JPH10284795A - Semiconductor laser element providing distortion amount and layer thickness modulating multiple quantum-well structure and manufacture therefor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To enhance a threshold current characteristic by suppressing a generation of a carrier overflow phenomenon, increase carrier injection efficiency, and obtain a stable light-emitting wavelength. SOLUTION: When this element has a p-type clad layer Cd1 and an n-type clad layer Cd2 which nip and active region Act which forms a plurality of quantum-well layers QW1 to QW4, the respective quantum-well layers QW1 to QW4 form potential barriers ΔEc1 to ΔEc4 between adjacent clad layers Cd1, Cd2 and/or barrier layers. Here, distortion amounts ε1 to ε4 of the respective quantum-well layers QW1 to QW4 are formed, or distortion amounts ε1 to ε4 and layer thicknesses T1 to T4 are formed, so that a difference between quantizing levels μ1 (-μ4) of carriers in the respective quantum-well layers QW1 to QW4 and the potential barriers ΔEc1 to ΔEc4 is a specific value.

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 having a multiple quantum well structure and a method of manufacturing the same, and more particularly to a semiconductor laser device having a multiple quantum well structure of a strain amount and layer thickness modulation type and a method of manufacturing the same. .

[0002]

2. Description of the Related Art Quantum well semiconductor lasers (QW lasers)
Is a semiconductor laser in which the active layer has a quantum well structure with a thickness of about the de Broglie wavelength of electrons and holes as carriers, and in particular, a quantum well layer (well) and a barrier layer (barrier) are alternately stacked, A multiple quantum well (MQW) semiconductor laser has two or more quantum well layers.

In such a quantum well semiconductor laser, the electron transition between the quantized levels formed in the active layer controls the laser oscillation, and the carrier state density is a step function. Price range narrows. As a result, the gain coefficient sharply increases at a small injection current density, and the threshold current Ith decreases.

Further, a strained quantum well semiconductor laser or a strained ultra-strained laser is used in which a lattice mismatched material is used for the quantum well layer and the barrier layer, and the thickness of the quantum well layer is less than the critical layer thickness so that misfit transition does not occur. Lattice semiconductor lasers are widely applied.

In these strain type lasers, the potential difference between the conduction band side of the quantum well layer and the barrier layer, that is, the potential barrier ΔEc of electrons, or /
Further, it is possible to change the band gap ΔEg by controlling the potential difference between the quantum well layer and the barrier layer on the valence band side, that is, the potential barrier ΔEv of holes.

For example, FIG. 14 shows a composition Ga (x) In (1
FIG. 11 is a diagram showing the dependence of the potential barrier ΔEc of electrons in the conduction band on the strain ε in the strained quantum well of −x) P. The strain amount ε is represented by 格子 q, the lattice constant of the quantum well of interest,
Set the lattice constant of the adjacent barrier layer or cladding layer to Λ
In the case of bc, ε = (Λq−Λbc) / Λq, where ε> 0 results in compressive strain, and ε <0 results in tensile strain. According to the figure, the band gap ΔEg
The electron potential barrier ΔEc normalized by
0, that is, the value increases at a compressive strain (ε> 0) and decreases at a tensile strain (ε <0) from the value at the time of no strain.

The introduction of strain changes not only the band gap but also the band structure. In the region of ε> 0 (compression strain), the band located at the top of the valence band has a small hole mass in the growth plane direction. For this reason, when a substance having the above composition is used as a gain medium of a semiconductor laser, the injection of a smaller number of holes easily increases the pseudo-Fermi level of holes and makes it easy to obtain a population inversion distribution. Low threshold oscillation becomes possible.

Also, in the region where ε> 0 (tensile strain), the optical transition probability between the state of the valence electrons and the conduction band is large, so that the differential gain is increased. The laser oscillation threshold can be reduced.

FIG. 15 shows the composition of a Ga (x) In (1-x) P well layer having a double quantum well structure laser oscillation threshold whose thickness is designed so that the oscillation wavelength becomes a constant value of 633 nm. This is dependent on the amount of strain (ε). Compared to a laser without distortion, the amount of distortion is an appropriate value for each of positive and negative, for example, ε =
A low oscillation threshold value Ith is realized at around 0.6% or ε = −0.5%. Note that oscillation occurs in the TE mode in the compression strain quantum well and in the TM mode in the tensile strain.

[0010] Thus, the strained crystal is an effective means for controlling the laser oscillation wavelength and gain. In addition, the distortion is conduction band,
Changing the energy level of the valence band changes the band discontinuity of the heterojunction, which is important in various heterojunction devices. Therefore, it also serves as a means for controlling the amount of band discontinuity.

FIG. 11 is a schematic diagram of an energy band gap in the conventional strained multiple quantum well (MQW) structure as described above. In the figure, the strain ε applied to the quantum well layer
Is defined by a lattice shift (Δa / a). In this structure, the quantum well layer is composed of a GaInP layer having ε of + 0.5%, and the barrier layer is (Al0.5Ga0.5) 0.5 having no distortion.
It is composed of an InP layer.

In this configuration, each quantum well QW101
ＱQW104 is constant at + 0.5%, the potential barrier ΔEc on the conduction band CBD side has the same value for each of the quantum wells QW101 to QW104, and similarly the potential barrier ΔEv on the valence band VBD side.
Is also equal for each of the quantum wells QW101 to QW104. Therefore, the band gap ΔEg is equal, and the quantization level μ of electrons on the conduction band CBD side and the valence band VBD
Of the quantization level ν of the hole on the side (= Fermi level difference ΔEf
ermi) have the same configuration.

The amount of strain is controlled by shifting the composition ratio of Ga and In from 0.5 to one of them to form a film. For example, by slightly increasing the In composition to 0.57 for In and 0.43 for Ga and forming a film on the In excess side (x <0.5), the lattice shift (Δa / a) becomes about + 0.65%. It is known that the potential barrier ΔEc on the conduction band CBD side increases and the energy band shrinks (IEEE Junalof Quantum El).
electronics, V29 No. 6 1863-1
867).

I, which is pulled on the Ga excess side (x> 0.5),
On the n excess side (x <0.5), a compressive biaxial stress acts,
Distortion occurs. Conversely, when the composition ratio of Ga is increased, tensile (minus) strain occurs, the potential barrier ΔEc on the conduction band CBD side decreases, and the energy band gap increases. Further, it is known that as an advantage caused by applying strain to the quantum well layer, the degeneracy of the valence band is released and the gain is easily obtained, so that the oscillation threshold of the laser element is lowered. For example, among the laser elements in the red wavelength band, the laser element of 635 nm has minus distortion, and 6
A positive distortion is applied to the 50 nm laser element.

FIG. 12 is a schematic diagram of the conduction band side energy level of the active region in a configuration in which each quantum well layer has the same layer thickness and the amount of strain differs for each quantum well layer. Only the conduction band side is shown. In the figure, the quantum well layers QW110 to QW113 are disposed between an n-type cladding layer N110 and a p-type cladding layer P110, and all the quantum well layers QW110 to QW113 have the same layer thickness T1.
10.

The amount of strain applied to each of the quantum well layers QW110 to QW113 is ε11 per quantum well layer QW110.
0 = 0% at no strain, ε111 per quantum well layer QW111
= 0.1%, ε112 = per quantum well layer QW112
0.3%, ε113 = 0.0.0 per quantum well layer QW113.
It is gradually increasing to 5%.

The potential barrier of each quantum well layer mainly depends on the amount of strain. Therefore, the strain-free quantum well layer Q
Assuming that the potential barrier of W110 is ΔEc110,
Potential barrier ΔEc111 of quantum well layer QW111
Is larger than that (the depth of the well is deeper), and the potential barrier ΔEc11 of the quantum well layers QW112 to QW113 in the following order.
2 to ΔEc113 are gradually increasing.

On the other hand, the carriers in each quantum well layer, that is, the quantization levels of the electrons in the figure mainly depend on the effective mass of the electrons and the layer thickness. Here, since the effective mass can be regarded as substantially the same, It will depend on the layer thickness. In this configuration, since the layer thickness is the same for each quantum well layer, the quantization level of each quantum well layer is located at the same height with the bottom of each well as the origin.

Since the potential barrier of each quantum well layer is different in each quantum well layer as described above, the quantum levels μ110 to μ113 of the electrons in the conduction band and the holes of the holes in the valence band (not shown) are thus determined. A difference occurs in the difference between the quantization levels ν (= Fermi level difference ΔEfermi). This is mainly because the profile of the quantization level ν of holes on the valence band side is different. For this reason, since the energy contributing to the light emitting process is different in each quantum well layer, the oscillation wavelength distribution becomes broad.

FIG. 13 is a schematic diagram of the energy level on the conduction band side of the active region in the conventional structure in which the quantum well layer thickness is adjusted. The structure shown in FIG. 13 is an attempt to improve the structure of FIG. It is a thing. Also, only the conduction band side is shown in FIG. As is clear from the description of FIG. 12, the energy band gap fluctuates depending on the magnitude of the distortion, and the oscillation wavelength varies. In order to solve this problem, the thickness of each quantum well layer is adjusted so as to keep the oscillation wavelength constant, given the amount of strain applied to each quantum well layer.

In the figure, the quantum well layers QW120 to QW12
4 is an n-type cladding layer N120 and a p-type cladding layer P120
And it is arranged between. Each quantum well layer QW120
ＷQW124 are applied to the quantum well layer QW1.
20 without strain at ε120 = 0%, quantum well layer QW12
Ε121 = 0.1% for each, ε122 = 0.3% for the quantum well layer QW122, ε123 = 0.3% for the quantum well layer QW123, and ε1 for the quantum well layer QW124.
24 = 0.5%, gradually increasing.

The potential barrier of each quantum well layer mainly depends on the amount of strain. Therefore, the strain-free quantum well layer Q
Assuming that the potential barrier of W120 is ΔEc120,
Potential barrier ΔEc121 of quantum well layer QW121
Is larger (the well is deeper), and the potential barrier ΔEc12 of the quantum well layers QW122 to
2 to ΔEc124 are leveling or gradually increasing.

Here, since the quantization level of the electrons in each quantum well layer depends on the layer thickness as in the above example, therefore, in this configuration, the quantization level of each quantum well layer is uniform μ1.
20 so that each of the quantum well layers QW120 to QW12
4 are independently adjusted. Thus, the oscillation wavelength distribution is sharpened.

[0024]

However, in the prior art as described above, since the layer thickness is adjusted so as to have a uniform quantization level, for example, the quantum well layer QW12 shown in FIG.
As shown in the layer thicknesses T122 to T124 of 2 to QW124, the design value may be such that the layer thickness of a specific well becomes extremely thin. For example, if the quantum well layer has a very small thickness of about 30 angstroms or less, it becomes difficult to form the quantum well layer, and it becomes difficult to control the quantum well layer thickness.

When the thickness of the quantum well layer is reduced, the effective area in the active region related to the output is reduced, and the gain is reduced. Therefore, in order to obtain a sufficient gain, it is necessary to increase the number of quantum wells (multi number) in the active region as shown in FIG. 13, but this leads to an increase in the number of barriers and injection of carriers into the quantum well layer. There has been a problem that the efficiency is deteriorated and the threshold value is increased and the efficiency is deteriorated.

Further, if the layer thickness is smaller than the minimum limit layer thickness, sagging often occurs in actual production. In this case, the well-type potential is deteriorated to raise the bottom of the well, which causes a short emission wavelength, and also causes a difference in the emission wavelength of each quantum well layer, resulting in a change in operating conditions and a decrease in gain. Was.

As described above, when the absolute value of the amount of distortion is increased, gain is easily obtained and the deflection ratio is increased, but there is a disadvantage that the limit of the layer thickness is narrowed. On the other hand, when the layer thickness is increased, the carrier is easily trapped, the manufacturing is easy, the influence of the layer thickness fluctuation is reduced, and there is an advantage that the sag is small. However, it is difficult to uniformly inject the carrier by MQW.
There is a disadvantage that the W effect (large gain, large deflection selection) is reduced, and optimization is not easy. Therefore, the prior art cannot be an effective technique for improving the overflow characteristics related to the effect of confining carriers, particularly electrons, and the threshold current characteristics.

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned problems in the prior art, and effectively confine carriers, suppress the occurrence of overflow phenomenon, improve the threshold current characteristics, and simultaneously perform carrier injection. It is an object of the present invention to provide a semiconductor laser device having a multiple quantum well structure and a manufacturing method capable of improving the efficiency and obtaining a stable emission wavelength.

[0029]

A semiconductor laser device having a multiple quantum well structure according to the present invention has an active region and a p-type cladding layer and an n-type cladding layer sandwiching the active region. A semiconductor laser device having a multiple quantum well structure in which the active region includes a plurality of quantum well layers and each of the quantum well layers forms a potential barrier between the adjacent cladding layer and / or barrier layer. The amount of strain or the amount of strain and the thickness of each of the quantum well layers are formed such that the difference between the quantization level of carriers in the quantum well layer and the potential barrier becomes a predetermined value. .

According to the semiconductor laser device having the multiple quantum well structure according to the present invention having the above-described structure, the amount of strain, or both the amount of strain and the layer thickness, are adjusted, so that each quantum well layer has The difference between the quantization level of the carrier and the potential barrier can be set to a desired value, so that the carrier is effectively confined and the overflow characteristics are improved.

Alternatively, in the semiconductor laser device having the multiple quantum well structure according to the present invention, when the thickness of each quantum well layer becomes narrow, the amount of minus strain is reduced or the amount of plus strain is increased beforehand. When the band gap is adjusted, it is possible to prevent the deterioration of the well-type potential caused in the quantum well layer in advance.

Alternatively, in the semiconductor laser device having the multiple quantum well structure according to the present invention, the thickness of the quantum well layer adjacent to at least one of the p-type cladding layer and the n-type cladding layer is the same as that of another quantum well layer. When the thickness is thicker, the overflow characteristics of electrons and / or holes, particularly the overflow characteristics of electrons, are improved, the number of heterointerfaces is reduced, the carrier injection efficiency is improved, and the threshold current characteristics are improved. Improvements are made.
Further, the effective output area in the active area is enlarged.

Alternatively, in the semiconductor laser device having a multiple quantum well structure according to the present invention, the thickness of the quantum well layer adjacent to at least one of the p-type cladding layer and the n-type cladding layer is the same as that of another quantum well layer. When the band gap is adjusted by reducing the amount of negative strain in advance or increasing the amount of positive strain in the case where the quantum well layer is configured to be thicker and the layer thickness of each quantum well layer becomes narrower, the conventional technology has a problem. The deterioration of the well-type potential generated in the quantum well layer as described above can be avoided, the overflow characteristics of electrons and / or holes are improved, the effective output area in the active region is enlarged, and the barrier layer By suppressing the number, carrier injection efficiency is improved, and threshold current characteristics are improved.

Alternatively, in the semiconductor laser device having the multiple quantum well structure according to the present invention, when the carrier density in each quantum well layer is different, a strain amount corresponding to the carrier density is formed in each quantum well layer. When the configuration is such that the emission wavelength variation is suppressed, the emission wavelength variation is effectively suppressed by accurate distortion amount control.

Alternatively, in the semiconductor laser device having a multiple quantum well structure according to the present invention, when the thickness of each quantum well layer is reduced, the amount of minus strain is reduced or the amount of plus strain is increased beforehand. When the band gap is adjusted, and when the carrier density in each quantum well layer is different, a configuration in which the amount of distortion according to the carrier density is formed in each quantum well layer to suppress the emission wavelength variation, The deterioration of the well-type potential generated in the quantum well layer can be prevented, and the fluctuation of the emission wavelength can be effectively suppressed by controlling the amount of distortion with high accuracy.

Alternatively, in the semiconductor laser device having a multiple quantum well structure according to the present invention, the thickness of the quantum well layer adjacent to at least one of the p-type cladding layer and the n-type cladding layer is the same as that of another quantum well layer. Thicker and the carrier density in each quantum well layer is different,
When the configuration is such that a variation in emission wavelength is suppressed by forming a strain amount corresponding to the carrier density in each quantum well layer,
The overflow characteristics of electrons and / or holes, especially the overflow characteristics of electrons, are improved, the number of heterointerfaces is reduced, carrier injection efficiency is improved, and threshold current characteristics are improved. Further, the effective output area in the active region is expanded, and the fluctuation of the emission wavelength is effectively suppressed by accurate distortion amount control.

Alternatively, in the semiconductor laser device having a multiple quantum well structure according to the present invention, when the thickness of each of the quantum well layers becomes narrow, the amount of minus strain is reduced or the amount of plus strain is increased beforehand. And the thickness of the quantum well layer adjacent to at least one of the p-type cladding layer and the n-type cladding layer is thicker than the other quantum well layers. When the carrier density of the quantum well layer is different, the variation of the emission wavelength is suppressed by forming a strain amount corresponding to the carrier density in each quantum well layer. Can be prevented.

Further, the overflow characteristics of electrons and / or holes, especially the overflow characteristics of electrons, are improved, the effective output area in the active region is enlarged, and the number of barrier layers is suppressed, so that the carrier injection efficiency is improved. The threshold current characteristics are improved. Further, the variation of the emission wavelength is effectively suppressed by the accurate distortion amount control.

Next, a method for manufacturing a semiconductor laser device having a multiple quantum well structure according to the present invention has an active region, a p-type cladding layer and an n-type cladding layer sandwiching the active region, and the active region has a plurality of quantum wells. In a semiconductor laser device having a multiple quantum well structure in which a quantum well layer is formed, and each quantum well layer forms a potential barrier between adjacent cladding layers and / or barrier layers, the quantization level and potential of carriers in each quantum well layer The manufacturing method is to form the strain amount of each quantum well layer or to form the strain amount and the layer thickness so that the difference from the barrier becomes a predetermined value.

According to the method of manufacturing a semiconductor laser device having a multiple quantum well structure according to the present invention having the above-described structure, the amount of strain or both the amount of strain and the layer thickness are adjusted to form the semiconductor laser device. The difference between the quantization level of the carriers in each quantum well layer and the potential barrier is set to a desired value, so that a semiconductor laser device having improved overflow characteristics can be manufactured.

Alternatively, in the method of manufacturing a semiconductor laser device having a multiple quantum well structure according to the present invention, when the thickness of each quantum well layer becomes narrow, the amount of minus strain is reduced or the amount of plus strain is reduced in advance. When the band gap is adjusted at most, a semiconductor laser device capable of preventing the deterioration of the well-type potential caused in the quantum well layer as seen in the related art is manufactured.

Alternatively, in the method of manufacturing a semiconductor laser device having a multiple quantum well structure according to the present invention, the thickness of a quantum well layer adjacent to at least one of a p-type clad layer and an n-type clad layer is changed to another quantum well layer. When it is formed thicker than the layer thickness, the overflow characteristics of electrons and / or holes, especially the overflow characteristics of electrons are improved, and the carrier injection efficiency is improved.
A semiconductor laser device with an improved threshold current can be manufactured.

Alternatively, in the method of manufacturing a semiconductor laser device having a multiple quantum well structure according to the present invention, the thickness of a quantum well layer adjacent to at least one of a p-type cladding layer and an n-type cladding layer may be changed to another quantum well layer. When the band gap is adjusted by reducing the amount of negative strain in advance or increasing the amount of positive strain when the thickness of each quantum well layer is reduced and the layer thickness of each quantum well layer is narrowed, It is possible to prevent the well-type potential from deteriorating in the well layer and further improve the overflow characteristics of electrons and / or holes, in particular, the overflow characteristics of electrons, and also improve the carrier injection efficiency, thereby improving the threshold current. In this way, it becomes possible to manufacture a semiconductor laser device in which the above-mentioned operation is performed.

Alternatively, in the method of manufacturing a semiconductor laser device having a multiple quantum well structure according to the present invention, when the carrier density in each quantum well layer is different, a strain amount corresponding to the carrier density is formed in each quantum well layer. In this case, it becomes possible to manufacture a semiconductor laser device in which the fluctuation of the emission wavelength is effectively suppressed by accurate distortion amount control.

Alternatively, in the method of manufacturing a semiconductor laser device having a multiple quantum well structure according to the present invention, when the thickness of each quantum well layer becomes narrow, the amount of minus strain is reduced or the amount of plus strain is reduced in advance. When the band gap is adjusted and the carrier density in each quantum well layer is different, and a strain amount corresponding to the carrier density is formed in each quantum well layer, a well-type potential is formed in the quantum well layer. Of the semiconductor laser device in which the deterioration of the light emission wavelength is prevented, and the fluctuation of the emission wavelength is effectively suppressed by accurate distortion amount control.

Alternatively, in the method of manufacturing a semiconductor laser device having a multiple quantum well structure according to the present invention, the quantum well layer adjacent to at least one of the p-type clad layer and the n-type clad layer may have a different thickness. In the case where the quantum well layer is formed to be thicker than the layer thickness of each of the layers and the carrier density in each quantum well layer is different, the amount of strain corresponding to the carrier density is formed in each quantum well layer. , Especially the overflow characteristics of electrons.

Furthermore, the number of heterointerfaces is reduced, carrier injection efficiency is improved, threshold current characteristics are improved, the effective output area in the active region is expanded, and the effect is improved by accurate distortion amount control. It is possible to manufacture a semiconductor laser device capable of effectively suppressing fluctuation in emission wavelength.

Alternatively, in the method of manufacturing a semiconductor laser device having a multiple quantum well structure according to the present invention, when the thickness of each quantum well layer becomes narrow, the amount of negative strain is reduced or the amount of positive strain is reduced in advance. In many cases, the band gap is adjusted, and the thickness of the quantum well layer adjacent to at least one of the p-type cladding layer and the n-type cladding layer is formed to be thicker than the other quantum well layers. If the quantum well layer has a structure in which a strain amount corresponding to the carrier density is formed when the carrier density in the layer is different, the well-type potential is prevented from deteriorating in the quantum well layer and electrons and / or holes are prevented. The overflow characteristics of electrons, especially the overflow characteristics of electrons,
The effective output area in the active region is expanded, and the number of barrier layers is suppressed to improve the carrier injection efficiency.
The threshold current characteristics are improved, and it becomes possible to manufacture a semiconductor laser device in which the emission wavelength variation is effectively suppressed by accurate distortion amount control.

[0049]

Preferred embodiments of the present invention will be described below in detail with reference to the accompanying drawings. The embodiment described below is a part of a preferred embodiment of the present invention,
Although various limitations that are preferable in terms of the technical configuration are given, the scope of the present invention is not limited to these embodiments unless otherwise specified in the following description.

FIG. 1 is a schematic diagram of the conduction band side energy level of the active region in the first embodiment of the multiple quantum well semiconductor laser device according to the present invention. As shown in FIG. 1, the active region Act of the multiple quantum well semiconductor laser device according to the present invention has p-type or n-type cladding layers Cd1 and n.
Sandwiched between the mold or p-type cladding layers Cd2.

The active region Act is the first quantum well layer QW1
(Strain amount ε1: layer thickness T1), barrier layer B1, second quantum well layer QW2 (strain amount ε2: layer thickness T2), barrier layer B2, third layer
Quantum well layer QW3 (strain ε3: layer thickness T3), barrier layer B
3. The fourth quantum well layer QW4 (strain ε4: layer thickness T4)
In this order, the layers are formed from the p-type or n-type cladding layer Cd1 to the n-type or p-type cladding layer Cd2.

Here, the thickness T1 of the first quantum well layer QW1 adjacent to the p-type or n-type cladding layer Cd1 is set to be large. Similarly, the layer thickness T4 of the fourth quantum well layer QW4 adjacent to the n-type or p-type cladding layer Cd2 is set to be large. As described above, by increasing the width of the quantum well layer adjacent to the clad layer, carrier capture is facilitated, and overflow of carriers from the quantum well layer to the clad layer is suppressed.

As described above, when the thickness of the quantum well layer is increased, the quantization level shifts toward the valence band. Therefore, in order to compensate for this shift, if the strain amount ε1 in the first quantum well layer QW1 is large for negative strain or small for positive strain, the potential barrier ΔEc1 decreases, and the quantized level becomes conductive. It shifts back to the band CBD side and becomes the quantization level μ1.

Similarly, in the fourth quantum well layer QW4, when the strain amount ε4 is large for negative strain or small for positive strain, the potential barrier ΔEc4 decreases, and the quantization level shifts to the conduction band CBD side. Shift back. At this time, the distortion level ε4 and the layer thickness T4 may be selected, and the quantization level may be set to μ1. The figure shows a case where the same quantization level μ1 is formed.

Here, when the quantization level μ1 is given a predetermined value, the potential barrier ΔEc1
The amount of strain, or the amount of strain and the thickness of each quantum well layer is selected and set so that the difference between the quantum well layer and ΔEc4 becomes the predetermined value.

Next, regarding the second quantum well layer QW2 and the third quantum well layer QW3 in the center, the layer thicknesses T2 and T3 are narrow and the positive strain amounts ε2 and ε3 are large (or the negative strain amounts ε2 and ε3 are large). Small), a high oscillation efficiency is secured, and the layer thickness T2 and the strain amount ε2, and the layer thickness T3 and the strain amount ε3 are regarded as controllable amounts, and a value that minimizes the fluctuation of the quantization level is selected and set. . In particular, it is preferable to select the quantization level to be the aforementioned μ1. As described above, the threshold current Ith can be improved (decreased) by setting the quantum well layer in the sandwiched region to have a narrow width and a high strain.

For these quantum well layers having a small layer thickness, it is preferable to select and set the minimum critical layer thickness as a limit value in selecting the layer thickness. This makes it possible to eliminate a layer thickness having such a size that a well-type potential is rounded.

As described above, in the present embodiment, the overflow of the carrier is prevented by the wide wells formed at both ends. As a result, 6
It is possible to improve the high-temperature operation of a 50 nm band AlGaInP-based laser. Further, by mixing the quantum well layers having such a thickness, the number of the entire heterointerfaces can be reduced, and the carrier injection efficiency and the reliability of the device can be improved.

FIG. 2 is a schematic diagram of the conduction band side energy level of the active region in the multiple quantum well semiconductor laser device according to the second embodiment of the present invention. In the configuration of the active region Act2 of the present embodiment, the first quantum well layer QW1 (strain amount ε1: layer thickness T1) of the first embodiment is changed to a first quantum well layer QW1 ′ (strain amount ε1 ′). And the amount of strain ε
1 ′ is slightly changed from the strain amount ε1 to make the well shallow. While the profile of the first embodiment is symmetric, the profile of the present embodiment is asymmetric. In the figure, in particular, the quantization level μ common to all the quantum well layers is shown.
1 shows that a quantization level μ1 ′ is formed, but the embodiment is not limited to this. The function and effect are the same as those of the first embodiment.

FIG. 3 is a schematic view showing the energy level on the conduction band side of the active region in the third embodiment of the multiple quantum well semiconductor laser device according to the present invention. FIG. 3 shows an example of an asymmetric distortion modulation QW structure. This is not a structure in which the p-type and n-type cladding layers are provided with the quantum wells having the respective layer thicknesses as in the first embodiment. In particular, the quantum well layer having the layer thickness is provided only on the p-type cladding layer Cd11 side. It is intended to store electrons that easily overflow. It is generally said that holes have a large effective mass, so that carrier overflow is smaller than electrons. Therefore, an asymmetric structure having a large effect only on electrons is adopted.

The active region Act3 of the multiple quantum well semiconductor laser device according to the third embodiment has a p-type cladding layer Cd1.
1 and n-type cladding layer Cd12. The active region Act3 includes a first quantum well layer QW11 (strain ε11: layer thickness T11), a barrier layer B11, and a second quantum well layer QW12.
(Strain amount ε12: layer thickness T12), barrier layer B12, third quantum well layer QW13 (strain amount ε13: layer thickness T13), barrier layer B13, and fourth quantum well layer QW14 (strain amount ε14: layer thickness T14). In this order, the p-type cladding layers Cd11 to n
It is formed up to the mold clad layer Cd12.

Here, the layer thickness T11 of the first quantum well layer QW11 adjacent to the p-type cladding layer Cd11 is set to be large. Further, as shown in the figure, a configuration in which the layer thickness T12 of the next adjacent second quantum well layer QW12 is similarly set to a large value is also possible. On the other hand, the thickness T4 of the fourth quantum well layer QW14 adjacent to the n-type cladding layer Cd12 is small. As described above, by increasing the width of the quantum well layer adjacent to the p-type cladding layer, the capture of electrons is facilitated, and the overflow of electrons from the quantum well layer to the cladding layer is suppressed.

As described above, in this embodiment, the structure is such that the overflow of electrons is prevented by the well having the layer thickness formed on the p-type cladding layer side. In addition, by mixing quantum well layers having a large thickness, the total number of heterointerfaces can be reduced, and carrier injection efficiency and device reliability can be improved.

FIG. 4 is a schematic view of the conduction band side energy level of the active region in the multiple quantum well semiconductor laser device according to the fourth embodiment of the present invention. In the configuration of the active region Act4 of the present embodiment, the second quantum well layer QW12 (strain ε12: layer thickness T12) of the third embodiment is changed to a second quantum well layer QW12 ′ (strain ε12 ′). The strain amount ε12 ′ is slightly changed from the strain amount ε12 to make the well shallower. Although the figure particularly shows the case where the quantization level μ12 ′ is formed in addition to the quantization level μ11 common to all the quantum well layers, the embodiment is not limited to this. The function and effect are similar to those of the third embodiment.

FIG. 5 is a schematic diagram of the conduction band side energy level of the active region in the multiple quantum well semiconductor laser device according to the fifth embodiment of the present invention. This embodiment has a configuration in which non-uniformity that tends to occur in hole carrier injection is corrected by distortion modulation.

The active region Act5 of the multiple quantum well semiconductor laser device according to the fifth embodiment has a p-type cladding layer Cd2.
1 and n-type cladding layer Cd22. The active region Act5 includes a first quantum well layer QW21 (strain amount ε21: layer thickness T21), a barrier layer B21, and a second quantum well layer QW22.
(Strain amount ε22: layer thickness T21), barrier layer B22, third quantum well layer QW23 (strain amount ε23: layer thickness T21), barrier layer B23, and fourth quantum well layer QW24 (strain amount ε24: layer thickness T21). In this order, the p-type cladding layers Cd21 to n
It is formed up to the mold clad layer Cd22. Thus, the thickness of all the quantum well layers is the same T21.

The strain amount ε21 is the largest plus value and the strain amount ε2
4 and gradually decreases. Here, considering that holes are injected into the first quantum well layer QW21 from the right side, for example, the first rightmost first quantum well layer QW2
1 is sufficiently filled with holes. However, the amount of holes moving through the quantum well layer gradually decreases with energy decay.

For this reason, the pseudo-Fermi level becomes smaller in the energy band in the left quantum well layer, so that the emission wavelength from each quantum well layer advances from the first quantum well layer QW21 to the fourth quantum well layer QW24. , To increase the wavelength. This is disadvantageous in terms of gain, and it is desirable that the emission wavelength from each quantum well layer be constant.

This correction can be performed in principle by modulation of the well width, that is, control by adjusting the thickness of the quantum well layer. However, control is not easy in practice, as will be described later. Thus, in the present embodiment, this is realized by easily controlled distortion modulation.

That is, when the carrier density in each quantum well layer is different, the amount of distortion corresponding to the carrier density is formed in each quantum well layer, thereby suppressing the emission wavelength fluctuation. This configuration changes the amount of distortion according to the carrier density in order to keep the emission wavelength constant. As a result, it is possible to output a desired emission wavelength by mixing structures that are easy to manufacture or the like.

FIG. 6 is a schematic diagram of the conduction band side energy level of the active region in the multiple quantum well semiconductor laser device according to the sixth embodiment of the present invention. The configuration of the active region Act6 of the present embodiment is obtained by combining the first quantum well layer QW21 (strain amount ε21: layer thickness T21) and the second quantum well layer QW22 (strain amount ε22: layer thickness T21) of the fifth embodiment. Replaced with a new code: the first 'quantum well layer QW21' (strain ε2
1 ': layer thickness T21) and second' quantum well layer QW22 '(strain ε22': layer thickness T21). Therefore, the maximum potential barrier is located in the second 2 'quantum well layer QW22' from the p-type cladding layer Cd21. The function and effect are the same as in the fifth embodiment.

FIG. 7 is a schematic diagram of the conduction band side energy level of the active region in the multiple quantum well semiconductor laser device according to the seventh embodiment of the present invention. In the present embodiment, the band gap is adjusted by reducing the amount of distortion in advance so that the well-type potential does not deteriorate when the thickness of each quantum well layer is reduced. Thus, the deterioration of the well-type potential caused can be avoided.

In FIG. 7, the active region Act7 of the multiple quantum well semiconductor laser device according to the seventh embodiment has a p-type or n-type cladding layer Cd31 and an n-type or p-type cladding layer Cd31.
d32.

The active region Act7 has a first quantum well layer QW
31 (strain ε31: layer thickness T31), barrier layer B31, second quantum well layer QW32 (strain ε32: layer thickness T32), barrier layer B32, third quantum well layer QW33 (strain ε33:
Layer thickness T33), barrier layer B33, fourth quantum well layer QW3
4 (strain amount ε34: layer thickness T34) are formed in this order from the p-type cladding layer Cd31 to the n-type cladding layer Cd32.

Here, in each of the quantum well layers, when the layer thickness is narrow and the surrounding cladding layer and barrier layer are in a state of “
The amount of distortion is adjusted in advance, and the band gap is adjusted in advance by predicting the quantum well layer that sagging (rounding) is likely to occur. In FIG. 7, the first quantum well layer QW31 and the fourth quantum well layer QW
The band gap is adjusted in advance by changing the strain amounts ε31 and ε34 with respect to 34 and adjusting the potential barriers ΔEc31 and ΔEc34 ′ in advance. As a result, undesired deterioration of the well-type potential (so-called “drip”)
Can be prevented from occurring.

FIG. 7 shows a correction in the case where the quantum well layer located at the end of the active region Act7 is easily sagged and its band gap is easily narrowed. That is, the strain amount of the quantum well layer located at the end is changed, and the band gap is adjusted in advance. Depending on the manufacturing conditions, the quantum well layer located at the center may be easily sagged. In this case, the distortion of the quantum well layer in the central region may be changed and set, contrary to FIG.

FIG. 8 is a schematic diagram of the conduction band side energy level of the active region in the multiple quantum well semiconductor laser device according to the eighth embodiment of the present invention. The configuration of the active region Act8 of the present embodiment is different from that of the seventh embodiment in that the fourth quantum well layer QW34 is changed to a fourth quantum well layer QW34 ',
The p-type cladding layer Cd3 is adjacent to the quantum well layer QW31.
1 ', an n-type cladding layer Cd32' is arranged adjacent to the fourth quantum well layer QW34 '. Therefore, the potential barrier of the quantum well layer adjacent to the p-type cladding layer Cd31 'is not the largest of the potential barriers of all the quantum well layers. The function and effect are the same as in the seventh embodiment.

As is apparent from the above, it is difficult to control the thickness of the quantum well layer, and the thickness of the quantum well layer tends to fluctuate. On the other hand, the strain control has higher accuracy than the control of the quantum well layer thickness. For example, the Δλ / Δ quantum well layer thickness has an accuracy of about 1.5 nm / 1 Å, whereas
For example, in the case of AlGaInP, the amount of / Δ strain can be precisely controlled with an accuracy of about 0.15 nm / 0.001%. Thus, the present invention is particularly effective in delicate energy band control by introducing distortion modulation MQW.

FIG. 9 is a schematic cross-sectional view of an embodiment of a multiple quantum well semiconductor laser device of the present invention, which is of a strain amount and layer thickness modulation type. The illustrated multiple quantum well semiconductor laser device has an AlGaInP-based mixed crystal stacked structure, and this stacked structure is manufactured by steps as shown in a sequence chart of one embodiment of the manufacturing method shown in FIG.

In FIG. 9, the AlGaIn according to the present invention is shown.
The P-based mixed crystal multiple quantum well semiconductor laser Lsc is made of GaAs.
GaAs buffer layer 2, AlGaIn
P clad layer 3, MQW of GaInP / AlGaInP
MQW active region 4 of (multiple quantum well) structure, Al
It has a structure in which a GaInP clad layer 5, a GaInP layer 6, and a GaAs cap layer 7 are sequentially stacked.

Further, the AlGaInP cladding layer 5, Ga
The InP layer 6 and the GaAs cap layer 7 form a mesa structure which is selectively etched using, for example, photolithography, and a GaAs current blocking layer 8 is laminated on both sides of the mesa portion. The dopant is Se or Si for the n-type and Zn for the p-type.

MQ having MQW (Multiple Quantum Well) structure
The W active region 4 includes a first quantum well layer QW1 (strain ε1: layer thickness T1), a barrier layer B1, a second quantum well layer QW2 (strain ε2: layer thickness T2), a barrier layer B2, and a third quantum well. Layer QW
3 (strain ε3: layer thickness T3), barrier layer B3, and fourth quantum well layer QW4 (strain ε4: layer thickness T4).

The MQW active region 4 is used for the purpose of increasing the differential gain, shortening the oscillation wavelength, etc., has a layer thickness of about the de Broglie wavelength of electrons or less, and has carriers confined on both sides by energy barriers. First to fourth quantum well layers QW1 to QW made of a material having an ultra-thin structure and a narrow band gap
This is realized by a heterojunction or the like composed of W4 and barrier layers B1 to B3 of a substance having a wide band gap.

In the first to fourth quantum well layers QW1 to QW4, the motion of the electrons in the direction perpendicular to the thin layer is quantized, and the energy of the electrons associated therewith has a discrete value (energy characteristic value). And the free movement of electrons
The degree of freedom in the layer thickness direction of the quantum well layer is restricted, and the quantum well layer becomes two-dimensional (only two-dimensional electrons) limited only in the direction parallel to the layer. As a result, the electrons stored in the quantum well layer form a two-dimensional electron gas. Reflecting this confinement,
The energy eigenvalue of the carrier has a significantly different energy from that of the bulk.

Therefore, the conventional thick active layer (having a thickness of 0.1 mm) can be used.
The laser oscillates with a smaller injection current than a DH laser having about 1 μm and electrons and holes are three-dimensional. That is, the threshold current density (the amount obtained by dividing the threshold current Ith by the effective current cross-sectional area of the active region) for laser oscillation is reduced. This is due to the difference in density of states.

In a conventional DH laser device having a thick active layer, the wave function of electrons is a three-dimensional system, and therefore, the density of states of electrons in the conduction band is １ ／ of E.
Although it changes in proportion to the power (E is the energy of electrons), since the electron wave function is a two-dimensional system in the multiple quantum well semiconductor laser device as described above, the state density of electrons in the conduction band is E. Becomes a step function. That is, in a quantum well structure having a nanometer-class width, the state density of the conduction band and the valence band becomes stepwise, greatly different from the parabolic state density in the bulk crystal.

As a result, it is involved in recombination with holes.
The state density of electrons having the lowest energy level is larger in a two-dimensional system than in a three-dimensional system, so that the threshold current density for laser oscillation is reduced and the current gain is further improved.

In terms of the quantum level of carriers in each quantum well layer, for example, focusing on the first quantum well layer QW1, a quantum well using a heterojunction having a finite barrier height is formed. Is confined in the z direction when the direction of the barrier is the z direction as described above, and x, y
It becomes a free two-dimensional electron in the direction. The energy eigenvalue E of the electron (taken from the bottom of the well as the origin) is represented by [Equation 1], reflecting that the motion in the z direction is quantized by the presence of the barrier when the barrier height is sufficiently lower than Vb. Is done.

[0089]

(Equation 1)

Where kx and ky are wave numbers in the x and y directions,
Lz is the width of the well, m 'is the effective mass, and n is a natural number.
For a quantum well in the conduction band of GaAs, the effective mass is 0.06.
Since 8me (me is the mass of free electrons), kx = k
When y = 0, L = 10 nm and E = 55 meV.

In the multiple quantum well structure, discrete energy levels are split into a plurality of energy levels by the number of quantum wells, and when the thickness of the barrier (barrier layer) is small, electrons are also tunneled in the z direction perpendicular to the layer. Propagate at The wave function in the z direction is represented by [Equation 2] with the origin of the center of the quantum well.

[0092]

(Equation 2)

As described above, the higher order term of the quantization level formed in the quantum well is inversely proportional to the effective mass of the carrier and inversely proportional to the square of the thickness (width) of the quantum well layer. . Therefore, the quantization level of the electrons in the conduction band can be controlled by changing the thickness of the quantum well layer. on the other hand,
Heavy holes (HH) with different effective masses in the valence band
A difference occurs between the quantization energy levels of the light and the light holes (LH), and the two kinds of holes that have been degenerated in the bulk crystal have different energies.

Since the multiple quantum well MQW has a structure in which a plurality of quantum wells QW are periodically stacked and the energy barrier between adjacent quantum wells is large, the energy barrier layer serving as a barrier is particularly preferable. In a structure that is extremely thin and has strong quantum mechanical coupling between quantum wells, a superlattice is formed.

The first to fourth quantum well layers QW1 to QW
No. 4 has a strain structure with strain amounts ε1 to ε4. In such a strained structure of the quantum well layer, the crystal lattice of the well is distorted by setting the lattice constant of the material forming the well to a value different from the lattice constant of the substrate crystal or the cladding layer. At this time, conditions are set such that lattice relaxation due to dislocation or the like does not occur. Generally, the lattice constant of a mixed crystal changes in proportion to the component ratio, and the physical properties change continuously with respect to the component ratio.

When a compressive stress is applied, the band gap is widened and an HH (heavy hole) band is located at the top of the valence band. Under compressive stress, the effective mass of HH in the in-plane direction of the substrate becomes small, and the threshold value is reduced. In addition, holes are concentrated near the γ point due to changes in the band structure, which greatly reduces Auger recombination and absorption between valence bands, resulting in low threshold and high efficiency operation, improved temperature characteristics, and improved differential gain. Increase, reduction in line width, high-speed modulation operation, and the like can be performed.

When a tensile stress is applied, the band gap becomes narrower, and either a heavy hole (HH) or a light hole (LH) is formed at the top of the valence band depending on the magnitude of the stress and the well width. Band will be located. Control of the band located at the top of these valence bands enables TE / TM mode control. As a result, the output of the strained quantum well is 125% of that of the unstrained quantum well, which is 15% of that of the bulk active layer LD.
It is improved to 0%.

When the oscillation wavelength is kept constant by minus distortion, the distortion is increased and the layer thickness is increased. It is also effective to pay attention to the critical layer thickness or to add distortion compensation to the barrier layer. When the oscillation wavelength is made constant by the positive distortion, the distortion is increased to make it easy to obtain the gain, but it is necessary to reduce the thickness of the layer at the same time, and it is necessary to increase the number of quantum well layers.

For manufacturing the AlGaInP-based semiconductor laser device Lsc according to the present invention, the method for manufacturing a semiconductor laser device having a multiple quantum well structure according to the present invention shown in FIG. 10 is applied. FIG. 10 is a sequence chart showing a combination of materials to be transported to the reaction region when each of the stacked semiconductor layers is grown, and the horizontal axis indicates time. Further, each semiconductor layer corresponds to each semiconductor layer shown in FIG. 9, and therefore, in the following description, FIG. 9 is appropriately referred to.

When the growth reaction is started, the GaAs buffer layer 2 is epitaxially grown on the GaAs substrate.
Here, on the substrate 1, TMG (trimethyl gallium),
AsH ₃ (arsenic trihydride: arsine) and H ₂ Se
(Hydrogen selenide) is supplied in a gaseous state. Thereby, the GaAs buffer layer 2 becomes n-type.

After the GaAs buffer layer 2 having a predetermined thickness is formed, an Al layer is formed on the GaAs buffer layer 2.
The GaInP cladding layer 3 is grown by lamination. Where TM
G (trimethyl gallium), TMA (trimethyl aluminum), TMI (trimethyl indium), P
H ₃ (phosphine) and H ₂ Se (hydrogen selenide)
Is supplied in a gaseous state. Thereby, AlGaIn
The P cladding layer 3 becomes n-type.

As described above, the AlGaI having a predetermined thickness
When the nP cladding layer 3 is formed, the AlGa
On the InP cladding layer 3, an MQW active region 4 having an MQW (multiple quantum well) structure is grown by lamination. MQW
The active region 4 includes a first quantum well layer QW1, a barrier layer B1,
The second quantum well layer QW2, the barrier layer B2, the third quantum well layer QW3, the barrier layer B3, and the fourth quantum well layer QW4 are stacked in this order.

In the meantime, during the formation period of the first quantum well layer QW1, for example, if the first quantum well layer QW1 is Ga (0.43) In (0.57) P ε1 = + 0.65%, the weight is reduced. TMG (trimethyl gallium), increased TMI (trimethyl indium),
PH ₃ (phosphine) is supplied in a gaseous state. Second
For the .about.4 quantum well layers QW2 to QW4, source gas corresponding to the specified composition is supplied at a concentration or / and flow rate corresponding to the specified composition ratio.

In the formation period of the barrier layers B1 to B3, TM
G (trimethyl gallium), TMA (trimethyl aluminum), TMI (trimethyl indium), P
H ₃ (phosphine) is supplied in a gaseous state.

When the MQW active region 4 having a predetermined thickness is formed, an AlGaInP clad layer 5 is grown by lamination. Where TMG (trimethyl gallium), TMA
(Trimethyl aluminum), TMI (trimethyl
Indium), DMZ (dimethylzinc), PH ₃ (phosphine) are supplied in gaseous phase. Thereby, Al
The GaInP cladding layer 5 becomes p-type.

An AlGaInP clad layer 5 having a predetermined thickness
Is formed, a GaInP layer 6 is then grown on the AlGaInP clad layer 5. Where TM
G (trimethyl gallium), TMI (trimethyl indium), DMZ (dimethyl zinc), and PH ₃ (phosphine) are supplied in a gas phase.

When the GaInP layer 6 is formed to a predetermined thickness in this way, the GaInP layer 6
The GaAs cap layer 7 is stacked and grown. Here, T
MG (trimethyl gallium) and AsH ₃ (arsine)
And DMZ (dimethylzinc) alone in the gas phase for time t6
Is supplied up to. After that, GaAs is used in the etching process.
The current block layer 8 is formed to form a mesa structure.

[0108]

As described in detail above, the present invention is mainly directed to an element structure which is optimized by using the amount of strain of the quantum well layer as a controllable amount, or the amount of strain and the layer thickness (well width) as a controllable amount. By setting the difference between the quantization level of carriers in the quantum well layer and the potential barrier to a predetermined value, the overflow characteristics of electrons or / and holes, especially the overflow characteristics of electrons, are improved. The carrier injection efficiency and the threshold current Ith can be improved, and the oscillation wavelength can be stabilized.

Further, by setting the thickness of the quantum well layer to be equal to or more than the minimum limit thickness, there is an effect that it is possible to avoid the deterioration of the well-type potential caused by the configuration having the minimum limit thickness or less. .

[Brief description of the drawings]

FIG. 1 is a schematic view of a conduction band side energy level of an active region in a multiple quantum well semiconductor laser device according to a first embodiment of the present invention.

FIG. 2 is a schematic diagram of a conduction band side energy level of an active region in a multiple quantum well semiconductor laser device according to a second embodiment of the present invention.

FIG. 3 is a schematic diagram of a conduction band side energy level of an active region in a multiple quantum well semiconductor laser device according to a third embodiment of the present invention.

FIG. 4 is a schematic diagram of a conduction band side energy level of an active region in a multiple quantum well semiconductor laser device according to a fourth embodiment of the present invention.

FIG. 5 is a schematic diagram of a conduction band side energy level of an active region in a multiple quantum well semiconductor laser device according to a fifth embodiment of the present invention.

FIG. 6 is a schematic diagram of a conduction band side energy level of an active region in a multiple quantum well semiconductor laser device according to a sixth embodiment of the present invention.

FIG. 7 is a schematic diagram of a conduction band side energy level of an active region in a multiple quantum well semiconductor laser device according to a seventh embodiment of the present invention.

FIG. 8 is a schematic diagram of a conduction band side energy level of an active region in an eighth embodiment of the multiple quantum well semiconductor laser device according to the present invention.

FIG. 9 is a schematic cross-sectional view of an embodiment of a multiple quantum well semiconductor laser device of a strain amount and layer thickness modulation type according to the present invention.

FIG. 10 is a sequence chart of an embodiment of a method for manufacturing a multiple quantum well semiconductor laser device of a strain amount and layer thickness modulation type according to the present invention.

FIG. 11 is a schematic diagram of an energy band gap in a conventional MQW structure having a constant distortion amount.

FIG. 12 is a schematic diagram of a conduction band side energy level of an active region in a configuration in which the strain amount is gradually increased with a constant quantum well layer thickness.

FIG. 13 is a schematic diagram of a conduction band side energy level of an active region in a conventional configuration in which the thickness of a quantum well layer is adjusted.

FIG. 14 is a diagram showing a strain amount dependence of an electron potential barrier in a conduction band.

FIG. 15 is a diagram showing the dependence of the oscillation threshold current on the amount of distortion in a double quantum well semiconductor laser.

[Explanation of symbols]

QW1 first quantum well layer, QW2 second quantum well layer, QW3 third quantum well layer, QW4 fourth quantum well layer, T1 layer thickness of first quantum well layer, T2 ... Layer thickness of second quantum well layer, T3... Layer thickness of third quantum well layer, T4
... Layer thickness of fourth quantum well layer, ε1... Strain amount of first quantum well layer, ε2... Strain amount of second quantum well layer, ε3... Strain amount of third quantum well layer, ε4. Strain amount of the fourth quantum well layer, ΔE
c1... potential barrier of the conduction band of the first quantum well layer;
ΔEc2: potential barrier of the conduction band of the second quantum well layer; ΔEc3: potential barrier of the conduction band of the third quantum well layer; ΔEc4: potential barrier of the conduction band of the fourth quantum well layer; Quantization level, CBD, conduction band, Cd1, p-type or n-type cladding layer, Cd2,
... n-type or p-type cladding layer, B1 ... first barrier layer, B2 ... second barrier layer, B3 ... third barrier layer

Claims (16)

[Claims] An active region includes a p-type cladding layer and an n-type cladding layer sandwiching the active region, wherein the active region includes a plurality of quantum well layers, and each of the quantum well layers is adjacent to the cladding layer or And / or a semiconductor laser device having a multiple quantum well structure forming a potential barrier between barrier layers, wherein a difference between a quantization level of carriers in each of the quantum well layers and the potential barrier is a predetermined value. A semiconductor laser device having a multiple quantum well structure, wherein a strain amount of each quantum well layer is formed, or a strain amount and a layer thickness are formed. 2. The band gap is adjusted by previously reducing the amount of negative strain or increasing the amount of positive strain when the thickness of each quantum well layer is reduced. A semiconductor laser device having the multiple quantum well structure according to the above. 3. The quantum well layer adjacent to at least one of the p-type cladding layer and the n-type cladding layer has a greater thickness than other quantum well layers. A semiconductor laser device having the multiple quantum well structure according to the above. 4. The quantum well layer adjacent to at least one of the p-type clad layer and the n-type clad layer is configured to be thicker than other quantum well layers, and each of the quantum well layers has a thickness. 2. The semiconductor laser device having a multiple quantum well structure according to claim 1, wherein the band gap is adjusted by decreasing the amount of negative strain or increasing the amount of positive strain in advance when the thickness becomes narrow. 5. When the carrier density in each of the quantum well layers is different, a variation in emission wavelength is suppressed by forming a strain amount corresponding to the carrier density in each of the quantum well layers. A semiconductor laser device having a multiple quantum well structure according to claim 1. 6. When the thickness of each of the quantum well layers is reduced, the band gap is adjusted by reducing the amount of negative strain or increasing the amount of positive strain in advance, and 2. The multiple quantum well structure according to claim 1, wherein when the carrier density is different, a variation in emission wavelength is suppressed by forming a strain amount corresponding to the carrier density in each of the quantum well layers. Semiconductor laser device. 7. The quantum well layer adjacent to at least one of the p-type clad layer and the n-type clad layer is formed to be thicker than the other quantum well layers, and each quantum well layer has 2. The multiple quantum well structure according to claim 1, wherein when the carrier density is different, a variation in emission wavelength is suppressed by forming a strain amount corresponding to the carrier density in each of the quantum well layers. Semiconductor laser device. 8. When the thickness of each quantum well layer is reduced, the band gap is adjusted by decreasing the amount of negative strain or increasing the amount of positive strain in advance, and
When the layer thickness of the quantum well layer adjacent to at least one of the n-type cladding layer or the n-type cladding layer is configured to be thicker than the layer thickness of the other quantum well layers, and the carrier density in each of the quantum well layers is different, 2. The semiconductor laser device having a multiple quantum well structure according to claim 1, wherein a variation in emission wavelength is suppressed by forming a strain amount corresponding to the carrier density in each of the quantum well layers. 9. An active region, comprising a p-type cladding layer and an n-type cladding layer sandwiching the active region, wherein the active region comprises a plurality of quantum well layers, and each of the quantum well layers is adjacent to the cladding layer or And / or a method of manufacturing a semiconductor laser device having a multiple quantum well structure in which a potential barrier is formed between barrier layers, wherein a difference between a quantization level of carriers in each of the quantum well layers and the potential barrier is a predetermined value. A method of manufacturing a semiconductor laser device having a multiple quantum well structure, wherein a strain amount of each of the quantum well layers is formed, or a strain amount and a layer thickness are formed. 10. The band gap is adjusted by previously reducing the amount of negative strain or increasing the amount of positive strain when the thickness of each quantum well layer becomes narrow. Of manufacturing a semiconductor laser device having a multiple quantum well structure. 11. The quantum well layer adjacent to at least one of the p-type clad layer and the n-type clad layer is formed to be thicker than other quantum well layers. Of manufacturing a semiconductor laser device having a multiple quantum well structure. 12. The quantum well layer adjacent to the p-type cladding layer and / or the n-type cladding layer is formed to be thicker than other quantum well layers, and the thickness of each of the quantum well layers is made larger. 10. The method of manufacturing a semiconductor laser device having a multi-quantum well structure according to claim 9, wherein the band gap is adjusted by reducing the amount of negative strain or increasing the amount of positive strain in advance when the width becomes narrow. . 13. The multiple quantum well structure according to claim 9, wherein when each of the quantum well layers has a different carrier density, a strain amount corresponding to the carrier density is formed in each of the quantum well layers. A method for manufacturing a semiconductor laser device comprising: 14. When the thickness of each of the quantum well layers is reduced, the band gap is adjusted by previously reducing the amount of negative strain or increasing the amount of positive strain, and 10. The method according to claim 9, wherein when the carrier density is different, a strain amount corresponding to the carrier density is formed in each of the quantum well layers. 15. The quantum well layer adjacent to at least one of the p-type clad layer and the n-type clad layer is formed to be thicker than the other quantum well layers. 10. The method according to claim 9, wherein when the carrier density is different, a strain amount corresponding to the carrier density is formed in each of the quantum well layers. 16. When the thickness of each of the quantum well layers is reduced, the band gap is adjusted by reducing the amount of negative strain or increasing the amount of positive strain in advance, and
Forming a layer thickness of the quantum well layer adjacent to at least one of the n-type cladding layer or the n-type cladding layer larger than the layer thickness of the other quantum well layers, and when the carrier density in each of the quantum well layers is different, 10. The method according to claim 9, wherein a strain amount corresponding to the carrier density is formed in each of the quantum well layers.