JP2006332714A - Semiconductor light-emitting device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To secure a high external quantum efficiency stably in a semiconductor light-emitting device. <P>SOLUTION: At least one recess portion (20) and/or protruding portion (21) is formed on the surface of a substrate (10) for scattering or diffracting light generated in a light-emitting region (12). The recess portion and/or protruding portion has a shape that precludes crystal defects from being produced in semiconductor layers (11 and 13). <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a semiconductor light emitting device, and in particular, in nitride compound semiconductor light emitting devices, the substrate is provided with irregularities that do not cause defects in the semiconductor, and the light guiding direction in the semiconductor layer is changed to increase the external quantum efficiency. It relates to the element made.

  In a semiconductor light emitting device, for example, a light emitting diode (LED), an n-type semiconductor layer, a light emitting region, and a p-type semiconductor layer are basically grown on a substrate in a stacked structure, while the p-type semiconductor layer and the n-type semiconductor layer are formed. A structure is adopted in which an electrode is formed and when light is generated in the light-emitting region due to recombination of holes and electrons injected from the semiconductor layer, the light is extracted from the translucent electrode or substrate on the p-type semiconductor layer. Has been. The translucent electrode is a translucent electrode made of a metal thin film or a transparent conductive film formed on almost the entire surface of the p-type semiconductor layer.

  In the light emitting diode having such a structure, the flatness of the substrate is processed to a mirror level because the laminated structure is controlled at the atomic level, so that the semiconductor layer, the light emitting region and the electrode on the substrate have a laminated structure parallel to each other. Moreover, the refractive index of the semiconductor layer is large, and the waveguide is constituted by the surface of the p-type semiconductor layer and the surface of the substrate. That is, a waveguide is formed by a structure in which a semiconductor layer having a high refractive index is sandwiched between a substrate having a low refractive index and a light-transmitting electrode.

  Therefore, when light is incident on the electrode surface or substrate surface at an angle greater than a predetermined critical angle, it is reflected at the electrode / p-type semiconductor layer interface or substrate surface and propagates laterally in the stacked structure of the semiconductor layer. Trapped in the waveguide, and there is a loss during lateral propagation, and the desired external quantum efficiency cannot be obtained. That is, light incident on the interface with the substrate or electrode at an angle larger than the critical angle repeats total reflection, propagates in the waveguide, and is absorbed therebetween. For this reason, a part of emitted light is attenuated and cannot be effectively extracted outside, and the external quantum efficiency is lowered.

  On the other hand, a method has been proposed in which a light emitting diode chip is processed into a hemispherical shape or a truncated pyramid shape, and light generated in the light emitting region is incident on the surface at less than a critical angle. However, it is difficult to process the chip. .

  Moreover, although the method of roughening the surface or side surface of the light emitting diode has been proposed, the pn junction may be partially broken, and the effective light emitting region may be reduced.

  On the other hand, a method has been proposed in which concave or convex portions are formed on the surface of the substrate to scatter light generated in the light emitting region, thereby improving external quantum efficiency (see Japanese Patent Application Laid-Open No. 11-274568). . In this method, in a GaN-based LED in which a sapphire substrate, n-type GaN, p-type GaN, and a transparent electrode are sequentially stacked, the surface of the sapphire substrate is randomly roughened by mechanical polishing or etching. Thereby, the light which injects into a sapphire substrate is scattered, and external quantum efficiency improves.

  However, in the light emitting diode described in the above-mentioned conventional publication, the external quantum efficiency may not be improved depending on the concave portion or the convex portion. That is, when roughening is performed without controlling the shape or size of the recesses or protrusions, the crystallinity of the grown GaN is lowered when the generated recesses or protrusions are increased to some extent. For this reason, the light emission efficiency (= internal quantum efficiency) in the GaN semiconductor layer is lowered, and the external quantum efficiency is lowered. Also, if the surface is simply roughened, the external quantum efficiency does not reach a sufficient level because the influence of light absorption in the waveguide is large.

  SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide a semiconductor light emitting device capable of stably ensuring improved external quantum efficiency.

  The semiconductor light-emitting device according to the present invention has a light-emitting region formed on a substrate surface with at least two semiconductor layers made of a material different from that of the substrate, and the light generated in the light-emitting region is emitted from the upper semiconductor layer or the substrate. In the semiconductor light emitting device that is taken out from the substrate, at least one concave portion and / or convex portion that scatters or diffracts the light generated in the light emitting region is formed on the surface portion of the substrate, and the concave portion and / or the convex portion is formed. The semiconductor layer has a shape that does not cause defects. In the present invention, “does not cause crystal defects in the semiconductor layer” means that there is no occurrence of a morphological abnormality such as pits on the semiconductor layer due to the formation of irregularities on the substrate, and the formation of irregularities on the substrate. It means that there is almost no increase in dislocations in the semiconductor layer.

  One of the features of the present invention is that a recess and / or a protrusion having a shape that does not allow defects to grow in the semiconductor layer is provided on the substrate surface portion, and the semiconductor layer is grown thereon. Providing a recess or projection that scatters or diffracts light at the interface between the semiconductor layer and the substrate rather than at the interface between the semiconductor layer and the electrode improves the crystallinity of the light emitting region (= active layer) and increases the output. effective. In particular, in the case of a gallium nitride compound semiconductor light emitting device, a substrate, an n-side nitride semiconductor layer, a light emitting region (= active layer), and a p-side nitride semiconductor layer are stacked in this order. The thickness is smaller than that of the n-side nitride semiconductor layer. For this reason, the concave or convex portions are provided not at the interface between the semiconductor layer and the electrode, but at the interface between the semiconductor layer and the substrate, so that the influence of the unevenness is mitigated by the thick n-side nitride semiconductor layer, and the light emitting region (= active region) The crystallinity of the layer) can be kept good.

  In the case of a conventional semiconductor light emitting device having a flat substrate, the light propagating in the lateral direction in the semiconductor layer is partially absorbed by the semiconductor layer and the electrode while propagating, and attenuated before exiting the semiconductor layer. To do.

  On the other hand, in the present invention, in the case of a conventional flat substrate, the light propagating in the lateral direction is scattered or diffracted in the concave and / or convex portions and efficiently extracted from the upper semiconductor layer or the lower substrate. As a result, the external quantum efficiency can be greatly improved. That is, first, due to the light scattering / diffraction effect due to the unevenness, the light flux above or below the substrate increases, and the luminance when the light emitting surface of the light emitting element is observed from the front (= front luminance) can be increased. . Second, the light scattering / diffraction effect due to the unevenness can reduce the light propagating in the lateral direction in the semiconductor layer, reduce the absorption loss during propagation, and increase the total amount of light emission.

  Moreover, even if the concave portion and / or the convex portion are formed on the substrate surface portion, crystal defects due to the concave and convex portions hardly grow on the semiconductor layer, so that the above-described high external quantum efficiency can be stably secured. In the present invention, it is preferable that the inside of the concave portion and the periphery of the convex portion are completely filled with the semiconductor layer. This is because if there is a cavity inside the recess or around the protrusion, the function of scattering or diffraction is hindered and the luminous efficiency is lowered.

  Either one of the concave portion and the convex portion may be formed on the surface portion of the substrate, or the same effect can be obtained even if they are formed in combination. However, it is preferable to form the convex portion rather than the concave portion because the semiconductor layer can easily fill the periphery without a cavity. If there is a cavity around the concave or convex portion, the scattering or diffraction function due to the concave and convex portions is hindered, and the output is reduced.

  The shape of the concave portion and / or the convex portion so that no defect grows in the semiconductor layer is specifically a shape having a straight line intersecting a plane substantially parallel to the growth stable surface of the semiconductor layer as a constituent side. More specifically, a straight line that intersects a plane substantially parallel to the growth stable surface is a straight line that is not parallel to the growth stable surface when viewed from the upper surface of the substrate. The growth stable surface refers to a surface having the slowest growth rate than other surfaces in the material to be grown. The growth stability surface generally appears as a facet surface during growth. For example, in the case of a gallium nitride-based compound semiconductor, a plane parallel to the A axis (particularly the M plane) is the growth stable plane. Therefore, when viewed from the top surface of the substrate, the concave portion or the convex portion is formed in a polygon having a straight line that is not parallel to a plane parallel to the A axis (= a straight line that is not parallel to the A axis). If the concave and / or convex portions are straight sides that are substantially parallel to the growth stable surface of the semiconductor layer, crystal defects will occur at the site when the semiconductor layer is formed, which reduces the internal quantum efficiency. This results in a decrease in external quantum efficiency.

More specifically, the concave portion and / or the convex portion has a vertex in a plane substantially parallel to the growth stable plane of the semiconductor layer and intersects with a plane substantially parallel to the growth stable plane of the semiconductor layer. Can be a polygon, for example, a triangle, a parallelogram or a hexagon, preferably a regular triangle, a rhombus or a regular hexagon.
In addition, in this specification, making a recessed part or a convex part a polygon means making the planar shape at the time of observing from a board | substrate upper surface into a polygon. The planar shape of the unevenness does not have to be a geometrically perfect polygon, and may have rounded corners for processing reasons.

  For example, when a GaN-based semiconductor is grown on the C-plane of a sapphire substrate, the growth starts in an island shape with a hexagonal shape surrounded by a plane including the A-axis of the GaN-based semiconductor, and the islands are combined to form a uniform semiconductor. Become a layer. Therefore, assuming a regular hexagon having the A axis of the GaN-based semiconductor as a constituting side, a polygon having a straight line perpendicular to a line connecting the center and apex of the regular hexagon (for example, a triangle, a hexagon, etc.) A recess or a protrusion is formed on the surface. A flat and excellent GaN-based semiconductor can be grown on the sapphire substrate having such irregularities.

  In addition, the number of the concave portions and / or convex portions may be one, but if the shape is formed in a repeated pattern, the efficiency of light scattering or diffraction is increased, and the external quantum efficiency can be further improved. In the present invention, even when the concave and / or convex portions are repeatedly provided on the substrate, by growing the semiconductor layer so as to suppress local crystal defects due to the concave or convex portions, The entire surface can be a light emitting surface.

  The present invention is characterized in that a concave portion and / or a convex portion are formed on the surface portion of the substrate to scatter or diffract light, and the substrate of the light emitting element and the semiconductor material itself can be any material. For example, the present invention can be applied to a semiconductor light emitting device in which the semiconductor layer is a III-V group semiconductor, specifically, a GaN semiconductor. The growth stable plane of the GaN-based semiconductor layer is an M plane {1-100} of hexagonal crystals. Here, {1-100} represents all of (1-100), (01-10), and (-1010). The M plane is one of the planes parallel to the A axis. Depending on the growth conditions, another plane (= plane other than the M plane) including the A axis of the GaN-based semiconductor may be a growth stable plane.

  Moreover, a sapphire substrate, a SiC substrate, or a spinel substrate can be used as the substrate. For example, a sapphire substrate having a C plane (0001) as a main surface can be used as the substrate. In this case, the M plane, which is the growth stable plane of the GaN-based semiconductor layer, is a plane parallel to the A plane {11-20} of the sapphire substrate. Here, the A plane {11-20} represents all of (11-20), (1-210), and (-2110).

  It is important that the depth of the concave portion or the level difference of the convex portion is 50 mm or more and the dimension is not more than the thickness of the semiconductor layer grown on the substrate. When at least the emission wavelength (for example, in the case of an AlGaInN-based light emitting layer, 206 nm to 632 nm) is λ, the light cannot be sufficiently scattered or diffracted without a depth or step of λ / 4 or more, This is because when the depth of the concave portion or the step difference of the convex portion exceeds the thickness of the semiconductor layer grown on the substrate, it becomes difficult for the current to flow in the lateral direction in the stacked structure, and the luminous efficiency decreases. . Therefore, the surface of the semiconductor layer may be concave and / or convex. In order to sufficiently scatter or diffract light, the depth or step is preferably λ / 4 or more, but if the depth or step is λ / 4n (n is the refractive index of the semiconductor layer) or more. Scattering or diffraction effects can be obtained.

  In addition, the size of the concave portion and / or the convex portion (that is, the length of one side serving as the constituent side of the concave portion and / or the convex portion) and the interval between them are the emission wavelength in the semiconductor as λ (380 nm to 460 nm). In this case, it is important that the size is at least λ / 4. This is because the light cannot be sufficiently scattered or diffracted unless it has a size of at least λ / 4. In order to sufficiently scatter or diffract light, the size of the recesses or projections and the distance between them are preferably λ / 4 or more, but λ / 4n (n is the refractive index of the semiconductor layer) or more. Scattering or diffraction effects can be obtained with the size and the distance between each other. In manufacturing, the size of the concave or convex portions and the interval between them are preferably 100 μm or less. Furthermore, it is preferable that the thickness is 20 μm or less because the scattering surface increases.

  Moreover, since the total film thickness of the semiconductor layer is generally 30 μm or less, it is preferable that the uneven pitch is 50 μm or less from the viewpoint of effectively reducing the number of total reflections by scattering or diffraction. Furthermore, from the viewpoint of the crystallinity of the GaN layer (= prevention of pit generation), it is preferable that the uneven pitch is 20 μm or less. More desirably, by setting the uneven pitch to 10 μm or less, the probability of scattering or diffraction increases, and the output can be further improved. In addition, the pitch of unevenness means the minimum distance among the distances between the centers of adjacent concave portions or convex portions.

Next, as shown in FIG. 9, the cross-sectional shape of the projections and depressions is preferably a trapezoid if it is a convex portion, and an inverted trapezoid if it is a concave portion. By setting it as such a cross-sectional shape, light scattering and diffraction efficiency can be improved. Note that the cross-sectional shape of the projections and depressions does not need to be a geometrically perfect trapezoid or inverted trapezoid, and the corners may be rounded for reasons such as processing. As shown in FIG. 9, the taper angle θ of the uneven side surface means an angle formed between the top surface and the side surface if it is a convex portion, and an angle formed between the bottom surface and the side surface if it is a concave portion. For example, when the taper angle θ is 90 °, the concavo-convex cross section is square, and when the taper angle θ is 180 °, there is a flat state with no concavo-convex. In order to fill the unevenness with the semiconductor layer, the taper angle θ of the unevenness needs to be at least 90 ° or more. Further, from the viewpoint of improving the output due to scattering or diffraction, the taper angle θ of the unevenness is preferably larger than 90 °, desirably 105 ° or more, more desirably 115 ° or more. On the other hand, if the taper angle θ of the unevenness is too large, the efficiency of scattering or diffraction is lowered, and pits in the semiconductor layer are easily generated. Therefore, the taper angle θ is preferably 160 ° or less, more preferably 150 ° or less, and further preferably 140 ° or less.
When the uneven side surface is inclined, the size of the unevenness and the interval between them are defined by the length on the top surface of the substrate (= bottom surface of the convex portion if it is a convex portion, flat surface of the substrate if it is a concave portion). Shall be.

In the light emitting device according to the present invention, it is preferable to form an ohmic electrode by forming a metal film having an opening. That is, when a semiconductor layer is formed on a substrate with unevenness as in the present invention, and a full-surface electrode with an opening is formed thereon, the light extraction efficiency is remarkably increased due to the synergistic effect of the two. improves. In particular, it is preferable that at least one uneven portion on the surface of the substrate is included in the opening of the electrode.

This is presumed to be due to the following reason.
First, when the luminance of a light emitting element using a concavo-convex substrate is observed from the front, the luminance near the step portion of the concavo-convex substrate becomes higher than the luminance of the flat portion of the substrate. For this reason, by providing the opening of the electrode above the stepped portion of the substrate unevenness, the output is improved in each step.
Secondly, in a light emitting device having a concavo-convex structure on a substrate, out of the light generated in the light emitting region, the light that is originally directed to the side or downward is extracted upward by scattering or diffracting at the concave and convex portions. be able to. However, in the configuration in which a normal translucent electrode is provided on the entire surface, the light reaching the upper side through scattering and diffraction is partially absorbed by the translucent electrode, and the light intensity is reduced. Therefore, in the case where a semiconductor layer is formed over a substrate provided with unevenness, an opening is provided in the translucent electrode, or a non-translucent electrode having an opening with high reflectivity is provided and a part of the semiconductor layer is formed. By providing the exposed portion, light that has reached the upper side through scattering and diffraction is easily extracted to the outside, and the light extraction efficiency is significantly improved.

In the case of a gallium nitride-based (including at least gallium and nitrogen) semiconductor light emitting device, the vicinity of the periphery of the p-electrode provided on the p-type nitride semiconductor layer has a property that it shines stronger than other portions. For this reason, by providing an opening in the electrode, the absorption of light is reduced, and the peripheral portion that shines strongly increases, so that the light extraction efficiency is improved. For example, it is preferable that L / S ≧ 0.024 μm / μm ² where L is the total perimeter of the opening of the electrode and S is the occupation area of the ohmic electrode including the inside of the opening. Thereby, the ratio of the electrode peripheral part which shines strongly can be increased, and light emission output can be improved further.

The ohmic electrode that forms the opening includes at least selected from Ni, Pd, Co, Fe, Ti, Cu, Rh, Au, Ru, W, Zr, Mo, Ta, Pt, Ag, and oxides and nitrides thereof. An alloy containing one kind or a multilayer film can be used. In particular, an alloy or multilayer film containing one of rhodium (Rh), iridium (Ir), silver (Ag), and aluminum (Al) is preferable.

  Hereinafter, the present invention will be described in detail based on specific examples shown in the drawings. 1 and 2 show a preferred embodiment of a semiconductor light emitting device according to the present invention. In the figure, a C-plane (0001) sapphire substrate having an orientation flat on the A-plane (11-20) is used for the substrate 10, and concave portions 20 are formed in a repetitive pattern on the surface portion of the sapphire substrate 10. In FIG. 2, etching is performed leaving a portion indicated by oblique lines.

  The recess 20 has a vertex on a growth stable plane (1-100), (01-10), (-1010) of the GaN-based semiconductor 11 grown on the sapphire substrate 10, that is, a plane substantially parallel to the M plane. In addition, it forms an equilateral triangle having a straight line that intersects with a plane substantially parallel to the growth stable plane. That is, as shown in FIG. 3, the equilateral triangle constituting the recess 20 has a vertex at a position where the M plane intersects when viewed from the upper surface of the substrate, and each constituent side of the equilateral triangle is 30 with respect to the M plane. Crossing at a degree or 90 degrees. More specifically, as shown in FIG. 3, when the concave portion 20 is viewed from the upper part of the substrate, each constituent side of the concave portion 20 is a line connecting the center and apex of a regular hexagon having the M plane of the GaN semiconductor 11 as a constituent side. It is orthogonal to. When observed from the upper surface of the sapphire substrate 10, the M-plane of the GaN semiconductor is parallel to the A-axis of the GaN-based semiconductor.

  Further, the depth of the recess 20 is about 1 μm, the size of one side a is 10 μm, and the interval b between the recess 20 and the recess 20 is 10 μm.

  An n-type GaN-based semiconductor layer 11 is formed on the sapphire substrate 10, an MQW light emitting region 12 is formed thereon, and a p-type AlGaN / p-type GaN-based semiconductor 13 is formed thereon.

When manufacturing the semiconductor light emitting device of this example, an SiO ₂ film 30 serving as an etching mask is formed on the sapphire substrate 10 as shown in FIG.

Next, using a photomask of a regular triangle having a side of 10 μm, aligning the photomask so that one side of the regular triangle is perpendicular to the orientation flat, and each side of the regular triangle is made of (1-100), (01- 10), (−1010), that is, substantially parallel to the M plane, and after etching the SiO ₂ film 30 and the sapphire substrate 10 by RIE about 1 μm as shown in FIGS. 4B and 4C, When the SiO ₂ film 30 is removed as shown in FIG. 4D, a repetitive pattern of the recesses 20 shown in FIG. 2 is formed on the surface portion of the sapphire substrate 10.

  An n-type GaN semiconductor layer 11 is grown on a sapphire substrate 10 having a repeated pattern of recesses 20, an MQW light emitting region 12 is grown thereon, and a p-type AlGaN / p-type GaN semiconductor layer 13 is grown thereon.

  Since the GaN lattice grows by 30 degrees with respect to the lattice of the sapphire substrate 10, the repetitive pattern of the recesses 20 formed on the sapphire substrate 10 is the GaN A-plane (11-20), (1-210), (-2110). ) Growth surface (1-100), (01-10), and (-1010) have vertices, and the GaN growth stability surface (1-100), (01-) 10), (−1010), that is, a polygon having no straight line parallel to the M plane.

  By forming irregularities in such a shape, GaN having excellent flatness and crystallinity can be grown. The principle will be described below. Since the principle is the same for both concave and convex portions, the convex portion will be described as an example. FIGS. 5A and 5B are SEM photographs in the middle of growing GaN on the sapphire substrate 10 on which equilateral triangular protrusions 20 are formed. FIG. 5A is observed from the upper surface of the substrate. FIG. 5B shows a state observed from obliquely above the substrate. As shown in FIGS. 5A and 5B, when GaN is grown on the sapphire substrate 10, the growth of GaN proceeds from the upper surface of the convex portion 20 and the flat surface where the convex portion 20 is not formed. Finally, the vicinity of the side surface of the convex portion 20 is filled. Therefore, when the growth stable surface of GaN and the side surface of the convex portion 20 are parallel when viewed from above the substrate, the vicinity of the side surface of the convex portion 20 is difficult to be buried, and the crystallinity of GaN is lowered.

Therefore, it is preferable to form the constituent sides of the convex part 20 of the equilateral triangle so as to intersect (= not to be parallel) with the M plane which is a growth stable plane of GaN when viewed from above the substrate. 5 (a) and 5 (b), a regular hexagon (= regular hexagon having an A axis as a component side) having a plane including the A axis as a growth stable surface of GaN as viewed from above the substrate. The constituent sides of the convex part 20 of the equilateral triangle are formed so as to be orthogonal to the line connecting the center and the vertex. By forming the protrusions 20 in this way, the periphery of the protrusions 20 can be filled flat and GaN with good crystallinity can be obtained.

  This is presumed to be because the growth rate of GaN increases at the portion where GaN grown from the upper surface of the convex portion 20 and GaN grown from a flat surface where the convex portion 20 is not formed are joined. That is, as shown in FIG. 5B, GaN grows in a hexagonal shape with the A axis as a constituent side from the upper surface of the convex portion 20, but GaN grown from the upper surface of the convex portion 20 The growth rate of GaN increases in the vicinity of the side surface of the convex portion where the GaN grown from the flat surface comes into contact. Therefore, the growth of GaN in the vicinity of the side surface of the protrusion 20 catches up with other regions, and flat GaN is obtained.

  This will be schematically described with reference to FIGS. As shown in FIG. 6A, when a convex portion is formed on the sapphire substrate 10 and GaN 11 is grown thereon, as shown in FIGS. 6B and 6C, the GaN 11 has a convex portion. It grows from the bottom surface and a flat surface on which no convex portion is formed, and the growth is delayed near the side surface of the convex portion. However, as shown in FIGS. 6D and 6E, when GaN 11 grown from the upper surface of the convex portion and GaN 11 grown from the flat surface meet each other, the growth rate of GaN 11 increases there. For this reason, the growth of GaN 11 in the vicinity of the side surface of the convex portion where the growth has been delayed significantly proceeds. Then, as shown in FIG. 6F, GaN 11 that is flat and excellent in crystallinity grows. On the other hand, when the growth stable surface of GaN and the side surface of the convex portion 20 are parallel when viewed from above the substrate, the growth rate does not increase in the vicinity of the side surface of the convex portion 20. The vicinity is difficult to fill, and the crystallinity of GaN is lowered.

  Thereafter, a device process is performed, electrodes and the like are appropriately formed, and finished into an LED chip.

  When holes and electrons are injected from the n-type GaN semiconductor layer 11 and the p-type AlGaN / p-type GaN semiconductor layer 13 into the MQW light emitting region 12 and recombination is performed, light is generated. This light is extracted from the sapphire substrate 10 or the p-type AlGaN / p-type GaN semiconductor layer 13.

  In the case of a conventional semiconductor light emitting device having a flat substrate, as shown in FIG. 7A, the light from the light emitting region 12 is above the critical angle at the interface between the p-type semiconductor layer 13 and the electrode or the surface of the substrate 10. When incident, it was trapped in the waveguide and propagated laterally.

  On the other hand, in the semiconductor light emitting device of this example, light having a critical angle or more with respect to the interface between the p-type semiconductor layer 13 and the electrode or the surface of the substrate 10 is scattered by the recess 21 as shown in FIG. Alternatively, the light is diffracted and incident on the interface between the p-type semiconductor layer 13 and the electrode or the surface of the substrate 10 at an angle smaller than the critical angle, and can be taken out.

  When the contact electrode on the p-type semiconductor layer 13 is a translucent electrode, it is effective in both cases of FU (face-up) and when it is a reflective electrode, FD (face-down). Even if the electrode is a reflective electrode, it is used for FU (face-up) when an opening or a cut is formed in the electrode. In that case, there is a particularly remarkable effect.

  FIG. 8 shows another embodiment of the semiconductor light emitting device according to the present invention. In the embodiment shown in FIG. 8A, the step surface of the recess 20 is formed to be inclined. Further, in the embodiment shown in FIG. 8B, the convex portion 21 is formed on the surface portion of the substrate 10 instead of the concave portion 20, and in this example, the convex portion 21 having a semicircular cross section is formed. Furthermore, in the embodiment shown in FIG. 8C, the n-type semiconductor layer 11, the light emitting region 12, and the p-type semiconductor layer 13 are recessed due to the influence of the recess 20.

  FIGS. 7C and 7D show examples of light propagation in the embodiment shown in FIGS. 8A and 8C. In any case, it can be seen that light can be extracted efficiently. In particular, as shown in FIG. 8A, the surface of the convex portion and the concave portion with a straight line (also referred to as a polygonal side in this case) intersecting with a plane substantially parallel to the growth stable surface of the semiconductor layer. The surface that is continuous with the surface of the surface (= the side surface of the concave or convex portion) is inclined with respect to the stacking direction of the semiconductor, so that the effect of light scattering or diffraction is remarkably increased, and the light extraction efficiency Is significantly improved. One factor for this is that by providing an inclined surface, the surface area of the surface continuous to the surface of the recess and the surface of the projection (= side surface of the recess or projection) increases, so that light scattering or diffraction occurs. It is thought that the number of times of occurrence increases.

  In other words, as shown in FIG. 9, the concave and convex cross-sectional shape is preferably a trapezoid if it is a convex part, and an inverted trapezoid if it is a concave part. By setting it as such a cross-sectional shape, the probability that the propagating light will be scattered and diffracted increases, and the absorption loss during the propagation of the light can be reduced. As shown in FIG. 9, the taper angle θ of the uneven side surface means an angle formed between the top surface and the side surface if it is a convex portion, and an angle formed between the bottom surface and the side surface if it is a concave portion. For example, when the taper angle θ is 90 °, the concavo-convex cross section is square, and when the taper angle θ is 180 °, there is a flat state with no concavo-convex.

  In order to fill the unevenness with the semiconductor layer, the taper angle θ of the unevenness needs to be at least 90 ° or more. Further, from the viewpoint of improving the output due to scattering or diffraction, the taper angle θ of the unevenness is preferably larger than 90 °, desirably 105 ° or more, more desirably 115 ° or more. On the other hand, if the taper angle θ of the unevenness is too large, the scattering or diffraction efficiency is lowered, and pits are easily generated in the semiconductor layer. Therefore, the taper angle θ is preferably 160 ° or less, more preferably 150 ° or less, and further preferably 140 ° or less.

FIG. 10 is a graph simulating the relationship between the taper angle on the side surface of the recess and the LED output. This also has the same tendency when viewed as the taper angle of the side surface of the convex portion. The vertical axis of the graph in FIG. 10 represents the output ratio when the LED output is 1 when a flat substrate (= taper angle θ is 180 °) is used, and the horizontal axis of the graph is the side surface of the recess. Represents the taper angle. As shown in the figure, the LED output changes greatly by changing the taper angle of the side surface of the concave portion (= the angle formed between the bottom surface and the side surface of the concave portion) between 90 degrees and 180 degrees.

  FIG. 11 shows an example of another shape of the concave portion 20 or the convex portion 21. In the figure, the hatched portion is the portion that remains without being etched.

  Further, when the concave portion 20 or the convex portion 21 is a regular hexagon, the direction of the orientation flat A of the sapphire substrate 10 shown in FIG. 12A is not the direction shown in FIG. ) Place a regular hexagon in the direction indicated by. As described above, when GaN is grown on the C surface of the sapphire substrate, the A surface of the sapphire substrate and the M surface of GaN become parallel. Therefore, by arranging concave and convex regular hexagons as shown in FIG. 12B, each side of the concave and convex regular hexagons is orthogonal to one of the M planes, which are GaN growth stable surfaces, when viewed from above the substrate. It becomes like this. In other words, when viewed from above the substrate, the line segment connecting the center and apex of the regular hexagon (= regular hexagon having the A axis as the component side) with the GaN M-plane as the component side is shown. This means that the constituent sides of the regular hexagons of irregularities are orthogonal to each other.

  In addition, the present invention is not particularly limited as long as it is an element in which a normal semiconductor layer such as a nitride semiconductor layer is formed on a substrate provided with irregularities that do not cause defects in the semiconductor, and electrodes and the like are further formed. Although it is not done, a remarkable effect is shown by making other configurations as follows.

(1) Electrode shape and material
[1] Aperture electrode Although it is necessary to provide an electrode on the semiconductor layer on the surface of the semiconductor light emitting device, the specific resistance is relatively high as in the p-type nitride semiconductor layer, and current diffusion is performed in that layer. For example, a translucent electrode is generally formed over the entire surface of the semiconductor layer on the difficult semiconductor layer. However, when light propagates through a waveguide composed of a translucent electrode, a semiconductor layer, and a substrate, not only the semiconductor layer but also the translucent electrode or the substrate due to the influence of “exudation” of reflected light. Luminescence is absorbed and attenuated. In particular, the translucent electrode has a large influence on the attenuation of light emission because of its high light absorptance in a short wavelength region of a general constituent material (for example, Au / Ni).

Therefore, in the light emitting device according to the present invention, it is preferable to form an electrode by forming a metal film having an opening. In particular, it is preferable that at least one uneven portion on the surface of the substrate is included in the opening of the electrode. Thus, it is preferable that the electrode formed on the surface of the semiconductor layer is an electrode having an opening, since light is extracted from the opening and the proportion of light absorbed by the electrode is reduced. It is desirable to provide a plurality of openings in the metal film, and providing the openings as large as possible is preferable in terms of improving light extraction efficiency. (Preferably, such an electrode is provided with a pad electrode that electrically connects the light emitting element to the outside.)

  In the case of a nitride semiconductor light emitting device, particularly a gallium nitride (including at least gallium and nitrogen) semiconductor light emitting device, an electrode having translucency is preferably formed on the entire surface of the p-type nitride semiconductor layer. In many cases, it is provided as an electrode, but the light-transmitting electrode absorbs light so that the vicinity of the periphery of the p-electrode provided on the p-type nitride semiconductor layer shines stronger than the other portions. Therefore, an opening may be provided in the translucent electrode, which reduces light absorption and increases the peripheral portion that shines strongly, thereby improving light extraction efficiency. In this case, it is preferable that the area of the opening is as large as possible from the viewpoint of improving the light extraction efficiency, and the light extraction efficiency is further improved by providing as long as possible the length of the peripheral portion of the p-electrode.

As in the present invention, when a semiconductor layer is formed on a substrate provided with unevenness and an electrode provided with the above-described opening is formed, the light extraction efficiency is remarkably improved by the synergistic effect of the both. This is presumed to be due to the following reason.
First, when the luminance of a light emitting element using a concavo-convex substrate is observed from the front, the luminance near the step portion of the concavo-convex substrate becomes higher than the luminance of the flat portion of the substrate. For this reason, by providing the opening of the electrode above the stepped portion of the substrate unevenness, the output is improved in each step.
Secondly, in a light emitting device having a concavo-convex structure on a substrate, out of the light generated in the light emitting region, the light that is originally directed to the side or downward is extracted upward by scattering or diffracting at the concave and convex portions. be able to. However, in the configuration in which a normal translucent electrode is provided on the entire surface, the light reaching the upper side through scattering and diffraction is partially absorbed by the translucent electrode, and the light intensity is reduced. Therefore, in the case where a semiconductor layer is formed over a substrate provided with unevenness, an opening is provided in the translucent electrode, or a non-translucent electrode having an opening with high reflectivity is provided and a part of the semiconductor layer is formed. By providing the exposed portion, light that has reached the upper side through scattering and diffraction is easily extracted to the outside, and the light extraction efficiency is significantly improved.

[2] Opening electrode material As described above, in the case of a nitride semiconductor light-emitting device, particularly a gallium nitride-based (including at least gallium and nitrogen) semiconductor light-emitting device, the p-type nitride semiconductor layer is formed on almost the entire surface. Although a light-transmitting electrode is provided as a p-electrode, as a more preferable form, the light extraction efficiency is improved by forming an electrode with an opening on almost the entire surface of the p-type nitride semiconductor layer. At this time, the material used as the electrode is a metal or an alloy made of two or more metals, and can be formed of a single layer or a plurality of layers. By using a metal material having a high reflectance for at least the wavelength of light emitted as the electrode material, the light component absorbed by the electrode can be reduced, and the light extraction efficiency to the outside can be improved.

  Preferred materials for the aperture electrode are selected from the group consisting of Ni, Pd, Co, Fe, Ti, Cu, Rh, Au, Ru, W, Zr, Mo, Ta, Pt, Ag and their oxides and nitrides. And an alloy or multilayer film containing at least one of the above. These can obtain good ohmic contact with the p-type semiconductor layer by annealing at a temperature of 400 ° C. or higher. In particular, a multilayer film of Au on Ni is preferable. The total thickness of the aperture electrode is preferably 50 to 10,000 mm. In particular, when used as a translucent electrode, 50 to 400 mm is preferable. Moreover, when setting it as a non-light-transmissive electrode, 1000 to 5000 mm is preferable.

  In particular, in a gallium nitride-based semiconductor light emitting device (including at least gallium and nitrogen), examples of the highly reflective metal material include rhodium (Rh), iridium (Ir), silver (Ag), and aluminum (Al). Used as a reflective electrode.

  In particular, it is also preferable that the material of the opening electrode is Rh. By using Rh, an electrode that is thermally stable and has low absorption can be obtained. In addition, the contact resistance can be lowered.

[3] Size and shape of the opening electrode The size relationship between the opening of the electrode and the unevenness of the substrate surface is not particularly limited, but it is preferable that at least one uneven step is formed in one opening. Thereby, the light scattered and diffracted by the unevenness can be extracted effectively, and at the same time, the uniformity of light emission is improved.

The opening electrode is an electrode that penetrates to the surface of the p-type semiconductor layer and has a plurality of openings surrounded by the electrode. The area of the portion surrounded by the outermost periphery (= inside the opening) It is preferable that L / S ≧ 0.024 μm / μm ^2, where S is the total area of the electrode including S and L is the total inner peripheral length of the opening. Thereby, light can be efficiently emitted from the surface of the p-type semiconductor layer to the outside, and a semiconductor light emitting element having a lower Vf can be obtained.

Each of the plurality of openings preferably has substantially the same shape. This makes it easy to form the openings and makes the in-plane distribution of light emission uniform. The plurality of openings preferably have substantially the same area, and this also makes the in-plane distribution of light emission uniform.

  In the case where the opening is provided by increasing the film thickness, by defining the shape and size of the opening, the light extraction efficiency can be increased and the light emission efficiency can be improved. In particular, by defining the inner peripheral length L of the opening, light can be emitted more efficiently. When L / S is reduced, that is, when the total L of the inner peripheral lengths of the openings is reduced with respect to the area S surrounded by the outermost periphery of the opening electrode, the output to the p-type semiconductor layer side is reduced. .

FIG. 13 shows the power conversion efficiency when the aperture ratio is the same, that is, the total area of the aperture is the same and the inner peripheral length is changed. Since the contact area between the p-type semiconductor layer and the opening electrode is the same because the area of the opening is the same, Vf and the quantum efficiency are considered to be the same. From this figure, it can be seen that even if the aperture ratio is the same, the output can be further increased by changing the inner peripheral length of the opening. Then, in the present invention, it is in the range that satisfies ^{L / S ≧ 0.024μm / μm 2} , may be a semiconductor light emitting device of high output. The upper limit is not particularly defined. However, if the upper limit is substantially larger than 1 μm / μm ² , the size of one opening becomes too small and becomes impractical.

  As described above, the output efficiency from the p-type semiconductor layer side is greatly influenced by the inner peripheral length of the opening because light emission is particularly strongly observed at the boundary between the electrode and the p-type semiconductor layer. The light can be efficiently emitted by increasing the boundary, that is, by increasing the inner peripheral length. In order to further increase the boundary, not only the opening, but also the outermost peripheral portion of the p-side ohmic electrode is provided along the end of the semiconductor layer by a refracted continuous line instead of a straight line. Since the boundary between the side ohmic electrode and the p-type semiconductor can be increased, the output can be further improved.

  By forming the plurality of openings as described above so as to have substantially the same shape, it becomes easy to efficiently form the plurality of openings. Furthermore, the in-plane distribution is likely to be uniform, and light emission without unevenness can be obtained. As the shape, various shapes such as a square, a circle, and a triangle can be used. Preferably, it is easy to obtain uniform light emission by forming a plurality of adjacent openings so as to be uniformly dispersed at a certain distance. Moreover, a preferable shape can be selected according to the position where an opening part is formed by forming so that the area of several opening part may become substantially the same.

  14 (a) to (d) show possible shapes of the aperture electrode. In FIG. 14, a p-side semiconductor layer 32 is formed on an n-side semiconductor layer 30, an opening electrode 34 that is a p-side ohmic electrode is formed thereon, and a p-side pad electrode 36 is formed on a part thereof. ing. An n-side pad electrode 38 is formed on the n-side semiconductor layer 30 exposed by etching the p-side semiconductor layer 32. A plurality of circular openings are arranged in the opening electrode 34. FIG. 14B shows an example where the size of the circular opening of the opening electrode 34 is large. 14C and 14D show only the opening electrode 34 and the p-side pad electrode 36 extracted. As shown in FIG. 14C, the opening provided in the p-side ohmic electrode may have a cut shape in which the periphery is not closed. In this case, the p-side ohmic electrode has a shape in which a plurality of linear electrodes are joined. The opening is preferably formed so that a large amount of current does not flow through a strong current path. Further, as shown in FIG. 14D, openings may be provided in a plurality of arcs arranged concentrically around an n-side pad electrode (not shown). By setting it as such an opening shape, the uniformity of light emission can be improved.

  Further, the end cross-sectional shape of the p-side ohmic electrode may be vertical as shown in FIG. 15A, but is preferably a mesa shape (trapezoidal shape) as shown in FIG. 15B. . In particular, in the case of a gallium nitride-based compound semiconductor light emitting device, since the light emission intensity at the peripheral portion of the p-side ohmic electrode is high, the end section has a mesa shape (trapezoidal shape), so that light can be efficiently extracted. Can do. In that case, the taper angle θ of the end section is preferably 30 ° ≦ θ <90 °. When the taper angle is less than 30 °, the resistance value of the p-side ohmic electrode in the taper portion is increased, so that it is difficult to effectively use the property that the electrode peripheral portion shines strongly.

(2) Shape of Semiconductor Light-Emitting Element In the present invention, at least two semiconductor layers made of a material different from the substrate and a light-emitting region are formed in a laminated structure on the substrate surface. That is, the materials of the substrate and the semiconductor layer are different. Here, when an insulating substrate is used as the substrate, for example, when a gallium nitride-based (including at least gallium and nitrogen) semiconductor layer is formed on a sapphire substrate, the electrode cannot be formed on the substrate. It is necessary to form two electrodes, an n electrode and a p electrode, on the same surface side. At this time, for example, a nitride semiconductor element formed in the order of an n-type semiconductor layer, a light emitting region, and a p-type semiconductor layer is etched until a part of the surface of the p-type semiconductor layer is exposed, A p-electrode is formed on the surface of the p-type semiconductor layer, and an n-electrode is formed on the surface of the exposed n-type semiconductor layer. The view seen from the surface of the semiconductor layer is shown at two opposing vertices of a rectangular semiconductor element as shown in FIG. These electrodes are arranged and formed.

  In this case, light exiting from the side surface of the semiconductor light emitting element is blocked by the external connection terminal such as an n electrode or a wire connected to the n electrode on the side surface formed when the n-type semiconductor layer is exposed. .

  Therefore, as shown in FIG. 17, the portion where the n-type semiconductor layer is exposed is the inside of the p-type semiconductor layer, and the n-type semiconductor layer is exposed inside the surface of the p-type semiconductor layer, thereby providing the n-type semiconductor. Since the light emitting region that is sandwiched between the p-type semiconductor layer and the p-type semiconductor layer is provided on the entire outer side surface of the semiconductor light emitting element, the light extraction efficiency to the outside is improved. In the case of an element laminated in the order of a p-type semiconductor layer, a light emitting region, and an n-type semiconductor layer on a substrate, the same effect can be obtained by providing an exposed surface of the p-type semiconductor layer inside the n-type semiconductor layer. .

  In addition, as shown in FIG. 17, when the inside of one conductive type semiconductor layer surface is etched to expose the other conductive type semiconductor layer surface, the former semiconductor layer surface or the opening is formed. In the case of forming an electrode having a current on the entire surface of the former semiconductor layer by providing a diffusion electrode extending from the pad electrode on the surface of the electrode having the former semiconductor layer and the opening, It is preferable that the light emission in the light emitting region is uniform and uniform. Further, this diffusion electrode is preferably provided inside the former semiconductor layer along the outer shape of the semiconductor light emitting element, so that more uniform light emission can be achieved.

  Further, the shape of the outer shape of the semiconductor light emitting device may be a square shape or a triangular shape as viewed from the surface of the semiconductor layer, and may be other polygonal shapes, but the surface formed by etching and the electrode formed on the exposed surface Is preferably stretched partially toward the apex constituting the outer shape of the semiconductor light-emitting element, whereby the current easily flows uniformly, and the light emission in the light-emitting region is uniform and uniform.

  For example, in the case of a gallium nitride-based (including at least gallium and nitrogen) semiconductor light-emitting element of the present invention, a phosphor containing YAG is mixed with a resin on the surface of the light-emitting element formed up to the electrode. Thus, a white light emitting element with high light extraction efficiency can be obtained, and a light emitting element with various light emission wavelengths and high light extraction efficiency can be obtained by selecting an appropriate phosphor.

  The p electrode and the n electrode used in the present invention are electrodes formed in contact with at least a semiconductor layer, and a material that exhibits good ohmic characteristics with the semiconductor layer in contact with the electrode is appropriately selected.

  As the substrate, a sapphire substrate having a C surface (0001) having an orientation flat on the A surface (11-20) as a main surface is used.

First, an SiO ₂ film 30 serving as an etching mask is formed on the sapphire substrate 10 as shown in FIG.

Next, using a photomask of a regular triangle having a side of 5 μm, aligning the photomask so that one side of the regular triangle is perpendicular to the orientation flat, and each side of the regular triangle is made of (1-100), (01- 10), (−1010), that is, substantially parallel to the M plane, and after etching the SiO ₂ film 30 and the sapphire substrate 10 by 3 to 4 μm by RIE as shown in FIGS. When the SiO ₂ film 30 is removed as shown in FIG. 4D, the convex portion 20 shown in FIG. 11B is repeatedly formed on the surface portion of the sapphire substrate 10 (the region where the hatched portion is not etched). A pattern is formed. The length of one side of the convex part is a = 5 μm, and the distance between the convex part and the convex part is b = 2 μm. The pitch of the convex portions (the distance between the centers of the adjacent convex portions) is 6.3 μm. Further, the inclination angle of the side surface of the convex portion was 120 °.

Next, on the sapphire substrate 10 having the repeated pattern of the protrusions 20, a low-temperature growth buffer layer of Al _x Ga _1-x N (0 ≦ x ≦ 1) is formed as an n-type semiconductor layer by 100 μm, and undoped GaN is 3 μm. Then, 4 μm of Si-doped GaN and 3000 μm of undoped GaN are stacked, and then, as an active layer of a multiple quantum well that becomes a light emitting region, (well layer, barrier layer) = (undoped InGaN, Si-doped GaN), respectively The film thickness is (60 mm, 250 mm), and the well layers are alternately stacked so that there are six well layers and seven barrier layers. In this case, the barrier layer to be finally stacked may be undoped GaN. In addition, by using undoped GaN as the first layer formed on the low-temperature growth buffer layer, it is possible to fill the protrusions 20 more uniformly and improve the crystallinity of the semiconductor layer formed thereon. .

  After stacking the active layers of the multi-quantum well, 200 p of Mg-doped AlGaN, 1000 p. Of undoped GaN, and 200 p. Of Mg-doped GaN are laminated as p-type semiconductor layers. An undoped GaN layer formed as a p-type semiconductor layer exhibits p-type due to diffusion of Mg from an adjacent layer.

  Next, in order to form an n-electrode, the Mg-doped GaN to the p-type semiconductor layer, the active layer, and a part of the n-type semiconductor layer are etched to expose the Si-doped GaN layer.

  Next, a light-transmitting p-electrode made of Ni / Au is formed on the entire surface of the p-type semiconductor layer, and a p-pad made of Au is placed on the light-transmitting p-electrode at a position facing the exposed surface of the n-type semiconductor layer. An electrode is formed, and an n electrode made of W / Al / W and an n pad electrode made of Pt / Au are formed on the exposed surface of the n-type semiconductor layer.

  Finally, the wafer is chipped into a square shape to obtain a 350 μm square semiconductor chip. This was mounted on a lead frame equipped with a reflecting mirror to produce a bullet-type LED.

  The LED thus obtained had a light emission wavelength of 400 nm and an external light output of 9.8 mW at a forward current of 20 mA.

[Comparative Example 1]
As a comparative example, when the sapphire substrate was not provided with irregularities, and other configurations were formed in the same manner as in Example 1, a bullet-type LED was formed. At a forward current of 20 mA, the light emission output to the outside was 8.4 mW. there were.

As the substrate, a sapphire substrate having a C surface (0001) having an orientation flat on the A surface (11-20) as a main surface is used.
The processing of the substrate and the lamination from the n-type semiconductor layer to the p-type semiconductor layer are performed in the same manner as in Example 1.
Next, in order to form an n-electrode, the p-type semiconductor layer made of Mg-doped GaN, the active layer, and a part of the n-type semiconductor layer are etched to expose the n-type semiconductor layer made of Si-doped GaN.

  Next, an opening made of a regular triangle having a side of 5 μm, and a patterning photomask in which the regular triangular opening as shown in FIG. A translucent p-electrode is formed on almost the entire surface of the p-type semiconductor layer.

  Further, a p-pad electrode made of Au is formed on the light-transmitting p-electrode at a position facing the exposed surface of the n-type semiconductor layer, and an n-electrode made of Ti / Al and a Pt / Pt on the exposed surface of the n-type semiconductor layer. An n-pad electrode made of Au is formed.

  Finally, the wafer is chipped into a square shape to obtain a semiconductor light emitting device. This is mounted on a lead frame provided with a reflecting mirror to produce a bullet-type LED.

  The LED thus obtained has a light emission output that is higher than that of the first embodiment due to the property that the vicinity of the periphery of the p-electrode shines stronger than other portions.

As the substrate, a sapphire substrate having a C surface (0001) having an orientation flat on the A surface (11-20) as a main surface is used.
The processing of the substrate and the lamination from the n-type semiconductor layer to the p-type semiconductor layer are performed in the same manner as in Example 1.

  Next, in order to form an n-electrode, the Mg-doped GaN to the p-type semiconductor layer, the active layer, and a part of the n-type semiconductor layer are etched to expose the Si-doped GaN layer.

  Next, a square having a side of 7.7 μm, arranged at intervals of 6.3 μm, and having an aperture ratio of 30%, a p-electrode made of Rh is formed on almost the entire surface of the p-type semiconductor layer.

Further, on the p-electrode, a p-pad electrode made of Pt / Au is formed at a position facing the exposed surface of the n-type semiconductor layer, and the n-electrode made of W / Al / W and the Pt / Au are formed on the exposed surface of the n-type semiconductor layer. An n-pad electrode made of Au is formed.
Finally, the wafer is chipped to obtain a semiconductor light emitting device. This was mounted on a lead frame equipped with a reflecting mirror to produce a bullet-type LED.

  The semiconductor light-emitting device obtained thereby utilizes the property that the periphery of the p-electrode shines stronger than the other parts, and further uses a material that highly reflects the emission wavelength for the electrode to absorb light at the electrode. As a result, the light emission output was improved as compared with Example 1 and Example 2. The light emission output of the bullet-type LED was 13.2 mW.

In the light emitting device of Example 3, the p-electrode is formed in a stripe shape as shown in FIG. By adopting such a stripe electrode structure, the current supplied from the p-side pad electrode to the semiconductor layer is made uniform in the plane, and the light emission efficiency is improved.
Since the p-electrode stripe gap is formed as an opening through which the semiconductor layer is exposed, the number of openings can be increased. As a result, light extraction efficiency is improved. At this time, the sum of the total area Sa of the opening 5 corresponding to the plurality of stripe gaps where the semiconductor layer is exposed and the area Sb of the electrode portion where the semiconductor layer 102 is not exposed is defined as S, It is preferable that L / S ≧ 0.024 μm / μm ² is satisfied, where L is the total circumference.

As the substrate, a sapphire substrate having a C surface (0001) having an orientation flat on the A surface (11-20) as a main surface is used.
The processing of the substrate and the lamination from the n-type semiconductor layer to the p-type semiconductor layer are performed in the same manner as in Example 1.

  Next, etching is performed inside the surface of the p-type semiconductor layer until the Si-doped GaN layer is exposed, particularly in the central portion. As shown in FIG. 17, the surface exposed by the etching at this time is formed by partially extending toward the three apexes constituting the outer shape of the semiconductor light emitting element.

  Next, using a photomask that is a regular triangle having a side of 5 μm and in which the regular triangle is filled most closely per unit area, the p-electrode 104 made of Rh is attached to almost the surface of the p-type semiconductor layer. A regular triangle shape is formed on the entire surface.

  Further, a p pad electrode / p diffusion electrode 106 made of Pt / Au is formed on the p electrode 104. As shown in FIG. 17, the p pad electrode / p diffusion electrode 106 is provided by extending a pad electrode inside the former semiconductor layer along the outer shape of the semiconductor light emitting element having a regular triangle. Providing this electrode makes it easier for a current to flow uniformly over the entire surface of the semiconductor layer, thus functioning as a diffusion electrode.

  An n electrode made of W / Al / W and an n pad electrode 103 made of Pt / Au are formed on the exposed surface of the n-type semiconductor layer.

  Finally, the wafer is chipped into a regular triangle to obtain a semiconductor light emitting device. FIG. 17 shows the light emitting element as viewed from above.

  The light-emitting element obtained by this utilizes the property that the periphery of the p-electrode shines stronger than the other parts, and further uses a material that highly reflects the emission wavelength for the electrode to reduce the light absorption component at the electrode. Since the reduced light emission region of the multiple quantum well structure is provided on the entire outer side surface of the semiconductor light emitting device, the light emission output is improved.

A light-transmitting material containing Y ₃ Al ₅ O ₁₂ Y: Ce (YAG: Ce) based on a yttrium-aluminum oxide phosphor as a phosphor on the upper surface and side surfaces of the semiconductor light-emitting device obtained in Example 5 Forming a resin.
The resulting semiconductor light emitting device emitted white light with a high light emission output.

  In this example, the effect of forming irregularities was confirmed with both the chip and the lamp for various irregular planar shapes. First, a sapphire substrate having a C surface (0001) having an orientation flat on the A surface (11-20) as a main surface is used as the substrate.

Next, four types of processing (i) to (iv) are performed on the sapphire substrate. Concavity and convexity formation on the surface of the sapphire substrate is performed in the same manner as in Example 1.
(I) On the surface of the sapphire substrate, a regular triangular convex portion as shown in FIG. 11B is formed. The convex portions of the equilateral triangle are arranged so that one side thereof is orthogonal to the orientation flat of the sapphire substrate, and are arranged so that the directions of the apexes are alternately left and right. One side of the convex portion of the regular triangle is 5 μm, and the interval between the convex portions is 2 μm.
(Ii) On the surface of the sapphire substrate, diamond-shaped convex portions as shown in FIG. One side of the rhombus convex portions is 4 μm, and the interval between the convex portions is 2 μm.
(Iii) A hexagonal convex portion as shown in FIG. 11 (m) is formed on the surface of the sapphire substrate. One side of the hexagonal convex portion is 3 μm, and the interval between the convex portions is 2 μm.
(Iv) No irregularities are formed on the surface of the sapphire substrate.

Next, on the four types of sapphire substrates 10, a low-temperature growth buffer layer of Al _x Ga _1-x N (0 ≦ x ≦ 1) as an n-type semiconductor layer is 100 μm, undoped GaN is 3 μm, and Si-doped GaN. 4 μm, 3000 μm of undoped GaN are stacked, and subsequently, as an active layer of a multi-quantum well that becomes a light emitting region, (well layer, barrier layer) = (undoped InGaN, Si doped GaN) each with a thickness of (60 μm). 250 cm), the well layers are alternately laminated so that there are 6 well layers and 7 barrier layers. In this case, the barrier layer to be finally stacked may be undoped GaN. Note that, when the first layer formed on the low-temperature growth buffer layer is made of undoped GaN, the recesses 20 can be filled more uniformly, and the crystallinity of the semiconductor layer formed thereon can be improved.

  After stacking the active layers of the multiple quantum wells, as a p-type semiconductor layer, 200 Ｍｇ of Mg-doped AlGaN and 200 Å of Mg-doped GaN are stacked.

  Next, in order to form an n-electrode, the Mg-doped GaN to the p-type semiconductor layer, the active layer, and a part of the n-type semiconductor layer are etched to expose the Si-doped GaN layer.

  Next, a light-transmitting p-electrode made of Ni / Au is formed on the entire surface of the p-type semiconductor layer with a thickness of 60/70 mm. Further, on the light-transmitting p-electrode, a p-pad electrode made of Au is formed at a position facing the exposed surface of the n-type semiconductor layer, and an n-electrode made of W / Al / W is formed on the exposed surface of the n-type semiconductor layer. An n-pad electrode made of Pt / Au is formed.

表１に示すように、凸部の形状がいずれの場合であっても、平坦なサファイア基板を用いた場合に比べて、４３％以上高い発光出力が得られる。このように、反射鏡を用いないチップ状態で正面輝度の評価を行うと、凹凸形成による発光出力の増大効果が顕著に現れる。 When a current is passed between the p pad electrode and the n pad electrode using a prober in the state of the wafer and the light emission output is examined, Table 1 shows. In Table 1, the intensity ratio of the light emission output is displayed with the light emission output when there is no unevenness being 1.

As shown in Table 1, regardless of the shape of the convex portion, a light emission output that is 43% or more higher than that obtained when a flat sapphire substrate is used is obtained. As described above, when the front luminance is evaluated in a chip state in which no reflecting mirror is used, the effect of increasing the light emission output due to the formation of the unevenness appears significantly.

  Next, the wafer is formed into a square shape to obtain a 350 μm square semiconductor chip. This was mounted on a lead frame equipped with a reflecting mirror to produce a bullet-type LED.

表２に示すように、凸部の形状がいずれの場合であっても、平坦なサファイア基板を用いた場合に比べて、１３％以上高い発光出力が得られる。特に、本実施例において、凸部の形状が六角形である場合に最も高い発光出力が得られる。 Table 2 shows the evaluation of the light emission output of the manufactured LED at Vf and 20 mA. Note that the emission wavelength of the LED is 460 nm.

As shown in Table 2, a light output of 13% or more higher than that obtained using a flat sapphire substrate can be obtained regardless of the shape of the convex portion. In particular, in the present embodiment, the highest light emission output is obtained when the shape of the convex portion is a hexagon.

  The same as Example 7 except that the p electrode was changed from the Ni / Au electrode to the Rh opening electrode. The opening shape of the Rh electrode is a square having a side of 7.7 μm, arranged at intervals of 6.3 μm, and the opening ratio is 30%.

表３に示すように、凸部の形状がいずれの場合であっても、平坦なサファイア基板を用いた場合に比べて、５４％以上高い発光出力が得られる。 When a current is passed between the p pad electrode and the n pad electrode using a prober in the state of the wafer and the light emission output is examined, Table 3 shows. In Table 3, the intensity ratio of the light emission output is displayed assuming that the light emission output is 1 when there is no unevenness.

As shown in Table 3, regardless of the shape of the convex portion, a light emission output that is 54% or more higher than that obtained when a flat sapphire substrate is used is obtained.

表４に示すように、凸部の形状がいずれの場合であっても、平坦なサファイア基板を用いた場合に比べて、１７％以上高い発光出力が得られる。特に、本実施例において、凸部の形状が六角形である場合に最も高い発光出力が得られる。
実施例７と実施例８の対比からわかるように、ｐ電極を開口電極とすることにより、開口電極と凹凸基板が相乗的に作用して、凹凸形成の効果が一層顕著に現れる。 A bullet-type LED is manufactured, and the light emission output at Vf and 20 mA is evaluated as shown in Table 4. Note that the emission wavelength of the LED is 460 nm.

As shown in Table 4, regardless of the shape of the convex portion, a light emission output that is 17% or more higher than that obtained when a flat sapphire substrate is used is obtained. In particular, in the present embodiment, the highest light emission output is obtained when the shape of the convex portion is a hexagon.
As can be seen from the comparison between Example 7 and Example 8, by using the p electrode as the opening electrode, the opening electrode and the uneven substrate act synergistically, and the effect of forming the unevenness appears more remarkably.

It is sectional drawing which shows preferable embodiment of the semiconductor light-emitting device based on this invention. It is a figure which shows the example of a pattern of the recessed part in the said embodiment. It is a schematic diagram which shows the relationship between the growth stable surface of a nitride semiconductor, and a recessed part shape. It is a figure which shows the manufacturing process of 1st Embodiment. It is the SEM photograph which observed the middle process of growing gallium nitride on the sapphire substrate which formed the convex part. It is a schematic diagram which shows the process of growing a gallium nitride on the sapphire substrate in which the convex part was formed. It is a figure which shows typically light propagation of this invention by contrast with the conventional structure. It is sectional drawing which shows other embodiment. It is sectional drawing which shows the example of the uneven | corrugated cross-sectional shape. It is a graph which shows the relationship between the inclination-angle of a recessed part side surface, and light emission output. It is a figure which shows the other example of a pattern of a recessed part or a convex part. It is a figure for demonstrating other embodiment which made the recessed part or the convex part the regular hexagon. It is a graph which shows the relationship between L / S (= area S of the p-side ohmic electrode and the inner peripheral length L of the opening) and the light emission output. It is a figure which shows the variation of the form of a p side ohmic electrode. It is a schematic diagram which shows the edge part cross-sectional shape of a p side ohmic electrode, and the relationship of light emission. The figure which looked at the semiconductor light-emitting device which concerns on other embodiment of this invention from the upper surface. The figure which looked at the semiconductor light-emitting device which concerns on other embodiment of this invention from the upper surface.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 ... Substrate 11 ... N-type semiconductor layer 12 ... Light emission region 13 ... P-type semiconductor layer 20 ... Concave part 21 ... Convex part 30 ... N side semiconductor layer 32 ... p-side semiconductor layer 34 ... p-side ohmic electrode 36 ... p-side pad electrode 38 ... n-side pad electrode 101 ... n-type semiconductor layer 102 ... p-type semiconductor layer 103 ... n-electrode And n pad electrode 104... P electrode 105... P pad electrode 106... P pad electrode and p diffusion electrode

Claims (27)

Semiconductor light emission in which at least two semiconductor layers of different materials from the substrate and a light emitting region are formed on the substrate surface in a laminated structure, and light generated in the light emitting region is extracted from the upper semiconductor layer or the lower substrate. In the element
At least one concave portion and / or convex portion that scatters or diffracts light generated in the light emitting region is formed on the surface portion of the substrate, and the at least one concave portion and / or convex portion causes crystal defects in the semiconductor layer. A semiconductor light emitting element having a shape that does not occur.   2. The semiconductor light emitting element according to claim 1, wherein the concave portion and / or the convex portion has a shape having a straight line intersecting a plane substantially parallel to a growth stable plane of the semiconductor layer as a constituent side.   The concave portion and / or the convex portion has a straight line having a vertex on a plane substantially parallel to the growth stable surface of the semiconductor layer and intersecting a plane substantially parallel to the growth stable surface of the semiconductor layer. The semiconductor light emitting device according to claim 1, wherein the semiconductor light emitting device is a polygon.   Assuming a regular polygon that has the growth stable surface of the semiconductor layer as a constituent side, a concave or convex part is formed in the polygon that has a straight line that is perpendicular to the line connecting the center and vertex of the polygon. The semiconductor light emitting element according to claim 1 or 2.   The semiconductor light emitting element according to claim 1, wherein the concave portion and / or the convex portion are formed in a pattern having a repeated shape.   6. The semiconductor light emitting device according to claim 1, wherein the semiconductor layer is a III-V group semiconductor.   The semiconductor light emitting element according to claim 1, wherein the semiconductor layer is a GaN-based semiconductor.   The semiconductor light-emitting device according to claim 2, wherein a growth stable surface of the semiconductor layer in the substrate is an M-plane {1-100} of hexagonal crystal.   9. The semiconductor light emitting device according to claim 1, wherein the substrate is a sapphire substrate, a SiC substrate, or a spinel substrate.   The semiconductor light-emitting device according to claim 1, wherein the substrate is a C-plane (0001) sapphire substrate.   The semiconductor light emitting element according to claim 10, wherein a growth stable surface in the semiconductor layer is a surface parallel to the A surface {11-20} of the substrate.   The semiconductor light-emitting element according to claim 3, wherein the polygon of the concave portion and / or the convex portion is a triangle, a parallelogram, or a hexagon.   The semiconductor light-emitting element according to claim 3, wherein the polygon of the concave portion and / or the convex portion is a regular triangle, a rhombus, or a regular hexagon.   The semiconductor light emitting device according to any one of claims 1 to 13, wherein the depth of the concave portion or the step of the convex portion is not less than 50 mm and not more than the thickness of the semiconductor layer grown on the substrate.   The semiconductor light emitting element according to any one of claims 2 to 14, wherein when the emission wavelength in the semiconductor is λ, the side of the concave portion and / or the convex portion is at least λ / 4.   The component side of the concave portion and / or the convex portion has a size of at least λ / 4n, where λ is an emission wavelength in the semiconductor and n is a refractive index of the semiconductor. The semiconductor light-emitting device described in 1.   17. The semiconductor light emitting element according to claim 2, wherein a side of the concave portion and / or the convex portion has a size of 100 μm or less.   18. The semiconductor light emitting element according to claim 2, wherein a side of the concave portion and / or the convex portion has a size of 20 μm or less.   The semiconductor light-emitting device according to claim 1, wherein the surface of the semiconductor layer has a concave shape and / or a convex shape. A plurality of semiconductor layers made of different materials from the substrate and an ohmic electrode formed on the uppermost layer of the semiconductor layer are stacked on the substrate, and light generated in the semiconductor layer is extracted from the ohmic electrode side or the substrate side. In such a semiconductor light emitting device,
At least one concave portion and / or convex portion that scatters or diffracts light generated in the semiconductor layer is formed on the surface portion of the substrate,
A semiconductor light-emitting element, wherein a cross-sectional shape of the concave portion is an inverted trapezoid and a cross-sectional shape of the convex portion is a trapezoid.   21. The semiconductor light emitting device according to claim 20, wherein the ohmic electrode covers substantially the entire surface of the uppermost layer of the semiconductor layer.   The semiconductor light emitting element according to claim 21, wherein a taper angle of the concave or convex side surface is larger than 90 ° and not larger than 160 °. A plurality of semiconductor layers made of different materials from the substrate and an ohmic electrode covering almost the entire uppermost layer of the semiconductor layer are stacked on the substrate, and light generated in the semiconductor layer is extracted from the ohmic electrode side. In a semiconductor light emitting device,
At least one concave portion and / or convex portion that scatters or diffracts light generated in the semiconductor layer is formed on the surface portion of the substrate,
At least one opening is formed in the said ohmic electrode, The semiconductor light-emitting device characterized by the above-mentioned.   24. The semiconductor light emitting device according to claim 23, wherein at least one step portion of the concave portion or the convex portion is formed inside the opening. 25. L / S ≧ 0.024 μm / μm ² where L is the total perimeter of the openings and S is the area occupied by the ohmic electrode including the inside of the openings. Semiconductor light emitting device.   The ohmic electrode is at least selected from the group consisting of Ni, Pd, Co, Fe, Ti, Cu, Rh, Au, Ru, W, Zr, Mo, Ta, Pt, Ag, and oxides and nitrides thereof. 26. The semiconductor light emitting device according to claim 23, wherein the semiconductor light emitting device is an alloy containing one kind or a multilayer film.   26. The ohmic electrode is an alloy or multilayer film including one selected from the group consisting of rhodium (Rh), iridium (Ir), silver (Ag), and aluminum (Al). The semiconductor light-emitting device according to any one of the above.

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