JPH07193314A - Manufacture of semiconductor multiwavelength laser - Google Patents

Abstract

PURPOSE:To display the excellent element characteristics by a method wherein passive wave guides are grown by controlling the thickness thereof by MOCVD process using growth blocking masks and then active layers are independently formed. CONSTITUTION:The growth blocking masks 20 in direction width orthogonal to the extending direction of a region 18 different per wave guide corresponding to the oscillation wavelength are formed. After the formation of the blocking masks 20, wave, guides 22 are formed using MOCVD process. Next, after the removal of the growth blocking masks 20, etching stopper layers are formed and then active layers are formed on the wave guides 22. Since the active layers are independently formed after growing the passive wave guide layers 22, no transition regions are to be formed at all within the boundry of active regions and passive regions (DBR regions) of a DBR laser. Accordingly, the passive wave guides can be grown by controlling the thickness thereof by MOCVD process using the growth blocking masks 20 further enabling excellent element characteristics to be displayed.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a semiconductor multi-wavelength laser used in the fields of optical wavelength division multiplex communication and optical switching, particularly D
The present invention relates to a method for manufacturing a BR laser.

[0002]

2. Description of the Related Art Conventionally, when a crystal is grown on a substrate by a selective MOCVD (Metal Organic Chemical Vapor Deposition) method, if growth preventing masks having various widths are provided to sandwich the growth region, the growth preventing is prevented in the growth region. It is known that the growth rate changes according to the width of the mask.

As a method of manufacturing a semiconductor laser using a growth blocking mask, for example, there is one described in Document 1: "Autumn 1993, Proceedings of Japan Society of Applied Physics, 27p-H-18". According to Document 1, a waveguide having a multiple quantum well (MQW) structure having different bandgap energies in the active region and the DBR region is formed at one time.

Further, in Document 1, even if the pitch of the diffraction grating (grating) is constant, the thickness of the waveguide is changed by changing the width of the growth blocking mask.
It is described that semiconductor lasers having different oscillation wavelengths can be obtained.

Reference 2: "LEOS '93, Con
ference Proceedings, pp. 18
9-190 ”and Document 3:“ OFC′92 (OPTI
CAL FIBER COMMUNICATION C
ONFERENCE), TECHNICAL DIGE
ST, p. 282, FB10 "describes a method for manufacturing a semiconductor laser using a growth blocking mask.

[0006]

However, in the method of manufacturing a semiconductor laser described in the above-mentioned Documents 1 to 3, when manufacturing a DBR laser, a waveguide (passive waveguide) in the DBR region and an active region are used. And the active layer are simultaneously formed. Therefore, the transition region is formed in the boundary region between the DBR region and the active region. Since the optimum bandgap energies of the DBR region and the active region are different from each other, the bandgap energy of the transition region gradually changes between both optimum bandgap energies. For example, FIG. The graph of 4 shows that the bandgap energy of the transition region is gradually changing over a distance of 55 μm on the waveguide. The band gap energy of the transition region is
It is not the optimum bandgap energy for either the DBR region or the active region. Therefore, there is a problem that the transition region becomes a region having a large absorption loss for the DBR laser, which causes deterioration of the device characteristics of the DBR laser.

Therefore, in manufacturing a semiconductor multi-wavelength laser, a waveguide layer of a portion which becomes a passive waveguide is grown by a MOCVD method using a growth blocking mask while controlling its thickness, and a good quality is obtained. It has been desired to realize a manufacturing method capable of obtaining device characteristics.

[0008]

A step of forming a single-pitch grating on a semiconductor substrate, extending along both sides of the region along which a passive waveguide is formed on the grating, and The step of forming a growth blocking mask in which the width of this area in the direction orthogonal to the extending direction differs depending on the area where the passive waveguide is formed according to the oscillation wavelength, and after the growth blocking mask is formed, the passive guiding mask is formed. The thickness of the portion to be the waveguide is different from that of the waveguide layer depending on the oscillation wavelength.
The method is characterized by including a step of forming using the VD method and a step of forming an active layer on the waveguide layer after removing the growth blocking mask.

Hereinafter, the portion of the waveguide layer that will be the passive waveguide will be referred to as the passive waveguide layer.

[0010]

According to the method of manufacturing a semiconductor multi-wavelength laser of the present invention, first, a passive waveguiding layer is grown by a MOCVD method using a growth blocking mask while controlling its thickness. Next, after growing the passive waveguiding layer, the active layer is independently formed. Therefore, the active region and the passive region (D
No transition region is formed at the boundary with the (BR region). Further, since the thicknesses of the passive waveguiding layer and the active layer can be independently controlled, the gain peak of the active layer can be optimally controlled according to the Bragg wavelength when manufacturing the DFB laser. Therefore, according to the present invention, it is possible to manufacture a semiconductor multi-wavelength laser in which a passive waveguiding layer is grown by a MOCVD method while controlling its thickness and a good device characteristic is obtained by using a growth blocking mask. You can

[0011]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An example of a semiconductor multi-wavelength laser of the present invention and a method of manufacturing the same will be described below with reference to the drawings. It should be noted that the drawings merely schematically show the sizes, shapes, and positional relationships of the respective constituent components to the extent that the present invention can be understood. Therefore, it is obvious that the present invention is not limited to this illustrated example.

The oscillation wavelength of the semiconductor laser depends on the Bragg wavelength of the grating. The Bragg wavelength (λ _b ) is determined by the pitch (Λ) of the grating and the effective refractive index (n _eff ) of the waveguide, as shown in equation (1) below.

Λ _b = 2 · n _eff · Λ (1) Further, the effective refractive index is determined by the composition, thickness and width of the waveguide. Here, FIG. 3 shows the dependence of the Bragg wavelength on the waveguide thickness. The horizontal axis of the graph in FIG. 3 is the thickness of the waveguide (μ
m), and the vertical axis represents the Bragg wavelength (μm). The curve I in the graph indicates the composition of the waveguide Eg = 1.3.
The dependence of the Bragg wavelength on the waveguide thickness when the width is 1 μm is shown. This waveguide allows single mode propagation up to a thickness of 0.35 μm, and the thicker the waveguide, the longer the Bragg wavelength. From curve I, change the thickness of the waveguide to 0.2μ
When changing from m to 0.35 μm, the Bragg wavelength is 17
It can be seen that the wavelength shifts to the longer wavelength side.

The thickness of the passive waveguiding layer is determined by MOCVD the waveguide.
It can be controlled by the width of the growth-inhibiting mask provided on both sides of the exposed portion of the substrate when growing using the method.
This is because the growth rate increases in proportion to the width of the growth blocking mask. Here, the width of the mask of the growth rate of the waveguide layer when InGaAs having a band gap wavelength of 1.3 μm is grown as an example of a crystal that forms the pattern of the growth blocking mask shown in FIG. Figure 5 shows the dependency
Is shown in the graph. Here, for growth, (00
1) on the n-InP substrate, as shown in FIG. 4, SiO ₂
Growth prevention mask 20 was formed in a stripe shape. The width of the growth region serving as the passive waveguiding layer is set to 20 μm and 350 μm
6 are provided at intervals of. The widths of the growth stop masks along the growth region are 5, 10, 20, 40, 80, 1 respectively.
The thickness was 60 μm and the thickness was 150 nm. Although not shown in FIG. 4, a waveguide having no growth prevention mask on both sides thereof was also formed. InGaAs (λg = 1.3 μm) was grown on the substrate on which the growth blocking mask was formed by MOCVD until the film thickness in the flat region away from the mask was 0.2 μm. The thickness of the growth layer at this time is shown in the graph of FIG. The horizontal axis of the graph is the mask width (μm)
And the vertical axis shows the growth rate (relative value). Curve II in the graph is obtained by connecting plots of the growth rate of each growth layer. It can be seen from curve II that the growth rate increases with the mask width.

Therefore, if a growth prevention mask is used, even if the grating has a single pitch, the semiconductor multi-wavelength laser having different oscillation wavelengths can be formed by forming the passive waveguide layers having different thicknesses by one growth. Can be manufactured.

Therefore, in the present invention, a semiconductor multi-wavelength laser is manufactured by utilizing this knowledge. Hereinafter, FIG. 1 and FIG.
With reference to, a method for manufacturing a DBR laser array will be described as an example of a method for manufacturing a semiconductor multi-wavelength laser according to the present invention. FIGS. 1A to 1C are process diagrams of the first half used to describe an embodiment of the present invention. 2 (A)-
FIG. 1C is a process drawing of the latter half of FIG. 1C.
Note that, in FIGS. 1 and 2, only two of the four waveguides formed in the embodiment are illustrated.

First, D of the (001) n-InP substrate 10
Only in the BR region 14, the pitch Λ = 24 by the interference exposure method.
A single pitch grating 12 of 40 A ° (A ° represents angstrom) is formed ((A) of FIG. 1).

Next, the DBR on this grating 12
The width of each of the regions 14 extending along both sides of the region 18 forming the passive waveguide, and extending in the direction orthogonal to the extending direction of the region 18 depends on the oscillation wavelength. A growth prevention mask 20 different from the above. In this embodiment, the width of the selective growth region 18 to be the passive waveguide layer 24 is set to 20 μm at 350 μm intervals, and the stripe-shaped growth blocking mask 20 made of SiO ₂ with the region 18 sandwiched therebetween.
Pattern is formed to extend in the (001) direction. Here, the width of the growth blocking mask 20 for each selective growth region 18 is set to 0, 15, 30 and 50 μm, and the thickness of the growth blocking mask 20 is set to 150 nm ((B) of FIG. 1).

Next, after forming the growth prevention mask 20,
The waveguide layer 22 is formed using the MOCVD method. In this embodiment, InGaAsP (λg = 1.3 μm) is selectively grown. The raw materials are TEGa, TMIn, AsH ₃ ,
Using PH ₃ , growth temperature: 650 ° C., growth pressure: 50To
It was grown under the condition of rr. In addition, in order to suppress the lattice mismatch in the selective growth region, the flatness is increased under the condition that the flat region away from the growth inhibition mask 20 has a tensile strain of 0.3% in anticipation that the group III composition becomes excessive in In. The region was grown to a thickness of 0.18 μm. In this case, the thickness of each passive waveguide layer is 0.18, 0.24, 0.28, 0.32 μm corresponding to the width of the growth blocking mask 20 ((C) of FIG. 1).

Next, after removing the growth blocking mask 20,
After forming an etching stop layer (not shown), an active layer 26 is formed on the waveguide layer 22. In this embodiment, the MQW active layer (InGaAs: 7) is used as the active layer 26.
0A °, barrier 1.3 μm composition InGaAsP: 140
A layer of A ° for 7 cycles) 26 is grown, and the active region 16 is removed by etching ((A) of FIG. 2).

Next, a p-InP clad layer 28 is formed on the entire surface of the laminated body on which the active layer 26 is formed (FIG. 2B).

Next, after performing mesa etching so that the width of the waveguide constituted by the passive waveguide 24 and the active layer 26 becomes 1.0 μm, the p-InP layers 30a, n- are formed.
The current blocking layer 30 is formed by sequentially stacking the InP layer 30b and the p-InP layer 30c. Next, the current blocking layer 30
A contact layer 32 made of p ⁺ -InGaAsP is formed on top. Next, an electrode (not shown) is vapor-deposited in the same manner as a normal semiconductor laser, and element-to-element isolation etching is performed for each laser (FIG. 2C). A cross-sectional view along the waveguide is shown in FIG.

Next, FIG. 7 shows a spectrum at the time of simultaneous oscillation of the semiconductor multi-wavelength laser manufactured in this example. Figure 7
From this, it can be seen that a 4-wavelength laser array in which the wavelength was shifted at 5 nm intervals was realized.

As described above, in this embodiment, the active layer is independently formed after growing the passive waveguiding layer. Therefore, the active region and passive region (DBR region) of the DBR laser
No transition region is formed at the boundary of the. Therefore,
According to the present invention, the MOCV using the growth prevention mask is used.
The passive waveguide layer is grown by controlling the thickness by the D method,
Moreover, it is possible to manufacture a semiconductor multi-wavelength laser capable of obtaining good device characteristics.

[0025]

According to the present invention, a semiconductor is obtained in which a waveguide layer is grown by controlling the thickness of a portion serving as a passive waveguide by the MOCVD method using a growth stop mask and excellent device characteristics are obtained. Multi-wavelength lasers can be manufactured.

[Brief description of drawings]

FIG. 1 (A) to (C) are process diagrams of the first half used to describe an embodiment of the present invention.

2A to 2C are process diagrams of the latter half of FIG. 1C.

FIG. 3 is a graph for explaining the dependency of the Bragg wavelength on the waveguide thickness.

FIG. 4 is an explanatory diagram of a pattern of a growth blocking mask.

FIG. 5 is a graph for explaining the mask width dependence of the growth rate.

FIG. 6 is a cross-sectional view of a semiconductor multi-wavelength laser manufactured in an example.

FIG. 7 is an oscillation spectrum of the semiconductor multi-wavelength laser manufactured in the example.

[Explanation of symbols]

 10: n-InP substrate 12: Grating 14: DBR region 16: Active region 18: Selective growth region 20: Growth blocking mask 22: Waveguide layer 24: Passive waveguide layer 26: Active layer 28: Clad layer 30: Current blocking Layer 30a: p-InP layer 30b: n-InP layer 30c: p-InP layer 32: Contact layer 34: Etching stop layer

Claims (1)

[Claims] 1. A step of forming a grating having a single pitch on a semiconductor substrate, and extending on both sides of the region along a region where a passive waveguide is formed on the grating, and extending the region. Forming a growth blocking mask in which the width in the direction orthogonal to the existing direction is different for each of the regions depending on the oscillation wavelength; and after forming the growth blocking mask, the thickness of the portion serving as the passive waveguide is A different waveguiding layer is used depending on the oscillation wavelength.
A method of manufacturing a semiconductor multi-wavelength laser, comprising: a step of forming by using a CVD method; and a step of forming an active layer on the waveguide layer after removing the growth blocking mask.