Method for producing a structure, structure, and optoelectronic device

Abstract

A method for producing a structure is specified. According to one embodiment, the method comprises providing a semiconductor nanocrystal (2) configured for converting a primary radiation into a secondary radiation, depositing a first layer (3) comprising a first semiconductor material and a metal dopant on the semiconductor nanocrystal (2), and exposing the first layer (3) to an oxygen-insertion agent (4) to form an intermediate layer (5) and an oxide layer (6) from the first layer (3), wherein the intermediate layer (5) is arranged between the semiconductor nanocrystal (2) and the oxide layer (6), wherein the oxide layer (6) comprises an oxide of the metal dopant, and wherein the intermediate layer (5) comprises a mixture of the first semiconductor material and the oxide of the metal dopant. Furthermore, a structure and an optoelectronic device, in particular comprising a micro-LED, are specified.

Description

[0001] Description

[0002] METHOD FOR PRODUCING A STRUCTURE, STRUCTURE, AND

[0003] OPTOELECTRONIC DEVICE

[0004] A method for producing a structure, a structure, and an optoelectronic device are specified.

[0005] It is an object to provide a simple method for producing a structure with improved efficiency. It is a further object to provide a structure with improved efficiency. Furthermore, it is an object to provide an optoelectronic device with improved efficiency.

[0006] A method for producing a structure, in particular for producing a plurality of structures, is specified. In particular, the method is provided for producing a structure that is a discrete nanoparticle. A nanoparticle is a small object with dimensions in the nanometer range. For example, the structure comprises an extension of at most 1000 nm along its largest dimension. The structure can be a spherical, a tetrahedral, and / or an elongated structure.

[0007] According to at least one embodiment, the method comprises providing a semiconductor nanocrystal configured for converting 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 500 nm and 2000 nm, for instance , between and including 500 nm and 1000 nm .

[0008] 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 , tetrahedral , 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 .

[0009] According to at least one embodiment , the method comprises depositing a first layer comprising or consisting of a first semiconductor material and a metal dopant on the semiconductor nanocrystal . In particular, the first layer is deposited on the semiconductor nanocrystal in such a way that the first layer at least partially, for example completely, surrounds the semiconductor nanocrystal . For instance , the first layer is an individual conformal coating of the semiconductor nanocrystal . For example , the first layer is epitaxially grown onto the semiconductor nanocrystal . In particular, the metal dopant is incorporated into the crystal lattice of the first semiconductor material during the deposition of the first layer . For example , the first layer is deposited on the semiconductor nanocrystal in a thickness between and including 0 . 3 nm and 5 nm .

[0010] According to at least one embodiment , the method comprises exposing the first layer to an oxygen-insertion agent to form an intermediate layer and an oxide layer from the first layer, wherein the intermediate layer is arranged between the semiconductor nanocrystal and the oxide layer, wherein the oxide layer comprises or consists of an oxide of the metal dopant , and wherein the intermediate layer comprises or consists of a mixture of the first semiconductor material and the oxide of the metal dopant . In particular, the first layer is partially oxidi zed by the exposition to an oxygeninsertion agent thereby forming the oxide of the metal dopant . In other words , oxygen atoms are incorporated into the crystal lattice of the first layer . For instance , anions of the first semiconductor material are replaced with oxygen atoms in the crystal lattice . For example , the oxygeninsertion agent reacts with the metal dopant by forming a hydroxide species of the metal dopant and subsequently trans forming it into the oxide of the metal dopant . For instance , the oxygen-insertion agent does not react with the first semiconductor material . For example , no oxidi zed species of the first semiconductor material are formed .

[0011] In particular, during exposition, the oxygen-insertion agent comes into contact , in particular into direct contact , with a first surface of the first layer facing away from the semiconductor nanocrystal . In other words , the first layer is oxidi zed starting from the first surface thereby forming the oxide layer at the first surface of the first layer . In particular, the intermediate layer is only partially oxidi zed . For example , the intermediate layer comprises the first semiconductor material and optionally the metal dopant at an interface of the intermediate layer and the semiconductor nanocrystal and the mixture of the first semiconductor material and the oxide of the metal dopant at an interface of the intermediate layer and the oxide layer .

[0012] According to at least one embodiment , the method comprises providing a semiconductor nanocrystal configured for converting a primary radiation into a secondary radiation, depositing a first layer comprising a first semiconductor material and a metal dopant on the semiconductor nanocrystal , and exposing the first layer to an oxygen-insertion agent to form an intermediate layer and an oxide layer from the first layer, wherein the intermediate layer is arranged between the semiconductor nanocrystal and the oxide layer, wherein the oxide layer comprises an oxide of the metal dopant , and wherein the intermediate comprises a mixture of the first semiconductor material and the oxide of the metal dopant .

[0013] 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 .

[0014] It is an idea of the present application to provide a method for producing a structure allowing for direct , in-situ growth of an oxide layer around a semiconductor nanocrystal , which allows the semiconductor nanocrystal to be fully protected prior to puri fication and further processing of the structure . This advantageously improves the processability of the structure . Instead of puri fying semiconductor nanocrystals and then inserting them into a new reaction mixture to grow an oxide encapsulation, the oxide layer produced with the method described herein is built from feedstock that is incorporated into the first layer itsel f and oxidi zed in-situ . This eliminates the need for external feedstock during the formation of the oxide layer . The protective oxide layer fully protects the semiconductor nanocrystal from deleterious species such as oxygen and water that can degrade the surface of the semiconductor nanocrystal leading to a loss in quantum yield, a shi ft in the semiconductor nanocrystal emission profile , and an overall decrease in the stability of the semiconductor nanocrystal . Furthermore , by depositing the first layer and subsequently exposing the first layer to an oxygen-insertion agent , a strain reduction within the structure is achieved . The strain reduction leads to a higher quantum yield in the structure produced with this method than would be possible i f an oxide layer was applied to a semiconductor nanocrystal with a di f ferent method such as a reverse-micelle chemistry . In addition, with the method described herein, a higher photoluminescence quantum yield can be achieved . Further, with the method described herein, the need for harmful species such as water or ammonia commonly found in reversemicelle chemistry can advantageously be eliminated .

[0015] According to at least one embodiment , the first semiconductor material is a sul fide semiconductor material or a phosphide semiconductor material . In particular, the first semiconductor material is a metal sul fide or a metal phosphide . For example , the first semiconductor material is zinc sul fide , a zinc selenide / sul f ide alloy, gallium phosphide , or indium gallium phosphide . A sul fide semiconductor material or a phosphide semiconductor material can advantageously be oxidi zed particularly well when exposed to the oxygen-inserting agent .

[0016] According to at least one embodiment , the oxide layer comprises direct chemical bonds to the intermediate layer . In particular, the intermediate layer and the oxide layer are chemically alloyed at their interface . This may result from the intermediate layer and the oxide layer being formed from the first layer . For example , the direct chemical bonds between the intermediate layer and the oxide layer are covalent bonds . The direct chemical bonds between the oxide layer and the intermediate layer are a direct result of the method described herein by forming the oxide layer in-situ by exposing the first layer to an oxygen-insertion agent .

[0017] According to at least one embodiment , a concentration of the metal dopant in the first layer increases from the semiconductor nanocrystal to a first surface of the first layer facing away from the semiconductor nanocrystal . In particular, the first layer comprises a gradient of the metal dopant . For example , a concentration of the metal dopant in comparison to a concentration of all cations at an interface of the first layer with the semiconductor nanocrystal is substantially 0 . For instance , a concentration of the metal dopant in comparison to a concentration of all cations at the first surface is substantially 1 . Further, a concentration of at least one cation, in particular of all cations , of the first semiconductor material in the first layer may decrease from the semiconductor nanocrystal to the first surface of the first layer . In particular, the increase of a concentration of the metal dopant in the first layer and optionally the decrease of the at least one cation, in particular of all cations , of the first semiconductor material in the first layer remains visible in the intermediate layer and the oxide layer after exposing the first layer to the oxygen-insertion agent . For example , the first layer is deposited by depositing the first semiconductor material and, as a concentration of the at least one cation, in particular of all cations , of the first semiconductor material begins to decrease , the concentration of the metal dopant is increased until the remaining reactants are the metal dopant and the source of the anion of the first semiconductor material and an optional trace presence of the at least one cation, in particular of all cations , of the first semiconductor material . By increasing the concentration of the metal dopant in the first layer from the semiconductor nanocrystal to the first surface of the first layer, a gradual change of the crystal lattice from the semiconductor nanocrystal to the metal oxide can be achieved in the structure . Thus , lattice mismatch is reduced and a strain reduction in the layers surrounding the semiconductor nanocrystal is reali zed .

[0018] According to at least one embodiment , a concentration of oxygen in the intermediate layer decreases from the oxide layer to the semiconductor nanocrystal . Further, a concentration of an anion of the first semiconductor material may increase from the oxide layer to the semiconductor nanocrystal . By increasing the concentration of the metal dopant in the first layer from the semiconductor nanocrystal to the first surface of the first layer, in particular by having a gradient of both the metal and non-metal content of the first layer, the intermediate layer and the oxide layer, a gradual change of the crystal lattice from the semiconductor nanocrystal to the metal oxide can be achieved in the structure . Thus , lattice mismatch is reduced and a strain reduction in the layers surrounding the semiconductor nanocrystal is reali zed .

[0019] According to at least one embodiment , the metal dopant is at least one of aluminum, zinc, titanium, hafnium, and zirconium . For example , the metal dopant is aluminum . In particular, the oxide of the metal dopant of the oxide layer is at least one of aluminum oxide , zinc oxide , titanium oxide , and zirconium oxide depending on the metal dopant . By using aluminum, zinc, titanium, and zirconium as metal dopants , an oxide layer is formed that advantageously protects the semiconductor nanocrystal from oxygen, water, or other deleterious chemical species .

[0020] According to at least one embodiment , the first layer is deposited at a temperature between and including 180 ° C and 350 ° C, in particular between and including 270 ° C and 320 ° C, for example of 300 ° C . By depositing the first layer at a temperature between and including 180 ° C and 350 ° C, the metal dopant can advantageously be incorporated into the crystal lattice of the first semiconductor material easily and ef ficiently .

[0021] According to at least one embodiment , the oxygen-insertion agent comprises at least one of hydrogen peroxide , a peroxy acid, a N-oxide , a trialkylamine N-oxide , ozone , oxygen gas , an inorganic base in the presence of water, an aqueous ammonia solution, a quaternary ammonium hydroxide , and an organic base in the presence of water . A chemical compound in the presence of water is to be understood in such a way that the chemical compound is solved or suspended in water . In particular, ozone and oxygen gas are provided in gaseous form and are bubbled through a reaction mixture comprising the semiconductor nanocrystals surrounded with the first layer. The inorganic base in the presence of water can be LiOH, NaOH, KOH, Mg(OH)2, Ca(OH)2, and other similar hydroxides and as delivered with or without the aid of additional compatible solvents. The aqueous ammonia solution can be a concentrated aqueous ammonia solution (NH4+OH) or dilutions of a concentrated ammonia solution in water or other compatible solvents. The quaternary ammonium hydroxide can be tetramethylammonium hydroxide, with or without the additional presence of water and as delivered with or without additional compatible solvents. The organic base in the presence of water can be an amine, a diamine, a triamine, a piperidine, or any amine containing the functional group R2-N (H) -R2and as delivered with or without additional compatible solvents. For example, the oxygen-insertion agent comprises at least one of hydrogen peroxide, a peroxy acid with the structure R- (C=0) -0-0H such as 3-chloroperoxybenzoic acid, a N-oxide such as pyridine N-oxide, a trialkylamine N-oxide such as trimethylamine N-oxide (TMAO, (CH3)3N-O) , and ozone. These oxygen-insertion agents are advantageously suited particularly well for oxidizing the first layer.

[0022] According to at least one embodiment, the first layer is exposed to the oxygen-insertion agent at a temperature between and including 0 °C and 270 °C. In particular, the temperature for exposing the first layer to the oxygeninsertion agent is dependent on the oxygen-insertion agent used. For example, the oxygen-insertion agent is pyridine N-oxide or 3-chloroperoxybenzoic acid. Pyridine N-oxide has a boiling point of 270 °C and can thus be utilized up to that temperature, for instance, in a high-boiling solvent with a higher boiling point than 270 °C. 3-Chloroperoxybenzoic acid has a melting point of approximately 70 ° C and a theoretical predicted boiling point of 250 ° C . In particular, the first layer is exposed to pyridine N-oxide or 3-chloroperoxybenzoic acid at a temperature between and including 180 ° C and 200 ° C . In this instance , an optimal reactivity of pyridine N-oxide or 3-chloroperoxybenzoic acid can advantageously be reali zed .

[0023] For example , the oxygen-insertion agent is hydrogen peroxide . In the instance that the hydrogen peroxide is delivered in a mixture of water, the first layer is exposed to hydrogen peroxide at a temperature between and including 0 ° C and 100 ° C .

[0024] For example , the oxygen-insertion agent is an inorganic base . In the instance that the inorganic base is delivered in an alcohol solution, the first layer is exposed to the inorganic base at a temperature below the boiling point of the alcohol . In the instance that the alcohol is methanol , the first layer is exposed to the inorganic base at a temperature between and including 0 ° C and 60 ° C . In the instance that the alcohol is isopropanol , the first layer is exposed to the inorganic base at a temperature between and including 0 ° C and 80 ° C .

[0025] For example , the oxygen-insertion agent is ammonia or an alkyl ammonium hydroxide . In the instance that the ammonia or the alkyl ammonium hydroxide is delivered in water, the first layer is exposed to the ammonia or the alkyl ammonium hydroxide at a temperature between and including 50 ° C and 100 ° C .

[0026] According to at least one embodiment , the first layer is exposed to the oxygen-insertion agent for between and including 1 minute and 24 hours . In particular, the duration of exposing the first layer to the oxygen-insertion agent is dependent on the oxygen-insertion agent used and the temperature . For example , for oxygen-insertion agents that require or are used at a lower temperature such as ammonia, ammonium hydroxides , or inorganic bases , the first layer is exposed to the oxygen-insertion agent for a longer duration such as between and including 16 hours and 24 hours . For instance , for oxygen-insertion agents that require or are used at a higher temperature , for example some N-oxides such as pyridine N-oxide or some peroxy acids such as 3-chloroperoxybenzoic acid, the first layer is exposed to the oxygen-insertion agent for a shorter duration such as between and including 1 hour and 2 hours .

[0027] According to at least one embodiment , exposing the first layer to the oxygen-insertion agent is performed in solution, wherein the oxygen-insertion agent is added to the solution . In particular, all method steps of the method for producing a structure are performed in solution . For example , the semiconductor nanocrystal is provided in a solvent . The semiconductor nanocrystal and the solvent can form a reaction mixture and the subsequent method steps of depositing the first layer and exposing the first layer to the oxygeninsertion agent are performed in the reaction mixture . For instance , the solvent is a high boiling solvent . A high boiling solvent is a solvent having a higher boiling point than the maximum temperature applied to the reaction mixture during the method . For example , the solvent is at least one of alkylamines , squalane , squalene , ethylene glycol , octadecene , tri-n-octylphosphine , molten salts , and ionic liquids . In particular, the oxygen-insertion agent is added to the solution in liquid form such as in solution or in suspension or in gaseous form, for example , by bubbling the gas through the solution . By exposing the first layer to the oxygen-insertion agent in solution, the oxide layer can advantageously be formed in solution and colloidally . A method step of forming an oxide layer by vapor deposition on a substrate can thus advantageously be omitted .

[0028] According to at least one embodiment , depositing the first layer and / or exposing the first layer to the oxygen-inserting agent is performed in a non-oxidi zing atmosphere . In particular, a non-oxidi zing atmosphere is free of oxygen, oxygen containing species , and oxygen-insertion agents . For example , the non-oxidi zing atmosphere is air- free . For instance , the non-oxidi zing atmosphere is argon or nitrogen . By performing the method steps in a non-oxidi zing atmosphere , the insertion of oxygen in the first layer can advantageously be performed in a controlled manner and uncontrolled oxidi zing reactions of the semiconductor nanocrystal and / or the first layer can be prevented .

[0029] According to at least one embodiment , the method further comprises heating the product obtained after exposing the first layer to the oxygen-insertion agent to a temperature between and including 100 ° C and 350 ° C . In particular, the product obtained after exposing the first layer to the oxygen-insertion agent comprises the semiconductor nanocrystal , the intermediate layer surrounding the semiconductor nanocrystal and the oxide layer surrounding the intermediate layer . For example , for oxygen-insertion agents that require or are used at a lower temperature such as ammonia, ammonium hydroxides , or inorganic bases , the product is heated to a temperature at a lower end of the above temperature range . For instance , for oxygen-insertion agents that require or are used at a higher temperature , for example some N-oxides such as pyridine N-oxide or some peroxy acids such as 3-chloroperoxybenzoic acid, the product is heated to a temperature at a higher end of the above temperature range . By heating the product obtained after exposing the first layer to the oxygen-insertion agent , the oxygen insertion into the oxide layer and the intermediate layer can a be further completed . For example , remaining hydroxide species of the metal dopant in the oxide layer are trans formed into the oxide of the metal dopant . Thus , a quality of the protective oxide layer can advantageously be improved .

[0030] According to at least one embodiment , the method further comprises depositing a second layer comprising or consisting of a second semiconductor material on the semiconductor nanocrystal prior to depositing the first layer . In this instance , the first layer is then deposited on the second layer . In particular, the second layer is deposited on the semiconductor nanocrystal in such a way that the second layer at least partially, for example completely, surrounds the semiconductor nanocrystal . For instance , the second layer is an individual conformal coating of the semiconductor nanocrystal . For example , the second layer is epitaxially grown onto the semiconductor nanocrystal . In particular, the second semiconductor material is a sul fide semiconductor material or phosphide semiconductor material . For example , the second semiconductor material is the first semiconductor material . In other words , the second layer can comprise the first semiconductor material and the first layer can comprise the first semiconductor material and the metal dopant . For instance , the second layer is deposited on the semiconductor nanocrystal in a thickness between and including 0 nm and 5 nm . A second layer between the semiconductor nanocrystal and the first layer can advantageously further protect the semiconductor nanocrystal against degradation . Further, the second layer can advantageously contribute to a strain reduction at the semiconductor nanocrystal .

[0031] According to at least one embodiment , the second layer is free of the metal dopant . In particular, the metal dopant is not present in the second layer .

[0032] According to at least one embodiment , the method further comprises growing a metal oxide encapsulation on the oxide layer . In particular, the product obtained after exposing the first layer to the oxygen-insertion agent is exposed to metal oxide growth conditions and a metal oxide precursor . For example , the metal oxide encapsulation comprises direct chemical bonds , in particular covalent bonds , to the oxide layer . For instance , the metal oxide encapsulation comprises or consists of the oxide of the metal dopant . For example , the metal oxide encapsulation comprises aluminum oxide and the metal oxide precursor comprises trimethylaluminum or aluminum tert-butoxide . By growing a metal oxide encapsulation on the oxide layer, a thickness of the protective oxide coating of the semiconductor nanocrystal comprising both the metal oxide encapsulation and the oxide layer can advantageously be increased thereby increasing the protection of the semiconductor nanocrystal .

[0033] According to at least one embodiment , the structure is free of organic linker molecules . In particular, the layers of the structure are arranged on one another without any intervening layers comprising or consisting of organic material . For example , the first layer and / or the second layer are grown on the semiconductor nanocrystal without the aid of organic linker molecules . For instance , the first layer is grown on the second layer without the aid of organic linker molecules . Dispensing of organic linker molecules during depositing the first layer and optionally the second layer can advantageously eliminate a source of porosity in the metal oxide shell thus ensuring conformal growth of the layers around the semiconductor nanocrystal . Further, a structure without organic linker molecules can advantageously eliminate the risk of degradation products from the organic linker molecules harming the semiconductor nanocrystal functions .

[0034] According to at least one embodiment , the semiconductor nanocrystal comprises a core or a core and at least one shell . In particular, the semiconductor nanocrystal consists of the core or has a core-shell structure . For example , the core has a diameter of between 2 nm and 5 nm . For instance , the at least one shell has a thickness between and including 0 nm and 3 nm . The core and / or the at least one shell may comprise at least one semiconductor material . In particular, the core comprises a di f ferent semiconductor material than the shell . For example , the core comprises or consists of indium phosphide , indium zinc phosphide , indium zinc gallium phosphide , or indium gallium phosphide . For example , the at least one shell comprises or consists of zinc selenide , gallium phosphide , or indium gallium phosphide . For instance , the at least one shell is epitaxially grown onto the core . The semiconductor nanocrystal can comprise further shells and / or layers . For instance , the semiconductor nanocrystal comprises a quantum well structure . In particular, the semiconductor nanocrystal is a core quantum dot or a coreshell quantum dot or a core-shell-shell quantum dot . Furthermore , a structure is speci fied . In particular, the structure is produced by the method for producing a structure described herein . Thus , embodiments , features , and advantages described in combination with the method for producing a structure also apply to the structure and vice versa .

[0035] According to at least one embodiment , the structure comprises a semiconductor nanocrystal , an intermediate layer at least partially surrounding the semiconductor nanocrystal , and an oxide layer at least partially surrounding the intermediate layer, wherein the intermediate layer comprises a mixture of a first semiconductor material and an oxide of a metal dopant , and wherein the oxide layer comprises the oxide of the metal dopant .

[0036] In such a structure , the semiconductor nanocrystal is fully protected by the oxide layer against deleterious species present in an environment of the structure . The protective oxide layer fully protects the semiconductor nanocrystal from deleterious species such as oxygen and water that can degrade the surface of the semiconductor nanocrystal leading to a loss in quantum yield, a shi ft in the semiconductor nanocrystal emission profile , and an overall decrease in the stability of the semiconductor nanocrystal . Furthermore , by introducing a gradual shi ft from the semiconductor nanocrystal to the metal oxide layer by the intermediate layer, a strain reduction within the structure is achieved which can allow semiconductor nanocrystals to reap the stability benefits of a protective oxide layer without sacri ficing the high quantum yield .

[0037] 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 method for producing a structure also apply to the optoelectronic device and vice versa .

[0038] 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 .

[0039] According to at least one embodiment , the optoelectronic device comprises a conversion element comprising at least one structure , in particular a plurality of structures , described herein . In particular, the conversion element is configured to convert at least a portion of the primary radiation into a secondary radiation . 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 .

[0040] According to at least one embodiment , the optoelectronic device comprises a semiconductor chip configured to emit a primary radiation, and a conversion element comprising at least one structure disclosed herein .

[0041] Advantageously, the optoelectronic device described herein has an improved ef ficiency, in particular, a high quantum yield, a high photoluminescence quantum yield and an increased operating li fetime due to the improved protective oxide layer around the semiconductor nanocrystal . In this way, the semiconductor nanocrystals can meet the stringent reliability requirements for displays and lighting devices .

[0042] 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 .

[0043] According to at least one embodiment , the optoelectronic device is used in any application with utili zes semiconductor nanocrystals to generate white light from blue LEDs such as in display applications and / or in general lighting applications .

[0044] Advantageous embodiments and developments of the method for producing a structure , the structure , and the optoelectronic device will become apparent from the exemplary embodiments described below in conj unction with the figures .

[0045] In the figures :

[0046] Figures 1A to ID, figures 3A and 3B, and figures 4A and 4B each show a schematic illustration of a method for producing a structure according to di f ferent exemplary embodiments ,

[0047] Figures 2 and 5 each show a schematic illustration of a structure according to di f ferent exemplary embodiment ,

[0048] Figure 6 shows a schematic illustration of an optoelectronic device according to an exemplary embodiment .

[0049] 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 .

[0050] A method for producing a structure 1 is shown in figures 1A to ID . In a first method step shown in figure 1A, a semiconductor nanocrystal 2 , in particular a plurality of nanocrystals 2 , is provided . The semiconductor nanocrystal 2 is configured for converting a primary radiation into a secondary radiation . The semiconductor nanocrystal 2 comprises a core of , for example , indium phosphide , indium zinc phosphide , indium zinc gallium phosphide , or indium gallium phosphide . The semiconductor nanocrystal 2 can further comprise at least one shell of , for example , zinc selenide around the core .

[0051] In a second method step shown in figure IB, a first layer 3 is deposited, in particular grown, on the semiconductor nanocrystal 2 . The first layer 3 is deposited at a temperature between and including 180 ° C and 350 ° C in a nonoxidi zing atmosphere such as argon or nitrogen . The first layer 3 comprises a first semiconductor material and a metal dopant . The first semiconductor material is a sul fide semiconductor material or a phosphide semiconductor material and the metal dopant is at least one of aluminum, zinc, titanium, hafnium, and zirconium .

[0052] At the beginning of the deposition reaction, only the first semiconductor material is applied to the semiconductor nanocrystal 2 . As a concentration of at least one cation, in particular all cations , of the first semiconductor material begins to decrease , a concentration of the metal dopant is increased until the remaining reactants are the metal dopant and the source of an anion of the first semiconductor material and a trace presence of the at least one cation, in particular all cations , of the first semiconductor material . In other words , the first layer 3 comprises a gradient of the metal dopant increasing from the semiconductor nanocrystal 2 to a first surface 31 of the first layer 3 . The cation primarily present at the first surface 31 is the metal dopant . In a third method step shown in figure 1C, the first layer 3 is exposed to an oxygen-insertion agent 4 . The first layer 3 is exposed to the oxygen-insertion agent 4 at a temperature between and including 0 ° C and 270 ° C and for a time between and including 1 minute to 24 hours in a non-oxidi zing atmosphere such as argon or nitrogen . The oxygen-insertion agent 4 comprises at least one of hydrogen peroxide , a peroxy acid, a N-oxide , a trialkylamine N-oxide , ozone , oxygen gas , an inorganic base in the presence of water, an aqueous ammonia solution, a quaternary ammonium hydroxide , and an organic base in the presence of water . For example , the oxygen-insertion agent 4 comprises hydrogen peroxide , a peroxy acid with the structure R- ( C=O) -O-OH such as 3-chloroperoxybenzoic acid, a N-oxide such as pyridine N-oxide , a trialkylamine N-oxide such as trimethylamine N-oxide ( TMAO, ( CH3)3N-O) , or ozone .

[0053] The third method step can be performed in solution 7 . In addition, the first method step and the second method step can also be performed in solution 7 . The solution 7 comprises a solvent , in particular a high boiling solvent such as alkylamines , squalane , squalene , ethylene glycol , octadecene , tri-n-octylphopshine , molten salts , or ionic liquids . The oxygen-insertion agent 4 is added to the solution 7 in liquid form such as in solution or in suspension or in gaseous form such as by bubbling through the solution 7 .

[0054] By exposing the first layer 3 to the oxygen-insertion agent 4 , oxygen atoms are inserted into the first layer 3 starting from the first surface 31 that comes into contact , in particular into direct contact , with the oxygen-insertion agent 4 . In particular, the oxygen-insertion agent 4 reacts with the metal dopant by forming a hydroxide species of the metal dopant and subsequently trans forming it into the oxide of the metal dopant . Depending on the reaction conditions during the third method step, a penetration depth of the oxygen atoms into the first layer 3 may vary . By inserting oxygen atoms into the first layer 3 , an intermediate layer 5 and an oxide layer 6 are formed from the first layer 3 ( figure ID) . The oxide layer 6 comprises or consists of an oxide of the metal dopant . The intermediate layer 5 comprises a mixture of the first semiconductor material and the oxide of the metal dopant . The oxide layer 6 comprises direct chemical bonds , in particular covalent bonds , to the intermediate layer 5 . The direct chemical bonds are a result from the oxide layer 6 and the intermediate layer 5 being formed from the first layer 3 .

[0055] After the third method step, a subsequent method step of heating to a temperature between and including 100 ° C and 350 ° C can be performed to further complete the insertion of oxygen atoms into the oxide layer 6 and / or the intermediate layer 5 .

[0056] For example , the structure 1 shown in figure ID can have one of the compositions 1-3 shown in table 1 . For the intermediate layer 5 , the material composition at the interface between the semiconductor nanocrystal 2 and the intermediate layer 5 as well as at the interface of the intermediate layer 5 and the oxide layer 6 are speci fied .

[0057] Table 1

[0058] The structure 1 according to the exemplary embodiment shown in figure 2 corresponds substantially to the structure 1 of the exemplary embodiment shown in figure ID . In contrast to the exemplary embodiment shown in figure ID, the structure 1 of figure 2 comprises a second layer 8 arranged between the semiconductor nanocrystal 2 and the intermediate layer 5 . The second layer 8 comprises a second semiconductor material . In particular, the second semiconductor material is a sul fide semiconductor material or phosphide semiconductor material . For example , the second semiconductor material is the first semiconductor material . The second layer 8 is free of the metal dopant .

[0059] The structure 1 according to the exemplary embodiment shown in figure 2 can be produced as follows :

[0060] The method steps described above for the method shown in figures 1A to ID are performed . After providing the semiconductor nanocrystal 2 and prior to depositing the first layer 3 , the second layer 8 is deposited, in particular grown, on the semiconductor nanocrystal 2 . Subsequently, the first layer 3 is deposited, in particular grown, on the second layer 8 instead of on the semiconductor nanocrystal 2 ( second method step, figure IB ) .

[0061] For example , the structure 1 shown in figure 2 can have one of the compositions 4- 6 shown in table 1 . For the intermediate layer 5 , the material composition at the interface between the second layer 8 and the intermediate layer 5 as well as at the interface of the intermediate layer

[0062] 5 and the oxide layer 6 are speci fied .

[0063] Table 1

[0064] Figures 3A and 3B show two method steps of a method for producing a structure 1 . With the method shown in figures 3A and 3B, a structure 1 having the composition 4 can be produced .

[0065] A semiconductor nanocrystal 2 is provided by coating a core of InP, InZnP, InZnGaP, or InGaP with a shell of ZnSe , and then with a second layer 8 of ZnS ( figure 3A) . A first layer 3 is deposited on the second layer 8 as follows : A coating of ZnS is deposited in which aluminum is a metal dopant . As the concentration of zinc in the reaction solution 7 begins to decrease , the concentration of aluminum is increased until the remaining reactants in the reaction mixture are aluminum and the sul fur source , for example S : TOP or DDT , and a trace presence of zinc . The composition of the first layer 3 can be described as ZnxAlYSA, where X+Y=l , X approaches 1 near the interface of the first layer 3 with the second layer 8 , and X approaches 0 at the first surface 31 of the first layer 3 facing away from the semiconductor nanocrystal 2 . After this growth, the outermost shell is ZnxAlYSA, where Y approaches 1 . After this is complete , and before puri fication, the first layer 3 is exposed to an oxygen-insertion agent 4 at a lower temperature than during the deposition of the first layer 3 such that the outermost AI2S3 is oxidi zed to form AI2O3 ( figure 3B ) . In particular, no sul fates are formed during exposing to the oxygen-insertion agent 4 . The intermediate layer 5 comprises AlZnOxat the interface of the intermediate layer 5 and the oxide layer 6 and ZnAlS at the interface of the intermediate layer 5 and the second layer 8 . In other words , the intermediate layer 5 may comprise a gradient of oxygen and sul fur as well as of zinc and aluminum whereas zinc and sul fur decrease and aluminum and oxygen increase from the second layer 8 to the oxide layer 6 .

[0066] In this exemplary embodiment , detectable technical features may include : direct chemical bond between the intermediate layer 5 comprising the sul fide semiconductor material and the oxide layer 6 with gradients of both metal and non-metal content such as pure zinc sul fide to pure aluminum oxide , oxidation of aluminum sul fide to form aluminum oxide in- situ, measurable aluminum content in the structure 1 , detectable aluminum-sul fur and aluminum-oxygen bonds in XPS .

[0067] Figures 4A and 4B show two method steps of a method for producing a structure 1 . With the method shown in figures 4A and 4B, a structure 1 having the composition 5 can be produced .

[0068] A semiconductor nanocrystal 2 comprising a core of InP, InZnP, InZnGaP, or InGaP is provided . The semiconductor nanocrystal 2 is coated with a second layer 8 of GaP . A first layer 3 is deposited on the second layer 8 as follows : A coating is then placed on the second layer 8 which transitions the second layer 8 of GaP to an outer shell of A1P, in the same fashion as described above for the alloying of a ZnS and AI2S3 shell in conj unction with figures 3A and 3B . The outer shell at the first surface 31 of the first layer 3 is primarily aluminum phosphide (A1P ) . The aluminum phosphide shell is covalently bonded to and alloyed with the underlying GaP shell ( figure 4A) . The aluminum phosphide shell is exposed to an oxygen-insertion agent 4 . The A1P shell reacts to form the oxide layer 6 of AI2O3. In particular, no phosphates are formed during exposing to the oxygen-insertion agent 4 . The oxide layer 6 remains chemically bonded to the underlying second layer 8 through the intermediate layer 5 . The intermediate layer 5 comprises AlGaOx, for example AlGaOs, at the interface of the intermediate layer 5 and the oxide layer 6 and GaAlP at the interface of the intermediate layer 5 and the second layer 8 . In other words , the intermediate layer 5 may comprise a gradient of oxygen and phosphor as well as of gallium and aluminum whereas gallium and phosphor decrease and aluminum and oxygen increase from the second layer 8 to the oxide layer 6 .

[0069] Alternatively to the exemplary embodiment shown in figures 4A and 4B, the second layer 8 can comprise InGaP and the first layer 3 can comprise InGaP and aluminum . In this case , a structure 1 having the composition 6 can be produced .

[0070] The structure 1 according to the exemplary embodiment shown in figure 5 corresponds substantially to the structure 1 of the exemplary embodiment shown in figure 2D . In contrast to the exemplary embodiment shown in figure 2D, the structure 1 of figure 5 comprises a metal oxide encapsulation 9 surrounding the oxide layer 6 . For example , the metal oxide encapsulation 9 comprises direct chemical bonds , in particular covalent bonds , to the oxide layer 6 . For instance , the metal oxide encapsulation 9 comprises or consists of the oxide of the metal dopant .

[0071] The structure 1 of figure 5 can be produced as follows : The method steps described above for the method shown in figures 1A to ID are performed . Subsequently, the product obtained after exposing the first layer 3 to the oxygen-insertion agent 4 is exposed to metal oxide growth conditions and a metal oxide precursor . For example , the metal oxide encapsulation 9 comprises aluminum oxide and the metal oxide precursor comprises trimethylaluminum or aluminum tert- butoxide .

[0072] Figure 6 shows a schematic illustration of an optoelectronic device 10 described herein according to a first exemplary embodiment . The optoelectronic device comprises a semiconductor chip 11 configured to emit a primary radiation of a first wavelength range . The semiconductor chip can be a micro-LED . For example , the first wavelength range is in the blue spectral region . A conversion element 12 is arranged on a radiation exit surface of the semiconductor chip 11 . The conversion element 12 can be arranged directly on the radiation exit surface or in a distance to the radiation exit surface . The conversion element 12 can be in the form of a layer or a casting . The conversion element 12 converts 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 .

[0073] 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 .

[0074] This patent application claims the priority of provisional US patent application 63 / 602 , 396 , the disclosure content of which is hereby incorporated by reference .

[0075] 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

[0076] 1 structure

[0077] 2 semiconductor nanocrystal 3 first layer

[0078] 31 first surface

[0079] 4 oxygen-insertion agent

[0080] 5 intermediate layer

[0081] 6 oxide layer 7 solution

[0082] 8 second layer

[0083] 9 metal oxide encapsulation

[0084] 10 optoelectronic device

[0085] 11 semiconductor chip 12 conversion element

Claims

Claims1. A method for producing a structure (1) comprising- providing a semiconductor nanocrystal (2) configured for converting a primary radiation into a secondary radiation,- depositing a first layer (3) comprising a first semiconductor material and a metal dopant on the semiconductor nanocrystal (2) , and- exposing the first layer (3) to an oxygen-insertion agent (4) to form an intermediate layer (5) and an oxide layer (6) from the first layer (3) , wherein the intermediate layer (5) is arranged between the semiconductor nanocrystal (2) and the oxide layer (6) , wherein the oxide layer (6) comprises an oxide of the metal dopant, and wherein the intermediate layer (5) comprises a mixture of the first semiconductor material and the oxide of the metal dopant .

2. The method according to the preceding claim, wherein the first semiconductor material is a sulfide semiconductor material or a phosphide semiconductor material.

3. The method according to at least one of the preceding claims , wherein the oxide layer (6) comprises direct chemical bonds to the intermediate layer (5) .

4. The method according to at least one of the preceding claims , wherein a concentration of the metal dopant in the first layer (3) increases at least partially from the semiconductornanocrystal (2) to a first surface (31) of the first layer (3) facing away from the semiconductor nanocrystal (2) .

5. The method according to at least one of the preceding claims , wherein a concentration of oxygen in the intermediate layer (5) decreases at least partially from the oxide layer (6) to the semiconductor nanocrystal (2) .

6. The method according to at least one of the preceding claims , wherein the metal dopant is at least one of aluminum, zinc, titanium, hafnium, and zirconium.

7. The method according to at least one of the preceding claims , wherein the first layer (3) is deposited at a temperature between and including 180 °C and 350 °C.

8. The method according to at least one of the preceding claims , wherein the oxygen-insertion agent (4) comprises at least one of hydrogen peroxide, a peroxy acid, a N-oxide, a trialkylamine N-oxide, ozone, oxygen gas, an inorganic base in the presence of water, an aqueous ammonia solution, a quaternary ammonium hydroxide, an organic base in the presence of water.

9. The method according to at least one of the preceding claims , wherein the first layer (1) is exposed to the oxygeninsertion agent (4) at a temperature between and including 0 °C and 270 °C.

10. The method according to at least one of the preceding claims , wherein the first layer (3) is exposed to the oxygeninsertion agent (4) for between and including 1 minute and 24 hours .

11. The method according to at least one of the preceding claims , wherein exposing the first layer (3) to the oxygen-insertion agent (4) is performed in solution, wherein the oxygeninsertion agent (4) is added to the solution.

12. The method according to at least one of the preceding claims , wherein depositing the first layer (3) and / or exposing the first layer (3) to the oxygen-insertion agent (4) is performed in a non-oxidizing atmosphere.

13. The method according to at least one of the preceding claims, further comprising- heating a product obtained after exposing the first layer (3) to the oxygen-insertion agent (4) to a temperature between and including 100 °C and 350 °C.

14. The method according to at least one of the preceding claims, further comprising- depositing a second layer (7) comprising a second semiconductor material on the semiconductor nanocrystal (2) prior to depositing the first layer (3) .

15. The method according to the preceding claim, wherein the second layer (7) is free of the metal dopant.

16. The method according to at least one of the preceding claims, further comprising- growing a metal oxide encapsulation (8) on the oxide layer (6) .

17. The method according to at least one of the preceding claims , wherein the structure (1) is free of organic linker molecules .

18. The method according to at least one of the preceding claims , wherein the semiconductor nanocrystal (2) comprises a core or a core and at least one shell.

19. A structure (1) comprising- a semiconductor nanocrystal (2) ,- an intermediate layer (5) at least partially surrounding the semiconductor nanocrystal (2) , and- an oxide layer (6) at least partially surrounding the intermediate layer (5) , wherein the intermediate layer (5) comprises a mixture of a first semiconductor material and an oxide of a metal dopant, and wherein the oxide layer (6) comprises the oxide of the metal dopant .

20. An optoelectronic device (10) comprising- a semiconductor chip (11) configured to emit a primary radiation, in particular a micro-LED,- a conversion element (12) configured to convert at least part of the primary radiation into a secondary radiation,wherein the conversion element (12) comprises or consists of at least one structure (1) according to the preceding claim.

Images