JP3237972B2 - Semiconductor light emitting device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a semiconductor light emitting device using a compound semiconductor material.

[0002]

2. Description of the Related Art In recent years, for the purpose of application to outdoor display boards, traffic signals, and the like, light-emitting diodes (LEDs) from green to yellow, lantern, and red have been actively developed. Among these, it is difficult to increase the luminance with the conventional material in a region having a wavelength shorter than 0.6 μm, such as green to yellow, and the development of a high-luminance LED using a new material has been desired.

[0003] InGaAlP-based mixed crystals, except nitride
It has the largest direct transition type energy gap in II-V compound semiconductor mixed crystals, and is attracting attention as a light emitting device material in the 0.5 to 0.6 μm band. In particular, a pn-junction LED having a GaAs substrate and a light-emitting portion of InGaAlP lattice-matched to the pn-junction LED has a higher luminance from red to green than a conventional device using an indirect transition material such as GaP or GaAsP. Light emission is possible. In order to form a high-brightness LED, it is important not only to increase the luminous efficiency but also to realize effective light extraction to the outside due to the light absorption inside the device and the relative positional relationship between the light emitting unit and the electrodes. It is.

FIG. 8 is a sectional view showing the structure of a conventional LED having an InGaAlP light emitting portion. In the figure, 81 is n-Ga
An As substrate, and n-InGa
AlP cladding layer 84, InGaAlP active layer 85, n
A double heterostructure portion (light emitting region layer) composed of an -InGaAlP cladding layer 86 is grown and formed. On the double heterostructure, a p-InGaP cap layer 82 and an n-InGaAlP current blocking layer 87 are grown and formed, and the current blocking layer 87 is processed into a circular shape by selective etching.

On the cap layer 82 and the current blocking layer 87, a p-GaAlAs current diffusion layer 88 and a p-GaAs
A contact layer 89 is formed, and the contact layer 89 is processed into a circular shape according to the shape of the current blocking layer 87. Then, a p-side electrode 91 is formed on the contact layer 89,
An n-side electrode 92 is formed on the back side of the substrate 81. The light emitting portion of this device is indicated by 93, and the current distribution is indicated by arrows.

[0006] By the way, the following points are problematic in this type of LED. First, an LED having a high luminance in a yellow region is realized by using an InGaAlP mixed crystal. However, if the wavelength is made shorter than that of yellow, the luminous efficiency is significantly reduced. This is because a method of increasing the Al composition for shortening the wavelength is usually used, but chemically active Al takes in oxygen during crystal growth, and this forms a non-emission center in the crystal. In actual LED,
In the case of yellow, a high efficiency of 1% or more is obtained, but in the case of green, the efficiency is reduced to 0.3%. As a means for avoiding this, improvement of light extraction efficiency such as providing a Bragg reflection layer below the light emitting layer has been performed, but this is not sufficient, and it is required to improve light emission efficiency at shorter wavelengths. Was.

When the light emitting layer has a multiple quantum well structure, the wavelength is shortened by the quantum level without increasing the Al composition of the light emitting layer. Therefore, the problem of Al taking in oxygen during crystal growth does not occur. Therefore, high efficiency is expected. However, in designing a multiple quantum well structure for the purpose of LEDs, the number of well layers must be increased to 20 or more (Sugawara et al., Applied Physics Lecture Meeting Spring 1993, III-13)
02). This is because injected carriers overflow from the well layer to the barrier layer, and non-radiative recombination occurs in the barrier layer. Therefore, it is necessary to increase the number of such well layers and to limit the density of carriers injected into each well to a certain level or less.

However, in a multiple quantum well structure having a large number of well layers designed from the viewpoint of the density of injected carriers, there is a serious problem that injected carriers, particularly holes, are not uniformly distributed. Holes injected from the p-type cladding layer have a short effective diffusion length due to the existence of the well layer / barrier layer interface, and are localized on the p-side portion. No effect could be obtained.

Second, in the LED shown in FIG. 8, the light generated in the light emitting portion is not absorbed in the current spreading layer 88, and the current spreads sufficiently.
A material having a band gap larger than 5, a p-type material and a sufficiently low resistivity must be selected. In _0.5 (Ga
_{In the case of 1-x} Al _x ) _0.5 (0 ≦ x ≦ 1), the value of x increases, and the resistivity particularly increases in the p-type, so that it is difficult to use the current diffusion layer 88. Therefore, GaAlAs having a lower resistivity than the n-InGaAlP cladding layer 84 and a larger band gap than the active layer 85 has been adopted as the current diffusion layer 88 even in the p-type.

However, in order to sufficiently spread the current even in GaAlAs, the film thickness must be increased to about 7 μm. When the film thickness is increased as described above, the growth time becomes longer, and the control of the growth temperature becomes difficult, so that the controllability of the composition is deteriorated. As a result, the purity of the crystal is lowered, and as a result, the morphology is reduced and light is absorbed from the light emitting portion. Further, longer growth times lead to lower productivity.

[0011]

As described above, the InGa
In a conventional LED using an AlP-based material, when a multiple quantum well structure is employed for the active layer, there is a problem that the distribution of holes becomes non-uniform and the luminous efficiency is significantly reduced. Further, in order to sufficiently spread the current in the current diffusion layer, it is necessary to increase the film thickness. However, this causes an increase in growth time, which leads to a decrease in morphology and a decrease in productivity. .

The present invention has been made in view of the above circumstances. It is an object of the present invention to uniformly inject carriers even in a multiple quantum well active layer having a large number of layers, to achieve a sufficiently high luminous efficiency, Another object of the present invention is to provide an excellent surface-emitting type semiconductor light-emitting device that is simple in method.

Another object of the present invention is to control the material and structure of the current diffusion layer, thereby significantly shortening the growth time of the current diffusion layer and improving the light extraction efficiency. A light emitting device is provided.

[0014]

In order to solve the above problems, the present invention employs the following configuration. That is,
The present invention (claim 1) provides a semiconductor substrate of a first conductivity type, and a double heterostructure formed on the semiconductor substrate and having a multiple quantum well active layer sandwiched between cladding layers of the first and second conductivity types. A structure, a second conductivity type current diffusion layer formed on the double heterostructure, a first electrode formed on a part of the current diffusion layer, and a back surface of the semiconductor substrate. A semiconductor light emitting device comprising:
The multiple quantum well active layer is characterized in that the thickness or the composition of at least one of the well layer and the barrier layer is varied in the stacking direction of the layers.

Further, according to the present invention (claim 2), a semiconductor substrate of a first conductivity type and an active layer formed on the semiconductor substrate are sandwiched between cladding layers of a first conductivity type and a second conductivity type. A double hetero structure, a second conductivity type current diffusion layer formed on the double hetero structure, a first electrode formed on a part of the current diffusion layer, and a back side of the semiconductor substrate. And a formed second electrode, wherein a superlattice structure is formed partially or entirely in the current spreading layer.

Here, a feature of the present invention (Claim 1) is that in a semiconductor light emitting device having a multiple quantum well structure as a light emitting portion, the multiple quantum well structure is directed from an electron injection side to a hole injection side. That is, each parameter of the multiple quantum well structure is set so that the quantum level of the well layer is increased, so that the injected carriers are uniformly distributed in the multiple quantum well structure. The parameters include well layer thickness, well layer composition, barrier layer thickness, barrier layer composition, and the like.

Preferred embodiments of the present invention include the following. (1) Each parameter of the multiple quantum well structure is set so that the quantum level of the well layer increases from the electron injection side to the hole injection side. (2) A part of the multiple quantum well structure is doped with an n-type impurity. (3) The multiple quantum well structure is made of InGaAlP.

The feature of the present invention (Claim 2) is that in order to shorten the growth time of the device and improve the light extraction efficiency at the interface between the device and air, the current spreads sufficiently even if the device is thin, and it is easy to use. The use of materials and structures that can control the refractive index in the current spreading layer.

Preferred embodiments of the present invention include the following. (1) The period of the superlattice formed in the current diffusion layer changes gradually. (2) The period of the superlattice constituting the current spreading layer is irregular. (3) The band gap of the material constituting the superlattice in the current diffusion layer changes gradually. (4) GaAs semiconductor substrate and In double heterostructure
Be composed of a GaAlP-based material.

[0020]

According to the present invention (claim 1), each parameter of the multiple quantum well structure is set such that the quantum level of the well layer increases from the electron injection side to the hole injection side. Thereby, carriers can be uniformly injected even in a multiple quantum well structure having a large number of layers. Therefore, it is possible to provide an excellent yellow and green surface-emitting LED having a sufficiently high luminous efficiency and a simple manufacturing method.

According to the present invention (Claim 2), a superlattice structure having an irregular mixed crystal ratio or a periodicity of the number of layers is formed in the current diffusion layer. The resistivity in the horizontal plane becomes very small, and the current spreads sufficiently even if the film thickness is reduced. Moreover, by gradually changing the mixed crystal ratio or period in the superlattice, the refractive index of the current diffusion layer can be gradually changed, and the light extraction efficiency at the interface with air can be improved. Therefore, a light-emitting element with high luminance can be manufactured in a short time.

[0022]

Embodiments of the present invention will be described below with reference to the drawings. The first to fourth embodiments described below are embodiments relating to (claim 1), and the fifth embodiment is an embodiment relating to (claim 2). (Embodiment 1) FIG. 1 shows an LE according to a first embodiment of the present invention.
It is sectional drawing which shows the element structure of D. In the figure, 11 is n-Ga
This is an As substrate, and the surface of the substrate 11 is inclined by 15 ° in the [011] direction from the (100) plane. On a substrate 11, an n-GaAs buffer layer 12, n-In _0.5 Al
_0.5 P (Si-doped, 5 × 10 ¹⁷ cm ⁻³ ) and n-GaAs
s (Si-doped, 3 × 10 ¹⁷ cm ⁻³ ) 10 pairs of Bragg reflection layers 13, n-In _0.5 (Ga _0.3 A
l _0.7 ) _0.5 P clad layer 14 (Si-doped, 5 × 10
¹⁷ cm ⁻³ ), multiple quantum well active layer 15 and p-In _0.5
A double heterojunction structure composed of a (Ga _0.3 Al _0.7 ) _0.5 P clad layer 16 (Zn-doped, 5 × 10 ¹⁷ cm ⁻³ ) is formed.

On the cladding layer 16, n-InGaAl
A P current confinement layer 17 (Si-doped, 1 × 10 ¹⁸ cm ⁻³ ) is formed in a circular shape, and p-Ga _0.8
A current diffusion layer 18 made of Al _0.2 As (Zn-doped, 2 × 10 ¹⁸ cm ⁻³ ) is formed. A p-GaAs contact layer 19 (Zn-doped, 5
× 10 ¹⁸ cm ^-3 ) is formed in a circular shape. And
A p-side electrode 21 made of Au-Zn is attached on the upper surface of the contact layer 19, and an n-side electrode 22 made of Au-Ge is attached on the lower surface of the substrate 11. Note that MOCVD was used to grow each layer, and 12 to 17 were formed in the first growth, and 18 and 19 were formed in the second growth.

In order to obtain an LED with high luminous efficiency, it is necessary to appropriately design structural parameters, here, the multiple quantum well active layer 15, and the details of the design will be described below. FIG. 2 shows an energy band diagram (the relationship between the barrier layer and the well layer) of the multiple quantum well active layer 15 employed in this embodiment. Thus, the energy band diagram has an asymmetric shape. here,
The well layer was In _0.5 (Ga _0.7 Al _0.3 ) _0.5 P, and the barrier layer was In _0.5 (Ga _0.5 Al _0.5 ) _0.5 P. The barrier layer thickness is constant at 4 nm, but the well layer thickness is 5 nm on the side closest to the n-cladding layer 14 and the p-cladding layer 16
The thickness is sequentially reduced to 4 nm and 3.5 nm on the side.

FIG. 9 shows an energy band diagram of a conventional multiple quantum well for comparison. Such a structure for increasing the luminous efficiency requires a very large number of layers. Therefore, the total thickness of the active layer is increased,
Due to the presence of a large number of heterointerfaces, uniform distribution of carriers, particularly holes, becomes extremely difficult and is localized in a part of the p-cladding layer side. Therefore, the luminous efficiency cannot be increased.

On the other hand, as shown in FIG. 2, the quantum level of holes can be set to be gradually deeper from the p side to the n side, and smooth injection becomes possible. The electron side becomes deepest at the n-side injection part, but the diffusion length is long, so that even in such a structure, the distribution is uniform. Although the quantum level, that is, the emission wavelength, differs depending on the setting when the thickness of the well layer is changed, there is no problem with the use purpose of the LED because the half value width of the emission spectrum is widened. The luminous efficiency was greatly improved by the uniform distribution of holes, and the external quantum efficiency was twice that of the conventional structure shown in FIG.

In an actual LED, a high luminance characteristic of 10 cd was obtained for green light. This is InGaAs
The brightness was about 5 times that of a double heterostructure LED using 1P as an active layer. (Embodiment 2) FIG. 3 shows an energy band diagram of a multiple quantum well active layer employed in a second embodiment of the present invention. The well layer is In _0.5 (Ga _0.7 Al _0.3 ) _0.5 P,
The barrier layer is In _0.5 (Ga _0.5 Al _0.5 ) _0.5 P. Here, the difference from the first embodiment is that the barrier layer thickness is changed together with the well layer thickness. Well layer thickness is n
5 nm closest to the cladding layer, 4 nm, 3
The barrier layer thickness is 5 nm on the side closest to the n-cladding layer, and is sequentially reduced to 4 nm and 3 nm.

As described above, since the thickness of the barrier layer is reduced on the p-clad layer side, the uniform distribution of holes is further facilitated. Further, as a feature of this embodiment, substantially the same emission wavelength can be obtained from each well layer. Therefore, L
The invention can be applied not only to EDs but also to semiconductor lasers.

According to this embodiment, high luminance characteristics of 10 cd with respect to green were obtained in the LED. In addition, with the laser, continuous oscillation at room temperature (yellow) was obtained at 595 nm. In addition, regarding the modulation of the well layer and the barrier layer, similar effects can be obtained by modulating not only the film thickness but also the composition. However, the modulation by the film thickness as described in the embodiment is easier to manufacture because the actual growth can be handled by controlling the time. Also,
A design in which only the barrier layer is modulated and gradually thinned from the n-clad layer side toward the p-clad layer side is also effective. (Embodiment 3) FIG. 4 shows an energy band diagram of a multiple quantum well active layer employed in a third embodiment of the present invention. The embodiment described here makes use of the effect that the energy band diagram depends on the impurity level of each layer when forming a heterojunction, and particularly when the level is deep, the Fermi level is pinned.

In the case of FIG. 4A, the barrier layer is undoped. Here, the well layer is made of In _0.5 (Ga _0.7 Al
_0.3 ) _0.5 P, barrier layer is In _0.5 (Ga _0.5 Al
_0.5 ) _0.5 P The heterojunction between the well layer and the barrier layer reflects the band discontinuity at the vacuum level of both,
It is shallow on the conduction band side and deeply connected on the valence band side. In this state, electrons easily overflow and holes are strongly confined, which is inconvenient for the above-described design of a multiple quantum well having a large number of layers for high efficiency.

On the other hand, when the barrier layer is doped with n-type (here, Si) as shown in FIG. 4B, a deep level called a DX center becomes a donor level, and a Fermi level on the conduction band side becomes pinning. The heterojunction between the well layer and the barrier layer shifts so as to be deeper toward the conduction band and shallower toward the valence band as shown in the figure. For this reason, even if a multiple quantum well is formed, holes are easily distributed uniformly, and luminous efficiency is improved. When only the barrier layer is doped with Si as in this embodiment, the external quantum efficiency is twice as high as that of the conventional structure. (Embodiment 4) FIG. 5 shows an energy band diagram of a multiple quantum well active layer employed in a fourth embodiment of the present invention. In this embodiment, in the multiple quantum well structure, only the well layer on the n-cladding layer side is doped with Zn. Holes are localized on the p-cladding layer side due to the multiple quantum well structure. At this time, the well layer on the n-cladding layer side where holes are depleted is intentionally doped with p-type to prepare a pair of electron recombination. Of course, it may be combined with the third embodiment.

Also in this embodiment, high efficiency was obtained, and high luminance characteristics of 5 cd for green light were obtained. this is,
Double heterostructure LED using InGaAlP as active layer
It was about three times brighter than

In each of the above embodiments, InGaAlP was used as the active layer.
It is also possible to use II-VI group compound semiconductors such as ZnSSe. Further, in the embodiment, the application example of the LED is shown. However, if consideration is given so that the quantum levels of the quantum wells are the same, the invention can be applied to a semiconductor laser. (Example 5) In order for a current to be sufficiently spread with a thin film, the resistivity in a direction from the p-type electrode to the n-type electrode in the current diffusion layer, that is, in a plane parallel to the substrate surface, is reduced. It is sufficient if the resistivity is sufficiently lower than the resistivity in the direction perpendicular to the direction. That is, a material such as a so-called two-dimensional conductor may be used. At the same time, the band gap energy in the direction perpendicular to the substrate surface needs to be larger than the band gap energy of the active layer so that the light generated in the light emitting portion is not absorbed. As a film satisfying such conditions, InGaAlP
A film composed of a superlattice using a system material can be considered.

However, if a film simply composed of a superlattice is used, the probability of total reflection at the interface between the current diffusion layer having a superlattice structure and air increases, and the light extraction efficiency decreases. Therefore, in the present invention, the refractive index of the current diffusion layer is gradually changed by gradually changing the mixed crystal ratio or period of the superlattice structure, and the light extraction efficiency at the interface with air is improved.

FIG. 6 shows an LE according to a fifth embodiment of the present invention.
It is sectional drawing which shows the element structure of D. In the figure, 31 is n-Ga
An As substrate, and on the main surface of the substrate 31, n-In
_0.5 (Ga _1-x Al _x ) _0.5 P cladding layer 34, In
_{0.5 (Ga 1-y Al y} ) 0.5 P active layer 35, p-In
_A double heterostructure portion (light-emitting region layer) composed of a _0.5 (Ga _{1 -z} Al _z ) _0.5 P clad layer 36 is formed by growth. A of each layer of InGaAlP forming a double heterostructure
The l compositions x, y, and z are set so that high luminous efficiency can be obtained.
≤ x, y ≤ z. That is, the active layer 3 serving as a light emitting layer
5, two cladding layers 34 having p and n band gaps,
A double heterojunction smaller than 36 is formed.

On the double heterostructure, p-In _0.5
(Ga _1-w Al _w ) _0.5 P and p-In _0.5 (Ga _1-v
A current diffusion layer 38 having a superlattice structure made of Al _v ) _0.5 P is formed by growth. On the current diffusion layer 38, p-In
A GaP contact layer 39a and a p-GaAs contact layer 39b are grown and formed, and these contact layers 39 are processed into, for example, a circular shape. And the contact layer 3
9, a p-side electrode 41 made of Au—Zn is formed, and an n-side electrode 42 made of Au—Ge is formed on the other main surface of the substrate 31.
Are formed. Note that the MOCVD method was used for growing each layer.

The InGa constituting the current diffusion layer 38
The Al composition w, v of each AlP layer is set to be transparent to the emission wavelength. The composition relationship with the light emitting layer is roughly
It is sufficient to set y ≦ (w + v) / 2. That is, y = 0.
5, when x = z = 1.0, the structure of the current diffusion layer 38 is (In _0.5 (Ga _0.7 Al _0.3 ) _0.5 P, 10
nm / InAlP, 10 nm), (In _{0.5
(Ga 0.7 Al 0.3) 0. 5} P, 5nm / InAlP, 5
nm) is 50 pairs, and (In _0.5 (Ga _0.7 Al _0.3 ) _0.5
P, 2 nm / InAlP, 2 nm) has a laminated structure of 100 pairs. This relationship is shown in FIG. Such a layer structure is transparent to the emission wavelength.

Although an LED having such a double hetero structure will be described below, the layer structure of the active layer portion is not essential from the viewpoint of light extraction efficiency, and the same applies to a single hetero junction structure and a homo junction structure. Can be considered.

The carrier concentration of each layer is set as shown in parentheses below. n-GaAs substrate 31 (80 μm, 3 × 10 ¹⁸ cm ⁻³ ) n-InGaAlP cladding layer 34 (1 μm, 5 × 10
¹⁷ cm ⁻³ ) InGaAlP active layer 35 (0.5 μm, undoped) p-InGaAlP cladding layer 36 (1 μm, 4 × 10
¹⁷ cm ^-3 ) p-InGaAlP current diffusion layer 38 (0.28 μm, 1
× 10 ¹⁸ cm ⁻³ ) p-InGaP contact layer 39a (0.025 μm,
3 × 10 ¹⁸ cm ⁻³ ) p-GaAs contact layer 39b (0.1 μm, 3 × 1
0 ¹⁸ cm ^-3 ).

The above structure is different from the conventional structure in that the current diffusion layer 38 is formed of a superlattice structure made of InGaAlP-based material and having a period that is gradually changed.
The advantages of this structure will be described below.

The p-InGaAlP current spreading layer 38
It is composed of a superlattice made of nGaAlP-based material.
If the InGaAlP-based material has a different Al mixed crystal ratio, the band gap energy is different, and a heterobarrier is generated at the interface between those having different Al mixed crystal ratios. In particular, current hardly flows in the p-type (K, Itaya et al., Jpn J. Appl. Phys. 5
A, 1919 (1993)).

In the direction from the p-side electrode 41 to the n-side electrode 42, carriers are easily scattered because the period of the superlattice is not constant, and the resistivity increases. For these reasons, the resistivity in the direction perpendicular to the inner surface that is horizontal to the substrate surface is higher. The ratio of the resistivity can be controlled by selecting the Al mixed crystal ratio and the period of the superlattice. Therefore, the current injected from the electrode 18 spreads sufficiently in the plane horizontal to the substrate by the p-InGaAlP current diffusion layer 38.

Light emitted from the light emitting layer is transmitted to the cladding layer 3.
After passing through 6, the light enters the current diffusion layer 38. In the current diffusion layer 38, the refractive index is different at each period of the superlattice structure and is set so as to gradually increase toward the upper surface, so that the traveling direction of light with respect to the substrate surface gradually approaches perpendicular. Therefore, even if the light has an incident angle greater than the critical angle when passing through the cladding layer 36, the light exits the current spreading layer 38 at a critical angle or less, and the probability of light to be extracted increases. Therefore, by adopting the superlattice, the reflectance increases, and light that cannot be extracted outside due to total reflection at the interface with air can be extracted outside. In addition, multiple reflections are possible depending on the reduction in loss due to the thinness and the design of the superlattice, and it is possible to further increase the light extraction efficiency as compared with the related art.

Actually, the diameter A of the p-side electrode 41 is formed to be 200 μmφ in the above-described laminated structure, and the In _0.5 (Ga
_1-y Al _y) constitute a device using _0.5 P active layer 35 0.5 Al composition y of, when a current flows by applying a voltage in the forward direction, have an emission wavelength in the 558 nm, luminous intensity 1 cd
Luminescence exceeding. This is 5 times less than the conventional device.
It was twice as bright.

As described above, according to this embodiment, InGaAl which is transparent to the emission wavelength and whose refractive index is gradually changed.
Since the current diffusion layer 38 is made of a superlattice made of a P-based material, even if the thin film has a thickness of about 0.1 to
The current injected from the substrate spreads sufficiently, and the light extraction efficiency can be increased. As a result, it is possible to produce high-brightness LEDs with a high yield in a short time.

The present invention is not limited to the embodiment described above. In the embodiment, the current I
Although the Al mixed crystal ratios w and v of nGaAlP are set to be constant, the refractive index gradually increases toward the light extraction side in the current diffusion layer if the combination is transparent to the emission wavelength. You may choose as follows. In the embodiment, the thickness of the current diffusion layer is set to 1.9 μm. However, the present invention is not limited to this. If a film thickness that is practically convenient is selected according to the resistivity ratio between the direction perpendicular to the substrate surface and the horizontal plane. Good. In order to further improve the light extraction efficiency, a GaAlAs cap layer having a low refractive index may be formed at the interface between the current diffusion layer and air.

In the embodiment, the InGaAlP-based material is used for both the double heterojunction and the current diffusion layer. However, the present invention is not limited to this, and the material combination may be such that the current diffusion layer is sufficiently transparent to the emission wavelength. I just need. The light-emitting portion may be a single-element system such as Si or a multi-element semiconductor of five or more elements, and the current spreading layer may be any combination of materials that can form a superlattice. Tribe, III-
The present invention can be applied to light emitting devices of various material types such as group V, II-VI, and chalcopyrite. In addition, various modifications can be made without departing from the scope of the present invention.

[0048]

As described in detail above, the present invention (claim 1)
According to the above, in the semiconductor light emitting device using the multiple quantum well active layer, from the electron injection side to the hole injection side,
By setting each parameter of the multiple quantum well structure so that the quantum level of the well layer becomes large, carriers can be injected uniformly even in the multiple quantum well active layer having a large number of layers, and the luminous efficiency is sufficiently high, and It is possible to realize an excellent surface-emitting type semiconductor light-emitting device with a simple method.

Further, according to the present invention (claim 2), by forming a superlattice structure in which the mixed crystal ratio or the number of layers is irregular in the current diffusion layer, a sufficient thickness can be obtained even if the film thickness is reduced. Current can be spread over the interface, and the light extraction efficiency at the interface with air can be improved. Therefore, it is possible to realize a semiconductor light emitting device with high productivity and high luminance by shortening the crystal growth time.

[Brief description of the drawings]

FIG. 1 is a sectional view showing an element structure of an LED according to a first embodiment.

FIG. 2 is a schematic diagram showing an energy band diagram of a multiple quantum well active layer adopted in the first embodiment.

FIG. 3 is a schematic diagram showing an energy band diagram of a multiple quantum well active layer employed in a second embodiment.

FIG. 4 is a schematic diagram showing an energy band diagram of a multiple quantum well active layer adopted in a third embodiment.

FIG. 5 is a schematic diagram showing an energy band diagram of a multiple quantum well active layer employed in a fourth embodiment.

FIG. 6 is a sectional view showing an element structure of an LED according to a fifth embodiment.

FIG. 7 is a schematic diagram showing an energy band diagram of a current spreading layer employed in a fifth embodiment.

FIG. 8 is a cross-sectional view showing the element structure of a conventional LED having an InGaAlP light emitting unit.

FIG. 9 is a schematic diagram showing an energy band diagram of a conventional multiple quantum well active layer.

[Explanation of symbols]

 11, 31 ... n-GaAs substrate 12 ... n-GaAs buffer layer 13 ... Bragg reflection layer 14, 34 ... n-InGaAlP cladding layer 15 ... multiple quantum well active layer 16, 36 ... p-InGaAlP cladding layer 17 ... n-InGaAlP Current confinement layer 18 p-GaAlAs current diffusion layer 19, 39b p-GaAs contact layer 21, 41 p-side electrode made of Au-Zn 22, 42 n-side electrode made of Au-Ge 35 InGaP active layer 38 ... Current diffusion layer including super lattice 39a ... p-InGaP contact layer

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-3-30486 (JP, A) JP-A-4-212479 (JP, A) JP-A-4-229665 (JP, A) JP-A-3-302 214683 (JP, A) (58) Field surveyed (Int. Cl. ⁷ , DB name) H01L 33/00

Claims (2)

(57) [Claims] 1. A semiconductor substrate of a first conductivity type, a double heterostructure portion formed on the semiconductor substrate and having a multiple quantum well active layer sandwiched between cladding layers of a first conductivity type and a second conductivity type; A second conductivity type current diffusion layer formed on the double heterostructure portion; a first electrode formed on a portion of the current diffusion layer; and a second electrode formed on a back surface of the semiconductor substrate. The multiple quantum well active layer has a well layer thickness, a well layer composition,
At least one of barrier layer thickness and barrier layer composition
A semiconductor light emitting device wherein the quantum level of the well layer is increased from the electron injection side to the hole injection side by changing the quantum level in the thickness direction . 2. A semiconductor substrate of a first conductivity type, a double hetero structure portion formed on the semiconductor substrate and having an active layer sandwiched between cladding layers of a first conductivity type and a second conductivity type; A second conductivity type current diffusion layer formed on the structure, a first electrode formed on a part of the current diffusion layer, and a second electrode formed on the back side of the semiconductor substrate; And a superlattice structure is formed in part or the whole of the current diffusion layer.