JP5533675B2 - Semiconductor light emitting device - Google Patents

Description

  The present invention relates to a positive electrode for a semiconductor light emitting device, and more particularly to a translucent positive electrode for a semiconductor light emitting device, which is suitable for a gallium nitride compound semiconductor light emitting device and can obtain strong light emission at a low driving voltage.

  In recent years, GaN-based compound semiconductor materials have attracted attention as semiconductor materials for short wavelength light emitting devices. GaN-based compound semiconductors include sapphire single crystals, various oxides and III-V compounds as substrates, and metalorganic vapor phase chemical reaction method (MOCVD method) or molecular beam epitaxy method (MBE method). And so on.

  A characteristic of the GaN-based compound semiconductor material is that current diffusion in the lateral direction is small. The cause is thought to be the presence of dislocations penetrating from the substrate present in the epitaxial crystal to the surface, but the details are not known. Furthermore, the p-type GaN-based compound semiconductor has a higher resistivity than the n-type GaN-based compound semiconductor, and there is almost no spread of lateral current in the p-type layer by simply laminating metal on the surface. In the case of an LED structure having a pn junction, light is emitted only directly below the positive electrode.

  For this reason, a translucent positive electrode is often used that emits light emitted directly under the positive electrode through the positive electrode. In particular, as a technology used in the market, Ni and Au are stacked on the p-type layer as a positive electrode about several tens of nanometers each, and then heated in an oxygen atmosphere for alloying treatment to reduce the resistance of the p-type layer. It has been proposed to simultaneously promote the formation of a positive electrode having translucency and ohmic properties (see Patent Document 1).

  Examples of the material for the light-transmitting electrode include a conductive metal oxide and an extremely thin metal. Since these materials and structures are difficult to bond directly, it is common to arrange a bonding pad electrode having a certain thickness so as to be electrically connected to a light-transmitting electrode. . However, since this pad electrode is a metal material having a certain thickness, there is a disadvantage that the pad electrode is not translucent and light emitted directly under the pad electrode cannot be extracted outside.

  In addition, in order to improve the adhesion of the pad electrode, a notch is formed in a part of the translucent electrode, and a pad electrode extending over this part and the adjacent translucent electrode is formed, so that the GaN semiconductor layer is directly formed. A structure has been disclosed in which bonding strength is obtained at the contacting portion and current diffusion is performed at the contacting portion on the translucent electrode. (See Patent Document 2)

  In addition, since the light emitted immediately below the pad electrode cannot be extracted to the outside, in order to efficiently use the current, no current has been injected immediately below the pad electrode and no light has been generated immediately below the pad electrode. Technology in the direction has been devised.

  For example, a technique is disclosed in which an insulating region is formed under a pad electrode and light can be efficiently obtained by not injecting current under the pad (see Patent Documents 3 and 4). In addition, a technique for preventing current from being injected into this region by forming the lowermost surface of the pad electrode with a metal having a high contact specific resistance with respect to the p-type layer has been disclosed (see Patent Document 5).

  However, according to our study, when these methods are used, the area in which the positive electrode is in ohmic contact with the p-type layer is reduced, so that the drive voltage is increased.

Japanese Patent No. 2803742 Japanese Patent Laid-Open No. 7-94782 JP-A-8-250768 JP-A-8-250769 JP-A-10-242516

  An object of the present invention is to provide a translucent positive electrode for a face-up chip capable of obtaining strong light emission with a low driving voltage in order to solve the above-mentioned problems. In the present invention, translucency means translucency with respect to light in the emission wavelength region. In the case of a gallium nitride-based compound semiconductor light emitting device, the emission wavelength region is usually in the range of 300 to 600 nm.

The present invention provides the following inventions.
(1) It is composed of a translucent electrode formed on a semiconductor layer and a bonding pad electrode formed on the translucent electrode, and the bonding pad electrode has a reflective layer at least on a surface in contact with the translucent electrode. A positive electrode for a semiconductor light emitting device.

(2) The positive electrode for a semiconductor light-emitting element according to the above item 1, wherein the adhesion strength between the reflective layer and the translucent electrode is 490 mN (50 gf) or more in terms of peel strength.

(3) The positive electrode for a semiconductor light-emitting element according to the above item 1 or 2, wherein the translucent electrode has a light transmittance of 60% or more at an emission wavelength at which the element emits light.

(4) The semiconductor light-emitting device according to any one of the above items 1 to 3, wherein the reflective layer is made of a metal selected from the group consisting of Al, Ag, Pt group metals and alloys containing at least one of these metals. Positive electrode.

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

(6) The semiconductor light-emitting element according to any one of 1 to 5 above, wherein the reflective layer is a metal selected from the group consisting of Al, Ag, Pt, and an alloy containing at least one of these metals. Positive electrode.

(7) The positive electrode for a semiconductor light-emitting element according to any one of the above items 1 to 6, wherein the reflective layer has a thickness of 20 to 3000 nm.

(8) The bonding pad electrode according to any one of the above items 1 to 7, wherein the bonding pad electrode has a layered structure and has a barrier layer made of Ti, Cr or Al and / or an uppermost layer made of Au or Al in addition to the reflective layer. The positive electrode for semiconductor light emitting elements as described in any one of.

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

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

(11) The positive electrode for a semiconductor light-emitting element according to the above item 10, wherein the translucent electrode is made of only a transparent material other than metal.

(12) The positive electrode for a semiconductor light-emitting element according to any one of (1) to (11), wherein a process for extracting light is performed on the outermost surface layer of the translucent electrode.

(13) The positive electrode for a semiconductor light-emitting element according to the above item 12, wherein the outermost surface layer of the translucent electrode is a transparent material.

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

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

(16) The positive electrode for a semiconductor light emitting device as described in 15 above, wherein the contact layer is platinum.
(17) The positive electrode for a semiconductor light-emitting element according to any one of the above 14 to 16, wherein the contact layer has a thickness of 0.1 to 7.5 nm.

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

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

(20) The positive electrode for a semiconductor light-emitting element according to the above item 19, wherein the current diffusion layer is gold or a gold alloy.
(21) The positive electrode for a semiconductor light-emitting element according to any one of the above 14 to 20, wherein the current diffusion layer has a thickness of 1 to 20 nm.

(22) The positive electrode for a semiconductor light-emitting element according to the above item 21, wherein the current diffusion layer has a thickness of 3 to 6 nm.

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

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

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

(26) The positive electrode for a semiconductor light-emitting element according to any one of the above 10, 11, 13, and 23 to 25, wherein the transparent material has a thickness of 10 to 5000 nm.

(27) The positive electrode for a semiconductor light-emitting element according to the above item 26, wherein the transparent material has a thickness of 100 to 1000 nm.
(28) A semiconductor light-emitting device using the positive electrode according to any one of items 1 to 27.

(29) An n-type semiconductor layer, a light-emitting layer, and a p-type semiconductor layer made of a gallium nitride compound semiconductor are provided in this order on a substrate, and a positive electrode and a negative electrode are provided on the p-type semiconductor layer and the n-type semiconductor layer, respectively. 28. A gallium nitride-based compound semiconductor light-emitting element, wherein the positive electrode is the positive electrode according to any one of 1 to 27 above.
(30) A lamp comprising the light emitting device as described in 28 or 29 above.

  Attenuation of light due to absorption of light at the surface in contact with the bonding pad electrode and the translucent electrode by providing a reflective layer on at least the surface in contact with the translucent electrode of the bonding pad electrode for passing a current through the translucent electrode The efficiency of extracting emitted light can be increased, and the emission intensity can be increased.

It is the schematic diagram which showed the cross section of an example of the semiconductor light-emitting device which has a positive electrode of this invention. It is the schematic diagram which showed the cross section of the gallium nitride type compound semiconductor light-emitting device which has the positive electrode of this invention produced in the Example. It is the schematic diagram which showed the plane of the gallium nitride type compound semiconductor light-emitting device which has the positive electrode of this invention produced in the Example.

  FIG. 1 is a schematic view showing a cross section of an example of a light emitting device having a positive electrode of the present invention. Reference numeral 10 denotes a positive electrode according to the present invention, which includes a translucent electrode (11) and a bonding pad electrode (13). The translucent electrode (11) is composed of, for example, a contact layer (111) and a current diffusion layer (112). The bonding pad electrode (13) has, for example, a three-layer structure of a reflective layer (131), a barrier layer (132), and an uppermost layer (133). Reference numeral 1 denotes a substrate. Reference numeral 2 denotes a GaN-based compound semiconductor layer, which includes an n-type semiconductor layer 3, a light emitting layer 4, and a p-type semiconductor layer 5. 6 is a buffer layer, and 20 is a negative electrode.

  In the face-up type chip provided with the translucent positive electrode, only the light emitted from the light emitting layer (4) toward the translucent electrode portion where the bonding pad electrode does not exist and the light directed toward the side surface of the chip. Take out to the outside.

  When the positive electrode of the present invention is used, the light directed to the bonding pad electrode (13) is reflected by the reflective layer (131) on the lowermost surface of the bonding pad electrode (the surface in contact with the translucent electrode), and a part thereof is scattered. Proceeding in the horizontal or diagonal direction, a part proceeds directly under the bonding pad electrode. The light that has been scattered and traveled in the lateral direction or the oblique direction is taken out from the side surface of the chip. On the other hand, the light traveling in the direction immediately below the bonding pad electrode is further scattered and reflected by the lower surface of the chip, and is extracted to the outside through the side surface and the translucent electrode (portion where the bonding pad electrode does not exist).

  As described above, by providing the reflective layer on the lowermost surface of the bonding pad electrode, light emitted immediately below the bonding pad electrode can be extracted to the outside, and high light emission intensity can be maintained. In the case where light is absorbed at the lowermost surface of the bonding pad electrode, most of the light emitted directly under the pad electrode is absorbed at the lowermost surface of the pad electrode and cannot be extracted outside.

  It is a requirement for the reflective layer to be in direct contact with the translucent electrode to manifest the effects of the present invention. For this reason, in order for the bonding pad to obtain sufficient strength, it is necessary that the reflective layer is firmly bonded to the translucent electrode. At the very least, it should not be peeled off in the step of connecting the gold wire to the bonding pad by a general method. For that purpose, it is desirable to have a peel strength of about 490 mN (50 gf). More desirably, it is 784 mN (80 gf) or more, and more desirably 980 mN (100 gf) or more.

  In order to enhance the adhesion strength between the reflective layer and the translucent electrode, there are methods such as devising a pretreatment of the surface of the translucent electrode, or performing a heat treatment after the formation of the reflective layer.

  The reflectance of the reflective layer varies greatly depending on the material constituting the reflective layer, but is preferably 60% or more. Further, it is preferably 80% or more, and more preferably 90% or more.

  The reflectance can be measured relatively easily with an apparatus called a spectrophotometer. However, since the bonding pad electrode itself has a small area, it is difficult to measure the reflectance. Therefore, a transparent “dummy substrate” made of glass, for example, having a large area is placed in the chamber when forming the bonding pad electrode, and at the same time, the same bonding pad electrode is created on the dummy substrate and measured. be able to.

  The reflective layer of the bonding pad electrode is preferably composed of a highly reflective metal, and is composed of a platinum group metal such as Pt, Rh, Ru, Ir, Al, Ag, and an alloy containing at least one of these metals. More preferably. Among these, Al, Ag, Pt, and alloys containing at least one of these metals are common as electrode materials, and are excellent in terms of easy availability and handling.

  The bonding pad electrode is formed directly on the translucent electrode without forming a notch or window in the translucent electrode. Since it is formed on the translucent electrode, the ohmic contact area is not reduced, and the contact resistance of the electrode does not increase even immediately under the bonding pad electrode, thereby preventing an increase in driving voltage. be able to. Further, since the light transmitted through the translucent electrode is reflected by the reflective layer on the lowermost surface of the bonding pad electrode, it is possible to suppress unnecessary absorption of light.

  The bonding pad electrode can be formed anywhere as long as it is on the translucent electrode. For example, it may be formed at a position farthest from the negative electrode, or may be formed at the center of the chip. However, if it is formed too close to the negative electrode, it is not preferable because a short circuit between wires and balls occurs during bonding.

  The bonding pad electrode area is as large as possible, but the bonding operation is easy, but it prevents the light emission from being taken out. For example, covering an area that exceeds half the area of the chip surface hinders the extraction of light emission, and the output is significantly reduced. On the other hand, if it is too small, the bonding work becomes difficult and the yield of the product is lowered. Specifically, it is preferably slightly larger than the diameter of the bonding ball, and generally has a circular shape with a diameter of 100 μm.

  When the reflective layer of the bonding pad electrode is formed of a metal having a high reflectance, the thickness is desirably 20 to 3000 nm. If the reflective layer is too thin, a sufficient reflection effect cannot be obtained. If it is too thick, there is no particular advantage, and only a long process time and material waste are caused. More desirably, the thickness is 50 to 1000 nm, and most desirably 100 to 500 nm.

  The bonding pad electrode can be made of only the metal having the high reflectance described above. That is, the bonding pad electrode may be composed only of the reflective layer. However, various structures using various materials are known as bonding pad electrodes, and the above-described reflective layer may be newly provided on the semiconductor layer side (translucent electrode side) of these known materials. Moreover, the lowermost layer on the semiconductor layer side of these known ones may be replaced with the above-described reflective layer.

  In the case of such a laminated structure, the laminated structure portion above the reflective layer is not particularly limited, and any structure can be used. For example, the layer formed on the reflective layer of the bonding pad electrode has a role of enhancing the strength of the entire bonding pad electrode. For this reason, it is necessary to use a relatively strong metal material or to sufficiently increase the film thickness. Desirable materials are Ti, Cr or Al. Among these, Ti is desirable in terms of material strength. When such a function is given, this layer is called a barrier layer.

  The barrier layer may also serve as a reflective layer. When a thick metal material having good reflectivity and mechanically strong is formed, it is not necessary to form a barrier layer. For example, when Al is used as the reflective layer, it is not necessary to form a barrier layer.

  The thickness of the barrier layer is preferably 20 to 3000 nm. If the barrier layer is too thin, a sufficient strength strengthening effect cannot be obtained, and if it is too thick, no particular advantage is produced and only an increase in cost is caused. More desirably, the thickness is 50 to 1000 nm, and most desirably 100 to 500 nm.

  The uppermost layer of the bonding pad electrode (on the side opposite to the reflective layer) is preferably made of a material having good adhesion to the bonding ball. Gold is often used for the bonding balls, and Au and Al are known as metals having good adhesion to the gold balls. Of these, gold is particularly desirable. The thickness of the uppermost layer is desirably 50 to 1000 nm, and more desirably 100 to 500 nm. If it is too thin, the adhesion to the bonding ball will be poor, and if it is too thick, no particular advantage will be produced, and only the cost will increase.

  Preferred performances required for the translucent electrode formed on the semiconductor layer (p-type layer) include a low contact resistance with the p-type layer and a face-up mount that extracts light from the light-emitting layer from the electrode surface side. In the case of the type light emitting device, excellent light transmittance and excellent conductivity for uniformly distributing the current over the entire surface of the p-type layer can be mentioned.

  Various structures using various materials are known as the translucent electrode, and these known translucent electrodes can be used without any limitation in the present invention. However, in order to satisfy the above-mentioned required performance, a translucent electrode having at least two layers of a contact layer in contact with the p-type layer and a current diffusion layer on the contact layer for assisting current diffusion is preferable. Of course, as long as the above-mentioned required performance is satisfied, a single layer having the functions of the contact layer and the current diffusion layer may be provided, and in the case of a single layer structure, there is an advantage that the process is not complicated.

  As the performance required for the contact layer, it is preferable that the contact resistance with the p-type layer is small. From this viewpoint, the material of the contact layer is platinum (Pt), ruthenium (Ru), osmium (Os), rhodium (Rh). ), Platinum group metals such as iridium (Ir) and palladium (Pd) or alloys thereof are preferred. Among these, Pt or an alloy thereof has a high work function and can obtain a good ohmic contact without heating to a relatively high resistance p-type GaN compound semiconductor layer not subjected to high-temperature heat treatment. preferable.

  When the contact layer is composed of a platinum group metal or an alloy thereof, it is necessary to make the thickness very thin from the viewpoint of light transmittance. The thickness of the contact layer is preferably in the range of 0.1 to 7.5 nm. If it is less than 0.1 nm, it is difficult to obtain a stable thin layer. When it exceeds 7.5 nm, the translucency is lowered, and more preferably 5 nm or less. In consideration of a decrease in translucency due to subsequent lamination of the current diffusion layer and stability of film formation, the range of 0.5 to 2.5 nm is particularly preferable.

  However, by reducing the thickness of the contact layer, the electrical resistance in the surface direction of the contact layer increases, and the current flows only in the periphery of the bonding pad electrode, which is the current injection portion, together with the p-type layer having a relatively high resistance. It does not spread, resulting in a non-uniform light emission pattern, and the light emission output decreases.

  Therefore, by arranging a high light transmittance and high conductivity current diffusion layer on the contact layer as a means to supplement the current diffusivity of the contact layer, the low contact resistance and light transmittance of the platinum group metal are not greatly impaired. It is possible to spread the current uniformly, and as a result, a light emitting element having a high light emission output can be obtained.

  The material of the current spreading layer is preferably a metal having a high conductivity, for example, a metal selected from the group consisting of gold, silver and copper, or an alloy containing at least one of them. Of these, gold is most preferable because of its high light transmittance when it is made into a thin film.

  On the other hand, the material of the current spreading layer should be made of a transparent material such as zinc sulfide and metal oxide having high conductivity, such as ITO, ZnO, aluminum zinc oxide, fluorine-doped tin oxide, titanium oxide, bismuth oxide and magnesium oxide. Can do. Such a transparent material is preferable because of its high light transmittance. Among them, ITO, ZnO, aluminum zinc oxide, and fluorine-doped tin oxide are known to have high conductivity and are most preferable.

  When the current spreading layer is formed of metal, the thickness is preferably 1 to 20 nm. If it is less than 1 nm, the current diffusion effect is not sufficiently exhibited. If it exceeds 20 nm, the light transmittance of the current diffusion layer is significantly reduced, and there is a fear that the light emission output is reduced. More preferably, it is 10 nm or less. Furthermore, by making the thickness in the range of 3 to 6 nm, the balance between the light transmittance of the current diffusion layer and the effect of current diffusion is the best, and by combining with the above contact layer, light is emitted uniformly over the entire surface of the positive electrode, In addition, high output light emission can be obtained.

  When the current diffusion layer is formed of a transparent material, the thickness is preferably 10 to 5000 nm. If it is less than 10 nm, the current diffusion effect is not sufficiently exhibited. If it exceeds 5000 nm, the light transmittance of the current diffusion layer is lowered, and there is a concern that the light emission output is lowered. 50 to 2000 nm is more preferable. Furthermore, by making the thickness in the range of 100 to 1000 nm, the balance between the light transmittance of the current diffusion layer and the effect of current diffusion is the best, and by combining with the above contact layer, light is emitted uniformly over the entire surface of the positive electrode, In addition, high output light emission can be obtained.

  When the bonding pad electrode is formed on the translucent electrode, the uppermost layer of the translucent electrode may be covered with a metal or a metal oxide.

  The uppermost layer of the translucent electrode may be a current diffusion layer, or a layer for bonding pad electrode bonding may be formed on the current diffusion layer. Since the light-transmitting property is deteriorated by forming a layer for bonding, the uppermost layer is preferably a current diffusion layer.

  In order to extract light, the surface of the translucent electrode may be uneven. For the production of the irregularities, a method using patterning or a method of providing irregularities by wet processing can be employed. As the uneven shape, a known shape such as a stripe shape, a lattice shape, or a dot shape can be used without any limitation.

  Further, the bonding strength of the pad can be increased by forming the bonding pad on the surface having such an uneven shape.

  The method for forming the contact layer, the current diffusion layer, and the bonding pad electrode is not particularly limited, and a known vacuum deposition method or sputtering method can be used.

  As shown in FIG. 1, the positive electrode of the present invention is a conventionally known nitridation in which a gallium nitride compound semiconductor is stacked on a substrate via a buffer layer to form an n-type semiconductor layer, a light emitting layer, and a p-type semiconductor layer. It can be used for semiconductor light emitting devices including gallium compound semiconductor light emitting devices without any limitation.

For the substrate, sapphire single crystal (Al ₂ O ₃ ; A plane, C plane, M plane, R plane), spinel single crystal (MgAl ₂ O ₄ ), ZnO single crystal, LiAlO ₂ single crystal, LiGaO ₂ single crystal, Substrate materials such as oxide single crystals such as MgO single crystals, Si single crystals, SiC single crystals, GaAs single crystals, AlN single crystals, GaN single crystals, and boride single crystals such as ZrB ₂ can be used without any limitation. . The plane orientation of the substrate is not particularly limited. Moreover, a just board | substrate may be sufficient and the board | substrate which provided the off angle may be sufficient.

The n-type semiconductor layer, the light emitting layer, and the p-type semiconductor layer can be used without any limitation including those of various known structures. In particular, the carrier concentration of the p-type semiconductor layer may be a general concentration, but the light-transmitting property of the present invention is also applied to a p-type semiconductor layer having a relatively low carrier concentration, for example, about 1 × 10 ¹⁷ cm ^−3. A sex electrode is applicable.

As the gallium nitride compound semiconductor constituting the n-type semiconductor layer, the light emitting layer, and the p-type semiconductor layer in the present invention, the general formula Al _x In _y Ga _1-xy N (0 ≦ x <1, 0 ≦ y <1,0) Semiconductors having various compositions represented by ≦ x + y <1) can be used without any limitation.

The growth method of these gallium nitride-based compound semiconductors is not particularly limited. Group III nitride semiconductors such as MOCVD (metal organic chemical vapor deposition), HVPE (hydride vapor deposition), MBE (molecular beam epitaxy), etc. All methods known to grow can be applied. A preferred growth method is the MOCVD method from the viewpoint of film thickness controllability and mass productivity. In the MOCVD method, hydrogen (H ₂ ) or nitrogen (N ₂ ) is used as a carrier gas, trimethyl gallium (TMG) or triethyl gallium (TEG) is used as a Ga source as a group III source, and trimethyl aluminum (TMA) or triethyl aluminum is used as an Al source. (TEA), trimethylindium (TMI) or triethylindium (TEI) as an In source, ammonia (NH ₃ ), hydrazine (N ₂ H ₄ ), or the like as an N source that is a group V source. In addition, as a dopant, monosilane (SiH ₄ ) or disilane (Si ₂ H ₆ ) is used as an Si raw material for n-type, germane (GeH ₄ ) or an organic germanium compound is used as a Ge raw material, and Mg raw material is used for a p-type. For example, biscyclopentadienyl magnesium (Cp ₂ Mg) or bisethylcyclopentadienyl magnesium ((EtCp) ₂ Mg) is used.

  In order to form a negative electrode in contact with an n-type semiconductor layer of a gallium nitride compound semiconductor in which an n-type semiconductor layer, a light-emitting layer, and a p-type semiconductor layer are sequentially stacked on a substrate, a part of the light-emitting layer and the p-type semiconductor layer To remove the n-type semiconductor layer. Thereafter, the positive electrode of the present invention is formed on the remaining p-type semiconductor layer, and the negative electrode is formed on the exposed n-type semiconductor layer. As the negative electrode, negative electrodes having various compositions and structures, including known negative electrodes, can be used without any limitation.

  In the case of an element using a substrate that is transparent with respect to the light emission wavelength, such as sapphire or SiC, a reflective film may be formed on the back surface of the substrate. Forming a reflective film is desirable because it can reduce the loss of light on the lower surface of the substrate and further improve the efficiency of extracting emitted light to the outside.

  In addition, the semiconductor layer, the transparent electrode layer, the back surface of the substrate, or the like can be processed to be uneven, and the efficiency of extracting emitted light to the outside can also be improved by this processing. In addition to forming a surface perpendicular to the substrate, the processing can be performed by forming an oblique surface. In order to prevent multiple reflection, it is desirable to form an oblique surface.

  The processing can be performed by scraping the semiconductor layer, the transparent electrode layer, or the back surface of the substrate, or by attaching a structure made of a transparent material.

  When the positive electrode for a semiconductor light-emitting device of the present invention is used, a gallium nitride compound semiconductor light-emitting device having high emission intensity can be obtained. In other words, since this technology can produce a high-intensity LED lamp, electronic devices such as mobile phones, displays, and panels incorporating a chip produced by this technology, automobiles, computers incorporating such electronic devices, Machine devices such as game machines can be driven with low power and can achieve high characteristics. In particular, the battery-powered devices such as mobile phones, game machines, toys, and automobile parts exhibit power saving effects.

  EXAMPLES Next, although an Example demonstrates this invention still in detail, this invention is not limited only to these Examples.

Example 1
FIG. 2 is a schematic view showing a cross section of the gallium nitride compound semiconductor light emitting device manufactured in this example, and FIG. 3 is a schematic view showing the plane thereof. An underlayer (3a) made of undoped GaN with a thickness of 8 μm and a Si-doped n-type GaN contact layer (3b) with a thickness of 2 μm on a substrate (1) made of sapphire via a buffer layer (6) made of AlN. Then, an n-type In _0.1 Ga _0.9 N cladding layer (3c) having a thickness of 250 nm, an Si-doped GaN barrier layer having a thickness of 16 nm, and an In _0.2 Ga _0.8 N well layer having a thickness of 2.5 nm are stacked five times, and finally the barrier A light emitting layer (4) having a multiple quantum well structure provided with a layer, a 0.01 μm-thick Mg-doped p-type Al _0.07 Ga _0.93 N cladding layer (5a), and a 0.15-μm-thick Mg-doped p-type GaN contact layer ( On the p-type GaN contact layer of a gallium nitride compound semiconductor in which 5b) are sequentially stacked, a Pt contact layer (111) having a thickness of 1.5 nm and an Au current diffusion layer (112) having a thickness of 5 nm are formed. 5 consisting of translucent electrode (11) and 50 nm Pt layer (13a), 20 nm Ti layer (13b), 10 nm Al layer (13c), 100 nm Ti layer (13d), 200 nm Au layer (13e) A positive electrode (10) of the present invention comprising a layered bonding pad electrode (13) was formed. Of the five layers forming the bonding pad electrode, the 50 nm Pt layer (13a) corresponds to the reflective layer having a high reflectance. Next, a light-emitting element in which a Ti / Au double-layer negative electrode (20) is formed on an n-type GaN contact layer and the light extraction surface is the semiconductor side. The shapes of the positive electrode and the negative electrode are as shown in FIG.

In this structure, the carrier concentration of the n-type GaN contact layer is 1 × 10 ¹⁹ cm ⁻³ , the Si doping amount of the GaN barrier layer is 1 × 10 ¹⁸ cm ⁻³ , and the carrier concentration of the p-type GaN contact layer is 5 is a × 10 ¹⁸ cm ^-3, Mg doping amount of p-type AlGaN cladding layer was 5 × 10 ¹⁹ cm ^-3.

  Lamination of the gallium nitride compound semiconductor layers was performed by MOCVD under normal conditions well known in the art. Moreover, the positive electrode and the negative electrode were formed in the following procedure.

  First, the n-type GaN contact layer for forming the negative electrode by the reactive ion etching method was exposed by the following procedure.

First, an etching mask was formed on the p-type semiconductor layer. The formation procedure is as follows. After uniformly applying the resist over the entire surface, the resist was removed from a region that was slightly larger than the positive electrode region using a known lithography technique. It was set in a vacuum deposition apparatus, and Ni and Ti were laminated by an electron beam method at a pressure of 4 × 10 ⁻⁴ Pa or less so that the film thicknesses were about 50 nm and 300 nm, respectively. Thereafter, the metal film other than the positive electrode region was removed together with the resist by a lift-off technique.

Next, the semiconductor laminated substrate is placed on the electrode in the etching chamber of the reactive ion etching apparatus, the pressure in the etching chamber is reduced to 10 ⁻⁴ Pa, and then Cl ₂ is supplied as an etching gas to expose the n-type GaN contact layer. Etched until After the etching, it was taken out from the reactive ion etching apparatus, and the etching mask was removed with nitric acid and hydrofluoric acid.

  Next, using a known photolithography technique and lift-off technique, a contact layer made of Pt and a current diffusion layer made of Au were formed only in the region where the positive electrode was formed on the p-type GaN contact layer. In the formation of the contact layer and the current diffusion layer, first, a substrate on which a gallium nitride compound semiconductor layer is stacked is placed in a vacuum deposition apparatus, and Pt is first deposited on the p-type GaN contact layer at 1.5 nm, and then Au is deposited at 5 nm. Laminated. Subsequently, after taking out from the vacuum chamber, it is processed in accordance with a well-known procedure generally called lift-off, and a reflection layer (13a) made of Pt and a barrier layer made of Ti (13b) are formed on a part of the current diffusion layer by a similar method. ), A barrier layer (13c) made of Al, a barrier layer (13d) made of Ti, and an uppermost layer (13e) made of Au were laminated in this order to form a bonding pad electrode (13). Thus, the positive electrode of the present invention was formed on the p-type GaN contact layer.

  Next, a 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.

  The wafer in which the positive electrode and the negative electrode were formed in this way was thinned and polished to a substrate thickness of 80 μm by grinding and polishing the back surface of the substrate, and a ruled line was entered from the semiconductor lamination side using a laser scriber. It was cut and cut into 350 μm square chips. Subsequently, when these chips were energized with a probe needle and the forward voltage was measured at a current application value of 20 mA, it was 2.9 V.

  After that, when mounted on a TO-18 can package and measured for light output by a tester, the light output at an applied current of 20 mA showed 4.5 mW. Moreover, it was confirmed that the light emission distribution on the light emitting surface emitted light on the entire surface under the positive electrode.

  Further, the reflectance of the reflective layer produced in this example was 92% in the wavelength region of 470 nm. This value was measured with a spectrophotometer using a glass dummy substrate placed in the same chamber when the bonding pad electrode was formed.

  Moreover, when the peeling strength of the bonding pad electrode was measured by a general apparatus called a shear tester, it was 980 mN (100 gf) or more on average, and there was no peeling between the bonding pad electrode and the transparent electrode.

(Comparative Example 1)
A light-emitting element was fabricated in the same manner as in Example 1 except that the translucent electrode was not provided on the portion where the bonding pad electrode was to be formed and the reflective layer (13a) was not provided on the bonding pad electrode. Therefore, in this comparative example, the lowermost layer (semiconductor side) of the bonding pad electrode is a layer (13b) made of Ti, and the layer is in direct contact with the p-type contact layer (5b).

  In order to make electrical contact between the bonding pad electrode and the translucent electrode, the periphery of the bonding pad electrode is in contact with the translucent electrode, and the contact area is about 5% of the area of the bonding pad electrode. did. A current flows from the bonding pad electrode to the translucent electrode through this contact portion.

  When the obtained light emitting device was evaluated in the same manner as in Example 1, the forward voltage was 3.1 V and the light emission output was 4.2 mW. In addition, it was confirmed that the light emission distribution on the light emitting surface did not emit light immediately below the bonding pad electrode. Ti has higher contact resistance with the p-type contact layer (5b) and lower reflectance than Pt.

(Example 2)
The thickness of the Pt contact layer (111) of the translucent electrode (11) is 1 nm, the current diffusion layer (112) is ITO having a thickness of 100 nm formed by sputtering, and the bonding pad electrode (13) A light emitting device was produced in the same manner as in Example 1 except that the reflective layer (13a) was formed using Al.

  When the obtained light emitting device was evaluated in the same manner as in Example 1, the forward voltage was 2.9 V and the light emission output was 5.0 mW.

  Further, when the peel strength of the bonding pad electrode was measured by a general apparatus called a shear tester, it was 980 mN (100 gf) or more on average. There were several samples in which peeling occurred between the bonding pad electrode and the transparent electrode.

(Comparative Example 2)
A light emitting device was fabricated in the same manner as in Example 2 except that the reflective layer (13a) of the bonding pad electrode (13) was not provided. When the obtained light emitting device was evaluated in the same manner as in Example 1, the forward voltage was 2.9 V, which was as low as in Example 2, but the light emission output decreased to 4.7 mW.

(Example 3)
In Example 3, an epitaxial substrate having the following laminated structure was prepared and used in the same manner as in Example 1. That is, an underlayer (3a) made of undoped GaN having a thickness of 6 μm and a Ge-doped n-type GaN contact layer having a thickness of 4 μm are formed on a substrate (1) made of sapphire via a buffer layer (6) made of AlN. 3b), an n-type In _0.1 Ga _0.9 N cladding layer (3c) doped with Si with a thickness of 180 nm, a Si-doped GaN barrier layer with a thickness of 16 nm and an In _0.2 Ga _0.8 N well layer with a thickness of 2.5 nm five times Multi-quantum well structure light-emitting layer (4) laminated and finally provided with a barrier layer, Mg-doped p-type Al _0.07 Ga _0.93 N clad layer (5a) with a thickness of 0.01 μm, Mg-doped with a thickness of 0.175 μm A p-type Al _0.02 Ga _0.98 N contact layer (5b) was sequentially stacked, and finally an n-type GaN tunnel layer (not shown) doped with Ge was formed to a thickness of 20 nm. On the n-type GaN tunnel layer gallium nitride compound semiconductor, a translucent electrode (11) consisting only of an ITO current diffusion layer (112) having a thickness of 250 nm, an Al layer (13a) of 50 nm, a Ti layer (13b) of 20 nm ) A positive electrode (10) of the present invention comprising a five-layer bonding pad electrode (13) comprising a 10 nm Al layer (13c), a 100 nm Ti layer (13d), and a 200 nm Au layer (13e) was formed. Of the five layers forming the bonding pad electrode, the Al layer (13a) of 50 nm corresponds to the reflective layer having a high reflectance. Next, a light-emitting element in which a Ti / Au double-layer negative electrode (20) is formed on an n-type GaN contact layer and the light extraction surface is the semiconductor side. The shapes of the positive electrode and the negative electrode are as shown in FIG.

In this structure, the carrier concentration of the n-type GaN contact layer is 8 × 10 ¹⁸ cm ⁻³ , the Si doping amount of the n-type InGaN cladding layer is 7 × 10 ¹⁸ cm ⁻³ , and the Si doping amount of the GaN barrier layer Was 1 × 10 ¹⁷ cm ⁻³ , the carrier concentration of the p-type AlGaN contact layer was 5 × 10 ¹⁷ cm ⁻³ , and the Mg doping amount of the p-type AlGaN cladding layer was 2 × 10 ²⁰ cm ⁻³ . . The doping amount of Ge in the n-type GaN tunnel layer was 2 × 10 ¹⁹ cm ⁻³ .

  When the obtained light emitting device was evaluated in the same manner as in Example 1, the forward voltage was 3.2 V and the light emission output was 8.5 mW.

  Moreover, when the peeling strength of the bonding pad was measured by a general apparatus called a shear tester, the average was 100 gf or more. There were several samples where peeling occurred between the bonding pad and the transparent electrode.

  The semiconductor light emitting device provided by using the positive electrode of the present invention is extremely useful as a material for a lamp or the like because of low driving voltage and high emission intensity.

DESCRIPTION OF SYMBOLS 1 Substrate 2 GaN-based compound semiconductor layer 3 n-type semiconductor layer 4 light emitting layer 5 p-type semiconductor layer 6 buffer layer 10 positive electrode 11 translucent electrode 13 bonding pad electrode 20 negative electrode

Claims (2)

A face-up comprising an n-type semiconductor layer, a light emitting layer and a p-type semiconductor layer made of a gallium nitride compound semiconductor on a substrate in this order, and a positive electrode and a negative electrode provided on the p-type semiconductor layer and the n-type semiconductor layer, respectively. In the type semiconductor light emitting device, the positive electrode includes a translucent electrode formed on the p-type semiconductor layer and a bonding pad electrode formed on the translucent electrode, and the bonding pad electrode includes at least the translucent electrode and The translucent electrode has a reflective layer on the surface in contact, and the translucent electrode is a single translucent electrode having the functions of a contact layer and a current diffusion layer, and is composed of only a transparent material other than metal, and the thickness of the transparent material 100 to 1000 nm, the thickness of the reflective layer is 20 to 500 nm, the reflective layer is made of a metal selected from the group consisting of Pt and its alloys, and is the outermost surface layer of the translucent electrode Processing for extracting light has been applied, a bonding pad electrode is layered structure, in addition to the reflective layer, Ti, a barrier layer made of Cr or Al, and / or to have a top layer made of Au or Al A face-up type semiconductor light emitting device characterized by the above. A lamp comprising using a face-up semiconductor light-emitting device according to claim 1.

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