JPH09270563A - Semiconductor laser element and manufacturing method thereof - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a high output element having a low noise characteristic and superior self-excited oscillation characteristic, without deteriorating the optical characteristic and reliability and increasing the operating current. SOLUTION: This semiconductor laser element has a laminate structure comprising at least a first conductivity type semiconductor substrate 1, first conductivity type first clad layer 3, active layer 4 and second conductivity type second clad layer 5, all formed on the substrate 1. On this laminate structure it has a current block functional members 9, 10 having stripe regions 7 and second conductivity type third clad layer 12 formed to bury the regions 7, and current block functional member 9, 10 which comprises at least a saturable absorption layer 9 having nearly the same forbidden band as that of the active layer 4.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a low-noise and high-output semiconductor laser device suitable for a light source for a recording / reproducing type magneto-optical disk and having a strong resistance to a return light of an emitted laser light. The present invention relates to a low-noise high-power semiconductor laser device utilizing a self-excited oscillation phenomenon by a saturable absorber and a manufacturing method thereof.

[0002]

2. Description of the Related Art When a semiconductor laser device is used as a signal reading light source for an optical disk device, when the emitted laser light is reflected by the disk surface and returns to the semiconductor laser device itself, the semiconductor laser device has a very large noise, so-called. The signal from the optical disc may not be read correctly due to the generation of return optical noise.

As a method of reducing the return light noise of such a semiconductor laser device, a method of utilizing a self-excited oscillation phenomenon is well known. In a self-excited oscillation type semiconductor laser device utilizing the self-excited oscillation phenomenon, the coherence of the laser beam is lowered by the self-excited oscillation, so that even if the laser beam is reflected by the disk surface and returned to the semiconductor laser device. , No interference occurs inside the device. As a result, low noise characteristics are ensured. It has been theoretically shown that this self-excited oscillation phenomenon occurs by forming a saturable absorber inside the active layer of a semiconductor laser device (M. Yamada: IE.
EEJ. Quantum Electron. , Vo
l. QE-29, No. 5, pp. 1330-1336
(See May 1993).

FIG. 12 shows a cross-sectional structure of a conventional semiconductor laser device 50 in which low noise operation is realized by self-excited oscillation (14th International Conference on Semiconductor Lasers Digest, Th4.1, pp.247-. 248 (1994)).

In this semiconductor laser device 50, an n-GaAs buffer layer 52 and n-Al _x Ga _1-x As are _{first formed} on an n-GaAs substrate 51 in a wafer state by metal organic chemical vapor deposition (MOCVD). (X = 0.4) First cladding layer 53, non-doped multiple quantum well active layer 54, p-A
The l _x Ga _1-x As (x = 0.4) second cladding layer 55 and the n-Al _x Ga _1-x As (x = 0.45) current blocking layer 56 are sequentially grown. After that, the wafer is taken out from the MOCVD apparatus, and stripe-shaped grooves (hereinafter referred to as “stripe portion”) 57 reaching the second cladding layer 55 from the surface of the current block layer 56 are formed. The stripe portion 57 functions as a current path during operation of the semiconductor laser device 50.

After that, the wafer is again subjected to MOCVD.
Introduced into the device, the stripe part 5 is formed by MOCVD.
P-Al so as to cover the current blocking layer 56 including
_x Ga _1-x As (x = 0.4) third cladding layer 58 and p
-The GaAs cap layer 59 is grown in order. After the growth is completed, the p-side electrode 60 is formed on the cap layer 59, and the n-side electrode 61 is formed on the back surface of the substrate 51. Further, by dividing the wafer into chips, individual semiconductor laser devices 50 can be obtained.

Further, in order to obtain a high-power semiconductor laser device, the end face on the light emitting side is coated with a reflectance of about 3%, and the end face on the opposite side has a reflectance of about 94%. Perform the coating as obtained.

When a voltage is applied between the electrodes 60 and 61 of the semiconductor laser device 50 thus formed, a current is injected into the active layer 54 through the stripe portion 57 to cause laser oscillation. At this time, the stripe portion 57
Due to the difference in effective refractive index between the inside and the outside of the laser, the oscillated laser light is guided in the region immediately below the stripe portion 57.

In such a semiconductor laser device 50, if the second cladding layer 55 is thickened to a certain extent or more and the effective refractive index difference between the inside of the stripe portion 57 and the outside thereof is made small, the inside of the stripe portion 57 is reduced. The light confinement to is weakened. As a result, a state in which the width of the spread of the laser light is larger than the width of the current injected into the active layer 54 is realized. In such a state, the active layer 54
Of these, a portion corresponding to the outside of the stripe portion 57 acts as a saturable absorber, and a self-excited oscillation operation is achieved.

On the other hand, FIG. 13 shows a sectional structure of another conventional semiconductor laser device 70 in which low noise operation utilizing the self-excited oscillation phenomenon is realized. In this semiconductor laser device 70, a saturable absorption layer 76 is provided in addition to the active layer 74, and self-excited oscillation is caused by the saturable absorption action (Proceedings of the 12th Semiconductor Laser Symposium,
p. 11 (March 1995)).

Specifically, in the semiconductor laser device 70,
on the n-GaAs substrate 71, n-GaAs buffer layer _{72, n-Al y Ga 1} -y As first cladding layer 73, Al
_x Ga _1-x As active layer 74 and _{p-Al y Ga 1-y} As second cladding layer 75, are laminated in this order. Also, the second
Striped p-AlGa is formed on the clad layer 75.
An As saturable absorption layer 76 is laminated.

Further, the p-AlGaAs saturable absorption layer 7
On top of _{6, p-Al y Ga 1} -y As third cladding layer 77
And a p-GaAs contact layer 78 are formed to form a stripe-shaped mesa region 79. Further, n-AlG is formed on the second cladding layer 75 and on both sides of the mesa region 79.
The aAs current blocking layer 80 is laminated. further,
A p-GaAs cap layer 81 is laminated so as to cover the stripe-shaped mesa region 79 and the current block layer 80. A p-side electrode 82 is formed on the cap layer 81, while an n-side electrode 83 is formed on the back surface of the substrate 71.

In the case of this semiconductor laser device 70, the Al composition ratio of the saturable absorption layer 76 (that is, the saturable absorption layer 7
The forbidden band width of 6 is the Al composition ratio of the active layer 74 (active layer 74
The forbidden band width) is set to be approximately equal to the saturable absorption characteristics. In the semiconductor laser device 50 described above, the region of the active layer 54 corresponding to the outside of the stripe portion 57 is operated as a saturable absorber. However, in the case of this semiconductor laser device 70, self-excited oscillation is The absorption saturation characteristic of the saturable absorption layer 76 provided separately from the active layer 74 is utilized.

[0014]

Among the structures of the two conventional semiconductor laser devices 50 and 70 described above, strong self-pulsation (that is, sufficient reduction of coherence) in the former semiconductor laser device 50 occurs. In order to realize it, it is necessary to make the saturable absorption effect sufficiently large. In order to achieve such an object, specifically, the following two methods can be adopted.

(1) The effective refractive index difference between the inside and outside of the stripe portion 57 is reduced to increase the leakage of light to the saturable absorber formed of the active layer 54 outside the stripe portion 57. .

(2) The active layer 54 is thickened to increase the volume of the saturable absorber.

However, the methods (1) and (2) have the following problems.

First, in the former method (1), the active layer 54 is
Of these, the amount of light seeping out to a portion corresponding to the outside of the stripe portion 57 is increased, so that the light spot size is expanded. Therefore, the radiation angle in the direction parallel to the active layer 54 becomes narrow. As a result, when compared with a semiconductor laser device in which self-sustained pulsation does not occur, there is a problem in optical characteristics that the coupling efficiency between the semiconductor laser device and the lens changes.

On the other hand, in the latter method (2), generally, when the active layer 54 is thickened, reliability in a high output state deteriorates.

Further, in the structure of the conventional semiconductor laser device 70, the active layer 74 outside the stripe portion 79 is not used as the saturable absorber, but the stripe portion 7 is used.
A saturable absorption layer 76 formed separately from the active layer 74 in a region corresponding to the inside of 9 is used for the self-excited oscillation operation. Therefore, since it is not necessary to increase the amount of light leaking to the active layer 74 outside the stripe portion 79 to increase the light spot size, the above-mentioned problems occurring in the semiconductor laser device 50 do not occur.

However, in order to secure a strong self-sustained pulsation characteristic for reducing noise in the structure of the semiconductor laser device 70, it is necessary to make the saturable absorption layer 76 relatively thick. In this case, since the saturable absorption layer 76 is formed very close to the central portion of the oscillation region, the light absorption in the unsaturated state of the saturable absorption layer 76 becomes large, which increases the oscillation start current and the differential efficiency. The operating current increases due to the decrease. as a result,
The operation characteristics of the semiconductor laser device 70 deteriorate.

The present invention has been made in order to solve the above problems, and its purpose is to have strong self-sustained pulsation characteristics excellent in low noise characteristics, and to deteriorate optical characteristics, poor reliability, or operation. It is an object of the present invention to provide a high-output semiconductor laser device and a method for manufacturing the same, which does not cause a problem in operating characteristics such as increase in current.

[0023]

According to one aspect of the present invention, a semiconductor laser device is formed on a semiconductor substrate of a first conductivity type and a first conductivity type semiconductor substrate formed on the semiconductor substrate.
A laminated structure including at least a clad layer, an active layer, and a second clad layer of the second conductivity type, a current blocking function body having a stripe-shaped region on the laminated structure, and the stripe portion And a third clad layer of the second conductivity type formed so as to fill the current blocking function body, wherein the current blocking function body has a forbidden band width substantially equal to the forbidden band width of the active layer. It comprises at least a saturable absorber layer, by means of which the above-mentioned object is achieved.

According to another aspect of the present invention, a semiconductor laser device is formed on a semiconductor substrate of a first conductivity type, a first clad layer of the first conductivity type and an active layer. And at least a second conductive type second clad layer, and at least a second conductive type third clad layer and a second conductive type contact layer formed on the stacked structure. A striped mesa region including the current blocking function body formed on the laminated structure on both sides of the stripe mesa region, wherein the current blocking function body has a forbidden band width of the active layer. At least including a saturable absorber layer having a bandgap substantially equal to the saturable absorber layer, the saturable absorber layer covering a side surface of the striped mesa region, thereby achieving the above object.

In one embodiment of the semiconductor laser device having any of the above structures, the current blocking function body has an n-type semiconductor layer provided on the laminated structure side, and the n-type semiconductor layer is provided. The saturable absorption layer is disposed on the side of the layer opposite to the substrate, and partly has a structure formed in p-type.

In one embodiment of the semiconductor laser device having any one of the above structures, the forbidden band width of a portion of the current blocking function body other than the saturable absorption layer has the first and second band gaps. It is larger than the forbidden band width of the clad layer and has no absorption effect on the laser light generated in the active layer due to current injection.

In another embodiment, an Al composition ratio x which gives an effective band gap of the active layer and an Al composition ratio y which gives an effective band gap of the saturable absorption layer are x- The relationship of 0.02 ≦ y ≦ x + 0.02 is satisfied.

In yet another embodiment, a region of the active layer corresponding to the outside of the striped region further functions as a saturable absorber.

According to still another aspect of the present invention, in the manufacturing process of the semiconductor laser device, the first conductivity type first cladding layer, the active layer and the second conductivity type are formed on the first conductivity type semiconductor substrate. And a saturable absorption layer having a forbidden band width substantially equal to the forbidden band width of the active layer are grown on the laminated structure. A step of growing a current blocking function body, a step of forming a stripe region in the current blocking function body by etching, and a second conductivity type third clad layer covering the stripe part and the current blocking function body. And the step of growing, thereby achieving the above object.

According to still another aspect of the present invention, there is provided a method of manufacturing a semiconductor laser device, comprising: a first conductivity type semiconductor substrate, a first conductivity type first cladding layer, an active layer, and a second conductivity type second cladding layer. A step of growing a laminated structure including at least a second conductivity type second clad layer, and a second conductivity type third clad layer and a second conductivity type contact layer are sequentially grown on the laminated structure. And a step of etching the third clad layer and the contact layer to form a stripe mesa region, and a forbidden band of the active layer on both sides of the laminated mesa region on the laminated structure. A step of growing a current blocking function body including at least a saturable absorption layer having a forbidden band width substantially equal to the width so that the saturable absorption layer covers the side surface of the stripe-shaped mesa region. By the above purpose It is achieved.

The step of growing the current blocking function body may include a step of forming a p-type saturable absorption layer after forming an n-type semiconductor layer.

The operation will be described below.

In the semiconductor laser device of the present invention, the saturable absorption layer is formed inside the current blocking function body. By utilizing the saturable absorption effect of the saturable absorption layer inside such a current blocking function body, a sufficiently strong self-excited oscillation operation is realized. As a result, low noise in the operating characteristics of the semiconductor laser device is achieved. Further, since the extent of light seeping out to the region corresponding to the outside of the stripe portion in the active layer or the thickness of the active layer can be reduced, deterioration of optical characteristics and poor reliability can be achieved. There is no problem.

Furthermore, since the saturable absorption layer formed inside the current blocking function body is formed away from the central portion of the oscillation region, the increase in light absorption can be suppressed to a relatively small level. As a result, the problem of increase in oscillation start current and drive current does not occur.

Further, by allowing the region of the active layer corresponding to the outside of the stripe portion to function as a saturable absorber and also utilizing the saturable absorber function of that portion, it is possible to solve the above problems. You can widen the range of values.

Alternatively, a laminated structure including a clad layer and an active layer is formed on a semiconductor substrate, and a stripe-shaped mesa region formed on the laminated structure is sandwiched between current blocking functional bodies. In the laser device, the current blocking function body includes the saturable absorption layer, and the side surface of the stripe-shaped mesa region is covered with the saturable absorption layer, whereby the self-excited oscillation characteristic (that is, noise characteristic) is further improved. Be improved.

When the saturable absorption layer of the current blocking function body is of p type, self-excited oscillation stronger than that of n type is obtained. The reason is that the amount of change in the light absorption characteristics of the saturable absorber layer with respect to the amount of change in the density of carriers generated by the light absorption of the saturable absorber layer is larger in the p-type than in the n-type,
This is because it is considered to be related to the ease and strength of self-sustained pulsation.

In addition, the saturable absorber layer is added in this manner.
When an n-type semiconductor layer is provided on the side of the laminated structure of the p-type semiconductor layer, the n-type semiconductor layer functions as a current blocking layer, which is lower than that in the case of using the p-type semiconductor layer. It becomes possible to perform current operation.

[0039]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below with reference to the drawings.

(First Embodiment) FIG. 1 shows a sectional structural view of a semiconductor laser device 100 according to a first embodiment of the present invention.

In this semiconductor laser device 100, n-G
on the aAs substrate 1, n-GaAs buffer layer (thickness _{0.5μm) 2, n-Al y} Ga 1-y As first cladding layer (y = 0.5, thickness 1.5 [mu] m) 3, undoped Al _x
Ga _1-x As active layer (x = 0.14, thickness 0.05 μ
_{m) 4, p-Al y} Ga 1-y As second cladding layer (y =
0.5, thickness 0.25 μm) 5, and p-GaAs
An etch stop layer (thickness 0.003 μm) 6 is sequentially stacked. On the etch stop layer 6, p-Al
_u Ga _1-u As etch stop layer (u = 0.6, thickness 0.
02 μm) 8, n-Al _v Ga _1-v as a saturable absorption layer
As 1st current blocking layer (v = 0.14, thickness 0.25
μm) 9, n-Al _w Ga _1-w As second current blocking layer (w = 0.6, thickness 0.35 μm) 10, and n−
A GaAs protective layer (thickness 0.01 μm) 11 is sequentially formed. In the present embodiment, the first current blocking layer 9 and the second current blocking layer 10 functioning as saturable absorption layers.
A current block function body is constituted by the and.

Further, a stripe-shaped groove, that is, a stripe portion 7, extending from the surface of the protective layer 11 to the surface of the etch stop layer 6, that is, the stripe portion 7, is formed.
The first current blocking layer 9, the second current blocking layer 10, and the protective layer 11 are all divided by the stripe portion 7. The width of the uppermost portion of the stripe portion 7 is about 2.5 μm.

Furthermore, the p-Al _z Ga _{1 -z} As third cladding layer (z is formed so as to cover the stripe portion 7 and the protective layer 11).
= 0.5, thickness 1.2 μm) 12 and p-GaAs cap layer (thickness 1.0 μm) 13 are sequentially stacked. Further, a p-side electrode 14 is formed on the cap layer 13, and an n-side electrode 15 is formed on the back surface of the substrate 1.

Next, a method of manufacturing the semiconductor laser device 100 will be described with reference to the sectional views of FIGS.

First, as shown in FIG. 2A, n-Ga
The As MOCVD method on the substrate 1, n-GaAs buffer layer _{2, n-Al y Ga 1} -y As first cladding layer 3,
Undoped AlGaAs active layer _{4, p-Al y Ga 1} -y A
s second cladding layer 5, p-GaAs etching stop layer _{6, p-Al u Ga 1} -u As etching stop layer 8, n-A
l _v Ga _1-v As first current blocking layer 9, n-Al _w Ga
_{The 1-w} As second current blocking layer 10 and the n-GaAs protective layer 11 are continuously grown in this order.

Next, this wafer is taken out from the MOCVD apparatus and, as shown in FIG. 2B, the p-GaAs etch stop layer 6 is formed from the surface of the protective layer 11 by using a photolithography method or a selective etching method. Forming a stripe portion 7 reaching

After that, the wafer on which the stripe portion 7 has been formed in this way is again introduced into the MOCVD apparatus, and as shown in FIG.
As shown in (c), the p-Al _z Ga _{1 -z} As third cladding layer 12 is formed so as to cover the stripe portion 7 and the protective layer 11.
And the cap layer 13 is grown.

Next, a part of the substrate 1 is removed from the back side by polishing or the like, and processed so that its thickness becomes about 100 μm. After that, the p-side electrode 1 is formed on the cap layer 13.
4 is formed, and the n-side electrode 15 is formed on the back surface of the substrate 1. Finally, the wafer is divided into chips, and end face coating for high output is performed to obtain the semiconductor laser device 1
00 is obtained.

In the method of manufacturing the semiconductor laser device 100 of the present embodiment described above, first, the layers including the first current blocking layer 9 functioning as a saturable absorber and the active layer 4 are laminated, and then, The stripe portion 7 is formed by etching. Therefore, the manufacturing method is simple, the yield is good, and the manufacturing cost is low.

When a voltage is applied between the electrodes 14 and 15 of the semiconductor laser device 100 thus formed,
A current is injected into the active layer 4 through the stripe portion 7 to start laser light oscillation. In the case of the semiconductor laser device 100 of the present embodiment, the Al composition of the second current block layer 10 is 0.6, which is sufficiently larger than the Al composition of 0.14 of the active layer 4. Therefore, this region is non-absorptive to the laser light generated in the active layer 4, whereby low current characteristics are realized. Typically, the oscillation start current of the semiconductor laser device 100 according to the present embodiment is 30 mA, and the operating current required to obtain an output of 35 mW is 70 m.
It is about A.

When a current is injected into the semiconductor laser device 100, the width of the current injection is limited by the width of the stripe portion 7, and most of the width is about the same width as the width of the stripe portion 7 in the active layer 4. Is injected into the region of. On the other hand, since the light confinement inside the stripe portion 7 is set to be weak, the light spreads wider than the width inside the stripe portion 7, and as a result, outside the stripe portion 7. The located active layer 4 acts as a saturable absorber. Further, the light partially spreads inside the first current blocking layer 9, so that the first current blocking layer 9 in this region also acts as a saturable absorber.

FIG. 3 is a graph showing the measurement results of the optical output dependence of the coherence index of the laser light which is a measure of the self-excited oscillation characteristic. As shown in FIG. 3, the coherence index starts to decrease when the light output is about 1 mW, and the coherence index shows a very low value when the light output is 2 mW. This characteristic is a CD
It is equivalent to the self-sustained pulsation characteristic of a low-noise low-power laser used in a player or the like.

FIG. 4 shows the semiconductor laser device 1 of this embodiment.
10 is a graph showing the measurement result of the return optical noise characteristic of No. 00.
Specifically, when the optical path length is 30 mm and the optical output is 3 mW, it is the measurement result of the relative noise intensity (RIN) obtained when the amount of returning light is changed in the range of 0.001% to 10%. . As shown in FIG. 4, the relative noise intensity was -130 dB / Hz in the range of all the measured returned light amounts.
A low value of about the same or less is obtained.

Further, FIG. 5 shows a first laser device which acts as a saturable absorber in the semiconductor laser device 100 of this embodiment.
The difference (Δn) in the effective refractive index inside and outside the stripe portion 7 with respect to the change in the thickness (d _block1 ) of the current blocking layer 9
6 is a graph showing a change in the graph. Specifically, the Al composition ratio (X _block1 ) of the first current blocking layer 9 is 0.12, 0.1.
4 and 0.16 are set to three different values, and the measurement results are shown.

As shown in FIG. 5, the thickness (d _block1 ) of the first current blocking layer 9 is approximately 0.03 μm ≦ d _block1 ≦ 0.13 μm, and 0.34 μm ≦ d _block1 ≦ 0. When it is within the range of 0.42 μm, the effective refractive index inside the stripe portion 7 becomes smaller than the effective refractive index outside the stripe portion 7 (Δn becomes 0 or less), which is an anti-guide mode. In such an anti-guide mode, it becomes difficult to confine light inside the stripe portion 7, and the laser oscillation characteristic becomes unstable.

The range shown as "anti-guide" in the drawing is for X _block1 = 0.14. This range changes depending on the value of X _block1 , but in principle, it corresponds to the range where Δn is 0 or less in the characteristics shown in FIG.

Regarding other characteristics described below, cases other than the anti-guide mode will be discussed.

FIG. 6 shows the semiconductor laser device 1 of this embodiment.
00 is a graph showing the change in coherence index with respect to the change in the thickness (d _blockl ) of the first current blocking layer 9 which acts as a saturable absorber at 00. However, the optical output is 3m
W. Specifically, the Al composition ratio (X _block1 ) of the first current blocking layer 9 is set to three values of 0.12, 0.14, and 0.16, and the measurement results for each are shown.

The coherence index must be 0.5 or less to realize the low noise characteristic, but the first current blocking layer 9
The coherence index tends to increase as the Al composition ratio X _block1 of the above increases. In particular, when X _block1 > 0.16, the area where the coherence index satisfies 0.5 or less is extremely small except the area corresponding to the anti-guide mode. Therefore, from the viewpoint of the coherence index characteristic, it is desirable to set the Al composition ratio X _block1 of the first current blocking layer 9 to 0.16 or less.

Next, FIG. 7 shows the thickness (d) of the first current blocking layer 9 in the semiconductor laser device 100 of this embodiment.
It is a graph showing a change in the operating current (I _op) to changes in _blockl). However, the optical output is 35 mW. Specifically, the Al composition ratio (X _block1 ) of the first current blocking layer 9 is set to three values of 0.12, 0.14, and 0.16, and the measurement results for each are shown.

As shown in FIG. 7, when the Al composition ratio X _block1 of the first current blocking layer 9 decreases, the operating current I _op tends to increase. Especially, X _block1 <0.12
In the case of, the operating current I _op increases to 110 mA or more. Therefore, from the viewpoint of operating current characteristics, it is desirable to set the Al composition ratio X _block1 of the first current blocking layer 9 to 0.12 or more.

From the above points, in the above description regarding the semiconductor laser device 100 shown in FIG. 1, the respective layers providing the forbidden band width of the active layer 4 and the first current blocking layer 9 functioning as the saturable absorption layer. Regarding the Al composition ratio of
The Al composition ratio (X _block1 ) of the current blocking layer 9 is the active layer 4
It is described that the Al composition ratio is 0.14, which is the same as the Al composition ratio of the above. In particular,
It is desirable to set in the range of 0.12 ≦ X _block1 ≦ 0.16 so as to satisfy the above condition described with reference to FIGS. 6 and 7.

The Al of the first current blocking layer 9 described above is used.
The range of the composition ratio (X _block1 ) is a value when the Al composition ratio x of the Al _x Ga _1-x As active layer 4 is 0.14.

More generally, for the Al composition ratio x of the active layer 4 which gives the effective forbidden band width of the active layer 4, the effective of the first current blocking layer 9 functioning as a saturable absorption layer is effective. Al composition ratio X of the first current blocking layer 9 that gives a forbidden band width
_{If block1} is set so as to satisfy the relationship of x- _{0.02≤X block1≤x} + 0.02, the same effect as that described above can be obtained. For example, even if the active layer or the saturable absorption layer has a quantum well structure or a superlattice structure and the Al composition ratio of each of these layers cannot be specified, the emission characteristics, the oscillation wavelength, or the absorption If the above relational expression is satisfied with respect to the equivalent Al composition of AlGaAs determined from operating characteristics such as characteristics, the effect of the present invention can be obtained.

Further, FIG. 8 shows the characteristics of the horizontal emission angle of the emitted laser light with respect to the change in the thickness (d _blockl ) of the first current blocking layer 9 in the semiconductor laser device 100 of this embodiment, that is, the emitted laser light. 3 is a graph showing a change in a horizontal half-value width (hereinafter, referred to as “θ horizontal”) in the far-field image of FIG. Specifically, the Al composition ratio (X _block1 ) of the first current blocking layer 9 is set to three values of 0.12, 0.14, and 0.16, and the measurement results for each are shown.

Generally, when the θ horizontal is less than 9 degrees, the optical characteristics are defective. From FIG. 8, the thickness (d _blockl ) of the first current blocking layer 9 where θ horizontal is 9 degrees or more is in the following range.

0.14 μm ≦ d _block1 ≦ 0.30 μm,
And 0.44 μm ≦ d _block1 ≦ 0.58 μm As described above, the thickness (d _block1 ) of the first current blocking layer 9 satisfies the above conditions described with reference to FIGS. 6 to 8. Thus, it is desirable to set it within the above range.

The semiconductor laser device 10 of this embodiment is used.
Reference numeral 0 has the etch stop layers 6 and 8, which are inserted to improve the reproducibility and controllability of the fabrication of the semiconductor laser device. Therefore, even when the etch stop layers 6 and 8 are not provided, the same effects as those described above can be obtained.

(Second Embodiment) FIG. 9 shows a sectional structural view of a semiconductor laser device 200 according to a second embodiment of the present invention.

This semiconductor laser device 200 is composed of n-Ga.
On the As substrate 21, n-GaAs buffer layer (thickness _{0.5μm) 22, n-Al y} Ga 1-y As first cladding layer (y = 0.5, thickness 1.5 [mu] m) 23, multiple quantum well active layer _{24, p-Al y Ga 1} -y As second cladding layer (thickness 0.30μm) 25, p-GaAs etching stop layer (thickness 0.003 .mu.m) 26 are laminated in this order.
Furthermore, p-Al _z G is formed on the etch stop layer 26.
a _1-z As third clad layer (z = y, thickness 1.2 μm)
27 and p-GaAs contact layer (thickness 0.5 μm)
A stripe-shaped mesa region 29 made of 28 is formed. The width of the mesa region 29 is about 2.5 μm.

Further, on the etch stop layer 26 on both sides of the mesa region 29, an n-type current blocking layer 30, p is formed.
-Al _w Ga _1-w As optical confinement layer (w = 0.7, thickness 0.43 μm) 31 and p-GaAs protective layer 32,
They are stacked in order. Of these, the current blocking layer 30 is
n-Al _v Ga _1-v As (v = 0.5, thickness 1 nm) and n
It has a superlattice structure composed of -GaAs (thickness: 2.5 nm), the average Al composition is 0.13, and the total thickness is 0.27 μm. This current blocking layer 3
0 functions as a saturable absorption layer for oscillated laser light. In the present embodiment, the current blocking function body is configured by the current blocking layer 30 that functions as the saturable absorption layer.

On the stripe-shaped mesa region 29 and the protective layer 32, a p-GaAs cap layer (thickness 1 μm) is formed.
33 are stacked. Further, a p-side electrode 34 is formed on the cap layer 33, and an n-side electrode 35 is formed on the back surface of the substrate 21.

The multiple quantum well active layer 24 is made of Al _0.3 Ga.
_0.7 As guide layer (thickness 200 Å),
A total of 5 layers of Al _0.1 Ga _0.9 As well layers (thickness 100 Å) and a total of 4 layers of Al _0.3 Ga _0.7 As
Barrier layers (thickness 80 Å) are alternately laminated.

In this structure, since the side surface of the stripe-shaped mesa region 29 is covered with the current block layer 30 functioning as a saturable absorber, the self-excited oscillation characteristic (noise characteristic) is further improved.

Next, a method of manufacturing the semiconductor laser device 200 will be described with reference to the sectional views of FIGS.

First, as shown in FIG. 10A, n-G
n-GaA is formed on the aAs substrate 21 by MOCVD.
s buffer layer _{22, n-Al y Ga 1} -y As first cladding layer 23, a multiple quantum active layer _{24, p-Al y Ga 1} -y As second cladding layer 25, p-GaAs etching stop layer 2
6, p-Al _z Ga _1-z As third cladding layer 27, and p
The -GaAs contact layer 28 is continuously grown in this order.

Next, this wafer is taken out from the MOCVD apparatus, and a SiN film (thickness 0.3 μm) is formed on the contact layer 28 by the plasma CVD method or the like. Next, the third clad layer 27 existing on the etch stop layer 26 is removed from the surface of the SiN film by using a photolithography method, a selective etching method, or the like, and a stripe shape as shown in FIG. To form the mesa region 29. However, in FIG. 10B, the SiN film on the mesa region 29 is omitted.

After that, the wafer on which the stripe-shaped mesa region 29 is formed is again introduced into the MOCVD apparatus, and as shown in FIG. 10C, a superlattice structure is formed on both sides of the mesa region 29. Te growing a current blocking layer 30 and _{p-Al w Ga 1-w} as optical confinement layer 31 and the p-GaAs protective layer 32, which functions as a saturable absorbing layer. At this time, the current block layer 30, the optical confinement layer 31, and the protective layer 32 are also laminated on the SiN film. After the growth of each of these films 30 to 32, the wafer is once taken out from the MOCVD apparatus and each of these films is removed. 30-32 and the SiN film are removed. After that, the wafer is MOCVD again.
The cap layer 33 is formed in the apparatus by MOCVD.

Next, a part of the substrate 21 is removed from the back surface by polishing or the like, and processed so that its thickness becomes about 100 μm. After that, the p-side electrode 3 is formed on the cap layer 33.
4 is formed, and the n-side electrode 35 is formed on the back surface of the substrate 21. Finally, the semiconductor laser device 2 is obtained by dividing the wafer into chips and performing end face coating for high output.
00 is obtained.

In the manufacturing method as described above, the interface between the etch stop layer 26 and the cladding layer 27 is maintained as it is in the initial state of formation, so that the interface is not disturbed. As a result, a reduction in operating current is realized.

In the semiconductor laser device 200 of this embodiment formed as described above, the oscillation start current is typically 27 mA, and the operating current required to obtain an output of 35 mW is 60 mA. Also, the coherence index is
Similar to the semiconductor laser device 100 in the first embodiment, a sufficiently low value is obtained, and a relative noise intensity is also sufficiently low value.

As described above, in the present embodiment, the saturable absorption characteristics are made steeper as compared with the ordinary saturable absorption layer of AlGaAs mixed crystal by forming the current blocking layer serving as the saturable absorption layer in the superlattice structure. Become. As a result, a strong self-sustained pulsation characteristic is obtained up to a lower level output, and as a result, a low noise characteristic is realized.

(Third Embodiment) In the present embodiment, the n-type current block is formed on the p-type etch stop layer (8 or 26) in the first and second embodiments. In contrast to the structure in which the current blocking function body composed of layers is provided, the layer of the n-type current blocking layer on the etch stop layer side is p-type, and the etch stop layer on the side in contact with this p-type layer is n-type. This is the case.

In the case of such a structure, the p-type layer on the etch stop layer side does not function as a current blocking layer, but functions mainly as a saturable absorption layer. Further, by making the etch stop layer on the side in contact with this p-type layer n-type, this layer comes to have a function as a current blocking layer.

FIG. 11 shows a sectional structural view of a semiconductor laser device 300 according to the third embodiment of the present invention.

In this semiconductor laser device 300, n-G
on the aAs substrate 101, n-GaAs buffer layer (thickness _{0.5μm) 102, n-Al y} Ga 1-y As first cladding layer (y = 0.5, thickness 1.5 [mu] m) 103, an undoped Al _x Ga _1-x As active layer (x = 0.14, thickness 0.
_{05μm) 104, p-Al y} Ga 1-y As second cladding layer (y = 0.5, thickness 0.25 [mu] m) 105, and p-GaAs etching stop layer (thickness 0.003 .mu.m)
106 are sequentially stacked. Etch stop layer 10
N-Al _u Ga _1-u As etch stop layer (u = 0.6, thickness 0.07 μm) 108, p-Al _v
Ga _1-v As saturable absorption layer (v = 0.14, thickness 0.2
5 μm) 109, n-Al _w Ga _1-w As current blocking layer (w = 0.6, thickness 0.35 μm) 110, and n
A -GaAs protective layer (thickness 0.01 µm) 111 is sequentially formed.

Further, a stripe-shaped groove, that is, a stripe portion 107, which extends from the surface of the protective layer 111 to the surface of the etch stop layer 106, is formed, and the etch stop layer 108, the saturable absorption layer 109, the current block layer 1 are formed.
10 and the protective layer 111 are all divided by the stripe portion 107. The stripe portion 10
The width of the uppermost part of 7 is about 2.5 μm.

Further, the stripe portion 107 and the protective layer 1
P-Al _z Ga _1-z As third cladding layer (z = 0.5, thickness 1.2 μm) 112 and p-Ga so as to cover 11
An As cap layer (thickness: 2.0 μm) 113 is sequentially stacked. Further, a p-side electrode 114 is formed on the cap layer 113, and the n-side electrode 1 is formed on the back surface of the substrate 101.
15 are formed.

In the semiconductor laser device of this embodiment having such a configuration, the saturable absorption layer 109 of the current blocking function body is of p-type. The reason is that, as described above, a self-sustained pulsation stronger than that of the n-type is obtained. Thus, when the saturable absorption layer 109 is made to be p-type and the underlying etch stop layer 108 is made to be p-type instead of n-type, the cap layer 113 moves to the third cladding layer 112 of the stripe portion 107. Since the current spreads laterally in the saturable absorption layer 109, a very large current spread occurs, causing an oscillation start current and an operating current to increase. Therefore, as in the present embodiment, by making the etch stop layer 108 n-type, the current spread can be reduced, that is, the n-type etch stop layer 108 functions as a current blocking layer, and the p-type It is possible to operate at a lower current than the case where the etch stop layer is used.

Therefore, in this embodiment, the etch stop layer 108, the saturable absorption layer 109, and the current block layer 110 constitute a current block function body. Regarding the etch stop layer 108 whose main function is a current block against the current spread in the saturable absorption layer 109, in order to improve the function, the thickness of the etch stop layer 108 is set to the optical characteristics and It is desirable to increase the thickness within a range that does not cause a problem in self-sustained pulsation characteristics.

In the present embodiment, the etch stop layer 108 is an n-type single layer, but the present invention is not limited to this.
A two-layer structure including an n-type layer having a current block as a main function and a p-type layer having an etch stop as a main function,
Various configurations are possible.

This semiconductor laser device 300 corresponds to the semiconductor laser device 100 according to the first embodiment described above, but this embodiment also applies to the semiconductor laser device 200 according to the second embodiment. The same can be done. Specifically, the semiconductor laser device 200
The n-type first current blocking layer 30 in 4 may be a p-type saturable absorption layer. Alternatively, the n-type first current blocking layer 30 is a p-type saturable absorption layer, and the saturable absorption layer and p
N-type Al _t Ga _1-t between the n-type etch stop layer 26 and
As current spreading prevention layer (t = 0.6, thickness 0.05 μ
m) may be provided.

In the above description of the first, second and third embodiments, for simplicity, only the AlGaAs semiconductor laser device is described. However, the present invention is also applicable to a semiconductor laser device made of a material system other than AlGaAs, such as InGaAIP system.

Further, the application of the present invention is not limited to the high power semiconductor laser device, but can be applied to the low power laser device for improving the self-sustained pulsation characteristic.

Further, as a method for growing a film used in the manufacturing process of a semiconductor laser device, in addition to the MOCVD method mentioned above, MBE (molecular beam epitaxy) is used.
Method, LPE (liquid phase epitaxy) method, MO-MBE method, or A
The LE (atomic epitaxy) method or the like can be applied.

[0096]

As described above, according to the present invention,
A high-power semiconductor laser device that has excellent low-noise characteristics and strong self-sustained pulsation characteristics and does not cause problems in device characteristics such as deterioration of optical characteristics, poor reliability, or increase in operating current is realized. .

Specifically, in a conventional semiconductor laser device (semiconductor laser device 50 described with reference to FIG. 12), the oscillation start current is 50 mA, and the operating current required to obtain an output of 35 mW is It is about 120 mA. On the other hand, in another conventional semiconductor laser device (semiconductor laser device 70 described with reference to FIG. 13), the oscillation start current is 5
It is 0 mA, and the operating current required to obtain an output of 35 mW is about 90 mA. On the other hand, the oscillation start current of the semiconductor laser device 100 according to the first embodiment is typically 30 mA, and the operating current required to obtain the output of 35 mW is typically about 70 mA. The oscillation start current of the semiconductor laser device 200 according to the second embodiment is typically 27 mA, and the output is 35 m.
The operating current required to obtain W is typically about 60 mA.

As is clear from comparing these values,
The semiconductor laser device according to each embodiment of the present invention exhibits dramatically improved operating characteristics as compared with the semiconductor laser device according to the related art.

[Brief description of drawings]

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

2A to 2C are sectional views showing manufacturing steps of the semiconductor laser device of FIG.

FIG. 3 is a graph showing coherence index characteristics of the semiconductor laser device of FIG.

FIG. 4 is a graph showing return light noise characteristics in the semiconductor laser device of FIG.

5 is a graph showing the relationship between the thickness of the first current blocking layer and the effective refractive index difference Δn in the semiconductor laser device of FIG.

6 is a graph showing the relationship between the thickness of the first current blocking layer and the coherence index in the semiconductor laser device of FIG.

7 is a graph showing the relationship between the thickness of the first current blocking layer and the operating current in the semiconductor laser device of FIG.

8 is a graph showing the relationship between the thickness of the first current blocking layer and the horizontal radiation angle in the semiconductor laser device of FIG.

FIG. 9 is a sectional structural view of a semiconductor laser device according to a second embodiment of the present invention.

10A to 10C are cross-sectional views showing a manufacturing process of the semiconductor laser device of FIG.

FIG. 11 is a sectional structural view of a semiconductor laser device according to a third embodiment of the present invention.

FIG. 12 is a sectional structural view of a conventional semiconductor laser device.

FIG. 13 is a sectional structural view of another conventional semiconductor laser device.

[Explanation of symbols]

50, 70, 100, 200, 300 Semiconductor laser device 1, 21, 101 Substrate 2, 22, 102 Buffer layer 3, 23, 103 First clad layer 4, 24, 104 Active layer 5, 25, 105 Second clad layer 6, 8, 26, 106, 108 Etch stop layer 7, 107 Stripe portion 9 First current blocking layer (saturable absorption layer) 30 Current blocking layer (saturable absorption layer) 10 Second current blocking layer 109 Saturable absorption layer 110 current blocking layer 11, 32, 111 protective layer 12, 27, 112 third cladding layer 13, 33, 113 cap layer 14, 15, 34, 35, 114, 115 electrode 28 contact layer 29 mesa region 31 light confinement layer 51 , 71 substrate 52, 72 buffer layer 53, 73 first cladding layer 54, 74 active layer 55, 75 second layer Rad layer 56, 80 Current blocking layer 57 Stripe portion 58, 77 Third cladding layer 59, 81 Cap layer 60, 61, 82, 83 Electrode 76 Saturable absorption layer 78 Contact layer 79 Mesa region

Claims (9)

[Claims] 1. A semiconductor substrate of a first conductivity type, a first cladding layer of a first conductivity type, an active layer, and a second cladding layer of a second conductivity type formed on the semiconductor substrate. At least a laminated structure, a current block function body formed with a stripe-shaped region on the laminated structure, and a second conductivity formed so as to fill the stripe portion and the current block function body. Laser device including a third clad layer of the type, wherein the current blocking function body includes at least a saturable absorption layer having a forbidden band width substantially equal to the forbidden band width of the active layer. . 2. A first conductivity type semiconductor substrate, a first conductivity type first clad layer, an active layer, and a second conductivity type second clad layer formed on the semiconductor substrate. A laminated structure including at least the same, a stripe-shaped mesa region formed on the laminated structure and including at least a third clad layer of the second conductivity type and a contact layer of the second conductivity type, and the mesa region on the laminated structure. And a current blocking function body formed on both sides of the striped mesa region, wherein the current blocking function body has a forbidden band width substantially equal to the forbidden band width of the active layer. A semiconductor laser device including at least a saturable absorption layer having the saturable absorption layer, the saturable absorption layer covering a side surface of the stripe mesa region. 3. The current blocking function body has an n-type semiconductor layer provided on the laminated structure side, and the saturable absorption layer is arranged on the opposite side of the n-type semiconductor layer from the substrate. A part of the structure having a p-type structure.
Alternatively, the semiconductor laser device according to item 2. 4. The forbidden band width of a portion of the current blocking function body other than the saturable absorption layer is larger than the forbidden band widths of the first and second cladding layers, and is generated in the active layer by current injection. 4. The semiconductor laser device according to claim 1, 2 or 3, which has no absorbing effect on the laser light generated. 5. An Al composition ratio x that gives an effective forbidden band width of the active layer and an Al composition ratio y that gives an effective forbidden band width of the saturable absorption layer are x-0.02 ≦ The semiconductor laser device according to claim 1, 2 or 3, wherein a relation of y ≦ x + 0.02 is satisfied. 6. The semiconductor laser device according to claim 1, wherein a region of the active layer corresponding to the outside of the striped region further functions as a saturable absorber. 7. A first conductive type semiconductor substrate is provided on the first conductive type semiconductor substrate.
A step of growing a laminated structure including at least a first clad layer of conductivity type, an active layer, and a second clad layer of second conductivity type, and a forbidden band width of the active layer on the laminated structure. Growing a current blocking function body including at least a saturable absorption layer having an equal forbidden band width, forming a stripe region in the current blocking function body by etching, the stripe portion and the current blocking function And a step of growing a second conductivity type third clad layer covering the body. 8. A first conductive type semiconductor substrate is provided on the first conductive type semiconductor substrate.
Growing a laminated structure including at least a first clad layer of conductivity type, an active layer, and a second clad layer of second conductivity type; and a third clad of second conductivity type on the laminated structure. A layer and a contact layer of the second conductivity type are grown in order; a step of etching the third cladding layer and the contact layer to form a stripe-shaped mesa region; On both sides of the stripe-shaped mesa region, a current blocking function body including at least a saturable absorption layer having a forbidden band width substantially equal to the forbidden band width of the active layer is provided. A method of manufacturing a semiconductor laser device, which comprises a step of growing so as to cover a side surface. 9. The semiconductor laser device according to claim 7, further comprising the step of forming a p-type saturable absorption layer after forming an n-type semiconductor layer in the step of growing the current blocking function body. Manufacturing method.