JP2010245378A - Nitride semiconductor laser device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To improve a kink level by suppressing generation of a higher order lateral mode during high output. <P>SOLUTION: A nitride semiconductor laser device includes: a laser structure 20 comprising an n-type Al<SB>x</SB>Ga<SB>1-x</SB>N clad layer 2, an In<SB>y</SB>Ga<SB>1-y</SB>N active layer 4, and a p-type Al<SB>x</SB>Ga<SB>1-x</SB>N clad layer 6 having a ridge structure, the layers being formed in order on a GaN substrate 1; a flat part current block layer 9 formed on a flat part of the p-type Al<SB>x</SB>Ga<SB>1-x</SB>N clad layer 6; a side face part current block layer 8 formed on a side face of the ridge structure; a p-type GaN contact layer 7 formed on a top surface of the ridge structure; a (p) electrode 10 formed so as to cover the side face part current block layer 8, flat part current block layer 9, and p-type GaN contact layer 7; and an (n) electrode 11 formed on a surface of the GaN substrate 1 on the opposite side from the laser structure 20. The side face part current block layer 8 has a larger refractive index than the flat part current block layer 9. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a nitride semiconductor laser device, and more particularly to a nitride semiconductor laser device including a cladding layer having a ridge structure.

  DVD equipment compatible with Blu-ray Disc (registered trademark), which can record high definition (HD) video of terrestrial digital broadcasting on a digital versatile disc (DVD) for a long time, is spreading. Yes. There is an urgent need to increase the output and cost of a nitride semiconductor laser device with a wavelength of 405 nm used for a light source for high-speed recording and price reduction of a DVD compatible with Blu-ray Disc (registered trademark). Yes.

  FIG. 10 shows a cross-sectional structure of a conventional nitride semiconductor laser device.

  As shown in FIG. 10, the conventional nitride semiconductor laser device includes an n-type aluminum gallium nitride (AlGaN) cladding layer 102, an n-type AlGaN guide layer 103, an indium gallium nitride (InGaN) on a gallium nitride (GaN) substrate 101. ) An active layer 104, a p-type AlGaN electron blocking layer 105, and a p-type AlGaN cladding layer 106 having a ridge structure are sequentially formed. A p-type GaN contact layer 107 is formed on the top surface of the ridge structure of the p-type AlGaN cladding layer 106, and current confinement is formed on the flat portion of the p-type AlGaN cladding layer 106 and on the side surface of the ridge structure. A dielectric current blocking layer 108 is formed. Furthermore, a p-electrode 109 ohmically joined to the p-type GaN contact layer 107 is formed so as to cover the p-type GaN contact layer 107 and the dielectric current blocking layer 108, and an n-electrode is formed on the lower surface of the GaN substrate 101. 110 is formed.

  In general, when a nitride semiconductor laser device is in a high output state, a kink in which the linearity of the optical output deteriorates with respect to the injection current is likely to occur, and it becomes difficult to obtain stable optical output characteristics. The cause of the kink is that the light confinement effect due to the heat generation in the ridge due to the light absorption and joule heat generation in the p-type AlGaN cladding layer 106 with the increase of the light output, and the refractive index of the p-type AlGaN cladding layer 106 increases. The increase is considered.

  FIG. 11A shows a diagram in which the cross-sectional structure of the nitride semiconductor laser device of FIG. 10 at low output is converted into a one-dimensional refractive index distribution by an effective refractive index approximation method, and FIG. FIG. 11 is a diagram in which the cross-sectional structure of the nitride semiconductor laser device of FIG. 10 at the time of output is converted into a one-dimensional refractive index distribution by an effective refractive index approximation method.

As shown in FIG. 11A, in the effective refractive index difference ΔN _low between the effective refractive index of the ridge portion at the time of low output and the effective refractive index of the flat portion (hereinafter simply referred to as the flat portion effective refractive index), Ten nitride semiconductor laser devices are set to satisfy a single transverse mode condition in which only the fundamental transverse mode can exist. On the other hand, at the effective refractive index difference ΔN _high at the time of high output, as shown in the region C of FIG. 11B, the refractive index of the ridge portion increases due to the influence of heat generation, etc. The transverse mode condition is not satisfied and the higher order transverse mode is likely to occur. For this reason, as the output of the nitride semiconductor laser device increases, interference between the fundamental transverse mode and the higher order transverse mode occurs, causing instability of the laser beam and causing kinks.

  Patent Documents 1 and 2 propose methods for improving the kink level by suppressing the interference between the fundamental transverse mode and the higher-order transverse mode as described above and stabilizing the light output characteristics of the nitride semiconductor laser device. Has been.

Japanese Patent No. 3300657 Japanese Patent No. 3849758

  In Patent Document 1, since there is an insulating layer only on the side surface of a p-type AlGaN cladding layer having a ridge structure, an electrode layer in contact with the p-type AlGaN cladding layer increases in the higher-order transverse mode as the optical output of the semiconductor laser device increases. A structure is proposed in which the absorption increases and the kink level improves. However, since there is an insulating layer only on the side surface of the ridge structure of the p-type AlGaN cladding layer, the absorption of fundamental transverse mode light leaking outside the ridge structure also increases, so that the threshold current increases and the injection current of the semiconductor laser device This is a structure in which an adverse effect such as a decrease in slope efficiency (hereinafter simply referred to as slope efficiency) defined by an increase in light output with respect to is likely to occur. In addition, the increase in absorption in the fundamental transverse mode of the semiconductor laser device means a waveguide structure with a large loss, which causes an increase in threshold current and a decrease in slope efficiency as the operation time becomes longer due to an increase in heat generation. As a result, there is a risk that reliability characteristics may be degraded.

  In Patent Document 2, the insulating layer of the p-type AlGaN cladding layer having a ridge structure is uniformly thinned on the flat portion of the p-type AlGaN cladding layer and the side surface of the ridge portion, thereby forming an upper portion of the insulating layer. 1 shows a structure in which a high-order transverse mode is absorbed by a light absorption layer composed of an amorphous silicon (Si) layer and an electrode layer formed to improve the kink level. In the structure shown in Patent Document 2, in order to significantly improve the kink level, it is necessary to sufficiently reduce the thickness of the insulating layer on the side surface of the p-type AlGaN cladding layer and the side surface of the ridge portion. For this reason, as in the structure shown in Patent Document 1, the absorption in the fundamental transverse mode is increased along with the absorption in the higher-order transverse mode, and thus adverse effects such as an increase in threshold current and a decrease in slope efficiency occur.

  Thus, although the conventional nitride semiconductor laser device can improve the kink level by increasing the absorption of the higher-order transverse mode that causes the kink level to decrease, the absorption of the fundamental transverse mode also increases. This results in sacrificing basic characteristics of the nitride semiconductor laser device such as current and slope efficiency. In addition, the conventional nitride semiconductor laser device described above is a nitride semiconductor that has a relatively small influence on the reliability characteristics even if the threshold current increases and the slope efficiency decreases, and the maximum optical output is about several tens of mW. This is effective in improving the kink level of the laser device. However, the improvement of the kink level of the nitride semiconductor laser device with higher output and the maximum optical output of several hundreds mW level is accompanied by deterioration of the basic characteristics, so that the nitride semiconductor laser device having good reliability characteristics Is difficult to realize.

  In view of the above-described conventional problems, the present invention aims to improve the kink level of the nitride semiconductor laser device and to improve the basic characteristics of the nitride semiconductor laser device such as threshold current and slope efficiency due to absorption of the fundamental transverse mode. It is to be able to maintain.

  In order to achieve the above object, according to the present invention, a nitride semiconductor laser device has a structure in which current blocking layers having different refractive indexes are provided on a flat portion of a cladding layer having a ridge structure and a side surface of the ridge structure.

  Specifically, a nitride semiconductor laser device according to the present invention is formed on a substrate, each made of a group III nitride semiconductor, an n-type cladding layer, and an active layer formed on the n-type cladding layer A p-type cladding layer having a ridge structure formed on the active layer, and a p-type contact layer formed on the top surface of the ridge structure of the p-type cladding layer, and a p-type cladding Formed on the flat portions on both sides of the ridge structure in the layer, and a flat portion current blocking layer for confining the current, and a side portion current blocking layer formed on the side surface of the ridge structure in the p-type cladding layer and confining the current A p-electrode formed so as to cover the flat portion current blocking layer, the side surface current blocking layer and the p-type contact layer, and an n-electrode formed on the surface of the substrate opposite to the laser structure, Side part Refractive index of the flow blocking layer, and greater than the refractive index of the flat portion the current blocking layer.

  According to the nitride semiconductor laser device of the present invention, since the refractive index of the side surface current blocking layer is larger than the refractive index of the flat portion current blocking layer, the absorption of the fundamental transverse mode is suppressed and only the absorption of the higher order transverse mode is suppressed. Can be increased. Therefore, the basic characteristics of the nitride semiconductor laser device such as the improvement of the kink level and the threshold current and the slope efficiency can be maintained, and the waveform distortion of the laser far field pattern (FFP) can be improved.

  In the nitride semiconductor laser device of the present invention, the side portion current blocking layer has a refractive index of 2.0 or more, and the flat portion current blocking layer has a refractive index of 1.3 to 1.6. preferable.

  In the nitride semiconductor laser device of the present invention, the side surface current blocking layer is preferably made of silicon nitride, tantalum pentoxide or zirconium dioxide.

  In the nitride semiconductor laser device of the present invention, the flat portion current blocking layer is preferably made of silicon dioxide.

  In the nitride semiconductor laser device of the present invention, the thickness of the side surface current blocking layer is preferably larger than the thickness of the flat portion current blocking layer.

  In the nitride semiconductor laser device of the present invention, it is preferable that the length of the bottom side of the side surface current blocking layer is set to 0.3 μm or more and 0.6 μm or less.

  In the nitride semiconductor laser device of the present invention, the flat portion current blocking layer is preferably formed also on the side surface of the side surface current blocking layer.

  According to the nitride semiconductor laser device of the present invention, the basic characteristics of the nitride semiconductor laser device such as improvement of the kink level and threshold current and slope efficiency can be maintained. Further, the waveform distortion of the laser beam far field image (FFP) can be improved.

1 is a cross-sectional view showing a structure of a nitride semiconductor laser device according to a first embodiment of the present invention. FIG. 3 is a diagram showing a one-dimensional effective refractive index distribution obtained by converting the cross-sectional structure of the nitride semiconductor laser device according to the first embodiment of the present invention by an effective refractive index approximation method, and light distributions of a fundamental transverse mode and a high-order transverse mode. is there. It is a graph which shows the result of having calculated the absorption coefficient of the fundamental transverse mode and the high order transverse mode with respect to the change of the film thickness of the side part current block layer of the nitride semiconductor laser device concerning a 1st embodiment of the present invention. 6 is a graph showing the results of calculating the absorption coefficients of the fundamental transverse mode and the higher order transverse mode with respect to the change in film thickness of the flat portion current blocking layer of the nitride semiconductor laser device according to the first embodiment of the present invention. 4 is a graph showing the light output characteristics of the nitride semiconductor laser device according to the first embodiment of the present invention and the conventional nitride semiconductor laser device. It is sectional drawing which shows the structure of the nitride semiconductor laser apparatus which concerns on the 2nd Embodiment of this invention. It is a graph which shows the result of having calculated the absorption coefficient of the fundamental transverse mode and the high order transverse mode with respect to the change of the film thickness of the flat part current block layer of the nitride semiconductor laser device concerning a 2nd embodiment of the present invention. It is a figure which shows the one-dimensional effective refractive index distribution which converted the cross-section of the nitride semiconductor laser apparatus concerning the 2nd Embodiment of this invention by the effective refractive index approximation method. 5 is a graph showing light output characteristics of a nitride semiconductor laser device according to a second embodiment of the present invention and a conventional nitride semiconductor laser device. It is sectional drawing which shows the structure of the conventional nitride semiconductor laser apparatus. (A) is a figure which shows the light distribution of the one-dimensional effective refractive index distribution and fundamental transverse mode which converted the cross-section of the conventional nitride semiconductor laser apparatus by the effective refractive index approximation method at the time of low output. FIG. 6B is a diagram showing a one-dimensional effective refractive index distribution obtained by converting a cross-sectional structure of a conventional nitride semiconductor laser device at a high output by an effective refractive index approximation method, and light distributions of a fundamental transverse mode and a high-order transverse mode. It is.

(First embodiment)
A nitride semiconductor laser device according to a first embodiment of the present invention will be described with reference to FIGS.

  FIG. 1 shows a cross-sectional structure of a nitride semiconductor laser device according to the first embodiment of the present invention. Hereinafter, x is an aluminum (Al) composition, and y is an indium (In) composition.

As shown in FIG. 1, for example, an n-type aluminum gallium nitride (Al _x Ga _1-x N) cladding layer 2 and an n-type Al _x Ga _1-x N guide layer are formed on a gallium nitride (GaN) substrate 1. 3 suppresses electron overflow from the well layers and barrier layers and InGaN having a structure quantum wells by _{(in y Ga 1-y N} ) active layer _{4, in y Ga 1-y} N active layer 4 A p-type Al _x Ga _1-x N electron blocking layer 5 and a p-type Al _x Ga _1-x N cladding layer 6 having a ridge structure are sequentially formed, and a laser structure 20 is formed. A p _- type GaN contact layer 7 is formed on the top surface of the ridge structure in the p-type Al _x Ga _1-x N cladding layer 6, and a side surface current blocking layer 8 is formed on the side surface of the ridge structure. A flat portion current block layer 9 is formed on the flat portion of the Al _x Ga _1-x N clad layer 6. A p-electrode 10 is formed so as to cover the p-type GaN contact layer 7, the side surface current blocking layer 8, and the flat portion current blocking layer 9. An n-electrode 11 is formed on the surface of the GaN substrate 1 opposite to the laser structure 20.

From the n-type Al _x Ga _1-x N cladding layer 2 to the p-type GaN contact layer 7 on the GaN substrate 1 is crystal-grown using a metal organic chemical vapor deposition method. The p-type Al _x Ga _1-x N cladding layer 6 is a mesa-shaped ridge that performs current injection and optical confinement into the In _y Ga _1-y N active layer 4 using dry etching techniques such as reactive ion etching. A structure is formed.

The side surface current blocking layer 8 is made of silicon nitride (SiN), tantalum pentoxide (Ta ₂ O ₅ ), zirconium dioxide (ZrO ₂ ) or the like having a refractive index of 2.0 or more, and a flat portion current blocking layer. 9 is formed by using a silicon dioxide (SiO ₂ ) having a refractive index of 1.3 or more and 1.6 or less and using a photolithography method such as a lift-off method on the flat portion and the side surface of the ridge portion. .

Thereafter, a p-electrode 10 made of a metal layer of titanium (Ti) / platinum (Pt) / gold (Au) ohmic-bonded on the p-type GaN contact layer 7 is formed. Here, in the nitride semiconductor laser device according to the present embodiment, a horizontal laser beam far field image (FFP) (hereinafter simply referred to as horizontal FFP) is in a range of 7 ° to 10 °, and vertical. N _- type Al _x Ga _1-x N cladding layer 2 and In _y Ga _1-y N active layer 4 so that the FFP in the direction (hereinafter simply referred to as vertical FFP) is in the range of 16 ° to 20 °. In addition, the Al composition, the In composition, and the film thickness of the p-type Al _x Ga _1-x N cladding layer 6 are adjusted to appropriate values.

  [Table 1] shows the Al composition, In composition, and film thickness of each layer constituting the nitride semiconductor laser device according to this embodiment.

  The ridge width W shown in FIG. 1 is set to a width that satisfies the single transverse mode condition in a low output state near the oscillation threshold. The bottom side L of the side current blocking layer 8 confines the light distribution in the fundamental transverse mode in the region A in the ridge structure, and the light distribution in the higher order transverse mode extends from the side current blocking layer 8 to the region B outside the ridge structure. It is set to the length that oozes out. The thickness of the side current block layer 8 and the flat current block layer 9 is such that only the fundamental transverse mode is confined and the higher order transverse mode is sufficiently absorbed by the p-electrode 10. The film thickness is set to be larger than the film thickness of the flat portion current blocking layer 9.

  In this embodiment, in order to obtain a nitride semiconductor laser device having a horizontal FFP of 8.5 ° and a vertical FFP of 18 °, the Al composition, the In composition, and the film thickness of each layer are set to the values shown in [Table 1]. The ridge width W is set to 1.4 μm. Further, the distance at which the fundamental transverse mode power amplitude of the nitride semiconductor laser device having the structure shown in [Table 1] is sufficiently attenuated with respect to the peak power is about 1.2 μm from the ridge center. And the flat portion current blocking layer 9 has a structure in which the bottom L of the side surface current blocking layer 8 is set to 0.45 μm so that the boundary between the flat portion current blocking layer 9 is about 1.2 μm from the center of the ridge and the absorption of the fundamental mode is suppressed. .

The side surface current blocking layer 8 is made of Ta ₂ O ₅ having a refractive index of about 2.2 in the oscillation wavelength region of 405 nm of the nitride semiconductor laser device, and its film thickness is set to 0.3 μm. The layer 9 is made of SiO ₂ having a refractive index of 1.5 in the oscillation wavelength region of 405 nm of the nitride semiconductor laser device, and its film thickness is set to 0.03 μm. The refractive index and the film thickness of the side surface current blocking layer 8 and the flat portion current blocking layer 9 are set in this way to weaken the light confinement effect on the side surface of the ridge portion. That is, the basic transverse mode is sufficiently confined in the region A because the side surface current blocking layer 8 is thick. On the other hand, since the higher-order transverse mode has a light confinement effect weaker than that of the fundamental transverse mode, only the bottom part of the light distribution of the higher-order transverse mode oozes out into the region B. Further, the absorption coefficient in the oscillation wavelength region of 405 nm of the nitride semiconductor laser device of the p-electrode 10 which is a metal layer of Ti / Pt / Au is generally very large, and is about 800,000 cm ⁻¹ in the measurement by the spectroscopic ellipsometry method. It is set. The width of the p-electrode 10 is set so as to sufficiently absorb the light distribution of the high-order transverse mode that has oozed into the region B, and the value is set to 10 μm on the left and right from the center of the ridge portion.

  Next, the operation of the nitride semiconductor laser device that improves the kink level by efficiently absorbing only the higher-order transverse mode in the present embodiment will be described.

The nitride semiconductor laser device oscillates in the fundamental transverse mode at the optical output near the oscillation threshold current, but the ridge portion is affected by the light absorption in the p-type Al _x Ga _1-x N cladding layer 6 due to the increase in the optical output. As the temperature rises, the single transverse mode condition is not satisfied, and the waveguide structure changes to a higher order transverse mode.

  FIG. 2 shows the effective refractive index distribution and the light distribution of the fundamental transverse mode and the high-order transverse mode in the high output state of the nitride semiconductor laser device according to the present embodiment.

  As shown in FIG. 2, at the time of high output, the refractive index of the region C increases due to the influence of heat generation or the like, so that the single transverse mode condition is not satisfied as the light output rises, and higher order transverse modes are likely to occur.

  The high-order transverse mode has a light confinement effect weaker than that of the fundamental transverse mode, and has a property that a large amount of light oozes out to the region B outside the ridge portion of the nitride semiconductor laser device. This property basically does not change even if the waveguide structure changes due to, for example, the ridge width W expanding. Therefore, by absorbing the light distribution of the high-order transverse mode that has oozed into the region B, the occurrence of the high-order transverse mode can be suppressed and the kink level can be improved.

In the present embodiment, by setting the refractive index of the side surface current blocking layer 8 to be higher than the refractive index of the flat portion current blocking layer 9, the effective refractive index Neq3 of the bottom L region of the side surface current blocking layer 8 is set to the region B. It can be higher than the effective refractive index Neq2. The value of the effective refractive index Neq3 changes due to a change in the refractive index of the side surface current blocking layer 8, decreases when the refractive index of the side surface current blocking layer 8 increases, and increases when the refractive index of the side surface current blocking layer 8 decreases. To do. Since the light distribution has such a property that the greater the effective refractive index, the greater the light confinement effect. Therefore, Neq3 is lowered by making the refractive index of the side surface current blocking layer 8 higher than the refractive index of the flat portion current blocking layer 9. The optical confinement effect in the fundamental transverse mode and the higher order transverse mode can be weakened. Therefore, the nitride semiconductor laser device according to the present embodiment, like the flat portion current blocking layer 9, has a higher-order transverse mode than the case where the side portion current blocking layer 8 is formed of SiO ₂ having a refractive index of 1.5. Confinement can be reduced.

  At this time, in the basic transverse mode, the thickness of the side surface current blocking layer 8 is sufficiently thick as 0.3 μm, so that light is almost confined in the region A inside the ridge portion. On the other hand, since the higher-order transverse mode has a property that the light confinement effect is weaker than that of the fundamental transverse mode, the region A is not sufficiently attenuated and the oozing into the region B becomes large. Further, by reducing the film thickness of the flat portion current blocking layer 9, reflected light and interference light that cause high-order transverse mode light distribution and horizontal FFP waveform ripple leaked from the region A are caused by the p electrode 10. Can be absorbed. At this time, the light distribution of the fundamental transverse mode is set such that the film thickness of the side current blocking layer 8 is set to a value that the fundamental transverse mode is sufficiently confined, and the bottom L of the side current blocking layer 8 is the bottom portion of the fundamental transverse mode. Is set so as not to ooze out to the region B, absorption by the p-electrode 10 can be suppressed.

  FIG. 3 shows the results of calculating the absorption coefficients of the basic transverse mode and the higher order transverse mode with respect to the thickness of the side surface current blocking layer 8 when the thickness of the flat portion current blocking layer 9 is 0.05 μm.

As shown in FIG. 3, the absorption coefficient increases as the side surface current blocking layer 8 becomes thinner. When the thickness of the side surface current blocking layer 8 becomes 0.2 μm or less, the absorption coefficient increases rapidly. Further, when the film thickness of the side surface current blocking layer 8 is 0.2 μm or more, the absorption coefficient of the high-order transverse mode is 19 cm ^−1, which is about 1.4 times the value of 14 cm ⁻¹ of the fundamental transverse mode. It can be confirmed that the higher-order transverse mode is larger in the light distribution to the p-electrode 10 as the absorption layer than the fundamental transverse mode.

  FIG. 4 shows the result of calculating the absorption coefficient when the thickness of the side surface current blocking layer 8 is constant at 0.3 μm and the thickness of the flat portion current blocking layer 9 is changed.

  As shown in FIG. 4, the absorption coefficient of the higher-order transverse mode increases as the film thickness of the flat part current blocking layer 9 decreases, and when the film thickness of the flat part current blocking layer 9 becomes 0.04 μm or less, the absorption coefficient increases. It can be confirmed that it increases rapidly. In addition, the absorption coefficient of the fundamental transverse mode at this time is set to a higher order because the bleeding of the light distribution to the p-electrode 10 is suppressed by setting the thickness of the side surface current blocking layer 8 to 0.3 μm. A sudden increase like the transverse mode cannot be confirmed.

As described above, in the nitride semiconductor laser device according to this embodiment, the refractive index and film thickness of the side surface current blocking layer 8 are made larger than the refractive index and film thickness of the flat portion current blocking layer 9. As a result, a current blocking layer of the same material is uniformly formed on the side surfaces of the flat portion and the ridge portion as in the prior art, and the film thickness is reduced and a higher-order transverse mode is formed by the light absorption layer above the current blocking layer. The nitride semiconductor laser device according to this embodiment can suppress an increase in the absorption coefficient of the fundamental transverse mode as compared with a structure that absorbs. Moreover, since it is formed thin flat portion current blocking layer 9 on top of the p-type _Al x _{Ga 1-x} N cladding layer 6, directly on the light at the top of p-type _Al x _{Ga 1-x} N cladding layer 6 It is possible to suppress an increase in the absorption coefficient of the fundamental transverse mode as compared with the structure forming the absorption layer.

  FIG. 5 shows the light output characteristics of the prototype device of the nitride semiconductor laser device according to this embodiment.

  As shown in FIG. 5, the kink level of the nitride semiconductor laser device according to the present embodiment is 550 mW, while the kink level of the nitride semiconductor laser device having the conventional structure shown in FIG. 10 is 400 mW. Therefore, it can be confirmed that the kink level can be improved by 150 mW. At this time, no adverse effects such as an increase in threshold current and a decrease in slope efficiency can be confirmed, and it has been confirmed that only absorption in the higher-order transverse mode increases while suppressing absorption in the fundamental transverse mode. In addition, the FFP characteristics at this time are 8.5 ° for horizontal FFP and 19.0 ° for vertical FFP, and it can be confirmed that no abnormal ripple or the like has occurred in the FFP waveform. Desired characteristics are obtained.

  In this embodiment, the Al composition, the In composition, and the film thickness of each layer are set as shown in [Table 1]. However, when the FFP design of the nitride semiconductor laser device is changed, the values are changed. Is also possible.

  The bottom side L of the side current blocking layer 8 is 0.3 μm in order to suppress the seepage to the region B outside the ridge portion of the basic transverse mode and to promote the seepage to the region B of the higher order transverse mode. It is desirable to set it above and below 0.6 micrometer.

  The film thickness of the side current blocking layer 8 is preferably 0.2 μm or more and 0.4 μm or less in order to suppress absorption of the fundamental transverse mode and absorb only the higher order transverse mode by the p-electrode 10. When the thickness of the side surface current blocking layer 8 is 0.2 μm or less, the absorption coefficient of the fundamental transverse mode increases as shown in FIG. 3, and the increase and absorption of the operating current due to the increase in the threshold current and the decrease in the slope efficiency. As the coefficient increases, the amount of heat generated by the nitride semiconductor laser device increases. As a result, the end face breakdown output level is lowered and the long-term reliability is adversely affected. Therefore, it is not desirable that the thickness of the side surface current blocking layer 8 is 0.2 μm or less. Further, when the film thickness of the side surface current blocking layer 8 is 0.4 μm or more, the base L of the side surface current blocking layer 8 may be larger than the set value, and absorption in the p-electrode 10 in the higher-order transverse mode. The coefficient decreases and the kink level improvement effect decreases.

  The film thickness of the flat portion current blocking layer 9 is set to 0.02 μm or more and 0.04 μm or less in order to suppress the increase of the absorption coefficient of the fundamental transverse mode and increase the absorption coefficient of only the higher order transverse mode. desirable. When the film thickness of the flat portion current blocking layer 9 is 0.02 μm or less, the absorption coefficient of the fundamental transverse mode increases as shown in FIG. 4, and the nitride semiconductor laser device such as an increase in threshold current and a decrease in slope efficiency is shown. Characteristic deterioration occurs. On the other hand, when the flat portion current blocking layer 9 is 0.04 μm or more, the absorption coefficient of the higher-order transverse mode is lowered, and the kink level improving effect is lowered, which is not desirable.

  The structure of the p-electrode 10 is not limited to the Ti / Pt / Au structure, and the nitride semiconductor laser device of this embodiment can be configured even if it is a metal electrode having a general absorption coefficient. The width of the p-electrode 10 is desirably set to 10 μm or more and 30 μm or less on the left and right sides from the ridge center. This is because the width of the p-electrode 10 needs to be set to a value that sufficiently absorbs the high-order transverse mode, and if the width is too narrow, the high-order transverse mode cannot be sufficiently absorbed. This is because if the width is increased too much, the parasitic capacitance of the nitride semiconductor laser device increases, which adversely affects response characteristics and the like.

  As described above, according to the nitride semiconductor laser device according to the first embodiment of the present invention, the refractive index and film thickness of the side surface current blocking layer 8 are set to be higher than the refractive index and film thickness of the flat portion current blocking layer 9. By setting it high, the absorption coefficient of the higher-order transverse mode can be increased without increasing the absorption coefficient of the fundamental transverse mode within a range that does not adversely affect the threshold current and the slope efficiency. Thereby, this embodiment can improve the kink level by 150 mW compared with the conventional structure. In addition, since the structure does not affect basic characteristics such as an increase in threshold current and a decrease in slope efficiency, the kink level can be improved without impairing the reliability of the nitride semiconductor laser device. Further, since unnecessary ripples and the like are not generated in the FFP waveform, it is possible to obtain a nitride semiconductor laser device that is desirable as a light source for an optical pickup.

(Second Embodiment)
A nitride semiconductor laser device according to the second embodiment of the present invention will be described below with reference to FIGS.

  FIG. 6 shows a cross-sectional structure of a nitride semiconductor laser device according to the second embodiment of the present invention. In FIG. 6, the same members as those in the nitride semiconductor laser device according to the first embodiment of the present invention shown in FIG. 1 are denoted by the same reference numerals, and the description thereof will be omitted. Only the differences will be described.

As shown in FIG. 6, in the nitride semiconductor laser device according to a second embodiment, the flat portion the current blocking layer 12 is not only on a flat portion of the p-type Al x _Ga 1-x _N cladding layer 6, It is also formed on the side surface of the side surface current blocking layer 8. As a result, as in the first embodiment, it is possible to increase only the absorption coefficient of the higher-order transverse mode without increasing the absorption coefficient of the fundamental transverse mode.

  FIG. 7 shows a nitride semiconductor laser device according to the second embodiment of the present invention, in which the thickness of the side current blocking layer 8 is constant at 0.3 μm and the thickness of the flat current blocking layer 12 is changed. The result of calculating the absorption coefficient is shown.

As shown in FIG. 7, the absorption coefficient of the fundamental transverse mode when the film thickness of the flat portion current blocking layer 12 is 0.03 μm is 14 cm ^−1, which is the case of the first embodiment of the present invention shown in FIG. about ^{1 cm -1} small compared with the 15cm ^-1. Further, the absorption coefficient of the high-order transverse mode of the second embodiment at this time is 32 cm ⁻¹ , which is about 1 cm ⁻¹ larger than 31 cm ^{−1 in} the case of the first embodiment.

  FIG. 8 shows the effective refractive index distribution in the high output state of the nitride semiconductor laser device according to the second embodiment of the present invention.

  As shown in FIG. 8, at the time of high output, the refractive index of the region C increases due to the influence of heat generation, etc., so that the single transverse mode condition is not satisfied as the light output rises, and higher order transverse modes are likely to occur.

  The reason why the absorption coefficient of the fundamental transverse mode of the second embodiment can be reduced more than the absorption coefficient of the fundamental transverse mode of the first embodiment is that the flat portion current blocking layer 12 is formed on the side surface of the side portion current blocking layer 8. This is because the radiation loss from the side current block layer 8 in the basic transverse mode can be reduced. Further, the reason why the absorption coefficient of the higher-order transverse mode of the second embodiment can be increased as compared with the first embodiment is that the flat portion current blocking layer 12 having a refractive index of 1.5 as shown in FIG. Is formed on the side surface of the side surface current blocking layer 8, the effective refractive index Neq4 of the base L of the side surface current blocking layer 8 becomes smaller than the effective refractive index Neq3 of the first embodiment, and as a result, the region This is because the light confinement effect of the higher-order transverse mode on A can be weakened.

  FIG. 9 shows the light output characteristics of a prototype device of the nitride semiconductor laser device according to the second embodiment of the present invention.

  As shown in FIG. 9, the kink level of the nitride semiconductor laser device of the second embodiment is 560 mW, whereas the kink level of the nitride semiconductor laser device of the conventional structure is 400 mW. Therefore, it can be confirmed that the kink level is improved by 160 mW. Further, the FFP characteristics at this time are 8.5 ° for horizontal FFP and 19.0 ° for vertical FFP, and it can be confirmed that no abnormal ripple or the like is generated in the FFP waveform, which is desirable as a light source for an optical pickup. Characteristics can be obtained.

  In the second embodiment, the base L of the side surface current blocking layer 8, the film thicknesses of the side surface current blocking layer 8 and the flat portion current blocking layer 12, and the width of the p-electrode 10 are the same as those in the first embodiment of the present invention. For the same reason as described, it is desirable to set within the same value range as in the first embodiment.

In the second embodiment, since the flat portion current blocking layer 12 is formed on the side surface of the side portion current blocking layer 8, the side portion current blocking layer 8 is hardly peeled off from the side surface of the ridge portion, and the nitride semiconductor laser device Therefore, it is possible to stabilize the basic characteristics and reduce the processing loss in the manufacturing process and improve the manufacturing yield. Further, since the side surface current blocking layer 8 is difficult to peel off from the side surface of the ridge portion, the side surface current blocking layer 8 is made of a material having a higher refractive index in addition to SiN _x , Ta ₂ O ₅ and ZrO _2. Even a material that is poor in adhesion to the side surface of the ridge portion can be used. For this reason, it becomes possible to widen the selection range of the material of the side surface current blocking layer 8.

  As described above, according to the nitride semiconductor laser device of the second embodiment of the present invention, as in the first embodiment, the oscillation threshold current and the slope efficiency are increased by increasing the absorption coefficient of the high-order transverse mode. It is possible to improve the kink level by 160 mW compared to the conventional structure without deteriorating. Further, since unnecessary ripples and the like are not generated in the FFP waveform, it is possible to obtain a nitride semiconductor laser device that is desirable as a light source for an optical pickup.

  The nitride semiconductor laser device according to the present invention can maintain the basic characteristics of the nitride semiconductor laser device such as the improvement of the kink level, the threshold current, and the slope efficiency, and the waveform of the laser beam far field image (FFP). The strain can be improved, and it is useful for a nitride semiconductor laser device having a cladding layer having a ridge structure.

1 GaN substrate 2 n-type Al _x Ga _1-x N cladding layer 3 n-type Al _x Ga _1-x N guide layer 4 In _y Ga _1-y N active layer 5 p-type Al _x Ga _1-x N electron blocking layer 6 p-type _Al x _{Ga 1-x} n cladding layer 7 p-type GaN contact layer 8 side portion current blocking layer 9 flats current blocking layer 10 p electrode 11 n electrode 12 flats current blocking layer 20 laser structure

Claims (7)

Each formed of a group III nitride semiconductor, having an n-type cladding layer, an active layer formed on the n-type cladding layer, and a ridge structure formed on the active layer a laser structure having a p-type cladding layer and a p-type contact layer formed on the top surface of the ridge structure of the p-type cladding layer;
A flat portion current blocking layer formed on the flat portions on both sides of the ridge structure in the p-type cladding layer and confining current;
A side-surface current blocking layer formed on a side surface of the ridge structure in the p-type cladding layer and confining current;
A p-electrode formed to cover the flat part current blocking layer, the side part current blocking layer and the p-type contact layer;
An n-electrode formed on a surface of the substrate opposite to the laser structure,
The nitride semiconductor laser device according to claim 1, wherein a refractive index of the side surface current blocking layer is larger than a refractive index of the flat portion current blocking layer. The side part current blocking layer has a refractive index of 2.0 or more,
The nitride semiconductor laser device according to claim 1, wherein the flat portion current blocking layer has a refractive index of 1.3 to 1.6.   The nitride semiconductor laser device according to claim 1, wherein the side surface current blocking layer is made of silicon nitride, tantalum pentoxide, or zirconium dioxide.   The nitride semiconductor laser device according to claim 1, wherein the flat portion current blocking layer is made of silicon dioxide.   5. The nitride semiconductor laser device according to claim 1, wherein a thickness of the side portion current blocking layer is larger than a thickness of the flat portion current blocking layer.   6. The nitride semiconductor according to claim 1, wherein a length of a bottom side of the side surface current blocking layer is set to 0.3 μm or more and 0.6 μm or less. Laser device.   The nitride semiconductor laser device according to claim 1, wherein the flat portion current blocking layer is also formed on a side surface of the side portion current blocking layer.

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