Method for preparing high-crystalline ii-v nanocrystal, ii-v nanocrystal prepared thereby and field-effect transistor comprising same

Abstract

The present invention relates to a method for preparing a high-crystalline II-V nanocrystal, to a II-V nanocrystal prepared thereby, and to a field-effect transistor comprising same. In the present invention, II-V nanocrystals are synthesized by means of a co-reduction method using halides of group II elements and group V elements as precursors, thereby preparing II-V nanocrystals which are difficult to synthesize using stable precursors. Particularly, in the present invention, by adjusting conditions such as a ratio of group II and group V elements in a precursor, and the reaction temperature and time after co-reduction, it is possible to prepare extremely high-crystalline II-V nanocrystals satisfying a stoichiometric ratio and improve particle uniformity. Accordingly, when the II-V nanocrystals of the present invention are applied as a p-type semiconductor material of a field-effect transistor, a transistor having excellent electrical performance can be manufactured.

Description

Method for manufacturing group II-V nanocrystals with excellent crystallinity, group II-V nanocrystals manufactured using the same, and field-effect transistors including the same

[0001] The present invention relates to a method for producing group II-V nanocrystals having excellent crystallinity, group II-V nanocrystals produced using the same, and a field-effect transistor including the same, and more particularly, to a method for producing group II-V nanocrystals having excellent crystallinity and uniformity by using a halide of zinc, a group II element, and a halide of a group V element as precursors and co-reducing the same, group II-V nanocrystals produced using the same, and a field-effect transistor including the same.

[0002] Zinc pnictide (Zn3Pn2) is a group II-V compound composed of zinc (Zn), a group II element, and a pnictogen (group V) element (Pn = P, As, or Sb), and is known to have high carrier mobility and a narrow band gap. The group II-V compound exhibits p-type characteristics due to defects that facilitate hole formation in the valence band, and colloidal nanocrystals can be synthesized to have various electrical and optical properties depending on their size. These group II-V nanocrystals are suitable for large-area processing and can be used in various fields such as energy harvesting and infrared imaging, and therefore, research is being conducted on the synthesis of group II-V nanocrystals such as Zn3As2 and Zn3P2.

[0003] For example, Korean Patent Publication No. 10-2007-0064554 describes a method for producing nanoparticles such as Zn3As2 by converting precursors containing ions into nanoparticles, and Korean Patent Registration No. 10-1593425 describes a method for producing zinc arsenide quantum dots by mixing and heating a zinc precursor and a surfactant, then injecting tristrimethylsilylarsenide as an arsenic precursor into the mixture and growing crystals.

[0004] However, zinc has low reactivity and the stability of precursors of group V elements (especially As) is low, so there are limitations in synthesizing group II-V nanocrystals. Even if synthesized, the stoichiometric ratio is not satisfied, so the crystallinity is very low, and there is a problem that many defects occur when a cation exchange process is used. In addition, when using the above-mentioned conventional technology, there was a problem that the reactivity of the zinc precursor and arsenic precursor is high, so oxidation may occur on the surface or the crystallinity may be reduced.

[0005] Accordingly, there is a need for the development of a technology that can manufacture II-V group nanocrystals that have high precursor stability, satisfy the stoichiometric ratio, and have excellent crystallinity, and use them to manufacture field-effect transistors with excellent electrical characteristics.

[0006] An object of the present invention is to provide a method for producing group II-V nanocrystals with high crystallinity using a stable precursor.

[0007] Another object of the present invention is to provide group II-V nanocrystals having high crystallinity and uniform size, manufactured by the above method.

[0008] Another object of the present invention is to provide a field effect transistor having excellent electrical performance including the above II-V group nanocrystals.

[0009] To achieve the above object, the present invention provides a method for producing group II-V nanocrystals, comprising the steps of: preparing a precursor mixture by mixing a group II precursor containing a zinc halide and a group V precursor containing a halide of a group V element; and synthesizing nanocrystals by adding a reducing agent to the precursor mixture and then performing a co-reduction reaction.

[0010] In the present invention, a method for producing a group II-V nanocrystal, wherein the zinc halide is at least one selected from the group consisting of zinc chloride (ZnCl2), zinc iodide (ZnI2), zinc fluoride (ZnF2), and zinc bromide (ZnBr2).

[0011] In the present invention, the halide of the group V element may be at least one selected from the group consisting of arsenic trichloride (AsCl3), arsenic tribromide (AsBr3), arsenic triiodide (AsI3), antimony trichloride (SbCl3), antimony tribromide (SbBr3), antimony triiodide (SbI3), phosphorus trichloride (PCl3), phosphorus tribromide (PBr3), and phosphorus triiodide (PI3).

[0012] In the present invention, the group II precursor and the group V precursor may each independently further include at least one ligand selected from a phosphine-based compound and an amine-based compound.

[0013] In the present invention, in the precursor mixture, the molar ratio of zinc and group V elements may be 1:1 to 8:1.

[0014] In the present invention, the reducing agent may include at least one selected from the group consisting of lithium triethylborohydride (superhydride), diisobutylaluminium hydride (DIBAL-H), lithium aluminum hydride (LiAlH4), lithium borohydride (LiBH4), sodium borohydride (NaBH4), alanine N,N-dimethylethylamine complex (DMEA-AlH3), and tris(dimethylamino)phosphine.

[0015] In the present invention, the above reduction reaction can be performed at a temperature of 200 to 400°C.

[0016] In the present invention, the above reduction reaction can be performed for 10 to 120 minutes.

[0017] The manufacturing method of the present invention may further include, after the above-described co-reduction step, a step of ligand substitution on the nanocrystal surface using a zinc halide solution.

[0018] In the present invention, the ligand substitution step can be performed by mixing and vortexing nanocrystals obtained through a co-reduction reaction and zinc halide.

[0019] In the present invention, the average particle diameter of the manufactured nanocrystals may be 5 to 50 nm.

[0020] In the present invention, the group II-V nanocrystals may be Zn3As2, Zn3P2 or Zn3Sb2 nanocrystals.

[0021]

[0022] The present invention also provides a group II-V nanocrystal manufactured by the above method.

[0023] In the present invention, the nanocrystal may include a crystal phase on space group P42 / nmc.

[0024]

[0025] The present invention also provides a field effect transistor including an active layer formed using the II-V group nanocrystals.

[0026] In the present invention, by synthesizing group II-V nanocrystals using halides of group II and group V elements as precursors and by co-reduction, group II-V nanocrystals, which are difficult to synthesize using stable precursors, can be manufactured. In particular, in the present invention, by controlling conditions such as the ratio of group II elements and group V elements in the precursor, the reaction temperature and time after co-reduction, group II-V nanocrystals satisfying the stoichiometric ratio and having excellent crystallinity can be manufactured, and the uniformity of nanocrystal particles can be improved. Accordingly, when the group II-V nanocrystals of the present invention are applied as a p-type semiconductor material of a field-effect transistor, a transistor with excellent electrical performance can be manufactured.

[0027] FIG. 1 schematically illustrates a manufacturing process of Zn3As2 nanocrystals according to one embodiment of the present invention.

[0028] Figure 2 shows transmission electron microscope images of Zn3As2 nanocrystals manufactured in one embodiment of the present invention according to the precursor ratio.

[0029] Figure 3 shows a UV-vis-absorption graph according to the precursor ratio for Zn3As2 nanocrystals manufactured in one embodiment of the present invention.

[0030] Figures 4a and 4b show the results of X-ray diffraction analysis (a) and the results of analysis (b) of enlarged X-ray diffraction peaks according to the precursor ratio for Zn3As2 nanocrystals manufactured in one embodiment of the present invention, respectively.

[0031] Figures 5a and 5b show a mapping image (a) of zinc (Zn) and arsenic (As) through energy dispersive spectroscopy (EDS) and a scanning transmission electron microscope image (b), respectively, of Zn3As2 nanocrystals manufactured in one embodiment of the present invention.

[0032] Figures 6a and 6b show transmission electron microscope images (a) and absorbance graphs (b) of Zn3P2 nanocrystals manufactured in one embodiment of the present invention, respectively.

[0033] Figures 7a and 7b show transmission electron microscope images (a) and absorbance graphs (b) of Zn3Sb2 nanocrystals manufactured in one embodiment of the present invention, respectively.

[0034] Figures 8a, 8b and 8c respectively show UV-vis-absorption graphs (a), absorbance graphs (b) and transmission electron microscope images (c) according to reaction temperature for Zn3As2 nanocrystals manufactured in one embodiment of the present invention.

[0035] Figures 9a and 9b respectively show Zn energy levels (a) and As energy levels (b) of X-ray photoelectron spectroscopy analysis according to precursor ratio for Zn3As2 nanocrystals manufactured in one embodiment of the present invention.

[0036] Figure 10 shows the results of inductively coupled plasma spectroscopy analysis according to the precursor ratio for Zn3As2 nanocrystals manufactured in one embodiment of the present invention.

[0037] Figure 11 shows the results of FT-IR analysis of Zn3As2 nanocrystals manufactured in one embodiment of the present invention after ligand substitution.

[0038] FIG. 12 schematically illustrates the structure of a field effect transistor including a Zn3As2 nanocrystal layer manufactured in one embodiment of the present invention.

[0039] Figure 13 shows the electrical characteristics of a field effect transistor manufactured in one embodiment of the present invention.

[0040] Figures 14a, 14b and 14c respectively show the results of analyzing the output electrical characteristics of nanocrystals in which ligands were substituted using ZnCl2 (a), ZnBr2 (b) and ZnI2 (c) for a field effect transistor manufactured in one embodiment of the present invention.

[0041] Figure 15 shows the results of analysis of the transfer electrical characteristics of ligand-substituted nanocrystals for a field effect transistor manufactured in one embodiment of the present invention.

[0042] Hereinafter, specific implementations of the present invention will be described in more detail. Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one skilled in the art to which the present invention pertains. In general, the nomenclature used herein is well known and commonly used in the art.

[0043]

[0044] The present invention relates to a method for producing group II-V nanocrystals by using a halide of zinc, a group II element, and a halide of a group V element as a group II precursor and a group V precursor, respectively, and co-reducing them.

[0045] In the present invention, a group II-V nanocrystal, which is difficult to synthesize, such as Zn3A2, can be manufactured using a ligand complex with excellent stability as a precursor and a co-reduction method, and in particular, group II-V nanocrystals satisfying the stoichiometric ratio can be manufactured by controlling the ratio of group II elements and group V elements in the precursor. In addition, the characteristics and uniformity of the nanocrystals can be improved by controlling the reaction temperature and time after co-reduction. In this way, according to the present invention, group II-V nanocrystals with high crystallinity and uniform size can be manufactured using a simple and stable method.

[0046] In the present invention, the group II-V nanocrystal is a nanocrystal formed by combining a group II element and a group V element (pnictogen), wherein the group II element may be zinc (Zn), and the group V element may be at least one of phosphorus (P), arsenic (As), and antimony (Sb). Specifically, the group II-V nanocrystal may be a Zn3As2, Zn3P2, or Zn3Sb2 nanocrystal.

[0047] In the present invention, the group II-V nanocrystals are prepared by mixing a group II precursor and a group V precursor and co-reducing them using a reducing agent. At this time, the group II precursor includes a zinc halide, and the group V precursor includes a halide of a group V element.

[0048] The group II precursor used in the method for producing group II-V nanocrystals according to the present invention may be a complex comprising a halide of zinc, a group II element, and a first ligand, and the group V precursor may be a complex comprising a halide of a group V element and a second ligand. In the present invention, by using a precursor in the form of a complex as described above, group II-V nanocrystals can be produced using a precursor with excellent stability.

[0049] Specifically, the zinc halide may include zinc chloride, bromide, iodide, fluoride, or a combination thereof. For example, the zinc halide may include one or more of zinc chloride (ZnCl2), zinc bromide (ZnBr2), zinc iodide (ZnI2), and zinc fluoride (ZnF2).

[0050] The Group V element may be a pnictogen element, for example, at least one of arsenic (As), antimony (Sb), and phosphorus (P). The halide of the Group V element may include a chloride, a bromide, an iodide, a fluoride, or a combination thereof of the Group V element. For example, the halide of the Group V element may include at least one of arsenic trichloride (AsCl3), arsenic tribromide (AsBr3), arsenic triiodide (AsI3), antimony trichloride (SbCl3), antimony tribromide (SbBr3), antimony triiodide (SbI3), phosphorus trichloride (PCl3), phosphorus tribromide (PBr3), and phosphorus triiodide (PI3).

[0051] The first ligand and the second ligand mixed with the Group II element and Group V element, respectively, may include at least one of a phosphine-based compound and an amine-based compound, and the ligands included in each precursor are independent of each other and may be the same or different.

[0052] In the present invention, the phosphine-based compound may be a phosphine, phosphine oxide, or phosphorous acid-based compound in which one or more hydrocarbon groups (R) are linked to a phosphorus (P) atom. Specifically, the phosphine-based compound may be R3P, R2PH, RPH2, R3PO, R2HPO, RH2PO, R2POOH, RHPOOH, RPO(OH)2, etc., wherein R may each independently be a substituted or unsubstituted aliphatic hydrocarbon group having 1 to 40 carbon atoms, or a substituted or unsubstituted aromatic hydrocarbon group having 6 to 40 carbon atoms. For example, the phosphine-based compound may be trioctylphosphine (TOP), trioctylphosphine oxide (TOPO), diphenylphosphine (DPP), etc.

[0053] In the present invention, the amine compound is a compound in which one or more hydrocarbon groups (R) are linked to a nitrogen (N) atom, and can be represented by RNH2 or R2NH. At this time, R can each independently be a substituted or unsubstituted aliphatic hydrocarbon group having 1 to 40 carbon atoms, or a substituted or unsubstituted aromatic hydrocarbon group having 6 to 40 carbon atoms. For example, the amine compound can be oleylamine, N,N-diisopropylethylamine, benzylamine, N,N,N,N-tetramethyleneethylenediamine, triethylamine, etc.

[0054] The halide of the Group II element can be dissolved in the first ligand to form a Group II precursor. In the Group II precursor, the concentration of the halide of the Group II element (i.e., zinc halide) can be 0.1 to 10 M, preferably 0.5 to 2 M.

[0055] The above Group II precursor can be prepared by mixing a halide of a Group II element and a first ligand at 80 to 200°C, preferably 100 to 150°C, and the reaction time for preparing the precursor can be 12 to 72 hours, preferably 36 to 60 hours.

[0056] The halide of the above group V element can be dissolved in the second ligand to form a group V precursor. In the group V precursor, the concentration of the halide of the group V element can be 0.05 to 5 M, preferably 0.1 to 0.5 M.

[0057] The above group V precursor can be prepared by mixing a halide of a group V element and a second ligand at 80 to 180°C, preferably 90 to 120°C, and the reaction time for preparing the precursor can be 6 to 60 hours, preferably 12 to 36 hours.

[0058] In the Group II precursor and Group V precursor used in the reaction of the present invention, the molar ratio of the Group II element and the Group V element may be 1:1 to 8:1, preferably 2:1 to 6:1, and more preferably 3:1 to 6:1. If the ratio of the Group II element is too low, the reactivity of zinc is too low, making it difficult to synthesize stoichiometric Zn3Pn2 nanocrystals and most of them exist in an amorphous state. However, when the molar ratio of the Group II element (Zn) and the Group V element is 2:1 or more, the synthesis of Zn3Pn2 nanocrystals is observed, and when the molar ratio is 3:1 or more, it is more preferable.

[0059] In this regard, in an embodiment of the present invention, Zn3As2 nanocrystals were synthesized by adjusting the molar ratio of the group II element (Zn) and the group V element (As) in the precursor to 1:1, 2:1, 3:1, and 4:1, respectively. As a result, it was confirmed that when the molar ratio was 4:1, the element ratio of Zn and As in the synthesized nanocrystals was approximately 3:2, which was close to the stoichiometric ratio. In this respect, the molar ratio of the group II element and the group V element is preferably 3:1 to 6:1, more preferably 4:1 to 6:1, and specifically 4:1 to 5:1.

[0060] In addition, in an embodiment of the present invention, when phosphorus (P) or antimony (Sb) is used as a group V element, when nanocrystals are synthesized by adjusting the molar ratio of Zn and group V elements to 2:1, 4:1, and 6:1, respectively, it was confirmed that scattering due to an amorphous surface does not occur when the ratio is 4:1 or higher. In this respect, the molar ratio of group II elements and group V elements is preferably 3:1 to 6:1, and specifically, may be 4:1 to 6:1.

[0061] In the method of the present invention, the Group II precursor and Group V precursor are co-reduced using a reducing agent. In the present invention, Group II-V nanocrystals with excellent crystallinity can be synthesized using a precursor with excellent stability as described above and a simple method for co-reducing them.

[0062] In the present invention, the reducing agent may include at least one of lithium triethylborohydride (superhydride), diisobutylaluminium hydride (DIBAL-H), lithium aluminum hydride (LiAlH4), lithium borohydride (LiBH4), sodium borohydride (NaBH4), alanine N,N-dimethylethylamine complex (DMEA-AlH3), and tris(dimethylamino)phosphine, and preferably, a hydride-based reducing agent may be included.

[0063] The above reducing agent can be used by dissolving it in an organic solvent. For example, the solvent can be one or more of dioctylether, octadecene, trioctylamine, and tetrahydrofuran.

[0064] The above II-V nanocrystal synthesis step can be performed by mixing the group II precursor and the group V precursor, adding a reducing agent, and reacting at high temperature. The above reaction can be performed by colloidal nanocrystal synthesis using heating-up, hot injection, etc.

[0065] Specifically, the reaction can be carried out at a temperature of 150°C or higher, for example, 200 to 400°C. Preferably, the reaction can be carried out at 250 to 350°C, and more preferably, it is carried out at 280 to 320°C. In this regard, in an embodiment of the present invention, nanocrystals were synthesized by adjusting the reaction temperature to 200, 220, 240, 260, 280, and 300°C, respectively, and the absorbance was measured. As a result, a rapid increase in absorbance was observed at 280°C, and it was confirmed that the absorbance was the highest when the nanocrystals were synthesized at 300°C.

[0066] In addition, the reaction can be carried out for 10 to 120 minutes, preferably 20 to 90 minutes. More preferably, the reaction can be carried out for 30 to 60 minutes. In this regard, in the embodiment of the present invention, it was confirmed that when the reaction time is too short, such as 10 minutes, the particles clump together, whereas when the reaction time is 30 minutes or longer, the dispersion is improved and particles of uniform size are synthesized.

[0067] In one embodiment of the present invention, after completion of the reaction, a step of cooling, a step of purifying, a step of washing, and / or a step of centrifuging may be further performed, as needed, to obtain nanocrystals.

[0068]

[0069] The crystals obtained according to the present invention may be nanocrystals having an average size (particle diameter) of 5 to 50 nm, preferably 6 to 20 nm, and include a crystalline substance having a space group (space group) of P42 / nmc. Generally, group II-V crystals in bulk form exhibit various morphologies including α, α', and β phases, but the group II-V crystals of the present invention have a nanocrystal form having an α" phase having a space group of P42 / nmc.

[0070] In this way, by using the present invention, it is possible to manufacture group II-V nanocrystals having excellent crystallinity and a pseudo-face-centered cubic crystal structure due to the α" phase, and in which Zn and As are uniformly distributed. In addition, the crystallinity and stability of the synthesized nanocrystals can be further improved by controlling the ratio of precursors and the reaction temperature.

[0071] In one embodiment of the present invention, the nanocrystals can be surface-treated using solution-ligand exchange, solid-state ligand exchange, etc. The electrical properties of the nanocrystals can be improved depending on the ligand exchange, and solution-state ligand exchange is preferably used.

[0072] For the above ligand substitution, a zinc halide may be used, and for example, one or more of zinc chloride (ZnCl2), zinc bromide (ZnBr2), and zinc iodide (ZnI2) may be used. In particular, from the perspective of the electrical properties of the nanocrystal, it is preferable to perform the ligand substitution with zinc bromide (ZnBr2) or zinc iodide (ZnI2), and zinc iodide (ZnI2) may be used more preferably.

[0073] The solvent used for the above ligand substitution may include at least one of dimethylformamide (N,N-dimethylformamide), formamide, and N-methylformamide.

[0074] The ligand substitution step can be performed by mixing the above nanocrystal solution and the zinc halide solution.

[0075] In an exemplary embodiment of the present invention, the concentration of the nanocrystal solution may be 10 to 100 mg / mL, preferably 30 to 50 mg / mL, and the concentration of the zinc halide solution may be 0.01 to 2 M, preferably 0.05 to 0.5 M. In this case, the nanocrystal solution and the zinc halide solution may be mixed in a volume ratio of 1:1 to 1:10.

[0076] The above nanocrystal solution and the zinc halide solution can be mixed and then vortexed to displace the surface ligands. For sufficient ligand displacement, the vortexing step can be performed for 10 seconds to 10 minutes, preferably 1 to 5 minutes.

[0077] After performing the above ligand substitution step, a purification step; a washing step; and / or a centrifugation step may be further performed, as necessary, to obtain ligand-substituted nanocrystals.

[0078] In this way, by performing a ligand substitution step on group II-V nanocrystals, the hole mobility of the synthesized nanocrystals can be improved, and this can be utilized in a field effect transistor device to manufacture a p-type semiconductor device.

[0079]

[0080] Accordingly, the present invention can also provide a device, preferably a field effect transistor, comprising the II-V group nanocrystal.

[0081] A field effect transistor (FET) is a transistor that controls the current of the source and drain electrodes by utilizing the principle that a gate electrode is energized by an electric field in the channel when a voltage is applied to the gate electrode, thereby generating a gate through which electrons or holes flow. The II-V nanocrystals of the present invention exhibit p-type semiconductor characteristics and have excellent crystallinity and electrical characteristics, thereby providing a field effect transistor with excellent output.

[0082] Specifically, the device of the present invention may include the II-V group nanocrystal layer as an active layer.

[0083] The above nanocrystal layer, which serves as the active layer of the device, can be formed by coating the II-V group nanocrystals of the present invention using a solution process. The coating can be performed using spin coating, drop coating, self-assembly coating, layer-by-layer coating, etc.

[0084] As a solvent for the above nanocrystal coating solution, one or more solvents such as dimethylformamide, octane, 1,2-ethanedithiol (EDT), sodium sulfide, sodium azide, 1-octanethiol, thiourea, and diethyl zinc may be used. The concentration of the nanocrystal coating solution may be, for example, 10 to 100 mg / mL, but is not limited thereto.

[0085] After coating the above nanocrystal coating solution, a nanocrystal layer can be formed by heat treatment at a temperature of 150 to 400°C for 10 to 60 minutes.

[0086] In the present invention, the thickness of the nanocrystal layer may vary depending on the type of device and the desired performance, and may be, for example, in the range of 5 nm to 100 μm, preferably in the range of 10 nm to 10 μm, and specifically in the range of 100 nm to 1 μm.

[0087] In the present invention, the device may further include components necessary for the device, such as a substrate, one or more electrodes, an electron transport layer, a hole transport layer, and a hole injection layer.

[0088] In the present invention, the electrode may be formed of a metal, a conductive oxide, or a conductive polymer, and for example, a metal such as Au, Ag, Pt, or Cu, or a conductive oxide such as ITO (indium tin oxide), FTO (fluorine-doped tin oxide), IZO (indium zinc oxide), AZO (aluminium-doped zinc oxide), or GZO (gallium zinc oxide) may be used, but is not limited thereto.

[0089] As the electron transport material forming the electron transport layer, known metal oxides may be applied. As such metal oxides, materials doped with or combined with fluorine in metals such as Al, Cd, Cs, Cu, Ga, Ge, In, and Li may be used, or titanium dioxide (TiO2), zinc oxide (ZnO), zirconium oxide (ZrO), tin oxide (SnO2), tungsten oxide (WO3), tantalum oxide (Ta2O3), etc. may be used, but are not limited thereto.

[0090] As the hole transport material forming the above hole transport layer, TFB (poly[(9,9-dioctylfluorenyl-2,7-diyl)-co-(4,4'-(N-(p-butylphenyl))diphenylamine)]), CBP (4,4'-N,N'-dicarbazolyl-biphenyl), polyaniline, polypyrrole, etc. can be used, but are not limited thereto.

[0091] As a hole injection material forming the above hole injection layer, one or more of PEDOT:PSS (poly(ethylenedioxy)thiophene):polystyrene sulfonate), PEDOT (poly(ethylenedioxy)thiophene), polyaniline, polypyrrole, polythiophene, polyacetylene, polyphenylene, etc. may be used, but is not limited thereto.

[0092] The nanocrystal layer used as an active layer in the device of the present invention exhibits p-type semiconductor characteristics, including the II-V group nanocrystals of the present invention, and has excellent crystallinity and electrical characteristics, and has advantages such as high mobility and a narrow band gap, which are characteristics of II-V group semiconductor compounds. Accordingly, the II-V group nanocrystals of the present invention can be usefully applied to the active layer of a field-effect transistor device.

[0093]

[0094] Example

[0095]

[0096] The present invention is described in more detail through the following examples. However, these examples are provided to illustrate some experimental methods and compositions for the purpose of illustratively explaining the present invention, and the scope of the present invention is not limited to these examples.

[0097]

[0098] Manufacturing Example 1: Synthesis of Zn3As2 nanocrystals using a co-reduction method

[0099]

[0100] As shown in Fig. 1, Zn3As2 nanocrystals were synthesized by co-reduction of a zinc precursor and a pnictogen (group 15) precursor.

[0101] For the zinc precursor, a 1 M precursor was prepared by mixing zinc halide substances, ZnCl2, and trioctylphosphine (TOP) and stirring on a hot plate at 120°C for 48 hours. For the pnictogen precursor, a 0.25 M precursor was prepared by reacting AsCl3 with degassed oleamine on a hot plate at 100°C for 24 hours. In addition, 2 M lithium triethylborohydride (super-hydride, SH) was prepared using degassed dioctyl ether (DOE) as a reducing agent. In this experiment, all precursor syntheses were performed in a glovebox.

[0102] To synthesize Zn3As2 nanocrystals, a group II-V semiconductor compound, 10 mL of degassed oleamine and 1 mL each of a zinc precursor and a pnictogen precursor were loaded into a 50 mL three-necked flask. 1.25 mL of lithium triethylborohydride (SH), a reducing agent, was added in a nitrogen atmosphere, and co-reduction was performed. The mixture was heated to 300°C and grown for 1 hour to synthesize nanocrystals.

[0103] Based on the above experimental method, nanocrystals were synthesized and used in the experiment by adjusting the molar ratio of Zn and As in the precursor to 1:1, 2:1, 3:1, and 4:1, respectively.

[0104]

[0105] Experimental Example 1: TEM image analysis of Zn3As2 nanocrystals according to the Zn / As ratio.

[0106]

[0107] Based on the method of Manufacturing Example 1, nanocrystals were synthesized by adjusting the ratio of Zn:As to 1:1, 2:1, 3:1, and 4:1, respectively, and the transmission electron microscope (TEM) images of each nanocrystal were analyzed.

[0108] Figure 2 shows a TEM image of the above nanocrystals. When the Zn / As ratio is low, such as 1 or 2, the nanocrystals are non-uniform in size, exhibit an amorphous surface, and tend to aggregate in an amorphous state. On the other hand, when the Zn precursor ratio is excessive, such as 3 or 4, the SAED pattern appears distinct, and it was confirmed that nanocrystals with uniform sizes of 6.35 ± 0.49 nm and 10.77 ± 1.06 nm, respectively, were synthesized.

[0109]

[0110] Experimental Example 2: UV-vis absorption analysis of Zn3As2 nanocrystals according to Zn / As ratio

[0111]

[0112] Based on the method of Manufacturing Example 1, nanocrystals were synthesized by adjusting the molar ratio of Zn:As to 1:1, 2:1, 3:1, and 4:1, respectively, and UV-visible spectroscopy analysis was performed on each nanocrystal. The UV-visible spectroscopy spectrum was recorded at 200 to 1400 nm using a SHIMADZU UV-2600 UV-vis spectrometer.

[0113] Figure 3 shows a UV-vis absorption graph of the nanocrystals, and a red shift in the absorption spectrum was observed as the Zn / As ratio increased. In addition, according to the Tauc plot, it can be confirmed that the size of the nanocrystals increases as the Zn / As ratio increases. However, when the Zn / As ratio was 1, severe scattering occurred due to the amorphous surface of the nanocrystals.

[0114] Accordingly, it was confirmed that when manufacturing Zn3As2 nanocrystals using the method of the present invention, it is preferable that the Zn / As ratio be at least 2.

[0115]

[0116] Experimental Example 3: Analysis of X-ray diffraction results of Zn3As2 nanocrystals according to the Zn / As ratio.

[0117]

[0118] Based on the method of Manufacturing Example 1, nanocrystals were synthesized by adjusting the ratio of Zn:As to 1:1, 2:1, 3:1, and 4:1, respectively, and X-ray diffraction analysis (XRD) was performed on each nanocrystal using a miniFlex 600 diffractometer (RIGAKU).

[0119] Figures 4a and 4b show the graph (a) and enlarged graph (b) of the X-ray diffraction analysis results of the nanocrystals. When the Zn / As ratio is 2 or less, the XRD pattern of the nanocrystals is broad, confirming poor crystallinity. On the other hand, when the Zn / As ratio is 3 or more, the crystallinity increases, and the peaks at 26.2° and 43.5° match the (202) and (224) of the tetragonal structure.

[0120] Bulk Zn3As2 generally exhibits various morphologies including α, α', and β phases, where the α phase generally has an I41cd structure and the α' phase has a P42 / nbc structure. However, the two XRD patterns for the α and α' phases did not match those of the nanocrystals of the present invention, and it was confirmed that the nanocrystals with a Zn / As ratio of 3 or 4 exhibited a P42 / nmc structure of the α" phase.

[0121] According to these results, it was confirmed that it is preferable that the Zn / As ratio be 3 or more in the production of the Zn3As2 nanocrystals of the present invention.

[0122]

[0123] Experimental Example 4: Analysis of HAADF-STEM and EDS mapping images of Zn3As2 nanocrystals.

[0124]

[0125] In Manufacturing Example 1, nanocrystals were synthesized with a Zn / As ratio of 4, and high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM) images were obtained for the synthesized Zn3As2 nanocrystals.

[0126] A mapping image of zinc (Zn) and arsenic (As) using energy dispersive spectroscopy (EDS) is shown in Fig. 5a, and a scanning transmission electron microscope (STEM) image of the nanocrystals is shown in Fig. 5b.

[0127] Referring to the image of the above nanocrystals, it can be confirmed that facets are developed and the crystallinity is high in the Zn3As2 nanocrystals with a Zn / As ratio of 4. In addition, the presence of Zn, As, Cl, and P elements inside the Zn3As2 nanocrystals was confirmed through EDS, and a triangular shape was observed in the Zn3As2 nanocrystals due to the α"-phase, confirming a pseudo-face-centered cubic crystal structure.

[0128] As a result, a uniform distribution of Zn and As was observed even though the sizes of the nanocrystals varied, and it was confirmed that Cl and P were not involved in the synthesis of the nanocrystals.

[0129]

[0130] Experimental Example 5: Characterization of Zn3P2 and Zn3Sb2 Nanocrystals

[0131]

[0132] Using the method of Manufacturing Example 1, Zn3P2 and Zn3Sb2 nanocrystals were synthesized using P or Sb precursor instead of As precursor as a pnictogen precursor.

[0133] In the case of Zn3P2, the P precursor was PCl3 with degassed oleamine reacted on a hot plate at 100°C for 24 hours, and in the case of Zn3Sb2, the Sb precursor was SbCl3 with degassed oleamine reacted on a hot plate at 100°C for 24 hours. Based on the above method, nanocrystals were synthesized by adjusting the molar ratios of Zn and P or Sb in the precursors to 2:1, 4:1, and 6:1, respectively.

[0134] Figures 6a and 6b show transmission electron microscopy images (a) and absorbance graphs (b) of Zn3P2 nanocrystals, respectively. Experimental results show that nanowires are formed when the ratio of Zn in Zn3P2 is 4 or higher, and lattice fringes appear at high magnification.

[0135] In addition, referring to the absorbance graph, it was found that when the Zn / P ratio was 2, severe scattering occurred due to the amorphous surface of the nanocrystal, and from this, it was found that a Zn / P ratio of 4 or higher is desirable.

[0136] Figures 7a and 7b show transmission electron microscopy images (a) and absorbance graphs (b) of Zn3Sb2 nanocrystals, respectively. Referring to the experimental results, it can be confirmed that when the Zn ratio in Zn3Sb2 is 4 or higher, relatively large particles are formed, and lattice fringes appear at high magnification. In addition, in the case of rectangular Zn3Sb2, the lattice fringe measurements confirmed that it had a hexagonal structure.

[0137] Referring to the absorbance graph of Zn3Sb2 nanocrystals, it was found that when the Zn / Sb ratio was 2, severe scattering occurred due to the amorphous surface of the nanocrystals, and smaller particles were formed compared to when the Zn / Sb ratio was 4 or higher.

[0138]

[0139] Experimental Example 6: Characterization of Zn3As2 Nanocrystals According to Synthesis Temperature and Growth Time

[0140]

[0141] Nanocrystals were manufactured using the method of Manufacturing Example 1 with a Zn / As ratio of 4, but the synthesis temperature was increased by 20°C in the range of 200 to 300°C, and a solution of nanocrystals was manufactured. For each synthesized nanocrystal, ultraviolet-visible spectroscopy was performed, and the crystal morphology was confirmed using TEM images.

[0142] Figure 8a shows UV-vis absorption graphs for nanocrystals at various temperatures. While a red shift was observed in the absorption spectrum as the Zn / As ratio and reaction temperature increased, no absorption peak was observed. From this, it is inferred that the nanocrystals of the present invention are larger than conventional quantum dots and do not exhibit quantum confinement effects, resulting in the absence of an absorption peak.

[0143] Figure 8b is a graph showing the photograph of the nanocrystal solution according to the reaction temperature and the absorbance at 600 nm. At low temperatures of 200 to 240°C, there was little change in absorbance and the solution was confirmed to be light beige, but at 260°C, nucleus formation began and the solution was confirmed to be dark brown. In addition, a rapid increase in absorbance was observed at 280°C, and the absorbance was highest when the nanocrystals were synthesized at 300°C.

[0144] Figure 8c shows transmission electron microscopy (TEM) images of nanocrystals grown at different temperatures and times. When grown at 260°C for 30 minutes, the nanocrystals remained in the form of clusters, and after 1 hour of growth, relatively larger particles with a size of 6 nm were formed. At 280°C, the synthesized nanoparticles were clumped together, but as time passed, the dispersion improved and particles of uniform size were synthesized. When synthesized at 300°C, an increase in particle size was observed from the beginning, and it was confirmed that a triangular shape developed as the growth time increased.

[0145] Accordingly, it was confirmed that 300℃ was the most suitable reaction temperature, and 30 minutes or more was preferable as the reaction time.

[0146]

[0147] Experimental Example 7: XPS analysis of Zn3As2 nanocrystals according to the Zn / As ratio

[0148]

[0149] Based on the method of Manufacturing Example 1, nanocrystals were synthesized by adjusting the ratio of Zn:As to 1:1, 2:1, 3:1, and 4:1, respectively, and the Zn energy level (a) and As energy level (b) of each nanocrystal were analyzed through X-ray photoelectron spectroscopy (XPS), and are shown in Figures 9a and 9b, respectively.

[0150] Experimental results showed that as the amount of Zn precursor increased, the binding energies of the Zn 2p level and the As 3d level decreased. In particular, the Zn 2p 1 / 2 and 2p 3 / 2 levels shifted from 1045 eV to 1044.3 eV and from 1021.8 eV to 1021.4 eV, respectively. Similarly, the As 3d 2 / 3 and 3d 5 / 2 levels showed similar trends, shifting from 42.2 eV to 41.2 eV and from 41.3 eV to 40.3 eV, respectively.

[0151] In addition, a peak around 44.1 eV related to the As-O bond peak was observed in nanocrystals synthesized with a Zn / As ratio of 1. However, as the content of the zinc precursor increased, the peak of arsenic oxidation decreased. This is because the reactivity of zinc is relatively low, making it difficult for all the zinc precursor to participate in the synthesis reaction. As a result, the surface of the nanocrystals becomes rich in arsenic, which has a high affinity for oxygen, and is easily oxidized, resulting in an amorphous and unstable structure. Consequently, a significant change in the XPS results was confirmed due to surface oxidation.

[0152] Accordingly, it was confirmed that when the Zn ratio was too low, the crystallinity was low and the surface oxidation was high, whereas when the Zn / As ratio was increased to 3 or more, the crystallinity was excellent.

[0153]

[0154] Experimental Example 8: ICP-OES Results Analysis of Zn3As2 Nanocrystals According to the Zn / As Ratio

[0155]

[0156] Based on the method of Manufacturing Example 1, nanocrystals were synthesized by adjusting the ratio of Zn:As to 1:1, 2:1, 3:1, and 4:1, respectively. The results of inductively coupled plasma optical spectroscopy (ICP-OES) analysis of the synthesized nanocrystals are shown in Fig. 10.

[0157] Experimental results showed that the amount of arsenic detected in the nanocrystals synthesized with a Zn / As ratio of 1 was more than twice that of zinc, indicating that arsenic was abundant on the surface and Zn was mixed into the nanocrystals. x As y We were able to confirm that it exists.

[0158] Meanwhile, as the zinc concentration increased, the amount of zinc detected also increased, and in particular, when the Zn / As ratio was 4, the atomic concentrations of Zn and As were calculated to be 61% and 39%, respectively. These values ​​are very close to the ideal stoichiometric ratio of 3:2, indicating that almost all As was consumed when the Zn / As ratio was 4.

[0159] That is, it was confirmed that when the Zn / As ratio was less than 2 due to the low reactivity of zinc, a significant amount of amorphous nanocrystals were synthesized, and when the ratio increased to 4, nanocrystals composed mostly of Zn3As2 were synthesized.

[0160]

[0161] Manufacturing Example 2: Manufacturing of nanocrystals ligand-substituted with zinc halides

[0162]

[0163] The nanocrystals manufactured according to Manufacturing Example 1 were dispersed in octane at a concentration of 50 mg / mL, and solution-phase ligand substitution was performed using zinc halogen inorganic materials, ZnCl2, ZnBr2, and ZnI2, respectively.

[0164] The solution used for ligand substitution was a mixture of 0.5 mmol of zinc halide, 0.3 mmol of ammonium acetate, and 5 mL of dimethylformamide. 5 mL of the zinc solution, 5 mL of octane, and 1 mL of the nanocrystal solution were added, and the mixture was vortexed for 1 minute to substitute the ligand. Toluene was added to the substituted solution to precipitate the nanocrystals, and the ligand-substituted nanocrystals were dispersed in dimethylformamide at 50 mg / mL.

[0165]

[0166] Experimental Example 9: FT-IR Analysis of Zn3As2 Nanocrystals Substituted with Halogenated Zinc

[0167]

[0168] According to Manufacturing Example 2, a solution-phase ligand substitution process was performed on Zn3As2 nanocrystals using zinc halide-based inorganic materials (ZnCl2, ZnBr2, and ZnI2), and Fourier transform infrared spectroscopy (FT-IR) was performed on each nanocrystal.

[0169] Figure 11 shows the FT-IR analysis results for each nanocrystal, and the peak (1570 cm) arising from the NH bond of oleamine after ligand exchange -1 and 3358 cm -1 ) was found to be extinguished. From this, it was confirmed that oleamine was replaced by a zinc halide substance during the solution ligand exchange process, and that there was no oleamine on the nanocrystal surface.

[0170]

[0171] Manufacturing Example 3: Fabrication of a Field-Effect Transistor Using Zn3As2 Nanocrystals

[0172]

[0173] The ligand-substituted Zn3As2 nanocrystal solution of Manufacturing Example 2 was spin-coated on a SiO2 substrate deposited to a thickness of 300 nm to produce a thin film. The thinned nanocrystal layer was baked at 250°C for 30 minutes, and gold (Au) was deposited as an electrode to produce a field effect transistor (FET).

[0174] Figure 12 schematically illustrates the structure of the fabricated field effect transistor. Referring to Figure 12, the fabricated field effect transistor has a structure in which an insulating layer and a nanocrystal layer are formed on a substrate, and an electrode (gold) is formed.

[0175]

[0176] Experimental Example 10: Electrical Characteristics Evaluation of Field-Effect Transistors

[0177]

[0178] The results of evaluating the electrical characteristics of the field effect transistor manufactured according to Manufacturing Example 3 are shown in Fig. 13. In addition, the electrical characteristics of the field effect transistor manufactured using the nanocrystal of Manufacturing Example 1 without performing ligand substitution were also evaluated, and the results were compared.

[0179] As a result of the experiment, the nanocrystals were observed to exhibit p-type characteristics at a bias of -80 V. In addition, sufficient p-type characteristics were observed even in the absence of ligand exchange, confirming that the Zn3As2 nanocrystals synthesized according to the present invention inherently exhibit p-type characteristics.

[0180]

[0181] Experimental Example 11: Electrical Characterization of Halogenated Zinc-Substituted Nanocrystals

[0182]

[0183] A solution-phase ligand substitution process was performed on Zn3As2 nanocrystals using ZnCl2, ZnBr2, and ZnI2 as zinc halide-based inorganic materials, and the electrical properties of each nanocrystal were evaluated.

[0184] Figures 14a, 14b, and 14c show the results of analysis of the output electrical characteristics of nanocrystals substituted with ZnCl2 (a), ZnBr2 (b), and ZnI2 (c), respectively, and Figure 15 shows the results of analysis of the transfer electrical characteristics of each nanocrystal.

[0185] For the output characteristics of ligand-substituted nanocrystals, the current increased as the size of the halide ion increased. Furthermore, when the nanocrystal thin film was treated with a halide compound, the hole mobility was confirmed to be enhanced in all cases of ZnCl2, ZnBr2, and ZnI2.

[0186] Accordingly, it was found that the electrical properties were improved when the nanocrystal surface of the present invention was ligand-substituted using zinc halide.

[0187]

[0188] Although some implementation forms of the present invention have been described above, the present invention is not limited to the implementation forms described above, and can be implemented by modifying and changing them within a scope that does not deviate from the gist of the present invention, and it should be understood that forms with such modifications and changes also fall within the technical spirit of the present invention.

Claims

1. A step of preparing a precursor mixture by mixing a Group II precursor containing a zinc halide and a Group V precursor containing a Group V element halide; and A step of synthesizing nanocrystals by adding a reducing agent to the above precursor mixture and then performing a co-reduction reaction. A method for producing a group II-V nanocrystal, comprising:

2. In paragraph 1, A method for producing a group II-V nanocrystal, wherein the zinc halide is at least one selected from the group consisting of zinc chloride (ZnCl2), zinc iodide (ZnI2), zinc fluoride (ZnF2), and zinc bromide (ZnBr2).

3. In paragraph 1, A method for producing a group II-V nanocrystal, wherein the halide of the group V element is at least one selected from the group consisting of arsenic trichloride (AsCl3), arsenic tribromide (AsBr3), arsenic triiodide (AsI3), antimony trichloride (SbCl3), antimony tribromide (SbBr3), antimony triiodide (SbI3), phosphorus trichloride (PCl3), phosphorus tribromide (PBr3), and phosphorus triiodide (PI3).

4. In paragraph 1, A method for producing a group II-V nanocrystal, wherein the group II precursor and the group V precursor each independently further comprise at least one ligand selected from a phosphine-based compound and an amine-based compound.

5. In paragraph 1, A method for producing group II-V nanocrystals, wherein the molar ratio of zinc and group V elements in the above precursor mixture is 1:1 to 8:

1.

6. In paragraph 1, A method for producing a group II-V nanocrystal, wherein the reducing agent comprises at least one selected from the group consisting of lithium triethylborohydride (superhydride), diisobutylaluminium hydride (DIBAL-H), lithium aluminum hydride (LiAlH4), lithium borohydride (LiBH4), sodium borohydride (NaBH4), alanine N,N-dimethylethylamine complex (DMEA-AlH3), and tris(dimethylamino)phosphine.

7. In paragraph 1, A method for producing group II-V nanocrystals, wherein the above reduction reaction is performed at a temperature of 200 to 400°C.

8. In paragraph 1, A method for producing group II-V nanocrystals, wherein the above reduction reaction is performed for 10 to 120 minutes.

9. In paragraph 1, A method for producing group II-V nanocrystals, further comprising, after the above-mentioned reduction step, a step of ligand substituting the nanocrystal surface using a zinc halide solution.

10. In paragraph 9, A method for producing group II-V nanocrystals, wherein the above ligand substitution step is performed by mixing and vortexing nanocrystals obtained through a co-reduction reaction and zinc halide.

11. In paragraph 1, A method for producing group II-V nanocrystals, wherein the average particle diameter of the nanocrystals is 5 to 50 nm.

12. In paragraph 1, A method for producing a group II-V nanocrystal, wherein the group II-V nanocrystal is a Zn3As2, Zn3P2 or Zn3Sb2 nanocrystal.

13. A group II-V nanocrystal manufactured by the method of any one of claims 1 to 12.

14. In paragraph 13, A group II-V nanocrystal comprising a crystalline phase of space group P42 / nmc.

15. A field effect transistor comprising an active layer formed using a group II-V nanocrystal of claim 13.

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