Semiconductor device

Abstract

The present invention increases on-state current of a semiconductor device. This semiconductor device (1) comprises a switch body (20) and a light-emitting element (10). The switch body (20) comprises a substrate (21), a channel layer (22) having a first band gap above the substrate (21), and a barrier layer (23) having a second band gap larger than the first band gap, in that order. Provided are a pair of electrodes (24, 25) provided above the barrier layer (23) so as to be apart from each other in a plan view of the substrate (21), and a pn gate layer (26) provided between at least a part of one electrode (24) and the other electrode (25) in a plan view of the substrate (21). The pn gate layer (26) includes a p-type layer (26p), an n-type layer (26n), and a light-absorbing layer (26a) provided between the p-type layer (26p) and the n-type layer (26n). The light-absorbing layer (26a) is capable of absorbing light of a wavelength longer than the wavelength band of light absorbed by the p-type layer (26p) and the n-type layer (26n), and absorbs light emitted by the light-emitting element (10).

Description

Semiconductor equipment

[0001] This disclosure relates to semiconductor devices.

[0002] Conventionally, relay devices utilizing photodetectors are known. For example, Patent Documents 1 to 3 disclose photodetectors having an AlGaN / GaN heterostructure. In the photodetectors disclosed in Patent Documents 1 to 3, a two-dimensional electron gas (2DEG: 2-Dimensional Electron Gas) generated near the interface of the heterojunction is used as a channel. By controlling the generation of 2DEG with light, it becomes possible to detect light or control conduction and non-conductivity with light.

[0003] International Publication No. 2007 / 135739, Japanese Patent Publication No. 2012-33773, Japanese Patent Publication No. 2010-73744

[0004] Conventional photodetectors have the problem of having a small on-current.

[0005] Therefore, this disclosure provides a semiconductor device that can increase the on-current.

[0006] A semiconductor device according to one aspect of the present disclosure comprises a switch body and a light-emitting element. The switch body comprises a substrate, a first nitride semiconductor layer having a first band gap, a second nitride semiconductor layer having a second band gap larger than the first band gap, a first electrode, a second electrode, and a third nitride semiconductor layer. The first nitride semiconductor layer is provided above the substrate. The second nitride semiconductor layer is provided above the first nitride semiconductor layer. The first electrode and the second electrode are provided above the second nitride semiconductor layer, spaced apart from each other in a plan view of the substrate. The third nitride semiconductor layer is provided above the second nitride semiconductor layer, between at least a portion of the first electrode and the second electrode in a plan view of the substrate. The third nitride semiconductor layer includes a first p-type nitride semiconductor layer, a first n-type nitride semiconductor layer, and a first light-absorbing layer provided between the first p-type nitride semiconductor layer and the first n-type nitride semiconductor layer. The first light-absorbing layer is capable of absorbing light with wavelengths longer than the wavelength band of light absorbed by the first p-type nitride semiconductor layer and the first n-type nitride semiconductor layer, and absorbs light emitted by the light-emitting element.

[0007] According to this disclosure, the on-current can be increased.

[0008] Figure 1 is a cross-sectional view showing the configuration of a semiconductor device according to Embodiment 1. Figure 2 is a cross-sectional view illustrating the switching between the ON and OFF states of the semiconductor device according to Embodiment 1. Figure 3 is an energy band diagram of a first example of a switch body provided in the semiconductor device according to Embodiment 1. Figure 4 is an energy band diagram of a second example of a switch body provided in the semiconductor device according to Embodiment 1. Figure 5 is an energy band diagram of a third example of a switch body provided in the semiconductor device according to Embodiment 1. Figure 6 is a cross-sectional view showing the relationship between the band gaps of each layer in the switch body provided in a semiconductor device according to a modified example of Embodiment 1. Figure 7 is a cross-sectional view showing the configuration of a switch body provided in a semiconductor device according to Embodiment 2. Figure 8 is a cross-sectional view showing the configuration of a switch body provided in a semiconductor device according to Embodiment 3. Figure 9 is a cross-sectional view showing the configuration of a switch body provided in a semiconductor device according to Embodiment 4.

[0009] (Summary of the Disclosure) A semiconductor device according to a first aspect of the Disclosure comprises a switch body and a light-emitting element. The switch body comprises a substrate, a first nitride semiconductor layer having a first band gap, a second nitride semiconductor layer having a second band gap larger than the first band gap, a first electrode and a second electrode, and a third nitride semiconductor layer. The first nitride semiconductor layer is provided above the substrate. The second nitride semiconductor layer is provided above the first nitride semiconductor layer. The first electrode and the second electrode are provided above the second nitride semiconductor layer, spaced apart from each other in a plan view of the substrate. The third nitride semiconductor layer is provided above the second nitride semiconductor layer, between at least a portion of the first electrode and the second electrode in a plan view of the substrate. The third nitride semiconductor layer includes a first p-type nitride semiconductor layer, a first n-type nitride semiconductor layer, and a first light-absorbing layer provided between the first p-type nitride semiconductor layer and the first n-type nitride semiconductor layer. The first light-absorbing layer is capable of absorbing light with wavelengths longer than the wavelength band of light absorbed by the first p-type nitride semiconductor layer and the first n-type nitride semiconductor layer, and absorbs light emitted by the light-emitting element.

[0010] As a result, since the light absorption layer is provided, light can be efficiently absorbed between the first p-type nitride semiconductor layer and the first n-type nitride semiconductor layer, and a high photovoltaic power can be generated. Therefore, even with a small amount of light, the switch body can be made conductive, and the on-current flowing between the first electrode and the second electrode can be increased. Further, light in a wavelength band that cannot be absorbed by the first p-type nitride semiconductor layer and the first n-type nitride semiconductor layer can also be absorbed by the light absorption layer. Thereby, the wavelength band of light that can control the switching of the switch body can be expanded. For this reason, the degree of freedom in selecting a light emitting element can be increased.

[0011] The semiconductor device according to the second aspect of the present disclosure is based on the semiconductor device according to the first aspect, and the band gap of the first light absorption layer is smaller than the energy of photons emitted by the light emitting element.

[0012] As a result, the light absorption layer can efficiently absorb the light emitted by the light emitting element, so that the loss of power consumption can be suppressed.

[0013] The semiconductor device according to the third aspect of the present disclosure is based on the semiconductor device according to the second aspect, and the first light absorption layer contains InGaN as a main component.

[0014] As a result, the light absorption layer can efficiently absorb light in the visible light band such as blue light. As the light emitting element, an inexpensive blue LED (Light Emitting Diode) or the like can be used.

[0015] The semiconductor device according to the fourth aspect of the present disclosure is based on the semiconductor device according to the third aspect, and the composition ratio of In in the first light absorption layer is 5% or more.

[0016] As a result, the absorption efficiency of blue light in the light absorption layer can be increased.

[0017] The semiconductor device according to the fifth aspect of the present disclosure is based on the semiconductor device according to the first aspect, and the first light absorption layer contains a p-type dopant and an n-type dopant.

[0018] As a result, the p-type and n-type dopants compensate for each other, and the light-absorbing layer effectively becomes an i-type nitride semiconductor layer. Since the light-absorbing region between the first p-type nitride semiconductor layer and the first n-type nitride semiconductor layer can be expanded, the switch body can be made to conduct even with a small amount of light, and the on-current can be increased. Furthermore, by utilizing the defect levels caused by the dopants added to the light-absorbing layer, light in a wavelength band longer than the wavelength of light corresponding to the band gap of the light-absorbing layer can also be absorbed. Therefore, the wavelength band of light over which the switching of the switch body can be controlled can be expanded.

[0019] A semiconductor device according to a sixth aspect of this disclosure is based on a semiconductor device according to a fifth aspect, wherein the p-type dopant is Mg or Be, and the n-type dopant is Si or Ge.

[0020] This allows for a larger on-current, similar to the semiconductor device according to the fifth embodiment. Furthermore, it expands the wavelength range of light over which the switching of the switch body can be controlled.

[0021] A semiconductor device according to a seventh aspect of this disclosure is based on a semiconductor device according to a first aspect, wherein the first light-absorbing layer comprises at least one element selected from the group consisting of C, F, and transition metal elements, 1 × 10 １６ cm －３ The above and 2 x 10 １９ cm －３ It contains the following concentrations.

[0022] As a result, carriers are trapped in deeper energy levels by the elements added to the light-absorbing layer. Since the trapped carriers can be excited by low-energy light, the light-absorbing layer can also absorb light in the long-wavelength range. Therefore, the wavelength range of light that can control the switching of the switch body can be expanded.

[0023] A semiconductor device according to the eighth aspect of this disclosure is based on a semiconductor device according to any one of the first to seventh aspects, wherein the energy of photons emitted by the light-emitting element is smaller than the band gap of either the first p-type nitride semiconductor layer or the first n-type nitride semiconductor layer.

[0024] This allows light incident on the switch body to pass through the first p-type nitride semiconductor layer and the first n-type nitride semiconductor layer, and be efficiently absorbed by the light absorption layer.

[0025] A semiconductor device according to the ninth aspect of this disclosure is based on a semiconductor device according to any one of the first to eighth aspects, wherein the thickness of the first light-absorbing layer is 100 nm or more.

[0026] This allows for a larger light absorption area, enabling the switch body to conduct electricity even with low light levels, thus increasing the on-current.

[0027] A semiconductor device according to a tenth aspect of the present disclosure is based on a semiconductor device according to any one of the first to ninth aspects, wherein the first band gap is smaller than the energy of the photons emitted by the light-emitting element.

[0028] This allows light to be absorbed even in the first nitride semiconductor layer, which includes the channel. This increases the amount of electrons in the first nitride semiconductor layer, lowers the on-resistance, and increases the on-current.

[0029] A semiconductor device according to an eleventh aspect of the present disclosure is based on a semiconductor device according to a tenth aspect, wherein the first nitride semiconductor layer mainly contains InGaN.

[0030] This allows the first nitride semiconductor layer to efficiently absorb light in the visible light band, such as blue light.

[0031] A semiconductor device according to a twelfth aspect of this disclosure is based on a semiconductor device according to an eleventh aspect, wherein the composition ratio of In in the first nitride semiconductor layer is 5% or more.

[0032] This makes it possible to increase the absorption efficiency of blue light in the first nitride semiconductor layer.

[0033] A semiconductor device according to a thirteenth aspect of the present disclosure is based on a semiconductor device according to any of the first to twelfth aspects, wherein the first electrode is electrically connected to a first n-type nitride semiconductor layer.

[0034] As a result, since the first n-type nitride semiconductor layer is electrically connected to the first electrode, even if holes accumulate in the first p-type nitride semiconductor layer during light irradiation (on state), in the off state, the accumulated holes can be released to the first electrode via the first n-type nitride semiconductor layer. Therefore, it is possible to suppress the potential of the first p-type nitride semiconductor layer from increasing in the off state, so that the 2DEG directly below the first p-type nitride semiconductor layer is sufficiently depleted and the off-leak current can be reduced.

[0035] A semiconductor device according to a fourteenth aspect of the present disclosure is based on a semiconductor device according to any one of the first to thirteenth aspects, wherein the conduction and non-conductivity between the first electrode and the second electrode are switched by the emission and non-emission of an emission-emitting element.

[0036] This makes it possible to switch the switch body by emitting and deemitting light from the light-emitting element.

[0037] A semiconductor device according to a 15th aspect of the present disclosure is based on a semiconductor device according to a first aspect, wherein a two-dimensional electron gas is generated at the interface between a first nitride semiconductor layer and a second nitride semiconductor layer, and when the light-emitting element is not emitting light, the two-dimensional electron gas disappears in the region below the first p-type nitride semiconductor layer.

[0038] This allows the switch itself to be switched by utilizing the generation and disappearance of 2DEG.

[0039] A semiconductor device according to a sixteenth aspect of the present disclosure is based on a semiconductor device according to a first aspect and further comprises a fourth nitride semiconductor layer provided above a second nitride semiconductor layer, between a third nitride semiconductor layer and at least a portion of the second electrode in a plan view of the substrate. The fourth nitride semiconductor layer includes a second p-type nitride semiconductor layer, a second n-type nitride semiconductor layer, and a second light-absorbing layer provided between the second p-type nitride semiconductor layer and the second n-type nitride semiconductor layer. The second light-absorbing layer is capable of absorbing light with wavelengths longer than the wavelength band of light absorbed by the second p-type nitride semiconductor layer and the second n-type nitride semiconductor layer, and absorbs light emitted by a light-emitting element.

[0040] This enables bidirectional switching.

[0041] A semiconductor device according to a 17th aspect of the present disclosure further includes a third electrode and a fifth nitride semiconductor layer, based on the semiconductor device according to the first aspect. The third electrode is provided above the second nitride semiconductor layer, spaced apart from the first electrode so as to sandwich the first electrode between the second electrode and the third electrode in a plan view of the substrate. The fifth nitride semiconductor layer is provided above the second nitride semiconductor layer, spaced between at least a portion of the first electrode and the third electrode in a plan view of the substrate. The fifth nitride semiconductor layer includes a third p-type nitride semiconductor layer, a third n-type nitride semiconductor layer, and a third light-absorbing layer provided between the third p-type nitride semiconductor layer and the third n-type nitride semiconductor layer. The third light-absorbing layer is capable of absorbing light with wavelengths longer than the wavelength band of light absorbed by the third p-type nitride semiconductor layer and the third n-type nitride semiconductor layer, and absorbs light emitted by a light-emitting element.

[0042] This enables bidirectional switching.

[0043] A semiconductor device according to an eighteenth aspect of the present disclosure is based on a semiconductor device according to a first aspect, wherein the third nitride semiconductor layer further includes a fourth n-type nitride semiconductor layer, a fourth p-type nitride semiconductor layer, and a fourth light-absorbing layer. The fourth n-type nitride semiconductor layer is provided between the first light-absorbing layer and the first n-type nitride semiconductor layer. The fourth p-type nitride semiconductor layer is provided between the fourth n-type nitride semiconductor layer and the first n-type nitride semiconductor layer. The fourth light-absorbing layer is provided between the fourth p-type nitride semiconductor layer and the first n-type nitride semiconductor layer. The fourth p-type nitride semiconductor layer is in ohmic contact with the fourth n-type nitride semiconductor layer.

[0044] This allows the voltage generated by the photovoltaic effect to be increased, thereby further increasing the concentration of 2DEG generated directly beneath the first p-type nitride semiconductor layer. Consequently, the on-resistance is reduced and can be further increased.

[0045] The embodiments will be described in detail below with reference to the drawings.

[0046] The embodiments described below are all comprehensive or specific examples. The numerical values, shapes, materials, components, arrangement and connection configurations of components, steps, and the order of steps shown in the following embodiments are examples only and are not intended to limit this disclosure. Furthermore, any components in the following embodiments that are not described in an independent claim will be described as optional components.

[0047] Furthermore, each figure is a schematic diagram and not necessarily a strictly accurate representation. Therefore, for example, the scale may not necessarily match in each figure. Also, in all figures, substantially identical components are given the same reference numerals, and redundant explanations are omitted or simplified.

[0048] Furthermore, in this specification, terms indicating relationships between elements such as parallel and perpendicular, terms indicating the shape of elements, and numerical ranges do not represent only strict meanings, but also include substantially equivalent ranges, such as differences of a few percent.

[0049] Furthermore, in this specification, the terms "upper" and "lower" do not refer to the upward (vertically upward) and downward (vertically downward) directions in absolute spatial perception, but rather are used as terms defined by the relative positional relationship based on the stacking order in a stacked configuration. Moreover, the terms "upper" and "lower" apply not only when two components are spaced apart and another component exists between them, but also when two components are placed in close proximity and touching each other.

[0050] Furthermore, in this specification, "main component" means the component with the highest content among all components constituting the member. For example, a component with a content of 50% or more is the main component. Components include materials, elements, or compounds. Also, "member A is composed of component B" means that member A substantially contains only component B. However, member A may contain impurities other than component B that are unavoidable to include during manufacturing. The content of such unavoidable impurities is 1% or less.

[0051] Furthermore, in this specification, a GaN layer means a nitride semiconductor layer containing GaN as the main component. An n-type GaN layer and a p-type GaN layer are formed by adding an n-type dopant (donor) or a p-type dopant (acceptor) to a GaN layer. Examples of n-type impurities include Si and Ge. Examples of p-type impurities include Mg and Be. However, the addition of impurities is not necessarily required to form an n-type or p-type GaN layer. For example, even an undoped GaN layer can be formed. １５ cm －３ A GaN layer that maintains a certain carrier concentration can be used as an n-type GaN layer. Note that "undoped" is a term meaning that n-type or p-type impurities are not doped, and does not mean that no impurities are doped at all. That is, a GaN layer doped with C, etc., or a GaN layer containing unavoidable impurities due to manufacturing, can also be considered "undoped." This undoped GaN layer is sometimes called an i-type GaN layer. Note that i-type refers to the characteristics of a layer manufactured without intrinsic doping, i.e., intentional doping.

[0052] Furthermore, in this specification, ordinal numbers such as "first," "second," etc., do not mean the number or order of components unless otherwise specified, but are used to avoid confusion and to distinguish similar components.

[0053] (Embodiment 1) [Configuration] First, the configuration of the semiconductor device according to Embodiment 1 will be described using Figure 1.

[0054] Figure 1 is a cross-sectional view of the semiconductor device 1 according to this embodiment. In Figure 1, the light-emitting element 10 is schematically represented by a circuit symbol.

[0055] The semiconductor device 1 according to this embodiment is a semiconductor relay that relays an input signal and outputs it to a predetermined circuit. Specifically, the semiconductor device 1 is an optically coupled semiconductor relay. Semiconductor relays are also called SSRs (Solid-State Relays).

[0056] As shown in Figure 1, the semiconductor device 1 comprises a light-emitting element 10 and a switch body 20. The light-emitting element 10 and the switch body 20 are supported by one or more mounting substrates or frames (not shown). The light-emitting element 10 and the switch body 20 may be integrally constructed or packaged together.

[0057] The light-emitting element 10 is an element that emits light. When the semiconductor device 1 is used as a semiconductor relay, an input signal is input to the light-emitting element 10. The light-emitting element 10 switches between emitting light and not emitting light according to the input signal. In this embodiment, the light-emitting element 10 emits light toward the switch body 20. The light-emitting element 10 is electrically insulated from the switch body 20. As will be described in detail later, the light-emitting element 10 emits light that is incident on the pn gate layer 26 of the switch body 20. At least a portion of this light may be incident on the channel layer 22 and barrier layer 23 of the switch body 20.

[0058] For example, the light-emitting element 10 is an LED (Light Emitting Diode) element. The light emitted by the light-emitting element 10 is, for example, blue light, but is not limited to this. The light emitted by the light-emitting element 10 may be other visible light such as violet light or white light, or it may be ultraviolet light. The light-emitting element 10 may also be an organic EL (Electroluminescence) element or a semiconductor laser element.

[0059] In this embodiment, the light-emitting element 10 is provided above the switch body 20. In this specification, "above" means the direction in which the channel layer 22, barrier layer 23, etc., are provided, as viewed from the substrate 21 of the switch body 20. "Below" is the opposite direction to "above". The light-emitting element 10 may also be provided below the switch body 20. For example, the light-emitting element 10 may be provided in direct contact with the substrate 21 of the switch body 20, or it may be provided via other layers such as an insulating layer.

[0060] The switch body 20 switches between conductive (on) and non-conductive (off) depending on the incident light. Specifically, in the switch body 20, the conductivity between electrodes 24 and 25 switches depending on whether the light-emitting element 10 is emitting or not.

[0061] As shown in Figure 1, the switch body 20 comprises a substrate 21, a channel layer 22, a barrier layer 23, electrodes 24 and 25, a pn gate layer 26, and a protective film 27. In Figure 1, the cross-sectional areas of the channel layer 22 and barrier layer 23 of the switch body 20 are not shown with shading. The same applies to Figure 2 and other cross-sectional views described later.

[0062] The substrate 21 is an electrically insulating substrate. The substrate 21 is, for example, a sapphire substrate, but is not limited to this. The substrate 21 may be formed using SiC or the like. The substrate 21 may also be a GaN substrate, a Si substrate, or the like.

[0063] The substrate 21 may be reflective to light from the light-emitting element 10. Alternatively, the substrate 21 may be a light-transmitting substrate that is transparent to light from the light-emitting element 10. By using a light-transmitting substrate 21, the light-emitting element 10 can be placed below the substrate 21. In this case, the substrate 21 has a single-layer structure and a uniform refractive index inside. Therefore, refraction and scattering of light from the light-emitting element 10 placed below the substrate 21 can be suppressed, and light can be efficiently propagated to the pn gate layer 26. The substrate 21 may also have a multilayer structure.

[0064] The channel layer 22 is an example of a first nitride semiconductor layer having a first band gap, and is provided above the substrate 21. The channel layer 22 is, for example, an i-type GaN layer mainly composed of undoped GaN, but is not limited to this. The channel layer 22 may also mainly contain other nitride semiconductors such as InGaN and AlGaN. The channel layer 22 is formed using a film deposition method such as epitaxial growth on the substrate 21. The thickness of the channel layer 22 is, for example, 100 nm or more and 1000 nm or less, but is not limited to this. Other layers such as a buffer layer and a back barrier layer may be provided between the channel layer 22 and the substrate 21.

[0065] The barrier layer 23 is an example of a second nitride semiconductor layer having a second band gap larger than the first band gap, and is provided above the channel layer 22. In this embodiment, the barrier layer 23 is in contact with the upper surface of the channel layer 22. The barrier layer 23 is, for example, an i-type AlGaN layer mainly composed of undoped AlGaN. The barrier layer 23 is formed continuously after the channel layer 22 formation process using a film formation method such as epitaxial growth. The thickness of the barrier layer 23 is, for example, 5 nm or more and 100 nm or less, but is not limited thereto.

[0066] A heterojunction is formed by the barrier layer 23 and the channel layer 22, and a 2DEG 28 is generated near the junction interface within the channel layer 22 due to spontaneous polarization and piezoelectric polarization. The 2DEG 28 functions as a current path when the switch body 20 is ON. Note that if a 2DEG 28 is generated within the channel layer 22, another layer may be provided between the channel layer 22 and the barrier layer 23.

[0067] Electrodes 24 and 25 are examples of first and second electrodes, respectively, provided spaced apart from each other in a plan view of the substrate 21, and are located above the barrier layer 23. In this embodiment, each of electrodes 24 and 25 is in contact with the upper surface of the barrier layer 23. Each of electrodes 24 and 25 is formed using a conductive material such as metal. For example, each of electrodes 24 and 25 has a laminated structure including a Ti layer and an Al layer laminated on the upper surface of the Ti layer, but is not limited to this.

[0068] The pn gate layer 26 is an example of a third nitride semiconductor layer, and is provided above the barrier layer 23 and between at least a part of the electrode 24 and the electrode 25 in a plan view of the substrate 21. In the present embodiment, the pn gate layer 26 is provided between the portion where the electrode 24 contacts the barrier layer 23 and the electrode 25.

[0069] As shown in FIG. 1, the pn gate layer 26 includes a p-type layer 26p, an n-type layer 26n, and a light absorption layer 26a. In the present embodiment, the p-type layer 26p, the light absorption layer 26a, and the n-type layer 26n are stacked in this order from the barrier layer 23.

[0070] The p-type layer 26p is an example of a first p-type nitride semiconductor layer, and is provided above the barrier layer 23. In the present embodiment, the p-type layer 26p is in contact with the upper surface of the barrier layer 23. The p-type layer 26p is a p-type GaN layer mainly containing GaN doped with a p-type dopant such as Mg or Be. The thickness of the p-type layer 26p is, for example, 50 nm or more and 300 nm or less, but is not limited thereto. Also, the concentration of the p-type dopant in the p-type layer 26p is, for example, 1×10 １７ cm －３ or more and 1×10 １９ cm －３ or less, but is not limited thereto. The p-type layer 26p may mainly contain other nitride semiconductors such as AlGaN or InGaN.

[0071] The light absorption layer 26a is an example of a first light absorption layer, and is provided between the p-type layer 26p and the n-type layer 26n. Specifically, the light absorption layer 26a is provided above the p-type layer 26p. In the present embodiment, the light absorption layer 26a is in contact with the upper surface of the p-type layer 26p. The light absorption layer 26a can absorb light having a wavelength longer than the wavelength band of light absorbed by the p-type layer 26p and the n-type layer 26n. Specifically, the light absorption layer 26a absorbs the emitted light 30 emitted by the light emitting element 10 (see (b) of FIG. 2 described later). The specific configuration of such a light absorption layer 26a will be described later.

[0072] The n-type layer 26n is an example of the first n-type nitride semiconductor layer and is provided above the light absorption layer 26a. In this embodiment, the n-type layer 26n is in contact with the upper surface of the light absorption layer 26a. The n-type layer 26n is an n-type GaN layer mainly composed of GaN with n-type dopants such as Si and Ge added. The thickness of the n-type layer 26n is, for example, 50 nm or more and 300 nm or less, but is not limited thereto. The concentration of the n-type dopant in the n-type layer 26n is, for example, 1 × 10⁻¹⁶. １７ cm －３ The above and 1 x 10 １９ cm －３ The following are, but are not limited to, the n-type layer 26n. As mentioned above, the n-type layer 26n may be an i-type GaN layer that can be considered as an n-type GaN layer. Furthermore, the n-type layer 26n may contain other nitride semiconductors such as AlGaN or InGaN as its main component.

[0073] The protective film 27 is a film that covers the upper surface of the barrier layer 23 and the side surface of the pn gate layer 26. In this embodiment, the protective film 27 covers the upper surface of the barrier layer 23, the side surface of the pn gate layer 26, and a part of the upper surface of the pn gate layer 26, specifically a part of the upper surface of the n-type layer 26n, in contact with each other. The protective film 27 covers the side surface of the pn gate layer 26 that faces the electrode 25 and the side surface that faces away from the electrode 25. The protective film 27 is, for example, SiN, SiO ２ These are insulating films. Note that the protective film 27 may not be provided.

[0074] The electrode 24 is electrically connected to the n-type layer 26n through an opening provided in the protective film 27. In this embodiment, the electrode 24 extends toward the electrode 25 from the contact portion with the barrier layer 23 so as to cover a part of the protective film 27 and is in contact with the upper surface of the n-type layer 26n. As a result, the potential of the n-type layer 26n is fixed to the potential of the electrode 24.

[0075] [Operation] Next, the operation of the semiconductor device 1 according to this embodiment will be explained using Figure 2. Figure 2 is a cross-sectional view illustrating the switching between the off state and the on state of the semiconductor device 1 according to this embodiment.

[0076] In the semiconductor device 1, the conduction and non-conductivity between electrodes 24 and 25 are switched by the emission and non-emission of the light-emitting element 10. That is, the switch body 20 receives light from the light-emitting element 10 and switches between conduction (on) and non-conductivity (off) between electrodes 24 and 25. In this embodiment, the switch body 20 becomes conductive when it receives light and non-conductive when it does not receive light. In other words, the switch body 20 is a switching element controlled by light. The switch body 20 has a configuration similar to that of a transistor that functions as a switching element. For this reason, electrode 24 can be called the source electrode and electrode 25 can be called the drain electrode. The pn gate layer 26 corresponds to the control terminal (gate) of the transistor. For example, a higher voltage than that of electrode 24 is applied to electrode 25 as a bias voltage. The magnitude of the bias voltage is, for example, about 5V to 10V.

[0077] First, the off state will be explained using Figure 2(a). In the off state, the light-emitting element 10 is not emitting light. In the off state, the 2DEG 28 generated in the channel layer 22 disappears in the region below the p-type layer 26p. This is because the energy at the lower end of the conduction band directly below the p-type layer 26p increases (see Figure 3, which will be described later), causing depletion. As a result, the channel between electrode 24 and electrode 25 is blocked, and the switch body 20 becomes non-conductive (off).

[0078] Next, the ON state will be explained using Figure 2(b). In the ON state, the light-emitting element 10 is emitting light. The light emitted 30 from the light-emitting element 10 is mainly absorbed by the light-absorbing layer 26a of the pn gate layer 26. In the light-absorbing layer 26a, the incident light emitted 30 is photoelectrically converted, generating electron-hole pairs. The generated electron-hole pairs separate into electrons and holes, with the electrons moving to the n-type layer 26n and the holes moving to the p-type layer 26p. As a result, the potential of the p-type layer 26p increases due to the so-called photovoltaic effect, and the energy at the lower end of the conduction band of the channel layer 22 decreases (see Figure 3, which will be described later). This generates a 2DEG 28 in the channel layer 22 directly below the pn gate layer 26, so that the electrode 24 and electrode 25 conduct through the 2DEG 28. That is, the switch body 20 becomes conductive (ON).

[0079] In the ON state, the ON current can be increased by the 2DEG 28 and the electrons generated in the pn gate layer 26 due to the photovoltaic effect. Furthermore, since 2DEG 28 is generated directly below each of the electrodes 24 and 25, the contact resistance is reduced. This also contributes to increasing the ON current.

[0080] In the ON state, holes can accumulate in the p-type layer 26p. If holes continue to remain in the p-type layer 26p after the light-emitting element 10 is deactivated, the decrease in the potential of the p-type layer 26p will be delayed, causing off-leak current. In contrast, in this embodiment, since the n-type layer 26n is electrically connected to the electrode 24, even if holes accumulate in the p-type layer 26p during light irradiation (ON state), the accumulated holes can be released to the electrode 24 via the n-type layer 26n. This suppresses the increase in the potential of the p-type layer 26p in the OFF state, thereby reducing off-leak current.

[0081] Thus, according to the semiconductor device 1 of this embodiment, it is possible to achieve both an increase in on-current and a decrease in off-leak current.

[0082] If the light-absorbing layer 26a is not provided, the p-type layer 26p and the n-type layer 26n come into contact, forming a depletion layer. The width (depth) of the depletion layer depends on the carrier concentration of the p-type layer 26p, and tends to decrease as the carrier concentration increases. For example, if the carrier concentration of the n-type layer 26n is 1 × 10⁻⁶ １９ cm －３ If the carrier concentration in the p-type layer 26p is approximately 5 × 10⁻¹⁰ １７ cm －３ When the above conditions are met, the width of the depletion layer will be less than 100 nm (specifically, about 80 nm).

[0083] Therefore, in the switch body 20 according to this embodiment, a light-absorbing layer 26a with a thickness of 100 nm or more is provided. This makes it possible to increase the width of the depletion layer, that is, the size of the light-absorbing region, compared to the case where the p-type layer 26p and the n-type layer 26n are in contact. As a result, the amount of light absorbed by the light-absorbing layer 26a can be increased, so that the switch body 20 can be made to conduct even with a small amount of light, and the ON current can be increased.

[0084] [Light Absorption Layer] Next, we will explain the specific configuration of the light absorption layer 26a. There are three specific examples of the configuration of the light absorption layer 26a, and each example will be explained in turn below.

[0085] <Example 1> In the switch body 20 according to Example 1, the light-absorbing layer 26a is a nitride semiconductor layer with a smaller band gap than both the p-type layer 26p and the n-type layer 26n. Specifically, the light-absorbing layer 26a mainly contains InGaN. The composition ratio of In in the light-absorbing layer 26a is, for example, 5% or more.

[0086] The composition ratio refers to the proportion of a target element among one or more elements excluding nitrogen (N) in a nitride semiconductor. For example, in the case of InGaN, the composition ratio of In is expressed as the amount of In in relation to In and Ga. ｘ Ga １－ｘ When denoted as N, the subscript "x" for In represents the composition ratio of In. The composition ratio of In is also called the molar ratio. The composition ratio of Al can be determined for AlGaN in the same way as for InGaN.

[0087] Figure 3 is an energy band diagram of a first example of a switch body 20 provided in the semiconductor device 1 according to this embodiment. In Figure 3, the horizontal position represents the position in the thickness (depth) direction of the switch body 20, and the vertical position represents the energy from the vacuum level. Figure 3 E ｃ E represents the energy at the lower end of the conduction band. ｖ This represents the energy at the top of the valence band. The solid line shows the E when the light-emitting element 10 is not irradiated. ｃ and E ｖ The dashed line shows the E when light from the light-emitting element 10 is irradiated. ｃ and E ｖ This is shown. The same applies to Figures 4 and 5, which will be discussed later. Furthermore, the band gap of GaN is given by E below. ｇＧａＮ This is indicated as follows, and the band gap of InGaN is E ｇＩｎＧａＮ This is how it is written.

[0088] The n-type layer, light-absorbing layer, p-type layer, barrier layer, and channel layer shown in Figure 3 correspond to the n-type layer 26n, light-absorbing layer 26a, p-type layer 26p, barrier layer 23, and channel layer 22 shown in Figure 1, respectively. The back barrier layer shown in Figure 3 is a layer not shown in Figure 1 and is provided between the channel layer 22 and the substrate 21. The back barrier layer is a layer mainly composed of i-type AlGaN. These are also the case in Figures 4 and 5, which will be described later.

[0089] The band gap of the light-absorbing layer 26a is smaller than the energy of the photons emitted by the light-emitting element 10. As a result, the light emitted by the light-emitting element 10 is absorbed by the light-absorbing layer 26a, generating electron-hole pairs. At this time, the light emitted by the light-emitting element 10 is light with photon energy smaller than the band gap of the p-type layer 26p and the n-type layer 26n. As a result, the light emitted by the light-emitting element 10 is less absorbed by the p-type layer 26p and the n-type layer 26n, and is efficiently absorbed by the light-absorbing layer 26a. Because a large number of electron-hole pairs are generated in the light-absorbing layer 26a, the photovoltaic effect also increases. Therefore, as shown in Figure 2(b), 2DEG28 is generated directly below the pn gate layer 26, and conductivity occurs between electrode 24 and electrode 25 via 2DEG28. That is, the switch body 20 becomes conductive (on).

[0090] Here, we consider the light-absorbing layer 26a made of InGaN. The thickness of the light-absorbing layer 26a is assumed to be 100 nm. As an example, assuming light of 385 nm, if the composition ratio of In is 5% or more, E ｇＩｎＧａＮ ≤ 3.2eV and E ｇＩｎＧａＮ Since the energy is near or below the energy of a photon, the light absorption rate in the light absorption layer 26a becomes 90% or more. In contrast, when the composition ratio of In is 0%, i.e., when the light absorption layer 26a is a GaN layer, E ｇＧａＮ Since the value is 3.4 eV, the absorption rate of light at 385 nm is less than 10%. Furthermore, the absorption rate of the n-type layer 26n, which is made of GaN, for light with a wavelength of 385 nm is the same as when the light absorption layer 26a is a GaN layer. In addition, the p-type layer 26p has a band gap that is larger than the energy of the photon, and the light is absorbed by the light absorption layer 26a above it, so it effectively does not absorb light. For this reason, when both the p-type layer 26p and the n-type layer 26n are GaN layers, and the light absorption layer 26a is an InGaN layer, the incident light can be efficiently absorbed by the light absorption layer 26a.

[0091] Furthermore, by increasing the composition ratio of In, the band gap of the light absorption layer 26a can be reduced, thereby increasing the absorption efficiency of longer wavelength light. For example, if the composition ratio of In is 10% (E ｇＩｎＧａＮ (=2.9 ​​eV), the absorption rate of light at 430 nm becomes 90% or more. When the composition ratio of In becomes 20%, (E ｇＩｎＧａＮ (=2.6 eV), the absorption rate of light at 460 nm becomes 90% or more. In this way, by increasing the composition ratio of In, the wavelength range of light that the light absorption layer 26a can absorb can be expanded towards longer wavelengths. However, if the composition ratio of In is too high, the potential generated in the p-type layer 26p due to the photovoltaic effect will decrease, and the amount of 2DEG28 generated in the channel layer 22 will decrease, so the ON current of the switch body 20 will decrease. For this reason, the composition ratio of In can be set to, for example, 50% or less.

[0092] On the other hand, the p-type layer 26p and n-type layer 26n, both made of GaN, have absorption rates for light with wavelengths of 430 nm and 460 nm, respectively, which are less than or equal to the absorption rate of the GaN-based light-absorbing layer 26a for light with a wavelength of 385 nm. In other words, the p-type layer 26p and n-type layer 26n do not substantially absorb light with wavelengths of 430 nm or greater. By using InGaN with an In composition ratio of 5% or more, the light-absorbing layer 26a can absorb light at wavelengths that the p-type layer 26p and n-type layer 26n do not substantially absorb.

[0093] Based on the above, by using InGaN with an In composition ratio of 5% or more in the light absorption layer 26a, light of wavelengths that are not substantially absorbed by the p-type layer 26p and the n-type layer 26n becomes absorbable.

[0094] <Second Example> In the switch body 20 according to the second example, the light-absorbing layer 26a is a co-dope layer containing a p-type dopant and an n-type dopant. The p-type dopant is, for example, Mg or Be. The n-type dopant is, for example, Si or Ge. The light-absorbing layer 26a mainly contains GaN. Since the p-type dopant and the n-type dopant compensate for each other, the light-absorbing layer 26a can be considered substantially as an i-type GaN layer. The concentrations of the p-type dopant and n-type dopant contained in the light-absorbing layer 26a are designed so that their respective activated dopant concentrations are equal. Because the design takes the activation rate into consideration, the concentrations of the p-type dopant and the n-type dopant contained in the light-absorbing layer 26a are generally different. For example, the concentrations of the p-type dopant and the n-type dopant are 1 × 10⁻⁶. １７ cm －３ The above and 1 x 10 １９ cm －３ The following are possible, but are not limited to these. Furthermore, the p-type dopant concentration and the n-type dopant concentration may have a concentration gradient within the light-absorbing layer 26a.

[0095] Figure 4 is an energy band diagram of a second example of a switch body 20 provided in the semiconductor device 1 according to this embodiment. In Figure 4, the horizontal position represents the position in the thickness (depth) direction of the switch body 20, and the vertical position represents the magnitude of the electron energy. The solid line shows the energy when the light-emitting element 10 is not irradiated, and the dashed line shows the energy when the light-emitting element 10 is irradiated. Figure 4 E ｃ E represents the energy at the lower end of the conduction band. ｖ This represents the energy at the upper end of the valence band. In the switch body 20 according to the second example, the light absorption layer 26a has a donor level E due to the impurities, p-type dopants and n-type dopants. ｄ and acceptor level E ａ There are energy levels at both. Furthermore, for GaN, when Si is used as the n-type dopant and Mg as the p-type dopant, the donor level E ｄ is, E ｃ It is formed at an energy level approximately 20 meV lower, and the acceptor level E ａ is, E ｖ It is formed at an energy level approximately 200 meV higher.

[0096] The main component of the light-absorbing layer 26a in the second example is GaN, the same as the main component of the p-type layer 26p and the n-type layer 26n. Therefore, the band gap of the light-absorbing layer 26a is greater than the energy of the light emitted by the light-emitting element 10. On the other hand, in the light-absorbing layer 26a, the donor level E is affected by the addition of p-type and n-type dopants. ｄ and acceptor level E ａ Therefore, in the light-absorbing layer 26a, the donor level E ｄ and acceptor level E ａ Electron-hole pairs are generated through this process. As a result, the light absorption layer 26a can efficiently absorb light in the long-wavelength band that is not substantially absorbed by the undoped GaN layer.

[0097] In the case of GaN, the carrier activation rate of p-type dopants is generally lower than that of n-type dopants. Therefore, in the light-absorbing layer 26a where p-type and n-type dopants are added, p-type dopants are added at a higher concentration than n-type dopants to cancel out the electron concentration and hole concentration. As a result, excess dopant, especially p-type dopants, may occur in the light-absorbing layer 26a. If excess dopant is added in the light-absorbing layer 26a, lattice defects, etc., may occur in the crystal constituting the light-absorbing layer, and donor levels E may be affected. ｄ or acceptor level E ａ This is formed at deeper energy levels. In that case, the light-absorbing layer 26 can absorb light in an even longer wavelength range.

[0098] <Third Example> In the switch body 20 according to the third example, the light-absorbing layer 26a contains at least one element selected from the group consisting of C, F, and transition metal elements as an impurity. Transition metal elements include, for example, Fe, Sc, Ti, V, Cr, Mn, Co, Ni, Cu, or Zn. The light-absorbing layer 26a may contain multiple different types of transition metal elements. The concentration of impurities contained in the light-absorbing layer 26a is 1 × 10⁻⁶. １６ cm －３ The above and 2 x 10 １９ cm －３ The following applies:

[0099] Figure 5 is an energy band diagram of a third example of the switch body 20 of the semiconductor device 1 according to this embodiment. In Figure 5, the horizontal position represents the position in the thickness (depth) direction of the switch body 20, and the vertical position represents the magnitude of the electron energy. The solid line shows the energy when the light-emitting element 10 is not irradiated, and the dashed line shows the energy when the light-emitting element 10 is irradiated. Figure 5 E ｃ E represents the energy at the lower end of the conduction band. ｖ represents the energy at the upper end of the valence band. In the switch body 20 according to the third example, the light absorbing layer 26a contains E due to the presence of impurities such as C, F, or transition metal elements. ｃ or E ｖ Deep energy levels E exist at energy positions several hundred meV or more away.ｍ It exists.

[0100] The main component of the light-absorbing layer 26a in the third example is GaN, the same as the main component of the p-type layer 26p and the n-type layer 26n. Therefore, the band gap of the light-absorbing layer 26a is greater than the energy of the photons emitted by the light-emitting element 10. On the other hand, the light-absorbing layer 26a contains impurities such as C, F, or transition metal elements, which results in a deep energy level E ｍ Carriers are trapped. The trapped carriers are excited by photon energies lower than the band gap, generating electron-hole pairs. Therefore, the light absorption layer 26a can efficiently absorb light in the long wavelength range.

[0101] In the first to third examples described above, the light-emitting element 10 may be positioned opposite to the pn junction layer 26 when viewed from the substrate 21. For example, the light-emitting element 10 may be provided in direct contact with the substrate 21. The substrate 21 is a transparent substrate (transparent substrate) that is transparent to light from the light-emitting element 10, such as a sapphire substrate or a GaN substrate. In this case, the light from the light-emitting element 10 will enter the light-absorbing layer 26a via the substrate 21, channel layer 22, barrier layer 23, and p-type layer 26p. However, the substrate 21 transmits the light from the light-emitting element 10. Furthermore, the band gaps of the channel layer 22, barrier layer 23, and p-type layer 26p are all larger than the energy of the photons from the light-emitting element 10. Therefore, the light from the light-emitting element 10 is not absorbed much by these layers, allowing a lot of light to reach the light-absorbing layer 26a and be absorbed there.

[0102] [Modified Version] Next, a modified version of Embodiment 1 will be described. In the following description, the differences from Embodiment 1 will be the main focus, and the similarities will be omitted or simplified.

[0103] Figure 6 is a cross-sectional view showing the configuration of the semiconductor device 1A according to this modified example. Also, in Figure 6, similar to Figure 2(b), the state of the light-emitting element 10 when it is emitting light is schematically represented.

[0104] The switch body 20A of the semiconductor device 1A according to this modified example differs from the switch body 20 according to Embodiment 1 in that it has a channel layer 22A instead of a channel layer 22. The channel layer 22A differs from the channel layer 22 in that it has a smaller band gap.

[0105] Specifically, the channel layer 22A is an example of a first nitride semiconductor layer having a first band gap, and is provided above the substrate 21. In this modified example, the band gap of the channel layer 22A is smaller than the energy of the light emitted by the light-emitting element 10. Specifically, the channel layer 22A is, for example, an i-type InGaN layer mainly composed of undoped InGaN. The composition ratio of In in the channel layer 22A is, for example, 5% or more.

[0106] As a result, the light emitted by the light-emitting element 10 is absorbed not only by the light-absorbing layer 26a but also by the channel layer 22A. The electrons generated by the light absorption of the channel layer 22A can increase the concentration of 2DEG28. Therefore, the on-resistance can be reduced and the on-current can be further increased.

[0107] Furthermore, the band gap of the barrier layer 23 is greater than the energy of the light emitted by the light-emitting element 10. As a result, the light from the light-emitting element 10 passes through the barrier layer 23 with almost no absorption. Therefore, the light from the light-emitting element 10 can be efficiently incident on the channel layer 22A, and the on-current reduction effect can be enhanced.

[0108] (Embodiment 2) Next, Embodiment 2 will be described.

[0109] Embodiment 2 differs from Embodiment 1 in that it has two pn gate layers, giving the switch body a so-called drain common double gate structure. Below, we will mainly explain the differences from Embodiment 1, and omit or simplify the explanation of the common points.

[0110] Figure 7 is a cross-sectional view of the switch body 120 of the semiconductor device according to Embodiment 2. The switch body 120 includes an electrode 125 and a protective film 127 instead of the electrode 25 and protective film 27 according to Embodiment 1. Furthermore, the switch body 120 includes a pn gate layer 126.

[0111] Electrode 125 corresponds to electrode 25, but differs in that it is electrically connected to the n-type layer 126n of the pn gate layer 126. Protective film 127 corresponds to protective film 27, but differs in that it further covers a portion of the upper surface and the side surface of the pn gate layer 126.

[0112] The pn gate layer 126 is an example of a fourth nitride semiconductor layer and is provided above the barrier layer 23, between the pn gate layer 26 and at least a portion of the electrode 125 in a plan view of the substrate 21. In this embodiment, the pn gate layer 126 is provided between the pn gate layer 26 and the portion of the electrode 125 that contacts the barrier layer 23.

[0113] As shown in Figure 7, the pn gate layer 126 includes a p-type layer 126p, an n-type layer 126n, and a light-absorbing layer 126a. In this embodiment, the p-type layer 126p, the light-absorbing layer 126a, and the n-type layer 126n are stacked in this order from the barrier layer 23.

[0114] The p-type layer 126p is an example of a second p-type nitride semiconductor layer and is provided above the barrier layer 23. In this embodiment, the p-type layer 126p is in contact with the upper surface of the barrier layer 23. The p-type layer 126p is a p-type GaN layer mainly composed of GaN to which p-type dopants such as Mg and Be have been added. The p-type layer 126p has the same configuration as, for example, the p-type layer 26p.

[0115] The light-absorbing layer 126a is an example of a second light-absorbing layer and is provided between the p-type layer 126p and the n-type layer 126n. Specifically, the light-absorbing layer 126a is provided above the p-type layer 126p. In this embodiment, the light-absorbing layer 126a is in contact with the upper surface of the p-type layer 126p. The light-absorbing layer 126a is capable of absorbing light with wavelengths longer than the wavelength band of light absorbed by the p-type layer 126p and the n-type layer 126n. Specifically, the light-absorbing layer 126a absorbs light emitted by the light-emitting element 10. The light-absorbing layer 126a has the same configuration as, for example, the light-absorbing layer 26a. Specifically, the light-absorbing layer 126a is a layer mainly composed of InGaN. Alternatively, the light-absorbing layer 126a may be a co-dope layer containing a p-type dopant and an n-type dopant. Alternatively, the light-absorbing layer 126a may be a layer mainly composed of GaN to which impurities such as C, F, or transition metal elements are added.

[0116] The n-type layer 126n is an example of a second n-type nitride semiconductor layer and is provided above the barrier layer 23. In this embodiment, the n-type layer 126n is in contact with the upper surface of the light absorption layer 126a and is not in contact with the barrier layer 23. The n-type layer 126n is an n-type GaN layer mainly composed of GaN doped with n-type dopants such as Si and Ge. The n-type layer 126n has the same configuration as, for example, the n-type layer 26n.

[0117] The electrode 125 is electrically connected to the n-type layer 126n through an opening provided in the protective film 127. In this embodiment, the electrode 125 extends toward the electrode 24 from the contact portion with the barrier layer 23 so as to cover a part of the protective film 127, and is in contact with the upper surface of the n-type layer 126n. As a result, the potential of the n-type layer 126n is fixed to the potential of the electrode 125.

[0118] The pn gate layer 126 has the same configuration as the pn gate layer 26. Therefore, when light from the light-emitting element 10 is not incident, the 2DEG 28 disappears directly below the pn gate layer 126. In other words, the switch body 120 can be made non-conductive (off).

[0119] When light from the light-emitting element 10 is incident near the light-absorbing layer 126a of the pn gate layer 126, a higher voltage is generated in the p-type layer 126p than in the n-type layer 126n due to the photovoltaic effect. As a result, the potential decreases directly below the pn gate layer 126, generating a 2DEG 28. The channel between electrode 24 and electrode 125 becomes conductive due to the 2DEG 28, causing the switch body 120 to conduct (turn on).

[0120] Thus, in this embodiment, the switch body 120 has pn gate layers 26 and 126, each of which can function as a gate. That is, the switch body 120 has a double gate structure. By changing the polarity of the bias voltage applied between electrode 24 and electrode 125, current can flow in both directions. In other words, the switch body 120 is capable of bidirectional switching.

[0121] (Embodiment 3) Next, Embodiment 3 will be described.

[0122] Embodiment 3 differs from Embodiment 1 in that it has two pn gate layers, giving the switch body a so-called source-common double-gate structure. Below, we will focus on explaining the differences from Embodiment 1, and omit or simplify the explanation of the common features.

[0123] Figure 8 is a cross-sectional view of the switch body 220 of the semiconductor device according to Embodiment 3. The switch body 220 includes an electrode 224 and a protective film 227 instead of the electrode 24 and protective film 27 according to Embodiment 1. Furthermore, the switch body 220 includes an electrode 225 and a pn gate layer 226.

[0124] Electrode 224 corresponds to electrode 24, but differs in that it is electrically connected not only to the n-type layer 26n of pn gate layer 26, but also to the n-type layer 226n of pn gate layer 226. Protective film 227 corresponds to protective film 27, but differs in that it further covers a portion of the upper surface and the side surface of pn gate layer 226.

[0125] Electrode 225 is an example of a third electrode and is provided above the barrier layer 23, spaced apart from electrode 224, so as to sandwich electrode 224 between it and electrode 25 in a plan view of the substrate 21. In this embodiment, electrode 225 is in contact with the upper surface of the barrier layer 23. Electrode 225 is formed using a conductive material such as metal. For example, electrode 225 has a laminated structure including a Ti layer and an Al layer laminated on the upper surface of the Ti layer, but is not limited to this.

[0126] The pn gate layer 226 is an example of a fifth nitride semiconductor layer and is provided above the barrier layer 23, between at least a portion of the electrode 224 and the electrode 225. In this embodiment, the pn gate layer 226 is provided between the portion of the electrode 224 that contacts the barrier layer 23 and the electrode 225.

[0127] As shown in Figure 8, the pn gate layer 226 includes a p-type layer 226p, an n-type layer 226n, and a light-absorbing layer 226a. The p-type layer 226p, the light-absorbing layer 226a, and the n-type layer 226n are stacked in this order from the barrier layer 23.

[0128] The p-type layer 226p is an example of a third p-type nitride semiconductor layer and is provided above the barrier layer 23. In this embodiment, the p-type layer 226p is in contact with the upper surface of the barrier layer 23. The p-type layer 226p is a p-type GaN layer mainly composed of GaN to which p-type dopants such as Mg and Be have been added. The p-type layer 226p has the same configuration as, for example, the p-type layer 26p.

[0129] The light-absorbing layer 226a is an example of a third light-absorbing layer and is provided between the p-type layer 226p and the n-type layer 226n. Specifically, the light-absorbing layer 226a is provided above the p-type layer 226p. In this embodiment, the light-absorbing layer 226a is in contact with the upper surface of the p-type layer 226p. The light-absorbing layer 226a is capable of absorbing light with wavelengths longer than the wavelength band of light absorbed by the p-type layer 226p and the n-type layer 226n. Specifically, the light-absorbing layer 226a absorbs light emitted by the light-emitting element 10. The light-absorbing layer 226a has the same configuration as, for example, the light-absorbing layer 26a. Specifically, the light-absorbing layer 226a is a layer mainly composed of InGaN. Alternatively, the light-absorbing layer 226a may be a co-dope layer containing a p-type dopant and an n-type dopant. Alternatively, the light-absorbing layer 226a may be a layer mainly composed of GaN to which impurities such as C, F, or transition metal elements are added.

[0130] The n-type layer 226n is an example of a third n-type nitride semiconductor layer and is provided above the barrier layer 23. In this embodiment, the n-type layer 226n is in contact with the upper surface of the light absorption layer 226a. The n-type layer 226n is an n-type GaN layer mainly composed of GaN with n-type impurities such as Si and Ge added. The n-type layer 226n has the same configuration as, for example, the n-type layer 26n.

[0131] The electrode 224 is electrically connected to the n-type layer 226n through an opening provided in the protective film 227. In this embodiment, the electrode 224 extends from the contact portion with the barrier layer 23 toward both the electrode 25 and the electrode 225 so as to cover a portion of the protective film 227, and is in contact with the upper surface of the n-type layer 26n and the upper surface of the n-type layer 226n, respectively. As a result, the potentials of the n-type layers 26n and 226n are fixed to the potential of the electrode 224.

[0132] The pn gate layer 226 has the same configuration as the pn gate layer 26. Therefore, when light from the light-emitting element 10 is not incident, the 2DEG 28 disappears directly below the pn gate layer 226. In other words, the switch body 220 can be made non-conductive (off).

[0133] When light from the light-emitting element 10 is incident near the light-absorbing layer 226a of the pn gate layer 226, a higher voltage is generated in the p-type layer 226p than in the n-type layer 226n due to the photovoltaic effect. As a result, the potential decreases in the direction directly below the pn gate layer 226, generating a 2DEG 28. The channel between electrode 224 and electrode 225 becomes conductive due to the 2DEG 28, and the switch body 220 becomes conductive (turns on).

[0134] Thus, in this embodiment, the switch body 220 has pn gate layers 26 and 226, each of which can function as a gate. In other words, the switch body 220 has a double gate structure. This means that the switch body 220 is capable of bidirectional switching.

[0135] (Embodiment 4) Next, Embodiment 4 will be described.

[0136] Embodiment 4 differs from Embodiment 1 in that the pn gate layer has multiple light-absorbing layers. Below, we will focus on explaining the differences from Embodiment 1, and omit or simplify the explanation of the common points.

[0137] Figure 9 is a cross-sectional view of the switch body 320 of the semiconductor device according to Embodiment 4. The switch body 320 is equipped with a pn gate layer 326 instead of the pn gate layer 26 of the switch body 20.

[0138] The pn gate layer 326 corresponds to the pn gate layer 26, but differs in that it has multiple light-absorbing layers. In other words, the pn gate layer 326 has multiple laminates in which a light-absorbing layer is sandwiched between p-type and n-type layers, and the structure is such that these multiple laminates are stacked in the stacking direction. Specifically, the pn gate layer 326 has a p-type layer 26p, a light-absorbing layer 26a, an n-type layer 326n, a p-type layer 326p, a light-absorbing layer 326a, and an n-type layer 26n. A laminated structure of light-absorbing layer 26a, n-type layer 326n, p-type layer 326p, and light-absorbing layer 326a is provided between the p-type layer 26p and the n-type layer 26n.

[0139] The n-type layer 326n is an example of a fourth n-type nitride semiconductor layer and is provided between the light absorption layer 26a and the n-type layer 26n. Specifically, the n-type layer 326n is provided between the light absorption layer 26a and the p-type layer 326p. The n-type layer 326n is in contact with the upper surface of the light absorption layer 26a and the lower surface of the p-type layer 326p. The n-type layer 326n is an n-type GaN layer mainly composed of GaN doped with n-type dopants such as Si and Ge. The n-type layer 326n has a configuration similar to that of the n-type layer 26n, for example.

[0140] The p-type layer 326p is an example of a fourth p-type nitride semiconductor layer and is provided between the n-type layer 326n and the n-type layer 26n. Specifically, the p-type layer 326p is in contact with the upper surface of the n-type layer 326n and the lower surface of the light absorption layer 326a. The p-type layer 326p is a p-type GaN layer mainly composed of GaN doped with p-type dopants such as Mg and Be. The p-type layer 326p has a similar structure to, for example, the p-type layer 26p.

[0141] In this embodiment, the p-type layer 326p is in ohmic contact with the n-type layer 326n. For example, by adjusting the respective impurity concentrations near the junction interface between the p-type layer 326p and the n-type layer 326n, the depletion layer formed near the junction interface between the p-type layer 326p and the n-type layer 326n is thinned. This effectively achieves ohmic contact by utilizing the tunneling effect.

[0142] The light-absorbing layer 326a is an example of a fourth light-absorbing layer and is provided between the p-type layer 326p and the n-type layer 26n. Specifically, the light-absorbing layer 326a is in contact with the upper surface of the p-type layer 326p and the lower surface of the n-type layer 26n. The light-absorbing layer 326a is capable of absorbing light with wavelengths longer than the wavelength band of light absorbed by the p-type layer 326p and the n-type layer 26n. Specifically, the light-absorbing layer 326a absorbs the emitted light 30 emitted by the light-emitting element 10. The light-absorbing layer 326a has, for example, the same configuration as the light-absorbing layer 26a. Specifically, the light-absorbing layer 326a is a layer mainly composed of InGaN. Alternatively, the light-absorbing layer 326a may be a co-dope layer containing a p-type dopant and an n-type dopant. Alternatively, the light-absorbing layer 326a may be a layer mainly composed of GaN to which impurities such as C, F, or transition metal elements are added. Note that the light-absorbing layer 326a and the light-absorbing layer 26a may have different configurations.

[0143] The pn gate layer 326 includes two light absorption layers 26a and 326a. This allows for a higher voltage to be generated when light is incident on the pn gate layer 326. Therefore, the concentration of 2DEG28 directly below the p-type layer 26p can be further increased, thereby reducing the on-resistance and further increasing the on-current.

[0144] Furthermore, the pn gate layer 326 may contain three or more light-absorbing layers. That is, the pn gate layer 326 may contain three or more laminates in which a light-absorbing layer is sandwiched between a p-type layer and an n-type layer.

[0145] (Other Embodiments) Although a nitride apparatus according to one or more embodiments has been described above based on embodiments, this disclosure is not limited to these embodiments. Without departing from the spirit of this disclosure, various modifications to these embodiments that a person skilled in the art can conceive of, and forms constructed by combining components from different embodiments are also included within the scope of this disclosure.

[0146] For example, in each embodiment and its modifications, the energy of the photons emitted by the light-emitting element 10 may be greater than the band gap of GaN. This allows light to be absorbed even in the channel layer 22, which mainly contains GaN. The electrons generated by photoelectric conversion in the channel layer 22 can increase the concentration of 2DEG28, thereby reducing on-resistance and increasing on-current.

[0147] Furthermore, for example, the barrier layer 23 may have a recess that is indented from the top surface toward the substrate 21 at a position overlapping the p-type layer 26p of the pn gate layer 26. This allows the voltage generated by the photovoltaic energy to be concentrated at the bottom of the recess, thereby increasing the concentration of 2DEG generated directly below the recess. This reduces the on-resistance and increases the on-current. Similarly, the barrier layer 23 may also have a recess in the case of the pn gate layers 126, 226, and 326.

[0148] Furthermore, for example, between the pn gate layer 26 and the barrier layer 23, SiN, SiO ２ An insulating film containing insulating materials such as the above as the main component may be provided. This can reduce the off-leak current. An insulating film may be provided between the pn gate layer 126, 226 or 326 and the barrier layer 23.

[0149] Furthermore, for example, in the pn gate layer 26, the p-type layer 26p, the light-absorbing layer 26a, and the n-type layer 26n may be arranged side by side in the lateral direction. For example, the n-type layer 26n, the light-absorbing layer 26a, and the p-type layer 26p may be arranged in the order from electrode 24 to electrode 25 so as to be in contact with each other, and each may be in contact with the upper surface of the barrier layer 23. The same may apply to the pn gate layers 126, 226, and 326.

[0150] Furthermore, for example, electrode 24 may extend toward electrode 25 to a position beyond the pn gate layer 26 or 326. This allows the extended portion of electrode 24 to function as a field plate, suppressing the concentration of the electric field generated by the potential difference between electrode 24 and electrode 25 on the side surface of the p-type layer 26p. This suppresses the formation of an inversion channel on the side surface of the p-type layer 26p due to electric field concentration, which would otherwise cause a large off-leak current to flow. Similarly, electrode 125 may extend toward electrode 24 to a position beyond the pn gate layer 126. Also, electrode 224 may extend toward electrode 25 to a position beyond the pn gate layer 26, and may extend toward electrode 225 to a position beyond the pn gate layer 226.

[0151] Furthermore, the concentration of the p-type dopant may be higher in the region near the side surface of the p-type layer 26p facing the electrode 25 than in other parts of the p-type layer 26p. This makes it less likely for an inversion channel to form in the region near the side surface of the p-type layer 26p, thereby suppressing off-leak current. The same applies to the p-type layers 126p, 226p, and 326p.

[0152] Furthermore, for example, the electrode 24 does not have to be electrically connected to the pn gate layer 26 or 326. The n-type layer 26n of the pn gate layer 26 or 326 may be electrically floating. Similarly, the n-type layer 126n of the pn gate layer 126 and the n-type layer 226n of the pn gate layer 226 may also be electrically floating.

[0153] Furthermore, in the above embodiment, for example, an example was shown where the switch body is conductive when the light-emitting element is emitting light and non-conductive when the light-emitting element is not emitting light, but the reverse is also possible. Specifically, the switch body may be non-conductive (off) when the light-emitting element is emitting light and conductive (on) when the light-emitting element is not emitting light.

[0154] Furthermore, the semiconductor devices according to each embodiment and each modified example may be used for purposes other than relay devices. The semiconductor devices can be used as various switching devices.

[0155] Furthermore, each of the above embodiments may be modified, replaced, added, or omitted in various ways within the scope of the claims or equivalent thereof.

[0156] This disclosure can be used as a semiconductor device that can reduce on-current, and can be used, for example, in relay devices, switching devices, and the like.

[0157] 1, 1A Semiconductor device 10 Light-emitting element 20, 20A, 120, 220, 320 Switch body 21 Substrate 22, 22A Channel layer 23 Barrier layer 24, 25, 125, 224, 225 Electrode 26, 126, 226, 326 pn gate layer 26a, 126a, 226a, 326a Light-absorbing layer 26n, 126n, 226n, 326n n-type layer 26p, 126p, 226p, 326p p-type layer 27, 127, 227 Protective film 28 2DEG 30 Emitted light

Claims

1. A switch comprising a switch body and a light-emitting element, wherein the switch body comprises a substrate, a first nitride semiconductor layer provided above the substrate and having a first band gap, a second nitride semiconductor layer provided above the first nitride semiconductor layer and having a second band gap larger than the first band gap, a first electrode and a second electrode provided above the second nitride semiconductor layer and spaced apart from each other in a plan view of the substrate, and a third nitride semiconductor layer provided above the second nitride semiconductor layer and between at least a part of the first electrode and the second electrode in a plan view of the substrate, wherein the third nitride semiconductor layer includes a first p-type nitride semiconductor layer, a first n-type nitride semiconductor layer, and a first light-absorbing layer provided between the first p-type nitride semiconductor layer and the first n-type nitride semiconductor layer. A semiconductor device wherein the first light-absorbing layer is capable of absorbing light with wavelengths longer than the wavelength band of light absorbed by the first p-type nitride semiconductor layer and the first n-type nitride semiconductor layer, and absorbs light emitted by the light-emitting element.

2. The semiconductor device according to claim 1, wherein the band gap of the first light-absorbing layer is smaller than the energy of the light emitted by the light-emitting element.

3. The semiconductor device according to claim 2, wherein the first light-absorbing layer mainly comprises InGaN.

4. The semiconductor device according to claim 3, wherein the composition ratio of In in the first light-absorbing layer is 5% or more.

5. The semiconductor device according to claim 1, wherein the first light-absorbing layer comprises a p-type dopant and an n-type dopant.

6. The semiconductor device according to claim 5, wherein the p-type dopant is Mg or Be, and the n-type dopant is Si or Ge.

7. The first light-absorbing layer comprises at least one element selected from the group consisting of C, F, and transition metal elements, 1 × 10 １６ cm －３ The above 2 x 10 １９ cm －３ The semiconductor device according to claim 1, comprising the following concentrations.

8. The semiconductor device according to any one of claims 1 to 7, wherein the energy of the light emitted by the light-emitting element is smaller than the band gap of either the first p-type nitride semiconductor layer or the first n-type nitride semiconductor layer.

9. The semiconductor device according to any one of claims 1 to 7, wherein the thickness of the first light-absorbing layer is 100 nm or more.

10. The semiconductor device according to any one of claims 1 to 7, wherein the first band gap is smaller than the energy of the light emitted by the light-emitting element.

11. The semiconductor device according to claim 10, wherein the first nitride semiconductor layer mainly comprises InGaN.

12. The semiconductor device according to claim 11, wherein the composition ratio of In in the first nitride semiconductor layer is 5% or more.

13. The semiconductor device according to any one of claims 1 to 7, wherein the first electrode is electrically connected to the first n-type nitride semiconductor layer.

14. The semiconductor device according to any one of claims 1 to 7, wherein the conduction and non-conductivity between the first electrode and the second electrode are switched by the emission and non-emission of the light-emitting element.

15. A semiconductor device according to claim 14, wherein a two-dimensional electron gas is generated at the interface between the first nitride semiconductor layer and the second nitride semiconductor layer, and when the light-emitting element is not emitting light, the two-dimensional electron gas disappears in the region below the first p-type nitride semiconductor layer.

16. The semiconductor device according to any one of claims 1 to 7, further comprising a fourth nitride semiconductor layer provided above the second nitride semiconductor layer and between at least a portion of the third nitride semiconductor layer and the second electrode in a plan view of the substrate, wherein the fourth nitride semiconductor layer includes a second p-type nitride semiconductor layer, a second n-type nitride semiconductor layer, and a second light-absorbing layer provided between the second p-type nitride semiconductor layer and the second n-type nitride semiconductor layer, wherein the second light-absorbing layer is capable of absorbing light with wavelengths longer than the wavelength band of light absorbed by the second p-type nitride semiconductor layer and the second n-type nitride semiconductor layer, and absorbs light emitted by the light-emitting element.

17. A semiconductor device according to any one of claims 1 to 7, further comprising: a third electrode provided above the second nitride semiconductor layer, spaced apart from the first electrode so as to sandwich the first electrode between the second electrode and the second electrode in a plan view of the substrate; and a fifth nitride semiconductor layer provided above the second nitride semiconductor layer, spaced apart from the third electrode in a plan view of the substrate, wherein the fifth nitride semiconductor layer comprises: a third p-type nitride semiconductor layer; a third n-type nitride semiconductor layer; and a third light-absorbing layer provided between the third p-type nitride semiconductor layer and the third n-type nitride semiconductor layer, wherein the third light-absorbing layer is capable of absorbing light with wavelengths longer than the wavelength band of light absorbed by the third p-type nitride semiconductor layer and the third n-type nitride semiconductor layer, and absorbs light emitted by the light-emitting element.

18. The semiconductor device according to any one of claims 1 to 7, wherein the third nitride semiconductor layer further includes: a fourth n-type nitride semiconductor layer provided between the first light-absorbing layer and the first n-type nitride semiconductor layer; a fourth p-type nitride semiconductor layer provided between the fourth n-type nitride semiconductor layer and the first n-type nitride semiconductor layer; and a fourth light-absorbing layer provided between the fourth p-type nitride semiconductor layer and the first n-type nitride semiconductor layer, wherein the fourth p-type nitride semiconductor layer is in ohmic contact with the fourth n-type nitride semiconductor layer.

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