JP5021693B2 - Semiconductor light emitting device - Google Patents

Description

The present invention relates to a semiconductor light emitting device, and more particularly to a semiconductor light emitting device using a nitride semiconductor, and in particular, a positive electrode and a negative electrode are arranged on the same surface side of a substrate.
About.

  FIG. 15A is a cross-sectional view of a semiconductor light emitting element disclosed in Patent Document 1 below. An n-type contact layer 202 made of n-type GaN, an n-type clad layer 203 made of n-type AlGaN, a light-emitting layer 204 made of InGaN, and a p-type clad made of p-type AlGaN on a sapphire substrate 200 via a buffer layer 201. A layer 205 and a p-type contact layer 206 made of p-type GaN are stacked in this order. In some regions, etching is performed from the p-type contact layer 206 to the surface layer portion of the n-type contact layer 202, and a part of the n-type contact layer 202 is exposed.

  A p-side ohmic electrode 207 is formed on the p-type contact layer 206, and an n-side ohmic electrode 208 is formed on the exposed region of the n-type contact layer 202. These laminated structures are covered with a light-transmitting insulating film 210. An opening 210 a that exposes the surface of the n-side ohmic electrode 208 and an opening 210 b that exposes part of the surface of the p-side ohmic electrode 207 are formed in the insulating film 210.

  A reflective film 211 is formed so as to cover the p-type ohmic electrode 207 via the insulating film 210. A p-side pad 213 is formed on a partial region of the surface of the reflective film 211, and an n-side pad 212 is formed on the n-side ohmic electrode 208.

  The reflective film 211 is formed of Al, Ag, or Rh, and reflects the light generated in the light emitting layer 204 toward the substrate 200 side. Light is extracted through the substrate 200. In order to increase the light extraction efficiency, it is desirable to increase the reflectance of the reflective film 211. Ag has a very high reflectance in the wavelength range from ultraviolet light to visible light. However, Ag is a metal that easily causes electrochemical migration. According to Tadashi Takemoto and Ryohei Sato, “High Reliability Micro Soldering Technology” (Industry Research Committee), the mechanism of Ag migration is explained as follows.

When an electric field is applied in the presence of moisture, Ag dissolves at the anode and hydrogen (H ₂ ) is generated at the cathode. In the vicinity of the anode, Ag ⁺ ions and OH ⁻ ions react to produce silver hydroxide AgOH. Chemically unstable silver hydroxide AgOH is decomposed to produce colloidal silver oxide Ag ₂ O. Silver oxide further reacts to produce Ag ⁺ ions. While repeating the above reaction, Ag ₂ O and Ag ⁺ ions move to the cathode, precipitate Ag, and silver grows in a dendritic shape on the anode.

  When silver migration occurs, the anode and the cathode are short-circuited by the dendritic silver and the leakage current increases. Patent Documents 2 and 3 below disclose inventions that suppress silver migration.

  FIG. 15B is a cross-sectional view of the semiconductor light emitting element disclosed in Patent Document 2. On the sapphire substrate 220, an AlN buffer layer 221, an n-type GaN layer 222, an InGaN light emitting layer 223, and a p-type GaN layer 224 are stacked in this order. The p-type GaN layer 224 and the light emitting layer 223 are partially etched, and a part of the n-type GaN layer 222 is exposed. An Ag layer 225 is formed on the surface of the p-type GaN layer, and this Ag layer 225 is covered with a silicon oxide film 227.

  A via hole exposing a part of the upper surface of the Ag layer 225 is formed in the silicon oxide film 227. An Au layer 228 is formed on the silicon oxide film 227. The Au layer 228 is connected to the Ag layer 225 via a via hole formed in the silicon oxide film 227.

  An n-side ohmic electrode 226 having a laminated structure of a V layer and an Al layer is formed on the exposed surface of the n-type GaN layer 222. Since the Ag layer 225 is covered with the silicon oxide film 227, Ag migration can be suppressed.

  FIG. 15C is a cross-sectional view of the semiconductor light emitting element described in Patent Document 3. On the sapphire substrate 230, an AlN buffer layer 231, an n-type GaN layer 232, an n-type GaN cladding layer 233, a light emitting layer 234, a p-type GaN cladding layer 235, and a p-type GaN contact layer 236 are stacked in this order. . The stack from the p-type GaN contact layer 236 to the n-type GaN cladding layer 233 is partially etched, and a part of the n-type GaN layer 232 is exposed.

  An Ag layer 237 is formed on part of the surface of the p-type GaN contact layer 236. The Ag layer 237 is covered with a vanadium (V) layer 238 and an Al layer 239. Since the Ag layer 237 is covered with the V layer 238 and the Al layer 239, migration of Ag can be suppressed.

JP 2003-224297 A JP 2003-168823 A JP-A-11-220171

  As disclosed in the above-mentioned Patent Documents 2 and 3, Ag migration is suppressed by covering the Ag layer used as the reflective film and the electrode with an insulating film or another metal film. However, the migration suppression effect is not sufficient. A semiconductor light emitting device capable of more effectively suppressing Ag migration is desired.

  SUMMARY OF THE INVENTION An object of the present invention is to provide a semiconductor light emitting device that can suppress migration and improve reliability in a semiconductor light emitting device using a metal that is easily migrated.

According to one aspect of the invention,
a first layer made of an n-type nitride semiconductor; and a second layer made of a p-type nitride semiconductor disposed on the first layer, wherein the first layer and the second layer A light emitting stacked structure in which a light emitting region is defined between the first layer and the first layer on the surface of the first layer, wherein the second layer is removed and the first layer appears.
It is disposed on the surface of the second layer, is electrically connected to the second layer, is formed of one metal selected from the group consisting of Pt, Rh, and Pd, and has a thickness of 1 nm. A p-side electrode that is ˜8 nm;
An insulating film covering the p-side electrode;
An n-side electrode electrically connected to the first layer in the first region;
On the insulating film, disposed so as to overlap the p-side electrode, formed of an alloy containing silver or silver, and not electrically connected to either the p-side electrode or the n-side electrode, but in an electrically floating state And a reflecting film made of
There is provided a semiconductor light emitting device in which the p-side electrode, the insulating film, and the reflective film constitute a multilayer reflective film.

According to another aspect of the invention,
a first layer made of an n-type nitride semiconductor; and a second layer made of a p-type nitride semiconductor disposed on the first layer, wherein the first layer and the second layer A light emitting stacked structure in which a light emitting region is defined between the first layer and the first layer on the surface of the first layer, wherein the second layer is removed and the first layer appears.
One metal disposed on the surface of the second layer, electrically connected to the second layer, transmitting light generated in the light emitting region, and selected from the group consisting of Pt, Rh, and Pd A p-side electrode having a thickness of 1 nm to 8 nm,
An insulating film covering the p-side electrode;
An n-side electrode electrically connected to the first layer in the first region;
On the insulating film, disposed so as to overlap the p-side electrode , formed of an alloy containing silver or silver, and not electrically connected to either the p-side electrode or the n-side electrode, but in an electrically floating state And a reflective film that reflects light generated in the light emitting region,
There is provided a semiconductor light emitting device in which the p-side electrode, the insulating film, and the reflective film constitute a multilayer reflective film.

The reflective film is in an electrically floating state and is not connected to the p-side electrode (anode). For this reason, ionization of the metal which comprises a reflecting film can be suppressed, and generation | occurrence | production of migration can be suppressed.

It is sectional drawing of the semiconductor light-emitting device by a 1st Example. It is a top view of the semiconductor light-emitting device by a 1st Example. It is a graph which shows the lifetime of the semiconductor light-emitting device by a 1st Example compared with the lifetime of the device by a comparative example. It is sectional drawing which shows the model of the laminated structure which performed the simulation of the reflectance. It is a graph which shows the relationship between the thickness of a p-side ohmic electrode, and a reflectance. It is a graph which shows the relationship between the thickness of a reflecting film, and a reflectance. It is a graph which shows the relationship between the thickness of an insulating film, and a reflectance for every thickness of the p side ohmic electrode. It is a graph which shows the relationship between the thickness of an insulating film, and a reflectance for every wavelength. It is a graph which shows the relationship between the thickness of an insulating film, and a reflectance for every wavelength. It is a graph which shows the relationship between a wavelength and a reflectance for every thickness of a p-side ohmic electrode. It is a top view of the semiconductor light-emitting device by the 2nd example. It is a schematic sectional drawing of the lamp | ramp which mounts the semiconductor light-emitting device by a 2nd Example. It is sectional drawing of the semiconductor light-emitting device by a 3rd Example. It is a top view of the semiconductor light-emitting device by a 3rd Example. It is a schematic sectional drawing of the lamp | ramp which mounts the semiconductor light-emitting device by a 3rd Example. It is sectional drawing of the semiconductor light-emitting device by a 4th Example. It is a top view of the semiconductor light-emitting device by the 4th example. It is sectional drawing of the conventional semiconductor light-emitting device using the reflecting film of Ag. It is sectional drawing of the conventional semiconductor light-emitting device which suppresses Ag migration. It is sectional drawing of the conventional semiconductor light-emitting device which suppresses Ag migration.

FIG. 1A shows a cross-sectional view of the semiconductor light emitting device according to the first embodiment, and FIG. 1B shows a plan view thereof. A cross section taken along one-dot chain line A1-A1 in FIG. 1B corresponds to FIG. On an underlying substrate 1 made of sapphire, an initial nucleation layer 2, an n-type contact layer 3, an n-type cladding layer 4, a light emitting layer 5, a p-type cladding layer 6 and a p-type contact layer 7 are laminated in this order. Yes. These layers are formed of a nitride compound semiconductor such as In _x Al _y Ga _z N (x + y + z = 1).

  In a part of the first region 25 in the substrate surface, each layer from the p-type contact layer 7 to the surface layer portion of the n-type contact layer 3 is etched, and a part of the n-type contact layer 3 is exposed.

  A p-side ohmic electrode 10 is formed on the p-type contact layer 7. The p-side ohmic electrode 10 is made of platinum (Pt) and has a thickness of about 5 nm. An n-side ohmic electrode 11 is formed on the surface of the n-type contact layer 3 in the first region 25. The n-side ohmic electrode 11 has a two-layer structure of an Al layer having a thickness of about 3 nm and a rhodium (Rh) layer having a thickness of about 100 nm. The p-side ohmic electrode 10 and the n-side ohmic electrode 11 are in ohmic contact with the p-type contact layer 7 and the n-type contact layer 3, respectively.

  On the p-side ohmic electrode 10 and the n-side ohmic electrode 11, an adhesive layer (not shown) having a thickness of 0.3 to 3 nm made of Ti, Ni, W, Mo or the like is formed. The adhesive layer can enhance the adhesion of the insulating film 15 deposited thereon.

  An insulating film 15 is formed on the substrate so as to cover the p-side ohmic electrode 10 and the n-side ohmic electrode 11. The insulating film 15 is made of, for example, silicon oxide and has a thickness of about 300 nm. Openings 15 a and 15 b are formed in the insulating film 15. A part of the surface of the p-side ohmic electrode 10 is exposed at the bottom surface of the opening 15a, and a part of the surface of the n-side ohmic electrode 11 is exposed at the bottom surface of the opening 15b.

  A reflective film 16 is formed on the insulating film 15. The reflective film 16 extends from the region overlapping the p-side ohmic electrode 10 to the n-side ohmic electrode 11 in the first region 25 and is electrically connected to the n-side ohmic electrode 11 exposed at the bottom surface of the opening 15b. Is done. The reflective film 16 is made of silver (Ag) and has a thickness of about 200 nm.

  An adhesive layer (not shown) made of Ti, Ni, Al, W, Mo or the like and having a thickness of 0.3 to 3 nm is inserted between the insulating film 15 and the reflective film 16. This adhesive layer improves the adhesion between the insulating film 15 and the reflective film 16. A similar adhesive layer (not shown) is also formed on the reflective film 16. This adhesive layer enhances the adhesion of the protective film 17 formed thereon. The thickness of the upper adhesive layer is, for example, 10 nm.

A p-side pad electrode 20 is formed on the p-side ohmic electrode 10 exposed on the bottom surface of the opening 15a, and an n-side pad electrode 21 is formed on the n-side ohmic electrode 11 exposed on the bottom surface of the opening 15b. The p-side pad electrode 20 and the n-side pad electrode 21 have a multilayer structure of Ti / Pt / Au / (Pt / Au) _n . Here, n indicates the number of repetitions of the two layers of the Pt layer and the Au layer. The thickness of the lowermost Ti layer is, for example, 3 nm, and the thicknesses of the Pt layer and the Au layer are, for example, 100 nm. The number of repetitions n is 2, for example. Note that the number of repetitions n is preferably 1 to 5 from the viewpoint of film formation and the amount of material used. When flip chip bonding is performed, the thickness of the third Au layer from the substrate side of the n-side pad electrode 21 is set to 100 nm to 1000 nm, and the height of the upper surface of the n-side pad electrode 21 is set to the p-side pad. It is preferable to align with the height of the upper surface of the electrode 20.

  On the p-side pad electrode 20 and the n-side pad electrode 21, an adhesive layer (not shown) having a thickness of 0.3 to 3 nm made of Ti, Ni, Al, W, Mo or the like is formed. This adhesive layer enhances the adhesion of the protective film 17 formed thereon.

  A protective film 17 is formed so as to cover the reflective film 16 and the pad electrodes 20 and 21. The protective film 17 is made of silicon oxide and has a thickness of 100 to 300 nm, preferably about 200 nm. Openings 17 a and 17 b are formed in the protective film 17. The upper surfaces of the p-side pad electrode 20 and the n-side pad electrode 21 are exposed at the bottom surfaces of the openings 17a and 17b, respectively.

  As shown in FIG. 1B, the planar shape of one semiconductor light emitting element is, for example, a square having a side of 300 μm. The first region 25 includes one vertex of the square and is composed of a region near the vertex. The shape is, for example, a sector shape with a central angle of 90 ° centered on one vertex. The p-side ohmic electrode 10 is disposed in a region excluding the first region 25 and occupies most of the surface of the semiconductor light emitting element. The p-side pad electrode 20 is disposed in the vicinity of the vertex on the side opposite to the vertex included in the first region 25. The reflective film 16 occupies most of the surface of the semiconductor light emitting device except for the region where the p-side pad electrode 20 is disposed.

  Next, a method for manufacturing the semiconductor light emitting device according to the first embodiment will be described. Each layer from the initial nucleation layer 2 to the p-type contact layer 7 on the base substrate 1 made of sapphire is formed by, for example, metal organic vapor phase epitaxy (MOVPE) or molecular beam epitaxy (MBE). After forming up to the p-type contact layer 7, the substrate surface is cleaned, and the p-side ohmic electrode 10 and the adhesive layer thereon are formed using electron beam evaporation and a lift-off method.

  Using the resist pattern in which the opening corresponding to the first region 25 is formed as a mask, the surface layer portion of the n-type contact layer 3 is etched by reactive ion etching to expose a part of the n-type contact layer 3. After the etching, the resist pattern used as a mask is removed. An n-side ohmic electrode 11 is formed on the exposed surface of the n-type contact layer 3 using electron beam evaporation and a lift-off method.

  Note that the p-side ohmic electrode 10 and the n-side ohmic electrode 11 may be formed after exposing a part of the surface of the n-type contact layer 3.

  An insulating film 15 is formed by sputtering. Openings 15 a and 15 b are formed in the insulating film 15. The openings 15a and 15b may be formed using a lift-off method. The lower adhesive layer, the reflective film 16 and the upper adhesive layer are formed using electron beam evaporation and a lift-off method. The edge of the reflective film 16 is set back from the edge of the opening 15a by 1 μm or more, preferably about 5 μm so that the reflective film 16 and the p-side ohmic electrode 10 exposed at the bottom of the opening 15a are not short-circuited. Further, the overlapping width of the reflective film 16 and the opening 15b is secured to about 3 to 5 μm so as to be electrically connected to the n-side ohmic electrode 11 exposed on the bottom surface of the opening 15b. Thereby, the reflective film 16 is not connected to the p-side ohmic electrode 10 but is electrically connected to the n-side ohmic electrode 11.

  The p-side pad electrode 20, the n-side pad electrode 21, and the adhesive layer thereon are formed using electron beam evaporation and a lift-off method. The p-side pad electrode 20 is preferably formed such that its outer periphery is disposed slightly inside the edge of the opening 15a. If the p-side pad electrode 20 does not contact the reflective film 16, the vicinity of the outer periphery of the p-side pad electrode 20 may overlap the insulating film 15.

  A protective film 17 is formed by sputtering. Thereafter, openings 17 a and 17 b are formed in the protective film 17. The openings 17a and 17b may be formed using a lift-off method. The surface of the p-side pad electrode 20 is exposed at the bottom surface of the opening 17a, and the surface of the n-side pad electrode 21 is exposed at the bottom surface of the opening 17b.

  The back surface of the base substrate 1 is ground and polished to reduce the thickness of the base substrate 1 to about 100 μm. The base substrate 1 may have a thickness of 60 μm to 210 μm. Scribing and braking are performed to separate the light emitting elements. The separated light emitting element is used in various forms. For example, flip chip bonding is performed on the submount substrate. In addition, the base substrate 1 may be attached to the light guide plate with a transparent adhesive, and the p-side pad electrode 20 and the n-side pad electrode 21 may be connected to the wiring provided on the light guide plate with a gold wire.

  When a forward voltage is applied to the laminated structure of the n-type cladding layer 4, the light emitting layer 5, and the p-type cladding layer 6, light emission occurs in the light emitting layer 5. The light generated in the light emitting layer 5 passes through the base substrate 1 and is emitted to the outside. Light generated in the light emitting layer 5 and propagating toward the p-type cladding layer 6 is transmitted through the p-side ohmic electrode 10 and the insulating film 15, reflected by the reflective film 16 toward the base substrate 1, and transmitted through the base substrate 1. And radiated to the outside.

  When an electric field is applied in the presence of moisture, the dissolution of Ag at the anode is considered to cause the migration of Ag. In the first embodiment, since the reflective film 16 formed of Ag is connected to the cathode (n-side ohmic electrode 11), dissolution of Ag does not occur. For this reason, Ag migration can be suppressed.

  FIG. 2 shows the result of the life evaluation test of the semiconductor light emitting device according to the first embodiment. The horizontal axis represents the elapsed time in the unit “time”, and the vertical axis represents the light emission output in a relative scale. As a comparative example, the results of a life evaluation test of a semiconductor light emitting device having a structure in which the p-side ohmic electrode 10 shown in FIG. 1A is formed of Ag and the p-side ohmic electrode 10 also serves as a reflective film are shown. Black square symbols in the figure indicate changes over time in the light emission output of the semiconductor light emitting device according to the first example, and black circles indicate changes over time in the light emission output of the semiconductor light emitting device of the comparative example. In the life evaluation test, the semiconductor light emitting device was flip-chip bonded to the submount substrate, and the light emission was measured by emitting light in the atmosphere. The emission wavelength was 405 nm.

  The light emission output of the semiconductor light emitting device according to the comparative example is rapidly reduced in several tens of hours, but the light emission output of the semiconductor light emitting device according to the example is hardly lowered even after 1000 hours. As described above, the life of the semiconductor light emitting device can be extended by connecting the reflective film 16 made of Ag to the cathode.

  In the first embodiment, the p-side ohmic electrode 10 is formed of Pt. However, the p-side ohmic electrode 10 is formed of another conductive material that transmits light in the emission wavelength region of the light-emitting layer 5 and can obtain ohmic contact with the p-type contact layer 7. May be. Examples of usable materials include rhodium (Rh) and palladium (Pd). In addition, a two-layer structure of a Pt layer and an Rh layer, or a two-layer structure of a Ni layer and an Au layer may be used. In the case of a two-layer structure of a Ni layer and an Au layer, it is necessary to perform heat treatment after film formation in order to obtain ohmic contact. Alternatively, a light-transmitting oxide film composed of an oxide of Au and Ni can be used. In this case, it is necessary to perform heat treatment in an oxidizing atmosphere after film formation.

  In the first embodiment, the n-side ohmic electrode 11 has a two-layer structure (Al / Rh structure) of an Al layer and an Rh layer. However, as another configuration capable of ohmic contact with the n-type contact layer 3 Also good. For example, an Al / Pt structure, an Al / Ir structure, an Al / Pd structure, a Ti / Al structure, or a V / Al structure may be used. When a Ti / Al structure or a V / Al structure is employed, heat treatment needs to be performed after film formation in order to obtain ohmic contact.

In the first embodiment, the insulating film 15 is formed of silicon oxide. However, the insulating film 15 may be formed of another insulating material that transmits light in the emission wavelength region of the light emitting layer 5. For example, oxides such as titanium oxide (TiO ₂ ), tantalum oxide (Ta ₂ O ₅ ), alumina (Al ₂ O ₃ ), zirconium oxide (ZrO ₂ ), hafnium oxide (HfO ₂ ) are used as the material of the insulating film 15. A heat-resistant organic polymer material such as polyimide can be used.

In the above embodiment, the p-side pad electrode 20 has a multi-layer structure of Ti / Pt / Au / (Pt / Au) _n , but in addition, a multi-layer structure of Ti / Rh / Au / (Pt / Au) _n , or Ni / A multilayer structure of Rh / Au / (Pt / Au) _n may be used.
The thickness of the lowermost Ti layer or Ni layer is, for example, 0.3 to 1 nm. The thickness of each of the Rh layer, Pt layer, and Au layer thereon is 100 nm. The number of repetitions n is 1 to 5. With such a multilayer structure, the p-side pad electrode 20 can have a function as a reflective film, and the light extraction efficiency can be increased.

  In the above embodiment, the reflective film 16 is made of Ag. However, the reflective film 16 may be made of an alloy containing Ag as a main component. The thickness of the reflective film 16 is preferably 80 nm or more so as not to transmit light generated in the light emitting layer 5. In addition, when the reflective film 16 is formed of a metal other than Ag that easily undergoes migration, a migration suppressing effect will be obtained. This is particularly effective when the reflective film 16 is formed of a metal that is more likely to migrate than the p-side ohmic electrode 10.

In the above embodiment, the protective film 17 is formed of silicon oxide. However, other insulating materials such as titanium oxide (TiO ₂ ), tantalum oxide (Ta ₂ O ₅ ), alumina (Al ₂ O ₃ ), zirconium oxide (ZrO) are used. ₂ ), an oxide such as hafnium oxide (HfO ₂ ), a heat-resistant organic polymer material such as polyimide, or the like.

  A conductive layer made of a metal such as Al, which has a higher ionization tendency than Ag, may be formed on the surface of the reflective film 16. By using together the dissimilar metal bonding utilizing the difference in ionization tendency, the electric corrosion of the reflective film 16 can be suppressed even in a state where no current is applied between the electrodes.

  In the first embodiment, the p-side ohmic electrode 10, the insulating film 15, and the reflecting film 16 constitute a multilayer reflecting film. The reflectivity depends on the thickness of these films. It is difficult to obtain a suitable condition for increasing the reflectance of a multilayer film composed of a metal thin film and a dielectric film by experiments. For this reason, the film thickness dependence of the reflectance of the multilayer reflective film was evaluated by simulation. Hereinafter, the evaluation result by simulation will be described.

FIG. 3 shows a model of the multilayer reflective film used in the simulation. On the contact layer 7 made of GaN, the adhesive layer 10a made of p-side ohmic electrode 10, Ti consisting of Pt, adhesive layer 16a made of an insulating film 15, Ti consisting of SiO _2, the reflective film 16 made of Ag this order Are stacked. The reflectance of light having a wavelength of 460 nm traveling from the contact layer 7 to the reflective film 16 was obtained by simulation.

  FIG. 4 shows the relationship between the thickness of the p-side ohmic electrode 10 and the reflectance. The horizontal axis represents the thickness of the p-side ohmic electrode 10 in the unit “nm”, and the vertical axis represents the reflectance in the unit “%”. The thicknesses of the adhesive layer 10a, the insulating film 15, the adhesive layer 16a, and the reflective film 16 were 0.3 nm, 285 nm, 0.3 nm, and 200 nm, respectively. In the region where the thickness of the p-side ohmic electrode 10 is 7 nm or less, the reflectance is hardly affected by the film thickness, and in the region where the thickness is 7 nm or more, the reflectance decreases as the film thickness increases.

  FIG. 5 shows the relationship between the thickness of the reflective film 16 and the reflectance. The horizontal axis represents the thickness of the reflective film 16 in the unit “nm”, and the vertical axis represents the reflectance in the unit “%”. The thicknesses of the p-side ohmic electrode 10, the adhesive layer 10a, the insulating film 15, and the adhesive layer 16a were 5 nm, 0.3 nm, 285 nm, and 0.3 nm, respectively. It can be seen that the reflectivity increases as the thickness of the reflective film 16 increases, and the reflectivity is saturated when the film thickness is around 80 nm. From this result, it can be seen that the thickness of the reflective film 16 is preferably 80 nm or more.

  FIG. 6 shows the relationship between the thickness of the insulating film 15 and the reflectance. The horizontal axis represents the thickness of the insulating film 15 in the unit “nm”, and the vertical axis represents the reflectance in the unit “%”. The thicknesses of the adhesive layer 10a, the adhesive layer 16a, and the reflective film 16 were 0.3 nm, 0.3 nm, and 200 nm, respectively. Three curves in the figure show the reflectance when the thickness of the p-side ohmic electrode 10 is 3 nm, 5 nm, and 8 nm. The reflectance varies periodically according to the variation of the thickness of the insulating film 15. The reflectance shows the maximum value when the thickness of the insulating film 15 is about 130 nm, 286 nm, and 440 nm.

  It can be seen that the reflectance at the position where the reflectance exhibits a minimum value decreases as the p-side ohmic electrode 10 becomes thicker. In order to suppress a decrease in reflectance when the thickness of the insulating film 15 varies, it is preferable to make the p-side ohmic electrode 10 thinner. However, if the thickness is too thin, the original purpose of injecting carriers uniformly into the p-type contact layer 7 cannot be achieved. In order to satisfy the requirements of both high reflectivity and uniform carrier injection, the thickness of the p-side ohmic electrode 10 is preferably 1 nm to 15 nm, and more preferably 3 nm to 8 nm. Moreover, the thickness of the p-side ohmic electrode 10 may be as thin as 1 to 5 nm, and a mesh-like auxiliary electrode made of Pt or Rh may be provided thereon. The width of one electrode constituting this mesh may be 2 to 5 μm, for example, and the distance between the electrodes may be 10 to 15 nm, for example.

  From the simulation, it has been found that the reflectance shows a maximum value when the thickness of the insulating film 15 is about 286 nm. However, when the evaluation sample was actually produced and the reflectance was measured, the thickness of the insulating film 15 was measured. Shows a maximum reflectance in the vicinity of 300 nm. The reason why the optimum film thickness of the insulating film 15 obtained by the experiment deviates from the optimum film thickness of the insulating film 15 obtained by the simulation is that the optical characteristics of each film used in the simulation and each actually formed film are This is considered to be because the optical characteristics of the above do not exactly match. From the viewpoint of ensuring insulation and etching time, the thickness of the insulating film 15 is preferably 100 to 600 nm, and more preferably 200 to 400 nm.

  7 and 8 show the relationship between the thickness of the insulating film 15 and the reflectance for various wavelengths. The horizontal axis represents the thickness of the insulating film 15 in the unit “nm”, and the vertical axis represents the reflectance in the unit “%”. The thicknesses of the p-side ohmic electrode 10, the adhesive layer 10a, the adhesive layer 16a, and the reflective film 16 were 5 nm, 0.3 nm, 0.3 nm, and 200 nm, respectively. The numerical value given to each of the plurality of curves shown in FIGS. 7 and 8 indicates the wavelength of light to be reflected.

  When the wavelength of the light to be reflected changes, the thickness of the insulating film 15 having the maximum reflectance changes. The insulating film 15 preferably has a thickness in the vicinity where the reflectance exhibits a maximum value in accordance with the wavelength of light generated in the light emitting layer.

  As described above, the film thickness condition for increasing the reflectance is obtained by performing the simulation, but actually, the refractive index and extinction coefficient of the film are somewhat different depending on the film forming method. The reflectance is also affected by the surface roughness of the film. For this reason, the optimum film thickness of each film can be determined by referring to the optimum film thickness obtained by the simulation and preparing a plurality of evaluation samples having different film thicknesses and actually measuring the reflectance. preferable. The simulation result is a scale for determining the thickness of each film of the evaluation sample.

Next, the result of actually producing an evaluation sample and measuring the reflectance will be described. In the sample for evaluation, a sapphire substrate having a thickness of 320 μm was used as the p-side contact layer 7 in FIG. The p-side ohmic electrode 10 is a Pt film having a thickness of 5 nm, 8 nm, and 10 nm, the adhesive layers 10a and 16a are Ti films having a thickness of 0.3 nm, the insulating film 15 is an SiO ₂ film having a thickness of 313 nm, and reflection The film 16 was an Ag film having a thickness of 200 nm.

  When a GaN film having a thickness of about 4 to 8 μm is formed on a sapphire substrate, the substrate is warped. When the substrate is warped, the incident angle of incident light for measuring the reflectance cannot be adjusted accurately. For this reason, in the measurement sample, a sapphire substrate on which no GaN layer was formed was used.

  FIG. 9 shows the measurement results of the reflectance. The horizontal axis represents the wavelength in the unit “nm”, and the vertical axis represents the reflectance in the unit “%”. In the prepared sample, the reflectance showed the maximum value when the wavelength was 350 to 360 nm and 510 to 520 nm. By producing various samples and measuring the reflectance, the relationship between the reflectance of the multilayer reflective film formed on the sapphire substrate and the reflectance of the multilayer reflective film formed on the GaN layer can be obtained. By utilizing this relationship, a preferable film thickness of the insulating film 15 can be predicted.

  Next, with reference to FIGS. 10 and 11, the semiconductor light emitting device according to the second embodiment will be described.

  FIG. 10 is a plan view of a semiconductor light emitting device according to the second embodiment. In the first embodiment shown in FIG. 1B, the reflective film 16 is a plain film and overlaps with most of the region of the p-side ohmic electrode 10. In the second embodiment, a grid-like reflection pattern 16 a is arranged instead of the reflection film 16. Other basic configurations are the same as those of the semiconductor light emitting device according to the first embodiment. FIG. 10 shows a case where the p-side pad electrode 20 and the n-side pad electrode 21 are arranged slightly inside the center of a pair of sides facing each other, but the case shown in FIG. As in the case of the first embodiment, it may be arranged near the vertex of a rectangle.

  In the semiconductor light emitting device according to the second embodiment, the light generated in the light emitting layer is radiated to the outside through the support substrate, and is also radiated to the side opposite to the support substrate through the opening of the reflective pattern 16a. Further, the light is scattered by the reflection pattern 16a, and light is also emitted to the side of the semiconductor light emitting element.

  FIG. 11 is a schematic cross-sectional view of a lamp mounted with the semiconductor light emitting device according to the second embodiment. The semiconductor light emitting element 28 shown in FIG. 10 is mounted on the bottom surface of the concave portion of the metal frame 30 having the concave portion with the support substrate facing the frame. A cathode lead 31 extends from the frame 30. The n-side pad electrode 21 of the semiconductor light emitting element 28 is connected to the frame 30 via a gold wire 35. The p-side pad electrode 20 is connected to the anode lead 32 through the gold wire 36.

  The concave portion of the frame 30 is embedded with a phosphor 37. The semiconductor light emitting element 28 is covered with the phosphor 37. The frame 30, the cathode lead 31, and the anode lead 32 are molded with a sealing resin 38.

  The light emitted below the semiconductor light emitting element 28 (on the support substrate side) is reflected by the frame 30 and enters the phosphor 37. Further, the light emitted to the side or upper side (opposite side of the support substrate) of the semiconductor light emitting element 28 also enters the phosphor 37. The phosphor 37 generates fluorescence by receiving light. This fluorescence is emitted to the outside of the resin mold 38.

  Since light is emitted below, to the side, and above the semiconductor light emitting element 28, color unevenness can be reduced.

  In the second embodiment, the reflection pattern 16a is formed in a lattice pattern, but may have other patterns that have openings and scatter light. For example, a striped pattern or a honeycomb pattern may be used.

  Next, with reference to FIGS. 12A, 12B, and 13, a semiconductor light emitting device according to a third embodiment will be described.

  FIG. 12A shows a sectional view of a semiconductor light emitting device according to the third embodiment, and FIG. 12B shows a plan view thereof. A cross-sectional view taken along one-dot chain line A12-A12 in FIG. 12B corresponds to FIG. Hereinafter, differences from the semiconductor light emitting device according to the first embodiment shown in FIGS. 1A and 1B will be described.

  In the first embodiment, the n-side pad electrode 21 is disposed on the n-side ohmic electrode 11. However, in the second embodiment, the n-side pad electrode 21 is disposed above the p-side ohmic electrode 10. , In contact with the reflective film 16. The p-side pad electrode 20 and the n-side pad electrode 21 are exposed at the bottom surfaces of the openings 17a and 17b formed in the protective film 17, respectively.

  As shown in FIG. 12B, the n-side ohmic electrode 11 is disposed in the vicinity of one side of the support substrate 1 along the side. The p-side pad electrode 20 is disposed in the vicinity of one end of the side facing the side along which the n-side ohmic electrode 11 extends. The reflective film 16 occupies most of the region where the p-side pad electrode 20 is not disposed. The n-side pad electrode 21 occupies most of the region where the reflective film 16 and the p-side ohmic electrode 10 overlap.

  FIG. 13 is a schematic cross-sectional view of a lamp on which the semiconductor light emitting device according to the third embodiment is mounted. The semiconductor light emitting device 50 according to the third embodiment is flip-chip bonded to the submount substrate 43. The p-side pad electrode 20 and the n-side pad electrode 21 of the semiconductor light emitting device 50 are connected to the anode wiring 44 and the cathode wiring 45 on the submount substrate 43, respectively. A submount substrate 43 is fixed to the stem 40. An anode lead 42 and a cathode lead 41 are fixed to the stem 40. The anode wiring 44 is connected to the anode lead 42 via the gold wire 46, and the cathode wiring 45 is connected to the cathode lead 41 via the gold wire 47.

  The semiconductor light emitting element 50 and the submount substrate 43 are sealed with a sealing resin 48. The light generated in the light emitting layer of the semiconductor light emitting element 50 is reflected by the reflective film 16 shown in FIG. 12A, passes through the support substrate 1 and the sealing resin 48, and is emitted to the outside.

  In the semiconductor light emitting device according to the third embodiment, the n-side pad electrode 21 occupies a wider area on the device surface than the semiconductor light emitting device according to the first embodiment. Heat generated in the element efficiently flows to the submount substrate 43 through the wide n-side pad electrode 21. For this reason, a favorable heat dissipation characteristic is securable.

  Next, with reference to FIGS. 14A and 14B, a semiconductor light emitting element according to the fourth embodiment will be described.

  FIG. 14A shows a cross-sectional view of a semiconductor light emitting device according to the fourth embodiment, and FIG. 14B shows a plan view thereof. A cross-sectional view along dashed-dotted line A14-A14 in FIG. 14B corresponds to FIG. In the fourth embodiment, the four n-side ohmic electrodes 11 are arranged along the four sides of the square support substrate 1, respectively. The reflective film 16 is connected to the four n-side ohmic electrodes 11. An opening 16 a is formed in the reflective film 16 so as to enclose the p-side pad electrode 20. By forming the opening 16a, a short circuit between the reflective film 16 and the p-side pad electrode 20 is avoided.

  In the fourth embodiment, since the four n-side ohmic electrodes 11 are formed, the contact area of the electrodes can be increased and the contact resistance can be reduced. Further, by arranging the four n-side ohmic electrodes 11 along the four sides of the square, it is possible to reduce the current bias in the substrate plane.

  The vicinity of the apex of the support substrate 1 is likely to be lost during element isolation. For this reason, it is preferable that the n-side ohmic electrode 11 does not extend to the vicinity of the apex of the support substrate 1.

  Further, in the fourth embodiment, the entire side surface of the mesa portion formed by stacking from the n-type cladding layer 4 to the p-type cladding layer 7 is covered with the reflective film 16. For this reason, the light radiated | emitted from the light emitting layer 5 to the side can be efficiently reflected to the support substrate 1 side, and the extraction efficiency of light can be improved. In order to further increase the light extraction efficiency, it is preferable to incline the side surface of the mesa portion. For example, the inclination angle of the side surface of the mesa portion is preferably 60 ° or less.

  Hereinafter, an example of a method for inclining the side surface of the mesa unit will be described. When a normal resist pattern is formed, exposure is performed by bringing a photomask into contact with the resist film. When the side surface of the mesa portion is inclined, exposure is performed with the photomask slightly lifted from the resist film. Since a gap is formed between the resist film and the photomask, the edge portion of the photomask pattern is blurred and transferred. When the resist film is developed, a resist pattern with inclined side surfaces is obtained.

  When the nitride semiconductor layer is dry-etched using this resist pattern as an etching mask, the resist pattern itself is also gradually etched. Therefore, the side surface of the mesa portion of the nitride semiconductor is inclined corresponding to the inclination of the side surface of the resist pattern. .

  In the above embodiment, the reflective film 16 is connected to the n-side ohmic electrode 11, but the reflective film 16 is not connected to either the p-side ohmic electrode 10 or the n-side ohmic electrode 11, and is in an electrically floating state. Also good. Even in the floating state, migration can be suppressed as compared with the case where the reflective film is connected to the anode as shown in FIGS. 15B and 15C.

  Although the present invention has been described with reference to the embodiments, the present invention is not limited thereto. It will be apparent to those skilled in the art that various modifications, improvements, combinations, and the like can be made.

DESCRIPTION OF SYMBOLS 1 Substrate 2 Initial nucleus formation layer 3 n-type contact layer 4 n-type cladding layer 5 light emitting layer 6 p-type cladding layer 7 p-type contact layer 10 p-side ohmic electrodes 10a and 16a adhesive layer 11 n-side ohmic electrode 15 insulating film 16 Reflective film 16a Reflective pattern 17 Protective film 20 P-side pad electrode 21 N-side pad electrode 25 First region 28, 50 Semiconductor light emitting element 30 Frame 31, 41 Cathode lead 32, 42 Anode lead 35, 36, 46, 47 Gold wire 37 Phosphor 38, 48 Sealing resin 40 Stem 43 Submount substrate 44 Anode wiring 45 Cathode wiring

Claims (10)

a first layer made of an n-type nitride semiconductor; and a second layer made of a p-type nitride semiconductor disposed on the first layer, wherein the first layer and the second layer A light emitting stacked structure in which a light emitting region is defined between the first layer and the first layer on the surface of the first layer, wherein the second layer is removed and the first layer appears.
It is disposed on the surface of the second layer, is electrically connected to the second layer, is formed of one metal selected from the group consisting of Pt, Rh, and Pd, and has a thickness of 1 nm. A p-side electrode that is ˜8 nm;
An insulating film covering the p-side electrode;
An n-side electrode electrically connected to the first layer in the first region;
On the insulating film, disposed so as to overlap the p-side electrode, formed of an alloy containing silver or silver, and not electrically connected to either the p-side electrode or the n-side electrode, but in an electrically floating state And a reflecting film made of
A semiconductor light emitting device in which the p-side electrode, the insulating film, and the reflective film constitute a multilayer reflective film. a first layer made of an n-type nitride semiconductor; and a second layer made of a p-type nitride semiconductor disposed on the first layer, wherein the first layer and the second layer A light emitting stacked structure in which a light emitting region is defined between the first layer and the first layer on the surface of the first layer, wherein the second layer is removed and the first layer appears.
One metal disposed on the surface of the second layer, electrically connected to the second layer, transmitting light generated in the light emitting region, and selected from the group consisting of Pt, Rh, and Pd A p-side electrode having a thickness of 1 nm to 8 nm,
An insulating film covering the p-side electrode;
An n-side electrode electrically connected to the first layer in the first region;
On the insulating film, disposed so as to overlap the p-side electrode , formed of an alloy containing silver or silver, and not electrically connected to either the p-side electrode or the n-side electrode, but in an electrically floating state And a reflective film that reflects light generated in the light emitting region,
A semiconductor light emitting device in which the p-side electrode, the insulating film, and the reflective film constitute a multilayer reflective film.   3. The insulating film according to claim 1, wherein the insulating film is formed of at least one material selected from the group consisting of silicon oxide, titanium oxide, tantalum oxide, alumina, zirconium oxide, hafnium oxide, and an insulating polymer material. The semiconductor light emitting element as described.   The semiconductor light-emitting element according to claim 1, further comprising an insulating protective film that covers the reflective film.   Furthermore, the intermediate layer which consists of at least 1 metal selected from the group which consists of Ti, Ni, Al, W, and Mo is arrange | positioned between the said reflecting film and the said protective film. Semiconductor light emitting device. Furthermore, a p-side pad for flip chip bonding disposed on a partial region of the surface of the p-side electrode;
The semiconductor light emitting element according to claim 1, further comprising an n-side pad for flip chip bonding disposed on a partial region of the surface of the n-side electrode. The reflective film has a planar shape that scatters light emitted from the light emitting region and traveling toward the reflective film,
Furthermore, the semiconductor light emitting element in any one of Claims 1-5 which have the fluorescent substance which generate | occur | produces fluorescence when the light scattered by the said reflecting film injects. Wherein on the surface of the reflective film, the reflective film made of a large metal ionization tendency than layers, the semiconductor light-emitting device according to any one of claims 1 to 7, which is further formed. The reflective layer has an opening, a semiconductor light-emitting device according to any one of claims 1-8, which is a pattern to scatter light. The thickness of the p-side electrode is 1 to 5 nm, further, the semiconductor light-emitting device according to any one of claims 1 to 9 mesh auxiliary electrode on the p-side electrode is formed.

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