Quantum dot photodiode, manufacturing method for the same, and electronic device including the same

Abstract

A quantum dot photodiode, a method for manufacturing the same, and an electronic device including the same are disclosed. The quantum dot photodiode comprises: a metal layer; an absorption layer formed on one surface of the metal layer; an electron transport layer formed on one surface of the absorption layer; a transparent electrode formed on one surface of the electron transport layer; and a metasurface portion formed on one surface of the transparent electrode. The absorption layer is composed of quantum dots, and the metasurface portion is configured to cause resonance at the absorption wavelength of the quantum dots. The metal layer and the transparent electrode may be provided to form an optical cavity structure that induces incident light irradiated from one side of the metasurface portion to be reflected multiple times between the metal layer and the transparent electrode.

Description

Technology Field

[0001] The present invention relates to a quantum dot photodiode, a method for manufacturing the same, and an electronic device including the same. Background Technology

[0002] Short-wave infrared (SWIR) is light with a wavelength range of approximately 900 nm to 2500 nm. It is safe for the human body and features an atmospheric transparent window with excellent atmospheric transmittance. Additionally, it has the advantage of achieving a high signal-to-noise ratio (SNR) even in outdoor environments due to minimal solar interference. Thanks to these characteristics, SWIR sensors are utilized in Time-of-Flight (TOF) sensors for indoor and outdoor environmental recognition. They can be used as core components for recognizing three-dimensional spatial information in LiDAR for autonomous vehicles, industrial machine vision, and VR / XR devices. Furthermore, they are being applied in various fields, such as non-destructive inspection in semiconductor manufacturing processes, free-space optical communication between satellite and Earth, and quantum key distribution technology, where they serve as signal receivers.

[0003] However, since SWIR corresponds to a wavelength range that silicon cannot absorb, it is difficult to implement with existing silicon-based sensors. To compensate for this, SWIR devices based on III-V compound semiconductors have been commercialized, but they require expensive epitaxial crystal growth technology, and the manufacturing cost is high due to the complex coupling process with silicon-based integrated circuits. Additionally, a cooling system for suppressing thermal noise is essential, which increases the complexity and cost of the entire system.

[0004] To overcome these limitations, low-cost SWIR sensors based on novel materials are being researched. Among them, Quantum Dot (QD)-based SWIR photodiodes offer the advantages of low manufacturing costs and large-area mass production due to the possibility of solution processing. However, quantum dot materials have lower charge mobility and shorter carrier lifetimes compared to single-crystal semiconductors, which imposes constraints on limiting the thickness of the light absorption layer. Consequently, if the light-absorbing layer becomes too thin, it fails to sufficiently absorb incident light, leading to a decrease in the device's photoelectric conversion efficiency.

[0005] The technology forming the background of this invention is disclosed in Korean Registered Patent Publication No. 10-1558801. The problem to be solved

[0006] The present invention aims to solve the problems of the aforementioned prior art by providing a quantum dot photodiode capable of operating in the short-wave infrared region and having polarization selectivity, and a method for manufacturing the same.

[0007] In addition, the invention aims to provide an electronic device comprising the above-mentioned quantum dot photodiode.

[0008] However, the technical problems that the embodiments of the present invention aim to solve are not limited to those described above, and other technical problems may exist. means of solving the problem

[0009] As a technical means for achieving the above-mentioned technical problem, the first aspect of the present invention relates to a quantum dot photodiode comprising: a metal layer; an absorption layer formed on one surface of the metal layer; an electron transport layer formed on one surface of the absorption layer; a transparent electrode formed on one surface of the electron transport layer; and a metasurface portion formed on one surface of the transparent electrode, wherein the absorption layer is composed of quantum dots, and the metasurface portion is configured to cause resonance at the absorption wavelength of the quantum dots, and the metal layer and the transparent electrode are provided to form an optical cavity structure that induces incident light irradiated from one side of the metasurface portion to be reflected multiple times between the metal layer and the transparent electrode.

[0010] In addition, the above quantum dot is a quantum dot that forms an absorption peak within the short-wave infrared wavelength band.

[0011] In addition, the metasurface portion is configured such that resonance occurs at the wavelength where the quantum dot forms an absorption peak, and a nanoantenna having an isotropic structure is configured to be arranged in a two-dimensional array so as to have the same resonance conditions regardless of the polarization of the incident light.

[0012] In addition, the metasurface portion is provided to induce optical interference by adjusting the phase difference between the incident light and the reflected light so that the amount of reflection in which the incident light fails to pass through the transparent electrode and is reflected is reduced compared to when the metasurface portion is not provided.

[0013] In addition, the light cavity structure is formed to enable multiple reflections by configuring the metal layer to reflect at least a portion of the light irradiated onto the metal layer from one side thereof, and the transparent electrode to reflect a portion of the light irradiated onto the transparent electrode to the other side thereof.

[0014] In addition, the metasurface portion is provided such that a nanoantenna having an anisotropic structure is arranged in a two-dimensional array so as to realize the polarization-selective characteristics of the metasurface.

[0015] In addition, the nanoantenna having the above anisotropic structure is configured such that the amount of light absorption for either TM polarization or TE polarization in the absorption layer is relatively larger.

[0016] The second aspect of the present invention relates to a quantum dot photodiode comprising: a metal layer; an absorption layer formed on one surface of the metal layer; an electron transport layer formed on one surface of the absorption layer; a transparent electrode formed on one surface of the electron transport layer; a glass layer formed on one surface of the transparent electrode; and a metasurface portion formed on one surface of the glass layer, wherein the absorption layer is composed of quantum dots, and the metasurface portion is configured to cause resonance at the absorption wavelength of the quantum dots, and the metal layer and the transparent electrode are provided to form an optical cavity structure that induces incident light irradiated from one side of the metasurface to be reflected multiple times between the metal layer and the transparent electrode.

[0017] In addition, the glass layer is provided with a thickness such that the reflected light and incident light on the glass layer undergo destructive interference.

[0018] In addition, due to destructive interference generated in the glass layer, the glass layer increases the rate at which light is absorbed in the absorption layer.

[0019] A third aspect of the present invention provides an electronic device comprising a quantum dot port diode according to the first aspect or the second aspect.

[0020] In addition, the electronic device includes at least one of a Time of Flight (TOF) sensor, a LiDAR sensor, machine vision, an infrared sensor, and an optical communication device.

[0021] The fourth aspect of the present invention relates to a method for manufacturing a quantum dot photodiode according to the first aspect, comprising the steps of: placing an absorption layer on one surface of a metal layer; placing an electron transport layer on one surface of the absorption layer; placing a transparent electrode on one surface of the electron transport layer; and placing a metasurface portion on one surface of the transparent electrode; wherein the absorption layer is composed of quantum dots, and the metasurface portion is configured to cause resonance at the absorption wavelength of the quantum dots, and the metal layer and the transparent electrode are provided to form an optical cavity structure that induces incident light irradiated from one side of the metasurface portion to be reflected multiple times between the metal layer and the transparent electrode.

[0022] The fifth aspect of the present invention relates to a method for manufacturing a quantum dot photodiode according to the second aspect, comprising the steps of: placing an absorption layer on one side of a metal layer; placing an electron transport layer on one side of the absorption layer; placing a transparent electrode on one side of the electron transport layer; placing a glass layer on one side of the transparent electrode; and placing a metasurface portion on one side of the glass layer; wherein the absorption layer is composed of quantum dots, and the metasurface portion is configured to cause resonance at the absorption wavelength of the quantum dots, and the metal layer and the transparent electrode are provided to form an optical cavity structure that induces incident light irradiated from one side of the metasurface portion to be reflected multiple times between the metal layer and the transparent electrode.

[0023] The means for solving the problem described above are merely exemplary and should not be interpreted as intended to limit the present invention. In addition to the exemplary embodiments described above, additional embodiments may exist in the drawings and the detailed description of the invention. Effects of the invention

[0024] According to the means for solving the problem of the present invention described above, a photodiode according to one embodiment of the present invention minimizes surface reflection through Mie resonance of the metasurface portion so that incident light is irradiated into the device. In addition, the absorption efficiency of the absorption layer can be improved by allowing light absorbed inside the photodiode to be absorbed in the absorption layer through the optical cavity structure between the metal layer and the transparent electrode of the photodiode.

[0025] In addition, by controlling the shape of the nanoantenna present on the metasurface of the photodiode, light can be absorbed selectively based on polarization, thereby enabling On-Off operation based on polarization even at the same wavelength.

[0026] In addition, the above photodiode can be used in various industrial fields, such as TOF sensors, LiDAR sensors used in autonomous vehicles, industrial machine vision, infrared detection sensors, and optical communication.

[0027] In addition, the above photodiode can be manufactured through a solution process, allowing for production at a lower cost compared to conventional III-V compound semiconductor-based SWIR (Short wave infrared) devices.

[0028] However, the effects obtainable from this invention are not limited to those described above, and other effects may exist. Brief explanation of the drawing

[0029] FIGS. 1a and FIGS. 1b are schematic diagrams of a photodiode according to one embodiment of the present invention. Figure 2 illustrates the structure of a photodiode according to one embodiment and a comparative example of the present invention. FIG. 3a is a graph showing the optical characteristics of a photodiode according to one embodiment of the present invention, FIG. 3b is for the reflectance of the photodiode, FIG. 3c is for the transmittance of the photodiode, and FIG. 3d is for the absorption rate of the photodiode. Figure 4(a) shows the electric field distribution inside the photodiode when light is irradiated onto the photodiode according to one embodiment of the present invention, (b) shows the magnetic field distribution inside the photodiode, (c) shows the light energy distribution absorbed in the photodiode according to one comparative example of the present invention, and (d) shows the light energy distribution absorbed in the photodiode of the above embodiment. FIG. 5a is a schematic diagram of a quantum dot photodiode according to one embodiment of the present invention, FIG. 5b shows the light absorption intensity of the absorption layer according to the thickness of the glass layer in the quantum dot photodiode, and FIG. 5c shows the electric field distribution in the photodiode. FIG. 6a is for surface reflectance in a quantum dot photodiode according to one embodiment and a comparative example of the present invention, and FIG. 6b is for light absorption rate of the absorption layer of the quantum dot photodiode according to the above embodiment and comparative example. FIGS. 7a and 7b are schematic diagrams of a quantum dot photodiode according to one embodiment of the present invention, FIG. 7c is of the light absorption rate of an absorption layer for polarized light irradiated on the quantum dot photodiode, and FIG. 7d is of the light energy distribution absorbed by the photodiode. Figures 8 (a) and (b) show the electric field distribution inside the nanoantenna of the quantum dot photodiode according to Figure 7a, and (c) and (d) show the magnetic field distribution. Specific details for implementing the invention

[0030] Below, embodiments of the present invention are described in detail with reference to the attached drawings so that those skilled in the art can easily implement them.

[0031] However, the present invention may be implemented in various different forms and is not limited to the embodiments described herein. Furthermore, in order to clearly illustrate the present invention in the drawings, parts unrelated to the description have been omitted, and similar parts throughout the specification have been given similar reference numerals.

[0032] Throughout this specification, when a part is described as being "connected" to another part, this includes not only cases where they are "directly connected," but also cases where they are "electrically connected" with other elements interposed between them.

[0033] Throughout the entire specification, when a component is described as being located "on," "on top," "on top," "under," "on bottom," or "on bottom" of another component, this includes not only cases where the component is in contact with the other component but also cases where another component exists between the two components.

[0034] Throughout this specification, when a part is described as "comprising" a certain component, this means that, unless specifically stated otherwise, it does not exclude other components but may include additional components.

[0035] Throughout this specification, polarization refers to the phenomenon in which the electric and magnetic fields constituting light vibrate in a specific direction as an electromagnetic wave propagates.

[0036] Throughout this specification, resonance refers to a phenomenon of vibrating with a large amplitude at a specific frequency, and may be described interchangeably with resonance.

[0037] Hereinafter, a quantum dot photodiode according to one embodiment of the present invention, a method for manufacturing the same, and an electronic device including the same will be described.

[0038] As a technical means for achieving the above-mentioned technical problem, the first aspect of the present invention relates to a quantum dot photodiode comprising: a metal layer; an absorption layer formed on one surface of the metal layer; an electron transport layer formed on one surface of the absorption layer; a transparent electrode formed on one surface of the electron transport layer; and a metasurface portion formed on one surface of the transparent electrode, wherein the absorption layer is composed of quantum dots, and the metasurface portion is configured to cause resonance at the absorption wavelength of the quantum dots, and the metal layer and the transparent electrode are provided to form an optical cavity structure that induces incident light irradiated from one side of the metasurface portion to be reflected multiple times between the metal layer and the transparent electrode.

[0039] FIGS. 1A and 1B are schematic diagrams of a photodiode according to one embodiment of the present invention. Referring to FIGS. 1A and 1B, the description of 'one surface' may mean the upper surface, and light irradiated inside the quantum dot photodiode is reflected from one surface of the metal layer and then repeatedly reflected from the other surface of the transparent electrode so as to be absorbed as much as possible in the absorption layer.

[0040] In addition, the above quantum dot is a quantum dot that forms an absorption peak within the short-wave infrared wavelength band.

[0041] The quantum dot photodiode according to the present invention is a quantum dot photodiode having an upper transparent metasurface and a lower optical cavity structure applied thereto, intended to amplify the light absorption rate of an absorption layer containing quantum dots. To this end, an absorption layer, an electron transport layer, and a transparent electrode are sequentially stacked on one side of a metal layer that serves as an electrode and simultaneously reflects incident light, and a metasurface portion that induces Mie resonance is applied on one side of the transparent electrode.

[0042] The above metasurface is composed of a two-dimensional periodic array of nanoantennas and is designed to generate resonance at the absorption peak wavelength of the absorption layer.

[0043] Through this structure, the transmittance of incident light irradiated from the metasurface portion of the quantum dot photodiode toward the metal layer can be increased, and light can be maximally absorbed within the absorption layer through multiple reflections caused by the optical cavity structure formed by the lower transparent electrode and the metal electrode.

[0044] Specifically, when incident light is irradiated from the top of the metasurface, the incident light undergoes resonance at the metasurface. Consequently, reflection from the surface of the quantum dot photodiode is minimized, and most of the light incident on the photodiode reaches the absorption layer. In this case, since a significant amount of light is reflected from the surface in the case of a transparent electrode without a metasurface, the use of a metasurface can minimize losses caused by such reflection. The light that passes through the transparent electrode and reaches the absorption layer is partially absorbed by the absorption layer, while the remaining portion is reflected by the metal layer and directed back toward the absorption layer. At this point, the light reflected from the metal layer passes through the absorption layer again, is partially absorbed, and then directed toward the transparent electrode. Since the other side of the transparent electrode has a high reflectivity, at least a portion is transmitted, and the remaining portion is reflected again toward the metal layer, passing through the absorption layer and being absorbed once more. As this process is repeated, the light incident on the photodiode is continuously absorbed as it passes through the absorption layer, thereby achieving a significant improvement in light absorption efficiency.

[0045] For example, when the upper metasurface is composed of a two-dimensional array of cylindrical TiO2 nanoantennas and the absorption layer contains PbS quantum dots, the reflectance reflected from the surface of the photodiode at a wavelength of 1550 nm was measured to be 0.38%, and the absorption rate of the absorption layer was measured to be 70.75%. Considering that the surface reflectance and the absorption rate of the absorption layer were measured to be 20.03% and 16.81%, respectively, in a photodiode with only a single metasurface and a single optical cavity structure, it can be seen that the quantum dot photodiode containing both the metasurface and the absorption layer containing quantum dots produces a synergistic effect in absorbing light.

[0046] Although the absorption layer may have a limited thickness due to the low charge mobility and lifetime of the quantum dots included in the absorption layer, in the case of a hybrid structure incorporating a metasurface and an optical cavity, such as the photodiode according to the present invention, a high light absorption rate can be achieved despite the thin thickness of the absorption layer.

[0047] In addition, the metasurface portion is provided to induce optical interference by adjusting the phase difference between the incident light and the reflected light so that the amount of reflection in which the incident light fails to pass through the transparent electrode and is reflected is reduced compared to when the metasurface portion is not provided.

[0048] In addition, the light cavity structure is formed to enable multiple reflections by configuring the metal layer to reflect at least a portion of the light irradiated onto the metal layer from one side thereof, and the transparent electrode to reflect a portion of the light irradiated onto the transparent electrode to the other side thereof.

[0049] The metal layer and the transparent electrode are configured to form a light cavity structure in which at least a portion of the light irradiated onto the metal layer by passing through the absorption layer is reflected to the absorption layer, and at least a portion of the light irradiated onto the transparent electrode by being reflected from the metal layer is reflected to the light absorption layer.

[0050] In addition, the metasurface portion is configured such that resonance occurs at the wavelength where the quantum dot forms an absorption peak, and a nanoantenna having an isotropic structure is configured to be arranged in a two-dimensional array so as to have the same resonance conditions regardless of the polarization of the incident light.

[0051] In addition, the metasurface portion is provided such that a nanoantenna having an anisotropic structure is arranged in a two-dimensional array so as to realize the polarization-selective characteristics of the metasurface.

[0052] The above anisotropic structure refers to a structure in which x-axis symmetry, y-axis symmetry, or origin symmetry does not hold, and may include, for example, a rectangular structure or an elliptical structure, but is not limited thereto.

[0053] The above metasurface may include a nanoantenna having an anisotropic structure capable of selectively responding to polarization of a specific direction among the polarizations included in the incident light, wherein resonance occurs at the wavelength where the quantum dot forms an absorption peak, or a nanoantenna having an isotropic structure capable of responding to polarizations included in the incident light.

[0054] In addition, the nanoantenna having the above anisotropic structure is configured such that the amount of light absorption for either TM polarization or TE polarization in the absorption layer is relatively larger.

[0055] Depending on the length and direction of the edges constituting the nano-antenna of the metasurface portion, resonance caused by polarization in a specific direction may occur selectively.

[0056] In the example, the nanoantenna having the anisotropic structure may have an anisotropic structure in which, in a planar view from the direction of light propagation, a first length in a first orthogonal direction and a second length in a second orthogonal direction that is orthogonal to both the direction of light propagation and the first orthogonal direction are different from each other, wherein the first length satisfies a first resonance condition for the first polarization and the second length satisfies a second resonance condition for the second polarization. In this case, when resonance for the first polarization (e.g., TM polarization) occurs at one edge of the nanoantenna having the anisotropic structure, resonance for the second polarization does not occur at the other edge.

[0057] In another example, the nanoantenna having the above isotropic structure has an isotropic structure in which, in a planar view from the direction of light propagation, the first length in the first orthogonal direction and the second length in the second orthogonal direction, which is orthogonal to both the direction of light propagation and the first orthogonal direction, are equal. In the case of the antenna having the above isotropic structure, since it has the same diameter in all directions, resonance for polarization occurs without distinguishing between TM polarization and TE polarization.

[0058] The above isotropic structure is a structure in which x-axis symmetry, y-axis symmetry, and origin symmetry all hold, and may include, for example, a cylindrical structure, but is not limited thereto.

[0059] By adjusting the period (P), radius (D), and height (H) of the nanoantenna included in the upper transparent metasurface, Mie resonance occurs at a specific wavelength, and transmission to the underlying structure is amplified. At this time, light that is not absorbed by the absorption layer is reflected multiple times from the optical cavity structure formed by the transparent electrode and metal layer within the underlying structure, and when multiple reflections occur within the quantum dot photodiode, the light absorption rate of the absorption layer increases.

[0060] In this case, if the upper metasurface is designed to have polarization selectivity, it is possible to achieve amplified light absorption or not achieve it depending on the polarization conditions of the incident light even at the same wavelength. Therefore, it is possible to design a quantum dot photodiode that generates different signals depending on polarization even at the same wavelength.

[0061] For example, in polarizations where resonance occurs, the light absorption rate of the absorption layer is amplified to produce a high output signal, whereas in polarizations where resonance does not occur, a very small signal can be produced. For instance, under the condition of an incident light wavelength of 1550 nm, if the horizontal (Lx) and vertical (Ly) lengths of the nanoantenna constituting the upper metasurface are varied, Mie resonance occurs in TM polarization, but no resonance occurs in TE polarization. In this case, the amount of light absorbed by the absorption layer becomes 72.36% and 17.95%, respectively, resulting in a significant difference in light absorption by the absorption layer depending on the polarization. Therefore, ON / OFF switching can be performed depending on the polarization.

[0062] The second aspect of the present invention relates to a quantum dot photodiode comprising: a metal layer; an absorption layer formed on one surface of the metal layer; an electron transport layer formed on one surface of the absorption layer; a transparent electrode formed on one surface of the electron transport layer; a glass layer formed on one surface of the transparent electrode; and a metasurface portion formed on one surface of the glass layer, wherein the absorption layer is composed of quantum dots, and the metasurface portion is configured to cause resonance at the absorption wavelength of the quantum dots, and the metal layer and the transparent electrode are provided to form an optical cavity structure that induces incident light irradiated from one side of the metasurface to be reflected multiple times between the metal layer and the transparent electrode.

[0063] The quantum dot photodiode according to the second aspect above has a structure in which a glass layer is formed between the metasurface portion and the transparent electrode.

[0064] Throughout the entire specification, the description of a 'glass layer' may be used interchangeably with the description of a 'SiO2 layer'.

[0065] In addition, the glass layer is provided with a thickness such that the reflected light and incident light on the glass layer undergo destructive interference.

[0066] In addition, due to destructive interference generated in the glass layer, the glass layer increases the rate at which light is absorbed in the absorption layer.

[0067] When a glass layer is positioned between a metasurface and a transparent electrode, the thickness of the glass layer is designed such that light reflected from the interface between the glass layer and the transparent electrode causes destructive interference with light incident on the glass layer, thereby amplifying the absorption of the absorption layer by the metasurface and the optical cavity. At this time, the thickness of the glass layer satisfying the corresponding condition satisfies a specific periodic condition.

[0068] For example, at an incident wavelength of 980 nm, the surface reflectance and light absorption rate in the absorption layer can be achieved at 3.82% and 78.18%, respectively. In this case, the device structure is a structure in which an absorption layer forms an absorption peak at a wavelength of 980 nm and a metasurface that resonates at that wavelength is applied.

[0069] If the thickness of the above glass layer is designed to meet the phase matching conditions, it can be seen that the optimal absorption amount is repeated with a period of 1000 nm for the thickness of the glass layer.

[0070] The quantum dot photodiode of the second aspect described above has a structure in which a metasurface is formed on one side of a glass layer, and a transparent electrode, electron transport layer, absorption layer, and metal layer are formed on the other side. Incident light is irradiated onto the quantum dot photodiode from one side of the glass layer where the metasurface is located. When resonance occurs at the metasurface, the irradiated incident light is not reflected but is mostly transmitted to the lower glass layer. When the transmitted light reaches the boundary between the glass layer and the transparent electrode, some of it is reflected at the boundary and some is transmitted to the lower absorption layer. At this time, by adjusting the thickness of the glass layer, destructive interference can occur between the reflected light and the incident light, thereby allowing most of the incident light to reach the absorption layer. Light that reaches the absorption layer but is not absorbed and is transmitted is reflected by the metal layer, and the light reflected from the metal layer moves toward the transparent electrode, then is reflected from the other surface of the transparent electrode and returns to the metal layer. This process is repeated, causing multiple reflections internally by the optical cavity structure, and as a result, most of the incident light can be absorbed by the absorption layer.

[0071] A third aspect of the present invention provides an electronic device comprising a quantum dot port diode according to the first aspect or the second aspect.

[0072] In addition, the electronic device includes at least one of a Time of Flight (TOF) sensor, a LiDAR sensor, machine vision, an infrared sensor, and an optical communication device.

[0073] The fourth aspect of the present invention relates to a method for manufacturing a quantum dot photodiode according to the first aspect, comprising the steps of: placing an absorption layer on one surface of a metal layer; placing an electron transport layer on one surface of the absorption layer; placing a transparent electrode on one surface of the electron transport layer; and placing a metasurface portion on one surface of the transparent electrode; wherein the absorption layer is composed of quantum dots, and the metasurface portion is configured to cause resonance at the absorption wavelength of the quantum dots, and the metal layer and the transparent electrode are provided to form an optical cavity structure that induces incident light irradiated from one side of the metasurface portion to be reflected multiple times between the metal layer and the transparent electrode.

[0074] The fifth aspect of the present invention relates to a method for manufacturing a quantum dot photodiode according to the second aspect, comprising the steps of: placing an absorption layer on one side of a metal layer; placing an electron transport layer on one side of the absorption layer; placing a transparent electrode on one side of the electron transport layer; placing a glass layer on one side of the transparent electrode; and placing a metasurface portion on one side of the glass layer; wherein the absorption layer is composed of quantum dots, and the metasurface portion is configured to cause resonance at the absorption wavelength of the quantum dots, and the metal layer and the transparent electrode are provided to form an optical cavity structure that induces incident light irradiated from one side of the metasurface portion to be reflected multiple times between the metal layer and the transparent electrode.

[0075] The fourth and fifth aspects of the present invention differ only in that a glass layer is placed between the transparent electrode and the metasurface portion, while other elements are identical.

[0076] First, an absorption layer is placed on one side of the metal layer.

[0077] Next, an electron transport layer is placed on one side of the absorption layer.

[0078] Next, a transparent electrode is placed on one side of the electron transport layer.

[0079] Next, a metasurface portion may be placed on one side of a transparent electrode, and a glass layer may be additionally placed between the transparent electrode and the metasurface portion.

[0080] The above metasurface is a two-dimensional arrangement of nanoantennas that generate resonance when irradiated with light, and the structure and spacing can be adjusted as needed.

[0081] At this time, the above process can be performed in reverse order. For example, a structure can be formed by placing a transparent electrode, placing an electron transport layer on one side of the transparent electrode, placing an absorption layer on one side of the electron transport layer, placing a metal layer on one side of the absorption layer, and then placing the structure in reverse. Since the electron transport layer is placed on the other side of the transparent electrode and a metasurface portion can be placed on one side of the transparent electrode while the structure is reversed, a photodiode identical to the first side can be manufactured even if the fourth side is performed in reverse order, and this can be applied equally to the fifth side.

[0082] In this regard, as in the fifth aspect, when a glass layer is placed on a metasurface portion and a transparent electrode is placed on one side of the glass layer, an electron transport layer and an absorption layer may be coated and placed sequentially through a solution process such as spin coating, and then a metal layer may be deposited.

[0083] The present invention is to be explained in more detail through the following examples, but the following examples are for illustrative purposes only and are not intended to limit the scope of the present invention.

[0084] [Example 1]

[0085] An absorption layer containing 270 nm thick PbS quantum dots was formed on a gold (Au) layer that serves as a bottom electrode and simultaneously reflects incident SWIR (short-wave infrared). Subsequently, a 30 nm thick ZnO electron transport layer (ETL) and a 100 nm thick ITO transparent electrode were sequentially stacked on the absorption layer, and a metasurface that induces Mie resonance at SWIR wavelengths was placed on the ITO transparent electrode.

[0086] At this time, the metasurface is composed of a two-dimensional periodic array of cylindrical TiO2 nanoantennas and is designed to generate resonance at a wavelength of 1550 nm. The radius (D) of the nanoantenna is 552 nm, the height (H) is 510 nm, and the period (P) is 920 nm.

[0087] [Comparative Example]

[0088] In Example 1 above, a glass layer was placed instead of a gold electrode layer, or a metasurface was not placed.

[0089] Figure 2 illustrates the structure of a photodiode according to one embodiment and a comparative example of the present invention.

[0090] In FIG. 2, Structure 3 represents a quantum dot photodiode of an example, Structure 1 is a quantum dot photodiode of a comparative example without a gold electrode layer at the bottom, and Structure 2 is a quantum dot photodiode of a comparative example without a metasurface.

[0091] FIG. 3a is a graph showing the optical characteristics of a photodiode according to one embodiment of the present invention, FIG. 3b is about the reflectance of a photodiode according to one embodiment and a comparative example of the present invention, FIG. 3c is about the transmittance of a photodiode according to the embodiment and a comparative example, and FIG. 3d is about the absorption rate of a photodiode according to the embodiment and a comparative example. In this case, FIG. 3b to FIG. 3d are graphs of the reflectance, transmittance, and absorption rate in structures 1 to 3 shown in FIG. 2.

[0092] Figure 3a shows the reflectance, transmittance, and absorption of a quantum dot photodiode corresponding to structure 3 of Figure 2, and a sharp decrease in reflectance and a corresponding sharp increase in transmittance and absorption are confirmed in the wavelength band of about 1550 nm.

[0093] Referring to FIG. 3b, when light, specifically SWIR in the 1550 nm wavelength band, is irradiated onto the quantum dot photodiodes according to the above examples and comparative examples, Mie resonance is induced in the nanoantennas of the upper metasurface, the electromagnetic field is locally strengthened, and a sharp reduction in reflection occurs in Structure 1 and Structure 3, which means that most of the incident light enters the device. On the other hand, Structure 2 shows that significant reflection of more than 70% occurs at the upper transparent electrode interface at the same wavelength.

[0094] In addition, in Figure 3b, in structures 1 and 3 containing a metasurface, a sharp decrease in reflectance for light at a wavelength of 1550 nm is observed due to the resonance of the metasurface, which means that most of the incident light enters the device. On the other hand, in structure 2, it can be seen that significant reflection occurs at the top ITO interface at the same wavelength.

[0095] Meanwhile, referring to Fig. 3c, the intensity of light reaching the absorption layer after passing through the transparent electrode layer and the electron transport layer can be observed. In structures 1 and 3 with applied metasurfaces, some of the incident SWIR is absorbed by the transparent electrode layer, and the intensity of light transmitted from the top of the device to nearly 100% is reduced to about 80% or less. In structure 2 as well, it is observed that some of the light incident into the device without reflection is absorbed by the transparent electrode layer.

[0096] Meanwhile, Figure 3d shows the light absorption intensity generated in the absorption layer. Structures 1 and 3 have relatively high light intensity reaching the absorption layer. However, in the case of Structure 1, since there is no bottom reflection structure, a significant portion of the reached light is lost by passing through the thin absorption layer. On the other hand, in Structure 3, the top transparent electrode and the bottom metal electrode form an optical cavity structure, so it can be confirmed that incident light of 1550 nm is reflected multiple times and effectively absorbed within the absorption layer.

[0097] In Structure 3, the light absorption rate of the absorption layer containing quantum dots is 70.75%, whereas in Structure 2, which has only a cavity without a metasurface, the reflectance is measured to be 75.45% and the absorption rate is 16.81%, and in the case of Structure 1, the reflectance is low and the absorption rate is also measured to be low.

[0098] Figure 4(a) shows the electric field distribution inside the photodiode when light is irradiated onto the photodiode according to one embodiment of the present invention, (b) shows the magnetic field distribution inside the photodiode, (c) shows the light energy distribution absorbed in the photodiode according to one comparative example of the present invention, and (d) shows the light energy distribution absorbed in the photodiode of the above embodiment.

[0099] Specifically, FIG. 4(a) shows the electric field distribution calculated in the xy plane inside the metasurface nanoantenna of structure 3 at a wavelength of 1550 nm, and FIG. 4(b) shows the magnetic field distribution. In addition, FIG. 4(c) shows the absorbed light energy distribution calculated in the xz plane perpendicular to the ITO layer in structure 2, and FIG. 4(d) shows the light energy distribution calculated in the xz plane perpendicular to the ITO layer passing through the center of the metasurface nanoantenna in structure 3.

[0100] Figures 4(a) and 4(b) show the electric and magnetic field distributions formed inside the device at a wavelength of 1550 nm, where the metasurface resonates. Figures 4(a) and 4(b) show the electric and magnetic field distributions calculated in the xy plane 280 nm above the bottom of the nanoantenna constituting the metasurface in Structure 3, and demonstrate that Mie resonance is occurring in the nanoantenna at the corresponding wavelength.

[0101] Meanwhile, Figure 4(c) shows the light energy absorption distribution within the transparent electrode, electron transport layer, quantum dot layer, and metal layer in Structure 2, plotted along a cross-section perpendicular to the transparent electrode layer, and Figure 4(d) shows the light energy absorption distribution in Structure 3, plotted along a cross-section perpendicular to the transparent electrode while passing through the center of the nanoantenna. Comparing the results of the two structures, it can be confirmed that in Structure 3, light is effectively absorbed within the quantum dot layer due to the resonance effect of the upper metasurface and the cavity structure formed by the metal electrode and the transparent electrode layer. That is, when comparing the absorption distributions in Figure 4(c) and (d), it can be confirmed that the light energy absorbed by the absorption layer in the hybrid structure of Structure 3 (metasurface + optical cavity) increases significantly compared to when it is composed only of optical cavities without a metasurface (Structure 2).

[0102] FIG. 5a is a schematic diagram of a quantum dot photodiode according to one embodiment of the present invention, FIG. 5b shows the light absorption intensity of the absorption layer according to the thickness of the glass layer in the quantum dot photodiode, and FIG. 5c shows the electric field distribution in the photodiode.

[0103] Specifically, FIG. 5a shows the structure of a quantum dot photodiode with a glass layer added to the structure 3 of FIG. 2 (or FIG. 1a), FIG. 5b shows the light absorption intensity of the quantum dot absorption layer according to the thickness of the glass layer of FIG. 5a, and FIG. 5c shows the electric field distribution calculated in the xz plane perpendicular to the top surface of the device while passing through the center of the metasurface when the thickness of the glass layer is 3650 nm.

[0104] The quantum dot photodiode of Fig. 5a was designed so that the light absorption of the quantum dot absorption layer is maximized when irradiated with 980 nm SWIR. Quantum dots that can be applied to this device include PbS and InAs quantum dots, and in this calculation, PbS quantum dots having an absorption peak at a wavelength of 980 nm were applied. The metasurface was designed so that the absorption peak wavelength of the quantum dot and the resonance wavelength of the metasurface match, and was designed as a two-dimensional array of cylindrical TiO2 nanoantennas having D=330 nm (diameter), H=340 nm (height), and Px=Py=P=550 nm (array period).

[0105] The quantum dot photodiode of Fig. 5a is configured such that, as with the structure of Fig. 1a, it transmits most of the incident light downwards by utilizing the resonance characteristics of the metasurface, and maximizes the light absorption efficiency of the quantum dot absorption layer through multiple reflections of the optical cavity composed of a transparent electrode and a metal electrode. At this time, the quantum dot photodiode of Fig. 5a varies depending on the thickness of the glass layer located between the metasurface and the transparent electrode.

[0106] Referring to Fig. 5b, it can be seen that the absorption intensity of the quantum dot layer reaches a maximum value with a glass layer thickness of 1000 nm. This can be explained by the electric field distribution in Fig. 5c. This is because when light transmitted toward the lower device without being reflected by the metasurface passes through the glass layer and reaches the interface between the transparent electrode and the glass layer, if a specific phase condition is satisfied, destructive interference occurs between the light reflected at the boundary between the glass layer and the transparent electrode and the light incident on the glass layer, allowing most of the light incident from the metasurface to be transmitted to the quantum dot photodiode without loss.

[0107] Therefore, regardless of the thickness of the glass layer, in a structure where a glass layer of thickness is applied that satisfies the phase condition of destructive interference between light reflected at the boundary between the glass layer and the transparent electrode and light incident on the glass layer, the surface reflectance of the top layer and the absorption rate of the absorption layer show similar trends of about 3% and 78%, respectively.

[0108] FIG. 6a is for surface reflectance in a quantum dot photodiode according to one embodiment and a comparative example of the present invention, and FIG. 6b is for light absorption rate of the absorption layer of the quantum dot photodiode according to the above embodiment and comparative example.

[0109] Figure 6a shows the surface reflectance of the structure of Figure 5a (hybrid) with a metasurface on one side of the glass layer, and the structure of Figure 5a with the metasurface removed (cavity). At the operating wavelength of the device, 980 nm, the hybrid structure of Figure 5a has a reflectance of 3.82%, whereas the structure with the metasurface removed (cavity) shows a reflectance of 52.91%. In addition, the absorption rate of the absorption layer in the two structures can be confirmed in Figure 6b; the absorption rate of 78.18% was confirmed in the hybrid structure with the metasurface, and the absorption rate of 38.17% was confirmed in the cavity structure without the metasurface.

[0110] FIGS. 7a and 7b are schematic diagrams of a quantum dot photodiode according to one embodiment of the present invention, FIG. 7c is of the light absorption rate of an absorption layer for polarized light irradiated on the quantum dot photodiode, and FIG. 7d is of the light energy distribution absorbed by the photodiode.

[0111] FIG. 7a is the structure of a quantum dot photodiode in which the shape of the nanoantenna included in the metasurface portion of FIG. 1a is changed to a rectangular parallelepiped, and FIG. 7b is a cross-section of FIG. 7a, where the left side represents the xy cross-section and the right side represents the yz cross-section. Additionally, FIG. 7c is the absorption spectrum for TE polarization and TM polarization in the quantum dot photodiode of FIG. 7a, and FIG. 7d shows the light absorption energy distribution in the absorption layer according to polarization in FIG. 7a, where the top side represents the TE polarization and yz cross-section and the bottom side represents the TM polarization and xz cross-section.

[0112] Figure 7a shows a structure in which the shape of the nanoantenna of the metasurface in the quantum dot photodiode structure operating at a wavelength of 1550 nm proposed in Figure 1a is changed from a cylindrical structure to a rectangular parallelepiped. In addition, Figure 7b is a cross-sectional view of the device viewed from two directions, in which the polarization-selective characteristics of the metasurface are implemented by varying the lengths of Lx and Ly. That is, when the incident light at a wavelength of 1550 nm is TM polarized (electric field direction is x direction), the metasurface satisfies the resonance condition, and the light absorption efficiency of the absorption layer is maximized; whereas, when the incident light is TE polarized (electric field is y direction), resonance does not occur, and a significant amount of incident light is reflected.

[0113] Figure 7c shows the degree of light absorption in the absorption layer when SWIR polarized by TE or TM with a wavelength band of 800 nm to 2000 nm is irradiated on Figure 7a. Since the absorption amount is 17.95% when TE polarized and 72.36% when TM polarized at a wavelength of 1550 nm, the On / Off selectivity according to polarization is clearly displayed, so even if incident light of the same wavelength is incident, the output signal strength of the photodiode can vary depending on the polarization state of the light.

[0114] In addition, Figure 7d shows the distribution of light energy absorption of the quantum dot absorption layer for each polarization, showing the contrast in light energy absorption in the yz plane for TE polarization and in the xz plane for TM polarization. In TM polarization, the light absorption efficiency of the absorption layer increases due to the induced Mie magnetic dipole resonance, whereas in TE polarization, no resonance occurs, so the light efficiency of the absorption layer is low.

[0115] Figures 8 (a) and (b) show the electric field distribution inside the nanoantenna of the quantum dot photodiode according to Figure 7a, and (c) and (d) show the magnetic field distribution.

[0116] FIGS. 8(a) to FIGS. 8(d) show the electric and magnetic field distributions formed inside the nanoantenna at a wavelength of 1550 nm, where the metasurface causes resonance. FIGS. 8(a) and (b) show the electric field distribution calculated in the xy plane 270 nm above the bottom of the nanoantenna in the structure of FIG. 7a, showing that Mie resonance occurs in TM polarization at the corresponding wavelength, but no resonance occurs in TE polarization. Additionally, FIGS. 8(c) and (d) show the magnetic field distribution in the xy plane, indicating that Mie magnetic dipole resonance occurs in TM polarization but not in TE polarization.

[0117] That is, when comparing FIG. 8(a) and (c) with TM polarization and FIG. 8(b) and (d) with TE polarization, it can be seen that ON / OFF switching operation can be performed depending on the polarization direction even at the same wavelength due to the stark difference.

[0118] The foregoing description of the present invention is for illustrative purposes only, and those skilled in the art will understand that other specific forms can be easily modified without altering the technical concept or essential features of the present invention. Therefore, the embodiments described above should be understood as illustrative in all respects and not restrictive. For example, each component described as a single unit may be implemented in a distributed manner, and components described as distributed may likewise be implemented in a combined form.

[0119] The scope of the present invention is defined by the claims set forth below rather than by the detailed description above, and all modifications or variations derived from the meaning and scope of the claims and the concept of equivalents thereof should be interpreted as being included within the scope of the present invention.

Claims

Claim 1 A quantum dot photodiode comprising: a metal layer; an absorption layer formed on one surface of the metal layer; an electron transport layer formed on one surface of the absorption layer; a transparent electrode formed on one surface of the electron transport layer; and a metasurface portion formed on one surface of the transparent electrode, wherein the absorption layer is composed of quantum dots, and the metasurface portion is configured to cause resonance at the absorption wavelength of the quantum dots, and the metal layer and the transparent electrode are configured to form an optical cavity structure that induces incident light irradiated from one side of the metasurface portion to be multiplely reflected between the metal layer and the transparent electrode, and the metasurface portion is configured such that a nanoantenna having an anisotropic structure is arranged in a two-dimensional array to realize the polarization-selective characteristics of the metasurface. Claim 2 A quantum dot photodiode according to claim 1, wherein the quantum dot is a quantum dot that forms an absorption peak within the short-wave infrared wavelength band. Claim 3 A quantum dot photodiode according to claim 2, wherein the metasurface portion is configured such that resonance occurs at the wavelength where the quantum dot forms an absorption peak, and a nanoantenna having an isotropic structure is configured to be arranged in a two-dimensional array so as to have the same resonance conditions regardless of the polarization of the incident light. Claim 4 A quantum dot photodiode according to claim 1, wherein the metasurface portion is configured to induce optical interference by adjusting the phase difference between the incident light and the reflected light so that the amount of reflection in which the incident light fails to pass through the transparent electrode and is reflected is reduced compared to when the metasurface portion is not provided. Claim 5 A quantum dot photodiode according to claim 1, wherein the optical cavity structure is formed to enable multiple reflections by configuring the metal layer to reflect at least a portion of the light irradiated onto the metal layer from one side thereof, and the transparent electrode to reflect a portion of the light irradiated onto the transparent electrode to the other side thereof. Claim 6 delete Claim 7 A quantum dot photodiode according to claim 1, wherein the nanoantenna having the anisotropic structure is configured such that the amount of light absorption for either TM polarization or TE polarization in the absorption layer is relatively larger. Claim 8 A quantum dot photodiode comprising: a metal layer; an absorption layer formed on one surface of the metal layer; an electron transport layer formed on one surface of the absorption layer; a transparent electrode formed on one surface of the electron transport layer; a glass layer formed on one surface of the transparent electrode; and a metasurface portion formed on one surface of the glass layer, wherein the absorption layer is composed of quantum dots, and the metasurface portion is configured to cause resonance at the absorption wavelength of the quantum dots, and the metal layer and the transparent electrode are configured to form an optical cavity structure that induces multiple reflections between the metal layer and the transparent electrode of incident light irradiated from one side of the metasurface, and the glass layer is configured with a thickness such that destructive interference occurs between the reflected light and the incident light of the glass layer. Claim 9 delete Claim 10 A quantum dot photodiode according to claim 8, wherein the glass layer increases the rate at which it absorbs light in the absorption layer due to destructive interference generated in the glass layer. Claim 11 An electronic device comprising a quantum dot port diode according to paragraph 1 or 8. Claim 12 An electronic device according to claim 11, wherein the electronic device comprises at least one of a Time of Flight (TOF) sensor, a LiDAR sensor, machine vision, an infrared sensor, and an optical communication device. Claim 13 A method for manufacturing a quantum dot photodiode according to claim 1, comprising: a step of placing an absorption layer on one surface of a metal layer; a step of placing an electron transport layer on one surface of the absorption layer; a step of placing a transparent electrode on one surface of the electron transport layer; and a step of placing a metasurface portion on one surface of the transparent electrode; wherein the absorption layer is composed of quantum dots, the metasurface portion is configured to cause resonance at the absorption wavelength of the quantum dots, and the metal layer and the transparent electrode are configured to form an optical cavity structure that induces incident light irradiated from one side of the metasurface portion to be reflected multiple times between the metal layer and the transparent electrode. Claim 14 A method for manufacturing a quantum dot photodiode according to claim 8, comprising: a step of placing an absorption layer on one surface of a metal layer; a step of placing an electron transport layer on one surface of the absorption layer; a step of placing a transparent electrode on one surface of the electron transport layer; a step of placing a glass layer on one surface of the transparent electrode; and a step of placing a metasurface portion on one surface of the glass layer; wherein the absorption layer is composed of quantum dots, the metasurface portion is configured to cause resonance at the absorption wavelength of the quantum dots, and the metal layer and the transparent electrode are configured to form an optical cavity structure that induces incident light irradiated from one side of the metasurface portion to be reflected multiple times between the metal layer and the transparent electrode.

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