JPH09298338A - Quantum well crystalline body and semiconductor laser - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a semiconductor laser oscillating at a wavelength of 2.0μm. SOLUTION: An InP clad layer 1a is formed on an InP substrate 1, and InGaAs strained quantum well layers 4 constituted of seven layers grown on the layer 1a, an InGaAs barrier layer 4, and an InP clad layer 7 are formed. Composition wavelength λg of the quantum well layers is 2.2μm, and the barrier layer is lattice-matching the InP clad layer and the InP substrate, and has composition wavelength λg=1.67μm. Compressive strain whose strain amount is 1.3% is introduced in the quantum well layers, and strain is not introduced in the barrier layer. Photo luminescence light emitting wavelength from the quantum well crystalline body is 2.0μm.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention oscillates at 1.6 .mu.m or more, and in particular, a semiconductor laser exhibiting high output and high efficiency characteristics at a wavelength near 1.8 .mu.m and a wavelength of 1.7 to 2.2 .mu.m can be received. The present invention relates to a simple light receiving element.

[0002]

2. Description of the Related Art In the conventional example, as shown in FIG. 9, the barrier layer is InGaAs (composition wavelength λ = 1.67 μm) lattice-matched with InP.
There is a strained quantum well laser whose well layer is composed of InGaAs having a compressive strain of about 1.5% (S. Follo et al.,
electronics. Letter 28 (1992) 1431). The laser was reported to pulse at room temperature, but not continuous wave. It is considered that, because InGaAs (composition wavelength λ = 1.67 μm) having a relatively small energy band gap was used for the barrier layer, carrier overflow occurred, and continuous oscillation at room temperature could not be performed.

In the conventional light receiving element, the light absorption layer is InGaAs.
Although it can receive light of 1.3 μm, it cannot efficiently absorb light of wavelength 1.67 μm or more, so when it receives light of wavelength 1.7 μm or more, its quantum efficiency is 40% or less. Was falling to.

[0004]

Therefore, the present invention is directed to 1.
It is an object to provide a semiconductor laser that oscillates at a long wavelength of 6 μm or more, particularly 1.8 μm or more, and a light receiving element that receives light of a long wavelength.

[0005]

According to the present invention, in order to realize a laser oscillating at a long wavelength, an InGaAs layer having a small bandgap is used for a well layer, and a barrier layer has a bandgap larger than that of a well layer. However, an InGaAs layer having a relatively small band gap is used.
This is because, in the present invention, in order to obtain a laser beam having a long wavelength, if the quantum level of the well layer is largely shifted, the laser beam is shifted from the long wave to the short wavelength direction. That is, a semiconductor layer having a relatively small bandgap is used for the barrier layer to the extent that the quantum level of the well layer does not cause a large quantum shift due to the quantum effect. The band gap is as shown in FIG. The difference (ΔEc) between the ground level of the conduction band of the well layer and the ground level of the barrier layer is 8
0 to 200 meV is preferable. This is because if it is larger than 200 meV, the well layer is accompanied by a large quantum shift, and if it is smaller than 80 meV, the overflow of electrons becomes too large and oscillation does not occur at room temperature.

As described above, the present invention uses InGaAs having a small energy band gap for the barrier layer, suppresses carrier overflow, and oscillates at room temperature. I am trying. As a result, a laser having a long wavelength of 1.6 to 2.2 μm can be obtained.

In order to oscillate at room temperature regardless of the number of well layers, tensile strain is introduced into the barrier layer to increase the energy band gap to the extent that electrons do not overflow into the well layer. . As a result, it is possible to obtain oscillation at room temperature without increasing the number of well layers. With this, a favorable laser oscillation characteristic of a wavelength of 1.8 μm to 2 μm can be obtained with a compressive strain of about 1% in the well layer.

When InGaAs layers are used for both the well layer and the barrier layer, since P is not used, it is not necessary to switch the phosphine gas (PH3) at the hetero interface, so that pressure fluctuation at the interface is suppressed and steep. It was possible to form a smooth interface.

In order to increase the sensitivity of the light receiving element, the energy band gap of the absorption layer of the light receiving element must be equal to or smaller than the energy of incident light. Therefore, light efficiency can be realized by manufacturing a light receiving element having an absorption layer with a structure similar to that of the active layer of the laser.

[0010]

BEST MODE FOR CARRYING OUT THE INVENTION Considering conventional lasers,
Our study revealed that the laser did not oscillate at room temperature because the number of laser well layers was as small as two. FIG. 14 shows a graph showing the threshold current of the laser. The horizontal axis represents the number of well layers, and the vertical axis represents the threshold current with respect to the number of well layers. The structure is a quantum well structure composed of an InGaAs well layer (composition wavelength: 2.2 μm, compressive strain 1.5%) and an InGaAs barrier layer (composition wavelength: 1.67 μm) sandwiched between InP clad layers.

As can be seen from FIG. 14, the well layer has three layers.
The layer did not oscillate at room temperature. It started to oscillate from 4 or more well layers. In particular, it became clear that the threshold current becomes low when the number of well layers is six. Considering this point, when the number of well layers is small, it is considered that it was difficult to oscillate at room temperature because many electrons necessary for oscillation must be accumulated in the well layers. The number of well layers is 2 and 7 photoluminescence (P
The characteristic of L) is shown in FIG. As you can see from this figure,
When the number of well layers is 2, the PL spectrum line width is broad, and it can be seen that there is light emission due to electrons overflowing from the well layer to the barrier layer. Therefore, it was found that increasing the number of well layers and reducing the current density per well layer is effective in preventing light emission from the barrier layer as much as possible and causing oscillation at room temperature.

A specific structure will be described below as an embodiment. (First Embodiment of the Invention) FIG. 1 is a sectional view showing an embodiment of a quantum well crystal body of the present invention. As shown in FIG. 1 (a), the quantum well crystal has an InP clad layer 1a formed on an InP substrate 1, and seven layers of InGa grown on the InP clad layer 1a.
An As strained quantum well layer 4, an InGaAs barrier layer 5, and an InP clad layer 7 are formed.

The composition wavelength λg of the well layer is 2.2 μm, and the film thickness is 6 nm. The barrier layer is lattice-matched to the InP clad layer and the InP substrate, and has a composition wavelength λg = 1.67.
The thickness is 10 nm in μm. A compressive strain with a strain amount of 1.3% was introduced into the well layer, and no strain was introduced into the barrier layer. The photoluminescence emission wavelength from this quantum well crystal was 2.0 μm.

As described above, seven layers of InGaAs having a composition wavelength of 2.2 μm are used for the quantum well layer, and the barrier layer has a band gap larger than that of the quantum well layer, but a band that does not increase the quantum shift of the well layer. InG with a gap (here 1.67 μm, ΔEc = 120 meV)
By using aAs, a laser beam having a long wavelength of 2.0 μm could be obtained. Here, the number of well layers is 7, but if the number of well layers is 4 or more, oscillation can be performed at room temperature. In order to reduce the threshold current, the number of well layers is preferably about 6 to 8.

The size of the bandgap of the barrier layer must, of course, be larger than that of the well layer. The conduction band difference (ΔEc) is preferably 80 to 200 meV, but in order to prevent electron overflow, 100
It is preferably about 150, especially about 120 meV. Therefore, a structure for ensuring this ΔEc at 120 meV will be described. InGaAs whose lattice is lattice matched to InP (lattice strain = 0%)
In this case, in order to make the energy gap 120 meV or more, 1% or more of compressive strain must be introduced into the well layer. This will be described with reference to FIG.

FIG. 2 is a graph in which the horizontal axis represents the lattice strain, which is the deviation from InP in this case, and the vertical axis represents the emission wavelength and the size of the energy band gap. A black circle indicates the band gap energy, and a white circle indicates the emission wavelength. From this graph, it can be seen that In
When GaAs (emission wavelength of about 1.67 μm, bandgap 0.74 eV) is used, the well layer is 120 meV (0.12 eV) smaller than the bandgap of the barrier layer.
Since GaAs is used, the band gap is 0.62 eV and the lattice strain is about 1%. Therefore, it is understood that when a strain of 1% or more is introduced into the well layer, the gap between the well layer and the barrier layer can be secured at 120 meV or more.

Further, when it is desired to increase the bandgap of the barrier layer, suppress carrier overflow, and reduce the strain introduced into the well layer to 1% or less, similarly, the strain of the barrier layer is 0 from FIG. From this, it is understood that tensile strain (minus side of strain in the figure) should be set.

FIG. 3 is a sectional structural view of a quantum well structure in which compressive strain is introduced into the well layer and tensile strain is introduced into the barrier layer. The quantum well crystal body is composed of seven InGaAs well layers 4 and InGaAs barrier layers 5 and an InP clad layer 7 grown on the InP substrate 1 via the InP clad layer 1a.

A compressive strain with a strain amount of 0.8% is introduced into the well layer, and the composition wavelength converted from energy is 1.9 μm.
m. The film thickness was 6 nm. The strain of the barrier layer is -0.6
% Tensile strain has been introduced, and the wavelength converted from energy is 1.5 μm. The film thickness was 10 nm.
The number of well layers is 7 to suppress carrier overflow.

This structure, as shown in FIG.
The energy band gap of the barrier layer can be increased by introducing tensile strain into the barrier layer, and as a result, the energy gap can be 120 meV or more even if the compressive strain of the well layer is small. This makes it possible to realize a quantum well structure for laser light having an oscillation wavelength of 1.8 μm.

The case of using ternary InGaAs for the barrier layer has been described, but the case of using quaternary InGaAsP will be described. By using the InGaAsP layer as the barrier layer, the energy band gap can be made larger than that when using InGaAs. FIG. 4 shows a cross-sectional structure diagram of the quantum well crystal structure using InGaAsP for the barrier layer.

The quantum well crystal is a waveguide layer 3 or 7 layers of InGaAs grown on the InP substrate 1 via the InP clad 1a.
Well layer 4, InGaAsP barrier layer 5, waveguide layer 6, and InP
It is composed of a clad layer 7.

Here, the well layer has a band gap of 0.
An InGaAs layer with a composition wavelength of 2 μm reduced to 62 eV is used, which introduces a compressive strain of 1%. As the barrier layer, an InGaAsP layer having a composition wavelength of 1.45 μm is used. The bandgap of the barrier layer is 0.85 compared to the well layer
Since it is as large as eV, a quantum shift effect of 70 meV occurs,
The photoluminescence wavelength of this quantum well structure is 1.8.
It became μm. In the case of this structure, although the quantum shift occurs, the oscillation wavelength can be set to 1.8 μm. Further, since the overflow of electrons is small, it is possible to oscillate even if the number of well layers is about four.

In this quantum well crystal, since a barrier layer having a large bandgap is used, ΔEc between the well layer and the barrier layer is large, and the barrier layer of InGaAs having a composition wavelength of 1.45 μm is used.
Since there is no light emission from the P layer, a thick layer structure like the waveguide layer 3 can be obtained. As a result, when used as a laser structure, high output can be achieved.

Further, in the strained quantum well structure including the barrier layer having tensile strain introduced therein as shown in FIG. 3, the waveguide layer is made of a crystal different from that of the barrier layer as shown in FIG. The film thickness can be increased by lattice-matching the mixed crystal that constitutes the waveguide layer to InP, so when used as a laser structure, the waveguide loss of laser light is reduced and higher output of laser light is possible. Becomes

Embodiment 2 of the Invention Embodiment 1 of the Invention
A structural diagram of a laser in the case where the strained quantum well crystal shown in 1 is used for a laser stripe-shaped active layer will be described with reference to FIG. The active layer of the present laser is lattice-matched to the InP substrate grown on the InP substrate 1 via the cladding layer 1a, the InGaAsP waveguide layer 3 having a composition wavelength of 1.45 μm, and the strain amount of 4 pairs of well layers. A 0.8% compressive strain InGaAs well layer 4, a strain amount of -0.6% tensile strain InGaAs barrier layer 5, a waveguide layer 6,
Further, it is composed of an InP clad layer 7. In order to efficiently inject current into the active layer, the current is concentrated in the active layer by the p-InP19a current injection layer, the n-InP current confinement layer 20, and the p-InP19b current injection layer. By passing a current through the electrodes 15 and 16, continuous oscillation at room temperature can be obtained at 1.8 μm. Laser cavity long wave 300μm, active layer width 1.2
μm.

FIG. 6 shows a process chart of an embodiment of the method for manufacturing a semiconductor laser of the present invention. First, the laser of the present invention is n-In
N-InGaAs is grown on the P substrate 1 by MOVPE at a growth temperature of 620 ° C.
P (λg = 1.45 μm, film thickness 50 nm, lattice matching with InP) waveguide layer 3 was grown, and 7 cycles of InGaAs (strain amount 0.8%, film thickness 6 n
m) Strain well layer 4 and InGaAs (strain amount -0.6%, film thickness 10 nm) barrier layer
After stacking 5 layers alternately, p-InGaAsP (λg = 1.45μm, film thickness
A strained quantum well structure is obtained by growing a waveguide layer 6 and a p-InP cladding layer (50 nm) (a).

Further, the clad layer and the InP substrate are removed by etching in stripes (b).

After that, buried growth is performed with the p-InP, n-InP and p-InP layers 19 and 20 to grow the contact layer 14 (c).

Finally, the electrodes 15 and 16 are formed by vapor deposition.
(d). With the embedded laser structure, a current can be effectively injected into the active layer, so that the threshold current can be lowered.

In the case of the strained quantum well structure of this embodiment, when the well layers and the barrier layers are alternately grown, both crystals do not contain P. Therefore, phosphine P which is a raw material of P is formed.
There is no need to supply H3, arsine A as a raw material for As
Since it is sufficient to supply sH3 at a constant flow rate, a crystal having a stable composition can be obtained as compared with the conventional example in which it is necessary to grow while alternately switching phosphine and arsine, so that laser characteristics can be stabilized.

(Embodiment 3 of the Invention) Embodiment of the Invention
FIG. 7 shows a structural diagram when the strained quantum well crystal shown in 1 is used for the light absorption layer of the light receiving element.

The light absorption layer 28 of the present light receiving element is the InP substrate 1
N-InP buffer layer 21 grown above, InGaAsP light transmitting layer 22 having a composition wavelength of 1.45 μm, strain amount of 7 pairs of well layers 0.8%
InGaAs well layer 4 with compressive strain and strain with tensile strain of -0.6%
It is composed of an InGaAs barrier layer 5, an InGaAsP light transmitting layer 23, and an nInP light transmitting layer 24. Finally, the electrodes 15 and 16 are formed by vapor deposition (d).

Zn is diffused in the light receiving region 27 at 1 × 10 ¹⁹ cm ⁻³ . The light receiving area has a diameter of 500 μm. By applying a reverse bias to the electrodes 15 and 16, the light absorption layer is depleted, and a photocurrent can be extracted when light is incident.
The photoluminescence wavelength of the quantum well structure forming the light absorption region was 2.0 μm. When 1.8 μm of light is incident on the light receiving element, the quantum efficiency increases from 20% to 90%.

(Embodiment 4) FIG. 8 shows a process chart of an embodiment of a method for manufacturing a light receiving element of the present invention. The light-receiving element of the present invention comprises an n-InP substrate 1, an n-InP buffer layer 21 at a growth temperature of 620 ° C., an InGaAsP light transmitting layer 22 having a composition wavelength of 1.45 μm, and a strain amount of 7 pairs of well layers. 0.8%
InGaAs well layer 4 with compressive strain and strain with tensile strain of -0.6%
Strained quantum well light absorption layer 28 composed of InGaAs barrier layer 5, n-InG
After the aAsP light transmitting layer 23 and the n-InP light transmitting layer 24 are successively grown, a silicon oxide film 25 is deposited on the surface (a). After the silicon oxide film in the light receiving region is removed by etching (b), the light receiving region 27 is formed by diffusion of Zn (c). After depositing the silicon nitride film 26 on the entire surface, the electrode pattern portion is removed by etching (d). By depositing the p-electrode 15 on the resist 28, the p-type electrode 15 is formed in the opening of the silicon nitride film. Further, the n-type electrode 16 is vapor-deposited on the back surface of the substrate. With the planar structure, a structure that is advantageous for integration and has a small dark current can be obtained.

(Fifth Embodiment) FIG. 12 shows a fiber inspection system using the semiconductor laser 31 and the light receiving element 33 described in the first to fourth embodiments. 1.7 μm from signal transmission base
The laser light of the wavelength is coupled with the signal light of the signal laser 30 and the coupler 38.
Are combined and emitted at the same time. On the receiving side, the light receiving element for signal 34 receives the light, and only the light having a wavelength of 1.7 μm is demultiplexed by the coupler 38b, and the light receiving element 33a of the present embodiment is used to receive the light. As shown in FIG. 12 (b), if the fiber 32 breaks somewhere, from the receiving side,
Since the light of 1.7 μm wavelength cannot be received, the abnormality of the fiber can be instantly detected. Also, on the transmitting side, the return light from the fiber is demultiplexed by the coupler 38a to 1.7 μm.
If the light of m wavelength is always received by the light receiving element 32, the reflected light from the end face generated by the breakage of the fiber is increased, so that the abnormality of the fiber can be detected.

(Embodiment 6) Semiconductor laser 31 of the present invention
A sensor system using the light receiving element 33 and the light receiving element 33 is shown in FIG. After the semiconductor laser light is collimated by the lens 35, it is condensed by the lens 36 and received by the light receiving element 33. Between the lenses,
When the object 38 that absorbs light having a wavelength of 1.7 μm passes, the output of the light receiving element 33 decreases, so that the object 38 can be detected. Also, as shown in FIG.
Even if the reflected light is split and received by the half mirror 37,
When the object 38 passes and blocks the laser beam of 1.7 μm, the reflected light from the object 38 increases, so that the object can be detected.

[0038]

According to the present invention, the following effects can be obtained.

InGa having a small band gap is formed in the well layer.
By using an As layer and an InGaAs layer having a relatively small bandgap also as a barrier layer, a large quantum shift of the well layer can be suppressed to form a semiconductor quantum well crystal having an oscillation wavelength of a long wavelength. . By using this crystal body for a laser, a semiconductor laser having an oscillation wavelength of 1.6 μm or more can be obtained.

Further, by using the above crystal for a light receiving element, it is possible to efficiently receive light having a wavelength of 1.6 μm or more. A quantum efficiency of 90% or more can be obtained.

[Brief description of drawings]

FIG. 1 is a cross-sectional view of a quantum well crystal body of the present invention.

FIG. 2 is a diagram showing a relationship between a strain amount, an energy band gap, and an emission wavelength of an InGaAs layer.

FIG. 3 is a sectional view of the quantum well crystal body of the present invention.

FIG. 4 is a sectional view of a quantum well crystal body of the present invention.

FIG. 5 is a sectional view of the quantum well crystal body of the present invention.

FIG. 6 is a manufacturing process diagram of the semiconductor laser of the present invention.

FIG. 7 is a sectional view of a light receiving element of the present invention.

FIG. 8 is a manufacturing process diagram of the light receiving element of the present invention.

FIG. 9 is a sectional view of a conventional quantum well crystal.

FIG. 10 is a conceptual diagram showing the composition range of the present invention.

FIG. 11 is a sectional view of a semiconductor laser of the present invention.

FIG. 12 is a block diagram of a fiber inspection system of the present invention.

FIG. 13 is a configuration diagram of a sensor system of the present invention.

FIG. 14 is a diagram showing the relationship between the number of well layers and the threshold current.

FIG. 15 is a diagram for explaining how the emission wavelength and emission intensity change depending on the number of well layers.

[Explanation of symbols] 1 InP substrate 3 Waveguide layer 4 Well layer 5 Barrier layer 6 Waveguide 7 Cladding layer 14 Contact layer 15 p-type barrier layer 16 n-type barrier layer 18 Submount 19 Current injection layer 20 Current confinement layer 21 Buffer Layer 22 Light transmission layer 23 Light transmission layer 24 Light transmission layer 25 Silicon oxide film 26 AR coat 27 Diffusion region 28 Light absorption layer 29 Resist 30 Transmitting base 31 Semiconductor laser 32 Fiber 33 Light receiving element 34 Receiving side 35 Lens 36 Lens 37 Half mirror 38 Coupler 39 Object

 ─────────────────────────────────────────────────── ─── Continued front page (72) Inventor Masato Ishino 1006 Kadoma, Kadoma, Osaka Prefecture Matsushita Electric Industrial Co., Ltd. (72) Yasushi Matsui 1006 Kadoma, Kadoma City, Osaka Matsushita Electric Industrial Co., Ltd.

Claims (23)

[Claims] 1. A lattice including a substrate, a quantum well active layer composed of an InGaAs well layer and an InGaAs barrier layer grown on the substrate, and an InP clad layer formed on the active layer, the lattice being introduced into the well layer. A quantum well crystal body having a strain amount of 0.4% or more and 2.0% or less, the barrier layer made of an InGaAs mixed crystal lattice-matched with InP, and having four or more well layers. 2. A lattice introduced into the well layer, comprising a substrate, a quantum well active layer composed of an InGaAs well layer and an InGaAs barrier layer grown on the substrate, and an InP clad layer formed on the active layer. A quantum well crystal body having a strain amount of 0.4% or more and 2.0% or less and the barrier layer made of an InGaAs mixed crystal having a lattice constant smaller than that of InP. 3. The amount of lattice strain introduced into the barrier layer is -1.5% or more 0
% Or less, The quantum well crystal body according to claim 2. 4. A substrate, a waveguide layer grown on the substrate, a quantum well active layer including an InGaAs well layer and an InGaAs barrier layer, and an InP clad layer on the active layer.
A quantum well crystal body in which the waveguide layer is composed of an InGaAsP mixed crystal having a composition wavelength λ = 1.45 to 1.67 μm. 5. The barrier layer of InGaAsP having a lattice constant smaller than that of InP.
The quantum well crystal body according to claim 4, wherein the quantum well crystal body is composed of a mixed crystal. 6. A substrate, a waveguide layer grown on the substrate, a quantum well active layer composed of an InGaAs well layer and an InGaAsP barrier layer, and an InP clad layer on the active layer, wherein the barrier layer is a composition. Quantum well crystal composed of InGaAsP mixed crystal with wavelength λ = 1.45 to 1.67 μm. 7. A substrate, a quantum well active layer composed of an InGaAs well layer and an InGaAs barrier layer grown on the substrate, and an InP clad layer on the active layer, wherein the amount of lattice strain introduced into the well layer is 0.4% to 2.0%, the barrier layer is composed of InGaAs mixed crystal lattice-matched to InP, and the number of well layers is 4
A semiconductor laser that is more than one layer. 8. A quantum well active layer composed of an InGaAs well layer and an InGaAs barrier layer, and an InP cladding layer, wherein the lattice strain introduced into the well layer is 0.4% or more and 2.0% or less, and the barrier layer is composed of InP. A semiconductor laser composed of InGaAsP mixed crystal with a small lattice constant. 9. A waveguide layer having a composition wavelength λ = 1.45 to 1.67 μm
8. The semiconductor laser according to claim 7, which is composed of a GaAsP mixed crystal. 10. The barrier layer is composed of In having a composition wavelength λ = 1.45 to 1.67 μm.
The semiconductor laser according to claim 8, which is composed of a GaAsP mixed crystal. 11. A step of growing a waveguide layer, a quantum well active layer composed of an InGaAs well layer and a barrier layer, and an InP clad layer on a substrate, and a step of etching away from the clad layer to the substrate in a stripe shape. A method for manufacturing a semiconductor laser, comprising: a step of burying and growing the stripe, and a step of forming an electrode. 12. An InP substrate and a first grown on the substrate.
A light transmission layer, a quantum well light absorption layer composed of an InGaAs well layer and an InGaAs barrier layer, and a second InP light transmission layer, and the lattice strain amount introduced into the well layer is 0.4% or more and 2.0% or less, A light-receiving element in which the barrier layer is composed of an InGaAs mixed crystal. 13. The barrier layer, I, having a lattice constant smaller than that of InP.
13. The light receiving element according to claim 12, which is composed of an nGaAs mixed crystal. 14. A light transmission layer comprising a substrate, a first light transmission layer grown on the substrate, a quantum well light absorption layer consisting of a well layer and a barrier layer, and a second InP light transmission layer. 13. The light receiving element according to claim 12, wherein is composed of an InGaAsP mixed crystal having a composition wavelength λ = 1.45 to 1.67 μm, and the barrier layer is composed of an InGaAs mixed crystal having a lattice constant smaller than that of InP. 15. The barrier layer has a composition wavelength λ = 1.45 to 1.67 μm.
13. The light-receiving element according to claim 12, which is composed of the InGaAsP mixed crystal. 16. A step of growing a light absorption layer, a quantum well light absorption layer composed of a well layer and a barrier layer, and an InP light transmission layer on a substrate, and after depositing an insulating film on the entire surface of the InP light transmission layer. A step of etching away the light receiving region, a step of diffusing a p-type impurity element in the light receiving region, a step of removing an electrode portion after depositing an antireflection film on the entire surface, and a step of forming an electrode by vapor deposition. A method of manufacturing a light receiving element having the same. 17. A fiber inspection apparatus comprising the semiconductor laser according to any one of claims 6 to 8 and the light receiving element according to any one of claims 10 to 12. 18. A quantum well active layer comprising a substrate and an InGaAs well layer and an InGaAs barrier layer grown on the substrate,
The number of well layers is 4 or more, and the emission wavelength is 1.6 μm.
A quantum well crystal in the range of m to 2.2 μm. 19. The quantum well crystal body according to claim 18, wherein compressive strain is introduced into the well layer, and a difference in ground level between the well layer and the barrier layer is 80 to 200 meV. 20. The quantum well crystal body according to claim 19, wherein tensile strain is introduced into the barrier layer. 21. The quantum well crystal body according to claim 19, wherein compressive strain is introduced into the well layer. 22. A substrate, and a quantum well active layer composed of an InGaAs well layer and an InGaAs barrier layer grown on the substrate,
The number of well layers is 4 or more, and the emission wavelength is 1.6 μm.
A light-receiving element in the range of m to 2.2 μm. 23. The quantum well crystal body according to claim 22, wherein compressive strain is introduced into the well layer.