JPH10117045A - Optical semiconductor element - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce an influence of a refractive index difference caused by photoabsorption between an n-type semiconductor substrate and a high-resistance embedded layer to be exerted on the photointensity distribution between an n-type semiconductor substrate and a high-resistance embedded layer. SOLUTION: A tapered waveguide part in which a size of a core layer 2, consisting of more than one layer for waveguiding of light inside a resonator is continuously decreased to an outgoing end face 5 of light, is integrated on an n-type semiconductor substrate 1. Now, along with at least making both sides of the core layer 2 to come in contact with a high-resistant semiconductor layer 4, out of the boundary surface between the n-type semiconductor substrate 1 and the high-resistant semiconductor layer 4, a distance between a part almost in parallel with the main surface of the n-type semiconductor substrate 1 at least in the outgoing end face 5 and the lower end of the core layer 2 is made not less than 2μm.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical semiconductor device, and more particularly, to an optical semiconductor device such as a semiconductor laser in which a spot size converter used for optical fiber communication is integrated.

[0002]

2. Description of the Related Art In recent years, since optical fiber communication can transmit a large amount of information with one optical fiber, its application range has been expanded from a conventional trunk system to a subscriber system or a network such as an optical LAN. It is requested to go.

[0003] In order to meet such demands, cost reduction is indispensable. In particular, optical coupling between an optical semiconductor element and an optical fiber in an optical module has become a major problem.

In order to solve such a problem, an optical semiconductor device in which a spot size converter having a structure in which the thickness or width of a core layer for guiding light is changed in a tapered shape toward an emission end face is integrated. In particular, a semiconductor laser with a spot size converter has been proposed. This semiconductor laser with a spot size converter can perform optical coupling with high coupling efficiency without using a lens and has a large margin of positional accuracy. Therefore, it is expected as an element that can simplify optical coupling.

[0005] As the semiconductor laser with a spot size converter, a semiconductor laser in which a spot size converter having a structure in which the thickness of a core layer for guiding light is reduced in a tapered shape toward an emission end face is required. Then H. Kob
ayashi et al. , IEEE Photo
n. Tech. Lett. , Vol. 6, 1994, p
p. 1080-1081, Sugie et al., "Butt-Joi"
1.3μmL with nt type selective growth spot size conversion
D ", 1995 IEICE General Conference Proceedings, p. 465, SC-4-5, or Y.I. Thom
ori et al. , Electronics Le
ters, vol. 31, 1995, p. 1069
-1070) and a semiconductor laser in which a spot size converter having a structure in which the width of a core layer for guiding light is reduced in a tapered shape toward an emission end face is integrated (if necessary, H.264).
Fukano, et al. , Electronics
Letters, vol. 31, No. 7,199
5, pp. 1439-1440).

Here, referring to FIG. 6, an example of a conventional semiconductor laser with a spot size converter having a structure in which the thickness of the former light waveguide core layer is tapered toward the emission end face. Will be described. FIG. 6A shows a semiconductor laser in which a tapered waveguide is formed by a butt joint by regrowth (if necessary, Y.To.
hmori, et al. , Electronics
Letters, vol. 31, 1995, p. 10
FIG. 69-1070).
After growing the MQW active layer on the P substrate 51, a part thereof is selectively removed by etching.

Next, after a tapered waveguide is regrown in the removed portion, a p-type InP cladding layer 54 is grown, and then a laser portion 52 and a tapered waveguide portion 53 are formed by mesa etching in a stripe shape. After that, the mesa stripe is buried by the high resistance InP burying layer 55.

FIG. 6B is a front view showing an emission end face 56 of the semiconductor laser with a spot size converter shown in FIG.
The spot size is enlarged at the emission end face 56, and the beam emission angle is reduced to about 1/3 as indicated by the light intensity distribution 57 shown by the broken line in the figure.

In this case, since a high resistance semiconductor layer is used for the buried structure, a pn current block structure is used (for example, the above-mentioned H. Kobayashi et al.).
l. , IEEE Photon. Tech. Let
t. , Vol. 6, 1994, p. 1080-108
1), there is an advantage that the modulation band of the laser can be increased and the jitter at the time of rising of the signal at the time of zero bias modulation can be reduced.

[0010]

However, in the case of the semiconductor laser with a spot size converter shown in FIG. 6, since almost no carriers are present in the high-resistance InP buried layer 55, light is absorbed by free carriers. And the electron concentration is 10 ¹⁸ cm ^-3.
As described above, a difference in the refractive index occurs between the n-type InP substrate 51 and the n-type InP substrate 51 having a large reduction in the refractive index.

In the case of an ordinary semiconductor laser, since the spot size is small, the intensity of the guided light is small in a portion where such a difference in refractive index occurs, and the core layer has a gain. This difference in the refractive index has little effect on the light intensity distribution at the emission end face.

Referring again to FIG. 6B, however, in the case of a semiconductor laser with a spot size converter in which the intensity distribution 57 of the light propagating through the waveguide in the vicinity of the emission end face 56 is widened, this difference in refractive index causes
Light does not spread much to the n-type InP substrate 51 having a smaller refractive index, and the light intensity distribution 5 is asymmetric with respect to the vertical direction.
It becomes 7.

As a result, there is a problem that the effect of improving the efficiency of coupling to an optical waveguide such as an optical fiber is reduced by reducing the thickness of the core layer toward the emission end face 56 to increase the spot size. Note that when a p-type semiconductor substrate is used, the effective mass of holes is larger than that of electrons, and the decrease in the refractive index due to light absorption is small.

Accordingly, an object of the present invention is to reduce the influence of a difference in refractive index on light intensity distribution caused by light absorption between an n-type semiconductor substrate and a high-resistance buried layer.

[0015]

FIG. 1 is an explanatory view of the principle configuration of the present invention. Referring to FIG. 1, means for solving the problems in the present invention will be described. 1 (a) and 1 (b) (1) According to the present invention, the size of the core layer 2 composed of one or more layers for guiding light continuously increases toward the light emitting end face 5 in the resonator. In an optical semiconductor device in which the reduced tapered waveguide portion is integrated on the n-type semiconductor substrate 1, at least both side surfaces of the core layer 2 are in contact with the high-resistance semiconductor layer 4, and the n-type semiconductor substrate 1 A portion substantially parallel to the main surface of the n-type semiconductor substrate 1 in the boundary surface with the high-resistance semiconductor layer 4 is at least 2 μm from the lower end of the core layer 2 at the emission end surface 5.
m or less.

As described above, of the boundary surface between the n-type semiconductor substrate 1 and the high-resistance semiconductor layer 4, a portion substantially parallel to the main surface of the n-type semiconductor substrate 1 is at least at the light-emitting end face 5,
To be at least 2 μm below the lower end of the
That is, the height of the mesa formed on the n-type semiconductor substrate 1 is 2 μm.
With the above, the n-type semiconductor substrate 1 having a small refractive index can be kept away from the core layer 2, whereby the phenomenon that the light intensity distribution 6 becomes asymmetric can be reduced.

Further, in order to greatly improve the coupling efficiency with a waveguide such as an optical fiber, it is necessary to enlarge the spot size at least twice, and for that purpose, the spot size in the gain region of 1 μm is required. 2μ of twice (radius)
It is necessary that a large refractive index difference does not occur within m, so that the height of the mesa formed on the n-type semiconductor substrate 1 needs to be 2 μm or more.

(2) Further, according to the present invention, in the resonator, the size of the core layer 2 composed of one or more layers for guiding light continuously decreases toward the light emitting end face 5. In an optical semiconductor device in which a waveguide portion is integrated on an n-type semiconductor substrate 1, an n-type semiconductor layer 7 having a carrier concentration of 5 × 10 ¹⁷ cm ⁻³ or less is provided at least directly below a core layer 2 and at least a core is provided. A feature is that both side surfaces of the layer 2 and the n-type semiconductor layer 7 are in contact with the high-resistance semiconductor layer 4.

As described above, by providing the n-type semiconductor layer 7 having a carrier concentration of 5 × 10 ¹⁷ cm ⁻³ or less and a small change in the refractive index between the core layer 2 and the n-type semiconductor substrate 1,
Light can be spread to the n-type semiconductor layer 7, and the coupling efficiency with the waveguide can be improved.

(3) The present invention is characterized in that, in the above (2), the thickness of the n-type semiconductor layer 7 is 2 μm or more.

As described above, the carrier concentration provided between the core layer 2 and the n-type semiconductor substrate 1 is 5 × 10 ¹⁷ cm ⁻³ or less.
By setting the thickness of the mold semiconductor layer 7 to 2 μm or more,
The light intensity distribution 6 can be made more symmetric, and the coupling efficiency with the waveguide can be greatly improved.

(4) Further, according to the present invention, in any one of the above (1) to (3),
It is characterized in that the thickness of the core layer 2 is continuously reduced toward the light emitting end face 5.

As described above, by devising the manufacturing process, the beam spot can be expanded by the tapered waveguide portion in which the thickness of the core layer 2 is continuously reduced toward the light emitting end face 5. In addition, light absorption can be reduced by increasing the effective bandgap of the tapered waveguide portion by the quantum effect.

(5) Further, according to the present invention, in any one of the above (1) to (3),
The width of the core layer 2 is continuously reduced toward the light emitting end face 5.

As described above, the size of the core layer 2 may be changed by continuously decreasing the width of the core layer 2 toward the light emitting end face 5 so as to enlarge the beam spot. In this case, the film forming process can be simplified.

(6) Further, according to the present invention, in the above (4) or (5), the number of core layers 2 of the tapered waveguide portion is:
It is characterized in that the number of core layers 2 in the gain region is the same.

As described above, by devising the manufacturing process, the optical semiconductor with the spot size converter is formed by the tapered waveguide portion and the gain region of the same core layer 2, that is, by the core layer 2 formed in a series of steps. An element can be formed, and the efficiency is improved as compared with the Butt-Joint type.

(7) Further, according to the present invention, in any one of the above (1) to (6), a p-type cladding layer 3 is provided on the core layer 2 and an electrode provided on the p-type cladding layer 3 side. The width of the contacting p-type semiconductor layer is wider than the width of the core layer 2.

As described above, by making the width of the p-type semiconductor layer in contact with the electrode, that is, the width of the contact layer larger than the width of the core layer 2, it is possible to reduce the element resistance while maintaining the current confined state. .

(8) In the present invention, the n-type semiconductor substrate 1 according to any one of the above (1) to (7),
an nP substrate, and the core layer 2 is made of one or more InGa
It is characterized by including an AsP layer.

Such an optical semiconductor device with a spot size converter becomes particularly important in an InGaAsP / InP system.

(9) The present invention is characterized in that, in the above (8), the high resistance semiconductor layer 4 is an Fe-doped InP layer.

As described above, in the InGaAsP / InP optical semiconductor device, the Fe-doped InP layer is most preferable as the high-resistance semiconductor layer 4 in which the mesa stripe is embedded.

[0034]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Here, a first embodiment of the present invention will be described with reference to FIG. FIG. 2 is a perspective view of a semiconductor laser with a spot size converter according to the first embodiment of the present invention. First, the electron concentration is 1.0 to 3.0 × 10 ¹⁸ cm ⁻³ , for example. 2.0 × 10
A selective growth mask (not shown) having a stripe-shaped opening is provided on the surface of an n-type InP substrate 11 of ¹⁸ cm ^-3 , and an optical guide layer 12, a quantum well layer 13, an optical guide layer 14, and a p-type I
The nP cladding layer 15 and the p-type InGaAs contact layer 16 are continuously grown.

At this time, the width of the stripe-shaped opening provided in the selective growth mask is adjusted so that the width gradually increases toward the emission end face 20 in a region of 200 μm in length where the tapered waveguide portion 18 is formed. And, on the other hand, length 30
In the region where the laser portion 17 of 0 μm is formed, the openings are made uniform and narrow so that the light guide layer 12, the quantum well layer 13 and the light guide layer 14 constituting the core layer are formed.
The thickness of the output end face 30 in the tapered waveguide portion 18 is
The thickness of the laser section 17 is reduced to 1/3 in a tapered shape over 200 μm, and the laser section 17 has a flat structure.

In the first embodiment,
As a thickness in a region where the laser portion is formed, the light guide layers 12 and 14 have a thickness of 50 to 150 nm, for example, 100 nm.
The quantum well layer 13 is composed of an InGaAsP layer having a wavelength composition of 1.1 μm, and the quantum well layer 13 has a thickness of 10 nm.
InGaAsP barrier layer having a wavelength composition of 1 μm and a thickness of 6 nm
InGaAsP well layers having a wavelength composition of 1.35 μm are alternately deposited so that five well layers are formed, and the thickness of the p-type InP cladding layer 15 is set to 1500 to 25.
00 nm, for example, 2000 nm (2 μm), and the thickness of the p-type InGaAs contact layer 16 is 200 to 100.
0 nm, for example, 500 nm (0.5 μm).

Next, a thickness of 0.2 to 0.5 μm is
For example, after depositing a 0.3 μm SiO ₂ film (not shown), the Si
The O ₂ film is removed, and then dry etching is performed using the SiO ₂ film as a mask to form p-type InGaAs.
The exposed portion of the s-contact layer 16 is removed.

This is because a 200 μm tapered waveguide section 18
In the vicinity of the laser section 17, light absorption occurs unless gain is provided, so that it is necessary to pass a current over a width of about 50 μm.
The SiO ₂ film is removed over 0 μm.

Next, after removing the SiO ₂ film, a new thickness of 0.2 to 0.5 μm, for example, 0.3 μm
a SiO ₂ film (not shown) having a width of 0.8 to
2.0 μm, for example, 1.5 μm stripe-shaped Si
After patterning on an O ₂ mask (not shown), 70 to 150 μm, for example, 120 μm from the emission end face 20 side.
The thickness of the SiO ₂ mask is reduced to about 1/3 over the range to form a thin film portion, and the SiO ₂ mask is used as a mask to perform mesa etching, so that the n-type InP substrate 11 has a thickness of 2 μm or more, for example, , 2.5 μm.

[0040] Then, by etching the SiO ₂ mask maskless removal of the thin film portion, using the remaining SiO ₂ mask as a selective growth mask, the thickness of the mesa top, 3.0～5.0Myuemu, e.g. The Fe-doped high-resistance InP buried layer 19 is grown to have a thickness of 4.0 μm, and the mesa of the tapered waveguide portion 18 is changed to the high-resistance InP buried layer 1.
Embed with 9.

Next, although not shown, p-type InGa
A p-side electrode is provided on the As contact layer 16 and n-type InP
By providing the n-side electrode on the back surface of the substrate 11, the basic structure of the semiconductor laser with a spot size converter is completed.

In this case, since the height of the mesa provided on the n-type InP substrate 11 is 2.5 μm, that is, 2.0 μm or more, the refractive index is significantly reduced due to light absorption by free carriers. Since the influence of the type InP substrate 11 is reduced, light is symmetrical in the tapered waveguide portion 18 and
It can be sufficiently widened, thereby greatly improving the coupling efficiency with a waveguide such as an optical fiber.

As is apparent from the drawing, on the emission end face 20 side constituting the tapered waveguide section 18, the high resistance InP made of the same Fe-doped InP all around the mesa is used.
Since it is buried by the burying layer 19, there is no difference in the refractive index that causes light scattering, the far-field image is not disturbed by the scattered light, and the scattering loss is reduced. I _{th is} also reduced.

Next, a second embodiment of the present invention will be described with reference to FIG. FIG. 3 is a perspective view of a semiconductor laser with a spot size converter according to a second embodiment of the present invention.
Just as in the embodiment, the electron concentration is 1.0 to 3.0.
× 10 ¹⁸ cm ^-3 , for example, 2.0 × 10 ¹⁸ cm ^-3 n
After providing a selective growth mask (not shown) having a stripe-shaped opening on the surface of the type InP substrate 11, growing the optical guide layer 12, the quantum well layer 13, and the optical guide layer 14, the thickness is 100 to 700 nm. , For example, 300 nm p
The type InP cladding layer 15 is continuously grown.

Then, a thickness of 0.2 to 0.5 μm is applied on the entire surface,
For example, a 0.3 μm SiO ₂ film (not shown) is deposited and patterned on a stripe-shaped SiO ₂ mask (not shown) having a width of 0.8 to 2.0 μm, for example, 1.5 μm. Mesa etching is performed using the SiO ₂ mask as a mask, and the n-type InP substrate 11 is
For example, 2.5 μm is removed.

Next, using this SiO ₂ mask as a selective growth mask, in the same process as that of the SI-PBH type laser, a Fe-doped high-resistance InP buried layer 21 and a thickness of 50 nm are formed.
An n-type InP current confinement layer 22 of 0 to 100 nm, for example, 700 nm is sequentially grown.

Next, after removing the SiO ₂ mask, the thickness of the n-type InP
000 nm, for example, 4000 nm, the p-type InP cladding layer 23 and 200 to 1000 nm,
For example, a 500 nm p-type InGaAs contact layer 2
4 is grown sequentially.

Next, a new thickness of 0.2 to 1.0 μm,
For example, by depositing and patterning 0.5 μm of SiO ₂ , an insulating film 25 having an opening corresponding to a stripe-shaped mesa is provided on the laser unit 17 side, and then a p-side electrode 26 and an n-side electrode 27 are formed. With this arrangement, the basic structure of the semiconductor laser with a spot size converter is completed.

Also in this case, since the height of the mesa provided on the n-type InP substrate 11 is 2.5 μm, that is, 2.0 μm or more, the refractive index is significantly reduced due to light absorption by free carriers. Since the influence of the n-type InP substrate 11 is reduced, the light can be symmetrically and sufficiently spread in the tapered waveguide portion 18, thereby greatly improving the coupling efficiency with a waveguide such as an optical fiber. You.

In this case, since the current confinement structure is the same as that of the SI-PBH type laser, the width of the p-type InGaAs contact layer 24 in the laser portion 17 is larger than the width of the stripe-shaped mesa. The element resistance can be reduced while maintaining the state where the current is confined in the quantum well layer 13.

Next, a third embodiment of the present invention will be described with reference to FIG.
It will be described with reference to FIG. FIG. 4 shows a third embodiment of the present invention.
FIG. 2 is a perspective view of a semiconductor laser with a spot size converter.
First, when the electron concentration is 1.0 to 3.0 × 10¹⁸cm^-3,
For example, 2.0 × 10¹⁸ cm^-3N-type InP substrate 11
On top, the electron concentration is 5.0 × 10¹⁷cm ^-3Below, for example,
3.0 × 10¹⁷cm^-3And the thickness is 2.0μm or more, for example
For example, an n-type InP buffer layer 28 of 2.5 μm was provided.
Thereafter, just like in the second embodiment, the n-type In
Selection having a stripe-shaped opening on the P buffer layer 28
A growth mask (not shown) is provided, and the light guide layer 12 and the quantum
After growing the well layer 13 and the light guide layer 14,
P-type I having a thickness of 100 to 700 nm, for example, 300 nm
The nP cladding layer 15 is continuously grown.

Thereafter, the basic structure of the semiconductor laser with a spot size converter is completed by the same steps as those in the second embodiment, but the lower end of the light guide layer 12 is used for mesa etching. May be 2.0 μm or more, and the depth of the mesa etching may or may not reach the n-type InP substrate 11 depending on the thickness of the n-type InP buffer layer 28.

In this case, since the n-type InP buffer layer 28 having a low electron concentration is provided, a decrease in the refractive index due to light absorption by free carriers in the n-type InP buffer layer 28 is reduced, and the n-type InP buffer layer 28 is reduced. The influence of the substrate 11 becomes smaller, and the light can be spread more symmetrically and sufficiently in the tapered waveguide portion 18, thereby greatly improving the coupling efficiency with a waveguide such as an optical fiber. .

Next, a fourth embodiment of the present invention will be described with reference to FIG.
It will be described with reference to FIG. FIG. 5 shows a fourth embodiment of the present invention.
FIG. 2 is a perspective view of a semiconductor laser with a spot size converter.
First, when the electron concentration is 1.0 to 3.0 × 10¹⁸cm^-3,
For example, 2.0 × 10¹⁸ cm^-3N-type InP substrate 31
On top, the electron concentration is 5.0 × 10¹⁷cm ^-3Below, for example,
3.0 × 10¹⁷cm^-3And the thickness is 2.0μm or more, for example
For example, an n-type InP buffer layer 32 of 2.5 μm is provided.
After that, the light guide layer 33, the quantum well layer 34, and the light guide layer
Layer 35 and the p-type InP cladding layer 36 continuously.
Let it grow.

In the fourth embodiment,
The light guide layers 33 and 35 are made of InGaAsP having a thickness of 50 to 150 nm, for example, 100 μm and a 1.1 μm wavelength composition.
And the quantum well layer 34 has a thickness of 10
an InGaAsP barrier layer having a wavelength of 1.1 μm,
InGaAsP well layers each having a thickness of 1.35 μm and having a composition of 6 nm are alternately deposited so that five well layers are formed, and the thickness of the p-type InP cladding layer 15 is set to 100.
To 700 nm, for example, 300 nm.

Next, a thickness of 0.2 to 0.5 μm
For example, a 0.3 μm SiO ₂ film (not shown) is deposited, and the laser section 37 having a length of 300 μm has a width of 0.8 μm.
A tapered waveguide portion 38 having a stripe-shaped portion having a uniform width of 2.0 μm, for example, 1.5 μm, and a length of 200 μm.
In the above, after patterning a SiO ₂ mask (not shown) having a width gradually narrowing from 1.5 μm to 0.6 μm or less, for example, 0.5 μm toward the emission end face 43, the SiO ₂ mask Is used as a mask to form a stripe-shaped mesa that reaches the n-type InP substrate 31.

Next, using this SiO ₂ mask as a selective growth mask, the Fe-doped high-resistance InP buried layer 39 and the thickness of 50 nm are formed in the same steps as in the SI-PBH type laser.
An n-type InP current confinement layer 40 of 0 to 1000 nm, for example, 700 nm is sequentially grown.

Then, after removing the SiO ₂ mask, the thickness of the n-type
000 nm, for example, 4000 nm, the p-type InP cladding layer 41 and 200 to 1000 nm,
For example, a 500 nm p-type InGaAs contact layer 4
2 are sequentially grown, and then a p-side electrode is provided on the p-type InGaAs contact layer 42, and an n-side electrode is provided on the back surface of the n-type InP substrate 31, whereby the basic structure of the semiconductor laser with a spot size converter is improved. Complete.

Also in this case, the light can be spread symmetrically and sufficiently at the emission end face 43, thereby greatly improving the coupling efficiency with a waveguide such as an optical fiber.

In this case, unlike the first to third embodiments, since the effect of expanding the quantum level by thinning cannot be expected, light absorption in the width tapered waveguide portion 38 is prevented. Therefore, it is necessary to allow a current to flow also in the width tapered waveguide section 38 to have a gain.

In the fourth embodiment,
Since the width tapered waveguide portion 38 is formed by gradually reducing the stripe width, the light guide layers 33 and 35 are formed.
In addition, when the quantum well layer 34 is grown, it is not necessary to use a selective growth method, which simplifies the manufacturing process. However, since the fine structure of the width tapered waveguide portion 38 depends on the etching accuracy, variation easily occurs. .

The embodiments have been described above. However, in the first embodiment, an n-type InP buffer layer having a low electron concentration similar to that of the third embodiment may be provided. In the fourth embodiment, the n-type InP
An optical guide layer or the like may be directly grown on the n-type InP substrate without using the buffer layer. In that case,
It is necessary to etch the n-type InP substrate by 2.0 μm or more.

In the second to fourth embodiments, the thickness of the n-type InP buffer layer is 2.0 μm or more, but may be 2.0 μm or less. The height of the mesa at the lower end of the light guide layer on the side is 2.0μ
It is necessary to etch the n-type InP substrate so that it becomes m or more.

In the above-described first to third embodiments, the tapered waveguide portion is formed by selective growth using a mask having a tapered opening. 1.1 μm wavelength composition of In which the film thickness changes to ３ in a tapered shape by regrowth
A GaAsP layer may be formed.

In the first and fourth embodiments, the quantum well layer has a thickness of 10 nm and a thickness of 1.1 μm.
An InGaAsP barrier layer having a wavelength composition and 6 nm thick 1.
InGaAsP well layers having a wavelength composition of 35 μm are formed by alternately depositing five well layers. However, the present invention is not limited to such a structure, and the wavelength required is, for example, 1.5 μm band. And the composition and thickness of each layer according to the output,
The number of layers may be arbitrarily selected.

In each of the above embodiments,
Although the present invention has been described as an nGaAsP / InP-based optical semiconductor device, the present invention is not limited to the InGaAsP / InP-based optical semiconductor device, but may be an InAlGaAs-based or InGaAs / Ga-based semiconductor device.
As / AlGaAs system or InGaP / AlIn
The present invention can also be applied to a GaP system or the like.

[0067]

According to the present invention, the flat surface of the n-type semiconductor substrate and the high-resistance semiconductor layer are formed so that the light intensity distribution in the tapered waveguide serving as the spot size converter is symmetrically expanded. 1. The distance between the interface and the lower end of the core layer is 2.
Since the thickness is set to 0 μm or more, the coupling efficiency with the optical waveguide can be greatly improved, which greatly contributes to the development of optical fiber communication.

[Brief description of the drawings]

FIG. 1 is an explanatory diagram of a basic configuration of the present invention.

FIG. 2 is a perspective view of a semiconductor laser with a spot size converter according to the first embodiment of the present invention.

FIG. 3 is a perspective view of a semiconductor laser with a spot size converter according to a second embodiment of the present invention.

FIG. 4 is a perspective view of a semiconductor laser with a spot size converter according to a third embodiment of the present invention.

FIG. 5 is a perspective view of a semiconductor laser with a spot size converter according to a fourth embodiment of the present invention.

FIG. 6 is an explanatory diagram of a conventional semiconductor laser with a spot size converter.

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 n-type semiconductor substrate 2 core layer 3 p-type cladding layer 4 high-resistance semiconductor layer 5 emission end face 6 light intensity distribution 7 n-type semiconductor layer 11 n-type InP substrate 12 light guide layer 13 quantum well layer 14 light guide layer 15 p Type InP cladding layer 16 p-type InGaAs contact layer 17 laser part 18 tapered waveguide part 19 high-resistance InP buried layer 20 emission end face 21 high-resistance InP buried layer 22 n-type InP current confinement layer 23 p-type InP cladding layer 24 p Type InGaAs contact layer 25 insulating film 26 p-side electrode 27 n-side electrode 28 n-type InP buffer layer 31 n-type InP substrate 32 n-type InP buffer layer 33 light guide layer 34 quantum well layer 35 light guide layer 36 p-type InP clad layer 37 laser part 38 width tapered waveguide part 39 high resistance InP buried layer 40 n-type InP current confinement layer Reference Signs List 41 p-type InP cladding layer 42 p-type InGaAs contact layer 43 emission end face 51 n-type InP substrate 52 laser section 53 tapered waveguide section 54 p-type InP cladding layer 55 high-resistance InP buried layer 56 emission end face 57 light intensity distribution

Claims (9)

[Claims] In a resonator, a tapered waveguide portion in which a size of one or more core layers for guiding light continuously decreases toward a light emitting end surface is formed on an n-type semiconductor substrate. In an optical semiconductor device integrated into, at least both side surfaces of the core layer are in contact with the high-resistance semiconductor layer,
A portion of the interface between the n-type semiconductor substrate and the high-resistance semiconductor layer, which is substantially parallel to the main surface of the n-type semiconductor substrate, is at least at the emission end face from the lower end of the core layer.
An optical semiconductor device, wherein the optical semiconductor device exists at least below μm. 2. An n-type semiconductor substrate in which a size of a core layer composed of one or more layers for guiding light continuously decreases toward a light emitting end face in a resonator. In the optical semiconductor device integrated in the above, at least an n-type semiconductor layer having a carrier concentration of 5 × 10 ¹⁷ cm ⁻³ or less is provided immediately below the core layer, and at least both side surfaces of the core layer and the n-type semiconductor layer. Is in contact with the high-resistance semiconductor layer. 3. The optical semiconductor device according to claim 2, wherein said n-type semiconductor layer has a thickness of 2 μm or more. 4. The tapered waveguide section according to claim 1, wherein the thickness of the core layer is continuously reduced toward the emission end face. Optical semiconductor device. 5. The light according to claim 1, wherein in the tapered waveguide portion, the width of the core layer continuously decreases toward the emission end face. Semiconductor element. 6. The optical semiconductor device according to claim 4, wherein the number of the core layers in the tapered waveguide portion is the same as the number of the core layers in the gain region. 7. A p-type cladding layer is provided on the core layer, and the p-type cladding layer is in contact with an electrode provided on the p-type cladding layer side.
The optical semiconductor device according to claim 1, wherein a width of the mold semiconductor layer is wider than a width of the core layer. 8. The optical semiconductor according to claim 1, wherein the n-type semiconductor substrate is an n-type InP substrate, and the core layer includes one or more InGaAsP layers. element. 9. The high-resistance semiconductor layer is made of Fe-doped InP.
9. The optical semiconductor device according to claim 8, wherein the optical semiconductor device is a layer.