High-efficiency infrared avalanche photodiode comprising colloidal quantum dot-based charge amplification layer and manufacturing method therefor

Abstract

An infrared avalanche photodiode according to an embodiment of the present invention comprises an electron transport layer, a light absorption layer, and a hole transport layer, and further comprises a quantum dot-based charge amplification layer between the charge transport layer and the light absorption layer.

Description

High-efficiency infrared avalanche photodiode including a colloidal quantum dot-based charge amplification layer and method for manufacturing the same

[0001] The present invention relates to optoelectronic devices, and more specifically, to an infrared avalanche photodiode that simultaneously achieves high photoresponse and fast response speed by including a colloidal quantum dot-based charge amplification layer, and a method for manufacturing the same.

[0002]

[0003] In the electromagnetic spectrum, the infrared (IR) region is a non-visible band with wavelengths longer than visible light, and is classified according to wavelength into near-infrared (Near-IR, 0.75-1.4 μm), short-wave infrared (Short-wave IR, 1.4-3 μm), mid-wave infrared (Mid-wave IR, 3-8 μm), and long-wave infrared (Long-wave IR, 8-15 μm). Among these, the 900-1600 nm region, which includes near-infrared and short-wave infrared, holds special technical importance. This wavelength range is a visual safety wavelength region with relatively little scattering in the atmosphere and a low likelihood of causing direct damage to the retina of the human eye; it is actively utilized in various advanced technology fields, such as LIDAR systems for autonomous vehicles, long-range object recognition, optical communication, medical imaging, and night surveillance systems.

[0004]

[0005] In these infrared applications, systems consisting of a light emitter and a light receiver are primarily used. The method involves the light emitter releasing infrared light, which is reflected back from an object, and the light sensor in the receiver detecting this to acquire the necessary information. Particularly in applications such as autonomous driving or object recognition, the light sensor in the receiver must simultaneously satisfy high bandwidth, high detection efficiency, and high current gain to respond to rapidly changing environments.

[0006]

[0007] The photodiode, the most widely used structure among optical sensor devices, features a junction of p-type and n-type semiconductors and operates on the principle that electron-hole pairs generated by the energy of incident light are separated by an electric field formed near the pn junction, thereby generating an electric current. Conventional photodiodes have the advantages of a simple structure, ease of manufacturing, and a relatively fast response time. However, a fundamental limitation is that the current gain is very low because a maximum of only one electron-hole pair is generated per incident photon. This acts as a serious constraint in high-sensitivity applications that require the detection of weak optical signals.

[0008]

[0009] To fabricate photosensors that operate in the infrared wavelength region, semiconductor materials with an appropriate bandgap capable of effectively absorbing incident infrared radiation are required. Silicon (Si) has a bandgap of 1.1 eV and cannot effectively absorb wavelengths longer than 1100 nm, so it is not suitable for fabricating photosensors in the single-infrared region. In contrast, indium gallium arsenide (InGaAs, 1.3-0.7 eV) and germanium (Ge, 0.8 eV) have been widely used as infrared photosensor materials because they exhibit high absorption efficiency in the single-infrared wavelength region.

[0010]

[0011] However, indium gallium arsenide or germanium-based optoelectronic devices often require high-temperature deposition processes, such as molecular beam epitaxy (MBE) or metal-organic chemical vapor deposition (MOCVD), to form high-quality crystalline thin films. These processes require expensive equipment and demanding process conditions, resulting in very high manufacturing costs. Furthermore, III-V compound semiconductors such as InGaAs have limitations, as they are difficult to integrate with silicon substrates due to differences in lattice constants and require separate, complex integration processes.

[0012]

[0013] Meanwhile, the Avalanche Photodiode (APD) was developed as a representative solution to overcome the current gain limit of photodiodes. The Avalanche Photodiode incorporates a region where a high electric field is applied into the structure of a standard photodiode, causing charge carriers generated by light absorption to accelerate in this region and trigger impact ionization. Impact ionization is a phenomenon in which charge carriers accelerated at high speed collide with other atoms within the semiconductor to create new electron-hole pairs, and as this process occurs in a chain reaction, it leads to a charge multiplication effect.

[0014]

[0015] Currently commercialized InGaAs-based avalanche photodiodes have a current gain of approximately 30, a photoresponse of approximately 0.8 A / W, and a bandwidth of approximately 900 MHz. While this represents improved performance compared to general photodiodes, it is still insufficient for applications requiring high speed and sensitivity, such as autonomous driving or long-distance object recognition. Furthermore, InGaAs-based avalanche photodiodes have faced limitations in mass commercialization because they are very expensive due to the manufacturing limitations of the aforementioned III-V compound semiconductors.

[0016]

[0017] To address the aforementioned problems, solution-processing-based materials such as perovskites, organic semiconductors, and colloidal quantum dots have recently been proposed as alternatives. In particular, colloidal quantum dots are semiconductor nanoparticles that possess a unique characteristic in that their bandgap can be easily controlled simply by adjusting the particle size due to the quantum confinement effect. For example, in the case of PbS and PbSe quantum dots, a bandgap in the range of 0.6 to 2.0 eV can be obtained by controlling the particle size within the 3-9 nm range, allowing for the fabrication of optoelectronic devices that cover a wide wavelength range from visible light to mid-infrared light.

[0018] Furthermore, colloidal quantum dots can control surface characteristics and inter-dot spacing through surface ligand exchange, enabling precise control of electrical properties such as charge mobility, trap density, and doping level. These characteristics provide significant flexibility for optimizing the performance of optoelectronic devices.

[0019] Above all, the greatest advantage of colloidal quantum dots is that low-temperature solution processing is possible. Quantum dots are manufactured through colloidal synthesis methods and exist in a dispersed form in organic solvents, and thin films can be formed using various solution processing technologies such as spin coating, spray coating, and inkjet printing. This is a factor that can significantly reduce processing costs compared to inorganic semiconductors such as InGaAs, which require high-temperature deposition processes.

[0020] Recently, research on lead sulfide (PbS) quantum dot-based optoelectronic devices has reported results showing a photoresponse of 0.6 A / W and a bandwidth of 140 MHz. However, these performance levels are still insufficient for application in actual fields such as autonomous driving, and there were limitations in absorbing light in the single-infrared band.

[0021]

[0022] Therefore, there is a need to develop photosensors with novel structures capable of simultaneously improving current gain and bandwidth while leveraging the advantages of quantum dots, such as ease of bandgap tuning, flexibility in controlling electrical characteristics, and low-cost solution processing. In particular, it is time to develop innovative technologies that can achieve both high photoresponse and fast response speeds by applying charge amplification mechanisms based on the avalanche effect to quantum dot-based optoelectronic devices.

[0023]

[0024] One objective of the present invention is to provide an avalanche photodiode capable of simultaneously achieving high signal amplification gain and bandwidth, which are difficult to achieve with existing quantum dot-based infrared photosensor structures.

[0025] Another objective of the present invention is to provide a device structure capable of effectively amplifying charge carriers generated by light absorption through impact ionization by introducing a quantum dot-based charge amplification layer.

[0026] Another objective of the present invention is to provide a low-cost solution-process-based colloidal quantum dot avalanche photodiode and a method for manufacturing the same, which can replace high-cost InGaAs-based avalanche photodiodes.

[0027] Another objective of the present invention is to provide a method for improving the photoresponse and noise characteristics of a device by optimizing the energy band structure between the charge amplification layer and the light absorption layer by utilizing the bandgap tuning characteristics of quantum dots.

[0028] Another objective of the present invention is to provide an avalanche photodiode with a SAM (Separated Absorption and Multiplication) structure that can independently optimize light absorption and amplification functions by separating the charge amplification layer and the light absorption layer.

[0029] Another objective of the present invention is to provide a high-performance infrared optical sensor applicable to various application fields, such as LIDAR for autonomous driving, infrared cameras / image sensors, gas / chemical sensors, night vision technology, and bioimaging.

[0030]

[0031] The above objectives of the present invention can be achieved by the configuration and operation of the invention described below, and the problems to be solved by the present invention are not limited to the above description. Furthermore, other objectives and advantages of the present invention may be more clearly understood from the specification and the attached drawings.

[0032]

[0033] To solve the problem described above, the following solution is proposed.

[0034] An infrared avalanche photodiode according to one embodiment of the present invention comprises: an electron transport layer; a light absorption layer; and a hole transport layer; and further comprises a quantum dot-based charge amplification layer between the charge transport layer and the light absorption layer.

[0035] According to one embodiment, the charge amplification layer comprises quantum dots, and the quantum dots may comprise one or more quantum dots selected from the group consisting of II-VI (CdS, CdSe, CdTe, HgS, HgSe, HgTe), IV-VI (PbS, PbSe, PbTe), III-V (InP, InAs, InSb), and I-VI (Ag2S, Ag2Se, Ag2Te).

[0036] According to one embodiment, the quantum dot may have a size of several nm and a band gap of 0.6 eV to 2.0 eV.

[0037] According to one embodiment, the quantum dot has a ligand attached to its surface, and the ligand may include one or more selected from the group consisting of a thiol-based functional group, a halide-based functional group, an amine-based functional group, and a carboxyl group.

[0038] According to one embodiment, the ligand may include an alkyl group having 1 to 12 carbon atoms.

[0039] According to one embodiment, the ligand may be an organic ligand that was originally bound to the quantum dot and is replaced and attached to the quantum dot.

[0040] According to one embodiment, the thickness of the quantum dot charge amplification layer may be 60 nm to 1000 nm.

[0041] According to one embodiment, the light absorption layer may absorb light in the wavelength range of 900 nm to 1600 nm.

[0042] According to one embodiment, the bandgap of the quantum dot charge amplification layer may be formed to be larger than the bandgap of the light absorption layer, thereby forming a structure in which the regions where light absorption and amplification functions are performed are physically separated.

[0043]

[0044] A method for manufacturing an infrared avalanche photodiode according to another embodiment of the present invention comprises: a step of preparing a transparent electrode; a step of coating a charge transport layer on the transparent electrode; a step of forming a quantum dot-based charge amplification layer on the charge transport layer; a step of forming a light absorption layer on the charge amplification layer; a step of forming a hole transport layer on the light absorption layer; and a step of depositing and forming a metal electrode on the hole transport layer.

[0045] According to one embodiment, the step of coating the charge transport layer material may involve coating the charge transport layer with a material selected from the group consisting of: a metal oxide including zinc oxide (ZnO), titanium oxide (TiO2) and tin oxide (SnO2); and an n-type semiconductor material including PCBM ([6,6]-phenyl-C61-butyric acid methyl ester).

[0046] According to one embodiment, the step of forming the hole transport layer comprises nickel oxide (NiO₂). x ), molybdenum oxide (MoO x A hole transport layer may be formed with a material comprising one or more selected from the group consisting of a metal oxide including ) and a p-type semiconductor material including Spiro-OMeTAD, P3HT, PTB7 and PM6.

[0047] According to one embodiment, the step of forming the quantum dot-based charge amplification layer may include: a step of spin-coating a colloidal quantum dot solution; and a step of substituting surface ligands of the coated quantum dots.

[0048] According to one embodiment, the step of forming the quantum dot-based charge amplification layer may include the process of forming a multilayer thin film in a layer-by-layer manner.

[0049] According to one embodiment, the infrared avalanche photodiode may be an infrared avalanche photodiode according to one embodiment of the present invention.

[0050]

[0051] A colloidal quantum dot-based infrared avalanche photodiode according to one embodiment of the present invention has the effect of simultaneously achieving high photoresponse and fast response speed by introducing a quantum dot-based charge amplification layer between a charge transport layer and a light absorption layer, so that when a reverse voltage is applied, a high electric field is concentrated in the charge amplification layer and charge amplification through collision ionization is effectively achieved.

[0052] An avalanche photodiode according to another embodiment of the present invention has the effect of improving noise characteristics and enhancing signal gain by designing the bandgap of the charge amplification layer to be larger than that of the light absorption layer to implement a SAM (Separated Absorption and Multiplication) structure that separates light absorption and amplification functions.

[0053] A colloidal quantum dot-based infrared avalanche photodiode according to another embodiment of the present invention has the effect of easily controlling the optical and electrical characteristics of the device by precisely controlling the band gaps of the charge amplification layer and the light absorption layer through size control of the quantum dots, and by optimizing the charge mobility and doping level through surface ligand exchange.

[0054] A method for manufacturing an avalanche photodiode according to another embodiment of the present invention forms a colloidal quantum dot layer through a low-temperature solution process, thereby enabling a solution process using ink, which significantly lowers production costs and enables large-area manufacturing, and thus has the effect of improving productivity.

[0055] According to an embodiment of the present invention, a semiconductor quantum dot-based charge amplification layer is introduced between the charge transport layer and the light absorption layer of a quantum dot-based photodiode structure to form a depletion region according to the difference in doping type within the junction under a reverse voltage application environment. Accordingly, a high electric field can be concentrated in the charge amplification layer, and through this, the photoresponse can be improved through high charge amplification even with a low optical signal.

[0056] In addition, according to an embodiment of the present invention, since a mechanism that does not utilize trap levels is utilized unlike other charge amplification mechanisms, it has the effect of simultaneously maintaining high photoresponse and fast response speed when used as a photosensor.

[0057] It should be added that even if an effect is not explicitly mentioned herein, the effects described in the following specification and the potential effects expected by the technical features of the present invention are treated as described in the specification of the present invention.

[0058]

[0059] FIG. 1 is a cross-sectional view showing the basic structure of a quantum dot-based infrared avalanche photodiode of the present invention, and is a schematic diagram showing a comparison between a structure without a quantum dot charge amplification layer (top) and a structure including a quantum dot charge amplification layer (bottom).

[0060] FIG. 2 is a cross-sectional SEM (scanning electron microscope) image of a device without a quantum dot charge amplification layer and a device with a quantum dot charge amplification layer according to the present invention.

[0061] Figure 3 is a band diagram showing the electric field distribution formed when a quantum dot charge amplification layer is introduced.

[0062] Figure 4 is a graph showing the current gain characteristics of the device depending on whether a quantum dot charge amplification layer is included (a) and a graph showing the breakdown voltage change according to temperature (b).

[0063] Figure 5 is a graph showing the absorption spectrum (a) of a quantum dot charge amplification layer with various band gaps and the change in electrical characteristics (b) of the device accordingly.

[0064] Figure 6 shows the simulation results of the energy band structure and electric field distribution according to the band gap change of the quantum dot charge amplification layer.

[0065] Figure 7 is a graph showing the time response characteristics of a fabricated quantum dot-based avalanche photodiode, showing the response characteristics according to quantum dot charge amplification layers with various band gaps.

[0066] It should be noted that the attached drawings are provided as examples for reference to help understand the technical concept of the present invention, and the scope of the rights of the present invention is not limited by them.

[0067]

[0068] The embodiments of the present invention are illustrative for the purpose of explaining the technical concept of the present invention. The scope of rights according to the present invention is not limited to the embodiments presented below or the specific description thereof.

[0069] All technical and scientific terms used in this invention, unless otherwise defined, have the meaning generally understood by those skilled in the art to which this invention pertains. All terms used in this invention are selected for the purpose of further explaining this invention and are not selected to limit the scope of rights according to this invention.

[0070] Expressions such as "comprising," "having," "having," etc. used in the present invention should be understood as open-ended terms implying the possibility of including other embodiments, unless otherwise stated in the phrase or sentence containing such expressions.

[0071] Unless otherwise stated, singular expressions described in the present invention may include the meaning of the plural form, and this applies likewise to singular expressions described in the claims.

[0072] Embodiments of the present invention will be described below with reference to the attached drawings. Furthermore, in the description of the following embodiments, the description of identical or corresponding components may be omitted. However, even if a description of a component is omitted, it is not intended that such component is not included in any embodiment.

[0073]

[0074] Basic structure of a quantum dot-based infrared avalanche photodiode

[0075] Referring to FIG. 1, the basic structure of a quantum dot-based infrared avalanche photodiode according to an embodiment of the present invention can be seen. The top of FIG. 1 shows a general photodiode structure without a charge amplification layer (comparative example), and the bottom shows an avalanche photodiode structure including a quantum dot charge amplification layer according to an embodiment of the present invention (example).

[0076] The avalanche photodiode of the present invention can be implemented by adding a quantum dot-based charge amplification layer to a conventional photodiode structure basically composed of an electron transport layer, a light absorption layer, and a hole transport layer. In particular, the charge amplification layer is located between the electron transport layer and the light absorption layer and performs the function of amplifying charge carriers generated in the light absorption layer through impact ionization in a high electric field environment.

[0077] Quantum dot-based infrared avalanche photodiodes generally consist of the following structure:

[0078] Electron transport layer formed on a transparent electrode (e.g., ITO);

[0079] Quantum dot charge amplification layer formed on an electron transport layer;

[0080] Light absorption layer formed on a quantum dot charge amplification layer;

[0081] A hole transport layer formed on a light absorption layer; and

[0082] Metal electrode formed on the hole transport layer

[0083]

[0084] Figure 2 shows cross-sectional SEM (scanning electron microscope) images of a device including a quantum dot charge amplification layer according to the present invention and a device not including it. Through this, a stacked structure in which each layer with a thickness of about 200 nm is clearly distinguished can be confirmed.

[0085]

[0086] Composition and characteristics of the quantum dot charge amplification layer

[0087] The quantum dot charge amplification layer is a key component of the present invention, and various types of colloidal quantum dots can be used to obtain an appropriate charge amplification effect.

[0088] The quantum dots used in the present invention may include semiconductor materials such as II-VI (CdS, CdSe, CdTe, HgS, HgSe, HgTe), IV-VI (PbS, PbSe, PbTe), III-V (InP, InAs, InSb), and I-VI (Ag2S, Ag2Se, Ag2Te).

[0089] These quantum dots are nanoparticles with a size of several nanometers (typically 3-9 nm) and are characterized by the ability to easily control their bandgap simply by adjusting their size due to the quantum confinement effect. In the present invention, quantum dots with a bandgap in the range of 0.6-2.0 eV are used, thereby enabling the optimization of light absorption and charge amplification characteristics across various wavelength ranges.

[0090] The surface of quantum dots can be substituted with various ligands to control their electrical properties. In this invention, ligands such as thiols, halides, amines, and carboxyl groups are used to control the spacing between quantum dots, charge mobility, and doping levels. In particular, charge transfer between quantum dots can be enhanced by using short ligands such as 1,2-ethanedithiol (EDT). The alkyl groups of these ligands generally have a carbon number in the range of C1 to C12.

[0091] The thickness of the quantum dot charge amplification layer can be controlled within the range of 60 nm to 1000 nm, which can have a significant impact on the overall performance of the device. If the thickness is too thin (less than 60 nm), it is difficult to obtain a sufficient charge amplification effect, and if it is too thick (more than 1000 nm), the response speed of the device may slow down; therefore, appropriate thickness optimization is required.

[0092]

[0093] Operating principle of quantum dot-based infrared avalanche photodiodes

[0094] The operating principle of the quantum dot-based infrared avalanche photodiode of the present invention can be understood by referring to FIGS. 3 and FIGS. 6.

[0095] Figure 3 is a band diagram showing the electric field distribution formed when a charge amplification layer is introduced.

[0096] Referring to Fig. 3, when a reverse voltage is applied to the device, a depletion region is formed depending on the difference in doping type within the junction, and a high electric field is concentrated particularly in the quantum dot charge amplification layer.

[0097] This is due to the band discontinuity between the charge amplification layer and the adjacent layer, which can be confirmed through the energy band structure simulation shown in Fig. 6.

[0098] When light is absorbed in the light absorption layer, electron-hole pairs are generated, and the generated charge carriers move under the applied electric field. In particular, electrons are injected into the quantum dot charge amplification layer and accelerated in a high electric field environment. The accelerated electrons collide with other atoms and transfer sufficient energy, causing an impact ionization phenomenon that generates new electron-hole pairs. As this process occurs in a chain reaction, a charge amplification effect takes place.

[0099] In particular, in this invention, by designing the bandgap of the quantum dot charge amplification layer to be larger than that of the light absorption layer, a Separated Absorption and Multiplication (SAM) structure is implemented in which light absorption and charge amplification functions are physically separated, thereby improving noise characteristics and enhancing signal gain.

[0100]

[0101] Method for manufacturing a quantum dot-based infrared avalanche photodiode

[0102] A method for manufacturing a quantum dot-based infrared avalanche photodiode according to the present invention is described step-by-step.

[0103] Step of preparing a transparent electrode

[0104] First, a substrate is prepared with an indium tin oxide (ITO) transparent electrode coated on a glass substrate. The surface of this substrate is cleaned and activated through UV-ozone treatment. This process takes about 15 to 30 minutes and serves to remove organic contaminants from the surface of the substrate and improve adhesion with subsequent layers.

[0105] Step of forming a charge transport layer

[0106] A charge transport layer is formed on a cleaned ITO substrate. As the material for the charge transport layer, metal oxides such as zinc oxide (ZnO), titanium oxide (TiO2), and tin oxide (SnO2), or n-type organic semiconductors such as PCBM ([6,6]-phenyl-C61-butyric acid methyl ester) can be used.

[0107] In the case of a ZnO charge transport layer, it can generally be prepared through a sol-gel method. In one embodiment, a ZnO charge transport layer can be formed by preparing a ZnO precursor solution by dissolving zinc acetate dihydrate and ethanolamine in 2-methoxyethanol, spin-coating the solution onto a substrate, and heat-treating it at 200-300°C for about 30 minutes to form a ZnO layer with a thickness of about 30-50 nm.

[0108]

[0109] Step of forming a quantum dot-based charge amplification layer

[0110] A quantum dot charge amplification layer is formed on the electron transport layer. This process can proceed in the following steps:

[0111] First, synthesize colloidal quantum dots with a target bandgap (0.6-2.0 eV) or prepare commercial products. In one embodiment, PbS quantum dots with a bandgap of about 1.13 eV can be used.

[0112] Next, the prepared quantum dots can be dispersed in a non-polar solvent such as hexane or octane at a concentration of about 60 mg / mL to prepare a quantum dot ink. The prepared quantum dot ink can be coated onto an electron transport layer using a spin coating method. At this time, spin coating can generally be performed for 30 to 60 seconds at a rotation speed of 2000 to 3000 rpm.

[0113] Surface ligands can be substituted by immersing a coated quantum dot layer in a ligand exchange solution (e.g., acetonitrile dissolved in 1,2-ethanedithiol (EDT)). In this process, long organic ligands (such as oleic acid) on the surface of the quantum dots are replaced with short ligands, thereby improving the charge transfer efficiency between quantum dots.

[0114] A charge amplification layer of a desired thickness (60-1000 nm) can be formed by repeating the above process in a layer-by-layer manner.

[0115]

[0116] Step of forming a light absorption layer

[0117] A light absorption layer can be formed on the quantum dot charge amplification layer. This layer may be composed of quantum dots with a narrow bandgap (about 0.82 eV) capable of effectively absorbing light in the single-infrared region (900-1600 nm). In one embodiment, PbS quantum dots substituted with halide ligands may be used.

[0118]

[0119] Halide ligand substitution can proceed through the following process:

[0120] Ligand exchange can be performed by reacting PbS quantum dot ink dispersed in non-polar octane with a dimethylformamide solution containing dissolved halide precursors, such as lead bromide (PbBr2) and lead iodide (PbI2), via a vortex process. After the reaction via a phase shift, octane is added again to perform a rinsing process, which removes removed ligands and unsubstituted quantum dots. Then, toluene, an antisolvent, is added to precipitate the quantum dots through centrifugation; following a drying process, the precipitates can be redispersed in a solvent mixture of n-butylamine and dimethylformamide. The PbS quantum dot ink prepared in this way can be coated onto a charge amplification layer using a spin coating method.

[0121] In this way, a light absorption layer with a thickness of about 350 nm can be formed.

[0122]

[0123] Step of forming a hole transport layer

[0124] A hole transport layer can be formed on the light absorption layer. Nickel oxide (NiO₂) can be used as the hole transport layer material. X ), copper oxide (CuO X ), molybdenum oxide (MoO X Metal oxides such as ) or p-type organic semiconductors such as Spiro-OMeTAD, P3HT, PTB7, PM6 can be used.

[0125] In one embodiment, MoO X It can be deposited to a thickness of approximately 10 nm using the thermal evaporation method. The deposition conditions are approximately 10 -6 It can be carried out at a deposition rate of 0.1-0.2 Å / s in a high vacuum environment of Torr.

[0126]

[0127] Step of forming a metal electrode

[0128] Finally, a metal electrode can be formed on the hole transport layer. Generally, metals such as gold (Au), silver (Ag), aluminum (Al), platinum (Pt), and copper (Cu) can be used.

[0129] In one embodiment, a gold (Au) electrode with a thickness of approximately 100 nm can be formed by thermal evaporation. At this time, the deposition conditions are approximately 10 -6 It can be carried out at a deposition rate of 1-2 Å / s in a high vacuum environment of Torr.

[0130]

[0131] Device Characterization and Analysis

[0132] Verification of charge amplification effect

[0133] Figure 4 shows the current gain characteristics of the device depending on whether a quantum dot charge amplification layer is included. As can be seen in Figure 4(a), the device including the charge amplification layer (blue line) exhibits significantly higher current values ​​under the same reverse voltage conditions compared to the device without it (gray line). In particular, an avalanche phenomenon is clearly observed in which the current gain increases sharply in the reverse voltage range of approximately 4V-6V.

[0134] Figure 4(b) is a graph showing the change in breakdown voltage with temperature, and in the device including the charge amplification layer, it shows a positive temperature coefficient in which the breakdown voltage increases as the temperature increases. This is a characteristic indicator of the avalanche phenomenon and proves that collision ionization-based charge amplification has been successfully implemented in the device.

[0135]

[0136] Optimization of characteristics based on changes in the charge amplification layer bandgap

[0137] Figure 5 shows the absorption spectrum (a) of a quantum dot charge amplification layer with various band gaps (0.82-1.39 eV) and the corresponding change in the electrical characteristics of the device (b). It can be seen that the absorption wavelength becomes shorter as the band gap increases, which is a result of the quantum confinement effect as the size of the quantum dots decreases.

[0138] Figure 5(b) shows the current-voltage characteristics under each bandgap condition, and it can be seen that lower dark current and higher signal gain can be obtained when the bandgap of the charge amplification layer is designed to be larger than that of the light absorption layer (0.82 eV) (0.95 eV, 1.139 eV). This means that a Separated Absorption and Multiplication (SAM) structure with separated light absorption and charge amplification functions has been effectively implemented.

[0139]

[0140] Energy band structure analysis

[0141] Figure 6 shows the simulation results of the energy band structure according to the band gap change of the quantum dot charge amplifier layer. Through TCAD (Technical Computer Aided Design) simulation, the conduction band profile and electric field distribution at two different band gap conditions (0.82 eV and 1.13 eV) were compared.

[0142] Simulation results show that when the bandgap of the quantum dot charge amplifier layer is larger than that of the light absorption layer (1.13 eV vs. 0.82 eV), a higher electric field is concentrated in the charge amplifier layer due to the conduction band discontinuity between the charge amplifier layer and the light absorption layer. Through this band structure optimization, collision ionization efficiency can be improved and noise characteristics can be enhanced.

[0143]

[0144] Evaluation of time response characteristics

[0145] Figure 7 shows the time response characteristics of the device according to the quantum dot charge amplification layer with various band gaps. All devices exhibit a fast response time of about 30ns, which means that the avalanche photodiode of the present invention is suitable for high-speed applications.

[0146] In particular, unlike conventional trap-based photodetectors, the avalanche photodiode of the present invention utilizes a collision ionization-based charge amplification mechanism, which has the advantage of simultaneously achieving high photoresponse and fast response speed.

[0147]

[0148] Examples

[0149] Hereinafter, we examine the configuration of the present invention as outlined by various embodiments of the present invention and the effects derived therefrom. In describing the present invention, detailed descriptions of related known functions are omitted if they are deemed obvious to a person skilled in the art and could unnecessarily obscure the essence of the invention.

[0150]

[0151] [Example 1] Fabrication of PbS Quantum Dot-Based Infrared Avalanche Photodiode

[0152] After surface-treating an ITO-coated glass substrate with UV-ozone, a 1M zinc acetate dihydrate solution was spin-coated and heat-treated at 245°C for 30 minutes to form a ZnO electron transport layer approximately 40 nm thick.

[0153] Quantum dot ink was prepared by dispersing PbS quantum dots with a bandgap of 1.13 eV (average particle size: approximately 3.3 nm) produced by colloidal synthesis in octane at a concentration of 60 mg / mL. This ink was spin-coated at 2500 rpm for 80 seconds, followed by immersion in a 0.1% EDT / acetonitrile solution for 30 seconds to perform ligand exchange. This process was repeated 8 times to form a quantum dot charge amplification layer approximately 250 nm thick.

[0154] Next, an ink in which PbS quantum dots with a bandgap of 0.82 eV (average particle size: approximately 5 nm) are dispersed in octane at a concentration of 60 mg / mL is reacted with a dimethylformamide solution containing dissolved halide precursors via a vortex process to perform ligand exchange. After the reaction in a phase-shift manner, octane is added again to perform a rinsing process to remove removed ligands and unsubstituted quantum dots. Then, toluene, an antisolvent, is added to precipitate the quantum dots through centrifugation, followed by a drying process, and then redispersed in a solvent mixed with n-butylamine and dimethylformamide. A light-absorbing layer approximately 350 nm thick was formed using the thus prepared PbS quantum dot ink by spin coating.

[0155] On top of that, 10nm thick MoO XThe device was completed by sequentially depositing a hole transport layer and a 100 nm thick Au electrode.

[0156] The fabricated device exhibited a high photoresponse of approximately 30,000 A / W and a fast response speed of 30 ns when a reverse voltage of 7 V was applied. This represents a performance improvement of approximately 5,000 times compared to conventional quantum dot photodiodes (approx. 0.6 A / W), making it suitable for high-sensitivity, high-speed applications such as LIDAR sensors for autonomous driving.

[0157]

[0158] [Example 2] Comparison of Quantum Dot Charge Amplification Layers with Various Band Gaps

[0159] In the same manner as in Example 1, four types of devices were fabricated with only the quantum dot band gap of the charge amplification layer different (0.82 eV, 0.95 eV, 1.13 eV, 1.39 eV) and their performance was compared.

[0160] As a result, devices with a bandgap of the charge amplification layer larger than that of the light absorption layer (0.82 eV), such as 0.95 eV and 1.13 eV, exhibited superior electrical and photoresponse characteristics. In particular, the device using a charge amplification layer with a bandgap of 1.13 eV exhibited the best photoresponse of 30,000 A / W under a reverse voltage condition of 7 V.

[0161]

[0162] These results demonstrate that device performance can be optimized by adjusting the bandgap of the charge amplification layer, and suggest that it is particularly important to design the bandgap of the charge amplification layer to be larger than that of the light absorption layer for the implementation of the SAM structure.

[0163]

[0164] The foregoing description is merely an illustrative explanation of the technical concept of the present invention, and those skilled in the art to which the present invention pertains will be able to make various modifications and variations within the scope of the essential characteristics of the present invention. Accordingly, the embodiments disclosed in the present invention are intended to explain, not limit, the technical concept of the present invention, and the scope of the technical concept of the present invention is not limited by these embodiments. The scope of protection of the present invention shall be interpreted by the claims below, and all technical concepts within an equivalent scope shall be interpreted as being included within the scope of rights of the present invention.

Claims

1. Electron transport layer; Light absorption layer; and In a photodiode comprising a hole transport layer, A quantum dot-based charge amplification layer between the charge transport layer and the light absorption layer; further comprising Infrared Avalanche Photodiode.

2. In Paragraph 1, The above charge amplification layer includes quantum dots, The above quantum point is, A quantum dot comprising one or more selected from the group consisting of II-VI (CdS, CdSe, CdTe, HgS, HgSe, HgTe), IV-VI (PbS, PbSe, PbTe), III-V (InP, InAs, InSb) and I-VI (Ag2S, Ag2Se, Ag2Te), Infrared Avalanche Photodiode.

3. In Paragraph 1, The above quantum point is, Having a size of several nanometers and a band gap of 0.6 eV to 2.0 eV, Infrared Avalanche Photodiode.

4. In Paragraph 1, The above quantum point is, It has ligands attached to the surface, The above ligand comprises one or more selected from the group consisting of thiol functional groups, halide functional groups, amine functional groups, and carboxyl groups, Infrared Avalanche Photodiode.

5. In Paragraph 4, The above ligand comprises an alkyl group having 1 to 12 carbon atoms. Infrared Avalanche Photodiode.

6. In Paragraph 4, The above ligand is one that is attached to the quantum dot after replacing the organic ligand that was primarily bound to the quantum dot. Infrared Avalanche Photodiode.

7. In Paragraph 1, The thickness of the quantum dot charge amplification layer is 60 nm to 1000 nm. Infrared Avalanche Photodiode.

8. In Paragraph 1, The light absorption layer absorbs light in the wavelength range of 900 nm to 1600 nm. Infrared Avalanche Photodiode.

9. In Paragraph 1, The bandgap of the quantum dot charge amplification layer is formed to be larger than the bandgap of the light absorption layer, thereby forming a structure in which the regions where light absorption and amplification functions are performed are physically separated. Infrared Avalanche Photodiode.

10. Step of preparing a transparent electrode; A step of coating a charge transport layer on the transparent electrode; A step of forming a quantum dot-based charge amplification layer on the charge transport layer; A step of forming a light absorption layer on the charge amplification layer; A step of forming a hole transport layer on the light absorption layer; and A step comprising forming a metal electrode by depositing it on the hole transport layer; Method for manufacturing an infrared avalanche photodiode.

11. In Paragraph 10, The step of coating the charge transport layer material described above is, Coating a charge transport layer with a material comprising one or more selected from the group consisting of: metal oxides including zinc oxide (ZnO), titanium oxide (TiO2), and tin oxide (SnO2); and an n-type semiconductor material including PCBM ([6,6]-phenyl-C61-butyric acid methyl ester). Method for manufacturing an infrared avalanche photodiode.

12. In Paragraph 10, The step of forming the hole transport layer above is, Nickel oxide (NiO₂) x ), molybdenum oxide (MoO x A hole transport layer formed with a material comprising one or more selected from the group consisting of a metal oxide comprising ) and a p-type semiconductor material comprising Spiro-OMeTAD, P3HT, PTB7, and PM6, Method for manufacturing an infrared avalanche photodiode.

13. In Paragraph 10, The step of forming the above-mentioned quantum dot-based charge amplification layer is, Step of spin-coating a colloidal quantum dot solution; and The method comprises the step of substituting the surface ligand of the coated quantum dot. Method for manufacturing an infrared avalanche photodiode.

14. In Paragraph 10, The step of forming the above-mentioned quantum dot-based charge amplification layer is, The process of forming a multilayer thin film in a layer-by-layer manner, Method for manufacturing an infrared avalanche photodiode.

15. In Paragraph 10, The above infrared avalanche photodiode is, The infrared avalanche photodiode of paragraph 1 Method for manufacturing an infrared avalanche photodiode.

Images