Optical semiconductor device

Abstract

An optical semiconductor device includes a multiple quantum well layer including a plurality of well layers and a plurality of barrier layers alternately overlapped with each other, an optical confinement layer, and a guide layer interposed between the multiple quantum well layer and the optical confinement layer. Each of the barrier layers is an undoped layer, and an outermost layer is one of the barrier layers. The optical confinement layer has a refractive index larger than a refractive index of the outermost layer and a band gap smaller than a band gap of the outermost layer. The guide layer includes a first adjacent layer in contact with the outermost layer, and the guide layer is thinner than the optical confinement layer. Each of the optical confinement layer and the guide layer is an n-type semiconductor layer. The first adjacent layer of the guide layer has a band gap larger than a band gap of the optical confinement layer.

Description

Technical Field

[0001] This disclosure relates to optical semiconductor devices. Background Technology

[0002] Typically, optical semiconductor devices used in optical communication can have multiple quantum well layers as active layers. A separate confinement heterostructure (SCH) is used where charge carriers and light are separately confined, with multiple quantum well layers interposed between the SCH layers. In some cases, to meet high-speed requirements, it may be necessary to increase the optical confinement factor of the multiple quantum well layers, and it may also be necessary to increase the relaxation oscillation frequency (fr) to improve the f3dB bandwidth of the optical semiconductor device (e.g., compared to conventional optical semiconductor devices).

[0003] Increasing the refractive index of the multi-quantum-well layer can further increase its optical confinement factor, affecting other properties such as light output and gain. Alternatively, increasing the refractive index of the SCH layer can increase the optical confinement factor due to the increased optical confinement factor in the region encompassing the upper and lower SCH layers. However, an energy barrier is formed between the SCH layer and the multi-quantum-well layer (barrier layer). In some cases, one side of the n-type SCH layer experiences a greater impact, thus blocking electrons from the energy barrier, which impedes electron flow at low frequencies.

[0004] In some cases, electron stagnation can be used to increase carrier trapping time and / or increase frequency modulation efficiency. However, using electron stagnation with intensity modulation can lead to a deterioration (roll-off) in the electro-optical response characteristics at low frequencies. Summary of the Invention

[0005] According to some possible implementations, the optical semiconductor device may include: a multiple quantum well layer comprising a number of well layers and a number of barrier layers that overlap each other alternately, wherein each barrier layer is an undoped layer, and the outermost layer is one of the barrier layers; an optical confinement layer having a refractive index greater than that of the outermost layer, wherein the optical confinement layer has a band gap smaller than that of the outermost layer; and a guiding layer interposed between the multiple quantum well layer and the optical confinement layer, wherein the guiding layer includes a first adjacent layer in contact with the outermost layer, and the guiding layer is thinner than the optical confinement layer, wherein each of the optical confinement layer and the guiding layer is an n-type semiconductor layer, and the first adjacent layer of the guiding layer has a band gap greater than that of the optical confinement layer.

[0006] Light can be confined within the optical confinement layer, ultimately increasing the optical confinement factor of the multi-quantum-well layer. Furthermore, the guiding layer can lower the energy barrier between the undoped layer and the n-type semiconductor layer, suppressing electron stagnation. Therefore, an improvement in the f3 dB bandwidth and a reduction in roll-off can be achieved. Attached Figure Description

[0007] Figure 1 This is a plan view of an exemplary optical semiconductor device described herein.

[0008] Figure 2 yes Figure 1 The exemplary optical semiconductor device shown is a cross-sectional view along line II-II.

[0009] Figure 3 This is the band diagram of the multi-quantum well layer, the guiding layer, and the optical confinement layer in the example embodiment.

[0010] Figure 4 This is the band diagram of the multi-quantum well layer, the guiding layer, and the optical confinement layer in the example embodiment.

[0011] Figure 5 This is the band diagram of the multi-quantum well layer, the guiding layer, and the optical confinement layer in the example embodiment.

[0012] Figure 6 This is the band diagram of the multi-quantum well layer, the guiding layer, and the optical confinement layer in the example embodiment.

[0013] Figure 7 This is the band diagram of the multi-quantum well layer, the guiding layer, and the optical confinement layer in the example embodiment.

[0014] Figure 8 This is a cross-sectional view of the example optical semiconductor device described in this article.

[0015] Figure 9 This is the band diagram of the multi-quantum well layer, the guiding layer, and the optical confinement layer in the example embodiment. Detailed Implementation

[0016] In the following description, some implementations are illustrated in detail with reference to the accompanying drawings. In all the drawings, components with the same reference numerals have the same or identical features, and their repeated descriptions will be omitted. The sizes of the drawings do not always correspond to the magnification.

[0017] Figure 1 This is a plan view of an example optical semiconductor device. Figure 2 yes Figure 1 The exemplary optical semiconductor device shown is a cross-sectional view along line II-II.

[0018] Example optical semiconductor devices can be direct-modulation semiconductor lasers, and can be any of the following: distributed feedback (DFB) lasers, Fabry-Perot (FP) lasers, distributed Bragg reflector (DBR) lasers, or distributed reflector (DR) lasers.

[0019] The example optical semiconductor device may have a mesa stripe structure 10. The example optical semiconductor device may have an upper electrode 12 and a lower electrode 14 on its upper and lower surfaces, respectively, to apply a voltage or inject current between the electrodes. This allows laser light to oscillate, for example, from the end face of the mesa stripe structure 10 in the 1.3 μm or 1.55 μm wavelength range. A dielectric antireflective coating 16 may be formed on the emitting end face of the mesa stripe structure 10. A dielectric high reflective coating 18 may be formed on the opposite end face of the mesa stripe structure 10.

[0020] Example optical semiconductor devices may include a semiconductor substrate 20 comprising p-type InP. A buffer layer 22 (e.g., a p-type cladding) may comprise p-type InP and may be stacked on the semiconductor substrate 20. A mesa stripe structure 10 may be disposed on the buffer layer 22.

[0021] The mesa stripe structure 10 may include, in order of proximity to the buffer layer 22, a p-type SCH layer 24, a multiple quantum well layer 26, a guiding layer 28, and an optical confinement layer 30. The guiding layer 28 and the optical confinement layer 30 may also be referred to as an n-type SCH layer 32. These layers form part of the lower mesa structure 34 of the mesa stripe structure 10.

[0022] This exemplary optical semiconductor device may have a structure in which an undoped multiple quantum well layer 26 is interposed between a p-type semiconductor multilayer and an n-type semiconductor multilayer. Another undoped layer may be interposed between the p-type semiconductor multilayer and the multiple quantum well layer 26.

[0023] Figure 3 This is an energy band diagram of the multi-quantum well layer 26, the guiding layer 28, and the optical confinement layer 30 in the example embodiment. The band gap is the energy difference between the top of the valence band and the bottom of the conduction band.

[0024] The multiple quantum well layer 26 may comprise undoped strained InGaAlAs. The multiple quantum well layer 26 may comprise alternating stacks of some well layers 36 and some barrier layers 38 (e.g., six pairs of well layers 36 and barrier layers 38). The well layers 36 and barrier layers 38 may have the same thickness (e.g., 8 nm). Each barrier layer 38 may be an undoped layer. The outermost layer 40 of the multiple quantum well layer 26 (each of the top and bottom layers) may be one of the barrier layers 38.

[0025] The optical confinement layer 30 can be an n-type semiconductor layer (e.g., an n-type InGaAlAs layer with a thickness of 80 nm and / or a composition wavelength of 1.15 μm). Si can be used as an n-type dopant.

[0026] The guiding layer 28 may be an n-type semiconductor layer (e.g., an n-type InGaAlAs layer with a thickness of 40 nm and / or a composition wavelength of 0.93 μm). Silicon may be used as the n-type dopant. The doping concentration of the guiding layer 28 and the optical confinement layer 30 may be the same or different. The concentration difference should be suitable for applying a sufficient electric field. The guiding layer 28 may be interposed between the multi-quantum well layer 26 and the optical confinement layer 30. The guiding layer 28 may include a first adjacent layer 42 in contact with the outermost layer 40 of the multi-quantum well layer 26. In some embodiments, the guiding layer 28 may include only the first adjacent layer 42. The guiding layer 28 (e.g., including only the first adjacent layer 42) may have the same composition wavelength as the outermost layer 40 of the multi-quantum well layer 26.

[0027] like Figure 3 As shown, the band gap Eg of the first adjacent layer 42 G1 The band gap Eg is greater than 30 of the optical confinement layer. C Therefore, an energy barrier (energy level difference in the conduction band) exists between the guiding layer 28 and the optical confinement layer 30. However, since the guiding layer 28 and the optical confinement layer 30 are n-type semiconductor layers, the resulting electron stagnation is smaller compared to the electron stagnation caused by the energy barrier between the n-type semiconductor layer and the undoped layer. This is because when a sufficient electric field is applied in the n-type layer, electrons move smoothly between the guiding layer 28 and the optical confinement layer 30 due to fewer electrons being stagnated by the energy barrier. This reduces the possibility of low-frequency electrical and / or optical response characteristic attenuation. In some embodiments, the band gap Eg of the first adjacent layer 42... G1 It can be equal to the band gap Eg0 of the outermost layer 40 of the multi-quantum well layer 26, so no energy barrier is formed.

[0028] Light generated in a multi-quantum-well layer (e.g., multi-quantum-well layer 26) can diffuse not only into the multi-quantum-well layer but also into its upper and lower layers (e.g., p-type semiconductor multilayer side and / or n-type semiconductor multilayer side). The region containing the light is defined by the p-type optical confinement layer, the multi-quantum-well layer, and the n-type optical confinement layer. The optical confinement layer can be configured to suppress light diffusion into other regions. In some embodiments, the refractive index of the optical confinement layer is less than the refractive index of the outermost layer of the multi-quantum-well layer (e.g., the barrier layer). This can improve carrier flow. Typically, the greater the refractive index of the optical confinement layer becomes, the smaller the band gap of the optical confinement layer becomes. In some embodiments, the optical confinement layer has a larger band gap than the barrier layer, which prevents the formation of energy barriers in the movement of carriers (e.g., electrons).

[0029] like Figure 3 As shown, the band gap Eg of the optical confinement layer 30 C It can be smaller than the band gap Eg0 of the outermost layer 40 of the multi-quantum-well layer 26. In the InGaAlAs layer, the larger the band gap, the smaller the refractive index. Therefore, the refractive index n of the optical confinement layer 30 is... C The refractive index n0 can be greater than that of the outermost layer 40 of the multi-quantum well layer 26. Therefore, compared to a structure where the refractive index of the optical confinement layer 30 is less than that of the outermost layer 40 of the multi-quantum well layer 26, the optical confinement factor in this region of the multi-quantum well layer 26 can be increased. This increases the optical confinement factor of the multi-quantum well layer 26 and thus improves the overall fr or f3 dB bandwidth.

[0030] Furthermore, as described above, the guiding layer 28 can reduce the influence of the energy barrier between the optical confinement layer 30 and the outermost layer 40 of the multi-quantum-well layer 26 on the electron flow. Therefore, electron stagnation is suppressed and roll-off is reduced. In some embodiments, the refractive index n of the first adjacent layer 42 is... G1 The refractive index n0 is equal to that of the outermost layer 40 of the multi-quantum well layer 26. The refractive index n of the optical confinement layer 30 is also equal to that of the outermost layer 40. C The refractive index n is greater than that of the guide layer 28 (first adjacent layer 42). G1 The strain (e.g., excluding strain) of the first adjacent layer 42 and the strain of the outermost layer 40 may differ, thus slightly distinguishing their respective final component wavelengths (band gaps). However, the individual component wavelengths may be substantially the same, such that the differences between component wavelengths have virtually no impact on the roll-off characteristics or optical constraint factor.

[0031] In some embodiments, the guiding layer 28 (first adjacent layer 42) may contact the optical confinement layer 30. The guiding layer 28 (first adjacent layer 42) may be thinner than the optical confinement layer 30 to confine light within the multi-quantum well layer 26.

[0032] like Figure 2 As shown, the lower mesa structure 34 may include an n-type cladding layer 44 adjacent to the optical confinement layer 30. The n-type cladding layer 44 may include a first n-type InP layer 46A, a diffraction grating layer 48 containing n-type InGaAsP, a second n-type InP layer 46B, and an n-type InGaAsP layer 50. The diffraction grating layer 48 may have a periodic diffraction grating structure, for example, perpendicular to... Figure 2 The cross-sectional view of the example optical semiconductor device shown is a λ / 4 shift structure in the direction.

[0033] The buried layer 52 of p-type InP may fill the lower mesa structure 34 (at least a portion thereof) on both sides. The buried layer 52 may include high-resistivity InP using Fe or Ru as dopants, or may be a stack of materials selected from the group consisting of p-type InP, n-type InP and high-resistivity InP.

[0034] The mesa stripe structure 10 may include an upper mesa structure 54 on top of the lower mesa structure 34. The upper mesa structure 54 may be narrower than the lower mesa structure 34. The upper mesa structure 54 may include a current injection layer 56 having n-type InP and an n-type contact layer 58 in order of proximity to the n-type InGaAsP layer 50. The current injection layer 56 may be part of the n-type cladding 44. Except for its top, the surface of the upper mesa structure 54 may be covered with an insulating layer 60 comprising SiO2. The upper electrode 12 may be electrically and physically connected to the n-type contact layer 58. The upper electrode 12 may have a Ti / Pt / Au three-layer structure that contacts the n-type contact layer 58 from the side. The lower electrode 14 may include an AuZn-based material.

[0035] Figure 4 This is the band diagram of the multi-quantum well layer, the guiding layer, and the optical confinement layer in the example embodiment.

[0036] The pilot layer 228 may consist only of the first adjacent layer 242. The bandgap Eg of the pilot layer 228 (first adjacent layer 242) G1 It can have a bandgap Eg greater than that of the optical confinement layer 230. C The bandgap Eg of the first adjacent layer 242 of the guide layer 228 G1 The band gap Eg0 of the outermost layer 240 of the multi-quantum well layer 226 can be smaller than that of the outermost layer 240. Therefore, there may be a difference in energy levels in the conduction band between the guiding layer 228 (first adjacent layer 242) and the outermost layer 240 of the multi-quantum well layer 226. However, this difference can be smaller than the energy level difference between the optical confinement layer 230 and the outermost layer 240 of the multi-quantum well layer 226. Therefore, the guiding layer 228 (first adjacent layer 242) reduces electron stagnation.

[0037] In the conduction band energy levels, the difference between the first adjacent layer 242 and the outermost layer 240 can be less than half (e.g., less than one-third) of the difference between the optical confinement layer 230 and the outermost layer 240. This can effectively reduce roll-off. In some embodiments, the refractive index n of the optical confinement layer 230 is... C The refractive index n of the guiding layer 228 (first adjacent layer 242) G1 The relationship between the refractive index n0 of the outermost layer 240 of the multi-quantum well layer 226 and the refractive index n0 is as follows: Figure 4 As shown.

[0038] Figure 5 This is the band diagram of the multi-quantum well layer, the guiding layer, and the optical confinement layer in the example embodiment.

[0039] The pilot layer 328 may consist only of the first adjacent layer 342. The bandgap Eg of the pilot layer 328 (first adjacent layer 342) G1 The band gap Eg0 can be greater than that of the outermost layer 340 of the multi-quantum well layer 326. This reduces electron stagnation, thereby reducing roll-off. Electron stagnation can occur even when they are identical n-type semiconductor layers, as the energy level difference between the guiding layer 328 (first adjacent layer 342) and the optical confinement layer 330 can be large. Therefore, the energy difference between the first adjacent layer 342 and the optical confinement layer 330 in the conduction band can be 0.6 eV or less. In some embodiments, the refractive index n of the optical confinement layer 330 is... C The refractive index n of the guiding layer 328 (first adjacent layer 342) G1 The refractive index n of the outermost layer 340 of the multi-quantum well layer 326 O The relationship between them is as follows Figure 5 As shown.

[0040] Figure 6 This is the band diagram of the multi-quantum well layer, the guiding layer, and the optical confinement layer in the example embodiment.

[0041] The guiding layer 428 may include multiple layers. These layers may include a first adjacent layer 442 in contact with the outermost layer 440. These layers may include a second adjacent layer 462 in contact with the optical confinement layer 430. The second adjacent layer 462 and the first adjacent layer 442 may be doped with the same concentration of Si. The thickness of the guiding layer 428 (the total thickness of the first adjacent layer 442 and the second adjacent layer 462) may be less than the thickness of the optical confinement layer 430.

[0042] The band gap Eg of the first adjacent layer 442 of the guide layer 428 G1 It can be equal to the band gap Eg0 of the outermost layer 440 of the multi-quantum-well layer 426. This reduces electron stagnation between the n-type semiconductor layer and the undoped layer.

[0043] The band gap Eg of the second adjacent layer 462G2 It can have a bandgap Eg greater than that of the optical confinement layer 430. C The band gap Eg of the second adjacent layer 462 G2 It can be smaller than the band gap Eg0 of the outermost layer 440 of the multi-quantum well layer 426. The band gap Eg of the second adjacent layer 462... G2 It can be smaller than the band gap Eg of the first adjacent layer 442. G1 This reduces electron stagnation because the energy level changes are stepped within the guiding layer 428 (first adjacent layer 442 and second adjacent layer 462). Furthermore, in some embodiments, the optical confinement layer 430 can increase the optical confinement factor of the multi-quantum-well layer 426. In some embodiments, the refractive index n of the optical confinement layer 430... C The refractive index n of the first adjacent layer 442 G1 The relationship between the refractive index n0 of the outermost layer 440 of the multi-quantum well layer 426 and the refractive index n0 is as follows: Figure 6 As shown.

[0044] Figure 7 This is the band diagram of the multi-quantum well layer, the guiding layer, and the optical confinement layer in the example embodiment.

[0045] The guiding layer 528 may include multiple layers. These layers may include a first adjacent layer 542 in contact with the outermost layer 540 of the multi-quantum-well layer 526. These layers may include a second adjacent layer 562 in contact with the optical confinement layer 530. These layers may 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 may be doped with Si at the same concentration as the first adjacent layer 542.

[0046] The band gap Eg of the first adjacent layer 542 G1 This can be equal to the band gap Eg0 of the outermost layer 540 of the multi-quantum-well layer 526. The band gap Eg of the second adjacent layer 562... G2 The band gap Eg can be greater than that of the optical confinement layer 530. C The band gap Eg of the second adjacent layer 562 G2 This can be equal to the band gap Eg0 of the outermost layer 540 of the multi-quantum-well layer 526. The band gap Eg of the second adjacent layer 562... G2 It can be equal to the band gap Eg of the first adjacent layer 542. G1 The band gap Eg of the intermediate layer 564 G3 It can be equal to the bandgap Eg of the optical confinement layer 530. C .

[0047] The thickness of the guiding layer 528 can be less than half the thickness of the multi-quantum-well layer 526. When the thickness of the guiding layer 528 is greater than half the thickness of the multi-quantum-well layer 526, the optical confinement effect may be insufficient. The thickness of the optical confinement layer 530 can be greater than half the thickness of the multi-quantum-well layer 526. Otherwise, the optical confinement layer 530 may be insufficient to confine light to the multi-quantum-well layer 526.

[0048] The thickness of the intermediate layer 564 can be less than the thickness of the first adjacent layer 542, which does not increase the effect of confining light to the multi-quantum well layer 526. However, the optical confinement layer 530, opposite the second adjacent layer 562, can confine the light entirely to the multi-quantum well layer 526. Therefore, when another layer is inserted between the first adjacent layer 542 and the optical confinement layer 530, a confinement effect is obtained. In some embodiments, the refractive index n of the optical confinement layer 530 is... C The refractive index n of the first adjacent layer 542 G1 The refractive index n of the second adjacent layer 562 G2 The refractive index n of the intermediate layer 564 G3 The relationship between the refractive index n0 of the outermost layer 540 of the multi-quantum well layer 526 and the refractive index n0 is as follows: Figure 7 As shown.

[0049] Figure 8 This is a cross-sectional view of an exemplary optical semiconductor device. The optical semiconductor device may have a semiconductor substrate 620 comprising n-type InP. A buffer layer 622 comprising n-type InP (e.g., an n-type cladding) may be stacked on the semiconductor substrate 620. An optical confinement layer 630, a guiding layer 628, a multiple quantum well layer 626, a p-type SCH layer 624, and a p-type cladding layer 644 may be stacked on the buffer layer 622 in order of proximity to the buffer layer 622. The optical confinement layer 630 and the guiding layer 628 may be referred to as the n-type SCH layer 632.

[0050] Figure 9 This is the band diagram of the multi-quantum well layer, the guiding layer, and the optical confinement layer in the example embodiment.

[0051] The multiple quantum well layer 626 may comprise undoped strained InGaAlAs. The multiple quantum well layer 626 may comprise alternating stacked well layers 636 and barrier layers 638 (e.g., six pairs of well layers 636 and barrier layers 638). The well layers 636 and barrier layers 638 may have the same thickness (e.g., 8 nm). Each barrier layer 638 may be an undoped layer. The outermost layer 640 of the multiple quantum well layer 626 (each of the top and bottom layers) may be one of the barrier layers 638.

[0052] The guiding layer 628 may be an n-type semiconductor layer (e.g., an n-type InGaAlAs layer with a thickness of 40 nm and / or a composition wavelength of 0.93 μm). Si may be used as an n-type dopant. The doping concentration of the guiding layer 628 and the optical confinement layer 630 may be the same or different. The concentration difference should be suitable for applying a sufficient electric field. The guiding layer 628 may be interposed between the multi-quantum well layer 626 and the optical confinement layer 630. The guiding layer 628 may include a first adjacent layer 642 in contact with the outermost layer 640 of the multi-quantum well layer 626. In some embodiments, the guiding layer 628 may include only the first adjacent layer 642. The guiding layer 628 (first adjacent layer 642) may have the same composition wavelength as the outermost layer 640 of the multi-quantum well layer 626.

[0053] The band gap Eg of the first adjacent layer 642 G1 It can have a bandgap Eg greater than that of the optical confinement layer 630. C Therefore, an energy barrier (energy level difference in the conduction band) exists between the guiding layer 628 and the optical confinement layer 630. However, the resulting electron stagnation is smaller than that caused by the energy barrier between the n-type semiconductor layer and the undoped layer because the guiding layer 628 and the optical confinement layer 630 are n-type semiconductor layers. This is because when a sufficient electric field is applied in the n-type layer, electrons move smoothly between the guiding layer 628 and the optical confinement layer 630 due to less electron stagnation caused by the energy barrier. This reduces the likelihood of roll-off in low-frequency electrical and / or optical response characteristics. In some embodiments, the band gap Eg of the first adjacent layer 642... G1 It can be equal to the band gap Eg0 of the outermost layer 640 of the multi-quantum well layer 626, so no energy barrier is formed.

[0054] The optical confinement layer 630 can be an n-type semiconductor layer (e.g., an n-type InGaAlAs layer with a thickness of 80 nm and / or a composition wavelength of 1.15 μm). Si can be used as an n-type dopant.

[0055] The band gap Eg of optical confinement layer 630 C It can be smaller than the band gap Eg0 of the outermost layer 640 of the multi-quantum-well layer 626. In the InGaAlAs layer, the larger the band gap, the smaller the refractive index. Therefore, the refractive index n of the optical confinement layer 630 is... C It can be greater than the refractive index n0 of the outermost layer 640 of the multi-quantum well layer 626. As mentioned above, this may increase the optical confinement factor of the multi-quantum well layer 626, which can improve the fr or improve the f3 dB bandwidth overall.

[0056] In some embodiments, the refractive index n of the first adjacent layer 642 G1The refractive index n0 of the outermost layer 640 of the multi-quantum well layer 626 can be equal to that of the optical confinement layer 630. The refractive index n0 of the optical confinement layer 630 can be greater than the refractive index n of the guiding layer 628 (the first adjacent layer 642). G1 .

[0057] The guiding layer 628 (first adjacent layer 642) can contact the optical confinement layer 630. The guiding layer 628 (first adjacent layer 642) can be thinner than the optical confinement layer 630 to confine light to the multi-quantum well layer 626.

[0058] like Figure 8 As shown, the p-type cladding 644 includes, in order of proximity to the p-type SCH layer 624, a p-type InP layer 666, a diffraction grating layer 648 containing p-type InGaAsP, a current injection layer 656 containing p-type InP, and a p-type contact layer 658. The diffraction grating layer 648 may have a periodic diffraction grating structure, for example, perpendicular to... Figure 8 The cross-sectional view of the example optical semiconductor device shown is a λ / 4 shift structure in the direction.

[0059] A stacked structure from the p-type InP layer 666 to the p-type contact layer 658 can be included in the mesa stripe structure 610. The insulating layer 660 containing SiO2 can be configured to extend from the side surface of the mesa stripe structure 610 to the top surface of the p-type SCH layer 624.

[0060] The upper electrode 612 can be electrically and physically connected to the p-type contact layer 658. The upper electrode 612 can have a Ti / Pt / Au three-layer structure that contacts the p-type contact layer 658 from the side. The lower electrode 614 can include an AuZn-based material.

[0061] The foregoing disclosure provides illustrations and descriptions, but is not intended to be exhaustive or to limit the implementation to the precise forms disclosed. Modifications and variations can be made based on the foregoing disclosure, or can be derived from the practice of implementation. Furthermore, any implementation described herein can be combined unless the foregoing disclosure expressly provides a reason why one or more implementations cannot be combined.

[0062] Even if a particular combination of features is referenced in the claims and / or disclosed in the specification, these combinations are not intended to limit the disclosure of various implementations. In fact, many of these features can be combined in ways not specifically stated in the claims and / or not disclosed in the specification. Although each dependent claim listed below may directly depend on only one claim, the disclosure of various embodiments includes each dependent claim as well as every other claim in the claim set. As used herein, the phrase “at least one” in the list of items refers to any combination of those items, including a single member. For example, “at least one of a, b, or c” is intended to cover any combination of a, b, c, ab, ac, bc, and abc, as well as a plurality of the same items.

[0063] Unless explicitly stated otherwise, the elements, actions, or instructions used herein should not be construed as critical or necessary. Furthermore, as used herein, the article “a” is intended to include one or more items and may be used interchangeably with “one or more.” Furthermore, as used herein, the article “the” is intended to include one or more items associated with the article “the” and may be used interchangeably with “the one or more.” Furthermore, as used herein, the term “group” is intended to include one or more items (e.g., related items, unrelated items, or a combination of related and unrelated items) and may be used interchangeably with “one or more.” When only one item is intended, the phrase “only one” or similar language is used. Furthermore, as used herein, the terms “having” and the like are intended to be open-ended terms. Furthermore, the phrase “based on” is intended to mean “at least partially based on” unless explicitly stated otherwise. Furthermore, as used herein, the term “or” is intended to be included when used in series and may be used interchangeably with “and / or” unless explicitly stated otherwise (e.g., if used in conjunction with “any” or “only one of them”). Furthermore, for ease of description, spatially relative terms such as “down,” “below,” “up,” “above,” etc., may be used herein to describe the relationship of one element or feature to another element or feature shown in the figure. In addition to the orientations shown in the figure, spatially related terms are intended to include different orientations of the equipment, apparatus, and / or element in use or operation. The equipment may be oriented in other ways (rotated 90 degrees or in other orientations), and the spatially relative descriptors used herein may be interpreted accordingly.

[0064] Cross-reference to related applications

[0065] This application claims priority to Japanese Patent Application JP2020-153686, filed on September 14, 2020, and JP2020-188541, filed on November 12, 2020, the contents of which are expressly incorporated herein by reference.

Claims

1. An optical semiconductor device, comprising: Lower countertop structure; An upper platform structure on the lower platform structure, wherein the upper platform structure is narrower than the lower platform structure; A multi-quantum-well layer is included in the lower mesa structure, the multi-quantum-well layer comprising well layers and barrier layers that alternately overlap each other. Each of these barrier layers is an undoped layer. The outermost layer is one of the barrier layers; An optical confinement layer is included in the lower mesa structure and has a refractive index greater than that of the outermost layer, wherein the band gap of the optical confinement layer is smaller than that of the outermost layer. An InGaAlAs guiding layer is interposed between a multi-quantum-well layer and an optical confinement layer. The guiding layer is in direct contact with the optical confinement layer; as well as The guiding layer includes a first adjacent layer that contacts the outermost layer, and the guiding layer is thinner than the optical confinement layer. in: Each of the optical confinement layer and the guiding layer is an n-type semiconductor layer, and The band gap of the first adjacent layer of the guiding layer is larger than that of the optical confinement layer; as well as An InP buried layer surrounds the lower platform structure.

2. The optical semiconductor device of claim 1, wherein the band gap of the first adjacent layer of the guiding layer is equal to the band gap of the outermost layer of the multiple quantum well layer.

3. The optical semiconductor device according to claim 1, wherein the band gap of the first adjacent layer of the guiding layer is smaller than the band gap of the outermost layer of the multiple quantum well layer.

4. The optical semiconductor device of claim 1, wherein the band gap of the first adjacent layer of the guiding layer is greater than the band gap of the outermost layer of the multiple quantum well layer.

5. The optical semiconductor device of claim 1, wherein the guiding layer comprises only the first adjacent layer.

6. The optical semiconductor device according to claim 1, wherein: The guiding layer includes a first adjacent layer in contact with the outermost layer and a second adjacent layer in contact with the optical confinement layer, and The band gap of the second adjacent layer is larger than that of the optically constrained layer.

7. The optical semiconductor device according to claim 6, wherein, The guiding layer also includes at least one intermediate layer between the first adjacent layer and the second adjacent layer.

8. The optical semiconductor device of claim 1, wherein in the conduction band, the energy level difference between the first adjacent layer and the outermost layer is half or less than the energy level difference between the optical confinement layer and the outermost layer.

9. The optical semiconductor device of claim 1, wherein in the conduction band, the energy level difference between the first adjacent layer and the outermost layer is one-third or less of the energy level difference between the optical confinement layer and the outermost layer.

10. The optical semiconductor device of claim 1, wherein in the conduction band, the energy level difference between the first adjacent layer and the optical confinement layer is 0.6 eV or less.

11. The optical semiconductor device of claim 1, wherein the thickness of the guiding layer is half or less than the thickness of the multiple quantum well layer.

12. The optical semiconductor device of claim 1, wherein the thickness of the optical confinement layer is half or more the thickness of the multiple quantum well layer.

13. The optical semiconductor device according to claim 1, further comprising: A p-type separated confined heterostructure layer is arranged adjacent to the multi-quantum well layer and opposite to the guiding layer.

14. An optical semiconductor device, comprising: Lower countertop structure; The upper platform structure located on the lower platform structure. The upper platform structure is narrower than the lower platform structure; A multi-quantum-well layer is included in the lower mesa structure, the multi-quantum-well layer comprising well layers and barrier layers that alternately overlap each other. Each of these barrier layers is an undoped layer, and The outermost layer is one of the barrier layers; An optical confinement layer is included in the lower mesa structure and has a refractive index greater than that of the outermost layer, wherein the band gap of the optical confinement layer is smaller than that of the outermost layer. An InGaAlAs guiding layer is interposed between the multiple quantum well layer and the optical confinement layer. The guiding layer is in direct contact with the optical confinement layer. The guiding layer includes a first adjacent layer in contact with the outermost layer, and the guiding layer is thinner than the optical confinement layer. The band gap of the first adjacent layer of the guiding layer is larger than the band gap of the optical confinement layer; as well as An InP buried layer surrounds the lower platform structure.

15. The optical semiconductor device of claim 14, wherein the band gap of the first adjacent layer of the guiding layer is greater than the band gap of the outermost layer of the multiple quantum well layer.

16. The optical semiconductor device of claim 14, wherein the guiding layer comprises only the first adjacent layer.

17. The optical semiconductor device of claim 14, wherein in the conduction band, the energy level difference between the first adjacent layer and the optical confinement layer is 0.6 eV or less.

18. The optical semiconductor device of claim 14, wherein the optical confinement layer and the guiding layer are contained in an n-type discrete confinement heterostructure layer.

19. An optical semiconductor device, comprising: Lower countertop structure; The upper platform structure located on the lower platform structure. The upper platform structure is narrower than the lower platform structure; A multi-quantum well layer is included in the lower mesa structure, the multi-quantum well layer comprising a number of well layers and a number of barrier layers that overlap each other alternately; Each of these barrier layers is an undoped layer, and The outermost layer is one of the barrier layers; An optical confinement layer is included in the lower mesa structure and has a refractive index greater than that of the outermost layer; The band gap of the optical confinement layer is smaller than that of the outermost layer; An InGaAlAs guiding layer is interposed between the multiple quantum well layer and the optical confinement layer. The guiding layer is in direct contact with the optical confinement layer; The guiding layer includes a first adjacent layer in contact with the outermost layer, and the guiding layer is thinner than the optical constraint layer. Each of the optical confinement layer and the guiding layer is an n-type semiconductor layer. The band gap of the first adjacent layer of the guiding layer is larger than the band gap of the optical confinement layer, and The optical confinement layer and the guiding layer are contained within an n-type separated confinement heterostructure layer; as well as An InP buried layer surrounds the lower platform structure.

20. The optical semiconductor device of claim 19, wherein the band gap of the first adjacent layer of the guiding layer is greater than the band gap of the outermost layer of the multiple quantum well layer.

21. The optical semiconductor device of claim 19, wherein the guiding layer comprises only the first adjacent layer.

22. The optical semiconductor device of claim 19, wherein in the conduction band, the energy level difference between the first adjacent layer and the optical confinement layer is 0.6 eV or less.

23. The optical semiconductor device of claim 19, wherein the InP buried layer comprises at least one of the following: InP doped with Fe or Ru, or A laminate comprising at least one of the following materials: p-type InP, n-type InP, or High resistance InP.

24. The optical semiconductor device of claim 1, wherein the InP buried layer comprises at least one of the following: InP doped with Fe or Ru, or A laminate comprising at least one of the following materials: p-type InP, n-type InP, or High resistance InP.

25. The optical semiconductor device of claim 14, wherein the InP buried layer comprises at least one of the following: InP doped with Fe or Ru, or A laminate comprising at least one of the following materials: p-type InP, n-type InP, or High resistance InP.

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