JPH07193210A - Semiconductor photointegrated element - Google Patents

Abstract

PURPOSE:To suppress cross talk caused by the transfer or the diffusion of carriers generated between a laser part when pulse modulation or frequency modulation are applied by forming a structure that separates elements by a semiconductor with a larger band gap than that of a photo guide layer. CONSTITUTION:On a semiconductor substrate 10 on which a diffraction grating 12 is partially formed, a SiO2 mask 8 is formed at a selective growth part 21b and other part on an upper part of the diffractory grating. After forming the mask, a photo waveguide layer 15, a quantum well layer 50, a photo waveguide layer 16 and a p-InP clad layer 60 are laminated sequentially. The opening part of the mask used for the selective growth is widened to be the form of stripes and after embedding and a p-InP a semiconductor layer 65 and a p<+>-Inlays contact layer 70, the elements are separated, and a SiO2 insulating film 80 and pad-shaped electrodes 91a and 91b are formed. With this structure, the crosstalk generated between the laser part by the transfer and the diffusion of the carrier is suppressed.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a semiconductor optical integrated device, and more particularly to a semiconductor optical integrated device having a modulator.

[0002]

2. Description of the Related Art Ultra-high-speed, large-capacity transmission and information processing using optical technology are rapidly advancing. Above all, a high-performance multi-quantum well semiconductor laser (MQW-LD) has been realized by the progress of growth techniques such as MOVPE (Metal Organic Chemical Vapor Deposition) method, and various devices such as ultra-high speed modulator, coherent transmission device or analog modulator have been realized. Research and development on system applications are becoming active. For example, as an ultrafast optical semiconductor device, a distributed feedback semiconductor laser (Distributed Fe
edback Laser Diode: DFB LD) and Distributed Bragg Reflector Diode: DBR
LD) etc. However, when the semiconductor laser is directly modulated, fluctuations in the refractive index of the laser medium caused by fluctuations in the injected carriers cause an increase in the spectral width, so-called dynamic wavelength chirping. Since this wavelength chirping becomes a factor that limits the transmission distance during high-speed modulation,
External modulators that do not rely on direct modulation have been proposed.

In a modulator using a semiconductor, a bulk semiconductor is used for the absorption layer, and a Franz-Keld (Franz-Keld) is used.
bulk structure modulator that utilizes the change in absorption edge due to the ysch) effect, and the quantum confined Stark effect (QCSE: Quantum Co
There is a quantum well structure modulator using the nfined Stark Effect). In addition, there is a Mach-Zehnder interferometer that applies the phase modulation of light, which is the principle of a Mach-Zehnder interferometer.

In recent years, as a crystal growth technique, with the rapid progress of thin film crystal growth techniques such as a metal organic vapor phase epitaxy (MOVPE) method and a molecular beam epitaxy (MBE) method, the thickness of a monoatomic layer can be accurately controlled. A high-quality semiconductor heterojunction interface having a sharp composition change has been manufactured.
The potential well structure and the superlattice structure formed by these heterojunctions have peculiar optical and electrical properties due to the wave nature of electrons, and research and development for device applications are becoming active. In particular, in recent years, a method of controlling the composition and layer thickness of the semiconductor layer within the substrate surface has been proposed and attracted attention. O. Kaiser, 1991, Journal of Crystal Growth, Volume 107, pages 989-998 (O. Kayser: Jo
urnal of Crystal Growth 107 (1991) 989-998), and E. Kolas et al., Vol. 107, pp. 226-230 (E. Colas et.
al .: Journal of Crystal Growth 107 (1991) 226-230)
Reported in detail on selective growth using SiO ₂ as a mask. In addition, T. Kato et al. Are the 1991 European Conference on Optical C
optical modulator integrated MQW-DFB-L using the above selective growth mechanism.
D, and S. Takano et al., 1992 International Conference ECOC '
TuB5-3 of 92 also reports a wavelength tunable MQW-DBR-LD that also utilizes selective growth. The integrated element as described above has advantages such as high output power without coupling loss with an optical fiber, easy handling and high stability since no complicated optical system is used.

FIG. 6 shows the shape (FIG. 6A) of the selective growth mask (SiO ₂ ) of the optical modulator integrated MQW-DFB-LD device to which the above selective growth mechanism is applied, and the optical growth of the selective growth layer. FIG. 7 shows a cross-sectional view of the element in the waveguide direction (FIG. 6B) and a band gap (FIG. 6C). In the figure, 9 is a SiO ₂ mask, 10 is a semiconductor substrate, 12 is a diffraction grating, 15 and 16 are optical waveguide layers, 21 is a selective growth portion, of which 21a is the modulator region side, 21b is the LD region side, and 51 is the LD region side. Is a quantum well layer, of which 51a is a modulator section and 51b is an LD section. Further, 60 is a p-InP clad layer, 65 is a p-InP layer, and 70 is p ⁺ -InGa.
AsP layers and 91a and 91b are electrodes.

[0006]

However, in the integrated device as described above, when the modulator section or the DBR section is pulse-modulated or frequency (FM) -modulated, carrier movement / diffusion with the laser section is performed. Due to the crosstalk caused by the above, there is a drawback that the laser operation becomes unstable, such as a decrease in the submode suppression ratio and an increase in noise. An object of the present invention is to provide a semiconductor optical integrated device that solves the above conventional problems.

[0007]

Means provided by the present invention for solving the above-mentioned problems are to provide a semiconductor optical integrated device in which a plurality of devices each including a semiconductor layer including an optical guide layer or a photoactive layer are integrated. The semiconductor optical integrated device is characterized in that at least two of the devices are separated by a semiconductor having a band gap larger than that of the light guide layer. Here, the photoactive layer or the optical guide layer preferably has a quantum well structure.

[0008]

Embodiments of the present invention will now be described with reference to the drawings. Embodiment 1 An optical modulator integrated type MQW as a first embodiment according to the present invention
The -DFB-LD element will be described in detail with reference to the drawings. 1A, 1B and 1C show the shape of the selective growth mask (SiO ₂ ) of the device according to the present invention, the device cross section of the selective growth layer in the optical waveguide direction and the band gap, respectively. 2 is a perspective view of the device according to the present invention. 1 and 2, 8 is a SiO ₂ mask, 10 is a semiconductor substrate, 12 is a diffraction grating, 15 and 16 are optical waveguide layers,
21a is a selective growth part (modulator region), 21b is a selective growth part (LD region), 50a and 50b are quantum well layers, 60 is a p-InP clad layer, 65 is a p-InP layer, and 70 is p.
⁺ -InGaAsP layer, and 91a and 91b are electrodes.
The present invention is different from the prior art in that as shown in FIG. 1A, the SiO ₂ mask is left in the transition region between the two regions and the LD
And diffusion of carriers by separating the selective growth portions of the modulator portion and the modulator portion and then performing buried growth in a semiconductor layer having a bandgap larger than that of the optical guide layer (FIGS. 1B and 1C). Is suppressed and crosstalk is reduced. Further, since the length of this portion is as short as 4 μm, the coupling efficiency of the LD light output to the modulator portion is 90% or more, which is extremely good.

Next, a method of manufacturing the above element will be described with reference to FIG.
To (c) are sequentially shown. First, the SiO ₂ mask 8 is formed on the semiconductor substrate 10 in which the diffraction grating 12 is partially formed, and the selective growth portion (LD region: length 420 μm) 21b on the diffraction grating is 12 μm wide, and the other portion (modulator region: length) is formed. 150 μm)
21a to a width of 4 μm. The width of the opening is 1.5 μm
Is. After forming the mask, the optical waveguide layer 15 (1.2 μm composition InGaAsP, layer thickness: 0.1 μm), quantum well layer 5
0 (seven wells), optical waveguide layer 16 (1.2 μm composition I
nGaAsP, layer thickness: 0.1 μm, p-InP clad layer 60 (layer thickness: 0.05 μm, carrier concentration: 5 × 1)
0 ¹⁷ cm ⁻³ ) was sequentially laminated to form the structure shown in FIG. In this case, as described above, the composition and the layer thickness differ within the element depending on the mask width (all of the above show the layer thickness in the modulation portion). That is, in the modulator area, LD
The composition has a shorter wavelength than the region, and the layer thickness is thinner.
That is, in the quantum well 50b in the LD region, the well layer is strained InGaAsP (compressive strain + 0.8%, wavelength composition 1.72).
(μm: layer thickness 5.5 nm), the barrier layer is InGaAsP
(Strain-free 1.15 μm composition: layer thickness 7 nm), 1.5
It has a bandgap energy (0.8 eV) corresponding to a wavelength of 5 μm. On the other hand, in the quantum well 50a in the modulator region, the well layer is strained InGaAsP (compressive strain +
0.5%, wavelength composition 1.66 μm: layer thickness 3.8 nm),
The barrier layer is InGaAsP (1.1 μm composition: layer thickness 5 n
m) and has a bandgap energy (0.84 eV) corresponding to a wavelength of 1.48 μm.

Next, the opening of the mask used for the selective growth is widened in a stripe shape to a width of about 5 μm, and the p-InP semiconductor layer 6 is formed.
5 (Layer thickness is about 1.3 μm, carrier concentration: 5 × 10 ¹⁷ c
m ^-3) , p ⁺ -InGaAs contact layer 70 (layer thickness of about 0.25 μm, carrier concentration: 8 × 10 ¹⁸ cm ^-3 ) after buried growth (FIG. 3B), InGa between devices.
Part of the As contact layer is removed to perform element isolation.
O ₂ insulating film 80 and pad-shaped electrodes 91a and 91b
Was formed (FIG. 3 (c), FIG. 2). FIG. 4 is a cross-sectional view of a portion separating the selective growth portion of the LD portion and the modulator portion. In this element, the LD characteristic has a threshold current of 10 m.
A, a light output of 20 mW or more, and a good extinction ratio of 15 dB or more at a modulation voltage of 3 V and a very high modulation characteristic at the time of 5 Gb / s modulation. Further, the sub-mode suppression ratio, which was 35 dB or less at the time of modulation in the past, is 45
It is improved to more than dB, and the relative noise intensity is -14 of the conventional one.
From about 0 dB / Hz to -155 dB / Hz or less, the crosstalk between the elements due to the generated carriers was significantly reduced. Further, since the selective growth is used as described above, the internal loss as a waveguide is small and a high output can be obtained, and the production process is based on vapor phase growth and patterning, so that the yield is also high.

Second Embodiment A second embodiment according to the present invention will be described with reference to the drawings. FIG. 5 shows an optical modulator integrated DFB- according to the present embodiment.
It is a perspective view and sectional view of LD. The difference from the first embodiment is that a bulk semiconductor is used as the active layer. The element structure is the so-called butt joint (butt
-joint) structure. The fabrication method is partially based on the diffraction grating 12
The optical waveguide layer 17 (1.3 μm composition InGaAsP, layer thickness: 0.1 μm), the bulk active layer 58 (1.55 μm composition InGaAsP, layer thickness 0.1 μm) on the substrate 10 on which
m), the optical waveguide layer 18 (1.3 μm composition InGaAs)
(P, layer thickness: 0.04 μm), the growth layers 18, 58 and 17 are partially removed by etching in order to form a modulator portion, and the optical waveguide layer 19 (1.47 μm) is formed on the entire surface.
Composition InGaAsP, layer thickness: 0.16 μm) is grown. Further, in the present invention, after the part between the LD part and the modulator part is removed, the p-InP semiconductor layer 65 (the layer thickness is about 1.5 μm) is formed.
m, carrier concentration: 7 × 10 ¹⁷ cm ⁻³ ),
p ⁺ -InGaAs contact layer 70 (layer thickness is about 0.2
5 μm, carrier concentration: 8 × 10 ¹⁸ cm ⁻³ ) were grown. After that, a waveguide is formed in a ridge shape, and semi-insulating In
After burying growth with P (Fe-doped) 62, SiO ₂
The insulating film 80 and the pad-shaped electrodes 91 and 92 were formed.

In this device, as the LD characteristics, a good extinction ratio of 15 mA or more was obtained with a threshold current of 15 mA and an optical output of 20 mW or more, and the modulation section at a modulation voltage of 3 V. Further, by embedding the semi-insulating semiconductor, extremely good modulation characteristics were obtained even at the time of modulation of 10 Gb / s. The secondary mode suppression ratio and the relative noise intensity are also good as in the first embodiment,
Crosstalk between elements was also greatly reduced. In the above embodiment, the InP semiconductor is taken as an example.
It is also effective for semiconductors.

[0013]

As described above, according to the present invention, in a semiconductor optical integrated device formed by integrating a plurality of devices each including a semiconductor layer including an optical guide layer or a photoactive layer,
By arranging at least two of the elements by a semiconductor having a bandgap larger than that of the optical guide layer, carrier movement between the laser section and the laser section occurs when pulse modulation or frequency (FM) modulation is performed. Crosstalk due to diffusion can be suppressed.

[Brief description of drawings]

FIG. 1 is an explanatory diagram of an embodiment of a semiconductor optical integrated device according to the present invention.

FIG. 2 is a perspective view of an embodiment of a semiconductor optical integrated device according to the present invention.

FIG. 3 is a process sectional view for explaining the manufacturing method of the embodiment of the semiconductor optical integrated device according to the present invention.

FIG. 4 is a cross-sectional view of a portion of the semiconductor optical integrated device according to the present invention which separates an LD growth portion and a modulator growth portion.

FIG. 5 is a perspective view and a sectional view of another embodiment of the semiconductor optical integrated device according to the present invention.

FIG. 6 is an explanatory diagram of a semiconductor optical integrated device according to a conventional example.

[Explanation of symbols]

8, 9 SiO ₂ mask 10 Semiconductor substrate 12 Diffraction grating 15, 16, 17, 18, 19 Optical waveguide layer 21a Selective growth part (modulator region) 21b Selective growth part (LD region) 50a Quantum well layer (modulator part) 50b Quantum well layer (LD part) 58 Bulk active layer 60 p-InP clad layer 62 Semi-insulating InP (Fe dope) layer 65 p-InP layer 70 p ⁺ -InGaAsP layer 80 Insulating film 91a, 91b Electrode

Claims (4)

[Claims] 1. A semiconductor optical integrated device in which a plurality of devices each composed of a semiconductor layer including an optical guide layer or a photoactive layer are integrated, and at least two of the devices are semiconductors having a band gap larger than that of the optical guide layer. A semiconductor optical integrated device characterized by being separated. 2. The semiconductor optical integrated device according to claim 1, wherein the optically active layer or the optical guide layer has a quantum well structure. 3. The semiconductor substrate is made of InP, and the photoactive layer and the light guide layer are made of In _X Ga _1-X As _Y P _1-Y (0 ≦ X ≦
2. The semiconductor optical integrated device according to claim 1, which is composed of 1,0 ≦ Y ≦ 1). 4. The semiconductor substrate is made of InP, and the well layer and the barrier layer forming the quantum well structure are In _X Ga _{1 -X} As.
The semiconductor optical integrated device according to claim 2, which is composed of _Y P _1-Y (0 ≦ X ≦ 1, 0 ≦ Y ≦ 1).