JP2013074071A - GaN-BASED LIGHT-EMITTING DIODE - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a GaN-based light-emitting diode which has an n-side electrode formed on a rear face of an m-plane GaN substrate and which improves luminous efficiency by control of a pathway of a current flowing in the element.SOLUTION: A GaN-based light-emitting diode comprises: a substrate which is an m-plane GaN substrate of an n-type conductivity; an epitaxial layer composed of a GaN-based semiconductor epitaxially grown on the substrate and including a pn junction light emitting structure; an n-side electrode formed on a rear face of the substrate; a translucent p-side ohmic layer formed on a top face of the epitaxial layer; and a p-side electrode pad formed on a part of the p-side ohmic electrode. In a region covered with the n-side electrode on the rear face of the substrate, a low contact resistance region which is a polishing finish region and a high contact resistance region which is a dry etching finish region are included. A whole or a part of orthogonal projection of the p-side electrode pad on the rear face of the substrate is included in the high contact resistance region.

Description

The present invention relates to a GaN-based light-emitting diode having a light-emitting structure formed using a GaN-based semiconductor, and more particularly to a GaN-based light-emitting diode having a pn junction type light-emitting structure formed by epitaxial growth on an m-plane GaN substrate. A GaN-based semiconductor is a compound semiconductor represented by the general formula Al _a In _b Ga _1-ab N (0 ≦ a ≦ 1, 0 ≦ b ≦ 1, 0 ≦ a + b ≦ 1), and is a nitride semiconductor. It is also called a nitride compound semiconductor.

  2. Description of the Related Art Semiconductor light emitting devices having a pn junction type light emitting structure formed by epitaxially growing a GaN-based semiconductor on an m-plane GaN substrate are known (Non-Patent Documents 1 to 4).

  Non-Patent Documents 1 to 3 disclose light emitting diodes (LEDs), and in each element, an n-side ohmic electrode is formed on an n-type Si-doped GaN layer epitaxially grown on an m-plane GaN substrate. ing. Non-Patent Document 4 discloses a laser diode (LD). In this element, an n-side ohmic electrode is formed on the back surface of an m-plane GaN substrate. The threshold current of this laser diode is 36 mA at the time of CW driving and 28 mA at the time of pulse driving, and the threshold voltage is about 7 to 8V.

  In a light emitting device having a light emitting structure formed on a GaN substrate, it is said that it is difficult to form a good n-side ohmic electrode on the back surface of the GaN substrate (Patent Documents 1 to 6). Therefore, in the method described in Patent Document 2, the contact resistance of the n-side ohmic electrode formed on the back surface is reduced by polishing the back surface of the GaN substrate with a polishing agent having a particle diameter of 10 μm or more. It has been. In the method described in Patent Document 3, for the same purpose, the back surface of the GaN substrate is roughened by wet etching or dry etching. On the other hand, according to Patent Document 4, a damaged layer is formed when the back surface is ground, lapped or polished in order to reduce the thickness of the GaN substrate, which inhibits the formation of a good ohmic electrode. . Therefore, in the method described in Patent Document 4, the back surface of the polished GaN substrate is shaved by dry etching or wet etching. However, Patent Document 5 describes that this purpose cannot be achieved by wet etching. In the method described in Patent Document 6, the contact resistance between the GaN substrate and the n-side ohmic electrode is reduced by dry-etching the back surface of the GaN substrate and scraping off the portion containing crystal defects generated by mechanical polishing. It has been. In addition, the knowledge and invention described in these Patent Documents 1 to 6 basically relate to a c-plane GaN substrate.

  An electrode pad formed using a metal material on the element surface is essential for a light emitting diode as a part to which a power feeding member such as a metal wire, a metal bump, or solder is bonded. Since the electrode pad does not have optical transparency, a light emitting diode in which the current flowing through the light emitting structure is concentrated in a portion that is a shadow of the electrode pad when viewed from the light extraction direction has low light emission efficiency. This is because the light generated at this site is shielded and absorbed by the electrode pad and cannot be extracted efficiently outside the device. Therefore, to prevent the current from concentrating on this part, a high resistance film (insulating film) or a high resistance region is provided as a current block structure between the electrode pad and the light emitting structure to control the path of the current flowing in the element. (Patent Documents 7 to 9).

JP-A-11-340571 JP 2002-16312 A JP 2004-71657 A JP 2003-51614 A JP 2003-347660 A Japanese Patent Laid-Open No. 2004-6718 JP-A-1-151274 JP-A-7-193279 Japanese Patent Laid-Open No. 10-229219

Kuniyoshi Okamoto et al., Japanese Journal of Applied Physics, Vol. 45, No. 45, 2006, pp. L1197-L1199 Mathew C. Schmidt et al., JapaneseJournal of Applied Physics, Vol. 46, No. 7, 2007, pp.L126-L128 Shih-Pang Chang et al., Journal of The Electrochemical Society, 157 (5) H501-H503 (2010) Kuniyoshi Okamoto et al., Japanese Journal of Applied Physics, Vol. 46, No. 9, 2007, pp. L187-L189

  The inventor succeeded in obtaining a light emitting diode in which an n-side electrode having a low contact resistance is formed on the back surface of an m-plane GaN substrate, and formed on the back surface of the m-plane GaN substrate by performing different treatments. It has been found that the contact resistance of the electrode can be changed.

  The present invention has been made on the basis of this finding, and has a n-side electrode formed on the back surface of an m-plane GaN substrate, and has improved luminous efficiency by controlling the path of current flowing in the device. The main purpose is to provide a diode.

According to the present invention, the following GaN-based light emitting diodes are provided.
(1) A substrate which is an n-type conductive m-plane GaN substrate, an epitaxial layer made of a GaN-based semiconductor epitaxially grown on the substrate and including a pn junction type light emitting structure, and an n-side formed on the back surface of the substrate An electrode, a translucent p-side ohmic electrode formed on the upper surface of the epi layer, and a p-side electrode pad formed on a part of the p-side ohmic electrode,
Of the back surface of the substrate, the region covered with the n-side electrode includes a low contact resistance region that is a polished region and a high contact resistance region that is a dry-etched region,
A GaN-based light emitting diode, wherein all or part of the orthogonal projection of the p-side electrode pad on the back surface of the substrate is included in the high contact resistance region.
(2) An auxiliary electrode connected to the p-side electrode pad is formed on the p-side ohmic electrode, and all or a part of the orthogonal projection of the auxiliary electrode to the back surface of the substrate is the high contact resistance. The GaN-based light emitting diode according to (1), which is not included in the region.
(3) A substrate which is an n-type conductive m-plane GaN substrate, an epi layer made of a GaN-based semiconductor epitaxially grown on the substrate and including a pn junction type light emitting structure, and a light transmission formed on the back surface of the substrate N-side ohmic electrode, an n-side electrode pad formed on a part of the n-side ohmic electrode, and a p-side electrode formed on the upper surface of the epi layer,
Of the back surface of the substrate, the region covered with the n-side ohmic electrode includes a low contact resistance region that is a polished region and a high contact resistance region that is a dry etched region,
A GaN-based light emitting diode, wherein all or part of an orthogonal projection of the n-side electrode pad on the back surface of the substrate is included in the high contact resistance region.
(4) An auxiliary electrode connected to the n-side electrode pad is formed on the n-side ohmic electrode, and all or a part of the orthogonal projection of the auxiliary electrode to the back surface of the substrate is the high contact resistance. The GaN-based light emitting diode according to (3), which is not included in the region.
(5) A substrate which is an n-type conductive m-plane GaN substrate, an epi layer including a pn junction type light emitting structure made of a GaN-based semiconductor epitaxially grown on the substrate, and partially formed on the back surface of the substrate An n-side electrode and a p-side electrode formed on the upper surface of the epi layer,
The n-side electrode has a pad part and an auxiliary part connected to the pad part,
Of the back surface of the substrate, the region covered with the n-side electrode includes a low contact resistance region that is a polished region and a high contact resistance region that is a dry etched region,
A GaN-based light emitting diode, wherein all or part of the orthogonal projection of the pad portion on the back surface of the substrate is included in the high contact resistance region.
(6) The GaN-based light emitting diode according to (5), wherein all or part of the orthogonal projection of the auxiliary portion on the back surface of the substrate is not included in the high contact resistance region.
(7) The GaN-based light-emitting diode according to any one of (1) to (6), wherein the substrate has a carrier concentration of 10 ¹⁷ cm ⁻³ .

  In the GaN-based light emitting diode according to the embodiment of the present invention, light is shielded or absorbed by an electrode pad included in at least one of the n-side electrode and the p-side electrode by controlling the path of the current flowing in the element. Can be suppressed. Further, by controlling the path of the current flowing in the element and making the density of the current flowing in the light emitting structure uniform, it is possible to suppress a decrease in light emission efficiency due to the droop phenomenon.

It is a schematic diagram which shows the structure of the GaN-type light emitting diode which this inventor made as an experiment, FIG. 1 (a) is a top view, FIG.1 (b) is sectional drawing in the position of the XX line of FIG. It is. It is drawing which shows typically the structure of the GaN light emitting diode which concerns on embodiment of this invention, FIG.2 (a) is the top view seen from the epi layer side, FIG.2 (b) is X- of FIG.2 (a). It is sectional drawing in the position of a X-ray. It is drawing which shows typically the structure of the GaN light emitting diode which concerns on embodiment of this invention, FIG.3 (a) is the top view seen from the epi layer side, FIG.3 (b) is X- of FIG.3 (a). It is sectional drawing in the position of a X-ray. It is drawing which shows typically the structure of the GaN light emitting diode which concerns on embodiment of this invention, FIG.4 (a) is the top view seen from the epi layer side, FIG.4 (b) is X- of FIG.4 (a). It is sectional drawing in the position of a X-ray. It is drawing which shows typically the structure of the GaN light emitting diode which concerns on embodiment of this invention, Fig.5 (a) is the top view seen from the board | substrate side, FIG.5 (b) is XX of Fig.5 (a). It is sectional drawing in the position of a line. It is drawing which shows typically the structure of the GaN light emitting diode which concerns on embodiment of this invention, Fig.6 (a) is the top view seen from the board | substrate side, FIG.6 (b) is XX of Fig.6 (a). It is sectional drawing in the position of a line. It is drawing which shows typically the structure of the GaN light emitting diode which concerns on embodiment of this invention, FIG.7 (a) is the top view seen from the board | substrate side, FIG.7 (b) is XX of Fig.7 (a). It is sectional drawing in the position of a line.

(Embodiment 1)
The structure of the GaN-based light emitting diode according to Embodiment 1 is schematically shown in FIG. The GaN-based light emitting diode 100 has a substrate 110 and an epi layer 120 made of a GaN-based semiconductor epitaxially grown thereon. FIG. 2A is a plan view of the GaN-based light emitting diode 100 as viewed from the epi layer 120 side, and FIG. 2B is a cross-sectional view taken along the line XX in FIG.

  The substrate 110 is an n-type conductive m-plane GaN substrate. The epi layer 120 includes an n-type layer 121 and a p-type layer 123 that form a pn junction. An active layer 122 is provided between the n-type layer 121 and the p-type layer 123 so that a double heterostructure is formed. An n-side electrode E100 that serves both as an ohmic electrode and an electrode pad is provided on the back surface of the substrate 110, and a p-side ohmic electrode E201 that is a translucent electrode is provided on the epi layer 120. Light emission occurs in the active layer 122 by applying a forward voltage to the epi layer 120 through the n-side electrode E100 and the p-side electrode pad E202 formed in part on the p-side ohmic electrode E201. This light is transmitted to the outside of the GaN-based light emitting diode through the p-side ohmic electrode E201. A part of this light is also emitted from the end face of the substrate 110 and the end face of the epi layer 120.

  The n-side electrode E100 preferably has a laminated structure. In that case, the portion in contact with the substrate 110 is formed using a material that forms ohmic contact with an n-type GaN-based semiconductor, such as Al, Ti, Cr, V, W, ITO, and the other portions are Au, Al, It is formed using a highly conductive metal such as Cu or Ag.

  The p-side ohmic electrode E201 is formed using a transparent conductive oxide (TCO) such as ITO. The p-side ohmic electrode E201 is preferably formed so as to cover the entire upper surface of the p-type layer 123. The p-side electrode pad E202 is formed using a metal, and preferably has a laminated structure. When the p-side electrode pad E202 has a laminated structure, the portion in contact with the p-side ohmic electrode E201 is formed of a metal having excellent adhesion to TCO, such as Cr, Ti, Ni, Pt, and Rh, and other portions. Is formed using a highly conductive metal such as Au, Al, Cu, or Ag. The thickness of the p-side ohmic electrode E201 formed of TCO is preferably 0.1 μm to 0.5 μm, and the thickness of the p-side electrode pad E202 formed of metal is preferably 0.5 μm to 5 μm.

  The n-side electrode E100 covers the entire back surface of the substrate 110. On the back surface of the substrate 110, there are a low contact resistance region 112a having a relatively low contact resistance with the n-side electrode E100 and a high contact resistance region 112b having a relatively high contact resistance. The low contact resistance region 112a is polished. That is, the last process (not including cleaning) performed on the low contact resistance region 112a before forming the n-side electrode E100 is a polishing process. On the other hand, the high contact resistance region 112b is dry-etched. That is, the last process performed on the high contact resistance region 112b before forming the n-side electrode E100 is a dry etching process such as reactive ion etching (RIE).

  As a result of experimental confirmation by the present inventors, an n-type conductive m-plane GaN substrate is polished using an acidic CMP slurry at a polishing rate as low as 0.5 μm / h or less. An electrode having a low contact resistance can be formed on the obtained surface (m-plane). On the other hand, an electrode formed on the surface of an m-plane GaN substrate that has been further subjected to dry etching after polishing exhibits higher contact resistance.

  The high contact resistance region 112b only needs to include at least a part of the orthogonal projection of the p-side electrode pad E202 on the back surface of the substrate 110, but is preferably formed to include all. With this configuration, the current flowing in the substrate 110 and the epi layer 120 is concentrated on the path connecting the p-side electrode pad E202 and the n-side electrode E100 with the shortest distance (the path indicated by the arrow in FIG. 2B). It is prevented. As a result, the shielding and absorption received by the p-side electrode pad E202 by the light generated in the active layer 122 is reduced as compared with the case where current is concentrated in this region. In addition, since the density of the current flowing across the active layer 122 becomes more uniform, a reduction in light emission efficiency due to the droop phenomenon (a phenomenon in which the light emission efficiency decreases as the current density increases, which is peculiar to a GaN-based light emitting diode) is suppressed. Is done.

(Embodiment 2)
The structure of a GaN-based light emitting diode according to Embodiment 2 is schematically shown in FIG. In FIG. 3, the same reference numerals are given to components common to the GaN-based light emitting diode of the first embodiment. FIG. 3A is a plan view of the GaN-based light emitting diode 100 as viewed from the epi layer 120 side, and FIG. 3B is a cross-sectional view taken along the line XX in FIG.

  In the GaN-based light emitting diode 100 shown in FIG. 3, four auxiliary electrodes E203 are connected to the p-side electrode pad E202. Therefore, the current supplied from the metal wire or the like to the p-side electrode pad E202 is expanded in the lateral direction (direction perpendicular to the thickness direction of the epi layer 120) by the line-shaped auxiliary electrode E203, and then the p-side ohmic electrode. It will flow to E201.

  In the region covered with the n-side electrode E100 on the back surface of the substrate 110, the high contact resistance region 112b is formed so as to include at least part, preferably all, of the orthogonal projection of the p-side electrode pad E202. Therefore, it is possible to prevent the current flowing in the substrate 110 and the epi layer 120 from being concentrated on the path connecting the p-side electrode pad E202 and the n-side electrode E100 with the shortest distance. Further, since the auxiliary electrode E203 is connected to the p-side electrode pad E202, the current flowing in the epi layer 120 is spread to a region sufficiently separated from the p-side electrode pad E202 in the lateral direction.

  In the GaN-based light emitting diode 100 of FIG. 3, the orthogonal projection of the auxiliary electrode E203 on the back surface of the substrate 110 is not included in the high contact resistance region 112b. Therefore, current flows in the direction immediately below from the auxiliary electrode E203, but the auxiliary electrode E203 is formed to be elongated unlike the p-side electrode pad E202, so the influence (shielding and absorption) on light emission that occurs immediately below the auxiliary electrode E203 is compared. Small. In one embodiment, the high contact resistance region 112b may be formed so as to include all or part of the orthogonal projection of the auxiliary electrode E203 onto the back surface of the substrate 110.

(Embodiment 3)
The structure of a GaN-based light emitting diode according to Embodiment 3 is schematically shown in FIG. In FIG. 4, the same reference numerals are given to components common to the GaN-based light emitting diode of Embodiment 1. 4A is a plan view of the GaN-based light emitting diode 100 as viewed from the epi layer 120 side, and FIG. 4B is a cross-sectional view taken along the line XX in FIG.

  In the GaN-based light emitting diode 100 shown in FIG. 4, an insulating film Z100 is formed between the epi layer 120 and the p-side ohmic electrode E201, at a position directly below the p-side pad electrode E100. By providing the two current block structures of the high contact resistance region 112b and the insulating film Z100 provided on the back surface of the substrate 110, the current flowing through the substrate 110 and the epi layer 120 is supplied to the p-side electrode pad E202 and the n-side electrode. Concentrating on the route connecting E100 with the shortest distance is effectively prevented.

(Embodiment 4)
The structure of a GaN-based light emitting diode according to Embodiment 4 is schematically shown in FIG. In FIG. 5, the same reference numerals are given to components common to the GaN-based light emitting diode of Embodiment 1. FIG. 5A is a plan view of the GaN-based light emitting diode 100 as viewed from the substrate 110 side, and FIG. 5B is a cross-sectional view taken along the line XX in FIG.

  In the GaN-based light emitting diode 100 shown in FIG. 5, an n-side ohmic electrode E101 that is a translucent electrode is provided on the back surface of the substrate 110, and a p-side electrode E200 that serves both as an ohmic electrode and an electrode pad is provided on the epi layer 120. It has been. By applying a forward voltage to the epi layer 120 through the n-side electrode pad E102 formed on a part of the n-side ohmic electrode E101 and the p-side electrode E200, the active layer 122 emits light. This light passes through the n-side ohmic electrode E101 and is emitted to the outside of the GaN-based light emitting diode. A part of this light is also emitted from the end face of the substrate 110 and the end face of the epi layer 120.

  The n-side ohmic electrode E101 is formed using a transparent conductive oxide (TCO) such as ITO. The n-side electrode pad E102 is formed using a metal, and preferably has a laminated structure. When the n-side electrode pad E102 has a laminated structure, the portion in contact with the n-side ohmic electrode E201 is formed of a metal having excellent adhesion to TCO, such as Cr, Ti, Ni, Pt, and Rh, and other portions. Is formed using a highly conductive metal such as Au, Al, Cu, or Ag. The thickness of the n-side ohmic electrode E101 formed of TCO is preferably 0.1 μm to 0.5 μm, and the thickness of the n-side electrode pad E102 formed of metal is preferably 0.5 μm to 5 μm.

  The p-side electrode E200 is preferably a laminated structure. In that case, the portion that contacts the p-type layer 123 is formed using a material that forms ohmic contact with the p-type GaN-based semiconductor, such as Ni, Au, Pt, Pd, Co, and ITO, and the other portion is Au. , Al, Cu, and Ag are used to form a highly conductive metal. The p-side electrode E200 is preferably formed so as to cover the entire top surface of the p-type layer 123.

  The n-side ohmic electrode E101 covers the entire back surface of the substrate 110. On the back surface of the substrate 110, there are a low contact resistance region 112a having a relatively low contact resistance with the n-side ohmic electrode E101 and a high contact resistance region 112b having a relatively high contact resistance. The low contact resistance region 112a is a polished region, and the high contact resistance region 112b is a dry etched region.

  The high contact resistance region 112b is provided immediately below the n-side electrode pad E102. The high contact resistance region 112b only needs to include at least a part of the orthogonal projection of the n-side electrode pad E102 onto the back surface of the substrate 110, but is preferably formed to include all. With this configuration, the current flowing in the substrate 110 and the epi layer 120 is concentrated on a path (path indicated by an arrow in FIG. 6B) connecting the p-side electrode E200 and the n-side electrode pad E102 with the shortest distance. It is prevented. As a result, the shielding and absorption received by the n-side electrode pad E102 by the light generated in the active layer 122 is reduced as compared with the case where current is concentrated in this region. In addition, since the density of the current flowing across the active layer 122 becomes more uniform, a reduction in light emission efficiency due to the droop phenomenon (a phenomenon in which the light emission efficiency decreases as the current density increases, which is peculiar to a GaN-based light emitting diode) is suppressed. Is done.

(Embodiment 5)
The structure of a GaN-based light emitting diode according to Embodiment 5 is schematically shown in FIG. In FIG. 6, the same reference numerals are given to components common to the GaN-based light emitting diode of the first embodiment. 6A is a plan view of the GaN-based light emitting diode 100 as viewed from the substrate 110 side, and FIG. 6B is a cross-sectional view taken along the line XX in FIG. 6A.

  In the GaN-based light emitting diode 100 shown in FIG. 6, four auxiliary electrodes E103 are connected to the n-side electrode pad E102. Therefore, the current supplied from the metal wire or the like to the n-side electrode pad E102 is expanded in the lateral direction (direction orthogonal to the thickness direction of the substrate layer 110) by the line-shaped auxiliary electrode E103, and then the n-side ohmic electrode. It will flow to E101.

  In the region covered with the n-side ohmic electrode E101 on the back surface of the substrate 110, the high contact resistance region 112b is formed so as to include at least a part, preferably all, of the orthogonal projection of the n-side electrode pad E102. . Therefore, it is possible to prevent the current flowing through the substrate 110 and the epi layer 120 from being concentrated on the path connecting the p-side electrode E200 and the n-side electrode pad E102 with the shortest distance. Further, since the auxiliary electrode E103 is connected to the n-side electrode pad E102, the current flowing in the epi layer 120 is spread to a region sufficiently separated from the n-side electrode pad E102 in the lateral direction.

  In the GaN-based light emitting diode 100 of FIG. 6, the orthogonal projection of the auxiliary electrode E103 onto the back surface of the substrate 110 is not included in the high contact resistance region 112b. Therefore, current flows also in the direction immediately below from the auxiliary electrode E103, but the auxiliary electrode E103 is formed in an elongated shape unlike the n-side electrode pad E202, so the influence (shielding and absorption) on the light emission that occurs immediately below is compared. Small. In one embodiment, the high contact resistance region 112b may be formed so as to include all or a part of the orthogonal projection of the auxiliary electrode E103 onto the back surface of the substrate 110.

(Embodiment 6)
The structure of a GaN-based light emitting diode according to Embodiment 6 is schematically shown in FIG. In FIG. 7, the same reference numerals are given to components common to the GaN-based light emitting diode of Embodiment 1. FIG. 7A is a plan view of the GaN-based light emitting diode 100 viewed from the substrate 110 side, and FIG. 7B is a cross-sectional view taken along the line XX in FIG.

  In the GaN-based light emitting diode 100 shown in FIG. 7, the n-side electrode E100 is an ohmic electrode, and the n-side electrode E100 is directly formed on the back surface of the substrate 110. The n-side electrode E100 includes a pad portion E100a that also serves as an electrode pad, and an auxiliary portion E100b that is connected to the pad portion E100a and presents a cross pattern (also referred to as a branched linear pattern).

  The n-side electrode E100 is preferably formed by using a material that forms ohmic contact with an n-type GaN-based semiconductor, such as Al, Ti, Cr, V, W, ITO, etc. The portion is formed using a highly conductive metal such as Au, Al, Cu, or Ag.

  In the region covered with the n-side electrode E100 in the back surface of the substrate 110, the high contact resistance region 112b is formed so as to include at least part, preferably all, of the orthogonal projection of the pad portion E100a of the n-side electrode. Yes. Accordingly, carriers (electrons) injected from the n-side electrode E100 into the substrate 110 are not directly from the pad portion E100a but are expanded in the lateral direction by the auxiliary portion E100b and then injected into the substrate 110. Therefore, the density of the current flowing through the light emitting structure in the epi layer 120 becomes uniform as compared with the case where the high contact resistance region 112b is not provided. Current flows from the auxiliary portion E100b in the direction immediately below, but the auxiliary portion E100b is formed to be elongated unlike the pad portion E100a, so that the influence (shielding and absorption) on the light emission that occurs immediately below the auxiliary portion E100b is small.

(Experimental result)
The results of trial manufacture and evaluation of a GaN-based light emitting diode (hereinafter also simply referred to as “LED”) by the present inventor will be described below.
1. Basic Structure of Prototype LED FIG. 1 schematically shows the basic structure of a prototype LED. 1A is a top view, and FIG. 1B is a cross-sectional view taken along the line XX in FIG. 1A. As shown to Fig.1 (a), the planar shape of LED1 is a rectangle, and a size is 350 micrometers x 340 micrometers.

As shown in FIG. 1B, the LED 1 has a semiconductor stacked body 20 made of a GaN-based semiconductor on a substrate 10. The substrate 10 is an m-plane GaN substrate, and the semiconductor stacked body 20 is disposed on the front surface 11 of the substrate 10. The semiconductor stacked body 20 includes, in order from the substrate 10 side, a first undoped GaN layer 21, a Si-doped n-type GaN contact layer 22, a second undoped GaN layer 23, a Si-doped n-type GaN cladding layer 24, an MQW. An active layer 25, a Mg-doped p-type Al _0.1 Ga _0.9 N clad layer 26, and an Mg-doped p-type Al _0.03 Ga _0.97 N contact layer 27 are provided.

The MQW active layer 25 has undoped In _0.04 Ga _0.96 N barrier layers and undoped In _0.16 Ga _0.84 N well layers that are alternately stacked. The number of undoped InGaN barrier layers is four, and the number of undoped InGaN well layers is three. Therefore, the lowermost layer and the uppermost layer of the MQW active layer 25 are both barrier layers. The composition of the well layer is adjusted so that the emission peak wavelength falls within the range of 445 to 465 nm.

  LED1 has two n-side electrodes and one p-side electrode. One of the n-side electrodes is a first n-side metal pad E11, which is provided so as to cover the entire back surface 12 of the substrate 10. The other is the second n-side metal pad E12, which is formed on the surface of the n-type GaN contact layer 22 exposed by partially removing the semiconductor stacked body 20. Both the first n-side metal pad E11 and the second n-side metal pad E12 also serve as ohmic electrodes. The p-side electrode is composed of an ohmic translucent electrode E21 formed on the upper surface of the p-type AlGaN contact layer 27 and a p-side metal pad E22 formed on a part of the translucent electrode E21. It is. The current application to the MQW active layer 25 can be performed through the first n-side metal pad E11 and the p-side metal pad E22, or can be performed through the second n-side metal pad E12 and the p-side metal pad E22. .

The first n-side metal pad E11 is a multilayer film, and includes a TiW layer, an Au layer, a Pt layer, an Au layer, a Pt layer, an Au layer, a Pt layer, and an Au layer in order from the substrate 10 side. The second n-side metal pad E12 is also a multilayer film having a similar laminated structure, and in order from the n-type GaN contact layer 22 side, a TiW layer, an Au layer, a Pt layer, an Au layer, a Pt layer, an Au layer, a Pt layer, It has an Au layer. The translucent electrode E21 is an ITO (indium tin oxide) film. The p-side metal pad E12 is a multilayer film having a laminated structure similar to that of the first n-side metal pad E11 and the second n-side metal pad E12, and sequentially includes a TiW layer, an Au layer, and Pt from the translucent electrode E21 side. A layer, an Au layer, a Pt layer, an Au layer, a Pt layer, and an Au layer.
2. LED Trial Production LED1 was produced by the following procedure.
2-1. Epitaxial growth Size is 7 mm (c-axis direction) x 15 mm (a-axis direction) x 330 μm (thickness), and the off-angle of the front surface (main surface on which the semiconductor laminate is provided) is 0 ± 0.5 ° The n-type conductive m-plane GaN substrate to which Si was added as an n-type impurity was prepared. The carrier concentration of the m-plane GaN substrate examined by hole measurement was 1.3 × 10 ¹⁷ cm ⁻³ .

A plurality of GaN-based semiconductor layers were epitaxially grown on the front surface of the m-plane GaN substrate using the atmospheric pressure MOVPE method to form a semiconductor laminate. TMG (trimethylgallium), TMI (trimethylindium) and TMA (trimethylaluminum) for Group III materials, ammonia for Group V materials, silane for Si materials, bisethylcyclopentadienylmagnesium ((EtCp) for Mg materials ) ₂ Mg) was used.

  Table 1 shows the growth temperature and film thickness of each layer.

  Table 2 shows the concentration of impurities added to the n-type GaN contact layer, n-type GaN clad layer, p-type AlGaN clad layer, and p-type AlGaN contact layer.

The activation of Mg added to the p-type AlGaN cladding layer and the p-type AlGaN contact layer is performed while the p-type AlGaN contact layer is grown for a predetermined time and then the substrate temperature is lowered to room temperature in the growth furnace of the MOVPE apparatus. This was carried out using a method for controlling the flow rates of nitrogen gas and ammonia gas flowing into the growth furnace.
2-2. Formation of p-side electrode and second n-side metal pad An ITO film having a thickness of 210 nm was formed on the surface of the semiconductor laminate formed by the epitaxial growth (surface of the p-type AlGaN contact layer) by electron beam evaporation. Subsequently, the ITO film was patterned into a predetermined shape using photolithography and etching techniques to form a translucent electrode. After patterning, a part of the semiconductor stacked body is removed by reactive ion etching (RIE) processing to expose the n-type GaN contact layer at the site where the second n-side metal pad is to be formed, and perform mesa formation. It was. In RIE processing, Cl ₂ was used as an etching gas, the antenna / bias was set to 100 W / 20 W, and the pressure in the chamber was set to 0.5 Pa.

  Subsequent to the RIE process, the produced ITO film was heat-treated at 520 ° C. for 20 minutes in the air atmosphere. Further, using an RTA (Rapid Thermal Annealing) apparatus, this ITO film was heat-treated at 500 ° C. for 1 minute in a nitrogen gas atmosphere.

After the heat treatment of the ITO film, a second n-side metal pad and a p-side metal pad were simultaneously formed in a predetermined pattern using a lift-off method. All layers (TiW layer, Au layer, and Pt layer) included in the metal multilayer film constituting the second n-side metal pad and the p-side metal pad were formed by sputtering. When forming a TiW film, a Ti-W target having a Ti content of 10 wt% is used as a target, Ar (argon) is used as a sputtering gas, sputtering conditions are RF power 800 W, Ar flow rate 50 sccm, sputtering gas pressure 2.2. × 10 ⁻¹ Pa. The thickness of the lowermost TiW layer and the Au layer laminated immediately above it was 108 nm, and the thicknesses of the other Pt layers and Au layers were all 89 nm.

After forming the second n-side metal pad and the p-side metal pad, a passivation film made of SiO ₂ was formed to a thickness of 230 nm on the exposed surface of the semiconductor stacked body and the surface of the translucent electrode.
2-3. Processing of Back Surface of m-plane GaN Substrate After the formation of the passivation film, four different processes described below as processing a to processing d were performed on the back surface of the m-plane GaN substrate.

  Process a: The thickness of the substrate was reduced to 200 μm by lapping and polishing the back surface of the m-plane GaN substrate in this order.

  In the lapping process, the grain size of the diamond abrasive used was gradually reduced in accordance with a conventional method.

  In the polishing step, a CMP slurry in which acid is added to acidic colloidal silica (particle size 70-100 nm) and the pH is adjusted to less than 2 is used, and the load is adjusted so that the polishing rate is 0.5 μm / h. The processing time was about 14 hours. The surface of the m-plane GaN substrate polished under these conditions has an arithmetic average roughness Ra in the range of 10 μm square measured using AFM (for example, DIMENSION 5000 manufactured by DIGITAL INSTRUMENTS) of 0.1 nm or less.

  The polished surface (the back surface of the m-plane GaN substrate) is washed with water, further washed with IPA and acetone at room temperature, and then dried with ultraviolet ozone cleaning (110 ° C., oxygen flow rate 5 L / min) for 5 minutes. gave.

  Process b: After process a, the surface layer portion was further removed from the back surface of the m-plane GaN substrate by RIE. The RIE condition is the above 2-2. The etching time was set to 60 seconds so that the etching depth was 0.1 μm under the same conditions as when the RIE processing was performed on the semiconductor laminate. When the roughness of the surface after RIE processing was measured with a stylus type step gauge (ET3000 manufactured by Kosaka Laboratory Ltd.), the arithmetic average roughness Ra was 0.02 μm, and the maximum height Rz was 0.04 μm.

  Processing c: After processing a, the surface layer portion was further scraped off from the back surface of the m-plane GaN substrate by RIE. The RIE condition is the above 2-2. The etching time was set to 610 seconds so that the etching depth was 1.0 μm under the same conditions as when the semiconductor laminate was subjected to RIE processing. When the surface roughness after RIE processing was measured with a stylus profilometer, the arithmetic average roughness Ra was 0.06 μm, and the maximum height Rz was 0.55 μm.

Processing d: After processing a, the surface layer portion was further scraped off from the back surface of the m-plane GaN substrate by RIE. The RIE condition is the above 2-2. The etching time was set to 1220 seconds so that the etching conditions were the same as those when the RIE processing was performed on the semiconductor laminate. When the surface roughness after RIE processing was measured with a stylus profilometer, the arithmetic average roughness Ra was 0.07 to 0.12 μm, and the maximum height Rz was 1.30 μm.
2-4. Formation of first n-side metal pad A metal multilayer film serving as a first n-side metal pad was formed on the back surface of the m-plane GaN substrate subjected to any of the above processes a to d. All layers (TiW layer, Au layer, and Pt layer) included in this metal multilayer film were formed by sputtering. When forming a TiW film, a Ti-W target having a Ti content of 10 wt% is used as a target, Ar (argon) is used as a sputtering gas, sputtering conditions are RF power 800 W, Ar flow rate 50 sccm, sputtering gas pressure 2.2. × 10 ⁻¹ Pa. The thickness of the lowermost TiW layer and the Au layer laminated immediately above it was 108 nm, and the thicknesses of the other Pt layers and Au layers were all 89 nm.

After the metal multilayer film was formed, the wafer was divided by scribing and breaking to form LED elements as chips. The metal multilayer film was cut together with the GaN substrate in this step. Therefore, the planar shape of the first n-side metal pad is the same as the shape of the back surface of the m-plane GaN substrate. The size of the first n-side metal pad was 350 μm × 340 μm, which was substantially the same as the chip size.
2-5. Evaluation of forward voltage Forward voltage (Vf ₁ ) when current is applied through the first n-side metal pad and p-side metal pad to the LED chip obtained by the above procedure, and the second n-side The forward voltage (Vf ₂ ) when current was applied through the metal pad and the p-side metal pad was compared. The applied current was a pulse current having a pulse width of 1 msec and a pulse period of 100 msec, and the current value was 20 mA and 60 mA. The results are shown in Table 3.

100 GaN-based light emitting diode 110 substrate 112a low contact resistance region 112b high contact resistance region 120 epi layer 121 n type layer 122 active layer 123 p type layer E100 n side electrode E101 n side ohmic electrode E102 n side electrode pad E103 auxiliary electrode E200 p Side electrode E201 p side ohmic electrode E202 p side electrode pad E203 Auxiliary electrode

Claims (7)

a substrate which is an n-type conductive m-plane GaN substrate, an epi layer comprising a pn-junction light emitting structure epitaxially grown on the substrate, an n-side electrode formed on the back surface of the substrate, A translucent p-side ohmic electrode formed on the upper surface of the epi layer, and a p-side electrode pad formed on a part of the p-side ohmic electrode;
Of the back surface of the substrate, the region covered with the n-side electrode includes a low contact resistance region that is a polished region and a high contact resistance region that is a dry-etched region,
A GaN-based light emitting diode, wherein all or part of the orthogonal projection of the p-side electrode pad on the back surface of the substrate is included in the high contact resistance region. An auxiliary electrode connected to the p-side electrode pad is formed on the p-side ohmic electrode, and all or part of the orthogonal projection of the auxiliary electrode on the back surface of the substrate is included in the high contact resistance region. The GaN-based light emitting diode according to claim 1, wherein a substrate which is an n-type conductive m-plane GaN substrate, an epi layer made of a GaN-based semiconductor epitaxially grown on the substrate and including a pn-junction light-emitting structure, and a translucent n formed on the back surface of the substrate A side ohmic electrode, an n-side electrode pad formed on a part of the n-side ohmic electrode, and a p-side electrode formed on the upper surface of the epi layer,
Of the back surface of the substrate, the region covered with the n-side ohmic electrode includes a low contact resistance region that is a polished region and a high contact resistance region that is a dry etched region,
A GaN-based light emitting diode, wherein all or part of an orthogonal projection of the n-side electrode pad on the back surface of the substrate is included in the high contact resistance region. An auxiliary electrode connected to the n-side electrode pad is formed on the n-side ohmic electrode, and all or part of the orthogonal projection of the auxiliary electrode on the back surface of the substrate is included in the high contact resistance region. The GaN-based light emitting diode according to claim 3, wherein a substrate which is an n-type conductive m-plane GaN substrate, an epi layer made of a GaN-based semiconductor epitaxially grown on the substrate and including a pn junction type light emitting structure, and an n-side partially formed on the back surface of the substrate An electrode and a p-side electrode formed on the upper surface of the epi layer,
The n-side electrode has a pad part and an auxiliary part connected to the pad part,
Of the back surface of the substrate, the region covered with the n-side electrode includes a low contact resistance region that is a polished region and a high contact resistance region that is a dry etched region,
A GaN-based light emitting diode, wherein all or part of the orthogonal projection of the pad portion on the back surface of the substrate is included in the high contact resistance region. The GaN-based light emitting diode according to claim 5, wherein all or a part of the orthogonal projection of the auxiliary portion on the back surface of the substrate is not included in the high contact resistance region. The GaN-based light emitting diode according to claim 1, wherein the substrate has a carrier concentration of 10 ¹⁷ cm ⁻³ .