TWI424592B - White light semiconductor light-emitting device with filtering layer - Google Patents

Description

White light semiconductor light-emitting element having a filter layer

The present invention relates to a white light semiconductor light-emitting device, and more particularly to a high efficiency white light semiconductor light-emitting element having a filtering layer.

Semiconductor light-emitting elements (eg, light-emitting diodes (LEDs)) are a class of relatively important solid state devices that convert electrical energy into light. A typical semiconductor light-emitting element typically comprises one or more layers of light-emitting layers made of a semiconductor material and sandwiched between layers of oppositely doped forms. When a bias voltage is applied through the doped layer, holes and electrons are injected into the light-emitting layer, and holes and electrons are recombined in the light-emitting layer to generate light. Light is emitted from the luminescent layer in all directions and is emitted from all surfaces of the semiconductor light emitting element. Useful light is typically light that is emitted toward the light exiting surface of the semiconductor light emitting element.

A disadvantage of conventional LEDs is that they do not produce white light from their luminescent layers. One of the methods for making conventional LEDs produce white light is to mix different colors of light emitted by different kinds of LEDs into white light. For example, light emitted from red, green, and blue LED light-emitting elements, or light emitted from blue and yellow LEDs, can be mixed to produce white light. One of the disadvantages of this approach is that it requires the use of multiple LEDs to produce a single color of light, which adds significant cost. In addition, different colors of light are usually produced by different types of LEDs. To combine these LEDs into one component requires a complicated process to achieve. The above completed components must have different control voltages due to different diode types, and complex control circuits must also be required. The long wavelength and stability of these components can also be degraded by the different ageing behavior of different types of LEDs.

Recently, a wavelength conversion material such as a yellow light phosphor, a polymer, or a dye mixed in a transparent encapsulating material such as epoxy resin or silicone resin has been used. Surround, to convert light emitted from a blue single-chip LED into white light. For a prior art of such a method, reference is made to U.S. Patent No. 5,813,753, U.S. Patent No. 5,959,316, and U.S. Patent No. 6,069,440. These surrounding wavelength converting materials downconvert the frequency of the portion of light emitted by the LED (the re-emitted light has a lower frequency), which in turn changes its color. For example, if a nitride-based blue LED is surrounded by yellow phosphor, a portion of the blue light it emits will pass through the phosphor without being altered, and the remaining light will be converted down to yellow. In the above case, the LED emits blue light combined with yellow light converted from phosphor powder to produce white light. This type of white light emitting diode is easy to manufacture and has a low production cost, so most of the white light emitting diodes currently on the market are of this type. Further, there has been proposed a technique in which a phosphor powder is coated on a light-emitting surface of a light-emitting diode wafer, and a technique of mixing the phosphor powder into the package material has been proposed. For the related art, please refer to U.S. Patent Publication No. 20080203410.

The above-mentioned LED which uses the blue light emitted by the wafer itself and the yellow light converted by the phosphor powder to be white light is subjected to total reflection of the blue light emitted from the wafer on the light-emitting surface of the wafer, and cannot be emitted. In the past, the surface of the LED wafer was roughened to overcome total reflection. For a prior art of such a method, reference is made to U.S. Patent No. 6,277,665, U.S. Patent No. 6,429,460, and U.S. Patent No. 6,441,403. Most of the prior art of surface roughening is achieved by an etching process, and therefore, the process is time consuming, and the roughness of the light emitting surface of the LED wafer is difficult to control to achieve uniformity. In addition, the yellow light emitted by the phosphor powder is also emitted in all directions. Therefore, part of the yellow light is incident on the LED chip and absorbed by the LED chip, thereby reducing the overall luminous efficiency of the LED. At present, no technology has been found which overcomes the total reflection caused by the blue light of the blue LED chip facing the blue light, and also reduces the absorption of the yellow light by the LED wafer.

Accordingly, it is a primary object of the present invention to provide a white light semiconductor light-emitting element having a filter layer to solve the above problems and further improve the light-emitting efficiency of the white light-emitting semiconductor light-emitting element as a whole.

A white light semiconductor light-emitting device according to a preferred embodiment of the present invention comprises a semiconductor multi-layer, a filter layer, a transparent encapsulating material, and a wavelength converting material. The semiconductor stack includes a light emitting layer. The luminescent layer can be excited by a current to emit light in a blue band. The semiconductor stack has a light exit surface. The filter layer is formed on the light exit surface of the semiconductor stack. The transparent encapsulating material encapsulates the semiconductor stack and the filter layer. The wavelength converting material is uniformly distributed in or coated on the transparent encapsulating material. The wavelength converting material absorbs a portion of the light in the blue light band and emits light in a yellow light band. In particular, the filter layer allows light in the blue band to pass through and reflect light in the yellow band. The light in the blue band and the light in the yellow band are further mixed into white light.

In one embodiment, the filter layer is alternately stacked into a multi-layer composite layer by a first material layer and a second material layer. The first material layer may be formed of TiO ₂ , Ti ₃ O ₅ , Y ₂ O ₃ , HfO ₂ , Ta ₂ O ₅ or ZrO ₂ . The second material layer may be formed of SiO ₂ , MgF ₂ , Na ₃ AF ₆ or Al ₂ O ₃ .

The advantages and spirit of the present invention will be further understood from the following detailed description of the invention.

Referring to FIG. 1, FIG. 1 is a cross-sectional view of a white light semiconductor light emitting device 1 according to a preferred embodiment of the present invention.

As shown in FIG. 1 , the white light semiconductor light emitting device 1 includes a semiconductor laminate 10 , a filter layer 12 , a transparent encapsulating material 14 , and a wavelength converting material 16 .

Also shown in FIG. 1, like a typical semiconductor light emitting device, the white light semiconductor stack 10 includes a substrate 102 and a plurality of epitaxial layers formed on the substrate 102. In practice, the substrate 102 may be glass (SiO ₂ ), germanium (Si), germanium (Ge), gallium nitride (GaN), gallium arsenide (GaAs), gallium phosphide (GaP), aluminum nitride ( AlN), sapphire, spinel, Al ₂ O ₃ , SiC, zinc oxide, magnesium oxide (MgO), lithium aluminum oxide (LiAlO) ₂ ), lithium gallium dioxide (LiGaO ₂ ) or magnesium aluminum oxide (MgAl ₂ O ₄ ), and the like for the substrate for epitaxy.

The multilayer epitaxial layer of the semiconductor stack 10 includes a light emitting layer 104. The luminescent layer 104 can be excited by a current to emit a first light. In one embodiment, the light-emitting layer 104 is formed of a II-VI compound or a III-V compound. In the case shown in FIG. 1, the luminescent layer 104 is a GaN-based light-emitting layer that can be excited by a current to emit light BL in the blue band. In a specific embodiment, the wavelength range of the light in the blue light band is between 445 and 475 nm.

As shown in FIG. 1, the semiconductor laminate 10 has a light exiting surface 108. In the case shown in FIG. 1, the semiconductor stack 10 includes a transparent conductive layer 106 (eg, an ITO layer or a ZnO layer) formed on a plurality of epitaxial layers. The transparent conductive layer 106 is provided as the light-emitting surface 108 of the semiconductor laminate 10. In practical applications, the light exit surface 108 of the semiconductor stack 10 may also be the top surface of the multilayer epitaxial layer.

Also shown in FIG. 1, the filter layer 12 is formed on the light exit surface 106 of the semiconductor stack 10. In particular, the composition and structure of the filter layer 12 are designed such that light directed into the blue light band of the filter layer 12 penetrates the filter layer 12. For example, the light BL of the blue light band emitted by the light-emitting layer 104 in FIG. 1 penetrates the filter layer 12.

As shown in FIG. 1, the semiconductor stack 10 comprises two electrodes 19. As with the packaging of a typical semiconductor light emitting device, a package substrate 18 is prepared first. Two terminals 182 are provided on the package substrate 18. The semiconductor laminate 10 is fixed to the package substrate 18. The two electrodes 19 are electrically connected to the two terminals 182 in a wire-bonding manner.

As shown in FIG. 1 , the transparent encapsulating material 14 covers the semiconductor laminate 10 and the filter layer 12 . The wavelength converting material 16 (eg, phosphor) is uniformly distributed within the transparent encapsulating material 14. In Figure 1, a phosphor powder 16 is deliberately exaggerated to illustrate the process of light conversion. The wavelength converting material 16 absorbs a portion of the light in the blue light band and emits light in a yellow light band. The light in the blue band and the light in the yellow band are further mixed into white light. In one embodiment, the wavelength of light in the yellow light band is between 480 and 700 nm.

In particular, the composition and structure of the filter layer 12 are designed such that light directed to the yellow light band of the filter layer 12 is reflected by the filter layer 12. In the case shown in Fig. 1, the phosphor powder 16 is a yellow phosphor powder, which can absorb the light BL of the blue light band and emit the light YL of the yellow light band. The light YL that is incident on the yellow light band of the filter layer 12 is reflected by the filter layer 12. Thereby, the light in the yellow light band is absorbed by the semiconductor laminate 10, thereby improving the overall luminous efficiency of the white light semiconductor light emitting element 1.

Referring again to FIG. 1, the filter layer 12 is formed on the side surface of the semiconductor laminate 10. Thereby, the light extraction rate of the blue light band emitted by the light emitting layer 104 can be further increased, and the amount of the yellow light band emitted by the wavelength converting material 16 can be further reduced by the semiconductor layer 10, and the white light is further reduced. The overall luminous efficiency of the semiconductor light emitting element 1 can be further improved.

Another variation of the white light-emitting semiconductor light-emitting element 1 shown in FIG. 1 is that the wavelength-converting material 16 is not mixed into the transparent encapsulating material 14, but is coated on the filter layer 12 to form a phosphor layer. Similarly, the wavelength converting material 16 coated on the filter layer 12 absorbs a portion of the light in the blue light band and emits light in a yellow light band. Similarly, the composition and structure of the filter layer 12 are designed such that light in the yellow wavelength band that is directed toward the filter layer 12 is reflected by the filter layer 12.

Referring to FIG. 2, the white light semiconductor light-emitting device 1 according to the present invention directly bonds the two electrodes 19 to the two terminals 182 by a flip-chip bonding method. Therefore, the light exit surface 108 of the semiconductor laminate 10 is provided as the bottom surface of the substrate 102. The filter layer 12 is formed on the bottom surface of the substrate 102. Similarly, the wavelength converting material 16 is uniformly distributed in or coated on the transparent encapsulating material 14. The component symbols in FIG. 2 are the same as those in FIG. 1, that is, the structures which have been described in detail above, and their functions are also the same, and will not be described here. It is to be emphasized that the filter layer 12 is formed on the side surface of the semiconductor laminate 10 to further enhance the overall luminous efficiency of the white light semiconductor light-emitting element 1.

Another variation of the white light semiconductor light-emitting element 1 shown in Fig. 2, the substrate 102 can be removed. Therefore, the light exiting surface 108 of the semiconductor laminate 10 is provided as a bottom surface of the multilayer epitaxial layer, and the filter layer 12 is formed on the bottom surface of the multilayer epitaxial layer.

In a specific embodiment, the filter layer 12 is a distributed Bragg reflector (DBR). That is, the filter layer 12 is alternately stacked into a multilayer composite layer by a first material layer having a higher refractive index and a second material layer having a lower refractive index. The multilayer composite layer consists essentially of (0.5 HL 0.5H) ^m , H is a 1/4 λ thick first material layer, and L is a 1/4 λ thick second material layer. The first material layer may be formed of TiO ₂ , Ti ₃ O ₅ , Y ₂ O ₃ , HfO ₂ , Ta ₂ O ₅ or ZrO ₂ . The second material layer may be formed of SiO ₂ , MgF ₂ , Na ₃ AF ₆ or Al ₂ O ₃ .

It should be emphasized that, in practical applications, the filter layer 12 serves as a passivation layer over the semiconductor stack 10 for protecting the semiconductor stack 10.

In one embodiment, the filter layer 12 in the form of a multilayer composite layer is formed by an electron beam evaporation process. In order to make the quality of each layer of the filter layer 12 better, the electron beam evaporation process may employ an ion-assisted electron-beam evaporation process.

It should be emphasized here that the thickness of the coating layer of each layer of the filter layer 12 according to the present invention requires consideration of the refraction of the material covered by the filter layer 12 in addition to the theory of the effective admittance of the multilayer film. The rate, more importantly, depends on the refractive index of the coating material itself to vary with the wavelength of the incident light. Therefore, in practical operation, it is necessary to first simulate the overall spectrum of the multilayer anti-reflection structure layer of different layers and different coating materials on a specific semiconductor material or a transparent conductive material by computer simulation.

For a computer simulation of the reflectance of the filter layer to incident light according to the present invention, please refer to FIG. 3A, FIG. 3B, FIG. 3C, FIG. 3D and FIG. In the simulation case, SiO ₂ and TiO _{2 were} alternately stacked on the ITO layer to form a 27-layer filter layer. The composition of the filter layer, the refractive index of each layer of the material, and the film thickness of each layer are shown in FIG.

In the simulation case, the incident light of different wavelengths is first simulated to emit from the GaN layer to the ITO layer, the filter layer and the epoxy resin shown in FIG. 3A at three different incident angles of 0°, 10° and 20°. The simulation results are shown in Figure 3B. From the results of FIG. 3B, it is clearly shown that the cutoff band shifts toward the short wavelength region as the incident angle increases, and the reflectance of the filter layer to 455 nm blue light can be reduced to less than 10% at an incident angle of 20° or less.

Figure 3C is a graph showing the reflectance of the incident light of 455 nm blue light emitted from a GaN-based semiconductor light-emitting element at an incident angle of 0° to 90° toward the filtered ITO layer, the filter layer, and the epoxy resin shown in Fig. 3A. The results of the same simulation in which the filter layer was replaced by the SiO ₂ passivation layer are shown in Fig. 3C. From the results of Fig. 3C, it is seen that the critical angle of total reflection caused by the intervening filter layer is about 22°, and the critical angle of total reflection caused by the intervening SiO ₂ passivation layer is about 27°. However, the overall extraction rate of the intervening filter layer for emitting blue light to the GaN-based semiconductor light-emitting element is not less than the overall extraction rate of the blue light emitted by the intervening SiO ₂ passivation layer for the GaN-based semiconductor light-emitting element.

In the simulation case, the incident light of different wavelengths is then simulated to be emitted from the epoxy resin to the filter layer shown in FIG. 3A at four different incident angles of 0°, 10°, 20°, 30°, and 40°, and ITO. The reflectance of the layer and the GaN layer is shown in Fig. 3D. From the results of Fig. 3D, it is clearly shown that the cutoff band shifts toward the short wavelength region as the incident angle increases, and the reflectance of the filter layer to 570 nm yellow light can be as high as 90% or more at an incident angle of 40 or less.

Figure 3E is a graph showing the reflectance of the incident light of 570 nm yellow light emitted by the phosphor from the epoxy resin to the filter layer, the ITO layer and the GaN layer shown in Fig. 3A at an incident angle of 0° to 90°. The result of the same simulation in which the filter layer was replaced by the SiO ₂ passivation layer is shown in Fig. 3E. From the results of Figure 3E, it is clearly shown that the reflectance of the intervening filter layer to 570 nm yellow light can be as high as 98%, while the reflectivity of the intervening SiO ₂ passivation layer to 570 nm yellow light is less than 10%.

The features and spirit of the present invention will be more apparent from the detailed description of the preferred embodiments. On the contrary, the intention is to cover various modifications and equivalents within the scope of the invention as claimed. Therefore, the scope of the patented scope of the invention should be construed as broadly construed in the

1. . . White light semiconductor light emitting element

10. . . Semiconductor stack

102. . . Substrate

104. . . Luminous layer

106‧‧‧Transparent conductive layer

108‧‧‧Glossy

12‧‧‧Filter layer

14‧‧‧Transparent packaging materials

16‧‧‧ wavelength conversion material

18‧‧‧Package substrate

182‧‧‧ terminals

19‧‧‧Electrode

BL‧‧‧Blue

YL‧‧‧Yuangguang

BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 is a cross-sectional view showing a white light semiconductor light emitting device in accordance with a preferred embodiment of the present invention.

2 is a cross-sectional view to schematically illustrate a white light semiconductor light emitting device according to the present invention packaged in a flip chip bonding manner.

Fig. 3A is a diagram showing the composition of the filter layer, the refractive index of each layer material, and the film thickness of each layer in the simulation case of the filter layer according to the present invention.

FIG. 3B is a graph showing the reflectance of the incident light of different wavelengths from the GaN layer to the ITO layer, the filter layer, and the epoxy resin shown in FIG. 3A at three different incident angles of 0°, 10°, and 20°.

Figure 3C is a graph showing the reflectance of the incident light of 455 nm blue light emitted from a GaN-based semiconductor light-emitting element at an incident angle of 0° to 90° toward the filtered ITO layer, the filter layer, and the epoxy resin shown in Fig. 3A. .

Figure 3D is a simulation of different wavelengths of incident light from 0 °, 10 °, 20 °, 30 °, and 40 ° four different angles of incidence from the epoxy resin to the filter layer, ITO layer and GaN shown in Figure A The reflectivity of the layer.

Fig. 3E is a graph showing the reflectance of the incident light of the 570 nm yellow light emitted by the phosphor from the epoxy resin toward the filter layer, the ITO layer and the GaN layer shown in Fig. 3A at an incident angle of 0° to 90°.

1. . . White light semiconductor light emitting element

10. . . Semiconductor stack

102. . . Substrate

104. . . Luminous layer

106. . . Transparent conductive layer

108. . . Glossy surface

12. . . Filter layer

14. . . Transparent packaging material

16. . . Wavelength conversion material

18. . . Package substrate

182. . . Terminal

19. . . electrode

BL. . . Blue light

YL. . . Huang Guang

Claims (15)

A white light semiconductor light emitting device comprising: a semiconductor stack, the semiconductor stack comprising a light emitting layer capable of being excited by a current to emit light in a blue light band, the semiconductor stack having a light emitting surface; a filter a layer, the filter layer is formed on the light-emitting surface of the semiconductor stack, and is alternately stacked into a multi-layer composite layer by a first material layer and a second material layer; and a wavelength conversion material, the wavelength conversion The material absorbs a portion of the light in the blue light band and then emits light in a yellow light band, wherein the filter layer allows the light in the blue light band to pass through and reflect the light in the yellow light band, and the light in the blue light band and the yellow light The light in the band is then mixed into a white light. The white light semiconductor light-emitting device according to claim 1, wherein the number of layers of the composite material layer is between 7 and 55 layers. The white light semiconductor light-emitting device according to claim 1, wherein the number of layers of the composite material layer is between 20 and 35 layers. The white light semiconductor light emitting device according to claim 1, wherein the first material layer is composed of selected from the group consisting of TiO ₂ , Ti ₃ O ₅ , Y ₂ O ₃ , HfO ₂ , Ta ₂ O ₅ and ZrO ₂ . One of the materials in one of the groups is formed. The white light semiconductor light-emitting device according to claim 1, wherein the second material layer is one selected from the group consisting of SiO ₂ , MgF ₂ , Na ₃ AF ₆ and Al ₂ O ₃ . The material is formed. A white light semiconductor light emitting device according to claim 1, wherein the The wavelength converting material is coated on the filter layer or distributed on the filter layer by a transparent encapsulating material. The white light semiconductor light-emitting device according to claim 1, wherein the light-emitting layer is formed of a II-VI compound or a III-V compound. The white light semiconductor light-emitting device according to claim 1, wherein the light wavelength of the blue light band is in the range of 445 to 475 nm. The white light semiconductor light-emitting device according to claim 1, wherein the yellow light band has a wavelength range of 480 to 700 nm. The white light semiconductor light-emitting device according to claim 1, wherein the filter layer has a reflectance of light in the blue light band of less than 20%. The white light semiconductor light-emitting device according to claim 1, wherein the filter layer has a reflectance of light of the yellow light band of more than 50%. The white light semiconductor light-emitting element according to claim 1, wherein the filter layer is formed on a side surface of the semiconductor laminate. The white light semiconductor light-emitting device of claim 1, wherein the filter layer is formed on a bottom surface of the semiconductor laminate. The white light semiconductor light-emitting element of claim 1, wherein the filter layer is also used as a passivation layer. The white light semiconductor light-emitting device of claim 1, wherein the semiconductor laminate does not comprise a substrate for epitaxy.