JP3548409B2 - Light emitting diode - Google Patents

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a light emitting diode, and more particularly, to a light emitting diode used in an optical printer head or the like, which is a light source for exposure of a page printer.
[0002]
[Prior art]
A conventional light emitting diode will be described with reference to FIG. 3, reference numeral 11 denotes a substrate, 12 denotes a buffer layer, 13 denotes a carrier injection layer, 14 denotes a light emitting layer, 15 denotes a carrier confinement layer, 17 denotes an individual electrode, and 18 denotes a common electrode. The substrate 11 is made of silicon, gallium arsenide, or the like, the buffer layer 12 is made of gallium arsenide, or the like, and the carrier injection layer 13, the light emitting layer 14, and the carrier confinement layer 15 are made of aluminum gallium arsenide. Note that contact layers 12a and 15a made of gallium arsenide or the like are formed on the surface portions of the buffer layer 12 and the carrier confinement layer 15.
[0003]
In such a light emitting diode, the optical band gap E ₁₃ of the carrier injection layer 13, the optical band gap E 14 of the light emitting layer ₁₄ , and the optical band gap E ₁₅ of the carrier confinement layer 15 obtain a carrier confinement effect. to _be set to _{E 13> E 14, E 15} > E 14. The carrier injection layer 13, luminescent layer 14, and the case of using an aluminum U gallium arsenide _{(Al x Ga 1-x As} ) as the material of the carrier confinement layer 15, the respective Al composition x _{x 13} (carrier injection layer 13 Al composition _{x), x 14} (Al composition x of the light-emitting layer _{14), x 15} (Al composition x of the carrier confinement layer 15) _then, the _{x 13> x 14, x 15} > x 14, 0 ≦ x 14 ≦ 0 .4, 0 <x ₁₃ , x ₁₅ ≦ 0.7, it is possible to set a light emitting diode having an optical band gap having the relationship described above.
[0004]
In this light-emitting diode, when a current flows in the forward direction, carriers are injected from the carrier injection layer 13 into the light-emitting layer 14, and light is generated by radiative recombination with majority carriers. In this case, the luminous efficiency of the light emitting diode is the product of the internal quantum efficiency and the light extraction efficiency (luminous efficiency (external quantum efficiency) = (internal quantum efficiency) × (light extraction efficiency)), so the luminous efficiency is increased. Therefore, it is necessary to increase the internal quantum efficiency and the light extraction efficiency.
[0005]
[Problems to be solved by the invention]
However, in the conventional light emitting diode, when Al _x Ga _1-x As is used as a material of the light emitting element, in order to increase the internal quantum efficiency, the carrier injection layer 13 and the carrier It is necessary to make the Al composition x of the confinement layer 15 as large as possible. On the other hand, in order to increase the light extraction efficiency, it is necessary to minimize reflection at the interface between the light emitting layer 14 and the carrier confinement layer 15. The critical angle for total reflection θ _c at the interface between the light emitting layer 14 and the carrier confinement layer 15 is sin θ _c = n ₁₅ / n ₁₄ (n ₁₄ is the refractive index of the light emitting layer 14, n ₁₅ is the refractive index of the carrier confinement layer 15). Is defined by
[0006]
Refractive index of Al _x Ga _1-x As as a function of Al composition x, represented as n = ^{(13.18-3.12x) 1/2,} total reflection larger the Al composition of the carrier confinement layer 15 The critical angle θ _C is reduced, and the light reflected at the interface between the light emitting layer 14 and the carrier confinement layer 15 is increased, and the light extraction efficiency is deteriorated.
[0007]
That is, light passing through substances having different refractive indexes has a relationship of n ₁ sin θ ₁ = n ₂ sin θ ₂ as shown in FIG. When θ ₁ > 90 °, light is totally reflected at the interface, and the critical angle θ _c is given by sin θ _c = n ₁ / n ₂ .
[0008]
Meanwhile, in order to increase the internal quantum efficiency in the light emitting diode, the optical band gap E ₁₃ and optical band gap E ₁₅ of the carrier confinement layer 15 of the carrier injection layer 13, an optical band gap of the light-emitting layer 14 E ₁₄ ( compared to the determined) by emission wavelength required, as large as possible (increasing the Al composition _{x 13} and _{x 15)} it is necessary to, but larger the Al composition, the refractive index _{n 13} and _{n 15} is the refractive smaller than the rate _{n 14.}
[0009]
Therefore, in order to increase the internal quantum efficiency, even a large optical band gap E ₁₅ of the carrier confinement layer 15 (the x ₁₅ large), and the total reflection critical angle of the interface between the light-emitting layer 14 and the carrier confinement layer 15 is Because of the small size, the light extraction efficiency is low, and the luminous efficiency cannot be greatly increased.
[0010]
The present invention has been made in view of such problems of the conventional device, and has as its object to provide a light emitting diode with high luminous efficiency by simultaneously improving internal quantum efficiency and light extraction efficiency. And
[0011]
[Means for Solving the Problems]
In order to achieve the above object, according to the light emitting diode according to claim 1, a carrier injection layer, a light emitting layer, and a carrier confinement layer are sequentially laminated on a substrate, and the carrier injection layer and the carrier confinement layer are formed. In a light emitting diode of a double hetero structure which is formed of a material having a lower refractive index than the light emitting layer and extracts light from the carrier confinement layer side, a light extraction path portion of the carrier confinement layer is removed and the carrier confinement is reduced. An electric current is applied between the light emitting layer, the light emitting layer, and the carrier injection layer to cause the light emitting layer to emit light.
[0012]
[Action]
With the configuration described above, it is possible to eliminate reflection at the interface between the carrier confinement layer and the light emitting layer while increasing the optical band gap between the carrier injection layer and the carrier confinement layer and improving the internal quantum efficiency. Accordingly, the light extraction efficiency can be improved.
[0013]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, the invention according to claim 1 will be described in detail with reference to the accompanying drawings.
FIG. 1 is a plan view showing one embodiment of the light emitting diode according to claim 1, and FIG. 2 is a sectional view of the same, wherein 1 is a substrate, 2 is a buffer layer, 3 is a carrier injection layer, 4 is a light emitting layer, and 5 is A carrier confinement layer, 6 is an insulating layer, 7 is an individual electrode, and 8 is a common electrode.
[0014]
The substrate 1 is formed of a single-crystal semiconductor substrate such as silicon or gallium arsenide, or a single-crystal insulating substrate such as sapphire (Al ₂ O ₃ ). When a semiconductor substrate is used, a substrate whose (100) plane is turned off by 2 to 7 ° in the <011> direction is preferably used. When sapphire is used, a C-plane substrate or the like is preferably used.
[0015]
The buffer layer 2 is made of GaAs or the like and has a thickness of about 0.5 to 3 μm. On the surface of buffer layer 2, contact layer 2a having a thickness of about 0.01 to 1.0 [mu] m containing a high concentration of one conductivity type semiconductor impurity such as silicon is formed.
[0016]
The carrier injection layer 3 is made of AlGaAs or the like and has a thickness of about 0.1 to 1.0 μm. This carrier injection layer 3 also has one conductivity type.
[0017]
The light emitting layer 4 is made of AlGaAs or the like having a thickness of about 0.1 to 1.0 μm and contains a semiconductor impurity of the opposite conductivity type such as zinc.
[0018]
The carrier confinement layer 5 is made of AlGaAs or the like having a thickness of about 0.1 to 1.0 μm and has a reverse conductivity type. On the surface of the carrier confinement layer 5, a contact layer 5a having a thickness of about 0.01 to 1.0 μm and containing a high concentration of a semiconductor impurity of the opposite conductivity type such as zinc is formed. In the carrier confinement layer 5, a region L serving as a light extraction path of the light emitting element is removed. That is, the carrier confinement layer 5 in a region that is not covered with the electrode 7 on the surface portion of the island-shaped semiconductor layers 2 to 5 is removed so as not to form an interface with the light emitting layer 4 in the light extraction direction. The carrier confinement layer 5 may remove a portion serving as a light extraction region L of the light emitting element into a circular or rectangular shape.
[0019]
Here, the band gap _{E 3} of the carrier injection layer 3, the band gap _{E 4} of the light-emitting layer 4, the band gap _{E 5} of the carrier confinement layer 5 _is set to _{E 3> E 4, E 5} > E 4. Carrier injection layer 3, a material of the light-emitting layer 4, and the carrier confinement layer _{5, Al X Ga 1-X} As when using the layers of Al composition x, the carrier injection layer 3 of the Al composition x of _x 3, emitting layer 4 of Al composition x of _{x 4,} when the Al composition x of the carrier confinement layer 5 and _{x 5,} since the x _3> x _4, x 5> _{x 4,} the refractive index n of each layer, _{n 3} <N ₄ , n ₅ <n ₄ (n ₃ is the refractive index of the carrier injection layer 3, n ₄ is the refractive index of the light emitting layer 4, and n ₅ is the refractive index of the carrier confinement layer 5).
[0020]
The surface portion of each of the semiconductor layers 2 to 5 is covered with an insulating film 6 made of a silicon nitride film having a thickness of about 3000 °. The insulating film 6 contact hole C ₁ individual electrode 7 via the formed are connected to the confining layer 5 carrier, common electrode 8 through the contact hole C ₂ is connected to the carrier injection layer 3.
[0021]
In such a light emitting diode, when a current flows in the forward direction, carriers are injected from the carrier injection layer 3 into the light emitting layer 4, and light is generated by light emission recombination with majority carriers. Of the generated light, most of the light traveling toward the substrate 1 is reflected at the interface between the light emitting layer 4 and the carrier injection layer 3 and travels upward. In addition, the upward light is directly extracted without passing through the carrier confinement layer 5 because a part of the carrier confinement layer 5 is removed. With this configuration, the internal quantum efficiency can be improved by increasing the band gap of the carrier confinement layer 5 without lowering the light extraction efficiency.
[0022]
Next, a method for manufacturing the above-described semiconductor light emitting device will be described. First, a buffer layer 2, a carrier injection layer 3, a light emitting layer 4, and a carrier confinement layer 5 are sequentially laminated on a substrate 1 by MOCVD or the like. When these semiconductor layers 2 to 5 are formed, the substrate temperature is first set to 400 to 500 ° C., an amorphous gallium arsenide film is formed to a thickness of about 100 to 1000 °, and then the substrate temperature is set to 600 to 900 ° C. Then, semiconductor layers 2 to 5 having a desired thickness are formed.
[0023]
In this case, TMG ((CH ₃ ) ₃ Ga), TEG ((C ₂ H ₅ ) ₃ Ga), arsine (AsH ₃ ), TMA ((CH ₃ ) ₃ Al), TEA ((C ₂ H ₅ ) ₃ Al) is used, and silane (SiH ₄ ), hydrogen selenide (H ₂ Se), DMZ ((CH ₃ ) ₂ Zn), etc. are used as a gas for controlling the conductivity type. H ₂ or the like is used as a carrier gas.
[0024]
Next, the carrier confinement layer 5 in the region L serving as a light extraction path of the light emitting element is removed by etching. Next, semiconductor layers 2 to 5 are patterned in an island shape so that adjacent elements are electrically separated. Next, the connection between the buffer layer 2 having the contact layer formed on the surface and the common electrode 8 is removed by etching so as to be exposed from the carrier injection layer 3, the light emitting layer 4, and the carrier confinement layer 5. Such etching of the semiconductor layers 2 to 5 is performed by wet etching using a sulfuric acid-hydrogen peroxide-based etchant, dry etching using CCl ₂ F ₂ gas, or the like.
[0025]
Next, after an insulating film 6 made of a silicon nitride film or the like is formed by a plasma CVD method using silane gas (SiH ₄ ) and ammonia gas (NH ₃ ), a predetermined portion is etched with a hydrofluoric acid (HF) -based etching solution. After removal, contact holes C ₁ and C ₂ are formed. Finally, a metal film to be the individual electrode 7 and the common electrode 8 is formed by a vapor deposition method or a sputtering method, and is completed by patterning.
[0026]
【The invention's effect】
As described above, according to the light-emitting diode according to claim 1, a carrier injection layer, a light-emitting layer, and a carrier confinement layer are sequentially provided on a substrate, and the carrier injection layer and the carrier confinement layer are connected to the light-emitting layer. In a light emitting diode of a double hetero structure which is formed of a material having a lower refractive index than that of the carrier confinement layer and takes out light from the carrier confinement layer side, a light extraction path portion of the carrier confinement layer is removed, and the carrier confinement layer and the light emission are removed. Since light is emitted in the light emitting layer by passing a current between the layer and the carrier injection layer, light emitted in the light emitting layer is not reflected at the interface between the light emitting layer and the carrier confinement layer, and light emission with improved light extraction efficiency A light-emitting diode with high efficiency is obtained. Further, since there is no light reflection at the interface between the light emitting layer and the carrier confinement layer, the Al composition of the carrier confinement layer can be increased (the refractive index can be reduced), the internal quantum efficiency can be increased, and the light emission efficiency can be increased. Light emitting diodes can be manufactured.
[Brief description of the drawings]
FIG. 1 is a plan view showing one embodiment of a light emitting diode according to the present invention.
FIG. 2 is a sectional view showing one embodiment of a light emitting diode according to the present invention.
FIG. 3 is a cross-sectional view illustrating a conventional light emitting diode.
FIG. 4 is a diagram showing a relationship between a refractive index of two substances and a critical angle.
[Explanation of symbols]
1 substrate, 2 buffer layer, 3 carrier injection layer, 4 light emitting layer, 5 carrier confinement layer

Claims (1)

A carrier injection layer, a light-emitting layer, and a carrier confinement layer are sequentially laminated on a substrate, and the carrier injection layer and the carrier confinement layer are formed of a material having a lower refractive index than the light-emitting layer. In a light emitting diode having a double hetero structure for extracting light from the side, a light extraction path portion of the carrier confinement layer is removed, and a current is caused to flow between the carrier confinement layer, the light emitting layer, and the carrier injection layer to cause the light emitting layer to emit light. A light-emitting diode, characterized in that:

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