WO2023148839A1 - Optical semiconductor element - Google Patents

Optical semiconductor element Download PDF

Info

Publication number
WO2023148839A1
WO2023148839A1 PCT/JP2022/003977 JP2022003977W WO2023148839A1 WO 2023148839 A1 WO2023148839 A1 WO 2023148839A1 JP 2022003977 W JP2022003977 W JP 2022003977W WO 2023148839 A1 WO2023148839 A1 WO 2023148839A1
Authority
WO
WIPO (PCT)
Prior art keywords
dielectric film
light
refractive index
film
semiconductor layer
Prior art date
Application number
PCT/JP2022/003977
Other languages
French (fr)
Japanese (ja)
Inventor
尚友 磯村
悦司 大村
Original Assignee
株式会社京都セミコンダクター
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by 株式会社京都セミコンダクター filed Critical 株式会社京都セミコンダクター
Priority to PCT/JP2022/003977 priority Critical patent/WO2023148839A1/en
Publication of WO2023148839A1 publication Critical patent/WO2023148839A1/en

Links

Images

Classifications

    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
    • H01L31/00—Semiconductor devices sensitive to infrared radiation, light, electromagnetic radiation of shorter wavelength or corpuscular radiation and specially adapted either for the conversion of the energy of such radiation into electrical energy or for the control of electrical energy by such radiation; Processes or apparatus specially adapted for the manufacture or treatment thereof or of parts thereof; Details thereof
    • H01L31/02—Details
    • H01L31/0232—Optical elements or arrangements associated with the device
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
    • H01L31/00—Semiconductor devices sensitive to infrared radiation, light, electromagnetic radiation of shorter wavelength or corpuscular radiation and specially adapted either for the conversion of the energy of such radiation into electrical energy or for the control of electrical energy by such radiation; Processes or apparatus specially adapted for the manufacture or treatment thereof or of parts thereof; Details thereof
    • H01L31/08—Semiconductor devices sensitive to infrared radiation, light, electromagnetic radiation of shorter wavelength or corpuscular radiation and specially adapted either for the conversion of the energy of such radiation into electrical energy or for the control of electrical energy by such radiation; Processes or apparatus specially adapted for the manufacture or treatment thereof or of parts thereof; Details thereof in which radiation controls flow of current through the device, e.g. photoresistors
    • H01L31/10—Semiconductor devices sensitive to infrared radiation, light, electromagnetic radiation of shorter wavelength or corpuscular radiation and specially adapted either for the conversion of the energy of such radiation into electrical energy or for the control of electrical energy by such radiation; Processes or apparatus specially adapted for the manufacture or treatment thereof or of parts thereof; Details thereof in which radiation controls flow of current through the device, e.g. photoresistors characterised by at least one potential-jump barrier or surface barrier, e.g. phototransistors
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
    • H01L33/00—Semiconductor devices with at least one potential-jump barrier or surface barrier specially adapted for light emission; Processes or apparatus specially adapted for the manufacture or treatment thereof or of parts thereof; Details thereof
    • H01L33/44—Semiconductor devices with at least one potential-jump barrier or surface barrier specially adapted for light emission; Processes or apparatus specially adapted for the manufacture or treatment thereof or of parts thereof; Details thereof characterised by the coatings, e.g. passivation layer or anti-reflective coating

Definitions

  • the present invention relates to an optical semiconductor device provided with an antireflection film that prevents reflection of incident or emitted light.
  • optical semiconductor elements for example, semiconductor light receiving elements for converting optical signals for optical communication into electrical signals, and semiconductor light emitting elements such as light emitting diodes used for lighting have been widely used.
  • an antireflection film is formed to prevent reflection of incident or emitted light in order to improve light receiving sensitivity in the semiconductor light receiving device and to improve light emission efficiency in the semiconductor light emitting device.
  • an antireflection film for example, in a glass substrate with a refractive index of about 1.45 to 1.5 used for lenses, display panels, etc., as in Patent Document 1, it reduces reflection of light with different wavelengths. Therefore, a multi-layer structure in which layers with different refractive indices are alternately laminated is known. Further, as disclosed in Japanese Unexamined Patent Application Publication No. 2002-100001, there is known a device in which an antireflection film having a four-layer structure is formed in order to prevent reflection of an optical multilayer filter formed on a glass substrate. These multi-layered antireflection films can expand the wavelength range of light to reduce reflection by causing interference of reflected light from a plurality of interfaces. However, in order to reduce the reflectance, it is necessary to precisely control the thickness and refractive index of each layer, which complicates the process of forming the antireflection film and increases the manufacturing cost.
  • optical semiconductor elements often have a fixed wavelength of light that is incident or emitted, and an antireflection film is required to reduce the reflection of light of this wavelength. Therefore, a dielectric film having a thickness corresponding to 1/4 of the wavelength ⁇ of incident or emitted light is often used as an antireflection film. In this case, light is reflected at the interface between the antireflection film and air, and at the interface between the semiconductor layer forming the light receiving portion or the light emitting portion of the optical semiconductor element and the antireflection film.
  • the refractive index of InP used for light receiving elements for optical communication is about 3.22 for infrared light for optical communication with a wavelength of 1550 nm in air.
  • the refractive index of GaN used for blue light emitting diodes is about 2.5 for blue light with a wavelength of 460 nm in air.
  • Other compound semiconductor materials also have a refractive index within the range of 3 to 3.8 for the light used.
  • a silicon nitride film having a refractive index of about 2 with respect to light in the wavelength range of 400 nm to 2000 nm is formed to a thickness corresponding to 1/4 of the wavelength ⁇ of light. It is often used as However, an antireflection film formed of a silicon nitride film has a large refractive index and does not satisfy the non-reflection condition, so the reduction of reflection is limited.
  • An object of the present invention is to provide an optical semiconductor device having an antireflection film capable of further reducing light reflection.
  • An optical semiconductor device is an optical semiconductor device comprising an antireflection film for preventing reflection of light incident on a light receiving portion or light emitted from a light emitting portion, wherein the antireflection film and a second dielectric film in contact with the first dielectric film, wherein the second dielectric film is in contact with the first dielectric film.
  • the second dielectric film has a smaller refractive index than the dielectric film and has a thickness of 1/4 of the wavelength of the light in the second dielectric film. It is formed so that the refractive index decreases in the thickness direction of the first dielectric film from the semiconductor layer side toward the second dielectric film side up to the square of the refractive index of the dielectric film.
  • the antireflection film that prevents reflection of light incident on the light receiving portion or light emitted from the light emitting portion is formed on the semiconductor layer forming the light receiving portion or the light emitting portion.
  • This antireflection film has a two-layer structure of a first dielectric film and a second dielectric film having a smaller refractive index than the first dielectric film, and is formed so that the first dielectric film is in contact with the semiconductor layer. ing. Since light is reflected at the interface between materials having different refractive indices, the light is reflected at the interface between the second dielectric film and air and at the interface between the first dielectric film and the second dielectric film.
  • the thickness of the second dielectric film is 1/4 of the wavelength of the light in this second dielectric film, the light reflected at the two interfaces interferes so as to cancel each other out, thereby reducing the reflection. can do.
  • the refractive index of the first dielectric film is the square of the refractive index of the second dielectric film, theoretically there is no reflection at all. It satisfies the non-reflection condition and can further reduce reflection.
  • the refractive index of the first dielectric film is equal to the refractive index of the semiconductor layer at the interface between the semiconductor layer and the first dielectric film, reflection of light at this interface is suppressed.
  • the refractive index of the first dielectric film decreases toward the second dielectric film. No light is reflected. Therefore, the reflection of light incident on the light-receiving portion or the reflection of light emitted from the light-emitting portion is reduced by the anti-reflection film, and the light-emitting efficiency or light-receiving sensitivity of the optical semiconductor element can be improved.
  • an optical semiconductor element according to the first aspect of the invention, wherein the first dielectric film is formed such that the refractive index of the first dielectric film decreases linearly in the thickness direction. It is characterized by According to the above configuration, since the refractive index of the first dielectric film changes continuously in the thickness direction, an interface that causes reflection of light due to a difference in refractive index is not formed. reflection can be suppressed. Also, the formation of the first dielectric film is facilitated.
  • an optical semiconductor device according to the first aspect of the invention, wherein the thickness of the first dielectric film increases toward the second dielectric film side in the thickness direction. It is characterized in that it is formed so that the decrease in refractive index is large.
  • the first dielectric film can be formed so that the refractive index smoothly continues at the interface between the semiconductor layer and the first dielectric film. Therefore, the reflection of light at the interface between the semiconductor layer and the first dielectric film can be reliably prevented, and the reflection of light can be further reduced.
  • an optical semiconductor element according to the first aspect of the invention, wherein the second dielectric film is a silicon oxide film, and the first dielectric film is It is characterized by being a silicon oxynitride film formed so that the proportion of contained oxygen increases and the proportion of contained nitrogen decreases toward the film side.
  • the first dielectric film is closer to the silicon nitride film having a higher refractive index toward the semiconductor layer forming the light emitting portion or the light receiving portion, and is more refractive than the silicon nitride film toward the second dielectric film. It is a silicon oxynitride film approaching a silicon oxide film with a small modulus.
  • the composition is changed so that the refractive index of the semiconductor layer in the thickness direction of the first dielectric film increases to the second power of the refractive index of the second dielectric film.
  • the refractive index of the dielectric film can be made small.
  • the second dielectric film is a silicon oxide film, the first dielectric film and the second dielectric film can be easily formed continuously, and the antireflection film can be collectively formed.
  • the reflection of light can be further reduced by the antireflection film that satisfies the non-reflection condition.
  • FIG. 1 is a cross-sectional view showing the structure of a semiconductor light receiving element according to Example 1 of the present invention
  • FIG. 1 is an explanatory diagram of the structure and function of an antireflection film of Example 1.
  • FIG. FIG. 10 is a diagram showing the relationship between the refractive index and the reflectance of the second dielectric film in the vicinity of the non-reflection condition; It is a figure which shows the refractive index distribution of an antireflection film.
  • 4 is a diagram showing the relationship between the composition and refractive index of the first dielectric film;
  • FIG. FIG. 4 is a diagram showing another example of refractive index distribution of an antireflection film;
  • FIG. 4 is a cross-sectional view showing the structure of a semiconductor light emitting device according to Example 2 of the present invention;
  • FIG. 10 is an explanatory diagram of the structure and function of the antireflection film of Example 2;
  • the semiconductor light receiving element 1A includes, for example, an n-InP substrate of an n-type semiconductor as a semiconductor substrate 10, an InGaAs layer as a light absorption layer 11 formed on one side of the semiconductor substrate 10, and a semiconductor layer formed on the light absorption layer 11. 12 has a p-InP layer of a p-type semiconductor.
  • the p-type semiconductor layer 12, the light absorption layer 11, and the n-type semiconductor substrate 10 form a light receiving portion 14 (PIN photodiode) that generates a photocurrent through photoelectric conversion.
  • a cathode electrode 15 connected to the semiconductor substrate 10 and an anode electrode 16 connected to the semiconductor layer 12 are formed to extract photocurrent from the light receiving portion 14 to the outside.
  • the conductivity type of the semiconductor layer 12 and the semiconductor substrate 10 described above is only an example, and the present invention is not limited to this.
  • the semiconductor light receiving element 1A is required to have improved light receiving sensitivity. Since part of the light I incident on the light receiving section 14 is reflected by the surface 12a of the semiconductor layer 12, the light receiving sensitivity can be improved by reducing this reflection. Therefore, the antireflection film 17 is formed so as to cover the surface 12a of the semiconductor layer 12. As shown in FIG.
  • the antireflection film 17 has a two-layer structure having a first dielectric film 17a in contact with the semiconductor layer 12 and a second dielectric film 17b in contact with the first dielectric film 17a.
  • FIG. 2 shows the structure of the antireflection film 17 with the horizontal direction as the thickness direction of the antireflection film 17 so that the light I is incident from the right side.
  • the light I perpendicularly incident on the surface 12a of the semiconductor layer 12 of the light receiving section 14 is, for example, infrared light with a wavelength ⁇ of 1550 nm used in optical communication.
  • the refractive index of air with respect to this light I be 1
  • the refractive index of the second dielectric film 17b be n 2
  • the refractive index of the first dielectric film 17a be n 1
  • the refractive index of the semiconductor layer 12 be ns .
  • the refractive index n2 is greater than 1
  • the refractive index n1 and the refractive index ns are greater than the refractive index n2 .
  • the second dielectric film 17b is a silicon oxide film ( SiO2 ).
  • the light I incident on the light receiving section 14 passes through the antireflection film 17 and reaches the semiconductor layer 12 like the light ray I1, for example.
  • part of the light I incident on the light receiving section 14, such as the light RF2 and RF1 is the interface between the second dielectric film 17b of the antireflection film 17 and the air, and the interface between the first dielectric film 17a and the second dielectric film 17a. They are reflected at the interface of the dielectric film 17b.
  • the thickness d of the second dielectric film 17b is 1/4 of the wavelength ⁇ of the light I in the second dielectric film 17b
  • the phases of the lights RF1 and RF2 reflected at these two interfaces are equivalent to half the wavelength. They shift and overlap, and interfere so as to cancel each other out. According to the law of conservation of energy, the light corresponding to the canceled light enters the first dielectric film 17a. Therefore, the reflection of the incident light I is reduced by the antireflection film 17, and the reflectance is reduced.
  • the first dielectric film 17a is formed so that the refractive index ns of the semiconductor layer 12 and the refractive index n1 of the first dielectric film 17a are equal. is formed in At the interface between the first dielectric film 17a and the semiconductor layer 12, since the semiconductor layer 12 and the first dielectric film 17a have the same refractive index, the light RFs reflected at this interface is suppressed as shown in FIG. Light enters the semiconductor layer 12 through the body film 17a.
  • the silicon oxynitride film (Si z O x N 1-x ), which is the first dielectric film 17a
  • the nitrogen content (1-x ) decreases
  • the refractive index n1 decreases.
  • This silicon oxynitride film is formed by changing the flow rates of raw material gases including, for example, silane (SiH 4 ), ammonia (NH 3 ), and oxygen (O 2 ) supplied to the reaction chamber during plasma CVD. can be changed to change the refractive index n1 .
  • the silicon oxynitride film is a Si - rich silicon oxynitride film with a large Si ratio (z) in the film. can be increased, and the refractive index n1 can be set to about 4.
  • the formation of the first dielectric film 17a is started.
  • the flow rate of the raw material gas is continuously changed as the film formation progresses so that the oxygen contained in the first dielectric film 17a increases at a constant rate and the nitrogen contained in the first dielectric film 17a decreases at a constant rate.
  • a body membrane 17a is formed.
  • the refractive index n1 of the first dielectric film 17a linearly decreases in the thickness direction of the first dielectric film 17a from the semiconductor layer 12 side to the second dielectric film 17b side. is formed.
  • the flow rate corresponding to the composition (x 0.833 in FIG. 5) where the refractive index n1 becomes equal to the square of the refractive index n2 of the second dielectric film 17b as the formation of the first dielectric film 17a progresses
  • the supply of ammonia for example, is stopped, and the process shifts to the formation of the second dielectric film 17b.
  • the second dielectric film 17b it may be formed in the same reaction chamber as the first dielectric film 17a under conditions suitable for forming the second dielectric film 17b. N 2 O) may be supplied.
  • the second dielectric film 17b can also be formed in a reaction chamber different from that for the first dielectric film 17a. As shown in FIG.
  • the antireflection film 17 consists of the first dielectric film 17a, the refractive index n1 of which decreases linearly in the thickness direction from the semiconductor layer 12 side to the second dielectric film 17b side, and the incident light I
  • the second dielectric film 17b has a thickness corresponding to 1/4 of the wavelength .lambda.
  • the refractive index n1 of the first dielectric film 17a is the square of the refractive index n2 of the second dielectric film 17b. , satisfies the non-reflection condition in the above formula (1), and the reflection of the incident light I is reduced. Therefore, most of the incident light I enters the first dielectric film 17a through the second dielectric film 17b.
  • the refractive index n1 of the first dielectric film 17a changes continuously in the thickness direction, there is no interface with a different refractive index in the first dielectric film 17a, and light passing through the first dielectric film 17a is reflected. not.
  • the refractive index n1 of the first dielectric film 17a is equal to the refractive index ns of the semiconductor layer 12. Reflection of light at the interface of the semiconductor layer 12 is suppressed. Therefore, the reflection of the light I incident on the light-receiving section 14 of the semiconductor light-receiving element 1A is reduced by the two-layered antireflection film 17 composed of the first dielectric film 17a and the second dielectric film 17b. Light receiving sensitivity can be improved.
  • the first dielectric film 17a extends from the refractive index ns of the semiconductor layer 12 to the second power of 2 of the refractive index n2 of the second dielectric film 17b in its thickness direction. It may be formed so that the rate at which the refractive index n1 decreases increases toward the body film 17b side.
  • the flow rate of the raw material gas is adjusted so that the refractive index n1 becomes equal to the refractive index ns of the semiconductor layer 12, and the formation of the first dielectric film 17a is started. Then, the first dielectric film 17a is formed while continuously changing the flow rate of the raw material gas so that the increase rate of the oxygen content increases and the decrease rate of the nitrogen content increases as the film formation progresses.
  • the supply of ammonia is stopped.
  • a second dielectric film 17b is formed in the same reaction chamber.
  • the rate of decrease in the refractive index n1 is increased toward the second dielectric film 17b side, in other words, the change in the refractive index n1 is decreased toward the semiconductor layer 12 side.
  • the change in the refractive index at the interface between the first dielectric film 17a and the semiconductor layer 12 is smoothed.
  • the antireflection film 17 further reduces the reflection of the light I incident on the light receiving portion 14 of the semiconductor light receiving element 1A, thereby improving the light receiving sensitivity.
  • the semiconductor light emitting device 1B has a light emitting portion 24 (light emitting diode) formed by laminating an n-type semiconductor layer 21 and a p-type semiconductor layer 22 on a sapphire substrate 20, for example, with a buffer layer 20a interposed therebetween.
  • the n-type semiconductor layer 21 is formed by stacking, for example, an n-GaN layer 21a, an n-AlGaN layer 21b, and an n-InGaN layer 21c from the buffer layer 20a side.
  • the p-type semiconductor layer 22 is formed by stacking, for example, a p-AlGaN layer 22a and a p-GaN layer 22b from the n-type semiconductor layer 21 side. Electrodes 25 and 26 are formed on both electrodes (n-GaN layer 21a and p-GaN layer 22b) of the light-emitting section 24 in order to supply electric power for light emission to the light-emitting section 24 from the outside.
  • the light E emitted in a direction perpendicular to the surface of the semiconductor layer 22 is not reflected at the interface with the air.
  • An antireflection film 17 similar to that of Example 1 is formed to cover the surface of the p-GaN layer 22b of the semiconductor layer 22.
  • the antireflection film 17 is composed of a first dielectric film 17a in contact with the p-GaN layer 22b of the semiconductor layer 22 forming the light emitting section 24, and a second dielectric film 17b in contact with the first dielectric film 17a. It is
  • FIG. 8 shows the structure of the antireflection film 17 with the horizontal direction as the thickness direction of the antireflection film 17 so that the light E is emitted rightward.
  • the second dielectric film 17b having a refractive index of n2 was formed to have a thickness of 1/4 of the wavelength ⁇ of the emitted light E in the second dielectric film 17b. It is a silicon oxide film.
  • the first dielectric film 17a has a composition such that the refractive index n1 of the first dielectric film 17a at the interface with the second dielectric film 17b is the square of the refractive index n2 of the second dielectric film 17b.
  • the refractive index n 2 is greater than 1, and the refractive index n 1 and the refractive index n s of the p-GaN layer 22b of the semiconductor layer 22 are greater than the refractive index n 2 .
  • the first dielectric film 17a has a refractive index n1 of The composition is adjusted to be equal to the refractive index n s of the p-GaN layer 22 b of the semiconductor layer 22 .
  • the first dielectric film 17a has a refractive index n s of the p-GaN layer 22b of the semiconductor layer 22 to the second power of the refractive index n 2 of the second dielectric film 17b from the semiconductor layer 22 side.
  • the composition is adjusted so that the refractive index n1 decreases continuously in the thickness direction of the first dielectric film 17a toward the 17b side.
  • the refractive index n1 of the first dielectric film 17a is equal to the square of the refractive index n2 of the second dielectric film 17b. .
  • the light E emitted from the light emitting section 24 passes through the p-GaN layer 22b of the semiconductor layer 22 and the antireflection film 17 and reaches the outside (air) like the light E1.
  • the refractive index n1 of the first dielectric film 17a is equal to the refractive index ns of the p-GaN layer 22b.
  • the light emitted from the light emitting section 24 is incident on the first dielectric film 17a while the light RFs reflected at this interface is suppressed. Since the refractive index n1 of the first dielectric film 17a decreases continuously from the p-GaN layer 22b side to the second dielectric film 17b side, light reflection occurs in the first dielectric film 17a. do not.
  • a portion of the light incident on the first dielectric film 17a is reflected at the interface between the first dielectric film 17a and the second dielectric film 17b, such as the light RF1. Also, part of the light incident on the second dielectric film 17b is reflected at the interface between the second dielectric film 17b and the air, such as the light RF2.
  • the light beams RF1 and RF2 emitted from the light emitting part 24 in the direction perpendicular to the surface of the p-GaN layer 22b and reflected by these two interfaces cancel each other out and interfere with each other, thereby reducing the reflection.
  • Reflected light emitted from the p-GaN layer 22b at an angle from the direction perpendicular to the surface of the p-GaN layer 22b is reflected at these two interfaces. Most of the light from is emitted to the outside. Therefore, the antireflection film 17 composed of the first dielectric film 17a and the second dielectric film 17b reduces the reflection of the light from the light emitting part 24, and most of the light is emitted to the outside like the light E. , the luminous efficiency of the semiconductor light emitting device 1B is improved.
  • the optical semiconductor element includes an antireflection film 17 for preventing reflection of light incident on the light receiving section 14 or light emitted from the light emitting section 24 .
  • the antireflection film 17 includes a first dielectric film 17a in contact with the semiconductor layer 12 forming the light receiving portion 14 or the semiconductor layer 22 forming the light emitting portion 24, and a second dielectric film 17a in contact with the first dielectric film 17a. It has a two-layer structure of the body membrane 17b.
  • the second dielectric film 17b has a smaller refractive index than the first dielectric film 17a and is formed to a thickness of 1/4 of the wavelength ⁇ of light in the second dielectric film 17b.
  • the first dielectric film 17a extends from the semiconductor layers 12, 22 side to the second dielectric film 17a from the refractive index n s of the semiconductor layers 12, 22 to the second power of the refractive index n 2 (n 2 2 ) of the second dielectric film 17b. It is formed such that the refractive index n1 continuously decreases in the thickness direction of the first dielectric film 17a toward the body film 17b.
  • the refractive index n1 of the first dielectric film 17a is equal to the refractive index ns of the semiconductor layers 12 and 22 at the interface between the semiconductor layer 12 or the semiconductor layer 22 and the first dielectric film 17a. Therefore, for light incident on the semiconductor layer 12 from the first dielectric film 17a and light incident on the first dielectric film 17a from the semiconductor layer 22, Reflections are suppressed.
  • the second dielectric film 17b is formed to have a thickness of 1/4 of the wavelength ⁇ of light in the second dielectric film 17b. Therefore, when light enters the second dielectric film 17b from the air, the light reflected at the interface between the second dielectric film 17b and the air Since the light reflected at the interface interferes so as to cancel each other out, the reflection of light is reduced.
  • the refractive index n1 of the first dielectric film 17a increases toward the second dielectric film 17b. decrease linearly. Since the refractive index n1 of the first dielectric film 17a changes continuously in the thickness direction, there is no interface in the first dielectric film 17a where light is reflected due to the difference in the refractive index. Reflection of light traveling through is suppressed.
  • the first dielectric film 17a can be easily formed so that the refractive index n1 decreases linearly by continuously changing the flow rate of the material gas during film formation.
  • the first dielectric film 17a may be formed so that the decrease in the refractive index n1 of the first dielectric film 17a increases toward the second dielectric film 17b.
  • the first dielectric film 17a can be formed so that the refractive index ns and the refractive index n1 are smoothly continuous at the interface between the semiconductor layers 12 and 22 and the first dielectric film 17a. Therefore, the reflection of light at the interface between the semiconductor layers 12 and 22 and the first dielectric film 17a can be reliably prevented, and the reflection of light can be further reduced.
  • the second dielectric film 17b is a silicon oxide film. 2
  • the silicon oxynitride film is formed such that the oxygen content (x) increases and the nitrogen content (1-x) decreases toward the dielectric film 17b.
  • This silicon oxynitride film has a composition closer to that of a silicon nitride film with a higher refractive index toward the semiconductor layer 12 forming the light receiving section 14 or toward the semiconductor layer 22 forming the light emitting section 24, and the composition of the silicon oxynitride film becomes closer to the second dielectric.
  • the composition closer to the body film 17b approaches that of a silicon oxide film having a smaller refractive index than that of a silicon nitride film.
  • the composition of the film is changed while forming the first dielectric film 17a.
  • the refractive index n1 of the first dielectric film 17a can be continuously decreased up to the square of the refractive index n2 ( n22 ).
  • the second dielectric film 17b is a silicon oxide film, the second dielectric film 17b can be easily continuously formed after the formation of the first dielectric film 17a, and the antireflection film 17 can be formed all at once. .
  • the first dielectric film 17a may be formed by reactive sputtering, for example. Also, the first dielectric film 17a is not limited to a silicon oxynitride film, and may be formed of an optical thin film material such as aluminum oxide or zirconium oxide. In addition, those skilled in the art can implement various modifications to the above embodiment without departing from the scope of the present invention, and the present invention includes such modifications.
  • semiconductor light receiving element 1B semiconductor light emitting element 10: semiconductor substrate 11: light absorbing layer 12: semiconductor layer 12a: surface 14: light receiving section 15: cathode electrode 16: anode electrode 17: antireflection film 17a: first dielectric film 17b: second dielectric film 20: sapphire substrate 20a: buffer layer 21: semiconductor layer 21a: n-GaN layer 21b: n-AlGaN layer 21c: n-InGaN layer 22: semiconductor layer 22a: p-AlGaN layer 22b: p -GaN layer 24: light-emitting portions 25, 26: electrodes

Abstract

[Problem] To provide an optical semiconductor element comprising an anti-reflection film that can further reduce the reflection of light. [Solution] An optical semiconductor element comprising an anti-reflection film (17) for preventing the reflection of light (I) incident on a light-receiving unit (14) or light (E) emitted from a light-emitting unit (24). The anti-reflection film (17) comprises: a first dielectric film (17a) contacting a semiconductor layer (12, 22) forming the light-receiving unit (14) or the light-emitting unit (24); and a second dielectric film (17b) contacting the first dielectric film (17a). The second dielectric film (17b) has a smaller refractive index than that of the first dielectric film (17a) and is formed with a thickness of one-fourth the wavelength (λ) of the light (I) or the light (E) at this second dielectric film (17b). The first dielectric film (17a) is formed such that the refractive index (n1) becomes smaller in the thickness direction of the first dielectric film (17a) from the semiconductor layer (12, 22) side to the second dielectric film (17b) side, ranging from the refractive index (ns) of the semiconductor layer (12,22) to the square of the refractive index (n2) of the second dielectric film (17b).

Description

光半導体素子Optical semiconductor device
　本発明は、入射又は出射する光の反射を防止する反射防止膜を備えた光半導体素子に関する。 The present invention relates to an optical semiconductor device provided with an antireflection film that prevents reflection of incident or emitted light.
　従来から、光半導体素子として、例えば光通信の光信号を電気信号に変換するための半導体受光素子、及び例えば照明に使用される発光ダイオードのような半導体発光素子が、広く利用されている。この光半導体素子において、半導体受光素子では受光感度向上のために、半導体発光素子では発光効率向上のために、入射又は出射する光の反射を防止するための反射防止膜が形成されている。 Conventionally, as optical semiconductor elements, for example, semiconductor light receiving elements for converting optical signals for optical communication into electrical signals, and semiconductor light emitting elements such as light emitting diodes used for lighting have been widely used. In this optical semiconductor device, an antireflection film is formed to prevent reflection of incident or emitted light in order to improve light receiving sensitivity in the semiconductor light receiving device and to improve light emission efficiency in the semiconductor light emitting device.
　反射防止膜としては、例えばレンズ、ディスプレイパネル等に使用される屈折率が１．４５～１．５程度のガラス基板において、特許文献１のように、異なる波長の光に対して反射を低減するために、屈折率が異なる層を交互に積層した多層構造のものが知られている。また、特許文献２のように、ガラス基板に形成された光学多層膜フィルタの反射を防止するために、４層構造の反射防止膜を形成したものが知られている。これらの多層構造の反射防止膜は、複数の界面での反射光を干渉させることによって、反射を低減する光の波長域を拡大することができる。しかし、反射率を低減するために各層の厚さ及び屈折率を精密に制御することが必要であり、反射防止膜の形成工程が複雑になり、製造コストが増加する。 As an antireflection film, for example, in a glass substrate with a refractive index of about 1.45 to 1.5 used for lenses, display panels, etc., as in Patent Document 1, it reduces reflection of light with different wavelengths. Therefore, a multi-layer structure in which layers with different refractive indices are alternately laminated is known. Further, as disclosed in Japanese Unexamined Patent Application Publication No. 2002-100001, there is known a device in which an antireflection film having a four-layer structure is formed in order to prevent reflection of an optical multilayer filter formed on a glass substrate. These multi-layered antireflection films can expand the wavelength range of light to reduce reflection by causing interference of reflected light from a plurality of interfaces. However, in order to reduce the reflectance, it is necessary to precisely control the thickness and refractive index of each layer, which complicates the process of forming the antireflection film and increases the manufacturing cost.
　一方、光半導体素子は、入射又は出射する光の波長が決まっている場合が多く、この波長の光の反射を低減することが反射防止膜に要求されている。それ故、入射又は出射する光の波長λの１／４相当の厚さの誘電体膜が反射防止膜として使用される場合が多い。この場合、反射防止膜と空気の界面、及び光半導体素子の受光部又は発光部を形成している半導体層と反射防止膜の界面で、夫々光が反射される。 On the other hand, optical semiconductor elements often have a fixed wavelength of light that is incident or emitted, and an antireflection film is required to reduce the reflection of light of this wavelength. Therefore, a dielectric film having a thickness corresponding to 1/4 of the wavelength λ of incident or emitted light is often used as an antireflection film. In this case, light is reflected at the interface between the antireflection film and air, and at the interface between the semiconductor layer forming the light receiving portion or the light emitting portion of the optical semiconductor element and the antireflection film.
　このとき、空気の屈折率を１、反射防止膜の屈折率をｎｆ、半導体層の屈折率をｎｓとすると、反射防止膜の厚さｄは、ｄ＝（１／ｎｆ）×（λ／４）のように表される。この反射防止膜によって、反射防止膜と空気の界面、及び半導体層と反射防止膜の界面で反射された光の位相が半波長ずれて重なり、互いに打ち消し合うように干渉するので、波長λの光の反射が低減されて反射率が小さくなる。そして、この反射防止膜の屈折率ｎｆの２乗が、空気の屈折率１と半導体層の屈折率ｎｓの積に等しいこと（ｎｆ ２＝１×ｎｓ）が、反射防止膜の反射率がゼロになる無反射条件になることが知られている。 At this time, when the refractive index of air is 1, the refractive index of the antireflection film is n f , and the refractive index of the semiconductor layer is ns , the thickness d of the antireflection film is d=(1/n f )×( λ/4). Due to this antireflection film, the phases of the light reflected at the interface between the antireflection film and air and at the interface between the semiconductor layer and the antireflection film are overlapped with a half-wavelength shift, and interfere with each other so as to cancel each other out. is reduced, resulting in a smaller reflectance. The square of the refractive index nf of this antireflection film is equal to the product of the refractive index 1 of air and the refractive index ns of the semiconductor layer (nf2 = 1 × ns ). It is known that a non-reflecting condition in which the reflectance becomes zero occurs.
特開昭６２－１４３００２号公報JP-A-62-143002 特開昭６４－９１１０４号公報JP-A-64-91104
　光半導体素子には、例えばＩｎＰ、ＩｎＧａＮ、ＩｎＧａＡｌＰ、ＧａＰ、ＡｌＧａＡｓ、ＧａＮのような多様な化合物半導体材料が利用される。例えば光通信の受光素子に利用されるＩｎＰの屈折率は、空気中での波長が１５５０ｎｍの光通信用の赤外光に対して３．２２程度である。また、例えば青色発光ダイオードに使用されるＧａＮの屈折率は空気中での波長が４６０ｎｍの青色光に対して２．５程度である。他の化合物半導体材料においても、使用する光に対して屈折率は３～３．８の範囲内である。 Various compound semiconductor materials such as InP, InGaN, InGaAlP, GaP, AlGaAs, and GaN are used for optical semiconductor devices. For example, the refractive index of InP used for light receiving elements for optical communication is about 3.22 for infrared light for optical communication with a wavelength of 1550 nm in air. Further, for example, the refractive index of GaN used for blue light emitting diodes is about 2.5 for blue light with a wavelength of 460 nm in air. Other compound semiconductor materials also have a refractive index within the range of 3 to 3.8 for the light used.
　このような光半導体素子の反射防止膜には、４００ｎｍ～２０００ｎｍの波長域の光に対して屈折率が２程度のシリコン窒化膜を、光の波長λの１／４相当の厚さに形成して使用する場合が多い。しかし、シリコン窒化膜によって形成された反射防止膜は、屈折率が大きいため上記無反射条件を満たさないので、反射の低減が限定的である。 As the antireflection film of such an optical semiconductor element, a silicon nitride film having a refractive index of about 2 with respect to light in the wavelength range of 400 nm to 2000 nm is formed to a thickness corresponding to 1/4 of the wavelength λ of light. It is often used as However, an antireflection film formed of a silicon nitride film has a large refractive index and does not satisfy the non-reflection condition, so the reduction of reflection is limited.
　本発明の目的は、光の反射を一層低減することができる反射防止膜を備えた光半導体素子を提供することである。 An object of the present invention is to provide an optical semiconductor device having an antireflection film capable of further reducing light reflection.
　請求項１の発明の光半導体素子は、受光部に入射する光又は発光部から出射する光の反射を防止するための反射防止膜を備えた光半導体素子において、前記反射防止膜は、前記受光部又は前記発光部を形成している半導体層に接する第１誘電体膜と、前記第１誘電体膜に接する第２誘電体膜を有し、前記第２誘電体膜は、前記第１誘電体膜よりも屈折率が小さく、且つこの第２誘電体膜における前記光の波長の１／４の厚さに形成され、前記第１誘電体膜は、前記半導体層の屈折率から前記第２誘電体膜の屈折率の２乗まで、前記半導体層側から前記第２誘電体膜側に向かう前記第１誘電体膜の厚さ方向に屈折率が小さくなるように形成されたことを特徴としている。 An optical semiconductor device according to claim 1 is an optical semiconductor device comprising an antireflection film for preventing reflection of light incident on a light receiving portion or light emitted from a light emitting portion, wherein the antireflection film and a second dielectric film in contact with the first dielectric film, wherein the second dielectric film is in contact with the first dielectric film. The second dielectric film has a smaller refractive index than the dielectric film and has a thickness of 1/4 of the wavelength of the light in the second dielectric film. It is formed so that the refractive index decreases in the thickness direction of the first dielectric film from the semiconductor layer side toward the second dielectric film side up to the square of the refractive index of the dielectric film. there is
　上記構成によれば、受光又は発光する光半導体素子において、受光部に入射する光又は発光部から出射する光の反射を防ぐ反射防止膜が、受光部又は発光部を形成している半導体層上に形成されている。この反射防止膜は、第１誘電体膜と、第１誘電体膜よりも屈折率が小さい第２誘電体膜の２層構造であり、第１誘電体膜が半導体層に接するように形成されている。光は屈折率が異なる物質の界面で反射するので、第２誘電体膜と空気の界面、及び第１誘電体膜と第２誘電体膜の界面で、光が夫々反射する。ここで、第２誘電体膜の厚さがこの第２誘電体膜における光の波長の１／４なので、上記２つの界面で夫々反射した光が互いに打ち消し合うように干渉して、反射を低減することができる。特に、第１誘電体膜と第２誘電体膜の界面において、第１誘電体膜の屈折率が第２誘電体膜の屈折率の２乗となっているので、理論的には全く反射しない無反射条件を満たし、反射を一層低減することができる。一方、半導体層と第１誘電体膜の界面において、第１誘電体膜の屈折率が半導体層の屈折率と等しいので、この界面における光の反射が抑制される。そして、半導体層の屈折率から第２誘電体膜の屈折率の２乗まで、第１誘電体膜の屈折率が第２誘電体膜側ほど小さくなっているので、第１誘電体膜中で光は反射されない。従って、受光部に入射する光の反射又は発光部から出射する光の反射が、反射防止膜によって低減され、光半導体素子の発光効率又は受光感度を向上させることができる。 According to the above configuration, in the optical semiconductor device that receives or emits light, the antireflection film that prevents reflection of light incident on the light receiving portion or light emitted from the light emitting portion is formed on the semiconductor layer forming the light receiving portion or the light emitting portion. is formed in This antireflection film has a two-layer structure of a first dielectric film and a second dielectric film having a smaller refractive index than the first dielectric film, and is formed so that the first dielectric film is in contact with the semiconductor layer. ing. Since light is reflected at the interface between materials having different refractive indices, the light is reflected at the interface between the second dielectric film and air and at the interface between the first dielectric film and the second dielectric film. Here, since the thickness of the second dielectric film is 1/4 of the wavelength of the light in this second dielectric film, the light reflected at the two interfaces interferes so as to cancel each other out, thereby reducing the reflection. can do. In particular, at the interface between the first dielectric film and the second dielectric film, since the refractive index of the first dielectric film is the square of the refractive index of the second dielectric film, theoretically there is no reflection at all. It satisfies the non-reflection condition and can further reduce reflection. On the other hand, since the refractive index of the first dielectric film is equal to the refractive index of the semiconductor layer at the interface between the semiconductor layer and the first dielectric film, reflection of light at this interface is suppressed. From the refractive index of the semiconductor layer to the second power of the refractive index of the second dielectric film, the refractive index of the first dielectric film decreases toward the second dielectric film. No light is reflected. Therefore, the reflection of light incident on the light-receiving portion or the reflection of light emitted from the light-emitting portion is reduced by the anti-reflection film, and the light-emitting efficiency or light-receiving sensitivity of the optical semiconductor element can be improved.
　請求項２の発明の光半導体素子は、請求項１の発明において、前記第１誘電体膜は、前記厚さ方向に前記第１誘電体膜の屈折率が直線的に小さくなるように形成されたことを特徴としている。
　上記構成によれば、第１誘電体膜の屈折率が厚さ方向に連続的に変化するので、屈折率の違いにより光の反射を発生させる界面が形成されず、第１誘電体膜中での反射を抑制することができる。また、この第１誘電体膜の形成が容易になる。 According to a second aspect of the invention, there is provided an optical semiconductor element according to the first aspect of the invention, wherein the first dielectric film is formed such that the refractive index of the first dielectric film decreases linearly in the thickness direction. It is characterized by
According to the above configuration, since the refractive index of the first dielectric film changes continuously in the thickness direction, an interface that causes reflection of light due to a difference in refractive index is not formed. reflection can be suppressed. Also, the formation of the first dielectric film is facilitated.
　請求項３の発明の光半導体素子は、請求項１の発明において、前記第１誘電体膜は、前記厚さ方向において、前記第２誘電体膜側に移行するほど前記第１誘電体膜の屈折率の低下が大きくなるように形成されたことを特徴としている。
　上記構成によれば、半導体層と第１誘電体膜の界面において、屈折率が滑らかに連続するように第１誘電体膜を形成することができる。従って、半導体層と第１誘電体膜の界面での光の反射を確実に防止して、光の反射を一層低減することができる。 According to a third aspect of the invention, there is provided an optical semiconductor device according to the first aspect of the invention, wherein the thickness of the first dielectric film increases toward the second dielectric film side in the thickness direction. It is characterized in that it is formed so that the decrease in refractive index is large.
According to the above configuration, the first dielectric film can be formed so that the refractive index smoothly continues at the interface between the semiconductor layer and the first dielectric film. Therefore, the reflection of light at the interface between the semiconductor layer and the first dielectric film can be reliably prevented, and the reflection of light can be further reduced.
　請求項４の発明の光半導体素子は、請求項１の発明において、前記第２誘電体膜はシリコン酸化膜であり、前記第１誘電体膜は、前記厚さ方向において、前記第２誘電体膜側に移行するほど含有酸素の割合が増加すると共に含有窒素の割合が減少するように形成されたシリコン酸窒化膜であることを特徴としている。
　上記構成によれば、第１誘電体膜は、発光部又は受光部を形成している半導体層側ほど屈折率が大きい窒化シリコン膜に近づき、第２誘電体膜側ほど窒化シリコン膜よりも屈折率が小さい酸化シリコン膜に近づくシリコン酸窒化膜である。この第１誘電体膜の形成時には組成を変化させるように形成して、第１誘電体膜の厚さ方向に半導体層の屈折率から第２誘電体膜の屈折率の２乗まで、第１誘電体膜の屈折率が小さくなるようにすることができる。また、第２誘電体膜がシリコン酸化膜なので、第１誘電体膜と第２誘電体膜を容易に連続的に形成することができ、反射防止膜を一括形成することができる。 According to a fourth aspect of the invention, there is provided an optical semiconductor element according to the first aspect of the invention, wherein the second dielectric film is a silicon oxide film, and the first dielectric film is It is characterized by being a silicon oxynitride film formed so that the proportion of contained oxygen increases and the proportion of contained nitrogen decreases toward the film side.
According to the above configuration, the first dielectric film is closer to the silicon nitride film having a higher refractive index toward the semiconductor layer forming the light emitting portion or the light receiving portion, and is more refractive than the silicon nitride film toward the second dielectric film. It is a silicon oxynitride film approaching a silicon oxide film with a small modulus. When the first dielectric film is formed, the composition is changed so that the refractive index of the semiconductor layer in the thickness direction of the first dielectric film increases to the second power of the refractive index of the second dielectric film. The refractive index of the dielectric film can be made small. In addition, since the second dielectric film is a silicon oxide film, the first dielectric film and the second dielectric film can be easily formed continuously, and the antireflection film can be collectively formed.
　本発明の光半導体素子によれば、無反射条件を満たす反射防止膜によって光の反射を一層低減することができる。 According to the optical semiconductor element of the present invention, the reflection of light can be further reduced by the antireflection film that satisfies the non-reflection condition.
本発明の実施例１に係る半導体受光素子の構造を示す断面図である。1 is a cross-sectional view showing the structure of a semiconductor light receiving element according to Example 1 of the present invention; FIG. 実施例１の反射防止膜の構造及び機能の説明図である。1 is an explanatory diagram of the structure and function of an antireflection film of Example 1. FIG. 無反射条件近傍の第２誘電体膜の屈折率と反射率の関係を示す図である。FIG. 10 is a diagram showing the relationship between the refractive index and the reflectance of the second dielectric film in the vicinity of the non-reflection condition; 反射防止膜の屈折率分布を示す図である。It is a figure which shows the refractive index distribution of an antireflection film. 第１誘電体膜の組成と屈折率の関係を示す図である。4 is a diagram showing the relationship between the composition and refractive index of the first dielectric film; FIG. 反射防止膜の屈折率分布の他の例を示す図である。FIG. 4 is a diagram showing another example of refractive index distribution of an antireflection film; 本発明の実施例２に係る半導体発光素子の構造を示す断面図である。FIG. 4 is a cross-sectional view showing the structure of a semiconductor light emitting device according to Example 2 of the present invention; 実施例２の反射防止膜の構造及び機能の説明図である。FIG. 10 is an explanatory diagram of the structure and function of the antireflection film of Example 2;
　以下、本発明を実施するための形態について実施例に基づいて説明する。 Hereinafter, the mode for carrying out the present invention will be described based on examples.
　図１に示すように、光半導体素子として半導体受光素子１Ａについて説明する。半導体受光素子１Ａは、例えば半導体基板１０としてｎ型半導体のｎ－ＩｎＰ基板と、半導体基板１０の片面に形成された光吸収層１１としてＩｎＧａＡｓ層と、光吸収層１１上に形成された半導体層１２としてｐ型半導体のｐ－ＩｎＰ層を有する。そして、ｐ型の半導体層１２と光吸収層１１とｎ型の半導体基板１０によって、光電変換により光電流を生成する受光部１４（ＰＩＮフォトダイオード）が形成されている。この受光部１４から光電流を外部に取り出すために、半導体基板１０に接続されたカソード電極１５と、半導体層１２に接続されたアノード電極１６が形成されている。尚、上記の半導体層１２及び半導体基板１０の導電型は１例であり、これに限定されるものではない。 As shown in FIG. 1, a semiconductor light receiving element 1A will be described as an optical semiconductor element. The semiconductor light receiving element 1A includes, for example, an n-InP substrate of an n-type semiconductor as a semiconductor substrate 10, an InGaAs layer as a light absorption layer 11 formed on one side of the semiconductor substrate 10, and a semiconductor layer formed on the light absorption layer 11. 12 has a p-InP layer of a p-type semiconductor. The p-type semiconductor layer 12, the light absorption layer 11, and the n-type semiconductor substrate 10 form a light receiving portion 14 (PIN photodiode) that generates a photocurrent through photoelectric conversion. A cathode electrode 15 connected to the semiconductor substrate 10 and an anode electrode 16 connected to the semiconductor layer 12 are formed to extract photocurrent from the light receiving portion 14 to the outside. The conductivity type of the semiconductor layer 12 and the semiconductor substrate 10 described above is only an example, and the present invention is not limited to this.
　半導体受光素子１Ａには、受光感度を向上させることが要求されている。受光部１４に入射する光Ｉの一部は半導体層１２の表面１２ａで反射されるので、この反射を低減することにより受光感度を向上させることができる。それ故、反射防止膜１７が半導体層１２の表面１２ａを覆うように形成されている。この反射防止膜１７は、半導体層１２に接する第１誘電体膜１７ａと、この第１誘電体膜１７ａに接する第２誘電体膜１７ｂを有する２層構造である。 The semiconductor light receiving element 1A is required to have improved light receiving sensitivity. Since part of the light I incident on the light receiving section 14 is reflected by the surface 12a of the semiconductor layer 12, the light receiving sensitivity can be improved by reducing this reflection. Therefore, the antireflection film 17 is formed so as to cover the surface 12a of the semiconductor layer 12. As shown in FIG. The antireflection film 17 has a two-layer structure having a first dielectric film 17a in contact with the semiconductor layer 12 and a second dielectric film 17b in contact with the first dielectric film 17a.
　図２には、右方から光Ｉが入射するように水平方向を反射防止膜１７の厚さ方向として、反射防止膜１７の構造が示されている。受光部１４の半導体層１２の表面１２ａに垂直に入射する光Ｉは、例えば光通信で使用される波長λが１５５０ｎｍの赤外光である。この光Ｉに対する空気の屈折率を１、第２誘電体膜１７ｂの屈折率をｎ２、第１誘電体膜１７ａの屈折率をｎ１、半導体層１２の屈折率をｎｓとする。屈折率ｎ２は１より大きく、屈折率ｎ１と屈折率ｎｓは屈折率ｎ２より大きい。 FIG. 2 shows the structure of the antireflection film 17 with the horizontal direction as the thickness direction of the antireflection film 17 so that the light I is incident from the right side. The light I perpendicularly incident on the surface 12a of the semiconductor layer 12 of the light receiving section 14 is, for example, infrared light with a wavelength λ of 1550 nm used in optical communication. Let the refractive index of air with respect to this light I be 1, the refractive index of the second dielectric film 17b be n 2 , the refractive index of the first dielectric film 17a be n 1 , and the refractive index of the semiconductor layer 12 be ns . The refractive index n2 is greater than 1, and the refractive index n1 and the refractive index ns are greater than the refractive index n2 .
　第２誘電体膜１７ｂはシリコン酸化膜（ＳｉＯ２）である。この第２誘電体膜１７ｂの厚さは、第２誘電体膜１７ｂにおける光Ｉの波長λの１／４である。第２誘電体膜１７ｂの厚さをｄとすると、ｄ＝（１／ｎ２）×（λ／４）である。また、この第２誘電体膜１７ｂの屈折率ｎ２は例えば１．４５である。 The second dielectric film 17b is a silicon oxide film ( SiO2 ). The thickness of the second dielectric film 17b is 1/4 of the wavelength λ of the light I in the second dielectric film 17b. Assuming that the thickness of the second dielectric film 17b is d, d=(1/n 2 )×(λ/4). Also, the refractive index n2 of the second dielectric film 17b is, for example, 1.45.
　受光部１４に入射する光Ｉは、例えば光線Ｉ１のように反射防止膜１７を通って半導体層１２に到達する。ここで、光がある物質から他の物質に入射する際には、例えば双方の屈折率が等しい特別な場合を除いて、これら物質同士の界面で光の反射が発生する。そのため、受光部１４に入射する光Ｉの一部は、例えば光ＲＦ２，ＲＦ１のように、反射防止膜１７の第２誘電体膜１７ｂと空気の界面、及び第１誘電体膜１７ａと第２誘電体膜１７ｂの界面で夫々反射される。 The light I incident on the light receiving section 14 passes through the antireflection film 17 and reaches the semiconductor layer 12 like the light ray I1, for example. Here, when light is incident from one substance to another substance, light reflection occurs at the interface between these substances, except for special cases where both have the same refractive index. Therefore, part of the light I incident on the light receiving section 14, such as the light RF2 and RF1, is the interface between the second dielectric film 17b of the antireflection film 17 and the air, and the interface between the first dielectric film 17a and the second dielectric film 17a. They are reflected at the interface of the dielectric film 17b.
　これら２つの界面で反射された光ＲＦ１，ＲＦ２は、第２誘電体膜１７ｂの厚さｄが第２誘電体膜１７ｂにおける光Ｉの波長λの１／４であるため、位相が半波長相当ずれて重なり、互いに打ち消し合うように干渉する。エネルギーの保存則により、打ち消し合った光に相当する光は第１誘電体膜１７ａに入射する。従って、反射防止膜１７によって入射する光Ｉの反射が軽減され、反射率が小さくなる。 Since the thickness d of the second dielectric film 17b is 1/4 of the wavelength λ of the light I in the second dielectric film 17b, the phases of the lights RF1 and RF2 reflected at these two interfaces are equivalent to half the wavelength. They shift and overlap, and interfere so as to cancel each other out. According to the law of conservation of energy, the light corresponding to the canceled light enters the first dielectric film 17a. Therefore, the reflection of the incident light I is reduced by the antireflection film 17, and the reflectance is reduced.
　その上、第２誘電体膜１７ｂの屈折率ｎ２の２乗と、空気の屈折率１と第１誘電体膜１７ａの屈折率ｎ１の積であるｎ１とが等しい場合（ｎ２ ２＝１×ｎ１＝ｎ１の場合）には、反射率がゼロになる。従って、第１誘電体膜１７ａの屈折率ｎ１が第２誘電体膜１７ｂの屈折率ｎ２の２乗に等しいこと（ｎ１＝ｎ２ ２）が、光Ｉの波長λの１／４相当の厚さの第２誘電体膜１７ｂを有する反射防止膜１７の反射率がゼロになる無反射条件である。 Moreover, when the square of the refractive index n2 of the second dielectric film 17b is equal to n1 , which is the product of the refractive index 1 of air and the refractive index n1 of the first dielectric film 17a ( n22 = 1 x n 1 = n 1 ), the reflectance becomes zero. Therefore, the fact that the refractive index n1 of the first dielectric film 17a is equal to the square of the refractive index n2 of the second dielectric film 17b ( n1 = n22 ) is 1/4 of the wavelength λ of the light I. This is a non-reflection condition in which the reflectance of the antireflection film 17 having the second dielectric film 17b with a considerable thickness is zero.
　図３は、第１誘電体膜１７ａの屈折率ｎ１＝１．４５２の場合に、無反射条件を満たす第２誘電体膜１７ｂの屈折率ｎ２＝１．４５近傍における屈折率ｎ２と反射率の関係を示している。屈折率ｎ２が屈折率ｎ１の平方根（１．４５）に近づくほど反射率がゼロに近づくことが分かる。 FIG . 3 shows the refractive index n 2 near the refractive index n 2 =1.45 of the second dielectric film 17b that satisfies the non-reflection condition when the refractive index n 1 =1.45 2 of the first dielectric film 17a. and reflectance. It can be seen that the reflectance approaches zero as the refractive index n2 approaches the square root (1.45) of the refractive index n1 .
　第１誘電体膜１７ａには、その膜の組成を変更しながら形成することができるシリコン酸窒化膜（ＳｉｚＯｘＮ１－ｘ）が使用される。シリコン酸窒化膜の組成に応じて屈折率が変化することを利用して、第１誘電体膜１７ａは、図４に示すように、第１誘電体膜１７ａと第２誘電体膜１７ｂの界面において、上記の無反射条件（ｎ１＝ｎ２ ２）を満たすように形成されている。 A silicon oxynitride film (Si z O x N 1-x ) that can be formed while changing the composition of the film is used for the first dielectric film 17a. Utilizing the fact that the refractive index changes according to the composition of the silicon oxynitride film, the first dielectric film 17a is formed at the interface between the first dielectric film 17a and the second dielectric film 17b as shown in FIG. is formed so as to satisfy the non-reflection condition (n 1 =n 2 2 ).
　一方、第１誘電体膜１７ａと半導体層１２との界面において、第１誘電体膜１７ａは、半導体層１２の屈折率ｎｓと第１誘電体膜１７ａの屈折率ｎ１とが等しくなるように形成されている。第１誘電体膜１７ａと半導体層１２の界面では、半導体層１２と第１誘電体膜１７ａの屈折率が等しいので、図２のようにこの界面で反射する光ＲＦｓが抑制され、第１誘電体膜１７ａから半導体層１２に光が入射する。 On the other hand, at the interface between the first dielectric film 17a and the semiconductor layer 12, the first dielectric film 17a is formed so that the refractive index ns of the semiconductor layer 12 and the refractive index n1 of the first dielectric film 17a are equal. is formed in At the interface between the first dielectric film 17a and the semiconductor layer 12, since the semiconductor layer 12 and the first dielectric film 17a have the same refractive index, the light RFs reflected at this interface is suppressed as shown in FIG. Light enters the semiconductor layer 12 through the body film 17a.
　図５に示すように、第１誘電体膜１７ａであるシリコン酸窒化膜（ＳｉｚＯｘＮ１－ｘ）は、含有酸素の割合（ｘ）が増加すると共に含有窒素の割合（１－ｘ）が減少するほど、屈折率ｎ１が小さくなる。このシリコン酸窒化膜は、プラズマＣＶＤ法による形成時に、反応室に供給される例えばシラン（ＳｉＨ４）、アンモニア（ＮＨ３）、酸素（Ｏ２）を含む原料ガスの流量を夫々変えることによって組成を変えて、屈折率ｎ１を変えることができる。尚、シリコン酸窒化膜は、膜中のＳｉの割合（ｚ）が大きいＳｉリッチのシリコン酸窒化膜にすることによって、含有酸素の割合（ｘ）にもよるが、屈折率ｎ１を２よりも大きくすることが可能であり、屈折率ｎ１を４程度にすることも可能である。 As shown in FIG. 5, in the silicon oxynitride film (Si z O x N 1-x ), which is the first dielectric film 17a, the nitrogen content (1-x ) decreases, the refractive index n1 decreases. This silicon oxynitride film is formed by changing the flow rates of raw material gases including, for example, silane (SiH 4 ), ammonia (NH 3 ), and oxygen (O 2 ) supplied to the reaction chamber during plasma CVD. can be changed to change the refractive index n1 . In addition, the silicon oxynitride film is a Si - rich silicon oxynitride film with a large Si ratio (z) in the film. can be increased, and the refractive index n1 can be set to about 4.
　第１誘電体膜１７ａの形成開始時には、原料ガスの流量が、屈折率ｎ１が半導体層１２の屈折率ｎｓと等しくなる組成（ここではｘ＝０．５７２）に対応する流量に調整され、第１誘電体膜１７ａの形成が開始される。そして、第１誘電体膜１７ａの含有酸素が一定の割合で増加すると共に含有窒素が一定の割合で減少するように、膜形成の進行と共に原料ガスの流量が連続的に変更され、第１誘電体膜１７ａが形成される。これにより、図４のように、半導体層１２側から第２誘電体膜１７ｂ側に向かう第１誘電体膜１７ａの厚さ方向に屈折率ｎ１が直線的に低下する第１誘電体膜１７ａが形成される。 At the start of the formation of the first dielectric film 17a, the flow rate of the raw material gas is adjusted to a flow rate corresponding to the composition (here, x=0.572) where the refractive index n1 is equal to the refractive index ns of the semiconductor layer 12. , the formation of the first dielectric film 17a is started. Then, the flow rate of the raw material gas is continuously changed as the film formation progresses so that the oxygen contained in the first dielectric film 17a increases at a constant rate and the nitrogen contained in the first dielectric film 17a decreases at a constant rate. A body membrane 17a is formed. As a result, as shown in FIG. 4, the refractive index n1 of the first dielectric film 17a linearly decreases in the thickness direction of the first dielectric film 17a from the semiconductor layer 12 side to the second dielectric film 17b side. is formed.
　第１誘電体膜１７ａの形成が進行して屈折率ｎ１が第２誘電体膜１７ｂの屈折率ｎ２の２乗に等しくなる組成（図５においてｘ＝０．８３３）に対応する流量まで原料ガスの流量が変更されると、例えばアンモニアの供給が停止されて第２誘電体膜１７ｂの形成に移行する。この第２誘電体膜１７ｂの形成時には、第１誘電体膜１７ａと同じ反応室で第２誘電体膜１７ｂの形成に適した条件で形成してもよく、例えば酸素の代わりに亜酸化窒素（Ｎ２Ｏ）を供給して形成してもよい。尚、第１誘電体膜１７ａと異なる反応室で第２誘電体膜１７ｂを形成することもできる。図４のように、第１誘電体膜１７ａと第２誘電体膜１７ｂの界面において上記の無反射条件を満たす屈折率ｎ２の第２誘電体膜１７ｂは、この第２誘電体膜１７ｂにおける光Ｉの波長λの１／４の厚さｄ（ｄ＝（１／ｎ２）×（λ／４））に形成される。 Until the flow rate corresponding to the composition (x=0.833 in FIG. 5) where the refractive index n1 becomes equal to the square of the refractive index n2 of the second dielectric film 17b as the formation of the first dielectric film 17a progresses When the flow rate of the raw material gas is changed, the supply of ammonia, for example, is stopped, and the process shifts to the formation of the second dielectric film 17b. When forming the second dielectric film 17b, it may be formed in the same reaction chamber as the first dielectric film 17a under conditions suitable for forming the second dielectric film 17b. N 2 O) may be supplied. The second dielectric film 17b can also be formed in a reaction chamber different from that for the first dielectric film 17a. As shown in FIG. 4, at the interface between the first dielectric film 17a and the second dielectric film 17b, the second dielectric film 17b having a refractive index n2 that satisfies the non-reflecting condition is the second dielectric film 17b. It is formed to have a thickness d (d=(1/n 2 )×(λ/4)) which is a quarter of the wavelength λ of the light I.
　以上のように反射防止膜１７は、半導体層１２側から第２誘電体膜１７ｂ側に向かう厚さ方向に屈折率ｎ１が直線的に小さくなる第１誘電体膜１７ａと、入射する光Ｉの波長λの１／４相当の厚さの第２誘電体膜１７ｂによって構成されている。そして、第１誘電体膜１７ａと第２誘電体膜１７ｂの界面において、第１誘電体膜１７ａの屈折率ｎ１が第２誘電体膜１７ｂの屈折率ｎ２の２乗になっているので、上記（１）式における無反射条件を満たし、入射する光Ｉの反射が低減される。それ故、入射する光Ｉの大部分が第２誘電体膜１７ｂを通って第１誘電体膜１７ａに入射する。 As described above, the antireflection film 17 consists of the first dielectric film 17a, the refractive index n1 of which decreases linearly in the thickness direction from the semiconductor layer 12 side to the second dielectric film 17b side, and the incident light I The second dielectric film 17b has a thickness corresponding to 1/4 of the wavelength .lambda. At the interface between the first dielectric film 17a and the second dielectric film 17b, the refractive index n1 of the first dielectric film 17a is the square of the refractive index n2 of the second dielectric film 17b. , satisfies the non-reflection condition in the above formula (1), and the reflection of the incident light I is reduced. Therefore, most of the incident light I enters the first dielectric film 17a through the second dielectric film 17b.
　第１誘電体膜１７ａの屈折率ｎ１が厚さ方向に連続的に変化するので、第１誘電体膜１７ａ中に屈折率が異なる界面がなく、第１誘電体膜１７ａを通る光は反射されない。そして、第１誘電体膜１７ａと半導体層１２の界面において、第１誘電体膜１７ａの屈折率ｎ１が半導体層１２の屈折率ｎｓと等しくなっているので、第１誘電体膜１７ａと半導体層１２の界面での光の反射が抑制される。従って、第１誘電体膜１７ａと第２誘電体膜１７ｂで構成された２層構造の反射防止膜１７によって、半導体受光素子１Ａの受光部１４に入射する光Ｉの反射が低減されるので、受光感度を向上させることができる。 Since the refractive index n1 of the first dielectric film 17a changes continuously in the thickness direction, there is no interface with a different refractive index in the first dielectric film 17a, and light passing through the first dielectric film 17a is reflected. not. At the interface between the first dielectric film 17a and the semiconductor layer 12, the refractive index n1 of the first dielectric film 17a is equal to the refractive index ns of the semiconductor layer 12. Reflection of light at the interface of the semiconductor layer 12 is suppressed. Therefore, the reflection of the light I incident on the light-receiving section 14 of the semiconductor light-receiving element 1A is reduced by the two-layered antireflection film 17 composed of the first dielectric film 17a and the second dielectric film 17b. Light receiving sensitivity can be improved.
　例えば図６に示すように、第１誘電体膜１７ａは、その厚さ方向において、半導体層１２の屈折率ｎｓから第２誘電体膜１７ｂの屈折率ｎ２の２乗まで、第２誘電体膜１７ｂ側に移行するほど屈折率ｎ１が低下する割合が大きくなるように形成されていてもよい。第１誘電体膜１７ａの形成開始時には、屈折率ｎ１が半導体層１２の屈折率ｎｓと等しくなるように原料ガスの流量を調整して第１誘電体膜１７ａの形成を開始する。そして、膜形成の進行と共に含有酸素の増加割合が増加し且つ含有窒素の減少割合が増加するように、原料ガスの流量を連続的に変更しながら第１誘電体膜１７ａを形成する。 For example, as shown in FIG. 6, the first dielectric film 17a extends from the refractive index ns of the semiconductor layer 12 to the second power of 2 of the refractive index n2 of the second dielectric film 17b in its thickness direction. It may be formed so that the rate at which the refractive index n1 decreases increases toward the body film 17b side. When starting the formation of the first dielectric film 17a, the flow rate of the raw material gas is adjusted so that the refractive index n1 becomes equal to the refractive index ns of the semiconductor layer 12, and the formation of the first dielectric film 17a is started. Then, the first dielectric film 17a is formed while continuously changing the flow rate of the raw material gas so that the increase rate of the oxygen content increases and the decrease rate of the nitrogen content increases as the film formation progresses.
　屈折率ｎ１が屈折率ｎ２の２乗に等しくなる組成（例えば図５においてｘ＝０．８３３）に対応する流量まで原料ガスの流量を変更した後は、例えばアンモニアの供給を停止して同じ反応室で第２誘電体膜１７ｂを形成する。屈折率ｎ２の第２誘電体膜１７ｂは、この第２誘電体膜１７ｂにおける光Ｉの波長λの１／４の厚さｄ（ｄ＝（１／ｎ２）×（λ／４））に形成される。 After changing the flow rate of the raw material gas to a flow rate corresponding to the composition where the refractive index n1 is equal to the square of the refractive index n2 (for example, x=0.833 in FIG. 5), for example, the supply of ammonia is stopped. A second dielectric film 17b is formed in the same reaction chamber. The second dielectric film 17b having a refractive index of n2 has a thickness d (d=(1/n 2 )×(λ/4)) which is 1/4 of the wavelength λ of the light I in the second dielectric film 17b. formed in
　直線的に屈折率ｎ１が変化する場合には、第１誘電体膜１７ａと半導体層１２の界面で屈折率の変化が滑らかでないので、光が反射する虞がある。そのため、第２誘電体膜１７ｂ側に移行するほど屈折率ｎ１が低下する割合が大きくなるようにして、言い換えると半導体層１２側に移行するほど屈折率ｎ１の変化が小さくなるようにして、第１誘電体膜１７ａと半導体層１２の界面で屈折率の変化を滑らかにしている。これにより第１誘電体膜１７ａと半導体層１２の界面で屈折率が滑らかに連続するので、この界面での反射を確実に防止することができる。従って、反射防止膜１７によって半導体受光素子１Ａの受光部１４に入射する光Ｉの反射が一層低減され、受光感度を向上させることができる。 If the refractive index n1 changes linearly, light may be reflected because the change in refractive index is not smooth at the interface between the first dielectric film 17a and the semiconductor layer 12. FIG. Therefore, the rate of decrease in the refractive index n1 is increased toward the second dielectric film 17b side, in other words, the change in the refractive index n1 is decreased toward the semiconductor layer 12 side. , the change in the refractive index at the interface between the first dielectric film 17a and the semiconductor layer 12 is smoothed. As a result, the refractive index smoothly continues at the interface between the first dielectric film 17a and the semiconductor layer 12, so that reflection at this interface can be reliably prevented. Therefore, the antireflection film 17 further reduces the reflection of the light I incident on the light receiving portion 14 of the semiconductor light receiving element 1A, thereby improving the light receiving sensitivity.
　図７に示すように、光半導体素子として半導体発光素子１Ｂについて説明する。半導体発光素子１Ｂは、例えばサファイア基板２０上にバッファ層２０ａを介して、ｎ型の半導体層２１とｐ型の半導体層２２を積層して形成された発光部２４（発光ダイオード）を有する。ｎ型の半導体層２１は、バッファ層２０ａ側から例えばｎ－ＧａＮ層２１ａ、ｎ－ＡｌＧａＮ層２１ｂ、ｎ－ＩｎＧａＮ層２１ｃを積層して形成されている。ｐ型の半導体層２２は、ｎ型の半導体層２１側から例えばｐ－ＡｌＧａＮ層２２ａ、ｐ－ＧａＮ層２２ｂを積層して形成されている。外部から発光部２４に発光用の電力を供給するために、発光部２４の両極（ｎ－ＧａＮ層２１ａ、ｐ－ＧａＮ層２２ｂ）に電極２５，２６が形成されている。 As shown in FIG. 7, a semiconductor light emitting device 1B will be described as an optical semiconductor device. The semiconductor light emitting device 1B has a light emitting portion 24 (light emitting diode) formed by laminating an n-type semiconductor layer 21 and a p-type semiconductor layer 22 on a sapphire substrate 20, for example, with a buffer layer 20a interposed therebetween. The n-type semiconductor layer 21 is formed by stacking, for example, an n-GaN layer 21a, an n-AlGaN layer 21b, and an n-InGaN layer 21c from the buffer layer 20a side. The p-type semiconductor layer 22 is formed by stacking, for example, a p-AlGaN layer 22a and a p-GaN layer 22b from the n-type semiconductor layer 21 side. Electrodes 25 and 26 are formed on both electrodes (n-GaN layer 21a and p-GaN layer 22b) of the light-emitting section 24 in order to supply electric power for light emission to the light-emitting section 24 from the outside.
　例えば空気中での波長λ＝４６０ｎｍを中心波長とする光が、発光部２４から出射される。出射される光の方向は様々であるが、例えば半導体層２２の表面（ｐ－ＧａＮ層２２ｂの表面）に垂直な方向に出射される光Ｅが空気との界面での反射されないように、上記実施例１と同様の反射防止膜１７が半導体層２２のｐ－ＧａＮ層２２ｂの表面を覆うように形成されている。この反射防止膜１７は、発光部２４を形成している半導体層２２のｐ－ＧａＮ層２２ｂに接する第１誘電体膜１７ａと、第１誘電体膜１７ａに接する第２誘電体膜１７ｂによって構成されている。 For example, light having a central wavelength of λ=460 nm in air is emitted from the light emitting section 24 . Although there are various directions of emitted light, for example, the light E emitted in a direction perpendicular to the surface of the semiconductor layer 22 (the surface of the p-GaN layer 22b) is not reflected at the interface with the air. An antireflection film 17 similar to that of Example 1 is formed to cover the surface of the p-GaN layer 22b of the semiconductor layer 22. FIG. The antireflection film 17 is composed of a first dielectric film 17a in contact with the p-GaN layer 22b of the semiconductor layer 22 forming the light emitting section 24, and a second dielectric film 17b in contact with the first dielectric film 17a. It is
　図８には、光Ｅが右方に向かって出射されるように水平方向を反射防止膜１７の厚さ方向として、反射防止膜１７の構造が示されている。この光Ｅに対する空気の屈折率を１として、屈折率ｎ２の第２誘電体膜１７ｂは、出射する光Ｅの第２誘電体膜１７ｂにおける波長λの１／４の厚さに形成されたシリコン酸化膜である。第１誘電体膜１７ａは、第２誘電体膜１７ｂとの界面において第１誘電体膜１７ａの屈折率ｎ１が第２誘電体膜１７ｂの屈折率ｎ２の２乗となるように、組成を調整して形成されたシリコン酸窒化膜である。尚、屈折率ｎ２は１より大きく、屈折率ｎ１と半導体層２２のｐ－ＧａＮ層２２ｂの屈折率ｎｓは屈折率ｎ２より大きい。 FIG. 8 shows the structure of the antireflection film 17 with the horizontal direction as the thickness direction of the antireflection film 17 so that the light E is emitted rightward. Assuming that the refractive index of air with respect to this light E is 1, the second dielectric film 17b having a refractive index of n2 was formed to have a thickness of 1/4 of the wavelength λ of the emitted light E in the second dielectric film 17b. It is a silicon oxide film. The first dielectric film 17a has a composition such that the refractive index n1 of the first dielectric film 17a at the interface with the second dielectric film 17b is the square of the refractive index n2 of the second dielectric film 17b. is a silicon oxynitride film formed by adjusting the The refractive index n 2 is greater than 1, and the refractive index n 1 and the refractive index n s of the p-GaN layer 22b of the semiconductor layer 22 are greater than the refractive index n 2 .
　図４又は図６に示すように、第１誘電体膜１７ａは、半導体層２２のｐ－ＧａＮ層２２ｂと第１誘電体膜１７ａの界面において、第１誘電体膜１７ａの屈折率ｎ１が半導体層２２のｐ－ＧａＮ層２２ｂの屈折率ｎｓと等しくなるように組成を調整して形成されている。ここでは、屈折率ｎｓは、波長λ＝４６０ｎｍの光Ｅに対してｎｓ＝２．５程度である。この第１誘電体膜１７ａは、半導体層２２のｐ－ＧａＮ層２２ｂの屈折率ｎｓから第２誘電体膜１７ｂの屈折率ｎ２の２乗まで、半導体層２２側から第２誘電体膜１７ｂ側に向かう第１誘電体膜１７ａの厚さ方向に、屈折率ｎ１が連続的に小さくなるように組成が調整されて形成されている。そして、第１誘電体膜１７ａと第２誘電体膜１７ｂの界面では、第１誘電体膜１７ａの屈折率ｎ１が第２誘電体膜１７ｂの屈折率ｎ２の２乗に等しくなっている。 As shown in FIG. 4 or FIG. 6, the first dielectric film 17a has a refractive index n1 of The composition is adjusted to be equal to the refractive index n s of the p-GaN layer 22 b of the semiconductor layer 22 . Here, the refractive index n s is approximately ns =2.5 for light E having a wavelength λ=460 nm. The first dielectric film 17a has a refractive index n s of the p-GaN layer 22b of the semiconductor layer 22 to the second power of the refractive index n 2 of the second dielectric film 17b from the semiconductor layer 22 side. The composition is adjusted so that the refractive index n1 decreases continuously in the thickness direction of the first dielectric film 17a toward the 17b side. At the interface between the first dielectric film 17a and the second dielectric film 17b, the refractive index n1 of the first dielectric film 17a is equal to the square of the refractive index n2 of the second dielectric film 17b. .
　図８に示すように、発光部２４から出射される光Ｅは、例えば光線Ｅ１のように半導体層２２のｐ－ＧａＮ層２２ｂと反射防止膜１７を通って外部（空気）に到達する。ここで、光がある物質から他の物質に入射する際には、例えば双方の屈折率が等しい特別な場合を除いて、これら物質同士の界面で反射する。しかし、ｐ－ＧａＮ層２２ｂと第１誘電体膜１７ａの界面では、第１誘電体膜１７ａの屈折率ｎ１がｐ－ＧａＮ層２２ｂの屈折率ｎｓと等しい。それ故、発光部２４から出射された光は、この界面で反射する光ＲＦｓが抑制されて第１誘電体膜１７ａに入射する。第１誘電体膜１７ａは、ｐ－ＧａＮ層２２ｂ側から第２誘電体膜１７ｂ側に向かって連続的に屈折率ｎ１が小さくなるので、第１誘電体膜１７ａ中で光の反射が発生しない。 As shown in FIG. 8, the light E emitted from the light emitting section 24 passes through the p-GaN layer 22b of the semiconductor layer 22 and the antireflection film 17 and reaches the outside (air) like the light E1. Here, when light enters from one substance to another substance, it is reflected at the interface between these substances, except for a special case where both have the same refractive index. However, at the interface between the p-GaN layer 22b and the first dielectric film 17a, the refractive index n1 of the first dielectric film 17a is equal to the refractive index ns of the p-GaN layer 22b. Therefore, the light emitted from the light emitting section 24 is incident on the first dielectric film 17a while the light RFs reflected at this interface is suppressed. Since the refractive index n1 of the first dielectric film 17a decreases continuously from the p-GaN layer 22b side to the second dielectric film 17b side, light reflection occurs in the first dielectric film 17a. do not.
　第１誘電体膜１７ａに入射した光の一部は、例えば光ＲＦ１のように第１誘電体膜１７ａと第２誘電体膜１７ｂの界面で反射される。また、第２誘電体膜１７ｂに入射した光の一部は、例えば光ＲＦ２のように第２誘電体膜１７ｂと空気の界面で反射される。ここで、第１誘電体膜１７ａと第２誘電体膜１７ｂは、その界面において上記の無反射条件（ｎ１＝ｎ２ ２）を満たすように形成されている。従って、発光部２４からｐ－ＧａＮ層２２ｂの表面に垂直な方向に出射されてこれら２つの界面で反射された光ＲＦ１，ＲＦ２は、互いに打ち消し合うように干渉して反射が低減される。 A portion of the light incident on the first dielectric film 17a is reflected at the interface between the first dielectric film 17a and the second dielectric film 17b, such as the light RF1. Also, part of the light incident on the second dielectric film 17b is reflected at the interface between the second dielectric film 17b and the air, such as the light RF2. Here, the first dielectric film 17a and the second dielectric film 17b are formed so as to satisfy the above non-reflection condition (n 1 =n 2 2 ) at their interface. Therefore, the light beams RF1 and RF2 emitted from the light emitting part 24 in the direction perpendicular to the surface of the p-GaN layer 22b and reflected by these two interfaces cancel each other out and interfere with each other, thereby reducing the reflection.
　ｐ－ＧａＮ層２２ｂの表面に垂直な方向から傾いて出射された光がこれら２つの界面で反射された反射光同士も、ある程度打ち消し合うように干渉して反射が低減されるので、発光部２４からの光の大部分が外部に出射される。従って、第１誘電体膜１７ａと第２誘電体膜１７ｂで構成された反射防止膜１７によって発光部２４からの光の反射が低減され、大部分が光Ｅのように外部に出射されるので、半導体発光素子１Ｂの発光効率が向上する。 Reflected light emitted from the p-GaN layer 22b at an angle from the direction perpendicular to the surface of the p-GaN layer 22b is reflected at these two interfaces. Most of the light from is emitted to the outside. Therefore, the antireflection film 17 composed of the first dielectric film 17a and the second dielectric film 17b reduces the reflection of the light from the light emitting part 24, and most of the light is emitted to the outside like the light E. , the luminous efficiency of the semiconductor light emitting device 1B is improved.
　上記実施例１，２に係る光半導体素子（半導体受光素子１Ａ、半導体発光素子１Ｂ）の作用、効果について説明する。
　光半導体素子は、受光部１４に入射する光又は発光部２４から出射する光の反射を防止するための反射防止膜１７を備えている。反射防止膜１７は、受光部１４を形成している半導体層１２又は発光部２４を形成している半導体層２２に接する第１誘電体膜１７ａと、第１誘電体膜１７ａに接する第２誘電体膜１７ｂの２層構造である。第２誘電体膜１７ｂは、第１誘電体膜１７ａよりも屈折率が小さく、且つこの第２誘電体膜１７ｂにおける光の波長λの１／４の厚さに形成されている。第１誘電体膜１７ａは、半導体層１２，２２の屈折率ｎｓから第２誘電体膜１７ｂの屈折率ｎ２の２乗（ｎ２ ２）まで、半導体層１２，２２側から第２誘電体膜１７ｂ側に向かう第１誘電体膜１７ａの厚さ方向に屈折率ｎ１が連続的に小さくなるように形成されている。 The operation and effects of the optical semiconductor devices (the semiconductor light receiving device 1A and the semiconductor light emitting device 1B) according to the first and second embodiments will be described.
The optical semiconductor element includes an antireflection film 17 for preventing reflection of light incident on the light receiving section 14 or light emitted from the light emitting section 24 . The antireflection film 17 includes a first dielectric film 17a in contact with the semiconductor layer 12 forming the light receiving portion 14 or the semiconductor layer 22 forming the light emitting portion 24, and a second dielectric film 17a in contact with the first dielectric film 17a. It has a two-layer structure of the body membrane 17b. The second dielectric film 17b has a smaller refractive index than the first dielectric film 17a and is formed to a thickness of 1/4 of the wavelength λ of light in the second dielectric film 17b. The first dielectric film 17a extends from the semiconductor layers 12, 22 side to the second dielectric film 17a from the refractive index n s of the semiconductor layers 12, 22 to the second power of the refractive index n 2 (n 2 2 ) of the second dielectric film 17b. It is formed such that the refractive index n1 continuously decreases in the thickness direction of the first dielectric film 17a toward the body film 17b.
　光がある物質から他の物質に入射する際には、例えば双方の屈折率が等しい特別な場合を除いて、これら物質同士の界面で反射する。ここで、半導体層１２又は半導体層２２と第１誘電体膜１７ａの界面において、第１誘電体膜１７ａの屈折率ｎ１が半導体層１２，２２の屈折率ｎｓと等しい。それ故、第１誘電体膜１７ａから半導体層１２に入射する光、及び半導体層２２から第１誘電体膜１７ａに入射する光について、半導体層１２，２２と第１誘電体膜１７ａの界面における反射が抑制される。 When light enters from one substance to another substance, it is reflected at the interface between these substances, except for a special case where both have the same refractive index. Here, the refractive index n1 of the first dielectric film 17a is equal to the refractive index ns of the semiconductor layers 12 and 22 at the interface between the semiconductor layer 12 or the semiconductor layer 22 and the first dielectric film 17a. Therefore, for light incident on the semiconductor layer 12 from the first dielectric film 17a and light incident on the first dielectric film 17a from the semiconductor layer 22, Reflections are suppressed.
　一方、第２誘電体膜１７ｂと空気の界面、及び第１誘電体膜１７ａと第２誘電体膜１７ｂの界面では、光の反射が発生する。ここで、第２誘電体膜１７ｂは、この第２誘電体膜１７ｂにおける光の波長λの１／４の厚さに形成されている。それ故、空気から第２誘電体膜１７ｂに光が入射する場合には、第２誘電体膜１７ｂと空気の界面で反射した光と、第１誘電体膜１７ａと第２誘電体膜１７ｂの界面で反射した光とが、互いに打ち消し合うように干渉するので、光の反射が低減される。これと同様に、第１誘電体膜１７ａから第２誘電体膜１７ｂに光が入射する場合には、第２誘電体膜１７ｂと空気の界面で反射した光と、第１誘電体膜１７ａと第２誘電体膜１７ｂの界面で反射した光とが、互いに打ち消し合うように干渉するので、光の反射が低減される。 On the other hand, reflection of light occurs at the interface between the second dielectric film 17b and the air and at the interface between the first dielectric film 17a and the second dielectric film 17b. Here, the second dielectric film 17b is formed to have a thickness of 1/4 of the wavelength λ of light in the second dielectric film 17b. Therefore, when light enters the second dielectric film 17b from the air, the light reflected at the interface between the second dielectric film 17b and the air Since the light reflected at the interface interferes so as to cancel each other out, the reflection of light is reduced. Similarly, when light is incident on the second dielectric film 17b from the first dielectric film 17a, the light reflected at the interface between the second dielectric film 17b and the air Since the light reflected at the interface of the second dielectric film 17b interferes so as to cancel each other out, the reflection of light is reduced.
　その上、第１誘電体膜１７ａと第２誘電体膜１７ｂの界面において、第１誘電体膜１７ａの屈折率ｎ１が第２誘電体膜１７ｂの屈折率ｎ２の２乗（ｎ１＝ｎ２ ２）となっているので、理論的には全く反射しない無反射条件を満たし、反射を一層低減することができる。従って、受光部１４に入射する光又は発光部２４から出射する光の反射が、反射防止膜１７によって低減され、光半導体素子の受光感度又は発光効率が向上する。 Moreover, at the interface between the first dielectric film 17a and the second dielectric film 17b, the refractive index n1 of the first dielectric film 17a is the square of the refractive index n2 of the second dielectric film 17b ( n1 = n 2 2 ), theoretically, it satisfies the non-reflection condition that no reflection is caused, and the reflection can be further reduced. Therefore, the reflection of the light incident on the light receiving section 14 or the light emitted from the light emitting section 24 is reduced by the antireflection film 17, and the light receiving sensitivity or light emitting efficiency of the optical semiconductor element is improved.
　第１誘電体膜１７ａは、半導体層１２，２２から第２誘電体膜１７ｂに向かう第１誘電体膜１７ａの厚さ方向において、第２誘電体膜１７ｂ側に移行するほど屈折率ｎ１が直線的に小さくなる。第１誘電体膜１７ａの屈折率ｎ１が厚さ方向に連続的に変化するので、屈折率の違いにより光が反射する界面が第１誘電体膜１７ａ中になく、第１誘電体膜１７ａ中を進む光の反射が抑制される。この第１誘電体膜１７ａは、膜形成時に原料ガスの流量を連続的に変化させることによって、屈折率ｎ１が直線的に小さくなるように容易に形成することができる。 In the thickness direction of the first dielectric film 17a from the semiconductor layers 12 and 22 toward the second dielectric film 17b, the refractive index n1 of the first dielectric film 17a increases toward the second dielectric film 17b. decrease linearly. Since the refractive index n1 of the first dielectric film 17a changes continuously in the thickness direction, there is no interface in the first dielectric film 17a where light is reflected due to the difference in the refractive index. Reflection of light traveling through is suppressed. The first dielectric film 17a can be easily formed so that the refractive index n1 decreases linearly by continuously changing the flow rate of the material gas during film formation.
　第１誘電体膜１７ａは、第２誘電体膜１７ｂ側に移行するほど第１誘電体膜１７ａの屈折率ｎ１の低下が大きくなるように形成されていてもよい。これにより半導体層１２，２２と第１誘電体膜１７ａの界面において、双方の屈折率ｎｓと屈折率ｎ１とが滑らかに連続するように第１誘電体膜１７ａを形成することができる。従って、半導体層１２，２２と第１誘電体膜１７ａの界面での光の反射を確実に防止して、光の反射を一層低減することができる。 The first dielectric film 17a may be formed so that the decrease in the refractive index n1 of the first dielectric film 17a increases toward the second dielectric film 17b. As a result, the first dielectric film 17a can be formed so that the refractive index ns and the refractive index n1 are smoothly continuous at the interface between the semiconductor layers 12 and 22 and the first dielectric film 17a. Therefore, the reflection of light at the interface between the semiconductor layers 12 and 22 and the first dielectric film 17a can be reliably prevented, and the reflection of light can be further reduced.
　第２誘電体膜１７ｂはシリコン酸化膜であり、第１誘電体膜１７ａは、半導体層１２，２２側から第２誘電体膜１７ｂ側に向かう第１誘電体膜１７ａの厚さ方向において、第２誘電体膜１７ｂ側に移行するほど含有酸素の割合（ｘ）が増加すると共に含有窒素の割合（１－ｘ）が減少するように形成されたシリコン酸窒化膜である。このシリコン酸窒化膜は、受光部１４を形成している半導体層１２側、又は発光部２４を形成している半導体層２２側ほど、屈折率が大きい窒化シリコン膜の組成に近づき、第２誘電体膜１７ｂ側ほど窒化シリコン膜よりも屈折率が小さい酸化シリコン膜の組成に近づく。 The second dielectric film 17b is a silicon oxide film. 2 The silicon oxynitride film is formed such that the oxygen content (x) increases and the nitrogen content (1-x) decreases toward the dielectric film 17b. This silicon oxynitride film has a composition closer to that of a silicon nitride film with a higher refractive index toward the semiconductor layer 12 forming the light receiving section 14 or toward the semiconductor layer 22 forming the light emitting section 24, and the composition of the silicon oxynitride film becomes closer to the second dielectric. The composition closer to the body film 17b approaches that of a silicon oxide film having a smaller refractive index than that of a silicon nitride film.
　第１誘電体膜１７ａの形成時にはその膜の組成を変えながら形成して、第１誘電体膜１７ａの厚さ方向に、半導体層１２，２２の屈折率ｎｓから第２誘電体膜１７ｂの屈折率ｎ２の２乗（ｎ２ ２）まで、第１誘電体膜１７ａの屈折率ｎ１が連続的に小さくなるようにすることができる。また、第２誘電体膜１７ｂがシリコン酸化膜なので、第１誘電体膜１７ａの形成後に第２誘電体膜１７ｂを容易に連続形成することができ、反射防止膜１７を一括形成することができる。 When forming the first dielectric film 17a, the composition of the film is changed while forming the first dielectric film 17a. The refractive index n1 of the first dielectric film 17a can be continuously decreased up to the square of the refractive index n2 ( n22 ). Further, since the second dielectric film 17b is a silicon oxide film, the second dielectric film 17b can be easily continuously formed after the formation of the first dielectric film 17a, and the antireflection film 17 can be formed all at once. .
　第１誘電体膜１７ａは、例えば反応性スパッタリング法によって形成されてもよい。また、第１誘電体膜１７ａはシリコン酸窒化膜に限定されるものではなく、例えば酸化アルミニウム系、酸化ジルコニウム系のような光学薄膜材料によって形成されてもよい。その他、当業者であれば、本発明の趣旨を逸脱することなく、上記実施形態に種々の変更を付加した形態で実施可能であり、本発明はその種の変更形態も包含するものである。 The first dielectric film 17a may be formed by reactive sputtering, for example. Also, the first dielectric film 17a is not limited to a silicon oxynitride film, and may be formed of an optical thin film material such as aluminum oxide or zirconium oxide. In addition, those skilled in the art can implement various modifications to the above embodiment without departing from the scope of the present invention, and the present invention includes such modifications.
１Ａ　：半導体受光素子
１Ｂ　：半導体発光素子
１０　：半導体基板
１１　：光吸収層
１２　：半導体層
１２ａ：表面
１４　：受光部
１５　：カソード電極
１６　：アノード電極
１７　：反射防止膜
１７ａ：第１誘電体膜
１７ｂ：第２誘電体膜
２０　：サファイア基板
２０ａ：バッファ層
２１　：半導体層
２１ａ：ｎ－ＧａＮ層
２１ｂ：ｎ－ＡｌＧａＮ層
２１ｃ：ｎ－ＩｎＧａＮ層
２２　：半導体層
２２ａ：ｐ－ＡｌＧａＮ層
２２ｂ：ｐ－ＧａＮ層
２４　：発光部
２５，２６：電極 1A: semiconductor light receiving element 1B: semiconductor light emitting element 10: semiconductor substrate 11: light absorbing layer 12: semiconductor layer 12a: surface 14: light receiving section 15: cathode electrode 16: anode electrode 17: antireflection film 17a: first dielectric film 17b: second dielectric film 20: sapphire substrate 20a: buffer layer 21: semiconductor layer 21a: n-GaN layer 21b: n-AlGaN layer 21c: n-InGaN layer 22: semiconductor layer 22a: p-AlGaN layer 22b: p -GaN layer 24: light-emitting portions 25, 26: electrodes

Claims (4)

  1. 　受光部に入射する光又は発光部から出射する光の反射を防止するための反射防止膜を備えた光半導体素子において、
    　前記反射防止膜は、前記受光部又は前記発光部を形成している半導体層に接する第１誘電体膜と、前記第１誘電体膜に接する第２誘電体膜を有し、
    　前記第２誘電体膜は、前記第１誘電体膜よりも屈折率が小さく、且つこの第２誘電体膜における前記光の波長の１／４の厚さに形成され、
    　前記第１誘電体膜は、前記半導体層の屈折率から前記第２誘電体膜の屈折率の２乗まで、前記半導体層側から前記第２誘電体膜側に向かう前記第１誘電体膜の厚さ方向に屈折率が小さくなるように形成されたことを特徴とする光半導体素子。     An optical semiconductor device provided with an antireflection film for preventing reflection of light incident on a light receiving part or light emitted from a light emitting part,
    The antireflection film has a first dielectric film in contact with a semiconductor layer forming the light receiving portion or the light emitting portion, and a second dielectric film in contact with the first dielectric film,
    the second dielectric film has a smaller refractive index than the first dielectric film and is formed to a thickness of 1/4 of the wavelength of the light in the second dielectric film;
    The first dielectric film has a refractive index ranging from the refractive index of the semiconductor layer to the square of the refractive index of the second dielectric film, from the semiconductor layer side to the second dielectric film side. An optical semiconductor element characterized by being formed so that a refractive index decreases in a thickness direction.
  2. 　前記第１誘電体膜は、前記厚さ方向に前記第１誘電体膜の屈折率が直線的に小さくなるように形成されたことを特徴とする請求項１に記載の光半導体素子。 2. The optical semiconductor device according to claim 1, wherein said first dielectric film is formed such that the refractive index of said first dielectric film decreases linearly in said thickness direction.
  3. 　前記第１誘電体膜は、前記厚さ方向において、前記第２誘電体膜側に移行するほど前記第１誘電体膜の屈折率の低下が大きくなるように形成されたことを特徴とする請求項１に記載の光半導体素子。 The first dielectric film is formed such that a decrease in refractive index of the first dielectric film in the thickness direction increases toward the second dielectric film side. Item 1. The optical semiconductor device according to item 1.
  4. 　前記第２誘電体膜はシリコン酸化膜であり、
    　前記第１誘電体膜は、前記厚さ方向において、前記第２誘電体膜側に移行するほど含有酸素の割合が増加すると共に含有窒素の割合が減少するように形成されたシリコン酸窒化膜であることを特徴とする請求項１に記載の光半導体素子。
          the second dielectric film is a silicon oxide film,
    The first dielectric film is a silicon oxynitride film formed so that the percentage of oxygen contained increases and the percentage of nitrogen contained decreases toward the second dielectric film in the thickness direction. 2. The optical semiconductor device according to claim 1, wherein:
PCT/JP2022/003977 2022-02-02 2022-02-02 Optical semiconductor element WO2023148839A1 (en)

Priority Applications (1)

Application Number Priority Date Filing Date Title
PCT/JP2022/003977 WO2023148839A1 (en) 2022-02-02 2022-02-02 Optical semiconductor element

Applications Claiming Priority (1)

Application Number Priority Date Filing Date Title
PCT/JP2022/003977 WO2023148839A1 (en) 2022-02-02 2022-02-02 Optical semiconductor element

Publications (1)

Publication Number Publication Date
WO2023148839A1 true WO2023148839A1 (en) 2023-08-10

Family

ID=87553351

Family Applications (1)

Application Number Title Priority Date Filing Date
PCT/JP2022/003977 WO2023148839A1 (en) 2022-02-02 2022-02-02 Optical semiconductor element

Country Status (1)

Country Link
WO (1) WO2023148839A1 (en)

Citations (7)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JPS59121886A (en) * 1982-12-21 1984-07-14 ウエスターン　エレクトリック　カムパニー，インコーポレーテッド Method of forming optical device
JPH07235684A (en) * 1994-02-23 1995-09-05 Hitachi Cable Ltd Solar cell
JP2005328066A (en) * 2004-05-14 2005-11-24 Magnachip Semiconductor Ltd Cmos image sensor
JP2007505771A (en) * 2003-10-30 2007-03-15 エス　オー　イ　テク　シリコン　オン　インシュレータ　テクノロジース Refractive index matched substrate
US20070113881A1 (en) * 2005-11-22 2007-05-24 Guardian Industries Corp. Method of making solar cell with antireflective coating using combustion chemical vapor deposition (CCVD) and corresponding product
JP2009140822A (en) * 2007-12-07 2009-06-25 Sony Corp Lighting system, color converting element, and display device
JP2011215440A (en) * 2010-04-01 2011-10-27 Canon Inc Anti-reflection structure and optical apparatus

Patent Citations (7)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JPS59121886A (en) * 1982-12-21 1984-07-14 ウエスターン　エレクトリック　カムパニー，インコーポレーテッド Method of forming optical device
JPH07235684A (en) * 1994-02-23 1995-09-05 Hitachi Cable Ltd Solar cell
JP2007505771A (en) * 2003-10-30 2007-03-15 エス　オー　イ　テク　シリコン　オン　インシュレータ　テクノロジース Refractive index matched substrate
JP2005328066A (en) * 2004-05-14 2005-11-24 Magnachip Semiconductor Ltd Cmos image sensor
US20070113881A1 (en) * 2005-11-22 2007-05-24 Guardian Industries Corp. Method of making solar cell with antireflective coating using combustion chemical vapor deposition (CCVD) and corresponding product
JP2009140822A (en) * 2007-12-07 2009-06-25 Sony Corp Lighting system, color converting element, and display device
JP2011215440A (en) * 2010-04-01 2011-10-27 Canon Inc Anti-reflection structure and optical apparatus

Similar Documents

Publication Publication Date Title
US7683378B2 (en) Light emitting diode and method for fabricating same
KR20080070696A (en) Nitride semiconductor light emitting device
JP2012502472A (en) Monochromatic light source
JP4186725B2 (en) Photoelectric conversion element
US9190545B2 (en) Optical device including three-coupled quantum well structure having multi-energy level
CN111868942A (en) Optoelectronic semiconductor chip
JP2009164506A (en) Semiconductor light-emitting element
JP2010021337A (en) Semiconductor photodetector
JP2014067894A (en) Semiconductor light-emitting element and manufacturing method of the same
CN103022297B (en) High-power gamma-irradiation-resisting super-radiation light-emitting diode
CN107492586A (en) Light emitting diode
Lin et al. Enhancement of InGaN–GaN Indium–Tin–Oxide Flip-Chip Light-Emitting Diodes With TiO $ _2 $–SiO $ _2 $ Multilayer Stack Omnidirectional Reflector
JP2005268601A (en) Compound semiconductor light-emitting device
US8233514B2 (en) Semiconductor laser device
CN114530532A (en) Prague reflector and LED with same
WO2023148839A1 (en) Optical semiconductor element
JP2009070929A (en) Surface emitting diode
JP5524517B2 (en) Light receiving element
US20230343893A1 (en) Led epitaxial structure and led chip
KR20190133382A (en) A surface-emitting laser device and light emitting device including the same
US20170084784A1 (en) Light-emitting device and production method therefor
KR100880635B1 (en) Light emitting device
JPH0738151A (en) Optical semiconductor device
JP2006270073A (en) Light-emitting diode and method of manufacturing it
KR20140127034A (en) Edge emitting laser diode and method for manufacturing the same

Legal Events

Date Code Title Description
121 Ep: the epo has been informed by wipo that ep was designated in this application

Ref document number: 22924752

Country of ref document: EP

Kind code of ref document: A1