JP3341425B2 - Semiconductor laser - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a semiconductor laser, and more particularly, to a so-called pulsation laser.

[0002]

2. Description of the Related Art Conventionally, when designing a self-pulsation type low noise laser, a part of the active layer is generally made of a saturable absorber outside the stripe-shaped resonator portion of the active layer. FIG. 4 is a schematic sectional view of a conventional semiconductor laser of this kind. In this case, for example, a base 1 made of an n-type GaAs substrate is used.
A first cladding layer 2 made of n-type AlGaAs, G
Active layer 3 of aAs, second layer of p-type AlGaAs
And a cap layer 5 made of p-type GaAs, and current blocking layers 6 are formed on both sides of the current path on the stripe-shaped resonator component.

In this configuration, as shown by hatching on both sides of the active layer 3, a saturable absorber region K is formed. In this case, self-excited oscillation does not occur unless light is expanded to the saturable absorber region K and light is intentionally absorbed. Therefore, it is necessary to reduce the refractive index difference Δn between the inside and the outside of the stripe portion as small as possible, for example, Δn <3 × 10 ⁻³ , so that the index property is weakened and the astigmatic difference is increased.

On the other hand, for example, when a semiconductor laser is used as a recording light source for magneto-optical recording, a semiconductor laser having a high output of, for example, 30 to 40 mW is required. Compared with the output case, since the number of photons increases very quickly, the saturable absorber region K is saturated immediately, and once the absorption loss decreases, the threshold carrier density decreases, but if the number of photons is too large, Since the supersaturated absorber region K constantly keeps the supersaturated state, there is a problem that the absorption loss does not increase again, the oscillation does not stop, and pulsation hardly occurs.

As described above, a general self-sustained pulsation type semiconductor laser has a problem that it is difficult to achieve high output and low astigmatism.

[0006]

SUMMARY OF THE INVENTION The present invention solves the problems of high output and low astigmatic difference in a self-pulsation type semiconductor laser, that is, a so-called pulsation type semiconductor laser.

[0007]

SUMMARY OF THE INVENTION The present invention relates to an II-VI
In a group III-V semiconductor laser, a first cladding layer of a first conductivity type, an active layer, and a second cladding layer of a second conductivity type are sequentially epitaxied to form a second cladding layer. Concave portions are formed on both sides of the current path portion, and a saturable absorber layer having the same composition as the active layer is epitaxially formed on the surface of the second clad layer in the concave portions, and the current is passed through the saturable absorber layer. The block layer is epitaxy, the refractive index of the current blocking layer is selected to be smaller than the refractive index of the second cladding layer, and the distance between the saturable absorber layer and the active layer is set to 10 nm or more and 200 nm or less.

The present invention also provides a III-V group semiconductor laser containing Al (aluminum), comprising a first cladding layer of a first conductivity type, an active layer, and a second cladding layer of a second conductivity type. Are successively epitaxied to form a concave portion on both sides of the current path portion of the second clad layer, and a supersaturated absorber layer having the same composition as the active layer is formed on the surface of the second clad layer in the concave portion by epitaxy. Then, the current blocking layer is epitaxied through the saturable absorber layer, and the refractive index of the current blocking layer is selected to be smaller than the refractive index of the second clad layer, and the saturable absorber layer and the active layer are Distance of 10nm or more 2
The thickness is set to be equal to or less than 00 nm. Further, according to the present invention, in the above-described semiconductor laser, the saturable absorber layer is configured to be non-doped.

The present invention also relates to a III-V group 4 containing Al.
In the source semiconductor laser, a first cladding layer of the first conductivity type, an active layer, and a second cladding layer of the second conductivity type are sequentially epitaxied to sandwich the current passage portion of the second cladding layer. To form recesses on both sides thereof,
A supersaturated absorber layer having the same composition as the active layer is epitaxied on the surface of the clad layer, and the current block layer is epitaxied through the supersaturated absorber layer to reduce the Al content of the current block layer to that of the second clad layer. The distance between the saturable absorber layer and the active layer is selected to be larger than the Al content by 10 nm or more.
The thickness is set to be equal to or less than 00 nm. Further, according to the present invention, in the above-described semiconductor laser, the saturable absorber layer is configured to be non-doped.

[0010]

According to the present invention described above, the saturable absorber layer 26 having the same composition as the active layer 23 is provided in the recess 25, that is, very close to the active layer 23. The self-excited oscillation can be achieved even when the output is increased due to the effect of increasing.

According to the configuration of the present invention described above, the injection of carriers into the saturable absorber layer 26 is prevented by the current blocking layer 27, so that the saturable absorber layer 2
6, it is possible to avoid a decrease in light absorption due to carrier injection.

That is, as shown in FIG. 2, the relationship between the carrier density and the gain is shown. In the saturable absorber, when the carrier is injected into the saturable absorber and is injected above the so-called threshold carrier density N _th , The increase / decrease in carrier density due to light absorption and emission (change a shown on the horizontal axis) is only manifested as an increase / decrease in gain (change a shown on the vertical axis), and is related to an essential element of pulsation, ie, stopping laser oscillation. It is an area without. On the other hand, in the threshold carrier density N _th is relatively high carrier density even less area, the oscillation stop and self-lasing since no remainder decrease of loss as indicated by the change b in FIG. 2 Not very effective. Therefore, in order to effectively generate pulsation, as shown by a change c in FIG.
It is necessary to change in a region where the carrier density is as low as possible.

On the other hand, in the configuration of the present invention, since the current blocking layer 27 is formed on the saturable absorber layer 26, injection of carriers into the saturable absorber layer 26 is prevented. Since the carrier density increases and decreases due to light absorption and emission in a state where the carrier density is low, a reliable pulsation operation can be performed.

Further, in the structure of the present invention, a current blocking layer 27 having a larger amount of Al than the second cladding layer 24 is disposed on both sides in the plane direction opposite to the active layer 23. Therefore, an astigmatic difference can be improved by generating a built-in refractive index difference.

[0015]

DESCRIPTION OF THE PREFERRED EMBODIMENTS A semiconductor laser according to the present invention has a II-VI
Group, III-V, etc. compound semiconductor configuration. An embodiment of a semiconductor laser according to the present invention will be described with reference to FIG.
An example of a -V semiconductor will be described together with an example of a manufacturing method thereof with reference to the process chart of FIG.

As shown in FIG. 3A, a semiconductor substrate 2 of a first conductivity type, for example, an n-type GaAs compound semiconductor substrate.
, A buffer layer 21 made of AlGaAs of the same conductivity type and a clad layer 22 made of the first AlGaAs are epitaxially grown thereon, and then a non-doped or low impurity concentration GaAs or clad layer 22 is formed thereon. AlGaAs with a small Al content compared to
An active layer 23 of s and a second cladding layer 24 of a second conductivity type, for example, p-type AlGaAs are further epitaxied thereon.

As shown in FIG. 3B, the second clad layer 2
4 is formed on the mask layer 30 made of, for example, SiN, SiO ₂ or the like in a stripe shape extending in a direction perpendicular to the paper surface of FIG. 3B by photolithography, and dry etching such as chemical etching or RIE (reactive ion etching) is performed. The recess 25 is formed on both sides of the second cladding layer 24 while leaving the ridge 31 in a stripe shape from the surface side of the second cladding layer 24.

A saturable absorber layer 26 is formed in the recess 25 on both sides made of GaAs or AlGaAs having the same composition as the active layer 23 and having a low impurity concentration or non-doping.
An n-type current blocking layer of the first conductivity type, that is, a current blocking layer 27 is epitaxied thereon.

After that, the mask layer 30 is removed, and a p-type cap layer of, for example, GaAs of the second conductivity type is epitaxially formed on the entire surface.

In this configuration, the first and second cladding layers are made of Al _Y Ga _{1 -Y} As, and the current blocking layer 27 is made of Al _X Ga _{1 -X} As, where x> y. That is, the Al amount of the current block layer 27 is increased.
The y value is 0.3 ≦ y ≦ 0.6, for example, y = 0.5,
The x value is selected to be 0.4 ≦ x ≦ 1.0, for example, x = 0.7.

The thickness of the active layer 23 is, for example, 30 nm, and the active layer 23 and the saturable absorber
6 is d <200 nm, preferably 10 nm to
It is selected to be 300 nm, for example, d = 50 nm. The thickness of the saturable absorber layer 26 is selected to be, for example, 30 nm.

According to the semiconductor laser having this configuration, the active layer 23 faces the portion forming the stripe-shaped resonator, that is, the outer side of the main current supply portion in the stripe shape where the current block layer 27 does not exist, with a small interval d. Since the saturable absorber layer 26 is present and the current blocking layer 27 is formed on the saturable absorber layer 26, injection of carriers into the saturable absorber layer 26 is suppressed, as described in FIG. Since the number of carriers is increased or decreased in a region where the carrier density is low, self-sustained pulsation is reliably performed even when the output is increased.

In this structure, since the Al content of the current blocking layer 27 is made larger than that of the second cladding layer 24, the difference in the refractive index between the inside and the outside of the stripe portion becomes large and the actual refractive index becomes large. The difference can be set in-built, and a low astigmatic difference can be realized.

In the above-described example, an AlGaAs-based semiconductor laser is formed, but an AlGaInP quaternary visible light semiconductor laser can also be formed. In this case, a GaAs substrate is used as the semiconductor substrate, and the first and second cladding layers 22 and 24 are made of Al _Y Ga _1-Y InP of the first conductivity type and the second conductivity type, respectively. 27 is Al _X Ga _1-X I
Let nP and x> y. In this case, the y value is 0.3 ≦ y
≦ 0.8, for example, y = 0.6, and the x value is 0.4 ≦
x ≦ 1.0, for example, x = 0.7 is selected. The active layer 23 and the saturable absorber layer 26 have the same composition, for example, GaI.
Although the quaternary system is constituted by nP, the supersaturated absorber layer 26 is also non-doped because the band gap of the quaternary system may be increased due to impurity doping and the light absorber may not operate.

Further, the semiconductor laser according to the present invention is not limited to the above-described configuration.
te Confinement Heterostructure) MQW (Multi-Quan
When a semiconductor laser having a (tum well) structure is formed, the active layer has a SCHMQW structure corresponding to the active layer, a structure in which a guide layer is interposed therebetween, and a saturable absorber layer 26 is formed.
Also has a similar SCHMQW configuration.

In the example described above, the first conductivity type is n-type and the second conductivity type is p-type, but they may be of opposite conductivity types.

[0027]

As described above, according to the present invention, even when the output is increased, the self-pulsation operation is reliably performed, and the increase of the astigmatic difference can be avoided. Therefore, using the semiconductor laser according to the present invention as a light source for recording with a high power of an optical recording medium, the recording can be reliably performed, and an optical spot with small astigmatism and therefore small spot distortion can be obtained. It provides many benefits, such as being suitable for high density recording.

[Brief description of the drawings]

FIG. 1 is a schematic sectional view of an example of a semiconductor laser according to the present invention.

FIG. 2 is a diagram illustrating a carrier density dependency of a gain used for describing the present invention.

FIG. 3 is a process chart showing an example of a method for manufacturing a semiconductor laser according to the present invention. A is a process diagram. B is a process diagram thereof.

FIG. 4 is a cross-sectional view of a conventional semiconductor laser.

[Explanation of symbols]

 Reference Signs List 20 semiconductor substrate 21 buffer layer 22 first cladding layer 23 active layer 24 second cladding layer 25 recess 26 saturable absorber layer 27 current blocking layer 28 cap layer

Claims (5)

(57) [Claims] In a semiconductor laser, a first cladding layer of a first conductivity type, an active layer, and a second cladding layer of a second conductivity type are sequentially epitaxied, and a current path of the second cladding layer is provided. A concave portion is formed on both sides of the portion, and a saturable absorber layer having the same composition as the active layer is epitaxially formed on the surface of the second clad layer in the concave portion, and a current blocking layer is formed via the saturable absorber layer. Is epitaxy, the refractive index of the current blocking layer is selected to be smaller than the refractive index of the second cladding layer, and the distance between the saturable absorber layer and the active layer is 10 nm or more and 200 nm or less. A semiconductor laser characterized by the above-mentioned. 2. A group III-V semiconductor laser containing Al, wherein a first cladding layer of a first conductivity type, an active layer, and a second cladding layer of a second conductivity type are sequentially epitaxied, Concave portions are formed on both sides of the current path portion of the second clad layer, and a saturable absorber layer having the same composition as the active layer is epitaxied on the surface of the second clad layer in the concave portions, The current blocking layer is epitaxied via the body layer, the refractive index of the current blocking layer is selected to be smaller than the refractive index of the second cladding layer, and the distance between the saturable absorber layer and the active layer is reduced. A semiconductor laser having a thickness of 10 nm or more and 200 nm or less. 3. The semiconductor laser according to claim 2, wherein said saturable absorber layer is non-doped. 4. A group III-V quaternary semiconductor laser containing Al, wherein a first cladding layer of a first conductivity type, an active layer, and a second cladding layer of a second conductivity type are sequentially epitaxied. A concave portion is formed on both sides of the current path portion of the second clad layer, and a saturable absorber layer having the same composition as the active layer is epitaxied on the surface of the second clad layer in the concave portion; The current block layer is epitaxied via the saturable absorber layer, and the Al content of the current block layer is selected to be larger than the Al content of the second clad layer. A semiconductor laser, wherein a distance from an active layer is 10 nm or more and 200 nm or less. 5. The semiconductor laser according to claim 4, wherein said saturable absorber layer is non-doped.