Resonant tunneling diode and high frequency device

Abstract

[Problem] Output can be improved. [Solution] This resonant tunneling diode comprises: a first electrode layer that is disposed on a support substrate which contains a nitride semiconductor material; a first spacer layer that is disposed on the first electrode layer; an active layer that is disposed on the first spacer layer; a second spacer layer that is disposed on the active layer; and a second electrode layer that is disposed on the second spacer layer. The average value of the band gap in the second spacer layer is smaller than the average value of the band gaps in the first electrode layer and the second electrode layer.

Description

Resonant tunneling diodes and high-frequency devices

[0001] This disclosure relates to resonant tunneling diodes and high-frequency devices.

[0002] In the field of semiconductor technology, research and development of tunneling devices is progressing. Among tunneling diodes, those that utilize the resonant tunneling phenomenon are also called resonant tunneling diodes (RTDs). Resonant tunneling diodes can oscillate at high frequencies of 1 THz or higher at room temperature, and their application to semiconductor memory and antennas has been proposed.

[0003] Currently, research and development of resonant tunneling diode devices using GaN-based materials is underway. For example, a resonant tunneling diode device with faster operation than conventional devices has been proposed by introducing a potential gradient in the well layer of a quantum well (see Patent Document 1).

[0004] Japanese Patent Publication No. 2018-67727

[0005] Resonant tunneling diode elements using GaN-based materials can experience significant potential changes due to the effects of spontaneous polarization and piezoelectric polarization. For example, piezoelectric polarization generated in the barrier layer can increase the potential of the spacer layer between the collector layer and the barrier layer (potential rise). This makes it difficult for the resonant tunneling current to flow, reducing the output of the resonant tunneling diode element. Patent Document 1 does not disclose a solution to this problem.

[0006] Therefore, this disclosure provides a resonant tunneling diode and a high-frequency device that can improve output.

[0007] To solve the above problems, the present disclosure provides a resonant tunneling diode comprising: a first electrode layer disposed on a support substrate containing a nitride semiconductor material; a first spacer layer disposed on the first electrode layer; an active layer disposed on the first spacer layer; a second spacer layer disposed on the active layer; and a second electrode layer disposed on the second spacer layer, wherein the average value of the band gap in the second spacer layer is smaller than the average value of the band gaps in the first electrode layer and the second electrode layer.

[0008] The impurity concentration of the second spacer layer may be lower than the impurity concentrations of the first electrode layer and the second electrode layer.

[0009] The second spacer layer may be positioned in contact with the active layer.

[0010] The band gap in the second spacer layer may be smallest on the first surface in contact with the active layer and largest on the second surface opposite to the first surface.

[0011] The second spacer layer may have a first nitride semiconductor layer containing indium (In).

[0012] The first nitride semiconductor layer may be arranged in contact with the active layer.

[0013] The second spacer layer may have a second nitride semiconductor layer that is laminated on the first nitride semiconductor layer and does not contain indium (In).

[0014] The average composition ratio of indium (In) in the first nitride semiconductor layer of the second spacer layer may be 1% or more and 30% or less.

[0015] The first nitride semiconductor layer may have a thickness of 0.1 nm or more and 20 nm or less.

[0016] The surface of the support substrate on which the first electrode layer is placed may be a C-surface.

[0017] The active layer comprises a first barrier layer disposed on the first spacer layer, a second barrier layer disposed on the first barrier layer, and a well layer disposed between the first barrier layer and the second barrier layer, having a smaller band gap than the first barrier layer and the second barrier layer, wherein the average band gap of the well layer may be smaller than the average band gap of the first electrode layer and the second electrode layer.

[0018] The impurity concentration of the well layer may be lower than the impurity concentrations of the first electrode layer and the second electrode layer.

[0019] The well layer may be arranged in contact with the first barrier layer.

[0020] The band gap in the well layer may be smallest on the third surface in contact with the first barrier layer and largeest on the fourth surface opposite to the third surface.

[0021] The well layer may have a third nitride semiconductor layer containing indium (In).

[0022] The third nitride semiconductor layer may be arranged in contact with the first barrier layer.

[0023] The well layer may have a fourth nitride semiconductor layer laminated on the third nitride semiconductor layer and not containing indium (In).

[0024] The average composition ratio of indium (In) in the third nitride semiconductor layer of the well layer may be 1% or more and 30% or less.

[0025] The third nitride semiconductor layer may have a thickness of 0.1 nm or more and 20 nm or less.

[0026] Furthermore, the present disclosure provides a high-frequency device comprising a resonant tunneling diode and an antenna connected in parallel between the resonant tunneling diode and a reference voltage node, the antenna having a capacitor and an inductor that resonate at a specific frequency.

[0027] A perspective view showing the configuration of a high-frequency device according to the first embodiment of this disclosure. A cross-sectional view of the high-frequency device in Figure 1. A circuit diagram showing the equivalent circuit of the high-frequency device according to the first embodiment of this disclosure. A cross-sectional view showing the configuration of a resonant tunneling diode according to a basic example. A waveform diagram of the energy band in the resonant tunneling diode in Figure 4. A cross-sectional view showing the configuration of a resonant tunneling diode according to the first embodiment of this disclosure. A waveform diagram showing the relationship between the composition ratio of InGaN and the band gap. A waveform diagram of the energy band in the resonant tunneling diode in Figure 6. A waveform diagram showing the I-V characteristics in a resonant tunneling diode. A waveform diagram showing the relationship between the In composition of the upper spacer first layer and PVCR. A waveform diagram showing the relationship between the film thickness of the upper spacer first layer and PVCR. A cross-sectional view showing the configuration of a resonant tunneling diode according to the second embodiment of this disclosure. A cross-sectional view showing the configuration of a resonant tunneling diode according to the third embodiment of this disclosure. A cross-sectional view showing the configuration of a resonant tunneling diode according to the fourth embodiment of this disclosure. A block diagram showing an example of the schematic configuration of a vehicle control system. An explanatory diagram showing an example of the installation positions of the external information detection unit and the imaging unit.

[0028] Embodiments of resonant tunneling diodes and high-frequency devices will be described below with reference to the drawings. While the main components of resonant tunneling diodes and high-frequency devices will be described below, there may be components and functions not shown or described. The following description does not exclude any components or functions not shown or described.

[0029] (First Embodiment) Figure 1 is a perspective view showing the configuration of a high-frequency device 1 comprising a resonant tunnel diode 10 according to the first embodiment of the present disclosure. Figure 2 is a cross-sectional view of the high-frequency device 1 of Figure 1. Figure 2 shows a cross-section along the line A-A' in Figure 1.

[0030] The high-frequency device 1 in Figure 1 is, for example, a patch antenna type high-frequency device. The high-frequency device 1 can be used as an oscillator or a receiver.

[0031] The high-frequency device 1 shown in Figures 1 and 2 comprises an emitter electrode 2, a collector electrode 3, a dielectric 4, a power supply circuit 5, a resonant tunnel diode 10, an emitter layer (first electrode layer) 11, a collector layer (second electrode layer) 12, and a support substrate 13. Figure 1 illustrates the emitter electrode 2, collector electrode 3, dielectric 4, and power supply circuit 5. Figure 2 illustrates the emitter electrode 2, collector electrode 3, dielectric 4, resonant tunnel diode 10, emitter layer 11, collector layer 12, and support substrate 13.

[0032] The emitter electrode 2 and the collector electrode 3 are, for example, metal electrodes. As shown in Figure 2, the emitter electrode 2 and the collector electrode 3 are arranged so as to sandwich the resonant tunnel diode 10, the emitter layer 11, and the collector layer 12 (hereinafter collectively referred to as the resonant tunnel diode 10) and at least a part of the dielectric 4.

[0033] The emitter electrode 2, collector electrode 3, and dielectric 4 form at least a part of the antenna 20. In this specification, the collector electrode 3 may be referred to as the antenna 20.

[0034] The potential of the emitter electrode 2 is set to a reference level (e.g., ground). In this specification, the emitter electrode 2 is also referred to as the ground electrode.

[0035] The collector electrode 3 inputs a signal based on the voltage supplied from the power supply circuit 5 to the resonant tunnel diode 10. In this specification, the collector electrode 3 is also referred to as the signal electrode.

[0036] The dielectric 4 is arranged so as to surround the power supply circuit 5 and the resonant tunnel diode 10 in a plan view.

[0037] The power supply circuit 5 in FIG. 1 has a filter section (MIM Filter) 6 and a power supply section (power supply Pad) 7. The filter section 6 functions as a low-pass filter that separates IF (Intermediate Frequency) signals and DC signals from RF (Radio Frequency) signals. The filter section 6 has, for example, MIM (Metal-Insulator-Metal). The power supply section 7 supplies power to the collector electrode 3 via the filter section 6. The collector electrode 3, one terminal of the filter section 6, and the power supply terminal of the power supply section 7 may be integrally formed. The other terminal of the filter section 6 may be integrally formed with the emitter electrode 2.

[0038] As shown in FIG. 2, the resonant tunneling diode 10 is disposed in the slot portion 8 of the dielectric 4. The resonant tunneling diode 10 is disposed so as to be sandwiched between the emitter layer 11 and the collector layer 12.

[0039] The emitter layer 11 is disposed between the support substrate 13 and the resonant tunneling diode 10. The collector layer 12 is disposed between the collector electrode 3 and the resonant tunneling diode 10, and electrically connects one end of the collector electrode 3 and the resonant tunneling diode 10.

[0040] The support substrate 13 is, for example, a semiconductor substrate containing a nitride semiconductor material. Also, the support substrate 13 is connected to the emitter electrode 2, for example, by an ohmic contact. The emitter electrode 2 is electrically connected to the emitter layer 11 via the support substrate 13.

[0041] FIG. 3 is a circuit diagram showing an equivalent circuit of the high-frequency device 1 according to the first embodiment of the present disclosure. The resonant tunneling diode 10 in FIG. 3 has a negative resistance -Grtd and a capacitor Crtd, which are connected in parallel between a reference voltage node n1 (for example, the emitter electrode 2) and a signal voltage node n2 (for example, the collector electrode 3). The negative resistance -Grtd can be realized by applying a bias voltage within a predetermined range (negative resistance region) to the resonant tunneling diode 10.

[0042] The antenna 20 in Figure 3 has a capacitor Cant, an inductor Lant, a resistor Gloss, and a resistor Grad connected in parallel with a negative resistor Grtd and a capacitor Crd. The resistor Gloss includes, for example, power loss (conductor loss) due to current generated on the surface of the collector electrode 3. The resistor Grad includes, for example, loss due to radiation from the antenna 20.

[0043] The resistive Gloss and resistive Grad act to attenuate the amplitude of the standing wave within the antenna 20. In contrast, the negative resistance -Grtd cancels out the effects of resistive Gloss and Grad, allowing the amplitude of the standing wave to be maintained (oscillate). The oscillation condition for antenna 20 can be expressed as Grtd > Gloss + Grad.

[0044] Here, the absolute value of the negative resistance -Grtd decreases as the oscillation frequency increases. Therefore, there is an upper limit to the oscillation frequency that satisfies the above oscillation conditions. Consequently, in order to make the antenna 20 oscillate at a higher oscillation frequency, it is desirable to increase the absolute value of Grtd over a wide oscillation frequency range.

[0045] One method to increase the absolute value of Grtd is to increase the bias current flowing through the resonant tunnel diode 10 in relation to the bias voltage.

[0046] The high-frequency device 1 in Figure 3 can be used as a receiver. In this case, the capacitor Can and the inductor Lan constitute a resonator 21 that resonates with radio signals of a specific frequency among the radio signals received by the antenna 20 (collector electrode 3).

[0047] Figure 4 is a cross-sectional view showing the configuration of a resonant tunnel diode 100 according to a basic example. The resonant tunnel diode 100 in Figure 4 has a lower spacer layer (first spacer layer) 22, an active layer 23, and an upper spacer layer (second spacer layer) 24, which are stacked in this order from the emitter layer 11 side. The active layer 23 also has a lower barrier layer (first barrier layer) 25, a well layer 26, and an upper barrier layer (second barrier layer) 27, which are stacked in this order from the lower spacer layer 22 side. In this specification, some or all of the components in Figure 4 may be referred to as semiconductor layers.

[0048] The resonant tunneling diode 100 in Figure 4 includes a nitride semiconductor material. Specifically, the emitter layer 11, collector layer 12, lower spacer layer 22, upper spacer layer 24, and well layer 26 include, for example, GaN (gallium nitride). The lower barrier layer 25 and upper barrier layer 27 include, for example, AlN (aluminum nitride).

[0049] The problems with the configuration in Figure 4 will be explained below using Figure 5. Figure 5 is a waveform diagram of the energy bands in the resonant tunnel diode 100 of Figure 4. The horizontal axis of Figure 5 represents the distance from the collector electrode 3 (Distance [A]), and the vertical axis represents the potential energy (Energy [eV]). Figure 5 also illustrates the potential energies of the collector layer 12, upper spacer layer 24, upper barrier layer 27, well layer 26, lower barrier layer 25, lower spacer layer 22, and emitter layer 11, respectively, from left to right.

[0050] Figure 5 illustrates curves W1 and W2. Curve W1 shows the energy band considering polarization (spontaneous polarization and piezoelectric polarization, etc.). Curve W2 shows the ideal energy band without considering polarization. In Figure 5, curve W1 is shown as a solid line and curve W2 as a dashed line.

[0051] As shown in Figure 4, the lower barrier layer 25 and the upper barrier layer 27 contain AlN and have a higher potential energy compared to other semiconductor layers containing GaN. Furthermore, as shown by curve W2 in Figure 5, in the ideal state where no polarization occurs, the energy band of the resonant tunnel diode 100 has a convex shape in the lower barrier layer 25 and the upper barrier layer 27, and a flat shape in the other semiconductor layers. The resonant tunnel diode 100 can obtain a large negative resistance due to the band gap difference between AlN and GaN.

[0052] The operation of the resonant tunnel diode 100 will now be explained. When no bias voltage is applied to the resonant tunnel diode 100, no current flows because the potentials of the emitter electrode 2 and the collector electrode 3 are lower than the conductor levels in the well layer 26.

[0053] When the bias voltage applied to the resonant tunneling diode 100 is increased, the charge tunnels through the potential barriers of the lower barrier layer 25 and the upper barrier layer 27, and a resonant tunneling current flows (also called the quantum tunneling effect). The film thickness of the lower barrier layer 25 and the upper barrier layer 27 is set to be thin enough to realize the above quantum tunneling effect. In this specification, the region in which the resonant tunneling current increases by increasing the bias voltage is also called the first positive resistance region.

[0054] If the bias charge is further increased, the resonant tunneling current decreases. The region in which increasing the bias voltage actually reduces the current flowing through the resonant tunneling diode 100 is also called the negative resistance region. In the negative resistance region, the current flowing through the resonant tunneling diode 100 decreases from the peak current to the valley current.

[0055] Further increasing the bias voltage generates a thermally excited current as the charge overcomes the potential barriers of the lower barrier layer 25 and the upper barrier layer 27. In this specification, the region in which the thermally excited current increases by increasing the bias voltage is also referred to as the second positive resistance region.

[0056] The output of the resonant tunneling diode 100 in the negative resistance region can be increased by increasing the ratio of the peak current to the valley current (hereinafter also called the PVCR: Peak to Valley Current Ratio). For this reason, it is desirable for a larger resonant tunneling current (i.e., peak current) to flow through the resonant tunneling diode 100.

[0057] As shown by curve W2 in Figure 5, in the ideal state where no polarization occurs, the thickness of the lower barrier layer 25 and the thickness of the upper barrier layer 27 become the barrier thickness that inhibits the resonant tunneling current.

[0058] On the other hand, as shown by curve W1 in Figure 5, the energy band of the resonant tunnel diode 100 actually changes significantly due to polarization. The potential energy of the well layer 26 is raised by the potential energies of the lower barrier layer 25 and the upper barrier layer 27. In addition, potential gradients are generated in the lower barrier layer 25, the well layer 26, and the upper barrier layer 27, respectively. Near the interface between the lower spacer layer 22 and the lower barrier layer 25, electrons accumulate, causing a potential constriction.

[0059] Furthermore, in the resonant tunneling diode 100, polarization causes the potential energy of the upper spacer layer 24 to rise significantly, as if being lifted by the upper barrier layer 27. As a result, the region of the upper spacer layer 24 near the interface with the upper barrier layer 27 effectively becomes a barrier layer that inhibits the resonant tunneling current. In other words, the effective barrier thickness B1 of the upper barrier layer 27 increases from the ideal barrier thickness. This makes it difficult for the resonant tunneling current to flow.

[0060] Furthermore, in the resonant tunneling diode 100, the potential energy of the well layer 26 on the side in contact with the lower barrier layer 25 also increases due to polarization, as if being lifted up to the lower barrier layer 25. In other words, the region of the well layer 26 near the interface with the lower barrier layer 25 also effectively becomes an effective barrier thickness B2 that inhibits the resonant tunneling current.

[0061] Figure 6 is a cross-sectional view showing the configuration of a resonant tunnel diode 10 according to the first embodiment of the present disclosure. The resonant tunnel diode 10 in Figure 6 has a lower spacer layer 22, a lower barrier layer 25, a well layer 26, and an upper barrier layer 27, similar to Figure 4. In addition, the resonant tunnel diode 10 in Figure 6 has an upper spacer first layer (first nitride semiconductor layer) 31 and an upper spacer second layer (second nitride semiconductor layer) 32 instead of the upper spacer layer 24 in Figure 4. In the resonant tunnel diode 10 in Figure 6, the upper spacer first layer 31 and the upper spacer second layer 32 are sometimes collectively referred to as the upper spacer layer (second spacer layer) 33.

[0062] The first upper spacer layer 31 is positioned in contact with the upper barrier layer 27. The second upper spacer layer 32 is positioned in contact with the collector layer 12.

[0063] The average bandgap energy (hereinafter also simply referred to as the bandgap) of the upper spacer layer 33 in Figure 6 is adjusted to be smaller than the average bandgap energy of the emitter layer 11 and the collector layer 12. Specifically, the first upper spacer layer 31 contains indium (In), while the second upper spacer layer 32 does not contain indium (In).

[0064] More specifically, the upper spacer first layer 31 includes, for example, InGaN. The upper spacer second layer 32 also includes, for example, GaN. More precisely, the upper spacer first layer 31 includes, In x Ga (1-x) N includes (0 < x < 1). Note that In below, x Ga (1-x) N is also sometimes simply written as InGaN.

[0065] Figure 7 shows In x Ga (1-x) This waveform diagram shows the relationship between the composition ratio of N and the band gap. The horizontal axis of Figure 7 represents the ratio of In (In content, i.e., molar ratio) x. In Figure 7, the minimum value of x is 0 (i.e., GaN), and the maximum value of x is 1 (i.e., InN). The vertical axis of Figure 7 represents the band gap energy.

[0066] As shown in Figure 7, In x Ga (1-x) The band gap of N decreases monotonically as the proportion of In increases. Therefore, the band gap of the upper spacer layer 1 31 containing In is smaller than the band gaps of the upper spacer layer 2 32, the emitter layer 11, and the collector layer 12, which do not contain In.

[0067] The emitter layer 11, collector layer 12, lower spacer layer 22, and well layer 26 in Figure 6 contain, for example, GaN. The lower barrier layer 25 and upper barrier layer 27 in Figure 6 contain, for example, AlN. The impurity concentrations in the lower spacer layer 22, well layer 26, upper spacer first layer 31, and upper spacer second layer 32 in Figure 6 are smaller than the impurity concentrations in the emitter layer 11 and collector layer 12. That is, impurities are injected during the formation of the emitter layer 11 and collector layer 12, while the impurity injection step can be omitted during the formation of the lower spacer layer 22, well layer 26, upper spacer first layer 31, and upper spacer second layer 32.

[0068] The above-mentioned nitride semiconductors (specifically GaN, AlN, and InGaN) have the C-plane as their primary plane orientation. That is, the plane on which the emitter layer 11 of the support substrate 13 is located is the C-plane.

[0069] Figure 8 is a waveform diagram of the energy bands in the resonant tunneling diode 10 shown in Figure 6. Similar to Figure 5, Figure 8 shows the potential energies of the collector layer 12, upper spacer layer 33, upper barrier layer 27, well layer 26, lower barrier layer 25, lower spacer layer 22, and emitter layer 11, respectively, from left to right.

[0070] Figure 8 illustrates curves W1 and W3. Curve W1 shows the energy band in the resonant tunneling diode 100 in Figure 4 (i.e., it is the same as curve W1 in Figure 5). Curve W3 shows the energy band in the resonant tunneling diode 10 in Figure 6. In Figure 8, curve W1 is shown as a dashed line and curve W3 as a solid line.

[0071] As shown in Figure 8, the potential energy of the upper spacer layer 33 of the resonant tunneling diode 10 according to the first embodiment of this disclosure is smaller than the potential energy of the upper spacer layer 24 of the resonant tunneling diode 100 according to the basic example. As a result, in the resonant tunneling diode 10, the effective barrier thickness B3 of the upper barrier layer 27 and the upper spacer layer 33 is smaller than the effective barrier thickness B1 of the resonant tunneling diode 100.

[0072] In other words, the resonant tunneling diode 10 in Figure 6 can pass a larger resonant tunneling current than the resonant tunneling diode 100 in Figure 4.

[0073] Figure 9 is a waveform diagram showing the I-V characteristics of resonant tunnel diodes 10 and 100. In Figure 9, the horizontal axis represents voltage (V) and the vertical axis represents current (Current (A)). Figure 6 also shows curves W4 and W5. Curve W4 shows the I-V characteristics of resonant tunnel diode 10 in Figure 6, and curve W5 shows the I-V characteristics of resonant tunnel diode 100 in Figure 4. In Figure 9, curve W4 is shown as a solid line and curve W5 as a dashed line. In Figure 9, the peak current (Peak) and valley current (Valley) are also shown for curves W4 and W5, respectively.

[0074] As shown in curves W4 and W5, the difference between the peak current and valley current of the resonant tunneling diode 10 is greater than the difference between the peak current and valley current of the resonant tunneling diode 100. That is, as shown in Figure 9, the PVCR of the resonant tunneling diode 10 is greater than that of the resonant tunneling diode 100. Therefore, the resonant tunneling diode 10 has a larger negative resistance than the resonant tunneling diode 100, and can oscillate the high-frequency device 1 over a wider oscillation frequency.

[0075] As shown in Figure 5, several methods can be considered to suppress the effects of interference with resonant tunneling current due to piezoelectric polarization, etc., in addition to the configuration shown in Figure 6. For example, one first method is to use a semi-polar or non-polar GaN substrate as the support substrate 13. However, semi-polar or non-polar substrates may be more difficult to manufacture, posing significant challenges in terms of productivity and cost. Furthermore, the crystal quality of semi-polar or non-polar substrates may be inferior to that of commonly used C-plane substrates, raising concerns about the impact on device performance.

[0076] A second approach involves using a barrier layer made of a material with low piezoelectric polarization, such as AlInGaN. However, the growth process for AlInGaN can be more difficult than that for AlN, and there are challenges in terms of crystallinity and productivity. Furthermore, since AlInGaN has a smaller band gap compared to AlN, sufficient barrier properties cannot be obtained, raising concerns about deterioration of the characteristics of the resonant tunneling diode.

[0077] Compared to these methods, the resonant tunneling diode 10 shown in Figure 6 uses a C-plane substrate, which is relatively easy to manufacture, and an AlN barrier layer, which is relatively easy to grow crystals in, thereby suppressing the effects of inhibition of the resonant tunneling current due to piezoelectric polarization, etc. For this reason, the resonant tunneling diode 10 according to the first embodiment of this disclosure is superior to the above methods in terms of productivity, cost, and characteristics.

[0078] Note that the resonant tunneling diode 10 in Figure 6 may have a configuration having multiple well layers. For example, a second well layer and a third barrier layer may be placed between the lower barrier layer 25 and the lower spacer layer 22. The second well layer is placed on the lower barrier layer 25 side, and the third barrier layer is placed on the lower spacer layer 22 side.

[0079] Next, the optimal design of the upper spacer first layer 31 will be examined using FIGS. 10 and 11. FIG. 10 is a waveform diagram showing the relationship between the In composition and PVCR of the upper spacer first layer 31. The horizontal axis of FIG. 10 indicates the In composition ratio (molar ratio) [%], and the vertical axis indicates the difference value ΔI [mA] between the peak current and the valley current. It is desirable that the difference value ΔI on the vertical axis of FIG. 10 be large.

[0080] As shown in FIG. 10, the difference value ΔI reaches a maximum value when the In composition is near 10%. Therefore, it is desirable that the In composition be around 10%. That is, the upper spacer first layer 31 preferably contains In 0.1 GaN. For example, by growing the upper spacer first layer 31 at 920° C., the In composition can be adjusted to around 10%.

[0081] Note that even if the In composition is not 10%, for example, if it is 1% or more and 30% or less, a sufficiently high difference value ΔI can be obtained effectively.

[0082] FIG. 11 is a waveform diagram showing the relationship between the film thickness of the upper spacer first layer 31 and PVCR. The horizontal axis indicates the film thickness of the upper spacer first layer 31 (InGaN film thickness [nm]), and the vertical axis indicates the difference value ΔI [mA] between the peak current and the valley current.

[0083] As shown in FIG. 11, the difference value ΔI reaches a maximum value when the film thickness of the upper spacer first layer 31 is 1 nm to 2 nm. Therefore, it is desirable that the film thickness of the upper spacer first layer 31 be 1 nm to 2 nm (for example, 1.5 nm). In addition to the above, if the film thickness of the upper spacer first layer 31 is, for example, 0.1 nm or less and 20 nm or less, a sufficiently high difference value ΔI can be obtained effectively.

[0084] Thus, the resonant tunneling diode 10 according to the first embodiment of the present disclosure is composed of a nitride semiconductor. Further, the resonant tunneling diode 10 includes a material having a lower bandgap than the collector layer 12 and the emitter layer 11 in a part of the upper spacer layer 33 between the collector layer 12 and the active layer 23. More specifically, In (more specifically, InGaN) is included on the surface side of the upper spacer layer 33 that contacts the active layer 23.

[0085] This suppresses the increase in the potential energy of the upper spacer layer 33 due to the effects of piezoelectric polarization, etc. As a result, a larger tunnel current can be passed through the resonant tunnel diode 10, increasing the negative resistance and improving the output of the oscillator (e.g., the high-frequency device 1).

[0086] Furthermore, when the upper spacer first layer 31 has an In composition of around 10% and a film thickness of 1 nm to 2 nm (for example, 1.5 nm), the output of the oscillator (for example, the high-frequency device 1) can be improved in particular.

[0087] Furthermore, the resonant tunnel diode 10 according to the first embodiment of this disclosure is superior in terms of productivity, cost, and characteristics to methods that use a semi-polar or non-polar GaN substrate as the support substrate 13, and methods that use a material with low piezoelectric polarization such as AlInGaN as a barrier layer.

[0088] (Second Embodiment) Figure 12 is a cross-sectional view showing the configuration of a resonant tunnel diode 10a according to the second embodiment of the present disclosure. As shown in Figure 12, the In composition of the upper spacer layer may be tilted.

[0089] Specifically, the resonant tunneling diode 10a in Figure 12 has an upper spacer layer 33a corresponding to the upper spacer layer 33 in Figure 6. The upper spacer layer 33a has an In composition that is graded. x Ga (1-x) It contains N. Of the upper spacer layer 33a, the In composition ratio is low on the interface side with the collector layer 12, and high on the interface side with the upper barrier layer 27.

[0090] The upper spacer layer 33a may contain GaN on the interface side with the collector layer 12. The upper spacer layer 33a may have an In composition ratio of approximately 10% (i.e., In 0.1 It may also be written as GaN.

[0091] As a result, the band gap of the upper spacer layer 33a is smallest at the interface in contact with the upper barrier layer 27 (first surface) and largest at the interface in contact with the collector layer 12 (second surface).

[0092] The In composition ratio of the upper spacer layer 33a may change linearly or nonlinearly depending on the distance from the collector layer 12.

[0093] (Third Embodiment) Figure 13 is a cross-sectional view showing the configuration of a resonant tunneling diode 10b according to the third embodiment of the present disclosure. As shown in Figure 13, a portion of the well layer may contain InGaN.

[0094] Specifically, the resonant tunneling diode 10b in Figure 13 has a first well layer (third nitride semiconductor layer) 41 and a second well layer (fourth nitride semiconductor layer) 42 instead of the well layer 26 in Figure 6. In this specification, the first well layer 41 and the second well layer 42 are collectively referred to simply as the well layer 43.

[0095] The first well layer 41 is arranged in contact with the lower barrier layer 25 and contains, for example, In. More specifically, the first well layer 41 contains, for example, InGaN. The second well layer 42 is arranged in contact with the upper barrier layer 27 and does not contain, for example, In. More specifically, the second well layer 42 contains, for example, GaN.

[0096] The average band gap of the well layer 43 is adjusted to be smaller than the average band gap of the emitter layer 11 and the collector layer 12.

[0097] As described above, by reducing the band gap on the lower barrier layer 25 side of the well layer 43, the increase in potential energy due to polarization can be suppressed. This makes it possible to reduce the effective barrier thickness B2 shown in Figure 5, and to increase the resonant tunneling current flowing through the resonant tunneling diode 10b.

[0098] Furthermore, the impurity concentration in the well layer 43 is lower than that in the emitter layer 11 and the collector layer 12. In other words, the impurity injection step can be omitted in the formation process of the well layer 43.

[0099] Similar to the upper spacer first layer 31 in Figure 6, the average In composition ratio of the first well layer 41 is preferably 1% or more and 30% or less. Furthermore, the film thickness of the first well layer 41 is preferably 0.1 nm or more and 20 nm or less.

[0100] The resonant tunneling diode 10b in Figure 13 does not contain InGaN in the upper spacer layer 24. However, the resonant tunneling diode 10b may contain InGaN on the interface side of the upper spacer layer 24 with the upper barrier layer 27. This reduces both the effective barrier thicknesses B1 and B2 in Figure 5, allowing a larger resonant tunneling current to flow through the resonant tunneling diode 10b.

[0101] The resonant tunneling diode 10b in Figure 13 may have a configuration having multiple well layers. For example, a second well layer and a barrier layer may be placed between the lower barrier layer 25 and the lower spacer layer 22. The second well layer is placed on the lower barrier layer 25 side, and the third barrier layer is placed on the lower spacer layer 22 side. The second well layer may also have a configuration that includes InGaN in a part of the interface with the third barrier layer, similar to the well layer 43 in Figure 13.

[0102] (Fourth Embodiment) Figure 14 is a cross-sectional view showing the configuration of a resonant tunneling diode 10c according to the fourth embodiment of the present disclosure. As shown in Figure 14, the In composition of the well layer may be tilted.

[0103] Specifically, the resonant tunneling diode 10c in Figure 14 has a well layer 43a corresponding to the well layer 43 in Figure 13. The well layer 43a has an In composition that is graded. x Ga (1-x) It contains N. In the well layer 43a, the In composition ratio is low on the interface side with the upper barrier layer 27, and high on the interface side with the lower barrier layer 25. That is, the band gap in the well layer 43a is smallest at the interface in contact with the lower barrier layer 25 (third surface) and largest at the interface in contact with the upper barrier layer 27 (fourth surface).

[0104] The well layer 43a on the interface side with the upper barrier layer 27 may contain GaN. The well layer 43a on the interface side with the lower barrier layer 25 may have an In composition ratio of around 10% (i.e., In 0.1 It may also be written as GaN.

[0105] The In composition ratio of the well layer 43a may change linearly or nonlinearly depending on the distance from the upper barrier layer 27.

[0106] (Application Examples) The technology disclosed herein can be applied to a variety of products. For example, the technology disclosed herein may be implemented as a device mounted on any type of mobile vehicle, such as automobiles, electric vehicles, hybrid electric vehicles, motorcycles, bicycles, personal mobility devices, airplanes, drones, ships, robots, construction machinery, or agricultural machinery (tractors).

[0107] Figure 15 is a block diagram showing a schematic configuration example of a vehicle control system 7000, which is an example of a mobile control system to which the technology of this disclosure may be applied. The vehicle control system 7000 comprises a plurality of electronic control units connected via a communication network 7010. In the example shown in Figure 15, the vehicle control system 7000 comprises a drive system control unit 7100, a body system control unit 7200, a battery control unit 7300, an external information detection unit 7400, an internal information detection unit 7500, and an integrated control unit 7600. The communication network 7010 connecting these plurality of control units may be an in-vehicle communication network conforming to any standard such as CAN (Controller Area Network), LIN (Local Interconnect Network), LAN (Local Area Network), or FlexRay®.

[0108] Each control unit comprises a microcomputer that performs calculations according to various programs, a storage unit that stores programs executed by the microcomputer or parameters used in various calculations, and a drive circuit that drives various controlled devices. Each control unit is equipped with a network interface for communication with other control units via the communication network 7010, and a communication interface for communication with devices or sensors inside or outside the vehicle via wired or wireless communication. Figure 15 shows the functional configuration of the integrated control unit 7600, which includes a microcomputer 7610, a general-purpose communication interface 7620, a dedicated communication interface 7630, a positioning unit 7640, a beacon receiver 7650, an in-vehicle equipment interface 7660, an audio / image output unit 7670, an in-vehicle network interface 7680, and a storage unit 7690. Other control units similarly include a microcomputer, a communication interface, and a storage unit.

[0109] The drivetrain control unit 7100 controls the operation of devices related to the vehicle's drivetrain according to various programs. For example, the drivetrain control unit 7100 functions as a control device for generating driving force for the vehicle, such as an internal combustion engine or a drive motor; a driving force transmission mechanism for transmitting driving force to the wheels; a steering mechanism for adjusting the steering angle of the vehicle; and a braking device for generating braking force for the vehicle. The drivetrain control unit 7100 may also function as a control device such as an ABS (Antilock Brake System) or an ESC (Electronic Stability Control).

[0110] A vehicle state detection unit 7110 is connected to the drive system control unit 7100. The vehicle state detection unit 7110 includes, for example, a gyro sensor for detecting the angular velocity of the axial rotation motion of the vehicle body, an acceleration sensor for detecting the acceleration of the vehicle, or at least one of the sensors for detecting the amount of operation of the accelerator pedal, the amount of operation of the brake pedal, the steering angle of the steering wheel, the engine speed, or the rotational speed of the wheels. The drive system control unit 7100 performs calculation processing using the signals input from the vehicle state detection unit 7110 and controls the internal combustion engine, drive motor, electric power steering system, brake system, etc.

[0111] The body system control unit 7200 controls the operation of various devices mounted on the vehicle body according to various programs. For example, the body system control unit 7200 functions as a control device for a keyless entry system, a smart key system, a power window system, or various lamps such as headlights, reverse lights, brake lights, turn signals, or fog lights. In this case, the body system control unit 7200 may receive radio waves transmitted from a portable device that replaces a key or signals from various switches. The body system control unit 7200 receives these radio waves or signals and controls the vehicle's door lock system, power window system, lamps, etc.

[0112] The battery control unit 7300 controls the secondary battery 7310, which is the power source for the drive motor, according to various programs. For example, the battery control unit 7300 receives information such as battery temperature, battery output voltage, or remaining battery capacity from the battery device equipped with the secondary battery 7310. The battery control unit 7300 uses these signals to perform calculations and controls the temperature of the secondary battery 7310 or the cooling device provided in the battery device.

[0113] The external information detection unit 7400 detects information from outside the vehicle equipped with the vehicle control system 7000. For example, at least one of the imaging unit 7410 and the external information detection unit 7420 is connected to the external information detection unit 7400. The imaging unit 7410 includes at least one of the following: a Time of Flight (ToF) camera, a stereo camera, a monocular camera, an infrared camera, and other cameras. The external information detection unit 7420 includes at least one of the following: an environmental sensor for detecting the current weather or climate, or an ambient information detection sensor for detecting other vehicles, obstacles, or pedestrians around the vehicle equipped with the vehicle control system 7000.

[0114] The environmental sensor may be at least one of the following: a raindrop sensor for detecting rain, a fog sensor for detecting fog, a sunshine sensor for detecting the degree of sunlight, and a snow sensor for detecting snowfall. The ambient information detection sensor may be at least one of the following: an ultrasonic sensor, a radar device, and a LIDAR (Light Detection and Ranging, Laser Imaging Detection and Ranging) device. These imaging unit 7410 and external information detection unit 7420 may be provided as independent sensors or devices, or as a device in which multiple sensors or devices are integrated.

[0115] Here, Figure 16 shows an example of the installation location of the imaging unit 7410 and the external information detection unit 7420. The imaging units 7910, 7912, 7914, 7916, and 7918 are installed, for example, at least one of the following locations on the vehicle 7900: the front nose, side mirrors, rear bumper, back door, and the upper part of the windshield inside the passenger compartment. The imaging unit 7910 installed on the front nose and the imaging unit 7918 installed on the upper part of the windshield inside the passenger compartment mainly acquire images of the front of the vehicle 7900. The imaging units 7912 and 7914 installed on the side mirrors mainly acquire images of the sides of the vehicle 7900. The imaging unit 7916 installed on the rear bumper or back door mainly acquires images of the rear of the vehicle 7900. The imaging unit 7918 installed on the upper part of the windshield inside the passenger compartment is mainly used for detecting preceding vehicles, pedestrians, obstacles, traffic lights, traffic signs, or lanes.

[0116] Figure 16 shows an example of the imaging range of each imaging unit 7910, 7912, 7914, and 7916. Imaging range a shows the imaging range of imaging unit 7910 located on the front nose, imaging ranges b and c show the imaging ranges of imaging units 7912 and 7914 located on the side mirrors, respectively, and imaging range d shows the imaging range of imaging unit 7916 located on the rear bumper or back door. For example, by superimposing the image data captured by imaging units 7910, 7912, 7914, and 7916, an overhead view image of the vehicle 7900 can be obtained.

[0117] The external information detection units 7920, 7922, 7924, 7926, 7928, and 7930, which are installed on the front, rear, sides, corners, and the upper part of the windshield inside the vehicle 7900, may be, for example, ultrasonic sensors or radar devices. The external information detection units 7920, 7926, and 7930, which are installed on the front nose, rear bumper, back door, and the upper part of the windshield inside the vehicle 7900, may be, for example, LIDAR devices. These external information detection units 7920 to 7930 are mainly used for detecting preceding vehicles, pedestrians, or obstacles.

[0118] Returning to Figure 15, the explanation continues. The external information detection unit 7400 causes the imaging unit 7410 to capture images of the area outside the vehicle and receives the captured image data. The external information detection unit 7400 also receives detection information from the connected external information detection unit 7420. If the external information detection unit 7420 is an ultrasonic sensor, radar device, or LIDAR device, the external information detection unit 7400 emits ultrasonic waves or electromagnetic waves and receives information on the received reflected waves. Based on the received information, the external information detection unit 7400 may perform object detection processing such as detecting people, vehicles, obstacles, signs, or characters on the road surface, or distance detection processing. Based on the received information, the external information detection unit 7400 may perform environmental recognition processing to recognize rainfall, fog, or road surface conditions. Based on the received information, the external information detection unit 7400 may calculate the distance to an object outside the vehicle.

[0119] Furthermore, the external information detection unit 7400 may perform image recognition processing or distance detection processing to recognize people, vehicles, obstacles, signs, or characters on the road surface based on the received image data. The external information detection unit 7400 may perform distortion correction or alignment processing on the received image data, and may also synthesize image data captured by different imaging units 7410 to generate an overhead view image or a panoramic image. The external information detection unit 7400 may also perform viewpoint transformation processing using image data captured by different imaging units 7410.

[0120] The in-vehicle information detection unit 7500 detects information inside the vehicle. The in-vehicle information detection unit 7500 is connected to, for example, a driver status detection unit 7510 that detects the driver's state. The driver status detection unit 7510 may include a camera that images the driver, a biosensor that detects the driver's biometric information, or a microphone that collects sounds inside the vehicle. The biosensor is installed, for example, on the seat or steering wheel and detects the biometric information of an occupant sitting in the seat or a driver holding the steering wheel. Based on the detection information input from the driver status detection unit 7510, the in-vehicle information detection unit 7500 may calculate the driver's level of fatigue or concentration, or determine whether the driver is dozing off. The in-vehicle information detection unit 7500 may perform processing such as noise cancellation on the collected audio signals.

[0121] The integrated control unit 7600 controls the overall operation of the vehicle control system 7000 according to various programs. An input unit 7800 is connected to the integrated control unit 7600. The input unit 7800 is implemented by a device that can be operated by the passenger, such as a touch panel, buttons, a microphone, a switch, or a lever. The integrated control unit 7600 may also receive data obtained by voice recognition of voice input from the microphone. The input unit 7800 may be, for example, a remote control device using infrared or other radio waves, or an externally connected device such as a mobile phone or PDA (Personal Digital Assistant) that is compatible with the operation of the vehicle control system 7000. The input unit 7800 may be, for example, a camera, in which case the passenger can input information by gesture. Alternatively, data obtained by detecting the movement of a wearable device worn by the passenger may be input. Furthermore, the input unit 7800 may include, for example, an input control circuit that generates an input signal based on the information input by the passenger using the above input unit 7800 and outputs it to the integrated control unit 7600. Passengers and others can input various data or instruct the vehicle control system 7000 to perform processing operations by operating this input unit 7800.

[0122] The storage unit 7690 may include a ROM (Read Only Memory) for storing various programs executed by a microcomputer, and a RAM (Random Access Memory) for storing various parameters, calculation results, or sensor values. The storage unit 7690 may also be implemented using a magnetic storage device such as an HDD (Hard Disk Drive), a semiconductor storage device, an optical storage device, or a magneto-optical storage device.

[0123] The general-purpose communication interface 7620 is a general-purpose communication interface that mediates communication between the external environment 7750 and various devices present in the external environment 7750. The general-purpose communication interface 7620 may implement cellular communication protocols such as GSM (Global System of Mobile communications), WiMAX (registered trademark), LTE (registered trademark) (Long Term Evolution), or LTE-A (LTE-Advanced), or other wireless communication protocols such as wireless LAN (also known as Wi-Fi (registered trademark)) and Bluetooth (registered trademark). The general-purpose communication interface 7620 may connect, for example, to devices (e.g., application servers or control servers) located on an external network (e.g., the Internet, a cloud network, or a carrier-specific network) via a base station or access point. Furthermore, the general-purpose communication I / F 7620 may connect to terminals located near the vehicle (for example, terminals belonging to the driver, pedestrians, or shops, or MTC (Machine Type Communication) terminals) using, for example, P2P (Peer To Peer) technology.

[0124] The dedicated communication interface 7630 is a communication interface that supports communication protocols developed for use in vehicles. The dedicated communication interface 7630 may implement standard protocols such as WAVE (Wireless Access in Vehicle Environment), DSRC (Dedicated Short Range Communications), or cellular communication protocols, which are combinations of lower-layer IEEE 802.11p and upper-layer IEEE 1609. The dedicated communication interface 7630 typically performs V2X communication, a concept that includes one or more of the following: vehicle-to-vehicle communication, vehicle-to-infrastructure communication, vehicle-to-home communication, and vehicle-to-pedestrian communication.

[0125] The positioning unit 7640 performs positioning by receiving, for example, GNSS (Global Navigation Satellite System) signals from GNSS satellites (for example, GPS signals from GPS (Global Positioning System) satellites) and generates location information including the vehicle's latitude, longitude, and altitude. The positioning unit 7640 may also determine its current location by exchanging signals with a wireless access point, or it may acquire location information from a terminal such as a mobile phone, PHS, or smartphone that has a positioning function.

[0126] The beacon receiver 7650 receives radio waves or electromagnetic waves transmitted from, for example, a radio station installed on a road, and acquires information such as the current location, traffic congestion, road closures, or travel time. The functions of the beacon receiver 7650 may also be included in the dedicated communication interface 7630 described above.

[0127] The in-vehicle equipment interface 7660 is a communication interface that mediates connections between the microcomputer 7610 and various in-vehicle equipment 7760 located inside the vehicle. The in-vehicle equipment interface 7660 may establish a wireless connection using wireless communication protocols such as wireless LAN, Bluetooth®, NFC (Near Field Communication), or WUSB (Wireless USB). Furthermore, the in-vehicle equipment I / F 7660 may establish a wired connection such as USB (Universal Serial Bus), HDMI (High-Definition Multimedia Interface), or MHL (Mobile High-definition Link) via connection terminals (and, if necessary, cables) not shown. The in-vehicle equipment 7760 may include, for example, at least one of the following: a mobile device or wearable device owned by a passenger, or an information device brought into or installed in the vehicle. The in-vehicle equipment 7760 may also include a navigation device that searches for a route to any destination. The in-vehicle equipment I / F 7660 exchanges control signals or data signals with these in-vehicle equipment 7760s.

[0128] The in-vehicle network interface 7680 is an interface that mediates communication between the microcomputer 7610 and the communication network 7010. The in-vehicle network interface 7680 transmits and receives signals and other data in accordance with a predetermined protocol supported by the communication network 7010.

[0129] The microcomputer 7610 of the integrated control unit 7600 controls the vehicle control system 7000 according to various programs based on information acquired via at least one of the general-purpose communication I / F 7620, dedicated communication I / F 7630, positioning unit 7640, beacon receiver 7650, in-vehicle equipment I / F 7660, and in-vehicle network I / F 7680. For example, the microcomputer 7610 may calculate control target values ​​for the drive force generator, steering mechanism, or braking device based on acquired information from inside and outside the vehicle, and output control commands to the drive system control unit 7100. For example, the microcomputer 7610 may perform coordinated control aimed at realizing ADAS (Advanced Driver Assistance System) functions, including vehicle collision avoidance or impact mitigation, following driving based on distance between vehicles, maintaining vehicle speed, vehicle collision warning, or vehicle lane departure warning. Furthermore, the microcomputer 7610 may perform cooperative control for purposes such as autonomous driving, where the vehicle drives autonomously without driver intervention, by controlling the drive force generating device, steering mechanism, or braking device, etc., based on the acquired information about the vehicle's surroundings.

[0130] The microcomputer 7610 may generate three-dimensional distance information between the vehicle and surrounding structures, people, and other objects based on information acquired via at least one of the general-purpose communication I / F 7620, dedicated communication I / F 7630, positioning unit 7640, beacon receiver 7650, in-vehicle equipment I / F 7660, and in-vehicle network I / F 7680, and create local map information including surrounding information of the vehicle's current location. The microcomputer 7610 may also predict dangers such as vehicle collision, proximity of pedestrians, or entry into a closed road based on the acquired information, and generate a warning signal. The warning signal may be, for example, a signal to generate a warning sound or to illuminate a warning lamp.

[0131] The audio-image output unit 7670 transmits at least one of an audio or image output signal to an output device capable of visually or audibly notifying the vehicle's occupants or those outside the vehicle. In the example in Figure 15, the output devices are exemplified as an audio speaker 7710, a display unit 7720, and an instrument panel 7730. The display unit 7720 may include, for example, at least one of an onboard display and a head-up display. The display unit 7720 may also have an AR (Augmented Reality) display function. The output device may be other devices besides these, such as headphones, wearable devices such as glasses-type displays worn by occupants, projectors, or lamps. If the output device is a display device, the display device visually displays the results obtained from various processes performed by the microcomputer 7610 or information received from other control units in various formats such as text, images, tables, and graphs. If the output device is an audio output device, the audio output device converts the audio signal, consisting of reproduced audio data or sound data, into an analog signal and outputs it audibly.

[0132] In the example shown in Figure 15, at least two control units connected via the communication network 7010 may be integrated into a single control unit. Alternatively, each control unit may be composed of multiple control units. Furthermore, the vehicle control system 7000 may include other control units not shown. Also, in the above description, some or all of the functions performed by one control unit may be assigned to other control units. In other words, as long as information is transmitted and received via the communication network 7010, predetermined calculation processing may be performed by any of the control units. Similarly, a sensor or device connected to one control unit may be connected to another control unit, and multiple control units may transmit and receive detection information to and from each other via the communication network 7010.

[0133] In the vehicle control system 7000 described above, the high-frequency device 1 according to this embodiment, as described with reference to Figure 1, can be applied to the general-purpose communication interface 7620 or dedicated communication interface 7630, etc., as shown in the application example in Figure 15. By applying the high-frequency device 1 of Figure 1, the general-purpose communication interface 7620 or dedicated communication interface 7630 can be realized as a compact and high-output communication device.

[0134] Furthermore, this technology can take the following configurations: (1) A resonant tunneling diode comprising: a first electrode layer disposed on a support substrate containing a nitride semiconductor material; a first spacer layer disposed on the first electrode layer; an active layer disposed on the first spacer layer; a second spacer layer disposed on the active layer; and a second electrode layer disposed on the second spacer layer, wherein the average value of the band gap in the second spacer layer is smaller than the average value of the band gaps in the first electrode layer and the second electrode layer. (2) The resonant tunneling diode according to (1), wherein the impurity concentration of the second spacer layer is lower than the impurity concentration of the first electrode layer and the second electrode layer. (3) The resonant tunneling diode according to (1) or (2), wherein the second spacer layer is disposed in contact with the active layer. (4) The resonant tunneling diode according to (3), wherein the band gap in the second spacer layer is smallest on the first surface in contact with the active layer and largest on the second surface opposite to the first surface. (5) The resonant tunnel diode according to any one of (1) to (4), wherein the second spacer layer has a first nitride semiconductor layer containing indium (In). (6) The resonant tunnel diode according to (5), wherein the first nitride semiconductor layer is arranged in contact with the active layer. (7) The resonant tunnel diode according to (6), wherein the second spacer layer is laminated on the first nitride semiconductor layer and has a second nitride semiconductor layer that does not contain indium (In). (8) The resonant tunnel diode according to (7), wherein the average value of the indium (In) composition ratio of the first nitride semiconductor layer in the second spacer layer is 1% or more and 30% or less. (9) The resonant tunnel diode according to any one of (5) to (8), wherein the first nitride semiconductor layer has a film thickness of 0.1 nm or more and 20 nm or less. (10) The resonant tunnel diode according to any one of (1) to (9), wherein the surface of the support substrate on which the first electrode layer is arranged is the C-plane.(11) The resonant tunnel diode according to any one of (1) to (10), wherein the active layer comprises a first barrier layer disposed on the first spacer layer, a second barrier layer disposed on the first barrier layer, and a well layer disposed between the first barrier layer and the second barrier layer and having a smaller band gap than the first barrier layer and the second barrier layer, and the average value of the band gap in the well layer is smaller than the average value of the band gaps in the first electrode layer and the second electrode layer. (12) The resonant tunnel diode according to (11), wherein the impurity concentration of the well layer is lower than the impurity concentration of the first electrode layer and the second electrode layer. (13) The resonant tunnel diode according to (11) or (12), wherein the well layer is disposed in contact with the first barrier layer. (14) The resonant tunnel diode according to (13), wherein the band gap in the well layer is smallest on the third surface in contact with the first barrier layer and largest on the fourth surface opposite to the third surface. (15) The resonant tunnel diode according to any one of (11) to (14), wherein the well layer has a third nitride semiconductor layer containing indium (In). (16) The resonant tunnel diode according to (15), wherein the third nitride semiconductor layer is arranged in contact with the first barrier layer. (17) The resonant tunnel diode according to (16), wherein the well layer has a fourth nitride semiconductor layer laminated on the third nitride semiconductor layer and does not contain indium (In). (18) The resonant tunnel diode according to (17), wherein the average value of the indium (In) composition ratio of the third nitride semiconductor layer in the well layer is 1% or more and 30% or less. (19) The resonant tunnel diode according to any one of (15) to (18), wherein the third nitride semiconductor layer has a film thickness of 0.1 nm or more and 20 nm or less. A high-frequency device comprising: a resonant tunneling diode as described in any one of paragraphs (20)(1) to (19); and an antenna having a capacitor and an inductor that resonate at a specific frequency, connected in parallel between the resonant tunneling diode and a reference voltage node.

[0135] The aspects of this disclosure are not limited to the individual embodiments described above, but include various modifications that a person skilled in the art could conceive, and the effects of this disclosure are not limited to those described above. In other words, various additions, modifications, and partial deletions are possible, as long as they do not depart from the conceptual idea and spirit of this disclosure derived from the claims and their equivalents.

[0136] 1 High-frequency device, 2 Emitter electrode, 3 Collector electrode, 4 Dielectric, 5 Power supply circuit, 6 Filter section, 7 Power supply section, 8 Slot section, 10, 10a, 10b, 10c, 100 Resonant tunnel diode, 11 Emitter layer, 12 Collector layer, 13 Support substrate, 20 Antenna, 21 Resonator, 22 Lower spacer layer, 23 Active layer, 24, 33, 33a Upper spacer layer, 25 Lower barrier layer, 26, 43, 43a Well layer, 27 Upper barrier layer, 31 Upper spacer 1st layer, 32 Upper spacer 2nd layer, 41 First well layer, 42 Second well layer

Claims

1. A resonant tunneling diode comprising: a first electrode layer disposed on a support substrate containing a nitride semiconductor material; a first spacer layer disposed on the first electrode layer; an active layer disposed on the first spacer layer; a second spacer layer disposed on the active layer; and a second electrode layer disposed on the second spacer layer, wherein the average value of the band gap in the second spacer layer is smaller than the average value of the band gaps in the first electrode layer and the second electrode layer.

2. The resonant tunneling diode according to claim 1, wherein the impurity concentration of the second spacer layer is lower than the impurity concentrations of the first electrode layer and the second electrode layer.

3. The resonant tunneling diode according to claim 1, wherein the second spacer layer is arranged in contact with the active layer.

4. The band gap in the second spacer layer is smallest on the first surface in contact with the active layer and largest on the second surface opposite to the first surface, according to claim 3.

5. The resonant tunneling diode according to claim 1, wherein the second spacer layer has a first nitride semiconductor layer containing indium (In).

6. The resonant tunneling diode according to claim 5, wherein the first nitride semiconductor layer is arranged in contact with the active layer.

7. The resonant tunnel diode according to claim 6, wherein the second spacer layer is laminated on the first nitride semiconductor layer and has a second nitride semiconductor layer that does not contain indium (In).

8. The resonant tunnel diode according to claim 7, wherein the average composition ratio of indium (In) in the first nitride semiconductor layer of the second spacer layer is 1% or more and 30% or less.

9. The resonant tunneling diode according to claim 5, wherein the first nitride semiconductor layer has a film thickness of 0.1 nm or more and 20 nm or less.

10. The surface on which the first electrode layer of the support substrate is arranged is a C-plane, as described in claim 1.

11. The resonant tunneling diode according to claim 1, wherein the active layer comprises a first barrier layer disposed on the first spacer layer, a second barrier layer disposed on the first barrier layer, and a well layer disposed between the first barrier layer and the second barrier layer and having a smaller band gap than the first barrier layer and the second barrier layer, wherein the average value of the band gap in the well layer is smaller than the average value of the band gaps in the first electrode layer and the second electrode layer.

12. The resonant tunneling diode according to claim 11, wherein the impurity concentration of the well layer is lower than the impurity concentrations of the first electrode layer and the second electrode layer.

13. The resonant tunneling diode according to claim 11, wherein the well layer is arranged in contact with the first barrier layer.

14. The resonant tunneling diode according to claim 13, wherein the band gap in the well layer is smallest on the third surface in contact with the first barrier layer and largest on the fourth surface opposite to the third surface.

15. The resonant tunneling diode according to claim 11, wherein the well layer has a third nitride semiconductor layer containing indium (In).

16. The resonant tunnel diode according to claim 15, wherein the third nitride semiconductor layer is arranged in contact with the first barrier layer.

17. The resonant tunnel diode according to claim 16, wherein the well layer is laminated on the third nitride semiconductor layer and has a fourth nitride semiconductor layer that does not contain indium (In).

18. The resonant tunnel diode according to claim 17, wherein the average composition ratio of indium (In) in the third nitride semiconductor layer having the well layer is 1% or more and 30% or less.

19. The resonant tunneling diode according to claim 15, wherein the third nitride semiconductor layer has a film thickness of 0.1 nm or more and 20 nm or less.

20. A high-frequency device comprising: a resonant tunneling diode according to claim 1; and an antenna connected in parallel between the resonant tunneling diode and a reference voltage node, having a capacitor and an inductor that resonate at a specific frequency.

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