JPH07176822A - Semiconductor light source and its manufacture - Google Patents

Abstract

PURPOSE:To make larger in order the absorption coefficient of the photo absorption layer of a modulator by a method wherein the further the photoabsorption layer recedes from the side of a laser, the smaller the band gap of the photoabsorption layer is made in order. CONSTITUTION:A diffraction grating 6 is formed in a substrate 5 and thereafter, an SiO2 film is deposited. A pair of stripe width-modulation patterns 7, which consist of the SiO2 film and have a width of 18mum and a length of 500mum at an interval of 1.5mum, subsequently, a width of 4 to 15mum and a length of lengths changed in order to 200mum, are formed. An N-type InGaAsP guide layer of a thickness of 0.1mum, a non-doped InGaAs well layer having a band gap long wave of 1.56mum in a laser part, a seven-layer multiple quantum well layer 9 using non-doped InGaAsP layers of a wavelength composition of 1.15mum as barrier layers and a clad layer 10, which consists of a P-type InP layer and has a thickness of 0.1mum, are grown in order. At this time, as the widths of the patterns 7 become wider in order in a modulation part, the growth rate of the layers is accelerated and the thickness of the layer 9 becomes thicker in order. Accordingly, the further a photoabsorption layer of a modulator recedes from the side of a the smaller a band gap of the photoabsorption layer becomes and the absorption coefficient of the photoabsorption layer can be made larger in order.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a modulator-integrated semiconductor light source used for optical communication, and more particularly to an external modulator-integrated semiconductor light source suitable for high output operation and a manufacturing method thereof.

[0002]

2. Description of the Related Art With the progress of optical fiber communication technology, development of a transmission system having a longer distance and a larger capacity has been promoted. Currently used for commercial use is a method of directly modulating a semiconductor laser, but this method changes the injection current into the active layer, so the refractive index also changes, which is called chirping. Wavelength fluctuation occurs. On the other hand, for increasing the distance, it is effective to change the wavelength of the semiconductor laser to be used from 1.3 μm band to 1.55 μm band in terms of transmission loss of the optical fiber.
When using light in the 1.55 μm band, if you try to perform gigabit transmission with an already installed optical fiber without dispersion compensation, sensitivity deterioration occurs on the receiving side due to chromatic dispersion, and transmission is performed using the existing optical fiber. This is an obstacle to increasing the distance and capacity. As a means for solving this problem, a method in which the laser is driven by DC and the chirping of the laser is suppressed by modulating the light intensity by an external modulator has been receiving attention in recent years, and in particular, the external modulator and the laser are integrated. The semiconductor light source has advantages such as miniaturization of the device and easy assembly, and there are great expectations for its development.

As shown in FIG. 13, the bandgap diagram of the conventional modulator integrated semiconductor light source is such that the bandgap of the modulator section 1 is set to be slightly larger than the photon energy of the laser section 2, and a reverse bias voltage is applied to the Franz. The intensity of the laser output light is modulated by modulating the absorption coefficient by the Keldysh effect or the quantum confined Stark effect. The band gap of the modulator section 1 is constant, and the absorption of the modulator section light absorption layer is fixed. The coefficient is also constant [for example, 1993 IEICE Fall Conference Proceedings C-98].

[0004]

In this conventional modulator integrated semiconductor light source, as shown in FIG. 13, the band gap of the light absorption layer of the modulator is constant in the optical waveguide direction. Therefore, the absorption coefficient is also constant in the optical waveguide direction, and the power density of the laser light absorbed at the time of modulation becomes maximum at the entrance end 3 of the modulator and attenuates exponentially toward the exit end 4 as shown in FIG. Distribution. Therefore, when the incident power becomes large, there is a problem that absorption saturation occurs near the incident end 3, and as a result, response deterioration and extinction ratio deterioration that cause sensitivity deterioration on the receiving side occur.

The present invention solves the above problems and provides a semiconductor light source that suppresses absorption saturation in the modulator section at high output, prevents extinction ratio deterioration, and response deterioration, and a method of manufacturing the same. To aim.

[0006]

In order to achieve the above object, the present invention is a semiconductor light source in which an electro-absorption modulator is integrated, wherein the modulator is higher than the photon energy of laser light. A semiconductor light source having an electroabsorption modulator having a large bandgap and a bandgap gradually or stepwise becomes smaller as the distance from the laser side is increased.

Further, in a method of manufacturing a semiconductor light source in which an electro-absorption modulator is integrated, an organometallic vapor is formed in a region sandwiched by a stripe pattern composed of _two SiO ₂ films formed on an InP substrate. In a manufacturing process for collectively forming a light-emitting layer and a light-absorbing layer having a multiple quantum well structure by a phase growth method, a stripe pattern width of a portion where the light-absorbing layer is formed is sequentially or gradually widened from the light-emitting layer side. The method of manufacturing a semiconductor light source configured as described above is characterized.

[0008]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a bandgap diagram in the optical waveguide direction of a modulator integrated light source of the first embodiment of the present invention, FIG. 2 is a diagram showing absorbed light power density in the modulator section 1 of the first embodiment, and FIG.
Is a plan view for explaining the manufacturing process of the modulator integrated light source of the first embodiment, FIGS. 4 and 5 are sectional views thereof, and FIG.
FIG. 7 is an external view of a modulator integrated light source of the embodiment, and FIG.
8 is a band gap diagram of the modulator integrated light source of the embodiment, FIG. 8 is a diagram showing the absorbed light power density in the modulator portion 1 of the second embodiment, and FIG. 9 is a manufacturing process of the modulator integrated semiconductor light source of the second embodiment. 10 and 11 are cross-sectional views thereof, FIG. 12 is an external view of the modulator integrated light source of the second embodiment, and FIG. 13 is a band gap in the optical waveguide direction of a conventional modulator integrated light source. FIG. 14 is a diagram showing the absorbed light power density in the conventional modulator section.

Embodiment 1 In this embodiment, the band gap of the laser section 2 is 1.5 wavelength.
6 μm, and the band gap of the modulator is 1.43 μm at the laser light entrance end 3 and 1.49 μm at the exit end 4 depending on the wavelength composition.
It is set to be m. The oscillation wavelength of the LD is set by the diffraction grating to be 1.55 μm.

3 to 5 are manufacturing process diagrams of the modulator integrated light source of this embodiment. Of these, FIG. 3 is a plan view, and FIGS.
Shows a cross section taken along the line AA 'in FIG. A diffraction grating 6 having a period of 241.7 nm is formed in the <011 bar> direction on the laser forming portion by interference exposure and wet etching on the substrate 5 made of n-InP having the (100) plane orientation. Next, SiO ₂ is deposited to a thickness of 150 nm by the thermal CVD method, and <01
1 bar> direction with a gap of 1.5 μm and width of 18 μm and length of 50
A pair of SiO ₂ stripe width modulation patterns 7 having a length of 0 μm and successively a width of 4 μm to 15 μm and a length of 200 μm are formed by ordinary photolithography and wet etching (FIG. 3).

Next, the wavelength composition was 1.13 μm at a growth pressure of 75 Torr and a growth temperature of 625 ° C. by MO-VPE growth method.
n-InGaAs with a carrier concentration of m of 5 × 10 ¹⁷ cm ^-3
The guide layer 8 made of P has a thickness of 0.1 μm, and the laser region has a non-doped I band gap wavelength of 1.56 μm.
A well layer of nGaAs and a barrier layer of non-doped InGaAsP having a wavelength composition of 1.15 μm are used as a multiple quantum well layer 9 of seven layers, and a clad layer 10 made of p-InP having a carrier concentration of 1 × 10 ¹⁷ cm ⁻³ is 0.1 μm. Grow sequentially (Fig. 4). At this time, in the modulator portion, the width of the stripe width modulation pattern 7 is gradually increased to accelerate the growth rate, and the thickness of the multiple quantum well layer 9 is gradually increased to sequentially increase the bandgap wavelength.

Next, the opening width of the stripe width modulation pattern 7 is expanded to 7 μm by ordinary photolithography and wet etching, and a buried layer made of p-InP having a carrier concentration of 5 × 10 ¹⁷ cm ^-3 is again formed by MO-VPE growth method. 11 is 1.8 μm, and the contact layer 12 made of p-InGaAs having a carrier concentration of 5 × 10 ¹⁸ cm ⁻³ is 0.3 μm.
m (FIG. 5).

Next, SiO ₂ is added to 350 by the thermal CVD method.
nm, a contact window is opened by ordinary photolithography and wet etching, Ti / Au is deposited by a 100/300 nm sputtering method, and a p-side electrode 13 is formed by ordinary photolithography and wet etching. Is polished to 100 μm, Ti / Au to be the n-side electrode 14 is deposited on the back surface by a 100/300 nm sputtering method, and sintering is performed at 430 ° C. in an N ₂ atmosphere. Finally cleave, S
The iNx film is formed by the sputtering method to form the high reflection film 15 on the end face on the laser unit 2 side and the non-reflection film 16 on the end face on the modulator unit 1 side to complete the element. FIG. 6 is an external view of the modulator integrated light source of this embodiment.

Since the absorption coefficient of the light absorption layer of the modulator section 1 of this embodiment gradually increases from the entrance end 3, the absorption power density becomes constant in the modulator. FIG. 13 is a bandgap diagram in the optical waveguide direction of the conventional modulator integrated light source, and FIG. 14 is an absorption power density distribution in the conventional modulator part. In this case, the bandgap of the modulator part 1 is constant. Therefore, the absorption coefficient is also constant, and the absorption power density becomes maximum at the incident end and decreases exponentially. Turning on the light absorption layer of a conventional modulator
Absorption coefficient is A, length is L, laser output power is Po
Then, the maximum absorption power density Pmax1 in the modulator and the total power Pab absorbed are

[0015]

## EQU1 ## Pmax1 = APo Pab = Po (1-e- ^AL )

[0016] If the absorption power is the same as the conventional one,
The maximum absorption power density Pmax2 of this embodiment is

[0017]

[Formula 2] Pmax2 = Pab / L

Therefore, in this embodiment, the maximum absorption power density is

[0019]

## EQU3 ## Pmax2 / Pmax1 = (1-e- ^AL ) / AL

Is reduced to In the case of this embodiment, the modulator length is 200 μm, the absorption loss at the time of OFF is 8 dB, and the extinction ratio is 1
It becomes 5 dB. The maximum absorption power density is reduced to 45% as compared with the conventional one having the same element length and the same characteristics. Absorption saturation occurs in the modulator section 1 due to higher output, resulting in deterioration of the extinction ratio, but in the present embodiment, absorption saturation can be suppressed up to 2.2 times the laser output of the conventional one.

Embodiment 2 FIG. 7 is a bandgap diagram in the optical waveguide direction of the modulator integrated light source of the second embodiment, and FIG. 8 is an absorption power density distribution in the modulator section. In this embodiment, the bandgap of the laser section 2 is 1.56 μm, and the bandgap of the modulator section 1 is 1.44 μm in the wavelength composition of 1/3 from the incident end of the laser light and 1/3 of the next. The portion is set to 1.46 μm, and the next ⅓ portion is set to 1.48 μm. The oscillation wavelength of the laser is 1.55 due to the diffraction grating.
It is set to be μm.

9 to 11 are manufacturing process diagrams of the modulator integrated light source of this embodiment. Of these, FIG. 9 is a plan view, FIG.
FIG. 11 shows a cross section taken along the line BB 'in FIG. In the manufacturing process, the substrate 5 made of n-InP having the (100) plane orientation is formed on the laser forming portion by <0.
The diffraction grating 6 having a period of 241.7 nm is formed in the 11> direction. Next, SiO ₂ is deposited to a thickness of 150 nm by the thermal CVD method, and the interval is 1.5 μm and the width is 18 μm in the <011> direction.
m, length 500 μm, width 5 μm, 10 μ
m, the stripe width modulation pattern 7 of a pair of SiO ₂ was changed stepwise to 120μm intervals to 15μm is formed by conventional photolithography and wet etching (FIG. 9).

Next, the wavelength composition was 1.13 at a growth pressure of 150 Torr and a growth temperature of 625 ° C. by MO-VPE growth method.
n-InGaA with a carrier concentration of 5 × 10 ¹⁷ cm ^-3
The guide layer 8 made of sP has a thickness of 0.1 μm, the LD portion has a non-doped InGaAs well layer having a bandgap wavelength composition of 1.54 μm, and In having a wavelength composition of 1.15 μm.
7 multi-quantum well layers 9 using GaAsP as a barrier layer,
A cladding layer 10 made of p-InP having a carrier concentration of 1 × 10 ¹⁷ cm ⁻³ is sequentially grown to a thickness of 0.1 μm (see FIG. 1).
0). At this time, the SiO ₂ width of the modulator portion becomes wider stepwise, and the bandgap wavelength of the multiple quantum well layer 9 also becomes longer stepwise.

Next, the opening width of SiO ₂ is expanded to 7 μm by ordinary photolithography and wet etching.
The carrier concentration is 5 × 10 ¹⁷ by the MO-VPE growth method again.
cm- ³ of the buried layer 11 made of p-InP having a thickness of 1.8 μm.
m, carrier concentration 5 × 10 ¹⁸ cm ⁻³ p-InGaAs
The contact layer 12 made of is grown to 0.3 μm (FIG. 11).

Next, the SiO ₂ film is heated to 350 by the thermal CVD method.
nm, a contact window is opened by ordinary photolithography and wet etching, Ti / Au is deposited by a 100/300 nm sputtering method, and a p-side electrode 13 is formed by ordinary photolithography and wet etching to form a wafer. Polished to 100 μm, and Ti / Au to be the n-side electrode 14 on the back surface 1
It is deposited by a 00/300 nm sputtering method and sintered at 430 ° C. in an N ₂ atmosphere. Finally, cleavage is performed at the center of the laser portion and the modulator portion, and a high reflection film 15 is formed on the end surface on the laser side of the SiNx film by the sputtering method, and a non-reflective film 16 is formed on the end surface on the modulator side to complete the device. FIG. 12 is an external view of the modulator integrated light source of this embodiment.

The absorption coefficient when the light absorption layer of the modulator section 1 of this embodiment is ON is A1, 2A1, 3 in three steps from the entrance end.
It is set to be larger than A1. Since the total absorption power Pab is the same as that of the conventional one having the same absorption coefficient and the same element length and the same characteristics,

[0027]

[Equation 4] Pab = Po (1-e- ^AL ) = Po (1-e-1 / ^{3 (A1 + 2A1 + 3A1) L} )

Therefore, A1 = 1 / 2A Therefore, the maximum absorption power density Pmax of this embodiment is higher than the conventional one.
3 is

[0029]

(5) Pmax3 = Pab / 2A = Pmax1 / 2

In the case of this embodiment, the maximum absorption power density is reduced to 50% as compared with the conventional one. Although a higher output causes absorption saturation in the modulator section 1 and deterioration of the extinction ratio, this embodiment can suppress the absorption saturation up to a laser output twice as high as the conventional one.

[0031]

As described above, according to the present invention, the absorption coefficient is sequentially or stepwise increased by gradually or gradually decreasing the bandgap of the light absorption layer of the modulator away from the laser side. As a result, local power concentration is eased and the maximum absorption power density is suppressed to 50% or less.
It is possible to prevent the extinction ratio from deteriorating with respect to the output which is more than twice that of the conventional output.

[Brief description of drawings]

FIG. 1 is a bandgap diagram in a light guide direction of a modulator integrated light source according to a first embodiment of the present invention.

FIG. 2 is a diagram showing an absorption power density distribution in the modulator section of the first embodiment.

FIG. 3 is a plan view for explaining a manufacturing process of the modulator integrated light source of the first embodiment.

FIG. 4 is a sectional view taken along the line AA ′ of FIG.

5 is a cross-sectional view taken along the line AA ′ of FIG.

FIG. 6 is an external view of a modulator integrated light source according to the first embodiment.

FIG. 7 is a bandgap diagram in the optical waveguide direction of the modulator integrated light source according to the second embodiment of the present invention.

FIG. 8 is a diagram showing an absorption power density distribution in the modulator section of the second embodiment.

FIG. 9 is a plan view for explaining the manufacturing process of the modulator integrated light source of the second embodiment.

10 is a sectional view taken along line BB ′ of FIG.

11 is a sectional view taken along line BB ′ of FIG.

FIG. 12 is an external view of a modulator integrated light source of the second embodiment.

FIG. 13 is a bandgap diagram in the optical waveguide direction of a conventional modulator integrated light source.

FIG. 14 is a diagram showing an absorption power density distribution in a conventional modulator section.

[Explanation of symbols]

 1 modulator part 2 laser part 3 entrance end 4 exit end 5 substrate 6 diffraction grating 7 stripe width modulation pattern 8 guide layer 9 multiple quantum well layer 10 clad layer 11 buried layer 12 contact layer 13 p-side electrode 14 n-side electrode 15 high Reflective film 16 Non-reflective film

Claims (2)

[Claims] 1. A semiconductor light source in which an electro-absorption modulator is integrated, wherein the modulator has a band gap larger than the photon energy of laser light, and the band gap increases as the distance from the laser side increases. A semiconductor light source, comprising an electro-absorption modulator that becomes smaller sequentially or stepwise. 2. A method of manufacturing a semiconductor light source in which an electro-absorption modulator is integrated, comprising: a semiconductor light source formed on an InP substrate;
Forming a light absorbing layer and a light absorbing layer having a multiple quantum well structure by a metalorganic vapor phase epitaxy method in a region sandwiched between stripe patterns of the present SiO ₂ film A method of manufacturing a semiconductor light source, characterized in that the stripe pattern width of a portion is formed sequentially or stepwise from the light emitting layer side.