Photodiodes and Light Sensitive Devices

Abstract

To provide a semiconductor photodiode having an electrode configuration in which a strength of adhesion with a Mg2Si material is high and total performance also including photosensitivity is improved.SOLUTION: The present invention relates to a photodiode including: a pn bond of a magnesium silicide crystal; an electrode containing a material in contact with a p-type magnesium silicide; and an electrode containing a material in contact with an n-type magnesium silicide. The material in contact with the p-type magnesium silicide is a material of which the work function is 4.81 eV or more and which reacts with silicon to form a silicide or form an alloy with magnesium, and consists of nickel, etc. The material in contact with the n-type magnesium silicide is a material of which the work function is less than 4.81 eV and which reacts with silicon to form a silicide or form an alloy with magnesium, and consists of aluminum, etc. In the photodiode, spectral sensitivity has a peak in a wavelength of 1350 nm in a spectral sensitivity spectrum and is 0.14 A / W or more.SELECTED DRAWING: Figure 3

Description

[Technical field]

[0001] The present invention relates to a photodiode using magnesium silicide. [Background technology]

[0002] With the recent dramatic technological innovation in artificial intelligence (AI), etc., research and development of systems that automatically monitor and control instead of human eyes and hands is also being actively conducted. In such automatic monitoring and automatic control systems, appropriate response actions are determined based on various input information such as light, temperature, and voice, so the hardware for sensing the input signals is one of the key devices that plays an important role in the entire system. In particular, in terms of sensing optical input signals, it is possible to realize advanced automatic monitoring and automatic control by using a device that can replace the human eye or, in some cases, detect information in areas that the human eye cannot detect.

[0003] Devices that are sensitive to optical input signals include those that have an element that converts the optical signal into an electrical signal that can be electronically processed. A basic example of such an element is a photodetector element that uses semiconductor materials, and among them, a photodiode that uses a pn junction is well known.

[0004] Photodiodes using semiconductor materials are sensitive to different wavelength ranges depending on the band gap of the semiconductor material. To perform advanced control such as automatic nighttime surveillance and automatic driving of automobiles, input information on infrared light is required in addition to light and image information in the visible light range. Therefore, there is a strong demand for elements and devices including photodiodes that can detect light input in the infrared range with high sensitivity, and active research and development using various semiconductor materials is underway.

[0005] Photodiodes using compound semiconductor materials such as InGaAs, HgCdTe, and InAsSb are already known as photodiodes intended to detect light in the infrared region of short wavelengths (approximately 0.9 to 2.5 μm). However, these semiconductor materials have the disadvantages of containing rare elements in the compound materials, being harmful to living organisms, and having a high environmental impact. Therefore, the present inventors have prepared a crystalline material of magnesium silicide (Mg2Si), which is a compound semiconductor composed of magnesium (Mg) and silicon (Si), which are naturally abundant resources and are less harmful to living organisms and highly safe materials (Non-Patent Document 1), proposed and prepared a photodiode using this, and have achieved certain results so far (Non-Patent Documents 2 and 3).

[0006] As electrodes used in semiconductor devices, gold (Au) electrodes are often used from the viewpoints of electrical conductivity, chemical stability, and ease of formation, as also used in Non-Patent Document 2. However, since Au is chemically stable, it does not react easily, particularly with Si or Si-based compounds, and tends to have poor adhesion at the contact interface with the semiconductor. Therefore, the electrode is prone to peeling and detachment from the contact interface with the semiconductor, and when considering the realistic usage environment of a practical device, there are problems with the durability and operability of the device.

[0007] In order to solve such problems, in Si-based semiconductor devices, another metal material is interposed between the contact surface of the Au electrode and the semiconductor to improve the adhesion at the contact interface between the electrode material and the semiconductor material. Non-Patent Document 3 discloses interposing titanium (Ti) between the contact surface of the Au electrode and the semiconductor material Mg2Si. This makes it possible to obtain an electrode with an adhesion strength that does not pose a problem when a practical device is assumed, even in a photodiode using Mg2Si as the semiconductor material.

[0008] However, when the specific physical properties of Mg2Si were subsequently taken into consideration, it became clear that in order to improve not only the adhesion between the electrode and the semiconductor material but also overall device performance, including photosensitivity, it was not necessarily optimal to use Ti as the electrode material in direct contact with Mg2Si, and that it was necessary to consider electrode materials from a different perspective. [Prior art documents] [Non-patent literature]

[0009] [Non-Patent Document 1] K. Sekino et al., Phys. Proc., Vol. 11, 2011, pp. 170-173 [Non-Patent Document 2] T. Akiyama et al., Proc. Asia-Pacific Conf. Semicond. Silicides Relat. Mater. 2016, JJAP Conf. Proc. Vol. 5, 2017, pp. 011102-1-011102-5 [Non-Patent Document 3] K. Daitoku et al., Proc. Int. Conf. Summer School Adv. Silicide Technol. 2014, JJAP Conf. Proc. Vol. 3, 2015, pp. 011103-1-011103-4 Summary of the Invention [Problem to be solved by the invention]

[0010] The technology disclosed herein is intended to solve the above-mentioned technical problems, and aims to provide a semiconductor photodiode that uses Mg2Si as a semiconductor material, and that has an electrode configuration that not only has high adhesion to the Mg2Si material, but also improves overall performance including photosensitivity. [Means for solving the problem]

[0011] As the basic knowledge on which the technology of the present disclosure is based, the present inventors focused on the inherent physical property values ​​related to the energy level of Mg2Si in the process of clarifying the fundamental physical properties of the compound semiconductor Mg2Si. Although many of the detailed physical properties of the compound Mg2Si were unclear, the present inventors further investigated the matter based on the contents disclosed in Non-Patent Document 1 and recognized the fact that the electron affinity (energy level difference between the vacuum level and the conduction band) in Mg2Si is 4.51 eV. Then, taking into consideration the inherent physical property values ​​of Mg2Si, they came up with a technical means for further improving the characteristics of Mg2Si photodiodes by appropriately selecting the electrode material.

[0012] Specifically, as shown below, this is a technology that prevents an energy barrier from occurring in the transport direction of photocarriers at the semiconductor / electrode interface by appropriately adjusting the relationship between the energy levels of Mg2Si and the electrode material. Figure 1 shows an example of the basic configuration of an Mg2Si photodiode, and Figure 2 shows an energy level diagram of the pn junction and the region near the electrode when the electrode material 103 directly connected to the p-type Mg2Si part 102 in the configuration of Figure 1 is Ti (a material also used in Non-Patent Document 3), and the electrode material 105 directly connected to the n-type Mg2Si part 101 is Al. Of the electron-hole pairs that are photocarriers generated in the depletion layer (and diffusion length) 201 of the pn junction by the incidence of light, the electrons 202 tend to move toward a lower energy level, and the holes 203 tend to move toward a higher energy level.

[0013] The problem here is the difference in work function between the p-type Mg2Si and the electrode. The work function of a semiconductor is the electron affinity multiplied by the energy difference ΔE from the conduction band to the Fermi level. F The Fermi level changes with the carrier concentration in the semiconductor, and in Mg2Si, the n-type is ΔE F is between 0 and 0.3 eV, and ΔE Ftakes a value between 0.3 and 0.6 eV. From the electron affinity of Mg2Si shown above, the work function of p-type Mg2Si is between 4.81 and 5.11 eV. The work function of Ti, which is the material of the electrode conventionally used here, is about 4.33 eV, which is lower than the minimum work function value of Mg2Si shown above, 4.81 eV. Therefore, an energy barrier 204 against holes is generated at the interface between p-type Mg2Si and the electrode, and the ratio of the generated holes that can reach the electrode is reduced, and there is a concern that the generated photocarriers cannot be effectively detected as a photocurrent.

[0014] In contrast, as shown in Figure 3, if the electrode material in contact with the p-type Mg2Si has a work function of 4.81 eV or more, there will be no energy barrier for holes at the interface between the p-type Mg2Si and the electrode, or the effect of the energy barrier can be reduced to a level that does not pose a practical problem. Many of the holes among the electron-hole pairs generated as photocarriers will be able to reach the electrode and effectively contribute to the photocurrent value.

[0015] Based on these findings and ideas, the present disclosure provides the following inventions. 1) A photodiode including a pn junction of magnesium silicide crystal, an electrode including a material in contact with the p-type magnesium silicide, and an electrode including a material in contact with the n-type magnesium silicide, the material in contact with the p-type magnesium silicide has a work function of 4.81 eV or more and reacts with silicon to form a silicide or with magnesium to form an alloy; The material in contact with the p-type magnesium silicide is nickel. In can be, a material in contact with the n-type magnesium silicide has a work function smaller than 4.81 eV and reacts with silicon to form a silicide or reacts with magnesium to form an alloy; The material in contact with the n-type magnesium silicide is aluminum. In can be, The spectral sensitivity has a peak at 1350 nm in the spectral sensitivity spectrum and is 0.14 A / W have A photodiode characterized by: 2) The photodiode according to 1) above, wherein the electrode containing a material in contact with the p-type magnesium silicide further contains a material in contact with the p-type magnesium silicide and another material in contact with the material. 3) The photodiode according to 2) above, characterized in that the other material is at least one metal or alloy selected from the group consisting of gold, palladium, and platinum, except when the other material is a metal selected as a material in contact with the p-type magnesium silicide; 4) The photodiode according to any one of 1) to 3) above, characterized in that the material in contact with the p-type magnesium silicide is a thin film having a thickness of 1 to 1000 nm; 5) The photodiode according to any one of 1) to 4), wherein the p-type magnesium silicide is magnesium silicide doped with silver. 6) The photodiode according to any one of 1) to 5), wherein at least one of the electrodes is a ring-shaped electrode having an opening on the inside. 7) A photosensitive device comprising the photodiode according to any one of 1) to 6) above. Effect of the Invention

[0016] According to the technology disclosed herein, in a photodiode using a pn junction of Mg2Si, a compound semiconductor, not only is the adhesion between Mg2Si and the electrode material strong, but the number of photocarriers that can reach the electrode from Mg2Si, in particular the number of holes that can reach the electrode from p-type Mg2Si, can be significantly increased, making it possible to provide a semiconductor photodiode with improved overall performance, including photosensitivity. [Brief description of the drawings]

[0017] [Figure 1] Basic structure of Mg2Si photodiode [Diagram 2]Energy level diagram for a conventional Ti electrode [Diagram 3] Energy level diagram of the disclosed technology [Figure 4] Spectral sensitivity spectra of Example 1 and Comparative Example 1 DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0018] The photodiode according to the technology of the present disclosure has, as a basic configuration, a pn junction of Mg2Si crystal, an electrode containing a material in contact with the p-type Mg2Si, and an electrode containing a material in contact with the n-type Mg2Si. The Mg2Si is preferably made of a crystalline material and is a single crystal. Non-doped Mg2Si usually exhibits n-type conductivity, but a pn junction of Mg2Si is formed by introducing p-type impurities into a part of it, etc., as the central configuration of the diode, and an electrode for extracting photocurrent is provided to this to form the photodiode of the present disclosure.

[0019] The photodiode of the present disclosure is characterized in that the material of the electrode in direct contact with the p-type Mg2Si has a work function of 4.81 eV or more, and is a material that reacts with Si to form a silicide or forms an alloy with magnesium. As described above, the electron affinity of Mg2Si is 4.51 eV, and its work function changes depending on the carrier concentration, being between 4.51 and 4.81 eV for n-type Mg2Si and between 4.81 and 5.11 eV for p-type Mg2Si. Therefore, if the material of the electrode in contact with the p-type Mg2Si has a work function of 4.81 eV or more, it is possible to eliminate the energy barrier at the interface between the p-type Mg2Si and the electrode for the holes transported to the electrode among the electron-hole pairs of the photocarriers formed in the depletion layer and diffusion region of the pn junction, or to reduce the effect of the energy barrier to a level that does not cause practical problems, and the carrier collection efficiency can be greatly improved.

[0020] Furthermore, the material of the electrode in direct contact with the p-type Mg2Si has a work function of 4.81 eV or more as described above, and is a material that reacts with Si to form a silicide or an alloy with magnesium. In this way, if the material of the electrode in direct contact with the Mg2Si is a material that reacts with Si to form a silicide or an alloy with magnesium, a strong bond can be formed by reacting a part of the Si in the Mg2Si with a part of the electrode material at the interface where the Mg2Si and the electrode material are in contact, and the adhesive force between the p-type Mg2Si and the electrode can be made high enough to withstand use as a practical device.

[0021] In the photodiode of the present disclosure, the electrode material that is in direct contact with p-type Mg2Si and has a work function of 4.81 eV or more and reacts with Si to form a silicide or an alloy with magnesium can be, for example, at least one metal or alloy selected from the group consisting of nickel (Ni), cobalt (Co), platinum (Pt), palladium (Pd), iridium (Ir), rhenium (Re), rhodium (Rh), beryllium (Be), selenium (Se), and tellurium (Te). If such a metal material is used as the electrode material in direct contact with p-type Mg2Si, the adhesive strength at the interface between the metals can be excellent when an electrode configuration is formed by providing another metal material on this metal material.

[0022] As mentioned above, in the conventional known technology, the energy barrier formed at the interface between p-type Mg2Si and the electrode directly in contact with it is a problem, but the same problem exists at the interface between n-type Mg2Si and the electrode directly in contact with it. Since the majority carriers at the interface between n-type Mg2Si and the electrode are electrons, in order to prevent the energy barrier from being formed against the electrons transported to the electrode at the interface, the work function of the electrode material directly in contact with n-type Mg2Si is set to 4.81 eV, which is the work function of n-type Mg2Si, or less. In addition, by using a material that reacts with silicon to form a silicide or forms an alloy with magnesium as the electrode material, it is possible to obtain good adhesion with Mg2Si.

[0023] As described above, examples of materials that have a work function of 4.81 eV or less and react with Si to form a silicide or an alloy with magnesium include at least one metal or alloy selected from the group consisting of aluminum (Al), silver (Ag), titanium (Ti), gallium, indium, arsenic, antimony, bismuth, copper, zinc, cadmium, vanadium (V), chromium (Cr), manganese (Mn), iron (Fe), yttrium (Y), zirconium (Zr), niobium (Nb), molybdenum (Mo), hafnium (Hf), tantalum (Ta), and tungsten (W). In addition, in Non-Patent Document 3, which is a conventional technique, Ag with a work function of 4.26 eV is used as the electrode material that directly contacts n-type Mg2Si.

[0024] In the photodiode of the present disclosure, the electrode in contact with the p-type Mg2Si may be an electrode having a configuration including a material in direct contact with the p-type Mg2Si and another material in contact with the material. By adopting such a configuration, it becomes possible to change the characteristics of the entire electrode to the desired characteristics and to further improve the characteristics, compared with the case where the electrode material is composed of only one type of material in direct contact with the p-type Mg2Si. For example, by adopting an electrode having a configuration in which a material having a higher conductivity than the material in direct contact with the p-type Mg2Si is combined, or a material having a higher chemical stability is combined, it is possible to improve the electrical characteristics, durability, and weather resistance of the entire electrode.

[0025] Such a material may be, for example, at least one metal or alloy selected from the group consisting of Au, Pd, and Pt. By forming a structure in which only the Au or Pd or alloy portion of the electrode is exposed by an appropriate passivation treatment, it is possible to prevent the electrode material from deteriorating even if the electrode material in direct contact with the p-type Mg2Si is a material that is easily degraded by oxidation or the like, and to realize a photodiode with high durability and weather resistance.

[0026] In the photodiode of the present disclosure, the specific arrangement of the material in direct contact with the p-type Mg2Si is not particularly limited, but a specific embodiment may be a thin film having a thickness of 1 to 1000 nm. If the thickness is less than 1 nm, sufficient adhesion to the p-type Mg2Si may not be obtained. If the thickness exceeds 1000 nm, the electrode may easily peel off, or the electrical resistance of the electrode may increase, resulting in a decrease in photocurrent. The thickness may be 5 nm or more, or 8 nm or more, or 500 nm or less, or 100 nm or less.

[0027] As described above, the pn junction of the Mg2Si crystal, which is the core component of the photodiode of the present disclosure, can be formed by doping a part of a non-doped Mg2Si crystal that is normally n-type with an impurity that becomes p-type, and an example of such a dopant impurity is Ag. Ag is an element that diffuses into the inside of the Mg2Si crystal by heat treatment, and can relatively easily form an Mg2Si structure locally doped with Ag.

[0028] Furthermore, in the photodiode of the present disclosure, the specific structure and shape of the electrode are not particularly limited, but as a specific embodiment, an example can be given in which the electrode on at least one side is configured as a ring-shaped electrode having an opening on the inside. As described above, if a ring-shaped electrode having an opening on the inside is formed on the surface on at least one side of a structure in which a pn junction is formed at a predetermined position in the depth direction from the surface of Mg2Si, light passing through the opening of the electrode can excite photocarriers in a wide range of pn junctions, thereby realizing a photodiode with high light sensitivity.

[0029] In the configuration of Fig. 1, the electrode in contact with the p-type Mg2Si is formed in a ring shape, but this is not limited to this, and the electrode in contact with the n-type Mg2Si may be formed in a ring shape, or both electrodes may be formed in a ring shape. In addition, the "ring shape" in this disclosure is not limited to a circular shape, but refers to an annular shape including an elliptical shape and a polygonal shape.

[0030] The Mg2Si photodiode having the above-mentioned configuration can be used as a basic element configuration to configure various photosensitive devices such as photodetectors and imaging devices. In particular, the Mg2Si photodiode disclosed herein has good sensitivity characteristics to infrared rays in the wavelength region of 900 to 1900 nm in the short-wavelength infrared region, and can be suitably used in photosensitive devices intended for use in such wavelength region.

[0031] The photodiode of the present disclosure is not particularly limited in its manufacturing method, and may be manufactured by any method including any means as long as the above-mentioned photodiode configuration can be realized. An example of a manufacturing method and a technical means related to manufacturing that can be used to realize the photodiode configuration of the present disclosure is shown below, but is not limited to this.

[0032] First, in order to form a pn junction of Mg2Si crystal, which is the central component of the photodiode of the present disclosure, a crystalline material of Mg2Si is prepared. As described above, a single crystalline material of Mg2Si is preferable as the crystalline material of Mg2Si, and the single crystalline material of Mg2Si can be obtained by a known method such as that disclosed in Non-Patent Document 1. In order to form the photodiode of the present disclosure, it is preferable in terms of the process that the crystalline material of Mg2Si is formed into a plate-shaped substrate having a thickness of about 0.1 to 5 mm in advance and the surface is polished before use.

[0033] To form a pn junction of Mg2Si, a part of the Mg2Si crystalline material prepared as described above is doped with p-type impurities. Since undoped Mg2Si exhibits n-type conductivity, by doping a part of it with p-type impurities to make a part of the Mg2Si crystalline material into p-type Mg2Si, a pn junction of Mg2Si is formed at the boundary with the undoped region.

[0034] The means for doping a part of the Mg2Si crystalline material with a p-type impurity and the p-type impurity species (dopant) are not particularly limited, and any desired means and dopants can be used. Here, a method of doping by thermal diffusion using Ag as a dopant is given as an example. Ag is placed on the surface of the Mg2Si crystalline material as a diffusion source, and is heated in an inert atmosphere to thermally diffuse Ag from the surface of the Mg2Si crystalline material to the inside. The amount of Ag that serves as the diffusion source that is required for thermal diffusion to the inside can be placed and formed on the surface of the Mg2Si crystalline material by vacuum deposition, sputtering, or the like. The conditions of the above-mentioned heat treatment can be adjusted and set in consideration of the diffusion speed and the depth of the diffusion region to be formed, that is, the position where the pn junction is formed. For example, the heat treatment temperature can be set to 400 to 550°C, and the heat treatment time can be set to a range of 30 seconds to 30 minutes as a guideline.

[0035] Next, electrodes necessary for extracting and detecting photocurrent are formed in each of the p-type and n-type regions of the Mg2Si crystal where the pn junction is formed. There is no particular limitation on the specific means for forming the electrodes on the surface of the Mg2Si crystal in each of the p-type and n-type regions, and they may be formed by applying known means such as vacuum deposition, sputtering, plating, etc., depending on the electrode material, etc. At this time, as disclosed in Non-Patent Documents 2 and 3, ring-shaped electrodes or desired electrode patterns can also be formed using masking, photolithography, etc.

[0036] In addition to the above, additional operations may be performed as necessary, such as forming an electrode of another material to form a multilayer electrode, forming a protective layer, partially removing unnecessary components by etching, polishing, etc. The means and conditions specifically mentioned above are merely examples, and there is no impediment to the application of other means and conditions as long as they provide the essential configuration of the Mg2Si photodiode of the present disclosure. EXAMPLES

[0037] The technical content of the present disclosure will be specifically described below based on examples and comparative examples. The following examples and comparative examples are merely specific examples for facilitating understanding of the technical content of the present disclosure, and the technical scope of the present invention is not limited by these specific examples.

[0038] Example 1 As the crystalline material of Mg2Si, a single crystal material of n-type Mg2Si was prepared by growing it by the vertical Bridgman method according to the method disclosed in Non-Patent Document 1. This was cut on the (110) plane, and both sides were mirror-polished and cleaned to obtain a single crystal Mg2Si substrate with a thickness of 1 mm. The carrier concentration of the substrate was 6×10 15 cm -3 An Ag layer with a diameter of 800 μm was formed as a diffusion source on a portion of one surface of this substrate by vacuum deposition, and then heat treatment was performed at 450°C for 10 minutes in an argon (Ar) atmosphere to thermally diffuse Ag from one surface of the n-type Mg2Si substrate in the depth direction, forming a p-type Mg2Si layer in a portion of the n-type Mg2Si crystal.

[0039] Next, a circular ring-shaped Ni layer with an inner diameter of 500 μm, width of 75 μm, and thickness of 10 nm was formed by sputtering on the surface of the formed p-type Mg2Si layer. Then, a 300 nm thick Au layer of the same size as the Ni layer was formed directly on the formed Ni layer by vacuum deposition. In this example, in the pn junction of the Mg2Si crystal, the material in direct contact with the p-type Mg2Si is Ni with a work function of 5.15 eV, and the structure including this Ni layer and the Au layer formed directly on it becomes the electrode on the p-type Mg2Si side. Furthermore, a 300 nm thick layer of Al with a work function of 4.28 eV was formed by vacuum deposition on the entire surface of the n-type Mg2Si on the opposite side of the substrate, and this was used as the electrode on the n-type Mg2Si side. Note that the carrier concentration in the p-type region is 1×10 19 cm -3 From the carrier concentrations in the p-type and n-type regions, the work function of p-type Mg2Si is estimated to be approximately 5.09 eV, and the work function of n-type Mg2Si is estimated to be approximately 4.62 eV.

[0040] The spectral sensitivity characteristics of the Mg2Si photodiode thus fabricated were evaluated by measuring the spectral sensitivity spectrum. The measurement was performed by splitting the light from a halogen lamp with a spectroscope, irradiating the light from the opening side of the ring-shaped electrode on the photodiode fabricated as described above, amplifying the obtained photocurrent with a circuit using an operational amplifier, and detecting it with a lock-in amplifier.

[0041] Figure 4 (solid line) shows the spectral sensitivity spectrum from 1300 to 2200 nm. From this spectrum, it was confirmed that the spectral sensitivity had a peak at a wavelength of 1350 nm, with a maximum value of approximately 0.14 A / W. Furthermore, when the adhesion strength of the electrodes was evaluated using a tape test method in accordance with JIS H8504, the area of ​​the electrodes attached to the tape on both pn sides was 5% or less of the electrode area, and no problematic points were found regarding the adhesion strength of the electrodes.

[0042] Comparative Example 1 A photodiode was fabricated in the same manner as in Example 1, except that the material of the electrode layer in direct contact with the surface of the p-type Mg2Si layer was Ti. That is, in this example, in the pn junction of the Mg2Si crystal, the material in direct contact with the p-type Mg2Si is a Ti layer with a work function of 4.33 eV, and the configuration including this Ti layer and the Au layer formed directly on it becomes the electrode on the p-type Mg2Si side. The electrode in contact with the entire surface of the n-type Mg2Si on the opposite side is Al as in Example 1. And, in this example, the spectral sensitivity characteristics were evaluated by the same means and conditions as in Example 1. Note that, as in Example 1, the work function of the p-type Mg2Si at this time is estimated to be about 5.09 eV and the work function of the n-type Mg2Si is estimated to be about 4.62 eV from the carrier concentration of each of the p-type and n-type regions.

[0043] FIG. 4 (dashed line) also shows the spectral sensitivity spectrum at wavelengths of 1300 to 2200 nm. The shape of the spectrum is generally similar to that of Example 1. However, it was confirmed that the maximum value of the spectral sensitivity at the peak position was less than about 0.08 A / W, approximately 57% of that of Example 1. In this example, the evaluation result of the adhesion of the electrodes by the tape test method according to JIS H8504 showed that the area of ​​the electrodes attached to the tape on both pn sides was 5% or less of the electrode area, and no problematic points were found with respect to the adhesion of the electrodes.

[0044] These results are summarized in Table 1. [Table 1]

[0045] From the above results, no significant problem was found in any of the examples regarding the adhesion between the electrode and Mg2Si. This is believed to be because all of the materials in direct contact with Mg2Si react with Si to form silicide. However, a significant difference was found in the spectral sensitivity values ​​between the examples and the comparative examples. In Example 1, in which the material in direct contact with p-type Mg2Si is Ni with a work function of 5.15 eV, no energy barrier is formed against the transport of holes at the interface between the p-type Mg2Si and the Ni electrode layer, so it is believed that holes, which are majority carriers, can efficiently reach the electrode.

[0046] In contrast, in Comparative Example 1, where the material in direct contact with p-type Mg2Si is Ti with a work function of 4.33 eV, even if photocarriers are generated by the incidence of light, some of the holes are prevented from being transported to the electrode by the energy barrier formed at the interface between the p-type Mg2Si and the Ti electrode layer, and are therefore not effectively detected as photocurrent. From these findings, it was confirmed that appropriately selecting and adjusting the work function of the material in direct contact with p-type Mg2Si based on the technical concept of this disclosure is extremely effective in significantly improving the performance of Mg2Si photodiodes. [Industrial Applicability]

[0047] According to the technology disclosed herein, in a photodiode using a pn junction of Mg2Si, the photosensitivity can be significantly improved compared to the conventional technology. Therefore, it is possible to dramatically improve the performance of various devices intended for sensing and imaging in the short wavelength (approximately 0.9 to 2.5 μm) infrared region, which is assumed for photodiodes using Mg2Si. Accordingly, it is expected to make a great contribution to various image analysis, image diagnosis, and other technologies in the wavelength region, as well as automatic monitoring and automatic control technologies using these technologies, and to industrial fields using these technologies. [Explanation of symbols]

[0048] 104 Electrode made of another material in direct contact with p-type Mg2Si 301 Depletion Layer and Diffusion Length 302 Electronic 303 holes

Claims

1. A photodiode including a pn junction of magnesium silicide crystal, an electrode including a material in contact with the p-type magnesium silicide, and an electrode including a material in contact with the n-type magnesium silicide, a material in contact with the p-type magnesium silicide has a work function of 4.81 eV or more and reacts with silicon to form a silicide or with magnesium to form an alloy; the material in contact with the p-type magnesium silicide is nickel; a material in contact with the n-type magnesium silicide has a work function smaller than 4.81 eV and reacts with silicon to form a silicide or reacts with magnesium to form an alloy; the material in contact with the n-type magnesium silicide is aluminum; A photodiode having a spectral sensitivity of 0.14 A / W, the spectral sensitivity spectrum having a peak at a wavelength of 1350 nm.

2. 2. The photodiode according to claim 1, wherein the electrode including a material in contact with the p-type magnesium silicide further includes a material in contact with the p-type magnesium silicide and another material in contact with the material.

3. 3. The photodiode of claim 2, wherein the other material is at least one metal or alloy selected from the group consisting of gold, palladium, and platinum, except when the other material is a metal selected as a material in contact with the p-type magnesium silicide.

4. 2. The photodiode according to claim 1, wherein the material in contact with the p-type magnesium silicide is a thin film having a thickness of 1 to 1000 nm.

5. 2. The photodiode of claim 1, wherein the p-type magnesium silicide is silver-doped magnesium silicide.

6. 2. The photodiode according to claim 1, wherein at least one of the electrodes is a ring-shaped electrode having an opening on the inside.

7. A light-sensitive device comprising a photodiode according to any one of claims 1 to 6.

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