TW201409745A - LED with high light extraction efficiency - Google Patents

Abstract

An LED with high light extraction efficiency comprises an epitaxial substrate, a semiconductor unit, and an electrode unit. The epitaxial substrate has a substrate and a plurality of conical microstructures formed upwards from the substrate surface. The semiconductor unit is disposed on the surface of the epitaxial substrate having the conical microstructures. The electrode unit is used to supply electrical energy to the semiconductor unit. Particularly, each conical microstructure has a bottom surface and a height being perpendicular to the bottom surface and extended towards the apex of the conical microstructure, wherein the width of the bottom surface is defined as D, the height is defined as H, and the distance between the centers of any two adjacent conical microstructures is defined as P while P ≥ 400nm, 0.4 ≤ D/P ≤ 1.0, and 0.4 ≤ H/D ≤ 1.4.

Description

High light extraction rate LED

The present invention relates to an LED, and more particularly to an LED having a high light extraction rate.

LED is considered to be the most energy-efficient lighting technology of the next generation because it is energy-saving, light and environmentally friendly, and has the effect of saving energy and reducing greenhouse gas emissions. It is widely used in daily life. In general, the photoelectric efficiency of an LED is expressed as the product of the internal quantum efficiency and the light extraction rate; and the light extraction rate is the ratio of the photons produced by the LED to the amount of photons that have successfully left the LED. Taking a gallium nitride (GaN)-based semiconductor luminescent material currently used for LEDs as an example, since the refractive index difference between gallium nitride and air is large (the refractive index (n) of air is 1, the refractive index of GaN ( n) is about 2.5), so when the light generated by the gallium nitride is in contact with the interface between the gallium nitride and the air, most of the light cannot be emitted due to total reflection, so that the actual light extraction rate of the LED is only 4 %, which seriously affects the photoelectric efficiency of the LED.

Referring to FIG. 1 , the current methods for improving the LED light extraction rate are mostly formed by etching a rough or regular shape on the surface of the epitaxial substrate of the LED. FIG. 1 shows a regular columnar shape. The epitaxial substrate 11 of the structure 12 is roughened, but since the columnar roughened structures 12 are regularly arranged and the top surface thereof is a flat surface, the improvement in light extraction efficiency is limited, and the light is formed into a regular reflection. The path causes a problem that the intensity of the emitted light is uneven.

Referring to Figure 2, in order to further enhance the light extraction rate, the United States US Patent No. 8,013,354 discloses an epitaxial substrate 13 having a multi-level microstructure pattern 14 by which light that contacts the multi-level microstructure pattern 14 produces different angles of reflection, reducing the exiting light. Total reflection between the interface between the semiconductor material and the air to increase the light extraction rate. However, although the multi-level microstructure pattern 14 can be used to increase the light extraction rate, the processing time and cost are relatively increased due to the complicated pattern.

Accordingly, it is an object of the present invention to provide a high light extraction rate LED that utilizes a microstructure design of an epitaxial substrate to enhance light extraction efficiency.

Thus, the present invention has a high light extraction rate LED comprising an epitaxial substrate, a semiconductor unit, and an electrode unit.

The epitaxial substrate has a substrate and a plurality of tapered microstructures formed upward from the surface of the substrate, each tapered microstructure having a bottom surface and a vertex perpendicular to the bottom surface and facing the tapered microstructure The height of the extension defines the width of the bottom surface as D, and the height is H. The center distance of any two adjacent pyramidal microstructures is P, and the D, H, and P respectively satisfy P≧400 nm, 0.4≦D/P≦1.0. And 0.4≦H/D≦1.4.

The semiconductor unit is disposed on a surface of the epitaxial substrate having the tapered microstructures to emit light by photoelectric effect when receiving electrical energy.

The electrode unit can be used to provide electrical energy to the semiconductor unit.

The foregoing and other technical contents, features, and advantages of the present invention will be described in the following detailed description of a preferred embodiment with reference to the drawings. Clear presentation.

Referring to Figures 3 and 4, a high light extraction rate LED of the present invention comprises an epitaxial substrate 2, a semiconductor unit 3, and an electrode unit 4.

The epitaxial substrate 2 has a substrate 21 and a plurality of tapered microstructures 23 projecting upward from the surface 22 of the substrate 21.

The substrate 21 may be selected from materials such as alumina, tantalum carbide, niobium, or aluminum nitride.

Each of the tapered microstructures 23 has a bottom surface and a height perpendicular to the bottom surface and extending toward an apex of the tapered microstructures 23, respectively defining a width D of the bottom surface 231, the height being H, and adjacent two micros The distance from the center point of the structure is P, and the D, H, and P satisfy P≧400 nm, 0.4≦D/P≦1.0, and 0.4≦H/D≦1.4, respectively.

It is to be noted that the present invention enhances the reflection effect of light by the tapered microstructures 23, but when the height/width ratio of the tapered microstructures 23 is not within a predetermined range or the density (D/P) is too high The reflective effects of the tapered microstructures 23 are poor, and the light reflected from one side of the tapered microstructures 23 is also easily blocked by the immediately adjacent tapered microstructures 23 and enters the substrate 21, which in turn reduces the light. The reflection effect; therefore, preferably, 0.4 ≦ D / P ≦ 0.8, 0.4 ≦ H / D ≦ 1.0; more preferably, 0.4 ≦ D / P ≦ 0.6, 0.6 ≦ H / D ≦ 1.0.

The tapered microstructures 23 of the present invention are microstructures having a nanometer size, and the fabrication method thereof will be described below.

First, a plurality of nanopores having a pitch and a predetermined height/width ratio are formed on a substrate, and then the nanopores are filled with polydecane oxyresin (PDMS), and after the polyalkylene oxide resin is hardened, Removed from the substrate, A master mold made of the polydecane oxide resin is obtained, and then an acrylic resin is filled in the pores of the master mold, and the master mold having the acrylic resin is reversely transferred to a surface to be etched. a sapphire substrate of the barrier layer, and a microstructure pattern formed by the acryl resin on the surface of the etch barrier layer, and then etching the etch barrier layer by using the microstructure pattern as an etch mask After the etch barrier layer has a pattern corresponding to the microstructure pattern, the residual microstructure pattern is removed, and finally the etched barrier layer is etched by using the patterned etch barrier layer as an etch mask. The epitaxial substrate 2 having the tapered microstructures 23 is obtained.

It is to be noted that, since the tapered microstructures 23 are patterned corresponding to the master mold, when the H/D values of the tapered microstructures 23 are greater than 1.0, the numbers formed on the substrate are indicated. The height/width ratio of the nanopores needs to be large, and the higher the height/width ratio, the less likely the PDMS is to be completely removed from the nanopores, thereby increasing the difficulty of the process and reducing the yield. Therefore, preferably, the tapered microstructures 23 have an H/D value of not more than 1.0.

The semiconductor unit 3 is disposed on the surface 22 of the substrate 21 to emit light with a photoelectric effect upon receiving electrical energy. a semiconductor layer 31 having a surface formed on the surface of the tapered microstructures 23 and the surface 22, a semiconductor light-emitting layer 32 formed on a portion of the surface of the first semiconductor layer 31, and a layer formed on the semiconductor The second type semiconductor layer 33 having the surface of the light emitting layer 32 and electrically opposite to the first type semiconductor layer 31 is not known to the present invention because the material selection of the semiconductor unit 3 is well known in the art, and therefore is not More explanations.

The electrode unit 4 can cooperate to provide electrical energy to the semiconductor unit 3 due to The position of the electrode unit 4 can be changed according to the structure of the LED, and the change is well known to those skilled in the art, so the description will not be repeated. In this embodiment, the electrode unit 4 has one formed in the first type. A bottom electrode 41 on the surface of the semiconductor layer 31 and a top electrode 42 formed on the surface of the second type semiconductor layer 33 are exemplified.

When external power is supplied to the semiconductor unit 3 via the bottom and top electrodes 41, 42, the semiconductor unit 3 emits light outward by a photoelectric effect, and light emitted from the semiconductor unit 3 contacts the second type semiconductor layer 33. When it is at the interface with the outside (air), part of the light is emitted outward through the refraction; and the other part of the light travels toward the epitaxial substrate 2 via total reflection. When the light traveling toward the epitaxial substrate 2 is in contact with the tapered microstructures 23, the incident angles are changed due to the tapered microstructures 23, so that the light contacts the tapered microstructures. After the reflected light of different traveling directions is generated, the chance of total reflection when contacting the interface between the second type semiconductor layer 33 and the air is reduced, thereby achieving the purpose of improving the light extraction rate of the LED; in addition, the tapered microstructures are matched The spacing design of 23 allows the reflected light to be reflected and refracted multiple times to obtain more reflected light in different directions of travel, which not only further improves the LED light extraction rate, but also improves the light uniformity.

Referring to FIG. 5, FIG. 5 is that the D/P values of the tapered microstructures are fixed at 0.6, and the distance P of different tapered microstructures is measured under different height/width ratio (H/D) conditions. The light extraction rate increase value (γ), wherein the light extraction rate increase value is the light extraction rate value of the preferred embodiment divided by the light extraction rate value of the conventional planar substrate.

As can be seen from FIG. 5, when the P value of the tapered microstructures 23 is ≦400 nm, since the sizes of the tapered microstructures 23 are too small, the contribution to the light extraction rate of the LED is small; and when the P value is When the thickness is >400 nm, the size of the tapered microstructures 23 is sufficient to affect the reflection of light, and the influence thereof is related to the inclination angle α of the tapered microstructures 23, when the inclination angle α is increased (indicating that the H/D value is also When added, the tapered microstructures 23 can increase the light to escape the light of the LED and increase the light extraction rate; however, when the tilt angle α continues to increase, the light passes through the reflection when contacting the tapered microstructures 23. The amount of entering the substrate 21 is more than that of the outwardly emitted light, and therefore, the light extraction effect is rather deteriorated; preferably, 0.4 ≦H/D ≦ 1.4; more preferably, 0.4 ≦ H/D ≦ 1.0 And, more preferably, 0.6≦H/D≦1.0. It can be seen from Fig. 5 that when P>400nm, the H/D value is 0.4, the light extraction rate is improved, and at P=1120nm, the best light extraction rate is improved when H/D=1. .

Referring to FIG. 6, the H/D value is fixed to 1.0, and the distance P of the different tapered microstructures 23 is measured, and the light extraction rate is improved under different D/P conditions, wherein the light extraction rate is increased (γ). As defined above.

It can be seen from Fig. 6 that when P < 640 nm, a larger D/P value is required to have a better light extraction lifting effect; and when P ≧ 640 nm, a smaller D/P value (about 0.4), The light extraction lifting effect can be attained; therefore, preferably, P ≧ 640 nm, 0.4 ≦ D / P ≦ 0.8; more preferably, 640 nm ≦ P ≦ 1120 nm 0.4 ≦ D / P ≦ 0.6.

From the foregoing results, it is shown that the increase in the LED light extraction rate is not only related to the size ratio (H/D) of the tapered microstructures 23, but the pitch P and the density of the tapered microstructures 23 at the same time (D). /P) Work together to get the best results.

Referring to FIG. 7 to FIG. 9 , FIG. 7 and FIG. 8 respectively show the light-emitting intensity of an LED obtained by using a planar substrate and an epitaxial substrate 11 having a roughened structure 12 as shown in FIG. 1 . As a result of the simulation, Fig. 9 is a high light extraction rate LED of the preferred embodiment of the present invention.

As can be seen from the results of FIGS. 7 to 9, the LED having the planar epitaxial substrate has a light-intensity due to severe total light reflection, and the light intensity is the weakest; and the LED having the regular columnar roughened structure 12 is The problem of total reflection of light can be reduced, but the improvement of light extraction efficiency is limited, and there is a problem of uneven light intensity; in contrast, the tapered microstructure 23 of the present invention can reflect the reflected light multiple times and Refraction gives more reflected light in different directions of travel, so it can simultaneously improve the LED light extraction rate and uniformity of light output.

In summary, the present invention adjusts the size and spacing of the tapered microstructures 23 of the epitaxial substrate so that the distance between the center points of any two adjacent microstructures is P, and each of the tapered microstructures The D and H of 23 satisfy the conditions of P≧400nm, 0.4≦D/P≦1.0, and 0.4≦H/D≦1.4, respectively, so that the light contacting the tapered microstructures 23 is caused by the tapered microstructures. 23 causes a change in the incident angle to generate reflected light in different directions of travel; and the pitch control of the tapered microstructures 23 allows the reflected light to be reflected and refracted multiple times to obtain more reflections in different directions of travel. Light, in this way, can reduce the chance of total reflection when contacting the interface between the second type semiconductor layer 33 and the air, and achieve the purpose of improving the light extraction rate of the LED, so that the object of the present invention can be achieved.

However, the above is only the preferred embodiment of the present invention, when not The scope of the invention is to be construed as being limited by the scope of the invention and the scope of the invention.

2‧‧‧ epitaxial substrate

21‧‧‧Substrate

22‧‧‧ Surface

23‧‧‧Cone microstructure

3‧‧‧Semiconductor unit

31‧‧‧First type semiconductor layer

32‧‧‧Semiconductor light-emitting layer

33‧‧‧First type semiconductor layer

4‧‧‧Electrode unit

41‧‧‧ bottom electrode

42‧‧‧ top electrode

H‧‧‧ Height

D‧‧‧Width

P‧‧‧ distance

‧‧‧‧ inclination

1 is a schematic view showing an epitaxial substrate having a regular columnar roughened structure; FIG. 2 is a schematic view showing a conventional epitaxial substrate having a multi-layer microstructure pattern; FIG. 3 is a schematic view The preferred embodiment of the high light extraction rate LED of the present invention is illustrated; FIG. 4 is a schematic view for explaining the epitaxial substrate of the preferred embodiment; FIG. 5 is that the D/P values of the tapered microstructures are fixed at 0.6, LEE results at different height/width ratios (H/D); Figure 6 shows the LEE results for the tapered microstructures with H/D values fixed at 1.0 and under different D/P conditions FIG. 7 is a simulation result of light-emitting intensity of an LED having a planar epitaxial substrate; FIG. 8 is a simulation result of light-emitting intensity of an LED obtained by using an epitaxial substrate having a roughened structure; and FIG. The simulation results of the light output intensity of the LED of the preferred embodiment of the present invention.

21‧‧‧Substrate

22‧‧‧ Surface

23‧‧‧Cone microstructure

H‧‧‧ Height

D‧‧‧Width

P‧‧‧ distance

‧‧‧‧ inclination

Claims (9)

A high light extraction rate LED comprising: an epitaxial substrate having a substrate; and a plurality of tapered microstructures formed upward from the surface of the substrate, each of the tapered microstructures having a bottom surface and a vertical surface And the height extending toward the apex of the tapered microstructure defines the width of the bottom surface as D, the height is H, and the center distance of any two adjacent tapered microstructures is P, and the D, H, and P respectively satisfy P≧ 400 nm, 0.4 ≦D/P ≦ 1.0, and 0.4 ≦H/D ≦ 1.4; a semiconductor unit disposed on the surface of the epitaxial substrate having the tapered microstructures to emit light by photoelectric effect when receiving electrical energy; And an electrode unit for supplying electrical energy to the semiconductor unit. The high light extraction rate LED according to claim 1, wherein the center distance of any two adjacent tapered microstructures is 400 nm ≦P ≦ 1120 nm, and 0.4 ≦ D / P ≦ 1.0. The high light extraction rate LED according to claim 2, wherein a center distance of any two adjacent tapered microstructures is 640 nm ≦ P ≦ 1120 nm. The high light extraction rate LED according to claim 2, wherein a ratio of a height of any one of the tapered microstructures to a center distance of the adjacent two tapered microstructures satisfies 0.4 ≦ D / P ≦ 0.8. The high light extraction rate LED according to claim 2, wherein the ratio of the height of any one of the tapered microstructures to the center distance of the adjacent two tapered microstructures satisfies 0.4 ≦ D / P ≦ 0.6. The high light extraction rate LED according to claim 1, wherein the ratio of the height to the width of each of the tapered microstructures satisfies 0.4 ≦H/D ≦ 1.0. The high light extraction rate LED according to claim 6, wherein the ratio of the height to the width of each of the tapered microstructures satisfies 0.6 ≦H/D ≦ 1.0. The high light extraction rate LED according to claim 1, wherein the constituent material of the substrate comprises aluminum oxide, tantalum carbide, niobium, or aluminum nitride. The high light extraction rate LED according to claim 1, wherein the semiconductor unit has a first type semiconductor layer, a light emitting layer, and an electric layer formed in this order from the surface of the epitaxial substrate. A second type semiconductor layer of electrically opposite polarity of the second type semiconductor layer.