Infrared Optical Elements

Abstract

An infrared optical element capable of improving optical performance is provided. [Solution] The infrared optical element comprises a substrate (10), and a unit element comprising a first conductivity type semiconductor layer (21) including a first region (211) and a second region (212), an active layer (22), and a second conductivity type semiconductor layer (23), wherein the second region, the active layer, and the second conductivity type semiconductor layer form a first mesa structure (26), and the first region and a part of the substrate form a second mesa structure (27), the refractive indexes of the semiconductor materials of the first mesa structure and the second mesa structure are in the range of 2.0 to 4.1, the angle at the intersection between the slope of the first mesa structure and the top surface of the second mesa structure is in the range of 45° to 78°, and where A is the height between the upper flat part of the first mesa structure and the top surface of the second mesa structure and B is the height of the second mesa structure, the relationship 0.8≦A / (A+B)≦0.95 is satisfied.

Description

[Technical Field]

[0001] The present disclosure relates to infrared optical elements. [Background technology]

[0002] In general, infrared rays in the long wavelength band, with wavelengths of 2 μm or more, are used in gas sensors due to the effect of infrared absorption by gases. In particular, the wavelength range from 2.5 μm to 10 μm has many absorption bands specific to various gases, making it a wavelength range suitable for use in gas sensors. Non-dispersive infrared absorption gas sensors are known that take advantage of the fact that different types of gas absorb different wavelengths of infrared light and measure the concentration of a desired gas by detecting the amount of infrared light absorbed at a specific wavelength.

[0003] Here, the performance of devices such as gas sensors can be improved by using an infrared optical element (high-performance infrared optical element) that has high sensitivity or high luminous efficiency. A high-performance infrared optical element can be realized, for example, by connecting a large number of photoelectric conversion elements (e.g., photodiodes) in series. For example, Patent Document 1 discloses an optical device with improved reliability that has a structure in which a large number of photoelectric conversion elements are connected in series. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Patent No. 5352857 Summary of the Invention [Problem to be solved by the invention]

[0005] Here, infrared optical elements using photoelectric conversion elements with mesa structures are known. In such infrared optical elements, by designing them with consideration given to the reflection (total reflection) of light at the side surfaces of the mesa structure, it is possible to increase the amount of light reaching the active layer from outside the infrared optical element or the amount of light emitted from the active layer to the outside of the infrared optical element. In other words, it is possible to further improve optical performance. However, until now, quantitative evaluation of the configuration of the mesa structure has not been performed.

[0006] The present disclosure has been made in consideration of the above circumstances, and has an object to provide an infrared optical element that can improve optical performance. [Means for solving the problem]

[0007] (1) An infrared optical element according to an embodiment of the present disclosure comprises: A substrate and a unit element are provided, the unit element comprises a first conductive type semiconductor layer disposed on the substrate, an active layer disposed on the first conductive type semiconductor layer, and a second conductive type semiconductor layer disposed on the active layer, the first conductive type semiconductor layer being 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 conductivity type semiconductor layer form a first mesa structure, and the first region and a portion of the substrate form a second mesa structure; the refractive index of the semiconductor material of the first mesa structure and the second mesa structure is in the range of 2.0 to 4.1; an angle at a portion where the slope of the first mesa structure intersects with the top surface of the second mesa structure is within a range of 50° to 78°; When the height between the upper flat portion of the first mesa structure and the upper surface of the second mesa structure is A and the height of the second mesa structure is B, 0.8≦A / (A+B)≦0.95 is satisfied.

[0008] (2) As one embodiment of the present disclosure, in (1), The surface of the substrate on which the first conductivity type semiconductor layer is not disposed is used as a light incident surface or a light emitting surface.

[0009] (3) As an embodiment of the present disclosure, in (1) or (2), The active layer is made of a material containing In and Sb.

[0010] (4) As an embodiment of the present disclosure, in any one of (1) to (3), The refractive index of the semiconductor material of the first mesa structure and the second mesa structure is in the range of 3.0 to 4.1.

[0011] (5) As an embodiment of the present disclosure, in any one of (1) to (4), The angle at the intersection between the slope of the first mesa structure and the top surface of the second mesa structure is within the range of 51° to 68°.

[0012] (6) As an embodiment of the present disclosure, in any one of (1) to (5), 0.85≦A / (A+B)≦0.95 is satisfied.

[0013] (7) As an embodiment of the present disclosure, in any one of (1) to (6), 6μm≦(A+B)≦8μm is satisfied.

[0014] (8) As an embodiment of the present disclosure, in any one of (1) to (7), 4.5 μm≦(A+B)≦8 μm is satisfied.

[0015] (9) As an embodiment of the present disclosure, in any one of (1) to (8), When the dimension of the upper flat portion is C (μm), the relationship 0.04≦A / C≦0.30 is satisfied.

[0016] (10) As an embodiment of the present disclosure, in any one of (1) to (9), When the distance of the slope of the first mesa structure is DA and the creepage distance of the second mesa structure is DB, 1≦(DA / DB)≦4 is satisfied, and 6 μm≦(A+B)≦8 μm is satisfied.

[0017] (11) As an embodiment of the present disclosure, in any one of (1) to (10), The conditions 1≦(DA / DB)≦2 are satisfied, and 4.5 μm≦(A+B)<6 μm are satisfied.

[0018] (12) As an embodiment of the present disclosure, in any one of (1) to (11), When the thickness of the active layer is T, the relationship 0.7≦T / A is satisfied.

[0019] (13) As an embodiment of the present disclosure, in any one of (1) to (12), When the total dimension of the slope of the first mesa structure and the upper flat portion is DC and the creepage distance of the second mesa structure is DB, the relationship 6≦DC / DB≦10 is satisfied. [Effects of the Invention]

[0020] According to the present disclosure, it is possible to provide an infrared optical element capable of improving optical performance. [Brief explanation of the drawings]

[0021] [Figure 1] FIG. 1 is a schematic configuration diagram (bird's-eye view) of an infrared optical element according to an embodiment of the present disclosure. [Figure 2] FIG. 2 is a partial cross-sectional view of the infrared optical element of FIG. [Figure 3] FIG. 3 is a diagram for explaining the configuration of the mesa structure. [Figure 4A] FIG. 4A is a diagram for explaining the difference in the amount of light reaching the active layer and the ratio of the step height between the first mesa structure and the second mesa structure. [Figure 4B] FIG. 4B is a diagram for explaining the difference in the amount of light reaching the active layer depending on the ratio of the step between the first mesa structure and the second mesa structure. [Figure 5]FIG. 5 is a diagram illustrating the simulation results. [Figure 6A] FIG. 6A is a diagram showing the results of verifying (A+B), which is the sum of the step heights (A and B) of the first and second mesa structures. [Figure 6B] FIG. 6B is a diagram showing the results of verifying (A+B), which is the sum of the step heights (A and B) of the first and second mesa structures. [Figure 7A] FIG. 7A is a diagram showing the results of examining (A / C), which is the ratio of the step (height) of the first mesa structure to the size of the upper flat portion. [Figure 7B] FIG. 7B is a diagram showing the results of verifying (A / C), which is the ratio of the step (height) of the first mesa structure to the size of the upper flat portion. [Figure 8A] FIG. 8A is a diagram showing the results of verifying the ratio (DA / DB) of the slope distance of the first mesa structure to the creepage distance of the second mesa structure when A+B=4.5 μm. [Figure 8B] FIG. 8B is a diagram showing the results of verifying the ratio (DA / DB) of the slope distance of the first mesa structure to the creepage distance of the second mesa structure when A+B=4.5 μm. [Figure 9A] FIG. 9A is a diagram showing the results of verifying the ratio (DA / DB) of the slope distance of the first mesa structure to the creepage distance of the second mesa structure when A+B=6 μm. [Figure 9B] FIG. 9B is a diagram showing the results of verifying the ratio (DA / DB) of the slope distance of the first mesa structure to the creepage distance of the second mesa structure when A+B=6 μm. [Figure 10A] FIG. 10A is a diagram showing the results of verifying the ratio (DA / DB) of the slope distance of the first mesa structure to the creepage distance of the second mesa structure when A+B=8 μm. [Figure 10B] FIG. 10B is a diagram showing the results of verifying the ratio (DA / DB) of the slope distance of the first mesa structure to the creepage distance of the second mesa structure when A+B=8 μm. [Figure 11A]FIG. 11A shows the results of verifying (DC / DB), which is the ratio of the total dimension of the slope and upper flat portion of the first mesa structure to the creepage distance of the second mesa structure, when A+B=8 μm and C=34 μm. [Figure 11B] FIG. 11B shows the results of verifying (DC / DB), which is the ratio of the total dimension of the slope and upper flat portion of the first mesa structure to the creepage distance of the second mesa structure, when A+B=8 μm and C=34 μm. DETAILED DESCRIPTION OF THE INVENTION

[0022] Hereinafter, embodiments of the present disclosure will be described with reference to the drawings. In the following description of the drawings, the same parts are designated by the same reference numerals. However, the drawings are schematic. For example, the relationship between thickness and planar dimensions may differ from the actual relationship. Furthermore, the embodiments shown below are merely examples of products that embody the technical ideas of the present disclosure, and are not intended to limit the materials, shapes, structures, arrangements, etc. of the components to those described below.

[0023] (infrared optical element) FIG. 1 is a schematic diagram showing an infrared optical element according to this embodiment. FIG. 1 shows a bird's-eye view. FIG. 2 is a partial cross-sectional view of the infrared optical element shown in FIG. 1, showing a plurality of unit elements 20 electrically connected to a pad electrode 40. The infrared optical element includes a substrate 10 and unit elements 20. The infrared optical element according to this embodiment further includes a pad electrode 40. The term "infrared optical element" refers to an infrared light receiving element or an infrared light emitting element, and is a collective term for both. The infrared optical element receives and emits infrared rays. Here, "receives and emits" means having at least one function of receiving and emitting light. An infrared light receiving element can be realized with the structure shown in FIGS. 1 and 2, and an infrared light emitting element can also be realized with the same structure. The unit elements 20 are photoelectric conversion elements, and in this embodiment, they are photodiodes (PDs) or light-emitting diodes (LEDs) in their minimum configuration.

[0024] The infrared optical element according to this embodiment can be used as a component of a gas sensor (concentration measurement device) that measures the concentration of a gas to be measured. The gas sensor may be, for example, a non-dispersive infrared (NDIR) type, or a photoacoustic type that measures the gas concentration by picking up the vibrations of gas molecules that have absorbed light as sound using a high-performance microphone. Furthermore, the infrared optical element according to this embodiment is not limited to gas sensors, and may also be used in infrared thermometers, infrared spectroscopic imaging, human body detection sensors, and the like.

[0025] The infrared optical element according to this embodiment has a configuration in which a large number of photoelectric conversion elements (multiple unit elements 20) are connected in series to achieve high sensitivity or high light-emitting efficiency. However, the infrared optical element may be configured to include one or more unit elements 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. In the configuration example shown in FIG. 1 , the pad electrodes 40 that do not contribute to receiving or emitting infrared light are arranged at ends away from the center portion (CP) of the infrared optical element. For example, when the infrared optical element is a light-receiving element, more photodiodes can be arranged in the center portion (CP) where infrared light is concentrated, thereby improving sensitivity compared to a configuration in which the pad electrodes 40 are located only in a portion of the center portion (CP). Furthermore, when the infrared optical element is a light-emitting element, only light-emitting diodes can be arranged in the center portion (CP), thereby forming a more uniformly luminous surface compared to a configuration in which the pad electrodes 40 are located only in a portion of the center portion (CP). Compared with a light-emitting element having an irregular light-emitting surface (part of which does not emit light), a light-emitting element having a uniform light-emitting surface facilitates the optical design of a device that uses the light-emitting element.

[0026] (substrate) The substrate 10 of this embodiment is not limited in doping with donor impurities or acceptor impurities. However, from the viewpoint of enabling serial connection of a plurality of unit elements 20 formed on the substrate 10, it is desirable that the substrate 10 be semi-insulating or capable of being insulated and separated from the first conductivity type semiconductor layer 21. In this embodiment, the substrate 10 is an insulating semiconductor.

[0027] Here, when light is incident or emitted from the substrate 10 side, it is necessary to use a material for the substrate 10 that has a larger band gap than the active layer 22. As an example, the substrate 10 may be, but is not limited to, a GaAs substrate, a Si substrate, an InP substrate, or an InSb substrate.

[0028] (unit element) The unit element 20 includes a first conductivity type semiconductor layer 21 disposed on a substrate 10, an active layer 22 disposed on the first conductivity type semiconductor layer 21, and a second conductivity type semiconductor layer 23 disposed on the active layer 22. The first conductivity type 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.

[0029] (mesa structure) As shown in FIG. 2, the first-conductivity-type semiconductor layer 21 (second region 212), the active layer 22, and the second-conductivity-type semiconductor layer 23 form a mesa structure. The first-conductivity-type semiconductor layer 21 (first region 211) and a portion of the substrate 10 form another mesa structure. FIG. 3 is a diagram for explaining the configuration of the mesa structure, and corresponds to a cross-sectional view of one unit element 20 in FIG. 2 , from which the first contact electrode portion 24 and the second contact electrode portion 25 are removed. The mesa structure formed by the second region 212, the active layer 22, and the second-conductivity-type semiconductor layer 23 is hereinafter referred to as a 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 a second mesa structure 27. As shown in FIG. 3, the unit element 20 has a shape in which the bottom surface of the first mesa structure 26 is in contact with the top surface of the second mesa structure 27 in a cross-sectional view. The angle (acute angle) at the intersection between the slope of the first mesa structure 26 and the top surface of the second mesa structure 27 is indicated by θ.

[0030] Here, the first mesa structure 26 includes a photodiode structure using a PN junction or a PIN junction. The first conductivity type semiconductor layer 21 and the second conductivity type semiconductor layer 23 are of opposite conductivity types. For example, if the first conductivity type semiconductor layer 21 is n-type, the second conductivity type semiconductor layer 23 is p-type. For example, if the first conductivity type semiconductor layer 21 is p-type, the second conductivity type semiconductor layer 23 is n-type. Materials for the first conductivity type semiconductor layer 21 and the second conductivity type semiconductor layer 23 include, but are not limited to, InSb, InAsSb, AlInSb, etc. Furthermore, the first conductivity type semiconductor layer 21 and the second conductivity type semiconductor layer 23 may have a stacked structure using multiple materials. The active layer 22 preferably contains In and Sb as constituent elements (i.e., is made of a material containing In and Sb). As a specific example, the material for the active layer 22 may be InSb, InAsSb, or AlInSb.

[0031] Furthermore, in the infrared optical element according to this embodiment, the surface of the substrate 10 on which the first conductivity type semiconductor layer 21 is not disposed serves as a light incident surface or a light emitting surface. The infrared optical element may be, for example, a backside illuminated infrared light receiving element, and the surface of the substrate 10 on which the first conductivity type semiconductor layer 21 is not disposed serves as a light incident surface. The infrared optical element may be, for example, a backside illuminated infrared light emitting element, and the surface of the substrate 10 on which the first conductivity type semiconductor layer 21 is not disposed serves as a light emitting surface.

[0032] (refractive index) In this embodiment, the first mesa structure 26 and the second mesa structure 27 include a semiconductor material and have a predetermined refractive index, where the refractive index of the semiconductor material of the first mesa structure 26 and the second mesa structure 27 is a refractive index in a wavelength band to which the infrared optical element is sensitive.

[0033] (contact electrode) The infrared optical element according to this embodiment includes a first contact electrode portion 24 disposed on the first region 211 of the first conductivity type semiconductor layer 21, and a second contact electrode portion 25 disposed on the second conductivity type semiconductor layer 23 (see FIG. 2). The material of the contact electrode (first contact electrode portion 24 or second contact electrode portion 25) preferably has low contact resistance with the semiconductor layer and low electrical resistance. Specific examples of the material of the contact electrode include Ti, Ni, Pt, Cr, Al, Cu, and Au. The contact electrode may also be formed of a laminate of multiple types of materials.

[0034] (internal wiring section) The infrared optical element according to this embodiment includes an internal wiring portion 30 that connects the first contact electrode portion 24 of one unit element 20 with the second contact electrode portion 25 of an adjacent and electrically connected unit element 20. That is, the internal wiring portion 30 electrically connects the multiple unit elements 20. The material of the internal wiring portion 30 is preferably one with low electrical resistance. Specific examples of the material of the internal wiring portion 30 include Ti, Ni, Pt, Cr, Al, Cu, and Au.

[0035] (insulation part) The unit element 20 of the infrared optical element of this embodiment may further include an insulating portion 60 to prevent direct electrical connection between the side surface 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. The insulating portion 60 may also be formed from a laminate of multiple types of materials.

[0036] (pad electrode) The pad electrode 40 is electrically connected to devices external to the infrared optical element via the connection portion 70 and the connection wiring 71. The infrared optical element according to this embodiment has a configuration in which a plurality of pad electrodes 40 and a plurality of unit elements 20 are electrically connected in series with the pad electrode 40 as both ends. The material of the pad electrode 40 is preferably one with low electrical resistance. Specific examples of the material of the pad electrode 40 include Ti, Ni, Pt, Cr, Al, Cu, and Au. The material of the pad electrode 40 may be different from that of the contact electrode.

[0037] (Connection) As described above, the connection portion 70 is provided for electrical connection to the outside, and may be made of metal and conductive adhesive, for example. For example, the connection portion 70 and the connection wiring 71 may be wire-bonded onto the pad electrode 40.

[0038] As described above, in an infrared optical element in which the unit element 20 has a mesa structure, by taking into consideration the reflection of light on the side surfaces, it is possible to 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. FIGS. 4A and 4B are diagrams illustrating the ratio of the step heights of the first mesa structure 26 and the second mesa structure 27 and the difference in the amount of light reaching the active layer 22. In FIGS. 4A and 4B, the first mesa structure 26 and the second mesa structure 27 are each shown as a simplified trapezoid. The step height is the distance between the top and bottom surfaces of the mesa structure and can also be referred to as the height of the mesa structure in the stacking direction. In FIG. 3, the step height of the first mesa structure 26 is indicated by A, and the step height of the second mesa structure 27 is indicated by B.

[0039] As shown in FIG. 4A , for example, when the step of the first mesa structure 26 is approximately half the total step of the first mesa structure 26 and the second mesa structure 27, the amount of light that is not reflected by the slope of the first mesa structure 26 (does not reach the active layer 22) increases. As shown in FIG. 4B , for example, when the step of the first mesa structure 26 occupies almost the entire total step of the first mesa structure 26 and the second mesa structure 27, the amount of light that is reflected by the slope of the first mesa structure 26 and reaches the active layer 22 increases. However, whether total reflection occurs at the slope of the first mesa structure 26 also depends on the refractive index, the angle of incidence of light, the angle indicated by θ, and other factors. Thus, the shapes of the first mesa structure 26 and the second mesa structure 27, among others, affect the optical performance of the infrared optical element. As a result of extensive research, the present inventors have confirmed that when a predetermined relationship is satisfied between the refractive index, angle, and step ratio of the mesa structure described below, it is possible to increase the amount of light reaching the active layer 22 from the outside or the amount of light emitted to the outside from the active layer 22. The configuration of a mesa structure that can improve the optical performance of an infrared optical element will be described below.

[0040] As an appropriate condition for improving optical performance, first, the unit element 20 is configured so that the refractive index of the semiconductor material of the first mesa structure 26 and the second mesa structure 27 (refractive index of the mesa structure) falls within the range of 2.0 to 4.1. From the viewpoint of widening the range of θ that causes total reflection at the slope of the first mesa structure 26, it is more preferable that the refractive index of the mesa structure falls within the range of 3.0 to 4.1.

[0041] Furthermore, the unit element 20 is configured so that the angle (θ in FIG. 3) falls within the range of 50° to 78°. Here, the first mesa structure 26 may be designed so that θ falls within the range of 51° to 68° to further increase the incident light intensity ratio (see FIG. 5).

[0042] The unit element 20 is configured so that the ratio of the step height of the first mesa structure 26 (A in FIG. 3 ) to the step height of the second mesa structure 27 (B in FIG. 3 ) satisfies 0.8≦A / (A+B)≦0.95. To further increase the ratio of the incident light amounts (see FIG. 5 ), the unit element 20 may be configured so that 0.85≦A / (A+B)≦0.95 is satisfied. The step height of the mesa structure is not limited to a specific value. For example, the sum of the step heights of the first mesa structure 26 and the second mesa structure 27 may satisfy 4.5 μm≦(A+B)≦8 μm, and more preferably, 6 μm≦(A+B)≦8 μm. The lower limit of A+B is determined from the viewpoint of the effect of increasing the incident light amount and the stability of the etching process of the first mesa structure. The upper limit of A+B is determined taking into consideration the risk of increased manufacturing costs, increased etching time, and loss of resist. Figures 6A and 6B show the results of verifying (A+B), which is the sum of the step heights of the first and second mesa structures. The verification of Figures 6A and 6B is premised on the satisfaction of A / (A+B)=0.85, and the incident light intensity ratio is set to 1 when A / (A+B)=0.4 and the mesa angle is 45 degrees.

[0043] Furthermore, the dimension of the upper flat portion may be C (μm), and the relationship 0.04≦A / C≦0.30 may be satisfied. As the value of A / C increases, the proportion of light reflected by the slope of the first mesa structure increases, thereby increasing the effect of increasing the amount of incident light. Therefore, the lower limit of A / C is determined based on the effect of increasing the amount of incident light. On the other hand, as the value of A / C increases, the effect of leakage current flowing through the side surface of the semiconductor becomes significant. Therefore, the upper limit of A / C is determined in consideration of the risk of performance degradation. Figures 7A and 7B show the results of verifying (A / C), which is the ratio of the step (height) of the first mesa structure to the dimension of the upper flat portion. The verification of Figures 7A and 7B is premised on the following conditions: A / (A+B) = 0.8, A+B = 4.5 μm, the refractive index is 3.9, and the incident light ratio is set to 1 when A / (A+B) = 0.4 and the mesa angle is 45 degrees. The legend on the graph indicates "dimension C, mesa angle θ."

[0044] Here, instead of the condition regarding the step ratio, the unit element 20 may be configured so that DA, the distance along the slope of the first mesa structure 26, and DB, the creepage distance of the second mesa structure 27, satisfy the condition 1≦(DA / DB)≦4. As shown in FIG. 3 , DA is the distance along the slope of the first mesa structure 26. DB is the creepage distance from the intersection of the slope of the first mesa structure 26 and the top surface of the second mesa structure 27 to the bottom surface of the second mesa structure 27. FIGS. 8A and 8B show the results of verifying DA / DB when A+B=4.5 μm. FIGS. 9A and 9B show the results of verifying DA / DB when A+B=6 μm. FIGS. 10A and 10B show the results of verifying DA / DB when A+B=8 μm. The incident light intensity ratio is defined as 1 when A / (A+B)=0.4.

[0045] Thus, the appropriate conditions for the unit element 20 can be determined as follows: the refractive index of the mesa structure is in the range of 2.0 to 4.1, θ is in the range of 50° to 78°, 0.8≦A / (A+B)≦0.95 is satisfied, 4.5 μm≦(A+B)≦8 μm is satisfied, and 0.04≦A / C≦0.30 is satisfied. Furthermore, when the above DA and DB are used, the appropriate conditions for the unit element 20 can be determined as follows: the refractive index of the mesa structure is in the range of 2.0 to 4.1, θ is in the range of 50° to 78°, 1≦(DA / DB)≦4 is satisfied, 4.5 μm≦(A+B)≦8 μm is satisfied, and 0.04≦A / C≦0.30 is satisfied.

[0046] Furthermore, when DC is the total dimension of the slope (DA) and the upper flat portion (C) of the first mesa structure shown in FIG. 3 and DB is the creepage distance of the second mesa structure, the relationship 6≦DC / DB≦10 may be satisfied. FIGS. 11A and 11B show the results of examining DC / DB when A+B=8 μm and C=34 μm. The incident light intensity ratio is defined as 1 when A / (A+B)=0.4. The larger the DC region relative to DB, the greater the amount of light reflected within the first mesa structure and incident on the active layer. The lower limit of DC / DB is determined in consideration of the effect of increasing the incident light intensity and the dimensional constraints that allow the shape of the first mesa structure to be stably manufactured. The upper limit of DC / DB is determined in consideration of the increase in manufacturing costs associated with increasing the mesa size. Furthermore, as shown in FIG. 3, when T is the film thickness of the active layer, the relationship 0.7≦T / A may be satisfied.

[0047] Figure 5 shows the results of a simulation in which the incident light intensity ratio was calculated by changing the refractive index, angle, and step ratio in the mesa structure of the unit element 20. Zemax OpticStudio software from Zemax was used for the simulation. The incident light intensity ratio is the relative ratio of the incident light intensity, where the incident light intensity (the amount of light reaching the active layer 22) when the above "A / (A+B)" is 0.4 is 1. The refractive index is the refractive index of the semiconductor material of the first mesa structure 26 and the second mesa structure 27. θ is the angle at which the slope of the first mesa structure 26 intersects with the top surface of the second mesa structure 27 (see Figure 3). As shown in Figure 5, when the above appropriate conditions are met, the incident light intensity increased by at least 5%, demonstrating improved optical performance. Here, in the graph for a refractive index of 2.0, the incident light intensity ratio when θ is 45° overlaps with the incident light intensity ratio when θ is 78°.

[0048] As described above, by determining the step ratio and the like 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.

[0049] Although the embodiments of the present disclosure have been described based on the drawings and examples, it should be noted that those skilled in the art can easily make various modifications or alterations based on the present disclosure, and therefore, it should be noted that these modifications and alterations are included within the scope of the present disclosure. [Explanation of symbols]

[0050] 10 Substrate 20 unit elements 21 First conductivity type semiconductor layer 22 Active layer 23 Second conductivity type semiconductor layer 24 First contact electrode portion 25 Second contact electrode part 26 First Mesa Structure 27 Second Mesa Structure 30 Internal wiring section 40 Pad Electrode 60 Insulation section 70 Connection 71 Connection wiring 211 First area 212 Second area

Claims

1. A substrate and a unit element are provided, the unit element comprises a first conductive type semiconductor layer disposed on the substrate, an active layer disposed on the first conductive type semiconductor layer, and a second conductive type semiconductor layer disposed on the active layer, the first conductive type semiconductor layer being configured with 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 conductivity type semiconductor layer form a first mesa structure, and the first region and a portion of the substrate form a second mesa structure; the refractive index of the semiconductor material of the first mesa structure and the second mesa structure is in the range of 2.0 to 4.1; an angle at a portion where the slope of the first mesa structure intersects with the top surface of the second mesa structure is within a range of 50° to 78°; an infrared optical element, wherein 0.8≦A / (A+B)≦0.95 is satisfied, where A is the height between the upper flat portion of the first mesa structure and the upper surface of the second mesa structure, and B is the height of the second mesa structure.

2. 2. The infrared optical element according to claim 1, wherein a surface of the substrate on which the first conductivity type semiconductor layer is not disposed is used as a light incident surface or a light emitting surface.

3. 3. The infrared optical element according to claim 1, wherein the active layer is made of a material containing In and Sb.

4. 3. The infrared optical element according to claim 1, wherein the refractive index of the semiconductor material of the first mesa structure and the second mesa structure is in the range of 3.0 to 4.

1.

5. 3. The infrared optical element according to claim 1, wherein an angle at a portion where the inclined surface of the first mesa structure intersects with the top surface of the second mesa structure is within a range of 51° to 68°.

6. 3. The infrared optical element according to claim 1, wherein 0.85≦A / (A+B)≦0.95 is satisfied.

7. 3. The infrared optical element according to claim 1, wherein 6 μm≦(A+B)≦8 μm is satisfied.

8. 3. The infrared optical element according to claim 1, wherein 4.5 μm≦(A+B)≦8 μm is satisfied.

9. 3. The infrared optical element according to claim 1, wherein the dimension of the upper flat portion is C (μm), and 0.04≦A / C≦0.30 is satisfied.

10. 3. The infrared optical element according to claim 1, wherein DA is a distance between the slopes of the first mesa structure and DB is a creepage distance of the second mesa structure, and 1≦(DA / DB)≦4 is satisfied, and 6 μm≦(A+B)≦8 μm is satisfied.

11. 3. The infrared optical element according to claim 1, wherein 1≦(DA / DB)≦2 and 4.5 μm≦(A+B)<6 μm are satisfied.

12. 3. The infrared optical element according to claim 1, wherein when the thickness of the active layer is T, the relationship 0.7≦T / A is satisfied.

13. 3. The infrared optical element according to claim 1, wherein when a total dimension of the slope of the first mesa structure and the upper flat portion is defined as DC and a creepage distance of the second mesa structure is defined as DB, 6≦DC / DB≦10 is satisfied.

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