JP2006140357A - Nitride semiconductor light emitting device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a structure inside a device that effectively scatters light and thereby to improve light extraction efficiency without complicating a light-emitting device manufacturing process. <P>SOLUTION: In the device structure of a GaN-based light emitting device, a light scattering layer 50 is provided as a layer other than a light emitting layer 30 in a laminated layer that contains an n-type layer 20, the light emitting layer 30, and a p-type layer 40. Light emitted from the light emitting layer is configured to be scattered by an uneven interface between a first GaN based crystal 51 and an embedding layer 52 that constitute the light scattering layer 50. The light scattering layer 50 is structured such that the first GaN-based crystal 51 having a refractive index of n1 is vapor-deposited in a form having projections and/or recesses on a surfactant-processed base surface 50B, and the crystal 51 is embedded by a second GaN-based crystal (refractive index n2 (≠n1)) 52. The level difference between the projections and depressions of the surface of the crystal 51 is set to be a quarter or more of a wavelength of light in the light layer 50 that is emitted from the light emitting layer 30. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a nitride semiconductor light emitting device, and more particularly to an LED device structure with improved light extraction efficiency.

The nitride semiconductor light emitting device is a light emitting device using a nitride semiconductor at least in a light emitting layer.
The nitride semiconductor is a compound semiconductor made of a group III nitride determined by the formula Al _a In _b Ga _1-ab N (0 ≦ a ≦ 1, 0 ≦ b ≦ 1, 0 ≦ a + b ≦ 1). . By selecting the composition ratios a and b in the above formula, an arbitrary mixed crystal of binary to quaternary such as GaN, AlGaN, InGaN, AlInGaN, etc. can be obtained. Here, a part of the group 3 element is substituted with B (boron), Tl (thallium) or the like, or a part of N (nitrogen) is P (phosphorus), As (arsenic), Sb (antimony), Those substituted with Bi (bismuth) or the like are also included in the nitride semiconductor.
Hereinafter, the nitride semiconductor is also abbreviated as “GaN-based”, and the conventional technology and the present invention will be described using GaN-based crystals, GaN-based light emitting devices, GaN-based LEDs, and the like as necessary.

The GaN-based LED has a problem that the light extraction efficiency is low. The light extraction efficiency is a ratio indicating how much light is extracted out of the element out of the total amount of light generated in the light emitting layer. The reason why the light extraction efficiency of the GaN-based LED is low is the high refractive index of the GaN-based crystal as described below.
First, the element structure of a GaN-based light-emitting element is obtained by growing a GaN-based crystal layer on a substrate, but sapphire, which is widely used as the most preferable substrate material, has a lower refractive index than a GaN-based crystal. On the other hand, on the upper side of the element, the material and medium surrounding the element (for example, a passivation film (such as silicon dioxide), a sealing resin (such as an epoxy resin), air (when not resin-sealed)) and the GaN-based crystal layer are in contact. However, in most cases, these materials and media also have a lower refractive index than GaN-based crystals. When an electrode made of a transparent conductive film material such as indium tin oxide (ITO) or zinc oxide (ZnO) is used as the p-side electrode, the refractive index of the electrode is lower than that of the GaN-based crystal.

In this way, since the GaN-based crystal layer, which is the main part of the light-emitting structure, is sandwiched from above and below by a material having a lower refractive index, a part of the light emitted from the light-emitting layer can The light is totally reflected at the interfaces on both sides (for example, [interface between the substrate and the GaN-based crystal layer] and [interface between the GaN-based crystal layer and air]) and confined inside the device by multiple reflection. This light is attenuated by internal absorption while propagating inside the element without going out of the element.
In a GaN-based LED mounted by flip-chip bonding, the p-side electrode is entirely formed on one surface of the GaN-based crystal layer (in some cases, it is formed via a transparent conductive film such as ITO). ) Since this electrode is made light reflective, a problem of multiple reflection occurs.

As a method of solving such a problem of multiple reflections and improving light extraction efficiency, a refractive index interface capable of generating light scattering is provided inside the element, thereby inhibiting the occurrence of multiple reflections and increasing the amount of light. A method of directing outside the element is known.
For example, in the “light-emitting element with enhanced light scattering” of Patent Document 1, light is scattered by providing irregularities called “textured layer” formed by etching or selective growth in the element.
Also, in “Light-emitting element, manufacturing method thereof and LED lamp” of Patent Document 2, pits by high-temperature treatment, unevenness by selective etching, unevenness by selective growth are provided in the element, light is scattered, and light extraction efficiency is increased. Has improved.
In addition, in the “semiconductor light-emitting device” of Patent Document 3, a surface that is a basis for crystal growth (substrate surface, etc.) is subjected to uneven processing, and further concavo-convex is created by facet growth of a GaN-based crystal. Providing light extraction efficiency.

However, any of the light scattering structures formed by the above-described conventional processing methods (etching processing, selective growth using a mask, uneven processing on a substrate surface, etc.) makes the element formation process more complicated.
JP 2004-193619 A Japanese Patent Laid-Open No. 2004-200523 JP 2002-280611 A Japanese Patent Laid-Open No. 10-79501 JP-A-11-354842 Japanese Patent Laid-Open No. 11-354843

  An object of the present invention is to improve the light extraction efficiency by providing a structure that effectively generates light scattering without complicating the manufacturing process of the light emitting element.

  As a result of diligent research to solve the above problems, the present inventors have conducted a phenomenon that a fine dot-like nitride semiconductor crystal is formed by subjecting a surface (base surface) serving as a base for crystal growth to a surfactant treatment. The present invention has been conceived to be applied as a method for forming a light scattering structure, not as a method for forming a quantum dot structure, which is a conventionally known application, or as a method for growing a nitride semiconductor crystal with a reduced dislocation density. Completed. That is, the present invention has the following characteristics.

(1) A nitride semiconductor light emitting device configured to have a laminate composed of a nitride semiconductor crystal layer, wherein the laminate includes an n-type layer, a light emitting layer, and a p-type layer. And as a layer other than the light emitting layer, the light scattering layer of the following (A) is included,
A nitride semiconductor light emitting element configured to scatter light emitted from a light emitting layer at an interface between a first nitride semiconductor crystal and a second nitride semiconductor crystal constituting the light scattering layer.
(A) A base surface on which a nitride semiconductor crystal can grow two-dimensionally is subjected to a surfactant treatment, and the first nitride semiconductor crystal having a refractive index n1 has a protrusion and / or a recess on the surface. A light scattering layer that is vapor-grown into a shape, and wherein the first nitride semiconductor crystal is embedded by a second nitride semiconductor crystal having a refractive index n2 different from the refractive index n1.
(2) The nitride semiconductor light emitting element according to (1), wherein the surface of the first nitride semiconductor crystal has a height difference of ¼ or more of the wavelength of light emitted from the light emitting layer.
(3) The nitride semiconductor light emitting device according to (2), wherein the light scattering layer of (A) is located in the laminate with the base surface side facing away from the light emitting layer.
(4) The nitride semiconductor light emitting device according to (2), wherein the light scattering layer of (A) is located in the laminate with the base surface side facing the light emitting layer.
(5) The light scattering layer of (A) so that the driving current of the nitride semiconductor light emitting element flowing between the n-type layer and the p-type layer crosses the light scattering layer of (A) in the layer thickness direction. The nitride semiconductor light emitting device according to (3), wherein is located in the stacked body.
(6) The first nitride semiconductor crystal and the second nitride are such that the light extraction direction of the nitride semiconductor light-emitting element is a direction away from the base surface, and the refractive index n2 <the refractive index n1. The nitride semiconductor light emitting device according to any one of (2) to (5), wherein a semiconductor crystal is selected.
(7) The first nitride semiconductor crystal and the second nitride are so arranged that the light extraction direction of the nitride semiconductor light emitting element is a direction approaching the base surface, and the refractive index n1 <the refractive index n2. The nitride semiconductor light emitting device according to any one of (2) to (5), wherein a semiconductor crystal is selected.
(8) The nitride semiconductor light-emitting element according to any one of (2) to (7), wherein oblique facets are exposed as side walls of the protrusions and / or depressions of the first nitride semiconductor crystal.

  Two-dimensional growth is a technical term in the field to which the present invention belongs, and crystal growth is performed while maintaining a flat growth surface (two-dimensional growth surface) by so-called step flow growth in which crystal growth proceeds for each atomic layer. Means the crystal growth mode.

After applying a surfactant treatment to the base surface (for example, the surface of the substrate on which the buffer layer is formed or the surface of the GaN-based crystal layer grown two-dimensionally on the substrate) capable of two-dimensional growth of GaN-based crystals, When a GaN-based crystal is vapor-phase-grown, the surface energy of the base surface is reduced, so that the three-dimensional growth occurs even under the growth conditions in which the two-dimensional growth occurs when the surfactant treatment is not performed. A structure in which minute dot-like GaN-based crystals are dispersed on the base surface is formed. Since the promoting action of three-dimensional growth by such a surfactant treatment continues until the base surface is filled with GaN-based crystals, further growth of the above-mentioned fine dot-like crystal results in a larger three-dimensional structure. The crystal can be easily formed.
On the other hand, if the base surface is completely filled with GaN-based crystals, the force that hindered the two-dimensional growth will not work. Grown crystals can be embedded.

Therefore, a surfactant treatment is applied to a base surface capable of two-dimensional growth, and a first GaN-based crystal having a refractive index n1 is first grown three-dimensionally on the base surface. When the first GaN crystal is grown, the surface of the first GaN crystal can be embedded. As a result, a crystal layer including a structure in which the first GaN-based crystal and the second GaN-based crystal having different refractive indexes are joined at the non-flat planar interface can be formed.
The crystal layer including such an interface acts as a light scattering layer having a function of irregularly changing the propagation direction of incident light by reflection or diffraction.
The nitride semiconductor light emitting device of the present invention includes such a light scattering layer in the laminated structure, and multiple reflections are less likely to occur inside the device due to the action of the light scattering layer, so that the light extraction efficiency is improved. It becomes the light emitting element made.

An additional effect is an improvement in crystal quality.
One of the effects of improving the crystal quality occurs when the first GaN-based crystal grows on the base surface. From the layer that provides the base surface by the surfactant treatment (hereinafter referred to as “base layer”). This is because dislocation propagation to the first GaN-based crystal is suppressed.
Another of the improvement effects is that, in the stage where the growth mode of the GaN-based crystal growing on the base surface changes from three-dimensional growth to two-dimensional growth, the lateral direction extends from the side wall of the three-dimensionally grown crystal. The crystal growth occurs, and the direction of dislocation is bent laterally at that time.
Due to these phenomena, the dislocation density is reduced above the light scattering layer, and the crystal quality is improved.
Therefore, it is preferable to grow the light scattering layer before growing the light emitting layer, since the crystal quality of the light emitting layer is improved.

GaN-based light emitting device products include those from which the substrate that is the basis for crystal growth has been removed, and those that are mounted with the front and back reversed (flip chip mounting). The explanation about the light extraction direction may be unclear. In this specification, in order to eliminate such ambiguity, the side on which the substrate on which crystal growth is based (the side on which the substrate exists) is referred to as “lower side”, and each GaN-based crystal layer is “ It is assumed that a laminated body is formed by being laminated to the “upper side”.
Further, in the present specification, the term “lateral direction” refers to a direction orthogonal to the vertical direction (stacking direction of the stacked body) defined above.

As shown in FIGS. 1A and 1B, the GaN-based light emitting device according to the present invention includes a stacked body S composed of GaN-based crystal layers. The mold layer 20, the light emitting layer 30, and the p-type layer 40 are included, and the light scattering layer 50 of the above (A) shown in the above (1) is included as a layer other than the light emitting layer. Hereinafter, the light scattering layer (A) is also simply referred to as “light scattering layer”.
In the example of the figure, an element structure is formed in which the stacked body S is grown on the substrate 10 with the n-type layer as the substrate side. Is not limited.
In the present invention, reflection or diffraction occurs irregularly at the non-planar planar interface between the first GaN-based crystal 51 and the second GaN-based crystal 52 constituting the light-scattering layer 50, whereby the light-emitting layer The light emitted from is scattered so that the above-described effects can be obtained.

As shown in FIG. 2A, the light scattering layer of the above (A) is shown in FIG. 2B after a surfactant treatment is applied to a base surface 50B on which a GaN-based crystal can grow two-dimensionally. As described above, the first GaN-based crystal 51 is vapor-phase grown on the surface 50B, so that the first GaN-based crystal 51 is discretely grown on the surface 50B as dot-like crystals protruding on the base surface. Further, as shown in FIG. 2C, the second GaN-based crystal 52 is obtained by growing the dot-shaped first GaN-based crystal 51 so as to be buried.
In the figure, for the purpose of explanation, the first GaN-based crystals 51 in the form of dots are drawn so as to be equally arranged with the same size, but the arrangement pattern is actually random, and the shape and size are random. Although they are generally the same, they are strictly different from each other. The same applies to the other figures.

Further, when the first GaN-based crystal 51 is further grown from the state of FIG. 2B, the base surface 50B is formed by the dot-shaped first GaN-based crystal 51 as shown in FIG. It is filled up (the exposed surface of the base surface 50B is eliminated). The crystal growth after this state is achieved is not affected by the surface treatment of the base surface 50B. Therefore, two-dimensional growth occurs by using appropriate growth conditions.
For example, immediately after the state shown in FIG. 2D is achieved, when a growth condition in which two-dimensional growth occurs is applied, a space (concave portion) between the first GaN-based crystals 51 in a dot shape is embedded. Therefore, as shown in FIG. 2E, the first GaN-based crystal 51 has a shape having protrusions and depressions on the surface. At this time, non-uniformity occurs in the embedding speed, and a shape in which hollow concave portions are dispersed in some places on the flat surface may occur. At this stage, when the composition of the GaN-based crystal to be grown is changed and the second GaN-based crystal 52 is grown until the surface of the growth surface becomes flat, the light scattering layer 50 having the structure shown in FIG. It is formed.

  After the state shown in FIG. 2D is achieved, the first GaN-based crystal can be grown under growth conditions that promote three-dimensional crystal growth. In that case, the dot-shaped first GaN-based crystal is integrated without generating a flat portion on the surface, and grows in the thickness (height) direction while maintaining the uneven shape on the surface. After that, if the growing crystal is switched to the second GaN-based crystal and the growth condition is changed to a condition that causes two-dimensional growth, the second GaN-based crystal fills the first GaN-based crystal and flattens it. The resulting structure is obtained.

The light scattering layer 50 formed as described above is preferably formed so that the surface of the first GaN-based crystal 51 has a height difference of ¼ or more of the wavelength of light emitted from the light emitting layer.
When the growth stage of the first GaN-based crystal 51 is the stage shown in FIG. 2 (b) or FIG. 2 (d), the surface height difference means that the base surface 50B and the dot-shaped first GaN-based crystal. It is a difference in height from the top of (projecting part) 51.
When the growth stage of the first GaN-based crystal 51 is the stage shown in FIG. 2 (e), the difference in height of the surface is the bottom of the recessed portion and the top of the protruding portion on the surface of the first GaN-based crystal 51. The height difference between.
If the height difference of the surface of the first GaN-based crystal 51 is set to ¼ or more of the wavelength of light emitted from the light emitting layer, the action of the side walls of the protrusions and recesses to reflect or diffract this light becomes strong. In addition, the scattering effect on the light emitted from the light emitting layer is enhanced.
Here, the wavelength of light emitted from the light emitting layer means the wavelength inside the light scattering layer, and is a length obtained by dividing the wavelength in air by the refractive index of the nitride semiconductor constituting the light scattering layer. It becomes.

The base surface that is the basis for the growth of the light scattering layer may be any surface that allows two-dimensional growth of GaN-based crystals, and is formed on the upper surface of any GaN-based crystal layer in the stack or on the substrate. The surface of the buffer layer suitable for the growth of GaN-based crystals is exemplified.
The base surface may be present when the light scattering layer is formed, and after the light scattering layer is formed, the layer providing the base surface may be removed in a process of forming an element. For example, the surface of the buffer layer formed on the substrate is used as a base surface, the light scattering layer is formed, and further a necessary GaN-based crystal layer is sequentially grown to form a laminate, which is separately prepared on the top surface of the laminate. For example, the support substrate may be bonded and the first substrate may be removed.

The surfactant reduces the surface energy of the base surface when growing the GaN-based crystal layer, thereby lowering the wettability of the base surface with respect to the growing GaN-based crystal and inhibiting two-dimensional growth. It is a substance that acts to promote three-dimensional growth (= island-like growth).
The material that can be used as the surfactant may be any substance that exhibits the above-described action. Specific examples include tetraethylsilane, silane, disilane, and cyclopentadienylmagnesium.

The surfactant treatment is a treatment in which a gaseous surfactant is brought into contact with a base surface to leave the surfactant or atoms or molecules generated by the decomposition thereof on the base surface.
The surfactant treatment referred to in the present invention is performed on the surface of a surfactant (referred to as anti-surfactant in Patent Documents 5 and 6), which is performed in the conventionally known quantum dot forming methods described in Patent Documents 4 to 6. These processes are the same as the processes to be performed, and these patent documents can be referred to for detailed methods, processing conditions, and the like.
As an example, as a surfactant treatment of the surface of a GaN-based crystal grown on a substrate, there is a method of bringing tetraethylsilane into contact with the surface using H ₂ (hydrogen gas) as a carrier gas. In this method, the substrate is placed on a susceptor in a crystal growth furnace and heated to the growth temperature of a GaN-based crystal, and tetraethylsilane is cooled to −12 ° C. in a sealed container to be in a liquid state. The gas is made gaseous by bubbling hydrogen gas to the surface of the GaN-based crystal.
In this method, the degree of surfactant treatment on the surface of the GaN-based crystal can be adjusted by changing the amount of tetraethylsilane supplied to the substrate. Specifically, for example, the adjustment can be performed by changing the flow rate of the carrier gas that is bubbled into a sealed container containing tetraethylsilane.

The growth conditions used when growing the first GaN-based crystal on the surfactant-treated base surface may be growth conditions in which two-dimensional growth occurs unless the surfactant treatment is performed, or in the case where the surfactant treatment is not performed. However, it may be a growth condition in which three-dimensional growth occurs (a growth condition that actively promotes three-dimensional growth), and is not limited. When the latter growth condition is used, the first GaN-based crystal can easily grow into a hexagonal pyramid shape to be described later.
The first GaN-based crystal is generated as a fine dot-like crystal on the surface that has been subjected to the surfactant treatment, and thereafter grows using this dot-like crystal as a seed. Accordingly, the propagation of dislocations from the base layer to the first GaN-based crystal occurs substantially only at the stage where the minute dot-like crystal grows, so that the dislocation density of the first GaN-based crystal is reduced. It will be.

When the first GaN-based crystal grows in a dot shape on the surface of the surface treated with Surfactant, the bottom is a regular hexagon and the top has a sharp hexagonal pyramid shape, or the top of the hexagonal pyramid is cut off and flattened. A surface shape (hexagon frustum shape) may occur as a stable shape. In this case, the oblique facet that is easily exposed as the side wall surface is, for example, a {1-101} facet. This facet has an angle of about 60 ° with respect to the base surface (= surface parallel to the substrate surface). Also, the {11-22} facet may be exposed.
The aspect ratio (ratio of width to height) when the dot-like crystal is hexagonal pyramid shape or hexagonal frustum shape or the hexagonal frustum shape is the ratio of the growth rate in the horizontal and height directions of the crystal. It depends on. In general, GaN-based crystals grow laterally as the growth temperature is lower, the hydrogen concentration in the atmosphere is higher, the growth atmospheric pressure is higher, and the composition ratio of Al or In contained in the GaN-based semiconductor is higher. There is a tendency that the speed is lowered and the growth in the height direction is promoted (= a three-dimensional growth tendency). The larger the growth rate in the height direction with respect to the growth rate in the horizontal direction, the smaller the top surface area, and the hexagonal pyramid or a shape close to the hexagonal pyramid grows.
Therefore, by controlling the growth conditions and the composition of the GaN-based crystal, the dot-like crystal can be intentionally grown into a hexagonal pyramid shape or a hexagonal frustum shape. For this purpose, it is preferable that the growth temperature is less than 1000 ° C., the hydrogen concentration in the atmosphere is 50% or more, and the growth atmosphere pressure is 600 Torr or more.
The hexagonal pyramid shape and the hexagonal frustum shape are effective in suppressing multiple reflections because the area of the surface parallel to the substrate surface is smaller, and the height difference between the bottom and the top is large, and light scattering It is an effective shape.

As described above, when the first GaN-based crystal is grown on the surfactant-treated base surface, initially, a minute dot-like crystal is generated to the extent that the quantum effect occurs. (Including those caused by coalescence and fusion with adjacent dot crystals), and the base surface is densely filled with dot crystals.
When the growth of the first GaN-based crystal is stopped in this process and the growth is switched to the growth of the second GaN-based crystal, in order to effectively generate light scattering at the interface of these GaN-based crystals, The first GaN-based crystal is grown until the height from the base surface of the dot-shaped crystal made of the GaN-based crystal becomes ¼ or more of the wavelength of light emitted from the light emitting layer. In order to produce light scattering more effectively, the height is more preferably ½ or more of the wavelength, and even more preferably the same as or more than the wavelength.

Here, the wavelength of light emitted from the light emitting layer is a wavelength in the light scattering layer as described above. On the other hand, the “emission wavelength of the light emitting element” usually refers to the wavelength in the air. For example, when the emission wavelength (in the air) is 400 nm, the wavelength of the light in the light scattering layer is When the refractive index of the GaN-based crystal is calculated as about 2.5 which is the refractive index of GaN, it is about 160 nm (= 400 nm ÷ about 2.5). For light with such a wavelength, the scattering phenomenon can be generated by setting the height of the dot-like crystal to about 1/4 or more of this wavelength of about 160 nm, that is, 40 nm or more. A more preferable height is 80 nm or more, and a more preferable height is 160 nm or more.
The height of the dot-like crystal can be measured by observing using a SEM (scanning electron microscope) or a TEM (transmission electron microscope). If a sample in which the first GaN-based crystal is grown while changing the growth time under a predetermined growth condition is prepared and the height thereof is measured, the growth rate under the growth condition can be obtained. From the growth rate thus determined, the time required to grow the dot-like crystal to a desired height can be determined.
Since the emission wavelength of the GaN-based light emitting element is about 360 nm to 550 nm in a normal product, an optimum dot-shaped crystal height may be selected according to each wavelength.

A case will be described in which the growth of the first GaN-based crystal is continued even after the state in which the dot-like crystal is densely filled on the base surface is formed.
When the surfactant-treated base surface is filled with the first GaN-based crystal, the factors that hindered the two-dimensional growth are virtually eliminated, so two-dimensional growth is generated by setting the growth conditions appropriately. Can be made. When the growth mode is switched to two-dimensional growth, lateral growth occurs from the side wall of the crystal that has been grown three-dimensionally (for example, oblique facets), and the concave portion on the surface of the first GaN-based crystal is formed. It is embedded, and finally a flat two-dimensional growth surface is formed.
When stopping the growth of the first GaN crystal in this process and switching to the growth of the second GaN crystal, in order to effectively cause light scattering at the interface of these GaN crystals, When the depth of the recess is ¼ or more of the wavelength of light emitted from the light emitting layer, the growth of the first GaN-based crystal is stopped and the growth is switched to the growth of the second GaN-based crystal. In order to produce light scattering more effectively, the depth is more preferably ½ or more of the wavelength, and even more preferably the same as or more than the wavelength.

Regardless of the stage at which growth is switched from the first GaN-based crystal to the second GaN-based crystal, the shape of the interface between the two crystals is determined by how far the first GaN-based crystal is grown. The growth condition of the second GaN-based crystal is not substantially affected.
Therefore, it is preferable that the second GaN-based crystal is grown under the condition that the surface is flattened from the viewpoint of improving the production efficiency.
The growth condition that the surface is flattened is a growth condition that has a higher lateral growth rate, and is opposite to the growth condition that promotes the growth of the dot-shaped crystal in the height direction. That is, the growth conditions are such that the growth temperature is higher, the hydrogen concentration in the atmosphere is lower, and the growth atmosphere pressure is lower.
Further, the lower the composition ratio of Al or In in the GaN-based crystal, the faster the planarization of the surface.

When growing the first GaN-based crystal on the surfactant-treated base surface, if the distribution density of the microcrystals formed initially is kept low, the base surface is filled until the base surface is filled with dot-like crystals. By effectively utilizing the effect of promoting the three-dimensional growth caused by the surfactant treatment, individual dot crystals can be grown greatly.
As a method for controlling the distribution density of the microcrystals, for example, Patent Document 4 can be referred to. Depending on the degree of surfactant treatment of the base surface and the growth temperature of the first GaN-based crystal, the distribution density of microcrystals can be controlled in the range of 10 ⁷ to 10 ¹⁰ cm ⁻² . The higher the degree of surfactant treatment and the higher the growth temperature, the lower the distribution density of microcrystals on the base surface.
Above the distribution density range, in order to average occupation area per crystallites becomes 0.01 [mu] m ² 10 .mu.m ^2, dots of the exposed hexagonal pyramid shape as a side wall {1-101} facets of above Then, before the base surface is completely filled with dot-like crystals, it is sufficiently possible to grow to a height of 40 nm or more.

  The composition of the first GaN crystal and the second GaN crystal may be selected so that the refractive indexes are different from each other. A preferable refractive index difference is 0.01 or more, more preferably 0.05 or more, and particularly preferably 0.1 or more. For example, when both the first and second GaN-based crystals are made of AlGaN, AlGaN can change the refractive index from about 2.0 of AlN to about 2.5 of GaN. An interface with a refractive index difference of 0.5 can be formed.

  Doping to the base layer, the first GaN-based crystal, and the second GaN-based crystal may be arbitrarily performed for the purpose of controlling conductivity. Further, since Si has an effect of increasing the growth rate in the height direction (thickness direction) of the crystal, it may be added for the purpose of growing the first GaN-based crystal. On the other hand, Mg has an effect of increasing the lateral growth rate, and for this purpose, Mg may be added during the growth of the second GaN-based crystal.

  The light scattering layer (A) may be formed at any position in the laminate. In the order of growth, as shown in FIG. 1A, the light emitting layer 30 may be formed before the growth (that is, on the substrate side), or as shown in FIG. It may be formed after growth of layer 30 (ie, on the side far from the substrate). In the former case, the light scattering layer of (A) is located in the laminate with the base surface side facing away from the light emitting layer, and in the latter case, the light scattering layer (A) The light scattering layer is positioned in the laminated body with the base surface side facing the light emitting layer.

As described above, the light scattering layer (A) suppresses the propagation of dislocations to the layer stacked above the light scattering layer, so that the light scattering layer is formed before the light emitting layer 30 is grown. When formed, the crystal quality of the light emitting layer is improved, which is preferable.
In this case, it is particularly preferable to form the light scattering layer (A) above the n-type contact layer. An n-type contact layer is a layer on which an n-side electrode is formed, and since it is necessary to increase conductivity and lower contact resistance with the electrode, n-type impurities such as Si are doped at a high concentration. Therefore, the crystal quality tends to be low. Therefore, if the light scattering layer is formed above the n-type contact layer, the adverse effect of the crystal quality of the n-type contact layer on the crystal quality of the light emitting layer can be reduced.
In addition, between the n-type contact layer and the light emitting layer is in a path through which the driving current of the light emitting element flows, but the light scattering layer of (A) can be formed in such a conductive path. This is because the surfactant process does not substantially form a layer serving as an insulating film.
On the other hand, for example, in the conventional technique using a mask made of SiO ₂ or the like to form a concavo-convex crystal by selective growth, a relatively thick mask acts as an insulator. When applied, there is a problem that light emission is limited.

In the light scattering layer (A), from the viewpoint of improving the light extraction efficiency, the magnitude relationship between the refractive index n1 of the first GaN-based crystal and the refractive index n2 of the second GaN-based crystal is It is preferable to determine as follows according to the light extraction direction.
(A) As shown in FIG. 3A, when the direction away from the base surface is the light extraction direction of the light emitting element, n2 <n1.
(B) As shown in FIG. 3B, when the light extraction direction of the light emitting element is the direction approaching the base surface, n1 <n2.
This relationship is the same regardless of whether the light scattering layer (A) is formed above or below the light emitting layer. The reason for this is explained as follows.

[When n2 <n1]
Light incident from the base surface side easily enters the light scattering layer, and light incident from a surface opposite to the base surface is easily reflected. Because the first GaN-based crystal having a high refractive index exists on the surface of the base surface side of the light scattering layer, the surface opposite to the base surface side is made of the second GaN-based crystal having a low refractive index. It is.
For the same reason, light that has once entered the light scattering layer is unlikely to be emitted from the base surface side and is likely to be emitted from the surface opposite to the base surface side.
On the other hand, the light traveling from the first GaN-based crystal to the second GaN-based crystal in the light scattering layer is likely to be reflected at the interface between the two crystals due to the refractive index, but this interface is light scattering. This tendency is alleviated.
Therefore, in summary, the light scattering layer in which n2 <n1 transmits light incident from the base surface side and reflects light incident from the opposite direction to the base surface side (that is, from the base surface). The light traveling in the direction away from the light is transmitted, and the light traveling in the direction approaching the base surface is reflected.
Therefore, in the light emitting element in which the direction away from the base surface is the light extraction direction, it is advantageous in terms of light extraction efficiency that n2 <n1.

[When n1 <n2]
Light incident from the base surface side is easily reflected on the light scattering layer, and light incident from a surface opposite to the base surface is likely to enter. Because the first GaN-based crystal having a low refractive index exists on the surface of the base surface side of the light scattering layer, the surface opposite to the base surface side is made of the second GaN-based crystal having a high refractive index. It is.
For the same reason, light that has once entered the light scattering layer is likely to be emitted from the base surface side, and is difficult to be emitted from the surface opposite to the base surface side.
On the other hand, the light traveling from the second GaN-based crystal toward the first GaN-based crystal in the light-scattering layer is likely to be reflected at the interface between the two crystals due to the refractive index, but this interface is light-scattering. This tendency is alleviated.
Therefore, in summary, the light scattering layer in which n1 <n2 has a tendency to reflect light incident from the base surface side and transmit light incident from a direction opposite to the base surface side (that is, to the base surface). The light traveling in the approaching direction is transmitted, and the light traveling in the direction away from the base surface is reflected.
Therefore, in the light emitting element in which the direction closer to the base surface is the light extraction direction, it is advantageous in terms of light extraction efficiency that n1 <n2.

  In the nitride semiconductor device according to the present invention, the surface of the light emitting layer is used as a base surface, a surfactant treatment is performed, and a first GaN-based crystal and a second GaN-based crystal are grown thereon to produce the light of (A) above. A scattering layer may be formed. In this case, the light scattering layer may be doped with p-type impurities to form a p-type cladding, and a p-type contact layer doped with a larger amount of p-type impurities may be formed thereon.

  Layers other than the light emitting layer for constituting the light emitting element structure, for example, n-type and p-type contact layers and cladding layers, may have the function of the base layer and the light scattering layer of (A) above, Or you may form separately from a base layer and a light-scattering layer.

The element structure of FIG. 1A is [sapphire substrate 10 / undoped GaN layer L / light scattering layer 50 / Si doped GaN layer 20 / light emitting layer 30 / Mg doped AlGaN layer 41 / Mg doped GaN layer 42 in order from the bottom. The upper surface of the undoped GaN layer L is the base surface, and the light scattering layer 50 is also undoped.
In addition, the element structure of FIG. 1B is formed in order from the bottom [sapphire substrate 10 / undoped GaN layer L / Si doped GaN layer 20 / light emitting layer 30 / Mg doped AlGaN layer 41 / light scattering layer 50 / Mg doped GaN. The upper surface of the Mg-doped AlGaN layer 41 is a base surface, and the light scattering layer 50 is also p-type by Mg doping.

  The n-type layer, the light-emitting layer, and the p-type layer are preferably laminated in the order of lamination. Since it is necessary to add a large amount of dopant to sufficiently increase the conductivity of the p-type layer, the crystal quality of the p-type layer tends to deteriorate, but if a layer with poor crystal quality is first grown, This is because it adversely affects the quality of the crystal layer that grows.

When the light extraction direction is upward, according to the preferred stacking order, a p-type layer having low conductivity is formed on the light emitting layer. Therefore, the entire surface of the uppermost layer of the GaN-based crystal layer is formed on the entire surface. It is preferable to form a light-transmitting p-side electrode so as to cover the surface.
In general, the uppermost layer of the GaN-based crystal layer forming the p-side electrode is a p-type contact layer. Further, an n-type tunneling layer or a p-type impurity and A co-doped layer of type impurities may be interposed.
Examples of the light transmissive electrode include a transparent electrode made of a metal thin film, a transparent electrode made of an oxide semiconductor such as ITO, and an opening electrode in which an opening for light extraction is provided in a thick film metal layer. An opening may be formed in the transparent electrode.
When the aperture electrode is used, the GaN-based crystal is in direct contact with air, a resin material, or a passivation film having a low refractive index at the aperture. When a transparent electrode made of a metal thin film is used, the GaN crystal is in contact with air, a resin material, or a passivation film through the thin metal layer over the entire surface of the p-type layer. Therefore, when these electrodes are used, the present invention is particularly useful because reflection due to a difference in refractive index is likely to occur on the surface of the p-type layer.

When the light extraction direction is set to the lower side, it is necessary to use a transparent substrate when an element is formed with the substrate remaining.
It is possible to remove the substrate after the growth of the GaN-based semiconductor crystal layer regardless of the light extraction direction, and whether the substrate is a transparent substrate or an opaque substrate. Similarly, when the substrate is a base layer, the substrate can be removed.

  A plurality of the light scattering layers (A) may be included in one element. A plurality of light emitting layers may be provided on one side of the light emitting layer, or may be provided on both sides of the light emitting layer.

A surface layer above the light-emitting layer is used as a base layer, and a surface treatment is performed on the upper surface, and then a first GaN-based crystal is grown in a shape having protrusions and / or depressions on the surface, and a second GaN-based layer is grown. The uneven surface obtained without forming crystals may be used as the light extraction surface. When forming irregularities at this position, the advantage of using the surfactant treatment is the same as the advantage of forming the light scattering layer under the light emitting layer.
When a light-transmitting p-side electrode is formed on this surface, the first GaN crystal may be doped with p-type impurities to be p-type. Alternatively, the base layer may be p-type, and the undoped or p-type doped first GaN-based crystal may be formed in discrete dots so as not to completely cover the base layer. Further, biscyclopentadienyl magnesium used for doping magnesium, which is a p-type impurity, can be preferably used as a surfactant.

After the p-type layer above the light emitting layer is used as a base layer and the upper surface thereof is subjected to a surfactant treatment, the first GaN-based crystal is grown in a shape having a protrusion and / or a recess on the surface. In an embodiment in which the uneven surface obtained without forming the second GaN-based crystal is a light extraction surface, the first GaN-based crystal is made n-type by n-type doping, and ITO (indium oxide) is embedded so as to embed the uneven surface. A transparent electrode made of an oxide semiconductor such as tin) or ZnO can be formed.
In this case, using a substance containing Si as a surfactant, a surfactant having a lower resistance value than the p-type layer and the first GaN-based crystal is formed on the surface of the p-type layer. Process. When an n-type layer is formed on a p-type layer through such a low resistance region, the interface between the p-type layer and the n-type layer can be made ohmic, and an oxide formed on the n-type layer A current can be supplied from the semiconductor electrode to the p-type layer (see Japanese Patent Application Laid-Open No. 2004-179369).
In this embodiment, the light extraction direction is away from the base surface. However, since ITO and ZnO have a lower refractive index than GaN-based crystals, embedding the first GaN-based crystal with ITO or ZnO results in light extraction efficiency. It becomes a preferable structure for improving the above.

The material of the substrate is not limited as long as the GaN-based crystal can be epitaxially grown. For example, sapphire (C plane, A plane, R plane), SiC (6H, 4H, 3C), GaN, AlN, Si, spinel, ZnO , GaAs, NGO and the like.
A sapphire substrate is preferable as a substrate for growing a GaN-based crystal, but has a problem in light extraction efficiency because of a large difference in refractive index from the GaN-based crystal, and the usefulness of the present invention is remarkably increased. It is the substrate shown.
On the other hand, since SiC has a refractive index close to that of GaN (slightly higher than GaN), the use of a SiC substrate reduces the problem of reflection at the interface between the GaN-based crystal layer and the substrate. Again, the problem of multiple reflections arises due to reflection at the bottom surface (if a reflective electrode is formed, reflection by the electrode). Also, when a substrate made of Si or GaAs that does not transmit visible light is used, the surface of the substrate becomes highly reflective by mirror polishing, which causes a problem of multiple reflection. Therefore, the present invention is useful even when these substrates are used.

Example 1
(Production of LED wafer)
A C-plane sapphire substrate having a diameter of 2 inches and a thickness of about 300 μm is mounted on a susceptor provided in the growth furnace of the MOVPE apparatus, and the substrate temperature is raised to 1100 ° C. in a hydrogen atmosphere to perform thermal cleaning of the surface. It was.
Next, the substrate temperature was lowered to 330 ° C., and an AlGaN low-temperature buffer layer was grown to 20 nm using trimethylgallium (TMG) and trimethylaluminum (TMA) as Group 3 materials and ammonia as Group 5 materials. After this step, hydrogen gas was used as the raw material and the surfactant carrier gas, and nitrogen gas was flowed into the growth furnace as a subflow gas in order to adjust the flow of the raw material gas.
Next, the substrate temperature was raised to 1000 ° C., TMG and ammonia were supplied as raw materials, and an undoped GaN layer was grown by 2 μm.
Next, the supply of TMG and ammonia was stopped, and as a surfactant, gaseous tetraethylsilane was supplied into the growth reactor and brought into contact with the surface of the undoped GaN layer. Tetraethylsilane was cooled to −12 ° C. in a closed vessel, and hydrogen gas was supplied at a flow rate of 30 cm ³ / min and bubbled to supply it into the growth furnace.
After the supply of tetraethylsilane was stopped, TMG, TMA (trimethylaluminum), and ammonia were supplied to grow undoped Al _0.5 Ga _0.5 N in a dot shape. The growth time at this time was determined such that the dot height was 200 nm.
Next, the supply of TMA was stopped, and undoped GaN was grown so as to embed Al _0.5 Ga _0.5 N grown in a dot shape. The undoped GaN was formed such that the film thickness from the surface of the previously grown undoped GaN layer treated with the surfactant was 2 μm.
Next, silane was supplied to grow a Si-doped GaN layer having a Si concentration of 5 × 10 ¹⁸ cm ⁻³ by 2 μm.
Next, the substrate temperature was lowered to 800 ° C. to form a light emitting layer having an MQW (multiple quantum well) structure in which a GaN barrier layer and 10 InGaN well layers (emission wavelength of 405 nm) were alternately stacked. Trimethylindium was used as an In raw material for the well layer growth.
Next, the substrate temperature is increased to 1000 ° C., and bis (ethylcyclopentadienyl) magnesium (EtCp ₂ Mg), TMG, TMA, and ammonia as Mg raw materials are supplied, and the Mg concentration is 5 × 10 ¹⁹ cm ⁻³ . A Mg-doped AlGaN layer was grown to 50 nm.
Next, the supply of TMA was stopped, and an Mg-doped GaN layer having an Mg concentration of 1 × 10 ²⁰ cm ⁻³ was grown to 100 nm.
Thus, a wafer on which a near ultraviolet LED structure having an emission wavelength of 405 nm was formed was obtained.

(Formation of p-side electrode)
The p-side electrode was an aperture electrode.
Prior to the formation of the electrode film, a photoresist film is formed on the upper surface of the Mg-doped GaN layer, and the photoresist film is used to form a window portion where the surface of the Mg-doped GaN layer is exposed in the shape of the opening electrode by using a photolithography technique. Formed.
The aperture electrode has a size that covers almost the entire upper surface of the Mg-doped GaN layer when chipped, and is a pattern in which square-shaped apertures of 6 μm × 6 μm are arranged in a square matrix at intervals of 2 μm vertically and horizontally ( A pattern in which the electrode portions are in a square lattice pattern).
Next, a 1 nm-thickness Ni film and a 250 nm-thickness Au film are stacked in this order on the exposed Mg-doped GaN layer surface and the photoresist film using an electron beam evaporation method. By lifting off the resist film, a square lattice-shaped electrode was formed on the surface of the Mg-doped GaN layer.
On the surface of the p-side electrode, a wire electrode pad electrode was further formed by laminating a 20 nm thick Ti film and a 400 nm thick Au film in this order. Later, in order to promote ohmic contact between the p-side electrode and the Mg-doped GaN layer, a heat treatment was performed at 500 ° C. for 5 minutes.

(Formation of n-side electrode)
The n-side electrode is formed by removing part of the Mg-doped GaN layer, Mg-doped AlGaN layer, and light-emitting layer by reactive ion etching from the side of the LED wafer on which the GaN-based crystal laminate is formed, and then doping with Si. After forming the concave portion where GaN is exposed, an Al film having a thickness of 50 nm, a Ti film having a thickness of 30 nm, and an Au film having a thickness of 400 nm are formed on the surface of the exposed Si-doped GaN layer by electron beam evaporation. This was done by laminating in this order. Thereafter, in order to promote ohmic contact with the Si-doped GaN layer, a heat treatment was performed at 500 ° C. for 5 minutes (simultaneously with the treatment on the p-side electrode).
After the formation of the n-side electrode, the back surface of the sapphire substrate was polished to a thickness of 90 μm, and element separation was performed by ordinary scribing and braking to obtain a 350 μm square LED chip.

Comparative Example 1
In Example 1 above, without performing tetraethylsilane treatment on the surface of the undoped GaN layer and growth of dot-shaped undoped Al _0.5 Ga _0.5 N, an undoped GaN layer was grown 4 μm on the AlGaN buffer layer, and then An LED chip (conventional LED) was fabricated in the same process as in Example 1 except that the Si-doped GaN layer was grown.

(Evaluation)
After the LED chip produced by the above procedure was die-bonded to the stem base, it was put into a state in which it could be energized by wire bonding, and the element characteristics of each LED of Example 1 and Comparative Example 1 were evaluated.
As a result, the example product and the comparative product were almost the same (about 3.4 V) with respect to the forward voltage (at the time of 20 mA energization), but the output measured using an integrating sphere (at the time of 20 mA energization) was The example product was about 15% higher than the comparative product.

Example 2
In this embodiment, the p-side electrode made of Ni (lower layer) / Au (surface layer) is formed to have a size that covers almost the entire upper surface of the Mg-doped GaN layer after chip formation without forming an opening. At the same time, an LED chip was produced in the same manner as in Example 1 except that the pad electrode on the surface of the p-side electrode was omitted.

Comparative Example 2
In Example 2, the undoped GaN layer was grown to 4 μm on the AlGaN buffer layer without performing tetraethylsilane treatment on the surface of the undoped GaN layer and the growth of dot-like undoped Al _0.5 Ga _0.5 N, An LED chip (conventional LED) was fabricated in the same process as in Example 2 except that the Si-doped GaN layer was grown.

(Evaluation)
The obtained LED chip was flip-chip bonded onto the ceramic package on which the lead electrode pattern was formed so that the p-side electrode and the n-side electrode were on the lower side, and each of the LEDs of Example 2 and Comparative Example 2 was The device characteristics were evaluated.
As a result, the forward voltage (20 mA energization) of the example product and the comparative example product was almost the same (about 3.3 V), but the output (using 20 mA energization) measured using an integrating sphere was The example product was about 20% higher than the comparative example product.
Compared to the case of Example 1, the rate of increase in output relative to the comparative example product was larger, in the direction in which the light extraction direction of the chip approaches the upper surface of the undoped GaN layer corresponding to the base surface of the surfactant treatment. Because the refractive index of undoped Al _0.5 Ga _0.5 N formed in the shape of dots on the surface of the undoped GaN layer is smaller than the refractive index of undoped GaN grown by embedding this, light extraction This is considered to be a more preferable configuration in terms of efficiency.

Example 3
First, without performing tetraethylsilane treatment on the surface of the undoped GaN layer and growth of dot-like undoped Al _0.5 Ga _0.5 N, an undoped GaN layer was grown to 4 μm on the AlGaN buffer layer, and then the Si-doped GaN layer A nitride semiconductor crystal layer up to an Mg-doped AlGaN layer having an Mg concentration of 5 × 10 ¹⁹ cm ⁻³ was grown on the sapphire substrate in the same manner as in Example 1 except that the above was grown.
Next, the supply of EtCp ₂ Mg, TMG, TMA, and ammonia was stopped, and as a surfactant, gaseous tetraethylsilane was supplied into the growth reactor and brought into contact with the surface of the Mg-doped AlGaN layer. The method for supplying tetraethylsilane was the same as in Example 1.
After the supply of tetraethylsilane was stopped, EtCp ₂ Mg, TMG, TMA (trimethylaluminum) and ammonia were supplied again, and Mg-doped Al _0.5 Ga _0.5 N with an Mg concentration of 5 × 10 ¹⁹ cm ⁻³ was added. , Grown in dots. The growth time at this time was determined such that the dot height was 50 nm.
Next, the supply of TMA was stopped, and Mg-doped GaN having an Mg concentration of 1 × 10 ²⁰ cm ⁻³ was grown so as to embed Al _0.5 Ga _0.5 N grown in a dot shape. This Mg-doped GaN was designed such that the film thickness from the surface of the Mg-doped AlGaN layer grown earlier was treated with a surfactant was 150 nm.
After forming the p-side electrode and the n-side electrode on the near-ultraviolet LED wafer having the emission wavelength of 405 nm thus obtained by the same method as in Example 1, the chip is formed by the same method as in Example 1. went.

Comparative Example 3
In Example 3, the Mg-doped GaN layer was grown to 150 nm on the Mg-doped AlGaN layer without performing tetraethylsilane treatment on the surface of the Mg-doped AlGaN layer and growing the dot-like Mg-doped Al _0.5 Ga _0.5 N. Except for this, an LED chip (conventional LED) was fabricated in the same process as in Example 3 above.

(Evaluation)
After the obtained LED chip was die-bonded to the stem base in the same manner as in Example 1, the device could be energized by wire bonding, and the element characteristics of the LEDs in Example 3 and Comparative Example 3 were evaluated.
As a result, the example product and the comparative product had almost the same forward voltage (at the time of 20 mA energization) (about 3.4 V), but the output measured using the integrating sphere (at the time of 20 mA energization) The example product was about 7% higher than the comparative product.

Example 4
In this embodiment, the p-side electrode made of Ni (lower layer) / Au (surface layer) is formed to have a size that covers almost the entire upper surface of the Mg-doped GaN layer after chip formation without forming an opening. At the same time, an LED chip was produced in the same manner as in Example 3 except that the pad electrode on the surface of the p-side electrode was omitted.

Comparative Example 4
In Example 4 above, the Mg-doped GaN layer was grown to 150 nm on the Mg-doped AlGaN layer without performing the tetraethylsilane treatment on the surface of the Mg-doped AlGaN layer and the growth of the dot-like Mg-doped Al _0.5 Ga _0.5 N. Except for this, an LED chip (conventional LED) was fabricated in the same process as in Example 4 above.

(Evaluation)
The obtained LED chip was flip-chip bonded onto the ceramic package on which the lead electrode pattern was formed so that the p-side electrode and the n-side electrode were on the lower side, and each LED of Example 4 and Comparative Example 4 was The device characteristics were evaluated.
As a result, the example product and the comparative product had almost the same forward voltage (at the time of 20 mA energization) (about 3.4 V), but the output measured using the integrating sphere (at the time of 20 mA energization) The example product increased about 9% over the comparative example product.

Example 5
In this example, as in Example 1, after the thermal cleaning of the sapphire substrate surface and the growth of the AlGaN low-temperature buffer layer, the substrate temperature was raised to 1000 ° C., and the Si concentration was 5 × 10 ¹⁸ cm ⁻³ . A Si-doped GaN layer was grown to 2 μm.
Next, tetraethylsilane was brought into contact with the surface of this Si-doped GaN layer in the same manner as in Example 1, and then Si-doped Al _0.5 Ga _0.5 N with a Si concentration of 5 × 10 ¹⁸ cm ^−3. Was grown in dots. The growth time at this time was determined such that the dot height was 200 nm. Thereafter, the supply of TMA was stopped, and Si-doped GaN having a Si concentration of 5 × 10 ¹⁸ cm ⁻³ was grown so as to embed Si-doped Al _0.5 Ga _0.5 N grown in a dot shape. This Si-doped GaN was formed so that the film thickness from the surface of the previously grown Si-doped GaN layer treated with the surfactant was 400 nm.
Thereafter, a light emitting layer, an Mg doped AlGaN layer, and an Mg doped GaN layer were sequentially grown on the Si doped GaN by the same method as in Example 1 to obtain a near ultraviolet LED wafer having an emission wavelength of 405 nm.
Next, a p-side electrode made of Ni (lower layer) / Au (surface layer) was formed on the entire surface of the Mg-doped GaN layer of this wafer, and heat treatment was performed at 500 ° C. for 5 minutes.
Next, a Au-Sn eutectic was used to bond a GaAs substrate to the surface of the p-side electrode, and then the sapphire substrate was abraded by grinding and polishing to expose the grown Si-doped GaN layer. On the exposed surface of the Si-doped GaN layer, Al (lower layer) / Ti (middle layer) / Au (surface layer) are used as pad electrodes for wire bonding, one for each region separated into individual chips by element isolation. An electrode consisting of was formed.
The wafer was separated to obtain an LED chip.

(Evaluation)
When the device characteristics were evaluated by energizing the LED chip obtained in Example 5 through the GaAs substrate and the pad electrode, a higher output than the LED chip obtained in Example 2 was obtained. Obtained.
This is considered to be because the reflection based on the difference in refractive index at the interface between sapphire and air was suppressed because the sapphire substrate on the light extraction surface side was removed.

  In any of the LEDs according to Examples 1 to 5, in addition to the improvement in output as compared with the LED having the conventional structure in which the surfactant treatment and the growth of the dot-like GaN-based crystal were not performed, the leakage of the element A decrease in current was observed. This is considered to be due to a reduction in the dislocation density of the GaN-based crystal as an accompanying effect accompanying the surfactant treatment.

  In the present invention, the light scattering layer (A) incorporated in the device can be formed only by performing a surfactant treatment on the base surface, and is effective without complicating the manufacturing process of the light emitting device. Causes light scattering and improves light extraction efficiency.

It is the schematic diagram which showed the structural example of the GaN-type light emitting element of this invention. Hatching is appropriately used to distinguish the areas. It is the figure which showed the formation process of a light-scattering layer. In FIG. 2A, the gaseous surfactant is schematically represented by dots. It is a figure explaining the advantage by determining the magnitude relationship of the refractive index n1 of a 1st GaN-type crystal, and the refractive index n2 of a 2nd GaN-type crystal regarding a light extraction direction.

Explanation of symbols

10 substrate 20 n-type layer 30 light emitting layer 40 p-type layer 50 light scattering layer 51 first GaN-based crystal 52 second GaN-based crystal S laminate

Claims (8)

A nitride semiconductor light emitting device configured to have a laminate composed of a nitride semiconductor crystal layer, the laminate including an n-type layer, a light emitting layer, and a p-type layer, and As a layer other than the light emitting layer, the following light scattering layer (A) is included,
A nitride semiconductor light emitting element configured to scatter light emitted from a light emitting layer at an interface between a first nitride semiconductor crystal and a second nitride semiconductor crystal constituting the light scattering layer.
(A) A base surface on which a nitride semiconductor crystal can grow two-dimensionally is subjected to a surfactant treatment, and the first nitride semiconductor crystal having a refractive index n1 has a protrusion and / or a recess on the surface. A light scattering layer that is vapor-grown into a shape, and wherein the first nitride semiconductor crystal is embedded by a second nitride semiconductor crystal having a refractive index n2 different from the refractive index n1.   The nitride semiconductor light emitting element according to claim 1, wherein the surface of the first nitride semiconductor crystal has a height difference of ¼ or more of a wavelength of light emitted from the light emitting layer.   The nitride semiconductor light emitting element according to claim 2, wherein the light scattering layer (A) is located in the multilayer body with the base surface side facing away from the light emitting layer.   The nitride semiconductor light emitting device according to claim 2, wherein the light scattering layer (A) is located in the multilayer body with the base surface side facing the light emitting layer.   The light scattering layer of (A) is stacked in the stack so that the driving current of the nitride semiconductor light emitting element flowing between the n-type layer and the p-type layer crosses the light scattering layer of (A) in the layer thickness direction. The nitride semiconductor light emitting device according to claim 3, which is located at   The first nitride semiconductor crystal and the second nitride semiconductor crystal are such that the light extraction direction of the nitride semiconductor light emitting element is a direction away from the base surface, and the refractive index n2 <refractive index n1. The nitride semiconductor light emitting device according to claim 2, wherein is selected.   The light extraction direction of the nitride semiconductor light emitting element is a direction approaching the base surface, and the first nitride semiconductor crystal and the second nitride semiconductor crystal are set such that the refractive index n1 <the refractive index n2. The nitride semiconductor light emitting device according to claim 2, wherein is selected.   The nitride semiconductor light-emitting element according to claim 2, wherein oblique facets are exposed as side walls of the protruding portion and / or the recessed portion of the first nitride semiconductor crystal.

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