KR100895452B1 - Positive electrode for semiconductor light-emitting device - Google Patents

Abstract

An object of the present invention is to provide a transparent positive electrode used in a face-up chip that can emit strong light even with a low driving voltage. The positive electrode for a semiconductor light emitting device of the present invention comprises a transparent electrode formed on a semiconductor layer and a bonding pad electrode formed on the transparent electrode, wherein the bonding pad electrode has a reflective layer at least in contact with the transparent electrode.

Description

Positive electrode for semiconductor light emitting device {POSITIVE ELECTRODE FOR SEMICONDUCTOR LIGHT-EMITTING DEVICE}

(Cross-reference of related applications)

This application claims 35 U.S.C. In accordance with § 111 (b), the benefit of the date of filing of Provisional Application No. 60 / 599,571, filed August 9, 2004, is 35 U.S.C. An application filed under 35 U.S.C. § 111 (a), alleging under §119 (e) (1).

The present invention relates to a positive electrode for a semiconductor light emitting device, and more particularly to a transparent positive electrode suitable for a gallium nitride compound semiconductor light emitting device capable of emitting strong light at a low driving voltage.

In recent years, GaN-based compound semiconductor materials have attracted interest as semiconductor materials used for short wavelength light emitting devices. The GaN compound semiconductor is formed on a substrate (for example, an oxide single crystal such as sapphire single crystal or a group III-V compound single crystal) by a technique such as organometallic chemical vapor deposition (MOCVD) or molecular beam deposition (MBE).

One characteristic characteristic of GaN-based compound semiconductor materials is that current spreading in a direction parallel to the light emitting surface is small. This lack of current diffusion may be due to the presence of a large number of penetrating potentials present throughout the epitaxial crystal from the bottom (substrate side) to the top surface. However, the reason has not yet been elucidated. On the other hand, p-type GaN-based compound semiconductors have higher resistivity than n-type GaN-based compound semiconductors. Therefore, when the metal layer is laminated on the surface of the p-type GaN based compound semiconductor layer, current diffusion does not occur in a direction substantially parallel to the p-type layer. Therefore, when the LED structure is manufactured by the pn junction of such a semiconductor, light emission is limited only to the portion directly under the positive electrode.

In order to overcome the above drawbacks, transparent positive electrodes for extracting light emitted directly under the positive electrode are generally used. Specifically, in one proposed technique used in commercially available transparent electrode products, a plurality of Ni and Au layers each having a thickness of several tens of nm are laminated on a p-type layer to form a laminated layer, and the layer contains oxygen. By heating and alloying in the atmosphere, the resistance of the p-type layer is promoted, and at the same time, a positive electrode having good transparency and ohmic characteristics is formed (see Japanese Patent No. 2803742).

The transparent electrode is made from a material such as a conductive metal oxide or an ultrathin metal film. Direct bonding is difficult with such materials or structures. Therefore, in general, a bonding pad electrode having a sufficient thickness is positioned so that electrical contact is made between the pad electrode and the transparent electrode. However, because of its relatively large thickness, the metal pad electrode does not exhibit transparency and becomes a problem because it cannot extract light emitted from the portion directly under the pad electrode to the outside.

In the structure of the prior art for improving the adhesion of the pad electrode, the transparent electrode is partially cut and the pad electrode is formed to crosslink with the neighboring transparent electrode, whereby the bonding strength is improved by the portion in direct contact with the GaN semiconductor layer, Current spreading occurs at the part in contact with the transparent electrode (see Japanese Patent Application Laid-Open No. 7-94782).

As described above, since light emitted from a portion directly below the pad electrode cannot be extracted to the outside, techniques for efficiently using current that do not emit light in the portion through suppression of current injection into the portion directly below the pad electrode are provided. Developed.

Specifically, some techniques have been disclosed in which the injection of current directly under the pad is suppressed by the formation of an insulating region directly below the pad electrode (see Japanese Patent Laid-Open Nos. 8-250768 and 8-250769). . Also disclosed is a technique of suppressing current injection into a portion directly below the pad electrode in which the lowest layer of the pad electrode is formed of a metal having a high contact specific resistance with respect to the p-type layer (see Japanese Patent Application Laid-open No. Hei 10-242516).

However, from the research conducted by the present inventors, it has been found that using any of the above techniques has a problem of increasing the driving voltage by reducing the ohmic contact area of the positive electrode with respect to the p-type layer.

SUMMARY OF THE INVENTION The present invention has been made to solve the above problems, and an object of the present invention is to provide a transparent positive electrode for use in a face-up chip that emits strong light even when a low driving voltage is used. As used herein, the term "transparency" refers to transparency to light having a wavelength in the luminescent wavelength region. In the case of a gallium nitride-based light emitting device, the light emission wavelength region is generally 300 to 600 nm.

The present invention provides the following.

(1) An electrode comprising a transparent electrode formed on a semiconductor layer and a bonding pad electrode formed on the transparent electrode, wherein the bonding pad electrode has at least a reflective layer in contact with the transparent electrode.

(2) In the positive electrode for semiconductor light emitting element according to (1), the adhesion strength between the reflective layer and the transparent electrode is 490 mN (50 gf) or more in terms of peel strength.

(3) In the positive electrode for semiconductor light emitting device according to (1) or (2), the transparent electrode has a transmission rate of 60% for light having a wavelength in the light emitting wavelength region of the semiconductor light emitting device.

(4) The positive electrode for semiconductor light emitting element according to any one of (1) to (3), wherein the reflecting layer contains at least one metal of Al, Ag, and Pt group metals, and Al, Ag, and Pt group metals. It consists of a metal selected from the group consisting of alloys.

(5) The positive electrode for semiconductor light emitting element according to any one of (1) to (4), wherein the semiconductor light emitting element is a gallium nitride compound semiconductor light emitting element.

(6) The positive electrode for semiconductor light emitting element according to any one of (1) to (5), wherein the reflective layer is made of Al, Ag, Pt, and an alloy containing at least one metal of Al, Ag, and Pt. It is made of a metal selected from the group.

(7) The positive electrode for semiconductor light emitting element according to any one of (1) to (6), wherein the reflective layer has a thickness of 20 to 3,000 nm.

(8) The positive electrode for semiconductor light emitting element according to any one of (1) to (7), wherein the bonding pad electrode has a layer structure and a barrier layer made of Ti, Cr or Al and / or Au in addition to the reflective layer. It includes the top layer made of Al.

(9) The positive electrode for semiconductor light emitting element according to any one of (1) to (8), wherein the transparent electrode includes a layer made of metal on the bonding pad electrode side.

(10) The positive electrode for semiconductor light emitting element according to any one of (1) to (8), wherein the transparent electrode includes a layer made of a transparent material on the bonding pad electrode side.

(11) In the positive electrode for semiconductor light emitting element according to (10), the transparent electrode is made of only conductive transparent material other than metal.

(12) In the positive electrode for semiconductor light emitting element according to any one of (1) to (11), a step of extracting emitted light from the uppermost surface of the transparent electrode is performed.

(13) In the positive electrode for semiconductor light emitting element according to (12), the uppermost surface of the transparent electrode is formed of a transparent material.

(14) The positive electrode for semiconductor light emitting element according to any one of (1) to (13), wherein the transparent electrode has a contact layer in contact with the p-type semiconductor layer and a current diffusion layer formed on the contact layer.

(15) The positive electrode for semiconductor light emitting element according to (14), wherein the contact layer is made of a platinum group metal or an alloy thereof.

(16) The positive electrode for semiconductor light emitting element according to (15), wherein the contact layer is made of platinum.

(17) The positive electrode for semiconductor light emitting element according to any one of (14) to (16), wherein the contact layer has a thickness of 0.1 to 7.5 nm.

(18) The positive electrode for semiconductor light emitting element according to (17), wherein the contact layer has a thickness of 0.5 to 2.5 nm.

(19) The positive electrode for semiconductor light emitting element according to any one of (14) to (18), wherein the current spreading layer is a metal selected from the group consisting of gold, silver and copper, or at least one of gold, silver and copper. It consists of an alloy containing metal.

(20) The positive electrode for semiconductor light emitting element according to (19), wherein the current spreading layer is made of gold or gold alloy.

(21) The positive electrode for semiconductor light emitting element according to any one of (14) to (20), wherein the current spreading layer has a thickness of 1 to 20 nm.

(22) In the positive electrode for semiconductor light emitting element according to (21), the current spreading layer has a thickness of 3 to 6 nm.

(23) The positive electrode for semiconductor light emitting element according to any one of (14) to (18), wherein the current spreading layer is made of a conductive transparent material.

(24) The positive electrode for semiconductor light emitting element according to any one of (10), (11), (13) or (23), wherein the transparent material is made of ITO, zinc oxide, zinc oxide, F-doped tin oxide. At least one material selected from the group consisting of titanium oxide, zinc sulfide, bismuth oxide and magnesium oxide.

(25) The positive electrode for semiconductor light emitting element according to (24), wherein the transparent material is at least one material selected from the group consisting of ITO, zinc oxide, zinc oxide, and F-doped tin oxide.

(26) The positive electrode for semiconductor light emitting element according to any one of (10), (11), (13), (23) to (25), wherein the transparent material has a thickness of 10 to 5,000 nm.

(27) In the positive electrode for semiconductor light emitting element according to (26), the transparent material has a thickness of 100 to 1,000 nm.

(28) A semiconductor light emitting element using the positive electrode according to any one of (1) to (27).

(29) substrates; An n-type semiconductor layer, a light emitting layer, and a p-type semiconductor layer, which are sequentially stacked on the substrate and made of a gallium nitride compound semiconductor layer; A positive electrode formed on the p-type semiconductor layer; And a negative electrode formed on the n-type semiconductor layer, wherein the positive electrode is a gallium nitride compound semiconductor light emitting device according to any one of (1) to (27).

(30) A lamp using the light emitting element according to the above (28) or (29).

According to the present invention, at least a reflective layer in contact with the transparent electrode is formed on the coupling pad electrode through which current flows to the transparent electrode, and thus the light attenuates due to light absorption at the interface between the coupling pad electrode and the transparent electrode. Can be reduced. Therefore, the extraction efficiency and the intensity of the emitted light can be improved.

1 is a schematic cross-sectional view of a light emitting device using the positive electrode of the present invention. Reference numeral 10 denotes a positive electrode of the present invention consisting of a transparent electrode 11 and a bonding pad electrode 13. The transparent electrode 11 is made of, for example, a contact layer 111 and a current spreading layer 112. The bonding pad electrode 13 is made of, for example, a reflective layer 131, a barrier layer 132, and an uppermost layer 133; That is, it has a three layer structure. Reference numeral 1 denotes a substrate, 2 denotes a GaN compound semiconductor layer composed of an n-type semiconductor layer 3, a light emitting layer 4 and a p-type semiconductor layer 5, and 6 denotes a buffer layer. , 20 denotes a negative electrode.

In a face-up chip having a transparent positive electrode, light emitted from the light emitting layer 4 is extracted only through the transparent electrode which is not covered with the side of the chip and the bonding pad electrode.

With the use of the positive electrode of the present invention, the light emitted toward the bonding pad electrode 13 is reflected by the reflective layer as the bottom surface of the bonding pad electrode (ie, the surface in contact with the transparent electrode). Some reflected light rays are scattered in the transverse direction or diagonal direction, and the remaining light rays are reflected directly below the coupling pad electrode. The light scattered in the transverse or oblique direction is extracted to the outside through the side of the chip, while the light reflected directly below the bonding pad electrode is scattered or reflected by the bottom of the chip, and the side of the chip and the transparent electrode It is extracted through the part (not covered by the bonding pad electrode).

The reflective layer as the lowest layer of the bonding pad electrode thus formed allows light emitted directly under the bonding pad electrode to be extracted to the outside, thereby obtaining high emission intensity. In contrast, when the lowest layer of the bonding pad electrode absorbs light, light emitted directly under the bonding pad electrode is almost absorbed by the lowest layer of the pad electrode and is not extracted to the outside.

In order to secure the effects of the present invention, the reflective layer needs to be in direct contact with the transparent electrode. As a result, the reflective layer needs to be strongly adhered to the transparent electrode so that the bonding pad electrode has sufficient strength. The bonding pad electrode should not be peeled from the transparent electrode in the step of connecting the gold wire to the bonding pad electrode in a conventional manner. Therefore, the adhesion strength of the reflective layer and the transparent electrode is preferably 490 mN (50 gf) or more in terms of peel strength. Peel strength is more preferably 784mN (80gf), the peel strength of 980mN (100gf) or more is most preferred. In order to improve the adhesion strength between the reflective layer and the transparent electrode, for example, there are methods of pretreating the surface of the transparent electrode or performing heat treatment after forming the reflective layer.

The reflectance of the reflective layer varies depending on the material forming the reflective layer, and is preferably at least 60%, more preferably at least 80%, even more preferably at least 90%.

Reflectance can be easily measured using a device such as a spectrophotometer. However, since the electrode itself has a very small surface area, it is difficult to measure the reflectance of the bonding pad electrode. Thus, in an alternative method, for example, a glass transparent dummy substrate made of glass is provided to the chamber when the bonding pad electrode is formed, thereby forming the bonding pad electrode on the dummy substrate. The reflectance of the bonding pad electrode on the dummy substrate is measured.

The reflective layer of the bonding pad electrode is preferably formed of a metal having high reflectance. Specifically, the reflective layer may be a platinum group metal such as Pt, Rh, Ru, or Ir; Al; Ag; Or an alloy containing at least one metal element selected from these metals. Among these metals, alloys containing Al, Ag, Pt, and at least one metal element selected from these metals are generally used as the electrode material, and are preferable in view of availability and ease of handling.

The bonding pad electrode is formed directly on the transparent electrode without the formation of openings or windows therein. When the bond pad electrode is formed on the transparent electrode, the ohmic contact area is not reduced, so that the contact resistance of the electrode does not rise in part even under the bond pad electrode. Thus, an increase in driving voltage can be prevented. In addition, the light passing through the transparent electrode is reflected by the reflective layer as the lowest surface of the bonding pad electrode, whereby excess light absorption can be suppressed.

The bonding pad electrode may be formed at any position on the transparent electrode. For example, the bonding pad electrode may be formed at a position furthest from the negative electrode or at the center of the chip. However, the bond pad electrode formed at a position excessively close to the negative electrode is not preferable because a short circuit may occur between the wire or the ball at the time of joining.

The bonding pad electrode preferably has the largest surface area possible to facilitate the bonding operation. However, as the surface area increases, extraction of emitted light is inhibited. As a result, the output of the chip is considerably lowered. For example, when more than half of the surface area of the chip is covered by the pad electrode, the extraction of the emitted light is inhibited and the output is considerably lowered. On the other hand, when the surface area of the pad electrode is too small, the coupling operation becomes difficult and the production yield is reduced. . Therefore, the surface area of the pad electrode is preferably slightly larger than the diameter of the coupling ball. In general, the pad electrode has a circular plan view with a diameter of about 100 μm.

When the reflective layer of the bonding pad electrode is formed of a high reflectance metal, the thickness of the reflective layer is preferably 20 to 3,000 nm. If the reflecting layer is excessively thin, sufficient reflection cannot be achieved, while if the thickness is excessively thick, the time required for forming the reflecting layer is long, thereby increasing the cost of the material; That is no advantage. More preferably, the thickness is 50 to 1,000 nm, most preferably 100 to 500 nm.

The bonding pad electrode may be formed only of the high reflectance metal. In other words, the bonding pad electrode may consist only of a reflective layer. On the other hand, coupling pad electrodes of various materials and structures are already known. Thus, the reflective layer may be provided on the semiconductor layer side (ie, transparent electrode side) of any known bonding pad electrode. Alternatively, the lowest layer (semiconductor layer side) of any known bonding pad electrode may be replaced with the reflective layer.

In the case of the laminated structure of the bonding pad electrodes, without any particular limitation on the stacked portion on the reflective layer, an appropriate portion of any structure can be used. In the laminated bonding pad electrode, the layer formed on the reflective layer serves to improve the strength of the entire bonding pad electrode. Therefore, this layer must be formed of a metal material having a relatively high strength or must be thick enough. In this respect, Ti, Cr, and Al are preferred materials. Among them, Ti is preferable in view of material strength. When the layer strengthens the bond pad electrode, the layer is called a "barrier layer".

The reflective layer may also be a barrier layer. If the reflective layer is formed of a metal material having high reflectivity and high strength and is thick, no additional barrier layer needs to be formed. For example, when the reflective layer is formed of Al, no barrier layer is necessary.

The barrier layer preferably has a thickness of 20 to 3,000 nm. If the barrier layer is excessively thin, the effect of improving strength is insufficient, while if the layer is excessively thick, no special advantage is obtained, and only an increase in cost occurs. More preferably, the thickness is 50 to 1,000 nm, most preferably 100 to 500 nm.

The uppermost layer (opposite side of the reflection layer) of the bonding pad electrode is preferably formed of a material that firmly bonds to the bonding ball. Bonding balls are generally made of gold, and Au and Al are known to have excellent bonding performance to metal bonding balls. Among these, gold is particularly preferred. The uppermost layer preferably has a thickness of 50 to 1,000 nm, more preferably 100 to 500 nm. If the top layer is too thin, the bonding performance to the bonding balls is insufficient, while if the layer is too thick, no special advantage is obtained, only the cost increases.

The transparent electrode formed on the p-type semiconductor layer satisfies the performance requirements. Examples of preferred performances include low contact resistance with the p-type layer, excellent optical transmittance (when the light emitting element is a face-up-mount type in which light emitted from the light emitting layer is extracted through the electrode side), P-type layers include those having excellent conductivity for uniform diffusion currents.

Transparent electrodes of various materials and structures are already known, and any known transparent electrode can be used in the present invention without limitation. However, in order to meet the above performance requirements, the transparent electrode preferably has at least two layers; That is, it has a structure including a contact layer in contact with the p-type layer and a current spreading layer formed on the contact layer and promoting current spreading. If the performance requirements are met, one layer with the performance of both contact layer and current spreading layer can be used. If a single layer structure is used, the manufacturing process has the advantage of being less complex.

The contact layer is required to have a low contact resistance to the p-type layer. In this respect, the contact layer is preferably formed of a platinum group metal such as platinum (Pt), ruthenium (Ru), osmium (Os), rhodium (Rh), iridium (Ir), or palladium (Pd) or an alloy thereof. Do. Of these, Pt and Pt alloys are particularly preferable because they have a high work function for a p-type GaN compound semiconductor layer having a relatively high resistance without high temperature heat treatment, and can realize excellent ohmic contact without any heat treatment. to be.

If the contact layer is formed of a platinum group metal or an alloy thereof, the layer thickness should be considerably reduced in view of optical transparency, and preferably 0.1 to 7.5 nm. When the thickness is 0.1 nm or less, such a thin film is not formed reliably, while when the thickness exceeds 7.5 nm, the transparency is reduced. More preferably, the thickness is 5 nm or less. In consideration of the transparency due to the continuous lamination of the current diffusion layer and the deterioration of the stability of the formed film, the thickness is particularly preferably 0.5 to 2.5 nm.

However, when the thickness of the contact layer is reduced, the electrical resistance of the contact layer increases in the plane direction, and current spreading is limited to the periphery of the bonding pad electrode as the current injection because of the relatively high resistance of the p-type layer. As a result, the uniformity of the light emission pattern is reduced and the light emission output is lowered.

When a current diffusion layer having a high light transmittance and a high conductivity as a means for promoting the current diffusivity of the contact layer is disposed on the contact layer, uniform diffusion of current does not significantly impair the low contact resistance and light transmittance of the platinum group metal. It can be realized, a light emitting device of high output can be manufactured.

The current spreading layer is a metal material having high conductivity, for example, a metal selected from the group consisting of gold, silver and copper; Or an alloy containing at least one of these metals. Among them, gold is most preferred because the thin film exhibits high light transmittance.

Alternatively, the current spreading layer may be formed of a transparent material having high conductivity such as zinc sulfide and a metal oxide such as ITO, zinc oxide, zinc oxide, F-doped tin oxide, titanium oxide, bismuth oxide, and magnesium oxide. . Such a transparent material is preferable in view of high light transmittance. Among them, ITO, zinc oxide, zinc oxide aluminum and F-doped tin oxide are most preferred because they are known to have conductivity.

When the current spreading layer is formed of a metal, the layer thickness is preferably 1 to 20 nm. When the thickness is less than 1 nm, the current diffusion effect is bad, whereas when the thickness exceeds 20 nm, the optical transparency of the current diffusion layer is significantly lowered, so that the light emission output may be reduced. More preferably, the thickness is 10 nm or less. In addition, when the thickness is adjusted to 3 to 6 nm, the current diffusion layer balances optical transparency and current diffusion effect. Through the combination of the current diffusion layer and the contact layer described above, uniform light emission can be achieved over the entire surface of the positive electrode having a high light emission output.

When the current spreading layer is formed of a transparent material, the thickness of the layer is preferably 10 to 5,000 nm. When the thickness is less than 10 nm, the current diffusion effect is bad, whereas when the thickness exceeds 5,000 nm, the optical transparency of the current diffusion layer is significantly lowered, so that the light emission output may be reduced. More preferably, the thickness is 50 to 2,000 nm. In addition, when the thickness is adjusted to 100 to 1,000 nm, the current diffusion layer balances optical transparency and current diffusion effect. Through the combination of the current diffusion layer and the contact layer described above, uniform light emission can be achieved over the entire surface of the positive electrode having a high light emission output.

When the bonding pad electrode is formed on the transparent electrode, the uppermost layer of the transparent electrode may be coated with metal or metal oxide.

The uppermost layer of the transparent electrode may be a current diffusion layer, or the current diffusion layer may be applied as a layer for bonding the bonding pad electrode. Since the formation of a layer for bonding impairs transparency, it is preferable that the uppermost layer is a current spreading layer.

The process for extracting luminescence can be carried out on the top surface of the transparent electrode. In this process, for example, recesses and / or protrusions are formed on the uppermost surface of the transparent electrode. The recesses and / or convexities may be formed using patterning or by wet treatment. There are no particular restrictions on the shape of the recesses and / or the convexities, and known forms such as stripes, gratings and dots can be used.

In addition, when the bonding pad electrode is formed on the surface having such concave and / or convex portions, the adhesion strength of the reflective layer and the transparent electrode can be improved.

There is no particular limitation on the method of forming the contact layer, the current spreading layer and the bonding pad electrode, and a known method such as vacuum deposition or sputtering can be used.

The positive electrode of the present invention is, for example, a substrate; A gallium nitride system such as an element as shown in FIG. 1 including a gallium nitride compound semiconductor layer (i.e., an n-type semiconductor layer, a light emitting layer, and a p-type semiconductor layer) laminated on a substrate by mediation of a buffer layer. It can be applied to a conventionally known semiconductor light emitting device including a compound semiconductor light emitting device.

The material of the substrate is not particularly limited, and the substrate may be formed of a known material. Examples of known materials include sapphire single crystal (Al ₂ O ₃ ; A-plane, C-plane, M-plane, or R-plane), spinel single crystal (MgAl ₂ O ₄ ), ZnO single crystal, LiAlO ₂ Oxidized single crystals such as single crystal, LiGaO ₂ single crystal, and MgO single crystal; Si single crystal; SiC single crystal; GaAs single crystal; AlN single crystal; GaN single crystal; And boride single crystals such as ZrB ₂ single crystal. There is no particular limitation on the crystal orientation of the substrate. The crystal surface of the substrate may or may not be inclined with respect to the specific crystal surface.

There is no particular limitation on the structures of the n-type semiconductor layer, the light emitting layer, and the p-type semiconductor layer, and these layers may have various known structures. The p-type semiconductor layer may have a usual carrier concentration. In particular, the transparent electrode of the present invention may be applied to a p-type semiconductor layer having a low carrier concentration (for example, about 1 × 10 ¹⁷ cm ⁻³ ).

In the present invention, there is no particular limitation on the gallium nitride compound semiconductor type for forming the n-type semiconductor layer, the light emitting layer, and the p-type semiconductor layer, and the general formula Al _x In _y Ga _{1 -xy} N (0 ≦ x < A conventionally known semiconductor represented by 1, 0 ≦ y <1, 0 ≦ x + y <1 can be used.

There is no particular limitation on the method for growing these gallium nitride semiconductors, and there are known methods for growing group III nitride semiconductors such as MOCVD (organic metal chemical vapor deposition), HVPE (hydrogen compound vapor deposition), or MBE (molecular beam growth method). Any method of may be used. MOCVD is preferably used in view of layer thickness controllability and mass productivity. In the case of MOCVD, hydrogen (H ₂ ) or nitrogen (N ₂ ) is used as the carrier gas, trimethylgallium (TMG) or triethylgallium (TEG) is used as the Ga (Group III element) source, and trimethylaluminum (TMA ) Or triethylaluminum (TEA) is used as the Al (group III element) source, trimethylindium (TMI) or triethylindium (TEI) is used as the In (group III element) source, ammonia (NH ₃ ), hydrazine (N ₂ H ₄ ) and the like are used as the N (Group V element) source. In addition, a monosilane (SiH ₄ ) or a disilane (Si ₂ H ₆ ), which is a Si source, or a Germanic (GeH ₄ ) or an organic Germanic compound, which is a Ge source, is used as an n-type dopant, while bis (cyclopentadienyl, which is an Mg source) is used. Magnesium (Cp ₂ Mg) or bis (ethylcyclopentadienyl) magnesium ((EtCp) ₂ Mg) is used as the p-type dopant.

In order to bring the negative electrode into close contact with the n-type semiconductor layer, the negative electrode is brought into close contact with a gallium nitride compound semiconductor structure including a substrate and an n-type semiconductor layer, a light emitting layer, and a p-type semiconductor layer continuously formed on the substrate. A portion of and a portion of the p-type semiconductor layer are removed to expose the n-type semiconductor layer. Then, the positive electrode of the present invention is formed on the remaining p-type semiconductor layer, and the negative electrode is formed on the exposed n-type semiconductor layer. There is no particular limitation on the composition and structure of the negative electrode, and a known negative electrode may be used.

When substrates such as sapphire and SiC that have a wavelength within the emission wavelength range and are transparent to light are used, a reflective film can be formed on the back surface of the substrate. When the reflective film is formed, the loss of light emission at the bottom of the substrate can be reduced. Therefore, the extraction efficiency of the emitted light can be further improved.

In addition, processing may be performed to form the concave portion and / or the convex portion on the surface of the semiconductor or the transparent electrode or on the back surface of the substrate. As a result, the extraction efficiency of the emitted light can be further improved. By the above processing, not only the surface perpendicular to the substrate but also the inclined surface can be formed. In order to prevent multiple reflections, an inclined surface is preferably formed. The processing can be performed by grinding the surface of the semiconductor or the transparent electrode or the back surface of the substrate. Alternatively, the processing can be carried out by attaching a structure of transparent material.

With respect to the semiconductor light emitting device, the gallium nitride compound semiconductor light emitting device exhibiting high emission intensity can be manufactured by using the positive electrode of the present invention. In other words, a high brightness LED can be manufactured based on the above technique. Therefore, electronic devices such as mobile phones and display panels using chips manufactured on the basis of the above technology; and machines and devices such as automobiles, computers, and game machines using electronic devices, respectively, can operate at low power and are excellent. Characteristics can be realized. In particular, significant power savings are obtained in battery powered cell phones, game machines, toys and automotive parts.

1 is a schematic cross-sectional view of a light emitting device using the positive electrode of the present invention.

2 is a schematic cross-sectional view of a gallium nitride compound semiconductor light emitting device manufactured in Example using the positive electrode of the present invention.

3 is a schematic plan view of a gallium nitride compound semiconductor light emitting device prepared in Example using the positive electrode of the present invention.

Hereinafter, the present invention will be described in more detail by examples, but the present invention is not limited thereto.

<Example 1>

FIG. 2 is a sectional view of a gallium nitride based semiconductor light emitting device manufactured in this embodiment, and FIG. 3 is a plan view thereof. A gallium nitride compound semiconductor laminate structure is manufactured through the following process. An AlN buffer layer 6 was formed on the sapphire substrate 1, and the following layers were successively formed on the buffer layer: an undoped GaN base layer (thickness: 8 mu m) 3a; Si-doped n-type GaN contact layer (thickness: 2 mu m) (3b); n- type In _{0 .1} Ga _{0 .9} N cladding layer (thickness: 250㎚) (3c); Light-emitting layer of multiple quantum well structure comprising Si-doped GaN barrier layer (5 layers and one final layer, each thickness: 16 nm) and In _0.2 Ga _0.8 N well layer (5 layers, each thickness: 2.5 nm) ); Mg-doped p-type Al _0.07 Ga _0.93 N clad layer (thickness: 0.01 mu m) (5a); And a Mg-doped p-type GaN contact layer (thickness: 0.15 mu m) (5b). The positive electrode 10 of the present invention was formed on the p-type GaN contact layer of the gallium nitride compound semiconductor stacked structure, and the positive electrode was a Pt contact layer (thickness: 1.5 nm) 111 and an Au current diffusion layer (thickness: 5 nm) (112); transparent electrode 11; and Pt layer (thickness: 50 nm) 13a, Ti layer (thickness: 20 nm) 13b, Al layer (thickness: 10 nm) (13c) ), Ti layer (thickness: 100 nm) (13d), and Au layer (thickness: 200 nm) (13e). Of the five layers forming the bonding pad electrode, a Pt layer (thickness: 50 nm) 13a having a high reflectance was used as the reflective layer. A negative electrode 20 having a Ti / Au double layer structure was formed on the n-type GaN contact layer. The semiconductor side of the thus-produced light emitting device was the light extraction side. 3 shows the structure of the positive electrode and the negative electrode.

In the stacked structure, the n-type GaN contact layer has a carrier concentration of 1 × 10 ¹⁹ cm ⁻³ , the GaN barrier layer has a Si dopant concentration of 1 × 10 ¹⁸ cm ⁻³ , and the p-type GaN contact layer is It has a carrier concentration of 5 × 10 ¹⁸ cm ⁻³ , and the p-type AlGaN cladding layer has an Mg dopant concentration of 5 × 10 ¹⁹ cm ⁻³ .

These gallium nitride compound semiconductor layers were deposited by MOCVD under well-known representative conditions. The positive electrode and the negative electrode were formed by the following procedure.

A portion of the n-type GaN contact layer that would form the negative electrode was exposed by reactive ion etching through the following procedure.

First, an etching mask was formed on a p-type semiconductor layer by the following procedure. The photoresist was applied over the entire surface of the semiconductor laminate structure and a portion of the resist, slightly larger than the positive electrode, was removed by known photolithography techniques. The laminated structure thus treated was placed in a vacuum deposition apparatus, and Ni (thickness: about 50 nm) and Ti (thickness: about 300 nm) were laminated at 4 × 10 ^-4 Pa or less by the electron beam method. The metal film laminated with the resist was then removed in a region other than the positive electrode region by lift-off.

The semiconductor laminated structure was disposed on the electrode set in the etching chamber of the reactive ion etching apparatus. The etching chamber was decompressed to 10 ^-4 Pa, and etching gas (Cl ₂ ) was supplied to the decompressed chamber. Etching was performed until the n-type GaN contact layer was exposed. After the end of the etching, the structure was taken out of the reactive etching apparatus and the etching mask was removed with nitric acid and hydrofluoric acid.

Then, through well-known photolithography and lift-off techniques, a contact layer made of Pt and Au formed on the p-type contact layer only in the region forming the positive electrode was formed. In forming the contact layer and the current diffusion layer, a gallium nitride compound semiconductor layer stack structure was placed in a vacuum deposition apparatus, and Pt (1.5 nm) and Au (5 nm) were successively laminated on the p-type GaN contact layer. After the laminate was removed from the vacuum chamber, the laminate was subjected to a well-known lift off treatment. In a similar manner, a Pt reflective layer 13a, a Ti barrier layer 13b, an Al barrier layer 13c, a Ti barrier layer 13d, and an Au top layer 13e are successively formed on a portion of the current spreading layer, thereby providing a bonding pad. The electrode 13 was formed. In this way, the positive electrode of the present invention was formed on the p-type GaN contact layer.

A negative electrode was formed on the exposed n-type GaN contact layer through the following process. First, the resist was applied to the entire surface of the structure and a portion of the resist for forming the negative electrode on the exposed n-type GaN contact layer was removed by known photolithography techniques. Ti (100 nm) and Au (200 nm) were successively deposited on a semiconductor layer by vacuum deposition, which was commonly used to form a negative electrode. The resist was then removed in the usual way.

After grinding the substrate back surface of the wafer having the positive electrode and the negative electrode thus formed, the thickness of the substrate is adjusted to 80 占 퐉, and then the laser scriber is used to scribe the wafer on the side of the semiconductor layer and cut along the chip dividing line to make a square chip. (350 µm x 350 µm) was prepared. The forward voltage of each chip was found to be 2.9V as measured by the probe at 20mA of applied current.

The chip was mounted in a TO-18 package can. The emission power of the chip was found to be 4.5 mA by the tester at 20 mA of applied current. The light emission distribution on the light emitting surface showed that light emission occurred in the entire area of the light emitting surface corresponding to the positive electrode on the surface.

It was found that the reflective layer prepared in Example 1 had a reflectance of 92% in the 470 nm wavelength region. The reflectance was measured with a spectrophotometer using a glass dummy substrate that was placed in the same chamber when the bonding pad electrode was formed.

In addition, the peeling strength of the bonding pad electrode was measured by a conventional shear tester. The peel strength was found to be 980 mN (100 gf) or more on average, and there was no peeling from the transparent electrode.

Comparative Example 1

The light emitting device was manufactured by repeating the process of Example 1 except that the transparent electrode was not provided in the region where the bonding pad electrode was formed and the bonding pad electrode did not have the reflective layer 13a. Therefore, in Comparative Example 1, the lowest layer (semiconductor side) of the bonding pad electrode was the Ti layer 13b, which was in direct contact with the p-type contact layer 5b.

In order to make electrical contact, the peripheral portion of the bonding pad electrode was brought into contact with the transparent electrode, and the contact area was made about 5% of the region of the bonding pad electrode. The current flowed from the bonding pad electrode to the transparent electrode via the contact portion.

The light emitting device thus manufactured was evaluated in a similar manner to Example 1, and it was found that the forward voltage and the light output were 3.1V and 4.2 kV, respectively. The light emission distribution on the light emitting surface showed no light emission in the region corresponding to the bonding pad electrode in the region. The results showed that, in comparison with Pt, Ti has higher contact resistance and lower reflectance with respect to the p-type contact layer 5b.

<Example 2>

The thickness of the Pt contact layer 111 of the transparent electrode 11 is adjusted to 1 nm; Using an ITO film having a thickness of 100 nm formed through sputtering as a current diffusion layer; A light emitting device was manufactured by repeating the process of Example 1, except that the reflective layer 13a of the bonding pad electrode was formed of Al.

The light emitting device thus manufactured was evaluated in a similar manner to Example 1, and it was found that the forward current and the light emission output were 2.9 V and 5.0 mA, respectively.

In addition, the peeling strength of the bonding pad electrode was measured by a conventional shear tester. Although the peel strength was on average 980 mN (100 gf) or more, it was found in some samples that there was peeling at the interface between the bonding pad electrode and the transparent electrode.

Comparative Example 2

The light emitting device was manufactured by repeating the process of Example 1 except that the coupling electrode 13 did not have the reflective layer 13a. The light emitting device thus manufactured was evaluated in a similar manner to Example 1. As a result, it was found that the forward current was 2.9 V, which was similarly low as Example 2, but the luminous output was reduced to 4.7 mA.

<Example 3>

In this embodiment, a gallium nitride compound semiconductor laminate structure was prepared in the same manner as in Example 1 through the following process. An AlN buffer layer 6 was formed on the sapphire substrate 1, and the following layers were successively formed on the buffer layer: an undoped GaN base layer (thickness: 6 mu m) 3a; Ge-doped n-type GaN contact layer (thickness: 4 mu m) 3b; Si- doped n- type In _{0 .1} Ga _{0 .9} N cladding layer (thickness: 180㎚) (3c); Light-emitting layer of multiple quantum well structure including Si-doped GaN barrier layer (5 layers and one final layer, each thickness: 16 nm) and In _0.2 Ga _0.8 N well layer (5 layers, each thickness: 2.5 nm) ); Mg- doped p- type Al _{0 .07} Ga _{0 .93} N cladding layer (thickness: 0.01㎛) (5a); Mg-doped p-type Al _0.02 Ga _0.98 N contact layer (thickness: 0.175 mu m) (5b); And Ge-doped n-type GaN tunnel layer (thickness: 20 nm) (not shown). The positive electrode 10 of the present invention was formed on a Ge-doped n-type GaN tunnel layer having a gallium nitride compound semiconductor stacked structure, which was an ITO current diffusion layer (thickness: 250 nm) 112; and an Al layer (thickness). : 50 nm (13a), Ti layer (thickness: 20 nm) (13b), Al layer (thickness: 10 nm) (13c), Ti layer (thickness: 100 nm) (13d), and Au layer (200 nm) A transparent electrode 11 composed only of a bonding pad electrode 13 having a five-layer structure composed of a (13e). Of the five layers constituting the bonding pad electrode, an Al layer (thickness: 50 nm) 13a having a high reflectance was used as the reflective layer. A negative electrode 20 having a Ti / Au double layer structure was formed on the n-type GaN contact layer. The light emitting device thus manufactured had a semiconductor side as a light extraction side. 3 shows the structure of the positive electrode and the negative electrode.

In the stacked structure, the n-type GaN contact layer has a carrier concentration of 8 × 10 ¹⁸ cm ⁻³ , the n-type InGaN cladding layer has a Si dopant concentration of 7 × 10 ¹⁸ cm ⁻³ , and the GaN barrier layer is Si dopant concentration of 1 × 10 ¹⁷ cm ⁻³ , p-type AlGaN contact layer has a carrier concentration of 5 × 10 ¹⁷ cm ⁻³ , and p-type AlGaN clad layer has a Mg of 2 × 10 ²⁰ cm ⁻³ The dopant concentration and the n-type GaN tunnel layer had a Ge dopant concentration of 2 × 10 ¹⁹ cm ⁻³ .

The light emitting device thus manufactured was evaluated in a similar manner to Example 1, and it was found that the forward current and the light emitting output were 3.2V and 8.5 mA, respectively.

In addition, the peel strength of the bonding pad electrode was measured by a conventional shear tester. Peel strength was above 980mN (100gf) on average, but some samples showed that peeling occurred at the interface between the bonding pad electrode and the transparent electrode.

The semiconductor light emitting device using the positive electrode of the present invention exhibits low driving voltage and high light emission intensity. Thus, light emitting devices are very useful for the manufacture of lamps or similar devices.

Claims (30)

An electrode comprising a transparent electrode formed on a semiconductor layer, and a bonding pad electrode formed on the transparent electrode, the transparent electrode having a contact layer in contact with a p-type semiconductor layer and a current diffusion layer formed on the contact layer, The contact layer is made of an alloy containing at least one of a platinum group metal or a platinum group metal, and the bonding pad electrode includes a reflective layer in contact with the transparent electrode, a barrier layer made of Ti, Cr or Al, and a top layer made of Au or Al. A positive electrode for a face-up semiconductor light emitting device, characterized in that it has a layer structure comprising a. The positive electrode for a semiconductor light emitting device according to claim 1, wherein the adhesion strength between the reflective layer and the transparent electrode is 490 mN (50 gf) or more in terms of peel strength. The positive electrode of claim 1, wherein the transparent electrode has a transmission rate of 60% with respect to light having a wavelength in a light emitting wavelength region of the semiconductor light emitting device. According to claim 1, wherein the reflective layer is one metal selected from the group consisting of Al, Ag and Pt metal; Or an alloy containing at least one metal of Al, Ag, and Pt group metals. The positive electrode for a semiconductor light emitting device according to claim 1, wherein the semiconductor light emitting device is a gallium nitride compound semiconductor light emitting device. The method of claim 1, wherein the reflective layer is selected from the group consisting of Al, Ag and Pt; Or an alloy containing at least one metal of Al, Ag, and Pt. The positive electrode for a semiconductor light emitting device according to claim 1, wherein the reflective layer has a thickness of 20 to 3,000 nm. delete The positive electrode for a semiconductor light emitting device according to claim 1, wherein the transparent electrode includes a metal layer on the bonding pad electrode side. The positive electrode for a semiconductor light emitting device according to claim 1, wherein the transparent electrode includes a layer made of a transparent material on the bonding pad electrode side. The positive electrode for a semiconductor light emitting device according to claim 10, wherein the transparent electrode is made of only a conductive transparent material other than metal. The positive electrode for a semiconductor light emitting device according to claim 1, wherein the step of extracting the emitted light from the top layer of the transparent electrode is performed. The positive electrode of claim 12, wherein the uppermost surface of the transparent electrode is formed of a transparent material. delete delete The positive electrode for a semiconductor light emitting device according to claim 1, wherein the contact layer is made of platinum. The positive electrode of claim 1, wherein the contact layer has a thickness of about 0.1 nm to about 7.5 nm. 18. The positive electrode of claim 17, wherein the contact layer has a thickness of 0.5 to 2.5 nm. According to claim 1, wherein the current spreading layer is one metal selected from the group consisting of gold, silver and copper; Or an alloy containing at least one metal of gold, silver and copper. 20. The positive electrode of claim 19, wherein the current spreading layer is made of gold or gold alloy. The positive electrode for a semiconductor light emitting device according to claim 1, wherein the current spreading layer has a thickness of 1 to 20 nm. 22. The positive electrode of claim 21, wherein the current spreading layer has a thickness of 3 to 6 nm. The positive electrode of claim 1, wherein the current spreading layer is made of a conductive transparent material. The semiconductor material according to claim 10, wherein the transparent material is at least one material selected from the group consisting of ITO, zinc oxide, zinc oxide, zinc oxide, F-doped tin oxide, titanium oxide, zinc sulfide, bismuth oxide, and magnesium oxide. Positive electrode for light emitting element. 25. The positive electrode as claimed in claim 24, wherein the transparent material is at least one material selected from the group consisting of ITO, zinc oxide, zinc oxide, and F-doped tin oxide. 11. The positive electrode of claim 10, wherein the transparent material has a thickness of 10 to 5,000 nm. 27. The positive electrode for semiconductor light emitting device according to claim 26, wherein the transparent material has a thickness of 100 to 1,000 nm. The semiconductor light emitting element using the positive electrode of Claim 1. A n-type semiconductor layer, a light emitting layer, and a p-type semiconductor layer sequentially stacked on the substrate and formed of a gallium nitride compound semiconductor layer; A positive electrode formed on the p-type semiconductor layer; And a negative electrode formed on the n-type semiconductor layer, wherein the positive electrode is a positive electrode according to claim 1; and a gallium nitride compound semiconductor light emitting device. A lamp using the light emitting element according to claim 28.

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