JP2008198654A - Semiconductor laser, and process for fabricating semiconductor laser - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a semiconductor laser having such a structure that stabilities of threshold current and oscillation wavelength are enhanced not only in the vicinity of room temperature but also at a higher temperature. <P>SOLUTION: In a light-emitting region 17 provided between a first conductivity type clad region 13 and a second conductivity type clad region 15, quantum wires 19a-19e are arranged at a cycle Λ and the intermediate semiconductor region 21 is located between the quantum wires 19. The semiconductor laser 11 having a complex distribution return structure includes each quantum wire 19a-19e having a gain responsive to current application and the intermediate semiconductor region 21 not having a gain and has a comparatively wide stop band. The peak of edge on the long wavelength side of the stop band corresponds to the oscillation wavelengths λ<SB>1</SB>-λ<SB>4</SB>of a DFB resonator. Since the quantum wires 19a-19e in the light-emitting region 17 have various widths (Wa-We), the gain spectrum of whole light-emitting region becomes wider than the gain spectrum of each individual quantum wire 19a-19e. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a semiconductor laser and a method for manufacturing the semiconductor laser.

  Non-Patent Document 1 describes a distributed feedback semiconductor laser having a multiple quantum wire active region. In this semiconductor laser, the minimum threshold current is obtained at −90 degrees Celsius, and good temperature dependence of the threshold current is obtained in the range of −120 degrees Celsius to −20 degrees Celsius.

Non-Patent Document 2 describes a distributed feedback semiconductor laser. This distributed feedback semiconductor laser uses a Fe-doped InP buried and a trench structure in the buried region, and the semiconductor laser achieves a direct modulation of 10 Gb / s at 100 degrees Celsius.
H. Yagi et al .: Appl. Phys. Lett., 87 (2005) pp.223120-1 1. JK White et al. ECOC2002, Lasers 5.3.3 (2002)

  However, in the semiconductor laser described in Non-Patent Document 1, a rapid increase in threshold current is observed at a temperature of room temperature or higher. This increase is considered to be due to the spread of the gain spectrum accompanying the temperature increase.

  Further, in the semiconductor laser described in Non-Patent Document 2, a complex coupled distributed feedback structure is formed using wet etching, except for the upper three layers of the multilayer quantum well structure. As described above, although a high-speed direct modulation operation can be obtained even in a high temperature region, good temperature characteristics are not obtained for the threshold current.

  The present invention has been made in view of such circumstances, and has a structure capable of improving the stability of threshold current and oscillation wavelength in a wide temperature range including not only around room temperature but also higher temperatures. It is an object of the present invention to provide a semiconductor laser having a semiconductor laser, and to provide a method for manufacturing the semiconductor laser.

  According to one aspect of the present invention, a semiconductor laser includes a first conductivity type cladding region, a second conductivity type cladding region, and a light emitting region. The light emitting region is provided between the first conductivity type cladding region and the second conductivity type cladding region, and the light emitting region is an intermediate semiconductor provided between the plurality of quantum wires and the quantum wires. Each of the quantum wires has a quantum well structure including a barrier layer and a well layer, the quantum wires are periodically arranged along a predetermined axis, and each of the quantum wires Has a quantum wire width defined in the predetermined axial direction, and a quantum wire width of one quantum wire of the plurality of quantum wires is a quantum wire of another quantum wire of the plurality of quantum wires. Different from width.

  In this semiconductor laser, each quantum wire has a gain in response to application of current to the semiconductor laser and the intermediate semiconductor region has no gain. For this reason, the arrangement of the plurality of quantum wires and the intermediate semiconductor region provides a distributed feedback structure. This distributed feedback structure has a relatively wide stop band, and a spectrum peak of the distributed feedback structure is located on one of the edges of the stop band. Also, since the quantum wire width of one quantum wire in the light emitting region is different from the quantum wire width of another quantum wire in the light emitting region, the gain spectrum of the entire light emitting region is It becomes wider than the gain spectrum of the thin line. Although the relative positional relationship between the peak wavelength of the gain spectrum and the peak wavelength of the distributed feedback structure changes due to the temperature change, the gain spectrum and the spectrum of the distributed feedback structure can be matched over a wide temperature range.

  The semiconductor laser according to the present invention includes a first conductivity type cladding region, a second conductivity type cladding region, and a light emitting region. The light emitting region is provided between the first conductivity type cladding region and the second conductivity type cladding region, and the light emitting region is an intermediate semiconductor provided between the plurality of quantum wires and the quantum wires. The plurality of quantum wires and the intermediate semiconductor region are arranged such that the light emitting region forms a complex coupled distributed feedback structure, and each of the quantum wires includes a barrier layer and a well layer. The gain spectrum of the plurality of quantum wires is distributed such that the width of the gain spectrum of the entire light emitting region is larger than the width of the gain spectrum of each quantum wire.

In this semiconductor laser, a quantum wire made of a material having a relatively high refractive index and an intermediate semiconductor region made of a material having a relatively low refractive index are arranged so that the light emitting region forms a complex coupled distributed feedback structure. This distributed feedback structure has a relatively wide stop band due to these large refractive index differences. The gain spectrum of multiple quantum wires is distributed so that the width of the gain spectrum of the entire light-emitting region is larger than the width of the gain spectrum of each quantum wire, so it is located at one of the stopband edges in a wide temperature range. The peak of the distributed feedback structure spectrum matches the gain spectrum of the entire light emitting region.

  In the semiconductor laser according to the present invention, it is preferable that an average value of the quantum wire width of the quantum wires is 30 nanometers or less. If the quantum wire width exceeds 30 nm, the lateral confinement of carriers peculiar to the quantum wires cannot be obtained, and desired characteristics cannot be obtained. In the semiconductor light emitting device according to the present invention, the maximum value of the quantum wire width of the quantum wire is larger than 1.1 times the average value, and the minimum value of the quantum wire width of the quantum wire is 0 of the average value. It is preferably less than 9 times. If the quantum wire width is distributed in such a value, the gain spectrum width of the entire light emitting region is suitable.

  In the semiconductor laser according to the present invention, the quantum well structure may be strain compensated. In this semiconductor laser, the strain compensation quantum well structure in which compressive strain is applied to the well layer and tensile strain is applied to the barrier layer, thereby suppressing the influence of triaxial strain generated during the manufacturing process, and at the regrowth interface. Non-radiative recombination current components can be reduced.

  In an example of the semiconductor laser according to the present invention, the well layer may be made of a GaInAsP semiconductor, and the intermediate semiconductor region may be made of an InP semiconductor.

  Another aspect of the present invention relates to a method for fabricating a semiconductor laser. This method includes (a) a step of forming a semiconductor stack for a quantum well structure on a first conductivity type cladding layer, and (b) a mask having a plurality of mask patterns periodically arranged on the semiconductor stack. And etching the semiconductor stack to form a plurality of quantum wires, and (c) embedding the plurality of quantum wires with a semiconductor, and the width of one of the mask patterns is: Of the mask patterns, the width of another mask pattern is intentionally changed to form a quantum wire width distribution.

  Etching a semiconductor stack to form a plurality of quantum wires and embedding a plurality of quantum wires with a semiconductor provides a periodically arranged gain region comprising each of the quantum wires, thereby providing a complex coupled distributed feedback structure Is formed. Also, the width of one of the mask patterns for forming a plurality of quantum wires is intentionally changed from the width of another mask pattern, so that the width of the quantum wires in the light emitting region is distributed. Thus, the width of the gain spectrum of the entire light emitting region becomes larger than the width of the gain spectrum of each quantum wire.

  The above and other objects, features, and advantages of the present invention will become more readily apparent from the following detailed description of preferred embodiments of the present invention, which proceeds with reference to the accompanying drawings.

  As described above, according to the present invention, there is provided a semiconductor laser having a structure capable of improving the stability of the threshold current and the oscillation wavelength not only near room temperature but also at a higher temperature. Provides a method for fabricating this semiconductor laser.

  The knowledge of the present invention can be easily understood by considering the following detailed description with reference to the accompanying drawings shown as examples. Subsequently, embodiments of the semiconductor laser of the present invention and the method for manufacturing the semiconductor laser will be described with reference to the accompanying drawings. Where possible, the same parts are denoted by the same reference numerals.

  FIG. 1A is a perspective view showing the structure of the semiconductor laser according to the present embodiment. The semiconductor laser 11 includes a first conductivity type cladding region 13, a second conductivity type cladding region 15, and a light emitting region 17. The light emitting region 17 is provided between the first conductivity type cladding region 13 and the second conductivity type cladding region 15. The light emitting region 17 includes a plurality of quantum wires 19 a, 19 b, 19 c, 19 d, 19 e and an intermediate semiconductor region 21. The first conductivity type cladding region 13, the second conductivity type cladding region 15 and the light emitting region 17 constitute a semiconductor mesa 25 extending along a predetermined axis.

  In the semiconductor laser 11, the quantum wires 19a to 19e are arranged with a period Λ (lambda) in a predetermined axial direction. The intermediate semiconductor region 21 is provided between the quantum wires 19.

FIG.1 (b) shows the quantum wire 19 as a representative for showing the layer structure of quantum wire 19a-19e. The quantum wire 19 has a quantum well structure 23, and the quantum well structure 23 includes a barrier layer 23a and a well layer 23b. Respect quantum wire 19a to 19e, a quantum wire width _{L W} is defined in a predetermined axial direction. The quantum wire width of one quantum wire (for example, quantum wire 19a) among the quantum wires 19a to 19e in the light emitting region 17 is at least one of other quantum wires (for example, quantum wires 19b, 19c, 19d, and 19e). Quantum wire width) is different.

  In the semiconductor laser 11, the quantum wires 19a to 19e and the intermediate semiconductor region 21 are arranged so that the light emitting region 17 forms a complex coupled distributed feedback structure, and the gain spectrum of each of the quantum wires 19a to 19e is The width of the gain spectrum of the entire light emitting region 17 is distributed so as to be larger than the width of the gain spectrum in each of the quantum wires 19a to 19e.

  FIG. 2A is a diagram illustrating a refractive index distribution and a gain distribution of a light emitting region of a semiconductor mesa, and FIG. 2B is a diagram illustrating an example of a spectrum of a DFB structure. In this semiconductor laser, as shown in FIG. 2A, each quantum wire 19a to 19e has a gain in response to application of current to the semiconductor laser, and the intermediate semiconductor region 21 includes each quantum wire 19a to 19e. Less than or no gain. Therefore, the arrangement of the plurality of quantum wires 19a, 19b, 19c, 19d, 19e and the intermediate semiconductor region 21 (for example, the arrangement shown in FIG. 2A) provides a complex distributed feedback structure. This distributed feedback structure has a relatively wide stop band due to a large refractive index difference between the plurality of quantum wires 19a to 19e and the intermediate semiconductor region 21, as shown in FIG. In addition, a spectrum peak of the distributed feedback structure is located at one of the edges of the stop band.

  Further, since the quantum wires 19a to 19e of the light emitting region 17 have various widths (for example, the widths Wa, Wb, Wc, Wd, We shown in FIG. 2A), the gain spectrum of the entire light emitting region is It becomes wider than the gain spectrum of the quantum wires 19a to 19e. Although the relative positional relationship between the peak wavelength of the gain spectrum and the peak wavelength of the spectrum of the distributed feedback structure changes due to temperature change, the gain spectrum and the spectrum of the distributed feedback structure can be matched over a wide temperature range.

  Next, the semiconductor laser 11 will be described. The semiconductor laser 11 can include first and second optical confinement layers 27 and 29. The first light confinement layer 27 is located between the first conductivity type cladding region 13 and the light emitting region 17, and the second light confinement layer 29 is formed between the second conductivity type cladding region 15 and the light emitting region 17. Located between. The semiconductor mesa 25 can include a first conductivity type cladding region 13, a first light confinement layer 27, a light emitting region 17, a second light confinement layer 29, and a second conductivity type cladding region 15. Further, the semiconductor mesa 25 is embedded by the embedded region 31. The buried region 31 can be made of, for example, Fe-doped InP. A second conductivity type cladding region 33 is provided on the semiconductor mesa 25 and the buried region 31. A contact layer 35 is provided on the second conductivity type cladding region 33. The contact layer 35 is in ohmic contact with a first electrode (for example, an anode) 39a. The semiconductor mesa 25 and the buried region 31 are mounted on the main surface 37a of the semiconductor substrate 37, and the second electrode (for example, cathode) 39b is in ohmic contact with the back surface 37b.

The relationship between the gain spectrum and the spectrum of the distributed feedback structure will be further described with reference to FIGS. 3 and 4. An example semiconductor laser includes a quantum well structure quantum wire composed of a GaInAsP well layer and a GaInAsP barrier layer, and an InP semiconductor located between the quantum wires. For this reason, the complex coupled DFB laser has a diffraction grating having a large refractive index difference in the light emitting region as compared with the refractive index coupled DFB laser. That is, a large refractive index difference occurs between the GaInAsP quantum wires and the InP buried between the quantum wires. As a result, the value of the refractive index coupling coefficient (ki) of the complex coupled DFB laser is about an order of magnitude larger than that of the refractive index coupled DFB laser (for example, about 200 cm ⁻¹ ). A relatively wide stop band appears in the characteristics.

  FIG. 3A and FIG. 3B show the relationship between the gain spectrum of a semiconductor laser having a uniform width of quantum wires in the light emitting region and the spectrum of the distributed feedback structure. The relationship shown in FIG. 3A is a positional relationship at room temperature (for example, 25 degrees Celsius), and the relationship shown in FIG. 3B is a positional relationship at a high temperature (for example, 100 degrees Celsius).

The gain spectrum of the quantum wire shows a temperature coefficient of about 0.5 nm / degree, for example, and the Bragg wavelength of the DFB structure shows a temperature coefficient of about 0.1 nm / degree, for example. Therefore, at room temperature, as shown in Fig. 3 (a), there overlap sufficiently with the oscillation wavelength lambda ₁ and the gain spectrum G _T1 in the spectrum S _DFB1 of distributed feedback structure, it is capable of lasing When the temperature rises, the overlap becomes smaller due to the difference in temperature coefficient, and the threshold current rises. In yet a high temperature, as shown in FIG. 3 (b), there is no overlap between the oscillation wavelength lambda ₂ and the gain spectrum G _T2 in the spectrum S _DFB2, no longer single-mode oscillation, rather than operating as a DFB laser, a Fabry Operation as a Perot laser.

  That is, when the width of the quantum wire is uniform, if the gain spectrum of the quantum wire and the oscillation wavelength of the DFB resonator exceed a temperature range (for example, a high temperature region) due to a difference in temperature coefficient, single mode oscillation Cannot be obtained.

  4A and 4B show the relationship between the gain spectrum of a semiconductor laser having a distribution in the width of the quantum wire in the light emitting region and the spectrum of the distributed feedback structure, as in this embodiment. The relationship shown in FIG. 4A is a positional relationship at room temperature (for example, 25 degrees Celsius), and the relationship shown in FIG. 4B is a positional relationship at a high temperature (for example, 100 degrees Celsius).

If a distribution having various values (for example, a distribution D having a substantially single peak) is given to the width of the quantum wire, a distributed feedback structure is formed at room temperature as shown in FIG. In the spectrum S _DFB3, the oscillation wavelength λ ₃ and the gain spectrum D _T1 are sufficiently overlapped, and single mode oscillation is possible. Even if the temperature rises, as shown in FIG. 4 (b), even if there is a difference in the above temperature coefficient, there is a sufficient overlap between the oscillation wavelength λ ₄ and the gain spectrum D _T2 in the spectrum S _DFB4 , Single mode oscillation is possible even at high temperatures.

  When the width of the quantum wire is not uniform, the gain spectrum spreads due to the size distribution even if there is a difference in the temperature coefficient between the oscillation wavelength and gain spectrum of the DFB resonator due to the distribution of the quantum wire width. The oscillation wavelength and gain spectrum of the DFB resonator are matched even in a high temperature range, and as a result, single mode oscillation is obtained.

  In the semiconductor laser 11, as described above, a plurality of quantum wires (active regions) are periodically arranged. The semiconductor laser 11 has a relatively wide stop band unique to the complex coupled DFB laser and a light emitting region. And a wide-band gain spectrum obtained by forming the quantum wires so that the widths thereof are not uniform. For this reason, in the wide temperature range, matching between the oscillation wavelength of the DFB resonator (the wavelength at the end of the long wavelength side of the stop band) and the gain spectrum can be obtained. Further, the temperature dependency of the threshold current, the oscillation wavelength, and the submode suppression ratio (SMSR) is stabilized. Since the width of the quantum wire in the light emitting region is intentionally formed so as not to be uniform, the gain spectrum width is widened. When the gain spectrum width is widened, there is a possibility that the maximum gain value is lowered to affect the laser characteristics. However, the complex coupling type DFB laser has a very large refractive index coupling coefficient (κi). In other words, in the complex coupled DFB laser, high internal reflection can be obtained (reflector loss is very small). As a result, a low threshold is obtained. Therefore, in the complex coupled DFB laser, there is almost no influence due to the widening of the gain spectrum width.

  Further, the DFB cycle is detuned in order to obtain stable laser characteristics over a range from a temperature near room temperature to a high temperature. Specifically, the gain spectrum (for example, the temperature coefficient of 0.5 nm per unit temperature) and the difference in temperature change between the Bragg wavelength (for example, the temperature coefficient of 0.1 nm per unit temperature) are used to calculate the gain spectrum and Detuning is performed so that the Bragg wavelength matches in a temperature range including a temperature higher than room temperature (for example, 100 degrees Celsius).

  In a semiconductor laser, as the dimension of the quantum structure of the active layer, such as a quantum thin film and a quantum wire, is lowered, carriers are tightly confined in the quantum structure and the optical gain spectrum becomes sharper. That is, laser oscillation is possible with a small number of carriers. For this reason, a low threshold current / high efficiency semiconductor laser is realized. In addition, since the gain is concentrated at a certain energy corresponding to the oscillation wavelength, a semiconductor laser having a low wavelength chirp characteristic is realized.

FIG. 5 shows the carrier density dependence of the maximum gain of the quantum wire (Q _WIRE ) and the quantum thin film (Q _FILM ). FIG. 5 shows a quantum well structure using Ga _0.22 In _0.78 As _0.81 P _0.19 , carrier density dependence at a temperature of 27 degrees Celsius, and an in-band relaxation time (τ _{in) of} 0.1 psec. ). As understood from this figure, as the width (W) of the quantum wire is increased (10 nm, 20 nm, 30 nm, 40 nm), the maximum gain characteristic of the quantum wire (Q _WIRE ) becomes the maximum gain of the quantum thin film (Q _FILM ). As the characteristics approach, the difference between the two becomes smaller in the maximum gain characteristics. In order to obtain the advantage of the quantum wire in the maximum gain characteristic, the width W of the quantum wire must be less than 40 nm, and the width W of the quantum wire is preferably 30 nm or less.

  As understood from the characteristics of FIG. 5, in the semiconductor laser 11 in which the quantum wire width is distributed, the average value of the quantum wire width is preferably 30 nm or less. When the quantum wire width exceeds 30 nm, it is difficult to obtain desired values for carrier confinement and laser characteristics.

  In the semiconductor laser 11, the maximum value of the quantum wire width of the quantum wire is larger than 1.1 times the average value, and the minimum value of the quantum wire width of the quantum wire is smaller than 0.9 times the average value. preferable. If the quantum wire width is distributed in such a value, the gain spectrum width of the entire light emitting region is suitable.

  In the semiconductor laser 11, the quantum well structure can be strain compensated. According to the strain compensated quantum well structure in which compressive strain is applied to the well layer and tensile strain is applied to the barrier layer in this semiconductor laser, the influence of triaxial strain generated during the manufacturing process can be suppressed, and non-reproduction at the regrowth interface can be suppressed. The light emission recombination current component can be reduced.

  In an example of the semiconductor laser 11, the well layer and the barrier layer can be made of GaInAsP semiconductors having different compositions. The intermediate semiconductor region can be made of an InP semiconductor. According to the combination of these materials, processing becomes relatively easy. The realization of the semiconductor laser 11 is not limited to the semiconductor material described above.

  With reference to FIGS. 6 and 7, the main steps in the method of manufacturing the semiconductor laser according to the above embodiment will be described.

  As shown in FIG. 6A, a p-type InP clad layer 53 is grown on the p-type InP substrate 51. This growth is performed using, for example, a metal organic vapor phase growth furnace. Next, a semiconductor stack 55 for a quantum well structure is formed on the p-type InP cladding layer 53. The semiconductor stack 55 can include, for example, a first undoped GaInAsP light confinement layer 57, a multiple quantum well structure 59 made of GaInAsP, and a second undoped GaInAsP light confinement layer 61. The semiconductor film in the semiconductor stack 55 is grown using, for example, a metal organic chemical vapor deposition furnace. The GaInAsP multiple quantum well structure 59 has a plurality of well layers and barrier layers. In one example of the semiconductor stack 55, a strain compensated quantum well structure including a compressive strain well layer and a tensile strain barrier layer is preferable. In order to compensate for a decrease in effective gain due to a decrease in active layer volume accompanying the quantum wire structure, the number of well layers is preferably four or more.

  As shown in FIG. 6B, a mask for quantum wires is formed on the semiconductor stack 55. An insulating film 63, for example, a silicon-based inorganic compound film such as a silicon oxide film is deposited for the mask. This deposition is performed by, for example, chemical vapor deposition. A resist mask 65 for transferring a plurality of periodically arranged patterns is formed on the insulating film 63. The formation of the resist mask 65 can be performed using, for example, an electron beam exposure method or a lithography technique such as nanoimprint.

  To obtain the appropriate temperature characteristics (ie improved temperature characteristics), the DFB period is detuned. For example, when a Bragg wavelength (for example, 1550 nanometer wavelength band) is made to correspond to a temperature increase of 80 degrees Celsius, the period (LAMBDA) is set to 240 nm assuming that the temperature change coefficient of the Bragg wavelength is 0.1 nm per unit temperature. To 246.25 nm.

  Furthermore, in order to realize the temperature dependence of the stable threshold current density, the gain spectrum of the light emitting region composed of quantum wires (active layer) is widened. That is, in consideration of the influence on the refractive index coupling coefficient and the gain characteristics, a distribution of about −10% to + 10% is given to the thin line width around the average value of the thin line width (W) of the quantum thin line. For example, for the average value of the fine line width of 30 nm, the fine line width of the quantum fine line is distributed with a standard deviation of 3 nm. This distribution formation is realized by the mask pattern 67.

As shown in FIG. 6C, the silicon oxide film is etched using the resist mask 65. For this etching, for example, reactive ion etching using CF ₄ gas can be used. In one example, it is preferable to use a silicon oxide film having a thickness of about 20 nm or more in order to secure a selection ratio between a resist and a silicon oxide film (for example, SiO ₂ ). When the resist mask 65 is removed after the etching, a mask pattern 67 for the DFB pattern of the quantum wire is formed. Each mask 67a of the mask pattern 67, 67b, 67c, 67d, 67e has to correspond to the distribution of the width of the quantum wire, respectively the width _{W A, W B, W C} , W D, W E. The masks 67a to 67e are arranged with a period LAMBDA.

As shown in FIG. 7A, the semiconductor stack 55 is etched using the mask pattern 67 to form a plurality of quantum wires. In this step, the optical confinement layer 61 and the multiple quantum well structure 59 of the semiconductor stack 55 are etched. In this example of etching, RIE using CH ₄ / H ₂ is used. For example, by repeating RIE etching using CH ₄ / H ₂ and O ₂ ashing for removing carbon polymer deposited on the semiconductor surface during this etching, a multilayer quantum wire structure with excellent perpendicularity is formed. it can. As a result of this etching, an array of semiconductor thin wires 69 a to 69 e is formed on the optical confinement layer 57. The semiconductor thin wires 69a, 69b, 69c, 69d, and 69e include optical confinement layers 61a, 61b, 61c, 61d, and 61e and multiple quantum well structures 59a, 59b, 59c, 59d, and 59e, respectively. The semiconductor thin wires 69 a to 69 e are periodically arranged, and the thin wire widths of the semiconductor thin wires 69 a to 69 e are distributed according to the mask pattern 67.

  In order to remove the damaged layer by dry etching, wet etching is performed. For this etching, for example, a sulfuric acid-based solution is used. After the wet etching, the mask pattern 67 is removed. For example, a pattern made of silicon oxide is removed with buffered hydrofluoric acid.

  Next, as shown in FIG. 7B, the semiconductor 71 for burying the semiconductor thin wires 69a to 69e is regrown. This embedding is performed with undoped InP. Further, it is desirable that the growth rate of InP for filling is as low as about 250 nm / h in order to obtain a flat regrowth interface. In the embedding process, a periodic structure is formed in which a gain region provided by each semiconductor thin wire and an intermediate semiconductor region without gain are alternately arranged in a predetermined axis direction.

  As shown in FIG. 7C, the n-type GaInAsP optical confinement layer 73, the n-type InP cladding layer 75, and the n-type GaInAs contact layer 77 are regrown. These growth rates are a normal growth rate, for example, about 1 μm / h. Thereafter, if necessary, a refractive index waveguide structure such as a buried heterostructure is formed.

  In this manufacturing method, the width of one mask (for example, mask 67a) of the mask pattern 67 is intentionally the same as the width of one of the masks 67b, 67c, 67d, and 67e (for example, mask 67b). has been edited. As a result, a quantum wire width distribution is formed.

An example will be described in which a size distribution is given to the quantum wires for lithography and development.
Average quantum wire width: 30 nm
Standard deviation of distribution: 3 nm (10% of average value)
And The Gaussian distribution formula is
exp (− (W−W ₀ ) ² / (2 × DW ² )) / (sqrt (2 × pi) × DW)
DW: Standard deviation W ₀ : Average value of fine line width W: Quantum fine line width pi: Circumferential ratio exp: Expressed by symbol of exponential function (natural logarithm). Using this, the relative frequency is obtained as follows.
0.133 when W = 30 nm
0.126 when W = 31 nm, 29 nm
0.107 when W = 32 nm, 28 nm
0.081 when W = 33 nm, 27 nm,
It becomes. Therefore, a size distribution is given to the thin line width by reflecting these relative frequencies. As a specific example,
Resonator length: 240 μm,
DFB cycle: 240 nm
Bragg wavelength: 1550nm
Then, 1000 quantum wires can be formed. Therefore, 133 quantum wires having a width of W = 30 nm and 126 quantum wires having a width of W = 31 and 29 nm are respectively distributed. The arrangement of these quantum wires can use a random distribution, but is not limited to this.

  When the Bragg wavelength is 1550 nm, the period of the quantum wire array (DFB period) is 240 nm. As understood from the matters already described, it is preferable to detune the Bragg wavelength in order to improve the temperature characteristics. For example, the detuning amount of the DFB cycle is preferably 6.25 nm or more. In order to obtain a wideband gain spectrum, a size distribution of about 10% is given to the quantum wire as described above, and matching between the Bragg wavelength (stop band) and the gain peak is obtained in a wide temperature range.

  While the principles of the invention have been illustrated and described in the preferred embodiments, it will be appreciated by those skilled in the art that the invention can be modified in arrangement and detail without departing from such principles. The present invention is not limited to the specific configuration disclosed in the present embodiment. We therefore claim all modifications and changes that come within the scope and spirit of the following claims.

FIG. 1A is a perspective view showing the structure of the semiconductor laser according to the present embodiment. FIG.1 (b) is drawing which shows the layer structure of a quantum wire. FIG. 2A is a diagram illustrating a refractive index distribution and a gain distribution of a light emitting region of a semiconductor mesa, and FIG. 2B is a diagram illustrating an example of a spectrum of a DFB structure. FIG. 3A and FIG. 3B show the relationship between the gain spectrum of a semiconductor laser having a uniform width of quantum wires in the light emitting region and the spectrum of the distributed feedback structure. 4A and 4B show the relationship between the gain spectrum of a semiconductor laser having a distribution in the width of the quantum wire in the light emitting region and the spectrum of the distributed feedback structure, as in this embodiment. FIG. 5 is a diagram showing the carrier density dependence of the maximum gain of the quantum wire (Q _WIRE ) and the quantum thin film (Q _FILM ). FIG. 6 is a drawing showing main steps in the method of manufacturing the semiconductor laser according to the present embodiment. FIG. 7 is a drawing showing main steps in the method of manufacturing the semiconductor laser according to the present embodiment.

Explanation of symbols

DESCRIPTION OF SYMBOLS 11 ... Semiconductor laser, 13 ... 1st conductivity type clad area | region, 15 ... 2nd conductivity type clad area | region, 17 ... Light emission area | region, 19, 19a, 19b, 19c, 19d, 19e ... Quantum wire, 21 ... Intermediate semiconductor area | region, 23 Quantum well structure, 23a ... barrier layer, 23b ... well layer, 25 ... semiconductor mesa, Wa, Wb, Wc, Wd, We ... quantum wire width, 27, 29 ... optical confinement layer, 31 ... buried region, 33 ... first 2-conductivity-type cladding region, 35 ... contact layer, 37 ... semiconductor substrate, 39a, 39b ... electrode, S _DFB1 , S _DFB2 , S _DFB3 , S _DFB4 ... spectrum of distributed feedback structure, λ ₁ , λ ₂ , λ ₃ , λ ₄ ... oscillation wavelength of the DFB _{resonator, G T1, G T2, D} T1, D T2 ... gain spectrum, 51 ... p-type InP substrate, 53 ... p-type InP cladding layer, 55 ... semiconductor Lamination 57: Undoped GaInAsP light confinement layer 59 ... Multiple quantum well structure 61 ... Undoped GaInAsP light confinement layer 63 ... Mask insulating film 65 ... Resist mask 67 ... Mask pattern 67a 67b 67c 67d 67e ... Mask pattern mask, 69a, 69b, 69c, 69d, 69e ... Semiconductor thin wire, 61a, 61b, 61c, 61d, 61e ... Optical confinement layer, 59a, 59b, 59c, 59d, 59e ... Multiple quantum well structure, 71 ... Embedded semiconductor, 73 ... n-type GaInAsP optical confinement layer, 75 ... n-type InP cladding layer, 77 ... n-type GaInAs contact layer

Claims (6)

A first conductivity type cladding region;
A second conductivity type cladding region;
With a light emitting area,
The light emitting region is provided between the first conductivity type cladding region and the second conductivity type cladding region,
Each of the quantum wires has a quantum well structure including a barrier layer and a well layer,
The light emitting region includes a plurality of quantum wires and an intermediate semiconductor region provided between the quantum wires,
The quantum wires are periodically arranged along a predetermined axis,
Each of the quantum wires has a quantum wire width defined in the predetermined axial direction,
A semiconductor laser characterized in that a quantum wire width of one quantum wire of the plurality of quantum wires is different from a quantum wire width of another quantum wire of the plurality of quantum wires. A first conductivity type cladding region;
A second conductivity type cladding region;
With a light emitting area,
The light emitting region is provided between the first conductivity type cladding region and the second conductivity type cladding region,
Each of the quantum wires has a quantum well structure including a barrier layer and a well layer,
The light emitting region includes a plurality of quantum wires and an intermediate semiconductor region provided between the quantum wires,
The plurality of quantum wires and the intermediate semiconductor region are arranged such that the light emitting region forms a complex coupled distributed feedback structure,
The gain spectrum of the plurality of quantum wires is distributed such that the width of the gain spectrum of the entire light emitting region is larger than the width of the gain spectrum of each quantum wire. The average value of the quantum wire width of the quantum wires is 30 nanometers or less,
The maximum value of the quantum wire width of the quantum wires is greater than 1.1 times the average value,
2. The semiconductor laser according to claim 1, wherein the minimum value of the quantum wire width of the quantum wires is smaller than 0.9 times the average value.   4. The semiconductor laser according to claim 1, wherein the quantum well structure is strain-compensated. 5. The well layer is made of a GaInAsP semiconductor,
The semiconductor laser according to claim 1, wherein the intermediate semiconductor region is made of an InP semiconductor. A method for fabricating a semiconductor laser, comprising:
Forming a semiconductor stack for the quantum well structure on the first conductivity type cladding layer;
Etching the semiconductor stack using a mask having a plurality of mask patterns periodically arranged on the semiconductor stack to form a plurality of quantum wires; and
Embedding the plurality of quantum wires with a semiconductor,
The width of one mask pattern of the mask patterns is intentionally changed from the width of another mask pattern of the mask patterns so as to form a distribution of quantum wire widths.

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