JP3385985B2 - Manufacturing method of strained quantum well crystal - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a semiconductor laser, a manufacturing method thereof, a strained quantum well crystal and a manufacturing method thereof.

[0002]

2. Description of the Related Art A conventional strained quantum well semiconductor laser will be described with reference to FIGS. 15 (a) and 15 (b). Such a strained quantum well type semiconductor laser is disclosed in, for example, Temkin et al., Journal of Crystal Growth J. Cryst. Growth, 93, 353 (1988).

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

The stripe-shaped 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 is passed from the p-side electrode 8 to the n-side electrode 9, holes and electrons are confined in the multiple quantum well portion 5,
There, the holes and electrons recombine and 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 into the well layer 3, the hole band structure is made similar to the electron band structure. 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 the long wavelength side as the temperature of the semiconductor laser rises. Therefore, there is a problem that the oscillation wavelength changes due to the change of the environmental temperature.

Further, when the current injected into the semiconductor laser is increased, the temperature of the semiconductor laser rises, so that there is a problem that the laser oscillation wavelength largely changes depending on the injected current.

Further, when the strained quantum well structure is applied to a DFB (distributed feedback type) laser, the single mode property is deteriorated due to a change in environmental temperature of the semiconductor laser. That is, there is a problem that the side mode appears and the suppression ratio between the peak of the oscillation wavelength and the side mode cannot be obtained. This phenomenon was particularly noticeable in the strained quantum well laser. The reason is that the introduction of lattice strain lowers the threshold carrier density, resulting in steep laser gain.

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

As shown in FIG. 12A, the distortion-free MQ
In the case of W, since the gain is not large, there is a substantially flat gain distribution in a wide wavelength range. The peak wavelength of this gain distribution shifts to a longer wavelength side as the temperature (T) of the laser becomes higher (larger T). However, distortion-free MQ
In the case of W, since the gain distribution is flat, even if the peak wavelength of gain and the DFB oscillation wavelength are separated due to temperature change, D
Since it has a gain at the FB oscillation wavelength, laser oscillation is preferentially performed at the DFB wavelength, and the side mode suppression ratio becomes large. Therefore, the monomodality is high.

On the other hand, in the case of the distorted MQW, FIG.
As shown in (3), the gain locally increases in the wavelength region of the specific range by introducing the distortion. When the temperature is low (small T) and the gain peak and the DFB oscillation wavelength are slightly deviated, the DFB oscillation causes the side mode suppression ratio to increase. However, when the temperature rises (large T), the gain peak has no distortion MQW. As in the case, since the wavelength shifts to the long wavelength side, the gain at the DFB oscillation wavelength becomes almost zero. As a result, the gain at the DFB oscillation wavelength decreases, and laser oscillation also occurs at the gain peak.
The single mode suppression ratio is reduced and the single mode property is deteriorated. That is, in the case of a strained quantum well laser, since the gain is particularly steep, 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 characteristic deteriorates. become. Therefore, compared with the non-strained quantum well laser, the strained quantum well laser deteriorates the single mode property even with a small amount of detuning, and thus it is strongly desired that the temperature dependence of the gain wavelength is small.

The present invention provides a semiconductor laser which has a small temperature variation of an oscillation wavelength and an injection current dependency and has a high single mode characteristic in a wide temperature range and an injection current range, a manufacturing method thereof, and a semiconductor crystal. To aim.

[0013]

A semiconductor laser according to the present invention is a semiconductor laser including 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.

A first optical waveguide layer and a second optical waveguide layer sandwiching the strained quantum well structure may be further provided.

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

A 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 includes the step of forming the well layer. And a step of forming at least one of the barrier layers from an ordered mixed crystal, whereby the above object is achieved.

In one embodiment, in the step of forming the well layer, the strain amount (%) = 1.0−0.10 × (the number of well layers).
Introducing a lattice strain not less than the strain amount shown in
Crystal growth is performed at 0 degrees or less.

In the step of forming the well layer, the strain amount (%)
= 1.2-0.02x (the number of well layers), the lattice strain of the strain amount or more may be introduced, and the crystal growth may be performed at 600 degrees or less.

In the step of forming the well layer, the strain amount (%)
= 1.6-0.02x (the number of well layers), the lattice strain of the strain amount or more may be introduced, and the crystal growth may be performed at 700 degrees or less.

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

The method for producing a strained quantum well crystal of the present invention is a method for producing 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. In the step of forming the well layer, strain of 1% or more is applied to the well layer and crystal growth is performed at 620 ° C. or more, thereby achieving the above object.

[0022]

BEST MODE FOR CARRYING OUT THE INVENTION The present invention introduces ordering into at least one of a well layer and a barrier layer,
Disclosed is a strained quantum well crystal suitable for a light emitting device such as a semiconductor laser having a small dependence of gain peak wavelength on temperature variation.

Generally, 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 atom and B atom are uniformly mixed. Crystals are obtained. However, when the mixed crystal is formed at a low temperature, the A atom and the B atom are not uniformly mixed, and the AC
A mixed crystal in which the compound and the BC compound are layered may be 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 arranged alternately is observed. In addition, since the superlattice is automatically created in low temperature crystal growth, it is called a natural superlattice in distinction from an artificial superlattice such as a quantum well structure. In the present specification, it is stated that such a natural superlattice is formed even partially.
It will be referred to as “having ordering” or “ordering has occurred”. The present invention is described below.
The AsP crystal will be described. The InGaAsP crystal grown at 620 ° C. or higher did not cause ordering without strain. This time, in this crystal, it was found that ordering occurs under a certain condition while conducting experiments by changing the strain amount, the number of well layers and the growth temperature.

Specifically, it was confirmed by experiments that ordering is likely to occur when (1) the strain amount of the InGaAsP crystal is large, (2) the number of well layers is large, and (3) the growth temperature is low. . It was found that ordering was likely to occur under any of the above conditions (1) to (3), but at first it was thought that dislocations were included in the crystal. Observation with a transmission electron microscope revealed that dislocations were not observed in the crystal and that ordering had occurred in the InGaAsP crystal. It was also found that the temperature dependence of the PL emission intensity of this crystal was small in the difference between the PL intensity peak at room temperature and the peak at 77K, as shown in the graph of FIG. 1 (b). Figure 1 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 was considered that PL characteristics would deteriorate if ordering occurred in the strained quantum well structure. On the other hand, the present inventor has found that by positively utilizing the ordering phenomenon, it is possible to provide a semiconductor laser in which the temperature variation of the oscillation wavelength and the injection current dependency are small.

InGaA will be described below with reference to the drawings.
The present invention will be described with reference to examples using sP crystals.

Example 1 An example 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 is a schematic sectional view 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. Shows. 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 = 1.0
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 is composed of seven layers of InGaAs which are alternately stacked.
I ordered with P strained well layer (0.8% compressive strain) 3
and 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 this example, 0.8% compressive strain was introduced into the strain well layer 3 and the crystal growth temperature was set to 580 ° C., whereby ordering occurred in the barrier layer 4. The energy band gap of the laminated structure is schematically shown in FIG. 2 (b).

The present inventor confirmed that the ordering exists in the barrier layer 4 by observing it with a transmission electron microscope. However, it is fully conceivable that the well layer 3 is also affected by ordering. In this example, since the compressive strain is introduced into the well layer 3, tensile strain is generated in the barrier layer 4. Therefore, it is considered that tensile strain is more likely to occur in ordering. In order to preferentially generate ordering in the well layer 3, it is considered that the composition of the well layer should be adjusted 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 a strained quantum well crystal without ordering, and FIG. 3B shows a PL peak of a strained quantum well crystal with ordering.
If there is no ordering, the temperature should be room temperature (T = 300
K) to 77K causes a short wavelength shift of 60 meV.
Almost no short wavelength shift of about 0 meV is recognized. Further, it can be seen that at room temperature, the emission intensity does not decrease as compared with the case where there is no ordering even if there is ordering. As described above, the strained quantum well crystal with ordering exhibits 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 when there is no ordering.
It can be seen that it is reduced to / 5 or less.

The reason 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 strain quantum well layer, the internal energy of the crystal increases by the strain energy. However, when In—As bonds having a large lattice constant are naturally oriented in the crystal growth direction and ordering occurs, the strain energy of the strained quantum well layer becomes small.

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

U = H-TSH is enthalpy, T is temperature, and 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 it is considered that the entropy S tends to be small, and thereby the internal energy U tends to be lowered. In other words, it is necessary to introduce a large strain into the quantum well to increase the enthalpy H and reduce S. On the other hand, the relationship between the crystal growth temperature and the ordering is considered as follows. U
Since H 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, causing a decrease in S, that is, ordering. It will be easier.

The inventor considers that the reason why the temperature dependence becomes smaller when the ordering is caused is as follows. When the entropy S becomes small due to ordering, the temperature dependence of the internal energy U becomes small.
Since the energy bandgap Eg that determines the oscillation wavelength varies depending on the internal energy U, the bandgap Eg can be reduced by reducing the temperature dependence of the internal energy U.
The temperature fluctuation of g can be reduced. In this way, the temperature fluctuation of the wavelength can be reduced by the ordering.

FIG. 5 shows that the growth temperatures Tg are 580, 600,
And 700 ° C., the relationship between the amount of strain that causes ordering and the number of quantum well layers is shown. 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 amount _{580 at which} ordering occurs is
It is expressed by the following equation 1 using the number of well layers.

Strain amount ₅₈₀ (%) = 1.0−0.10 × number of well layers Equation 1 That is, when a strain amount larger than the strain amount ₅₈₀ obtained by Equation 1 is applied, ordering occurs and It can be said that if a strain amount smaller than the strain amount ₅₈₀ obtained in 1 is applied, 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 less than 580 ° C., ordering is considered to occur in the region represented by the inequality of strain amount (%) ≧ 1.0−0.10 × well layer number.

Similarly, the growth temperature Tg is 600 ° C., 700
When the temperature is ° C, ordering occurs in the regions shown by the following formulas 2 and 3, respectively.

Strain amount (%) ≧ 1.2-0.02 × number of well layers Equation 2, Tg = 600 ° C. Strain amount (%) ≧ 1.6-0.02 × number of well layers Formula 3, Tg = 700 ° C. When actually manufacturing a semiconductor laser, 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 a range of optimum conditions that does not reduce the optical output of the semiconductor laser. Therefore, when crystal growth is performed at about 600 ° C., it is necessary to form a compressive strain of about 1% in order to generate ordering. On the other hand, when the crystal growth temperature is lowered to 580 ° C., if the number of well layers is 7, the 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 as a light source for exciting a fiber amplifier. In order to obtain a 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, which causes 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. Therefore, even if the drive current is increased, it is easy to maintain the oscillation wavelength within the predetermined range required by the fiber amplifier.

Further, even if the active layer width of the semiconductor laser varies from element to element, and thus the amount of heat generated for the same drive current (injection current) differs for each laser, the oscillation wavelength is maintained constant. Therefore, according to the present invention, it is possible to remarkably improve the manufacturing yield of the semiconductor laser that satisfies the desired specifications.

FIG. 6 is a graph showing the relationship between the amount of strain (%) causing ordering and the crystal growth temperature (° C.) when the number of InGaAsP strain quantum well layers is 10. In a region where the distortion shown in the graph of FIG. 6 is larger than that shown by the curve,
Ordering occurs. Crystal growth of the InGaAsP strained quantum well layer is usually performed in the range of about 600 to 620 ° C. Therefore, in order to prevent the ordering, it is necessary to grow the crystal 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, the ordering does not occur if the condition shown in the region B of the graph is adopted.

It is an object of the present invention to provide a strained quantum well crystal having a light emission characteristic that is hard to change depending on temperature by intentionally causing ordering. However, in the process of finding the conditions that cause ordering, conversely, the conditions that do not cause ordering were clarified. It is understood that when the PL characteristics of FIG. 1A are to be exerted while giving a large strain to the quantum well layer, the crystal growth may be performed under the condition of the region B in the graph of FIG.

Example 2 An example 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 striped ridge (width: 1.2 to 1.5 μm, height: 1.5 to 2.5 μm).
m), an Sn-doped InP semiconductor single crystal substrate 1,
1 schematically shows the structure of a semiconductor laser including a stripe-shaped laminated structure provided on a ridge of a Sn-doped InP semiconductor single crystal substrate 1. This stripe-shaped laminated structure comprises InGaAsP (λg = 1.05 μm) first optical waveguide layer 2, multiple quantum well structure 5, and InGaAs.
The P (λg = 1.05 μm) 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 is composed of seven layers of InGaA.
The sP strain well layer (0.8% compressive strain) 3 and the ordered InGaAsP (λg = 1.15 μm) barrier layer 4 are alternately laminated. 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 this multiple quantum well structure 5 was 1.3 μm. In this example, 0.8% compressive strain was introduced into the strain well layer 3 and the crystal growth temperature was set to 580 ° C., whereby ordering occurred in the barrier layer 4. Note that 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 striped 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 the semiconductor laser.

Next, a method of manufacturing the strained quantum well laser of FIG. 7A will be described with reference to FIGS. 8A to 8D. First, as shown in FIG. 8A, the InP substrate 1
On top of the first InGaAsP optical waveguide layer 2, InGaA
A first crystal growth step of 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 into stripes is performed.

Thereafter, as shown in FIG. 8C, after performing a second crystal growth step of growing the current confinement structure 7, as shown in FIG. 8D, the p-side electrodes 8 and n are formed. An electrode forming step of forming the side electrode 9 is performed.

To cause ordering, the well layer 3
0.8% strain was introduced and the growth temperature was increased to 580
C, and the supply ratio V / III of the group V and group III gases is 250
And This crystal growth condition is indicated by a point A on the graph of FIG. As described above, the semiconductor laser of the present embodiment includes the same crystal as the strained quantum well crystal of the first embodiment in the stripe-shaped laminated structure. Such a strained quantum well crystal is produced under the conditions described in the first embodiment.

The oscillation wavelength of the semiconductor laser having the strained quantum well crystal with ordering was 1.3 μm, and the maximum optical output was 300 mW. This is at the same level as the laser output of a semiconductor laser without ordering, and laser oscillation occurred at the same 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 strained quantum well semiconductor laser without ordering is changed from 1.26 μm to 1.44 μm, whereas the strained quantum with ordering is changed. The oscillation wavelength of the well-type semiconductor laser is 1.29 μm to 1.31 μm
Changes to. Thus, the ordering reduced the amount of wavelength variation to ⅕ or less. Since the amount of change in the oscillation wavelength with respect to the temperature is reduced, it is possible to provide a semiconductor laser that stably oscillates in the temperature range of -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.
It shows in 0. Usually, when the injection current to the semiconductor laser increases, Joule heat is generated due to the internal resistance of the semiconductor laser and the temperature of the semiconductor laser rises. Therefore, the oscillation wavelength changes. However, according to the semiconductor laser of the present embodiment, since the oscillation wavelength has little temperature dependence, the oscillation wavelength hardly changes even when the injection current is changed. In particular, a high-power semiconductor laser that injects a large current is required to have a small change in oscillation wavelength. There is also an advantage that the oscillation wavelength at high output can be easily estimated from the PL emission wavelength.

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

(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 striped ridge,
1 schematically shows the structure of a semiconductor laser including a stripe-shaped laminated structure provided on a ridge of a Sn-doped InP semiconductor single crystal substrate 1. A diffraction grating 10 having a pitch of 180 nm is formed on the upper surface of the striped ridge. The striped laminated structure is 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 includes 7 InGaAsP strain well layers (0.8%).
Compressive strain 3 and ordered InGaAsP (λg =
1.15 μm) The barrier layer 4 is included. The thickness of each semiconductor layer may be within the thickness range described in the third embodiment. The photoluminescence (PL) emission wavelength of the multiple quantum well structure 5 was 1.3 μm. In this example, 0.8% compressive strain was introduced into the strain well layer 3 and the crystal growth temperature was set to 580 ° C., whereby ordering occurred in the barrier layer 4. Note that FIG. 11 (b)
Shows the energy band structure of the laminated structure.

As shown in FIG. 11B, p-InGaAsP / p-I is formed on both sides of the striped laminated structure.
An nP / n-InP / p-InP current confinement structure 7 is provided, and a groove is provided in a part of the current confinement structure 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 the semiconductor laser.

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

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

Ideally, the DFB laser oscillates in a single mode. However, as shown in FIG. 12B, when the difference between the “DFB oscillation wavelength” determined by the pitch of the diffraction grating and the “gain peak wavelength” is larger than 20 nm, the probability of single mode oscillation of the laser is Falls sharply. Figure 13
The temperature dependence of the appearance rate of single-mode characteristics is shown. When a semiconductor laser without ordering is driven without temperature control, the temperature range in which single mode oscillation can be realized is 0.
It goes from 40 ° C to 40 ° C. On the other hand, when a semiconductor laser is prototyped using a strained quantum well crystal with ordering, -8
Single mode oscillation is maintained even if the temperature of the semiconductor laser is changed within the range of 0 ° C to 120 ° C. As a result, there is no need to use a Peltier element for temperature control, and the cost 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 the single mode decreases at 300 mA or more, but when the ordering exists, the single mode property is maintained even at 600 mA or more, and the low optical output is obtained. It is possible to realize a high-power DFB laser exhibiting single-mode oscillation from high to high optical output with high yield.

As described above, according to this embodiment, it is possible to provide the DFB laser whose single-mode characteristics are not easily influenced by the ambient temperature and the injection current, and at the same time, the inexpensive laser module which does not need the Peltier element is provided. can do.

In the description of each of the above embodiments, the barrier layer 1
4 was formed from InGaAsP (λg = 1.15 μm), but if formed from InGaAsP (λg = 1.05 μm), ordering is more likely to occur,
Further, ordering can be effectively generated in the barrier layer. In addition, SCH (spectrum confinment hetero
I have explained a semiconductor laser with a structure,
The present invention is also applicable to other semiconductor lasers. Also,
In addition to InGaAsP / InP, AlGaAs / G
aAs and InGaP / AlGaInP, ZnSe
The same effect can be achieved with the GaN-based and GaN-based materials.

The type of the semiconductor laser is not limited to the Fabry-Perot type or the DFB type, but may be a semiconductor laser having a high added value such as a DBR type. Further, when the strained quantum well crystal of the present invention is applied to not only a light emitting element such as a semiconductor laser but also a light receiving element and a high-speed electronic element such as an HFET, the temperature fluctuation characteristics of these 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 in which the oscillation wavelength is not affected by the ambient temperature and the injected current, and also possible to provide a low-cost DFB laser module that does not require a temperature control element such as a Peltier element. , Its practical effect is extremely large.

[Brief description of drawings]

FIG. 1A is a graph showing a shift of PL light emission depending on temperature without ordering, and FIG. 1B is a graph showing a shift of PL light emission according to temperature with ordering.

2A is a structural cross-sectional view of an example 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.

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

FIG. 4 is a graph illustrating a difference in 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 strain 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 strain quantum well layers is 10.
It is a graph which shows the relationship with.

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

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

FIG. 9 is a graph illustrating the 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.

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 emission intensity of a multiple quantum well structure depending on the presence or absence of strain.

FIG. 13 is a graph for explaining 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 for explaining the difference in the injection current dependency of the appearance rate of single-mode oscillation depending on the presence or absence of ordering.

FIG. 15 (a) is an energy band diagram of a strained quantum well structure of a conventional strained quantum well semiconductor laser,
FIG. 3B is a perspective view of the semiconductor laser.

[Explanation of symbols]

1 Single crystal substrate 2 First waveguide layer 3 Strain well layer 4 Barrier layer 5 Strained quantum well structure 6 Second Waveguide Layer 7 Current constriction layer 8 p-side electrode 9 n-side electrode

   ─────────────────────────────────────────────────── ─── Continued front page    (72) Inventor Yasushi Matsui               1006 Kadoma, Kadoma-shi, Osaka Matsushitaden               Instrument industry Co., Ltd.                (56) Reference JP-A-5-55699 (JP, A)                 Japanese Patent Laid-Open No. 7-7217 (JP, A)

Claims (4)

(57) [Claims] 1. A semiconductor crystal composed of InP and InGa having a lattice constant different from that of the semiconductor crystal.
AsP crystal, and a method for manufacturing a strained quantum well crystal comprising the well layer and a barrier layer, wherein in the step of forming the well layer, 1% is added to the well layer. A method for producing a strained quantum well crystal, characterized in that the well layer and the barrier layer are not ordered by giving a strain in an amount exceeding 620 ° C. and performing crystal growth. 2. The method for manufacturing a strained quantum well crystal according to claim 1, wherein the number of the well layers is 10. 3. The strain amount of the well layer is: strain amount (%) = (1.0345 × 10 ⁻⁶ ) × (growth temperature)
^The method for producing a strained quantum well crystal according to claim 1, wherein the value is not more than a value given by a function of ³ −0.0021252 × (growth temperature) ² + 1.4575 × (growth temperature) 332.27. 4. A semiconductor crystal composed of InP and InGa having a lattice constant different from that of the semiconductor crystal.
An AsP crystal and a method for manufacturing a strained quantum well crystal, the strained quantum well crystal including a well layer and a barrier layer, wherein the number of the well layers is 10 or less. In the forming step, the strain amount (%) is added to the well layer.
= 1.2-0.02x (the number of well layers), and the strain amount (%) = 1.6-0.02x (the number of well layers) Give a small distortion, 620
A method for producing a strained quantum well crystal, wherein the well layer and the barrier layer are not ordered by performing crystal growth at a temperature in the range of 100 to 700 degrees.