JPH0636460B2 - Method for manufacturing semiconductor optical integrated circuit - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention is applied to a semiconductor optical integrated circuit using a quantum well structure. In particular, it relates to a semiconductor structure around a quantum well structure.

〔Overview〕

The present invention relates to a method for manufacturing a semiconductor optical integrated circuit by integrating semiconductor optical devices provided with a quantum well structure, wherein crystal growth is performed in two steps, and a quantum well structure and an optical guide are formed by the first crystal growth. By introducing impurities and forming a rib-shaped waveguide structure before the second growth, the waveguide loss due to the impurities for disordering is reduced and the bending waveguide and This enables a waveguide structure suitable for an optical device such as a directional coupler.

[Prior art]

In the case of forming an optical integrated circuit by forming various optical elements operating in the same wavelength band on the same substrate, it is necessary to use semiconductors having different optical characteristics, particularly band gaps, depending on the type of optical element. In order to optically couple semiconductors having different band gaps on the same substrate, conventionally, a method of partially etching a semiconductor thin film once crystal-grown and then re-growing semiconductors having different band gaps has been used. . For this method, for example, Shigeru Murata, Ikuo Mito, Kouro Kobayashi,
"Spectral Characteristic for
1.5 μm DBR Laser with Frequency Tuning Region ", IEEE Journal of Quantum Electronics Volume QE-23, No. 6, 1987, 6
Moon (S.Murata, I.Mito and K.Kobayashi, "Spectral Char
acteristics for a 1.5 μm DBR Laser with Freguency-
Tuning Region ", IEEE Journal of Quantum Electronic
s, Vol.QE-23, No.6, June 1987).

[Problems to be solved by the invention]

However, in the conventional method, since semiconductors having different band gaps are grown separately, it is necessary to repeat etching and crystal growth many times, and it is difficult to grow each semiconductor layer flat. In addition, it is difficult to increase the coupling efficiency between the elements because the structure of the waveguide is different.

Furthermore, when used for GaAs, selective regrowth of AlGaAs was difficult.

On the other hand, when the disordered quantum well structure is used, it is not necessary to repeat etching and regrowth, the process is simple, and almost perfect coupling between elements can be obtained. However, heretofore, no consideration has been given to the increase in waveguide loss due to impurities for disordering, and the waveguide structure suitable for optical devices such as curved waveguides and directional couplers. These have a great influence on the device characteristics and manufacturing yield, and an optical integrated circuit cannot be manufactured without solving these problems.

The present invention solves such a problem, has a small increase in waveguide loss due to impurities for disordering, and is a semiconductor optical integrated device for forming a waveguide structure suitable for a curved waveguide or a directional coupler. The purpose is to provide a circuit.

[Means for solving problems]

A method for manufacturing a semiconductor optical integrated circuit according to the present invention is a method for manufacturing a semiconductor optical integrated circuit in which a quantum well structure is formed on a substrate and at least a part of the quantum well structure is disordered by ion implantation and heat treatment. A first growth step of growing a guide layer adjacent to the quantum well structure together with the structure, and another semiconductor layer is formed on the semiconductor layer formed by the first growth step to form an optical element structure. Including a second growth step, following the first growth step, the rib waveguide structure and the diffraction grating are formed in the guide layer by etching, and ion implantation is performed, and after the ion implantation is completed, the second growth step is performed. It is characterized by executing a growth process.

A rib-shaped waveguide structure in which the quantum well structure is disordered includes a Bragg reflection region, a variable wavelength Bragg reflection region, a Resonant Optical Reflector (hereinafter referred to as “ROR”), a variable wavelength ROR, an optical coupler, and a phase. Adjustment areas, PM modulation areas, AM modulation areas, etc. can be formed.

The degree of disorder can be controlled by controlling at least one of the dose amount and the implantation energy in ion implantation for disordering the quantum well structure. Also, the degree of disordering can be controlled by selecting the implanted ion species.

It is desirable that the heat treatment be performed concurrently with the formation of the semiconductor layer by the temperature increase in the second growth step.

[Work]

As the quantum well structure becomes disordered, the effective well width decreases, the first quantum level changes, and the band gap increases. When the disorder becomes completely disordered, the band gap increases up to the value of the barrier layer. Therefore, a region that is not disordered at all is used as a light emitting region, and an optical waveguide, a DBR region, a phase adjustment region, a PM modulation region, an AM modulation region, and the like are formed in the at least partially disordered region.

At this time, the crystal growth is divided into two steps, the quantum well structure and the optical guide layer are grown in the first crystal growth, and the impurity is introduced and the rib waveguide structure is formed before the second growth. And do. This causes the disordered quantum well structure to be close to the surface.
Since impurities are introduced after the second growth, the impurity material required for disordering can be reduced and the impurities can be easily introduced. In addition, there are few impurities required for disordering, and
Since it exists only in the layer formed by the second growth, an increase in waveguide loss due to impurities can be suppressed.

Since the waveguide structure is formed after the first growth, a buried rib waveguide structure can be adopted for the optical waveguide. The greatest advantage of the embedded rib waveguide in the optical integrated circuit is that the required etching amount is as small as several tens of nm. For this reason, it becomes easy to manufacture an optical element such as a directional coupler, which requires processing accuracy on the order of submicrons. Further, since there is no influence of the plane orientation dependence of etching, which is a problem in deep etching, it becomes easy to manufacture an optical element such as a curved waveguide in which the plane orientation differs depending on the location.

The only difference between the integrated waveguide and the active waveguide is the change in the refractive index due to disordering. By using a single quantum well, this difference can be reduced, and almost perfect optical coupling between elements can be obtained.

There are advantages such as.

〔Example〕

1 and 2 are views showing a reference example of a method for manufacturing a semiconductor optical integrated circuit, in which crystal growth is performed in two steps.
A manufacturing method in which a quantum well structure and an optical guide layer are grown by the second crystal growth and impurities are introduced before the second growth is shown.

Here, as a quantum well structure, GRIN-SCH-SQW (Graded
Index-Separate Confinement Heterostructure-Si
An example will be described in which a tunable growth Bragg reflection laser, an AM modulator and a PM modulator are integrated on the same substrate by using the ngle Quantum Well). In this example, disorder is controlled by the dose amount in Si ion implantation, the growth process is divided into first and second growth processes, ion implantation is performed after the first growth process, and the temperature rise in the second growth process is performed. Will be described as a heat treatment step for ion implantation.

First, as shown in FIG. 1A, a buffer layer 2, a cladding layer 3, a GRIN layer 4, an active layer 5, a GRIN layer 6 and a guide layer 7 are sequentially grown on a substrate 1. Here, GRIN layer 4,
The active layer 5 and the GRIN layer 6 are formed by the quantum well structure.

Next, the quantum well structure is disordered by ion implantation and heat treatment. At the time of ion implantation, a mask 8 having a window is provided on the surface of the guide layer 7 in a region where an optical element is to be formed, and the dose amount is controlled according to the band gap required for the optical element. 1 (b) to (d), a waveguide region for connecting individual optical elements, a refractive index control region for variably controlling the refractive index for radiated light, and an absorption coefficient for radiated light are variable. The shapes of the masks for forming the absorption coefficient control regions for the control are shown respectively.
Si is used as the implanted ions, and the dose amount for each region is S ₁ , S ₂ and S ₃ , respectively. However, S ₁ > S ₂ > S ₃ .

The quantum well structure is disordered by heat treatment after ion implantation. The degree of disordering depends on the dose in that region. Regarding disordering of quantum well structure by ion implantation and heat treatment, see, for example, Ueyama, Yamagawa, "Compositional Disordering of Si Implanted GaAs / AlGaAs Superiorizes by Rapid Thermal Annealing", Japanese Journal.・ Applied Physics No.
Vol. 26, No. 8, August 1987, L1470-L1409 (Masashi
Uematsu, Fumihiko Yamagawa, "Compositional DIsorder
ing of Si-Implanted GaAs / AlGaAs Superlatices by Ra
pid Thermal Annealing ", Japanese Journal of Applied
Physics, Vol.26, No.8, August, 1987, pp.L1407-L1409)
Explained.

FIG. 2 shows the steps after the ion implantation process is completed.

In the step after the end of the ion implantation process, as shown in FIG. 2A, the diffraction grating 9 is formed on the surface of the guide layer 7 corresponding to the place where the DBR region is to be formed. Then, the second
As shown in FIG. 2B, the cladding layer 10 and the cap layer 11
As shown in FIG. 2 (c), the cap layer 11 and the cladding layer 10 are etched into a mesa structure,
As shown in (d), a lower electrode 12-1 and an upper electrode 12-2 are formed. The temperature rise during the growth of the cladding layer 10 and the cap layer 11 also serves as the heat treatment after the ion implantation.

FIG. 3 is a sectional view taken along the length direction of the mesa structure of the semiconductor optical device obtained by the above method, and FIG. 4 is a sectional view taken along the line AB in FIG.

In this semiconductor optical device, a quantum well structure which is not disordered is used as a light emitting region 21, a waveguide 22 is formed in a waveguide region, and a phase adjustment region 23, a DBR region 24 and a PM modulation region 25 are formed in a refractive index control region. Form the AM modulation area in the absorption control area
Formed 26.

FIG. 5 is a diagram showing a change in energy band due to disordering. In this figure, (a) shows a state before disordering, (b) and (c) show a disordered state, and (d) shows a completely disordered state. As the disordering progresses, the effective well width decreases, the first quantum level changes,
Bandgap increases.

The non-disordered region maintains the band gap during crystal growth. Therefore, this region is used as the light emitting region 21. The oscillation wavelength of this light emitting region 21 is determined by its band gap.

In the absorption control region, the band gap is expanded due to disordering, and the absorption edge is correspondingly shifted to a wavelength side slightly shorter than the oscillation wavelength. Therefore, the absorption edge corresponding to the band gap shifts to the shorter wavelength side than the oscillation wavelength of the light emitting region 21. Therefore, it becomes transparent in the steady state. But,
When a current or voltage is applied to this region, the absorption edge shifts to the long wavelength side and the absorption coefficient changes. By utilizing this change in absorption coefficient, this region can be used as the AM modulation region 26.

Since the refractive index control region has a larger dose amount than the absorption region,
The degree of disorder is large. Therefore, the band gap is larger than that in the absorption control region, and the change in absorption coefficient due to current or voltage is small. However, when a current or voltage is applied, the refractive index changes due to the plasma effect, Stark shift and other effects. Utilizing this change in the refractive index, this area is adjusted to the phase adjustment area 23, the DBR area 24 and
It can be used as the PM modulation area 25.

In the waveguide region, disorder is further promoted and the band gap is further increased. Therefore, the absorption edge shifts to the short wavelength side, and the waveguide loss is small. Therefore, this region can be used as the waveguide 22.

The light emitting region 21, the phase adjusting region 23, the DBR region 24 and the structure around it form a variable wavelength Bragg reflection laser, the AM modulation region 26 and the structure around it form an AM modulator, and the PM modulation region 25 and Due to the surrounding structure
A PM modulator is formed. Regarding the operation of the tunable wavelength Bragg reflection type laser, for example, Murata, Mito, Kobayashi,
"Over 720 GHz (5.8 nm) frequency tuning by a 1.5 μm DBR laser with phase and Bragg wavelenx control
Regions ", Electronics Letters Vol. 23, No. 8, April 9, 1987 (S. Murata, I. Mito, K. Kobayash
i, "Over 720GHz (5.8nm) Frequency Tuning by a 1.5μ
mDBR Laser with Phase and Bragg Wavelength Contro
l Regions ", ELECTRONICS LETTERS, Vol.23, No.8,9th Apr
il 1987).

FIG. 6 shows the quantum well structure of an actually manufactured semiconductor optical device.
The Al mixed crystal ratio is shown.

In this example, GaAs is used as the active layer 5, and the GRIN layers 4 and 6 are used.
And Al _x Ga _1-x As is used as the guide layer 7. The width (quantum well width) Lz of the active layer 5 is 7.5 nm, the GRIN layer 4,
The width L _G of 6 is 150 nm, and the width Lg of the guide layer 7 is 50 nm. For this quantum well structure, Si is used as the implanted ion species.
(1) Waveguide region Injection energy 100 KeV dose amount S ₁ = 1 × 10 ¹² to 1 × 10 ¹⁵ cm ^-2 (2) Refractive index control region, absorption control region Injection energy 100 KeV dose amount S ₂ , Ion implantation was performed under the condition of S ₃ = 1 × 10 ¹¹ to 1 × 10 ¹³ cm ^-2 .

After this, the processing shown in FIG. 2 is performed, and the processing shown in FIGS.
It was confirmed that a semiconductor device having the structure shown in the figure was produced and that it actually operates. The temperature rise in the second growth step (Fig. 2 (b)) is 770 ° C and 40 minutes.

The table shows the measurement results of the waveguide loss with respect to the Si dose.

This table shows that substrate 1: GaAs, buffer layer 2: n-type GaAs, cladding layer 3: n-type Al _0.6 Ga _0.4 As, GRIN layer 4: undoped Al _x Ga _1-x As, undoped quantum well layer is disordered. Layer, GRIN layer 6: undoped Al _x Ga _1-x As, guide layer 7: undoped Al _0.3 Ga _0.7 As, clad layer 10: p-type Al _0.6 Ga _0.4 As layer structure, waveguide width: 6 μm The result is measured under the condition of 845 nm. In this case, Si
By setting the dose amount to about 1.0 × 10 ¹³ cm _-2 , a waveguide with low loss can be obtained.

In the above-mentioned reference example, an example in which the degree of disordering is controlled by the ion implantation amount is shown, but it can be controlled by the implanted ion species. For example, May, Venkatesan, Schwartz, Stoffel, Harbison, Heart, Florets,
"Comparative Studies of Ion Inducing Mixing of GaAs-AlAs Superiors", Applied Physics Letters Vol. 52, Vol. 18
Issue 1487-1479, May 2, 1988 (P. Mei, T. Venkatesa
n, SASchwarz, NGStoffel, JPHarbison, DLHart, an
d LAFlorez, ”Comparetive studies of ion-induced m
ixing of GaAs-AlAs superlattices ”, Appl.Phys.Let
According to t.52 (18), 2may 1988, pp.1487-1479), the degree of disorder can be controlled by the implanted ion species even under the same heat treatment conditions.

As such an example, in the quantum well structure shown in FIG. 6, the quantum well width Lz = 7.5 nm and the width L of the GRIN layers 4 and 6
_G = 100 nm, the width Lg of the guide layer 7 = 50 nm, and for this quantum well structure, (1) Waveguide region Implanted ion species Si implantation energy 75 KeV Dose amount S ₁ = 1 × 10 ¹² to 1 × 10 ¹⁴ cm ^-2 (2) Refractive index control area, Absorption control area Implanted ion species As Implantation energy 400 KeV Dose amount S ₂ , S ₃ = 1 × 10 ¹² 〜 1 × 10 ¹⁴ cm ⁻² Good.

In this way, if impurities are introduced after the first growth in which the disordered quantum well structure is close to the surface, the amount of impurities required for disordering can be reduced and the introduction of impurities can be simplified. Further, since the amount of impurities required for disordering is small and the impurities are present only in the layer formed by the first growth, an increase in waveguide loss due to impurities can be suppressed.

In the above reference example, a waveguide structure suitable for an optical element such as a curved waveguide or a directional coupler is not considered.
By dividing the crystal growth into two, it becomes possible to adopt a waveguide structure suitable for manufacturing an optical integrated circuit. Such an embodiment will be described below.

FIGS. 7 to 10 show a method of manufacturing a DBR laser, a variable wavelength DBR laser, a ROR laser, and a variable wavelength ROR laser, respectively, as a first embodiment to a fourth embodiment of the present invention. For ROR and tunable ROR lasers,
Plan views are shown in FIG. 9 (f) and FIG. 10 (f), respectively.

When manufacturing a DBR laser, a light emitting region and a DBR region are formed in the rib waveguide 20 in the same manner as the process shown in FIG. In this example, DBR regions are provided on both sides of the light emitting region. A diffraction grating 9 is provided in the DBR region to disorder the quantum well layer in that region. In FIG. 7 and FIG. 8, reference numeral 30 indicates an ion-implanted region. Upper electrode 12
As for -2, the light emitting region is left as it is, and the remaining part is used as the driving electrode 12-3.

In the case of a variable wavelength DBR laser, a light emitting region, a phase adjusting region and a DBR region are formed in the rib waveguide 20.
The upper electrode 12-2 is divided into the respective regions, and the driving electrode 12-3, the phase adjusting electrode 12-4 and the wavelength sweeping electrode 12 are divided.
Form -5.

The ROR laser has a structure in which the light emitting region 21 and the DBR region 24 are formed in separate waveguides, and the coupling region 40 is provided so that the electro-optical light is coupled between the separate waveguides. The DBR regions 24 are provided on both sides of the coupling region 40.

In order to make the oscillation wavelength of the ROR laser variable, a phase adjustment region 23 is provided in the waveguide on the side of the light emission region 21, the light emission region 21 is provided with a drive electrode 12-3, and the phase adjustment region 23 is provided with a phase adjustment electrode 12 -Four,
Wavelength sweep electrode 12-5 in DBR region 24 and the region in between
To provide.

For ROR, see Gazalinoff et al. (Rudolf F. Kazar
inov, Charles H. Henry and N. Anders Olsson, "Narrow-
Band Resonant Optical Reflectors and Resonant Tran
sformers for Laser Stabilization and Wavelength Di
vision Multiplexing ", IEEE J. Quantum Electron., Vol.
QE-23, No. 9, September 1987). Regarding a semiconductor laser using an ROR as an external cavity, a paper by Olson et al. (NAOlsson, CHHenr
y, RFKazarinov, HJLee, BHJohnson and KJOrlows
ky, "Narrow linewidth 1.5 μm semiconductor laser wi
th a resonant optical reflector ", Appl.Phys.Lett.51
(15), 12 Oct. 1987). further,
The applicant has already filed a patent for the technology of integrating a semiconductor laser and ROR on the same substrate (Japanese Patent Application No.
63-218981).

In the above embodiments, ²⁸ Si is used as the implanted ions, but the present invention can be similarly implemented by using other ions.

As for the structure of the semiconductor laser, any other structure such as a light confinement structure may be used as long as it uses a quantum well structure. Therefore, the present invention can be similarly implemented even when manufacturing a broad area semiconductor laser or a laser array.

〔The invention's effect〕

As described above, in the method for manufacturing a semiconductor optical integrated circuit of the present invention, crystal growth is divided into two steps, and impurity introduction and waveguide structure formation are performed between the first growth and the second growth. This makes it possible to combine the method of manufacturing an optical integrated circuit utilizing the disorder of the quantum well structure and the rib waveguide structure with good matching and a simple process. This is a unique advantage of the combination of both. With this combination, the manufacturing process is simplified, low-loss waveguides can be integrated, almost complete optical coupling between elements can be obtained, and a waveguide structure suitable for optical elements such as curved waveguides and directional couplers can be obtained. There is an effect that can be realized.

[Brief description of drawings]

FIG. 1 is a diagram showing a reference example of a method for manufacturing a semiconductor optical integrated circuit. FIG. 2 is a diagram showing a process after ion implantation. FIG. 3 is a sectional view of a reference example. FIG. 4 is a sectional view of a reference example. FIG. 5 is a diagram showing changes in energy band due to disordering. FIG. 6 is a diagram showing a band structure of a quantum well structure. FIG. 7 is a diagram showing a method of manufacturing a DBR laser according to the first embodiment of the present invention. FIG. 8 is a diagram showing a method of manufacturing a variable wavelength DBR laser according to a second embodiment of the present invention. FIG. 9 is a view showing a method of manufacturing the ROR laser according to the third embodiment of the present invention. FIG. 10 is a view showing a method of manufacturing a variable wavelength ROR laser according to a fourth embodiment of the present invention. 1 ... Substrate, 2 ... Buffer layer, 3, 10 ... Cladding layer, 4, 6 ... GRIN layer, 5 ... Active layer, 7 ... Guide layer, 8 ... Mask, 9 ... Diffraction grating, 11 …… Cap layer, 12-1 …… Lower electrode, 12-2 …… Upper electrode, 12-3 …… Drive electrode, 12-4 …… Phase adjustment electrode, 12-5 …… Wavelength reference electrode , 20 …… rib waveguide, 21 …… light emitting area, 22 …… waveguide, 23 …… phase adjusting area, 24 …… DBR area, 25 …… PM
Modulation region, 26 ... AM modulation region, 30 ... Ion-implanted region, 40 ... Coupling region.

Continued from the front page Application for application of Article 30 (1) of the Patent Act September 27, 1989 The Japan Society of Applied Physics held at Fukuoka Institute of Technology 1989 (1989) The 50th Autumn Meeting of Japan Society of Applied Physics Presented at the Lecture Meeting Patent Law Article 30 Clause 1 Application for Application The Journal of Applied Physics, The 50th Autumn Meeting of the Applied Physics Society of Japan, 3rd Volume (Heisei Era) (September 27, 1991) Published in Japan Society of Applied Physics, page 879, paper number 27P-ZG-5

Claims (5)

[Claims] 1. A method for manufacturing a semiconductor optical integrated circuit, wherein a quantum well structure is formed on a substrate, and at least a part of this quantum well structure is disordered by ion implantation and heat treatment. A first growth step of growing a guide layer adjacent to the first growth step, and a second growth step of forming another semiconductor layer on the semiconductor layer formed by the first growth step to form an optical device structure. Including the step of forming a rib waveguide structure and a diffraction grating in the guide layer by etching subsequent to the first growth step and performing the ion implantation, and the second growth after the ion implantation is completed. A method for manufacturing a semiconductor optical integrated circuit, comprising performing steps. 2. The method of manufacturing a semiconductor optical integrated circuit according to claim 1, wherein the Bragg reflection region is formed in a rib-shaped waveguide structure having a disordered quantum well structure. 3. The variable wavelength Bragg reflection region is formed in a rib waveguide structure in which a quantum well structure is disordered.
A method for manufacturing the semiconductor optical integrated circuit described. 4. The method of manufacturing a semiconductor optical integrated circuit according to claim 1, wherein the resonant optical reflector is formed in a rib waveguide structure having a disordered quantum well structure. 5. The method of manufacturing a semiconductor optical integrated circuit according to claim 1, wherein the variable wavelength resonant optical reflector is formed in a rib waveguide structure having a disordered quantum well structure.