JP2004047760A - Light emitting diode and epitaxial wafer therefor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an epitaxial wafer for high-luminant light-emitting diodes and a light emitting diode structure suitable for mass production by enabling easy formation of current blocking layers. <P>SOLUTION: A first conductivity-type cladding layer 6, an active layer 5, a second conductivity-type cladding layer 4, and a second conductivity-type current diffusing layer 2 are epitaxially grown in this order on a first conductivity-type substrate 8. A circular or near-circular surface-side electrode 1 is arranged cyclically on the surface of the second conductivity-type current diffusing layer 2, and a rear-side electrode 9 occupying the entire rear surface or a part of the rear surface of the first conductivity type substrate 8 is cyclically arranged. A second conductivity-type or insulator-type current blocking region 7 or 10 is arranged with its center in alignment with the center of the surface-side electrode 1 in between the substrate 8 and the rear-surface electrode 9, so that power currents spread as far as the neighborhood of the chip. <P>COPYRIGHT: (C)2004,JPO

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a light-emitting diode epitaxial wafer and a structure of a light-emitting diode capable of obtaining high luminance.
[0002]
[Prior art]
Light emitting diodes (LEDs) are widely used as industrial or consumer display elements because they can emit light of various colors by selecting the type of semiconductor. Conventionally, red LEDs of AlGaAs have been used as high-brightness LEDs. On the other hand, there were GaAsP and GaP LEDs as LEDs having a shorter wavelength than red, but only LEDs with low luminance were obtained. Recently, high-quality epitaxial layers of AlGaInP and GaN can be grown by MOVPE (organic metal vapor phase epitaxy). It has become.
[0003]
FIG. 3 shows a typical sectional structure of an AlGaInP-based light-emitting diode chip having a light emission wavelength of 590 nm.
[0004]
As shown in FIG. 3, in the conventional AlGaInP-based light emitting diode, an undoped AlGaInP active layer 25, an n-type AlGaInP lower cladding layer 26 doped with selenium or silicon, and a zinc-doped p-type A light emitting region layer (light emitting portion) 23 having a double hetero structure sandwiched between an upper cladding layer 24 of the AlGaInP type and a p-type AlGaInP current spreading layer 22 doped with zinc (a “window layer”) is formed on the light emitting region layer 23. ), A circular surface-side electrode 21 is provided on a part of the surface of the p-type current dispersion layer 22 (usually at the center of the surface), and a back-side electrode 29 is provided on the entire back surface of the n-type substrate 28. It has a structure provided.
[0005]
In this light emitting diode chip structure, the carriers injected from the circular surface side electrode 21 are injected into the active layer 25 to emit light. At this time, if the resistance of the epitaxial layer existing between the surface-side electrode 21 and the active layer 25 is high, carriers will be injected into the active layer in a portion directly below the electrode. That is, the spread of the current in the upper cladding layer 24 is small, and only the area directly below the electrode 21 is the light emitting area. Then, the light emitted at that portion is blocked by the electrodes and does not come out of the chip, and as a result, the luminous efficiency cannot be increased.
[0006]
Therefore, in the conventional LED shown in FIG. 3, a GaAlAs layer having a band gap energy larger than that of the active layer 25 and the upper cladding layer 24 is adopted as the current dispersion layer 22 and provided on the upper cladding layer 24. . Thereby, the current injected from the electrode 21 on the light emitting surface side is diffused in the current distribution layer 22 on the light emitting surface side before reaching the active layer 25.
[0007]
[Problems to be solved by the invention]
However, if an attempt is made to increase the thickness of the current dispersion layer in order to obtain high luminance, there is a problem that the cost of the LED epitaxial wafer increases.
[0008]
More specifically, in order to distribute the current uniformly over the entire surface of the active layer, the resistance of the epitaxial layer between the surface-side electrode 21 and the active layer 25 is reduced or the thickness of the epitaxial layer is increased. It is necessary to spread the current spreading. However, since an AlGaInP cladding layer or a window layer cannot provide an epitaxial layer with low resistance, another semiconductor material such as GaP or AlGaAs has been used as the window layer (current distribution layer 22). In the case of such a structure, although the current of the active layer 25 can be dispersed, it is still necessary to grow the epitaxial layer thickly in order to uniformly distribute the current. Even if the current is dispersed, the current density immediately below the surface-side electrode 21 is the highest, and the light emitted at that portion cannot be taken out, which causes a reduction in efficiency.
[0009]
Therefore, as a method of obtaining high luminance by suppressing light emission immediately below the electrodes while keeping the current spreading layer thin, a current blocking region 27 (current blocking portion) is inserted in the current spreading layer 22 as shown in FIG. (Japanese Patent Laid-Open No. Hei 4-229665) and a method of inserting a current blocking region 27 between an epitaxial layer and a substrate as shown in FIG. 5 (Japanese Patent No. 1950123).
[0010]
However, although these methods can suppress light emission immediately below the electrodes, there are problems such as the formation of a reverse mesa portion by processing the current blocking region and the oxidation of the surface, which makes subsequent epitaxial growth difficult. there were.
[0011]
SUMMARY OF THE INVENTION It is an object of the present invention to solve the above-mentioned problems, to provide a structure of a light-emitting diode epitaxial wafer and a light-emitting diode having a high luminance suitable for mass production, in which a current blocking region is formed more easily.
[0012]
[Means for Solving the Problems]
In order to achieve the above object, the present invention is configured as follows.
[0013]
The epitaxial wafer for a light-emitting diode according to the first aspect of the present invention comprises a first-conductivity-type substrate, a first-conductivity-type clad layer, an active layer, a second-conductivity-type clad layer, and a second-conductivity-type current-spreading layer, which are sequentially epitaxially grown on a first-conductivity-type substrate. In a light-emitting diode epitaxial wafer in which a circular or nearly circular front-side electrode is formed on the front side, and a back-side electrode made of a whole or partial electrode is periodically disposed on the back side, A current blocking region of the second conductivity type having a center aligned with the front electrode is disposed between the back electrode and the back electrode.
[0014]
In the epitaxial wafer for a light emitting diode according to the second aspect of the present invention, a first conductivity type clad layer, an active layer, a second conductivity type clad layer, and a second conductivity type current spreading layer are sequentially epitaxially grown on a first conductivity type substrate. In a light-emitting diode epitaxial wafer in which a circular or nearly circular front-side electrode is formed on the front side, and a back-side electrode made of a whole or partial electrode is periodically disposed on the back side, An insulating current blocking region having the same center as that of the front electrode is disposed between the back electrode and the back electrode.
[0015]
According to a third aspect of the present invention, in the epitaxial wafer for a light emitting diode according to the first or second aspect, the substrate is GaAs, and the first conductive type clad layer, the active layer, and the second conductive type clad forming a light emitting portion. The layer is made of AlGaInP or GaInP. The current spreading layer can be made of, for example, GaP or AlGaAs.
[0016]
A light-emitting diode according to a fourth aspect of the present invention is manufactured using the light-emitting diode epitaxial wafer according to any one of the first to third aspects.
[0017]
<The gist of the invention>
The gist of the present invention is that, in order to achieve the above object, a current blocking region (pn inversion layer) or an insulating current blocking region (high resistance layer) of a conductivity type different from that of the substrate is provided between the substrate and the back side electrode. The structure is such that the current is spread to the periphery of the chip by the insertion, thereby improving the brightness of the light emitting diode. A typical example of a current blocking region of a conductivity type different from that of the substrate is an AlGaAs layer, which can be easily provided by, for example, liquid phase epitaxial growth. A typical example of the insulating current blocking region is an SiO ₂ film, which can be easily formed by, for example, forming the film by a plasma CVD method and selectively etching the SiO ₂ film in a photolithography process. Therefore, it is suitable for mass production.
[0018]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, embodiments of the present invention will be described with reference to examples shown in the drawings.
[0019]
<Example 1>
FIG. 1 shows a structure of a light emitting diode (LED) for explaining a first embodiment of the present invention.
[0020]
An n-type AlGaInP lower cladding layer 6 having a thickness of 0.5 μm and a carrier concentration of 1 × 10 ¹⁸ cm ⁻³ , an undoped AlGaInP active layer 5 having a thickness of 0.5 μm on an n-type GaAs substrate 8 by MOVPE; A p-type AlGaInP upper cladding layer 4 having a thickness of 0.5 μm and a carrier concentration of 5 × 10 ¹⁷ cm ⁻³ , and a p-type AlGaAs current dispersion layer 2 having a thickness of 5 μm and a carrier concentration of 2 × 10 ¹⁸ cm ^−3. It grew sequentially.
[0021]
This is because a light emitting region layer 13 (light emitting portion) having a double hetero structure in which an undoped AlGaInP active layer 5 is sandwiched between an n-type AlGaInP lower cladding layer 6 and a p-type AlGaInP upper cladding layer 4 on an n-type GaAs substrate 8. And an AlGaInP-based light emitting diode structure in which the p-type AlGaAs current spreading layer 2 is stacked on the light emitting region layer 13.
[0022]
Thereafter, a p-type current blocking region 7 of a conductivity type different from that of the substrate 8, that is, a p-type inversion layer made of a pn inversion layer was periodically formed on the back surface so that the center of the p-type current blocking region 7 coincided with the center of the front surface electrode 1. That is, a p-type AlGaAs layer having a carrier concentration of 1 × 10 ¹⁸ cm ⁻³ and a thickness of 0.1 μm is formed on the back surface of the substrate by a liquid phase epitaxial growth. Formed the p-type current blocking region 7 having a diameter of 200 μm periodically.
[0023]
Metal electrodes were periodically formed on this epitaxial wafer. To be more precise, the front surface electrode 1 having a circular shape or a shape close thereto is periodically arranged on the front surface side of the wafer, and the back surface electrode 9 composed of the entire surface or a partial electrode is periodically arranged on the back surface side.
[0024]
Thus, a p-type current blocking region 7 of a conductivity type different from that of the n-type substrate 8 is periodically disposed between the substrate 8 and the back surface electrode 9 so that the center of the p-type current blocking region 7 coincides with the center of the front surface electrode 1. did.
[0025]
According to this structure, the current blocking region 7 of a conductivity type different from that of the substrate 8 is partially inserted between the substrate 8 and the back surface electrode 9, so that the surface side electrode 1 to the back surface electrode 9 As shown in FIG. 1, the current 3 flows so as to avoid the current blocking region 7, thereby spreading the current to the periphery of the chip, thereby improving the brightness of the light emitting diode.
[0026]
LED chips of about 300 μm square were manufactured from the epitaxial wafer on which the metal electrodes were formed, and their characteristics were evaluated. The LED chip of this example had an emission output of 2.4 mW, which was about 20% higher than that of the LED chip having no current blocking region 7, and Vf was 1.9 V without change.
[0027]
<Example 2>
FIG. 2 shows the structure of a light emitting diode (LED) for explaining a second embodiment of the present invention.
[0028]
An n-type AlGaInP lower cladding layer 6 having a thickness of 0.5 μm and a carrier concentration of 1 × 10 ¹⁸ cm ⁻³ , an undoped AlGaInP active layer 5 having a thickness of 0.5 μm on an n-type GaAs substrate 8 by MOVPE; A p-type AlGaInP upper cladding layer 4 having a thickness of 0.5 μm and a carrier concentration of 5 × 10 ¹⁷ cm ⁻³ , and a p-type AlGaAs current dispersion layer 2 having a thickness of 5 μm and a carrier concentration of 2 × 10 ¹⁸ cm ^−3. It grew sequentially. Reference numeral 13 denotes a light emitting region layer.
[0029]
Thereafter, an insulating current blocking region 10 was periodically arranged on the back surface so that the center of the electrode 1 coincided with the center of the front electrode 1. That is, an insulating SiO ₂ film having a thickness of 0.1 μm is formed on the back surface of the substrate by a plasma CVD method, and a current blocking region 10 having a diameter of 200 μm and a thickness of 0.1 μm is formed by a photolithography process. Was formed periodically.
[0030]
Metal electrodes were periodically formed on this epitaxial wafer. To be more precise, the front surface electrode 1 having a circular shape or a shape close thereto is periodically arranged on the front surface side of the wafer, and the back surface electrode 9 composed of the entire surface or a partial electrode is periodically arranged on the back surface side.
[0031]
Thus, the insulating current blocking region 10 was periodically arranged between the substrate 8 and the back surface electrode 9 so that the center of the insulating current blocking region 10 coincided with the center of the front surface electrode 1.
[0032]
According to this structure, since the insulating current blocking region 10 is partially inserted between the substrate 8 and the back surface electrode 9, the current 3 flowing from the front surface electrode 1 to the back surface electrode 9 is reduced. As shown in FIG. 2, the current flows so as to avoid the current blocking region 10, whereby the current spreads to the periphery of the chip, thereby improving the brightness of the light emitting diode.
[0033]
After metal electrodes were periodically formed on the front and back of the epitaxial wafer, LED chips of about 300 μm square were manufactured and evaluated for characteristics. The LED chip of this example had an emission output of 2.4 mW, about 20% higher than that of the LED chip having no current blocking layer, and Vf was 1.9 V without change.
<Other Embodiments and Modifications>
In the first and second embodiments, after forming the LED epitaxial structure, the AlGaAs layer as the p-type current blocking region 7 and the SiO ₂ film as the insulating current blocking region 10 were formed. Even if the LED epitaxial structure is manufactured after forming the layer or the SiO ₂ film, the same effect of blocking and diffusing the current can be obtained.
[0034]
In the first embodiment, the AlGaAs layer is used as the p-type current blocking region 7, but the same effect can be obtained even if another material is used as long as the layer has conductivity different from that of the substrate. .
[0035]
In the second embodiment, the SiO ₂ film is used as the insulating current blocking region 10. However, the present invention is not limited to the SiO ₂ film. For example, another insulating material such as a SiN film or an undoped AlGaAs layer may be used. Even so, the same effect can be obtained.
[0036]
In the first embodiment, an AlGaAs layer serving as a p-type current blocking region 7 is formed by liquid phase epitaxial growth. In the second embodiment, an SiO ₂ film formed by a plasma CVD method is selectively etched by a photolithography process. Thus, the SiO ₂ film serving as the insulating current blocking region 10 was formed, but it can also be manufactured by other methods, and the same effect can be obtained in the current blocking region obtained thereby. For example, in Example 1 described above, the p-type AlGaAs layer on the rear surface side of the substrate was formed by liquid phase epitaxial growth. However, a dopant having conductivity different from that of the substrate may be implanted into the substrate by a method such as ion plantation. Similar effects can be obtained.
[0037]
In the case of the above embodiment, the current blocking region 7 or 10 is located within the thickness of the back-side electrode 9, but may be located on the substrate side surface of the back-side electrode.
[0038]
【The invention's effect】
As described above, the epitaxial wafer for a light emitting diode and the light emitting diode according to the present invention include a current blocking region having a conductivity type different from that of the substrate or an insulating current blocking region inserted between the substrate and the back surface side electrode, thereby forming a chip periphery. The brightness of the light emitting diode is improved by spreading the current to the portion.
[0039]
Therefore, according to the light emitting diode of the present invention, the following effects can be obtained as compared with a conventional light emitting diode having a structure in which a current blocking region is provided in an LED epitaxial layer.
[0040]
Since the current blocking region can be grown by liquid phase epitaxial growth or plasma CVD with high productivity, the manufacturing cost of the LED epitaxial wafer and the LED can be significantly reduced as compared with the conventional LED structure. .
[0041]
Further, since the current blocking region is formed on the back surface side of the substrate, an epitaxial wafer for LED having good surface morphology can be easily manufactured as compared with the conventional LED structure.
[Brief description of the drawings]
FIG. 1 is a cross-sectional view illustrating a structure of a light emitting diode according to a first embodiment of the present invention.
FIG. 2 is a sectional view illustrating a structure of a light emitting diode according to a second embodiment of the present invention.
FIG. 3 is an external view of a conventional light emitting diode chip.
FIG. 4 is a cross-sectional view illustrating a structure of a conventional light emitting diode.
FIG. 5 is a sectional view showing another structure of a conventional light emitting diode.
[Explanation of symbols]
REFERENCE SIGNS LIST 1 front-side electrode 2 p-type current dispersion layer 4 p-type AlGaInP upper cladding layer 5 undoped AlGaInP active layer 6 n-type AlGaInP lower cladding layer 7 p-type current blocking region 8 n-type GaAs substrate 9 backside electrode 10 insulating current Blocking region 13 Light emitting region layer

Claims (4)

On the substrate of the first conductivity type, the first conductivity type clad layer, the active layer, the second conductivity type clad layer, the second conductivity type current dispersion layer is epitaxially grown sequentially, and the surface side of the surface side of a circle or a shape close to it is formed. In the epitaxial wafer for the light emitting diode, the electrode, and the back surface side electrode consisting of the entire surface or the partial electrode on the back side, respectively, are arranged periodically.
An epitaxial wafer for a light emitting diode, wherein a current blocking region of the second conductivity type having a center aligned with the front electrode is disposed between the substrate and the rear electrode. On the substrate of the first conductivity type, the first conductivity type clad layer, the active layer, the second conductivity type clad layer, the second conductivity type current dispersion layer is epitaxially grown sequentially, and the surface side of the surface side of a circle or a shape close to it is formed. In the epitaxial wafer for the light emitting diode, the electrode, and the back surface side electrode consisting of the entire surface or the partial electrode on the back side, respectively, are arranged periodically.
An epitaxial wafer for a light-emitting diode, wherein an insulating current blocking region having a center aligned with the front electrode is disposed between the substrate and the rear electrode. The epitaxial wafer for a light emitting diode according to claim 1 or 2,
An epitaxial wafer for a light emitting diode, wherein the substrate is GaAs, and the first conductivity type clad layer, the active layer, and the second conductivity type clad layer constituting the light emitting portion are made of AlGaInP or GaInP. A light emitting diode manufactured using the light emitting diode epitaxial wafer according to claim 1.

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