JP2014099434A - Semiconductor light-emitting element - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a semiconductor light-emitting element which can avoid current concentration and light shielding thereby to obtain good reflectance and achieve high performance such as high luminous efficiency and excellent reliability.SOLUTION: A semiconductor light-emitting element comprises: a semiconductor film including a first conductivity type first semiconductor layer, a second conductivity type second semiconductor layer and a luminescent layer provided between the first semiconductor layer and the second semiconductor layer; a first electrode provided on the first semiconductor layer; a transparent electrode layer formed on the second semiconductor layer; a reflection electrode layer formed on the transparent electrode layer; and a support substrate bonded to the reflection electrode layer via a bonding layer. The bonding layer includes a high resistance part buried in the bonding layer. The high resistance part has electric resistance higher than that of the bonding layer and is provided in a region opposite to the first electrode across the semiconductor film.

Description

  The present invention relates to a semiconductor light emitting element such as a light emitting diode (LED).

  In recent years, there has been a demand for semiconductor light emitting devices such as LED devices with improved device characteristics such as luminous efficiency. For example, an LED having a so-called thin film structure or a paste structure has been developed. In such an LED, after growing the semiconductor layer, the growth substrate is removed, and an n-electrode is partially formed on the exposed n-type semiconductor layer. In such an element, current concentrates on the semiconductor film immediately below the n electrode, and the light emission efficiency in the light emitting layer immediately below the n electrode is the highest. However, the light emitted from the light emitting layer immediately below the n-electrode is blocked by the n-electrode above it, so that the light extraction efficiency is lowered. For example, in Patent Document 1, the p-electrode and the n-electrode are arranged at positions shifted from each other in the direction parallel to the semiconductor film in order to avoid light shielding by the electrode and improve the light extraction efficiency. Is disclosed.

JP-A-8-125225

  In order to solve the above-described problems, for example, the p electrode is patterned so that the p electrode (transparent electrode) such as ITO does not face the n electrode, and a reflective metal layer is formed on the patterned p electrode. Forming is also conceivable. Although such a configuration can avoid current concentration and light shielding, it has been found that there are various problems. For example, the film quality of transparent conductive films such as ITO varies greatly depending on the film formation conditions, and residues are likely to remain during etching. In addition, resist residues may remain during patterning. There is a problem that decreases. Furthermore, the adhesiveness of the bonding interface between the reflective metal layer such as Ag (silver) and the semiconductor layer is poor, and Ag tends to aggregate at the bonding interface, which tends to cause defects. Therefore, it has been found that there is a problem that the reflectance of the reflective layer is lowered. Moreover, even if Ti, Ni, or the like is added to the interface between the p-type semiconductor layer and Ag to improve the adhesion at the junction interface, the reflectance from the reflective layer via the transparent electrode is reduced. There's a problem.

  The present invention has been made in view of the above points, and is capable of avoiding current concentration and light shielding, obtaining good reflectivity, high luminous efficiency and high reliability, and the like. The purpose is to provide.

The semiconductor light emitting device according to the present invention includes a first conductive type first semiconductor layer, a second conductive type second semiconductor layer, and a light emitting layer provided between the first semiconductor layer and the second semiconductor layer. And a semiconductor film containing
A first electrode provided on the first semiconductor layer;
A transparent electrode layer formed on the second semiconductor layer;
A reflective electrode layer formed on the transparent electrode layer;
A support substrate bonded to the reflective electrode layer via the bonding layer,
The bonding layer has a high resistance portion embedded in the bonding layer, and the high resistance portion has a higher electric resistance than the bonding layer and is provided in a region facing the first electrode with the semiconductor film interposed therebetween. It is characterized by.

It is the top view and sectional drawing of the semiconductor light-emitting device which are the Examples of this invention. It is a figure which shows typically the case where a high resistance part and n electrode are projected on the plane parallel to a semiconductor film. It is a partial expanded sectional view which shows typically the high resistance part and its vicinity when an element structure is joined to a support body. It is a partial expanded sectional view which shows typically the case where a high resistance part contacts an element structure. It is sectional drawing of the semiconductor light-emitting device of a comparative example. (A) is sectional drawing which shows typically the current pathway of the semiconductor light-emitting device of an Example, (b) is the simple equivalent circuit. (A) is sectional drawing which shows typically the electric current path | route of the semiconductor light-emitting device of a comparative example, (b) is the simple equivalent circuit. It is a top view of the semiconductor light-emitting device which is a modification of this invention. It is a figure which shows typically the case where the high resistance part and n electrode of a modification are projected on the plane parallel to a semiconductor film.

Embodiments of the present invention will be described below with reference to the drawings. In the drawings, substantially the same or equivalent components and parts are denoted by the same reference numerals. In the following description, the present invention is applied to a semiconductor light emitting device including a semiconductor film made of Al _x In _y Ga _z N (0 ≦ x ≦ 1, 0 ≦ y ≦ 1, 0 ≦ z ≦ 1, x + y + z = 1). Although the case where the invention is applied will be described as an example, the semiconductor film may be made of another material.

  FIG. 1 shows a semiconductor light emitting device 10 which is an embodiment of the present invention. FIG. 1A is a plan view schematically showing the arrangement of the semiconductor film 20, the support substrate 60, and the electrode 70. FIG. 1B is a plan view schematically showing the arrangement of the bonding layer 50 and the high resistance portion 51 when viewed from the vertical direction toward the semiconductor film 20 at the interface between the bonding layer 50 and the support substrate 60. . FIG.1 (c) is sectional drawing along the WW line of Fig.1 (a).

  As shown in FIGS. 1A to 1C, the semiconductor light emitting device 10 includes a semiconductor film 20, a second electrode 30 formed on the semiconductor film 20, and a reflection formed on the second electrode 30. The structure includes an electrode layer 40, a bonding layer 50 formed on the reflective electrode layer 40, and a support substrate 60 formed on the bonding layer 50. The semiconductor film 20 includes a first conductivity type first semiconductor layer 21, a second conductivity type second semiconductor layer 22, and a light emission provided between the first semiconductor layer 21 and the second semiconductor layer 22. It has a layer 23. A first electrode 70 is formed on a part of the surface of the semiconductor film 20 on the first semiconductor layer 21 side. In the following, the first conductivity type and the second conductivity type are n-type and p-type, respectively, and the first electrode 70 and the second electrode 30 are n-electrode and p-electrode (transparent electrode), respectively. Will be described. The entire first electrode 70, second electrode 30, reflective electrode layer 40, and semiconductor film 20 are also referred to as an element structure 25, the bonding layer 50, and the entire support substrate 60 are also referred to as a support 55.

  As described above, the semiconductor film 20 has a structure including the n-type semiconductor layer 21, the p-type semiconductor layer 22, and the light emitting layer 23 provided between the n-type semiconductor layer 21 and the p-type semiconductor layer 22. ing. The n-type semiconductor layer 21 is doped with an n-type dopant such as Si, and has a thickness of 3 to 7 μm, for example. The p-type semiconductor layer 22 is added with a p-type dopant such as Mg, and has a thickness of 50 to 300 nm, for example. The light emitting layer 23 has a multiple quantum well structure in which, for example, an InGaN well layer having a thickness of 2.2 nm and a GaN barrier layer having a thickness of 15 nm are repeatedly stacked for 3 to 10 periods.

  As shown in FIG. 1A, a strip-shaped n-electrode 70 having a width a (FIG. 1C) is formed on the n-type semiconductor layer 21. As shown in FIG. The n-electrode 70 has a structure in which, for example, Ti / Al / Pt / Au or Ti / Ni / Au are sequentially stacked. The n electrode 70 forms an ohmic junction with the n-type semiconductor layer 21. FIG. 1 shows a case where a plurality (four) of n electrodes 70 are arranged, but the number of n electrodes 70 is not limited to this, and at least one n electrode 70 is an n-type. What is necessary is just to be provided on the semiconductor layer 21.

  The transparent electrode layer (p electrode) 30 is formed on the p-type semiconductor layer 22 of the semiconductor film 20. The transparent electrode layer 30 is made of indium tin oxide (ITO). The transparent electrode layer 30 is made of a conductive metal oxide film, and in addition to ITO, for example, indium zinc oxide (IZO) can be used. The transparent electrode layer 30 has a thickness of about 1 to 30 nm, for example. The transparent electrode layer 30 forms an ohmic junction with the p-type semiconductor layer 22.

  The reflective electrode layer 40 is made of a highly reflective metal, for example, Ag. Further, an alloy containing Ag, Al, Rh, Pt, or a composite material thereof can be used as the reflective electrode layer 40. The transparent electrode layer 30 described above does not have an opening that exposes the p-type semiconductor layer 22 and covers the p-type semiconductor layer 22. That is, the reflective electrode layer 40 is formed in a non-contact state with the p-type semiconductor layer 22 via the transparent electrode layer 30.

  In order to obtain a high reflectance, the film thickness of the transparent electrode layer 30 (ITO) is preferably 1 to 30 nm. The thickness of the reflective electrode layer 40 (Ag) is preferably 40 nm or more. However, in order to prevent current diffusion in the transparent electrode layer (p electrode) 30, the thickness of the reflective electrode layer 40 (Ag) is preferably 300 nm or less. The reflective electrode layer 40 is formed by sputtering, for example. The reflective electrode layer 40 may cover the side surface of the transparent electrode layer 30.

As the bonding layer 50, the semiconductor film 20 and the support substrate 60 are bonded, and eutectic bonding such as Au / Sn bonding or metal / metal bonding such as Au / Au bonding can be used. Then, as shown in FIG. 1C, a high resistance portion 51 is embedded in the bonding layer 50. The high resistance portion 51 is a high resistance body having an electric resistance higher than that of at least the bonding layer 50, and functions as a current blocking portion or a current limiting portion. For example, SiO ₂ or SiN can be used for the high resistance portion 51. Moreover, the high resistance part 51 may be comprised with the other material which has insulation or high resistance, or may be a space | gap.

  More specifically, the high resistance portion 51 is provided in a region facing the n electrode 70 with the semiconductor film 20 interposed therebetween. More specifically, a plurality of high resistance portions (high resistance bodies) 51 corresponding to each of the plurality of n electrodes 70 are provided. Further, the high resistance portion 51 is formed in such a size and shape as to include the opposing n-electrode 70 when viewed from the top of the semiconductor light emitting element 10, that is, when viewed from a direction perpendicular to the semiconductor film 20. It is preferable. This point will be further described with reference to FIG. FIG. 2 schematically shows a case where the high resistance part 51 and the n-electrode 70 are projected onto the plane P parallel to the semiconductor film 20. The projected shapes of the high resistance part 51 and the n electrode 70 are indicated using the same reference numerals. As shown in FIG. 2, when the high resistance portion 51 and the n electrode 70 facing the high resistance portion 51 are projected onto the plane P parallel to the semiconductor film 20, the high resistance portion 51 is formed so as to include the n electrode 70. It is preferable. Specifically, the n-electrode 70 has, for example, a rectangular shape (width a = 10 μm), and the high resistance portion 51 has a rectangular shape (width b = 40 μm) in a cross section parallel to the semiconductor film 20. The length is longer than that of the n-electrode 70.

  Below, the formation method of the high resistance part 51 and joining of the element structure 25 and the support body 55 are demonstrated. First, a bonding metal is formed on the support substrate 60 to form the bonding layer 50. The bonding layer 50 is partially removed by etching to form a formation region of the high resistance portion 51. In the following, a case where a concave portion is formed in the bonding layer 50 as a formation region of the high resistance portion 51 will be described. However, a groove that penetrates the bonding layer 50 and reaches the support substrate 60 may be formed.

  Next, a resist is formed on the bonding layer 50 other than the formation region of the high resistance portion 51 by photolithography. Then, after depositing a high resistance material by a sputtering method, a vapor deposition method or the like, the high resistance material is buried in the formation region (concave portion) by a lift-off method or the like to form the high resistance portion 51. In addition, the formation method of the high resistance part 51 is not restricted to this. For example, after forming a recess or groove in the bonding layer 50, a high resistance material is deposited by sputtering, vapor deposition, or the like, and the high resistance material deposited on the bonding layer 50 is removed by polishing to form the high resistance portion 51. You may do it. In addition, when the element structure 25 is bonded to the support body 55, the element structure 25 is placed on the bonding layer 50, and thus the upper surface of the high resistance portion 51 is formed to be lower than the bonding layer 50. Is done.

  Next, the support body 55 having the bonding layer 50 in which the high resistance portion 51 is formed and the element structure 25 are bonded. FIG. 3A is a partial enlarged cross-sectional view schematically showing the high resistance portion 51 and its vicinity (indicated by a broken line in FIG. 1C) when the element structure 25 is bonded to the support body 55.

  As described above, when the height c of the upper surface of the high resistance portion 51 is lower than the height d of the bonding layer 50, a gap 52 (gap: e) is formed above the high resistance portion 51. Depending on the formation process of the high resistance part 51, the gap 52 may be formed also on the side part of the high resistance part 51. Further, such a gap may not be formed, and the high resistance portion 51 may be in contact with the reflective electrode layer 40. Moreover, although the case where the concave portion is formed in the bonding layer 50 and the high resistance portion 51 is embedded in the concave portion has been described, the high resistance portion 51 is provided on the support substrate 60 as shown in FIG. It may be embedded in. Or as shown in FIG. 4, the high resistance part 51 may be embed | buried so that the element structure 25 (namely, reflective electrode layer 40) may be contact | connected.

  As shown in FIG. 4, the element structure 25 including the concave portion in which the high resistance portion 51 is formed by the molten metal of the bonding layer 45 at the time of bonding to the support body 55 (that is, the reflective electrode layer 40). A bonding layer 45 may be formed so as to cover the whole. Alternatively, the bonding layer 45 may be formed on the reflective electrode layer 40 in advance, and the bonding layer 45 and the bonding layer 50 may be bonded. More specifically, in this case, the bonding layer 45 has a structure in which, for example, Ti / Pt / Au are sequentially stacked. Normally, a metal layer having such a structure is formed as a bonding layer in a thickness of 500 to 2000 nm. In the present invention, the total thickness of the transparent electrode layer (p electrode) 30 and the reflective electrode layer 40 is used to suppress current diffusion. When the bonding layer 45 is used, the total layer thickness of the transparent electrode layer (p electrode) 30, the reflective electrode layer 40, and the bonding layer 45 is formed within a thickness range of 50 to 300 nm. Note that the bonding layer 45 may also function as a migration preventing layer that prevents migration of the metal (Ag) of the reflective electrode layer 40, so that it covers the side surfaces of the transparent electrode layer (p electrode) 30 and the reflective electrode layer 40. good.

  The support body 55 and the element structure 25 are bonded to the reflective electrode layer 40 by, for example, thermocompression bonding. It is desirable to use Si for the support substrate 60 from the viewpoints of various physical properties such as matching of the thermal expansion coefficient with the semiconductor film 20 (for example, a semiconductor film made of GaN) and cost. Further, Ge, CuW, AlN, SiC, Cu or the like may be used for the support substrate 60.

  In the above description, the case where the plurality of n-electrodes 70 are formed separately has been described. However, an n-electrode or a wiring electrode that connects these electrodes may be provided on the n-type semiconductor layer 21. In addition, a high resistance corresponding to the n electrode may be embedded in the bonding layer 50. Furthermore, the wiring electrode may be in ohmic contact with the n-type semiconductor layer 21 or may not be in ohmic contact.

  FIG. 5 shows a comparative semiconductor light emitting device 110 for comparison with the semiconductor light emitting device 10 of the example. The semiconductor light emitting device 110 is different from the semiconductor light emitting device 10 in that the high resistance portion 51 is not provided in the bonding layer 50.

  Next, referring to FIGS. 6A, 6B, 7A, and 7B, current paths and currents between the semiconductor light emitting device 10 of the example according to the present invention and the semiconductor light emitting device 110 of the comparative example. The distribution will be described. FIG. 6A is a cross-sectional view schematically showing a path of a current flowing between the electrodes of the semiconductor light emitting device 10 of this example, and FIG. 6B is a simple equivalent circuit of the semiconductor light emitting device 10. . 7A is a cross-sectional view schematically showing a path of a current flowing between the electrodes of the semiconductor light emitting device 10 of the comparative example, and FIG. 7B is a simple equivalent circuit of the semiconductor light emitting device 110. is there. More specifically, in the semiconductor light emitting device 10 of the example, four current paths 1A to 4A from the bonding layer 50 to the n electrode 70 through the reflective electrode layer 40, the transparent electrode layer 30, and the semiconductor film 20 are equivalent circuits. Based on the simulation. Similarly, in the semiconductor light emitting device 110 of the comparative example, the current flowing through the four current paths 1B to 4B from the bonding layer 50 to the n electrode 70 through the reflective electrode layer 40, the transparent electrode layer 30, and the semiconductor film 20 is as follows. A simulation based on a simple equivalent circuit was performed. In the equivalent circuit, R (Ag1) and R (Ag2) are resistances in the horizontal and vertical directions (parallel and vertical to the semiconductor film 20) of the reflective electrode layer 40 (Ag), and R (pc) is R (pc). The resistances R (epi1) and R (epi2) of the transparent electrode layer 30 (ITO) are the resistances of the semiconductor film 20 in the horizontal direction and the vertical direction, respectively.

  More specifically, the current values of the current paths 1A to 4A and 1B to 4B in the case where a current of I = 350 mA was passed through the semiconductor light emitting devices 10 and 110 were obtained. Further, the simulation was performed in increments of 10 nm in the range where the total film thickness t of the transparent electrode layer 30 and the reflective electrode layer 40 was 10 to 300 nm.

  As a result, the currents flowing in the current paths 1B, 2B, 3B, and 4B of the semiconductor light emitting device 110 of the comparative example were 61 mA, 74 mA, 92 mA, and 123 mA (t = 10 to 300 nm), respectively. That is, even if the film thickness t (10 to 300 nm) is changed, the current value of each path is substantially constant, but the difference in current value between the current paths 1B, 2B, 3B, and 4B is large. For example, it was found that about twice as much current flows in the current path 4B having the maximum current value as compared to the current path 1B having the minimum current value.

  On the other hand, the currents flowing in the current paths 1A, 2A, 3A, and 4A of the semiconductor light emitting device 10 of the example are 82 to 80 mA, 86 to 85 mA, 89 to 90 mA, and 93 to 95 mA (t = 10 to 300 nm), respectively. there were. That is, even if the film thickness t (10 to 300 nm) is changed, the current value of each path is substantially constant, and the difference in current value between the current paths 1A, 2A, 3A, and 4A is small. For example, the current value increases only by about 16% in the current path 4A having the maximum current value compared to the current path 1A having the minimum current value.

  From this simulation, in the current distribution of the semiconductor light emitting device 110 of the comparative example, the current concentrates on the path 4B immediately below the n-electrode 70, so that the current flowing through the path 4B is the largest and goes to the path 3B, path 2B, and path 1B. It is clear that the current gradually decreases. That is, the light emission efficiency in the light emitting layer 23 on the path 4B is the highest, and the light emission is blocked by the n electrode 70 thereabove, so that the light extraction efficiency is lowered, and the light emission efficiency of the semiconductor light emitting device 110 is lowered.

  On the other hand, in the semiconductor light emitting device 10 of the example, current concentration is greatly suppressed as compared with the semiconductor light emitting device 110 of the comparative example. That is, in the semiconductor light emitting device 10 of the example, the current diffusion is improved and the uniformity of the in-plane current distribution is high. Therefore, light shielding by the n-electrode 70 is reduced, and a semiconductor light emitting device with high light extraction efficiency and high light emission efficiency can be provided.

  As described above, in the semiconductor light emitting device 10 of the example, the reflective electrode layer 40 (Ag) is not directly formed on the p-type semiconductor layer 22. Therefore, when the reflective electrode layer 40 (Ag) is directly formed on the p-type semiconductor layer 22, the adhesiveness at the bonding interface between the p-type semiconductor layer 22 and the reflective electrode layer 40 is reduced, and the adhesiveness is reduced. Problems such as a decrease in reflectance due to the decrease can be avoided. That is, while the reflective electrode layer 40 is formed on the entire surface of the transparent electrode layer 30 (that is, without patterning the transparent electrode layer 30), it is possible to suppress a decrease in reflectance and current concentration, so that semiconductor light emission with high emission efficiency can be achieved. An element can be provided. In addition, a highly reliable semiconductor light emitting element can be provided.

  FIG. 8 shows a semiconductor light emitting device 10 which is a modification of the above embodiment. FIG. 8A is a plan view schematically showing the arrangement of the semiconductor film 20, the support substrate 60, and the n electrode 70. FIG. 8B is a plan view schematically showing the arrangement of the bonding layer 50 and the high resistance portion 51 when viewed from the vertical direction toward the semiconductor film 20 at the interface between the bonding layer 50 and the support substrate 60. .

  As shown in FIG. 8A, an n-electrode 70 having a comb shape (comb shape) is formed. In this case, as shown in FIG. 8B, a high resistance portion 51 having a comb-shaped cross section in a plane parallel to the semiconductor film 20 is formed. More specifically, as illustrated in FIG. 9, when the high resistance portion 51 projects the high resistance portion 51 and the n electrode 70 facing the high resistance portion 51 onto the plane P parallel to the semiconductor film 20, the high resistance portion 51 is 70 is preferably included. Alternatively, the n-electrode 70 has a comb shape by combining or combining a plurality of electrodes having a strip shape, and the high resistance portion 51 includes a plurality of high resistance bodies having a rectangular parallelepiped shape. Can be said to have a comb shape by being synthesized or combined.

  In the above-described embodiments, the thin film structure element has been described as an example. However, the present invention can also be applied to a flip chip structure element. Further, the shapes of the semiconductor film 20, the high resistance portion 51, the support substrate 60, and the first electrode 70 (n electrode) are not limited to the shapes of the above-described embodiments, and are, for example, polygonal, circular, and elliptical. Also good.

DESCRIPTION OF SYMBOLS 10 Semiconductor light emitting element 20 Semiconductor film 21 1st semiconductor layer 22 2nd semiconductor layer 23 Light emitting layer 30 2nd electrode (transparent electrode layer)
40 reflective electrode layer 50 bonding layer 51 high resistance part 52 gap 60 support substrate 70 first electrode

Claims (6)

A semiconductor film including a first semiconductor layer of a first conductivity type, a second semiconductor layer of a second conductivity type, and a light emitting layer provided between the first semiconductor layer and the second semiconductor layer; ,
A first electrode provided on the first semiconductor layer;
A transparent electrode layer formed on the second semiconductor layer;
A reflective electrode layer formed on the transparent electrode layer;
A support substrate bonded to the reflective electrode layer via a bonding layer,
The bonding layer has a high resistance portion embedded in the bonding layer, the high resistance portion has a higher electric resistance than the bonding layer, and is a region facing the first electrode with the semiconductor film interposed therebetween A semiconductor light emitting element provided in the above.   2. The semiconductor light emitting element according to claim 1, wherein the high resistance portion has a shape including the first electrodes facing each other when viewed from a direction perpendicular to the semiconductor film.   The first electrode is formed as a plurality of strip-shaped electrodes, and the high-resistance portion is formed of a plurality of high-resistance bodies each provided corresponding to each of the plurality of strip-shaped electrodes. The semiconductor light emitting device according to claim 1 or 2.   The semiconductor light emitting element according to claim 1, wherein the first electrode has a comb shape.   5. The semiconductor light emitting element according to claim 1, wherein the reflective electrode layer is formed in contact with the second semiconductor layer via the transparent electrode layer. 6.   6. The semiconductor light emitting element according to claim 1, wherein the high resistance portion is embedded in a groove extending from the support substrate to the inside of the support substrate.

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