JP2007109793A - Semiconductor light-emitting element and light scattering substrate - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a semiconductor light-emitting element capable of improving light extraction efficiency. <P>SOLUTION: A light emitter 30 is provided on a transparent light scattering substrate 12 to an emission wavelength, and light generated by the emitter 30 is emitted from the side of the light scattering substrate 12. The light scattering substrate 12 has a plurality of projecting light scatters 11 on a substrate 10 (a sapphire substrate). For the light scatters 11, a number of scattering particles 14 made of, for example, Si (silicon) are dispersed inside a medium 13 made of, for example, SiO<SB>2</SB>(silicon oxide). Emission light is refracted on an inclined surface at the light scatter 11, and is scattered by the scattering particles 14 inside the light scatter 11 for changing to an angle less than a critical angle. As a result, the light extraction efficiency is improved. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a semiconductor light emitting device that emits light from a substrate side, and a light scattering substrate used therefor.

  The external quantum efficiency of a semiconductor light emitting device such as a light emitting diode (LED) is composed of two elements, an internal quantum efficiency and a light extraction efficiency. By improving these efficiency, long life and low power consumption are achieved. In addition, a high-power semiconductor light emitting device can be realized. Here, the former internal quantum efficiency is, for example, a layer structure capable of accurately controlling the growth conditions so as to obtain a high-quality crystal with few crystal defects and dislocations and suppressing the occurrence of carrier overflow. It is improved by doing. On the other hand, the latter light extraction efficiency has a geometric shape or layer structure in which the light emitted from the active layer is incident on the exit window at a angle less than the critical angle before being absorbed by the substrate or the active layer. Can be improved.

  For example, when a semiconductor layer made of a material different from the substrate is stacked on the substrate, there are techniques described in Patent Document 1 and Patent Document 2, for example, as measures for improving the external quantum efficiency. In these techniques, unevenness is formed in advance on the substrate surface, and a semiconductor layer is grown in the lateral direction on the uneven substrate surface.

JP 2004-6931 A JP 2004-6937 A

  However, in the techniques described in Patent Document 1 and Patent Document 2, if the structure of the projections and depressions provided on the substrate surface and the crystal growth conditions are not appropriate, gaps are formed in the semiconductor layer or high crystal defects are widespread. An element that cannot be improved in external quantum efficiency, such as spreading, is formed.

  Therefore, the same applicant and the same applicant have proposed a technique for forming a semiconductor layer without any gaps under the growth conditions in which predetermined irregularities are provided on the substrate surface and a predetermined plane is formed on the substrate during crystal growth. ing. As a result, the internal quantum efficiency can be greatly improved, and the light extraction efficiency can also be improved by adjusting the inclination angle and area of the side surface of the convex portion.

  However, with the previously proposed technology, there was room for improvement in light extraction efficiency because the focus was on improving internal quantum efficiency.

  The present invention has been made in view of such problems, and an object thereof is to provide a semiconductor light emitting device capable of further improving the light extraction efficiency and a light scattering substrate used therefor.

  The light scattering substrate of the present invention has one or a plurality of light scattering portions protruding on the surface of the substrate transparent to the emission wavelength, and a plurality of light scattering particles are dispersed inside the light scattering portion. Has been. The semiconductor light emitting device of the present invention includes a light emitting section including an active layer for guiding light emitted from the active layer to the substrate side on the light scattering substrate.

  In this semiconductor light-emitting device, most of the light emitted from the active layer that enters the substrate at an angle greater than the critical angle is refracted by the slope of the light scattering portion or enters the light scattering portion. It is changed to an angle less than the critical angle by being scattered by the dispersed scattering particles.

  According to the semiconductor light emitting device of the present invention, since the light scattering portion in which a plurality of scattering particles are dispersed is provided on the substrate, the light traveling toward the substrate, particularly the light traveling at an angle greater than the critical angle. Scattered. For this reason, the ratio of the emitted light incident on the substrate at less than the critical angle increases, thereby improving the light extraction efficiency. Therefore, a high-output light emitting diode can be realized.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

  FIG. 1 shows a cross-sectional structure of a light emitting diode (LED) 1 according to an embodiment of the present invention. The light emitting diode 1 is provided with a light emitting portion 30 on a light scattering substrate 12, and FIG. 2 is a perspective view of only the light scattering substrate 12 extracted. 1 and 2 are schematically shown, and are different from actual dimensions and shapes.

  The light scattering substrate 12 is formed by periodically forming a plurality of light scattering portions 11 having a trapezoidal cross section on one side of a substrate 10, for example, a sapphire substrate. Here, each light scattering portion 11 extends in a band shape in the <1-100> direction of the substrate 10.

  In the substrate 10, the surface (main surface) on which the light scattering portion 11 is formed is a c-plane, and the c-plane is a flat surface. In addition, the light-scattering part 11 may be formed in surfaces other than c surface. The substrate 10 only needs to be transparent with respect to the emission wavelength of light generated from the light emitting unit 30, and may be made of a material other than sapphire, for example, GaN (gallium nitride).

  The light scattering unit 11 has a trapezoidal cross section with an upper base width of 2 μm and a height of 1 μm, for example, and has a gap of 2 μm with the adjacent light scattering unit 11, for example. The light scattering portion 11 is obtained by dispersing a plurality of scattering particles 14 in a medium portion 13, and emitted light directed toward the substrate 10 is refracted on its slope when passing through the light scattering portion 11, or a large number of insides. Are scattered by the scattering particles 14.

  In addition to the trapezoidal shape, the light scattering portion 11 may have, for example, a hemispherical cross section as shown in FIG. 3, or a triangular cross section as shown in FIG. It may be. As described above, by providing a large area of the inclined surface, the ratio of the incident light refracted on the inclined surface to be incident on the exit window at less than the critical angle increases, and the light extraction efficiency can be improved.

The medium portion 13 is made of a material that has a refractive index smaller than that of the scattering particles 14 and transmits the emitted light, for example, SiO ₂ , TiO ₂ , Sb ₂ O ₃ , CaO, or In ₂ O ₃ . The scattering particles 14 are particles having a refractive index larger than that of the constituent material of the medium portion 13 and having a band gap larger than the energy corresponding to the emission wavelength of the emitted light. For example, the emission wavelength of the emitted light has a wavelength of 300 nm. When it is 1000 nm or less, it is composed of Si, Ti, Sb, Ca, or In having a diameter of 0.5 nm or more and 5 nm or less.

  The light emitting unit 30 provided on the light scattering substrate 12 described above is formed by a laminated structure of, for example, a group III-V nitride semiconductor. The group III-V nitride semiconductor here is a gallium nitride-based compound containing gallium (Ga) and nitrogen (N). For example, GaN, AlGaN (aluminum nitride / gallium), or AlGaInN (nitride). (Aluminum, gallium, indium) and the like. These may be n-type impurities composed of group IV and group VI elements such as Si (silicon), Ge (germanium), O (oxygen), Se (selenium), or Mg (magnesium), Zn (zinc as required) ), C (carbon) and other p-type impurities composed of group II and group IV elements.

  Specifically, the light emitting unit 30 includes an n-type GaN layer 15, an n-type GaInN layer 16, an n-type GaN layer 17, an n-type GaInN layer 18, an active layer 19, a p-type GaInN layer 20, a p-type AlInN layer 21, p. A type GaN layer 22 and a p-type GaInN layer 23 are stacked in this order. Here, in the active layer 19, a region that emits light when current is injected by a p-side electrode 25 and an n-side electrode 26 described later is referred to as a light-emitting region 19A. Hereinafter, a direction in which the light emitting units 30 are stacked is referred to as a vertical direction, an emission direction of emitted light is referred to as an axial direction, and a direction perpendicular to the axial direction and the vertical direction is referred to as a horizontal direction.

  The n-type GaN layer 15 has a facet surface ((1-) that is inclined with respect to the main surface in a region where the light scattering portion 11 is not formed on the surface of the light scattering substrate 12, that is, a region between the light scattering portions 11. 101) surface) is formed on an inclined surface under a growth condition in which lateral growth is dominant. As a result, there is no gap between the light emitting unit 30 and the light scattering substrate 12, and high crystal defects do not spread over a wide range in the light emitting unit 30, so that the defect density becomes extremely small. As a result, the internal quantum efficiency is reduced. It can be greatly improved.

  After the p-type GaInN layer 23 is formed in the light emitting unit 30, the p-type GaInN layer 23, the p-type GaN layer 22, the p-type AlInN layer 21, p, for example, by RIE (Reactive Ion Etching). The ridge portion 24 is formed by selectively etching the n-type GaInN layer 20, the active layer 19, the n-type GaInN layer 18 and the n-type GaN layer 17.

  In the light emitting portion 30, the p-side electrode 25 is formed on the upper surface of the ridge portion 24, that is, on the surface of the p-type GaInN layer 23, while on the exposed surface of the n-type GaInN layer 16. An n-side electrode 26 is formed. The p-side electrode 25 has, for example, a structure in which a Ti (titanium) layer, a Pt (platinum) layer, and an Au (gold) layer are stacked in this order on the surface of the p-type GaInN layer 23. And are electrically connected. The n-side electrode 26 has, for example, a structure in which an alloy layer of Au and Ge (germanium), a Ni (nickel) layer, and an Au layer are stacked in this order, and is electrically connected to the n-type GaInN layer 16. It is connected to the.

  The light emitting diode 1 having such a configuration can be manufactured, for example, as follows.

  First, a SiOx (0 <x <2) layer 11A containing excessive Si is formed on the surface of the substrate 10 by using, for example, a plasma CVD (Chemical Vapor Deposition) method or a simultaneous sputtering method.

In the plasma CVD method, for example, the temperature of the substrate 10 is 400 ° C., the flow rate of SiH ₄ is 100 sccm, the flow rate of N ₂ O is 2000 sccm, the pressure is 3.3 × 10 ² Pa, the RF power is 150 to 300 W, and the RF power is The SiOx layer 11A is formed under the condition that the gap between the parallel plates for application is 14 mm.

On the other hand, in the simultaneous sputtering method, for example, a plurality of Si chips are arranged on the SiO ₂ target under the condition that the flow rate of Ar (argon) is 20 sccm, the pressure is 1 × 10 ⁻⁴ Pa, and the RF power is 500 W, the SiO ₂ target and Si chip to form the SiOx layer 11A by simultaneously sputtering with Ar.

  In both the plasma CVD method and the co-sputtering method, the film thickness and composition of the SiOx layer 11A vary depending on the application of the light emitting diode 1, and therefore the film formation conditions may be changed depending on each application.

After forming the SiOx layer 11A, as shown in FIG. 5A, the SiOx layer 11A is selectively etched to form a band-like region periodically, followed by Ar (argon) or N ₂ (nitrogen). In an inert atmosphere such as, annealing is performed at a temperature of about 700 ° C. to 1400 ° C., for example. Then, as shown in FIG. 5 (B), and SiOx is SiO _2, separated into the Si, a state where Si particles are dispersed in SiO ₂ medium. In this way, a large number of scattering particles 14 are dispersed in the medium portion 13 to form a light scattering substrate 12 having a plurality of light scattering portions 11.

Next, the light emitting unit 30 is formed on the light scattering substrate 12. That is, first, an isosceles triangular prism-shaped crystal (seed crystal) having a facet surface ((1-101) plane) inclined with respect to the main surface in the region between the light scattering portions 11 of the light scattering light scattering substrate 12. ) (Not shown), the n-type GaN layer 15 is formed by lateral growth. Subsequently, on this n-type GaN layer 15, an n-type GaInN layer 16, an n-type GaN layer 17, an n-type GaInN layer 18, an active layer 19, a p-type GaInN layer 20, a p-type AlInN layer 21, and a p-type GaN layer. 22 and a p-type GaInN layer 23 are stacked in this order. As a growth method of each layer, for example, MOCVD (Metal Organic Chemical Vapor Deposition) method is used, and as a source of donor impurities, for example, hydrogen selenide (H ₂ Se) is used. For example, dimethyl zinc (DMZn) is used as the impurity source.

  Next, the ridge portion 24 is formed by selectively etching the laminated structure from the p-type GaInN layer 23 by using RIE, and then p is formed on the upper surface of the ridge portion 24 (the surface of the p-type GaInN layer 23). The side electrode 25 is formed, and the n-side electrode 26 is formed on the exposed surface of the n-type GaInN layer 16. In this way, the light emitting diode 1 of the present embodiment is manufactured.

  Next, operations and effects of the light-emitting diode 1 of the present embodiment will be described.

  In the light emitting diode 1 according to the present embodiment, when a predetermined voltage is applied between the p-side electrode 25 and the n-side electrode 26, electrons are activated from the n-side electrode 26, and holes are activated from the p-side electrode 25. Implanted into layer 19. Then, electrons and holes injected into the active layer 19 are recombined to generate photons from the light emitting region 19A. As a result, emitted light is emitted from the back surface of the substrate 10 to the outside.

  At this time, most of the light emitted from the light emitting region 19 </ b> A is refracted on the slopes of the plurality of light scattering portions 11 or light scattering portions 11. It is changed to an angle less than the critical angle by being scattered by the scattering particles 14 dispersed inside.

  As described above, in the light emitting diode 1 according to the present embodiment, the light traveling toward the substrate 10, particularly the light traveling at an angle greater than the critical angle, is scattered by the scattering particles 14 dispersed inside the light scattering portion 11. For this reason, the rate at which the emitted light is incident on the substrate 10 at less than the critical angle is increased, thereby improving the light extraction efficiency. Therefore, it is possible to realize a high-output light emitting diode 1.

  The present invention has been described with reference to the embodiment. However, the present invention is not limited to the above embodiment, and various modifications can be made. For example, in the above embodiment, the surface of the substrate 10 is a flat surface, but a groove may be formed in a region between the light scattering portions 11 adjacent to each other on the surface of the substrate 10. In addition, the light emitting unit 30 is not limited to a III-V nitride semiconductor, but may be formed of other material systems.

It is a section lineblock diagram of a light emitting diode concerning one embodiment of the present invention. It is a perspective view of a sapphire substrate and a light scattering part. It is a cross-sectional block diagram showing the modification of a light-scattering part. It is a cross-sectional block diagram showing the other modification of a light-scattering part. It is a cross-sectional block diagram for demonstrating the manufacturing process of a light emitting diode.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Light emitting diode, 10 ... Substrate (sapphire substrate), 11 ... Light scattering part, 11A ... SiOx layer, 12 ... Light scattering substrate, 13 ... Medium part, 14 ... Scattering particle, 15 ... n-type GaN layer, 16 ... n Type ... GaInN layer, 17 ... n-type GaN layer, 18 ... n-type GaInN layer, 19 ... Active layer, 19A ... Light emitting region, 20 ... p-type GaInN layer, 21 ... p-type AlInN layer, 22 ... p-type GaN layer, 23 ... p-type GaInN layer, 24 ... ridge portion, 25 ... p-side electrode, 26 ... n-side electrode 26, 30 ... light emitting portion

Claims (6)

A substrate that is transparent to the emission wavelength, and a light-scattering substrate that is provided on the surface of the substrate and has one or a plurality of light-scattering portions having a plurality of light-scattering particles dispersed therein,
A semiconductor light emitting device comprising: a light emitting portion that is provided on the light scattering substrate and includes an active layer and guides light emitted from the active layer to the substrate side. The semiconductor light-emitting element according to claim 1, wherein the scattering particles have a size that makes a band gap larger than energy corresponding to an emission wavelength. The light scattering portion includes particles made of Si, Ti, Sb, Ca or In as scattering particles in a medium portion made of SiO ₂ , TiO ₂ , Sb ₂ O ₃ , CaO or In ₂ O _3. The semiconductor light emitting device according to claim 1. The semiconductor light-emitting element according to claim 1, wherein the light scattering portion extends in a band shape along the surface of the substrate. The semiconductor light-emitting element according to claim 1, wherein the light scattering portion has a trapezoidal, hemispherical, or triangular cross section. A light-scattering substrate including an active layer formed on the surface and transmitting light emitted from the active layer,
A substrate transparent to the emission wavelength;
A light scattering substrate comprising: one or a plurality of light-scattering portions provided on a surface of the substrate and having a plurality of light scattering particles dispersed therein.

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