suited for passivating a semiconductor nanocrystal to improve the semiconductor nanocrystals optical properties .

According to at least one embodiment , the single- faceted layer and the multi faceted layer each comprise a di f ferent semiconductor material , in particular, the semiconductor material of the single- faceted layer is ZnS and the semiconductor material of the multi faceted layer is MgS . In this instance , due to the high lattice mismatch between the semiconductor nanocrystal and MgS , MgS can grow in a multi faceted manner on the single- faceted layer of ZnS .

According to at least one embodiment , the single- faceted layer comprises a thickness of at most ten monolayers . In particular, the thickness of the single- faceted layer comprises at least one monolayer . For example , the singlefaceted layer comprises a thickness of between and including two monolayers and three monolayers at its smallest thickness . For instance , the single- faceted layer comprises between and including five monolayers and six monolayers at its largest thickness . In particular, the thickness of the single- faceted layer depends on the semiconductor material of the semiconductor nanocrystal , the semiconductor material of the single- faceted layer, and the lattice match between these semiconductor materials . For example , a single- faceted layer comprising or consisting of ZnS comprises a thickness between and including two monolayers and six monolayers. A singlefaceted layer comprising a thickness of at most ten monolayers can advantageously improve the optical properties of the semiconductor nanocrystal and provide a basis for growing the multifaceted layer.

According to at least one embodiment, the multifaceted layer comprises a thickness of at most 30 monolayers. In particular, the multifaceted layer comprises a thickness of at most 30 monolayers at its largest thickness. For example, the multifaceted layer comprises a thickness of at most 20 monolayers at its largest thickness.

According to at least one embodiment, the structure comprises an extension of at most 100 nm, in particular of at most 50 nm, along its largest dimension. In particular, the semiconductor nanocrystal surrounded with the passivation layer comprises an extension of at most 100 nm, in particular of at most 50 nm, along its largest dimension.

According to at least one embodiment, the semiconductor nanocrystal comprises or consists of a core. In particular, the core has a diameter of between and including 2 nm and 5 nm. For example, the core is spherical or elongated. In other words, the core is a dot or a rod. For instance, the semiconductor nanocrystal is a core quantum dot. The core can comprise at least one semiconductor material. For example, the semiconductor material is a metal chalcogenide semiconductor material or a metal pnictide semiconductor material. For instance, the core comprises or consist of CdSe, CdS, CdSeS, CdZnSe, CdZnS, CdZnSeS, ZnSe, ZnS, ZnSeS, InP, InGaP, GaP, InAs, PbS, PbSe, CuInSe₂, CuInS₂, or CuInS . Alternatively, the core can comprise a doped semiconductor material. For example, the core comprises or consists of Cu:ZnSe, Cu,In:ZnSe, Cu,Ga:ZnSe, or Cu,Al:ZnSe.

According to at least one embodiment, the semiconductor nanocrystal further comprises a shell at least partially, in particular completely, surrounding the core. In particular, the shell forms a conformal coating of the core. For example, the shell is epitaxially grown onto the core. For instance, the semiconductor nanocrystal is a core-shell quantum dot. In particular, the shell has a thickness between and including 0 nm and 3 nm. For example, the shell comprises a different semiconductor material than the core. For instance, the shell comprises or consists of CdSe, CdS, ZnSe, CdZnSe, CdZnS, GaP, InGaP, InP, or InAs .

According to at least one embodiment, the core is configured to convert the primary radiation into the secondary radiation. In particular, the semiconductor nanocrystal is a core quantum dot or a core-shell quantum dot comprising an emissive core. For example, the core comprises or consists of a semiconductor material configured to convert the primary radiation into the secondary radiation. For instance, the core comprises or consists of CdSe, CdS, CdSeS, CdZnSe, CdZnS, CdZnSeS, ZnSe, ZnSeS, InP, InGaP, InAs, PbS, PbSe, CuInSe₂, CuInS₂, CuInS, Cu:ZnSe, Cu,In:ZnSe, Cu,Ga:ZnSe, or Cu,Al:ZnSe. In particular, the shell comprises a semiconductor material having a higher bandgap than the core. For example, the shell comprises or consists of CdS, ZnSe, CdZnSe, CdZnS, GaP, InGaP, or InP.

According to at least one embodiment, the shell is configured to convert the primary radiation into the secondary radiation. In particular, the structure forms a quantum well structure having an emissive shell between a core and a further semiconductor layer . In this instance , the passivation layer can form the further semiconductor layer of the quantum well structure . For example , the shell comprises or consists of a semiconductor material configured to convert the primary radiation into the secondary radiation . For instance , the shell comprises or consist of ZnSe , CdSe , CdS , InP, or InAs . In particular, the core comprises a semiconductor material having a higher bandgap than the shell . For example , the core comprises or consist of ZnS , CdS , ZnSe , CdZnSe .

According to at least one embodiment , the structure further comprises a barrier layer at least partially surrounding the passivation layer . In particular, the barrier layer is configured to protect the semiconductor nanocrystal against degradation, for example , by chemical species present in the environment of the structure such as water or moisture . For example , the barrier layer comprises or consists of a metal oxide such as silica . A barrier layer surrounding the passivation layer can advantageously further improve the protection of the semiconductor nanocrystal .

Furthermore , a method for producing a structure is speci fied . In particular, the structure described herein is produced by the method for producing a structure . Thus , embodiments , features , and advantages described in combination with the structure also apply to the method for producing a structure and vice versa .

According to at least one embodiment , the method comprises providing a first solution comprising a semiconductor nanocrystal configured to convert a primary radiation into a secondary radiation and oleic acid . The first solution can further comprise a solvent . For example , the solvent is trioctylphosphine oxide , 1-octadecene , oleylamine , squalane , squalene , or trioctylphosphine . In particular, the semiconductor nanoparticles are dispersed in the first solution .

According to at least one embodiment , the method comprises adding a metal alkyl and a chalcogen precursor or a pnictogen precursor to the first solution to form a single- faceted layer of a semiconductor material around the semiconductor nanocrystal . In particular, the metal of the metal alkyl is the metal of the metal chalcogen semiconductor material or the metal pnictide semiconductor material of the singlefaceted layer . For example , the chalcogen of the chalcogen precursor is the chalcogen of the metal chalcogenide semiconductor material of the single- faceted layer such as a sul fur precursor, a selenium precursor, or a tellurium precursor . For instance , the chalcogen precursor is trioctylphosphine sul fide . For example , the pnictogen of the pnictogen precursor is the pnictogen of the metal pnictide semiconductor material of the single- faceted layer such as a phosphorus precursor, or an arsenic precursor . In particular, the metal of the metal alkyl reacts with the oleic acid in the first solution to form a reactive species . The reactive species subsequently can deposit the metal for the semiconductor material on the semiconductor nanocrystal , whereas the chalcogen precursor or the pnictogen precursor can deposit the chalcogen or the pnictogen for the semiconductor material . In particular, the single- faceted layer can be grown on the semiconductor nanocrystal . According to at least one embodiment , the method comprises adding a metal alkyl and a chalcogen precursor or a pnictogen precursor to the first solution to form a multi faceted layer of a semiconductor material around the single- faceted layer . The metal alkyl and the chalcogen precursor or the pnictogen precursor can be the same or di f ferent than the metal alkyl and the chalcogen precursor or the pnictogen precursor in the preceding method step of forming the single- faceted layer . In particular, the metal of the metal alkyl is the metal of the semiconductor material of the multi faceted layer . For example , the chalcogen of the chalcogen precursor or the pnictogen of the pnictogen precursor is the chalcogen or the pnictogen of the metal chalcogenide semiconductor material or the metal pnictide semiconductor material of the multi faceted layer . In particular, the metal of the metal alkyl reacts with the oleic acid in the first solution to form a reactive species . The reactive species subsequently can deposit the metal for the semiconductor material on the single- faceted layer, whereas the chalcogen precursor or the pnictogen precursor can deposit the chalcogen or the pnictogen for the semiconductor material . In particular, the multi faceted layer can be grown on the single- faceted layer .

According to at least one embodiment , the single- faceted layer and the multi faceted layer form a passivation layer . In particular, the passivation layer is a passivation layer for the semiconductor nanocrystal .

According to at least one embodiment , the method for producing a structure comprises providing a first solution comprising a semiconductor nanocrystal configured to convert a primary radiation into a secondary radiation and oleic acid, adding a metal alkyl and a chalcogen precursor or a pnictogen precursor to the first solution to form a singlefaceted layer of a semiconductor material around the semiconductor nanocrystal , and adding a metal alkyl and a chalcogen precursor or a pnictogen precursor to the first solution to form a multi faceted layer of a semiconductor material around the single- faceted layer, wherein the singlefaceted layer and the multi faceted layer form a passivation layer .

In particular, the method for producing a structure is a method for producing a plurality of structures . In this instance , a plurality of semiconductor nanocrystals is provided and the subsequent method steps are performed with the plurality of semiconductor nanocrystals .

With such a method, a structure having improved protective properties can advantageously be produced simply and cost- ef ficiently . By using a metal alkyl as the metal source for the semiconductor materials of the passivation layer, the reaction can be performed in a simple and controlled fashion . Further, using metal alkyl as the metal source has been found to increase the roughness of the multi faceted layer . In other words , by using a metal alkyl , the multi faceted layer can be produced with an increased bumpiness . Furthermore , the metal alkyl is advantageous for controlling the reaction of forming the single- faceted layer and the multi faceted layer .

According to at least one embodiment , the metal alkyl is ( C2H₅ ) ₂M, wherein M is a divalent metal element , or the metal alkyl is ( C2H₅ ) ₃M, wherein M is a trivalent metal element , or the metal alkyl is ( C2H5 ) ₄M, wherein M is a tetravalent metal element . In particular, the metal alkyl is diethyl zinc or diethyl magnesium . Diethyl zinc is advantageously suited for depositing zinc and diethyl magnesium is advantageously suited for depositing magnesium. (C2H₅)₂M, (C2H₅)₃M, and (C2H5) ₄M can advantageously be suited for forming reactive species in the first solution.

According to at least one embodiment, the metal alkyl and the chalcogen precursor or the metal alkyl and the pnictogen precursor are the same for forming the single-faceted layer and the multifaceted layer. In particular, the method step of forming the multifaceted layer can be performed directly subsequent to the method step of forming the single-faceted layer. In other words, any purification steps to remove any precursor materials from the first solution that were added in the method step of forming the single-faceted layer can be omitted. For example, the metal alkyl can be diethyl zinc and the chalcogen precursor can be a sulfur precursor such as trioctylphosphine sulfide in both method steps. In this instance, the reaction of forming both the single-faceted layer and the multifaceted layer can be controlled by the reactiveness of the reactive species formed from the metal alkyl in the first solution and the lattice strain in the growing layers. First, the reactive species can form the single-faceted layer on a surface of the semiconductor nanocrystal. When the single-faceted layer reaches its maximum thickness, in particular when the strain in the single-faceted layer becomes too large, the reactive species can start to form the multifaceted layer.

Furthermore, an optoelectronic device is specified. In particular, the optoelectronic device comprises at least one structure described herein. Thus, embodiments, features, and advantages described in combination with the structure and the method for producing a structure also apply to the optoelectronic device and vice versa .

According to an embodiment , the optoelectronic device comprises a semiconductor chip configured to emit a primary radiation . In other words , the semiconductor chip is configured to emit electromagnetic radiation of a first wavelength range . In particular, the primary radiation comprises wavelengths in the ultraviolet to blue spectral region, for example of 450 nm .

According to at least one embodiment , the optoelectronic device comprises a conversion element configured to convert at least a part of the primary radiation into a secondary radiation, wherein the conversion element comprises or consists of at least one structure , in particular a plurality of structures , described herein . In other words , the conversion element converts the electromagnetic radiation of the first wavelength range into electromagnetic radiation of a second wavelength range . For example , the first wavelength range is at least partially di f ferent from the second wavelength range . For instance , the second wavelength range comprises wavelengths having a lower energy compared to the wavelengths in the first wavelength range . In particular, an ability of the conversion element to convert electromagnetic radiation is attributed to the structure which comprises the semiconductor nanocrystal converting primary radiation into secondary radiation .

According to at least one embodiment , the optoelectronic device comprises a semiconductor chip configured to emit a primary radiation, and a conversion element configured to convert at least a part of the primary radiation into a secondary radiation, wherein the conversion element comprises or consists of at least one structure described herein .

Advantageously, the optoelectronic device described herein has an improved ef ficiency, in particular at high flux of the semiconductor chip, due to the improved properties of the passivation layer . The multi faceted layer on top of the single- faceted layer improves the photoluminescence quantum yield maintenance , in particular at high fluxes of the semiconductor chip, of the structure . In this way, the conversion element can have an improved performance compared to conversion elements comprising structures without the multi faceted layer .

According to at least one embodiment , the semiconductor chip is a micro-LED . Here and in the following, LED is an abbreviation for the term " light-emitting diode" . Micro-LEDs may have a width, a length, a thickness and/or a diameter smaller than or equal to 100 micrometers , in particular smaller than or equal to 70 micrometers , for example smaller than or equal to 50 micrometers . In particular, micro-LEDs , for example rectangular micro-LEDs , have an edge length, for instance in plan view of layers of a layer stack, of a luminous surface smaller than or equal to 70 micrometers , for example smaller than or equal to 50 micrometers . For example , the micro-LED is a light-emitting diode , wherein a growth substrate is removed, such that a thickness of the micro-LED is , for instance , between and including 1 . 5 micrometers and 10 micrometers . For example , the micro-LED is provided on a wafer having releasable retaining structures . The micro-LED can be detached from the wafer in a non-destructive manner . According to at least one embodiment , the conversion element is arranged on the semiconductor chip . In particular, the conversion element is arranged in a beam path of the semiconductor chip . For example , the conversion element is in direct mechanical contact to the semiconductor chip . Alternatively, the conversion element and the semiconductor chip can be spaced apart . For example , further layers such as adhesive layers can be arranged between the conversion element and the semiconductor chip .

According to at least one embodiment , the conversion element comprises a matrix material and the at least one structure is arranged in the matrix material . In particular, the at least one structure is dispersed in the matrix material . For example , the matrix material is silicone . For instance , further phosphors can be dispersed in the matrix material together with the at least one structure .

According to at least one embodiment , the optoelectronic device has a high photoluminescence quantum yield at a flux of the semiconductor chip of between and including 0 W/cm² and 100 W/cm² . In particular, it should be noted that the photoluminescence quantum yield is depending on the flux . For example , the photoluminescence quantum yield decreases with increasing flux . Therefore , a high photoluminescence quantum yield in this context means that the photoluminescence quantum yield exceeds a speci fic value at each flux . In particular, the photoluminescence quantum yield of the optoelectronic device described herein exceeds the photoluminescence quantum yield of an optoelectronic device having structures without a multi faceted layer at each flux . For example , the photoluminescence quantum yield of the optoelectronic device described herein is at least 55 at a flux of 5 W/cm² and at least 20 at a flux of 75 W/cm² . Additionally, the photoluminescence quantum yield of the optoelectronic device described herein can be at least 35 at a flux of 50 W/cm² . The optoelectronic device can advantageously have a signi ficantly higher photoluminescence quantum yield at both low fluxes and high fluxes of the semiconductor chip than optoelectronic devices comprising structures having only a single- faceted layer and no multi faceted layer .

According to at least one embodiment , the optoelectronic device has a photoluminescence quantum yield of at least 45 at a flux of the semiconductor chip between and including 0 W/cm² and 100 W/cm² . In particular, the optoelectronic device has a photoluminescence quantum yield of at least 45 at each flux of the semiconductor chip between and including 0 W/cm² and 100 W/cm² . The optoelectronic device can advantageously have a signi ficantly higher photoluminescence quantum yield at high fluxes of the semiconductor chip than optoelectronic devices comprising structures having only a single- faceted layer and no multi faceted layer . As a result , the optoelectronic device can be particularly suited for applications requiring a high photoluminescence quantum yield at high fluxes such as fluxes of at least 50 W/cm² .

According to at least one embodiment , the optoelectronic device has a photoluminescence quantum yield of at least 50 , in particular of at least 65 , at a flux of the semiconductor chip of at most 20 W/cm² . In particular, the optoelectronic device has a photoluminescence quantum yield of at least 55 , in particular of at least 75 , at a flux of the semiconductor chip of at most 10 W/cm² . The optoelectronic device can advantageously have a signi ficantly higher photoluminescence quantum yield at low fluxes of the semiconductor chip than optoelectronic devices comprising structures having only a single- faceted layer and no multi faceted layer . As a result , the optoelectronic device can be particularly suited for lighting applications requiring a high photoluminescence quantum yield at low fluxes such as fluxes of at most 10 W/cm² .

According to at least one embodiment , the optoelectronic device has a photoluminescence quantum yield of at least 30 , in particular of at least 45 , at a flux of the semiconductor chip of at least 60 W/cm² and at most 70 W/cm² . The optoelectronic device can advantageously have a signi ficantly higher photoluminescence quantum yield at high fluxes of the semiconductor chip than optoelectronic devices comprising structures having only a single- faceted layer and no multi faceted layer . As a result , the optoelectronic device can be particularly suited for applications requiring a high photoluminescence quantum yield at high fluxes such as fluxes of at least 50 W/cm² .

According to at least one embodiment , the optoelectronic device is used in lighting applications , in particular in high flux lighting applications .

Advantageous embodiments and developments of the structure , the method for producing a structure , and the optoelectronic device will become apparent from the exemplary embodiments described below in conj unction with the figures .

In the figures : Figures 1 , 2 , and 3 each show a schematic illustration of a structure according to di f ferent exemplary embodiments ,

Figures 4A, 4B, and 4C show a schematic illustration of a method for producing a structure according to an exemplary embodiment ,

Figures 5A, 5B, and 5C each show a transmission electron microscopy ( TEM) images of semiconductor nanocrystals , intermediate products , and structures obtained with a method for producing a structure according to an exemplary embodiment ,

Figure 6 shows a schematic illustration of an optoelectronic device according to an exemplary embodiment , and

Figure 7 shows the photoluminescence quantum yield as a function of the flux of an optoelectronic device according to an exemplary embodiment and a comparative example .

In the exemplary embodiments and figures , similar or similarly acting constituent parts are provided with the same reference signs . The elements illustrated in the figures and their si ze relationships among one another should not be regarded as true to scale . Rather, individual elements may be represented with an exaggerated si ze for the sake of better representability and/or for the sake of better understanding .

The structure 1 of the exemplary embodiment of figure 1 comprises a semiconductor nanocrystal 2 and a passivation layer 3 . The semiconductor nanocrystal 2 comprises a core 21 . The core 21 is spherical , i . e . a dot . Alternatively, the core 21 can be elongated, i . e . a rod . The core 21 is configured to convert a primary radiation into a secondary radiation . The core 21 comprises a semiconductor material .

The passivation layer 3 comprises a single- faceted layer 31 surrounding the semiconductor nanocrystal 2 . The singlefaceted layer comprises a semiconductor material , in particular a semiconductor material di f ferent from the semiconductor material of the core 21 . The single- faceted layer 31 has a thickness of at least one monolayer and of at most ten monolayers of the semiconductor material . The single- faceted layer 31 forms a regularly shaped layer around the semiconductor nanocrystal 2 with no apparent defects . In other words , the single- faceted layer 31 forms continuously grown monolayers around the semiconductor nanocrystal 2 .

The passivation layer 3 further comprises a multi faceted layer 32 surrounding the single- faceted layer 31 . The multi faceted layer 32 comprises a semiconductor material , in particular the same semiconductor material as the singlefaceted layer 31 . The multi faceted layer 32 has a thickness of most 30 monolayers of the semiconductor material at its largest thickness . As can be seen in figure 1 , the multi faceted layer 32 does not form continues monolayers around the single- faceted layer 31 . Instead, the multi faceted layer 32 comprises islands of semiconductor material growth around the single- faceted layer 31 .

The structure 1 of the exemplary embodiment of figure 2 corresponds essentially to the structure 1 of the exemplary embodiment shown in figure 1 . In addition, the semiconductor nanocrystal 2 of the structure 1 shown in figure 2 comprises a shell 22 surrounding the core 21 . The shell comprises a semiconductor material , in particular a semiconductor material different from the semiconductor material of the core 21. Both the core 21 and the shell 22 are spherical, i.e. forming a dot. The core 21 can be configured to convert the primary radiation into the secondary radiation. In this instance, the structure 1, in particular the semiconductor nanocrystal 2, forms a core-shell quantum dot with an emissive core 21 and a shell 22 having a higher bandgap semiconductor material than the core 21. Alternatively, the shell 22 can be configured to convert the primary radiation into the secondary radiation. In this instance, the structure 1 forms a quantum well structure with the emissive shell 22 arranged between a core 21 and the passivation layer 3 both having a higher bandgap semiconductor material than the shell 22.

The structure 1 of the exemplary embodiment of figure 3 corresponds essentially to the structure 1 of the exemplary embodiment shown in figure 2. In contrast, the semiconductor structure comprises a shell 22 that is elongated, i.e. a rod. In other words, the semiconductor nanocrystal of figure 3 comprises a dot-in-a-rod configuration.

In the following, a combination of semiconductor materials for the structures 1 according to at least one of the exemplary embodiments of figures 1, 2, and 3 is provided. In each of the structures 1 below, the semiconductor materials are listed in order radially in the form core 21/passivation layer 3 or core 21/shell 22/passivation layer 3, and any core 21 or shell 22 or passivation layer 3 can be spherical or elongated, i.e. a dot or a rod.

Structures 1 having a core 21 configured to convert the primary radiation into the secondary radiation are: CdSe/ZnS, CdS/ZnS, CdSe/CdS/ZnS, CdSeS/ZnS, CdZnSe/ZnS, CdZnSeS/ZnS, ZnSe/ZnS, ZnSeS/ZnS, CdSe/ZnSe/ZnS, CdZnSe/CdS/ZnS, CdZnSeS/CdS/ZnS, CdZnS/ZnS, CdSe/CdZnSe/ZnS, CdS/CdZnS/ZnS, InP/ZnS, InP/GaP/ZnS, InP/InGaP/ZnS, InGaP/ZnS, InAs/ZnS, InAs/InP/ZnS, PbS/ZnS, PbSe/ZnS, PbSe/ZnSe/ZnS, CuInSe₂/ZnS, CuInS₂/ZnS, CuInS/ZnS.

Structures 1 having a shell 22 configured to convert the primary radiation into the secondary radiation, i.e. quantum well structures, are: ZnS/ZnSe/ZnS, CdS/CdSe/ZnS, ZnS/CdSe/ZnS, ZnS/CdS/ZnS, ZnSe/CdSe/ZnS, CdZnSe/CdSe/ZnS, CdS/InP/ZnS, ZnSe/InP/ZnS, ZnS/InP/ZnS, ZnSe/InAs/ZnS, GaP/InP/ZnS.

Structures 1 having a doped core 21 configured to convert the primary radiation into the secondary radiation are: Cu:ZnSe/ZnS, Cu, In: ZnSe/ZnS, Cu, Ga : ZnSe/ZnS, Cu, Al : ZnSe/ZnS .

The structures 1 according to the exemplary embodiments of figures 1, 2, and 3 can be produced by the method for producing a structure 1 as described in conjunction with figures 4A, 4B, and 4G. In particular, figures 4A, 4B, and 4G illustrate the method for producing a structure 1 using the structure 1 as shown in the exemplary embodiment of figure 3.

In the method step shown in figure 4A, a semiconductor nanocrystal 2, in particular a plurality of semiconductor nanocrystals 2, is provided. The semiconductor nanocrystal 2 is provided in a first solution. The first solution further comprises oleic acid.

In the method step shown in figure 4B, a single-faceted layer

31 is formed around the semiconductor nanocrystal 2. By forming the single- faceted layer 31 around the semiconductor nanocrystal 2 , an intermediate product 100 is formed . The single- faceted layer 31 is formed by adding a metal alkyl and a chalcogen precursor or a pnictogen precursor to the first solution . For producing a single- faceted layer 31 of ZnS , the metal alkyl is diethyl zinc and the chalcogen precursor is trioctylphosphine sul fide . The metal alkyl reacts with the oleic acid in the first solution to form a reactive species . The reactive species then deposits the metal onto the semiconductor nanocrystal 2 whereas the chalcogen precursor or the pnictogen precursor deposits the chalcogen or the pnictogen onto the semiconductor nanocrystal 2 thereby forming the semiconductor material of the single- faceted layer 31 .

In the method step shown in figure 4C, a multi faceted layer 32 is formed around the single- faceted layer 31 . The multi faceted layer 32 is formed by adding a metal alkyl and a chalcogen precursor or a pnictogen precursor to the first solution . For producing a multi faceted layer 32 of MgS , the metal alkyl is diethyl magnesium and the chalcogen precursor is a sul fur precursor such as trioctylphosphine sul fide . For producing a multi faceted layer 32 of ZnS , the metal alkyl is diethyl zinc and the chalcogen precursor is trioctylphosphine sul fide . The metal alkyl reacts with the oleic acid in the first solution to form a reactive species . The reactive species then deposits the metal onto the single- faceted layer 31 whereas the chalcogen precursor or the pnictogen precursor deposits the chalcogen or the pnictogen onto the singlefaceted layer 31 thereby forming the semiconductor material of the multi faceted layer 32 . In the instance that both the single- faceted layer 31 and the multi faceted layer 32 comprise the same semiconductor material , for example ZnS , puri fication steps between the method steps of forming the single- faceted layer 31 and forming the multi faceted layer 32 can be omitted . In this case , the single- faceted layer 31 is grown until a thickness limit for a single- faceted growth of the semiconductor material is reached . This can be the case , for example , when the strain in the single- faceted layer 31 due to the lattice mismatch between the semiconductor material of the semiconductor nanocrystal 2 and the semiconductor material of the single- faceted layer 31 becomes too large . When the thickness limit is reached, further semiconductor material is deposited on the single- faceted layer 31 in a multi faceted growth thereby forming the multi faceted layer 32 .

Figure 5A shows a TEM image of semiconductor nanocrystals 2 as provided in the method step shown in figure 4A. The semiconductor nanocrystals 2 have a dot-in-a-rod configuration with a core 21 of CdSe and a shell 22 of CdS . The semiconductor nanocrystals 2 comprise an average diameter of 6 . 9 nm along their smallest dimension and an average diameter of 18 . 7 nm along their largest dimension . The average diameters were determined from an average of 440 particles by an automated si zing that approximated the particle shapes as ellipses .

Figure 5B shows a TEM image of intermediate products 100 as formed in the method step shown in figure 4B . The intermediate products 100 comprise a single- faceted layer 31 around the semiconductor nanocrystals 2 shown in figure 5A. The single- faceted layer 31 comprises ZnS . The intermediate products 100 comprise an average diameter of 7 . 5 nm along their smallest dimension and an average diameter of 23 . 6 nm along their largest dimension . The average diameters were determined from an average of 344 particles by an automated si zing that approximated the particle shapes as ellipses . This data shows that the thickness of the single- faceted layer 31 is about two monolayers of ZnS at its smallest thickness and about five to six monolayers of ZnS at its largest thickness .

Figure 5C shows a TEM image of structures 1 as formed in the method step shown in figure 4C . The structures 1 comprise a multi faceted layer 32 around the intermediate products 100 shown in figure 5B . The multi faceted layer 32 comprises ZnS . The structures 1 comprise an average diameter of 8 . 7 nm along their smallest dimension and an average diameter of 22 . 9 nm along their largest dimension . The average diameters were determined from an average of 56 particles by an automated si zing that approximated the particle shapes as ellipses .

The optoelectronic device 10 of the exemplary embodiment of figure 6 comprises a semiconductor chip 20 configured to emit a primary radiation of a first wavelength range . The semiconductor chip 20 can be a micro-LED . For example , the first wavelength range is in the blue spectral region, for instance 450 nm .

A conversion element 30 is arranged on a radiation exit surface of the semiconductor chip 20 . The conversion element 30 can be arranged directly on the radiation exit surface or in a distance to the radiation exit surface . The conversion element 30 can be in the form of a layer or a casting . The conversion element 30 can comprise a matrix material , for example silicone . The at least one structure 1 can be dispersed in the matrix material . Further phosphors can be dispersed in the matrix material together with the at least one structure 1 . The conversion element 30 converts at least a part of the primary radiation into secondary radiation of a second wavelength range . The conversion element comprises or consists of at least one structure 1 described herein .

In figure 7 , the photoluminescence quantum yield PLQY of an optoelectronic device is plotted as a function of the flux F in W/cm² . Curve 7-2 shows the data obtained with an optoelectronic device comprising a semiconductor chip emitting a wavelength of 450 nm and a conversion element comprising a plurality of intermediate products 100 as shown in figure 5B . Curve 7- 1 shows the data obtained with an optoelectronic device 10 described herein comprising a semiconductor chip 30 emitting a wavelength of 450 nm and a conversion element comprising a plurality of structures 1 as shown in figure 5C . Figure 7 shows that the optoelectronic device 10 described herein exhibits a higher photoluminescence quantum yield over the entire measured flux range . In particular, the optoelectronic device 10 described herein exhibits a photoluminescence quantum yield of at least 50 , in particular of at least 65 , at a flux of the semiconductor chip 30 of at most 20 W/cm² . For example , the optoelectronic device 10 has a photoluminescence quantum yield of at least 55 , in particular of at least 75 , at a flux of the semiconductor chip 30 of at most 10 W/cm² . For instance , the optoelectronic device 10 has a photoluminescence quantum yield of at least 30 , in particular of at least 45 , at a flux of the semiconductor chip 30 of at least 60 W/cm² and at most 70 W/cm² . The features and exemplary embodiments described in connection with the figures can be combined with each other according to further exemplary embodiments , even i f not all combinations are explicitly described . Furthermore , the exemplary embodiments described in connection with the figures may have alternative or additional features as described in the general part .

This patent application claims the priority of US provisional patent application 63/ 613 , 539 , the disclosure content of which is hereby incorporated by reference .

The invention is not restricted to the exemplary embodiments by the description on the basis of said exemplary embodiments . Rather, the invention encompasses any new feature and also any combination of features , which in particular comprises any combination of features in the patent claims and any combination of features in the exemplary embodiments , even i f this feature or this combination itsel f is not explicitly speci fied in the patent claims or exemplary embodiments .

References

1 structure

2 semiconductor nanocrystal 21 core

22 shell

3 passivation layer

31 single- faceted layer

32 multi faceted layer

10 optoelectronic device

20 semiconductor chip

30 conversion element 100 intermediate product

7- 1 curve

7-2 curve

Claims

1. A structure (1) comprising

- a semiconductor nanocrystal (2) configured to convert a primary radiation into a secondary radiation, and

- a passivation layer (3) at least partially surrounding the semiconductor nanocrystal (2) , wherein the passivation layer (3) comprises a single-faceted layer (31) and a multifaceted layer (32) , wherein the single-faceted layer (31) is arranged between the semiconductor nanocrystal (2) and the multifaceted layer (32) , and wherein the single-faceted layer (31) and the multifaceted layer (32) each comprise a semiconductor material.

2. The structure (1) according to the preceding claim, wherein the single-faceted layer (31) and the multifaceted layer (32) each comprise the same semiconductor material.

3. The structure (1) according to the preceding claim, wherein the semiconductor material is ZnS .

4. The structure (1) according to at least one of the preceding claims, wherein the single-faceted layer (31) comprises a thickness of at most ten monolayers.

5. The structure (1) according to at least one of the preceding claims, wherein the multifaceted layer (32) comprises a thickness of at most 30 monolayers.

6. The structure (1) according to at least one of the preceding claims, wherein the structure (1) comprises an extension of at most 100 nm along its largest dimension.

7. The structure (1) according to at least one of the preceding claims, wherein the semiconductor nanocrystal (2) comprises a core (21) .

8. The structure (1) according to the preceding claim, wherein the semiconductor nanocrystal (2) further comprises a shell (22) at least partially surrounding the core (21) .

9. The structure (1) according to at least one of the claims 7 or 8 , wherein the core (21) is configured to convert the primary radiation into the secondary radiation.

10. The structure (1) according to claim 8, wherein the shell (22) is configured to convert the primary radiation into the secondary radiation.

11. The structure (1) according to at least one of the preceding claims, further comprising:

- a barrier layer (4) at least partially surrounding the passivation layer.

12. A method for producing a structure comprising

- providing a first solution comprising a semiconductor nanocrystal (20) configured to convert a primary radiation into a secondary radiation and oleic acid, - adding a metal alkyl and a chalcogen precursor or a pnictogen precursor to the first solution to form a singlefaceted layer (31) of a semiconductor material around the semiconductor nanocrystal, and

- adding a metal alkyl and a chalcogen precursor or a pnictogen precursor to the first solution to form a multifaceted layer (32) of a semiconductor material around the single-faceted layer (31) , wherein the single-faceted layer (31) and the multifaceted layer (32) form a passivation layer (3) .

13. The method according to the preceding claim, wherein the metal alkyl is (C2H₅)₂M, wherein M is a divalent metal element, or wherein the metal alkyl is (C2H₅)₃M, wherein M is a trivalent metal element, or wherein the metal alkyl is (C2H5) ₄M, wherein M is a tetravalent metal element.

14. The method according to at least one of the claims 12 or 13, wherein the metal alkyl and the chalcogen precursor or the metal alkyl and the pnictogen precursor are the same for forming the single-faceted layer and the multifaceted layer.

15. An optoelectronic device (10) comprising:

- a semiconductor chip (20) configured to emit a primary radiation, and

- a conversion element (30) configured to convert at least a part of the primary radiation into a secondary radiation, wherein the conversion element (30) comprises or consists of at least one structure (1) according to at least one of the claims 1 to 11.

16. The optoelectronic device (10) according to the preceding claim, wherein the semiconductor chip (20) is a micro-LED.

17. The optoelectronic device (10) according to at least one of the claims 15 or 16, wherein the conversion element (30) is arranged on the semiconductor chip (20) .

18. The optoelectronic device (10) according to at least one of the claims 15 to 17, wherein the conversion element (30) comprises a matrix material and the at least one structure (1) is arranged in the matrix material.

19. The optoelectronic device (10) according to at least one of the claims 15 to 18, wherein the optoelectronic device (10) has a photoluminescence quantum yield of at least 50 at a flux of the semiconductor chip of at most 20 W/cm².

20. The optoelectronic device (10) according to at least one of the claims 15 to 19, wherein the optoelectronic device (10) has a photoluminescence quantum yield of at least 30 at a flux of the semiconductor chip of at least 60 W/cm² and at most 70 W/cm².