JP2000277854A - Semiconductor laser - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a semiconductor laser with superior effect of optical con finement or optical absorption by forming a current block layer with sufficient thickness, along with a large composition of Al and In, while crystallinity deteri oration such as cracks and the like is restrained. SOLUTION: A semiconductor laser has an InGaN active layer 7. A current block layer 12 as a constriction for a current carried in the active layer 7 has a superlattice structure composed of a first GaN layer 12a and a second AlGaN layer 12b, each laminated alternately. As a result, the current block layer 12 with a desired thickness can be formed, while crystallinity deterioration such as cracks and the like is restrained, and the composition of Al and In is made large. In this way, a semiconductor laser with superior effect in optical confinement or optical absorption is obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a nitride-based semiconductor laser.

[0002]

2. Description of the Related Art In recent years, research and development of nitride semiconductor lasers have been conducted as light sources for recording or reproduction used in high-density, large-capacity optical disk systems.

In this nitride-based semiconductor laser,
In order to be used as a light source in an optical disk system, transverse mode control is required, as is the case with semiconductor lasers that emit infrared light or red light. A refractive index guided semiconductor laser suitable for this transverse mode control has been proposed. Have been.

In a nitride-based semiconductor laser, in order to realize a refractive index waveguide structure, a current blocking layer for narrowing a current flowing through an active layer is formed by, for example, a mixed crystal ratio of AlN (hereinafter, referred to as an Al composition). There are two methods: a real refractive index guide structure in which the band gap is larger than the Al composition of the cladding layer, and a loss guide structure in which the band gap of the current block layer is smaller than the band gap of the active layer.

However, in order to form a semiconductor laser having a loss guide structure, InGaN having a mixed crystal ratio of InN (hereinafter referred to as In composition) larger than that of the active layer can sufficiently block current and sufficiently absorb light. When the current blocking layer is formed by growing the layer to a thickness as large as possible (for example, about 0.5 μm or more), the current blocking layer exceeds the critical thickness, and there is a problem that the crystallinity of the grown layer is significantly reduced.

In order to form a real refractive index guide structure, AlGaN having an Al composition larger than that of the cladding layer can sufficiently block current and can sufficiently confine light (for example, a thickness of about 0.5 μm or more). In the case where the current blocking layer is formed by growing the current blocking layer, the cladding layer containing Al and the current blocking layer become brittle, cracks are generated, and the crystallinity of the grown layer is significantly reduced.

[0007]

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned drawbacks of the prior art, and is intended to reduce the crystallinity of a current blocking layer having a large Al composition, In composition, etc. It is an object of the present invention to provide a semiconductor laser which can be formed to a thickness that can sufficiently block the laser beam.

[0008]

According to the present invention, there is provided a semiconductor laser having an active layer made of a nitride-based semiconductor material, wherein a current blocking layer for narrowing a current flowing through the active layer has a plurality of layers. Characterized by a superlattice structure consisting of

In the semiconductor laser having such a configuration, since the thickness of each layer of the superlattice structure constituting the current blocking layer is reduced, the distortion between the underlying layer such as the cladding layer and the current blocking layer is reduced. Is relaxed.

Further, in the semiconductor laser according to the present invention, the current blocking layer is made of Al _x Ga ₁ -xN (where 0 ≦ X ≦ 1) and the superlattice structure is made up of a plurality of layers having different values of X. It is characterized by being.

In this case, even if the average Al composition in the entire current block layer is increased, or the thickness of the current block layer is increased, a decrease in the crystallinity of the current block layer can be suppressed. For this reason, for example, A
It is possible to further increase the l-composition and to realize a semiconductor laser having a real refractive index structure having an excellent effect of confining light in a waveguide.

For example, when the current blocking layer has a superlattice structure in which a first layer made of GaN and a second layer made of AlGaN are alternately and repeatedly laminated, the second layer containing Al is an individual layer. Since the thickness of the layer may be small, the distortion based on the difference in the coefficient of thermal expansion between the current blocking layer and the underlying layer such as the cladding layer is reduced.

In this case, the second layer must have a thickness of about 200 to 500 ° when the Al composition ratio is 0.5 or less, and when the Al composition ratio is 0.75 or less, The thickness needs to be about 100 to 200 °, and when the Al composition ratio is 1 or less, the layer thickness needs to be about 10 to 100 °. The thickness of the first layer can be about 10 to 1000 ° regardless of the thickness of the second layer and the Al composition ratio, but is preferably about the same as the thickness of the second layer.

Further, the current blocking layer is made of a first layer made of AlGaN, and an Al composition having a larger Al composition than the first layer.
In the case of a superlattice structure in which second layers made of GaN are alternately and repeatedly laminated, the second layer having a large Al composition may have a small layer thickness of each layer. The distortion due to the difference in the coefficient of thermal expansion between the base layer and the underlying layer is reduced.

Further, according to the present invention, in the above-mentioned semiconductor laser in which the current blocking layer is made of Al _x Ga ₁ -xN, among the layers constituting the superlattice structure of the current blocking layer, A
A layer having a large l composition has a lower carrier concentration than a layer having a small Al composition or a layer containing no Al.

In this case, the band barrier in the current blocking layer is increased, and the current blocking function in the current blocking layer is improved.

Further, in the semiconductor laser according to the present invention, the current blocking layer is made of In _Y Ga ₁ -YN (where 0 ≦ Y ≦ 1), and the superlattice structure is made up of a plurality of layers having different values of Y. It is characterized by being.

In this case, even if the average In composition in the entire current block layer is increased, or the thickness of the current block layer is increased, a decrease in crystallinity of the current block layer can be suppressed. For this reason, for example, I
The n composition can be further increased, and a semiconductor laser having a loss guide structure excellent in light absorption in the current blocking layer can be realized.

For example, when the current blocking layer has a superlattice structure in which a first layer made of GaN and a second layer made of InGaN are alternately and repeatedly laminated, the individual layers of the second layer containing In Since the thickness of the layer may be small, distortion based on the difference in lattice constant between the current blocking layer and the underlying layer such as the cladding layer is reduced.

In this case, when the composition ratio of In is 0.4 or less, the thickness of the second layer needs to be about 100 to 300 °, and when the composition ratio of In is 0.6 or less, The thickness is 1
It needs to be about 0 to 100 °. Also, the first layer is
10 to 1000 regardless of the thickness of the second layer and the In composition ratio
Although it is possible to make it about Å, it is preferably about the same as the thickness of the second layer.

Further, the current blocking layer has a first layer made of InGaN, and an In composition having a larger In composition than the first layer.
In the case of a superlattice structure in which second layers made of GaN are alternately and repeatedly laminated, the thickness of each of the second layers having a large In composition may be small, and thus the current blocking layer and the cladding layer may be used. Distortion due to the difference in lattice constant between the underlying layer and the underlying layer is reduced.

Further, according to the present invention, the current blocking layer is preferably made of In.
_{In the} semiconductor laser composed of YGa ₁ -YN, a layer having a large In composition among layers constituting the superlattice structure of the current blocking layer has a higher carrier than a layer having a small In composition or a layer not containing In. It is characterized by high concentration.

In this case, the band barrier in the current block layer is increased, and the current constriction action in the current block layer is improved.

Further, in the semiconductor laser according to the present invention, a first clad layer, an active layer, and a second clad layer made of a nitride-based semiconductor material are sequentially formed, and the second clad layer is formed on the active layer.
In a semiconductor laser in which a current blocking layer for narrowing a current flowing through the active layer is formed on the cladding layer side, the current blocking layer is a layer in which a first current blocking layer and a second current blocking layer are sequentially formed, The first current blocking layer has a superlattice structure including an i-type semiconductor layer.

In the semiconductor laser having such a configuration, the first
Since the thickness of each layer of the superlattice structure constituting the current blocking layer is reduced, the strain between the second cladding layer and the current blocking layer is reduced. In addition, since a high-resistance first current blocking layer exists between the second current blocking layer and the second cladding layer, when a forward voltage is applied, the second current blocking layer and the second cladding layer may be in contact with each other. The space is depleted, the element capacitance is reduced, and as a result, the rise and fall of the light output become faster.

Further, in the semiconductor laser according to the present invention,
The current blocking layer is a layer having a semiconductor layer of a conductivity type different from that of the second cladding layer.

In this case, the function of blocking the current in the current blocking layer is enhanced in the above-described semiconductor laser having a fast rising and falling light output.

Further, the present invention is characterized in that the second current blocking layer has a superlattice structure composed of a plurality of layers.

In this case, even if the average Al composition or In composition in the entire second current block layer is increased, or the thickness of the current block layer is increased, the crystallinity of the second current block layer does not decrease. Can be suppressed. Thus, for example,
By increasing the Al composition further than the second cladding layer, by increasing the In composition further than the semiconductor laser having a real refractive index structure excellent in the light confinement effect in the waveguide or the second cladding layer, A semiconductor laser having a loss guide structure excellent in light absorption in the current blocking layer can be realized.

Further, in the semiconductor laser according to the present invention, the first current blocking layer is doped with at least one of Zn, Be, Ca and C.

In this case, the first current blocking layer has a thickness of 1.5
It becomes a layer having a sufficiently high resistance of Ω · cm or more.

In the semiconductor laser according to the present invention, the first current blocking layer is formed of i-type GaN or i-type In.
It has a superlattice structure in which a first layer made of GaN and a second layer made of i-type InGaN having an In composition larger than that of the first layer are alternately and repeatedly stacked.

In this case, even in a semiconductor laser having a current blocking layer containing In and having a small band gap, the device capacity can be sufficiently reduced, and as a result,
The current blocking effect can be enhanced, and the rise and fall of the light output can be accelerated.

Further, in the semiconductor laser according to the present invention, the first layer is in contact with the second clad layer.

As a result, the first bandgap having a large band gap can be obtained.
Since the layer is in contact with the second cladding layer, the band gap can be gradually reduced from the second cladding layer toward the current blocking layer. As a result, the rise and fall of the light output become faster.

[0036]

Embodiments of the present invention will be described below in detail with reference to the drawings.

FIG. 1 is a sectional view showing the structure of a semiconductor laser according to a first embodiment of the present invention.

The semiconductor laser of the first embodiment is a ridge waveguide type semiconductor laser, and undoped i-Al _{0.5 is formed} on the c-plane of the sapphire substrate 1 by MOCVD.
Ga _{0 .5} thickness 300Å consisting of N buffer layer 2, a thickness of 3μm consisting n-GaN of the i-GaN layer 3, Si-doped thick 2μm of undoped i-GaN n-
A GaN layer 4, a _0.1 μm thick n-crack prevention layer 5 made of Si-doped n-In _0.1 Ga _0.9 N, and a 0.7 μm thick n-made of Si-doped n-Al _0.10 Ga _0.90 N
A cladding layer 6, an active layer 7 having a multiple quantum well structure made of Si-doped n-InGaN, and Mg-doped p-Al
_A 0.7 μm thick p-cladding layer 8 made of _0.10 Ga _0.90 N and a 0.2 μm thick Mg-doped p-GaN
Are formed by a semiconductor wafer in which the p-cap layers 9 are sequentially laminated.

The active layer 7 is made of GaN and has a thickness of 0.1 mm.
In _0.03 Ga _0.97 N between a pair of 1 μm light guide layers.
Is a multiple quantum well structure in which barrier layers having a thickness of 60 ° and alternately well layers having a thickness of 30 ° made of In _0.13 Ga _0.87 N are formed.

The semiconductor wafer is removed to a predetermined depth of the p-cladding layer 8 by reactive ion etching or reactive ion beam etching to form a stripe-shaped ridge portion 10.
The electrode forming surface 11 is removed to a predetermined depth of the GaN layer 4.
Are formed. The ridge portion 1 of the p-cladding layer 8
The thickness of the flat portion other than 0 is set to perform the transverse mode control.
It is preferably from 0.05 to 0.4 μm.

A 0.5 μm-thick current blocking layer 12 having a superlattice structure, which will be described later, is formed in the etched portion on the p-cladding layer 8. 12, Mg-doped p-Ga
A p-contact layer 13 made of N and having a thickness of 0.2 μm is formed. A p-electrode 14 is formed on the upper surface of the p-contact layer 13, and an n-electrode 15 is formed on the electrode forming surface 11 of the n-cladding layer 4.

As shown in FIG. 2, the current blocking layer 12 has a first layer 12a made of Si-doped n-GaN and having a thickness of 250 ° and a small amount of undoped i-Al _0.30 Ga _0.70 N or Si. It has a superlattice structure in which second layers 12b each made of n-Al _0.30 Ga _0.70 N and having a thickness of 250 ° are alternately formed in ten layers.

The first layer 12a has a Si-doped carrier concentration of 3 × 10 ¹⁸ cm ⁻³ . When the second layer 12b is a layer doped with Si, the carrier concentration of the Si doping is 1 × 10 ¹⁷ cm ^{−3 which} is lower than that of the first layer 12a.
is there.

In the semiconductor laser of the first embodiment as described above, the current blocking layer 12 has the first layer 12 containing no Al.
a and a second layer 12b containing Al have a superlattice structure in which the layers are alternately and repeatedly laminated, and the second layer 12b containing an Al composition has a small individual layer thickness. The distortion based on the difference between the expansion coefficients is reduced. For this reason, the current blocking layer 12 can increase the Al composition and the thickness without lowering the crystallinity as compared with the case where the current blocking layer 12 is formed as a single layer.

In the current block layer 12, the first layer 12a containing no Al has a high carrier concentration, and the second layer 12b containing Al has a low carrier concentration. 3, the current blocking effect is improved.

As another example of the first embodiment, the current blocking layer 12 is made of Si-doped n-Al _0.05 Ga _0.95 N
The first layer 12a having a thickness of 250 ° and the second layer 12b having a thickness of 250 ° made of undoped i-Al _0.25 Ga _0.75 N or n-Al _0.25 Ga _0.75 N doped with a small amount of Si are alternately formed by 10. A superlattice structure formed layer by layer may be used.

This is an example in which the current blocking layer 12 is formed by a super lattice structure of the first layer 12a having a small Al composition and the second layer 12b having a large Al composition. Since the thickness of each of the two layers 12b is small, distortion due to a difference in thermal expansion coefficient between the two layers 12b and the p-clad layer 8 is reduced. Therefore, the current blocking layer 12
Can increase the Al composition and increase the thickness without lowering the crystallinity as compared with the case where a single layer is formed.

In the current blocking layer 12, the first layer 12a having a small Al composition has a high carrier concentration, and the second layer 12b having a large Al composition has a low carrier concentration. 3, the current blocking effect is improved.

As described above, in the semiconductor laser of the first embodiment, the current blocking layer 12 can have a large Al composition and a large thickness without deteriorating the crystallinity. Since the light is sufficiently confined and the current blocking effect is improved, the semiconductor laser has a real refractive index guide structure with good luminous efficiency.

As the semiconductor laser of the second embodiment of the present invention, the current blocking layer 12 is replaced with an undoped i-GaN or an undoped i-GaN, as shown in FIG. N-G lightly doped with Si
The first layer 12c having a thickness of 250 ° made of aN and the second layer 12c having a thickness of 250 ° made of n-In _0.3 Ga _0.7 N doped with Si.
A superlattice structure in which the layers 12d and the layers 12d are alternately formed every ten layers may be used.

The carrier concentration of Si-doped second layer 12d is 3 × 10 ¹⁸ cm ⁻³ . When the first layer 12c is a layer doped with Si, the carrier concentration of Si doping is 1 × 10 ¹⁷ cm ⁻³ which is lower than that of the second layer 12d.

In the semiconductor laser of the second embodiment as described above, the current blocking layer 12 has the first layer 12 containing no In.
a superlattice structure in which c and second layers 12d containing In are alternately and repeatedly laminated, and the second layer 12 containing In
Since d has a small individual layer thickness, the strain due to the difference in lattice constant from the p-cladding layer 8 is reduced. Therefore, as compared with the case where the current block layer 12 is formed as a single layer, the In composition can be increased and the thickness can be increased without lowering the crystallinity.

In the current blocking layer 12, the first layer 12c containing no In has a low carrier concentration, and the second layer 12d containing In has a high carrier concentration. As shown in FIG. 5, the current blocking effect is improved.

As another example of the second embodiment, the current blocking layer 12 is made of undoped i-In _0.05 Ga _0.95 N
Alternatively, n-In _0.05 Ga _0.95 N doped with a small amount of Si
A superlattice structure in which first layers 12c having a thickness of 250 ° made of Si and n-In _0.25 Ga _0.75 N doped with Si and having second layers 12d having a thickness of 250 ° are alternately formed by 10 layers may be used.

This is an example in which the current blocking layer 12 has a superlattice structure of the first layer 12c having a small In composition and the second layer 12d having a large In composition. In this case, the current blocking layer 12 also has a large In composition. Since the thickness of each of the two layers 12d is small, the distortion based on the difference in lattice constant between the two layers 12d and the p-clad layer 8 is reduced. Therefore, the current blocking layer 12
Compared with the case where a single layer is formed, the In composition can be increased and the thickness can be increased without lowering the crystallinity.

In the current blocking layer 12, the first layer 12c having a small In composition has a low carrier concentration, and the second layer 12d having a large In composition has a high carrier concentration. As shown in FIG. 5, the height is increased, and the current blocking effect is improved.

As described above, in the semiconductor laser according to the second embodiment, the current blocking layer 12 can have a large In composition and a large thickness without deteriorating crystallinity. At 12, the light is attenuated enough,
In addition, since the current blocking effect is improved, the semiconductor laser has a loss guide structure with good luminous efficiency.

In the first and second embodiments described above, the case where the present invention is applied to a ridge waveguide type semiconductor laser has been described. However, the present invention is not limited to such a structure, for example, as shown in FIG. Even in a semiconductor laser having a self-aligned structure, the current blocking layer may be configured in the same manner as in the above-described embodiment.

In FIG. 6, reference numeral 21 denotes a sapphire substrate. On the c-plane of the sapphire substrate 21, a buffer layer 22 made of undoped i-Al _0.5 Ga _0.5 N having a thickness of 300 ° and a thickness of 2 μm is formed by MOCVD. Undoped i-GaN layer 23, 3 μm thick Si-doped n-Ga
An N layer 24; a _0.1 μm-thick crack preventing layer 25 made of Si-doped n-In _0.1 Ga _0.9 N;
A 0.7 μm thick n-cladding layer 26 made of -Al _0.1 Ga _0.9 N, a multiple quantum well structure active layer 27 made of Si-doped n-InGaN, and Mg-doped p-Al _0.1
A first p-cladding layer 28 of 0.2 μm in thickness of Ga _0.9 N, a current blocking layer 29 of 0.5 μm in thickness of a superlattice structure, and a 0.5 μm thickness of p-Al _0.1 Ga _0.9 N doped with Mg. Second p-clad layer 30, Mg-doped p
-P-contact layer 3 made of GaN and having a thickness of 0.2 μm
1 are sequentially stacked.
In the current block layer 29, the window 35 serving as a current path is removed by etching. The electrode formation surface 32 is formed on the semiconductor wafer by removing the n-GaN layer 24 to a predetermined depth by reactive ion etching or reactive ion beam etching. A p-electrode 33 is formed on the upper surface of the p-contact layer 31, and an n-
An n-electrode 34 is formed on the electrode forming surface 32 of the cladding layer 24.

The current blocking layer 29 is formed of a superlattice structure having the same structure as the above-mentioned ridge waveguide type current blocking layer 12, and has a real refractive index guide structure or a light guide structure with high luminous efficiency. Semiconductor laser.

Although the sapphire substrate is used as the substrate in the above-described embodiment, the substrate may be made of another material such as SiC, spinel, and GaN.

The semiconductor material of the current blocking layer may be a material having P or As as a group V element.

As a doping material for a layer constituting the superlattice structure of the current blocking layer, Ge may be used instead of Si.
Other elements may be used. Further, a high resistance current block layer may be formed by doping Zn or the like.

Next, a description will be given of a semiconductor laser according to a third embodiment of the present invention.

FIG. 7 is a sectional view showing the structure of the semiconductor laser according to the third embodiment. The same parts as those in FIG. 1 are denoted by the same reference numerals, and their description will be omitted.

In the semiconductor laser according to the third embodiment, the current blocking layer 12 includes an i-type first current blocking layer 121 formed from both side surfaces of the ridge portion 10 to the upper surface of the p-cladding layer 8. An n-type second current block layer 122 is formed on the first current block layer 121.

As shown in FIG. 8, the first current blocking layer 121 includes a first layer 121a having a thickness of 250 ° made of i-GaN doped with an impurity and an i-GaN doped impurity.
A high-resistance superlattice structure in which second layers 121b each having a thickness of 250 ° and made of -InGaN are alternately formed in ten layers. The impurities doped into the first layer 121a and the second layer 121b include Zn (zinc), Be (beryllium),
At least one of Ca (calcium) and C (carbon) is used, and by doping this impurity, the first layer 121a and the second layer 121b become i-type semiconductor layers,
It becomes a high resistance layer. The first layer 121a is in contact with the p-clad layer 8.

Further, the second current blocking layer 122 corresponds to FIG.
As shown in FIG. 1, a first layer having a thickness of 250 ° made of undoped i-GaN or n-GaN lightly doped with Si.
It has a superlattice structure in which five layers are alternately formed by layers 122a and 250 ° -thick second layers 122b made of Si-doped n-In _0.3 Ga _0.7 N. The p-contact layer 13 is formed on the second current block layer 122.

In the semiconductor laser according to the third embodiment, the first current block layer 121 and the second current block layer 122 constituting the current block layer 12 each have a superlattice structure composed of thin layers. , Current block layer 1
The distortion generated based on the difference between the lattice constants of p-cladding layer 2 and p-cladding layer 8 is reduced. For this reason, in the first current block layer 121 and the second current block layer 122, the composition ratio of In can be increased, and the overall film thickness can be increased.

Since the high-resistance first current block layer 121 is formed between the p-type p-clad layer 8 and the n-type second current block layer 122, the p-electrode 14 and the n-type
When a voltage is applied between the second current blocking layer 122 and the p-cladding layer 8 when a voltage is applied in the forward direction to the electrode 15, the depletion between the second current blocking layer 122 and the p-cladding layer 8 is sufficiently reduced, and the element capacitance is sufficiently reduced. For this reason,
The function of blocking the current in the current blocking layer 12 is enhanced, and the rise and fall of the optical output when the element is pulse-driven is increased. In particular, in the third embodiment, the first layer 121 of the first current blocking layer 121 in contact with the p-cladding layer 8 is used.
Since a does not contain In and has a larger band gap than the other second layer 121b, the rise and fall of the optical output become faster.

In the above-described third embodiment, the first layer 121a of the first current blocking layer 121 and the first layer 122a of the second current blocking layer 122 are formed of GaN. layer containing in at least one layer of 122a, for example, may be formed by in _0.05 Ga _0.95 N.

In such a configuration, as in the third embodiment described above, the function of blocking the current in the current blocking layer 12 is enhanced, and the rise and fall of the optical output when the element is pulse-driven are fast. Become. In particular, the first layer 121a of the first current blocking layer 121 in contact with the p-clad layer 8
However, the composition ratio of In is smaller than that of the other second layer 121b,
In the case of a layer having a large band gap, the rise and fall of the light output become faster.

As described above, in the semiconductor laser according to the third embodiment, the current blocking layer 12 can have a large In composition and a large thickness without deteriorating crystallinity. At 12, the light is attenuated enough,
In addition, since the current blocking effect is improved and the element capacitance is reduced, a semiconductor laser having a light guide structure with good luminous efficiency and high-speed operation can be obtained.

In the third embodiment described above, the case where the present invention is applied to a ridge waveguide type semiconductor laser has been described. However, the present invention is not limited to such a structure, for example, a self-aligned structure as shown in FIG. In semiconductor lasers with a structure,
The current blocking layer may be configured in the same manner as in the above-described embodiment.

Although the sapphire substrate is used as the substrate in the third embodiment, it may be made of other materials such as SiC, spinel, and GaN.

The semiconductor material of the current blocking layer may be a material having P or As as a group V element.

Further, as a doping material for the layer constituting the superlattice structure of the second current blocking layer, another element such as Ge may be used instead of Si. Further, a high resistance current block layer may be formed by doping Zn or the like.

In the embodiment of the present invention, n-type, p-type
The type and i-type are abbreviated as n-, p-, and i-, respectively.

[0079]

According to the present invention, the current block layer can be formed with a sufficient thickness while suppressing the crystallinity such as cracks, and the Al composition, the In composition and the like can be increased. Accordingly, a semiconductor laser having an excellent light confinement effect or light absorption effect in the current blocking layer can be provided.

Further, according to the present invention, in addition to the above-mentioned effects, since the element capacitance is reduced, the semiconductor laser which can improve luminous efficiency and operate at high speed can be provided.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view showing an overall configuration of a ridge waveguide type semiconductor laser according to first and second embodiments using the present invention.

FIG. 2 is a sectional view showing a configuration of a current blocking layer in the semiconductor laser according to the first embodiment of the present invention.

FIG. 3 is a diagram showing an energy band of a current blocking layer in the semiconductor laser according to the first embodiment of the present invention.

FIG. 4 is a sectional view showing a configuration of a current blocking layer in a semiconductor laser according to a second embodiment of the present invention.

FIG. 5 is a diagram showing an energy band of a current blocking layer in a semiconductor laser according to a second embodiment of the present invention.

FIG. 6 is a cross-sectional view showing the entire configuration of a semiconductor laser having a self-aligned structure corresponding to the first and second embodiments.

FIG. 7 is a cross-sectional view showing an overall configuration of a ridge waveguide type semiconductor laser according to a third embodiment using the present invention.

FIG. 8 is a sectional view showing a configuration of a current blocking layer in a semiconductor laser according to a third embodiment of the present invention.

FIG. 9 is a sectional view showing a configuration of a current blocking layer in a semiconductor laser according to a third embodiment of the present invention.

FIG. 10 is a cross-sectional view showing the entire configuration of a semiconductor laser having a self-aligned structure corresponding to the third embodiment.

[Explanation of symbols]

 7 active layer 12 current blocking layer 12a first layer 12b second layer 12c first layer 12d second layer 27 active layer 29 current blocking layer 121 first current blocking layer 121a first layer 121b second layer 122 second current blocking layer 122a first layer 122b second layer

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Takashi Kano 2-5-5 Keihanhondori, Moriguchi-shi, Osaka Sanyo Electric Co., Ltd. (72) Inventor Yasuhiko Nomura 2-5-5 Keihanhondori, Moriguchi-shi, Osaka No. 5 Sanyo Electric Co., Ltd.

Claims (15)

[Claims] 1. A semiconductor laser having an active layer made of a nitride-based semiconductor material, wherein a current block layer for narrowing a current flowing through the active layer has a superlattice structure made up of a plurality of layers. Semiconductor laser. 2. The method according to claim 1, wherein said current blocking layer is made of Al _x Ga ₁ -xN.
2. The semiconductor laser according to claim 1, wherein the semiconductor laser has a superlattice structure including a plurality of layers (0 ≦ X ≦ 1) and different values of X. 3. The semiconductor laser according to claim 2, wherein said current blocking layer has a superlattice structure in which a first layer made of GaN and a second layer made of AlGaN are alternately and repeatedly laminated. . 4. A current blocking layer comprising a first layer made of AlGaN, and an AlGa having a larger Al composition than the first layer.
3. The semiconductor laser according to claim 2, wherein the semiconductor laser has a superlattice structure in which second layers made of N are alternately and repeatedly stacked. 5. A layer comprising a superlattice structure of the current blocking layer, wherein a layer having a large Al composition has a lower carrier concentration than a layer having a small Al composition or a layer not containing Al. The semiconductor laser according to claim 2, 3 or 4, wherein: Wherein said current blocking layer is In _Y Ga _1-Y N
2. The semiconductor laser according to claim 1, wherein the semiconductor laser has a superlattice structure including a plurality of layers (0 ≦ Y ≦ 1) and different values of Y. 7. The semiconductor laser according to claim 6, wherein the current blocking layer has a superlattice structure in which a first layer made of GaN and a second layer made of InGaN are alternately and repeatedly stacked. . 8. A first layer in which the current blocking layer is made of InGaN, and InGa having an In composition larger than that of the first layer.
7. The semiconductor laser according to claim 6, wherein the semiconductor laser has a superlattice structure in which second layers made of N are alternately and repeatedly laminated. 9. A layer comprising a superlattice structure of the current blocking layer, wherein a layer having a large In composition has a higher carrier concentration than a layer having a small In composition or a layer not containing In. 9. The semiconductor laser according to claim 6, 7 or 8, wherein: 10. A first cladding layer, an active layer, and a second cladding layer made of a nitride-based semiconductor material are sequentially formed, and a current flowing through the active layer is provided on the side of the second cladding layer with respect to the active layer. In a semiconductor laser having a constricted current block layer, the current block layer is a layer in which a first current block layer and a second current block layer are sequentially formed, and the first current block layer is an i-type semiconductor. A semiconductor laser having a superlattice structure composed of layers. 11. The semiconductor laser according to claim 10, wherein said second current blocking layer is a layer having a semiconductor layer of a conductivity type different from that of said second cladding layer. 12. The semiconductor laser according to claim 11, wherein said second current blocking layer has a superlattice structure composed of a plurality of layers. 13. The first current blocking layer includes Zn,
13. The semiconductor laser according to claim 10, wherein at least one of Be, Ca, and C is doped. 14. The first current blocking layer comprises an i-type G layer.
It has a superlattice structure in which a first layer made of aN or i-type InGaN and a second layer made of i-type InGaN having a larger In composition than the first layer are alternately and repeatedly laminated. Claims 10, 11, 12, or 13
A semiconductor laser as described in the above. 15. The semiconductor laser according to claim 14, wherein said first layer is in contact with said second cladding layer.