Resonant tunneling diode, oscillator, detection system and method for manufacturing the resonant tunneling diode
Patent Information
- Application Number
- JP2022012278
- Authority / Receiving Office
- JP · JP
- Patent Type
- Applications
- Current Assignee / Owner
- Filing Date
- 2022-01-28
- Publication Date
- 2025-01-30
- Estimated Expiration
- 2042-01-28
Smart Images
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Abstract
Description
[Technical Field]
[0001] The technology disclosed herein relates to resonant tunneling diodes, oscillators, and detection systems. [Background technology]
[0002] Development is underway on terahertz oscillators that integrate resonant tunneling diodes (RTDs) and antennas, for use in imaging systems and high-capacity wireless communication systems utilizing terahertz waves.
[0003] For example, Patent Document 1 discloses a terahertz oscillator using a single solid-state element in which a patch antenna is integrated into an RTD.
[0004] In order to realize an RTD terahertz oscillator, 10 5 ~10 6 A / cm 2 It is necessary to apply a high current density to the RTD. To achieve this high current density, it is necessary to fabricate a mesa structure with a diameter of approximately 0.5 to 5 μm and a multi-barrier structure by processing a compound semiconductor epitaxial wafer. Examples of multi-barrier structures include a double-barrier structure in which a quantum well layer with a small band gap is sandwiched between barrier layers with a large band gap. Typically, mesa structures of this size are fabricated using the dry etching method. [Prior art documents] [Patent Documents]
[0005] [Patent Document 1] Japanese Patent Publication No. 2020-57739 [Overview of the project] [Problems that the invention aims to solve]
[0006] When a compound semiconductor epitaxial layer (compound semiconductor single crystal layer) is processed by dry etching, a considerable amount of damage occurs to the surface region (a region of several tens of nanometers) of the semiconductor crystal layer left behind by etching. It is known that this region has many more crystal defects than the undamaged semiconductor crystal layer.
[0007] In order to realize an RTD terahertz oscillator, a mesa structure with a diameter of approximately 0.5 to 5 μm is formed by dry etching, and the outer edge of this structure contains many crystal defects. Therefore, when current is injected into a region containing many crystal defects, the barrier layers and quantum well layers of the multi-barrier structure collapse, preventing the RTD from exhibiting negative resistance characteristics due to the resonant tunneling effect, and causing a short circuit.
[0008] In view of the above, the technology disclosed herein aims to provide a resonant tunneling diode that operates stably without short-circuiting when current is applied to the resonant tunneling diode. [Means for solving the problem]
[0009] The resonant tunneling diode related to the technology disclosed herein is circuit board and A mesa structure comprising a compound semiconductor layer including a heterojunction portion having a multi-barrier structure disposed on the substrate, and an electrode disposed on the upper surface of the compound semiconductor layer, It has, The outer edge portion of the compound semiconductor layer is a crystalline region containing crystal defects. The crystal region and the electrode are spaced apart. The present invention includes a resonant tunneling diode characterized by the following features.
[0010] Furthermore, the oscillator related to the technology disclosed herein is Having one or more of the above-mentioned resonant tunneling diodes, One or more of the aforementioned resonant tunneling diodes are connected to an antenna and integrated to form a single solid-state device structure. Includes an oscillator characterized by the following features.
[0011] In addition, the oscillator according to the technology disclosed in this case has a plurality of the above-mentioned oscillators, and a plurality of the oscillators are combined and operate synchronously with each other. It includes an oscillator characterized by this.
[0012] In addition, the detection system according to the technology disclosed in this case uses the above-mentioned resonant tunneling diode as an oscillation element, a receiving element that receives high-frequency waves from the oscillation element, a processing circuit that processes signals from the receiving element, and has a detection system characterized by this.
Effect of the Invention
[0013] According to the technology disclosed in this case, for example, even when a high current density on the order of 10 5 ~10 6 A / cm2 is applied to a mesa with a diameter of about 0.5 to 5 μm, the characteristics of the resonant tunneling diode do not short-circuit during current application, and a resonant tunneling diode that operates stably can be provided.
Brief Description of the Drawings
[0014] [Figure 1] Schematic diagram for explaining the configuration of the RTD according to Embodiment 1 [Figure 2] Schematic diagram for explaining the configuration of the side wall of the RTD mesa structure according to Embodiment 1 [Figure 3] Diagram for explaining the characteristics of the RTD according to Embodiment 1 [Figure 4] Schematic diagram for explaining the manufacturing method of the RTD mesa structure part according to Embodiment 1 [Figure 5] Schematic diagram for explaining the configuration of the RTD according to Embodiment 1 [Figure 6] Schematic diagram for explaining the configuration of the RTD with two mesa structures arranged according to Embodiment 2 [Figure 7]A schematic perspective diagram illustrating the configuration of the RTD terahertz oscillator according to Embodiment 3. [Figure 8] Schematic cross-sectional diagram illustrating the configuration of the RTD terahertz oscillator according to Embodiment 3. [Figure 9] A schematic perspective diagram illustrating the configuration of the RTD terahertz oscillator according to Embodiment 4. [Figure 10] Schematic cross-sectional diagram illustrating the configuration of the RTD terahertz oscillator according to Embodiment 4. [Figure 11] A schematic diagram illustrating the configuration of the detection system according to Embodiment 5. [Modes for carrying out the invention]
[0015] Preferred embodiments of the technology disclosed herein will be described below with reference to the drawings. Note that the drawings are for illustrative purposes only, and the dimensions of the illustrated components do not necessarily reflect actual dimensions. Furthermore, the same reference numerals are used for identical components or elements in each drawing, and redundant explanations will be omitted below. For example, the following embodiments show a resonant tunneling diode as an example of a semiconductor device to which the present invention can be applied, but the present invention is also applicable to light-emitting elements such as surface-emitting lasers and light-emitting diodes.
[0016] According to the technology disclosed herein, when a compound semiconductor mesa structure and an electrode are placed in contact with the mesa structure, unlike conventional structures, the structure is such that the crystalline region containing crystal defects formed in the mesa structure and the electrode are spaced apart. In other words, the electrode is placed in contact with the compound semiconductor mesa structure. The configuration employs an electrode in which the outer diameter is smaller than the outer diameter of the upper part of the compound semiconductor mesa structure. Embodiments of the technology disclosed herein will be described below.
[0017] (Embodiment 1) Embodiment 1 describes a single resonant tunneling diode (RTD). Figure 1 shows a schematic diagram illustrating the configuration of the RTD in this embodiment.
[0018] Figure 1 is a schematic cross-sectional view of the RTD1 in this embodiment. As shown in the figure, a lower contact layer (n + A (n-InGaAs) 102 is formed. A compound semiconductor mesa structure (hereinafter referred to as "mesa structure") 120 is formed on the lower contact layer 102. The mesa structure 120 consists of a lower spacer layer (n-InGaAs) 104, a double barrier structure (InAs / InGaAs / InAs) 106, an upper spacer layer (n-InGaAs) 108, and an upper contact layer (n + The RTD1 has a compound semiconductor layer 130 containing (-InGaAs) 110. Thus, the compound semiconductor layer (hereinafter referred to as the "semiconductor layer") 130 includes a heterojunction consisting of a double barrier structure as a multi-barrier structure. An upper electrode 112 is positioned on top of the mesa structure 120 so as to be in contact with the upper surface of the semiconductor layer 130, i.e., the upper surface of the upper contact layer 110. A lower electrode 116 is positioned so as to be in contact with the lower contact layer 102. Furthermore, the entire RTD1 is covered with a passivation film (dielectric film) 114 so as to expose the upper electrode 112 and the lower electrode 116. The passivation film 114 is a dielectric film. For example, the passivation film 114 is preferably composed of silicon nitride, silicon oxide, or aluminum oxide. The passivation film 114 covers at least from the crystalline region 200 to at least a part of the upper electrode 112. The crystalline region 200 contains crystal defects, which can be caused, for example, by dry etching. Details of the crystalline region 200 will be described later. Furthermore, the passivation film 114 may be arranged in the order of semiconductor substrate 100, lower contact layer 102, and passivation film 114, and may cover the lower contact layer 102. In this embodiment, a part of the electrode 118 may function as the upper electrode 112. The electrode 118 extends from the mesa structure 120 onto the passivation film 114.
[0019] Figure 2 is an enlarged view of the area enclosed by circle A in Figure 1, and schematically shows the configuration of the outer edge portion of the mesa structure 120 of the RTD1 in this embodiment. As shown in Figure 2, a crystalline region 200 containing crystal defects caused by dry etching is formed at the outer edge portion of the semiconductor layer 130 of the mesa structure 120 formed by the dry etching method. Similarly, a crystalline region 200 containing crystal defects caused by dry etching is also formed at the outer edge portion of the double barrier structure 106. Therefore, in the crystalline region 200 containing crystal defects caused by dry etching, energy levels called resonance levels are not formed, and current flows more easily compared to the crystalline region without crystal defects (regions where resonance levels are formed). However, as shown in Figure 2, the upper electrode 112 and the crystalline region 200 containing crystal defects caused by dry etching are spaced apart. Therefore, current does not flow through the crystalline region 200 containing crystal defects caused by dry etching, which allows current to flow easily, but instead flows through the double barrier structure 106 which does not have crystal defects. As a result, the RTD1 can stably obtain the resonance tunneling effect.
[0020] For example, consider a case in RTD1 where a mesa structure 120 is formed by dry etching as a mesa structure with a mesa diameter of 1 μm and a mesa height of 0.15 μm. In this case, it is thought that a crystalline region 200 containing crystal defects generated by dry etching is formed within a region with a thickness of 20 nm extending from the outer edge of the mesa structure 120 toward the center.
[0021] Therefore, in order to prevent current from flowing through the crystal region 200 containing crystal defects caused by dry etching, the difference between the outer diameter of the electrode 112 and the outer diameter of the upper part of the mesa structure 120 must be 20 It is preferable to space them apart so that the spacing is 20 nm or more. That is, as shown in Figure 2, in a cross-section parallel to the thickness direction of the substrate 100 (vertical direction of the paper), the outer edge of the upper surface of the mesa structure 120 is spaced a predetermined distance (distance d in the figure) from the outer edge of the electrode 112 in a direction perpendicular to the thickness direction of the substrate 100 (horizontal direction of the paper). Here, the predetermined distance is 20 nm or more.
[0022] Figure 3 shows a graph of the voltage-current characteristics of RTD1 when the crystal region 200 containing crystal defects formed by dry etching on the mesa structure 120 and the electrode 112 are spaced apart. Figure 3 also shows a graph of the voltage-current characteristics of RTD1 when the crystal region 200 containing crystal defects formed by dry etching on the mesa structure 120 and the electrode 112 are not spaced apart. In Figure 3, characteristic curve 300 shows the voltage-current characteristics of RTD1 when the crystal region 200 containing crystal defects formed by dry etching on the mesa structure 120 and the electrode 112 are spaced apart. Characteristic curve 302 shows the voltage-current characteristics of RTD1 when it is assumed that the crystal region 200 containing crystal defects formed by dry etching on the mesa structure 120 and the electrode 112 are not spaced apart. Thus, characteristic curve 300 shows negative resistance characteristics due to the resonant tunneling effect. On the other hand, characteristic curve 302 shows that the resonant tunneling effect does not occur, and the current increases with increasing voltage, exhibiting a so-called short-circuit characteristic where current flows through the crystalline region containing crystal defects.
[0023] Furthermore, characteristic curve 304 shows the voltage-current characteristics of RTD1 in a different case from characteristic curve 302, assuming that the crystal region 200 containing crystal defects caused by dry etching in the mesa structure 120 and the electrode 112 are placed without separation. In characteristic curve 304, the current increases sharply at a certain voltage value (a voltage value between 0.4 and 0.5V in the figure), and when voltage is further applied to RTD1, it exhibits a short-circuit characteristic similar to characteristic curve 302. This assumes the case where the crystal region 200 containing crystal defects caused by dry etching in the mesa structure 120 and the electrode 112 are placed without separation. In this case, unstable operation occurs, such as RTD1 not exhibiting the resonant tunneling effect, or RTD1 ceasing to exhibit the resonant tunneling effect when driven continuously. Therefore, according to the RTD1 of this embodiment, a stable operating RTD1 can be obtained by arranging the crystal region 200 containing crystal defects generated by dry etching formed in the semiconductor layer 130 of the mesa structure 120 and the upper electrode 112 at a distance from each other.
[0024] Figures 4A to 4E are diagrams schematically showing a method for fabricating the mesa structure 120 of the RTD1 in the present embodiment. As shown in Figure 4A, first, each layer is sequentially formed on the n-type InP substrate 100. The layers to be formed are n + -type InGaAs lower contact layer 102, undoped InGaAs spacer layer 104, undoped AlAs / InGaAs / AlAs double barrier structure 106. Further, on the double barrier structure 106, an undoped InGaAs spacer layer 108, n + -type InGaAs upper contact layer 110 is formed. Each layer is formed by epitaxial growth using the molecular beam epitaxy (MBE) method. Note that each layer may also be formed by epitaxial growth by methods such as metal organic chemical vapor deposition (MOCVD). Then, an upper electrode 112 made of a tungsten layer, which is an ohmic electrode material, is formed by sputtering. Subsequently, a silicon oxide layer 400 serving as a mask during dry etching is formed using the plasma enhanced chemical vapor deposition (PECVD) method.
[0025] Next, as shown in Figure 4B, a resist pattern 402 is formed using photolithography technology, and then the silicon oxide layer 400 is processed by a dry etching method using a fluorine-based gas. Subsequently, the resist pattern 402 is removed (not shown).
[0026] Next, as shown in Figure 4C, using the processed silicon oxide layer 404 as a mask, the upper electrode 112 is processed by a dry etching method using a fluorine-based gas.
[0027] Next, as shown in Figure 4D, the processed silicon oxide layer 404 is used as a mask, and the upper contact layer 110, upper spacer layer 108, double barrier structure 106, lower spacer layer 104, and lower contact layer 102 are processed by dry etching using a chlorine-based gas. At this time, by adjusting the dry etching conditions, side etching occurs on the sidewalls of the processed tungsten layer 412. Specifically, by setting the dry etching conditions to conditions that promote the chemical reaction between chlorine-based radicals and tungsten based on the chlorine-based gas, side etching occurs on the sidewalls of the processed tungsten layer 412.
[0028] Next, as shown in Figure 4E, when the processed silicon oxide layer 404 is removed, the center (central axis AX) of the upper electrode 112 and the mesa structure 120 approximately coincide, as also shown in Figure 4F. Furthermore, the separation distance between the outer edge of the electrode 112 and the outer edge of the mesa structure 120 becomes 20 nm or more. In this way, a mesa structure 120 is formed in which the upper electrode 112 and the crystalline region 200 containing crystal defects created by dry etching are separated.
[0029] By performing the processes described in Figure 4C and Figure 4D consecutively and using the same processed silicon oxide layer 404, the centers of the upper electrode 112 and the semiconductor layer 130 can be made to approximately coincide when viewed from above on the substrate 100. Figure 5 schematically shows the positional relationship between the upper electrode 112 and the semiconductor layer 130 when viewed from above on the substrate 100 of the RTD1. Note that in Figure 5, components other than the substrate 100, semiconductor layer 130, and upper electrode 112 are omitted. As shown in Figure 5, the centers (central axis AX) of the electrode 112 and the semiconductor layer 130 approximately coincide when viewed from above on the substrate 100. By adopting a configuration in which the central axis of the upper electrode 112 and the center of the semiconductor layer 130 approximately coincide, a mesa structure can be formed in which the outer edge of the electrode 112 and the outer edge of the semiconductor layer 130 are spaced apart. As a result, in the RTD1 of this embodiment, 10 5 ~10 6 A / cm 2 This makes it possible to stably apply high current densities of the order of magnitude to the mesa structure 120.
[0030] Although not shown in Figures 4A to 4E, as a step after the formation of the mesa structure 120, a silicon nitride layer is deposited as a passivation film (dielectric layer) 114, and then the lower contact layer 102 is exposed. Subsequently, a tungsten layer is deposited, and then the lower electrode 116 is formed using photolithography and dry etching. After that, an opening is formed in the passivation film 114 on top of the mesa structure 120 using lithography and dry etching, exposing the upper electrode 112 made of tungsten. Then, an Au / Ti second electrode (electrode 118 in Figure 1), which will be a wiring electrode or pad electrode connected to the upper electrode 112, is formed using lithography, electron beam evaporation, and lift-off techniques.
[0031] The above process makes it possible to form the RTD1 shown in Figure 1. Note that the RTD fabrication process and method described here are just examples, and other processes and methods may be used as long as the above configuration is obtained. Furthermore, although this embodiment describes an InGaAs / InAs-based RTD formed on an InP substrate, it is not limited to this. For example, a GaAs / AlGaAs-based RTD formed on a GaAs substrate, a GaN / AlGaN-based RTD formed on a GaN or Si substrate, or a Si / SiGe-based RTD formed on a Si substrate may also be used. Even with other materials, the above configuration and effects can be obtained. Furthermore, although tungsten was used as the upper electrode 112 in this embodiment, it is not limited to this. For example, the above configuration and effects can also be obtained with molybdenum or tantalum.
[0032] Therefore, according to this embodiment, 10 5 ~10 6 A / cm 2 Even when high current densities are applied to a mesa with a diameter of approximately 0.5 to 5 μm, the RTD does not short-circuit and exhibits negative resistance characteristics. We can provide an RTD that can be expressed stably.
[0033] (Embodiment 2) Next, we will describe the RTD1 according to Embodiment 2. Note that in the following description, we will omit explanations of configurations and processes similar to those in Embodiment 1.
[0034] In Embodiment 1, a configuration of RTD1 in which a single mesa structure 120 is provided on a substrate 100 was described. However, it is also possible to fabricate an RTD1 having an RTD array configuration in which multiple mesa structures 120 are arranged on the substrate 100. Figure 6 shows a schematic cross-sectional view of an RTD1 with two mesa structures 120 arranged on it. As shown in Figure 6, even in the array configuration, in each mesa structure 120, the upper electrode 112 and the crystal region 200 containing crystal defects created by dry etching are spaced apart, similar to Embodiment 1. Therefore, current does not flow through the crystal region 200 containing crystal defects created by dry etching, which is prone to current flow, but current flows through the region containing the double barrier structure 106 which is free of crystal defects. As a result, the RTD1 of this embodiment can also stably exhibit the resonant tunneling effect, similar to Embodiment 1. The RTD1 can be fabricated in accordance with the fabrication method described in Embodiment 1.
[0035] (Embodiment 3) The RTD1 described in Embodiment 1 can be configured as an oscillator by connecting it to an external resonator. Therefore, Embodiment 3 describes a resonant tunnel diode (RTD) terahertz oscillator, which is an oscillator that forms a small solid-state element structure by connecting one RTD and a patch antenna (microstrip antenna) as an external resonator and integrating them.
[0036] Figure 7 is a schematic perspective view illustrating the configuration of the RTD terahertz oscillator in this embodiment, and Figure 8 is a schematic cross-sectional view thereof, specifically a cross-sectional view taken along the line A-A' in Figure 8.
[0037] The configuration of the RTD terahertz oscillator 600 will be described with reference to Figure 7. The RTD terahertz oscillator 600 mainly consists of a resonator 602 for oscillating terahertz waves and a bias circuit 604. The resonator 602 also has an RTD 606 and a patch antenna 608.
[0038] Next, the resonator 602 will be described using Figure 8. The resonator 602 is composed of a semiconductor substrate 100, a lower contact layer 102, a semiconductor layer 700, a first upper electrode 112, a first dielectric layer 114, a lower electrode 116, a second dielectric layer 702, a second upper electrode 118, a third dielectric layer 704, and a patch antenna 608. The semiconductor layer 700 includes the lower spacer layer 104, the double barrier structure 106, the upper spacer layer 108, and the upper contact layer 110 in Figure 1. The arrangement of these layers constituting the semiconductor layer 700 is the same as shown in Figure 2. The patch antenna 608 corresponds to the third upper electrode.
[0039] Furthermore, the RTD606 is composed of a lower contact layer 102, a semiconductor layer 700, a first upper electrode 112, a first dielectric layer 114, a lower electrode 116, and a second upper electrode 118. The mesa structure of the RTD606 is composed of the semiconductor layer 700 and the first upper electrode 112, and, as in Figure 2, the outer edge of the crystalline region 200 containing crystal defects generated by dry etching in the semiconductor layer 700 and the outer edge of the upper electrode 112 are spaced at a predetermined distance apart. Because the above configuration is adopted in the RTD606 according to this embodiment, the RTD terahertz oscillator 600 has gain in the terahertz wave frequency band.
[0040] Furthermore, the resonator 602 is formed by two conductors, the lower electrode 116 and the third upper electrode 608. The second dielectric layer 702 and the third dielectric layer 704 are sandwiched together. This configuration is known as a microstrip type resonator. Therefore, in this embodiment, we will describe the case in which a patch antenna 608, which is a typical microstrip type resonator, is used.
[0041] The lower electrode 116 is formed on a lower contact layer 102 formed on a semiconductor substrate 100. Furthermore, the semiconductor layer 700 formed on the lower contact layer 102 is electrically connected via a first upper electrode 112, a second upper electrode 118, and a third upper electrode (patch antenna) 608. It is preferable that the lower electrode 116 connected to the lower contact layer 102 and the first upper electrode 112 connected to the semiconductor layer 700 (upper contact layer 110) have low-resistance ohmic connections from the viewpoint of loss suppression, i.e., high output power, and parasitic oscillation suppression. In Embodiment 1, n + Type InGaAs lower contact layer, and n + It is assumed that a type InGaAs upper contact layer will be used. Preferably, the lower electrode 102 and upper electrode 112 are composed of one of the following: Au (gold) and Ti (titanium), Au and Pd (palladium) and Ti, Au and Pt (platinum) and Ti, W (tungsten), Mo (molybdenum), or Ta (tantalum). Then, using the upper electrode 112 configured in this way, the RTD1 is formed using the fabrication method described in Embodiment 1 to form a mesa structure. This makes it possible to form a mesa structure 120 such that the crystalline region containing crystal defects generated by dry etching in the semiconductor layer 700 and the upper electrode 112 are spaced apart. In order to make it a terahertz band oscillator, it is preferable that the mesa structure 120 of the RTD606 be a cylindrical structure with a diameter of about 0.5 to 5 μm.
[0042] In this embodiment, three dielectric materials are used from the following perspectives.
[0043] The first dielectric layer 114 and the second dielectric layer 702 are preferably formed using inorganic dielectric materials such as silicon nitride, silicon oxide, and aluminum oxide, from the viewpoint of insulation, barrier properties (prevention of electrode metal diffusion), and submicron processability. By using such materials for the first dielectric layer 114 and the second dielectric layer 702, miniaturization and high current density of the RTD 606 become possible. As a result, the RTD terahertz resonator 600 in the RTD 606 can be made more powerful and faster. The reason for separating the first and second dielectric layers is to form the lower electrode 116 on the lower contact layer 102.
[0044] The third dielectric layer 704 is preferably thick from the viewpoint of the radiation efficiency of the patch antenna 608. However, if the third dielectric layer 704 is too thick, multimode resonance may occur, so it is preferable to have a thickness of λ / 10 (λ: effective wavelength of the 0th-mode terahertz wave) or less. Also, from the viewpoint of impedance matching with the surrounding space (atmosphere), it is preferable to use a material with a low dielectric constant. From these viewpoints, it is preferable that the third dielectric layer 704 be made of a material with a lower dielectric constant than the material of the second dielectric layer, and that it is an organic dielectric material such as BCB (benzocyclobutene) or polyimide, which is processable by semiconductor processing processes.
[0045] Furthermore, in the patch antenna 608, the length (width) of the patch antenna 608 in the AA' direction (resonance direction) shown in Figures 7 and 8 is set to be a λ / 2 resonator (λ: effective wavelength of the 0th-order mode terahertz wave).
[0046] For example, in the case of an oscillator with a frequency of 0.45 terahertz, it is preferable that the patch antenna 608 be a 170 μm square (when the effective wavelength is 340 μm). Furthermore, from the viewpoint of suppressing multimode oscillation, it is preferable that the RTD 606 be positioned 34 μm (when the effective wavelength is 340 μm) away from the center of gravity (center) of the patch antenna 608 in the resonant direction (AA' direction) when viewed from above the substrate 100.
[0047] In this embodiment, the patch antenna 608 is connected to the RTD 606 via the second upper electrode 118, but the patch antenna 608 and the RTD 606 may be connected directly without the second upper electrode 118. However, from the viewpoint of processing stability or power supply stability to the RTD 606, it is preferable to form the second upper electrode on the second dielectric 702 made of an inorganic material, and then form the third dielectric layer 704 made of an organic material. This constitutes the patch antenna (third upper electrode) 608.
[0048] Furthermore, although the RTD 606 is supplied with power via the patch antenna (third upper electrode) 608 in this embodiment, the invention is not limited to this, and a power supply line may be formed on the second dielectric layer 702. Also, although a patch antenna is used as the antenna in this embodiment, the invention is not limited to this, and a slot antenna, throttling antenna, tapered slot antenna, ring antenna, etc., may also be used.
[0049] By applying the above configuration, 10 5 ~10 6 Even when a high current density of the order of A / cm² is applied to a mesa with a diameter of approximately 0.5 to 5 μm, the characteristics of the resonant tunnel diode do not short-circuit, and an RTD capable of stably exhibiting negative resistance characteristics can be obtained. Therefore, in this embodiment as well, it is possible to provide a small, single-solid-state RTD terahertz oscillator that operates stably.
[0050] (Embodiment 4) In Embodiment 3, an RTD terahertz oscillator 600 having one RTD 606 was described, but it is also possible to configure an oscillator by connecting multiple RTDs, as described in Embodiment 2, to an external resonator. Therefore, in Embodiment 4, an RTD terahertz oscillator 800 equipped with two RTD 606s will be described with reference to Figures 9 and 10. Figure 9 is a schematic perspective view illustrating the configuration of the RTD terahertz oscillator in this embodiment, and Figure 10 is a schematic cross-sectional view thereof, which is a cross-sectional view taken along the line A-A' in Figure 9. As in this embodiment, increasing the number of RTD 606s makes it possible to increase the current flowing through the resonator 602, thereby enabling higher output power of the oscillator.
[0051] The configuration of the RTD terahertz oscillator 800 having multiple RTD606s in this embodiment is basically the same as in Embodiment 3, but the positional relationship between the RTD606 and the patch antenna 608 differs from Embodiment 3. Specifically, for example, in the case of an oscillator with a frequency of 0.45 terahertz, the patch antenna 608 is assumed to be a 170 μm square (when the effective wavelength is 340 μm). In this case, from the viewpoint of radiation efficiency and multimode oscillation suppression, it is preferable that the two RTD606a and 606b are positioned 34 μm offset from the center of gravity of the antenna in the resonance direction (AA' direction) when viewed from above the substrate 100. In this case, the distance between the two RTD606a and 606b is 68 μm, and the effective wavelength is 340 μm. By arranging the RTD606a and 606b in this way, the RTD606a and RTD606b will be in a state where their phases are inverted relative to each other, and will oscillate in mutual injection synchronization. Thus, the oscillator according to this embodiment has multiple oscillators of Embodiment 3, and these multiple oscillators are coupled together and operate in synchronous manner with one another.
[0052] In this embodiment, a patch antenna was used as the antenna, but it is not limited to this, and slot antennas, throttling antennas, tapered slot antennas, ring antennas, etc., may also be used.
[0053] By applying the above configuration, 10 5 ~106 A / cm 2 Even when a current density of the order of magnitude is applied to a mesa with a diameter of approximately 0.5 to 5 μm, the characteristics of the resonant tunnel diode do not short-circuit, and an RTD capable of stably exhibiting negative resistance characteristics can be obtained. Therefore, in this embodiment as well, a small, single solid-state device structure that operates stably can be constructed. This makes it possible to provide high-power RTD terahertz oscillators.
[0054] Furthermore, by arranging the resonators 602 described in Figure 8 in an array (for example, 6 x 6 = 36), it is possible to realize an RTD array terahertz oscillator with even higher output. The multiple RTD terahertz resonators constituting the array resonator are coupled via microstrip lines, allowing each RTD to oscillate in mutual injection synchronization.
[0055] (Embodiment 5) The RTD described in the above embodiment can be applied to, for example, a detection system. Therefore, the detection system according to this embodiment will be described with reference to Figure 11. The detection system may be a system capable of image capture, for example, a camera system. In this embodiment, a camera system will be described as an example. Figure 11 is a schematic diagram illustrating the configuration of a camera system 2300 using terahertz waves.
[0056] The camera system 2300 includes an oscillator 2301, a detection device 2302, and a processing unit 2303. In the oscillator 2301, the RTD described in each embodiment can be applied as the oscillating element. The detection device 2302 has a receiving element that receives terahertz waves, which are high-frequency waves transmitted from the oscillator 2301. Thus, the detection device 2302 is capable of detecting electromagnetic waves transmitted from an antenna device, and may be an antenna device using other semiconductor elements such as a Schottky barrier diode. The terahertz waves emitted from the oscillator 2301 are reflected by the subject 2305 and detected by the detection device 2302. The processing unit 2303 has a processing circuit that processes the signal detected by the detection device 2302. Image data generated by the processing unit 2303 is output from the output unit 2304. With this configuration, the camera system 2300 can acquire terahertz images.
[0057] The oscillator 2301 and the detection device 2302 may be provided with an optical section having a lens through which terahertz waves can pass. The optical section may consist of multiple layers and may include at least one material that is transparent to terahertz waves, such as polyethylene, Teflon®, high-resistance silicon, or polyolefin resin.
[0058] The camera system described in this embodiment is merely an example, and other configurations are possible. In particular, the information acquired by the system is not limited to image information; it may also be a detection system that detects signals. [Explanation of Symbols]
[0059] 1 Resonant tunneling diode, 100 Substrate, 112 Top electrode, 130 Semiconductor layer, 120 Mesa structure, 200 Crystalline region containing crystal defects created by dry etching
Claims
1. A substrate; a mesa structure including a compound semiconductor layer including a heterojunction having a multi-barrier structure disposed on the substrate, and an electrode disposed on an upper surface of the compound semiconductor layer; having an outer edge portion of the compound semiconductor layer is a crystalline region including crystal defects; The crystal region and the electrode are disposed apart from each other, the mesa structure further includes a dielectric film covering at least a region from the crystal region to the electrode; The dielectric film is disposed so as to cover a portion of the upper surface of the electrode.
1. A resonant tunneling diode comprising:
2. In a cross section parallel to the thickness direction of the substrate, the outer edge of the upper surface of the compound semiconductor layer is spaced a predetermined distance from the outer edge of the electrode in a direction perpendicular to the thickness direction of the substrate.
2. The resonant tunneling diode according to claim 1 .
3. The predetermined distance is 20 nm or more.
3. The resonant tunneling diode according to claim 2.
4. When viewed from above, the center of the electrode and the center of the compound semiconductor layer are substantially aligned.
4. The resonant tunneling diode according to claim 1, wherein the first and second electrodes are arranged in a first direction.
5. The dielectric film is made of any one of silicon nitride, silicon oxide, and aluminum oxide.
5. The resonant tunneling diode according to claim 1, wherein the first and second electrodes are electrically connected to each other.
6. The electrodes are made of any one of gold and titanium, gold, palladium and titanium, gold, platinum and titanium, tungsten, molybdenum, and tantalum.
6. The resonant tunneling diode according to claim 1, wherein the first and second electrodes are electrically connected to each other.
7. The crystalline region including the crystal defects includes crystal defects caused by dry etching.
7. The resonant tunneling diode according to claim 1, wherein the first and second electrodes are arranged in a first direction.
8. A resonant tunneling diode as claimed in any one of claims 1 to 7, further comprising an electrode extending over the dielectric film.
9. A resonant tunneling diode according to any one of claims 1 to 8, One or more of the resonant tunneling diodes are connected to an antenna and integrated to form a single solid-state device structure.
1. An oscillator comprising:
10. A plurality of oscillators according to claim 9, A plurality of the oscillators are coupled to operate in synchronization with each other.
1. An oscillator comprising:
11. The resonant tunneling diode according to any one of claims 1 to 8 is used as an oscillation element, a receiving element for receiving a high frequency wave from the oscillation element; A processing circuit for processing signals from the receiving elements; have A detection system comprising:
12. A method of manufacturing a compound semiconductor layer including a heterojunction having a multi-barrier structure disposed on a substrate, forming an electrode made of tungsten, molybdenum or tantalum on an upper surface of the compound semiconductor layer; forming a silicon oxide layer on the electrode; patterning the silicon oxide layer to form a mask on the electrode; processing the electrodes by dry etching using a fluorine-based gas and the mask of the patterned silicon oxide; a step of processing the compound semiconductor layer by performing dry etching using a chlorine-based gas and the mask made of the patterned silicon oxide so that side etching occurs on the sidewalls of the electrode, the compound semiconductor layer is patterned to have a mesa structure, and an outer edge of the electrode and an outer edge of the compound semiconductor layer are spaced apart; 4. A method for manufacturing a resonant tunneling diode comprising the steps of:
13. The method for manufacturing a resonant tunneling diode according to claim 12, wherein the silicon oxide layer is patterned by a dry etching method using a fluorine-based gas and a resist pattern as a mask.
14. A method for manufacturing a resonant tunnel diode as described in claim 12 or 13, characterized in that the resonant tunnel diode is a resonant tunnel diode as described in any one of claims 1 to 8.