JPH08148717A - Blue light emitting diode - Google Patents

Abstract

PURPOSE: To reduce the deterioration of a blue high-brightness LED by providing a light emitting chip for reducing the deterioration of resin where the LED is molded. CONSTITUTION: In a light emitting diode where a light emitting chip in that a semiconductor material 2 is laminated on a substrate 1 is molded by resin and where the main light emitting wavelength of the light emitting chip is 500nm or less and output is 500μW or more at a forward current of 20mA, a thin film 3 for absorbing a wavelength which is at least shorter than the main light emitting wavelength is formed on the reverse side of a light emitting chip, thus cutting short wavelength components and reducing the deterioration in resin.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a high-intensity blue light emitting diode made of a semiconductor material that emits light having a wavelength of 500 nm or less.

[0002]

2. Description of the Related Art Green to infrared light emitting diodes (LE
In D), a compound semiconductor such as GaAs, GaP or AlInGaP is used as a light emitting source. On the other hand, as compound semiconductors that emit ultraviolet to blue light, ZnSe, II-VI group compound semiconductors represented by ZnS, gallium nitride compound semiconductors represented by GaN, SiC, diamond and the like are known, and recently nitrided. A high brightness blue LED using a gallium compound semiconductor was announced.

FIG. 4 shows one emission spectrum of a blue LED made of a gallium nitride compound semiconductor. This shows a spectrum of a blue LED having a double hetero structure having InGaN doped with Zn and Si as a light emitting layer. This blue LED has a high brightness L that achieves an output of 2.5 mW or more and a luminous intensity of 2 cd or more at a forward current (If) of 20 mA.
It is ED.

[0004]

However, when a high-intensity blue LED is realized, the conventional green LED and red L
A new problem that has never existed in ED has occurred. This is because a high-intensity blue LED of 1 cd or more has not been realized conventionally.

For example, one of the problems is that the resin molding the LED (generally, a colorless and transparent epoxy resin is used) is very easily deteriorated by the heat and light emitted from the blue LED. There is a problem. Epoxy resins with little deterioration against ultraviolet rays and good weather resistance are commercially available as mold resins, but generally epoxy resins have excellent weather resistance against external weak light such as sunlight and heat. , It is very weak against strong light and heat from inside the LED. Therefore, although the light emitting chip is not deteriorated, the mold resin is deteriorated and the luminous intensity is drastically reduced. For example, the luminous intensity is reduced to half in 1000 hours.

Therefore, the present invention has been made in view of the above circumstances, and an object thereof is to realize a high-intensity blue LED with little deterioration in luminous intensity. Specifically, the LED is molded. It is to reduce the deterioration of the blue LED by providing a light emitting chip that reduces the deterioration of the resin being processed.

[0007]

[Means for Solving the Problems]
As a result of diligent research on the emission spectrum of D and the mold resin, it was found that the resin is particularly likely to deteriorate below a specific wavelength of the emission spectrum of the light emitting chip, and the resin does not absorb the specific wavelength. The problems have been solved by improving the light emitting chip. That is, the blue LED of the present invention is an LED obtained by molding a light emitting chip in which a semiconductor material is laminated on a substrate with a resin, the main light emitting wavelength of the light emitting chip is 500 nm or less, and an output of 500 μW or more at If 20 mA. In the blue LED, the light emitting chip is characterized in that a thin film absorbing at least a wavelength shorter than a main emission wavelength is formed on the surface of the light emitting chip.

[0008] At present, gallium nitride compound semiconductor (In) is used for a light emitting chip which has an emission wavelength of 500 nm or less in a semiconductor layer constituting a light emitting chip and has an output of 500 μW or more at If 20 mA. _X Al _Y Ga _1-XY N, 0 ≦ X, 0 ≦ Y, X + Y ≦
1), or II-VI compound semiconductor containing Zn and _{Se (Zn a Cd 1-a} Se b Te 1-b, 0 ≦ a, 0 ≦ b) can be exemplified, as described before Gallium nitride-based compound semiconductors have already been put to practical use. To meet the conditions of the LED of the present invention with a gallium nitride-based compound semiconductor, for example,
A double heterostructure light emitting chip using an In _X Al _Y Ga _1-XY N layer with an X value of 0.5 or less as an active layer, or a homo or single layer in which a semiconductor layer with good crystallinity is laminated using SiC as a substrate. It is possible to realize a light emitting chip having a terrorism or double hetero structure, or a light emitting chip in which semiconductor layers having few crystal defects are stacked using a substrate having a lattice constant similar to that of a gallium nitride compound semiconductor.

In the LED of the present invention, the thin film formed on the surface of the light emitting chip may be any material as long as it absorbs a wavelength shorter than the main emission peak of the light emitting chip, for example, an alkali silicate glass. A glass composition such as soda lime glass, lead glass, barium glass, or an oxide such as SiO ₂ , TiO ₂ , or GeO ₂ , and a glass composition or an oxide for absorbing a necessary wavelength component. For example, a colorant containing a metal ion such as iron, chromium, nickel, copper, cobalt, a rare earth element (cerium, neodymium, etc.), or a metal colloid can be preferably formed. A glass material and an oxide containing a colorant have an advantage that they are hardly discolored by ultraviolet rays and are very stable even by heat.

Next, a method of forming the thin film on the surface of the light emitting chip will be described. First of all, in order to form the glass composition, it can be formed by masking a portion to be an electrode of the light emitting chip with an appropriate material and then immersing the light emitting chip or the wafer in a molten glass composition. is there.
The light emitting chip is immersed in the molten glass composition to form a thin film of the glass composition on the chip surface, and then the mask is removed by wet or dry etching. In order to form a thin film with high productivity, it is preferable to form a thin film of the glass composition in a wafer state. Second, the oxide thin film can be formed by forming a mask on a predetermined part of the semiconductor wafer in a predetermined shape, and then using a thin film forming technique such as vapor deposition or sputtering of the oxide material to be the thin film. Is. After formation, annealing may be performed for the purpose of firmly adhering the oxide thin film.

Further, in the LED of the present invention, it is particularly preferable to select a gallium nitride compound semiconductor as the material of the light emitting chip. This is because gallium nitride-based compound semiconductors have a GaN temperature of about 1100 ° C. and an AlN temperature of 1200 ° C. or higher.
Even InN has a high melting point of about 600 ° C., and the semiconductor itself is extremely stable. Therefore, when the thin film is formed as described above, the semiconductor does not decompose against the melting temperature of glass and the annealing heat. This is because a thin film can be formed.

[0012]

In FIG. 3, a broken line shows the transmittance curve of the thin film of one embodiment of the present invention. This is a glass colored by mixing Cu, nickel oxide and the like into potash glass so as to absorb a wavelength of 440 nm or less. Note that the transmittance curve shows the transmittance of air as 1
It is shown as 00%. Further, FIG. 4 shows an emission spectrum of a light emitting chip in which this colored glass is formed on the surface of a light emitting chip having an emission spectrum shown by the solid line in FIG.

As can be seen by comparing the spectra of FIGS. 3 and 4, in the blue LED of the present invention, the short wavelength component of the emission wavelength is largely cut. The LED in which the short-wavelength component is cut does not deteriorate the molding resin less than the LED in which the short-wavelength component is not cut, so that the life of the LED is dramatically improved. As a secondary effect, the full width at half maximum of the emission spectrum is narrowed and the color purity can be improved.

In the LED of the present invention, the transmittance of the thin film formed on the surface of the light emitting chip is preferably adjusted to 50% or less, more preferably 30% or less of the wavelength to be absorbed. If the transmittance is greater than 50%, there is an advantage that the light emission output of the LED is less reduced, but short wavelength absorption is insufficient and the mold resin tends to deteriorate. Although the thickness of the thin film is not particularly limited, it is formed to a thickness that can maintain the transmittance,
For example, it is preferably formed with a thickness of 10 μm or less.

Further, the present invention has a main emission wavelength of 500 nm.
In the following, it is necessary to apply to a blue LED having an emission output of 500 μW or more at 20 mA. In an LED having an emission peak at a wavelength longer than 500 nm, the intensity of a short-wavelength emission component is small, and therefore the mold resin is hardly deteriorated. In addition, even for a blue LED having an emission peak at a wavelength of 500 nm or less, an LED having an emission output of 500 μW or less has a weak wavelength component intensity lower than the main emission peak, and the heat generated in the chip is low, so that the mold is used. It hardly deteriorates the resin.

[0016]

【Example】

[Example 1] On a sapphire substrate 1, a buffer layer made of GaN, an n-type contact layer made of Si-doped n-type GaN, an n-type cladding layer made of Si-doped n-type AlGaN, and Si- and Zn-doped n-type Double hetero structure including a gallium nitride-based compound semiconductor layer 2 in which an active layer made of InGaN, a p-type clad layer made of Mg-doped p-type AlGaN, and a p-type contact layer made of Mg-doped p-type GaN are sequentially stacked. Wafers are prepared.
This wafer was separated into 350 μm square light emitting chips, and the LE was used as the emission observation surface on the sapphire substrate surface on which the gallium nitride based compound semiconductor layer was not formed as shown in FIG.
When D is realized, L having a directional characteristic with a full width at half maximum of 15 degrees
ED, if 20 mA, emission peak wavelength 450
nm, luminous intensity 4 cd, and light emission output 6.0 mW.

Next, an oxide thin film 3 is deposited on the surface of the sapphire substrate 1 facing the surface of the wafer on which the gallium nitride compound semiconductor layer 2 is formed. The raw material of the oxide thin film 3 is SiO ₂ containing a small amount of Fe ions and Cr as inorganic coloring substances.
By using a material containing ions and the like, as shown by the broken line in FIG. 4, adjustment is performed so that a transmittance curve of a wavelength of 440 nm or less has a transmittance of 90% or less.

After depositing the oxide thin film 3, the gallium nitride-based compound semiconductor layer of the wafer is etched to form a negative electrode 4 on the n-type contact layer and a positive electrode 5 on the p-type contact layer, and then separate into chips of 350 μm square. To do. A cross-sectional view of the chip after separation is shown in FIG. In FIG. 1, the gallium nitride-based compound semiconductor layer 2 is divided into each layer as described above, but the structure of each layer is not particularly shown.

Next, this chip is placed on a lead frame so that the oxide thin film 3 is on the side of the light emission observation surface, and is molded with epoxy resin to obtain LE having a directional characteristic of a half value width of 15 degrees.
D. This LED emits light at 40 mA, 500
When the decrease in the output after the lapse of time was measured, the output was decreased by only 5%. For comparison, when an LED having a chip on which an oxide thin film was not formed was similarly tested, the output decreased by 50% after 500 hours.

Example 2 A wafer having a sapphire substrate 1 on which a gallium nitride compound semiconductor layer 2'having a different InGaN composition of the active layer and having an emission peak at 490 nm is formed is used. Note that if this wafer is divided into 350 μm square light emitting chips to realize an LED in which the gallium nitride compound semiconductor layer 2 ′ side is the light emission observation surface side, If
It has a luminous intensity of 2 cd and an output of 2.5 mW at 20 mA.

After forming a mask having a predetermined shape on the surface of the p-type contact layer of the wafer, the gallium nitride compound semiconductor layer 2'is etched in the same manner as in Example 1 to form the negative electrode 4, p on the n-type contact layer. Positive electrode 5 on the mold contact layer
After providing, the chips are separated into 350 μm square chips.

On the other hand, when a coloring material such as Cu ion or Ni ion is mixed in sodium glass as a glass material,
A colored glass that absorbs 80% or more of a wavelength of 70 nm or less is prepared.

After masking the electrode surface of the light emitting chip,
The colored glass is deposited on the entire surface of the chip to form a glass thin film 3 '.
To form. After forming the glass thin film, annealing is performed at 400 ° C. or higher to firmly attach the glass thin film, and finally the mask is removed by etching. A cross-sectional view showing the structure of the light emitting chip after removing the mask is shown in FIG.

Next, this chip was placed on a lead frame with the electrode side facing the emission observation surface and molded with an epoxy resin to obtain an LED having a directional characteristic with a half value width of 15 degrees. Similarly, this LED is made to emit light at 40 mA, and 500
When the decrease in the output after the lapse of time was measured, the output was decreased by only 5%. For comparison, when an LED having a chip on which an oxide thin film was not formed was similarly tested, the output decreased by 35% after 500 hours.

[Comparative Example] Main emission wavelength 505 nm, 20 m
Example 2 for a light emitting chip with a light emission output of 800 μW in A.
Although a glass thin film absorbing a wavelength of 490 nm or less was formed in the same manner as above, the effect of the thin film was only the first output was lowered, and in the deterioration test of 40 mA, it was almost the same as that not forming a thin film. Yes, the decrease in output was very small, within 5%.

[0026]

As described above, according to the present invention, it is possible to realize a blue LED which has an improved life by improving the life of the LED having a specific wavelength region and output.
Moreover, since the thin film formed on the light emitting chip of the blue LED of the present invention acts as a filter, it is possible to narrow the half width of the emission spectrum and improve the visibility.
It is suitable for realizing a display. Although only the gallium nitride-based compound semiconductor has been described in the embodiments of the present invention, a blue LED having a main emission peak at 500 nm or less and an output of 500 μW or more is applicable to a light emitting chip made of another semiconductor material. It goes without saying that it is possible.

[Brief description of drawings]

FIG. 1 is a schematic cross-sectional view showing a structure of a light emitting chip of an LED according to an embodiment of the present invention.

FIG. 2 is a schematic sectional view showing the structure of a light emitting chip of an LED according to another embodiment of the present invention.

FIG. 3 is a diagram showing an emission spectrum of a conventional blue LED and a transmittance curve of a thin film formed on the light emitting chip of the present invention.

FIG. 4 is a diagram showing an emission spectrum of a blue LED according to an embodiment of the present invention.

[Explanation of symbols]

 1 ... Substrate 2, 2 '... Gallium nitride compound semiconductor layer 3, 3' ... Thin film 4 ... Negative electrode 5 ... Positive electrode

Claims (3)

[Claims] 1. A light emitting diode in which a light emitting chip formed by laminating a semiconductor material on a substrate is molded with a resin, and the main light emission wavelength of the light emitting chip is 500 nm or less,
A blue light emitting diode having an output of 500 μW or more at a forward current of 20 mA, wherein a thin film absorbing at least a wavelength shorter than a main emission wavelength is formed on the surface of the light emitting chip. 2. The blue light emitting diode according to claim 1, wherein the thin film is made of a glass material containing a colorant or an oxide containing a colorant. 3. The semiconductor material is a gallium nitride-based compound semiconductor (In _X Al _Y Ga _1-XY N, 0 ≦ X, 0 ≦ Y, X + Y.
≦ 1), The blue light emitting diode according to claim 1 or 2.