JP2007036077A - Pn-junction-type light-emitting diode - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To improve withstand voltage characteristics by preventing the short-circuiting circulation of a element drive current between electrodes in a pn-junction-type light-emitting diode. <P>SOLUTION: First, a laminated structure is formed, where it comprises a crystal substrate, a first conductive layer made of a first-conductivity-type compound semiconductor, a luminous layer made of a compound semiconductor, and a second conductive layer made of a second-conductivity-type compound semiconductor being present in a direction for taking out light emitted from the luminous layer to the outside successively on the surface of the crystal substrate. Then, a second ohmic electrode made of a conductive thin film in which an opening is provided, and a second pad electrode provided by making continuity with the second ohmic electrode are arranged on the second conductive layer. Then, a first pad electrode is arranged on the first conductive layer while the first pad electrode opposes the second one. The pn-junction-type light-emitting diode has a supplementary electrode that is extended in the direction of the fringe of the light-emitting diode from the second pad electrode and is made of a conductive thin band in contact with the second ohmic electrode. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a pn-junction light-emitting diode, and more particularly to a compound semiconductor pn-junction light-emitting diode excellent in the efficiency of extracting light emitted to the outside and having a high withstand voltage.

Recently, a light emitting diode (LED) having a pn junction structure that emits visible light having a relatively short wavelength is configured using various III-V group compound semiconductor materials (for example, see Non-Patent Document 1). . For example, an aluminum phosphide / gallium / indium mixed crystal (compositional formula Al _X Ga _Y In _Z P: 0 ≦ X, Y, Z ≦ 1, X + Y + Z = 1) is a material having a short wavelength visible from a yellow-orange band to a yellow-green band. It is used to construct a light emitting layer or a clad layer for constructing an LED that emits light. Further, as a semiconductor material for a short wavelength LED that emits light of a blue band or a green band, a gallium nitride (GaN) system such as Al _X Ga _Y In _ZN (0 ≦ X, Y, Z ≦ 1, X + Y + Z = 1) or the like. Compound semiconductors are known (see, for example, Patent Document 1).

The LED is configured by providing positive (+) and negative (−) ohmic electrodes on the III-V group compound semiconductor layer as described above. In particular, in a wide band gap (wide band gap) material such as Al _X Ga _Y In _Z P or Al _X Ga _Y In _Z N, the device driving current is spread over a wide range, for example, substantially over the entire surface of the light emitting layer. Difficult to diffuse. For this reason, a group III nitride semiconductor layer having a relatively high forbidden band width in the direction of light emission to the outside is provided as an ohmic electrode made of a metal thin film over almost the entire surface thereof to constitute an LED. (For example, refer to Patent Document 2). For example, a GaN pn junction type light emitting diode is configured by providing a p-type ohmic electrode from a metal thin film on substantially the entire surface of a p-type GaN layer in the light extraction direction (see Patent Document 2).

  As for a wide band gap compound semiconductor, a technique of forming an ohmic electrode from a metal film having an opening is also known (see, for example, Patent Document 3). Specifically, the ohmic electrode having an opening is a net-like or comb-like electrode (see the above-mentioned Patent Document 3). This is because an opening is provided in the ohmic electrode provided in the direction of taking out the emitted light to reduce the degree to which the light emitted from the light emitting layer is absorbed by the electrode material, and the emitted light is efficiently taken out to the outside.

Japanese Patent Publication No.55-3834 JP-A-6-314822 JP-A-6-69546 Supervised by Toshika Fukaumi, “Semiconductor Engineering”, Tokyo Denki University Press, published on March 20, 1993, first edition, 7th edition, pp. 206-208

  Even if an ohmic electrode made of a metal film with openings is provided over the entire surface of the wide band gap compound semiconductor layer, for example, considering the light extraction efficiency, the openings should be present at a substantially uniform density. As long as the device driving current can be evenly distributed in the compound semiconductor layer, the device driving current is not necessarily distributed. Even if the ohmic electrode is composed of a metal film having openings uniformly and evenly, conventionally, the element drive current flows in a short circuit through the region closest to the electrode of another polarity. It is normal. For this reason, since the element drive current is concentrated in a narrow region, the current density is increased and the electrode is thermally destroyed.

In addition, pn junction type light emitting diodes having electrodes configured and arranged so as to cause short-circuiting and concentrated distribution of element driving current generally have no withstand voltage against inadvertent application of a high voltage. ing. In particular, a conventional substrate having an insulating crystal such as sapphire (α-Al ₂ O ₃ single crystal), gallium lithium acid (LiGaO ₂ ), aluminum lithium acid (LiAlO ₂ ) or the like having high electrical insulation. In the pn junction type light emitting diode, the withstand voltage is particularly low. For this reason, the current situation is that, as a countermeasure against withstand voltage, a Si surge diode or the like is added to the light emitting diode as an external element.

In order to prevent the thermal damage or the withstand voltage failure of the electrode as described above, it is necessary to avoid a short-circuit flow from one polarity electrode to the other polarity electrode.
An object of the present invention is to avoid a short-circuit and concentrated distribution of element driving current between electrodes, and does not hinder the extraction of emitted light to the outside, and has excellent withstand voltage characteristics. It is to provide an element.

The present invention has been made to solve the above-described problems, and includes the inventions of the following items.
(1) From a first conductive layer made of a compound semiconductor of the first conductivity type, a light emitting layer made of a compound semiconductor, and a second conductive type compound semiconductor in the direction of taking out light emitted from the light emitting layer to the outside A laminated structure including a second conductive layer, a second ohmic electrode made of a conductive thin film having an opening provided on the second conductive layer, and a second ohmic electrode A pn junction in which a second pedestal (pad) electrode provided in electrical conduction with the first pedestal electrode is disposed on the first conductive layer so as to face the second pedestal electrode In the type light emitting diode, an incidental electrode made of a conductive thin strip that extends from the second pedestal electrode toward the outer edge of the light emitting diode element and contacts the second ohmic electrode is provided. A pn junction type light emitting diode.

(2) The second pedestal electrode is disposed at the corner of the light emitting element, the first pedestal electrode is disposed at the corner on the diagonal line of the second pedestal electrode, and the incidental electrode is connected to the light emitting element from the second pedestal electrode. The pn junction type light emitting diode according to (1), wherein the pn junction type light emitting diode extends in an outer edge direction on both sides.
(3) The second pedestal electrode is disposed on the side of the light emitting element, the first pedestal electrode is disposed on the opposite side of the second pedestal electrode, and the incidental electrode extends from the second pedestal electrode to the outer edge of the light emitting element. The pn junction type light-emitting diode according to (1), which extends in a direction.
(4) The above (1) to (3), wherein the shape of the side of the auxiliary electrode facing the first pedestal electrode is similar to the shape of the side of the first pedestal electrode facing the auxiliary electrode. Pn junction type light emitting diode in any one of 1).

(5) The aperture ratio of the opening of the second ohmic electrode decreases from the second pedestal electrode toward the first pedestal electrode. (1) to (4) above A pn junction type light emitting diode according to any one of the above.
(6) The pn junction type according to any one of the above (1) to (5), wherein the incidental electrode and the second ohmic electrode are made of a conductive material that transmits light emitted from the light emitting layer. Light emitting diode.
(7) A light emitting diode comprising a combination of the light emitting diode according to any one of (1) to (6) and a phosphor.
(8) A lighting fixture using the light emitting diode according to (7).

According to the present invention, the pedestal electrode is provided with the incidental electrode that can uniformly distribute the element driving current supplied from the pedestal electrode to the ohmic electrode. In addition, it is possible to provide a pn-junction light-emitting diode that is excellent in withstand voltage by avoiding a short-circuit element operating current.
In addition, since the ohmic electrode is composed of a conductive thin film having an opening, light emission can be directly transmitted from the opening to the outside, so that a pn junction type compound semiconductor light emitting device with excellent emission efficiency to the outside is provided. A diode can be provided.
On top of that, the electrostatic breakdown resistance was improved by providing an auxiliary electrode extending in the direction of the outer edge of the pedestal electrode that conducts to the electrode from which light is extracted.

  The light emitting diode of the present invention is characterized in that a specific incidental electrode is provided in addition to a known electrode in a laminated structure constituting a pn junction type light emitting diode. The stacked structure is formed on the surface of the crystal substrate in sequence, a first conductive layer that is a compound semiconductor of the first conductivity type, a light emitting layer made of the compound semiconductor, and a compound semiconductor of the second conductivity type. The first conductive layer. The second conductive layer made of the compound semiconductor of the second conductivity type is in a direction to extract light emitted from the light emitting layer to the outside. The first conductivity type and the second conductivity type can be either p-type or n-type. When the first conductivity type is n-type, the second conductivity type is p-type. When the conductivity type is p-type, the second conductivity type is n-type. The light emitting layer can be p-type, n-type or non-doped.

As the compound semiconductor, a III-V compound semiconductor, a II-VI group compound semiconductor, or the like can be used, and a III-V group compound semiconductor, particularly a gallium nitride group III nitride semiconductor is preferable.
A second ohmic electrode made of a conductive thin film having an opening is formed on the second conductive layer of the laminated structure. Then, the second ohmic electrode is electrically connected to the second pedestal (pad) electrode so as to face the second pedestal electrode, and the first ohmic electrode and the first Pedestal electrodes are arranged. The first pedestal electrode may also serve as the first ohmic electrode. These will be described in detail below.

The n-type (for example, first conductivity type) and p-type (for example, second conductivity type) ohmic electrodes are provided in direct contact with the surfaces of the n-type and p-type cladding layers. Alternatively, it is provided in contact with a contact layer of the same conductivity type as that of the cladding layer, which is bonded to the upper surface of one cladding layer or the lower surface of the other cladding layer. In the present invention, a pedestal electrode is provided in accordance with the polarity of the n-type or p-type ohmic electrode.
The light emitting device of the present invention is provided with an incidental electrode extending from the second pedestal electrode toward the outer edge of the light emitting diode device. The auxiliary electrode is made of a conductive thin ribbon and is in contact with the second pedestal electrode and the second ohmic electrode.

The laminated structure for constituting the pn junction type light emitting diode of the present invention includes sapphire (α-Al ₂ O ₃ single crystal), 4H crystal type or 6H crystal type hexagonal silicon carbide (SiC) or wurtzite. A hexagonal single crystal such as a mineral crystal type (Wurtzite) gallium nitride (GaN) or zinc oxide (ZnO) is formed as a substrate. Further, a zinc-blende semiconductor single crystal such as gallium phosphide (GaP), gallium arsenide (GaAs), and silicon (Si) is formed as a substrate.

  The laminated structure constituting the pn junction type compound semiconductor light emitting diode of the present invention may have a single heterojunction (single heterojunction) structure, but in order to obtain higher intensity light emission, a double heterojunction (double hetero: A light emitting portion having a (DH) structure is provided. The light emitting part is an n-type cladding layer (for example, the first conductivity type) and a p-type cladding layer (for example, the second conductivity type) that sandwiches the light emitting layer from both sides (upper surface side and lower surface side) and exerts a barrier action. Pn junction structure part.

For example, the light-emitting layer includes gallium phosphide indium (composition formula Ga _Y In _Z P: 0 ≦ Y, Z ≦ 1, Y + Z = 1), aluminum gallium arsenide (composition formula Al _X Ga _Y As: 0 ≦ X, Y ≦ 1, X + Y = 1), gallium indium nitride (compositional formula _{Ga Y In Z N: 0 ≦} Y, Z ≦ 1, Y + Z = 1), also nitride gallium phosphide (compositional formula GaN _1-a P a: It is formed from a direct transition type III-V group compound semiconductor material such as 0 ≦ a <1). Further, it is composed of a II-VI group compound semiconductor material such as zinc selenide sulfide (compositional formula ZnSe _{1 -Q} S _Q : 0 ≦ Q ≦ 1).

The light emitting layer may be composed of only a single layer, but has a quantum well structure in order to obtain light emission with more excellent monochromaticity. It consists of multiple quantum well structure (MQW) rather than single quantum well structure (SQW). The light emitting layer having a quantum well structure that emits light in a blue band or a green band includes, for example, a barrier layer made of Al _X Ga _Y N (0 ≦ X, Y ≦ 1, X + Y = 1), and Ga _Y In _Z N (0 ≦ Y, Z ≦ 1, Y + Z = 1) and the well layers are alternately stacked. Further, for example, direct transition type nitride gallium phosphide (compositional formula _{GaN 1-a P a: 0} ≦ a <1) consisting of a well layer and (well), more of the band gap large GaN _1-a P a (0 A barrier layer composed of ≦ a <1) is alternately and periodically stacked.
The light emitting layer having a quantum well structure that emits light in the green band can also be composed of a II-VI group compound semiconductor material such as ZnSe _{1 -Q} S _Q (0 ≦ Q ≦ 1).

When a multiple quantum well structure is composed of a GaN-based III-V group compound semiconductor material, the number of periods when alternately stacked is 3 or more and 20 or less, more preferably 5 or more and 10 or less. When a multiple quantum well structure is formed from Al _X Ga _Y As (0 ≦ X, Y ≦ 1, X + Y = 1), even if the number of periods is increased to 5 or more and 20 or less, a light emitting layer with a flat surface can be obtained. can get. The barrier layer and the well layer may have different carrier concentrations, but have the same conductivity type. The start and end of the quantum well structure may be either a well layer or a barrier layer. Also, it does not matter if the starting end is a barrier layer and the end is a well layer, or vice versa.

For example, when forming a well layer having a quantum well structure from a GaN-based III-V group compound semiconductor, the thickness of the well layer is preferably 2 nm or more and 12 nm or less. Rather than making the film thickness substantially uniform as in the prior art, the layer thickness is reduced locally (partially) to make the layer thickness non-uniform, for example, Ga _Y In _Z N (0 ≦ Y, Z ≦ 1, When a quantum well structure is formed using a well layer from Y + Z = 1), a pn junction type compound semiconductor light emitting diode having a low forward voltage is obtained. A well layer composed of Ga _Y In _Z N partially including a region having a layer thickness of 1.5 nm or less can be particularly preferably used to obtain a light emitting diode having a low forward voltage. In a quantum well structure consisting of a well layer with a non-uniform thickness including a partially thin film region and a barrier layer doped with impurities to reduce resistance, the piezoelectric layer extending from the barrier layer to the well layer is used. Distortion due to the (piezo) effect is reduced, and a light-emitting layer that emits light with a stable wavelength can be formed.

For example, for a light-emitting layer made of a GaN-based III-V group compound semiconductor, the n-type or p-type cladding layer has a larger forbidden band than the light-emitting layer. For example, the composition formula Al _x Ga _y In _z N _{1-a M a (0 ≦} X, Y, Z ≦ 1, X + Y + Z = 1, M represents a group V element other than nitrogen, 0 ≦ a <a 1.) GaN-based III-V representable It consists of a compound semiconductor. Further, it can be composed of a boron phosphide (BP) III-V compound semiconductor material containing phosphorus (P) and boron (B) as constituent elements. The n-type cladding layer is formed by doping a group IV element such as silicon (Si) or germanium (Ge) or a group VI element such as selenium (Se), for example. The p-type cladding layer is formed by doping a Group II element such as magnesium (Mg) or beryllium (Be) as a p-type impurity.

The carrier concentration of the compound semiconductor layer forming the cladding layer is preferably in the range of 1 × 10 ¹⁷ cm ^{−3 to} 5 × 10 ¹⁸ cm ⁻³ . From monomeric boron phosphide (BP), n-type and p-type having a carrier concentration in the above-mentioned preferable range in an undoped as-grown state without doping impurities. A conductive layer can be obtained. The thickness of the cladding layer is preferably 0.1 μm or more and 5 μm or less.

In addition to the MOCVD method, each layer constituting the laminated structure, such as a light emitting layer, a clad layer, or a contact layer to be described later, for forming a light emitting diode according to the present invention is, for example, molecular beam epitaxial (MBE). And vapor phase growth means such as hydride (hydride) vapor phase epitaxial growth (VPE) method. In order to form a barrier layer doped with silicon (Si) or germanium (Ge), silane (molecular formula: SiH ₄ ), disilane (molecular formula: Si ₂ H ₆ ), germane (molecular formula: GeH ₄ ), etc. are used during vapor phase growth. Is added as a doping gas. In order to form a quantum well structure in which the barrier layer is a GaN layer and the well layer is a Ga _Y In _Z N layer, 650 ° C. to 900 ° C. is suitable. In the case of a quantum well structure having this configuration, the barrier layer and the well layer can be formed at substantially the same growth temperature. When the barrier layer is made of Al _x Ga _y N containing aluminum (Al) instead of GaN, the growth temperature is set higher than that of the GaN barrier layer.

  In the present invention, the second ohmic electrode and the incidental electrode are provided in a direction in which light emitted from the light emitting layer is extracted to the outside. For example, in an n-side up pn junction type light emitting diode, the n-type ohmic electrode (negative electrode) is used as the second ohmic electrode. Conversely, in a p-side-up pn junction LED, the p-type ohmic electrode (positive electrode) is the second ohmic electrode.

  The incidental electrode is provided in mechanical and electrical contact with the second pedestal electrode on the second ohmic electrode. The auxiliary electrode is provided so as to extend from both sides of the base electrode toward the outer edge of the light emitting element. These will be described based on the planar square pn junction LED illustrated in FIGS. The base electrode 12 is provided at a corner portion of the light emitting element. Further, it can be provided so as to face the side of the light emitting element. The auxiliary electrode 14 is constituted by, for example, a band-like continuous metal film (conductive thin band) extending from the pedestal electrode 12 of one polarity to the two directions 15a and 15b along the outer edge 15 of the element. The auxiliary electrode 14 has a function of uniformly and evenly distributing an element driving current supplied from the pedestal electrode 12 as a feeding point to an ohmic electrode described later.

The pedestal electrode 12 for connecting a conductor for supplying an element driving current is formed of a thick film of a metal material having a layer thickness (total layer thickness in the case of a multilayer) of 0.5 μm or more and 5 μm or less. Is preferred. When metal electrodes are stacked in multiple layers to form a pedestal electrode, the surface is preferably composed of gold (Au) or an alloy film thereof for easy connection. The base electrode 12 and the auxiliary electrode 14 are provided in electrical contact.
A first ohmic electrode forming portion 13a is provided on a diagonal line in the plan view of the second pedestal electrode, and the second pedestal electrode 13 is arranged in the 13a. The first ohmic electrode forming portion 13a is a portion obtained by etching the semiconductor layer until the first conductor layer is exposed. A first pedestal electrode is formed on the exposed first ohmic electrode forming portion via the first ohmic electrode or directly on the first conductor layer.

  The shape of the surface 14a of the auxiliary electrode 14 on the side facing the pedestal electrode 13 is preferably substantially similar to the shape of the first ohmic electrode forming portion 13a (including the same shape). That is, as long as the shapes are similar, the sizes may be different. This is to keep the distance between the ohmic electrode forming portion 13a and the incidental electrode 14 at a constant interval. For example, as shown in the drawing, both are linear and have a parallel relationship. Further, if the first ohmic electrode forming portion 13a is a ¼ circle, the shape of the inner surface 14a of the auxiliary electrode 14 is a substantially similar arc shape. As a result, the distance between the first ohmic electrode forming portion and the inner surface 13a of the auxiliary electrode 14 is kept constant. Here, the auxiliary electrode 14 does not necessarily need to be made of the same material as the second ohmic electrode.

  The plane area occupied by the auxiliary electrode 14 is ½ or less, more preferably ¼ or less, of the plane area of the light emitting surface (planar region exhibiting light emission). This is because if an incidental electrode having a large flat area is provided, the efficiency of taking out emitted light to the outside decreases.

  The auxiliary electrode 14 is in contact with an ohmic electrode made of a conductive thin film provided with an electrically conductive opening 11. The planar shape of the opening 11 is arbitrarily selected from squares, rectangles, parallelograms, rhombuses, regular hexagons, regular polygons such as regular octagons, and the like. It has a shape that can efficiently extract light emitted from the light emitting layer to the outside, and it does not prevent planar and even diffusion of the element driving current to the light emitting portion by providing an opening of that shape. I just need it. The planar shape of the opening may be the same and the same, or may be different for each region. For example, a case where a square opening is provided in a region near the incidental electrode and an opening provided in another region is circular can be exemplified.

  When the auxiliary electrode 14 and the ohmic electrode 10 are formed of a conductive thin film such as a thin metal film that can transmit light, a pn junction type light emitting diode that is superior in the efficiency of extracting light emitted to the outside can be obtained. In order to ensure sufficient transmission of light emission to the outside, the thickness of the conductive thin film is preferably in the range of 1 nm to 100 nm. An ultra-thin film with a thickness of less than 1 nm is excellent in light emission transmittance, but increases resistance when passing element driving current, and therefore has sufficient action to diffuse the element driving current to the light emitting portion in a plane. Does not reach. In addition, in the electrode forming process, there arises a disadvantage that it is easily damaged. For this reason, it is preferable that the electroconductive thin film which comprises a translucent ohmic electrode has the film thickness which provides the transmittance | permeability of the range of 30% to 80% with respect to the light emission from a light emitting layer. As the materials for the auxiliary electrode 14 and the ohmic electrode 10, various metals such as transition metals, alloys, and metal oxides can be used. These layers may be multi-layered, and in that case, the film thickness is preferably in the range of 1 nm to 100 nm. Such a thin film can be formed by thin film forming means such as high-frequency sputtering or vacuum deposition.

In the present invention, as illustrated in FIG. 2, for example, the ohmic electrode 10 can be configured from a metal film in which the aperture ratio of the second ohmic electrode is decreased from the pedestal electrode 12 toward the pedestal electrode 13. it can. The aperture ratio is the ratio of the total plane area of the openings 11 to the plane area of the region including the openings where the conductive thin film forming the ohmic electrode 10 is installed (laying area of the ohmic electrode 10).
The opening ratio of the second ohmic electrode is preferably 20 to 80% as a whole (average).
The aperture ratio in the region in the vicinity of the incidental electrode 14 is preferably 10% or more and 90% or less, and more preferably 15% or more and 85% or less. The vicinity means a region surrounded by a distance that is not more than twice the width of the incidental electrode from the incidental electrode.
In the vicinity of the first pedestal electrode, the aperture ratio is preferably 20 to 80%.

  When the aperture ratio of the conductive thin film is different depending on the region from one pedestal electrode to the other pedestal electrode, it is not necessary to combine different materials having different aperture ratios. For example, a conductive thin film provided with an opening having a different opening ratio depending on the region uses a photomask in which the shape of the opening is drawn with the opening ratio, and a photoresist material is applied by a known photolithography technique. By patterning and selective etching, it can be easily formed from the same material.

Examples of the n-type ohmic electrode (negative electrode) material suitable for forming the ohmic electrode and the auxiliary electrode include aluminum (Al), titanium (Ti), nickel (Ni), gold (Au), chromium (Cr), tungsten ( W) and vanadium (V). The p-type ohmic electrode and the incidental electrode (positive electrode) are, for example, platinum (Pt), palladium (Pd), gold (Au) chromium (Cr), nickel (Ni), copper (Cu), and cobalt (Co). It can be composed of a thin film. In addition, oxides such as NiO and CoO (the ratio of O to O is not necessarily 1: 1) can be used for any electrode.
When the aperture ratio is particularly small on the first pedestal electrode side of the second ohmic electrode, it is better not to place the conductive thin film in the region and the incidental electrode in direct contact with each other. . This is to prevent the element drive current supplied to the auxiliary electrode 14 via the base electrode 12 from flowing directly into the metal film having a small aperture ratio. In addition, this is for avoiding a short-circuited element driving current between the pedestal electrode 12 and the pedestal electrode 13 having the other polarity via the conductive thin film having a small aperture ratio.
Ti, Zr, W, Mo, Cr, Al, Ni, Au, Sn, etc., and their alloys and laminated structures can be used for the other first pedestal electrode and ohmic electrode (the pedestal electrode may also serve). . The outermost surface layer is preferably made of Au or Al in order to improve bonding properties.

(Function)
With the ohmic electrode made of a conductive thin film provided in conduction with the auxiliary electrode, the auxiliary electrode has an action of evenly distributing the element driving current supplied from the pedestal electrode to the ohmic electrode.
The opening provided in the ohmic electrode has a function of transmitting light emitted from the light emitting layer to the outside.
The conductive thin film whose aperture ratio decreases toward the first ohmic electrode side exhibits an effect of equalizing the potential in a region adjacent to the electrode.

A blue light emitting device made of a nitride compound semiconductor was produced as follows.
A 4 μm-thick underlayer made of undoped GaN on an sapphire substrate via an AlN layer, a 2 μm-thick n-side contact layer made of Ge-doped (concentration 1 × 10 ¹⁹ / cm ³ ), Si-doped (concentration 1 × 10 ¹⁸ / cm ³ ) An n-side cladding layer made of In _0.1 Ga _0.9 N having a thickness of 12.5 nm, a barrier layer made of GaN having a thickness of 16 nm, and a well layer made of In _0.2 Ga _0.8 N having a thickness of 2.5 nm. After alternately laminating five times, a light emitting layer having a multi-quantum well structure finally provided with a barrier layer, Mg doped (concentration 1 × 10 ²⁰ / cm ³ ) Al _0.07 Ga _0.93 N, 2.5 nm thick p A nitride compound semiconductor multilayer structure was formed by sequentially laminating a side cladding layer and a p-side contact layer made of Mg-doped (concentration 8 × 10 ¹⁹ / cm ³ ) Al _0.02 Ga _0.98 N and having a thickness of 0.16 μm.

A positive electrode having the pattern of FIG. 2 was formed at a predetermined position on the p-side contact layer of the nitride-based compound semiconductor multilayer structure by using a known photolithography technique and lift-off technique. The positive electrode has a structure in which Pt and Au are laminated in order from the p-side contact layer side. The incidental electrode 14 constituting the positive electrode has a width of 50 μm, and the mesh electrode 10 has a width of 6 μm. The aperture ratio of the mesh electrode was 50% in the vicinity of the incidental electrode 14 and 10% in the vicinity of the first ohmic electrode forming portion 13a. The overall average aperture ratio was 50%.
Subsequently, a positive electrode bonding pad having an Au / Ti / Al / Ti / Au layer structure was formed from the semiconductor side using a known photolithography technique.

Subsequently, the n-type GaN contact layer where the negative electrode was to be formed was exposed by reactive ion etching, and the negative electrode was formed on the exposed n-type GaN contact layer by the following procedure. After uniformly applying the resist to the entire surface, the resist is removed from the negative electrode forming portion on the exposed n-type GaN contact layer using a known lithography technique, and Ti is sequentially applied from the semiconductor side by a commonly used vacuum deposition method. A negative electrode having a thickness of 100 nm and Au of 200 nm was formed. Thereafter, the resist was removed by a known method.
After that, it was cut into a 350 μm square LED chip, placed on a lead frame, and a gold lead was connected to the lead frame so that an element driving current could flow from the lead frame to the LED chip.
An element driving current was passed between the positive electrode 10 and the negative electrode 13 in the forward direction via the lead frame. When the forward current was 20 mA, the forward voltage was 3.5V. Further, the central wavelength of emitted blue band light when a forward current of 20 mA was passed was 460 nm. In addition, the intensity of light emission measured using a general integrating sphere reached 5 mW, and a group III nitride semiconductor light-emitting device that gave high intensity light emission was obtained.
Moreover, as a result of performing electrostatic withstand voltage measurement (ESD) of the obtained light-emitting element by the Human body model (HB model), all of 20 points in the plane were 2000 V or more.

(Comparative example)
A wafer having the same layered structure as in the example was used, and the layered structure of the p-layer was the same, except that the p-side electrode pattern was changed so as to cover the entire surface without providing an opening, and a device was fabricated. . The n-electrode pattern and the laminated structure were the same as in the example.
When the obtained light emitting device was evaluated in the same manner as in the example, the forward voltage was 3.5 V when the forward current was 20 mA. Further, the central wavelength of emitted blue band light when a forward current of 20 mA was passed was 460 nm. The intensity of light emission measured using a general integrating sphere was 3 mW, and the intensity of light emission was clearly weaker than in the examples.
Furthermore, in electrostatic withstand voltage measurement (ESD), only 3 points out of 20 points in the plane showed 2000 V or more.

According to the present invention, it is possible to obtain a pn junction type light emitting diode having excellent withstand voltage by avoiding local and short-circuited element operating current flow between the electrodes, and emitting light directly from the opening to the outside. Pn-junction compound semiconductor light-emitting diode with excellent light extraction efficiency, so it can be transmitted to the outside, so various displays, various indicators, various traffic signals, automobile blinkers, rear lights, daytime lights, etc. Can be suitably used.
Further, by combining this light emitting diode and a phosphor, it can be used as a light emitting diode for white light or the like in an automobile headlamp, or a lighting device such as a spotlight, a ceiling light, or a streetlight.

It is a plane schematic diagram of LED for demonstrating the structure of the electrode of this invention. It is a plane schematic diagram of LED for demonstrating the structure of the opening part of the electrode of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Metal ohmic electrode which provided opening 11 Opening part 12 2nd base electrode 13 1st base electrode 13a 1st ohmic electrode formation part 14 Auxiliary electrode 14a Inner side surface of an accompanying electrode 15 Outer edge of a light emitting diode 15a One direction of outer edge 15b Other direction of outer edge of light emitting diode

Claims (8)

  A first conductive layer made of a compound semiconductor of the first conductivity type, a light emitting layer made of a compound semiconductor, and a second made of a compound semiconductor of the second conductivity type in the direction of taking out light emitted from the light emitting layer to the outside. And a second ohmic electrode made of a conductive thin film having an opening on the second conductive layer, and a second ohmic electrode electrically A pn-junction light emitting diode in which a second pedestal (pad) electrode provided in conduction with the first pedestal electrode is disposed on the first conductive layer so as to face the second pedestal electrode In this case, a pn junction type is provided, which is provided with an auxiliary electrode made of a conductive ribbon extending from the second pedestal electrode in the direction of the outer edge of the light-emitting diode element and in contact with the second ohmic electrode. Light emitting diode.   The second pedestal electrode is disposed at a corner portion of the light emitting element, the first pedestal electrode is disposed at a diagonal corner of the second pedestal electrode, and the auxiliary electrode is disposed at the outer edges of both sides of the light emitting element from the second pedestal electrode. The pn junction type light emitting diode according to claim 1, which extends in a direction.   The second pedestal electrode is disposed on the side of the light emitting element, the first pedestal electrode is disposed on the opposite side of the second pedestal electrode, and the auxiliary electrode extends from the second pedestal electrode toward the outer edge of the light emitting element. The pn junction type light emitting diode according to claim 1, wherein the pn junction type light emitting diode is present.   The shape of the side facing the first pedestal electrode of the incidental electrode and the shape of the side facing the incidental electrode of the first pedestal electrode are similar in any one of claims 1 to 3. The pn junction type light emitting diode as described.   The aperture ratio of the opening part of a 2nd ohmic electrode is reducing toward the direction of a 1st base electrode from a 2nd base electrode, The one in any one of Claims 1-4 characterized by the above-mentioned. A pn junction type light emitting diode.   The pn junction light emitting diode according to any one of claims 1 to 5, wherein the auxiliary electrode and the second ohmic electrode are made of a conductive material that transmits light emitted from the light emitting layer.   A light emitting diode comprising a combination of the light emitting diode according to claim 1 and a phosphor. The lighting fixture using the light emitting diode of Claim 7.

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