JP5191937B2 - Light emitting device and manufacturing method thereof - Google Patents

Description

  The present invention relates to a light emitting device and a method for manufacturing the same.

  A light emitting element used for a lighting device, a display device, or the like is required to have high luminance. In the case where the upper side of the light emitting element is the light extraction side, the light extraction efficiency can be improved by reflecting the light traveling downward of the light emitting layer.

  In this case, a metal film or a dielectric film can be used as the light reflecting layer. However, the reflectance of the metal film often decreases as the wavelength becomes shorter. In addition, although the dielectric has a multilayer film structure and the reflectance can be increased by the difference in refractive index, the obtained reflectance has a limit.

There is a technology disclosure example including a main metal layer that reflects light traveling downward from a light emitting layer (Patent Document 1). In this example, a contact metal layer for reducing the contact resistance is selectively disposed between the compound semiconductor layer including the light emitting layer and the main metal layer.
However, when the alloying heat treatment of the contact metal layer is performed, ohmic contact can be easily obtained, but light absorption occurs in the alloyed layer, making it difficult to increase the light extraction efficiency.

Japanese Patent Laid-Open No. 2005-19424

  Provided are a light-emitting element in which the reflectance of light toward the substrate side is increased and the light extraction efficiency is improved, and a method for manufacturing the light-emitting element.

According to one embodiment of the present invention, a semiconductor comprising a substrate, a light emitting layer provided on the substrate and capable of emitting emitted light, and a contact layer having a convex cross section smaller than a planar size of the light emitting layer. A layer, a first electrode provided on the first surface of the contact layer so as to be substantially the same size as the contact layer, and at least two media, and a quarter wavelength of the emitted light within the medium A photonic crystal layer having a periodic structure with a pitch within a range of 1 to 3/4 and capable of reflecting the emitted light; and an adhesive metal layer provided on the substrate and bonded to the first electrode And the photonic crystal layer is formed between the non-contact region of the first surface of the semiconductor layer and the adhesive metal layer so as to be adjacent to the contact layer and the first electrode. originating, characterized in that provided between Element is provided.

According to another aspect of the present invention, a step of forming a semiconductor layer having a light emitting layer capable of emitting emitted light and a contact layer on a crystal growth substrate; and the contact layer of the light emitting layer. Processing to a convex cross section smaller than a planar size, forming the first electrode on the first surface of the contact layer so as to have substantially the same planar size as the contact layer, and the first The contact layer non-formation region on the first surface of the semiconductor layer has a periodic structure with a pitch smaller than the wavelength within the medium of the emitted light so that one electrode is exposed. The step of forming a photonic crystal layer, the step of forming an adhesive metal layer on the substrate, the first electrode, and the adhesive metal layer are heat bonded in a bonded state, and then the crystal growth substrate is removed. Craft When manufacturing method of the light emitting element characterized by comprising a are provided.

  Provided are a light-emitting element having improved reflectance of light toward the substrate side and improved light extraction efficiency, and a method for manufacturing the same.

1 is a schematic cross-sectional view of a light emitting device according to a first embodiment. Schematic perspective view of photonic crystal layer Schematic sectional view of a light emitting device according to a comparative example Process sectional drawing of the manufacturing method of the light emitting element concerning 1st Embodiment Schematic sectional view of a light emitting device according to a second embodiment Sectional drawing of the process of the manufacturing method of the light emitting element concerning 2nd Embodiment Schematic diagram of a light emitting device according to the third embodiment

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
FIG. 1 is a schematic cross-sectional view of a light emitting device according to a first embodiment of the present invention.
The first contact layer 20, the first cladding layer 18, the light emitting layer 16, the second cladding layer 14, and the second contact layer 12, and the semiconductor layer 21 made of a compound semiconductor is a first electrode 48. It is bonded to the laminate 44 via. If the light emitting layer 16 is an InGaAlP-based material, light having a wavelength in the visible light range can be emitted. The first contact layer 20 is smaller than the planar size of the light emitting layer 16 and has a convex cross section.

Note that InGaAlP is a material represented by a composition formula of In _x (Ga _y Al _1-y ) _1-x P (where 0 ≦ x ≦ 1, 0 ≦ y ≦ 1), and p-type impurities and Including those doped with n-type impurities.

  The contact layer 20 has a convex cross section that is smaller than the planar size of the light emitting layer 16. In addition, a first electrode 48 having substantially the same size as the contact layer 20 is provided on the first surface 20 a of the contact layer 20.

  The photonic crystal layer 30 is adjacent to the contact layer 20 and the first electrode 48, and is provided in a non-formation region of the contact layer 20 on the first surface 21 a of the semiconductor layer 21. On the other hand, the laminate 44 includes a substrate 40 made of Si or the like and an adhesive metal layer 42. Further, the first electrode 48 and the adhesive metal layer 42 are bonded at the bonding interface 50. When Si having a high carrier concentration is used as the substrate 40, the resistance can be reduced and the mechanical strength can be increased.

  The photonic crystal layer 30 has a minute periodic structure composed of at least two media having different refractive indexes, and can reflect light in a wavelength range determined by this structure. The photonic crystal layer will be described later.

  A second electrode 46 is formed on the surface of the second contact layer 12. The second contact layer 12 is made of, for example, GaAs. However, if the second contact layer 12 has substantially the same size as the second electrode 46, it is possible to suppress the emission lights G1 and G2 from being absorbed on the light extraction side.

  In FIG. 1, the contact layer 20 is provided in the vicinity of the center portion of the chip when viewed from above, and the second contact layer 12 and the second electrode 46 are disposed at positions separated from the center portion of the chip. . However, the present invention is not limited to this arrangement. That is, the second contact layer 12 and the second electrode 46 are located in the vicinity of the center portion of the chip, the first contact layer 20 is separated from the center portion, and the center portion is a non-formation region of the first contact layer 20. The photonic crystal layer 30 may be provided in a nearby recess.

  The adhesive metal layer 42 and the contact layer 20 can form an ohmic contact, and the second electrode 46 and the second contact layer 12 can form an ohmic contact. Light emission recombination is caused by the injected current, and emitted light can be emitted from the light emitting layer 16 on the contact layer 20. The emitted light G1 can be extracted from the surface 21b side of the semiconductor layer 21.

  Further, light traveling downward from the light emitting layer 16 is reflected by the photonic crystal layer 30 and can be extracted from the surface 21b (G2). That is, even if it is the light which goes to the downward direction, absorption in the board | substrate 40 is suppressed or it escapes to a side, Therefore Light extraction efficiency can be improved.

  FIG. 2 is a schematic perspective view of the photonic crystal layer. 2A shows a one-dimensional photonic crystal, and FIG. 2B shows a three-dimensional photonic crystal.

If the pitch P is equal to or less than the in-medium wavelength λm, the light may be diffracted or scattered, and follow wave optics rather than a straight beam. In other words, such a micro periodic structure can be treated as a medium uniformly filled with a medium having an effective refractive index n _eff . When the wavelength in the free space is λ ₀ , it is expressed by the medium wavelength λm = λ ₀ / n _eff .

Here, the effective refractive index n _eff falls within the range of the refractive indexes of the two media. If the first medium is SiO ₂ (refractive index is approximately 1.5) and the second medium is air (refractive index is 1), the effective refractive index n _eff can vary between 1 and 1.5. is there. The wavelength range of light transmitted through this periodic structure is called a photonic band, and the wavelength range of light blocked by reflection or the like is called a photonic band gap.

The one-dimensional photonic crystal 31 shown in FIG. 2A is composed of repeated two-layer films 31a and 31b. For example, a combination of SiO ₂ and Si ₃ N ₄ can be used. When the pitch P is set in a range from ¼ to ¾ of the in-medium wavelength λm determined by the effective refractive index n _{eff, the} light is strengthened by the periodic structure and the reflectance can be increased. For example, in a Bragg reflection structure in which two dielectric films having different refractive indexes are laminated so that the pitch P is approximately a half wavelength, the reflectance increases exponentially with respect to the number of laminated layers.
Here, at least one of silicon dioxide, silicon nitride, and aluminum nitride can be used as the dielectric film.

FIG. 2B shows a woodpile photonic crystal, which is a stacked first prism-shaped first dielectric 31c. For example, the refractive index of the first dielectric 31c is as follows. The range may be from 1.3 to 2.6. Examples of such a dielectric include SiO ₂ (refractive index is approximately 1.5), Si ₃ N ₄ (refractive index is approximately 2.0), and AlN (refractive index is approximately 2.0). . In this figure, a photonic crystal layer 31 is provided adjacent to the first cladding layer 18 constituting the semiconductor layer. In the photonic crystal layer 31, prisms made of the dielectric as described above are alternately stacked. The hollow area between these prisms can be, for example, the air layer 31e.

  In order to reflect light emitted from the light emitting element, it is preferable to use a one-dimensional or three-dimensional photonic crystal. In particular, since light emitted from the light emitting element spreads three-dimensionally, a three-dimensional photonic crystal layer is more preferable because the reflectance can be easily maintained regardless of the incident angle to the photonic crystal layer.

The effective refractive index n _eff in the photonic crystal can be controlled by the periodic structure and the material constituting them. In the case of visible light, the pitch P of the periodic structure is, for example, 200 to 440 nm.

FIG. 3 is a schematic cross-sectional view of a light emitting device according to a comparative example.
In FIG. 3A, the adhesive metal layer 142 provided on the substrate 140 is bonded to the first contact layer 120 of the semiconductor layer at the adhesive interface 150. When an alloy layer is formed between the contact layer 120 and the adhesive metal layer 142, an ohmic contact can be obtained. However, the light absorption layer 119 is generated in this alloy layer, and the light output is likely to decrease (G10).

  The adhesive metal layer 142 also absorbs light. For example, in Au, the reflectance in the green to red wavelength range is 90% or more, but the reflectance in blue decreases to 50% or less. Further, in Cu, the reflectance in red is approximately 97%, but decreases to approximately 60% in the blue to green wavelength range. Thus, the reflectance of the metal film may decrease on the short wavelength side of the visible light wavelength range.

  On the other hand, in FIG. 3B, the planar size of the first contact layer 120 is reduced, and a dielectric such as an oxide film 122 having a refractive index lower than that of the semiconductor layer is provided around the first contact layer 120 to provide a first contact. Light absorption in the layer 120 is reduced. If the refractive index of the oxide film 122 is 1.5 and the refractive index of the semiconductor layer is 3.5, the critical angle θc is approximately 25 degrees. For this reason, light G11 having an incident angle larger than 25 degrees is reflected at the interface between the first cladding layer 118 and the oxide film 122, but light G12 having an incident angle smaller than 25 degrees is reflected by the oxide film 122. After being transmitted, a part is absorbed by the adhesive metal layer 142. That is, the optical loss cannot be reduced sufficiently in the comparative example shown in FIG.

  On the other hand, in the present embodiment, by appropriately setting the pitch of the fine periodic structure, it is easy to increase the reflectance within the wavelength range of the photonic band gap and further reduce the optical loss. For example, when the pitch P is approximately one-half of the in-medium wavelength, the reflectance becomes closer to 100%, and a high output (high luminance) light emitting element can be obtained.

FIG. 4 is a process cross-sectional view of the method for manufacturing the light emitting device according to the first embodiment.
As shown in FIG. 4A, on the crystal growth substrate 10 made of GaAs or the like, the second contact layer 12 made of p-type GaAs or the like (thickness: 0.1 μm, carrier concentration: 2 × 10 ¹⁸ cm ⁻³ ). A second clad layer 14 (thickness: 0.6 μm) made of p-type InAlP, a light-emitting layer 16 made of In _0.5 (Ga _y Al _1-y ) _0.5 P, n-type InAlP, etc. The first cladding layer 18 (thickness: 0.6 μm) and the first contact layer 20 (carrier concentration: 2 × 10 ¹⁸ cm ⁻³ ) made of n-type GaAs or the like are grown in this order.

  For crystal growth, MOCVD (Metal Organic Chemical Vapor Deposition) method, MBE (Molecular Beam Epitaxy) method and the like can be used. The conductivity type is not limited to this, and may be an opposite conductivity type.

When the light emitting layer 16 has an MQW (Multi Quantum Well) structure, it becomes easy to control the emission wavelength and reduce the operating current. The MQW structure can be realized, for example, by arranging a plurality of well layers with y = 0.96 and a width of 5 nm and a barrier layer with y = 0.2 and a width of 8 nm.

  The contact layer 20 is patterned into a convex cross-sectional shape, and a first electrode 48 is formed on the first surface 20a (FIG. 4B). The structure shown in FIG. 4B can also be obtained by forming a film to be the first electrode on the contact layer 20 and then patterning the first electrode 48 and further patterning the contact layer 20. .

Further, on the first surface 21 a of the semiconductor layer 21, the first surface 48 a of the first electrode 48 is exposed in the non-formation region of the contact layer 20 adjacent to the contact layer 20 and the first electrode 48. Then, the photonic crystal layer 30 is formed. In this case, for example, after forming a first dielectric such as SiO ₂ , a first layer composed of a prismatic first dielectric is formed using a photolithography method or the like. Further, the second layer is formed using a photolithography method or the like so as to be substantially orthogonal to the prisms constituting the first layer. Similarly, the photonic crystal layer 30 having a three-dimensional structure can be formed by stacking the third and subsequent layers.

  If the hollow region of each prism is an air layer, the structure and the manufacturing method can be simplified. Such a fine periodic structure can be formed using a photolithography method or the like in a semiconductor manufacturing process. Note that the one-dimensional photonic crystal in FIG. 2A has a simpler structure.

  On the other hand, as shown in FIG. 4D, a stacked body 44 is formed in which an adhesive metal layer 42 containing Au or the like is provided on a substrate 40 made of n-type Si or the like. Further, as shown in FIG. 4E, the first electrode 48 and the photonic crystal layer 30 and the adhesive metal layer 42 of the stacked body 44 are bonded together, for example, in a hydrogen atmosphere or an inert gas while applying a load. Heat in an atmosphere. As a result, bonding is performed at the bonding interface 50 as shown in FIG.

  The first electrode 48 can have a structure of Ti / Pt / Au, for example, from the contact layer 20 side. Further, the adhesive metal layer 42 can have a structure of Ti / Pt / Au from the substrate 40 side, for example. In the case of such a combination, when heating is performed for 30 minutes in a temperature range of 350 to 500 ° C., the first electrode 48 and the adhesive metal layer 42 are bonded.

  Further, eutectic solder may be included in at least one of the first electrode 48 and the adhesive metal layer 42. In this case, a eutectic solder layer such as AuSb (melting point approximately 270 ° C.), AuGe (melting point approximately 356 ° C.), AuSi (melting point approximately 370 ° C.) or the like is provided on the first layer made of Ti / Pt / Au. Furthermore, if an Au layer is provided thereon, oxidation of the eutectic solder can be suppressed. In this way, high adhesive strength can be achieved at a temperature slightly higher than the melting point of the eutectic solder.

Subsequently, the substrate 10 is removed by using at least one of an etching method and a mechanical polishing method (FIG. 4G). Further, when the second electrode 46 made of AuZn or the like is formed and the second contact layer 12 is etched, the structure shown in FIG. 4H is obtained.
When the substrate 40 is a low resistance Si substrate, the current from the adhesive metal layer 42 can be taken out to the conductive portion of the mounting member via the substrate 40.

FIG. 5 is a schematic cross-sectional view of a light emitting device according to the second embodiment.
The contact layer 20 is not a convex cross section and has the same size as the light emitting layer 16, and the conductive photonic crystal layer 30 and the first electrode 48 are laminated on the entire surface. That is, light traveling downward from the light emitting layer 16 can be reflected by the entire surface of the photonic layer 30, and it becomes easier to improve the light extraction efficiency. Examples of the medium constituting the conductive photonic crystal layer 30 include ITO (Indium Tin Oxide), IZO (Indiumu Zinc Oxide), NiO (nickel oxide), zinc oxide, and titanium nitride. including.

FIG. 6 is a process cross-sectional view of the manufacturing method of the present embodiment.
As shown in FIG. 6A, the contact layer 20 is left on the entire surface of the wafer. Further, as shown in FIG. 6B, the photonic crystal layer 30 is formed on the entire first surface 20 a of the contact layer 20. In the second embodiment, the first surface 20 a of the contact layer 20 coincides with the first surface 21 a of the semiconductor layer 21. Further, as shown in FIG. 6C, the first electrode 48 is formed on the entire first surface 30 a of the photonic crystal layer 30. That is, since the contact layer 20, the photonic crystal layer 30, and the first electrode 48 do not require a patterning process, the process can be simplified.

  The first electrode 48 and the adhesive metal layer 42 can be Ti / Pt / Au, for example. Further, at least one of them may further include a eutectic solder such as AuSb. In the present embodiment, since the bonding area between the first electrode 48 and the adhesive metal layer 42 can be increased, it is easier to increase the adhesive strength.

FIG. 7 is a schematic view of a light emitting device according to the third embodiment. 7A is a plan view, FIG. 7B is a cross-sectional view taken along line AA, and FIG. 7C is a bottom view taken along line BB.
The semiconductor layer 21 includes a first contact layer 20, a current diffusion layer 19, a cladding layer 18, a light emitting layer 16, a cladding layer 14, a current diffusion layer 13, and a second contact layer 12 stacked from the stacked body 44 side. Has been. The current diffusion layers 13 and 19 are made of, for example, In _0.5 (Ga _0.3 Al _0.7 ) _0.5 P, and can easily spread the current injected from the electrode 46 in the plane of the light emitting layer 16. However, if the current can be diffused by the cladding layers 14 and 18, it can be omitted.

  Further, the current from the light emitting layer 16 and the clad layer 18 flows along the current diffusion layer 19, and becomes a current path that flows through the contact layer 20 and the adhesive metal layer 42. When the photonic crystal layer 30 is an insulating material, it is preferable to provide the current diffusion layer 19 in order to increase reflection by increasing the areas of the photonic crystal layer 30 and the contact layer 20.

  The first electrode 48 is provided on the contact layer 20 patterned to have a convex cross section, and is bonded to the adhesive metal layer 42.

  The second electrode 46 includes a wire bonding pad portion 46a and a thin wire portion 46b surrounding the pad portion 46a. The width of the thin wire portion 46b is, for example, 3 to 6 μm, and the interval between the pad portion 20a and the thin wire portion 20b is, for example, 6 to 50 μm. A current flows between the second electrode 46 and the first electrode 48.

  The photonic crystal layer 30 has an annular shape so that the first surface 48a of the first electrode 48 is exposed in the concave portion adjacent to the convex contact layer 20 and the first electrode 48 provided thereon. Provided. Light traveling downward from the light emitting layer 16 can be reflected upward by the photonic crystal layer 30. That is, the light emitting region is widened by the thin wire electrode 46b, and light can be reflected upward by the photonic crystal layer 30, so that it is easy to increase the output of the emitted light G2. Of course, the emitted light is emitted upward from the light emitting layer 16, but is omitted in this figure.

  In the present embodiment, the light emitting layer 16 is made of an InGaAlP-based semiconductor, but the present invention is not limited to this, and may be made of, for example, a GaAlAs-based semiconductor or an InGaAlN-based semiconductor. Further, the substrate 40 may be any of Ge, SiC, GaN, and GaP.

  The light-emitting element according to this embodiment can easily obtain high luminance, and can be widely used in applications such as lighting devices, display devices, and traffic lights.

  The embodiment of the present invention has been described above with reference to the drawings. However, the present invention is not limited to these embodiments. Even if a person skilled in the art makes various design changes with respect to the material, size, shape, arrangement, etc. of a semiconductor layer including a substrate, a photonic crystal layer, a light emitting layer contact layer, and the like constituting a light emitting element, an electrode, etc. It is included in the scope of the present invention without departing from the gist of the invention.

 10 crystal growth substrate, 20, 20a first contact layer, 21, 21a, 21b semiconductor layer, 16 light emitting layer, 30, 30a, 31 photonic crystal layer, 40 substrate, 42 adhesive metal layer, 44 laminate, 48 first 1 electrode, G1, G2 emission light

Claims (6)

A substrate,
A semiconductor layer provided on the substrate and capable of emitting emitted light; and a contact layer having a convex cross section smaller than a planar size of the light emitting layer ;
A first electrode provided on the first surface of the contact layer so as to be substantially the same size as the contact layer ;
A photonic crystal layer composed of at least two media, having a periodic structure with a pitch within a range of ¼ to ¾ of an in-medium wavelength of the emitted light, and capable of reflecting the emitted light;
An adhesive metal layer provided on the substrate and bonded to the first electrode;
Equipped with a,
The photonic crystal layer is adjacent to the contact layer and the first electrode,
A light-emitting element provided between the non-formation region of the contact layer on the first surface of the semiconductor layer and the adhesive metal layer . The periodic structure, the light emitting device of claim 1, wherein the spread one-dimensional or three-dimensional. The pitch, the light-emitting device according to claim 1 or 2, characterized in that it is a 1 substantially half of the medium wavelength. The medium is a dielectric film, conductive film, and a light-emitting element according to any one of claims 1 to 3, characterized in that it comprises one of air. The light emitting device according to claim 4, wherein the conductor film includes indium tin oxide, indium zinc oxide, zinc oxide, nickel oxide, and titanium nitride. Forming a semiconductor layer having a light emitting layer capable of emitting emitted light and a contact layer on a crystal growth substrate;
Processing the contact layer into a convex cross section smaller than the planar size of the light emitting layer;
Forming the first electrode on the first surface of the contact layer so as to have substantially the same planar size as the contact layer;
A periodic structure made of at least two media and having a pitch smaller than the in-medium wavelength of the emitted light in the contact layer non-formation region of the first surface of the semiconductor layer so that the first electrode is exposed. Forming a photonic crystal layer having:
Forming an adhesive metal layer on the substrate;
Removing the crystal growth substrate after heat-bonding the first electrode and the adhesive metal layer in a bonded state;
A method for manufacturing a light-emitting element, comprising:

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