JPH0695587B2 - Semiconductor laser device - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a semiconductor laser device, and more particularly to a semiconductor laser device having a plurality of active layers in a vertical direction and having a far-field pattern which is substantially a perfect circle.

[Prior Art] It is expected that the semiconductor laser device will be applied more and more in the future as a light source for an optical disk, optical communication or a laser printer. In the process of such development, the semiconductor laser device has a higher output,
Characteristics such as low noise and short wavelength are required. Among them, especially the demand for high output is very important for high speed and high performance of the application system. For this purpose, semiconductor laser arrays are being actively developed, and the maximum output has reached the 10 W level.

3A to 3C are views showing a conventional semiconductor device, in particular, FIG. 3A is a view showing a cross-sectional structure of a semiconductor laser device, and FIG. 3B is a view of the semiconductor laser device shown in FIG. 3A. FIG. 3C is a view showing a far-field image in the vertical direction on the active layer, and FIG. 3C is a view showing a far-field image in the same horizontal direction.

The conventional semiconductor laser device shown in FIG. 3A to FIG. 3C described above is prepared by DRScifres et al. In Electronics Letters,
Vol.19 (5), 169th to 171st pages (1983). In FIG. 3A, on the n-type GaAs substrate 101, an n-Ga _0.6 Al _0.4 As clad layer 102, an active layer 103, and p-Ga are formed.
_{The 0.6} Al _0.4 As clad layer 104, the p-GaAs cap layer 105 and the electrode 106 are sequentially laminated.

Of the output far-field image of the light oscillated by the semiconductor laser device shown in FIG. 3A, the characteristics in the direction perpendicular to the laser active layer are shown in FIG. 3B, and the characteristics in the parallel direction are shown in FIG. 3C. Has been done. As a high output characteristic, 800mW was obtained in the continuous drive system, but the horizontal far-field image has two peaks as shown in Fig. 3C, and when converging at one point, Only one can be used. In addition, the full width at half maximum of the peak is narrow at about 2.0 °. This is because light from a plurality of light emitting points located in the lateral direction is phase-synchronized, and thus the light is diffracted with the maximum light emitting width as an aperture.

However, the full width at half maximum of the beam in the direction perpendicular to the active layer is 3C.
As shown in the figure, it is 22 °, which is the same thickness as a single laser element. As a result, the far-field image has a vertically elongated elliptical shape with an aspect ratio of about 11, which is far from a perfect circle. In this way, if the beam whose aspect ratio deviates from 1, it is difficult to use all the light when narrowing it down to one point with the lens, and the amount of light that actually enters the lens is 10% or less of the total power. I will end up. For these two reasons,
In the semiconductor laser device shown in FIG. 3A, only light of 40 mW or less out of the total output of 800 mW contributes to focusing.

To solve the above mentioned drawbacks, App by DGDeppe et al.
lied Physics Letters Vol.50 (7), pages 392-third
A structure having a plurality of active regions in a vertical direction in a layer as described in page 94 (1987) and phase-locking light emitted from them is considered.

FIGS. 4A to 4C are views showing such a semiconductor laser device, in particular, FIG. 4A shows a sectional structure, and FIG. 4B shows a far-field image in a direction perpendicular to the active layer of the semiconductor laser device. , FIG. 4C also shows a horizontal far-field image.

In FIG. 4A, the semiconductor laser device is an n-GaAs substrate 30.
N on the top of the substrate by molecular beam epitaxy (MBE)
-AlxGa1 _- xAs buffer layer 302, four p-AlxGa1 _- xAs cladding layers 303, 305, 307, 309, three p-quantum well (QW) structure active layers 304, 306, 308 alternately and GaAs contact layer 312
Are continuously grown, silicon is diffused on both sides of the light emitting region so as to reach the n-AlxGa1 _- xAs buffer layer 302 to form an n-type region 310. Finally, zinc 311 is diffused into the entire surface at a concentration lower than that of silicon and is shallowly diffused 311 to make the surface other than the silicon diffusion region 310 p-type. The laser resonator is manufactured by cleavage.

In a semiconductor laser device, three active layers 304, 306, 308
Electrons are injected from the interface 320 with the silicon diffusion region 310 to emit light. And these three active layers 304, 30
Since 6,308 are in optical proximity and are in a coupled state,
The oscillated laser light is in a phase locked state. Thus, the active layers 304, 306, 308 are formed in the same manner as the semiconductor laser device described above.
The aperture in the vertical direction can be increased, and the far-field pattern has a full-width half-maximum angle of 8.7 degrees as shown in Fig. 4B, which is 1/3 of the value of the conventional semiconductor laser device having only one active layer. Is becoming thinner. However, since the electrons are injected at the six places 320 on the side surface of the active layer in a very narrow region, the light emission is localized near the six places 320. To this end, as shown in FIG. 4C, the active layers 304, 306,
The far-field image in the direction parallel to 308 has a shape having two peaks, and a single beam close to a perfect circle is not realized at present.

As the above-mentioned current injection type semiconductor laser element, an element in which zinc is deeply diffused is also known, and a multiple active layer semiconductor laser element to which this structure is applied is also proposed.

5A to 5C are views showing such a semiconductor laser device, in particular, FIG. 5A shows a cross-sectional structure, and FIG. 5B is perpendicular to the active layer of the semiconductor laser device shown in FIG. 5A. FIG. 5C also shows a horizontal far-field image in the horizontal direction.

The semiconductor laser device shown in FIG. 5A has four layers of n-AlxGa1 _- xAs cladding layers 402, 404, 406, 408 and three layers of n-AlyGa1 _- yAs active layer 4 on a semiconductor insulating or n-type GaAs substrate 401.
03, 405, and 407 are alternately formed, and finally, an n-GaAs contact layer 409 is grown to be formed. As a growth method at this time, a liquid phase epitaxial (LPE) method, a metal organic vapor phase epitaxial (DM-VPE) method, an MBE method, or the like can be applied. Next, zinc diffusion 410 is performed from the surface so as to reach the lowermost n-AlxGa1 _- xAs cladding layer 402. After that, by heat treatment, 1-2 μm around the first diffusion region 410
A region 411 having a relatively low zinc concentration is formed. Due to the difference in carrier density, this region 411 becomes an optical waveguide by having a higher refractive index than the high-concentration zinc diffusion region 410 and the non-diffused region. The GaAs contact layer 409 on the region 411 is removed by etching, and an insulator 4 is
After forming 40, a p-type electrode 420 and an n-type electrode 421 are created. This wafer separates the elements forming the resonator by cleavage.

[Problems to be Solved by the Invention] In the conventional semiconductor laser device configured as described above, in the same manner as the semiconductor laser device shown in FIG. As shown in the figure, a thin beam that is about 1/3 that of a normal single active layer device is obtained. However, as described above, since the optical waveguide is formed by re-diffusion of zinc by heat treatment, it lacks controllability and the width of the optical waveguide region 411 becomes as small as about 2 μm. Therefore, the far-field image in the horizontal direction is a beam thicker than that in the vertical direction, as shown in FIG. 5C.
In addition, the narrow waveguide width causes an increase in the light density at the end face when a high output is emitted.
The semiconductor laser device shown in FIG. 5A is considered not suitable as a high-power laser device.

In addition, it has been attempted to stack double heterojunctions of a normal laser two to three times and tunnel a carrier at a pn reverse bias interface where no active layer exists, but the voltage during driving increases, There were problems such as deterioration due to heat generation. As described above, none of the conventional semiconductor laser devices can emit a beam close to a perfect circle and high output light.

Therefore, a main object of the present invention is to provide a semiconductor laser device capable of emitting a perfect circular pattern of light having a high output of 1 W or more and a divergence ratio of vertical and horizontal beams being substantially equal to 1.

[Means for Solving the Problems] The present invention is a second type semiconductor layer which emits light of two or more layers and a second type semiconductor layer which is located above and below the first type semiconductor layer and has a larger forbidden band and a smaller refractive index than the first type semiconductor layer. In a semiconductor laser device including a first-type semiconductor layer and a third-type semiconductor layer, the second-type and third-type semiconductor layers have opposite conductivity types, and each second-type semiconductor layer is the same as the second-type semiconductor layer. Since each third-type semiconductor layer is in contact with a region having a conductivity type and each third-type semiconductor layer is in contact with a region having the same conductivity type as that of the third-type semiconductor layer, regions having different conductivity types form a comb shape, On the other hand, it is configured to emit light in the horizontal direction.

[Operation] Since the semiconductor laser device according to the present invention is formed such that the boundaries between regions having different conductivity types are comb-shaped, by selecting a small forbidden band width at this boundary portion, the rising voltage at this portion is low. Therefore, a current flows selectively, and light can be efficiently emitted in the horizontal direction with respect to the first-type semiconductor layer.

[Embodiment of the Invention] FIGS. 1A to 1D are views showing an embodiment of the present invention. In particular, FIG. 1A shows a sectional structure, and FIG. 1B shows a pn interface shape. FIG. 1C shows a far-field image in the vertical direction on the active layer of the semiconductor laser device shown in FIG. 1A, and FIG. 1D shows a far-field image in the horizontal direction.

First, the configuration of one embodiment of the present invention will be described with reference to FIG. 1A. The semiconductor laser device is a semi-insulating GaAs
P-Al x Ga _1- x As clad layer 2 on the substrate 1 by MBE method
Is 1.5 μm thick and the undoped multiple quantum well active layer 3 is 0.1
0 μm thick, n-AlxGa _1- xAs cladding layer 4 1.8 μm thick, undoped multiple quantum well active layer 5 0.10 μm thick, p-AlxGa
_{The 1-} xAs clad layer 6 is formed to have a thickness of 1.8 μm, the undoped multiple quantum well active layer 7 is formed to have a thickness of 0.10 μm, and finally the n-AlxGa _1- xAs clad layer 8 is formed to have a thickness of 1.5 μm. At this time, the forbidden band width of each multiple quantum well active layer 3, 5, 7 is smaller than each cladding layer 2, 4, 6, 8 and the refractive index is larger than each cladding layer 2, 4, 6, 8. So that the structure is selected.

Next, a part of the above-mentioned grown wafer was formed into a stripe shape with Si ₃ N ₄
The film is covered with the film 13 and the other parts are etched to the position of the GaAs substrate 1. Then, the p-AlyGa _1- yAs cladding layer 9 is grown on the right side of the etched portion, and the n-AlyGa _1- yAs cladding layer 10 is grown on the left side. As the growth method at this time, the LPE method or the OM-VPE method can be applied.While the growth on one side is performed, the other etching surface or the growth surface is a dielectric such as SiO ₂ or Si ₃ N _4. By covering with a body film, crystal growth on that portion is prevented.

At the time of the above-mentioned growth, the n-AlyGa _1- yAs cladding layers 9 and 10 are grown on both sides at once, and only the region 9 is made to have the conductivity type of p-type by using the technique of ion implantation or thermal diffusion. You may make it reverse. However, the cladding layers on both sides 9,
It is important to determine the material of 10 so that the refractive index is smaller than that of the multiple quantum well active layers 3, 5, and 7 and the band gap is increased. In this example, x = y was selected. Finally, a p-type electrode 11 is formed on the p-AlyGa _1- yAs clad layer 9, an n-type electrode 12 is formed on the n-AlyGa _1- yAs clad layer 10, and a resonator having a length of 360 μm is cleaved. Form.

A p-type region of a semiconductor laser device formed as described above
The shapes of 15 and n-type region 16 are shown in FIG. 1B. However, since the GaAs substrate 1 is an insulating one, it can be considered that no current flows through the substrate 1. In this way, the pn interface is comb-shaped, and only the portion where the active layers 3, 5, and 7 are present forms the double dissimilar junction structure 20. Others
AlxGa _1- xAs results in the same type of junction. As described in the explanation of the device fabrication procedure, the forbidden band width of the active layers 3, 5, 7 is larger than that of the clad layers 2, 4, 6, 8, 9, 10 surrounding these active layers 3, 5, 7. Since the rising voltage at the pn interface is low only in the double dissimilar junction 20, and when a voltage is applied to both electrodes, the current is selectively applied to this dissimilar junction 20. Will flow.

In this way, the carriers are injected into the active layers 3, 5, 7 from the p-side and the n-side and are recombined, so that light emission is efficiently realized. As is clear from comparison between this example and the examples shown in FIGS. 3A to 3C and FIGS. 4A to 4C described above, the interface where carriers are injected has a significantly higher interface in this example. Has become wide. This is because in the semiconductor laser device according to this example, carriers are injected from above and below in a plane, whereas in the conventional semiconductor laser device,
This is based on the fact that the points of linear injection in the lateral direction are greatly different. As a result, uniform carrier injection is realized over the entire area of the active layers 3, 5, 7 and, like the conventional semiconductor laser device shown in FIGS. 4A to 4C,
There will never be two output beams horizontally (1D
Figure).

Also, the far-field image in the vertical direction is 3% as shown in FIG. 1C.
The light oscillated in the one active layer 3, 5, 7 seeps into the cladding layers 4, 6 between them, and the tails of the attenuated light overlap each other to form a phase-locked pattern. The half-width of the beam in the vertical direction is 10.3 °, and the half-width of the beam in the horizontal direction is 9.5 °. The ratio is 1.08, which is very close to 1.

In this way, a beam close to a perfect circle can have about 80% of its light incident on the lens, and the light can be narrowed down to a single circular spot. High output characteristics include active layer
Since there are three 3, 5, and 7, it is possible to generate an output three times as high as that of a single laser element, similar to the effect of the conventional semiconductor laser element shown in FIG. 3A. In this example, an output of about 200 mW could be observed during continuous driving at room temperature.

The measurement shown in Fig. 1C and Fig. 1D shows an output of 180 mW.
It was done in. As described above, by applying the present invention, it is understood that the semiconductor laser device according to the present embodiment can emit a high-power laser beam as high as 200 mW with a beam having a substantially perfect circle.

Next, an embodiment in which the present invention is applied to a two-dimensionally arranged laser will be described.

FIG. 2A is a sectional structure diagram thereof. In the embodiment shown in FIG. 2A, the n-GaAs substrate 201 is firstly n-typed by the LPE method.
AlxGa _1- xAs clad layer 202 with a thickness of 2.0 μm and undoped AlxGa
_1- yAs active layer 203 is 0.08 μm thick, p-AlxGa _1- xAs clad layer
204 is 1.0 μm thick, n-Al x Ga _1- x As clad layer 205 is 1.0 μm thick
Thick, undoped AlyGa _1- yAs active layer 206 with a thickness of 0.08 μm, p-AlxGa
_{The 1-} xAs clad layer 207 has a thickness of 1.0 μm, the n-AlxGa _1- xAs clad layer 208 has a thickness of 1.0 μm, and the undoped AlyGa _1- yAs active layer 209 has a thickness of 0.0 μm.
8 μm thick, p-Al x Ga _1- x As clad layer 210 1.0 μm thick, n−A
lxGa _1- xAs clad layer 211 1.0 μm thick, undoped AlyGa _1- yA
The active layer 212 is 0.08 μm thick, and the p-Al x Ga _1- x As clad layer 213 is formed.
A 1.5 μm thick undoped GaAs contact layer 214 is successively grown to a thickness of 0.3 μm. However, x <y.

Next, boron or hydrogen is ion-implanted into the entire surface to a depth of 0.5 μm from the surface to increase the resistance of this portion 230.
As a region for connecting the stacked n-type cladding layers 202, 205, 208, 211, Si is implanted using a focused ion beam to
The die penetrating region 221 is formed with a width of about 2 μm and a period of 10 μm. Similarly, as the p-type through region 220, a Zn ion beam having a width of 2 μm is implanted. This is the n-type through region 221.
Located in the center of. As a result, the region that is not ion-implanted has a shape of 3 μm width and 5 μm period.

It is important that these ion-implanted regions 220 and 221 penetrate the active layer located closest to the substrate. Then, n
An insulating film 240 such as a Si ₃ N ₄ film is formed so as to cover the surface of the die penetrating region. The insulating film on the surface of the p-type through region is removed by etching. Finally, an n-type electrode 215 is formed on the wafer surface, an n-type electrode 216 is formed on the substrate side, and the resonator is formed by cleavage.

FIG. 2B is a diagram showing the pn interface shape of the semiconductor laser device produced by the above procedure. In FIG. 2B, the shaded area is the p region 251, and the other is the n region 250. However, the region 230 where only boron is implanted on the surface
Has a high resistance and is not included in both regions 250 and 251.
Similar to the embodiment shown in FIGS. 1A to 1C, the p-n semiconductor laser device according to the embodiment of the present invention is used.
It can be seen that the interface has a comb shape and the shapes are arranged in the lateral direction. A portion of the pn interface having a low rising voltage is a portion 252 indicated by a thick line. This is because only this part has a double dissimilar junction structure. When an appropriate voltage is applied between both electrodes, carriers are efficiently injected at this heterojunction pn interface 252, thereby realizing laser oscillation.

FIG. 2C (a) is an energy band diagram in the direction of line AA ′ in FIG. 2A, and FIG. 2C (b) is a diagram showing the refractive index distribution 260 and the light intensity distribution 261 at that time.

From the energy band diagram shown in Fig. 2C (a), four active layers
It can be seen that recombination of electrons and holes occurs efficiently only at 203,206,209,212. The refractive index distribution 260 shows the active layer AlyGa _1- yA
Since the mixed crystal ratio of s and the cladding layer AlxGa _1- xAs has a relation of x> y, the refractive index becomes large only in the active layers 203, 206, 209, 212. The period is about 2 μm. Due to this refractive index distribution 260, the light intensity distribution 261 becomes the active layers 203, 206, 209, 212.
The peak has a localized shape, and the skirts of the peaks overlap each other in the cladding layer 10. This overlap causes light coupling in the vertical direction (A-A 'direction).

FIG. 2D shows the refractive index distribution 27 along the line BB ′ shown in FIG. 2A.
It is a figure showing 0 and light intensity distribution 271. In the n-type penetrating region 221 and the p-type penetrating region 220, the lower refractive index is
This is because the carrier concentration in this portion is as high as 5 to 10 × 10 ¹⁸ cm ⁻³ . However, the carrier concentration in each clad layer is 1 to 1.5 × 10 ¹⁸ cm ⁻³ . Line A
Similarly to the −A ′ direction, the n or p type penetrating regions 220, 22
At 1, the light intensity is attenuated, and the peak is localized at the double heterojunction pn interface 252. The coupling of light is also performed according to the same principle as the direction of line AA '.

As described above, the laser light from the two-dimensionally arranged light emitting points 252 is in a phase-locked state by optical coupling. Output 80
As shown in Fig. 2D (vertical direction) and Fig. 2E (horizontal direction), the far-field image at 0 mW has a vertical half-width of 4.2 ° and a horizontal half-width of 2.5 °. The ellipticity is 1.68, which is a larger value than that in the above-mentioned embodiment, but it can be judged to be a value that does not pose a problem in application, considering the ability to emit high output light. Also, here, 4 × 4 2
In principle, an arbitrary matrix-shaped array can be produced by showing the dimensional phase-locked laser array.

In addition to the above-mentioned embodiment, the structure of the active layer is GR
IN-SCH (Graded Index Separate Confinement Het
It is also possible to apply erostructure) or insert a light guide layer. The active layer has a multiple quantum well structure,
It is also possible to create a refractive index difference in the lateral direction by disordering by ion implantation or impurity diffusion. Other,
It is also conceivable that the materials constituting the laser are different, that all the conductivity types are opposite to those of the above-mentioned embodiment, that the crystal growth method is different.

[Effects of the Invention] As described above, according to the present invention, by forming the boundaries of regions having different conductivity types in a comb shape, a high output is emitted and the ellipticity of the output beam is close to 1 (beam. Laser light (close to a perfect circle) can be efficiently emitted horizontally to the semiconductor layer.

[Brief description of drawings]

FIG. 1A is a sectional structural view of an embodiment of the present invention. 1B
The figure shows the pn interface shape of one embodiment of the present invention. FIG. 1C is a diagram showing a far-field image in a direction perpendicular to an active layer according to an embodiment of the present invention. Similarly, FIG. 1D is a diagram showing a horizontal far-field image. FIG. 2A is a sectional structural view of another embodiment of the present invention. FIG. 2B is a diagram showing a pn interface shape of another embodiment of the present invention. FIG. 2C (a) is a diagram showing the energy band in the direction of line AA ′ shown in FIG. 2A, and FIG. 2C (b) is the same as the refractive index distribution and light intensity distribution in the direction of line AA ′. FIG. 2C is a diagram showing a refractive index distribution and a light intensity distribution in the direction of line BB ′ in the same manner. FIG. 2D is a diagram showing a far-field image in the direction perpendicular to the active layer of another embodiment of the present invention. FIG. 2E is a diagram similarly showing a far-field image in the horizontal direction. FIG. 3A, FIG. 4A, and FIG. 5A are diagrams showing a cross-sectional structure of a conventional semiconductor laser device. Third B
Figures 4, 4B and 5B are views showing a far-field image in the direction perpendicular to the active layer of the conventional semiconductor laser device. 3C, 4C
Similarly, Fig. 5C is a diagram showing a horizontal far-field image. In the figure, 1 is a GaAs substrate, 2 and 6 are p-AlxGa _1- xAs cladding layers, 3 and 5 and 7 are multiple quantum well active layers, and 4 and 8 are n-AlxGa.
_1- xAs clad layer, 9 is p-AlyGa _1- yAs clad layer, 10
Is an -AlyGa _1- yAs clad layer, 11 is a p-type electrode, 12 is an n-type electrode, 203,206,209,212 is an undoped AlyGa _1- yAs active layer, 202,2
05,208,211 are n-AlxGa1 _- xAs cladding layers, 204,207,210,
213 is a p-AlxGa1 _- xAs cladding layer, 214 is an undoped GaAs contact layer, 220 is a p-type through region, and 221 is an n-type through region.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Kansai Matsui, 22-22 Nagaike-cho, Abeno-ku, Osaka City, Osaka Prefecture (56) References JP-A-58-225680 (JP, A) JP-A-SHO 59-152683 (JP, A) JP-A-56-15094 (JP, A) JP-A-57-115892 (JP, A)

Claims (1)

[Claims] 1. A first-type semiconductor layer that emits two or more layers of light,
The semiconductor layer of the first type includes semiconductor layers of the second type and the third type which are located above and below the first type semiconductor layer and have a forbidden band width larger than that of the first type semiconductor layer and a small refractive index. In a semiconductor laser device that guides laser light in a direction parallel to each other, the second-type semiconductor layer and the third-type semiconductor layer have opposite conductivity types, and each of the second-type semiconductor layers is The third type semiconductor layer is in contact with a region having the same conductivity type as the second type semiconductor layer,
Since the seed semiconductor layer is in contact with a region having the same conductivity type as that of the third seed semiconductor layer, the boundary between the regions having different conductivity types has a comb shape, and the laser light generated in the adjacent first seed semiconductor layer is generated. The semiconductor laser device is characterized in that the first-type semiconductor layers are arranged so as to be optically coupled to each other.