JPH08264889A - Semiconductor laser element - Google Patents

Abstract

PURPOSE: To provide a semiconductor laser element in which the noise or the increase of the drive power is prevented and which has excellent characteristics such as low power consumption and low noise in a real refractive index guided laser in which the inhibit band gap of a current light confinement layer is narrower than that of a clad layer. CONSTITUTION: A current light confinement layer 106 is formed of a structure which has an inhibit band gap larger than that of an active layer 104 and smaller than those of first and second clad layers 103, 105 and in which the layer is thinner than 1μm and its Al composition ratio is 0.35 or less, and the stripe groove 107 is wider than 1.0 but narrower than 4μm.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a semiconductor laser device, and more particularly to improving the characteristics of a semiconductor laser device used for optical disks and the like.

[0002]

2. Description of the Related Art A semiconductor laser having a wavelength band of 780 nm is
CD (Compact Disk), MD (Mini
Disk) and MO (Magneto-Optica)
l) Widely used as a light source for disk devices.
The specifications required for these semiconductor lasers are (1)
To reduce the power consumption by reducing the drive current and drive voltage as much as possible. (2) When used in an optical disk device,
One of the reasons is that there is little noise induced by the returning light from the optical disc and other optical parts during signal reproduction.

Regarding the power consumption reduction of (1), since the drive voltage is almost determined by the forbidden band width of the light emitting layer and the large reduction is impossible, the reduction of the drive current is mainly studied.

Regarding the laser return light noise reduction of (2), the self-sustained pulsation phenomenon of a semiconductor laser is actively used. In self-sustained pulsation, when the laser is driven with a constant current, the light intensity of the emitted light of the laser is not constant and
It becomes a time-varying state at a high frequency of about GHz. When the self-excited oscillation occurs, the coherence of the emitted laser light is lowered because the oscillation spectrum line width increases and the oscillation spectrum becomes multimode. As a result, the interference between the emitted laser light and the return light is reduced, and the optical coherence noise of the laser can be reduced.

Regarding the reduction of the driving current of the laser described in (1), a laser using a semiconductor layer which does not absorb light as a current / light confinement layer has been proposed and its performance has been verified. This type of laser utilizes a difference in the real part of the refractive index for confining light, that is, a substantial difference in the refractive index between the laser oscillation part and the other region, and therefore, the real index guided type laser is used. Called a laser. The conventional example will be described below.

(Conventional Example 1) A real index guided laser (Appl. Phys. Lett., Vo reported by Takayama et al.
l. 65, pp. 1211 (1994)) will be described. FIG. 2 shows a cross-sectional structure of this real index guided laser device.

In the figure, reference numeral 200 designates the real refractive index guided laser element, which is formed on an n-GaAs substrate 201 of n-Ga.
Laminated structure 20 formed via As buffer layer 202
It has 0a. The laminated structure 200a is made of AlGaA.
The s-active layer 204 is sandwiched between the n-AlGaAs first cladding layer (lower cladding layer) 203 and the p-AlGaAs second cladding layer (upper cladding layer) 205.

On the upper cladding layer 205, an n-AlGaAs current / light confinement layer 206 having a stripe-shaped groove 207 reaching the surface of the layer in the central portion is provided, and on the current / light confinement layer 206, A p-AlGaAs third cladding layer 208 is formed so as to fill the stripe-shaped groove 207. This third clad layer 20
8 through p-GaAs contact layer 209.
The mold electrode 210 is formed, and n is formed on the back surface side of the substrate 201.
The mold electrode 211 is formed.

Next, the manufacturing method will be described.

First, n-G is formed on an n-GaAs substrate 201.
After forming the aAs buffer layer 202 to a layer thickness of about 1.0 μm, an n-Al _0.55 Ga _0.45 As first cladding layer 203 is formed on the aAs buffer layer 202 to a layer thickness of about 1.5 μm and undoped Al _0.14 G.
The a _0.86 As active layer 204 is grown to a layer thickness of about 0.06 μm, and the p-Al _0.55 Ga _0.45 As second clad layer 205 is grown to a layer thickness of about 0.1 μm to form a laminated structure 200a. Then, n-Al is formed on the second cladding layer 205.
_0.65 Ga _0.35 AS Current / light confinement layer 206 with a layer thickness of 1.0
It grows to about μm. Here, the growth of each semiconductor layer is MO
It is performed by a CVD (metal organic chemical vapor deposition) method.

Then, in the central portion of the current / light confinement layer 206, a width of 2.0 μ reaching the p-second cladding layer 205.
m stripe stripe 207 is formed, and then the p-Al _0.55 Ga _0.45 As third clad layer 2 is formed so as to fill the groove 207.
08 was grown to a layer thickness of about 2.0 μm, and p-GaA
The s contact layer 209 is formed to have a layer thickness of about 1.0 μm. Here, the growth of each of the above semiconductor layers is the second MOC.
The VD method is used.

Next, p is formed on the exposed surface of the contact layer 209.
The mold electrode 210 is formed, and the n-type electrode 211 is formed on the back surface side of the substrate 201.

Then, the resonator length is 100 by the cleavage method.
dividing the substrate so that the [mu] m, thereby the reflectance cavity facet obtained forms an Al ₂ O ₃ film to be 32%.

In this laser device, the oscillation start current is 15.2 mA when a forward voltage is applied between the p-type electrode 210 and the n-type electrode 211, and the slope efficiency of the current-light output characteristic is 0.66 W / A. Has become. Further, the present laser element can observe a self-excited oscillation phenomenon in which the light intensity changes with time at a high frequency of about 1 GHz at an optical output of 3 mW, and the noise due to the returning light can be sufficiently suppressed.

In the laser device of Conventional Example 1, assuming that the forbidden band width of the current / light confinement layer 206 is Eg1, the forbidden band width of the active layer 204 is Eg2, and the forbidden band widths of the cladding layers 203 and 205 are Eg3 and Eg4, respectively. The forbidden band widths of the semiconductor layers satisfy Eg2 <Eg3 and Eg4 <Eg1.

Here, since the forbidden band width of the current / light confinement layer is wider than the forbidden band width of the active layer, the light generated in the active layer is not absorbed in the current / light confinement layer.

Further, since the forbidden band width of the current / light confinement layer is wider than the forbidden band width of the cladding layer, and the forbidden band width and the refractive index are in inverse proportion to each other, the refractive index of the current / light confinement layer is the refractive index of the cladding layer. Will be lower than. Therefore, the equivalent refractive index in the layer thickness direction outside the stripe groove becomes lower than the equivalent refractive index in the layer thickness direction inside the stripe groove, and optical confinement (real refractive index guiding) due to the difference in actual refractive index is possible. Become. Also,
In this element, self-pulsation is realized by adjusting the equivalent refractive index difference (Δn) in the layer thickness direction inside and outside the stripe groove.

(Prior art example 2) Real refractive index guided laser reported by Shima et al. (Proceedings of the 1994 Spring Applied Physics Society of Japan 28p-
K-4) will be described. FIG. 3 is a sectional view showing the device structure of this real index guided laser.

In the figure, reference numeral 300 designates a real refractive index guided laser device, on the n-GaAs substrate 301 of which a TQW is provided.
(Triple Quantum Well) Active Layer 3
03 is sandwiched between an n-AlGaAs first clad layer (lower clad layer) 302 and a p-AlGaAs second clad layer (upper clad layer) 304.
a is provided.

AlGa is formed on the upper cladding layer 304.
An As etching stop layer 305 is formed, and p-AlGaA is formed in the central portion of the etching stop layer 305.
A ridge stripe portion 308 is formed by stacking a p-GaAs layer 307 on the third cladding layer 306, and a p-AlGaAs current / light confinement layer is formed on both sides of the ridge stripe portion 308 so as to fill the side surface of the ridge. Thirty
9 is formed.

A p-type electrode 311 is formed on the ridge stripe portion 308 and the photocurrent confinement layer 309 via a p-GaAs contact layer 310, and an n-type electrode 312 is formed on the back surface of the substrate 301. Has been formed.

Next, the manufacturing method will be described.

On the n-GaAs substrate 301, n-Al
_0.48 Ga _0.52 As First cladding layer 302, TQW (Tr
an active layer 303 of the triple quantum well),
The p-Al _0.48 Ga _0.52 As second cladding layer 304 is MO
Sequential growth is performed by the CVD method to form a laminated structure 300a. Then, on the second cladding layer 304, p-Al
_0.69 Ga _0.31 As Etching stop layer 305, p-A
l _0.48 Ga _0.52 As Third cladding layer 306, p-GaA
The s layer 307 is sequentially laminated by MOCVD.

Next, a dielectric stripe mask is formed on the surface of the p-GaAs layer 307 in a predetermined region, and then an etching process is performed to form a ridge stripe portion 308 reaching the etching stop layer 305. continue,
N− by a chlorine-added MOCVD method so as to fill the side surface (ridge side surface) on both sides of the ridge stripe portion 308.
An Al _0.7 Ga _0.3 As current / light confinement layer 309 is formed,
A p-GaAs contact layer 310 is formed on the entire surface by MOCVD. After that, the p-type electrode 311 is formed on the front surface of the contact layer 310, and the n-type electrode 3 is formed on the rear surface side of the substrate 301.
12 is formed.

The resonator length is 600 μ by the cleavage method.
The substrate is divided so as to have a thickness of m, and a predetermined treatment is applied to the end face of the resonator thus obtained so that the reflectance thereof is 4% to 90%.

In the present laser device 300, the p-type electrode 311 is used.
The oscillation start current when a forward voltage is applied between the n-type electrode 312 and the n-type electrode 312 is 32 mA, and the slope efficiency of the current-optical output characteristic is 1.05 W / A.

Also in the laser of Conventional Example 2, since the forbidden band width of the current / light confinement layer is wider than the forbidden band width of the cladding layer, the forbidden band width and the refractive index are in inverse proportion to each other.
The refractive index of the current / light confinement layer is lower than that of the cladding layer. Therefore, the equivalent refractive index in the layer thickness direction outside the ridge stripe portion becomes lower than the equivalent refractive index in the layer thickness direction inside the ridge stripe portion, and optical confinement due to the difference in the actual refractive index (actual refractive index guide ) Is possible.

(Conventional Example 3) The forbidden band width Eg1 of the current / light confinement layer, the forbidden band width Eg2 of the active layer, and the forbidden band width Eg3 of the cladding layer satisfy the relationship of Eg2 <Eg1 <Eg3.
A real refractive index guided laser has been reported by Yano et al. (See Japanese Patent Publication No. 57-5070). FIG. 4 is a sectional view showing the element structure disclosed in this publication.

In the figure, reference numeral 400 denotes the real refractive index waveguide type laser device, on the n-GaAs substrate 401, an undoped AlGaAs active layer 403, an n-AlGaAs first cladding layer (lower cladding layer) 402 and p. -AlGa
A laminated structure 400a sandwiched between As second clad layers (upper clad layer) 404 is provided.

On the upper cladding layer 404, an n-AlGaAs current / light confinement layer 405 having a stripe-shaped groove 406 reaching the surface of the layer is provided in the central portion, and on the current / light confinement layer 405. A p-AlGaAs third cladding layer 407 is formed so as to fill the stripe groove 406. This third clad layer 40
7 through p-GaAs contact layer 408.
A mold electrode 409 is formed, and n is formed on the back surface side of the substrate 401.
A mold electrode 410 is formed.

Next, the manufacturing method will be described.

First, on the n-GaAs substrate 401, n-
Al _0.6 Ga _0.4 As 1st clad layer 402 layer thickness 1.5
μm, undoped Al _0.20 Ga _0.80 As active layer 403
To a layer thickness of 0.1 μm, and a p-Al _0.6 Ga _0.4 As second cladding layer 404 to a layer thickness of 0.2 μm.
00a, and then the n-Al _0.4 Ga _0.6 As current / light confinement layer 405 is formed to have a layer thickness of 1.0 μm.

Next, a stripe groove 406 reaching the p-second cladding layer 404 is formed in the central portion of the current / light confinement layer 405, and then p-Al _0.6 Ga _0.4 As is filled so as to fill the stripe groove 406. Third cladding layer 407
Is formed to have a layer thickness of 2.0 μm, and p-Ga is further formed thereon.
The As contact layer 408 is grown to a layer thickness of 1.0 μm.
Then, a p-type electrode 409 is formed on the surface of the contact layer 408.
Then, the n-type electrode 410 is formed on the back surface side of the substrate 401.

Then, the resonator length is 250 by the cleavage method.
The substrate is divided to have a thickness of 400 μm.

In the laser device of Conventional Example 3, the p-type electrode 40 is used.
The oscillation start current when a forward voltage is applied between the 9 and the n-type electrode 410 is 100 mA.

Here, since the forbidden band width of the current confinement layer is wider than the forbidden band width of the active layer, the light generated in the active layer is not absorbed in the current light confinement layer.

Since the forbidden band width of the current / light confinement layer is narrower than the forbidden band width of the cladding layer, and the forbidden band width and the refractive index are in inverse proportion to each other, the refractive index of the current / light confinement layer is larger than that of the cladding layer. It will be higher than the refractive index.

However, since the equivalent refractive index in the laser oscillation mode selected outside the stripe groove is lower than the equivalent refractive index in the layer thickness direction inside the stripe groove, the optical confinement due to the difference in the actual refractive index (real refraction Index guiding) is possible.

The optimum design range of the laser device of Conventional Example 3 is described in the above publication, and the stripe width (width of the stripe groove) W, the layer thickness of the current / light confinement layer and the forbidden band width are respectively d. And Eg1, and the forbidden band width of the cladding layer is Eg3, the stripe width is W = 4 to 7 μm.
m is appropriate, and under the conditions of W <3 μm and W> 8 μm, the effect of lateral light confinement is not exhibited, and the layer thickness of the current light confinement layer is appropriately d = 1 to 2 μm. It is desirable that the difference between the forbidden band widths Eg1 and Eg3 is relatively small.

In the optical confinement mechanism in the laser device of Conventional Example 3, self-sustained pulsation has not been studied at all.

[0041]

In the semiconductor laser device 200 of Conventional Example 1, the forbidden band width of the current / light confinement layer 206 is wider than the forbidden band width of the cladding layer. In the AlGaAs material, the forbidden band width and the Al composition ratio are in a proportional relationship, so that the current light confinement layer satisfying this condition has a considerably high Al composition ratio. Therefore, in the process of forming a groove in the current / light confinement layer, the surface of the current / light confinement layer is easily oxidized, and a growth defect occurs in the MOCVD growth for filling the groove thereafter, so that a desired element structure is formed. There is a problem that it becomes very difficult.

Further, the semiconductor laser device 300 of the second conventional example.
Then, since the forbidden band width of the current / light confinement layer is set to be wider than the forbidden band width of the cladding layer,
The composition ratio becomes considerably high. Therefore, when the current and light confinement layers are embedded and grown on both sides of the ridge stripe portion,
It is necessary to add a highly reactive gas such as chlorine so that the growth material is not deposited on the surface of the dielectric mask. As a result, there is a problem that abnormal reaction or corrosion occurs inside the growth apparatus.

On the other hand, in the semiconductor laser device 400 of Conventional Example 3, the forbidden band width of the current / light confinement layer is narrower than the forbidden band width of the cladding layer. Therefore, the Al composition ratio of the current / light confinement layer that satisfies this condition can be set relatively low. Therefore, in the manufacturing process of the element having the groove burying structure similar to that of the conventional example 1, the surface oxidation at the time of forming the groove is suppressed, so that the growth failure is less likely to occur in the groove burying MOCVD growth.

However, in the stripe width W, the layer thickness d of the current / light confinement layer, and the forbidden band width (Al composition ratio) of the current / light confinement layer disclosed as the optimum design range in Conventional Example 3, the following problems occur. Occurs.

That is, in the technique described in the above publication, it is said that the stripe width W is appropriately set to W = 4 to 7 μm. However, when this value W is 4 μm or more, the self-sustained pulsation of the laser is hard to occur, and therefore, Moreover, the noise reduction of the laser cannot be realized. Further, when the stripe width is 4 μm or more, the oscillation start current increases, so that it is difficult to reduce the current.

The current / light confinement layer d is d = 1 to 2 μm.
Although it is considered that m is appropriate, when d is 1 μm or more, the layer thickness of the stripe region becomes large, so that the element resistance increases and the driving voltage increases. Furthermore, d is 1 μm
In the above case, the self-sustained pulsation of the laser is unlikely to occur, and the noise reduction of the laser cannot be realized.

Further, it is said that it is more appropriate that the forbidden band width of the current / light confinement layer is closer to the forbidden band width of the cladding layer. In that case, however, the Al composition ratio of the current / light confinement layer becomes high. Surface oxidation of the current / light confinement layer is likely to occur at the time of forming the stripe groove, and defective growth may occur at the time of crystal growth for filling the groove. Moreover, even when the Al composition ratio is high, self-sustained pulsation is less likely to occur, and the noise reduction of the laser cannot be realized as in the above case.

As described above, in Conventional Example 3, since the element structure for causing self-sustained pulsation has not been examined, it is difficult to realize low noise. Further, since the drive voltage necessary for reducing the power consumption is insufficiently studied, it is difficult to reduce the power consumption by reducing the drive voltage. Further, from the viewpoint of achieving the low noise and low power consumption, in the manufacturing process of the device using the AlGaAs material described in the above publication, the set values such as dimensions in the device structure are in the optimum range. Not really.

The present invention has been made in order to solve the above problems, and in a real refractive index guided laser in which the forbidden band width of the current / light confinement layer is narrower than the forbidden band width of the cladding layer, noise of It is an object of the present invention to provide a semiconductor laser device which is excellent in characteristics of low power consumption and low noise by preventing generation and increase in driving power.

[0050]

A semiconductor laser device according to the present invention is a semiconductor laser device using a semiconductor material containing Al as a constituent material, wherein a first conductivity type first clad layer comprises: A laminated structure formed by sequentially laminating an active layer and a second conductivity type second cladding layer; a stripe-shaped semiconductor layer formed on a surface of the second cladding layer;
And a current / light confinement layer formed on both sides of the striped semiconductor layer on the surface of the clad layer. The current / light confinement layer has a forbidden band width larger than the forbidden band width of the active layer and smaller than the forbidden band width of the first and second cladding layers, and has a layer thickness smaller than 1 μm and a The stripe-shaped semiconductor layer is formed to have a composition ratio of 0.35 or less and a width of 1.0 μm.
It is formed so as to have a value within the above range and less than 4 μm. Thereby, the above object is achieved.

In the semiconductor laser device according to the present invention, the difference Δn between the equivalent refractive index in the layer thickness direction inside the striped semiconductor layer and the equivalent refractive index in the layer thickness direction outside the striped semiconductor layer is Δn. ^Is 1 × 10 ⁻³ or more and 1 × 10
Values are in the range of ^-2 or less.

According to the present invention, in the above semiconductor laser device, the current light confinement layer has a layer thickness of 0.4 μm or more and 0.8 μm or less.

[0053]

In the present invention, the forbidden band width of the current / light confinement layer is narrower than that of the cladding layer, so that the Al composition ratio of the current / light confinement layer can be set relatively low. As a result, the surface oxidation of the current / light confinement layer that occurs when the stripe groove is formed is suppressed, and the growth failure of the semiconductor layer grown on the current / light confinement layer by MOCVD growth embedded in the groove can be suppressed.

Further, since the width W of the stripe groove is 4 μm or less, self-excited oscillation is likely to occur and noise reduction can be realized, and the width of the stripe groove is 4 μm or less and 1.0 μm or more. Therefore, the oscillation start current Ith can be reduced and power consumption can be reduced.

Further, since the thickness of the current / light confinement layer is less than 1 μm, it is possible to prevent the driving voltage from increasing, and it becomes easy for self-sustained pulsation to occur, so that the noise can be reduced. Further, the Al composition ratio of the current / light confinement layer is set to 0.35.
As described below, when a semiconductor layer is formed by the second crystal growth on the semiconductor layer formed by the first crystal growth, crystal defects are less likely to occur, and the drive voltage is increased as the resistance due to the crystal defects increases. Can be suppressed. Further, it is possible to suppress the deposition of the film-forming substance on the SiN mask for selective growth used when burying the ridge stripe portion. Further, since the Al composition ratio X1 is 0.35 or less, the maximum self-excited oscillation light output Pmax can be maintained at a certain value or more, and noise can be reduced.

[0056]

Embodiments of the present invention will be described below.

(Embodiment 1) FIG. 1 is a diagram showing a sectional structure of a semiconductor laser device according to a first embodiment of the present invention.

In the figure, reference numeral 100 denotes a real index guided laser device of this embodiment, which has a laminated structure 100a formed on an n-GaAs substrate 101 via an n-GaAs buffer layer 102. . In the laminated structure 100a, the undoped AlGaAs active layer 104 is made into n-AlGaAs.
First cladding layer (lower cladding layer) 103 and p-AlG
It is configured by being sandwiched by the aAs second cladding layer (upper cladding layer) 105.

On the upper clad layer 105, a n-AlG layer having a layer thickness of 0.5 μm and having a 2.5 μm wide stripe-shaped groove 107 reaching the surface of the clad layer in the central portion.
An aAs current / light confinement layer 106 is provided, and a p-AlGaAs third cladding layer 108 is formed on the current / light confinement layer 106 so as to fill the stripe groove 107. On the third clad layer 108, p−
A p-type electrode 110 is formed via the GaAs contact layer 109, and an n-type electrode 111 is formed on the back surface side of the substrate 101.

Next, the manufacturing method will be described.

A layer thickness of 0.5 μm on the n-GaAs substrate 101.
m n-GaAs buffer layer 102 is grown, and subsequently,
On top of that, n-Al _0.6 Ga _0.4 As having a layer thickness of 1.0 μm
Clad layer 103, undoped Al with a layer thickness of 0.06 μm
_0.14 Ga _0.86 As active layer 104, p− with a layer thickness of 0.3 μm
The Al _0.6 Ga _0.4 As second cladding layer 105 is grown to form the laminated structure 100a. After that, n-Al _0.2 Ga _0.8 As having a layer thickness of 0.5 μm is formed on the second cladding layer 105.
The current / light confinement layer 106 is grown. Here, the growth of each semiconductor layer is performed by crystal growth by the first MOCVD method.

Next, by selective etching, a stripe groove 107 having a width of 2.5 μm and reaching the p− second cladding layer 105 is formed in the central portion of the current / light confinement layer 106.

Then, the p-Al _0.6 Ga _0.4 As third cladding layer 108 is formed so as to fill the stripe groove 107 on the entire surface.
To a layer thickness of 1.5 μm, and then p
The GaAs contact layer 109 is grown to have a layer thickness of 1.5 μm. Here, the third cladding layer 108 and the contact layer 109 are grown by the second MOCVD.
It is performed by crystal growth according to the method.

After that, p is formed on the surface of the contact layer 109.
The mold electrode 110 is formed, and the n-type electrode 111 is formed on the back surface side of the substrate 101.

Then, the resonator length is 200 by the cleavage method.
dividing the substrate so as to be [mu] m, thereby the reflectance cavity facet obtained forms an Al ₂ O ₃ film to be 30%.

In the laser device 100 of this embodiment, the oscillation starting current when a forward voltage is applied between the p-type electrode 110 and the n-type electrode 111 is 19.7 mA, and the slope efficiency of the current-light output characteristic is 0. It was 0.46 W / A, and low current operation could be realized.

Further, when the light output is 3 mW, the light intensity is 1
A self-excited oscillation phenomenon that changes with time at a high frequency of about GHz could be observed. When such self-excited oscillation occurs, the coherence of the emitted laser light is lowered because the oscillation spectrum line width increases and the oscillation spectrum becomes multimode. Therefore, in the device of this embodiment, the interference between the emitted laser light and the returning light is small, and the optical coherence noise of the device can be reduced. Such an element is suitable for use in which return light is generated, such as an optical disk device.

In the sectional structure of the device 100 of this embodiment shown in FIG. 1, the width of the stripe groove 107 (stripe width) is W, the layer thickness of the current / light confinement layer 106 is d, and the Al composition of the current / light confinement layer 106 is Al. When the ratio is X1, when d is 0.5 μm and X1 is 0.2 as in the present embodiment, the change of the oscillation start current (Ith) with respect to the change of W,
And maximum self-oscillation light output (Pmax) for changes in W
Changes are as shown in FIGS. 6 and 7, respectively.

When Pmax is larger than 0 mW, self-excited oscillation occurs, and the noise of the element with respect to the return light is reduced. The larger Pmax is, the stronger the self-excited oscillation intensity is, and the noise is further reduced. On the other hand, it can be seen from FIG. 7 that Pmax = 0 mW when the stripe width W is 4 μm or more, so that self-excited oscillation does not occur and noise reduction cannot be realized. Further, it can be seen from FIG. 6 that the oscillation start current Ith tends to rapidly increase when the stripe width W has a value of 4 μm or more and a value of less than 1.0 μm.

From the above, it was found that it is important to set 1.0 μm ≦ W <4 μm in order to achieve both low noise characteristics and low current characteristics.

Next, FIG. 8 shows changes in the drive voltage Vop (light output 3 mW) when the layer thickness d of the current / light confinement layer changes when W = 2.5 μm and X1 = 0.25. When the layer thickness d becomes thicker than 1 μm, the element resistance increases, so that the driving voltage Vop increases to 2 V or more. Further, FIG. 9 shows changes in the maximum self-excited oscillation light output Pmax with respect to changes in the layer thickness d when the oscillation start current is constant. It can be seen that when the layer thickness d increases, Pmax sharply decreases, and noise reduction cannot be realized. From the above, it is necessary to set the layer thickness d of the current / light confinement layer to be smaller than 1 μm.

The stripe width W is W = 2.5 μm,
When the Al composition ratio X2 of the active layer 104 is X2 = 0.14, the Al composition ratio X3 of the cladding layer is X3 = 0.6, and the layer thickness d of the current / light confinement layer is d = 0.55 μm, FIG. 10 shows the ratio of the normal growth portion in the wafer surface to the Al composition ratio X1 of the confinement layer. Here, the normal growth portion has a driving voltage of 2 when a forward voltage is applied.
It was assumed to be V or less. If a crystal defect occurs in the second crystal growth, the drive voltage increases as the resistance increases.
When the Al composition ratio X1 is greater than 0.35, the rate of normal growth is less than 50%, and the occurrence of poor growth increases.

Further, the maximum self-excited oscillation light output Pma with respect to the above Al composition ratio X1 when the oscillation start current is constant.
x is shown in FIG. As X1 increases, Pmax tends to decrease. In particular, when X1 becomes larger than 0.35, Pmax sharply decreases, and it can be seen that noise reduction cannot be realized. From the above, it is necessary to set X1 to 0.35 or less.

From the above, in order to solve the problem of manufacturing the device due to defective crystal growth, realize the low power consumption by the low current and low voltage, and suppress the noise generation due to the returning light, the stripe width W, Layer thickness d of current / light confinement layer and AlG
It was found that it is important to set the Al composition ratio X1 of the aAs current / light confinement layer to 1.0 μm ≦ W <4 μm, 0 μm <d <1 μm, and X1 ≦ 0.35.

Further, as a precondition for causing self-sustained pulsation in the device of this embodiment, the stripe groove 10 is used.
7 Equivalent refractive index difference (Δn) in the layer thickness direction inside and outside
Need to be suppressed.

FIG. 12 shows the relationship between the oscillation start current (Ith) and the equivalent refractive index difference Δn, and FIG. 13 shows the relationship between the maximum self-oscillation light output (Pmax) and the equivalent refractive index difference Δn. It can be seen that by setting Δn to 10 × 10 ⁻³ or less, desired self-excited oscillation occurs and noise reduction can be realized. However, when Δn is less than 1 × 10 ⁻³ , the intensity of self-excited oscillation is too strong, and the oscillation start current Ith is 30 m.
It increases above A, and low current driving becomes difficult. Therefore, it is important to set 1 × 10 ⁻³ ≦ Δn ≦ 1 × 10 ⁻² .

FIG. 14 shows the relationship between the equivalent refractive index difference Δn and the layer thickness d of the current / light confinement layer. Here, the Al composition ratio X1 of the current / light confinement layer is taken as a parameter, and 0.15 (black circles), 0.20 (black squares),
Five cases of 0.25 (white circle), 0.30 (white square), and 0.35 (white triangle) are shown. The other conditions are the same as those of the element structure of the first embodiment.

In order for Δn to satisfy the above range, it is desirable to set d to 0.4 μm ≦ d ≦ 0.8 μm. Within this range, the Al composition ratio X1 of the current / light confinement layer is adjusted. For example, the equivalent refractive index difference Δn can be set within the above required range.

When the layer thickness d is 0.9 μm or more,
When the layer thickness d is 0.3 μm or less, there is a problem that the driving voltage increases and it is difficult to reduce the noise. Deterioration becomes a problem.

(Embodiment 2) FIG. 5 shows a sectional structure of a semiconductor laser device according to a second embodiment of the present invention. The element of this embodiment is a high-power laser capable of emitting high-power emitted light for signal rewriting in an optical disk device capable of signal rewriting.

In the figure, reference numeral 500 denotes a high-power laser device of this embodiment, on the n-GaAs substrate 501,
Laminated structure 500 via n-GaAs buffer layer 502
a is provided, and the laminated structure 500a is configured by sandwiching the undoped active layer 504 between the n-AlGaAs first cladding layer (lower cladding layer) 503 and the p-AlGaAs second cladding layer (upper cladding layer) 505. Has been done.

The upper cladding layer 505 has a ridge stripe portion 507 in the center thereof, and a p-GaAs layer 506 is formed on the ridge stripe portion 507. Further, p-AlGaAs current / light confinement layers 508 are formed on both sides of the ridge stripe portion 507 so as to fill the side surfaces of the ridge.

A third clad layer 509 is formed on the entire surface of the p-GaAs layer 506 and the photocurrent confinement layer 508 on the ridge stripe portion 507, and a p-GaAs contact layer 510 is formed on the third clad layer 509. Has been done.

Then, a p-type electrode 5 is formed on the contact layer.
11 is formed, and the n-type electrode 5 is formed on the back surface side of the substrate 501.
12 are formed.

Next, the manufacturing method will be described.

First, an n-GaAs buffer layer 502 having a layer thickness of 0.5 μm is grown on an n-GaAs substrate 501, and then n-Al _0.5 Ga _0.5 having a layer thickness of 1.5 μm is formed thereon.
As first clad layer 503, undoped Al _0.14 Ga _0.86 As active layer 504 having a layer thickness of 0.05 μm, layer thickness 1.5 μm
Then, a p-Al _0.5 Ga _0.5 As second cladding layer 505 of m is sequentially grown to form a laminated structure 500a. Then, p-GaAs having a layer thickness of 0.1 μm is formed on the second cladding layer 505.
Grow layers. Here, the growth of each semiconductor layer is performed by crystal growth by the first MOCVD method.

Next, the p-GaAs layer and the second cladding layer 505 are selectively etched by using the SiN stripe film as a mask to form a ridge stripe 507 and a p-GaAs layer 506 thereon. The etching is performed so that the layer thickness of the remaining portion of the etched portion of the p− second cladding layer 505 is 0.45 μm.

Next, by the second crystal growth by the MOCVD method, n-Al _0.2 Ga _0.8 As is formed on both sides of the ridge stripe 507 by using the SiN stripe film as a mask.
The current / light confinement layer 508 is grown to have a layer thickness of 0.5 μm, and the ridge stripe portion 507 is embedded.

Further, the SiN stripe film is removed,
By the third crystal growth by the MOCVD method, a p-Al _0.5 Ga _0.5 As third cladding layer 509 is grown to a thickness of 0.5 μm on the entire surface, and a p-GaAs contact layer 510 is further formed to a thickness of 1 μm. It grows to 0.5 μm.

After that, p is formed on the surface of the contact layer 510.
The mold electrode 511 is formed, and the n-type electrode 512 is formed on the back surface side of the substrate 501.

Then, the resonator length is 375 by the cleavage method.
The substrate is divided to have a thickness of μm, and the end facet on the light emission side of the resonator thus obtained is made of Al so that the reflectance is 12%.
_{A 2} O ₃ film is formed, and its reflectance is 75 on the opposite end face.
The Si film is formed so that the content becomes%.

In the laser device of this embodiment, the p-type electrode 51 is used.
When a forward voltage was applied between the 1 and n-type electrode 512, the oscillation start current was 39 mA, the slope efficiency of the current-light output characteristics was 0.70 W / A, and low current operation could be realized.

Furthermore, a self-excited oscillation phenomenon can be observed at an optical output of 3 mW, and when the element of this example is used for signal reproduction, low noise operation for returned light can be realized. Therefore, in the past, in order to reduce noise during signal reproduction in a high-power laser, a method of lowering coherence by superposing a high frequency wave on a driving current and causing laser light to oscillate in multimode has been used. Therefore, it is not necessary to superimpose a high frequency, so that the driving circuit can be simplified and the size and weight can be reduced.

A laser device 500 of the second embodiment shown in FIG.
In the cross-sectional structure of FIG. 5, the width of the lower portion of the ridge stripe 507 is W, the layer thickness of the current / light confinement layer 508 is d, and its Al
When the composition ratio is X1, d is 0.5 as in the present embodiment.
When μm and X1 are 0.2, the change of the oscillation start current (Ith) with respect to the change of W and the change of the maximum self-excited oscillation light output (Pmax) with respect to the change of W are shown in FIG.
5 and as shown in FIG.

When Pmax is larger than 0 mW, self-sustained pulsation occurs, and the noise of the element with respect to the return light is reduced. The larger Pmax is, the stronger the self-excited oscillation intensity is, and the noise is further reduced. On the other hand, it can be seen from FIG. 16 that Pmax = 0 mW when W is 4 μm or more, so that self-sustained pulsation does not occur and noise reduction cannot be realized. Further, when W is 4 μm or more, or when W is less than 1.0 μm, Ith tends to rapidly increase as shown in FIG.
I understand more.

Regarding the current / light confinement layer thickness d,
It is necessary to set the thickness to less than 1 μm in order to prevent an increase in driving voltage and reduce noise.

Also, the Al composition ratio X1 of the current / light confinement layer
However, if it is larger than 0.35, a film forming material is deposited on the SiN stripe film at the time of manufacturing the device, and its removal requires a very complicated process. Further, in order to prevent such deposition of the film forming material, if a reactive gas is used as in Conventional Example 2, problems such as corrosion in the growth apparatus occur. On the other hand, when the Al composition ratio X1 is 0.35 or less, deposition on the SiN stripe film does not occur.

From the above, in order to solve the problem in manufacturing the device due to defective crystal growth, realize the low power consumption by the low current and low voltage, and suppress the noise generation due to the returning light,
It is important to select W, d, and X1 as 1.0 μm ≦ W <4 μm, 0 μm <d <1 μm, and X1 ≦ 0.35.

The structure of the semiconductor laser device is not limited to that of the above-mentioned embodiment, and the layer thickness and Al composition ratio other than that of the embodiment may be any as long as the effects of the present invention can be obtained. Good.

Further, in each of the above embodiments, the AlGaAs-based material is given as an example of the Al-containing semiconductor material, but the present invention is also applicable to other AlGaInP-based materials.

In each of the above embodiments, MOCV is used as a method for growing each semiconductor layer forming the semiconductor laser device.
Although the D method is used, it is not limited to this, and other growth methods such as LPE (liquid phase epitaxy) method, MBE (molecular beam epitaxy) method, MOMBE method, and ALE (atomic layer epitaxial growth) method are also used. Can also be used.

[0102]

As described above, according to the semiconductor laser device of the present invention, the width of the stripe-shaped portion as the light emitting region of the laser beam, the layer thickness of the current / light confinement layer located on both sides of the stripe-shaped portion, and Al. By optimizing the composition ratio and the equivalent refractive index difference between the inside and the outside of the stripe-shaped portion, both low current characteristics and low noise characteristics can be achieved, and the current / light confinement layer thickness is optimized. Low voltage drive can be achieved. Further, by optimizing the Al composition ratio of the current / light confinement layer, it is possible to avoid problems caused by the manufacturing process of the laser device.

As described above, according to the present invention, low power consumption and low noise can be realized without causing a problem in manufacturing the device.

[Brief description of drawings]

FIG. 1 is a diagram showing a cross-sectional structure of a semiconductor laser device according to a first embodiment of the present invention.

FIG. 2 is a cross-sectional view showing the structure of a real index guided laser device reported by Takayama et al. As a conventional semiconductor laser device.

FIG. 3 is a cross-sectional view showing a structure of an actual refractive index guided laser device reported by Shima et al. As a conventional semiconductor laser device.

FIG. 4 is a cross-sectional view showing a structure of a real index guided laser device reported by Yano et al. As a conventional semiconductor laser device.

FIG. 5 is a diagram showing a cross-sectional structure of a semiconductor laser device according to a second embodiment of the present invention.

FIG. 6 shows an oscillation start current (I) with respect to a change in stripe width W in the semiconductor laser device according to the first embodiment.
It is a figure which shows the change of th).

FIG. 7 is a diagram showing a change in maximum self-excited oscillation light output (Pmax) with respect to a change in stripe width W in the semiconductor laser device according to the first example.

FIG. 8 is a diagram showing the relationship between the layer thickness d of the current / light confinement layer and the drive voltage Vop (optical output 3 mW) in the semiconductor laser device according to the first example.

FIG. 9 is a diagram showing changes in the maximum self-excited oscillation light output Pmax with respect to the layer thickness d when the oscillation start current is constant in the semiconductor laser device according to the first example.

FIG. 10 is a diagram showing a ratio of a normal growth portion in a wafer surface to an Al composition ratio X1 of a current / light confinement layer in the first embodiment.

FIG. 11 is a diagram showing a change in the maximum self-excited oscillation light output Pmax with respect to the Al composition ratio X1 when the oscillation start current is constant in the first embodiment.

FIG. 12 shows the oscillation start current (I
It is a figure which shows the relationship of th).

FIG. 13 is a diagram showing the relationship between the maximum self-oscillation light output (Pmax) and the equivalent refractive index difference Δn.

FIG. 14 is a diagram showing the relationship between the equivalent refractive index difference Δn and the layer thickness d of the current / light confinement layer.

FIG. 15 is an oscillation start current (It) with respect to a change in stripe width W in the semiconductor laser device of the second embodiment.
It is a figure which shows the change of h).

FIG. 16 is a diagram showing a change in maximum self-excited oscillation light output (Pmax) with respect to a change in stripe width W in the semiconductor laser device according to the second embodiment.

[Explanation of symbols]

 100,500 Semiconductor laser device 100a, 500a Laminated structure 101,501 n-GaAs substrate 102,502 n-GaAs buffer layer 103,503 n-AlGaAs first cladding layer 104,504 Undoped AlGaAs active layer 105,505 p-AlGaAs first layer 2 clad layer 106,508 n-AlGaAs current / light confinement layer 107 striped groove 108,509 p-AlGaAs third clad layer 109,510 p-GaAs contact layer 110,511 p-type electrode 111,512 n-type electrode 506 p- GaAs layer 507 Ridge stripe part

Claims (3)

[Claims] 1. A semiconductor laser device using a semiconductor material containing Al as a constituent material, wherein an active layer and a second conductivity type second clad layer are provided on a first conductivity type first clad layer. A laminated structure formed by sequentially laminating, a stripe-shaped semiconductor layer formed on the surface of the second cladding layer, and a current formed on both sides of the stripe-shaped semiconductor layer on the surface of the second cladding layer. A current confinement layer, the current light confinement layer having a forbidden band width larger than the forbidden band width of the active layer and smaller than the forbidden band width of the first and second cladding layers, and having a layer thickness of The stripe-shaped semiconductor layer is formed to have an Al composition ratio of 0.35 or less and a width of 1.0 μm or more and less than 4 μm. Laser diode device 2. The semiconductor laser device according to claim 1, wherein a difference between an equivalent refractive index in the layer thickness direction inside the striped semiconductor layer and an equivalent refractive index in the layer thickness direction outside the striped semiconductor layer. A semiconductor laser device in which Δn is a value in the range of 1 × 10 ⁻³ or more and 1 × 10 ⁻² or less. 3. The semiconductor laser device according to claim 1, wherein the current / light confinement layer is 0.4 μm or more and 0.8 μm.
A semiconductor laser device having the following layer thickness.