JP2007165725A - Semiconductor light-emitting diode - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a semiconductor light-emitting diode capable of restraining the influence of damage by dry etching at a level difference section and improving element characteristics and reliability. <P>SOLUTION: A p-side electrode 21 and an n-side electrode 22 are provided at a first region 10A and a second region 10B, respectively. A boundary region 10C between both of them is set to a two-stage structure of a first level difference section 31 in a p-type cladding layer 13 and a second level difference section 33 straddling over a pn junction section 14 with a flat section 32 in between. The thickness of the p-type cladding layer 13 in the flat section 32 becomes small, thus preventing current from spreading laterally. Current C injected from the p-side electrode 21 enters the n-type cladding layer 12 after lowering to the flat section 32 along the first level difference section 31, and flows toward the n-side electrode 22 laterally; and the path of the current C is separated from the second level difference section 33. Even if a pn structure on the surface of the second level difference section 33 is damaged by dry etching, the generation of a leak path, or the like is restrained. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a semiconductor light emitting diode in which a first electrode and a second electrode are provided on one side of a substrate, and more particularly to a semiconductor light emitting diode suitable for one that generates blue to green light.

  A GaInN mixed crystal, which is a typical nitride-based III-V group compound semiconductor (hereinafter referred to as “nitride semiconductor”), has a band gap varying from 0.8 eV to 3.2 eV depending on the indium composition ratio. It is a direct transition semiconductor material, and is expected as a constituent material for light emitting / receiving elements over a wide wavelength range from the ultraviolet region, the entire visible region, and the infrared region. Already, ultraviolet, blue, green, and white light emitting diodes (LEDs) and lasers with an oscillation wavelength of 405 nm in accordance with the Blu-ray standard have been put into practical use, and their performance has been improved. . Furthermore, a pure blue laser having an oscillation wavelength of 450 nm is almost in practical use. Further, since this material has a high saturation rate in a high electric field and is excellent in heat resistance and radiation resistance, it is also attracting attention as a material constituting electronic devices such as high-power high-frequency transistors.

  FIG. 25 shows an example of a conventional semiconductor light emitting diode using such a GaInN mixed crystal. This semiconductor light emitting diode is formed on a substrate 111 made of an insulating material such as sapphire, and a pn junction 114 is constituted by the n-type layer 112 and the p-type layer 113. A p-side electrode 121 made of a highly reflective material is provided on the p-type layer 113. Part of the p-type layer 113 and the n-type layer 112 in the thickness direction is removed by dry etching, for example, to form a stepped portion 130, and an n-side electrode 122 is provided on the exposed surface of the n-type layer 112. As described above, in the semiconductor light emitting diode in which the p-side electrode 121 and the n-side electrode 122 are provided on one side of the substrate 111, the generated light is extracted from the back side of the substrate 111 to the outside.

  As the substrate 111, a conductive material such as SiC or GaN may be used. Since these substrates are transparent to the emission wavelength, a p-side electrode and an n-side electrode are provided on one side of the substrate as in the case of the sapphire substrate, and a flip-chip type structure in which light is extracted from the back side of the substrate. There are many. This is due to the element performance design reason that if an electrode or the like is provided on the back side of the substrate, the loss of light absorbed by the electrode or the like becomes large.

Thus, in the semiconductor light emitting diode in which the p-side electrode and the n-side electrode are provided on one side of the substrate, the current C injected from the p-side electrode 121 flows in the n-type layer 112 in a direction parallel to the substrate surface (hereinafter referred to as “horizontal”). Direction).) Further, in order to increase the light extraction efficiency by increasing the area of the p-side electrode 121 made of a highly reflective material, the p-side electrode 121 is formed up to the level of the step portion 130 around the p-type layer 113. The distance X _LED between the end of the electrode 121 and the pn junction 114 exposed at the stepped portion 130 is close to, for example, several μm, which is the lithography control limit. As a result, the current C flows in the vicinity of the step portion 130.
Japanese Patent No. 3576963 (paragraph 0013)

  However, the stepped portion 130 has an effect on element characteristics and reliability, such as damage to the pn structure on the surface due to dry etching and the occurrence of a leak path on the surface.

  For example, Patent Document 1 discloses that in a nitride semiconductor light emitting device, since a light emitting component emitted from the end face of the light emitting layer is relatively large, the p-type semiconductor layer is etched to provide a comb-shaped recess, and light emission A structure is described in which the light extraction efficiency is increased by increasing the end face of the region. However, in this structure, the stepped portion due to dry etching also increases, so that the influence on the device characteristics and reliability due to the damage of the stepped portion becomes more difficult to overlook. In addition, although the light extraction efficiency is increased by providing the concave portion, the area of the p-type semiconductor layer, that is, the light emitting region is decreased, so that there is a problem that the current density is increased with respect to the same current and the light emission efficiency is decreased. It was.

Incidentally, in the case of a semiconductor laser, the configuration is almost the same as that of a semiconductor light emitting diode except that a protrusion (ridge) 113A is provided on a p-type cladding layer 113 as shown in FIG. . However, the width of the protrusion 113A is, for example, 1 μm to 2 μm, which is sufficiently narrow as compared with the laser stripe width W _LD of, for example, 300 μm. Therefore, the distance X _LD between pn junction 114 which is exposed at the end and the step portion 130 of the p-side electrode 121 on the ridge 113A is, for example, can be designed to be sufficiently apart about 20Myuemu～70myuemu. Since the current mainly flows below the protrusion 113A and hardly flows in the vicinity of the stepped portion 130, even if the stepped portion 130 is damaged by dry etching, the effect is hardly exhibited.

  Further, when the structure in which the current C flows in the lateral direction is used, the resistance of the n-type layer 112 needs to be low in order to reduce the operating voltage. For this reason, the contact resistance of the n-type layer 112 or the n-side electrode 122 does not significantly affect the increase in the operating voltage of the element, depending on the impurity addition conditions and thickness design of the n-type layer 112. However, when the n-type layer 112 is remarkably thick, not only the crystal growth time increases, but also the warpage due to the difference in thermal expansion coefficient between the substrate 111 and the n-type layer 112 becomes large, and lithography, chip pelletization, etc. There was a problem of affecting the manufacturing process and the mounting process.

  As long as the resistance of the n-type layer 112 is finite and the current C flows in the lateral direction, the current concentrates in the vicinity of the step portion 130 at the pn boundary as shown schematically in FIG. A so-called current crowding phenomenon in which a current does not flow so much has occurred in a place where the distance from the portion 130 is long. Since the light output depends on the current injection density, if the current injection is not uniform, the light emission efficiency and the device characteristics are deteriorated. In order to shorten the distance through which the current C flows, the element size may be reduced. However, a high output element could not be designed.

  The present invention has been made in view of such problems, and a first object of the present invention is to provide a semiconductor light-emitting diode capable of suppressing the influence of damage due to dry etching of a stepped portion and improving device characteristics and reliability. It is to provide.

  A second object of the present invention is to provide a semiconductor light emitting diode capable of reducing nonuniformity of current injection and improving luminous efficiency.

  It is a third object of the present invention to provide a semiconductor light emitting diode that can improve light extraction efficiency and light emission efficiency.

  A first semiconductor light emitting diode according to the present invention includes a first conductive semiconductor layer and a second conductive semiconductor layer constituting a pn junction, and a first electrode having a first electrode on the surface of the first conductive semiconductor layer. A second region having a second electrode on the surface of the second conductivity type semiconductor layer, and a second region including a part of the second conductivity type semiconductor layer, and a second region having a second electrode; A first stepped portion formed from the surface of the one-conductivity-type semiconductor layer to a part in the thickness direction, continuous to the first stepped portion, a flat portion formed in the first-conductivity-type semiconductor layer, and continuous to the flat portion. , A boundary region having a second step portion formed across the pn junction.

  In the first semiconductor light emitting diode of the present invention, the boundary region has a two-stage structure of a first step portion in the first conductivity type semiconductor layer and a second step portion straddling the pn junction portion with a flat portion in between. Therefore, the thickness of the first conductivity type semiconductor layer in the flat portion is small, and the current is difficult to spread in the lateral direction. Therefore, the current injected from the first electrode descends to the flat portion along the first step portion and enters the second conductive type semiconductor layer, then flows laterally toward the second electrode, and the current path is Move away from the second step. Accordingly, even if the pn structure on the surface of the second step portion is damaged, the occurrence of a leak path or the like can be suppressed.

  A second semiconductor light emitting diode according to the present invention includes a first conductive type semiconductor layer and a second conductive type semiconductor layer constituting a pn junction, and has a first electrode on the surface of the first conductive type semiconductor layer. A second region having a second electrode on the surface of the second conductive semiconductor layer, and a boundary provided between the first region and the second region; The first electrode is formed so as to surround the recess, while the second electrode is formed on the bottom surface of the recess. The shortest distance M to the second electrode is 70 μm or less at all positions of the first electrode.

  Here, the shortest distance M is the maximum value when the distance to the closest second electrode is obtained for each coordinate of the first electrode.

  In the second semiconductor light emitting diode of the present invention, since the shortest distance M from the second electrode is 70 μm or less at all positions of the first electrode, the distance in which the current actually flows in the lateral direction is shortened. Current injection unevenness between the peripheral portion and the central portion of one electrode is improved. Therefore, the operating voltage is lowered and the light emission efficiency is increased.

  A third semiconductor light emitting diode according to the present invention includes a first conductive type semiconductor layer and a second conductive type semiconductor layer constituting a pn junction, and a first electrode having a first electrode on the surface of the first conductive type semiconductor layer. A second region having a second electrode on the surface of the second conductive semiconductor layer, and a boundary provided between the first region and the second region; The first region has a recess, the bottom surface of the recess is a second region, the area S of the first region and the total peripheral length L satisfy Equation 1, and the area S Is 70% or more of the total area of the first region, the second region, and the boundary region.

(Equation 1)
a = L / √S
a> 10
(In Equation 1, a represents an index of the complexity of the shape of the first region.)

  In the third semiconductor light emitting diode of the present invention, the area S of the first region and the total peripheral length L satisfy Equation 1, and the area S is 70 of the total area of the first region, the second region, and the boundary region. Since the total peripheral length L is increased to increase the light extraction efficiency, a sufficiently large area S is secured, and the current density does not increase for the same current. Reduction in efficiency is suppressed.

  According to the first semiconductor light emitting diode of the present invention, the boundary region is divided into the first stepped portion in the second conductivity type semiconductor layer and the second stepped portion straddling the pn junction with the flat portion in between. Therefore, even if the first electrode is provided as far as the first step portion to increase the current injection efficiency, it is possible to suppress the influence of damage due to dry etching of the second step portion. Therefore, element characteristics and reliability can be improved.

  According to the second semiconductor light emitting diode of the present invention, since the shortest distance M with respect to the second electrode is 70 μm or less at all positions of the first electrode, the distance in which the current actually flows in the lateral direction is shortened, Current injection unevenness can be improved. Therefore, the operating voltage can be lowered to increase the light emission efficiency, and the device performance can be improved.

  According to the third semiconductor light emitting diode of the present invention, the area S of the first region and the total peripheral length L satisfy the expression 1, and the area S can be set to the first region, the second region, and the boundary region. Since it is 70% or more of the total area, it is possible to secure a sufficient area S while increasing the total peripheral length L to improve the light extraction efficiency. Therefore, the current density does not increase with respect to the same current, and a decrease in light emission efficiency can be suppressed.

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

(First embodiment)
FIG. 1 shows a cross-sectional configuration of the semiconductor light emitting diode according to the first embodiment of the present invention, and FIG. 2 schematically shows a planar configuration thereof. This semiconductor light emitting diode is used for display elements such as traffic lights, lights or displays, and is formed on a substrate 11 made of an insulating material such as sapphire. The semiconductor light-emitting diode has a square first region 10A and a second region 10B surrounding the first region 10A in a frame shape, and a boundary region 10C is provided therebetween. Although the actual element shape is close to FIG. 2, the boundary region 10C is shown slightly wider in FIG. 1 for easy understanding.

  The first region 10A includes an n-type layer 12 and a p-type layer 13, and a pn junction portion 14 is constituted by these layers. A p-side electrode 21 is provided on the surface of the p-type layer 13. The n-type layer 12 has, for example, a thickness in the stacking direction (hereinafter simply referred to as “thickness”) of about 1 μm to 6 μm and is composed of n-type AlGaInN, n-type AlGaN, n-type GaInN, or n-type GaN. . For example, the p-type layer 13 has a thickness of about 0.1 μm to 1 μm and is made of p-type AlGaInN, p-type AlGaN, p-type GaInN, or p-type GaN. The p-side electrode 21 uses, for example, a palladium (Pd) layer or a nickel (Ni) layer as a first layer. For example, a palladium (Pd) layer, a platinum (Pt) layer, and a gold (Au) layer are arranged on the p-type layer 13 side. And are electrically connected to the p-type layer 13. The p-side electrode 21 does not need to be formed in the entire first region 10A, and may be formed in a part of the first region 10A.

  Second region 10 </ b> B includes a partial region of n-type layer 12, and n-side electrode 22 is provided on the surface of n-type layer 12. The n-side electrode 22 has a configuration in which, for example, a titanium (Ti) layer, a platinum (Pt) layer, and a gold (Au) layer are sequentially stacked from the n-type layer 12 side, and is electrically connected to the n-type layer 12. ing. The n-side electrode 22 does not have to be formed in the entire second region 10B, and may be formed in a part of the second region 10B.

  A part of the p-side electrode 21 and the n-side electrode 22 is provided with a pad region (not shown) having a diameter of about 100 μm, for example, in order to provide a bump, a solder adhesive layer, etc. for taking out the electrode. For example, three or more pad regions may be provided depending on the reliability at the time of mounting.

  In the boundary region 10C, a first step portion 31, a flat portion 32, and a second step portion 33 are successively formed in this order from the first region 10A side. The first step portion 31 is formed from the surface of the p-type layer 13 to a part in the thickness direction. The flat portion 32 is continuous with the first step portion 31 and is formed in the p-type layer 13. The second step portion 33 is continuous with the flat portion 32 and is formed across the pn junction portion 14. Thereby, in this semiconductor light emitting diode, the thickness of the p-type cladding layer 13 in the flat portion 32 is reduced to reduce the spread of the current C in the lateral direction, and the path of the current C is kept away from the second stepped portion 33. The influence of damage due to dry etching of the second stepped portion 33 can be suppressed.

  The thickness T of the p-type layer 13 in the flat portion 32 is preferably 0.05 μm or more and 0.2 μm or less, for example. Although the thickness T is preferably small from the viewpoint of the current path, the controllability of the etching process and damage (depth of 0.05 μm to 0.1 μm or less) due to dry etching on the surface of the flat portion 32 are caused in the pn junction 14. Since it is necessary not to reach, the thickness T is set in the above range.

  Further, the width W of the flat portion 32 is preferably, for example, not less than 0.5 μm and not more than 3 μm. If the width W is larger than the thickness T (W> T), it is sufficient from the viewpoint of current control. However, since there are actually problems in dimensions and alignment accuracy in the wafer process, the width W is controlled to be less than 1 μm. On the other hand, increasing the width W is not necessary for effective use of the element area.

  The inclination angle θ of the first step portion 31 and the second step portion 33 with respect to the exposed surface of the n-type layer 12 is preferably, for example, 30 ° to 40 °. This is because the angle at which the light reflected by the first step portion 31 or the second step portion 33 enters the substrate 11 can be increased, so that the light extraction efficiency can be increased.

  The length D (element size) passing through the center of the semiconductor light emitting diode is preferably 250 μm or more. Nitride semiconductors have a large current dependency on efficiency, and as shown in FIG. 3, the operating current is generally larger than the maximum efficiency condition. This is because it is necessary to increase the size. Moreover, it is because it is advantageous for a high output design that the element size is larger from the viewpoint of exhaust heat.

  This semiconductor light emitting diode can be manufactured, for example, as follows.

  First, for example, as shown in FIG. 4A, a substrate 11 made of sapphire is prepared, and on this substrate 11, for example, by MOCVD (Metal Organic Chemical Vapor Deposition) method, The n-type layer 12 and the p-type layer 13 made of the above-described thickness and material are sequentially formed. Next, as shown in FIG. 4A, a palladium (Pd) layer, a platinum (Pt) layer, and a gold (Au) layer are sequentially stacked on the p-type layer 13 by, eg, vapor deposition. A metal film 21 </ b> A for forming the side electrode 21 is formed.

  Subsequently, as shown in FIG. 4B, a photoresist film 41 is formed on the metal film 21A so as to cover only the formation region 10A1 of the first region 10A, and this photoresist film 41 is used as a mask. For example, the metal film 21A is selectively removed by RIE (Reactive Ion Etching). Further, a part of the p-type layer 13 in the thickness direction is selectively removed to form the first step portion 31. After that, the photoresist film 41 is removed. Thereby, the first region 10 </ b> A including the n-type layer 12 and the p-type layer 13 constituting the pn junction 14 and having the p-side electrode 21 on the surface of the p-type layer 13 is formed.

  After forming the first region 10A, as shown in FIG. 5A, a photoresist film 42 is formed so as to cover the first region 10A and the first step portion 31. At this time, in order to form the flat portion 32, the photoresist film 42 extends beyond the first step portion 31 to the flat surface of the p-type cladding layer 13. 5A, using the photoresist film 42 as a mask, the remainder in the thickness direction of the p-type cladding layer 13 and a part in the thickness direction of the n-type cladding layer 12, for example, by RIE. Then, the n-type cladding layer 12 is exposed, and the second stepped portion 33 is formed across the pn junction portion 14. After that, the photoresist 42 is removed. As a result, a boundary region 10 </ b> C having a two-step structure of the first step portion 31 and the second step portion 33 is formed with the flat portion 32 therebetween.

  After forming the boundary region 10C, as shown in FIG. 5B, the n-side electrode 22 is formed on the exposed surface of the n-type cladding layer 12 by, for example, vapor deposition. Thereby, the semiconductor light emitting diode shown in FIGS. 1 and 2 is completed.

  In this semiconductor light emitting diode, when a predetermined voltage is applied between the p-side electrode 21 and the n-side electrode 22, a current is injected and light emission occurs due to electron-hole recombination. Here, the boundary region 10 </ b> C has a two-stage structure of a first step portion 31 in the p-type cladding layer 13 and a second step portion 33 straddling the pn junction portion 14 with the flat portion 32 interposed therebetween. Therefore, the thickness of the p-type cladding layer 13 in the flat portion 32 is small, and the current is difficult to spread in the lateral direction. Therefore, the current C injected from the p-side electrode 21 descends to the flat portion 32 along the first step portion 31 and enters the n-type cladding layer 12, and then flows toward the n-side electrode 22 in the lateral direction. The path of the current C moves away from the second step portion 33. Therefore, even if the pn structure on the surface of the second step portion 33 is damaged, the occurrence of a leak path or the like can be suppressed.

  As described above, in the semiconductor light emitting diode according to the present embodiment, the boundary region 10C is separated from the first step portion 31 in the p-type cladding layer 13 and the second step portion across the pn junction portion 14 with the flat portion 32 in between. Since the p-side electrode 21 is provided as far as the first step portion 31 in order to increase the current injection efficiency, the influence of damage due to dry etching of the second step portion 33 can be suppressed. it can. Therefore, element characteristics and reliability can be improved.

  Although the case where the substrate 11 is made of sapphire has been described in the present embodiment, a GaN substrate may be used.

  In the present embodiment, the case where the first region 10A is square has been described, but the shape of the first region 10A is not particularly limited. For example, the first region 10A may be circular as shown in FIG. 6 or rectangular as shown in FIG.

  Further, the width of the second region 10B is not necessarily uniform, and may be partially different. For example, as shown in FIG. 8, the width of the second region 10B may be widened at one corner of the first region 10A, for example, a square that is about one third of one side of the first region 10A. Alternatively, as shown in FIG. 9, the width of the second region 10B may be widened at the center of the two opposite sides of the first region 10A.

  Furthermore, a plurality of first regions 10A can be arranged to constitute one semiconductor light emitting diode. For example, as shown in FIG. 10, a boundary region 10C and a second region 10B may be provided in a frame shape around the four rectangular first regions 10A, respectively. In this case, the number of the first regions 10A is preferably about 1 to 5 or less so that the area of the pn junction portion 14 is not reduced, and each first region 10A is preferably rectangular or a shape close thereto.

(Second Embodiment)
FIG. 11 shows a cross-sectional configuration of a semiconductor light emitting diode according to the second embodiment of the present invention, and FIG. 12 schematically shows a planar configuration thereof. In this semiconductor light emitting diode, a boundary region 10C is provided between the first region 10A and the second region 10B, as in the first embodiment. Accordingly, the corresponding components will be described with the same reference numerals.

  In the present embodiment, the second region 10B is formed around the square first region 10A. The width of the second region 10B is widened at one corner of the first region 10A, and is substantially square, for example, about one third of one side of the first region 10A. The boundary region 10C has, for example, a step portion 34. The step 34 is formed from the surface of the p-type cladding layer 13 to the exposed surface of the n-type cladding layer 12. As in the first embodiment, the length D (element size) passing through the center of the semiconductor light emitting diode is preferably 250 μm or more.

  Each side of the first region 10A is provided with a notch-shaped recess 10D extending from the periphery to the inside, and the bottom surface of the recess 10D is a second region 10B. The p-side electrode 21 is formed so as to surround the recess 10D, while the n-side electrode 22 is formed on the bottom surface of the recess 10D. The side surface of the recess 10D is a boundary region 10C.

  The shortest distance M from the n-side electrode 22 at all positions of the p-side electrode 21 is preferably 70 μm or less, and more preferably 30 μm or less. If it is within this range, the distance over which current actually flows in the lateral direction can be shortened, current injection unevenness can be improved, the operating voltage can be lowered, and the luminous efficiency can be increased. In the drawing, the arrow indicating the shortest distance M is shown as a distance on a plane when the semiconductor light emitting diode is viewed from the p-side electrode 21 side. However, this distance is not necessarily the current in the horizontal direction. It is not always the same as the flowing distance.

  The shortest distance M is, in a broad sense, the maximum value when the distance to the n-side electrode 22 for each coordinate of the p-side electrode 21 is obtained with respect to the element dimensions (one side, long side, or diameter). In other words, the smaller this value (approximately M <0.1), the closer the p-side electrode 21 is to the n-side electrode 22. Expressed qualitatively, this indicates that the first region 10A is not a circle or a rectangle, but a long or complicated shape.

  In terms of device performance, the shortest distance M is not a relative value, but is a problem that a current actually flows in the lateral direction. That is, even if the first region 10A is a square, the lateral current path does not become more than half of one side. For example, the first region 10A having a frame shape around the square first region 10A having a side of 200 μm. In the semiconductor light emitting diode having the two regions 10B, the distance in which the current flows in the lateral direction is 100 μm at the maximum. However, if one side of the first region 10A is 1 mm, the distance in which the current flows in the lateral direction may be as much as 500 μm, which may cause uneven current injection.

  Further, the area S and the total peripheral length L of the first region 10A satisfy Expression 2, and the area S is 70% or more of the total area of the first region 10A, the second region 10B, and the boundary region 10C. Is preferred. The total peripheral length L can be increased to improve the light extraction efficiency, and can be optimized to ensure a sufficient area S. The current density does not increase for the same current, and the light emission efficiency is improved. This is because the decrease can be suppressed.

(Equation 2)
a = L / √S
a> 10
(In Equation 2, a represents an index of the complexity of the shape of the first region 10A.)

  a is the ratio of the total peripheral length L to the area S and represents the degree of intricacy of the shape of the first region 10A. That is, the larger the value of a, the more complicated the shape of the first region 10A.

  Increasing the value of a and making the shape of the first region 10A intricate leads to improved light extraction efficiency. That is, in the generated light, there is a component that is not output to the outside of the substrate 11, which is the interface between the inside and outside of the element or the interface between layers having different refractive indexes in the element, and the p-side electrode. Reflected between 21. Since the reflectance at the p-side electrode 21 is not 100%, an absorption loss occurs every time it is reflected, and it attenuates as reflection is repeated. As shown in FIG. 13A, when the recess 10D is not provided, the width of the first region 10A is large, the number of reflections until the generated light reaches the boundary region 10C, and the absorption loss is also large. growing. On the other hand, as shown in FIG. 13B, when the recess 10D is provided, the number of reflections until the generated light reaches the boundary region 10C can be reduced, and light absorption loss can be reduced. It can be reduced to increase the extraction efficiency. Further, at this time, it is preferable that the inclination angle θ of the stepped portion 34 is made shallow, for example, about 30 ° to 40 °. This is because the light reflected by the step portion 34 is incident on the substrate 11 at a deep angle and can be efficiently extracted outside the device. As shown in FIG. 13C, when the inclination angle θ of the stepped portion 34 is an angle close to vertical, the light reflected by the stepped portion 34 returns to the inside of the element and is output to the outside of the substrate 11. It becomes difficult.

  Table 1 shows the total peripheral length L and area S when the shape of the first region 10A is changed as shown in Calculation Examples 1 and 2, the shortest distance M between the p-side electrode 21 and the n-side electrode 22, and It shows a simple calculation result of the index a. In the calculation, the width of the recess 10D and the width of the boundary region 10C are ignored. Further, when the recess 10D is provided, the area S is also reduced by, for example, 10% to 20%, but is ignored in Table 1 for simplicity.

  In Calculation Example 1, as shown in FIG. 14, the first region 10A is rectangular, the long side X is about 1 mm, and the short side is a quarter of the long side (X / 4), which is about 250 μm. Fifteen cut-in recesses 10D are provided at equal intervals on the long side of the first region 10A. The length of the recess 10D is about one third (X / 12) of the short side.

  In Calculation Example 2, as shown in FIG. 15, four rectangular first regions 10A shown in FIG. 14 are arranged side by side, and a square having a side of about 1 mm as a whole is formed.

  Further, as Reference Examples 1 to 6, when the concave portion 10D is not provided, the total peripheral length L and area S, the shortest distance M between the p-side electrode 21 and the n-side electrode 22, The index a is also shown in Table 1.

  In Reference Example 1, as shown in FIG. 16, the first region 10A is a circle having a radius Z, and an annular second region 10B is provided around the first region 10A. In Reference Example 2, as shown in FIG. 17, the first region 10A is a square with one side Z, and a frame-shaped second region 10B is provided around the first region 10A. In Reference Example 3, as shown in FIG. 18, in one corner of the first region 10A similar to Reference Example 2, the width of the second region 10B is widened and one third (Z) of the width of the first region 10A (Z / 3) square. In Reference Example 4, as shown in FIG. 19, the width of the second region 10B is widened at the center of the two opposite sides of the first region 10A similar to Reference Example 2, and the width of the first region 10A is 3 It is a fraction (Z / 3). In Reference Example 5, as shown in FIG. 20, the first region 10A is a rectangle, the long side Z, the short side is a quarter of the long side (Z / 4), and the frame-shaped second region around the first side 10A. Region 10B is provided. In Reference Example 6, as shown in FIG. 21, four first regions 10A similar to Reference Example 5 are arranged side by side.

  Here, since the total peripheral length for a certain area is minimum when the shape is a circle, L = 2√π (≈3.5) is the minimum value of L. As can be seen from Table 1, in the first and second calculation examples 1 and 2 in which the concave portion 10D is provided, a> 10, whereas in Reference Examples 1 to 6 in which the concave portion is not provided, a ≦ 10.

  This semiconductor light emitting diode is the same as the first embodiment except that the concave portion 10D is provided when the first region 10A is formed and the step portion 34 is formed by one etching. Can be manufactured.

  In this semiconductor light emitting diode, as in the above embodiment, when a predetermined voltage is applied between the p-side electrode 21 and the n-side electrode 22, a current is injected and light is emitted by electron-hole recombination. Happens. Here, since the shortest distance M with respect to the n-side electrode 22 is 70 μm or less at all positions of the p-side electrode 21, the distance in which the current actually flows in the lateral direction is shortened. Current injection unevenness between the central portion and the central portion is improved. Therefore, the operating voltage is lowered and the light emission efficiency is increased.

  Further, the area S and the total peripheral length L of the first region 10A satisfy Equation 2, and the area S is 70% or more of the total area of the first region, the second region, and the boundary region. A sufficiently large area S is secured while increasing the total peripheral length L to increase the light extraction efficiency, so that the current density does not increase with respect to the same current, and a decrease in light emission efficiency is suppressed.

  On the other hand, conventionally, the current distribution is not uniform with respect to the p-side electrode 121, and the current density is high in the peripheral portion of the p-side electrode 121, and the current injection amount decreases as the distance from the current density increases. Such uneven current injection becomes more prominent as the distance that the current C actually flows in the lateral direction becomes longer, leading to an increase in operating voltage and a decrease in luminous efficiency.

  In order to change the distance through which the current C flows in the lateral direction, conventionally, the resistivity has been adjusted by designing the thickness and concentration of the p-type cladding layer 113 and the n-type cladding layer 112. However, this method has a limitation on the crystal growth process and the wafer process. For example, if the thickness of the p-type cladding layer 113 is increased, the growth time becomes longer, which may cause adverse effects on impurity diffusion and the pn junction 114, and patterning of the wafer process by increasing the etching depth. The technology was also limited.

  In addition, by the manufacturing method described above, a semiconductor light-emitting diode capable of obtaining λ≈520 nm green light emission in which a recess 10D is provided on each side of a square first region 10A having a side of 0.3 mm as shown in FIGS. Was actually made. Further, on the same wafer, those having the same configuration except that the recess 10D was not provided were made close to each other. Regarding the obtained semiconductor light-emitting diode, when the current value was both constant (40 mA) and the light output was examined, the one provided with the recess 10D was equivalent to the one not provided, and at least the luminance variation distribution in the peripheral elements in the wafer Within a few percent, there was no significant difference. In the case where the concave portion 10D is provided, the area of the first region 10A is as small as about 85% compared to the case where the concave portion 10D is not provided, and the current output is high, but the optical output is not inferior. From this, it is considered that the amount of light emission per unit area is larger when the concave portion 10D is provided than when the concave portion 10D is not provided. Further, when the wavelength was examined, it was almost the same at the center wavelength when Δλ ≦ 1 nm.

  As described above, in the present embodiment, the shortest distance M from the n-side electrode 22 at all positions of the p-side electrode 21 is set to 70 μm or less, more preferably 30 μm or less, so that the current actually flows in the lateral direction. To improve the current injection unevenness, lower the operating voltage and increase the light emission efficiency.

  Further, the area S and the total peripheral length L satisfy Equation 2, and the area S is set to 70% or more of the total area of the first region, the second region, and the boundary region, thereby increasing the total peripheral length L. Thus, while increasing the light extraction efficiency, a sufficiently large area S is ensured, the current density is not increased with respect to the same current, and a decrease in light emission efficiency can be suppressed.

  In addition, semiconductor light-emitting diodes are general-purpose components that have already been widely used in the market, and it is desirable to reduce costs as much as possible. However, in this embodiment, only a few process changes are involved, and light emission efficiency is suppressed while minimizing cost increases. And performance such as light extraction efficiency can be improved.

  14 and 15, the description has been given of the case where the concave portion 10D is provided on the long side of the first region 10A. However, the position where the concave portion 10D is provided may be the peripheral portion of the first region 10A. It is also possible to put in.

  In the case of flip chip mounting, the second region 10B does not necessarily have a continuous shape when seen in a plan view. Therefore, as shown in FIG. 22, for example, four circular recesses 10D may be provided in the first region 10A. Needless to say, the planar shape of the recess 10D is not limited to a circle, and the number of the recesses 10D is not particularly limited.

(Third embodiment)
FIG. 23 shows a cross-sectional configuration of a semiconductor light emitting diode according to the third embodiment of the present invention, and FIG. 24 schematically shows a planar configuration thereof. This semiconductor light emitting diode has the same configuration as that of the semiconductor light emitting diode of the second embodiment, except that the boundary region 10C has a two-stage structure similar to that of the first embodiment. . The manufacturing method and operation are the same as those in the first embodiment.

  In the present embodiment, the boundary region 10C has a two-stage structure similar to that of the first embodiment. Therefore, even if the total peripheral length L is increased by providing the recess 10D in the first region 10A, the first The influence of damage due to dry etching of the two stepped portions 33 can be suppressed. Therefore, element characteristics and reliability can be improved.

  While the present invention has been described with reference to the embodiment, the present invention is not limited to the above embodiment, and various modifications can be made. For example, in the above embodiment, the case where the first stepped portion 31 and the second stepped portion 33 are inclined surfaces has been described, but the first stepped portion 31 and the second stepped portion 33 are not necessarily inclined surfaces. It may be a curved surface.

  Further, the material and thickness of each layer described in the above embodiment, or the film formation method and film formation conditions are not limited, and other materials and thicknesses may be used, or other film formation methods and film formation. It is good also as conditions. For example, in the above-described embodiment, the constituent material of the semiconductor layer 10 is specifically described, but the semiconductor layer 10 is made of aluminum (Al), gallium (Ga), and indium (In) among the group 3B elements. And other nitride semiconductors containing nitrogen (N) among group 5B elements.

  Further, the p-side electrode 21 uses silver (Ag) or an alloy containing silver (Ag) having a high reflectivity for reasons of device design, for example, a silver (Ag) layer, a platinum (Pt) layer, and gold (Au). It is good also as a structure which laminated | stacked the layer in order from the p-type cladding layer 13 side. In this case, tungsten (W) or molybdenum (Mo) may be used as a barrier metal for suppressing electrode diffusion / alloying instead of the platinum (Pt) layer. Further, when heat-treating the n-side electrode 22, titanium (Ti) or aluminum (Al) system may be used.

  Further, for example, in the above embodiment, the case where the n-type layer 12 and the p-type layer 13 are formed by the MOCVD method has been described. However, the n-type layer 12 and the p-type layer 13 may be formed by other metal organic vapor phase epitaxy methods such as the MOVPE method, Alternatively, MBE (Molecular Beam Epitaxy) method or the like may be used.

  In addition, for example, in the above-described embodiment, the configuration of the semiconductor light emitting diode has been specifically described, but it is not necessary to include all the layers, and other layers may be further included. For example, an active layer may be provided between the n-type layer 12 and the p-type layer 13. Further, a contact layer for improving the contact property with the p-side electrode 21 or the n-side electrode 22 is provided between the p-type layer 13 and the p-side electrode 21 or between the n-type layer 12 and the n-side electrode 22. You may have. Further, a buffer layer may be provided between the substrate 11 and the n-type layer 12.

It is sectional drawing showing the structure of the semiconductor light-emitting diode which concerns on the 1st Embodiment of this invention. FIG. 2 is a plan view illustrating a configuration of the semiconductor light emitting diode illustrated in FIG. 1 viewed from a p-side electrode side. It is a figure showing the relationship between internal efficiency and operating current in the semiconductor light emitting diode using a nitride semiconductor. FIG. 2 is a cross-sectional view illustrating a method of manufacturing the semiconductor light emitting diode illustrated in FIG. 1 in order of steps. FIG. 5 is a cross-sectional view illustrating a process that follows the process illustrated in FIG. 4. It is a top view showing the modification of the semiconductor light emitting diode shown in FIG. FIG. 10 is a plan view illustrating another modification of the semiconductor light emitting diode illustrated in FIG. 1. FIG. 10 is a plan view illustrating still another modification of the semiconductor light emitting diode illustrated in FIG. 1. FIG. 10 is a plan view illustrating still another modification of the semiconductor light emitting diode illustrated in FIG. 1. FIG. 10 is a plan view illustrating still another modification of the semiconductor light emitting diode illustrated in FIG. 1. It is sectional drawing showing the structure of the semiconductor light-emitting diode based on the 2nd Embodiment of this invention. It is a top view showing the structure which looked at the semiconductor light emitting diode shown in FIG. 11 from the p side electrode side. It is a figure for demonstrating the improvement of the light extraction efficiency in the semiconductor light-emitting diode shown in FIG. It is a top view for showing the example which changed the shape of the 1st field and calculated the value of M and a. It is a top view for showing the other example which changed the shape of the 1st field and calculated the value of M and a. It is a top view for showing the other example which changed the shape of the 1st field and calculated the value of M and a. It is a top view for showing the other example which changed the shape of the 1st field and calculated the value of M and a. It is a top view for showing the other example which changed the shape of the 1st field and calculated the value of M and a. It is a top view for showing the other example which changed the shape of the 1st field and calculated the value of M and a. It is a top view for showing the other example which changed the shape of the 1st field and calculated the value of M and a. It is a top view for showing the other example which changed the shape of the 1st field and calculated the value of M and a. It is the top view and sectional drawing showing the modification of the semiconductor light-emitting diode shown in FIG. It is sectional drawing showing the structure of the semiconductor light-emitting diode which concerns on the 3rd Embodiment of this invention. It is a top view showing the structure which looked at the semiconductor light emitting diode shown in FIG. 23 from the p side electrode side. It is sectional drawing showing the structure of the conventional semiconductor light-emitting diode. It is sectional drawing showing the structure of the conventional semiconductor laser. FIG. 26 is a diagram schematically illustrating a current injection distribution in the semiconductor light emitting diode illustrated in FIG. 25.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 ... Semiconductor light emitting diode, 10A ... 1st area | region, 10B ... 2nd area | region, 10C ... Boundary area | region, 10D ... Recessed part, 11 ... Substrate, 12 ... n-type cladding layer, 13 ... p-type cladding layer, 14 ... pn junction part 21 ... p-side electrode, 22 ... n-side electrode, 31 ... first step, 32 ... flat portion, 33 ... second step, 34 ... step

Claims (10)

a first region including a first conductivity type semiconductor layer and a second conductivity type semiconductor layer constituting a pn junction, and having a first electrode on a surface of the first conductivity type semiconductor layer;
A second region including a partial region of the second conductivity type semiconductor layer and having a second electrode on a surface of the second conductivity type semiconductor layer;
A first step portion provided between the first region and the second region and formed from the surface of the first conductivity type semiconductor layer to a part in a thickness direction; the first step portion; and the first step portion. 1. A semiconductor comprising: a flat portion formed in a one-conductivity-type semiconductor layer; and a boundary region having a second stepped portion that is continuous with the flat portion and straddles the pn junction portion. Light emitting diode.   The first conductive type semiconductor layer and the second conductive type semiconductor layer include at least one of aluminum (Al), gallium (Ga), and indium (In) among group 3B elements and nitrogen among group 5B elements. 2. The semiconductor light emitting diode according to claim 1, wherein the semiconductor light emitting diode is composed of a nitride-based III-V group compound semiconductor containing (N). A recess is provided in the first region, and the bottom surface of the recess is the second region,
The first electrode is formed so as to surround the recess, while the second electrode is provided on the bottom surface of the recess,
2. The semiconductor light emitting diode according to claim 1, wherein a shortest distance M from the second electrode at all positions of the first electrode is 70 μm or less. The semiconductor light emitting diode according to claim 3, wherein the recess is a cut extending from the periphery of the first region to the inside. A recess is provided in the first region, and the bottom surface of the recess is the second region,
The area S and the total peripheral length L of the first region satisfy the formula 1,
2. The semiconductor light emitting diode according to claim 1, wherein the area S is 70% or more of a total area of the first region, the second region, and the boundary region.
(Equation 1)
a = L / √S
a> 10
(In Equation 1, a represents an index of the complexity of the shape of the first region.) The semiconductor light emitting diode according to claim 5, wherein the recess is a cut extending from the periphery of the first region to the inside. a first region including a first conductivity type semiconductor layer and a second conductivity type semiconductor layer constituting a pn junction, and having a first electrode on a surface of the first conductivity type semiconductor layer;
A second region including a partial region of the second conductivity type semiconductor layer and having a second electrode on a surface of the second conductivity type semiconductor layer;
A boundary region provided between the first region and the second region,
A recess is provided in the first region, and the bottom surface of the recess is the second region,
The first electrode is formed so as to surround the recess, while the second electrode is provided on the bottom surface of the recess,
The shortest distance M from the second electrode at all positions of the first electrode is 70 μm or less. The semiconductor light emitting diode according to claim 7, wherein the recess is a cut extending from the periphery of the first region to the inside. a first region including a first conductivity type semiconductor layer and a second conductivity type semiconductor layer constituting a pn junction, and having a first electrode on a surface of the first conductivity type semiconductor layer;
A second region including a partial region of the second conductivity type semiconductor layer and having a second electrode on a surface of the second conductivity type semiconductor layer;
A boundary region provided between the first region and the second region,
A recess is provided in the first region, and the bottom surface of the recess is the second region,
The area S and the total peripheral length L of the first region satisfy the formula 2,
The area S is 70% or more of the total area of the first region, the second region, and the boundary region.
(Equation 2)
a = L / √S
a> 10
(In Equation 2, a represents an index of the complexity of the shape of the first region.) The semiconductor light-emitting diode according to claim 9, wherein the recess is a cut extending from the periphery of the first region to the inside.

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