Semiconductor device

Abstract

A semiconductor device (1) comprises a switch body (20) and a light-emitting element (10). The switch body (20) is provided with a substrate (21) having a first band gap, a buffer layer (22) provided above the substrate (21) and having a second band gap, a back gate layer (23) provided above the buffer layer (22) and having a third band gap smaller than any of the first band gap and the second band gap, a channel layer (24) provided above the back gate layer (23) and having a fourth band gap, a barrier layer (25) provided above the channel layer (24) and having a fifth band gap larger than the fourth band gap, and electrodes (27, 28) provided above the barrier layer (25) so as to be separated from each other in a plan view of the substrate (21). Light emitted by the light-emitting element (10) passes through the substrate (21) and is incident on the back gate layer (23).

Description

Semiconductor Devices

[0001] The present disclosure relates to semiconductor devices.

[0002] Patent Document 1 and Non-Patent Documents 1 and 2 disclose a HEMT (High Electron Mobility Transistor) photodetector. When light is irradiated from the top surface of the HEMT photodetector, a photocurrent flows between the source electrode and the drain electrode, allowing light to be detected.

[0003] Japanese Patent Application Publication No. 7-131056

[0004] Atsuki Miyata et al., “Suppression of decay time in transient drain current of back-gated GaN HEMT under UV exposure”, Japanese Journal of Applied Physics, Apr. 2022, Vol. 61Wanglong Wu et al., “Wafer-scale high sensitive UV photodetectors based on novel AlGaN / n-GaN / p-GaN heterostructure HEMT”, Applied Surface Science, Feb. 2023, Vol. 618

[0005] There is room for further reduction in on-resistance compared to the conventional photodetector.

[0006] Therefore, the present disclosure provides a semiconductor device that can reduce the on-resistance.

[0007] a buffer layer having a second band gap provided above the substrate; a p-type nitride semiconductor layer having a third band gap smaller than both the first band gap and the second band gap provided above the buffer layer; a first nitride semiconductor layer having a fourth band gap provided above the p-type nitride semiconductor layer; a second nitride semiconductor layer having a fifth band gap larger than the fourth band gap provided above the first nitride semiconductor layer; and 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, wherein light emitted by the light-emitting element is transmitted through the substrate and enters the p-type nitride semiconductor layer.

[0008] According to the semiconductor device according to the present disclosure, the on-resistance can be reduced.

[0009] FIG. 1 is a perspective view of a semiconductor device according to a first embodiment. FIG. 2A is a cross-sectional view illustrating an ON state of the semiconductor device according to the first embodiment. FIG. 2B is a cross-sectional view illustrating an OFF state of the semiconductor device according to the first embodiment. FIG. 3 is a diagram illustrating an example of an emission spectrum of a light-emitting element. FIG. 4 is a diagram illustrating an example of an Al ｘ Ga １－ｘ FIG. 5 is a diagram showing the light absorption spectrum of Al. ｘ Ga １－ｘ FIG. 6 is a diagram showing the total absorption rate of light versus the molar ratio of N. FIG. 6 is a diagram showing the relationship between the on-current of the switch body and the thickness of the back gate layer. FIG. 7 is a cross-sectional view of a switch body according to a first modification of the first embodiment. FIG. 8 is a cross-sectional view of a switch body according to a second modification of the first embodiment. FIG. 9 is a cross-sectional view of a switch body according to the second embodiment. FIG. 10 is a cross-sectional view of a switch body according to a first modification of the second embodiment. FIG. 11 is a cross-sectional view of a switch body according to a second modification of the second embodiment. FIG. 12 is a cross-sectional view of a switch body according to a third embodiment. FIG. 13 is a cross-sectional view of a switch body according to a third modification of the third embodiment.

[0010] a first nitride semiconductor layer having a fourth band gap provided above the p-type nitride semiconductor layer; a second nitride semiconductor layer having a fifth band gap provided above the first nitride semiconductor layer; and 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, wherein light emitted by the light-emitting element is transmitted through the substrate and enters the p-type nitride semiconductor layer.

[0011] As a result, two-dimensional electron gas (2DEG) can be generated near the heterojunction interface between the second nitride semiconductor layer and the first nitride semiconductor layer due to spontaneous polarization and piezoelectric polarization. The 2DEG functions as a current path (channel) between the first electrode and the second electrode. In the semiconductor device according to this aspect, since a p-type nitride semiconductor layer is provided, the potential of the first nitride semiconductor layer directly above the p-type nitride semiconductor layer increases, causing the 2DEG to disappear and become depleted. In this state, the channel is blocked, and the switch body is in a non-conducting state (off).

[0012] In the semiconductor device according to this aspect, the band gaps of the substrate and buffer layer are large, which suppresses light absorption in the substrate and buffer layer, enabling illumination of the switch body from below (so-called backside illumination).Since light is not blocked by the electrodes provided on the top surface, the light input efficiency is increased.

[0013] Light incident from the back surface of the substrate is absorbed by at least the p-type nitride semiconductor layer, generating electron-hole pairs. The generated electron-hole pairs are separated into electrons and holes, with the electrons moving to the first nitride semiconductor layer and the holes remaining in the p-type nitride semiconductor layer. As a result, the so-called photovoltaic effect increases the potential of the p-type nitride semiconductor layer and decreases the potential of the first nitride semiconductor layer. This generates a 2DEG near the interface with the second nitride semiconductor layer, causing the switch body to become conductive (ON).

[0014] In this way, in the semiconductor device according to this embodiment, the switch body can be switched between conductive (ON) and non-conductive (OFF) states by illuminating the backside of the switch body. Backside illumination increases the light input efficiency, further enhancing the effect of reducing the ON resistance due to the 2DEG and electrons generated by the photovoltaic effect. Furthermore, backside illumination allows the semiconductor device (switch body) to be flip-chip mounted.

[0015] A semiconductor device according to a second aspect of the present disclosure is the semiconductor device according to the first aspect, wherein the p-type nitride semiconductor layer is located between the first electrode and the second electrode in a planar view of the substrate, and does not overlap either the first electrode or the second electrode.

[0016] As a result, the 2DEG does not disappear in the region that does not overlap with the p-type nitride semiconductor layer in plan view, so that the 2DEG concentration can be increased and the on-resistance can be further reduced.

[0017] A semiconductor device according to a third aspect of the present disclosure is the semiconductor device according to the first or second aspect, wherein the p-type nitride semiconductor layer has a thick film portion and a thin film portion thinner than the thick film portion, and the thick film portion is located between the first electrode and the second electrode in a plan view of the substrate, and does not overlap either the first electrode or the second electrode.

[0018] As a result, the 2DEG does not disappear in the region overlapping the thin film portion in plan view, so that the 2DEG concentration can be increased and the on-resistance can be further reduced.

[0019] A semiconductor device according to a fourth aspect of the present disclosure is a semiconductor device according to any one of the first to third aspects, wherein the second nitride semiconductor layer has a recess located between the first electrode and the second electrode in a planar view of the substrate.

[0020] As a result, the 2DEG does not disappear in the region that does not overlap the recess in plan view, so the 2DEG concentration can be increased and the on-resistance can be further reduced.

[0021] A semiconductor device according to a fifth aspect of the present disclosure is the semiconductor device according to any one of the first to fourth aspects, comprising an n-type nitride semiconductor layer provided between the buffer layer and the p-type nitride semiconductor layer, and a third electrode electrically connected to the n-type nitride semiconductor layer.

[0022] This allows the pn junction between the p-type nitride semiconductor layer and the n-type nitride semiconductor layer to promote separation of electron-hole pairs when light is incident. Since the number of holes accumulated in the p-type nitride semiconductor layer can be increased, the potential of the p-type nitride semiconductor layer can be further increased, thereby increasing the 2DEG concentration. Furthermore, since the potential of the n-type nitride semiconductor layer can be fixed using the third electrode, fluctuations in the potential of the p-type nitride semiconductor layer can be suppressed. This allows leakage current to be reduced.

[0023] A semiconductor device according to a sixth aspect of the present disclosure is a semiconductor device according to any one of the first to fourth aspects, wherein the thickness of the p-type nitride semiconductor layer is thinner than the sum of four times the penetration depth of light emitted by the light-emitting element and the diffusion length of electrons in the first nitride semiconductor layer.

[0024] As a result, light incident from the back surface of the substrate is absorbed not only by the p-type nitride semiconductor layer but also by the first nitride semiconductor layer, generating electron-hole pairs. The generated electron-hole pairs are separated into electrons and holes, with the electrons contributing to an increase in the 2DEG concentration and the holes migrating to the p-type nitride semiconductor layer. The holes migrating to the p-type nitride semiconductor layer increase the potential of the p-type nitride semiconductor layer, further reducing the on-resistance.

[0025] A semiconductor device according to a seventh aspect of the present disclosure is the semiconductor device according to any one of the first to sixth aspects, wherein the buffer layer is Al ｘ Ga １－ｘ The semiconductor device further includes an AlGaN layer made of N (0<x<1), and the second band gap is the band gap of the AlGaN layer.

[0026] This allows the buffer layer, p-type nitride semiconductor layer, first nitride semiconductor layer, and second nitride semiconductor layer to be formed successively by epitaxial growth, thereby improving the film quality of each layer while avoiding the inclusion of impurities.

[0027] A semiconductor device according to an eighth aspect of the present disclosure is the semiconductor device according to the seventh aspect, wherein x is 0.05 or greater.

[0028] This makes it possible to suppress the absorption of light by the buffer layer, and therefore, in the case of backside illumination, the efficiency of light input to the p-type nitride semiconductor layer can be increased.

[0029] A semiconductor device according to a ninth aspect of the present disclosure is the semiconductor device according to the seventh or eighth aspect, wherein the buffer layer has a stacked structure in which a plurality of the AlGaN layers, each having a different value of x, are stacked, and the value of x of each of the plurality of AlGaN layers decreases in order upward.

[0030] This effectively reduces the lattice mismatch between the buffer layer and the p-type nitride semiconductor layer.

[0031] A semiconductor device according to a tenth aspect of the present disclosure is the semiconductor device according to any one of the first to ninth aspects, wherein the light-emitting element is provided on the lower surface of the substrate.

[0032] This allows the switch body and the light emitting element to be integrated, thereby realizing miniaturization of the semiconductor device.

[0033] Hereinafter, the embodiments will be specifically described with reference to the drawings.

[0034] The embodiments described below are all comprehensive or specific examples. The numerical values, shapes, materials, components, component placement and connection configurations, steps, and step order shown in the following embodiments are merely examples and are not intended to limit the present disclosure. Furthermore, among the components in the following embodiments, components not described in the independent claims are described as optional components.

[0035] Furthermore, each figure is a schematic diagram and is not necessarily an exact illustration. Therefore, for example, the scales of the figures do not necessarily match. Furthermore, in each figure, substantially the same components are given the same reference numerals, and redundant explanations are omitted or simplified.

[0036] Furthermore, in this specification, terms indicating the relationship between elements, such as parallel or perpendicular, terms indicating the shape of elements, and numerical ranges are not expressions that only express a strict meaning, but are expressions that also include a substantially equivalent range, for example, a difference of about a few percent.

[0037] Furthermore, in this specification, the terms "above" and "below" do not refer to the upward direction (vertically upward) and downward direction (vertically downward) in absolute spatial recognition, but are used as terms defined by a relative positional relationship based on the stacking order in a stacked configuration. Furthermore, the terms "above" and "below" are applied not only to a case where two components are arranged with a gap between them and another component exists between the two components, but also to a case where two components are arranged closely together and the two components are in contact with each other.

[0038] In this specification, "thickness direction" refers to the thickness direction of the semiconductor device, and is the direction perpendicular to the main surface of the substrate. Furthermore, "plan view" refers to the view from a direction perpendicular to the main surface of the substrate, unless otherwise specified. In the case of a flat member such as a plate or layer, the "main surface" refers to the main surface of the member, for example, the surface with the largest area or the surface opposite to the surface with the largest area. The main surface is usually flat, but may include minute irregularities or curvatures.

[0039] In this specification, the term "major component" refers to the component that is contained in the largest proportion, expressed in mole percent, in a material.

[0040] In this specification, AlGaN refers to a ternary mixed crystal Al ｘ Ga １－ｘ It represents N (0<x<1). The subscript "x" of Al indicates the content ratio (composition ratio) of Al excluding N in AlGaN, and is also called the molar ratio of Al. Similarly, the subscript "1-x" of Ga indicates the molar ratio of Ga. Hereinafter, multi-element mixed crystals may be abbreviated by the arrangement of the symbols of the respective constituent elements, for example, AlInN, GaInN, etc.

[0041] Furthermore, a layer made of material A such as GaN or AlGaN, and a layer constituted by material A, means that the layer contains substantially only material A. However, the layer may contain other elements as impurities, such as elements that are unavoidable in the manufacturing process, at a rate of 1 at % or less.

[0042] Furthermore, in this specification, ordinal numbers such as "first" and "second" do not refer to the number or order of components unless otherwise specified, but are used for the purpose of avoiding confusion and distinguishing between components of the same type.

[0043] First Embodiment [Configuration of Semiconductor Device] First, the configuration of a semiconductor device according to a first embodiment will be described with reference to FIGS. 1, 2A, and 2B.

[0044] FIG. 1 is a perspective view of a semiconductor device 1 according to this embodiment. FIGS. 2A and 2B are cross-sectional views illustrating the on and off states of the semiconductor device 1 according to this embodiment. Note that FIGS. 2A and 2B illustrate a cross section of a switch body 20, the light-emitting element 10 is represented schematically by a circuit symbol, and the support substrate 30, the resin member 50, and the like are omitted from the illustration. The positional relationship between the light-emitting element 10 and the switch body 20 shown in FIGS. 2A and 2B is upside down compared to the positional relationship shown in FIG. 1 . That is, "upward" in FIGS. 2A and 2B refers to the direction from the light-emitting element 10 toward the switch body 20, and corresponds to "downward" in FIG. 1 . In the following description, unless otherwise specified, the up-down direction is defined as shown in FIGS. 2A and 2B . That is, the direction from the light-emitting element 10 toward the switch body 20 is defined as "upward," and the opposite direction is defined as "downward."

[0045] 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. A semiconductor relay is also called an SSR (Solid-State Relay).

[0046] 1 , the semiconductor device 1 includes a light-emitting element 10 and a switch body 20. The semiconductor device 1 also includes a support substrate 30, a plurality of terminals 41 a, 41 b, 41 c, 41 d, 45 a, and 45 b, external terminals 43 a, 43 b, and 43 c, wires 44 a and 44 b, and a resin member 50.

[0047] The light-emitting element 10 is an element that emits light and is electrically insulated from the switch body 20. 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 and not emitting light depending on the input signal. In this embodiment, the light-emitting element 10 emits light toward the switch body 20. As shown by the wavy arrow in FIG. 2A , the light emitted by the light-emitting element 10 passes through the substrate 21 provided in the switch body 20 and enters the back gate layer 23. At least a portion of the light emitted by the light-emitting element 10 may enter the channel layer 24 provided in the switch body 20.

[0048] In this embodiment, the light-emitting element 10 is provided on the lower surface (back surface, "upper surface" in FIG. 1 ) of the switch body 20. For example, the light-emitting element 10 is bonded to the lower surface of the switch body 20 via an insulating layer (not shown). The insulating layer is formed using an insulating resin material such as epoxy. The insulating layer is translucent to the light emitted by the light-emitting element 10. By adjusting the material and thickness of the insulating layer, it is possible to easily ensure electrical insulation between the light-emitting element 10 and the switch body 20. Note that the light-emitting element 10 may also be bonded directly to the lower surface of the switch body 20.

[0049] For example, the light-emitting element 10 is an LED (Light Emitting Diode) element. The light emitted by the light-emitting element 10 is ultraviolet light, but may be visible light. An example of the spectrum of the light emitted by the light-emitting element 10 will be described later with reference to FIG. 3. The light-emitting element 10 may be an organic EL (Electroluminescence) element or a semiconductor laser element.

[0050] The switch body 20 switches between conductive (ON) and non-conductive (OFF) states in response to incident light. Specifically, in the switch body 20, the electrodes 27 and 28 shown in Figures 2A and 2B are switched between conductive and non-conductive states depending on whether the light-emitting element 10 emits light or not. The specific configuration of the switch body 20 will be described later.

[0051] The support substrate 30 is an example of a support member that supports the switch body 20. The support substrate 30 is a ceramic substrate, a glass epoxy substrate, or the like, but is not limited to these.

[0052] As shown in FIG. 1 , conductive terminals 41 a, 41 b, 41 c, and 41 d are provided on the mounting surface (main surface on the switch body 20 side) of the support substrate 30. External terminals 43 a, 43 b, and 43 c are provided on the back surface (main surface opposite the mounting surface) of the support substrate 30. The external terminals 43 a, 43 b, and 43 c correspond to the terminals 41 a, 41 b, and 41 c, respectively, and are electrically connected to each other via vias (not shown) that penetrate the support substrate 30. In addition, an external terminal (not shown) corresponding to the terminal 41 d is provided on the back surface of the support substrate 30, and this external terminal and the terminal 41 d are connected via a via (not shown). The external terminal corresponding to the terminal 41 d and the external terminal 43 c are external input terminals of the semiconductor device 1. The external terminals 43 a and 43 b are external output terminals of the semiconductor device 1. An input signal is input to an external terminal corresponding to the terminal 41d and to an external terminal 43c, and an output signal corresponding to the input signal is output from the external terminals 43a and 43b.

[0053] For example, the switch body 20 is flip-chip mounted on the support substrate 30. Although not shown, the electrode 27 of the switch body 20 and the terminal 41a are electrically and mechanically connected via a bump. The electrode 28 of the switch body 20 and the terminal 41b are electrically and mechanically connected via a bump.

[0054] In this embodiment, as shown in Fig. 1, the light emitting element 10 is stacked on the main surface of the switch body 20. The light emitting element 10 is provided with terminals 45a and 45b. The terminal 45a is connected to the terminal 41c by a wire 44a. The terminal 45b is connected to the terminal 41d by a wire 44b. The terminals 45a and 45b are electrically connected to the anode electrode and the cathode electrode of the light emitting element 10 (LED), respectively. As a result, an input signal input to the semiconductor device 1 is supplied to the light emitting element 10.

[0055] The terminals, vias, external terminals, bumps, and wires provided on the support substrate 30 are each formed using a conductive material such as a metal. Examples of metals used for the terminals, vias, external terminals, bumps, and wires include, but are not limited to, copper, silver, gold, and aluminum.

[0056] The resin member 50 seals the light emitting element 10, the switch body 20, and at least a part of the support substrate 30. The resin member 50 is provided to protect the light emitting element 10 and the switch body 20. The resin member 50 can be made of a resin typically used for molding semiconductor elements.

[0057] The semiconductor device 1 does not necessarily have to include the support substrate 30, the terminals 41a, 41b, 41c, 41d, 43a, 43b, 43c, 45a, and 45b, the wires 44a and 44b, and the resin member 50. For example, instead of these components, the semiconductor device 1 may include a first frame member that supports the light-emitting element 10 and a second frame member that supports the switch body 20. The first frame member and the second frame member are each formed using a conductive material such as metal. The first frame member functions as part of a transmission path for an input signal to the light-emitting element 10, and the second frame member functions as part of a transmission path for an output signal from the switch body 20.

[0058] [Specific Configuration of Switch Main Body] Next, a specific configuration of the switch main body 20 will be described with reference to FIGS. 2A and 2B.

[0059] 2A and 2B , the switch body 20 includes a substrate 21, a buffer layer 22, a back gate layer 23, a channel layer 24, a barrier layer 25, electrodes 27 and 28, and a protective film 29. Note that in FIGS. 2A and 2B , the hatching representing the cross section is omitted for the channel layer 24 and the barrier layer 25 of the switch body 20. The same applies to the cross-sectional views from FIG. 7 onwards, which will be described later.

[0060] The substrate 21 is a substrate having a first band gap. For example, the substrate 21 is electrically insulating. Specifically, the substrate 21 is a sapphire substrate, but is not limited to this. The substrate 21 may also be formed using SiC or the like.

[0061] The substrate 21 is a light-transmitting substrate that is transparent to the light from the light-emitting element 10. The substrate 21 has a single-layer structure and has a uniform refractive index inside. This makes it possible to suppress refraction and scattering of light from the light-emitting element 10, and to efficiently propagate the light to the back gate layer 23. The substrate 21 may have a multi-layer structure.

[0062] The buffer layer 22 has a second band gap and is provided above the substrate 21. Specifically, the buffer layer 22 is provided in contact with the upper surface of the substrate 21. The buffer layer 22 is formed using a nitride semiconductor such as undoped AlN or AlGaN.

[0063] The back gate layer 23 is an example of a p-type nitride semiconductor layer having a third band gap smaller than both the first band gap and the second band gap. That is, the band gap of the back gate layer 23 is smaller than both the band gap of the substrate 21 and the band gap of the buffer layer 22.

[0064] The back gate layer 23 is, for example, a layer made of p-type GaN, but is not limited to this. The back gate layer 23 may be formed using other nitride semiconductors such as InGaN, AlGaN, or AlInGaN. The back gate layer 23 is provided above the buffer layer 22. Specifically, the back gate layer 23 is provided in contact with the upper surface of the buffer layer 22. In this embodiment, the back gate layer 23 has a substantially uniform thickness and is provided so as to cover almost the entire upper surface of the buffer layer 22. That is, in a plan view of the substrate 21, the back gate layer 23 overlaps each of the electrodes 27 and 28.

[0065] The channel layer 24 is an example of a first nitride semiconductor layer having a fourth band gap, and is provided above the back gate layer 23. The band gap of the channel layer 24 is smaller than both the band gap of the substrate 21 and the band gap of the buffer layer 22. The band gap of the channel layer 24 is substantially the same size as the band gap of the back gate layer 23.

[0066] The channel layer 24 is, for example, a layer made of undoped GaN, but is not limited to this. The channel layer 24 may be formed using other nitride semiconductors such as InGaN, AlGaN, and AlInGaN. The thickness of the channel layer 24 is, for example, not less than 100 nm and not more than 1000 nm, but is not limited to this.

[0067] The barrier layer 25 is an example of a second nitride semiconductor layer having a fifth band gap larger than the fourth band gap, and is provided above the channel layer 24. That is, the band gap of the barrier layer 25 is larger than the band gap of the channel layer 24. In this embodiment, the barrier layer 25 is in contact with the upper surface of the channel layer 24. The barrier layer 25 is, for example, an undoped AlGaN layer. The thickness of the barrier layer 25 is, for example, not less than 5 nm and not more than 100 nm, but is not limited to this.

[0068] A heterojunction is formed between the barrier layer 25 and the channel layer 24, and 2DEG 26 (see FIG. 2A ) can be generated near the junction interface in the channel layer 24 due to spontaneous polarization and piezoelectric polarization. The 2DEG 26 functions as a current path when the switch body 20 is on. Note that, as long as the 2DEG 26 is generated in the channel layer 24, another layer may be provided between the channel layer 24 and the barrier layer 25.

[0069] The electrodes 27 and 28 are an example of a first electrode and a second electrode that are spaced apart from each other, and are provided above the barrier layer 25. In the present embodiment, the electrodes 27 and 28 are each in contact with the upper surface of the barrier layer 25. The electrodes 27 and 28 are formed using a conductive material such as a metal. For example, the electrodes 27 and 28 have a layered structure including a Ti layer and an Al layer stacked on the upper surface of the Ti layer, but are not limited to this.

[0070] The protective film 29 is a film that covers the upper surface of the barrier layer 25. In this embodiment, the protective film 29 is in contact with and covers the upper surface of the barrier layer 25. The protective film 29 is made of, for example, SiN or SiO ２The protective film 29 is an insulating film formed using an insulating material such as a SiO 2 film or the like. The protective film 29 does not necessarily have to be provided. The protective film 29 may have a light-blocking property against the light emitted by the light-emitting element 10. For example, the protective film 29 may be a reflective film that reflects the light emitted by the light-emitting element 10. The protective film 29 can further increase the light utilization efficiency by reflecting the light that has not been absorbed by the back gate layer 23 and the channel layer 24.

[0071] To manufacture the switch body 20, for example, first, a buffer layer 22, a back gate layer 23, a channel layer 24, and a barrier layer 25 are formed in this order on the upper surface of the substrate 21 by epitaxial growth. By sequentially depositing the layers while varying the growth conditions, such as the introduced gas and additives, for each layer, impurities can be prevented from being mixed between or within the layers. This improves the film quality of each layer, resulting in a highly reliable switch body 20. After the barrier layer 25 is formed, an insulating film is deposited as a protective film 29 by plasma CVD (chemical vapor deposition) or the like. Portions of the deposited protective film 29 are then removed to form openings in the protective film 29 for contact with the electrodes 27 and 28. The openings are formed by, for example, photolithography and etching. A metal film is then formed by sputtering or vapor deposition to fill the openings in the protective film 29, and the metal film is then patterned into a predetermined shape to form the electrodes 27 and 28. The metal film is patterned by photolithography, etching, etc. In this manner, the switch body 20 shown in Figures 2A and 2B can be formed. Note that the method for forming the switch body 20 is not particularly limited.

[0072] [Characteristic Configuration and Operation] Next, the main characteristic configuration of the semiconductor device 1 (specific configurations of the buffer layer 22 and the back gate layer 23) will be described while explaining the operation of the semiconductor device 1 according to this embodiment.

[0073] In the semiconductor device 1, the electrode 27 and the electrode 28 are switched between conductive and non-conductive states depending on whether the light-emitting element 10 emits light or not. That is, the switch body 20 receives light from the light-emitting element 10 through the underside of the substrate 21, switching between conductive (ON) and non-conductive (OFF) states between the electrode 27 and the electrode 28. In this embodiment, the switch body 20 is conductive when it receives light and non-conductive when it does not receive light. That is, the switch body 20 is a switching element controlled by light. The switch body 20 has a configuration similar to a transistor that functions as a switching element. Therefore, the electrode 27 can be referred to as a source electrode, and the electrode 28 can be referred to as a drain electrode. The back gate layer 23 corresponds to the control terminal (gate) of the transistor. For example, a bias voltage higher than that of the electrode 27 is applied to the electrode 28. The magnitude of the bias voltage is, for example, approximately 5 V to 10 V.

[0074] First, the off state will be described using Figure 2B. In the off state, the light-emitting element 10 does not emit light. In the off state, the 2DEG 26 generated in the channel layer 24 disappears. This is because the back gate layer 23 increases the potential of the channel layer 24, causing it to become depleted. As a result, the channel between the electrode 27 and the electrode 28 is blocked, and the switch body 20 becomes non-conductive (off).

[0075] Next, the on state will be described with reference to FIG. 2A . In the on state, the light-emitting element 10 emits light. Light from the light-emitting element 10 is incident on the lower surface of the substrate 21, passes through the substrate 21 and the buffer layer 22, and reaches the back gate layer 23 where it is absorbed. In the back gate layer 23, electron-hole pairs are generated by the incident light. The generated electron-hole pairs separate into electrons and holes, with the electrons moving to the channel layer 24 and the holes remaining in the back gate layer 23. As a result, the potential of the back gate layer 23 increases and the potential of the channel layer 24 decreases. This generates a 2DEG 26 near the interface between the channel layer 24 and the barrier layer 25. The channel between the electrode 27 and the electrode 28 is conductive due to the 2DEG 26, so the switch body 20 is conductive (ON).

[0076] Furthermore, a portion of the light incident from the substrate 21 passes through the back gate layer 23 and is absorbed by the channel layer 24, generating electron-hole pairs in the channel layer 24. The generated electron-hole pairs separate into electrons and holes, and the holes move to the back gate layer 23. As a result, the potential of the back gate layer 23 becomes higher, which increases the carrier concentration (2DEG concentration) of the 2DEG 26 and further reduces the on-resistance. The separated electrons also move near the interface between the channel layer 24 and the barrier layer 25, contributing to a reduction in the on-resistance.

[0077] Thus, in the switch body 20, the higher the concentration of electrons generated in the channel layer 24 when light is incident, the lower the on-resistance. Specifically, the more light is incident on the back gate layer 23 and the channel layer 24, that is, the higher the light input efficiency, the lower the on-resistance can be. The light input efficiency can be expressed as the proportion of light emitted by the light-emitting element 10 that contributes to the generation of electron-hole pairs in the back gate layer 23 and the channel layer 24. In order to increase the light input efficiency, it is necessary to suppress light absorption in the substrate 21 and the buffer layer 22.

[0078] In the switch body 20 according to this embodiment, the band gap energy of each of the substrate 21 and the buffer layer 22 is greater than the energy of the light from the light emitting element 10. As a result, the substrate 21 and the buffer layer 22 are unable to generate electron-hole pairs due to the lack of energy of the light from the light emitting element 10, and the light passes through the substrate 21 and the buffer layer 22.

[0079] Here, the emission spectrum of the light-emitting element 10 according to the present embodiment will be described with reference to Fig. 3. Fig. 3 is a diagram showing an example of the emission spectrum of the light-emitting element 10. In Fig. 3, the horizontal axis represents wavelength, and the vertical axis represents relative intensity. The relative intensity is the intensity converted with the peak intensity of light being 100%.

[0080] As shown in Figure 3, the light from the light-emitting element 10 is narrowband light having a peak wavelength at approximately 365 nm. The half-width of the light from the light-emitting element 10 is approximately 12 nm. The relative intensity of the light from the light-emitting element 10 is substantially zero in the wavelength band of 340 nm or less and the wavelength band of 390 nm or less. Note that the emission spectrum shown in Figure 3 is merely an example. For example, the peak wavelength of the light from the light-emitting element 10 may be in the range of 360 nm to 370 nm, and the half-width may be 20 nm or less, or 15 nm or less. It is sufficient that the absorption rate in the substrate 21 and the buffer layer 22 is low and the absorption rate in the back gate layer 23 is high.

[0081] First, the absorption characteristics of the buffer layer 22 will be described. In this embodiment, the buffer layer 22 is made of Al ｘ Ga １－ｘ The AlGaN layer includes an AlGaN layer consisting of N (0<x<1). The smaller the molar ratio x of Al, the smaller the band gap and the higher the light absorption rate. The larger the molar ratio x, the larger the band gap and the lower the light absorption rate.

[0082] FIG. ｘ Ga １－ｘ 4 is a graph showing the light absorption spectrum of N. In Fig. 4, the horizontal axis represents wavelength and the vertical axis represents absorption ratio. The five curves shown in Fig. 4 are for four types of Al with different molar ratios x. ｘ Ga １－ｘ The absorption spectra of N and GaN are shown. ｘ Ga １－ｘ The thickness of the N and GaN layers is 1 μm. The absorption spectra at x=0, 0.11, 0.2, and 0.38 are measured data, whereas the absorption spectrum at x=0.05 is interpolated data. By calculating the convolution integral between the emission spectrum shown in FIG. 3 and each absorption spectrum shown in FIG. 4, the Al absorption spectrum for the light from the light emitting element 10 can be calculated. ｘ Ga １－ｘ The absorption characteristics of N can be obtained.

[0083] FIG. 5 shows the Al ｘ Ga １－ｘ5 is a diagram showing the total light absorption rate versus the molar ratio x of N. In Fig. 5, the horizontal axis represents the molar ratio x, and the vertical axis represents the total light absorption rate. The plots (white circles) for x = 0, 0.11, 0.2, and 0.38 are values ​​based on actual measurement data, while the other plots (black circles) are values ​​based on interpolated data.

[0084] As shown in FIG. ｘ Ga １－ｘ The larger the molar ratio x of N, the higher the total light absorption rate, and the smaller the molar ratio x, the lower the total light absorption rate. In order to allow a sufficient amount of light to be incident on the back gate layer 23, for example, the total absorption rate in the buffer layer 22 needs to be approximately 30% or less. That is, as shown in FIG. 5, the molar ratio x needs to be 0.05 or more. However, depending on the emission spectrum of the light-emitting element 10 and the thickness of the buffer layer 22 (AlGaN), there are cases where the molar ratio x may be less than 0.05.

[0085] The thickness of the buffer layer 22 is, for example, not less than 100 nm and not more than 10,000 nm, and is, for example, 1 μm, but is not limited to this. Increasing the thickness of the buffer layer 22 makes it easier to alleviate the lattice mismatch between the substrate 21 and the back gate layer 23, thereby improving the film quality of the back gate layer 23 and the channel layer 24. In addition, decreasing the thickness of the buffer layer 22 makes it possible to suppress light absorption in the buffer layer 22, thereby increasing the light input efficiency.

[0086] If the substrate 21 is a sapphire substrate, the band gap of the substrate 21 is larger than the band gap of the buffer layer 22 (AlGaN), thereby sufficiently suppressing light absorption. Therefore, the thickness of the substrate 21 can be increased. For example, the thickness of the substrate 21 is 10 μm or more and 1000 μm or less, e.g., 400 μm, but is not limited thereto. The thickness of the substrate 21 may be 100 μm or more, 200 μm or more, or 300 μm or more. When the light-emitting element 10 is disposed on the underside of the substrate 21, the thicker the substrate 21, the greater the capacitance between the input and output, thereby improving the high-frequency characteristics of the semiconductor device 1. Furthermore, the thickness of the substrate 21 may be 800 μm or less, 600 μm or less, 500 μm or less, or 400 μm or less. Reducing the thickness of the substrate 21 allows the switch body 20 to be thinner.

[0087] The on-resistance can be further reduced if the light from the light-emitting element 10 is absorbed not only by the back gate layer 23 but also partially by the channel layer 24. For this reason, the thickness of the back gate layer 23 is set to a predetermined value or less. Specifically, the thickness of the back gate layer 23 is thinner than the sum of four times the penetration depth of the light emitted by the light-emitting element 10 and the diffusion length of electrons in the channel layer 24.

[0088] The penetration depth d0 of light is expressed by the following equation (1).

[0089] (1) d0={1+ln(1-R)} / A

[0090] A is the absorption coefficient of light. In the case of GaN, A>100,000 [1 / cm]. R is the reflection coefficient of light. In the case of GaN, R can be considered to be substantially 0. Therefore, in the case of GaN, d0 is greater than 100 nm. By setting the thickness of the back gate layer 23 to a value four times d0 or less, light can be transmitted through the back gate layer 23 and reach the channel layer 24. The penetration depth of light is the depth at which the light intensity becomes 1 / e (approximately 37%), and four times the penetration depth of light is the depth at which the light intensity becomes approximately 2%.

[0091] Specifically, the penetration depth d0 of GaN is approximately 250 nm. Furthermore, the diffusion distance of electrons is approximately 10 nm in the case of p-type GaN. Therefore, by making the thickness of the back gate layer 23 thinner than approximately 260 nm, a portion of the light incident on the switch body 20 can be transmitted through the back gate layer 23 and reach the channel layer 24, thereby reducing the on-resistance. It is not essential that light is transmitted through the back gate layer 23, and the thickness of the back gate layer 23 may be thicker than approximately 260 nm. The thickness of the back gate layer 23 can be, for example, in the range of 0.1 μm to 1.2 μm.

[0092] In the on-state, the on-current can be increased by the 2DEG 26 and electrons generated in the channel layer 24 due to the photovoltaic effect. In addition, the 2DEG 26 is generated directly below each of the electrodes 27 and 28, reducing the contact resistance. This also increases the on-current.

[0093] 6 is a diagram showing the relationship between the on-current of the switch body 20 and the thickness of the back gate layer 23. In Fig. 6, the horizontal axis represents the bias voltage applied between the electrodes 27 and 28, and the vertical axis represents the current (on-current) that flows between the electrodes 27 and 28 when the switch is on.

[0094] As shown in Figure 6, when the thickness of the back gate layer 23 made of p-type GaN is 0.1 μm and 0.3 μm, a high on-current of approximately 0.25 A is obtained at a bias voltage of 3 V. It can also be seen that even when the back gate layer 23 is 1 μm thick, a sufficient on-current of approximately 0.2 A is obtained at a bias voltage of 3 V. On the other hand, when the thickness of the back gate layer 23 is 1.5 μm or 2 μm, the current value is less than 0.05 A even at a bias voltage of 3 V, indicating a low on-current. This indicates that a high on-current can be obtained if the thickness of the back gate layer 23 is 1 μm or less. It can also be inferred that a high current can be obtained even when the thickness of the back gate layer 23 is approximately 1.1 μm or 1.2 μm.

[0095] As described above, the semiconductor device 1 according to this embodiment can reduce the on-resistance and increase the on-current. Furthermore, because backside illumination can be utilized, a field plate formed of a light-shielding metal material can be disposed on the upper surface of the switch body 20. Since there are no restrictions on the shape of the field plate, optimization of the shape is possible, thereby alleviating electric field concentration and improving the breakdown voltage.

[0096] [Modifications] Next, a description will be given of modifications of embodiment 1. The following description will focus on differences from embodiment 1, and description of commonalities will be omitted or simplified.

[0097] <Modification 1> Fig. 7 is a cross-sectional view of a switch body 20A (ON) according to Modification 1 of Embodiment 1. As shown in Fig. 7, the switch body 20A differs from the switch body 20 in that it includes a buffer layer 22A instead of the buffer layer 22.

[0098] 7, the buffer layer 22A includes an AlN layer 22a and an AlGaN layer 22b. The AlGaN layer 22b is substantially the same as the buffer layer 22. In other words, the switch body 20A according to this modification has a configuration in which the AlN layer 22a is inserted between the buffer layer 22 and the substrate 21 in the configuration of the switch body 20 shown in FIG.

[0099] The AlN layer 22a is provided so as to contact and cover the upper surface of the substrate 21. The AlN layer 22a is made of undoped AlN. ｘ Ga １－ｘ This corresponds to the case where the molar ratio x of N is 1. The band gap of the AlN layer 22a is larger than the band gap of the AlGaN layer 22b, and the absorption rate of light from the light emitting element 10 is sufficiently low. Therefore, even if the AlN layer 22a is provided, there is almost no effect on the light input efficiency. The thickness of the AlN layer 22a is, for example, not less than 100 nm and not more than 10,000 nm, but is not limited to this.

[0100] The provision of the AlN layer 22a can alleviate the lattice mismatch between the substrate 21 and the AlGaN layer 22b, thereby improving the film quality of the AlGaN layer 22b, the back gate layer 23, the channel layer 24, and the barrier layer 25, and increasing the reliability of the switch body 20A.

[0101] <Modification 2> Fig. 8 is a cross-sectional view of a switch body 20B (ON) according to Modification 2 of Embodiment 1. As shown in Fig. 8, the switch body 20B differs from the switch body 20 in that it includes a buffer layer 22B instead of the buffer layer 22.

[0102] 8, the buffer layer 22B includes an AlN layer 22a and an AlGaN layer 22c. The AlN layer 22a is the same as the AlN layer 22a according to Modification 1. Note that in this modification, the AlN layer 22a does not necessarily have to be provided.

[0103] The AlGaN layer 22c has a stacked structure in which a plurality of AlGaN layers 22c_1, 22c_2, ..., 22c_n are stacked. Although Fig. 8 shows an example in which the AlGaN layer 22c has a stacked structure of three or more layers, the number of layers n included in the AlGaN layer 22c may be two. The plurality of AlGaN layers 22c_1 to 22c_n each have an Al ｘ Ga １－ｘ N, and each layer has a different value of x. Specifically, the x values ​​of the plurality of AlGaN layers 22c_1 to 22c_n decrease in ascending order. That is, the Al molar ratio x of the bottommost AlGaN layer 22c_1 is the smallest, and the Al molar ratio x of the topmost AlGaN layer 22c_n is the largest. The thicknesses of the plurality of AlGaN layers 22c_1 to 22c_n are equal to one another and are, for example, not less than 1 nm and not more than 10 nm, but are not limited to this.

[0104] In this way, by providing the AlGaN layer 22b configured so that the Al molar ratio decreases stepwise, it is possible to alleviate the lattice mismatch between the substrate 21 and the back gate layer 23. This makes it possible to improve the film quality of the back gate layer 23, the channel layer 24, and the barrier layer 25, thereby increasing the reliability of the switch body 20B.

[0105] When the buffer layer 22B has a stacked structure of multiple layers, as in the switch body 20B according to this modification, the second band gap of the buffer layer 22B can be considered to be the smallest band gap among the band gaps of the multiple layers. In this modification, the band gap of the AlGaN layer 22c_n is the second band gap. In other words, the buffer layer 22B does not include any layer having a band gap smaller than the band gap of the back gate layer 23 and the band gap of the channel layer 24.

[0106] Although the present modification shows an example in which the Al molar ratio x decreases stepwise, the Al molar ratio x may decrease smoothly. That is, the AlGaN layer 22c does not need to have a clearly stacked structure, and may be configured so that the Al molar ratio decreases smoothly (for example, linearly).

[0107] Second Embodiment Next, a second embodiment will be described.

[0108] The main difference between the second embodiment and the first embodiment is that 2DEG is generated partially even when the device is off. The following description will focus on the differences from the first embodiment, and the description of the commonalities will be omitted or simplified.

[0109] 9 is a cross-sectional view of a switch body 120 (off) according to the present embodiment. The switch body 120 shown in FIG. 9 differs from the switch body 20 in that it includes a back gate layer 123 instead of the back gate layer 23.

[0110] The back gate layer 123 corresponds to the back gate layer 23, but has a different shape (arrangement) in a plan view. Specifically, the back gate layer 123 is provided so as to cover only a partial region of the upper surface of the buffer layer 22. Specifically, the back gate layer 123 is located between the electrode 27 and the electrode 28 in a plan view of the substrate 21, and does not overlap with either the electrode 27 or the electrode 28.

[0111] The back gate layer 123 is formed, for example, by forming a film made of p-type GaN by epitaxial growth on the upper surface of the buffer layer 22, and then patterning the film into a predetermined shape by photolithography and etching. Specifically, the back gate layer 123 can be formed by removing a portion of the film made of p-type GaN until the upper surface of the buffer layer 22 is exposed.

[0112] 2DEG 26 is generated in a region of the substrate 21 that does not overlap with the back gate layer 123 in a planar view. As shown in FIG. 9 , when light from the light-emitting element 10 (not shown) is not incident, 2DEG 26 is not generated in a region that overlaps with the back gate layer 123 in a planar view. Therefore, the electrode 27 and the electrode 28 are blocked, and the switch body 120 is non-conductive (off). When light from the light-emitting element 10 is incident, 2DEG 26 is generated in a region that overlaps with the back gate layer 123 in a planar view, and the switch body 120 is conductive, similar to the switch body 20 according to the first embodiment.

[0113] In this way, when the switch body 120 is turned off, the 2DEG 26 disappears only in a certain area, and the 2DEG 26 is generated in other areas. The carrier concentration increases in the areas where the 2DEG 26 does not disappear, further reducing the on-resistance. Furthermore, with the switch body 120 according to this embodiment, the distance between the back gate layer 123 and the electrode 28 can be increased in the planar direction, thereby improving the breakdown voltage.

[0114] [Modification] Next, a description will be given of a modification of embodiment 2. The following description will focus on the differences from embodiment 1 or 2, and the description of commonalities will be omitted or simplified.

[0115] 10 is a cross-sectional view of a switch body 120A (off) according to Modification 1 of Embodiment 2. As shown in FIG. 7 , the switch body 120A differs from the switch body 20 in that it includes a back gate layer 123A instead of the back gate layer 23.

[0116] The back gate layer 123A corresponds to the back gate layer 23, and differs from the back gate layer 23 in that the thickness thereof is partially different. Specifically, the back gate layer 123A has a thin film portion 123a and a thick film portion 123b.

[0117] The thin film portion 123a is thinner than the thick film portion 123b. The thin film portion 123a is provided at a position overlapping the electrode 27 or 28 when the substrate 21 is seen in a plan view.

[0118] In a plan view of the substrate 21, the thick film portion 123b is located between the electrode 27 and the electrode 28, and does not overlap either the electrode 27 or the electrode 28. The thick film portion 123b corresponds to the back gate layer 123 according to embodiment 2. The thickness of the thick film portion 123b is, for example, not less than 100 nm and not more than 1200 nm, similar to the thickness of the back gate layer 23 according to embodiment 1, but is not limited to this.

[0119] By providing the thin film portion 123a and the thick film portion 123b, the thickness of the channel layer 24 differs above the thin film portion 123a and the thick film portion 123b. Due to the difference in thickness of the channel layer 24, when no light is incident, the 2DEG 26 disappears above the thick film portion 123b, but the 2DEG 26 does not disappear above the thin film portion 123a. For example, the thickness of the channel layer 24 above the thin film portion 123a is greater than 200 nm, and the thickness of the channel layer 24 above the thick film portion 123b is 100 nm to 200 nm. The thicknesses of the thin film portion 123a and the thick film portion 123b are adjusted to desired values ​​so that the thickness of the channel layer 24 is an appropriate value.

[0120] The back gate layer 123A is formed, for example, by forming a film made of p-type GaN by epitaxial growth on the upper surface of the buffer layer 22, and then removing a portion of the formed film by photolithography and etching. Specifically, the back gate layer 123A can be formed by partially removing a portion of the film made of p-type GaN so that the upper surface of the buffer layer 22 is not exposed.

[0121] In the area overlapping with the thin film portion 123a in plan view, the potential of the channel layer 24 does not increase sufficiently, and the 2DEG 26 is generated even in the off state. Therefore, as in the second embodiment, in the area overlapping with the thin film portion 123a in plan view, the carrier concentration of the 2DEG 26 increases, and the on-resistance can be further reduced.

[0122] 11 is a cross-sectional view of a switch body 120B (off) according to Modification 2 of Embodiment 2. As shown in Fig. 11 , the switch body 120B differs from the switch body 20 in that it includes a barrier layer 125 instead of the barrier layer 25.

[0123] The barrier layer 125 corresponds to the barrier layer 25, and differs in that a recess 125r is provided. The recess 125r is located between the electrodes 27 and 28 in a plan view of the substrate 21. The recess 125r is also called a recess portion, and is formed so as to recess downward from the upper surface of the barrier layer 125. The bottom surface of the recess 125r is part of the barrier layer 125, and the channel layer 24 is not exposed.

[0124] By providing the recess 125r, the polarization is weakened in the direction directly below the recess 125r, and the 2DEG 26 disappears. In this modification, the 2DEG 26 is generated in the region other than the region directly below the recess 125r, i.e., the region that does not overlap with the recess 125r in a planar view, even in the off state. In this way, in a state where no light is incident, the 2DEG 26 disappears in the direction directly below the recess 125r, and in order to maintain the state where the 2DEG 26 is generated in the region other than the direction directly below the recess 125r, the thickness of the channel layer 24 in this modification is, for example, 100 nm to 200 nm.

[0125] In this way, in the switch body 120B of this modified example, as in embodiment 2, the carrier concentration of the 2DEG 26 increases in the area that does not overlap with the recess 125r in a planar view, thereby further reducing the on-resistance.

[0126] The switch bodies 120, 120A, and 120B according to the present embodiment and the modifications may each include the buffer layer 22A or 22B according to the modification of the first embodiment, instead of the buffer layer 22. The switch bodies 120 and 120A according to the present embodiment and the modifications may each include a barrier layer 125 provided with a recess 125r, instead of the barrier layer 25.

[0127] Third Embodiment Next, a third embodiment will be described.

[0128] The main difference between the third embodiment and the first embodiment is that an n-type nitride semiconductor layer is provided between a p-type back gate layer and a buffer layer. The following description will focus on the differences from the first embodiment, and the description of the commonalities will be omitted or simplified.

[0129] 12 is a cross-sectional view of a switch body 220 (off) according to this embodiment. The switch body 220 shown in FIG. 12 includes an n-type GaN layer 223n and an electrode 227 in addition to the configuration of the switch body 20.

[0130] The n-type GaN layer 223n is an example of an n-type nitride semiconductor layer provided between the buffer layer 22 and the back gate layer 23. In this embodiment, the n-type GaN layer 223n is provided in contact with the upper surface of the buffer layer 22 and the lower surface of the back gate layer 23, respectively. The n-type GaN layer 223n is made of n-type GaN. Note that, instead of the n-type GaN layer 223n, a layer made of n-type InGaN, AlGaN, AlInGaN, or the like may be provided. The band gap of the n-type GaN layer 223n is smaller than both the band gap of the substrate 21 and the band gap of the buffer layer 22. The band gap of the n-type GaN layer 223n is, for example, the same as the band gap of the back gate layer 23.

[0131] The n-type GaN layer 223n forms a p-n junction with the p-type back gate layer 23. This can promote the separation of electron-hole pairs generated near the p-n junction interface when light is incident. This can increase the number of holes accumulated in the back gate layer 23, thereby further increasing the potential of the back gate layer 23. This can increase the carrier concentration of the 2DEG 26, further reducing the on-resistance.

[0132] The thickness of the n-type GaN layer 223n is adjusted, for example, so that the total thickness of the back gate layer 23 and the n-type GaN layer 223n is thinner than the sum of the penetration depth of light emitted by the light emitting element 10 and the diffusion length of electrons in the channel layer 24. This allows part of the light from the light emitting element 10 to pass through the n-type GaN layer 223n and the back gate layer 23 and reach the channel layer 24.

[0133] The electrode 227 is an example of a third electrode and is electrically connected to the n-type GaN layer 223 n. Specifically, the electrode 227 is provided in contact with the upper surface of the n-type GaN layer 223 n. An opening is provided through the barrier layer 25, the channel layer 24, and the back gate layer 23 to expose the upper surface of the n-type GaN layer 223 n.

[0134] The electrode 227 is formed using a conductive material such as a metal, etc. For example, the electrode 227 has a layered structure including a Ti layer and an Al layer stacked on the top surface of the Ti layer, but is not limited to this.

[0135] The electrode 227 is supplied with the same potential as the lower-potential electrode of the electrodes 27 and 28. For example, the electrodes 227 and 27 are electrically connected and supplied with a ground potential (0 V). This allows the potential of the n-type GaN layer 223n to be fixed. By fixing the potential of the n-type GaN layer 223n, the potential of the p-type back gate layer 23 can be indirectly fixed. In other words, fluctuations in the potential of the back gate layer 23 can be suppressed, thereby suppressing leakage current. For example, holes accumulated in the back gate layer 23 during on-state can be quickly released to the n-type GaN layer 223n during off-state, preventing the back gate layer 23 from reaching a high potential during off-state, thereby suppressing off-state leakage current.

[0136] 13, an i-type GaN layer 223i may be provided between the n-type GaN layer 223n and the back gate layer 23. Fig. 13 is a cross-sectional view of a switch body 220A (off) according to a modification of the present embodiment.

[0137] The i-type GaN layer 223i is provided in contact with the upper surface of the n-type GaN layer 223n and the lower surface of the back gate layer 23. The i-type GaN layer 223i is made of undoped GaN. Note that instead of the i-type GaN layer 223i, a layer made of undoped InGaN, AlGaN, AlInGaN, or the like may be provided. The band gap of the i-type GaN layer 223i is smaller than both the band gap of the substrate 21 and the band gap of the buffer layer 22. The band gap of the i-type GaN layer 223i is, for example, the same as the band gap of the back gate layer 23.

[0138] In this way, the switch body 220A including the i-type GaN layer 223i also provides the same effects as the switch body 220. That is, it is possible to achieve a reduction in on-resistance and a reduction in off-leak current.

[0139] The thickness of the i-type GaN layer 223i is adjusted, for example, so that the total thickness of the back gate layer 23, the i-type GaN layer 223i, and the n-type GaN layer 223n is thinner than the sum of the penetration depth of light emitted by the light emitting element 10 and the diffusion length of electrons in the channel layer 24. This allows part of the light from the light emitting element 10 to pass through the n-type GaN layer 223n, the i-type GaN layer 223i, and the back gate layer 23 and reach the channel layer 24.

[0140] The switch bodies 220 and 220A according to the present embodiment and the modification may each include the buffer layer 22A or 22B according to the modification of the first embodiment, instead of the buffer layer 22. The switch bodies 220 and 220A may also include the back gate layer 123 or 123A according to the second embodiment and the modification, instead of the back gate layer 23. The switch bodies 220 and 220A may also include the barrier layer 125 provided with a recess 125r, instead of the barrier layer 25.

[0141] While the semiconductor device according to one or more aspects has been described above based on the embodiments, the present disclosure is not limited to these embodiments. As long as they do not deviate from the gist of the present disclosure, various modifications conceivable by those skilled in the art to the present embodiments and configurations constructed by combining components of different embodiments are also included within the scope of the present disclosure.

[0142] For example, in the above embodiment, the light-emitting element 10 is provided on the underside of the switch body 20, but this is not limiting. For example, the light-emitting element 10 may be mounted on the support substrate 30. For example, the semiconductor device 1 may include a reflective member that reflects light emitted by the light-emitting element 10, and the light reflected by the reflective member may be incident on the underside of the substrate 21 of the switch body 20. The reflective member may be, for example, a reflector made of a metal material. Alternatively, the reflective member may be a translucent member having a refractive index different from that of the resin member 50, and may be provided to cover the light-emitting element 10 and the switch body 20. In this case, the light emitted by the light-emitting element 10 enters the translucent member (reflective member) and is incident on the underside of the substrate 21 of the switch body 20 by utilizing total reflection at the interface between the translucent member and the resin member 50.

[0143] Furthermore, for example, at least one of the back gate layer 23, 123, or 123A and the channel layer 24 may be made of InGaN. Since the band gap of InGaN is smaller than that of GaN, the barrier layer 25 or 125 may be made of GaN, AlInGaN, or the like. Furthermore, the buffer layer 22, 22A, or 22B may include a layer made of GaN, AlInGaN, or the like.

[0144] The bandgap of the channel layer 24 may be larger or smaller than the bandgap of the back gate layer 23, 123 or 123A.

[0145] In addition, for example, in the above embodiment, an example was shown in which the switch body is conductive when emitting light and non-conductive when 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.

[0146] Furthermore, various modifications, substitutions, additions, omissions, etc. can be made to the above-described embodiments within the scope of the claims or their equivalents.

[0147] The present disclosure can be used as a semiconductor device capable of reducing on-resistance, and can be used in, for example, a relay device, a switch device, and the like.

[0148] REFERENCE SIGNS LIST 1 semiconductor device 10 light emitting element 20, 20A, 20B, 120, 120A, 120B, 220, 220A switch body 21 substrate 22, 22A, 22B buffer layer 22a AlN layer 22b, 22c AlGaN layer 23, 123, 123A back gate layer 24 channel layer 25, 125 barrier layer 26 2DEG 27, 28, 227 electrode 29 protective film 30 support substrate 41a, 41b, 41c, 41d, 45a, 45b terminal 43a, 43b, 43c external terminal 44a, 44b wire 50 resin member 123a thin film portion 123b thick film portion 125r recess 223n n-type GaN layer 223i i-type GaN layer

Claims

1. A semiconductor device comprising: a switch body; and a light-emitting element electrically insulated from the switch body, wherein the switch body comprises: a substrate having a first band gap; a buffer layer having a second band gap provided above the substrate; a p-type nitride semiconductor layer provided above the buffer layer and having a third band gap smaller than both the first band gap and the second band gap; a first nitride semiconductor layer having a fourth band gap provided above the p-type nitride semiconductor layer; a second nitride semiconductor layer provided above the first nitride semiconductor layer and having a fifth band gap larger than the fourth band gap; and a first electrode and a second electrode provided above the second nitride semiconductor layer and spaced apart from each other in a planar view of the substrate, wherein light emitted by the light-emitting element passes through the substrate and enters the p-type nitride semiconductor layer.

2. The semiconductor device according to claim 1, wherein the p-type nitride semiconductor layer is located between the first electrode and the second electrode in a plan view of the substrate, and does not overlap either the first electrode or the second electrode.

3. The semiconductor device according to claim 1, wherein the p-type nitride semiconductor layer has a thick film portion and a thin film portion thinner than the thick film portion, and the thick film portion is located between the first electrode and the second electrode in a plan view of the substrate, and does not overlap either the first electrode or the second electrode.

4. The semiconductor device according to claim 1, wherein the second nitride semiconductor layer has a recess located between the first electrode and the second electrode in a plan view of the substrate.

5. The semiconductor device according to claim 1, further comprising: an n-type nitride semiconductor layer provided between said buffer layer and said p-type nitride semiconductor layer; and a third electrode electrically connected to said n-type nitride semiconductor layer.

6. The semiconductor device according to any one of claims 1 to 4, wherein the thickness of the p-type nitride semiconductor layer is thinner than the sum of four times the penetration depth of light emitted by the light emitting element and the diffusion length of electrons in the first nitride semiconductor layer.

7. The buffer layer is Al ｘ Ga １－ｘ 6. The semiconductor device according to claim 1, further comprising an AlGaN layer made of N (0<x<1), wherein the second band gap is the band gap of the AlGaN layer.

8. The semiconductor device according to claim 7, wherein x is 0.05 or more.

9. The semiconductor device according to claim 7, wherein the buffer layer has a layered structure in which a plurality of the AlGaN layers, each having a different value of x, are stacked, and the value of x of each of the plurality of AlGaN layers decreases in order upward.

10. The semiconductor device according to any one of claims 1 to 5, wherein the light emitting element is provided on the lower surface of the substrate.

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