JP2006237574A - GaN-BASED LIGHT EMITTING DIODE - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a GaN-based light emitting diode whose emission efficiency is improved. <P>SOLUTION: The GaN-based light emitting diode comprises: a p-type GaN-based semiconductor layer 5 formed by being laminated on a light emitting layer 3; a p-type ohmic electrode P2 formed on a front surface of the p-type GaN-based semiconductor layer 5; and a p side pad electrode P3 electrically connected to the p-type ohmic electrode P2. The p-type ohmic electrode P2 consists of: a portion formed on a pattern having a window part through which a light occurring at the light emitting layer 3 can pass; and a portion in which an opening is provided, and the p side pad electrode P3 is formed so that the electrode P3 touches the p-type GaN-based semiconductor layer 5 inside the opening and a periphery portion thereof is overlapped on the p-type ohmic electrode P2, and thereby a region where the p side pad electrode P3 and the p-type ohmic electrode P2 are overlapped becomes a strip and annular region along a border line of the p side pad electrode P3. The diode is so designed that any current may not directly flow from the p side pad electrode P3 to the p-type GaN-based semiconductor layer 5. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a GaN-based light emitting diode. More specifically, a GaN-based light emitting diode configured such that a p-type ohmic electrode formed on the surface of a p-type GaN-based semiconductor layer is formed in a pattern having a window portion and light can be extracted through the window portion. About.

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

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

A GaN-based LED is formed on a crystal substrate made of sapphire or the like by using a vapor phase growth method such as an organic metal compound vapor phase growth (MOVPE) method, a hydride vapor phase growth (HVPE) method, or a molecular beam epitaxy (MBE) method. , An n-type GaN-based semiconductor layer, a light emitting layer, and a p-type GaN-based semiconductor layer are sequentially stacked, and then an ohmic electrode is formed on each of the n-type GaN-based semiconductor layer and the p-type GaN-based semiconductor layer. be able to.
In this specification, in the description of the element structure, the thickness direction of the substrate and the semiconductor layer is also referred to as the vertical direction, and the crystal substrate is located on the lower side, and the GaN-based semiconductor layer is formed thereon. Distinguish between upward and downward as stacked. In addition, a direction orthogonal to the vertical direction is also referred to as a horizontal direction. The p-type GaN-based semiconductor layer is also simply referred to as a p-type layer, and the n-type GaN-based semiconductor layer is also simply referred to as an n-type layer.

FIG. 12 is a cross-sectional view showing an example of the GaN-based LED manufactured as described above. On the sapphire substrate 41, an n-type layer 42, a light-emitting layer 43, and a p-type layer (p-type cladding layer 44, p-type). N-type ohmic electrode P41 is formed on the surface of the n-type layer 42, and the p-type ohmic electrode P42 is formed on the surface of the p-type layer 45. Each is formed. P43 is a p-side pad electrode, and is laminated on the p-type ohmic electrode P42 so as to be electrically connected to the p-type ohmic electrode P42.
The p-type ohmic electrode formed on the surface of the p-type layer is formed so as to cover the surface as widely as possible. This is because the conductivity of the p-type GaN-based semiconductor is low, so that the current supplied from the p-type ohmic electrode hardly spreads in the lateral direction inside the p-type layer, and the light emission in the light-emitting layer is p-type ohmic. This is because it occurs only below the electrodes.
Therefore, in order to extract light from the surface side of the p-type layer, it is necessary to form the p-type ohmic electrode with a transparent material or a pattern having a window portion through which light can pass. Among these, in the method of forming the p-type ohmic electrode in the pattern having the window portion, it is not necessary to form the electrode film transparently, so that the sheet resistance of the electrode is lowered by appropriately increasing the film thickness. Can do. When the sheet resistance of the p-type ohmic electrode is low, the current diffusivity in the lateral direction is good, so that the in-plane uniformity of the light emission intensity in the light emitting layer is improved.

When light is extracted from the surface side of the p-type layer, a p-side pad electrode for wire bonding is formed in contact with the p-type ohmic electrode in order to supply power to the p-type ohmic electrode with an Au wire.
FIGS. 8A and 8B are top views of a conventional GaN-based LED including a p-type ohmic electrode formed in a pattern having a window portion, respectively. In the GaN-based LED of FIG. 8A, the p-side pad electrode P23 is formed on a portion of the p-type ohmic electrode P22 that does not have a window (Patent Document 1). In the GaN-based LED of FIG. 8B, the p-type ohmic electrode P32 is formed in a pattern (lattice pattern) having windows over the entire surface of the p-type layer 35, and the p-side pad electrode P33 is a part of the pattern. (Patent Document 2, Patent Document 3). 8A, the entire p-side pad electrode P23 is formed on the p-type ohmic electrode P22, and light emission below the p-side pad electrode P23 is not suppressed at all. However, since this light emission is difficult to be emitted above the element due to the p-side pad electrode P23 being an obstacle, the light emission efficiency of the LED is lowered when this is not suppressed at all. In particular, most of the light emission below the central portion of the p-side pad electrode P23 is a loss.
8B, when the p-side pad electrode P33 is formed of Au (gold) or Ni (nickel), the contact between the p-side pad electrode P33 and the p-type layer 35 becomes an ohmic contact, and the p-side Since light emission occurs below the entire pad electrode P33, a problem similar to the problem in the embodiment of FIG. On the other hand, when the lowermost layer portion of the p-side pad electrode P33 is formed of Ti (titanium), the contact between the p-side pad electrode P33 and the p-type layer 35 becomes a Schottky contact, and the p-side pad electrode P33 becomes the p-type layer 35. Light emission does not occur below the contact area. However, under the p-side pad electrode P33, the p-type ohmic electrode P32 is formed in a uniform lattice pattern as in the other regions, and light emission below the p-side pad electrode P33 is particularly suppressed. The above problem is not improved because there is no.

JP 2003-318441 A JP 2000-174339 A JP 2003-46127 A JP-A-10-303502 JP 2004-172189 A

  An object of the present invention is to solve the above-described problems of the prior art and provide a GaN-based LED with improved luminous efficiency.

The present invention has the following features.
(1) A p-type GaN-based semiconductor layer formed on a light-emitting layer made of a GaN-based semiconductor, a p-type ohmic electrode formed on the surface of the p-type GaN-based semiconductor layer, and the p-type ohmic electrode A GaN-based light emitting diode comprising a p-side pad electrode electrically connected, wherein the p-type ohmic electrode is formed in a pattern having a window through which light generated in the light emitting layer can pass The p-side pad electrode is in contact with the p-type GaN-based semiconductor layer inside the opening, and its outer peripheral portion is on the p-type ohmic electrode. The region where the p-side pad electrode and the p-type ohmic electrode overlap is a band-like and annular region along the contour line of the p-side pad electrode. Side pad The contact between the electrode and the p-type GaN-based semiconductor layer is made non-ohmic, or the surface of the p-type GaN-based semiconductor layer in contact with the p-side pad electrode is increased in resistance. A GaN-based light-emitting diode configured to prevent current from flowing directly from the side pad electrode to the p-type GaN-based semiconductor layer.
(2) The GaN according to (1), wherein the p-side pad electrode has at least a portion in contact with the p-type GaN-based semiconductor layer formed of a metal material in Schottky contact with the p-type GaN-based semiconductor. Light emitting diode.
(3) The p-type ohmic electrode includes an Au layer, and the portion of the p-side pad electrode in contact with the p-type GaN-based semiconductor layer has a portion formed of Al as the p-type ohmic electrode. The GaN-based light emitting diode according to (2), which is provided so as not to contact.
(4) Plasma treatment is performed on a portion of the surface of the p-type GaN-based semiconductor layer where the p-side pad electrode is in contact, whereby a current is directly applied from the p-side pad electrode to the p-type GaN-based semiconductor layer. The GaN-based light emitting diode according to (1), which is configured not to flow.
(5) The GaN-based light-emitting diode according to (4), wherein the p-side pad electrode has at least a portion in contact with the p-type GaN-based semiconductor layer formed of a platinum group element.
(6) The GaN-based light emitting diode according to any one of (1) to (5), wherein the thickness of the p-type ohmic electrode is 30 nm or more.
(7) The thickness of the p-type ohmic electrode is 30 nm or more, and the ratio of the area of the belt-like and annular regions to the area of the p-side pad electrode is larger than the area ratio of the electrode portion in the pattern. The GaN-based light emitting diode according to (1) above.
(8) The GaN-based light emitting diode according to (7), wherein the p-type ohmic electrode includes one or more layers selected from an Ag layer, a Cu layer, an Au layer, and an Al layer.
(9) The GaN-based light emitting diode according to any one of (1) to (8), wherein a width of the belt-like and annular region is 1 μm to 25 μm.

In the GaN-based LED of the present invention, the p-side pad electrode is formed so that the central portion thereof is in contact with the p-type GaN-based semiconductor layer through the opening provided in the p-type ohmic electrode, and the p-side pad electrode is separated from the p-side pad electrode. Since no current flows directly to the type GaN-based semiconductor layer, light emission below the center portion of the p-side pad electrode is suppressed. Therefore, the light emission efficiency is improved as compared with the GaN-based LED according to the related art in which the light emission below the central portion of the p-side pad electrode is not suppressed at all.
In the GaN-based LED of the present invention, the p-side pad electrode is formed so that the outer peripheral portion thereof overlaps the p-type ohmic electrode, whereby the p-side pad electrode and the p-type ohmic electrode overlap each other. Is a band-like and annular region along the contour line of the p-side pad electrode. By doing in this way, the effect that the variation in the forward voltage (Vf) of LED becomes small is acquired.

Hereinafter, the present invention will be specifically described with reference to the drawings.
1A and 1B are schematic views showing the structure of a GaN-based LED according to an embodiment of the present invention. FIG. 1A is a top view, and FIG. 1B is a cross-sectional view taken along line xy in FIG. It is.
In FIG. 1, 1 is a sapphire substrate, 2 is a 3 μm thick n-type GaN cladding layer doped with Si (silicon), and 3 is an In _X1 Ga _{1 -X1} N well layer and In _X2 Ga _{1 -X2} N (0 ≦ X2 <X1) Light emitting layer having a quantum well structure in which barrier layers are alternately stacked, 4 is a p-type AlGaN cladding layer having a thickness of 30 nm doped with Mg (magnesium), and 5 is a thickness having been doped with Mg A p-type GaN contact layer with a thickness of 200 nm, P1 is an n-type ohmic electrode formed by laminating an Al (aluminum) layer with a thickness of 1000 nm on a Ti (titanium) layer with a thickness of 20 nm, and P2 has a thickness of 20 nm. A p-type ohmic electrode obtained by laminating an Au (gold) layer with a thickness of 200 nm on a Ni (nickel) layer and heat-treating, P3 is an Au layer with a thickness of 1000 nm on a Ti layer with a thickness of 30 nm Is a p-side pad electrode formed by stacking and heat-treating. A buffer layer (not shown) made of AlGaN is formed between the sapphire substrate 1 and the n-type GaN cladding layer 2.

A p-type ohmic electrode P2 is formed on the surface of the p-type GaN contact layer 5 in a lattice pattern so as to cover almost the entire surface of the p-type GaN contact layer 5 except for the region where the p-side pad electrode P3 is formed. This lattice pattern is formed by regularly arranging square window portions W each having a side of 15 μm in an electrode film in a square matrix shape at intervals of 3 μm in two orthogonal directions. The surface of the p-type GaN contact layer 5 is exposed. When the area ratio of the electrode portion in the pattern having the window portion is defined as the ratio of the area of the electrode portion to the total area of the electrode portion and the area of the window portion, the area ratio of the electrode portion in this lattice pattern is as shown in FIG. As shown in FIG.
FIG. 3A illustrates only the p-type ohmic electrode P2 included in the GaN-based LED of FIG. 1, and includes a portion formed in a lattice pattern and a portion provided with an opening Q. ing.

On the upper surface of the element, a square p-side pad electrode P3 having a side of 100 μm is formed so as to be in contact with both the surface of the p-type GaN contact layer 5 and the p-type ohmic electrode P2. The p-side pad electrode P3 is in contact with the p-type GaN contact layer 5 inside the opening of the p-type ohmic electrode P2, and the outer peripheral portion thereof overlaps the p-type ohmic electrode P2.
A region indicated by hatching in FIG. 1A is a region S in which the p-side pad electrode P3 is in contact with the p-type ohmic electrode P2 so that these electrodes are in contact with each other. This region S has a band shape with a band width of about 10 μm along the contour line of the p-side pad electrode P3 and has an annular shape. In FIG. 1A, the dotted line that defines the inner edge of the annular region S is the outline of the p-type ohmic electrode P2 hidden under the p-side pad electrode P3. (= Inside the opening of the p-type ohmic electrode P2), the p-side pad electrode P3 is in contact with the surface of the p-type GaN contact layer 5. The area of the strip-shaped region S is approximately 3600μm ^2, the area ratio to the area of the p-side pad electrode P3 (10000 ²⁾ is about 36%.

  When the GaN-based LED of FIG. 1 is wire-bonded and energized, light is emitted from the light-emitting layer 3 below the p-type ohmic electrode P2, and emitted through the window W to the top of the device. On the other hand, since the p-side pad electrode P3 is made of Ti at the portion in contact with the p-type GaN contact layer 5, no light emission occurs below the region where the p-side pad electrode P3 is in contact with the surface of the p-type GaN contact layer 5. . This is because the contact between Ti and p-type GaN is a Schottky contact, so that no current flows directly from the p-side pad electrode P3 to the p-type GaN contact layer 5. Therefore, in the GaN-based LED of FIG. 1, no light emission occurs below the central portion of the p-side pad electrode P3. On the other hand, under the band-like region S, current flows from the p-type ohmic electrode P2 to the p-type GaN contact layer 5, and thus light emission occurs. This light emission occurs below the edge of the p-side pad electrode P3. Compared with the light emission under the central portion of the p-side pad electrode, which is generated in the conventional GaN-based LED, the light is easily emitted to the outside of the element through the window portion W.

  FIG. 2 is a top view of a GaN-based LED examined by the present inventors for comparison. 2 differs from the GaN-based LED shown in FIG. 1 in that the p-side pad electrode is stacked on the p-type ohmic electrode, and the p-side pad electrode is in contact with the p-type layer. However, a part of the shape of the p-type ohmic electrode is changed so as to be alternately arranged along the contour line of the p-side pad electrode. In FIG. 2, the black area is the area where the p-side pad electrode P <b> 13 overlaps the p-type ohmic electrode P <b> 12. FIG. 3B illustrates only the p-type ohmic electrode P12 included in the GaN-based LED of FIG. In the GaN-based LED of FIG. 2, the area of the region where the p-side pad electrode overlaps the p-type ohmic electrode is about 1/6 of the GaN-based LED of FIG.

As a result of studies by the present inventors, it has been found that the characteristics of the GaN-based LED of FIG. 2 are extremely unstable. Specifically, this GaN-based LED has a large variation in forward voltage, and along with this, the value of the average forward voltage of an element obtained from one wafer has also increased. In addition, as a defective product, when the element is viewed from above, an element that emits light only in the vicinity of the p-side pad electrode P13, that is, a current is normally transferred from the p-side pad electrode P13 to the p-type ohmic electrode P12. Many elements that did not flow occurred. These problems did not occur in the GaN-based LED of FIG. 1, and the GaN-based LED of FIG. 1 is more electrically connected to the p-type ohmic electrode and the p-side pad electrode than the GaN-based LED of FIG. This suggests that the general connection is good.
Thus, from the comparison of the GaN-based LED shown in FIG. 1 and the GaN-based LED shown in FIG. 2, in the GaN-based LED of the present invention, the region where the p-side pad electrode overlaps the p-type ohmic electrode is It is understood that it is important to form a band-like and annular region along the contour line of the pad electrode.

Next, a manufacturing procedure of the GaN-based LED of FIG. 1 will be described.
As a method for forming the GaN-based semiconductor layer on the sapphire substrate, a conventionally known vapor phase growth method such as a MOVPE method, an HVPE method, or an MBE method can be appropriately used.
When using the MOVPE method, first, the sapphire substrate 1 is mounted in a growth furnace of a MOVPE apparatus, and the substrate is heated to 1100 ° C. in a hydrogen atmosphere to perform thermal etching of the surface. Thereafter, the substrate temperature is lowered to a range of about 300 ° C. to 600 ° C., and trimethylgallium (TMG) and trimethylaluminum (TMA) are supplied as Group 3 materials and ammonia is supplied as a Group 5 material to form an AlGaN low temperature buffer layer.

After growing the AlGaN low-temperature buffer layer, the substrate temperature is raised to 900 ° C. to 1100 ° C., and TMG, ammonia and silane are supplied to grow the n-type GaN cladding layer 2. The concentration of Si doped in the n-type GaN cladding layer 2 is preferably 1 × 10 ¹⁸ cm ^{−3 to} 5 × 10 ¹⁹ cm ⁻³ .
When growing the light emitting layer 3, the substrate temperature is lowered to a range of 600 ° C. to 800 ° C., and the gas supply is adjusted so that the hydrogen gas concentration in the growth furnace is lowered. This is because the decomposition temperature of InGaN constituting the light emitting layer 3 is low and the decomposition of InGaN is promoted by the presence of hydrogen gas. By using trimethylindium (TMI) as the In raw material and changing the supply amount of TMI between the growth of the well layer and the growth of the barrier layer, the In composition can be changed. The well layer and the barrier layer may be appropriately doped with n-type impurities and / or p-type impurities. In order to generate light emission between bands, the well layer is preferably undoped, and the emission wavelength of the LED can be changed by adjusting the In composition of the well layer. For the thicknesses of the well layers and the barrier layers and the number of layers to be stacked, known techniques can be referred to as appropriate.

After the light emitting layer 3 is grown, the substrate temperature is raised again to 900 ° C. to 1100 ° C., and TMG, TMA, ammonia, bis (cyclopentadienyl) magnesium (Cp ₂ Mg) is supplied, and p-type AlGaN The cladding layer 4 is grown. Bis (ethylcyclopentadienyl) magnesium can also be used instead of Cp ₂ Mg. The Mg concentration doped in the p-type AlGaN cladding layer 4 is preferably 1 × 10 ¹⁸ cm ^{−3 to} 5 × 10 ²⁰ cm ⁻³ .
After the p-type AlGaN cladding layer 4 is grown to a predetermined thickness, the supply of TMA is stopped and the p-type GaN contact layer 5 is grown. In order to reduce the contact resistance with the p-type ohmic electrode P2, the p-type GaN contact layer 5 is preferably doped with Mg at a high concentration, for example, 1 × 10 ¹⁹ cm ⁻³ to 1 × 10 ²¹ cm. ^-3 .
About these layers, you may perform the process for activating the doped Mg as needed. Examples of such a process include an electron beam irradiation process and an annealing process.

When the formation of the GaN-based semiconductor layer is completed, the p-type ohmic electrode P2 is formed on the surface of the p-type GaN contact layer 5.
The p-type ohmic electrode P2 can be patterned using a normal photolithography technique. For example, after a photoresist film is formed so as to cover the entire surface of the p-type GaN contact layer 5, exposure is performed using a predetermined photomask, and development is performed, so that only the portion where the electrode film is to be formed is p-type. The photoresist film is patterned so that the surface of the GaN contact layer 5 is exposed. When an electrode film is formed thereon by electron beam evaporation and the photoresist film is lifted off, the electrode film can be left at a predetermined site.
As another method, an electrode film and a photoresist film are sequentially formed on the entire surface of the p-type GaN contact layer 5, and the photoresist film is patterned so that only a portion where the electrode film is to be removed is exposed, and then exposed. It is also possible to employ a method in which the electrode film at the part is removed by etching, the photoresist film is finally removed, and the electrode film is left only at a predetermined part.
The electrode film formed by laminating the Ni film and the Au film is preferably annealed at 400 ° C. or higher in order to reduce the contact resistance with the p-type contact layer 5. This annealing may be performed simultaneously with the annealing of the p-side pad electrode P3 described later.

  After the formation of the p-type ohmic electrode P2, the p-side pad electrode P3 has an outer peripheral portion overlapping the p-type ohmic electrode P2 at the position of the opening Q of the p-type ohmic electrode, and a central portion at the p-type GaN contact layer 5 It forms so that it may touch the surface of. Patterning of the p-side pad electrode P3 can also be performed by a lift-off method using a photolithography technique, similarly to the p-type ohmic electrode P2. The electrode film formed by laminating the Ti film and the Au film by the electron beam evaporation method improves the adhesion with the p-type GaN contact layer 5 and improves the electrical contact with the p-type ohmic electrode P2. Therefore, it is preferable to anneal at 400 ° C. or higher.

  In order to form the n-type ohmic electrode P1 on the n-type GaN cladding layer 2, first, the p-type GaN contact layer 5 is formed from the surface side of the p-type GaN contact layer 5 by a reactive ion etching method using chlorine gas. The p-type AlGaN cladding layer 4 and the light emitting layer 3 are partially removed to expose the n-type GaN cladding layer 2. Next, an electrode film in which a Ti film and an Al film are stacked is formed on the exposed surface of the n-type GaN cladding layer 2 by electron beam evaporation. This electrode film is preferably annealed at 400 ° C. or higher in order to reduce the contact resistance with the n-type GaN cladding layer 2.

  After the formation of the electrodes is completed, the wafer is cut using means such as scribing and dicing to perform chip separation. If the light emitting layer in the region along the dividing line is removed from the surface side of the p-type GaN contact layer 5 by a reactive ion etching method or the like before dividing, the light emitting layer is propagated by the impact at the time of dividing. Can reduce damage. Further, it is preferable that the end face of the GaN-based semiconductor layer including the end face of the light emitting layer 3 exposed in this step is protected with an insulating protective film made of silicon oxide or the like before chip separation. It is preferable to protect the surface of the exposed p-type GaN contact layer 5 and the surface of each electrode except for the portion that needs to be exposed for bonding.

As mentioned above, although embodiment of this invention was described using FIG. 1, the structure of GaN-type LED which concerns on this invention is not limited to the structure shown in FIG.
As a substrate for growing a GaN-based semiconductor layer, a substrate suitable for the growth of a GaN-based semiconductor crystal can be used without limitation. In addition to a sapphire substrate (C-plane, A-plane, R-plane), a SiC substrate ( 6H, 4H, 3C), GaN substrate, AlGaN substrate, AlN substrate, Si substrate, GaAs substrate, GaP substrate, spinel substrate, ZnO substrate, NGO (NdGaO ₃ ) substrate, LGO (LiGaO ₂ ) substrate, LAO (LaAlO ₃ ) A substrate, a ZrB ₂ substrate, a TiB ₂ substrate, or the like can be used. A template in which a GaN-based semiconductor crystal layer is previously grown as a base layer on the surface of a sapphire substrate or the like can also be used.
In the case of using a conductive substrate such as a SiC substrate, a GaN substrate, a Si substrate, a GaAs substrate, or a ZnO substrate among the above-exemplified substrates, an n-side electrode can be formed on the lower surface of the substrate.
On the crystal growth surface of the substrate, a mask pattern made of SiO ₂ or the like can be formed or the concavo-convex shape can be processed before the growth of the GaN-based semiconductor is started.
A reflective layer made of a metal film or a dielectric multilayer film may be provided on the lower surface of the substrate.
The substrate included in the GaN-based LED according to the present invention does not have to be a substrate used for the growth of the GaN-based semiconductor layer constituting the device, but is a separately prepared substrate used for the growth of the GaN-based semiconductor layer. It may be bonded after the is removed.

In the n-type layer, light-emitting layer, and p-type layer constituting the pn junction diode structure, electrons injected into the n-type layer and holes injected into the p-type layer are recombined in the light-emitting layer to emit light. There is no particular limitation on the crystal composition of each layer, the type / concentration of impurities, the thickness, and the like. For example, each layer may have a uniform or non-uniform crystal composition and impurity type / concentration in the thickness direction, and layers with different crystal composition and impurity type / concentration are laminated. A multilayer structure may be included, and a structure in which the crystal composition and the impurity concentration are inclined may be included. In order to increase the light emission efficiency, it is preferable to form a double hetero structure, and the light emitting layer preferably has a quantum well structure. A substrate made of an n-type GaN-based semiconductor can also be used as the n-type layer.
In the GaN-based LED shown in FIG. 1, the n-type GaN clad layer also serves as a contact layer, but the n-type clad layer and the n-type contact layer may be provided as separate layers. In addition to the cladding layer and contact layer, a layer for controlling dislocation propagation, a layer for suppressing impurity diffusion, a layer for controlling light reflectivity and transparency, and a layer for suppressing impurity diffusion Layers with various functions, such as layers, layers to relieve lattice mismatch and associated strain, layers to enhance carrier confinement in the light emitting layer, layers to protect the light emitting layer containing In, The n-type layer, the light-emitting layer, and the p-type layer constituting the pn junction diode structure may be provided as appropriate or all of them.

  The p-type ohmic electrode may be formed of a metal material that is in ohmic contact with the p-type GaN-based semiconductor at least at a portion in contact with the p-type layer. Metal materials that make ohmic contact with p-type GaN-based semiconductors are known. For example, Au (gold), Ni (nickel), Pd (palladium), Rh (rhodium), Ag (silver), Pt (platinum), Ir ( Examples thereof include simple substances such as iridium) and In (indium) and alloys thereof. The p-type ohmic electrode may be a single-layer film made of any of such metal materials, or may have a multilayer structure made of such a metal material at a portion in contact with the p-type layer. In the case of a multilayer structure, it is preferable to include an Ag layer, a Cu (copper) layer, an Au layer, an Al layer, or the like as a part of the multilayer structure in order to improve the conductivity and thermal conductivity of the electrode.

The p-type ohmic electrode is preferably formed to a thickness that hardly transmits light. This is because when the p-type ohmic electrode is formed of a transparent metal thin film, the light transmittance of the electrode fluctuates due to subtle changes in the electrode film thickness, slight differences in heat treatment conditions, etc. This is because it is sensitive to the influence. This problem can be solved if the electrode portion of the p-type ohmic electrode is formed to a thickness that hardly transmits light, and most of the emitted light is emitted outside the device through the window portion. The metal thin film exhibits a considerable translucency when the film thickness is about 20 nm or less, but reflects light well when formed with a film thickness of 30 nm or more. Therefore, the film thickness of the p-type ohmic electrode is preferably 30 nm. It is above, More preferably, it is 60 nm or more, More preferably, it is 100 nm or more.
Further, when a p-type ohmic electrode having a small film thickness so as to exhibit high light transmittance is further formed in a pattern having a window portion, the sheet resistance of the electrode becomes excessively high, and current flows laterally in the electrode. Therefore, the in-plane uniformity of the light emission intensity in the light emitting layer is lowered. In order to avoid such a problem, the thickness of the p-type ohmic electrode is preferably 60 nm or more, and more preferably 100 nm or more.
When the film thickness of the p-type ohmic electrode is too large, the p-type ohmic electrode tends to be easily peeled off from the surface of the p-type layer. Therefore, the film thickness is preferably 1 μm or less, more preferably 500 nm or less. Particularly preferably, it is 300 nm or less.

  When the p-type ohmic electrode has a multilayer structure, as an example of a preferred embodiment, a portion in contact with the surface of the p-type layer is a transparent Au film, and a highly reflective layer made of Ag, Al, Rh, or Pt is laminated thereon. An embodiment is mentioned. The reason why the Au film is in contact with the surface of the p-type layer is that the contact resistance is particularly small. In order to improve the adhesion to the p-type layer, a transparent thin film made of Ni or Pd is used. It may be formed first and an Au film may be laminated thereon. The highly reflective layer uses Ag, Al, Rh, Pt or the like having a high reflectance at a green to near ultraviolet wavelength, which is a typical emission wavelength of a GaN-based LED, so that light absorption by the p-type ohmic electrode is reduced. Thus, the film is formed to a thickness of 30 nm or more.

Examples of the pattern of the p-type ohmic electrode having a window include a net shape, a dendritic shape, a comb shape, a radial shape, a spiral shape, and a meander shape. These patterns can also be mixed.
Among these, the net-like pattern is the most preferable pattern because the current diffusibility is good. The shape of the window when the electrode is a net pattern may be any shape such as a triangle, a rectangle, a polygon, a circle, an ellipse, an irregular shape, an irregular shape, the size and orientation of each window, The arrangement or the like may be regular or irregular. In order to improve the in-plane uniformity of the emitted light intensity on the light extraction surface (the upper surface of the element), it is preferable to arrange the windows regularly, and to make the shape and size of each window uniform. preferable. For the purpose of simplifying the design of the window part and the design of the photomask used in the patterning process of the window part, it is preferable that the window part has a simple shape and the arrangement is regular. Therefore, in the case of a net pattern, a lattice pattern in which square windows are regularly arranged is most preferable.
In any case, it is preferable to form the electrode portion and window portion finely within the range where the electrode characteristics do not become unstable, and the band width or dot shape in the region where the electrode portion or window portion is formed in a band shape. The vertical and horizontal sizes of the dots in the formed region are preferably 1 μm to 25 μm, more preferably 2 μm to 20 μm, and particularly preferably 3 μm to 15 μm.

  The area ratio of the electrode part in the pattern having a window part is preferably 20% to 80%. The smaller the area ratio of the electrode portion, the higher the density of current supplied from the electrode film to the p-type layer immediately below the device during operation, but the lower the In composition of the GaN-based semiconductor forming the light emitting layer, the emission wavelength In a short GaN-based LED, the current density at which the saturation tendency of output begins is high, and the shift of the emission wavelength with respect to the change in current density is small. It is advantageous to improve the light emission efficiency to operate (the portion located immediately below the electrode film of the p-type ohmic electrode) at a high current density. Therefore, in an LED having an emission wavelength of violet to near-ultraviolet using InGaN for the light emitting layer, the area ratio of the electrode portion is preferably 20% to 40%.

The p-side pad electrode is formed of a metal material that is in Schottky contact with the p-type GaN-based semiconductor so that no current flows directly from the p-side pad electrode to the p-type layer. . Such metal materials are known, and examples thereof include simple substances such as Ti, Ta (tantalum), Cr (chromium), Mo (molybdenum), Al, and W (tungsten), and alloys thereof. The p-side pad electrode may be a single layer film made of such a metal material, or may have a multilayer structure in which a portion in contact with the p-type layer is made of the above metal material. In the case of a multilayer structure, Ag, Cu, Au, Al, Pt, Pd, Ni, etc. are preferably laminated on top. Considering the bonding property with the Au wire, the uppermost layer is most preferably made of Au.
Since Al has a particularly good light reflectivity in the visible to near-ultraviolet wavelength region, when the portion of the p-side pad electrode in contact with the p-type layer is formed of Al, the light generated in the light-emitting layer is absorbed by the p-side pad electrode. Loss received when reflected by the lower surface is reduced, and the luminous efficiency of the LED is improved. However, when the p-type ohmic electrode includes an Au layer, it is desirable that the portion formed of Al does not contact the p-type ohmic electrode. This is because when Al and Au come into contact, an alloying reaction accompanied by the generation of a light-absorbing colored substance may occur. Specifically, for example, as shown in FIG. 10, of the p-side pad electrode, a lower part P3a in contact with the p-type layer 5 and a part P3a-1 not in contact with the p-type ohmic electrode are formed of Al. The portion P3a-2 is formed of a metal material other than Al that is in Schottky contact with the p-type GaN-based semiconductor. In this case, as the metal material other than Al, it is preferable to use a refractory metal such as Ta, Mo, or W that has a high function as a barrier for preventing the alloying reaction of Al or Au.

As another method for preventing current from flowing directly from the p-side pad electrode to the p-type layer, plasma treatment is performed on the surface of the p-type layer that the p-side pad electrode is in contact with before the p-side pad electrode is formed. There is a method to apply. Such plasma treatment can be performed using a reactive ion etching apparatus. The plasma treatment includes, for example, dry etching treatment using Cl ₂ , SiCl ₄ , BCl ₃ or the like, or a gas obtained by adding Ar, H ₂ or the like to these. By performing the dry etching process, the surface of the p-type GaN-based semiconductor becomes non-ohmic or increases in resistance. Therefore, by performing dry etching in advance on a predetermined region of the surface of the p-type layer. The current can be prevented from flowing directly from the p-side pad electrode formed in the region to the p-type layer (Patent Document 4). The plasma treatment may be exposure to plasma using a gas such as Ar or H ₂ as a raw material. On the surface of a p-type GaN-based semiconductor that has been exposed to such plasma beyond the extent to which the natural oxide film is removed, a surface layer having a high resistance is formed by physically damaging the crystal structure. Therefore, this phenomenon can be used to prevent current from flowing directly from the p-side pad electrode to the p-type layer (Patent Document 5).

When the p-side pad electrode is formed by the lift-off method, the photoresist film used in the lift-off method can be preferably used as a protective mask in plasma processing. In the lift-off method, as shown in FIG. 11, a photoresist film PR is formed so as to cover the surface of the p-type GaN contact layer 5 on which the p-type ohmic electrode P2 is formed (FIG. 11A). An opening is formed in a predetermined portion of the resist film PR (FIG. 11B), and then an electrode film is formed on the surface of the p-type GaN contact layer 5 and the photoresist film PR exposed in the opening by vapor deposition or the like. Finally, the p-side pad electrode P3 is formed at the predetermined position by lifting off the photoresist film (FIG. 11C). Therefore, in the state shown in FIG. 11B, if plasma processing is performed using the photoresist film PR as a protective mask, only the minimum necessary region on the surface of the p-type GaN contact layer 5 is exposed to plasma. Therefore, even a region where the p-side pad electrode P3 is not formed can be prevented from being damaged by the plasma treatment. In addition, since the number of mask processes can be reduced (since a mask process for only plasma treatment is unnecessary), it is preferable in terms of manufacturing efficiency.
Further, when the plasma treatment is performed in the state shown in FIG. 11B, the p-side pad electrode is laminated, and the surface of the p-type ohmic electrode is also exposed to the plasma. System foreign matter (for example, photoresist residue) is removed, thereby improving the contact state between the p-side pad electrode and the p-type ohmic electrode, reducing the contact resistance between them, The effect of improving can be expected.

  When the surface of the p-type layer in contact with the p-side pad electrode is subjected to plasma treatment so that no current flows directly from the p-side pad electrode to the p-type layer, the p-side pad electrode is formed of an arbitrary metal material. it can. That is, it is not essential to form the portion of the p-side pad electrode that contacts the p-type layer with a metal material that is in Schottky contact with the p-type GaN-based semiconductor. Therefore, in order to improve the light emission efficiency of the LED, the portion of the p-side pad electrode is formed of a platinum group element such as Rh, Pt, or Ir having high light reflectivity in the visible to near-ultraviolet wavelength region. It is possible to reduce the loss received when the light generated in the light emitting layer is reflected by the lower surface of the p-side pad electrode. Since platinum group elements are chemically stable, contact with Au does not cause an alloying reaction accompanied by generation of a colored substance.

The shape of the p-side pad electrode may be any shape such as a square, a rectangle, a polygon, a circle, a semicircle, and an irregular shape. Since the p-side pad electrode is an obstacle to light extraction from above the element, it is preferable that the p-side pad electrode has a minimum size. Considering the area necessary for wire bonding including the yield, the p-side pad electrode is circular. The preferred diameter is 70 μm to 150 μm, and in the case of another shape, the size may include a circle of this size.
If the p-side pad electrode has a film thickness of 50 nm or more, peeling in the wire bonding process is difficult to occur. On the other hand, even if the film thickness is 2 μm or more, there is no particular effect, and only the amount of material used is increased. Therefore, the film thickness of the p-side pad electrode is preferably 50 nm to 2 μm, more preferably 200 nm to 1 0.5 μm, particularly preferably 500 nm to 1 μm.
Forming a plurality of p-side pad electrodes in contact with one p-type ohmic electrode is not prevented.

In the GaN-based LED according to the present invention, a region where the p-side pad electrode overlaps the p-type ohmic electrode is a band-shaped region along the contour line of the p-side pad electrode. The strip shape along the contour line of the electrode is a strip shape in which the direction along the contour line is the longitudinal direction, and may be a linear strip shape or a curved strip shape according to the shape of the contour line. There may be.
By making this belt-like region annular along the entire circumference of the contour line of the p-side pad electrode, the contact state between the p-side pad electrode and the p-type ohmic electrode can be stabilized.

  The width of the band-like region along the outline of the p-side pad electrode in which the p-side pad electrode overlaps the p-type ohmic electrode is preferably 1 μm to 25 μm, and more preferably 3 μm to 20 μm. It is especially preferable to set it as 5 micrometers-10 micrometers. If the width of the band-like region is less than 1 μm, it is difficult to align during manufacturing, which may increase the number of defective products. When the width of the band-shaped region exceeds 25 μm, light emission generated below the portion near the center of the p-side pad electrode in the band-shaped region tends to be difficult to be emitted out of the element from the window.

4 to 7 are top views of the GaN-based LEDs according to the embodiments of the present invention, respectively.
In the example of FIG. 4, the p-type ohmic electrode P <b> 2 includes a portion formed in a net-like pattern having an elongated window portion and a portion provided with a square opening, and the square p-side A pad electrode P3 is formed so as to cover the opening. A region S where the p-side pad electrode P3 overlaps the p-type ohmic electrode P2 is a band-like and annular region along the contour line of the p-side pad electrode.
In the example of FIG. 5, the p-type ohmic electrode P2 is composed of a part formed in a kind of comb pattern and a part provided with a pentagonal opening. A pentagonal p-side pad electrode P3 is formed so as to cover the opening, and a region S where the p-side pad electrode P3 overlaps the p-type ohmic electrode P2 is an outline of the p-side pad electrode P3 It is a belt-like and annular region along the line.
In the example of FIG. 6, the p-type ohmic electrode P <b> 2 includes a portion formed in a net-like pattern combining concentric linear electrode patterns and radial linear electrode patterns, and a circular shape located at the center of the portion. And a portion provided with an opening. A circular p-side pad electrode P3 is formed so as to cover the opening, and a region S where the p-side pad electrode P3 overlaps the p-type ohmic electrode P2 follows the contour line of the p-side pad electrode P3. It is a belt-like and annular region. The example of FIG. 6 shows a case where a conductive substrate is used, and the n-type ohmic electrode is formed on the lower surface of the substrate.
In the example of FIG. 7, the planar shape of the element is a rectangular shape, and the p-type ohmic electrode P <b> 2 includes a comb-shaped portion and an annular portion formed at one end thereof. The outer peripheral portion of the p-side pad electrode P3 is formed in contact with the annular portion of the p-type ohmic electrode P2, and the belt-like region S where both electrodes overlap is along the outline of the p-side pad electrode P3. It is a ring.

A metal film formed to a thickness that hardly transmits light has high thermal conductivity due to the action of free electrons. Therefore, when the p-type ohmic electrode is formed of such a metal film, it is advantageous in terms of heat dissipation of the element, and effects such as an increase in the lifetime of the element and stabilization of characteristics can be expected. For heat dissipation through the p-type ohmic electrode, heat generated inside the GaN-based semiconductor layer flows from the p-side pad electrode to the p-side pad electrode through the p-type ohmic electrode. Since it is generated by flowing out of the element via the Au wire to be bonded, it is desirable to increase the contact area between the p-type ohmic electrode and the p-side pad electrode.
In a preferred embodiment, the region where the p-side pad electrode overlaps the p-type ohmic electrode is a band-like and annular region along the outline of the p-side pad electrode, This is an aspect in which the area ratio of the annular region is made larger than the area ratio of the electrode portion in the portion where the p-type ohmic electrode has a pattern having a window portion. By doing in this way, luminous efficiency can be improved and heat dissipation can be ensured at the same time.
Furthermore, when the p-type ohmic electrode has a single layer or multilayer structure including at least one layer selected from an Ag layer, a Cu layer, an Au layer, and an Al layer, the heat dissipation is further improved. This is because Ag, Cu, Au, and Al are materials having the best thermal conductivity among metal materials.

When an n-type ohmic electrode is formed on the surface of an n-type layer exposed by etching, an n-side pad electrode for bonding an Au wire connected to the n-type ohmic electrode is separately formed on the n-type ohmic electrode. Alternatively, the n-type ohmic electrode itself may be formed in a thick film, and the n-side pad electrode may also be used. In the case where the n-type ohmic electrode itself is an n-side pad electrode, the thickness of the electrode is preferably 50 nm to 2 μm.
There is no limitation on the planar shape of the n-type layer surface exposed by etching and the n-type ohmic electrode formed thereon, and various shapes can be used. For example, see JP-A-2000-164930. it can.
The n-type ohmic electrode may be formed of a material in ohmic contact with the n-type GaN-based semiconductor at least at a portion in contact with the n-type layer. Materials that make ohmic contact with n-type GaN-based semiconductors are known. For example, simple metals such as Al, Ti, W, Nb (niobium), alloys thereof, indium tin oxide (ITO), zinc oxide, etc. And a transparent conductive film material made of an oxide semiconductor. The n-type ohmic electrode may be a single layer film made of any of the above materials, or may have a multilayer structure in which a portion in contact with the n-type layer is made of the above material.
When a conductive substrate is used, instead of exposing the n-type layer by etching and forming an n-type ohmic electrode on the surface, an n-side electrode can be formed on the lower surface of the conductive substrate. In that case, an electrode material having low contact resistance with the conductive substrate may be used in accordance with the type of the conductive substrate.

[Example]
As an example, the GaN-based LED of FIG. 1 was produced by the above-described procedure. The emission wavelength of the LED was set to 400 nm by controlling the In composition of the well layer. Ten wafers were produced using a 2-inch diameter sapphire substrate, and the forward voltage of the element after chip separation obtained from each wafer was measured using an auto prober. The number of elements obtained from one wafer is about 15,000. Further, 20 elements were sampled from each wafer, die-bonded on the stem, wire-bonded, and the output was measured with an integrating sphere.
As a result of the evaluation, the average value of the forward voltage of the element is 3.2 to 3.3 V for all the wafers, and the deviation from the average value of the forward voltage is 0.1 V or more in any wafer. The number of elements was less than 10% of the total. Moreover, the average value of the output was 5 mW.

[Comparative Example 1]
As Comparative Example 1, GaN having the same configuration as that of the example except that a p-type ohmic electrode having the same lattice pattern as that of the example was formed below the p-side pad electrode in the same manner as other regions. A system LED was produced by the same method as in the example and evaluated by the same method as in the example.
As a result of the evaluation, no significant difference was found between the examples and the forward voltage of the device. On the other hand, the average value of the output of the element was about 10% lower than that of the example.

[Comparative Example 2]
As Comparative Example 2, a GaN-based LED shown in FIG. In the GaN-based LED of Comparative Example 2, the region where the p-side pad electrode overlaps the p-type ohmic electrode is not a band-like and annular region along the outline of the p-side pad electrode. The region in contact with the p-type ohmic electrode and the region in which the p-side pad electrode is in contact with the p-type GaN contact layer are alternately arranged along the contour line of the p-side pad electrode. Thus, except that a part of the pattern of the p-type ohmic electrode is changed, the other configuration is the same as that of the GaN-based LED of the example. The area of the region where the p-side pad electrode overlaps the p-type ohmic electrode is about 1/6 of the LED of Example 1.
As a result of measuring the forward voltage by the same method as in the example, the average value of each wafer was 3.4V to 3.6V. This is because the variation in the forward voltage is large, and a large number of elements having a deviation from the average value of the forward voltage of 0.1 V or more are generated in each wafer. Moreover, although it was not seen in the Example, the element from which the deviation from the average value of a forward voltage was 0.3V or more also generate | occur | produced from each wafer.

In the GaN-based LEDs of Comparative Example 1 and Comparative Example 2, a defect in which “chip” occurs at the edge of the p-side pad electrode often occurred in the lift-off process when forming the p-side pad electrode. When the portion where the “chip” occurs is observed in detail, the electrode film of the p-side pad electrode is broken at the boundary between the portion where the p-side pad electrode is in contact with the p-type ohmic electrode and the portion where the p-type GaN contact layer is in contact. Has occurred. On the other hand, in the device of the example, no such defect occurred.
The details of the cause of the breakage of the electrode film of the p-side pad electrode are unknown, but the present inventors consider as follows. That is, the p-type GaN-based semiconductor layer and the p-type ohmic electrode have different adhesive strengths with the p-side pad electrode and also have different thermal expansion coefficients. Mechanical stress and thermal stress tend to concentrate at the boundary between the portion in contact with the portion and the portion in contact with the p-type GaN contact layer. Therefore, if the boundary portion exists at the edge portion of the p-side pad electrode, the p-side pad electrode is easily broken at the boundary portion in a lift-off process or the like. On the other hand, in the GaN-based LED of the present invention, the edge of the p-side pad electrode is overlapped on the p-type ohmic electrode over the entire circumference, so that such a problem is improved.

It is a figure which shows the GaN-type light emitting diode which concerns on embodiment of this invention, Fig.1 (a) is a top view, FIG.1 (b) is sectional drawing in the xy line | wire of Fig.1 (a). It is a top view which shows the GaN-type light emitting diode which concerns on a comparative example. FIG. 3A is a diagram showing a form of a p-type ohmic electrode, FIG. 3A is a plan view of the p-type ohmic electrode included in the GaN-based light emitting diode of FIG. 1, and FIG. 3B is a GaN-based light emission of FIG. It is a top view of the p-type ohmic electrode contained in a diode. It is a top view which shows the GaN-type light emitting diode which concerns on other embodiment of this invention. It is a top view which shows the GaN-type light emitting diode which concerns on other embodiment of this invention. It is a top view which shows the GaN-type light emitting diode which concerns on other embodiment of this invention. It is a top view which shows the GaN-type light emitting diode which concerns on other embodiment of this invention. It is a top view which shows the conventional GaN-type light emitting diode. It is a figure for demonstrating the area ratio of the electrode part in the pattern which has a window part. It is sectional drawing for demonstrating the suitable aspect of the p side pad electrode in the GaN-type light emitting diode which concerns on embodiment of this invention. It is sectional drawing for demonstrating the suitable formation method of the p side pad electrode in the GaN-type light emitting diode which concerns on embodiment of this invention. It is sectional drawing which shows the conventional GaN-type light emitting diode.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Sapphire substrate 2 n-type GaN clad layer 3 Light emitting layer 4 p-type AlGaN clad layer 5 p-type GaN contact layer P1 n-type ohmic electrode P2 p-type ohmic electrode P3 p-side pad electrode

Claims (9)

A p-type GaN-based semiconductor layer formed on a light-emitting layer made of a GaN-based semiconductor, a p-type ohmic electrode formed on the surface of the p-type GaN-based semiconductor layer, and the p-type ohmic electrode electrically A p-side pad electrode connected to the GaN-based light emitting diode,
The p-type ohmic electrode consists of a part formed in a pattern having a window part through which light generated in the light emitting layer can pass, and a part provided with an opening,
The p-side pad electrode is formed so as to be in contact with the p-type GaN-based semiconductor layer inside the opening and to have an outer peripheral portion overlapping the p-type ohmic electrode, whereby the p-side pad electrode is formed. And the region where the p-type ohmic electrode overlaps is a band-like and annular region along the contour line of the p-side pad electrode,
Contact between the p-side pad electrode and the p-type GaN-based semiconductor layer is non-ohmic, or the surface of the p-type GaN-based semiconductor layer in contact with the p-side pad electrode is increased in resistance. Accordingly, a current is prevented from flowing directly from the p-side pad electrode to the p-type GaN-based semiconductor layer. 2. The GaN-based light-emitting diode according to claim 1, wherein at least a portion of the p-side pad electrode that is in contact with the p-type GaN-based semiconductor layer is formed of a metal material that is in Schottky contact with the p-type GaN-based semiconductor. The p-type ohmic electrode includes an Au layer, and the portion of the p-side pad electrode that contacts the p-type GaN-based semiconductor layer does not contact the p-type ohmic electrode. The GaN-based light emitting diode according to claim 2, wherein the GaN-based light emitting diode is provided. Plasma treatment is performed on the surface of the p-type GaN-based semiconductor layer where the p-side pad electrode contacts, so that no current flows directly from the p-side pad electrode to the p-type GaN-based semiconductor layer. The GaN-based light emitting diode according to claim 1, wherein 5. The GaN-based light-emitting diode according to claim 4, wherein at least a portion of the p-side pad electrode in contact with the p-type GaN-based semiconductor layer is formed of a platinum group element. The GaN-based light emitting diode according to claim 1, wherein the p-type ohmic electrode has a thickness of 30 nm or more. The thickness of the p-type ohmic electrode is 30 nm or more, and the ratio of the area of the band-like and annular regions to the area of the p-side pad electrode is larger than the area ratio of the electrode portion in the pattern. 2. A GaN-based light emitting diode according to 1. The GaN-based light emitting diode according to claim 7, wherein the p-type ohmic electrode includes one or more layers selected from an Ag layer, a Cu layer, an Au layer, and an Al layer. The GaN-based light emitting diode according to any one of claims 1 to 8, wherein a width of the band-like and annular region is 1 µm to 25 µm.