JP4911957B2 - Semiconductor laser device and application system - Google Patents

Description

  The present invention relates to a semiconductor laser device and an application system including the same.

  High-power broad area type semiconductor laser elements can obtain a watt-class optical output and are used in the processing field and the medical field using laser light. On the other hand, in recent years, development of a semiconductor laser element that emits blue-violet laser light having a wavelength of about 400 nm for pickup of an optical disk has been advanced, and is approaching a practical stage. If the wavelength of blue-violet laser light is short and a watt-class light output can be obtained, it is expected that the range of use in the processing field and the medical field will be further expanded. Note that the broad area type semiconductor laser element described here refers to a semiconductor laser element that has a wide current confinement width and emits a laser beam in a first-order or higher-order horizontal transverse mode. The current confinement structure of the broad area type element includes an electrode stripe type and a wide ridge type.

For example, a broad area type semiconductor laser device using a GaInN multiple quantum well formed on a GaN substrate as an active layer has been reported (see Non-Patent Document 1 and Non-Patent Document 2). According to this document, the current confinement width of the semiconductor laser element is 10 μm, 50 μm and 100 μm, and it is disclosed that a very high light output of about 1 watt can be obtained.
S. Goto et al., “Super high-power AlGaInN-based laser diodes with a single broad-area stripe emitter fabricated on a GaN substrate”, phys. Stat. Sol. (A) 200, No.1 (2003), p.122-125 M. TAKEYA et al., “High-power AlGaInN lasers”, phys. Stat. Sol. (A) 192, No. 2 (2002), p.269-276

  A broad area type semiconductor laser oscillates with a large number of horizontal and transverse modes, and as the laser output increases, the number of modes changes and the position shifts. For this reason, there is a problem that the near-field image and the far-field image are deformed and the current-light output characteristic is likely to be kinked. If the near-field image / far-field image is deformed / shifted, the lens coupling efficiency of the output light may fluctuate, leading to a decrease in light utilization efficiency in a system using laser light. Further, if a kink occurs in the current-light output characteristic, the light output value cannot be controlled linearly by the current.

  An object of the present invention is to stabilize a light distribution in the horizontal direction of an active layer in a semiconductor laser element that emits laser light including a first-order or higher-order horizontal transverse mode. An object of the present invention is to provide an excellent semiconductor laser device in which an image does not fluctuate and does not cause kinking in current-light output characteristics. Another object of the present invention is to provide an application system including the semiconductor laser element.

  The semiconductor laser device of the present invention comprises an upper clad layer, a lower clad layer, an active layer between the upper clad layer and the lower clad layer, and a stripe-shaped current confinement structure on the substrate, and the longitudinal direction of the stripe A semiconductor laser element having a pair of end surface reflecting mirrors orthogonal to each other and generating laser oscillation in a first-order or higher-order horizontal transverse mode, and in the region where the laser beam exists in the semiconductor laser element, the length of the stripe The structure is characterized in that the refractive index varies in a direction perpendicular to the direction and parallel to the substrate.

  The structure in which the refractive index varies preferably has an aspect in which the shape varies periodically, and the variation pitch is preferably 0.5 μm or more and 6 μm or less. Moreover, the structure in which the refractive index varies is preferably provided in a layer other than the active layer and has a concavo-convex shape. It is preferable that the uneven shape is provided on the upper cladding layer, or between the active layer and the upper cladding layer, or the lower cladding layer, or between the active layer and the lower cladding layer, or on the surface of the substrate.

  As another preferred embodiment according to the semiconductor laser device of the present invention, a layer having a refractive index variation is provided in a layer other than the active layer, and a layer having a refractive index variation structure is included in the layer. There is an embodiment in which a layer made of a material having a refractive index different from that of the layer is discretely embedded. A structure in which layers made of materials having different refractive indexes are discretely embedded is an upper cladding layer, or between an active layer and an upper cladding layer, or between a lower cladding layer, or between an active layer and a lower cladding layer. A mode of providing is preferable. On the other hand, as another preferred embodiment according to the semiconductor laser device of the present invention, there is an embodiment in which the structure in which the refractive index varies has a slit-like groove provided in the upper cladding layer.

The structure in which the refractive index fluctuates is desirably provided at least in the vicinity of the emitting end face reflecting mirror in front of the semiconductor laser element. In addition, the structure in which the refractive index fluctuates is a line that bisects the current confinement structure when viewed from the longitudinal direction of the stripe-shaped current confinement structure, and is a line having a line perpendicular to the substrate as an axis of symmetry. An embodiment that is symmetrical is preferred. The semiconductor laser element is preferably made of Al _x Ga _{1 -xy} In _y N (0 ≦ x ≦ 1,0 ≦ y ≦ 1).

  An application system of the present invention includes the above-described semiconductor laser element and a phosphor that absorbs at least a part of the laser light emitted from the semiconductor laser element and emits light having a wavelength different from that of the emitted laser light. It is characterized by that. As this system, a white illumination device including a semiconductor laser element and a phosphor that absorbs laser light having a wavelength shorter than 420 nm emitted from the semiconductor laser element and emits white light is preferable. In addition, a white illumination device including a semiconductor laser element and a phosphor that absorbs part of blue laser light emitted from the semiconductor laser element and emits light having at least red and green spectral components is preferable. In the present invention, “same” includes not only completely the same case but also substantially the same case.

  According to the present invention, in a semiconductor laser device that emits laser light of a first-order or higher-order horizontal transverse mode, fluctuations in the light distribution in the horizontal direction when the light output is increased are suppressed, and current-light output characteristics are reduced. There is no kink and the near-field and far-field images are stable. In particular, it is effective when the material of the semiconductor laser element is made of AlGaInN.

Embodiment 1
FIG. 1 illustrates a perspective view of the semiconductor laser device according to the first embodiment of the present invention. FIG. 1A is an overall view of the semiconductor laser device, and a part of the semiconductor laser device is deleted to clarify the internal structure. FIG. 1B is a partially enlarged view. The semiconductor laser device 100 according to the first embodiment is an electrode stripe type broad area laser device that emits laser light of a first-order or higher-order horizontal transverse mode. This laser element has a periodic concavo-convex structure K at the boundary between the p-type optical waveguide layer 110 and the p-type upper cladding layer 111 above the active layer. The uneven structure is characterized in that it is provided in a direction (X direction) perpendicular to the longitudinal direction (Z direction) of the stripe-shaped current confinement structure and parallel to the substrate.

Here, the main semiconductor laminated portion of the semiconductor laser device 100 of the first embodiment is formed on the substrate 101 made of n-type GaN, the buffer layer 102 made of n-type GaN having a layer thickness of 0.5 μm, and n having a layer thickness of 2 μm. A lower cladding layer 103 made of type Al _0.05 Ga _0.95 N, a lower guide layer 104 made of non-doped GaN having a layer thickness of 0.05 μm, a well layer 105 made of InGaN having a thickness of 5 nm, a barrier layer 106 made of InGaN having a thickness of 10 nm, Well layer 107 made of InGaN with a layer thickness of 5 nm, upper guide layer 108 made of non-doped GaN with a layer thickness of 0.05 μm, carrier block layer 109 made of p-type Al _0.3 Ga _0.7 N with a layer thickness of 0.02 μm, average layer thickness 0 optical waveguide layer 110 made of p-type GaN of .05Myuemu, the average layer thickness 0.5 [mu] m p-type Al _0.05 Ga _0.95 on consisting of N cladding layer 11 , And it can be composed of the contact layer 112 made of p-type GaN having a thickness of 0.1 [mu] m.

Except for the semiconductor laminated portion, a protective film 113 made of silicon nitride with a thickness of 50 nm, an ohmic electrode 114 made by laminating a Pd layer with a thickness of 15 nm and a Mo layer with a thickness of 15 nm in this order, and the n-type GaN substrate 101 An ohmic electrode 115 formed by laminating an Hf layer having a thickness of 5 nm and an Al layer having a thickness of 150 nm on the back surface in this order can be used. Here, Mg is doped as the p-type impurity, and Si is doped as the n-type impurity. The current confinement width w of the current confinement structure provided by the protective film 113 made of silicon nitride can be 10 μm. Further, both end surfaces of the semiconductor laser element 100 are cleaved to obtain a Fabry-Perot resonator, and the pair of end surface reflecting mirrors are positioned so as to be orthogonal to the longitudinal direction of the stripe-shaped current confinement structure. Here, a low reflection film (not shown) made of an Al ₂ O ₃ film having a thickness of 80 nm and a reflectivity of emitted laser light of 5% is formed on the cleaved front end face, and is formed on the rear end face. Is a highly reflective film comprising four pairs of SiO ₂ film and TiO ₂ film, having a thickness of ¼ of the wavelength of the emitted laser light, and a reflectivity of the emitted laser light of 95% (Not shown). The resonator length of the Fabry-Perot resonator (the shortest distance between the front end face and the rear end face) can be 1.5 mm.

  In the semiconductor laser device 100, the boundary portion between the p-type cladding layer 111 and the p-type guide layer 110, which is the region where the laser beam exists therein, is orthogonal to the longitudinal direction of the stripe (Z direction) and the substrate. A periodic uneven structure K having a pitch (period) of 2.5 μm is provided in a parallel direction (X direction), and the refractive index periodically varies in the same direction. This concavo-convex structure is parallel to the longitudinal direction (Z direction) of the stripe-shaped current confinement portion and has a structure that extends uniformly. In addition, the concave and convex structure is disposed in the central portion in the X direction of the stripe-shaped current confinement portion, and the concave and convex structure is viewed from the longitudinal direction (Z direction) of the stripe-shaped current confinement structure, It is a line that bisects the current confinement structure and is line-symmetric with a line perpendicular to the substrate (Y direction) as the axis of symmetry.

When the semiconductor laser device 100 is mounted on a copper heat sink by junction down, sealed in a package with excellent heat dissipation, and a current is passed through the semiconductor laser device 100, a laser beam is emitted with a threshold current of 0.3 A, and a maximum of 1 Continuous oscillation up to 5W can be obtained. The wavelength of this laser beam is 405 nm. The near-field image when the laser light is emitted emits light stably in a state where a plurality of longitudinal modes exist. Further, the laser beam is emitted with a high internal quantum efficiency in which the internal quantum efficiency η _i exceeds 90%.

  The current-light output characteristics of the semiconductor laser element 100 are illustrated as A in FIG. For comparison, FIG. 5 differs only in that an uneven structure is not provided at the boundary between the p-type cladding layer 111 and the p-type optical waveguide layer 110, and the other points are the same as those of the laser element in the first embodiment. As for the semiconductor laser element, the current-light output characteristic is exemplified as B. As is clear from FIG. 5A, in the semiconductor laser device 100 of the present invention, the current-light output characteristics change linearly from the start of oscillation, and so-called kink does not occur. On the other hand, in the case of the semiconductor laser element not provided with the concavo-convex structure, as is apparent from FIG. 5B, kinks occur and the current-light output characteristics do not change linearly.

  FIG. 6 shows the number of emission intensity peaks (number of modes) in the horizontal direction of the near-field image for the light outputs indicated by P1 to P4 in the current-light output characteristics of FIG. In the case of A of the present invention, the number of peaks is four at any light output as shown in FIG. 6A, and the four peaks have the same intensity and the position is stable. is there. On the other hand, in the semiconductor laser shown as B, P1 has two as shown in FIG. 6B, P2 has four as shown in FIG. 6C, and P3 has five. The number of P4 and the number of P4 is 6 (none of which are shown), and changes according to the output, and at the time when the number of peaks of the near-field image changes, a kink occurs in the current-light output characteristics.

  In the case of a conventional broad area type semiconductor laser element in which the concavo-convex structure is not provided, since the horizontal transverse mode inside the laser resonator is not controlled, horizontal hole burning occurs as the laser output is increased. The peak position of the horizontal transverse mode and the number of modes change discontinuously, and when the injection current is increased due to the influence, the light output changes discontinuously and a kink occurs. According to the study of the present inventor, it has been found that such a change in the position of the horizontal transverse mode is noticeably caused particularly in a blue or blue-violet laser using an AlGaInN-based material and oscillating in a wavelength band of 400 nm. . This is presumably because the AlGaInN-based material has poor crystallinity and crystal surface flatness compared to other material systems, and thus the light intensity distribution in the current path is not stable.

  On the other hand, in the broad area type semiconductor laser device according to the present embodiment, the periodic unevenness is perpendicular to the longitudinal direction (Z direction) of the stripe-shaped current confinement portion and parallel to the substrate (X direction). Structure K is provided. For this reason, a periodic refractive index distribution is created in the horizontal direction in the current constriction. The horizontal and horizontal modes of laser oscillation in a broad area laser element are complicated including a number of higher-order modes. By creating a refractive index distribution in the horizontal direction, for example, horizontal and horizontal The mode peak is stably present, and the valley portion of the horizontal transverse mode is stably present in the portion where the refractive index is low. In other words, the light distribution is fixed so that the overlap between the spatial distribution of the refractive index in the horizontal direction and the light intensity distribution is maximized. It does not occur and the far-field and near-field images are not deformed. When the horizontal transverse mode light distribution is determined so that the overlap between the horizontal transverse mode light distribution and the refractive index distribution is the largest, it stabilizes the position and shape of the horizontal transverse mode most. It can be said. At this time, as in the first embodiment, the uneven structure is a line that bisects the current confinement structure when viewed from the longitudinal direction (Z direction) of the stripe-shaped current confinement structure, and is formed on the substrate. By making line symmetry with the orthogonal line (Y direction) as the axis of symmetry, the light distribution is arranged symmetrically with a good balance with respect to the current confinement structure, so that the stability of the mode shape is improved. In the first embodiment, the concave portion of the concavo-convex structure is arranged at the center portion in the X direction of the current confinement structure, but it goes without saying that the convex portion may be arranged.

  A structure in which the refractive index varies due to an uneven structure or the like does not necessarily have to be periodic in principle, but the mode shape has better stability if it is periodic. FIG. 7 shows the relationship between the period (pitch) when the concavo-convex structure is periodic and the output at which kinks appear. As shown in FIG. 7, when the period is in a certain range, the light output until the kink is generated can be increased. In particular, when the period (pitch) is 0.5 to 6 μm, a remarkable effect can be obtained. It can be seen.

  A structure in which the refractive index fluctuates, such as a concavo-convex structure, is formed in a region where laser light exists inside the laser element, and is formed in an upper cladding layer, or between an active layer and an upper cladding layer, or a lower cladding layer, or It is effective to form it between the active layer and the lower cladding layer. In Embodiment 1, the unevenness is provided in the layer provided above the active layer, but it is also possible to provide in an arbitrary layer below the active layer. For example, it can be provided between the lower cladding layer 103 and the lower guide layer 104. Further, it is also effective as a configuration in which unevenness is provided on the surface of the substrate or the buffer layer and a lower cladding layer is provided thereon. In particular, when unevenness is provided in the lower part of the active layer, in addition to the structure modulation by the uneven structure itself, the effect of slight periodic modulation of the composition inherent in the crystal grown on the uneven structure is largely due to the effect of most elements including the active layer. Therefore, the effect of stabilizing the horizontal and transverse modes is increased, which is more effective. In particular, when unevenness is provided on the surface of the substrate, the uneven layer can be formed by a single crystal growth, so that manufacture is easy and inexpensive.

Embodiment 2
FIG. 2 illustrates a perspective view of the semiconductor laser device according to the second embodiment of the present invention. FIG. 2A is an overall view of the semiconductor laser device, in which a part is deleted to clarify the internal structure. FIG. 2B is a partially enlarged view. The semiconductor laser device 200 according to the second embodiment is a wide ridge stripe type broad area laser device that emits laser light of a first-order or higher-order horizontal transverse mode. In this laser element, a periodic different refractive index portion 211 is formed in a p-type upper cladding layer 210 above the active layer, and the length of the stripe-shaped current confinement portion is formed by forming the different refractive index portion 211. It is characterized in that the refractive index varies in a direction (X direction) orthogonal to the direction (Z direction) and parallel to the substrate 201.

The main semiconductor stacked portion of the semiconductor laser device 200 of the second embodiment is formed on a substrate 201 made of n-type GaN, a buffer layer 202 made of n-type GaN having a layer thickness of 0.5 μm, and an n-type Al _{0.05 having} a layer thickness of 2 μm. Lower cladding layer 203 made of Ga _0.95 N, lower guide layer 204 made of non-doped GaN with a thickness of 0.05 μm, well layer 205 made of InGaN with a thickness of 5 nm, barrier layer 206 made of InGaN with a thickness of 10 nm, layer thickness of 5 nm Well layer 207 made of InGaN, upper guide layer 208 made of non-doped GaN having a thickness of 0.05 μm, carrier block layer 209 made of p-type Al _0.3 Ga _0.7 N having a thickness of 0.02 μm, p having a thickness of 0.5 μm structure from the mold Al _0.05 Ga _0.95 upper cladding layer 210 composed of N contact layer 212 and a p-type GaN having a thickness of 0.1 [mu] m, It can be.

  In the upper clad layer 210, a different refractive index portion 211 made of p-type GaN with a layer thickness of 0.2 μm and a pitch of 4 μm is embedded. Except for the semiconductor stacked portion, a current confinement layer 213 made of polyimide, a Pd layer having a thickness of 15 nm and a Mo layer having a thickness of 15 nm are stacked in this order, and the thickness of the back surface of the n-type GaN substrate 201 is 5 nm. The ohmic electrode 215 is formed by stacking the Hf layer and the 150 nm thick Al layer in this order. Here, Mg is doped as the p-type impurity, and Si is doped as the n-type impurity.

By providing the current confinement layer 213 of polyimide, a current confinement structure is formed, and the current confinement width w can be 20 μm. Further, both end faces of the semiconductor laser element 200 are cleaved to obtain a Fabry-Perot resonator, and the pair of end face reflecting mirrors are orthogonal to the longitudinal direction (Z direction) of the stripe-shaped current confinement structure. Here, a low reflection film (not shown) made of an Al ₂ O ₃ film having a thickness of 80 nm and a reflectivity of emitted laser light of 5% is formed on the cleaved front end face, and is formed on the rear end face. Is a highly reflective film comprising four pairs of SiO ₂ film and TiO ₂ film, having a thickness of ¼ of the wavelength of the emitted laser light, and a reflectivity of the emitted laser light of 95% (Not shown) is formed, and the resonator length (the shortest distance between the front end face and the rear end face) of the Fabry-Perot resonator can be 1.5 mm.

  In the semiconductor laser element 200, a periodic different refractive index portion 211 is formed in a p-type upper cladding layer 210, and this different refractive index portion 211 is formed along the longitudinal direction (Z direction) of the stripe-shaped current confinement portion. They are arranged in a direction (X direction) that is orthogonal and parallel to the substrate. Further, the different refractive index portion 211 has a structure that extends uniformly in parallel with the longitudinal direction (Z direction) of the stripe-shaped current confinement portion, but is not on the entire surface of the resonator, and is a front surface from which laser light is emitted. It is provided only within a certain range (can be set to 500 μm) from the end surface reflecting mirror. As described above, in this embodiment, the structure in which the refractive index varies is provided in a layer other than the active layer, and the layer provided with the structure in which the refractive index varies is included in the layer. In a direction (X direction) perpendicular to the longitudinal direction (Z direction) of the stripe-shaped current confining portion and parallel to the substrate 201 (layer X direction). The refractive index of fluctuates.

When the semiconductor laser element 200 is mounted on a copper heat sink by junction down, sealed in a package with excellent heat dissipation, and a current is passed through the semiconductor laser element 200, a laser beam is emitted with a threshold current of 0.6 A, and a maximum of 1 Continuous oscillation up to 5W can be obtained. The current-light output characteristic changes linearly from the start of oscillation to the light output of 1.5 W, and so-called kink is not seen. The only difference is that the different refractive index portion 211 is not provided. In other respects, the semiconductor laser device having the same configuration has kinks, and the current-light output characteristics do not change linearly. Effectiveness is demonstrated. The wavelength of the laser light emitted from the semiconductor laser element in the present embodiment is 405 nm, and the near-field image when the laser light is emitted is stable in the state where there are a plurality of longitudinal modes. Further, laser light is emitted with a high internal quantum efficiency of 90% or more of the internal quantum efficiency η _i .

  In the first embodiment, an example in which periodic irregularities are formed inside the element is shown, whereas in the second embodiment, an example in which a periodic different refractive index portion is embedded in the element is shown. . In any configuration, the horizontal transverse mode is the same in that it is stabilized by a periodic refractive index variation in the horizontal direction, and the same effect can be obtained. In the first embodiment, the refractive index variation structure is provided in the entire resonator from the front end surface to the rear end surface, whereas in the second embodiment, the variation structure is provided only in the vicinity of the front end surface. Yes. As in Embodiment 2, if the horizontal transverse mode is stabilized at least in the vicinity of the front end face reflector where the laser light is emitted to the outside, unstable phenomena such as kinks do not appear outside, which is effective. is there. By providing the different refractive index portion, it is more preferable that the region where the refractive index fluctuates is 50 μm or more from the front exit end reflecting mirror. This point is the same in the configuration provided with the periodic unevenness shown in the first embodiment. In addition, the structure in which layers made of materials having different refractive indexes are discretely embedded is formed in a region where laser light exists inside the laser element. For example, the effect of the present invention is effectively exhibited by providing the upper cladding layer, or between the active layer and the upper cladding layer, or between the lower cladding layer or the active layer and the lower cladding layer.

Embodiment 3
FIG. 3 illustrates a perspective view of the semiconductor laser device according to the third embodiment. FIG. 3A is an overall view of the semiconductor laser device, and FIG. 3B is a partially enlarged view. The semiconductor laser device 300 according to the third embodiment is a wide ridge stripe type broad area laser device that emits a laser beam of a first-order or higher order horizontal transverse mode. In this laser element, periodic slit-shaped grooves are provided in a p-type contact layer and a p-type upper clad layer above the active layer. Since this slit is arranged in parallel to the longitudinal direction (Z direction) of the stripe-shaped current confinement portion, it is a direction orthogonal to the longitudinal direction (Z direction) of the stripe and parallel to the substrate (X direction). ) Is characterized in that the refractive index fluctuates periodically.

Here, the main semiconductor stacked portion of the semiconductor laser device 300 of the third embodiment includes an n-type GaN buffer layer 302 and an n-type GaN buffer layer 302 on a substrate 301 made of n-type GaN. A lower cladding layer 303 made of type Al _0.05 Ga _0.95 N, a lower guide layer 304 made of non-doped GaN with a thickness of 0.05 μm, a well layer 305 made of InGaN with a thickness of 5 nm, a barrier layer 306 made of InGaN with a thickness of 10 nm, Well layer 307 made of InGaN with a layer thickness of 5 nm, upper guide layer 308 made of non-doped GaN with a layer thickness of 0.05 μm, carrier block layer 309 made of p-type Al _0.3 Ga _0.7 N with a layer thickness of 0.02 μm, upper cladding layer 310 made of 5μm of p-type Al _0.05 Ga _0.95 N contact layer 31 and made of p-type GaN having a thickness of 0.1 [mu] m, Consisting of. The contact layer and the upper clad layer are provided with slit grooves 314 having a depth of 0.4 μm and a pitch of 5 μm, and the slit grooves can be filled with polyimide. Except for the semiconductor laminated portion, an insulating layer 312 made of polyimide, an ohmic electrode 313 obtained by laminating a Pd layer having a thickness of 15 nm and a Mo layer having a thickness of 15 nm in this order, and a back surface of the n-type GaN substrate 301 having a thickness of 5 nm. An ohmic electrode 315 is formed by stacking an Hf layer and an Al layer having a thickness of 150 nm in this order. Here, Mg is doped as a p-type impurity, and Si is doped as an n-type impurity.

The current confinement width w of the current confinement structure formed by the insulating layer 312 is 25 μm. Further, both end faces of the semiconductor laser element 300 are cleaved to obtain a Fabry-Perot resonator. Here, a low reflection film (not shown) made of an Al ₂ O ₃ film having a thickness of 80 nm and a reflectivity of the emitted laser light of 5% is formed on the cleaved front end face, and the rear end face is formed on the rear end face. A highly reflective film comprising four pairs of SiO ₂ film and TiO ₂ film, having a thickness of ¼ of the wavelength of the emitted laser light, and a reflectivity of the emitted laser light of 95% (see FIG. Not shown). The resonator length of the Fabry-Perot resonator (the shortest distance between the front end face and the rear end face) is 1.0 mm.

In the semiconductor laser device 300, the p-type upper cladding layer 310 is provided with slit-shaped grooves periodically in the direction (X direction) perpendicular to the longitudinal direction (Z direction) of the stripe-shaped current confinement portion and parallel to the substrate. 314 is arranged. The slit has a structure that extends uniformly in parallel to the longitudinal direction (Z direction) of the stripe-shaped current confinement portion, is orthogonal to the longitudinal direction (Z direction) of the stripe-shaped current confinement portion, and The refractive index in the parallel direction (X direction) varies. The semiconductor laser device 300 was mounted on a copper heat sink by junction down and sealed in a package with excellent heat dissipation. When a current was passed through the semiconductor laser element 300, a laser beam was emitted with a threshold current of 0.5A, and continuous oscillation was obtained up to a maximum of 1.5W. From the start of oscillation to the light output of 1.5 W, the current-light output characteristics changed linearly, and so-called kink was not observed. For comparison, in the case of a semiconductor laser device having the same configuration except that no slit-shaped groove is provided, kinks are observed and the current-light output characteristics do not change linearly. Wavelength of the laser light is 405 nm, was observed with near-field pattern when a laser beam emitted stably in a state in which a plurality of longitudinal modes were present, with a high internal quantum efficiency internal quantum efficiency eta _i is more than 90% Laser light is emitted.

  In this embodiment, unlike Embodiments 1 and 2 in which periodic irregularities or different refractive index portions are provided inside the element, slit-like grooves extending from the contact layer to the middle of the upper cladding layer are periodically provided. Yes. In any configuration, the horizontal transverse mode is the same in that it is stabilized by a periodic refractive index variation in the horizontal direction (X direction), and the same effect can be obtained. However, the structure provided with the slit is excellent in that it can be manufactured relatively inexpensively and with good reproducibility because the element is completed if it is dug into a slit shape by etching without the need for crystal regrowth. In this embodiment, the digged slit portion is embedded with polyimide. However, in the embodiment in which the slit portion is left hollow, it is embedded in an arbitrary material having a refractive index different from that of the p-type cladding layer. The present invention is effective. The slit-shaped digging may be provided in the entire resonator from the front end face to the rear end face as in the present embodiment, or may be provided only in the vicinity of the front end face as in the second embodiment. It is.

  In the first to third embodiments, a semiconductor laser element having an electrode stripe structure or a wide ridge structure is shown as an example of a broad area type laser element. The present invention can be applied to any semiconductor laser element that emits laser light in the above high-order horizontal transverse mode.

In the semiconductor laser device of the present invention, the material of the p-type cladding layer, the n-type cladding layer and the active layer is not particularly limited as long as it is a semiconductor material, and among these, the p-type cladding layer, the n-type cladding layer and the active layer are not limited. When the material of the layer is made of a nitride semiconductor material represented by the composition formula of Al _x Ga _1-xy In _y N (0 ≦ x ≦ 1,0 ≦ y ≦ 1), the effect of the present invention is sufficiently obtained. Obtainable. In this composition formula, x represents a mixed crystal ratio of Al, y represents a mixed crystal ratio of In, and 1-xy represents a mixed crystal ratio of Ga. Further, for nitride semiconductor materials represented by the composition formula of Al _x Ga _{1 -xy} In _y N (0 ≦ x ≦ 1,0 ≦ y ≦ 1), group III elements (boron etc.) and group V elements ( Arsenic, phosphorus, bismuth, etc.) can be mixed as appropriate, and impurity elements (zinc, beryllium, tellurium, magnesium, sulfur, selenium, silicon, etc.) can be appropriately blended.

  In the semiconductor laser device of the present invention, each of the p-type cladding layer and the n-type cladding layer may be a single layer or a plurality of layers. In the present invention, the p-type layer is arranged above the active layer and the n-type layer is arranged below the active layer. However, the upper and lower arrangements can be reversed. The structure of the active layer is not particularly limited, and for example, a single quantum well structure (SQW) or a multiple quantum well structure (MQW) can be applied. Further, there is no limitation on the strain amount or the well layer thickness of the layer constituting the active layer, and compressive or tensile strain may be introduced into the barrier layer constituting the active layer.

  In the semiconductor laser device of the present invention, the wavelength of the emitted laser light is not particularly limited and can be appropriately adjusted according to the application. The substrate is not particularly limited, and for example, a single crystal substrate such as a sapphire substrate, a silicon carbide substrate, a silicon substrate, or a gallium arsenide substrate can be used. Note that when these substrates are manufactured by crystal growth, they can be manufactured by any crystal growth method using any raw material. In the present invention, “upper” indicates a direction away from the substrate, and “lower” indicates a direction approaching the substrate.

Embodiment 4
The application system of the present invention includes the semiconductor laser element described above and a phosphor that absorbs at least a part of the laser light emitted from the semiconductor laser element and emits light having a wavelength different from the absorbed laser light. For example, a white illumination device including a semiconductor laser element and a phosphor that absorbs laser light having a wavelength shorter than 420 nm emitted from the semiconductor laser element and emits white light is exemplified. FIG. 4 shows a schematic principle diagram of a white illumination device as a preferred example of the application system of the present invention. As shown in FIG. 4, the basic configuration of the illumination device 400 includes a semiconductor laser element 401 having an oscillation wavelength of 405 nm, a lens system 402, and a phosphor 403 that converts laser light having a wavelength of 405 nm into white light. The semiconductor laser element 401 can be, for example, a semiconductor laser element having the same configuration as the semiconductor laser element 100 of the first embodiment. The phosphors 403 are red (Y ₂ O ₂ S: Eu ³⁺ ), green (ZnS: Cu, Al) and blue ((Sr, Ca, Ba, Mg) ₁₀ (PO ₄ ) ₆ Cl ₂ : Eu ^2+. ) Phosphor. In this illuminating device, when laser light is emitted from the semiconductor laser element 401, laser light having an oscillation wavelength of 405 nm is condensed on the phosphor 403, and white fluorescence 404 is emitted.

  Since the illumination device 400 uses the semiconductor laser element of the first embodiment as an excitation element for the phosphor, the amount and luminance of white light can be controlled linearly in accordance with the injection current to the semiconductor laser. And a small and high-brightness point light source can be obtained. In addition, an illumination system using a semiconductor laser as a light source is superior in that the electro-optical conversion efficiency is extremely high as compared with conventional illumination, the lifetime is long, and no toxic substance such as mercury is contained. Therefore, it is useful as an alternative device for fluorescent lamps and incandescent lamps.

  The wavelength of the laser beam used as the excitation light source is not necessarily 405 nm and can be adjusted according to the absorption line of the phosphor. For example, by including a semiconductor laser element and a phosphor that absorbs a part of blue laser light emitted from the semiconductor laser element and emits light having at least red and green spectral components, It is possible to provide a white illumination device that uses a blue (for example, wavelength 445 nm) semiconductor laser as a light source and converts blue laser light into red and green fluorescence. This white illuminating device is an excellent illuminating device having a small size, high luminance, high electro-optical conversion efficiency, and a long lifetime.

  The application system provided with the semiconductor laser device of the present invention is not limited to the illumination device of the fourth embodiment, but can output high-power and high-efficiency laser light such as a laser knife and various processing lasers or various excitation light sources. It can be applied to various necessary application systems. The oscillation wavelength of the semiconductor laser used as the excitation light source is not necessarily 405 nm, and can be appropriately selected according to the application form.

  The embodiment disclosed this time should be considered as illustrative in all points and not restrictive. The scope of the present invention is defined by the terms of the claims, rather than the description above, and is intended to include any modifications within the scope and meaning equivalent to the terms of the claims.

  It is possible to provide an application system such as an excellent white lighting device that is small, has high luminance, has high electro-optical conversion efficiency, and has a long lifetime.

1 is a perspective view of a semiconductor laser element in Embodiment 1. FIG. FIG. 6 is a perspective view of a semiconductor laser element in a second embodiment. FIG. 10 is a perspective view of a semiconductor laser element in a third embodiment. It is a typical principle figure of the white illuminating device in Embodiment 4. It is a figure which shows the electric current-light output characteristic of a semiconductor laser element. It is a figure which shows the peak of the emitted light intensity in the horizontal direction of a near-field image. It is a figure which shows the relationship between the period of an unevenness | corrugation, and the output from which a kink appears.

Explanation of symbols

  100, 200, 300, 401 Semiconductor laser element 101, 201, 301 Substrate, 102, 202, 302 Buffer layer, 103, 203, 303 Lower cladding layer, 104, 204, 304 Lower guide layer, 105, 107, 205, 207, 305, 307 Well layer, 106, 206, 306 Barrier layer, 108, 208, 308 Upper guide layer, 109, 209, 309 Carrier block layer, 110 Optical waveguide layer, 111, 210, 310 Upper cladding layer, 112, 212, 311 Contact layer, 113 Protective film, 211 Different refractive index part, 213 Current confinement layer, 312 Insulating layer, 314 Slit groove, 400 Illumination device, 403 phosphor, 404 White fluorescence.

Claims (10)

An upper clad layer, a lower clad layer, an active layer between the upper clad layer and the lower clad layer, and a ridge stripe-shaped current confinement structure are provided on the substrate, and are orthogonal to the longitudinal direction of the ridge stripe. A semiconductor laser element having a pair of end surface reflecting mirrors and generating laser oscillation in a first-order or higher-order horizontal transverse mode, wherein a longitudinal direction of the ridge stripe is provided in a region where laser light is present inside the semiconductor laser element Having a structure in which the refractive index varies in a direction perpendicular to the substrate and parallel to the substrate,
The ridge stripe-shaped current confinement structure includes a part of the upper cladding layer and a contact layer laminated thereon,
The structure in which the refractive index varies has a depth that reaches from the contact layer to the middle of the upper cladding layer constituting the current confinement structure, and has a depth shorter than the height of the ridge stripe. A semiconductor laser device having a plurality of slit-like grooves periodically provided in the structure . The semiconductor laser device according to claim 1, wherein the upper cladding layer and the refractive index in the slit-like grooves are different materials embedded. 2. The semiconductor laser device according to claim 1 , wherein the slit-shaped groove is hollow inside. 2. The semiconductor laser device according to claim 1 , wherein the plurality of slit-shaped grooves are provided at a pitch of 0.5 μm to 6 μm.   2. The semiconductor laser device according to claim 1, wherein the structure in which the refractive index fluctuates is provided at least in the vicinity of the emitting end surface reflecting mirror on the front surface of the semiconductor laser device.   The structure in which the refractive index fluctuates is a line that bisects the current confinement structure when viewed from the longitudinal direction of the stripe-shaped current confinement structure, and is line symmetric with respect to a line perpendicular to the substrate as an axis of symmetry. The semiconductor laser device according to claim 1. Said semiconductor laser device, a semiconductor laser device according to claim 1, characterized in that the _{Al x Ga 1-xy In y} N (0 ≦ x ≦ 1,0 ≦ y ≦ 1) of material.   2. An application system comprising: the semiconductor laser device according to claim 1; and a phosphor that absorbs at least part of laser light emitted from the semiconductor laser device and emits light having a wavelength different from that of the laser light. Said semiconductor laser device, the semiconductor wavelength emitted from the laser element absorbs the shorter laser beam than 420 nm, in claim 8, characterized in that a white illumination device comprising a phosphor that emits white light Application system described. A white illumination device comprising: the semiconductor laser element; and a phosphor that absorbs part of blue laser light emitted from the semiconductor laser element and emits light having at least red and green spectral components. The application system according to claim 8 .

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