Variable capacitance diode and method for producing variable capacitance diode

Abstract

Provided is a variable capacitance diode and a method for producing the same, the diode being configured, with a simple technique, for improved electrostatic properties. A variable capacitance diode 1 according to the present disclosure is a compound semiconductor in which a pn junction is formed between a p-type semiconductor 10 and an n-type semiconductor 20, and at least one of the p-type semiconductor 10 and n-type semiconductor 20 contains a metal cation and an anion of Groups 15 through 17 of the Periodic Table. This compound semiconductor does not contain a dopant and has a gradient coefficient of 0.6 or greater.

Description

Variable capacitance diode and method of manufacturing the same

[0001] FIELD OF THE DISCLOSURE The present disclosure relates to variable capacitance diodes and methods for manufacturing variable capacitance diodes.

[0002] In recent years, variable capacitance diodes have been developed that utilize the technological concept of changing the width of the depletion layer of a pn junction depending on the applied voltage. One known example is a variable capacitance diode with a hyperabrupt junction, in which an n-type semiconductor in which silicon (Si) is doped with arsenic (As) is joined to a p-type semiconductor in which silicon (Si) is doped with boron (B), resulting in an elemental distribution in which the dopant concentration (boron concentration) of the p-type semiconductor increases toward the pn junction interface.

[0003] Furthermore, Patent Document 1 discloses a manufacturing method for a variable capacitance diode with a hyperabrupt junction, which includes the steps of forming a semiconductor single crystal substrate pre-doped with a dopant (e.g., As), a diffusion material layer (e.g., a boron diffusion layer) on the semiconductor single crystal substrate and exhibiting a carrier conduction type opposite to that of the dopant, and an epitaxial layer made of a semiconductor material formed on the diffusion material layer, in which the diffusion material layer is carefully polished, etched, and cleaned before growing the epitaxial layer on the diffusion material layer, and the growth temperature of the epitaxial layer is set to a range of 850 to 1400° C. This manufacturing method is said to realize a hyperabrupt junction in which the dopant and / or diffusion material diffuse, resulting in an elemental distribution in which the dopant concentration (boron concentration) of the p-type semiconductor increases toward the p-n junction interface.

[0004] U.S. Pat. No. 3,149,395

[0005] The inventors of the present invention have noticed that there are problems to be overcome in conventional variable capacitance diodes from the viewpoint of capacitance characteristics and practicality of manufacturing processes, and have found the need to take measures to address these problems.

[0006] The present disclosure has been made in view of the above-mentioned problems. That is, a main object of the present disclosure is to provide a variable capacitance diode that improves capacitance characteristics by a simpler method, and to provide a method for manufacturing a variable capacitance diode.

[0007] The inventors of the present application have attempted to solve the above problems by taking a new approach rather than simply extending the conventional technology, and as a result have been able to disclose a variable capacitance diode and a method for manufacturing a variable capacitance diode in which the above-mentioned primary object has been achieved.

[0008] The variable capacitance diode according to the present disclosure comprises a pn junction between a p-type semiconductor and an n-type semiconductor, at least one of the p-type semiconductor and the n-type semiconductor being a compound semiconductor containing a metal cation and an anion of Groups 15 to 17 of the periodic table, the compound semiconductor containing no dopant, and having a gradient coefficient of 0.6 or more.

[0009] The method for manufacturing a variable capacitance diode according to the present disclosure includes: a pn-junction step of forming a pn-junction between a p-type semiconductor and an n-type semiconductor, wherein at least one of the p-type semiconductor and the n-type semiconductor is a compound semiconductor containing a metal cation and an anion of Groups 15 to 17 of the periodic table, by a liquid phase method; and a thermal diffusion step of performing thermal diffusion after the joining step to set the gradient coefficient to 0.6 or more, wherein the compound semiconductor does not contain a dopant.

[0010] According to the present disclosure, it is possible to provide a variable capacitance diode in which the capacitance characteristics are improved by a simple technique, and to provide a method for manufacturing a variable capacitance diode.

[0011] FIG. 1 is a diagram showing the correspondence between space charge distribution and junction name; FIG. 2 is a graph showing the space charge distribution of a conventionally known hyperabrupt junction variable capacitance diode; FIG. 3 is a graph showing the element distribution of a conventionally known hyperabrupt junction variable capacitance diode; FIG. 4 is a cross-sectional view of a variable capacitance diode according to the present disclosure; FIG. 5 is a conceptual diagram showing the space charge distribution of a variable capacitance diode according to the present disclosure; FIG. 6 is a conceptual diagram showing the element distribution of a variable capacitance diode according to the present disclosure; FIG. 7 is a table showing evaluation results of variable capacitance diodes of examples and comparative examples; FIG. 8 is a table showing evaluation results of a comparative hyperabrupt silicon variable capacitance diode; FIG. 9 is a graph showing diffusion at a pn interface.

[0012] [Findings that Form the Basis of the Present Disclosure] As described above, the present inventors have found that conventional variable capacitance diodes have problems to be overcome from the viewpoints of capacitance characteristics and practicality of the manufacturing process. The findings from the viewpoints of capacitance characteristics and practicality of the manufacturing process are described in detail below.

[0013] - Knowledge Regarding Capacitance Characteristics - Before describing the variable capacitance diode of the present disclosure, the form of the pn junction used in the variable capacitance diode will be described with reference to FIG.

[0014] A variable capacitance diode has a space charge in the depletion layer, which is the origin of capacitance, and the distribution near the end of the depletion layer is q(x) ∝ x ｎ It can be approximated by the following equation. Here, x is the displacement of the axis along the direction from the p-type semiconductor to the n-type semiconductor in the pn junction, and x = 0 refers to the junction interface of the pn junction. In this space charge distribution, n is called the power coefficient; when n = 1, the space charge distribution is proportional, when n = 0, the space charge distribution is constant, and when n = -1, the space charge distribution is inversely proportional. Furthermore, the gradient coefficient γ is one of the indicators of the performance of a variable capacitance diode. The gradient coefficient γ and the power coefficient n are related by the equation γ = 1 / (n + 2).

[0015] As shown in FIG. 1, the pn junction of a variable capacitance diode generally has a space charge distribution pattern such as a linearly graded junction, an abrupt junction, or a hyperabrupt junction.

[0016] The linearly graded junction refers to a junction in which the space charge distribution in the p-type and n-type semiconductors changes linearly. As shown in Figure 1, the space charge distribution q(x) is proportional to x.

[0017] In a linearly graded junction, the space charge distribution q(x) is x １ Since the junction is proportional to the power factor n, the power factor n is 1. Also, the gradient factor γ in the linearly graded junction is γ=1 / 3.

[0018] As shown in Figure 1, the abrupt junction has a space charge distribution q(x) that is a constant (x ０) In other words, the power coefficient n = 0 and the gradient coefficient γ = 1 / 2. As shown in Figure 1, in a hyperabrupt junction, the space charge distribution q(x) is inversely proportional to x (power coefficient n = -1) and the gradient coefficient γ = 1.

[0019] In terms of the gradient factor γ, a hyperabrupt junction can increase the gradient factor γ. Increasing the gradient factor γ can increase the capacitance change when the reverse voltage is changed. Therefore, it has been found that the gradient factor γ in a variable capacitance diode is an important factor in increasing the capacitance change.

[0020] - Knowledge regarding the practicality of the manufacturing process - Variable capacitance diodes are known that have a hyperabrupt junction with an element distribution (Figure 2B) in which the dopant concentration (boron (B) concentration) of the p-type semiconductor increases as it approaches the p-n junction interface. However, when conventional heat treatment is performed, the boron doped in the p-type semiconductor diffuses toward the n-type semiconductor side, reducing the boron concentration at the p-n junction interface on the p-type semiconductor layer side, preventing the formation of a hyperabrupt junction.

[0021] In Patent Document 1, a diffusion material layer (boron diffusion layer) is provided to increase the boron concentration at the pn junction interface on the p-type semiconductor layer side, but designing the boron concentration of the diffusion material layer to achieve a desired hyperabrupt junction is not practical from the viewpoint of the manufacturing process. Specifically, to form a hyperabrupt junction, the diffusion material (boron) needs to have a diffusion coefficient much larger than that of the dopant (arsenic), but it is difficult to select a dopant, diffusion material, and / or process temperature that satisfies such a diffusion coefficient.

[0022] [Varactor Diode of the Present Disclosure] Based on the above findings, the present inventors have come up with the disclosure of a variable capacitance diode of the present disclosure. The following describes a variable capacitance diode of the present disclosure. While the description will refer to drawings as necessary, the illustrated contents are merely schematic and illustrative for understanding the present disclosure, and the appearance, dimensional ratios, and the like may differ from the actual product. Note that, unless otherwise specified, various numerical ranges referred to in this specification are intended to include the lower and / or upper limits. For example, a numerical range such as 1 to 10 can be interpreted as including both the lower limit of "1" and the upper limit of "10." Furthermore, various numerical values ​​may be accompanied by the terms "about" or "approximately," and these terms mean that the range may include a variation of a few percent, for example, ±10%, ±5%, ±3%, ±2%, and / or ±1%.

[0023] In the variable capacitance diode 1 of the present disclosure, a p-type semiconductor 10 and an n-type semiconductor 20 are formed as a pn junction (see FIG. 3 ), and at least one of the p-type semiconductor 10 and the n-type semiconductor 20 is a compound semiconductor containing a metal cation and an anion of Groups 15 to 17 of the periodic table, and the compound semiconductor does not contain a dopant and has a gradient coefficient of 0.6 or more. Hereinafter, as one embodiment of the present disclosure, a mode in which the p-type semiconductor 10 is a compound semiconductor containing a metal cation and an anion of Groups 15 to 17 of the periodic table will be described in detail.

[0024] P-type Semiconductor The p-type semiconductor 10 may be a compound semiconductor containing metal cations and anions of groups 15 to 17 of the periodic table. Examples of metal cations include Ni ２＋ , Cu ２＋ and / or Co ２＋ (or Co ３＋ Examples of anions in Groups 15 to 17 include O ２－ Examples include:

[0025] The p-type semiconductor 10 functions by the conduction of holes resulting from metal cation vacancies present in the crystal. NiO, for example, functions as a p-type semiconductor because of a shortage of metal cations (Ni ions) due to the presence of crystal defects at Ni sites, and the metal cation vacancies become the source of holes, which are space charges. In other words, the p-type semiconductor 10 used in this embodiment does not contain a dopant (e.g., boron) as in conventional technology. In other words, the p-type semiconductor 10 of this embodiment does not function by using a dopant as the source of space charges.

[0026] The definition of a dopant is an impurity introduced into a base material for the purpose of generating carriers, and the amount introduced is such that the crystal structure of the base material is not changed. Among dopants, those that generate holes are called acceptors, and those that generate electrons are called donors, and the net dopant concentration is defined here as the difference between the product of the effective charge and concentration of the acceptor and donor. In this specification, "dopant-free" means that the dopant does not function as a p-type semiconductor by generating space charge. Generally, even if an element that functions as a dopant is inevitably included, a net dopant concentration of 1.0 x 10 １５ cm －３ If the concentration is below this range, the compound semiconductor containing metal cations and anions of Groups 15 to 17 of the periodic table is not considered to contain a dopant. The lower limit may be 0. If the concentration is below this range, the vacancies due to the metal cations are dominant as space charges in the compound semiconductor, and the compound semiconductor functions as a p-type semiconductor that functions due to the metal cation vacancies.

[0027] In a preferred embodiment, the compound semiconductor may be an oxide semiconductor, which has high weather resistance, and thus can be used to produce a variable capacitance diode whose characteristics are less susceptible to fluctuations due to moisture, etc.

[0028] Specific examples of oxide semiconductors include NiO, Co ３ O ４and CuO. This material is known as a material with a relatively high dielectric constant and / or a wide band gap. By using this material, a variable capacitance diode with high withstand voltage and / or high capacitance can be realized. Among them, NiO has a band gap of 3.7 eV, so that a variable capacitance diode with particularly high withstand voltage can be realized.

[0029] The dielectric constant of a preferred compound semiconductor may be 15 or more. NiO is an example of a material having such a dielectric constant. By using a material having such a dielectric constant, a variable capacitance diode with a higher capacitance than conventional Si variable capacitance diodes (dielectric constant 11.7) can be realized.

[0030] The n-type semiconductor 20 may be a semiconductor having a dopant (donor) as a space charge source. An example of the n-type semiconductor 20 having a dopant (donor) as a space charge source is La-doped BaTiO. ３ BaTiO ３ has a high relative permittivity of about 2000 and a wide band gap of 3.2 eV, making it possible to realize a variable capacitance diode with high withstand voltage and / or high capacitance.

[0031] The compound semiconductor containing the dopant may be a polycrystalline body. By sintering the compound semiconductor containing the dopant, a polycrystalline body can be obtained, which facilitates diffusion of elements along grain boundaries and facilitates the formation of hyperabrupt junctions, as will be described later.

[0032] Hyperabrupt Junction Structure The variable capacitance diode 1 of this embodiment is constructed by forming a pn junction between a p-type semiconductor 10, which is a compound semiconductor containing the above-mentioned metal cations and anions of Groups 15 to 17 of the periodic table, and an n-type semiconductor 20 containing a dopant (donor), and then performing a predetermined heat treatment (see FIG. 3).

[0033] By performing heat treatment, Ni elements diffuse from the p-type side to the n-type side, and the concentration of Ni vacancies, which are the source of space charge in the p-type semiconductor, increases at the p-n interface. As a result, as shown in FIG. 4A , a space charge distribution based on a hyperabrupt junction is formed on the p-type semiconductor 10 side. Meanwhile, a space charge distribution based on an abrupt junction is formed on the n-type semiconductor 20 side. Because the n-type semiconductor 20 has a higher carrier concentration and the depletion layer extends toward the p-type semiconductor 10 side, even if the space charge distribution on the n-type semiconductor side is not a hyperabrupt junction, the overall p-n junction becomes a hyperabrupt junction, resulting in improved electrical characteristics compared to conventional variable capacitance diodes. In this specification, the term "hyperabrupt junction" refers to a junction having the aforementioned gradient coefficient γ of 0.6 or greater. In addition, the term "abrupt junction" refers to a junction having the aforementioned gradient coefficient γ of approximately 0.5.

[0034] As described above, the variable capacitance diode of this embodiment includes a p-type semiconductor in which metal cation vacancies are the origin of space charge, and therefore does not require the design of a diffusion coefficient (design of the dopant amount) to realize a hyperabrupt junction as in conventional technology, and can be manufactured by simple thermal diffusion, making it practical. Furthermore, as will be described in detail in the examples, the variable capacitance diode of this embodiment can have better capacitance characteristics than conventional variable capacitance diodes.

[0035] Other Embodiments In the above, an embodiment has been described in which the p-type semiconductor is a compound semiconductor containing metal cations whose vacancies are the origin of space charge and anions from Groups 15 to 17 of the periodic table, and the n-type semiconductor is a compound semiconductor containing a dopant (donor), but this is not limiting. For example, the p-type semiconductor may be a compound semiconductor containing a dopant (acceptor), and the n-type semiconductor may be a compound semiconductor containing metal cations whose vacancies are the origin of space charge and anions from Groups 15 to 17 of the periodic table. For example, Li-doped NiO may be used as the p-type semiconductor, and undoped BaTiO where oxygen vacancies are the origin of space charge may be used as the n-type semiconductor. ３ In this case, the n-type semiconductor becomes deficient in anions (for example, oxygen ions) due to the heat treatment, and the anion vacancies become the origin of space charge, so that the n-type semiconductor functions as an n-type semiconductor.

[0036] The variable capacitance diode of this other embodiment does not require the design of a diffusion coefficient (design of the dopant amount) to realize a hyperabrupt junction as in the conventional technology, and the manufacturing process is practical, and the capacitance characteristics can be improved compared to conventional variable capacitance diodes.

[0037] In yet another embodiment, for example, both the p-type semiconductor and the n-type semiconductor may be compound semiconductors containing metal cations whose vacancies are the origin of space charge and anions of Groups 15 to 17 of the periodic table. In such an embodiment, both the p-type semiconductor side and the n-type semiconductor side can be hyperabrupt junctions, further improving the capacitance characteristics of the variable capacitance diode.

[0038] In the above-described embodiment, the n-type semiconductor is La-doped BaTiO ３ Although the p-type semiconductor is described as being NiO (polycrystalline), it may be a single crystal of Si, etc. However, from the viewpoint of facilitating diffusion of elements of the semiconductor on the side that forms the hyperabrupt junction through grain boundaries, the semiconductor on the side that does not form the hyperabrupt junction may be polycrystalline.

[0039] [Method for Manufacturing the Variable Capacitance Diode of the Present Disclosure] Next, a method for manufacturing the variable capacitance diode 1 of the present disclosure will be described. As an example, a method for manufacturing a variable capacitance diode in which the p-type semiconductor is a compound semiconductor containing metal cations and anions of Groups 15 to 17 of the periodic table, and the n-type semiconductor is a compound semiconductor containing a dopant (donor) will be described in detail. The method for manufacturing the variable capacitance diode includes a pn junction step and a thermal diffusion step.

[0040] First, a compound semiconductor having a dopant (donor) is prepared as an n-type semiconductor. For example, BaTiO ３ The powder is molded into a tablet shape with a diameter of 8 mm and a thickness of approximately 0.7 mm. ２ / N ２ By performing reduction baking in a reducing atmosphere at 1350° C. for 2 hours, a compound semiconductor containing a dopant (donor) can be prepared.

[0041] Next, a p-type semiconductor is formed on the n-type semiconductor. For example, NiO is formed. Specifically, La-doped BaTiO ３ A NiO film is formed on the polycrystalline body by chemical solution deposition to a thickness of approximately 60 nm. Chemical solution deposition is a method of applying a metal salt solution to a substrate by a method such as spin coating, followed by heat treatment in the atmosphere to obtain a metal oxide thin film. When forming NiO, the metal salt solution may be a solution of nickel acetate tetrahydrate dissolved in dimethylformamide. The heat treatment is preferably performed at a temperature at which the counter anions of the metal salt decompose. The method for forming the NiO film is not limited to this method, and other methods may also be used. A pn ​​junction is formed through this process.

[0042] After forming a p-type semiconductor on an n-type semiconductor to form a pn junction, a heat treatment is performed in an oxidizing atmosphere to diffuse Ni into the n-type semiconductor, thereby forming a space charge distribution on the p-type semiconductor side with a gradient coefficient of 0.6 or more.

[0043] A suitable heat treatment temperature will be described in detail in the Examples below, but may be 900°C or higher. By performing heat treatment at 900°C or higher, a space charge distribution with a gradient coefficient of 0.6 or higher can be formed on the p-type semiconductor side. Note that if the heat treatment temperature is set to 1200°C or higher, oxygen vacancies will be filled with oxygen and La will volatilize and escape, resulting in insulation, so the upper limit of the heat treatment temperature may be set to 1200°C.

[0044] According to the manufacturing method of the variable capacitance diode 1 described above, it is not necessary to design the diffusion coefficient (design the amount of dopant) to realize a hyperabrupt junction as in the prior art, and therefore it is possible to manufacture a variable capacitance diode with good capacitance characteristics by a simple method.

[0045] Although the above-described embodiment describes a method for manufacturing a varactor diode in which the p-type semiconductor is a compound semiconductor containing metal cations whose vacancies are the origin of space charge and anions from Groups 15 to 17 of the periodic table, and the n-type semiconductor is a compound semiconductor containing a dopant (donor), the present invention is not limited to this embodiment. For example, the present invention may be a method for manufacturing a varactor diode in which the p-type semiconductor is a compound semiconductor containing a dopant (acceptor) and the n-type semiconductor is a compound semiconductor containing metal cations whose vacancies are the origin of space charge and anions from Groups 15 to 17 of the periodic table, or a method for manufacturing a varactor diode in which both the p-type semiconductor and the n-type semiconductor are compound semiconductors containing metal cations whose vacancies are the origin of space charge and anions from Groups 15 to 17 of the periodic table.

[0046] The variable capacitance diodes were evaluated for Examples 1 and 2 and Comparative Examples 1 to 6. The evaluation results are shown in Figures 5A and 5B.

[0047] Example 1 p-type semiconductor: NiO n-type semiconductor: La-doped BaTiO ３ Polycrystalline body Heat treatment temperature in thermal diffusion process: 900°C (RTA equipment: Model MILA-5050, manufactured by ADVANCE RIKO)

[0048] Example 2 p-type semiconductor: NiO n-type semiconductor: La-doped BaTiO ３ Polycrystalline body Heat treatment temperature in thermal diffusion process: 1050°C (electric furnace: model number KSB, manufactured by Motoyama Co., Ltd.)

[0049] Comparative Example 1 p-type semiconductor: NiO n-type semiconductor: La-doped BaTiO ３ Polycrystalline body Heat treatment temperature in thermal diffusion process: 400°C (RTA equipment: Model MILA-5050, manufactured by ADVANCE RIKO)

[0050] Comparative Example 2 p-type semiconductor: NiO n-type semiconductor: La-doped BaTiO ３ Polycrystalline body Heat treatment temperature in thermal diffusion process: 550°C (RTA equipment: Model MILA-5050, manufactured by ADVANCE RIKO)

[0051] Comparative Example 3 p-type semiconductor: NiO n-type semiconductor: La-doped BaTiO ３ Polycrystalline body Heat treatment temperature in thermal diffusion process: 600°C (RTA equipment: Model MILA-5050, manufactured by ADVANCE RIKO)

[0052] Comparative Example 4 p-type semiconductor: NiO n-type semiconductor: La-doped BaTiO ３ Polycrystalline body Heat treatment temperature in thermal diffusion process: 700°C (RTA equipment: Model MILA-5050, manufactured by ADVANCE RIKO)

[0053] Comparative Example 5: Si hyperabrupt junction variable capacitance diode (variable capacitance diode product number: 1SV101, manufactured by Toshiba Corporation)

[0054] Comparative Example 6: Si hyperabrupt junction variable capacitance diode (variable capacitance diode product number: 1SV149, manufactured by Toshiba Corporation)

[0055] The variable capacitance diode was evaluated by evaluating (1) the gradient coefficient γ, (2) the capacitance, and (3) the amount of Ni diffusion into the n-type semiconductor side.

[0056] (1) Evaluation results of the gradient coefficient γ The gradient coefficient γ was calculated by measuring the reverse voltage dependence of the capacitance. The measurement method was to deposit a gold dot pattern of 1 mm diameter as an upper electrode on the NiO film by vapor deposition, and then deposit a La-doped BaTiO ３ An InGa paste was applied to the polycrystalline body as a lower electrode. The capacitance was measured using an LCR meter (model number 4284A, Keysight Technologies) while applying an AC voltage of 1 kHz and 100 mV. The capacitance was measured while changing the reverse voltage Vr (i.e., the reverse voltage, i.e., the direction in which the n-type semiconductor side has a higher potential, is positive) from 4 V to -0.6 V in increments of -0.1 V.

[0057] The slope coefficient γ was calculated by fitting a graph of the reverse voltage dependence of the measured capacitance. Specifically, the graph of the reverse voltage dependence of the capacitance of the variable capacitance diode was modeled using the following equation: C=C ０ (1+Vr / Vbi) －γ In addition, C ０: capacitance when the reverse voltage is 0 V, Vr: reverse voltage, Vbi: built-in potential of the variable capacitance diode, γ: gradient coefficient.

[0058] In Examples 1 and 2, the gradient coefficient γ was 0.6 or more, while in Comparative Examples 1 to 4, the gradient coefficient γ was less than 0.6.

[0059] (2) Capacitance Evaluation Results The capacitance was evaluated by measuring the capacitance per unit area when the reverse voltage was 1 V. For Examples 1 and 2 and Comparative Examples 1 to 4, the capacitance per unit area was calculated by dividing the area of ​​the upper electrode, which was 1 mm in diameter. For Comparative Examples 5 and 6, the capacitance was calculated by dividing the area of ​​the external dimensions (4.2 mm wide x 2.6 mm deep) of the variable capacitance diode when viewed from above. The capacitance ratio was calculated by dividing the capacitance when the reverse voltage was 0 V by the capacitance when the reverse voltage was 4 V.

[0060] In Examples 1 and 2, the gradient coefficient γ was 0.6 or more, and the capacitance ratio was 1.6 or more, which was larger than that of Comparative Examples 1 to 4, which had a gradient coefficient of less than 0.6. In addition, in Examples 1 and 2, the capacitance was 6 nF / mm ２ This was higher than that of the conventional variable capacitance diodes using Si (Comparative Examples 5 and 6).

[0061] (3) Evaluation results of the amount of Ni diffusion into the n-type semiconductor side As a method for evaluating the amount of Ni diffusion into the n-type semiconductor side, Dynamic-SIMS (model number IMS-7f, CAMECA Corporation) was used to measure Cs ＋ The element distribution of Ni in the depth direction was obtained for each sample of each example or comparative example while digging NiO by irradiating the NiO surface with ions. Note that depth=0 indicates the p-type semiconductor surface, and the direction of increasing depth indicates the depth direction of the n-type semiconductor side (La-doped BaTiO ３ The amount of Ni diffused into the n-type semiconductor side is shown in FIG. 5A, and the distribution of the amount of Ni in the depth direction is shown in FIG.

[0062] In Examples 1 and 2, the average value of the Ni secondary ion intensity in the region 2.5 μm or more deep from the surface was 50 cps or more.３ The results showed that Ni was diffused to the polycrystalline side. In other words, the amount of Ni element was reduced on the NiO side as shown in Figure 4B, and it is thought that a hyperabrupt junction like that shown in Figure 4A was formed on the NiO side.

[0063] On the other hand, in Comparative Examples 1 and 4, the average value of the Ni secondary ion intensity in the region 2.5 μm or more deep from the surface was less than 20 cps, and therefore, the La-doped BaTiO ３ The results showed that Ni diffusion into the polycrystalline body was less than in Examples 1 and 2. This is thought to be why the hyperabrupt junctions shown in FIG. 4A were not formed in Comparative Examples 1 and 4. Elemental analysis using Dynamic-SIMS revealed that Cs ＋ It is known that ion beam irradiation causes a knock-on effect, in which elements on the sample surface are pushed into the sample. Based on this, it can be inferred that the detection of Ni at approximately 10 cps in Comparative Examples 1 and 4 is due to the knock-on effect, and that the La-doped BaTiO ３ It can be determined that the amount of Ni diffused into the polycrystalline body is very small.

[0064] According to the above evaluation results (1) to (3), it can be seen that the variable capacitance diode of the present disclosure has improved electrical characteristics compared to conventional variable capacitance diodes.

[0065] The variable capacitance diode of the present disclosure includes the following aspects: <1> A variable capacitance diode in which a p-type semiconductor and an n-type semiconductor are formed at a pn junction, at least one of the p-type semiconductor and the n-type semiconductor is a compound semiconductor containing a metal cation and an anion of Groups 15 to 17 of the periodic table, the compound semiconductor does not contain a dopant, and the gradient coefficient is 0.6 or more. <2> The variable capacitance diode according to <1>, in which the compound semiconductor is an oxide semiconductor. <3> The oxide semiconductor is a compound semiconductor containing NiO, Co ３ O ４and CuO. <4> The variable capacitance diode according to any one of <1> to <3>, wherein the compound semiconductor has a relative dielectric constant of 15 or more. <5> The variable capacitance diode according to any one of <1> to <4>, wherein the other of the p-type semiconductor and the n-type semiconductor is a compound semiconductor containing a dopant. <6> The compound semiconductor containing a dopant is BaTiO doped with La. ３ <7> The variable capacitance diode according to <5>, wherein the compound semiconductor containing a dopant is a polycrystalline material. <8> The variable capacitance diode according to any one of <5> to <7>, wherein the compound semiconductor containing a dopant is an n-type semiconductor. <9> The variable capacitance diode according to any one of <1> to <8>, wherein the compound semiconductor containing a metal cation and an anion of Groups 15 to 17 of the periodic table is a p-type semiconductor. <10> A method for manufacturing a variable capacitance diode in which a p-type semiconductor and an n-type semiconductor are junctioned together by a p-n junction, and at least one of the p-type semiconductor and the n-type semiconductor is a compound semiconductor containing a metal cation and an anion of Groups 15 to 17 of the periodic table, and the compound semiconductor does not contain a dopant, the method comprising: a p-n junction step of forming at least one of the compound semiconductors forming the p-n junction by a liquid phase method; and a thermal diffusion step of performing thermal diffusion after the p-n junction step to set the gradient coefficient to 0.6 or more. <11> The method for manufacturing a variable capacitance diode according to <10>, wherein the heat treatment temperature in the thermal diffusion step is 900° C. or higher.

[0066] It should be noted that the embodiments disclosed herein are illustrative in all respects and are not intended to be limiting. Therefore, the technical scope of the present disclosure should not be interpreted solely by the above-described embodiments, but should be defined based on the claims. The technical scope of the present disclosure also includes all modifications within the scope and meaning equivalent to the claims.

[0067] The present disclosure can be used for a variable capacitance diode in which the capacitance characteristics are improved by a simple technique.

[0068] 1 variable capacitance diode 10 p-type semiconductor 20 n-type semiconductor

Claims

1. A variable capacitance diode comprising a p-type semiconductor and an n-type semiconductor formed as a pn junction, at least one of the p-type semiconductor and the n-type semiconductor being a compound semiconductor containing a metal cation and an anion of Groups 15 to 17 of the periodic table, the compound semiconductor containing no dopant, and having a gradient coefficient of 0.6 or more.

2. The variable capacitance diode according to claim 1, wherein the compound semiconductor is an oxide semiconductor.

3. The oxide semiconductor is NiO, Co ３ O ４ 3. The variable capacitance diode of claim 2, wherein the at least one selected from the group consisting of CuO and CuO.

4. The variable capacitance diode according to any one of claims 1 to 3, wherein the compound semiconductor has a relative dielectric constant of 15 or more.

5. A variable capacitance diode according to any one of claims 1 to 4, wherein the other of the p-type semiconductor and the n-type semiconductor is a compound semiconductor containing a dopant.

6. The compound semiconductor containing the dopant is La-doped BaTiO ３ 6. The variable capacitance diode according to claim 5, 7. The variable capacitance diode according to claim 5 or 6, wherein the compound semiconductor containing the dopant is a polycrystalline material.

8. The variable capacitance diode according to any one of claims 5 to 7, wherein the compound semiconductor containing a dopant is an n-type semiconductor.

9. The variable capacitance diode according to any one of claims 1 to 8, wherein the compound semiconductor containing the metal cation and the anion of Groups 15 to 17 of the periodic table is a p-type semiconductor.

10. A method for manufacturing a variable capacitance diode, the method comprising: a pn junction step of forming at least one of a p-type semiconductor and an n-type semiconductor into a pn junction, the p-type semiconductor and the n-type semiconductor being a compound semiconductor containing a metal cation and an anion of Groups 15 to 17 of the periodic table, by a liquid phase method; and a thermal diffusion step of carrying out thermal diffusion after the pn junction step to set the gradient coefficient to 0.6 or more.

11. The method for manufacturing a variable capacitance diode according to claim 10, wherein in the thermal diffusion step, the heat treatment temperature is higher than 900°C.

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