JPH06209139A - Semiconductor laser - Google Patents

Abstract

PURPOSE:To provide a semiconductor laser of a structure, wherein a recombination current in light guide layers under a high-temperature environment is inhibited leaving as an optical confinement coefficient is held without reducing the coefficient and an oscillation takes place in a low threshold current over a wide range covering from room temperature to a high temperature. CONSTITUTION:An N-type light guide layer 16 and a P-type light guide layer 18 having a conduction band lower end Ec higher than that of barrier layers 10 with an electronic energy as a reference are respectively provided on one side of the sides of a quantum well active layer 14 formed by laminating alternately the burrier layers 10 and well layers 12 and on the other side of the layer 14 in such a way as to hold the layer 14 between them and an N-type clad layer 20 and a P-type clad layer 22 are respectively provided on the outsides of these layers 16 and 18. A hole blocking layer 24, whose valence band upper end Ev is higher than that of the layer 16 with the energy of a hole as a reference, is provided at the boundary between the layers 14 and 16.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a semiconductor laser device, and more particularly to a quantum well laser device used as a light source for optical communication and optical interconnection. Semiconductor laser devices are used for information transmission through optical fibers, but in order to expand the applicable area from conventional trunk lines to optical subscriber lines, optical LANs (Local Area Networks), etc. There is a demand for a semiconductor laser device having a low oscillation threshold current in a wide temperature range up to a high temperature environment.

[0002]

2. Description of the Related Art Conventionally, in order to realize a semiconductor laser device having a low threshold current characteristic, a quantum well structure has been introduced into an active layer to separate optical confinement from carrier confinement.
A quantum well laser device using an H (Separate-Confinement Heterostructure) structure is used.

FIGS. 7A and 7B are energy band diagrams showing a band structure at the time of current injection in a quantum well laser device having a typical SCH structure. In FIG. 7A, an n-type light guide layer 86 and a p-type light guide layer 88 are provided with a quantum well active layer 84 in which barrier layers 80 and well layers 82 are alternately stacked. Also, these n-type and p
Outside the type optical guide layers 86 and 88, an n-type cladding layer 90 and a p-type cladding layer 92 having a bandgap energy Eg larger than the bandgap energy Eg of the n-type and p-type optical guide layers 86 and 88, respectively. It is provided.

Here, the well layer 82 of the quantum well active layer 84
Barrier layer 80 of the quantum well active layer 84 and the n-type and p-type light guide layer 86 having a bandgap energy Eg intermediate between the bandgap energy Eg of the n-type and p-type cladding layers 90 and 92. ,
88 is provided because the carrier is the barrier layer 80 and the well layer 8.
2 is confined in the well layer 82 due to the difference in bandgap energy from the n-type and n-type and p-type optical guide layers 86, 8
This is for confining due to the difference in refractive index between the n-type and p-type clad layers 90 and 92. In this way, by separating the confinement of light from the carriers, the confinement coefficient Γ of light showing the ratio of the light energy confined in the well layer 82 is increased, thereby decreasing the gain coefficient required for laser oscillation, It is possible to reduce the threshold current.

[0005]

In such a quantum well laser device having an SCH structure, the threshold current near room temperature is mainly determined by the optical confinement of the quantum well active layer 84 in the well layer 82. However, under a high temperature environment, the carriers in the well layer 82 overflow into the barrier layer 80 and further into the n-type and p-type optical guide layers 86 and 88, and recombination occurs in these layers. Recombination currents in layers other than the well layers 82, especially n-type and p-type optical guide layers 86 having a large volume,
The carrier recombination current at 88 is a major factor and raises the threshold current.

The conventional SCH structure in which the barrier layer 80 shown in FIG. 7A and the n-type and p-type optical guide layers 86 and 88 have the same band gap energy, and the carriers in the well layer 82 are n-type and p-type. In order to suppress the overflow to the type optical guide layers 86 and 88, a band lineup in which the band gap energy difference between the well layer 82 and the barrier layer 80 and the n-type and p-type optical guide layers 86 and 88 becomes large. If so, the light confinement in the well layer 82 becomes small and the threshold current at room temperature rises.

That is, in the normal SCH structure, the well layer 82 of the quantum well active layer 84, the barrier layer 80, the n-type and the p-type.
When the band gap energy difference between the optical guide layers 86 and 88 is reduced to increase the light confinement coefficient Γ, the carriers that recede into the n-type and p-type optical guide layers 86 and 88 recombine, resulting in high temperature. On the contrary, if the bandgap energy difference is increased to confine carriers in the well layer 82, the optical confinement in the well layer 82 becomes small and the threshold current at room temperature increases. There was a problem that would rise.

Further, instead of the n-type light guide layer 86 and the p-type light guide layer 88 of FIG. 7A, the refractive index changes stepwise or continuously as shown in FIG. 7B. GRIN having n-type light guide layer 94 and p-type light guide layer 96
A quantum well laser device having a (Graded Index) -SCH structure has also been manufactured. However, also in this quantum well laser device having the GRIN-SCH structure, when the band gap energy Eg of the n-type and p-type optical guide layers 94 and 96 is increased from near the boundary with the quantum well active layer 84, carriers overflow. Although the region can be suppressed in the vicinity of the quantum well active layer 84, the refractive index suddenly becomes small, so that the confinement of light in the well layer 82 of the quantum well active layer 84 is reduced. On the contrary, if the change in the bandgap energy Eg is relaxed, the situation is normal SCH.
It becomes the same as the case of the structure.

Therefore, in the conventional quantum well laser device, whether the ordinary SCH structure or the GRIN-SCH structure is adopted, the light is confined in the quantum well active layer 84 and the high temperature environment is obtained. It was difficult to simultaneously confine carriers in the vicinity of the well layer 82.
Therefore, the present invention suppresses the recombination current of carriers in the optical guide layer under a high temperature environment while keeping the optical confinement coefficient Γ without decreasing, and provides a low threshold current in a wide range from room temperature to high temperature. An object is to provide a semiconductor laser device that oscillates.

[0010]

FIG. 1 is an energy band diagram showing the band structure of a quantum well laser device for explaining the principle of the present invention. Barrier layer 10 and well layer 12
The n-type optical guide layer 16 is provided on one side of the quantum well active layer 14 in which and are alternately stacked, and the energy level Ec (hereinafter,
P type optical guide layer 1 having a conduction band lower end Ec higher than the conduction band lower end Ec) based on electron energy.
8 are provided. That is, this p-type light guide layer 18
Is the band offset ΔE of the conduction band from the barrier layer 10.
c is made of a material that is positive with respect to the energy of the electron.

An n-type cladding layer 20 having a bandgap energy Eg larger than the bandgap energy Eg of the n-type light guide layer 16 is provided outside the n-type light guide layer 16, and the p-type clad layer 20 is provided. A p-type cladding layer 22 having a bandgap energy Eg larger than the bandgap energy Eg of the p-type light guide layer 18 and the barrier layer 10 is provided outside the light guide layer 18.

At the boundary between the quantum well active layer 14 and the n-type light guide layer 16, the energy level Ev at the upper end of the valence band (hereinafter abbreviated as “valence band upper end Ev”) is the n-type light guide layer. A hole blocking layer 24 is provided which is higher than the upper end Ev of the valence band of 16 with respect to the energy of holes. That is, the hole block layer 24 is
A significant feature of the present invention is that the band offset ΔEv of the valence band from the barrier layer 10 and the n-type optical guide layer 16 is made of a material whose positive value is based on the energy of holes.

[0013]

In general, when trying to confine carriers in the vicinity of the quantum well layer, the situation is quite different between electrons and holes. Since electrons have a lighter effective mass than holes, they easily tunnel through barriers, and because the pseudo-Fermi level rises near the bottom of the conduction band Ec of the optical guide layer that sandwiches the quantum well active layer, electrons with high energy are generated. Many. Therefore,
Even if a potential barrier for electrons is provided, if the thickness is thin, electrons will tunnel through the potential barrier, and if the height is low, electrons will exceed the barrier. On the other hand, holes have a larger effective mass than electrons, and the pseudo-Fermi level is far from the valence band upper end Ev of the light guide layer, that is, the situation is opposite, so it is relatively easier than electrons. Can be confined near the quantum well layer.

In the present invention, the valence band upper end Ev of the hole blocking layer 24 provided at the boundary between the quantum well active layer 14 and the n-type optical guide layer 16 is the barrier layer 1 of the quantum well active layer 14.
Since the energy of the hole is higher than the upper end Ev of the valence band of the 0 and n-type optical guide layers 16 on the basis of the hole energy, it becomes a potential barrier for the hole, and the well layer 12 of the quantum well active layer 14 under high temperature environment. The holes overflowing from the inside are retained up to the barrier layer 10, and the n-type light guide layer 16
Overflow is suppressed. As a result, the recombination current in the n-type light guide layer 16 can be suppressed.

The position where the hole blocking layer 24 is provided is not limited to the boundary between the quantum well active layer 14 and the n-type light guide layer 16, and even in the n-type light guide layer 14 near this boundary, It is possible to exert the effect of becoming a potential barrier for holes. Further, it is desirable that tensile strain is applied to the hole blocking layer 24. In this case, when no tensile strain is applied, the degeneration of the heavy hole band and the light hole band, which had been degenerated at the top of the valence band, is resolved and separated, and the potential barrier for the heavy hole with many carriers increases in the barrier layer 10. ,
Moreover, since the ratio ΔEc / ΔEv of the band offset ΔEc of the conduction band and the band offset ΔEv of the valence band becomes large, it is possible to more effectively suppress the entry of holes into the n-type optical guide layer 16.

Further, it is desirable that the conduction band lower end Ec of the hole block layer 24 is lower than the height which becomes a potential barrier for electrons. For example, the conduction band lower end Ec of the hole block layer 24 is substantially equal to the conduction band lower end Ec of the n-type light guide layer 16, or the n-type light guide layer 16 is formed.
This is because, if it is lower than the lower end Ec of the conduction band, the traveling of the electrons injected from the n-type cladding layer 20 is not hindered.

Further, even if the conduction band lower end Ec of the hole blocking layer 24 is such a height that it becomes a potential barrier for electrons existing in the n-type optical guide layer 16, the thickness of the hole blocking layer 24 is It may be thick enough to prevent tunneling and thin enough to allow electrons to tunnel. Also in this case, the electrons injected from the n-type cladding layer 20 easily reach the quantum well active layer 14.

Further, in the present invention, the conduction band lower end Ec of the p-type light guide layer 18 is the barrier layer 10 and the n-type light guide layer 16.
Since the electron energy is higher than the lower end of the conduction band Ec of the quantum well active layer, it becomes a potential barrier for electrons, and the electrons overflowing from the well layer 12 of the quantum well active layer 14 under the high temperature environment are retained by the barrier layer 10. , P-type light guide layer 18 is prevented from overflowing. As a result, the recombination current in the p-type light guide layer 18 can be suppressed.

The conduction band lower end Ec of the p-type optical guide layer 18 is
To increase the bandgap energy Eg
When the value is increased, the refractive index is decreased, and the light confinement is lowered. However, the decrease in the light confinement is caused by the p-type light guide layer 1
This can be mitigated by the presence of the n-type light guide layer 16 having a refractive index larger than 8. Especially, the hole block layer 2
4 is provided, the well layer 1 of the quantum well active layer 14 is provided.
Since it becomes possible to keep the holes overflowing from 2 up to the barrier layer 10, the valence band upper end Ev of the n-type optical guide layer 16 is lower than the valence band upper end Ev of the barrier layer 10 based on the hole energy. You can also do it. Therefore, even if the bandgap energy Eg is made smaller than that of the barrier layer 10 in order to increase the refractive index of the n-type optical guide layer 16, recombination of carriers in the n-type optical guide layer 16 does not increase, and the optical confinement is suppressed. It is possible to increase only.

In this way, the carriers can be confined in the vicinity of the well layer 12 while maintaining the optical confinement coefficient Γ without lowering, so that the n-type optical guide layer 16 and the p-type optical guide layer 18 can be maintained even at high temperatures. Since the recombination of the carriers can be suppressed, it is possible to oscillate with a low threshold current in a wide range from room temperature to high temperature.

[0021]

EXAMPLES The present invention will be specifically described below based on examples. 2A is a sectional view showing the quantum well laser device according to the first embodiment of the present invention, and FIG. 2B is an energy band diagram showing its band structure. On the n-type InP substrate 30, an n-type InP clad layer 32 having a thickness of 1 μm, a thickness of 0.13 μm, and a bandgap wavelength λg = 1.25.
The n-type InGaAsP light guide layer 34 having a thickness of 10 μm is laminated in this order, and the n-type InGaAsP hole block layer 36 having a thickness of 10 nm and a bandgap wavelength λg of 1.1 μm is formed on the n-type InGaAsP light guide layer 34. .

On the n-type InGaAsP hole blocking layer 36, the thickness is 10 nm and the band gap wavelength is λg.
= 1.25 μm i-type InGaAsP barrier layer 38 and 7 nm-thick i-type In _0.53 Ga _0.47 As well layer 40 are alternately laminated to form a quantum well active layer 42 having a four-layer multi-quantum well structure. ing. Furthermore, on the quantum well active layer 42, a p-type InGaAsP optical guide layer 4 having a thickness of 0.16 μm and a bandgap wavelength λg = 1.1 μm is formed.
4, p-type InP clad layer 46 having a thickness of 2 μm, and p-type InGaAs having a bandgap wavelength λg = 1.25 μm
The P contact layer 48 is sequentially stacked. Although not shown, a p-side electrode is formed on the p-type InGaAsP contact layer 48, and an n-side electrode is formed on the bottom surface of the n-type InP substrate 30.

As described above, according to the first embodiment, the n-type I
The n-type InGaAsP hole blocking layer 36 provided at the boundary between the nGaAsP optical guide layer 34 and the quantum well active layer 42.
The valence band upper end Ev of is higher than the valence band upper end Ev of the n-type InGaAsP optical guide layer 34 and the i-type InGaAsP barrier layer 38 on the basis of the hole energy, and thus becomes a potential barrier for holes, and I-type In _0.53 Ga _0.47 As of the well active layer 42
The holes overflowing from the well layer 40 can be suppressed from overflowing into the n-type InGaAsP light guide layer 34, and the recombination current in the n-type InGaAsP light guide layer 34 can be suppressed.

Further, the p-type InGaAsP optical guide layer 44
Since the conduction band lower end Ec of the i-type InGaAsP barrier layer 38 is higher than the conduction band lower end Ec of the i-type InGaAsP barrier layer 38 on the basis of electron energy, it becomes a potential barrier against electrons, and the i-type In _0.53 Ga _{0.47 of the} quantum well active layer 42 is formed.
Electrons overflowing from the As well layer 40 can be prevented from overflowing into the p-type InGaAsP optical guide layer 44, and p
The recombination current in the InGaAsP optical guide layer 44 can be suppressed.

As a result, the quantum well laser device of the conventional GRIN-SCH structure shown in FIG.
It was possible to improve the optical confinement coefficient Γ to the well layer which did not reach the value of 5.1%. Since the optical confinement coefficient Γ is improved and the carrier confinement can be maintained even in a high temperature environment, the threshold current can be lowered in a wide range from room temperature to high temperature.

In the first embodiment, the hole block layer is provided at the boundary between the quantum well active layer and the n-type optical guide layer. However, the hole block layer is provided at the quantum well active layer. Near the boundary between the and n-type light guide layer
It may be in the mold light guide layer. However, since the recombination of carriers occurs in the n-type light guide layer between the quantum well active layer and the hole block layer as the hole block layer moves away from the boundary between the quantum well active layer and the n-type light guide layer, The hole blocking layer is preferably provided at the boundary between the quantum well active layer and the n-type optical guide layer, or as close to the boundary as possible.

Next, a quantum well laser device according to a second embodiment of the present invention will be described with reference to FIG. FIG. 3A is a sectional view showing a quantum well laser device according to the second embodiment,
FIG. 3B is an energy band diagram showing the band structure. The same components as those of the quantum well laser device shown in FIG. 2 are designated by the same reference numerals and the description thereof will be omitted.

In the second embodiment, instead of the n-type InGaAsP optical guide layer 34 in the first embodiment shown in FIG. 2, the thickness is 0.13 μm and the bandgap wavelength λg =
The n-type InGaAsP light guide layer 50 of 1.35 μm is used, and the refractive index of the n-type InGaAsP light guide layer 50 is made larger than that of the i-type InGaAsP barrier layer 38. As a result, the upper edge of the valence band Ev of the n-type InGaAsP light guide layer 50 is lower than the upper edge of the valence band Ev of the i-type InGaAsP barrier layer 38 based on the hole energy.

In such a band lineup, the recombination of carriers in the n-type InGaAsP optical guide layer 50 is usually increased, but the n-type InGaAsP hole blocking layer 36 causes the holes to be n-type InGaAsP.
In order to prevent the light guide layer 50 from overflowing, n-type I
Even if the bandgap energy Eg of the nGaAsP optical guide layer 50 is made smaller than the bandgap energy Eg of the i-type InGaAsP barrier layer 38, the recombination of carriers does not increase. Then, the bandgap energy Eg of the n-type InGaAsP optical guide layer 50 is reduced to
The larger the refractive index, the greater the light confinement.

As described above, according to the second embodiment, the refractive index value is larger than that of the i-type InGaAsP barrier layer 38, and the band gap energy Eg is i-type InGaAs.
N-type InGaAsP smaller than that of the P barrier layer 38
By using the optical guide layer 50, the quantum well active layer 4
The optical confinement coefficient Γ to the i-type In _0.53 Ga _0.47 As well layer 40 of _No. 2 could be further increased to 5.3%. As the optical confinement coefficient Γ is increased, carriers can be kept confined in the vicinity of the i-type In _0.53 Ga _0.47 As well layer 40, so that the threshold value can be further reduced.

Next, a quantum well laser device according to a third embodiment of the present invention will be described with reference to FIG. FIG. 4A is a sectional view showing a quantum well laser device according to a third embodiment,
FIG. 4B is an energy band diagram showing the band structure. The same components as those of the quantum well laser device shown in FIG. 2 are designated by the same reference numerals and the description thereof will be omitted.

The third embodiment is the n-type InGaAsP hole blocking layer 36 in the first embodiment shown in FIG.
Tensile strain is applied to the n-type InGaAsP strained hole blocking layer 52. As described above, according to the third embodiment, since the n-type InGaAsP strained hole blocking layer 52 has tensile strain, the heavy hole (hh) band and the light hole (lh) band are separated even at the top of the valence band, As shown by the broken line in the figure, the potential barrier for the heavy hole (hh) with a large number of carriers is the light hole (lh).
Higher than the potential barrier to.

Further, the band offset ΔE between the n-type InGaAsP strained hole block layer 52 and the n-type InGaAsP optical guide layer 34 and the i-type InGaAsP barrier layer 38.
In c and ΔEv, the ratio ΔEv / ΔEc between the band offset ΔEv on the valence band side and the band offset ΔEc on the conduction band side is larger than that in the case of lattice matching. Therefore, the holes can be more effectively confined, and the threshold value can be further lowered.

Next, a quantum well laser device according to a fourth embodiment of the present invention will be described with reference to FIG. FIG. 5 is a sectional view showing a quantum well laser device according to the fourth embodiment.
The same components as those of the quantum well laser device shown in FIG. 2 are designated by the same reference numerals and the description thereof will be omitted.

The fourth embodiment is the i-type InGaAsP barrier layer 38 and the i-type I in the first embodiment shown in FIG.
Instead of the quantum well active layer 42 in which n _0.53 Ga _0.47 As well layers 40 are alternately laminated, an i-type InGaAsP barrier layer 54 having a thickness of 10 nm and a bandgap wavelength λg = 1.25 μm and an i-type having a thickness of 3 nm are used. The strained quantum well active layer 58 has a four-layered multiple quantum well structure in which In _0.62 Ga _0.38 As well layers 56 are alternately laminated.

As described above, according to the fourth embodiment, by using the strained quantum well active layer 58 as an active layer, the carrier density required for laser oscillation can be lowered,
Therefore, it is possible to further reduce the threshold value. The hole blocking layer in the first to fourth embodiments is formed at the boundary between the barrier layer of the quantum well active layer or the strained quantum well active layer and the n-type optical guide layer. It may be formed at the boundary with the mold light guide layer. However, in this case, it should be noted that the carrier energy level in the well layer in contact with the hole block layer varies.

Next, a quantum well laser device according to a fifth embodiment of the present invention will be described with reference to FIG. FIG. 6 is a sectional view showing a quantum well laser device according to the fifth embodiment.
In the fifth embodiment, while the first to fourth embodiments shown in FIGS. 2 to 5 are made of InP, Ga is used.
It is composed of an As system.

That is, a thickness of 1 is formed on the n-type GaAs substrate 60.
A μm n-type Al _0.3 Ga _0.7 As clad layer 62 and a 0.06 μm-thick n-type Al _0.15 Ga _0.85 As optical guide layer 64 are sequentially stacked, and on the n-type Al _0.15 Ga _0.85 As optical guide layer 64, I-type In _0.5 Ga with a thickness of 10 nm
_{A 0.5} P hole blocking layer 66 is formed. Also,
On the i-type In _0.5 Ga _0.5 P hole blocking layer 66,
A quantum well active layer 72 having a single quantum well structure is formed with two i-type Al _0.15 Ga _0.85 As barrier layers 68 having a thickness of 5 nm sandwiching an i-type GaAs well layer 70 having a thickness of 5 nm.

Further, on the quantum well active layer 72, a thickness
0.08 μm p-type Al_0.25Ga _0.75As light guide layer
74, 2 μm thick p-type Al_0.3Ga_0.7As clad
The layer 76 and the p-type GaAs contact layer 78 are sequentially stacked.
Has been done. Thus, according to the fifth embodiment, GaA
Also in the s-based quantum well laser device, i-type In_0.5Ga
_0.5By providing the P-hole block layer 66,
InP-based quantum well lasers in the first to fourth embodiments
The same effect as that of the device can be obtained.

In the above first to fifth embodiments,
As the active layer, an unstrained quantum well active layer or a strained quantum well active layer having a multiple quantum well structure or a single quantum well structure is used. Instead of such a quantum well structure, a quantum wire or a quantum box is used. Good. In this case, the density of states changes due to an increase in the confinement dimension of carriers, and the carriers that do not contribute to laser oscillation can be reduced, so that the threshold value can be further reduced.

Further, in the first to fifth embodiments, the hole blocking layer is a so-called type I straddling type heterojunction,
Although it forms a small potential barrier against electrons, it may be a hole blocking layer forming a so-called type II staggered heterojunction.
In this case, the hole blocking layer does not form a potential barrier for electrons but serves as a potential barrier only for holes, and the electrons can be injected into the well layer without being blocked by the hole blocking layer.

The conductivity type of this hole block layer is
Although n-type or i-type is used, whichever conductivity type is used, it can function as a potential barrier for holes to confine the holes in the quantum well layer of the quantum well active layer. Further, in the above-mentioned first to fifth embodiments, the p-type optical guide layer has a single conduction band lower end Ec higher than the conduction band lower end Ec of the barrier layer of the quantum well active layer with reference to the electron energy. Although a layer having a composition is used, the p-type light guide layer may be a p-type light guide layer having a GRIN-SCH structure having a multilayer structure as shown in FIG. 7B. Whether to employ this structure depends on the adjustment of carrier confinement and optical confinement in the quantum well active layer.

[0043]

As described above, according to the present invention, an n-type cladding layer, an n-type light guide layer, a quantum well active layer in which well layers and barrier layers are alternately laminated, and a p-type light guide layer. Layers and
In a semiconductor laser device in which a p-type cladding layer is sequentially formed, an n-type light guide layer and a barrier layer are formed in the n-type light guide layer at or near the boundary between the quantum well active layer and the n-type light guide layer. Since the hole block layer having a higher energy level Ev at the upper end of the valence band than the energy level Ev at the upper end of the valence band is provided, the hole block layer serves as a potential barrier for holes. Therefore, the holes overflowing from the well layer can be suppressed from overflowing to the n-type light guide layer, and the recombination current in the n-type light guide layer can be suppressed.

Since the energy level Ec at the bottom of the conduction band of the p-type optical guide layer is higher than the energy level Ec at the bottom of the conduction band of the barrier layer on the basis of electron energy, It is possible to suppress overflow electrons from overflowing to the p-type light guide layer, and to suppress recombination current in the p-type light guide layer. Therefore, carriers can be confined in the vicinity of the well layer while maintaining the optical confinement coefficient Γ without being lowered, and recombination of carriers in the n-type optical guide layer and the p-type optical guide layer can be suppressed. Therefore, it becomes possible to oscillate the semiconductor laser device with a low threshold current in a wide range from room temperature to high temperature.

[Brief description of drawings]

FIG. 1 is an energy band diagram showing a band structure of a quantum well laser device for explaining a principle diagram of the present invention.

FIG. 2 is a sectional view showing a quantum well laser device according to a first embodiment of the present invention and an energy band diagram showing its band structure.

FIG. 3 is a sectional view showing a quantum well laser device according to a second embodiment of the present invention and an energy band diagram showing its band structure.

FIG. 4 is a sectional view showing a quantum well laser device according to a third embodiment of the present invention and an energy band diagram showing its band structure.

FIG. 5 is a sectional view showing a quantum well laser device according to a fourth embodiment of the present invention.

FIG. 6 is a sectional view showing a quantum well laser device according to a fifth embodiment of the present invention.

FIG. 7 is an energy band diagram showing a band structure of a conventional SCH quantum well laser device.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 10 ... Barrier layer 12 ... Well layer 14 ... Quantum well active layer 16 ... N-type optical guide layer 18 ... P-type optical guide layer 20 ... N-type clad layer 22 ... P-type clad layer 24 ... Hole block layer 30 ... N-type InP Substrate 32 ... n-type InP clad layer 34 ... n-type InGaAsP optical guide layer 36 ... n-type InGaAsP hole blocking layer 38 ... i-type InGaAsP barrier layer 40 ... i-type In _0.53 Ga _0.47 As well layer 42 ... quantum well active layer 44 ... p-type InGaAsP optical guide layer 46 ... p-type InP clad layer 48 ... p-type InGaAsP contact layer 50 ... n-type InGaAsP optical guide layer 52 ... n-type InGaAsP strain hole blocking layer 54 ... i-type InGaAsP barrier layer 56 ... i-type In _0.62 Ga _0.38 As well layer 58 ... strained quantum well active layer 60 ... n-type GaAs substrate 62 ... n-type l _0.3 Ga _0.7 As cladding layer 64 ... n-type Al _0.15 Ga _0.85 As optical guide layer 66 ... i-type In _0.5 Ga _0.5 P a hole blocking layer 68 ... i-type Al _0.15 Ga _0.85 As barrier layers 70 ... i-type GaAs well layers 72 Quantum well active layer 74 p-type Al _0.25 Ga _0.75 As optical guide layer 76 p-type Al _0.3 Ga _0.7 As clad layer 78 p-type GaAs contact layer 80 barrier layer 82 well layer 84 quantum well active layer 86 ... N-type light guide layer 88 ... P-type light guide layer 90 ... N-type clad layer 92 ... P-type clad layer 94 ... N-type light guide layer 96 ... P-type light guide layer

Claims (7)

[Claims] 1. An n-type clad layer, an n-type optical guide layer formed on the n-type clad layer, and an n-type optical guide layer, wherein well layers and barrier layers are alternately laminated. A quantum well active layer, a p-type optical guide layer formed on the quantum well active layer, and a p-type cladding layer formed on the p-type optical guide layer. An n-type or i-type hole blocking layer is provided in the n-type light guiding layer near the boundary between the active layer and the n-type light guiding layer or near the boundary between the quantum well active layer and the hole blocking layer. The semiconductor laser is characterized in that the energy level Ev at the upper end of the valence band is higher than the energy level Ev at the upper end of the valence band of the n-type optical guide layer and the barrier layer on the basis of hole energy. apparatus. 2. The semiconductor laser device according to claim 1, wherein the energy level Ec at the lower end of the conduction band of the p-type optical guide layer.
Is higher than the energy level Ec at the lower end of the conduction band of the barrier layer on the basis of electron energy. 3. The semiconductor laser device according to claim 1, wherein the n-type light guide layer has a refractive index higher than that of the barrier layer. 4. The semiconductor laser device according to claim 1, wherein a tensile strain is applied to the hole blocking layer. 5. The semiconductor laser device according to claim 1, wherein the energy level E at the bottom of the conduction band of the hole blocking layer is E.
A semiconductor laser device characterized in that c is lower than a height which becomes a potential barrier for electrons. 6. The semiconductor laser device according to claim 1, wherein the hole blocking layer has a thickness that allows electrons to pass therethrough by a tunnel effect. 7. The semiconductor laser device according to claim 1, wherein the quantum well active layer is a strained quantum well active layer.