JP2905123B2 - Semiconductor laser, manufacturing method thereof, and strained quantum well crystal - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a semiconductor laser and a method for manufacturing the same, and a strained quantum well crystal and a method for manufacturing the same.

[0002]

2. Description of the Related Art A conventional strained quantum well semiconductor laser will be described with reference to FIGS. Such a strained quantum well type semiconductor laser is disclosed in, for example, Temkin et al., Journal of Crystal Cloth J. Cryst. Growth, 93, 353 (1988).

As shown in FIG. 15B, this semiconductor laser is composed of an InP single crystal substrate 1, a stripe-shaped laminated structure provided on the substrate 1, and Fe-InP that covers both side surfaces of the laminated structure. And a current blocking layer 7. An n-side electrode 9 is on the bottom surface of the semiconductor laser, and a p-side electrode 8 is on the top surface.
Is provided, SiO ₂ and Si on the end face of the semiconductor laser
Is provided.

[0004] The striped laminated structure includes a first optical waveguide layer 2, a multiple quantum well portion 5 composed of a strain well layer 3 and a barrier layer 4, and a second optical waveguide layer 6. The energy band gap of this portion is shown in FIG.

When a current flows from the p-side electrode 8 to the n-side electrode 9, holes and electrons are confined in the multiple quantum well 5,
Then, the holes and electrons recombine to emit light. as a result,
Laser oscillation occurs. In this conventional example, the strain well layer 3 has a mixed crystal composition of In _0.7 Ga _0.3 As and is formed to have a compressive strain of 1%. By introducing compressive strain to the well layer 3, the band structure of holes is made similar to the band structure of electrons. As a result, laser oscillation occurs even if the carrier injection amount is low.

[0006]

However, in such a semiconductor laser, the laser oscillation wavelength shifts to a longer wavelength side as the temperature of the semiconductor laser increases. Therefore, there is a problem that the oscillation wavelength fluctuates due to a change in environmental temperature.

In addition, when the current injected into the semiconductor laser is increased, the temperature of the semiconductor laser rises, so that the laser oscillation wavelength varies greatly depending on the injection current.

Further, when this strained quantum well structure is applied to a DFB (distributed feedback) laser, the single mode characteristic is deteriorated due to a change in the ambient temperature of the semiconductor laser. That is, there is a problem that a side mode appears and a suppression ratio between the peak of the oscillation wavelength and the side mode cannot be obtained. This phenomenon was observed particularly remarkably in the strained quantum well laser. The cause is that the gain of the laser becomes steep because the threshold carrier density is reduced by introducing lattice distortion.

FIG. 12A shows a distortion-free multiple quantum well (MQ).
FIG. 12B shows the temperature dependence of the gain profile in the semiconductor laser having the W) structure, and FIG. 12B shows the temperature dependence of the gain profile in the semiconductor laser having the strained MQW structure. The vertical axis of the graphs in FIGS. 12A and 12B is the gain,
The horizontal axis is the wavelength.

[0010] As shown in FIG.
In the case of W, since the gain is not large, a substantially flat gain distribution exists in a wide wavelength region. The peak wavelength of this gain distribution shifts to the longer wavelength side (larger T) as the temperature (T) of the laser increases. However, no distortion MQ
In the case of W, since the gain distribution is flat, even if the temperature changes and the gain peak wavelength and the DFB oscillation wavelength are separated, D
Since there is gain at the FB oscillation wavelength, laser oscillation occurs preferentially at the DFB wavelength, and the side mode suppression ratio increases. Therefore, the single mode property is enhanced.

On the other hand, in the case of the distortion MQW, FIG.
As shown in (1), the gain is locally increased in a specific range of wavelength region by introducing distortion. When the temperature is low (small T), if the gain peak slightly deviates from the DFB oscillation wavelength, the DFB oscillation occurs and the side mode suppression ratio increases. However, when the temperature increases (large T), the gain peak changes to the distortion-free MQW. As in the case, since the wavelength shifts to the longer wavelength side, the gain at the DFB oscillation wavelength is almost eliminated. As a result, the gain at the DFB oscillation wavelength decreases, and the laser oscillates even at the gain peak,
The single mode suppression ratio is reduced, and the single mode property is degraded. That is, in the case of a strained quantum well laser, the gain is steep, so that even if the difference (detuning) between the DFB oscillation wavelength and the gain peak wavelength is small, the side mode suppression ratio decreases and the single mode property deteriorates. become. Therefore, it is strongly desired that the strained quantum well laser has less temperature dependence of the gain wavelength because the single mode property is deteriorated even with a small detuning amount, as compared with the non-strained quantum well laser.

It is an object of the present invention to provide a semiconductor laser having a small single-mode characteristic over a wide temperature range and a wide range of injection current, which has a small oscillation wavelength dependence on temperature and injection current, a method of manufacturing the same, and a semiconductor crystal. Aim.

[0013]

A semiconductor laser according to the present invention includes a strained quantum well structure including a well layer and a barrier layer, and a semiconductor substrate supporting the strained quantum well structure. At least one of the well layer and the barrier layer is formed of an ordered mixed crystal, thereby achieving the above object.

[0014] The semiconductor device may further include a first optical waveguide layer and a second optical waveguide layer sandwiching the strained quantum well structure.

In one embodiment, the semiconductor substrate is I
Each of the well layer and the barrier layer is formed of InGaAs having a different energy band gap.
It is formed from a P crystal.

The method of manufacturing a semiconductor laser according to the present invention is a method of manufacturing a semiconductor laser having a strained quantum well structure including a well layer and a barrier layer, wherein the step of forming the strained quantum well structure comprises the steps of: And forming at least one of the barrier layers from an ordered mixed crystal, thereby achieving the above object.

In one embodiment, the step of forming the well layer includes the step of distorting (%) = 1.0-0.10 × (the number of well layers)
Is introduced into the well layer at a strain amount equal to or larger than
Crystal growth is performed at 0 degrees or less.

In the step of forming the well layer, the amount of strain (%)
Lattice strain greater than or equal to 1.2−0.02 × (the number of well layers) may be introduced, and crystal growth may be performed at 600 degrees or less.

In the step of forming the well layer, the amount of strain (%)
The crystal growth may be performed at 700 degrees or less by introducing a lattice strain equal to or greater than the strain amount represented by = 1.6-0.02 × (the number of well layers).

The strained quantum well crystal of the present invention is a strained quantum well crystal comprising a semiconductor crystal and an InGaAsP crystal having a lattice constant different from the lattice constant of the semiconductor crystal, wherein the InGaAsP crystal is ordered. Therefore, the above object is achieved.

[0021]

[0022]

DESCRIPTION OF THE PREFERRED EMBODIMENTS According to the present invention, an ordering is introduced into at least one of a well layer and a barrier layer.
Provided is a strained quantum well crystal suitable for a light emitting device such as a semiconductor laser in which the gain peak wavelength has little dependence on temperature fluctuation.

In general, when a mixed crystal of a diatomic compound represented by AC and a diatomic compound represented by BC is prepared, a mixture of (AB) C _{2 in} which A atoms and B atoms are uniformly mixed. A crystal is obtained. However, when a mixed crystal is formed at a low temperature, A atoms and B atoms are not uniformly mixed, and AC
In some cases, a mixed crystal in which the compound and the BC compound are stacked in layers is obtained. As a result, a superlattice structure in which the lattice planes of the AC compound and the lattice planes of the BC compound are alternately arranged is observed. In addition, when a crystal is grown at a low temperature, a superlattice is automatically created. Therefore, the superlattice is called a natural superlattice to distinguish it from an artificial superlattice such as a quantum well structure. In the present specification, such a natural superlattice is formed even partially,
It is referred to as "having an ordering" or "ordering has occurred". The present invention will be described below with reference to InGa.
The AsP crystal will be described. The InGaAsP crystal grown at 620 ° C. or higher did not cause ordering without distortion. In this study, it was found that ordering occurs under certain conditions in experiments with changing the amount of strain, the number of well layers, and the growth temperature.

Specifically, it was confirmed by experiments that ordering easily occurs when (1) the amount of strain of the InGaAsP crystal is large, (2) when the number of well layers is large, and (3) when the growth temperature is low. . It was found that ordering was likely to occur under any of the conditions (1) to (3) above, but it was initially thought that dislocations were present in the crystal. By observation with a transmission electron microscope, no dislocation was observed in the crystal, and it was found that ordering had occurred in the InGaAsP crystal. Further, as shown in the graph of FIG. 1B, the temperature dependence of the PL emission intensity of this crystal showed that the difference between the PL intensity peak at room temperature and the peak at 77K was small. If there is no ordering,
As shown in (a), the difference between the PL intensity peak at room temperature and the peak at 77K is large. Conventionally, based on the graph of FIG. 1B, it has been considered that when ordering occurs in the strained quantum well structure, the PL characteristic deteriorates. On the other hand, the present inventor has found that a semiconductor laser with small temperature fluctuation of the oscillation wavelength and small injection current dependency can be provided by actively utilizing the ordering phenomenon.

Hereinafter, InGaAs will be described with reference to the drawings.
The present invention will be described with reference to examples using sP crystals.

(Embodiment 1) An embodiment of a strained quantum well crystal according to the present invention will be described with reference to FIGS. 2 (a) and 2 (b).

FIG. 2A schematically shows a cross section of a strained quantum well crystal including a Sn-doped InP semiconductor single crystal substrate 1 and a laminated structure provided on the Sn-doped InP semiconductor single crystal substrate 1. Is shown. This laminated structure is made of InGa
AsP (λg = 1.05 μm) First optical waveguide layer 2, multiple quantum well structure 5, and InGaAsP (λg = 1.05 μm)
(5 μm) The second optical waveguide layer 6 is grown on the InP semiconductor single crystal substrate 1 in this order. The multiple quantum well structure 5 has seven layers of InGaAs alternately stacked.
I ordered with P strain well layer (0.8% compressive strain) 3
nGaAsP (λg = 1.15 μm) barrier layer 4. The photoluminescence (PL) emission wavelength of the multiple quantum well structure 5 was 1.3 μm. In the present example, ordering was generated in the barrier layer 4 by introducing a compressive strain of 0.8% into the strain well layer 3 and setting the crystal growth temperature to 580 degrees. The energy band gap of the laminated structure is schematically shown in FIG.

The present inventor has confirmed by transmission electron microscope observation that the ordering exists in the barrier layer 4. However, it is sufficiently conceivable that the ordering influence is exerted on the well layer 3 as well. In this embodiment, since a compressive strain is introduced into the well layer 3, a tensile strain is generated in the barrier layer 4. Therefore, it is considered that tensile strain is more likely to occur in ordering. It is considered that the ordering is preferentially generated in the well layer 3 by adjusting the composition of the well layer to generate tensile strain in the well layer.

The PL emission spectrum of the strained quantum well crystal was measured. FIG. 3A shows a PL emission peak of the strained quantum well crystal without ordering, and FIG. 3B shows a PL peak of the strained quantum well crystal having ordering.
If there is no ordering, the temperature is set to room temperature (T = 300
Although the short wavelength shift of 60 meV is caused by lowering from K) to 77 K, when there is ordering, 1
A short wavelength shift of about 0 meV is hardly recognized. Also, it can be seen that the emission intensity at room temperature does not decrease even if there is an ordering as compared to the case where there is no ordering. As described above, a strained quantum well crystal having ordering exhibits light emission characteristics with low temperature dependence.

FIG. 4 shows the temperature dependence of the PL emission peak wavelength. When there is ordering, the temperature dependence of the PL emission peak wavelength is 1 compared to the case without ordering.
It can be seen that it has been reduced to / 5 or less.

The inventor's view as to why the ordering is likely to occur when the crystal is strained and the crystal growth temperature T is lowered as described above is as follows.

For example, when compressive strain is introduced into the InGaAsP strained quantum well layer, the internal energy of the crystal increases by the energy of the strain. However, when the In-As bond having a large lattice constant is naturally oriented in the crystal growth direction and ordering occurs, the strain energy of the strained quantum well layer decreases.

The internal energy U of the crystal is generally expressed by the following equation.

U = H-TS H is enthalpy, T is temperature, S is entropy (S <
0). The smaller the internal energy U, the more stable the crystal. When strain is introduced into the crystal, the enthalpy H increases, so that it is considered that the entropy S tends to decrease and thereby the internal energy U tends to decrease. In other words, it is understood that it is necessary to introduce a large strain into the quantum well to increase the enthalpy H and reduce the S. On the other hand, the relationship between the crystal growth temperature and the ordering is considered as follows. Since U and H change in proportion to the square of T, when the crystal growth temperature T decreases, S also changes in proportion to T and decreases, and a decrease in S, that is, ordering occurs. Easier to do.

The inventor considers the reason why the ordering causes the temperature dependency to be smaller as follows. When the entropy S decreases due to the ordering, the temperature dependency of the internal energy U decreases.
Since the energy band gap Eg that determines the oscillation wavelength changes depending on the internal energy U, the band gap Eg can be reduced by reducing the temperature dependence of the internal energy U.
g can be reduced. Thus, the temperature fluctuation of the wavelength can be reduced by the ordering.

FIG. 5 shows that the growth temperatures Tg are 580 and 600,
7 shows the relationship between the amount of strain that causes ordering and the number of quantum well layers at 700 ° C. and 700 ° C. It can be seen that when the strain amount is increased and the number of well layers is increased, ordering easily occurs. From this experiment, the growth temperature T
When g is 580 ° C, the strain _{580 at which} ordering occurs is
It is expressed by the following equation 1 using the number of well layers.

Strain ₅₈₀ (%) = 1.0−0.10 × the number of well layers Equation 1 That is, if a strain larger than the strain ₅₈₀ obtained by Equation 1 is given, ordering occurs, and If a distortion amount smaller than the distortion amount ₅₈₀ obtained in 1 is given, it can be said that ordering does not occur.

As shown in FIG. 5, as the growth temperature Tg is increased, ordering tends to be less likely to occur. Therefore, even when the growth temperature Tg is lower than 580 ° C., it is considered that ordering occurs in a region represented by an inequality of strain amount (%) ≧ 1.0−0.10 × the number of well layers.

Similarly, when the growth temperature Tg is 600.degree.
At ° C., ordering occurs in the regions represented by the following equations 2 and 3, respectively.

Strain amount (%) ≧ 1.2−0.02 × the number of well layers Formula 2, Tg = 600 ° C. Strain amount (%) ≧ 1.6-0.02 × the number of well layers Equation 3, Tg = 700 ° C. When a semiconductor laser is actually manufactured, the crystal growth is 600
It is often performed at a temperature of about ° C or higher, and the number of well layers needs to be 10 or less as an optimum condition that does not reduce the optical output of the semiconductor laser. Therefore, in order to generate ordering when crystal growth is performed at about 600 ° C., it is necessary to form a compressive strain of about 1%. On the other hand, when the crystal growth temperature is lowered to 580 ° C., if the number of well layers is seven, ordering can be generated by applying a compressive strain of about 0.7%.

The amount of strain may be adjusted by adjusting the composition of the crystal to be grown to grow a crystal having a desired lattice constant.

The strained quantum well crystal structure of the present invention is particularly suitable for a light emitting region of a semiconductor laser used for a light source for excitation of a fiber amplifier. In order to obtain sufficient gain with a fiber amplifier, it is necessary to use laser light having a specific wavelength. However, when a large drive current of 500 mA or more is applied to the semiconductor laser, the amount of heat generated by the semiconductor laser changes significantly by modulating the magnitude of the drive current, and thus there is a problem that the laser oscillation wavelength changes. According to the semiconductor laser of the present invention, the temperature dependence of the oscillation wavelength is small. For this reason, even if the drive current is increased, it is easy to maintain the oscillation wavelength within a predetermined range required by the fiber amplifier.

Further, even if the active layer width and the like of the semiconductor laser vary from element to element, the oscillation wavelength is kept constant even if the amount of heat generated for the same drive current (injection current) differs for each laser. Therefore, according to the present invention, the manufacturing yield of semiconductor lasers satisfying desired specifications can be significantly improved.

FIG. 6 is a graph showing the relationship between the amount of strain (%) that causes ordering and the crystal growth temperature (° C.) when the number of InGaAsP strained quantum well layers is 10. In the region where the distortion is larger than the distortion indicated by the curve in the graph of FIG.
Ordering occurs. The crystal growth of the InGaAsP strained quantum well layer is usually performed at a temperature in the range of about 600 to 620 ° C. For this reason, in order to prevent the ordering from occurring, it is necessary to perform the crystal growth under the condition of the region A. On the other hand, when the crystal growth of the InGaAsP strained quantum well layer is performed at 620 ° C. or higher, no ordering occurs if the conditions shown in the region B of the graph are adopted.

An object of the present invention is to provide a strained quantum well crystal having a light emission characteristic which is hardly changed depending on temperature by intentionally causing ordering. However, in the process of finding the conditions that cause ordering, the conditions that do not cause ordering were clarified. It can be seen that when trying to exert the PL characteristic of FIG. 1A while applying a large strain to the quantum well layer, the crystal should be grown under the conditions of the region B in the graph of FIG.

(Embodiment 2) An embodiment of a strained quantum well semiconductor laser according to the present invention will be described with reference to FIGS. 7 (a) and 7 (b). FIG. 7A shows a stripe-shaped ridge (width: 1.2 to 1.5 μm, height: 1.5 to 2.5 μm).
m) a Sn-doped InP semiconductor single crystal substrate 1 having:
1 schematically illustrates a structure of a semiconductor laser including a striped laminated structure provided on a ridge of a Sn-doped InP semiconductor single crystal substrate 1. This striped laminated structure is composed of an InGaAsP (λg = 1.05 μm) first optical waveguide layer 2, a multiple quantum well structure 5, and InGaAsP.
P (λg = 1.05 μm) A second optical waveguide layer 6 is grown on the InP semiconductor single crystal substrate 1 in this order. First optical waveguide layer 2 and second optical waveguide layer 6
Are set to 30 and 150 nm, respectively.

The multiple quantum well structure 5 has seven layers of InGaAs.
The sP strain well layers (0.8% compressive strain) 3 and the ordered InGaAsP (λg = 1.15 μm) barrier layers 4 are alternately stacked. The thickness of the InGaAsP strain well layer 3 is set to 3 to 6 nm, and the thickness of the InGaAsP barrier layer 4 is set to 5 to 20 nm. The photoluminescence (PL) emission wavelength obtained from the multiple quantum well structure 5 was 1.3 μm. In the present example, ordering was generated in the barrier layer 4 by introducing a compressive strain of 0.8% into the strain well layer 3 and setting the crystal growth temperature to 580 degrees. FIG. 7B shows the energy band structure of the laminated structure.

As shown in FIG. 7B, p-InG having a thickness of 3 to 6 μm is formed on both sides of the stripe-shaped laminated structure.
An aAsP / p-InP / n-InP / p-InP current confinement structure 7 is provided, and a groove is provided in a part of the current confinement layer 7. The surface of the groove is covered with a SiO ₂ layer. A p-side electrode 8 is provided above the semiconductor laser, and an n-side electrode 9 is provided below.

Next, a method of manufacturing the strained quantum well laser shown in FIG. 7A will be described with reference to FIGS. 8A to 8D. First, as shown in FIG.
On top of the first InGaAsP optical waveguide layer 2, InGaAs
A first crystal growth step for growing the sP strain well layer 3, the InGaAsP barrier layer 4, the multiple quantum well structure 5, and the second InGaAsP optical waveguide layer 6 is performed. Next, as shown in FIG. 8B, an etching step of etching these layers in a stripe shape is performed.

After that, as shown in FIG. 8C, a second crystal growth step for growing the current confinement structure 7 is performed, and then, as shown in FIG. An electrode forming step of forming the side electrode 9 is performed.

In order to cause the ordering, the well layer 3
At a growth temperature of 580
° C, and the supply ratio V / III of the group V and group III gas is 250
And This crystal growth condition is indicated by a point A on the graph of FIG. As described above, the semiconductor laser according to the present embodiment includes the same crystal as the strained quantum well crystal according to the first embodiment in the striped laminated structure. Such a strained quantum well crystal is formed under the conditions described in the first embodiment.

The oscillation wavelength of the semiconductor laser having the strained quantum well crystal having the ordering was 1.3 μm, and the maximum light output was 300 mW. This was at the same level as the laser output of the semiconductor laser without ordering, and laser oscillation occurred at the same level of threshold current.

FIG. 9 shows the temperature dependence of the laser oscillation wavelength. When the temperature of the semiconductor laser is changed from −40 ° C. to 100 ° C., the oscillation wavelength of the strain quantum well semiconductor laser without ordering changes from 1.26 μm to 1.44 μm, whereas the strain quantum well having ordering changes. The oscillation wavelength of the well type semiconductor laser is 1.29 μm to 1.31 μm.
Changes to In this way, the ordering reduced the wavelength variation to 1/5 or less. Since the change amount of the oscillation wavelength with respect to the temperature is reduced, it is possible to provide a semiconductor laser that stably oscillates in a temperature range from −40 ° C. to 100 ° C. without particularly controlling the temperature of the semiconductor laser.

FIG. 1 shows the dependence of the oscillation wavelength on the injection current.
0 is shown. Normally, when the injection current to the semiconductor laser increases, Joule heat is generated by the internal resistance of the semiconductor laser, and the temperature of the semiconductor laser rises. As a result, the oscillation wavelength fluctuates. However, according to the semiconductor laser of this embodiment, the oscillation wavelength hardly changes even if the injection current is changed because the temperature dependence of the oscillation wavelength is small. In particular, a high-power semiconductor laser to which a large current is injected is required to have a small change in oscillation wavelength. Another advantage is that the oscillation wavelength at high output can be easily estimated from the PL emission wavelength.

As described above, according to the present embodiment, there is provided a semiconductor laser having a small dependence of the oscillation wavelength on temperature and injection current.

(Embodiment 3) An embodiment of another strained quantum well semiconductor laser according to the present invention will be described with reference to FIGS. 11 (a) and 11 (b). FIG. 11A shows an Sn-doped InP semiconductor single crystal substrate 1 having a stripe-shaped ridge,
1 schematically illustrates a structure of a semiconductor laser including a striped laminated structure provided on a ridge of a Sn-doped InP semiconductor single crystal substrate 1. On the upper surface of the stripe-shaped ridge, a diffraction grating 10 having a pitch of 180 nm is formed. The striped laminated structure is made of InGaAsP.
(Λg = 1.05 μm) First optical waveguide layer 2, multiple quantum well structure 5, and InGaAsP (λg = 1.05 μm)
m) The second optical waveguide layer 6 is grown on the InP semiconductor single crystal substrate 1 in this order. The multiple quantum well structure 5 has seven InGaAsP strained well layers (0.8%
InGaAsP (λg =
1.15 μm) barrier layer 4. The thickness of each semiconductor layer may be within the range of the thickness described in the third embodiment. The photoluminescence (PL) emission wavelength of the multiple quantum well structure 5 was 1.3 μm. In the present example, ordering was generated in the barrier layer 4 by introducing a compressive strain of 0.8% into the strain well layer 3 and setting the crystal growth temperature to 580 degrees. Note that FIG.
Shows the energy band structure of the laminated structure.

As shown in FIG. 11B, p-InGaAsP / p-I is provided on both sides of the stripe-shaped laminated structure.
An nP / n-InP / p-InP current confinement structure 7 is provided, and a part of the current confinement structure 7 is provided with a groove. The surface of the groove is covered with a SiO ₂ layer. A p-side electrode 8 is provided above the semiconductor laser, and an n-side electrode 9 is provided below.

The present semiconductor laser is characterized in that it oscillates at an oscillation wavelength determined by the pitch of the diffraction grating 10 and is called a distributed feedback laser (DFB laser).

The temperature or injection current dependence of the gain peak wavelength of the present semiconductor laser is the same as that of the semiconductor laser of the second embodiment.

Ideally, a DFB laser oscillates in a single mode. However, as shown in FIG. 12B, when the difference between the “DFB oscillation wavelength” and the “gain peak wavelength” determined by the pitch of the diffraction grating is larger than 20 nm, the probability of single mode oscillation of the laser is It drops sharply. FIG.
The temperature dependence of the appearance rate of the single mode characteristic is shown. If a semiconductor laser without ordering is driven without temperature control, the temperature range in which single mode oscillation can be realized is 0
From 40 ° C to 40 ° C. On the other hand, when a semiconductor laser is prototyped using a strained quantum well crystal having ordering, -8
Even when the temperature of the semiconductor laser is changed within a range from 0 ° C. to 120 ° C., the single mode oscillation is maintained. As a result, there is no need to use a Peltier element for temperature control, and the price of the laser module can be greatly reduced.

Further, it is possible to drive the DFB laser at a high output. As shown in FIG. 14, when there is no ordering, the appearance rate of a single mode decreases at 300 mA or more, but when ordering is performed, the single mode property is maintained at 600 mA or more, and the low light output is obtained. A high-power DFB laser exhibiting single mode oscillation from high to high optical output can be realized with a high yield.

As described above, according to the present embodiment, it is possible to provide a DFB laser whose single mode characteristics are hardly affected by the ambient temperature and the injection current, and to provide an inexpensive laser module which does not require a Peltier element. can do.

In the description of each of the above embodiments, the barrier layer 1
Although No. 4 was formed from InGaAsP (λg = 1.15 μm), if it was formed from InGaAsP (λg = 1.05 μm), ordering would occur more easily.
Further, the ordering can be effectively generated in the barrier layer. In addition, SCH (spectrum confinment hetero
structure)
The present invention is applicable to other semiconductor lasers. Also,
In addition to the InGaAsP / InP system, AlGaAs / G
aAs and InGaP / AlGaInP, ZnSe
A similar effect can be achieved with a GaN-based system.

The type of the semiconductor laser is not limited to the Fabry-Perot type or the DFB type, but may be a high value-added semiconductor laser such as a DBR type. Further, even if the strained quantum well crystal of the present invention is applied to not only light emitting elements such as semiconductor lasers but also light receiving elements and high-speed electronic elements such as HFETs, the temperature fluctuation characteristics of those elements are improved.

[0065]

As described above, according to the present invention,
By providing ordering in the strained quantum well layer, it is possible to provide a semiconductor laser whose oscillation wavelength is not affected by environmental temperature or injection current, and to provide a low-cost DFB laser module that does not require a temperature control element such as a Peltier element. The practical effect is extremely large.

[Brief description of the drawings]

FIG. 1A is a graph showing a shift of PL light emission due to a temperature when there is no ordering, and FIG. 1B is a graph showing a shift of PL light emission due to a temperature when ordering is present.

2A is a structural sectional view of an embodiment of a strained quantum well crystal structure according to the present invention, and FIG. 2B is an energy band diagram of the strained quantum well structure.

FIGS. 3A and 3B are graphs for explaining a difference in PL emission intensity depending on the presence or absence of ordering.

FIG. 4 is a graph illustrating a difference in a gain peak wavelength shift amount depending on the presence or absence of ordering.

FIG. 5 is a graph showing the relationship between the presence or absence of ordering, the number of well layers, and the amount of lattice distortion when the growth temperature is used as a parameter.

FIG. 6 shows the amount of strain (%) that causes ordering and the crystal growth temperature (° C.) when the number of InGaAsP strained quantum well layers is 10.
6 is a graph showing a relationship with the graph.

7A is a structural sectional view of an embodiment of a strained quantum well semiconductor laser according to the present invention, and FIG. 7B is an energy band diagram of the strained quantum well structure.

FIGS. 8A to 8D are process cross-sectional views illustrating a method for manufacturing a strained quantum well laser according to the present invention.

FIG. 9 is a graph illustrating a difference in gain peak wavelength depending on the presence or absence of ordering.

FIG. 10 is a graph showing the injection current dependency of the oscillation wavelength for the present invention and the conventional example.

FIG. 11A is a structural cross-sectional view of another embodiment of the strained quantum well semiconductor laser according to the present invention, and FIG. 11B is an energy band diagram of the strained quantum well structure.

12A and 12B are graphs for explaining a difference in light emission intensity of a multiple quantum well structure depending on the presence or absence of strain.

FIG. 13 is a graph illustrating the difference in the temperature dependence of the appearance rate of single mode oscillation depending on the presence or absence of ordering.

FIG. 14 is a graph illustrating the difference in the injection current dependence of the appearance rate of single mode oscillation depending on the presence or absence of ordering.

FIG. 15A is an energy band diagram of a strained quantum well structure of a conventional strained quantum well semiconductor laser,
(B) is a perspective view of the semiconductor laser.

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 single crystal substrate 2 first waveguide layer 3 strained well layer 4 barrier layer 5 strained quantum well structure 6 second waveguide layer 7 current confinement layer 8 p-side electrode 9 n-side electrode

────────────────────────────────────────────────── ─── Continuing from the front page (72) Yasushi Matsui 1006 Kazuma Kadoma, Kadoma City, Osaka Prefecture Matsushita Electric Industrial Co., Ltd. (56) References JP-A-5-55699 (JP, A) JP-A-7- 7217 (JP, A) Lightwave Technology 12 [1] (1994) p. 28-37 J.C. Appl. Phys. 72 [9] (1992) p. 4118-4124 (58) Field surveyed (Int. Cl. ⁶ , DB name) H01S 3/18

Claims (6)

(57) [Claims] 1. A strained quantum well structure including a well layer and a barrier layer.
When a semiconductor substrate for supporting the strained quantum well structure, a semiconductor laser with a first optical waveguide layer and the second optical waveguide layers sandwiching the strained quantum well structure, and the barrier layer, Formed from ordered mixed crystals
Yes, a semiconductor laser. 2. A strained quantum well structure including a well layer and a barrier layer.
And an InP substrate that supports the strained quantum well structure.
And a semiconductor laser, each of the well layers and the barrier layers are formed from different InGaAsP crystals energy band gap, the
The barrier layer is made of ordered mixed crystals
That, semiconductor laser. 3. A strained quantum well structure including a well layer and a barrier layer.
A method of manufacturing a semiconductor laser comprising a step of forming a strained quantum well structure, a step of forming a mixed crystal that ordering a said barrier layer
And a crystal strain at a temperature of 580 ° C. or less by introducing a lattice strain equal to or more than the strain amount represented by strain amount (%) = 1.0−0.10 × (number of well layers). and forming a manufacturing method of a semiconductor laser. 4. A strained quantum well structure including a well layer and a barrier layer.
A method of manufacturing a semiconductor laser comprising a step of forming a strained quantum well structure, a step of forming a mixed crystal that ordering a said barrier layer
If, strain amount (%) = 1.2-0.02 × well layer by performing crystal growth at a strain amount or more of lattice strain introduced to 6 00 degrees or less temperature represented by (the number of well layers) and forming a manufacturing method of a semiconductor laser. 5. A strained quantum well structure including a well layer and a barrier layer.
A method of manufacturing a semiconductor laser comprising a step of forming a strained quantum well structure, a step of forming a mixed crystal that ordering a said barrier layer
If, strain amount (%) = 1.6-0.02 × well layer by performing crystal growth at a strain amount or more introduce lattice distortion to 7 00 degrees or less temperature represented by (the number of well layers) and forming a manufacturing method of a semiconductor laser. 6. A strained quantum well crystal comprising a semiconductor crystal and an InGaAsP crystal having a lattice constant different from the lattice constant of the semiconductor crystal, wherein a portion of the InGaAsP crystal where a barrier layer is formed is formed. Ordered strained quantum well crystal.