JP3146821B2 - Manufacturing method of semiconductor optical integrated device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a semiconductor optical integrated device and
It relates to the manufacturing method .

[0002]

2. Description of the Related Art Ultra-high-speed large-capacity transmission and information processing using optical technology are rapidly advancing. Among them, a high performance multiple quantum well structure semiconductor laser (MQW-LD) has been realized by the development of growth technology such as MOVPE (metal organic chemical vapor deposition), and various devices such as an ultra-high-speed modulation device, a coherent transmission device, and an analog modulation device have been realized. R & D on system applications is active. For example, a distributed feedback semiconductor laser (Distributed Fe
edback Laser Diode: DFB LD and Distributed Bragg Reflector Diode: DBR
LD). However, when the semiconductor laser is directly modulated, the spectral width increases, that is, so-called dynamic wavelength chirping occurs due to the refractive index fluctuation of the laser medium caused by the fluctuation of the injected carrier. This wavelength chirping is a factor that limits the transmission distance during high-speed modulation.
External modulators that do not rely on direct modulation have been proposed.

[0003] In a modulator using a semiconductor, a bulk semiconductor is used for an absorption layer, and a Franz-Keld
modulator using the change of the absorption edge due to the ysch) effect, and the quantum confined Stark effect (QCSE: Quantum Co
There is a quantum well structure modulator using an nfined stark effect). In addition, there is a Mach-Zehnder modulator that applies phase modulation of light, which is the principle of a Mach-Zehnder interferometer.

In recent years, with the rapid progress of thin film crystal growth techniques such as metalorganic vapor phase epitaxy (MOVPE) and molecular beam epitaxy (MBE) as crystal growth techniques, the accuracy of the thickness of a monoatomic layer has been increased. A high-quality semiconductor heterojunction interface having a steep composition change has been manufactured.
The potential well structure and the superlattice structure formed by these heterojunctions have unique optical characteristics and electric characteristics due to the wave nature of electrons, and research and development for device application is active. In particular, in recent years, a method for controlling the composition and thickness of a semiconductor layer within a substrate surface has been proposed and attracted attention. O. Kaiser, 1991, Journal of Crystal Growth, Vol. 107, pp. 989-998 (O. Kayser: Jo
urnal of Crystal Growth 107 (1991) 989-998). Colas et al., Vol. 107, pp. 226-230 (E. Colas et.
al .: Journal of Crystal Growth 107 (1991) 226-230)
Report on selective growth using SiO ₂ as a mask. Also, T.I. Kato et al., 1991, European Conference on Optical C
Optical modulator integrated MQW-DFB-L using the selective growth mechanism described above in WebB 7-1
D; Takano and others at the 1992 International Conference ECOC '
92 TuB5-3 similarly reports on a wavelength tunable MQW-DBR-LD utilizing selective growth. The integrated device as described above has advantages in that high output can be obtained because there is no coupling loss with the optical fiber, and handling is easy and stability is high because a complicated optical system is not used.

FIG. 6 shows the shape of a selective growth mask (SiO ₂ ) (FIG. 6A) of an optical modulator integrated type MQW-DFB-LD device to which the above-described selective growth mechanism is applied, and FIG. FIG. 6 shows a cross-sectional view of the element in the wave path direction (FIG. 6B) and a band gap (FIG. 6C). In the figure, 9 is an 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, 21a is a modulator region side, 21b side is an LD region side, 51 Is a quantum well layer, of which 51a is a modulator section and 51b is an LD section. 60 is a p-InP cladding layer, 65 is a p-InP layer, 70 is p ⁺ -InGa
AsP layers, 91a and 91b are electrodes.

[0006]

However, in the above-mentioned integrated device, when the modulator and the DBR are pulse-modulated or frequency-modulated (FM), the movement and diffusion of carriers between the laser and the laser are performed. However, there is a disadvantage that the laser operation becomes unstable such as a decrease in the sub-mode suppression ratio and an increase in noise due to the occurrence of crosstalk due to the above. An object of the present invention is to provide a semiconductor optical integrated device which solves such a conventional problem.

[0007]

In order to solve the above-mentioned problems, a means provided by the present invention is formed to prevent crystal growth in a region between adjacent device regions on a semiconductor substrate,
In the adjacent element regions , cells having different widths are used.
Simultaneously forming a plurality of semiconductor layers including a light guide layer by crystal growth on each of the adjacent element regions of the semiconductor substrate exposed from the mask; Embedding and growing a semiconductor layer having a larger band gap than the light guide layer in a region between the matching element regions, wherein the light guide layer included in each of the adjacent elements is adjacent to the light guide layer by the semiconductor layer having a larger band gap. It is interrupted in the area between the matching element areas,
A method of manufacturing a semiconductor optical integrated device, wherein the thickness of the semiconductor layer is different for each of the adjacent element regions. Here, the light guide layer preferably has a quantum well structure.

[0008]

Next, an embodiment of the present invention will be described with reference to the drawings. Embodiment 1 As a first embodiment according to the present invention, an optical modulator integrated type MQW
This will be described in detail with reference to the drawings, taking a DFB-LD element as an example. 1 (a), 1 (b) and 1 (c) show the shape of the selective growth mask (SiO ₂ ), the cross section of the selective growth layer in the optical waveguide direction, and the band gap, respectively, of the device according to the present invention. FIG. 2 is a perspective view of an element 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 portion (modulator region), 21b is a selective growth portion (LD region), 50a and 50b are quantum well layers, 60 is a p-InP cladding layer, 65 is a p-InP layer, and 70 is a p-InP layer.
⁺ -InGaAsP layers, 91a and 91b are electrodes.
The present invention differs from the prior art, as shown in FIG. 1 (a), leaving the SiO ₂ mask the transition region between both regions, LD
By selectively burying the semiconductor layer having a band gap larger than that of the optical guide layer (FIGS. 1 (b) and 1 (c)), the carrier is moved and diffused by separating the selective growth portion between the portion and the modulator portion. And the crosstalk is reduced. In addition, 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 extremely good at 90% or more.

Next, a method of manufacturing the above-described device is shown in FIG.
To (c). First, an SiO ₂ mask 8 is formed on a semiconductor substrate 10 on which a diffraction grating 12 is partially formed by using a selective growth portion (LD region: length 420 μm) 21b on the diffraction grating 21b with a width of 12 μm, and another portion (modulator region: length) 150 μm)
21a was formed with a width of 4 μm. The width of the opening is 1.5 μm
It is. After forming the mask, the optical waveguide layer 15 (1.2 μm composition InGaAsP, layer thickness: 0.1 μm), the quantum well layer 5
0 (7-well), optical waveguide layer 16 (1.2 μm composition I)
nGaAsP, layer thickness: 0.1 μm), p-InP cladding layer 60 (layer thickness: 0.05 μm, carrier concentration: 5 × 1)
0 ¹⁷ cm ^-3 ) were sequentially laminated to obtain a structure shown in FIG. In this case, as described above, the composition and the layer thickness are different in the device according to the mask width (the above all show the layer thickness in the modulation section). That is, LD in the modulator area
The composition is shorter in wavelength and the layer thickness is smaller than in the region.
That is, in the quantum well 50b in the LD region, the well layer has strained InGaAsP (compression strain + 0.8%, wavelength composition 1.72).
μm: 5.5 nm in thickness), and the barrier layer is InGaAsP
(Strain-free 1.15 μm composition: layer thickness 7 nm) and 1.5
It has a band gap 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 has strained InGaAsP (compressive strain +
0.5%, wavelength composition 1.66 μm: layer thickness 3.8 nm),
The barrier layer is composed of 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 expanded 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⁾ , after buried growth by ap ⁺ -InGaAs contact layer 70 (layer thickness: about 0.25 μm, carrier concentration: 8 × 10 ¹⁸ cm ⁻³ ) (FIG. 3B),
Part of the As contact layer is removed to perform element isolation, and the Si contact layer is removed.
O ₂ insulating film 80 and pad-shaped electrodes 91a and 91b
Was formed (FIGS. 3C and 2). FIG. 4 is a cross-sectional view of a portion separating a selective growth portion between an LD portion and a modulator portion. In this device, the threshold current is 10 m as the LD characteristic.
A, the optical output was 20 mW or more, and the modulation section obtained a good extinction ratio of 15 dB or more at a modulation voltage of 3 V and extremely good modulation characteristics even at the time of modulation of 5 Gb / s. Further, the sub-mode suppression ratio which was 35 dB or less in the conventional modulation is 45 dB.
dB, and the relative noise intensity is -14
From about 0 dB / Hz to -155 dB / Hz or less, crosstalk between elements due to the generated carriers was significantly reduced. Further, since selective growth is used as described above, a high output can be obtained with a small internal loss as a waveguide, and the yield is high because the manufacturing process is performed by vapor phase growth and patterning.

Embodiment 2 A second embodiment of the present invention will be described with reference to the drawings. FIG. 5 shows an optical modulator integrated DFB-
It is the 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 a so-called butt joint.
-joint) structure. The manufacturing method partially includes the diffraction grating 12.
An optical waveguide layer 17 (1.3 μm composition InGaAsP, layer thickness: 0.1 μm), a bulk active layer 58 (1.55 μm composition InGaAsP, 0.1 μm layer thickness)
m), the optical waveguide layer 18 (1.3 μm composition InGaAs)
After growing P, a layer thickness: 0.04 μm), the growth layers 18, 58, and 17 were partially removed by etching in order to form a modulator portion, and the entire surface of the optical waveguide layer 19 (1.47 μm) was removed.
A composition InGaAsP (layer thickness: 0.16 μm) is grown. Further, in the present invention, after a portion between the LD section and the modulator section is partially removed, the p-InP semiconductor layer 65 (having a thickness of 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 ). Thereafter, a waveguide portion is formed in a ridge shape, and semi-insulating In
After burying and growing by P (Fe doping) 62, SiO ₂
An insulating film 80 and pad-shaped electrodes 91 and 92 were formed.

In this device, a threshold current of 15 mA and an optical output of 20 mW or more were obtained as LD characteristics, and a good extinction ratio of 15 dB or more was obtained in the modulation section at a modulation voltage of 3 V. Also, by embedding the semi-insulating semiconductor, very good modulation characteristics were obtained even at the time of modulation of 10 Gb / s. The submode suppression ratio and the relative noise intensity are also good as in the first embodiment,
The crosstalk between elements has also been significantly reduced. In the above embodiment, an InP-based semiconductor has been described as an example.
It is also effective for system semiconductors.

[0013]

As described above, according to the present invention, there is provided a semiconductor optical integrated device in which a plurality of devices including a semiconductor layer including an optical guide layer or an optical active layer are integrated.
A structure in which at least two of the elements are separated by a semiconductor having a band gap larger than that of the optical guide layer, so that when a pulse modulation or a frequency (FM) modulation is performed, the movement of carriers generated between the laser unit and the laser unit. Crosstalk due to diffusion can be suppressed.

[Brief description of the drawings]

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

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

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

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

[Description of Reference Numerals] 8, 9 SiO ₂ mask 10 Semiconductor substrate 12 Diffraction grating 15, 16, 17, 18, 19 Optical waveguide layer 21a Selective growth portion (modulator region) 21b Selective growth portion (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-doped) layer 65 p-InP layer 70 p ⁺ -InGaAsP layer 80 Insulating film 91a, 91b electrode

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-54-37595 (JP, A) JP-A-5-29602 (JP, A) JP-A-1-339996 (JP, A) JP-A-4- 268765 (JP, A) JP-A-5-82909 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) H01L 27/15 H01S 5/00-5/50

Claims (3)

(57) [Claims] A step of forming masks having different widths in the adjacent element regions to prevent crystal growth in a region between adjacent element regions on the semiconductor substrate; A step of simultaneously crystal-growing and stacking a plurality of semiconductor layers including a light guide layer in each of the adjacent element regions of the semiconductor substrate exposed from the mask, and in a region between the adjacent element regions. Burying and growing a semiconductor layer having a band gap larger than that of the light guide layer, wherein the light guide layers included in the adjacent elements are formed by the semiconductor layer having a larger band gap in a region between the adjacent element regions. A method for manufacturing a semiconductor optical integrated device, wherein the semiconductor layer is discontinuous and the thickness of the semiconductor layer is different for each of the adjacent device regions. 2. The method according to claim 1, wherein the light guide layer has a quantum well structure. 3. The semiconductor substrate is made of InP, and the light guide layer is made of In _x Ga ₁ -x As _Y P _{1 -y} (0 ≦ X ≦ 1,0
≦ Y ≦ 1). The method of manufacturing a semiconductor optical integrated device according to claim 1, wherein