Patent Publication Number: US-2021184428-A1

Title: Semiconductor laser element

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     The present application claims priority from Japanese Application JP2019-224740, the content of which is hereby incorporated by reference into this application. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     One aspect of the disclosure relates to a semiconductor laser element. 
     2. Description of the Related Art 
     In recent years, the use of blue laser light or green laser light emitted from a nitride-based semiconductor has been attracting attention for next generation applications such as directional lights, projectors, or televisions. Since the visibility of laser light is required in these applications, high radiation quality of the laser light is required. However, since a substrate for a normal nitride-based semiconductor is transparent, stray light from an active layer leaks from the substrate. 
     A semiconductor laser element  500  disclosed in JP 2018-195749 A, for example, is provided as a semiconductor laser element in which stray light leaking from a substrate is reduced.  FIG. 24  is a perspective view of the semiconductor laser element  500  of JP 2018-195749 A. As illustrated in FIG.  24 , in the semiconductor laser element  500  disclosed in JP 2018-195749 A, a semiconductor layered film  510  is layered on an upper surface of a substrate  502 , and a waveguide  531  is formed by the semiconductor layered film  510 . Further, grooves  543  extending in a direction intersecting the waveguide  531  are provided in a lower surface of the substrate  502 , and this can reduce stray light leaking from the substrate  502 . 
     SUMMARY OF THE INVENTION 
     One aspect of the disclosure is to reduce stray light leaking from a substrate and reduce the possibility of element cracking of a semiconductor laser element. 
     To solve the above problem, a semiconductor laser element according to one aspect of the disclosure is a semiconductor laser element configured to emit laser light and includes a substrate and a semiconductor layer provided on the substrate. The semiconductor layer includes a waveguide extending in a predetermined direction and configured to emit the laser light from one end face of the waveguide, the substrate includes a plurality of cavity sections intersecting the predetermined direction and extending, the plurality of cavity sections are provided in the substrate such that at least parts of at least two cavity sections of the plurality of cavity sections overlap with each other along the predetermined direction, and a length of each of the plurality of cavity sections in a direction perpendicular to the predetermined direction is shorter than a length of the semiconductor laser element in the perpendicular direction. 
     According to one aspect of the disclosure, the stray light leaking from the substrate can be reduced, and the possibility of the element cracking of the semiconductor laser element can be reduced. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a perspective view illustrating a configuration of a semiconductor laser element according to a first embodiment of the disclosure. 
         FIG. 2  is a front view illustrating a layered structure of an active layer of the semiconductor laser element according to the first embodiment of the disclosure. 
         FIG. 3  is a schematic cross-sectional view when a cavity section of the semiconductor laser element according to the first embodiment of the disclosure is cut along a plane perpendicular to a bottom surface of the semiconductor laser element in a Y direction. 
       In  FIG. 4 , a reference numeral  401  indicates a top view of the semiconductor laser element according to the first embodiment of the disclosure, and a reference numeral  402  indicates a diagram illustrating another example of the cavity section. 
         FIG. 5  is a schematic perspective view illustrating a structure of a plurality of cavity sections of the semiconductor laser element according to the first embodiment of the disclosure. 
         FIG. 6  is a schematic front view illustrating a structure when the cavity section of the semiconductor laser element according to the first embodiment of the disclosure is viewed from an emission surface. 
         FIG. 7  is a flowchart illustrating an example of a manufacturing process of the semiconductor laser element according to the first embodiment of the disclosure. 
         FIG. 8  is a bottom view illustrating a chip dividing groove forming step in a wafer according to the first embodiment of the disclosure. 
         FIG. 9  is a bottom view illustrating a cavity section forming step in the wafer according to the first embodiment of the disclosure. 
         FIG. 10  is a top view illustrating a bar dividing groove forming step in the wafer according to the first embodiment of the disclosure. 
         FIG. 11  is a perspective view illustrating an end face coating film forming step in a bar according to the first embodiment of the disclosure. 
         FIG. 12  is a diagram illustrating a forming pattern of cavity sections of a semiconductor laser element according to a second embodiment of the disclosure. 
         FIG. 13  is a diagram illustrating a forming pattern of cavity sections of a semiconductor laser element according to a third embodiment of the disclosure. 
         FIG. 14  is a diagram illustrating a forming pattern of cavity sections of a semiconductor laser element according to a fourth embodiment of the disclosure. 
         FIG. 15  is a diagram illustrating a forming pattern of cavity sections of a semiconductor laser element according to a fifth embodiment of the disclosure. 
         FIG. 16  is a diagram illustrating a forming pattern of cavity sections of a semiconductor laser element according to a sixth embodiment of the disclosure. 
         FIG. 17  is a diagram illustrating a forming pattern of cavity sections of a semiconductor laser element according to a seventh embodiment of the disclosure. 
         FIG. 18  is a diagram illustrating a forming pattern of cavity sections of a semiconductor laser element according to an eighth embodiment of the disclosure. 
         FIG. 19  is a diagram illustrating a forming pattern of cavity sections of a semiconductor laser element according to a ninth embodiment of the disclosure. 
         FIG. 20  is a diagram illustrating test results for comparative examples. 
         FIG. 21  is a diagram illustrating test results for semiconductor laser elements according to one aspect of the disclosure. 
         FIG. 22  is a schematic front view illustrating a structure of a cavity section of a semiconductor laser element according to a tenth embodiment of the disclosure when viewed from an emission surface. 
         FIG. 23  is a schematic perspective view illustrating a structure of a plurality of cavity sections of the semiconductor laser element according to the tenth embodiment of the disclosure. 
         FIG. 24  is a perspective view of a semiconductor laser element of JP 2018-195749 A. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     First Embodiment 
     An embodiment of the disclosure will be described in detail below. 
     Configuration of Nitride Semiconductor Laser Element 
     A case in which a semiconductor laser element  100  is a nitride semiconductor laser element is described herein as an example. 
       FIG. 1  is a perspective view illustrating a configuration of the semiconductor laser element  100  according to a first embodiment.  FIG. 2  is a front view illustrating a layered structure of an active layer  14  of the semiconductor laser element  100  according to the first embodiment.  FIG. 3  is a schematic cross-sectional view when a cavity section  43  of the semiconductor laser element  100  according to the first embodiment is cut along a plane perpendicular to a bottom surface of the semiconductor laser element  100  in a Y direction. A reference numeral  401  in  FIG. 4  indicates a top view of the semiconductor laser element  100  according to the first embodiment. A reference numeral  402  in  FIG. 4  indicates a cavity section  43 ′, in a case in which a recessed and protruding portion is provided on a side surface of the cavity section  43  of the semiconductor laser element indicated by the reference numeral  401  in  FIG. 4 .  FIG. 5  is a schematic perspective view illustrating a structure of a plurality of cavity sections  43  of the semiconductor laser element  100  according to the first embodiment.  FIG. 6  is a schematic front view illustrating a structure when the cavity section  43  of the semiconductor laser element  100  according to the first embodiment is viewed from an emission surface  1 A. 
     Note that  FIG. 1  is a diagram schematically illustrating the configuration of the semiconductor laser element  100  according to the present embodiment, and does not limit the number of each member constituting the semiconductor laser element  100  and the dimensions of the members. Additionally, in coordinate axes illustrated in  FIG. 1 , a Z axis positive direction side is defined as “upper”, and a surface of each member on the positive Z direction side is referred to as an “upper surface”. This also applies to other drawings. “A to B” used herein indicates “A or greater and B or less”. 
     As illustrated in  FIG. 1 , the semiconductor laser element  100  includes a substrate  2 , a semiconductor layer  10 , a buried layer  21 , a p-side lower layer electrode  22 , a p-side upper layer electrode  23 , and a ridge portion  30 . As illustrated in  FIG. 1 , the semiconductor laser element  100  further includes an n-side electrode  24  on a lower side surface of the substrate  2 , and a pad electrode  25  on a lower side surface of the n-side electrode  24 . 
     In a case where voltage is applied between the p-side upper layer electrode  23  and the n-side electrode  24 , the semiconductor layer  10  emits laser light. The semiconductor layer  10  is a semiconductor layered structure that is epitaxially grown on an upper surface of the substrate  2 . The semiconductor layer  10  includes an underlayer  11 , a lower cladding layer  12 , a lower guide layer  13 , an active layer  14 , an upper guide layer  15 , an evaporation preventing layer  16 , an upper cladding layer  17 , and an upper contact layer  18  in this order from the substrate  2 . 
     The substrate  2  is a conductive nitride semiconductor substrate, and is made of, for example, GaN. 
     The underlayer  11  is a layer provided to reduce stress or scratches received on the substrate  2  when the substrate  2  is surface-processed. In a case where the underlayer  11  is layered on the substrate  2 , the surface of the substrate  2  can be flattened. The underlayer  11  is a layer that facilitates application of current or voltage from the n-side electrode  24  to the active layer  14 . The underlayer  11  is a layer formed of n-type GaN and has a film thickness from 0.1 to 10 μm (for example, 4 μm). 
     The lower cladding layer  12  is a layer that confines current and light generated in the active layer  14 . The lower cladding layer  12  is formed of n-type Al 1 Ga 1-x1 N (0&lt;x1&lt;1) and has a film thickness from 0.5 to 3.0 μm (for example, 2 μm). 
     The lower guide layer  13  is a layer that facilitates propagation of light in the active layer  14 . The lower guide layer  13  is formed of In x4 Ga 1-4x N (0≤x2&lt;0.1) and has a film thickness of 0.3 μm or less (for example, 0.1 μm). An n-type lower guide layer  13  in which Si or the like is doped is also possible. 
     The active layer  14  is an active portion that has optical amplification action by stimulated emission. As illustrated in  FIG. 2 , the active layer  14  has a multi quantum well (MQW) structure in which, for example, four barrier layers  14 A and three quantum well layers  14 B are alternately layered. The quantum well layer  14 B is formed of, for example, In x3 Ga 1-x3 N having a film thickness of 4 nm. The barrier layer  14 A is formed of, for example, In x4 Ga 1-4x N (where x3&gt;x4) having a film thickness of 8 nm. x3 and x4 can be x3=0.05 to 0.35 and x4=0 to 0.1, for example. 
     The upper guide layer  15  is a layer that facilitates propagation of light in the active layer  14 . The upper guide layer  15  is formed of In y2 Ga 1-y2 N (0≤y2&lt;0.1) and has a film thickness of 0.3 μm or less (for example, 0.1 μm). A p-type upper guide layer  15  in which Mg or the like is doped is also possible. 
     The evaporation preventing layer  16  is a layer that prevents In in a nitride semiconductor containing In from evaporating. The evaporation preventing layer  16  is a layer formed of p-type Al y1 Ga 1-y1 N (0&lt;y1&lt;1) and has a film thickness of 0.02 μm or less (for example 0.01 μm). 
     The upper cladding layer  17  is a layer that confines current and light generated in the active layer  14 . The upper cladding layer  17  is a layer formed of p-type Al y3 Ga 1-y3 N (0&lt;y3&lt;1). The upper cladding layer  17  has a film thickness from 0.01 to 1 μm (for example, 0.5 μm). 
     The ridge portion  30  limits an area in which current flows along the Y direction and causes laser oscillation in an area of the active layer  14  corresponding to the area. The area where the laser oscillation occurs in the active layer  14  functions as a waveguide  31 . For example, a protruding portion formed by etching a part of the upper cladding layer  17  to an intermediate position in a thickness direction (Z direction) by a photolithography technique functions as the ridge portion  30 . As illustrated in  FIG. 1 , the ridge portion  30  is formed so as to extend in the Y direction. Note that a method for forming the ridge portion  30  is described in more detail in the following manufacturing method. 
     The upper contact layer  18  is a layer that facilitates application of current or voltage to the active layer  14 . The upper contact layer  18  is provided on the protruding portion of the upper cladding layer  17  that forms the ridge portion  30 . The upper contact layer is formed of p-type GaN and has a film thickness from 0.01 to 1 μm (for example, 0.05 μm). 
     The buried layer  21  is a layer that functions as a current constriction layer. The buried layer  21  is formed of an insulating material such as SiO 2  and has a film thickness from 0.1 to 0.3 μm (for example, 0.15 μm). As illustrated in  FIG. 1 , light may be confined in the ridge portion  30  in an operation mode by covering both side surfaces of the ridge portion  30  with the buried layer  21 . 
     The p-side lower layer electrode  22  is a conductive layer having Pd or Ni as a main component. The p-side lower layer electrode  22  is in ohmic contact with the upper contact layer  18 . 
     The p-side upper layer electrode  23  is an electrode for injecting a carrier from the upper surface of the ridge portion  30 . The p-side upper layer electrode  23  is formed on the upper surface of the ridge portion  30  (on the upper contact layer  18  and the buried layer  21  of the ridge portion  30 ). The p-side upper layer electrode  23  is an example of a metal layer formed of Au, for example. 
     The n-side electrode  24  is an electrode for injecting a carrier from below the substrate  2 . The n-side electrode  24  is in ohmic contact with the substrate  2 . The n-side electrode  24  is formed, for example, of a single layer of Ti or a Ti/Al multilayer body in which Ti is layered and Al is further layered thereon. 
     The pad electrode  25  is a layer for easily connecting and fixing the semiconductor laser element  100  to a submount or the like. The pad electrode  25  is formed of, for example, Au. 
     Additionally, an end face coating film  26  (see  FIG. 11 ; the end face coating film  26  of  FIG. 11  is formed so as to cover end faces of the substrate  2 , end faces of the semiconductor layered film  10 , and end faces of the ridge portion  30 ) is provided on the emission surface  1 A and an opposing surface  1 B (see  FIG. 4 ) of the semiconductor laser element  100 . The end face coating film  26  on the emission surface  1 A is formed of a low reflective film such as Al 2 O 3 . The end face coating film  26  on the opposing surface  1 B is formed of a highly reflective film in which Al 2 O 3  and Ta 2 O 5  are alternately layered (for example, nine layers). The waveguide  31  extending in the Y direction constitutes a resonator with the end face coating films  26  on the emission surface  1 A and the opposing surface  1 B. This allows laser light to be emitted from an emitting portion  31 A, which is one end face of the waveguide  31 , in a case where current is injected from the p-side upper layer electrode  23  into the active layer  14  via the ridge portion  30 . In other words, the semiconductor layer  10  includes the waveguide  31  that extends in the Y direction and emits laser light from the emitting portion  31 A. 
     Further, as illustrated in  FIGS. 4 and 5 , a plurality of cavity sections  43  are provided in the lower surface of the substrate  2 . The substrate  2  of the semiconductor laser element  100  is usually made of a transparent material. Thus, laser light generated in the active layer  14  may not only be emitted from the emitting portion  31 A, which is the one end face of the waveguide  31 , but also leak from the substrate  2  as stray light. The cavity section  43  provided in the substrate  2  is configured to reduce an amount of stray light leaking from the substrate  2  by utilizing a change in a reflective index or the like. The detailed configuration and effect of the cavity section  43  will be described in detail below. 
     Cavity Section 
     As illustrated in  FIGS. 4 and 5 , in the semiconductor laser element  100  according to the first embodiment, three cavity sections  43  having a groove structure are formed at different distances from the emission surface  1 A. Further, the cavity sections  43  overlap with each other along the Y direction and each extend so as to intersect the waveguide  31 . The cavity section  43  is formed in the lower surface of the substrate  2  by, for example, laser scribing. As illustrated in  FIG. 6 , the cavity section  43  has a length W A  in the X direction perpendicular to the Y direction and a height H A  in a thickness direction of the substrate of the semiconductor laser element  100  (Z direction). For the three cavity sections  43 , the length W A  of each cavity section  43  is shorter than a length W of the semiconductor laser element  100  in the X direction. 
     Further, in the present embodiment, the length W A  of the cavity section  43  in the X direction is preferably long in order to shield stray light and reduce laser light leaking from the substrate  2 . On the other hand, when the cavity section  43  reaches both ends of the semiconductor laser element  100  in the X direction, the possibility of element cracking increases. Thus, the length W A  of the cavity section  43  in the X direction is preferably from 30% to 80%, more preferably from 50% to 70% of the length W of the semiconductor laser element  100  in the X direction. 
     In the example of  FIGS. 4 and 5 , the three cavity sections  43  have substantially the same shape. In other words, the length W A  and the height H A  of the three cavity sections  43  are substantially the same. Specifically, each of the three cavity sections  43  extends substantially linearly when viewed from the upper surface side of the substrate  2 , and has a substantially trapezoidal shape when viewed from the emission surface  1 A side. In this example, in the X direction, one cavity section  43  is disposed inside the substrate  2  (for example, substantially in a center) and one end portions of two cavity sections  43  are exposed on the side surface of the substrate  2 . Specifically, one end portion of one cavity section  43  of the two cavity sections  43  is in contact with one side surface of the substrate  2  (exposed on the side surface), and one end portion of another cavity section  43  is in contact with another side surface of the substrate  2 . In other words, at least one end portion of each of the three cavity sections  43  is not in contact with the side surface of the substrate  2 . Additionally, the three cavity sections  43  are disposed at different distances from the emission surface  1 A, and at least parts of the three cavity sections  43  overlap with each other across the entire X direction of the substrate  2  in the Y direction when viewed from the emission surface  1 A side. In this example, the cavity section  43  disposed inside in the X direction and each of the two other cavity sections  43  overlap with each other in the Y direction. 
     Note that  FIG. 5  is a schematic view for illustrating an arrangement of a plurality of cavity sections  43 , and a width (length in the Y direction) of the cavity section  43  is ignored in the drawing. The width of the cavity section  43  is not particularly limited to a specific width, but any width of the cavity section  43  can be obtained by changing a frequency and a sweeping velocity of laser when the cavity section  43  is formed by laser scribing. 
     Note that the number of cavity sections  43  provided in the semiconductor laser element  100  is not limited to three, and may be two or more. Further, it is not always necessary that all the plurality of cavity sections  43  overlap with each other along the Y direction. It is sufficient that at least two cavity sections  43  overlap, and at least parts of the two cavity sections  43  may overlap. In addition, the cavity section  43  may extend in a direction not orthogonal to the waveguide  31  as long as the cavity section  43  extends in a direction intersecting the waveguide  31 , or need not extend intersecting the waveguide  31 . Further, in the first embodiment, as illustrated in  FIG. 3 , the cavity section  43  is illustrated in a shape of a groove including an opening on the lower surface of the substrate  2 . However, the shape of the cavity section  43  is not limited to the shape of the groove, and the cavity section having a light-shielding function may be formed in a direction intersecting the waveguide  31 . In other words, it is not always necessary that all the cavity sections  43  be implemented as grooves. Furthermore, the plurality of cavity sections  43  need not have the same shape as each other, and do not necessarily have the shape illustrated in  FIGS. 4 and 5  and are not necessarily formed with the arrangement pattern illustrated in  FIGS. 4 and 5 . Examples of a plurality of cavity sections having shapes different from that of the first embodiment, and examples of a plurality of cavity sections formed with arrangement patterns different from that of the first embodiment will be described in other embodiments described below. 
     Method for Manufacturing Semiconductor Laser Element  100   
     Hereinafter, a manufacturing process of the semiconductor laser element  100  according to the present embodiment will be described with reference to  FIGS. 7 to 11 . In the following description, a wafer-shaped intermediate in the middle of the process may be simply referred to as a wafer  50 . Also, a bar-shaped intermediate obtained by dividing the wafer  50  in the middle of the process may be simply referred to as a bar  51 .  FIG. 7  is a flowchart illustrating an example of a manufacturing process of the semiconductor laser element  100  according to the present embodiment.  FIG. 8  is a bottom view illustrating a step of forming a chip dividing groove  42  in the wafer  50  according to the present embodiment.  FIG. 9  is a bottom view illustrating a step of forming the cavity section  43  in the wafer  50  according to the present embodiment.  FIG. 10  is a top view illustrating a step of forming a bar dividing groove  41  in the wafer  50  according to the present embodiment.  FIG. 11  is a perspective view illustrating a step of forming the end face coating film  26  in the bar  51  according to the present embodiment. 
     As illustrated in  FIG. 7 , a method for manufacturing the semiconductor laser element  100  according to the present embodiment includes steps S 1  to S 15 . In the present embodiment, the semiconductor laser element  100  is manufactured in this order as an example. However, the present embodiment is not limited to the manufacturing steps described above as long as the semiconductor laser element  100  having the layered structure illustrated in  FIG. 1  can be manufactured. The above steps will be described below. 
     In step S 1  illustrated in  FIG. 7 , the semiconductor layer  10  is epitaxially grown on the upper surface of the substrate  2  (epitaxial growth step). The epitaxial growth is performed by, for example, a metal organic chemical vapor deposition (MOCVD) method or the like. 
     In other words, the underlayer  11 , the lower cladding layer  12 , and the lower guide layer  13  are sequentially grown on the upper surface of the substrate  2 . Next, the four barrier layers  14 A and the three quantum well layers  14 B (see  FIG. 3 ) are alternately grown on the upper surface of the lower guide layer  13  to obtain the active layer  14 . Subsequently, the upper guide layer  15 , the evaporation preventing layer  16 , the upper cladding layer  17 , and the upper contact layer  18  are sequentially grown on the active layer  14 . 
     When forming the semiconductor layer  10  using the MOCVD method, trimethylgallium, ammonia, trimethylaluminum, trimethylindium, silane, or bis-cyclopentadienyl magnesium can be used as a raw material. Further, hydrogen or nitrogen can be used as a carrier gas. 
     Subsequently, in step S 2 , the p-side lower layer electrode  22  is formed on the upper contact layer  18  of the wafer  50  by vacuum vapor deposition, sputtering, or the like (p-side lower layer electrode forming step). 
     Subsequently, in step S 3 , the ridge portion  30  is formed (ridge portion forming step). Specifically, a resist (not illustrated) is formed by photolithography in an area where the ridge portion  30  on the p-side lower layer electrode  22  of the wafer  50  is to be formed. The resist is formed in a band shape extending in the Y direction. Next, reactive ion etching (RIE) is performed using SiCl 4  gas, Cl 2  gas, Ar gas, or the like to etch a portion where the resist is not formed. As a result, the ridge portion  30  including the protruding portion at the upper end portion of the upper cladding layer  17 , the upper contact layer  18 , and the p-side lower layer electrode  22  is formed. By forming the ridge portion  30 , the waveguide  31  (see  FIG. 1 ) extending in the Y direction is obtained below the ridge portion  30 . 
     Note that etching in the ridge portion forming step may be performed by dry etching such as the above RIE or wet etching. 
     Alternatively, a mask layer of, for example, SiO 2  may be provided in the forming area of the ridge portion  30  instead of the resist. In this case, a resist is provided in an area where the ridge portion  30  is not formed by photolithography, and after film formation of SiO 2 , the resist and SiO 2  on the resist are removed to form a mask layer. The mask layer can be removed using, for example, an etchant such as buffered hydrogen fluoride (BHF). 
     Subsequently, in step S 4 , the buried layer  21  made of SiO 2  or the like is formed on the upper surface of the resist, both side walls of the ridge portion  30 , and the upper cladding layer  17  by sputtering or the like. Thereafter, the buried layer  21  on the resist is removed together with the resist, and the p-side lower layer electrode  22  is exposed (buried layer forming step). 
     Subsequently, in step S 5 , the p-side upper layer electrode  23  is formed on the upper surface of the p-side lower layer electrode  22  disposed on the ridge portion  30  and the buried layer  21  by vacuum vapor deposition, sputtering, or the like (p-side upper layer electrode forming step). Note that, as illustrated in  FIG. 8 , a plurality of p-side upper layer electrodes  23  are provided in a patterned manner according to the layout of the semiconductor laser element  100  to be formed in a chip shape by dividing the wafer  50 . 
     Subsequently, in step S 6 , the lower surface of the substrate  2  is polished so that a thickness of the substrate  2  is from 80 to 150 μm (for example 130 μm) (polishing step). This allows the wafer  50  and the bar  51  (see  FIG. 11 ) to be easily divided in a first cutting step and a second cutting step described below. Note that the substrate  2  may be physically polished with an abrasive or may be chemically polished with a chemical. 
     Subsequently, in step S 7 , a plurality of chip dividing grooves  42  are formed in the lower surface of the substrate  2  of the wafer  50  by, for example, laser scribing (chip dividing groove forming step) (see  FIG. 8 ). The chip dividing groove  42  extends in the Y direction and is disposed between the ridge portions  30 . 
     After dividing the wafer  50  into a plurality of bars  51  in the first cutting step described below, the chip dividing groove  42  is used to dice the bars  51  into chips in the second cutting step. Therefore, the chip dividing groove  42  is disposed at a position based on the ridge portion  30 , such as a center between the ridge portions  30 , for example. This allows desired chips to be obtained with a good yield when the bar  51  is divided into the chips. 
     The chip dividing groove  42  is more preferably formed at a depth from approximately 5 to 60 μm from the lower surface of the substrate  2 . This makes it possible to remove the possibility in that the bar cannot be divided into chips because the chip dividing groove  42  is too shallow, or to prevent the wafer  50  from being damaged during handling because the chip dividing groove  42  is too deep. Additionally, the chip dividing groove  42  is formed in a straight line extending between both end faces of the wafer  50  in the Y direction. This can reduce the possibility in that when dividing the bar  51  into the chip shaped semiconductor laser elements  100 , the bar  51  cracks in an unintended direction. 
     Subsequently, in step S 8 , a plurality of cavity sections  43  are formed in the lower surface of the substrate  2  of the wafer  50  by, for example, laser scribing (cavity section forming step) (see  FIG. 9 ). The cavity sections  43  extend so as to intersect the ridge portion  30 , and are provided in plurality corresponding to the respective semiconductor laser elements  100  that are to be diced into chips. Further, the plurality of cavity sections  43  are provided so as to overlap with each other in the Y direction in each semiconductor laser element  100 . As described above, the plurality of cavity sections  43  need not intersect the ridge portion  30 , and may be provided so as to intersect the Y direction. Further, it is sufficient that at least parts of at least two cavity sections  43  of the plurality of cavity sections  43  may be provided so as to overlap with each other in the Y direction. 
     In the semiconductor laser element  100 , in a case where the height H A  of the cavity section  43  is one tenth or greater of the thickness H of the substrate  2 , approximately 10% of stray light can be shielded. Further, in a case where the height H A  of the cavity section  43  is one third or greater of the thickness H of the substrate  2 , 30% or greater of stray light can be shielded. On the other hand, in a case where the height H A  of the cavity section  43  is greater than the thickness H of the substrate  2 , the substrate  2  is divided and the strength of the semiconductor laser element  100  is significantly reduced. Therefore, the height H A  of the cavity section  43  is less than the thickness H of the substrate  2 . In other words, the height H A  of the cavity section  43  is preferably less than the thickness H of the substrate  2  and is one tenth or greater, and the height H A  of the cavity section  43  is more preferably one third or greater of the thickness H of the substrate  2 . 
     In addition, in a case where the cavity section  43  is formed by laser scribing, a coating film  27  (see  FIG. 3 ) containing a metal and/or a metal oxide is formed on an inner wall of the cavity section  43  by using a laser having a pulse width on the order of nanoseconds. Ga is an example of the metal contained in the coating film  27 . Further, Ga 2 O 3  is an example of the metal oxide contained in the coating film  27 . In the present embodiment, the n-side electrode  24  and the pad electrode  25  are formed after the cavity section  43  is formed, but the cavity section  43  may be formed by laser scribing after the n-side electrode  24  and the pad electrode  25  are formed. In this case, the coating film  27  contains a metal such as Ti or Au, and/or a metal oxide such as Ga 2 O 3  or Ti 2 . 
     Further, by changing a sweep speed of a laser pulse having a pulse width on the order of nanoseconds at a repetition frequency of several tens of kHz, the width of the cavity section  43  can be changed periodically. As a result, a recessed and protruding portion (recessed portion  45  and protruding portion  46 ) having a periodic wavy shape can be formed in a longitudinal direction (Y direction) on a side wall of the cavity section  43 . The cavity section  43 ′ in which the side wall of the cavity section  43  is provided with the recessed and protruding portion is indicated by a reference numeral  402  in  FIG. 4 . Instead of the recessed and protruding portion, one or more recessed portions  45  or one or more protruding portions  46  may be formed on the side wall of the cavity section  43 . 
     Subsequently, in step S 9 , debris generated by forming the chip dividing groove  42  and the cavity section  43  by laser scribing is removed (debris removing step). The debris is attached to the lower surface of the substrate  2  along the chip dividing groove  42  and the cavity section  43 , and is mainly composed of group III metal such as Ga, Al, or In. 
     The debris removing step is performed by, for example, wet etching. Specifically, the wafer  50  is immersed in an acid or alkaline etchant to dissolve and remove the debris. The etchant is not particularly limited to a specific etchant, and examples thereof include the etchant containing an acid such as nitric acid, sulfuric acid, hydrochloric acid, or phosphoric acid, or the etchant containing an alkali such as sodium hydroxide or potassium hydroxide. In a case where the etchant may corrode the p-side upper layer electrode  23  and the like, the wafer  50  may be immersed in the etchant after that portion is covered with a resist or the like. 
     Debris may be removed by dry etching using a chlorine based gas (SiCl 4 , Cl 2 , or the like), Ar gas, or the like. 
     Subsequently, in step S 10 , the n-side electrode  24  is formed on the lower surface of the substrate  2  by vacuum vapor deposition or sputtering (n-side electrode forming step). 
     When the n-side electrode  24  such as the above-mentioned single layer of Ti or Ti/Al multilayer body is formed on the lower surface of the substrate  2 , the metal film  24 A of Ti, Al, or Ga is also formed on the inner wall of the cavity section  43  (see  FIG. 3 ). When the n-side electrode  24  is formed, heat treatment is performed to reduce contact resistance between the substrate  2  and the n-side electrode  24  and ensure ohmic contact. 
     Subsequently, in step S 11 , the pad electrode  25  is formed on the n-side electrode  24  by vacuum vapor deposition or sputtering (pad electrode forming step). When the pad electrode  25  made of Au or the like described above is formed on the n-side electrode  24 , the metal film  25 A made of Au is also formed on the inner wall of the cavity section  43  (see  FIG. 3 ). 
     In the present embodiment, the metal film  24 A and the metal film  25 A are formed in accordance with the formation of the n-side electrode  24  and the pad electrode  25 , but the metal films may be formed separately from the formation of the n-side electrode  24  and the pad electrode  25 . Further, either one of the metal films  24 A and  25 A may be formed on the inner wall of the cavity section  43 . 
     Subsequently, in step S 12 , a plurality of bar dividing grooves  41  are formed by a diamond point in the semiconductor layer  10  of the wafer  50  (bar dividing groove forming step) (see  FIG. 10 ). The bar dividing groove  41  is formed at one end portion of the substrate  2  in the X direction, extends in the X direction orthogonal to the ridge portion  30 , and is disposed between the p-side upper layer electrodes  23 . 
     By forming the bar dividing grooves  41  only at one end portion of the substrate  2 , it is possible to reduce workloads compared to a case of forming the bar dividing grooves  41  on the entire wafer  50 . In the first cutting step described below, the wafer  50  is divided at the bar dividing groove  41 , and the side walls of the bar dividing groove  41  form the emission surface  1 A and the opposing surface  1 B of the semiconductor laser element  100  (see  FIG. 4 ). Thus, the distance between the bar dividing grooves  41  is a resonator length of the waveguide  31  of the semiconductor laser element  100  (see  FIG. 4 ), and the resonator length is formed to be approximately 600 μm, for example. 
     The bar dividing groove  41  may be formed by laser scribing. In this case, the debris removing step of step S 9  is more preferably performed after the bar dividing groove forming step of step S 12 . 
     Subsequently, in step S 13 , the wafer  50  is cleaved by applying a blade into each bar dividing groove  41 , to form a plurality of bars  51  that are bar-shaped intermediates (first cutting step). In this step, as described above, a resonator end face of the waveguide  31  is formed by a cleavage surface. 
     In the first cutting step, when cleavage occurs from the bar dividing groove  41  in the upper surface of the wafer  50  toward the cavity section  43  in the lower surface, the resonator end face is not formed flat. Thus, the cavity section  43  is formed at a position that does not overlap with the bar dividing groove  41 . When the cavity section  43  is separated from the bar dividing groove  41  by 10 μm or greater in the longitudinal direction of the ridge portion  30 , the wafer  50  can be reliably cleaved from the bar dividing groove  41  in a direction perpendicular to the lower surface of the semiconductor laser element  100 . As a result, when the semiconductor laser element  100  is diced, the cavity section  43  separates from the end face of the waveguide  31  by 10 μm or greater in the longitudinal direction of the waveguide  31 . 
     Subsequently, in step S 14 , the end face coating film  26  is formed on the resonator end faces, which are both ends of the bar  51 , by vacuum vapor deposition or sputtering (end face coating film forming step) (see  FIG. 11 ). The end face coating film  26  on the emission surface  1 A is formed of the low reflective film, and the end face coating film  26  on the opposing surface  1 B is formed of the highly reflective film. As a result, light can be efficiently emitted from the emitting portion  31 A (see  FIG. 1 ), and the surfaces of both end faces can be protected. 
     Subsequently, in step S 15 , the bar  51  is cleaved by applying a blade into each chip dividing groove  42  and is diced into a plurality of chips (second cutting step). As a result, the semiconductor laser element  100  illustrated in  FIG. 1  is obtained. 
     Summary of First Embodiment 
     The semiconductor laser element  100  that emits laser light according to a first aspect of the disclosure includes the substrate  2  and the semiconductor layer  10  provided on the substrate  2 . The semiconductor layer  10  includes the waveguide  31  that extends in the Y direction (predetermined direction) and emits laser light from the emission surface  1 A (one end face). The substrate  2  includes the plurality of cavity sections  43  intersecting the Y direction and extending, and the plurality of cavity sections  43  are provided in the substrate  2  such that at least parts of at least two cavity sections  43  of the plurality of cavity sections  43  overlap with each other along the Y direction. The length W A  of each of the plurality of cavity sections  43  in the direction perpendicular to the Y direction (X direction) is shorter than the length W of the semiconductor laser element  100  in the X direction. 
     According to the above configuration, since the cavity sections  43  are formed in the substrate  2 , the stray light incident on the substrate  2  from the waveguide  31  is shielded, and the stray light leaking from the substrate  2  can be reduced. Further, the length W A  of each of the cavity sections  43  is shorter than the length W. As a result, it is possible to reduce the possibility that the semiconductor laser element  100  cracks at a position other than the desired cleavage surface. 
     In the semiconductor laser element  100  according to a second aspect of the disclosure, in the first aspect, the cavity sections  43  may overlap with each other so that any one cavity section  43  of the plurality of cavity sections  43  exists across the entirety of the semiconductor laser element  100  in the X direction. 
     According to the above configuration, when viewed from the emission surface  1 A of the semiconductor laser element  100 , the cavity sections  43  can be disposed in a wider area in the substrate  2 . As a result, in the semiconductor laser element  100 , stray light leaking from the substrate  2  can be more effectively reduced. 
     In the semiconductor laser element  100  according to a third aspect of the disclosure, in the above-described first or second aspect, at least one cavity section  43  of the plurality of cavity sections  43  may be the groove including the opening on the lower surface of the substrate  2 . 
     According to the above configuration, in a case where the groove including the opening on the lower surface of the substrate  2  is formed as the cavity section  43  for reducing stray light leaking from the substrate  2 , the cavity section  43  can be easily formed by laser scribing or the like. 
     In the semiconductor laser element  100  according to a fourth aspect of the disclosure, in the third aspect, the height H A  (groove depth) of the cavity section  43  may be one third or greater of the height H of the substrate  2  (thickness of the substrate  2 ). 
     According to the above configuration, stray light leaking from the substrate  2  can be reduced more effectively. 
     In the semiconductor laser element  100  according to a fifth aspect of the disclosure, in the third or fourth aspect, the metal film  24 A and/or  25 A may be disposed on the inner wall of the cavity section  43 , which is the groove. 
     According to the above configuration, since the metal film  24 A and/or  25 A is disposed on the inner wall of the cavity section  43 , which is the groove, the stray light can be reflected by the metal film  24 A and/or  25 A. As a result, the stray light leaking from the substrate  2  can be further reduced. 
     In the semiconductor laser element  100  according to a sixth aspect of the disclosure, in the fifth aspect, the coating film  27  containing at least one of the metal or the metal oxide may be provided between the inner wall of the cavity section  43 , which is the groove, and the metal film  24 A. 
     According to the above configuration, since the coating film  27  containing the metal and/or the metal oxide is provided on the inner wall of the cavity section  43 , the adhesion strength of the n-side electrode  24  to the substrate  2  can be improved. 
     In the semiconductor laser element  100  according to a seventh aspect of the disclosure, in any of the above third to sixth aspects, at least the recessed portion  45  or the protruding portion  46  may be provided on the side wall of the cavity section  43 . 
     According to the above configuration, since the recessed portion  45  and/or the protruding portion  46  is provided on the side wall of the cavity section  43 , the stray light that has entered the cavity section  43  from the substrate  2  can be diffusely reflected, and the stray light leaking from the substrate  2  can be further reduced. 
     In the semiconductor laser element  100  according to an eighth aspect of the disclosure, in any one of the above first to seventh aspects, at least a part of at least one cavity section  43  of the plurality of cavity sections  43  may be inclined with respect to the X direction when the semiconductor laser element  100  is viewed from the upper surface side. Specific examples of the eighth aspect of the disclosure will be described in detail in other fourth to ninth embodiments below. 
     According to the above configuration, since the cavity section  43  is inclined with respect to the X direction, the stray light can be reflected in a direction different from the emission direction of the laser light (a direction parallel to the waveguide  31 ). As a result, the stray light leaking from the substrate  2  can be further reduced. 
     In the semiconductor laser element  100  according to a ninth aspect of the disclosure, in any one of the above first to eighth aspects, each of the plurality of cavity sections  43  may be provided inside the substrate  2  when the semiconductor laser element  100  is viewed from the upper surface side. 
     According to the above configuration, since the cavity sections  43  are not in contact with the end portion of the semiconductor laser element  100  in the X direction, the strength of the semiconductor laser element  100  can be increased and the possibility of element cracking can be further reduced. Note that a specific example of the ninth aspect of the disclosure will be described in detail in other third to sixth embodiments below. 
     In the semiconductor laser element  100  according to a tenth aspect of the disclosure, in any one of the above first to ninth aspects, the length W A  of each of the plurality of cavity sections  43  in the X direction may be 80% or less of the length W of the semiconductor laser element  100  in the X direction. 
     According to the above configuration, the possibility of element cracking of the semiconductor laser element  100  can be further reduced. 
     In the semiconductor laser element  100  according to an eleventh aspect of the disclosure, in any one of the above first to tenth aspects, the plurality of cavity sections  43  may be provided at the distance of 10 μm or greater from the emission surface  1 A along the Y direction. 
     The method for manufacturing the semiconductor laser element  100  of the present embodiment includes the step of cleaving the wafer to obtain the bar, and the step of cleaving the bar to obtain the semiconductor laser element  100 . In the step of cleaving the bar, in a case where the emission surface  1 A and the cavity section  43  are close to each other, the cleavage surface may not be formed flat, and may cause division failure. The cavity section  43  is provided at the distance of 10 μm or greater from the emission surface  1 A, thereby reducing the possibility of causing the division failure. 
     However, as illustrated in  FIGS. 4 and 5 , the plurality of cavity sections  43  may be formed at positions closer to the emission surface  1 A than the opposing surface  1 B. For example, all of the plurality of cavity sections  43  may be provided closer to the emission surface  1 A than a center of the semiconductor laser element  100  in the Y direction. In this case, the stray light leaking from the substrate  2  can be efficiently reduced. 
     Hereinafter, other embodiments of the disclosure will be described. Note that, for convenience of explanation, components having the same function as those described in the above-described embodiment will be denoted by the same reference signs, and descriptions of those components will be omitted. 
     Second Embodiment 
     Hereinafter, a second embodiment of the disclosure will be described with reference to  FIG. 12 .  FIG. 12  is a diagram illustrating a forming pattern of cavity sections  43 A of a semiconductor laser element  101  according to the second embodiment of the disclosure. Note that  FIG. 12  is a bottom view of the substrate  2  of the semiconductor laser element  101 , and members other than the substrate  2  and the cavity sections  43 A are omitted for clarity. This also applies to  FIGS. 13 to 19 . 
     In the semiconductor laser element  101  according to the second embodiment, the forming pattern (shape and arrangement pattern) of the cavity sections  43 A is different from the forming pattern of the cavity sections  43  of the semiconductor laser element  100  according to the first embodiment. 
     Specifically, as illustrated in  FIG. 12 , the semiconductor laser element  101  is different from that in the first embodiment in that two cavity sections  43 A of three cavity sections  43 A are formed at the same distance from the emission surface  1 A. One end of one cavity section  43 A of the two cavity sections  43 A is in contact with one side surface of the substrate  2 , and one end portion of another cavity section  43 A is in contact with another side surface of the substrate  2 . Further, each of the two cavity sections  43 A, in a part thereof, overlaps with still another cavity section  43 A (the cavity section  43 A formed closer to the emission surface  1 A) along the Y direction. 
     The three cavity sections  43 A extend in a direction intersecting the Y direction in the semiconductor laser element  101 . Further, parts of the two cavity sections  43 A overlap with each other so that any one of the three cavity sections  43 A exists across the entire X direction of the substrate  2  when viewed from the emission surface  1 A side. Further, a length W A  of each of the cavity sections  43 A in the X direction is shorter than a length W of the semiconductor laser element  101  in the X direction. 
     According to the above configuration, since the plurality of cavity sections  43 A are provided across the entire X direction of the substrate  2  when viewed from the emission surface  1 A side, in the semiconductor laser element  101 , stray light can be effectively reduced as in the first embodiment. Further, in the semiconductor laser element  101 , when the semiconductor laser element  101  is viewed from the upper surface side, one of the plurality of cavity sections  43 A is provided inside the substrate  2 . Thus, in the semiconductor laser element  101 , the possibility of element cracking at a position other than a desired cleavage surface can be reduced. 
     Note that  FIG. 12  is a diagram schematically illustrating a part of the configuration of the semiconductor laser element  101  according to the present embodiment, and does not limit the dimensions of the members. This also applies to other embodiments. 
     Third Embodiment 
     Hereinafter, a third embodiment of the present disclosure will be described with reference to  FIG. 13 .  FIG. 13  is a diagram illustrating a forming pattern of cavity sections  43 B of a semiconductor laser element  102  according to the third embodiment of the disclosure. The cavity section  43 B of the semiconductor laser element  102  according to the present embodiment differs from those in the first and second embodiments in that both end portions of each of the cavity sections  43 B in the X direction are not in contact with both end portions of the semiconductor laser element  102  in the X direction. 
     Specifically, the semiconductor laser element  102  according to the third embodiment includes two cavity sections  43 B. The two cavity sections  43 B each extend in a direction intersecting the Y direction and overlap with each other along the Y direction. In addition, each of the two cavity sections  43 B is not in contact with both end portions of the semiconductor laser element  102  in the X direction. In other words, each of the two cavity sections  43 B is provided inside the substrate  2  when the semiconductor laser element  102  is viewed from the upper surface side. Further, the two cavity sections  43 B have the same length W A  in the X direction, and all portions thereof overlap with each other along the Y direction. 
     According to the above configuration, since the semiconductor laser element  102  according to the third embodiment is provided with the two cavity sections  43  overlapping along the Y direction, stray light leaking from the substrate  2  can be reduced. Additionally, since each of the cavity sections  43 B is not in contact with the side surface of the substrate  2  (the end portion of the semiconductor laser element  102  in the X direction), strength of the semiconductor laser element  102  is increased as compared to those in the first and second embodiments, and the possibility of element cracking can be further reduced. 
     Fourth Embodiment 
     Hereinafter, a fourth embodiment of the present disclosure will be described with reference to  FIG. 14 .  FIG. 14  is a diagram illustrating a forming pattern of cavity sections  43 C of a semiconductor laser element  103  according to the fourth embodiment of the disclosure. The cavity section  43 C of the semiconductor laser element  103  according to the present embodiment differs from that in the third embodiment in that the cavity section  43 C is inclined with respect to the X direction. 
     Specifically, the semiconductor laser element  103  according to the fourth embodiment includes two cavity sections  43 C. The two cavity sections  43 C each extend in a direction intersecting the Y direction and overlap with each other along the Y direction. Further, each of the two cavity sections  43 C has a linear shape when viewed from the upper surface side of the substrate  2 , and is inclined with respect to the X direction. Furthermore, each of the two cavity sections  43 C is not in contact with both end portions of the semiconductor laser element  102  in the X direction. Additionally, the two cavity sections  43 C have the same length W A  in the X direction (length when viewed from the emission surface  1 A side), and all the portions thereof overlap with each other along the Y direction. 
     According to the above configuration, similar to the third embodiment, in the semiconductor laser element  103  according to the fourth embodiment, the possibility of element cracking can be further reduced. Additionally, since the cavity section  43 C is inclined with respect to the X direction, stray light can be reflected in a direction different from an emission direction of laser light. As a result, the stray light leaking from the substrate  2  can be further reduced as compared to the third embodiment. 
     Fifth Embodiment 
     Hereinafter, a fifth embodiment of the present disclosure will be described with reference to  FIG. 15 .  FIG. 15  is a diagram illustrating a forming pattern of cavity sections  43 D of a semiconductor laser element  104  according to the fifth embodiment of the disclosure. The cavity section  43 D of the semiconductor laser element  104  according to the present embodiment differs from that in the third embodiment in that the cavity section  43 D has a zigzag shape. 
     Specifically, the semiconductor laser element  104  according to the fifth embodiment includes two cavity sections  43 D. The two cavity sections  43 D each extend in a direction intersecting the Y direction and overlap with each other along the Y direction. The two cavity sections  43 D each have a zigzag shape. The zigzag shape is, in other words, a combination of portions having different inclinations with respect to the X direction. The angle of inclination may be different in each portion of the cavity section  43 D, and the cavity section  43 D may include a portion substantially parallel to the X direction (angle≈0°). Further, each of the two cavity sections  43 D is not in contact with both end portions of the semiconductor laser element  104  in the X direction. Furthermore, the two cavity sections  43 D have the same length W A  in the X direction (length when viewed from the emission surface  1 A side), and all the portions thereof overlap with each other along the Y direction. 
     According to the above configuration, similar to the fourth embodiment, in the semiconductor laser element  104  according to the fifth embodiment, the possibility of element cracking can be further reduced. In addition, since each portion of the cavity section  43 D is inclined with respect to the X direction, stray light can be reflected in directions different from the emission direction of laser light. As a result, as in the fourth embodiment, the stray light leaking from the substrate  2  can be further reduced. 
     Sixth Embodiment 
     Hereinafter, a sixth embodiment of the present disclosure will be described with reference to  FIG. 16 .  FIG. 16  is a diagram illustrating a forming pattern of cavity sections  43 E of a semiconductor laser element  105  according to the sixth embodiment of the disclosure. The cavity section  43 E of the semiconductor laser element  105  according to the present embodiment differs from that in the third embodiment in that the cavity section  43 E has a curved shape. 
     Specifically, the semiconductor laser element  105  according to the sixth embodiment includes two cavity sections  43 E. The two cavity sections  43 E each extend in a direction intersecting the Y direction and overlap with each other along the Y direction. The two cavity sections  43 E each have a curved shape. A tangent at any point of the cavity section  43 E intersects the Y direction. Further, the tangent is inclined with respect to the X direction. That is, the curved shape can be said to be a combination of portions having different inclinations with respect to the X direction. The angle of the inclination may be different in each portion of the cavity section  43 E, and the cavity section  43 E may include a portion substantially parallel to the X direction. Further, each of the two cavity sections  43 E is not in contact with both end portions of the semiconductor laser element  105  in the X direction. Furthermore, the two cavity sections  43 E have the same length W A  in the X direction (length when viewed from the emission surface  1 A side), and all the portions thereof overlap with each other along the Y direction. 
     According to the above configuration, similar to the fourth embodiment, in the semiconductor laser element  105  according to the sixth embodiment, the possibility of element cracking can be reduced. Additionally, since the direction of the tangent at any point of the cavity section  43 E is inclined with respect to the X direction, the stray light can be reflected in directions different from the emission direction of laser light. As a result, as in the fourth embodiment, the stray light leaking from the substrate  2  can be further reduced. 
     Seventh Embodiment 
     Hereinafter, a seventh embodiment of the present disclosure will be described with reference to  FIG. 17 .  FIG. 17  is a diagram illustrating a forming pattern of cavity sections  43 F of a semiconductor laser element  106  according to the seventh embodiment of the disclosure. The cavity section  43 F of the semiconductor laser element  106  according to the present embodiment differs from that in the fourth embodiment in that one end portion of each of the cavity sections  43 F in the X direction is in contact with the side surface of the substrate  2 . 
     Specifically, the semiconductor laser element  106  according to the seventh embodiment includes two cavity sections  43 F. The two cavity sections  43 F each extend in a direction intersecting the Y direction. Further, parts of the two cavity sections  43 F overlap with each other such that at least one cavity section  43 F exists across the entire X direction of the substrate  2  when viewed from the emission surface  1 A side. 
     According to the above configuration, in the semiconductor laser element  106  according to seventh embodiment, stray light leaking from the substrate  2  can be more effectively reduced as compared to the fourth embodiment. In addition, since one end portion of the two cavity sections  43 F is not in contact with the side surface, in the semiconductor laser element  106 , the possibility of element cracking can be reduced. 
     Eighth Embodiment 
     Hereinafter, an eighth embodiment of the present disclosure will be described with reference to  FIG. 18 .  FIG. 18  is a diagram illustrating a forming pattern of cavity sections  43 G of a semiconductor laser element  107  according to the eighth embodiment of the disclosure. The cavity section  43 G of the semiconductor laser element  107  according to the present embodiment differs from that in the fifth embodiment in that one end portion of each of the cavity sections  43 G in the X direction is in contact with the side surface of the substrate  2 . 
     Specifically, the semiconductor laser element  107  according to the eighth embodiment includes two cavity sections  43 G. A description of the zigzag shape of the cavity section  43 G is the same as that of the fifth embodiment. The two cavity sections  43 G each extend in a direction intersecting the Y direction. In addition, parts of the two cavity sections  43 G overlap with each other such that at least one cavity section  43 G exists across the entire X direction of the substrate  2  when viewed from the emission surface  1 A side. 
     According to the above configuration, in the semiconductor laser element  107  according to the eighth embodiment, stray light leaking from the substrate  2  can be more effectively reduced compared to the fifth embodiment. In addition, since one end portion of the two cavity sections  43 G is not in contact with the side surface, in the semiconductor laser element  107 , the possibility of element cracking can be reduced. 
     Ninth Embodiment 
     Hereinafter, a ninth embodiment of the present disclosure will be described with reference to  FIG. 19 .  FIG. 19  is a diagram illustrating a forming pattern of cavity sections  43 H of a semiconductor laser element  108  according to the ninth embodiment of the disclosure. The cavity section  43 H of the semiconductor laser element  108  according to the present embodiment differs from that in the sixth embodiment in that one end portion of each of the cavity sections  43 H in the X direction is in contact with the side surface of the substrate  2 . 
     Specifically, the semiconductor laser element  108  according to the ninth embodiment includes two cavity sections  43 H. A description of the curved shape of the cavity section  43 H is the same as that of the sixth embodiment. Further, parts of the two cavity sections  43 H overlap with each other such that at least one cavity section  43 H exists across the entire X direction of the substrate  2  when viewed from the emission surface  1 A side. 
     According to the above configuration, in the semiconductor laser element  108  according to the ninth embodiment, stray light leaking from the substrate  2  can be more effectively reduced compared to the sixth embodiment. In addition, since one end portion of the two cavity sections  43 H is not in contact with the side surface, in the semiconductor laser element  108 , the possibility of element cracking can be reduced. 
     Tenth Embodiment 
     Hereinafter, a tenth embodiment of the present disclosure will be described with reference to  FIGS. 22 and 23 .  FIG. 22  is a schematic front view illustrating a structure of a cavity section  44  of a semiconductor laser element  109  according to the tenth embodiment when viewed from the emission surface  1 A.  FIG. 23  is a schematic perspective view illustrating a structure of a plurality of cavity sections  44  of the semiconductor laser element  109  according to the tenth embodiment. 
     The cavity section  44  of the semiconductor laser element  109  according to the present embodiment differs from that in the first embodiment in that the cavity section  44  is formed inside the substrate  2  without including an opening on the lower surface of the substrate  2 . In other words, it can be said that the cavity section  44  is a cavity provided in the substrate  2 . The cavity section  44  is formed in the substrate  2  by, for example, stealth dicing with a laser. 
     Note that in  FIGS. 22 and 23 , the forming pattern of the cavity sections  44  is similar to that of the first embodiment, but is not limited to this forming pattern. The forming pattern of the cavity sections  44  may be, for example, a pattern similar to any of the second to ninth embodiments. For example, as in the first embodiment, a part of the cavity section  44  may be in contact with the side surface of the substrate  2 . The embodiment is not limited to this, a part of the cavity section  44  may be in contact with the upper surface of the substrate  2 . In other words, the cavity section  44  may be provided at least separated from the lower surface of the substrate  2 . 
     Further, it is not always necessary that all the plurality of cavity sections formed in the substrate  2  be the cavity sections  44 . Some of the cavity sections formed in the substrate  2  may be the cavity section  44 , and another cavity section may be, for example, at least one of the cavity sections  43 ,  43 D, or  43 E. 
     Summary of Tenth Embodiment 
     In the semiconductor laser element  109  according to a twelfth aspect of the disclosure, in the above first or second aspect, at least one cavity section  44  of the plurality of cavity sections  44  is provided at least separated from the lower surface of the substrate  2 . 
     According to the above configuration, the cavity section  44  as a cavity is separated from the lower surface of the substrate  2 . In this case as well, similar to the case in which the plurality of cavity sections  43 , which are the grooves, are provided in the substrate  2 , stray light leaking from the substrate  2  can be reduced. Additionally, since the cavity section  44  does not include an opening on the lower surface of the substrate  2 , the possibility of element cracking of the semiconductor laser element  109  can be further reduced. 
     Further, in the semiconductor laser element  109  according to a thirteenth aspect of the disclosure, in the above twelfth aspect, a height He (length in the thickness direction of the substrate) of the cavity section  44 , which is the cavity, may be one third or greater of the height H of the substrate  2  (thickness of the substrate). 
     According to the above configuration, stray light leaking from the substrate  2  can be reduced more effectively. 
     Further, in the semiconductor laser element  109  according to a fourteenth aspect of the disclosure, at least a recessed portion or a protruding portion may be provided on an inner wall of the cavity section  44 , which is the cavity, in the above twelfth or thirteenth aspect. 
     According to the above configuration, since the recessed portion and/or the protruding portion is provided on the inner wall of the cavity section  44 , stray light that has entered the cavity section  44  from the substrate  2  can be diffusely reflected, and stray light leaking from the substrate  2  can be further reduced. 
     Further, in the semiconductor laser element  109  according to a fifteenth aspect of the disclosure, in any one of the above twelfth to fourteenth aspects, each of the plurality of cavity sections  44 , which are the cavities, may be provided inside the substrate  2  when the semiconductor laser element  109  is viewed from the upper surface side. 
     According to the above configuration, since the cavity section  44 , which is the cavity, is not in contact with the end portion of the semiconductor laser element  109  in the X direction, the cavity section  44  includes no opening on any of the upper surface, the side surface, and the lower surface (bottom surface) of the substrate  2 . As a result, the strength of the semiconductor laser element  109  is increased, and the possibility of element cracking can be further reduced. 
     Further, in the semiconductor laser element  109  according to a sixteenth aspect of the disclosure, in any one of the above twelfth to fifteenth aspects, the length W A  of each of the plurality of cavity sections  44 , which are the cavities, in the X direction may be 80% or less of the length W of the semiconductor laser element  100  in the X direction. 
     According to the above configuration, the possibility of element cracking of the semiconductor laser element  109  can be further reduced. 
     Further, in the semiconductor laser element  109  according to a seventeenth aspect of the disclosure, in any one of the above twelfth to sixteenth aspects, the plurality of cavity sections  44 , which are the cavities, may be provided at a distance of 10 μm or greater from the emission surface  1 A along the Y direction. 
     The cavity sections  44  are provided at the distance of 10 μm or greater from the emission surface  1 A, thereby reducing the possibility of causing the division failure. 
     Results of Verification Test 
     Here, a test conducted to confirm effect of representative semiconductor laser elements (semiconductor laser elements  100 ,  101 , and  102 ) according to one aspect of the disclosure will be described with reference to  FIGS. 20 and 21 . 
     In this test, as comparative examples, a semiconductor laser element in which no cavity section (groove) was formed (Comparative Example 1) and a semiconductor laser element including one cavity section (groove) (Comparative Example 2) were used. As the representative examples of the semiconductor laser element according to the one aspect of the disclosure, the semiconductor laser elements (semiconductor laser elements  100 ,  101 , and  102 ) according to the first to third embodiments were used. With the two comparative examples and the three semiconductor laser elements according to the one aspect of the disclosure, a state in which laser light was actually emitted was photographed from the emission surface  1 A side, and stray light leaking from the substrate  2  was examined. 
       FIG. 20  is a diagram illustrating test results for the comparative examples.  FIG. 21  is a diagram illustrating test results for the semiconductor laser elements according to the one aspect of the disclosure. 
     As illustrated in  FIG. 20 , in the comparative examples, it is possible to visually recognize how stray light is leaking in an area of the substrate  2  surrounded by a broken line. As illustrated in  FIG. 21 , in the semiconductor laser elements  100  to  102  of the first to third embodiments according to the one aspect of the disclosure, in an area of the substrate  2  surrounded by a broken line, it is possible to visually recognize how stray light leaking from the substrate  2  is reduced as compared to Comparative Examples 1 and 2. That is, this test demonstrated that in the semiconductor laser elements according to one aspect of the disclosure represented by the semiconductor laser elements  100 ,  101 , and  102 , stray light leaking from the substrate  2  can be reduced. In other words, this test demonstrated that by providing the substrate  2  with a plurality of cavity sections overlapping along the Y direction, stray light leaking from the substrate  2  can be reduced as compared to the case in which the cavity section is not provided in the substrate  2  or only one cavity section is provided in the substrate  2 . 
     Further, this test demonstrated that in the semiconductor laser elements  100  and  101  of the first and second embodiments, stray light leaking from the substrate  2  can be further reduced as compared to the semiconductor laser element  102  of the third embodiment. In other words, it was demonstrated that stray light leaking from the substrate  2  can be reduced by forming a plurality of cavity sections such that at least one of a plurality of cavity sections exists across the entire X direction of the substrate  2  when viewed from the emission surface  1 A side. 
     Supplementary Information 
     The disclosure is not limited to each of the above-described embodiments. It is possible to make various modifications within the scope of the claims. An embodiment obtained by appropriately combining technical elements each disclosed in different embodiments falls also within the technical scope of the disclosure. Furthermore, technical elements disclosed in the respective embodiments may be combined to provide a new technical feature. 
     While there have been described what are at present considered to be certain embodiments of the invention, it will be understood that various modifications may be made thereto, and it is intended that the appended claims cover all such modifications as fall within the true spirit and scope of the invention.