JP7561580B2 - Semiconductor Optical Device - Google Patents

Description

The present invention relates to a semiconductor optical element.

In semiconductor optical devices used in optical communications, a multiple quantum well layer is used in the active layer. In a separate confinement heterostructure (SCH), which confines carriers and light separately, the multiple quantum well layer is sandwiched between SCH layers. In order to meet the recent demand for higher speeds, it is expected that the optical confinement coefficient in the multiple quantum well layer will be increased, the relaxation oscillation frequency (fr) will be increased, and the f3 dB bandwidth will be improved (Patent Document 1).

JP 2018-56212 A Japanese Unexamined Patent Publication No. 7-183617

Increasing the refractive index of the multiple quantum well layer itself can increase the optical confinement coefficient of the multiple quantum well layer, but this affects characteristics such as the optical output and gain characteristics. Alternatively, increasing the refractive index of the SCH layer increases the optical confinement coefficient of the region including the upper and lower SCH layers, and therefore increases the optical confinement coefficient of the multiple quantum well layer. However, an energy barrier is created between the SCH layer and the multiple quantum well layer (barrier layer). This effect is particularly large on the n-type SCH layer side, where electrons are retained by the energy barrier and the flow of electrons at low frequencies is reduced.

Patent Document 2 discloses that electron retention is used to increase the carrier capture time and improve frequency modulation efficiency. However, in intensity modulation, the retention of electrons leads to deterioration (roll-off) of electrical/optical response characteristics in the low frequency range, which is undesirable.

The aim of this invention is to achieve both improved f3 dB bandwidth and reduced roll-off.

The semiconductor optical element includes a plurality of alternating well layers and a plurality of barrier layers, each of which is an undoped layer, a multiple quantum well layer whose outermost layer is one of the barrier layers, an optical confinement layer having a refractive index greater than that of the outermost layer and a band gap smaller than that of the outermost layer, and a guide layer interposed between the multiple quantum well layer and the optical confinement layer, including a first adjacent layer in contact with the outermost layer, and being thinner than the optical confinement layer, each of the optical confinement layer and the guide layer being an n-type semiconductor layer, and the first adjacent layer of the guide layer having a larger band gap than that of the optical confinement layer.

According to the present invention, light is confined in the optical confinement layer, and as a result, the optical confinement coefficient in the multiple quantum well layer can be increased. In addition, the presence of the guide layer reduces the energy barrier between the undoped layer and the n-type semiconductor layer, making it possible to suppress the retention of electrons.

1 is a plan view of a semiconductor optical device according to a first embodiment. 2 is a cross-sectional view taken along line II-II of the semiconductor optical device shown in FIG. 3 is a band diagram of a multiple quantum well layer, a guide layer, and an optical confinement layer in the first embodiment. 5 is a band diagram of a multiple quantum well layer, a guide layer, and an optical confinement layer in the second embodiment. 13 is a band diagram of a multiple quantum well layer, a guide layer and an optical confinement layer in the third embodiment. 13 is a band diagram of a multiple quantum well layer, a guide layer and an optical confinement layer in the fourth embodiment. 13 is a band diagram of a multiple quantum well layer, a guide layer and an optical confinement layer in the fifth embodiment. FIG. 13 is a cross-sectional view of a semiconductor optical device according to a sixth embodiment. 13 is a band diagram of a multiple quantum well layer, a guide layer and an optical confinement layer in the sixth embodiment.

The following describes an embodiment of the present invention in detail with reference to the drawings. Components with the same reference numerals in all the drawings have the same or equivalent functions, and their repeated explanation will be omitted. Note that the size of the figures does not necessarily correspond to the magnification.

[First embodiment]
Fig. 1 is a plan view of the semiconductor optical device according to the first embodiment, and Fig. 2 is a cross-sectional view of the semiconductor optical device shown in Fig. 1 taken along line II-II.

The semiconductor optical element is a directly modulated semiconductor laser, and may be any of a DFB (Distributed Feedback) laser, a FP (Fabry-Perot) laser, a DBR (Distributed Bragg Reflector) laser, and a DR (Distributed Reflector) laser.

The semiconductor optical element has a mesa stripe structure 10. The semiconductor optical element has an upper electrode 12 and a lower electrode 14 on the upper and lower surfaces, respectively, and a voltage is applied (current is injected) between them. This allows laser light to be emitted from the end face of the mesa stripe structure 10, for example in the 1.3 μm band or the 1.55 μm band. A dielectric anti-reflective coating film 16 is formed on the end face on the emission side. A dielectric highly reflective coating film 18 is formed on the end face on the opposite side.

The semiconductor optical device has a semiconductor substrate 20 made of p-type InP. A buffer layer 22 (p-type cladding layer) made of p-type InP is laminated on the semiconductor substrate 20. The mesa stripe structure 10 is provided on the buffer layer 22.

The mesa stripe structure 10 includes, in order from closest to the buffer layer 22, a p-type SCH layer 24, a multiple quantum well layer 26, a guide layer 28, and an optical confinement layer 30. The guide layer 28 and the optical confinement layer 30 can also be referred to as an n-type SCH layer 32. These constitute a part of the lower mesa structure 34 of the mesa stripe structure 10.

The semiconductor optical element has a structure in which an undoped multiple quantum well layer 26 is sandwiched between a p-type semiconductor multilayer and an n-type semiconductor multilayer. Note that another undoped layer may be sandwiched between the p-type semiconductor multilayer and the multiple quantum well layer 26.

Figure 3 shows a band diagram of the multiple quantum well layer 26, the guide layer 28, and the optical confinement layer 30 in the first embodiment. The energy difference between the top of the valence band and the bottom of the conduction band is the band gap.

The multiple quantum well layer 26 is made of undoped strained InGaAlAs. The multiple quantum well layer 26 includes multiple well layers 36 and multiple barrier layers 38 (e.g., six pairs of well layers 36 and barrier layers 38) that are alternately stacked. The well layers 36 and barrier layers 38 may have the same thickness (e.g., 8 nm). Each of the multiple barrier layers 38 is an undoped layer. The outermost layer 40 (each of the top and bottom layers) of the multiple quantum well layer 26 is one of the multiple barrier layers 38.

The optical confinement layer 30 is an n-type semiconductor layer (for example, an n-type InGaAlAs layer with a thickness of 80 nm and a composition wavelength of 1.15 μm). Si is used as the n-type dopant.

The guide layer 28 is an n-type semiconductor layer (for example, an n-type InGaAlAs layer having a thickness of 40 nm and a composition wavelength of 0.93 μm). Si is used as the n-type dopant. The doping concentrations of the guide layer 28 and the optical confinement layer 30 may be the same or different, but it is preferable that the concentration difference is sufficient to apply an electric field. The guide layer 28 is interposed between the multiple quantum well layer 26 and the optical confinement layer 30. The guide layer 28 includes a first adjacent layer 42 that contacts the outermost layer 40 of the multiple quantum well layer 26. The guide layer 28 is composed of only the first adjacent layer 42. The guide layer 28 (first adjacent layer 42) has the same composition wavelength as the outermost layer 40 of the multiple quantum well layer 26.

As shown in FIG. 3, the band gap Eg _G1 of the first adjacent layer 42 is larger than the band gap Eg _C of the optical confinement layer 30. Therefore, an energy barrier (difference in energy levels in the conduction band) exists between the guide layer 28 and the optical confinement layer 30, but since both are n-type semiconductor layers, there is less electron retention compared to the energy barrier between an n-type semiconductor layer and an undoped layer. This is because a sufficient electric field is applied in the n-type layer. In this way, there is little electron retention due to the energy barrier between the guide layer 28 and the optical confinement layer 30, so that the electrons move smoothly, and the roll-off in the low range of the electrical/optical response characteristics does not become a problem. Note that the band gap Eg _G1 of the first adjacent layer 42 is equal to the band gap Eg _O of the outermost layer 40 of the multiple quantum well layer 26, so there is no energy barrier.

Generally, the light generated in the multiple quantum well layer does not remain only in the multiple quantum well layer, but spreads to the upper and lower layers (the p-type semiconductor multilayer side and the n-type semiconductor multilayer side). The region where the light mainly stays is the region surrounded by the p-type optical confinement layer, the multiple quantum well layer, and the n-type optical confinement layer. As the name suggests, the optical confinement layer has the function of suppressing the light from spreading to other regions. Generally, the refractive index of the optical confinement layer is smaller than that of the outermost layer (barrier layer) of the multiple quantum well layer. This is to improve the flow of carriers. The larger the refractive index, the smaller the band gap. In the above-mentioned structure, the optical confinement layer has a larger band gap than the barrier layer, and no energy barrier occurs in the movement of carriers, for example, electrons. In this embodiment, as shown in FIG. 3, the band gap Eg _C of the optical confinement layer 30 is smaller than the band gap Eg _O of the outermost layer 40 of the multiple quantum well layer 26. In the InGaAlAs layer, the larger the band gap, the smaller the refractive index. Therefore, the refractive index n _C of the optical confinement layer 30 is larger than the refractive index n _O of the outermost layer 40 of the multiple quantum well layer 26. Therefore, compared with a structure in which the refractive index of the optical confinement layer 30 is smaller than the refractive index of the outermost layer 40 of the multiple quantum well layer 26, the optical confinement coefficient of the region from the optical confinement layer 30 to the multiple quantum well layer 26 can be increased. As a result, the optical confinement coefficient of the multiple quantum well layer 26 can also be increased, and it is possible to improve fr, that is, to improve the f3 dB band in total. Furthermore, as described above, because of the presence of the guide layer 28, the influence on the flow of electrons due to the energy barrier between the optical confinement layer 30 and the outermost layer 40 of the multiple quantum well layer 26 can be reduced, and the retention of electrons can be suppressed and the roll-off can be reduced. The refractive index n _G1 of the first adjacent layer 42 is equal to the refractive index n _O of the outermost layer 40 of the multiple quantum well layer 26. The refractive index n _C of the optical confinement layer 30 is larger than the refractive index n _G1 of the guide layer 28 (first adjacent layer 42). Here, the amount of strain (including no strain) of the first adjacent layer 42 differs from the amount of strain of the outermost layer 40, and the composition wavelength (band gap) of the actual finished product differs slightly. However, this difference does not have a significant effect on the roll-off characteristics or the optical confinement factor, and there is no problem in regarding them as having substantially the same composition wavelength.

The guide layer 28 (first adjacent layer 42) also contacts the optical confinement layer 30. In order to strongly confine light in the multiple quantum well layer 26, the guide layer 28 (first adjacent layer 42) is preferably thinner than the optical confinement layer 30.

2, the lower mesa structure 34 includes an n-type cladding layer 44 adjacent to the optical confinement layer 30. The n-type cladding layer 44 includes a first n-type InP layer 46A, a diffraction grating layer 48 made of n-type InGaAsP, a second n-type InP layer 46B, and an n-type InGaAsP layer 50. The diffraction grating layer 48 has a periodic diffraction grating structure, and for example, a λ/4 shift structure is introduced in the direction perpendicular to the paper surface.

A buried layer 52 made of p-type InP buries the lower mesa structure 34 (at least a part of it) on both sides. The buried layer 52 may be made of high-resistance InP doped with Fe or Ru, or may be a laminate of materials selected from the group consisting of p-type InP, n-type InP, and high-resistance InP.

The mesa stripe structure 10 includes an upper mesa structure 54 on the lower mesa structure 34. The upper mesa structure 54 is narrower than the lower mesa structure 34. The upper mesa structure 54 includes, in order from the n-type InGaAsP layer 50 closer to the n-type InP, a current injection layer 56 and an n-type contact layer 58. The current injection layer 56 is a part of the n-type cladding layer 44. The surface of the upper mesa structure 54 is covered with an insulating layer 60 made of SiO ₂ , except for its upper portion. The upper electrode 12 is electrically and physically connected to the n-type contact layer 58. The upper electrode 12 has a three-layer structure of Ti/Pt/Au from the side in contact with the n-type contact layer 58. The lower electrode 14 is made of an AuZn-based material.

Second Embodiment
FIG. 4 is a band diagram of the multiple quantum well layer, the guide layer and the optical confinement layer in the second embodiment.

The guide layer 228 is composed of only the first adjacent layer 242. The band gap Eg _G1 of the guide layer 228 (first adjacent layer 242) is larger than the band gap Eg _C of the optical confinement layer 230. Also, the band gap Eg _G1 of the first adjacent layer 242 of the guide layer 228 is smaller than the band gap Eg _o of the outermost layer 240 of the multiple quantum well layer 226. Therefore, a difference in energy level in the conduction band occurs between the guide layer 228 (first adjacent layer 242) and the outermost layer 240 of the multiple quantum well layer 226. However, this difference is smaller than the difference in energy level between the optical confinement layer 230 and the outermost layer 240 of the multiple quantum well layer 226. Therefore, the presence of the guide layer 228 (first adjacent layer 242) reduces the retention of electrons.

In the energy level of the conduction band, the difference between the first adjacent layer 242 and the outermost layer 240 is half or less (preferably 1/3 or less) of the difference between the optical confinement layer 230 and the outermost layer 240. This can effectively reduce roll-off. The relationship between the refractive index n _C of the optical confinement layer 230, the refractive index n _G1 of the guide layer 228 (first adjacent layer 242), and the refractive index n _O of the outermost layer 240 of the multiple quantum well layer 226 is as shown in FIG. 4.

[Third embodiment]
FIG. 5 is a band diagram of the multiple quantum well layer, the guide layer and the optical confinement layer in the third embodiment.

The guide layer 328 is composed of only the first adjacent layer 342. The band gap Eg _G1 of the guide layer 328 (first adjacent layer 342) is larger than the band gap Eg _O of the outermost layer 340 of the multiple quantum well layer 326. Therefore, the electrons hardly stay, and the roll-off is excellent in terms of reduction. However, if the difference in energy level between the guide layer 328 (first adjacent layer 342) and the optical confinement layer 330 is too large, there is a risk of electrons staying, even if they are the same n-type semiconductor layer. Therefore, the difference in energy level of the conduction band between the first adjacent layer 342 and the optical confinement layer 330 is 0.6 eV or less. The relationship between the refractive index n _C of the optical confinement layer 330, the refractive index n _G1 of the guide layer 328 (first adjacent layer 342), and the refractive index n _O of the outermost layer 340 of the multiple quantum well layer 326 is as shown in FIG. 5.

[Fourth embodiment]
FIG. 6 is a band diagram of the multiple quantum well layer, the guide layer and the optical confinement layer in the fourth embodiment.

The guide layer 428 is made up of multiple layers. The multiple layers include a first adjacent layer 442 in contact with the outermost layer 440. The multiple layers include a second adjacent layer 462 in contact with the optical confinement layer 430. The second adjacent layer 462 is doped with Si at the same concentration as the first adjacent layer 442. The thickness of the guide layer 428 (the total thickness of the first adjacent layer 442 and the second adjacent layer 462) is thinner than the thickness of the optical confinement layer 430.

The band gap Eg _G1 of the first adjacent layer 442 of the guide layer 428 is equal to the band gap Eg _O of the outermost layer 440 of the multiple quantum well layer 426. This makes it possible to reduce the retention of electrons between the n-type semiconductor layer and the undoped layer.

The band gap Eg _G2 of the second adjacent layer 462 is larger than the band gap Eg _C of the optical confinement layer 430. The band gap Eg _G2 of the second adjacent layer 462 is smaller than the band gap Eg _O of the outermost layer 440 of the multiple quantum well layer 426. The band gap Eg _G2 of the second adjacent layer 462 is smaller than the band gap Eg _G1 of the first adjacent layer 442. Therefore, in the guide layer 428 (the first adjacent layer 442 and the second adjacent layer 462), the energy level changes stepwise, so that the retention of electrons can be effectively reduced. In this embodiment, the optical confinement layer 430 is also present, so that the optical confinement coefficient of the multiple quantum well layer 426 can be increased. The relationship between the refractive index n _C of the optical confinement layer 430, the refractive index n _G1 of the first adjacent layer 442, and the refractive index n _GO of the outermost layer 440 of the multiple quantum well layer 426 is as shown in FIG. 6.

[Fifth embodiment]
FIG. 7 is a band diagram of the multiple quantum well layer, the guide layer and the optical confinement layer in the fifth embodiment.

The guide layer 528 is made up of multiple layers. The multiple layers include a first adjacent layer 542 in contact with the outermost layer 540 of the multiple quantum well layer 526. The multiple layers include a second adjacent layer 562 in contact with the optical confinement layer 530. The multiple layers further include at least one intermediate layer 564 between the first adjacent layer 542 and the second adjacent layer 562. The second adjacent layer 562 and the intermediate layer 564 are doped with Si at the same concentration as the first adjacent layer 542.

The band gap Eg _G1 of the first adjacent layer 542 is equal to the band gap Eg _O of the outermost layer 540 of the multiple quantum well layer 526. The band gap Eg _G2 of the second adjacent layer 562 is larger than the band gap Eg _C of the optical confinement layer 530. The band gap Eg _G2 of the second adjacent layer 562 is equal to the band gap Eg _O of the outermost layer 540 of the multiple quantum well layer 526. The band gap Eg _G2 of the second adjacent layer 562 is equal to the band gap Eg _G1 of the first adjacent layer 542. The band gap Eg _G3 of the intermediate layer 564 is equal to the band gap Eg _C of the optical confinement layer 530.

The thickness of the guide layer 528 is less than half the thickness of the multiple quantum well layer 526. If it is thicker than half, there is a risk that the light confinement effect will not be sufficient. The thickness of the light confinement layer 530 is more than half the thickness of the multiple quantum well layer 526. If the light confinement layer 530 is thin, it will be difficult to sufficiently confine light in the multiple quantum well layer 526.

The thickness of the intermediate layer 564 is thinner than that of the first adjacent layer 542. Therefore, the intermediate layer 564 alone has little effect of increasing the confinement of light to the multiple quantum well layer 526. However, since the optical confinement layer 530 is arranged with the second adjacent layer 562 sandwiched therebetween, the light can be confined to the multiple quantum well layer 526 side as a whole. Therefore, even if another layer is sandwiched between the first adjacent layer 542 and the optical confinement layer 530, the effect can be obtained. The relationship between the refractive index n _C of the optical confinement layer 530, the refractive index n _G1 of the first adjacent layer 542, the refractive index n _G2 of the second adjacent layer 562, the refractive index n _G3 of the intermediate layer 564, and the refractive index n _G0 of the outermost layer 540 of the multiple quantum well layer 526 is as shown in FIG. 7.

Sixth embodiment
8 is a cross-sectional view of a semiconductor optical device according to the sixth embodiment. The semiconductor optical device has a semiconductor substrate 620 made of n-type InP. A buffer layer 622 (n-type cladding layer) made of n-type InP is laminated on the semiconductor substrate 620. In the buffer layer 622, an optical confinement layer 630, a guide layer 628, a multiple quantum well layer 626, a p-type SCH layer 624, and a p-type cladding layer 644 are laminated in order from the side closest to the buffer layer 622. The optical confinement layer 630 and the guide layer 628 can also be referred to as an n-type SCH layer 632.

Figure 9 shows a band diagram of the multiple quantum well layer, guide layer, and optical confinement layer in the sixth embodiment.

The multiple quantum well layer 626 is made of undoped strained InGaAlAs. The multiple quantum well layer 626 includes multiple well layers 636 and multiple barrier layers 638 (e.g., six pairs of well layers 636 and barrier layers 638) that are alternately stacked. The well layers 636 and the barrier layers 638 may have the same thickness (e.g., 8 nm). Each of the multiple barrier layers 638 is an undoped layer. The outermost layer 640 (each of the top and bottom layers) of the multiple quantum well layer 626 is one of the multiple barrier layers 638.

The guide layer 628 is an n-type semiconductor layer (for example, an n-type InGaAlAs layer having a thickness of 40 nm and a composition wavelength of 0.93 μm). Si is used as an n-type dopant. The doping concentrations of the guide layer 628 and the optical confinement layer 630 may be the same or different, but it is preferable that the concentration difference is sufficient to apply an electric field. The guide layer 628 is interposed between the multiple quantum well layer 626 and the optical confinement layer 630. The guide layer 628 includes a first adjacent layer 642 that contacts the outermost layer 640 of the multiple quantum well layer 626. The guide layer 628 is composed of only the first adjacent layer 642. The guide layer 628 (first adjacent layer 642) has the same composition wavelength as the outermost layer 640 of the multiple quantum well layer 626.

The band gap Eg _G1 of the first adjacent layer 642 is larger than the band gap Eg _C of the optical confinement layer 630. Therefore, an energy barrier (difference in energy levels in the conduction band) exists between the guide layer 628 and the optical confinement layer 630, but since both are n-type semiconductor layers, there is less electron retention compared to the energy barrier between an n-type semiconductor layer and an undoped layer. This is because a sufficient electric field is applied in the n-type layer. In this way, there is less electron retention due to the energy barrier between the guide layer 628 and the optical confinement layer 630, so the electrons move smoothly, and the roll-off in the low range of the electrical/optical response characteristics does not become a problem. Note that the band gap Eg _G1 of the first adjacent layer 642 is equal to the band gap Eg _O of the outermost layer 640 of the multiple quantum well layer 626, so there is no energy barrier.

The optical confinement layer 630 is an n-type semiconductor layer (for example, an n-type InGaAlAs layer with a thickness of 80 nm and a composition wavelength of 1.15 μm). Si is used as the n-type dopant.

The band gap Eg _C of the optical confinement layer 630 is smaller than the band gap Eg _O of the outermost layer 640 of the multiple quantum well layer 626. In the InGaAlAs layer, the larger the band gap, the smaller the refractive index. Therefore, the refractive index n _C of the optical confinement layer 630 is larger than the refractive index n _O of the outermost layer 640 of the multiple quantum well layer 626. In this embodiment, as described in the first embodiment, the optical confinement coefficient in the multiple quantum well layer 626 can be increased, and it is possible to improve fr, that is, to improve the f3 dB band in total. The refractive index n _G1 of the first adjacent layer 642 is equal to the refractive index n _O of the outermost layer 640 of the multiple quantum well layer 626. The refractive index n _C of the optical confinement layer 630 is larger than the refractive index n _G1 of the guide layer 628 (first adjacent layer 42).

The guiding layer 628 (first adjacent layer 642) also contacts the optical confinement layer 630. The guiding layer 628 (first adjacent layer 642) is preferably thinner than the optical confinement layer 630 in order to strongly confine light in the multiple quantum well layer 626.

As shown in FIG. 8, the p-type cladding layer 644 includes, in order from closest to the p-type SCH layer 624, a p-type InP layer 666, a diffraction grating layer 648 made of p-type InGaAsP, a current injection layer 656 made of p-type InP, and a p-type contact layer 658. The diffraction grating layer 648 has a periodic diffraction grating structure, and for example, a λ/4 shift structure is introduced in the direction perpendicular to the paper surface.

The stacked body from the p-type InP layer 666 to the p-type contact layer 658 is included in the mesa stripe structure 610. An insulating layer 660 made of SiO ₂ is disposed on the side surface of the mesa stripe structure 610 and on the upper surface of the p-type SCH layer 624.

The upper electrode 612 is electrically and physically connected to the p-type contact layer 658. The upper electrode 612 has a three-layer structure of Ti/Pt/Au from the side in contact with the p-type contact layer 658. The lower electrode 614 is made of an AuZn-based material.

The present invention is not limited to the above-described embodiment, and various modifications are possible. For example, the configuration described in the embodiment can be replaced with a substantially identical configuration, a configuration that provides the same action and effect, or a configuration that can achieve the same purpose.

10 mesa stripe structure, 12 upper electrode, 14 lower electrode, 16 dielectric anti-reflective coating film, 18 dielectric high-reflective coating film, 20 semiconductor substrate, 22 buffer layer, 24 p-type SCH layer, 26 multiple quantum well layer, 28 guide layer, 30 optical confinement layer, 32 n-type SCH layer, 34 lower mesa structure, 36 well layer, 38 barrier layer, 40 outermost layer, 42 first adjacent layer, 44 n-type cladding layer, 46A first n-type InP layer, 46B second n-type InP layer, 48 diffraction grating layer, 50 n-type InGaAsP layer, 52 buried layer, 54 upper mesa structure, 56 current injection layer, 58 n-type contact layer, 60 insulating layer, 226 multiple quantum well layer, 228 guide layer, 230 optical confinement layer, 240 outermost layer, 242 First adjacent layer, 326 Multiple quantum well layer, 328 Guide layer, 330 Optical confinement layer, 340 Outermost layer, 342 First adjacent layer, 426 Multiple quantum well layer, 428 Guide layer, 430 Optical confinement layer, 440 Outermost layer, 442 First adjacent layer, 462 Second adjacent layer, 526 Multiple quantum well layer, 528 Guide layer, 530 Optical confinement layer, 540 Outermost layer, 542 First adjacent layer, 562 Second adjacent layer, 564 Intermediate layer, 610 Mesa stripe structure, 612 Upper electrode, 614 Lower electrode, 620 Semiconductor substrate, 622 Buffer layer, 624 p-type SCH layer, 626 Multiple quantum well layer, 628 Guide layer, 630 Optical confinement layer, 632 n-type SCH layer, 636 Well layer, 638 Barrier layer, 640 Outermost layer, 642 first adjacent layer, 644 p-type cladding layer, 648 diffraction grating layer, 656 current injection layer, 658 p-type contact layer, 660 insulating layer, 666 p-type InP layer, Eg _C band gap, Eg _G1 band gap, Eg _G2 band gap, Eg _G3 band gap, Eg _O band gap, n _C refractive index, n _G1 refractive index, n _G2 refractive index, n _G3 refractive index, n _O refractive index.

Claims (19)

a multiple quantum well layer including a plurality of well layers and a plurality of barrier layers that are alternately stacked, each of the plurality of barrier layers being an undoped layer, and an outermost layer being one of the plurality of barrier layers;
an optical confinement layer having a refractive index larger than that of the outermost layer and a band gap smaller than that of the outermost layer;
a guide layer interposed between the multiple quantum well layer and the optical confinement layer, including a first adjacent layer in contact with the outermost layer, the guide layer being thinner than the optical confinement layer;
having
each of the optical confinement layer and the guide layer is an n-type semiconductor layer;
the first adjacent layer of the guiding layer is larger in band gap than the optical confinement layer;
The first adjacent layer of the guiding layer has a band gap larger than that of the outermost layer of the multiple quantum well layer . a multiple quantum well layer including a plurality of well layers and a plurality of barrier layers that are alternately stacked, each of the plurality of barrier layers being an undoped layer, and an outermost layer being one of the plurality of barrier layers;
an optical confinement layer having a refractive index larger than that of the outermost layer and a band gap smaller than that of the outermost layer;
a guide layer interposed between the multiple quantum well layer and the optical confinement layer, including a first adjacent layer in contact with the outermost layer, the guide layer being thinner than the optical confinement layer;
having
each of the optical confinement layer and the guide layer is an n-type semiconductor layer;
the first adjacent layer of the guiding layer is larger in band gap than the optical confinement layer;
The first adjacent layer of the guiding layer has a band gap smaller than that of the outermost layer of the multiple quantum well layer. 3. The semiconductor optical device according to claim 1,
The guide layer is a semiconductor optical device consisting of only the first adjacent layer. 3. The semiconductor optical device according to claim 1,
the guide layer is made up of a plurality of layers including the first adjacent layer in contact with the outermost layer and a second adjacent layer in contact with the optical confinement layer;
The second adjacent layer has a larger band gap than the optical confinement layer. a multiple quantum well layer including a plurality of well layers and a plurality of barrier layers that are alternately stacked, each of the plurality of barrier layers being an undoped layer, and an outermost layer being one of the plurality of barrier layers;
an optical confinement layer having a refractive index larger than that of the outermost layer and a band gap smaller than that of the outermost layer;
a guide layer interposed between the multiple quantum well layer and the optical confinement layer, including a first adjacent layer in contact with the outermost layer, the guide layer being thinner than the optical confinement layer;
having
each of the optical confinement layer and the guide layer is an n-type semiconductor layer;
the first adjacent layer of the guiding layer is larger in band gap than the optical confinement layer;
the guide layer is made up of a plurality of layers including the first adjacent layer in contact with the outermost layer and a second adjacent layer in contact with the optical confinement layer;
the second adjacent layer has a larger band gap than the optical confinement layer;
The second adjacent layer has a band gap smaller than that of the outermost layer of the multiple quantum well layer. a multiple quantum well layer including a plurality of well layers and a plurality of barrier layers that are alternately stacked, each of the plurality of barrier layers being an undoped layer, and an outermost layer being one of the plurality of barrier layers;
an optical confinement layer having a refractive index larger than that of the outermost layer and a band gap smaller than that of the outermost layer;
a guide layer interposed between the multiple quantum well layer and the optical confinement layer, including a first adjacent layer in contact with the outermost layer, the guide layer being thinner than the optical confinement layer;
having
each of the optical confinement layer and the guide layer is an n-type semiconductor layer;
the first adjacent layer of the guiding layer is larger in band gap than the optical confinement layer;
the guide layer is made up of a plurality of layers including the first adjacent layer in contact with the outermost layer and a second adjacent layer in contact with the optical confinement layer;
the second adjacent layer has a larger band gap than the optical confinement layer;
The second adjacent layer has a band gap equal to that of the outermost layer of the multiple quantum well layer. a multiple quantum well layer including a plurality of well layers and a plurality of barrier layers that are alternately stacked, each of the plurality of barrier layers being an undoped layer, and an outermost layer being one of the plurality of barrier layers;
an optical confinement layer having a refractive index larger than that of the outermost layer and a band gap smaller than that of the outermost layer;
a guide layer interposed between the multiple quantum well layer and the optical confinement layer, including a first adjacent layer in contact with the outermost layer, the guide layer being thinner than the optical confinement layer;
having
each of the optical confinement layer and the guide layer is an n-type semiconductor layer;
the first adjacent layer of the guiding layer is larger in band gap than the optical confinement layer;
the guide layer is made up of a plurality of layers including the first adjacent layer in contact with the outermost layer and a second adjacent layer in contact with the optical confinement layer;
the second adjacent layer has a larger band gap than the optical confinement layer;
The semiconductor optical device, wherein the plurality of layers constituting the guide layer further includes at least one intermediate layer between the first adjacent layer and the second adjacent layer. 8. The semiconductor optical device according to claim 7 ,
The at least one intermediate layer has the same band gap as the optical confinement layer. 9. The semiconductor optical device according to claim 1,
A semiconductor optical device, wherein a difference in energy level of a conduction band between the first adjacent layer and the outermost layer is half or less of a difference between the optical confinement layer and the outermost layer. 9. The semiconductor optical device according to claim 1,
A semiconductor optical device, wherein a difference in energy level of a conduction band between the first adjacent layer and the outermost layer is 1/3 or less of a difference between the optical confinement layer and the outermost layer. 11. The semiconductor optical device according to claim 1,
A semiconductor optical device, wherein the difference in energy level of the conduction band between the first adjacent layer and the optical confinement layer is 0.6 eV or less. 12. The semiconductor optical device according to claim 1,
The thickness of the guide layer is equal to or less than half the thickness of the multiple quantum well layer. 13. The semiconductor optical device according to claim 1,
A semiconductor optical device in which the thickness of the optical confinement layer is at least half the thickness of the multiple quantum well layer. A lower mesa structure;
an upper mesa structure located above the lower mesa structure and having a width narrower than that of the lower mesa structure;
a multiple quantum well layer, the multiple quantum well layer being included in the lower mesa structure but not in the upper mesa structure, the multiple quantum well layer including a plurality of well layers and a plurality of barrier layers which are alternately stacked, each of the plurality of barrier layers being an undoped layer, and an outermost layer being one of the plurality of barrier layers;
an optical confinement layer that is not included in the upper mesa structure but is included in the lower mesa structure, the optical confinement layer having a refractive index larger than that of the outermost layer and a band gap smaller than that of the outermost layer;
a guide layer interposed between the multiple quantum well layer and the optical confinement layer, in direct contact with the optical confinement layer, including a first adjacent layer in contact with the outermost layer, and thinner than the optical confinement layer;
a buried layer surrounding the lower mesa structure without surrounding the upper mesa structure;
A semiconductor optical element comprising: 15. The semiconductor optical device according to claim 14,
A semiconductor optical device in which a first adjacent layer of the guiding layer has a larger band gap than the outermost layer of the multiple quantum well layer. 15. The semiconductor optical device according to claim 14,
The guide layer is a semiconductor optical device consisting of only the first adjacent layer. 15. The semiconductor optical device according to claim 14,
A semiconductor optical device, wherein the difference in energy level of the conduction band between the first adjacent layer and the optical confinement layer is 0.6 eV or less. 15. The semiconductor optical device according to claim 14,
The optical confinement layer and the guide layer are n-type separate confinement heterolayers. 15. The semiconductor optical device according to claim 14,
The buried layer is a semiconductor optical device including at least one of InP doped with Fe or Ru, or a laminate of materials including at least one of p-type InP, n-type InP, and high-resistance InP.

Images