Nitride semiconductor material and thermal flow switching element equipped therewith

Abstract

To provide a nitride semiconductor material with low lattice thermal conductivity and a heat flow switching device comprising the same.SOLUTION: A nitride semiconductor material according to the present invention is a metal nitride represented by M-Si-N-Te (provided that M represents at least one transition metal element and Te is an optional element) and has a thermal effusivity of less than 2,000 Ws0.5 / m2K. Particularly, M is at least one element from Cr, Mn, Ni, Mo and W. A heat flow switching element according to the present invention comprises an N-type semiconductor layer 3, an insulating layer 4 stacked on the N-type semiconductor layer, and a P-type semiconductor layer 5 stacked on the insulating layer, wherein at least one of the N-type semiconductor layer and the P-type semiconductor layer is formed from the nitride semiconductor material.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a nitride semiconductor material having low lattice thermal conductivity and a heat flow switching element equipped therewith. [Background technology]

[0002] Conventionally, as a heat flow switch that actively changes the thermal conductivity by a bias voltage, for example, Non-Patent Document 1 describes two sheets of polyimide tape exhibiting electrical insulation properties as a semiconductor material: Ag2S 0.6 Se 0.4 A heat flow switching element has been proposed that changes thermal conductivity by sandwiching it between two elements and applying an electric field. [Prior art documents] [Non-patent literature]

[0003] [Non-Patent Document 1] Takuya Matsunaga, et al., "Fabrication of a Heat Flow Switching Element Operated by Bias Voltage," The 15th Annual Conference of the Thermoelectric Society of Japan, September 13, 2018. [Overview of the project] [Problems that the invention aims to solve]

[0004] The above conventional technologies still have the following challenges. In the technology described in Non-Patent Literature 1, by applying a voltage, a heat-conductive charge is generated at the interface between the semiconductor material and the insulating material, and heat can be carried by this charge. Therefore, it is possible to immediately transition to a state in which the heat conduction has changed, and relatively good thermal response can be obtained. However, in order to change the heat conduction originating from the material interface in response to this external electric field (external voltage) and increase the amount of change in the heat conduction of the entire element, it is necessary to reduce the intrinsic thermal conductivity of the materials constituting the element under zero bias (a state in which no external voltage is applied). Thermal conductivity is a function proportional to the square of the thermal permeability, and it is necessary to reduce the intrinsic thermal permeability of the materials constituting the element under zero bias. The intrinsic thermal conductivity of the material under zero bias is expressed as the sum of the lattice thermal conductivity and the electronic thermal conductivity. Thermal conductivity = Lattice thermal conductivity + Electronic thermal conductivity

[0005] Lattice thermal conduction is heat conduction due to vibrations (phonons, lattice vibrations) propagating between crystal lattices. Electronic thermal conduction, on the other hand, is heat conduction due to conduction electrons, and generally, as electrical conductivity increases, electronic thermal conductivity tends to increase. Of these, for semiconductors, in order to maintain the conductivity of the semiconductor, the material's inherent electronic thermal conductivity at zero bias needs to be adjusted to an appropriate value so as not to increase the total heat conduction. Note that insulating materials do not possess electronic thermal conduction. On the other hand, a lower lattice thermal conductivity is preferable. Materials with low lattice thermal conductivity can lower the overall thermal conductivity of the element at zero bias, thereby increasing the rate of change of interface-induced thermal conductivity in response to the external electric field and improving the overall heat flow switching performance of the element. For this reason, there is a demand for the use of low thermal conductivity (low thermal permeability) semiconductor materials and insulating materials, which are derived from low lattice thermal conductivity. Furthermore, to improve the heat resistance of heat flow switching elements, it is desirable to use nitride materials as constituent materials.

[0006] The present invention has been made in view of the aforementioned problems, and aims to provide a nitride semiconductor material with low lattice thermal conductivity and a heat flow switching element equipped therewith. [Means for solving the problem]

[0007] In order to solve the above problems, the present invention adopts the following configuration. That is, the nitride semiconductor material according to the first invention is a metal nitride represented by M-Si-N-Te (where M represents at least one transition metal element and Te is an optional element), and has a thermal diffusivity of 2000 Ws 0.5 / m 2 less than KK. In this nitride semiconductor material, it is a metal nitride represented by M-Si-N-Te (where M represents at least one transition metal element and Te is an optional element), and has a thermal diffusivity of 2000 Ws 0.5 / m 2 less than K. Therefore, it has P-type or N-type semiconductor characteristics and a low lattice thermal conductivity, so that a low thermal diffusivity indicating low thermal conductivity can be obtained. Among the constituent elements, M being at least one transition metal element improves the conductivity, and Si can crystallize the crystal structure into nanocrystals (the crystal size is 5 nm or less, including amorphous) and reduce the lattice thermal conductivity, so that the thermal diffusivity can be reduced. Note that the notation "Te is an optional element" indicates that the inclusion of Te (tellurium) is optional. That is, it indicates that Te may or may not be included. In other words, it becomes M-Si-N, or M-Si-N-Te (where M represents at least one transition metal element).

[0008] The nitride semiconductor material according to the second invention is characterized in that, in the first invention, the metal nitride is represented by M-Si-N (where M represents at least one transition metal element).

[0009] The nitride semiconductor material according to the third invention is characterized in that, in the first or second invention, the electrical resistivity is less than 10 Ωcm. That is, this nitride semiconductor material is a nitride containing a transition metal element and is a compound having a transition metal-nitrogen bond that is likely to have conductivity, so an electrical resistivity of less than 10 Ωcm can be obtained, and it is suitable as a semiconductor material with excellent conductivity.

[0010] The nitride semiconductor material according to the fourth invention is characterized in that, in any one of the first to third inventions, M is at least one of Cr, Mn, Ni, Mo, and W. That is, in this nitride semiconductor material, since M is at least one of Cr, Mn, Ni, Mo, and W, a low thermal penetration rate can be obtained, and a metal nitride material with a low electrical resistivity can be obtained.

[0011] The nitride semiconductor material according to the fifth invention is characterized in that, in any one of the first to fourth inventions, it is used as a low thermal conductivity material. That is, in this nitride semiconductor material, since a low thermal penetration rate is obtained, it is suitable for use as a low thermal conductivity semiconductor material for a heat flow switching element or the like.

[0012] The heat flow switching element according to the sixth invention includes an N-type semiconductor layer, an insulator layer laminated on the N-type semiconductor layer, and a P-type semiconductor layer laminated on the insulator layer, and at least one of the N-type semiconductor layer and the P-type semiconductor layer is formed of the nitride semiconductor material according to any one of the first to fifth inventions.

[0013] That is, in this heat flow switching element, since it includes an N-type semiconductor layer, an insulator layer laminated on the N-type semiconductor layer, and a P-type semiconductor layer laminated on the insulator layer, when an external voltage is applied to the N-type semiconductor layer and the P-type semiconductor layer, charges are induced mainly at the interfaces between the P-type semiconductor layer, the N-type semiconductor layer, and the insulator layer, and these charges carry heat, thereby changing the thermal conductivity. In particular, since at least one of the N-type semiconductor layer and the P-type semiconductor layer is formed of the nitride semiconductor material according to any one of the first to third inventions, the lattice thermal conductivity is low and the thermal penetration rate is low, and the rate of change of the thermal conductivity can be increased by an external electric field (external voltage). Also, when the insulator layer is a nitride, since at least one of the N-type semiconductor layer and the P-type semiconductor layer is a nitride, the bonding property at the interface between the semiconductor layer and the insulator layer is improved.

[0014] The rate of increase in thermal conductivity Δk after voltage application, which is the heat flow switching performance, is evaluated by the following formula. Δk = k(V) / k(0) - 1 Δk = b(V) 2 / b(0) 2 - 1 k(V): Thermal conductivity (W / mK) when voltage is applied k(0): Thermal conductivity (W / mK) without voltage application b(V): Thermal penetration rate (Ws 0.5 / m 2 K) b(0): Thermal penetration rate (Ws 0.5 / m 2 K) The thermal conductivity caused by the interface that changes with the above external voltage is defined as the "third thermal conductivity", and is distinguished for convenience from the material-specific thermal conductivity (the sum of the lattice thermal conductivity and the electron thermal conductivity) that does not change with the external voltage.

[0015] k(V) = Electron thermal conductivity of semiconductor + Lattice thermal conductivity of semiconductor + Lattice thermal conductivity of insulator + Third thermal conductivity k(0) = Electron thermal conductivity of semiconductor + Lattice thermal conductivity of semiconductor + Lattice thermal conductivity of insulator Thus, in order to improve the heat flow switching performance, it is preferable to select a material with a small electron thermal conductivity and a small lattice thermal conductivity. Among these, regarding the electron thermal conduction of the semiconductor, in order to maintain the conductivity of the semiconductor, the material-specific electron thermal conductivity at zero bias needs to be adjusted to an appropriate value so as not to increase the total thermal conduction significantly. On the other hand, regarding the lattice thermal conductivity, if the material has a low lattice thermal conductivity, k(0) can be reduced, and the thermal conductivity of the entire device at zero bias can be lowered. Therefore, the lower the lattice thermal conductivity, the greater the contribution of the third thermal conductivity that responds to the external electric field from zero bias, and the greater the rate of change in thermal conductivity in response to the external electric field, resulting in an improvement in the heat flow switching performance.

[0016] Furthermore, since charge is generated at both the interface between the N-type semiconductor layer and the insulator layer and its vicinity, and at the interface between the P-type semiconductor layer and the insulator layer and its vicinity, a large amount of charge is generated, resulting in a significant change in thermal conductivity and high thermal responsiveness. In addition, since this mechanism physically changes the thermal conductivity without using a chemical reaction mechanism, it can immediately transition to a state where the thermal conductivity has changed, resulting in good thermal responsiveness. Furthermore, since the amount of charge induced at the interface changes in proportion to the magnitude of the external voltage, it is possible to adjust the thermal conductivity by adjusting the external voltage, thus enabling active control of heat flow through this element. Furthermore, since the insulating layer is an insulator and no current is generated when voltage is applied, no Joule heating occurs. Therefore, heat flow can be actively controlled without self-heating. [Effects of the Invention]

[0017] The present invention provides the following effects. In other words, the nitride semiconductor material according to the present invention is a metal nitride represented by M-Si-N-Te (where M represents at least one transition metal element and Te is an arbitrary element), and has a thermal permeability of 2000 Ws 0.5 / m 2 Since it is less than K, it has P-type or N-type semiconductor properties and low lattice thermal conductivity, resulting in low thermal conductivity with low thermal permeability. As described above, the nitride semiconductor material of the present invention is suitable for use as a low thermal conductivity semiconductor material in thermal flow switching elements and the like, because it provides a low thermal permeability. Therefore, in the heat flow switching element of the present invention, at least one of the N-type semiconductor layer and the P-type semiconductor layer is formed of the nitride semiconductor material of the present invention. As a result, the N-type and P-type semiconductor layers have low lattice thermal conductivity, which increases the rate of change of thermal conductivity in response to the external electric field, thereby improving the heat flow switching performance. [Brief explanation of the drawing]

[0018] [Figure 1]This is a perspective view showing one embodiment of the nitride semiconductor material and a thermal flow switching element equipped therewith according to the present invention. [Figure 2] This embodiment is a conceptual diagram for explaining the principle. [Figure 3] This is a cross-sectional SEM image showing a comparative example of a nitride semiconductor material and a thermal flow switching element equipped therewith according to the present invention. [Figure 4] This is a cross-sectional SEM image showing an embodiment of the nitride semiconductor material according to the present invention and a thermal flow switching element equipped therewith. [Figure 5] This is a cross-sectional TEM image showing an embodiment of the nitride semiconductor material and a thermal flow switching element equipped therewith according to the present invention. [Figure 6] This is a cross-sectional TEM image showing an embodiment of the nitride semiconductor material and a thermal flow switching element equipped therewith according to the present invention. [Modes for carrying out the invention]

[0019] Hereinafter, an embodiment of the nitride semiconductor material and a thermal flow switching element equipped therewith according to the present invention will be described with reference to Figures 1 and 2. In the drawings used in the following description, the scale has been appropriately changed as necessary to make each part recognizable or easily recognizable.

[0020] As shown in Figures 1 and 2, the heat flow switching element 1 of this embodiment comprises an N-type semiconductor layer 3, an insulating layer 4 laminated on the N-type semiconductor layer 3, and a P-type semiconductor layer 5 laminated on the insulating layer 4. Furthermore, the heat flow switching element 1 of this embodiment includes an N-side electrode 6 connected to an N-type semiconductor layer 3 and a P-side electrode 7 connected to a P-type semiconductor layer 5.

[0021] The above-mentioned N-type semiconductor layer 3 and P-type semiconductor layer 5 are nitride semiconductor materials with low thermal conductivity, and are metal nitrides represented by M-Si-N-Te (where M represents at least one transition metal element and Te is an arbitrary element), with a thermal permeability of 2000 Ws 0.5 / m2 It is less than K and has an electrical resistivity of less than 10 Ωcm. Furthermore, the above nitride semiconductor material is a nanocrystal. In this specification, materials with a crystal size of 5 nm or less are referred to as nanocrystals, including amorphous materials. Furthermore, the crystal size mentioned above was determined by randomly selecting 10 crystals from cross-sectional TEM images and calculating the average of their equivalent circle diameters.

[0022] The above M is at least one of Cr, Mn, Ni, Mo, or W. In other words, the above metal nitrides include Cr-Si-N, Mn-Si-N, Ni-Si-N, Mo-Si-N, W-Si-N, Cr-W-Si-N, Cr-Si-N-Te, W-Si-N-Te, etc. These film deposition methods employ various techniques, such as sputtering and molecular beam epitaxy (MBE). Regarding the sputtering method, the above-mentioned metal nitride can be deposited in a sputtering apparatus using targets with various composition ratios, under a mixed gas atmosphere of Ar gas and nitrogen gas, by varying the sputtering gas pressure, nitrogen gas partial pressure, etc. Furthermore, it is acceptable for the film to contain trace amounts of oxygen (O) as an unavoidable impurity during film formation. Furthermore, if voltage can be applied directly to the N-type semiconductor layer 3 and the P-type semiconductor layer 5, the N-side electrode 6 and the P-side electrode 7 are unnecessary.

[0023] Furthermore, the heat flow switching element 1 of this embodiment includes an insulating substrate 2, on which the N-side electrode 6 is formed. That is, the N-side electrode 6, N-type semiconductor layer 3, insulating layer 4, P-type semiconductor layer 5, and P-side electrode 7 are stacked on the substrate 2 in this order. Note that the layers may be stacked on the substrate 2 in the reverse order. Also, the substrate 2 itself may be the P-side electrode 7 or the N-side electrode 6.

[0024] An external power supply V is connected to the N-side electrode 6 and P-side electrode 7, and a voltage is applied. The arrows in Figure 1 indicate the direction of voltage (electric field) application. The N-type semiconductor layer 3 and the P-type semiconductor layer 5 are formed as thin films with a thickness of less than 1 μm. In particular, since the charge e (positive charge, negative charge) generated at and near the interface with the insulator layer 4 mainly accumulates in the thickness range of 5 to 10 nm, it is more preferable that the N-type semiconductor layer 3 and the P-type semiconductor layer 5 be formed with a film thickness of 100 nm or less. However, a film thickness of 5 nm or more is preferable for the N-type semiconductor layer 3 and the P-type semiconductor layer 5. Furthermore, the insulating layer 4 is preferably 40 nm or thicker, and its thickness is set to a level that does not cause dielectric breakdown. However, if the insulating layer 4 is too thick, it becomes difficult to carry the charge e, so it is preferable to have a thickness of less than 1 μm.

[0025] In Figure 2, the type of charge e generated at and near the interface between the N-type semiconductor layer 3 and the insulator layer 4 is electrons, and is represented by white circles. Similarly, the type of charge e generated at and near the interface between the P-type semiconductor layer 5 and the insulator layer 4 is a hole, and is represented by black circles. (A hole is a void created by a deficiency of electrons in the valence band of a semiconductor, and appears to have a relatively positive charge.) The N-type and P-type characteristics of the N-type semiconductor layer 3 and P-type semiconductor layer 5 are determined by the selection of the M element, the Si / (M+Si) composition ratio, and the nitrogen (N) content. Furthermore, the N-type and P-type characteristics can also be determined by adding N-type and P-type metal elements as dopants to the above nitride semiconductor material.

[0026] The insulating layer 4 is preferably made of an insulating material with low thermal conductivity. Insulators such as SiO2, dielectrics such as HfO2 and BiFeO3, and organic materials such as polyimide (PI) can be used. Dielectric materials with a high dielectric constant are particularly preferred. The substrate 2 can be, for example, a glass substrate. The N-side electrode 6 and the P-side electrode 7 are formed from a metal such as Mo or Al.

[0027] As shown in Figure 2, the heat flow switching element 1 of this embodiment generates a heat-conductive charge e at and near the interface between the N-type semiconductor layer 3 and the insulating layer 4 when an electric field (voltage) is applied. The generated charge e carries heat, causing a change in thermal conductivity.

[0028] To obtain a larger change in thermal conductivity due to the charge generated at and near the interface by applying an electric field (voltage), a material with low lattice thermal conductivity is suitable. The nitride semiconductor material in this embodiment has low lattice thermal conductivity, that is, it is a material with low thermal conductivity. Furthermore, the third thermal conductivity defined above increases in proportion to the amount of charge e generated in response to the applied external electric field (voltage). Furthermore, since charge e is generated at the interface between the N-type semiconductor layer 3 and the P-type semiconductor layer 5 and the insulator layer 4, increasing the total surface area of ​​the interface can increase the amount of charge e generated.

[0029] The above method for measuring thermal conductivity is performed using the pulsed optical heating thermoreflectance method, which involves instantaneously heating a thin film sample formed on a substrate with a pulsed laser and measuring the rate of decrease or increase in surface temperature due to thermal diffusion into the thin film to determine the thermal diffusivity or thermal osmosis in the thickness direction of the thin film. Note that, among the pulsed optical heating thermoreflectance methods, the method that directly measures thermal diffusion (backside heating / surface temperature measurement (RF) method) requires the use of a transparent substrate through which the pulsed laser can penetrate. Therefore, if the substrate is not transparent, the thermal conductivity is measured using the surface heating / temperature measurement (FF) method, which measures thermal osmosis and converts it to thermal conductivity. This measurement requires a metal film, such as Mo or Al. In this embodiment, the thermal osmosis is measured using the surface heating / temperature measurement (FF) method.

[0030] In the heat flow switching element 1 of this embodiment, charge e is generated at both the interface between the N-type semiconductor layer 3 and the insulator layer 4 and its vicinity, and at the interface between the P-type semiconductor layer 5 and the insulator layer 4 and its vicinity. As a result, a large amount of charge is generated, allowing for a significant change in thermal conductivity and high thermal responsiveness. Furthermore, since this mechanism physically changes the thermal conductivity without using a chemical reaction mechanism, it can immediately transition to a state where the thermal conductivity has changed, resulting in excellent thermal responsiveness.

[0031] Furthermore, since the amount of charge induced at the interface changes in proportion to the magnitude of the external voltage, it is possible to adjust the thermal conductivity by adjusting the external voltage, thus enabling active control of heat flow through this element. Furthermore, since the insulating layer 4 is an insulator and no current is generated when voltage is applied, no Joule heating occurs. Therefore, heat flow can be actively controlled without self-heating. Furthermore, when the insulating layer is a nitride, at least one of the N-type semiconductor layer and the P-type semiconductor layer is a nitride, which improves the bonding strength at the interface between the semiconductor layer and the insulating layer.

[0032] Thus, the nitride semiconductor material of this embodiment (N-type semiconductor layer 3 and P-type semiconductor layer 5) is a metal nitride represented by M-Si-N-Te (where M represents at least one transition metal element and Te is an arbitrary element), and has a thermal permeability of 2000 Ws 0.5 / m 2 Since the temperature is less than K, it has P-type or N-type semiconductor properties and low lattice thermal conductivity, resulting in low thermal conductivity with low thermal permeability. Furthermore, the conductivity is improved by the fact that M is at least one transition metal element among the constituent elements, and Si has been made into a nanocrystal structure (crystal size of 5 nm or less, including amorphous material) and has reduced thermal permeability.

[0033] Furthermore, the nitride semiconductor material of this embodiment is a nitride containing a transition metal element and is a compound having a transition metal-nitrogen bond that is prone to conductivity, so it can obtain an electrical resistivity of less than 10 Ωcm and is suitable as a semiconductor material with excellent conductivity. Furthermore, since M is at least one of Cr, Mn, Ni, Mo, and W, a metal nitride material with low thermal sensitivity and low electrical resistivity can be obtained. In the heat flow switching element 1 of this embodiment, an N-type semiconductor layer 3, an insulating layer 4 laminated on the N-type semiconductor layer 3, and a P-type semiconductor layer 5 laminated on the insulating layer 4 are provided. When an external voltage is applied to the N-type semiconductor layer 3 and the P-type semiconductor layer 5, a charge e is induced mainly at the interface between the P-type semiconductor layer 5 and the N-type semiconductor layer 3 and the insulating layer 4. This charge e carries heat, causing a change in thermal conductivity.

[0034] In particular, since the N-type semiconductor layer 3 and the P-type semiconductor layer 5 are formed from the above-mentioned nitride semiconductor material, low thermal conductivity is obtained when there is a low lattice thermal conductivity and low thermal permeability when there is zero bias, and the rate of change of thermal conductivity can be greatly increased by an external electric field (external voltage). That is, the lower the lattice thermal conductivity, the greater the contribution of interface-induced thermal conductivity in response to the external electric field from zero bias, and the larger the rate of change of thermal conductivity in response to the external electric field, improving the heat flow switching performance. [Examples]

[0035] Based on the above embodiments, the materials listed in Table 1 below (Cr-Si-N, Mn-Si-N, Ni-Si-N, Mo-Si-N, W-Si-N, Cr-W-Si-N, Cr-Si-N-Te, W-Si-N-Te) were deposited on SiO2 by reactive sputtering in a nitrogen-containing atmosphere. In the examples of the present invention, the crystal structure, thermal permeability, and electrical resistivity were measured. The results are shown in Table 1. The composition of each example was determined by changing the nitrogen fraction (N2 / (Ar+N2)) and the Si / (M+Si) ratio.

[0036] Compositional analysis was performed using X-ray photoelectron spectroscopy (XPS) for elemental analysis. In XPS, quantitative analysis was performed on the sputtered surface up to a depth of 20 nm from the outermost surface, using Ar sputtering. The quantitative accuracy was ±2% for N / (M+Si+N) and ±1% for Si / (M+Si). Electrical resistivity (specific resistivity) was measured at 25°C using the four-terminal method (van der Pauw method). The N-type and P-type of the semiconductor were determined by Hall effect measurement. The applied magnetic field during Hall effect measurement was set to 0.5 Tesla. Furthermore, as a comparative example, Table 1 shows the results of measurements of thermal turbidity and electrical resistivity for films deposited with columnar crystalline structures (Cr-N, Cr-Si-N, Mn-N, Mo-N, WN).

[0037] The above thermal osmotic coefficient was measured using the pulsed light heating thermoreflectance method (FF method: surface heating / surface temperature measurement) (measurement device: PicoTR, Picotherm). The measurement was performed at room temperature. Thermal conductivity is calculated from thermal osmosis using the following formula. Thermal conductivity k = (thermal osmosis b) 2 / Volumetric heat capacity =(thermal effusivity b) 2 (Specific heat × Density)

[0038] [Table 1] [Table 2]

[0039] These results indicate that in each comparative example, the crystalline structure was columnar, and the thermal osmotic coefficient was 2500 Ws. 0.5 / m 2 While the temperature is above K, each embodiment of the present invention has a nanocrystalline structure and a thermal osmotic coefficient of 2000 Ws. 0.5 / m 2 The materials exhibited low thermal conductivity of less than K. Furthermore, the electrical resistivity of each embodiment of the present invention was less than 10 Ωcm. In particular, in Examples 1 to 13, the electrical resistivity was less than 1 Ωcm. Furthermore, in Examples 21, 24-26, which contain 9 at% or more of Te, the thermal osmosis was 1000 Ws 0.5 / m 2 It was a low thermal conductivity material with a temperature of less than K. Furthermore, Examples 21-26, which included Te, were P-type semiconductors. Furthermore, as Example 27 of the present invention, a material (Ni-Si-N-Te) was also prepared in which Te was added to the Ni-Si-N N-type semiconductor of Example 6. Furthermore, the thermal permeability of Example 27 (Ni-Si-N-Te), in which the Te content is less than 9 at%, is 1163 Ws. 0.5 / m 2 The value was K, and the thermal fusibility was significantly lower compared to the Ni-Si-N of Example 6. Furthermore, the electrical resistivity of this Example 27 (Ni-Si-N-Te) was 9.46 × 10⁻⁶. -3 It had a density of Ωcm and was an N-type semiconductor. In Examples 1 to 27, the composition ranges for each element of M-Si-N-Te were as follows: M: 27.5 to 63.1 at%, Si: 10.8 to 33.7 at%, N: 7.8 to 46.8 at%, Te: 0 to 29.6 at%, and the total for each element was 100 at%. Furthermore, the Si / (M+Si) ratio was 14.6 to 49.4 at%.

[0040] Next, cross-sectional SEM images (45-degree oblique field of view) of some of the above comparative examples and examples are shown in Figures 3 and 4. Figure 3 shows the cross-sectional and surface structures of the Cr-Si-N film of Comparative Example 3 and the WN film of Comparative Example 8. Figure 4 shows the cross-sectional and surface structures of the Cr-Si-N film of Example 2, the Mn-Si-N film of Example 4, the Mo-Si-N film of Example 8, and the W-Si-N film of Example 11. The substrates used were obtained by cleavage fracture, and for example, the fracture of columnar crystals occurred when the substrate was cleaved. Furthermore, cross-sectional TEM:HAADF-STEM (high-angle scattering annular dark-field scanning transmission microscopy) images of some of the above comparative examples and examples are shown in Figures 5 and 6. Figure 5 shows the cross-sectional microstructure of the Mo-Si-N film of Example 8 and the W-Si-N film of Example 11. Figure 6 shows the cross-sectional microstructure of the W-Si-N-Te film of Example 25. As can be seen from these images, the crystalline structure of the comparative example is columnar crystals with a diameter of 10-20 nm, whereas the crystalline structure of the examples of the present invention is dense nanocrystals with a crystal size of 5 nm or less. Furthermore, electron diffraction was performed on the cross-section of the film for the examples in which cross-sectional TEM observation was conducted, and in all cases, no electron diffraction patterns showing long-period crystallinity, which would suggest a relatively large crystal size, were detected, confirming that they are nanocrystals with a very small crystal size. In this specification, if the crystal size is 5 nm or less, it is referred to as a nanocrystal, including amorphous materials.

[0041] Grazing Incidence X-ray Diffraction (thin-film XRD) was also performed. While peaks indicating a crystallized film were observed in the comparative example's columnar crystalline material, no long-period crystallization peaks suggesting a relatively large crystal size were detected in the example, indicating that it is a nanocrystal with a very small crystal size. (In this specification, materials with a crystal size of 5 nm or less are referred to as nanocrystals, including amorphous materials.)

[0042] Furthermore, the nanocrystal film in the example exhibits high surface smoothness, density, and high density. This indicates that the low thermal conductivity is not due to low density such as voids, but rather that the nitride material itself possesses low thermal conductivity. These results suggest that nanocrystallization reduces thermal conduction due to vibrations (phonons, lattice vibrations) transmitted between crystal lattices, thereby reducing lattice thermal conduction and achieving a thermal permeability of 2000 Ws. 0.5 / m 2 This indicates that a semiconductor material with low thermal conductivity below K was obtained.

[0043] Next, a thermal flow switching element was fabricated using the nitride semiconductor material of the above embodiment of the present invention as a P-type semiconductor layer, and the thermal permeability with respect to voltage and the rate of increase in thermal conductivity after voltage application were measured. The results are shown in Table 3. Furthermore, an embodiment of the present invention was constructed by laminating an insulator layer, a P-type semiconductor layer, and a P-side electrode on an N-type semiconductor layer using the following materials, and the change in thermal conductivity was measured. N-type semiconductor layer: N-type semiconductor Si substrate (thickness 0.38 mm) Insulating layer: SiO2 (thickness 100 nm) P-type semiconductor layer: CrSiN (Example 3) WSiN (Example 11) WSiNTe (Example 25) (Each thickness 40nm) P-side electrode: Mo (thickness 100 nm)

[0044] Furthermore, it has been confirmed that the SiO2 (100 nm thick) and P-type semiconductor layer (40 nm thick) each have a thermal conductivity of less than 2 W / mK as single films. An Au wire was connected to the Si substrate and the Mo electrode on the P side of the above-mentioned N-type semiconductor, and a voltage was applied. The measurement was performed at room temperature.

[0045] [Table 3]

[0046] The thermal osmosis was measured using the pulsed light heating thermoreflectance method (FF method: surface heating / surface temperature measurement) (measurement device: PicoTR, Picotherm). The measurement was performed at room temperature. Thermal conductivity is calculated from thermal osmosis using the following formula. Thermal conductivity k = (thermal osmosis b) 2 / Volumetric heat capacity =(thermal effusivity b) 2 (Specific heat × Density)

[0047] Therefore, the rate of increase in thermal conductivity Δk after voltage application is evaluated by the following formula. Δk = k(V) / k(0) - 1 Δk=b(V) 2 / b(0) 2 -1 k(V): Thermal conductivity when voltage is applied (W / mK) k(0): Thermal conductivity without voltage application (W / mK) b(V): Thermal conductivity (Ws) when voltage is applied. 0.5 / m 2 K) b(0): Thermal conductivity (Ws) without applied voltage 0.5 / m 2 K)

[0048] The pulsed optical heating thermoreflectance (FF) method described above involves instantaneously heating the element with a pulsed laser from the Mo film side of the P-side electrode, and measuring the rate at which the surface temperature decreases due to thermal diffusion into the thin film, thereby measuring the thermal permeability of the thin film. A high thermal conductivity, or thermal osmosis, means that heat is transferred more rapidly, resulting in a faster decrease in temperature.

[0049] As can be seen from these results, in each embodiment of the present invention, the thermal osmosis at zero bias (no external voltage applied) is 2000 Ws. 0.5 / m 2 The temperature is less than K, and the rate of increase in thermal conductivity after voltage application increases with increasing voltage. In particular, in the thermal flow switching element using the nitride semiconductor material of Example 25 containing Te as the P-type semiconductor layer, the thermal penetration rate at zero bias is smaller, and the rate of increase in thermal conductivity after voltage application is even greater as the voltage increases. The thermal permeability of a nitride semiconductor material containing 9 at% or more of Te is 1000 Ws 0.5 / m 2 The material exhibits low thermal permeability of less than K. In Example 25, by using an extremely low thermal conductivity material, the thermal permeability b(0) of the heat flow switching element at zero bias was reduced. This allowed for a larger rate of change in interface-induced thermal conductivity in response to the external electric field, increasing the rate of increase Δk of thermal conductivity after voltage application and improving heat flow switching performance.

[0050] It should be noted that the technical scope of the present invention is not limited to the embodiments and examples described above, and various modifications can be made without departing from the spirit of the invention.

[0051] For example, in the nitride semiconductor material of the present invention, M is at least one transition metal element, but if a large amount of Ta and Hf is included, the insulating properties increase and semiconductor properties cannot be obtained, so Ta and Hf are undesirable as the main component elements of M. However, if M is a transition metal element such as at least one of the above-mentioned Cr, Mn, Ni, Mo, and W, then at least one of Ta and Hf may be included in trace amounts as long as semiconductor properties can be obtained. [Explanation of symbols]

[0052] 1…Heat flow switching element, 3…N-type semiconductor layer, 4…Insulator layer, 5…P-type semiconductor layer

Claims

1. It is a metal nitride represented by M-Si-N-Te (where M represents at least one transition metal element) and has a thermal permeability of 2000 Ws ０．５ / m ２ It is less than K, A nitride semiconductor material characterized in that M is at least one of Cr and W.

2. In the nitride semiconductor material according to claim 1, A nitride semiconductor material characterized by having an electrical resistivity of less than 10 Ωcm.

3. In the nitride semiconductor material according to claim 1 or 2, Heat effusivity 1000Ws ０．５ / m ２ A nitride semiconductor material characterized by being used as a low thermal conductivity material with a thermal conductivity of less than K.

4. N-type semiconductor layer, An insulating layer stacked on the aforementioned N-type semiconductor layer, The insulator layer comprises a P-type semiconductor layer laminated on the aforementioned insulating layer, A thermal flow switching element characterized in that at least one of the N-type semiconductor layer and the P-type semiconductor layer is formed of a nitride semiconductor material according to any one of claims 1 to 3.

Images