JPH04151886A - Optical semiconductor device - Google Patents

Abstract

PURPOSE:To make it possible to obtain an optical coupler which is easy to process, excellent in reliability and reproducibility and suitable to a semiconductor optical integrated circuit by forming a region which has a reflectance in a part of waveguide passage structure so as to divide the wave front of waveguide optical field distribution in the horizontal direction. CONSTITUTION:An epitaxial film, which comprises a first clad layer 2, an active layer 3, a second clad layer 4 and a cap layer 5, is arranged to grow on a substrate 1 successively where a ridge section is formed by carrying out reactive ion beam etching and further focusing ion beam etching is carried out so as to process the end face which reaches the lower part of the active layer 3, thereby forming a slit groove 10. The slit groove 10 is formed to proceed from the center of the branch/junction of a ridge waveguide passage in the direction of waveguide of light wave, say, at an angle of 45 deg., thereby constituting a total reflection mirror. This total reflection mirror forces the light wave 11 which has entered the active layer 3 to be branched at the branch/ junction section into light wave 12 (reflected) and light wave 13 (transmitted) virtually at the same rate. It is, therefore, possible to obtain an optical coupler which is easy to process, and excellent in reliability and reproducibility.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to optical semiconductor devices used in optoelectronic integrated circuits and the like required in the field of optical communication, particularly channel waveguide structures in which optical couplers are configured. The present invention relates to an optical semiconductor device having the present invention.

[Prior Art] Conventionally, as an optical coupler, an interference laser, which is a type of composite resonator laser, including a Y-branch type optical coupler 100 as shown in FIG.
et al, “Sem1conductor i
terferometric 1aser”App
l, Phys, Lett, 41.2. pp, 112-1
14 (July 1982)).

Furthermore, an interference type laser including X-branch type optical couplers 110a and 110b as shown in FIGS. 11(a) and 11(b) is also known (J, Salzman et al.
, ”Crossco
u p 1 e d c a vity
semiconductor 1aser”
Appl, Phys, Lett, 52. L.O., pp.
, 767-769 (March 1988
)reference). Here, R, ~R4 are resonance surfaces, L + ~L, 4
indicate the resonator length, respectively.

[Problems to be Solved by the Invention] However, the conventional example described above has the following drawbacks. First, in the case of the example including the Y-branch type optical coupler shown in FIG. However, since the element length is 1 mm or more, the size is too large compared to other optical devices, making it difficult to integrate.

In addition, in the case of the example including the X-branch type optical coupler shown in FIG. 11, the process accuracy such as positional accuracy and depth accuracy required for the In other words, the mode of branching and merging is determined by how the X-branch is formed with respect to the field distribution of light waves propagating through the optical waveguide.
Strict precision is required for the process.

Therefore, in view of the above problems, an object of the present invention is to provide an optical semiconductor device including an optical coupler that is easy to process, has excellent reliability and reproducibility, and is suitable for semiconductor optical integrated circuits.

[Means for solving the problem] In the optical semiconductor device of the present invention that achieves the above object,
A coupler section for coupling light waves to a single channel waveguide structure is constructed on the semiconductor substrate. (Wavefront division of the waveguide optical field distribution in the vertical direction or depth direction may also be carried out) The waveguide structure may include an active layer, the coupler section may include a slit-shaped section (formed only in a part of the waveguide structure in the horizontal direction) beyond the active layer, or the coupler section may include a slit-shaped section (formed only in a part of the waveguide structure in the horizontal direction). is formed by forming a part of the waveguide structure (with respect to the horizontal direction) with a different processing depth, and the coupler part is a T-shaped part of the waveguide structure,
The coupler section may be provided at an intersection point or a non-intersection section such as an X-type or a Y-shape (it may be provided at a non-intersection section to form a composite resonator laser), or the coupler section may be provided in the above-mentioned manner so as to branch light waves in multiple directions. It may include multiple parts with different reflectances, or the coupler part may be configured by forming a slit groove that becomes a total reflection mirror (45° mirror) in a part of the part where the optical waveguide structure branches and merges (in the horizontal direction). do.

[Example] FIG. 1 shows an optical semiconductor device including a T-branch coupler according to a first embodiment of the present invention, in which (a) is a schematic top view, and (b) is a schematic top view of A in FIG. -A' sectional view, the same figure (c) is the first
The sectional view taken along the line B-B' in the figure, and FIG. 1(d) is an enlarged view of the main part of FIG. 1(a).

First, the process procedure of the first embodiment will be explained.

An epitaxial film consisting of a first cladding layer 2, an active layer 3, a second cladding layer 4, and a cap layer 5 is grown in order on a substrate 1 by molecular beam epitaxy (MBE). A buffer layer made of GaAs may be formed at the interface with the substrate 1 if necessary. The film thickness of the first and second cladding layers 2.4 is 1μ
m, and the thickness of the active layer 3 was approximately 0.1 μm. next,
A desired pattern (T-shaped pattern in the illustrated example) with a width of 3 μm is formed on the top by photolithography, and a ridge portion (see FIG. 1(b)) is formed by reactive ion beam etching (RIBE). A striped structure was adopted to perform lateral confinement (Fig. 1 (a), (b)).
)reference).

Furthermore, by using a focused ion beam etching (FIBE) method, the end face of the active layer 3 is processed down to the bottom of the slit groove 1.
0 as shown in FIG.
(See Figure 1(c)) At an angle of φ = 45° from the center of the branching/merging part of the ridge waveguide to the light wave guiding direction (see Figure 1(c))
(see Figure (d)), forming a 45° mirror, that is, a total reflection mirror.

Next, the end face of this element was cleaved to allow light to enter and exit.

By this total reflection mirror, the light wave 11 incident on the active layer 3 in the direction B-B' in FIG. At this time, the light wave 12 is totally reflected by the slit groove 10 in the lower half of the branching/merging section shown in FIG.
The light wave 13 is generated by passing through the upper half of this branching/merging section as it is.

The branching/merging section, that is, the optical coupler in this example is as follows:
Since this forms a branching coupler of wavefront splitting type in the horizontal direction (the direction of extension of the substrate l on which the channel waveguide structure is formed), the machining depth of the end face of the slit groove 10 is equal to that of the active layer 3.
(The waveguide layer that is the center of the channel waveguide structure) can be etched (there is no need for precise depth control. Also, by controlling the position of the 45° mirror, it is possible to The transmission/reflection ratio can be set to a desired value.

In this embodiment, a ridge waveguide has been described as the channel waveguide structure, but a refractive index waveguide can also be used.

2 and 3 show a modification of the first embodiment, and in the T-type coupler of FIG. 2, the slit groove 20 is located at a position symmetrical to that of the first embodiment, that is, in the first embodiment, it is a transparent part. In the T-type coupler shown in Fig. 3, the slit groove 21 is formed at the center of the branching/merging section at an angle of 45° with respect to the waveguide direction. .

FIG. 4 shows a second embodiment of the Y-branch coupler, in which slit grooves 25 are formed as shown in the figure, and light waves are branched and merged as shown by arrows in FIG.

FIG. 5 shows a third embodiment. The third embodiment is an example in which the present invention is applied to an optical node that includes a transmitting section and a receiving section.

6 and 7 show a sectional view taken along line AA' and line BB' in FIG. 5, respectively. This embodiment is an example in which the processed end surface of the first embodiment is used in an integrated coupler.
are slit grooves formed by FIB, 30a, 30
b is an amplification region equipped with an optical amplifier (not shown) that has a gain by current injection; 31a and 31b are photodetection regions equipped with photodetectors operated by applying a reverse bias;
8a and 38b are AR coats formed on the end faces;
1゜Q 3 + Z r O2 as electron beam (E
B) Deposited by vapor deposition. 39 is a waveguide.

The waveguide 39 is formed in a cross shape on the upper surface, and the waveguide portions in the vertical direction from the center are amplification regions 30a and 30b.
The left and right directions are defined as detection areas 38a and 38b. The slit groove 29 is formed approximately at the center of the waveguide 39 so that its elongate direction is inclined at 45 degrees with respect to each longitudinal direction of the cross-shaped waveguide 39 and extends from the lower left end to the center. It is provided. As a result, the waveguide 39
The central portion is an integrated coupler portion 32 indicated by a broken line.

Next, the process procedure of the third embodiment will be explained.

First, as can be seen from FIGS. 6 and 7, n-type GaAs 42 as a buffer layer is sequentially deposited on an n-type GaAs substrate 41 using the MBE method. g m thickness, n-type A 10.4 Gao as cladding layer, c As43 1.5
It was formed with a thickness of ILm. Next, undoped GaΔ5 (10
0 person thickness), A 10.2 G an, a A S
(30 layers thick) 4 times (repeatedly layered, and finally 1 layer of GaAs)
The active layer 44 having a multi-quantum well structure is formed by stacking the active layer 44 to a thickness of 0.000 nm, and on top of this, a p-type A 1 (1,
4'Gao6A S 45 was formed to a thickness of 1.51jm, and GaAs46 as a cap layer was formed to a thickness of 0.5μm.

Next, a desired cross-shaped mask pattern (pattern of the waveguide 39) with a width of 3 μm is formed on this semiconductor laser wafer by a photolithography process, and an active layer 44 is formed through the mask by the RIBE method in a chlorine gas atmosphere.
The striped structure was etched to 0.2 μm in front of the ridge to form a ridge to provide lateral confinement.

Next, S is applied onto the laser wafer on which this ridge has been formed.
An insulating film 47 (thickness: 1200 nm) made of iN was formed by plasma CVD, a resist was applied to the SiN insulating film 47-F, and an O+tm coating was applied. After that, 4 Pa
By RIBE method in 02 atmosphere, only the deposited resist is removed and the SiN insulating film 47 in the ridge area
RI in a CF4 gas atmosphere of 4 Pa
B IE method was performed to expose the top of the ridge.
The insulating film was selectively etched. Thereafter, the remaining resist was removed by the RIBE method in an 02 atmosphere of 4 Pa.

Next, the surface oxide film formed on the top of the ridge is wet-etched with hydrochloric acid to form a current injection window, and then a Cr-Au ohmic electrode 48 is formed as an upper electrode by vacuum evaporation, and the GaAS substrate 41 is wrapped. de1
After cutting to a thickness of 00 μm, an AuGe-Au electrode was deposited as an n-type ohmic electrode 49. And p
Heat treatment was performed to establish ohmic contact between the type and n-type electrodes, resulting in a ridge-type semiconductor element.

Furthermore, FI using Ga + ions with an accelerating voltage of 40 KeV
By etching using Method B, the slit 29 of the coupler portion 32 was formed in the manner shown in FIG. The grooves 1 to 29 are as described above (inclined, and the depth is lower than the active layer 44).
m deep, and the inclination angle of the groove was 85° or more (see Figure 7).Finally, a resonant surface was formed by cleaving,
A1゜03+ by EB (electron beam) evaporation
ZrO2 was deposited to form AR coats 38a and 38b, which were separated by scribing, and the electrodes were taken out by wire bonding.

Next, the operation will be explained. The incident light wave 33 is
The incident wave 34 is amplified in the amplification region 30a and enters the integrated coupler section 32, where it is separated into a transmitted wave 36 and a reflected wave 35 as described in the embodiment of FIG. The reflected wave 35 is photoelectrically converted in the photodetection area 31a of the incident wave 33, and the light wave 33
Monitoring of the signal components within is performed. On the other hand, the transmitted wave 36 is further amplified in the amplification region 30b, and the output light 3
It is output as 7. When the light enters from the opposite direction (via the AR coat 38b), monitoring is performed in the photodetection region 31b, and other amplification operations are the same.

If the optical amplification factor (gain) is set in such a way as to compensate for the loss of the coupler 32 and the end-coupling loss, it appears to function as a lossless light-receiving optical node and can be connected in multiple stages.

Although the above description has been made on the assumption that the optical node performs only reception, it is possible to realize an optical node capable of transmitting and receiving by providing a transmitting section and a receiving section.

FIG. 8 shows a fourth embodiment of the present invention, and FIG. 9 is a sectional view taken along the line AA' of the coupler section in FIG.

In this embodiment, the optical amplifying section 8 arranged in the path line direction
0a and 80b are formed, and branch waveguides 82 and 83 to the receiving section and transmitting section intersect with the waveguide in the path line direction. The branch coupler 88 performs branch coupling by forming an eight-shaped groove 81 at the intersection. The ratio of branching and coupling can be adjusted by controlling the optical electromagnetic field distribution and the length of the waveguide (position control). To form such grooves 81, microfabrication techniques such as etching using a Ga focused ion beam (FIB) and etching using a reactive ion beam (RIT'3E) can be used.

The parts other than the branching cup and the bra part 88 can be realized with the same structure as the third embodiment.

The wing type branching coupler 81 in this embodiment has different branching ratios into the left and right branching waveguides 82 and 83. Usually, in order to improve the coupling toward the receiving section, it is preferable to arrange the upper part (the narrower side) of the wing shape toward the receiving section side branch waveguide 82. If the branching ratio of the groove is -3 dB and excess loss is ignored, the branching ratio to the receiver side is -3 dB and the branching ratio to the transmitter side is -6 dB. In addition, when light enters the lower part (open side) of the wing type, there is a reflection of -6 dB, so it is necessary to insert an isolator to stabilize the frequency on the transmitter side (not shown). ).

In FIG. 8, 83a is the AR coat that the end face of the fiber 91 comes into contact with, 83b is the AR coat that the end face of the fiber 92 is in contact with, 83c is the AR coat that the fiber 94 on the receiving side is in contact with, and 83d is the AR coat on the transmitting side. The operation of the fourth embodiment will be described in which the AR coat is in contact with the fiber 95 of FIG.

Optical fiber 91. The light wave that has entered through the AR coat 83a enters the integrated coupler section 88 as an incident wave that has been amplified by the amplification section 80a, and is transmitted and reflected by the slit groove 81 and the unfilled portion, so that the light wave is directed to the receiving section on the left side. waveguide 8
2, the light wave entering the waveguide 83 to the transmitting section on the right side (this is blocked by the above-mentioned isolator), and the amplifying section 80
It is split into a light wave entering b. Waveguide 82. fiber 9
The light wave that enters the receiving section via the optical fiber 4 is detected as a signal there, and the light wave that enters the amplifying section 80b is further amplified there and output to the fiber 92. The same applies to the light waves incident from the opposite direction (via the Al1 R coat 83b). The light waves entering the coupler section 88 from the transmitting section via the fiber 95 and the waveguide 83 are the same (transmitted and reflected by the slit groove 81 and the part without grooves, and the waveguide 82
．． 83 (the light wave reflected by the waveguide 83 is blocked by the isolator) and the light wave enters the amplification sections 80a and 80b. The light wave entering the receiving section via the waveguide 82 and the fiber 94 is monitored for signal components, and then sent to the amplifying section 80.
Light waves entering a and 80b are amplified there and output to fibers 91 and 92, respectively.

In the above embodiments, an example was shown in which the resonant surface of the laser was formed by cleavage, but an etched end surface formed by etching such as RIBE method or dry etching such as reactive ion etching may also be used.

In addition, in the above embodiments, the active region is formed with an MQW (multiple quantum well structure), but the present invention is not limited to this, and the active region is formed with a DH (double hetero) structure, a 5QW
(Hyaku-Quantum Well) structure etc. may be used.

In addition, in the above embodiments, GaAs system was used and edge wave structure was used as an example, but BH (buried heterostrive) structure, CPS structure (channel substrate planar strive), and current light confinement It is also effective for refractive index waveguide type lasers, such as structures in which the absorption layer is provided near the active layer.It is also effective for gain waveguide type lasers, such as striped electrode type and proton bombarded type lasers. .

In addition, the material of the semiconductor laser is GaAs/AlGa.
In addition to As-based, I nP ・I'nGaAsP-based AIGa
Needless to say, the same applies to materials such as InP.

[As described in detail, the present invention is configured to perform wavefront division of the field distribution at least in the horizontal direction, so the degree of wavefront division in the depth direction is set as strictly as shown. (This means that couplers such as Y branch and
Compared to the conventional example shown in the figure, it is easier, has superior reliability and reproducibility, and improves yield. Furthermore, it has become possible to realize an optoelectronic integrated device in which an optical coupler is configured.

[Brief explanation of the drawing]

FIGS. 1(a), (b), (c), and (d) are the first embodiments of the present invention.
A plan view of the embodiment, an A-A' cross-sectional view, a B-B' cross-sectional view, a partially enlarged view, and FIGS. 2 and 3 are views of modifications of the first embodiment,
4 is a plan view of the second embodiment, FIG. 5 is a plan view of the third embodiment, FIG. 6 is a sectional view taken along line AA' in FIG. 5, and FIG.
8 is a plan view of the fourth embodiment, FIG. 9 is a sectional view taken along A-A' in FIG. 8, and FIGS. 10 and 11 are views showing the conventional example. be. l, 41...Substrate, 2.4.43.45...
・Clad layer, 3.44...Active layer 5.46...
... Cap layer, 10.20.21.25.29.8
1...Slit groove, 47...Insulating film, 48
．． 49...electrode, 80a, 80b...'-light beam width portion 82, 83---waveguide, 83a, 83b
, 83c83d...AR coat, 88...
Coupler part, 91.92.94.95...Optical fiber

Claims (1)

[Claims] 1. A coupler section for coupling light waves is configured in a channel waveguide structure configured on a semiconductor substrate,
An optical semiconductor device characterized in that the coupler portion is formed by forming portions with different reflectances in a part of the waveguide structure so as to perform wavefront division of the waveguide optical field distribution in at least the horizontal direction. 2. Claim 1, wherein the channel waveguide structure includes an active layer.
The optical semiconductor device described above. 3. The optical semiconductor device according to claim 2, wherein the coupler portion includes a slit-shaped portion extending beyond the active layer. 4. The optical semiconductor device according to claim 1, wherein the coupler portion is formed by forming a portion of a channel waveguide structure with a different processing depth. 5. The optical semiconductor device according to claim 4, wherein the portions of the coupler portion having different processing depths are processed into slit shapes. 6. The optical semiconductor device according to claim 1, wherein the coupler portion is provided at an intersection of the channel waveguide structures. 7. Claim 6: The intersection portion is T-shaped, X-shaped, or Y-shaped.
The optical semiconductor device described above. 8. The coupler part has at least one slit groove formed at the intersection part that extends halfway or partially in the horizontal direction at a predetermined angle with respect to the optical waveguide direction. 7. The optical semiconductor device according to claim 6, comprising: 9. The channel waveguide structure is formed in plurality including intersection parts forming coupler parts, one set of which becomes an optical amplification region, and the other set is connected to at least one of a transmitting part and a receiving part. 2. The optical semiconductor device according to claim 1, which constitutes an optical node exhibiting branching, merging, and amplifying functions. 10. The optical semiconductor device according to claim 1, wherein the coupler portion includes a plurality of portions having different reflectances so as to branch light waves in a plurality of directions.