JP2004158778A - Semiconductor light-emitting device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a semiconductor light-emitting device with improved luminance and light extraction efficiency. <P>SOLUTION: In the semiconductor light-emitting device 1 comprising an active layer 3 (light-emitting layer), a current diffusion layer 5 laminated on the active layer 3, and a mesa structure 9 formed by etching the surface of the current diffusion layer 5, a prospective half angle r1 of a top face 9a of the mesa structure 9 is set approximately as the totally reflecting angle. <P>COPYRIGHT: (C)2004,JPO

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a semiconductor light emitting device, and more particularly, to a light emitting device used for display and communication, particularly a light emitting diode.
[0002]
[Prior art]
Prior art documents related to the present invention include the following.
[0003]
[Patent Document 1]
Japanese Patent No. 2901823 (FIG. 1)
[0004]
As shown in FIG. 8, the conventional light emitting device 100a has a multilayer structure including an active layer 101 (light emitting layer), a p-cladding layer 102, and a current spreading layer 103. And-an electrode 104 is provided. When a current flows through the light emitting element 100, the active layer 101 emits light. Light generated from the active layer 101 is emitted in the same direction and emitted from the element surface 105 to the outside of the crystal. At this time, light emitted from the active layer 101 and emitted to the outside is limited to light (for example, paths a and b indicated by arrows) whose incident angle on the element surface 105 is within the total reflection angle. Light having an incident angle equal to or larger than the total reflection angle (for example, a path c shown by an arrow) is totally reflected on the element surface 105 and returns to the inside of the crystal.
[0005]
As shown in FIG. 9, in the other light emitting element 100 b, light having an incident angle equal to or larger than the total reflection angle (for example, a path d indicated by an arrow) is extracted to the outside of the light emitting element by roughening the element surface 105. I have to. However, if the current spreading layer 103 is composed of GaP and _{(Al x Ga x-1)} y In 1-y P (0 ≦ x ≦ 1,0 ≦ y ≦ 1) material, such as, HF or HCl boil There has been a problem that the element surface 105 cannot be roughened by using such a method.
[0006]
In order to solve this problem, a light emitting element 100c shown in FIG. 10 has a light emitting element surface 105 provided with a mesa structure 106. At this time, light having an incident angle equal to or larger than the total reflection angle (for example, paths e and f indicated by arrows) can be extracted to the outside of the element 100c, and the luminance of the light emitting element 100c is improved.
[0007]
The light extraction efficiency of the light emitting element 100c having the mesa structure will be discussed. In the light emitting device model, as shown in FIG. 11, the vertical distance h1 from the upper surface of the active layer to the device surface was 5 μm, and the mesa height h2 from the device surface to the top surface of the mesa structure was 4 μm. The top surface width m of the mesa structure is 14 μm. The angle t between the slope of the mesa structure and the vertical direction is 41 °. The light extraction efficiency refers to light emitted at an angle θ with respect to the horizontal direction at an emission position P (x, 0) on the active layer of the light emitting element model when the angle θ is in the range of 0 to π. It is determined whether or not light is totally reflected on the element surface at every angle θ of 1 °, and is the ratio of light that is not totally reflected at this time (however, multiple reflection within the crystal and the current diffusion layer / air interface). Is not considered. The light extraction efficiency of 1 indicates the light extraction efficiency when the light emitting element is not provided with a mesa structure.
[0008]
FIG. 12 shows the light extraction efficiency according to the light emitting position P (x, 0) obtained as described above. According to this, the light extraction efficiency is such that the light emission position P is about 10 μm away from the center point (origin O) of the active layer corresponding to the center point Q (shown in FIG. 11) of the top surface of the mesa structure in plan view. This is lower than when the light emitting element is not provided with a mesa structure. At a position where the light emitting position P is at least 10 μm away from the origin O, it is almost equal to the case where the light emitting element is not provided with a mesa structure. This indicates that the luminance of the light emitting element is not improved even if the light emitting position P is provided at a position distant from the mesa structure below the active layer.
[0009]
Therefore, as in the light emitting element 100d shown in FIG. 13, a current confinement layer 107 having an opening 107a is provided below the mesa structure 106, and the current density is increased by performing current confinement during energization as indicated by an arrow. Are known (for example, see Patent Document 1). Thus, in the light emitting element 100d, the light emitting region R is limited in the active layer 101 (light emitting layer) below the mesa structure 106, and the light extraction efficiency of the mesa structure 106 is improved.
[0010]
[Problems to be solved by the invention]
In the light emitting device 100d, the light extraction efficiency was determined according to each value of the mesa height h2 and the top surface width m of the mesa structure. At this time, the light extraction efficiency was obtained when the mesa height h2 was 4, 6, 8 μm and when the top surface width m of the mesa structure was 40, 48, 56, 64, 72 μm.
[0011]
As a result, as shown in FIGS. 14, 15 and 16, it was found that the light extraction efficiency was increased in proportion to the mesa height h2 of the mesa structure (in particular, the light emission position P (x, 0) was higher). At a position away from the center point (origin O) of the active layer by about −10 to 10 μm, the light extraction efficiency is high in proportion to the mesa height h2 of the mesa structure). In order to set the mesa height h2 to 4 μm or more, particularly 12 μm or more, the material of the current diffusion layer 103 in which the mesa structure 106 is formed is made of AlGaAs or (Al _x Ga _{x -1} ) _y In _1-y P (0 ≦ x ≦ 1, 0 ≦ y ≦ 1) may be used. At this time, the current diffusion layer 103 is lattice-matched and degradation due to distortion is suppressed. However, when other materials are used, lattice mismatch occurs. Therefore, it is necessary to limit the mesa height h2 and suppress deterioration due to distortion. Note that the material of the p-clad layer 102 on which the current diffusion layer 103 is stacked is selected so that lattice mismatch with the light emitting layer 101 does not occur.
[0012]
Further, it was found from the graph that the light extraction efficiency was not improved even if the top surface width m of the mesa structure 106 was increased. Conversely, if it is narrow, the light extraction efficiency at the central portion of the light emitting portion (where the light emitting position P (x, 0) is about -10 to 10 μm away from the center point (origin O) of the active layer) is improved, but the light emitting portion Does not improve the efficiency of taking out the peripheral portion, and the effect is rather reduced as a whole. For example, in the case of an AlGaInP-based light-emitting diode having an emission wavelength of 570 nm, the luminous intensity dropped from 30 mcd to 20 mcd.
[0013]
Thus, simply providing a mesa structure does not improve luminous intensity, and a semiconductor light emitting device having a mesa structure having an appropriate shape has been required.
[0014]
In view of the above, it is an object of the present invention to provide a semiconductor light emitting device having improved luminance and light extraction efficiency.
[0015]
[Means for Solving the Problems]
The present invention, as means for solving the above problems,
A light-emitting layer, a current diffusion layer laminated on the light-emitting layer, and a semiconductor light-emitting element including a mesa structure formed by etching the surface of the current diffusion layer;
The expected half angle of the top surface of the mesa structure is substantially equal to the total reflection angle.
[0016]
According to the invention, since the expected half angle of the top surface of the mesa structure is substantially the total reflection angle, light incident from the light emitting layer on the top surface of the mesa structure at an angle within the expected half angle is equal to the top surface of the mesa structure. Through the device to improve the brightness of the light emitting device. Here, the expected half angle of the top surface of the mesa structure refers to an incident angle when the light enters the outer edge of the top surface of the mesa structure from the light emitting position of the light emitting layer corresponding to the center point of the top surface of the mesa structure in a plane. .
[0017]
The current spreading _{layer, (Al x Ga x-1} ) consists of _{y In 1-y P (0} ≦ x ≦ 1,0 ≦ y ≦ 1), the visual angle of the side surface of the mesa structure, 35 ° or 150 ° or less. When formed by a current diffusion layer _{(Al x Ga x-1)} y In 1-y P (0 ≦ x ≦ 1,0 ≦ y ≦ 1), the total reflection angle is about 17 °. At this time, the estimated half angle of the top surface of the mesa structure is 14 ° to 17 °, preferably 17 °. Further, the upper limit value of the prospect angle of the side surface of the mesa structure is set to 150 ° because the prospect angle becomes approximately 150 ° when the angle between the side surface (slope) of the mesa structure and the vertical direction is 41 °. It is. Thus, the expected half angle of the top surface of the mesa structure becomes the total reflection angle, and the light that has returned to the inside out of the emitted light can be extracted to the outside from the side surface of the mesa structure, and the luminance of the light emitting element can be improved. Here, the expected angle of the side surface of the mesa structure is twice as large as the incident angle when the light enters the outer edge of the side surface of the mesa structure from the light emitting position of the light emitting layer corresponding to the center point of the top surface of the mesa structure in the plane. Is an angle having In addition, since the current diffusion layer is lattice-matched to the light emitting layer, the height of the mesa structure can be formed to a height of 12 μm or more. Further, the present invention can be applied to a light emitting element having a short wavelength.
[0018]
Further, it is preferable that the current diffusion layer is made of AlGaAs, and a prospect angle of a side surface of the mesa structure is 35 ° or more and 150 ° or less. When the current diffusion layer is formed of AlGaAs, the total reflection angle is about 17 °. At this time, the estimated half angle of the top surface of the mesa structure is 17 °. Thus, the expected half angle of the top surface of the mesa structure becomes the total reflection angle, and the light that has returned to the inside out of the emitted light can be extracted to the outside from the side surface of the mesa structure, and the luminance of the light emitting element can be improved. In addition, since the current diffusion layer is lattice-matched to the light emitting layer, the height of the mesa structure can be formed to a height of 12 μm or more.
[0019]
The light emitting layer _is preferably made of _{(Al x Ga x-1)} y In 1-y P (0 ≦ x ≦ 1,0 ≦ y ≦ 1). At this time, the emission wavelength of the light emitted from the light emitting layer is 570 nm.
[0020]
Preferably, the height of the mesa structure is 4 μm or more and 12 μm or less. In order to improve the light extraction efficiency by increasing the height of the mesa structure, it is necessary to increase the thickness of the current diffusion layer in which the mesa structure is formed. At this time, if the current diffusion layer has a lattice mismatch with the light emitting layer, the current diffusion layer including the mesa structure is deteriorated due to strain when the current diffusion layer is thickened. In order to prevent the deterioration of the mesa structure, the height of the mesa structure is set to 4 μm or more and 12 μm or less. When the height of the mesa structure is 4 μm or more and 12 μm or less, it is preferable that the height be controlled by controlling the thickness of the current diffusion layer.
[0021]
The mesa structure is formed in a dome shape by etching the surface of the current diffusion layer a plurality of times, so that light extraction efficiency is improved.
[0022]
The present invention provides, as another means for solving the above problems,
A light-emitting layer, a current diffusion layer laminated on the light-emitting layer, and a semiconductor light-emitting element including a mesa structure formed by etching the surface of the current diffusion layer;
Providing an electrode on the top surface of the mesa structure,
The light emitting layer is disposed so as to surround the periphery of the electrode in a plane, and the distance between the outer edge of the electrode and the outer edge of the light emitting layer is made uniform.
[0023]
According to the invention, since the distance from the electrode to the light emitting layer is uniform, when the semiconductor light emitting element is energized, the current is uniformly diffused in the current diffusion layer, and the light emission of the light emitting element can be uniform.
[0024]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings.
[0025]
FIG. 1 is a sectional view of a semiconductor light emitting device 1 according to the present invention. The semiconductor light emitting device 1 has a multilayer structure including a substrate 2, an active layer 3 (light emitting layer), a p-clad layer 4, and a current diffusion layer 5. The back electrode 6 is provided on the lower surface of the substrate 2, and the p-electrode 7 is provided on the upper surface of the current diffusion layer 5. The active layer 3 and the current diffusion layer 5 _is composed of _{(Al x Ga x-1)} y In 1-y P (0 ≦ x ≦ 1,0 ≦ y ≦ 1). When the light emitting element 1 is energized, the active layer 3 emits light. Further, between the p-cladding layer 4 and the current diffusion layer 5, a current confinement layer 8 for increasing the current density by constricting the current is formed as in the conventional light emitting element.
[0026]
Further, a mesa structure 9 is formed on the upper surface 5a (device surface) of the current diffusion layer 5. The mesa height h2 of the mesa structure 9, that is, the height from the surface of the current diffusion layer 5 to the top surface of the mesa structure 9 is 4 μm or more and 12 μm or less, and the top surface width m of the mesa structure is 3 to 9 μm.
[0027]
The expected half angle r1 of the top surface 9a of the mesa structure 9 is substantially the total reflection angle (about 17 °). Here, the estimated half angle r1 of the top surface of the mesa structure is incident on the outer edge of the top surface 9a of the mesa structure 9 from the light emitting position O of the active layer 3 corresponding to the center point Q of the top surface 9a of the mesa structure 9 in a plane. The angle of incidence at that time.
[0028]
The expected angle r2 of the side surface 9b of the mesa structure 9 is 35 °. Here, the expected angle r2 of the side surface of the mesa structure is an angle r2 having a magnitude twice as large as the incident angle r3 when the light enters the outer edge of the side surface 9b of the mesa structure 9 from the light emitting position O. In the present embodiment, the estimated angle r2 of the side surface 9b of the mesa structure 9 is 35 °, but may be 35 ° or more and 150 ° or less.
[0029]
Next, a manufacturing method for manufacturing the semiconductor light emitting device 1 will be described.
[0030]
As shown in FIG. 2A, first, an active layer 3 made of (Al _x Ga _x-1 ) _y In _1-y P (0 ≦ x ≦ 1, 0 ≦ y ≦ 1) is formed on a substrate 2. A cladding layer 4, a current confinement layer 8, and a current diffusion layer 5 composed of (Al _x Ga _x-1 ) _y In _1-y P (0 ≦ x ≦ 1, 0 ≦ y ≦ 1) are sequentially stacked. Here, the height h3 from the upper surface of the p-cladding layer 4 to the surface of the current diffusion layer 5 is 14 μm, and the height h4 from the upper surface of the active layer 3 to the surface of the current diffusion layer 5 is 13 μm. .
[0031]
Next, as shown in FIG. 2B, a part of the upper surface of the current diffusion layer 5 is protected by the resist 10. Then, as shown in FIG. 2C, the current diffusion layer 5 is etched to form a mesa structure 9. As the etchant used at the time of this etching, a sulfuric acid-based etchant can be etched only at about 1 μm even if it is etched at 60 ° C. for 10 minutes. At that time, the etching is started about 15 minutes after the etchant is formed. This is because, as shown in FIG. 3, when looking at the etching rate one hour after the etchant was created, the etching rate was greatly different, and the etch rate was the fastest immediately after the etchant was created, but the etching variation was increased. One hour after the formation, the etching rate becomes slow, and it becomes difficult to perform etching.
[0032]
Subsequently, as shown in FIG. 2D, after the resist 10 is peeled off, a thin film of an electrode material is formed on the upper surface of the current diffusion layer 5 by a sputtering method or a vapor deposition method, and a p-electrode 7 is formed. Further, a back electrode 6 is deposited on the lower surface of the substrate 2.
[0033]
Next, the operation of the semiconductor light emitting device 1 having the above configuration will be described.
[0034]
In the light emitting diode 1 manufactured as described above, of the light emitted from the light emitting region R shown in FIG. 1, the light incident on the top surface 9a of the mesa structure 9 at an angle within the expected half angle r1 is expected. Since the half angle r1 is substantially the total reflection angle (about 17 °), the light is emitted outward without being reflected by the top surface 9a. Further, of the light emitted from the light emitting region R, the light incident on the side surface 9b of the mesa structure 9 is reflected by the side surface 9b because the estimated angle r2 of the side surface 9b of the mesa structure 9 is 35 ° or more. It is injected outward without being. Thereby, light extraction efficiency is improved. Further, the luminous intensity of the emitted light could be improved. When the present invention is applied to an AlGaInP-based light emitting diode having an emission wavelength of 570 nm, the luminous intensity, which was 30 mcd in the conventional light emitting element, could be improved to 58 mcd.
[0035]
As a modified example of the above embodiment, as shown in FIG. 4, the mesa structure 9 may be formed in a dome shape. This is one in which the additional etching is further performed after the resist 10 is stripped off in the manufacturing method of manufacturing the semiconductor light emitting device 1 described above. Thereby, the luminous intensity of the emitted light can be improved in the same manner as in the above embodiment.
[0036]
FIG. 5A is a cross-sectional view of a semiconductor light emitting device 1 ′ according to another embodiment of the present invention. In this semiconductor light emitting device 1 ′, as shown in FIG. 5B, a p-electrode 7 ′ is formed on the top surface 9 a of the mesa structure 9. Further, a ring-shaped active layer 3 '(light emitting layer) is arranged so as to surround the periphery of the p-electrode 7' in plan view. Further, the current confinement layer 8 of the above embodiment is not provided. The same parts as those in the other embodiments are denoted by the same reference numerals, and the detailed description is omitted.
[0037]
In the semiconductor light emitting device 1 'having the above configuration, since the distance between the outer edge of the p-electrode 7' and the outer edge of the ring-shaped active layer 3 'is equal, the current diffusion of the current flowing in the light emitting region R is uniform. It becomes. On the other hand, as shown in FIG. 6, when the distance between the outer edge of the p-electrode 7 'and the outer edge of the active layer 3' is uneven, the current diffusion becomes uneven and the light emitting region (in particular, the active layer 3 ' The brightness of the corners of 'is reduced. Further, as shown in FIG. 7, instead of providing the ring-shaped active layer 3 ', a polygonal shape is formed so that the distance between the outer edge of the p-electrode 7' and the outer edge of the ring-shaped active layer 3 'becomes uniform. May be formed.
[0038]
【The invention's effect】
As is clear from the above description, the present invention provides a light emitting layer, a current diffusion layer stacked on the light emitting layer, and a semiconductor light emitting device including a mesa structure formed by etching the surface of the current diffusion layer. Since the expected half angle of the top surface of the mesa structure is set to almost the total reflection angle, light that enters the top surface of the mesa structure from the light emitting layer at an angle within the expected half angle is reflected by the top surface of the mesa structure without being reflected. It is taken out to improve the luminance and the light taking-out efficiency of the light emitting element.
[Brief description of the drawings]
FIG. 1 is a sectional view of a semiconductor light emitting device of the present invention.
2 (a), 2 (b), 2 (c), 2 (d) are cross-sectional views showing the light emitting diode of FIG. 1 during manufacture.
FIG. 3 is a graph showing an etching rate according to a standing time after an etchant is formed.
FIG. 4 is a sectional view showing a modification of the semiconductor light emitting device of FIG. 1;
FIG. 5A is a cross-sectional view of a semiconductor light emitting device according to another embodiment of the present invention. (B) is a plan view of (a).
FIG. 6 is a plan view of the semiconductor light emitting device showing a case where the distance between the outer edge of the p-electrode and the outer edge of the active layer is unequal.
FIG. 7 is a plan view showing a modification of FIG. 5;
FIG. 8 is a sectional view of a conventional semiconductor light emitting device.
FIG. 9 is a sectional view of a conventional semiconductor light emitting device.
FIG. 10 is a sectional view of a conventional semiconductor light emitting device.
FIG. 11 is a light-emitting element model of a conventional semiconductor light-emitting element.
12 is a graph showing light extraction efficiency in the light emitting device model of FIG.
FIG. 13 is a sectional view of a conventional semiconductor light emitting device.
14 is a graph showing light extraction efficiency of the semiconductor light emitting device of FIG.
15 is a graph showing light extraction efficiency of the semiconductor light emitting device of FIG.
FIG. 16 is a graph showing light extraction efficiency of the semiconductor light emitting device of FIG.
[Explanation of symbols]
1. Semiconductor light emitting element 3. Active layer (light emitting layer)
5 ... current diffusion layer 9 ... mesa structure r1 ... estimated half angle r2 of the top surface of the mesa structure ... estimated angle of the side surface of the mesa structure

Claims (7)

A light-emitting layer, a current diffusion layer laminated on the light-emitting layer, and a semiconductor light-emitting device including a mesa structure formed by etching the surface of the current diffusion layer;
A semiconductor light-emitting device, wherein an estimated half angle of a top surface of the mesa structure is substantially equal to a total reflection angle. The current spreading _{layer, (Al x Ga x-1} ) consists of _{y In 1-y P (0} ≦ x ≦ 1,0 ≦ y ≦ 1), the visual angle of the side surface of the mesa structure, 35 ° or 150 2. The semiconductor light emitting device according to claim 1, wherein the angle is equal to or less than 0 °. 2. The semiconductor light emitting device according to claim 1, wherein the current diffusion layer is made of AlGaAs, and an estimated angle of a side surface of the mesa structure is 35 ° or more and 150 ° or less. 3. 4. The light-emitting layer according to claim 1, wherein the light-emitting layer is made of (Al _x Ga _x-1 ) _y In _1-y P (0 ≦ x ≦ 1, 0 ≦ y ≦ 1). 5. Semiconductor light emitting device. 5. The semiconductor light emitting device according to claim 1, wherein the height of the mesa structure is 4 μm or more and 12 μm or less. 6. The semiconductor light emitting device according to claim 1, wherein the mesa structure is formed in a dome shape by etching the surface of the current diffusion layer a plurality of times. A light-emitting layer, a current diffusion layer laminated on the light-emitting layer, and a semiconductor light-emitting device including a mesa structure formed by etching the surface of the current diffusion layer;
Providing an electrode on the top surface of the mesa structure,
A semiconductor light-emitting device, wherein the light-emitting layer is disposed so as to surround the periphery of the electrode in a plane, and the distance between the outer edge of the electrode and the outer edge of the light-emitting layer is equalized.

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