JP5310271B2 - Semiconductor laser element - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a semiconductor laser device capable of reducing electrical resistance and a light loss at a high level. <P>SOLUTION: The semiconductor laser device 1A includes: an n-type semiconductor substrate 3; an active layer 12; a diffraction lattice layer 15; and an n-type clad layer 18. The diffraction lattice layer 15 includes: a plurality of regions 15a disposed in an optical waveguide direction at a cycle corresponding to an output wavelength; and a region 15b that is provided among the plurality of regions 15a and has an impurity concentration lower than that of the plurality of regions 15a. Each of the plurality of regions 15a includes a p-type semiconductor layer 16 formed on the active layer 12 and an n-type semiconductor layer 17 formed on the p-type semiconductor layer 16, and the p-type semiconductor layer 16 and the n-type semiconductor layer 17 mutually constitute a tunnel junction. <P>COPYRIGHT: (C)2011,JPO&amp;INPIT

Description

  The present invention relates to a semiconductor laser device.

  Non-Patent Document 1 describes a ridge type laser diode. This laser diode includes a diffraction grating layer made of n-type InGaAsP formed on an n-type InP substrate, a multiple quantum well active layer made of AlGaInAs provided on the diffraction grating layer, and provided on the active layer. and a ridge-shaped upper cladding layer made of p-type InP.

  Non-Patent Document 2 describes a laser diode having a tunnel junction layer. The laser diode includes an n-type InP substrate, an n-type InP layer provided on the n-type InP substrate, a p-type InP layer provided on the n-type InP layer, an n-type InP layer, and a p-type InP layer. And a multiple quantum well active layer provided between the two. In addition, this laser diode further includes another n-type InP layer (second n-type InP layer) on the p-type InP layer, and between the p-type InP layer and the second n-type InP layer. In this case, a tunnel junction layer is interposed.

K. Takagi, et al., “120 ℃ 10-Gb / sUncooled Direct Modulated 1.3-μm AlGaInAs MQW DFB Laser Diodes”, IEEE Photonics Technology Letters, VOL. 16, NO. 11, pp.2415-2417 (2004)

S. Sekiguchi, et al., “Long WavelengthGaInAsP / InP Laser with nn Contacts Using AlAs / InP Hole Injecting Tunnel Junction”, Japanese Journal of Applied Physics, vol.38, Part 2, no.4B, pp.L443-445 (1999 )

  The conventional ridge type semiconductor laser device having the configuration described in Non-Patent Document 1 has the following problems. That is, since the width of the upper cladding layer in the direction orthogonal to the optical waveguide direction is narrow and the upper cladding layer is made of a p-type semiconductor, 1. a current passes through a p-type semiconductor having a relatively high resistivity. In this case, the amount of heat generated becomes large, and the maximum value of the laser light output intensity is kept low. 2. Since the light absorption rate of the p-type semiconductor is higher than that of the n-type semiconductor, the light loss is large, and the laser oscillation threshold value is increased. At the same time as the current increases, the maximum value of the laser beam output intensity is kept low.

  To solve these problems, for example, a tunnel junction layer as described in Non-Patent Document 2 is provided in the upper clad layer, and the conductivity type of the upper clad layer is changed from p-type to n-type. Can be made thinner.

  However, the impurity concentration of the tunnel junction layer is generally much higher than other semiconductor layers. Semiconductors tend to have higher light absorptance when the impurity concentration is higher, and light loss occurs in the tunnel junction layer, so that the above problem 2 cannot be effectively solved. Further, if the impurity concentration of the tunnel junction layer is lowered in order to reduce the optical loss, the electric resistance at the tunnel junction surface increases and the above problem 1 cannot be effectively solved.

  The present invention has been made in view of the above-described problems, and an object of the present invention is to provide a semiconductor laser device capable of realizing a reduction in electric resistance and optical loss at a high level.

  In order to solve the above problems, a semiconductor laser device according to the present invention is a semiconductor laser device that outputs laser light of a predetermined wavelength, and includes a first n-type semiconductor cladding region and a first n-type semiconductor cladding region. The active layer provided on the active layer, the diffraction grating layer provided on the active layer, and the width provided in the direction intersecting with the optical waveguide direction are made narrower than the first n-type semiconductor cladding region. A second n-type semiconductor clad region, and a diffraction grating layer is provided between the plurality of first regions arranged in the optical waveguide direction at a period corresponding to a predetermined wavelength, and the plurality of first regions. A second region having a lower impurity concentration than the plurality of first regions, and each of the plurality of first regions includes a p-type semiconductor layer provided on the active layer, and a p-type semiconductor layer An n-type semiconductor layer provided on a p-type semiconductor layer and n Wherein the semiconductor layer forms a tunnel junction with each other.

  This semiconductor laser device has a tunnel junction structure composed of a p-type semiconductor layer and an n-type semiconductor layer. This tunnel junction structure is provided in the entire region on the active layer as in the conventional semiconductor laser device. Instead, it is provided in each of the plurality of first regions arranged in the optical waveguide direction with a period corresponding to a predetermined wavelength. A second region having an impurity concentration lower than that of the plurality of first regions is provided between the plurality of first regions. Therefore, compared with the case where the tunnel junction layer is provided in the entire region on the active layer, the total length of the tunnel junction structure in the optical waveguide direction is shortened, so the volume of the tunnel junction structure is reduced and the tunnel junction structure is reduced. Can effectively reduce the optical loss.

  Further, the flow path of the current injected into the semiconductor laser element is secured by the tunnel junction structure provided in each of the plurality of first regions, and the optical loss can be reduced as described above in this semiconductor laser element. It is not necessary to reduce the impurity concentration of the p-type semiconductor layer and the n-type semiconductor layer constituting the tunnel junction structure. Therefore, the electrical resistance at the tunnel junction can be effectively reduced with an impurity concentration sufficient to develop the tunnel effect. As described above, according to the semiconductor laser element described above, reduction of electric resistance and optical loss can be realized at a high level.

  The balance between the electrical resistance and the optical loss can be easily adjusted by the ratio (duty ratio) of the first region in one period of the diffraction grating layer. In other words, by increasing this duty ratio, the degree of reduction in electrical resistance can be made greater than the degree of reduction in optical loss. Conversely, by reducing the duty ratio, the degree of reduction in optical loss is made greater than the degree of reduction in electrical resistance. be able to.

  In the semiconductor laser device, the diffraction grating layer has a relatively low impurity concentration (that is, a small optical loss) between the plurality of first regions having a relatively high impurity concentration (that is, a large optical loss). Since the region 2 is provided, gain modulation can be performed on light resonating in the vicinity of the active layer, and laser light having a predetermined wavelength can be suitably output.

  In the semiconductor laser element, the width of the active layer and the diffraction grating layer in the direction crossing the optical waveguide direction is narrower than that of the first n-type semiconductor cladding region, and the active layer, the diffraction grating layer, and the second n The semiconductor device may further include a semi-insulating or insulating embedded region that embeds both side surfaces of the type semiconductor cladding region. Alternatively, the semiconductor laser element may have a ridge structure in which the width of the active layer and the diffraction grating layer in the direction intersecting the optical waveguide direction is wider than that of the second n-type semiconductor cladding region. Alternatively, the active layer has a ridge structure in which the width of the active layer in the direction crossing the optical waveguide direction is wider than that of the second n-type semiconductor cladding region, and the ridge structure includes a diffraction grating layer and a second n-type semiconductor cladding region. It may be characterized by being included. The operational effects exhibited by the semiconductor laser element are particularly effective in a semiconductor laser element having such a buried type or ridge type configuration.

  According to the semiconductor laser device of the present invention, reduction in electrical resistance and optical loss can be realized at a high level.

FIG. 1 shows the configuration of a semiconductor laser device 1A according to the first embodiment of the present invention. FIG. 1A is a view showing a cross section orthogonal to the optical waveguide direction of the semiconductor laser device 1A, and FIG. 1B is a side cross sectional view taken along the line Ib-Ib in FIG. FIG. 2A and FIG. 2B are diagrams sequentially illustrating the manufacturing steps of the semiconductor laser element 1A, and show side cross-sections along the optical waveguide direction. FIG. 3A and FIG. 3B are diagrams sequentially illustrating the manufacturing steps of the semiconductor laser element 1A. 3A shows a side cross section along the optical waveguide direction, and FIG. 3B shows a cross section perpendicular to the optical waveguide direction. FIG. 4 is a diagram showing a manufacturing process of the semiconductor laser device 1A, and shows a cross section perpendicular to the optical waveguide direction. FIG. 5 shows a cross section perpendicular to the optical waveguide direction of the semiconductor laser element 1B according to a modification of the first embodiment. FIG. 6A and FIG. 6B are diagrams sequentially illustrating a manufacturing process of a gain modulation type semiconductor laser device as a comparative example, and show side cross-sections along the optical waveguide direction. FIG. 7A and FIG. 7B are diagrams sequentially illustrating a manufacturing process of a gain modulation type semiconductor laser device as a comparative example. FIG. 7A shows a side cross section along the optical waveguide direction, and FIG. 7B shows a cross section perpendicular to the optical waveguide direction. FIG. 8 is a diagram showing a manufacturing process of a gain modulation type semiconductor laser device as a comparative example, and shows a cross section perpendicular to the optical waveguide direction. FIG. 9 is a graph showing the current-light output characteristics of the semiconductor laser element 1A and the current-light output characteristics of a normal gain modulation type semiconductor laser element. FIG. 10 is a graph showing current-operating resistance characteristics of the semiconductor laser element 1A and current-operating resistance characteristics of a normal gain modulation type semiconductor laser element. FIG. 11 shows a configuration of a semiconductor laser element 1C according to the second embodiment of the present invention. 11A is a diagram showing a cross section orthogonal to the optical waveguide direction of the semiconductor laser device 1C, and FIG. 11B is a side cross sectional view taken along the line XIb-XIb in FIG. 11A. FIG. 12A and FIG. 12B are diagrams sequentially illustrating manufacturing steps of the semiconductor laser element 1C. 12A shows a side cross section along the optical waveguide direction, and FIG. 12B shows a cross section perpendicular to the optical waveguide direction. FIG. 13A and FIG. 13B are diagrams sequentially illustrating a manufacturing process of the semiconductor laser device 1C, and show cross sections perpendicular to the optical waveguide direction.

  Embodiments of a semiconductor laser device according to the present invention will be described below in detail with reference to the accompanying drawings. In the description of the drawings, the same elements are denoted by the same reference numerals, and redundant description is omitted.

(First embodiment)
The semiconductor laser device 1A according to this embodiment is a so-called distributed feedback (DFB) laser device that outputs laser light having a predetermined wavelength. Referring to FIGS. 1A and 1B, a semiconductor laser element 1A includes a semiconductor substrate 3 having a main surface 3a. The semiconductor substrate 3 is mainly made of an n-type semiconductor, and in one embodiment, is made of n-type InP. The semiconductor substrate 3 constitutes a first n-type semiconductor cladding region together with an n-type buffer layer 11 to be described later, and functions as a lower cladding region for light guided through the semiconductor laser element 1A.

  In addition, the semiconductor laser device 1A includes an n-type buffer layer 11, an active layer 12, a p-type carrier stop layer 13, a p-type spacer layer 14, a diffraction grating layer 15, an n-type cladding layer 18, and an n-type contact layer 19. ing. The n-type buffer layer 11 is provided on the main surface 3a of the semiconductor substrate 3, and is made of, for example, an n-type semiconductor having the same composition as the semiconductor substrate 3 (Si-doped n-type InP in one embodiment). The layer thickness of the n-type buffer layer 11 is, for example, 100 [nm].

  The active layer 12 is provided on the n-type buffer layer 11 and is made of a semiconductor having a composition corresponding to a desired emission wavelength. As an example, the active layer 12 has a multiple quantum well structure, and is formed by alternately laminating barrier layers (barrier layers) made of undoped AlGaInAs and well layers.

  The p-type carrier stop layer 13 is a layer for reducing carrier overflow, and is provided on the active layer 12. The p-type carrier stop layer 13 is made of, for example, Zn-doped p-type AlInAs, and the layer thickness is, for example, 50 [nm]. The p-type spacer layer 14 is made of, for example, Zn-doped p-type InP, and its layer thickness is, for example, 50 [nm].

  The diffraction grating layer 15 is provided on the p-type spacer layer 14. The diffraction grating layer 15 includes a plurality of regions (first regions) 15a arranged along the active layer 12, and a region (second region) 15b formed so as to be embedded between the plurality of regions 15a. It is configured to include.

The plurality of regions 15a are formed with the direction perpendicular to the optical waveguide direction as the longitudinal direction, and are arranged in the optical waveguide direction at intervals with a period Λ corresponding to a predetermined wavelength to be output by the semiconductor laser device 1A. Has been. Each region 15a includes a p-type semiconductor layer 16 and an n-type semiconductor layer 17 that form a tunnel junction with each other. The p-type semiconductor layer 16 is provided on the active layer 12 and is made of a high-concentration p-type semiconductor, for example, C-doped p ^++- type AlGaInAs, and its layer thickness is, for example, 15 [nm]. The n-type semiconductor layer 17 is provided on the p-type semiconductor layer 16 and is made of a high-concentration n-type semiconductor, for example, Si-doped n ^++- type AlGaInAs, and its layer thickness is, for example, 15 [nm].

The impurity concentration of the p-type semiconductor layer 16 is preferably 1 × 10 ¹⁹ [cm ⁻³ ] or higher, and the impurity concentration of the n-type semiconductor layer 17 is preferably 3 × 10 ¹⁸ [cm ⁻³ ] or higher. In addition to C, Zn, Be, or Mg is preferably used as the impurity of the p-type semiconductor layer 16. As impurities of the n-type semiconductor layer 17, S, Se, or Te is preferably used in addition to Si. In addition to the above, the composition of the p-type semiconductor layer 16 includes, for example, GaInAsP, InGaAs, AlInAs, or InP. In addition to the above, the composition of the n-type semiconductor layer 17 includes, for example, GaInAsP, InGaAs, or InP.

  The region 15b is made of a semiconductor having a lower impurity concentration than the plurality of regions 15a, for example, Si-doped n-type InP. Since the optical absorptance of the semiconductor increases as the impurity concentration increases, a region 15b having a relatively low impurity concentration (that is, light loss is small) between the plurality of regions 15a having a relatively high impurity concentration (that is, light loss is large). , Gain modulation can be performed on light resonating in the vicinity of the active layer 12.

  The n-type clad layer 18 is a second n-type semiconductor clad region in the present embodiment, and functions as an upper clad region with respect to light guided through the semiconductor laser device 1A. The n-type cladding layer 18 is provided on the diffraction grating layer 15. The n-type cladding layer 18 is made of, for example, Si-doped n-type InP, and its layer thickness is, for example, 2.0 [μm]. The n-type contact layer 19 is provided on the n-type cladding layer 18 and is made of, for example, n-type InGaAs. The layer thickness of the n-type contact layer 19 is, for example, 100 [nm].

  The n-type cladding layer 18 and the contact layer 19 are included in a ridge portion 24 whose width in the direction intersecting the optical waveguide direction is narrower than that of the semiconductor substrate 3 and the n-type buffer layer 11. Extending in the direction. With such a configuration, it is possible to preferably realize a ridge structure in which the width of the n-type cladding layer 18 in the direction intersecting the optical waveguide direction is narrower than the widths of the active layer 12 and the diffraction grating layer 15. In the semiconductor laser element 1 </ b> A, a refractive index type waveguide is formed by an effective refractive index distribution inside the active layer 12 generated by current injection into the ridge portion 24. The width of the ridge portion 24 in the direction orthogonal to the optical waveguide direction is, for example, 1.5 [μm], and the height of the ridge portion 24 is, for example, 2 [μm].

Insulating films 25 made of SiO ₂ are provided on both side surfaces of the ridge portion 24. The insulating film 25 of this embodiment is provided over the surface of the diffraction grating layer 15 exposed from the ridge portion 24 in addition to the both side surfaces of the ridge portion 24.

  An electrode 20 is provided on the n-type contact layer 19, and the electrode 20 and the n-type contact layer 19 are in ohmic contact. Further, an electrode 21 is provided on the back surface of the semiconductor substrate 3 opposite to the main surface 3a, and the electrode 21 and the semiconductor substrate 3 are in ohmic contact.

  Next, a manufacturing method of the semiconductor laser device 1A according to the present embodiment will be described with reference to FIGS. First, as shown in FIG. 2A, an n-type buffer layer 11, an active layer 12, a p-type carrier stop layer 13, a p-type spacer layer 14, and a p-type semiconductor layer 16 are formed on the main surface 3 a of the semiconductor substrate 3. Then, the n-type semiconductor layer 17 and the cover layer 26 are formed. The cover layer 26 is made of, for example, Si-doped n-type InP, and its layer thickness is, for example, 30 [nm]. The growth of these semiconductor layers is performed using, for example, a metal organic vapor phase growth furnace.

  Next, a plurality of regions 15a to be the diffraction grating layer 15 are formed. That is, a resist is applied on the cover layer 26, and a pattern corresponding to the plurality of regions 15a is transferred using, for example, an interference exposure method. Then, dry etching is performed on the cover layer 26, the n-type semiconductor layer 17, and the p-type semiconductor layer 16. At this time, the etching is stopped when the p-type spacer layer 14 is exposed. Thus, as shown in FIG. 2B, a plurality of regions 15a each including the p-type semiconductor layer 16 and the n-type semiconductor layer 17 are formed.

  Subsequently, after removing the resist, the semiconductor substrate 3 is re-introduced into the growth furnace, and the n-type cladding layer 18 and the n-type contact layer 19 are sequentially grown as shown in FIG. When the n-type cladding layer 18 is grown, a region 15b is formed by filling gaps between the plurality of regions 15a with n-type InP, whereby the diffraction grating layer 15 is completed. Thereafter, as shown in FIG. 3B, the n-type cladding layer 18 and the n-type contact layer 19 are etched to form a striped ridge portion 24.

Subsequently, as shown in FIG. 4, an insulating film 25 made of SiO ₂ is formed so as to cover the surface of the ridge portion 24 and the surface of the diffraction grating layer 15 exposed from the ridge portion 24. Then, an opening is formed in the insulating film 25 located above the ridge portion 24, an electrode 20 in contact with the n-type contact layer 19 is deposited through the opening, and an electrode 21 is further deposited on the back surface of the semiconductor substrate 3. Finally, the antireflection film (AR film) and the high reflection film (HR film) are coated on both end faces serving as the resonator, thereby completing the semiconductor laser device 1A according to the present embodiment.

  The operation and effect of the semiconductor laser device 1A having the above configuration will be described. In this semiconductor laser device 1A, a tunnel junction structure including a p-type semiconductor layer 16 and an n-type semiconductor layer 17 is provided in each of a plurality of regions 15a periodically arranged in the optical waveguide direction. A region 15b having an impurity concentration lower than that of the plurality of regions 15a is provided between the plurality of regions 15a. Therefore, compared with the case where the tunnel junction layer is provided in the entire region on the active layer 12, the total length of the tunnel junction structure in the optical waveguide direction is shortened, so that the volume of the tunnel junction structure is reduced and the tunnel junction structure is reduced. The optical loss due to the structure can be effectively reduced.

  Further, the flow path of the current injected into the semiconductor laser element 1A is secured by the tunnel junction structure provided in each of the plurality of regions 15a. However, in the semiconductor laser element 1A, the optical loss is reduced as described above. Therefore, it is not necessary to reduce the impurity concentration of the p-type semiconductor layer 16 and the n-type semiconductor layer 17 constituting the tunnel junction structure. Therefore, the electrical resistance at the tunnel junction (p-type semiconductor layer 16 and n-type semiconductor layer 17) can be effectively reduced with an impurity concentration sufficient to develop the tunnel effect. Thus, according to the semiconductor laser device 1A of the present embodiment, it is possible to achieve a reduction in electrical resistance and optical loss at a high level.

  The balance between the electrical resistance and the optical loss can be easily adjusted by the ratio (duty ratio) of the region 15a in one period of the diffraction grating layer 15. In other words, by increasing this duty ratio, the degree of reduction in electrical resistance can be made greater than the degree of reduction in optical loss. Conversely, by reducing the duty ratio, the degree of reduction in optical loss is made greater than the degree of reduction in electrical resistance. be able to.

  A modification of this embodiment will be described. FIG. 5 shows a configuration of a semiconductor laser element 1B according to a modification of the first embodiment, and shows a cross section orthogonal to the optical waveguide direction of the semiconductor laser element 1B. In the first embodiment described above, the diffraction grating layer 15 is formed on the active layer 12 and the p-type spacer layer 14 and is not included in the ridge portion 24 as shown in FIG. As shown, the ridge portion 26 may be formed so that the diffraction grating layer 15 is included in the ridge portion 26. The ridge portion 26 is formed so that the width in the direction intersecting the optical waveguide direction is narrower than that of the semiconductor substrate 3 and the n-type buffer layer 11 as in the ridge portion 24 of the first embodiment. It is.

  In this case, it is desirable that the diffraction grating layer 15 be positioned in a range from the bottom surface of the ridge portion 26 (the surface connecting the lower ends of both side surfaces of the ridge portion 26) to a height of 0.5 [μm]. This is because the electrical resistance of the semiconductor laser element 1B can be limited to a predetermined value or less by limiting the thickness of the p-type semiconductor layer such as the p-type spacer layer 14 included in the ridge portion 26 to some extent. Even in the structure of the present modification, the total length of the tunnel junction structure in the optical waveguide direction is shorter than the case where the tunnel junction layer is provided in the entire region on the active layer 12, so that the volume of the tunnel junction structure can be reduced. The optical loss due to the tunnel junction structure can be effectively reduced. In addition, the electrical resistance at the tunnel junction can be effectively reduced with an impurity concentration sufficient to develop the tunnel effect. In this way, reduction in electrical resistance and optical loss can be achieved at a high level.

  Here, a normal gain modulation type semiconductor laser device will be described as a comparative example of the first embodiment shown in FIG. 6 to 8 are views showing a method of manufacturing a conventional gain modulation type semiconductor laser device. First, as shown in FIG. 6A, on the main surface of the semiconductor substrate 103, an n-type buffer layer 111 (thickness 100 [nm]), an active layer 112, and a p-type carrier stop layer 113 (thickness 50 [ nm]), p-type spacer layer 114 (thickness 50 [nm]), light absorption layer 115 (thickness 30 [nm]), and cover layer 126 (thickness 30 [nm]). In one example, the n-type buffer layer 111 is made of n-type InP, the active layer 112 is made of AlGaInAs multiple quantum wells, the p-type carrier stop layer 113 is made of p-type AlInAs, and the p-type spacer layer 114 is made of p-type InP. The light absorption layer 115 is made of p-type GaInAsP, and the cover layer 126 is made of p-type InP.

  Next, the light absorption layer 115 is divided into a plurality of light absorption regions arranged in the optical waveguide direction at a period corresponding to the output wavelength. That is, a resist is applied on the cover layer 126, and patterns corresponding to a plurality of light absorption regions are transferred using, for example, an interference exposure method. Then, dry etching is performed on the cover layer 126 and the light absorption layer 115. Thus, as shown in FIG. 6B, a plurality of light absorption regions 115a are formed.

  Subsequently, after removing the resist, as shown in FIG. 7A, a p-type cladding layer 118 and a p-type contact layer 119 are grown sequentially. The p-type cladding layer 118 is made of, for example, p-type InP, and the p-type contact layer 119 is made of, for example, p-type InGaAs. Thereafter, as shown in FIG. 7B, the p-type cladding layer 118 and the p-type contact layer 119 are etched to form a striped ridge portion 124.

Subsequently, as shown in FIG. 8, an insulating film 125 made of SiO ₂ is formed so as to cover the surface of the ridge portion 124 and the surface of the light absorption region 115 a exposed from the ridge portion 124. Then, an opening is formed in the insulating film 125 located above the ridge portion 124, the electrode 120 in contact with the p-type contact layer 119 is deposited through the opening, and the electrode 121 is further deposited on the back surface of the semiconductor substrate 103. Finally, an antireflection film (AR film) and a high reflection film (HR film) are coated on both end faces serving as a resonator.

  The characteristics of a normal gain modulation type semiconductor laser device manufactured by the above manufacturing method are compared with the characteristics of the semiconductor laser device 1A according to the first embodiment. FIG. 9 is a graph showing the current-light output characteristics of the semiconductor laser element 1A and the current-light output characteristics of a normal gain modulation type semiconductor laser element, and shows the characteristics at an element temperature of 85.degree. In the graphs G1 to G3 shown in FIG. 9, in the semiconductor laser element 1A, the ratio (duty ratio) of the region 15a in one period of the diffraction grating layer 15 is set to 0.3, 0.5, and 0.7, respectively. The current-light output characteristics are shown. A graph G4 shows current-light output characteristics of a normal gain modulation type semiconductor laser element (see FIG. 8).

  The threshold current of a normal gain modulation type semiconductor laser device was 25 [mA], and the maximum light output was 15 [mW]. On the other hand, the threshold current of the semiconductor laser device 1A of the present embodiment is 25 [mA] at a duty ratio of 0.7, 21 [mA] at a duty ratio of 0.5, and 21 [mA] at a duty ratio of 0.3. The maximum light output was 16 [mA] at a duty ratio of 0.7, 18 [mA] at a duty ratio of 0.5, and 19.5 [mA] at a duty ratio of 0.3.

  FIG. 10 is a graph showing the current-operating resistance characteristics of the semiconductor laser element 1A and the current-operating resistance characteristics of a normal gain modulation type semiconductor laser element, showing the characteristics at an element temperature of 85 ° C. Yes. Graphs G5 to G7 shown in FIG. 10 show current-operating resistance characteristics when the duty ratio of the diffraction grating layer 15 is 0.3, 0.5, and 0.7 in the semiconductor laser device 1A, respectively. . A graph G8 shows current-operating resistance characteristics of a normal gain modulation type semiconductor laser element.

  The differential resistance value in the vicinity of the threshold value of a normal gain modulation type semiconductor laser element was 9.5 [Ω]. On the other hand, the differential resistance value in the vicinity of the threshold value of the semiconductor laser device 1A of the present embodiment is 6.2 [Ω] when the duty ratio is 0.7, 7.0 [Ω] when the duty ratio is 0.5, and the duty ratio. 0.3 was 8.7 [Ω].

  As can be seen from the above results, the optical output characteristics and operating resistance characteristics of the semiconductor laser device 1A of the present embodiment are the same as those of the normal gain modulation type semiconductor laser device shown in FIG. 8 regardless of the duty ratio of the region 15a. It is better than the characteristics. The improvement of the light output characteristics (that is, the reduction of the threshold current value) is achieved by introducing a tunnel junction structure (p-type semiconductor layer 16 and n-type semiconductor layer 17) into the diffraction grating layer 15 so that the p-type cladding layer has a high light absorption rate. This is because 118 (see FIG. 8) is replaced with the n-type cladding layer 18 having a low light absorption rate. Further, the improvement of the operating resistance characteristics (that is, the reduction of the differential resistance value) is achieved by introducing a tunnel junction structure into the diffraction grating layer 15 so that the p-type cladding layer 118 having a high resistivity is replaced with an n-type cladding layer having a low resistivity. This is due to the replacement with 18.

  The larger the duty ratio of the region 15a, the larger the area occupied by the tunnel junction structure in the plane perpendicular to the current direction, so the resistance value decreases. Conversely, the smaller the duty ratio of the region 15a, the smaller the tunnel junction structure. Since the volume of the structure is reduced, the light absorption loss is reduced. As a result, the threshold current value is reduced and the maximum light output is increased. That is, in order to obtain desired characteristics, the duty ratio of the region 15a may be adjusted to an appropriate range. For example, a preferable range of the duty ratio in the above-described embodiment, that is, a range in which both the light output characteristic and the operating resistance characteristic can be improved as compared with a normal gain modulation type semiconductor laser element is 0.3 to 0.7. It becomes as follows.

(Second Embodiment)
The semiconductor laser element 1C according to this embodiment is a so-called distributed feedback (DFB) laser element that outputs laser light having a predetermined wavelength. The difference from the semiconductor laser device 1A of the first embodiment is that the semiconductor laser device 1C has a so-called high resistance current confinement buried type (SI-BH) structure. Referring to FIGS. 11A and 11B, a semiconductor laser device 1C includes a semiconductor substrate 3 as a first n-type semiconductor clad region, and an n-type buffer layer stacked on the semiconductor substrate 3 in order. 31, an active layer 32, a p-type carrier stop layer 33, a p-type spacer layer 34, a diffraction grating layer 35, an n-type cladding layer 38, and an n-type contact layer 39. The constituent materials and the layer thicknesses of these layers are the same as those of the n-type buffer layer 11, the active layer 12, the p-type carrier stop layer 13, the p-type spacer layer 14, the diffraction grating layer 15, n of the first embodiment described above. The same applies to the type cladding layer 18 and the n-type contact layer 19.

  The diffraction grating layer 35 includes a plurality of regions (first regions) 35 a arranged along the active layer 32 and a region (second region) 35 b formed so as to be embedded between the plurality of regions 35 a. It is configured to include. The configurations of these regions 35a and 35b are the same as the regions 15a and 15b of the first embodiment.

In this embodiment, the n-type buffer layer 31, the active layer 32, the p-type carrier stop layer 33, the p-type spacer layer 34, the diffraction grating layer 35, the n-type cladding layer 38, and the n-type contact layer 39 are in the optical waveguide direction. The mesa portion 44 whose width in the direction intersecting with the semiconductor substrate 3 is narrower than the semiconductor substrate 3 extends in the optical waveguide direction. The width of the mesa unit 44 in the direction orthogonal to the optical waveguide direction is, for example, 1.5 [μm], and the height of the mesa unit 44 is, for example, 3 [μm]. Further, on both sides of the mesa portion 44, semi-insulating or insulating buried regions 47 are provided so as to bury both side surfaces of these layers. The buried region 47 is made of, for example, Fe-doped InP. An insulating film 45 made of SiO ₂ is provided on the surface of the buried region 47.

  An electrode 40 is provided on the n-type contact layer 39, and the electrode 40 and the n-type contact layer 39 are in ohmic contact. In addition, an electrode 41 is provided on the back surface of the semiconductor substrate 3 opposite to the main surface 3a, and the electrode 41 and the semiconductor substrate 3 are in ohmic contact.

  Next, a manufacturing method of the semiconductor laser device 1C according to the present embodiment will be described with reference to FIGS. First, as in the first embodiment, on the main surface 3a of the semiconductor substrate 3, an n-type buffer layer 31, an active layer 32, a p-type carrier stop layer 33, a p-type spacer layer 34, a p-type semiconductor layer 36, n A mold semiconductor layer 37 and a cover layer are formed. Then, dry etching is performed on the n-type semiconductor layer 37 and the p-type semiconductor layer 36, thereby forming a plurality of regions 35a to be the diffraction grating layer 35. Thereafter, an n-type cladding layer 38 and an n-type contact layer 39 are grown sequentially (FIG. 12A).

Subsequently, as shown in FIG. 12B, by performing etching from the n-type contact layer 39 to the n-type buffer layer 31, a striped mesa portion 44 is formed. Then, as shown in FIG. 13A, an embedded region 47 is grown on the exposed main surface 3 a of the semiconductor substrate 3 so as to bury both side surfaces of the mesa portion 44. An insulating film 45 made of SiO ₂ is formed so as to cover the surface of the buried region 47. An opening is formed in the insulating film 45 located above the mesa portion 44, an electrode 40 in contact with the n-type contact layer 39 is deposited through the opening, and an electrode 41 is further deposited on the back surface of the semiconductor substrate 3. Finally, the antireflection film (AR film) and the high reflection film (HR film) are coated on both end faces serving as a resonator, thereby completing the semiconductor laser device 1C according to the present embodiment.

  In the semiconductor laser device 1C having the above configuration, a tunnel junction structure including a p-type semiconductor layer 36 and an n-type semiconductor layer 37 is provided in each of a plurality of regions 35a periodically arranged in the optical waveguide direction. In addition, since the region 35b having an impurity concentration lower than the plurality of regions 35a is provided between the plurality of regions 35a, the same operational effects as those of the semiconductor laser device 1A of the first embodiment can be obtained. In the semiconductor laser device 1C of the present embodiment, when the duty ratio of the region 35a is 0.5, the threshold current value is 22 [mA], the maximum light output is 17 [mW], and the vicinity of the threshold current value The differential resistance value at 7.5 was 7.5 [Ω].

  The semiconductor laser device according to the present invention is not limited to the above-described embodiment, and various other modifications are possible. For example, in each of the above embodiments, an InP-based compound semiconductor is exemplified as the semiconductor substrate and each semiconductor layer, but the configuration of the present invention can be suitably realized even with other III-V compound semiconductors and other semiconductors.

  1A, 1B, 1C ... semiconductor laser element, 3 ... semiconductor substrate, 11, 31 ... n-type buffer layer, 12, 32 ... active layer, 13, 33 ... p-type carrier stop layer, 14, 34 ... p-type spacer layer, 15, 35 ... diffraction grating layer, 15a, 35a ... (first) region, 15b, 35b ... (second) region, 16, 36 ... p-type semiconductor layer, 17, 37 ... n-type semiconductor layer, 18, 38 ... n-type cladding layer, 19, 39 ... n-type contact layer, 20, 21, 40, 41 ... electrode, 24 ... ridge portion, 25, 45 ... insulating film, 26 ... cover layer, 44 ... mesa portion, 47 ... Embedded area.

Claims (4)

A semiconductor laser element that outputs laser light of a predetermined wavelength,
A first n-type semiconductor cladding region;
An active layer provided on the first n-type semiconductor cladding region;
A diffraction grating layer provided on the active layer;
A second n-type semiconductor clad region provided on the diffraction grating layer and having a width in a direction intersecting the optical waveguide direction narrower than the first n-type semiconductor clad region;
The diffraction grating layer is provided between the plurality of first regions arranged in the optical waveguide direction at a period corresponding to the predetermined wavelength, and the plurality of first regions, and the impurity concentration is the plurality of first regions. A second region lower than the region,
Each of the plurality of first regions includes a p-type semiconductor layer provided on the active layer and an n-type semiconductor layer provided on the p-type semiconductor layer, and the p-type semiconductor layer and the p-type semiconductor layer A semiconductor laser device, wherein the n-type semiconductor layers form a tunnel junction with each other. A width of the active layer and the diffraction grating layer in a direction intersecting the optical waveguide direction is narrower than the first n-type semiconductor cladding region;
2. The semiconductor according to claim 1, further comprising a semi-insulating or insulating buried region filling both side surfaces of the active layer, the diffraction grating layer, and the second n-type semiconductor cladding region. Laser element.   2. The semiconductor laser device according to claim 1, wherein a width of the active layer and the diffraction grating layer in a direction crossing an optical waveguide direction has a ridge structure wider than that of the second n-type semiconductor cladding region. .   The active layer in the direction intersecting the optical waveguide direction has a ridge structure wider than the second n-type semiconductor cladding region, and the ridge structure includes the diffraction grating layer and the second n-type semiconductor. The semiconductor laser device according to claim 1, further comprising a cladding region.

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