JP2000357842A - Semiconductor laser - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a semiconductor laser using nitride based III-V compound semiconductor which can easily realize decrease of a driving voltage, stabilization in transverse mode, increase of a divergence angle of beams in the horizontal direction of a far field pattern, prevention of deterioration of laser characteristic which is to be caused by irregularity of the form of a resonator end surface, and improvement of noise characteristic. SOLUTION: In a GaN based semiconductor laser of a refractive index waveguide type in which SiO2 current constriction layers 11 absorbing no lights from a GaInN active layer 5 are formed on both sides of a ridge part 9 composed of an upper layer of a P-type AlGaN clad layer 7 and a P-type GaN contact layer 8, tapered regions 9a whose width decreases from the central part of the resonator lengthwise direction toward both ends of the resonator lengthwise direction are formed in both end parts of the ridge 9 in the resonator lengthwise direction. The central part of the ridge 9 in the resonator lengthwise direction is made a straight region 9b halving a constant width. The width W1 of both ends of the ridge 9 in the resonator lengthwise direction is made at most 3 μm. The width W2 of the central part of the ridge 9 in the resonator lengthwise direction is made at least 4 μm.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a semiconductor laser, and more particularly, to a semiconductor laser using a nitride III-V compound semiconductor.

[0002]

2. Description of the Related Art Nitride III-V represented by GaN
Group compound semiconductor (hereinafter also referred to as "GaN-based semiconductor")
Is promising as a material for a semiconductor laser capable of oscillating in a short wavelength band from blue to ultraviolet region because it can increase the energy band gap as compared with other group III-V compound semiconductors. In particular, a semiconductor laser using this GaN-based semiconductor reads / writes using an existing optical system.
Since an oscillation wavelength of about 400 nm, which is the limit wavelength of an optical disk on which writing is performed, can be obtained, it has attracted much attention as a light source for an optical disk device having a high recording density.

FIGS. 4 and 5 show an example of a conventional GaN-based semiconductor laser realized so far (for example, FIG.
Japanese Journal of Physics Letters vol.36 p.L156
8). Here, FIG. 4 is a perspective view, and FIG. 5 is a plan view. The conventional GaN-based semiconductor laser shown here is of a refractive index guided type.

As shown in FIGS. 4 and 5, in this conventional GaN-based semiconductor laser, an n-type GaN semiconductor laser is placed on a c-plane sapphire (Al ₂ O ₃ ) substrate 101 via an undoped GaN buffer layer 102. Contact layer 10
3, n-type AlGaN cladding layer 104, GaInN active layer 105, p-type AlGaN cap layer 106, p-type Al
A GaN cladding layer 107 and a p-type GaN contact layer 108 are sequentially stacked.

The upper layer of the p-type AlGaN cladding layer 107 and the p-type GaN contact layer 108 have a straight-stripe ridge shape extending in one direction. Reference numeral 109 denotes these p-type AlGaN cladding layers 107.
2 shows a ridge portion formed by an upper layer portion and a p-type GaN contact layer 108. The ridge 109 has a uniform width W in the resonator length direction. The ridge 10
The width W (also referred to as a ridge width) W of 9 indicates the width at the bottom of the ridge portion 109.

An n-type AlGaN cladding layer 104, GaI
The lower layers of the nN active layer 105, the p-type AlGaN cap layer 106, and the p-type AlGaN cladding layer 107 have a predetermined mesa shape extending in one direction. Reference numeral 110 is
The mesa section is shown. In FIG. 5, a portion corresponding to the mesa unit 110 is shown, and a portion adjacent thereto is not shown.

[0007] GaI is formed on both sides of the ridge 109.
A SiO ₂ current confinement layer 111 that does not absorb light from the nN active layer 105 is formed, thereby forming a current confinement structure. The SiO ₂ current confinement layer 111 is also provided on the side surface of the mesa unit 110 in order to prevent a short circuit between the electrodes. In addition, since the SiO ₂ current confinement layers 111 are formed on both sides of the ridge portion 109 in this manner, a portion corresponding to the ridge portion 109 has a high refractive index and portions on both sides thereof have a low refractive index. A refractive index distribution is built in the direction parallel to the junction.

[0008] p-type GaN contact layer 108 and Si
On the O ₂ current confinement layer 111, a p-side electrode 112 such as a Ni / Pt / Au electrode is provided. On the n-type GaN contact layer 103 adjacent to the mesa 110, a Ti / Al
An n-side electrode 113 such as an electrode is provided.

[0009] Both cavity end faces of the conventional GaN-based semiconductor laser are quasi-cleaved surfaces formed by cleaving (pseudo-cleavage) the sapphire substrate 101 together with a GaN-based semiconductor layer forming a laser structure thereon. It consists of. Here, in a GaN-based semiconductor laser using a sapphire substrate, a GaN-based semiconductor layer forming a laser structure is etched by a reactive ion etching (RIE) method, and a cut surface (etched facet) formed by the etching is etched. It is also possible to use a resonator end face. However, in this case, the sapphire substrate is
Since it is difficult to perform etching by the method, a part of the laser light emitted from the end face of the resonator is reflected on the surface of the sapphire substrate, and the far-field pattern (FFP) is disturbed. When such a GaN-based semiconductor laser is used as a light source for an optical disk device, the performance as an optical pickup is reduced. On the other hand, in the conventional GaN-based semiconductor laser in which the cavity facet is formed by the pseudo-cleavage plane, the laser light emitted from the cavity facet is not reflected on the sapphire substrate surface, and the laser light is distant. The shape of the field image is good.

In the conventional GaN-based semiconductor laser configured as described above, the effective refractive index difference Δn between the inside and outside of the ridge, that is, the effective refractive index difference Δn between the portion corresponding to the ridge portion 109 and the portions on both sides thereof, A so-called refractive index guide (actual refractive index guide) in which a light field in a direction (horizontal direction) parallel to the junction is confined in a portion corresponding to the ridge portion 109 is realized. As a result, in the conventional GaN-based semiconductor laser, a low threshold current and relatively stable oscillation in the horizontal and transverse modes are obtained.

[0011]

However, the above-described conventional GaN-based semiconductor laser, that is, a GaN-based semiconductor laser having a straight-stripe ridge structure has the following problems.

That is, the conventional G shown in FIGS.
In the aN-based semiconductor laser, the transverse mode of the laser beam emitted from the cavity facet is strongly affected by the ridge width at the cavity facet. It is desirable that the thickness be about 3 μm or less. However, in the conventional GaN-based semiconductor laser, when the ridge width W is reduced, the contact area between the p-type GaN contact layer 108 and the p-side electrode 112 is reduced, so that the current path is narrowed and the differential resistance is increased. , The driving voltage increases. In this case, GaIn
As the width of the gain region in the N active layer 105 decreases and the waveguide loss increases, the driving current may also increase.

As described above, in the conventional GaN-based semiconductor laser, the ridge width W cannot be made much smaller than 3 μm from the viewpoint of suppressing an increase in driving voltage, and therefore, higher-order horizontal and transverse modes are likely to occur. There was a problem. When a higher-order mode occurs in the horizontal and transverse modes, nonlinearity (kink) appears in the current-light output characteristics, and the emission angle and emission direction of the laser light change, deteriorating the laser characteristics. In particular, when the non-linearity of the current-light output characteristic occurs at a lower level than the used light output, the jitter is extremely deteriorated, so that such a semiconductor laser cannot be used as a light source of an optical disk device.

When a GaN-based semiconductor laser is used as a light source for an optical disk device, a conventional AlGaAs-based semiconductor laser or AlGaInP-based laser can be used as long as the beam spread angle θ // in the horizontal direction of the far-field image is substantially the same. Strict positional accuracy is required at the time of assembling as compared with a semiconductor laser or the like. Therefore, when a GaN-based semiconductor laser is used as a light source for an optical disk device, the beam diameter at the emission end face is reduced, and the beam divergence angle θ // in the horizontal direction of the far-field image is increased to, for example, about 8 ° or more. There is a need. For this reason, the ridge width W of 3 μm is insufficient.

Further, in this conventional GaN-based semiconductor laser, it is desirable that the ridge width W be set further narrower for the following reasons.

That is, the conventional G shown in FIGS.
In the aN-based semiconductor laser, the refractive index of the portion corresponding to the ridge portion 109 decreases due to the plasma effect of the injected carriers during the operation, causing a change in the refractive index distribution inside and outside the ridge. Mode may occur. To prevent this and make the horizontal transverse mode more stable, the effective refractive index difference Δ
n is the amount of decrease in the refractive index due to the plasma effect (2 × 10 ⁻³
Degree).

Here, FIG. 6 shows a G having a straight stripe type ridge structure similar to that shown in FIGS.
The oscillation conditions of the fundamental mode in the aN-based semiconductor laser are shown. In FIG. 6, the horizontal axis represents the effective refractive index difference Δ inside and outside the ridge.
n, and the vertical axis indicates the ridge width W. Curve A is
The cut-off condition of the first-order mode obtained by giving the condition that the refractive index of GaN is n = 2.504 and the wavelength λ = 400 nm, and the broken line B indicates the decrease in the refractive index due to the carrier plasma effect. The lower limit of the effective refractive index difference Δn (Δn
= 2 × 10 ⁻³ ). In order to cause the GaN-based semiconductor laser to oscillate in the fundamental mode, usually, in FIG.
The effective refractive index difference Δn inside and outside the ridge and the ridge width W may be set in the lower region of the curve A, but the oscillation conditions of the fundamental mode when the plasma effect of the carrier is considered include the curve A, the broken line B and the horizontal line. The region is a region surrounded by the axis (the hatched portion in FIG. 6). In this case, the ridge width W needs to be set to 2 μm or less.

In addition, Ga formed on a sapphire substrate
In the case of the N-based semiconductor laser, since the sapphire substrate itself does not have a cleavage property, another type of semiconductor laser manufactured on a substrate that is easily cleaved such as a GaAs substrate, specifically, a G laser
AlGaAs semiconductor laser using AlAs substrate or Al
Unlike a GaInP-based semiconductor laser, it is not easy to form a resonator end face by mechanical processing. Therefore, in the conventional GaN-based semiconductor laser shown in FIGS. 4 and 5, two opposing resonator end faces may not be perpendicular to the extension direction of the ridge portion 109, that is, to the resonator length direction. When the cavity facet is inclined with respect to the cavity length direction in this way, the optical axis of the laser beam emitted from the cavity facet is also inclined. This is clear from the relationship between the horizontal inclination of the cavity end face and the emission direction of the laser light shown in FIG.

The inclination of the cavity facet not only changes the emission direction of the laser beam as described above, but also causes a decrease in the facet reflectivity, an increase or decrease in the slope efficiency, an increase in the threshold current, and the like. Have a serious impact. Therefore,
The inventor of the present invention has found that, in a GaN-based semiconductor laser having a straight-stripe ridge structure similar to that shown in FIGS. 4 and 5, when the cavity facet is inclined in the horizontal direction, how much the facet reflectivity and the threshold current change I checked what to do.
8 and 9 show the results. FIG. 8 shows the relationship between the horizontal inclination of the end face of the resonator and the end face reflectivity, and FIG.
6 shows the relationship between the horizontal inclination of the resonator end face and the increase in threshold current. 8 and 9, a curve A shows the results when the ridge width W is 4 μm, a curve B shows the results when the ridge width W is 3 μm, and a curve C shows the results when the ridge width W is 2 μm. From FIGS. 8 and 9, it can be seen that as the inclination of the cavity facet increases, the facet reflectivity decreases and the threshold current increases.

Since such phenomena are different between chips formed in mutually adjacent regions on the wafer, variations in the characteristics of the semiconductor laser in the same lot become large,
This is a factor that lowers the production yield.

FIGS. 8 and 9 show that as the ridge width W gradually decreases from 4 μm → 3 μm → 2 μm, the degree of decrease in the end face reflectivity and the increase in the threshold current due to the inclination of the cavity end face are reduced. It is understood that it is done. Therefore, in a conventional GaN-based semiconductor laser having a ridge structure, as the ridge width W is reduced, the laser characteristics are not deteriorated due to the variation in the shape (mainly the inclination) of the cavity end face, and the manufacturing yield is improved.

In a conventional GaN-based semiconductor laser,
The larger the ridge width W at the resonator end face, the more easily the ridge width W is affected by the disturbance due to the return light. Therefore, it is preferable to reduce the ridge width W from the viewpoint of improving noise characteristics.

However, as described above, in the conventional GaN-based semiconductor laser, the lower limit of the ridge width W is limited to about 3 μm from the viewpoint of suppressing an increase in driving voltage. Therefore, in a conventional GaN-based semiconductor laser,
It has been extremely difficult to reduce the adverse effect on the laser characteristics due to the quality of the cavity facets without increasing the driving voltage, and to improve the noise characteristics.

Accordingly, it is an object of the present invention to reduce the driving voltage, stabilize the transverse mode, increase the beam divergence angle in the horizontal direction of the far-field image, prevent the laser characteristics from deteriorating due to variations in the shape of the cavity end face, and reduce noise. It is an object of the present invention to provide a semiconductor laser using a nitride-based III-V compound semiconductor that can easily improve characteristics.

[0025]

To achieve the above object, the present invention provides a first cladding layer of a first conductivity type, an active layer on the first cladding layer, and a second cladding layer on the active layer. A current confinement layer having a conductive type second cladding layer, and a current constriction layer made of a material that does not absorb light from the active layer is provided on both sides of a ridge portion provided on the second cladding layer; In a semiconductor laser using a nitride-based III-V compound semiconductor having a structure, a ridge portion is formed at both ends in the resonator length direction from a central portion in the resonator length direction to both ends in the resonator length direction. It has a tapered region in which the width is reduced.

In the present invention, the nitride-based III-V compound semiconductor comprises at least one group III element selected from the group consisting of Ga, Al, In, B and Tl;
It is composed of a group V element containing at least N and possibly further containing As or P.

In the present invention, as a material of the current confinement layer, for example, a dielectric such as silicon oxide (SiO ₂ ) or silicon nitride (SiN), AlGaN, GaInN,
Nitride-based III-V compound semiconductors such as GaN, Zn
II-VI compound semiconductors such as S are used.

In the present invention, in order to suppress the rise of the driving voltage and to stably maintain the transverse mode, the width of the ridge at the center in the resonator length direction is preferably 4 μm.
m and the width of the ridge portion at both end faces in the resonator length direction is selected to be 3 μm or less. In particular, since the transverse mode of the emitted laser light is strongly affected by the width of the ridge portion at both ends in the resonator length direction (width at the resonator end face), the transverse mode at the both end faces of the ridge portion in the resonator length direction is obtained. The width is more preferably 2 μm or more and 3 μm or less, and still more preferably 2 μm or less.

According to the present invention configured as described above, the width of the ridge portion is reduced at both ends in the resonator length direction from the center in the resonator length direction to the both ends in the resonator length direction. By having the tapered region, the width of the ridge at the center in the resonator length direction is wider than the width of the ridge at both end surfaces in the resonator length direction. Therefore, even when the width of the ridge portion at both end faces in the resonator length direction is set to be narrow in order to stably maintain the transverse mode, independently of the width at the center portion of the ridge portion in the resonator length direction. The width can be set wider. As a result, the contact area with the electrode can be increased and the resistance component at the ridge can be reduced, so that the drive voltage of the semiconductor laser can be reduced. In particular, in the present invention, when the width of the ridge at the center in the resonator length direction is set to 4 μm or more, and the width of the ridge at both end faces in the resonator length direction is set to 3 μm or less, , The lateral mode can be stabilized. Regarding stabilization of the transverse mode, when the width of the ridge portion at both end faces in the resonator length direction is set to 2 μm or less, the occurrence of higher-order horizontal transverse mode can be suppressed, which is more effective.

According to the present invention, the beam divergence angle in the horizontal direction of the far-field image can be increased by the wavefront shaping effect in the tapered regions at both ends of the ridge portion in the resonator length direction. By reducing the width of the ridge portion at both end faces in the resonator length direction, the beam divergence angle of the far-field image in the horizontal direction can be further increased. Therefore, when this semiconductor laser is used as a light source of an optical disc device,
Strict positional accuracy required during assembly can be reduced. At this time, the width of the ridge at the center in the resonator length direction is set to be wide independently of the width of the ridge at both end faces in the resonator length direction, so that the electrode contact area is reduced without reducing the electrode contact area. Since the beam divergence angle in the horizontal direction of the field image can be increased, the far-field image can be shaped with high reliability.

According to the present invention, when the width of the ridge portion at both end faces in the resonator length direction is reduced, the end face reflectivity decreases, the threshold current increases, and the slope efficiency changes due to the end face shape of the resonator. Can be suppressed. As a result, it is possible to prevent the laser characteristics from deteriorating due to variations in the shape of the cavity end face, so that a semiconductor laser having good characteristics can be obtained with a high production yield. Further, when the width of the ridge portion at both end surfaces in the resonator length direction is reduced, the degree of disturbance of the semiconductor laser by the return light is suppressed, so that noise induced by the return light can be reduced. In this case, according to the present invention, the width of the ridge portion at the central portion in the resonator length direction can be set to be large independently of the width of the ridge portion at both end surfaces in the resonator length direction. The advantage obtained by reducing the width at both end surfaces in the long direction can be obtained without increasing the driving voltage.

[0032]

Embodiments of the present invention will be described below with reference to the drawings. In all the drawings of the embodiments, the same or corresponding portions are denoted by the same reference numerals.

First, a first embodiment of the present invention will be described. 1 and 2 show a GaN-based semiconductor laser according to a first embodiment of the present invention. Here, FIG. 1 is a perspective view, and FIG. 2 is a plan view. This GaN semiconductor laser is of a refractive index guided type.

As shown in FIGS. 1 and 2, in the GaN-based semiconductor laser according to the first embodiment, for example, an n-type GaN semiconductor layer is formed on a c-plane sapphire substrate 1 via an undoped GaN buffer layer 2. Contact layer 3, n-type AlGaN cladding layer 4, GaInN active layer 5, p-type A
An lGaN cap layer 6, a p-type AlGaN cladding layer 7, and a p-type GaN contact layer 8 are sequentially stacked.
The Al composition of the n-type AlGaN cladding layer 4 and the p-type AlGaN cladding layer 7 is, for example, about 6 to 8%.
The In composition of the InN active layer 5 is, for example, about 15%.
The emission wavelength of this GaN-based semiconductor laser is about 400 nm. The Al composition of the p-type AlGaN cap layer 6 is about 20%.

The upper layer portion of the p-type AlGaN cladding layer 7 and the p-type GaN contact layer 8 have a tapered stripe ridge shape extending in one direction. Reference numeral 9 denotes an upper layer portion of the p-type AlGaN cladding layer 7 and a ridge portion formed by the p-type GaN contact layer 8. The configuration of the ridge portion 9 will be described later in detail.

N-type AlGaN cladding layer 4, GaInN
Active layer 5, p-type AlGaN cap layer 6, and p-type Al
The lower part of the GaN cladding layer 7 has a predetermined mesa shape extending in one direction. Reference numeral 10 indicates the mesa portion. In FIG. 2, a portion corresponding to the mesa unit 10 is shown, and a portion adjacent thereto is not shown.

The portions on both sides of the ridge portion 9 are, for example, G
An SiO ₂ current confinement layer 11 that does not absorb the light from the aInN active layer 5 is formed, thereby forming a current confinement structure. The SiO ₂ current confinement layer 11 is also provided on the side surface of the mesa unit 10 to prevent a short circuit between the electrodes. Further, SiO ₂ thus on both sides of the ridge portion 9
By forming the current confinement layer 11, the ridge portion 9 is formed.
Is formed in a direction parallel to the junction, in which the refractive index of the portion corresponding to is high and the refractive index of the portions on both sides thereof is low. The effective refractive index difference Δn between the inside and outside of the ridge is preferably, for example, 2 × 10 ⁻³ or more in consideration of the fact that the refractive index of the portion corresponding to the ridge portion 9 is reduced by the plasma effect of carriers. To be elected. In the case of this example, the effective refractive index difference Δn inside and outside the ridge is, for example, 2 × 1
It is set to 0 ^-3.

P-type GaN contact layer 8 and SiO ₂
A p-side electrode 12 such as a Ni / Pt / Au electrode is provided on the current constriction layer 11, and a Ti / Al
An n-side electrode 13 such as an electrode is provided.

Further, both cavity end faces of the GaN-based semiconductor laser are composed of a pseudo-cleavage plane formed by cleaving (pseudo-cleavage) the sapphire substrate 1 together with a GaN-based semiconductor layer forming a laser structure thereon. . In this case, the laser light emitted from the cavity end face is reflected on the sapphire substrate 1.
Therefore, the shape of the far-field image of the laser light is good.

In the GaN-based semiconductor laser according to the first embodiment configured as described above, the effective refractive index difference Δn between the inside and outside of the ridge, that is, the effective refraction between the portion corresponding to the ridge portion 9 and the portions on both sides thereof. Due to the rate difference Δn, the horizontal light field is confined in a portion corresponding to the ridge portion 9.
So-called refractive index guiding (real refractive index guiding) is realized. Thereby, in the GaN-based semiconductor laser, a low threshold current and relatively stable oscillation in the horizontal and transverse modes are obtained. Further, in this GaN-based semiconductor laser, the width of the ridge portion 9 at both end faces in the resonator length direction is preferably set to 3 μm or less, more preferably 2 μm or less, to further stabilize the transverse mode. It is possible to achieve.

Hereinafter, the GaN according to the first embodiment will be described.
The configuration of the ridge 9 in the system semiconductor laser will be described in detail.

That is, as shown in FIGS. 1 and 2,
The width of the ridge portion 9 in this GaN-based semiconductor laser is continuously reduced in the respective regions at both ends in the cavity length direction from the central portion in the cavity length direction toward both ends in the cavity length direction. And has a tapered region 9a which is tapered. The ridge portion 9 has a straight region 9b having a uniform width in the central region in the resonator length direction.

[0043] In this ridge 9, two tapered regions 9a provided at both ends of the resonator length direction has a length substantially equal to L ₁ to each other. These tapered regions 9a
Total length 2L ₁ of, as well wavefront shaping effect is obtained, for example, the resonator length _{L (L = 2L 1 + L} 2, L 2
Is 1/10 or more of the length of the straight region 9b), that is, 2L ₁ ≧ L / 10.

In FIG. 2, W ₁ indicates the width of the ridge 9 at both end faces in the resonator length direction, and W ₂ indicates the width of the ridge 9 at the center in the resonator length direction. Here, the width W ₁ refers to the width at the bottom of the ridge 9 at both end faces in the resonator length direction, and the width W ₂ refers to the width at the bottom of the ridge 9 at the center in the resonator length direction. . The width W _{1 of} these ridges 9 at both end faces in the resonator length direction and the width W ₂ of the ridge 9 at the center in the resonator length direction are:
The relationship W ₁ <W ₂ is satisfied. Furthermore, the width W _{1 of} these ridges 9 at both end faces in the resonator length direction and the width W ₂ of the ridge 9 at the center in the resonator length direction are:
In order to stably maintain the transverse mode while suppressing the rise of the driving voltage, it is preferably selected so that W ₁ ≦ 3 μm and W ₂ ≧ 4 μm, and more preferably 2 μm ≦ W ₁ ≦ 3 μm.
m and W ₂ ≧ 4 μm, and more preferably, W ₁ ≦ 2 μm and W ₂ ≧ 4 μm.

Here, the GaN according to the first embodiment
As an example of the dimensions of each part of the system semiconductor laser, the cavity length L = 500 μm, the length L ₁ of the tapered region 9a of the ridge portion 9 = 100 μm, and the length L ₂ of the straight region 9b = ₂
The width W _{1 is} 2 μm at both end faces of the ridge 9 in the resonator length direction, and the width W ₂ is 4 μm at the center of the ridge 9 in the resonator length direction.

According to the GaN-based semiconductor laser according to the first embodiment of the present invention configured as described above, the ridges 9 are respectively provided at the respective regions at both ends in the resonator length direction at the center in the resonator length direction. By having the tapered region 9a whose width decreases in the direction from the portion to the both ends in the resonator length direction, the following various advantages can be obtained.

That is, the Ga according to the first embodiment is
In N-based semiconductor laser, by the ridge portion 9 has a tapered region 9a on both ends of the resonator length direction, than the width W ₁ at the end faces of the resonator length direction of the ridge portion 9, the resonance of the ridge portion 9 Width W _{2 at} the center in the container length direction
Is wider. Therefore, in order to stably maintain the transverse mode, even when the width W ₁ of the ridge portion 9 at both end surfaces in the resonator length direction is set to 3 μm or less, specifically, 2 μm as illustrated, independently, the width W ₂ 4 [mu] m or more at the center of the resonator length direction of the ridge portion 9, and specifically can be set wide and 4 [mu] m as illustrated. Thereby, the contact area between the p-type GaN contact layer 8 and the p-side electrode 11 is increased, and the ridge 9
Can reduce the resistance component of the GaN
It is possible to reduce the drive voltage of the system semiconductor laser.

As described above, according to the first embodiment, it is possible to stably maintain the transverse mode without increasing the driving voltage. In particular, the resonator length L = 500
μm, the length L ₁ of the tapered region 9a = 100 μm, the length L ₂ of the straight region 9b = 300 μm, the width W _{1 at} both end surfaces in the resonator length direction of the ridge portion 9 = 2 μm, and the resonator length direction of the ridge portion 9 In the case of the GaN-based semiconductor laser according to the first embodiment in which the width W ₂ is set to 4 μm at the center of the GaN-based semiconductor laser shown in FIGS. 4 and 5, the resonator length L = 500 μm and the ridge Since the electrode contact area can be made larger than when the width W of the portion 109 is set to 3 μm, the driving voltage can be reduced while stabilizing the transverse mode. In the first embodiment, since the width W ₁ of the ridge portion 9 at both end faces in the resonator length direction is set to 2 μm, the oscillation condition of the fundamental mode taking the plasma effect of the carrier into account is considered. Is satisfied (see FIG. 6), and therefore, the occurrence of higher-order horizontal and transverse modes can be suppressed, so that the transverse modes can be more stably maintained.

According to the first embodiment, the beam divergence angle θ // in the horizontal direction of the far-field pattern is obtained by the wavefront shaping effect in the tapered regions 9a at both ends of the ridge portion 9 in the resonator length direction. Can be widened. In addition to this, in the first embodiment, the width W ₁ of the ridge portion 9 at both end faces in the resonator length direction is set as small as 2 μm, so that the beam divergence angle θ in the horizontal direction of the far-field image is obtained. // has been further expanded. Specifically, in the conventional GaN-based semiconductor laser in which the width W of the ridge portion 109 is 3 μm, the beam divergence angle θ // in the horizontal direction of the far-field image is 6 °, while the resonance of the ridge portion 9 Width W at both end faces in container length direction
G according to the first embodiment in which ₁ is narrowed to 2 μm.
In the aN-based semiconductor laser, the beam divergence angle θ // in the horizontal direction of the far-field image can be increased to about 8 °. Accordingly, when this GaN-based semiconductor laser is used as a light source of an optical disk device, strict positional accuracy required during assembly can be reduced. At this time, the width W ₂ of the ridge portion 9 at the center in the resonator length direction is set to be wide independently of the width W _{1 at} both end surfaces of the ridge portion 9 in the resonator length direction. Since the beam divergence angle θ // in the horizontal direction can be increased without reducing the distance, it is possible to reliably shape the far-field image.

Further, according to the first embodiment, the width W _{1 of} the ridge portion 9 at both end faces in the resonator length direction is 2 μm.
With such a narrow setting, it is possible to suppress a decrease in end face reflectivity, an increase in threshold current, and a change in slope efficiency due to the shape (mainly the inclination) of the end face of the resonator. As a result, it is possible to prevent the laser characteristics from deteriorating due to variations in the shape of the cavity end face, so that a semiconductor laser having good characteristics can be obtained with a high production yield. Further, the width W _{1 of} the ridge portion 9 at both end faces in the resonator length direction is set.
Is set as narrow as 2 μm, this GaN
Since the degree to which the system semiconductor laser is disturbed by the return light is suppressed, noise induced by the return light can also be reduced. At this time, in the first embodiment, the width W at the center of the ridge portion 9 in the resonator length direction is set.
₂ is the width W at both end faces of the ridge portion 9 in the resonator length direction.
Since the width can be set to be wide independently of _1, it is possible to obtain these advantages obtained by reducing the width W ₁ at both end surfaces of the ridge portion 9 in the resonator length direction without increasing the drive voltage. it can.

As described above, according to the first embodiment, the ridges 9 are provided in the respective regions at both ends in the resonator length direction from the center in the resonator length direction to both ends in the resonator length direction. The width W _{1 at} both end surfaces of the ridge portion 9 in the resonator length direction and the width W ₂ at the center portion of the ridge portion in the resonator length direction are optimized by having the tapered region 9a whose width decreases toward the portion. Drive voltage reduction, transverse mode stabilization, far-field image horizontal beam divergence angle θ //, laser characteristic deterioration prevention due to variations in cavity end face shape, and noise characteristics Improvement can be easily realized. Therefore, according to the first embodiment, it is possible to obtain a GaN-based semiconductor laser having good characteristics and suitable for a light source of an optical disk device.

Next, a second embodiment of the present invention will be described. FIG. 3 shows a G according to a second embodiment of the present invention.
It is a top view of an aN type semiconductor laser. In the GaN-based semiconductor laser according to the second embodiment, the width of the ridge portion 9 is made constant in a predetermined region near both end faces in the resonator length direction in consideration of the tolerance in the process. The structure of the GaN-based semiconductor laser according to the second embodiment in a direction perpendicular to the junction is the same as that of the GaN-based semiconductor laser according to the first embodiment.

As shown in FIG. 3, the ridge portion 9 in the GaN-based semiconductor laser according to the second embodiment has respective regions between the tapered regions 9a at both ends in the resonator length direction and both resonator end faces. to further have a uniform width W ₁ of the straight region 9c. In FIG. 3, L ₃ represents the length of the straight region 9c. Here, these straight regions 9c is provided in order to reliably W ₁ the width of both end faces of the resonator length direction of the ridge portion 9, the length L ₃ of these straight regions 9c as much as possible It is desirable to shorten it. In this case, the upper limit of the length L ₃ of these straight regions 9c, for example 20~25μm
Chosen by degree.

Here, the GaN according to the second embodiment
As an example of the dimensions of each part of the system semiconductor laser, the cavity length L = 500 μm, the length L ₁ of the tapered region 9a of the ridge portion 9 = 100 μm, and the length L of the central straight region 9b in the cavity length direction. ₂ = 250 μm, length L ₃ of straight region 9c at both ends in the resonator length direction = 25 μm, width W _{1 of} ridge portion 9 at both ends in the resonator length direction = 2 μm
m, the width W _{2 at} the center of the ridge portion 9 in the resonator length direction.
= 4 μm.

The other structure of the GaN-based semiconductor laser according to the second embodiment is the same as that of the Ga-based semiconductor laser according to the first embodiment.
The description is omitted because it is the same as that of the N-based semiconductor laser.

According to the second embodiment, the same advantages as in the first embodiment can be obtained, and
The following advantages can be obtained together. That, in the second embodiment, by straight region 9c of the resonator length direction of the end regions to a uniform width W ₁ of the ridge portion 9 is provided, in processing the resonator, the width of both end faces of the resonator length direction of the ridge portion 9 can be reliably and W _1. Thus, a width of W ₁ of the ridge portion 9 in the both end faces of the resonator length direction,
It is possible to obtain a GaN-based semiconductor laser having a ridge structure of a tapered stripe type as the width of the ridge portion 9 is W ₂ at the center of the resonator length direction with a high production yield.

Although the embodiments of the present invention have been specifically described above, the present invention is not limited to the above embodiments, and various modifications based on the technical concept of the present invention are possible.

For example, the numerical values, structures, materials, and the like described in the first and second embodiments are merely examples, and different numerical values, structures, materials, and the like may be used as necessary.

Specifically, the resonator length L, the length L ₁ of the tapered region 9a at both ends of the ridge portion 9 in the resonator length direction, and the resonance of the ridge portion 9 in the first and second embodiments described above. The length L ₂ of the straight region 9b at the center in the container length direction,
Straight regions 9 at both ends of the ridge portion 9 in the resonator length direction
The values of the length L _{3 of} c, the width W _{1 of} the ridge portion 9 at both end faces in the resonator length direction, and the width W ₂ of the ridge portion 9 at the center portion in the resonator length direction are given in the first and second embodiments. Can be set arbitrarily as long as the conditions described in are satisfied.

In the first and second embodiments described above, two tapered regions 9a provided in the respective regions of the ridge portion 9 at both ends in the resonator length direction are provided on the front side and the rear side. It is not necessary to be symmetrical, and furthermore, both side surfaces of the ridge portion 9 may be asymmetrical. If the width of the tapered region 9a of the ridge portion 9 monotonically decreases in the direction from the central portion in the resonator length direction to both end portions in the resonator length direction, its side surface needs to be formed as a flat surface. However, it may be constituted by a curved surface curved inward or outward, for example. Furthermore, 0 the length L ₂ of the straight region 9b of the central portion of the resonator length direction of the ridge portion 9, a ridge portion 9 only tapered region 9a at both ends of the resonator length direction, or the tapered region 9a and a straight Area 9
Only c may be used.

In the first and second embodiments, SiO ₂ is used as the material of the current confinement layer embedded on both sides of the ridge portion 9. Other than this, AlGaN, GaI
A nitride III-V compound semiconductor such as nN or GaN, a dielectric such as SiN, or a II-VI compound semiconductor such as ZnS may be used.

In the first and second embodiments, the conductivity type of each semiconductor layer forming the laser structure may be reversed.

In the first and second embodiments described above, the sapphire substrate is used as the substrate.
This is because a sapphire substrate is replaced by a spinel substrate, SiC
A substrate, a ZnO substrate, a GaP substrate, or the like may be used,
Alternatively, a substrate on which a nitride III-V compound semiconductor layer is grown on these substrates, and after growing a nitride III-V compound semiconductor layer on these substrates, the substrate is removed by polishing or the like. A substrate having only a nitride III-V compound semiconductor layer, a nitride III- such as a GaN substrate
A substrate made of a V-group compound semiconductor itself may be used.

In the first and second embodiments, the present invention is applied to a DH structure (Double Heterostructu).
re) was applied to a GaN-based semiconductor laser, but the present invention relates to an SCH structure (Separate Confineme).
It is also possible to apply the present invention to a GaN-based semiconductor laser having a nt heterostructure.

[0065]

According to the present invention constructed as described above, the ridge portions are formed at both ends in the resonator length direction in the direction from the central portion in the resonator length direction to both end portions in the resonator length direction. Since the width of the ridge portion at the central portion in the resonator length direction and the width of the ridge portion at both end surfaces in the resonator length direction can be optimized, the drive voltage can be reduced, Stabilization of the transverse mode, enlargement of the beam divergence angle in the horizontal direction of the far-field image, prevention of deterioration of laser characteristics due to variations in the shape of the cavity end face, and improvement of noise characteristics can be easily realized. Thus, a semiconductor laser using a nitride III-V compound semiconductor having good characteristics and suitable for a light source of an optical disk device can be obtained.

[Brief description of the drawings]

FIG. 1 is a perspective view of a GaN-based semiconductor laser according to a first embodiment of the present invention.

FIG. 2 is a plan view of the GaN-based semiconductor laser according to the first embodiment of the present invention.

FIG. 3 is a plan view of a GaN-based semiconductor laser according to a second embodiment of the present invention.

FIG. 4 is a perspective view of a conventional GaN-based semiconductor laser.

FIG. 5 is a plan view of a conventional GaN-based semiconductor laser.

FIG. 6 is a graph showing oscillation conditions of a fundamental mode in a GaN-based semiconductor laser.

FIG. 7 is a graph showing the relationship between the inclination of a cavity facet and the emission direction of laser light in a GaN-based semiconductor laser.

FIG. 8 is a graph showing the relationship between the inclination of the cavity facet and the facet reflectivity in a GaN-based semiconductor laser.

FIG. 9 is a graph showing the relationship between the inclination of the cavity facet and the increase in threshold current in a GaN-based semiconductor laser.

[Explanation of symbols]

1 ... sapphire substrate, 2 ... GaN buffer layer,
3 ... n-type GaN contact layer, 4 ... n-type AlG
aN cladding layer, 5 ... GaInN active layer, 6 ...
p-type AlGaN cap layer, 7 ... p-type AlGaN cladding layer, 8 ... p-type GaN contact layer, 9 ...
Ridge part, 9a ... taper area, 9b, 9c ...
Straight region, 10 ... SiO ₂ current confinement layer, 11
... p-side electrode, 12 ... n-side electrode

 ──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Shiro Uchida 6-7-35 Kita-Shinagawa, Shinagawa-ku, Tokyo Inside Sony Corporation (72) Inventor Teruji Hirata 6-35, Kita-Shinagawa, Shinagawa-ku, Tokyo No. Sony Corporation F term (reference) 5F041 AA06 CA04 CA34 CA40 CA46 5F073 AA13 AA35 BA06 CA07 CB05 EA19 EA27

Claims (4)

[Claims] 1. A first cladding layer of a first conductivity type, an active layer on the first cladding layer, and a second cladding layer of a second conductivity type on the active layer, A nitride-based I having a current confinement structure in which a current confinement layer made of a material that does not absorb light from the active layer is provided on both sides of the ridge provided in the second cladding layer.
In a semiconductor laser using a II-V compound semiconductor, the ridge portion has a width decreasing at both ends in a cavity length direction in a direction from a center portion in the cavity length direction to both ends in the cavity length direction. 1. A semiconductor laser having a tapered region. 2. The method according to claim 1, wherein the width of the ridge at the central portion in the resonator length direction is 4 μm or more, and the width of the ridge at both end surfaces in the resonator length direction is 3 μm or less. Item 2. The semiconductor laser according to item 1. 3. The width of the ridge portion at the central portion in the resonator length direction is 4 μm or more, and the width of the ridge portion at both end surfaces in the resonator length direction is 2 μm or more and 3 μm or less. The semiconductor laser according to claim 1, wherein 4. The width of the ridge portion at the central portion in the resonator length direction is 4 μm or more, and the width of the ridge portion at both end surfaces in the resonator length direction is 2 μm or less. Item 2. The semiconductor laser according to item 1.