JP5205901B2 - Semiconductor laser device manufacturing method and semiconductor laser device - Google Patents

Description

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

Non-Patent Document 1 describes a distributed feedback (DFB) semiconductor laser element having thin line-like active regions arranged periodically. In this semiconductor laser device, a buried heterostructure including the active region is formed on a p-type InP substrate. Non-Patent Document 2 also describes a semiconductor laser device having a thin linear active region. In this document, when a semiconductor laser device is manufactured by forming a thin line active region by etching and embedding between active regions, the threshold current density is higher when a p-type InP substrate is used than when an n-type InP substrate is used. It is described that it is reduced. Note that a DFB semiconductor laser element having thin line-shaped active regions arranged periodically may be called a complex coupling type (or active layer separation type) DFB laser element.
N.Nunoya et al., “High-Performance1.55-μm Wavelength GaInAsP-InP Distributed-Feedback Lasers With Wirelike ActiveRegions”, IEEE JOURNAL ON SELECTED TOPICS IN QUANTUM ELECTRONICS, VOL. 7, NO.2, MARCH / APRIL (2001 ) Y.Miyake et al., “Threshold Current Reduction of GaInAs / GaInAsP / InP SCH Quantum-Well Lasers with Wire-Like ActiveRegion by Using p-Type Substrates”, IEEE PHOTONICS TECHNOLOGY LETTERS, VOL 4, NO 9, SEPTEMBER (1992)

  Non-Patent Document 2 states that it is preferable to use a p-type InP substrate when a thin-line active region is formed by etching and embedded between the active regions. FIG. 13 is a cross-sectional view showing the structure of a conventional complex coupled DFB laser device, and shows an enlarged cross section along the laser oscillation direction of a light emitting layer including a thin-line active region and its peripheral structure. As shown in FIG. 13, a conventional complex coupled DFB laser device 100 includes a p-type InP substrate 102, a p-type InP cladding layer 104, a p-type GaInAsP light confinement layer 106, an n-type GaInAsP light confinement layer 108, and an n-type. An InP cladding layer 110 is provided. A light-emitting layer 112 is provided between the p-type GaInAsP light confinement layer 106 and the n-type GaInAsP light confinement layer 108. The light-emitting layer 112 includes a plurality of thin-line active regions 114 arranged periodically. And an intermediate semiconductor region 116 made of undoped InP provided between the plurality of active regions 114. Each active region 114 includes a quantum well structure 114a in which barrier layers and well layers are alternately stacked.

  FIG. 14 is a diagram showing a band structure in the complex coupled DFB laser device 100 shown in FIG. In FIG. 14, BG1 represents the band gap of the active region 114, BG2 represents the band gap of the p-type GaInAsP optical confinement layer 106, BG3 represents the band gap of the p-type InP cladding layer 104, and BG4 represents the n-type GaInAsP light. The band gap of the confinement layer 108 is shown, and BG5 shows the band gap of the n-type InP clad layer 110.

  When the complex coupled DFB laser device 100 is manufactured, a method in which the active region 114 is formed by etching and the gap between the active regions 114 is filled with the intermediate semiconductor region 116 may be employed. In this case, the constituent material (undoped InP) of the intermediate semiconductor region 116 is deposited thinly on the active region 114 as well. As a result, when a deposited layer is formed between the active region 114 and the n-type GaInAsP optical confinement layer 108, the band structure of the complex coupled DFB laser device 100 is changed by the deposited layer. Note that BG6 shown in FIG. 14 indicates the band gap of this deposited layer. For example, when the deposited layer is made of InP, the band offset on the conduction band side of InP is smaller than that on the valence band side, and electrons have a higher mobility than holes. It is difficult for electrons moving toward the region 114 to be a barrier.

  On the other hand, FIG. 15 is a diagram showing a band structure when a complex coupled DFB laser element is formed on an n-type InP substrate. In this case, BG7 represents the band gap of the n-type GaInAsP optical confinement layer, BG8 represents the band gap of the n-type InP cladding layer, BG9 represents the band gap of the p-type GaInAsP optical confinement layer, and BG10 represents the p-type InP cladding. The band gap of the layer is shown. As shown in FIG. 15, the band offset on the valence band side of the InP deposited layer (BG6) is larger than that on the conduction band side, and holes have a lower mobility than electrons. Therefore, when a complex coupled DFB laser element is formed on an n-type InP substrate, the band structure change due to the deposited layer becomes a barrier for holes moving toward the active region 114. This is the reason why p-type InP substrates have been used in conventional complex coupled DFB laser elements.

  However, it is desirable that a complex coupled DFB laser element using an n-type InP substrate is also put into practical use. As long as a complex coupled DFB laser element can be manufactured regardless of the conductivity type of the InP substrate, it can flexibly cope with any manufacturing process. When integrating a modulator or the like, it is more advantageous to dispose a p-type InP cladding layer for supplying holes with low mobility using an n-type InP substrate above the active layer from the viewpoint of element isolation. It is. In order to put a complex coupled DFB laser element using an n-type InP substrate into practical use, it is necessary to improve the light emission efficiency of the complex coupled DFB laser element formed on the n-type InP substrate.

  The present invention has been made in view of the above-described problems, and an object of the present invention is to provide a method for manufacturing a semiconductor laser element and a semiconductor laser element that can improve light emission efficiency using an n-type InP substrate.

  In order to solve the above-described problems, a method of manufacturing a semiconductor laser device according to the present invention includes a first cladding layer, an first optical confinement layer, and an InP compound semiconductor including an n type InP compound semiconductor on an n type InP substrate. A first growth step of growing an active layer containing a second optical confinement layer containing a p-type InP-based compound semiconductor, and a mask having a plurality of mask patterns periodically arranged on the second optical confinement layer And etching the second optical confinement layer and the active layer to form a plurality of fine line regions arranged periodically, and the side surface of the active layer included in the plurality of fine line regions is defined as an InP-based compound semiconductor. And a second cladding layer containing a p-type InP-based compound semiconductor is grown so as to be adjacent to the second optical confinement layer included in the plurality of thin line regions. Characterized in that it comprises a second growth step.

  In this method of manufacturing a semiconductor laser device, in the first growth step, a second optical confinement layer is further grown thereon in addition to the active layer that should originally be a thin line region. In the fine line forming step, the active layer and the second optical confinement layer are etched to form a plurality of fine line regions, so that each fine line region includes the second optical confinement layer. Thereafter, the side surface of the active layer included in the thin line region is embedded in the embedding process. At this time, a thin deposited layer formed on the thin line region is formed on the second optical confinement layer included in the thin line region. Then, since the second cladding layer is formed adjacent to the second optical confinement layer in the second growth step, the thin deposited layer described above is positioned between the second optical confinement layer and the second cladding layer. Will be. Therefore, no deposited layer is formed between the active layer included in the thin line region and the second optical confinement layer, and therefore the band structure change due to the deposited layer is unlikely to be a hole barrier. That is, according to this method for manufacturing a semiconductor laser element, the light emission efficiency can be improved while using the n-type InP substrate.

  In addition, a semiconductor laser device manufacturing method is such that the second cladding layer is made of p-type InP, the second optical confinement layer and the active layer have a band gap narrower than the band gap of InP, and the InP-based compound semiconductor in the embedding step. May be made of undoped InP. When the band gap of the active layer and the second optical confinement layer is narrower than the band gap of InP and the InP compound semiconductor in the embedding process is made of undoped InP, the conventional complex coupled DFB laser device shown in FIG. The barrier action due to the deposited layer becomes significant (see FIG. 15). On the other hand, since the deposition layer in the above-described method for manufacturing a semiconductor laser device is formed between the second optical confinement layer and the second cladding layer, the deposition layer (InP) having the same composition and the second cladding layer (p Type InP) are in contact with each other, and the deposited layer is unlikely to be a barrier against holes. Therefore, the luminous efficiency can be further improved.

  In addition, in the method of manufacturing the semiconductor laser element, a p-type InP layer is further grown on the second optical confinement layer during the first growth step, and the p-type InP layer and the second light are formed during the thin line formation step. A plurality of thin line regions may be formed by etching the confinement layer and the active layer using a mask. In this case, each fine line region formed by the fine line forming step includes a p-type InP layer. In the embedding process, InP moves (mass transport) from the p-type InP layer to the gap in the thin line region. Thereby, for example, even when the gap between the thin line regions is narrow and deep, deterioration of the crystallinity of the embedded InP (for example, generation of voids) can be suppressed.

  The semiconductor laser device manufacturing method may be characterized in that Ru or / and Fe are doped into the InP-based compound semiconductor in which the side surface of the active layer is embedded in the embedding step. As a result, the InP-based compound semiconductor that embeds the side surface of the active layer can be made semi-insulating, and carriers can be more effectively confined in the thin line region. When Fe is doped, it is preferable to further grow an undoped InP-based compound semiconductor on the InP-based compound semiconductor. When Fe is doped into the InP-based compound semiconductor that embeds the side surface of the active layer, resistance distribution occurs in the layer thickness direction of the InP-based compound semiconductor due to mutual diffusion of p-type dopants Zn and Fe contained in the second cladding layer. Also, a distribution occurs in the density of carriers injected into the active layer. In such a case, mutual diffusion of Zn and Fe can be suitably suppressed by further providing an undoped InP-based compound semiconductor layer between the InP-based compound semiconductor and the second cladding layer.

  The semiconductor laser device according to the present invention includes an n-type InP substrate, a first clad layer including an n-type InP-based compound semiconductor provided on the n-type InP substrate, and an n-type provided on the first clad layer. A first optical confinement layer including an InP-based compound semiconductor; an active layer formed on the first optical confinement layer; the active layer formed of an InP-based compound semiconductor; and a second including a p-type InP-based compound semiconductor provided on the active layer. A plurality of fine line regions having a light confinement layer and periodically arranged, a plurality of intermediate semiconductor regions including an InP-based compound semiconductor provided between the plurality of fine line regions, and a plurality of fine line regions adjacent to the second light confinement layer And a second cladding layer including a p-type InP-based compound semiconductor provided on the thin wire region and the intermediate semiconductor region.

  In this semiconductor laser device, each thin line region includes a second optical confinement layer in addition to the active layer. As described above, when manufacturing such a semiconductor laser device, a thin deposited layer formed on the fine line region when the gap in the fine line region is filled is formed on the second optical confinement layer. Since the second cladding layer is provided so as to be adjacent to the second optical confinement layer, the thin deposited layer described above is located between the second optical confinement layer and the second cladding layer. Therefore, no deposited layer is formed between the active layer included in the thin line region and the second optical confinement layer, and therefore the band structure change due to the deposited layer is unlikely to be a hole barrier. That is, according to this semiconductor laser device, the light emission efficiency can be improved while the n-type InP substrate is provided.

  In the semiconductor laser device, the second cladding layer is made of p-type InP, the second optical confinement layer and the active layer have a band gap narrower than the band gap of InP, and the intermediate semiconductor region is made of undoped InP. It is good. When the band gap of the active layer and the second optical confinement layer is narrower than the band gap of InP and the intermediate semiconductor region is made of undoped InP, the barrier action due to the InP deposited layer becomes significant in the conventional complex coupled DFB laser element ( FIG. 15). On the other hand, when the semiconductor laser device described above is manufactured, the deposition layer is formed between the second optical confinement layer and the second cladding layer, so that the deposition layer (InP) having the same composition and the second cladding are formed. The layer (p-type InP) is in contact with each other, and the deposited layer is unlikely to be a barrier against holes. Therefore, the luminous efficiency can be further improved.

  The semiconductor laser element may be characterized in that the intermediate semiconductor region is doped with Ru or / and Fe. Thereby, the intermediate semiconductor region can be made semi-insulating, and carriers can be more effectively confined in the thin line region. When Fe is doped, it is preferable to further include an undoped InP-based compound semiconductor layer between the intermediate semiconductor region and the second cladding layer. When Fe is doped in the intermediate semiconductor region, a resistance distribution is generated in the layer thickness direction of the intermediate semiconductor region due to mutual diffusion of Zn and Fe, which are p-type dopants contained in the second cladding layer, and is injected into the active layer. Distribution also occurs in the density of carriers. In such a case, the mutual diffusion of Zn and Fe can be suitably suppressed by further providing an undoped InP-based compound semiconductor layer between the intermediate semiconductor region and the second cladding layer.

  According to the method for manufacturing a semiconductor laser device and the semiconductor laser device according to the present invention, the n-type InP substrate can be used and the light emission efficiency can be improved.

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

(First embodiment)
FIG. 1 is a partially cutaway perspective view showing the structure of the semiconductor laser device according to the first embodiment of the present invention. FIG. 2 is an enlarged side sectional view showing a portion A shown in FIG. The semiconductor laser device 10 of this embodiment has a configuration of a complex coupled DFB laser and outputs laser light having a predetermined wavelength. Referring to FIG. 1, the semiconductor laser device 10 includes an n-type InP substrate 37 having a main surface 37a.

  The semiconductor laser element 10 also includes a first optical confinement layer 13, a plurality of fine wire regions 15, an intermediate semiconductor region 17, a first cladding layer 27, and a second cladding layer 29. Among these, the 1st optical confinement layer 13, the some thin wire | line area | region 15, and the intermediate | middle semiconductor region 17 comprise the semiconductor mesa 25 extended along a predetermined direction (laser oscillation direction). The first optical confinement layer 13 is provided on the first cladding layer 27 and mainly includes an n-type InP-based compound semiconductor having a narrower band gap than the first cladding layer 27. As an example, the first optical confinement layer 13 is made of n-type GaInAsP.

  The plurality of thin line regions 15 are formed on the first optical confinement layer 13 with the direction perpendicular to the laser oscillation direction as the longitudinal direction, and are periodically arranged in the laser oscillation direction. The fine line width W (see FIG. 2) of the fine line region 15 is set to, for example, 80 to 90 [nm] so that the semiconductor laser element 10 operates with a smaller current, and the fine line region 15 has a quantum fine line structure. Is set to, for example, 30 [nm] or less in order to obtain a high differential gain. The period Λ (see FIG. 2) of the thin line region 15 is set according to the wavelength of the laser beam to be output. For example, when the wavelength of the laser beam is 1550 [nm], it is set to 240 [nm]. When the wavelength of the laser beam is 1300 [nm], it is set to 200 [nm].

  As shown in FIG. 2, each of the plurality of thin line regions 15 includes an active layer 21 provided on the first optical confinement layer 13 and a second optical confinement layer 23 provided on the active layer 21. Yes. The active layer 21 mainly includes an InP-based compound semiconductor. As an example, the active layer 21 has a multiple quantum well structure and is undoped (that is, not actively doped with impurities). Barrier layers (barrier layers) 21a and well layers 21b made of GaInAsP are alternately stacked. As an example, two well layers 21b and three barrier layers 21a are provided. The layer thickness of the well layer 21b is, for example, 6 [nm], and the layer thickness of the barrier layer 21a is, for example, 9 [nm].

  The multiple quantum well structure of the active layer 21 is preferably a strain compensated quantum well structure including a compressive strain well layer 21b and a tensile strain barrier layer 21a. In this case, it is more preferable that the compressive strain amount of the well layer 21b is about 1.0% and the tensile strain amount of the barrier layer 21a is about -0.15%.

  The second optical confinement layer 23 mainly includes a p-type InP-based compound semiconductor having a narrower band gap than the second cladding layer 29. As an example, the second optical confinement layer 23 is made of p-type GaInAsP. The layer thickness of the second optical confinement layer 23 is preferably adjusted according to the layer thickness of the active layer 21 (that is, the number of barrier layers 21a and well layers 21b in the multiple quantum well structure). For example, the thickness is as described above. In the case where two well layers 21b having a thickness of 6 [nm] and three barrier layers 21a having a thickness of 9 [nm] are provided, the thickness of the second optical confinement layer 23 is 140 [nm] or less. Good. That is, in the manufacturing process (described later) of the semiconductor laser element 10, the fine line region 15 is formed by etching. In order to set the etching depth to a predetermined depth or less (for example, 200 [nm] or less), the second region 15 is formed. The layer thickness of the optical confinement layer 23 is set to a value obtained by subtracting the layer thickness of the active layer 21 and the etching depth for the first optical confinement layer 13 from the etching depth.

  Gaps between the plurality of thin line regions 15 are filled with the intermediate semiconductor region 17. The intermediate semiconductor region 17 mainly includes an InP compound semiconductor. As an example, the intermediate semiconductor region 17 is made of undoped InP. Alternatively, the intermediate semiconductor region 17 may be a semi-insulating region doped with at least one of Fe and Ru. The thickness of the intermediate semiconductor region 17 is set in a range that is thicker than the thickness of the active layer 21 and thinner than the total thickness of the active layer 21 and the second optical confinement layer 23. That is, the intermediate semiconductor region 17 embeds all the side surfaces of the active layer 21 and embeds part of the side surfaces of the second optical confinement layer 23.

  Please refer to FIG. 1 again. The first cladding layer 27 mainly includes an n-type InP-based compound semiconductor, and is provided between the first optical confinement layer 13 and the n-type InP substrate 37. As an example, the first cladding layer 27 is made of n-type InP. The second cladding layer 29 mainly includes a p-type InP-based compound semiconductor, is provided on the plurality of fine line regions 15 and the intermediate semiconductor region 17, and is adjacent to the second optical confinement layer 23. . As an example, the second cladding layer 29 is made of p-type InP. The first cladding layer 27 and the second cladding layer 29 are provided over the entire main surface 37a of the n-type InP substrate 37 and sandwich the semiconductor mesa 25 from above and below.

  Further, the side surface of the semiconductor mesa 25 is embedded by the embedded region 31. The buried region 31 is constituted by, for example, a first p-type current confinement layer 31a, an n-type current confinement layer 31b, and a second p-type current confinement layer 31c. The first p-type current confinement layer 31 a is provided in a region on the first cladding layer 27 excluding a region where the semiconductor mesa 25 is provided, and covers the region of the first cladding layer 27 and the side surface of the semiconductor mesa 25. Yes. The n-type current confinement layer 31b is provided on the first p-type current confinement layer 31a. The second p-type current confinement layer 31 c is provided between the n-type current confinement layer 31 b and the second clad layer 29 described above. These current confinement layers 31a to 31c are made of, for example, n-type (or p-type) InP.

  An insulating film 33 and a first (anode) electrode film 35 are formed on the second cladding layer 29. The insulating film 33 has an opening corresponding to the semiconductor mesa 25, and the second cladding layer 29 and the electrode film 35 are in ohmic contact through the opening. A second (cathode) electrode film 39 is provided on the back surface opposite to the main surface 37a of the n-type InP substrate 37, and the second electrode film 39 and the n-type InP substrate 37 form an ohmic contact. doing.

  Subsequently, main steps in the method of manufacturing the semiconductor laser device according to the present embodiment will be described with reference to FIGS.

[First growth process]
First, as shown in FIG. 3A, a first cladding layer 53 and a first optical confinement layer 55 mainly containing an n-type InP-based semiconductor are grown on an n-type InP substrate 51. This growth is performed using, for example, a metal organic chemical vapor deposition furnace. As an example, the first cladding layer 53 is made of n-type InP, and the first optical confinement layer 55 is made of n-type GaInAsP. Next, a semiconductor stack (active layer) 57 for the quantum well structure is formed on the first optical confinement layer 55. The semiconductor stack 57 includes a multiple quantum well structure made of an InP-based semiconductor (for example, GaInAsP), and has a plurality of well layers and barrier layers stacked alternately. Each layer in the semiconductor stack 57 is grown using, for example, a metal organic chemical vapor deposition reactor. As an example, two well layers and three barrier layers are provided. Further, the thickness of the well layer is, for example, 6 [nm], and the thickness of the barrier layer is, for example, 9 [nm]. In one example of the semiconductor stack 57, the multiple quantum well structure is preferably a strain compensation quantum well structure including a compressive strain well layer and a tensile strain barrier layer. Thereby, the non-light-emitting recombination current component at the regrowth interface can be reduced. In this case, it is more preferable that the compressive strain amount of the well layer is 1.0% and the tensile strain amount of the barrier layer is −0.15%.

  Then, a second optical confinement layer 59 mainly including a p-type InP-based semiconductor is grown on the semiconductor stack 57. This growth is performed using, for example, a metal organic chemical vapor deposition furnace. The second optical confinement layer 59 is made of an InP-based semiconductor having a band gap smaller than that of the second cladding layer formed in a later step, and is made of p-type GaInAsP as an example. The layer thickness of the second optical confinement layer 59 is preferably adjusted according to the layer thickness of the semiconductor stack 57, and as described above, there are two well layers having a thickness of 6 [nm] and a thickness of 9 [nm]. When three barrier layers are provided, the thickness of the second optical confinement layer 59 is preferably set to 140 [nm] or less, for example. That is, a thin line region is formed by etching in a later step, and in order to set the etching depth to a predetermined depth or less (for example, 200 [nm] or less), the layer thickness of the second optical confinement layer 59 is The etching depth may be set to be equal to or less than a value obtained by subtracting the layer thickness of the semiconductor stack 57 and the etching depth (for example, 20 [nm]) with respect to the first optical confinement layer 55 from the etching depth.

[Thin wire forming process]
Subsequently, a mask for forming a fine line region is formed on the second optical confinement layer 59. As shown in FIG. 3B, 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 65 is applied on the insulating film 63.

  Subsequently, as illustrated in FIG. 4A, a resist mask 67 is formed by transferring a plurality of periodically arranged patterns to the resist 65. In this step, the resist mask 67 is formed to have a pattern corresponding to the plurality of thin line regions 15 shown in FIG. The resist mask 67 is formed using, for example, an electron beam exposure method or a lithography technique such as nanoimprint.

Subsequently, the insulating film 63 (silicon oxide film) is etched using the resist mask 67. For this etching, for example, reactive ion etching using CF ₄ gas can be used. In this process, in order to secure a selection ratio between the resist mask 67 and the insulating film 63 (silicon oxide film, for example, SiO ₂ ), the thickness of the insulating film 63 is set to 15 to 20 nm in the previous process. It is preferable. When the resist mask 67 is removed after the etching, a plurality of mask patterns 69 for forming fine line regions are formed as shown in FIG. The arrangement period of the mask pattern 69 is set equal to the period Λ of the fine line region 15. That is, the arrangement period of the mask pattern 69 is set according to the wavelength of the laser beam to be output. For example, when the wavelength of the laser beam is 1550 [nm], it is set to 240 [nm]. Is 1300 [nm], it is set to 200 [nm]. The width of the mask pattern 69 is set equal to the thin line width W of the thin line region 15 shown in FIG. That is, the width of the mask pattern 69 is set to, for example, 80 to 90 [nm] for the semiconductor laser element to operate with a smaller current, and in order to obtain a high differential gain when the fine line region has a quantum fine line structure. For example, it is set to 30 [nm] or less.

Subsequently, as shown in FIG. 5A, the second light confinement layer 59 and the semiconductor stacked layer 57 are etched using the mask pattern 69 to form the fine line region 71. 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 to remove the carbon polymer deposited on the semiconductor surface during this etching, a multilayer thin wire region structure with excellent perpendicularity is formed. it can. As a result of this etching, a plurality of fine line regions 71 are arranged on the first optical confinement layer 55. The fine line region 71 includes a second optical confinement layer 59 and a semiconductor stacked layer (active layer) 57. The fine line regions 71 are arranged with the above-described period Λ, and the fine line width of the fine line region 71 is W.

  Thereafter, wet etching is performed to remove a damaged layer caused by dry etching. For this etching, for example, a sulfuric acid-based solution is used. After the wet etching, the mask pattern 69 is removed as shown in FIG. For example, the mask pattern 69 made of silicon oxide is removed using buffered hydrofluoric acid.

[Embedding process]
Subsequently, as illustrated in FIG. 6A, the side surface of the semiconductor stack 57 included in the plurality of thin line regions 71 is embedded with an InP-based compound semiconductor. As an example, this embedding is performed with undoped InP. Further, it is preferable that this embedding is performed until all the side surfaces of the semiconductor stack 57 are embedded and the thickness is such that half of the side surfaces of the second optical confinement layer 59 are embedded. By this embedding process, a periodic structure is formed in which a gain region provided by each thin line region 71 and an intermediate semiconductor region 73 having no gain are alternately arranged in a predetermined direction. In this embedding process, the growth rate of the InP-based compound semiconductor is desirably a low speed of 500 [nm / h] or less in order to uniformly fill the gaps between the thin lines and obtain a flat regrowth interface. The growth temperature of the InP-based compound semiconductor is desirably about 600 [° C.].

In this embedding process, the side surface of the semiconductor stack 57 may be embedded while doping an InP-based compound semiconductor with at least one of Ru and Fe. Thereby, the intermediate semiconductor region 73 that fills the side surface of the semiconductor stack 57 is made semi-insulating, and carriers can be more effectively confined in the semiconductor stack 57. In addition, suitable concentration of Ru or Fe to be doped is, for example, 2 × 10 ¹⁸ [cm ⁻³ ] for Ru and 6 × 10 ¹⁶ [cm ⁻³ ] for Fe.

[Second growth process]
Subsequently, as shown in FIG. 6B, a second cladding layer 75 containing a p-type InP-based compound semiconductor is grown over the thin line region 71 and the intermediate semiconductor region 73. In this step, the second cladding layer 75 is formed so as to embed the second light confinement layer 59 so as to be adjacent to the second light confinement layer 59 included in the thin line region 71. As an example, the second cladding layer 75 is made of p-type InP. In the case where the intermediate semiconductor region 73 and the second cladding layer 75 are made of an InP-based compound semiconductor (for example, InP) having the same composition, the above-described embedding process may be performed with or without doping Fe or Ru. When an InP-based compound semiconductor is grown and embedded to the middle of the second optical confinement layer 59, doping of a p-type dopant (for example, Zn) is started instead of the previous dopant, and then the InP-based compound semiconductor is It is good to grow. And after embedding the thin wire | line area | region 71, it is good to increase the growth rate (for example, 1 [micrometer / h]) and to complete the 2nd clad layer 75. FIG.

  After the second growth step, as shown in FIG. 7, a contact layer 77 made of, for example, p-type GaInAs is grown. The growth rate of the contact layer 77 is a normal growth rate, for example, about 1 [μm / h]. Thereafter, if necessary, a refractive index waveguide structure such as a buried heterostructure may be formed. That is, after forming a semiconductor mesa (for example, width 1.0 [μm]), the side surface of the semiconductor mesa is formed by the first p-type InP current confinement layer, the n-type current confinement layer, and the second p-type InP current confinement layer. Embed. Thereby, the semiconductor laser device having the configuration shown in FIGS. 1 and 2 is completed.

  The effects obtained by the semiconductor laser device 10 according to the present embodiment and the manufacturing method thereof will be described. In the manufacturing method of the semiconductor laser device 10 described above, in the first growth step shown in FIG. 3A, in addition to the semiconductor stack (active layer) 57 that should originally become the thin line region 71, the second light is further emitted. A confinement layer 59 is grown thereon. Then, in the fine line forming step shown in FIGS. 4A, 4B and 5A, the semiconductor stack 57 and the second optical confinement layer 59 are etched to form a plurality of fine line regions 71. Region 71 includes a second optical confinement layer 59. Thereafter, the side surface of the semiconductor stack (active layer) 57 included in the fine line region 71 is buried in the embedding step (FIG. 6A). At this time, the thin deposited layer formed on the fine line region 71 is the second light. A confinement layer 59 is formed. In the second growth step (FIG. 6B), the second cladding layer 75 is formed so as to be adjacent to the second optical confinement layer 59. Therefore, the thin deposited layer described above is the second optical confinement layer. 59 and the second cladding layer 75. That is, no deposition layer is formed between the semiconductor stack (active layer) 57 included in the thin line region 71 and the second optical confinement layer 59. Therefore, the band structure change due to the deposited layer is unlikely to be a hole barrier, and according to the manufacturing method of the semiconductor laser device 10 according to the present embodiment, the light emission efficiency can be improved while using the n-type InP substrate 51.

  In the semiconductor laser device 10 of the present embodiment, each thin line region 15 includes a second optical confinement layer 23 in addition to the active layer 21 as shown in FIG. As described above, when manufacturing such a semiconductor laser device 10, a thin deposited layer formed on the fine line region 15 when the gap of the fine line region 15 is buried is formed on the second optical confinement layer 23. Formed. Since the second cladding layer 29 is provided so as to be adjacent to the second optical confinement layer 23, the above-described thin deposited layer is located between the second optical confinement layer 23 and the second cladding layer 29. It will be. That is, no deposited layer is formed between the active layer 21 included in the thin line region 15 and the second optical confinement layer 23. Therefore, the band structure change due to the deposited layer is unlikely to be a hole barrier, and according to the semiconductor laser device 10 of the present embodiment, the light emission efficiency can be improved while the n-type InP substrate 37 is provided.

  Further, as in the present embodiment, in the semiconductor laser device 10 and the manufacturing method thereof, the second cladding layer 29 (75) is made of p-type InP, and the second optical confinement layer 23 (59) and the active layer 21 (57 ) Has a narrower band gap than that of InP, and the intermediate semiconductor region 17 (73) buried between the thin line regions 15 (71) is preferably made of undoped InP. When the band gap of the active layer 21 (57) and the second optical confinement layer 23 (59) is narrower than the band gap of InP and the intermediate semiconductor region 17 (73) is made of undoped InP, the conventional complex shown in FIG. In the coupled DFB laser element, the barrier action due to the InP deposited layer becomes significant (see FIG. 15). On the other hand, in this embodiment, the InP deposition layer is formed between the second optical confinement layer 23 (59) and the second cladding layer 29 (75), so that the same composition layer (i-type InP) and The second cladding layer (p-type InP) is in contact with each other, and the deposited layer is unlikely to be a barrier against holes. Therefore, the luminous efficiency can be further improved.

(Second Embodiment)
FIG. 8 is a side sectional view showing a second embodiment of the semiconductor laser device and the method for producing the same according to the present invention. FIG. 8 shows a cross section corresponding to FIG. 2 of the first embodiment. The difference between the semiconductor laser device 20 according to the present embodiment and the semiconductor laser device 10 of the first embodiment is that the intermediate semiconductor region 17 is doped with Fe, and the intermediate semiconductor region 17 and the second cladding layer 29 are different from each other. An offset layer 41 made of an undoped InP-based compound semiconductor is provided therebetween. As an example, the offset layer 41 is made of undoped InP. The layer thickness of the offset layer 41 is, for example, 50 [nm]. The offset layer 41 is formed, for example, so as to bury the side surface of the second light confinement layer 23 halfway.

  A method for producing the semiconductor laser device 20 of the present embodiment is as follows. That is, after finishing the first growth step and the fine line forming step in the first embodiment (the state of FIG. 5B), an InP-based compound semiconductor (for example, InP) is doped in the gap between the fine line regions 15 while doping Fe. The intermediate semiconductor region 17 is formed by growing. Then, after growing the intermediate semiconductor region 17 to a thickness that covers the side surface of the active layer 21, the doping of Fe is stopped and the growth of the InP-based compound semiconductor is continued, thereby forming the offset layer 41. At this time, the offset layer 41 may be grown to a thickness that covers about half of the side surface of the second optical confinement layer 23. Thereafter, doping of a p-type dopant (for example, Zn) is started, and the second cladding layer 29 is formed by subsequently growing the InP-based compound semiconductor.

  When the intermediate semiconductor region 17 that embeds the side surface of the active layer 21 is doped with Fe, the inter-diffusion of Zn and Fe, which are p-type dopants included in the second cladding layer 29, causes the intermediate semiconductor region 17 in the layer thickness direction. A resistance distribution occurs, and a distribution also occurs in the density of carriers injected into the active layer 21. In such a case, by providing an undoped InP-based compound semiconductor layer (offset layer 41) between the intermediate semiconductor region 17 and the second cladding layer 29 as in the present embodiment, it is preferable to achieve mutual diffusion of Zn and Fe. Can be suppressed.

(Third embodiment)
Next, a third embodiment relating to a method for producing a semiconductor laser device according to the present invention will be described. Consider a case where the number of active layers 21 is large as shown in FIG. In such a case, the gap between the thin line regions 15 becomes deep and it is necessary to form the intermediate semiconductor region 17 thick. However, if the thickness of the intermediate semiconductor region 17 is larger than a certain level (for example, 200 [nm]), Voids V are likely to be generated inside the intermediate semiconductor region 17.

  Therefore, in the manufacturing method of the present embodiment, as shown in FIG. 10, the first cladding layer (n-type InP) 53 and the first optical confinement layer (n-type) are formed on the n-type InP substrate 51 in the first growth step. After growing the GaInAsP) 55, the active layer (GaInAsP) 57, and the second optical confinement layer (p-type GaInAsP) 59, the p-type InP layer 61 is further grown on the second optical confinement layer 59. The layer thickness of the p-type InP layer 61 is, for example, 30 [nm]. Then, in the fine line forming step, the p-type InP layer 61, the second optical confinement layer 59, and the active layer 57 are etched to form a plurality of fine line regions 43 (FIG. 11). Accordingly, the thin line region 43 includes the p-type InP layer 61 in addition to the active layer 57 and the second optical confinement layer 59.

In the embedding step, the intermediate semiconductor region 73 is formed by embedding the gap between the thin wire regions 43 to the middle of the second optical confinement layer 23 with undoped (which may be Fe-doped or Ru-doped) InP (FIG. 12). . At this time, when InP is grown in the PH ₃ atmosphere, InP moves (mass transport) from the p-type InP layer 61 to the gap between the thin line regions 43. Thereby, for example, even when the gap between the thin line regions 43 is narrow and deep, deterioration of the crystallinity (such as generation of voids) of the embedded InP can be suppressed. Further, the side surface of the active layer 57 can be protected by an InP mass transport. In addition, the process after the 2nd growth process in this embodiment is the same as that of 1st Embodiment.

  The method for manufacturing a semiconductor laser device and the semiconductor laser device according to the present invention are not limited to the above-described embodiments, and various other modifications are possible. For example, in the above-described embodiment, InP is exemplified as the InP-based compound semiconductor constituting the first cladding layer, the second cladding layer, and the intermediate semiconductor region, but these layers are configured by various compositions including In and P. Can. In the above embodiment, GaInAsP is exemplified as the InP-based compound semiconductor constituting the first optical confinement layer, the second optical confinement layer, and the active layer. However, these layers also have various compositions including In and P. Can be configured.

FIG. 1 is a partially cutaway perspective view showing the structure of the semiconductor laser device according to the first embodiment of the present invention. FIG. 2 is an enlarged side sectional view showing a part of FIG. FIG. 3A is a diagram showing a first growth step in the method for producing a semiconductor laser element. FIG. 3B is a diagram showing a thin line forming step in the method of manufacturing the semiconductor laser element. FIG. 4A and FIG. 4B are diagrams showing a thin line forming step in the method of manufacturing the semiconductor laser element. FIG. 5A and FIG. 5B are diagrams showing a thin line forming step in a method of manufacturing a semiconductor laser element. FIG. 6A is a diagram showing an embedding process in the method for manufacturing the semiconductor laser device. FIG. 6B is a diagram showing a second growth step in the method for manufacturing the semiconductor laser element. FIG. 7 is a diagram showing a subsequent process of the second growth process in the method of manufacturing the semiconductor laser element. FIG. 8 is a side sectional view showing a second embodiment of the semiconductor laser device and the method for producing the same according to the present invention. FIG. 9 is a diagram showing a case where the number of active layers in the semiconductor laser device is large. FIG. 10 is a diagram showing a first growth step in the third embodiment of the method for manufacturing a semiconductor laser device. FIG. 11 is a diagram showing a thin line forming step in the third embodiment of the method for manufacturing a semiconductor laser device. FIG. 12 is a diagram showing an embedding process in the third embodiment of the method for manufacturing a semiconductor laser device. FIG. 13 is a cross-sectional view showing the structure of a conventional complex coupled DFB laser device. FIG. 14 is a diagram showing a band structure in the complex coupled DFB laser device shown in FIG. FIG. 15 is a diagram showing a band structure in the case where a conventional complex coupled DFB laser element is formed on an n-type InP substrate.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 10,20 ... Semiconductor laser element, 13, 55 ... 1st optical confinement layer, 15, 43, 71 ... Thin wire | line area | region, 17, 73 ... Intermediate semiconductor region, 21 ... Active layer, 23, 59 ... 2nd optical confinement layer, 25 ... Semiconductor mesa, 27, 53 ... First cladding layer, 29, 75 ... Second cladding layer, 31 ... Buried region, 33 ... Insulating film, 35 ... First electrode film, 37, 51 ... n-type InP substrate, 39 ... Second electrode film, 41 ... Offset layer, 57 ... Semiconductor stack (active layer), 61 ... p-type InP layer, 63 ... insulating film, 65 ... resist, 67 ... resist mask, 69 ... mask pattern, 77 ... Contact layer.

Claims (5)

A method for producing a semiconductor laser device, comprising:
A first cladding layer and a first optical confinement layer containing an n-type InP-based compound semiconductor, an active layer including an InP-based compound semiconductor, and a second optical confinement layer including a p-type InP-based compound semiconductor on an n-type InP substrate. grown, a first growth step of Ru and further growing a p-type InP layer on said second optical confinement layer,
By using a mask having a plurality of mask patterns are periodically arranged in the p-type InP layer, until said first optical confinement layer is exposed, the p-type InP layer, said second optical confinement layer and the active A thin wire forming step of forming a plurality of periodically arranged thin wire regions by etching the layer;
A step of embedding a side surface of the active layer included in the plurality of thin line regions with an InP-based compound semiconductor;
A second growth step of growing a second cladding layer containing a p-type InP-based compound semiconductor so as to be adjacent to the second optical confinement layer included in the plurality of thin line regions ,
During the embedding step, the gap between the thin line regions is embedded to the middle of the second optical confinement layer by embedding growth of the InP-based compound semiconductor, and the p-type InP layer is embedded during the embedding growth. A method for manufacturing a semiconductor laser device, wherein mass transport is performed to a gap in the thin line region . The second cladding layer is made of p-type InP;
The second optical confinement layer and the active layer have a narrower band gap than that of InP;
2. The method for manufacturing a semiconductor laser device according to claim 1, wherein the InP-based compound semiconductor in the embedding step is made of undoped InP.   2. The method of manufacturing a semiconductor laser device according to claim 1, wherein in the embedding step, Ru is doped into the InP-based compound semiconductor that embeds a side surface of the active layer. 3.   2. The method of manufacturing a semiconductor laser device according to claim 1, wherein, in the embedding step, Fe is doped into the InP-based compound semiconductor that embeds a side surface of the active layer. 3. 5. The method of manufacturing a semiconductor laser device according to claim 4 , wherein an undoped InP-based compound semiconductor is further grown on the InP-based compound semiconductor doped with Fe.

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