JPH09260776A - Semiconductor light element - Google Patents

Abstract

PROBLEM TO BE SOLVED: To restrict the diffusion of P-type dopant, improve emission efficiency at a laser portion, and enhance the quenching ratio at the modulating portion, by providing an N-type diffusion stopper layer between a P-type clad layer and an active layer. SOLUTION: An N-type diffusion stopper 13 is provided for restricting the diffusion of a P-type dopant to an active layer 3 between a P-type clad layer 2 and an active layer 3. That is, at the semiconductor laser 110, a Zn dope P-type InP clad layer 2 and a quantum well active layer 3 are laminated on a Zn dope P-type InP substrate 1, and the N-type InP diffusion stopper layer 13 is provided between the clad layer 2 and the active layer 3. By this N-type InP diffusion stopper layer 13, the diffusion of Zn from the P-type InP substrate 1 and Zn dope P-type InPclad layer 2 to the quantum well active layer 3 can be restricted. However, the carrier concentration and thickness of the N-type InP diffusion stopper layer must be smaller than the total amount of Zn, to which the total amount of electrons are diffused.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a semiconductor optical device such as a semiconductor laser, and more particularly to suppressing diffusion of P-type dopant into a quantum well active layer.

[0002]

2. Description of the Related Art FIG. 10 is a sectional view of a long-wavelength semiconductor laser which is a conventional semiconductor optical device. In the illustrated semiconductor laser 100, 1 is a P-type InP substrate and 2 is a P-type InP substrate.
Cladding layer, 3 quantum well active layer, 4 N-type InP cladding layer, 5 P-type InP buried layer, 6 N-type InP current blocking layer, 7 P-type InP current blocking layer, 8 P
A type electrode, 9 is an N type electrode, 10 is an insulating film, 11 is a P type light confinement layer, and 12 is an N type light confinement layer.

Conventionally, during crystal growth or process,
P-type InP substrate 1 and P-type InP clad layer 2 to P
Since the type dopant diffuses into the quantum well active layer 3, there have been problems that the threshold current of the laser increases and the luminous efficiency decreases.

A similar phenomenon occurs in a semiconductor laser with a modulator. FIG. 11 is a sectional view of a conventional semiconductor laser with a modulator. In the semiconductor laser 200 with a modulator shown in the figure, 30 is an N-type InP substrate, 31 is an N-type InP cladding layer, 32 is an N-type InGaAsP optical guide layer, 33 is a diffraction grating, 34 is a quantum well active layer, and 35 is a strain quantum. Well optical waveguide layer, 36 is a P-type InP clad layer, and 37 is a P-type I
nGaAsP contact layer, 38 P-type electrode of laser section, 39 P-type electrode of modulator section, 40 N-type electrode, 41
Is a P-type InGaAsP optical confinement layer.

This conventional semiconductor laser 200 with a modulator
Also, during the crystal growth or process, the P-type I
The P-type dopant diffuses from the nP cladding layer 36 into the quantum well active layer 34 and the strained quantum well optical waveguide layer 35. For this reason, there has been a problem that the extinction ratio of the modulator portion is lowered.

In order to solve this problem, there is a conventional method, for example, in the literature (M. Glade
et.al., GaAs and Related Compounds 1990 pp579-58
As described in 4), for example, P-type InP shown in FIG.
Undoped In between the clad layer 2 and the quantum well active layer 3
By inserting the P layer, P to the quantum well active layer 3 is inserted.
The diffusion of the type dopant was suppressed.

[0007]

As described above, in the conventional semiconductor optical device, the diffusion of the P-type dopant into the quantum well active layer is suppressed by, for example, undoping between the P-type InP clad layer and the quantum well active layer. Although this is done by inserting the InP layer, there is a problem that the diffusion of the P-type dopant cannot be sufficiently suppressed in the undoped InP layer.

The present invention has been made in order to solve the above problems of the conventional semiconductor laser, and can sufficiently suppress the diffusion of the P-type dopant, improve the luminous efficiency in the laser section, and extinction ratio in the modulation section. It is an object of the present invention to provide a semiconductor optical device having improved optical characteristics.

[0009]

In view of the above-mentioned object, the first invention of the present invention is such that between the P-type cladding layer and the active layer,
A semiconductor optical device is provided with an N-type diffusion stopper layer for suppressing diffusion of a P-type dopant into the active layer.

A second aspect of the present invention is characterized in that the N type diffusion stopper layer comprises an N type InP diffusion stopper layer inserted between the P type cladding layer and the active layer. 1. The semiconductor optical device described in 1.

According to a third aspect of the present invention, the N-type diffusion stopper layer is an optical confinement layer in which the optical confinement layer on the P-type clad layer side between the P-type clad layer and the active layer is N-type doped. The semiconductor optical device according to claim 1, wherein the semiconductor optical device comprises:

A fourth invention of the present invention is the semiconductor optical device according to claim 3, wherein the N-type doped optical confinement layer comprises an S-doped N-type InGaAsP optical confinement layer.

In a fifth aspect of the present invention, the N-type diffusion stopper layer forms an optical confinement layer on the P-type clad layer side between the P-type clad layer and the active layer with N-doped InGaA.
The semiconductor optical device according to claim 1, wherein the semiconductor optical device is formed of a multilayer of s (P) / undoped In (Ga) (As) P.

According to a sixth aspect of the present invention, the N-type diffusion stopper layer is formed from an N-type In (Ga) (As) P layer inserted between the P-type cladding layer and the P-type InP substrate. The semiconductor optical device according to claim 1, wherein

In a seventh aspect of the present invention, the semiconductor optical device comprises a semiconductor laser with a modulator having a laser section and a modulator section following the laser section, and the active layer is a quantum well active layer on the laser section side. 6. The semiconductor optical device according to claim 1, further comprising a strained quantum well optical waveguide layer on the modulator section side.

According to an eighth aspect of the present invention, a diffusion stopper layer for suppressing diffusion of a P-type dopant into the active layer is provided between the P-type cladding layer and the active layer, and the diffusion stopper layer is the above-mentioned. A semiconductor optical device is characterized in that the optical confinement layer on the side of the P-type cladding layer is formed by an undoped InGaAs (P) / In (Ga) (As) P multilayer.

According to a ninth aspect of the present invention, the semiconductor optical device comprises a semiconductor laser with a modulator having a laser section and a modulator section following the laser section, and the active layer is a quantum well active layer on the laser section side. 9. The semiconductor optical device according to claim 8, further comprising a strained quantum well optical waveguide layer on the side of the modulator section.

[0018]

BEST MODE FOR CARRYING OUT THE INVENTION First, the principle by which an N-type doping layer according to the present invention suppresses diffusion of a P-type dopant will be described. First, Zn, which is a P-type dopant, diffuses in a state where the following equilibrium relational expression is established.

(Interstitial Zn) + (In vacancy) ⇔ (Zn at the lattice position) + 2 (Hole)

The interstitial Zn settles at a lattice position at a certain ratio, and the remaining Zn diffuses into an adjacent layer while maintaining an equilibrium state with the right side of the above equation.

Next, the diffusion of Zn in the N-type doping layer will be considered. The interstitial Zn that has diffused causes a settled hole at the lattice position. However, since holes are present in the N-type doping layer, the generated holes are united with the electrons and disappear. Therefore, the reaction proceeds to the right side until there are no electrons in the N-type doping layer. Therefore, all interstitial Zn settles at the lattice position,
Does not diffuse to adjacent layers.

When there are no electrons in the N-type doping layer, the interstitial Zn diffuses into the adjacent layer as usual. According to this principle, the more electrons in the N-type doped layer, that is, the higher the N-type carrier concentration and the thicker the layer thickness, the greater the amount of Zn trapped, and the more effective the diffusion of Zn is.

Next, the principle of the InGaAs (P) layer suppressing the diffusion of the P-type dopant will be described. In of Zn
The solid solubility in the 1-xGaxAsyP1-y layer increases as the composition y increases. FIG. 1A shows a change in Zn concentration when the conventional InP layer is inserted, and FIG. 1B shows a change in Zn concentration when the InGaAs layer according to the present invention is inserted. As shown in FIG. 1, the InP layer to the InGaAs layer
In the case of diffusion to (y = 1), since the InGaAs layer has a higher solid solubility, Zn has a higher concentration in the InGaAs layer. That is, the InGaAs layer is Z
A large amount of n is trapped, which has an effect of further suppressing diffusion of Zn.

Embodiment 1. FIG. 2 is a sectional view of a semiconductor laser according to an embodiment of the present invention. In the semiconductor laser 110 of the figure, 1 is a Zn-doped P-type InP substrate
(Carrier concentration P = 5 × 18 cm ^-3 ), 2 is Zn-doped P
Type InP clad layer (thickness 2 μm, carrier concentration P = 1
× 18 cm ^-3 ), 3 is a quantum well active layer, 4 is S-doped N
Type InP clad layer (thickness 0.5 μm, carrier concentration N =
1 × 18 cm ⁻³ ), 5 is a Zn-doped P-type InP buried layer (thickness 1 μm, carrier concentration P = 1 × 18 cm ⁻³ ), 6
Is an S-doped N-type InP current blocking layer (thickness 1 μm, carrier concentration N = 5 × 18 cm ⁻³ ).

7 is a Zn-doped P-type InP current blocking layer
(Thickness 1 μm, carrier concentration P = 1 × 18 cm ⁻³ ), 8 is a P-type electrode (Ti / Pt / Au), 9 is an N-type electrode (Au / G)
e / Ni / Au), 10 is a SiO ₂ insulating film, 11 is an undoped InGaAsP optical confinement layer, and 12 is S-doped N.
Type InGaAsP optical confinement layer. 13 is N-type In
It is a P diffusion stopper layer.

In this embodiment, the N-type InP diffusion stopper layer 13 is used to form a Z from the P-type InP substrate 1 and the Zn-doped P-type InP clad layer 2 to the quantum well active layer 3.
The diffusion of n can be suppressed.

However, the carrier concentration and the thickness of the N-type InP diffusion stopper layer 13 must be made slightly smaller than the total amount of diffused Zn of the total amount of electrons. If there are many, an N-type layer will remain between the P-type InP clad layer 2 and the quantum well active layer 3. FIG. 3 shows a band near the active layer and how holes are injected into the active layer. Thus, the N-type layer 13 prevents injection of holes from the P-type InP cladding layer 2 into the quantum well active layer 3 during current injection due to the band structure as shown in FIG. I will end up.

Embodiment 2 FIG. 4 is a sectional view of a semiconductor laser according to another embodiment of the present invention. In the semiconductor laser 120 shown, 1 to 10 and 12 are the same as those in the above-mentioned embodiment. Reference numeral 14 is an S-doped N-type InGaAsP optical confinement layer.

In this embodiment, the P-side optical confinement layer 11 shown in FIG. 2 is an N-doped S-doped N-type InG.
By using the aAsP optical confinement layer 14, the P-type I
The diffusion of Zn from the nP substrate 1 and the Zn-doped P-type InP cladding layer 2 to the quantum well active layer 3 can be suppressed.

Embodiment 3 FIG. 5 is a sectional view of a semiconductor laser according to another embodiment of the present invention. In the semiconductor laser 130 shown in the figure, 1 to 10 and 12 are the same as those in the above embodiment. 15 is an optical confinement multilayer (undoped InGaAs (P) / In (Ga) (As)
P).

FIG. 6 is a sectional view near the optical confinement multilayer 15. In the figure, 150 is undoped InGa
The As layer, 152 is an undoped InP layer. The undoped InGaAs layer 150 has a thickness of 80 Å or less, and the multilayer 15
Have a quantum effect. Further, the multi-layer 15 has a band gap size as the quantum well layer larger than that of the quantum well active layer 3. This is to prevent laser oscillation in the multilayer 15.

The InGaAs layer 150 is made of In of the conventional composition.
Since the y composition is larger than that of the GaAsP optical confinement layer, Zn
Since the higher the composition y, the higher the solid solubility in the layer, the larger the amount of Zn trapped, and the more effective the diffusion of Zn is. With this layer, diffusion of Zn from the P-type InP substrate 1 and the Zn-doped P-type InP clad layer 2 to the quantum well active layer 3 can be suppressed.

Embodiment 4 FIG. FIG. 7 shows another example of the optical confinement multilayer according to the third embodiment. In the figure, 15a is an optical confinement multilayer (N-doped InGaAs (P) / undoped In (Ga) (As) P), and 152 is undoped InP.
The layer 154 is an N-type InGaAs layer. In this embodiment, the undoped InGaAs layer 150 of the optical confinement multilayer of the third embodiment is N-type.

N-type InGa in which the InGaAs layer is N-type
By using the As layer 154, a larger amount of Zn is trapped as compared with the undoped InGaAs layer of the third embodiment, and there is an effect of further suppressing Zn diffusion. Further, even if an N-type layer remains in this multilayer, the N-type layer does not hinder the injection of holes from the P-type InP cladding layer 2 to the quantum well active layer 3 during current injection.

Embodiment 5 FIG. FIG. 8 is a sectional view of a semiconductor laser according to another embodiment of the present invention. In the semiconductor laser 140 shown in the figure, 1 to 12 are the same as those in the above embodiment. 20 is N-type In (Ga) (As) P
It is a diffusion stopper layer.

The N-type In (Ga) (As) P diffusion stopper layer 20 can suppress the diffusion of Zn from the P-type InP substrate 1 into the Zn-doped P-type InP clad layer 2. If the diffusion of Zn from the P-type InP substrate 1 into the Zn-doped P-type InP clad layer 2 is large, the carrier concentration of the P-type InP clad layer 2 increases, so that the Zn from the P-type InP clad layer 2 to the active layer 3 increases. Increase the spread of. Therefore, P-type I
By suppressing the diffusion of Zn from the nP substrate 1 into the Zn-doped P-type InP cladding layer 2, the laser characteristics can be improved.

When the N-type InP diffusion stopper layer 13 of Embodiment 1 is further provided in this embodiment, the carrier concentration and thickness of this stopper layer 13 are such that the total amount of electrons diffuses. It is necessary to slightly reduce the total amount of Zn coming in.

Embodiment 6 FIG. FIG. 9 is a sectional view of a semiconductor laser with a modulator according to an embodiment of the present invention. In the semiconductor laser 210 with a modulator shown in FIG.
0 is an N-type InP substrate, 31 is an N-type InP clad layer, 3
2 is an N-type InGaAsP optical guide layer, 33 is a diffraction grating,
34 is a quantum well active layer, 35 is a strained quantum well optical waveguide layer,
36 is a P-type InP clad layer, 37 is a P-type InGaAs
Reference numeral 38 is a P contact layer, 38 is a P type electrode in the laser portion, 39 is a P type electrode in the modulator portion, 40 is an N type electrode, and 42 is a diffusion stopper layer.

The diffusion stopper layer 42 is used in the first to fourth embodiments.
As in the case of the semiconductor laser of FIG.
nP layer, N-type InGaAsP optical confinement layer of the second embodiment, undoped InGaAs (P) / In of the third embodiment
(Ga) (As) P multi-layer, N-doped In of the fourth embodiment
It is one of GaAs (P) / undoped In (Ga) (As) P multilayers.

Thus, the diffusion stopper layer 42 allows P
Type InP clad layer 36 to strained quantum well optical waveguide layer 35
Zn can be suppressed from diffusing into the film, and the extinction ratio in the modulator section can be improved.

[0041]

As described above, according to the first aspect of the present invention, between the P-type cladding layer and the active layer, the N-type diffusion stopper for suppressing the diffusion of the P-type dopant into the active layer is provided. Since the layer is provided, during the crystal growth or the process, P
It is possible to suppress the diffusion of the P-type dopant from the type clad layer into the active layer, reduce the threshold current in the laser section, and improve the luminous efficiency. can get.

According to the second aspect of the present invention, the N-type InP diffusion stopper layer is provided as the N-type diffusion stopper layer between the P-type cladding layer and the active layer. Can be suppressed from diffusing into the active layer, and a semiconductor optical device can be provided in which the threshold current can be reduced and the light emission efficiency can be improved more reliably in the laser portion.

According to the third aspect of the present invention, the N-type diffusion stopper layer is formed between the P-type clad layer and the active layer.
Since the optical confinement layer on the side of the clad layer is an N-type doped optical confinement layer, it is possible to suppress the diffusion of the P-type dopant from the P-type clad layer to the active layer without adding a new layer. Therefore, it is possible to provide an effect such as providing a semiconductor optical device in which the reduction of the threshold current and the improvement of the light emission efficiency can be realized more reliably in the laser portion.

According to the fourth aspect of the present invention, the N-type doped optical confinement layer is S-doped N-type InGaAsP.
Since it is a light confinement layer, it is possible to suppress the diffusion of the P-type dopant from the P-type cladding layer into the active layer without adding a new layer, and to reduce the threshold current in the laser portion and It is possible to obtain an effect such as providing a semiconductor optical device that can more surely improve the luminous efficiency.

According to the fifth aspect of the present invention, the N-type diffusion stopper layer is the optical confinement layer on the P-type clad layer side between the P-type clad layer and the active layer and is N-doped InGaAs.
Since it is formed of multiple layers of (P) / undoped In (Ga) (As) P, it is possible to prevent the P-type dopant from diffusing into the active layer from the P-type cladding layer without adding a new layer. It is possible to provide an effect such as providing a semiconductor optical device that can be suppressed and can more reliably realize the reduction of the threshold current and the improvement of the light emission efficiency in the laser portion.

According to the sixth aspect of the present invention, the N-type diffusion stopper layer is composed of the N-type In (Ga) (As) P layer inserted between the P-type cladding layer and the P-type InP substrate. Therefore, the diffusion of the P-type dopant from the P-type cladding layer to the active layer can be increased, and thus the diffusion of the P-type dopant from the P-type cladding layer to the active layer can be suppressed. It is possible to obtain an effect such as providing a semiconductor optical device that can realize reduction and improvement of luminous efficiency more reliably.

According to the seventh aspect of the present invention, the quantum well active layer has a laser section and a modulator section following the laser section, and the active layer is a quantum well active layer on the laser section side and a strained quantum well on the modulator section side subsequent thereto. In a semiconductor laser with a modulator consisting of an optical waveguide layer,
Since the N-type diffusion stopper layer according to any one of the first to fifth aspects is provided, it is possible to prevent the P-type dopant from diffusing into the active layer from the P-type cladding layer during crystal growth or during the process. It is possible to provide a semiconductor optical device in which the threshold current can be more reliably reduced and the luminous efficiency can be improved more reliably in the laser section, and the extinction ratio can be more surely improved in the modulator section.

According to the eighth aspect of the present invention, a diffusion stopper layer for suppressing diffusion of the P-type dopant into the active layer is provided between the P-type cladding layer and the active layer, and the diffusion stopper layer is provided. Since the optical confinement layer on the side of the P-type cladding layer is formed by the multiple layers of undoped InGaAs (P) / In (Ga) (As) P, P
It is possible to suppress the diffusion of the P-type dopant from the type clad layer into the active layer, reduce the threshold current in the laser section, and improve the luminous efficiency. can get. It is a semiconductor optical device characterized in that it is composed of one.

According to a ninth aspect of the present invention, a quantum well active layer having a laser section and a modulator section following the laser section is provided on the laser section side, and a strained quantum well on the modulator section side following the active layer. In a semiconductor laser with a modulator consisting of an optical waveguide layer,
Since the diffusion stopper layer according to the eighth aspect of the present invention is provided, during the crystal growth or the process, the P-type cladding layer is removed from the P-type cladding layer.
The diffusion of the type dopant into the active layer can be suppressed, the threshold current can be reduced and the luminous efficiency can be improved more reliably in the laser section, and the extinction ratio can be improved more reliably in the modulator section. It is possible to obtain an effect such that a semiconductor optical device that can be provided can be provided.

[Brief description of drawings]

FIG. 1A is Zn when a conventional InP layer is inserted.
FIG. 3B is a diagram showing a change in Zn concentration when the InGaAs layer according to the present invention is inserted.

FIG. 2 is a sectional view of a semiconductor laser according to an embodiment of the present invention.

FIG. 3 is a diagram for explaining how holes are injected into a band near the active layer and the active layer. InGaAs
It is explanatory drawing of the diffusion of Zn in a layer.

FIG. 4 is a sectional view of a semiconductor laser according to still another embodiment of the present invention.

FIG. 5 is a sectional view of a semiconductor laser according to still another embodiment of the present invention.

6 is a cross-sectional view of the vicinity of the optical confinement multilayer of FIG.

FIG. 7 is a cross-sectional view showing another example of the optical confinement multilayer.

FIG. 8 is a sectional view of a semiconductor laser according to still another embodiment of the present invention.

FIG. 9 is a sectional view of a semiconductor laser with a modulator according to an embodiment of the present invention.

FIG. 10 is a cross-sectional view of a long-wavelength semiconductor laser that is a conventional semiconductor optical device.

FIG. 11 is a sectional view of a conventional semiconductor laser with a modulator.

[Explanation of symbols]

1 Zn-doped P-type InP substrate, 2 Zn-doped P-type I
nP clad layer, 3 quantum well active layer, 4 S-doped N-type InP clad layer, 5 Zn-doped P-type InP buried layer, 6 S-doped N-type InP current blocking layer, 7 Zn
Doped P-type InP current blocking layer, 8 P-type electrode, 9
N-type electrode, 10 SiO ₂ insulating film, 11 undoped I
nGaAsP optical confinement layer, 12 S-doped N-type InG
aAsP optical confinement layer, 13 N-type InP diffusion stopper layer, 14 S-doped N-type InGaAsP optical confinement layer,
15 optical confinement multilayer, 20 N-type In (Ga) (As)
P diffusion stopper layer, 30 N type InP substrate, 31 N type InP clad layer, 32 N type InGaAsP optical guide layer, 33 diffraction grating, 34 quantum well active layer, 35 strained quantum well optical waveguide layer, 36 P type InP clad layer, Three
7 P-type InGaAsP contact layer, 38 P-type electrode of laser part, 39 P-type electrode of modulator part, 40 N-type electrode, 42 Diffusion stopper layer, 110, 120, 13
0,140 semiconductor laser, 210 semiconductor laser with modulator.

Claims (9)

[Claims] 1. A semiconductor optical device comprising an N-type diffusion stopper layer for suppressing diffusion of a P-type dopant into the active layer between the P-type cladding layer and the active layer. 2. The semiconductor optical device according to claim 1, wherein the N type diffusion stopper layer comprises an N type InP diffusion stopper layer inserted between the P type cladding layer and the active layer. . 3. The N-type diffusion stopper layer is composed of an optical confinement layer obtained by N-type doping the optical confinement layer on the P-type clad layer side between the P-type clad layer and the active layer. The semiconductor optical device according to claim 1. 4. The semiconductor optical device according to claim 3, wherein the N-type doped optical confinement layer is an S-doped N-type InGaAsP optical confinement layer. 5. The N-type diffusion stopper layer forms an N-doped InGaAs (P) / undoped In layer on the optical confinement layer on the P-type clad layer side between the P-type clad layer and the active layer.
2. The semiconductor optical device according to claim 1, wherein the semiconductor optical device is formed of multiple layers of (Ga) (As) P. 6. The N-type I, wherein the N-type diffusion stopper layer is inserted between the P-type cladding layer and the P-type InP substrate.
2. An n (Ga) (As) P layer.
3. The semiconductor optical device according to item 1. 7. The semiconductor optical device comprises a semiconductor laser with a modulator having a laser section and a modulator section following the laser section, wherein the active layer is a quantum well active layer on the laser section side and the modulator section following the quantum well active layer. 6. The semiconductor optical device according to claim 1, comprising a strained quantum well optical waveguide layer on the side. 8. A diffusion stopper layer for suppressing diffusion of a P-type dopant into the active layer is provided between the P-type cladding layer and the active layer, and the diffusion stopper layer is a light on the P-type cladding layer side. Unconfined InGaAs (P) /
A semiconductor optical device comprising a multi-layered structure of In (Ga) (As) P. 9. The semiconductor optical device comprises a semiconductor laser with a modulator having a laser section and a modulator section following the laser section, wherein the active layer is a quantum well active layer on the laser section side and the modulator section subsequent thereto. 9. The semiconductor optical device according to claim 8, comprising a strained quantum well optical waveguide layer on the side.