JP2011018703A - Multi-wavelength semiconductor laser and method of manufacturing the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a multi-wavelength semiconductor laser that eliminates the need for high-precision mechanical mounting for aligning optical axes of individual LDs emitting laser light beams differing in wavelength.SOLUTION: On a part of a substrate 10 made of n-type GaAs, a composition modulation buffer layer 20 made of n-type GaAsN(0≤x≤1) mixed crystal is formed. On the composition modulation buffer layer 20, first semiconductor layer 40 is formed which includes an active layer made of a nitride semiconductor. A second semiconductor layer 50 which includes an active layer made of AlGaAs is formed on the substrate 10 so as to be arranged in parallel with the composition modulation buffer layer 20. A third semiconductor layer 60 which includes an active layer made of AlGaInP or GaInP is formed on the substrate 10 so as to be arranged in parallel with the second semiconductor layer 50. The composition modulation buffer layer 20 is formed having an inclined composition increasing in N atom content from the substrate 10 toward the first semiconductor layer 40.

Description

  The present invention relates to a multiwavelength semiconductor laser that emits light having different wavelengths.

  Optical disks such as CDs, DVDs, and BDs (Blu-ray Discs) are currently actively used as large-capacity recording media. The oscillation wavelengths of laser diodes (hereinafter referred to as “LD”) used for recording / reproduction of these optical discs are different, the oscillation wavelength of CD LD is 780 nm band (infrared), and the oscillation wavelength of DVD LD is The oscillation wavelength of the 650 nm band (red) and the BD LD is the 405 nm band (blue-violet). Therefore, in order to handle CD, DVD, and BD information with one optical disk device, a light source that emits laser light of three colors of infrared, red, and blue-violet is required.

  As a conventional multi-wavelength semiconductor laser light source that emits three colors of infrared, red, and blue-violet laser light, a blue-violet LD formed on a GaN substrate and a red and infrared laser light formed on a GaAs substrate And a blue-violet LD placed on the submount via a solder layer and the two-wavelength LD placed face-down on the submount via the solder layer. Yes (see, for example, Patent Document 1).

JP 2007-201223 A (FIG. 1)

  However, in the conventional multi-wavelength semiconductor laser light source as described above, the two-wavelength LD that emits infrared and red laser light and the blue-violet LD exist as separate LDs, and these LDs are mounted on the submount. In this case, a highly accurate mounting technique is required to align the optical axes of the LDs, and it is difficult to obtain a high yield as a semiconductor laser light source.

  A semiconductor layer including an active layer made of AlGaAs, AlGaInP, or GaInP that emits infrared or red laser light, and a semiconductor layer containing an active layer made of a nitride semiconductor that emits blue-violet laser light have a crystal structure and Since the lattice constants are different, they cannot be formed monolithically on one common substrate.

  The present invention has been made to solve the above-described problems, and can be easily performed without requiring high-precision mechanical mounting for aligning the optical axes of individual LDs that emit laser beams having different wavelengths. A highly accurate multi-wavelength semiconductor laser is obtained.

The multiwavelength semiconductor laser according to the present invention includes a substrate made of GaAs, a composition modulation buffer layer formed on a part of the substrate and made of GaAs _x N _1-x (0 ≦ x ≦ 1), and the composition modulation A first semiconductor layer including an active layer made of a nitride semiconductor formed on the buffer layer, and a second semiconductor including an active layer made of AlGaAs formed in parallel with the composition modulation buffer layer on the substrate And a third semiconductor layer formed on the substrate in parallel with the second semiconductor layer and including an active layer made of AlGaInP or GaInP, wherein the composition modulation buffer layer is formed from the substrate. It is characterized by being formed with a gradient composition in which the N atom content increases toward one semiconductor layer.

  According to the present invention, a highly accurate multi-wavelength semiconductor laser can be easily obtained without requiring highly accurate mechanical mounting for aligning the optical axes of individual LDs that emit laser beams of different wavelengths.

It is sectional drawing which shows the structure of the multiwavelength semiconductor laser in embodiment of this invention. It is sectional drawing which shows the manufacturing process of the multiwavelength semiconductor laser in embodiment of this invention. It is sectional drawing which shows the manufacturing process of the multiwavelength semiconductor laser in embodiment of this invention. It is sectional drawing which shows the manufacturing process of the multiwavelength semiconductor laser in embodiment of this invention. It is sectional drawing which shows the manufacturing process of the multiwavelength semiconductor laser in embodiment of this invention. It is sectional drawing which shows the manufacturing process of the multiwavelength semiconductor laser in embodiment of this invention. It is sectional drawing which shows the manufacturing process of the multiwavelength semiconductor laser in embodiment of this invention. It is sectional drawing which shows the manufacturing process of the multiwavelength semiconductor laser in embodiment of this invention. It is sectional drawing which shows the manufacturing process of the multiwavelength semiconductor laser in embodiment of this invention. It is sectional drawing which shows the manufacturing process of the multiwavelength semiconductor laser in embodiment of this invention. It is sectional drawing which shows the manufacturing process of the multiwavelength semiconductor laser in embodiment of this invention. It is sectional drawing which shows the manufacturing process of the multiwavelength semiconductor laser in embodiment of this invention. It is sectional drawing which shows the manufacturing process of the multiwavelength semiconductor laser in embodiment of this invention. It is sectional drawing which shows the manufacturing process of the multiwavelength semiconductor laser in embodiment of this invention. It is sectional drawing which shows the manufacturing process of the multiwavelength semiconductor laser in embodiment of this invention. It is sectional drawing which shows the manufacturing process of the multiwavelength semiconductor laser in embodiment of this invention.

  FIG. 1 is a cross-sectional view showing a configuration of a multiwavelength semiconductor laser according to an embodiment of the present invention. FIGS. 2-16 is sectional drawing which shows the manufacturing process of the multiwavelength semiconductor laser in embodiment of this invention. FIGS.

First, referring to FIG. 1, the structure of multi-wavelength semiconductor laser 100 in the embodiment of the present invention will be described. A composition modulation buffer layer 20 made of an n-type GaAs _x N _1-x (0 ≦ x ≦ 1) mixed crystal is formed on a part of the substrate 10 made of n-type GaAs. The surface of the substrate 10 is preferably made of a (111) plane of GaAs.

  On the composition modulation buffer layer 20, a first semiconductor layer 40 (blue-violet LD portion) including an active layer made of a nitride semiconductor that emits blue-violet light is formed. A second semiconductor layer 50 (infrared LD portion) including an active layer made of AlGaAs that emits infrared light is formed on the substrate 10 in parallel with the composition modulation buffer layer 20. A third semiconductor layer 60 (red LD portion) including an active layer made of AlGaInP or GaInP that emits red light is formed on the substrate 10 in parallel with the second semiconductor layer 50.

  An n-side electrode 70 is formed on the back surface of the substrate 10. P-side electrodes 81, 82, and 83 are formed on the first, second, and third semiconductor layers 40, 50, and 60, respectively.

  Here, the composition modulation buffer layer 20 is formed with a gradient composition in which the N atom content increases from the substrate 10 toward the first semiconductor layer 40. The surface 20a on which the first semiconductor layer 40 is formed is formed with a composition close to GaN. The composition modulation buffer layer 20 may be formed of a superlattice buffer layer.

  Further, the surface 20a of the composition modulation buffer layer 20 is desirably formed as a close-packed surface, and the surface 20a of the composition modulation buffer layer 20 configured with a composition close to GaN is <1-100 with respect to the (0001) plane. It is preferably formed so as to have an off angle of 0.1 degrees to 1 degree in the> direction.

  In the first semiconductor layer 40 that is a blue-violet LD portion, an n-type AlGaN cladding layer 41, an active layer 42 containing InGaN that is a nitride semiconductor, a p-type AlGaN cladding layer 43, and a p-type layer are formed on the composition modulation buffer layer 20. A type contact layer 44 is sequentially laminated, and a p-side electrode 81 is formed on the p-type contact layer 44. A ridge waveguide is formed in the p-type AlGaN cladding layer 43 and the p-type contact layer 44.

  In the second semiconductor layer 50 that is an infrared LD portion, an n-type AlGaAs cladding layer 51, an active layer 52 containing AlGaAs, a p-type AlGaAs cladding layer 53, and a p-type contact layer 54 are sequentially formed on the substrate 10. A p-side electrode 82 is formed on the p-type contact layer 54. A ridge waveguide is formed in the p-type AlGaAs cladding layer 53 and the p-type contact layer 54.

  In the third semiconductor layer 60 which is a red LD portion, an n-type AlGaInP clad layer 61, an active layer 62 containing GaInP, a p-type AlGaInP clad layer 63, and a p-type contact layer 64 are sequentially laminated on the substrate 10. A p-side electrode 83 is formed on the p-type contact layer 64. A ridge waveguide is formed in the p-type AlGaInP cladding layer 63 and the p-type contact layer 64.

  The active layers 42, 52 and 62 of the first, second and third semiconductor layers 40, 50 and 60 are preferably formed in a multiple quantum well structure in which a well layer and a barrier layer are sequentially stacked. Further, an SCH (Separate Confinement Heterostructure) layer may be provided between each active layer and the n-type cladding layer and the p-type cladding layer. The light emitting points of the semiconductor layers 40, 50, 60 are on substantially the same plane. Here, “substantially the same plane” means that an error allowable in optical design may be included.

  The multiwavelength semiconductor laser 100 having such a structure applies a predetermined voltage between the p-side electrode 81 and the n-side electrode 70 formed on the first semiconductor layer 40 that is a blue-violet LD portion. As a result, blue-violet laser light is emitted from the active layer 42. Similarly, an infrared laser beam is emitted from the active layer 52 by applying a predetermined voltage between the p-side electrode 82 and the n-side electrode 70 formed on the second semiconductor layer 50 that is the infrared LD portion. The active layer 62 emits red laser light by applying a predetermined voltage between the p-side electrode 83 and the n-side electrode 70 formed on the third semiconductor layer 60.

  Next, with reference to FIGS. 2-16, the manufacturing method of the multiwavelength semiconductor laser 100 in this Embodiment is demonstrated.

(Composition modulation buffer layer forming step)
First, as shown in FIG. 2, an SiO ₂ film 11 having an opening 11a formed on a part of the surface of the GaAs substrate 10 is formed. The SiO ₂ film 11 may be another film such as a SiN film (the same applies to the subsequent processes). Then, as shown in FIG. 3, the temperature of the substrate 10 is raised to the growth temperature of the GaAsN layer. For example, AsH ₃ gas that is an As source, TMG (trimethylgallium) gas that is a Ga source, and NH ₃ that is an N source. By supplying a predetermined amount of gas into the reaction vessel together with H ₂ gas as a carrier gas, the GaAsN layer 21 is partially deposited on the GaAs substrate 10 and the SiO ₂ film 11 by MOCVD (Metal Organic Chemical Vapor Deposition) method. Epitaxially grow. At this time, the N raw material is grown in accordance with the growth of the GaAsN layer 21 so that the composition of the GaAsN layer 21 increases from the substrate 10 side toward the surface 21a so that the N atom content increases and the surface 21a has a composition close to GaN. The NH ₃ gas flow rate is gradually increased, and the AsH ₃ gas flow rate of the As raw material is gradually decreased. Thereafter, the SiO ₂ film 11 on the substrate 10 and the GaAsN layer 21 laminated on the SiO ₂ film 11 are removed by dry etching, whereby the composition modulation buffer layer 20 is formed on the substrate 10 as shown in FIG. Form.

(First semiconductor layer forming step)
Next, as shown in FIG. 5, a protective film made of the SiO ₂ film 13 having an opening 13 a in a part on the composition modulation buffer layer 20 is formed on the surface of the substrate 10. At this time, a region on the substrate 10 where the second and third semiconductor layers 50 and 60 are to be formed in a later process is necessarily covered with the protective film.

Thereafter, as shown in FIG. 6, an n-type AlGaN cladding layer 41, an active layer 42 containing InGaN, a p-type AlGaN cladding layer 43, and a p-type contact layer 44 are sequentially stacked on the composition modulation buffer layer 20 by MOCVD. Thus, the first semiconductor layer 40 is formed. For example, the growth temperature of the n-type AlGaN cladding layer 41 is 1100 ° C., the growth temperature of the active layer 42 is 740 ° C., and the growth temperature of the p-type AlGaN cladding layer 43 is 1100 ° C. Then, as shown in FIG. 7, the SiO ₂ film 13 is removed by dry etching.

(Second semiconductor layer forming step)
Next, as shown in FIG. 8, a protective film made of the SiO ₂ film 14 having an opening 14 a in a part on the composition modulation buffer layer 20 is formed on the surface of the substrate 10. At this time, a region on the substrate 10 where the third semiconductor layer 60 is to be formed in a later process is always covered with the protective film. Then, the surface of the substrate 10 is removed by etching at least one molecular layer through the opening 14a of the SiO ₂ film 14 by, for example, RIE.

Then, as shown in FIG. 9, the temperature of the substrate 10 is raised to 600 to 700 ° C., and an n-type AlGaAs clad layer 51, an active layer 52 containing AlGaAs, a p-type AlGaAs clad layer 53 and p are formed on the substrate 10 by MOCVD. The second contact layer 54 is sequentially stacked to form the second semiconductor layer 50. Then, as shown in FIG. 10, the SiO ₂ film 14 is removed by dry etching.

(Third semiconductor layer forming step)
Then, as in the third semiconductor layer forming step, as shown in FIG. 11, an SiO ₂ film 15 having an opening 15a formed on the substrate 10 is formed. Then, the surface of the substrate 10 is removed by etching at least one molecular layer through the opening 15a of the SiO ₂ film 15 by, for example, the RIE method.

Then, as shown in FIG. 12, the temperature of the substrate 10 is raised to 600 to 700 ° C., and an n-type AlGaInP clad layer 61, an active layer 62 containing GaInP, a p-type AlGaInP clad layer 63 and p are formed on the substrate 10 by MOCVD. The third contact layer 64 is sequentially stacked to form the third semiconductor layer 60. Then, as shown in FIG. 13, the SiO ₂ film 15 is removed by dry etching.

  Note that either the second semiconductor layer 50 or the third semiconductor 60 may be formed first after the formation of the first semiconductor layer 40.

(Ridge formation process)
Thereafter, as shown in FIG. 14, a resist is applied to the surface, and a resist pattern 16 corresponding to the shape of the mesa portion is formed by lithography. Using this resist pattern 16 as a mask, the p-type contact layers 44, 54, 64 and the p-type cladding layer 43 formed on the first, second, and third semiconductor layers 40, 50, 60 using, for example, chlorine-based gas. , 53 and 63 are etched in the same process, thereby forming a ridge to be an optical waveguide layer as shown in FIG. Thereafter, as shown in FIG. 16, the resist pattern 16 is removed using an organic solvent. Each semiconductor layer 40, 50, 60 may be etched in a separate process to form each ridge waveguide. However, as in the present embodiment, each semiconductor layer 40, 50, 60 is formed in the same process. Etching can greatly shorten the ridge formation step.

(Electrode formation process)
Then, p-side electrodes 81, 82, and 83 are formed on the first, second, and third semiconductor layers 40, 50, and 60, respectively, by a process that is not shown. Further, after polishing the back surface of the substrate 10, the n-side electrode 70 is formed on the back surface of the substrate 10.

  Through the above steps, a multiwavelength semiconductor laser 100 as shown in FIG. 1 can be manufactured.

  Thus, in the present embodiment, the composition modulation buffer layer 20 made of a GaAsN mixed crystal is formed on the substrate 10 made of GaAs. The composition modulation buffer layer 20 has a gradient composition in which the N atom content increases from the substrate 10 toward the surface 20a on which the first semiconductor layer 40 is formed.

  Thus, the first semiconductor layer 40 (blue-violet LD portion) including an active layer made of a GaN-based material (nitride semiconductor) having a different crystal structure and lattice constant on one common substrate 10 and the second made of AlGaAs. A multiwavelength semiconductor laser in which the semiconductor layer 50 (infrared LD portion) and the semiconductor layer 60 (red LD portion) including an active layer made of AlGaInP or GaInP are monolithically formed can be obtained.

  As a result, the mechanical mounting required for manufacturing the conventional multi-wavelength semiconductor laser light source becomes unnecessary, and a highly accurate multi-wavelength semiconductor laser can be easily obtained. Furthermore, since three LD portions can be formed monolithically on one substrate, a small and lightweight multi-wavelength semiconductor laser can be obtained.

  In addition, by forming a plurality of LD portions on one substrate 10, the n-side electrode 70 can be made one, and the wire bonding process can be shortened.

Further, by making the surface of the substrate 10 a (111) plane of GaAs, the superlattice buffer layer 20 made of a GaAs _x N _1-x mixed crystal can be easily epitaxially grown on the substrate 10.

  Further, the surface 20a of the composition modulation buffer layer 20 is formed on the surface 20a by providing an off angle of 0.1 degree or more and 1 degree or less in the <1-100> direction with respect to the (0001) plane. The flatness and crystallinity of the mold cladding layer 41 are improved. As a result, the electrical characteristics of the first semiconductor layer 40 that forms the blue-violet LD portion are improved, and the reliability is improved.

  In addition, according to the present embodiment, the multiwavelength semiconductor laser 100 is configured so that the light emitting points of the first, second, and third semiconductor layers 40, 50, 60 are substantially on the same plane. An optical system design of a laser light source using the semiconductor laser 100 as a light source becomes easy.

  Furthermore, according to the present embodiment, after the first semiconductor layer 40 to be the blue-violet LD portion having a high crystal growth temperature is formed first, the second semiconductor layer 50 to be the infrared LD portion and the red LD portion. Since the third semiconductor layer 60 is formed, the second and third semiconductor layers are grown during the crystal growth of the first semiconductor layer 40 having a crystal growth temperature higher than that of the second and third semiconductor layers 50 and 60. An LD part with high electrical characteristics and reliability can be formed without breaking the layer structure of 50 and 60.

In addition, since the protective film made of the SiO ₂ film 13 is formed in the region where the second and third semiconductor layers 50 and 60 are formed before the first semiconductor layer 40 is formed, the crystal growth temperature is high. During the formation of the first semiconductor layer 40, the constituent atoms Ga and As atoms can be prevented from evaporating from the substrate 10, so that the crystals of the second and third semiconductor layers 50 and 60 to be formed in a later step are used. Can be improved.

Further, after removing the SiO ₂ film 13, at least one molecular layer or more of the region where the second and third semiconductor layers 50 and 60 are formed on the surface of the substrate 10 is etched. Thereby, even if constituent atoms evaporate from the surface of the substrate 10 during the formation of the first semiconductor layer 40, the surface of the substrate 10 can be cleaned. Accordingly, the crystallinity and electrical characteristics of the second and third semiconductor layers 50 and 60 formed on the substrate 10 in a later process can be improved.

  In addition to the first semiconductor layer 40 that is the blue-violet LD portion, the second semiconductor layer 50 that is the infrared LD portion, and the third semiconductor layer 60 that is the red LD portion described in this embodiment. A high-frequency semiconductor element made of GaAs-based material or GaN-based material, an ultraviolet light LD element made of AlN-based material that emits ultraviolet light, and the like are formed on the substrate 10 through the same composition modulation buffer layer as in the present embodiment. May be.

  In this manner, by forming a plurality of LD elements on one substrate 10 via a composition modulation buffer layer, it is possible to easily combine with other semiconductor elements, and a small multifunction semiconductor device can be obtained. Can be easily obtained.

10 substrate, 13 SiO ₂ film (protective film), 20 composition modulation buffer layer, 40 first semiconductor layer, 42, 52, 62 active layer, 50 second semiconductor layer, 60 third semiconductor layer, 100 multiwavelength Semiconductor laser.

Claims (7)

A substrate made of GaAs;
A composition modulation buffer layer formed on a part of the substrate and made of GaAs _x N _1-x (0 ≦ x ≦ 1);
A first semiconductor layer including an active layer made of a nitride semiconductor formed on the composition modulation buffer layer;
A second semiconductor layer including an active layer made of AlGaAs formed in parallel with the composition modulation buffer layer on the substrate;
A third semiconductor layer formed on the substrate in parallel with the second semiconductor layer and including an active layer made of AlGaInP or GaInP;
The multi-wavelength semiconductor laser, wherein the composition modulation buffer layer is formed with a gradient composition in which an N atom content increases from the substrate toward the first semiconductor layer.   2. The multiwavelength semiconductor laser according to claim 1, wherein the surface of the substrate is made of a (111) plane of GaAs.   3. The multiwavelength semiconductor laser according to claim 1, wherein the light emitting points of the first, second and third semiconductor layers are substantially on the same plane. To a part of a substrate made of _{GaAs x N 1-x (0} <x <1), forming a compositionally modulated buffer layer made of _{GaAs x N 1-x (0} ≦ x ≦ 1),
Forming a first semiconductor layer including an active layer made of a nitride semiconductor on the composition modulation buffer layer; and forming a second semiconductor layer including an active layer made of AlGaAs after forming the first semiconductor layer. Forming, and
Forming a third semiconductor layer including an active layer made of AlGaInP or GaInP on the substrate in parallel with the second semiconductor layer.   5. The method of manufacturing a multi-wavelength semiconductor laser according to claim 4, wherein the composition modulation buffer layer is formed with a gradient composition in which the N atom content increases from the substrate toward the first semiconductor layer.   6. The protective film is formed on the substrate in a region where the second and third semiconductor layers are formed before forming the first semiconductor layer. 6. Of manufacturing a multi-wavelength semiconductor laser.   Before forming the second and third semiconductor layers, the protective film is removed, and the surface of the substrate corresponding to the region where the second and third semiconductor layers are formed is etched by at least one molecular layer. The method of manufacturing a multi-wavelength semiconductor laser according to claim 6, wherein the multi-wavelength semiconductor laser is removed.

Images