JPH04212479A - Semiconductor light-emitting device - Google Patents

Abstract

PURPOSE:To realize a semiconductor light-emitting device capable of giving out the emission of light of a high efficiency even in short-wavelength regions, such as yellow, green short-wavelength regions and the like, by a method wherein the carrier concentration and film thickness of an active layer are optimized. CONSTITUTION:In a semiconductor light-emitting device of a structure, in which a double heterostructure part constituted in such a way as to hold an active layer 13 consisting of an InGaAlP material between n-type and p-type clad layers 12 and 14 is formed on an n-type GaAs substrate 11, a first electrode 17 is formed at one part on this double heterostructure part, a second electrode 18 is formed on the surface on the opposite side to the structure part of the substrate 11 and light is led out through the upper part of the surface other than the electrode 17 formed at one part on the luminous surface on the opposite side to the surface on the side of the electrode 18 of the substrate 11, the carrier concentration of the layer 13 is set into a p-type carrier concentration of 1X10<17>cm<-3> or lower or an n-type carrier concentration of 5X10<16>cm<-3> or lower and the thickness of the layer 13 is set in the range of a thickness of 0.15 to 0.75mum.

Description

[Detailed description of the invention]

0001

[Industrial Field of Application] The present invention relates to a semiconductor light emitting device using a compound semiconductor material, and in particular InGaA in the active layer.
The present invention relates to a semiconductor light emitting device using lP-based materials.

0002

2. Description of the Related Art LEDs (light emitting diodes) are used as light sources with low power consumption, high efficiency, and high reliability in various fields such as optical communication and optical information processing. In particular, in the visible wavelength range, GaP (green) is used as a light-emitting layer material.
, GaAsP (yellow, orange, red), GaAlAs (red), and other compound semiconductors are used.

However, GaP and GaAsP are indirect transition type semiconductors, and their luminous efficiency is extremely low at about 0.5% or less even if a transparent substrate is used and the influence of absorption is eliminated. Further, although GaAlAs has an efficiency of about 8% at 660 nm, the efficiency at 635 nm is about 1% at shorter wavelengths due to the influence of indirect transition.

Considering the visibility of the human eye, GaAl
In the As system, 3cd (candela) at 660nm, 635n
m corresponds to 1 cd. On the other hand, GaP has only achieved 0.5 cd or less, and GaAsP has only 0.3 cd or less, and high brightness LEDs in the orange, yellow, and green regions have been realized.
There were strong expectations for the development of

[0005] InGaAlP mixed crystals exclude nitrides.
It has the largest direct transition type energy gap among the - group compound semiconductor mixed crystals, and is attracting attention as a material for light emitting devices in the 0.5 to 0.6 μm band. In particular, using GaAs as a substrate,
LEDs using InGaAlP, which is lattice-matched to this, have the possibility of emitting high-intensity light from green to red. However, even with this type of LED, the luminous efficiency in the short wavelength region cannot necessarily be said to be sufficiently high.

FIG. 30 shows a cross-sectional view of the element structure of a conventional LED having an InGaAlP light emitting section. 1 in the figure is n-G
aAs substrate, 2 is an n-InGaAlP cladding layer, 3 is an InGaAlP active layer, 4 is a p-InGaAlP cladding layer, 5 is a p-GaAlAs current diffusion layer, 6 is a p-Ga
As contact layer, 7 p-side electrode made of AuZn, 8
is an n-side electrode made of AuGe.

The mixed crystal composition is set so that the energy gap of the InGaAlP active layer 3 is smaller than that of the cladding layers 2 and 4, and light and carriers are transferred to the active layer 3.
It has a double heterostructure that confines the inside of the cell. Also, p
-The composition of the GaAlAs current spreading layer 5 is InGaAlP
It is set to be substantially transparent to the wavelength of light emitted from the active layer 3.

In the structure of FIG. 30, the active layer 3 has a thickness of 0.
．． 2 μm undoped In0.5 (Ga1-X A
When 1X)0.5P (x=0.4), the conductivity type was n type and the concentration was about 1 to 5 x 1016 cm-3. At this time, the emission wavelength is 565 nm (green),
The luminous efficiency was about 0.07% at DC 20 mA. Also, when x = 0.3, the emission wavelength is 585 nm (yellow), the luminous efficiency is low at about 0.4% at DC 20 mA, and the G
Characteristic advantages over aP and GaAsP systems were not necessarily observed. On the other hand, when x = 0.2, the emission wavelength is 620 nm (orange) and the luminous efficiency is about 1.5% at DC 20 mA, and Ga acts as an absorber for the emission wavelength.
Luminous efficiency exceeding that of the GaAlAs system was obtained without particularly removing the As substrate 1.

As a result of intensive studies by the present inventors regarding the cause of such compositional dependence of luminous efficiency, it was found that there is a strong correlation with the mobility in the n-conduction type. That is, the mobility decreased rapidly when the Al composition x was about 0.3. It was also observed that the donor level deepened accordingly. It was thought that the generation of deep levels in the n-conduction type caused non-radiative recombination, leading to a decrease in luminous efficiency. Furthermore, when the Al composition x of the active layer 3 is high and the emission wavelength is short, it is not possible to maintain a sufficient energy gap difference between the active layer 3 and the cladding layers 2 and 4. It was also thought that overflow became noticeable and this led to a decrease in luminous efficiency.

On the other hand, in the configuration shown in FIG. 30, the current diffusion layer 5 is provided to spread the current injected from the electrode 7, but if the current diffusion layer 5 is not provided, the spread of the injected current is reduced due to the following reasons. It becomes smaller, and the light emitting area is only near the area directly below the electrode. That is, the Al composition of the cladding layers 2 and 4 is the same as that of the active layer 3.
It is necessary to make the band gap sufficiently larger than that of the active layer 3 in order to have a band gap difference between the active layer 3 and the active layer 3. In the p-cladding layer 4, if the Al composition is large, the carrier concentration cannot be increased and the resistance becomes large. Therefore, the spread of current in the p-cladding layer 4 is small, and only the area directly below the electrode becomes a light-emitting region. In this case, in a configuration in which light is extracted from above, the electrode 7 blocks light from the light emitting region, resulting in a decrease in light extraction efficiency.

Furthermore, in semiconductor light emitting devices using InGaAlP-based materials, when the Al composition of the active layer is increased in order to obtain light emission with a shorter wavelength, the number of non-radiative centers in the active layer increases and non-radiative recombination occurs. There is a problem in that the luminous efficiency decreases due to the increase in the amount of light.

0012

[Problems to be Solved by the Invention] In this way, the conventional I
With nGaAlP-based LEDs, it has been difficult to obtain highly efficient light emission, especially in yellow and green. Furthermore, it has been difficult to achieve high brightness because current concentration occurs under the electrode in the light emitting part, resulting in a decrease in light extraction efficiency and an increase in non-radiative recombination in the active layer.

The present invention has been made in consideration of the above circumstances, and its purpose is to provide a semiconductor light emitting device capable of emitting light with high efficiency even in short wavelength regions such as yellow and green. .

Another object of the present invention is to provide a semiconductor light emitting device that can improve the current distribution in the light emitting section and improve the light extraction efficiency and brightness.

[0015]

[Means for Solving the Problems] The gist of the present invention is to
Optimize the carrier concentration and film thickness of the active layer in a semiconductor light emitting device that has an active layer made of aAlP and extracts light from a surface other than the electrode formed on a part of the light emitting surface opposite to the semiconductor substrate. By doing so, the purpose is to improve luminous efficiency.

That is, the present invention provides InGaA on a semiconductor substrate.
A double heterostructure is formed in which an active layer made of an lP-based material is sandwiched between cladding layers, a first electrode is formed on a part of the double heterostructure, and a first electrode is formed on the side of the substrate opposite to the double heterostructure. In the semiconductor light emitting device in which the electrode No. 2 is formed, the active layer is formed to be p-type with a carrier concentration of 1 x 1017 cm-3 or less or n-type with a carrier concentration of 5 x 1016 cm-3 or less, and the thickness of the active layer is 0. .15~0.75μ
It is set within a range of m.

More preferably, in the present invention, GaAs is used as the semiconductor substrate, and the plane orientation of the substrate is inclined from (100) to [011] direction by 10 to 20 degrees. A reflective layer and a transparent buffer layer are formed from the substrate side between the semiconductor substrate and the double heterostructure, and the thickness of the transparent buffer layer is set in a range of 20 to 100 μm. Among the cladding layers constituting the double heterostructure, the carrier concentration of the n-type cladding layer is set to 1 x 1016 cm-3 to 6 x 1017 cm-3.
3, and the carrier concentration of the p-type cladding layer is set to 5.
It is set in the range of ×1017 cm−3 to 2×1018 cm−3. In order to obtain this desired carrier concentration, the active layer is actively doped with one or both of p-type impurities and n-type impurities. Further, the active layer has a quantum well structure. Furthermore, a current diffusion layer made of GaAlAs is provided between the double heterostructure portion and the first electrode, and the film thickness of this current diffusion layer is set in the range of 5 to 30 μm, and the carrier concentration is set to 5×10 17 cm −3 ~5x1018cm
It is set in the range of -3. The present invention also provides a semiconductor light emitting device that extracts light from a surface other than an electrode provided on the side opposite to the substrate with respect to the active layer. ,
A transparent buffer layer of a first conductivity type formed on this reflective layer, and an InGaAl layer formed on this transparent buffer layer with an active layer sandwiched between cladding layers of a first conductivity type and a second conductivity type.
a double heterostructure made of a P-based material; a second conductivity type current diffusion layer formed on the double heterostructure;
A first electrode formed on a part of the current diffusion layer, a second electrode formed on the back side of the substrate, and a part between the double heterostructure part and the first electrode. , and a first conductivity type current blocking layer formed to face the first electrode. In this structure as well, conditions such as substrate orientation, material of each layer, carrier concentration, film thickness, etc.
The materials and ranges mentioned above are desirable.

[0018] Furthermore, the present invention provides InGaA on a semiconductor substrate.
A double heterostructure is formed in which an active layer made of an lP-based material is sandwiched between cladding layers, a first electrode is formed on a part of the double heterostructure, and a first electrode is formed on the side of the substrate opposite to the double heterostructure. In a semiconductor light emitting device in which a second electrode is formed, the substrate is made of GaAs (for example, n-type), and the plane orientation of the main growth surface of the substrate is changed from the (100) plane to the [011] direction.
It is designed to be tilted more than 100 degrees.

[0019]

[Operation] According to the present invention, the active layer made of InGaAlP is formed into a low concentration p-type (carrier concentration 1 x 1017 cm-
By using p-type with a carrier concentration of 3 or less) or n-type with a lower concentration (n-type with a carrier concentration of 5×10 16 cm −3 or less), it is possible to reduce the influence of the non-radiative recombination described above. In addition, the thickness of the active layer was optimized (0.15~0.7
5 μm), highly efficient light emission can be obtained. Further, by optimizing the inclination of the plane orientation of the substrate, the carrier concentration and film thickness of each layer, etc., it is possible to further improve the luminous efficiency.

[0020]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The details of the present invention will be explained below with reference to illustrated embodiments.

FIG. 1 is a sectional view showing a schematic structure of a semiconductor light emitting device according to a first embodiment of the present invention. In the figure, 11 is an n-GaAs substrate, and on this substrate 11 is an n-In
A double heterostructure consisting of a GaAlP cladding layer 12, a p-InGaAlP active layer 13, and a p-InGaAlP cladding layer 14 is grown. A p-GaAlAs current diffusion layer 15 is grown on the double heterostructure, and a GaAs contact layer 16 is grown on a portion of the current diffusion layer 15. Then, a p-side electrode 17 made of AuZn is formed on the contact layer 16,
An n-side electrode 18 made of AuGe is formed on the lower surface of the substrate 11.

The p-InGaAlP active layer 13 has a mixed crystal composition set so that the energy gap is smaller than that of the cladding layers 12 and 14, and forms a double heterostructure that confines light and carriers in the active layer 13. There is. The composition of the p-GaAlAs current diffusion layer 15 is set so that it is substantially transparent to the wavelength of light emitted from the active layer 13. Note that in this embodiment, the substrate side is of n-type conductivity type, but a structure in which the conductivity type is reversed can be considered in the same way.

In the structure shown in FIG. 1, the thickness of each layer,
The carrier concentration is set as follows. That is, n
-GaAs substrate 11 (250μm, 3x1018cm-
3), n-InGaAlP cladding layer 12 (1 μm, 5×10
17cm-3), p-InGaAlP active layer 13 (0.5μm, 5×10
16cm-3), p-InGaAlP cladding layer 14 (1μm, 7×10
17cm-3), p-GaAlAs current spreading layer 15 (7μm, 3×101
8cm-3), p-GaAs contact layer 16 (0.1μm, 3×10
18cm-3).

Furthermore, the p-side electrode 17 was circular with a diameter of 200 μm. The composition of the active layer 13 and cladding layers 12 and 14 is In0.5(Ga1-XAlX)0.5P
When expressed as 0.4 and 0.7, respectively, the emission wavelength is 565 nm (green) and the luminous efficiency is 0.7 at DC 20 mA.
%, which is 10 times more efficient than the conventional method.

FIG. 2 shows the dependence of luminous efficiency on carrier concentration in the active layer when the thickness of the active layer 13 is 0.5 μm. The p-type was made by Zn doping, the n-type less than 5×10 16 cm −3 was undoped, and the n-type more than 5×10 16 cm −3 was made by doping with Si. At this time, in the case of n-type, the luminous efficiency decreased as the concentration increased. This was thought to be due to an increase in non-radiative recombination and a decrease in the diffusion length of holes, which are minority carriers, due to generation at deep levels.

On the other hand, in the case of p-type, when the concentration was increased from 1×10 17 cm −3 , the luminous efficiency decreased significantly. This is Z
This is thought to be due to the formation of centers that cause non-radiative recombination due to the large amount of n doping. Also, Figure 2
The characteristic curve shown in FIG. 10 only shifted in the vertical direction even if the thickness of the active layer 13 was changed, and the range in which the luminous efficiency was high remained almost unchanged. Therefore, the active layer 13 is preferably p-type with a carrier concentration of 1×10 17 cm −3 or less or n-type with a carrier concentration of 5×10 16 cm −3 or less.

FIG. 3 shows that the carrier concentration of the active layer 13 is 5×1.
The graph shows the dependence of luminous efficiency on the active layer thickness when 016 cm-3 (p type). The thickness of the active layer 13 depends on the carrier concentration of the p-cladding layer 14, but is approximately 0.15
High luminous efficiency was obtained in the range of ~0.75 μm.

Although not shown in FIG. 3, an n-type active layer with a carrier concentration of 5×10 16 cm −3 or more has lower luminous efficiency than a Zn-doped p-type active layer at the same thickness. Moreover, the peak value of luminous efficiency was present on the thin film side. The decrease in efficiency in thin films is thought to be due to significant overflow into the cladding layer due to high injection density, since the injection carrier density in the active layer is determined by injection current density/active layer thickness. In the case where the active layer 13 is p-type, the majority carriers are holes and light emission occurs due to the injection of electrons, so it is considered that the influence of overflow is less compared to the undoped case. On the other hand, in thick films, when the diffusion length of injected carriers in the active layer becomes larger, the effect of the double heterostructure decreases, and light emission occurs due to absorption within the layer and an increase in relative non-radiative recombination at low carrier density. It is thought that a decrease in efficiency will occur. As described above, according to this embodiment, by optimizing the carrier concentration and film thickness of the active layer 13 made of InGaAlP, the influence of non-radiative recombination can be reduced and the luminous efficiency can be improved. can. Therefore, it is possible to realize a semiconductor light emitting device that can emit light with high efficiency even in short wavelength regions such as yellow and green.

In the above embodiment, the Al composition x of the active layer 13
Although we have described the case where Al is set to 0.4, other Al
Similar effects were obtained with regard to the composition. Here, regardless of the carrier concentration, changing the Al composition x will also change the emission wavelength, but as shown in Figure 4, the larger the Al composition x and the shorter the emission wavelength, the lower the emission efficiency. Become. In this case as well, the carrier concentration is 1×1017
p-type below cm-3 or carrier concentration 5 x 1016 cm
If the n-type is -3 or less, high luminous efficiency can be obtained. FIG. 5 is a sectional view showing a schematic structure of a semiconductor light emitting device according to a second embodiment of the present invention.

In the structure shown in FIG. 5, 31 is a first conductivity type semiconductor substrate, and on this substrate 31 are a first conductivity type buffer layer 32, a reflective layer 33, and a transparent buffer layer 34.
is growing and forming. On the transparent buffer layer 34 are a lower cladding layer (first conductivity type cladding layer) 35 and an active layer 3.
6 and an upper cladding layer (second conductivity type cladding layer) 37 is formed.

A second conductivity type current diffusion layer 38 is grown on the double heterostructure portion, and a second conductivity type contact layer 39 is formed on a portion of the current diffusion layer 38. Furthermore, a current blocking layer 40 of the first conductivity type is formed at a position corresponding to the contact layer 39 at the interface between the double heterostructure portion and the current diffusion layer 38 . An upper electrode 41 is formed on the contact layer 39, and a lower electrode 42 is formed on the lower surface of the substrate 31.

Next, the substrate, carrier concentration and film thickness of each layer, and other conditions in the above device will be explained. Note that this condition can be similarly applied to the first embodiment described above.

The first conductivity type semiconductor substrate 31 is n-GaAs.
The carrier concentration is 2 x 1018 cm-3 ~
It is 4 x 1018 cm-3. This is because a product with a low defect density cannot be obtained at a low concentration, and a layer made of InGaAlP formed on the substrate 31 cannot be formed satisfactorily at a high concentration. Moreover, its thickness is 50 to 450 μm. This is because thin films are difficult to handle as wafers, slight differences in lattice constant between the substrate and the layer formed on it can cause warping, and thick films are difficult to form into pellets. It depends.

The plane orientation of the n-GaAs substrate 31 is (100
) or inclined within a range of 25 degrees from (100). This is because the composition of the active layer 36 to obtain the same wavelength differs depending on the direction and angle of inclination, and the defect density also changes, which changes the crystallinity and affects the luminous efficiency. Figure 6 shows the angle of inclination of the substrate surface and 590
It is a characteristic diagram showing the relationship with the Al composition x for obtaining nanometer light emission, and from this diagram it can be seen that when the inclination angle is 7 degrees or more in the [011] direction, the Al composition x can be reduced to 0.3.

FIG. 7 is a characteristic diagram showing the relationship between the angle of inclination in the [011] direction and the half width of photoluminescence. From this figure, the smallest half width can be obtained when the inclination angle is 10 degrees to 20 degrees. Therefore, the preferred surface orientation of the substrate 31 is from the (100) direction to the [011] direction when the substrate is tilted by 7 degrees to 25 degrees, and the particularly desirable surface orientation is from the (100) direction to the [011] direction. 10 degrees ~ 2
This was the case when it was tilted at 0 degrees.

The buffer layer 32 is for preventing defects from occurring due to contamination on the substrate surface and from being transmitted to the light emitting layer, and is made of, for example, n-GaAs. Its carrier concentration is 4×10 17 cm −3 and its thickness is 0.6 μm. In this case, if the material satisfies the above objectives, n-Ga
For example, n-InGaP, n
-GaAlAs, n-InGaAlP, or n-Ga
A superlattice structure (total thickness of about 100 nm with a period on the order of atomic layers to 100 atomic layers) made of these materials including As may be used. Further, if there is no adverse effect on the light emitting layer, it is not necessary to provide the buffer layer 32.

The reflective layer 33 prevents light from reaching the substrate 31 and the buffer layer 32, which serve as light absorbers for the emission wavelength.
The purpose of this is to reflect light emitted in a direction opposite to the substrate 31. For this purpose, it is desirable to laminate two types of semiconductor layers having different refractive indexes η with respect to the emission wavelength λ to a thickness of λ/(4n).

For example, for an emission wavelength of 590 nm, n
-GaAs (η=3.94; thickness 37.5 nm), n
- By alternately stacking 20 or more layers of Ga0.3 Al0.7 As (η = 3.425; thickness 43 nm), approximately 30% of the light directed toward the substrate is absorbed before reaching the absorber such as the substrate. can be reflected, resulting in high luminous efficiency. The doping amount at this time may be set so as not to cause an increase in operating voltage due to a large voltage drop during energization, and is set to 4×10 17 cm −3 here. At this time, the n-GaAs in the reflective layer 33 is an absorber for the emission wavelength, but the reflection effect due to the effect of the refractive index is sufficient.

In addition to this, n-InGaAlP, n-I
nAlP, n-InGaP, n-InGaAsP, n-
High luminous efficiency can be obtained by similarly configuring the reflective layer using a combination of materials such as GaAlAs and n-GaAs and their compositions. Note that the reflective layer 33 may not be provided if light absorption on the substrate side does not have a large disadvantage on luminous efficiency.

The transparent buffer layer 34 is made of a transparent material having a sufficiently small absorption coefficient with respect to the emission wavelength, and contributes to effectively extracting light emission from the sides. As shown in FIG. 8, if the transparent buffer layer 34 is sufficiently thick, this will prevent light emitted toward the substrate side, or light emitted toward the opposite side of the substrate and then traveling toward the substrate again due to total reflection on the pellet surface. This is because the proportion of light that can be emitted from the side surfaces of the pellet increases before it reaches a light absorber such as a substrate.

For example, when the pellet size is 300 μm square and the emission wavelength is 590 nm, n-Ga0.3 A
By providing the l0.7 As transparent buffer layer 34 with a thickness of 30 μm, the amount of light that can be taken out from the side increases,
A luminous efficiency as high as about 30% can be obtained. This is thought to be due to the fact that light emitted near the side surfaces of the pellet can be effectively extracted within a distance range comparable to the thickness of the transparent buffer layer 34.

The doping amount of the transparent buffer layer 34 may be set so as not to cause an increase in the operating voltage due to a large voltage drop when energized, and in this case, it is set to 4×10 17 c.
It was set as m-3. In addition, the thickness of the transparent buffer layer 34 needs to be significantly larger than the size of the pellet in the area near the side surfaces of the pellet from which luminescence can be effectively extracted, and the thickness is approximately 5% or more of the pellet size. Become.

For example, in a 300 μm square chip, as shown in FIG. 9, a sufficient improvement in luminous efficiency was observed when the thickness of the transparent buffer layer 34 was set to about 15 μm or more. At this time, the thicker the transparent buffer layer 34 is, the higher the luminous efficiency can be obtained, but if the thickness is 100 μm or more, the luminous efficiency decreases due to defects caused by warpage of the wafer, in-plane distribution, etc.

By combining the transparent buffer layer 34 and the reflective layer 33, as shown in FIG.
Needless to say, total reflection on the pellet surface is repeated in a zigzag pattern, making it possible to effectively extract the light emitted from the sides. Moreover, such an effect can be obtained by using the transparent buffer layer 3.
It can also be obtained by forming 4 into a layered structure made of two or more types of materials and compositions having different refractive indexes. In this case, it is important to place the layer with a low refractive index on the substrate side.

Here, as the transparent buffer layer 34, n-
Although GaAlAs was used, n-InGaA
It goes without saying that materials transparent to the emission wavelength, such as lP and n-InAlP, have similar effects. Further, the reflective layer 33 may be included in the transparent buffer layer 34. Note that if light absorption on the substrate side does not have a large disadvantage on luminous efficiency, the transparent buffer layer 34 may not be provided.

The lower cladding layer 35 is for obtaining high luminous efficiency by confining carriers injected into the active layer 36. That is, active layer 3
When the conductivity type of 6 is n type and the carrier concentration is smaller than the injected carrier density (when the minority carrier is a hole), the active layer 3
When the conductivity type of 6 is p type and the carrier concentration is lower than the injected carrier density (when the minority carrier is an electron), or when the injected carrier density is higher than the carrier concentration of the active layer 36 (in the case of a so-called double injection state),
In either case, there is an effect of suppressing carriers injected into the active layer 36 from diffusing into the lower cladding layer 35. In this case, the lower cladding layer 35 needs to have a larger energy gap than the active layer 36.

Here, as the lower cladding layer 35, n
In the composition notation (x, y) of -In1-Y(Ga1-XAlX)YP, x=0.7 and y=0.5. This is because even when the emission wavelength of the active layer 36 is shortened to 555 nm, an energy gap that provides a sufficient carrier confinement effect can be obtained. Further, since the lattice constant matches that of the GaAs substrate 31, a good crystal can be obtained. The composition range of such a cladding layer was 0.6≦x≦1 in the above composition notation. This is the range in which n-InGaAlP has an almost indirect transition type energy gap. Since the energy gap in this region increases with the composition x, the carrier confinement effect is large when the composition x is large.

[0048] Furthermore, in InGaAlP-based materials, an ordered structure of atomic arrangement is likely to occur, and as a result, the energy gap changes even if the composition is the same. The energy gap in a random state with no ordered structure gives the largest energy gap for the same composition. A case without an ordered structure is advantageous for carrier confinement. Such a disordered structure could be easily formed by using the above-mentioned inclined orientation in the substrate 31.

On the other hand, the carrier concentration of the lower cladding layer 35 was set to 1×10 17 cm −3 . FIG. 11 shows the relationship between the carrier concentration of the n-cladding layer 35 and the luminous efficiency. As shown in this figure, from the viewpoint of luminous efficiency, the desired carrier concentration range is from 1 x 1016 cm-3 to 7 x 1017
cm-3. Due to the relationship with the resistivity of the upper cladding layer 37, current diffusion layer 38, etc., this increases the resistivity and lowers the carrier concentration in order to spread the current to areas other than directly under the electrode where light cannot be extracted by the electrode 41. What is desirable to set. Furthermore, dopants such as Si and Se form deep levels in InGaAlP according to their concentration, and carriers injected into the active layer 36 are transferred through these levels in the n-InGaAlP lower cladding layer 35 near the active layer. The reason for this was thought to be non-radiative recombination.

The lower limit of the desired carrier concentration is the minimum concentration necessary to prevent an increase in operating voltage due to a large voltage drop when current is applied, and the upper limit was determined because non-radiative recombination increases. be. In addition, a particularly desirable carrier concentration range is from 1 x 1016 cm-3 to 2 x
It was 1017 cm-3. The upper limit in this case was considered to be due to the fact that the current spreading effect becomes smaller due to lower resistance.

When the lower cladding layer 35 and the buffer layer 32 or the reflective layer 33 are directly bonded, n-InGaA
A heterojunction between lP and n-GaAs or the like is formed. At this time, when electrons are injected from the GaAs side where the energy gap is small, an excessive voltage drop is required to overcome the barrier caused by the heterojunction. Therefore, the current flows uniformly through this interface throughout the pellet, reducing the current density and preventing voltage drop, resulting in a large current spread. This is n-InG
It is highly dependent on the carrier concentration of aAlP, 1×1017
It was noticeable below cm-3.

The thickness of the lower cladding layer 35 was 1 μm. In order to have the effect of suppressing the diffusion of carriers injected into the active layer 36 to the lower cladding layer 35, it is necessary to have a thickness of about 0.5 μm or more, and to provide the effect of current spreading. This is determined by the fact that the thickness is about 2 μm or less. Further, the lower cladding layer 35 may be made of the same material and composition as the transparent buffer layer 34. That is, n-GaAlAs or the like may be used. In addition, if the carriers injected into the active layer are not suppressed to diffuse toward the substrate side, such as in a single heterostructure or a homojunction structure, but there is no significant disadvantage to luminous efficiency, the lower cladding layer 35 may not be provided. It's okay.

The active layer 36 is made of In1-Y (Ga1-X
The energy gap is determined by the composition x, y and the state of the ordered structure, and when the injected carriers are recombined radiatively, it emits light at a wavelength corresponding to the energy gap. As shown in FIG. 4, as the Al composition x increased, the emission wavelength became shorter, and the luminous efficiency decreased accordingly. This is because as the Al composition increases, the difference between the energy gap of the direct transition type and the energy gap of the indirect transition type becomes smaller, the occurrence of deep levels becomes more noticeable especially in n-type, and it becomes difficult to obtain good crystals. This is thought to be due to the following reasons.

Several methods can be considered to avoid these problems. To obtain the same wavelength, use Al as much as possible.
One way to achieve this with a low composition is to form the active layer 36 into a disordered structure. Such a disordered structure is
By using the above-mentioned inclined orientation on the substrate 31, it was possible to easily form the structure. In addition, multiple quantum well structure (
By adopting MQW), it was possible to shorten the wavelength by quantizing the energy level even if a layer with a low Al composition was used as a well layer serving as a light emitting layer.

For example, composition (x, y)=(0.3, 0.
5) is a well layer, (0.7, 0.5) is a barrier layer, each has a thickness of 2.5 to 5 nm, and has a period of 10 to 100.
By using the active layer as the active layer, the structure shown in FIG.
As shown in (0.4, 0.5) to (0.5, 0.5
) wavelength (575
~555 nm) was obtained.

In addition, it is possible to remove the lattice matching with GaAs, that is, change the lattice constant of the active layer InGaAlP to GaAs.
By making it smaller, the Al composition can be reduced. In addition, conversely, the lattice constant of the active layer InGaAlP is set to Ga
By making it larger than As, it is possible to increase the difference between the energy gap of the direct transition type and the energy gap of the indirect transition type. In both cases, the effect becomes noticeable at 0
．． The degree of lattice mismatch is about 5% or more, and the upper limit is due to an increase in non-radiative recombination due to the occurrence of dislocations. The occurrence of such a transition depends on the thickness, and a limit of about 1% appeared at about 0.3 μm.

An effective way to avoid this is to use a layer with a shifted lattice constant as a well layer of the active layer having the MQW structure. Since the thickness of the well layer is very thin, the degree of lattice mismatch that limits the occurrence of dislocation is about 3% or more, as shown in FIG. 13, and a very wide composition range can be used. Note that, as in the previous embodiment, the conductivity type of the active layer 36 is n-type of 5 x 1016 cm-3 or less, or p-type of 1 x 1017 cm-3 or less (see Fig. 2) to achieve high luminous efficiency. was gotten. In addition, the active layer 36
The thickness of the pellet is 300 μm as in the previous example.
A high luminous efficiency was obtained in the m-square size from 0.15 μm to 0.75 μm (see FIG. 3).

The upper cladding layer 37 is similar to the lower cladding layer 3.
5, the carriers injected into the active layer 36 are transferred to the active layer 3.
The purpose is to obtain high luminous efficiency by confining the light inside the 6. That is, the effect of suppressing the diffusion of carriers injected into the active layer 36 into the upper cladding layer 37 in any case when the minority carriers are holes, when the minority carriers are electrons, or in a double injection state. There is. In this case, the upper cladding layer 37 needs to have a larger energy gap than the active layer 36.

Here, p-In1-Y (Ga1-X
In the composition notation (x, y) of AlX)YP, x
=0.7, y=0.5. This is because even when the emission wavelength of the active layer 36 is shortened to 555 nm, an energy gap that provides a sufficient carrier confinement effect can be obtained. Further, since the GaAs substrate lattice constants match, a good crystal can be obtained. As shown in FIG. 14, the composition range of the p cladding layer 37 was 0.6≦x≦1 in the above composition notation. This is the range in which p-InGaAlP has an almost indirect transition type energy gap. Since the energy gap in this region increases with the composition x, the carrier confinement effect is large when the composition x is large.

[0060] Furthermore, in InGaAlP-based materials, an ordered structure of atomic arrangement is likely to occur, and as a result, the energy gap changes even if the composition is the same. The energy gap in a random state with no ordered structure gives the largest energy gap for the same composition. A case without an ordered structure is advantageous for carrier confinement. Such a disordered structure could be easily formed by using the above-mentioned inclined orientation in the substrate 31 and by performing sufficiently high doping.

On the other hand, the carrier concentration of the upper cladding layer 37 was set to 7×10 17 cm −3 . FIG. 15 shows the relationship between the carrier concentration of the p-cladding layer 37 and the luminous efficiency. As shown in this figure, from the viewpoint of luminous efficiency, the desired carrier concentration range is from 5 x 1017 cm-3 to 2 x 1018 cm-3.
cm-3. This is due to the relationship with the resistivity of the lower cladding layer 35, current diffusion layer 38, etc., and in order to spread the current to areas other than directly under the electrode where light cannot be extracted by the electrode 41, the resistivity is lowered and the carrier concentration is increased. This is because by doping as high as 5×10 17 cm −3 or more, a disordered structure can be easily formed and the energy gap can be increased, so that carrier confinement can be effectively performed.

The thickness of the upper cladding layer 37 was 1 μm. This requires a thickness of approximately 0.5 μm or more in order to have the effect of suppressing the diffusion of carriers injected into the active layer 36 to the upper cladding layer 37, and a thickness necessary to provide the effect of current spreading. This is determined by the fact that the thickness is about 2 μm or less. Further, the upper cladding layer 37 may be made of the same material and composition as the current diffusion layer 38 and the like. That is, p-GaAlAs or the like may be used. In addition, if the carriers injected into the active layer are not suppressed to diffuse to the side opposite to the substrate side in a single heterostructure or homojunction structure, but there is no significant disadvantage to luminous efficiency, the upper cladding layer It is not necessary to provide

The current spreading layer 38 is for spreading the current to areas other than directly under the electrode where light cannot be extracted by the electrode 41. The current diffusion layer 38 is made of a transparent material having a sufficiently small absorption coefficient with respect to the emission wavelength. For example, when the pellet size is 300 μm square, the electrode is circular with a diameter of about 150 μm, and the emission wavelength is 590 nm, p-Ga0.3Al0.7 A with a carrier concentration of 3 x 1018 cm-3
By providing s with a thickness of 15 μm, the current spread over the entire chip, and a luminous efficiency approximately 30 times higher than that without this was obtained.

The thickness of the current spreading layer 38 is desirably as large as possible to spread the current. As shown in FIG. 16, an effective current spreading effect was obtained at a thickness of 5 μm or more. On the other hand, when the thickness is 30 μm or more, the current spreading effect is saturated and the luminous efficiency decreases due to impurity diffusion from the upper cladding layer 37 to the active layer 36 due to long-term growth. Rather, the luminous efficiency of the device decreased.

The carrier concentration of the current diffusion layer 38 is shown in FIG.
As shown in Figure 2, in order to obtain sufficient current spread, 5 x 101
It is desirable that it is 7 cm −3 or more. On the other hand, 5×10
When doped to 18 cm-3 or more, the current spread is sufficient, but the absorption at the emission wavelength becomes large.
As a result, the luminous efficiency of the device decreased.

The Al composition x of the current diffusion layer 38 has an absorption coefficient of about 100 cm -1 or less for the emission wavelength, and is preferably as low as possible. At this time, as shown in FIG.
-Ga1-X AlX The larger the composition x of As, the smaller the absorption coefficient at a certain wavelength. For the emission wavelength region of InGaAlP, it is desirable that x be 0.6 or more. On the other hand, with GaAlAs having a large x value, it was difficult to obtain good crystallinity, and the absorption coefficient rather increased. For this reason, it was desirable that x be 0.8 or less.

At the junction between the current diffusion layer 38 and the upper cladding layer 37, a heterojunction between p-InGaAlP and p-GaAlAs is formed. At this time, holes are injected from the p-GaAlAs side where the energy gap is smaller. In this case, an excessive voltage drop was required to overcome the barrier caused by the heterojunction. Therefore, the current flows uniformly through this interface throughout the pellet, reducing the current density and preventing voltage drop, resulting in a large current spread. This largely depended on the carrier concentration of p-InGaAlP, and was noticeable below 1×10 18 cm −3 .

Here, p-Ga is used as the current diffusion layer 38.
Although AlAs was used, in addition to this, p-InGaAlP
It goes without saying that materials transparent to the emission wavelength, such as , p-InAlP, have similar effects. Further, if not providing the current diffusion layer 38 does not cause a large disadvantage to the luminous efficiency, the current diffusion layer 38 may not be provided.

The contact layer 39 is a layer for easily making ohmic contact with the electrode 41, for example, p-
GaAs was used. Specifically, as shown in FIG. 19, after a p-GaAs layer 39 is grown on a current diffusion layer 38, an upper electrode 41 is formed, and the electrode 41 and p-GaAs layer 39 are selected using a resist 44 as a mask. It was formed by etching and finally removing the resist 44.

The concentration of the contact layer 39 is preferably 1×10 18 cm −3 or more in order to easily lower the contact resistance sufficiently. Further, it was important that the thickness be 50 nm or more in order to make contact with good reproducibility. Contact layer 39 does not necessarily need to be transparent to the emission wavelength. This is because the absorption effect can be avoided by selectively removing parts other than the electrodes. In this case, there is also the advantage that damaged parts caused by alloying during electrode formation can be removed at the same time.

In this case, if the contact layer 39 is thick, the contact layer at the end of the electrode 41 will be lost during the removal process, and the electrode 41 will easily peel off. is 150nm
It is desirable that it be below the level of In addition, contact layer 3
If 9 is sufficiently thin, the absorption can be reduced, so it is not necessarily necessary to remove it at parts other than the electrodes.

Here, p-G is used as the contact layer 39.
aAs was used, but in addition to this, p-InGaP, p-
InGaAlP, p-GaAlAs, etc. may also be used. Further, the contact layer 39 may not be particularly provided, and the electrode may be directly formed on the current diffusion layer or the like.

The upper electrode 41 is made of AuZn/Au,
In addition to injecting current into the pellet, it also serves as a pad for wire bonding. It is important that the electrode 41 is effective in spreading the current throughout the pellet and does not block the light emission.

The current blocking layer 40 is for spreading the current to areas other than directly under the electrode where light cannot be extracted by the electrode 41. That is, by inserting a layer that functions to prevent current injection into a part or all of the area directly below the electrode 41, invalid current injection directly below the electrode is avoided. The current blocking layer 40 may be provided between the electrode 41 and the active layer 36. For example, between the upper cladding layer 37 and the current diffusion layer 38 as shown in FIG. 5, inside the current diffusion layer 38, and between the current diffusion layer 38 and the contact 39 as shown in FIG. Furthermore, as shown in FIG. 20(b), the contact layer 3
9 and the electrode 41. At this time,
In order to reduce the current flowing directly under the current blocking layer 40, it is desirable to be located as close to the active layer 36 as possible.

The current blocking layer 40 is made of a semiconductor having a conductivity type opposite to that of the upper cladding layer 37, such as n-GaAs.
, n-GaAlAs, n-InGaP, n-InAlP
, n-InGaAlP, etc., or high resistance semiconductors such as GaAs, InGaP, GaAlAs, InGaA
lP, InAlP, etc. can be used. In addition, a semiconductor layer having the same conductivity type as the upper cladding layer 37 and having a structure that requires an excessive voltage drop between it and a layer in contact with it to overcome a barrier due to a heterojunction, such as a p
-GaAs/p-InGaAlP, p-GaAs/p-
InAlP, p-GaAlAs/p-InGaAlP,
p-GaAlAs/p-InAlP or an insulator,
For example, SiO2, Al2 O3, Si3 N4, etc. can be used.

By making the current blocking layer 40 a material that is transparent to the emission wavelength, the emission can be extracted more effectively. That is, by providing the current blocking layer 40 that is transparent to the emission wavelength in a region including directly below the electrode 41, it is possible to reduce the reactive current directly below the electrode, and also to absorb the light emitted by the current that has passed to the area directly below the current blocking layer 40. It can be taken outside without being affected.

In this example, for example, the size of the pellet is 3
n-In1-Y (Ga1-X
In the composition notation (x, y) of AlX)YP, x=
0.7, y=0.5 as the current blocking layer 40, which was inserted between the upper cladding layer 37 and the current spreading layer 38. The concentration of the current blocking layer 40 is 1×10 18 cm −3 and the thickness is 150 nm.
It was set as m. In addition, its shape is 180 μm including the electrode 41.
The diameter of At this time, almost no current is injected directly below the electrode 41, and even if the light emission here is hidden by the electrode 41,
Luminous efficiency was not affected. In addition, the light emitted by the current flowing directly under the current blocking layer 40 was taken out to the outside through the transparent current blocking layer 40, and therefore did not become a reactive current. Note that the current blocking layer 40 may not be particularly provided if not inserting it will not cause a large disadvantage to the luminous efficiency.

[0078] The device pellets having the structure set as above, the size of the pellets being 300 μm square, and the electrodes being circular with a diameter of 150 μm, were molded with resin so that the width at half maximum was about 8 degrees, and the device was formed. By doing, In1
-Y(Ga1-XAlX)Y By setting the composition of the active layer 35 to x=0.2 and y=0.5, orange light emission with an emission wavelength of 610 nm (luminous intensity 10 candela) is achieved.
However, by setting x=0.3 and y=0.5, yellow light emission with an emission wavelength of 590 nm (luminous intensity 7 candela) becomes x
=0.4, y=0.5, the emission wavelength 5
70 nm yellow-green light emission (luminous intensity 3 candela), x = 0
．． 5, by setting y=0.5. Emission wavelength 555
A green emission (luminous intensity of 1 candela) of 1 nm was obtained in each case. In other words, by optimizing the carrier concentration and film thickness of each layer, selecting the plane orientation of the substrate, etc., it was possible to obtain high luminous efficiency even at short wavelengths.

In the second embodiment described above, an example was shown in which n-GaAs was used as the first conductivity type semiconductor substrate 31. However, p-GaAs having a different conductivity type may be used. At this time, it is necessary to reverse the conductivity type of each semiconductor layer. In this case, the thickness of each semiconductor layer is desirably set in the same way as when the n-GaAs substrate 31 is used.

On the other hand, regarding the carrier concentration, considering current spread and luminous efficiency, the optimum value is n-GaAs.
This is different from the case of the substrate 31. For the cladding layer, n-
In the case of the GaAs substrate 31, the lower cladding layer 35 is n-I
nGaAlP, upper cladding layer 37 is p-InGaAl
However, when a p-GaAs substrate is used, the upper cladding layer becomes n-InGaAlP and the lower cladding layer becomes p-InGaAlP.
It is only necessary to consider that the settings for IP and p-InGaAlP are the same.

The conductivity types of the buffer layer 32, reflective layer 33, transparent buffer layer 34, current diffusion layer 38, contact layer 39, and current blocking layer 40 may be reversed, and the carrier concentrations may be set the same. Regarding the active layer 36, settings similar to those for n-GaAs are desirable regardless of the conductivity type of the substrate.

The advantages of using a p-type conductivity type substrate are as follows:
Compared to the n-type case, the current spread can be expanded more easily. This is n-I compared to p-InGaAlP and p-GaAlAs in the above composition range.
With nGaAlP and n-GaAlAs, it is easier to obtain a layer with higher mobility and lower resistivity for the same composition and carrier concentration, and by placing this layer on the upper electrode side with respect to the active layer, the current spreads more easily. This is because the light emitting section can be easily enlarged. In particular, when n-GaAlAs is used for the current diffusion layer 38, the resistivity is 1/2 of that when p-GaAlAs is used, so as shown in FIG. Even when the ratio was reduced to 1/2, approximately the same current spread and, as a result, the luminous efficiency was obtained. This was effective in shortening crystal growth time and improving productivity.

Furthermore, as the first conductivity type semiconductor substrate 31, n
When -GaAs or p-GaAs is used, the substrate acts as a light absorber for the emission wavelength, as detailed in the Examples. Since the light absorbed by the substrate 31 cannot be extracted to the outside, approximately 1/2 of the light emitted from the active layer 36 does not contribute to the light emission efficiency. As a method for extracting this, as shown in FIG. 22, it is effective to remove the substrate 31 and the buffer layer 32 that serves as an absorber for the emission wavelength.

In this case, in order to maintain the mechanical strength of the pellet, the thickness of the transparent buffer layer 34 and current diffusion layer 38 may be set thick, and the wafer thickness after substrate removal may be set to approximately 50 μm or more. is important. At this time, the lower electrode 42 is formed on the transparent buffer layer 34. Lower electrode 42
Alternatively, the light emitted to the bottom can be taken out to the outside without being absorbed by a reflecting plate formed below this during assembly.

Furthermore, in the explanation up to this point, examples in which n-GaAs and p-GaAs are used as the first conductivity type semiconductor substrate 31 and in which these are removed have been shown. In addition, GaP, ZnS
Semiconductors such as E, ZnS, Si, and Ge, and mixed crystals made of these including GaAs may be used as the substrate. In this case, the above-mentioned concept of conductivity type applies as is, and these conductivity types may be n-type or p-type. GaP
, ZnSe, ZnS, GaAsP, InGaP, etc. as a substrate has the advantage that the substrate can be made transparent to the emission wavelength and there is no need to remove the substrate as described above.

However, in these cases, unlike GaAs, lattice matching between the active layer material and the substrate may not be achieved. In this case, it is important to suppress the generation of dislocations in the active layer and reduce non-radiative recombination by providing a gradient lattice constant layer of the same conductivity type as the substrate. In this case, the lattice constant of the lattice constant gradient layer is gradually changed from the lattice constant of the substrate to the lattice constant of the active layer from the substrate side toward the active layer side. At this time, the material of the gradient lattice constant layer is preferably a material transparent to the emission wavelength, such as InGaAlP. When the lattice constant of the active layer is the same as that of GaAs, by forming GaAlAs as a transparent buffer layer on the lattice constant gradient layer, a layer with the same lattice constant as the active layer is formed, which reduces dislocations. It is also effective for Figure 2 shows the configuration in this case.
Shown in 3. In the figure, reference numeral 51 indicates a transparent substrate, and reference numeral 52 indicates a gradient lattice constant layer.

Although Si and Ge are opaque to the emission wavelength, they are desirable substrate crystals from the viewpoint of mass production and productivity because they can provide substrate crystals of good quality. In the case of Si, lattice matching cannot be achieved between the active layer material and the substrate. It is important to suppress the generation of dislocations in the active layer and reduce non-radiative recombination by providing a gradient lattice constant layer of the same conductivity type as the substrate. In this case, the lattice constant of the lattice constant gradient layer is gradually changed from the lattice constant of the substrate to the lattice constant of the active layer from the substrate side toward the active layer side. At this time, the material of this lattice constant gradient layer is GaP, AlP, GaAs.
, InP, etc., or a superlattice is used. In the case of Ge, there is no problem with lattice matching.

In either case, forming GaAlAs as a transparent buffer layer is effective in reducing dislocations. Furthermore, as in the case of GaAs, it is effective to remove these substrates after crystal growth.

Even when crystals other than n-GaAs are used for the substrate, the effect of current spreading by the current diffusion layer, the effect of reducing reactive current by the current blocking layer, the carrier concentration and thickness of the active layer, cladding layer, etc. The effects on the luminous efficiency, such as the degree of disorder and the degree of disorder, are the same as in the embodiments described above.

FIG. 24 is a sectional view showing the element structure of a semiconductor light emitting device according to a third embodiment of the present invention. 6 in the diagram
1 is an n-GaAs substrate, and the main surface of this substrate 61 is (
100) is inclined by 15 degrees in the [011] direction. On the substrate 61, n-In0.5 (Ga1-X1AlX1)0.5P
Cladding layer 62In0.5 (Ga1-X2AlX2)
0.5 P active layer 63p-In0.5 (Ga1-X3
AlX3)0.5P cladding layer 64 (Zn doped), p-In0.5Ga0.5P intermediate bandgap layer 65, and p-GaAs contact layer 66 are sequentially laminated. And contact layer 66
A p-side electrode 67 made of AuZn is formed on the substrate 6.
An n-side electrode 68 made of AuGe is formed on the back surface of 1.

FIG. 25 is a schematic diagram showing the current distribution and light emitting region within the light emitting element shown in FIG. 24. In the same figure, the current distribution 72 within the light emitting element is indicated by broken line arrows, and the light emitting region 7
1 is indicated by a nodal dot. The Al composition of each InGaAlP layer is set to X2≦ to obtain high luminous efficiency.
Make sure that X1, X2≦X3 is satisfied. For example, X1=
Let X3=0.7 and X2=0.3.

In the structure shown in FIGS. 24 and 25,
The thickness and carrier concentration of each layer are set as shown in parentheses below. That is, an n-GaAs substrate 61 (80 μm, 3×10 18 cm
3) n-InGaAlP cladding layer 62 (1 μm, 5×
1017 cm-3) InGaAlP active layer 63 (0.5 μm, undoped)
p-InGaAlP cladding layer 64 (2 μm, 2×10
18cm-3) p-InGaP intermediate bandgap layer 65 (0.05μ
m, 1 x 1018 cm-3). Furthermore, the p-side electrode 67 was circular with a diameter of 200 μm.

The structure of this embodiment differs from the conventional structure in that the main growth surface of the GaAs substrate 61 on which the element structure is laminated is (10
This is because the surface is inclined by 15 degrees in the [011] direction from the 0) surface, and the advantages of this structure will be explained below.

In the conventional structure, that is, the structure in which the (100) plane is used as the main growth surface of the GaAs substrate 61, p-In
The current spread in the GaAlP cladding layer 64 is small because the p-cladding layer 64 has a high resistivity. p-cladding layer 6
It is possible to increase the current spread by increasing the film thickness of No. 4, but this InGaAlP material system has poor thermal conductivity, and increasing the film thickness deteriorates the crystal structure and may also have an adverse effect on the upper layer. It is not desirable because it appears. Furthermore, the growth rate of InGaAlP-based materials is limited due to crystal quality, and when growing a thick film, the growth time must be extended. This means that p-
When a highly diffusible impurity is used as the impurity in the cladding layer 64, the impurity diffuses into the active layer 63, causing deterioration of device characteristics. Therefore, p-InGaAl
It is difficult to grow the P cladding layer 64 thickly.

[0095] Furthermore, in this InGaAlP-based material, when doped with Zn, its activation rate is low;
It is difficult to obtain high carrier concentrations. In addition to this,
Zn is a highly diffusible impurity, and high concentration doping causes it to diffuse into the active layer 63, causing deterioration in device characteristics. The cladding layers 62 and 64 have a large band gap difference with the active layer 63, and the active layer 63
It is desirable to confine light and carriers to
For this purpose, the Al composition of the cladding layers 63 and 64 must be increased. However, when Zn is used as an impurity in the p-cladding layer 64, there is a problem that as the Al composition increases, the carrier concentration decreases and the resistance increases. Therefore, in the conventional structure, depending on the element structure on the GaAs substrate 61, the injection current could not be expanded, and light was emitted only directly below the electrode, resulting in very low light extraction efficiency.

On the other hand, as shown in FIGS. 24 and 25, the main growth surface of the GaAs substrate 61 is changed from the (100) plane to [
011], even if the p-cladding layer 64 has a high Al composition, Zn can be doped at a high concentration, resulting in a low-resistance p-InGaAlP cladding. Layer 64 may be formed.

FIG. 26 shows InG with an Al composition of 0.7.
Saturation hole concentration due to Zn for aAlP and GaA
The relationship between the angle of inclination of the s-substrate from the (100) plane to the [011] direction is shown. This figure shows that as the tilt angle increases, the saturated hole concentration increases, especially at a tilt angle of 5 degrees or more.
A sufficient saturated hole concentration of 0.018 cm-3 or more was obtained,
It has been found that a sufficient luminous intensity of three times or more can be obtained compared to that using a non-tilted substrate.

Therefore, by using the element structure of this embodiment, the current injected from the electrode 67 is transferred to a low resistance p-
The light can be spread over a wide area in the InGaAlP cladding layer 64, and light can be emitted in a wide area other than directly under the electrode 67, as shown by the current distribution in FIG. (1
GaA tilted 15 degrees from the 00) plane in the [011] direction
The p-InGaAlP cladding layer 64 of the device formed on the s-grown main surface and the p-InGaAlP cladding layer of the device formed on the conventional (100)-plane GaAs growth main surface have the same Al composition and the above carrier concentration. The resistivity is
0.2Ω・cm on a 15 degree inclined surface, (100
) surface is 2Ω・cm.

Furthermore, when the active layer 64 of the devices fabricated in this example and the conventional example was evaluated by photoluminescence (PL) etc., it was found that the light emitting efficiency was higher in the element fabricated in this example. FIG. 27 shows the relationship between the PL emission intensity and the tilt angle when the Al composition of the active layer is 0.3. In this way, as the tilt angle increases, the PL emission intensity increases, and at 5 degrees or more, a sufficient emission intensity of 3 times or more was obtained. Further, FIG. 28 shows cases where the inclination angle of the dependence on Al composition and PL emission intensity is 0 degree, that is, the (100) plane, and 15 degrees. The effect of increasing the emission intensity due to the tilted substrate was observed in a wide range of Al compositions.

From this reason as well, it is possible to increase the brightness in this embodiment. In addition, from the (100) plane, [01
1] InGa grown on a GaAs substrate tilted in the direction
It is known that AlP mixed crystals suppress the generation of natural superlattices and have a larger band gap than those grown on the (100) plane. This band gap increasing effect makes it possible to use an active layer with a smaller Al composition in order to obtain a certain emission wavelength, making it possible to achieve high brightness in a short wavelength region.

[0101] In0.5 (Ga1
-X2AlX2)0.5 Al composition X2 of P active layer 63
When an element was constructed using 0.3 and a voltage was applied in the forward direction to flow a current, the current distribution was as shown in Figure 25, and p
Light emission having a peak wavelength of 600 nm was obtained from a wide area on the surface of the device excluding the side electrode 67. In addition, InGaAlP
A similar effect can be obtained by providing a distribution of carrier concentration in the growth direction in the Zn-doped p-cladding layer on the light emitting section constructed of the above structure.

As described above, according to this embodiment, by using the main growth plane of the GaAs substrate 61 that is inclined by 15 degrees from the (100) plane toward the [011] direction, the light emitting portion InG
The resistivity of the p-InGaAlP cladding layer 64 on the aAlP active layer 63 can be lowered, and the current injected from the electrode 67 can be spread over a wide range in the p-cladding layer 64, allowing light to be emitted in areas other than directly under the electrode. You can expand your area. Therefore, it is possible to improve the efficiency of extracting light from around the electrodes, and thereby it is possible to increase the brightness.

FIG. 29 is a sectional view showing the element structure of a semiconductor light emitting device according to a fourth embodiment of the present invention. In addition,
Components that are the same as those in FIG. 24 are given the same reference numerals, and detailed explanation thereof will be omitted.

This embodiment differs from the third embodiment described above in that the p-InGaAlP cladding layer is composed of two layers with different Al compositions. That is, as the first p-cladding layer 64 adjacent to the active layer 63, p-In0.5 with a high Al composition necessary for confining light and carriers is used.
(Ga0.3 Al0.7 )0.5 P layer is formed, and a second p-In0.5 (Ga0.6 A
l0.4)0.5 A P cladding layer 73 is formed, and an intermediate bandgap layer 6 is formed on this second p-cladding layer 73.
5 and a contact layer 66 are formed.

[0105] The first p- cladding layer 64 and the second p- cladding layer 64
The film thickness and carrier concentration of the cladding layer 73 are 1 μm for the first p-cladding layer 64 and 2×10 17 cm −
3, the second p-cladding layer 73 is 3 μm, 6×101
It is 8 cm-3. The other layer structures were the same as those in the third example.

[0106] This embodiment differs from the conventional structure in the first
A second p-cladding layer 73 having a lower Al composition than that of the p-cladding layer 64 is formed on the p-cladding layer 64. As mentioned above, the carrier concentration of Zn-doped p-InGaAlP is highly dependent on the Al composition, and when the amount of Zn supplied is constant, the carrier concentration is lower and the resistivity is higher as the Al composition is higher. Become. Therefore, in the configuration of this embodiment, the first p-cladding layer 6
4 (Al composition 0.7), the second p-cladding layer 73
(Al composition 0.4) allows the resistivity to be lower.

In addition, the main growth surface of the GaAs substrate 61 is
By using a plane inclined by 15 degrees in the [011] direction from the 100) plane, the carrier concentration can be higher and the resistivity can be lowered. The difference in resistivity of layer 73 can be made larger. In this way, the p-cladding layers 64, 73
Since the distribution of resistivity can be widened within the electrode 67, the current injected from the electrode 67 can be spread over a wide area in the p-cladding layer 73, which has low resistivity, and light emission is possible in a wide area other than directly under the electrode. .

First p-cladding layer 6 used in this example
4 and the second p-cladding layer 73, the resistivities at the above carrier concentrations are 2 Ω·cm and 0.2 Ω·cm, respectively. Because of this large difference in resistivity, the current injected from the electrode is spread over a wide area in the second p-cladding layer 73 before reaching the first p-cladding layer 64. Therefore, the current distribution is similar to that of the third embodiment, and it is possible to obtain light from a wide area on the device surface excluding the p-side electrode. Furthermore, the device made with the laminated structure of this example emitted light having a peak wavelength of 600 nm as in the third example. In the fourth embodiment, the composition of the second p-cladding layer 73 is In0.5 (Ga0.6 Al
0.4) 0.5 P, but the Al composition is lower than that of the first p-cladding layer 64, which makes it possible to lower the resistance, and has a bandgap energy larger than that of the active layer 63. If so, the composition is not limited to this. A second p-cladding layer 73 with the same composition
A method of increasing the carrier concentration may also be used. Further, the second p-cladding layer 73 is not limited to one layer, and any InGaAlP layer having an Al composition smaller than that of the first p-cladding layer 64 and larger than the bandgap of the active layer 63 can be used. A similar effect can be obtained in a structure in which two or more different layers are laminated. Furthermore, the first p-cladding layer 6
A composition gradient layer may be formed in which the Al composition is gradually reduced from No. 4.

[0109] In addition, in the third and fourth embodiments, GaA
Although the main growth plane of the s-substrate was tilted from the (100) plane by 15 degrees in the [011] direction, the present invention is not limited to this tilt angle; Needless to say, the same effect can be obtained if there is. Furthermore, the layer structure of the light emitting section including the active layer is not limited to a double heterostructure, but may be a single heterostructure or a homojunction. In addition, various modifications can be made without departing from the gist of the present invention.

[0110]

As described in detail above, according to the present invention, the active layer is formed on a semiconductor substrate and is made of InGaAlP, and other than the electrode formed on a part of the surface opposite to the semiconductor substrate. In a semiconductor light emitting device that extracts light from the surface of the substrate, by making the active layer made of InGaAlP a low concentration p-type and having a thickness of 0.25 μm to 0.75 μm, highly efficient light emission can be achieved even at short wavelengths. A possible semiconductor light emitting device can be realized. Also, the main surface of the board is (100)
By tilting the surface by 5 degrees or more in the [011] direction, the current distribution in the light emitting part can be improved, and it becomes possible to realize a semiconductor light emitting device that can improve light extraction efficiency and brightness.

[Brief explanation of the drawing]

FIG. 1 is a cross-sectional view showing the element structure of a semiconductor light emitting device according to a first embodiment of the present invention;

[Fig. 2] Characteristic diagram showing the relationship between carrier concentration and luminous efficiency,

FIG. 3 is a characteristic diagram showing the relationship between active layer thickness and luminous efficiency;

[Figure 4] Characteristic diagram showing the relationship between wavelength and luminous efficiency,

[Figure 5
]A cross-sectional view showing a device structure for explaining a second embodiment of the present invention;

FIG. 6 is a characteristic diagram showing the relationship between the tilt angle of the substrate, the Al composition, and the half width;

FIG. 7 is a characteristic diagram showing the relationship between the tilt angle of the substrate, the Al composition, and the half width;

FIG. 8 is a cross-sectional view for explaining the action of the transparent buffer layer;

FIG. 9 is a characteristic diagram showing the relationship between the thickness of the transparent buffer layer and luminous efficiency;

FIG. 10 is a cross-sectional view for explaining the action of the transparent buffer layer;

FIG. 11 is a characteristic diagram showing the relationship between the carrier concentration of the n-cladding layer and the luminous efficiency;

FIG. 12 is a characteristic diagram showing the relationship between well layer thickness and wavelength;

FIG. 13 is a characteristic diagram showing the relationship between lattice mismatch of the well layer and luminous efficiency;

FIG. 14 is a characteristic diagram showing the relationship between the Al composition of the cladding layer and the energy gap;

FIG. 15 is a characteristic diagram showing the relationship between cladding layer carrier concentration and luminous efficiency;

FIG. 16 is a characteristic diagram showing the relationship between the film thickness of the current diffusion layer and luminous efficiency;

FIG. 17 is a characteristic diagram showing the relationship between the carrier concentration of the current diffusion layer and the luminous efficiency;

FIG. 18 is a characteristic diagram showing the relationship between the absorption coefficient of the current diffusion layer and the emission wavelength;

FIG. 19 is a cross-sectional view showing the upper electrode forming process;

[Figure 20]
A cross-sectional view showing the formation position of the current blocking layer,

FIG. 21 is a characteristic diagram showing the relationship between the film thickness of the current diffusion layer and the luminous efficiency, which is for explaining a modification of the present invention;

FIG. 22 is a cross-sectional view of an element structure showing an example in which the substrate is removed in a modified example of the present invention;

FIG. 23 is a cross-sectional view of an element structure showing an example using a transparent substrate in a modified example of the present invention;

FIG. 24 is a cross-sectional view showing the element structure of a semiconductor light emitting device according to a third embodiment of the present invention;

FIG. 25 is a schematic diagram showing the current distribution and light emitting region within the device in the third example;

FIG. 26 is a characteristic diagram showing the relationship between the tilt angle and the saturated hole concentration of Zn;

FIG. 27 is a characteristic diagram showing the relationship between tilt angle and PL emission intensity;

FIG. 28 is a characteristic diagram showing the relationship between Al composition and PL emission intensity,

FIG. 29 is a cross-sectional view showing the element structure of a semiconductor light emitting device according to a fourth embodiment of the present invention;

FIG. 30 is a cross-sectional view showing the element structure of a conventional semiconductor light emitting device;

[Explanation of symbols]

11,31...n-GaAs substrate, 12,35...n-In
GaAlP cladding layer, 13,36...p-InGaAl
P active layer, 14,37...p-InGaAlP cladding layer, 15,38...p-GaAlAs current spreading layer, 16,3
9... p-GaAs contact layer, 17, 41... p-side electrode, 18, 42... n-side electrode, 32... n-GaAs buffer layer, 33... reflective layer, 34... n-GaAlAs transparent buffer layer, 40... n- GaAs current blocking layer.

Claims (8)

[Claims] Claim 1: InGa formed on a semiconductor substrate.
A double heterostructure portion in which an active layer made of an AlP-based material is sandwiched between cladding layers, a first electrode formed on a part of the double heterostructure portion, and a first electrode formed on the side opposite to the double heterostructure portion of the substrate. the active layer is p-type with a carrier concentration of 1×10 cm or less or n-type with a carrier concentration of 5×10 cm or less,
A semiconductor light emitting device characterized in that the thickness of the active layer is set in a range of 0.15 to 0.75 μm. 2. The substrate is made of GaAs, and the plane orientation of the substrate is 10 to 20 in the (100) to [011] direction.
2. The semiconductor light emitting device according to claim 1, wherein the semiconductor light emitting device is tilted by a certain degree. 3. A reflective layer and a transparent buffer layer are formed from the substrate side between the substrate and the double heterostructure, and the thickness of the transparent buffer layer is set in a range of 20 to 100 μm. The semiconductor light emitting device according to claim 1, characterized in that: 4. Among the cladding layers constituting the double heterostructure, the carrier concentration of the n-type cladding layer is set to 1×
The carrier concentration of the p-type cladding layer is set to 1016 cm-3 to 7×1017 cm-3, and the carrier concentration of the p-type cladding layer is 5×1017.
2. The semiconductor light emitting device according to claim 1, wherein the semiconductor light emitting device is set in a range of cm-3 to 2 x 1018 cm-3. 5. The semiconductor light emitting device according to claim 1, wherein the active layer has a quantum well structure. 6. A current spreading layer made of GaAlAs is formed between the double heterostructure portion and the first electrode,
The thickness of this current diffusion layer is set in the range of 5 to 30 μm,
And the carrier concentration is 5 x 1017 cm-3 to 5 x 101
2. The semiconductor light emitting device according to claim 1, wherein the semiconductor light emitting device is set in a range of 8 cm<-3>. 7. A reflective layer of a first conductive type formed on a semiconductor substrate of a first conductive type, a transparent buffer layer of a first conductive type formed on the reflective layer, and a transparent buffer layer of a first conductive type formed on the transparent buffer layer. a double heterostructure made of an InGaAlP-based material in which an active layer is sandwiched between cladding layers of a first conductivity type and a second conductivity type; and a current diffusion layer of a second conductivity type formed on the double heterostructure. A first electrode formed on a part of the current diffusion layer, a second electrode formed on the back side of the substrate, and a portion between the double heterostructure portion and the first electrode. 1. A semiconductor light emitting device comprising: a first conductivity type current blocking layer formed to face a first electrode; 8. InGa formed on a semiconductor substrate.
A double heterostructure portion in which an active layer made of an AlP-based material is sandwiched between cladding layers, a first electrode formed on a part of the double heterostructure portion, and a first electrode formed on the side opposite to the double heterostructure portion of the substrate. the substrate is made of GaAs, and the main growth surface of the substrate has a plane orientation of (1
00) A semiconductor light emitting device, the semiconductor light emitting device is inclined by 5 degrees or more in the [011] direction from the 00) plane.