Through which chip manufacturing process technology measures, can improve chip light intensity and light output efficiency?
The brightness of the LED mainly depends on the quality of the epitaxial method and the quality of the epitaxy. Different methods can also be used to increase the light intensity in the chip manufacturing process, that is, to increase the external quantum efficiency, but the degree is limited. The most common method now used is the surface roughening process. The principle of roughening is to increase the light emitting area. This method is suitable for yellow, green, red and yellow. Wafers and other epitaxial wafers of GaPa, but also infrared LED can also use this method. This method can generally be increased by 30%.
Another way is to cover the AR coating. Since the refractive index of a light-emitting diode crystal is relatively high, when the light is directed toward the surface of the crystal, refraction occurs at the interface between the crystal and air. Assume that the crystal has a refractive index of N1, an incident angle of θ1, an air refractive index of N2, and a refraction angle of θ2, as shown in the figure:
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According to the law of refraction, available:
According to the law of refraction, available:
(1) NIsinθ1=N2sinθ2
From equation (1), when θ2 = 90°, θ1 is called the critical angle of incidence. It is denoted by θC, ie (2)θC = arcsinN2/N1
Obviously, when θ1 >=θC, the light is totally reflected toward the inside of the crystal. The critical angle θC can be increased if a dielectric layer with medium refractive index is coated between the LED crystal and air. For example, if GaP has N1=3.3, if there is no dielectric layer, the critical angle θC=17.7 degrees. After overlaying a dielectric layer with N2=1.66, the θC may increase to 30.3 degrees and the light intensity may increase to 2.5 times.
At present, through the improvement of the process and structure, the light extraction efficiency of the chip can be improved. In summary, there are several effective methods:
(1) Transparent Substrate Technology Generally, the substrate of the LED is made of GaAs material, but GaAs is a light-absorbing material, and the light emitted by the LED is absorbed by it, which reduces the light output efficiency. For this purpose, after epitaxially forming a PN junction, the GaAs substrate is removed by etching, and a light-transmissive GaP is pasted onto the substrate under high temperature conditions so that the PN junction emits light that is reflected off the metal substrate and the light output efficiency is improved. .
In this method, when fabricating the InGaAlP quadruple chip, after removing the GaAs substrate, a layer of a metal mirror reflective layer is formed by a paste method, and then the substrate is attached, so that the light emitted toward the substrate is radiated to the light exit surface, so that the chip emits light. to raise efficiency.
(2) chip surface roughening method GaN refractive index η1 = 2.3, and air refraction coefficient η1 = 1 is greater than the difference, the remaining reflection critical angle is only 25 °, so that most of the light can not escape to the air, the light Less efficient. For this reason, by changing the geometry of the interface between GaN and air, the critical angle of total reflection is increased and the light extraction efficiency is improved. This is achieved by the method of roughening the surface of the chip. FIG. 2 shows a schematic diagram of a chip light emitting surface.
NIsinθ1=N2sinθ2
From equation (1), when θ2 = 90°, θ1 is called the critical angle of incidence. It is denoted by θC, that is, θC = arcsinN2/N1 (2)
Obviously, when θ1 >=θC, the light is totally reflected toward the inside of the crystal. The critical angle θC can be increased if a dielectric layer with medium refractive index is coated between the LED crystal and air. For example, if GaP has N1=3.3, if there is no dielectric layer, the critical angle θC=17.7 degrees. After overlaying a dielectric layer with N2=1.66, the θC may increase to 30.3 degrees and the light intensity may increase to 2.5 times.
At present, through the improvement of the process and structure, the light extraction efficiency of the chip can be improved. In summary, there are several effective methods:
(1) Transparent Substrate Technology Generally, the substrate of the LED is made of GaAs material, but GaAs is a light-absorbing material, and the light emitted by the LED is absorbed by it, which reduces the light output efficiency. For this purpose, after epitaxially forming a PN junction, the GaAs substrate is removed by etching, and a light-transmissive GaP is pasted onto the substrate under high temperature conditions so that the PN junction emits light that is reflected off the metal substrate and the light output efficiency is improved. .
In this method, when fabricating the InGaAlP quadruple chip, after removing the GaAs substrate, a layer of a metal mirror reflective layer is formed by a paste method, and then the substrate is attached, so that the light emitted toward the substrate is radiated to the light exit surface, so that the chip emits light. to raise efficiency.
(2) chip surface roughening method GaN refractive index η1 = 2.3, and air refraction coefficient η1 = 1 is greater than the difference, the remaining reflection critical angle is only 25 °, so that most of the light can not escape to the air, the light Less efficient. For this reason, by changing the geometry of the interface between GaN and air, the critical angle of total reflection is increased and the light extraction efficiency is improved. This is achieved by the method of roughening the surface of the chip. FIG. 2 shows a schematic diagram of a chip light emitting surface.
![Chip light emitting surface]()
(3) The chip inverted ladder structure. CREE company has a chip with inverted trapezoidal structure also increased light intensity, as shown in Figure 3. Due to the fact that the critical angle of the total reflection of the edge portion of the chip of this structure increases, the photon escape rate increases and can be ejected from the bowl cavity to increase the light intensity and light extraction efficiency.
![MQW]()
The brightness of the LED mainly depends on the quality of the epitaxial method and the quality of the epitaxy. Different methods can also be used to increase the light intensity in the chip manufacturing process, that is, to increase the external quantum efficiency, but the degree is limited. The most common method now used is the surface roughening process. The principle of roughening is to increase the light emitting area. This method is suitable for yellow, green, red and yellow. Wafers and other epitaxial wafers of GaPa, but also infrared LED can also use this method. This method can generally be increased by 30%.
Another way is to cover the AR coating. Since the refractive index of a light-emitting diode crystal is relatively high, when the light is directed toward the surface of the crystal, refraction occurs at the interface between the crystal and air. Assume that the crystal has a refractive index of N1, an incident angle of θ1, an air refractive index of N2, and a refraction angle of θ2, as shown in the figure:
According to the law of refraction, available:
According to the law of refraction, available:
(1) NIsinθ1=N2sinθ2
From equation (1), when θ2 = 90°, θ1 is called the critical angle of incidence. It is denoted by θC, ie (2)θC = arcsinN2/N1
Obviously, when θ1 >=θC, the light is totally reflected toward the inside of the crystal. The critical angle θC can be increased if a dielectric layer with medium refractive index is coated between the LED crystal and air. For example, if GaP has N1=3.3, if there is no dielectric layer, the critical angle θC=17.7 degrees. After overlaying a dielectric layer with N2=1.66, the θC may increase to 30.3 degrees and the light intensity may increase to 2.5 times.
At present, through the improvement of the process and structure, the light extraction efficiency of the chip can be improved. In summary, there are several effective methods:
(1) Transparent Substrate Technology Generally, the substrate of the LED is made of GaAs material, but GaAs is a light-absorbing material, and the light emitted by the LED is absorbed by it, which reduces the light output efficiency. For this purpose, after epitaxially forming a PN junction, the GaAs substrate is removed by etching, and a light-transmissive GaP is pasted onto the substrate under high temperature conditions so that the PN junction emits light that is reflected off the metal substrate and the light output efficiency is improved. .
In this method, when fabricating the InGaAlP quadruple chip, after removing the GaAs substrate, a layer of a metal mirror reflective layer is formed by a paste method, and then the substrate is attached, so that the light emitted toward the substrate is radiated to the light exit surface, so that the chip emits light. to raise efficiency.
(2) chip surface roughening method GaN refractive index η1 = 2.3, and air refraction coefficient η1 = 1 is greater than the difference, the remaining reflection critical angle is only 25 °, so that most of the light can not escape to the air, the light Less efficient. For this reason, by changing the geometry of the interface between GaN and air, the critical angle of total reflection is increased and the light extraction efficiency is improved. This is achieved by the method of roughening the surface of the chip. FIG. 2 shows a schematic diagram of a chip light emitting surface.
NIsinθ1=N2sinθ2
From equation (1), when θ2 = 90°, θ1 is called the critical angle of incidence. It is denoted by θC, that is, θC = arcsinN2/N1 (2)
Obviously, when θ1 >=θC, the light is totally reflected toward the inside of the crystal. The critical angle θC can be increased if a dielectric layer with medium refractive index is coated between the LED crystal and air. For example, if GaP has N1=3.3, if there is no dielectric layer, the critical angle θC=17.7 degrees. After overlaying a dielectric layer with N2=1.66, the θC may increase to 30.3 degrees and the light intensity may increase to 2.5 times.
At present, through the improvement of the process and structure, the light extraction efficiency of the chip can be improved. In summary, there are several effective methods:
(1) Transparent Substrate Technology Generally, the substrate of the LED is made of GaAs material, but GaAs is a light-absorbing material, and the light emitted by the LED is absorbed by it, which reduces the light output efficiency. For this purpose, after epitaxially forming a PN junction, the GaAs substrate is removed by etching, and a light-transmissive GaP is pasted onto the substrate under high temperature conditions so that the PN junction emits light that is reflected off the metal substrate and the light output efficiency is improved. .
In this method, when fabricating the InGaAlP quadruple chip, after removing the GaAs substrate, a layer of a metal mirror reflective layer is formed by a paste method, and then the substrate is attached, so that the light emitted toward the substrate is radiated to the light exit surface, so that the chip emits light. to raise efficiency.
(2) chip surface roughening method GaN refractive index η1 = 2.3, and air refraction coefficient η1 = 1 is greater than the difference, the remaining reflection critical angle is only 25 °, so that most of the light can not escape to the air, the light Less efficient. For this reason, by changing the geometry of the interface between GaN and air, the critical angle of total reflection is increased and the light extraction efficiency is improved. This is achieved by the method of roughening the surface of the chip. FIG. 2 shows a schematic diagram of a chip light emitting surface.
(3) The chip inverted ladder structure. CREE company has a chip with inverted trapezoidal structure also increased light intensity, as shown in Figure 3. Due to the fact that the critical angle of the total reflection of the edge portion of the chip of this structure increases, the photon escape rate increases and can be ejected from the bowl cavity to increase the light intensity and light extraction efficiency.
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