JP2007103689A - Semiconductor light emitting device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To achieve a semiconductor light emitting device having a reflection electrode exhibiting high reflectivity even to emission light of ultraviolet region. <P>SOLUTION: The semiconductor light emitting device comprises a P type semiconductor layer 11, an active layer 12 of InGaN/GaN and a P type semiconductor layer 13 formed sequentially on a sapphire substrate 10, and an N side reflection electrode 14 including a reflective layer 14b formed on the P type semiconductor layer 13 to come into ohmic contact therewith and reflecting emission light 50 from the active layer 12. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a semiconductor light emitting device, and more particularly to a semiconductor light emitting device having a reflective electrode.

  In recent years, light emitting devices using semiconductors have been widely used in applications such as display light sources, liquid crystal backlight light sources, and illumination white light sources, and high output of semiconductor light emitting devices is strongly desired. ing. In particular, light emitting devices made of nitride semiconductors, that is, light emitting diode (LED: light emitting diode) devices capable of obtaining light emitted from the blue region to the ultraviolet region, due to high output, are used in large markets such as lighting applications and automotive headlamp applications. Can be expected. In order to realize a semiconductor light emitting device capable of high output, not only the luminous efficiency of the light emitting layer itself is increased, but also a structure that efficiently extracts emitted light generated in the light emitting layer to the outside, that is, the extraction efficiency is increased. It is extremely important to raise it.

  As a method for improving the extraction efficiency of emitted light, the electrode material formed on the semiconductor layer has translucency, the electrode is patterned, the surface of the electrode or the semiconductor layer is processed into an uneven shape, Various techniques for coating the semiconductor layer with a resin having a low refractive index have been proposed.

  Among them, a large effect is expected. A semiconductor light emitting device having a structure in which light is extracted from the back surface side of the substrate by using a metal having a high reflectance such as silver (Ag) as a reflective electrode, a so-called flip chip type semiconductor light emitting device. Device. Silver is a material having a high reflectance in the visible range, but on the other hand, there are problems such as large migration and weakness to heat, and it is difficult to put it into practical use as a reflective electrode. In addition, silver has a characteristic that its reflectance rapidly deteriorates with respect to light having a wavelength of 350 nm or less, and cannot be used for ultraviolet light with a wavelength of 350 nm or less.

Patent Document 1 below discloses a P-side reflective electrode using silver. However, since silver is used for the reflective layer, sufficient reflectivity cannot be obtained in the ultraviolet region. In addition, aluminum (Al) is mentioned as a material with a high reflectance with respect to ultraviolet light.
Japanese Patent Laid-Open No. 11-186598 Japanese Unexamined Patent Publication No. 07-045867

  As described above, the conventional semiconductor light emitting device has a problem that a reflective electrode having a high reflectance in the ultraviolet region cannot be realized.

  The present invention has been made in view of the above-described conventional problems, and an object thereof is to realize a semiconductor light-emitting device having a reflective electrode having a high reflectance even with respect to ultraviolet light.

  In order to achieve the above-described object, the present invention provides a semiconductor light-emitting device in which a reflective electrode having a high reflectance is provided on an N-type semiconductor layer in ohmic contact with the N-type semiconductor layer. To do.

  Specifically, a first semiconductor light emitting device according to the present invention is formed between an N-type first semiconductor layer, a P-type second semiconductor layer, and the first semiconductor layer and the second semiconductor layer. A reflective electrode including an active layer and a reflective layer formed on a surface of the first semiconductor layer opposite to the active layer and in ohmic contact with the first semiconductor layer and reflecting light emitted from the active layer; It is characterized by being.

  According to the first semiconductor light emitting device, the reflection is formed on the surface of the N-type first semiconductor layer opposite to the active layer, is in ohmic contact with the first semiconductor layer, and reflects the emitted light from the active layer. Since a reflective electrode including a layer is provided, even a material having high reflectivity in the ultraviolet region, such as aluminum (Al), which is a metal that cannot make ohmic contact with the P-type second semiconductor layer, is N-type. A reflective electrode can be formed over the first semiconductor layer. As a result, it is possible to realize a semiconductor light emitting device having a high light emission rate even in the ultraviolet region.

  In the first semiconductor light emitting device, the reflective layer preferably contains aluminum or rhodium. Thus, a reflective electrode having a sufficiently high reflectance can be formed even for ultraviolet light having a wavelength of 350 nm or less.

  In the first semiconductor light emitting device, the reflective layer preferably has a reflectance of 60% or more with respect to the emitted light.

  In the first semiconductor light emitting device, the thickness of the reflective layer is preferably 20 nm or more. If it does in this way, since the emitted light from an active layer will be reflected efficiently, without permeate | transmitting a reflective layer, the reflectance of a reflective electrode can be maintained high.

  In the first semiconductor light emitting device, the reflective electrode preferably includes a contact layer in ohmic contact with the first semiconductor layer. In this case, the contact resistance of the reflective electrode is reduced, so that the operating voltage of the light emitting device can be reduced. In addition, since the contact layer improves the adhesion between the reflective electrode and the first semiconductor layer, the reliability is improved.

  A second semiconductor light emitting device according to the present invention includes an N-type first semiconductor layer, a P-type second semiconductor layer, an active layer formed between the first semiconductor layer and the second semiconductor layer, An N-type third semiconductor layer formed on the surface of the second semiconductor layer opposite to the active layer and in ohmic contact with the second semiconductor layer, and on a surface of the third semiconductor layer opposite to the second semiconductor layer. And a first reflective electrode including a first reflective layer formed and in ohmic contact with the third semiconductor layer and reflecting light emitted from the active layer.

  According to the second semiconductor light-emitting device, the N-type third semiconductor layer that is in ohmic contact with the P-type second semiconductor layer, the second semiconductor light-emitting device that is in ohmic contact with the third semiconductor layer, and reflects the emitted light from the active layer. A material having a high reflectivity in the ultraviolet region, such as aluminum (Al), which is a metal that cannot make ohmic contact with the P-type second semiconductor layer. Even if it exists, it can be formed as a reflective electrode on the N-type third semiconductor layer. As a result, it is possible to realize a semiconductor light emitting device having a high light emission rate in the ultraviolet region. The ohmic contact between the P-type second semiconductor layer and the N-type third semiconductor layer can be realized by a tunnel junction.

  Therefore, in the second semiconductor light emitting device, the second semiconductor layer and the third semiconductor layer are preferably in ohmic contact with each other through a tunnel junction.

In the second semiconductor light emitting device, the impurity concentrations of the second semiconductor layer and the third semiconductor layer are each preferably 1 × 10 ¹⁹ cm ⁻³ or more.

  The second semiconductor light emitting device is formed on a part of the surface of the first semiconductor layer opposite to the active layer, and is in ohmic contact with the first semiconductor layer and reflects the light emitted from the active layer. It is preferable to further include a second reflective electrode including a layer.

  In this case, since the active layer is sandwiched between the first reflective electrode and the second reflective electrode, a so-called vertical device in which an injection current flows in a direction perpendicular to the active layer is obtained. Even in the case of this configuration, the emitted light can be taken out of the device by multiple reflection between the two reflective electrodes even on the surface of the second reflective electrode facing the first reflective electrode. A semiconductor light emitting device having a high light rate can be realized.

  In the second semiconductor light emitting device, it is preferable that at least the first reflective layer of the first reflective layer and the second reflective layer contains aluminum or rhodium.

  In the second semiconductor light emitting device, it is preferable that at least the first reflective layer of the first reflective layer and the second reflective layer has a reflectance of 60% or more with respect to the emitted light.

  In the second semiconductor light emitting device, it is preferable that at least the first reflective layer of the first reflective layer and the second reflective layer has a thickness of 20 nm or more.

  In the second semiconductor light emitting device, the first reflective electrode or the second reflective electrode preferably includes a contact layer in ohmic contact with each adjacent semiconductor layer.

  In the first or second semiconductor light emitting device, when a contact layer is formed, the contact layer preferably has a light-transmitting property with respect to emitted light. In this case, even if the contact layer has absorption with respect to the emission wavelength, the transmittance of the contact layer is increased by sufficiently reducing the thickness of the contact layer. The reflectance can be kept high.

  In this case, the thickness of the contact layer is preferably greater than 0 and 10 nm or less. In this way, even when the contact layer has absorption with respect to the emission wavelength, by sufficiently reducing the film thickness, the transmittance of the contact layer can be increased and the reflectance of the entire reflective electrode can be kept high. .

  In this case, the contact layer preferably contains titanium, aluminum, palladium, vanadium, indium tin oxide (ITO), or zinc oxide. In this way, a reflective electrode having good ohmic contact with the N-type semiconductor layer can be formed.

  The semiconductor light-emitting device according to the present invention can realize a reflective electrode having a high reflectance even with respect to ultraviolet light.

(First embodiment)
A first embodiment according to the present invention will be described with reference to the drawings.

  FIG. 1A shows a semiconductor light emitting device according to a first embodiment of the present invention, which shows a planar configuration of the LED device, and FIG. 1B is a cross-sectional configuration taken along line Ib-Ib in FIG. Is shown.

As shown in FIG. 1A and FIG. 1B, the semiconductor light emitting device according to the first embodiment is transparent to emitted light 50 from the light emitting device, for example, sapphire (single crystal) consists al ₂ O _3), and the substrate 10 of the planar dimensions are 350 .mu.m × 350 .mu.m, a P-type semiconductor layer 11 are sequentially formed by epitaxial growth on the main surface of the substrate 10, an active layer 12 having a multiple quantum well structure And an N-type semiconductor layer 13.

  On the N-type semiconductor layer 13, a peripheral portion is formed inward by 10 μm from the end face of the N-type semiconductor layer 13, a contact layer 14 a made of titanium (Ti) having a thickness of 3 nm, and aluminum having a thickness of 100 nm. A first mounting electrode formed by laminating an N-side reflective electrode 14 composed of a reflective layer 14b made of (Al), titanium (Ti) having a thickness of 50 nm, and gold (Au) having a thickness of 300 nm. A cover metal layer 15 is sequentially formed. On the region where a part of the P-type semiconductor layer 11 is exposed by etching, nickel (Ni) having a thickness of 50 nm and gold (Au) having a thickness of 150 nm are stacked in ohmic contact with the P-type semiconductor layer 11. A P-side electrode 16 and a mounting second cover metal layer 17 having the same configuration as that of the first cover metal layer 15 are sequentially formed. Here, the planar dimension of the P-side electrode 16 is 75 μm × 75 μm.

  The active layer 12 has a multiple quantum well structure or a superlattice structure made of, for example, InGaN. In the active layer 12, aluminum (Al) may be added to the barrier layer portion in the quantum well structure or the superlattice structure.

P-type semiconductor layer 11 is made of the 2μm of P-type GaN thick, N-type semiconductor layer 13, the thickness of 30nm undoped Al _0.15 Ga _0.85 N, a thickness of N-type 10 nm Al _0.3 Ga _0.7 N And N-type Al _0.15 Ga _0.85 N having a thickness of 50 nm, N-type GaN having a thickness of 15 nm, and N ⁺ -type GaN having a thickness of 5 nm.

  The semiconductor light emitting device according to the first embodiment is a so-called flip-chip type in which the first cover metal layer 15 and the second cover metal layer 17 are mounted so as to face the main surface of a mounting substrate (submount) (not shown). LED device.

  Hereinafter, a method for manufacturing the LED device configured as described above will be described.

  First, a buffer layer (not shown) made of GaN having a thickness of 200 nm is formed on the main surface of the substrate 10 made of sapphire by a metal organic chemical vapor deposition (MOCVD) method. An active layer 12 and an N-type semiconductor layer 13 having a multiple quantum well structure in which well layers made of, for example, InGaN and barrier layers made of GaN are alternately stacked are sequentially epitaxially grown.

Then, by plasma CVD (plasma-Chemical Vapor Deposition) method, a mask-forming film thickness over the entire surface is made of 400nm silicon oxide (SiO ₂₎ on the formed N-type semiconductor layer 13 (not shown) formed To do. Thereafter, a mask film having an opening in the upper part of the P-side electrode formation region in the mask formation film is formed on the formed mask formation film by a dry etching method using a lithography method and reactive ion etching (RIE). obtain. Subsequently, the N-type semiconductor layer 13, the active layer 12, and the P-type semiconductor layer 11 are formed by dry etching using, for example, ECR (Electron Cyclotron Resonance) plasma using chlorine (Cl ₂ ) gas, using the formed mask film. The upper part is sequentially removed to form a P-side electrode formation region in a part of the P-type semiconductor layer 11.

Next, the mask film is removed with a buffered hydrofluoric acid (BHF) solution, and then a first resist pattern (not shown) that opens the reflective electrode formation region is formed on the P-type semiconductor layer 13 by lithography. A Ni film having a thickness of 50 nm and an Au film having a thickness of 150 nm are sequentially formed on the formed first resist pattern by EB vapor deposition. Subsequently, the P-side electrode 16 made of Ni / Au is formed on the P-type semiconductor layer 11 by a so-called lift-off method in which the first resist pattern is removed together with the Ni film and the Au film deposited on the first resist pattern. Form. Thereafter, in order to reduce the contact resistance of the formed P-side electrode 16 with the P-type semiconductor layer 11, a heat treatment is performed in a nitrogen atmosphere at a temperature of 600 ° C. for 20 minutes. By this first heat treatment, the contact resistance of the P-side electrode 16 can realize a good ohmic contact with an order of 10 ⁻⁴ Ω · cm ² .

Next, a second resist pattern (not shown) that opens the reflective electrode formation region is formed on the P-type semiconductor layer 13 by lithography, and on the formed second resist pattern by EB vapor deposition. A contact layer 14a made of Ti having a thickness of 3 nm and a reflective layer 14b made of Al having a thickness of 100 nm are sequentially deposited. Subsequently, N is formed of the contact layer 14a and the reflective layer 14b on the N-type semiconductor layer 13 by a lift-off method in which the second resist pattern is removed together with unnecessary Ti and Al deposited on the second resist pattern. The side reflection electrode 14 is formed. Here, the N-side reflective electrode 14 is preferably formed so as to cover almost the entire upper surface of the N-type semiconductor layer 13. Thereafter, in order to reduce the contact resistance of the formed N-side reflective electrode 14 with the N-type semiconductor layer 13, heat treatment is performed for 1 minute in a nitrogen atmosphere at a temperature of 600 ° C. The second heat treatment, the contact resistance of the N-side reflecting electrode 14, the order can be achieved in 10 ^-6 Ω · cm ² good ohmic contact.

  Next, a protective film made of silicon oxide having a thickness of 300 nm is formed on the entire surface of the N-type semiconductor layer 13 and the P-type semiconductor layer 11 on which the N-side reflective electrode 14 and the P-side electrode 16 are formed by plasma CVD. A film (not shown) is formed. Subsequently, a second resist pattern (not shown) having openings for exposing the N-side reflective electrode 14 and the P-side electrode 16 is formed by lithography, and the formed second resist pattern is used as a mask. By performing wet etching with a buffered hydrofluoric acid solution on the protective film forming film, the entire periphery of each of the electrodes 14 and 16 is left leaving the peripheral portions of the N-side reflective electrode 14 and the P-side electrode 16 from the protective film forming film. A protective film (passivation film) having an opening exposing the film is formed.

  Next, a cover metal forming layer made of Ti having a thickness of 50 nm and Au having a thickness of 300 nm is deposited on the second resist pattern by EB vapor deposition. Thereafter, the first cover metal layer 15 is formed on the N-side reflective electrode 14 by a lift-off method in which the second resist pattern is removed together with unnecessary Ti and Au deposited on the second resist pattern. At the same time, the second cover metal layer 17 is formed on the P-side electrode 16. Here, since the flip-chip type LED device is electrically and mechanically connected to the submount by the cover metal layers 15 and 17, the first cover metal is used to enhance the heat dissipation of the LED device. It is preferable that the layer 15 is formed to have approximately the same size as the N-side reflective electrode 14.

  Through the above steps, the emitted light 50 emitted from the active layer 12 is reflected to the substrate 10 side by the N-side reflective electrode 14, and the emitted light 50 is extracted from the translucent substrate 10 side to the outside. An LED device is obtained.

  In the first embodiment, aluminum (Al) is used as the reflective layer 14b of the N-side reflective electrode 14 formed on the P-type semiconductor layer 13, but rhodium (Rh) is used instead of Al. A material having a high light reflectance in the ultraviolet region to the visible region can be used.

  FIG. 2 shows the wavelength dependence (calculated value) of the reflectance of the single-layer metal film in the air. Silver (Ag), aluminum (Al), and rhodium (Rh) have higher reflectivity than nickel (Ni) or platinum (Pt) used in conventional gallium nitride (GaN) -based semiconductors. It is promising as a material for the reflective electrode 14. However, Ag has an abrupt decrease in reflectance in a wavelength region of 350 nm or less, and thus is not suitable as a reflective electrode for a light-emitting device that outputs emitted light in the ultraviolet region. On the other hand, Al shows a high reflectance even in the ultraviolet region, and can be compatible with a low contact resistance, so is most suitable for the N-side reflective electrode 14.

  In the first embodiment, the thickness of the reflective layer 14b of the N-side reflective electrode 14 is set to 100 nm. However, the thickness is not limited to this.

  FIG. 3 shows the thickness dependence (calculated value) of the transmittance of light having wavelengths of 300 nm, 350 nm, and 400 nm in the reflective layer 14b made of aluminum (Al). As can be seen from FIG. 3, when the thickness of the reflective layer 14b is reduced, a decrease in the reflectance of the reflective layer 14b, that is, an increase in the transmittance cannot be ignored. Therefore, the thickness of the reflective layer 14b may be 20 nm or more. Preferably, it is more preferably 50 nm or more.

  As described above, according to the first embodiment, since the reflective layer 14b made of Al is used for the N-side reflective electrode 14, the N-type semiconductor layer 13 is the substrate above the element, that is, the active layer 12. The structure provided on the opposite side of 10 is adopted. Usually, in the case of a GaN-based light emitting device, a configuration in which a P-type semiconductor layer is provided on the upper part of the element is often used. In this configuration, the reflective electrode using Al is a good ohmic to the P-type semiconductor layer. You can't get in touch. For this reason, in the first embodiment, both the high reflectance and the low contact resistance can be achieved by turning the PN junction upside down and forming the reflective electrode as an N-side electrode. Therefore, it is possible to realize a semiconductor light emitting device having a reflective electrode having a high reflectivity even with respect to ultraviolet light 50 having a wavelength of 350 nm or less.

  In the first embodiment, titanium (Ti) is used as the contact layer 14 a of the N-side reflective electrode 14. As a result, the adhesion between the reflective layer 14b of the N-side reflective electrode 14 and the N-type semiconductor layer 13 is improved, so that the contact resistance of the reflective electrode 14 can be further reduced.

  Patent Document 2 describes a configuration in which an ohmic electrode using Ti and Al is provided on a GaN-based semiconductor. However, if only an ohmic contact is realized, the thickness and the composition ratio of Ti and Al are described. It is not very important.

  As in this embodiment, in order to achieve a high reflectance in the ohmic electrode, it is desirable that the thickness of Ti as the contact layer 14a is as thin as possible. That is, in order for Al to sufficiently function as the reflective layer 14b, the contact layer 14a needs to be thin enough to transmit the emitted light 50 sufficiently. In the present embodiment, the thickness of the contact layer 14a is 3 nm, but is preferably 10 nm or less, and more preferably 3 nm or less.

  Further, although Ti is used for the contact layer 14a, any material that can realize good ohmic contact with the N-type semiconductor layer 13 made of N-type GaN may be used. For example, Al (when Rh is used for the reflective layer 14b), palladium (Pd), V (vanadium), indium tin oxide (ITO), zinc oxide (ZnO), or the like can be used. When the transmittance of the contact layer 14a with respect to the emission wavelength is low, it is preferable that the contact layer 14a is thin as in the case of Ti. When the contact layer 14a is a light-transmitting conductive material such as ITO, it is not necessary to reduce the thickness.

  In the first embodiment, a laminate of Ti and Au is used as the first cover metal layer 15 and the second cover metal layer 17, but other metals may be used. It may be a single layer film or a multilayer film. For example, when a laminated body made of Ti / Pt / Au is used, thermal stability is improved and interdiffusion between Ti and Au is suppressed, so that a more stable device can be obtained. In addition to stability and oxidation resistance, the cover metal layers 15 and 17 preferably contain gold (Au) from the viewpoint of wire bonding adhesion.

In the first embodiment, sapphire is used as the substrate 10 for epitaxial growth. However, the material is not limited to sapphire as long as the material has translucency with respect to the emission wavelength. For example, gallium nitride (GaN) or gallium oxide (Ga ₂ O ₃ ) can be used.

(Second Embodiment)
Hereinafter, a second embodiment of the present invention will be described with reference to FIG.

  FIG. 4A is a semiconductor light emitting device according to the second embodiment of the present invention, and shows a planar configuration of the LED device, and FIG. 4B is a cross-sectional configuration taken along line IVb-IVb in FIG. Is shown. In FIG. 4A and FIG. 4B, the same components as those in FIG.

  As shown in FIGS. 4A and 4B, the semiconductor light emitting device according to the second embodiment includes a substrate 10 made of sapphire that is transparent to emitted light 50 from the light emitting device. The first N-type semiconductor layer 21 sequentially formed on the main surface of the substrate 10 by epitaxial growth, the active layer 12 having a multiple quantum well structure, the P-type semiconductor layer 23, the P-type semiconductor layer 23, And a second N-type semiconductor layer 24 in ohmic contact with the tunnel junction. The ohmic contact due to the tunnel junction is a tunnel junction in which the P-type semiconductor layer 23 and the second N-type semiconductor layer 24 are each doped at a high concentration, and when a reverse voltage is applied, It means that it does not show rectification and shows ohmic characteristics by tunnel current.

  A contact layer 14a made of titanium (Ti) having a thickness of 3 nm is formed on the second N-type semiconductor layer 24 with a peripheral portion formed inward by 10 μm from the end face of the second N-type semiconductor layer 24, and A P-side reflective electrode 25 constituted by a reflective layer 14b made of aluminum (Al) having a thickness of 100 nm, titanium (Ti) having a thickness of 50 nm, and gold (Au) having a thickness of 300 nm are laminated. A first cover metal layer 15 for mounting is sequentially formed. On a region where a part of the first N-type semiconductor layer 21 is exposed by etching, titanium (Ti) having a thickness of 3 nm and aluminum having a thickness of 100 nm are in ohmic contact with the first N-type semiconductor layer 21. An N-side electrode 26 formed by laminating (Al) and a second cover metal layer 17 for mounting having the same configuration as the first cover metal layer 15 are sequentially formed.

The first N-type semiconductor layer 21 is made of N-type GaN with a thickness of 4 μm, and the P-type semiconductor layer 23 is undoped Al _0.15 Ga _0.85 N with a thickness of 30 nm, and P-type Al _{0.3 with} a thickness of 10 nm. It consists of Ga _0.7 N, P-type Al _0.15 Ga _0.85 N with a thickness of 50 nm, P-type GaN with a thickness of 15 nm, and P ⁺ -type GaN with a thickness of 5 nm. The thickness of the second N-type semiconductor layer 24 is 20 nm.

  The semiconductor light emitting device according to the second embodiment is a flip chip type in which the first cover metal layer 15 and the second cover metal layer 17 are mounted so as to face the main surface of a mounting substrate (submount) (not shown). LED device.

  Hereinafter, a method for manufacturing the LED device configured as described above will be described.

First, on the main surface of the substrate 10 made of sapphire, a buffer layer (not shown) made of GaN having a thickness of 200 nm and a first N-type semiconductor layer 21 made of N-type GaN, such as InGaN, are formed by MOCVD. The active layer 12, the P-type semiconductor layer 23, and the second N-type semiconductor layer 24 having a multiple quantum well structure in which GaN is alternately stacked are sequentially epitaxially grown. Here, both the uppermost P ⁺ -type GaN layer constituting the P-type semiconductor layer 23 and the second N-type semiconductor layer 24 have a relatively high impurity concentration of about 1 × 10 ²⁰ cm ^−3. Doping makes the PN junction between the P ⁺ -type GaN layer and the second N-type semiconductor layer 24 a tunnel junction. The impurity concentration may be about 1 × 10 ¹⁹ cm ⁻³ .

  Next, a mask formation film (not shown) made of silicon oxide having a thickness of 400 nm is formed on the entire surface of the formed second N-type semiconductor layer 24 by plasma CVD. Thereafter, a mask film having an opening in an upper portion of the N-side electrode formation region in the mask formation film is obtained by a lithography method and a dry etching method by RIE on the formed mask formation film. Subsequently, using the formed mask film, the second N-type semiconductor layer 24, the P-type semiconductor layer 23, the active layer 12, and the first N-type semiconductor are formed by dry etching using, for example, ECR plasma using chlorine gas. The upper portion of the layer 21 is sequentially removed to form an N-side electrode formation region in a part of the first N-type semiconductor layer 21.

Next, the mask film is removed with a buffered hydrofluoric acid (BHF) solution, and then a P-side reflective electrode is formed on the second N-type semiconductor layer 24 and the exposed N-type semiconductor layer 21 by lithography. A first resist pattern (not shown) is formed to open the region and the N-side electrode formation region. Subsequently, a contact layer 14a made of Ti having a thickness of 3 nm and a reflective layer 14b made of Al having a thickness of 100 nm are sequentially deposited on the formed first resist pattern by EB vapor deposition. Subsequently, the contact layer 14a and the reflective layer 14b are formed on the second N-type semiconductor layer 24 by a lift-off method in which the first resist pattern is removed together with unnecessary Ti and Al deposited on the first resist pattern. A P-side reflective electrode 25 made of, and an N-side electrode 26 made of Ti and Al are formed on the N-type semiconductor layer 21. Here, the P-side reflective electrode 25 is preferably formed so as to cover almost the entire upper surface of the second N-type semiconductor layer 24. Thereafter, in order to reduce the contact resistance of the formed P-side reflective electrode 25 with the second N-type semiconductor layer 24, heat treatment is performed for 1 minute in a nitrogen atmosphere at a temperature of 600 ° C. By this first heat treatment, a good ohmic contact with an order of 10 ⁻⁶ Ω · cm ² can be realized for the contact resistance of the P-side reflective electrode 25. In the second embodiment, since the P-side reflective electrode 25 and the N-side electrode 26 can be formed in the same process, the process can be further simplified.

  Next, an oxidation of 300 nm in thickness over the entire surface of the second N-type semiconductor layer 24 and the first N-type semiconductor layer 21 on which the P-side reflective electrode 25 and the N-side electrode 26 are formed by plasma CVD. A protective film forming film (not shown) made of silicon is formed. Subsequently, a second resist pattern (not shown) having openings for exposing the P-side reflective electrode 25 and the N-side electrode 26 is formed by lithography, and the formed second resist pattern is used as a mask. By performing wet etching with a buffered hydrofluoric acid solution on the protective film forming film, the entire periphery of each of the electrodes 25 and 26 is left leaving the peripheral portions of the P-side reflective electrode 25 and the N-side electrode 26 from the protective film forming film. A protective film having an opening exposing the surface is formed.

  Next, a cover metal forming layer made of a Ti film having a thickness of 50 nm and an Au film having a thickness of 500 nm is deposited on the second resist pattern by EB vapor deposition. Thereafter, the first cover metal layer 15 is formed on the P-side reflective electrode 25 by a lift-off method in which the second resist pattern is removed together with unnecessary Ti and Au deposited on the second resist pattern. At the same time, the second cover metal layer 17 is formed on the N-side electrode 26. Here, since the flip-chip type LED device is electrically and mechanically connected to the submount by the cover metal layers 15 and 17, the first cover metal is used to enhance the heat dissipation of the LED device. It is preferable that the layer 15 is formed to be approximately the same size as the P-side reflective electrode 25.

  Through the above steps, the emitted light 50 emitted from the active layer 12 is reflected to the substrate 10 side by the P-side reflective electrode 25, and the emitted light 50 is extracted from the transparent substrate 10 side to the outside. An LED device is obtained.

As described above, in the second embodiment, as a contact layer for the P-side reflective electrode 25, the P ⁺ -type GaN layer formed on the P-type semiconductor layer 23 on the active layer 12 and the top thereof A tunnel contact layer using a tunnel junction with the second N-type semiconductor layer 24 made of N ⁺ -type GaN is introduced.

This tunnel junction is a high concentration of the PN junction, the reverse voltage is applied to the second N-type semiconductor layer 24 and the P ⁺ -type GaN layer to flow a tunnel current, a second N-type semiconductor layer 24 Can function as a contact layer for the P-type semiconductor layer 23. As a result, a metal electrode capable of making ohmic contact with the second N-type semiconductor layer 24 can be used as the P-side reflective electrode 25.

  In addition, the first N-type semiconductor layer 21, the active layer 12, and the P-type semiconductor layer 23 can be sequentially epitaxially grown on the main surface of the substrate 10 as in the conventional GaN-based LED device. That is, since it is easier to grow the N-type semiconductor layer on the main surface of the substrate 10 than the P-type semiconductor layer, the active layer 12 can be formed efficiently. Therefore, according to the second embodiment, it is possible to realize a semiconductor light emitting device having both the highly efficient active layer 12 and the P-side reflective electrode 25 having a high reflectance in the ultraviolet region.

(Third embodiment)
Hereinafter, a third embodiment of the present invention will be described with reference to FIG.

  FIG. 5A is a semiconductor light emitting device according to the third embodiment of the present invention, and shows a planar configuration of the LED device, and FIG. 5B is a cross-sectional configuration taken along line Vb-Vb in FIG. Is shown. In FIG. 5A and FIG. 5B, the same components as those in FIG. 1 and FIG.

  As shown in FIG. 5A and FIG. 5B, the semiconductor light emitting device according to the third embodiment uses the first N-type substrate 10 made of sapphire in the semiconductor light emitting device according to the second embodiment. After removing from the semiconductor layer 21, the N-side reflective electrode 30 and the cover metal layer 31 are provided in the central portion on the surface of the first N-type semiconductor layer 21 on the side opposite to the active layer 12.

  On the surface of the P-side reflective electrode 25 opposite to the second N-type semiconductor layer 24, a base metal layer 41 made of titanium (Ti) and gold (Au) is interposed, and gold ( A holding film 40 made of Au) is formed by bonding instead of the substrate 10.

  As described above, in the LED device according to the third embodiment, the N-side reflective electrode 30 formed on the first N-type semiconductor layer 21 and the second N-type semiconductor layer that tunnel-joins with the P-type semiconductor layer 23. Since the P-side reflective electrode 25 formed on the electrode 24 is formed so as to sandwich the active layer 12, the current injected into the LED device is the P-type semiconductor layer 23, the active layer 12, and the first N-type semiconductor. The layer 21 is formed as a so-called vertical device that flows in a direction substantially perpendicular to each semiconductor layer. Since the vertical device is not affected by the sheet resistance in the first N-type semiconductor layer 21, low voltage driving can be realized.

  Hereinafter, a method for manufacturing the LED device configured as described above will be described.

First, a buffer layer (not shown) made of GaN having a thickness of 200 nm and a first N-type semiconductor made of N-type GaN are formed on the main surface of a base material substrate (not shown) made of sapphire by MOCVD. An active layer 12, a P-type semiconductor layer 23, and a second N-type semiconductor layer 24 having a multiple quantum well structure in which InGaN and GaN are alternately stacked, for example, are epitaxially grown sequentially. Here, as in the second embodiment, the upper P ⁺ -type GaN layer constituting the P-type semiconductor layer 23 and the second N-type semiconductor layer 24 are both about 1 × 10 ²⁰ cm ⁻³ . By doping at a high concentration, the PN junction between the P ⁺ -type GaN layer and the second N-type semiconductor layer 24 is used as a tunnel junction.

Next, a first contact layer 14a made of Ti having a thickness of 3 nm and a first reflective layer 14b made of Al having a thickness of 100 nm are formed on the second N-type semiconductor layer 24 by EB vapor deposition. A P-side reflective electrode 25 is formed. Thereafter, in order to reduce the contact resistance of the formed P-side reflective electrode 25 with the second N-type semiconductor layer 24, heat treatment is performed for 1 minute in a nitrogen atmosphere at a temperature of 600 ° C. By this first heat treatment, a good ohmic contact with an order of 10 ⁻⁶ Ω · cm ² can be realized for the contact resistance of the P-side reflective electrode 25.

  Next, a base metal layer 41 made of titanium (Ti) having a thickness of 50 nm and gold (Au) having a thickness of 150 nm is formed on the P-side reflective electrode 25 by vacuum deposition. Subsequently, the holding film 40 made of Au plating having a thickness of 50 μm is formed on the base metal layer 41 by electroplating.

  Next, the first N-type semiconductor layer 21 is irradiated with a third harmonic (third harmonic) laser beam of YAG (yttrium aluminum garnet) having a wavelength of 355 nm through a base material substrate made of sapphire. The base material substrate is peeled from the first N-type semiconductor layer 21 by melting the interface portion of the first N-type semiconductor layer 21 with the base material substrate.

Next, an island having a diameter of about 70 μm is formed at a substantially central portion on the surface opposite to the active layer 12 in the first N-type semiconductor layer 21 from which the base material substrate has been peeled off by lithography, EB vapor deposition, and lift-off. The N-side reflective electrode 30 is selectively formed. Here, the N-side reflective electrode 30 is formed in order from the first N-type semiconductor layer 21 side, the second contact layer 30a made of Ti having a thickness of 3 nm and the first contact layer 30 made of Al having a thickness of 100 nm. 2 reflective layers 30b. Thereafter, in order to reduce the contact resistance of the formed N-side reflective electrode 30, heat treatment is performed for 1 minute in a nitrogen atmosphere at a temperature of 600 ° C. Note that the N-side reflective electrode 30 is not necessarily formed in an island shape at the center of the upper surface of the first N-type semiconductor layer 21. Similarly, on the periphery of the first N-type semiconductor layer 21, it may be formed in a ring shape or a ring shape in which a part thereof is missing. In this case, the width of the electrode of the annular portion may be about 10 μm or more and 20 μm or less. Next, a thickness of 50 nm is formed on the N-side reflective electrode 30 formed by lithography, EB vapor deposition, and lift-off. A cover metal layer 31 for wiring mounting made of Ti and Au having a thickness of 500 nm is selectively formed.

  Through the above steps, a vertical LED device is obtained in which the emitted light 50 emitted from the active layer 12 is reflected by the P-side reflective electrode 25 toward the N-side reflective electrode 30 and the emitted light 50 is extracted to the outside.

  According to the third embodiment, similarly to the second embodiment, it is possible to realize a semiconductor light emitting device having both the high-efficiency active layer 12 and the P-side reflective electrode 25 having a high reflectance in the ultraviolet region.

  In addition, in the third embodiment, a vertical LED structure is employed in which the N-side reflective electrode 30 and the P-side reflective electrode 25 sandwich the active layer 12 from above and below. Unlike the flip-chip LED device, the vertical LED device does not allow a current in the direction parallel to the active layer 12 (lateral direction) to flow in the first N-type semiconductor layer 21, thereby reducing the resistance of the element. Can do. As a result, the operating voltage of the device can be reduced.

  By the way, in a normal vertical device, since it is necessary to provide an electrode also on the light extraction side (the first N-type semiconductor layer 21 side), the emitted light 50 from directly below the electrode in the active layer 12 is emitted from the light extraction side. The electrode provided in the is an obstacle. For this reason, the emitted light 50 emitted from directly under the electrode cannot be effectively extracted outside.

  However, in the third embodiment, the N-side reflective electrode 30 on the light extraction side has the same configuration as the P-side reflective electrode 25 having a high reflectance, and is opposed to each other with the active layer 12 interposed therebetween. Due to the multiple reflection between the two reflection electrodes 25 and 30 provided on the first N-type semiconductor layer 21 and the second N-type semiconductor layer 24, the emitted light 50 from directly below the N-side reflection electrode 30 is also effective to the outside. Can be taken out.

  In the third embodiment, Au plating is used as the constituent material of the holding film 40, but a holding film made of silicon (Si), tungsten copper (CuW), or the like can be used. In this case, it is necessary to bond the first reflective layer 14b and the holding film by using a mixed crystal solder material made of gold tin (AuSn) or the like. In addition, since the holding film 40 functions as a mount part of the LED device, a material having high thermal conductivity is preferable.

  In the third embodiment, the base material substrate is peeled from the first N-type semiconductor layer 21 using laser light, but another method that does not use laser light is used for peeling the base material substrate. be able to. For example, silicon (Si) may be used for the base material substrate, and after forming the holding film 40 by the bonding process described above, the base material substrate made of Si may be peeled off by wet etching or gas etching.

  In each of the first to third embodiments, the contact layers 14a and 30a made of titanium (Ti) are provided on the N-side reflective electrodes 14 and 30 and the P-side reflective electrode 25, respectively. 30a is not necessarily provided.

  The semiconductor light-emitting device according to the present invention can realize a reflective electrode having a high reflectance even for light emitted in the ultraviolet region, and is useful as an ultraviolet LED device having a high output and a long life.

(A) And (b) shows the semiconductor light-emitting device concerning the 1st Embodiment of this invention, (a) is a top view, (b) is sectional drawing in the Ib-Ib line | wire of (a). . It is a graph which shows the wavelength dependence (calculated value) of the reflectance of the single layer metal film in the air. It is a graph which shows the film thickness dependence of the light transmittance in the reflective layer (Al) of the reflective electrode used for the semiconductor light-emitting device concerning the 1st Embodiment of this invention. (A) And (b) shows the semiconductor light-emitting device concerning the 2nd Embodiment of this invention, (a) is a top view, (b) is sectional drawing in the IVb-IVb line | wire of (a). . (A) And (b) shows the semiconductor light-emitting device concerning the 3rd Embodiment of this invention, (a) is a top view, (b) is sectional drawing in the Vb-Vb line | wire of (a). .

Explanation of symbols

10 substrate 11 P-type semiconductor layer 12 active layer 13 N-type semiconductor layer 14 N-side reflective electrode 14a (first) contact layer 14b (first) reflective layer 15 first cover metal layer 16 P-side electrode 17 second Cover metal layer 21 First N-type semiconductor layer 23 P-type semiconductor layer 24 Second N-type semiconductor layer 25 P-side reflective electrode 30 N-side reflective electrode 30a Second contact layer 30b Second reflective layer 31 Cover metal Layer 40 Holding film 41 Underlying metal layer 50 Emitted light

Claims (16)

An N-type first semiconductor layer;
A P-type second semiconductor layer;
An active layer formed between the first semiconductor layer and the second semiconductor layer;
A reflective electrode including a reflective layer formed on a surface of the first semiconductor layer opposite to the active layer and in ohmic contact with the first semiconductor layer and reflecting light emitted from the active layer; A semiconductor light emitting device characterized by comprising:   The semiconductor light emitting device according to claim 1, wherein the reflective layer contains aluminum or rhodium.   The semiconductor light emitting device according to claim 1, wherein the reflective layer has a reflectance of 60% or more with respect to the emitted light.   The semiconductor light-emitting device according to claim 1, wherein the reflective layer has a thickness of 20 nm or more.   5. The semiconductor light emitting device according to claim 1, wherein the reflective electrode includes a contact layer in ohmic contact with the first semiconductor layer. An N-type first semiconductor layer;
A P-type second semiconductor layer;
An active layer formed between the first semiconductor layer and the second semiconductor layer;
An N-type third semiconductor layer formed on the surface of the second semiconductor layer opposite to the active layer and in ohmic contact with the second semiconductor layer;
A first reflective layer formed on a surface of the third semiconductor layer opposite to the second semiconductor layer, the first reflective layer being in ohmic contact with the third semiconductor layer and reflecting light emitted from the active layer; A semiconductor light emitting device.   The semiconductor light emitting device according to claim 6, wherein the second semiconductor layer and the third semiconductor layer are in ohmic contact with each other through a tunnel junction. 8. The semiconductor light emitting device according to claim 7, wherein impurity concentrations of the second semiconductor layer and the third semiconductor layer are each 1 × 10 ¹⁹ cm ⁻³ or more.   A second reflective layer formed on a part of the first semiconductor layer on a surface opposite to the active layer and in ohmic contact with the first semiconductor layer and reflecting light emitted from the active layer; The semiconductor light emitting device according to claim 6, further comprising two reflective electrodes.   10. The semiconductor light emitting device according to claim 6, wherein at least a first reflective layer of the first reflective layer and the second reflective layer contains aluminum or rhodium.   10. At least a first reflective layer of the first reflective layer and the second reflective layer has a reflectance of 60% or more with respect to the emitted light. 10. The semiconductor light emitting device according to claim 1.   The at least 1st reflective layer of the said 1st reflective layer and a 2nd reflective layer is a film thickness of 20 nm or more, Any one of Claim 6, 9, 10, and 11 characterized by the above-mentioned. The semiconductor light-emitting device as described.   The first reflective electrode or the second reflective electrode includes a contact layer that is in ohmic contact with an adjacent semiconductor layer, respectively. The semiconductor light emitting device according to item.   The semiconductor light-emitting device according to claim 5, wherein the contact layer has a light-transmitting property with respect to the emitted light.   15. The semiconductor light emitting device according to claim 13, wherein the contact layer has a thickness of greater than 0 and not greater than 10 nm.   The semiconductor light emitting device according to claim 13, wherein the contact layer includes titanium, aluminum, palladium, vanadium, indium tin oxide (ITO), or zinc oxide.

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