JP4599836B2 - Semiconductor laser element - Google Patents

Description

The present invention relates to a semiconductor laser device having a band-like electrode confinement structure (ridge portion) in a part of a laminated structure including an active layer serving as a light emitting region.

  High-power semiconductor light-emitting elements are currently used in information terminal devices such as optical disk devices, laser beam printers, and copiers, and are also used for solid-state laser excitation, processing, and medical use. In addition, a semiconductor light emitting device with a maximum light output of 4 kW, which is unthinkable in the past, is commercially available.

  In general, the easiest way to increase the output of a semiconductor light emitting device is to make it a broad area, that is, to widen the width of the light emitting region. The so-called broad area type semiconductor light emitting device having such a wide light emitting region has a narrow stripe width (the width of the region through which the operating current is narrowed and passed) of an ordinary narrow stripe type semiconductor light emitting device having a narrow light emitting region. The stripe width is several tens μm to several hundreds μm while it is several μm.

  However, due to the broad area, (1) instability of transverse mode, (2) reduction in device lifetime, (3) occurrence of optical damage (COD), (4) occurrence of thermal saturation, etc. It has been pointed out that there are many undesirable problems.

  Both of these problems are caused by an increase in photon density and an increase in injected carriers. For example, an increase in photon density is caused by a spatial hole burning phenomenon (carriers are consumed by stimulated emission and the maximum light intensity is increased). Cause the carrier mode to become smaller than the surroundings) and destabilize the transverse mode. Also, the increase in injected carriers is a factor that causes the refractive index to decrease due to the plasma effect and destabilizes the transverse mode.

  Therefore, conventionally, (1) the width of the waveguide section is made equal to or less than the carrier diffusion length (2 to 3 μm), and the gain is made uniform. (2) The light spot diameter is increased to reduce the photon density (specifically, (3) A refractive index waveguide structure sufficient for the plasma effect, by thinning the active layer to increase the light seepage into the cladding layer, or by providing optical waveguide layers above and below the active layer to increase the spot diameter) Semiconductor light-emitting elements in which measures such as manufacturing are taken are provided.

  However, the high-power semiconductor light-emitting element in which such countermeasures have been taken has excellent characteristics such as high efficiency, small size, and low cost compared to solid-state lasers and gas lasers, It has a major drawback of inferior beam characteristics. FIG. 4 accurately represents the relationship between the light output (horizontal axis) of these light emitting elements and the like and M2 (no unit) representing the beam characteristics. In FIG. 4, A represents a conventional high-power semiconductor light emitting device, B represents a carbon dioxide laser, and C represents a solid-state laser. Here, M2 representing the beam characteristic indicates that the closer to 1, the higher the quality. That is, in this high-power semiconductor light emitting device A, M2 is close to 1 in a low-output region that can sufficiently cope with a device having a narrow stripe structure, and the beam characteristics are excellent. Becomes far from 1, and the beam characteristics deteriorate.

Non-Patent Documents 1 and 2 disclose a tapered stripe laser diode similar to the semiconductor light emitting device of the present invention. As shown in FIG. 5, the tapered stripe type semiconductor laser device 110 includes, for example, an n-type buffer layer 113 made of GaAs on the surface of an n-type substrate 112 made of GaAs (gallium arsenide), Al _x Ga _{1− x} n-type cladding layer 114 made of As (aluminum gallium arsenide) (0 <x <1), n-type light guide layer 115 made of Al _y Ga _1-y As (0 <y <1), Al _z Ga ₁ active layer 116 made of _-z As (0 <z <1), p-type light guide layer 117 made of Al _y Ga _1-y As (0 <y <1), Al _x Ga _1-x As (0 <x The p-type cladding layer 118 made of <1) and the p-type cap layer 119 made of GaAs are sequentially stacked. A portion from the surface of the laminated structure to the intermediate position of the p-type cladding layer 118 is selectively removed by, for example, RIE (Reactive Ion Etching) to form a belt-like ridge portion 120a. A p-side electrode 152 is provided on the surface of the ridge portion 120a. The p-side electrode 152 has a tapered shape, and the width Ww of one end face (exit-side end face) in the active layer 116 is wide. The end face width Wn is narrowed. The side surface of the ridge portion 120a and the upper region of the skirt portion 120b of the ridge structure 120 are embedded with a protective layer 121 made of SiO ₂ (silicon dioxide). An n-side electrode 153 is formed on the back surface of the n-type substrate 112.

In this semiconductor laser device, in particular, Ln, Wn, Ww, and ψ are structural parameters, and by finding an optimum condition together with the optical confinement coefficient Γ, the beam characteristics are improved, and for example, M2 = 2 at 2W oscillation.
Roland Diehl, “High-power Diode Laser Fundamentals, Technology, Applications”, Springer Takahisa Kanno et al., "Shaping Technology of Semiconductor Laser Beam", Laser Research May 2003

  However, this semiconductor laser device has problems such as complicated device design, difficulty in setting optimum conditions, complicated manufacturing process, and narrow range of optimum values.

The present invention has been made in view of the above problems, its object is to provide a semiconductor laser device having an improved bi chromatography beam characteristics.

A semiconductor laser device according to the present invention is a semiconductor laser device having a stacked structure in which at least a first conductivity type cladding layer, an active layer serving as a light emitting region, and a second conductivity type cladding layer are stacked in this order. A band-shaped ridge portion provided along the waveguide direction of light generated in the active layer in a portion from the surface of the structure to the intermediate position of the cladding layer of the second conductivity type, and provided on the surface of the ridge portion, Since the shape of at least one of the edges is a wave shape that periodically changes along the waveguide direction, the wide and narrow portions that are wide along the waveguide direction are alternately arranged. a second conductivity type electrode, while being continuously formed in the ridge portion by a portion of the second conductivity type cladding layer, the shape of the surface of that, same as the edge shape of the electrodes along the waveguide direction With a waveform shape that changes periodically with period The Rukoto, a skirt thickness of the thickness of the layer along the waveguide direction is larger thickness portion and the layers have alternately a small thin layer portion, an insulating layer covering the surface of the sides and bottom portion of at least the ridge portion The layer thickness part of the bottom part and the wide part of the electrode correspond to the end in the waveguide direction.

In the semiconductor laser device of the present invention, carriers injected from the second conductivity type electrode are activated by giving a gain to a region substantially the same as the shape of the electrode in the active layer. As a result, light is emitted, and the light is guided through the active region inside the active layer, is amplified while being repeatedly reflected at the end face of the resonator, and is emitted as laser light when amplified to a certain level. At this time, the shape of the edge of the second conductivity type electrode, and each shape of the surface of the skirt, not straight, because the waveform shape together periodically varies along the waveguiding direction, the electrode shape and In each skirt shape, an index guide region having a large effective refractive index difference (Δn) and a gain guide region having a small effective refractive index difference (Δn) are generated, and these regions work complementarily. That is, carriers and light are effectively confined in the active region, and the guided light is amplified while generating or suppressing filaments while expanding or narrowing the width in the active region. As a result, the transverse mode is stabilized, and light is emitted as a laser having a beam characteristic M2 close to 1.

According to the semiconductor laser device of the present invention, both the shape of the edge of the second conductivity type electrode on the surface of the ridge portion and the shape of the surface of the skirt portion periodically change along the waveguide direction. Since it has a corrugated shape, light and carriers can be efficiently confined in the active region in the active layer, the characteristics of the emitted laser can be controlled, and the beam characteristics can be improved.

  In particular, when the electrode has a shape in which the wide wide portion and the narrow narrow portion change periodically, and the wide portion is 10 μm or more, the amount of injected carriers can be increased, and the light emission output can be increased. Can be high.

  Embodiments of the present invention will be described below with reference to the drawings.

  FIG. 1 shows a cross-sectional structure of a semiconductor laser device according to an embodiment of the present invention. Here, as an example, a GaAs semiconductor laser element will be described. In the figure, each component schematically shows the shape, size, and arrangement relationship to the extent that the present invention can be understood, and is different from the actual size.

The semiconductor laser device 10 includes, for example, an n-type buffer layer 13 made of GaAs and an n _- type clad layer 14 made of Al _x Ga _1-x As (0 <x <1) on an n-type substrate 12 made of GaAs. N-type light guide layer 15 made of Al _y Ga _1-y As (0 <y <1), active layer 16 made of Al _z Ga _1-z As (0 <z <1), Al _y Ga _1-y A p-type light guide layer 17 made of As (0 <y <1), a p-type cladding layer 18 made of Al _x Ga _1-x As (0 <x <1), and a p-type cap layer 19 made of GaAs are sequentially formed. It has a laminated structure.

  An n-type impurity, for example, Se (selenium) is added as a dopant to the n-type buffer layer 13, the n-type cladding layer 14, and the n-type light guide layer 15. The p-type light guide layer 17, the p-type cladding layer 18 and the p-type cap layer 19 are added with a p-type impurity, for example, Zn (zinc) as a dopant.

  Specific layer thickness and width of each part are as follows, for example. The thickness of the n-type buffer layer 13 is 0.5 μm, the thickness of the n-type cladding layer 14 is 1.5 μm, the thickness of the n-type light guide layer 15 is 0.04 μm, and the thickness of the active layer 16 is 0.012 μm. The p-type light guide layer 17 has a thickness of 0.04 μm, the p-type cladding layer 18 has a thickness of 1 μm, the p-type cap layer 19 has a thickness of 0.5 μm, and the n-type substrate 12 has a thickness of 120 μm.

The upper part of this laminated structure, that is, the p-type cladding layer 18 and the p-type cap layer 19 have a ridge structure 20 composed of a ridge portion 20a and a skirt portion 20b. The ridge portion 20 a is formed by selectively removing a portion from the surface of the p-type cap layer 19 to the intermediate position of the p-type cladding layer 18. The ridge portion 20 a has a substantially trapezoidal cross section and is generated in the active layer 16. It has a shape extending in a band shape along the light guiding direction. The skirt portion 20b is constituted by the remaining lower region of the p-type cladding layer 18, and covers the entire upper surface of the active layer 16 together with the ridge portion 20a. A protective layer 21 made of, for example, SiO ₂ (silicon dioxide) is buried in the side surface of the ridge portion 20a and the upper surface region of the skirt portion 20b to form a current confinement structure together with the ridge portion 20a. On the surface of the ridge portion 20a, one electrode (p-side electrode 52) made of, for example, Au (gold) / Pt (platinum) / Ti (titanium) is formed, and on the back surface of the n-type substrate 12, for example, Au / AuGe The other electrode (n-side electrode 53) made of (gold / germanium) / Au is formed.

  The present embodiment is characterized in that the width of one p-side electrode 52 and the thickness of the p-type cladding layer 18 constituting the skirt 20b of the ridge structure 20 both change along the waveguide direction. is doing. In other words, the p-side electrode 52 has a substantially band shape along the surface of the ridge portion 20a, but has a shape in which the edges 52a on both sides thereof fluctuate in a direction perpendicular to the waveguide direction, for example, a shape that periodically changes to a waveform ( Waveform shape), which has wide portions 52b having a wide width and narrow portions 52c having a narrow width. Similarly, the surface of the skirt portion 20b of the ridge structure 20 also has a waveform shape that periodically fluctuates along the waveguide direction, and the thin layer portion 20b1 having a small layer thickness and the thick layer portion 20b2 having a large layer thickness. Alternately.

  With such a configuration, in the active layer 16, a region corresponding to the shape of the p-side electrode 52 is activated and emits light substantially in that portion, but the region corresponding to the wide portion 52 b of the p-side electrode 52 is effective. On the other hand, the region corresponding to the narrow portion 52c of the p-side electrode 52 is an index (refractive index) guide region having a large effective refractive index difference (Δn). Become.

  Note that the shape of the edge 52a of the p-side electrode 52 may be rectangular or indefinite, but it is preferable to have the waveform shape as described above because it is easy to manufacture. Further, the change of the edge 52a of the p-side electrode 52 is desirably periodic, but may be a non-periodic change. The periodic change of the p-side electrode 52 is preferably repeated three or more times.

  In the present embodiment, the shape of the edges 52a on both sides of the p-side electrode 52 is axisymmetric with respect to the center line of the p-side electrode 52, but may be asymmetric. However, by using line symmetry, the width difference between the wide portion 52b and the narrow portion 52c can be maximized, which is more effective.

  The width of the wide portion 52b of the p-side electrode 52 is preferably 10 μm or more, and more preferably 60 μm or more from the viewpoint of increasing the amount of injected carriers and increasing the output, for example. On the other hand, the width of the narrow portion 52c of the p-side electrode is, for example, from the viewpoint of making the gain of the active region in the active layer 16 uniform, suppressing the generation of filaments, and bringing the beam characteristic M2 of the laser that emits light closer to 1. It is preferably about 1 μm or more and 10 μm or less.

  The p-side electrode 52 has an end 52d, that is, a region corresponding to the end surface (resonator end surface) of the active layer 16 in the waveguide direction is a wide portion 52b. By making the wide portion 52b correspond to the resonator end face in this way, the laser output can be increased and the beam characteristic M2 can be improved.

  Here, the edge 52a of the p-side electrode 52 has a shape that changes on both sides here, but it may have a form in which only one side changes.

  The skirt 20b of the ridge structure 20 has a shape in which the surface fluctuates in the direction perpendicular to the waveguide direction along the waveguide direction. At this time, the p-side electrode formed inside the active layer 16 The region substantially the same as the shape of 52 is the activated region, but the region corresponding to the layer thickness portion 20b2 of the skirt portion 20b is a gain guide region having a small effective refractive index difference (Δn), and the layer of the skirt portion 20b. A region corresponding to the thin portion 20b1 is an index guide region having a large effective refractive index difference (Δn).

As the layer thickness d1 of the skirt 20b of the ridge structure 20 decreases, the effective refractive index difference in the active layer increases, and the gain guide region (Δn <0.001) to the weak index guide region (0.001 <0.001). The guiding changes from Δn <0.004) to the index guide region (0.004 <Δn). In the semiconductor laser device of the present embodiment, the effective refractive index difference can be changed in the range of 1 × 10 ⁻⁴ <Δn <5 × 10 ⁻³ .

  The shape of the surface of the skirt 20b of the ridge structure 20 is not limited to a periodic waveform, and may be an aperiodic waveform, a rectangle, or an indeterminate shape. Similarly, a periodic waveform is preferred. Further, it is desirable that the light emitting end face (that is, the resonator end face) in the active layer 16 correspond to the layer thickness portion 20b2 of the skirt portion 20b as shown in FIG. This is because the laser output can be increased and the beam characteristic M2 can be improved.

  In the semiconductor laser device 10 of the present embodiment, the number of periodic changes in the waveform shape of the p-side electrode 52 is the same as the number of periodic changes in the waveform shape of the surface of the skirt 20b of the ridge structure 20. In addition, the wide portion 52b of the p-side electrode 52 and the layer thickness portion 20b2 of the skirt portion 20b are both arranged corresponding to the end face of the resonator. That is, the region corresponding to the wide portion 52b of the p-side electrode 52 and the region corresponding to the layer thickness portion 20b2 of the skirt portion 20b coincide with each other to become a gain guide region. The region activated corresponding to the narrow portion 52c and the region corresponding to the thin layer portion 20b1 of the skirt portion 20b coincide with each other and become an index guide region.

  Next, a method for manufacturing the semiconductor laser device 10 of the present embodiment will be described.

  As shown in FIG. 2, the n-type buffer layer 13, the n-type cladding layer 14, and the n-type buffer layer 13 are formed on the (100) surface of the n-type substrate 12 by MOCVD (Metal Organic Chemical Vapor Deposition). The n-type light guide layer 15, the active layer 16, the p-type light guide layer 17, the p-type optical cladding layer 18 and the p-type cap layer 19 are sequentially epitaxially grown to produce a laminated structure. At this time, an n-type impurity, for example, Se (selenium) is used for the n-type buffer layer 13, the n-type cladding layer 14, and the n-type light guide layer 15 as dopants, and the p-type light guide layer 17, p-type cladding is used. A p-type impurity such as Zn (zinc) is added to the layer 18 and the p-type cap layer 19.

  Subsequently, a strip-like resist mask (not shown) is formed on the upper surface of the laminated structure in the light guiding direction, that is, in the direction of the resonator 23 by photolithography. Next, as shown in FIG. 3, using this resist mask, etching is performed from the surface of the laminated structure to the intermediate position of the p-type clad layer 18 by, for example, RIE, thereby having a ridge portion 20a and a skirt portion 20b. A ridge structure 20 is formed. At this time, the bottom 20b of the ridge structure 20 is etched so that the surface fluctuates in the direction perpendicular to the light guiding direction along the light guiding direction, and then the resist mask is removed.

  Next, as shown in FIG. 1, a protective layer 21 is deposited by MOCVD so as to cover the side surface of the ridge 20a and the surface of the skirt 20b of the ridge structure 20. Subsequently, the p-side electrode 52 made of, for example, Au / Pt / Ti and having the above-described pattern is formed on the surface of the ridge portion 20a of the ridge structure 20, and the n-side made of Au / AuGe / Au on the back surface of the substrate 12. An electrode 53 is formed.

  In the semiconductor laser device 10 according to the present embodiment formed in this way, carriers injected from the p-side electrode 52 gain gain in a region substantially the same as the shape of the p-side electrode 52 inside the active layer 16. Put on and activate. The light thus generated is guided through the active region inside the active layer 16 and amplified while being repeatedly reflected by the resonator 23. When the light is amplified to a certain level or more, it is output as a laser.

  In the present embodiment, since the wide portion 52b and the narrow portion 52c are formed in the p-side electrode 52, the active region corresponding to the wide portion 52b in the active layer 16 has an effective refractive index difference (Δn). The small gain guide region, on the other hand, the active region corresponding to the narrow portion 52c of the p-side electrode 52 is an index guide region having a large effective refractive index difference (Δn). Therefore, carriers and light are effectively confined in the active region inside the active layer 16, and the guided light generates or suppresses filaments while expanding or narrowing the width in the active region. It is amplified while. Therefore, the transverse mode is stabilized, and light is emitted as a laser having a beam characteristic M2 close to 1. In particular, when the wide portion 52b of the p-side electrode 52 is 10 μm or more, the amount of carriers to be injected can be increased, so that a high-power laser emits light.

  In addition, in the present embodiment, the layer thickness portion 20b2 and the layer thin portion 20b1 are also formed in the skirt portion 20b of the ridge structure 20, and a region corresponding to the layer thickness portion 20b2 of the active region in the active layer 16 Is a gain guide region having a small effective refractive index difference (Δn), and a region corresponding to the thin layer portion 20b1 is an index guide region having a large effective refractive index difference (Δn). Therefore, also by the layer thickness portion 20b2 and the layer thin portion 20b1, similarly to the p-side electrode 52, carriers and light are effectively confined in the active region inside the active layer 16, and this also stabilizes the transverse mode. And beam characteristics are improved.

  Furthermore, in the present embodiment, as described above, the region that becomes index guide (gain guide) by the p-side electrode 52 and the region that becomes index guide (gain guide) of the skirt 20b coincide. Therefore, both of them can confine carriers and light more effectively in the active region inside the active layer 16, the lateral mode is further stabilized, and the beam characteristics are further improved.

  While the present invention has been described with reference to the embodiment, the present invention is not limited to the above embodiment, and various modifications can be made. For example, the buffer layer, the grad layer, the light guide layer, and the active layer may be formed of materials such as InGaAs / InGaAsP, GaInNAs / GaAs, GaInP / AlGaInP, and GaN / InGaN. In addition, as a method of performing epitaxial growth, a halide vapor phase growth method, a molecular beam epitaxy (MBE) method, sputtering, a liquid phase epitaxy (LPE) method, or the like may be used. The etching process may be dry etching, wet etching, or a combination thereof.

The semiconductor laser device of the present invention can be used for solid laser excitation, processing, and medical use, for example.

It is sectional drawing showing the structure of the semiconductor laser element which concerns on one embodiment of this invention. FIG. 3 is a diagram showing a manufacturing process of the semiconductor laser element shown in FIG. 1. FIG. 3 is a diagram illustrating a manufacturing process subsequent to FIG. 2. It is the figure which showed the relationship between the light output and beam characteristic of the conventional high output semiconductor light-emitting device and another light-emitting device. It is sectional drawing showing the structure of the conventional taper stripe type semiconductor laser element.

Explanation of symbols

10 ... semiconductor laser device, 12, 112 ... n-type substrate (GaAs), 13,113 ... n-type buffer layer (GaAs), 14,114 ... n-type cladding layer _{(Al x Ga 1-x As} ), 15,115 ... n-type optical guide layer _{(Al y Ga 1-y As} ), 16,116 ... active layer _{(Al z Ga 1-z As} ), 17,117 ... p -type optical guide layer _{(Al y Ga 1-y As} ) 18, 118 ... p-type cladding layer (Al _x Ga _1-x As), 19, 119 ... p-type cap layer (GaAs), 20, 120 ... ridge structure, 20a, 120a ... ridge part, 20b, 120b ... skirt parts, 21, 121 ... protective layer (SiO _2), 23 ... cavity, 52, 152 ... p-side electrode, 52a ... edge, 52 b ... wide portion, 52c ... narrow portion, 52 d ... end, 53, 153 ... n Side electrode, 110 ... taper / striped semiconductor laser element

Claims (4)

A semiconductor laser device having a laminated structure in which at least a first conductivity type cladding layer, an active layer serving as a light emitting region, and a second conductivity type cladding layer are laminated in this order,
A band-shaped ridge portion provided along a waveguide direction of light generated in the active layer in a portion from the surface of the laminated structure to an intermediate position of the cladding layer of the second conductivity type;
A wide portion that is provided on the surface of the ridge portion and at least one edge of the ridge portion has a waveform shape that periodically changes along the waveguide direction. And second conductivity type electrodes having alternating narrow and narrow portions ,
Wherein together with the second being formed continuously with the ridge portion by a portion of the conductivity type of the cladding layer, the shape of the surface of its periodic shape the same period of the edge of the electrode along the guiding direction A skirt having alternating layer thickness portions with a large layer thickness and thin layer portions with a small layer thickness along the waveguide direction ,
An insulating layer covering at least the side surface of the ridge portion and the surface of the skirt portion , and
A semiconductor laser element in which a layer thickness portion of the skirt portion and a wide portion of the electrode correspond to an end in the waveguide direction . Periodic variation of the waveform shape of the electrode is Ru repeated more than 3 times
The semiconductor laser device 請 Motomeko 1 wherein. The shape of both side edges of said electrodes Ru axisymmetrical der each other with respect to a center line of the electrode
請 Motomeko 1 or claim 2 The semiconductor laser device according. Width of the narrow portion of the electrode is 1 to 10 [mu] m, the width of the wide portion is Ru der than 10μm
The semiconductor laser device 請 Motomeko 3 wherein.

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