JP3511993B2 - Light emitting device - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a light emitting device using a light emitting element having a nitride semiconductor and a phosphor that absorbs light from the light emitting element and converts the wavelength to emit fluorescence. The present invention relates to a light emitting device that has little color unevenness and can extract RGB emission wavelength components as peaks.

[0002]

2. Description of the Related Art A nitride-based compound semiconductor (In _x Ga _y Al _1-xy N, 0 ≦ x ≦ 1, 0 ≦ _y capable of emitting blue light with high brightness)
≤1) is used in combination with a phosphor capable of emitting blue light that absorbs blue light from the light emitting element and emits white light as shown in FIG. A diode was developed. In the white light emitting diode, an LED chip (303) electrically connected to a pair of lead electrodes (315) by a conductive wire (304) is arranged in a cavity of a housing (316). The cavity is filled with a resin (301) containing a phosphor (302). This light emitting diode is rapidly becoming widespread as a backlight of a liquid crystal device, a light source for a vehicle, and the like, because the light emitting diode has the characteristics of small size, light weight, low power consumption, and high reliability.

FIG. 4 shows an emission spectrum of such a light emitting diode. As shown in FIG. 4, although the light emitting diode emits blue light from the light emitting element having a monochromatic peak wavelength and a relatively broad emission spectrum as compared with the light emitting element, the phosphor emits reddish light. A mixed light with yellow light with a small wavelength range is emitted. Therefore, the color rendering property becomes low. When the white light from the light emitting diode is divided into RGB (red, green, blue) wavelength regions by using a coloring filter, the red component is small and the color reproducibility tends to be poor. In order to prevent these, it is possible to solve by adding a phosphor or a light emitting element that emits red light.

However, it is extremely difficult to adjust the color as new processes are added. Therefore, in some cases, color unevenness or color misregistration occurs and the yield decreases. In particular, when the white light emitting diode is used as a liquid crystal backlight light source, the light from the light emitting diode is RG which is the three primary colors of the light by the color filter.
Divide into B (red, green, blue) components. Each R
Multicolor display can be performed by controlling the transmittance of the GB component with liquid crystal. Therefore, if the RGB components cannot be displayed with high brightness, it is difficult to achieve brighter multicolor display with high color rendering.

[0005]

SUMMARY OF THE INVENTION Therefore, the present invention has a relatively simple structure and is capable of producing less color shift and color unevenness.
An object of the present invention is to provide a white light-emitting diode in which the light emitting component of B can emit light with high brightness. At present, when higher brightness and lower power consumption are required, the structure of the light emitting diode is not sufficient and further improvement is required.

[0006]

According to the present invention, the well layer is made of In.
A light emitting device having a plurality of nitride semiconductor layers having different concentrations, and a nitrogen-containing C activated by Eu and / or Cr which receives light from the light emitting device and emits fluorescence having a wavelength longer than that of the light emitting device.
and _{aO-Al 2} O 3 -SiO ₂ phosphor, a light emitting device white is capable of emitting light, characterized in that it comprises a. With such a relatively simple structure of one chip and two terminals, it is possible to form a light emitting diode having extremely high color rendering properties and capable of emitting mixed color light with high luminance at a high yield.

According to a second aspect of the present invention, in the light emitting device, a nitride semiconductor is formed on a substrate of the light emitting element, and a nitride semiconductor layer capable of emitting a monochromatic peak wavelength including a blue wavelength range, and A nitride semiconductor layer capable of emitting a monochromatic peak wavelength including a green wavelength region, and emits blue light.
The nitride semiconductor layer that emits green light is
Is also disposed on the substrate side, and the phosphor emits the light emitting element.
The fluorescent light emitted from the phosphor is excited mainly by the blue peak wavelength of the light emitted, and is a light emitting device including a red wavelength range. With this, it is possible to form a white light emitting diode capable of emitting RGB high brightness with a relatively simple structure. Further, the light emitting device according to claim 3 of the present application,
The light emitting device includes Ag paste (114) on a circuit board.
Are electrically connected using the phosphor
Resin is placed close to the light emitting device
A light-emitting device characterized by being used as fat
It This makes it possible to provide a light-emitting device that is simple and has high brightness and high reliability and is capable of emitting mixed color light.

[0008]

BEST MODE FOR CARRYING OUT THE INVENTION The present inventor combined a nitride semiconductor light emitting device capable of emitting blue and green light with a phosphor capable of emitting red light to balance RGB components with a relatively simple structure. The inventors have found that a white light emitting diode that can be taken out with high brightness can be obtained.

That is, it is said that a light emitting device using a nitride semiconductor can form a light emitting device capable of emitting light from ultraviolet to red by increasing or decreasing the In composition ratio. This is because by increasing the In content of the active layer, long-wavelength light emission tends to be obtained depending on the composition ratio. However, a nitride semiconductor containing a large amount of In is easily decomposed at high temperatures. Further, it is extremely difficult to form a nitride semiconductor layer having a high crystallinity and a large amount of In. Therefore, a light-emitting element capable of emitting blue, green, or yellow light can be formed with relatively good controllability and high brightness at present, but a light-emitting element capable of emitting a monochromatic peak wavelength including a red component. Is one of the reasons why it is difficult to form.

Therefore, the present invention forms a nitride semiconductor capable of emitting a blue component and a green component with relatively good controllability as a light emitting device utilizing a multiple quantum well structure. In other words, the mixed crystal ratios of the plurality of well layers are different, and the different color components, for example, the blue component and the green component are emitted from each well layer, and the combined light is extracted. On the other hand, a white light emitting diode is formed by utilizing a phosphor that excites the remaining red component by electromagnetic waves emitted from a light emitting element, for example, blue visible light, and converts it into visible light having a longer wavelength.

The light emitting device of the present invention is shown in FIG. 1 and the specific structure will be described in detail below, but needless to say, the present invention is not limited to this. The semiconductor of the present invention uses the MOCVD method and uses TMG (trimethylgallium) gas, TMA (trimethylaluminum) gas, T
MI (trimethylindium) gas, ammonia gas,
SiH ₄ (silane), Cp ₂ Mg (cyclopentadienyl magnesium) as an impurity gas and hydrogen gas as a carrier gas can be caused to flow according to various desired conditions to form a desired semiconductor film.

More specifically, the sapphire substrate (103)
A buffer layer made of GaN (1
04), an n-type GaN layer having a low n-type impurity concentration or undoped, and Si-containing G for forming an n-type electrode
An n-type contact layer made of aN, an n-type GaN layer having a low n-type impurity concentration or undoped (these three n-type nitride semiconductor layers are schematically referred to as 105), Si-containing AlGaN and Si-containing. N-type clad layer (not shown), which is preferably used by stacking a plurality of GaN, and Ga as a barrier layer having a quantum well structure
N (106) (108) (110) / I as a well layer
A light emitting layer in which a plurality of sets of nGaN (107) and (109) are stacked, Mg-doped GaN / Mg-doped G
A p-type clad layer (11
1), a p-type contact layer (112) made of GaN doped with Mg is laminated. The n-type and p-type contact layers of the semiconductor wafer thus laminated are exposed by etching, and the n-type and p-type electrodes (113) are formed on the semiconductor wafer by sputtering or the like. The surface other than the exposed surface of each electrode is covered with an insulating member of SiO ₂ . After that, the semiconductor wafer is cut into the size of each light emitting element by using a dicer or a scriber, so that each light emitting element can be obtained.

The feature of the present invention is that GaN (106) (108) / InGaN (107) which functions as a light emitting layer.
There are a plurality of pairs of (109) / GaN (106) (110) and at least two types of well layers (107) (109) having different In composition ratios. In particular, the In composition ratio is preferably selected so that at least one of them can emit blue light having a monochromatic peak wavelength from 420 nm to 490 nm. On the other hand, at least one of the remaining well layers is 495n
The In composition ratio is preferably selected so that green light having a monochromatic peak wavelength from m to 555 nm can be emitted. Therefore, as the light emitted from the light emitting element, for example, cyan, which is a mixed color light of blue and green, is observed. Since a light emitting layer which emits light of a shorter wavelength tends to be formed with better crystallinity, when a nitride semiconductor is formed on a sapphire substrate, a spinel substrate, a gallium nitride substrate or a SiC substrate, a well emitting blue light. It is preferable to dispose the layer closer to the substrate than the well layer that emits green light. In addition, in order to adjust the emission intensity of each color, the number of well layers may be increased or decreased to make the adjustment relatively easy.

Next, in the present invention, a phosphor which is excited by the light emitted from the light emitting element and is capable of emitting a reddish light having a wavelength longer than that thereof is used. It is more efficient for the phosphor to emit fluorescence having a longer wavelength than the excitation wavelength. In addition, although there are inorganic phosphors and organic phosphors as the phosphors, the organic phosphors can be such that the excitation wavelength and the emission wavelength can be relatively close to each other and the light can be efficiently emitted. Therefore, not only a fluorescent dye or an organic fluorescent pigment that can emit red light by receiving blue light from a light emitting element, but also a fluorescent dye or an organic fluorescent pigment that can absorb green light and emit red light can be used. This can also make it easier to adjust the tint. On the other hand, the inorganic phosphor tends to be able to reliably emit light for a long time even if it is provided closer to the light emitting element.

As such a phosphor (101), Ce
Activated Y ₂ O ₃ .5 / 3Al ₂ O ₃ , Eu and /
Or nitrogen-containing been activated with Cr _{CaO-Al 2} O 3 -S
iO ₂ may be mentioned. Besides, Mg ₅ Li ₆ Sb ₂ O ₁₃ :
Mn, Mg ₂ TiO ₄ : Mn, Y ₂ O ₃ : Eu, Y ₂ O ₂ S:
Eu, 3.5MgO.MgF ₂ .GeO ₂ : Mn, and perylene derivative can be preferably mentioned.

For example, the nitrogen-containing CaO-Al ₂ O ₃ -SiO ₂ phosphor activated with Eu and / or Cr is a rare earth material in a predetermined ratio to a material such as aluminum oxide, yttrium oxide, silicon nitride and calcium oxide. The powder mixed in 1300 ℃ to 1900 ℃ under nitrogen atmosphere
(More preferably from 1500 ° C. to 1750 ° C.) and melt and mold. The molded product can be ball-milled, washed, separated, dried, and finally passed through a sieve to form a phosphor. As a result, C excited by Eu and / or Cr capable of emitting red light by an excitation spectrum having a peak at 450 nm and blue light having a peak at about 450 nm.
It can be an a-Al-Si-O-N based oxynitride fluorescent glass.

C activated with Eu and / or Cr
The peak of the emission spectrum can be continuously shifted from 575 nm to 690 nm by increasing or decreasing the nitrogen content of the a-Al-Si-O-N oxynitride fluorescent glass. Similarly, the excitation spectrum can be continuously shifted. Therefore, light from a gallium nitride-based compound semiconductor containing GaN or InGaN doped with impurities such as Mg and Zn in the light emitting layer is emitted at about 580 n.
White light can be emitted by the combined light of the lights of the phosphors of m. In particular, it is also possible to ideally obtain light emission in combination with a light emitting element made of a gallium nitride-based compound semiconductor containing InGaN in the light emitting layer, which can emit light of approximately 490 nm with high brightness.

Similarly, if Y ₂ O ₂ S: Eu, then Y ₂ O ₃
And Eu ₂ O ₃ are dissolved in hydrochloric acid and coprecipitated as an oxalate. This precipitate is invited in air at 800 to 1000 ° C. to form an oxide. Further, sulfur, sodium carbonate and flux are mixed and put in an alumina crucible at 1000 ° C to 12 ° C.
The product is baked in air at 00 ° C for 2 to 3 hours to obtain a baked product. The fired product is crushed, washed, separated and dried, and finally passed through a sieve to obtain a Y ₂ O ₂ S: Eu phosphor. This phosphor is
It is possible to efficiently absorb blue light from the light emitting element and emit red fluorescence. The phosphors described above may be used alone or in combination of two or more.

The phosphor (101) is mixed with a binder (102) such as epoxy resin, silicone resin or low melting point glass to form a slurry. A phosphor-containing slurry is applied to the light-emitting element having a multi-quantum well structure having active layers capable of emitting blue and green lights, respectively, and cured to form a light-emitting device. Alternatively, they can be used together as a die bond resin. More specifically, after the light emitting element is arranged on the circuit board and electrically connected using a conductive wire such as a gold wire or a conductive paste (114) such as Ag paste, a phosphor is added. Applied resin,
It can be formed by various methods such as injection, printing, and attachment of a phosphor-containing substance. As long as it can absorb the light from the light emitting element and emit fluorescence, the light emitting element may be not only the one coated on the light emitting element but also the one closely arranged.

When a current is applied to the electrodes of the light emitting device thus formed from the outside, a monochromatic emission wavelength having a peak at about 460 nm and a monochromatic peak wavelength having a peak wavelength at about 535 nm are emitted as shown in FIG. The element emits light. Then, the phosphor is excited by the light from the light emitting element,
A reddish light having a longer wavelength than that can mainly emit light. Therefore, RGB can be converted by a very simple structure and a simple method such as coating one kind of phosphor on the light emitting element.
It is possible to emit white light that can emit strong light.

Needless to say, various phosphors and light-emitting elements can be used in addition to the above-mentioned phosphors as long as color unevenness and color misregistration can be suppressed.

[0022]

The light emitting device of the present invention utilizes a multicolor light emitting element that can be formed with relatively good controllability to form two of the three primary colors of light and the remaining one color to be a multicolor light emitting element. It is possible to provide a white light emitting diode capable of emitting RGB components with high brightness by using the light supplied from the light emitting diode. In particular, the light emitting diode of the present invention only causes one light emitting element to emit light by supplying a current from, for example, two terminals. Therefore, it is possible to obtain a white light emitting diode including RGB components with high brightness without color shift or color unevenness, despite the extremely simple structure. As described above, the light-emitting diode including the RGB components with high brightness can form a full-color or multi-color display device by using the RGB filter and the liquid crystal. Similarly, a light emitting diode for lighting having extremely high color rendering can be used.

[Brief description of drawings]

FIG. 1 shows a schematic cross-sectional view of a light emitting diode of the present invention.

FIG. 2 shows an emission spectrum diagram of the light emitting diode of the present invention.

FIG. 3 shows a schematic cross-sectional view of a light emitting diode for comparison with the present invention.

FIG. 4 shows an emission spectrum diagram of a light emitting diode shown for comparison with the present invention.

[Explanation of symbols]

101 ... Phosphor 102 ... binder 103 ... Sapphire substrate 104 ... Buffer layer 105 ... N-type nitride semiconductor layer 106, 108, 110 ... Barrier layer 107, 109 ... Well layer 111 ... P-type clad layer 112 ... p-type contact layer 113 ... Electrode 114 ... Solder 115 ... Lead electrode 116 ... Support 117 ... Insulating film 301 ... Resin 302 ... Phosphor 303 ... LED chip 304 ... Wire 315 ... Lead electrode 316 ... housing

─────────────────────────────────────────────────── ─── Continuation of the front page (58) Fields surveyed (Int.Cl. ⁷ , DB name) H01L 33/00 C09K 11/00-11/89

Claims (3)

(57) [Claims] 1. A light emitting device in which a well layer has a plurality of nitride semiconductor layers having different In concentrations, and Eu and / or C which receives light from the light emitting device and emits fluorescence having a wavelength longer than that of the light emitting device.
Nitrogen was activated by r-containing _CaO-Al 2 O 3 -SiO ₂
Can emit white light characterized by having a phosphor
Do the light-emitting device. 2. The light emitting device comprises a nitride semiconductor from above the substrate.
The body is formed, and has a nitride semiconductor layer capable of emitting a monochromatic peak wavelength including a blue wavelength range, and a nitride semiconductor layer capable of emitting a monochromatic peak wavelength including a green wavelength range, The nitride semiconductor layer that emits blue light emits green light
The nitride semiconductor layer is arranged closer to the substrate side than the nitride semiconductor layer.
The light source is mainly due to the blue peak wavelength emitted by the light emitting element.
The light-emitting device according to claim 1, wherein the fluorescence emitted by the phosphor is excited in the red wavelength range. 3. The light-emitting element is Ag-based on a circuit board.
(114) to be electrically connected,
A resin mixed with phosphor is placed near the light emitting device.
It is also used as a die bond resin.
The light emitting device according to claim 2.