JP4814538B2 - Semiconductor laser device and manufacturing method thereof - Google Patents

Description

  The present invention relates to a semiconductor laser device and a manufacturing method thereof, and more particularly to a semiconductor laser device for an optical pickup light source used in an optical information processing apparatus such as an optical disk system and a manufacturing method thereof.

  As a light source for next-generation high-density optical discs, it emits light in a short wavelength range (400 nm band) that allows the diameter of the focused spot on the optical disc to be reduced compared to light in the red and infrared regions, and the optical disc playback and recording density There is a demand for a laser light source in the blue-violet region that is effective in improving the above.

  In order to realize blue-violet laser light, research and development of a semiconductor laser device using a group III-V nitride semiconductor mainly composed of gallium nitride (GaN) has been actively conducted. From the viewpoint of such high-density optical disk applications, a high-power blue-violet semiconductor laser device capable of dealing with a high recording density has been demanded. At present, it is said that a light output of at least 65 mW or more by pulse oscillation is required. ing. Furthermore, in order to aim at high-speed writing, high output characteristics of 30 mW or more with continuous oscillation are desired.

FIG. 18 shows a cross-sectional configuration of a conventional nitride semiconductor laser device described in Patent Document 1. As shown in FIG. 18, the nitride semiconductor laser device includes an n-type cladding layer 151 and an active layer 152 which are sequentially formed on a substrate 150 made of sapphire by epitaxial growth, and a p-type cladding layer having a ridge portion 112a on the top. 112 and a p-type contact layer 101 formed on the ridge 112a. A first electrode layer 113 is formed on the p-type contact layer 101. On the upper surface of the p-type cladding layer 112 and on the side surface of the ridge portion 112 a including the p-type contact layer 101 and the first electrode layer 113. A dielectric film 102 made of silicon oxide, which is a current confinement layer, and a second electrode layer 114 are formed. As a result, a semiconductor laser device having a waveguide structure that has both a current confinement function and an optical confinement function is realized.
JP 2000-299528 A

  As a result of various studies on the conventional nitride semiconductor laser device, the present inventor has found that there are the following problems.

First, it is difficult for the conventional nitride semiconductor laser device to obtain a high output characteristic of 65 mW or more with required pulse oscillation or 30 mW or more with continuous oscillation. As described above, the conventional semiconductor laser device uses silicon oxide (SiO ₂ ) for the dielectric film 102 covering the ridge portion 112a. The refractive index of silicon oxide is 1.56, and the refractive index difference is one or more larger than 2.54 which is the refractive index of gallium nitride (GaN). This increases the difference in effective refractive index between the waveguide formed of the region including the ridge 112a in the direction perpendicular to the substrate surface in the active layer 152 and the outer portion of the waveguide. For this reason, the transverse mode of oscillation easily shifts from the basic mode to the higher order mode, and so-called kink phenomenon is likely to occur even at a low output. Therefore, there is a first problem that the conventional nitride semiconductor laser device cannot realize high output characteristics due to a decrease in the so-called kink level.

  In addition, the dielectric film 102 made of silicon oxide has a second problem that the adhesion with the second electrode layer 114 is insufficient.

  These first and second problems are not limited to gallium nitride semiconductor laser devices, but are common to ridge waveguide semiconductor laser devices having a ridge portion.

  In view of the above-described conventional problems, an object of the present invention is to obtain desired output characteristics by using a dielectric film that has excellent adhesiveness and can realize stable transverse mode characteristics.

  In order to achieve the above object, according to the present invention, the semiconductor laser device is configured to use a laminated structure having a different composition for the dielectric film covering the ridge portion.

  Specifically, a semiconductor laser device according to the present invention includes a light emitting layer, a semiconductor layer formed on the light emitting layer, having a ridge portion and having a refractive index smaller than that of the light emitting layer, and a ridge portion in the semiconductor layer. And a plurality of dielectric films formed in at least a side region.

  According to the semiconductor laser device of the present invention, for example, the semiconductor laser device includes a plurality of dielectric films formed in at least a side region of the ridge portion in the semiconductor layer that is a clad layer. A dielectric material having a refractive index larger than that of silicon oxide can be selected for one dielectric film in contact with the metal film, and the other dielectric film located outside the ridge portion and in contact with the metal electrode has the metal electrode It is possible to select a dielectric material that is excellent in adhesiveness. Therefore, since the range of selection of the material for the dielectric film covering the ridge portion is widened, process stability and high output characteristics can be realized at the same time.

  In the semiconductor laser device of the present invention, the plurality of dielectric films are composed of a first dielectric film and a second dielectric film sequentially formed from below, and the refractive index of the first dielectric film is equal to that of the semiconductor layer. The refractive index is preferably smaller than the refractive index. In this way, light emitted from the light emitting layer can be efficiently confined in the layer direction (lateral direction) of the light emitting layer, so that stable single transverse mode characteristics can be realized.

In this case, if the refractive index of the semiconductor layer is N ₀ , the refractive index of the first dielectric film is N _1, and the refractive index of the second dielectric film is N ₂ , each refractive index is N _0. It is preferable to satisfy the relationship> N ₂ > N ₁ . In this case, the light emitted from the light emitting layer can be confined by the relationship N ₀ > N ₁ , and the effective refractive index in the outer portion of the waveguide is increased by the relationship N ₂ > N ₁ . The difference in effective refractive index between the inside and the outside of the waveguide is reduced, and as a result, the generation level of kinks with respect to the output value is increased, so that stable single transverse mode characteristics can be realized.

  In the semiconductor laser device of the present invention, the plurality of dielectric films include a first dielectric film, a second dielectric film, and a third dielectric film sequentially formed from below, and the first dielectric film The refractive index of the film is preferably smaller than the refractive index of the semiconductor layer. Here, since the metal electrode formed on the third dielectric film is difficult to peel by disposing the dielectric material having good adhesion to the metal on the third dielectric film, the yield during manufacturing And the reliability is improved.

In this case, if the refractive index of the semiconductor layer is N ₀ , the refractive index of the first dielectric film is N _1, and the refractive index of the third dielectric film is N ₃ , each refractive index is N _0. It is preferable to satisfy the relationship> N ₃ > N ₁ . In this case, the light emitted from the light emitting layer can be confined by the relationship N ₀ > N ₁ , and the effective refractive index in the outer portion of the waveguide is increased by the relationship N ₃ > N ₁ . The difference in effective refractive index between the inside and the outside of the waveguide is reduced, and as a result, the generation level of kinks with respect to the output value is increased, so that stable single transverse mode characteristics can be realized.

  Furthermore, it is preferable that the second dielectric film has an absorption edge on the longer wavelength side than the oscillation wavelength in the light emitting layer. In this case, in the second dielectric film, the gain of the higher order mode can be reduced without loss of carriers injected into the light emitting layer, so that the gain difference between the fundamental mode and the higher order mode can be increased. It becomes possible. As a result, stable transverse mode characteristics for realizing high output characteristics can be obtained.

In the semiconductor laser device of the present invention, the light emitting layer and the semiconductor layer are made of Al _u Ga _v In _w N (where u, v and w are 0 ≦ u ≦ 1, 0 ≦ v ≦ 1, 0 ≦ w ≦ 1, It is preferable that the nitride semiconductor layer be u + v + w = 1. In this way, a semiconductor laser device that outputs laser light in the blue-violet region can be obtained.

In the semiconductor laser device of the present invention, the first dielectric film and the third dielectric film are SiO ₂ , SiN, ZrO ₂ , Ta ₂ O ₅ , Nb ₂ O ₅ , TiO ₂ , Al ₂ O ₃ , AlN. or preferably consists of Ga ₂ O _3.

  In the semiconductor laser device of the present invention, when the plurality of dielectric films are composed of three layers, the second dielectric film is preferably composed of Si, TiN or TaN.

  In the semiconductor laser device of the present invention, when the plurality of dielectric films are composed of three layers, the total thickness of the first dielectric film, the second dielectric film, and the third dielectric film is 20 nm or more. And it is preferable that it is 200 nm or less. In this way, the waveguide loss can be reduced, and an increase in operating current during high output operation can be suppressed. In addition, since the thickness of the plurality of dielectric films is relatively thin, the thickness on the side surface of the ridge portion becomes small, so that lift-off can be easily performed.

  The semiconductor laser device of the present invention preferably further includes a metal film that covers the ridge portion in the semiconductor layer together with a plurality of dielectric films. In this way, a metal film is also formed on the plurality of dielectric films. For this reason, since the area of the metal film can be increased, when the metal film is used as a pad electrode, wire bonding can be reliably performed on the pad electrode.

  In this case, the metal film preferably includes at least one of Ni, Pd, and Pt. In this way, the contact resistance with the contact layer located on the lower side of the metal film can be reduced, and the diffusion of carriers in the lateral direction can be suppressed. The characteristics can be realized.

  In the semiconductor laser device of the present invention, the width of the ridge portion is preferably 1.0 μm or more and 4.0 μm or less. For example, if the width of the ridge portion is smaller than 1.0 μm, the manufacturing yield decreases and the series resistance in the ridge portion increases. On the other hand, if the width of the ridge portion is larger than 4.0 μm, the kink generation level with respect to the output value is lowered. Therefore, the width of the ridge portion is preferably 1.0 μm or more and 4.0 μm or less.

  The method for manufacturing a semiconductor laser device according to the present invention includes a step (a) of forming a light emitting layer on a substrate and a step of forming a semiconductor layer having a refractive index smaller than that of the light emitting layer on the light emitting layer (b) And a step (c) of selectively etching the formed semiconductor layer to form a ridge portion in the semiconductor layer, and a plurality of dielectrics in a region on at least a side of the ridge portion on the semiconductor layer. And a step (d) of laminating a film.

  According to the method for manufacturing a semiconductor laser device of the present invention, since a plurality of dielectric films are stacked on at least a side region of the ridge on the semiconductor layer, the dielectric film having a stacked structure is in contact with the ridge portion. A dielectric material having a refractive index higher than that of silicon oxide can be selected for the dielectric film, and the other dielectric film outside the ridge portion in contact with the metal electrode has good adhesion to the metal electrode. An excellent dielectric material can be selected. Accordingly, since the range of selection of materials for the dielectric film covering the ridge portion is widened, long-term reliability and high output characteristics can be realized at the same time.

In the method of manufacturing a semiconductor laser device according to the present invention, the plurality of dielectric films include a first dielectric film, a second dielectric film, and a third dielectric film sequentially formed from below, When the refractive index is N ₀ , the refractive index of the first dielectric film is N _1, and the refractive index of the third dielectric film is N ₃ , each refractive index is N ₀ > N ₃ > N ₁ . The second dielectric film preferably satisfies the relationship, and has an absorption edge on the longer wavelength side than the oscillation wavelength in the light emitting layer.

In the method for manufacturing a semiconductor laser device of the present invention, the light emitting layer and the semiconductor layer are made of Al _u Ga _v In _w N (where u, v, w are 0 ≦ u ≦ 1, 0 ≦ v ≦ 1, 0 ≦ w). ≦ 1, u + v + w = 1) is preferable.

  In the method for manufacturing a semiconductor laser device of the present invention, in the step (d), the plurality of dielectric films are preferably formed by electron cyclotron resonance sputtering or magnetron sputtering. In this case, since the directivity at the time of depositing the dielectric film is high, it is difficult to deposit the dielectric film on the side surface of the ridge portion, so that lift-off to the dielectric film can be easily performed.

  In the method of manufacturing a semiconductor laser device of the present invention, it is preferable that the plurality of dielectric films are formed by a pulse laser deposition method in the step (d).

  The method for manufacturing a semiconductor laser device of the present invention preferably further includes a step (e) of forming a metal film so as to cover the ridge portion including a plurality of dielectric films after the step (d).

  According to the semiconductor laser device and the manufacturing method thereof according to the present invention, the dielectric film covering the ridge portion for current confinement formed in the laser structure has a laminated structure having different compositions, so that the adhesion is excellent and stable. Since the transverse mode characteristic can be realized, a desired output characteristic can be obtained.

(First embodiment)
A first embodiment of the present invention will be described with reference to the drawings.

FIG. 1 shows a cross-sectional configuration of a gallium nitride (GaN) based semiconductor laser device according to a first embodiment of the present invention. As shown in FIG. 1, the semiconductor laser device according to the first embodiment is formed, for example, sequentially on the main surface of a substrate 1 made of GaN, and lattice mismatch between the substrate 1 and an epitaxial layer grown thereon. Low-temperature growth buffer layer 2 made of AlGaN that relaxes, n-type contact layer 3 made of n-type GaN with a thickness of about 2 μm, and n-type cladding layer made of n-type Al _0.07 Ga _0.93 N with a thickness of about 1 μm 4, an n-type light guide layer 5 made of n-type GaN having a thickness of about 100 nm, an MQW active layer 6 having a multiple quantum well (MQW) structure, and a p-type made of p-type GaN having a thickness of about 100 nm. a light guide layer 7, the p-type cladding layer 8 having a thickness of the ridge portion 8a has a ridge portion 8a is composed of 0.5μm order of p-type Al _0.07 Ga _0.93 N, is formed on the ridge portion 8a, Thickness is about 100nm And a p-type contact layer 9 made of p-type GaN.

  A p-side electrode 10 is formed on the p-type contact layer 8 having the ridge portion 8 a, and on the upper surface of the p-type cladding layer 8 and the side surface of the ridge portion 8 a including the p-type contact layer 9 and the p-side electrode 10. The first dielectric film 11, the second dielectric film 12, and the third dielectric film 13 having a current confinement function for the ridge portion 8a are sequentially formed.

  A wiring electrode 15 made of a laminated film of titanium (Ti) and gold (Au) is formed on the p-side electrode 10 so as to cover the ridge portion 8 a including the third dielectric film 13.

  A side portion of the ridge portion 8a in the n-type contact layer 3 is exposed, and an n-side electrode 14 is formed on the exposed portion. A wiring electrode 15 is also formed on the n-side electrode 14.

Here, the MQW active layer 6 includes, for example, three pairs of a well layer made of Ga _0.92 In _0.08 N having a thickness of 4.0 nm and a barrier layer made of GaN having a thickness of 8.0 nm. Are laminated.

  In addition, the n-type cladding layer 4 and the p-type cladding layer 8 are generated by recombination of carriers and the carriers to the MQW active layer 6 using the difference in band gap and refractive index from the MQW active layer 6. Confine the light. The n-type light guide layer 5 and the p-type light guide layer 7 have a higher refractive index than the n-type clad layer 4 and the p-type clad layer 8, and make it easier to confine light generated using the difference in refractive index.

  Here, [Table 1] shows materials of each dielectric film applicable in the first embodiment.

The first dielectric film 11 is made of GaN so that the generated light is not absorbed or absorbed so as to reduce the waveguide loss in the waveguide, and the generated light is confined in the waveguide. It is necessary to use a dielectric having a refractive index smaller than the refractive index (2.54). Here, silicon oxide (SiO ₂ ) having the smallest refractive index in [Table 1] is used with a film thickness of 40 nm.

  For the second dielectric film 12, a dielectric material having an absorption edge on the longer wavelength side than the light of, for example, 405 nm, which is the oscillation wavelength of the semiconductor laser device according to the present embodiment, is used. Here, silicon (Si) having the largest absorption coefficient in [Table 1] is used with a film thickness of 30 nm. As described above, the laser light is absorbed by the second dielectric film 12, and thus the gain of the higher order mode can be reduced. Therefore, the gain difference between the fundamental mode and the higher order mode can be increased. For this reason, generation | occurrence | production of hole burning is suppressed and it becomes possible to suppress the fall of the generation | occurrence | production level of a kink.

The third dielectric film 13 has good adhesion to the wiring electrode 15 provided on the third dielectric film 13 and has high output characteristics, that is, increases the level of occurrence of kinks. Minimize the difference in refractive index between the inside and outside. In other words, it is necessary to use a dielectric material having a large refractive index that increases the effective refractive index difference in the direction perpendicular to the substrate 1 in the outer portion of the waveguide. Here, niobium oxide (Nb ₂ O ₅ ) having high adhesion to metal and a large refractive index in [Table 1] is used with a film thickness of 30 nm.

  Here, as materials applicable to the dielectric films 11, 12 and 13, there are combinations as shown below.

That is, the first dielectric film 11 has SiO ₂ , SiN, ZrO ₂ , Ta ₂ O ₅ , Nb ₂ O ₅ , Al ₂ O ₃ , AlN or Ga ₂ O ₃ , or a compound thereof such as SiON or AlON or the like can be used. For the second dielectric film 12, Si, TiO ₂ , AlN, TiN, or TaN that absorbs the oscillation wavelength can be used. For the third dielectric film 13, Nb ₂ O ₅ , ZrO ₂ , Ta ₂ O ₅ , TiO ₂ , AlN or SiN, or a compound thereof such as SiON or AlON can be used. Of these, the refractive index of the first dielectric film 11 and N _1, and the refractive index of the third dielectric film 13 and N _3, it is preferable to select a material which satisfies N ₁ <N _3.

More preferably, the first dielectric film 11 is selected from SiO ₂ , Al ₂ O _3, and SiN, the second dielectric film 12 is selected from Si and TiO ₂ , and the third dielectric film is selected. The film 13 may be selected from Nb ₂ O ₅ , ZrO ₂ and Ta ₂ O ₅ .

However, when AlN is selected for the second dielectric film 12, a material other than AlN is selected for the first dielectric film 11 and the third dielectric film 13. Similarly, when selecting the TiO ₂ in the second dielectric film 12 or the third dielectric film 13, the other dielectric film to select a material other than TiO _2.

  As described above, according to the first embodiment, the dielectric films covering at least the ridge portion 8a of the p-type cladding layer 8 and the lateral region thereof have different compositions, that is, the refractive index, the light absorption coefficient, etc. By using the first dielectric film 11, the second dielectric film 12, and the third dielectric film 13 having different physical properties, a single-layer dielectric film made of silicon oxide is used as in the prior art. In comparison, the current-light output (IL) characteristics are dramatically improved.

  FIG. 2 shows current-light output (IL) characteristics in the semiconductor laser device according to the first embodiment of the present invention in comparison with the conventional example. As shown in FIG. 2, in the semiconductor laser device according to the present embodiment, it is possible to realize output characteristics of 200 mW or more.

FIG. 3 shows a far-field image (far field pattern: FFP) of the semiconductor laser device according to the present embodiment. As shown in FIG. 3, by using the dielectric films 11, 12, and 13 having three layers, it is possible to simultaneously satisfy a device characteristic having an aspect ratio of 3 or less at the same time as a high kink generation level. Here, θ _v in FIG. 3 indicates the far viewing angle in the vertical direction, and θ _h indicates the far viewing angle in the horizontal direction.

  As can be seen from FIG. 4, the total film thickness of the three dielectric films 11, 12, and 13 is such that the lift-off can be performed with good yield and that the waveguide loss is small, specifically, the operating current at 30 mW. In order to make the waveguide loss within 5% in FIG. 2, it is necessary to be 20 nm or more and 200 nm or less, and in the first embodiment, it is 100 nm.

  Hereinafter, a method of manufacturing the semiconductor laser device configured as described above will be described with reference to the drawings.

  5 (a) to 5 (e) and FIGS. 6 (a) to 6 (d) show cross-sectional structures in the order of steps of the method of manufacturing the semiconductor laser device according to the first embodiment of the present invention. .

First, as shown in FIG. 5A, a low temperature growth buffer layer 2 made of AlGaN is grown on the main surface of the substrate 1 made of GaN at a growth temperature of about 500 ° C. by metal organic chemical vapor deposition (MOCVD). Form. When the buffer layer 2 is deposited at a temperature lower than about 1000 ° C., which is the growth temperature of this normal gallium nitride semiconductor, the crystal structure of AlGaN constituting the buffer layer 2 becomes slightly amorphous, and the original lattice constant The film is formed in a state shifted from the above. For this reason, it is possible to prevent crystal defects generated in the gallium nitride-based epitaxial layer grown on the low temperature growth buffer layer 2 and to improve the crystallinity. Here, for example, trimethylgallium (TMG), trimethylaluminum (TMA), and trimethylindium (TMI) are used as the organometallic raw material containing Ga, Al, or In, and ammonia (NH ₃ ) is used as the nitrogen raw material.

Subsequently, the growth temperature is set to 1000 ° C., and the n-type contact layer 3 made of n-type GaN, the n-type cladding layer 4 made of n-type Al _0.07 Ga _0.93 N, and the n-type GaN are formed on the low-temperature growth buffer layer 2. An n-type light guide layer 5, an MQW active layer 6, a p-type light guide layer 7 made of p-type GaN, a p-type cladding layer 8 made of p-type Al _0.07 Ga _0.93 N, and a p-type contact layer 9 made of p-type GaN. It is formed by sequential epitaxial growth. Here, since the MQW active layer 6 contains In in its composition, the growth temperature is set to 800 ° C. to prevent evaporation of In during growth.

  Next, as shown in FIG. 5B, a first resist pattern 201 that masks the laser structure formation region on the p-type contact layer 9 is formed by lithography. Subsequently, by using the formed first resist pattern 201 as a mask, the p-type contact layer 9 and the p-type cladding layer 8 are formed by reactive dry etching (RIE) using an etching gas containing chlorine as a main component. The p-type light guide layer 7, the MQW active layer 6, the n-type light guide layer 5, the n-type cladding layer 4 and the n-type contact layer 3 are etched to expose a part of the n-type contact layer 3.

  Next, as shown in FIG. 5C, after removing the first resist pattern 201 by ashing, a resist is again formed on the p-type contact layer 9 including the exposed surface of the n-type contact layer 3 by lithography. A film is applied, and then a second resist pattern 202 having an opening in the ridge portion formation region is formed from the applied resist film. Thereafter, for example, palladium (Pd) and gold (Au) are laminated on the formed second resist pattern 202 by, for example, vapor deposition to make the p-type contact layer 9 conductive. A P-side electrode 10 including a metal multilayer film and a second metal multilayer film for lift-off formed by laminating, for example, aluminum (Al) and nickel (Ni) is formed on the first metal multilayer film. To do.

  Here, the width of the second resist pattern 202, that is, the width of the waveguide is preferably as small as possible in order to increase the generation level of the kink. However, if the width of the waveguide is too small, the yield due to etching may be reduced in the waveguide forming process described later, and the series resistance in the waveguide is increased. Furthermore, since optical damage (COD: Catastrophic Optical Damage) occurs on the output end face of the waveguide and the light output is reduced, the width of the waveguide is preferably 1.0 μm or more from a practical viewpoint.

  In order to realize a practical kink generation level, the width of the waveguide is preferably 2.5 μm or less in the nitride semiconductor laser device according to the first embodiment. Similarly, in a GaAs infrared semiconductor laser device having an oscillation wavelength band of 780 nm and an AlGaInP red semiconductor laser device having a band of 650 nm, the width of the waveguide is preferably 4.0 μm or less. From the above, the width of the waveguide needs to be set in the range of 1.0 μm or more and 4.0 μm or less, and in the present embodiment, it is set to 1.6 μm.

  Further, the lowermost layer of the first metal laminated film constituting the lower part of the P-side electrode 10 is not limited to palladium (Pd), and nickel (Ni) or platinum (Pt) is preferably used. By using such a material, the contact resistance between the P-side electrode 10 and the p-type contact layer 9 can be reduced.

  Next, as shown in FIG. 5D, the second resist pattern 202 and the P-side electrode deposited on the second resist pattern 202 are formed by a so-called lift-off method using an organic solvent such as acetone. The P-side electrode 10 is formed in the ridge portion forming region on the p-type contact layer 9 by removing the metal laminated film.

  Next, as shown in FIG. 5E, deposition is performed on the uppermost layer of the second metal laminated film constituting the upper portion of the P-side electrode 10 by reactive dry etching (RIE) mainly containing chlorine. Using the nickel portion as a mask, a part of the p-type cladding layer 8 is etched into a ridge shape to form a ridge portion 8a. At this time, by using nickel as a mask for dry etching, the etching selectivity with gallium nitride or aluminum gallium nitride is increased, and therefore the mask does not retreat, so that the design value of the ridge width is 1.6 μm. Thus, a high controllability of 1.6 ± 0.1 μm can be obtained. As a result, it is possible to realize a semiconductor laser device having a high kink generation level, that is, a high-output laser oscillation characteristic.

  Here, the thickness (remaining film thickness) of the portion remaining in the region other than the ridge portion 8a in the p-type cladding layer 8 is set to 180 nm in order to realize a stable transverse mode characteristic in which spatial hole burning is suppressed. .

  The values of the waveguide width (ridge width) of 1.6 μm and the remaining film thickness of the p-type cladding layer 8 of 180 nm are determined in consideration of the variation caused by the process in the design data shown in FIG. . In the semiconductor laser device according to the present embodiment, in order to obtain a high light output characteristic that can be used for an optical pickup and can be recorded, the so-called kink is free and the horizontal divergence angle in the far field pattern (FFP) is high. It is desirable that the angle is 8 ° or more in the optical pickup system. Thus, although the ridge width W was designed to be 1.6 μm for the trial manufacture of the device, as can be seen from FIG. 7, if the remaining film thickness dp is larger than 205 nm, the FFP becomes 8 ° or less. In a region where the horizontal divergence angle is 8 ° or less, the level of kinks increases, but the transverse mode becomes unstable. Therefore, it was found that the light confinement function by the ridge portion 8a is lowered and the yield is also reduced.

  As described above, the horizontal divergence angle in the FFP is desirably 8 ° or more, and it is indispensable to fabricate the device within the design range as shown in FIG. It is.

Next, as shown in FIG. 6A, the p-type cladding layer 8 and the p-type exposed by etching including the p-side electrode 10 using a sputtering method using electron cyclotron resonance (ECR) plasma. A first dielectric film 11 made of SiO ₂ with a thickness of 40 nm and a first dielectric film made of Si with a thickness of 30 nm are formed on the upper surface of the contact layer 3 and further on the side surface of the semiconductor laminate such as the p-type light guide layer 7. A second dielectric film 12 and a third dielectric film 13 made of Nb ₂ O _{5 having} a thickness of 40 nm are sequentially deposited. Here, when depositing the first dielectric film 11, silicon is used as a target material in an oxygen atmosphere, and when depositing the second dielectric film 12, silicon is used as a target material in an argon atmosphere. Further, when depositing the third dielectric film 13, niobium is used as a target material in a nitrogen atmosphere. Next, as shown in FIG. 6B, by lift-off using a hydrochloric acid-based etchant, the second metal laminated film made of aluminum and nickel in the P-side electrode 10, and the second metal laminated film The first dielectric film 11, the second dielectric film 12, and the third dielectric film 13 deposited thereon are removed. In this lift-off process, since the nickel or aluminum constituting the second metal laminated film is exposed on the surface before lift-off, the p-side electrode 10 is silver, but after lift-off, nickel and aluminum The aluminum constituting the first metal laminated film is exposed by removing the aluminum. Accordingly, it is possible to easily check whether or not lift-off is performed due to a color change before and after the lift-off process. Therefore, the yield when the dielectric films 11, 12, and 13 deposited on the p-side electrode 10 are lifted off is improved.

Next, a resist pattern (not shown) that opens the n-side electrode formation region in the n-type contact layer 3 is formed on the third dielectric film 13 by lithography, and the formed resist pattern is used as a mask. Openings are formed in the dielectric films 11, 12 and 13 by reactive dry etching (RIE) and wet etching. Subsequently, an n-side electrode forming film is deposited on the resist pattern including the opening, and then the resist pattern is lifted off using an organic solvent such as acetone, as shown in FIG. An n-side electrode 14 made of, for example, a laminated film of titanium (Ti) and aluminum (Al) is formed on the mold contact layer 3. Here, the etching method for each of the dielectric films 11, 12, and 13 differs depending on the materials of the first dielectric film 11, the second dielectric film 12, and the third dielectric film 13, but in the present embodiment, Etch SiO ₂ , Si and Nb ₂ O ₅ by reactive dry etching (RIE) or buffered hydrofluoric acid (BHF) using a fluorine-based gas.

  Next, as shown in FIG. 6D, a resist pattern (not shown) having openings for exposing the p-side electrode 10 and the n-side electrode 14 is formed by lithography, and the resist pattern including the openings. A metal film for forming a wiring electrode made of, for example, a laminated film of (Ti) and gold (Au) is deposited thereon. Subsequently, the wiring electrode 15 is formed on the p-side electrode 10 and the n-side electrode 14 by lifting off the wiring electrode forming metal film using an organic solvent such as acetone.

  In the semiconductor laser device manufactured as described above, when one wiring electrode 15 formed on the n-side electrode 14 is grounded and a voltage is applied to the other wiring electrode 15 formed on the p-side electrode 10, Carriers are injected into the MQW active layer 6, an optical gain is generated in the MQW active layer 6, and laser oscillation occurs when the oscillation wavelength is around 400 nm. The oscillation wavelength can be changed by the composition and film thickness of gallium indium nitride (GaInN) constituting the MQW active layer 6.

  In addition, the manufacturing method according to the first embodiment includes a resist pattern that masks the ridge portion itself in a stripe shape as in the prior art in the mask formation step of the ridge portion 8a of the p-type cladding layer 8 shown in FIG. Instead, it is formed by lifting off the p-side electrode 10 using an inverted stripe pattern as in the second resist pattern 202. Furthermore, since nickel constituting the upper portion of the p-side electrode 10 is used as a mask, the selection ratio during dry etching is high and the mask made of nickel hardly retreats, so that compared with the case where a resist mask is used. The controllability of the stripe (ridge) width is improved. For this reason, when the stripe width is small, the kink occurrence level is increased, and the stripe width can be stably controlled, so that a high kink occurrence level can be maintained. As a result, a semiconductor laser device having high output characteristics can be realized.

  In this embodiment, an ECR plasma patch is used as a method for depositing the dielectric films 11, 12 and 13. One advantage of using ECR plasma sputtering is that the directivity is high, and as shown in the schematic diagrams of FIGS. 8 and 9, the amount of deposition on the side surface of the ridge portion of the dielectric film can be reduced. Thus, the lift-off of the dielectric film can be realized only when the deposited shape as shown in FIGS. 8 and 9 is obtained in the dielectric film deposited on the ridge portion.

  For example, in the case of using isotropically deposited plasma chemical vapor deposition (CVD) as shown in FIG. 10, the dielectric deposited on the side surface of the ridge portion is used. Since no breaks (step breaks) occur in the film, lift-off cannot be realized.

Another advantage of using ECR plasma sputtering is that it is possible to select a metal target that can be highly purified, such as Zr, Ta, Al, Si, Nb, and Ti, so that it is excellent in adaptability to various materials. It is. Therefore, for example, ZrO ₂ , Ta ₂ O ₅ , Nb ₂ O ₅ , AlN, TiO ₂ and TiN can be deposited with high quality.

  Due to the above two advantages, it can be said that deposition of a dielectric film by ECR sputtering is essential. In place of the ECR plasma sputtering method, a magnetron sputtering method or a pulsed laser deposition method can be used.

  As described above, according to the ridge type nitride semiconductor laser device according to the first embodiment, the current confinement function formed on at least the side surface of the ridge portion 8a and the outer region of the p type cladding layer 8 is provided. By making the dielectric film have a three-layer structure, the effective refractive index difference between the inside and the outside of the ridge portion 8a can be reduced as compared with the case where the dielectric film is formed of only one layer.

  Further, by using a material that absorbs laser light, such as Si, for the second dielectric film 12 of the second layer, the gain difference between the fundamental mode and the higher-order mode can be increased.

Furthermore, a stable process can be realized by using a material having high adhesion to the P-side electrode 10 such as Nb ₂ O ₅ for the third dielectric film 13 of the third layer. As a result, it is possible to obtain a ridge waveguide semiconductor laser device having stable lateral mode characteristics that can realize high output characteristics and high yield.

  In the step shown in FIG. 6B, the hydrochloric acid-based etchant is used when the aluminum layer included in the P-side electrode 10 is etched and lift-off is performed, but the invention is not limited to this. For example, when titanium is used for the lower layer of the second metal laminated film of the P-side electrode 10, a hydrofluoric acid-based etchant may be used, and when nickel is used for the lower layer, a nitric acid-based etchant may be used.

(One modification of the first embodiment)
Hereinafter, a modification of the first embodiment of the present invention will be described with reference to the drawings.

  FIG. 11 shows a cross-sectional configuration of a GaN-based semiconductor laser device according to a modification of the first embodiment of the present invention. In FIG. 11, the same components as those shown in FIG.

  As shown in FIG. 11, in the semiconductor laser device according to this modification, instead of forming the n-side electrode 14 on the n-type contact layer 3 made of n-type GaN, low-temperature growth on the substrate 1 made of n-type GaN. It is formed on the opposite surface (back surface) of the buffer layer 2.

  Thereby, the n-type contact layer 3 is etched, and the first dielectric film 11, the second dielectric film 12 and the third dielectric film 13 deposited on the exposed surface of the n-type contact layer 3 are formed. The step of forming the opening for forming the n-side electrode can be omitted. Furthermore, the chip area of the semiconductor laser device itself can be reduced.

  Another difference in manufacturing is that, before the n-side electrode 14 is formed on the back surface of the substrate 1, in order to reduce the series resistance of the substrate 1, the back surface of the substrate 1 is polished to have a thickness of 100 μm to 100 μm. The point is that the film thickness is reduced to about 150 μm.

(Second Embodiment)
Hereinafter, a second embodiment of the present invention will be described with reference to the drawings.

  FIG. 12 shows a cross-sectional configuration of a GaN-based semiconductor laser device according to the second embodiment of the present invention. In FIG. 12, the same components as those shown in FIG.

  The semiconductor laser device according to the second embodiment is different from the first embodiment in the formation method of the p-side electrode. In other words, in the first embodiment, the p-side electrode 10 is formed in advance including the first metal laminated film for electrodes and the second metal laminated film for lift-off. In the second embodiment, Then, a metal laminate film for lift-off is formed first, a dielectric film consisting of three layers is lifted off, and then a metal laminate film for forming a p-side electrode is formed.

  As shown in FIG. 12, the p-side electrode 17 is formed on the third dielectric film 13 as well as on the upper surface of the p-type contact layer 9 formed on the ridge portion 8 a of the p-type cladding layer 8. It is formed so as to cover the side portion of the portion 8a.

  Hereinafter, a method of manufacturing the semiconductor laser device configured as described above will be described with reference to the drawings.

  13 (a) to 13 (e) and FIGS. 14 (a) to 14 (e) show cross-sectional structures in the order of steps of the method of manufacturing the semiconductor laser device according to the second embodiment of the present invention. .

First, as shown in FIG. 13A, the low temperature growth buffer layer 2 made of AlGaN is formed on the main surface of the substrate 1 made of GaN by MOCVD. Subsequently, the growth temperature is set to 1000 ° C., and the n-type contact layer 3 made of n-type GaN, the n-type cladding layer 4 made of n-type Al _0.07 Ga _0.93 N, and the n-type GaN are formed on the low-temperature growth buffer layer 2. An n-type light guide layer 5, an MQW active layer 6, a p-type light guide layer 7 made of p-type GaN, a p-type cladding layer 8 made of p-type Al _0.07 Ga _0.93 N, and a p-type contact layer 9 made of p-type GaN. It is formed by sequential growth.

  Next, as shown in FIG. 13B, a first resist pattern 201 that masks the laser structure formation region on the p-type contact layer 9 is formed by lithography. Subsequently, a part of the n-type contact layer 3 is exposed by reactive dry etching (RIE) using an etching gas containing chlorine as a main component by using the formed first resist pattern 201 as a mask.

  Next, as shown in FIG. 13C, after removing the first resist pattern 201 by ashing, a resist is again formed on the p-type contact layer 9 including the exposed surface of the n-type contact layer 3 by lithography. A film is applied, and then a second resist pattern 202 having an opening in the ridge portion formation region is formed from the applied resist film. Subsequently, for example, aluminum (Al) and nickel (Ni) are stacked on the formed second resist pattern 202 by, for example, vapor deposition to lift off a dielectric film to be formed in a later process. A lift-off metal film 16 is formed. As described in the first embodiment, the waveguide width (ridge width) needs to be set in a range of 1.0 μm or more and 4.0 μm or less, and is 1.6 μm in this embodiment as well. The lowermost layer of the lift-off metal film 16 is made of Ni or Al, and is preferably made of Al. By this material selection, the lift-off metal film 16 can be removed by lift-off using a hydrochloric acid-based etchant.

  Next, as shown in FIG. 13D, the second resist pattern 202 and the lift-off metal film 16 deposited on the second resist pattern 202 are removed by a lift-off method using an organic solvent such as acetone. As a result, the lift-off metal film 16 is formed in the ridge portion formation region on the p-type contact layer 9.

  Next, as shown in FIG. 13E, by reactive dry etching (RIE) containing chlorine as a main component, the nickel portion constituting the upper portion of the lift-off metal film 16 is used as a mask to form a p-type cladding layer 8. The portion is etched into a ridge shape to form a ridge portion 8a. Here, the thickness (remaining film thickness) of the portion remaining in the region other than the ridge portion 8a in the p-type cladding layer 8 is 180 nm.

Next, as shown in FIG. 14A, the p-type cladding layer 8 and the p-type contact layer 3 exposed by etching including the lift-off metal film 16 using a sputtering method using electron cyclotron resonance (ECR) plasma. A first dielectric film 11 made of SiO ₂ having a thickness of 40 nm and a _second dielectric made of Si having a thickness of 30 nm are formed on the upper surface and further on the side surface of the semiconductor laminate such as the p-type light guide layer 7. A film 12 and a third dielectric film 13 made of Nb ₂ O _{5 having} a thickness of 40 nm are sequentially deposited.

  Next, as shown in FIG. 14B, the lift-off metal film 16 and the first and second dielectric films 11 and 11 deposited on the lift-off metal film 16 by lift-off using a hydrochloric acid-based etchant. The film 12 and the third dielectric film 13 are removed. In this lift-off process, before the lift-off, nickel or aluminum constituting the lift-off metal film 16 appears on the surface so that it is silver, but after the lift-off, the nickel and aluminum are removed and the p-type contact is removed. Layer 9 is exposed. Accordingly, it is possible to easily check whether or not lift-off is performed due to a color change before and after the lift-off process. Therefore, the yield when the dielectric films 11, 12, and 13 deposited on the lift-off metal film 16 are lifted off is improved.

  Next, a resist pattern (not shown) that opens the p-side electrode formation region is formed on the third dielectric film 13 including the p-type contact layer 9 by lithography. Subsequently, a p-side electrode forming film made of palladium (Pd) and gold (Au) is deposited on the resist pattern including the opening, and then the resist pattern is lifted off using an organic solvent such as acetone. As shown in FIG. 14C, the p-side electrode 17 straddling the side portion of the ridge portion 8a on the p-type contact layer 9 and the third dielectric film 13 is formed. Thus, it is preferable to use Ni or Pt in addition to Pd for the lowermost layer of the p-side electrode 17. Thereby, the contact resistance between the p-side electrode 17 and the p-type contact layer 9 can be reduced.

  Next, a resist pattern (not shown) that opens the n-side electrode formation region in the n-type contact layer 3 is formed on the third dielectric film 13 by lithography, and the formed resist pattern is used as a mask. Openings are formed in the dielectric films 11, 12 and 13 by reactive dry etching (RIE) and wet etching. Subsequently, an n-side electrode forming film is deposited on the resist pattern including the opening, and then the resist pattern is lifted off by using an organic solvent such as acetone, as shown in FIG. An n-side electrode 14 made of, for example, a laminated film of titanium (Ti) and aluminum (Al) is formed on the mold contact layer 3.

  Next, as shown in FIG. 14E, a resist pattern (not shown) having openings for exposing the p-side electrode 17 and the n-side electrode 14 is formed by lithography, and the resist pattern including the openings. A metal film for forming a wiring electrode made of a laminated film of, for example, titanium (Ti) and gold (Au) is deposited thereon. Subsequently, the wiring electrode 15 is formed on the p-side electrode 17 and the n-side electrode 14 by lifting off the wiring electrode forming metal film using an organic solvent such as acetone.

  In the semiconductor laser device manufactured as described above, when one wiring electrode 15 formed on the n-side electrode 14 is grounded and a voltage is applied to the other wiring electrode 15 formed on the p-side electrode 17, Carriers are injected into the MQW active layer 6, an optical gain is generated in the MQW active layer 6, and laser oscillation occurs when the oscillation wavelength is around 400 nm. The oscillation wavelength can be changed by the composition and film thickness of gallium indium nitride (GaInN) constituting the MQW active layer 6.

  In addition, the manufacturing method according to the second embodiment uses a second resist pattern instead of the conventional stripe-shaped resist pattern in the mask forming process of the ridge portion 8a of the p-type cladding layer 8 shown in FIG. The lift-off metal film 16 is formed by lift-off using an inverted stripe pattern as in 202. Furthermore, by using nickel constituting the upper part of the lift-off metal film 16 as a mask, the selectivity at the time of dry etching is high, and there is almost no receding of the mask made of nickel, so compared with the case of using a resist mask, The controllability of the stripe (ridge) width is improved.

  As described above, according to the ridge type nitride semiconductor laser device according to the second embodiment of the present invention, the current confinement function formed on at least the side surface of the ridge portion 8a of the p-type cladding layer 8 and the outer region thereof. By providing the provided dielectric film with a three-layer structure, the effective refractive index difference between the inside and outside of the ridge portion 8a can be reduced as compared with the case where the dielectric film is formed of only one layer.

  Further, by using a material that absorbs laser light, such as Si, for the second dielectric film 12 of the second layer, the gain difference between the fundamental mode and the higher-order mode can be increased.

Furthermore, a stable process can be realized by using a material having high adhesion to the P-side electrode 10 such as Nb ₂ O ₅ for the third dielectric film 13 of the third layer. As a result, it is possible to obtain a ridge waveguide semiconductor laser device having stable lateral mode characteristics that can realize high output characteristics and high yield.

  In the step shown in FIG. 14C, the hydrochloric acid-based etchant is used when the aluminum layer included in the lift-off metal film 16 is etched to perform the lift-off, but the present invention is not limited to this. For example, when titanium is included in the lower layer of the lift-off metal film 16, a hydrofluoric acid-based etchant may be used, and when nickel is used as the lower layer, a nitric acid-based etchant may be used.

  Also in the second embodiment, the n-side electrode 14 may be formed on the back surface of the substrate 1 as in a modification of the first embodiment.

(Third embodiment)
Hereinafter, a third embodiment of the present invention will be described with reference to the drawings.

  FIG. 15 shows a cross-sectional structure of a GaN-based semiconductor laser device according to the third embodiment of the present invention. In FIG. 15, the same components as those shown in FIG.

  The semiconductor laser device according to the third embodiment is characterized in that the dielectric laminated film covering the outer portion of the ridge portion 8a has a two-layer structure of the first dielectric film 11 and the second dielectric film 12. Different from the first embodiment.

In the third embodiment, a material having a small absorption with respect to the oscillation wavelength is used for the first dielectric film 11 in order to make the waveguide loss as small as possible, and the light is confined inside the waveguide. Therefore, it is necessary to use a dielectric having a refractive index lower than that of GaN (2.54). Therefore, in the third embodiment, gallium oxide (Ga ₂ O ₃ ) having a film thickness of 40 nm and a refractive index of 1.82 is used. As a result, the gain of the higher order mode can be reduced, and the gain difference between the fundamental mode and the higher order mode can be increased. As a result, hole burning is suppressed and a decrease in the generation level of kink can be suppressed.

The second dielectric film 12 has good adhesion to the wiring electrode 15 formed on the second dielectric film 12 and realizes high output characteristics, that is, an increase in kink generation level. It is necessary to apply a dielectric film having a large refractive index so as to make the difference in refractive index between the inside and outside of the waveguide as small as possible (increase the effective refractive index difference outside the waveguide). Therefore, in the third embodiment, zirconium oxide (ZrO ₂ ) having a film thickness of 30 nm and a refractive index of 2.22 is used.

  Here, as materials applicable to the dielectric films 11 and 12, there are combinations as shown below.

For example, Ga ₂ O ₃ , TiO _2, or AlN that absorbs the oscillation wavelength can be used for the first dielectric film 11. The second dielectric film _12, it is possible to use _{SiO 2, SiN, ZrO 2,} Ta 2 O 5, Nb 2 O 5 or Al ₂ O _3. Of these, the refractive index of the first dielectric film 11 and N _1, the refractive index of the second dielectric film 12 and N _2, it is preferable to select a material which satisfies N ₁ <N _2. More preferably, the combinations are expressed in the order of the first dielectric film 11 / second dielectric film 12, Ga ₂ O ₃ / ZrO ₂ , Ga ₂ O ₃ / Ta ₂ O ₅ , Ga ₂ O ₃ / Nb. _{It is a combination of 2} O ₅ , TiO ₂ / ZrO ₂ , TiO ₂ / Ta ₂ O ₅ , and TiO ₂ / Nb ₂ O ₅ .

Furthermore, as another combination, for example, SiO ₂ , SiN, ZrO ₂ , Ta ₂ O ₅ , Nb ₂ O _5, or Al ₂ O ₃ can be used for the first dielectric film 11. At this time, Ga ₂ O ₃ , TiO ₂ , AlN, TiN, TaN, or Si having absorption with respect to the oscillation wavelength can be used for the second dielectric film 12. Of these, the refractive index of the first dielectric film 11 and N _1, the refractive index of the second dielectric film 12 and N _2, it is preferable to select a material which satisfies N ₁ <N _2. More preferably, when the combinations are expressed in the order of the first dielectric film 11 / second dielectric film 12, SiO ₂ / Si, SiO ₂ / TiO ₂ , Al ₂ O ₃ / TiO ₂ , ZrO ₂ / Si, A combination of Ta ₂ O ₅ / Si and Nb ₂ O ₅ / Si.

  The total film thickness of the two dielectric films 11 and 12 needs to be 20 nm or more and 200 nm or less in order to keep the waveguide loss within 5% at an operating current of 30 mW, for example. Then, it is 70 nm.

  Hereinafter, a method of manufacturing the semiconductor laser device configured as described above will be described with reference to the drawings.

  16 (a) to 16 (d) and FIGS. 17 (a) to 17 (e) show cross-sectional structures in the order of steps of the method of manufacturing a semiconductor laser device according to the third embodiment of the present invention. .

First, as shown in FIG. 16A, the low temperature growth buffer layer 2 made of AlGaN is formed on the main surface of the substrate 1 made of GaN by MOCVD. Subsequently, the growth temperature is set to 1000 ° C., and the n-type contact layer 3 made of n-type GaN, the n-type cladding layer 4 made of n-type Al _0.07 Ga _0.93 N, and the n-type GaN are formed on the low-temperature growth buffer layer 2. An n-type light guide layer 5, an MQW active layer 6, a p-type light guide layer 7 made of p-type GaN, a p-type cladding layer 8 made of p-type Al _0.07 Ga _0.93 N, and a p-type contact layer 9 made of p-type GaN. It is formed by sequential growth.

  Next, as shown in FIG. 16B, a first resist pattern 201 that masks the laser structure formation region on the p-type contact layer 9 is formed by lithography. Subsequently, a part of the n-type contact layer 3 is exposed by reactive dry etching (RIE) using an etching gas containing chlorine as a main component by using the formed first resist pattern 201 as a mask.

  Next, as shown in FIG. 16C, after removing the first resist pattern 201 by ashing, a resist is again formed on the p-type contact layer 9 including the exposed surface of the n-type contact layer 3 by lithography. A film is applied, and then a second resist pattern 202 having an opening in the ridge portion formation region is formed from the applied resist film. Subsequently, for example, palladium (Pd) and gold (Au) for laminating the p-type contact layer 9 are laminated on the formed second resist pattern 202 by, for example, vapor deposition. A P-side electrode 10 including a metal multilayer film and a second metal multilayer film formed by laminating aluminum (Al) and nickel (Ni), for example, is formed on the first metal multilayer film. As described in the first embodiment, the waveguide width (ridge width) needs to be set in a range of 1.0 μm or more and 4.0 μm or less, and is 1.6 μm in this embodiment as well.

  Further, the lowermost layer of the first metal laminated film constituting the lower part of the P-side electrode 10 is not limited to palladium (Pd), and nickel (Ni) or platinum (Pt) is preferably used. By using such a material, the contact resistance between the P-side electrode 10 and the p-type contact layer 9 can be reduced.

  Next, as shown in FIG. 16D, a metal for forming the second resist pattern 202 and the P-side electrode deposited on the second resist pattern 202 by a lift-off method using an organic solvent such as acetone. By removing the laminated film, the P-side electrode 10 is formed in the ridge portion formation region on the p-type contact layer 9.

  Next, as shown in FIG. 17A, deposition is performed on the uppermost layer of the second metal laminated film constituting the upper portion of the P-side electrode 10 by reactive dry etching (RIE) mainly containing chlorine. Using the nickel portion as a mask, a part of the p-type cladding layer 8 is etched into a ridge shape to form a ridge portion 8a. Here, the thickness (remaining film thickness) of the portion remaining in the region other than the ridge portion 8a in the p-type cladding layer 8 is set to 180 nm in order to realize a stable transverse mode characteristic in which spatial hole burning is suppressed. .

Next, as shown in FIG. 17B, the p-type cladding layer 8 and the p-type contact layer 3 exposed by etching including the p-side electrode 10 using a sputtering method using electron cyclotron resonance (ECR) plasma. A first dielectric film 12 made of Ga ₂ O ₃ with a film thickness of 40 nm and a _second dielectric film made of ZrO _{2 with a} film thickness of 30 nm are formed on the upper surface and further on the side surface of the semiconductor laminate such as the p-type light guide layer 7. The dielectric films 12 are sequentially deposited. Here, when depositing the first dielectric film 11, gallium is used as the target material in an oxygen atmosphere, and when depositing the second dielectric film 12, zirconium is used as the target material in the oxygen atmosphere.

  Next, as shown in FIG. 17C, by lift-off using a hydrochloric acid-based etchant, the second metal laminated film made of aluminum and nickel in the P-side electrode 10 and the second metal laminated film The first dielectric film 11 and the second dielectric film 12 deposited thereon are removed. In this lift-off process, since the nickel or aluminum constituting the second metal laminated film is exposed on the surface before lift-off, the p-side electrode 10 is silver, but after lift-off, nickel and aluminum The aluminum constituting the first metal laminated film is exposed by removing the aluminum. Accordingly, it is possible to easily check whether or not lift-off is performed due to a color change before and after the lift-off process. Therefore, the yield when the dielectric films 11 and 12 deposited on the p-side electrode 10 are lifted off is improved.

Next, a resist pattern (not shown) that opens an n-side electrode formation region in the n-type contact layer 3 is formed on the second dielectric film 11 by lithography, and the formed resist pattern is used as a mask. Openings are formed in the dielectric films 11 and 12 by reactive dry etching (RIE) and wet etching. Subsequently, an n-side electrode forming film is deposited on the resist pattern including the opening, and then the resist pattern is lifted off by using an organic solvent such as acetone, so that n as shown in FIG. An n-side electrode 14 made of, for example, a laminated film of titanium (Ti) and aluminum (Al) is formed on the mold contact layer 3. Here, the etching method for the dielectric films 11 and 12 differs depending on the materials of the first dielectric film 11 and the second dielectric film 12, but in this embodiment, the reactivity using a fluorine-based gas is used. Etching of Ga ₂ O ₃ and ZrO ₂ is performed using dry etching (RIE) or buffered hydrofluoric acid.

  Next, as shown in FIG. 17E, a resist pattern (not shown) having openings for exposing the p-side electrode 10 and the n-side electrode 14 is formed by lithography, and the resist pattern including the openings. A metal film for forming a wiring electrode made of a laminated film of, for example, titanium (Ti) and gold (Au) is deposited thereon. Subsequently, the wiring electrode 15 is formed on the p-side electrode 10 and the n-side electrode 14 by lifting off the wiring electrode forming metal film using an organic solvent such as acetone.

  In the semiconductor laser device manufactured as described above, when one wiring electrode 15 formed on the n-side electrode 14 is grounded and a voltage is applied to the other wiring electrode 15 formed on the p-side electrode 10, Carriers are injected into the MQW active layer 6, an optical gain is generated in the MQW active layer 6, and laser oscillation occurs when the oscillation wavelength is around 400 nm. The oscillation wavelength can be changed by the composition and film thickness of gallium indium nitride (GaInN) constituting the MQW active layer 6.

  Further, in the manufacturing method according to the third embodiment, as in the first embodiment, the conventional striped resist is used in the mask forming process of the ridge portion 8a of the p-type cladding layer 8 shown in FIG. It is formed by lifting off the p-side electrode 10 using an inverted stripe pattern like the second resist pattern 202 instead of the pattern. Furthermore, by using nickel constituting the upper part of the p-side electrode 10 as a mask, the selectivity at the time of dry etching is high, and there is almost no receding of the mask made of nickel, so compared with the case of using a resist mask, The controllability of the stripe (ridge) width is improved. For this reason, when the stripe width is small, the kink occurrence level is increased, and the stripe width can be stably controlled, so that a high kink occurrence level can be maintained. As a result, a semiconductor laser device having high output characteristics can be realized.

  As described above, according to the ridge type nitride semiconductor laser device according to the third embodiment of the present invention, the current confinement function formed at least on the side surface of the ridge portion 8a of the p-type cladding layer 8 and in the outer region thereof. By providing the provided dielectric film with a two-layer structure, the effective refractive index difference between the inside and outside of the ridge portion 8a can be reduced as compared with the case where the dielectric film is formed of only one layer.

Further, by using a material having a small laser light absorption coefficient such as Ga ₂ O ₃ for the first dielectric film 11 of the first layer, the gain difference between the fundamental mode and the higher order mode can be increased. it can.

Furthermore, a stable process can be realized by using a material having high adhesion to the P-side electrode 10 such as ZrO ₂ for the second dielectric film 12 of the second layer. As a result, it is possible to obtain a ridge waveguide semiconductor laser device having stable lateral mode characteristics that can realize high output characteristics and high yield.

  In the step shown in FIG. 17C, the hydrochloric acid-based etchant is used when the aluminum layer included in the P-side electrode 10 is etched and lift-off is performed. However, the present invention is not limited to this. For example, when titanium is used for the lower layer of the second metal laminated film of the P-side electrode 10, a hydrofluoric acid-based etchant may be used, and when nickel is used for the lower layer, a nitric acid-based etchant may be used.

  Also in the third embodiment, the n-side electrode 14 may be formed on the back surface of the substrate 1 as in a modification of the first embodiment.

In each of the first to third embodiments, an example in which gallium nitride (GaN) is used for the substrate 1 has been described. For example, sapphire substrate, ELOG (Epitaxial Lateral Over Growth) or ABLEG on GaN or sapphire substrate. (Air Bridge Lateral Epitaxial Growth) The same effect can be obtained by using a low dislocation substrate in which dislocation defects are reduced by growth, a GaN template substrate from which a sapphire substrate is removed by a laser lift-off method, or a silicon carbide (SiC) substrate. . Alternatively, a substrate made of GaAs, NGO (NdGaO ₃ ), LGO (LiGaO ₃ ), Si, or the like may be used.

  In each embodiment, the GaN-based semiconductor laser device has been described as an example. However, the present invention can also be applied to a semiconductor laser device using another material, for example, an AlGaInP-based semiconductor, an AlGaAs-based semiconductor, or an InGaAsP-based semiconductor. .

  In the semiconductor laser device and the manufacturing method thereof according to the present invention, the dielectric film covering the ridge portion for current confinement has a laminated structure having different compositions, so that it is possible to realize a stable lateral mode characteristic with excellent adhesion, It has the effect of obtaining desired output characteristics, and is useful for a semiconductor laser device capable of high output for an optical pickup light source used in an optical information processing apparatus such as an optical disk system, a manufacturing method thereof, and the like.

1 is a structural cross-sectional view showing a semiconductor laser device according to a first embodiment of the present invention. It is the graph which compared the electric current-light output (IL) characteristic in the semiconductor laser apparatus which concerns on the 1st Embodiment of this invention with the prior art example. 4 is a graph showing far field pattern (FFP) characteristics in the semiconductor laser device according to the first embodiment of the present invention. 5 is a graph showing the relationship of the operating current value with respect to the film thickness of the dielectric film that confines the operating current in the semiconductor laser device according to the first embodiment of the present invention. (A)-(e) is the structure sectional drawing of the order of a process which shows the manufacturing method of the semiconductor laser apparatus concerning the 1st Embodiment of this invention. (A)-(d) is the structure sectional drawing of the order of a process which shows the manufacturing method of the semiconductor laser apparatus concerning the 1st Embodiment of this invention. 4 is a graph showing a relationship between a waveguide width (ridge width) and a remaining film thickness of a cladding layer and a design range in the semiconductor laser device according to the first embodiment of the present invention. FIG. 4 is a diagram schematically illustrating a cross-sectional shape of a ridge portion and a dielectric film deposited in the vicinity thereof when using the ECR sputtering method, which is a method for manufacturing a semiconductor laser device according to the first embodiment of the present invention. . FIG. 6 is a diagram schematically illustrating another cross-sectional shape of the dielectric film deposited in the vicinity of the ridge portion and the vicinity thereof when the ECR sputtering method is used in the method for manufacturing the semiconductor laser device according to the first embodiment of the present invention. It is. It is a figure for comparison, and it is a figure showing typically the section shape of the dielectric film deposited in the ridge part at the time of using plasma CVD method, and its neighborhood. FIG. 6 is a structural cross-sectional view showing a semiconductor laser device according to a modification of the first embodiment of the present invention. It is a structure sectional view showing a semiconductor laser device concerning a 2nd embodiment of the present invention. (A)-(e) is the structure sectional drawing of the order of a process which shows the manufacturing method of the semiconductor laser apparatus concerning the 2nd Embodiment of this invention. (A)-(e) is the structure sectional drawing of the order of a process which shows the manufacturing method of the semiconductor laser apparatus concerning the 2nd Embodiment of this invention. It is a structure sectional view showing a semiconductor laser device concerning a 3rd embodiment of the present invention. (A)-(d) is the structure sectional drawing of the order of a process which shows the manufacturing method of the semiconductor laser apparatus concerning the 3rd Embodiment of this invention. (A)-(e) is the structure sectional drawing of the order of a process which shows the manufacturing method of the semiconductor laser apparatus concerning the 3rd Embodiment of this invention. It is a cross-sectional view showing a conventional GaN-based semiconductor laser device.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Substrate 2 Low-temperature growth buffer layer 3 n-type contact layer 4 n-type cladding layer 5 n-type light guide layer 6 multiple quantum well (MQW) active layer (light emitting layer)
7 p-type light guide layer 8 p-type cladding layer (semiconductor layer)
8a Ridge portion 9 p-type contact layer 10 p-side electrode 11 first dielectric film 12 second dielectric film 13 third dielectric film 14 n-side electrode 15 wiring electrode 16 lift-off metal film 17 p-side electrode 201 first 1 resist pattern 202 2nd resist pattern

Claims (9)

A light emitting layer;
A semiconductor layer formed on the light emitting layer, having a ridge portion and having a refractive index smaller than that of the light emitting layer;
A plurality of dielectric films formed in at least a lateral region of the ridge portion in the semiconductor layer;
The plurality of dielectric films include a first dielectric film, a second dielectric film, and a third dielectric film, which are sequentially formed from below .
The light emitting layer and the semiconductor layer are Al _u Ga _v In _w N (where u, v, and w are 0 ≦ u ≦ 1, 0 ≦ v ≦ 1, 0 ≦ w ≦ 1, u + v + w = 1). Consists of
The first dielectric film is made of SiO _2,
The second dielectric film is made of Si, TiN or TaN,
The third dielectric film, a semiconductor laser device comprising SiN, in that it consists of _{ZrO 2, Ta 2 O 5,} Nb 2 O 5, TiO 2, Al 2 O 3, AlN or Ga ₂ O _3. 2. The semiconductor laser device according to claim 1, wherein a total thickness of the first dielectric film, the second dielectric film, and the third dielectric film is 20 nm or more and 200 nm or less. The semiconductor laser device according to claim 1 or 2, characterized in that it further comprises a metal layer covering the ridge portion in the semiconductor layer with the plurality of dielectric films. The semiconductor laser device according to claim 3 , wherein the metal film includes at least one of Ni, Pd, and Pt. Width of the ridge portion, a semiconductor laser device according to any one of claims 1 to 4, characterized in that at 1.0μm or more and 4.0μm or less. Forming a light emitting layer on the substrate (a);
(B) forming a semiconductor layer having a refractive index smaller than that of the light emitting layer on the light emitting layer;
A step (c) of selectively etching the formed semiconductor layer to form a ridge portion in the semiconductor layer;
A step (d) of laminating a plurality of dielectric films on at least a side region of the ridge portion on the semiconductor layer;
The plurality of dielectric films include a first dielectric film, a second dielectric film, and a third dielectric film, which are sequentially formed from below .
The light emitting layer and the semiconductor layer are Al _u Ga _v In _w N (where u, v, and w are 0 ≦ u ≦ 1, 0 ≦ v ≦ 1, 0 ≦ w ≦ 1, u + v + w = 1). Consists of
The first dielectric film is made of SiO _2,
The second dielectric film is made of Si, TiN or TaN,
The third dielectric film, the production of the semiconductor laser device comprising SiN, in that it consists of _{ZrO 2, Ta 2 O 5,} Nb 2 O 5, TiO 2, Al 2 O 3, AlN or Ga ₂ O ₃ Method. 7. The method of manufacturing a semiconductor laser device according to claim 6 , wherein in the step (d), the plurality of dielectric films are formed by electron cyclotron resonance sputtering or magnetron sputtering. 7. The method of manufacturing a semiconductor laser device according to claim 6 , wherein in the step (d), the plurality of dielectric films are formed by a pulse laser deposition method. 9. The method according to claim 6 , further comprising a step (e) of forming a metal film so as to cover the ridge portion including the plurality of dielectric films after the step (d). A manufacturing method of the semiconductor laser device according to claim 1.

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