KR20010007396A - Semiconductor laser - Google Patents

Abstract

PURPOSE: 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. CONSTITUTION: 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

Semiconductor Laser {SEMICONDUCTOR LASER}

TECHNICAL FIELD This invention relates to a semiconductor laser. Specifically, It is related with the semiconductor laser using the nitride system group III-V compound semiconductor.

Nitride III-V compound semiconductors (hereinafter also referred to as "GaN-based semiconductors") represented by GaN can increase the energy band gap as compared with other III-V compound semiconductors. It is promising as a material of the semiconductor laser which can oscillate in the short wavelength band of the ultraviolet region. In particular, a semiconductor laser using this GaN-based semiconductor has a large attention as a light source of an optical disk device having a high recording density since a wavelength of about 40 nm, which is the limit wavelength of an optical disk on which reading and writing is performed using an existing optical system, is obtained. It is becoming.

1 and 2 show an example of a conventional GaN semiconductor laser that has been realized so far (for example, Japanese Jounal of Physics Letters vol. 36 p.L1568). 1 is a perspective view and FIG. 2 is a top view. The conventional GaN-based semiconductor laser shown here is of an index-guided type.

As shown in Figs. 1 and 2, in this conventional GaN semiconductor laser, an undoped GaN buffer layer 102 is formed on a c-sapphire (Al ₂ O ₃ ) substrate 101. N-type GaN contact layer 103, n-type AlGaN cladding layer 104, GaInN active layer 105, p-type AlGaN cap layer 106, p-type AlGaN cladding layer 107 And the p-type GaN contact layer 108 are sequentially stacked.

The upper portion 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 an upper portion of the p-type AlGaN cladding layer 107 and a ridge portion constituted by the p-type GaN contact layer 108. The ridge portion 109 has a uniform width W in the resonator length direction. The width W (also referred to as ridge width) W of the ridge portion 109 indicates the width at the bottom of the ridge portion 109.

The lower layers of the n-type AlGaN cladding layer 104, the GaInN active layer 105, the p-type AlGaN cap layer 106, and the p-type AlGaN cladding 107 have a predetermined mesa shape extending in one direction. Reference numeral 110 denotes the mesa portion. 2, the part corresponding to this mesa part 110 appears, and the part adjacent to this mesa part is abbreviate | omitted.

On both sides of the ridge portion 109, a SiO ₂ current confinement layer 111 which does not absorb light from the GaInN active layer 105 is formed, thereby forming a current confinement structure. The SiO ₂ current confinement layer 111 is also formed on the side surface of the mesa portion 110 to prevent short circuit between the electrodes. In addition, since SiO ₂ current confinement layers 111 are formed on both sides of the ridge portion 109 in this manner, a stepped refractive index distribution having a high refractive index of a portion corresponding to the ridge portion 109 and a low refractive index of both portions thereof is formed. Is attached in the direction parallel to the joint.

On the p-type GaN contact layer 108 and the SiO ₂ current confinement layer 111, a p-side electrode 112 such as a Ni / Pt / Au electrode is formed. On the n-type GaN contact layer 103 adjacent to the mesa portion 110, an n-side electrode 113 such as a Ti / Al electrode is formed.

The cross section of both resonators of the conventional GaN semiconductor laser is a pseudo cleaved surface formed by cleaving the sapphire substrate 101 together with the GaN semiconductor layer forming the laser structure thereon. It consists of. Here, in a GaN semiconductor laser using a sapphire substrate, the GaN semiconductor layer forming the laser structure is etched by the reactive ion etching (RIE) method, and the etched facets formed by the etching are the resonator end faces. It is also possible. However, in this case, since it is difficult to etch the sapphire substrate by the RIE 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 thus a far field (FFP; far-field) There is confusion in pattern. When such a GaN semiconductor laser is used as a light source of the optical disk device, the performance as an optical pickup is degraded. In contrast, in this conventional GaN-based semiconductor laser having a resonator cross section formed by a pseudo cleaved surface, laser light emitted from the resonator cross section is not reflected on the sapphire substrate surface. The far field image shape of the laser beam is good.

In the conventional GaN-based semiconductor laser constructed as described above, the effective refractive index difference Δn inside and outside the ridge, that is, the effective refractive index difference Δn between the portion corresponding to the ridge portion 109 and the both sides thereof. A so-called refractive index waveguide (real refractive index waveguide) in which an optical field in the junction and parallel direction (horizontal direction) is confined to a portion corresponding to the ridge portion 109 is realized. Accordingly, in this conventional GaN-based semiconductor laser, oscillation in the horizontal transverse mode where the low threshold current is relatively stable is obtained.

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

That is, in the conventional GaN semiconductor laser shown in Figs. 1 and 2, since the lateral mode of the laser light emitted from the end face of the resonator is strongly influenced by the ridge width at the end face of the resonator, in order to maintain the lateral mode stably, It is preferable to make the ridge width W about 3 micrometers or less. However, in this conventional GaN-based semiconductor laser, when the ridge width W is narrowed, the contact area between the p-type GaN contact layer 108 and the p-side electrode 112 is reduced, whereby the current path is narrowed and differentiated. The driving voltage increases because the resistance is high. In this case, the width of the gain region in the GaInN active layer 105 is reduced, and the waveguide increases, which may cause an increase in the drive current.

As described above, in the conventional GaN-based semiconductor laser, the ridge width W cannot be made narrower than 3 µm from the viewpoint of suppressing the increase in the driving voltage, so that a high-order horizontal transverse mode is likely to occur. There was a problem. When the higher-order mode occurs in the horizontal transverse mode, non-linearity in the current-light output characteristics is exhibited, and the emission angle and the emission direction of the laser light are changed, and the laser characteristics are deteriorated. In particular, when the non-linearity of the current-light output characteristic occurs at a lower position than the use light output, the jitter is extremely deteriorated, so that such semiconductor laser light cannot be used as a light source of the optical disk device.

In the case of using a GaN semiconductor laser as a light source of an optical disk device, when the beam diffusion angle (θ //) in the horizontal direction of the far field image is about the same, it is compared with an AlGaAs semiconductor laser, an AlGaInP semiconductor laser, or the like which is conventionally used. In assembly, strict positioning accuracy is required. Therefore, when the GaN semiconductor laser is used as a light source of the optical disk device, the beam diameter at the emission cross section is reduced, and the beam diffusion angle θ // in the horizontal direction of the far field is, for example, It is necessary to enlarge it by more than 8 degrees. Also from this reason, the ridge width W is insufficient as 3 µm.

In this conventional GaN semiconductor laser, the ridge width W is preferably set narrower for the following reason.

That is, in the conventional GaN-based semiconductor laser shown in Figs. 1 and 2, the refractive index of the portion corresponding to the ridge portion 109 is lowered due to the plasma effect of the injection carrier during the operation, and the refractive index distribution in and out of the ridge is reduced. A change occurs, and in extreme cases, a higher order mode may occur in the horizontal transverse mode. In order to prevent this and to make the horizontal transverse mode more stable, it is necessary to make the effective refractive index difference Δn inside and outside the ridge larger than the decrease of the refractive index (about 2x10 ^-3 ) by the plasma effect.

Here, FIG. 3 shows the oscillation conditions of the conventional mode in the GaN semiconductor laser having the same straight stripe ridge structure as shown in FIGS. 1 and 2. In FIG. 3, the horizontal axis represents the effective refractive index difference Δn in and out of the ridge, and the vertical axis represents the ridge width W. In FIG. Further, curve A is a cutoff condition of the first mode obtained by giving GaN refractive index (N) of 2.504 and wavelength (λ) of 400 nm, and broken line B shows a decrease in refractive index due to the plasma effect of the carrier. The lower limit (Δn = 2 × 10 ⁻³ ) of the effective refractive index difference Δn when minutes are taken into account is shown. In order to oscillate the GaN semiconductor laser in the basic mode, the effective refractive index difference Δn and the ridge width W within and outside of the ridge may be generally set in the lower region of the curve A in FIG. 3. When the plasma effect is taken into consideration, the oscillation condition of the basic mode is a region surrounded by the curve (A), the broken line (B), and the abscissa (the diagonal line in Fig. 3), in which case, the ridge width It is necessary to set (W) to 2 micrometers or less.

In the GaN semiconductor laser fabricated on a sapphire substrate, since the sapphire substrate itself has no cleavage, another type of semiconductor laser fabricated on a cleavable substrate such as a GaAs substrate, specifically, an AlGaAs substrate using a GaAs substrate. Like the semiconductor laser and the AlGaInP semiconductor laser, it is not easy to form the end face of the resonator by mechanical processing. Therefore, in the conventional GaN semiconductor laser shown in Figs. 1 and 2, two resonator cross sections facing each other may not be perpendicular to the extending direction of the ridge portion 109, that is, the resonator length direction. Thus, when the resonator cross section is inclined with respect to the resonator longitudinal direction, the optical axis of the laser light emitted from the resonator cross section is also inclined. This is evident in the relationship between the horizontal inclination of the cross section of the resonator shown in Fig. 4 and the emission direction of the laser light.

As described above, the inclination of the cross section of the resonator not only changes the emission direction of the laser light, but also decreases the cross-sectional reflectance, increases or decreases the slope efficiency, and increases the threshold current, thereby seriously affecting the laser characteristics. give. Thus, the inventors of the present invention have shown that the GaN-based semiconductor laser having the same straight stripe ridge structure as shown in Figs. 1 and 2 changes the cross-sectional reflectance and the threshold current when the cross section of the resonator is inclined in the horizontal direction. Investigated. 5 and 6 show the results. FIG. 5 shows the relationship between the horizontal slope of the resonator cross section and the cross-sectional reflectance, and FIG. 6 illustrates the relationship between the horizontal slope of the resonator cross section and the rise of the threshold current. 5 and 6, curve A shows a ridge width W of 4 占 퐉, curve B shows a ridge width W of 3 占 퐉, and curve C shows a ridge width W of 2 占 퐉. The result of the case was shown. 5 and 6 show that as the slope of the cross section of the resonator increases, the cross-sectional reflectance decreases and the threshold current rises.

Since these phenomena differ between chips formed in adjacent regions on the wafer, the nonuniformity of semiconductor laser characteristics in the same lot becomes large, which causes a factor of lowering the manufacturing yield.

5 and 6, as the ridge width W gradually decreases from 4 μm to 3 μm → 2 μm, the decrease in the cross-section reflectivity and the increase in the threshold current due to the inclination of the cross section of the resonator are reduced. It can be seen that. Therefore, in a GaN semiconductor laser having a conventional ridge structure, as the ridge width W is narrowed, deterioration of laser characteristics due to unevenness of the resonator cross-sectional shape (mainly its inclination) is prevented, and the production yield is improved.

In the conventional GaN semiconductor laser, as the ridge width W at the cross section of the resonator becomes wider, the ridge width W is more susceptible to disturbance caused by feedback light. It is desirable to narrow it.

However, as described above, in the conventional GaN semiconductor laser, the lower limit of the ridge width W is limited to about 3 µm from the viewpoint of suppressing the increase in the driving voltage. Therefore, in the conventional GaN-based semiconductor laser, it was very difficult to reduce the adverse effect of both parts of the resonator cross section formation on the laser characteristics without increasing the driving voltage, and to improve the noise characteristics.

Accordingly, it is an object of the present invention to easily realize reduction of driving voltage, stabilization of the lateral mode, expansion of the beam diffusion angle in the horizontal direction of the prismatic field image, prevention of deterioration of laser characteristics due to unevenness of the cross section of the resonator, and improvement of noise characteristics. It is providing the semiconductor laser using the nitride type III-V compound semiconductor which can be used.

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

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

3 is a graph showing oscillation conditions in a basic mode in a GaN semiconductor laser.

Fig. 4 is a graph showing the relationship between the inclination of the resonator end face of the GaN semiconductor laser and the emission direction of the laser light.

Fig. 5 is a graph showing the relationship between the inclination of the cross section of the resonator and the cross-sectional reflectance in a GaN semiconductor laser.

Fig. 6 is a graph showing the relationship between the inclination of the cross section of the resonator and the rise of the threshold current in the GaN semiconductor laser.

Fig. 7 is a perspective view of a GaN semiconductor laser according to the first embodiment of the present invention.

8 is a plan view of a GaN semiconductor laser according to the first embodiment of the present invention.

9 is a plan view of a GaN semiconductor laser according to a second embodiment of the present invention.

<Description of the code | symbol about the principal part of drawing>

1: sapphire substrate, 2: GaN buffer layer, 3: n-type GaN contact layer, 4: n-type AlGaN cladding layer, 5: GaInN active layer, 6: p-type AlGaN-type cap layer, 7: p-type AlGaN cladding layer, 8: p Type GaN contact layer, 9: ridge portion, 9a: tapered region, 9b, 9c: straight region, 10: SiO ₂ current confinement layer, 11: p-side electrode, 12: n-side electrode.

According to the present invention, a first cladding layer of the first conductivity type, an active layer on the first cladding layer, and a second cladding layer of the second conductivity type on the active layer, are formed on both sides of the ridge portion formed in the second cladding layer. In the semiconductor laser using the nitride system III-V group compound semiconductor which has a current confinement structure in which the current confinement layer which consists of a material which does not absorb the light from an active layer is formed,

The ridge portion is provided with a semiconductor laser having a tapered region whose width decreases in the direction toward the both ends of the resonator longitudinal direction from the center portion of the resonator longitudinal direction to both ends of the resonator longitudinal direction.

In the present invention, the nitride III-V compound semiconductor contains at least one group III element selected from the group consisting of Ga, Al, In, B, and Tl, and at least N, and optionally As Or a group V element containing P.

In the present invention, examples of the material of the current blocking layer include dielectrics such as silicon oxide (SiO ₂ ) and silicon nitride (SiN), nitride III-V group semiconductors such as AlGaN, GaInN, GaN, and ZnS. Group II-VI compound semiconductors are used.

In the present invention, in order to stably maintain the lateral mode while suppressing the increase of the driving voltage, the width at the center of the resonator longitudinal direction of the ridge portion is preferably 4 µm or more, and the resonator longitudinal direction of the ridge portion The width | variety in both end surfaces of is 3 micrometers or less. In particular, since the lateral mode of the emitted laser light is largely influenced by the width (width at the end face of the resonator) at both ends of the ridge resonator in the longitudinal direction, the width at both end faces of the ridge resonator in the longitudinal direction is further increased. Preferably they are 2 micrometers or more and 3 micrometers or less, More preferably, they are 2 micrometers or less.

According to the present invention configured as described above, both ends of the ridge portion in the resonator length direction are provided by having a tapered region in which the ridge portion decreases in the direction from the central portion in the resonator longitudinal direction to the both ends in the resonator longitudinal direction at both ends in the longitudinal direction of the resonator. The width at the center of the resonator longitudinal direction of the ridge is wider than the width at. Therefore, in order to maintain the lateral mode stably, even when the widths at both end faces in the longitudinal direction of the ridge resonator are narrowly set, the width at the central portion in the longitudinal direction of the ridge resonator is set independently. Can be. Thereby, since the contact area with an electrode can be enlarged and the resistance component in a ridge part can be reduced, it is possible to reduce the drive voltage of a semiconductor laser. In particular, in the present invention, when the width at the center of the resonator longitudinal direction of the ridge portion is set to 4 µm or more, and the width at both end surfaces of the ridge portion of the resonator longitudinal direction is set to 3 µm or less, the driving voltage It is possible to stabilize the transverse mode without raising. Regarding the stabilization of the lateral mode, when the widths at both end faces in the longitudinal direction of the ridge portion of the ridge portion are set to 2 µm or less, generation of higher order horizontal lateral mode can be suppressed, which is more efficient.

According to the present invention, the wave diffusion angle in the horizontal direction of the far field is widened by the wavefront shaping effect in the tapered regions of both ends of the ridge resonator in the longitudinal direction. By narrowing the width at both ends in the longitudinal direction of the resonator, the beam diffusion angle in the horizontal direction of the far field can be further widened. Therefore, when this semiconductor laser is used as a light source of the optical disk device, the strict position accuracy required at the time of assembly is required. Can alleviate At this time, the width in the center of the resonator longitudinal direction of the ridge portion is set to be wider independent of the width at both end surfaces of the resonator longitudinal direction of the ridge portion, thereby reducing the electrode contact area and reducing the horizontal direction of the prismatic field image. Since the beam diffusion angle can be increased, it is possible to form the primitive night image with good reliability.

Moreover, according to this invention, when the width | variety in both end surfaces of the ridge part longitudinal direction is narrowed, the fall of the cross-sectional reflectance by the shape of the resonator cross section, the raise of threshold current, and the change of slope efficiency can be suppressed. . As a result, deterioration of the laser characteristics due to unevenness of the cross-sectional shape of the resonator can be prevented, so that a semiconductor laser having good characteristics can be obtained with a high production yield. Moreover, when the width | variety in both end surfaces of the ridge resonator longitudinal direction is narrowed, the degree to which a semiconductor laser is disturbed by feedback light is suppressed, and the noise induced by feedback light can be reduced. At this time, in the present invention, since the width at the center portion in the longitudinal direction of the ridge portion in the resonator length can be set independently of the width at both end surfaces in the longitudinal direction of the ridge portion in the ridge portion, The advantage obtained by narrowing the width can be obtained without raising the driving voltage.

EMBODIMENT OF THE INVENTION Hereinafter, embodiment of this invention is described, referring drawings. In all the drawings of the embodiment, the same or corresponding parts are denoted by the same reference numerals.

First, the first embodiment of the present invention will be described. 7 and 8 show a GaN semiconductor laser according to the first embodiment of the present invention. Here, FIG. 7 is a perspective view and FIG. 8 is a top view. This GaN semiconductor laser is of refractive index waveguide.

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

The upper 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 these p-type AlGaN cladding layer 7 and a ridge portion constituted by the p-type GaN contact layer 8. The structure of this ridge part 9 is demonstrated in detail later.

Lower layers of the n-type AlGaN cladding layer 4, the GaInN active layer 5, the p-type AlGaN capping layer 6, and the p-type AlGaN cladding layer 7 have a predetermined mesa shape extending in one direction. Reference numeral 10 denotes the mesa portion. 8, the part corresponding to this mesa part 10 appears, and the part adjacent to this is abbreviate | omitted.

On both sides of the ridge portion 9, a SiO ₂ current confinement layer 11 which does not absorb light from the GaInN active layer 5 is formed, thereby forming a current confinement structure. The SiO ₂ current confinement layer 11 is also formed on the side surface of the mesa portion 10 to prevent a short circuit between the electrodes. In addition, since the SiO ₂ current confinement layer 11 is formed on both sides of the ridge portion 9 in this manner, a stepped refractive index distribution having a high refractive index of a portion corresponding to the ridge portion 9 and a low refractive index of both portions thereof is formed. Is attached in the direction parallel to the joint. In addition, the effective refractive index difference (Δn) in and out of the ridge here considers that the refractive index of the portion corresponding to the ridge portion 9 decreases due to the plasma effect of the carrier, and preferably, for example, 2 x 10 ^-3 or more is selected. In this example, the effective refractive index difference Δn inside and outside the ridge is set to 2 × 10 ⁻³ , for example.

On the p-type GaN contact layer 8 and the SiO ₂ current confinement layer 11, for example, a p-side electrode 12 such as a Ni / Pt / Au electrode is formed. On the n-type GaN contact layer 3 adjacent to the mesa portion 10, for example, an n-side electrode 13 such as a Ti / Al electrode is formed.

The cross section of both resonators of the GaN semiconductor laser is formed on the pseudo cleaved surface formed by cleaving the sapphire substrate 1 together with the GaN semiconductor layer forming the laser structure thereon. In this case, the laser light emitted from the end face of the resonator is not reflected on the surface of the sapphire substrate 1, and therefore the shape of the far field image of the laser light is good.

In the GaN semiconductor laser according to the first embodiment configured as described above, the effective refractive index difference Δn in and out of the ridge, that is, the effective refractive index difference between the portion corresponding to the ridge portion 9 and both sides thereof ( By (n), what is called refractive index waveguide (real refractive index waveguide) which the horizontal square is trapped in the part corresponding to the ridge part 9 is implement | achieved. Accordingly, in this GaN semiconductor laser, oscillation in the horizontal transverse mode where the low threshold current is relatively stable is obtained. In this GaN semiconductor laser, the width at both end faces of the ridge portion 9 in the longitudinal direction of the resonator is preferably set to 3 µm or less, more preferably 2 µm or less, thereby further stabilizing the lateral mode. It is possible to plan.

Hereinafter, the structure of the ridge part 9 in the GaN type semiconductor laser which concerns on this 1st Embodiment is demonstrated in detail.

That is, as shown in Figs. 7 and 8, the ridge portions 9 in this GaN semiconductor laser are directed from the central portion in the longitudinal direction of the resonator to the both ends in the longitudinal direction of the resonator in respective regions of both ends of the resonator longitudinal direction. This has a tapered area 9a which is tapered so that the width is continuously reduced. The ridge portion 9 also has a straight region 9b having a uniform width in the central region of the resonator longitudinal direction.

In this ridge portion 9, the two tapered regions 9a formed at both ends of the resonator longitudinal direction have almost the same length L ₁ . The length 2L ₁ of the sum of these tapered regions 9a is such that the resonator length L (L = 2L ₁ + L ₂ , L ₂ is the length of the straight region 9b so that a sufficient wavefront shaping effect can be obtained. Is determined to be at least 1/10, i.e., 2L ₁ ? L / 10.

Further, in Fig. 8, W ₁ denotes a width at both end faces of the resonator length direction of the ridge portion (9), W ₂ represents the width at the central portion of the cavity length direction of the ridge portion (9). Here, the width W ₁ indicates the width at the bottom of the ridge portion 9 at both end faces in the resonator longitudinal direction, and the width W ₂ indicates the bottom of the ridge portion 9 at the center in the longitudinal direction of the resonator. Indicates the width at. The width W ₁ at both end faces of the ridge portion 9 in the longitudinal direction of the ridge portion 9 and the width W ₂ at the center portion of the ridge portion 9 in the longitudinal direction of the ridge portion 9 satisfy a relationship of W ₁ <W ₂ . I'm making it. In addition, the width W ₁ at both end faces of the ridge part 9 in the longitudinal direction of the resonator and the width W ₂ at the center part of the resonator length direction of the ridge part 9 suppress the rise of the driving voltage. In order to stably maintain the transverse mode, preferably, W ₁ ≤ ₃ μm and W ₂ ≧ ₄ μm, more preferably ₂ μm ≦ W ₁ ≦ ₃ μm and W ₂ ≧ ₄ μm, more preferably W _It is determined to satisfy ₁ ≦ ₂ μm and W ₂ ≧ ₄ μm.

Here, as an example of the dimensions of each part of the GaN semiconductor laser according to the first embodiment, the resonator length L is 500 µm and the length L ₁ of the tapered region 9a of the ridge portion 9 is 100. The length L ₂ of the straight region 9b is 300 μm, and the width W ₁ at both ends of the resonator length direction of the ridge portion 9 is ₂ μm, and the length of the resonator length of the ridge portion 9 is ₂ μm. The width W ₂ at the center portion is 4 μm.

According to the GaN semiconductor laser according to the first embodiment of the present invention configured as described above, the ridge portion 9 is directed from the central portion in the longitudinal direction of the resonator to the both ends in the longitudinal direction of the resonator in respective regions of both ends of the resonator longitudinal direction. By having the taper area | region 9a whose width | variety decreases in the direction, the following various advantages can be acquired.

That is, in the GaN semiconductor laser according to the first embodiment, the ridge portions 9 have tapered regions 9a at both ends in the resonator longitudinal direction, so that the ridge portions 9 at both end surfaces in the resonator longitudinal direction of the ridge portions 9 are provided. the width (W ₁₎ is wider than, the ridge portion 9, the width in the central portion of the cavity length direction (W ₂₎ side. Therefore, in order to maintain the lateral mode stably, even when the width W ₁ at both end surfaces of the resonator longitudinal direction of the ridge portion 9 is set to 3 µm or less, specifically 2 µm as narrowly illustrated. Independently of this, the width W ₂ at the central portion of the resonator longitudinal direction of the ridge portion 9 can be set to 4 µm or more, specifically 4 µm as illustrated. As a result, the contact area between the p-type GaN contact layer 8 and the p-side electrode 11 can be increased to reduce the resistance component of the ridge portion 9, so that the driving voltage of the GaN semiconductor laser is reduced. It is possible to reduce.

As described above, according to the first embodiment, it is possible to stably maintain the lateral mode without raising the driving voltage. In particular, the resonator length L is 500 µm, the length L ₁ of the tapered region 9a is 100 µm, the length L ₂ of the straight region 9b is 300 µm, and the resonator length direction of the ridge portion 9 is shown. width at both end faces of the (W ₁₎ is 2㎛, the ridge portion 9, the width in the central portion of the cavity length direction (W ₂₎ when the GaN compound semiconductor according to the first embodiment is set to 4㎛, In the conventional GaN semiconductor laser shown in Figs. 1 and 2, the electrode contact area can be made wider than the case where the resonator length L is 500 mu m and the width W of the ridge portion 109 is 3 mu m. The driving voltage can be reduced while stabilizing the lateral mode. In addition, the oscillation conditions of the first embodiment, the ridge portion 9, the basic mode resonator length so that the width (W ₁₎ at both end faces of the direction is set to 2㎛, into the plasma effect of the carrier on a consideration of the It is possible to satisfy (see Fig. 3), and therefore, it is possible to suppress the occurrence of the higher-order horizontal mode, so that the lateral mode can be kept more stable.

In addition, according to the first embodiment, the beam diffusion angle θ // in the horizontal direction of the far-field image is adjusted by the wavefront shaping effect in the tapered region 9a of both ends of the ridge portion 9 in the longitudinal direction of the resonator. Can be widened. In addition, in this first embodiment, since the width W ₁ at both end surfaces of the resonator longitudinal direction of the ridge portion 9 is set narrow to 2 μm, the beam diffusion angle θ / /) Is further expanded. Specifically, in the conventional GaN-based semiconductor laser having a width W of the ridge portion 109 of 3 µm, the ridge portion (6) has a beam diffusion angle θ // of 6 ° in the horizontal direction of the far field. In the GaN-based semiconductor laser according to the first embodiment, in which the width W ₁ at both end faces in the longitudinal direction of the resonator in 9) is narrowed to 2 µm, the beam diffusion angle (θ //) in the horizontal direction of the far field image Can be expanded to about 8 °. As a result, when the GaN semiconductor laser is used for the light source of the optical disk device, the strict positioning accuracy required for assembly can be alleviated. At this time, the width W ₂ at the central portion of the resonator longitudinal direction of the ridge portion 9 is set wider than the width W ₁ at both end surfaces of the resonator length direction of the ridge portion 9. Since the beam diffusion angle [theta] // in the horizontal direction can be enlarged without reducing the electrode contact area, it is possible to shape the far field image with high reliability.

In addition, according to the first embodiment, since the width W ₁ at both end faces of the ridge part 9 in the longitudinal direction of the resonator is set narrow to 2 μm, the cross section by the shape of the resonator cross section (mainly its inclination) is The fall of a reflectance, the raise of a threshold current, and the change of slope efficiency can be suppressed. As a result, deterioration of the laser characteristics due to unevenness of the cross-sectional shape of the resonator can be prevented, so that a semiconductor laser having good characteristics can be obtained with a high production yield. In addition, since the width W ₁ at both end faces of the resonator in the longitudinal direction of the ridge portion 9 is set narrow to 2 μm, the degree of disturbance of the GaN semiconductor laser by feedback light is suppressed. The noise induced by can be reduced. At this time, in this first embodiment, the width W ₂ at the central portion of the resonator longitudinal direction of the ridge portion 9 is equal to the width W ₁ at both end surfaces of the ridge portion 9 in the longitudinal direction of the resonator portion 9. Since can be set independently and widely, these advantages obtained by narrowing the width W ₁ at both end surfaces of the resonator longitudinal direction of the ridge portion 9 can be obtained without increasing the driving voltage.

As mentioned above, according to this 1st Embodiment, the taper area | region in which the width | variety decreases in each direction of the ridge part 9 toward the both ends of a resonator longitudinal direction from the center part of a resonator longitudinal direction to each area | region of both ends of a resonator longitudinal direction. By having 9a, the width W ₁ at both end surfaces of the resonator longitudinal direction of the ridge part 9 and the width W ₂ at the center part of the resonator longitudinal direction of the ridge part can be optimized, respectively. Reduction of voltage, stabilization of the lateral mode, expansion of the beam diffusion angle (θ //) in the horizontal direction of the far field image, prevention of deterioration of laser characteristics due to unevenness of the cross section of the resonator, and improvement of noise characteristics can be easily realized. Therefore, according to this first embodiment, a GaN semiconductor laser can be obtained which is suitable for the light source of the optical disk device and has good characteristics.

Next, a second embodiment of the present invention will be described. 9 is a plan view of a GaN semiconductor laser according to the second embodiment of the present invention. In the GaN semiconductor laser according to the second embodiment, the width of the ridge portion 9 is constant in a predetermined region near both end surfaces of the resonator longitudinal direction in consideration of the tolerance in the process. And the structure of the junction and the perpendicular direction of the GaN semiconductor laser which concerns on this 2nd Embodiment is comprised similarly to the GaN semiconductor laser which concerns on 1st Embodiment.

As shown in Fig. 9, the ridge portion 9 in the GaN semiconductor laser according to the second embodiment is uniform in each of the regions between the tapered regions 9a at both ends of the resonator longitudinal direction and the cross sections of both resonators. width has an additional straightening region (9c) of (W _1). In Fig. 9, L ₃ represents the length of these straight regions 9c. Here, these straight regions 9c are formed so as to ensure the width at both end faces of the resonator longitudinal direction of the ridge portion 9 to be W ₁ , and the length L ₃ of these straight regions 9c is Very short is desirable. In this case, the upper limit of the length (L ₃₎ of these straight region (9c), for example, is about 20 ~ 25㎛.

Here, as an example of the dimensions of each part of the GaN semiconductor laser according to the second embodiment, the resonator length L is 500 µm and the length L ₁ of the tapered region 9a of the ridge portion 9 is 100. The length L ₂ of the central straight region 9b in the resonator longitudinal direction is 250 μm, the length L ₃ of the straight region 9c at both ends of the resonator longitudinal direction is 25 μm, and the resonator length of the ridge portion 9. The width W ₁ at both end surfaces in the direction is ₂ μm, and the width W ₂ at the center portion of the resonator longitudinal direction of the ridge portion 9 is 4 μm.

Since the structure other than the above of the GaN type semiconductor laser which concerns on this 2nd Embodiment is the same as that of the GaN type semiconductor laser which concerns on 1st Embodiment, it abbreviate | omits description.

According to this second embodiment, the same advantages as those in the first embodiment can be obtained, and the following advantages can be obtained. That is, in this second embodiment, since the ridge portion 9 is straight region (9c) of the width (W ₁₎ uniform on both end regions of the cavity length direction is formed of, when machining a cavity, ridge portion (9 The width at both end faces in the longitudinal direction of the resonator can be set to W ₁ . This has a tapered stripe ridge structure in which the width of the ridge portion 9 at both end faces in the longitudinal direction of the resonator is W ₁ and the width of the ridge portion 9 at the center in the longitudinal direction of the resonator is W ₂ . GaN semiconductor lasers can be obtained with high production yields.

As mentioned above, although embodiment of this invention was described concretely, this invention is not limited to embodiment mentioned above, Various deformation | transformation according to the technical idea of this invention is possible.

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

Specifically, in the above-described first and second embodiments, the resonator length L, the length L ₁ of the tapered region 9a at both ends of the resonator longitudinal direction of the ridge part 9, and the ridge part 9 Length L ₂ of the straight region 9b of the central portion in the longitudinal direction of the resonator of the resonator, length L ₃ of the straight region 9c of the both ends of the resonator longitudinal direction of the ridge portion 9, and the resonator of the ridge portion 9 If the width W ₁ at both end surfaces in the longitudinal direction and the width W ₂ at the central portion in the resonator longitudinal direction of the ridge portion 9 satisfy the conditions mentioned in the first and second embodiments, Can be set arbitrarily.

In addition, in the above-described first and second embodiments, the two tapered regions 9a formed in the respective regions of both ends of the resonator longitudinal direction of the ridge portion 9 are symmetrical at the front side and the rear side. It does not need to be, and both sides of the ridge part 9 may also be left-right asymmetrical. Moreover, the taper area | region 9a of the ridge part 9 is monotonically reduced in the direction toward the both ends of a resonator longitudinal direction from the center part of a resonator longitudinal direction, and the side does not need to be comprised flat, for example, For example, it may be comprised by the curved surface curved inward or outward. But also, the ridge portion 9, the cavity length the length (L ₂₎ of the straight area (9b) of the central portion in the direction to zero, and the ridge portion 9, the resonator length end portions tapered zone (9a) in the direction of, or, It is good also as only the taper area | region 9a and the straight area | region 9c.

Moreover, in the above-mentioned first and second embodiments, SiO ₂ is used as the material of the current blocking layer embedded in both sides of the ridge portion 9, but as the material of this current blocking layer, AlGaN, A nitride III-V compound semiconductor such as GaInN or GaN, a dielectric such as SiN, or a II-VI compound semiconductor such as ZnS may be used.

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

In addition, although the sapphire substrate is used as a board | substrate in the above-mentioned 1st and 2nd embodiment, this may use a spinel substrate, a SiC substrate, a ZnO substrate, a GaP substrate, etc. instead of a sapphire substrate, or After growing a nitride III-V compound semiconductor layer on these substrates and growing a nitride III-V compound semiconductor layer on these substrates, the substrate is removed by polishing or the like to remove only the nitride III-V compound semiconductor layer. You may use the board | substrate which consists of a nitride-type III-V compound semiconductor, such as a GaN substrate, and the like.

In the above-described first and second embodiments, the present invention has been described in the case where the present invention is applied to a GaN semiconductor laser having a double heterostructure, but the present invention is a GaN semiconductor laser having a SCH structure (seperate confinement heterostructure). It is also possible to apply to.

According to the present invention configured as described above, the ridge portion has a tapered region in which the width decreases in the direction toward the both ends of the resonator longitudinal direction from the central portion of the resonator longitudinal direction to both ends of the resonator longitudinal direction, thereby Since the width at the center and the width at both ends of the resonator length in the ridge can be optimized, the reduction of the driving voltage, the stabilization of the lateral mode, the expansion of the beam diffusion angle in the horizontal direction in the far field and the cross-sectional shape of the resonator Prevention of deterioration of the laser characteristic due to unevenness and improvement of the noise characteristic can be easily realized. Thereby, the semiconductor laser which used the nitride type III-V compound semiconductor suitable for the light source of an optical disk apparatus, and has favorable characteristics can be obtained.

Claims (4)

A ridge portion including 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, and formed on the second cladding layer. In a semiconductor laser using a nitride-based III-V compound semiconductor having a current blocking structure formed on both sides of a ridge portion, a current blocking layer made of a material that does not absorb light from the active layer is formed. , And the ridge portion at both ends in the longitudinal direction of the resonator, the taper region having a width decreasing in the direction from the center portion in the longitudinal direction of the resonator to both ends in the longitudinal direction of the resonator. The method of claim 1, A semiconductor laser having a width at a central portion of the ridge portion in the longitudinal direction of the resonator is 4 µm or more, and a width at both end surfaces of the ridge portion in the longitudinal direction of the resonator portion is 3 µm or less. The method of claim 1, A semiconductor laser having a width at the central portion of the ridge portion in the longitudinal direction of the resonator is 4 µm or more, and a width at both end surfaces of the ridge portion in the longitudinal direction of the ridge portion is 2 µm or more and 3 µm or less. The method of claim 1, A semiconductor laser having a width at a central portion of the ridge portion in the longitudinal direction of the resonator is 4 μm or more, and a width at both end surfaces of the ridge portion in the longitudinal direction of the resonator portion is 2 μm or less.