JP2011258713A - Method of manufacturing distributed feedback type semiconductor laser element - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce the difference between an oscillation wavelength and a gain peak wavelength in a DFB laser element where a grating is provided between an active layer and a semiconductor substrate.SOLUTION: The method of manufacturing a distributed feedback type semiconductor laser element includes a grating formation step S11 for forming a semiconductor layer including a grating on a semiconductor substrate, an active layer formation step S12 for forming an active layer on the semiconductor layer, a measurement step S13 for measuring a gain peak wavelength of the active layer, and a mesa formation step S15 for forming an optical waveguide by forming at least the active layer in a mesa shape extending in a predetermined direction. In the mesa formation step S15, width of the active layer is determined so that the difference between the oscillation wavelength of the distributed feedback type semiconductor laser element which depends on the width of the active layer in a direction crossing the predetermined direction and the period of the grating, and the gain peak wavelength of the active layer obtained at the measurement step falls within a predetermined range.

Description

  The present invention relates to a method for manufacturing a distributed feedback semiconductor laser element.

  In Patent Document 1, a DFB laser element group composed of a plurality of distributed feedback (DFB) laser elements that satisfy a predetermined detuning condition and emit a plurality of laser beams having different wavelengths is included in one wafer. Describes a method that is intended to be produced in batches. The method described in this document includes a stacked structure forming step of forming a stacked structure of compound semiconductor layers including active layers whose gain peak wavelengths are periodically different in each region in the wafer surface, and a gain of the active layer. A diffraction grating that forms a diffraction grating having a period such that the detuning amount falls within a predetermined range based on a measurement process for measuring the peak wavelength in the wafer plane and the distribution of the measured gain peak wavelength of the active layer in the wafer plane. Forming step.

  Patent Document 2 discloses that in a DFB laser element having a phase shift unit in a diffraction grating, a diffraction grating coupling coefficient / element length product κL, which are element parameters governing transmission characteristics, and a detuning amount Δλ from a gain peak of an oscillation wavelength. A method is described that is intended to suppress waveform chirping during direct modulation by limiting the range. In the method described in this document, the resonator of the semiconductor laser is divided into two regions in the length direction of the resonator, and a diffraction grating having the same period is formed in the light guide layer of each region. A phase shift unit having a phase shift amount λ / n (16> n> 4) is provided. κL and Δλ satisfy the relational expression of κL + ξΔλ ≧ σ (0.06 nm ≧ ξ ≧ 0.04 nm−1, 5.0 ≧ σ ≧ 3.0). ξ and σ are obtained from κL + ξΔλ = σ, which is a straight line that roughly divides an element with good transmission characteristics and an element with poor transmission characteristics in the Δλ-κL plane.

Japanese Patent Laid-Open No. 2003-069145 JP 2003-204114 A

  The detuning amounts described in Patent Documents 1 and 2 described above correspond to the difference between the oscillation wavelength mainly based on the pitch of the diffraction grating and the emission wavelength caused by the composition of the active layer. In a DFB laser element that oscillates in a single longitudinal mode, it is necessary to keep the detuning amount within a preferable range in order to obtain a single mode operation in a wide temperature range. Further, as a method for increasing the relaxation oscillation frequency that defines the upper limit of the modulation speed, a so-called minus detuning method is known in which the oscillation wavelength based on the diffraction grating pitch of the DFB structure is set on the short wavelength side with respect to the gain peak wavelength. Yes. In Patent Document 1 described above, the detuning amount is controlled by measuring the emission wavelength distribution of the active layer after forming the active layer and determining the diffraction grating pitch on the active layer based on the measurement result. .

  However, some DFB laser elements have a diffraction grating disposed under the active layer, that is, between the active layer and the substrate (see, for example, Patent Document 2). In such a DFB laser element, since it is necessary to create a diffraction grating prior to the active layer, the method described in Patent Document 1 cannot be used. For this reason, the fluctuation of the emission wavelength (that is, the gain peak wavelength) due to the fluctuation of the composition of the active layer leads to the fluctuation of the detuning amount as it is, and the oscillation current threshold, the sub-mode suppression ratio (SMSR), There is a problem that light emission characteristics such as relaxation oscillation frequency vary between wafers and it is difficult to obtain desired light emission characteristics.

  The present invention has been made in view of such problems, and in a DFB laser element in which a diffraction grating is provided between an active layer and a semiconductor substrate, the oscillation wavelength mainly based on the pitch of the diffraction grating, and the active It is an object of the present invention to provide a method for manufacturing a DFB laser device capable of reducing a difference from an emission wavelength (gain peak wavelength) due to a layer composition.

  In order to solve the above-described problem, a first distributed feedback semiconductor laser device fabrication method according to the present invention includes a diffraction grating forming step of forming a semiconductor layer including a diffraction grating on a semiconductor substrate, and an active on the semiconductor layer. An active layer forming step of forming a layer, a measuring step of measuring a gain peak wavelength of the active layer, and a mesa forming step of forming an optical waveguide by forming at least the active layer into a mesa shape extending in a predetermined direction, In the mesa formation process, the oscillation wavelength of the distributed feedback semiconductor laser element, which depends on the width of the active layer in the direction intersecting the predetermined direction and the period of the diffraction grating, and the gain peak wavelength of the active layer obtained in the measurement process The width of the active layer is determined so that the difference is within a predetermined range.

  In this first method for fabricating a DFB laser element, since the diffraction grating forming step is performed before the active layer forming step, a DFB laser element having a diffraction grating between the active layer and the semiconductor substrate is fabricated. Then, after forming the active layer, the gain peak wavelength of the active layer is measured, and the difference between the gain peak wavelength and the oscillation wavelength of the DFB laser element is within a predetermined range. The manufacturing method includes the following steps. That is, the oscillation wavelength of the DFB laser element depends not only on the period of the diffraction grating but also on the effective refractive index of the optical waveguide, and the effective refractive index of the optical waveguide depends on the width of the active layer. In the mesa formation step performed after the step, the width of the active layer is determined so that the difference between the oscillation wavelength and the gain peak wavelength is within a predetermined range. Thereby, the difference between the oscillation wavelength of the DFB laser element and the emission wavelength (gain peak wavelength) due to the composition of the active layer can be reduced.

  The second distributed feedback semiconductor laser device fabrication method according to the present invention includes a diffraction grating forming step of forming a semiconductor layer including a diffraction grating on a semiconductor substrate, and an active layer formation of forming an active layer on the semiconductor layer. A step of measuring the gain peak wavelength of the active layer, and a step of forming a light confinement layer having a band gap energy larger than that of the active layer on the active layer. The difference between the oscillation wavelength of the distributed feedback semiconductor laser element, which depends on the thickness of the optical confinement layer and the period of the diffraction grating, and the gain peak wavelength of the active layer obtained in the measurement process is within a predetermined range. Determining the thickness of the optical confinement layer.

  In this second DFB laser element manufacturing method, a DFB laser element having a diffraction grating between the active layer and the semiconductor substrate is manufactured as in the first manufacturing method described above. Then, after forming the active layer, the gain peak wavelength of the active layer is measured, and the difference between the gain peak wavelength and the oscillation wavelength of the DFB laser element is within a predetermined range. The manufacturing method includes the following steps. That is, the oscillation wavelength of the DFB laser element depends not only on the period of the diffraction grating but also on the effective refractive index of the optical waveguide, and the effective refractive index of the optical waveguide depends on the thickness of the optical confinement layer. In the optical confinement layer formation step performed after the formation step, the thickness of the optical confinement layer is determined so that the difference between the oscillation wavelength and the gain peak wavelength is within a predetermined range. Thereby, the difference between the oscillation wavelength of the DFB laser element and the emission wavelength (gain peak wavelength) due to the composition of the active layer can be reduced.

  The third distributed feedback semiconductor laser device fabrication method according to the present invention includes a diffraction grating forming step of forming a semiconductor layer including a diffraction grating on a semiconductor substrate, and an active layer formation of forming an active layer on the semiconductor layer. A step of measuring the gain peak wavelength of the active layer, and a step of forming a light confinement layer having a band gap energy larger than that of the active layer on the active layer. Depending on the composition of the optical confinement layer and the period of the diffraction grating, the difference between the oscillation wavelength of the distributed feedback semiconductor laser element and the gain peak wavelength of the active layer obtained in the measurement step is within a predetermined range. The composition of the optical confinement layer is determined.

  In this third method for fabricating a DFB laser element, a DFB laser element having a diffraction grating between the active layer and the semiconductor substrate is fabricated, as in the first fabrication method described above. Then, after forming the active layer, the gain peak wavelength of the active layer is measured, and the difference between the gain peak wavelength and the oscillation wavelength of the DFB laser element is within a predetermined range. The manufacturing method includes the following steps. In other words, the oscillation wavelength of the DFB laser element depends not only on the period of the diffraction grating but also on the effective refractive index of the optical waveguide, and the effective refractive index of the optical waveguide depends on the composition of the optical confinement layer. In the optical confinement layer forming step performed after the step, the composition of the optical confinement layer is determined so that the difference between the oscillation wavelength and the gain peak wavelength is within a predetermined range. Thereby, the difference between the oscillation wavelength of the DFB laser element and the emission wavelength (gain peak wavelength) due to the composition of the active layer can be reduced.

  In the first to third distributed feedback semiconductor laser device fabrication methods described above, the optical confinement layer is provided on the first layer having the band gap energy larger than that of the active layer, and on the first layer. And a second layer having a band gap energy larger than that of the first layer.

  According to the method for manufacturing a distributed feedback semiconductor laser device according to the present invention, in a DFB laser device in which a diffraction grating is provided between an active layer and a semiconductor substrate, an oscillation wavelength mainly based on the pitch of the diffraction grating, The difference from the emission wavelength (gain peak wavelength) due to the composition can be reduced.

FIG. 1 is a flowchart showing a method for manufacturing a DFB laser device according to an embodiment of the present invention. FIG. 2A is a diagram schematically showing a diffraction grating forming step of a method for producing a DFB laser. FIG. 2B is a diagram schematically showing an active layer forming step of the method for manufacturing the DFB laser. FIG. 3A is a diagram schematically showing a step of forming an optical confinement layer in the method for manufacturing the DFB laser. FIG. 3B is a diagram schematically showing a mesa formation step of the method for manufacturing the DFB laser. FIG. 4A is a diagram schematically showing a current block region forming step of the method for manufacturing the DFB laser. FIG. 4B is a diagram schematically showing the upper clad layer forming step of the method for manufacturing the DFB laser. FIG. 5A is a diagram schematically showing a contact layer forming step of a method for manufacturing a DFB laser. FIG. 5B is a diagram schematically showing a groove forming step of the method for manufacturing the DFB laser. FIG. 6 is a diagram schematically showing an electrode forming step of a method for manufacturing a DFB laser. FIG. 7 is a chart showing the calculation results of the oscillation wavelength (Bragg wavelength) when the active layer width and the thicknesses of the first and second layers of the upper optical confinement layer are changed.

  Embodiments of a method for manufacturing a distributed feedback 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.

  FIG. 1 is a flowchart showing a method for manufacturing a distributed feedback semiconductor laser element (hereinafter referred to as a DFB laser element) according to an embodiment of the present invention. 2 to 6 are diagrams schematically showing each step of the method for manufacturing the DFB laser according to the present embodiment. FIG. 2A is a cross-sectional view of the DFB laser manufacturing process viewed from a direction perpendicular to the optical waveguide direction. 2B and 3 to 6 are cross-sectional views of the manufacturing process of the DFB laser as seen from the optical waveguide direction.

  As shown in FIG. 1, the manufacturing method of this embodiment includes a diffraction grating formation step S11, an active layer formation step S12, a measurement step S13, a light confinement layer formation step S14, a mesa formation step S15, a current block region formation step S16, It includes an upper clad layer forming step S17, a contact layer forming step S18, an electrode forming step S19, and a chip forming step S20.

  First, in the diffraction grating forming step S <b> 11, as shown in FIG. 2A, the semiconductor layer 10 including the diffraction grating 10 a is formed on the semiconductor substrate 20. As an example, an n-type InP substrate is used as the semiconductor substrate 20. An n-type InP cladding layer having a thickness of 550 nm is grown on the n-type InP substrate, and an InGaAsP diffraction grating layer having a thickness of 60 nm and a band gap wavelength of 1.1 μm is grown thereon. Thereafter, a resist for electron beam (EB) drawing is applied, and EB drawing is performed using an EB drawing apparatus to form a resist film having a diffraction grating pattern with a period Λ = 243.8 nm. Thereafter, etching is performed so as to penetrate the InGaAsP diffraction grating layer through the resist film, thereby forming the diffraction grating 10a. At this time, it is preferable to perform etching by dry etching having excellent reproducibility of the diffraction grating 10a. After this etching, the resist for EB drawing is removed. Then, an undoped InP layer having a thickness of 140 nm is grown on the InGaAsP diffraction grating layer to embed the diffraction grating 10a. Thus, the semiconductor layer 10 including the diffraction grating 10a is formed.

  Next, in the active layer forming step S12, the active layer 12 is formed on the semiconductor layer 10 as shown in FIG. As an example, a layer made of undoped InGaAsP with a thickness of 30 nm and a band gap wavelength of 1.1 μm and a layer made of undoped InGaAsP with a thickness of 20 nm and a band gap wavelength of 1.225 μm are grown in order, thereby A step-type GRIN-SCH (Graded-Index Separate-Confinement Heterostructure) layer is formed as the confinement layer 11. Subsequently, on the lower optical confinement layer 11, seven InGaAsP well layers having a thickness of 6.6 nm and generating 1.55 μm band light, and a band gap wavelength of 1.225 μm having a thickness of 10 nm. The active layer 12 having a multiple quantum well (MQW) structure is formed by alternately growing the eight InGaAsP barrier layers.

  Subsequently, in the measurement step S13, the gain peak wavelength of the active layer 12 is measured. In one embodiment, photoluminescence (PL) measurement is performed on a substrate product having the semiconductor substrate 20, the semiconductor layer 10, and the active layer 12, and the active layer 12 is determined based on the PL spectrum obtained by the PL measurement. Gain peak wavelength is obtained. Since this PL spectrum is a spectrum in which the emission wavelengths of the semiconductor layer 10 and the semiconductor substrate 20 overlap in addition to the active layer 12, information on gain peak wavelengths of the semiconductor substrate 20, the semiconductor layer 10, and the active layer 12 is included. . However, since the band gap energy of the active layer 12 is the smallest, the spectrum on the long wavelength side (side with the smallest band gap energy) can be specified as the PL spectrum for the active layer 12. Further, carriers (electrons, holes) excited by light fall into the layer having the smallest band gap energy and recombine, so that the PL spectrum of the active layer 12 appears the largest. Therefore, the gain peak wavelength of the active layer 12 can be measured.

  Subsequently, in the light confinement layer forming step S14, as shown in FIG. 3A, the upper light confinement layer 13 is formed on the active layer. The upper optical confinement layer 13 has a larger band gap energy than the active layer 12. As an example, the active layer 12 includes a first layer made of InGaAsP having a thickness of 20 nm and a band gap wavelength of 1.225 μm, and a second layer made of InGaAsP having a thickness of 30 nm and a band gap wavelength of 1.1 μm in this order. By growing it on top, a step type GRIN-SCH layer as the upper optical confinement layer 13 is formed. Thus, the upper optical confinement layer 13 includes a first layer having a band gap energy larger than that of the active layer 12 and a second layer provided on the first layer and having a band gap energy larger than that of the first layer. May be included.

  Here, as will be described later, the oscillation wavelength of the DFB laser element depends not only on the period of the diffraction grating 10 a but also on the effective refractive index of the optical waveguide, and the effective refractive index of the optical waveguide depends on the thickness of the optical confinement layer 13. Depends on sheath composition. Therefore, in order to reduce the difference between the oscillation wavelength of the DFB laser element and the emission wavelength due to the composition of the active layer, in the optical confinement layer forming step S14, the difference between the oscillation wavelength and the gain peak wavelength is within a predetermined range. Thus, at least one of the thickness and the composition of the optical confinement layer 13 is determined.

  After the light confinement layer forming step S14, as shown in FIG. 3B, the clad layer 14 (for example, a p-type InP clad layer having a thickness of 400 nm) is grown on the light confinement layer 13. Good.

  Subsequently, in the mesa formation step S15, as shown in FIG. 4A, the cladding layer 14, the optical confinement layer 13, the active layer 12, and the semiconductor layer 10 are formed into a mesa shape extending in a predetermined direction (optical waveguide direction). By doing so, the optical waveguide 15 is formed. As an example, dry etching or wet etching is performed on the cladding layer 14, the optical confinement layer 13, the active layer 12, and the semiconductor layer 10. The width of the mesa in the direction intersecting the optical waveguide direction is, for example, 1.25 μm.

  Here, as will be described later, the oscillation wavelength of the DFB laser element depends not only on the period of the diffraction grating 10a but also on the effective refractive index of the optical waveguide, and the effective refractive index of the optical waveguide intersects with the optical waveguide direction. It also depends on the width of the active layer 12 in the direction in which it is generated. Therefore, in order to reduce the difference between the oscillation wavelength of the DFB laser element and the emission wavelength (gain peak wavelength) due to the composition of the active layer, in the mesa formation step S15, the difference between the oscillation wavelength and the gain peak wavelength is a predetermined value. The width W of the active layer 12 is determined so as to be within the range. In this step, when the width of the active layer 12 is determined in this way, the determination of the thickness and composition of the light confinement layer 13 according to the gain peak wavelength in the light confinement layer forming step S14 may be omitted. it can. Further, when at least one of the thickness and the composition of the light confinement layer 13 is determined according to the gain peak wavelength in the light confinement layer forming step S14, the width of the active layer 12 according to the gain peak wavelength in this step is determined. The decision can be omitted.

  Subsequently, in the current block region forming step S16, the current block region 16 is formed as shown in FIG. As an example, a p-type InP layer 16a and an n-type InP layer 16b are sequentially grown on a region excluding a region where the mesa structure including the active layer 12 is formed on the semiconductor substrate 20, and the mesa is formed by these layers. Embed both sides of the structure. Thereby, the current block region 16 having a pn junction is preferably formed.

  Subsequently, in the upper clad layer forming step S <b> 17, as shown in FIG. 5A, the upper clad layer 17 is grown on the mesa structure including the active layer 12 and on the current blocking region 16. As an example, an upper cladding layer 17 made of p-type InP having a thickness of 1600 nm is grown. Subsequently, in the contact layer forming step S <b> 18, as shown in FIG. 5A, the contact layer 18 is grown on the upper cladding layer 17. As an example, a contact layer 18 made of p-type InGaAs having a thickness of 500 nm is grown. After the contact layer forming step S18, as shown in FIG. 5B, grooves 19 reaching the semiconductor substrate 20 from the contact layer 18 may be formed along both side surfaces of the mesa structure.

  Subsequently, in the electrode forming step S19, as shown in FIG. 6, after the insulating film 21 is formed on the surface of the contact layer 18 and the inner surface of the groove 19, the insulating film formed above the active layer 12 is formed. An anode electrode 22 is formed in the opening 21. A cathode electrode 23 is formed on the back surface of the semiconductor substrate 20.

  Finally, in the chip forming step S20, the laser resonant end face is formed by cleaving the semiconductor substrate 20, and further, the DFB laser element is formed by cutting into a chip shape. The interval between the resonance end faces, that is, the resonator length is, for example, 300 μm.

  Actions and effects obtained by the method for manufacturing the DFB laser device according to this embodiment will be described. First, in order to facilitate understanding of the operation and effect in the present embodiment, as a comparative example, a method for manufacturing a DFB laser element in which a diffraction grating is provided on the upper side of an active layer and a method for adjusting an oscillation wavelength will be briefly described.

  On a semiconductor substrate (for example, an InP substrate), a cladding layer (n-type InP), a lower optical confinement layer (InGaAsP), a multiple quantum well active layer (InGaAsP), an upper optical confinement layer (InGaAsP), a spacer layer (p-type InP) ) And a diffraction grating layer (p-type InGaAsP). Next, PL measurement is performed on the substrate product to obtain the gain peak wavelength of the active layer. Then, the diffraction grating pitch is determined so that the difference (detuning amount) between the oscillation wavelength of the desired DFB laser element and the gain peak wavelength of the active layer 12 is included in the desired range, and the diffraction grating is formed. At that time, it is necessary to form a diffraction grating pattern not by interference exposure but by EB exposure. Thereafter, a layer for embedding the diffraction grating (p-type InP) and a cladding layer (p-type InP) are grown.

  Thus, when fabricating a DFB laser element having a diffraction grating on the upper side of the active layer, the gain peak wavelength of the active layer is measured during the process, and the result is reflected in the diffraction grating pitch. The amount of tuning can be kept small. However, when fabricating a DFB laser device in which a diffraction grating is provided below the active layer, that is, between the semiconductor substrate and the active layer, it is necessary to form the diffraction grating before the active layer. Cannot be used. Therefore, in this embodiment, the detuning amount is kept small as described below.

The oscillation wavelength λ _DFB of the DFB laser element can be expressed by the following formula (1) using the period Λ of the diffraction grating 10 a and the effective refractive index neff of the optical waveguide 15.
λ _DFB = 2 × neff × Λ (1)
Therefore, the oscillation wavelength λ _DFB can be controlled by adjusting the period Λ and the effective refractive index neff. For example, when the configuration of the upper optical confinement layer 13 is the above-described embodiment (step type GRIN-SCH layer), the effective refractive index neff of the optical waveguide 15 is 3.1891, and the oscillation wavelength λ _DFB is
λ _DFB = 2 × neff × Λ = 2 × 3.11891 × 243.8 × 10 ⁻⁹ = 1555 nm
It becomes.

  Here, when the gain peak wavelength of the active layer 12 is 1565 nm, the difference (detuning amount) between the oscillation wavelength of the DFB laser element and the emission wavelength of the active layer 12 is 1555 nm−1565 nm = −10 nm. On the other hand, since the gain peak wavelength of the active layer 12 is determined by the internal structure of the active layer 12 (thickness and composition of the well layer and the barrier layer), it depends on the crystal quality during epitaxial growth, and is approximately ± A few nm varies. When the gain peak wavelength shifts from the target value in this way, the detuning amount varies, and the relaxation oscillation frequency and single mode characteristics also vary.

In the present embodiment, the oscillation wavelength λ _DFB is controlled by adjusting the effective refractive index neff of the optical waveguide 15 so that the detuning amount falls within a predetermined range. That is, the gain peak wavelength of the active layer 12 is measured by performing PL measurement after growing the active layer 12. Then, by adjusting at least one of the thickness and composition of the upper optical confinement layer 13 and / or the width of the active layer 12, the effective refractive index of the optical waveguide 15 is changed, and the oscillation wavelength (Bragg wavelength) λ _{DFB is changed.} Adjust.

  Specifically, the width of the active layer 12 (reference value 1.25 μm) is adjusted within a range of ± 0.25 μm, that is, 1.00 μm to 1.50 μm. Further, the thickness (reference value 20 nm) of the first layer (the layer closer to the active layer 12) of the upper optical confinement layer 13 is adjusted within the range of +15 nm to −10 nm, that is, 10 nm to 35 nm. The band gap wavelength of this first layer is 1.225 μm. Further, the thickness (reference value 30 nm) of the second layer (the layer far from the active layer 12) of the upper optical confinement layer 13 is adjusted within a range of ± 15 nm, that is, 15 nm to 45 nm. The band gap wavelength of this second layer is 1.1 μm.

FIG. 7 shows the calculation result of the oscillation wavelength (Bragg wavelength) λ _DFB when the width of the active layer 12 and the thicknesses of the first and second layers of the upper optical confinement layer 13 are changed as described above. It is a chart. The results shown in FIG. 7 are _subjected to a multiple regression analysis using the oscillation wavelength λ _DFB as a dependent variable and the width of the active layer 12 and the thicknesses of the first and second layers of the upper optical confinement layer 13 as explanatory variables. As a result, the oscillation wavelength λ _DFB is calculated by the following equation (2).
Oscillation wavelength (nm) = 8.9823 × {active layer width (μm)}
+ 0.03724 × {first layer thickness (nm)}
+ 0.09045 × (the thickness of the second layer (nm))
+1540.3 (nm) (2)

Therefore, based on the formula (2), for example, by adjusting the width of the active layer 12 by ± 0.1 μm and the thicknesses of the first and second layers of the upper optical confinement layer 13 by ± 10 nm, respectively, the oscillation wavelength λ _{The DFB} can be tuned over about ± 2 nm. That is, even when the gain peak wavelength of the active layer 12 fluctuates by ± 2 nm, the difference (detuning amount) between the oscillation wavelength of the DFB laser element and the emission wavelength of the active layer 12 is within a predetermined range close to the target value. Can fit in.

In the above description, the oscillation wavelength λ _DFB is adjusted by the width of the active layer 12 and the thickness of the upper optical confinement layer 13, but the same effect can be obtained by adjusting the composition of the upper optical confinement layer 13. Can be obtained. This is because the effective refractive index neff of the optical waveguide 15 also depends on the composition of the upper optical confinement layer 13.

As described above, according to the method for manufacturing the DFB laser device of this embodiment, in the DFB laser device in which the diffraction grating 10a is provided between the active layer 12 and the semiconductor substrate 20, the oscillation wavelength λ _DFB and the emission wavelength are determined. Difference (detuning amount) can be reduced.

  The manufacturing method of the DFB laser device according to the present invention is not limited to the above-described embodiment, and various other modifications are possible. For example, the manufacturing method shown in the above embodiment includes a diffraction grating formation step, an active layer formation step, a measurement step, a light confinement layer formation step, and a mesa formation step, but only by the thickness or composition of the light confinement layer. When adjusting the oscillation wavelength, the mesa forming step can be omitted. Further, when the oscillation wavelength is adjusted only by the active layer width, the optical confinement layer forming step can be omitted.

  DESCRIPTION OF SYMBOLS 10 ... Semiconductor layer, 10a ... Diffraction grating, 11 ... Lower light confinement layer, 12 ... Active layer, 13 ... Upper light confinement layer, 14 ... Cladding layer, 15 ... Optical waveguide, 16 ... Current blocking region, 17 ... Upper clad layer , 18 ... contact layer, 19 ... groove, 20 ... semiconductor substrate, 21 ... insulating film, 22 ... anode electrode, 23 ... cathode electrode.

Claims (4)

A method for producing a distributed feedback semiconductor laser device, comprising:
A diffraction grating forming step of forming a semiconductor layer including a diffraction grating on a semiconductor substrate;
An active layer forming step of forming an active layer on the semiconductor layer;
A measurement step of measuring a gain peak wavelength of the active layer;
A mesa forming step of forming an optical waveguide by forming at least the active layer into a mesa shape extending in a predetermined direction,
In the mesa formation step, the oscillation wavelength of the distributed feedback semiconductor laser element depends on the width of the active layer and the period of the diffraction grating in the direction intersecting the predetermined direction, and the active layer obtained in the measurement step A method of manufacturing a distributed feedback semiconductor laser device, wherein the width of the active layer is determined so that a difference from a gain peak wavelength of the active layer falls within a predetermined range. A method for producing a distributed feedback semiconductor laser device, comprising:
A diffraction grating forming step of forming a semiconductor layer including a diffraction grating on a semiconductor substrate;
An active layer forming step of forming an active layer on the semiconductor layer;
A measurement step of measuring a gain peak wavelength of the active layer;
Forming an optical confinement layer on the active layer having a larger band gap energy than the active layer,
In the optical confinement layer forming step, the oscillation wavelength of the distributed feedback semiconductor laser element, which depends on the thickness of the optical confinement layer and the period of the diffraction grating, and the gain peak wavelength of the active layer obtained in the measurement step The thickness of the optical confinement layer is determined so that the difference between the two is within a predetermined range. A method for producing a distributed feedback semiconductor laser device, comprising:
A diffraction grating forming step of forming a semiconductor layer including a diffraction grating on a semiconductor substrate;
An active layer forming step of forming an active layer on the semiconductor layer;
A measurement step of measuring a gain peak wavelength of the active layer;
Forming an optical confinement layer on the active layer having a larger band gap energy than the active layer,
In the optical confinement layer forming step, the oscillation wavelength of the distributed feedback semiconductor laser element, which depends on the composition of the optical confinement layer and the period of the diffraction grating, and the gain peak wavelength of the active layer obtained in the measurement step, A method of manufacturing a distributed feedback semiconductor laser device, wherein the composition of the optical confinement layer is determined so that the difference between the two is within a predetermined range. The optical confinement layer
A first layer having a larger band gap energy than the active layer;
4. The distributed feedback semiconductor laser device according to claim 2, further comprising: a second layer provided on the first layer and having a band gap energy larger than that of the first layer. 5. Method.

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