JPH10178236A - Semiconductor laser - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a semiconductor laser which prevents the resistance of an Fe-InP constriction layer from being lowered by a method wherein a p-type InP layer is provided on a buried layer in which an active InP layer is laminated and in which an iron-doped InP layer and an n-type layer are laminated on both sides sequentially and the produce of an n-type impurity concentration in the n-type InP layer multiplied by a layer thickness satisfies a formula. SOLUTION: S P-type InP layer 4B is provided on a buried layer in which an active layer 2 is laminated and in which an iron-doped InP layer 5 and an n-type InP layer 6 are laminated sequentially on other sides of the active layer 3. The product of an n-type impurity concentration (n-type concentration) in the n-type InP layer (Si-InP layer) 6 multiplied by a layer thickness (an n-layer thickness) satisfies a formula of 5.0×10<19> (cm<-3> nm)<(n-type concentration)×(n-layer thickness)<3.0×10<21> (cm<-3> ×nm). Thereby, it is possible to prevent the resistance of an Fe-InP construction layer doe to the diffusion Zn, and the strain of an optical intensity distribution due to the existence of an n-type InP current stop layer can be suppressed to a negligible degree. In addition, the formulas is established with reference to all n-type dopants without being limited to Si.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a semiconductor laser having a buried structure in which a spot size converter is integrated, and more particularly to an iron (Fe) doped (Fe-) InP layer and an n-type InP as buried layers.
Buried laser (Semi-Insulated Planer Buried Heterostructure)
Laser; SIPBH laser).

[0002]

2. Description of the Related Art A SIBH laser (Semi-Insulated Buri) having a high-resistance current confinement layer formed of Fe-InP as a buried layer.
The ed Heterostructure Laser) can be expected to have low threshold current and high efficiency laser oscillation due to the efficient current confinement structure.

FIG. 6 is an explanatory view of an SIBH laser having a (tapered) spot size converter whose cross section gradually decreases toward the emission end. In the figure, 1 is an n-type (n-) InP substrate, 2 is a laser gain region (active layer), 3 is a waveguide region,
4 is a p-type (p-) InP cladding layer, and 5 is a Fe-InP constriction layer.

In this structure, in the laser gain region (active layer) 2, the current injected from the p-side electrode is confined by the Fe—InP constriction layer and flows efficiently only to the active layer. In the waveguide region 3, since the thickness of the waveguide decreases from the laser gain region toward the emission end, the confinement rate of light in the waveguide decreases. Therefore, the spot size increases as the light emitted from the laser gain region approaches the emission end.

As described above, in a semiconductor laser in which a spot size converter is integrated in the resonator direction in series with the laser gain region, it is possible to increase the light spot size toward the emission end and to approach the spot size of the optical fiber. it can. Accordingly, when assembling the optical module, the coupling with the optical fiber can be facilitated, so that a coupling lens or the like is not required, and a low-cost optical module can be manufactured.

Therefore, an SIBH laser with an integrated spot size converter is an important element in the future for optical fiber communication subscribers as a low-cost laser capable of high-speed modulation.

[0007] In the structure of the conventional SIBH laser, the series resistance increases due to the small current transmission area of the p-InP cladding layer and the contact layer deposited thereon. Therefore, it has been found that when the injection current is large, the luminous efficiency is reduced and the device is destroyed due to the temperature rise of the device due to the resistance component.

Therefore, as shown in FIG. 7, it has been found that it is necessary to make the SIPBH structure capable of increasing the current transmission area of the p-InP cladding layer 4 and the contact layer 8 into a buried structure. FIG. 3 is an explanatory diagram of a SIPBH laser in which a tapered waveguide is integrated as a size converter.

In the figure, 1 is an n-InP substrate, 2 is a laser gain region (active layer), 3 is a waveguide region, 4 is a p-InP cladding layer, 5 is a Fe-InP confinement layer, 6 is n-InP A current blocking layer, 8 is a contact layer, 9 is an n-side electrode, 10 is an insulating film, and 11 is a p-side electrode.

[0010]

However, in the SIPBH structure, the zinc (Zn) -doped p-InP cladding layer (Zn-InP cladding layer) 4 and the Fe-InP current confinement layer 5 are adjacent to each other. It diffuses into the Fe-InP constriction layer. As a result, the Fe-InP constriction layer becomes p-type, the resistance decreases, and a leakage current that does not pass through the active layer is generated. To prevent this, Zn-InP cladding layer 4 and Fe
It is necessary to insert the n-InP current blocking layer 6 between the -InP constriction layer 5.

The higher the carrier concentration of the n-InP current blocking layer 6 and the greater its thickness, the more the diffusion of Zn atoms can be prevented. On the other hand, when a spot size converter is integrated at the emission end, the beam spot size increases near the emission end, and the Zn-InP cladding layer 4 including the n-InP current blocking layer 6
Spread out. At this time, the refractive index of the n-InP current blocking layer 6 was significantly different from that of the Zn-InP cladding layer 4 and the Fe-InP constriction layer 5, indicating that the light intensity distribution was distorted.

For example, silicon (Si) doped n-InP (Si-
(InP) Assuming that the current blocking layer 6 has a layer thickness of 1 μm and a carrier concentration of 4 × 10 ¹⁸ cm ^-3 , the refractive index difference Δn of the Si-InP current blocking layer 6 and the other layers is Δn = 0.02. The cross section has the light intensity distribution shown in FIG.

In FIG. 8, the x axis is parallel to the InP substrate, and the y axis is
Taken perpendicular to the InP substrate, the origin (x = 0, y = 0) is the central axis of the waveguide. The center of the light intensity at the emission end (+
1) is shifted upward from the central axis of the waveguide. From this result, it can be seen that light is not sufficiently guided in the waveguide.

The distortion of the light intensity distribution is caused by the n-InP current blocking layer 6.
Is larger as the carrier concentration is higher and as the layer thickness is larger. Therefore, in order to determine the layer thickness and the carrier concentration of the n-InP current blocking layer 6, there is a trade-off between the effect of preventing the diffusion of the Zn dopant and the effect of the light intensity distortion as described above. It is necessary to determine that Zn atoms are prevented from diffusing into the Fe-InP constriction layer 5 and the light intensity distribution is not increased.

An object of the present invention is to prevent the Fe—InP constriction layer from lowering in resistance due to the diffusion of Zn atoms and to reduce the distortion of the light intensity distribution.

[0016]

Means for solving the above problems are as follows: 1) A spot size converter formed at the emission end, and an iron (Fe) -doped InP layer and an n-type InP layer on both sides of the active layer in order. A p-type InP layer formed on the active layer and the buried layer; and a product of an n-type impurity concentration of the n-type InP layer and a layer thickness of the n-layer thickness Is 5.0 × 10 ¹⁹ [cm ⁻³ × nm] <[n-type concentration] × [n-layer thickness] <
A semiconductor laser satisfying 3.0 × 10 ²¹ [cm ⁻³ × nm]. 2) The spot size converter is achieved by the semiconductor laser as described in 1 above, wherein the cross section gradually decreases toward the emission end.

The diffusion of Zn atoms into the Fe-InP confining layer 5 is based on Zn-I
It is known that it can be reduced by inserting an n-InP layer between the nP layer and the Fe-InP layer. In the following description, n-InP
Take the Si-InP layer as an example. The Zn diffusion in InP can be explained by the following model.

Zn _i ⁺ + V _In = Zn _sb ⁻ +2 h where Zn _i ⁺ is Zn ion between lattices, V _In is vacancy of In, Z
n _sb ^- is a Zn ion at the lattice position, and h is a hole.

Zn atoms in InP have a small diffusion coefficient
Zn _sb ^- and, in a large equilibrium with Zn _i ⁺ diffusion coefficient. In the Si-InP layer, the electrons generated when the Si atoms enter the lattice position are combined with the holes h and canceled, and the equilibrium state in the above equation moves to the right side. Thereby, the interstitial ions Zn _i ⁺ contributing to the diffusion decrease, and the Zn diffusion speed decreases.

According to experiments conducted by the inventors, the diffusion rate of Zn in the Si-InP layer was found to be lower as the Si concentration was higher, as shown in FIG. In addition, in the Zn diffusion layer in the Si-InP layer, the Zn concentration coincided with the Si concentration, and as shown in FIG. 3, it was found that the total diffusion amount did not depend on the Si concentration. Here, the total diffusion separation amount can be expressed by the following equation.

Total diffusion separation = Zn concentration × Diffusion distance = Si concentration × Diffusion distance In order to prevent Zn atoms from passing through the Si-InP layer during laser structure growth requiring about 5 hours, the following equation is used from FIG. Relationship is needed.

Total diffusion separation = 5.0 × 10 ¹⁹ [cm ⁻³ × nm] <
[Si concentration] × [Si-InP layer thickness] On the other hand, when the carrier concentration of the n-InP layer is high and the layer thickness is large, the refractive index difference Δn between the n-InP layer and the other layers is as shown in FIG. The light intensity distribution at the emission end is distorted.

According to the calculation made by the inventor, as shown in FIG. 4, when the thickness of the n-InP layer is 1 μm (10 ³ nm),
When the refractive index difference of the n-InP layer is Δn = 0.01 or less, the center of light intensity coincides with the central axis (x = 0, y = 0) of the waveguide.

FIG. 5 (Ref .; J. Stone and MSWha)
rten, Appl. Phs. Lett. 41, 1141 (1982).) As shown in the experiment showing the change in the refractive index difference when the n-type carrier concentration was changed, the n-type carrier concentration was less than 3.0 × 10
^{At 18} cm ^-3 , Δn <0.01 is achieved. Therefore, the following equation must be satisfied.

[N-type concentration] × [n-layer thickness] <3.0 × 10 ²¹ [cm ⁻³ × nm] From the above considerations, the carrier concentration and thickness of the n-InP current blocking layer are set to 5.0 × 10 ¹⁹ [ cm ⁻³ × nm] <[n-type concentration] × [n-layer thickness] <3.0 × 10 ²¹ [cm ⁻³ × nm] (1) The resistance of the -InP constriction layer can be prevented from being lowered, and the distortion of the light intensity distribution due to the presence of the n-InP current blocking layer can be suppressed to a negligible level. Note that the above relational expression (1) holds true not only for Si but also for all n-type dopants.

[0026]

FIG. 1 is an explanatory diagram of an embodiment of the present invention. In the figure, 1 is an n-InP substrate, 2 and 3 are InGaAsP to be the laser gain region (active layer) and the waveguide region.
Layers, 4A, 4B: Zn-InP layer (p-InP cladding layer), 5: Fe-InP
Current confinement layer, 6 is Si-InP layer (n-InP current blocking layer), 7 is
An Si-InP buffer layer, 8 is a Zn-InGaAs contact layer, 9 is an n-side electrode, 10 is an insulating film, and 11 is a p-side electrode.

The details of each layer are as follows. In the laser gain region, the thickness of the Si-InP buffer layer 7 is 0.2 μm.
m, the carrier concentration is 5 × 10 ¹⁷ cm ^-3 , and the InGaAsP active layer 2 is 0.3 μm thick and undoped with a wavelength of 1.3 μm.
The InP cladding layer 4A has a thickness of 0.7 μm and a carrier concentration of 7 × 10
¹⁷ cm ^-3 .

At the exit end of the waveguide, the Si-InP buffer layer has a thickness of 0.07 μm, a carrier concentration of 5 × 10 ¹⁷ cm ^-3 , and InGaA
The sP waveguide layer is 0.1 μm thick and undoped with a 1.3 μm composition in terms of wavelength, and the Zn-InP cladding layer is 0.23 μm thick and has a carrier concentration of 7 × 10 ¹⁷ cm ⁻³ .

The thickness of each layer changes gradually from the laser gain region toward the emission end. Fe-InP current confinement layer 5
Is 2 μm thick and has a carrier concentration of 5 × 10 ¹⁶ cm ^-3 , and the Si-InP current blocking layer 6 has a thickness of 0.3 μm and has a carrier concentration of 5 × 10 ¹⁸ cm ^-3 , Z
The n-InP cladding layer 4 has a thickness of 1.5 μm and a carrier concentration of 2 × 1
0 ¹⁸ cm ⁻³ , Zn—InGaAs contact layer 8 has a thickness of 0.5 μm and a carrier concentration of 2 × 10 ¹⁸ cm ⁻³ .

In this embodiment, [thickness] × [carrier concentration] of the Si—InP current blocking layer 6 is 5 × 10 ¹⁸ cm ⁻³ × 0.3 μm = 5 × 10 ¹⁸ × 3 × 10 ² [cm ^{− 3} × nm] = 1.5 × 10 ²¹ [cm ^-3 × nm], which satisfies the expression (1).

In the embodiment, the case where the thickness is changed as the tapered waveguide of the spot size converter has been described. However, the same effect can be obtained by changing the width of the waveguide as shown in FIG. Of course, it can be obtained.

[0032]

According to the present invention, according to the present invention, Fe
-The resistance of the InP constriction layer can be prevented from being lowered, and the distortion of the light intensity distribution can be reduced.

[Brief description of the drawings]

FIG. 1 is an explanatory diagram of an embodiment of the present invention.

Fig. 2 Illustration of Zn diffusion in Si-InP (diffusion distance vs. diffusion time)

FIG. 3 is an explanatory view of Zn diffusion in Si-InP (n-type concentration × diffusion distance vs. diffusion time)

FIG. 4 is a diagram showing a light intensity distribution in the embodiment of the present invention.

FIG. 5 is a diagram showing a relationship between an n-type carrier concentration and a refractive index difference.

FIG. 6 is an explanatory diagram of a SIBH laser (with a tapered waveguide).

FIG. 7 is an explanatory view of a SIPBH laser (with a tapered waveguide).

FIG. 8 is a diagram showing a light intensity distribution of a conventional example.

FIG. 9 is an explanatory view of another embodiment of the present invention.

[Explanation of symbols]

1 n-InP substrate 2, 3 InGaAsP layer for laser gain region (active layer) and waveguide region 4, 4A, 4B Zn-InP layer (p-InP cladding layer) 5 Fe-InP confining layer 6 Si-InP layer (n-InP current blocking layer) 7 Si-InP buffer layer 8 Zn-InGaAs contact layer 9 n-side electrode 10 insulating film 11 p-side electrode

Claims (2)

[Claims] 1. A spot size converter formed at an emission end, an iron (Fe) doped InP layer and an n-type InP layer on both sides of an active layer.
A p-type InP layer formed on the active layer and the buried layer.
The product of the n-type impurity concentration [n-type concentration] of the P layer and the layer thickness [n-layer thickness] is 5.0 × 10 ¹⁹ [cm ⁻³ × nm] <[n-type concentration] × [n-layer thickness] <
A semiconductor laser satisfying 3.0 × 10 ²¹ [cm ⁻³ × nm]. 2. The spot size converter according to claim 1, wherein a cross section of the spot size converter is gradually reduced toward an emission end.
A semiconductor laser as described in the above.