JP2013012709A - Nitride-based light-emitting diode element and light-emitting method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a nitride-based LED including a configuration favorable for effectively transferring heat generated in an active region to the element outside.SOLUTION: A nitride-based light-emitting diode element comprise: a nitride semiconductor laminate including a p-type layer, an n-type layer laminated on the p-type layer and a luminescent layer sandwiched by the p-type layer and the n-type layer; a p-side electrode provided on a surface of the p-type layer; and an n-side electrode connected to the n-type layer. The p-side electrode includes: an ohmic contact layer having a contact surface with the p-type layer; and a thermal conductive metal layer provided so as to sandwich the ohmic contact layer with the p-type layer. A projection area of the thermal conductive metal layer with respect to an element plane which is a plane orthogonal to a lamination direction of the nitride semiconductor laminate is larger than a projection area of the contact surface with respect to the element plane.

Description

The present invention relates to a nitride-based light-emitting diode element (hereinafter also referred to as a nitride-based LED) having a light-emitting structure formed of a nitride semiconductor. The nitride semiconductor is represented by a general formula such as Al _x Ga _y In _1-xy N (0 ≦ x ≦ 1, 0 ≦ y ≦ 1, 0 ≦ x + y ≦ 1), (Al, Ga, In) N. This compound semiconductor is also called a group III nitride semiconductor, nitride semiconductor, gallium nitride (GaN) semiconductor, or the like.

  Semiconductor devices using nitride semiconductors such as GaN, GaInN, AlGaN, and AlGaInN have been put into practical use. A typical device is a light emitting element such as a light emitting diode or a laser diode, in which a double hetero pn junction type light emitting structure is formed of a nitride semiconductor. In particular, nitride LEDs having a light-emitting structure heteroepitaxially grown on a c-plane sapphire substrate are produced in large quantities as light sources for backlights and illumination.

A nitride LED obtained by homoepitaxial growth of a light emitting structure on a GaN substrate has a low density of crystal defects in the light emitting structure, and is expected to be excellent in luminous efficiency and lifetime.
A GaN substrate having a c-plane as a main surface usually has a defect assembly region. For example, a c-plane GaN substrate called a stripe core substrate has a plurality of defect collection regions formed in parallel straight lines (Patent Documents 1 and 2). When a nitride semiconductor is epitaxially grown on a stripe core substrate, a portion having a high defect density is formed in the epitaxial layer corresponding to the stripe core of the substrate. In a light emitting device using a GaN substrate, an active region (a region where light emission occurs) is usually provided in a portion that is not such a high defect density portion in the epitaxial layer (Patent Document 3).

JP 2004-335646 A JP 2006-196609 A JP 2009-295893 A

A light output device using a nitride LED is required to have a high output as a substitute for an incandescent bulb, a fluorescent lamp, a mercury lamp, and the like. Accordingly, nitride-based LEDs are required to have good efficiency when driven with a large current.
Since the efficiency of a light-emitting diode element usually decreases as the temperature rises, in order to satisfy the above requirements, it is important to efficiently release heat generated in the active region during driving to the outside of the element. Accordingly, a main object of the present invention is to provide a nitride LED having a preferable configuration for efficiently releasing heat generated in the active region to the outside of the device, and a preferable light emitting method using the nitride LED. That is.

In one embodiment, a nitride-based light emitting diode device having the following configuration is provided:
a nitride semiconductor stack including a p-type layer, an n-type layer stacked on the p-type layer, and a light emitting layer sandwiched between the p-type layer and the n-type layer;
A p-side electrode provided on the surface of the p-type layer;
An n-side electrode connected to the n-type layer;
A nitride-based light emitting diode device comprising:
The p-side electrode has an ohmic contact layer having a contact surface with the p-type layer, and a thermally conductive metal layer provided so as to sandwich the ohmic contact layer between the p-type layer,
A nitride-based light-emitting diode element, wherein a projected area of the thermally conductive metal layer with respect to an element plane is larger than a projected area of the contact surface with respect to the element plane.

The term “element plane” as used herein refers to a plane parallel to the nitride semiconductor layer (n-type layer, light-emitting layer, p-type layer) that is the main component of the light-emitting diode element (a plane orthogonal to the layer thickness direction). ).
In addition, the “projection area” here is an area of an orthographic projection of an object to a predetermined plane (a shadow formed on the plane when light projected perpendicular to the plane is blocked by the object). Say. Therefore, when the contact surface is a plane, the projected area of the contact surface with respect to the element plane is equal to the area of the contact surface. On the other hand, when the contact surface is an uneven surface, the projected area of the contact surface with respect to the element plane is smaller than the area of the contact surface.

The threading dislocation density on the surface of the p-type layer in the portion in contact with the ohmic contact layer may be less than 1 × 10 ⁷ cm ⁻² . In this case, a GaN substrate may be bonded to the nitride semiconductor multilayer body on the n-type layer side as viewed from the light emitting layer. In addition, a high dislocation density portion having a surface threading dislocation density higher than a portion in contact with the ohmic contact layer may be present on the surface of the p-type layer. It is preferable to cover at least a part of the high dislocation density part.

Preferably, an insulating film may be inserted between the surface of the p-type layer and the thermally conductive metal layer.
Preferably, the insulating film is a transparent thin film having a lower refractive index than the p-type layer.
It is preferable that the contact surface and the n-side electrode do not overlap in a direction parallel to the element plane. In that case, the distance from an arbitrary point on the contact surface to the n-side electrode when the element is viewed in plan is preferably within 75 μm, more preferably within 50 μm.

The n-side electrode may be disposed on a side opposite to the side on which the p-side electrode is formed when viewed from the nitride semiconductor multilayer body.
Preferably, the projected area of the thermally conductive metal layer with respect to the element plane is 1.5 to 10 times the projected area of the contact surface with respect to the element plane.
Preferably, the total thickness of the heat conductive metal layer is 1 μm to 1 mm.
Preferably, the ohmic contact layer is a translucent thin film containing a transparent conductive oxide, or a metal thin film containing a platinum group element.
When the ohmic contact layer is a translucent thin film containing a transparent conductive oxide, preferably, the thermally conductive metal layer has a highly reflective layer at a portion in contact with the ohmic contact layer.

Preferably, the highly reflective layer includes Ag, Al, or Rh.
The thermally conductive metal layer may have an opening at a portion facing the contact surface.
Preferably, the thermally conductive metal layer includes at least one of an Au layer, a Cu layer, an Ag layer, or an Al layer.
The thermally conductive metal layer may include a thick film layer having a thickness of 5 μm to 1 mm made of Cu or Ni.

  The wavelength of light emitted by the light emitting layer may be less than 400 nm.

In the nitride-based light-emitting diode element, when the threading dislocation density on the surface of the p-type layer in the portion in contact with the ohmic contact layer is less than 1 × 10 ⁷ cm ⁻² , preferably, for the light-emitting diode element, Light can be emitted by supplying current so that the current per projected area of the contact surface with respect to the element plane is 150 to 300 A / cm ² .

  The nitride-based LED according to the embodiment of the present invention has a preferable configuration for efficiently radiating heat generated in the active region to the outside of the device. Therefore, the light emitting efficiency due to increase in device temperature when driven with a large current is provided. Reduction is suppressed.

FIG. 1A shows a structure of a nitride LED, FIG. 1A is a plan view, and FIG. 1B is a cross-sectional view taken along line XX in FIG. 1A. It is a top view for demonstrating the structure of the GaN board | substrate contained in the nitride-type LED shown in FIG. It is sectional drawing which shows the example of mounting of nitride type LED shown in FIG. It is sectional drawing which shows the structure of nitride type LED. It is sectional drawing which shows the structure of nitride type LED. It is sectional drawing which shows the structure of nitride type LED. It is a top view of a dot core board. FIGS. 8A and 8B are cross-sectional views showing the structure of a nitride LED. FIG. 9A shows a structure of a nitride-based LED, FIG. 9A is a plan view, and FIG. 9B is a cross-sectional view taken along the line XX in FIG. 9A. FIG. 10A is a plan view and FIG. 10B is a cross-sectional view taken along the line XX in FIG. FIG. 11A is a plan view, and FIG. 11B is a cross-sectional view taken along the line XX in FIG. 11A, illustrating the structure of a nitride-based LED. FIG. 12A is a plan view, and FIG. 12B is a cross-sectional view taken along the line XX of FIG. 12A. It is sectional drawing of an ultraviolet light-emitting device. It is sectional drawing of an ultraviolet light-emitting device.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. In order to simplify the description, the same components are denoted by the same reference numerals.

[Light emitting diode element]
(Embodiment 1-1)
1A and 1B are schematic views showing the structure of a nitride-based LED 101 according to Embodiment 1-1 of the present invention. FIG. 1A is a plan view, and FIG. 1B is an XX of FIG. It is sectional drawing in the position of a line.

  The nitride-based LED 101 has a structure in which an n-type layer 12, a light emitting layer 13, and a p-type layer 14 made of a nitride semiconductor are stacked on one main surface of a GaN substrate 11. Each layer is an epitaxial layer formed using a vapor phase growth method such as the MOVPE method. The epitaxial layer located at the top is the p-type layer 14, and the p-side electrode 15 is formed on the surface thereof. The p-side electrode 15 includes an ohmic contact layer 15a and a heat conductive metal layer 15b. An n-side electrode 16 is formed on the surface of the n-type layer 12 exposed by partially removing the p-type layer 14 and the light emitting layer 13.

The GaN substrate 11 is a stripe core substrate, and has a stripe core A which is a defect assembly region at both ends, and a single crystal region B having a low dislocation density at the center. As shown in FIG. 2, the stripe core A is a defect gathering region that is linear when the GaN substrate 11 is viewed in plan, and has a width of 20 to 100 μm. The p-type layer 14 has a high defect density portion C immediately above the stripe core A of the GaN substrate 11. The other part of the p-type layer 14 is a low defect density portion D having a defect density lower than that of the high defect density portion C. The low defect density portion D includes a portion where the density of threading dislocations on the surface is less than 1 × 10 ⁷ cm ⁻² . The low defect density portion D preferably includes a portion where the density of threading dislocations on the surface is less than 1 × 10 ⁶ cm ⁻² , and further includes the density of threading dislocations on the surface less than 1 × 10 ⁵ cm ^−2. It is more preferable.

  The ohmic contact layer 15a is formed on the surface of the low defect density portion D and does not contact the surface of the high defect density portion C. This is to prevent carriers from diffusing and deactivating in a portion having a high defect density in the epitaxial layer. Inside the p-type layer 14 having low conductivity, carriers injected from the p-side electrode 15 through the ohmic contact layer 15a hardly diffuse in the lateral direction (direction perpendicular to the thickness direction), and substantially the ohmic contact layer. Since the ohmic contact layer 15a is formed at a position away from the surface of the high defect density portion C of the p-type layer 14 so that the carrier has a defect density inside the epitaxial layer. It is possible to prevent diffusion to a high part.

  The heat conductive metal layer 15b is formed on the ohmic contact layer 15a and is electrically connected to the ohmic contact layer. The thermally conductive metal layer 15 b is formed from the low defect density portion D to the high defect density portion C of the p-type layer 14. As described above, since the p-type carrier injection into the light emitting layer 13 occurs substantially only in the region immediately below the ohmic contact layer 15a, the area of the active region is substantially equal to the area of the ohmic contact layer 15a. The same can be said. Therefore, it can be said that the area of the heat conductive metal layer 15b is larger than the area of the active region.

  The mounting of the nitride-based LED 101 includes, for example, a conductive bonding material such as solder (for example, AuSn alloy), conductive paste (for example, Ag paste), the heat conductive metal layer 15b of the p-side electrode 15 and the external electrode. This can be done by joining. FIG. 3 shows a mounting example of the nitride LED 101 using such a method. FIG. 3 is a sectional view, and a nitride LED 101 is fixed on a mounting substrate 200 having an anode terminal 22 and a cathode terminal 23 on an insulating substrate 21. The nitride LED 101 is flip-chip mounted with the epitaxial layer side facing the mounting substrate 200. Between the anode terminal 22 of the mounting substrate and the thermally conductive metal layer 15b of the nitride LED, and between the cathode terminal 23 of the mounting substrate and the n-side electrode 16 of the nitride LED, there is a conductive property, respectively. Bonding is performed by the adhesive bonding material E.

  Since the area of the heat conductive metal layer 15b is larger than the area of the active region (≈the area of the ohmic contact layer 15a), heat generated in the active region is generated inside the heat conductive metal layer 15b and the conductive bonding material E. In FIG. 5, the diffusion may be performed not only in the direction immediately below but also in the lateral direction (direction parallel to the element surface). Therefore, the temperature rise of the active region when the nitride LED 101 is driven with a large current is suppressed. This effect becomes more prominent as the area ratio of the heat conductive metal layer 15b to the area of the ohmic contact layer 15a is increased. This area ratio can be, for example, 1.5 to 10 times, and preferably 2 to 4 times.

(Embodiment 1-2)
FIG. 4 shows a cross-sectional view of the nitride LED 102 according to Embodiment 1-2 of the present invention. The nitride-based LED 102 is different from the embodiment 1-1 in that the ohmic contact layer 15a included in the p-side electrode 15 is formed from the low defect density portion D to the high defect density portion C of the p-type layer 14. This is different from the nitride LED 101 according to the above. In the case of the nitride-based LED 102, the ohmic contact layer 15a and the high defect density portion are covered with the insulating film 17 covering the surface of the high defect density portion C of the p-type layer 14 while the ohmic contact layer 15a is formed in this way. Since C is insulated, carriers are not injected from the p-side electrode 15 into the high defect density portion C. Therefore, the region immediately below the portion where the ohmic contact layer 15a and the p-type layer 14 are in contact becomes the active region. The thermally conductive metal layer 15b is formed from the low defect density portion D to the high defect density portion C, and the area thereof is larger than the area of the active region.

  In the nitride-based LED 102, if the insulating film 17 is a transparent thin film having a refractive index lower than that of the p-type layer, light that is incident on the lower surface of the p-side electrode 15 from the p-type layer 14 side without the insulating film 17 is used. Since a part of the light is efficiently reflected by the insulating film 17, the improvement of the light emission efficiency can be expected.

(Embodiment 1-3)
FIG. 5 shows a cross-sectional view of the nitride LED 103 according to Embodiment 1-3 of the present invention. In the nitride LED 102 according to Embodiment 1-2 described above, the insulating film 17 is sandwiched between the ohmic contact layer 15a of the p-side electrode 15 and the p-type layer 14, whereas in the nitride LED 103, An ohmic contact layer 15 a is sandwiched between the insulating film 17 and the p-type layer 14. The insulating film 17 has a plurality of through holes in a portion formed on the ohmic contact layer 15a, and the ohmic contact layer 15a and the heat conductive metal layer 15b are connected through the plurality of through holes.

  Also in the nitride LED 103, if the insulating film 17 is a transparent thin film having a refractive index lower than that of the p-type layer, if the insulating film 17 is not present, the light enters the lower surface of the heat conductive metal layer 15b from the p-type layer 14 side. Since a part of the light to be efficiently reflected by the insulating film 17, an improvement in luminous efficiency can be expected.

(Embodiment 1-4)
FIG. 6 shows a cross-sectional view of the nitride LED 104 according to Embodiment 1-4 of the present invention. In the nitride-based LEDs according to the above-described embodiments 1-1 to 1-3, the n-side electrode 16 is formed on the surface of the partially exposed n-type layer 12, whereas in the nitride-based LED 104, An n-side electrode 16 is formed on the single crystal region B on the back surface of the GaN substrate 11.

What is common to Embodiments 1-1 to 1-4 described above is that the surface of the high defect density portion C, which is not suitable for providing an active region, is effective in order to increase the area of the heat conductive metal layer 15b. It is used for.
In each of the above embodiments 1-1 to 1-4, it is obvious that the high defect density portion can be effectively used in the same manner even when the GaN substrate 11 is replaced from a stripe core substrate to a dot core substrate. I will. The dot core substrate is a substrate in which a defect gathering region A having a dot shape in a plan view is arranged in a predetermined pattern and surrounded by a single crystal region B having a low dislocation density.
A plan view of a dot core substrate according to an example is shown in FIG. 7, and a nitride LED 105 (Embodiment 1-5) and a nitride LED 106 according to an embodiment of the present invention using the dot core substrate 11 shown in FIG. Sectional views of Embodiment 1-6 are shown in FIGS. 8A and 8B, respectively.

(Preferred embodiment)
Next, a preferable configuration of each part that can be employed in the nitride-based LED according to the above-described embodiments 1-1 to 1-6 will be described.

  Each of the n-type layer 12, the light emitting layer 13 and the p-type layer 14 epitaxially grown on the GaN substrate 11 does not have to have a constant semiconductor crystal composition or impurity concentration in the thickness direction. You may have. Further, nitriding having various functions between the GaN substrate 11 and the n-type layer 12, between the n-type layer 12 and the light-emitting layer 13, and between the light-emitting layer 13 and the p-type layer 14 with reference to known techniques. A physical semiconductor layer can be inserted. For example, a defect reduction layer, a strain relaxation layer, a carrier block layer, and the like.

  The ohmic contact layer 15a formed on the surface of the p-type layer 14 is preferably a translucent thin film containing a transparent conductive oxide. It is desirable to use a transparent conductive oxide having high transmittance. Specifically, indium oxide-based TCO such as ITO and IZO (indium zinc oxide), AZO (aluminum zinc oxide), GZO ( Examples include zinc oxide based TCO such as gallium zinc oxide) and tin oxide based TCO such as FTO (fluorine doped tin oxide). Since the transparent conductive oxide has a refractive index lower than that of the nitride semiconductor, when the ohmic contact layer 15a is formed of the transparent conductive oxide, the interface between the p-type layer 14 and the ohmic contact layer 15a is a high-quality reflective surface. Become.

  Another preferred example of the ohmic contact layer 15a is a metal thin film containing a platinum group element. Among platinum group elements, it is desirable to use Rh having a particularly high reflectance. Ni / Au can also be used for the ohmic contact layer 15a.

  The heat conductive metal layer 15b desirably has a high reflection layer formed of a metal having a high reflectance with respect to light generated in the light emitting layer 13 on the lower surface side. Since a typical emission wavelength of a nitride LED is 360 to 500 nm, examples of preferable metals used for the highly reflective layer include Al, Ag, and Rh. Al to which elements such as Ti, Nd, Si, Cu, Mg, Mn, Cr are added, Cu, Au, Pd, Nd, Si, Ir, Ni, W, Zn, Ga, Ti, Mg, Y, In Ag added with an element such as Sn can also be preferably used as a material for the highly reflective layer. When the ohmic contact layer 15a is made of a transparent conductive oxide film having high translucency, the effect of the high reflection layer is particularly remarkable.

  The heat conductive metal layer 15b may include a high heat conductive layer formed of a metal such as Au, Cu, Ag, or Al having high heat conductivity. The thermally conductive metal layer 15b may include a thick film layer made of Cu or Ni and having a thickness of 5 μm to 1 mm. Suitable methods for forming this thick film layer are electrolytic plating, electroless plating, and the like. The heat conductive metal layer 15b desirably has a surface layer that is difficult to oxidize, such as an Au layer.

  The total thickness of the heat conductive metal layer 15b is preferably 1 μm to 1 mm, more preferably 5 to 500 μm, and particularly preferably 10 to 400 μm.

  In the n-side electrode 16, the portion in contact with the n-type layer 12 or the GaN substrate 11 is formed of a simple substance of Al, Ti, W, Ni, Cr, or V, or an alloy containing one or more metals selected from these. It is preferable. Among these, Al is a particularly preferable material. Al may contain additive elements such as Ti, Nd, Si, Cu, Mg, Mn, and Cr. The n-side electrode 16 is made of a transparent conductive oxide film, that is, indium oxide, ITO, IZO, zinc oxide, AZO, GZO, tin oxide, FTO, or the like, at a portion in contact with the n-type layer 12 or the GaN substrate 11. You may have a translucent thin film. The n-side electrode 16 preferably has a surface layer that is difficult to oxidize, such as an Au layer.

  As described above, the insulating film 17 desirably has a refractive index lower than that of the p-type layer 14. For example, the insulating film 17 is a metal oxide such as silicon oxide, magnesium oxide, spinel, aluminum oxide, zirconium oxide, or PSG. , BPSG, and glass such as spin-on glass.

  The thickness of the GaN substrate 11 is preferably 400 μm or more at the time of use for forming the epitaxial layer. It can be reduced to 100 μm or less. In particular, when the above-described thick film layer is formed to a thickness of 50 μm or more on the heat conductive metal layer 15b, the thickness of the GaN substrate 11 can be reduced to 50 μm or less, and the GaN substrate 11 is worn down. You may.

In order to improve the light extraction efficiency, the back surface of the GaN substrate 11 is roughened (textured).
surface) is effective. The back surface of the GaN substrate 11 can be roughened by wet etching or KEC using KOH, or by dry etching using an etching mask. The etching mask may be patterned into a predetermined shape using a photolithography technique or a laser interference exposure method. In addition, the etching mask is a nanomask formed by utilizing the ball-up phenomenon that occurs spontaneously when a metal thin film is heated and the microphase separation phenomenon that occurs spontaneously when an incompatible polymer is mixed. It may be.

(Embodiment 2-1)
FIG. 9 is a schematic view showing the structure of the nitride-based LED 201 according to Embodiment 2-1 of the present invention. FIG. 9A is a plan view, and FIG. 9B is an XX in FIG. It is sectional drawing in the position of a line. FIG. 9A shows the nitride LED 201 viewed from the conductive substrate 21 side.

  The nitride-based LED 201 has a structure in which an n-type layer 22, a light emitting layer 23, and a p-type layer 24 made of a nitride semiconductor are sequentially stacked on the first main surface 21 a of the conductive substrate 21. Each layer is an epitaxial layer formed using a vapor phase growth method such as the MOVPE method. The uppermost epitaxial layer is a p-type layer 24, and a p-side electrode 25 is formed on the surface thereof. The p-side electrode 25 includes an ohmic contact layer 25a and a heat conductive metal layer 25b. An n-side electrode 26 is formed on a part of the second main surface 21 b of the conductive substrate 21.

The conductive substrate 21 is a substrate that can transmit light generated in the light emitting layer 23, and may be, for example, a SiC substrate or a gallium oxide substrate, but is preferably manufactured using a liquid phase growth method or a solvothermal method. The GaN substrate does not have a defect assembly region. When the conductive substrate 21 is such a GaN substrate, the density of threading dislocations on the surface of the p-type layer 24 can be less than 1 × 10 ⁶ cm ^{−2 and even} less than 1 × 10 ⁵ cm ⁻² . When the dislocation density in the epitaxial layer is reduced to a level of less than 1 × 10 ⁶ cm ^−2, a decrease in internal quantum efficiency (so-called droop) when a large current is applied is reduced, so that the forward direction flows across the active region It is possible to apply a large current to the LED so that the current density is 150 to 300 A / cm ² .

As shown in FIG. 9A, the n-side electrode 26 formed on the second main surface 21b of the conductive substrate 21 is supplied to a pad portion 26a that is a portion to which a bonding wire is bonded, and the pad portion 26a. It is formed in a pattern having a grid portion 26b for spreading the current to be generated in the lateral direction.
On the other hand, the broken line in FIG. 9A shows the outer periphery of the ohmic contact layer 25 a formed on the surface of the p-type layer 24. That is, in the nitride-based LED 201, the pattern formed by the contact surface between the p-type layer 24 and the ohmic contact layer 25a and the pattern of the n-side electrode 26 do not overlap when viewed in plan (the outer periphery of the ohmic contact layer 25a). Is equal to the outer periphery of the contact surface between the p-type layer 24 and the ohmic contact layer 25a).

With this configuration, light generated in the active region immediately below the ohmic contact layer 25a is emitted to the outside from the second main surface 21b of the conductive substrate 21 without being blocked by the n-side electrode 26. It will be.
In addition, the heat conductive metal layer 25b provided so as to sandwich the ohmic contact layer 25a with the p-type layer 24 is formed in a larger area than the ohmic contact layer 25a. By thermally connecting to a heat sink, the heat generated in the active region can be effectively dissipated through the thermally conductive metal layer 25b.

(Embodiment 2-2)
FIG. 10A is a plan view of the nitride LED 202 according to Embodiment 2-2 of the present invention, and FIG. 10B is the nitride LED 202 at the position of line XX in FIG. FIG. FIG. 10A shows the nitride LED 202 viewed from the conductive substrate 21 side.

As shown in FIG. 10A, the n-side electrode 26 formed on the second main surface 21b of the conductive substrate 21 is supplied to a pad portion 26a that is a portion to which a bonding wire is bonded, and the pad portion 26a. It is formed in a pattern having a grid portion 26b for spreading the current to be generated in the lateral direction.
On the other hand, the broken line in FIG. 10A shows the outer periphery of the insulating film 27 formed on the surface of the p-type layer 24. That is, in the nitride-based LED 202, the p-type layer 24 and the p-type layer 24 are arranged so that the pattern formed by the contact surface between the p-type layer 24 and the ohmic contact layer 25a and the pattern of the n-side electrode 26 do not overlap when viewed in plan. The pattern of the insulating film 27 that separates the ohmic contact layers 25a is determined.

(Embodiment 2-3)
Fig.11 (a) is a top view of nitride-type LED203 which concerns on Embodiment 2-3 of this invention, FIG.11 (b) is the nitride-type LED203 in the position of the XX line of Fig.11 (a). FIG. FIG. 11A shows the nitride-based LED 203 viewed from the conductive substrate 21 side.

As shown in FIG. 11A, the n-side electrode 26 formed on the second main surface 21b of the conductive substrate 21 is supplied to a pad portion 26a that is a portion to which a bonding wire is bonded, and the pad portion 26a. It is formed in a pattern having a grid portion 26b for spreading the current to be generated in the lateral direction.
On the other hand, the broken line in FIG. 11A shows the outer periphery of the ohmic contact layer 25 a formed on the surface of the p-type layer 24. That is, in the nitride-based LED 203, when viewed in plan, the pattern formed by the contact surface between the p-type layer 24 and the ohmic contact layer 25a and the pattern of the n-side electrode 26 do not overlap (the outer periphery of the ohmic contact layer 25a). Is equal to the outer periphery of the contact surface between the p-type layer 24 and the ohmic contact layer 25a).

  The nitride-based LED 203 is different from the nitride-based LED 201 according to the above-described embodiment 2-1. In the nitride-based LED 203, only the ohmic contact layer 25a is provided between the p-type layer 24 and the thermally conductive metal layer 25b. Instead, the insulating film 27 is sandwiched. The insulating film 27 covers substantially the entire surface of the p-type layer 24 exposed without being covered by the ohmic contact layer 25a, and covers a part of the ohmic contact layer 25a. The insulating film 27 has a through hole in a portion formed on the ohmic contact layer 25a, and the ohmic contact layer 25a and the heat conductive metal layer 25b are connected through the through hole.

(Embodiment 2-4)
FIG. 12A is a plan view of the nitride LED 204 according to Embodiment 2-4 of the present invention, and FIG. 12B is the nitride LED 204 at the position of line XX in FIG. FIG. FIG. 12A shows the nitride LED 204 viewed from the n-type layer 22 side.

The nitride-based LED 204 does not have a conductive substrate, and the n-side electrode 26 is formed on the main surface of the n-type layer 22 opposite to the light emitting layer 23 side.
As shown in FIG. 12A, the n-side electrode 26 formed on the n-type layer 22 has a pad portion 26a, which is a portion to which a bonding wire is bonded, and a current supplied to the pad portion 26a in the horizontal direction. It is formed in a pattern having a grid portion 26b for spreading it.
On the other hand, the broken line in FIG. 12A shows the outer periphery of the ohmic contact layer 25 a formed on the surface of the p-type layer 24. Therefore, also in the nitride-based LED 203, the pattern formed by the contact surface between the p-type layer 24 and the ohmic contact layer 25a does not overlap with the pattern of the n-side electrode 26 when viewed in plan.

  The growth substrate used for forming the epitaxial layer (including the n-type layer 22, the light emitting layer 23, and the p-type layer 24) included in the nitride-based LED 204 has an n-side electrode 26 in the manufacturing process of the nitride-based LED 204. Prior to being formed, it is removed from the epitaxial layer using any suitable method (eg, laser lift-off, chemical lift-off, machining, etc.). The growth substrate may be any substrate that can grow the epitaxial layer, and may be, for example, a SiC substrate, a sapphire substrate, a Si substrate, a gallium oxide substrate, a GaN substrate, or the like.

(Preferred embodiment)
In the nitride-based LEDs according to Embodiments 2-1 to 2-4, an epitaxial layer (including the n-type layer 22, the light-emitting layer 23, and the p-type layer 24), an ohmic contact layer, a thermally conductive metal layer, and an insulating film A preferred configuration is the same as that of the nitride-based LED according to Embodiments 1-1 to 1-6.
The pattern of the n-side electrode 26 formed on the second main surface 21b of the conductive substrate 21 or the surface of the n-type layer 22 is not only a square lattice grid pattern, but also a triangular lattice pattern, a honeycomb lattice It can be various patterns such as a pattern, a comb pattern, a radial pattern, and a pattern in which a radial pattern and a concentric pattern are combined. Whatever pattern the n-side electrode 26 has, when the LED is viewed in plan, the pattern of the contact surface between the p-type layer 24 and the ohmic contact layer 25a overlaps the pattern of the n-side electrode 26. It is determined not to.

  In order to improve the light extraction efficiency, it is effective to make a region of the second main surface 21b of the conductive substrate 21 not covered with the n-side electrode 26 a textured surface by etching. is there. When removing the growth substrate as in the embodiment 2-4, it is desirable to etch the surface of the n-type layer 22 to make it rough.

  In any of Embodiments 1-1 to 1-6 and 2-1 to 2-4, the p-type layers 14 and 24 when the device is viewed in plan so that the uniformity of the current density in the active region is high. The distance from any point on the contact surface between the ohmic contact layers 15a and 25a to the n-side electrode is preferably within 75 μm, and more preferably within 50 μm. Since the conductivity of an n-type nitride semiconductor is lower than that of a metal n-side electrode, there is a limit to the distance at which electron carriers can diffuse parallel to the element surface inside a GaN substrate or n-type layer.

[Light emitting device]
An ultraviolet light emitting device as shown in FIG. 13 can be configured using the nitride LED according to the embodiment of the present invention. The ultraviolet light emitting device 301 of FIG. 13 is a visible light that also serves as a nitride LED (ultraviolet LED) 31 that emits ultraviolet light, a circuit board 33 on which the ultraviolet LED 31 is mounted, and a sealing material that seals the ultraviolet LED 31. And a light emitting unit 35. In this example, the ultraviolet LED 31 has the same element structure and mounting structure as those in FIG. A small amount of phosphor is added to the visible light emitting unit 35.

  The ultraviolet light emitting device 301 is used as a light source of an ultraviolet irradiation device for curing an ultraviolet curable resin used as a printing ink, coating, adhesive, or the like. In such an application, since a large current is applied to the LED for the purpose of obtaining a sufficient light output, it is desirable that the LED be radiated efficiently. In this regard, in the ultraviolet light emitting device 301, the nitride LED according to one embodiment of the present invention is used as the ultraviolet LED 31, so that heat generated in the active region of the LED is efficiently circuitized through the thermally conductive metal layer. It is escaped to the substrate 33.

  In the visible light emitting unit 35, a part of the ultraviolet light from the ultraviolet LED 31 is converted into visible light by the added phosphor. This visible light is taken out together with the ultraviolet light from the ultraviolet LED 31. Therefore, in the ultraviolet light emitting device 301, the ultraviolet LED 31 can be easily turned on / off by the naked eye, which is safe.

  In the visible light emitting part 35, the base material to which the phosphor is added is a translucent molding material that is usually used for sealing an ultraviolet LED. Preferable examples include inorganic glass and silicone resin, which are materials having good resistance to ultraviolet rays.

  Although the emission color of the visible light emitting unit 35 is not limited, it is advantageous to use green or yellow with high visibility because a small amount of phosphor is used. As the phosphor that emits green or yellow light, a silicate or sialon phosphor using Eu as an activator, or a garnet or nitride phosphor using Ce as an activator is preferable. . Alternatively, the emission color of the visible light emitting unit 35 can be purple to express an ultraviolet image. In that case, a blue phosphor and a red phosphor may be added to the visible light emitting portion 35.

  In the emission spectrum of the ultraviolet light emitting device 301, the emission peak intensity based on the emission of the ultraviolet LED 31 is the emission peak intensity based on the emission from the visible light emitting unit 35 so that the ultraviolet light from the ultraviolet LED 31 is not converted to visible light more than necessary. The amount of the phosphor added to the visible light emitting unit 35 is adjusted so as to be 10 times or more, preferably 20 times or more.

FIG. 14 shows a configuration example of another ultraviolet light emitting device configured to provide a visible light emitting unit so that the lighting / non-lighting of the ultraviolet LED can be safely confirmed.
The ultraviolet light emitting device 302 in FIG. 14 includes an ultraviolet LED 31, a circuit board 33 on which the ultraviolet LED 31 is mounted, a sealing material 37 that seals the ultraviolet LED 31, and a visible light emitting unit 35. Sealing of the ultraviolet LED 31 can be omitted.

  In the ultraviolet light emitting device 302, a visible light emitting unit 35 that converts a part of ultraviolet light emitted from the ultraviolet LED 31 into visible light is disposed on the side of the ultraviolet LED 301 so as not to prevent extraction of ultraviolet light from the ultraviolet LED 31. Yes. The reason is that the efficiency of the ultraviolet light emitting device 302 as an ultraviolet light source is not lowered. Furthermore, in the ultraviolet light emitting device 302, since the visible light emitting unit 35 is installed outside the sealing material 37 that seals the ultraviolet LED 31, the light emitted from the ultraviolet LED 31 is not converted to visible light more than necessary. . On the other hand, when a phosphor is added in the sealing material for sealing the ultraviolet LED, wavelength conversion more than necessary may occur. This is because the light emitted from the ultraviolet LED tends to be trapped inside the sealing material.

The ultraviolet light emitting devices 301 and 302 embody the invention described below:
(1) An ultraviolet light emitting element and a light emitter that absorbs part of the light from the ultraviolet light emitting element and converts it into visible light,
An ultraviolet light emitting device capable of confirming with the naked eye whether or not the ultraviolet light emitting element is lit by observing whether or not the light emitter emits visible light.
(2) The ultraviolet light emitting device according to (1), wherein the ultraviolet LED is sealed with a sealing material.
(3) The ultraviolet light emitting device according to (2), wherein at least a part of the sealing material also serves as the light emitter.
(4) The ultraviolet light emitting device according to (1) or (2), wherein the light emitter is disposed at a position that does not interfere with extraction of light from the ultraviolet light emitting element.
(5) The ultraviolet light emitting device according to (4), wherein the ultraviolet LED is sealed with a sealing material, and the light emitter is disposed outside the sealing material.
(6) The ultraviolet light emitting device according to any one of (1) to (5), wherein a light emission color of the light emitter is green, yellow, or purple.
(7) In the emission spectrum of the ultraviolet light emitting device, the intensity of the light emission peak based on the light emission of the ultraviolet LED is 10 times or more the intensity of the light emission peak based on the light emission from the light emitter. The ultraviolet light-emitting device according to any one of 6).

101, 102, 103, 104, 105, 201, 202, 203, 204 Nitride LED
11, 21 GaN substrate 12, 22 n-type layer 13, 23 Light-emitting layer 14, 24 p-type layer 15, 25 p-side electrode 15a, 25a ohmic contact layer 15b, 25b thermally conductive metal layer 16, 26 n-side electrode 17, 27 Insulating films 301 and 302 Ultraviolet light emitting device 31 Ultraviolet LED
33 Circuit board 35 Visible light emitting part 37 Sealing material

Claims (19)

a nitride semiconductor stack including a p-type layer, an n-type layer stacked on the p-type layer, and a light emitting layer sandwiched between the p-type layer and the n-type layer;
A p-side electrode provided on the surface of the p-type layer;
An n-side electrode connected to the n-type layer;
A nitride-based light emitting diode device comprising:
The p-side electrode has an ohmic contact layer having a contact surface with the p-type layer, and a thermally conductive metal layer provided so as to sandwich the ohmic contact layer between the p-type layer,
A nitride system, wherein a projected area of the thermally conductive metal layer with respect to an element plane which is a plane orthogonal to a stacking direction of the nitride semiconductor multilayer body is larger than a projected area of the contact surface with respect to the element plane Light emitting diode element. 2. The nitride-based light-emitting diode element according to claim 1, wherein a threading dislocation density on a surface of the p-type layer in a portion in contact with the ohmic contact layer is less than 1 × 10 ⁷ cm ⁻² .   The nitride-based light-emitting diode element according to claim 2, wherein a GaN substrate is bonded to the n-type layer side of the nitride semiconductor multilayer body as viewed from the light-emitting layer.   The surface of the p-type layer has a high threading dislocation density portion whose surface has a high threading dislocation density compared to the portion in contact with the ohmic contact layer, and the thermally conductive metal layer has at least the high dislocation density portion. The nitride-based light-emitting diode element according to claim 2 or 3, wherein a part thereof is covered.   The nitride-based light-emitting diode element according to claim 1, wherein an insulating film is partially inserted between the surface of the p-type layer and the thermally conductive metal layer.   The nitride-based light-emitting diode element according to claim 5, wherein the insulating film is a transparent thin film having a lower refractive index than the p-type layer.   The nitride-based light-emitting diode element according to claim 1, wherein the contact surface and the n-side electrode do not overlap in a direction parallel to the element plane.   The nitride-based light-emitting diode element according to claim 1, wherein when the element is viewed in plan, a distance from an arbitrary point on the contact surface to the n-side electrode is within 75 μm.   The nitride according to any one of claims 1 to 8, wherein the n-side electrode is disposed on a side opposite to the side on which the p-side electrode is formed when viewed from the nitride semiconductor multilayer body. Light emitting diode element.   The nitriding according to any one of claims 1 to 9, wherein a projected area of the thermally conductive metal layer with respect to the element plane is 1.5 times to 10 times a projected area of the contact surface with respect to the element plane. Physical light emitting diode element.   11. The nitride-based light-emitting diode element according to claim 1, wherein the total thickness of the thermally conductive metal layer is 1 μm to 1 mm.   The nitride-based light emission according to any one of claims 1 to 13, wherein the ohmic contact layer is a light-transmitting thin film containing a transparent conductive oxide or a metal thin film containing a platinum group element. Diode element.   The said ohmic contact layer is a translucent thin film containing a transparent conductive oxide, The said heat conductive metal layer has a highly reflective layer in the part which contact | connects the said ohmic contact layer. Nitride-based light emitting diode device.   The nitride-based light-emitting diode element according to claim 11, wherein the highly reflective layer contains Ag, Al, or Rh.   The nitride-based light-emitting diode element according to claim 1, wherein the thermally conductive metal layer has an opening at a portion facing the contact surface.   The nitride-based light-emitting diode element according to any one of claims 1 to 15, wherein the thermally conductive metal layer includes at least one of an Au layer, a Cu layer, an Ag layer, or an Al layer.   The nitride-based light-emitting diode element according to claim 1, wherein the thermally conductive metal layer includes a thick film layer made of Cu or Ni and having a thickness of 5 μm to 1 mm.   The nitride-based light-emitting diode element according to claim 1, wherein the wavelength of light emitted from the light-emitting layer is less than 400 nm. Supplied to the nitride-based light-emitting diode device according, the current to the projected area per current of the contact surface with respect to the optical device plane becomes the 150~300A / cm ² to one of the claims 2-6 Luminescent method.

Images