JP2933051B2 - Multiple quantum well structure optical semiconductor device and method of manufacturing the same - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical semiconductor device having a multiple quantum well structure typified by, for example, a semiconductor laser and a method of manufacturing the same, and more particularly, to strain well layers and barrier layers in opposite directions. An optical semiconductor device having a strained multiple quantum well structure and a method of manufacturing the same.

[0002]

2. Description of the Related Art Multi-quantum well structures
1, hereinafter referred to as an MQW structure) as an active layer, when a strain stress is applied to the active layer by using a crystal having a lattice constant different from the lattice constant of the substrate in a well layer (hereinafter referred to as a well layer). It is known that light output characteristics are greatly improved. At this time, recently, attempts are often made to apply a strain in a direction opposite to the strain of the well layer to a barrier layer (hereinafter referred to as a barrier layer) to prevent the accumulation of strain stress and prevent the introduction of crystal defects. This technique is generally called distortion compensation.

[0003] As an example of distortion compensation, I
A "semiconductor optical device" having an nGaAs compressive strain well layer and a GaAsP tensile strain barrier layer is disclosed in JP-A-3-3384. Also, 1995, Journal of Applied Physics, Volume 15, H. Ooha
shi, et al, "1.3μm InAsP compressively strained mul
tiple-quantum-well lasers for high-temperature ope
ration ", (J. Appl. Phys., 15, p. 4119 (1995)) includes InA
s _0.52 P _0.48 compressive strain well layer and 1.1 at −0.6% strain
A strain-compensated MQW using a combination of InGaAsP barrier layers corresponding to a band gap of μm has been proposed.
Further, assuming that the same strain MQW is used,
In 1995, the Institute of Electronics, Information and Communication Engineers, Ohashi et al., "InP Compressive Strain MQW Laser for High Temperature Operation" reported excellent high temperature characteristics.

When compressive strain is applied to the well layer, applying tensile strain to the barrier layer has not only the effect of compensating for strain but also the effect of improving the behavior of carrier injection by changing the band lineup. The tensile strain barrier layer increases the barrier of electrons, thereby preventing the overflow of electrons having a small effective mass, and reducing the barrier of holes (hereinafter, referred to as holes). To be uniformly injected.

However, in such distortion compensation,
There is a disadvantage that a large difference in lattice constant occurs at the interface between the well layer and the barrier layer, and crystal defects easily enter from this interface. In order to avoid this problem, attempts have been made to eliminate a sudden change in the lattice constant by inserting a layer having a lattice constant between the well layer and the barrier layer between the two. Published in 1995, Electronics Letters, Vol. 31, A. Ougazzaden, A. Mircea and C. Kaz
mierski, "High temperature characteristic To and lo
w threshold current density of 1.3μm InAsP / InGaP /
InP compensated strain multiquantum well structure
lasers ", (Electronics Letters, 31, p. 803 (1995)), a 1.7% compressive strain InAsP well layer and -1.4%.
Two atomic layers of In between the tensile strained InGaP barrier layers
By inserting the P layer, the quality of the crystal is improved. Sectional structure and its surrounding strained MQW as used herein is as shown in FIG. 16, InP insertion layer 108 is interposed between the compressive strain InAs _y P _1-y well layer 6 and the tensile strained InGaP barrier layer 207 Have been.

FIG. 17 shows the composition of the material used in the strain MQW. In the case of this material system, the compressive strain InAs _y P _1-y well layer 6 and the InP insertion layer 1
08, the only difference is whether As is present or not.
nP insertion layer 108 and tensile strained InGaP barrier layer 20
7, the only difference is the presence or absence of Ga, and the interface switching during crystal growth is easy. FIG. 18 shows a band diagram of the distortion MQW. In this structure, since a high barrier called a tensile strained InGaP barrier layer 207 is used, holes having a large effective mass are not uniformly injected into each well layer. For this reason, although this structure has good crystallinity, when a semiconductor laser is formed, the lasing threshold is not sufficiently lowered, and the internal differential quantum efficiency cannot be increased any more.

As described above, InGaP / InP / InA
In the sP system, there was a problem that the barrier was too high. However, the "multiple quantum well structure semiconductor laser" disclosed in Japanese Patent Application Laid-Open No. Hei 8-116129 proposes a method that does not cause this kind of problem. The details will be described below with reference to the drawings. A strained MQW in a conventional semiconductor laser of this type and its periphery have a cross-sectional structure as shown in FIG.

In the manufacturing process, InP / I
The epitaxial growth of nGaAsP is performed by metal organic vapor phase epitaxy (hereinafter referred to as MO).
-VPE) method. Source gas MO-VPE is trimethyl indium (hereinafter referred to as TMI), trimethyl gallium (hereinafter referred to as TMG), trimethyl aluminum (hereinafter, referred to as TMAl), arsine (hereinafter referred to as AsH _3), phosphine ( hereinafter, reference to referred to as PH _3), organometallic supplies by bubbling of hydrogen. Regarding doping, disilane (hereinafter, referred to as
Si ₂ referred to as H _6), dimethyl zinc (hereinafter referred to as DMZn) using gas diluted with hydrogen.

First, an n-InP buffer layer 2 is grown to a thickness of 0.5 μm on an n-type InP substrate 1 having a (100) plane orientation, and then the composition is In _0.84 Ga _0.16 As.
_0.35 P _0.65 unstrained n-InGaAsP guide layer 3
A strained MQW layer 5 is grown sequentially from 0 to 100 nm. Distortion M
QW layer 5, and a five-layer compressive strain _{In 1-x Ga x As y} P 1-y well layer 206, sandwiched between unstrained _{In 1-x Ga x As y} P 1-y intermediate layer 8 therebetween tensile strain _{in 1-x Ga x as y} P 1-y barrier layer 107 in which is disposed. Specifically, compressive strain _{In 1-x Ga x As y} P 1-y well layers 206, 4 nm
Undoped In _0.96 Ga _0.04 As with a thickness of 1.4% and a strain of 1.4%
_0.54 P _0.46 . Tensile strain _{In 1-x Ga x As y} P
_{The 1-y} barrier layer 107 is undoped In _0.71 Ga _0.29 As _0.46 P _0.54 with a thickness of 6 nm and a strain of −0.6%. Unstrained _{In 1-x Ga x As y} P 1-y intermediate layer 8 is In _0.84 Ga _0.16 As _0.35 P _0.65 of 2nm thick.

On the strained MQW layer 5, an InGaAsP layer having a composition equal to that of the n-InGaAsP guide layer 3 is formed.
The guide layer 10 is grown. Further, a p-InP cladding layer 11 is grown.

Using this strained MQW structure, the resonator length 30
When a semiconductor laser having a front end face coating film of 0 μm and a reflectivity of 30% and a rear end face coating film of a reflectivity of 75% is prepared, a semiconductor laser device having a threshold current of 6 mA and a slope efficiency of 0.6 W / A is obtained. Is obtained. In addition,
Slope efficiency is defined as the rate of increase in light output from the front end face relative to the injected current after oscillation.

In the above-described strained MQW, stress compensation is possible, and there is no large change in lattice constant at the interface.
A large distortion amount of 1.4% is also possible. However, for example, the well layer 206 of In _0.96 Ga _0.04 As _0.54 P _0.46 , the intermediate layer 8 of In _0.84 Ga _0.16 As _0.35 P _0.65 , the barrier layer 107 of In _0.71 Ga _0.29 As _0.46 P _0.54
The composition of all the atomic species must be switched during the sequential formation of InGaP / InP /
There are not a few atomic species that are switched at the interface as in the InAsP system. Therefore, the influence of roughness and segregation at the interface is likely to occur. Therefore, if an attempt is made to realize a large strain amount as in the case of the InAsP well, it is difficult to stably manufacture the MO-VPE.

[0013]

That is, the conventional distortion MQ
The optical semiconductor device having the W structure has the following problems. The first problem is that when an intermediate layer is inserted to reduce the difference in lattice constant at the well layer / barrier layer interface of the stress-strain compensation type MQW, the switching interface in crystal growth increases, and the adverse effect of the interface is reduced. It is easy to receive. In a system such as InGaP / InP / InAsP, switching of the interface is simple, and the problem of the interface can be ignored. However, since the barrier barrier is too high, carrier injection cannot be performed with good uniformity. That is, in the prior art, it was impossible to achieve both the point that the carrier injection was not hindered and the point that the switching of the interface was not complicated. As a result, when this structure was applied to a semiconductor laser, sufficient optical characteristics could not be obtained. The reason is that in the problem of switching of the interface, there is a fluctuation at the time of switching the material supply in the MO-VPE, so that segregation at the interface is likely to occur, and in the problem of carrier injection,
If the barrier is high, holes having a large effective mass cannot move between the wells, and are injected unevenly in the p-side well layer.

The second problem is that the presence of the intermediate layer between the well layer and the barrier layer makes carrier injection not sufficiently uniform. The reason is that, in a compressive strained well / tensile strained barrier without an intermediate layer, the energy difference between the heavy hole level in the well layer and the edge of the light hole band in the barrier layer is generally small. It is easy to move and the injection of holes becomes uniform, but if there is an intermediate layer, its flow is obstructed. In particular, since the InGaAsP-based material has a large valence band discontinuity, non-uniformity of hole carrier injection greatly affects device characteristics.

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned problems. In a stress-strain compensation type MQW structure in which an intermediate layer is inserted between a well layer and a barrier layer, the present invention does not impair carrier injection. An object of the present invention is to eliminate problems such as interface segregation and turbulence. Another purpose is to use the distortion MQW
The purpose is to make the hole injection into the holes uniform. Further, based on the above points, it is an object to provide an optical semiconductor device capable of realizing a reduction in threshold current of a strained MQW semiconductor laser, an improvement in slope efficiency, and an improvement in high output and high temperature characteristics, and a method for manufacturing the same. .

[0016]

In order to achieve the above object, an MQW structure optical semiconductor device of the present invention comprises: (1) a substrate having a well layer and a barrier layer made of a group III-V compound semiconductor on a substrate; In the optical semiconductor device provided with the MQW structure, an intermediate layer is provided between the well layer and the barrier layer, and the well layer and the intermediate layer constitute these layers.
The group V compound semiconductors have the same composition ratio, and the barrier layer and the intermediate layer are composed of the group III-V compound semiconductors II.
(2) the intermediate layer and the substrate made of a III-V compound semiconductor have the same lattice constant;
(3) The substrate is InP and the barrier layer is InG
aAsP.

The method of manufacturing an optical semiconductor device having an MQW structure according to the present invention is directed to a method of manufacturing an optical semiconductor device having an MQW structure having a well layer and a barrier layer made of a group III-V compound semiconductor on a substrate. the intermediate layer was formed between the layer and the barrier layer, while the crystal growth of the well layer and the intermediate layer supplies the V group material while maintaining the supply amount of group V raw material constant, and the well layer and the intermediate layer Switch
Sometimes, only the supply amount of the group III raw material is changed, and the supply amount of the group III raw material is kept constant during the crystal growth of the intermediate layer and the barrier layer.
It supplies the III group material while maintaining an intermediate layer
When switching to the barrier, only the supply amount of the group V raw material is changed.

Another aspect of the present invention is an optical semiconductor device having a strained MQW structure in which (1) a well layer subjected to compressive strain and a barrier layer subjected to tensile strain are provided. (2) In an optical semiconductor device having a strained MQW structure in which a light hole band end of a layer is equal to a light hole band end of a barrier layer, and (2) a well layer subjected to tensile strain and a barrier layer subjected to compressive strain are provided. (3) In (1) and (2), an unstrained thin film intermediate layer is provided between the well layer and the barrier layer, wherein the heavy hole band edge of the layer is equal to the heavy hole band edge of the barrier layer. Respectively.

In the MQW structure composed of a group III-V compound semiconductor, it is necessary to switch the source gas serving as a source of group III and group V elements at the interface between the well layer and the barrier layer. The problem of segregation at the interface occurs due to the problem of the switching timing. In particular, when an intermediate layer is provided between the well layer and the barrier layer, the number of interfaces increases, so that the stress at the weak interface has a considerable adverse effect on the entire strain MQW. On the other hand, when only the group III is switched between the well layer and the intermediate layer and only the group V is switched between the intermediate layer and the barrier layer as in the present invention, the intermediate layer is inserted without increasing the number of times of gas switching. Therefore, the crystallinity of the strained MQW can be kept good.

Further, in the compressive strain MQW, the hole injection can be made uniform by making the level of the light hole bulk and making the p-side SCH layer a tensile strain. This is because if the p-side SCH is in tensile strain, the injected hole becomes a light hole when entering the SCH and enters the MQW. The SCH is Sepa
Rate Confinement Heterostructure (separated confinement heterostructure), which has the function of confining guided light. Here, if the number of light hole levels in the MQW is one, the light hole can spread in the MQW without feeling a potential barrier. And
The widened light hole falls equally to the heavy hole level of each well. Also, when heat is released from a hole at the level of a heavy hole in a well, the hole is released to a light hole as a bulk, so that the hole can be moved to a farther well. Therefore, hole injection can be easily made uniform between the wells.

As described above, in the semiconductor laser using the strained MQW as the active layer, the reduction of the threshold current, the improvement of the slope efficiency, the improvement of the maximum light output, the improvement of the temperature characteristic, and the improvement of the reliability are achieved.

[0022]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, a first embodiment of the present invention will be described with reference to FIGS. FIG. 1 is a sectional view showing an MQW structure of a semiconductor laser (optical semiconductor device) according to the present embodiment.

As shown in FIG. 1, in the case of the semiconductor laser according to the present embodiment, an n-InP buffer layer 2 has a thickness of 0.1 to 1 μm on an n-type InP substrate 1 having a (100) plane orientation.
m, n-InGaAsP guide layer 3 is 30 to 100 n
m, tensile strain In _1-x Ga _x AsP-SCH layer 4
20 nm, strained MQW layer 5, tensile strained In _1-x Ga _x As
P-SCH layer 9 is 4 to 20 nm, InGaAsP guide layer 10 is 30 to 100 nm, p-InP cladding layer 11
Are sequentially laminated.

In the above laminated structure, the strained MQW layer 5
Unstrained _{In 1-x Ga x As y} P 1-y intermediate layer 8 compressive strain InAs _y P _1-y well layers 6 sandwiched by the provided 15 layers of three layers,
Tensile strain In _1-x Ga _x AsP barrier layer 7 between them
Are arranged. And the compression strain InAs _y P
_1-y well layers 6 and unstrained _{In 1-x Ga x As y} P 1-y intermediate layer 8
, The values of the composition ratio y are equal. Further, the tensile strained In _1-x Ga _x AsP barrier layer 7 and the unstrained In _1-x
Looking at the Ga _x As _y P _{1 -y} intermediate layer 8, the values of the composition ratio x are equal. Further, tensile strain In _1-x Ga _x As
P-SCH layer 4 and tensile strain In _1-x Ga _x AsP-SC
The H layer 9 has the same composition as the tensile strained In _1-x Ga _x AsP barrier layer 7.

The compressive strain InAs _y P _{1 -y} well layer 6 has a strain amount of 1.3 to 1.7% and a composition y of 0.43 to 0.53.
It is. If the thickness is adjusted in the range of 7 nm to 3 nm,
It becomes the active layer of the semiconductor laser for the 1.3 μm band. The tensile strained In _1-x Ga _x AsP barrier layer 7 has a thickness of 15 nm.
The tensile strain amount is set so that the average value weighted by the layer thickness with the compressive strain of the well layer becomes 0 as much as possible.
The thickness of the unstrained _{In 1-x Ga x As y} P 1-y intermediate layer 8, 0.3
It may be about nm to 2.4 nm.

FIG. 2 is a band diagram of the MQW structure of the semiconductor laser. As shown in this figure, the conduction band ends of the n-InGaAsP guide layer 3 and the InGaAsP guide layer 10 have tensile strain In _1-x Ga _x As.
P-SCH layer 4 and the tensile strain In _1-x Ga _x AsP-
The height is higher than the conduction band edge of the SCH layer 9 so that electron carriers do not overflow. In addition, the compression strain InAs
_The composition is selected so that the ends of the light hole bands of the _y P _1-y well layer 6 and the tensile strained In _1-x Ga _x AsP barrier layer 7 are as equal as possible. Furthermore, no strain _{In 1-x Ga x As y} P 1-y
It is preferable to make the thickness of the intermediate layer 8 sufficiently thin so that no quantum level of a light hole can be formed in the strained MQW layer 5. At this time, the light hole carriers in the strained MQW layer 5 behave as in a bulk.

FIG. 3 is a sectional view of a semiconductor laser according to a modification of the present embodiment. In this example, instead of the compressive strain InAs _y P _1-y well layer 6 of the above embodiment, a compressive strain InG
It is used aAs _y P _1-y well layers 106. This makes it suitable for a semiconductor laser in the band of 1.4 to 1.65 μm. FIG. 4 is a band diagram in this case.

Next, a method of forming an MQW structure according to the present embodiment will be described in detail with reference to FIGS. Crystal growth is performed using MO-VPE. First, in a PH ₃ atmosphere in a growth furnace, n-type In
The P substrate 1 is heated to 650 ° C. Next, TMI, TM
G, AsH ₃ , and PH ₃ are supplied to provide an n-InP buffer layer 2, an n-InGaAsP guide layer 3, and a tensile strain In.
_{A 1-x} Ga _x AsP-SCH layer 4, a strained MQW layer 5, a tensile strained In _1-x Ga _x AsP-SCH layer 9, an InGaAsP guide layer 10, and a p-InP cladding layer 11 are sequentially grown. Tertiary butyl arsine and tertiary butyl phosphine may be used instead of AsH ₃ and PH ₃ . For doping, Si ₂ H ₆ and DMZn gas are used as appropriate.

In the strained MQW layer 5, the compression strain InAs _y P
The _1-y well layers 6 or compressive strain InGaAs _y P _1-y well layer 106 / unstrained _{In 1-x Ga x As y} P 1-y intermediate layer 8 / tensile strain In _1-x Ga _x AsP barrier layer 7 The method of switching the interface during growth is as follows. Well layer 6,
When switching between the growth of the intermediate layer 8 and the growth of the
Without stopping supply of AsH ₃ (Group V raw material) and PH ₃ (Group V raw material), the flow is continued at a constant flow rate, and only the supply of TMG (Group III raw material) is switched. The interface switching between the intermediate layer 8 and the barrier layer 7 is performed by using TMI (Group III raw material), TM
The supply of G (Group III raw material) and PH ₃ (Group V raw material) is not stopped and is continued to flow at a constant flow rate so that only the AsH ₃ (Group V raw material) flow value is changed.

Note that, instead of the configuration of the strained MQW layer 5 in the above embodiment, an InAsP well layer / InGaAlAsP intermediate layer / InGaAlAsP barrier layer on an InP substrate can be used. That is, the distortion-free I
Using nGaAlAsP, using InGaAsP in which Al is removed from the intermediate layer for the well layer, and using A from the intermediate layer for the barrier layer.
Tensile strain InGa with only s / V ratio (composition ratio y) changed
AlAsP may be used. When the crystal is grown in this strained MQW structure, the gas switching of the well layer / intermediate layer is performed by TM
Only ON / OFF of Al is performed, and gas switching of the intermediate layer / barrier layer is only switching of the flow rate of AsH ₃ .

Further, the above structure is changed to a strain M on a GaAs substrate.
Of course, it can be applied to the QW layer. Further, a structure in which the group V ratio is switched between the intermediate layer and the barrier layer continuously or stepwise may be adopted. In this case, there is an effect that the change of the lattice constant becomes more gradual, and the possibility of introducing dislocations is further reduced.

Hereinafter, a second embodiment of the present invention will be described with reference to FIGS.
This will be described with reference to FIG. FIG. 6 is a cross-sectional view showing the MQW structure of the semiconductor laser (optical semiconductor device) of the present embodiment.

The semiconductor laser according to the present embodiment shown in FIG. 6 has a compressively strained InAs _y P _{1 -y} well layer 6 and a strain _- free In ₁ -xG layer.
a _x As _y P _1-y intermediate layer 8, tensile strain In _1-x Ga x As _y
The composition of the P _1-y barrier layer 107 is obtained by linearly changing y versus x. And tensile strain In _{1-x
Ga x As y P 1-y} SCH layer 104 and the tensile strain In _1-x G
The composition of _{a x As y P 1-y} SCH layer 109, tensile strain I
equal to the composition of the _{n 1-x Ga x As y} P 1-y barrier layers 107.

FIG. 7 is a band diagram of the semiconductor laser of this embodiment. Compression strain InA
s _y P _1-y well layers 6 and unstrained _{In 1-x Ga x As y} P 1-y intermediate layer 8 and tensile strain _{In 1-x Ga x As y} P 1-y barrier layers 10
Each composition is determined such that all light hole band edges of 7 are equal.

Further, as a modification of the present embodiment, there is a strained MQW for a semiconductor laser in a band of 1.4 μm to 1.65 μm as shown in FIG. In this structure, instead of the 3-way compressive strain in FIG. 6 InAs _y P _1-y well layer 6, quaternary compressive strain _{In 1-x Ga x As y} P 1-y well layers 20
6 is used. FIG. 9 is a band diagram in that case.

FIG. 10 is a composition diagram. Although gas switching cannot be simplified as in the first embodiment, gas switching is performed so as to be linear in the composition diagram, so that the gas switching amount is minimized. Moreover, this straight line is not a straight line but a straight line in which the light hole band edge of the strained epitaxial crystal on InP is constant. Therefore, this strain MQW can make the edge of the light hole band in the strain MQW uniform, as shown in FIGS. 7 and 9, while minimizing the amount of gas switching. Further, in the present embodiment, the tensile strain of the strained MQW layer 5 and both sides thereof _{In 1-x Ga x As y} P 1-y S
CH layer 104, tensile strain _{In 1-x Ga x As y} P 1-y SC
Since there is no obstacle to the light hole in the H layer 109, there is an advantage that the uniform injection of the hole into each well is further improved.

As described above, here, InGa on the InP substrate is used.
AsP system was described, but InP with Al added thereto
The same can be applied to the InGaAlAsP system on the substrate.

Further, the compressive strain well / tensile strain barrier has been described so far. However, like a visible laser in the 630 nm band, an InGaAlP-based tensile strain well / tensile strain barrier is used.
In the case where a compression strain barrier is used, the edge of the heavy hole band can be made constant. In this case, the distortion M
The heavy holes move freely within the QW, and are uniformly injected into the light hole levels in each well.

In this crystal growth method, as shown in FIG. 11, first, an n-Ga
0.5 μm of n-InGaAs
The 1P cladding layer 103 is grown by 1 μm. Next, the compression strain InAlP guide layer 304, the strain MQW layer 5, the compression strain I
A nAlP guide layer 309 is grown. Strained MQW layer 5
Is composed of four tensile-strained InGaP well layers 306 sandwiched between non-strained InGaAlP intermediate layers 208 and a compression-strained InAlP barrier layer 307 interposed therebetween. The composition of the tensile strained InGaP well layer 306 is −
The strain is 0.6% strain In _0.4 Ga _0.6 P and has a thickness of 8 nm. Compression strain InAlP guide layer 304 and compression strain InAl
P barrier layer 307 and compression-strained InAlP guide layer 309
Is + 1.2% strain In _0.64 Al _0.36 P and has a thickness of 4 nm. The composition of the unstrained InGaAlP intermediate layer 208 is In _0.48 Ga _0.4 Al _0.12 P. Finally, p-
The InGaAlP cladding layer 110 and the p-GaAs cap layer 111 are grown. The composition of the n-InGaAlP cladding layer 103 and the p-InGaAlP cladding layer 110 is In _0.47 Ga _0.17 Al _0.36 P.

In the case of the distortion compensation MQW for the visible laser,
As shown in the band diagram of FIG. 12, the edge of the heavy hole differs between the well and the barrier. However, since the energy difference is small, it is possible to cause the heavy hole to behave like a bulk in the strained MQW layer 5. it can.

[0041]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A description will now be given of a semiconductor laser according to an embodiment prepared to demonstrate the effects of the present invention. The semiconductor laser of this embodiment be based on the configuration of the above-described embodiment, as shown in FIG. 5, no strain _{In 1-x Ga x As y} P 1-y
The intermediate layer 8 having a bandgap wavelength of 1.22 μm
The original composition was used. The compressive strain InAs _y P _1-y well layer 6
Unstrained In the 1.22μm composition _{1-x Ga x As y P} 1-y As / V ratio from the composition of the intermediate layer 8 (y) as a constant Ga / III
Only the ratio (x) was changed to 1.5% strain. On the other hand, the tensile strain In _1-x Ga _x AsP barrier layer 7, no strain _{In 1-x Ga x As y} P 1 Ga / III the composition of _-y intermediate layer 8
With the ratio (x) kept constant, only the As / V ratio (y) was changed to obtain a distortion amount of -0.5%. Stated another way, the tensile strained In _1-x Ga _x AsP barrier layer 7 has a thickness of 1.1 μm.
InGaAsP of composition, Ga / III with constant As / V ratio
It can also be said that only the ratio was changed and a distortion of -0.5% was applied.

The thickness of the compressively strained InAs _y P _1-y well layer 6 is 4.5 nm, and the tensile strained In _1-x Ga _x AsP
The thickness of the barrier layer 7 was 10 nm. At this time, when the calculation is performed using the weighted average based on the layer thickness, the average strain amount of the strained MQW layer 5 is almost zero, so that the accumulation of stress is small,
It was found that misfit transition did not occur even when the number of well layers was five.

[0043] The thickness of the unstrained _{In 1-x Ga x As y} P 1-y intermediate layer 8 and a thickness of 0.6 nm. With such a thin film, in FIG. 2 of the band diagram view, the quantum level of the light holes from the unstrained _{In 1-x Ga x As y} P 1-y intermediate layer 8 is expelled. With the composition described above, the compressive strain InAs _y P _1-y well layer 6 and the tensile strain In
_Since the light hole band edges of the _{1- x} Ga _x AsP barrier layer 7 are approximately equal, the light hole becomes bulk-like in the strained MQW layer 5.

Next, tensile strain In _1-x Ga _x AsP-S
CH layer 4 and tensile strained In _1-x Ga _x AsP-SCH layer 9
About the tensile strain In _1-x Ga _x AsP barrier layer 7
And the thickness was 10 nm. n
-The InGaAsP guide layer 3 and the InGaAsP guide layer 10 were formed to have a composition of 1.0 µm and each to have a thickness of 50 nm so that the conduction band edge was higher than the tensile strained In _1-x Ga _x AsP barrier layer 7.

When a semiconductor laser using this strained MQW layer as an active layer was actually manufactured, a semiconductor laser having a cavity length of 300 μm and a length of 30 μm was manufactured.
%, A semiconductor laser having a threshold current of 5 mA and a slope efficiency of 0.7 W / A was obtained in a structure in which a front end coating film having a reflectance of 75% and a rear end coating film having a reflectance of 75% were applied.

Meanwhile, as the use 1.55μm band semiconductor laser, as unstrained _{In 1-x Ga x As y} P 1-y intermediate layer 8 1.
Compression-strained InAs _y P _1-y well layer 1 of 45 μm composition
06 is obtained from InGaAsP having a composition of 1.45 μm,
/ V ratio is kept constant and only the Ga / III ratio is changed,
The one with 1.5% strain is used. In addition, tensile strain In
_{1 -x} Ga _x AsP barrier layer 7, no strain In _1-x Ga x As _y
From the P _{1 -y} intermediate layer 8, the Ga / III ratio is kept constant and the As / V
By changing only the ratio, a strain amount of -0.7% was obtained. Alternatively, the tensile strained In _1-x Ga _x AsP barrier layer 7 is formed by adding InGaAsP having a composition of 1.27 μm to As / V.
The ratio was constant, and only the Ga / III ratio was changed to -0.7%
It can be said that the distortion was applied. The n-InGaAsP guide layer 3 and the InGaAsP guide layer 10 have a 1.1 μm composition as shown in FIG.

The compressive strain InAs _y P _{1 -y} well layer 10
6, the thickness is 3.7 nm, and the tensile strain In _1-x Ga _x A
The thickness of the sP barrier layer 7 is 7 nm. At this time, the distortion MQ
The average amount of strain of the W layer 5 is almost zero, so-called zero net strain, and crystal deterioration due to stress accumulation is eliminated.

[0048]

As described above, according to the present invention, the following effects can be obtained. A first effect is that in the strain MQW, a larger strain can be applied without deteriorating the crystallinity, and a good optical output characteristic of the semiconductor laser can be obtained. For example, the characteristics of the threshold current and the slope efficiency are 10 to 2
0% improvement. The reason for this is that in stress-strain compensation MQW in which an intermediate layer is provided at the interface between the well layer and the barrier layer, gas switching during crystal growth is suppressed to the minimum necessary.

The second effect is that the uniformity of hole injection is improved. Thereby, the characteristics of the semiconductor laser can be further improved. The reason is that, in the strain MQW of the compressive strain well, the level of the light hole in the strain MQW or, in addition, the light hole in the p-side SCH layer is constant, so that the light hole can move freely in the strain MQW. Since holes injected from the holes or holes released from the wells can move to farther wells, uniformity of the hole density in each well is achieved, improving the gain,
This is because the improvement in the oscillation threshold carrier density is achieved.
This is the same when the level of the heavy hole is constant in the strain MQW of the tensile strain.

[Brief description of the drawings]

FIG. 1 is a sectional view showing a semiconductor laser having an MQW structure according to a first embodiment of the present invention.

FIG. 2 is a diagram showing a band diagram of the semiconductor laser.

FIG. 3 is a sectional view showing a modification of the semiconductor laser.

FIG. 4 is a diagram showing a band diagram in the same modified example.

FIG. 5 is a composition diagram of a semiconductor laser according to an example of the present invention.

FIG. 6 is a sectional view showing a semiconductor laser having an MQW structure according to a second embodiment of the present invention.

FIG. 7 is a diagram showing a band diagram of the semiconductor laser.

FIG. 8 is a sectional view showing a modified example of the semiconductor laser.

FIG. 9 is a diagram showing a band diagram in the same modification.

FIG. 10 is a composition diagram of the same semiconductor laser.

FIG. 11 is a sectional view showing a semiconductor laser according to another embodiment of the present invention.

FIG. 12 is a diagram showing a band diagram of the semiconductor laser.

FIG. 13 is a sectional view showing a conventional semiconductor laser having an MQW structure.

FIG. 14 is a composition diagram of the same semiconductor laser.

FIG. 15 is a diagram showing a band diagram of the semiconductor laser.

FIG. 16 is a cross-sectional view showing another conventional semiconductor laser having an MQW structure.

FIG. 17 is a composition diagram of the same semiconductor laser.

FIG. 18 is a diagram showing a band diagram of the semiconductor laser.

[Explanation of symbols]

1 n-type InP substrate 2 n-InP buffer layer 3 n-InGaAsP guide layer 4, 9 tensile strain _{In 1-x Ga x AsP-} SCH layer 5 strained MQW layer 6 compressive strain InAs _y P _1-y well layers 7 tensile strain In _1-x Ga _x AsP barrier layer 8 unstrained _{In 1-x Ga x As y} P 1-y intermediate layer 10 InGaAsP guide layer 11 p-InP cladding layer 101 n-type GaAs substrate 102 n-GaAs buffer layer 103 n- InGaAlP cladding layer 104 and 109 tensile strain _{In 1-x Ga x As y} P 1-y S
Tensile CH layer 106 compressive strain InGaAs _y P _1-y well layers 107 strain _{In 1-x Ga x As y} P 1-y barrier layers 108 InP insertion layer 110 p-InGaAlP cladding layer 111 p-GaAs cap layer 204 and 209 pull strain InGaP SCH layer 206 compressively strained _{In 1-x Ga x As y} P 1-y well layers 207 tensile strain InGaP barrier layer 208 unstrained InGaAlP intermediate layer 304 compressive strain InAlP guide layer 306 tensile strain InGaP well layer 307 compressive strain InAlP barrier Layer 309 Compressive strain InAlP guide layer

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-4-369830 (JP, A) JP-A-8-102566 (JP, A) JP-A-4-49689 (JP, A) JP-A-8-108 250798 (JP, A) JP-A-8-56045 (JP, A) JP-A 8-288586 (JP, A) JP-A 8-78786 (JP, A) JP-A 9-270567 (JP, A) JP-A-4-234184 (JP, A) JP-A-7-86696 (JP, A) (58) Fields investigated (Int. Cl. ⁶ , DB name) H01S 3/18

Claims (7)

(57) [Claims] 1. An optical semiconductor device in which a multiple quantum well structure having a well layer and a barrier layer made of a group III-V compound semiconductor is provided on a substrate, wherein an intermediate layer is provided between the well layer and the barrier layer. The well layer and the intermediate layer have the same group V composition ratio of the group III-V compound semiconductor forming these layers, and the barrier layer and the intermediate layer have the same group III-V compound semiconductor forming these layers. II
An optical semiconductor device having a multiple quantum well structure, wherein the composition ratio of group I is equal. 2. The multiple quantum well structure optical semiconductor device according to claim 1, wherein said intermediate layer and said substrate made of a III-V compound semiconductor have the same lattice constant. Semiconductor device. 3. The multiple quantum well structure optical semiconductor device according to claim 1, wherein said substrate is made of InP, and said barrier layer is made of InGaAsP.
An optical semiconductor device having a multiple quantum well structure, characterized in that: 4. A method of manufacturing an optical semiconductor device having a multi-quantum well structure having a well layer and a barrier layer made of a group III-V compound semiconductor on a substrate, wherein an intermediate layer is formed between the well layer and the barrier layer. Formation of a layer, and supply of group V raw material during crystal growth of the well layer and the intermediate layer.
It supplies the V group material while keeping the amount constant, before
At the time of switching between the well layer and the intermediate layer, only the supply amount of the group III source is changed, and while the crystal growth of the intermediate layer and the barrier layer is performed, the supply amount of the group III source is kept constant.
While supplying the group III raw material, the intermediate layer and the barrier
A method for manufacturing an optical semiconductor device having a multiple quantum well structure, characterized in that only a supply amount of a group V raw material is changed when switching between layers . 5. An optical semiconductor device having a strained multiple quantum well structure provided with a well layer subjected to compressive strain and a barrier layer subjected to tensile strain, wherein a light hole band edge of the well layer and a light of the barrier layer are provided. An optical semiconductor device having a multiple quantum well structure, wherein hole band edges are equal. 6. An optical semiconductor device having a strained multiple quantum well structure provided with a well layer subjected to tensile strain and a barrier layer subjected to compressive strain, wherein a heavy hole band edge of the well layer and a heavy layer of the barrier layer are provided. An optical semiconductor device having a multiple quantum well structure, wherein hole band edges are equal. 7. The multiple quantum well structure optical semiconductor device according to claim 5, wherein a strainless thin film intermediate layer is provided between said well layer and said barrier layer. Well-structured optical semiconductor device.