Short-wave infrared detector

Abstract

To provide a short-wave infrared detector that achieves improved detection sensitivity for short-wave infrared radiation.SOLUTION: A short-wave infrared detector 1A includes a substrate 2, a thin film layer 3 provided on one surface side of the substrate 2, an anode electrode 4 and a cathode electrode 5 electrically connected to the thin film layer 3, and a metal layer 7 disposed in proximity to the thin film layer 3 on one surface side of the substrate 2. The metal layer 7 is formed by a plurality of island-like pieces 15 distributed in the direction of the surface of the substrate 2, separated from each other by grooves 16 forming a brain-like groove pattern.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present disclosure relates to short-wave infrared detectors. [Background technology]

[0002] An example of a conventional infrared detector is the infrared detector described in Patent Document 1. This conventional infrared detector includes a first lower superlattice layer of a first conductivity type, a second lower superlattice layer of the first conductivity type formed on the first lower superlattice layer, a superlattice absorption layer formed on the second lower superlattice layer, and an upper superlattice layer of a second conductivity type formed on the superlattice absorption layer. The second lower superlattice layer, the superlattice absorption layer, and the upper superlattice layer are formed with the same superlattice structure. The first lower superlattice layer is formed with a superlattice structure made of a different material from that of the second lower superlattice layer. As a result, the effective bandgap of the first lower superlattice layer is equal to or greater than the effective bandgap of the second lower superlattice layer. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Publication No. 2019-57639 Summary of the Invention [Problem to be solved by the invention]

[0004] In recent years, there has been remarkable progress in laser sensing technology for vehicle autonomous driving and collision prevention functions. Accordingly, the development of inexpensive, high-performance photodetectors in the infrared band has been progressing. Currently, for example, in the shortwave infrared (SWIR) band, which includes wavelengths of 1 μm to 2.5 μm, semiconductor photodetectors using substrates such as InGaAs are the mainstream. However, such elements are generally expensive, and for broader market applications, the emergence of elements using cheaper light-absorbing materials is desired.

[0005] The present disclosure has been made to solve the above-mentioned problems, and has an object to provide a short-wave infrared detector that improves detection sensitivity for short-wave infrared rays. [Means for solving the problem]

[0006] The gist of the present disclosure is as follows.

[0007] [1] A shortwave infrared detector comprising: a substrate; a thin film layer provided on one side of the substrate and sensitive to light in the shortwave infrared region; an anode electrode and a cathode electrode electrically connected to the thin film layer; and a metal layer arranged adjacent to the thin film layer on one side of the substrate, wherein the metal layer is composed of a plurality of island-shaped pieces separated from each other by sulci-like grooves distributed in the surface direction of the substrate.

[0008] In this shortwave infrared detector, a thin film layer sensitive to light in the shortwave infrared region is provided on one side of a substrate. While a thin film layer alone is likely to be insufficiently thick and therefore unlikely to provide sufficient shortwave infrared absorption, this shortwave infrared detector employs a metal layer disposed adjacent to the thin film layer to compensate for this shortwave infrared absorption. Increasing the volume of the metal layer can shift the resonance wavelength of the surface plasmon toward longer wavelengths, improving shortwave infrared absorption. However, increasing the thickness of the metal layer with increasing volume increases the reflection of incident light by the metal layer, reducing the amount of light incident on the thin film layer, potentially resulting in insufficient detection sensitivity. In contrast, in this shortwave infrared detector, the metal layer contains multiple island-shaped pieces separated from each other by sulci-like grooves distributed in the plane direction of the substrate. The island-shaped pieces separated by the grooves are distributed in a thin layer in the metal layer, achieving a good balance between ensuring the volume of the metal layer and maintaining the amount of light incident on the thin film layer. Therefore, this short wave infrared detector has improved detection sensitivity for short wave infrared rays.

[0009] [2] A shortwave infrared detector as described in [1], wherein when the width of an island-shaped piece is defined as the length of the longest line segment that passes through any two points that equally divide the length of the outer edge of the island-shaped piece and equally divides the area of ​​the island-shaped piece, the width of the island-shaped piece is greater than the thickness of the island-shaped piece along the direction perpendicular to the substrate.

[0010] In this case, by making the width of the island-shaped pieces larger than the thickness, the island-shaped pieces become thinner layers, which allows a better balance to be maintained between ensuring a sufficient volume of the metal layer and maintaining the amount of light incident on the thin film layer, thereby further improving the detection sensitivity for short-wave infrared radiation.

[0011] [3] The shortwave infrared detector according to [1] or [2], wherein the island-shaped pieces have a thickness of 3 nm or more and less than 20 nm. By making the island-shaped pieces 3 nm or more thick, the volume of the metal layer can be secured sufficiently, and the absorption of shortwave infrared rays can be sufficiently increased. By making the island-shaped pieces less than 20 nm thick, an increase in the reflection of incident light by the metal layer can be avoided, and a sufficient amount of light can be maintained incident on the thin film layer.

[0012] [4] The short-wave infrared detector according to any one of [1] to [3], wherein the groove width is 10 nm or less. By setting the groove width to 10 nm or less, a strong electric field enhancement effect due to surface plasmon resonance is achieved in the minute gaps between the island-shaped pieces formed by the grooves. This allows for more sufficient improvement in the absorbency of short-wave infrared radiation.

[0013] [5] The short-wave infrared detector according to any one of [1] to [4], wherein the metal layer is made of Au or Ag. By making the metal layer of Au or Ag, surface plasmon resonance in the metal layer can be more effectively induced, thereby further enhancing the absorption of short-wave infrared radiation.

[0014] [6] The shortwave infrared detector according to any one of [1] to [5], wherein the grooves penetrate the metal layer in the thickness direction, and a layer underlying the metal layer is exposed at the positions of the grooves in a plan view of the metal layer. In this case, since the grooves penetrate the metal layer in the thickness direction, reflection of incident light by the metal layer is reduced, and it is possible to increase the amount of light incident on the thin film layer.

[0015] [7] The shortwave infrared detector according to any one of [1] to [6], further comprising an insulating layer covering the thin film layer, the anode electrode, and the cathode electrode, and the metal layer being disposed on the insulating layer. In this case, the insulating layer can effectively prevent short-circuiting between the anode electrode and the cathode electrode. Furthermore, by selecting a material with a high refractive index for incident light as the material for the insulating layer underlying the metal layer, the resonance wavelength of the surface plasmon can be shifted to a longer wavelength side. Therefore, the absorption of shortwave infrared light can be further enhanced.

[0016] [8] The shortwave infrared detector according to any one of [1] to [6], further comprising: an insulating layer covering the thin film layer, the anode electrode, and the cathode electrode; and a surface layer disposed on the insulating layer and having higher wettability with respect to the metal constituting the metal layer than the insulating layer, the metal layer being disposed on the surface layer. In this case, the metal layer is easily wetted and spread on the surface layer during formation, making it easy to form island-shaped pieces having a sufficient width relative to its thickness. This allows for an even better balance between ensuring a sufficient volume of the metal layer and maintaining the amount of light incident on the thin film layer.

[0017] [9] The short-wave infrared detector according to any one of [1] to [8], wherein the anode electrode and the cathode electrode are provided on the substrate, and the thin film layer has a first portion in contact with the substrate and a second portion that overlaps the anode electrode and the cathode electrode. In this case, a sufficient contact area between the anode electrode and the thin film layer and the cathode electrode can be ensured, resulting in good electrical conduction. This improves the efficiency of photocurrent extraction.

[0018]

[10] The shortwave infrared detector according to any one of [1] to [8], wherein the entire thin film layer is provided in contact with the substrate, and the anode electrode and the cathode electrode are provided on the thin film layer. In this case, the thin film layer can be formed flat on the substrate, thereby improving the uniformity of the thin film layer. By improving the uniformity of the thin film layer, the occurrence of areas in which the photoelectric conversion efficiency is lower than the surrounding area is suppressed, and the detection sensitivity for shortwave infrared rays is improved.

[0019]

[11] The short-wave infrared detector according to any one of [1] to

[10] , wherein the metal layer is disposed on the thin film layer. In this case, the thin film layer underlying the metal layer has a relatively high refractive index for incident light, which can shift the resonance wavelength of the surface plasmon to a longer wavelength. This can further enhance the absorption of short-wave infrared light. Furthermore, the proximity of the metal layer, which is the excitation source of the surface plasmon, to the thin film layer can further improve the detection sensitivity for short-wave infrared light.

[0020]

[12] The short-wave infrared detector according to any one of [1] to

[11] , wherein a light-reflecting layer is provided on the other side of the substrate. In this case, when light is incident from the metal layer side, light that is not absorbed by the thin film layer and passes through the substrate can be returned to the thin film layer by the light-reflecting layer. Therefore, it is possible to increase the amount of light incident on the thin film layer.

[0021]

[13] The short-wave infrared detector according to any one of [1] to

[11] , further comprising a dielectric layer as the outermost layer on one side of the substrate, and a light-reflecting layer on the dielectric layer. In this case, when light is incident from the substrate side, light that is not absorbed by the thin film layer and passes through the metal layer can be returned to the thin film layer by the light-reflecting layer. Therefore, it is possible to increase the amount of light incident on the thin film layer.

[0022]

[14] The shortwave infrared detector according to any one of [1] to

[13] , wherein the thin film layer is made of a carbon nanomaterial. Carbon nanomaterials are direct optical transition materials and have a high absorption coefficient over a wide wavelength range of shortwave infrared radiation. By using a carbon nanomaterial as the thin film layer and arranging a metal layer adjacent to it, the absorption of shortwave infrared radiation is sufficiently compensated for. Therefore, the detection sensitivity for shortwave infrared radiation is improved.

[0023]

[15] The shortwave infrared detector according to any one of [1] to

[14] , wherein the thin film layer is made of carbon nanotubes. Carbon nanotubes are direct optical transition materials and have a high absorption coefficient over a wide wavelength range of shortwave infrared rays. By using carbon nanotubes as the thin film layer and arranging the metal layer 7 adjacent to them, the absorption of shortwave infrared rays is sufficiently compensated for. Therefore, the detection sensitivity for shortwave infrared rays is improved. [Effects of the Invention]

[0024] According to the present disclosure, the detection sensitivity for short-wave infrared rays is improved. [Brief explanation of the drawings]

[0025] [Figure 1] 1 is a schematic cross-sectional view showing a short-wave infrared detector according to a first embodiment of the present disclosure. [Figure 2] FIG. 2 is a schematic enlarged view of a main part of a metal layer. [Figure 3] FIG. 4 is a schematic cross-sectional view showing a short-wave infrared detector according to a second embodiment of the present disclosure. [Figure 4] FIG. 10 is a schematic cross-sectional view showing a short-wave infrared detector according to a third embodiment of the present disclosure. [Figure 5] FIG. 11 is a schematic cross-sectional view showing a short-wave infrared detector according to a modified example of the third embodiment. [Figure 6] FIG. 10 is a schematic cross-sectional view showing a short-wave infrared detector according to a fourth embodiment of the present disclosure. [Figure 7] FIG. 10 is a schematic cross-sectional view showing a short-wave infrared detector according to a fifth embodiment of the present disclosure. [Figure 8] FIG. 10 is a schematic cross-sectional view showing a short-wave infrared detector according to a sixth embodiment of the present disclosure. [Figure 9] 1(a) to 1(d) are diagrams showing the relationship between the thickness of a metal layer formed by vapor deposition and the film formation state. [Figure 10] FIG. 10 is a diagram showing the relationship between the thickness of the metal layer and the extinction spectrum in the short wavelength band. [Figure 11] FIG. 10 is a diagram showing the relationship between the thickness of a metal layer and detection sensitivity. [Figure 12] FIG. 10 is a diagram showing the relationship between the thickness of an insulating layer and detection sensitivity. DETAILED DESCRIPTION OF THE INVENTION

[0026] Hereinafter, preferred embodiments of a short-wave infrared detector according to one aspect of the present disclosure will be described in detail with reference to the drawings.

[0027] In the following embodiments and drawings of the short-wave infrared detector, one constituent unit of the incident region of incident light to be detected is shown as a main part. In an actual photodetector, these constituent units may be arrayed at a predetermined pitch on a substrate.

[0028] [First embodiment] 1 is a schematic cross-sectional view showing a short-wave infrared detector according to a first embodiment of the present disclosure. As shown in FIG. 1, a short-wave infrared detector 1A according to the first embodiment includes a substrate 2, a thin film layer 3, an anode electrode 4, a cathode electrode 5, an insulating layer 6, and a metal layer 7.

[0029] For ease of explanation, the substrate 2 side will be defined as the back surface of the shortwave infrared detector 1A, and the metal layer 7 side will be defined as the front surface of the shortwave infrared detector 1A. The shortwave infrared detector 1A may be either a front-illuminated type in which incident light I is incident from the front surface, or a back-illuminated type in which incident light I is incident from the back surface. In this embodiment, a front-illuminated type shortwave infrared detector will be exemplified.

[0030] In the shortwave infrared detector 1A, when light in the shortwave infrared region (for example, a wavelength range including wavelengths of 1 μm to 2.5 μm) is incident as incident light I, the incident light I generates a localized inhomogeneous electric field in and near the metal layer 7. In the shortwave infrared detector 1A, by utilizing the effect of this localized inhomogeneous electric field, direct optical transition in the thin film layer 3 becomes possible, and sufficient light absorption can occur in the thin film layer 3. In the shortwave infrared detector 1A, the light absorption occurring in the thin film layer 3 is extracted to the outside as a photocurrent, thereby realizing detection of shortwave infrared. As described above, a wavelength range including wavelengths of 1 μm to 2.5 μm is exemplified as the range of the shortwave infrared region, but the detection range of the shortwave infrared detector 1A need only include at least this wavelength range, and may be a wider wavelength range.

[0031] The substrate 2 has, for example, a Si layer 11 and a SiO2 layer 12 provided on one side of the Si layer 11. When viewed in the thickness direction of the substrate 2, the substrate 2 has, for example, a rectangular shape. The thickness of the Si layer 11 is, for example, 50 μm or more and 600 μm or less. The thickness of the SiO2 layer 12 is, for example, 0.2 μm or more and 10 μm or less.

[0032] The anode electrode 4 and the cathode electrode 5 are electrically connected to the thin film layer 3 and extract photocurrent generated in the thin film layer 3 by the formation of a localized non-uniform electric field. The anode electrode 4 and the cathode electrode 5 have, for example, a rectangular cross section and are provided on the SiO2 layer 12 of the substrate 2 with equal thickness and width. The anode electrode 4 and the cathode electrode 5 are spaced apart from each other and extend parallel to each other in a straight line in one in-plane direction of the substrate 2. The thickness of the anode electrode 4 and the cathode electrode 5 is, for example, approximately several hundred nanometers. The distance between the anode electrode 4 and the cathode electrode 5 is, for example, 10 μm or less.

[0033] The anode electrode 4 is formed of a metal with a relatively high work function, such as Pd (palladium), Au (gold), or Pt (platinum). The anode electrode 4 may be formed of a compound material containing these metals. The anode electrode 4 is not limited to a single layer, and may be formed of multiple layers. The cathode electrode 5 is formed of a metal with a relatively low work function, such as Sc (scandium), Y (yttrium), or Th (thorium). The cathode electrode 5 may be formed of a compound material containing these metals. The cathode electrode 5 is not limited to a single layer, and may be formed of multiple layers.

[0034] The thin film layer 3 is a layer sensitive to light in the short-wave infrared region. Examples of materials that constitute the thin film layer 3 include quantum dots, graphene, and carbon nanomaterials. In this embodiment, the thin film layer 3 is a layer formed of carbon nanotubes. Carbon nanotubes are cylindrical nanomaterials made of carbon atoms. Carbon nanotubes are direct optical transition materials for incident light I and have a high absorption coefficient over a wide wavelength range of short-wave infrared light. When viewed from the thickness direction of the substrate 2, the thin film layer 3 has, for example, a rectangular shape, and is arranged so as to overlap with the anode electrode 4 and the cathode electrode 5. The thickness of the thin film layer 3 is, for example, several nm to several hundred nm.

[0035] In this embodiment, the thin film layer 3 has a first portion 3A in contact with the substrate 2 and a second portion 3B that overlaps the anode electrode 4 and the cathode electrode 5. The first portion 3A is provided flat on the SiO2 layer 12 of the substrate 2 so as to connect the anode electrode 4 and the cathode electrode 5. The second portion 4B has a portion that overlaps the side surfaces of the anode electrode 4 and the cathode electrode 5, and a portion that overlaps the top surfaces of the anode electrode 4 and the cathode electrode 5. The second portion 3B may overlap the entire top surfaces of the anode electrode 4 and the cathode electrode 5, or may overlap only a portion of them.

[0036] The insulating layer 6 is a layer having electrical insulation properties. In this embodiment, the insulating layer 6 is provided so as to cover the thin film layer 3, the anode electrode 4, and the cathode electrode 5, and serves as a base layer for the metal layer 7. From the viewpoint of bringing the metal layer 7 close to the thin film layer 3, it is preferable that the thickness of the insulating layer 6 is smaller than the thicknesses of the anode electrode 4 and the cathode electrode 5, for example. The lower limit of the thickness of the insulating layer 6 is set based on the minimum thickness that can maintain electrical insulation, and the upper limit of the thickness of the insulating layer 6 is set based on the penetration depth of surface plasmons. As an example, the thickness of the insulating layer 6 is 10 nm to 50 nm, for example.

[0037] From the viewpoint of shifting the resonance wavelength of surface plasmons generated in the metal layer 7 to the longer wavelength side, it is preferable to select a material having a relatively high refractive index for short-wave infrared rays as the constituent material of the insulating layer 6. Examples of such constituent materials include Al2O3 (alumina) and SiN (silicon nitride film). In the short-wave infrared region, the refractive index of Al2O3 (alumina) is approximately 1.7 to 1.8, and the refractive index of SiN (silicon nitride film) is approximately 2.0 to 2.2.

[0038] The metal layer 7 is a nanostructured layer formed using a metal. Examples of metals include Au (gold) and Ag (silver). The metal layer 7 is disposed adjacent to the thin film layer 3 on one side of the substrate 2. In this embodiment, the metal layer 7 is provided flat on the insulating layer 6. As shown in FIG. 2 , the metal layer 7 is composed of multiple island-shaped pieces 15 separated from each other by sulcus-like grooves 16 distributed in the plane direction of the substrate 2. The sulcus-like shape refers to the overall shape of the two-dimensionally extending grooves 16 in a planar view of the metal layer 7. The shape is not a simple straight line or a curved line according to a geometric rule, but rather a state in which the island-shaped pieces 15 extend in a seemingly random manner with fine bends. Due to the sulcus-like grooves 16, each island-shaped piece 15 is not a simple circle or ellipse, but has a distorted shape, with different shapes and areas. In a planar view, the metal layer 7 does not resemble a collection of particles, but rather a thin layer (similar to a thin film) with gaps formed by the grooves 16.

[0039] The width W of the island-shaped piece 15 is greater than the thickness T of the island-shaped piece 15. Here, the width W of the island-shaped piece 15 is the length of the longest line segment that passes through any two points that equally divide the length of the outer edge of the island-shaped piece 15 and equally divides the area of ​​the island-shaped piece 15. The thickness T of the island-shaped piece 15 is the length along the direction perpendicular to the substrate 2 (see FIG. 1). Here, the thickness T of the island-shaped piece 15 is equivalent to the distance between one surface and the other surface of the metal layer 7.

[0040] The thickness T of the island-shaped pieces 15 is, for example, not less than 3 nm and less than 20 nm. The thickness T of the island-shaped pieces 15 is preferably close to the percolation threshold due to the surface energy at the interface between the insulating layer 6 and the metal layer 7. When the insulating layer 6 is made of Al2O3 (alumina) and the metal layer 7 is made of Au (gold), the percolation threshold due to the surface energy at the interface between the insulating layer 6 and the metal layer 7 is about 5 nm to 10 nm, and the thickness T of the island-shaped pieces 15 is also preferably about 5 nm to 10 nm.

[0041] The average width W of the island-shaped pieces 15 is, for example, 15 nm or more and 100 nm or less. The average width W of the island-shaped pieces 15 is preferably three times or more, and more preferably five times or more, the thickness T of the island-shaped pieces 15. When the metal layer 7 is formed by metal vapor deposition as described below, the average width W of the island-shaped pieces 15 tends to increase as the thickness T of the metal layer 7 increases. As an example, when the thickness T of the island-shaped pieces 15 is 6 nm, the lower limit of the average width W of the island-shaped pieces 15 is about 20 nm.

[0042] The dimensions of the island pieces 15 can be measured using, for example, a scanning electron microscope (SEM). For example, the metal layer 7 is imaged with the scanning electron microscope (SEM), and an image analysis tool (ImageJ, for example) is applied to the image to measure the area of ​​each island piece 15. The diameter of a circle having an area equal to the area of ​​each island piece 15 is then calculated, and the calculated diameter is used as the width W of each island piece 15. Statistical analysis can also be used to calculate the lower limit of the average width W of the island pieces 15. For example, a histogram of the diameter values ​​of the circles corresponding to each island piece 15 is generated using statistical analysis software, and the diameter range with the largest count is used as the lower limit of the average width W of the island pieces 15.

[0043] In this embodiment, all of the island-shaped pieces 15 constituting the metal layer 7 satisfy the relationship between the width W of the island-shaped pieces 15 and the thickness T of the island-shaped pieces 15, but it is also possible for some of the island-shaped pieces 15 constituting the metal layer 7 to satisfy the relationship between the width W of the island-shaped pieces 15 and the thickness T of the island-shaped pieces 15. In this case, 50% or more of the island-shaped pieces 15 constituting the metal layer 7 may satisfy the relationship between the width W of the island-shaped pieces 15 and the thickness T of the island-shaped pieces 15, or 70% or more may satisfy the relationship between the width W of the island-shaped pieces 15 and the thickness T of the island-shaped pieces 15.

[0044] The grooves 16 separating the island pieces 15 form a random mesh pattern surrounding each of the randomly shaped island pieces 15. The width Tm of the grooves 16 is sufficiently smaller than the width W of the island pieces 15. The width Tm of the grooves 16 does not necessarily have to be constant and may vary depending on the position. Here, the width Tm of the grooves 16 is the distance between the point where a line segment perpendicular to a line segment passing through the center of the groove 16 intersects with one adjacent island piece 15 and the point where the line segment intersects with the other adjacent island piece 15. The width Tm of the grooves 16 is, for example, 10 nm or less. In this case, the width Tm of all parts of the grooves 16 may be 10 nm or less (the maximum value of the width Tm of the grooves 16 may be 10 nm or less), or the average value of the width Tm of all parts of the grooves 16 may be 10 nm or less.

[0045] In this embodiment, the grooves 16 are formed across one surface and the other surface of the metal layer 7 and penetrate the metal layer 7 in the thickness direction. Therefore, in a plan view of the metal layer 7, the layer underlying the metal layer 7 (here, the insulating layer 6) is exposed at the locations of the grooves 16. As an example, the entire grooves 16 may penetrate the metal layer 7 in the thickness direction. In this case, adjacent island-shaped pieces 15, 16 are separated from each other by the grooves 16. The entire grooves 16 do not necessarily have to penetrate the metal layer 7 in the thickness direction; at least a portion or the entire grooves 16 may have a bottom on the underlying layer side. In this case, adjacent island-shaped pieces 15, 16 are connected to each other at the locations where the bottoms are formed.

[0046] The metal layer 7 having the above-described configuration can be formed, for example, by vapor deposition of a thin metal film on an underlayer. In this embodiment, the thin film layer 3 is formed on one side of the substrate 2, for example, by spray coating, so as to cover the anode electrode 4 and the cathode electrode 5. Next, the insulating layer 6 is formed so as to cover the thin film layer 3, for example, by atomic layer deposition (ALD) or chemical vapor deposition (CVD). After the insulating layer 6 is formed, polyimide tape such as Kapton (registered trademark) tape is placed on the insulating layer 6 so as to sandwich the area where the metal layer 7 is to be formed, and nanostructures made of a thin metal film are formed on the insulating layer 6 by resistance heating using the tape. After the metal layer 7 is formed, the tape is peeled off from the insulating layer 6, and organic cleaning is performed.

[0047] In this method, as the thickness of the metal layer 7 formed by vapor deposition (thickness T of the island-shaped pieces 15) increases, the width W of the island-shaped pieces 15 tends to increase. Therefore, when forming multiple island-shaped pieces 15 separated from each other by the above-mentioned sulcus-like grooves 16, it is preferable to adjust the deposition rate and accurately control the thickness of the metal layer 7. The deposition rate is preferably, for example, from 0.5 Å / sec to 2.0 Å / sec, and more preferably from 0.1 Å / sec to 0.5 Å / sec.

[0048] As described above, in the shortwave infrared detector 1A, the thin film layer 3, which is sensitive to light in the shortwave infrared region, is provided on one side of the substrate 2. It is expected that the thin film layer 3 alone will be too thin and will not be able to absorb shortwave infrared light. However, in the shortwave infrared detector 1A, the metal layer 7 is disposed in close proximity to the thin film layer 3, thereby compensating for the shortwave infrared absorption. If the volume of the metal layer 7 increases, the resonance wavelength of the surface plasmon can be shifted to longer wavelengths, thereby increasing the absorption of shortwave infrared light. However, if the thickness of the metal layer 7 increases with the increase in volume, the reflection of incident light I by the metal layer 7 increases, reducing the amount of light incident on the thin film layer 3. As a result, it is thought that sufficient detection sensitivity cannot be obtained.

[0049] In contrast, in the shortwave infrared detector 1A, a plurality of island-like pieces 15 separated from each other by sulcus-like grooves 16 are distributed in the metal layer 7 in the surface direction of the substrate 2. The island-like pieces 15 separated by the grooves 16 are distributed in the metal layer 7 in the form of thin layers, which makes it possible to maintain a good balance between ensuring the volume of the metal layer 7 and maintaining the amount of light incident on the thin film layer 3. Therefore, the shortwave infrared detector 1A improves the detection sensitivity to shortwave infrared rays.

[0050] In this embodiment, the width W of the island-shaped pieces 15 is larger than the thickness T of the island-shaped pieces 15. By making the width W of the island-shaped pieces 15 larger than the thickness T, the island-shaped pieces 15 become thinner layers, which makes it possible to maintain a better balance between ensuring a sufficient volume of the metal layer 7 and maintaining the amount of light incident on the thin film layer 3. This further improves the detection sensitivity for short-wave infrared rays.

[0051] In this embodiment, the thickness T of the island-shaped pieces 15 is 3 nm or more and less than 20 nm. By setting the thickness T of the island-shaped pieces 15 to 3 nm or more, a sufficient volume of the metal layer 7 can be ensured, and the absorption of short-wave infrared rays can be sufficiently enhanced. On the other hand, by setting the thickness T of the island-shaped pieces 15 to less than 20 nm, an increase in the reflection of the incident light I by the metal layer 7 can be avoided, and a sufficient amount of light incident on the thin film layer 3 can be maintained.

[0052] In this embodiment, the width Tw of the grooves 16 is 10 nm or less. By setting the width Tw of the grooves 16 to 10 nm or less, a strong electric field enhancement effect due to surface plasmon resonance is achieved in the minute gaps between the island pieces 15, 16 formed by the grooves 16. This allows the absorbency of short-wave infrared radiation to be further improved.

[0053] In this embodiment, the metal layer 7 is made of Au or Ag. By making the metal layer 7 of Au or Ag, surface plasmon resonance can be more effectively generated in the metal layer 7. Therefore, the absorbency of short-wave infrared rays can be further sufficiently improved.

[0054] In this embodiment, the grooves 16 penetrate the metal layer 7 in the thickness direction, and in a plan view of the metal layer 7, the layer underlying the metal layer 7 is exposed at the positions of the grooves 16. In this way, since the grooves 16 penetrate the metal layer 7 in the thickness direction, the reflection of the incident light I by the metal layer 7 is reduced, and it is possible to increase the amount of light incident on the thin film layer 3.

[0055] In this embodiment, an insulating layer 6 is provided so as to cover the thin film layer 3, the anode electrode 4, and the cathode electrode 5, and the metal layer 7 is provided on the insulating layer 6. With this configuration, the insulating layer 6 can effectively prevent short circuits between the anode electrode 4 and the cathode electrode 5. Furthermore, by selecting a material with a high refractive index for incident light I as the material for the insulating layer 6, which serves as an underlayer for the metal layer 7, the resonance wavelength of the surface plasmon can be shifted to a longer wavelength side. Therefore, the absorbency for short-wave infrared light can be further improved.

[0056] In this embodiment, the anode electrode 4 and the cathode electrode 5 are provided on the substrate 2, and the thin film layer 3 has a first portion 3A in contact with the substrate 2 and a second portion 3B that overlaps the anode electrode 4 and the cathode electrode 5. This configuration ensures a sufficient contact area between the anode electrode 4 and the cathode electrode 5 and the thin film layer 3, thereby achieving good conduction. This improves the efficiency of extracting photocurrent.

[0057] In this embodiment, the thin film layer 3 is made of a carbon nanomaterial or carbon nanotubes. Carbon nanomaterials and carbon nanotubes are direct optical transition materials and have a high absorption coefficient for a wide wavelength band of short-wave infrared light. By using a carbon nanomaterial or carbon nanotubes as the thin film layer 3 and arranging the metal layer 7 in close proximity thereto, the absorption of short-wave infrared light is sufficiently compensated for. Therefore, the detection sensitivity for short-wave infrared light is improved.

[0058] [Second embodiment] Fig. 3 is a schematic cross-sectional view showing a shortwave infrared detector according to a second embodiment of the present disclosure. As shown in Fig. 3, the shortwave infrared detector 1B according to the second embodiment differs from the first embodiment in the positional relationship between the thin film layer 3 and the anode electrode 4 and cathode electrode 5. More specifically, in the shortwave infrared detector 1B, the thin film layer 3 is provided flat so that the entire thin film layer 3 is in contact with the substrate 2 (SiO2 layer 12), and the anode electrode 4 and cathode electrode 5 are provided on the flat thin film layer 3.

[0059] In this shortwave infrared detector 1B, as in the first embodiment, a good balance can be maintained between ensuring the volume of the metal layer 7 and maintaining the amount of light incident on the thin film layer 3. This improves the detection sensitivity for shortwave infrared rays. Furthermore, in the shortwave infrared detector 1B, the thin film layer 3 can be formed flat on the substrate 2, which improves the uniformity of the thin film layer 3. The improved uniformity of the thin film layer 3 prevents the occurrence of areas where the photoelectric conversion efficiency is inferior to the surrounding areas, thereby improving the detection sensitivity for shortwave infrared rays.

[0060] [Third embodiment] FIG. 4 is a schematic cross-sectional view showing a shortwave infrared detector according to a third embodiment of the present disclosure. As shown in FIG. 4, a shortwave infrared detector 1C according to the third embodiment differs from the first embodiment in the positional relationship between the thin film layer 3 and the metal layer 7. More specifically, in the shortwave infrared detector 1C, the metal layer 7 is formed on the thin film layer 3. As in the first embodiment, the thin film layer 3 has a first portion 3A in contact with the substrate 2 and a second portion 3B that overlaps the anode electrode 4 and the cathode electrode 5. The metal layer 7 has a first portion 7A that overlaps the first portion 3A of the thin film layer 3 and a second portion 7B that overlaps the second portion 3B of the thin film layer 3. An insulating layer 6 is provided to cover the thin film layer 3 and the metal layer 7.

[0061] In this short-wave infrared detector 1C, as in the first embodiment, a good balance can be maintained between ensuring the volume of the metal layer 7 and maintaining the amount of light incident on the thin film layer 3. Therefore, the detection sensitivity for short-wave infrared rays is improved. Furthermore, because the thin film layer 3, which serves as the base layer for the metal layer 7, has a relatively high refractive index with respect to the incident light I, the resonance wavelength of the surface plasmon can be shifted to the longer wavelength side. Therefore, the absorption of short-wave infrared rays can be further sufficiently improved. Furthermore, since the metal layer 7, which is the excitation source of the surface plasmon, is located close to the thin film layer 3, the detection sensitivity for short-wave infrared rays is further improved.

[0062] FIG. 5 is a schematic cross-sectional view showing a shortwave infrared detector according to a modification of the third embodiment. As shown in FIG. 5, the shortwave infrared detector 1Ca according to this modification differs from the shortwave infrared detector 1C in that the metal layer 7 on the thin film layer 3 has only a first portion 7A that overlaps the first portion 3A of the thin film layer 3. The second portion 7B of the metal layer 7 is removed by photolithography or the like after the metal layer 7 is formed on the thin film layer 3. This configuration also achieves the same effects as the shortwave infrared detector 1C. Furthermore, because the metal layer 7 is spaced apart from the anode electrode 4 and the cathode electrode 5, the occurrence of short circuits between the metal layer 7 and the anode electrode 4 and the cathode electrode 5 can be effectively suppressed.

[0063] [Fourth embodiment] Fig. 6 is a schematic cross-sectional view showing a short-wave infrared detector according to a fourth embodiment of the present disclosure. As shown in Fig. 6, a short-wave infrared detector 1D according to the fourth embodiment differs from the first embodiment in that a light-reflecting layer 21 is provided on the other surface side of the substrate 2. In the example of Fig. 6, the light-reflecting layer 21 is provided flatly over the entire surface of the other surface side of the substrate 2 (the surface of the Si layer 11 opposite the SiO2 layer 12). An example of a material for the light-reflecting layer 21 is a thin film of Au having a thickness of 50 nm or more.

[0064] In this short-wave infrared detector 1D, as in the first embodiment, a good balance can be maintained between ensuring the volume of the metal layer 7 and maintaining the amount of light incident on the thin film layer 3. Therefore, the detection sensitivity for short-wave infrared rays is improved. Furthermore, in the short-wave infrared detector 1D, when light is incident from the metal layer 7 side, incident light I that is not absorbed by the thin film layer 3 and passes through the substrate 2 can be returned to the thin film layer 3 by the light reflecting layer 21. Therefore, it is possible to increase the amount of light incident on the thin film layer 3.

[0065] [Fifth embodiment] 7 is a schematic cross-sectional view showing a short-wave infrared detector according to a fifth embodiment of the present disclosure. As shown in Fig. 7, a short-wave infrared detector 1E according to the fifth embodiment differs from the first embodiment in the configuration of layers outside the metal layer 7 on one surface side of the substrate 2.

[0066] More specifically, the short-wave infrared detector 1E includes a dielectric layer 31 on the metal layer 7 as the outermost layer on one surface of the substrate 2, and a light-reflecting layer 32 on the dielectric layer 31. Examples of materials for the dielectric layer 31 include SiN and SiO2. Examples of materials for the light-reflecting layer 32 include a thin film of Au having a thickness of 50 nm or more. In the example of FIG. 7, the dielectric layer 31 is provided so as to cover the entire metal layer 7, and the surface on which the light-reflecting layer 32 is provided is a flat surface. The light-reflecting layer 32 is provided flat on the surface of the dielectric layer 31 opposite the metal layer 7.

[0067] In this short-wave infrared detector 1E, as in the first embodiment, a good balance can be maintained between ensuring the volume of the metal layer 7 and maintaining the amount of light incident on the thin film layer 3. Therefore, the detection sensitivity for short-wave infrared rays is improved. Furthermore, by using the short-wave infrared detector 1E as a back-illuminated type in which incident light I is incident from the back surface, light that is not absorbed by the thin film layer 3 and that passes through the metal layer 7 can be returned to the thin film layer 3 by the light-reflecting layer 32. Therefore, it is possible to increase the amount of light incident on the thin film layer 3.

[0068] [Sixth embodiment] Fig. 8 is a schematic cross-sectional view showing a shortwave infrared detector according to a sixth embodiment of the present disclosure. As shown in Fig. 8, the shortwave infrared detector 1F according to the sixth embodiment differs from the first embodiment in that a surface layer having higher wettability with respect to the metal constituting the metal layer 7 than the insulating layer 6 is provided on the insulating layer 6. In the example of Fig. 8, a surface layer 41 is provided so as to cover the entire surface of the insulating layer 6, and the metal layer 7 is provided on the surface layer 41. The surface layer 41 is an electrically insulating layer, similar to the insulating layer 6. When the insulating layer 6 is made of Al2O3 (alumina), the surface layer 41 can be made of, for example, ZnO (zinc oxide).

[0069] In this shortwave infrared detector 1F, as in the first embodiment, a good balance can be maintained between ensuring the volume of the metal layer 7 and maintaining the amount of light incident on the thin film layer 3. Therefore, the detection sensitivity for shortwave infrared rays is improved. Furthermore, in the shortwave infrared detector 1F, the metal layer 7 is more likely to wet and spread on the surface layer 41 during formation, making it easier to form island-shaped pieces 15 that have a sufficient width relative to their thickness. Therefore, an even better balance can be maintained between ensuring the volume of the metal layer 7 and maintaining the amount of light incident on the thin film layer 3.

[0070] [Example] Hereinafter, examples of the present disclosure will be described.

[0071] 9(a) to 9(d) are diagrams showing the relationship between the thickness and deposition state of a metal layer formed by vapor deposition. FIG. 9(a) shows the deposition state of a metal layer when the metal layer is 3 nm thick, and FIG. 9(b) shows the deposition state of a metal layer when the metal layer is 6 nm thick. FIG. 9(c) shows the deposition state of a metal layer when the metal layer is 9 nm thick, and FIG. 9(d) shows the deposition state of a metal layer when the metal layer is 20 nm thick. In this example, in a sample of a short-wave infrared detector conforming to the configuration of the first embodiment, Au (gold) was deposited on an insulating layer made of Al2O3 (alumina) using resistance heating, and the deposition state of the metal layer was observed with a scanning electron microscope (SEM). The thickness of the metal layer is equivalent to the thickness of the island-shaped pieces.

[0072] The results shown in Figures 9(a) to 9(d) reveal that the film formation state of the metal layer differs depending on the thickness of the metal layer formed by vapor deposition. When the metal layer is 3 nm thick, sulci-like grooves and multiple island-like pieces separated by these grooves can be seen, but the island shapes are not particularly distorted, and when viewed from above, the metal layer appears to be more like a collection of particles. When the metal layer is 6 nm or 9 nm thick, the sulci-like grooves have a more complex shape and the island shapes are more distorted than when the metal layer is 3 nm thick. Therefore, when viewed from above, the metal layer appears to be a thin layer with gaps caused by the grooves (close to a thin film). On the other hand, when the metal layer is 20 nm thick, the grooves are shallower and the island outlines are unclear. Therefore, when viewed from above, the metal layer appears to be almost identical to a thin film.

[0073] Figure 10 shows the relationship between the thickness of the metal layer and the extinction spectrum in the shortwave wavelength band. In Figure 10, the horizontal axis represents wavelength, and the vertical axis represents the extinction rate. The extinction rate is calculated by subtracting the amount of reflection and the amount of transmission from the amount of incident light, and is calculated as "1 - amount of reflection - amount of transmission" where the amount of incident light is set to 1. In other words, the extinction rate here is a parameter that indicates the absorption efficiency of incident light in the carbon nanotube layer.

[0074] The results in Figure 10 show that without a metal layer, the extinction ratio is nearly zero at wavelengths longer than 1200 nm. However, when the metal layer is 3 nm thick, the range in which the extinction ratio is near 0.1 extends toward the longer wavelength side, up to approximately 1350 nm. Furthermore, when the metal layer is 6 nm or 9 nm thick, the extinction spectrum is mountain-shaped, peaking near 1300 nm, and an extinction ratio of approximately 0.1 to 0.2 is maintained even at wavelengths longer than 1600 nm. The peak near 1300 nm is thought to be due to thin-film interference caused by the SiO2 layer. On the other hand, when the metal layer is 20 nm thick, the extinction ratio is nearly flat at around 0.1 in the range from 1000 nm to 1600 nm.

[0075] FIG. 11 shows the relationship between the thickness of the metal layer and the detection sensitivity. In FIG. 11, the horizontal axis represents wavelength and the vertical axis represents sensitivity multiplication. The results shown in FIG. 11 indicate that the sensitivity multiplication depends on the thickness of the metal layer. When the metal layer is 3 nm thick, the sensitivity multiplication peaks near 1400 nm, with a multiplication factor of 2.5. When the metal layer is 6 nm thick, the sensitivity multiplication peaks near 1550 nm, with a multiplication factor of just over 3. When the metal layer is 9 nm thick, although not shown in FIG. 11, the slope of the graph near 1400 nm to 1650 nm suggests that a peak of approximately 3x sensitivity multiplication exists near 1700 nm.

[0076] Fig. 12 is a diagram showing the relationship between the thickness of the insulating layer and the detection sensitivity. Fig. 12 shows the detection multiplication factor for each wavelength when the insulating layer is 10 nm thick. From the results in Fig. 12, it was confirmed that when the insulating layer is thinned to 10 nm, a detection multiplication factor of approximately 3 to 8 times is obtained, regardless of the thickness of the metal layer.

[0077] Furthermore, regarding the relationship between the presence or absence of a surface layer and the state of the metal layer deposition, the relationship between the thickness of the metal layer formed by vapor deposition and the width of the island-shaped pieces was investigated for cases with and without a surface layer on the insulating layer. As a result, when the metal layer thickness was 6 nm, the width of the island-shaped pieces was approximately 80 nm with the surface layer, while it was approximately 40 nm without the surface layer. This confirmed that by providing a metal layer on a surface layer that has higher wettability to metal than the insulating layer, the width of the island-shaped pieces can be increased even if the metal layer thickness is the same. [Explanation of symbols]

[0078] 1A to 1F...shortwave infrared detector, 2...substrate, 3...thin film layer (carbon nanomaterial, carbon nanotube), 3A...first part, 3B...second part, 4...anode electrode, 5...cathode electrode, 6...insulating layer, 7...metal layer, 15...island-like piece, 16...groove portion, 31...dielectric layer, 21, 32...light-reflecting layer, 41...surface layer, T...island-like piece thickness, W...island-like piece width.

Claims

1. A substrate; a thin film layer provided on one surface of the substrate and sensitive to light in the short-wave infrared region; an anode electrode and a cathode electrode electrically connected to the thin film layer; a metal layer disposed adjacent to the thin film layer on one surface side of the substrate, The short-wave infrared detector, wherein the metal layer is configured by a plurality of island-shaped pieces separated from each other by sulci-like grooves distributed in the surface direction of the substrate.

2. 2. The shortwave infrared detector of claim 1, wherein when the width of an island-shaped piece is defined as the length of the longest line segment that passes through any two points that equally divide the length of the outer edge of the island-shaped piece and equally divides the area of ​​the island-shaped piece, the width of the island-shaped piece is greater than the thickness of the island-shaped piece along a direction perpendicular to the substrate.

3. 2. The short-wave infrared detector according to claim 1, wherein the island-shaped pieces have a thickness of 3 nm or more and less than 20 nm.

4. 2. The short-wave infrared detector according to claim 1, wherein the groove has a width of 10 nm or less.

5. 2. The short-wave infrared detector according to claim 1, wherein the metal layer is made of Au or Ag.

6. The shortwave infrared detector according to claim 1 , wherein the groove penetrates the metal layer in a thickness direction, and when viewed from above, a layer underlying the metal layer is exposed at the position of the groove.

7. an insulating layer provided so as to cover the thin film layer, the anode electrode, and the cathode electrode; 7. The short-wave infrared detector according to claim 1, wherein the metal layer is provided on the insulating layer.

8. an insulating layer provided so as to cover the thin film layer, the anode electrode, and the cathode electrode; a surface layer provided on the insulating layer and having a higher wettability with respect to a metal constituting the metal layer than the insulating layer; 7. The short-wave infrared detector according to claim 1, wherein the metal layer is provided on the surface layer.

9. the anode electrode and the cathode electrode are provided on the substrate, 7. The short-wave infrared detector according to claim 1, wherein the thin film layer has a first portion in contact with the substrate and a second portion that covers the anode electrode and the cathode electrode.

10. the entire thin film layer is provided in contact with the substrate, 7. The short-wave infrared detector according to claim 1, wherein the anode electrode and the cathode electrode are provided on the thin film layer.

11. 7. The short-wave infrared detector according to claim 1, wherein the metal layer is provided on the thin film layer.

12. 7. The short-wave infrared detector according to claim 1, further comprising a light-reflecting layer provided on the other surface of said substrate.

13. a dielectric layer as an outermost layer on one surface of the substrate; 7. The short-wave infrared detector according to claim 1, further comprising a light-reflecting layer provided on the dielectric layer.

14. 7. The short-wave infrared detector according to claim 1, wherein the thin film layer is made of a carbon nanomaterial.

15. 7. The short-wave infrared detector according to claim 1, wherein the thin film layer is made of carbon nanotubes.

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