KR100245192B1 - Light emitting diode - Google Patents

Abstract

A light emitting diode is described. The light emitting diode may include a chip having a triangular prism shape or a quadrilateral shape having at least one acute angle in its body, and the chip may have a structure in which its cross-sectional area is increased or decreased in the vertical direction. This structure suppresses total reflection inside the chip so that photons generated in the active region are emitted to the outside of the chip as much as possible, making most of the photons practically available. As a result, high luminance light can be generated with low power consumption, and the life of the chip is extended by the low power consumption and efficient use of photons.

Description

Light emitting diode

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to light emitting diodes, and more particularly, to a light emitting diode having maximum light utilization efficiency and improved durability at low power consumption.

Conventional light-emitting diodes have upper and lower crystal layers (3), (4) and upper and lower crystal layers physically associated with the active region 2 in the middle and the upper and lower active regions as shown in FIG. It has a rectangular parallelepiped chip 1 having electrodes 5 and 6 provided therein, wherein (1) is protected by a mold forming the appearance of a light emitting diode. According to the chip 1 on the rectangular parallelepiped, a large part of the photons generated in the active region 2 are lost from the inside of the chip 1 due to total internal reflection from the walls of the chip 1. Can't come out. Total reflection occurs when the incident angle θ _i of the photon is greater than the critical angle θ _c .

In the above Equation 1, n _e is the refractive index of the mold surrounding the chip 1, for example, about 1.5 in the case of epoxy, n _s is the refractive index of the crystalline layer of the chip (1) in the exact sense Although the values vary from layer to layer, in general there is no significant difference, the refractive index of all the crystal layers can be regarded as having a value of usually about 3.5. . Here, the critical angle θ _c calculated when the refractive index of the mold is 1.5 and the refractive index of the crystal layer is 3.5 is about 25.4 °. 2 is a plan view showing an example of a reflection routine on the chip wall surface of photons generated at an arbitrary point 7 of the active region 2. Photons generated at the random point 7 must escape into the cone-shaped escape area 12 having an angle smaller than the critical angle θ _c with respect to the wall surface 11, that is, a vertex angle of 2θ _c , and then escape out of the chip 1. can do. However, photons incident on the wall surface of the chip 1 at an angle greater than the critical angle θ _c are primarily totally reflected at the wall surface. Even though the traveling path is changed by total reflection, the incident angle θ _i with respect to the wall surface of the chip 1 is Since it becomes larger than the critical angle θ _c , photons do not escape to the outside of the chip 1 but continue to circulate inside the chip. This is because the escape area is cone-shaped because photons emitted from any point are diverged in all directions, and the center axis of the cone-shaped escape area is perpendicular to the wall surface on which the photons are incident. In conclusion, photons generated at any point in the active region are emitted with the same probability in all directions, but only photons emitted into the cone-shaped escape region having a vertex angle of 2θ _c can dehydrate the chip to avoid total reflection.

For this reason, in the conventional light emitting diodes, the amount of photons actually used among the total photons emitted is usually about 20% or less. Therefore, in order to obtain a desired amount of light, a large amount of current must be applied to the light emitting diode, and the limit of the maximum current for the chip is limited as well as the durability of the light emitting diode is increased by increasing the current.

It is an object of the present invention to provide a light emitting diode having a high luminous luminance even at low current due to increased light utilization efficiency.

Another object of the present invention is to provide a light emitting diode having improved durability.

1 is a schematic perspective view of a chip of a conventional light emitting diode.

FIG. 2 is a plan view showing an example of an internal total reflection trajectory of photons emitted from an active region and an arbitrary point of the active region of the conventional light emitting diode shown in FIG.

3 is a schematic perspective view of a first embodiment of a light emitting diode according to the present invention.

FIG. 4 is a plan view showing the total internal reflection trajectory and the exit trajectory of photons emitted from the active region and the random region of the light emitting diode according to the present invention shown in FIG.

5 is a schematic perspective view of a second embodiment of a light emitting diode according to the present invention.

FIG. 6 is a plan view showing an example of the total internal reflection trajectory and the exit trajectory of photons emitted from the active region and the random region of the light emitting diode according to the present invention shown in FIG.

FIG. 7 is a schematic perspective view of a third embodiment of a light emitting diode according to the present invention showing a modification of the light emitting diode according to the present invention shown in FIG.

FIG. 8 is a schematic perspective view of a fourth embodiment of a light emitting diode according to the present invention showing a modification of the light emitting diode according to the present invention shown in FIG.

FIG. 9 is a plan view of an active region of Embodiments 2 and 4 according to the present invention shown in FIGS. 5 and 7 showing a trajectory of photons totally reflected on one side to enter the other side.

10A to 10D are function graphs showing the expansion and contraction of the total reflection area according to the change of the angle between two adjacent wall surfaces.

FIG. 11 is a schematic perspective view of the wafer showing a cutting line of the wafer for obtaining the chip of the first embodiment according to the present invention shown in FIG.

FIG. 12 is a schematic perspective view of the wafer showing the cutting line of the wafer for obtaining the chip of the second embodiment according to the present invention shown in FIG.

FIG. 13 is a schematic perspective view of the wafer showing a cutting line of the wafer for obtaining the chip of the third embodiment according to the present invention shown in FIG. And

FIG. 14 is a schematic perspective view of the wafer showing the cutting line of the wafer for obtaining the chip of the fourth embodiment according to the present invention shown in FIG.

In order to achieve the above object, according to the present invention, there is provided a crystal layer including an active region, the body having a plurality of wall surface through which photons emitted from the active region and the body for supplying current to the active region It is provided with an electrode means, and a light emitting diode is provided, characterized in that the horizontal cross-section of at least some vertical area of the body is a triangle.

In the present invention, it is preferable that the cross-sectional area of the vertical region having a triangular cross section is gradually increased or decreased.

In addition, according to another type of the present invention, in order to achieve the above object, a crystal layer including an active region is provided, and a body having a plurality of wall surfaces through which photons emitted from the active region are transmitted, and in the active region. Provided with an electrode means provided in the body for supplying a current, the light emitting diode is characterized in that the cross section of at least some vertical area of the body is a quadrilateral having at least one acute angle. In the present invention, it is preferable that the cross sectional area of the vertical region having a quadrilateral cross section is gradually increased or decreased.

Hereinafter, exemplary embodiments of the light emitting diode according to the present invention will be described in detail with reference to the accompanying drawings.

Embodiments described below with reference to the drawings include an active region and a crystal layer related to the active region above and below it. The active region is also part of a crystal layer, and generally has a crystal layer arrangement structure of a light emitting diode. The arrangement of the crystal layer may be applied to, for example, homojunction, single heterojunction, or double heterojunction or double heterostructure. Most high-brightness LEDs follow a double heterojunction structure, while GaP-based green and red LEDs follow homogeneous or single heterojunction structures. The active region of the crystal layer arrangement structure as described above and other functional layers such as a window layer generally included in the light emitting diode are excluded from the description of the drawings and the embodiments, but such a general functional layer may be used for the light emitting diode of the present invention. Can be optionally included depending on the design conditions.

Example 1

As shown in FIG. 3, the chip 100 is triangular in shape. An active region 200 is provided in the middle portion of the chip 100, and crystal layers 300 and 400 are provided above and below the chip 100. In the upper and lower surfaces of the chip 100, the crystal layer, in particular, the active region 200 is provided. Electrodes 500 and 600 as means for supplying current are formed.

4 is a view of the photons generated at an arbitrary point 700 of the active region 300, which is directed out of the cone-shaped escape region 120 and is primarily formed on the vertical wall surface 110 of the chip 100. This is a cross-sectional view of the chip 100 showing the progress trajectory of the photons totally reflected. In FIG. 4 and in all the drawings described below, 2θ _c denotes a range of incidence angles at which photons can escape from inside the chip, that is, a critical angle.

As shown in FIG. 4, the photons 701 directly incident on the first escape region 120 of the wall 110 among the photons emitted from the arbitrary point 700 are emitted to the outside of the chip 100. Photons incident to the region outside the first escape region 120 are first totally reflected at the first total reflection point 130 of one wall and then proceed to the other wall surface. At this time, when the incident angle of the photon to the other wall is within the critical angle, that is, when the primary reflected photon is incident into the second escape area 180, the photon escapes through the area. Meanwhile, after the first total reflection, the second total reflection point 140 of the other wall surface is totally reflected and then reflected on another wall in the vertical direction to undergo a series of total reflection processes. When the incident angle of the photon is gradually decreased and undergoes a certain number of total reflection processes, the photon exits the chip by being incident into the second escape area 180 of the wall in one vertical direction at an angle smaller than the critical angle. In other words, the chip having the triangular cross-sectional structure as described above is designed to allow the photons that have undergone one or more total reflection processes to enter the escape area while circulating in a direction in which the incident angle of the photons to the wall gradually decreases. The photons of E will escape to the outside of the chip and become actual usable light. The escape effect of photons by this cyclic process is particularly strong in photons traveling in parallel to the plane of the active region.

Example 2

As shown in FIG. 5, the chip 101 is not square but quadrilateral, for example, a quadrilateral having a cross section with two acute angles. As in the above-described embodiment, an active region 201 is provided in the middle portion of the chip 101, and crystal layers 301 and 401 associated with the active region 201 are provided above and below. On the upper and lower surfaces of the chip 101, electrodes 501 and 601 are formed as a means for supplying current to the crystal layer, particularly the active region 201. In the above structure, the horizontal cross-sectional shape of the chip is a quadrilateral having two acute angles as described above, and may have one or three acute angles in some cases.

FIG. 6 shows the total reflection at the vertical wall surface 111 of the chip 101 as it proceeds out of the cone-shaped escape region 120 among photons exerted at an arbitrary point 701 of the active region 301. It is sectional drawing of the chip 101 which shows an example of the progress trajectory of the photon.

As shown in FIG. 6, the light totally reflected on the wall surface 111 of the chip among photons emitted from the arbitrary point 701 undergoes one or more total reflection processes as in the first embodiment described above. It escapes to the outside of the chip 101 through the escape region 180 of the wall surface 111. Photons 701 directly incident on the first escape area 120 of the wall surface 111 of the photons emitted from an arbitrary point 701 are emitted to the outside of the chip 101. Photons incident to the region outside the first escape region 120 are first totally reflected at the first total reflection point 130 of one wall and then proceed to another wall surface. At this time, when the incident angle of the photon to the other wall is within the critical angle, that is, when the first reflected photon is incident into the second escape area 180, it escapes to the outside of the chip through this area. On the other hand, after the first reflection, photons that are totally reflected on the second and other walls are reflected back to another wall and undergo a series of total reflection processes. At this time, the incident angle of the photons to the wall gradually decreases during the series of total reflection processes. When the total reflection process is performed, the light is incident into the second escape area 180 of one wall at an angle smaller than the critical angle, so that photons escape from the chip. In other words, the chip having the horizontal cross-sectional structure of the triangle as described above allows the photons that have undergone one or more series of total reflection processes to enter the escape area in a direction in which the incident angle of the photons to the wall gradually decreases. Most of the photons will escape to the outside of the chip, making it practically available light. The escape effect of photons by this series of total reflections is particularly strong in photons traveling in parallel directions with respect to the plane of the active region.

[Examples 3 and 4]

In Examples 1 and 2, structural symmetry in the direction parallel to the active area is removed, that is, structurally changed so that the walls in the vertical direction are not parallel or perpendicular to each other, but structurally in the direction perpendicular to the active area. Since the symmetry remains, that is, the wall surface is perpendicular to the top and bottom surfaces of the chip, some of the photons traveling in the vertical direction of the chip, that is, in the vertical direction of the active region, are caused by cyclic total reflection in the chip. You may not be able to escape outside of. 7 and 8 show the structure of the chip in which the symmetry between the wall surface is removed with respect to the vertical direction of the chip, and in particular, the wall surface is inclined at a constant angle with respect to the plane of the active region. According to this structure, the photon generated in the active region can be more efficiently escaped to the outside of the chip through the internal reflection process as in the first and second embodiments.

FIG. 7 shows the structure of a chip in which the horizontal cross-sectional shape of the chip is triangular, and FIG. 8 schematically shows the structure of a quadrilateral chip in which the horizontal cross-sectional shape of the chip has two acute angles.

In Examples 3 and 4, all vertical wall surfaces from which photons escape have a constant inclination angle with respect to the plane of the active region, so that the external quantum efficiency is higher than those of the first and second embodiments. The degree of improvement of the external quantum efficiency can be expressed by the following equation.

In Equation 2 above, n _e is the refractive index surrounding the chip molds water, n _s is a refractive index of a crystal layer that forms the chips.

In the above embodiments, in a quadrilateral or quadrilateral chip having at least one acute angle, the top and bottom surfaces are parallel to each other in the structure of the wafer for fabricating the chip. In the triangular prism chip of the first embodiment and the third embodiment, the angle formed between one wall surface and one wall surface may form a right angle, an acute angle, or an obtuse angle. In the case of the quadrilateral chip of Example 2 and Example 4, when the angle between adjacent wall surfaces forms an acute angle, it is preferable to set the angle between 20 ° and 85 °. FIG. 9 illustrates that photons generated at an arbitrary point 701 enter the wall at an angle θ ₁ greater than the critical angle θ _c at the first total reflection point 130 of the first side, and then at θ _{2 on} the second wall. The case where incident at an angle is shown is shown. The incident angle θ ₂ of the photons with respect to the second wall surface is expressed by Equation 3 below.

In Equation 3 above, α ₁ is an angle between two adjacent walls. That is, according to the above equation, θ ₂ is given as a function of α ₁ and θ ₁ . As can be seen from the above equation, by adjusting the angle α ₁ between the walls properly, the photons totally reflected on the first wall can be totally avoided on the second wall. If the relational expression of equation (3) is expressed as the parameter α ₁ as a parameter, a function graph as shown in FIGS. 10A to 10D can be obtained.

FIG. 10A shows a case where α ₁ = π / 2, which corresponds to the structure of a conventional light emitting diode. The problem in this case can be seen in Equation 4 below.

As can be seen from Equation 4 above, the absolute value of the incident angle θ ₂ at the second wall surface is larger than the critical angle θ c for the incident angle θ ₁ in a relatively wide range (the shaded area in FIG. 10a). Conforms. That is, photons incident under the condition of Equation 4 are totally reflected on the second wall as well as on the first wall. If, as in the conventional light emitting diode, all three remaining angles of the planar cross section are π / 2, that is, the photons that are totally reflected once cannot be escaped to the outside of the chip due to cyclic total reflection, the light cannot be used. 10C and 10D show that the total reflection area (the area indicated by the shade) is greatly reduced when the angle α ₁ is set to π / 2 or less. In particular, when α ₁ is set to 2θ _c as shown in FIG. 10C (α ₁ = 2θc), photons are totally reflected on the second wall only for a relatively narrow range of θ ₁ as shown in Equation (5) below.

However, in an actual light emitting diode, since photons are generated in the center portion of the active region, it is very unlikely that the incident angle θ ₁ with respect to the vertical wall surface has a value of 76.1 ° (= 3θ _c ) or more.

Thus, most photons can avoid total reflection on the first or second wall. On the other hand, if α ₁ is selected to be smaller than 2θ _c as shown in FIG. 10d, a total reflection occurs on the second wall, that is, an area of θ ₁ is enlarged and disadvantageously given that the absolute value of θ ₂ is larger than the critical angle θ c. . Setting the angle to be an acute angle between one of the flat end surface of the chip as described above, there is possible to efficiently escape to the outside of the chip to the photons generated in the active region, the upper limit value of a between the α ₁ to maximize the effect, and The lower limit value can be determined based on the above-described FIG. 10B and FIG. 10D. In the case of the upper limit of the angle α ₁ , the improvement effect may be insignificant when the shaded region of FIG. 10b is about 75% or more of the maximum shaded region of FIG. 10a. Therefore, the upper limit of α ₁ can be obtained by Equation 6 below.

On the other hand, as for the lower limit of α ₁ when α ₁ be set to less than two θc it becomes significantly disadvantageous because larger than the given range is in the range of the angle of incidence θ ₁ Figure 10a causing a total reflection on the second wall surface. If α ₁ = θ _c , the width of θ ₁ , which causes total reflection on the second wall, is given by π / 2-2θ _c as in the case of FIG. 10a, but is much more advantageous than that of FIG. 10a. Can be. The reason for this is that as mentioned above, since photons are mainly generated in the center of the active region, the probability that the incident angle θ ₁ is large is relatively low. Therefore, the lower limit of α ₁ is represented by Equation 7 below.

In conclusion, the preferred range α ₁ is in Equation 8 below.

The chip of the light emitting diode according to the present invention as described above is obtained by a general wafer processing process, in the case of Example 3 and Example 4 by cutting the chip on which the chip is left, the wall surface of the active region It can be formed to be inclined at an angle with respect to the plane.

In addition, the condition of Equation 8 may be applied to the inclination angle of the wall surface with respect to the third and fourth embodiments, that is, the plane of the active area, the principle is as described above.

11 to 14 are schematic perspective views of the wafer showing the cutting direction of the wafer for obtaining Examples 1 to 4 in the order thereof. In Figures 11 to 12, 333 denotes a cutting line.

In the above embodiments, the overall appearance of the chip can be pure triangular, quadrilateral, as described above, and only described above with respect to a portion of the chip, e. The structure as described may be applied. Such structural modification may be accompanied by external requirements such as an arrangement of electrodes of the light emitting diode.

According to the present invention as described above, the photons isolated inside the chip by the cyclic total reflection inside the chip effectively escapes to the outside of the chip to make the actual usable light. Therefore, the power consumption for obtaining a constant amount of light is lower than that of the conventional light emitting diode, and as a result, the driving current is significantly lowered. In addition, the life of the chip is extended by the reduction of the driving current, and internal heat generation is greatly suppressed by the effective emission of isolated photons, which is one of the heat concentration factors inside the chip.

Claims (6)

A crystal layer comprising an active region, the body having a plurality of wall surfaces through which photons emitted from the active region pass, and electrode means provided on the body to supply current to the active region; A light emitting diode according to claim 1, wherein a horizontal cross section of at least one portion of the vertical region of the body is a triangle, wherein a cross sectional area of the vertical region having a triangular cross section is gradually increased or decreased in the vertical direction. The light emitting diode of claim 1, wherein at least one of the wall surfaces of the vertical region having a triangular cross section is inclined in a range of 20 ° to 85 ° with respect to a plane of the active region. A crystal layer including an active region, the body having a plurality of wall surfaces through which photons emitted from the active region pass, and electrode means provided in the body to supply current to the active region; A light emitting diode having a horizontal cross section of at least one portion of a vertical region of which is a quadrilateral having at least one acute angle, wherein the cross-sectional area of the vertical region having a quadrilateral cross-sectional shape is gradually increased or decreased in the vertical direction. diode. 4. The light emitting diode according to claim 3, wherein at least one of the walls of the vertical region having a quadrilateral cross section is inclined in a range of 20 to 85 degrees with respect to the plane of the active region. The light emitting diode of claim 3, wherein at least one angle of the horizontal cross section of the vertical region has a value of 20 degrees to 85 degrees. The light emitting diode of claim 5, wherein at least one of the wall surfaces of the vertical region having a quadrilateral cross section is inclined in a range of 20 to 85 degrees with respect to a plane of the active region.

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