Infrared detector and preparation method thereof

Abstract

The invention relates to the technical field of photoelectric detection, and discloses an infrared detector and a preparation method thereof, and the infrared detector comprises a substrate, a metal sensitive film, a light absorption enhancement structure and a current transmission structure. The light absorption enhancing structure comprises a Schottky junction, the Schottky junction passes through an array pattern etched on a silicon substrate, the array pattern is filled with metal, the silicon substrate is in contact with the metal to form the Schottky junction, and a 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. Current generated by the light absorption enhancing structure is led out from the P-type conductive structure and the N-type conductive structure. According to the invention, the Schottky interface is subjected to roughening treatment to enhance hot electron absorption, and a backside illumination type incidence method is adopted to shorten a hot electron transmission free path so as to improve the quantum efficiency of the detector.

Description

Technical Field

[0001] The present invention relates to the field of photoelectric detection technology, and in particular to an infrared detector and a preparation method thereof. Background Art

[0002] Photodetectors (PDs) are devices that capture and collect light signals within a specific wavelength range in real time and convert them into electrical signals. They have been widely used in optoelectronic imaging, optical communications, and biosensing. In recent years, near-infrared (NIR, 780-2526nm) photoelectric detection technology has received widespread attention.

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

[0004] The Schottky junction is a simple interface between metal and semiconductor. It is similar to the PN junction and has nonlinear impedance characteristics. The basic principle is that the work function of semiconductors is generally smaller than that of metals. Therefore, when metals and semiconductors (taking N-type as an example) come into contact, electrons flow from the semiconductor into the metal, forming a space charge region composed of positively charged immovable impurity ions in the surface layer of the semiconductor. In this region, there is an electric field pointing from the semiconductor to the metal, just like building a high wall to prevent electrons in the semiconductor from continuing to flow into the metal. From the energy band diagram of the Schottky barrier, it can be seen that the energy band of the semiconductor bends at the interface to form a high potential energy region, which is the Schottky barrier. Electrons must have an energy higher than this barrier to cross the barrier and flow into the metal. When in equilibrium, the height of the Schottky barrier is the difference between the work functions of the metal and the semiconductor.

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

[0006] In view of the above-mentioned shortcomings of the prior art, the object of the present invention is to provide an infrared detector and a method for preparing the same, which enhances light absorption by forming a Schottky junction between an arrayed pattern etched on a silicon substrate and metal contact, thereby improving the light response of photoelectric detection.

[0007] The technical solution of this application is:

[0008] In a first aspect of the present application, an infrared detector is provided, comprising a metal sensitive film, a light absorption enhancement structure and a current transmission structure;

[0009] The metal sensitive film interface is roughened, a disordered nanohole light trapping structure is etched, or nanoparticles are deposited on the silicon substrate interface to increase the probability of hot electron injection at the Schottky interface. The increase in the probability of hot electron injection is due to the fact that the rough interface can be equivalent to an electronic random grating, which increases the range of momentum directions of hot electrons injected into silicon, thereby increasing the injection probability;

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

[0011] 1) Preparation of cleaning solution: No. Ⅰ cleaning solution is a solution obtained by mixing concentrated sulfuric acid and hydrogen peroxide in proportion; II

[0012] Cleaning solution No. 1 is a solution obtained by mixing ammonia water, hydrogen peroxide and deionized water in a set ratio; cleaning solution No. 3 is a solution obtained by mixing concentrated hydrochloric acid, hydrogen peroxide and deionized water in a set ratio; the silicon wafer is placed in cleaning solution No. 1, cleaning solution No. 2 and cleaning solution No. 3 in sequence for ultrasonic cleaning, and finally ultrasonically cleaned with deionized water, taken out and dried; it is mainly used to remove two types of pollutants: one is the oxide layer produced by slight oxidation of the surface of the silicon wafer when it has the opportunity to be exposed to the air during storage and transportation; the other is dust, organic matter and metal salts adhered to the silicon substrate during the production, cutting and packaging process.

[0013] 2) Prepare the deposition solution: the concentration of silver nitrate is 0.0125-0.05 mol / L, and the ionized water, hydrofluoric acid and silver nitrate solution are prepared in a certain volume ratio;

[0014] 3) Silver particle deposition: Place the sample after EBL etching in the deposition solution and take it out after 5s, 10s, 15s, and 20s;

[0015] 4) preparing an etching solution: mixing hydrogen peroxide and hydrofluoric acid in a set ratio to prepare an etching solution;

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

[0017] 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 on the surface of microstructured silicon. Place the etched sample in the dilute nitric acid solution for 20-40 minutes to completely dissolve the residual silver ions and then take it out.

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

[0019] The light absorption enhancement structure includes a Schottky junction, and the Schottky junction is formed by contacting an arrayed pattern etched on a silicon substrate with a metal;

[0020] The current transmission structure comprises 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 respectively derived from the P-type and N-type conductive structures.

[0021] Furthermore, a layer of silicon oxide is provided 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 is in contact with silicon to form the Schottky junction.

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

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

[0024] Furthermore, an aluminum layer is arranged around the top of the silicon substrate, and the aluminum layer contacts the silicon substrate to form an ohmic contact. The aluminum layer is covered with a metal layer to form an outer ring electrode. The silicon oxide is covered with a chromium layer, and the chromium layer is covered by the metal layer to form a central electrode. After the light absorption enhancement structure generates current, the current is conducted through the central electrode and the outer ring electrode.

[0025] In a second aspect of the present application, a method for preparing an infrared detector as described above is provided, wherein the method comprises the following steps:

[0026] 1) Design and process the mask;

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

[0028] 3) Spin-coat LOR and S1805 as the first layer of glue, use micro-nano lithography exposure process to form electrode patterns on the silicon oxide surface, use lift-off process on the silicon wafer, perform exposure and development, transfer the first layer of mask pattern to silicon oxide, and make marks and center electrodes;

[0029] 4) Deposit metal by magnetron sputtering, plate 10-30nm chromium and 30-100nm gold on silicon wafer, and remove the glue;

[0030] 5) Spin-coat AZ3100 as the second layer of adhesive, perform exposure and development, transfer the second layer of 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 glue, expose and develop, plate 200nm aluminum on the outer circle, 10nm metal to make N electrode, and remove the glue;

[0032] 7) annealing;

[0033] 8) Etching an array pattern in the hole at the center of the silicon oxide using EBL;

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

[0035] Furthermore, the marks made in step 3) include silicon wafer marks and EBL processing marks, and the marks are 10-30nm for chromium and 40-70nm for metal.

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

[0037] Compared with the prior art, the present invention has the following beneficial effects:

[0038] (1) The arrayed pattern etched on the silicon substrate contacts the metal to form a Schottky junction, 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 made 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 improving the sensitivity of the detector.

[0040] (3) Using back-illuminated light source irradiation method, the initial position of thermal electron generation is closer to the Schottky interface, shortening the free path of thermal electron transmission, so as to improve the quantum efficiency of the detector.

[0041] (4) The rough interface caused by the manufacturing process can not only form a local high-intensity electric field at the sharp edge, but also break the momentum conservation rule of electron injection at the interface. Therefore, the hot electrons that might have been completely reflected back to the metal can smoothly enter the silicon, thereby significantly improving the injection efficiency of hot electrons. The present invention enhances light absorption by forming a Schottky junction in contact with the metal through the arrayed pattern etched on the silicon substrate, and enhances the absorption of hot electrons by roughening the Schottky interface, and adopts a back-illuminated incidence method to shorten the free path of hot electron transmission, so as to improve the quantum efficiency of the detector. BRIEF DESCRIPTION OF THE DRAWINGS

[0042] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on the structures shown in these drawings without paying creative work.

[0043] Figure 1 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 stereoscopic view.

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

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

[0046] Figure 4 1 is a diagram of the energy transfer and loss process in the three stages of hot electron generation, transmission and injection according to an embodiment of the present invention.

[0047] Figure 5 Graph showing the effect of metal material type on the initial energy distribution of hot electrons according to an embodiment of the present invention.

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

[0049] Figure 7 FIG. 4 is a schematic diagram of a conical distribution of hot electron momentum that can be injected into silicon according to an embodiment of the present invention.

[0050] Figure 8 1 is a structural diagram of a mask according to an embodiment of the present invention, wherein: (a) a first mask layer; (b) a second mask layer; (c) a third mask layer; and (d) a fourth mask layer.

[0051] Fig. 9 Schematic diagram of the simulated structure of a back-illuminated absorption-enhanced photodetector according to an embodiment of the present invention.

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

[0053] Fig.11 The graph is a distribution curve of absorption rate versus wavelength obtained after simulation using a back-illuminated absorption-enhanced photodetector according to an embodiment of the present invention.

[0054] Fig.12 The figure is a flow chart of a method for preparing an infrared detector according to an embodiment of the present invention.

[0055] Fig.13 FIG. 4 is a flow chart of preparing a metal sensitive film according to an embodiment of the present invention. DETAILED DESCRIPTION

[0056] The following describes the embodiments of the present invention by specific examples, and those skilled in the art can easily understand other advantages and effects of the present invention from the contents disclosed in this specification. The present invention can also be implemented or applied through other different specific embodiments, and the details in this specification can also be modified or changed in various ways based on different viewpoints and applications without departing from the spirit of the present invention. It should be noted that the following embodiments and features in the embodiments can be combined with each other without conflict.

[0057] In the description of the present invention, unless otherwise specified, "plurality" means two or more than two; the orientations or positional relationships indicated by the terms "upper", "lower", "left", "right", "inner", "outer", "front end", "rear end", "head", "tail", etc. are based on the orientations or positional relationships shown in the drawings, and are only for the convenience of describing the present invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, be constructed and operate in a specific orientation, and therefore cannot be understood as limiting the present invention. In addition, the terms "first", "second", "third", etc. are only used for descriptive purposes and cannot be understood as indicating or implying relative importance.

[0058] In the description of the present invention, it should be noted that, unless otherwise clearly specified and limited, the terms "connected" and "connection" should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection or an indirect connection through an intermediate medium. For ordinary technicians in this field, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

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

[0060] Embodiment 1:

[0061] An embodiment of the present invention provides an infrared detector, which is a back-illuminated absorption-enhanced photodetector comprising a substrate, a metal sensitive film, a light absorption-enhanced structure and a current transmission structure; the light absorption-enhanced structure comprises a Schottky junction, and the Schottky junction is formed by contacting an arrayed pattern etched on a silicon substrate with a metal; the current transmission structure comprises a silicon substrate, a P-type conductive structure, an N-type conductive structure and a dielectric material, and the current produced by the light absorption-enhanced structure is respectively derived from the P-type and N-type conductive structures.

[0062] In some embodiments, 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 is in contact with silicon to form the Schottky junction.

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

[0064] For example, Figure 1 As shown, a layer of silicon oxide 2 is disposed on 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, the array pattern is filled with metal, and the metal is in contact with silicon to form the Schottky junction. Figure 2 As shown, the array pattern is a rectangular square hole, an aluminum layer 3 is arranged around the top of the silicon substrate 1, the aluminum layer 3 is in contact with the silicon substrate 1 to form an ohmic contact, the aluminum layer 3 is covered with a gold layer 4 to form an outer ring electrode, the silicon oxide 2 is covered with a chromium layer 5, and the chromium layer 5 is covered by the gold layer 4 to form a central electrode, and the light absorption enhancement structure generates current, which is conducted out through the central electrode and the outer ring electrode. Among them, the aluminum layer 3 between the gold layer 4 and the silicon substrate 1 is used as a metal sensitive film, and the gold layer 4 is a P-type conductive structure.

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

[0066] The process of metal and silicon forming a Schottky junction is a physical process involving charge redistribution and electron energy level adjustment. Figure 3 As shown in (a), for N-type silicon, after the metal and silicon come into contact, the Fermi level of N-type silicon is generally higher than that of the metal, causing the electrons of N-type silicon to flow to the metal. In this process, an electric field is formed at the interface where the semiconductor and the metal come into contact due to the 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 the potential decrease (which is also the direction of the electron's potential energy increase), the energy band of N-type silicon is warped upward, forming the following Figure 3 The energy band structure shown in (b) is shown in Figure 1. Under ideal conditions, the barrier height of the Schottky junction formed by metal and N-type silicon can be expressed by the formula Calculated, where is the Schottky junction barrier height, W metal is the work function of the metal, χ si is the affinity of electrons in silicon, representing the energy distance from the bottom of the silicon conduction band to vacuum. Figure 3 As shown in (c), the process of forming a Schottky junction between metal and P-type silicon is similar to that of N-type silicon. The main difference between the two is that the hot carriers corresponding to the N-type silicon Schottky junction are generally hot electrons, while the hot carriers corresponding to the P-type silicon Schottky junction are usually hot holes.

[0067] The introduction of an external bias voltage will break the thermal equilibrium state of the Schottky junction, causing the Fermi level between the metal and silicon to no longer be equal, thereby changing the relative height of the Fermi level and the Schottky junction barrier. Specifically, when forward biased, the relative height of the barrier will decrease, allowing electrons to flow from the metal to the silicon, forming a forward current; when reverse biased, the relative height of the barrier will increase, preventing the flow of electrons, and the current will be almost zero, showing rectification characteristics, such as Figure 3 As shown in (d). In actual situations, the height of the Schottky barrier is determined by many complex factors, including the properties of the interface, the properties of the material, and the preparation conditions. When a Schottky barrier is formed between metal and silicon, these factors can significantly change its height. In particular, interface states may induce a pinning effect at the Fermi level, resulting in a large deviation between the actual Schottky barrier height and the theoretically predicted value. Therefore, in practical applications, the height of the Schottky barrier is generally determined by experimental measurements.

[0068] When infrared light shines on the metal-silicon Schottky junction detector, the photons interact with the electrons in the metal, exciting the electrons to transition from a low energy state to a high energy state, forming hot electrons. These hot electrons have a certain initial momentum distribution and are transmitted inside the metal. Among them, some hot electrons will move toward the Schottky junction and have a certain probability of crossing the Schottky barrier and being injected into the silicon material.

[0069] The hot electrons successfully injected into silicon will continue to move toward the electrode and eventually form a measurable current, namely photocurrent. Figure 4 As shown in Figure 1, the formation of photocurrent involves multiple processes: first, photon absorption leads to the generation of hot electrons, second, the transmission of hot electrons within the metal, and finally, the hot electrons cross the Schottky barrier and are injected into the silicon material.

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

[0071] On the one hand, the photoelectric conversion efficiency of the detector can be improved by making the initial energy of the electrons higher than the Schottky barrier and the initial momentum (speed) of the electrons toward the Schottky interface, thereby increasing the probability of them reaching the Schottky junction interface.

[0072] Specifically, there are two main ways to generate hot electrons in metals. The first way is that incident light directly excites hot electrons in bulk metals. In this case, the absorption rate of light plays a decisive role in the excitation efficiency of hot electrons, and bulk metals reflect most of the incident light, so the hot electron excitation efficiency of this method is low. The second way is that light irradiates metal nanostructures to excite surface plasmon resonance. These plasmons relax on an ultrafast time scale (about 1-10 femtoseconds). In this process, plasmons may decay in a variety of ways, including degenerating into hot electron-hot hole pairs through Landau damping, emitting energy in the form of photons through radiation decay, or directly forming 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, the loss caused by light reflection, the radiation loss of plasmons, and the heat loss constitute the main energy loss pathways. In order to improve the efficiency of hot electron generation, it is crucial to reduce these loss mechanisms.

[0073] The spatial distribution, initial energy and momentum distribution of excited hot electrons have an important impact on the photoelectric conversion efficiency of metal-silicon Schottky detectors. First, the spatial distribution of hot electrons is not uniform, which is attributed to the difference in light intensity in different areas of the metal, resulting in more hot electrons in areas with higher light intensity. 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 usually consists of multiple frequencies, the frequency needs to be integrated when calculating the hot electron distribution n. In the design of the detector, optimizing the spatial distribution of hot electrons to ensure that they are as close to the Schottky junction interface as possible 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 hot electrons originally at the Fermi level (E f ) below, after absorbing the incident light energy or the plasmon excited by the incident light degenerates into hot electrons, their energy will increase by ΔE, so that the energy range of hot electrons is within E f With E f +ΔE. When the electron excitation process occurs in the same energy band (i.e., intra-band transition), the excited electron state density is between E f The following usually presents a relatively uniform distribution, so that the energy of the excited hot electrons is also within E f +ΔE. However, when the electrons make interband transitions, the situation is completely different. At this time, the state density of the electrons may become extremely non-uniform, resulting in uneven energy distribution of the hot electrons, such as Figure 5 shown.

[0077] Taking metal gold as an example, its d-band electrons are mainly located at about 2.6 eV below the Fermi level. When the energy of the incident photon exceeds this value, a large number of d-band electrons will be triggered to make inter-band transitions. Most of these electrons after the transition are located near the Fermi level and cannot form effective hot electrons to cross the Schottky barrier, which has an adverse effect on the photoelectric conversion efficiency. On the other hand, the initial momentum distribution of hot electrons is also affected by many factors, including the orientation of the metal crystal relative to the silicon interface, the electric field direction of the incident light, and the inter-band transition. For the back-illuminated absorption-enhanced photodetector proposed in this embodiment, the initial energy of the electrons is higher than the Schottky barrier (rather than at the E f +ΔE range is uniformly distributed, or below the potential barrier height), the initial momentum (speed) direction of the electron can be toward the Schottky interface, which increases the probability of it reaching the Schottky junction interface and improves the photoelectric conversion efficiency of the detector.

[0078] On the other hand, for the thermal electron transmission process, in order to increase the probability of thermal electrons successfully reaching the Schottky junction interface, this embodiment starts from two directions. The first is to increase the free path of thermal electrons. Under the premise that there are fewer defects inside the metal material, the free path of thermal electrons is mainly determined by the type of material itself, so materials with a longer free path can be used. The second is to shorten the distance between the initial position of the thermal electrons and the Schottky interface. The generation position of thermal electrons can be made as close to the Schottky junction interface as possible by adjusting the electric field distribution of the incident light, or ultra-thin metal materials can be used to confine thermal electrons near the Schottky interface.

[0079] Specifically, after being generated, hot electrons must be transmitted to the interface of the Schottky junction before they can be successfully injected into silicon. During the transmission process, hot electrons will undergo a variety of scattering processes, mainly including electron-electron scattering and electron-phonon scattering. From a dynamic point of view, hot electrons exhibit three main states in different time scales after being excited. Figure 6 As shown in (a), in a time of less than 10 femtoseconds, the hot electrons are excited after the metal absorbs light. In the time scale of about 10-100 femtoseconds, the hot electrons are mainly affected by the electron-electron scattering process, which causes their energy to gradually decrease. The energy between electrons is redistributed to form a quasi-Fermi distribution. When the time scale exceeds 100 femtoseconds, the electron-phonon mutual scattering process dominates, causing energy exchange between electrons and the lattice, and the hot electrons gradually cool to equilibrium, and the entire system returns to its initial state. Therefore, in the transmission process of hot electrons, the two processes of electron-electron scattering and electron-phonon scattering are crucial, which directly determine whether the hot electrons can successfully reach the metal-silicon interface. These two scattering processes can be described by the mean free path, where the mean free path corresponding to electron-electron scattering is l ee , and the mean free path corresponding to electron-phonon scattering is l ep In particular, the mean free path of electron-electron scattering, l ee is not a constant, but is closely related to the energy of the hot electrons. Specifically, hot electrons with higher energy are more likely to collide with other electrons, so their free paths are relatively short, while hot electrons with lower energy have longer free paths. On the other hand, the mean free path of electron-phonon scattering is l ep It is mainly affected by the number of phonons and has no significant relationship with the electron energy. Since the number of phonons is related to temperature, it can be considered that at a specific temperature, l ep It is a relatively stable value. Figure 6 (b) shows the mean free path l of gold ee and l ep , it can be seen that in the range where the hot electron energy is less than 2eV, both free paths reach more than 20 nanometers.

[0080] After electron-electron scattering and electron-phonon scattering, the probability of hot electrons being transmitted from the initial position to the Schottky interface is exponentially decayed with the distance between the excitation point and the interface, which can be given by the following formula [:

[0081]

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

[0083] Therefore, in order to increase the probability of hot electrons successfully reaching the Schottky junction interface, we can start from two aspects. The first is to increase the free path of hot electrons. Under the premise that there are fewer defects inside the metal material, the free path of hot electrons is mainly determined by the type of material itself, so materials with a longer free path can be used. The second is to shorten the distance between the initial position of the hot electrons and the Schottky interface. The electric field distribution of the incident light can be adjusted to make the generation position of the hot electrons as close to the Schottky junction interface as possible, or ultra-thin metal materials can be used to confine the hot electrons near the Schottky interface.

[0084] The last aspect is to improve the strategy of enhancing photoelectric conversion efficiency from 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 also meet certain conditions. Specifically, according to the Fowler model, the kinetic energy component of hot electrons perpendicular to the Schottky interface must be higher than the barrier height before they can be injected into silicon. It can be considered that hot electrons are higher than the Fermi level E f The energy part of is kinetic energy. In this case, let the energy of the hot electron above the Fermi level be E d , then:

[0086]

[0087] in is the momentum of the hot electron, is the mode of the wave vector corresponding to the momentum. According to the above formula, the energy part perpendicular to the gold-silicon interface can be expressed as:

[0088]

[0089] In the above formula, k d⊥ represents the momentum perpendicular to the gold-silicon interface. Therefore, only the hot electrons with energy greater than the Schottky barrier height can be injected into silicon, that is, the following conditions are met:

[0090]

[0091] The image corresponding to the injection condition expressed in the above formula is as follows Figure 7As shown. That is, in momentum space, only those hot electrons whose momentum is distributed in the red cone area can be injected. The critical angle corresponding to this cone area is Ω, which satisfies the relationship Therefore, the probability of electron injection is the integral of the solid angle of this shadow area, divided by the total solid angle, that is:

[0092]

[0093] Also because Can be simplified to Therefore, the above formula can be further simplified as:

[0094]

[0095] From the above formula, we can see that the injection probability of hot electrons is related to their energy E d Closely related. d The larger the value, the higher the injection efficiency. d Much larger than the barrier height When , 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 points to the metal-silicon interface; but hot electrons with slightly lower energy can only be injected if their momentum direction is within the solid angle Ω, such as Figure 7 As shown. The hot electrons that fail to be injected will be reflected back into the metal at the interface, and their energy will gradually decrease due to various scattering processes, which greatly reduces the possibility of them being injected into silicon again. In order to increase the injection probability of hot electrons, a variety of strategies can be adopted. One strategy is to use double Schottky junctions, body Schottky junctions, rough surfaces, etc. These structures increase the contact surface between metal and silicon, expand the injection angle range, and thus improve the injection efficiency. Another strategy is to reduce the Schottky junction potential height, but it will also increase the dark current, thereby affecting the signal-to-noise ratio of the detector. Therefore, it is necessary to comprehensively consider the signal-to-noise ratio of the detector to decide whether to use this method.

[0096] In this embodiment, Fig.13 As shown, the steps for making the metal sensitive film are as follows:

[0097] Step 1, preparation of cleaning solution: No. Ⅰ cleaning solution is a solution obtained by mixing concentrated sulfuric acid and hydrogen peroxide in proportion; No. Ⅱ cleaning solution is a solution obtained by mixing ammonia water, hydrogen peroxide and deionized water in a set ratio; No. Ⅲ cleaning solution is a solution obtained by mixing concentrated hydrochloric acid, hydrogen peroxide and deionized water in a set ratio; the silicon wafer is placed in No. Ⅰ cleaning solution, No. Ⅱ cleaning solution and No. Ⅲ cleaning solution in turn for ultrasonic cleaning, and finally ultrasonic cleaning with deionized water, and then taken out for drying; it is mainly used to remove two types of pollutants: one is the oxide layer produced by slight oxidation of the surface of the silicon wafer when it has the opportunity to be exposed to the air during storage and transportation; the other is the dust, organic matter and metal salt adhered to the silicon substrate during the production, cutting and packaging process.

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

[0099] Step 3, silver particle deposition: Place the sample after EBL etching in the deposition solution and take it out after timing for 5s, 10s, 15s, and 20s.

[0100] Step 4, preparing etching solution: hydrogen peroxide and hydrofluoric acid are mixed in a set ratio to prepare etching solution.

[0101] Step 5, metal-assisted etching: Place the sample in the etching solution, set the etching temperature to 50-70 degrees Celsius, time it for 5-20 minutes, take it out, and the overall reaction formula 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 on the surface of the microstructured silicon. Place the etched sample in the dilute nitric acid solution for 20-40 minutes to completely dissolve the residual silver ions and then take it out.

[0103] Step 7, cleaning and storage: Wash the sample using an ultrasonic cleaner, repeat several times, blow dry the washed sample with nitrogen gas, and store it in a constant temperature drying oven.

[0104] Embodiment 2:

[0105] The present invention provides a method for preparing an infrared detector. Fig.12 As shown, the preparation method comprises the following steps:

[0106] 1) Design and process the mask.

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

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

[0109] 3) Spin-coat LOR and S1805 as the first layer of glue, use micro-nano lithography exposure process to form an electrode pattern on the silicon oxide surface, use lift-off process on the silicon wafer to perform exposure and development, transfer the first layer of mask pattern to silicon oxide, and make marks and center electrodes (P).

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

[0111] 4) Deposit metal by magnetron sputtering, plate 10nm chromium and 50nm gold on the silicon wafer, and remove the glue.

[0112] 5) Spin-coat AZ3100 as the second layer of adhesive, perform exposure and development, transfer the second layer of mask pattern to silicon oxide, and etch holes in the center and around the silicon wafer. Remove the adhesive.

[0113] The silicon hole etching method adopts dry etching. The spin coating speed of AZ3100 photoresist is 5000 rpm for 25 seconds, and then 5500 rpm for 3 seconds.

[0114] 6) Spin-coat the third layer of photoresist, expose and develop, transfer the third layer mask pattern to silicon oxide, plate 200nm aluminum and 10nm gold on the outer circle to make N electrode. Remove the resist.

[0115] Among them, the outer circle electrode is AL with a thickness of 200nm and gold with a thickness of 10nm.

[0116] 7) Perform annealing.

[0117] 8) Etch an array pattern in the hole at the center of the silicon oxide using EBL.

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

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

[0120] Based on an infrared detector prepared by the above method, this embodiment carries out a simulation experiment, wherein Fig. 9is a schematic diagram of the simulated structure corresponding to the back-illuminated absorption-enhanced photodetector. Fig.10 and Fig.11 The electric field distribution diagram and the absorption rate versus wavelength distribution curve obtained by simulating the back-illuminated absorption enhanced photodetector are shown in Figure 2. Fig.10 and Fig.11 It can be found that the infrared detector proposed in the present invention has high-performance photoelectric conversion efficiency and detector sensitivity.

[0121] The above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit the same. Although the present invention has been described in detail with reference to the above embodiments, those skilled in the art should understand that the technical solutions described in the above embodiments may still be modified, or some or all of the technical features may be replaced by equivalents. Such modifications or replacements do not deviate the essence of the corresponding technical solutions from the scope of the technical solutions of the embodiments of the present invention, and should all be included in the scope of the claims and specification of the present invention.

Claims

1. An infrared detector, characterized in that: It includes a substrate, a metal sensitive film, a light absorption enhancement structure and a current transmission structure; The metal sensitive film interface is roughened, a disordered nano-hole light trapping structure is etched, or nano-particles are deposited on the silicon substrate interface to increase the probability of hot electron injection at the Schottky interface; The steps for making the metal sensitive film are as follows: 1) Preparation of cleaning solution: No. Ⅰ cleaning solution is a solution obtained by mixing concentrated sulfuric acid and hydrogen peroxide in a certain proportion; No. Ⅱ cleaning solution is a solution obtained by mixing ammonia water, hydrogen peroxide and deionized water in a certain proportion; No. Ⅲ cleaning solution is a solution obtained by mixing concentrated hydrochloric acid, hydrogen peroxide and deionized water in a certain proportion; the silicon wafer is placed in No. Ⅰ cleaning solution, No. Ⅱ cleaning solution and No. Ⅲ cleaning solution in turn for ultrasonic cleaning. Finally, use deionized water to ultrasonically clean it, take it out and dry it; 2) Prepare the deposition solution: the concentration of silver nitrate is 0.0125-0.05 mol / L, and the ionized water, hydrofluoric acid and silver nitrate solution are prepared in a certain volume ratio; 3) Silver particle deposition: Place the sample after EBL etching in the deposition solution and take it out after 5s, 10s, 15s, and 20s; 4) preparing an etching solution: mixing hydrogen peroxide and hydrofluoric acid in a set ratio to prepare an etching solution; 5) Metal-assisted etching: Place the sample in the etching solution, set the etching temperature to 50-70 degrees Celsius, time for 5-20 minutes, take it out, the overall reaction formula is: Si+4AgNO3+4HF→H2SiF6+4Ag+4HNO3 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 on the surface of microstructured silicon. Place the etched sample in the dilute nitric acid solution for 20-40 minutes to completely dissolve the residual silver ions and then take it out. 7) Cleaning and storage: Wash the sample using an ultrasonic cleaner, repeat several times, blow dry the washed sample with nitrogen gas, and store it in a constant temperature drying oven; The light absorption enhancement structure includes a Schottky junction, and the Schottky junction is formed by contacting an arrayed pattern etched on a silicon substrate with a metal; The current transmission structure comprises 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 respectively derived from the P-type and N-type conductive structures.

2. An infrared detector according to claim 1, characterized in that: 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 completely filled with metal, and the metal is in contact with silicon to form the Schottky junction.

3. An infrared detector according to claim 2, characterized in that: The array pattern is a rectangular structure.

4. The infrared detector according to claim 1, characterized in that: The metal film includes one of metal particles or films of Au, Pt, Ni, Co, Ti, ITO and silicides thereof.

5. The infrared detector according to claim 2, characterized in that: An aluminum layer is arranged around the top of the silicon substrate, and the aluminum layer contacts the silicon substrate to form an ohmic contact. The aluminum layer is covered with a gold layer to form an outer ring electrode. The silicon oxide is covered with a chromium layer, and the chromium layer is covered by the gold layer to form a central electrode. After the light absorption enhancement structure generates current, the current is conducted through the central electrode and the outer ring electrode.

6. A method for preparing an infrared detector according to any one of claims 1 to 5, characterized in that: The preparation method comprises the following steps: 1) Design and process the mask; 2) obtaining a silicon wafer, wherein a layer of silicon dioxide is provided on the front side of the silicon wafer; 3) Spin-coat LOR and S1805 as the first layer of glue, use micro-nano lithography exposure process to form electrode patterns on the silicon oxide surface, use lift-off process on the silicon wafer, perform exposure and development, transfer the first layer of mask pattern to silicon oxide, and make marks and center electrodes; 4) Deposit metal by magnetron sputtering, plate 10-30nm chromium and 30-100nm gold on silicon wafer, and remove the glue; 5) Spin-coat AZ3100 as the second layer of adhesive, perform exposure and development, transfer the second layer of mask pattern to silicon oxide, etch holes in the center and around the silicon wafer, and remove the adhesive; 6) Spin-coat LOR and S1805 as the third layer of glue, expose and develop, plate 100-300nm aluminum and 10-30nm gold on the outer circle to make N electrode, and remove the glue; 7) performing annealing to form a Schottky contact; 8) Etching an array pattern in the hole at the center of the silicon oxide using EBL; 9) Spin-coat LOR and S1805 as the fourth layer of glue, expose and develop, plate metal, fill the array pattern with metal, make P electrodes, and remove glue.

7. The preparation method according to claim 6, characterized in that: The marks made in step 3) include silicon wafer marks and EBL processing marks, and the marks are 10-30 nm for chromium and 40-70 nm for metal layer.

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

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