JP3503551B2 - Light emitting diode - Google Patents

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a nitride semiconductor (Al
_X In _Y Ga _1-XY N, 0 ≦ X ≦ 1, 0 ≦ Y ≦ 1) Related to a light-emitting element, and particularly a light-emitting diode capable of highly efficiently emitting a red-based light which is a long-wavelength component of visible light. Is.

[0002]

2. Description of the Related Art Today, as a light emitting device using a nitride semiconductor, a light emitting device capable of emitting red light from the ultraviolet region is formed. In particular, practical high-power emission is possible in the ultraviolet region to the yellow region. RG in visible light
By emitting B (red, green, blue) with substantially the same semiconductor with high brightness, various emission colors including white can be emitted, and not only various indicators but also liquid crystal backlights, various light sources and lighting, etc. Is being used by.

A light emitting device using a gallium nitride-based compound semiconductor can emit light from ultraviolet to red by adjusting the In composition ratio of the light emitting layer. As a specific example, n is formed on a sapphire substrate via a buffer layer.
-Type GaN n-type contact layer, multi-quantum well GaN and InGaN light-emitting layer, p-type A
Electrodes are formed on each of the n-type and p-type contact layers, which are laminated from the p-type clad layer of lGaN and the contact layer of p-type GaN. By increasing the In concentration in InGaN of the well layer forming the light emitting layer of this light emitting element, it is possible to obtain a light emitting element containing a red component in visible light.

However, it is extremely difficult to form a light emitting layer containing a large amount of In in a gallium nitride compound semiconductor with good crystallinity. Therefore, in the present situation, a light emitting device capable of emitting red light with high brightness has not been put into practical use in gallium nitride compound semiconductors. for that reason,
Although a light emitting element capable of emitting red light using another semiconductor material is used, there are inconveniences when different semiconductors are used due to differences in temperature characteristics and driving voltage peculiar to the semiconductor.

On the other hand, as a light emitting diode capable of emitting white light with two terminals on one chip, a light emitting diode utilizing a fluorescent substance which absorbs light from the light emitting element and converts the wavelength to emit fluorescent light of a complementary color has been developed. It was However, at present, there are few red components, and as the field of use spreads, there is a demand for a light emitting diode having a higher red component.

Further, a light emitting diode capable of emitting red light by converting ultraviolet light from a light emitting element with a phosphor is conceivable, but it has a problem that handling, reliability and mass productivity are difficult because it emits ultraviolet light.

[0007]

SUMMARY OF THE INVENTION It is, therefore, an object of the present invention to provide a light emitting diode capable of emitting red and white with high color rendering, which has a relatively simple structure and is highly reliable and practical.

[0008]

The present invention is a light emitting diode in which a gallium nitride-based compound semiconductor light emitting layer capable of emitting light in the ultraviolet region to the yellow region is formed on a substrate, wherein the substrate is a gallium nitride based material. An α-alumina substrate containing Cr that absorbs light in the ultraviolet region to the yellow region emitted from the compound semiconductor light emitting layer and emits visible light of a longer wavelength, wherein the light emitting layer has a plurality of In concentrations. And a well layer having an emission peak of about 410 nm or about 550 nm and a well layer having an emission peak of 420 nm to 490 nm.

In the light emitting diode according to claim 2 of the present invention, the emission peak is about 410 nm or about 550 nm.
The light emitting diode according to claim 1, wherein the certain well layer is provided on the p-type contact layer side of the light emitting layer.

In the light emitting diode according to claim 3 of the present invention, Cr contained in the alumina substrate is 550 nm.
The light emitting diode according to claim 1 or 2, wherein the absorbance at the wavelength is 10 cm ^-1 or more.

A light emitting diode according to a fourth aspect of the present invention is the light emitting diode according to the first to third aspects, wherein the substrate has a thickness of 150 μm or less. The light emitting diode according to claim 5 of the present invention is a light emitting diode according to any one of claims 1 to 4, wherein white light can be emitted by the mixed light of the light emitted from the light emitting layer and the visible light wavelength-converted by the substrate. Is.

[0012]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS As a result of various experiments, the present inventors have confirmed that a nitride semiconductor capable of emitting visible light and a substrate supporting and forming the nitride semiconductor as a specific substrate are highly reliable and practical. The inventors have found that a light-emitting element capable of emitting red-colored light on the long wavelength side in visible light with a particularly high brightness can be obtained.

That is, in order to easily manufacture a reliable and practical light emitting element, it is considered to use visible light. Based on this idea, the present invention uses an α-alumina substrate containing Cr as a substrate on which a nitride semiconductor capable of emitting high brightness in visible light can be formed with good crystallinity. This is a light-emitting diode whose red component, which is a wavelength side component, can efficiently emit light with high brightness.

According to the present invention, as shown in FIG. 2, on a ruby substrate 210 which is an α-alumina substrate containing Cr,
An n-type contact layer made of a first n-type GaN layer in which Si is undoped via a GaN buffer layer and a second n-type GaN in which Si is contained on the first n-type GaN layer to form an electrode. , A third n-type GaN layer undoped with Si formed on Si-containing n-type GaN, and a light emitting layer 202 in which three GaN (barrier layers) / InGaN (well layers) having a multiple quantum well structure are stacked. , Mg-doped p-type AlG
cN layer made of aN, p-type GaN doped with Mg
And a p-type electrode formed on the p-type contact layer, and an n-type electrode formed on the n-type contact layer. The In composition ratio of the light emitting layer 202 having a multiple quantum well structure is selected so that a blue light having a main emission peak of about 420 nm can be emitted by energization.

The Cr concentration contained in the α-alumina substrate 201 is 150 cm ⁻¹ in terms of absorbance at 550 nm.
That is, after forming the nitride semiconductor film, the α-alumina substrate is polished to a thickness of 120 μm in order to separate the individual LED chips from the semiconductor wafer.

The light emitting device having the above structure is electrically connected to the electrodes of the light emitting device by using gold bumps on the glass epoxy 204 on which a pair of lead electrodes 205 and 206 of copper foil are formed. It is arranged in a chip type. Next, an epoxy resin is applied and cured by screen printing while a part of the lead electrode is exposed using a mask. As a result, it is possible to form the translucent mold member 203 that serves as a protective layer.

Thus, a light emitting diode having a semiconductor light emitting layer made of a nitride-based compound semiconductor capable of emitting blue light having a main light emission peak in the range of 420 nm to 490 nm on an α-alumina substrate containing Cr is obtained. Can be formed. When a current is passed between the lead electrodes of the light emitting diode, red light having a main emission peak at about 694 nm can be emitted from the LED chip through the α-alumina substrate. It can be used as a light emitting diode capable of emitting substantially red light to human eyes.

The light emission output emitted from this light emitting element is
Absorption spectrum of α-alumina substrate activated with Cr
To select visible light emitted from nitride semiconductors
Therefore, it can be adjusted. That is, it emits visible light
By adjusting the In composition ratio of the shining nitride semiconductor,
The most efficient absorption of Cr-containing α-alumina substrate
To improve the high output by selecting the appropriate wavelength.
You can Specifically, light emission made of nitride semiconductors
The layer can emit high brightness at about 410 nm or about 550 nm.
It is preferable that the light emitting element is a light emitting element having high performance. Also, α-aluminum
By increasing or decreasing the concentration of Cr contained in the substrate
It is also possible to adjust the output of the red component. Furthermore, C
To adjust the film thickness of the alumina substrate containing r
Therefore, the output of the red component can be adjusted. Special
In addition, a light emitting device that uses a nitride semiconductor for the light emitting layer is
Practical with high crystallinity and high efficiency by being formed on the substrate
LED chips can be formed, but
Mina substrate is hard and gallium nitride semiconductor has no cleavage
Therefore, gallium nitride compound semiconductor was once formed
In order to produce each light emitting element from a semiconductor wafer, Cr
The contained α-alumina substrate must be thin.
However, thinning the Cr-containing α-alumina substrate
Then, the red component emission output decreases, so
550n when using the Cr-containing alumina substrate below
Absorbance at a wavelength of m is 10 cm^{- 1}Be above
Is preferred, more preferably the absorbance is 25 cm^{- 1}that's all
More preferably 125 cm^{- 1}By the above
It This makes it possible to use nitride semiconductors for practical red
Color light can be emitted. Hereinafter, specific examples of the present invention will be described.
The details will be described, but the present invention is not limited to this.

[0019]

EXAMPLE As a light emitting device, an InGaN semiconductor having a multiple quantum well structure capable of emitting light mainly at emission peaks of about 420 nm and about 550 nm was used. The LED chip is prepared by flowing TMG (trimethylgallium) gas, TMA (trimethylaluminum) gas, nitrogen gas and dopant gas together with a carrier gas onto a cleaned Cr-activated α-alumina (ruby) substrate, and using gallium nitride by the MOCVD method. It was formed by depositing a system compound semiconductor. By switching SiH ₄ and Cp ₂ Mg as a dopant gas, a gallium nitride semiconductor having n-type conductivity and a gallium nitride semiconductor having p-type conductivity were formed to form a pn junction. Specifically, on a ruby substrate, which is an α-alumina substrate containing Cr, an undoped GaN layer, an n-type contact layer made of Si-doped GaN, an n-type GaN and an n-type n
An n-type superlattice layer of InGaN, an active layer having a multiple quantum well structure, a p-type cladding layer made of Mg-doped AlGaN, and a p-type contact layer made of Mg-doped GaN are sequentially formed. The well layer of the multiple quantum well structure is I
nGaN and the barrier layer is GaN. Note that p
The amount of In contained in the well layer on the side of the type contact layer is larger than that of the well layer on the side of the n-type contact layer. Further, the p-type semiconductor is annealed at 400 ° C. or higher after the film formation.

Next, after exposing each pn semiconductor surface by etching, each electrode was formed by sputtering. After polishing the Cr-containing alumina substrate of the semiconductor wafer thus completed to a thickness of about 100 μm, a scribe line is drawn and the LED chip 102 is formed as a light emitting element by dividing by a external force.

The alumina substrate containing Cr is formed by using the Bernoulli method while adjusting the Cr concentration. Here, the absorbance at 550nm and the concentration of Cr of about 27cm ^- is a ^1. The α-alumina substrate may contain Ti and / or Eu in addition to Cr.

Next, LE is mounted on the mount lead 105 having a cup at the tip of a silver-plated copper lead frame.
The D chip was die bonded with an epoxy resin. LE
Each electrode of the D chip and the mount lead 105 and the inner lead 106 were wire-bonded with a gold wire 103 to establish electrical continuity.

After that, a translucent epoxy resin was formed as a mold member for the purpose of protecting the LED chip and the photoluminescent phosphor from external stress, moisture and dust. For the molding member 104, after inserting the lead frame into the shell-shaped mold and mixing the translucent epoxy resin, 1
It was cured at 50 ° C. for 5 hours. The light emitting diode thus formed can be a white light emitting diode having an emission spectrum as shown in FIG. 3 and excellent color rendering properties.

From FIG. 3, blue light and yellow-green light from the light-emitting layer having a plurality of well layers having different In concentrations, and the yellow-green light from the light-emitting layer are absorbed by the alumina substrate, and wavelength conversion is performed to obtain a blue color. It can be seen that the light emitting diode emits red light having a main emission peak on a wavelength side longer than the main emission peaks of yellowish green and white light by mixed color light. Further, this light emitting diode has a temperature resistance of 25 ° C. and a current of 60 mA as a weather resistance test.
No change due to the substrate was observed even in the respective tests of the current application of mA and the current application of 20 mA at 60 ° C. and 90% RH, and there is no difference in life characteristics from the light emitting diode using a normal sapphire substrate. Further, this light emitting diode has a well layer of In
In addition to the composition ratio, the number of stacked well layers having different In composition ratios, and the thickness of the barrier layer, the amount of Cr contained in the α-alumina substrate and α
-It is possible to provide a light emitting element capable of emitting various emission colors with high brightness depending on the thickness of the alumina substrate.

[0025]

By using the light emitting diode having the structure of the present invention, it is possible to obtain a practical light emitting diode which can emit white light with high brightness and high color rendering using visible light. In particular, by using an α-alumina substrate containing Cr, which efficiently absorbs light emitted from a nitride semiconductor and emits light containing a red component, for growth of gallium nitride-based compound semiconductor, high color mixing and high reliability can be obtained. It is possible to use a high light emitting diode.

[Brief description of drawings]

FIG. 1 is a schematic sectional view of a bullet type light emitting diode capable of emitting white light according to the present invention.

FIG. 2 is a schematic cross-sectional view of an SMD type light emitting diode capable of emitting red light according to the present invention.

FIG. 3 shows an emission spectrum of a light emitting diode capable of emitting white light according to the present invention.

[Explanation of symbols]

101 ... Bullet type light emitting diode 102 ... LED chip 103 made of a nitride-based compound semiconductor having a light emitting layer capable of emitting a plurality of main emission peaks ... Wire 104 ... Translucent mold member 105 ... Mount lead 106 ... Inner lead 200 ... SMD type light emitting diode 201 ... Ruby substrate 202 ... Light emitting layer 203 having a multiple quantum well structure ... Translucent mold member 204 ... Glass epoxy substrates 205, 206 ... Lead electrodes

Claims (4)

(57) [Claims] 1. A light emitting diode having a gallium nitride-based compound semiconductor light-emitting layer capable of emitting light in the ultraviolet to yellow region formed on the substrate, wherein the substrate is emitted from the gallium nitride-based compound semiconductor light-emitting layer. An α-alumina substrate containing Cr that absorbs light in the ultraviolet region to the yellow region and emits visible light of a longer wavelength, wherein the light emitting layer has a plurality of well layers having different In concentrations and emits light. Well layer with a peak of about 410m or about 550m
And a well layer whose emission peak is from 420 nm to 490 nm
A light-emitting diode having at least . 2. The emission peak is about 410 nm or about
550 nm well layer is the p-type contact layer side of the light emitting layer
The light emitting diode according to claim 1, which is included in 3. The Cr contained in the alumina substrate is
Absorbance at a wavelength of 550 nm is 10 cm ^-1 or more
The light emitting diode according to claim 1 or 2 , wherein the alumina substrate has a thickness of 150 µm or less . 4. The light emitted from the light emitting layer and the substrate
White light is emitted by the mixed color of visible light whose wavelength is converted.
A light emitting diode according to claims 1 to 3 which is possible .