Semiconductor laser and method for manufacturing semiconductor laser

Abstract

A semiconductor laser (100) according to the present invention is provided with: a ridge structure (16) that is formed on an n-type semiconductor substrate (1); and an embedded layer (13) that is embedded so as to cover the both sides of the ridge structure (16), the both sides being opposite to each other in a direction that is perpendicular to the extending direction of the ridge structure (16). The ridge structure (16) comprises an n-type clad layer (4), an active layer (5) and a p-type clad layer (6), which are sequentially formed from the n-type semiconductor substrate (1) side. The embedded layer (13) has a semi-insulating layer (8) and a p-type semiconductor layer (7b) that is in contact with both lateral surfaces of the p-type clad layer (6) and the active layer (5) of the ridge structure (16); and the p-type semiconductor layer (7b) is not in contact with the n-type clad layer (4) of the ridge structure (16).

Description

[Technical field]

[0001] The present application relates to a semiconductor laser and a method for manufacturing a semiconductor laser. [Background technology]

[0002] Patent Document 1 discloses an optical semiconductor device including a mesa stripe structure s2 having an n-type InP cladding layer s3, an active layer s4, and a p-type InP cladding layer s5 stacked in order, and buried layers s7 buried on both sides of the mesa stripe structure s2, the active layer s4 being a multiple quantum well structure having a well layer and a barrier layer to which carbon is added, and the buried layer s7 having a p-type InP layer s10, an Fe-doped InP layer s11, and an n-type InP layer s12 stacked in order. The sides of the n-type InP cladding layer s3 and the p-type InP cladding layer s5 in the mesa stripe structure s2 are covered with the p-type InP layer s10, and the side of the active layer s4 in the mesa stripe structure s2 is not in contact with the p-type InP layer s10 but is in contact with the Fe-doped InP layer s11. The symbols used in Patent Document 1 are distinguished from the symbols in the present specification by adding "s".

[0003] The optical semiconductor device of Patent Document 1 has a modulation doped structure in which carbon is added to the barrier layer of the active layer s4, and in order to prevent the modulation doped structure from collapsing due to diffusion of the p-type dopant zinc (Zn) from the p-type InP layer s10 to the active layer s4, the side of the active layer s4 is not in contact with the p-type InP layer s10 but is in contact with the iron (Fe)-doped InP layer s11.

[0004] In general, a structure is adopted in which the side surface of the active layer s4 is in contact with the p-type InP layer s10. This structure is disclosed in FIG. 8 of Patent Document 1. In the optical semiconductor device disclosed in FIG. 8 of Patent Document 1 (the optical semiconductor device of the comparative example), the p-type InP layer s10 is in contact with the side surface of the p-type InP cladding layer s5. Therefore, when a hole current is caused to flow from the p-type InP cladding layer s5 to the active layer s4 and an electron current is caused to flow from the n-type InP cladding layer s3 to the active layer s4 to generate laser light, some holes leak to the p-type InP layer s10 on the side surface before holes are injected from the p-type InP cladding layer s5 to the active layer s4, which causes a problem of generating a reactive current that does not pass through the active layer s4. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] JP 2016-31970 A (Fig. 1) Summary of the Invention [Problem to be solved by the invention]

[0006] The optical semiconductor device of Patent Document 1 employs a structure in which the p-type InP layer s10 does not contact the side surface of the active layer s4, thereby avoiding the deterioration of the characteristics of the optical semiconductor device due to the optical loss caused by carrier absorption and inter-valence band absorption in the active layer s4, which would occur if the side surface of the active layer s4 were in contact with the p-type InP layer s10.

[0007] On the other hand, the p-type InP layer s10 has a role of preventing the electronic current injected into the active layer s4 from overflowing due to the influence of heat and leaking outward from the side surface of the active layer s4, that is, a role of an energy barrier against electrons. In the optical semiconductor device of Patent Document 1, since the p-type InP layer s10 is not in contact with the side surface of the active layer s4, the energy barrier against the electronic current is insufficient, and there is a concern that electron overflow occurs, particularly during high-temperature operation, and that this may result in a decrease in optical output characteristics and a decrease in high-speed operation characteristics. In particular, zinc (Zn), which is a dopant in the surrounding p-type InP layer s10, may diffuse into the Fe-doped InP layer s11 in contact with the side surface of the active layer s4, and when the Fe-doped InP layer s11 no longer functions as a high-resistance semiconductor layer or a semi-insulating semiconductor layer, the performance degradation becomes significant.

[0008] The technology disclosed in the present specification aims to realize a semiconductor laser capable of reducing reactive current that does not pass through the active layer and improving optical output characteristics and high-speed operation performance. [Means for solving the problem]

[0009] The semiconductor laser disclosed in the present specification is a semiconductor laser including a ridge structure formed on an n-type semiconductor substrate and a buried layer buried in such a way as to cover both sides of the ridge structure that face each other in a direction perpendicular to the extension direction of the ridge structure. , life sex layer, An n-type cladding layer is formed so as to contact the n-type semiconductor substrate side of the active layer, and an n-type cladding layer is formed so as to contact the opposite side of the active layer to the n-type semiconductor substrate. The buried layer has a p-type semiconductor layer in contact with both side surfaces of the p-type cladding layer and the active layer of the ridge structure, a semi-insulating layer, and has other p-type semiconductor layers on the n-type semiconductor substrate side on both side surfaces of the n-type cladding layer of the ridge structure, the p-type semiconductor layer is not in contact with the n-type cladding layer of the ridge structure, and a separation portion separating the p-type semiconductor layer from the other p-type semiconductor layer is formed on the active layer side on both side surfaces of the n-type cladding layer of the ridge structure, and a semi-insulating layer is buried in the separation portion. Effect of the Invention

[0010] In the semiconductor laser as an example disclosed in the present specification, the p-type semiconductor layers in contact with both side surfaces of the p-type cladding layer and active layer of the ridge structure are not in contact with the n-type cladding layer of the ridge structure, and therefore it is possible to reduce reactive current that does not pass through the active layer and to improve the optical output characteristics and high-speed operation performance. [Brief description of the drawings]

[0011] [Figure 1] 1 is a diagram showing a cross-sectional structure of a semiconductor laser according to a first embodiment. [Diagram 2] FIG. 2 is an enlarged view of the periphery of the active layer in FIG. [Diagram 3] FIG. 2 is a diagram showing the active layer of FIG. [Figure 4] FIG. 2 is an enlarged view of the periphery of an active layer of a comparative example. [Diagram 5] 11 is a diagram showing a cross-sectional structure of a semiconductor laser according to a second embodiment. FIG. [Figure 6] FIG. 6 is an enlarged view of the periphery of the active layer in FIG. 5. [Figure 7] 11 is a diagram showing a cross-sectional structure of a semiconductor laser according to a third embodiment. [Figure 8] 8A to 8C are diagrams illustrating a method for manufacturing the semiconductor laser of FIG. [Figure 9] 8A to 8C are diagrams illustrating a method for manufacturing the semiconductor laser of FIG. [Figure 10] 8A to 8C are diagrams illustrating a method for manufacturing the semiconductor laser of FIG. [Figure 11] 8A to 8C are diagrams illustrating a method for manufacturing the semiconductor laser of FIG. [Figure 12] 8A to 8C are diagrams illustrating a method for manufacturing the semiconductor laser of FIG. [Figure 13] 8A to 8C are diagrams illustrating a method for manufacturing the semiconductor laser of FIG. [Figure 14] FIG. 11 is a diagram showing a cross-sectional structure of a first semiconductor laser according to the fourth embodiment. [Figure 15] 15A to 15C are diagrams illustrating a method for manufacturing the semiconductor laser of FIG. [Figure 16] 15A to 15C are diagrams illustrating a method for manufacturing the semiconductor laser of FIG. [Figure 17] 15A to 15C are diagrams illustrating a method for manufacturing the semiconductor laser of FIG. [Figure 18] FIG. 11 is a diagram showing a cross-sectional structure of a second semiconductor laser according to the fourth embodiment. [Figure 19] FIG. 13 is a diagram showing a cross-sectional structure of a third semiconductor laser according to the fourth embodiment. [Figure 20] FIG. 13 is a diagram showing a cross-sectional structure of a semiconductor laser according to a fifth embodiment. [Figure 21] FIG. 21 is an enlarged view of the periphery of the active layer in FIG. 20. [Figure 22] 22 is a diagram showing the energy bands of the extension base layer and the p-type semiconductor layer of FIG. 21. FIG. [Diagram 23] FIG. 13 is a diagram showing a cross-sectional structure of a semiconductor laser according to a sixth embodiment. [Figure 24] FIG. 24 is an enlarged view of the periphery of the active layer in FIG. 23. [Diagram 25] 24A to 24C are diagrams illustrating a method for manufacturing the semiconductor laser of FIG. 23. [Figure 26] 24A to 24C are diagrams illustrating a method for manufacturing the semiconductor laser of FIG. 23. [Figure 27] FIG. 13 is a diagram showing a cross-sectional structure of a semiconductor laser according to a seventh embodiment. [Figure 28] FIG. 28 is an enlarged view of the periphery of the active layer in FIG. [Figure 29] 28A to 28C are diagrams illustrating a method for manufacturing the semiconductor laser of FIG. 27. [Diagram 30] 28A to 28C are diagrams illustrating a method for manufacturing the semiconductor laser of FIG. 27. [Diagram 31] 28A to 28C are diagrams illustrating a method for manufacturing the semiconductor laser of FIG. 27. [Diagram 32] 28A to 28C are diagrams illustrating a method for manufacturing the semiconductor laser of FIG. 27. [Diagram 33] 28A to 28C are diagrams illustrating a method for manufacturing the semiconductor laser of FIG. 27. [Diagram 34] 28A to 28C are diagrams illustrating a method for manufacturing the semiconductor laser of FIG. 27. [Diagram 35] 13A to 13C are diagrams illustrating a method for manufacturing a semiconductor laser according to an eighth embodiment. [Diagram 36] FIG. 13 is a diagram showing a cross-sectional structure of a semiconductor laser according to a ninth embodiment. [Figure 37]FIG. 37 is an enlarged view of the periphery of the active layer in FIG. 36. [Figure 38] 37A to 37D are diagrams illustrating a method for manufacturing the semiconductor laser of FIG. 36. [Figure 39] 37A to 37D are diagrams illustrating a method for manufacturing the semiconductor laser of FIG. 36. [Diagram 40] 37A to 37D are diagrams illustrating a method for manufacturing the semiconductor laser of FIG. 36. [Diagram 41] 37A to 37D are diagrams illustrating a method for manufacturing the semiconductor laser of FIG. 36. [Diagram 42] 13A to 13C are diagrams illustrating a method for manufacturing a semiconductor laser according to a tenth embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0012] Embodiment 1 Fig. 1 is a diagram showing a cross-sectional structure of a semiconductor laser according to a first embodiment, and Fig. 2 is an enlarged view of the periphery of an active layer in Fig. 1. Fig. 3 is a diagram showing the active layer in Fig. 1, and Fig. 4 is an enlarged view of the periphery of an active layer of a comparative example. The semiconductor laser 100 of the first embodiment includes a first n-type cladding layer 2 of n-type InP formed on the surface of an n-type semiconductor substrate 1 which is an n-type InP substrate, a ridge structure 16 having a part of the first n-type cladding layer 2, a diffraction grating layer 3, a second n-type cladding layer 4 of n-type InP, an active layer 5, and a first p-type cladding layer 6 of p-type InP, p-type semiconductor layers 7a and 7b of p-type InP formed on both side surfaces facing each other in a direction perpendicular to the extension direction of the ridge structure 16, and both side surfaces of a part of the second n-type cladding layer 4. The semiconductor laser 100 includes a semi-insulating layer 8 covering the n-type semiconductor substrate 1 and the p-type semiconductor layers 7a and 7b, a block layer 9 of n-type InP formed on the surface of the semi-insulating layer 8, a second p-type cladding layer 10 of p-type InP formed on the surface of the block layer 9 and the surface of the first p-type cladding layer 6, a contact layer 11 of p-type InGaAs formed on the surface of the second p-type cladding layer 10, an anode electrode 51 formed on the surface of the contact layer 11, and a cathode electrode 52 formed on the back surface opposite to the front surface of the n-type semiconductor substrate 1. The semiconductor layer consisting of the p-type semiconductor layers 7a and 7b, the semi-insulating layer 8, and the block layer 9 is a buried layer 13 buried so as to cover both sides facing each other in a direction perpendicular to the extension direction of the ridge structure 16. The semiconductor laser 100 shown in FIG. 1 is an example of a distributed feedback laser diode (DFB-LD). The direction perpendicular to the n-type semiconductor substrate 1 is the z-direction, the extension direction of the ridge structure 16 perpendicular to the z-direction is the y-direction, and the direction perpendicular to the z-direction and the y-direction is the x-direction. The first n-type cladding layer 2, diffraction grating layer 3, second n-type cladding layer 4, active layer 5, and first p-type cladding layer 6 that constitute the ridge structure 16 are formed in this order on the positive side in the z direction. Both side surfaces of the ridge structure 16 in the x direction and the side surfaces of the ridge structure 16 in the x direction will be referred to as both side surfaces of the ridge structure 16 and the side surfaces of the ridge structure 16 as appropriate.

[0013] The p-type semiconductor layer 7a is formed on the surface on the positive side in the z direction of the first n-type cladding layer 2 and on the side surface of the ridge structure 16 facing the n-type semiconductor substrate 1. The p-type semiconductor layer 7b is formed on the positive side in the z direction on both side surfaces of the ridge structure 16, sandwiching an isolation portion 17 separated from the p-type semiconductor layer 7a. The area between the dashed lines 54a and 54b is the region 53 in the x direction of the ridge structure 16, and the area between the dashed lines 55a and 55b is the isolation portion 17. In the isolation portion 17, the semi-insulating layer 8 contacts both side surfaces of the second n-type cladding layer 4, i.e., both side surfaces in the x direction.

[0014] The material of the diffraction grating layer 3 is a material having a refractive index larger than that of InP, such as InGaAsP. If the semiconductor laser 100 is not a DFB-LD, the diffraction grating layer 3 is not formed. The active layer 5 generally has a quantum well structure and an SCH (Separate Confinement) structure. t FIG. 3 shows an active layer 5 including a quantum well structure 35 in which well layers 32 and barrier layers 33 are alternately stacked, a light confinement layer 31 formed on the second n-type cladding layer 4 side of the quantum well structure 35, and a light confinement layer 34 formed on the first p-type cladding layer 6 side. The quantum well structure 35 of the active layer 5 shown in FIG. 3 includes four well layers 32 and three barrier layers 33 formed between the well layers 32. The SCH structure includes light confinement layers 31 and 34 that confine electrons and holes in the quantum well structure 35 as shown in FIG. 3. The material of each of the well layers 32, the barrier layers 33, and the light confinement layers 31 and 34 is, for example, AlGaInAs.

[0015] The end of the p-type semiconductor layer 7b on the n-type semiconductor substrate 1 side is preferably below the starting interface of the quantum well structure 35 of the active layer 5, i.e., the interface between the light confinement layer 31 on the second n-type cladding layer 4 side and the well layer 32 formed on the surface of the light confinement layer 31. In terms of the separation portion 17, the end of the separation portion 17 on the p-type semiconductor layer 7b side is preferably below the starting interface of the quantum well structure 35 of the active layer 5 on the n-type semiconductor substrate 1 side, i.e., on the n-type semiconductor substrate 1 side. The separation length L, which is the length of the separation portion 17 in the z direction, may be long enough to block the hole current. For example, the separation length L is about 0.2 um.

[0016] A method for forming the ridge structure 16 will be described in the manufacturing method for manufacturing the semiconductor laser 100 of the third embodiment. The p-type semiconductor layers 7a, 7b separated by the separation portion 17 are formed, for example, as follows. In the case of the active layer 5 using a compound semiconductor containing aluminum (Al), an oxide layer is formed on the side surface of the active layer 5, so that the p-type semiconductor layers 7a, 7b are not grown on the side surface of the active layer 5. For this reason, in the manufacturing process for manufacturing the semiconductor laser of the comparative example shown in FIG. 4, hydrogen chloride (HCl) is added into a crystal growth furnace to remove the oxide layer on the side surface of the active layer 5, and then the p-type semiconductor layer 7 is grown. However, in the first embodiment, the p-type semiconductor layers 7a, 7b are grown without removing the oxide layer by adding hydrogen chloride. This allows the p-type semiconductor layers 7a, 7b to have a structure that does not contact the side surface of the active layer 5. After the p-type semiconductor layers 7a, 7b are formed on both side surfaces of the ridge structure 16, hydrogen chloride is added to remove the oxide layer on the side surfaces of the active layer 5, and then the semi-insulating layer 8 is grown to form the p-type semiconductor layers 7a, 7b and the semi-insulating layer 8 in the buried layer 13. The manufacturing process thereafter is the same as that of the third embodiment.

[0017] In order to operate the semiconductor laser 100 to generate laser light, a hole current is injected into the semiconductor layers of the semiconductor material, i.e., the contact layer 11, the second p-type cladding layer 10, the first p-type cladding layer 6 in the ridge structure 16, and the active layer 5, via the anode electrode 51, and an electron current is injected into the n-type semiconductor substrate 1 and the semiconductor layers of the ridge structure 16, i.e., the first n-type cladding layer 2, the diffraction grating layer 3, the second n-type cladding layer 4, and the active layer 5, via the cathode electrode 52. The semiconductor laser 100 of the first embodiment generates laser light by recombining holes 14 and electrons 15 in the active layer 5.

[0018] Holes 14, which are majority carriers in the contact layer 11 and the second p-type cladding layer 10, move toward the active layer 5, and a hole current Ih flows. The hole current Ih is composed of a main current I1 that flows from the first p-type cladding layer 6 to the active layer 5, and a bypass current I2 that flows from the first p-type cladding layer 6 to the active layer 5 via the p-type semiconductor layer 7b. The bypass current I2 is a hole current component that leaks from the first p-type cladding layer 6 to the p-type semiconductor layer 7b. However, this bypass current I2 cannot flow through the separation portion 17 where the semi-insulating layer 8 is present, and flows toward the valence band of the active layer 5, which is at a lower energy level than the valence band of the p-type semiconductor layer 7b, and is therefore injected into the active layer 5.

[0019] Electrons 15, which are majority carriers in the n-type semiconductor substrate 1 and the first n-type cladding layer 2, move to the active layer 5, and an electron current Ie flows. The electron current Ie flows through the diffraction grating layer 3 and the second n-type cladding layer 4 to the active layer 5. The side surface of the active layer 5, i.e., the x-direction side surface, is in contact with the p-type semiconductor layer 7b, and the energy level of the conduction band of the p-type semiconductor layer 7b is higher than the energy level of the conduction band of the active layer 5. Therefore, the p-type semiconductor layer 7b forms an energy barrier against the electron current Ie, and the electron current Ie does not overflow from the active layer 5 to the semi-insulating layer 8, i.e., in the x-direction. Therefore, unlike the optical semiconductor device of Patent Document 1, the semiconductor laser 100 of the first embodiment does not deteriorate in the characteristics of the semiconductor laser, i.e., the optical output characteristics and the high-speed operation characteristics, even in a high-temperature environment.

[0020] Furthermore, the second n-type cladding layer 4 and the semi-insulating layer 8 are in contact with each other at the separation portion 17. At this time, an energy barrier formed by the junction between the two prevents overflow of the electron current Ie into the semi-insulating layer 8. Furthermore, if the semi-insulating layer 8 is, for example, an iron (Fe)-doped semi-insulating layer so that it has a particularly high resistance to electrons, the performance of suppressing the overflow of the electron current Ie from the second n-type cladding layer 4 to the semi-insulating layer 8 is further improved.

[0021] In the semiconductor laser of the comparative example shown in FIG. 4, the p-type semiconductor layer 7 is formed on the side of the ridge structure without the separation portion 17 interposed therebetween. The hole current Ih for driving the semiconductor laser of the comparative example is composed of a main current I1 flowing from the first p-type cladding layer 6 to the active layer 5, and a bypass current I3 flowing from the first p-type cladding layer 6 to the second n-type cladding layer 4 and the first n-type cladding layer 2 via the p-type semiconductor layer 7. The electron current Ie for driving the semiconductor laser of the comparative example passes through the diffraction grating layer 3 and the second n-type cladding layer 4 and flows to the active layer 5. The semiconductor laser of the comparative example generates laser light by recombining holes 14 and electrons 15 in the active layer 5, similar to the semiconductor laser 100 of the first embodiment.

[0022] In the semiconductor laser of the comparative example, a bypass current I3, which is a part of the hole current Ih, leaks from the x-direction side surface of the first p-type cladding layer 6 to the p-type semiconductor layer 7. The bypass current I3 does not flow into the active layer 5, but flows into the second n-type cladding layer 4 and the first n-type cladding layer 2, and therefore the bypass current I3 is a reactive current that does not pass through the active layer 5. Therefore, in the semiconductor laser of the comparative example, since there is a reactive current that does not pass through the active layer 5, unlike the semiconductor laser 100 of the first embodiment, the semiconductor laser characteristics, i.e., the optical output characteristics and high-speed operation characteristics, are deteriorated, and a high-output, high-speed semiconductor laser cannot be realized.

[0023] The semiconductor laser 100 of the first embodiment differs from the semiconductor laser of the comparative example in that the p-type semiconductor layer 7b arranged farther from the n-type semiconductor substrate 1 than the separation portion 17 covers the x-direction side surface of the quantum well structure 35 in the active layer 5, so that the bypass current I2, which is a part of the hole current Ih that has passed from the first p-type cladding layer 6 through the p-type semiconductor layer 7b, can be injected into the active layer 5, and the electron current Ie does not overflow from the active layer 5. Therefore, the semiconductor laser 100 of the first embodiment can prevent a reactive current that does not pass through the active layer 5, and can improve the optical output characteristics and high-speed operation performance.

[0024] In the semiconductor laser of the comparative example, the area of ​​the p-type layer connection part, which is the part where the x-direction side surface of the first p-type cladding layer 6 and the p-type semiconductor layer 7 are connected, varies during the manufacturing process. When the area of ​​the p-type layer connection part varies, the amount of hole current leaking to the p-type semiconductor layer 7, i.e., the amount of bypass current I3, varies, and the amount of reactive current varies. For this reason, the semiconductor laser of the comparative example also has large variations in laser characteristics.

[0025] The semiconductor laser 100 of the first embodiment also has a p-type layer connection portion, which is a portion where the x-direction side surface of the first p-type cladding layer 6 is connected to the p-type semiconductor layer 7b. This p-type layer connection portion is affected by manufacturing variations, and the area of ​​the p-type layer connection portion varies. However, in the semiconductor laser 100 of the first embodiment, the hole current Ih leaked to the p-type semiconductor layer 7b, i.e., the bypass current I2, is injected into the active layer 5 and contributes to the laser operation, so that the characteristics do not vary depending on the amount of the bypass current I2 leaked to the p-type semiconductor layer 7b. Therefore, the semiconductor laser 100 of the first embodiment can reduce the characteristic variation due to manufacturing variations in the p-type layer connection portion, which is a portion where the x-direction side surface of the first p-type cladding layer 6 is connected to the p-type semiconductor layer 7.

[0026] As described above, the semiconductor laser 100 of the first embodiment is a semiconductor laser including the ridge structure 16 formed on the n-type semiconductor substrate 1 and the buried layer 13 buried so as to cover both sides facing each other in a direction perpendicular to the extension direction of the ridge structure 16. The ridge structure 16 includes an n-type cladding layer (second n-type cladding layer 4), an active layer 5, and a p-type cladding layer (first p-type cladding layer 6) formed in this order from the n-type semiconductor substrate 1 side. The buried layer 13 includes a p-type semiconductor layer 7b in contact with both side surfaces of the p-type cladding layer (first p-type cladding layer 6) and the active layer 5 of the ridge structure 16, and a semi-insulating layer 8, and the p-type semiconductor layer 7b is not in contact with the n-type cladding layer (second n-type cladding layer 4) of the ridge structure 16. In the semiconductor laser 100 of the first embodiment, due to this configuration, the p-type semiconductor layer 7b in contact with the p-type cladding layer (first p-type cladding layer 6) of the ridge structure 16 and both side surfaces of the active layer 5 is not in contact with the n-type cladding layer (second n-type cladding layer 4) of the ridge structure 16, so that reactive current that does not pass through the active layer 5 can be prevented, and the optical output characteristics and high-speed operating performance can be improved.

[0027] In the semiconductor laser 100 of the first embodiment, the embedded layer 13 may have another p-type semiconductor layer 7a on the n-type semiconductor substrate 1 side of both side surfaces of the n-type cladding layer (second n-type cladding layer 4) of the ridge structure 16. In this case, a separation portion 17 is formed on the active layer 5 side of both side surfaces of the n-type cladding layer (second n-type cladding layer 4) of the ridge structure 16, where the p-type semiconductor layer 7b and the other p-type semiconductor layer 7a are separated, and a semi-insulating layer 8 is buried in the separation portion 17. With this configuration, in the semiconductor laser 100 of the first embodiment, even if there is another p-type semiconductor layer 7a on the side of the n-type semiconductor substrate 1 on both side surfaces of the n-type cladding layer (second n-type cladding layer 4) of the ridge structure 16, the p-type semiconductor layers 7b in contact with both side surfaces of the p-type cladding layer (first p-type cladding layer 6) of the ridge structure 16 and the active layer 5 are not in contact with the n-type cladding layer (second n-type cladding layer 4) of the ridge structure 16, so that reactive current that does not pass through the active layer 5 can be prevented, and the optical output characteristics and high-speed operating performance can be improved.

[0028] Embodiment 2 Fig. 5 is a diagram showing a cross-sectional structure of a semiconductor laser according to the second embodiment, and Fig. 6 is an enlarged view of the periphery of the active layer in Fig. 5. The semiconductor laser 100 of the second embodiment is different from the semiconductor laser 100 of the first embodiment in that the p-type semiconductor layer 7 is in contact with the first p-type cladding layer 6 and the active layer 5 on both side surfaces of the ridge structure 16, and the p-type semiconductor layer 7 is not in contact with both side surfaces of each layer of the ridge structure 16 from the active layer 5 to the n-type semiconductor substrate 1 side. Figs. 5 and 6 show an example in which the p-type semiconductor layer 7 covers both side surfaces of the first p-type cladding layer 6 and the active layer 5 up to a specific position on both side surfaces of the ridge structure 16. The specific position in Fig. 5 and Fig. 6 is a position that is farther from the n-type semiconductor substrate 1 side than the near end of the active layer 5 on the n-type semiconductor substrate 1 side in the quantum well structure 35 of the active layer 5, that is, a position that does not reach the near end on the n-type semiconductor substrate 1 side in the quantum well structure 35 of the active layer 5, that is, the starting interface of the quantum well structure 35, and is an end including the near end on the n-type semiconductor substrate 1 side in the quantum well structure 35, that is, a position in the middle of the light confinement layer 31 on the n-type semiconductor substrate 1 side of the active layer 5. The p-type semiconductor layer 7 covers both side surfaces of the quantum well structure 35 of the active layer 5. The specific position of the active layer 5 may be the near end on the n-type semiconductor substrate 1 side of the active layer 5. The following mainly describes the parts that are different from the semiconductor laser 100 of the first embodiment.

[0029] In the semiconductor laser 100 of the second embodiment, the semi-insulating layer 8 is in contact with both side surfaces of the first n-type cladding layer 2, the diffraction grating layer 3, and the second n-type cladding layer 4 on the n-type semiconductor substrate 1 side in the ridge structure 16. In the semiconductor laser 100 of the second embodiment, like the semiconductor laser 100 of the first embodiment, holes 14, which are majority carriers in the contact layer 11 and the second p-type cladding layer 10, move to the active layer 5 side when the semiconductor laser is driven, and a hole current Ih flows. The hole current Ih is composed of a main current I1 that flows from the first p-type cladding layer 6 to the active layer 5, and a bypass current I2 that flows from the first p-type cladding layer 6 to the active layer 5 via the p-type semiconductor layer 7. The bypass current I2 is a hole current component that leaks from the first p-type cladding layer 6 to the p-type semiconductor layer 7. However, this bypass current I2 cannot flow along the side of the second n-type cladding layer 4 where the semi-insulating layer 8 is present, and instead flows toward the valence band of the active layer 5, which is at a lower energy level than the valence band of the p-type semiconductor layer 7, and is therefore injected into the active layer 5.

[0030] The semiconductor laser 100 of the second embodiment is similar to the semiconductor laser 100 of the first embodiment except that the p-type semiconductor layer 7 is not in contact with both side surfaces of each layer on the n-type semiconductor substrate 1 side of the active layer 5 of the ridge structure 16, and therefore has the same effects as the semiconductor laser 100 of the first embodiment.

[0031] As described above, the semiconductor laser 100 of the second embodiment is a semiconductor laser including the ridge structure 16 formed on the n-type semiconductor substrate 1 and the buried layer 13 buried so as to cover both sides of the ridge structure 16 that face each other in a direction perpendicular to the extension direction. The ridge structure 16 includes an n-type cladding layer (second n-type cladding layer 4), an active layer 5, and a p-type cladding layer (first p-type cladding layer 6) that are successively formed from the n-type semiconductor substrate 1 side. The buried layer 13 includes a p-type semiconductor layer 7 that contacts both side surfaces of the p-type cladding layer (first p-type cladding layer 6) and the active layer 5 of the ridge structure 16, and a semi-insulating layer 8. The p-type semiconductor layer 7 is not in contact with the n-type cladding layer (second n-type cladding layer 4) of the ridge structure 16, and the semi-insulating layer 8 contacts both side surfaces of the n-type cladding layer (second n-type cladding layer 4) of the ridge structure 16. In the semiconductor laser 100 of the second embodiment, due to this configuration, the p-type semiconductor layers 7 in contact with the p-type cladding layer (first p-type cladding layer 6) of the ridge structure 16 and both side surfaces of the active layer 5 are not in contact with the n-type cladding layer (second n-type cladding layer 4) of the ridge structure 16, so that reactive current that does not pass through the active layer 5 can be prevented, and the optical output characteristics and high-speed operating performance can be improved.

[0032] Embodiment 3 Fig. 7 is a diagram showing a cross-sectional structure of a semiconductor laser according to embodiment 3. Figs. 8 to 13 are diagrams showing a method for manufacturing the semiconductor laser of Fig. 7. Semiconductor laser 100 of embodiment 3 differs from semiconductor laser 100 of embodiment 1 in that ridge structure 16 has ridge main body 63 and ridge extensions 64 extending in the x-direction from both side surfaces of ridge main body 63, and separation portion 17 is formed on the n-type semiconductor substrate 1 side of ridge extension 64. The differences from semiconductor laser 100 of embodiment 1 will be mainly described.

[0033] In the third embodiment, an example will be described in which the ridge intermediate layer 39 in which the ridge extension 64 is formed is the active layer 5. In the first embodiment, a case in which the active layer 5 is a compound semiconductor containing Al has been described as an example of a method for forming the p-type semiconductor layers 7a and 7b separated from each other with the separation portion 17 interposed between both side surfaces of the ridge structure 16. In the third embodiment, a method will be described in which the p-type semiconductor layers 7a and 7b separated from each other with the separation portion 17 interposed between them easily even when the active layer 5 does not contain Al.

[0034] 8 to 10 are diagrams for explaining a ridge structure forming step of forming a basic ridge structure 16 on an n-type semiconductor substrate 1. FIG. 11 is a diagram for explaining an extension forming step of etching layers other than the ridge intermediate layer 39 on both side surfaces of the basic ridge structure 16 to form ridge extensions 64 extending in the x-direction from both side surfaces of the ridge structure 16 in the ridge intermediate layer 39. FIG. 12 is a diagram for explaining a p-type semiconductor layer forming step of forming p-type semiconductor layers 7a, 7b so as to cover both side surfaces of the ridge structure 16 and the surface of the ridge extension 64 opposite to the n-type semiconductor substrate 1. FIG. 13 is a diagram for explaining a semi-insulating layer forming step of forming a semi-insulating layer 8 so as to cover the surfaces of the p-type semiconductor layers 7a, 7b and the exposed surface of the ridge extension 64 on the n-type semiconductor substrate 1 side, and a step of forming a block layer 9.

[0035] On the surface of an n-type semiconductor substrate 1, a first n-type cladding layer 2, a diffraction grating layer 3, and then a second n-type cladding layer 4, an active layer 5, and a first p-type cladding layer 6 are epitaxially grown in sequence on the upper surface thereof, i.e., on the positive surface in the z direction, by using a metal organic chemical vapor deposition (MOCVD) method, that is, each layer of a ridge semiconductor layer, which is a semiconductor layer of a ridge structure 16, is formed in sequence (ridge semiconductor layer formation process). An insulating film 18 such as SiO2 is formed on the upper surface thereof, i.e., on the positive surface in the z direction. The semiconductor laser 100 shown in FIG. 7 is an example of a DFB-LD. If the semiconductor laser 100 is not a DFB-LD, the diffraction grating layer 3 is not formed.

[0036] As shown in FIG. 9, the insulating film 18 is processed by etching to leave a portion for forming the basic ridge structure 16. The insulating film 18 is processed by a general semiconductor photolithography process. As shown in FIG. 10, the insulating film 18 is used as a mask to process the first n-type cladding layer 2, the diffraction grating layer 3, the second n-type cladding layer 4, the active layer 5, and the first p-type cladding layer 6 by etching to form the basic ridge structure 16 with both side surfaces in the x direction exposed. The width in the x direction of the basic ridge structure 16 shown in FIG. 10 is the width in the x direction of the ridge intermediate layer 39 having the ridge main body 63 and the ridge extensions 64 extending from both sides of the ridge main body 63 in the x direction in the ridge structure 16 of the final shape. The ridge structure formation process for forming the basic ridge structure 16 shown in FIG. 10 is a process for forming a ridge structure having the maximum width in the x direction of the ridge structure 16 of the final shape on all both side surfaces, i.e., the ridge structure 16 in the process of being formed.

[0037] Next, an extension forming step is performed to form a ridge extension 64. For the basic ridge structure 16 formed in the ridge structure forming step, an etching solution, gas, or the like that does not etch the active layer 5 is used to etch each layer other than the active layer 5 so that the active layer 5 has an active layer main body 65 and active layer extensions 66 extending from both sides of the active layer main body 65 in the x direction, that is, so that active layer extensions 66 extending from both side surfaces of the ridge main body 63 in the x direction are formed in the active layer 5. The area between the dashed lines 54a and 56a and the area between the dashed lines 56b and 54b are the ridge extension 64. The area between the dashed lines 56a and 56b is the ridge main body 63. In the third embodiment, since the ridge intermediate layer 39 is only the active layer 5, the ridge main body 63 is the active layer main body 65, and the ridge extension 64 is also the active layer extension 66. In the extension formation step, layers other than the ridge intermediate layer 39 on both side surfaces in the x direction of the basic ridge structure 16 are etched. The surface of the active layer extension 66 facing the n-type semiconductor substrate 1 in the z direction faces the surface of the first n-type cladding layer 2 other than the ridge main body 63 on the opposite side to the n-type semiconductor substrate 1, and the active layer extension 66 serves as a so-called eaves.

[0038] When the material of the active layer 5 is InGaAsP or AlGaInAs, the active layer 5 can be shaped to have the active layer main body 65 and the active layer extension 66 by using concentrated sulfuric acid for etching an InP layer, for example. When the material of the active layer 5 is AlGaInAs, the active layer 5 can be shaped to have the active layer main body 65 and the active layer extension 66 by etching each InP layer using hydrogen chloride gas in an apparatus for forming a film by MOCVD. The length in the x direction of the active layer extension 66 of the active layer 5 is set to a length that provides a shadow effect when forming the p-type semiconductor layer 7. Here, the shadow effect refers to an effect in which a material gas required for crystal growth is not sufficiently supplied to the surface of the ridge extension 64 extending from the ridge main body 63 on the n-type semiconductor substrate 1 side, i.e., the surface on the negative side in the z direction, so that crystals do not grow on the surface on the negative side in the z direction of the ridge extension 64.

[0039] Next, as shown in FIG. 12, a p-type semiconductor layer forming step is performed to form a p-type semiconductor layer 7. The p-type semiconductor layers 7a and 7b are crystal-grown by epitaxial growth using the MOCVD method on the ridge structure 16 in the final shape shown in FIG. 11. At this time, since the active layer extension 66 of the active layer 5 extends in the x direction further than the ridge main body 63, the shadow effect of the active layer extension 66, which is the ridge extension 64, can be utilized to prevent the p-type semiconductor layers 7a and 7b from growing on the surface of the active layer extension 66, which is the ridge extension 64, on the n-type semiconductor substrate 1 side. By performing the p-type semiconductor layer forming step on the ridge structure 16 in the final shape shown in FIG. 11, the p-type semiconductor layers 7a and 7b can be formed to cover both side surfaces of the ridge structure 16 and the surface of the ridge extension 64 opposite to the n-type semiconductor substrate 1. In other words, since the p-type semiconductor layer 7a and the p-type semiconductor layer 7b are separated, a separation portion 17 that separates the p-type semiconductor layer 7a and the p-type semiconductor layer 7b can be formed on the n-type semiconductor substrate 1 side of the ridge extension portion 64 where the p-type semiconductor layers 7a, 7b are not formed.

[0040] After the p-type semiconductor layer forming step, as shown in FIG. 13, a semi-insulating layer forming step of forming a semi-insulating layer 8 and a step of forming a block layer 9 are performed. The semi-insulating layer 8 and the block layer 9 are epitaxially grown on the intermediate product after the p-type semiconductor layer forming step shown in FIG. 12, that is, the semi-insulating layer 8 and the block layer 9 are formed. In the semi-insulating layer forming step, the semi-insulating layer 8 is formed so as to cover the surfaces of the p-type semiconductor layers 7a and 7b and the exposed surface of the ridge extension 64 on the n-type semiconductor substrate 1 side, that is, the surface of the ridge extension 64 on the negative side in the z direction. Thereafter, the block layer 9 is formed on the surface of the semi-insulating layer 8. Note that the semi-insulating layer forming step and the step of forming the block layer 9 are performed consecutively to the p-type semiconductor layer forming step. That is, the p-type semiconductor layer forming step, the semi-insulating layer forming step, and the step of forming the block layer 9 are performed in the same device. Next, the insulating film 18 is removed using hydrofluoric acid, buffered hydrofluoric acid, or the like.

[0041] After removing the insulating film 18, the second p-type cladding layer 10 and the contact layer 11 are crystal-grown by epitaxial growth. The second p-type cladding layer 10 is formed on the surface of the block layer 9 and the surface of the ridge structure 16, and the contact layer 11 is formed on the surface of the second p-type cladding layer 10. Thereafter, an anode electrode 51 is formed in contact with the contact layer 11, and a cathode electrode 52 is formed in contact with the rear surface of the n-type semiconductor substrate 1, i.e., the surface on the negative side in the z direction.

[0042] In the third embodiment, by appropriately setting the length in the x direction of the ridge extension 64 in the ridge intermediate layer 39 of the ridge structure 16, i.e., the length in the x direction of the active layer extension 66 of the active layer 5, it is possible to easily form the separation portion 17 that separates the p-type semiconductor layer 7a and the p-type semiconductor layer 7b on the negative side in the z direction of the active layer extension 66 without adding any complicated steps. The appropriate length of the x direction of the active layer extension 66 is a length that provides a shadow effect. Even if the active layer 5 does not contain Al, the semiconductor laser 100 of the third embodiment can be manufactured to have the same structure as the semiconductor laser 100 of the first embodiment, i.e., a structure in which the p-type semiconductor layer 7a and the p-type semiconductor layer 7b separated from each other by the separation portion 17 are formed on both side surfaces of the ridge structure 16.

[0043] As described above, the semiconductor laser 100 of the third embodiment is a semiconductor laser including the ridge structure 16 formed on the n-type semiconductor substrate 1 and the buried layer 13 buried so as to cover both sides facing each other in a direction perpendicular to the extension direction of the ridge structure 16. The ridge structure 16 includes an n-type cladding layer (second n-type cladding layer 4), an active layer 5, and a p-type cladding layer (first p-type cladding layer 6) successively formed from the n-type semiconductor substrate 1 side. The buried layer 13 includes a p-type semiconductor layer 7b in contact with both side surfaces of the p-type cladding layer (first p-type cladding layer 6) and the active layer 5 of the ridge structure 16, and a semi-insulating layer 8, and the p-type semiconductor layer 7b is not in contact with the n-type cladding layer (second n-type cladding layer 4) of the ridge structure 16. The buried layer 13 has another p-type semiconductor layer 7a on the n-type semiconductor substrate 1 side of both side surfaces of the n-type cladding layer (second n-type cladding layer 4) of the ridge structure 16, and a separation portion 17 is formed on the active layer 5 side of both side surfaces of the n-type cladding layer (second n-type cladding layer 4) of the ridge structure 16, in which the p-type semiconductor layer 7b and the other p-type semiconductor layer 7a are separated, and a semi-insulating layer 8 is embedded in the separation portion 17. The stacking direction of each layer of the ridge structure 16 is the z direction, the extension direction in which the ridge structure extends is the y direction, and the direction perpendicular to the z direction and the y direction is the x direction. The ridge structure 16 has a ridge main body 63 and a ridge extension portion 64 extending in the x direction from both side surfaces of the ridge main body 63. The ridge extension portion 64 is an active layer extension portion 66 in which the active layer 5 extends in the x direction. The p-type semiconductor layer 7b is in contact with both side surfaces in the x direction of the p-type cladding layer (first p-type cladding layer 6) and the active layer 5 and the surface of the active layer extension 66 opposite to the n-type semiconductor substrate 1, and the separation portion 17 is formed on the n-type semiconductor substrate 1 side of the active layer extension 66. With this configuration, even if there is another p-type semiconductor layer 7a on the n-type semiconductor substrate 1 side on both side surfaces of the n-type cladding layer (second n-type cladding layer 4) of the ridge structure 16, the p-type semiconductor layer 7b in contact with both side surfaces of the p-type cladding layer (first p-type cladding layer 6) and the active layer 5 of the ridge structure 16 is not in contact with the n-type cladding layer (second n-type cladding layer 4) of the ridge structure 16, so that reactive current that does not pass through the active layer 5 can be prevented, and the optical output characteristics and high-speed operation performance can be improved.

[0044] The semiconductor laser manufacturing method for manufacturing the semiconductor laser 100 of the third embodiment is a method for manufacturing a semiconductor laser 100 including a ridge structure 16 formed on an n-type semiconductor substrate 1 and an embedded layer 13 embedded so as to cover both opposing sides in a direction perpendicular to the extension direction of the ridge structure 16. The embedded layer 13 has p-type semiconductor layers 7a, 7b and a semi-insulating layer 8. The stacking direction of the layers of the ridge structure 16 is defined as the z direction, the extension direction of the ridge structure 16 is defined as the y direction, and the direction perpendicular to the z direction and the y direction is defined as the x direction. The semiconductor laser manufacturing method of the third embodiment includes a ridge structure forming step of sequentially forming an n-type cladding layer (second n-type cladding layer 4), a ridge intermediate layer 39 including an active layer 5, and a p-type cladding layer (first p-type cladding layer 6) on an n-type semiconductor substrate 1, and forming a ridge structure 16 having the n-type cladding layer (second n-type cladding layer 4), the ridge intermediate layer 39, and the p-type cladding layer (first p-type cladding layer 6) with both side surfaces exposed by etching. The semiconductor laser manufacturing method of the third embodiment further includes an extension part forming step of, after performing the ridge structure forming step, etching layers other than the ridge intermediate layer 39 on both side surfaces of the ridge structure 16, and forming ridge extension parts 64 in the ridge intermediate layer 39 extending in the x direction from both side surfaces of the ridge structure 16 (both side surfaces of the processed ridge main body part 63). Furthermore, the semiconductor laser manufacturing method of the third embodiment includes, after performing the extension forming step, a p-type semiconductor layer forming step of forming p-type semiconductor layers 7a, 7b so as to cover both side surfaces of the ridge structure 16 (both side surfaces of the ridge main body 63 and the ridge extension 64) and the surface of the ridge extension 64 opposite to the n-type semiconductor substrate 1, and a semi-insulating layer forming step of forming a semi-insulating layer 8 so as to cover the surfaces of the p-type semiconductor layers 7a, 7b and the exposed surface of the ridge extension 64 on the n-type semiconductor substrate 1 side. The semiconductor laser manufacturing method of the third embodiment for manufacturing the semiconductor laser 100 can manufacture the semiconductor laser 100 in which, even if the p-type semiconductor layer 7a is present on the n-type semiconductor substrate 1 side on both side surfaces of the n-type cladding layer (second n-type cladding layer 4) of the ridge structure 16 on the side of the n-type cladding layer 1, the p-type semiconductor layer 7b in contact with both side surfaces of the p-type cladding layer (first p-type cladding layer 6) and the active layer 5 of the ridge structure 16 is not in contact with the n-type cladding layer (second n-type cladding layer 4) of the ridge structure 16.Therefore, the semiconductor laser 100 manufactured by the semiconductor laser manufacturing method of the third embodiment can prevent reactive current that does not pass through the active layer 5, and can improve the optical output characteristics and high-speed operation performance.

[0045] Embodiment 4 FIG. 14 is a diagram showing a cross-sectional structure of a first semiconductor laser according to embodiment 4. FIGS. 15 to 17 are diagrams showing a manufacturing method for the semiconductor laser of FIG. 14. FIG. 18 is a diagram showing a cross-sectional structure of a second semiconductor laser according to embodiment 4, and FIG. 19 is a diagram showing a cross-sectional structure of a third semiconductor laser according to embodiment 4. The semiconductor laser 100 of embodiment 4 differs from the semiconductor laser 100 of embodiment 3 in that the ridge intermediate layer 39 of the ridge extension portion 64 in the ridge structure 16 has an extension portion base layer 21 and an active layer 5. The parts different from the semiconductor laser 100 of embodiment 3 will be mainly described.

[0046] The first and third semiconductor lasers 100 of the fourth embodiment are examples in which the ridge intermediate layer 39 of the ridge extension 64 has the extension base layer 21, the third n-type cladding layer 20, and the active layer 5. The second semiconductor laser 100 of the fourth embodiment is an example in which the ridge intermediate layer 39 of the ridge extension 64 has the extension base layer 21 and the active layer 5. The ridge structure 16 in the first semiconductor laser 100 of the fourth embodiment has the extension base layer 21 of AlGaInAs or InGaAsP and the third n-type cladding layer 20 of n-type InP, which are successively formed from the n-type semiconductor substrate 1 side between the second n-type cladding layer 4 and the active layer 5. As in the third embodiment, when the material of the active layer 5 is InGaAsP or AlGaInAs, the extension base layer 21 is the same material as the active layer 5, so that the ridge extension 64 can be formed using an etchant such as concentrated sulfuric acid having an etching rate slower than the etching rate of the InP layer. In addition, when the material of the active layer 5 and the extension base layer 21 is AlGaInAs, the ridge extension 64 can be formed using hydrogen chloride gas. By forming the third n-type cladding layer 20 sandwiched between the active layer 5 and the extension base layer 21 as a thin film, the third n-type cladding layer 20 is not etched, and the third n-type cladding layer 20 can be left as a part of the ridge extension 64 as shown in FIG. 15. The thickness of the third n-type cladding layer 20 is a minimum thickness equal to or greater than the crystal lattice, for example, 1 nm. The thickness at which the third n-type cladding layer 20 is not etched depends on the etching material used, the state of the semiconductor layer surface during etching, and the like. The third n-type cladding layer 20 only needs to have a thickness that remains even after the ridge extension 64 is formed by etching, so it is not necessary to make the third n-type cladding layer 20 have a maximum thickness. If confirmation of the maximum thickness at which the third n-type cladding layer 20 is not etched is confirmed by experimentation to confirm the thickness remaining after etching.

[0047] The extension base layer 21 may be made of a material other than AlGaInAs and InGaAsP, so long as it is a material that is not etched by the etching solution or etching gas for forming the ridge extension 64. In addition, the ridge intermediate layer 39 may be in direct contact with the active layer 5 and the extension base layer 21, and the lengths of the active layer 5 and the extension base layer 21 in the ridge intermediate layer 39 in the x direction may be different. The second semiconductor laser 100 of the fourth embodiment shown in FIG. 18 is an example in which the ridge intermediate layer 39 is in direct contact with the active layer 5 and the extension base layer 21. The third semiconductor laser 100 of the fourth embodiment shown in FIG. 19 is an example in which the lengths of the active layer 5 and the extension base layer 21 in the x direction in the ridge intermediate layer 39 are different. In FIG. 19, the extension base layer 21 is shorter than the active layer 5, so that the third n-type cladding layer 20 has the same length in the x direction as the extension base layer 21. In any of the first to third semiconductor lasers 100 of the fourth embodiment, the ridge extension 64 can be formed by etching.

[0048] When the ridge intermediate layer 39 has the extension portion base layer 21, the third n-type cladding layer 20, and the active layer 5, in the ridge semiconductor layer formation step, the extension portion base layer 21, the third n-type cladding layer 20, the active layer 5, and the first p-type cladding layer 6 are epitaxially grown in sequence on the surface of the second n-type cladding layer 4 to form each layer of the ridge semiconductor layer which is the semiconductor layer of the ridge structure 16. When the ridge intermediate layer 39 has the extension portion base layer 21 and the active layer 5, in the ridge semiconductor layer formation step, the extension portion base layer 21, the active layer 5, and the first p-type cladding layer 6 are epitaxially grown in sequence on the surface of the second n-type cladding layer 4 to form each layer of the ridge semiconductor layer.

[0049] In the ridge structure forming step, a basic ridge structure 16 is formed using the insulating film 18 as a mask, and in the extension portion forming step, layers other than the ridge intermediate layer 39 of the basic ridge structure 16 are etched in the x direction to form a ridge structure 16 having a ridge main body 63 and ridge extension portions 64. Figure 15 shows an intermediate product of the first semiconductor laser 100 of the fourth embodiment after the extension portion forming step is completed.

[0050] In the p-type semiconductor layer formation step, p-type semiconductor layers 7a, 7b are formed on ridge structure 16 in the final shape shown in Fig. 15 so as to cover both side surfaces of ridge structure 16 and the surface of ridge extension portion 64 opposite to n-type semiconductor substrate 1. Fig. 16 shows an intermediate product of first semiconductor laser 100 according to embodiment 4 after the p-type semiconductor layer formation step has been completed. Since ridge structure 16 has ridge extension portion 64 extending from ridge main body 63, a separation portion 17 that separates p-type semiconductor layer 7a and p-type semiconductor layer 7b can be formed on the surface of ridge extension portion 64 on the negative side in the z direction by the shadow effect.

[0051] In the semi-insulating layer forming step, a semi-insulating layer 8 is formed on the intermediate product of semiconductor laser 100 shown in Fig. 16, and in the subsequent step of forming a block layer 9, a block layer 9 is formed on the surface of semi-insulating layer 8. Fig. 17 shows the intermediate product of first semiconductor laser 100 of the fourth embodiment after the semi-insulating layer forming step and the step of forming block layer 9 are completed and insulating film 18 is removed.

[0052] Thereafter, as described in the third embodiment, the second p-type cladding layer 10 and the contact layer 11 are formed on the surface of the block layer 9 and the surface of the ridge structure 16 in the z direction. Specifically, the second p-type cladding layer 10 is formed on the surface of the block layer 9 and the surface of the ridge structure 16, and the contact layer 11 is formed on the surface of the second p-type cladding layer 10. Thereafter, an anode electrode 51 is formed in contact with the contact layer 11, and a cathode electrode 52 is formed in contact with the rear surface of the n-type semiconductor substrate 1, i.e., the surface on the negative side in the z direction.

[0053] Like the semiconductor laser 100 of the third embodiment, even if the active layer 5 does not contain Al, the semiconductor laser 100 of the fourth embodiment can be manufactured to have the same structure as the semiconductor laser 100 of the first embodiment, that is, a structure in which the p-type semiconductor layer 7a and the p-type semiconductor layer 7b separated from each other by the separation portion 17 are formed on both side surfaces of the ridge structure 16. Therefore, the semiconductor laser 100 of the fourth embodiment can reduce the reactive current that does not pass through the active layer 5 compared to the semiconductor laser of the comparative example shown in FIG. 4, and can improve the optical output characteristics and high-speed operation performance.

[0054] In the first semiconductor laser 100 of the fourth embodiment, the third n-type cladding layer 20 is provided between the active layer 5 and the extension base layer 21, so that the bypass current I2 of the holes 14 flowing through the p-type semiconductor layer 7 is injected into the third n-type cladding layer 20 and the extension base layer 21 together with the active layer 5. In the third n-type cladding layer 20 and the extension base layer 21, the holes 14 and the electrons 15 are recombined. Note that the energy level of the valence band of the extension base layer 21 is higher than the energy level of the valence band of the p-type semiconductor layer 7b, as described later. Therefore, due to the energy barrier between the extension base layer 21 and the p-type semiconductor layer 7b, the number of holes 14 moving from the p-type semiconductor layer 7b to the extension base layer 21 is much smaller than the number of holes 14 moving from the p-type semiconductor layer 7b to the third n-type cladding layer 20. Therefore, the first semiconductor laser 100 of the fourth embodiment generates a somewhat larger amount of reactive current than the semiconductor laser 100 of the third embodiment, but the reactive current can be reduced compared to the semiconductor laser of the comparative example.

[0055] The second semiconductor laser 100 of embodiment 4 does not have the third n-type cladding layer 20 between the active layer 5 and the extension portion base layer, and therefore can reduce the reactive current that does not pass through the active layer 5 more than the first semiconductor laser 100 of embodiment 4.

[0056] Embodiment 5. Fig. 20 is a diagram showing a cross-sectional structure of a semiconductor laser according to embodiment 5. Fig. 21 is an enlarged view of the active layer periphery in Fig. 20, and Fig. 22 is a diagram showing the energy bands of the extension base layer and p-type semiconductor layer in Fig. 21. The semiconductor laser 100 of embodiment 5 differs from the semiconductor laser 100 of embodiment 4 in that the valence band energy level of the extension base layer 21a of the ridge intermediate layer 39 is higher than the valence band energy level of the p-type semiconductor layer 7b, compared to the extension base layer 21 of embodiment 4. The following mainly describes the parts different from the semiconductor laser 100 of embodiment 4.

[0057] The energy band shown in FIG. 22 is an energy band between position A1 of the extension base layer 21a and position A2 of the p-type semiconductor layer 7b shown in FIG. 21. In FIG. 21, the pattern of the extension base layer 21a is omitted. The horizontal axis of FIG. 22 is position, and the vertical axis is energy [au (arbitrary unit)]. Along with the conduction band energy 71 and valence band energy 72 shown by solid lines, the conduction band energy 73 and valence band energy 74 in the extension base layer 21 of the fourth embodiment are shown by dashed lines. The conduction band energy and valence band energy of the third n-type cladding layer 20 are higher than the conduction band energy 73 and valence band energy 74 shown by dashed lines, that is, they are on the upper side (y-axis positive side) in FIG. 22, and the energy barrier, which is the energy difference between the third n-type cladding layer 20 and the p-type semiconductor layer 7b, is smaller than the energy barrier between the extension base layer 21, 21a and the p-type semiconductor layer 7b. The bypass current I2 of the holes 14 that leak into the p-type semiconductor layer 7b flows through the valence band side of the p-type semiconductor layer 7b. For this reason, the bypass current I2 of the holes 14 that flows from the p-type semiconductor layer 7b to the ridge intermediate layer 39 flows mainly through the third n-type cladding layer 20.

[0058] In order to prevent the bypass current I2 of the holes 14 leaked to the p-type semiconductor layer 7b from flowing into the extension base layer 21 of the fourth embodiment, it is necessary to increase the energy level of the valence band of the extension base layer 21 relative to the energy level of the valence band of the p-type semiconductor layer 7b. Note that the positive side of the y-axis in FIG. 22 has a lower energy than the holes 14. To achieve this, the extension base layer 21 of the fourth embodiment may be made of a highly n-type doped material, or the extension base layer 21 of the fourth embodiment may be replaced with an n-type AlInAs layer having a larger band gap than the p-type semiconductor layer 7b. The extension base layer 21a is an n-type AlGaInAs layer or an n-type AlInAs layer, which is an n-type semiconductor layer.

[0059] In the semiconductor laser 100 of the fifth embodiment, the energy level of the valence band in the extension portion base layer 21a of the ridge intermediate layer 39 is higher than that of the extension portion base layer 21 of the fourth embodiment, and therefore a higher energy barrier exists for the p-type semiconductor layer 7b than that of the extension portion base layer 21 of the fourth embodiment, so that the movement of the holes 14 to the extension portion base layer 21a is reduced and recombination with the electrons 15 in the extension portion base layer 21a is reduced. Therefore, the semiconductor laser 100 of the fifth embodiment can reduce the reactive current that does not pass through the active layer 5 more than the semiconductor laser 100 of the fourth embodiment.

[0060] Embodiment 6 FIG. 23 is a diagram showing a cross-sectional structure of a semiconductor laser according to the sixth embodiment, and FIG. 24 is an enlarged view of the periphery of the active layer in FIG. 23. FIGS. 25 and 26 are diagrams showing a method for manufacturing the semiconductor laser in FIG. 23. The semiconductor laser 100 of the sixth embodiment is a semiconductor laser that can easily realize the characteristic structure of the semiconductor laser 100 of the second embodiment, that is, the structure in which the p-type semiconductor layer 7 is in contact only with the first p-type cladding layer 6 and the active layer 5 on both side surfaces of the ridge structure 16. The semiconductor laser 100 of the sixth embodiment is different from the semiconductor laser 100 of the second embodiment in that the buried layer 13 has a semi-insulating layer 8, a p-type semiconductor layer 7, a semi-insulating layer 22, and a block layer 9, and the p-type semiconductor layer 7 is formed to extend in a direction away from the ridge structure 16 on the surface of the semi-insulating layer 8 opposite to the n-type semiconductor substrate 1. The parts different from the semiconductor laser 100 of the second embodiment will be mainly described.

[0061] In the semiconductor laser 100 of the sixth embodiment, similarly to the semiconductor laser 100 of the second embodiment, holes 14, which are majority carriers in the contact layer 11 and the second p-type cladding layer 10, move to the active layer 5 side when the semiconductor laser is driven, and a hole current Ih flows. The hole current Ih is composed of a main current I1 flowing from the first p-type cladding layer 6 to the active layer 5 and a bypass current I2 flowing from the first p-type cladding layer 6 to the active layer 5 via the p-type semiconductor layer 7. The bypass current I2 is a hole current component leaking from the first p-type cladding layer 6 to the p-type semiconductor layer 7. In a portion where the p-type semiconductor layer 7 spreads in a direction away from the ridge structure 16, i.e., in the x-direction, the p-type semiconductor layer 7 is sandwiched between the semi-insulating layer 8 and the semi-insulating layer 22, and since there are no electrons 15 in the semi-insulating layer 8 and the semi-insulating layer 22, there is no recombination with the holes 14. Therefore, this bypass current I2 cannot flow through the side surface of second n-type cladding layer 4 where semi-insulating layer 8 is present, and flows toward the valence band of active layer 5, which is at a lower energy level than the valence band of p-type semiconductor layer 7, and is injected into active layer 5. For this reason, in the semiconductor laser 100 of the sixth embodiment, like the semiconductor laser 100 of the second embodiment, no reactive current is generated.

[0062] A semiconductor laser manufacturing method for manufacturing the semiconductor laser 100 of the sixth embodiment will be described. The steps up to the ridge structure forming step of forming the ridge structure 16 are the same as those up to the ridge structure forming step described in the third embodiment. The semiconductor laser 100 of the sixth embodiment does not have a ridge extension 64, so after the ridge structure forming step, a first semi-insulating layer forming step is performed to form a semi-insulating layer 8 on the n-type semiconductor substrate 1 side of both side surfaces of the ridge structure 16. In the first semi-insulating layer forming step, the semi-insulating layer 8 is formed by epitaxial growth so as to cover both side surfaces of the ridge structure 16 from the n-type semiconductor substrate 1 side to a specific position of the active layer 5. Here, the specific position of the active layer 5 is a position (first specific position) of the near end of the active layer 5 on the n-type semiconductor substrate 1 side, or a position (second specific position) that is farther from the n-type semiconductor substrate 1 side than the near end of the active layer 5 and does not reach the near end of the quantum well structure 35 of the active layer 5 on the n-type semiconductor substrate 1 side. FIG. 25 shows an intermediate product of the semiconductor laser 100 after the first semi-insulating layer forming step. By appropriately setting the epitaxial growth conditions for the semi-insulating layer 8, the semi-insulating layer 8 can be formed so as to cover the surface of the first n-type cladding layer 2 on the positive side in the z direction, both side surfaces of the ridge structure 16 in the x direction, and both side surfaces of the diffraction grating layer 3 and the second n-type cladding layer 4 in the x direction. In addition, the semi-insulating layer 8 can be formed so as to cover both side surfaces of the ridge structure 16 from the n-type semiconductor substrate 1 side to a specific position of the active layer 5.

[0063] After the first semi-insulating layer formation step, a p-type semiconductor layer formation step of forming a p-type semiconductor layer 7 and a second semi-insulating layer formation step of forming a semi-insulating layer 22 are performed. In the p-type semiconductor layer formation step, the p-type semiconductor layer 7 is formed by epitaxial growth so as to cover the surface of the semi-insulating layer 8 and both side surfaces from a specific position of the exposed active layer 5 of the ridge structure 16 to the far end opposite the n-type semiconductor substrate 1. In the second semi-insulating layer formation step, the semi-insulating layer 22 is formed by epitaxial growth so as to cover the p-type semiconductor layer 7.

[0064] After the second semi-insulating layer forming step, the block layer 9 is formed by epitaxial growth. Fig. 26 shows an intermediate product of the semiconductor laser 100 according to the sixth embodiment after the second semi-insulating layer forming step and the block layer 9 forming step are completed.

[0065] Thereafter, as described in the third embodiment, the insulating film 18 is removed, and the second p-type cladding layer 10 and the contact layer 11 are formed on the surface of the block layer 9 and the surface of the ridge structure 16 in the z direction. Specifically, the second p-type cladding layer 10 is formed on the surface of the block layer 9 and the surface of the ridge structure 16, and the contact layer 11 is formed on the surface of the second p-type cladding layer 10. Thereafter, an anode electrode 51 is formed in contact with the contact layer 11, and a cathode electrode 52 is formed in contact with the rear surface of the n-type semiconductor substrate 1, i.e., the surface on the negative side in the z direction.

[0066] The semiconductor laser 100 of the sixth embodiment is the same as the semiconductor laser 100 of the second embodiment except that the p-type semiconductor layer 7 extends in a direction away from the ridge structure 16 on the surface of the semi-insulating layer 8 opposite the n-type semiconductor substrate 1 and the p-type semiconductor layer 7 is sandwiched between the semi-insulating layer 8 and the semi-insulating layer 22, and therefore has the same effects as the semiconductor laser 100 of the second embodiment.

[0067] In the manufacturing method of the semiconductor laser 100 of the second embodiment shown in FIG. 5, for example, after the p-type semiconductor layer forming step in the manufacturing method of the semiconductor laser 100 of the sixth embodiment, a step of etching the p-type semiconductor layer 7 on the surface on the positive side in the z direction of the semi-insulating layer 8 is added, and then the second semi-insulating layer forming step and subsequent steps are performed. The etching of the p-type semiconductor layer 7 is processed using a semiconductor photolithography process. The semi-insulating layer 8 and the semi-insulating layer 22 are integrated, so they can also be called an integrated semi-insulating layer 8. In the embodiment shape The manufacturing method of the semiconductor laser 100 of the second embodiment is more complicated than the manufacturing method of the semiconductor laser 100 of the sixth embodiment. Therefore, the semiconductor laser 100 of the sixth embodiment can easily realize the characteristic structure of the semiconductor laser 100 of the second embodiment, that is, the structure in which the p-type semiconductor layer 7 is in contact only with the first p-type cladding layer 6 and the active layer 5 on both side surfaces of the ridge structure 16.

[0068] As described above, the semiconductor laser 100 of the sixth embodiment is a semiconductor laser including the ridge structure 16 formed on the n-type semiconductor substrate 1 and the buried layer 13 buried so as to cover both sides of the ridge structure 16 that face each other in a direction perpendicular to the extension direction. The ridge structure 16 includes an n-type cladding layer (second n-type cladding layer 4), an active layer 5, and a p-type cladding layer (first p-type cladding layer 6) that are successively formed from the n-type semiconductor substrate 1 side. The buried layer 13 includes a p-type semiconductor layer 7 in contact with both side surfaces of the p-type cladding layer (first p-type cladding layer 6) and the active layer 5 of the ridge structure 16, a semi-insulating layer 8, and a semi-insulating layer 22. The p-type semiconductor layer 7 is not in contact with the n-type cladding layer (second n-type cladding layer 4) of the ridge structure 16, and the semi-insulating layer 8 is in contact with both side surfaces of the n-type cladding layer (second n-type cladding layer 4) of the ridge structure 16. Moreover, the p-type semiconductor layer 7 is formed to spread in a direction away from the ridge structure 16 on the surface of the semi-insulating layer 8 opposite the n-type semiconductor substrate 1. The surface of the p-type semiconductor layer 7 opposite the n-type semiconductor substrate 1 and the surface on the ridge structure 16 side are covered with a semi-insulating layer 22. With this configuration, the semiconductor laser 100 of the sixth embodiment has the p-type semiconductor layer 7 in contact with the p-type cladding layer (first p-type cladding layer 6) of the ridge structure 16 and both side surfaces of the active layer 5 not in contact with the n-type cladding layer (second n-type cladding layer 4) of the ridge structure 16, thereby preventing reactive current that does not pass through the active layer 5 and improving the optical output characteristics and high-speed operation performance.

[0069] The semiconductor laser manufacturing method for manufacturing the semiconductor laser 100 of the sixth embodiment is a semiconductor laser manufacturing method for manufacturing the semiconductor laser 100 including a ridge structure 16 including an active layer 5 formed on an n-type semiconductor substrate 1, and an embedded layer 13 embedded so as to cover both opposing sides in a direction perpendicular to the extension direction of the ridge structure 16. The embedded layer 13 has a first semi-insulating layer (semi-insulating layer 8), a p-type semiconductor layer 7, and a second semi-insulating layer (semi-insulating layer 22). The specific position of the active layer is set to a position of a near end of the active layer 5 on the n-type semiconductor substrate 1 side, or a position farther from the n-type semiconductor substrate 1 side than the near end of the active layer 5 and not reaching the near end of the quantum well structure 35 of the active layer 5 on the n-type semiconductor substrate 1 side. The semiconductor laser manufacturing method of the sixth embodiment includes a ridge structure formation step of sequentially forming an n-type cladding layer (second n-type cladding layer 4), an active layer 5, and a p-type cladding layer (first p-type cladding layer 6) on an n-type semiconductor substrate 1, and forming a ridge structure 16 having the n-type cladding layer (second n-type cladding layer 4), the active layer 5, and the p-type cladding layer (first p-type cladding layer 6), both side surfaces of which are exposed by etching. Furthermore, the semiconductor laser manufacturing method of the sixth embodiment includes, after performing the ridge structure forming step, a first semi-insulating layer forming step of forming a first semi-insulating layer (semi-insulating layer 8) so as to cover both side surfaces of the ridge structure 16 from the n-type semiconductor substrate 1 side to a specific position of the active layer 5, a p-type semiconductor layer forming step of forming a p-type semiconductor layer 7 so as to cover a surface of the first semi-insulating layer (semi-insulating layer 8) and both side surfaces of the exposed active layer 5 of the ridge structure 16 from the specific position to the far end opposite to the n-type semiconductor substrate 1, and a second semi-insulating layer forming step of forming a second semi-insulating layer (semi-insulating layer 22) so as to cover the p-type semiconductor layer 7. The semiconductor laser manufacturing method of the sixth embodiment for manufacturing the semiconductor laser 100 can manufacture the semiconductor laser 100 in which the p-type cladding layer (first p-type cladding layer 6) of the ridge structure 16 and the p-type semiconductor layer 7 in contact with both side surfaces of the active layer 5 are not in contact with the n-type cladding layer (second n-type cladding layer 4) of the ridge structure 16. Therefore, the semiconductor laser 100 manufactured by the semiconductor laser manufacturing method of the sixth embodiment can prevent reactive current that does not pass through the active layer 5, and can improve the optical output characteristics and high-speed operation performance.

[0070] Embodiment 7 FIG. 27 is a diagram showing a cross-sectional structure of a semiconductor laser according to the seventh embodiment, and FIG. 28 is an enlarged view of the active layer periphery of FIG. 27. FIGS. 29 to 34 are diagrams showing a method for manufacturing the semiconductor laser of FIG. 27. The semiconductor laser 100 of the seventh embodiment is an example of a semiconductor laser in which the p-type semiconductor layer 40 is in contact with the first p-type cladding layer 27 and the active layer 5 on both side surfaces of the ridge structure 16, and the undoped semiconductor layer 23 is in contact with both side surfaces of each layer on the n-type semiconductor substrate 1 side from the active layer 5 of the ridge structure 16. The semiconductor laser 100 of the seventh embodiment is different from the semiconductor laser 100 of the second embodiment in that the undoped semiconductor layer 23 is in contact with both side surfaces of each layer on the n-type semiconductor substrate 1 side from the active layer 5 of the ridge structure 16, the first p-type cladding layer 27 is provided on the positive side of the active layer 5 of the ridge structure 16 in the z direction, and the semi-insulating layer 42 in which zinc is diffused and the block layer 41 in which zinc is diffused are provided on both side surfaces of the ridge structure 16. 27 and 28 show an example in which the p-type semiconductor layer 40 covers both side surfaces of the ridge structure 16 up to a specific position of the first p-type cladding layer 27 and the active layer 5. The specific position is as described in embodiment 2. The following mainly describes the differences from the semiconductor laser 100 of embodiment 2.

[0071] The p-type semiconductor layer 40 is a semiconductor layer made p-type by diffusing zinc atoms into the InP undoped semiconductor layer 23. The first p-type cladding layer 27 is a p-type cladding layer made by diffusing zinc into the p-type InP first p-type cladding layer 6. The buried layer 13 covering both sides of the ridge structure 16 includes the undoped semiconductor layer 23, the p-type semiconductor layer 40, semi-insulating layers 8 and 42, and a block layer 9.

[0072] In the semiconductor laser 100 of the seventh embodiment, similarly to the semiconductor laser 100 of the second embodiment, holes 14, which are majority carriers in the contact layer 11 and the second p-type cladding layer 10, move to the active layer 5 side when the semiconductor laser is driven, and a hole current Ih flows. The hole current Ih is composed of a main current I1 flowing from the first p-type cladding layer 27 to the active layer 5, and a bypass current I2 flowing from the first p-type cladding layer 27 to the active layer 5 via the p-type semiconductor layer 40. The bypass current I2 is a hole current component leaking from the first p-type cladding layer 27 to the p-type semiconductor layer 40. Since the undoped semiconductor layer 23 in contact with the first n-type cladding layer 2, the diffraction grating layer 3, and the second n-type cladding layer 4 has a high resistance, the bypass current I2 cannot flow through the undoped semiconductor layer 23 to the first n-type cladding layer 2 and the second n-type cladding layer 4. Therefore, in the semiconductor laser 100 of the seventh embodiment, the hole current leaking to the p-type semiconductor layer 40 is injected into the active layer 5 and does not become a reactive current, similar to the semiconductor laser 100 of the second embodiment. Moreover, by making the p-type semiconductor layer 40, which has been made p-type by zinc diffusion, contact the side surface of the active layer 5, it is possible to suppress the overflow of the electron current from the active layer 5 to the buried layer 13.

[0073] A semiconductor laser manufacturing method for manufacturing the semiconductor laser 100 of the seventh embodiment will be described. The steps up to the ridge structure forming step for forming the ridge structure 16 are the same as those up to the ridge structure forming step described in the third embodiment. After the ridge structure forming step, the undoped semiconductor layer 23 is formed by epitaxial growth so as to cover both side surfaces of the ridge structure 16 (undoped semiconductor layer forming step). After the undoped semiconductor layer forming step, the semi-insulating layer 8 is formed by epitaxial growth so as to cover the surface of the undoped semiconductor layer 23 (semi-insulating layer forming step). After the semi-insulating layer forming step, the block layer 9 is formed by epitaxial growth. FIG. 29 shows an intermediate product of the semiconductor laser 100 of the seventh embodiment, which has been completed up to the semi-insulating layer forming step and the block layer 9 forming step. Thereafter, as shown in FIG. 30, the insulating film 18 is removed.

[0074] Next, a zinc diffusion process for diffusing zinc in a region from the far end of the undoped semiconductor layer 23 opposite to the n-type semiconductor substrate 1 to a specific position of the active layer 5 will be described. First, a diffusion prevention film 24 such as SiO2 is formed on the surface of the block layer 9 and the surface of the ridge structure 16 in the z direction, and an opening 25 having a width in the x direction including the active layer 5 and the undoped semiconductor layer 23 in contact with the active layer 5 is formed in the diffusion prevention film 24. The opening 25 is processed using a semiconductor photolithography process. FIG. 31 shows an intermediate product of the semiconductor laser 100 of the seventh embodiment in which the diffusion prevention film 24 having the opening 25 exposing a region including the undoped semiconductor layer 23 on the surface of the ridge structure 16 opposite to the n-type semiconductor substrate 1 and the surface of the buried layer 13 opposite to the n-type semiconductor substrate 1 is arranged in the buried layer 13.

[0075] Next, as shown in FIG. 32, a zinc oxide film (ZnO film) 26 is formed on the diffusion prevention film 24, the surface of the ridge structure 16 exposed by the opening 25 on the positive side in the z direction, and the surface of the buried layer 13.

[0076] Next, the intermediate product of the semiconductor laser 100 of the seventh embodiment shown in FIG. 32 is heat-treated. In the semiconductor layer in contact with the zinc oxide film 26 in the region of the opening 25, zinc (Zn) atoms in the zinc oxide film 26 are diffused into the semiconductor layer. The zinc atoms are diffused into the undoped semiconductor layer 23 and the first p-type cladding layer 6 in contact with both side surfaces of the ridge structure 16 from the end farthest from the n-type semiconductor substrate 1 on the positive side in the z direction to a specific position of the active layer 5, and the undoped semiconductor layer 23 is converted to p-type. That is, the zinc atoms are diffused into the undoped semiconductor layer 23 in contact with both side surfaces of the ridge structure 16 from the positive end in the z direction of the active layer 5 to a specific position, and the undoped semiconductor layer 23 is converted to p-type. The heat treatment conditions set are heat treatment conditions under which zinc atoms diffuse to a specific position of the active layer 5 toward the negative side in the z direction in the semiconductor layer in contact with the ridge structure 16 in the region of the opening 25, and zinc atoms do not diffuse into the undoped semiconductor layer 23 in contact with the first n-type cladding layer 2, the diffraction grating layer 3, and the second n-type cladding layer 4. The heat treatment conditions set further are heat treatment conditions under which zinc atoms diffuse into the first p-type cladding layer 6 in the ridge structure 16 in the region of the opening 25, and zinc atoms do not diffuse into the active layer 5. The first p-type cladding layer 6 becomes the first p-type cladding layer 27 as a result of the diffusion of zinc atoms. Furthermore, zinc atoms are also diffused into the semiconductor layer in the region of the opening 25, i.e., the block layer 9 and the semi-insulating layer 8 on the ridge structure 16 side, and become p-type. The block layer 9 and the semi-insulating layer 8 into which zinc has been diffused are the semi-insulating layer 42 and the block layer 41.

[0077] In the heat treatment of the zinc diffusion step, zinc atoms from the zinc oxide film 26 cannot diffuse through the diffusion prevention film 24 in the portion covered by the diffusion prevention film 24, and therefore the zinc atoms do not diffuse into the semiconductor layer directly below the diffusion prevention film 24. Fig. 34 shows an intermediate product of the semiconductor laser 100 of the seventh embodiment after the heat treatment of the zinc diffusion step.

[0078] After the zinc diffusion step, the zinc oxide film 26 and the diffusion prevention film 24 are removed, and the second p-type cladding layer 10 and the contact layer 11 are formed on the surface of the block layer 9 and the surface of the ridge structure 16 in the z direction. Specifically, the second p-type cladding layer 10 is formed on the surface of the block layer 9 and the surface of the ridge structure 16, and the contact layer 11 is formed on the surface of the second p-type cladding layer 10. Thereafter, an anode electrode 51 is formed in contact with the contact layer 11, and a cathode electrode 52 is formed in contact with the back surface of the n-type semiconductor substrate 1, i.e., the surface on the negative side in the z direction.

[0079] In addition, the width of the opening 25 of the diffusion prevention film 24 in FIG. 31 is appropriately adjusted so that the undoped semiconductor layer 23 in contact with the active layer 5 becomes p-type and the semi-insulating layer 8 in the x-direction of the p-type semiconductor layer 40 that has been made p-type does not become p-type due to zinc diffusion.

[0080] The semiconductor laser 100 of the seventh embodiment is the same as the semiconductor laser 100 of the second embodiment except for the differences described above, and therefore provides the same effects as the semiconductor laser 100 of the second embodiment.

[0081] As described above, the semiconductor laser 100 of the seventh embodiment is a semiconductor laser including the ridge structure 16 formed on the n-type semiconductor substrate 1 and the buried layer 13 buried so as to cover both sides facing each other in a direction perpendicular to the extension direction of the ridge structure 16. The ridge structure 16 has an n-type cladding layer (second n-type cladding layer 4), an active layer 5, and a p-type cladding layer (first p-type cladding layer 27) formed in this order from the n-type semiconductor substrate 1 side. The buried layer 13 has a p-type semiconductor layer 40 in contact with both side surfaces of the p-type cladding layer (first p-type cladding layer 27) and the active layer 5 of the ridge structure 16, an undoped semiconductor layer 23, and a semi-insulating layer 8, and the p-type semiconductor layer 40 is not in contact with the n-type cladding layer (second n-type cladding layer 4) of the ridge structure 16. The undoped semiconductor layer 23 contacts both side surfaces of the n-type cladding layer (second n-type cladding layer 4) of the ridge structure 16, and the p-type semiconductor layer 40 and the p-type cladding layer (first p-type cladding layer 27) contain zinc. With this configuration, the semiconductor laser 100 of the seventh embodiment has the p-type semiconductor layer 40 in contact with both side surfaces of the p-type cladding layer (first p-type cladding layer 27) of the ridge structure 16 and the active layer 5 not in contact with the n-type cladding layer (second n-type cladding layer 4) of the ridge structure 16, thereby preventing reactive current that does not pass through the active layer 5 and improving the optical output characteristics and high-speed operation performance.

[0082] The semiconductor laser manufacturing method for manufacturing the semiconductor laser 100 of the seventh embodiment is a semiconductor laser manufacturing method for manufacturing a semiconductor laser 100 including a ridge structure 16 including an active layer 5 formed on an n-type semiconductor substrate 1, and an embedded layer 13 embedded so as to cover both opposing sides in a direction perpendicular to the extension direction of the ridge structure 16. The embedded layer 13 has an undoped semiconductor layer 23, a p-type semiconductor layer 40, and a semi-insulating layer 8. The specific position of the active layer is set to a position of a near end of the active layer 5 on the n-type semiconductor substrate 1 side, or a position farther from the n-type semiconductor substrate 1 side than the near end of the active layer 5 and not reaching the near end of the quantum well structure 35 of the active layer 5 on the n-type semiconductor substrate 1 side. The semiconductor laser manufacturing method of the seventh embodiment includes a ridge structure forming step of sequentially forming an n-type cladding layer (second n-type cladding layer 4), an active layer 5, and a p-type cladding layer (first p-type cladding layer 6) on an n-type semiconductor substrate 1, and forming a ridge structure 16 having the n-type cladding layer (second n-type cladding layer 4), the active layer 5, and the p-type cladding layer (first p-type cladding layer 6) with both side surfaces exposed by etching. The semiconductor laser manufacturing method of the seventh embodiment further includes an undoped semiconductor layer forming step of forming an undoped semiconductor layer 23 so as to cover both side surfaces of the ridge structure 16, a semi-insulating layer forming step of forming a semi-insulating layer 8 so as to cover the surface of the undoped semiconductor layer 23, and a zinc diffusion step of diffusing zinc into a region of the undoped semiconductor layer 23 from a far end on the opposite side to the n-type semiconductor substrate 1 to a specific position of the active layer 5, and diffusing zinc into the p-type cladding layer (first p-type cladding layer 6) after the ridge structure forming step is performed. The semiconductor laser manufacturing method for manufacturing the semiconductor laser 100 of the seventh embodiment can manufacture the semiconductor laser 100 in which the zinc-diffused p-type cladding layer (first p-type cladding layer 27) of the ridge structure 16 and the p-type semiconductor layer 40 in contact with both side surfaces of the active layer 5 are not in contact with the n-type cladding layer (second n-type cladding layer 4) of the ridge structure 16. Therefore, the semiconductor laser 100 manufactured by the semiconductor laser manufacturing method of the seventh embodiment can prevent reactive current that does not pass through the active layer 5, and can improve the optical output characteristics and high-speed operation performance.

[0083] Embodiment 8 35 is a diagram showing a method for manufacturing a semiconductor laser according to the eighth embodiment. The semiconductor laser 100 of the eighth embodiment is the same as the semiconductor laser 100 of the seventh embodiment. The semiconductor laser manufacturing method for manufacturing the semiconductor laser 100 of the eighth embodiment is different from the semiconductor laser manufacturing method of the seventh embodiment in that zinc is diffused into the semiconductor layer by gas phase diffusion using the MOCVD method in the zinc diffusion step. The differences from the semiconductor laser manufacturing method of the seventh embodiment will be mainly described.

[0084] The intermediate product of the semiconductor laser 100 of the eighth embodiment when diffusing zinc is the same as the intermediate product of the semiconductor laser 100 of the seventh embodiment shown in FIG. 31. When diffusing zinc, a diffusion prevention film 24 having an opening 25 exposing a region including the undoped semiconductor layer 23 on the surface of the ridge structure 16 opposite to the n-type semiconductor substrate 1 and the surface of the buried layer 13 opposite to the n-type semiconductor substrate 1 is disposed on the buried layer 13. This intermediate product is placed in an apparatus for forming a film by the MOCVD method, and dimethyl zinc 28 is introduced into the apparatus. By setting the pressure and temperature in the apparatus to predetermined conditions, the dimethyl zinc 28 is decomposed and zinc is vapor-phase diffused into the semiconductor layer from the opening 25, that is, zinc is diffused into the semiconductor layer in the region of the opening 25. The predetermined pressure and temperature conditions, i.e., zinc diffusion conditions, are conditions under which zinc diffuses in the semiconductor layer in contact with ridge structure 16 in the region of opening 25 toward the negative z-direction up to a specific position in active layer 5, and zinc does not diffuse into undoped semiconductor layer 23 in contact with first n-type cladding layer 2, diffraction grating layer 3, and second n-type cladding layer 4. Furthermore, the zinc diffusion conditions are conditions under which zinc atoms diffuse into first p-type cladding layer 6 in ridge structure 16 in the region of opening 25, but do not diffuse into active layer 5.

[0085] The steps after the zinc diffusion step are the same as those in the semiconductor laser manufacturing method of the seventh embodiment. The semiconductor laser 100 of the eighth embodiment is the same as the semiconductor laser 100 of the seventh embodiment, and therefore has the same effects as the semiconductor laser 100 of the seventh embodiment.

[0086] Embodiment 9 FIG. 36 is a diagram showing a cross-sectional structure of a semiconductor laser according to the ninth embodiment, and FIG. 37 is an enlarged view of the periphery of the active layer in FIG. 36. FIGS. 38 to 41 are diagrams showing a method for manufacturing the semiconductor laser in FIG. 36. The semiconductor laser 100 of the ninth embodiment is different from the semiconductor laser 100 of the seventh embodiment in that a first p-type cladding layer 6 is formed on the positive side of the active layer 5 in the z direction. FIGS. 36 and 37 show an example in which the p-type semiconductor layer 40 covers both side surfaces of the first p-type cladding layer 6 and the active layer 5 up to a specific position on both side surfaces of the ridge structure 16. The specific position is as described in the second embodiment. The parts different from the semiconductor laser 100 of the seventh embodiment will be mainly described.

[0087] The p-type semiconductor layer 40 is a semiconductor layer that has been made p-type by diffusing zinc atoms into the InP undoped semiconductor layer 23. The buried layer 13 covering both sides of the ridge structure 16 includes the undoped semiconductor layer 23, the p-type semiconductor layer 40, semi-insulating layers 8 and 42, and a block layer 9.

[0088] In the semiconductor laser 100 of the ninth embodiment, similarly to the semiconductor lasers 100 of the second and seventh embodiments, holes 14, which are majority carriers in the contact layer 11 and the second p-type cladding layer 10, move to the active layer 5 side when the semiconductor laser is driven, and a hole current Ih flows. The hole current Ih is composed of a main current I1 flowing from the first p-type cladding layer 6 to the active layer 5, and a bypass current I2 flowing from the first p-type cladding layer 6 to the active layer 5 via the p-type semiconductor layer 40. The bypass current I2 is a hole current component leaking from the first p-type cladding layer 6 to the p-type semiconductor layer 40. Since the undoped semiconductor layer 23 in contact with the first n-type cladding layer 2, the diffraction grating layer 3, and the second n-type cladding layer 4 has a high resistance, the bypass current I2 cannot flow through the undoped semiconductor layer 23 to the first n-type cladding layer 2 and the second n-type cladding layer 4. Therefore, in the semiconductor laser 100 of the ninth embodiment, the hole current leaking to the p-type semiconductor layer 40 is injected into the active layer 5 and does not become a reactive current, similar to the semiconductor lasers 100 of the second and seventh embodiments. In addition, by bringing the p-type semiconductor layer 40, which has been made p-type by zinc diffusion, into contact with the side surface of the active layer 5, the overflow of the electron current from the active layer 5 to the buried layer 13 can be suppressed.

[0089] In the semiconductor laser 100 of the ninth embodiment, the region where zinc is diffused is limited to the portion including the undoped semiconductor layer 23, so that zinc is not diffused into the first p-type cladding layer 6, and the optical absorption loss of the laser light due to zinc is suppressed, compared with the semiconductor laser 100 of the seventh embodiment. Therefore, the semiconductor laser 100 of the ninth embodiment can output a laser light with a higher optical output than the semiconductor laser 100 of the seventh embodiment.

[0090] A semiconductor laser manufacturing method for manufacturing the semiconductor laser 100 of the 9th embodiment will be described. The ridge structure forming step of forming the ridge structure 16, the subsequent undoped semiconductor layer forming step of forming the undoped semiconductor layer 23, the semi-insulating layer forming step of forming the semi-insulating layer 8, and the step of forming the block layer 9 are the same as those of the semiconductor laser manufacturing method of the 7th embodiment. Thereafter, as shown in Fig. 30, the insulating film 18 is removed, and then a zinc diffusion step of diffusing zinc into the semiconductor layer is carried out.

[0091] 38, a diffusion prevention film 24 such as SiO2 is formed on the surface of the block layer 9 and the surface in the z direction of the ridge structure 16, and two openings 29 having a width in the x direction that includes the undoped semiconductor layer 23 in contact with the active layer 5 are formed in the diffusion prevention film 24. The openings 29 are processed using a semiconductor photolithography process. FIG. 38 shows an intermediate product of the semiconductor laser 100 of the ninth embodiment in which the diffusion prevention film 24 having the openings 29 that expose the region including the undoped semiconductor layer 23 on the surface of the buried layer 13 opposite to the n-type semiconductor substrate 1 is disposed in the buried layer 13.

[0092] Next, as shown in FIG. 39, a zinc oxide film 26 is formed on the diffusion prevention film 24 and the surface of the buried layer 13 exposed by the opening 29.

[0093] Next, the intermediate product of the semiconductor laser 100 of the ninth embodiment shown in FIG. 39 is heat-treated. In the semiconductor layer in contact with the zinc oxide film 26 in the region of the opening 29, zinc atoms in the zinc oxide film 26 are diffused into the semiconductor layer. The zinc atoms are diffused into the undoped semiconductor layer 23 in contact with both side surfaces of the ridge structure 16 from the end farthest from the n-type semiconductor substrate 1 on the positive side in the z direction to a specific position of the active layer 5, and the undoped semiconductor layer 23 is changed to a p-type. That is, the zinc atoms are diffused into the undoped semiconductor layer 23 in contact with both side surfaces of the ridge structure 16 from the positive end of the active layer 5 in the z direction to a specific position, and the undoped semiconductor layer 23 is changed to a p-type. The heat treatment conditions set are heat treatment conditions under which zinc atoms are diffused into the semiconductor layer in the region of the opening 29 toward the negative side in the z direction to a specific position of the active layer 5, and zinc atoms are not diffused into the undoped semiconductor layer 23 in contact with the first n-type cladding layer 2, the diffraction grating layer 3, and the second n-type cladding layer 4. In addition, in the semiconductor layer in the region of the opening 29, i.e., in the block layer 9 and the semi-insulating layer 8 on the ridge structure 16 side, Moa The lead atoms are diffused to form a p-type layer. The block layer 9 and the semi-insulating layer 8 into which zinc is diffused form the semi-insulating layer 42 and the block layer 41.

[0094] In the heat treatment of the zinc diffusion step, zinc atoms from the zinc oxide film 26 cannot diffuse through the diffusion prevention film 24 in the portion covered by the diffusion prevention film 24, and therefore the zinc atoms do not diffuse into the semiconductor layer directly below the diffusion prevention film 24. Fig. 40 shows an intermediate product of the semiconductor laser 100 of the ninth embodiment after the heat treatment of the zinc diffusion step has been completed.

[0095] After the zinc diffusion step, the zinc oxide film 26 and the diffusion prevention film 24 are removed, and the second p-type cladding layer 10 and the contact layer 11 are formed on the surface of the block layer 9 and the surface of the ridge structure 16 in the z direction. Specifically, the second p-type cladding layer 10 is formed on the surface of the block layer 9 and the surface of the ridge structure 16, and the contact layer 11 is formed on the surface of the second p-type cladding layer 10. Thereafter, an anode electrode 51 is formed in contact with the contact layer 11, and a cathode electrode 52 is formed in contact with the back surface of the n-type semiconductor substrate 1, i.e., the surface on the negative side in the z direction.

[0096] In addition, the width of the opening 29 of the diffusion prevention film 24 in FIG. 38 is appropriately adjusted so that the undoped semiconductor layer 23 in contact with the active layer 5 becomes p-type and the semi-insulating layer 8 in the x-direction of the p-type semiconductor layer 40 that has been made p-type does not become p-type due to zinc diffusion.

[0097] The semiconductor laser 100 of the ninth embodiment is the same as the semiconductor laser 100 of the seventh embodiment except for the above-mentioned differences, and therefore has the same effects as the semiconductor laser 100 of the seventh embodiment. Furthermore, as described above, the semiconductor laser 100 of the ninth embodiment does not have zinc diffused into the first p-type cladding layer 6, and the optical absorption loss of the laser light due to zinc is suppressed, so that the semiconductor laser 100 can output a laser light with a higher optical output than the semiconductor laser 100 of the seventh embodiment.

[0098] As described above, the semiconductor laser 100 of the ninth embodiment is a semiconductor laser including the ridge structure 16 formed on the n-type semiconductor substrate 1 and the buried layer 13 buried so as to cover both sides of the ridge structure 16 that face each other in a direction perpendicular to the extension direction. The ridge structure 16 has an n-type cladding layer (second n-type cladding layer 4), an active layer 5, and a p-type cladding layer (first p-type cladding layer 6) that are successively formed from the n-type semiconductor substrate 1 side. The buried layer 13 has a p-type semiconductor layer 40 that contacts both side surfaces of the p-type cladding layer (first p-type cladding layer 6) and the active layer 5 of the ridge structure 16, an undoped semiconductor layer 23, and a semi-insulating layer 8, and the p-type semiconductor layer 40 does not contact the n-type cladding layer (second n-type cladding layer 4) of the ridge structure 16. The undoped semiconductor layer 23 contacts both side surfaces of the n-type cladding layer (second n-type cladding layer 4) of the ridge structure 16, and the p-type semiconductor layer 40 contains zinc. In the semiconductor laser 100 of the ninth embodiment, due to this configuration, the p-type semiconductor layer 40 in contact with the p-type cladding layer (first p-type cladding layer 6) of the ridge structure 16 and both side surfaces of the active layer 5 is not in contact with the n-type cladding layer (second n-type cladding layer 4) of the ridge structure 16, so that reactive current that does not pass through the active layer 5 can be prevented, and the optical output characteristics and high-speed operating performance can be improved.

[0099] The semiconductor laser manufacturing method for manufacturing the semiconductor laser 100 of the ninth embodiment is a method for manufacturing a semiconductor laser 100 including a ridge structure 16 including an active layer 5 formed on an n-type semiconductor substrate 1, and an embedded layer 13 embedded so as to cover both sides facing each other in a direction perpendicular to the extension direction of the ridge structure 16. The embedded layer 13 has an undoped semiconductor layer 23, a p-type semiconductor layer 40, and a semi-insulating layer 8. The specific position of the active layer is set to a position of a near end of the active layer 5 on the n-type semiconductor substrate 1 side, or a position farther from the n-type semiconductor substrate 1 side than the near end of the active layer 5 and not reaching the near end of the quantum well structure 35 of the active layer 5 on the n-type semiconductor substrate 1 side. The semiconductor laser manufacturing method of the ninth embodiment includes a ridge structure forming step of sequentially forming an n-type cladding layer (second n-type cladding layer 4), an active layer 5, and a p-type cladding layer (first p-type cladding layer 6) on an n-type semiconductor substrate 1, and forming a ridge structure 16 having the n-type cladding layer (second n-type cladding layer 4), the active layer 5, and the p-type cladding layer (first p-type cladding layer 6) with both side surfaces exposed by etching. The semiconductor laser manufacturing method of the ninth embodiment further includes, after the ridge structure forming step, an undoped semiconductor layer forming step of forming an undoped semiconductor layer 23 so as to cover both side surfaces of the ridge structure 16, a semi-insulating layer forming step of forming a semi-insulating layer 8 so as to cover a surface of the undoped semiconductor layer 23, and a zinc diffusion step of diffusing zinc into a region of the undoped semiconductor layer 23 from a far end opposite the n-type semiconductor substrate 1 to a specific position of the active layer 5. The semiconductor laser manufacturing method for manufacturing the semiconductor laser 100 of the ninth embodiment can manufacture the semiconductor laser 100 in which the p-type cladding layer (first p-type cladding layer 27) of the ridge structure 16 and the p-type semiconductor layer 40 in contact with both side surfaces of the active layer 5 are not in contact with the n-type cladding layer (second n-type cladding layer 4) of the ridge structure 16. Therefore, the semiconductor laser 100 manufactured by the semiconductor laser manufacturing method of the ninth embodiment can prevent reactive current that does not pass through the active layer 5, and can improve the optical output characteristics and high-speed operation performance.

[0100] Embodiment 10 42 is a diagram showing a method for manufacturing a semiconductor laser according to the tenth embodiment. The semiconductor laser 100 of the tenth embodiment is the same as the semiconductor laser 100 of the ninth embodiment. The semiconductor laser manufacturing method for manufacturing the semiconductor laser 100 of the tenth embodiment is different from the semiconductor laser manufacturing method of the ninth embodiment in that zinc is diffused into the semiconductor layer by gas phase diffusion using the MOCVD method in the zinc diffusion step. The parts different from the semiconductor laser manufacturing method of the ninth embodiment will be mainly described.

[0101] The intermediate product of the semiconductor laser 100 of the tenth embodiment when diffusing zinc is the same as the intermediate product of the semiconductor laser 100 of the ninth embodiment shown in FIG. 38. When diffusing zinc, a diffusion prevention film 24 having an opening 29 exposing a region including the undoped semiconductor layer 23 on the surface of the buried layer 13 opposite to the n-type semiconductor substrate 1 is disposed on the buried layer 13. This intermediate product is placed in an apparatus for forming a film by the MOCVD method, and dimethyl zinc 28 is introduced into the apparatus. By setting the pressure and temperature in the apparatus to predetermined conditions, the dimethyl zinc 28 is decomposed and zinc is vapor-phase diffused into the semiconductor layer from the opening 29, that is, zinc is diffused into the semiconductor layer in the region of the opening 29. The predetermined pressure and temperature conditions, i.e., zinc diffusion conditions, are conditions under which zinc diffuses into the semiconductor layer in contact with the ridge structure 16 in the region of the opening 29 toward the negative z-direction up to a specific position in the active layer 5, and zinc does not diffuse into the undoped semiconductor layer 23 in contact with the first n-type cladding layer 2, the diffraction grating layer 3, and the second n-type cladding layer 4.

[0102] The steps after the zinc diffusion step are the same as those in the semiconductor laser manufacturing method of embodiment 9. Since the semiconductor laser 100 of embodiment 10 is the same as the semiconductor laser 100 of embodiment 9, it has the same effects as the semiconductor laser 100 of embodiment 9.

[0103] In the above description, the semiconductor laser 100 in each of the first to tenth embodiments is an example of a DFB-LD. However, as described in the first and third embodiments, if the semiconductor laser 100 is not a DFB-LD, the diffraction grating layer 3 is not formed.

[0104] In addition, although various exemplary embodiments and examples are described in this application, various features, aspects, and functions described in one or more embodiments are not limited to application in a specific embodiment, but can be applied to the embodiments alone or in various combinations. Therefore, countless modifications not illustrated are expected within the scope of the technology disclosed in this specification. For example, this includes cases in which at least one component is modified, added, or omitted, and further cases in which at least one component is extracted and combined with components of other embodiments. [Explanation of symbols]

[0105] 1...n-type semiconductor substrate, 2...first n-type cladding layer, 3...diffraction grating layer, 4...second n-type cladding layer, 5...active layer, 6...first p-type cladding layer, 7, 7a, 7b...p-type semiconductor layer, 8...semi-insulating layer, 13...buried layer, 16...ridge structure, 17...separation portion, 20...third n-type cladding layer, 21, 21a...extension portion base layer, 22...semi-insulating layer, 23...undoped semiconductor layer, 24...diffusion prevention film, 25...opening, 26...zinc oxide film, 29...opening, 35...quantum well structure, 39...ridge intermediate layer, 40...p-type semiconductor layer, 63...ridge main body, 64...ridge extension, 66...active layer extension, 72...valence band energy, 74...valence band energy, 100...semiconductor laser

Claims

1. 1. A semiconductor laser comprising: a ridge structure formed on an n-type semiconductor substrate; and a buried layer buried in such a manner as to cover both sides opposed to each other in a direction perpendicular to an extension direction of the ridge structure, the ridge structure includes an active layer, an n-type cladding layer formed in contact with the active layer on a side of the n-type semiconductor substrate, and a p-type cladding layer formed in contact with the active layer on a side opposite to the n-type semiconductor substrate, The buried layer is the ridge structure includes p-type semiconductor layers in contact with both side surfaces of the p-type cladding layer and the active layer, and a semi-insulating layer, and the ridge structure includes other p-type semiconductor layers on both side surfaces of the n-type cladding layer on the n-type semiconductor substrate side, the p-type semiconductor layer is not in contact with the n-type cladding layer of the ridge structure, a separation portion in which the p-type semiconductor layer and the other p-type semiconductor layer are separated is formed on both side surfaces of the n-type cladding layer of the ridge structure on the side of the active layer, The semi-insulating layer is embedded in the isolation portion. Semiconductor laser.

2. 2. The semiconductor laser according to claim 1, wherein said semi-insulating layer contacts both side surfaces of said n-type cladding layer of said ridge structure.

3. a stacking direction of each layer of the ridge structure is defined as a z direction, an extension direction in which the ridge structure extends is defined as a y direction, and a direction perpendicular to the z direction and the y direction is defined as an x ​​direction, the ridge structure has a ridge main body and ridge extensions extending in the x-direction from both side surfaces of the ridge main body, the ridge extension portion is an active layer extension portion in which the active layer extends in the x-direction, the p-type semiconductor layer is in contact with both side surfaces of the p-type cladding layer and the active layer in the x-direction and with a surface of the active layer extension portion opposite to the n-type semiconductor substrate, the separation portion is formed on the n-type semiconductor substrate side of the active layer extension portion; 2. The semiconductor laser according to claim 1.

4. A semiconductor laser comprising a ridge structure formed on an n-type semiconductor substrate, and an embedded layer embedded so as to cover both sides facing each other in a direction perpendicular to an extension direction of the ridge structure, a stacking direction of each layer of the ridge structure is defined as a z direction, an extension direction in which the ridge structure extends is defined as a y direction, and a direction perpendicular to the z direction and the y direction is defined as an x ​​direction, The ridge structure is a ridge intermediate layer including an active layer, an n-type cladding layer formed in contact with the n-type semiconductor substrate side of the ridge intermediate layer, and a p-type cladding layer formed in contact with the ridge intermediate layer on the side opposite to the n-type semiconductor substrate, and a ridge extension portion extending in the x-direction from both side surfaces of the ridge main body, the ridge intermediate layer includes the active layer, an intermediate layer portion n-type cladding layer which is an n-type cladding layer formed on the n-type semiconductor substrate side of the active layer, and an extension portion base layer formed on the n-type semiconductor substrate side of the intermediate layer portion n-type cladding layer, The ridge extension portion has the ridge intermediate layer extending in the x direction, The buried layer is the ridge structure includes a p-type semiconductor layer in contact with both side surfaces in the x-direction of the p-type cladding layer and the ridge intermediate layer and a surface of the ridge extension portion opposite the n-type semiconductor substrate, and another p-type semiconductor and a semi-insulating layer are provided on both side surfaces of the n-type cladding layer of the ridge structure in the x-direction facing the n-type semiconductor substrate, the p-type semiconductor layer is not in contact with the n-type cladding layer of the ridge structure, a separation portion in which the p-type semiconductor layer and the other p-type semiconductor layer are separated from each other is formed on the n-type semiconductor substrate side of the ridge extension portion, The semi-insulating layer is embedded in the isolation portion. Semiconductor laser.

5. a stacking direction of each layer of the ridge structure is defined as a z direction, an extension direction in which the ridge structure extends is defined as a y direction, and a direction perpendicular to the z direction and the y direction is defined as an x ​​direction, The ridge structure is an extension base layer formed between the n-type cladding layer and the active layer; and a ridge extension portion extending in the x-direction from both side surfaces of the ridge main body, the ridge extension portion is such that the extension portion base layer and the active layer extend in the x-direction, the p-type semiconductor layer is in contact with both side surfaces of the p-type cladding layer, the extension base layer, and the active layer in the x-direction, and with a surface of the ridge extension portion opposite to the n-type semiconductor substrate, the isolation portion is formed on the n-type semiconductor substrate side of the ridge extension portion, 2. The semiconductor laser according to claim 1.

6. 6. The semiconductor laser according to claim 4, wherein the extension base layer has a valence band whose energy level is higher than the valence band whose energy level is higher than the valence band whose energy level is higher than the p-type semiconductor layer.

7. 7. The semiconductor laser according to claim 6, wherein the extension base layer is an n-type semiconductor layer.

8. 8. The semiconductor laser according to claim 7, wherein the extension base layer is an n-type AlGaInAs layer or an n-type AlInAs layer.

9. A semiconductor laser comprising a ridge structure formed on an n-type semiconductor substrate, and an embedded layer embedded so as to cover both sides facing each other in a direction perpendicular to an extension direction of the ridge structure, the ridge structure includes an active layer, an n-type cladding layer formed in contact with the active layer on a side of the n-type semiconductor substrate, and a p-type cladding layer formed in contact with the active layer on a side opposite to the n-type semiconductor substrate, The buried layer is a semi-insulating layer in contact with both side surfaces of the n-type cladding layer of the ridge structure and formed on the n-type semiconductor substrate side; a p-type semiconductor layer in contact with both side surfaces of the p-type cladding layer and the active layer of the ridge structure and formed to extend in a direction away from the ridge structure on a surface of the semi-insulating layer opposite to the n-type semiconductor substrate; and another semi-insulating layer; the p-type semiconductor layer is not in contact with the n-type cladding layer of the ridge structure, the other semi-insulating layer covers a surface of the p-type semiconductor layer opposite to the n-type semiconductor substrate and a surface of the p-type semiconductor layer facing a ridge structure; Semiconductor laser.

10. A semiconductor laser comprising a ridge structure formed on an n-type semiconductor substrate, and a buried layer buried in such a way as to cover both sides facing each other in a direction perpendicular to the extension direction of the ridge structure, the ridge structure includes an active layer, an n-type cladding layer formed in contact with the active layer on a side of the n-type semiconductor substrate, and a p-type cladding layer formed in contact with the active layer on a side opposite to the n-type semiconductor substrate, The buried layer is a p-type semiconductor layer in contact with both side surfaces of the p-type cladding layer and the active layer of the ridge structure, a semi-insulating layer, and an undoped semiconductor layer; the undoped semiconductor layer is in contact with both side surfaces of the n-type cladding layer of the ridge structure, the p-type semiconductor layer contains zinc and is not in contact with the n-type cladding layer of the ridge structure; Semiconductor laser.

11. the ridge structure has a first n-type cladding layer which is an n-type cladding layer formed on the n-type semiconductor substrate side of the n-type cladding layer via a diffraction grating layer; 11. The semiconductor laser according to claim 1.

12. 1. A method for manufacturing a semiconductor laser comprising: a ridge structure formed on an n-type semiconductor substrate; and a buried layer buried in such a manner as to cover both sides opposed to each other in a direction perpendicular to an extension direction of the ridge structure, the method comprising the steps of: the buried layer includes a p-type semiconductor layer and a semi-insulating layer, The ridge structure is a ridge base layer including an n-type cladding layer formed in contact with the ridge intermediate layer on the side of the n-type semiconductor substrate, and a p-type cladding layer formed in contact with the ridge intermediate layer on the side opposite to the n-type semiconductor substrate, the n-type cladding layer of the ridge base layer is in contact with the ridge intermediate layer, a stacking direction of each layer of the ridge structure is defined as a z direction, an extension direction in which the ridge structure extends is defined as a y direction, and a direction perpendicular to the z direction and the y direction is defined as an x ​​direction, a ridge structure forming step of sequentially forming the ridge base layer, the ridge intermediate layer, and the p-type cladding layer on the n-type semiconductor substrate, and forming the ridge structure having the ridge base layer, the ridge intermediate layer, and the p-type cladding layer, both side surfaces of which are exposed by etching; an extension portion forming step of etching layers other than the ridge intermediate layer on both side surfaces of the ridge structure to form ridge extension portions in the ridge intermediate layer extending in the x-direction from both side surfaces of the ridge structure; a p-type semiconductor layer forming step of forming the p-type semiconductor layer so as to cover both side surfaces of the ridge structure and a surface of the ridge extension portion opposite to the n-type semiconductor substrate; a semi-insulating layer forming step of forming the semi-insulating layer so as to cover a surface of the p-type semiconductor layer and an exposed surface of the ridge extension portion on the n-type semiconductor substrate side; A method for manufacturing a semiconductor laser comprising the steps of:

13. 13. The method for producing a semiconductor laser according to claim 12, wherein the ridge intermediate layer is made up of only the active layer.

14. 13. The method for producing a semiconductor laser according to claim 12, wherein the ridge intermediate layer includes an extension base layer on the ridge base layer side of the active layer.

15. 15. The method for producing a semiconductor laser according to claim 14, further comprising the step of: providing an intermediate n-type cladding layer between said extension base layer and said active layer, said intermediate n-type cladding layer being an n-type cladding layer.

16. 1. A method for manufacturing a semiconductor laser comprising: a ridge structure including an active layer formed on an n-type semiconductor substrate; and a buried layer buried in such a manner as to cover both sides opposed to each other in a direction perpendicular to an extension direction of the ridge structure, the method comprising the steps of: the buried layer includes a first semi-insulating layer, a p-type semiconductor layer, and a second semi-insulating layer; The ridge structure is the active layer, a ridge base layer including an n-type cladding layer formed in contact with the active layer on a side of the n-type semiconductor substrate, and a p-type cladding layer formed in contact with the active layer on a side opposite to the n-type semiconductor substrate, the n-type cladding layer of the ridge base layer is in contact with the active layer, A specific position of the active layer is A position of a near end of the active layer on the n-type semiconductor substrate side, or a position that is farther from the n-type semiconductor substrate side than a near end of the active layer and does not reach a near end of a quantum well structure of the active layer that is on the n-type semiconductor substrate side, a ridge structure forming step of sequentially forming the ridge base layer, the active layer, and a p-type cladding layer on the n-type semiconductor substrate, and forming the ridge structure having the ridge base layer, the active layer, and the p-type cladding layer, both side surfaces of which are exposed by etching; a first semi-insulating layer forming step of forming the first semi-insulating layer so as to cover both side surfaces of the ridge structure from the n-type semiconductor substrate side to the specific position of the active layer; a p-type semiconductor layer forming step of forming the p-type semiconductor layer so as to cover a surface of the first semi-insulating layer and both side surfaces of the active layer from the specific position where the ridge structure is exposed to a far end opposite the n-type semiconductor substrate; a second semi-insulating layer forming step of forming the second semi-insulating layer so as to cover the p-type semiconductor layer; A method for manufacturing a semiconductor laser comprising the steps of:

17. 1. A method for manufacturing a semiconductor laser comprising: a ridge structure including an active layer formed on an n-type semiconductor substrate; and a buried layer buried in such a manner as to cover both sides opposed to each other in a direction perpendicular to an extension direction of the ridge structure, the method comprising the steps of: the buried layer includes an undoped semiconductor layer, a p-type semiconductor layer, and a semi-insulating layer; The ridge structure is the active layer, a ridge base layer including an n-type cladding layer formed in contact with the active layer on a side of the n-type semiconductor substrate, and a p-type cladding layer formed in contact with the active layer on a side opposite to the n-type semiconductor substrate, the n-type cladding layer of the ridge base layer is in contact with the active layer, A specific position of the active layer is A position of a near end of the active layer on the n-type semiconductor substrate side, or a position that is farther from the n-type semiconductor substrate side than a near end of the active layer and does not reach a near end of a quantum well structure of the active layer that is on the n-type semiconductor substrate side, a ridge structure forming step of sequentially forming the ridge base layer, the active layer, and a p-type cladding layer on the n-type semiconductor substrate, and forming the ridge structure having the ridge base layer, the active layer, and the p-type cladding layer, both side surfaces of which are exposed by etching; an undoped semiconductor layer forming step of forming the undoped semiconductor layer so as to cover both side surfaces of the ridge structure; a semi-insulating layer forming step of forming the semi-insulating layer so as to cover a surface of the undoped semiconductor layer; a zinc diffusion step of diffusing zinc into a region from a far end of the undoped semiconductor layer opposite to the n-type semiconductor substrate to the specific position of the active layer; A method for manufacturing a semiconductor laser comprising the steps of:

18. In the zinc diffusion step, a diffusion prevention film having openings exposing a region including the undoped semiconductor layer on a surface of the ridge structure opposite to the n-type semiconductor substrate and on a surface of the buried layer opposite to the n-type semiconductor substrate is disposed in the buried layer, 18. The method for manufacturing a semiconductor laser according to claim 17, further comprising diffusing said zinc from a zinc oxide film disposed so as to cover said opening into said undoped semiconductor layer and said p-type cladding layer.

19. In the zinc diffusion step, a diffusion prevention film having openings exposing a region including the undoped semiconductor layer on a surface of the ridge structure opposite to the n-type semiconductor substrate and on a surface of the buried layer opposite to the n-type semiconductor substrate is disposed in the buried layer, 18. The method for producing a semiconductor laser according to claim 17, further comprising vapor-phase diffusing said zinc from said opening into said undoped semiconductor layer and said p-type cladding layer.

20. In the zinc diffusion step, a diffusion prevention film having an opening exposing a region including the undoped semiconductor layer on a surface of the buried layer opposite to the n-type semiconductor substrate is disposed on the buried layer and the surface of the ridge structure opposite to the n-type semiconductor substrate, 18. The method for manufacturing a semiconductor laser according to claim 17, further comprising diffusing said zinc into said undoped semiconductor layer from a zinc oxide film disposed so as to cover said opening.

21. In the zinc diffusion step, a diffusion prevention film having an opening exposing a region including the undoped semiconductor layer on a surface of the buried layer opposite to the n-type semiconductor substrate is disposed on the buried layer and the surface of the ridge structure opposite to the n-type semiconductor substrate, 18. The method for producing a semiconductor laser according to claim 17, further comprising vapor-phase diffusing said zinc from said opening into said undoped semiconductor layer.

22. The ridge base layer has a diffraction grating layer and a first n-type clad layer and a second n-type clad layer as the n-type clad layer, The ridge structure forming step includes: forming the first n-type cladding layer, the diffraction grating layer, and the second n-type cladding layer in sequence on a surface of the n-type semiconductor substrate to form the ridge base layer, and then forming the ridge intermediate layer including the active layer and the p-type cladding layer in sequence; forming a ridge structure having the first n-type cladding layer, the diffraction grating layer, the second n-type cladding layer, the ridge intermediate layer, and the p-type cladding layer, both side surfaces of which are exposed by etching; 16. A method for manufacturing a semiconductor laser according to claim 12.

23. The ridge base layer has a diffraction grating layer and a first n-type clad layer and a second n-type clad layer as the n-type clad layer, The ridge structure forming step includes: forming the first n-type cladding layer, the diffraction grating layer, and the second n-type cladding layer in sequence on a surface of the n-type semiconductor substrate to form the ridge base layer, and then forming the active layer and the p-type cladding layer in sequence; forming the ridge structure having the first n-type cladding layer, the diffraction grating layer, the second n-type cladding layer, the active layer, and the p-type cladding layer, both side surfaces of which are exposed by etching; 22. A method for manufacturing a semiconductor laser according to claim 16.

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