JP2000049374A - White LED - Google Patents

Abstract

(57) [Summary] [Purpose] To provide a long-life, high-brightness white LED that can be manufactured at a low cost with a simple structure. [Constitution] An active layer and a pn junction are formed by laminating an epitaxial thin film of a GaInN-based mixed crystal on a GaN single crystal substrate doped with oxygen or carbon or having nitrogen vacancies. The white light is obtained by synthesizing the light and the yellow fluorescence from the fluorescence emission center of the GaN substrate excited by the blue / blue-green light.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a novel semiconductor light emitting device capable of emitting white light with a single device. There is a great demand for white light. White light is most suitable as a light source for illumination. The liquid crystal backlight uses white light. The present invention relates to a semiconductor white LED that can be used for lighting, display, a liquid crystal backlight, and the like.

[0002]

2. Description of the Related Art Light-emitting diodes (LEDs) of a single color such as red, yellow, green, and blue have already been manufactured and sold. As a red high-intensity light-emitting diode (LED), one having several Cd (candela) or more is already on the market.
Red L with a light emitting layer of AlGaAs or GaAsP
ED. It is a low-cost LED and is used for a wide range of applications. Green / yellow-green LEDs using GaP as a light emitting layer are also manufactured and sold. Some blue LEDs use SiC as an active layer. Blue and green LEDs include GaInN as an active layer. Orange / yellow elements include AlGaInP as a light emitting layer. Both are inexpensive and practical LEDs. Among them, GaP and SiC are indirect transition type semiconductors, so their efficiency is low, and they have not reached candela-class output.

[0003] Since all of these LEDs utilize the electronic transition between the bands of the light emitting layer material, they emit only monochromatic light.
That's why LEDs were monochromatic. This is natural. Monochromatic LEDs have many uses, such as display LEDs. However, monochromatic LEDs alone cannot replace all light sources. Monochromatic light sources are useless for applications such as lighting, special displays, and liquid crystal backlights. When monochromatic light is used for lighting, all objects appear in that color. When monochromatic light is used for the liquid crystal backlight, only the shaded image of that color can be seen.

A white light source including all colors is absolutely necessary. However, there is no semiconductor light emitting element which emits white light.
Incandescent lamps, fluorescent lamps and the like are still widely used as illumination light sources. Incandescent bulbs are inefficient. Also, the life is short. Fluorescent lamps are not efficient, but have a short life. A heavy object such as a ballast is required. Also the size is too big. There are such difficulties.

It is desired for a white light source to have a small size, a simple peripheral circuit, a long life, a high luminous efficiency, and a low cost.
It seems that only semiconductor light emitting devices can satisfy these requirements. However, as described above, since the semiconductor light emitting device uses an electronic transition between band gaps, it is inevitably only monochromatic light. A semiconductor element alone cannot generate white light.

[0006]

The use of blue, green, and red LEDs, which are the three primary colors, could produce a white LED. Blue LEDs using GaInN are also commercially available, and LEDs of three primary colors are available. However, combining three light emitting elements results in high cost.
It requires three times the power as well as the product cost, which is not efficient. It is also necessary to adjust the balance among the three primary colors. The circuit must be complicated. It is also disadvantageous in terms of size. There is little benefit in producing white light by combining a plurality of LEDs in this way. Again a single LE
I want to get white with D.

An LED having sapphire as a substrate and GaInN as an active layer is a GaInN-based LED or simply GaN.
It is called system LED. A trial of a white LED combining a GaInN-based LED and a YAG-based phosphor has been proposed.
For example, there is a white semiconductor light emitting device introduced in the following literature. "Optical Functional Materials Manual" Optical Functional Materials Manual Editing Board Edition, Optronics, p. 457, 19
June 1997

This device uses GaInN as an active layer.
It has a structure in which an N-based LED chip is embedded in a YAG fluorescent material that emits yellow light. This is shown in FIG. A first lead 2 and a second lead 3 are fixed in a transparent mold 1 made of resin. The upper part of the first lead 2 has a Γ shape, and a depression 4 is formed. A GaN-based LED chip 5 having a GaInN active layer is fixed in the depression 4. The recess 4 is filled with a yellow YAG phosphor 6 so as to completely cover the LED 5. An anode electrode and a cathode electrode are provided on the upper surface of the GaN-based LED, and these are connected to the leads 2 and 3 by wires 7 and 8.

Since a normal light emitting element and a light receiving element use a conductive substrate, the chip bottom surface becomes an electrode and is directly attached to a lead.
Therefore, only one wire connecting the other upper electrode and the lead is required. However, a GaN-based blue LED has a GaN or GaInN layer laminated on a sapphire substrate. Since sapphire is an insulator, the bottom surface cannot be used as a cathode.
Therefore, an n-electrode (cathode) and a p-electrode (anode) are formed side by side on the upper surface of the chip. So you need two wires. When current flows from the anode to the cathode, GaN-based LE
D emits blue. Part of the blue light passes through the YAG phosphor and is emitted to the outside. The rest is absorbed by the phosphor 6 to emit yellow light having a longer wavelength. Blue light and yellow light overlap. The synthesized light is white. That is, this is Ga
The blue color of the N-based LED and the fluorescent light excited by the N-type LED are superimposed to emit white light.

The light emission of the LED is aggressive light emission due to the inter-band transition of electrons. The phosphor absorbs the light and emits light when the electrons inside are excited from the base band to the upper band and the electrons fall into the base band via a level called the emission center. Naturally, in this excitation light emission, light having lower energy than the light of the LED is emitted. Surrounding the LED with a suitable phosphor will emit the intrinsic light of the LED and longer wavelength fluorescence. Since the YAG phosphor emits just yellow light, it is combined with the blue color of the LED to become white. In visible light, blue has a short wavelength and high energy. This is possible because a blue light emitting element is present.

FIG. 2 shows an emission spectrum of the GaInN / YAG light emitting device. The horizontal axis represents wavelength, and the vertical axis represents light intensity (arbitrary scale). The sharp peak at 460 nm is GaInN
This is due to the light of the system LED. The broad peak around 550 nm is the fluorescence from the YAG phosphor. The naked eye does not separate the colors and cannot be observed.

However, the GaInN / YAG light emitting device has some disadvantages. An extra YAG phosphor, which is a material completely different from GaInN-based LEDs, is required. This is the first difficulty. Since the YAG phosphor having poor transparency is filled on the chip, much of the light from the LED is absorbed.
With only blue GaN LED used for this, brightness 1C
d, and the external quantum efficiency is 5% or more. However, GaInN / YAG has a luminance of 0.5.
Cd, external quantum efficiency is only about 3.5%. The brightness decreases because the YAG phosphor absorbs light. Further, the light conversion efficiency of the YAG phosphor is as low as about 10%. Therefore, in order to obtain a warm white color in which yellow is dominant, the fluorescent material layer must be thicker. Then, absorption is further increased, and both luminance and efficiency are reduced. This is the second difficulty. A third difficulty is that a complicated manufacturing process is required.

[0013]

SUMMARY OF THE INVENTION The present invention proposes a white LED having a simple structure in which a GaN substrate including a fluorescent center and a GaInN-based blue light emitting element are combined. When a p-type GaInN thin film is grown on an n-type GaN substrate having a fluorescent center, a blue LED that emits light at 400 nm to 500 nm is obtained. The present invention takes advantage of this structure to produce a white LED. This is an extremely simple structure that combines only a GaN substrate and a GaInN-based LED lattice-matched to the GaN substrate. No phosphor is required, and the GaN substrate also serves as the phosphor. GaInN can be epitaxially grown on GaN, and the materials of the same system are used as a luminous body and a phosphor. This is a device which is originally a blue light emitting diode and is converted into a white LED with a little contrivance. GaInN
A semiconductor crystal substrate is always required for a blue light emitting device.
It is merely that the substrate is doped with a fluorescent center to cause fluorescence. The originally required substrate is used instead of the phosphor. It is a very clever idea.

Conventionally, it has been considered impossible to manufacture a large GaN substrate with few defects. GaN itself does not easily melt even at high temperature and high pressure, and the Czochralski method, Bridgman method, etc. cannot be used. So conventionally, GaInNLEDs have been formed on sapphire substrates. The present invention cannot be implemented without a GaN substrate. In recent years, it has become possible to manufacture a GaN substrate by a melt growth method or a vapor phase growth method. This has enabled the present invention. In the melt growth method, G is added to Ga melt.
This is a method of dissolving aN and applying pressure and heat to form a Ga-GaN melt and grow a GaN single crystal. Small crystals can be made.

In the vapor phase growth method, a mask having a large number of dot holes and linear holes is provided on a (111) GaAs substrate, and GaN is vapor grown at a low temperature through the mask to form a buffer layer. An epitaxial layer is grown thick thereon at a high temperature, and the GaAs substrate is removed to produce a large GaN single crystal substrate. In other words, the substrate was grown using a thin film growth method. HVPE (halide vapor phase epitaxy), MOC (organic metal chloride vapor phase epitaxy), MOCVD (organic metal CV)
D method). A Ga metal melt is placed in an HVPE hot wall type furnace, and hydrogen and HCl gas are blown to produce GaCl and react with ammonia near the substrate to form G.
aN is synthesized. MOC uses organic metals such as TMG,
React with H ₂ + HCl gas in a hot wall type furnace
Cl is synthesized and reacted with ammonia NH ₃ to form G
Make aN. In MOCVD, an organic metal such as TMG is transported by H ₂ in a cold wall reactor and reacted with ammonia to produce GaN. The method of manufacturing these GaN substrates is disclosed in Japanese Patent Application No.
No. 171276. It is very recently that large GaN substrates can be manufactured. The present invention provides a white LED using such a GaN substrate as a starting material.
Is prepared.

When a GaN substrate is grown by vapor phase growth or melt growth, impurities such as oxygen and carbon (dopants) can be doped, and crystal defects (nitrogen vacancies) can be introduced. Impurities such as oxygen and carbon, or crystal defects such as nitrogen vacancies are centers for generating fluorescence. 48
When light having a wavelength shorter than 0 nm is applied, 520 nm to 65
It emits fluorescence over a wide range of 0 nm. This emission center can be called a fluorescence emission center or simply a fluorescence center. The center wavelength of the fluorescence emission and the half width of the emission spectrum are
It can be adjusted according to the type of dopant (oxygen or carbon), the doping amount, or the amount of crystal defects (nitrogen vacancies). Fluorescence changes from yellow to red (520 nm to 650 nm)
Since it is widely distributed, there is one obtained by adding this and the blue color of GaInNLED. This is synthesized by the naked eye and looks like white light. White light is synthesized from the two lights such as white light = blue light of GaInN + fluorescence of GaN.

That is, the device of the present invention is composed of two parts: (1) GaInN-based LED: blue light emission (400 to 500 nm) by band-to-band transition (2) GaN substrate: yellow to red fluorescence (fluorescence: 520 to 520)
650 nm). The GaN substrate may be n-type or p-type. In each case, a pn junction is formed in the epitaxial growth layer. The epitaxial growth layer has a light emitting structure. The substrate becomes the phosphor.

The advantage of this device lies in its simplicity.
In general, a light emitting element forms an active layer on some substrate, and the substrate is always present. In a normal device, the substrate merely holds the active layer and only allows a current to flow, and is passive. However, in the present invention, the substrate itself is cleverly used as a fluorescent light emitting layer. Therefore, the white LED of the present invention is GaN in the GaInN blue LED.
Impurities (dopants) that create fluorescent emission centers on the substrate
And only lattice defects are added, and only one step is added. It does not add a different material.

There are various types of white. When blue is predominant, the color becomes cool white, and when red is predominant, the color tends to warm. When the GaN substrate is thicker, the blue color of the GaInNLED is absorbed and reduced, and the yellow color of the fluorescent light is prevailed. Ga
If the N substrate is thin, the blue color of the GaInNLED is superior, and the fluorescence emission is weak. By changing the thickness of the GaN substrate, the intensity of the fluorescent light emission can be adjusted. That is, the ratio of the fluorescent light emission to the blue light emission from the LED can be changed depending on the substrate thickness. However, other conditions impose limitations on the substrate thickness. When the thickness is 50 μm or less, the rate of breakage increases in a later step. Yield decreases and costs increase. Conversely, if the substrate thickness is 2 mm or more, the size of the LED becomes too large. In addition, the ratio of yellow light is excessively increased, and the light is not white. So the substrate thickness is 50μm ~ 2m
m.

As described above, the center wavelength of fluorescent light emission can be changed by adjusting the kind, concentration and defect density of the dopant. The ratio of the fluorescence can be changed by the thickness of the substrate. Therefore, by freely adjusting parameters such as impurity type, concentration, defect density, and substrate thickness, any white color from warm color to cool color can be obtained.

There are several options for the geometric arrangement. The same arrangement (erect) as a conventional LED in which a substrate is placed below and a thin film is placed above is also possible. Conversely, an inverted (epi-side down) arrangement in which the thin film is placed below and the substrate is placed above is also possible. It is also possible to adopt a structure that prevents only blue from being emitted to the outside.

The electrodes of the LED are formed on the epitaxial side and the back side of the substrate, respectively (an n-type substrate has an n-side electrode on the back side, a p-type electrode on the epitaxial side; N electrode). The electrode on the surface attached to the stem may be an electrode covering the entire surface, but the light emitting side must be an electrode with a wide opening.

When mounting by episide down, it is desirable to have the following structure. The electrode on the epitaxial side needs to be as large as possible to prevent blue and blue-green from the light emitting layer from being emitted outside the chip. The electrode on the epitaxial side is preferably an electrode which covers the entire surface of the chip or 80% or more of the entire surface of the chip. On the other hand, since the substrate side is the light emission side, it is necessary to reduce the electrode area. Any of a ring shape and a dot shape may be used, but for a chip having a standard chip size of 0.25 mm × 0.25 mm, the area ratio is set to 40% or less. More preferably, it is set to 16% or less.

When an n-type GaN substrate is used, if epi-side down is used, a p-electrode having a large area can be formed on the p-type epitaxial layer, which is difficult to have a low specific resistance, and the contact resistance can be reduced. Since n-type GaN is easily reduced in resistance, it may be a ring-shaped narrow electrode. Thus, an electrically preferable structure is obtained. Since the GaN substrate is a single crystal, it has higher transparency than the YAG phosphor. The efficiency of converting blue and blue-green light to yellow light is also 15% higher than that of the YAG phosphor. Since both the transparency and the conversion efficiency are high, the GaInN / GaN LED of the present invention is a white LED having higher luminance than the conventional GaInN / YAG. Also, simply by changing the thickness of the GaN substrate,
White light of warm to cool colors can be obtained. Since the transparency is high, the luminance does not decrease even when the thickness is increased.

There is no need to embed a fluorescent material. By a simple process, a high-brightness white LED can be manufactured. The GaN substrate can be conductive. Since there is one less wire bonding than the element on the conventional sapphire substrate (insulator), the manufacturing process is simplified. A low-cost white LED can be made.

[0026]

DESCRIPTION OF THE PREFERRED EMBODIMENTS (1) Upright GaN White LED FIG. 3 shows an example of the structure of a white LED according to the present invention.
FIG. 3A is a longitudinal sectional view, and FIG. 3B is a sectional view of only a chip. The leads 12 and 13 and the LED chip 15 are embedded in the transparent mold 11. Such a structure is tailored to conventional LEDs. Transparent molds are the cheapest LED packages. Of course, it can also be stored in a metal can type package. Packages and leads can be freely selected depending on the purpose. Γ type lead 12
The top 14 has no depression and is a flat surface. On the flat surface 14, the GaInNLED 15 is fixed upright. The LED 15 includes a GaN substrate 16 having impurities (oxygen and carbon) serving as fluorescent emission centers and crystal defects (nitrogen vacancies), and a light emitting structure (thin film) 17 epitaxially grown thereon.

The light emitting structure 17 is a GaInN thin film,
Includes n-junction. The epitaxial light emitting structure 17 is a laminate of thin films mainly composed of GaN, and has a ring-shaped or small-area p-electrode at the top having a pn junction. This should not exceed 40% of the total area so as not to block light. The p electrode is connected to the lead 13 by a wire 18. The n electrode on the substrate side is directly connected to the lead 12. Only one wire is required. The lead 12 becomes a cathode and the lead 13 becomes an anode. When a current flows through the pn junction, a band gap transition occurs to emit light E of 400 nm to 500 nm.
Part goes down and enters the substrate. Here, the GaN substrate has oxygen, carbon, or nitrogen vacancies, and absorbs blue light, and
It emits fluorescence at 20-650 nm. The fluorescent light F in the substrate is reflected on the bottom surface or directly out of the thin film 17. The mixed light of the LED light E and the fluorescent light F goes out and looks like white light W (W = E + F). This is an upright structure for bonding the substrate 16 to the lead surface 14. All ordinary LEDs are so. But this is LE
The ratio of D light E always exceeds 50%, and the fluorescence emission is weakened.

(2) Inverted GaN White LED FIG. 4 shows an example of the structure of an inverted white LED according to the present invention. FIG. 4A is a longitudinal sectional view, and FIG. 4B is a sectional view of only a chip. The lead 2 is placed inside the transparent mold 21.
2, 23 and the LED chip 25 are embedded. Such a structure is tailored to conventional LEDs. The top 24 of the リ ー ド -shaped lead 22 has no depression. It is a flat surface. A GaInNLED 25 is fixed on the lead top 24. L
The ED 25 has an impurity serving as a fluorescent emission center and a G having a defect.
An aN substrate 26 and a light emitting structure (GaInN-based thin film) 27 epitaxially grown thereon are formed. The epitaxial light emitting structure (thin film) 27 is a GaInN thin film and includes a pn junction. The LED is fixed to the lead surface 24 in the opposite direction. When an n-type GaN substrate is used, there is a p-electrode on the thin film surface, which is directly joined to the lead surface 24 (stem). The electrode attached to the stem is 80% of the chip area
It may be 100%. There is a ring-shaped or small-area n-electrode on the GaN substrate side. This is 40% of the chip area
The following area is assumed. The n-electrode is connected to the lead 23 by a wire 28. Again, only one wire is required. In this case, the lead 23 becomes a cathode and the lead 22 becomes an anode. Of course, when a p-type substrate is used, the cathode and anode are reversed.

When a current flows through the leads 22 to 23, a band gap transition occurs and the epitaxial thin film 2
7 emits light E of 400 nm to 500 nm. Everything goes up and enters the substrate. The transmitted light goes out to the outside as blue light. Part of the light is absorbed and promotes fluorescence emission by the fluorescence center in the GaN substrate. The fluorescence emission F in the substrate also goes upward. Both the LED light E and the fluorescent light F go upward.
The two dissimilar lights mix to become white. With this structure, the fluorescence increases in proportion to the thickness of the substrate. 50% fluorescence
The above is also easy. Easy to control the color tone of white light. However, care must be taken because the normal LED and the anode and cathode pins are reversed.

(3) Inverted shielding type GaN white LED In FIG. 4, blue light and blue-green light emitted from the thin film 27 almost in parallel to the substrate surface cannot be mixed with fluorescent light because they do not pass through the substrate. It just becomes. When viewed from the side, color unevenness occurs. In order to avoid this, the shape of the lead may be devised. FIG. 5 shows an example of the structure of an inverted shielded white LED according to the present invention. FIG. 5A is a longitudinal sectional view, and FIG. 5B is a sectional view of only a chip. The leads 32 and 33 and the LED chip 35 are embedded in the transparent mold 31. Such a structure is tailored to conventional LEDs. A deep recess 39 is formed in the top 34 of the Γ-shaped lead 32. Ga is formed at the bottom of the deep depression 39 of the lead top 34.
The InNLED 35 is inverted and fixed with the light emitting structure facing down. The area of the upper opening viewed from the LED 35 is small, so that light is not emitted to the side.

The LED 35 is composed of a GaN substrate 36 having a dopant as a fluorescent light emission center and a light emitting structure (GaInN thin film) 37 epitaxially grown thereon. The epitaxial light emitting structure (thin film) 37 is a GaInN thin film and includes a pn junction. The LED is fixed in the opposite direction to the bottom 34 of the depression 39. On the upper surface of the thin film 37, there is an electrode having an area of 80% to 100% of the entire surface, which is directly joined to the bottom of the recess of the lead 32. When an n-type substrate is used, the thin-film electrode is a p-electrode. There is a ring-shaped or small-area electrode on the GaN substrate side. It shall be 40% or less of the whole area. In the case of an n-type substrate, this is an n-electrode. The n-electrode is connected to the lead 33 by a wire 38. Again, only one wire is required. Also in this case, the lead 33 is a cathode and the lead 32 is an anode. A ring-shaped reflector 40 is joined to the upper surface of the recess 39. In the case of a p-type substrate, the electrode on the substrate side is a p-electrode and the electrode on the light-emitting mechanism (thin film) side is an n-electrode.

When a current is passed, the epitaxial thin film 37 emits light E of 400 to 500 nm. Everything goes up and enters the substrate. The transmitted light goes out to the outside as blue light. Part of the light is absorbed and causes fluorescence emission by the fluorescence center of the GaN substrate. Fluorescence emission F in substrate
(520 nm to 650 nm) also goes upward. Both the LED light E and the fluorescent light F go upward. Together, they exhibit a white color. Any light emitted obliquely to the surface is blocked by the hollow wall. Only light that exits perpendicular to the surface can go upward and out of the dent. This results in a directional LED.

(4) Inverted Substrate Shielding GaN White LED Since there is no light emitted to the side in FIG. 5, it always becomes white light. That's good, but it has the drawback of being too directional. An LED with less directivity may be required. 5 also has the disadvantage that the shape of the leads is complicated and it is difficult to mount them on an LED chip. LEDs with low directivity and no blue or blue-green leakage
Will be described with reference to FIG. This is one in which the GaN substrate itself is given a concave shape and the light emitting structure is embedded in the substrate.

FIG. 6A is a longitudinal sectional view, and FIG. 6B is a sectional view of only a chip. The leads 42 and 43 and the LED chip 45 are embedded in the transparent mold 41. A unique shape LED is provided on the top 44 of the ＬＥＤ-shaped lead 42.
The chip 45 is bonded in the opposite direction. The center of the LED 45 is a deep depression 49 in which the GaInN-based epitaxial light emitting structure 47 is formed. That is, the epitaxial thin film 47 has a shape surrounded by the GaN substrate 46. All light emitted from the epitaxial thin film 47 passes through the substrate 46.

The insulating layer 50 and the GaN layer 5
There is one. The LED 45 is bonded to the lead surface 44 by the GaN layer 51. However, no current flows from the lead surface 44 to the device because of the insulating layer 50. A bump 52 is provided at the center of the lead surface 44. The ridge 52 is fixed in contact with the p-electrode of the epitaxial light emitting layer. The p electrode and the lead 42 are thereby electrically connected. The bottom side of the GaN substrate 46 is on the top. There is a ring or small area electrode on the bottom. If it is an n-type substrate, it is an n-electrode. The n-electrode is connected to the lead 43 by a wire 48. Lead 4
2 is the anode and the lead 43 is the cathode.

When a current is passed, the epitaxial thin film 47 emits light E of 400 to 500 nm. Both light traveling upward and light traveling laterally enter the peripheral substrate 46.
The transmitted light goes out to the outside as blue light. Part of the light is absorbed by the substrate 46 and causes fluorescence emission by the fluorescent center such as impurities and defects of the GaN substrate. Both the LED emission E and the fluorescence F go upward and sideways. Together, they exhibit a white color. Light emitted not only in the direction perpendicular to the substrate surface but also obliquely or laterally becomes all white light. The resulting LED has no directivity. Use is much wider.

[0037]

[Example 1] (Gas-grown GaN substrate, GaIn
N active layer, erect)] The GaN single crystal is grown by vapor phase growth (HVPE, MOC, MOCVD) or melt growth as described above. The GaN free-standing film is used as a substrate. The GaN substrate is provided with dopants such as oxygen and carbon or defects such as nitrogen vacancies. Oxygen, carbon, and nitrogen vacancies serve as fluorescent centers. The thickness of the GaN substrate is 5
It is preferably about 0 μm to 2000 μm. G on GaN substrate
A crystal thin film of aInN is epitaxially grown. For example, epitaxial growth can be performed by MOCVD.

FIG. 7 shows a GaN epitaxial wafer-60.
The structure of is shown. On an n-type GaN substrate 62, an n-type GaN buffer layer 63, an n-type AlGaN cladding layer 64, a GaI
An nN active layer 65, a p-type AlGaN cladding layer 66, and a p-type GaN contact layer 67 are provided. In the epitaxial layer, Mg was used as a p-type dopant and Si was used as an n-type dopant. A more specific composition will be described.

(1) n-type GaN substrate 62 (2) n-type GaN buffer layer 63 (3) n-type Al _0.20 Ga _0.80 N cladding layer 64 (4) Zn-doped Ga _0.88 In _0.12 N active layer 65 (5) p-type Al _0.20 Ga _0.80 N clad layer 66 (6) p-type GaN contact layer 67

The contact layer must be in ohmic contact with the p-electrode and have a low resistance, and have a high p-type concentration. AlGaN
The cladding layer has a wide band gap and has the effect of confining carriers in the active layer. The GaInN active layer has a thin I
An nN film and a GaN film are alternately stacked in any number of layers.

A p-electrode made of Pd / Au was formed on the p-type contact layer of this epitaxial wafer. On the n-type GaN on the back surface, an In n electrode was formed. In / TiAu can also be used for the n-electrode. Photolithography is used to form the pattern electrodes. After the electrodes were formed, the epitaxial wafer was cut out to a size of 300 μm × 300 μm square and fixed to the stem 14 of the lead 12 as shown in FIG. The n-electrode was down and the p-electrode was up. That is, the GaN substrate 16 comes into contact with the stem 14. The p-electrode was attached to another lead 13 by a wire. These were molded with a transparent resin.

This LED was measured in a constant current mode. High intensity white light was emitted. Typical luminance was 1.5 Cd for a drive current of 20 mA. FIG. 8 shows this LE.
3 shows the emission spectrum of D. As designed, LED light emission from the epitaxial light emitting layer having a sharp peak at 430 nm is combined with fluorescent light emission from a broad GaN substrate having a dull peak at 550 nm. The synthesized light is white. The yellow color was a little stronger warm white.

Embodiment 2 Three Types of GaN Substrates of Melt Growth Method, Inverted, and Substrate Thickness] Three types of GaN substrates having different thicknesses manufactured using the melt growth method were prepared. The thickness is 100μ
m, 500 μm, and 1 mm. On this GaN substrate, a homoepitaxial structure similar to that of Example 1 was formed by MOCVD.
It was produced by the method. It has the structure of FIG. 7, and the p-type dopant is Mg and the n-type dopant is Si.

(1) n-type GaN substrate 62 (2) n-type GaN buffer layer 63 (3) n-type Al _0.20 Ga _0.80 N cladding layer 64 (4) Zn-doped Ga _0.88 In _0.12 N active layer 65 (5) p _-Type Al _0.20 Ga _0.80 N clad layer 66 (6) p-type GaN contact layer 67

A p-electrode Pd is formed on the p-type GaN contact layer.
/ Au. The p-electrode is formed on the entire epitaxial surface. 100 μm × 1 on the bottom of the n-type GaN substrate
A 00 μm In n electrode was provided. The chip coverage of the p electrode is 100%, and the chip coverage of the n electrode is 11%.
This was cut out into a 300 μm × 300 μm square chip, and attached to the stem with the back surface facing upward as shown in FIG. It is also called episide down because the epitaxial surface is down. The p-electrode is directly attached to the stem. Only the n-electrode is connected to the stem by a wire. This was molded with a transparent resin.

When this LED was caused to emit light in a constant current mode, high-luminance white light could be obtained. L of Example 1
In the ED, white color tone unevenness was observed, but this light receiving element has no such unevenness in the direction perpendicular to the element surface. This is because the light emitted in the vertical direction, which is episide down, is a mixture of fluorescent light and LED light. Typical brightness is 2
At 0 mA, it was 1.5-2 Cd. Substrate thickness (100
.mu.m, 500 .mu.m, 1 mm). (C) 100 μm thick LED: white with a bluish, cool color tone (D) 500 μm thick LED: neutral white (E) 1000 μm thick LED: fairly yellow, strong warm white. FIG. 9 shows the chromaticity C, D, and E of each white light emission in chromaticity coordinates.

The chromaticity diagram is obtained by numerically stimulating the three primary colors red, green, and blue (stimulation amounts perceived by three human visual sensory organs) for a general visible light source color or object color. FIG. 5 is a diagram devised for displaying on plane coordinates. In the emission spectrum of a certain light source, when the stimulus amount corresponding to red is x, the stimulus amount corresponding to green is y, and the stimulus amount corresponding to blue is z, these are normalized by the total stimulus amount, X = FIG. 10 is a chromaticity diagram showing plane coordinates defined by x / (x + y + z) and Y = y / (x + y + z) shown in FIG. 9. In this coordinate system, a color having any spectrum is represented as one point on the coordinates. Of these, from 400 nm to 67
Monochromatic light in a range of up to 5 nm draws a Λ-shaped curve in the figure. All other colors are composite light of these monochromatic lights and can be represented by internal points surrounded by Λ-shaped curves in the figure. The white light is a portion surrounded by a broken line near the center. It is assumed that two colors P and Q are set to these two-dimensional coordinates. These arbitrary ratios of mixed colors are represented as points on a line connecting two points PQ.

In FIG. 9, point A indicates light emission only from the LED light emitting structure having a peak at 460 nm. Since it has good color purity, it is located at the corner of the chromaticity diagram curve. Point B is 580
The chromaticity of fluorescence emission centered on nm is shown. Since it is a broad peak and contains various lights, it is inside the Λ curve. The light obtained by combining the light at the point A and the light at the point B is on the straight line AB. When the GaN substrate is thin, the fluorescence is weakened and this depends on the A side. When the substrate is thick, the fluorescence becomes strong and depends on the B side.

Point C: GaN substrate thickness is 100 μm. Closest to point A. Point D: GaN substrate thickness is 500 μm. It is in the middle. Point E: GaN substrate thickness is 1000 μm (1 mm). Closest to point B. These white colors can be expressed by the color tone temperature. Point C: Cool white with a little blue color and color temperature 8000K
degree. Point D: Neutral white with a color tone temperature of about 5000K. Point E: A warm yellowish white with a color tone temperature of about 3000K. By changing the thickness of the substrate in this way, white with different color tones can be obtained. This is a case where the impurity concentration of the substrate is constant.

It has also been found that when the impurity concentration of the substrate is changed, the absorption coefficient of the substrate changes, and the relationship between the substrate thickness and the color tone of the LED changes from the above relationship. G of active layer
The emission wavelength can be changed between 40 nm and 500 nm by changing the composition x of a _1-x In _x N. It was also found that even if the LED emission wavelength was changed within this range, white light could be obtained by optimizing the substrate thickness.

[Embodiment 3] Inverted Reflector] In the second embodiment, the LED is mounted on the stem in an inverted manner. As a result, the color is uniform and white as seen from above. However, when viewed from the side of the chip, there is an angle at which only blue light is emitted. Therefore, a depression was provided in the stem, and a chip was mounted in the depression. This is shown in FIG. The bottom surface of the depression 39 was mirror-finished.
The chip was inverted and attached to the depression 39. In this case, all the light emitted to the side is blocked by the wall surface of the depression 39 and is not outside. The opening is further narrowed by the reflection plate 40. Light comes only upward.

Light emitted from the epitaxial thin film must pass through the GaN substrate 36 in order to be emitted upward. Be sure to mix the blue light with the yellow fluorescent light. Thus, an LED emitting uniform white light was obtained. The mounting surface 34 of the stem is mirror-finished, and a thin aluminum plate is used as a reflection plate. Since the blue light is reflected and enters the GaN substrate, the yellow orange intensity is increased by the reflection. Directivity is improved due to the reflector and the concave structure. 1.8 to 2.5C due to reflection
d.

Embodiment 4 Inversion, Selective Growth] In the third embodiment, a recess is formed in the stem, and the LED is mounted in the recess in an inverted manner. Light comes out only upwards. High directivity and high brightness. However, it is difficult to form such a deep recess in the stem. Boost stem costs. In some cases, it is better to provide the chip with anisotropy. This is because the chip can be easily given shape anisotropy by a wafer process.

Thus, a chip stem having a shape as shown in FIG. 6 was manufactured. The manufacturing method will be described with reference to FIGS. A lattice-like SiN mask pattern 80 was formed on a GaN wafer 78. FIG. 10A shows a mask 80.
Is a cross-sectional view of a part of the wafer on which is mounted. FIG.
(D) shows a plan view of the same. The white portion of the square is the exposed portion 79 of GaN. The square portion will later become the light emitting portion. About 3 parts other than the mask (opening)
Etching was performed to a depth of μm. A concave portion 83 is formed as shown in FIG. The portion immediately below the mask 80 is undercut and remains in the shape of the inverted mesa 81. The exposed portion becomes a plane 82.

A light emitting structure was grown on the wafer having the concave portions 83 by MOCVD in the same manner as in Examples 1 to 3. Selective growth occurs and a light emitting structure is formed only in the concave portion 82, and no single crystal epitaxial film is formed on the mask 80. Further, the light emitting structure is completely separated due to the undercut shape just below the mask. That is, the GaN films are not connected above and below the mask. FIG. 10C shows this state. Epitaxial light emitting structure 84 inside recess 83
Is provided with an electrode, etc.
It was cut into mx 300 μm chips. An LED chip having a recess at the center is manufactured. The stem 44 of the lead 42 itself has an irregular shape having the convex portion 52.

The chip was inverted and the p-type layer was fixed so as to contact the stem ridge 52. FIGS. 6A and 6B
become that way. The n-electrode was connected to another lead 43 by a wire 48. This is because the epitaxial light emitting structure 47 is GaN
Since it is embedded in the substrate, there is no blue or blue-green leakage light. The LED emits white light uniformly for all viewing angles. This is designed to emit uniform light by devising the shape of the chip. This embodiment, in which an epitaxial layer is embedded in a chip, has a low directivity and is a full-field type. It emits light at a wide angle and is suitable for display.

Embodiment 5 (Inverted, Reflector-Shaped Stem) FIG. 11 shows an embodiment in which the stem has a reflecting function. As in the case of the second and third embodiments, the stem is inverted. Example 2 had a flat stem and Example 3 had a deep recess. The one shown in FIG. 11 is an intermediate one, and a concave portion not deeper than that of the third embodiment is provided in the stem. FIG.
(A) is a plan view of a chip. (B) is a front view,
(C) is a bottom view. (D) is a front view of the element.
In this LED, a small disk-shaped n-electrode 87 is provided on the back surface of the n-type GaN substrate 62 instead of a ring electrode. Under the p-type contact layer 67, a p-electrode 88 is provided on the entire surface. The top of the lead 89 has a frame shape that expands, and the epitaxial growth layer side (p electrode side) of the chip is fixed here. The n-electrode 87 is connected to another lead 90 by a wire 92. The whole of the stem, the chip, the wires, etc. is molded with the transparent resin 93.

[0058]

According to the present invention, a GaInN-based thin film is epitaxially grown on a GaN substrate having a fluorescent center.
The GaInN thin film emits blue light as an LED, emits yellow or yellow-green fluorescent light when blue passes through the substrate, and emits white light in combination. It can be manufactured in a process that is almost the same as making a single color LED. Since the substrate is not sapphire, it is cleaved and it is easy to cut into chips. When the substrate is sapphire, wire bonding is required twice, but since the present invention uses a conductive GaN substrate, only one wire bonding is required. The LED is easy to manufacture. The conductive single crystal GaN substrate has higher transparency and less absorption than the conventional YAG fluorescent material. Further, the conversion efficiency of converting blue, blue, and green light into yellow light is high (15% or more).
Since both transparency and conversion efficiency are high, GaInN / GaNL
The ED is a white LED with higher luminance than the conventional GaInN / YAG LED.

Since the main component is GaInNLED, it has a long life. Various white colors can be generated from a warm color system to a cool color system depending on the dopant type, concentration, crystal defect amount, and the like of the GaN substrate. Further, the color tone can be changed from a warm color system to a cool color system simply by changing the thickness of the substrate. No extra phosphor is required. The GaN substrate itself is effectively used as a fluorescent light emitter. A semiconductor element requires a substrate, but since it is used as a yellow light emitter, the structure is simple and easy to manufacture.

[Brief description of the drawings]

FIG. 1 is a diagram showing an example of a white LED according to a conventional example in which a GaN-based LED and a YAG phosphor are combined. (A) is the whole longitudinal section including a package. (B) is an enlarged sectional view near the LED chip.

FIG. 2 shows a GaI comprising a GaN-based LED and a YAG phosphor
FIG. 3 is an emission spectrum diagram of an nN / YAG white LED. The horizontal axis represents wavelength, and the vertical axis represents light intensity (arbitrary scale).

FIG. 3 is a diagram showing an example of a white LED according to Example 1 of the present invention in which an LED combining a GaN substrate and a GaInN-based thin-film light emitting structure is fixed upright to a stem. (A) is the whole longitudinal section including a package. (B) is an enlarged sectional view near the LED chip.

FIG. 4 is a diagram showing an example of a white LED according to a second embodiment of the present invention in which an LED combining a GaN substrate and a GaInN-based thin-film light emitting structure is invertedly fixed to a stem. (A) is the whole longitudinal section including a package. (B) is an enlarged sectional view near the LED chip.

FIG. 5 is a diagram showing an example of a white LED according to a third embodiment of the present invention in which an LED is inverted and fixed between valleys of a stem having a concave portion. (A) is the whole longitudinal section including a package. (B) Enlarged cross section near the LED chip

FIG. 6 is a diagram showing an example of a white LED according to a fourth embodiment of the present invention in which an LED having a structure in which a GaN-based thin film light emitting structure is embedded in a GaN substrate is invertedly fixed to a stem having a convex portion.
(A) is the whole longitudinal section including a package. (B) is LE
FIG. 4 is an enlarged cross-sectional view near a D chip.

FIG. 7: LE of Example 1 having GaInN as an active layer
The figure which shows the layer structure of the epitaxial wafer of D.

FIG. 8 is an emission spectrum diagram of an LED used in the present invention having GaInN as an active layer.

FIG. 9 is a diagram showing light emitting points of three kinds of LEDs having different thicknesses of Example 2 as C, D, and E in a chromaticity coordinate system indicating chromaticity with the horizontal axis being X and the vertical axis being Y. A is GaInNLE
D indicates light emission and B indicates fluorescence. X indicates the ratio of the red component among the three primary colors, and Y indicates the ratio of the green component among the three primary colors.

FIG. 10 is a diagram for explaining a wafer process for manufacturing an LED chip of Example 4 in which a concave portion is formed in a central portion of a chip, an epitaxial light emitting structure is formed in the concave portion, and the light emitting structure is surrounded by a substrate. .

FIG. 11 is a diagram showing an LED chip and an LED element in a fifth embodiment of the inverted mounting. (A) is a plan view of a chip, (b) is a front view, (c) is a bottom view, and (d) is a view of a light emitting device in which a chip is attached to a lead and molded with a transparent resin.

[Explanation of symbols]

 1 Transparent Mold 2 First Lead 3 Second Lead 4 Depression 5 GaN InLED 6 YAG Phosphor 7 Wire 8 Wire 11 Transparent Mold 12 Lead 13 Lead 14 Top 15 GaInNLED 16 GaN Substrate 17 Epitaxial Light Emitting Structure (Thin Film) 18 Wire 21 Transparent Mold 22 Lead 23 Lead 24 lead top surface 25 GaInNLED 26 GaN substrate 27 epitaxial light emitting structure (thin film) 28 wire 31 transparent mold 32 lead 33 lead 34 lead top surface 35 GaInNLED 36 GaN substrate 37 epitaxial light emitting structure (thin film) 38 wire 39 recess 40 reflector 41 transparent mold 42 lead 43 Lead 44 Lead top surface 45 GaInNLED 46 GaN substrate 47 Epitaxial light emitting structure (thin film) 48 Wire 49 Depression 50 Insulating layer 51 aN layer 52 protrusion of lead 60 GaInN LED chip 62 n-type GaN substrate 63 n-type GaN buffer layer 64 n-type AlGaN cladding layer 65 GaInN active layer 66 p-type AlGaN cladding layer 67 p-type GaN contact layer 78 GaN substrate 79 substrate surface 80 mask 81 convex portion 82 bottom surface 83 depression 84 Epitaxial light emitting structure 85 Non-epitaxial layer 87 n electrode 88 p electrode 89 lead 90 lead

Claims (7)

[Claims] 1. An n-type or p-type GaN single crystal substrate containing an oxygen atom, a carbon atom, or a nitrogen vacancy as a fluorescent center;
a blue-blue-green light-emitting structure of a GaInN-based mixed crystal compound provided by epitaxial growth so as to include a pn junction on an aN single-crystal substrate; an n-electrode or p-electrode provided on the bottom surface of a GaN substrate; A p-electrode or n-electrode provided in the upper layer of the structure, a support mechanism for supporting the GaN substrate or the light-emitting structure, and a lead for flowing a current to the electrode,
A GaN substrate, a light-emitting structure, and a package surrounding the supporting mechanism. The blue or blue-green light from the light-emitting structure excites the fluorescent center of the GaN substrate to emit yellow or orange light. A white LED characterized in that white light is obtained by synthesizing both yellow and orange light from a GaN substrate fluorescent center. 2. The light-emitting structure has a multilayer structure including Ga _1-x In _x N, the wavelength of light emitted from the light-emitting structure is in a range of 450 nm to 510 nm, and the wavelength of fluorescence emitted from a GaN substrate. 2 is 520 nm to 650 nm. 3. The thickness of the GaN substrate is set to 50 μm to 2 mm.
3. The color tone of the obtained white light can be changed from a cool color system to a warm color system by adjusting the light emission wavelength from the light emitting structure by adjusting the light emission wavelength from the light emitting structure. The white LED described in 1. 4. The lead mechanism according to claim 3, wherein the support mechanism is a Γ-shaped lead having a stem at the top, and the substrate side is opposite to the stem and the surface having the light emitting structure is fixed to the stem surface. The white LED described in 1. 5. A リ ー ド -shaped lead in which a support mechanism has a stem including a concave portion at a top portion, wherein a substrate side is opposite to the stem and a surface having a light emitting structure is fixed to the concave portion of the stem, and is provided at an upper end of the concave portion. 4. The white LED according to claim 3, wherein the white LED has a reflector and reflects a part of the blue, blue and green light from the light emitting structure to irradiate the GaN substrate. 6. The GaN substrate has a concave portion, and G is provided at the bottom of the concave portion.
a _1-x In _x N light emitting structure is formed, and the light emitting structure is Ga
4. The white LED according to claim 3, wherein the white LED is surrounded by an N substrate, and the substrate side is opposite to the stem and the surface of the light emitting structure is fixed so as to contact the stem. 7. The electrode on the light emitting structure side has a total area of 8
7. The white LED according to claim 4, wherein the white LED covers an area of 0% to 100%, and the electrode on the GaN substrate side covers an area of 40% or less of the substrate area. 8.