KR102649305B1 - Substrate for UV photodetector comprising plasmonic hybrid nanoparticles, zinc oxide quantum dots and transition metal dichalcogenide and hybrid UV photodetector using the same - Google Patents

Abstract

The present invention relates to a substrate for a UV photodetector containing plasmonic hybrid nanoparticles (HNP), titanium dioxide (TiO ₂ ), and graphene quantum dots (GQD), and a UV photodetector using the same. More specifically, the present invention relates to a substrate for a high-performance UV photodetector with high photocurrent and photoresponsiveness, which is made by stacking GQD/TiO ₂ /HNP on a sapphire substrate, and a UV photodetector based on the same.

Description

Substrate for UV photodetector comprising plasmonic hybrid nanoparticles, zinc oxide quantum dots and transition metal dichalcogenide and hybrid UV photodetector using the same}

The present invention relates to a substrate for a UV photodetector containing plasmonic hybrid nanoparticles (HNP), ZnO quantum dots, and transition metal dichalcogenide, and a UV photodetector using the same. More specifically, the present invention relates to a substrate for a high-performance UV photodetector having high photocurrent and photoresponsiveness, which is a layered layer of MoS ₂ /ZnO/HNP, and a UV photodetector based on the same.

Due to its wide range of applications in pollution monitoring, biochemical analysis, flame detection, inter-satellite communication, factory automation, and missile launch detection, ultraviolet (UV) light detection has attracted much research interest. UV photodetectors used in these applications are composed of materials with excellent photon absorption, linearity and stable photocurrent. The hybrid photodetector structure composed of a hybrid material system has shown scientific and economic value due to its flexibility in material selection.

The combination of various UV-sensitive materials in a single nano-device structure may provide a promising route to achieve improved photoresponsivity, detectability, and quantum efficiency. For example, the quantum- and nanostructured semiconductors such as GaN, SiC, AlN and ZnO have shown great potential in UV photodetectors. In addition, plasmonic nanoparticles (NPs) are capable of ultrafast charge transfer by hot-electron injection induced by localized surface plasmon resonance (LSPR), making them useful in photodetector applications. showed considerable potential.

As background technology for the present invention, Korean Patent Publication No. 10-2018-0075898 (published on July 5, 2018) describes a method of manufacturing a UV photodetector.

Republic of Korea Patent Publication No. 10-2018-0075898

The purpose of the present invention is to provide a substrate for a UV photodetector that can manufacture a high-performance UV photodetector with high photocurrent and photoresponsiveness.

Another object of the present invention is to provide a high-performance UV photodetector with high photocurrent and photoresponsiveness.

Another object of the present invention is to provide a manufacturing method that can efficiently manufacture a high-performance UV photodetector with high photocurrent and photoresponsiveness.

Other objects and advantages of the present invention will become more apparent from the following detailed description, claims, and drawings.

According to one aspect, a base substrate; A hybrid nanoparticle layer containing hybrid nanoparticles (HNPs) formed on the base substrate; A ZnO quantum dot (QDs) layer formed on the hybrid nanoparticle layer; and a transition metal dichalcogenide layer, wherein the hybrid nanoparticles (HNPs) include a core containing a palladium (Pd) element; A substrate for a UV photodetector is provided, including hybrid nanoparticles (HNPs) with a core-shell structure and a plurality of Ag nanoparticles, including a shell layer containing a silver (Ag) element.

According to one embodiment, the base substrate may be a sapphire (Al ₂ O ₃ ) substrate for a UV photodetector.

According to one embodiment, the shell layer may have a thickness of 5 nm or more and less than 20 nm, and may be a substrate for a UV photodetector.

According to one embodiment, the ZnO quantum dots (QDs) may be a substrate for a UV photodetector, which has a wide band gap of 150 to 300 μm between electrodes and an average thickness of 50 nm to 300 nm.

According to one embodiment, the transition metal dichalcogenide layer may be a substrate for a UV photodetector composed of MoS ₂ nanoflakes.

According to another aspect, a substrate for a UV photodetector according to the present invention; and an Au electrode formed on the UV detector substrate. A UV photodetector is provided, including a.

According to another aspect, a hybrid nanoparticle layer forming step of forming a hybrid nanoparticle layer containing hybrid nanoparticles (HNPs) on a base substrate; A quantum dot layer forming step of forming a ZnO quantum dot layer on the hybrid nanoparticle layer; and forming a transition metal dichalcogenide layer on the ZnO quantum dot layer.

According to one embodiment, the hybrid nanoparticle layer forming step includes forming a plurality of nanoparticle islands of a first metal separated from each other on the base substrate; And it may include depositing a second metal on the nanoparticle island of the first metal and annealing it at 550 to 650°C.

According to one embodiment, the first metal may be Pd, the second metal may be Ag, and the hybrid nanoparticles (HNPs) may be PdAg.

According to one embodiment, the thickness of the deposited second metal may be 1 nm or more and less than 20 nm.

According to one embodiment, MoS ₂ /ZnO/hybrid nanoparticles (HNPs), including ZnO quantum dots and transition metal dichalcogenide MoS ₂ nanoflakes (NFs) included in the substrate for the photodetector according to the present invention. The resulting hybrid nanostructure has excellent optical properties and can significantly improve the high hot spot, high photocurrent, and photoresponsiveness of the photodetector, providing excellent LSPR.

According to one embodiment, the substrate structure according to the present invention can provide efficient light transmission using the transition metal dichalcogenide MoS ₂ nanoflake according to the present invention, thereby providing a great advantage for photodetector applications. can be provided.

According to one embodiment, the UV photodetector of the present invention can have high photocurrent and photoresponsiveness due to the hybrid nanostructure of MoS ₂ /ZnO/HNPs with excellent light availability and optical properties.

According to one embodiment, the UV photodetector according to the present invention has high light absorption efficiency, exhibits a strong localized surface plasmon resonance (LSPR) effect even in the near-infrared, visible, and ultraviolet regions, and can improve photoresponsiveness.

According to one embodiment, the method for manufacturing a UV photodetector according to the present invention can efficiently manufacture a high-performance UV photodetector with high photocurrent and photoresponsiveness.

Figure 1 (a) shows a schematic diagram of the architecture of a photodetector including MoS ₂ nanoflake/ZnO quantum dots (QDs)/PdAg hybrid nanoparticles (HNP) according to an embodiment of the present invention.
Figure 1(b) shows the photoresponse of various devices, namely, MoS ₂ /ZnO/HNPs hybrid device, ZnO/HNPs and pure ZnO device according to the present invention, under 385 nm illumination of 54.9 mW/mm ² at 10V. .
Figure 1(c) schematically shows the method for producing PdAg HNPs according to the present invention.
Figure 1(d) shows the localized surface plasmon resonance (LSPR) effect of PdAg HNPs according to the present invention.
Figure 1(e) schematically shows the charge transfer and photocurrent enhancement of the MoS ₂ /ZnO/HNPs hybrid device architecture according to the present invention.
Figure 2 shows the evolution of PdAg hybrid nanoparticles prepared by coating 10 nm of Ag on a Pd NP template and then annealing at various temperatures between 0 and 600 °C for 120 seconds. (a) schematically shows the manufacturing steps of PdAg HNPs, and (b) to (e) show AFM top views of bare Pd NPs and PdAg HNPs. (b-1) to (e-1) show enlarged top views showing core-shell PdAg NPs and background Ag NPs. (b-2) to (e-2) show the line-profiles of primary NPs. (c-3) to (e-3) show line-profiles of background Ag NPs. (f) shows a summary plot of total surface area ratio (SAR) and root mean square (RMS) roughness (Rq).
Figure 3 shows SEM and EDS elemental analysis of PdAg HNPs prepared with 10 nm Ag coating at 400 and 600 °C. (a-1) to (a-4) show EDS phase maps corresponding to Pd Lα1, Ag Lα1, Al Kα1, and O Kα1. (b) to (b-1) show the AFM side view and line profile of the corresponding HNPs at 400 °C. (c) to (c-2) show the EDS line profiles of Ag Lα1 and Pd Lα1. (d) to (e) show SEM images of HNPs at 600 °C. (e-1) to (e-4) show EDS phase maps of various elements shown in the SEM image corresponding to (e).
Figure 4 shows the localized surface plasmon resonance (LSPR) response of PdAg HNPs prepared with 10 nm Ag coating, based on UV-VIS-NIR spectra. (a) shows the extinction spectrum in the 270-1100 nm region. (a-1) represents the normalized spectrum corresponding to the 400-700 nm region. (a-2) shows contour plots showing the quenching peak location and area based on the generation of HNPs. (b) to (c) show the reflection and transmission spectra of PdAg HNPs. (d) shows the simulation schematic of Pd, Au, core-shell PdAg, and PdAg hybrid NPs. (e) to (h) show the local electric field (Local e-field) distribution of various NPs according to the finite-difference time-domain (FDTD). (e-1) to (h-1) show the corresponding side views of the FDTD simulation.
Figure 5 shows an AFM top view of MoS ₂ /ZnO/HNP according to the present invention. (a-1) shows the line profile of (a) AFM plan view. (b) shows the cross-sectional backscattering electron detector (BSE) image of the cross section of MoS ₂ /ZnO/HNP. (c) shows the SEM image of the cross section of MoS ₂ /ZnO/HNP. (c-1) to (c-5) show EDS maps of labeled elements. (d) shows an enlarged cross-section of the ZnO/HNP interface. (d-1) to (d-5) show EDS line analysis according to the EDS line. (e) shows the Raman spectrum of ZnO QDs. (f) shows the Raman spectrum of MoS ₂ nanoflake. (f-1) represents an expanded spectrum between 300 and 500 cm ^-1 .
Figure 6 shows the photoresponse characteristics of pure ZnO, ZnO/HNP, and MoS ₂ /ZnO/HNP photodetectors under the illumination of a 385 nm light emitting diode (LED). (a) schematically shows the MoS ₂ /ZnO/HNP hybrid photodetector architecture. (b) shows the photocurrent response of various devices at 54.9 mW/mm ² at ±10 V, and the inset indicates the dark current of each device. (c) shows the photocurrent variation of the MoS ₂ /ZnO/HNP hybrid photodetector at different power densities. (d) to (f) show the photocurrent responses of the device at various incident powers of 10 V. (g) to (i) are summary plots of photoresponsivity, detection sensitivity, and external quantum efficiency (EQE) based on the change in incident power of the 385 nm LED at 10 V. indicates.
Figures 7 (a) to (c) show the transient photoresponse of the photodetector based on on/off switching of 385 nm at 10 V. The LED power density was fixed at 54.9 mW/mm ² . (d) to (f) show transient analyzes of various devices at 10 V with UV on and off. (g) shows the voltage-dependent responsivity at 1, 5 and 10 V under 385 nm illumination at 54.9 mW/mm ² . (h) shows the local electric field (Local e-field) distribution of MoS ₂ /ZnO/HNP according to the finite-difference time-domain (FDTD). (i) schematically shows the energy Venn diagram of the MoS ₂ /ZnO/HNP hybrid photodetector.
Figures 8 (a) to (b) show AFM top views of pure and degassed sapphire (0001) substrates. (a-1) to (a-2) and (b-1) to (b-2) show AFM side views and corresponding line profiles of pure and degassed sapphire, respectively. (c) to (d) show reflection and transmission spectra between 270 and 1100 nm. The sapphire wafer was cut to a sample size of 6 × 6 mm ² and degassed in a pulsed laser deposition (PLD) chamber at 1.0 × 104 torr, 600° C. for 30 min. After degassing, a smooth surface, flat optical transmittance, and reflection with a modulation of less than 0.3 nm were observed in the UV-VIS-NIR region.
Figures 9 (a) to (e) show a schematic diagram of the HNPs/ZnO/MoS ₂ photodetector architecture. (b-1) shows SEM and EDS elemental phase maps of typical HNPs. (f) shows the extinction spectra of pure ZnO, HNPs, ZnO/HNPs, and MoS ₂ /ZnO/HNPs. (g) shows the photoresponse of various devices such as pure ZnO, NPs/ZnO, and NPs/ZnO/MoS ₂ at 10 V under 385 nm illumination. (h) shows the corresponding photoresponsivity of the photodetector with 385 nm excitation at various power densities.
Figure 10 shows a monometallic pure Pd NP template fabricated from a 30 nm Pd film annealed at 800 °C for 450 s on sapphire (0001). (a) shows a side view of the Pd template. (a-1) shows the cross-sectional line profile of the Pt template. (a-2) shows the height distribution of Pd NPs. (a-3) shows the diameter distribution of Pd NPs. (a-4) shows the transmission (T), reflection (R), and extinction (E) spectra of Pd NPs in the 280 - 1100 nm region.
Figure 11 shows the large-scale morphology of core-shell PdAg hybrid nanoparticles (HNPs) coated with 10 nm Ag. (a) to (c) show AFM side views of PdAg HNPs (3 × 3 μm ² ). (a-1) to (c-1) represent the corresponding line profiles. (d) to (f) show summary plots of average roughness (Ra), root mean square (RMS) roughness (Rq) and surface area ratio (SAR).
Figure 12 (a) to (c) show EDS spectra for PdAg HNPs annealed at different temperatures labeled after coating with 10 nm Ag. (a-1) to (c-1) show enlarged intensities and peak positions of the corresponding elements. (a-2) to (c-2) show the EDS element composition table with weight and atomic percentage indicated.
Figure 13 shows core-shell PdAg HNPs coated with 5 nm Ag on a 30 nm Pd NP template and then annealed from 0 to 600 °C. (a) to (d) show the AFM top view (3 × 3 μm ² ). (a-1) to (d-1) show enlarged AFM top views of 750 × 750 nm ² . (a-2) to (d-2) show enlarged side views of typical PdAg HNPs. (a-3) to (d-3) show cross-sectional line profiles on core-shell NPs. (b-4) to (d-4) show cross-sectional line profiles on background Ag NPs. (e) shows a summary plot of Rq and SAR.
Figure 14 shows large-scale morphology analysis of PdAg HNPs annealed after 5 nm Ag coating. (a) to (c) show AFM side views of PdAg hybrid NPs (3 × 3 μm ² ). (a-1) to (c-1) represent the corresponding line profiles. (d) to (g) show summary plots of Ra, Rq and SAR.
Figure 15 shows the EDS spectrum of PdAg HNPs coated with 5 nm Ag. (a) to (c) show EDS spectra. (a-1) to (c-1) represent the enlarged peak positions of the corresponding elements. (a-2) to (c-2) represent a summary of elemental compositions indicated by weight and atomic percentage.
Figures 16 (a) to (c) show the extinction, transmission, and reflection spectra of PdAg HNPs coated with 5 nm Ag. (a) shows the extinction spectrum in the 270 - 1100 nm region. (a-1) represents the normalized spectrum within the 400 - 700 nm region. (a-2) shows contour plots showing the movement of the extinction peak position.
Figure 17 shows large-scale morphology analysis of fully alloyed PdAg NPs, coated with 20 nm Ag on 30 nm Pd NPs and then annealed at different temperatures. (a) to (c) show AFM side views of fully alloyed PdAg NPs (3 × 3 μm ² ). (a-1) to (c-1) show the corresponding line profiles. (d) to (f) show summary plots of Ra, Rq and SAR.
Figure 18 shows SEM and EDS elemental mapping of fully alloyed PdAg NPs coated with 20 nm Ag on 30 nm Pd NPs at 400 °C. (a) shows the SEM image, (b) to (b-1) show the AFM image and the corresponding line profile. (c) to (f) show the Pd, Ag, Al and O maps in the SEM image in (a). (g) to (i) show EDS line profile analysis.
Figure 19 shows the large-scale morphology of fully alloyed PdAg coated with 20 nm Ag on 30 nm Pd NPs. (a) to (c) show AFM (3 × 3 μm ² ) top views. (b-1) to (b-3) show SEM images and corresponding phase maps of NPs alloyed with PdAg at 400 °C. (d) to (f) show plots of Rq, SAR and atomic percentage.
Figure 20 shows EDS spectra of fully alloyed PdAg NPs coated with 20 nm Ag at different temperatures. (a) to (c) show EDS spectra. (a-1) to (c-1) show enlarged peak positions. (a-2) to (c-2) represent the EDS element composition table.
Figure 21 (a) to (c) show the extinction, reflection and transmission spectra of fully alloyed PdAg and PtAg NPs coated with 20 nm Ag. (a) shows the extinction spectrum in the 270 - 1100 nm region. (a-1) represents the intensity of the normalized spectrum in the 400 - 700 nm region. (a-2) shows a contour plot showing the movement of the LSPR peak position.
Figure 22 shows finite difference time domain (FDTD) simulations of various NP and hybrid configurations. (a) to (e) show schematic diagrams of typical Pd, Ag, core-shell PdAg, hybrid PdAg, and MoS ₂ /ZnO/HNP configurations. (a-1) to (e-1) show top views of local electric field distribution. (a-2) to (e-2) show side views of the corresponding local electric field distribution.
Figures 23 (a) to (b) show ZnO QDs on sapphire and ZnO QDs on PdAg HNPs (ZnO/HNP). (a-1) to (b-1) show the line profiles of the corresponding AFM images of (a) and (b). (c) shows the plot of Rq and SAR. (d) shows a schematic diagram of the optical measurement system. (e) to (g) show the extinction, transmission, and reflection spectra of pure ZnO, ZnO/HNP, and MoS ₂ /ZnO/HNP.
Figure 24 (a) shows the EDS spectrum of pure ZnO QDs on sapphire. (b) shows the elemental map of ZnO QDs on sapphire. (c) shows the EDS spectrum of ZnO on PdAg HNPs (ZnO/HNP).
Figure 25 shows cross-sectional EDS analysis at the ZnO QD and HNP interface. (a) shows the assembled EDS map. (b) shows the SEM image of the EDS spectral region. (c) shows the EDS spectrum. (d) shows the corresponding EDS element composition table with weight and atomic percentage indicated.
Figures 26 (a) to (c) show the voltage dependence characteristics of pure ZnO QD, ZnO/HNP, and MoS ₂ /ZnO/HNP devices under 385 nm illumination of 54.9 mW/mm ² at 1, 5, and 10 V. (d) to (f) show summary plots of responsivity, detection sensitivity and EQE measured with excitation at 385 nm at different voltages.
Figure 27 shows the voltage and wavelength dependence characteristics of pure ZnO QD, ZnO/HNP, and MoS ₂ /ZnO/HNP devices under illumination of 275 nm at 1.6 mW/mm ² . (a) to (c) show the photoresponse of various UV photodetectors at 275 nm at 1.6 mW/mm ² at 1, 5, and 10 V. (d) to (f) show summary plots of wavelength-dependent responsivity, detection sensitivity and EQE between the UV and NIR regions with a fixed power density of 1.6 mW/mm ² at 10 V.

The terms used in this application are only used to describe specific embodiments and are not intended to limit the invention. Singular expressions include plural expressions unless the context clearly dictates otherwise.

In this application, terms such as 'include' or 'have' are intended to designate the presence of features, numbers, steps, operations, components, parts, or combinations thereof described in the specification, but are not intended to indicate the presence of one or more other features. It should be understood that this does not exclude in advance the possibility of the existence or addition of elements, numbers, steps, operations, components, parts, or combinations thereof.

In this application, when a part “includes” a certain component, this means that it may further include other components rather than excluding other components unless specifically stated to the contrary. In addition, throughout the specification, “on” means located above or below the object part, and does not necessarily mean located above the direction of gravity.

Since the present invention can be modified in various ways and can have various embodiments, specific embodiments will be illustrated in the drawings and described in detail in the detailed description. However, this is not intended to limit the present invention to specific embodiments, and should be understood to include all transformations, equivalents, and substitutes included in the spirit and technical scope of the present invention. In describing the present invention, if it is determined that a detailed description of related known technologies may obscure the gist of the present invention, the detailed description will be omitted.

Terms such as first and second are used to distinguish various components in the present invention, and the components are not limited numerically by the terms.

The inventors of the present application have developed a hybrid UV method combining plasmonic PdAg hybrid nanoparticles (HNPs), wide-bandgap ZnO quantum dots (QDs), and transition metal dichalcogenide MoS ₂ nanoflakes for improved performance of UV photodetectors. A photodetector device was designed. The MoS ₂ /ZnO _/ HNPs hybrid device of the present invention is configured as shown in Figure 1 (a).

The MoS ₂ /ZnO _/ HNPs device showed a significant improvement in photodetector performance, specifically, a significantly increased photocurrent (I _ph ) of 4 × 10 ⁻³ A under 385 nm illumination of 54.9 mW/mm ² at 10 V. indicated. In addition, it was confirmed that the photoresponsivity of 21,111 mA/W, detection sensitivity of 7.9 × 10 ¹¹ jones, and EQE of 6,800% were superior compared to the ZnO-based UV photodetector.

The present invention was completed by confirming that the cause of the increase in the above-mentioned high photo current is related to the original photo-induced carriers of the HNP and ZnO QD layers and the photo carriers from 2-D MoS ₂ nanoflakes and hot carrier injection through them. did. In addition, this connection is systematically described below based on the surface morphology, optical properties, and FDTD simulation of the photodetector substrate.

According to one aspect, a base substrate; A hybrid nanoparticle layer containing hybrid nanoparticles (HNPs) formed on the base substrate; A ZnO quantum dot (QDs) layer formed on the hybrid nanoparticle layer; and a transition metal dichalcogenide layer, wherein the hybrid nanoparticles (HNPs) include a core containing a palladium (Pd) element; A substrate for a UV photodetector is provided, including hybrid nanoparticles (HNPs) with a core-shell structure and a plurality of Ag nanoparticles, including a shell layer containing a silver (Ag) element.

The substrate for photodetector of the present invention has high photoresponsiveness, excellent detection sensitivity, and high sensitivity by generating and transmitting optical carriers from the HNP and ZnO QD layers and additional optical carriers from transition metal dichalcogenides, especially 2-D MoS ₂ nanoflakes. It is characterized by representing photocurrent.

In this regard, Figure 1(b) shows that the MoS ₂ /ZnO/HNP hybrid device structure shows significantly improved photocurrent (I _ph ) of less than 4 mA under 385 nm illumination of 54.9 mW/mm ² at 10 V. there is. Compared to pure ZnO, the photocurrent increased rapidly as each hybrid layer according to the present invention was added. Specifically, the increased photocurrent was induced by 2-D MoS ₂ on top of the pristine photo-induced carriers on the PdAg HNPs and ZnO QD layers. It may be related to hot carrier injection through localized surface plasmon resonance (LSPR), which is strongly enhanced by additional optical carriers by nanoflakes. This HNP configuration provided a very high density of hot spots and significantly improved LSPR. The photocurrent enhancement of the MoS ₂ /ZnO/HNP architecture was systematically studied by finite-difference time-domain (FDTD) simulations.

The combination of various UV-sensitive materials in a single nano-device structure can be used to achieve improved photoresponsivity, detection sensitivity and quantum efficiency, such as protonated and nanostructured semiconductors such as GaN, SiC, AlN and ZnO, etc. was explored, and the semiconductor zinc oxide (ZnO), which has a wide bandgap below 3.37 eV and high excitation binding energy, has been proven to have excellent properties in various types of UV light detectors such as layers, wires, rods, and quantum dots.

Plasmonic nanoparticles are capable of ultrafast charge transfer by thermo-electron injection induced by localized surface plasmon resonance (LSPR), and thus have found significant potential in photodetector applications. Ag NPs showed a strong LSPR response due to their high light-trapping efficiency, and in particular, Pd NPs showed a high bulk-plasma frequency of LSPR in the UV region. Therefore, it was judged that it would be advantageous for UV light detection if both Ag and Pd were combined into a single nanoparticle (NP) configuration.

Meanwhile, molybdenum disulfide (MoS ₂ ), which belongs to a class of materials called transition metal dichalcogenides (TMDs), can provide a direct bandgap and can be formed into nano-sheets or nano-flakes. The same 2D shape can provide sufficient absorption and efficient transmission, providing great benefits for photodetector applications.

Therefore, hybrid photodetector structures composed of ZnO quantum dots (QDs), plasmonic hybrid NPs and 2D MoS ₂ nanoflakes can benefit from the physical and optical properties offered by these materials, allowing the UV This can provide significant advantages for photodetectors.

Regarding the core-shell structure of the present invention, Figure 2 shows the production of PdAg hybrid nanoparticles (HNPs) by depositing a 10 nm thick Ag coating on a Pd NP template. The PdAg HNP is composed of core-shell structured PdAg NPs and high-density small background Ag NPs. PdAg HNP preparation involves two steps: preparation of template Pd NPs followed by growth of core-shell and background NPs.

In Figure 2(a-1), well-separated 3D islands of Pd NPs on a thin Pd film on sapphire were prepared by solid-state dewetting (SSD) as a first step ( (see Figure 2(b)). The SSD of Pd NPs is based on the reduction of the total surface free energy through optimization of the interfacial energy between the film and the substrate. As shown in Figure 2 (b-2), after the dewetting, the Pd NPs reached a height of 110 nm or less and a width of 400 nm. In the second step, PdAg core-shell NPs are prepared together with background Ag NPs through Ag film deposition followed by annealing, as shown in (a-3) and (a-4) of Figure 2. The Ag adatoms can diffuse into high chemical potential sites of primary Pd NPs, forming a core-shell configuration.

Figure 3 shows SEM and EDS analysis of hybrid PdAg NPs at 400 and 600 °C. The corresponding EDS spectrum with the corresponding elemental peaks is shown in Figure 12. First, in Figures 3(a-1) and 3(e-1), the phase maps clearly indicate the presence of Pd atoms only at the primary NP position. In Figures 3(a-2) and 3(e-4), Ag atoms were observed anywhere on the surface with higher intensity on the Pd NP positions. This clearly shows that Pd NPs shelled by Ag and background Ag NPs were fabricated throughout the surface. As discussed, the Ag count may be higher at the sites of Pd NPs due to preferential diffusion to the higher chemical potential sites of the Pd NPs. EDS line-profiles of the primary NPs are shown in Figures 3(c) to 3(c-2), showing the presence of Pd and Ag on the original Pd NP sites. The hybrid NPs maintained stability without any significant sublimation of Ag, which was confirmed by the elemental ratio of Ag and Pd, as shown in Figure 12.

Meanwhile, in Figures 18 and 19, the 20 nm Ag coating set showed completely different phases of the elemental maps. First, no background NPs were observed in this set. Additionally, the Pd and Ag maps showed exact agreement with the SEM morphology. This shows that the Pd and Ag atoms were well distributed within the NPs, and the resulting NPs were perfectly alloyed without any background.

Although not limited thereto, the base substrate may be made of sapphire (Al ₂ O ₃ ). Sapphire substrates were chosen for the growth of plasmonic nanoparticles (NPs) due to their high thermal conductivity and high stability, and are also desirable because the optical properties of NPs can be easily extracted due to their high optical transparency and low losses in a wide electromagnetic spectral range. .

Although not limited thereto, the thickness of the shell layer may be 5 nm or more to less than 20 nm and may be adjusted. The thickness range of the shell layer may be suitable in terms of improving photocurrent and photoresponsiveness.

Mixing of Ag and Pd atoms can occur at the Ag and Pd interface, while primary Pd NPs remain in their original form due to the limited amount of Ag atoms. The rapid growth of Ag NPs in the background can be attributed to the high diffusivity of Ag adsorption atoms.

After depositing 10 nm Ag on the Pd NP template, the surface morphology was very similar to that of pristine Pd NPs, as shown in Figure 2(c). However, through subsequent annealing, preferential Ag diffusion into Pd NPs and gradual development of background Ag NPs were observed in Figure 2 (d) to (e). In (d-2) to (e-2) of Figure 2, the PdAg core-shell NPs did not show much change, while the background Ag NPs in (d-3) to (e-3) of Figure 2 changed dramatically. developed. The height of the Ag NPs reached less than 20 nm at 600 °C, and the height of the Ag NPs almost doubled between 400 and 600 °C. The overall surface roughness of surface area ratio (SAR) and root mean squared (Rq) tended to slightly decrease up to 400°C due to the development of the background. As the background develops, the effective height of primary PdAg NPs and subsequent SAR and Rq can be slightly reduced. At 600 °C, the SAR showed a sharp jump, as background NPs developed larger. Furthermore, morphological and optical analyzes on pure Pd NP templates are shown in Figure 9. Additionally, additional morphological and EDS analyzes of PdAg HNPs with 10 nm Ag coating are shown in Figures 11 and 12. PdAg HNPs coated with 5 nm Ag in Figures 13 to 15 show a similar production trend.

On the other hand, when a higher thickness of Ag coating layer, i.e., 20 nm Ag, was applied to the same Pd NPs, the NP production was totally different, as shown in Figures 17 to 19. That is, instead of HNP composition, alloy PdAg NPs with an overall very large size were fabricated. In Figures 17 to 19, it was not observed that the background NPs had a 20 nm Ag film. As mentioned, mixing of Ag and Pd atoms is possible at the interface of PdAg NPs. Therefore, with a thin Ag film, the available Ag adsorption atoms were limited during mixing, so the pristine Pd NPs were retained. However, if the amount of Ag adsorbed atoms greatly increases, mixing at the NP interface can be further enhanced. When Pd and Ag atoms are completely mixed, fully alloyed PdAg NPs can be formed through redistribution of surface energy.

In conclusion, depending on the thickness of the coating layer and annealing temperature, unique surface morphologies of bimetallic HNPs can be formed.

Regarding the annealing temperature, Figure 4 shows the extinction, reflection, and transmission spectra of 10 nm Ag coated PdAg core-shell HNPs at different temperatures. In general, HNPs exhibit significantly enhanced extinction peaks in the UV and visible regions, and the optical properties varied significantly based on the morphology and element of the NPs. The extinction spectrum of PdAg HNPs was very different from that of pure Pd NPs, which may be due to the distinct surface morphology as well as elemental composition-dependent plasmonic behavior. The tremendous enhancement in LSPR properties can be related to the unique surface morphology, i.e., the synergistic effect of the core-shell configuration of Ag shell with Pd core and high-density pure background Ag NPs. FDTD simulation studies clearly show that the PdAg HNPs are superior and have advantages for photodetector applications with very high electromagnetic field strengths and widely distributed hot spots.

According to one embodiment, the ZnO quantum dots (QDs) may have a wide band gap of 150 to 300 μm between electrodes and an average thickness of 50 nm to 300 nm.

The quantum dots (QDs) can be widely used in optoelectronic applications due to their size-dependent band gap, strong absorption in near to deep UV, high carrier mobility, and quantum confinement. To this end, the combination of various UV-sensitive materials in a single nanodevice architecture could be a promising route to achieve improved photoresponsiveness, detection sensitivity, and quantum efficiency of photodetectors.

According to one embodiment, the transition metal dichalcogenide layer may be composed of MoS ₂ nanoflakes.

According to another aspect, a substrate for a UV photodetector described herein; and an Au electrode formed on the UV detector substrate. A UV photodetector is provided, including a.

The MoS ₂ /ZnO _/ HNPs device showed a dramatic improvement in photodetector performance. As described above, the photocurrent was dramatically improved compared to a device made of pure ZnO.

Although not limited thereto, the base substrate of the photodetector may be made of sapphire.

According to another aspect, a hybrid nanoparticle layer forming step of forming a hybrid nanoparticle layer containing hybrid nanoparticles (HNPs) on a base substrate; A quantum dot layer forming step of forming a ZnO quantum dot layer on the hybrid nanoparticle layer; and forming a transition metal dichalcogenide layer on the ZnO quantum dot layer. A method of manufacturing a UV photodetector is provided.

According to one embodiment, the hybrid nanoparticle layer forming step includes forming a plurality of first metal nanoparticle islands separated from each other on the base substrate; And it may include depositing a second metal on the first metal nanoparticle island and annealing it at 550 to 650°C. As shown in Figure 1(c), it is manufactured by a two-step solid-state dewetting technique. According to the above configuration, the first metal can be more uniformly coated on the base substrate.

Forming a hybrid nanoparticle layer under the above conditions may be suitable for improving the photocurrent and photoresponsiveness of a UV photodetector.

The first metal may be Pd, and the second metal may be Ag. Additionally, the hybrid nanoparticles (HNPs) may be PdAg.

Although not limited to this, the hybrid nanoparticle may be formed by coating a second metal on a first metal.

According to one embodiment, but not limited thereto, the thickness of the deposited second metal may be 1 nm or more and less than 20 nm. If the deposited thickness is less than 1 nm, it cannot have the effect of the Ag shell layer, and if it is more than 20 nm, PdAg of a large size is generated, so it cannot have the effect of hybrid NPs.

Hereinafter, the present invention will be described in more detail through examples. However, these examples are only for illustrating the present invention, and the scope of the present invention is not to be construed as limited by these examples.

Example

MoS ₂ /ZnO/HNP hybrid photodetector manufacturing

1-1. Preparation of bimetallic plasmonic hybrid nanoparticles ((HNPs)

In this study, double-sided polished 430-μm thick c-plane sapphire (0001) with ±0.1° off-axis (iNexus Inc., South Korea) was coated with various PdAg hybrid nanoparticles (HNPs). ) and is used as a substrate for the manufacture of photodetectors. The surface morphology of pure sapphire before and after degassing is shown in Figure 8. For the fabrication of various PdAg NPs, various thicknesses of metal films were deposited on the substrate in a plasma-assisted sputter chamber. The basal pressure, ionization current, and deposition rate were 1 × 10 ¹ torr, 3 mA, and 0.05 nm/s, respectively. A single metal Pd template was prepared as a 30 nm film annealed at 800 °C for 450 sec. Afterwards, Ag films were deposited on top of them at various thicknesses (5, 10 and 20 nm) and ramped at 4 °C s ¹ under 1 × 10 ⁴ torr in a pulsed laser deposition (PLD) chamber. ), and were re-annealed for 120 seconds at each target temperature between 0 and 600 °C.

In this study, double-sided polished 430-μm thick c-plane sapphire (0001) with ±0.1° off-axis (iNexus Inc., South Korea) was coated with various PdAg hybrid nanoparticles (HNPs). ) and is used as a substrate for the manufacture of photodetectors. The surface morphology of pure sapphire before and after degassing is shown in Figure 8. For the fabrication of various PdAg NPs, various thicknesses of metal films were deposited on the substrate in a plasma-assisted sputter chamber. The basal pressure, ionization current, and deposition rate were 1 × 10 ¹ torr, 3 mA, and 0.05 nm/s, respectively. A single metal Pd template was prepared as a 30 nm film annealed at 800 °C for 450 sec. Afterwards, Ag films were deposited on top of them at various thicknesses (5, 10 and 20 nm) and ramped at 4 °C s ¹ under 1 × 10 ⁴ torr in a pulsed laser deposition (PLD) chamber. ), and were re-annealed for 120 seconds at each target temperature between 0 and 600 °C.

1-2. ZnO quantum dots (QDs) and MoS ₂ Nanoflake (NF) solution manufacturing

To synthesize the ZnO QD solution of the present invention, 0.97 g of zinc acetate dehydrate (Zn (CH ₃ COO) ₂ 2H ₂ O, 99.99%) was dissolved in 42 mL of methanol and stirred with magnetic stirring. It was heated to 60°C while stirring. A solution of 0.426 g potassium hydroxide (KOH) in 23 mL methanol was slowly added to the zinc acetate dihydrate methanol solution over 5 minutes. The mixed solution was kept stirred at 60°C for 2.5 h. The obtained solution was allowed to precipitate for 4 hours, and the supernatant of the solution was removed. Afterwards, the product was repeatedly precipitated and washed twice by adding 50 ml methanol. Finally, the remaining product was dispersed in a mixed solution of 4 ml chloroform and 2 ml methanol by ultrasonication for 5 minutes. To prepare molybdenum disulfide (MoS ₂ ) nanoflake (NF) solution, 2 mg of MoS ₂ NFs was dissolved in 1 ml of ethanol. The as-received MoS ₂ NFs in powder form had less than three layers with a diameter of less than 1000 nm. Typically, over time, the MoS ₂ NFs settle to the bottom of the vial, so the solution was sonicated for 10 min before application to improve dispersion of the dose. All reagents (chemicals) were purchased from Sigma Aldrich, USA.

1-3. MoS ₂ /ZnO/HNP hybrid photodetector manufacturing

The photodetector was fabricated by depositing a ZnO QD layer and MoS ₂ NFs on a PdAg hybrid nanoparticle (HNP) sample prepared at 600 °C. In particular, 10 μL of the as-prepared ZnO QDs solution was drop-cast on HNPs and then spin-coated at 2000 rpm for 30 s. ZnO spin coating was repeated five times to form a thin uniform layer of ZnO QDs on PdAg HNPs. Thereafter, the ZnO deposited sample was subjected to three conditions: 100°C for 10 min in vacuum, 200°C for 10 min under 10 cc O ₂ flow, and finally 550°C for 1 hour under 20 cc O ₂ flow in a PLD chamber. Annealed in different stages. A pair of Au electrodes (less than 100 nm thick) were deposited on top of the ZnO layer with a wide gap of 200 μm between the Au electrodes, using a shadow mask. Finally, the MoS ₂ NF solution was deposited on the active area of the device by drop-casting. The step-by-step manufacturing process is shown in Figure 9.

2. Experimental example

2-1. Feature analysis

Non-contact atomic force microscope (AFM) (XE-70, Park Systems Corp., South Korea) and scanning electron microscopes (SEM) (Regulus 8230, HITACHI, Japan and COXEM Corp. , South Korea) was adopted for morphology analysis. Energy-dispersive x-ray spectroscopes (EDS) (Noran System 7, Thermo Fisher, United States and Ultimax, Oxford Instruments, United Kingdom) were used for elemental analysis. An optical system (NOST I, Nostoptiks, South Korea) equipped with an ANDOR sr-500i spectrometer, CCD detector and coupled halogen-deuterium light source was used for extinction, reflection and transmission characterization. The IV responses of the various devices were measured in dark conditions using a B2902A precision source/measurement unit (Keysight Technologies, United States). A tungsten carbide tip was used to contact the Au electrode of the device. Finite-difference time-domain (FDTD) (Lumerical Solutions, Canada) was used to simulate the distribution of electromagnetic fields of various PdAg NPs. Accordingly, the refractive indices of Pd, Ag, and sapphire were referred to.

2-2. Experiment result

After depositing 10 nm Ag on the Pd NP template, the surface morphology was very similar to that of pristine Pd NPs, as shown in Figure 2(c). Through subsequent annealing, preferential Ag diffusion into Pd NPs and gradual development of background Ag NPs were observed in Figure 2(d) to Figure 2(e). In Figures 2(d-2) to 2(e-2), the PdAg core-shell NPs did not show much change, whereas in Figures 2(d-3) to 2(e-3), the background Ag NPs have developed dramatically. The height of the Ag NPs reached ~20 nm or less at 600 °C, and the height of the Ag NPs almost doubled at 400 and 600 °C. The overall surface roughness of surface area ratio (SAR) and root mean squared (Rq) tended to slightly decrease up to almost 400 °C due to the development of the background. As the background develops, the effective height of primary PdAg NPs and subsequent SAR and Rq can be slightly reduced. At 600 °C, the SAR showed a sharp jump, as background NPs developed larger. Furthermore, morphological and optical analyzes on pure Pd NP templates can be found in Figure 9. Additionally, additional morphological and EDS analyzes of PdAg HNPs with 10 nm Ag coating can be found in Figures 11 and 12. 13 to 15, PdAg HNPs coated with 5 nm Ag show a similar evolution trend.

On the other hand, when a higher thickness of the Ag coating layer, i.e., 20 nm Ag, was applied to the same Pd NPs, the NP evolution was entirely different, as shown in Figures 17 to 19. Instead of HNP composition, alloyed PdAg NPs with overall, very large size were fabricated. In Figures 17 to 19, it was not observed that the background NPs had a 20 nm Ag film. As mentioned, mixing of Ag and Pd atoms is possible at the interface of PdAg NPs. With a thin Ag film, the available Ag adsorption atoms were limited during mixing, so the pristine Pd NPs were retained. However, if the amount of Ag adsorbed atoms greatly increases, mixing at the NP interface can be further enhanced. When Pd and Ag atoms are completely mixed, fully alloyed PdAg NPs can be formed through redistribution of surface energy. Depending on the thickness of the coating layer and annealing temperature, unique surface morphologies of bimetallic HNPs can be formed.

Figure 3 shows SEM and EDS analysis of hybrid PdAg NPs at 400 and 600 °C. The corresponding EDS spectrum with the corresponding elemental peaks is shown in Figure 12. First, in Figures 3(a-1) and 3(e-1), the phase maps clearly indicate the presence of Pd atoms only at the primary NP position. In Figures 3(a-2) and 3(e-4), Ag atoms were observed anywhere on the surface with higher intensity on the Pd NP site. This clearly shows that Pd NPs surrounded by Ag and background Ag NPs were fabricated throughout the surface. As discussed, the Ag content may be higher at the Pd NPs sites due to preferential diffusion to the higher chemical potential sites of the Pd NPs. EDS line-profiles of the primary NPs are shown in Figures 3(c) to 3(c-2), showing the presence of Pd and Ag on the original Pd NP sites. The hybrid NPs maintained stability without any significant sublimation of Ag, which was confirmed by the elemental ratio of Ag and Pd, as shown in Figure 12.

Meanwhile, in Figures 18 and 19, the 20 nm Ag coating set showed completely different phases of the elemental maps. First, no background NPs were observed in this set. Additionally, the Pd and Ag maps showed exact agreement with the SEM morphology. This shows that the Pd and Ag atoms were well distributed within the NPs, and the resulting NPs were perfectly alloyed without any background.

Figure 4 shows the extinction, reflection, and transmission spectra of 10 nm Ag coated PdAg core-shell HNPs at different temperatures.

The extinction was determined by the relationship E% = 100% (R% + T%). In general, HNPs exhibit significantly enhanced extinction peaks in the UV and visible regions, and the optical properties vary considerably based on the morphology and element of the NPs. In Figure 3, the extinction spectrum of PdAg HNPs was very different from that of pure Pd NPs, which may be due to the distinct surface morphology as well as elemental composition-dependent plasmonic behavior. The dipole extinction peak in the VIS region by the Ag thin film was extended throughout the visible and infrared regions, whereas the Pd template peaked at 465 nm. The extinction spectrum of PdAg HNPs showed two peaks. There is one smaller peak in the UV region and a broader peak in the visible region, which may be attributed to the quadrupolar resonance (QR) and dipole resonance (DR) modes of the NPs. The stronger VIS peak may be due to a pronounced DR mode. The tremendous enhancement in LSPR properties can be related to the unique surface morphology, i.e., the synergistic effect of the core-shell configuration of Ag shell with Pd core and high-density pure background Ag NPs. The enlarged and normalized extinction spectrum in (a-1) of Figure 4 shows the LSPR peak position in the VIS region. In general, the development of background Ag NPs and the reduction of effective height for samples annealed at higher temperatures resulted in a blue shift of the LSPR peak position. The HNPs exhibited a blue shift in the peak position and a narrower LSPR bandwidth as clearly visible in the contour plot in (a-2) of FIG. 4. In particular, the peak position was observed below 520 nm at 0 °C, which resulted in a blue shift mainly at 485 and 465 nm for PdAg HNPs. Additionally, reflection and transmission spectra were provided in Figures 4(b) and 4(c). The strong peaks observed in the UV and VIS regions for HNPs due to the QR and DR resonance modes were observed as dips in the reflection and transmission spectra. Additional reflection and transmission spectra for the 5 and 20 nm coating sets can be found in Figures 16 and 21. Figures 4(d) to 4(h) show finite-difference time-domain (FDTD) simulations of bare Pd, Ag, core-shell AgPd, and hybrid AgPd NPs. The design diagram for the simulation is shown in Figure 4(d). For systematic comparison, the sizes of Pd, Ag, and core-shell AgPd NPs were kept the same. In Figures 4(e) to 4(g), all three NP configurations of Pd, Ag, and core-shell AgPd exhibited electromagnetic (EM) hotspots at the boundaries. As shown in the side views of Figures 4(e-1) to 4(g-1), EM hotspots generally appeared at the edges of NPs with excitation of surface plasmons. Meanwhile, the maximum local e-field intensity (MLEI, E _max ) gradually increases from E _max = 4 for Pd NPs to 6.2 for Ag NPs and up to 9.8 for the core-shell NPs. increased. This indicates that core-shell NPs can provide higher electromagnetic field strengths and are therefore advantageous for photodetection applications. Finally, Figure 4(h) shows that the HNP composition showed a significantly increased MLEI of 25.1 and greatly increased hotspot distribution. This increased distribution of hot spots may be due to the small high-density Ag background NPs. As mentioned, the EM hot spans typically form at sharp edges and boundaries of NPs. The unique composition of HNPs provided a very high density of background Ag NPs along with core-shell PdAg NPs. Ag NPs based on the general SSD approach generally exhibit very large sizes and low densities. FDTD simulation studies clearly show that the PdAg HNPs are superior and have advantages for photodetector applications with very high electromagnetic field strengths and widely distributed hot spots.

Figure 5 shows characterization of the MoS ₂ /ZnO/HNP photodetector configuration. In the MoS ₂ /ZnO/HNP hybrid configuration, the ZnO QD layer was first prepared on PdAg HNPs and then MoS ₂ nanoflakes were deposited on the active region of the ZnO QD layer. The ZnO QD layer can provide a light-current path with very efficient electron-hole pair (EHP) generation. The MoS ₂ nanoflake is a two-dimensional layered transition metal dichalcogenide (TMD) semiconductor, which can provide additional photo-current through absorption of extra photons. Since the MoS ₂ nanoflakes have an average width of hundreds of nanometers with a thickness of less than three layers, they are expected to increase the absorption while allowing light transmission. Here, since a dispersion solution was used, the actual thickness of the MoS ₂ nanoflake layer can actually be higher. The surface morphology after MoS ₂ nanoflake deposition is shown in Figure 5 (a) to Figure 5 (a-1), and became more rough with some splitting. Alternatively, electrophoresis can be employed to enhance partitioning, which can provide site-selective integration of MoS ₂ nanoflakes. The cross-sectional backscattering electron detector (BSE) image is shown in the electrode region, showing the Au electrode, ZnO QDs and PdAg HNPs. The cross section of the active area where MoS ₂ was deposited was easily destroyed during ion milling. The ZnO QDs were aggregated, the total thickness was less than 300 nm, and the Au electrode was made less than 100 nm. FE-SEM micrograph clearly reveals the granular structure of ZnO QDs with nanopores in the ZnO QD layer. The cross-sectional elemental maps of Figures 5(c) to 5(c-5) clearly revealed the presence of ZnO QDs and PdAg HNPs in the hybrid configuration. Similarly, EDS line profiles clearly show ZnO QDs and PdAg HNPs in Figures 5(d) to 5(d-5). For example, the Zn content was higher at the ZnO site, and the Pd and Ag contents were higher at the NPs site. Additional properties of ZnO, ZnO/HNP, and MoS ₂ /ZnO/HNP are shown in Figures 23 and 24, and the plan view elemental map clearly shows the uniform distribution of MoS ₂ and ZnO in the active region of Figure 24. As shown in (c) of Figure 27, the EDS spectrum of the MoS ₂ /ZnO/HNP indicates the presence of Ag, Pd, Mo, S, Zn, and O, and the Mo L series peak below 2.29 KeV is MoS ₂ It overlapped with the SK series peak (below 2.31 KeV). Raman spectra of the ZnO/HNP and MoS ₂ are shown in Figure 5 (e) and Figure 5 (f). The high intensity peak at 440 cm ^-1 can be attributed to the high E ₂ phonon mode of wurtzite crystalline ZnO. Additionally, the peak at 381 cm ^-1 may be in the A1 mode, and the peak at 331 cm ^-1 of the ZnO sample may be due to multiple phonon scattering.

Structural defects in the ZnO layer may be associated with the small peak at 580 cm ^-1 . Raman of ZnO QD confirmed that the quality of the QD layer was sufficient for use. Figure 5 (f-1) shows that the MoS ₂ layer exhibits characteristic peaks at 380 and 411 cm ^-1 , which are mainly assigned to the E ¹ _2g and A _1g modes of the MoS ₂ nanoflake. The E ¹ _2g mode is due to in-plane motion of Mo and S atoms, and the A _1g mode vibration is due to out-of-plane vibration. Because the layer was thin, the Raman intensity was weaker. Figure 6 shows the photoresponse characteristics of pure ZnO and ZnO/HNP devices and MoS ₂ /ZnO/HNP hybrid architecture under 385 nm illumination with 54.9 mW/cm ^-2 at 10 V. Based on optical and simulation analysis, PdAg HNPs at 600 °C were selected for photodetector application. The sample can provide highly-enhanced LSPR with core-shell configuration and hotspots with well-dewetted high-density small background Ag NPs, which are suitable for photodetector applications. The hybrid device architecture was composed of a combination of MoS ₂ nanoflakes and a ZnO QD layer on a PdAg HNPs layer, as shown in (a) of Figure 6. The current versus voltage ( IV ) characteristics measured under the illumination of a UV LED (385 nm, 54.9 mW/cm ^-2 ) at 10 V in Figure 6 (b) demonstrate the successful photocurrent from pure ZnO to MoS ₂ /ZnO/HNP devices. The improvement was clearly visible. The pure ZnO has 54.9 mW/cm ^-2 at 10 V. It showed 6 × 10 ^-5 A under illumination of 385 nm. Then, the ZnO/NPs composition exhibited an order of magnitude higher I _pH of approximately 5 × 10 ^-4 A or less. Finally, the hybrid configuration of the MoS ₂ /ZnO/HNP device showed a very high photo-current of less than 5 × 10 ⁻³ A for the same excitation. The photocurrent ( I _ph ) enhancement was approximately one order of magnitude with each additional hybrid layer. That is, the I _ph of the MoS ₂ /ZnO/HNP composition rapidly increased by less than 2 times compared to pure ZnO under the same UV excitation. The enhancement may be due to the original electron-hole pair (EHP) generation from ZnO and additional carriers generated from plasmonic hybrid NPs and MoS ₂ nanoflakes. The inset (b) of Figure 6 shows the dark current accompanying the formation of an ohmic contact between the ZnO and Au contacts, compared to the other two configurations, which may be due to the increased concentration of carriers present in the MoS ₂ layer. increased slightly in the MoS ₂ /ZnO/HNP composition. Figure 6(c) shows the power-dependent photoresponse of the MoS ₂ /ZnO/HNP composition under 385 nm illumination at different power densities between 0.34 and 54.9 mW/mm ² at 10 V. In general, I _ph increased gradually with increasing excitation power at a fixed bias due to the production of increased photocarriers. Similarly, all of the above device configurations in Figures 6(d) to 6(f) exhibited highly linear power-dependent photoresponse. The photo responsivities ( R ) of each device configuration are summarized in Figure 6(g), and were calculated based on the following formula: , where I _ph is the photocurrent, I _d is the dark current, and P _d is the power density and A is the active geometrical area of the device. Power-dependent photo responsivities ( R ), detection sensitivity ( D ), and external quantum efficiency ( EQE ) are provided in Table 1 below under 385 nm illumination at each power density. Specifically, Table 1 shows the power photoresponsivity (R), detection _sensitivity (D), and external quantum efficiency ( EQE) is summarized.

Additionally, in Table 2, the device performance parameters were compared with the previously reported ZnO-based UV photodetector. As expected, greatly improved photoresponsivity was obtained with the addition of each hybrid layer, with a maximum R of 21,111 mA/W ^-1 achieved by the MoS ₂ /ZnO/HNP configuration at a power density of 0.34 mW/mm ² . was achieved, which is 533 times higher than the maximum R of pure ZnO composition. The photoresponsivity calculations show that the MoS ₂ /ZnO/HNP configuration is superior even compared to the best results of previously reported ZnO-based UV photodetectors. With the increased power density, photoresponsiveness gradually decreased due to saturation of optical carrier production or increased recombination rates. The detection sensitivity ( D ) is expressed by the following equation, was calculated according to where A is the active area, R is the photoresponsiveness, I _d is the dark current, and e is the elementary charge. As summarized in (d) of FIG. 6, the MoS ₂ /ZnO/HNP photodetector showed the highest detection sensitivity of 7.92 × 10 ¹¹ jones at 0.34 mW/mm ² , which was comparable to that of pure ZnO and It was significantly higher than that of the ZnO/HNP photodetector. Additionally, as shown in Table 2, most of the previous results did not include detection sensitivity, but since detection sensitivity D is directly proportional to light sensitivity (R), it can be seen that the MoS ₂ /ZnO/HNP composition is excellent. Similarly, the external quantum efficiency (EQE) of each device is Calculated based on , where: is the monochromatic wavelength (nm) of light. The maximum EQE for pure ZnO, ZnO/HNP, and MoS ₂ /ZnO/HNP was 12.7, 177, and 6,800 % at 0.34 mW/mm ² , respectively. In other words, the EQE of the MoS ₂ /ZnO/HNP composition was better. Overall, the performance parameters of the photodetector were calculated for the demonstrated device architectures, and as summarized in Table 2, the hybrid device configuration of MoS ₂ /ZnO/HNP clearly exhibited the best parameters; This indicated that the proposed hybrid configuration of MoS ₂ /ZnO/HNP was an efficient photodetector architecture (MoS ₂ /ZnO/HNP in Table 2 below represents the architecture of the present invention).

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7(a) to 7(c) show the photocurrent over time of pure ZnO, ZnO/HNP, and MoS ₂ /ZnO/HNP photodetectors irradiated with a density of 54.9 mW/mm ² and a wavelength of 385 nm at room temperature. It shows on-off characteristics. The irradiation source was turned on and off at 20 second intervals. From the curves, it can be seen that all devices show stable photocurrent response. The current increased rapidly upon UV irradiation, showing excellent stability and repeatability. Figures 7(d) to 7(f) show the time-dependent photoresponses of pure ZnO, ZnO/HNP, and MoS ₂ /ZnO/HNP photodetectors under 385 nm illumination at 10 V. Rise time (t _r ) and fall time (t _f ) were defined as the time required for the maximum photocurrent to reach 90% (t _r ) and 10% (t _f ). t _r and t _f were found to be 6 and 0.34 s, 4 and 0.45 s, and 5 and 4.5 s for the three devices, as shown in Figures 7 (d) to 7 (f). Although the above values are in a similar range, the MoS ₂ /ZnO/HNP composition showed a longer t _f of 4.5 s, which may be due to delayed remixing caused by the increased density of charge trapping centers with the addition of MoS ₂ nanoflakes. You can. As shown in (g) of Figure 7, measurements were made at different biasing voltages of 1, 5 and 10 V for a fixed intensity of 54.9 mW/mm ² , which shows that with increased biasing and Shows a gradually increased R. The generated optical carriers can be collected more quickly at increased bias. Furthermore, in Figures 27 (d) and (f), the wavelength-dependent photoresponsiveness was investigated under different wavelengths of illumination between 275 and 850 nm. For all three devices, negligible photoresponsiveness was obtained in the visible and near-infrared (NIR) regions, while high photoresponsiveness was observed at 275 and 385 nm. Specific values of photoresponsivity, detection sensitivity and EQE values at different voltages and wavelengths are presented in Tables 3 and 4. Additional transient response, voltage-dependent characteristics, and more photo-response are provided in Figures 26 and 27.

Figure 7 (h) shows a finite difference time domain simulation of the local e-field distribution for the MoS ₂ /ZnO/HNP configuration. In Figure 4 (h), the maximum local e-field intensity (MLEI) of 25.1 for PdAg HNPs significantly increased to 45.53 after the addition of ZnO QDs and MoS ₂ nanoflakes, up to 1.8 times. Additionally, the hotspots were highly enhanced around HNPs. This confirms that the hybrid configuration of MoS ₂ /ZnO/HNP can provide greatly increased LSPR with greatly improved hot spot. Figure 7 (i) shows a schematic energy band diagram of the hybrid device architecture of MoS ₂ /ZnO/HNP to visualize photocurrent ( I _ph ) enhancement. The increased I _pH is due to hot carrier (Korea Sensor Research Institute) injection through the strongly improved LSPR of HNPs and native photo-induced carriers in the ZnO QD layer, as clearly visible in the induced band in the diagram. This may be related to the injection of additional optical carriers from MoS ₂ NFs into the phase. Initially, the I _pH contribution originated from electron-hole pair (EHP) generation within the ZnO QD layer. Due to the larger work function of ZnO (5.2 ~ 5.3 eV) compared to Ag (4.26 eV) and Pd (5.22 eV) NPs, a slight upward bending is expected on the surfaces of PdAg HNPs and ZnO. You can. The work function of an alloy material lies between two work functions depending on its composition. As shown in Figure 7(h), additional hot electrons can be injected from HNPs by their strong LSPR under UV illumination. This can result in a significant enhancement of the photocurrent and thus increase the sensitivity of the device, as discussed. Similarly, additional photocarriers can be created by adding several layers of MoS ₂ nanoflakes and transferred to the guided band of the ZnO QD layer. It is quite surprising that a thin layer of 2D TMD MoS ₂ nanoflakes can induce this much current. MoS ₂ nanoflakes with a bandgap of less than 1.4 eV demonstrate the generation of significant photocarriers with sufficient UV absorption.

2-3. conclusion

In summary, a unique configuration of PdAg hybrid NPs was successfully fabricated based on a two-step solid-state dewetting technique, and highly enhanced LSPR properties were demonstrated by optical analysis. The FDTD simulation confirmed that the MELI of PdAg HNPs was significantly improved. At 600 °C, typical PdAg HNPs were assembled in a MoS ₂ /ZnO/HNP configuration, where the ZnO QD layer and MOS ₂ flakes were tailored to a unique UV detector architecture. Initially, template NPs of pure Pd were fabricated on sapphire (0001) by systematic control of SSD and Ag coating thickness, and hybrid HNPs were fabricated with background Ag NPs. The unique core-shell configuration with high density background NPs exhibited highly enhanced LSPR and hot spots. With the optimized device architecture, excellent performance parameters, i.e., a response of 21,111 mA/W, a detection sensitivity ^{of 7.9} This is a significant performance improvement compared to previously reported results for similar breeds. Additionally, the MELI of the MoS ₂ /ZnO/HNP hybrid architecture was also greatly increased with the application of ZnO QDs and MoS ₂ nanoflakes.

Although the present invention has been described in detail through specific examples, this is for detailed explanation of the present invention, and the present invention is not limited thereto, and can be understood by those skilled in the art within the technical spirit of the present invention. It is clear that it can be modified or improved. All simple modifications or changes of the present invention fall within the scope of the present invention, and the specific scope of protection of the present invention will be made clear by the appended patent claims.

Claims (10)

base substrate;
A hybrid nanoparticle layer containing hybrid nanoparticles (HNPs) formed on the base substrate;
A ZnO quantum dot (QDs) layer formed on the hybrid nanoparticle layer; and
comprising a transition metal dichalcogenide layer,
The hybrid nanoparticles (HNPs) include a core containing the element palladium (Pd); and
Containing core-shell structured hybrid nanoparticles (HNPs) and a plurality of Ag nanoparticles, including a shell layer containing a silver (Ag) element,
The base substrate is sapphire (Al ₂ O ₃ ), a substrate for a UV photodetector. delete According to paragraph 1,
A substrate for a UV photodetector, wherein the shell layer has a thickness of 5 nm or more and less than 20 nm. According to paragraph 1,
The ZnO quantum dots (QDs) have a wide band gap of 150 to 300 μm between electrodes and an average thickness of 50 nm to 300 nm. According to paragraph 1,
A substrate for a UV photodetector, wherein the transition metal dichalcogenide layer is composed of MoS ₂ nanoflakes. A substrate for a UV photodetector according to any one of claims 1 and 3 to 5; and
A UV photodetector comprising; an Au electrode formed on the UV photodetector substrate. The method for manufacturing the UV photodetector described in paragraph 6,
A hybrid nanoparticle layer forming step of forming a hybrid nanoparticle layer containing hybrid nanoparticles (HNPs) on a base substrate;
A quantum dot layer forming step of forming a ZnO quantum dot layer on the hybrid nanoparticle layer; and
A method of manufacturing a UV photodetector comprising forming a transition metal dichalcogenide layer on a ZnO quantum dot layer. In clause 7,
The hybrid nanoparticle layer forming step includes forming nanoparticle islands of a plurality of first metals separated from each other on the base substrate; and
A method of manufacturing a UV photodetector, comprising depositing a second metal on the nanoparticle island of the first metal and annealing at 550 to 650°C. According to clause 8,
The first metal is Pd, the second metal is Ag, and the hybrid nanoparticles (HNPs) are PdAg. According to clause 8,
A method of manufacturing a UV photodetector, wherein the thickness of the deposited second metal is 1 nm or more and less than 20 nm.