Infrared optical elements

Abstract

This invention provides an infrared optical element that improves optical performance. The infrared optical element comprises: a substrate (10); a unit element comprising a first conductive semiconductor layer (21) including a first region (211) and a second region (212), an active layer (22), and a second conductive semiconductor layer (23). The second region, the active layer, and the second conductive semiconductor layer constitute a first mesa structure (26), and the first region and a portion of the substrate constitute a second mesa structure (27). The refractive index of the semiconductor materials of the first and second mesa structures is in the range of 2.0 to 4.1. The angle between the inclined surface of the first mesa structure and the upper surface of the second mesa structure is in the range of 45° to 78°. Let A be the height between the upper flat portion of the first mesa structure and the upper surface of the second mesa structure, and B be the height of the second mesa structure, satisfying 0.8 ≤ A / (A+B) ≤ 0.95.

Description

Technical Field

[0001] This disclosure relates to infrared optical elements. Background Technology

[0002] Typically, long-wavelength infrared light (wavelengths above 2 μm) is used in gas sensors due to the infrared absorption effect of gases. Particularly in the region from 2.5 μm to 10 μm, various gases possess numerous inherent absorption bands, making it a suitable band for use in gas sensors. A known non-dispersive infrared gas sensor utilizes the fact that different wavelengths of infrared light are absorbed depending on the type of gas, detecting the amount of absorption at specific wavelengths of infrared light to determine the desired gas concentration.

[0003] Here, by using infrared optical elements with high sensitivity or high luminous efficiency (high-performance infrared optical elements), the performance of devices such as gas sensors can be improved. High-performance infrared optical elements can be achieved, for example, by connecting multiple photoelectric conversion elements (e.g., photodiodes) in series. For example, Patent Document 1 discloses an optical device with a structure of multiple photoelectric conversion elements connected in series, which improves reliability.

[0004] Existing technical documents

[0005] Patent documents

[0006] Patent Document 1: Japanese Patent No. 5352857 Utility Model Content

[0007] The problem to be solved by the utility model

[0008] Here, infrared optical elements using photoelectric conversion elements with mesa structures are known. In such infrared optical elements, by considering the reflection (total internal reflection) of light on the side surfaces of the mesa structure in the design, the amount of light reaching the active layer from the outside of the infrared optical element or the amount of light emitted from the active layer to the outside of the infrared optical element can be increased. That is, optical performance can be further improved. However, the structure of the mesa structure has not been quantitatively evaluated in the past.

[0009] This disclosure was made in view of the following circumstances, and its purpose is to provide an infrared optical element that can improve optical performance.

[0010] Methods for solving problems

[0011] (1) An infrared optical element according to one embodiment of the present disclosure includes a substrate and a unit element.

[0012] The unit element includes a first conductive semiconductor layer disposed on the substrate, an active layer disposed on the first conductive semiconductor layer, and a second conductive semiconductor layer disposed on the active layer. The first conductive semiconductor layer is composed of a first region disposed on the substrate and a second region disposed on the first region.

[0013] The second region, the active layer, and the second conductive semiconductor layer constitute a first mesa structure, and the first region and a portion of the substrate constitute a second mesa structure.

[0014] The refractive index of the semiconductor materials in both the first and second mesa structures is within the range of 2.0 to 4.1.

[0015] The angle at the intersection of the inclined surface of the first platform structure and the upper surface of the second platform structure is within the range of 50° to 78°.

[0016] When the height between the upper flat portion of the first platform structure and the upper surface of the second platform structure is set as A, and the height of the second platform structure is set as B, the condition 0.8≤A / (A+B)≤0.95 is satisfied.

[0017] (2) As one embodiment of this disclosure, in (1),

[0018] The side of the substrate that is not provided with the first conductive semiconductor layer is designated as the light incident surface or the light emitting surface.

[0019] (3) As one embodiment of this disclosure, in (1) or (2),

[0020] The active layer is made of a material containing In and Sb.

[0021] (4) As one embodiment of the present invention, in any one of (1) to (3),

[0022] The refractive index of the semiconductor materials of the first mesa structure and the second mesa structure is in the range of 3.0 to 4.1.

[0023] (5) As one embodiment of this disclosure, in any one of (1) to (4),

[0024] The angle at which the inclined surface of the first platform structure intersects the upper surface of the second platform structure is within the range of 51° to 68°.

[0025] (6) As one embodiment of this disclosure, in any one of (1) to (5),

[0026] It satisfies 0.85≤A / (A+B)≤0.95.

[0027] (7) As one embodiment of this disclosure, in any one of (1) to (6),

[0028] It satisfies 6μm≤(A+B)≤8μm.

[0029] (8) As one embodiment of this disclosure, in any one of (1) to (7),

[0030] It satisfies 4.5μm≤(A+B)≤8μm.

[0031] (9) As one embodiment of this disclosure, in any one of (1) to (8),

[0032] When the size of the upper flat portion is set to C (μm), the condition 0.04 ≤ A / C ≤ 0.30 is satisfied.

[0033] (10) As one embodiment of this disclosure, in any one of (1) to (9),

[0034] When the distance of the inclined surface of the first platform structure is set as DA and the creepage distance of the second platform structure is set as DB, 1≤(DA / DB)≤4 and 6μm≤(A+B)≤8μm are satisfied.

[0035] (11) As one embodiment of this disclosure, in any one of (1) to (10),

[0036] It satisfies 1≤(DA / DB)≤2 and 4.5μm≤(A+B)<6μm.

[0037] (12) As one embodiment of this disclosure, in any one of (1) to (11),

[0038] When the thickness of the active layer is set to T, 0.7 ≤ T / A is satisfied.

[0039] (13) As one embodiment of this disclosure, in any one of (1) to (12),

[0040] When the total dimension of the inclined surface of the first platform structure and the upper flat part is set as DC, and the creepage distance of the second platform structure is set as DB, the following condition is met: 6≤DC / DB≤10.

[0041] Utility Model Effect

[0042] According to this disclosure, it is possible to provide infrared optical elements that can improve optical performance. Attached Figure Description

[0043] Figure 1 This is a schematic structural diagram (top view) of an infrared optical element according to an embodiment of the present disclosure;

[0044] Figure 2 yes Figure 1 A partial cross-sectional view of the infrared optical element;

[0045] Figure 3 It is a structural diagram used to illustrate the countertop structure.

[0046] Figure 4A This is a diagram used to illustrate the difference between the step ratio between the first and second mezzanine structures and the amount of light reaching the active layer;

[0047] Figure 4B This is a diagram used to illustrate the difference between the step ratio between the first and second mezzanine structures and the amount of light reaching the active layer;

[0048] Figure 5 This is a graph illustrating the simulation results.

[0049] Figure 6A This is a diagram showing the results of verifying the total height of the steps (A+B) of the first and second platform structures.

[0050] Figure 6B This is a diagram showing the results of verifying the total height of the steps (A+B) of the first and second platform structures.

[0051] Figure 7A This is a diagram showing the results of verifying the ratio (A / C) of the step (height) of the first platform structure to the size of the upper flat section.

[0052] Figure 7B This is a diagram showing the results of verifying the ratio (A / C) of the step (height) of the first platform structure to the size of the upper flat section.

[0053] Figure 8A This is a graph showing the results of verifying the ratio (DA / DB) of the inclined plane of the first mezzanine structure to the creepage distance of the second mezzanine structure when A+B=4.5μm.

[0054] Figure 8B This is a graph showing the results of verifying the ratio (DA / DB) of the inclined plane of the first mezzanine structure to the creepage distance of the second mezzanine structure when A+B=4.5μm.

[0055] Figure 9AThis is a graph showing the results of verifying the ratio (DA / DB) of the inclined plane of the first mezzanine structure to the creepage distance of the second mezzanine structure when A+B=6μm.

[0056] Figure 9B This is a graph showing the results of verifying the ratio (DA / DB) of the inclined plane of the first mezzanine structure to the creepage distance of the second mezzanine structure when A+B=6μm.

[0057] Figure 10A This is a graph showing the results of verifying the ratio (DA / DB) of the inclined plane of the first mezzanine structure to the creepage distance of the second mezzanine structure when A+B=8μm.

[0058] Figure 10B This is a graph showing the results of verifying the ratio (DA / DB) of the inclined plane of the first mezzanine structure to the creepage distance of the second mezzanine structure when A+B=8μm.

[0059] Figure 11A This is a graph showing the results of verifying the ratio (DC / DB) of the total dimensions of the inclined surface and the upper flat portion of the first mezzanine structure to the creepage distance of the second mezzanine structure when A+B=8μm and C=34μm.

[0060] Figure 11B This is a graph showing the results of verifying the ratio (DC / DB) of the total dimensions of the inclined surface and the upper flat portion of the first mezzanine structure to the creepage distance of the second mezzanine structure when A+B=8μm and C=34μm.

[0061] Label Explanation

[0062] 10 substrate

[0063] 20 unit components

[0064] 21 First conductivity type semiconductor layer

[0065] 22 Active layer

[0066] 23 Second conductivity type semiconductor layer

[0067] 24 First contact electrode section

[0068] 25 Second contact electrode section

[0069] 26 First tabletop structure

[0070] 27 Second countertop structure

[0071] 30 Internal Wiring Section

[0072] 40 Pad Electrode

[0073] 60 Insulation section

[0074] 70 Connecting part

[0075] 71 Connection wiring

[0076] 211 First District

[0077] 212 Second Area Detailed Implementation

[0078] Hereinafter, embodiments of the present disclosure will be described with reference to the accompanying drawings. In the following description of the drawings, the same reference numerals are used to label the same parts. However, the drawings are schematic. For example, the relationship between film thickness and planar dimensions may differ from reality. Furthermore, the embodiments shown below exemplify aspects used to embody the technical concept of the present disclosure, and the materials, shapes, structures, and arrangements of the constituent components are not limited to the following descriptions.

[0079] (Infrared optical element)

[0080] Figure 1 This is a schematic structural diagram showing the infrared optical element of this embodiment. Figure 1 This represents a top view. Figure 2 yes Figure 1 The diagram shows a partial cross-sectional view of an infrared optical element, illustrating multiple unit elements 20 electrically connected to pad electrodes 40. The infrared optical element comprises a substrate 10 and unit elements 20. The infrared optical element of this embodiment also includes pad electrodes 40. An infrared optical element is a collective term encompassing both infrared light-receiving and infrared light-emitting elements. The infrared optical element performs infrared light reception and emission. Here, emission means having at least one of the functions of light reception and emission. Figure 1 and Figure 2 The structure shown implements an infrared light-receiving element, and the same structure is used to implement an infrared light-emitting element. Furthermore, the unit element 20 is a photoelectric conversion element, which in this embodiment is a minimal photodiode (PD) or light-emitting diode (LED).

[0081] For example, the infrared optical element of this embodiment can be used as a component of a gas sensor (concentration measuring device) for measuring, for example, the concentration of a target gas. The gas sensor can be, for example, a non-dispersive infrared absorption (NDIR) type, or a photoacoustic type that measures gas concentration by using a high-performance microphone to pick up the vibrations of light-absorbing gas molecules as sound. Furthermore, the infrared optical element of this embodiment is not limited to gas sensors, and can also be used in infrared radiation thermometers, infrared spectral imaging, human body detection sensors, etc.

[0082] The infrared optical element of this embodiment has a structure in which multiple photoelectric conversion elements (multiple unit elements 20) are connected in series to achieve high sensitivity or high luminous efficiency. However, the infrared optical element can be configured to include more than one unit element 20. Furthermore, the unit elements 20 located at the ends of the multiple unit elements 20 connected in series are electrically connected to different pad electrodes 40. Figure 1 In the structural example, the pad electrode 40, which does not contribute to the emission of infrared light, is positioned at an end offset from the center portion (CP) of the infrared optical element. For example, when the infrared optical element is a light-receiving element, since more photodiodes can be positioned in the center portion (CP) where infrared light is concentrated, sensitivity can be improved compared to a configuration where the pad electrode 40 is present only in a portion of the center portion (CP). Furthermore, for example, when the infrared optical element is a light-emitting element, since only the light-emitting diodes can be positioned in the center portion (CP), a more uniform brightness surface can be formed compared to a structure where the pad electrode 40 is present only in a portion of the center portion (CP). Compared to a light-emitting element with a skewed (partially non-emitting) light-emitting surface, a light-emitting element with a uniform light-emitting surface simplifies the optical design in devices using light-emitting elements.

[0083] (Substrate)

[0084] In this embodiment, the substrate 10 is not limited by donor or acceptor impurities in terms of doping. However, from the viewpoint that multiple unit elements 20 formed on the substrate 10 can be connected in series, it is preferable to be semi-insulating or to be insulated from the first conductivity semiconductor layer 21. In this embodiment, the substrate 10 is an insulating semiconductor.

[0085] Here, when light is incident or emitted from the substrate 10 side, a material with a band gap larger than that of the active layer 22 is required for the substrate 10. As an example, the substrate 10 can be, but is not limited to, a GaAs substrate, a Si substrate, an InP substrate, or an InSb substrate.

[0086] (Unit Component)

[0087] The unit element 20 includes a first conductive semiconductor layer 21 disposed on the substrate 10, an active layer 22 disposed on the first conductive semiconductor layer 21, and a second conductive semiconductor layer 23 disposed on the active layer 22. In addition, the first conductive semiconductor layer 21 is composed of a first region 211 disposed on the substrate 10 and a second region 212 disposed on the first region 211.

[0088] (Countertop structure)

[0089] like Figure 2As shown, the first conductive semiconductor layer 21 (second region 212), the active layer 22, and the second conductive semiconductor layer 23 constitute a mesa structure. Additionally, the first conductive semiconductor layer 21 (first region 211) and a portion of the substrate 10 constitute another mesa structure. Figure 3 This is a structural diagram used to illustrate the countertop structure, corresponding to... Figure 2 A cross-sectional view of a unit element 20 excluding the first contact electrode portion 24 and the second contact electrode portion 25. The mesa structure formed by the second region 212, the active layer 22, and the second conductive semiconductor layer 23 is hereinafter referred to as the first mesa structure 26. The mesa structure formed by the first region 211 and a portion of the substrate 10 is hereinafter referred to as the second mesa structure 27. Figure 3 As shown, the unit element 20, when viewed in section, has a shape in which the bottom surface of the first platform structure 26 is in contact with the upper surface of the second platform structure 27. Furthermore, the angle (as an acute angle) at the intersection of the inclined surface of the first platform structure 26 and the upper surface of the second platform structure 27 is represented by θ.

[0090] Here, the first mesa structure 26 includes a photodiode structure with a PN junction or a PIN junction. The first conductivity semiconductor layer 21 and the second conductivity semiconductor layer 23 have opposite conductivity types. For example, if the first conductivity semiconductor layer 21 is n-type, then the second conductivity semiconductor layer 23 is p-type. For example, if the first conductivity semiconductor layer 21 is p-type, then the second conductivity semiconductor layer 23 is n-type. Materials for the first conductivity semiconductor layer 21 and the second conductivity semiconductor layer 23 include InSb, InAsSb, AlInSb, etc., but are not limited to these. Furthermore, the first conductivity semiconductor layer 21 and the second conductivity semiconductor layer 23 can be a stacked structure formed of multiple materials. The active layer 22 preferably contains In and Sb as constituent elements (i.e., it is composed of a material containing In and Sb). As a specific example, the material of the active layer 22 can be InSb, InAsSb, or AlInSb.

[0091] Furthermore, in the infrared optical element of this embodiment, the side of the substrate 10 without the first conductive semiconductor layer 21 is designated as the light incident surface or the light emitting surface. The infrared optical element is, for example, a back-illuminated infrared light-receiving element, and the side of the substrate 10 without the first conductive semiconductor layer 21 is designated as the light incident surface. Alternatively, the infrared optical element is, for example, a back-illuminated infrared light-emitting element, and the side of the substrate 10 without the first conductive semiconductor layer 21 is designated as the light emitting surface.

[0092] (Refractive index)

[0093] In this embodiment, the first mesa structure 26 and the second mesa structure 27 comprise semiconductor materials having a predetermined refractive index. Here, the refractive index of the semiconductor materials of the first mesa structure 26 and the second mesa structure 27 is the refractive index in the wavelength band where the infrared optical element has sensitivity.

[0094] (Contact electrode)

[0095] The infrared optical element of this embodiment includes a first contact electrode portion 24 disposed on a first region 211 of the first conductive semiconductor layer 21 and a second contact electrode portion 25 disposed on the second conductive semiconductor layer 23 (see [link]). Figure 2 The material of the contact electrode (first contact electrode portion 24 or second contact electrode portion 25) is preferably a material with low contact resistance to the semiconductor layer and low overall resistance. As specific examples, the material of the contact electrode can be Ti, Ni, Pt, Cr, Al, Cu, or Au, etc. Furthermore, the contact electrode can be composed of a laminate of various materials.

[0096] (Internal wiring section)

[0097] The infrared optical element of this embodiment includes an internal wiring section 30 that connects the first contact electrode portion 24 of one unit element 20 to the second contact electrode portion 25 of an adjacent and electrically connected unit element 20. That is, multiple unit elements 20 are electrically connected via the internal wiring section 30. The material of the internal wiring section 30 is preferably a material with low electrical resistance. As a specific example, the material of the internal wiring section 30 may be Ti, Ni, Pt, Cr, Al, Cu, or Au, etc.

[0098] (Insulation section)

[0099] The unit element 20 of the infrared optical element in this embodiment may further include an insulating portion 60 to prevent direct electrical connection between the side of the mesa structure and the internal wiring portion 30. The insulating portion 60 is disposed between the first mesa structure 26 and the second mesa structure 27 and the internal wiring portion 30. The material of the insulating portion 60 may be, for example, silicon nitride, silicon oxide, or aluminum oxide, but is not limited to these. In addition, the insulating portion 60 may be composed of a laminate of various materials.

[0100] (Pad electrode)

[0101] The pad electrodes 40 are electrically connected to devices outside the infrared optical element via the connection portion 70 and the connection wiring 71. The infrared optical element of this embodiment has a structure in which multiple pad electrodes 40 and multiple unit elements 20 are connected in series with the pad electrodes 40 as both ends. The material of the pad electrodes 40 is preferably a material with low resistance. As a specific example, the material of the pad electrodes 40 can be Ti, Ni, Pt, Cr, Al, Cu, Au, etc. The material of the pad electrodes 40 can be different from that of the contact electrodes.

[0102] (Connecting part)

[0103] As described above, the connection portion 70 is provided for external electrical connection, and as a specific example, it can be made of metal and conductive adhesive. For example, the connection portion 70 and the connection wiring 71 can be wire bonded on the pad electrode 40.

[0104] Here, as described above, in the infrared optical element with a mesa structure in unit element 20, by taking into account the reflection of light from the side, the amount of light reaching the active layer 22 from the outside or the amount of light emitted from the active layer 22 to the outside can be increased, thereby improving optical performance. Figure 4A and Figure 4B This is a diagram illustrating the difference between the step ratio between the first mesa structure 26 and the second mesa structure 27 and the amount of light reaching the active layer 22. Figure 4A and Figure 4B In the diagram, the first platform structure 26 and the second platform structure 27 are represented by simplified figures (trapezoidal). Furthermore, a step is the distance between the upper surface and the bottom surface of the platform structure, which can also be referred to as the height of the platform structure in the stacking direction. Figure 3 In the diagram, the steps of the first platform structure 26 are represented by A, and the steps of the second platform structure 27 are represented by B.

[0105] like Figure 4A As shown, for example, when the steps of the first mezzanine structure 26 are approximately half the total steps of the first mezzanine structure 26 and the second mezzanine structure 27, the amount of light not reflected by the slope of the first mezzanine structure 26 (not reaching the active layer 22) increases. Figure 4BAs shown, for example, when the steps of the first mesa structure 26 occupy almost the entire sum of the steps of the first mesa structure 26 and the second mesa structure 27, the amount of light reflected from the slope of the first mesa structure 26 and reaching the active layer 22 increases. However, whether total internal reflection occurs on the slope of the first mesa structure 26 depends on the refractive index, the angle of incidence of light, the angle represented by θ mentioned above, etc. Therefore, the shapes of the first mesa structure 26 and the second mesa structure 27 affect the optical performance of the infrared optical element. The inventors of this application have conducted intensive research and confirmed that when the specified relationships regarding the refractive index, angle, and step ratio of the mesa structure are satisfied, the amount of light reaching the active layer 22 from the outside or the amount of light emitted from the active layer 22 to the outside is increased. The structure of the mesa structure that can improve the optical performance of the infrared optical element will be described below.

[0106] As appropriate conditions for improving optical performance, the unit element 20 is first configured such that the refractive index of the semiconductor material of the first mesa structure 26 and the second mesa structure 27 (the refractive index of the mesa structure) is within the range of 2.0 to 4.1. From the viewpoint of expanding the range of θ mentioned above for total internal reflection generated by the inclined surface of the first mesa structure 26, it is more preferable that the refractive index of the mesa structure is within the range of 3.0 to 4.1.

[0107] Additionally, as with angle ( Figure 3 The unit element 20 is constructed such that θ is contained within the range of 50° to 78°, depending on the conditions related to θ. Here, the first platform structure 26 can be designed such that θ is contained within the range of 51° to 68°, thereby increasing the incident light intensity ratio (see reference). Figure 5 ).

[0108] Furthermore, the unit element 20 is configured as a step (with the first platform structure 26) Figure 3 A) and the steps of the second platform structure 27 ( Figure 3 The condition related to the ratio of A to B is that 0.8 ≤ A / (A+B) ≤ 0.95. Here, the unit element 20 can be configured to satisfy 0.85 ≤ A / (A+B) ≤ 0.95, so as to increase the incident light intensity ratio more significantly (see reference). Figure 5 Furthermore, the steps of the mezzanine structure are not limited to a specific value. For example, the total number of steps between the first mezzanine structure 26 and the second mezzanine structure 27 can satisfy 4.5μm ≤ (A+B) ≤ 8μm, and more preferably 6μm ≤ (A+B) ≤ 8μm. Here, the lower limit of A+B is determined from the viewpoint of the effect of increased incident light and the stability of the etching process of the first mezzanine structure. The upper limit of A+B is determined considering risks such as increased manufacturing costs, increased etching time, and resist disappearance. Figure 6A and Figure 6BThis represents the result of verifying the total step (height) of the first and second platform structures, i.e., (A+B). Figure 6A and Figure 6B The premise for verification is that A / (A+B) = 0.85, and the incident light ratio is set to 1 when A / (A+B) = 0.4 and the table angle is 45 degrees.

[0109] Furthermore, when the size of the upper flat portion is set to C (μm), the condition 0.04 ≤ A / C ≤ 0.30 can be satisfied. As the value of A / C increases, the proportion of light reflected from the inclined surface of the first mesa structure increases, thus amplifying the effect of increasing the incident light amount. Therefore, the lower limit of A / C is determined by the effect of increasing the incident light amount. On the other hand, if the value of A / C increases, the effect of leakage current flowing through the semiconductor sidewalls cannot be ignored. Therefore, the upper limit of A / C is determined considering the risk of performance degradation. Figure 7A and Figure 7B This represents the result of verifying the ratio (A / C) between the height of the step and the size of the upper flat section of the first platform structure. Figure 7A and Figure 7B The verification premise is that A / (A+B) = 0.8, A+B = 4.5μm, and the refractive index is 3.9. When A / (A+B) = 0.4 and the stage angle is 45 degrees, the incident light ratio is set to 1. In addition, the legend in the chart represents "dimension C, stage angle θ".

[0110] Here, instead of the condition related to the step ratio, the unit element 20 can also be configured such that, when the distance of the inclined plane of the first platform structure 26 is set as DA and the creepage distance of the second platform structure 27 is set as DB, 1≤(DA / DB)≤4. Figure 3 As shown, DA is the distance along the inclined surface of the first platform structure 26. DB is the creepage distance from the portion where the inclined surface of the first platform structure 26 intersects with the upper surface of the second platform structure 27 to the bottom surface of the second platform structure 27. Figure 8A as well as Figure 8B This is a graph showing the results of verifying DA / DB when A+B = 4.5μm. Figure 9A as well as Figure 9B This is a graph showing the results of verifying DA / DB when A+B = 6μm. Figure 10A as well as Figure 10B This graph shows the results of verifying DA / DB when A+B = 8 μm. The incident light ratio was set to 1 when A / (A+B) = 0.4.

[0111] Thus, appropriate conditions can be specified as follows: for a unit element 20, at least the refractive index of the mesa structure is within the range of 2.0 to 4.1, θ is within the range of 50° to 78°, satisfying 0.8 ≤ A / (A+B) ≤ 0.95, satisfying 4.5 μm ≤ (A+B) ≤ 8 μm, and satisfying 0.04 ≤ A / C ≤ 0.30. Furthermore, when using the aforementioned DA and DB, appropriate conditions can be specified as follows: for a unit element 20, at least the refractive index of the mesa structure is within the range of 2.0 to 4.1, θ is within the range of 50° to 78°, satisfying 1 ≤ (DA / DB) ≤ 4, satisfying 4.5 μm ≤ (A+B) ≤ 8 μm, and satisfying 0.04 ≤ A / C ≤ 0.30.

[0112] In addition, in the Figure 3 The total dimension of the inclined surface (DA) and the upper flat part (C) of the first platform structure shown is set as DC. When the creepage distance of the second platform structure is set as DB, it can satisfy 6≤DC / DB≤10. Figure 11A and Figure 11B This graph shows the results of verifying the DC / DB ratio when A+B = 8 μm and C = 34 μm. The incident light ratio is set to 1 when A / (A+B) = 0.4. As the DC region increases relative to DB, the amount of light reflected and incident on the active layer in the first mesa structure increases. Here, the lower limit of DC / DB is determined considering the effect of increased incident light and the dimensional limitations of the shape that allows for stable fabrication of the first mesa structure. The upper limit of DC / DB is determined based on the increased manufacturing cost associated with the increased size of the mesa. Additionally, as... Figure 3 As shown, when the thickness of the active layer is set to T, 0.7 ≤ T / A can be satisfied.

[0113] Figure 5 This represents the simulation results of calculating the incident light ratio by varying the refractive index, angle, and step ratio in the mesa structure of unit element 20. Zemax OpticStudio from Zemax Corporation was used as the simulation software. The incident light ratio is the relative ratio of the incident light amount (the amount of light reaching the active layer 22) when "A / (A+B)" is 0.4 and the incident light amount is set to 1. The refractive index is the refractive index of the semiconductor material of the first mesa structure 26 and the second mesa structure 27. Additionally, θ is the angle at which the inclined surface of the first mesa structure 26 intersects the upper surface of the second mesa structure 27 (refer to...). Figure 3 ).like Figure 5 As shown, under the appropriate conditions described above, an increase in incident light amount of at least 5% resulted in an improvement in optical performance. Here, in the graph with a refractive index of 2.0, the incident light amount ratio at θ = 45° overlaps with the incident light amount ratio at θ = 78°.

[0114] As described above, by determining the step ratio and other parameters as described above, the infrared optical element of this embodiment can increase the amount of light reaching the active layer 22 from the outside or the amount of light emitted from the active layer 22 to the outside, thereby improving optical performance.

[0115] The embodiments of this disclosure have been described with reference to the accompanying drawings and examples. However, it should be noted that those skilled in the art can readily make various modifications or alterations based on this disclosure. Therefore, it should be understood that these modifications or alterations are included within the scope of this disclosure.

Claims

1. An infrared optical element, characterized in that, The infrared optical element comprises a substrate and unit elements. The unit element includes a first conductive semiconductor layer disposed on the substrate, an active layer disposed on the first conductive semiconductor layer, and a second conductive semiconductor layer disposed on the active layer. The first conductive semiconductor layer is composed of a first region disposed on the substrate and a second region disposed on the first region. The second region, the active layer, and the second conductive semiconductor layer constitute a first mesa structure, and the first region and a portion of the substrate constitute a second mesa structure. The refractive index of the semiconductor materials in both the first and second mesa structures is within the range of 2.0 to 4.

1. The angle at the intersection of the inclined surface of the first platform structure and the upper surface of the second platform structure is within the range of 50° to 78°. When the height between the upper flat portion of the first platform structure and the upper surface of the second platform structure is set as A, and the height of the second platform structure is set as B, the condition 0.8≤A / (A+B)≤0.95 is satisfied.

2. The infrared optical element according to claim 1, characterized in that, The side of the substrate that is not provided with the first conductive semiconductor layer is designated as the light incident surface or the light emitting surface.

3. The infrared optical element according to claim 1 or 2, characterized in that, The active layer is made of a material containing In and Sb.

4. The infrared optical element according to claim 1 or 2, characterized in that, The refractive index of the semiconductor materials of the first mesa structure and the second mesa structure is in the range of 3.0 to 4.

1.

5. The infrared optical element according to claim 1 or 2, characterized in that, The angle at which the inclined surface of the first platform structure intersects the upper surface of the second platform structure is within the range of 51° to 68°.

6. The infrared optical element according to claim 1 or 2, characterized in that, It satisfies 0.85≤A / (A+B)≤0.

95.

7. The infrared optical element according to claim 1 or 2, characterized in that, It satisfies 6μm≤(A+B)≤8μm.

8. The infrared optical element according to claim 1 or 2, characterized in that, It satisfies 4.5μm≤(A+B)≤8μm.

9. The infrared optical element according to claim 1 or 2, characterized in that, When the size of the upper flat portion is set to C (μm), the condition 0.04 ≤ A / C ≤ 0.30 is satisfied.

10. The infrared optical element according to claim 1 or 2, characterized in that, When the distance of the inclined surface of the first platform structure is set as DA and the creepage distance of the second platform structure is set as DB, 1≤(DA / DB)≤4 and 6μm≤(A+B)≤8μm are satisfied.

11. The infrared optical element according to claim 1 or 2, characterized in that, It satisfies 1≤(DA / DB)≤2 and 4.5μm≤(A+B)<6μm.

12. The infrared optical element according to claim 1 or 2, characterized in that, When the thickness of the active layer is set to T, 0.7 ≤ T / A is satisfied.

13. The infrared optical element according to claim 1 or 2, characterized in that, When the total dimension of the inclined surface of the first platform structure and the upper flat part is set as DC, and the creepage distance of the second platform structure is set as DB, the following condition is met: 6≤DC / DB≤10.

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