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EP-4415061-B1 - LIGHT-EMITTING DIODE ELEMENT

EP4415061B1EP 4415061 B1EP4415061 B1EP 4415061B1EP-4415061-B1

Inventors

  • NODA, SUSUMU
  • KASHIWAGI, HIROYUKI
  • Ide, Shunya
  • IWASAKI, Tessei
  • KAWAKAMI, YASUYUKI
  • YOKOBAYASHI, YUSUKE

Dates

Publication Date
20260506
Application Date
20221101

Claims (8)

  1. A light-emitting diode element (10, 50, 61) comprising: a substrate (11) with a moth-eye nano pattern (11M) on a surface of the substrate (11) in which cone-shaped protrusions are periodically formed and are arranged in a lattice; a first semiconductor layer (21) formed on the moth-eye nano pattern (11M) and having a photonic crystal layer (21P); an active layer (23) formed on the first semiconductor layer (21) and having a light-emitting layer (23A); and a second semiconductor layer (25) formed on the active layer (23), characterized in that P < λ / ns is satisfied, wherein a period of the protrusions is P, an emission wavelength of the light-emitting layer (23A) is λ, and a refractive index of a medium on a light-emitting layer side of the moth-eye nano pattern (11M) is ns.
  2. The light-emitting diode element according to claim 1, wherein the photonic crystal layer (21P) has only photonic crystals satisfying a square lattice arrangement and a ≠ mλw/neff for any natural number m, or the photonic crystal layer (21P) has only photonic crystals satisfying a triangular lattice arrangement and a ≠ mλw x 2/(3/2 x neff) for any natural number m, wherein a lattice constant of the photonic crystal layer (21P) is a, a refractive index of a material of the first semiconductor layer (21) is neff, and an arbitrary wavelength in a vacuum within a full width at half maximum of an emission spectrum of the light-emitting layer (23A) is λw.
  3. The light-emitting diode element according to claim 1 or 2, wherein a first layer (21P) and a second layer (25) having an effective refractive index lower than the active layer (23) are formed with the active layer (23) sandwiched therebetween, and the photonic crystal layer (21P) is the first layer (21P).
  4. The light-emitting diode element according to any one of claims 1 to 3, wherein the photonic crystal layer (21P) has air holes (22) having a cylindrical shape and arranged at square lattice point positions, wherein 0.3 ≤ d/a is satisfied, wherein a lattice constant of the air holes (22) is a, and a diameter of the air holes (22) is d.
  5. The light-emitting diode element according to claim 4, wherein the first semiconductor layer (21) is made of GaN, and a depth of the air holes (22) of the photonic crystal layer (21P) is equal to or more than a penetration depth of evanescent light in TE0 mode light from the light-emitting layer (23A).
  6. The light-emitting diode element according to any one of claims 1 to 3, wherein the active layer (23) includes a spacer layer (23B) formed on the light-emitting layer (23A), and has a layer thickness such that only TE0 to TE5 mode light is guided.
  7. The light-emitting diode element according to any one of claims 1 to 6, wherein an LED structural layer (20) including the first semiconductor layer (21), the active layer (23), and the second semiconductor layer (25) has a rectangular parallelepiped shape, and a reflective film (51) covering at least four sides of the light-emitting layer (23A) is formed, wherein the reflective film (51) is a dielectric multilayer film in which high refractive index films and low refractive index films are alternately stacked, and wherein the following formula holds: n h d h cos α = λ 4 or n h d h cos α = 3 λ 4 wherein an emission wavelength of the light-emitting layer (23A) is λ, an incidence angle of the TE0 mode light is α, a refractive index of the high refractive index film is n h , and a film thickness is d h .
  8. The light-emitting diode element according to any one of claims 1 to 7, wherein a center position of the light-emitting layer (23A) coincides with a peak position of a light intensity distribution of the TE0 mode light of the active layer (23).

Description

Technical Field The present invention relates to a light-emitting diode element including a photonic crystal. Background Art In recent years, efforts toward autonomous driving of vehicles such as automobiles or moving objects have progressed rapidly, and the demands placed on lighting equipment such as headlamps are also changed. For example, headlamps are required to have value not only as a single lamp but also as a lamp system that incorporates sensors and the like. However, for example, in automobile headlamps, light-emitting diode (LED) elements are sometimes arranged in parallel to increase output for use, but there is a problem in that it is difficult to secure a space for installing sensors and the like. In general, spontaneous emission LEDs have a Lambertian light emission distribution, which spreads the light distribution, resulting in loss due to light that deviates from the lens in a headlamp. In order to reduce the loss of light and further increase the amount of light, it is necessary to increase the size of the lens (that is, increase an aperture ratio NA), but this is not preferable from the viewpoint of the space for the headlamp. In order to increase the amount of LED light taken in without changing the NA of the lens, it is necessary to narrow the light emission distribution of the LED light source itself in angle. For example, JP 2015-109477 A discloses forming a structure called a moth-eye nano pattern with a sapphire substrate (NPSS) on a sapphire substrate or the like to increase light extraction efficiency. Further, it is disclosed that depending on the period of the NPSS, it is possible to narrow a part of the light for extraction. However, the proportion of light that can be narrowed by the effect of NPSS is not high. Liu, Jia-Zhe et al.: "Efficiency Improvement of Blue LEDs Using a GaN Burried Air Void Photonic Crystal With High Air Filling Fraction", IEEE Journal of Quantum Electronics, IEEE, USA, vol. 50, No. 5, May 2014, pages 314-320, ISSN: 0018-9197, DOI: 10.1109/JQE.2014.2309137, discloses an investigation of the efficiency enhancement of blue InGaN/GaN light-emitting diodes (LEDs) by incorporating a buried air void photonic crystal (BAVPC) layer within the epitaxial structure. As compared with the conventional patterned sapphire substrate (C-PSS) LEDs and flat sapphire substrate LEDs with BAVPC, the fabricated patterned sapphire substrate (PSS) LEDs with BAVPC exhibit the lowest full-width at half-maximum of (002) and (102) diffraction peaks, the highest light output power of 20.6 mW, and the highest external quantum efficiency of 37.4%. Remarkable performance improvement in the PSS LED with BAVPC is attributed to the better epitaxial quality with threading dislocations terminated by the BAVPC and the higher scattering at interface between GaN and air-void. By positioning the BAVPC directly below the multiple quantum wells (MQWs), it would cause the reduction in the number of trapped optical modes. The methodology optically isolates the MQWs from the underlying substrate and increases the optical output power. Moreover, threading dislocations are significantly suppressed using the BAVPC with high air filling fraction of {sim}{50%}. It is well proposed that this methodology provides a promising alternative to C-PSS LEDs. CN 108 511 572 A discloses an LED with a photonic crystal structure. The LED comprises a nano graphical sapphire substrate, a non-doped GaN layer, an n type GaN layer, a multi-quantum well active region, a p type AlGaN electron barrier layer, a p type GaN ohmic contact layer and an ITO layer arranged successively from bottom to top, the LED further comprises a p type ohmic electrode led out of the ITO layer and an n type ohmic electrode led out of the n type GaN layer, and the reflective photonic crystal structure is prepared on the non-doped GaN layer. Summary of Invention Technical Problem An object of the present invention is to provide a highly efficient light-emitting diode element having a light distribution characteristic that is highly efficiently narrowed in angle. Solution to Problem According to the present invention, a light-emitting diode element is provided as set forth in claim 1. Preferred embodiments of the present invention may be gathered from the dependent claims. Brief Description of Drawings FIG. 1A is a plan view schematically showing the upper surface of a light-emitting diode element 10 according to a first comparative example.FIG. 1B is a cross-sectional view schematically showing a cross-sectional structure taken along the line A-A shown in FIG. 1A.FIG. 2A is a view showing a dispersion relationship in which a horizontal axis is a wave number kx (= ksinθ) and a vertical axis is a normalized frequency a/λ.FIG. 2B is a view showing an enlarged portion of the maximum value of TE0.FIG. 3A is a view showing experimental results of the dependence of PL detection intensity (vertical axis) with respect to d/a (horizontal axis).FIG. 3B is a