JPS6290968A - Optical integrated circuit and manufacture thereof - Google Patents

Abstract

PURPOSE:To efficiently obtain an element having high coupling efficiency by growing a protective layer of specific band gap wavelength on an active layer, removing the protective layer of an optical and the active layer, melting back the protective layer, and growing the optical guide layer of specific band gap wavelength. CONSTITUTION:A Te-doped N<+> type InP buffer layer 2, an InGaAsP active layer 3 of band gap wavelength lambdag=1.3mum, and an InGaAs protective layer 10 of lambdag=1.5mum are sequentially epitaxially grown on an S-doped N<+> type InP substrate 1. Then, with a laser A as a mask the layer 10 of an optical guide B and the layer 3 are selectively removed. The protective layer is melt back by the second epitaxial growth, and a Zn-doped P<-> type InGaAsP optical guide layer 6 of lambdag=1.1mum shorter than the wavelength of the active layer, a Zn-doped P<+> type InP clad layer 4, a Zn-doped P<+> type InGaAsP contacting layer 5 are sequentially grown. Thus, an optical integrated circuit having high yield planar structure and high coupling efficiency is obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to an integrated external cavity laser (MEC-LD).
), DBR-lasers, monolithic switch-integrated lasers, etc., and their manufacturing method.

Conventional technology The technology to monolithically couple an optical waveguide and a semiconductor laser on the same substrate is an integrated external cavity laser (MEC-
It is indispensable for manufacturing LD), DBR-I, D, and even monolithic optical switch integrated lasers. Up until now, this coupling technology has been advanced mainly in the development of DBR-LD. As an example of this, a pad joint type 1.66 μm band DBR with relatively good coupling efficiency is used.
-There is an LD [Electronics Letters (EllCt
-rOn, Lett,) Vol, 17. P9
45.1981:]. Figure 3 shows this structure in the 1.3 μm band Ml! : Shows a structural sectional view when applied to C-LD.

Here, 1 is an S-doped r''-InP substrate, 2 is a To-doped ri'-InP buffer layer, and 3 is λg = 1-3 μ
m (7) InGaAsP monolayer, 4 is Zn-doped.
-InP cladding layer, 6 is Zn-doped p+InGaASP with λg = 1.1 μm: y y tact layer, 6 is λg =
1.1μEII InGaAsP optical waveguide layer, 7 is InP
This is the cladding layer. When manufacturing such a structure by liquid phase epitaxial growth, first, 2 to 4 layers are epitaxially grown in sequence on an n-1nP substrate, and then the P-InP cladding layer 4 and the InGaAsP active layer 3 of the optical waveguide section B are selected. On the epitaxial substrate having the steps removed by etching, a second epitaxial growth is performed to form an InGaAsP layer with λg = 1.1 μm, which becomes the contact layer 5 in the laser part A and the optical waveguide layer 6 in the optical waveguide part B, and then an InP cladding layer 7. grow sequentially. Next, the InP cladding layer 7 of the laser section is removed by selective etching to expose the InGaAsP contact layer. Furthermore, current narrowing and lateral confinement of light waves are performed by means such as buried epitaxial growth. In such a structure, the active layer 3 of the laser and the optical waveguide layer 6 of the optical waveguide section B are almost on the same optical axis, and a high coupling efficiency of 80 coefficients or more can be expected.

However, when this structure is actually grown by liquid phase epitaxy (LPE method), 2. Side 8 in the second epitaxial growth
In addition, the epitaxial layers 6 and 7 may not grow and a V-shaped groove is formed, or the thickness of the optical waveguide layer 6 at the coupling portion may become abnormally thick due to abnormal growth of the optical waveguide layer 6 on the side surface of the step. It is difficult to make the surfaces of the laser section B and the optical waveguide section B at the same height, and a step is inevitably formed. The presence of V-shaped grooves and steps is extremely disadvantageous from the standpoint of planarization of the device. That is, if the strip becomes locally thick during subsequent stripe formation, it may cause disconnection of the wiring. Further, abnormal growth causes a decrease in coupling efficiency between the active layer and the optical waveguide. In this way, the knot joint structure that utilizes epitaxial growth on steps does not have a planar structure, and the coupling efficiency is not as good as expected.

On the other hand, an LD structure with an integrated optical waveguide has been announced in recent years, which has good coupling efficiency and a planar type element.

(OQEBB-7P, 47) This is Bundle -Integrated-Gu
It is called the IDE (BIG) structure, and its cross-sectional structure is shown in FIG. The feature of this structure is that the Japanese laser
A P--InP intermediate layer 9 of about 0.1 μm exists between the GaAsP active layer 3 and the F"'L InGaAsP optical waveguide layer 6, and the optical waveguide layer 6 and the p-InP cladding layer 4 form a laser beam and an optical waveguide. This is a common layer in part B. The manufacturing method of this structure using the LPE method is shown in Figure 5. First, as the first growth, T is grown on the S-doped n-InP substrate 1.
.

Doped ♂-InP buffer layer 2, I with λg=1.3μm
The nGaAsP1 layer 3 is further grown to a Zn doped IIn intermediate layer 9 of about 0.1 μm. (Figure 6 (2L
).

Next, mask the laser Japanese and insert the InP intermediate layer 9°InG.
The aAsP active layer 3 is removed using a selective etchant (fifth
Figure (b)). After removing the mask, a Zn-doped p-InGaA film with λg = 1.1 μm was grown for the second time.
sP optical waveguide layer 6, Zn-doped--rnP cladding layer 4,
λ1= 1.1 μm (7:) Zn doped f (n
GaAsP-t y tact layers are sequentially grown (FIG. 6(C)). In this way, the surface of this structure can be completely flattened (planar structure), and subsequent buried epitaxial growth and other processes can be performed very easily. In addition, the coupling efficiency was determined by setting the film thickness of the InGaAsP monolayer 3 to 0.16 μn, and the thickness of the In intermediate layer 9 to 1 μm.
When the thickness of the InGaAsP optical waveguide layer 6 is 0.3 μm, a directivity of 97% can be obtained, and the loss at the coupling portion can be almost ignored.

However, in this manufacturing method, a thin InP layer of about 0.1 μm is exposed on the active layer 3 when the temperature is raised before the second LPX growth, and defects due to thermal damage to the InP occur in the active layer/
It reaches the hetero interface of the InP intermediate layer and causes a decrease in laser light emission efficiency. To alleviate this, rnP
If the intermediate layer is made thicker, the laser section will oscillate in multiple modes, reducing the coupling efficiency with the optical waveguide.

Problems to be Solved by the Invention As mentioned above, the E-joint type shown in FIG. 3 does not have a planar structure and the coupling efficiency does not become as high as expected. Further, although the BIG structure shown in FIG. 4 has a planar structure, it is difficult to obtain a laser with good characteristics. Other conventional structures also have similar problems.

As described above, the optical integrated circuit having the conventional structure has the problem that it is difficult to obtain a device with high coupling efficiency at a high yield without impairing the characteristics of the semiconductor laser.

Means for Solving the Problems In order to overcome the above-mentioned problems, the present invention provides a layer of λg=1, F
After growing a 5 μm InGaAsP or InGaAs protective layer and removing the protective layer and active layer of the original waveguide, the protective layer is selectively melted back in the second epitaxial growth, and the InGaAsP optical waveguide layer and InGaAsP optical waveguide layer are grown.
This is obtained by growing a P cladding layer and an InGaAsP contact layer, and provides an optical integrated circuit in which the structure of the laser section is such that an optical waveguide layer exists directly on the active layer.

By adopting this structure and manufacturing method, the planar structure has high coupling efficiency, but defects are introduced at the active layer heterointerface due to thermal damage during leakage at high temperatures before the second growth. The characteristics of the laser do not deteriorate. Furthermore, it is possible to easily obtain an optical waveguide-integrated semiconductor laser device in which the single mode condition is not compromised even by slight variations in film thickness in the laser portion.

EXAMPLE Hereinafter, a case will be described in which an example of the present invention is applied to a MEO laser. FIG. 1 shows a cross section of the structure of the invention. This structure is divided into a Japanese laser and an optical waveguide part B. The Japanese laser has an S-doped n''-InP substrate 1 and a To-doped n±
-InP buffer layer 2, InGaA with λg=1.3 μn
sP active layer 3, λg: 1.1 μm Zn-doped p-I
The optical waveguide B is composed of an nGaAsP optical waveguide layer 6, a Zn-doped 7°p''-InP layer 4, and a Zn-doped p''-InGaAsP:ry tact layer 6.
, ntInP buffer 7 layer 2, p-1nGaAgP optical waveguide layer 6, p-InP cladding layer 4, p+-button GaAsP:
It is composed of an r7 tact layer 5.

The manufacturing method for this structure is as shown in FIG. 2. First, a Te-doped n+-InP buffer layer 2 is formed on an S-doped n+-InP substrate 1 with a length of 5 μm and λg = 1-3 μm.
(7) InGaAsP active layer 3 with a thickness of 0.15 μm,
InGaAs protective layer 0.1μm? The epitaxial growth was performed sequentially by the LPE method (Fig. 2(a)). Next K
After masking the laser beam with a CVD 5in2 film, the InGaAs protective layer 10 of the optical waveguide section B and the InGaAs
The sP active layer 3 is selectively removed using a sulfuric acid-based etchant (FIG. 2(b)).

Using this epitaxial substrate with minute steps, 2
In the second epitaxial growth, the Znn-1n GaAsP optical waveguide layer 6 with λg = 1.1 μm was grown by 0.3 μm.
m, Zn-doped p-InP cladding layer 4f2 μm.

ZnnDog--rnGaAsP:+7-j' tact layer f 0.54 m is sequentially grown by LPE method (FIG. 2(C)).

On the InGaAs protective layer 10, λg (I of 1.1 μm
nGaAsP does not originally grow, and the p-InGaAsP optical waveguide layer (λg=1.1 μm)6? They are selectively melted back as they grow. In particular, if the film thickness is 0.1 μm or less, it will completely melt back and the InGaAs protective layer 1o will not remain between the active layer 3 and the optical waveguide layer 6. Since the InGaAsP monolayer 3 is covered with the InGaAs protective layer 10 during soaking at high temperature during LPE growth, defects are not introduced to the active layer interface and reduce the luminous efficiency of the semiconductor laser. This is because InP suffers heat damage to a considerable depth due to p flying off during high-temperature treatment above 550°C, whereas InGaS suffers thermal damage to a considerable depth near the growth temperature (56°C).
This is because there is almost no thermal damage at temperatures between 0°C and 6°C.

In addition, the second epitaxial growth gives the surface an almost flat planar structure, which facilitates subsequent processes such as current confinement, three-dimensional optical waveguide fabrication, and wiring, which improves yield. When mounting, P-side down is used. You can increase the laser power.

On the other hand, in this case, the coupling efficiency can be more than 90%, and since there is no InP intermediate layer between the active layer and the optical waveguide layer, multimode oscillation will not occur in the laser part even if the film thickness becomes somewhat thick. .

I using such an optical waveguide-integrated semiconductor laser device
The PC type laser has a low threshold value and a narrow oscillation spectrum of several hundred kilohertz or less, and can suppress chirping during high-speed modulation and reduce noise due to returned light. DB
Good characteristics can also be expected when applied to R lasers and other optical integrated circuits.

By the way, in the present invention, InGaAs is used to protect the active layer.
(λg=1-7μm) was used, but this is λg=1.
InGaAsP with a thickness of 5 to 1.7 μm is also suitable. But λ
As g becomes smaller, InGaA with λg = 1.1 μm
Since it is difficult to melt back against spP, the composition of InGaAsP in the optical waveguide layer needs to be set in a direction in which λg is smaller.

Effects of the Invention As described above, in the present invention, the laser section is made of an InP substrate, an InP substrate, and an InP substrate.
P buffer layer, InGaAsP active layer, InGaAsP
It is composed of an optical waveguide layer, an InP cladding layer, and an InGaAsP contact layer, and the optical waveguide section is composed of an InP substrate, an InP buffer layer, an InGaAsP optical waveguide layer, an InP cladding layer, and an InP cladding layer.
In an optical waveguide integrated semiconductor laser structure composed of an nGaAsP contact layer, InGaAsP is grown in the -th growth.
InGaA with λg = 1.5 ~ 1-774 m on the active layer
After growing the sP or InGaAS protective layer, the protective layer and active layer in the optical waveguide are removed, and a second LPE is performed.
By melting back the protective layer during growth and sequentially growing the optical waveguide layer, cladding layer, and contact layer, it has a brainer structure with high yield and high coupling efficiency without impairing the characteristics of a single semiconductor laser. Moreover, an optical integrated circuit in which the laser can be easily converted into a single mode can be obtained, and various devices based on this can obtain good characteristics.

[Brief explanation of drawings]

FIG. 1 is a cross-sectional view of an MEC laser according to an embodiment of the present invention, FIG. 2 is a process diagram showing a method for manufacturing the same MEC laser, FIG. 3 is a cross-sectional view of a conventional butt joint type MIEC laser, and FIG. The figure is a cross-sectional view of a conventional BIG structure MEC laser.
FIG. 5 is a process diagram showing a method for manufacturing the laser shown in FIG. 4. 1... S-doped f-InP substrate, 3...
・InGaAsP active layer, 6...Znn-doped--InGaAsP optical waveguide layer, 9...Znn-doped--InP intermediate layer, 10...InGaAS
Protective layer, M... Laser section, B... Optical waveguide section. Name of agent: Patent attorney Toshio Nakao and 1 other person No. 1
Figure 2 (λ) /θ (b), Figure 3 122B- Figure 4

Claims (3)

[Claims] (1) The device has a laser part and an optical waveguide part, and the light emitting part has an InP substrate and a bandgap wavelength (λg).
1. An optical integrated circuit comprising an InGaAsP active layer and an InGaAs optical waveguide layer (λg<λa) in which the wavelength is λa, and the optical waveguide section has an InP substrate and an InGaAsP optical waveguide layer (λg<λa). (2) InP by liquid phase or vapor phase epitaxial growth method
InGaAsP active layer on the substrate, and InGaAs with a bandgap wavelength (λg) of 1.5 μm to 1.7 μm.
After forming a P or InGaAs protective layer and selectively removing the protective layer and the active layer of the optical waveguide, the InGaAsP optical waveguide layer is grown using a melt necessary for growing the InGaAsP optical waveguide layer by liquid phase epitaxial growth. The protective layer is selectively melted back and the InGaAsP optical waveguide layer is formed, and then the InP cladding layer and the InGaA
A method for manufacturing an optical integrated circuit in which an sP contact layer is formed. (3) The method for manufacturing an optical integrated circuit according to claim 2, wherein the thickness of the InGaAsP or InGaAs protective layer with λg=1.5 to 1.7 μm is 0.1 μm or less.