An infrared detector and its preparation method

Abstract

The application relates to the technical field of photoelectric detection, and discloses an infrared detector and a preparation method thereof. The infrared detector comprises a substrate, a metal sensitive film, a light absorption enhancement structure and a current transmission structure. The light absorption enhancement structure comprises a Schottky junction. The Schottky junction is formed by etching an arrayed pattern on a silicon substrate, the arrayed pattern is filled with metal, the silicon substrate is in contact with the metal to form the Schottky junction, and the Schottky interface is subjected to roughening treatment to enhance hot electron absorption. The current transmission structure comprises a silicon substrate, a P-type conductive structure, an N-type conductive structure and a dielectric material. The current generated by the light absorption enhancement structure is led out from the P-type and N-type conductive structures. The Schottky interface is subjected to roughening treatment to enhance hot electron absorption, a back-illumination method is adopted, and the free path of hot electron transmission is shortened, so that the quantum efficiency of the detector is improved.

Description

Technical Field

[0001] This invention relates to the field of photoelectric detection technology, and in particular to an infrared detector and its fabrication method. Background Technology

[0002] Photodetectors (PDs) are devices that capture and convert light signals within a specific wavelength range into electrical signals in real time. They have been widely used in optoelectronic imaging, optical communication, and biosensing. In recent years, near-infrared photodetector technology, which detects the spectrum in the near-infrared (NIR, 780–2526 nm) band, has attracted widespread attention.

[0003] Compared with ultraviolet (200–400 nm) and visible light (400–780 nm), NIR photons have a penetration depth of 1–20 mm, and have advantages such as less photodamage to biological samples, strong penetration ability to deep tissues, and less interference with the autofluorescence of living biological systems. They are considered to be a powerful tool for medical diagnosis and surgical treatment.

[0004] A Schottky junction is a simple metal-semiconductor interface, similar to a PN junction, exhibiting nonlinear impedance characteristics. Its basic principle is as follows: the work function of a semiconductor is generally smaller than that of a metal. Therefore, when a metal and a semiconductor (taking an N-type junction as an example) come into contact, electrons flow from the semiconductor into the metal, forming a space charge region composed of positively charged, immobile impurity ions within the semiconductor surface layer. Within this region, an electric field exists pointing from the semiconductor to the metal, acting like a high wall to prevent electrons from the semiconductor from further flowing into the metal. As can be seen from the Schottky barrier's band diagram, the energy bands of the semiconductor bend at the interface, forming a high-potential region—this is the Schottky barrier. Electrons must possess energy higher than this barrier to overcome it and flow into the metal. At equilibrium, the height of the Schottky barrier is the difference in work functions between the metal and the semiconductor.

[0005] Currently, most existing technologies utilize plasma structures to effectively enhance the light absorption rate and local electric field of photodetectors, thereby improving photoelectric conversion efficiency. How to utilize Schottky junctions to enhance light absorption and thus improve photoelectric conversion efficiency and detector sensitivity is a technical problem that urgently needs to be solved. Summary of the Invention

[0006] In view of the shortcomings of the prior art described above, the purpose of this invention is to provide an infrared detector and its fabrication method, which enhances light absorption by forming a Schottky junction through contact between an array pattern etched on a silicon substrate and a metal, thereby improving the photodetector's light response.

[0007] The technical solution of this application is:

[0008] A first aspect of this application provides an infrared detector, including a metal sensitive film, a light absorption enhancement structure, and a current transmission structure;

[0009] The interface of the metal sensitive film is roughened by etching a disordered nanopore light-trapping structure or depositing nanoparticles on the silicon substrate interface to improve the hot electron injection probability of the Schottky interface. The increase in the hot electron injection probability is because the roughened interface can be equivalent to an electron random grating, which increases the range of momentum direction of hot electrons injected into silicon, thereby improving the injection probability.

[0010] The steps for manufacturing the metal-sensitive film are as follows:

[0011] 1) Preparation of cleaning solution: Washing solution I is a solution obtained by mixing concentrated sulfuric acid and hydrogen peroxide in a specific ratio; II

[0012] Washing solution No. I is a solution obtained by mixing ammonia, hydrogen peroxide, and deionized water in a set ratio; Washing solution No. III is a solution obtained by mixing concentrated hydrochloric acid, hydrogen peroxide, and deionized water in a set ratio; the silicon wafer is placed in washing solution No. I, washing solution No. II, and washing solution No. III in sequence for ultrasonic cleaning, and finally ultrasonically cleaned with deionized water, then removed and dried; it is mainly used to remove two types of contaminants: one is the oxide layer formed by slight oxidation of the surface of the silicon wafer when it may be exposed to air during storage and transportation; the other is the dust, organic matter, and metal salts that adhere to the silicon substrate during production, cutting, and packaging.

[0013] 2) Preparation of precipitation solution: The concentration of silver nitrate is 0.0125-0.05 mol / L, and deionized water, hydrofluoric acid and silver nitrate solution are prepared in a certain volume ratio;

[0014] 3) Silver particle deposition: The EBL-etched sample was placed in the deposition solution and removed after 5s, 10s, 15s, and 20s.

[0015] 4) Prepare the etching solution: Mix hydrogen peroxide and hydrofluoric acid in a set ratio to prepare the etching solution;

[0016] 5) Metal-assisted etching: Place the sample in the etching solution, set the etching temperature to 50-70 degrees Celsius, and time for 5-20 minutes. Remove the sample. The overall reaction is: Si + 4AgNO3 + 4HF → H2SiF6 + 4Ag + 4HNO3

[0017] 6) Silver ion removal: Prepare a dilute nitric acid solution by mixing nitric acid solution and deionized water in a certain proportion to remove residual silver ions from the microstructured silicon surface. Place the etched sample in the dilute nitric acid solution for 20-40 minutes to completely dissolve the residual silver ions before removing it.

[0018] 7) Cleaning and storage: Wash the sample with an ultrasonic cleaner, repeat several times, dry the washed sample with nitrogen gas, and store it in a constant temperature drying oven.

[0019] The light absorption enhancement structure includes a Schottky junction, which is formed by contacting a metal with an array pattern etched onto a silicon substrate;

[0020] The current transport structure includes a silicon substrate, a P-type conductive structure, and an N-type conductive structure. The current generated by the light absorption enhancement structure is derived from the P-type and N-type conductive structures, respectively.

[0021] Furthermore, a layer of silicon oxide is disposed on the silicon substrate, an array pattern is etched in the middle of the silicon oxide, the array pattern is in contact with the silicon substrate, the array pattern is filled with metal, and the metal and silicon contact to form the Schottky junction.

[0022] Furthermore, the array pattern is a rectangular structure.

[0023] Furthermore, the metal thin film includes one of the following: metal particles or thin films of Au, Pt, Ni, Co, Ti, ITO, and their silicides.

[0024] Furthermore, an aluminum layer is disposed around the silicon substrate, and the aluminum layer contacts the silicon substrate to form an ohmic contact. A metal layer is covered on top of the aluminum layer to form an outer ring electrode. A chromium layer is covered on top of the silicon oxide, and the metal layer covers the chromium layer to form a central electrode. After the light absorption enhancement structure generates current, it is led out through the central electrode and the outer ring electrode.

[0025] A second aspect of this application provides a method for fabricating an infrared detector as described above, characterized in that the fabrication method includes the following steps:

[0026] 1) Design and fabricate photomasks;

[0027] 2) Obtain a silicon wafer, wherein a layer of silicon dioxide is provided on the front side of the silicon wafer;

[0028] 3) Spin-coating LOR and S1805 as the first layer of adhesive, forming electrode patterns on the silicon oxide surface using micro-nano photolithography, and then using a lift-off process on the silicon wafer for exposure and development, transferring the first layer of mask pattern to the silicon oxide to create markings and center electrodes;

[0029] 4) Deposit metal using magnetron sputtering, plating 10-30nm chromium and 30-100nm gold on the silicon wafer, then remove the resist;

[0030] 5) Spin-coat AZ3100 as the second layer of adhesive, expose and develop, transfer the second layer mask pattern to silicon oxide, etch holes in the center and around the silicon wafer, and remove the adhesive.

[0031] 6) Spin-coat LOR and S1805 as the third layer of adhesive, expose and develop, then deposit 200nm aluminum and 10nm metal on the outer ring to make the N electrode, and then remove the adhesive.

[0032] 7) Perform annealing;

[0033] 8) An array pattern is etched into the holes in the silicon oxide center using EBL;

[0034] 9) Spin-coat the fourth layer of photoresist, expose and develop, plate metal, fabricate the P electrode, and remove the photoresist.

[0035] Furthermore, the markings produced in step 3) include silicon wafer markings and EBL processing markings, with markings of chromium 10-30nm and metal 40-70nm.

[0036] Furthermore, in the outer electrode of step 6), the aluminum thickness is 100-300 nm and the metal thickness is 10-30 nm.

[0037] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0038] (1) The array pattern etched on the silicon substrate forms a Schottky junction in contact with the metal, which can promote the generation of hot electrons in the detector by enhancing light absorption, thereby improving the photoelectric conversion efficiency.

[0039] (2) Disordered nanopores are fabricated at the interface of the metal sensitive film to increase the roughness of the Schottky junction, thereby increasing the injection probability of hot electrons and thus improving the detector sensitivity.

[0040] (3) A back-illuminated light source is used to make the initial position of the hot electron generation closer to the Schottky interface, shortening the hot electron transport free path and thus improving the quantum efficiency of the detector.

[0041] (4) The roughened interface caused by the manufacturing process can not only form a local high-intensity electric field at the sharp edges, but also break the momentum conservation rule of electron injection at the interface. Therefore, hot electrons that might otherwise be completely reflected back to the metal can smoothly enter the silicon, thereby significantly improving the hot electron injection efficiency. This invention enhances light absorption by forming a Schottky junction between the arrayed pattern etched on the silicon substrate and the metal, and enhances hot electron absorption by roughening the Schottky interface. By using a back-illuminated incident method, the hot electron transport free path is shortened to improve the quantum efficiency of the detector. Attached Figure Description

[0042] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on the structures shown in these drawings without creative effort.

[0043] Figure 1 This is a schematic diagram of the structure of an infrared detector according to an embodiment of the present invention; wherein, (a) is a cross-sectional view; and (b) is a perspective view.

[0044] Figure 2 This is a schematic diagram of a metal marking pattern of an infrared detector according to an embodiment of the present invention.

[0045] Figure 3 The diagram below illustrates the principle of metal-silicon Schottky junction formation according to an embodiment of the present invention, wherein: (a) energy band diagram before metal and silicon contact; (b) Schottky junction energy band diagram after metal and N-type silicon contact; (c) Schottky junction energy band diagram after metal and P-type silicon contact; and (d) typical current-voltage characteristic curve of the Schottky junction.

[0046] Figure 4 This diagram illustrates the energy transfer and loss process during the three stages of thermionic generation, transport, and injection according to an embodiment of the present invention.

[0047] Figure 5 This diagram illustrates the influence of the type of metallic material on the initial energy distribution of hot electrons according to an embodiment of the present invention.

[0048] Figure 6 The diagram illustrates the principle of hot electron transport according to an embodiment of the present invention, wherein (a) the scattering process and time scale of hot electrons; and (b) the relationship between the mean free path of hot electrons scattered by electrons and phonons and the energy of hot electrons.

[0049] Figure 7 This is a schematic diagram of the cone-shaped distribution of the momentum of hot electrons that can be injected into silicon according to an embodiment of the present invention.

[0050] Figure 8 The diagram shows the structure of a photomask according to an embodiment of the present invention, wherein: (a) a first photomask; (b) a second photomask; (c) a third photomask; and (d) a fourth photomask.

[0051] Figure 9 This is a schematic diagram of a simulated back-illuminated absorption-enhanced photodetector according to an embodiment of the present invention.

[0052] Figure 10This is an electric field distribution diagram obtained by simulation using a back-illuminated absorption-enhanced photodetector according to an embodiment of the present invention.

[0053] Figure 11 This is a graph showing the absorptivity distribution as a function of wavelength obtained after simulation using a back-illuminated absorption-enhanced photodetector according to an embodiment of the present invention.

[0054] Figure 12 This is a flowchart of a method for fabricating an infrared detector according to an embodiment of the present invention.

[0055] Figure 13 This is a flowchart illustrating the preparation process of a metal-sensitive membrane according to an embodiment of the present invention. Detailed Implementation

[0056] The following specific examples illustrate the implementation of the present invention. Those skilled in the art can easily understand other advantages and effects of the present invention from the content disclosed in this specification. The present invention can also be implemented or applied through other different specific embodiments, and various details in this specification can also be modified or changed based on different viewpoints and applications without departing from the spirit of the present invention. It should be noted that, unless otherwise specified, the following embodiments and features described therein can be combined with each other.

[0057] In the description of this invention, unless otherwise stated, "a plurality of" means two or more; the terms "upper," "lower," "left," "right," "inner," "outer," "front end," "rear end," "head," "tail," etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings, and are only for the convenience of describing the invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation of the invention. Furthermore, the terms "first," "second," "third," etc., are used for descriptive purposes only and should not be construed as indicating or implying relative importance.

[0058] In the description of this invention, it should be noted that, unless otherwise explicitly specified and limited, the terms "connected" and "linked" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium. Those skilled in the art can understand the specific meaning of the above terms in this invention according to the specific circumstances.

[0059] The invention will now be further described with reference to the accompanying drawings.

[0060] Example 1:

[0061] This invention provides an infrared detector, a back-illuminated absorption-enhanced photodetector comprising a substrate, a metal sensitive film, a light absorption enhancement structure, and a current transport structure; the light absorption enhancement structure includes a Schottky junction, which is formed by contacting a metal with an array pattern etched on a silicon substrate; the current transport structure includes a silicon substrate, a P-type conductive structure, an N-type conductive structure, and a dielectric material, wherein the current generated by the light absorption enhancement structure is derived from the P-type and N-type conductive structures, respectively.

[0062] In some embodiments, a layer of silicon oxide is disposed above the silicon substrate, an array pattern is etched in the middle of the silicon oxide, the array pattern is in contact with the silicon substrate, the array pattern is filled with metal, and the metal and silicon contact to form the Schottky junction.

[0063] In some embodiments, the metal thin film includes metal particles or thin films of Au, Pt, Ni, Co, Ti, and ITO, as well as their silicides.

[0064] For example, such as Figure 1 As shown, a layer of silicon oxide 2 is disposed on top of the silicon substrate 1. An array pattern is etched in the middle of the silicon oxide 2. The array pattern is in contact with the silicon substrate and is filled with metal. The metal and silicon contact to form the Schottky junction. Figure 2 As shown, the array pattern is a rectangular aperture. An aluminum layer 3 is disposed around the top of the silicon substrate 1, forming an ohmic contact with the silicon substrate 1. A gold layer 4 covers the aluminum layer 3 to form an outer ring electrode. A chromium layer 5 covers the silicon oxide 2, and the gold layer 4 covers the chromium layer 5 to form a central electrode. After the light absorption enhancement structure generates current, it is conducted through the central electrode and the outer ring electrode. The aluminum layer 3 between the gold layer 4 and the silicon substrate 1 serves as a metal-sensitive film, and the gold layer 4 is a P-type conductive structure.

[0065] This back-illuminated absorption-enhanced photodetector forms a Schottky junction by etching an array of patterns on a silicon substrate and contacting a metal element. By enhancing light absorption, it promotes the generation of hot electrons in the detector, thereby improving photoelectric conversion efficiency. Its working principle is as follows:

[0066] The formation of a Schottky junction between a metal and silicon is a physical process involving charge redistribution and electronic energy level adjustment. For example... Figure 3 As shown in (a), for N-type silicon, after the metal comes into contact with silicon, the Fermi level of N-type silicon is generally higher than that of the metal, causing electrons in N-type silicon to flow towards the metal. During this process, an electric field is formed at the interface between the semiconductor and the metal due to electron transfer. The direction of the electric field is from the semiconductor to the metal. Since the direction of the electric field is the direction of decreasing potential (which is also the direction of increasing electron potential energy), the energy bands of N-type silicon warp upwards, forming a shape like... Figure 3 The band structure is shown in (b). Ideally, the barrier height of a Schottky junction formed by a metal and N-type silicon can be expressed by the formula... Calculated, where For the height of the Schottky barrier, W metal Let χ be the work function of the metal. si This represents the electron affinity in silicon, indicating the energy distance from the bottom of the silicon conduction band to vacuum. For example... Figure 3 As shown in (c), the process of metal forming a Schottky junction with P-type silicon is similar to that of N-type silicon. The main difference is that the hot carriers in an N-type silicon Schottky junction are generally hot electrons, while the hot carriers in a P-type silicon Schottky junction are usually hot holes.

[0067] The introduction of an external bias voltage disrupts the thermal equilibrium of the Schottky junction, causing the Fermi levels between the metal and silicon to become unequal, thus altering the relative height of the Fermi level and the Schottky junction barrier. Specifically, forward bias lowers the relative barrier height, allowing electrons to flow from the metal to the silicon, forming a forward current; reverse bias increases the relative barrier height, hindering electron flow, resulting in almost zero current and exhibiting rectification characteristics, such as... Figure 3 As shown in (d), the height of a Schottky barrier in practice is determined by many complex factors, including the properties of the interface, material properties, and fabrication conditions. These factors can significantly alter the height of a Schottky barrier when it is formed between a metal and silicon. In particular, interface states can induce pinning effects at the Fermi level, leading to a large deviation between the actual Schottky barrier height and the theoretical prediction. Therefore, in practical applications, the height of a Schottky barrier is generally determined through experimental measurement.

[0068] When infrared light shines on a metal-silicon Schottky junction detector, photons interact with electrons within the metal, exciting them to transition from low-energy states to high-energy states, forming hot electrons. These hot electrons possess a certain initial momentum distribution and propagate within the metal. Some of these hot electrons move towards the Schottky junction and have a chance to overcome the Schottky barrier and be injected into the silicon material.

[0069] Thermionic electrons successfully injected into silicon continue to move towards the electrodes, eventually forming a measurable current, namely the photocurrent. Figure 4 As shown, the formation of photocurrent involves multiple processes: first, photon absorption leads to the generation of hot electrons; second, hot electrons are transported within the metal; and finally, hot electrons cross the Schottky barrier and are injected into the silicon material.

[0070] In some embodiments, considering that energy losses occur in multiple processes involved in the formation of photocurrent, including radiation losses, heat losses, and losses caused by electron-electron and electron-phonon interactions, most of the energy is converted into heat energy rather than electrical energy. To improve the photoelectric conversion efficiency of this back-illuminated absorption-enhanced photodetector, this embodiment establishes an effective strategy to suppress these losses and enhance photocurrent generation.

[0071] On the one hand, by making the initial energy of electrons higher than the Schottky barrier and the initial momentum (velocity) of electrons oriented towards the Schottky interface, the probability of electrons reaching the Schottky junction interface can be increased, thereby improving the photoelectric conversion efficiency of the detector.

[0072] Specifically, there are two main ways hot electrons are generated in metals. The first is through direct excitation of hot electrons in the bulk metal by incident light. In this case, the light absorption rate plays a decisive role in the excitation efficiency, but since the bulk metal reflects most of the incident light, the excitation efficiency of this method is relatively low. The second method is through light irradiation onto a metal nanostructure to excite surface plasmon resonances. These plasmons relax on an ultrafast timescale (approximately 1–10 femtoseconds). During this process, plasmons may decay in various ways, including degenerating into hot electron-hot hole pairs through Landau damping, emitting energy as photons through radiative decay, or directly causing heat loss. The proportion of these decay mechanisms is affected by factors such as the size of the metal nanostructure, the type of material, and the lifetime of hot carriers. Therefore, in the generation of hot electrons, losses due to light reflection, radiative losses from plasmons, and heat losses constitute the main energy loss pathways. To improve the generation efficiency of hot electrons, reducing these loss mechanisms is crucial.

[0073] The spatial distribution, initial energy, and momentum distribution of excited hot electrons all significantly influence the photoelectric conversion efficiency of metal-silicon Schottky detectors. First, the spatial distribution of hot electrons is not uniform, attributed to differences in light intensity across different regions of the metal, resulting in higher light intensity regions generating more hot electrons. Specifically, the spatial distribution of hot electrons can be given by the following formula:

[0074]

[0075] Where n is the number of hot electrons, E is the electric field of the incident light, ω is the frequency of the incident light, and ε is the dielectric function of the metal. Since the incident light typically consists of multiple frequencies, the frequency must be integrated when calculating the hot electron distribution n. In detector design, optimizing the spatial distribution of hot electrons to ensure they are as close as possible to the Schottky junction interface can increase the probability of hot electron injection into silicon.

[0076] Secondly, the initial energy and momentum distribution of hot electrons may also be non-uniform. Inside the metal, the energy and momentum initially located at the Fermi level (E) may be non-uniform. f Electrons below a certain size will have their energy increase by ΔE after absorbing incident light energy or after plasmons excited by incident light degenerate into hot electrons. Therefore, the energy range of hot electrons is within the range of E. f With E f Between +ΔE. When the excitation process of electrons occurs within the same energy band (i.e., intra-band transition), the density of excited electronic states is between E and ΔE. f The following distribution is usually relatively uniform, so that the energy of the excited hot electrons is also at E f The electrons are uniformly distributed within the range of +ΔE. However, when interband transitions occur, the situation is quite different. At this point, the electron density of states can become extremely non-uniform, leading to a non-uniform energy distribution of hot electrons, such as... Figure 5 As shown.

[0077] Taking gold as an example, its d-band electrons are mainly located at approximately 2.6 eV below the Fermi level. When the energy of the incident photon exceeds this value, it triggers a large number of interband transitions of d-band electrons. Most of these transitioned electrons are located near the Fermi level and cannot form effective hot electrons to overcome the Schottky barrier, thus negatively impacting the photoelectric conversion efficiency. On the other hand, the initial momentum distribution of hot electrons is also affected by various factors, including the orientation of the metal crystal relative to the silicon interface, the direction of the electric field of the incident light, and interband transitions. For the back-illuminated absorption-enhanced photodetector proposed in this embodiment, the initial energy of the electrons is kept above the Schottky barrier (rather than at E...). f When the +ΔE range is uniformly distributed (or below the barrier height), the initial momentum (velocity) of electrons can be directed toward the Schottky interface, which increases the probability of them reaching the Schottky junction interface and improves the photoelectric conversion efficiency of the detector.

[0078] On the other hand, regarding the hot electron transport process, to increase the probability of hot electrons successfully reaching the Schottky junction interface, this embodiment takes two approaches. First, it increases the free path of the hot electrons. Given a small number of internal defects in the metallic material, the free path of the hot electrons is mainly determined by the type of material itself; therefore, materials with a longer free path can be used. Second, it shortens the distance between the initial position of the hot electrons and the Schottky interface. This can be achieved by adjusting the electric field distribution of the incident light to bring the hot electron generation position as close as possible to the Schottky junction interface, or by using an ultrathin metallic material to confine the hot electrons near the Schottky interface.

[0079] Specifically, after being generated, hot electrons must be transported to the interface of a Schottky junction in order to be successfully injected into silicon. During this transport, hot electrons undergo various scattering processes, primarily electron-electron scattering and electron-phonon scattering. From a dynamical perspective, hot electrons exhibit three main states at different time scales after excitation. Figure 6 As shown in (a), within a timescale of less than 10 femtoseconds, the hot electrons are excited after the metal absorbs light. In the timescale of approximately 10–100 femtoseconds, the hot electrons are primarily affected by electron-electron scattering, leading to a gradual decrease in their energy and a redistribution of energy among the electrons, forming a quasi-Fermi distribution. When the timescale exceeds 100 femtoseconds, electron-phonon scattering becomes dominant, causing energy exchange between the electrons and the crystal lattice. The hot electrons gradually cool to an equilibrium state, and the entire system returns to its initial state. Therefore, electron-electron scattering and electron-phonon scattering are crucial in the transport of hot electrons, directly determining whether they can successfully reach the metal-silicon interface. These two scattering processes can be described by the mean free path, where the mean free path for electron-electron scattering is l. ee The mean free path corresponding to electron-phonon scattering is l ep In particular, the mean free path l of electron-electron scattering ee It is not a constant, but closely related to the energy level of the hot electrons. Specifically, higher-energy hot electrons are more likely to collide with other electrons, and therefore have a relatively shorter mean free path, while lower-energy hot electrons have a longer mean free path. On the other hand, the mean free path l of electron-phonon scattering... ep Primarily influenced by the number of phonons, its relationship with electron energy is not significant. Since the number of phonons is temperature-dependent, at a specific temperature, it can be considered that l... ep It is a relatively stable value. Figure 6 (b) shows the mean free path of gold. ee and l ep It can be seen that in the range where the hot electron energy is less than 2 eV, both free paths reach more than 20 nanometers.

[0080] After electron-electron scattering and electron-phonon scattering, the probability of hot electrons transporting from their initial position to the Schottky interface decreases exponentially with the distance between the excitation point and the interface, as given by the following formula:

[0081]

[0082] in, Let be the probability that a hot electron with energy E excited at point r reaches the gold-silicon interface. Let be the distance from the hot electron to the gold-silicon interface at point r, θ be the direction of the hot electron's momentum, and l(E) be the free path of the hot electron. ee and l ep According to Matthiassen's rule, 1 / l(E) = 1 / l ee +1 / l ep .

[0083] Therefore, to increase the probability of hot electrons successfully reaching the Schottky junction interface, two approaches can be taken. First, increase the free path of the hot electrons. Given a relatively small number of internal defects in the metallic material, the free path of the hot electrons is mainly determined by the material type itself; therefore, materials with a longer free path can be used. Second, shorten the distance between the initial position of the hot electrons and the Schottky interface. This can be achieved by adjusting the electric field distribution of the incident light to bring the hot electron generation position as close as possible to the Schottky junction interface, or by using ultrathin metallic materials to confine the hot electrons near the Schottky interface.

[0084] Finally, there are strategies to improve photoelectric conversion efficiency by focusing on the hot electron injection process.

[0085] When hot electrons reach the metal-silicon Schottky interface, they are not necessarily injected into silicon; their energy must meet certain conditions. Specifically, according to the Fowler model, the kinetic energy component of the hot electron perpendicular to the Schottky interface must be higher than the potential barrier height for it to be injected into silicon. This can be considered as the hot electron's energy being higher than the Fermi level E. f The energy component is kinetic energy. In this case, let the energy of the hot electron above the Fermi level be E. d Then we have:

[0086]

[0087] in The magnitude of the momentum of the hot electrons. Let be the modulus of the wave vector corresponding to the momentum. According to the above equation, the energy component perpendicular to the gold-silicon interface can be expressed as:

[0088]

[0089] In the above formula, k d⊥ This represents the momentum perpendicular to the gold-silicon interface. Therefore, only thermionic electrons with energy greater than the height of the Schottky barrier can be injected into silicon, i.e., the following condition must be met:

[0090]

[0091] The image corresponding to the injection conditions expressed in the above formula is as follows: Figure 7As shown, in momentum space, only the hot electrons whose momentum distribution is within the red cone region can be injected. The critical angle corresponding to this cone region is Ω, satisfying the relationship... Therefore, the probability of electron injection is the integral of the solid angle over this shaded region, divided by the total solid angle, which gives:

[0092]

[0093] And because It can be simplified to Therefore, the above formula can be further simplified to:

[0094]

[0095] As can be seen from the above formula, the injection probability of hot electrons is related to their energy E. d Closely related. E d The larger the value of E, the higher the injection efficiency. d Much greater than the height of the barrier At this point, the injection probability approaches 0.5. This means that high-energy hot electrons have a chance to be injected as long as their momentum direction is pointing towards the metal-silicon interface; however, slightly lower-energy hot electrons can only be injected if their momentum direction is within the solid angle Ω. Figure 7 As shown, unimplanted hot electrons are reflected back into the metal at the interface, their energy gradually decreasing due to various scattering processes, which greatly reduces their likelihood of re-implantation into silicon. To improve the injection probability of hot electrons, several strategies can be adopted. One strategy is to use double Schottky junctions, bulk Schottky junctions, rough surfaces, etc. These structures increase the contact area between the metal and silicon, expanding the injectable angle range and thus improving the injection efficiency. Another strategy is to reduce the Schottky junction potential height, but this also increases the dark current, thus affecting the detector's signal-to-noise ratio. Therefore, the signal-to-noise ratio of the detector must be comprehensively considered to determine whether to adopt this method.

[0096] In this embodiment, as Figure 13 As shown, the fabrication steps of the metal-sensitive film are as follows:

[0097] Step 1: Preparation of cleaning solutions: Washing solution I is a solution obtained by mixing concentrated sulfuric acid and hydrogen peroxide in a certain proportion; Washing solution II is a solution obtained by mixing ammonia, hydrogen peroxide, and deionized water in a set proportion; Washing solution III is a solution obtained by mixing concentrated hydrochloric acid, hydrogen peroxide, and deionized water in a set proportion; The silicon wafer is placed in washing solution I, washing solution II, and washing solution III in sequence for ultrasonic cleaning, and finally ultrasonically cleaned with deionized water, then removed and dried; It is mainly used to remove two types of contaminants: one is the oxide layer formed by slight oxidation of the silicon wafer surface when it is exposed to air during storage and transportation; the other is the dust, organic matter, and metal salts that adhere to the silicon substrate during production, cutting, and packaging.

[0098] Step 2: Prepare the precipitation solution: The concentration of silver nitrate is 0.0125-0.05 mol / L. Deionized water, hydrofluoric acid and silver nitrate solution are prepared in a certain volume ratio.

[0099] Step 3, Silver particle deposition: Place the EBL-etched sample in the deposition solution and remove it after 5s, 10s, 15s, and 20s.

[0100] Step 4: Prepare the etching solution: Mix hydrogen peroxide and hydrofluoric acid in a set ratio to prepare the etching solution.

[0101] Step 5, Metal-assisted etching: Place the sample in the etching solution, set the etching temperature to 50-70 degrees Celsius, and time for 5-20 minutes. Remove the sample. The overall reaction is: Si + 4AgNO3 + 4HF → H2SiF6 + 4Ag + 4HNO3.

[0102] Step 6: Silver ion removal: Mix nitric acid solution and deionized water in a certain proportion to prepare a dilute nitric acid solution to remove residual silver ions from the microstructured silicon surface. Place the etched sample in the dilute nitric acid solution for 20-40 minutes to completely dissolve the residual silver ions before removing it.

[0103] Step 7, Cleaning and Storage: Wash the sample using an ultrasonic cleaner, repeating several times. Dry the washed sample with nitrogen gas and store it in a constant temperature drying oven.

[0104] Example 2:

[0105] This invention provides a method for preparing an infrared detector, such as... Figure 12 As shown, the preparation method includes the following steps:

[0106] 1) Design and fabricate the photomask.

[0107] like Figure 3 As shown, (a) to (d) illustrate schematic diagrams of the first to fourth layers of photomasks, respectively.

[0108] 2) Obtain silicon wafers with 300nm silicon dioxide on the front side, a total thickness of 500μm, light doping, and a resistivity of 1-10Ω·cm (N-type).

[0109] 3) Spin-coating LOR and S1805 as the first layer of adhesive, and forming electrode patterns on the silicon oxide surface using micro-nano photolithography exposure process. Then, using a lift-off process on the silicon wafer, exposure and development are performed to transfer the first layer of mask pattern to the silicon oxide to create the marker and center electrode (P).

[0110] The LOR spin coating process involves first spin coating at 500 rpm for 5 seconds, then at 4000 rpm for 40 seconds. The substrate is then baked at 170 degrees Celsius for 10 minutes. Next, S1805 is spin coated at 500 rpm for 5 seconds, then at 4000 rpm for 40 seconds. The substrate is then baked on a hot plate for 3-10 minutes. The markings include silicon wafer markings and EBL processing markings, with chromium at 10nm and gold at 40-70nm.

[0111] 4) Deposit metal using magnetron sputtering, plating 10nm chromium and 50nm gold on the silicon wafer, then remove the adhesive.

[0112] 5) Spin-coat AZ3100 as the second resist layer, expose and develop, transfer the second mask pattern to silicon oxide, and etch holes in the center and around the silicon wafer. Remove the resist.

[0113] The silicon via etching method employed was dry etching. The spin coating speed for the AZ3100 photoresist was 5000 rpm for 25 seconds, followed by 5500 rpm for 3 seconds.

[0114] 6) Spin-coat the third layer of photoresist, expose and develop it, then transfer the third photomask pattern to silicon oxide. Deposit 200nm aluminum and 10nm gold on the outer ring to fabricate the N-electrode. Remove the photoresist.

[0115] The outer electrode is made of AL with a thickness of 200nm and gold with a thickness of 10nm.

[0116] 7) Perform annealing.

[0117] 8) An array pattern is etched into the hole in the center of the silicon oxide using EBL.

[0118] 9) Spin-coat the fourth layer of photoresist, expose and develop, transfer the fourth layer mask pattern to silicon oxide, plate with gold, and fabricate the P electrode. Remove the photoresist.

[0119] In steps 4), 5), 6), and 9), acetone is used to remove the adhesive layer.

[0120] An infrared detector prepared based on the above method was subjected to simulation experiments in this embodiment. Figure 9This is a schematic diagram of a simulated structure corresponding to this back-illuminated absorption-enhanced photodetector. Figure 10 and Figure 11 These are, respectively, the electric field distribution diagram and the absorptivity versus wavelength distribution curve obtained after simulation using this back-illuminated absorption-enhanced photodetector. Figure 10 and Figure 11 It can be seen that the infrared detector proposed in this invention has high photoelectric conversion efficiency and detector sensitivity.

[0121] The above embodiments are only used to illustrate the technical solutions of the present invention, and are not intended to limit it. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features therein. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention, and they should all be covered within the scope of the claims and specification of the present invention.

Claims

1. An infrared detector, characterized by The metal sensitive film, the light absorption enhancement structure and the current transmission structure are arranged on the substrate. The interface of the metal sensitive film is roughened, etched with disordered nanopore light trapping structure or deposited with nanoparticles on the interface of the silicon substrate to improve the hot electron injection probability of the Schottky interface. The manufacturing steps of the metal sensitive film are as follows: 1) Preparation of cleaning solution: No. 1 cleaning solution is a solution prepared by mixing concentrated sulfuric acid and hydrogen peroxide in a certain proportion; No. 2 cleaning solution is a solution prepared by mixing ammonia, hydrogen peroxide and deionized water in a certain proportion; No. 3 cleaning solution is a solution prepared by mixing concentrated hydrochloric acid, hydrogen peroxide and deionized water in a certain proportion; the silicon wafer is sequentially placed in No. 1 cleaning solution, No. 2 cleaning solution and No. 3 cleaning solution for ultrasonic cleaning, and finally cleaned with deionized water and dried; 2) Preparation of deposition solution: the concentration of silver nitrate is 0.0125-0.05 mol / L, and ionized water, hydrofluoric acid and silver nitrate solution are configured in a certain volume ratio; 3) Silver particle deposition: the sample after EBL etching is placed in the deposition solution, and taken out after timing for 5s, 10s, 15s and 20s; 4) Preparation of etching solution: hydrogen peroxide and hydrofluoric acid are mixed in a certain proportion to obtain the etching solution; 5) Metal-assisted etching: the sample is placed in the etching solution, the etching temperature is set to 50-70℃, and the total reaction formula is: Si+4AgNO3+4HF→H2SiF6+4Ag+4HNO3 6) Silver ion removal: dilute nitric acid solution is prepared by mixing nitric acid solution and deionized water in a certain proportion to remove residual silver ions on the surface of the microstructure silicon; the sample after etching is placed in the dilute nitric acid solution for 20-40 minutes, and the residual silver ions are completely dissolved before being taken out; 7) Cleaning and preservation: the sample is washed repeatedly using an ultrasonic washing instrument, and then dried with a small nitrogen air flow and stored in a constant temperature drying box. The light absorption enhancement structure includes a Schottky junction formed by an array pattern etched on the silicon substrate and a metal contact. The current transmission structure includes a silicon substrate, a P-type conductive structure and an N-type conductive structure, and the current generated by the light absorption enhancement structure is conducted from the P-type and N-type conductive structures respectively.

2. The infrared detector of claim 1, wherein, A layer of silicon oxide is arranged above the silicon substrate, an array pattern is etched in the middle of the silicon oxide, the array pattern is in contact with the silicon substrate, the array pattern is filled with metal, and the metal is in contact with the silicon to form the Schottky junction.

3. An infrared detector according to claim 2, wherein The array pattern is a rectangular structure.

4. The infrared detector of claim 1, wherein, The metal sensitive film includes one of Au, Pt, Ni, Co, Ti, ITO metal particles or thin films and silicides thereof.

5. The infrared detector of claim 2, wherein, An aluminum layer is arranged around the top of the silicon substrate, the aluminum layer is in contact with the silicon substrate to form an ohmic contact, a gold layer is arranged above the aluminum layer to form an outer electrode, a chromium layer is arranged above the silicon oxide, and the chromium layer is covered by the gold layer to form a center electrode, and the current generated by the light absorption enhancement structure is conducted through the center electrode and the outer electrode.

6. A method of producing an infrared detector as claimed in any one of claims 1 to 5, characterized in that The preparation method includes the following steps: 1) Mask design and processing; 2) Obtain a silicon wafer, and a layer of silicon dioxide is arranged on the front surface of the silicon wafer. 3) Spin-coat LOR and S1805 as the first layer of glue, using micro-nano lithography exposure process to form electrode pattern on the surface of silicon oxide, using lift-off process on the silicon wafer, exposure and development, transfer the first layer of mask pattern to the silicon oxide, make the mark and center electrode; 4) Using magnetron sputtering to deposit metal, 10-30nm chromium and 30-100nm gold on the silicon wafer, and then remove the glue; 5) Spin-coat AZ3100 as the second layer of glue, exposure and development, transfer the second layer of mask pattern to the silicon oxide, etch the hole in the center and around the silicon wafer, and then remove the glue; 6) Spin-coat LOR and S1805 as the third layer of glue, after exposure and development, 100-300nm aluminum and 10-30nm gold are plated on the outer ring to make N electrode, and then remove the glue; 7) Annealing to form Schottky contact; 8) Using EBL to etch array pattern in the hole in the center of the silicon oxide; 9) Spin-coat LOR and S1805 as the fourth layer of glue, exposure and development, and then plate metal to fill the array pattern with metal and make P electrode, and then remove the glue.

7. The process for the preparation of a compound according to claim 6, characterized in that, The mark made in step 3) includes silicon wafer mark and EBL processing mark, the mark is 10-30nm chromium and 40-70nm metal layer.

8. The preparation method according to claim 6, characterized in that, In step 6), the thickness of aluminum in the outer ring electrode is 100-300nm, and the metal is 10-30nm.

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