WO2025171984A1

WO2025171984A1 - Semiconductor nanocrystal structure, method for producing thereof and optoelectronic device

Info

Publication number: WO2025171984A1
Application number: PCT/EP2025/051025
Authority: WO
Inventors: Robert FITZMORRIS; Aidan CORYELL
Original assignee: Ams Osram International GmbH
Current assignee: Ams Osram International GmbH
Priority date: 2024-02-13
Filing date: 2025-01-16
Publication date: 2025-08-21
Anticipated expiration: 2026-08-13

Abstract

A structure is specified. According to one embodiment, the structure (1) comprises a semiconductor nanocrystal (2) and a first shell (3) at least partially surrounding the semiconductor nanocrystal (2), wherein the structure (1) is configured to convert a primary radiation into a secondary radiation, wherein the first shell (3) comprises a metal selenide semiconductor material or a metal phosphide semiconductor material, and wherein the first shell (3) is rod-shaped. Furthermore, methods for producing a structure and an optoelectronic device, in particular comprising a micro-LED, are specified.

Description

SEMICONDUCTOR NANOCRYSTAL STRUCTURE, METHOD FOR PRODUCING THEREOF AND OPTOELECTRONIC DEVICE

A structure, methods 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 simple methods 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, a cubic, and/or an elongated structure.

According to at least one embodiment, the structure comprises a semiconductor nanocrystal. 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 size, semiconductor nanocrystals have different properties than a bulk material formed from the same material. It is possible that the semiconductor nanocrystal is spherical, spheroidal, rodshaped, or cubic. For example, a surface of the semiconductor nanocrystal is uniform 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 first shell at least partially, in particular completely, surrounding the semiconductor nanocrystal . In particular, the first shell is configured for electronic passivation . The first shell may further improve robustness and/or confinement . Alternatively, the first shell can be configured for converting a primary radiation into a secondary radiation .

According to at least one embodiment , the structure is configured to convert a primary radiation into a secondary radiation . The primary radiation and the secondary radiation can at least partially di f fer from each other . For example , the structure 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 .

According to at least one embodiment the first shell comprises a metal selenide semiconductor material or a metal phosphide semiconductor material . The metal selenide semiconductor material can have a wurtzite crystal structure . In particular, the metal selenide semiconductor material is a zinc-containing selenide semiconductor material . For example , the metal selenide semiconductor material is zinc selenide ( ZnSe ) , cadmium zinc selenide ( CdZnSe ) , zinc selenide sul fide ( ZnSeS ) , or zinc telluride selenide ( ZnTeSe ) . For instance , the bandgap and/or the lattice parameters of the ZnSe are adj usted by exchanging a part of the Zn with Cd and/or a part of the Se with Te or S . In particular, the metal phosphide semiconductor material is an indium-containing and/or gallium-containing phosphide semiconductor material . For example , the metal phosphide semiconductor material is indium phosphide ( InP ) , gallium phosphide ( GaP ) or indium gallium phosphide ( InGaP ) .

According to at least one embodiment , the first shell is rodshaped . In particular, the first shell is elongated . For example , a first dimension of the first shell is larger than a second dimension and a third dimension both perpendicular to the first dimension . For instance , an outer shape of the first shell surrounding the semiconductor nanocrystal is that of a cuboid, a hexagonal prism, an ellipsoid, or a cylinder .

According to at least one embodiment , the structure comprises a semiconductor nanocrystal and a first shell at least partially surrounding the semiconductor nanocrystal , wherein the structure is configured to convert the primary radiation into a secondary radiation, wherein the first shell comprises a metal selenide semiconductor material or a metal phosphide semiconductor material , and wherein the first shell is rodshaped .

It is an idea of the present application to provide a structure having a rod-shaped first shell of a metal selenide semiconductor material or a metal phosphide semiconductor material . The rod-shaped first shell reduces particle-to- particle sel f-absorption, increases absorption in the UV and blue region, reduces red shi fting of the emission wavelength and provides additional corrosion resistance . Thus , the rodshaped first shell enables the protection of the semiconductor nanocrystal . Further, a rod-shaped first shell can be thicker than a spherical or cubic first shell while avoiding issues that thick spherical or cubic first shells present such as increased core-shell strain, increased introduction of trap-sites , decreased photoluminescent quantum yield, increased excited-state li fetime , and deactivation of the structure due to non-radiative pathways such as auger recombination . These issues of thick spherical or cubic first shells arise from the lattice mismatch between the semiconductor nanocrystal and the shell material which limits the thickness that can be deposited before crystal defects become a source of trap-sites . By using a rod-shaped first shell , the strain due to the lattice mismatch is focused in only one axis of the shell whereas , in the other directions , the strain is less than in spherical or cubic shells . In particular, for the same amount of material of the first shell , a rod-shaped first shell avoids more deficits and achieves more advantages than spherical or cubic first shells .

According to at least one embodiment , an aspect ratio of the first shell is at least 1 . 5 , for example 2 . In particular, the aspect ratio of the first shell is the ratio of the extension of the first shell along its largest dimension, i . e . its length, and the extension of the first shell along its shortest dimension, i . e . its width and/or its height . In other words , the first shell has an elongated structure . It should be noted that the extension of the first shell is not limited to its thickness . Instead, the extension of the first shell includes all components such as the semiconductor nanocrystal surrounded by the first shell in the direction of the extension . In other words , for a first shell surrounding semiconductor nanocrystal , the extension of the first shell along a speci fic direction includes the thickness of the first shell on one side of the semiconductor nanocrystal in that direction, the thickness or diameter of the semiconductor nanocrystal in that direction, and the thickness of the first shell on the other side of the semiconductor nanocrystal in that direction . A first shell having an aspect ratio of at least 1 . 5 is advantageously rodshaped .

According to at least one embodiment , the semiconductor nanocrystal comprises a core or consists of a core . In particular, the core has a diameter of between and including 2 nm and 9 nm . For example , the core is spherical , cubic, tetrahedral , or elongated . In other words , the core is a dot , a cube , 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 . 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 . 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 instance , the core comprises or consists of CdSe , CdS , CdZnSe , ZnSe , ZnS , InP, InAs , PbS , PbSe , or CuInSe₂ . 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 second shell at least partially, in particular completely, surrounding the core. In particular, the second shell forms a conformal coating of the core. For example, the second shell is epitaxially grown onto the core. For instance, the semiconductor nanocrystal is a core-shell quantum dot. In particular, the second shell has a thickness between and including 0 nm and 3 nm. For example, the second shell comprises a different semiconductor material than the core. The semiconductor material of the second shell can be a chalcogenide semiconductor material or a pnictide semiconductor material. For instance, the second shell comprises or consists of CdSe, InP, or InAs . In particular, the second shell is arranged between the core and the first shell .

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, CdZnSe, InP, InAs, PbS, PbSe, CuInSe₂, Cu:ZnSe, Cu,In:ZnSe, Cu,Ga:ZnSe, or Cu,Al:ZnSe. In particular, in the case a second shell is present, the second shell comprises a semiconductor material having a wider bandgap than the core. For example, the second shell comprises or consists of InP. According to at least one embodiment , the second shell is configured to convert the primary radiation into the secondary radiation . In particular, the structure forms a quantum well structure having an emissive second shell between a core and a further semiconductor layer . In this instance , the first shell can form the further semiconductor layer of the quantum well structure . For example , the second shell comprises or consists of a semiconductor material configured to convert the primary radiation into the secondary radiation . For instance , the second shell comprises or consists of CdSe , InP, or InAs . In particular, the core comprises a semiconductor material having a wider bandgap than the shell . For example , the core comprises or consists of ZnS , CdS , ZnSe , CdZnSe , GaP, InGaP, or InP .

According to at least one embodiment , the first shell comprises a thickness in a first direction larger than a thickness in a second direction perpendicular to the first direction . Here and in the following, the thickness of the first shell is a height of the first shell on a surface of the semiconductor nanocrystal . The first shell can comprise a thickness in a third direction perpendicular to the first direction and the second direction . The thickness in the third direction can be equal to or larger than the thickness in the second direction and smaller than the thickness in the first direction . In particular, the first direction is the extension along the length of the first shell . The thickness of the first shell along the first direction, the second direction and/or the third direction can depend on the strain due to the lattice mismatch between the material of the semiconductor nanocrystal and the material of the first shell . In general , the higher the lattice mismatch, the thinner the first shell can be grown before defects are introduced . For example , the thickness of the first shell in the first direction is at least three monolayers . For example , the thickness of the first shell in the second direction is at least one monolayer . For instance , the thickness of the first shell in the second direction is at most three monolayers . A first shell comprising a thickness in a first direction larger than a thickness in a second direction is advantageously rod-shaped .

According to at least one embodiment , the first shell is free of cadmium . For example , the first shell comprises or consists of ZnSe , ZnSeS , ZnTeSe , InP, GaP, or InGaP . By using a semiconductor material for the first shell that is free of cadmium, the structure can advantageously comprise much less or no cadmium and, therefore , more structures can be loaded into an optoelectronic device while adhering to cadmium limit regulations .

According to at least one embodiment , an aspect ratio of the semiconductor nanocrystal , in particular of the core of the semiconductor nanocrystal , is smaller than an aspect ratio of the first shell . In other words , the first shell is more elongated than the semiconductor nanocrystal . For example , the core is spherical or cubic and thus has an aspect ratio of 1 . Alternatively, the core can be rod-shaped and have a smaller aspect ratio than the first shell .

According to at least one embodiment , an aspect ratio of the semiconductor nanocrystal , in particular of the core of the semiconductor nanocrystal , is equal to an aspect ratio of the first shell . For example , the semiconductor nanocrystal is rod-shaped and has the same aspect ratio as the first shell . According to at least one embodiment , an aspect ratio of the semiconductor nanocrystal , in particular of the core of the semiconductor nanocrystal , is larger than an aspect ratio of the first shell . In other words , the semiconductor nanocrystal is more elongated than the first shell . For example , the semiconductor nanocrystal is rod-shaped and has a larger aspect ratio than the first shell .

According to at least one embodiment , the semiconductor nanocrystal comprises , in particular consists of , a rodshaped core . In particular, the core is elongated . For example , a first dimension of the core is larger than a second dimension and a third dimension both perpendicular to the first dimension . For instance , an outer shape of the core is that of a cuboid, a hexagonal prism, an ellipsoid, or a cylinder . In particular, the semiconductor nanocrystal is free of any shells .

According to at least one embodiment , the first shell comprises a similar thickness in all directions around the rod-shaped core . Here and in the following, similar means that the thickness of the first shell varies by at most 5% , in particular by at most 1 % . In other words , the first shell comprises a constant thickness . In particular, the first shell is symmetrical around the rod-shaped core . For example , the first shell is in direct mechanical contact to the rodshaped core . A first shell comprising a similar thickness in all directions around a rod-shaped core is advantageously rod-shaped .

According to at least one embodiment , the first shell comprises a chemical element not present in the rod-shaped core , and a concentration of the chemical element in the first shell increases with increasing distance from the rodshaped core . In other words , the concentration of the chemical element in the first shell increases from the rodshaped core to a surface of the first shell facing away from the rod-shaped core . In particular, the first shell comprises a gradient of the chemical element . For example , the chemical element is a cation . In particular, a concentration of the chemical element in comparison to a concentration of all cations is substantially 0 at an interface of the first shell with the rod-shaped core . For example , the concentration of the chemical element in comparison to a concentration of all cations at the surface of the first shell facing away from the rod-shaped core is substantially 1 . Further, a concentration of at least one cation, in particular of all cations , of the semiconductor material of the rod-shaped core may decrease in the first shell with increasing distance from the rod-shaped core . For example , the rod-shaped core comprises CdSe and the first shell comprises CdZnSe with an increasing concentration of Zn and a decreasing concentration of Cd with increasing distance from the rod-shaped core . Such a configuration can advantageously reduce the lattice mismatch between rod-shaped core and first shell and, therefore , a strain reduction in the first shell can be reali zed .

According to at least one embodiment , an aspect ratio of the rod-shaped core is larger than an aspect ratio of the first shell . In other words , the rod-shaped core is more elongated than the first shell .

According to at least one embodiment , the rod-shaped core and the first shell comprise the same anion . In other words , all anions of the semiconductor materials of the rod-shaped core and the first shell are identical or the same . In particular, the semiconductor materials of the rod-shaped core and the first shell only di f fer in the composition of the cations . For example , the core comprises CdSe and the first shell comprises CdZnSe . In this instance , the rod-shaped core and the first shell both comprise selenium as the anion . This can advantageously further reduce strain due to lattice mismatch of the rod-shaped core and the first shell .

According to at least one embodiment , the structure further comprises a third shell at least partially, in particular completely, surrounding the first shell . In particular, the third shell is configured for electronic passivation . Furthermore , the third shell can be configured for protecting the first shell against reactions with oxygen . The third shell may further improve robustness and/or confinement . For example , the third shell comprises or consists of a metal sul fide semiconductor material such as ZnS .

According to at least one embodiment , the first shell is configured to convert the primary radiation into the secondary radiation . In particular, the structure forms a quantum well structure having an emissive first shell between a core and a further semiconductor layer . In this instance , the third shell can form the further semiconductor layer of the quantum well structure . For example , the first shell comprises or consists of a semiconductor material configured to convert the primary radiation into the secondary radiation . For instance , the first shell comprises or consists of ZnSe , CdZnSe , ZnSeS , or ZnTeSe . In particular, the core and the third shell comprise a semiconductor material having a wider bandgap than the first shell . For example , the core and/or the third shell comprises or consists of ZnS .

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 described in the following . Thus , embodiments , features , and advantages described in combination with the structure also apply to the method for producing a structure described in the following and vice versa .

According to at least one embodiment , the method comprises providing a semiconductor nanocrystal capped, in particular completely, with first ligands . The semiconductor nanocrystal capped with first ligands can be provided in a reaction mixture . In particular, the first ligands are bonded to a surface of the semiconductor nanocrystal via physical and/or chemical bonds such as van der Waals forces , hydrogen bonds , coordinative bonds , ionic bonds and/or covalent bonds . For example , the first ligands are at least one of phosphonates or carboxylates . In particular, each region on the surface of the semiconductor nanocrystal binding first ligands is referred to as a first region .

According to at least one embodiment , the method comprises partially exchanging the first ligands with second ligands . The second ligands can be added to the reaction mixture comprising the semiconductor nanocrystal capped with first ligands . In particular, the second ligands are bonded to a surface of the semiconductor nanocrystal via physical and/or chemical bonds such as van der Waals forces , hydrogen bonds , coordinative bonds , ionic bonds and/or covalent bonds . For example , the second ligands are at least one of metal carboxylates , amines , or phosphines . In particular, each region on the surface of the nanocrystal binding second ligands is referred to as a second region . For example , by partially exchanging the first ligands with second ligands , at least a part of the first regions on the surface of the semiconductor nanocrystal is converted to second regions . For instance , the binding strength of the first ligands in di f ferent first regions di f fers from one another depending on the surface structure and composition of the underlying surface of the semiconductor nanocrystal . In particular, the first ligands in first regions having the smallest binding strength are exchanged with second ligands , whereas the first ligands in first regions having the highest binding strength are not exchanged with second ligands . For example , the second regions are arranged on opposite faces of the semiconductor nanocrystal and the first regions are arranged on faces perpendicular to the second regions .

According to at least one embodiment , the method comprises growing a first shell on the semiconductor nanocrystal . In particular, precursors of the semiconductor material of the first shell are added to the reaction mixture . For example , a crystal structure of the first shell is templated by a crystal structure of the semiconductor nanocrystal . In addition, the growth conditions of the growth reaction can facilitate the growth of a first shell having a speci fic crystal structure . For instance , the crystal structure of the first shell is a wurtzite crystal structure .

According to at least one embodiment , a growth of the first shell is faster in second regions comprising the second ligands than in first regions comprising the first ligand . In particular, faster growth in second regions is a result of the second ligands ease of desorption compared to the first ligands . In other words , the second ligands can be desorbed from the second regions more easily than the first ligands can be desorbed from the first regions . For example , the first shell is grown in second regions and, due to the first ligands , the first regions are inhibited from the growth of the first shell . In particular, the growth of the first shell is faster in one direction comprising the second regions on the surface of the semiconductor nanocrystal than in perpendicular directions comprising the first regions .

According to at least one embodiment , the method for producing a structure comprises providing a semiconductor nanocrystal capped with first ligands , partially exchanging the first ligands with second ligands , and growing a first shell on the semiconductor nanocrystal , wherein a growth of the first shell is faster in second regions comprising the second ligands than in first regions comprising the first ligand .

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 a rod-shaped first shell can advantageously be produced simply and cost- ef ficiently . By using a partial ligand exchange , the growth of the first shell can be initiated and facilitated on surfaces of the seminar nanocrystal that underwent the ligand exchange . This allows the first shell to grow thicker on these surfaces than on perpendicular surfaces thereby forming a rod-shaped first shell comprising the benefits of rodshaped first shells over spherical or cubic first shells .

According to at least one embodiment , the first shell comprises a metal selenide semiconductor material or a metal phosphide semiconductor material . In particular, the first- shell is free of a metal sul fide semiconductor material , for example , of CdS . Metal selenide semiconductor materials and metal phosphide semiconductor materials can advantageously enable the protection of the semiconductor nanocrystal and provide corrosion resistance .

According to at least one embodiment , the first shell is rodshaped . Due to the rod-shape , the first shell can advantageously be grown thicker than spherical or cubic first shells and, thus , provide the benefits associated with a thicker first shell growth while avoiding the issues that thick spherical or cubic first shell growth presents .

According to at least one embodiment , the first ligands form a stronger bond with the semiconductor nanocrystal than the second ligands . In particular, the binding strength of the first ligands to a speci fic region of the surface of the semiconductor nanocrystal is higher than the binding strength of the second ligands to the same region . Further, the binding strength of the first ligands to any region of the surface of the seminar nanocrystal can be higher than the binding strength of the second ligands to any region of the surface of the semiconductor nanocrystal . As a result , the second ligands can advantageously be desorbed more easily from the surface of the semiconductor nanocrystal than the first ligands and, therefore , crystal growth of the first shell is much faster in the second regions . According to at least one embodiment , further first ligands are exchanged with second ligands during growing the first shell on the semiconductor nanocrystal . In particular, the start of the growth of the first shell in the second region initiates and facilitates the ligand exchange of first ligands to second ligands in first regions on the surface of the semiconductor nanocrystal . For example , the further ligand exchange is not initiated externally, but takes place due to the kinetics of the shell growth reaction that enables the first ligands to be exchanged during the growth of the first shell . After all first ligands are exchanged with second ligands , the growth of the first shell proceeds at an equal rate on all surfaces of the semiconductor nanocrystal . The further ligand exchange can advantageously enable a faster growth of the first shell , thereby enabling control over the rod growth of the first shell .

According to at least one embodiment , the method comprises providing a rod-shaped semiconductor nanocrystal . In particular, the rod-shaped semiconductor nanocrystal comprises or consists of a semiconductor material , for example , a selenide semiconductor material or a phosphide semiconductor material . According to at least one embodiment , the method comprises performing a cation exchange of a semiconductor material of the rod-shaped semiconductor nanocrystal in an outer region of the rod-shaped semiconductor nanocrystal to form a first shell of the outer region around an inner region of the rodshaped semiconductor nanocrystal . In other words , by performing the cation exchange , the composition of the semiconductor material of the outer region of the rod-shaped semiconductor nanocrystal is converted from the semiconductor material of the rod-shaped semiconductor nanocrystal to the semiconductor material of the first shell . In particular, the inner region of the rod-shaped semiconductor nanocrystal and the first shell di f fer in the composition of the cations . For example , the first shell comprises at least one cation not present in the inner region . For instance , the inner region and the first shell comprise the same anion . In particular, the semiconductor material of the inner region remains unchanged . The inner region can form a semiconductor nanocrystal , in particular a core , of the structure produced with this method . In particular, both the inner region and the first shell are rod-shaped .

According to at least one embodiment , the method for producing a structure comprises providing a rod-shaped semiconductor nanocrystal and performing a cation exchange of a semiconductor material of the rod-shaped semiconductor nanocrystal in an outer region of the rod-shaped semiconductor nanocrystal to form a first shell of the outer region around an inner region of the rod-shaped semiconductor nanocrystal .

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

With such a method, a structure having a rod-shaped first shell can advantageously be produced simply and cost- ef ficiently . By using cation exchange on a rod-shaped semiconductor nanocrystal , a rod-in-rod structure can be achieved in a simple manner .

According to at least one embodiment , the first shell is formed with a similar thickness in all directions around the inner region of the rod-shaped semiconductor nanocrystal . In particular, the cation exchange is performed on all surfaces of the rod-shaped semiconductor nanocrystal at the same time and in the same amount . By using cation exchange , a first shell having a similar thickness in all directions around the inner region of the rod-shaped semiconductor nanocrystal can be achieved in a simple manner .

According to at least one embodiment , the first shell comprises an element not present in the inner region of the rod-shaped semiconductor nanocrystal and a concentration of the element in the first shell increases with increasing distance from the inner region . By using cation exchange , a first shell comprising a gradient can advantageously be achieved in a simple manner .

Furthermore , an optoelectronic device is speci fied . 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 methods 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 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 due to the rod-shaped first shell of the structure . The rod-shaped first shell can be thicker and thereby improve the protection of the semiconductor nanocrystal . In this way, the conversion element can have an improved performance compared to conversion elements comprising structures with a spherical or cubic first shell .

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 optoelectronic device is used in lighting applications , in particular in automotive applications , for example in automotive display 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 to 4 and 7 each show a schematic illustration of a structure according to di f ferent exemplary embodiments ,

Figures 5A to 5D and 8A and 8B show schematic illustrations of methods for producing a structure according to di f ferent exemplary embodiments ,

Figures 6A and 6B each show a transmission electron microscopy ( TEM) images of semiconductor nanocrystals and structures obtained with a method for producing a structure according to an exemplary embodiment , and

Figure 9 shows a schematic illustration of an optoelectronic device according to an exemplary embodiment .

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 first shell 3 . The semiconductor nanocrystal 2 comprises a core 21. The core

21 is spherical, i.e. a dot. The core 21 comprises a semiconductor material, for example CdSe or InP.

The first shell 3 surrounds the core 21 at least partially, in particular completely. The first shell 3 comprises a metal selenide semiconductor material, for example ZnSe, CdZnSe, ZnSeS, or ZnTeSe, or a metal phosphide semiconductor material, for example InP, GaP or InGaP. The first shell 3 is rod-shaped and has an aspect ratio of at least 1.5, for example of 2. In other words, the structure 1 of figure 1 comprises a dot-in-a-rod configuration.

The first shell 3 is thicker in one direction than in perpendicular directions. In the exemplary embodiment of figure 1, the first shell 3 is thicker in the direction of the c-axis than in the directions of the a-axis and the b- axis. The core 21 can be arranged in a center of the first shell 3 or, as shown in figure 1, off-center.

The core 21 is configured to convert primary radiation into secondary radiation. In this instance, the structure 1 forms a core-shell quantum dot with an emissive core 21 and a first shell 3 having a wider bandgap semiconductor material than the core 21.

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 second shell 22 surrounding the core 21. The second shell 22 comprises a semiconductor material, in particular a semiconductor material different from the semiconductor material of the core 21. Both the core 21 and the second 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 forms a core-shell-shell quantum dot with an emissive core 21 and a second shell 22 and a first shell 3 having wider bandgap semiconductor materials than the core 21. Alternatively, the second 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 an emissive second shell 22 arranged between a core 21 and a first shell 3 both having a wider bandgap semiconductor material than the second 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 1. In contrast, the core 21 is elongated, i.e. a rod. In other words, the structure 1 of figure 3 comprises a rod-in-a-rod configuration. The aspect ratio of the core 21 can be smaller than, equal to or larger than the aspect ratio of the first shell 3.

The structure 1 of the exemplary embodiment of figure 4 corresponds essentially to the structure 1 of the exemplary embodiment shown in figure 1. In addition, the structure 1 comprises a third shell 4 at least partially, in particular completely, surrounding the first shell 3. The third shell 4 is spherical, i.e. a dot. Alternatively, the third shell 4 can be elongated, i.e. a rod. For example, the third shell 4 comprises or consists of ZnS . In the exemplary embodiment of figure 4, the core 21 can be configured to convert the primary radiation into the secondary radiation. In this instance, the structure 1 forms a core-shell-shell quantum dot with an emissive core 21 and a first shell 3 and a third shell 4 having wider bandgap semiconductor materials than the core 21. Alternatively, the first shell 3 can be configured to convert the primary radiation into the secondary radiation. In this instance, the structure 1 forms a quantum well structure with an emissive first shell 3 arranged between a core 21 and a third shell 4 both having a wider bandgap semiconductor material than the first shell 3.

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, 3, and 4 is provided. In each of the structures 1 below, the semiconductor materials are listed in order radially in the form core 21/first shell 3 or core 21/second shell 22/first shell 3 or core 21/first shell 3/third shell 4, and any core 21 or second shell 22 or third shell 4 can be spherical or elongated, i.e. a dot or a rod. The first shell 3 is rodshaped. The shape of the cores 21, the second shells 22, the third shells 4, and the first shells 3 are indicated for each combination of semiconductor materials for the structures 1 in parentheses. It is to be understood, that the shapes of the cores 21, the second shells 22, and the third shells 4 are meant as examples only. In each of the structures 1 below, the fist shell 3 is ZnSe(rod) or CdZnSe(rod) .

Structures 1 having a core 21 configured to convert the primary radiation into the secondary radiation are: CdSe (dot) /ZnSe (rod) /ZnS (dot) , CdSe (rod) /ZnSe (rod) , CdZnSe (dot) /ZnSe (rod) , CdSe (dot) /CdZnSe (rod) , CdSe (rod) /CdZnSe (rod) , InP (dot) /ZnSe (rod) , InAs (dot) /ZnSe (rod) , InAs (dot) /InP (dot) /ZnSe (rod) , PbSe (dot) /ZnSe (rod) , PbS (dot) /ZnSe (rod) , CuInSe₂ (dot) /ZnSe (rod) .

Structures 1 having a second shell 22 configured to convert the primary radiation into the secondary radiation, i.e. quantum well structures, are:

ZnS (dot) /CdSe (dot) /ZnSe (rod) , CdS (dot) /CdSe (dot) /ZnSe (rod) , CdS (rod) /CdSe (dot) /ZnSe (rod) , ZnSe (dot) /CdSe (dot) /ZnSe (rod) , CdZnSe (dot) /CdSe (dot) /ZnSe (rod) , CdS (dot) /InP (dot) /ZnSe (rod) , ZnSe (dot) /InP (dot) /ZnSe (rod) , ZnS (dot) /InP (dot) /ZnSe (rod) , GaP (dot) /InP (dot) /ZnSe (rod) , InGaP (dot) /InP (dot) /ZnSe (rod) , ZnSe (dot) /InAs (dot) /ZnSe (rod) , InP (dot) /InAs (dot) /ZnSe (rod) , ZnSe (dot ) /CuInS (dot ) /ZnSe (rod) , ZnS (dot) /CuInS (dot) /ZnSe (rod) .

Structures 1 having a first shell 3 configured to convert the primary radiation into the secondary radiation, i.e. quantum well structures, are:

ZnS (dot) /ZnSe (rod) /ZnS (dot) , ZnS (rod) /ZnSe (rod) /ZnS (dot) .

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

The structures 1 according to the exemplary embodiments of figures 1, 2, 3 and 4 can be produced by the method for producing a structure 1 as described in conjunction with figures 5A to 5D. In particular, figures 5a to 5D 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 5A, a semiconductor nanocrystal 2 , in particular plurality of semiconductor nanocrystals 2 , is provided . The semiconductor nanocrystal 2 consists of a core 21 of , for example , CdSe or InP . The core 21 is cubic . The semiconductor nanocrystal 2 is capped with first ligands 5 , for example , phosphonates or carboxylates . The first ligands 5 are bonded to a surface of the semiconductor nanocrystal 2 in first regions 51 . In particular, the first ligands 5 cover the surface of the semiconductor nanocrystal 2 completely .

In the method step shown in figure 5B, a part of the first ligands 5 is exchanged with second ligands 6 , such as metal carboxylates , amines , or phosphines . The regions on the surface of the semiconductor nanocrystal 2 that undergo the partial ligand exchange are converted into second region 61 . In particular, the ligands 5 having the lowest binding strength to the surface of the semiconductor nanocrystal 2 are exchanged with second ligands 6 . In the exemplary embodiment shown in figure 5B, the first ligands 5 on the c- axis faces of the semiconductor nanocrystal 2 are replaced with second ligands 6 .

In the method step shown in figure 5C, the growth of the first shell 3 is initiated . The crystal faces comprising the second region 61 with second ligands 6 have a head-start in growing the first shell 3 , whereas the crystal faces comprising the first regions 51 with first ligands undergo little-to-no growth . This is a result of the di f ferent binding strengths of the first ligands 5 and the second ligands 6 to the surface of the semiconductor nanocrystal 2 . The first ligands 5 bind more tightly to the surface of the semiconductor nanocrystal 2 than the second ligands 6 . Thus , the second ligands 6 can be easily desorbed from the second regions 61 and the first shell 3 can be grown in the second regions 61 .

Further, the method step of figure 5C also shows that a further ligand exchange takes place . Further first ligands 5 are exchanged with second ligands 6 . In particular, the start of the growth of the first shell 3 in the second region 61 initiates and facilitates the ligand exchange of first ligands 5 to second ligands 6 in first regions 51 on the surface of the semiconductor nanocrystal 2 due to the kinetics of the shell growth reaction .

In the method step shown in figure 5D, the growth of the first shell 3 proceeds on all surfaces of the semiconductor 2 . After all first ligands 5 are exchanged with second ligands 6 , the growth of the first shell 3 proceeds at an equal rate on all surfaces of the semiconductor nanocrystal 2 . Due to the head-start of the c-axis crystal faces in the growth of the first shell 3 , the first shell 3 is rod-shaped .

Figure 6A shows a TEM image of semiconductor nanocrystals 2 as provided in the method step shown in figure 5A. The semiconductor nanocrystals 2 consist of cores 21 that are near-spherical CdSe particles . The semiconductor nanocrystals 2 comprise an average diameter of 5 . 0 nm along their smallest dimension and an average diameter of 5 . 8 nm along their largest dimension . The average diameters were determined from an average of 1834 particles by an automated si zing that approximated the particle shapes as ellipses . The aspect ratio of the semiconductor nanocrystals 2 is 1 . 16 .

Figure 6B shows a TEM image of structures 1 as formed in the method step shown in figure 5D . The structures 1 comprise a rod-shaped first shell 3 of ZnSe around the semiconductor nanocrystals 2 as shown in figure 6A. The structures 1 comprise an average diameter of 5 . 3 nm along their smallest dimension and an average diameter of 8 . 7 nm along their largest dimension . The average diameters were determined from an average of 1321 particles by an automated si zing that approximated the particle shapes as ellipses . The aspect ratio increased to 1 . 64 after the ZnSe rod growth .

The structure 1 of the exemplary embodiment of figure 7 comprises a semiconductor nanocrystal 2 and a first shell 3 . The semiconductor nanocrystal 2 comprises a rod-shaped core 21 . The first shell 3 comprises a similar thickness in all directions around the rod-shaped core 21 . In other words , the structure 1 is symmetrical . In particular, the aspect ratio of the rod-shaped core 21 is larger than an aspect ratio of the first shell 3 . The rod-shaped core 21 comprises a semiconductor material , for example , CdSe . The first shell 3 comprises a semiconductor material having the same anion as the semiconductor material of the rod-shaped core 21 . Further, the semiconductor material of the first shell comprises the cation of the semiconductor material of the rod-shaped core 21 and a further cation that is not present in the rod-shaped core 21 . For example , the first shell 3 comprises zinc cations and the semiconductor material of the first shell 3 is CdZnSe . A concentration of the cation that is not present in the rod-shaped core 21 increases with increasing distance from the rod-shaped core 21 . At the same time , a concentration of the cation that is present in the rod-shaped core 21 decreases with increasing distance from the rod-shaped core 21 . In other words , the first shell 3 comprises a gradient .

The structure 1 can further comprise a third shell 4 at least partially, in particular completely, surrounding the first shell 3 (not shown here ) .

The structures 1 according to the exemplary embodiments of figure 7 can be produced by the method for producing a structure 1 as described in conj unction with figures 8A and 8B . In particular, figures 8A and 8B illustrate the method for producing a structure 1 using the structure 1 as shown in the exemplary embodiment of figure 7 .

In the method step shown in figure 8A, a rod-shaped semiconductor nanocrystal 7 , in particular a plurality of rod-shaped semiconductor nanocrystals 7 , is provided . The rod-shaped semiconductor nanocrystal 7 comprises an outer region 8 and an inner region 9 . The outer region 8 surrounds the inner region 9 , in particular completely . The rod-shaped semiconductor nanocrystal 7 comprises or consists of a semiconductor material , for example , CdSe .

In the method step shown in figure 8B, a cation exchange of the semiconductor material of the rod-shaped semiconductor nanocrystal 7 is performed in the outer region 8 . For example , Cd of the CdSe is replaced with Zn . A first shell 3 is formed of the outer region 8 . The resulting structure 1 as shown in figure 8B is identical to the structure explained in conj unction with figure 7 . The inner region 9 forms the semiconductor nanocrystal 2 , in particular the rod-shaped core 21 , of the structure 1 and the outer region 8 forms the first shell 3 . Due to the nature of the cation exchange , the semiconductor material of the first shell 3 comprises a gradient . For example , the semiconductor material of the first shell 3 is CdZnSe with an increasing concentration of Zn and a decreasing concentration of Cd with increasing distance from the inner region 9 .

In particular, the aspect ratio of the inner region 9 is larger than the aspect ratio of the rod-shaped semiconductor nanocrystal 7 and thus of the structure 1 . As the cation exchange is performed in the same amount on all surfaces of the rod-shaped semiconductor nanocrystal 7 , the thickness of the inner region 7 in the direction of the a-axis is reduced in a greater percentage than the thickness of the inner region 7 in the direction of the c-axis , wherein the thickness of the outer region 8 is the same in both the direction of the a-axis and the direction of the c-axis .

The optoelectronic device 10 of the exemplary embodiment of figure 9 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 .

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/ 552 , 680 , 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 second shell

3 first shell

4 third shell

5 first ligand

51 first region

6 second ligand

61 second region

7 rod-shaped semiconductor nanocrystal

8 outer region

9 inner region

10 optoelectronic device

20 semiconductor chip

30 conversion element

Claims

1. A structure (1) comprising

- a semiconductor nanocrystal (2) , and

- a first shell (3) at least partially surrounding the semiconductor nanocrystal (2) , wherein the structure (1) is configured to convert a primary radiation into a secondary radiation, wherein the first shell (3) comprises a metal selenide semiconductor material or a metal phosphide semiconductor material, and wherein the first shell (3) is rod-shaped.

2. The structure (1) according to the preceding claim, wherein an aspect ratio of the first shell (3) is at least 1.5.

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

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

5. The structure (1) according to at least one of the preceding claims, wherein the first shell (3) comprises a thickness in a first direction larger than a thickness in a second direction perpendicular to the first direction.

6. The structure (1) according to at least one of the preceding claims, wherein the first shell is free of cadmium.

7. The structure (1) according to at least one of the claims 1 to 3, wherein the semiconductor nanocrystal (2) comprises a rodshaped core (21) , wherein the first shell (3) comprises a similar thickness in all directions around the rod-shaped core (21) , wherein the first shell (3) comprises a chemical element not present in the rod-shaped core (21) , and wherein a concentration of the chemical element in the first shell (3) increases with increasing distance from the rodshaped core (21) .

8. The structure according to the preceding claim, wherein an aspect ratio of the rod-shaped core (21) is larger than an aspect ratio of the first shell (3) .

9. The structure (1) according to at least one of the claims 7 or 8 , wherein the rod-shaped core (21) and the first shell (3) comprise the same anion.

10. The structure (1) according to at least one of the preceding claims, further comprising a third shell (4) at least partially surrounding the first shell (3) .

11. A method for producing a structure (1) comprising: - providing a semiconductor nanocrystal (2) capped with first ligands ( 5 ) ,

- partially exchanging the first ligands (5) with second ligands ( 6 ) , and

- growing a first shell (3) on the semiconductor nanocrystal (2) , wherein a growth of the first shell (3) is faster in second regions (61) comprising the second ligands (6) than in first regions (51) comprising the first ligands (5) .

12. The method according to the preceding claim, wherein the first shell (3) comprises a metal selenide semiconductor material or a metal phosphide semiconductor material .

13. The method according to at least one of the claims 11 or

12, wherein the first shell (3) is rod-shaped.

14. The method according to at least one of the claims 11 to

13, wherein the first ligands (5) form a stronger bond with the semiconductor nanocrystal (2) than the second ligands (6) .

15. The method according to at least one of the claims 11 to 14, wherein further first ligands (5) are exchanged with second ligands (6) during growing the first shell (3) on the semiconductor nanocrystal (2) .

16. A method for producing a structure (1) comprising:

- providing a rod-shaped semiconductor nanocrystal (7) , and - performing a cation exchange of a semiconductor material of the rod-shaped semiconductor nanocrystal (7) in an outer region (8) of the rod-shaped semiconductor nanocrystal (7) to form a first shell (3) of the outer region (8) around an inner region (9) of the rod-shaped semiconductor nanocrystal (7) .

17. The method according to the preceding claim, wherein the first shell (3) is formed with a similar thickness in all directions around the inner region (9) of the rod-shaped semiconductor nanocrystal (7) .

18. The method according to at least one of the claims 16 or 17, wherein the first shell (3) comprises an element not present in the inner region (9) of the rod-shaped semiconductor nanocrystal (7) , and wherein a concentration of the element in the first shell (3) increases with increasing distance from the inner region (9) .

19. 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 10.

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