Manufacturing method for optical semiconductor device and design method for low reflectance film

Abstract

A manufacturing method for an optical semiconductor device according to the present disclosure includes: calculating a minimum value Rmin 0 of a reflectance by making, equal to each other, a characteristic matrix of a single-layer coating film (12) having a film thickness of λ0 / 4 / nfl, and a characteristic matrix of multilayer coating films (13, 14, 15), using at least two types of materials for which a refractive index of one of the materials is lower than a refractive index nfl and a refractive index of another of the materials is higher than the refractive index nfl; and forming the multilayer coating films (13, 14, 15) on end surfaces on the basis of each film thickness obtained by matching a minimum value Rmin at a wavelength λmin of the multilayer coating films (13, 14, 15) with a minimum reflectance R0, by making, equal to each other, the characteristic matrix of the single-layer coating film (12) having a film thickness of λ0 / 4 / nfl 1, and a characteristic matrix of the multilayer coating films (13, 14, 15), using at least two types of materials for which a refractive index of one of the materials is lower than a refractive index nfl 1 and a refractive index of the other of the materials is higher than the refractive index nfl 1.

Description

Optical semiconductor device manufacturing method and low reflectance film design method

[0001] The present disclosure relates to a method for manufacturing an optical semiconductor device and a method for designing a low-reflectivity film.

[0002] As disclosed in Non-Patent Document 1, the effective refractive index n c (=3.6, GaAs) is applied to the output end face of the optical semiconductor device. f When a coating film of (=1.72, Al2O3) is provided, the reflectance of the coating film changes periodically with respect to the film thickness, and the film thickness d f is λ0 / (4n f The reflectance becomes a minimum value when the reflectance is an integer multiple of R0. The minimum reflectance R0 at this time is expressed by the following equation (1) and is uniquely determined.

[0003] In other words, the minimum reflectance R for the wavelength λ is the effective refractive index n c and the refractive index n of the coating film provided on the light-emitting end face (front end face) of the optical semiconductor device. f The minimum reflectance R0 was determined uniquely by the formula:

[0004] For example, in a semiconductor laser device, when controlling the mirror loss calculated from the facet reflectivity and cavity length of the semiconductor laser device from the viewpoint of reducing the threshold current or improving efficiency, it has not been possible to change the value of the mirror loss to a desired value.

[0005] I. Ladany et. al. , “Al2O3 half-wave films for long-life cw lasers,” Appl. Phys. Lett. , vol. 30, no. 2, pp. 87-88, 1977

[0006] Conventional methods for manufacturing optical semiconductor devices and methods for designing low reflectance films have had the problem that the minimum reflectance R0 at a desired wavelength λ0 cannot be controlled to the desired minimum reflectance.

[0007] The present disclosure has been made to solve the above-mentioned problems, and aims to provide a method for manufacturing an optical semiconductor device having a low-reflectivity film that is controlled to a desired minimum reflectivity at a desired wavelength, by replacing a single-layer coating film with a multilayer coating film of three or more layers using a characteristic matrix, and to provide a method for designing a low-reflectivity film.

[0008] The method for manufacturing an optical semiconductor device according to the present disclosure includes: c and a method for manufacturing an optical semiconductor device having a low reflectance film formed thereon, the low reflectance film having a desired minimum reflectance R at a desired wavelength λ, wherein the refractive index n fl is expressed by the following formula,

[0009] The film thickness is λ0 / 4 / n fl and the refractive index of at least one material is the refractive index n fl and the refractive index of at least one other material is lower than the refractive index n fl By making the characteristic matrix of a multilayer coating film consisting of three or more coating films using two or more materials higher than min 0 The refractive index n of the coating film consisting of a single layer that realizes the preset reflectance R1 is calculated. fl 1 is expressed by the following formula,

[0010] The film thickness is λ0 / 4 / n fl 1 The refractive index of at least one material is the refractive index n fl 1 and the refractive index of at least one other material is lower than the refractive index n fl 1 By making the characteristic matrix of a multilayer coating film consisting of three or more coating films using two or more materials having a reflectance higher than min The minimum reflectance value R min is made to coincide with the minimum reflectance R0, and the wavelength λ minThe minimum value R min A multilayer coating film is formed on the end face based on the thicknesses of the three or more coating films obtained by matching the reflectance R0 at the wavelength λ0 with the minimum reflectance R0 at the wavelength λ0.

[0011] The method for designing a low-reflectivity film according to the present disclosure is to c A method for designing a low reflectance film having a minimum reflectance R0, which is a desired minimum reflectance other than zero, on an end face of an optical semiconductor device having a refractive index n fl The refractive index n fl and calculating

[0012] At the desired wavelength λ0, the film thickness is λ0 / 4 / n fl and the refractive index of at least one material is the refractive index n fl and the refractive index of at least one other material is lower than the refractive index n fl By making the characteristic matrix of a multilayer coating film consisting of three or more coating films using two or more materials higher than min 0 and calculating the refractive index n of a coating film consisting of a single layer that realizes a preset set reflectance R1. fl 1 using the following formula:

[0013] The film thickness is λ0 / 4 / n fl 1 The refractive index of at least one material is the refractive index n fl 1 and the refractive index of at least one other material is lower than the refractive index n fl 1 By making the characteristic matrix of a multilayer coating film consisting of three or more coating films using two or more materials having a reflectance higher than min The minimum reflectance value R min to coincide with the minimum reflectance R0; and minThe minimum value R min and determining each thickness of the multilayer coating film based on each thickness of the three or more coating films obtained by matching

[0014] According to the method for manufacturing an optical semiconductor device and the method for designing a low-reflectivity film of the present disclosure, by replacing a single-layer coating film with a multilayer coating film of three or more layers using a characteristic matrix, it becomes possible to manufacture an optical semiconductor device having a low-reflectivity film that is controlled to a desired minimum reflectivity at a desired wavelength, and it also becomes possible to obtain a method for designing a low-reflectivity film.

[0015] FIG. 1 is a schematic view of a quantum cascade laser device which is an example of an optical semiconductor device according to the first embodiment. FIG. 2 is a cross-sectional view taken along line A-A in FIG. 1 of the quantum cascade laser device which is an example of an optical semiconductor device according to the first embodiment. FIG. 3 is a schematic view for explaining a method for designing a low reflectance film having an extremely small reflectance of the optical semiconductor device according to the first embodiment. FIG. 4 is a graph showing the wavelength dependence of the reflectance of a low reflectance film designed by the method for designing a low reflectance film having an extremely small reflectance of the optical semiconductor device according to the first embodiment. FIG. 5 is a schematic view for explaining a method for designing a low reflectance film having an extremely small reflectance of the optical semiconductor device according to the first embodiment. FIG. 6 is a schematic view for explaining a method for designing a low reflectance film having an extremely small reflectance of the optical semiconductor device according to the second embodiment. FIG. 7 is a graph showing the wavelength dependence of the reflectance of a low reflectance film designed by the method for designing a low reflectance film having an extremely small reflectance of the optical semiconductor device according to the second embodiment. FIG. 1 is a schematic diagram for explaining a design method for a low-reflectivity film having a minimum reflectivity of an optical semiconductor device according to embodiment 2. FIG. 2 is a diagram showing the wavelength dependence of the reflectivity of a low-reflectivity film designed by the design method for a low-reflectivity film having a minimum reflectivity of an optical semiconductor device according to embodiment 2. FIG. 3 is a schematic diagram for explaining a design method for a low-reflectivity film having a minimum reflectivity of an optical semiconductor device according to embodiment 3. FIG. 4 is a diagram showing the wavelength dependence of the reflectivity of a low-reflectivity film designed by the design method for a low-reflectivity film having a minimum reflectivity of an optical semiconductor device according to embodiment 3. FIG. 5 is a schematic diagram for explaining a design method for a low-reflectivity film having a minimum reflectivity of an optical semiconductor device according to embodiment 4. FIG. 6 is a diagram showing the wavelength dependence of the reflectivity of a low-reflectivity film designed by the design method for a low-reflectivity film having a minimum reflectivity of an optical semiconductor device according to embodiment 4.10 is a schematic diagram for explaining a method for designing a low-reflectivity film having a minimum reflectivity of an optical semiconductor device according to Embodiment 4. FIG. 11 is a diagram showing the wavelength dependency of the reflectivity of a low-reflectivity film designed by the method for designing a low-reflectivity film having a minimum reflectivity of an optical semiconductor device according to Embodiment 4.

[0016] 1 is a schematic diagram showing a quantum cascade laser device 100, which is an example of an optical semiconductor device according to a first embodiment. The quantum cascade laser device 100 according to the first embodiment includes an n-type first electrode 1, an n-type InP substrate 2, an n-type InP buffer layer 3, an n-type GaInAs first optical confinement layer 4, a core region 5 consisting of 30 to 40 stages, an n-type GaInAs second optical confinement layer 6, an n-type InP cladding layer 7, an n-type GaInAs contact layer 8, and an n-type second electrode 9. Hereinafter, the quantum cascade laser device 100 may also be referred to as an optical semiconductor device 11.

[0017] The first stage of the core region 5 has a multi-quantum well (MQW) structure in which many GaInAs well layers and AlInAs barrier layers are stacked, and the oscillation wavelength is mid-infrared light in the range of 3 to 24 μm. Note that the low-reflectivity film 10 provided on the front end facet is not shown in FIG.

[0018] Figure 2 is a cross-sectional view of quantum cascade laser device 100 taken along line A-A in Figure 1. The emission end face of quantum cascade laser device 100 is provided with low-reflectivity film 10, which is made up of multiple coating films (hereinafter referred to as a multilayer coating film) and has a minimum reflectivity at wavelength λ0.

[0019] The effective refractive index is n c The optical semiconductor device 11 has a refractive index of n f and the film thickness is λ0 / (4n f ), the reflectance of the single-layer coating film becomes the minimum reflectance R0, which is expressed by the above-mentioned formula (1).

[0020] Conversely, from equation (1), the refractive index n of the coating film to realize the desired minimum reflectance R0 is fl , and the refractive index nfh is calculated using the following formula (2).

[0021]

[0022] For example, the effective refractive index n c is 3.2 and the minimum reflectance R = 0.005 (0.5%), the refractive index n fl and refractive index n fh are calculated to be 1.666535 and 1.920152, respectively. However, there are currently no materials that constitute the coating film that have these refractive index values ​​and are applicable to optical semiconductor devices. Therefore, in the present disclosure, the above-mentioned refractive index values ​​are achieved by substituting known materials.

[0023] First, the refractive index n fl The case where the refractive index of the single-layer coating film is n fl and a material with a refractive index lower than n fl Consider replacing the material with a three-layer coating of two materials, one of which has a higher refractive index than the other.

[0024] FIG. 3 shows the refractive index n fl and the film thickness d fl is λ0 / (4n fl 3 is a schematic diagram showing a case where the single-layer coating film 12 having an effective refractive index n1 and a thickness d1, a three-layer coating film having an effective refractive index n2 and a thickness d2, and a three-layer coating film having an effective refractive index n1 and a thickness d3. c The refractive index n fl (=1.66535) and the film thickness d fl =λ / (4n fl ) is replaced with a three-layer coating film consisting of a first coating film 13 with a refractive index n1 and a thickness d1, a second coating film 14 with a refractive index n2 and a thickness d2, and a third coating film 15 with a refractive index n1 and a thickness d3. If the single-layer coating film 12 can be replaced with a three-layer coating film, the characteristic matrices of both will be equal, as expressed by the following equation (3).

[0025] The phase terms φ1, φ2, and φ3 of the coating films in equation (3) are expressed by the following equation (4).

[0026]

[0027] In equation (3), the refractive indexes n1 and n2 are known, so there are three unknowns: film thicknesses d1, d2, and d3. Each film thickness can be calculated by solving equation (3).

[0028] The wavelength λ0 is 10 μm, and the first coating film 13 and the third coating film 15 have a refractive index of n fl YF3 having a refractive index n1 = 1.40 lower than that of the second coating film 14 is used. fl Taking ZnS, which has a refractive index n2 = 2.20 higher than that of ZnS, as an example, solving equation (3) gives the thicknesses of the coating films d1 = 654.371 nm, d2 = 277.806 nm, and d3 = 654.371 nm, respectively. The wavelength dependency of the reflectance in this case is shown by the dashed-dotted line 22 in Figure 4. The reflectance is 0.5% at a wavelength of 10 μm, but this value is not the minimum value, but the minimum value R of the reflectance of the three-layer coating film. min 0 In the present disclosure, R min and R min 0 The meanings of (1) R are as follows: min : The minimum reflectance of the multilayer coating film when the set reflectance R1 of the single-layer coating film is replaced with the multilayer coating film (2) R min 0 : The minimum reflectance of a multilayer coating film when the desired minimum reflectance R of a single-layer coating film is replaced with a multilayer coating film

[0029] The minimum reflectance R of the single-layer coating film is 0.5%, while the minimum reflectance R of the triple-layer coating film is min 0 The minimum reflectance R of the triple-layer coating film is 0.4857%, which is lower than the minimum reflectance R of the single-layer coating film. min In order to achieve the desired minimum reflectance R0, the set reflectance R1 is set high. The target of the reflectance increment ΔR0 is R0 - R min 0= 0.0143%, and adjust the increment ΔR0 until it matches the desired minimum reflectance R0. In the first embodiment, the increment ΔR0 = 0.0146%, and the set reflectance R1 is 0.51460%. From the following equation (5), the refractive index n of the single-layer coating film to achieve the set reflectance R1 = 0.51460% is fl 1 is calculated as 1.6648189.

[0030]

[0031] That is, from the formula (5), the refractive index n of the single-layer coating film to realize R1 = 0.51460% is fl 1 The thickness of each coating film is calculated by solving the following equation (6): d1 = 655.839 nm, d2 = 276.062 nm, d3 = 655.839 nm.

[0032]

[0033] The wavelength dependency of the reflectance in this case is shown by the two-dot chain line 23 in Figure 4. The minimum value R of the reflectance of the three-layer coating film min is the wavelength λ min = 9.876 μm, the desired minimum reflectance of 0.5% can be obtained.

[0034] Next, the wavelength λ at which the reflectance becomes minimum min is set to the desired wavelength λ0. The thickness of each coating film is set to λ0 / λ min Multiplying this by 1, we get d = 664.074 nm, d = 279.528 nm, and d = 664.074 nm. The wavelength dependency of reflectance in this case is shown by the solid line 24 in Figure 4. It can be seen that the reflectance reaches a minimum of 0.5% at a wavelength λ = 10 μm.

[0035] The broken line 21 in FIG. fl The film thickness is λ0 / (4n fl 4 shows the wavelength dependence of reflectance for a single-layer coating film having a reflectance of 0.015 μm / cm. The solid line 24 and the dashed line 21 in FIG. 4 do not perfectly coincide, but they show almost the same wavelength dependence of reflectance, and the minimum reflectance and the wavelength at which the minimum reflectance occurs are completely coincident.

[0036] The minimum reflectance R0 = 0.5% and the wavelength λ0 = 10 μm are merely examples, and are not limited to these and can be set to desired values. In the above example, YF3 is used for the first coating film 13 and the third coating film 15, and ZnS is used for the second coating film 14, but the present invention is not limited to these and any other suitable material may be used, such as a material having a refractive index of n fl and n fl 1 and one or more materials with refractive indexes higher than n fl and n fl 1 The refractive index of the material can be determined by the refractive index of the material.

[0037] FIG. 5 shows the refractive index n fl The film thickness is λ0 / (4n fl 5 is a schematic diagram showing a method of replacing a single-layer coating film having a refractive index n fl The film thickness λ0 / (4n fl ) and shows a minimum reflectance R0 at wavelength λ0.

[0038] The above-mentioned replacement method will be explained below. (1) In order to replace the single-layer coating film (broken line 21a) with a three-layer coating film, the thickness of each of the three-layer coating films is determined so that the characteristic matrices of both are equal. In this case, the minimum reflectance R0 occurs at wavelength λ0, but the value of the minimum reflectance of the three-layer coating film (minimum value R min 0 ) and the wavelength at which the minimum reflectance is reached (λ min ) deviates. The wavelength dependency of the reflectance in this case is represented by the dashed line 22a in Figure 5. (2) The set reflectance R1 of the single-layer coating film is set as R1 = R0 + ΔR0 (broken line 21b), and the thicknesses of the three-layer coating film that make the characteristic matrices equal are calculated, and the wavelength λ min The minimum reflectance value R of the three-layer coating film is desired to have a minimum reflectance. min = minimum reflectance R0. In other words, the minimum value R minThe minimum reflectance R1 of the single-layer coating is set to R0 + ΔR0 so that R0 coincides with the desired minimum reflectance R0. The wavelength dependency of the reflectance in this case is represented by the two-dot chain line 23a in Figure 5. (3) The thicknesses of the three-layer coating are set to λ0 / λ0 so that the minimum reflectance R0 is obtained at wavelength λ0. min The wavelength dependency of the reflectance in this case is represented by a solid line 24a in FIG.

[0039] The method for setting the set reflectance R1 will be described in more detail below. The minimum reflectance of the three-layer coating film at the time of the initial substitution is R min 0(0) If R0 is not satisfied, the difference ΔR0 from the desired reflectance R0 at this time is (0) is ΔR (0) = R0 - R min 0(0) Next, the set reflectance R of the single-layer coating film for the first loop is (1) , R1 (1) = R0 + ΔR0 (0) and replaced with a three-layer coating film to achieve the minimum reflectance R min 0(1) As a result of the calculation, R min 0(1) If ΔR0 = ΔR0, the calculation ends here. (0) , R1=R1 (1) This becomes:

[0040] R min 0(1) If R0, the process moves to the second loop. The difference ΔR0 from the desired reflectance R0 at this time (1) is ΔR (1) = R0 - R min 0(1) The set reflectance R1 of the single-layer coating film (2) , R1 (2) = R0 + ΔR0 (1) and replaced with a three-layer coating film to achieve the minimum reflectance R min 0(2) Calculate.

[0041] As a result of the calculation, R min 0(2) If ΔR0 = ΔR0, the calculation ends here. (1) , R1=R1 (2) It becomes. Rmin 0(2) If R0, the process moves to the third loop and the calculation is repeated in the same way. min 0(k) By looping k times until the set reflectance R1 = R1 (k) The above is the method for setting the set reflectance R1.

[0042] Similarly, the refractive index n fh The case where the refractive index of the single-layer coating film is n fh and a material with a refractive index lower than n fh Consider replacing the material with a triple coating of at least two materials with a higher refractive index than the material ...

[0043] FIG. 6 shows the refractive index n fh and the film thickness d fh is λ0 / (4n fh 6 is a schematic diagram showing a case where a single-layer coating film 31 having an effective refractive index n1 and a thickness d1, a three-layer coating film having an effective refractive index n2 and a thickness d2, and a three-layer coating film having an effective refractive index n1 and a thickness d3, respectively. c The refractive index n fh (=1.920152) and the film thickness d fh =λ / (4n fh The single-layer coating film 31 having a refractive index of n1 and a thickness of d1 is replaced with a three-layer coating film consisting of a first coating film 32 having a refractive index of n2 and a thickness of d2, a second coating film 33 having a refractive index of n1 and a thickness of d2, and a third coating film 34 having a refractive index of n1 and a thickness of d3. fl This is the same as in the case of (1), and is performed by solving the following equation (7).

[0044]

[0045] The wavelength λ0 is 10 μm, and the first coating film 32 and the third coating film 34 have a refractive index of n fh The second coating film 33 is made of YF3 having a refractive index n1 = 1.40, which is lower than that of the first coating film 33. fhTaking ZnS, which has a refractive index n = 2.20 higher than that of ZnS, as an example, solving equation (7) gives d = 434.257 nm, d = 547.934 nm, and d = 434.257 nm, respectively. The wavelength dependency of reflectance in this case is shown by the dashed-dotted line 36 in Figure 7. The reflectance is 0.5% at a wavelength of 10 μm, but this value is not the minimum value, but the minimum value R of the reflectance of the three-layer coating film. min 0 is 0.4715%.

[0046] The minimum reflectance R of the single-layer coating film is 0.5%, while the minimum reflectance R of the triple-layer coating film is min 0 is 0.4715%, which is lower than the minimum reflectance R of the single-layer coating film. fl As in the case of min In order to achieve the desired minimum reflectance R0, the set reflectance R1 is set high at 0.53032%. From the following formula (8), the refractive index n of the single-layer coating film to achieve the set reflectance R1 = 0.53032% is fh 1 is calculated as 1.9243333.

[0047] The thickness of each coating film is calculated by solving the following equation (9): d1 = 430.513 nm, d2 = 552.699 nm, d3 = 430.513 nm.

[0048]

[0049] The wavelength dependency of the reflectance in this case is shown by the two-dot chain line 37 in Figure 7. The minimum value R of the reflectance of the three-layer coating film min is the wavelength λ min = 10.174 μm, the desired minimum reflectance of 0.5% can be obtained.

[0050] Next, the wavelength λ at which the reflectance becomes minimum min is set to the desired wavelength λ0. The thickness of each of the three coating layers is set to λ0 / λ minMultiplying these values, we get d = 423.150 nm, d = 543.247 nm, and d = 423.150 nm. The wavelength dependency of reflectance in this case is shown by the solid line 38 in Figure 7. It can be seen that the reflectance reaches a minimum of 0.5% at a wavelength λ = 10 μm.

[0051] The broken line 35 in FIG. fh The film thickness is λ0 / (4n fh 7 shows the wavelength dependence of reflectance for a single-layer coating film having a reflectance of 0.015 μm / cm2 (where 0.015 μm / cm2) and a reflectance of 0.015 μm / cm2 (where 0.015 μm / cm2) are shown. Although the solid line 38 and the dashed line 35 in FIG. 7 do not perfectly coincide, they show almost the same wavelength dependence of reflectance, and the minimum reflectance and the wavelength at which the minimum reflectance is obtained are completely coincident.

[0052] The minimum reflectance R0 = 0.5% and the wavelength λ0 = 10 μm are merely examples, and are not limited to these, and can be set to desired values. In the above example, YF3 is used for the first coating film 32 and the third coating film 34, and ZnS is used for the second coating film 33, but the present invention is not limited to these, and any other suitable material may be used, such as a material having a refractive index of n fh and n fh 1 and one or more materials with refractive indexes higher than n fh and n fh 1 As a result, it is possible to realize a desired minimum reflectance at a desired wavelength using a material with a known refractive index.

[0053] Effect of First Embodiment As described above, according to the method for manufacturing an optical semiconductor device and the method for designing a low-reflectivity film according to the first embodiment, by replacing a single-layer coating film with a three-layer multilayer coating film by utilizing a characteristic matrix, it is possible to manufacture an optical semiconductor device having a low-reflectivity film that is controlled to a desired minimum reflectivity at a desired wavelength, and also to obtain a method for designing a low-reflectivity film.

[0054] The above-described method for manufacturing an optical semiconductor device utilizes the concept of the above-described method for designing a low-reflectivity film, and it does not matter if the coating films of the multilayer coating film do not strictly match during manufacturing. In other words, the present disclosure includes a method for manufacturing a low-reflectivity film designed by the following method and provided on an optical semiconductor device.

[0055] First, to obtain a desired minimum reflectance (R0) at a desired wavelength (λ0), a single-layer coating film that provides the desired minimum reflectance (R0) is replaced with a multilayer coating film, and the minimum value of the reflectance (R0) of the multilayer coating film is obtained. min 0 ) and the wavelength at which the minimum reflectance is reached (λ min Next, the minimum value of the reflectance of the multilayer coating film (R min The minimum reflectance R of the single-layer coating is set to R + ΔR so that the reflectance R coincides with the desired minimum reflectance (R). Furthermore, the thickness of each layer of the multilayer coating is calculated so that the desired minimum reflectance (R) is obtained at the desired wavelength (λ).

[0056] Second Embodiment The minimum reflectance R0 can be set to a desired value. In the method for manufacturing an optical semiconductor device and the method for designing a low reflectance film according to the second embodiment, an example of the minimum reflectance R0 = 0.01 (1%) is shown. The effective refractive index n c If we set the value to 3.2, then from the above equation (2), n fl and n fh are calculated to be 1.618080 and 1.977653, respectively.

[0057] First, the refractive index n fl = 1.618080. At least one single layer coating film has a refractive index n fl and at least one of the materials has a refractive index n fl Consider replacing the film with a three-layer coating of three materials, each of which has a higher refractive index than the other.

[0058] FIG. 8 shows the refractive index n fl and the film thickness d fl is λ0 / (4n fl 8 is a schematic diagram showing a case where a single-layer coating film 41 having an effective refractive index n1 and a thickness d1, a three-layer coating film having an effective refractive index n2 and a thickness d2, and a three-layer coating film having an effective refractive index n3 and a thickness d3. c The refractive index n fl (=1.618080) and the film thickness d fl =λ / (4n fl) is replaced with a three-layer coating film consisting of a first coating film 42 with a refractive index n and a thickness d, a second coating film 43 with a refractive index n and a thickness d, and a third coating film 44 with a refractive index n and a thickness d. If the single-layer coating film 41 can be replaced with a three-layer coating film, the characteristic matrices of both will be equal, as expressed by the following equation (10):

[0059] In equation (10), the phase terms φ1, φ2, and φ3 of each coating film are expressed as the following equation (11).

[0060]

[0061] In equation (10), the refractive indexes n1, n2, and n3 are known, so there are three unknowns: film thicknesses d1, d2, and d3. By solving equation (10), the film thickness of each coating film can be calculated.

[0062] The wavelength λ0 is 10 μm, and the refractive index of the first coating film 42 is n fl The second coating film 43 is YF3 having a refractive index n1 = 1.40 lower than that of the first coating film 42. fl The third coating film 44 is made of ZnS having a refractive index n = 2.20, which is higher than that of the first coating film 41. fl When equation (10) is solved using CeF3 with n3 = 1.45, which is lower than the above, as an example, the thicknesses of the coating films are d1 = 640.642 nm, d2 = 206.894 nm, and d3 = 763.646 nm. The wavelength dependency of the reflectance in this case is shown by the dashed-dotted line 46 in Figure 9. The reflectance is 1.0% at a wavelength of 10 μm, but this value is not the minimum value, but the minimum value R of the reflectance of the three-layer coating film. min 0 is 0.9836%.

[0063] The minimum reflectance R of the single-layer coating film is 1.0%, while the minimum reflectance R of the triple-layer coating film is min 0 The minimum reflectance R of the single-layer coating film is 0.9836%, which is lower than the minimum reflectance R of the single-layer coating film. min In order to achieve the desired minimum reflectance R0, the set reflectance R1 is set to a high value of 1.01648%. In this case, from equation (5), n fl 1The film thickness of each coating film is calculated by solving the following equation (12): d1 = 641.123 nm, d2 = 205.474 nm, d3 = 765.332 nm.

[0064]

[0065] The wavelength dependency of the reflectance in this case is shown by the two-dot chain line 47 in Figure 9. The minimum value R of the reflectance of the three-layer coating film min is the wavelength λ min = 9.864 μm, the desired minimum reflectance of 1.0% can be obtained.

[0066] Next, the wavelength λ at which the reflectance becomes minimum min is set to the desired wavelength λ0. Each film thickness is set to λ0 / λ min Multiplying by 1, we get d1 = 649.962 nm, d2 = 208.307 nm, and d3 = 775.884 nm. The wavelength dependency of the reflectance in this case is shown by the solid line 48 in FIG. 9. It can be seen that the reflectance reaches a minimum of 1.0% at the wavelength λ0. The broken line 45 in FIG. 9 indicates the refractive index n fl The film thickness is λ0 / (4n fl 9 shows the wavelength dependence of reflectance for a single-layer coating film having a reflectance of 0.015 μm / cm. The solid line 48 and the dashed line 45 in FIG. 9 show almost the same wavelength dependence of reflectance, and the minimum reflectance and the wavelength at which the minimum reflectance occurs are completely the same.

[0067] The minimum reflectance R0 = 1.0% and the wavelength λ0 = 10 μm are examples, and are not limited to these, and can be set to desired values. Also, although YF3 was used for the first coating film 42, ZnS for the second coating film 43, and CeF3 for the third coating film 44, the present invention is not limited to these, and the refractive index may be set to any value other than n fl and n fl 1 and one or more materials with refractive indexes higher than n fl and n fl 1 The refractive index of the material can be determined by the refractive index of the material.

[0068] Similarly, n fh= 1.977653. At least one single-layer coating film has a refractive index n fh and at least one of the materials has a refractive index n fh Consider a three-layer coating of three materials, each of which has a higher refractive index than the other.

[0069] FIG. 10 shows the refractive index n fh and the film thickness d fh is λ0 / (4n fh 10 is a schematic diagram showing a case where the single-layer coating film 49 having an effective refractive index n1 and a thickness d1, a three-layer coating film having an effective refractive index n2 and a thickness d2, and a three-layer coating film having an effective refractive index n3 and a thickness d3, respectively. c The refractive index n fh (=1.977653) and the film thickness d fh =λ / (4n fh ) is replaced with a three-layer coating film consisting of a first coating film 50 with a refractive index n and a thickness d, a second coating film 51 with a refractive index n and a thickness d, and a third coating film 52 with a refractive index n and a thickness d. The method for replacing the single-layer coating film with the three-layer coating film is the same as in the case of the low refractive index described above, and is performed by solving the following equation (13).

[0070]

[0071] The wavelength λ0 is 10 μm, and the refractive index of the first coating film 50 is n fl The second coating film 51 is YF3 having a refractive index n1 = 1.40, which is lower than that of the first coating film 51. fl The third coating film 52 is made of ZnS having a refractive index n = 2.20, which is higher than that of the first coating film 51. fl Taking CeF3, which has n3 = 1.45, as an example, solving equation (13) gives d1 = 370.115 nm, d2 = 607.246 nm, and d3 = 395.897 nm, respectively. The wavelength dependency of reflectance in this case is shown by the dashed line 54 in Figure 11. The reflectance is 1.0% at a wavelength of 10 μm, but this value is not the minimum value, but the minimum value R of the reflectance of the three-layer coating film. min 0 is 0.94561%.

[0072] The minimum reflectance R of the single-layer coating film is 1.0%, while the minimum reflectance R of the triple-layer coating film is min 0 The minimum reflectance R of the single-layer coating film is 0.94561%, which is lower than the minimum reflectance R of the single-layer coating film. min In order to achieve the desired minimum reflectance R0, the set reflectance R1 is set as high as 1.057485%. The refractive index n of the single-layer coating film to achieve the set reflectance R1 = 1.057485% is fh 1 is obtained from equation (8) as fh 1 When the thickness of each coating film is calculated by solving the following equation (14), the thicknesses are calculated as d1 = 364.825 nm, d2 = 614.601 nm, and d3 = 390.009 nm, respectively.

[0073]

[0074] The wavelength dependency of the reflectance in this case is shown by the two-dot chain line 55 in Figure 11. The minimum value R of the reflectance of the three-layer coating film min is the wavelength λ min = 10.243 μm, the desired minimum reflectance of 1.0% can be obtained.

[0075] Next, the wavelength λ at which the reflectance becomes minimum min is set to the desired wavelength λ0. The thickness of each coating film is set to λ0 / λ min Multiplying these values, we get d = 356.170 nm, d = 600.021 nm, and d = 380.757 nm. The wavelength dependency of reflectance in this case is shown by the solid line 56 in Figure 11. It can be seen that the reflectance reaches a minimum of 1.0% at wavelength λ.

[0076] The broken line 53 in FIG. 11 indicates the refractive index n fh The film thickness is λ0 / (4n fh 11 shows the wavelength dependence of reflectance for a single-layer coating film having a reflectance of 0.015 μm / cm2 (where 0.015 μm / cm2) and a reflectance of 0.015 μm / cm2 (where 0.015 μm / cm2) are shown. Although the solid line 56 and the dashed line 53 in FIG. 11 do not perfectly coincide, they show almost the same wavelength dependence of reflectance, and the minimum reflectance and the wavelength at which the minimum reflectance occurs are completely coincident.

[0077] The minimum reflectance R0 = 1.0% and the wavelength λ0 = 10 μm are examples, and are not limited to these, and can be set to desired values. Also, although YF3 was used for the first coating film 50, ZnS for the second coating film 51, and CeF3 for the third coating film 52, the present invention is not limited to these, and any other suitable material may be used as long as the refractive index is n fh and n fh 1 and one or more materials with refractive index higher than n fh and n fh 1 The refractive index of the material can be determined by the refractive index of the material.

[0078] Effect of Second Embodiment As described above, according to the method for manufacturing an optical semiconductor device and the method for designing a low-reflectivity film according to the second embodiment, by replacing a single-layer coating film with a three-layer multilayer coating film by utilizing a characteristic matrix, it is possible to manufacture an optical semiconductor device having a low-reflectivity film that is controlled to a desired minimum reflectivity at a desired wavelength, and also to obtain a method for designing a low-reflectivity film.

[0079] The above-described method for manufacturing an optical semiconductor device utilizes the concept of the above-described design method for a low-reflectivity film, and it does not matter if the coating films of the multilayer coating film do not strictly match during manufacturing. In other words, the present disclosure includes a method for manufacturing a low-reflectivity film designed by the design method of the second embodiment and provided in an optical semiconductor device.

[0080] Embodiment 3 In embodiment 3, a method for realizing a desired minimum reflectance at a desired wavelength using four or more materials with different refractive indices will be described. As an example of a multilayer coating film made of four or more materials, a five-layer coating film will be described.

[0081] In the third embodiment, the minimum reflectance R0 = 0.01 (1%) is taken as an example. c If the refractive index is 3.2, then from equation (2), fl and refractive index n fh are calculated to be 1.618080 and 1.977653, respectively.

[0082] First, the refractive index n fl = 1.618080. At least one single layer coating film has a refractive index n fl and at least one of the materials has a refractive index n fl Consider a five-layer coating of five materials, each of which has a higher refractive index than the other.

[0083] FIG. 12 shows the refractive index n fl and the film thickness d fl is λ0 / (4n fl 12 is a schematic diagram showing a case where a single-layer coating film 41 having an effective refractive index n1 and a thickness d1, a refractive index n2 and a thickness d2, a refractive index n3 and a thickness d3, a refractive index n4 and a thickness d4, and a refractive index n5 and a thickness d5 is replaced with a five-layer coating film having an effective refractive index n c The refractive index n fl and the film thickness d fl is λ0 / (4n fl ) is replaced with a five-layer coating film consisting of a first coating film 61 with a refractive index n and a thickness d, a second coating film 62 with a refractive index n and a thickness d, a third coating film 63 with a refractive index n and a thickness d, a fourth coating film 64 with a refractive index n and a thickness d, and a fifth coating film 65 with a refractive index n and a thickness d. If the single-layer coating film can be replaced with a five-layer coating film, the characteristic matrices of both will be equal, as expressed by the following equation (15).

[0084] The phase terms φ1, φ2, φ3, φ4, and φ5 of the coating films in equation (15) are expressed by the following equation (16).

[0085]

[0086] However, since the number of unknowns calculated from Equation (15) is limited to three, the film thicknesses of two of the five materials are set to predetermined film thicknesses. Here, as an example, the film thicknesses d1 and d2 of the first coating film 61 and the second coating film 62 are set to predetermined film thicknesses.

[0087] The wavelength λ0 is 10 μm, and the refractive index of the first coating film 61 is n fl The second coating film 62 has a refractive index nfl The third coating film 63 is made of ZnS having a refractive index n = 2.20 and a film thickness d = 100 nm, which is higher than the refractive index n fl YF3 has a refractive index of n3 = 1.40 and a film thickness of d3, which is lower than the refractive index of the fourth coating film 64. fl ZnSe has a refractive index n4 = 2.41 and a thickness d4, which is higher than the refractive index n fl When equation (15) is solved using CeF3 with n5 = 1.45 and film thickness d5, which is lower than n5 = 1.45, the film thicknesses of the coating films are d3 = 738.670 nm, d4 = 151.598 nm, and d5 = 333.010 nm, respectively.

[0088] The wavelength dependency of the reflectance in this case is shown by the dashed line 67 in Figure 13. The reflectance is 1.0% at a wavelength of 10 μm, but this value is not the minimum value, but the minimum value R min 0 is 0.998474%.

[0089] The minimum reflectance R of the single-layer coating film is 1.0%, while the minimum reflectance R of the five-layer coating film is min 0 The minimum reflectance R of the five-layer coating film is 0.998474%, which is lower than the minimum reflectance R of the single-layer coating film. min In order to achieve the desired minimum reflectance R0, the set reflectance R1 is set as high as 1.00153%. In this case, from equation (5), the refractive index n of the single-layer coating film to achieve the set reflectance R1 = 1.00153% is fl 1 The thickness of each coating film is calculated by solving the following equation (17), and the calculated values ​​are d3 = 738.955 nm, d4 = 151.533 nm, and d5 = 332.847 nm, respectively.

[0090]

[0091] The wavelength dependency of the reflectance in this case is shown by the two-dot chain line 68 in Figure 13. The minimum value R of the reflectance of the five-layer coating film min is the wavelength λ min = 10.040 μm, the desired minimum reflectance of 1.0% can be obtained.

[0092] Next, the wavelength λ at which the reflectance becomes minimum min is set to the desired wavelength λ0. The thickness of each coating film is set to λ0 / λ min Multiplying these values, the calculated values ​​are d1 = 199.203 nm, d2 = 99.602 nm, d3 = 736.011 nm, d4 = 150.929 nm, and d5 = 331.521 nm. Note that the first coating film 61 and the second coating film 62 also have a λ0 / λ min The wavelength dependency of the reflectance in this case is shown by a solid line 69 in Fig. 13. It can be seen that the reflectance reaches a minimum of 1.0% at a wavelength λ0 = 10 µm.

[0093] The broken line 66 in FIG. 13 indicates the refractive index n fl The film thickness is λ0 / (4n fl 13 shows the wavelength dependence of reflectance for a single-layer coating film having a reflectance of 0.015 μm / cm2 (where 0.015 μm / cm2) and a reflectance of 0.015 μm / cm2 (where 0.015 μm / cm2) are shown. Although the solid line 69 and the dashed line 66 in FIG. 13 do not perfectly match, they show almost the same wavelength dependence of reflectance, and the minimum reflectance and the wavelength at which the minimum reflectance is obtained are completely the same.

[0094] The minimum reflectance R0 = 1.0% and the wavelength λ0 = 10 μm are examples, and are not limited to these, and can be set to desired values. In the example described above, CeO2 was used for the first coating film 61, ZnS for the second coating film 62, YF3 for the third coating film 63, ZnSe for the fourth coating film 64, and CeF3 for the fifth coating film 65, but the present invention is not limited to these, and any other suitable materials may be used, such as those having a refractive index of n fl and n fl 1 and one or more materials with refractive indexes higher than n fl and n fl 1 It is sufficient to have one or more materials having a lower viscosity than the above, and the order of the materials can be selected arbitrarily.

[0095] In addition, the two coating films with preset thicknesses can also be arbitrarily selected from the five-layer coating film. In the third embodiment, a five-layer coating film is exemplified as an example of a coating film with four or more layers, but by performing the same procedure, a desired minimum reflectance at a desired wavelength can be achieved even with a multi-layer coating film.

[0096] Similarly, the refractive index n fh= 1.977653. At least one single-layer coating film has a refractive index n fh and at least one of the materials has a refractive index n fh Consider a five-layer coating of five materials, each of which has a higher refractive index than the other.

[0097] FIG. 14 shows the refractive index n fh and the film thickness d fh is λ0 / (4n fh 14 is a schematic diagram showing a case where a single-layer coating film 49 having an effective refractive index n1 and a thickness d1, a refractive index n2 and a thickness d2, a refractive index n3 and a thickness d3, a refractive index n4 and a thickness d4, and a refractive index n5 and a thickness d5 is replaced with a five-layer coating film having an effective refractive index n c The refractive index n fh (=1.977653) and the film thickness d fh =λ / (4n fh ) is replaced with a five-layer coating film consisting of a first coating film 71 with a refractive index n1 and a thickness d1, a second coating film 72 with a refractive index n2 and a thickness d2, a third coating film 73 with a refractive index n3 and a thickness d3, a fourth coating film 74 with a refractive index n4 and a thickness d4, and a fifth coating film 75 with a refractive index n5 and a thickness d5. The method for replacing the single-layer coating film with the five-layer coating film is the same as in the case of the low refractive index film described above, and is performed by solving the following equation (18).

[0098]

[0099] The wavelength λ0 is 10 μm, and the refractive index of the first coating film 71 is n fh The second coating film 72 has a refractive index n fh The third coating film 73 is made of ZnS having a refractive index n = 2.20 and a film thickness d = 100 nm, which is higher than the refractive index n fh YF3 has a refractive index of n3 = 1.40 and a film thickness of d3, which is lower than the refractive index of the fourth coating film 74. fh ZnSe has a refractive index n4 = 2.41 and a thickness d4, which is higher than the refractive index n4 of the fifth coating film 75. fhWhen equation (18) is solved using CeF3 with n5 = 1.45 and film thickness d5, which is lower than n5 = 1.45, the film thicknesses of the coating films are d3 = 282.491 nm, d4 = 387.869 nm, and d5 = 366.354 nm, respectively.

[0100] The wavelength dependency of the reflectance in this case is shown by the dashed line 77 in Figure 15. The reflectance is 1.0% at a wavelength of 10 μm, but this value is not the minimum value, but the minimum value R min 0 is 0.975517%.

[0101] The minimum reflectance R of the single-layer coating film is 1.0%, while the minimum value R of the five-layer coating film is min 0 The minimum reflectance R of the five-layer coating film is 0.975517%, which is lower than the minimum reflectance R of the single-layer coating film. min In order to achieve the desired minimum reflectance R0, the set reflectance R1 is set as high as 1.025357%. In this case, the refractive index n of the single-layer coating film to realize the set reflectance R1 = 1.025357% is fh 1 is obtained from equation (8) as fh 1 The film thickness of each coating film is calculated by solving the following equation (19): d3 = 280.332 nm, d4 = 389.708 nm, d5 = 365.369 nm.

[0102]

[0103] The wavelength dependency of the reflectance in this case is shown by the two-dot chain line 78 in Figure 15. The minimum value R of the five-layer coating film min is the wavelength λ min = 10.159 μm, the desired minimum reflectance of 1.0% can be obtained.

[0104] Next, the wavelength λ at which the reflectance becomes minimum min is set to the desired wavelength λ0. Each film thickness is set to λ0 / λ minBy multiplying these, the film thicknesses of the coating films are calculated as d1 = 196.870 nm, d2 = 98.435 nm, d3 = 275.944 nm, d4 = 383.609 nm, and d5 = 359.651 nm. Note that the first coating film 71 and the second coating film 72 also have a λ0 / λ min The wavelength dependency of the reflectance in this case is shown by a solid line 79 in Fig. 15. It can be seen that the reflectance reaches a minimum of 1.0% at a wavelength λ0 = 10 µm.

[0105] The broken line 76 in FIG. 15 indicates the refractive index n fh The film thickness is λ0 / (4n fh 15 shows the wavelength dependence of reflectance for the single-layer coating film 49. Although the solid line 79 and the dashed line 76 in FIG. 15 do not perfectly coincide with each other, they show almost the same wavelength dependence of reflectance, and the minimum reflectance and the wavelength at which the minimum reflectance is obtained are completely coincident.

[0106] The minimum reflectance R0 = 1.0% and the wavelength λ0 = 10 μm are examples, and are not limited to these, and can be set to desired values. Also, CeO2 was used for the first coating film 71, ZnS for the second coating film 72, YF3 for the third coating film 73, ZnSe for the fourth coating film 74, and CeF3 for the fifth coating film 75, but the present invention is not limited to these, and any other suitable material may be used as long as the refractive index is n fh and n fh 1 and one or more materials with refractive indexes higher than n fh and n fh 1 It is sufficient to have one or more materials having a lower viscosity than the above, and the order of the materials can be selected arbitrarily.

[0107] In addition, the two coating films with preset thicknesses can also be arbitrarily selected from the five-layer coating film. In the third embodiment, a five-layer coating film is exemplified as an example of a coating film with four or more layers, but by performing the same procedure, a desired minimum reflectance at a desired wavelength can be achieved even with a multi-layer coating film.

[0108] Effect of Third Embodiment As described above, according to the method for manufacturing an optical semiconductor device and the method for designing a low-reflectivity film according to the third embodiment, by replacing a single-layer coating film with a five-layer multilayer coating film by utilizing a characteristic matrix, it is possible to manufacture an optical semiconductor device having a low-reflectivity film that is controlled to a desired minimum reflectivity at a desired wavelength, and also to obtain a method for designing a low-reflectivity film.

[0109] The above-described method for manufacturing an optical semiconductor device utilizes the concept of the above-described design method for a low-reflectivity film, and it does not matter if the coating films of the multilayer coating film do not strictly match during manufacturing. In other words, the present disclosure includes a method for manufacturing a low-reflectivity film designed by the following design method and provided on an optical semiconductor device.

[0110] In the case of a multilayer coating film having more than three coating layers, the thickness of the excess coating layer is preset. Then, to obtain a desired minimum reflectance (R0) at a desired wavelength (λ0), the single-layer coating film that provides the desired minimum reflectance (R0) is replaced with a multilayer coating film, and the minimum reflectance (R0) of the multilayer coating film is calculated. min 0 ) and the wavelength at which the minimum reflectance is reached (λ min Next, the minimum value of the reflectance of the multilayer coating film (R min The minimum reflectance R of the single-layer coating is set to R + ΔR so that the reflectance R coincides with the desired minimum reflectance (R). Furthermore, the thickness of each layer of the multilayer coating is calculated so that the desired minimum reflectance (R) is obtained at the desired wavelength (λ).

[0111] Fourth Embodiment The mirror loss of an optical semiconductor device is defined by the following equation (20).

[0112]

[0113] In formula (20), R f , R r and L are the front facet reflectivity, the rear facet reflectivity, and the cavity length, respectively. In applications requiring a narrow band of mirror loss, it is necessary to narrow the band near the minimum reflectivity.

[0114] 16 is a schematic diagram showing a method for narrowing the band near the minimum reflectance, taking the minimum reflectance shown in the second embodiment (FIG. 8) as an example. As shown in FIG. 16, in the fourth embodiment, a and the film thickness d a is λ0 / (2n a ) is provided. The other coating films are the same as the coating films shown in FIG. 8 of the second embodiment. The characteristic matrix of the four-layer coating film of the fourth embodiment is expressed by the following equation (21).

[0115] In equation (21), the phase terms φ, φ, φ and φ of each coating are a is expressed by the following formula (22), and the thickness d a is expressed by the following equation (23).

[0116] The reflectance of the coating is given by the matrix element m 11 , m 12 , m 21 , m 22 Using the above, it is expressed by the following equation (24).

[0117]

[0118] An example of the material of the inserted coating film 81 is a material having a refractive index n a The thickness d of the coating film 81 is 1.70. a If the wavelength λ0 is 10 μm, a = λ / (2n a ) is set to 2941.176 nm.

[0119] In the second embodiment, the set reflectance R1 is set to 1.0165%, and equation (12) is solved to calculate the thicknesses of the coating films. The coating film 81 is inserted between the second and third coating films of a three-layer coating film consisting of d1 = 641.123 nm, d2 = 205.474 nm, and d3 = 765.332 nm. The wavelength dependency of the reflectance is shown by the dashed-dotted line 82 in Figure 17. min 0 is 0.9609%.

[0120] So, λmin In order to set the minimum reflectance R to 1.0%, the set reflectance R is set to 1.05761% and equation (12) is solved. The thicknesses of the coating films are calculated as d = 642.718 nm, d = 201.981 nm, and d = 769.510 nm, respectively. min = 9.908 μm, the minimum value R of the reflectance of the four-layer coating min = 1.0% (double-dashed line 83 in FIG. 17). At this time, the refractive index n a is 1.70, and the film thickness d a is 2941.176 nm.

[0121] Next, the thickness of each coating film is calculated as λ0 / λ min By multiplying the thickness of each coating film, d1 = 648.686 nm, d2 = 203.856 nm, and d a = 2968.486 nm, and d = 776.655 nm. The wavelength dependency of reflectance in this case is shown by a solid line 84 in Figure 17. It can be seen that the reflectance reaches a minimum of 1.0% at a wavelength λ = 10 μm.

[0122] For comparison, the wavelength dependence of the reflectance of the three-layer coating film of the second embodiment is shown by the dashed line 48 in Figure 17. It can be seen that the reflectance band is narrowed in the vicinity of the desired wavelength λ0.

[0123] Similarly, taking the minimum reflectance shown in the second embodiment (FIG. 10) as an example, when the refractive index is high (n fh ) a method for narrowing the band near the minimum reflectance will be described below.

[0124] 18 is a schematic diagram showing the structure of the coating film. In FIG. 18, the coating film 81 has a refractive index of n a and the film thickness d a is λ0 / (2n a The other coating films are the same as those in FIG. 10 of the second embodiment.

[0125] In the second embodiment, the set reflectance R1 is set to 1.057485%, and equation (14) is solved to calculate the thicknesses of the coating films, where d1 = 364.825 nm, d2 = 614.601 nm, and d3 = 390.009 nm. The wavelength dependency of the reflectance when the above-described coating film 81 is inserted between the second coating film 51 and the third coating film 52 of the three-layer coating film is shown by the dashed-dotted line 85 in Figure 19. The minimum value R of the reflectance of the four-layer coating film min 0 is 0.9950%.

[0126] Therefore, the wavelength λ min In order to set the minimum reflectance at wavelength λ to 1.0%, the set reflectance R is set to 1.0627% and equation (14) is solved. The thicknesses of the coating films are calculated as d = 364.348 nm, d = 615.265 nm, and d = 389.478 nm, respectively. min = 10. The minimum reflectance value R of the four-layer coating at 110 μm min = 1.0% (double-dashed line 86 in FIG. 19). At this time, the refractive index n a is 1.70, and the film thickness d a is 2941.176 nm.

[0127] Next, the thickness of each coating film is calculated as λ0 / λ min When multiplied, d1 = 360.384 nm, d2 = 608.571 nm, d a = 2909.175 nm, and d = 385.240 nm. The wavelength dependency of reflectance in this case is shown by a solid line 87 in Figure 19. It can be seen that the reflectance reaches a minimum of 1.0% at a wavelength λ = 10 μm.

[0128] For comparison, the wavelength dependency of the reflectance of the three-layer film of the second embodiment is shown by the dashed line 56 in Figure 19. It can be seen that the reflectance band is narrowed in the vicinity of the desired wavelength λ0.

[0129] In the fourth embodiment, the desired refractive index n a and the film thickness d a is λ0 / (2n a ), the thickness of the coating film 81 is λ0 / (4n a ) and 3λ0 / (4na ) it is possible to narrow the reflectance band.

[0130] In the fourth embodiment, the characteristic matrix of the three-layer coating film is solved to derive the film thickness of each coating film, and then the coating film is inserted to calculate the wavelength dependency of the reflectance, and the minimum value R of the reflectance of the four-layer coating film is calculated. min 0 is adjusted to the desired minimum reflectance R0, and then the desired minimum reflectance R0 is obtained at the desired wavelength λ0. However, as shown in the third embodiment, it is assumed in advance that there are four coating layers, and the thickness of the inserted coating layer is set to d a = λ / (2n a ) or d a = λ min / (2n a ) and then determine the thickness of each of the three coating layers.

[0131] Furthermore, in the fourth embodiment, between the second coating film and the third coating film, d a = λ / (2n a ) was inserted, but it may be inserted at other interfaces, for example, between the optical semiconductor device and the first coating film, between the first coating film and the second coating film, or between the third coating film and air (free space), or at multiple interfaces, such as between the optical semiconductor device and the first coating film and between the second coating film and the third coating film.

[0132] Effect of Fourth Embodiment As described above, according to the method for manufacturing an optical semiconductor device and the method for designing a low-reflectivity film according to the fourth embodiment, by replacing a single-layer coating film with a four-layer multilayer coating film by utilizing a characteristic matrix, it is possible to manufacture an optical semiconductor device having a low-reflectivity film that is controlled to a desired minimum reflectivity at a desired wavelength, and also to obtain a method for designing a low-reflectivity film.

[0133] The above-described method for manufacturing an optical semiconductor device utilizes the concept of the above-described design method for a low-reflectivity film, and it does not matter if the coating films of the multilayer coating film do not strictly match during manufacturing. In other words, the present disclosure includes a method for manufacturing a low-reflectivity film designed by the following design method and provided on an optical semiconductor device.

[0134] The desired wavelength is λ0 and the refractive index of the coating film to be inserted is n aIn this case, the thickness of the inserted coating film is set to λ0 / (4n a ) and 3λ0 / (4n a ) is preset in a range thinner than that. Then, in order to obtain a desired minimum reflectance (R0) at a desired wavelength (λ0), the single-layer coating film that provides the desired minimum reflectance (R0) is replaced with a multilayer coating film, and the minimum value of the reflectance (R0) of the multilayer coating film is obtained. min 0 ) and the wavelength at which the minimum reflectance is reached (λ min Next, the minimum value of the reflectance of the multilayer coating film (R min The minimum reflectance R of the single-layer coating is set to R + ΔR so that the reflectance R coincides with the desired minimum reflectance (R). Furthermore, the thickness of each layer of the multilayer coating is calculated so that the desired minimum reflectance (R) is obtained at the desired wavelength (λ).

[0135] In the first to fourth embodiments, the desired minimum reflectance R of 0.5% and 1.0% and the desired wavelength λ of 10 μm are merely examples, and are not limited to these. Similar designs can be made for other desired minimum reflectances and desired wavelengths.

[0136] In the first to fourth embodiments, the minimum value R of the reflectance of the multilayer coating film when replaced with the multilayer coating film min 0 is lower than the minimum reflectance R0 of the single-layer coating film, but even if it is higher, a desired minimum reflectance can be achieved at a desired wavelength in the same manner.

[0137] Although the present disclosure describes various exemplary embodiments and examples, the various features, aspects, and functions described in one or more embodiments are not limited to application to a particular embodiment, but may be applied to the embodiments alone or in various combinations.

[0138] Therefore, countless variations not illustrated are conceivable within the scope of the technology of the present disclosure, including, for example, cases where at least one component is modified, added, or omitted, and cases where at least one component is extracted and combined with a component of another embodiment.

[0139] 1 n-type first electrode, 2 n-type InP substrate, 3 n-type InP buffer layer, 4 n-type GaInAs first optical confinement layer, 5 core region, 6 n-type GaInAs second optical confinement layer, 7 n-type InP cladding layer, 8 n-type GaInAs contact layer, 9 n-type second electrode, 10 low-reflectivity film, 11 optical semiconductor device, 12, 31, 41, 49 single-layer coating film, 13, 32, 42, 50, 61, 71 first coating film, 14, 33, 43, 51, 62, 72 second coating film, 15, 34, 44, 52, 63, 73 third coating film, 21, 21a, 21b, 35, 45, 48, 53, 56, 66, 76 dashed line, 21a Dotted lines, 22, 22a, 36, 46, 54, 67, 77, 82, 85 One-dot chain lines, 23, 23a, 37, 47, 55, 68, 78, 83, 86 Two-dot chain lines, 24, 24a, 38, 48, 56, 69, 79, 84, 87 Solid lines, 64, 74 Fourth coating film, 65, 75 Fifth coating film, 81 Coating film, 100 Quantum cascade laser device

Claims

1. Effective refractive index is n c A method for manufacturing an optical semiconductor device having a low reflectance film formed thereon, the low reflectance film having a desired minimum reflectance R0 at a desired wavelength λ0, the refractive index n fl is expressed by the following formula, The film thickness is λ0 / 4 / n fl The characteristic matrix of the coating film consisting of a single layer is n fl and the refractive index of at least one other material is lower than said refractive index n fl By making the characteristic matrix of a multilayer coating film consisting of three or more coating films using two or more materials having a wavelength dependency higher than min 0 The refractive index n of the coating film consisting of a single layer that realizes the preset reflectance R1 is calculated. fl 1 is expressed by the following formula, The film thickness is λ0 / 4 / n fl 1 The characteristic matrix of the coating film consisting of a single layer of the material, and the refractive index of at least one material is the refractive index n fl 1 and the refractive index of at least one other material is lower than the refractive index n fl 1 By making the characteristic matrix of a multilayer coating film consisting of three or more coating films using two or more materials having a reflectance higher than min The minimum reflectance value R min is made to coincide with the minimum reflectance R0, and the wavelength λ min The minimum value R min and forming a multilayer coating film on the end face based on each film thickness of the three or more coating films obtained by matching the minimum reflectance R at the wavelength λ.

2. Effective refractive index is n c A method for manufacturing an optical semiconductor device having a low reflectance film formed thereon, the low reflectance film having a desired minimum reflectance R0 at a desired wavelength λ0, the refractive index n fh is expressed by the following formula, The film thickness is λ0 / 4 / n fh The characteristic matrix of the coating film consisting of a single layer is n fh and the refractive index of at least one other material is lower than the refractive index n fh By making the characteristic matrix of a multilayer coating film consisting of three or more coating films using two or more materials having a wavelength dependency higher than min 0 The refractive index n of the coating film consisting of a single layer that realizes the preset reflectance R1 is calculated. fh 1 is expressed by the following formula, The film thickness is λ0 / 4 / n fh 1 The characteristic matrix of the coating film consisting of a single layer of the material, and the refractive index of at least one material is the refractive index n fh 1 and the refractive index of at least one other material is lower than the refractive index n fh 1 By making the characteristic matrix of a multilayer coating film consisting of three or more coating films using two or more materials having a reflectance higher than min The minimum reflectance value R min is made to coincide with the minimum reflectance R0, and the wavelength λ min The minimum value R min and forming a multilayer coating film on the end face based on each film thickness of the three or more coating films obtained by matching the minimum reflectance R at the wavelength λ.

3. Refractive index is n fl and n fl 1 A coating film made of at least one material having a refractive index lower than n fl and n fl 1 2. The method for manufacturing an optical semiconductor device according to claim 1, further comprising forming a three-layer coating film on the end surface, the three-layer coating film including a coating film made of at least one other material having a higher resistivity than the end surface.

4. Refractive index is n fh and n fh 1 A coating film made of at least one material having a refractive index lower than n fh and n fh 1 3. The method for manufacturing an optical semiconductor device according to claim 2, further comprising forming a three-layer coating film on the end surface, the three-layer coating film including a coating film made of at least one other material having a higher resistivity than the end surface.

5. Refractive index is n fl and n fl 1 A coating film made of at least one material having a refractive index lower than n fl and n fl 1 2. The method for manufacturing an optical semiconductor device according to claim 1, further comprising forming a three-layer coating film made of three kinds of materials on the end surface, the three-layer coating film including a coating film made of at least one other material having a higher thermal conductivity than the end surface of the optical semiconductor device.

6. Refractive index is n fh and n fh 1 A coating film made of at least one material having a refractive index lower than n fh and n fh 1 3. The method for manufacturing an optical semiconductor device according to claim 2, further comprising forming a three-layer coating film made of three kinds of materials on the end surface, the three-layer coating film including a coating film made of at least one other material having a higher thermal conductivity than the end surface.

7. Refractive index is n fl and n fl 1 and at least one material having a refractive index lower than n fl and n fl 1 and forming a multilayer coating film on the end surface, the multilayer coating film including a three-layer coating film each composed of three of the four or more materials and a coating film having a predetermined thickness composed of a material other than the three materials.

8. Refractive index is n fh and n fh 1 and at least one material having a refractive index lower than n fh and n fh 1 and at least one other material having a higher thermal conductivity than the first material, and a multilayer coating film including a three-layer coating film composed of three of the four or more materials, and a coating film having a predetermined thickness composed of a material other than the three materials, is formed on the end surface.

9. Refractive index is n a and the film thickness is λ0 / (4n a ) thicker than 3λ0 / (4n a 9. The method for manufacturing an optical semiconductor device according to claim 3, further comprising providing a coating film thinner than the thickness of the multilayer coating film between the end face, between each coating film of the multilayer coating film, or on the outermost surface of the multilayer coating film.

10. Effective refractive index is n c A method for designing a low reflectance film having a minimum reflectance R0, which is a desired minimum reflectance other than zero, on an end face of an optical semiconductor device having a refractive index n fl The refractive index n fl and calculating At the desired wavelength λ0, the film thickness is λ0 / 4 / n fl The characteristic matrix of the coating film consisting of a single layer is n fl and the refractive index of at least one other material is lower than the refractive index n fl By making the characteristic matrix of a multilayer coating film consisting of three or more coating films using two or more materials having a wavelength dependency higher than min 0 A step of calculating a refractive index n of a coating film consisting of a single layer that realizes a preset reflectance R1. fl 1 using the following formula: The film thickness is λ0 / 4 / n fl 1 The characteristic matrix of the coating film consisting of a single layer of the material, and the refractive index of at least one material is the refractive index n fl 1 and the refractive index of at least one other material is lower than the refractive index n fl 1 By making the characteristic matrix of a multilayer coating film consisting of three or more coating films using two or more materials having a reflectance higher than min The minimum reflectance value R min to the minimum reflectance R0; and min The minimum value R min and determining each thickness of the multilayer coating film based on each thickness of the three or more coating films obtained by matching the minimum reflectance R at a wavelength λ.

11. Effective refractive index is n c A method for designing a low reflectance film having a minimum reflectance R0, which is a desired minimum reflectance other than zero, on an end face of an optical semiconductor device having a refractive index n fh The refractive index n fh and calculating At the desired wavelength λ0, the film thickness is λ0 / 4 / n fh The characteristic matrix of the coating film consisting of a single layer is n fh and the refractive index of at least one other material is lower than the refractive index n fh By making the characteristic matrix of a multilayer coating film consisting of three or more coating films using two or more materials having a wavelength dependency higher than min 0 A step of calculating a refractive index n of a coating film consisting of a single layer that realizes a preset set reflectance R1. fh 1 using the following formula: The film thickness is λ0 / 4 / n fh 1 The characteristic matrix of the coating film consisting of a single layer of the material, and the refractive index of at least one material is the refractive index n fh 1 and the refractive index of at least one other material is lower than the refractive index n fh 1 By making the characteristic matrix of a multilayer coating film consisting of three or more coating films using two types of materials with a reflectance higher than min The minimum reflectance value R min to the minimum reflectance R0; and min The minimum value R min and determining each thickness of the multilayer coating film based on each thickness of the three or more coating films obtained by matching the minimum reflectance R at the wavelength λ.

12. Refractive index is n fl and n fl 1 A coating film made of at least one material having a refractive index lower than n fl and n fl 1 11. The method for designing a low reflectance film according to claim 10, further comprising forming a three-layer coating film on the end surface, the three-layer coating film including a coating film made of at least one other material having a reflectance higher than that of the end surface.

13. Refractive index is n fh and n fh 1 A coating film made of at least one material having a refractive index lower than n fh and n fh 1 12. The method for designing a low reflectance film according to claim 11, further comprising forming a three-layer coating film on the end surface, the three-layer coating film including a coating film made of at least one other material having a reflectance higher than that of the end surface.

14. Refractive index is n fl and n fl 1 A coating film made of at least one material having a refractive index lower than n fl and n fl 1 and forming a coating film made of at least one other material having a reflectance higher than that of the end surface on the facet.

15. Refractive index is n fh and n fh 1 A coating film made of at least one material having a refractive index lower than n fh and n fh 1 and forming a coating film made of at least one other material having a reflectance higher than that of the end surface on the facet.

16. Refractive index is n fl and n fl 1 and at least one material having a refractive index lower than n fl and n fl 1 and at least one other material having a reflectance higher than 100 nm, and a multilayer coating film including a three-layer coating film composed of three materials among the four or more materials, and a coating film having a preset thickness composed of a material other than the three materials is formed on the end face.

17. Refractive index is n fh and n fh 1 and at least one material having a refractive index lower than n fh and n fh 1 and at least one other material having a reflectance higher than 100 nm, and a multilayer coating film including a three-layer coating film composed of three materials among the four or more materials, and a coating film having a preset thickness composed of a material other than the three materials is formed on the end surface.

18. Refractive index is n a and the film thickness is λ0 / (4n a ) thicker than 3λ0 / (4n a 18. The method for designing a low reflectance film according to claim 12, further comprising providing a coating film thinner than the thickness of the multilayer coating film between the end face, between each coating film of the multilayer coating film, or on the outermost surface of the multilayer coating film.

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