JPH05198894A - Semiconductor laser and its manufacture - Google Patents

Abstract

PURPOSE:To restrain breakdown of modulation doping structure, increase differential gain, and realize a semiconductor laser with a low threshold value and high slope efficiency, by forming a dopant diffusion stopper layer, and constituting a modulation doping structure wherein diffusion of dopant is restrained. CONSTITUTION:The title semiconductor laser is constituted by laminating in order an N-InGaAsP waveguide layer 2, a modulation doping quantum well layer 7, a P-InGaAsP layer 8, and a P-InP clad layer 9, on an Sn-doped InP substrate 1, and arranging in order a PNP current blocking layer 10, a mesa type active layer lead 11, an N side electrode 12 composed of Au/Sn, and a P side electrode 13 composed of Au/Zn. The modulation doping quantum well layer 7 is formed by laminating in order barrier layers composed of an InGaAs well layer, an undoped InGaAsP layer, and a P-InGaAsP modulation doping layer. The diffusion of Zn from the P-InP clad layer 9 is restrained by the P-InGaAsP layer 8.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a high performance semiconductor laser required for optical fiber communication and the like and a method for manufacturing the same.

[0002]

2. Description of the Related Art Conventionally, in order to improve the characteristics of a semiconductor laser, a single quantum well (SQW) laser or a multiple quantum well (MQW) having an active layer of the semiconductor laser having a quantum well structure is used.
Research on QW) lasers is being conducted. Due to the quantum size effect, the semiconductor laser having this quantum well active layer can be expected to have good characteristics not found in a normal bulk type active layer. For example, by increasing the differential gain and reducing TM emission, it is possible to operate with high efficiency and high output at a low threshold value, and by increasing the relaxation oscillation frequency and decreasing the line width increase coefficient, fast response and low chirping can be obtained. ..

However, in order to further increase the differential gain, in addition to application of a strained quantum well and thinning of the barrier layer, application of a modulation-doped MQW structure in which the barrier layer of the quantum well is doped is being studied. Umi, Tee Mishima, N Chinone, Japan Journal Affiliate Physics, 51 (199
0) 88 (K. Uomi, T. Mishima, N. Chinone, Jpn. J. App
L. Phys., 51 (1990) 88)].

FIG. 8 shows an example of a conventional semiconductor laser. Three
1 n-GaAs substrate, 32 is n-GaAs buffer layer 33 is n-In _0.6 Al _0.4 As cladding layer, an undoped AlGaAs optical confinement layer 34, an undoped GaAs well layers 35, 36 an undoped Ga _0.8 Al _0.2 A
s layer, 37 is Be-doped Ga _0.8 Al _0.2 As, 38 is modulation-doped quantum Iodo layer, 39 is p-AlGaAs cladding layer, 40 is n-GaAs current narrowing layer, and 41 is SiO _2.
An insulating layer, a Zn diffusion region 42, a p-side electrode 43 made of Au / Cr, and an n-side electrode 44 made of AuGeNi.

The structure of the modulation-doped quantum well layer of FIG. 8 is shown in FIG.
As shown in (b), the undoped GaAs well layer 35, the undoped GaAlAs barrier layer 36, and the modulation doped layer 37.
It consists of a barrier layer.

In the conventional modulation-doped quantum well semiconductor laser device constructed as described above, a current is applied to the p-side electrode 4
After being introduced from No. 3 and confined by the Zn diffusion region 42, it is injected into the modulation-doped quantum well layer 38. It was confirmed that the relaxation oscillation frequency increased by the increase of the differential gain was increased in the modulation-doped quantum well structure shown in FIG. 8 with respect to the undoped quantum well structure.

[0007]

The modulation-doped quantum well layer 38 of the semiconductor laser of the modulation-doped quantum well structure having the above-described structure shown in FIG. 8 has the undoped GaAs well layer 35, as described above. Undoped AlGaAs barrier layer 36 and Be-doped AlGaAs modulation doped layer 37
And a barrier layer consisting of.

Comparison of the relaxation oscillation frequency between this semiconductor laser and a semiconductor laser having a uniformly-doped quantum well structure in which the well layer and the barrier layer are uniformly doped as shown in FIG. 9D shows no doping. Only an equal increase in relaxation oscillation frequency was observed compared to the quantum well semiconductor laser. It is considered that this is because the modulation doping structure shown in FIG. 9B or 9C became a uniform doping structure due to the diffusion of the doping element and the disappearance of the modulation doping structure in the subsequent heat treatment step. It is shown in FIG. 9 (a). In the modulation-doped quantum well structure having the structure shown in FIG. 6B, the Be concentration was high only in the modulation-doped layer before the heat treatment, but Be diffused from the modulation-doped layer after the heat treatment. It is uniform.
As a result, it is believed that there is no difference between lasers with uniform doping and modulation doping. This is because the element used for doping diffuses at high temperature.

In view of the above problems, the present invention suppresses the diffusion of the dopant element in the modulation-doped quantum well layer having the modulation-doping structure to prevent the modulation-doping structure from being destroyed and suppresses the destruction of the cladding layer. Provided is a semiconductor laser having a structure that suppresses the diffusion of a dopant into a modulation-doped quantum well layer and suppresses the destruction of the modulation-doping structure of the modulation-doped quantum well layer.

[0010]

To achieve this object, a semiconductor laser according to the present invention comprises a first conductivity type compound semiconductor substrate, a first waveguide layer on the substrate, a well layer and a barrier. A layer in which layers are alternately laminated, a modulation-doped quantum well layer that is modulation-doped in the barrier layer, a stop layer that stops diffusion of a dopant, and a second conductive clad layer are sequentially laminated, The first waveguide layer has the same or smaller energy gap than the substrate, the well layer has a smaller energy gap than the first waveguide layer,
The barrier layer is an energy gap intermediate between the first waveguide layer and the well layer, and partially includes a modulation dope layer having a conductivity type that is the same as or different from that of the substrate, and the stop layer is formed from the barrier layer. The semiconductor laser is a crystal in which the energy gap is the same as or larger than that of the crystal, and the dopant is added below its solid solubility limit.

A first semiconductor having a first conductivity type and a first semiconductor having a smaller energy gap than the first semiconductor on the compound semiconductor substrate.
Growing a first waveguide layer having a conductivity type of
A well layer having an energy gap smaller than that of the first waveguide layer, an undoped first barrier layer, a modulation-doped layer, and an undoped second barrier layer are alternately arranged at an energy gap in the middle of the well layer. Growing a stacked modulation-doped quantum well layer; growing a stop layer having an energy gap larger than that of the barrier layer to stop diffusion of a dopant; and having an energy gap larger than that of the stop layer and the second conductive type. A step of growing a clad layer having a layer, an etching step of etching the substrate up to the stripe shape, and a side surface of the stripe of the second conductive type crystal, the first conductive type crystal, and the second conductive type crystal. A method of manufacturing a semiconductor laser, comprising a step of growing a crystal to embed the stripe.

[0012]

In order to preserve the modulation dope structure, first, the concentration of the dopant added to the modulation dope layer needs to be equal to or lower than the saturation concentration of the dopant depending on the composition of the crystal.
However, even when the amount of the dopant in the modulation dope layer is below the saturation concentration, the modulation dope structure may disappear. This occurs when there is a layer to which a dopant having a saturation concentration or higher is added near the modulation-doped layer. Therefore, it is necessary to dispose the layer having a low saturation concentration away from the modulation dope layer and set the amount of the dopant to be equal to or less than the saturation concentration. In the present invention, the undoped layer is inserted between the cladding layer and the modulation-doped layer even when the Zn concentration in the cladding layer is set to be equal to or lower than the Zn saturation concentration, or when the cladding layer is doped with Zn near the saturation concentration. Therefore, diffusion can be prevented. However, when the laser structure is produced, it is necessary to dope the inside of the waveguide layer. Therefore, for example, a layer of InGaAsP or the like is inserted in place of InP or the like having a low Zn saturation concentration, which is a dopant. Save is realized.

[0013]

EXAMPLES The following preliminary experiments were attempted in order to realize the examples shown below.

As shown in FIG. 14, the well layer has a thickness of 5n.
In a 10-pair modulation-doped MQW structure in which the barrier layer has a thickness of 10 nm and the central region of 3 nm is doped with Zn at 1 × 10 ¹⁸ cm ⁻³ , a p-type cladding layer is usually formed after growth of the modulation-doping structure. InP layer 300n
grow. The growth temperature was 620 degrees and the growth time was 90 minutes. As a result of measuring the modulation doping structure after growth by SIMS, it was confirmed that the modulation doping structure was preserved.

However, in order to obtain a PBH structure (laser embedded structure), a liquid layer growth method (Liquid Phase) is used.
After the current confinement layer was embedded and grown by a p-n-p-InP layer by Epitaxy), the modulation doping structure was measured again by SIMS. As a result, the modulation doping structure disappeared.

On the other hand, after the modulation doping structure is grown, as shown in FIG. 10A, an undoped-InP layer is grown to 300 nm instead of the p-InP layer, and then p-In is grown.
As a result of growing the P layer and measuring the modulation-doped structure by SIMS, it was confirmed that the modulation-doped structure was preserved.

From the result of FIG. 10, when the concentration of the InP layer grown after growing the modulation doping structure is 0 (in the case of b), it is found that the modulation doping structure is preserved from the result of (a). As can be seen, the concentration of InP is 1 × 10 ¹⁸ c
In the case of m ^-3 (case of c), the modulation dope structure disappears. Therefore, adjacent to the modulation doped layer, undoped In
It can be seen that although P can be grown, the doped p-InP crystal cannot be grown.

From the above experimental results, the modulation doping structure disappears when there is a doped p-InP layer near the modulation doping layer, but the modulation doping structure disappears when the p-InP layer is not doped. It has not changed at all. The disappearance of the modulation-doped structure is considered to be that Zn doped into the p-InP layer diffuses into the modulation-doped layer as interstitial atoms Zni to destroy the modulation-doped structure. Therefore, there are two possible ways to preserve the modulation-doped structure.

1. As shown in FIG. 3A, the doped p-InP layer 9 is placed away from the modulation-doped quantum well layer 7, and the number of interstitial atoms Zni of Zn diffused from the p-InP layer 9 is set. Lower. As shown in FIG. 3A, a p-InGaAsP layer 8 that stops the diffusion of Zn was provided under the p-InP cladding layer 9. This p
-The InGaAsP layer 8 also functions as the second waveguide. Since the InGaAsP layer 8 has a high solid solubility limit of Zn,
Even if Zn diffuses from the cladding layer 9, this In
Zn stops at the GaAsP layer 8. Therefore, I
The nGaAsP layer 8 acts as a low resistance layer between the p-InP cladding layer 9 and the modulation dope layer 7 without generating Zn interstitials Zni.

2. As shown in FIG. 3B, p-InP
The Zn concentration of the layer 9 is reduced. The amount of Zn that can be solid-dissolved in the p-InP layer 9 depends on the crystal growth temperature and the total gas amount during crystal growth, but is considered to be approximately 1 × 10 ¹⁸ cm ⁻³ . When a concentration near the solid solubility limit is used, a large amount of interstitial atoms Zni are generated. Therefore, the p-InP clad layer 9 is 5 × 10 5 in which interstitials Zni are hardly generated.
^It is necessary to dope to about ¹⁷ cm ^-3 .

The above two means were to prevent the Zn element from diffusing into the modulation-doped quantum well layer from the outside of this layer. By this means alone, it is possible to prevent the doping element that diffuses into the modulation dope layer from outside the modulation dope layer, but to prevent the element doped in the modulation dope layer itself from diffusing and destroying the modulation dope layer. It is not possible. Therefore, in addition to these means, FIG.
As shown in (a), the doping element (Z
It is necessary to prevent n) from diffusing and diffusing out of the modulation doped layer. There are three ways to do this:

1. The modulation doping concentration of the p-InGaAsP modulation doping layer 5 is set to the solid solubility limit of the InGaAsP crystal or less. This is because, as with the p-InP clad layer 9 described above, when Zn exceeding the solid solubility limit is doped, the modulation dope layer disappears due to interstitials Zni generated in the modulation doping layer itself. In FIG. 11, p-In
The Zn concentration of the GaAsP modulation doped layer was set to 1 × 10 ¹⁸ cm
^{-3, 2 × 10 18 cm -3} , showing a change of a modulation doped structure as 5 × 10 ¹⁸ cm ^-3. As a result, the Zn concentration was set to 2 × 10.
Below ¹⁸ cm ^-3 , the modulation dope structure is preserved and Z
It was found that the n concentration needs to be 2 × 10 ¹⁸ cm ⁻³ or less.

2. Since the p-InGaAsP modulation-doped layer 5 is modulation-doped, since the Zn concentration is high,
Zn tries to diffuse out of this layer. To prevent the diffusion of Zn, p-InGaA is formed by diffusion of Zn.
The diffusion of Zn should be suppressed by increasing the crystal energy of the sP modulation-doped layer to make it unstable.

For example, when the lattice constant of the crystal of the layer to be modulation-doped (modulation-doped layer) is larger than the lattice constant of the adjacent barrier layer, the layer to be modulation-doped causes compressive strain and becomes unstable. As a result, the internal energy of the crystal rises, but as the concentration of Zn to be doped increases, the lattice constant of the modulation-doped layer becomes smaller.
By compressing, the compressive strain is reduced and the crystal becomes stable.

That is, when the compressive strain is applied to the modulation dope layer in advance (the lattice constant of the modulation dope layer is made larger than that of the adjacent barrier layer), Zn is removed from the modulation dope layer.
Zn diffusion is suppressed because the Zn concentration is lowered by the diffusion of Zn and the crystal energy is increased. Therefore, by making the lattice constant of the modulation-doped layer larger than that of the adjacent barrier layer, the undoped-InGaA
The diffusion of Zn into the sP layer could be suppressed. In this case, the Zn concentration added to the modulation dope layer could be increased to 5 × 10 ¹⁸ cm ⁻³ .

3. The energy states of the well layer and the barrier layer of the modulation-doped quantum well layer are shown in FIG. 4 (b). As shown in FIG. 4 (c), the InGaAsP crystal forming the barrier layer is
Z has a crystal composition with a small energy gap.
The saturation concentration of n increases. However, when the energy gap of the crystal of the barrier layer is reduced, there is a problem that the energy gap difference between the well layer and the barrier layer is reduced, and the electrons supplied to the laser overflow from the well layer and the luminous efficiency is reduced. Therefore, the energy gap of the crystal of the modulation dope layer 5 in the barrier layer is not made small, but only the composition of the undoped-InGaAsP layer 4 has a small energy gap, and a crystal having a high Zn saturation concentration can be used instead. Therefore, Zn atoms diffused from the modulation doped layer 5 are not doped with the undoped-InGaAsP layer 4
You can stop at. That is, undoped-
The composition of the InGaAsP layer 4 is changed to the modulation dope layer 5 of the barrier layer.
By interposing the composition between the above composition and the composition of the well layer 3, the solid solubility limit of Zn in the undoped-InGaAsP layer 4 is increased and diffusion is suppressed. In this case, as shown in FIG. 13, the concentration of Zn added to the modulation dope layer increased to 8 × 10 ¹⁸ cm ⁻³ .

In the barrier layer, the undoped layer having a large energy gap is sandwiched by the modulation doped layers having a small energy gap, and the Zn doping concentration is increased in the structure in which the energy gap between the well layer and the barrier layer is increased. I made it big.

Further, by making the energy gap of the modulation doped layer small and making the energy gap of the undoped layer large, the Zn doping concentration can be made large in the structure in which the energy gap of the well layer and the barrier layer is made large.

(Embodiment 1) A semiconductor laser according to an embodiment of the present invention will be described below with reference to the drawings.

FIG. 1 is a structural diagram of a strained quantum well semiconductor laser according to an embodiment of the present invention. 1 and 2, 1 is a Sn-doped InP substrate, 2 is n-InGa
AsP waveguide layer, 3 is a 5 nm thick InGaAs well layer, 4 is a 3.5 nm thick undoped-InGaAsP
Layer 5 is a p-InGaAsP modulation doped layer having a thickness of 3 nm, and 6 is undoped-InGaAsP having a thickness of 3.5 nm.
Layer, 7 is a modulation-doped quantum well layer having 10 wells, 8 is a p-InGaAsP layer having a thickness of 90 nm, 9 is a p-InP clad layer (Zn = 7 × 10 ¹⁷ cm −3), and 10 is p-n-
p current blocking layer, 11 is a mesa-shaped active layer region, 12
Is an n-side electrode made of Au / Sn, and 13 is a p-side electrode made of Au / Zn. FIG. 2 shows a detailed view of the modulation-doped quantum well layer and its energy state diagram. As shown in FIG. 2, the modulation-doped quantum well layer 7 includes the InGaAs well layer 3, the undoped InGaAsP layer, and the p-InGa.
It is made of a barrier layer composed of an AsP modulation doped layer.

The operation of the structure of the semiconductor laser of this embodiment having the above structure will be described below with reference to FIG. The current introduced from the p-side electrode 13 is narrowed by the current blocking layer 10 and then injected into the modulation-doped quantum well 7.

The modulation dope layer 5 contains 2 × 10 ¹⁸ cm of Zn.
^{-3 is} doped. As shown in FIG. 11, this doping amount is a concentration at which the modulation dope layer 5 is not destroyed.

The thickness of the well layer depends on the composition of the well layer.
It was set to 5 nm to obtain an emission wavelength of 55 μm.
In the first embodiment, the p-InGaAsP layer 8 is laminated between the p-InP cladding layer 9 and the modulation-doped quantum well layer 7 to suppress the diffusion of Zn from the p-InP cladding layer 9, Interstitial atoms Z in the p-InGaAsP layer 8
It was confirmed that the Ni concentration was attenuated and the Zn profile of the modulation doped layer in the modulation doped quantum well layer 7 was preserved.

Actually, as a result of manufacturing the laser shown in this example and evaluating various characteristics, the relaxation oscillation frequency was 10 GHz /
It was mW, which was 1.7 times as high as 6 GHz / mW in the case of the same structure but without modulation doping. this is,
It is considered that the differential gain increases due to the adaptation of the modulation-doped structure.

(Second Embodiment) A second embodiment of the present invention will be described below with reference to the drawings.

FIG. 5 is a structural diagram of the strained quantum well semiconductor laser of the second embodiment of the present invention. The composition of the p-InGaAsP modulation doped layer 5 in FIG.
In0.76Ga0.24As0.61P so that compressive strain of
The strain modulation doped layer 14 is 0.39. As a result, the strain modulation doped layer 14 was further adjusted to have a modulation doping concentration of 5 × 10 ¹⁸ cm ⁻³ from the adjacent barrier layer. As shown in FIG. 11, with this doping amount, the modulation dope layer is destroyed, but by using the strain modulation dope layer 14 in which a compression strain is applied to the modulation dope layer as in this embodiment, the doping concentration is increased. The modulation dope layer was not destroyed even when the value was increased.

In the structure of the semiconductor laser of this embodiment configured as described above, since the diffusion of Zn in the modulation dope layer is suppressed, the concentration of Zn can be 2.5 times that of the first embodiment. As a result, the relaxation oscillation frequency f _r is further improved and 13 GHz.

(Third Embodiment) A third embodiment of the present invention will be described below with reference to the drawings.

FIG. 6 is a structural diagram of a strained quantum well semiconductor laser of the second embodiment of the present invention. The stepped barrier layer 15 in which the composition of the undoped-InGaAsP layer 4 adjacent to the p-InGaAsP strain modulation doped layer 14 in FIG. 5 is set between the composition of the modulation doped layer and the composition of the well layer.
By this, the solid solubility limit of Zn in the undoped-InGaAsP layer is increased, and diffusion is suppressed. The modulation doping concentration was 8 × 10 ¹⁸ cm ⁻³ . This doping amount is also shown in FIG.
The concentration is higher than the concentration at which the modulation dope layer shown in FIG.
By doing so, the amount of doping in the modulation dope layer can be increased.

In the structure of the semiconductor laser of this embodiment configured as described above, Zn can be made to have a concentration four times that of the first embodiment because the diffusion of Zn in the modulation doped layer is suppressed. As a result, the relaxation oscillation frequency f _r is further improved and 15 GHz.

(Embodiment 4) FIG. 4 shows a method for manufacturing a semiconductor laser according to an embodiment of the present invention.

An n-InGaAsP waveguide layer 2 having a thickness of 60 nm is formed on the Sn-doped InP substrate 1 by MOVPE method.
To grow. Next, an InGaAs well layer 3 having a film thickness of 5 nm, an undoped-InGaAsP barrier layer 4 having a film thickness of 3.5 nm, a p-InGaAsP modulation-doped layer 5 having a film thickness of 3 nm, and an undoped-InGaAsP barrier layer 6 having a film thickness of 3.5 nm are formed. As one pair, the well layer 3 and the barrier layers 4 to 6 composed of three layers are repeatedly grown to form a modulation-doped quantum well layer 7 having 10 pairs.

Further, p-InGa is used as a Zn stop layer.
AsP layer 8 (Zn = 5 × 10¹⁷cm ^-3), P-InP
Rad layer 9 (Zn = 5 × 10)¹⁷cm^-3) Grows continuously
Then, the crystal growth step (FIG. 7A) is performed.

Next, from the p-InP clad layer 9 to the n-
A mesa etching step of etching the InGaAsP waveguide layer 2 into a mesa 11 (FIG. 7B).

Then, p-InP, n-InP, p-In
A buried growth step of LPE growing the P current block layer 10 (FIG. 7C).

Finally, an electrode vapor deposition step (FIG. 7D) for forming the n-side electrode 12 and the p-side electrode 13 by vapor deposition is performed to obtain a laser structure.

The determination of the Zn concentration of the modulation doped layer 5 and the p-InP layer 9 of the semiconductor laser of this embodiment manufactured as described above will be described below.

As a result of obtaining the relation between the flow rate of DMZn (dimethyl Zn) and the hole concentration, the result of FIG. 12 was obtained. Here, in InP, the hole concentration is saturated at 9 × 10 ¹⁷ cm ⁻³ , and in InGaAsP, it is saturated at 5 × 10 ¹⁸ cm ⁻³ . Therefore, the concentration of Zn doped into InP is ½ of the saturation concentration, 5 × 10 ¹⁷ cm ⁻³ , InG
The concentration of Zn doped into aAsP is 3 × 10 ¹⁸ c
m ^-3 . Total flow rate is 5 L / min, growth temperature is 640
℃.

The semiconductor laser of the first embodiment is realized by the method of manufacturing a semiconductor laser described above.

The method of manufacturing the semiconductor laser shown in the second and third embodiments is also substantially the same as the method of manufacturing the first embodiment. The difference is that the InGaAsP strain modulation doped layer 14 is grown as a modulation doped layer in the second embodiment, and the undoped barrier layer is grown as an undoped InGaAsP step barrier layer in the third embodiment. ..

In the above embodiments, the crystal of InP type compound semiconductor is used, but other crystal such as Si is used.
System, GaAs system, ZnSeS system, InAlAs system, Al
A semiconductor material such as GaAs-based InGaAlAsP-based may be used. Moreover, although Zn is used as a dopant,
It may be e, Mg, Cd, Se, S, Te or C. Although the laser structure is the DH laser, it can be applied to a high-value-added laser such as a DFB laser or a DBR laser. Further, although the structure of the active layer is the PBH type, other structures may be used. Further, although the modulation-doped structure is applied to the laser in this embodiment, it can be applied to the waveguide, the light receiving element, and the like. Further, p-InGaAsP is used as a Zn stop layer.
However, undoped-InP, undoped-InGa
AsP and more graded undoped-InGa
It may be AsP.

Although the device is a laser in this embodiment, it may be an electronic device (for example, HEMT, HFET, HBT, etc.) as long as the device uses doping.

Although the crystal growth method is the MOVPE method, other growth methods such as the hydride VPE method may be used as well as the gas source MBE method and the MOMBE method. Further, although the method of manufacturing the semiconductor laser is shown in the embodiment, the optical waveguide can be manufactured by the same method.

Further, although the n-type substrate is used as the conductivity of the crystal substrate, the p-type substrate is used in order to reduce the contact resistance between the metal of the p-side electrode and the semiconductor in the case of a high light output laser device. Also in this case, the additional element may be p-type.

Further, although the p-type is shown as the dopant added to realize the modulation-doped structure, it may be the n-type.

[0056]

As described above, according to the present invention, a dopant diffusion stop layer made of a crystal having an energy gap larger than that of the well layer and a solid solubility limit of the dopant larger than that of the cladding layer is provided, and the modulation doping in which the diffusion of the dopant is suppressed is suppressed. With the structure, the differential gain can be increased to realize a semiconductor laser having a low threshold value, a high slope efficiency, a high operating speed, and a low distortion.

Further, since the waveguide layers are present on both sides of the quantum well layer, the portion where the optical output is maximum comes to the center of the quantum well layer, the confinement coefficient Γ of light is improved, and the optical output is increased.

[Brief description of drawings]

FIG. 1 is a modulation-doped MQ according to a first embodiment of the present invention.
Structural cross section of W laser

FIG. 2 is a diagram showing the structure and energy state of a modulation-doped quantum well layer.

FIG. 3 is a diagram showing the behavior of Zn in a cladding layer and a Zn stop layer.

FIG. 4A is a diagram showing Zn behavior in a modulation-doped layer, FIG. 4B is an energy state diagram of the modulation-doped layer, and FIG. 4C is a diagram showing a relationship between energy gap and Zn saturation concentration.

FIG. 5 is a modulation-doped MQ according to the second embodiment of the present invention.
Structural cross section of W laser

FIG. 6 is a modulation-doped MQ according to the third embodiment of the present invention.
Structural cross section of W laser

FIG. 7 is a modulation-doped MQ according to the fourth embodiment of the present invention.
The figure which shows the manufacturing process cross section of W laser

FIG. 8 is a schematic diagram of a conventional modulation-doped MQW laser.

9A is a diagram showing a Be concentration distribution of a conventional modulation-doped quantum well. FIG. 9B is a conventional modulation-doped quantum well structure diagram. FIG. 9C is a conventional modulation-doped quantum well structure diagram. Of the modulation-doped quantum well structure when a laser is manufactured using the above-mentioned modulation-doped quantum well

FIG. 10 is a diagram showing a storage state of a modulation-doped structure during growth of a p-InP crystal.

FIG. 11 is a diagram showing a modulation doping concentration and a storage state of a modulation doping structure.

FIG. 12 is a diagram showing the relationship between the flow rate of DMZn and the hole concentration for InP and InGaAsP.

FIG. 13 is a diagram showing the modulation doping concentration and the storage state of the modulation doping structure.

FIG. 14 is a diagram showing a cross-sectional structure and energy level of a conventional modulation-doped quantum well.

[Explanation of symbols]

 1 Sn-doped InP substrate 2 n-InGaAsP waveguide layer 3 InGaAs well layer 4 Non-doped-InGaAsP barrier layer 5 p-InGaAsP modulation-doped layer 6 Non-doped-InGaAsP barrier layer 7 Modulation-doped quantum well 8 p-InGaAsPZn stop layer 9 p-InP Cladding layer 10 pnp current blocking layer 11 Mesa-shaped region 12 Au / Sn n-side electrode 13 Au / Zn p-side electrode 14 p-InGaAsP strain modulation doped layer 15 Non-doped-InGaAsP step barrier layer 16 Non-doped-InGaAsP step type barrier layer

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Yasushi Matsui 1006 Kadoma, Kadoma City, Osaka Prefecture Matsushita Electric Industrial Co., Ltd.

Claims (7)

[Claims] 1. A modulation-doped quantum device in which a first conductivity type compound semiconductor substrate, a first waveguide layer, a well layer and a barrier layer are alternately laminated on the substrate, and the barrier layer is modulation-doped. A well layer, a stop layer for stopping the diffusion of a dopant, and a second conductive clad layer are sequentially stacked, and the first waveguide layer has the same or smaller energy gap than the substrate, The well layer has an energy gap smaller than that of the first waveguide layer, and the barrier layer is an energy gap intermediate between the first waveguide layer and the well layer, and has a conduction part which is the same as or different from that of the substrate. A semiconductor layer including a modulation-doped layer having a type, wherein the stop layer is a crystal having an energy gap equal to or larger than that of the barrier layer, and a dopant added below its solid solubility limit. . 2. The semiconductor laser according to claim 1, wherein the amount of dopant added to the cladding layer is below the solid solubility limit. 3. The semiconductor laser according to claim 1, wherein the amount of dopant added to the barrier layer is not more than the solid solubility limit. 4. The semiconductor laser according to claim 1, wherein the modulation doped layer has a lattice mismatch. 5. The modulation doping layer has an energy gap different from that of the barrier layer.
Alternatively, the semiconductor laser as described in 3 above. 6. The conductivity type of the compound semiconductor substrate and the conductivity type of the modulation dope layer included in the barrier layer are both p-type. A semiconductor laser according to item. 7. A step of growing, on a compound semiconductor substrate having a first conductivity type, a first waveguide layer having a first conductivity type having an energy gap smaller than that of the substrate, and the first conductivity type. A modulation-doped quantum layer in which a well layer having an energy gap smaller than that of a waveguide layer, an undoped first barrier layer, a modulation-doped layer, and an undoped second barrier layer are alternately stacked with an energy gap in the middle of the well layer. A step of growing a well layer, a step of growing a stop layer having an energy gap larger than that of the barrier layer to stop diffusion of a dopant, and a step of forming a cladding layer having an energy gap larger than that of the stop layer and having the second conductivity type. Growing step, etching step of etching up to the substrate in a stripe shape, and a second conductive type crystal on the side surface of the stripe. Method for manufacturing a semiconductor laser, characterized by a step of first conductivity type of the crystal and the crystal of the second conductivity type grown bury the stripe.