JP6807541B2 - Semiconductor light emitting device - Google Patents

Description

The present invention relates to a semiconductor light emitting device used for an in-vehicle headlamp, a projector light source, or the like.

Conventionally, a semiconductor laser device described in, for example, Patent Document 1 is known as a semiconductor light emitting device made of a group III nitride semiconductor such as GaN or AlGaN. This conventional semiconductor light emitting device will be described with reference to FIG.

Conventional semiconductor light emitting element, a buffer layer ₁₀₂ made of _Al 0.05 _{Ga 0.95} N on the substrate 101 made of GaN, Al _{0.05 Ga 0.95} n-type contact layer 103 made of N, _{an In 0. A} crack prevention layer 104 made of ₀₆ Ga _0.94 N is formed. On it, an n-type clad layer 105 formed by alternately forming a layer made of Al _0.05 Ga _0.95 N and a layer made of GaN, and an n-type optical guide layer 106 made of GaN are formed. Active layers 107 and Al _0.3 formed by alternately forming a barrier layer made of undoped In _0.05 Ga _0.95 N and a well layer made of undoped In _0.32 Ga _0.68 N on the barrier layer. A p-type electron confinement layer 108 made of Ga _0.7 N is formed. Then, a p-type optical guide layer 109 made of GaN, a p-type clad layer 110 made of Al _0.05 Ga _0.95 N and a layer made of GaN are alternately formed on the p-type clad layer 110 made of GaN, and a p-type made of GaN. The contact layer 111 is sequentially formed. Then, the side surface of the ridge structure and the p-type optical guide layer formed by etching from the p-type contact layer 111 to the middle of the p-type optical guide layer 109 until the remaining thickness of the p-type optical guide layer 109 becomes 0.1 μm. A protective film 162 made of Zr oxide is formed on the upper surface of 109. A p-electrode 120 made of Ni / Au is formed on the p-type contact layer 111 and the second protective film 162. Further, the n-type contact layer 103 is etched until a part is exposed, and an n-electrode 121 made of Ti / Al is formed on the surface of the n-type contact layer 103, and the n-electrode 121, the p-electrode 120 and the n-type contact layer 103 are formed. A dielectric multilayer film 164 made of SiO ₂ and TiO ₂ is formed so as to cover the film. A pad electrode 122 is provided in the opening on the p-type contact layer 111 side of the dielectric multilayer film 164 so as to be in contact with the p electrode 120, and a pad electrode 123 is provided in the opening in the n electrode 121 of the dielectric multilayer film 164. Is provided.

Japanese Unexamined Patent Publication No. 2002-27971

In such a conventional semiconductor light emitting device, it is difficult to suppress lattice irregularity between the substrate 101 and the n-type clad layer 105 and the p-type clad layer 110 and to confine light in the direction perpendicular to the substrate 101. Was a problem.

That is, in the above-mentioned conventional semiconductor light emitting device, when trying to increase the light confinement in the vertical direction, it is necessary to lower the refractive index of the n-type clad layer 105 and the p-type clad layer 110, so that it is necessary to increase the Al composition, for example. There is. On the other hand, if the Al composition of the n-type clad layer 105 and the p-type clad layer 110 is increased, the lattice irregularity with the substrate 101 becomes large. When the lattice irregularity becomes large, lattice defects are likely to occur, leading to a decrease in luminous efficiency. Therefore, since the Al composition of the n-type clad layer 105 and the p-type clad layer 110 cannot be made too large, AlGaN having a low Al composition of 10% or less is used. In this case, the difference in refractive index between the n-type or p-type clad layer and the active layer becomes small, the light distribution tends to spread widely above and below the active layer, and the electrode formed on the top of the ridge waveguide or the waveguide light on the substrate. The base is reached and absorption loss is likely to occur. In order to reduce the light absorption of such waveguide light, it is necessary to increase the thickness of the clad layer so that the base of the light distribution does not reach the electrodes or the substrate formed on the ridge. Become. However, when the thickness of the p-type clad layer 110 on which the ridge-type waveguide is formed increases, the series resistance of the element increases and the operating voltage increases. For this reason, heat generation during laser oscillation operation becomes large, and the light output tends to be thermally saturated. As a result, the suppression of lattice irregularity between the substrate 101 and the n-type clad layer 105 and the p-type clad layer 110, the prevention of the increase in the thickness of the p-type clad layer 110, and the vertical light confinement are all satisfied. It was getting harder.

Therefore, in the present invention, even if the thickness of the conductive clad layer on which the ridge is formed is thin, the lattice between the substrate and the first clad layer and the second clad layer is reduced while reducing the absorption loss at the electrodes on the ridge. The purpose is to suppress irregularities and satisfy all vertical light confinement.

In order to solve the above problems, the semiconductor light emitting device of the present invention includes a substrate, a monoconductive first clad layer made of a group III nitride semiconductor having Al formed on the substrate, and a first clad layer. It has an active layer made of a group III nitride semiconductor formed on the clad layer. Then, a second clad layer of the inverse conductive type made of a group III nitride semiconductor having Al formed on the active layer, a conductive compound layer formed on the second clad layer, and a conductive compound. Has a ridge structure having a second clad layer as a lower surface and a second clad layer as a lower surface. The Al composition of the second clad layer is smaller than the Al composition of the first clad layer, and the refractive index of the conductive compound layer is smaller than the refractive index of the second clad layer.

With this configuration, the Al composition of the second clad layer is smaller than the Al composition of the first clad layer, so that the second clad layer has a relatively higher refractive index than the first clad layer, so that the light distribution is high. The shape depends on the second clad layer. Further, since the refractive index of the conductive compound is smaller than the refractive index of the second clad layer, the light distribution immediately below the ridge is distributed between the first clad layer and the second clad layer. The vertical light confinement coefficient of the light distribution to the active layer increases. As a result, the effective refractive index difference (ΔN) inside and outside the ridge increases.

Further, in the semiconductor light emitting device of the present invention, the ridge structure preferably propagates in a higher-order transverse mode of a second order or higher. According to this preferable configuration, even if the horizontal modes of different orders interfere with each other, the light distributions are coupled, and the light distribution is deformed, the influence is small, and a kink having a large non-linearity is less likely to occur.

The semiconductor light emitting device of the present invention further has a waveguide formed by a front end surface and a rear end surface, a ridge structure is formed between the front end surface and the rear end surface, and is included in the side surface of the ridge structure. It is preferable that the direction from the front end surface to the rear end surface and the direction of the waveguide form a predetermined angle. According to this preferable configuration, since the waveguide has a taper, spatial hole burning is less likely to occur.

In the semiconductor light emitting device of the present invention, when the reflectance of the front end surface is Rf, the reflectance of the rear end surface is Rr, the width of the ridge on the front end surface is Wf, and the width of the ridge on the rear end surface is Wr, then Rf <Rr. It is preferable that Wf> Wr.

In the semiconductor light emitting device of the present invention, the angle formed by the direction from the front end surface to the rear end surface and the direction of the waveguide is preferably 0.05 ° or more and 0.15 ° or less. According to this preferable configuration, spatial hole burning is less likely to occur.

In the semiconductor light emitting device of the present invention, the film thickness of the second clad layer is preferably 0.3 μm or more and 0.6 μm or less. According to this preferable configuration, when the film thickness of the second clad layer is 0.3 μm or more, the light confinement rate of the active layer can be increased, and the layer thickness of the second clad layer is 0.6 μm or less. , The series resistance of the semiconductor light emitting element can be reduced.

In the semiconductor light emitting device of the present invention, it is preferable that the conductive compound layer is further made of an oxide containing indium and tin, and the thickness is 0.15 μm or more and 0.3 μm or less. According to this preferable configuration, the waveguide loss can be reduced, ΔN and the optical confinement coefficient can be increased, and the electric resistance of the semiconductor light emitting device can be reduced.

In the semiconductor light emitting element of the present invention, the first clad layer is further composed of Al _X1 Ga _1-X1 N, the second clad layer is composed of Al _X2 Ga _1-X2 N, and X1-X2 ≧ 0.02, X1. It is preferable to satisfy the relationship of ≤0.1 and 0.03≤X2≤0.07.

In the semiconductor light emitting device of the present invention, the layer thickness of the second clad layer outside the ridge structure is preferably larger than 0 nm and 50 nm or less. According to this preferable configuration, a large difference in effective refractive index can be obtained between the inside and the outside of the ridge structure.

The semiconductor light emitting device of the present invention preferably has a current block layer having a refractive index smaller than that of the second clad layer formed on the side surface of the ridge structure.

According to the semiconductor light emitting device of the present invention, even in a semiconductor laser using a group III nitride, particularly a green semiconductor laser having an oscillation wavelength in the 530 nm band, the optical confinement coefficient and ΔN are large, the occurrence of lattice defects is suppressed, and the induction is performed. A laser with low waveguide loss can be realized. Therefore, it is possible to realize a semiconductor laser having excellent temperature characteristics and capable of long-term reliable operation.

FIG. 3 is a cross-sectional view of the semiconductor light emitting device according to the first embodiment of the present invention. The figure which shows the ridge height dependence of the stress distribution in the horizontal direction generated in the active layer 14 of the semiconductor light emitting device. Al composition X1 and the second clad layer of the first clad layer 12 having a waveguide loss, a light confinement coefficient, and an effective refractive index difference (ΔN) when the thickness of the second clad layer 16 in the semiconductor light emitting device is 0.3 μm. The figure which shows the dependence of 16 Al composition X2 and the relationship between X1 and X2. The second clad layer showing the dependence of the waveguide loss, the optical confinement coefficient, and the effective refractive index difference (ΔN) of the Al composition X1 of the first clad layer 12 and the Al composition X2 of the second clad layer 16 in the semiconductor light emitting device. The figure when the film thickness of 16 is 0.2 μm. The figure in the case where the film thickness of the 2nd clad layer 16 is 0.3 μm. The figure in the case where the film thickness of the 2nd clad layer 16 is 0.4 μm. The figure when the film thickness of the 2nd clad layer 16 is 0.5 μm. The figure in the case where the film thickness of the 2nd clad layer 16 is 0.6 μm. In the structure in which the conductive oxide layer 18 is eliminated for the semiconductor light emitting device, the Al composition X1 of the first clad layer 12 and the Al of the second clad layer 16 having a waveguide loss, a light confinement coefficient, and an effective refractive index difference (ΔN). The figure in the case where the thickness | thickness of the 2nd clad layer 16 which shows the dependence of composition X2 is 0.2 μm. The figure in the case where the film thickness of the 2nd clad layer 16 is 0.3 μm. The figure in the case where the film thickness of the 2nd clad layer 16 is 0.4 μm. The figure when the film thickness of the 2nd clad layer 16 is 0.5 μm. The figure in the case where the film thickness of the 2nd clad layer 16 is 0.6 μm. The figure which shows the waveguide loss when the layer thickness of the conductive oxide layer 18 is changed in the semiconductor light emitting device. It is a figure which shows the change of ΔN when the layer thickness of the conductive oxide layer 18 is changed in the semiconductor light emitting device. The plan view of the stripe shape of the semiconductor light emitting element in the 2nd Embodiment of this invention. The figure when the conductive oxide layer 18 which shows the current-light output characteristic of the semiconductor light emitting element is used. The figure when the same conductive oxide layer is not used. The plan view which shows the modification of the stripe shape of the semiconductor light emitting element. The plan view which shows the modification of the stripe shape of the semiconductor light emitting element. The plan view which shows the modification of the stripe shape of the semiconductor light emitting element. Sectional drawing of the conventional semiconductor light emitting element.

(First Embodiment)
Hereinafter, the semiconductor light emitting device according to the first embodiment of the present invention will be described with reference to the drawings. In the following, AlGaN means Al _x Ga _1-x N (0 <x <1), and InGaN means In _y Ga _1-y N (0 <y <1). In addition, the InAlGaN is that _{In z Al t Ga 1-z} -t N of (0 <z <1,0 <t <1). The x, y, z, and t representing the composition can be appropriately determined depending on the layer structure of the semiconductor light emitting device.

(1) Structure of Semiconductor Light Emitting Element As shown in FIG. 1, the semiconductor light emitting device of the present embodiment has a substrate 11 made of GaN and an n-type first clad layer 12 made of AlGaN provided on the substrate 11. It is provided with an optical guide layer 13 made of n-type GaN provided on the first clad layer 12, and an active layer 14 having a quantum well structure provided on the optical guide layer 13. Then, the p-type electron barrier layer 15 made of p-type AlGaN provided on the active layer 14, the p-type second clad layer 16 made of AlGaN, and the p-type second clad layer 16 provided above the p-type second clad layer 16. The p-type contact layer 17 made of GaN is provided. Further, a conductive oxide layer 18 made of indium tin oxide (hereinafter referred to as ITO) provided on the p-type contact layer 17 is provided. Further, a ridge 23 is formed on the p-type second clad layer 16, and a current block layer 20 made of SiO ₂ is provided on the side wall of the ridge 23. The current block layer 20 and the conductive oxide layer 18 are provided. A p-type electrode 22 is provided on the top. Further, an n-type electrode 21 is provided on the back surface of the substrate 11.

In the above, the n-type semiconductor layer is doped with Si, and the p-type semiconductor layer is doped with Mg.

The active layer 14 has a multiple quantum well structure using a well layer made of InGaN having a thickness of 3 nm and an In composition of 0.3 and a quantum barrier layer made of GaN having a thickness of 7.5 nm. It is advantageous that the number of wells is as large as possible because the coefficient of light confinement in the vertical direction to the active layer can be increased, but if the number of wells is four or more, the operating carrier density of each quantum well layer is not uniform. It causes a decrease in luminous efficiency. In the present embodiment, the number of well layers is three. As a result, it is possible to increase the light confinement coefficient while making the operating carrier density in each well uniform. Further, GaN is used as the quantum barrier layer, and the occurrence of lattice defects due to lattice irregularities that occur in the InGaN well layer having a high In composition is suppressed by sandwiching the top and bottom of the well layer with GaN.

In the semiconductor light emitting device of the present embodiment, the direction perpendicular to the paper surface of FIG. 1 is the direction of the resonator, and the two surfaces perpendicular to the direction of the resonator are the end faces. That is, the semiconductor light emitting device of this embodiment is a semiconductor laser. Incidentally, the front and rear facets of the two end faces of which is coated with a multilayer film of AlN film and the Al ₂ O ₃ film, 5% for each of reflectivity front facet is 95% for the rear end face. That is, the reflectance of the front end face is made smaller than the reflectance of the rear end face.

The emission wavelength of the semiconductor light emitting device in this embodiment is 530 nm.

The semiconductor light emitting device in the present embodiment is a semiconductor laser device having a striped structure when the two side walls of the ridge 23 are parallel to the direction of the resonator when viewed from above the substrate 11.

In the semiconductor light emitting device of the present embodiment, the Al composition of the first clad layer 12 is X1, and the Al composition of the second clad layer 16 is X2. Further, as shown in FIG. 1, the width of the ridge 23 is W, the thickness of the second clad layer 16 inside the ridge 24 is M2, the height of the ridge 23 is H, and the layer of the second clad layer 16 inside the ridge 25 is 25. Let the thickness be dp. Further, the effective refractive index difference between the ridge inner 24 and the ridge outer 25 is ΔN. The ridge 23 is created by performing etching (usually dry etching). That is, since the second clad layer 16 in the ridge outer 25 is made thinner than the second clad layer 16 in the ridge inner 24 by etching, dp is referred to as the etching residual thickness of the second clad layer 16 in the ridge outer 25. You can also do it.

As is clear from FIG. 1, the relational expression shown in the following (Equation 1) is established between M2, H, and dp.
(Equation 1) M2 = H + dp
(2) Examination The inventor of the present application relates to the semiconductor light emitting device of the present embodiment using the conductive oxide layer 18 of X1, X2, W, M2, H, ΔN, dp and the conductive oxide layer 18. We examined what kind of thickness is desirable. The results of the study will be described below.

(2-1) About dp Explaining the size of the layer thickness dp, it is preferable that dp is as small as possible because ΔN becomes small when dp is large. However, if the dp is made too small, the effect of damage to the crystal structure due to dry etching will reach the active layer 14 due to variations in the etching depth in the wafer surface when etching, especially dry etching, and long-term reliability It becomes a factor that hinders the guarantee. Therefore, the etching is controlled so that the dp is in the range of 0 nm to 50 nm.

Since M2 does not change even if dp changes from 0 nm to 50 nm, there is almost no change in the light confinement coefficient in the vertical direction and the waveguide loss that occurs in the light distribution in the p-type contact layer 17 and the p-type electrode 22.

On the other hand, when dp changes from 0 nm to 50 nm, the effective refractive index at the outside of the ridge 25 changes, so that ΔN changes. In the case of this embodiment, since SiO ₂ having a low refractive index is used as the current block layer 20, if the dp increases, the effective refractive index in the ridge outer 25 increases. That is, ΔN becomes smaller as dp increases.

As will be described later, ΔN should be as high as possible in order to stably oscillate the second-order or higher-order transverse mode. Therefore, in the case where dp at which ΔN is the smallest is 50 nm, X1 and X2 are determined so that ΔN as large as possible can be obtained without causing a large increase in waveguide loss. At dp smaller than 50 nm, ΔN becomes larger. Therefore, in the following description, dp is set to 50 nm.

(2-2) SiO ₂ on stress applied to the semiconductor light-emitting device to the current blocking layer 20 (thermal expansion ^{coefficient: 0.6 × 10 -6 /K~0.9×10 -6 /} K) in the case of using the Since the coefficient of thermal expansion is smaller than that of GaN (coefficient of thermal expansion: 5.6 × ^10-6 / K) and AlN (coefficient of thermal expansion: 4.2 × ^10-6 / K), the current block layer 20 A stress is generated between the ridge and the ridge 23 due to the difference in the coefficient of thermal expansion. Therefore, in the second clad layer 16 between the current block layer 20 and the active layer 14, compressible stress is generated in the plane parallel to the active layer 14 in the regions on both sides of the lower end portion of the ridge 23, resulting in crystals. The structure is distorted. When the crystal structure is distorted, the refractive index of that part changes. In general, the refractive index of group III nitride semiconductors increases when compressible stress is applied. Therefore, the refractive index of the second clad layer 16 in the region near the lower end of the ridge 23 changes so as to increase its magnitude due to the compressive stress. As a result, ΔN decreases.

Further, since the bandgap energy in the active layers 14 on both lower ends of the ridge 23 becomes small, the current injected into the ridge 23 easily flows through the regions on both sides of the ridge 23. Therefore, the current is not uniformly injected into the active layer immediately below the ridge 23, which leads to a decrease in slope efficiency. Therefore, it is necessary to reduce the strain based on the difference in the coefficient of thermal expansion between the current block layer 20 and the second clad layer 16 generated on both sides of the lower end portion of the ridge 23 as much as possible.

The inventor of the present application examined the relationship between the thickness M2 of the second clad layer 16 at the ridge inner 24 and the stress applied to the second clad layer 16 at the ridge inner 24 and the ridge outer 25 for the semiconductor light emitting device shown in FIG. did. FIG. 2 shows the examination results. In FIG. 2, the horizontal axis represents the position of the second clad layer 16 with the center of the ridge 23 as the origin, parallel to the GaN substrate 11 and parallel to the end face, and the vertical axis represents the position of the second clad layer 16 at a predetermined position. The magnitude of the stress applied to the layer 16 is expressed in arbitrary units. If it is larger than 0 on the vertical axis, compressive stress is applied to the second clad layer 16, and if it is smaller than 0, tensile stress is applied to the second clad layer 16. For the semiconductor light emitting device examined, the ridge width W was set to 16 μm. In addition, three M2s, 0.3 μm, 0.6 μm, and 0.8 μm, were examined.

As shown in FIG. 2, it was found that the larger M2, that is, the higher the height H of the ridge 23, the larger the compressive stress inside the ridge 24. In particular, it was found that the compressive stress was remarkably large in the vicinity of the boundary between the ridge inside 24 and the ridge outside 25. It was also found that the larger M2, the more uneven the distribution of compressive stress inside the ridge 24. From this, as the height H of the ridge 23 is higher, the compressive stress of the ridge inner 24 near the boundary with the ridge outer 25 becomes remarkably large, the band gap there becomes smaller, and the ridge inner 24 becomes the ridge outer 25. Current flows near the boundary of. Then, it is found that it is difficult to apply a current uniformly to the ridge 23. From this, it can be seen that the higher the height H of the ridge 23, the narrower the current path for the current flowing through the ridge 23, and the greater the electrical resistance of the semiconductor light emitting element.

That is, it is necessary to reduce the height H of the ridge 23 in order to reduce the stress generated in the regions on both sides of the lower end portion of the ridge 23 and to reduce the electric resistance of the semiconductor light emitting element.

From FIG. 2, it can be seen that when M2 is reduced from 0.8 μm to 0.3 μm, the strain generated in the active layers on both sides of the lower end of the ridge 23 is almost halved, and the stress distribution is flat. That is, if M2 ≦ 0.3 μm, the electric resistance of the semiconductor light emitting device can be reduced.

(2-3) ΔN The effective refractive index difference ΔN between the ridge inner 24 and the ridge outer 25 will be described.

When ΔN is small, even if the ridge width W is widened, the confinement mechanism of the horizontal horizontal light distribution (horizontal horizontal mode) with respect to the secondary or higher horizontal mode is weak, and only in the basic (0th) horizontal mode and the primary horizontal mode. It will be easier to operate. As a result, the interaction due to interference between the transverse modes becomes large, the shape of the light distribution changes significantly, a kink in which the current-light output characteristic shows non-linearity occurs, and the light output tends to become unstable.

On the other hand, when the transverse mode of the second order or higher oscillates, the transverse modes of different orders interfere with each other, and even if the optical distribution is deformed due to the coupling of the optical distribution, the influence becomes small and the kink having a large nonlinearity Is less likely to occur, so that the linearity of the current-light output characteristic is improved.

That is, in order to reduce the occurrence of kink and improve the linearity of the current-light output characteristic, a semiconductor light emitting device that oscillates in a second or higher transverse mode is desirable.

A semiconductor light emitting device used as a projector light source or the like is required to have a high output operation of several hundred mW or more. On the other hand, in a high-power laser, the ridge width W is 5 μm in order to reduce the light density at the end face of the resonator and suppress the occurrence of COD (Catastrophic Optical Damage) in which the end face is melt-broken by the laser's own light. The above so-called wide stripe structure is used. For such a wide stripe structure, at least 2.5 × 10 ^-3 is required as the value of ΔN in order to confine the secondary transverse mode light inside the ridge and oscillate the laser. If ΔN is further increased, the horizontal light confinement rate in the second-order or higher-order transverse mode becomes larger, and laser oscillation including the second-order or higher-order transverse mode becomes stable.

(2-4) Light Confinement Coefficient In order to obtain good temperature characteristics in a semiconductor light emitting device, particularly a semiconductor light emitting device having a wavelength of around 530 nm, the light confinement coefficient in the direction perpendicular to the active layer 14 should be set. The larger the better, it is necessary to have a light confinement coefficient (vertical direction) of at least 1%. Hereinafter, the light confinement coefficient in the vertical direction is referred to as a vertical / transverse mode confinement coefficient.

(2-5) Values of X1 and X2 Next, the values of the Al composition X1 of the first clad layer 12 and the Al composition X2 of the second clad layer 16 will be described.

When the Al composition X1 of the first clad layer 12 is increased, the refractive index of the first clad layer 12 is lowered, the difference in refractive index from the active layer 14 can be increased, and the optical confinement coefficient in the vertical direction can be increased. .. When the optical confinement coefficient is increased, a large gain can be obtained even when the injection current to the active layer is small, so that the oscillation threshold current value and the operating carrier density in the active layer are reduced. Therefore, it is possible to suppress the overflow of carriers that are thermally excited by the carriers injected into the active layer and leak into the clad layer during high-temperature operation. For this reason, an increase in the optical confinement coefficient in the vertical direction increases the heat-saturated light output in the current-light output characteristic even during high-temperature and high-power operation, and realizes a laser having a low operating current value and excellent temperature characteristics. It is effective.

However, if X1 is made too large, both the difference in the lattice constant and the difference in the coefficient of thermal expansion between the substrate 11 made of GaN and the first clad layer 12 made of AlGaN become large, which leads to the occurrence of lattice defects and cracks. .. Therefore, it is necessary to set X1 ≦ 0.1.

Further, if the Al composition X2 of the second clad layer 16 is also increased in the same manner as X1, the vertical light confinement coefficient to the active layer is increased. However, if it is made too large, the activation rate of Mg, which is a p-type impurity, decreases, the electric resistance of the second clad layer 16 increases, and the electric resistance of the semiconductor light emitting device increases. An increase in the electrical resistance of the semiconductor light emitting device increases self-heating during the laser oscillation operation of the semiconductor light emitting device, leading to a decrease in the heat-saturated light output level in the current-light output characteristic. Therefore, in order to obtain the effect of increasing the light confinement coefficient in the vertical direction and not to increase the resistance of the second clad layer 16, it is necessary to set X2 ≦ 0.07.

As X2 is reduced, the light distribution in the vertical direction approaches the second clad layer 16, so that ΔN increases. However, if X2 is made too small, the light distribution becomes too close to the second clad layer 16, and free carrier absorption loss due to impurities in the p-type contact layer 17 and the second clad layer 16 and absorption loss in the p-type electrode 22 occur. It increases and the waveguide loss increases. An increase in waveguide loss leads to a decrease in the ratio of change in optical output (slope efficiency) to a change in the amount of injection current after laser oscillation in the current-optical output characteristic, resulting in a decrease in the heat-saturated optical output level during high-temperature operation. Leads to. Therefore, the value of X2 needs to be 0.03 or more in order to suppress a large increase in waveguide loss.

(2-6) Relationship between X1 and X2 In the semiconductor light emitting device as shown in FIG. 1, since the second clad layer 16 is thin at the ridge outer 25, it is perpendicular to the active layer 14 at the ridge outer 25. The light distribution in the direction (vertical transverse mode) depends on the first clad layer 12 side. In the ridge interior 24, the vertical transverse mode is substantially symmetrical with respect to the active layer 14.

Here, when the Al composition X1 of the first clad layer 12 is larger than the Al composition X2 of the second clad layer 16, the refractive index of the first clad layer 12 is smaller than the refractive index of the second clad layer 16. The effective refractive index inside the ridge 25 can be further smaller than the effective refractive index inside the ridge 24. That is, ΔN can be increased, and the light confinement rate in the horizontal and transverse mode can be increased.

Therefore, the inventor of the present application determined ΔN for the semiconductor light emitting device shown in FIG. 1 with X1 and X2 as parameters and N2 = 0.3 μm. In addition, W was set to 6 μm, and the layer thickness of the conductive oxide layer 18 was set to 0.17 μm. The result is shown in FIG. In FIG. 3, 1%, 1.1%, 1.2%, 1.3%, and 1.4% are the vertical-transverse mode confinement coefficients, which are 1.5 × 10 ^-3 , 2 ×. 10 ^-3 , 2.5 × 10 ^-3 , 3 × 10 ^-3 , 3.5 × 10 ^-3 are ΔN. Moreover, the ^{curve cm -1} are assigned as ^{6 cm -1} and 10 cm ^-1 represents the waveguide loss in the semiconductor light emitting element. Further, in FIG. 3, the waveguide loss is shown by a solid line, the vertical transverse mode confinement coefficient is shown by a dashed line, and the effective refractive index difference (ΔN) is shown by a broken line.

As shown in FIG. 3, the relationship between X1 and X2 in which ΔN is 2.5 × 10 ^-3 or more is such that X1 ≦ 0.1 and X2 ≦ 0.07.
(Equation 2) X1-X2 ≧ 0.02
, That is, the region on the right side of the straight line AB in FIG.

To summarize the above, for the semiconductor light emitting device shown in FIG. 1, in order to reduce the electrical resistance of the semiconductor light emitting device while having a ΔN of 2.5 × 10 ^-3 or more and obtaining the effect of increasing the light confinement coefficient in the vertical direction. Is
(Equation 2) X1-X2 ≧ 0.02
(Equation 3) X1 ≤ 0.1
(Equation 4) 0.03 ≤ X2 ≤ 0.07
Is required.

(2-8) Examination of Layer Thickness of Conductive Oxide Layer 18 Next, when M2 was changed in order to investigate the effect of the conductive oxide layer 18 and the condition of the layer thickness of the conductive oxide layer 18. The characteristics of the semiconductor light emitting device will be described.

The characteristics of the semiconductor light emitting device when the thickness of the conductive oxide layer 18 is changed to 0.17 μm, W is 6 μm, and M2 is 0.2 μm to 0.6 μm are shown in FIGS. 4A to 4E. Further, as a comparison, when there is no conductive oxide layer 18, that is, when the semiconductor light emitting device in which the conductive oxide layer 18 is removed from the semiconductor light emitting device shown in FIG. 1 is changed to 0.2 μm to 0.6 μm as M2. The characteristics of the semiconductor light emitting device shown in FIG. 5A to 5E are shown in FIGS. 5A to 5E. Table 1 shows the relationship between the values of FIGS. 4A to 4E and 5A to 5E and the values of M2 and the presence or absence of the conductive oxide layer 18.

In FIGS. 4A to 4E and 5A to 5E, 1%, 1.1%, 1.2%, 1.3%, and 1.4% are vertical and transverse mode confinement coefficients. , 1.5 × 10 ^-3 , 2 × 10 ^-3 , 2.5 × 10 ^-3 , 3 × 10 ^-3, etc. are ΔN. Moreover, the ^{curve cm -1} are assigned as ^{6 cm -1} and 10 cm ^-1 is a curve representing the waveguide loss in the semiconductor light emitting element.

Further, in FIGS. 4 and 5, the waveguide loss is shown by a solid line, the vertical transverse mode confinement coefficient is shown by a chain line, and the effective refractive index difference (ΔN) is shown by a broken line. Further, the regions (hatched regions) shown by diagonal lines in these figures satisfy (Equation 2) to (Equation 4), have a light confinement coefficient of 1% or more, and ΔN of 2.5 × 10 ^-3 or more. Indicates the area of.

As shown in FIGS. 4A to 4E, when M2 is 0.3 μm or more, (Equation 1) to (Equation 3) are satisfied, the vertical-transverse mode confinement coefficient is 1% or more, and ΔN is 2.5 × 10. ^It can be seen that there are ^-3 or more regions. Further, it can be seen that as M2 is larger, ΔN in the region satisfying (Equation 1) to (Equation 3) becomes larger, while the waveguide loss becomes smaller. When M2 is 0.8 μm or more, the ridge height H becomes high, and the strain generated in the active layer and the resistance of the element become large. In order not to increase the series resistance of the semiconductor light emitting device, M2 ≦ 0.6 μm may be set.

Therefore, from the results shown in FIGS. 2 and 4A to 4E, the occurrence of strain in the active layers on both sides of the lower end of the ridge is suppressed, the light confinement coefficient is 1% or more, and ΔN is 2.5 × 10 ^-3 or more. It can be seen that in order to obtain the above, it is sufficient that (Equation 1) to (Equation 3) are satisfied and M2 is 0.3 μm or more and 0.6 μm or less. In this case, it can be seen that the maximum waveguide loss is 12.5 cm ^-1 .

(2-9) Examination of Effect of Conductive Oxide Layer 18 Next, the effect of the conductive oxide layer 18 will be examined. In FIGS. 5A to 5E, in the region satisfying (Equation 2) to (Equation 4), the optical confinement coefficient is 1% or more, ΔN is 2.5 × 10 ^-3 or more, and the waveguide loss is 12.5 cm ^-1. The following range is shown in the hatch area. This region of the semiconductor light emitting device without the conductive oxide layer 18 is much smaller than the region shown in FIGS. 4A to 4E of the semiconductor light emitting device having the conductive oxide layer 18. This is because when ITO is used for the conductive oxide layer 18, the refractive index is as small as 2.02, so that the light distribution in the vertical direction is rapidly attenuated by the conductive oxide layer 18, and the p-type contact layer. This is because the ratio of the light distribution in 17 becomes small and the waveguide loss is reduced. This effect is greater as M2 is smaller, and when comparing FIGS. 4D and 5D, FIGS. 4C and 5C, and FIGS. 4B and 5B, the waveguide loss is relatively small even if M2 is the same. I understand. By providing the conductive oxide layer 18 in this way, it is possible to simultaneously realize a light confinement coefficient of 1% or more, a ΔN of 2.5 × 10 ^-3 or more, and a waveguide loss of 12.5 cm ^-1 or less. It will be possible. As a result, it is possible to realize high output characteristics that do not cause thermal saturation even during high-temperature operation. Further, since the strain in the active layers 14 on both sides of the lower end of the ridge 23 is small, not only the in-plane distribution of the band gap in the active layer 14 can be reduced, but also the occurrence of lattice defects in the active layer 14 can be suppressed. Therefore, it is possible to realize a highly reliable nitride laser in the 530 nm band that can operate at high output for a long period of time.

In particular, even in a region where M2 is 0.4 μm or less, a light confinement coefficient of 1% or more, ΔN of 2.5 × 10 ^-3 or more, and a low waveguide loss of 12.5 cm ^-1 or less can be realized at the same time. It is possible to reduce the strain in the active layers on both sides of the lower end of the ridge 23. As a result, the electrical resistance of the semiconductor light emitting device is further reduced. Further, since the occurrence of lattice defects in the active layer 14 can be further suppressed, a highly reliable semiconductor laser device capable of high output operation for a long period of time can be obtained.

(2-10) Layer Thickness of Conductive Oxide Layer 18 Further, the minimum thickness of the conductive oxide layer 18 required when ITO is used as the conductive oxide layer 18 will be described. 6A and 6B show the examination results of the waveguide loss and ΔN when the film thickness of ITO is changed in the semiconductor light emitting device of the present embodiment. In both FIGS. 6A and 6B, the horizontal axis represents the thickness of the conductive oxide layer 18, the vertical axis represents the waveguide loss in FIG. 6A, and ΔN in FIG. 6B. As shown in FIGS. 6A and 6B, it can be seen that as the thickness of the conductive oxide layer 18 is increased from 0 μm to 0.15 μm, the waveguide loss decreases, while ΔN increases. That is, by forming the conductive oxide layer 18 having a thickness of 0.15 μm or more on the p-type contact layer 17, not only the effect of reducing the waveguide loss but also ΔN is increased, and the higher order of the second order or higher is obtained. It can be seen that it has the effect of stabilizing the transverse mode oscillation.

It can be seen that when the thickness of the ITO film is 0.15 μm or more, the waveguide loss, ΔN, and the optical confinement coefficient are all substantially constant. Therefore, it can be seen that in the structure in which ITO is used as the conductive oxide layer 18, the thickness of the conductive oxide film layer may be 0.15 μm or more. If the ITO film is made too thick, the electric resistance of the semiconductor light emitting device may increase due to the electric resistance of the ITO film. Therefore, the thickness of the ITO film is preferably 0.3 μm or less.

(2-11) Summary A conductive oxide layer 18 having a refractive index smaller than that of AlGaN having a refractive index of 2.36 having an Al composition of 0.1 is formed on the p-type contact layer 17, and is a layer of the second clad layer 16. The thickness (M2) was set from 0.3 μm to 0.6 μm, and a structure satisfying (Equation 2) to (Equation 4) was examined. When the stripe width W is 5 μm or more and the higher-order transverse mode is not cut off, the above structure is derived even if the height of the ridge 23 is lowered as compared with the structure without the conductive oxide layer 18. Waveguide loss is reduced. It can be seen that stable high-order transverse mode oscillation of the second or higher order can be realized by the effect of increasing ΔN, and distortion in the region near both sides of the lower end of the ridge due to low ridge can be reduced.

The reduction of strain leads to the prevention of a decrease in ΔN. As a result, kink suppression in the current-light output characteristic, increase in slope efficiency, and improvement in the heat-saturated light output level during high-temperature operation are realized. Not only that, the in-plane strain of the active layer 14 directly under the ridge 23 is reduced, the variation in the bandgap energy of the active layer 14 can be suppressed, the decrease in the luminous efficiency of the semiconductor light emitting device and the growth of lattice defects are suppressed. , It is possible to improve long-term operation reliability. Further, if the thickness (M2) of the second clad layer 16 is 0.3 μm or more and 0.5 μm or less, the electric resistance of the semiconductor light emitting element can be reduced, so that further high temperature and high output operating characteristics can be obtained. preferable.

(3) Example of Semiconductor Light Emitting Element of the Present Embodiment Next, an example of the semiconductor light emitting device of the present embodiment examined above will be briefly described.

In the semiconductor light emitting device according to the present embodiment, X1 is 0.09, X2 is 0.05, and M2 is 0.4 μm. Table 2 summarizes the layer structure of the semiconductor light emitting device of this embodiment. In Table 2, the refractive index is a value with respect to the emission wavelength of 530 nm.

In the semiconductor light emitting device shown in Table 2 above, the waveguide loss was 8.0 cm ^-1 , the optical confinement coefficient was 1.4%, and ΔN was 3.6 × 10 ^-3 . The emission wavelength was 530 nm, and green laser oscillation was obtained.

(Second Embodiment)
(1) Tapered Stripe Structure The semiconductor light emitting device according to the first embodiment is a semiconductor laser device having a stripe structure when the two side walls of the ridge 23 are parallel to the direction of the resonator when viewed from above the substrate 11. Is.

The semiconductor light emitting device according to the second embodiment of the present invention is a semiconductor light emitting device having a so-called tapered stripe structure. The laminated structure of each semiconductor layer and the conductive oxide layer 18 constituting the semiconductor light emitting device, and the structure of the electrodes are the same as those in the first embodiment. Further, the end face reflectance is the same as that of the first embodiment.

Here, as shown in FIG. 7, the angle formed by the direction along the ridge side wall and the direction of the resonator is θ. This angle θ is the taper angle. In the semiconductor laser device having a striped structure having a taper angle θ of 0 ° described in the first embodiment, the light density in the active layer in the waveguide on the front end face side having low end face reflectance is increased. Therefore, the number of electrons and holes injected into the active layer 14 on the front end face side increases due to stimulated emission, and the operating carrier density of the active layer 14 on the front end face side increases. Spatial Hole Burning (SHB for short) occurs. Here, as the taper angle θ is increased, the ridge width on the front end surface side becomes larger, so that the width of the light distribution in the horizontal and horizontal directions perpendicular to the resonator direction becomes wider and the light density decreases. Therefore, as the taper angle θ increases, the number of electrons and holes consumed per unit time on the front end surface side decreases. On the other hand, on the rear end face side, as the taper angle increases, the width of the light distribution in the horizontal and horizontal directions narrows and the light density increases, so the number of electrons and holes consumed per unit time on the rear end face side increases. Increase. As a result, if the taper angle is made too large, the operating carrier density in the active layer 14 on the rear end surface side becomes small, and SHB is generated. When the degree of SHB increases, electrons and holes are thermally excited in the active layer 14 on the side where the operating carrier concentration in the active layer 14 is large, and the active layer leaks from the active layer to the first clad layer 12 or the second clad layer 16. Carriers (carrier overflow) increase and the thermal saturation level of the light output decreases.

Further, when SHB occurs in the resonator direction, the wavelength at which the maximum amplification gain is obtained varies inside the active layer 14, leading to an increase in the oscillation threshold current value. When the oscillation threshold current value increases, carrier overflow during high-temperature operation increases, leading to deterioration of temperature characteristics. Further, if the taper angle θ is large, propagation loss occurs in the waveguide light propagating in the waveguide. Therefore, the taper angle θ is preferably set within the range of 0.1 ° ± 0.05 ° (0.05 ° or more, 0.15 ° or less). In this case, the generation of SHB is suppressed in the active layer 14 under the ridge 23, and the occurrence of carrier overflow is suppressed. Further, the uniformity of the operating carrier concentration is improved, and the wavelength at which the maximum amplification gain is obtained in the active layer 14 becomes uniform, so that the slope efficiency and the temperature characteristics are improved, and further high-temperature and high-output operation becomes possible.

Further, when the ridge width Wr on the rear end surface side becomes narrower, higher-order horizontal transverse modes cannot be guided and cut off, so that the number of horizontal transverse modes that can be oscillated decreases. When the higher-order transverse mode is not cut off and the order of the higher-order transverse mode that can oscillate at the same time becomes smaller, the optical distribution shape in the resonator direction is greatly deformed when the transverse modes are coupled during laser oscillation. Large non-linearity occurs in the current-optical output characteristics, and the temperature characteristics deteriorate. In order to prevent this, Wr needs to have a width in which a higher-order transverse mode of at least a third-order mode or higher is guided. In the case of a wide stripe width in which the higher-order transverse mode is not cut off, it is effective that the third-order mode or higher can be guided in the current-optical output characteristic in order to prevent large non-linearity due to kink. For example, in the case of a waveguide that can be guided up to the third-order transverse mode, the effective refractive index of the third-order mode, which is the highest order that can be guided, is almost the same as the effective refractive index of the region outside the ridge, so that it is lateral On the other hand, the light distribution has a large spread with a large base outside the ridge. In this case, since the third-order transverse mode exudes a large amount of light distribution to the outside of the ridge, a large amount of current injection is required to oscillate the laser. Therefore, the oscillation threshold current value in the third-order mode is relatively higher than that in the basic (0th-order) transverse mode, the primary transverse mode, and the secondary transverse mode, and the third-order mode can be guided. However, the actual laser oscillation is in three modes from the basic transverse mode to the secondary transverse mode. If the laser oscillates in the horizontal modes of at least three orders at the same time, the interaction due to the interference between the horizontal modes can be made relatively small, and even if the horizontal modes interfere with each other and are coupled, the change in the light distribution shape can be made small. Therefore, a kink occurs in the current-light output characteristic, and the non-linearity can be reduced, so that the light output can be stabilized.

If a waveguide having such a tapered shape is formed for the semiconductor light emitting device according to the present embodiment, the height of the ridge 23 can be lowered, so that the electric resistance of the semiconductor light emitting device is further lowered, and the high temperature and high output are obtained. It is advantageous for operation. Further, even if the height of the ridge 23 is lowered, the use of the conductive oxide layer 18 has the effect of increasing ΔN as shown in FIG. 6B. Therefore, even if the Wr is narrowed, the third-order or higher-order transverse mode is not cut off, so that it is possible to prevent the occurrence of a kink having a large non-linearity in the current-optical output. In the case of this embodiment, Wr may be at least 4 μm. The effect of increasing ΔN is more effective as the exudation of the light distribution to the conductive oxide layer 18 is larger, and therefore, it is more advantageous as the thickness of the second clad layer (M2) is smaller. If the waveguide shape is tapered in the range of M2 of 0.3 μm or more and 0.5 μm or less, the series resistance of the element is further reduced, the slope efficiency and temperature characteristics are improved, and the current-light output characteristics are improved. Further high temperature and high output operation is possible while suppressing the generation of kink with large non-linearity.

(2) An Example of a Semiconductor Light Emitting Element of the Present Embodiment and Its Characteristics In the semiconductor light emitting device according to the second embodiment of the present invention, X1 is 0.05, X2 is 0.09, and the second clad layer thickness is 0. The resonator length is .4 μm and the resonator length is 600 μm. Table 2 shows the parameters of each layer of the semiconductor light emitting device. The width of the ridge 23 is 6 μm on the rear end surface side and widens toward the front end surface side. The taper angle θ on the side surface of the ridge 23 is θ = 0.1 °.

The waveguide loss of this semiconductor light emitting device is 7.9 cm ^-1 , the optical confinement coefficient is 1.45%, and ΔN is 3.7 × 10 ^-3 .

The current-light output characteristics of the semiconductor light emitting device according to the second embodiment of the present invention are shown in FIG. 8A. Further, a comparative example of the current-light output characteristics of a semiconductor light emitting device having a structure in which the conductive oxide layer 18 having a thickness of 0.17 μm is eliminated from the structure of the semiconductor light emitting device according to the second embodiment of the present invention. Is shown in FIG. 8B. The waveguide loss of the semiconductor light emitting device according to this comparative example is 13.5 cm ^-1 , the optical confinement coefficient is 1.4%, and ΔN is 3.3 × 10 ^-3 . Regarding the element temperature of the semiconductor light emitting device, the case of 25 ° C. and the case of 50 ° C. were examined.

Comparing FIG. 8A and FIG. 8B, it can be seen that the slope efficiency is improved by 1.4 times by using the conductive oxide layer 18. It is considered that the high slope efficiency is improved because the absorption loss at the metal electrode is reduced even if the film thickness of the second clad layer 16 is reduced to 0.4 μm by using the conductive oxide layer 18. Further, it can be seen that the use of the conductive oxide layer 18 also increases ΔN and has a function of increasing the confinement rate in the transverse mode.

That is, the semiconductor light emitting device of the present embodiment using the conductive oxide layer 18 has improved slope efficiency and improved the confinement rate in the lateral mode as compared with the semiconductor light emitting device not using the conductive oxide layer 18. You can do it.

(3) Deformation Example of Tapered Stripe Structure In the second embodiment, the shape of the tapered stripe structure seen from above the substrate 11 is not limited to the shape shown in FIG. 7. For example, as shown in FIG. 9A, a semiconductor light emitting device having a striped shape with a taper angle of 0 ° in the vicinity of the front end surface and the vicinity of the rear end surface and having a taper angle of not 0 ° between the front end surface and the rear end surface is also described above. A similar effect can be obtained.

Further, the rate of change of the ridge width with respect to the resonator direction does not have to be constant. For example, as shown in FIGS. 9B and 9C, it may be a curved tapered stripe.

Further, in the striped structure of the ridge 23 including FIGS. 7 and 9A to 9C, it is more preferable that the maximum value of the angle formed by the ridge 23 in the resonator normal direction is 0.05 ° or more and 0.15 ° or less. ..

(Other embodiments)
Indium tin oxide (ITO) is used for the conductive oxide layer 18 used in the semiconductor light emitting device shown in the first embodiment and the second embodiment, but the present invention is not limited to this. For example, in the case of a conductive oxide having a refractive index smaller than the refractive index of 2.36 of AlGaN having an Al composition of 0.1 in the wavelength band of 530 nm, the effect of reducing the waveguide loss by lowering the ridge height (H) It is possible to obtain. Specifically, it may be a conductive oxide composed of an oxide containing at least one of indium (In), zinc (Zn), tin (Sn), gallium (Ga), and magnesium (Mg). Further, for example, it may be a conductive oxide such as In ₂ O ₃ , SnO ₂ , ZnO, Zn ₂ SnO ₄ , In ₂ O _3- ZnO, MgInO ₄ , or Ga ₂ O ₃ .

Further, instead of the conductive oxide, a conductive nitride such as TiN or ZrN can be used. In the conductive oxide layer 18 having a low refractive index, the light distribution in the vertical direction is rapidly attenuated, so that the influence of the absorption loss in the p-type electrode 22 can be reduced.

Table 3 lists examples of conductive oxides, conductive nitrides, and conductive materials that can be used in the above embodiments and modifications.

Although SiO ₂ having a refractive index smaller than that of the second clad layer 16 is used as the current block layer 20 in the above embodiment, it is not limited to SiO ₂ and is composed of another insulator having a refractive index smaller than that of the second clad layer 16. Layers such as Al ₂ O ₃ and SiN can be used.

Further, in the semiconductor light emitting device according to the above embodiment, the Al composition of the first clad layer 12 is X1, but the first clad layer can be a superlattice layer composed of AlGaN and GaN. In this case, X1 may be the average Al composition in the superlattice layer. That is, when the superlattice layer is formed of an AlGaN layer having a thickness of 3 nm and an Al composition of 0.2 and a superlattice layer made of GaN having a thickness of 3 nm, X1 is 0.1. Further, when the superlattice layer is formed of an AlGaN layer having a thickness of 4 nm and an Al composition of 0.2 and a superlattice layer made of GaN having a thickness of 6 nm, X1 is 0.08.

Further, in the semiconductor light emitting device according to the above embodiment, the Al composition of the second clad layer 16 is X2, but the second clad layer may be a superlattice layer composed of AlGaN and GaN. In this case, X2 may be the average Al composition in the superlattice layer. That is, when the superlattice layer is formed of an AlGaN layer having a thickness of 3 nm and an Al composition of 0.1 and a superlattice layer made of GaN having a thickness of 3 nm, X2 is 0.05.

Further, in the semiconductor light emitting device according to the above embodiment, the light emitting wavelength is 530 nm, but the light emitting wavelength can be changed by changing the composition or layer structure of the active layer 14. The present invention can be applied to a semiconductor light emitting device from a near-ultraviolet region having an emission wavelength of about 370 nm to a red region having a wavelength of about 600 nm.

The semiconductor light emitting device of the present invention can achieve both reduction of series resistance of the device, current-light output characteristics with excellent linearity due to stable high-order lateral mode oscillation, reduction of waveguide loss, and light confinement in the vertical direction. It has the effect of being able to be used, and is useful for in-vehicle head lamps, projector light sources, and the like.

11 Substrate 12 1st clad layer 13 Optical guide layer 14 Active layer 15 Electronic barrier layer 16 2nd clad layer 17 p-type contact layer 18 Conductive oxide layer 20 Current block layer 21 n-type electrode 22 p-type electrode 23 Ridge

Claims (10)

With the board
A monoconductive first clad layer made of a group III nitride semiconductor having Al formed on the substrate, and
An active layer made of a group III nitride semiconductor formed on the first clad layer and
A reverse conductive second clad layer made of a group III nitride semiconductor having Al formed on the active layer, and
The conductive compound layer formed on the second clad layer and
A ridge structure having the conductive compound as the upper surface and the second clad layer as the lower surface.
Have,
The Al composition of the second clad layer is smaller than the Al composition of the first clad layer.
The refractive index of the conductive compound layer is smaller than the refractive index of the second clad layer.
Ri the ridge inside thickness der or more and 0.4μm or less 0.3μm of the second cladding layer,
A semiconductor light emitting device, wherein the conductive compound layer is made of an oxide containing indium and tin, and the thickness of the conductive compound layer is 0.15 μm or more and 0.3 μm or less . The semiconductor light emitting device according to claim 1, wherein the ridge structure has a width for propagating a second-order or higher-order transverse mode. It has a waveguide formed by a front end surface and a rear end surface, the ridge structure is formed between the front end surface and the rear end surface, is included in the side surface of the ridge structure, and is said from the front end surface to the said. The semiconductor light emitting device according to claim 1 or 2, wherein the direction toward the rear end surface and the direction of the waveguide form a predetermined angle. When the reflectance of the front end surface is Rf, the reflectance of the rear end surface is Rr, the width of the ridge on the front end surface is Wf, and the width of the ridge on the rear end surface is Wr, Rf <Rr and Wf> Wr. The semiconductor light emitting device according to claim 3, characterized in that. The semiconductor according to claim 3 or 4, wherein the angle formed by the direction from the front end surface to the rear end surface and the direction of the waveguide is 0.05 ° or more and 0.15 ° or less. Light emitting element. The first clad layer is made of Al _X1 Ga _1-X1 N, the second clad layer is made of Al _X2 Ga _1-X2 N, X1-X2 ≧ 0.02, X1 ≦ 0.1, 0. The semiconductor light emitting element according to any one of claims 1 to 5 , wherein the relationship of 03 ≦ X2 ≦ 0.07 is satisfied. The semiconductor light emitting device according to any one of claims 1 to 6 , wherein the layer thickness of the second clad layer on the outside of the ridge structure is larger than 0 nm and 50 nm or less. The semiconductor light emitting device according to any one of claims 1 to 7 , wherein a current block layer having a refractive index smaller than that of the second clad layer is formed on the side surface of the ridge structure. The semiconductor light emitting device according to claim 1, further comprising a contact layer containing a group III nitride semiconductor between the conductive compound layer and the second clad layer. The semiconductor light emitting device according to claim 1, further comprising an electron barrier layer containing a group III nitride semiconductor having AI between the second clad layer and the active layer.

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