JP2006261609A - Garium nitride based light emitting diode and light emitting device using the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a GaN based LED provided with a structure reflecting the light moving in the opposite direction from a light extracting direction inside an element more efficiently and having improved efficiency of extracting light. <P>SOLUTION: A GaN-based light emitting diode has: a laminate including an n-type GaN-based semiconductor layer 2, a light emitting layer 3 comprising a GaN based semiconductor, and a p-type GaN based semiconductor layer 4 in this order; a semiconductor electrode layer P2a formed on the surface of the p-type GaN based semiconductor layer 4 and comprising the n-type semiconductor transmitting the light generated in the light emitting layer; a metal electrode P2b formed on the surface of the semiconductor electrode layer partially; a transparent insulating film Ins formed on the surface of the semiconductor electrode layer P2a with the metal electrode P2b in-between, and having a refractive index lower than that of the semiconductor electrode layer P2a; and a metallic reflective film R formed on the surface of the transparent insulating film Ins. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a GaN-based light-emitting diode suitable for flip-chip mounting and a light-emitting device including a GaN-based light-emitting diode mounted on a flip chip.

  A GaN-based light emitting diode (hereinafter also referred to as a “GaN-based LED”) is a semiconductor light emitting device having a pn junction diode structure in which p-type and n-type GaN-based semiconductors are joined with a light-emitting layer made of a GaN-based semiconductor interposed therebetween. By selecting the composition of the GaN-based semiconductor that constitutes the light-emitting layer of the device, light ranging from red to ultraviolet can be emitted.

A GaN-based semiconductor is a compound semiconductor made of a group III nitride determined by the chemical formula Al _a In _b Ga _1-ab N (0 ≦ a ≦ 1, 0 ≦ b ≦ 1, 0 ≦ a + b ≦ 1). For example, those having an arbitrary composition such as GaN, InGaN, AlGaN, AlInGaN, AlN, and InN are exemplified. In the above chemical formula, a part of the group 3 element is substituted with boron (B), thallium (Tl), or the like, and a part of N (nitrogen) is phosphorus (P), arsenic (As), antimony ( Those substituted with Sb) or bismuth (Bi) are also included in the GaN-based semiconductor.

A GaN-based LED is formed on a crystal substrate made of sapphire or the like by using a vapor phase growth method such as an organic metal compound vapor phase growth (MOVPE) method, a hydride vapor phase growth (HVPE) method, or a molecular beam epitaxy (MBE) method. An electrode for growing a stacked body including an n-type GaN-based semiconductor layer, a light-emitting layer, and a p-type GaN-based semiconductor layer in this order from the n-type GaN-based semiconductor layer side, and then supplying power to the n-type GaN-based semiconductor layer And an electrode for supplying power to the p-type GaN-based semiconductor layer.
In this specification, when the GaN-based semiconductor layer is manufactured by the vapor deposition method, it is assumed that the crystal substrate is on the lower side and the GaN-based semiconductor layer is stacked thereon, and this upper and lower distinction is made. This also applies to the description of the element structure. A direction perpendicular to the vertical direction (also the thickness direction of the crystal substrate or the GaN-based semiconductor layer) is referred to as a horizontal direction. The p-type GaN-based semiconductor layer is also simply referred to as a p-type layer, and the n-type GaN-based semiconductor layer is also simply referred to as an n-type layer.

FIG. 10 is a schematic diagram showing the structure of a conventional GaN-based LED disclosed in Japanese Patent Application Laid-Open No. 2004-179347 (Patent Document 1). 10A is a top view, and FIG. 10B is a cross-sectional view taken along line XY in FIG. 10A. In FIG. 10, 11 is a crystal substrate made of sapphire, 12 is an n-type layer made of a Si-doped GaN contact layer and a Si-doped AlGaN cladding layer laminated thereon, and 13 is an MQW (multiple quantum well) structure made of InGaN. A light emitting layer, p is a p-type layer composed of an Mg-doped AlGaN cladding layer and an Mg-doped GaN contact layer laminated thereon, P11 is a lower electrode formed by laminating Ti (titanium) and Al (aluminum), P12a and P12b constitute an upper electrode, P12a is a transparent layer made of ITO (indium tin oxide), and P12b is a reflective layer made of Ag (silver), Al, Rh (rhodium) or the like.
In the element shown in FIG. 10, light generated in the light emitting layer 13 is extracted from the lower surface side of the crystal substrate 11. Therefore, as a mounting form of this element, the lower electrode P11 and the reflective layer P12a of the upper electrode are bonded to the positive and negative lead electrodes provided on the surface of the mounting substrate with Au-Sn solder or the like, respectively. Flip chip mounting, which is fixed by doing so, is suitable.

JP 2004-179347 A

The light generated in the light-emitting layer 13 of the GaN-based LED shown in FIG. 10 always includes a component that goes upward in the element, that is, a component that goes in the direction opposite to the lower surface of the crystal substrate 11. In addition, the light traveling in the downward direction inside the element may be reflected at the refractive index interface existing inside the element or the interface separating the inside and outside of the element, thereby changing the traveling direction upward. When light traveling upward in the device enters the interface between the p-type layer 14 and the transparent layer P12a from the p-type layer 14 side, the refractive index of ITO (about 2) is changed to the refractive index of GaN (about 2.5) is approximately 80%, and according to Snell's law, light having an incident angle larger than approximately 53 degrees is totally reflected at the interface, and light having an incident angle smaller than this is reflected on the transparent layer P12a. Enter inside.
In the conventional GaN-based LED shown in FIG. 10, the light that has entered the transparent layer P12a is reflected by the metal reflective layer P12b and directed toward the crystal substrate 11, thereby improving the light extraction efficiency. For this reason, the reflective layer P12b is formed of Ag, Al, Rh or the like having good light reflectivity.
However, since the reflection by the metal reflecting member involves a relatively large loss, the light extraction efficiency is improved by selecting the metal material constituting the reflecting member in the light-emitting diode in which multiple reflection is likely to occur inside the element. Has its limits.

  The present invention has been made in view of the above problems of the prior art, and is provided with a structure that more efficiently reflects light traveling in the direction opposite to the light extraction direction from the inside of the element. An object of the present invention is to provide a GaN-based LED with improved extraction efficiency.

(1) A stack including an n-type GaN-based semiconductor layer, a light-emitting layer made of a GaN-based semiconductor, and a p-type GaN-based semiconductor layer in this order, and the surface formed on the surface of the p-type GaN-based semiconductor layer, A semiconductor electrode layer made of an n-type semiconductor that transmits light generated in the light emitting layer, a metal electrode partially formed on the surface of the semiconductor electrode layer, and a surface of the semiconductor electrode layer with the metal electrode interposed therebetween A GaN-based light emitting diode, comprising: a formed transparent insulating film having a refractive index lower than that of the semiconductor electrode layer; and a metal reflective film formed on a surface of the transparent insulating film.
(2) The GaN-based light emitting diode according to (1), wherein the semiconductor electrode layer is made of an oxide semiconductor.
(3) The GaN-based light emitting diode according to (2), wherein the oxide semiconductor is ITO.
(4) The GaN-based light-emitting diode according to (1), wherein the semiconductor electrode layer is made of a GaN-based semiconductor.
(5) The GaN-based light emitting diode according to any one of (1) to (4), wherein the transparent insulating film is made of SiO ₂ .
(6) The GaN-based light emitting diode according to any one of (1) to (5), wherein a portion of the reflective film that reflects light generated in the light emitting layer is made of Ag or Al.
(7) The GaN-based light emitting diode according to any one of (1) to (6), wherein the metal electrode has a portion made of Ag or Al that reflects light generated in the light emitting layer.
(8) A light-emitting device comprising a mounting substrate and the GaN-based light-emitting diode according to any one of (1) to (7), which is flip-chip mounted on the surface thereof.

  In the GaN-based LED described in (1) above, a metal reflecting member is not directly formed on the surface of the semiconductor electrode layer formed on the surface of the p-type GaN-based semiconductor layer, but is partially formed on the surface. A transparent insulating film having a refractive index lower than that of the semiconductor electrode layer is formed with the metal electrode thus formed interposed therebetween, and a metallic reflective film is formed on the surface thereof. Therefore, at least a part of the light entering the semiconductor electrode layer from the p-type GaN-based semiconductor layer side is not reflected by the metal electrode or the metal reflection film, but the semiconductor electrode layer and the transparent insulating film It will be totally reflected at the interface. Due to the high light transmittance of the insulating material, the loss due to this total reflection, and the loss received when a part of the light incident on the transparent insulating film propagates in the transparent insulating film is small. Therefore, the light extraction efficiency is improved as compared with a conventional GaN-based LED that mainly uses reflection by a metallic reflecting member.

Hereinafter, the present invention will be specifically described with reference to the drawings.
1A and 1B are schematic views showing the structure of a GaN-based LED according to an embodiment of the present invention. FIG. 1A is a top view, and FIG. 1B is a cross section taken along line XY in FIG. FIG.
In FIG. 1, 1 is a crystal substrate, 2 is an n-type layer, 3 is a light emitting layer, 4 is a p-type layer, P1 is a lower electrode, P2a and P2b are upper electrodes, P2a is a semiconductor electrode layer, P2b is a metal electrode, Ins is a transparent insulating film, and R is a reflective film. The broken line in FIG. 1A indicates the outline of the metal electrode P2b hidden under the reflective film R and the transparent insulating film Ins, and the alternate long and short dash line indicates the transparent insulation hidden under the reflective film R. An outline of an opening provided in the film Ins is shown.

The detailed configuration of each part of the element shown in FIG. 1 is as follows.
The crystal substrate 1 is a sapphire substrate, and the dimensions after element separation are, for example, about 350 μm in length and width and 100 μm in thickness.
The n-type layer 2 is a 3 μm-thick GaN layer doped with Si (silicon) at a concentration of 5 × 10 ¹⁸ cm ⁻³ .
The light emitting layer 3 is an MQW layer formed by alternately stacking 10 GaN barrier layers having a thickness of 8 nm and InGaN well layers having a thickness of 2 nm.
The p-type layer 4 includes, in order from the lower layer side, a p-type Al _0.1 Ga _0.9 N cladding layer having a thickness of 30 nm doped with Mg (magnesium) at a concentration of 5 × 10 ¹⁸ cm ⁻³ , and 5 Mg. A p-type GaN contact layer with a thickness of 200 nm doped at a concentration of × 10 ¹⁹ cm ⁻³ is laminated.
The lower electrode P1, in order from the lower layer side, is Ti with a thickness of 20 nm, Al with a thickness of 100 nm, Pt with a thickness of 100 nm, Au with a thickness of 100 nm, Pt with a thickness of 100 nm, Au with a thickness of 100 nm, and 100 nm with a thickness of 100 nm. Pt and Au with a film thickness of 400 nm are laminated and heat-treated.
The semiconductor electrode layer P2a is ITO having a film thickness of 150 nm.
The metal electrode P2b is 100 nm thick Al.
The transparent insulating film Ins is SiO ₂ having a film thickness of 300 nm.
The reflective film R is formed by laminating 100 nm thick Al, 100 nm thick Pt, and 100 nm thick Au in order from the lower layer side. The reflective film R also serves as an electrode for bonding to the upper electrode.

The GaN-based LED shown in FIG. 1 can be manufactured by the following method.
(Crystal growth)
A c-plane sapphire substrate having a diameter of 2 inches and a thickness of 400 μm is used as the crystal substrate 1, and an n-type layer 2, light emission is appropriately formed on the growth surface by appropriately using a known GaN-based semiconductor crystal growth method such as the MOVPE method. Layer 3 and p-type layer 4 are formed sequentially. Preferably, before the n-type layer 2 is grown, a low-temperature buffer layer made of GaN, AlGaN or the like is grown on the surface of the crystal substrate 1 at a temperature lower than the growth temperature of the n-type layer 2. After the crystal growth is completed, heat treatment is performed in an inert gas atmosphere in order to activate Mg added to the p-type layer 4 as necessary.

(Formation of the upper electrode)
A semiconductor electrode layer P2a is formed on the entire surface of the p-type layer 4. For the formation of the semiconductor electrode layer P2a made of ITO, sputtering, vacuum vapor deposition, spray pyrolysis, cluster beam vapor deposition, pulsed laser vapor deposition, ion plating, sol-gel method, laser ablation, and other known ITO thin film production methods Can be used as appropriate.
FIG. 2A is a top view of the wafer that has been subjected to the formation of the semiconductor electrode layer P2a in this way. For convenience, only a region corresponding to one element is illustrated, but the process before element separation is performed in a wafer state. The same applies to FIGS. 2B, 2C, and 3D to 3F.
After the formation of the semiconductor electrode layer P2a, a metal electrode P2b made of Al is partially formed on the surface as shown in FIG. The patterning of the metal electrode P2b can be performed by a lift-off method using a known photolithography technique. In the lift-off method, first, a photoresist film is formed on the entire surface of the semiconductor electrode layer P2a. Next, using a photolithography technique, an opening is formed in the shape of the metal electrode P2b to be formed in the photoresist film, and the surface of the semiconductor electrode layer P2a is exposed in the opening. Next, using the photoresist film as a mask, an electrode film of the metal electrode P2b is formed by appropriately using a known method for producing a metal thin film such as vapor deposition, sputtering, or CVD. Thereafter, the photoresist film is lifted off leaving the electrode film formed in the shape of the opening on the surface of the semiconductor electrode layer P2a.
As another method, first, an electrode film of the metal electrode P2b is formed on the entire surface of the semiconductor electrode layer P2a, and then an unnecessary portion is formed using a photoresist film patterned in a predetermined shape by a photolithography technique as an etching mask. The metal electrode P2b can be formed into a predetermined shape by etching away.
The patterning of the transparent insulating film Ins, the reflective film R, the lower electrode P1, and the p-side bonding electrode P2c can also be performed by the same method.

(Dry etching)
By reactive ion etching using chlorine gas, the semiconductor electrode layer P2a, the p-type layer 4, and the light emitting layer 3 are partially removed from the surface side of the semiconductor electrode layer P2a, and as shown in FIG. The surface of the n-type layer 2 is exposed.

(Formation of transparent insulating film)
As shown in FIG. 3D, a transparent insulating film Ins made of SiO ₂ is formed on the surface of the semiconductor electrode layer P2a with the metal electrode P2b interposed therebetween. The broken line shown in FIG. 3D is the outline of the metal electrode P2b hidden under the transparent insulating film Ins, and the same applies to FIGS. 3E and 3F. For the formation of the transparent insulating film Ins, a known method for producing a SiO ₂ thin film such as CVD, sputtering, vapor deposition, sol-gel method, or the like can be appropriately used. In order to form the reflective film R in contact with the metal electrode P2b in a later step, the transparent insulating film Ins is provided with an opening through which the surface of the metal electrode P2b is exposed.

(Formation of reflective film)
As shown in FIG. 3E, a reflective film R is formed on the surface of the transparent insulating film Ins by appropriately using a known method for producing a metal thin film such as vapor deposition, sputtering, or CVD. The reflective film R is formed so as to be electrically connected to the metal electrode P2b in the opening formed in the transparent insulating film Ins. A dash-dot line shown in FIG. 3E is the outline of the opening hidden under the reflective film R, and the same applies to FIG.

(Formation of lower electrode)
As shown in FIG. 3F, a lower electrode P1 is formed on the surface of the n-type layer 2 exposed in the dry etching process by appropriately using a known metal thin film manufacturing method such as vapor deposition, sputtering, or CVD. To do.
Thereafter, although not shown, the upper surface side of the element is made to be SiO ₂ , Si ₃ N while leaving a part of the surface of the lower electrode P1 and the reflective film R that need to be exposed for electrode bonding. It is preferable to cover with an insulating protective film made of ₄ or the like. At this time, if the surface of the lower electrode P1 or the reflective film R to be covered with the insulating protective film is made of a metal that is difficult to oxidize, such as Au, before the insulating protective film is formed, If a Ti thin film or Ni thin film having a thickness of about 10 nm is formed, the adhesion with the insulating protective film is improved.

(Heat treatment)
In order to reduce the contact resistance between the electrode and the semiconductor, the entire wafer is heat-treated to promote adhesion between the electrode and the GaN-based semiconductor. Such heat treatment is a normal treatment performed when an ohmic electrode is formed on the surface of the semiconductor. The temperature and time of the heat treatment depend on the material of the electrode, but the temperature is 350 ° C. to 900 ° C., and the time is It can be 1 minute to 60 minutes.

(Element isolation)
The lower surface of the crystal substrate 1 is ground and / or polished so that the thickness is reduced to 100 μm or less, and then element isolation is performed by appropriately using a known element isolation method such as scribing, dicing, or laser fusing. .
The above is the manufacturing method of the GaN-based LED shown in FIG.

In the GaN-based LED shown in FIG. 1, one of the light traveling upward in the element by being reflected directly from the light emitting layer 3 or at the interface between the crystal substrate 1 and the n-type layer 2. The portion is reflected downward by the metal electrode P2b, but most of the remaining portion is incident on the interface between the p-type layer 4 and the semiconductor electrode layer P2a. Among these, light incident on this interface at an incident angle smaller than about 53 degrees enters the semiconductor electrode layer P2a. As described above, the light incident on the interface between GaN and ITO from the GaN side is totally reflected when the incident angle is larger than about 53 degrees.
Of the light that enters the semiconductor electrode layer P2a, light that enters the interface with the transparent insulating film Ins at an incident angle greater than about 49 degrees has a refractive index of SiO ₂ (about 1.5) that is refracted by ITO. Since it is about 75% of the rate, it is totally reflected at this interface according to Snell's law. Therefore, in consideration of the refraction generated at the interface between the p-type layer 4 and the semiconductor electrode layer P2a, the incident angle smaller than about 53 degrees from the p-type layer 4 to the interface between the p-type layer 4 and the semiconductor electrode layer P2a. Incident light enters the semiconductor electrode layer P2a, and light having an incident angle larger than about 36 degrees is totally reflected at the interface between the semiconductor electrode layer P2a and the transparent insulating film Ins. .

In the GaN-based LED shown in FIG. 1, unlike the conventional GaN-based LED shown in FIG. 10, the light incident on the interface between the p-type layer 4 and the semiconductor electrode layer P2a at an incident angle of about 36 degrees to about 53 degrees. Is not reflected by the metallic reflecting member (the reflecting layer P12b in the element of FIG. 10), but is totally reflected at the interface between the semiconductor electrode layer P2a and the transparent insulating film Ins, so that the light extraction efficiency is improved. . This is because the light absorption of SiO ₂ that is an insulator is small, the loss associated with the total reflection at the interface with the transparent insulating film Ins is smaller than the loss associated with the reflection on the surface of the metallic reflecting member, This is because it becomes smaller.
In view of the fact that multiple reflections are likely to occur inside the light emitting diode, reducing the loss due to light reflection inside the element has a great effect on improving the light extraction efficiency.

FIG. 4 is a schematic view showing a state where the GaN-based LED shown in FIG. 1 is flip-chip mounted on the surface of the mounting base material.
In FIG. 4, S is a mounting base material, and a pattern of lead electrodes S2 and S3 made of Au is formed on the mounting surface side of an insulating substrate S1 made of AlN or the like. In the GaN-based LED, the lower electrode P1 is bonded to the lead electrode S2 and the reflective film R is bonded to the lead electrode S3 with the conductive bonding material C, with the upper surface side facing the mounting surface of the mounting substrate S. It is fixed by. Here, the conductive bonding material C is, for example, a conductive paste in which a brazing material such as Au—Sn solder or conductive fine particles are dispersed in a resin binder.

  As described above, the present invention has been described based on the specific embodiment, but the present invention is not limited to the embodiment.

The crystal substrate used for the GaN-based LED according to the embodiment of the present invention may be a substrate applicable to the growth of a GaN-based semiconductor crystal and a transparent substrate that transmits light generated in the light-emitting layer, and sapphire Other examples include substrates made of SiC, GaN, ZnO, AlN, spinel, NGO, and the like. When an n-type semiconductor substrate made of SiC, GaN, ZnO or the like is used, a lower electrode can be formed on the lower surface of the crystal substrate, so that a step of exposing the n-type layer by dry etching is not necessary. In flip chip mounting, only the upper electrode needs to be fixed to the lead electrode of the mounting substrate with a conductive bonding material, and wire bonding can be performed on the lower electrode formed on the lower surface of the substrate. In the mounting process, a short circuit between the electrodes due to the conductive bonding material is less likely to occur, and an improvement in yield can be expected.
If a concavo-convex structure capable of scattering light generated in the light emitting layer is provided on the lower surface and / or the upper surface of the crystal substrate, the light extraction efficiency of the device is further improved.

  The GaN-based LED according to the embodiment of the present invention includes a stacked body in which an n-type layer, a light-emitting layer, and a p-type layer are sequentially stacked so that a pn junction type light-emitting element structure is formed. The thickness, impurity concentration, carrier concentration, and the like can be designed by appropriately referring to conventionally known techniques. Between the laminated body and the crystal substrate, or inside the laminated body, there is a function of relaxing the distortion of the crystal layer, a function of suppressing unwanted diffusion of impurities, a function of preventing the decomposition of the light emitting layer, and a light emitting layer. Layers having various functions other than the function of scattering the generated light can be provided as appropriate.

In the GaN-based LED according to the implementation of the present invention, the material of the semiconductor electrode layer may be an n-type semiconductor that transmits light generated in the light emitting layer, and in addition to ITO, indium oxide, tin oxide, zinc oxide, etc. Various oxide semiconductors exhibiting n-type conductivity can be used. An n-type GaN-based semiconductor can also be used. In the case of using an n-type GaN-based semiconductor, the growth of the semiconductor electrode layer can be performed in the same manufacturing apparatus by using the same method in succession to the growth of the p-type layer.
When the semiconductor electrode layer is formed of any material, it is desirable to increase the carrier concentration so that the junction barrier with the p-type layer becomes thin. In addition, a known structure for reducing the resistance of the semiconductor electrode layer, the p-type layer, and the bonding portion, such as interposing a transparent or island-shaped thin film made of a metal such as Au at the bonding interface, can be appropriately employed.

  In the GaN-based LED according to the embodiment of the present invention, the lower electrode and the metal electrode are Ni (nickel), Au (gold), Pt (platinum), Pd (palladium), Rh (rhodium), Ru (ruthenium), Os ( Osmium), Ir (iridium), Ti (titanium), Al (aluminum), Zr (zirconium), Hf (hafnium), V (vanadium), Nb (niobium), Ta (tantalum), Co (cobalt), Fe ( Iron, Mn (manganese), Mo (molybdenum), Cr (chromium), W (tungsten), La (lanthanum), Cu (copper), Ag (silver), Y (yttrium), etc. It is also possible to adopt a laminated structure. In addition, an oxide semiconductor layer can be interposed between the lower electrode and the n-type layer. The same applies to the case where the lower electrode is provided on the lower surface of the n-type semiconductor substrate.

The metal electrode is partially formed on the surface of the semiconductor electrode layer so that the semiconductor electrode layer and the transparent insulating film stacked with the metal electrode in between can be brought into contact with each other. In the element shown in FIG. 1, the metal electrode P2b is formed in a coarse lattice pattern, but the shape of the metal electrode is not limited to this, and may be another net pattern, stripe shape, comb shape, It may be formed in a radial shape, a ring shape, a meander shape, a spiral shape, a dendritic shape, or the like, or a pattern in which these are combined.
When the sheet resistance of the metal electrode pattern is high according to the sheet resistance of the semiconductor electrode layer, the sheet resistance is set so that the electrode film of the metal electrode is densely dispersed on the surface of the semiconductor electrode layer. When it is low, it is preferable to form the electrode film so as to be sparsely dispersed on the surface. This is because when the sheet resistance of the semiconductor electrode layer is high, it is necessary to supplement the current diffusion in the lateral direction with a metal electrode, whereas when the sheet resistance is low, this is not necessary, and light reflectivity is higher than that. This is because it is preferable to increase the area of the interface between the semiconductor electrode layer and the transparent insulating film.

  The film thickness of the metal electrode is not particularly limited, but it is desirable to form the film so as to generate sufficient light reflectivity in order to improve the light extraction efficiency of the element. Therefore, the film thickness of the metal electrode is preferably 30 nm or more, more preferably 50 nm or more, and particularly preferably 100 nm or more. When the film thickness is larger than a certain value, the effect is saturated, and when the film thickness is larger than that, the material is wasted. From this, the preferable film thickness of the metal electrode is 1 μm or less.

The thickness of the lower electrode may be any thickness as long as it can withstand the impact received during mounting and does not easily cause peeling, and can be, for example, 200 nm to 3 μm. It is also possible to select a thickness at which the upper surface of the lower electrode and the upper surface of the bonding electrode with respect to the upper electrode have substantially the same height.
In the lower electrode P1 of the element shown in FIG. 1, the uppermost layer portion is formed of Au having good wettability with the brazing material. When this Au causes an alloying reaction with Al contained in the lower layer portion, There is a risk that the characteristics of the lower electrode, and thus the characteristics of the element, will deteriorate. Therefore, in order to suppress this, Au is not directly laminated on Al, and a refractory metal (W, Mo, Zr, Ti, a simple substance selected from the platinum group or between the Al layer and the Au layer, or A layer made of Pt, which is one of those alloys, is interposed as a barrier layer.

  When the lower electrode or the metal electrode is configured to reflect the light generated in the light emitting layer, at least a portion of the electrode that reflects the light is reduced so that the loss due to the reflection is reduced. It is preferable to use Ag, Al, Rh, Pt, Ir, Pd, etc., which are metals having good light reflectivity. Ag and Al are the most preferable materials because they have a particularly high reflectance in a wavelength region from green to near ultraviolet, which is a typical emission wavelength of a GaN-based LED.

In the GaN-based LED according to the embodiment of the present invention, the material of the transparent insulating film may be any material that transmits light generated in the light emitting layer and whose refractive index is smaller than that of the semiconductor electrode layer. From the viewpoint of thermal and chemical stability, it is preferable to use an inorganic insulator. As such an inorganic insulator, various metal oxides and metal nitrides such as Al ₂ O ₃ , spinel, ZrO ₂ , TiO ₂ , Si ₃ N ₄ , and AlN can be used in addition to SiO ₂ . According to the material of the semiconductor electrode layer, a material having a smaller refractive index may be selected as appropriate.
The refractive index of the transparent insulating film is preferably 85% or less of the refractive index of the semiconductor electrode layer so that reflection due to the refractive index difference is sufficiently generated at the interface between the semiconductor electrode layer and the transparent insulating film, and 80% More preferably, it is more preferably 75% or less. SiO ₂ having a low refractive index is one of the most preferable materials for the transparent insulating film regardless of the material of the semiconductor electrode layer.

  The thickness of the transparent insulating film is not particularly limited as long as the effect of the present invention is produced, but when the light is totally reflected at the interface between the semiconductor electrode layer and the transparent insulating film, The thickness of the transparent insulating film is preferably 100 nm or more, more preferably 200 nm or more, and particularly preferably 300 nm or more so that the light that penetrates to the inside is less absorbed by the reflective film.

  The transparent insulating film may be formed so as to extend not only the upper surface portion of the semiconductor electrode layer but also partially extend the semiconductor electrode layer, the p-type layer, and the light emitting layer exposed by dry etching. . An example of a cross-sectional structure of the element according to such an embodiment is shown in FIG. In the element shown in FIG. 5, a part of the transparent insulating film Ins is formed to extend so as to cover the surface of the n-type layer 2 exposed by dry etching except for the portion where the lower electrode P1 is formed. Yes.

In the GaN-based LED according to the embodiment of the present invention, the reflection film may be a metal film having light reflectivity. When the film thickness is thinner than 20 nm, even a metal film exhibits a considerable light transmittance, and therefore the thickness of the reflective film is preferably 30 nm or more. A more preferable thickness of the reflective film is 50 nm or more, and a particularly preferable thickness is 100 nm or more. It is preferable that at least a portion of the reflective film that reflects light generated in the light emitting layer is formed of Ag, Al, Rh, Pt, Ir, Pd, or the like, which is a metal having good light reflectivity. Or it is preferable to form with Al.
When Ag or Al is used for the material of the metal electrode or the reflective film, it is preferable to use Ag or Al alone from the viewpoint of light reflectivity, but various elements may be added to improve chemical stability and heat resistance. An added Ag alloy or Al alloy can also be suitably used. Ag alloys and Al alloys with improved chemical stability and heat resistance without significantly impairing light reflectivity have been developed for wiring materials for various display devices such as liquid crystal display devices. An alloy or an Al alloy can be suitably used as a material for a metal electrode or a reflective film.

  Since the reflective film R of the element shown in FIG. 1 also serves as an electrode for bonding to the upper electrode, its uppermost layer portion is formed of Au having good wettability with the brazing material. On the other hand, since the lowermost layer portion is made of Al, Pt is not formed between the lowermost layer portion and the uppermost layer portion so that the light reflectivity of the reflective film R is not lowered by the alloying reaction between Al and Au. This layer is provided as a barrier layer.

The reflective film can be formed so as to be electrically connected to the lower electrode instead of the upper electrode, or integrally with the lower electrode. In that case, the reflective film can also be used as an electrode for bonding to the lower electrode.
6 (a) and 6 (b) are schematic views showing an example of the structure of a GaN-based LED according to such an embodiment, where FIG. 6 (a) is a top view and FIG. 6 (b) is FIG. 6 (a). It is sectional drawing in the XY line. In the element shown in FIG. 6, the reflective film R and the lower electrode P1 are integrally formed. However, a part of the transparent insulating film Ins is prevented so that the p-type layer side and the n-type layer side of the element are not short-circuited. Are extended so as to cover the end surfaces of the semiconductor electrode layer P2a, the p-type layer 4 and the light emitting layer 3 exposed by dry etching. In this embodiment, in order to reliably prevent a short circuit between the reflective film and the upper electrode separated by the transparent insulating film, the transparent insulating film is formed using a plasma CVD method in which pinholes are unlikely to occur. Is preferred.
In FIG. 6, P2c is a p-side bonding electrode that forms a part of the upper electrode, and is formed in contact with the metal electrode P2b at the position of the opening provided in the transparent insulating film Ins. The material of the p-side bonding electrode P2c is not particularly limited, but it is preferable that at least the surface portion is formed of Au, Sn, In or the like having good wettability with the brazing material.
Such an embodiment in which the reflective film and the lower electrode are connected or integrated is particularly suitable when Ag is used as the material of the reflective film. Ag is the metal having the best light reflectivity, but there is a problem in that it tends to cause electrochemical migration when placed in a high potential state, whereas in this embodiment, the reflective film is an electrode on the low potential side. This problem is alleviated because it is connected to a certain lower electrode.

  A part of the reflective film can be connected to or integrated with the lower electrode, and the other part can also be used as a bonding electrode for the upper electrode. An example of the structure of a GaN-based LED according to such an embodiment is schematically shown in FIG. 7A is a top view of the element, and FIG. 7B is a cross-sectional view taken along line XY in FIG. 7A. In the element shown in FIG. 7, the reflective film R1 is formed integrally with the lower electrode P1, and the reflective film R2 also serves as an electrode for bonding to the upper electrodes P2a and P2b.

The reflective film can also be formed independently of either the lower electrode or the upper electrode. A structural example of a GaN-based LED according to such an embodiment is schematically shown in FIG. 8A is a top view of the element, and FIG. 8B is a cross-sectional view taken along line XY in FIG. 8A.
In FIG. 8A, the broken line indicates the outline of the metal electrode P2b hidden under the reflective film R and the transparent insulating film Ins. The metal electrode P2b is composed of a rectangular portion on which the p-side bonding electrode P2c is stacked, and two stripe-shaped portions extending from the rectangular portion.

In the GaN-based LED according to one embodiment of the present invention, the crystal substrate used for the growth of the GaN-based semiconductor layer is finally removed from the device. An example of the structure and manufacturing process of a GaN-based LED according to such an embodiment will be described with reference to FIG. FIGS. 9A to 9C are cross-sectional views, and for convenience, only a region corresponding to one element is displayed. However, a process before element separation is performed in a wafer state.
In FIG. 9A, an n-type layer 2, a light emitting layer 3, and a p-type layer 4 are sequentially grown on the growth surface of the crystal substrate 1, and further, a semiconductor electrode layer P2a, a metal electrode P2b, a transparent insulating film Ins, The place where the reflective film R is formed is shown. The structure of each part is the same as that which can be adopted in the embodiment in which the crystal substrate is not removed.
FIG. 9B shows a state where the holding substrate B is bonded onto the reflective film R via a conductive bonding material (not shown). The conductive bonding material is, for example, a brazing material or a conductive paste. The holding substrate B may be any conductive substrate, and various semiconductor substrates and metal substrates can be used. By bonding the holding substrate B, the wafer and the element can be handled by a normal method even after the crystal substrate 1 is removed. Instead of bonding the holding substrate B with a conductive bonding material, a thick film of a metal such as Ni can be deposited on the surface of the reflective film R by plating, and this can be used as the holding substrate B.
FIG. 9C shows that the crystal substrate 1 is removed and the lower electrode P1 is formed on the exposed surface of the n-type layer 2. The crystal substrate 1 can be removed using a conventionally known technique. For example, the crystal substrate 1 is peeled off from the n-type layer 2 using a method of abrasion of the crystal substrate 1 by grinding or polishing, or a laser lift-off technique. A method of causing the crystal substrate 1 to disappear by selectively dissolving the crystal substrate 1 itself or a buffer layer (not shown) formed in advance between the crystal substrate 1 and the n-type layer 2; Alternatively, a method of peeling from the n-type layer 2 can be used. The surface of the n-type layer 2 exposed by removing the crystal substrate 1 is cleaned by polishing or etching as necessary before forming the lower electrode P1. Thereafter, element isolation is performed using a conventionally known method.
When the laser lift-off technique is used, an element manufactured by a normal method can be flip-chip mounted without removing the crystal substrate, and then the crystal substrate can be peeled off from the mounted element.

It is a figure explaining the structure of the GaN-type light emitting diode which concerns on embodiment of this invention. It is a figure explaining the manufacturing process of the GaN-type light emitting diode shown in FIG. It is a figure explaining the manufacturing process of the GaN-type light emitting diode shown in FIG. It is a figure explaining the flip-chip mounting example of the GaN-type light emitting diode which concerns on embodiment of this invention. It is a figure explaining the structure of the GaN-type light emitting diode which concerns on embodiment of this invention. It is a figure explaining the structure of the GaN-type light emitting diode which concerns on embodiment of this invention. It is a figure explaining the structure of the GaN-type light emitting diode which concerns on embodiment of this invention. It is a figure explaining the structure of the GaN-type light emitting diode which concerns on embodiment of this invention. It is a figure explaining the structure and manufacturing process of the GaN-type light emitting diode which concern on embodiment of this invention. It is a figure which shows the structure of the GaN-type light emitting diode which concerns on a prior art.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Crystal substrate 2 n-type GaN-type semiconductor layer 3 Light emitting layer 4 p-type GaN-type semiconductor layer P1 Lower electrode P2a Semiconductor electrode layer P2b Metal electrode P2c P side bonding electrode Ins Transparent insulating film R Reflective film

Claims (8)

a laminate including an n-type GaN-based semiconductor layer, a light-emitting layer made of a GaN-based semiconductor, and a p-type GaN-based semiconductor layer in this order;
A semiconductor electrode layer formed on the surface of the p-type GaN-based semiconductor layer and made of an n-type semiconductor that transmits light generated in the light-emitting layer;
A metal electrode partially formed on the surface of the semiconductor electrode layer;
A transparent insulating film having a refractive index lower than that of the semiconductor electrode layer formed on the surface of the semiconductor electrode layer with the metal electrode interposed therebetween;
A metal reflective film formed on the surface of the transparent insulating film;
A GaN-based light emitting diode having:   The GaN-based light emitting diode according to claim 1, wherein the semiconductor electrode layer is made of an oxide semiconductor.   The GaN-based light emitting diode according to claim 2, wherein the oxide semiconductor is ITO.   The GaN-based light-emitting diode according to claim 1, wherein the semiconductor electrode layer is made of a GaN-based semiconductor. The GaN-based light-emitting diode according to claim 1, wherein the transparent insulating film is made of SiO ₂ .   The GaN-based light emitting diode according to any one of claims 1 to 5, wherein a portion of the reflective film that reflects light generated in the light emitting layer is made of Ag or Al.   The GaN-based light emitting diode according to claim 1, wherein the metal electrode has a portion made of Ag or Al that reflects light generated in the light emitting layer. A light-emitting device comprising a mounting substrate and the GaN-based light-emitting diode according to claim 1 mounted on the surface thereof in a flip-chip manner.

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