JP2010098238A - Semiconductor light-emitting element - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a crack-free semiconductor light-emitting element by achieving a thinner film and higher Al composition of a clad layer without continuously forming metal films from a trench to the back surface of a substrate. <P>SOLUTION: The semiconductor light-emitting element includes: a conductive substrate 1; a first clad layer 2 of a first conductivity type, comprising a nitride semiconductor and formed on the conductive substrate 1; an active layer 4 formed on the first clad layer 2; and a second clad layer 6 of a second conductivity type formed on the active layer 4, wherein an optical waveguide 7 is formed in the second clad layer 6. On the conductive substrate 1 at least right under the optical waveguide 7, a groove penetrating the conductive substrate 1 is formed. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to improvement of characteristics of a semiconductor light emitting device.

  A GaN-based semiconductor laser element which is a semiconductor light emitting element is indispensable as a light source for a next-generation high-density optical disk apparatus. A GaN-based semiconductor laser device having an emission wavelength band of 405 nm that is currently in practical use has a ridge-type waveguide.

In general, a GaN-based semiconductor laser device is formed by laminating an n-type cladding layer made of an AlGaN layer, an active layer, a p-type cladding layer made of an AlGaN layer, and a p-type contact layer on a GaN substrate. A ridge portion is constituted by a part of the p-type contact layer and the p-type cladding layer. A dielectric film such as SiO ₂ having a lower refractive index than the ridge portion is formed on the side surface of the ridge portion and on the p-type cladding layer other than the ridge portion, and current confinement and lateral light confinement are performed.

  The refractive index of the GaN substrate is higher than that of AlGaN forming the n-type cladding layer, and oscillation light may leak to the GaN substrate and propagate (substrate mode). In order to prevent this, the n-type cladding layer is formed with a relatively large thickness of about 2 μm.

In the n-type cladding layer on the GaN substrate, cracks often occur because tensile strain is accumulated during crystal growth of Al _x Ga _1-x N. This occurs particularly when the n-type cladding layer is thick or when the n-type cladding layer has a high Al composition. The total thickness of the p-side cladding layer and the n-side cladding layer is about 2.5 μm. In this configuration, in order to realize crack-free, the Al composition is generally about x = 0.03 to 0.07.

  In the laser structure, the higher the Al composition of the cladding layer, the lower the oscillation threshold current and the operating current, and the better the temperature characteristics. There are two main reasons for this. One reason is that the larger the refractive index difference between the cladding layer and the active layer, the larger the value of the optical confinement coefficient Γ in the active layer (from the viewpoint of optical confinement). The other is that the band discontinuity between the active layer and the clad layer can be increased, and the overflow of carriers from the active layer can be suppressed (in view of carrier confinement). However, in the actual laser structure design, as described above, the Al composition cannot be increased so much from the viewpoint of suppressing cracks.

  If the GaN substrate can be removed, there is no substrate mode propagation, so a thick n-type cladding layer is not necessary. Moreover, if the n-type cladding layer can be made thin, the Al composition that can be realized without cracks can be increased, which is advantageous from the viewpoint of optical confinement and carrier confinement. However, it is technically difficult to remove the entire substrate with a laser structure. In addition, there is a problem that chip handling becomes difficult in a cleavage step or the like.

Patent Document 1 discloses a configuration in which a trench is formed on the back side of a substrate. If the width of the trench is only a portion related to the near field of the laser oscillation light, the chip handling property is hardly deteriorated. The substrate is a high-resistance sapphire substrate with low thermal conductivity. By continuously covering the back surface of the substrate and the bottom of the trench with the metal film, heat can be efficiently released from the active layer.
Japanese Patent Laid-Open No. 2002-232003

  However, at present, when it is common to use a GaN substrate having good thermal conductivity as the substrate, the structure in which the trench is provided for heat dissipation has a small heat dissipation effect. Furthermore, it is very difficult to continuously form a metal film from the trench to the back surface of the substrate with respect to the trench having a depth corresponding to the thickness of the substrate (usually 100 to 400 μm).

  The present invention provides a crack-free semiconductor light emitting device having high heat dissipation efficiency without forming a metal film continuously from the trench to the back surface of the substrate, and realizing a thin cladding layer and a high Al composition. For the purpose.

  The semiconductor light emitting device of the present invention includes a conductive substrate, a first conductivity type first cladding layer made of a nitride semiconductor formed on the conductive substrate, and an active layer formed on the first cladding layer. And a second conductivity type second cladding layer formed on the active layer, and an optical waveguide is formed in the second cladding layer. In order to solve the above problems, the conductive substrate has conductivity, and the conductive substrate at least directly below the optical waveguide is formed with a groove penetrating the conductive substrate. To do.

  According to the present invention, by forming a trench in a conductive substrate, it has high heat dissipation efficiency without forming a metal film continuously from the trench to the back surface of the substrate, and the cladding layer is thinned and the Al composition is high. Thus, it is possible to provide a crack-free semiconductor light-emitting device that realizes the above.

The semiconductor light emitting device of the present invention can take various modes based on the above-described configuration. That is, in the semiconductor light emitting device of the present invention, the conductive substrate is made of Al _y Ga _1-y N (y ≧ 0), and the first cladding layer is made of Al _x Ga _1-x N (x> 0). The value (xy) obtained by subtracting the Al composition ratio y of the conductive substrate from the Al composition ratio x of the first cladding layer is 0.15 or less, and the thickness of the first cladding layer is It can be set as the structure which is 0.3 micrometer or more.

  The width of the groove may be wider than the width of the optical waveguide.

  Moreover, it can be set as the structure by which resin was embedded in the said groove | channel. Furthermore, it is preferable that the resin embedded in the groove has a refractive index of 2 or less at the light emission wavelength of the element.

  Hereinafter, embodiments of the semiconductor light emitting device of the present invention will be described with reference to the drawings, taking a semiconductor laser device as an example.

(First embodiment)
FIG. 1 is a cross-sectional view showing the structure of the semiconductor laser device according to the first embodiment of the present invention. The substrate 1 is a conductive substrate made of n-type GaN. On one main surface (front surface) of the substrate 1, an n-type cladding layer 2 made of n-type Al _x Ga _1-x N (x = 0.15) is formed to a thickness of 0.5 μm. On the n-type cladding layer 2, an n-type light guide layer 3 made of n-type Al _x Ga _1-x N (x = 0.003) is formed to a thickness of 0.1 μm. On the n-type optical guide layer 3, the barrier layer and the thickness of 3nm consisting of thickness _{8nm In z Ga 1-z N} (z = 0.02) In z Ga 1-z N (z = 0.08 The triple quantum well active layer 4 in which the well layers made of

A p-type light guide layer 5 made of p-type GaN is formed on the triple quantum well active layer 4 to a thickness of 0.1 μm. A p _- type cladding layer 6 made of p-type Al _x Ga ₁ -xN (x = 0.15) is formed on the p-type light guide layer 5. A part of the p-type cladding layer 6 is formed in a ridge shape. The thickness from the bottom surface of the p-type cladding layer 6 to the upper end of the ridge-shaped portion is 0.5 μm, and the thickness other than the ridge-shaped portion is 60 nm. On the ridge-shaped portion of the p-type cladding layer 6, a contact layer 8 made of p-type GaN is formed to a thickness of 60 nm. Hereinafter, the ridge-shaped portion of the p-type cladding layer 6 and the contact layer 8 are collectively referred to as a ridge portion 7.

A dielectric film 9 made of SiO ₂ is formed on the p-type cladding layer 6 other than the ridge portion 7 and on a part of the side surface of the ridge portion 7. Since the dielectric film 9 has a refractive index smaller than that of the ridge portion 7, the ridge portion 7 serves as a waveguide. Here, the waveguide means a current-carrying portion of the current confinement structure. For example, in the case of a ridge structure, it means a ridge portion, and in the case of a buried structure shown in a third embodiment to be described later, the opening portion of the current blocking layer. Say that.

  A p-type ohmic electrode 10 made of Pd / Pt is formed on the contact layer 8. A p-type pad electrode 11 made of Ti (50 nm) / Pt (35 nm) / Au (500 nm) is formed on the ohmic electrode 10 and the dielectric film 9.

  In the substrate 1, a trench 12 penetrating at a position facing the ridge portion 7 is formed. An n-type ohmic electrode 13 made of a Ti (5 nm) / Pt (100 nm) / Au (1 μm) layer is formed on the back surface of the substrate 1 on which the n-type cladding layer 2 is formed. The n-type ohmic electrode 13 is not formed on the n-type cladding layer 2. Since the trench 12 is formed at a position facing the ridge portion 7 of the substrate 1, the substrate mode can be suppressed even if the thickness of the cladding layers 2 and 6 is reduced.

In a general semiconductor laser element, a layer having an Al composition of about x = 0.03 to 0.07 and a thickness of about 2 μm is used for an n-type Al _x Ga _1-x N cladding layer. In the semiconductor laser device according to this embodiment, the n-type cladding layer 2 has an Al composition of x = 0.15 and a thickness of 0.5 μm. The Al composition of the p-type cladding layer 6 is also x = 0.15. Since the thickness of the n-type cladding layer 2 is thin, no crack is generated even when the Al composition is increased to x = 0.15.

  Here, the thickness of each of the n-type cladding layer 2 and the p-type cladding layer 6 is preferably about 0.3 μm or more. This is because the component where the guided light leaks to the outside of the cladding layer becomes conspicuous and the waveguide loss cannot be ignored.

Further, the higher the Al composition of the n-type cladding layer 2 and the p-type cladding layer 6 is desirable, but when GaN is used as the substrate 1, the upper limit of the Al composition is about x = 0.15. This is from the viewpoint of avoiding the occurrence of cracks. Note that the substrate 1 is not limited to this when a free-standing AlGaN substrate manufactured by a laser lift-off method or the like is used. In the free-standing AlGaN substrate, the force applied to the substrate 1 by the strain caused by the growth of the cladding layers 2 and 6 applied to the AlGaN substrate can be reduced, so that the Al composition of the cladding layers 2 and 6 can be further increased. In this case, it is possible to increase the Al composition of the substrate _{1 (Al y Ga 1-y} N) y, the Al composition of the cladding layers 2 and 6 to about x = 0.15 + y When x.

  As described above, in the semiconductor laser device according to this embodiment, the trench 12 is formed in the substrate 1 at a position facing the ridge portion 7. For this reason, even if the cladding layers 2 and 6 are combined and thinned to a thickness of 1 μm, the guided light can be prevented from leaking out of the cladding layers 2 and 6. Since the cladding layers 2 and 6 can be made thin, the Al composition of the cladding layers 2 and 6 can be increased. As a result, the oscillation threshold current and the operating current of the semiconductor laser element can be reduced, and the temperature characteristics are improved.

  Next, a method for manufacturing the semiconductor laser device according to this embodiment will be described. 2A to 2M are cross-sectional views showing the manufacturing process of the semiconductor laser device according to this embodiment. In the present embodiment, a plurality of semiconductor laser elements are formed on a wafer-like substrate 1 and then divided for each element.

First, as shown in FIG. 2A, an n-type cladding layer 2, an n-type light guide layer 3, a triple quantum well active layer 4, and a p-type are formed on a wafer-like substrate 1 using metal organic chemical vapor deposition (MOCVD). The light guide layer 5, the p-type cladding layer 6, and the contact layer 8 are laminated. Next, an SiO ₂ mask 21 is formed on the contact layer 8. Next, the SiO ₂ mask 21 is patterned into a stripe shape having a width of 1.5 μm by reactive ion etching (RIE).

Next, as shown in FIG. 2B, the contact layer 8 and part of the p-type cladding layer 6 are etched using Cl ₂ gas in an inductively coupled dry etching apparatus using the SiO ₂ mask 21 as a mask. At this time, etching is performed so that a portion other than the ridge portion 7 of the p-type cladding layer 6 has a thickness of 60 nm. Therefore, the height of the ridge portion 7 is 0.5 μm (60 nm (contact layer 8) +440 nm (p-type cladding layer 6)).

  FIG. 2B shows a case where the contact layer 8 and a part of the p-type cladding layer 6 are etched, and the p-type cladding layer 6 in a region other than the ridge portion 7 is left by a thickness of 60 nm. However, the p-type cladding layer 6 in a region other than the ridge portion 7 may be completely removed by etching.

Next, as shown in FIG. 2C, the SiO ₂ mask 21 is removed by buffered hydrofluoric acid (BHF). Thereafter, as shown in FIG. 2D, a dielectric film 9 made of SiO ₂ is formed to a thickness of 800 nm on the entire surface by a thermal CVD (Chemical Vapor Deposition) method.

In the thermal CVD method, monosilane SiH ₄ is used as a source gas in order to form the dielectric film 9 made of SiO ₂ . Therefore, hydrogen H is mixed into the deposited dielectric film 9. Since hydrogen can make p-type impurities electrically inactive, it is desirable to remove hydrogen. Therefore, a heat treatment at 900 ° C. is performed for 4 minutes in the state shown in FIG. 2D where the dielectric film 9 is deposited. An RTA (Rapid Thermal Anneal) furnace is used for the heat treatment.

  Next, as shown in FIG. 2E, a resist 22 is applied on the dielectric film 9 to form an opening in the resist 22 on the ridge portion 7. The width of the opening of the resist 22 is approximately the same as the width of the upper portion of the ridge portion 7. Next, as shown in FIG. 2F, the dielectric film 9 on the ridge 7 is removed by wet etching using BHF using the resist 22 as a mask.

  Next, as shown in FIG. 2G, an ohmic electrode 10 made of Pd / Pt is deposited on the contact layer 8. When the resist 22 is removed after the ohmic electrode 10 is deposited, the ohmic electrode 10 other than the ridge portion 7 is lifted off together with the resist 22, as shown in FIG. 2H.

  In this step, it is desirable that the width of the opening of the resist 22 be approximately the same as the ridge width 7 as described above. If the opening of the resist 22 is too narrow, the ohmic electrode 10 can be formed only on a part of the top of the ridge, the contact area with the p-type pad electrode 11 (see FIG. 1) decreases, and the p-type ohmic electrode 10 And the p-type electrode pad 11 increase in contact resistance. The required opening width of the resist 22 includes the incident angle of the vapor deposition material in the vapor deposition apparatus for depositing the ohmic electrode 10, the thickness of the resist 22, and the thickness above the ridge portion 7 of the dielectric film 9 (opening of the resist 22 The distance between the bottom edge and the top edge of the ridge is determined geometrically. For example, as an extreme example, when the ohmic electrode 10 is deposited by normal deposition, the width of the opening of the resist 22 must be larger than the width of the upper portion of the ridge portion 7.

  Next, as shown in FIG. 2I, the pad electrode 11 made of Ti / Pt / Au is formed on the dielectric film 9 and the p-type ohmic electrode 10, and the processing on the surface side of the substrate 1 is completed.

  Next, as shown in FIG. 2J, the back surface of the surface of the substrate 1 on which the n-type cladding layer 2 is formed is ground and polished so that the thickness of the substrate 1 is about 80 μm. Next, as shown in FIG. 2K, a resist 23 is formed on the back surface of the substrate 1 and patterned so that a portion of the resist 23 facing the ridge portion 7 remains. Next, Ti (5 nm) / Pt (100 nm) / Au (1 μm) to be the n-type ohmic electrode 13 is deposited on the back surface of the substrate 1.

  Next, as shown in FIG. 2L, the resist 23 is removed, and the n-type ohmic electrode 13 in contact with the resist 23 is lifted off. As a result, the back surface of the substrate 1 has a pattern in which the n-type ohmic electrode 13 is not formed in a portion facing the ridge portion 7 formed on the front surface side of the substrate 1. That is, a pattern in which the n-type ohmic electrode 13 is not formed immediately below the waveguide.

Next, as shown in FIG. 2M, using with the n-type ohmic electrode 13 as a mask Cl ₂ gas, dry etching until the n-type cladding layer 2 through the substrate 1 is exposed. At this time, it is desirable that the bottom width a of the trench 12 is at least wider than the width (waveguide width) b of the ridge portion 7. Further, it is preferably wider than the near field width of the guided light.

  The width of the trench 12 is preferably as short as possible. As described above, the n-type ohmic electrode 13 is formed in a portion other than the trench 12. If the width of the trench 12 is too large, the area of the n-type ohmic electrode 13 decreases and the resistance increases. As a result, the drive voltage increases. Further, if the width of the trench 12 is too wide, the substrate 1 may be cracked starting from the trench 12 in a cleavage process described later.

  In the semiconductor laser device according to the present embodiment, since the expansion of the near field pattern in the width direction of the ridge portion 7 is about 3 μm, the width a at the bottom of the trench 12 is preferably 3 to 10 μm as a larger value.

  Through the above steps, a plurality of semiconductor laser elements in which trenches (grooves) 12 are formed in the wafer-like substrate 1 are completed at least directly below the waveguide.

  Next, although not shown, the wafer-shaped substrate 1 is cleaved into strip-shaped laser bars (primary cleavage process). Next, a coating is applied to the end face for the purpose of reflectance control and end face protection on the primary cleavage plane (resonator end face). Next, the laser bar is cleaved into individual chips (secondary cleaving step). Finally, the chip is packaged to complete the semiconductor laser device shown in FIG.

  Next, a description will be given of the results of a characteristic evaluation performed by junction-down mounting the semiconductor laser device according to the present embodiment and a general ridge type semiconductor laser device. The general ridge-type semiconductor laser device referred to here is an n-type cladding layer 2 of the semiconductor laser device according to the present embodiment having an Al composition x = 0.03 and a thickness of 2.5 μm. The Al composition x = 0.03 and the thickness 0.5 μm.

  The semiconductor laser device according to the present embodiment and a general ridge type semiconductor laser device have a resonant length L of 600 μm, and are coated with a reflective coating having a reflectance of 10% on the front surface of the resonator and a reflectance of 90% on the rear surface. ing. In the general ridge type semiconductor laser device formed in this way, the threshold current is 27 mA, whereas in the semiconductor laser device according to the present embodiment, the threshold current is reduced to 23 mA. Further, in the general ridge type semiconductor laser device, the operating current at an optical output of 200 mW is 145 mA, whereas in the semiconductor laser device according to the present embodiment, the operating current is reduced to 127 mA.

  As described above, in the semiconductor laser device according to this embodiment, the trench 12 is formed in the substrate 1 at a position facing the ridge portion 7. For this reason, even if the clad layers 2 and 6 are reduced to a thickness of 1 μm, the guided light can be prevented from leaking out of the clad layers 2 and 6. Since the cladding layers 2 and 6 can be made thin, the Al composition of the cladding layers 2 and 6 can be increased. As a result, the oscillation threshold current and the operating current of the semiconductor laser element can be reduced, and the temperature characteristics are improved.

Incidentally, illustrating the configuration in which the substrate 1 is formed of GaN, but is not limited to this configuration and may be formed by Al _y Ga _1-y N. In this case, if the value of (x−y) is larger than 0 (that is, x> 0) and 0.15 or less, the oscillation threshold current and the operating current of the semiconductor element can be reduced, and the temperature characteristics are further improved. Can be improved.

  Further, the thickness of the n-type cladding layer 2 is preferably 0.3 μm or more in order to suppress the generation of cracks and increase the optical confinement coefficient Γ of guided light in the triple quantum well active layer 4. . Note that the thickness of the n-type cladding layer 2 is equal to or less than the thickness (for example, 2 μm) of the n-type cladding layer of a general semiconductor laser element.

(Second Embodiment)
FIG. 3 is a sectional view showing the structure of a semiconductor laser device according to the second embodiment of the present invention. The semiconductor laser device according to the present embodiment has a configuration in which the trench 12 of the semiconductor laser device according to the first embodiment is filled with BCB (benzocyclobutene) resin 14. Other components of the semiconductor laser device according to this embodiment are the same as those of the semiconductor laser device according to the first embodiment, and the same components are denoted by the same reference numerals and description thereof is omitted.

  In the semiconductor laser device according to the first embodiment, since the trench 12 is formed in a part of the substrate 1, the substrate 1 may be broken starting from the trench 12 during the cleavage process or chip handling. Since the semiconductor laser device according to this embodiment has a configuration in which the trench 12 is filled with the BCB resin 14, the strength of the substrate 1 in the trench 12 portion is increased, and the substrate 1 can be prevented from being broken.

The BCB resin 14 has a refractive index of about 1.6 with respect to the oscillation light (wavelength 405 nm) of the semiconductor laser element. This value is sufficiently smaller than the refractive index 2.48 of Al _0.15 Ga _0.85 N used for the cladding layers 2 and 6. Therefore, the leakage of the guided light to the BCB resin 14 is negligibly small. Any material other than the BCB resin can be used as a reinforcing material as long as the refractive index with respect to the oscillation light is 2 or less.

Next, a method for manufacturing the semiconductor laser device according to this embodiment will be described. The steps up to the step shown in FIG. 2M in the first embodiment are the same as those in the first embodiment. Next, as shown in FIG. 4A, a BCB resin 14 is applied on the back surface of the wafer-like substrate 1 to fill the trench 12. Thereafter, the BCB resin 14 is cured by baking at 300 ° C. Next, as shown in FIG. 4B, dry etching is performed on the BCB resin 14 using a mixed gas of SF ₆ / O ₂ until the n-type ohmic electrode 13 is exposed.

  Next, although not shown, the wafer-shaped substrate 1 is cleaved into strip-shaped laser bars (primary cleavage process). Next, a coating is applied to the end face for the purpose of reflectance control and end face protection on the primary cleavage plane (resonator end face). Next, the laser bar is cleaved into individual chips (secondary cleaving step). Finally, the chip is packaged to complete the semiconductor laser device shown in FIG.

  As described above, in the semiconductor laser device according to this embodiment, the BCB resin 14 having a refractive index of 2 or less is filled in the trench formed in the substrate 1 at a position facing the ridge portion 7. For this reason, even if the clad layers 2 and 6 are reduced to a thickness of 1 μm, the guided light can be prevented from leaking out of the clad layers 2 and 6. Since the cladding layers 2 and 6 can be made thin, the Al composition of the cladding layers 2 and 6 can be increased. As a result, the oscillation threshold current and the operating current of the semiconductor laser element can be reduced, and the temperature characteristics are improved.

  Furthermore, by filling the trench of the substrate 1 with the BCB resin 14, it is possible to reduce the bending of the substrate 1 as compared with the semiconductor laser device of the first embodiment.

(Third embodiment)
FIG. 5 is a cross-sectional view showing a configuration of a semiconductor laser device according to the third embodiment of the present invention. The semiconductor laser element shown in FIG. 5 is a buried type semiconductor laser element. The substrate 31 is a conductive substrate made of n-type GaN. On one main surface (front surface) of the substrate 31, an n-type cladding layer 32 made of n-type Al _x Ga _1-x N (x = 0.10) is formed to a thickness of 0.5 μm. On the n-type cladding layer 32, an n-type light guide layer 33 made of n-type Al _x Ga _1-x N (x = 0.003) is formed to a thickness of 0.1 μm. On the n-type optical guide layer 33, the barrier layer and the thickness of 3nm consisting of thickness _{8nm In z Ga 1-z N} (z = 0.02) In z Ga 1-z N (z = 0.08 The triple quantum well active layer 34 in which the well layers made of) are stacked is formed.

A p-type light guide layer 35 made of p-type GaN is formed on the triple quantum well active layer 34 to a thickness of 0.1 μm. On the p-type light guide layer 35, a current blocking layer 36 made of n-type Al _x Ga _1-x N (x = 0.20) is formed. An opening 37 is formed in the current block layer 36. On the p-type light guide layer 35 and the current blocking layer 36 exposed by the opening 37, a p _- type cladding layer 38 made of p-type Al _x Ga _1-x N (x = 0.10) has a thickness of 0. .5 μm. On the p-type cladding layer 38, a contact layer 39 made of p-type GaN is formed to a thickness of 60 nm. A p-type ohmic electrode 40 made of Pd / Pt is formed on the contact layer 39. A p-type pad electrode 41 made of Ti / Pt / Au is formed on the p-type ohmic electrode 40.

  Further, a trench 42 penetrating the substrate 31 at a position facing the opening 37 is formed. An n-type ohmic electrode 43 made of a Ti / Pt / Au layer is formed on the back surface of the surface of the substrate 31 on which the n-type cladding layer 32 is formed. The n-type ohmic electrode 43 is not formed on the n-type cladding layer 32.

  With the configuration as described above, the semiconductor laser device according to the present embodiment is thinned to a thickness of 1 μm together with the cladding layers 32 and 38. For this reason, even if the Al composition is set to a high ratio of 10%, the occurrence of cracks in the cladding layers 32 and 38 can be reduced. In addition, the oscillation threshold current and the operating current can be reduced, and the temperature characteristics are improved.

Next, a method for manufacturing the semiconductor laser device according to this embodiment will be described. 6A to 6E are cross-sectional views showing the manufacturing process of the semiconductor laser device according to this embodiment. First, as shown in FIG. 6A, an n-type cladding layer 32, an n-type light guide layer 33, a triple quantum well active layer 34, and a p-type are formed on a wafer-like substrate 31 using metal organic chemical vapor deposition (MOCVD). The light guide layer 35 and the current blocking layer 36 are stacked. Next, the SiO ₂ mask 51 is formed on the current blocking layer 36 is patterned so that an opening is provided in the central portion of the portion made of SiO ₂ mask 51 and the semiconductor laser element. Next, as shown in FIG. 6C, the opening 37 is formed by removing the current blocking layer 36 using the photoelectrochemical (PEC) etching technique with the SiO ₂ mask 51 as a mask.

FIG. 7 is a side view schematically showing PEC etching. A current blocking layer 36 of a plurality of semiconductor laser elements formed up to the state shown in FIG. 6B on the wafer 61 is connected to a cathode 62 made of platinum (Pt) or the like, and the wafer 61 is made alkaline with potassium hydroxide (KOH) or the like. Immerse in the solution 63. Further, etching is performed by irradiating the current blocking layer 36 exposed from the SiO ₂ mask 51 in the wafer 61 immersed in the solution 63 with ultraviolet light. In the PEC etching, the n-type current blocking layer 36 is selectively etched, and the p-type nitride semiconductor layer (p-type light guide layer 35) is not etched. The opening 37 is formed by etching the current blocking layer 36.

Next, as shown in FIG. 6C, the SiO ₂ mask 51 is removed. Next, as shown in FIG. 6D, a p-type cladding layer 38 and a contact layer 39 are laminated on the p-type light guide layer 35 and the current blocking layer 36 exposed from the opening 37 by using MOCVD. Next, a p-type ohmic electrode 40 made of Pd / Pt is formed on the contact layer 39. Next, a p-type pad electrode 41 made of Ti / Pt / Au is formed on the p-type ohmic electrode 40.

  Next, as shown in FIG. 6E, the trench 42 and the n-type ohmic electrode 43 of the substrate 31 are formed. The formation of the trench 42 and the n-type ohmic electrode 43 is the same as the formation method of the trench 12 and the n-type ohmic electrode 13 according to the first embodiment. Omitted.

  Next, although not shown, the wafer-like substrate 31 is cleaved into strip-like laser bars (primary cleavage step). Next, a coating is applied to the end face for the purpose of reflectance control and end face protection on the primary cleavage plane (resonator end face). Next, the laser bar is cleaved into individual chips (secondary cleaving step). Finally, the chip is packaged to complete the semiconductor laser device shown in FIG.

  As described above, in the semiconductor laser device according to this embodiment, the trench 42 is formed in the substrate 31 at a position facing the opening 37. For this reason, even if the cladding layers 32 and 38 are combined and thinned to a thickness of 1 μm, the guided light can be prevented from leaking to other than the cladding layers 32 and 38. Since the cladding layers 32 and 38 can be made thin, the Al composition of the cladding layers 32 and 38 can be increased. As a result, the oscillation threshold current and operating current of the semiconductor laser element can be reduced, and the temperature characteristics are also improved. Furthermore, since it is not necessary to form the n-type ohmic electrode 43 in the n-type cladding layer 32 in the trench 42, the semiconductor laser device can be easily manufactured.

Incidentally, illustrating the configuration in which the substrate 31 is formed of GaN, but is not limited to this configuration and may be formed by Al _y Ga _1-y N. In this case, if the value of (xy) is larger than 0 and 0.15 or less, the oscillation threshold current and the operating current of the semiconductor element can be reduced, and the temperature characteristics can be further improved. .

  Further, the thickness of the n-type cladding layer 32 is preferably 0.3 μm or more in order to suppress the generation of cracks and increase the optical confinement coefficient Γ of guided light in the triple quantum well active layer 34. .

  The semiconductor laser device according to the present invention can reduce the oscillation threshold current and the operating current of the semiconductor laser device and can further improve the temperature characteristics, and can be used as a light source for an optical disk.

Sectional drawing which shows the structure of the semiconductor laser element which concerns on the 1st Embodiment of this invention Sectional drawing which shows the manufacturing process of the semiconductor laser element concerning 1st Embodiment Sectional drawing which shows the next process of FIG. 2A Sectional drawing which shows the next process of FIG. 2B Sectional drawing which shows the next process of FIG. 2C Sectional drawing which shows the next process of FIG. 2D Sectional drawing which shows the next process of FIG. 2E Sectional drawing which shows the next process of FIG. 2F Sectional drawing which shows the next process of FIG. 2G Sectional drawing which shows the next process of FIG. 2H Sectional drawing which shows the next process of FIG. 2I Sectional drawing which shows the next process of FIG. 2J Sectional drawing which shows the next process of FIG. 2K Sectional drawing which shows the next process of FIG. 2L Sectional drawing which shows the structure of the semiconductor laser element which concerns on the 2nd Embodiment of this invention. Sectional drawing which shows the manufacturing process of the semiconductor laser element concerning 2nd Embodiment Sectional drawing which shows the next process of FIG. 4A Sectional drawing which shows the structure of the semiconductor laser element concerning the 3rd Embodiment of this invention. Sectional drawing which shows the manufacturing process of the semiconductor laser element concerning 1st Embodiment Sectional drawing which shows the next process of FIG. 6A Sectional drawing which shows the next process of FIG. 6B Sectional drawing which shows the next process of FIG. 6C Sectional drawing which shows the next process of FIG. 6D Side view showing outline of PEC etching

Explanation of symbols

1, 31 Substrate 2, 32 n-type cladding layer 3, 33 n-type light guide layer 4, 34 triple quantum well active layer 5, 35 p-type light guide layer 6, 38 p-type cladding layer 7 ridge portion 8, 39 contact layer 9 Dielectric film 10, 40 p-type ohmic electrode 11, 41 p-type pad electrode 12, 42 trench 13, 43 n-type ohmic electrode 14 BCB resin 21 SiO ₂ mask 22, 23 resist 36 current blocking layer 37 opening

Claims (5)

A conductive substrate;
A first cladding layer of a first conductivity type made of a nitride semiconductor formed on the conductive substrate;
An active layer formed on the first cladding layer;
A second cladding layer of a second conductivity type formed on the active layer,
In the semiconductor light emitting device in which an optical waveguide is formed in the second cladding layer,
A semiconductor light-emitting element, wherein a groove penetrating the conductive substrate is formed in the conductive substrate at least directly below the optical waveguide. The conductive substrate is made of Al _y Ga _1-y N (y ≧ 0),
The first cladding layer is made of Al _x Ga _1-x N (x> 0),
A value (xy) obtained by subtracting the Al composition ratio y of the conductive substrate from the Al composition ratio x of the first cladding layer is 0.15 or less,
The semiconductor light emitting element according to claim 1, wherein the first cladding layer has a thickness of 0.3 μm or more.   The semiconductor light emitting element according to claim 1, wherein a width of the groove is wider than a width of the optical waveguide.   The semiconductor light emitting element according to claim 1, wherein a resin is embedded in the groove.   The semiconductor light-emitting element according to claim 4, wherein the resin embedded in the groove has a refractive index of 2 or less at an emission wavelength of the element.

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