JP3037111B2 - Semiconductor lasers and composite semiconductor lasers - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a semiconductor laser capable of operating at a high output of several tens of watts, which is used as a light source for optical measurement and excitation of a solid-state laser. The present invention relates to a semiconductor laser and a composite semiconductor laser.

[0002]

2. Description of the Related Art In the field of optical measurement and the like, a point ranging device for measuring a distance to a certain point has been developed, and a high-power laser diode which generates a watt-class or tens of watt-class optical output has been required as a light source. It is becoming possible.

As a first conventional example, in order to increase the output in the case of a single laser diode chip, the width of the light emitting region is widened to form a so-called broad area laser diode (FIG. 9). (B)), a light output of 6 W is obtained by Yamanaka et al. At a light emitting region width of 600 μm (Yamanaka et al., Laser Research, Vol. 18, No. 55)
5, p. 1990). In addition, a large number of laser elements have been arranged in an array, and a light output of 100 W or more has been obtained by Harnagei et al. In a total light emitting region width of 7200 μm (Applied Physics Letter). Journal 49, 1418, 1
986, GL Harnagei et al., Appl. Phys. Lett., Vo
l.49, p.1418, 1986).

As a second conventional example, there is a method in which a semiconductor laser having a flare structure having a shape in which an active layer width is widened in a resonator direction, and a stable large-power operation in a transverse fundamental mode up to the watt class. is there. Such a semiconductor laser is expected to be used in various applications such as an optical measurement system. In Fig. 11, reported by Shigihara et al. (1988, Electronics Letters, Vol. 24, No. 18, No. 1
FIG. 18 shows a perspective view of a flare structure semiconductor laser.

In this example, a buffer layer 2
2. After growing the current block layer 23, a part of the current block layer 23 is removed by etching so as to change the width in the resonator direction, and the lower clad layer 24 and the active layer are entirely formed thereon. 25, an upper cladding layer 26, and a contact layer 27 are sequentially laminated, and an electrode 28 is formed on the epitaxial growth layer side and the substrate side.
29, and a high-reflection film 10 is formed on the narrow end face from which the current blocking layer 23 has been removed to obtain a desired flare structure semiconductor laser. Since the current is injected only into the portion where the current blocking layer 23 is removed, the width of the light emitting region 9 changes in the light resonance direction in the element plan view shown in FIG. Spread) shape.

By using such an element, a light output of 4 W is obtained in a light emitting region having a width of 200 μm (1).
Published by IEE Photonics Technology Letters, Vol. 5, Section 605, published in 993, ESKintzer et al.,
IEEE Photon. Technol. Lett., 5, p.605, 1993).

Further, as a third conventional example, a master oscillator power amplifier (Master Osc
illator Power Amplifier: MOPA: For example, literature IEE Photonics Technology Letters, Vol. 5, pp. 297-300, R. Parke et al., IEEE Pho
ton. Tech. Lett. Vol. 5, pp. 297-300) (see FIG. 9 (d)), and a light output of 2 W or more can be obtained in a light emitting region having a width of 200 μm. Have been.

[0008]

When a semiconductor laser is applied to an optical measuring device or the like, it is necessary to convert the output from the laser into a parallel beam using a lens, but the optical system must be kept within a certain size. For this reason, the width of the light emitting region of the semiconductor laser is limited. For this reason, a semiconductor laser capable of obtaining a large output in a narrow light emitting region is required.

In the method of increasing the light output by widening the light emitting area of the semiconductor laser or increasing the number of semiconductor lasers arranged in an array as in the first conventional example, the light emitting area becomes large. Therefore, there is a disadvantage that the optical system becomes large when configuring an apparatus for optical measurement.

In the flare structure semiconductor laser of the second conventional example, light is extracted from a portion having a narrow active region width, and the light output is increased by enlarging the light emitting region width in a portion having a wide active region width. Although a large output is obtained, the divergence angle of the light emitting region is limited due to mode control. To increase the output, it is necessary to lengthen the resonator. -The conversion efficiency of the light output is reduced. For this reason, this conventional example has a drawback that the capacity of the current source for driving the laser is increased when configuring an apparatus for optical measurement.

In the third conventional example, the current density cannot be increased in order to suppress the oscillation in the amplifier region, and in order to increase the output, the amplifier region must be lengthened or the light emitting region width of the amplifier must be increased. To respond. In the former, the loss in the amplifier area increases,
As in the second conventional example, the capacity of the laser driving current source increases. Further, in the latter case, since the light emitting area becomes large, there is a disadvantage that the optical system becomes large when configuring an apparatus for optical measurement.

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned problems of the prior art, and has as its object to achieve a high power-to-light output conversion efficiency and a light-emitting far-field in a narrow light-emitting region. An object of the present invention is to provide a semiconductor laser having a single peak image and a high output.

[0013]

According to the present invention, there is provided a semiconductor laser according to the present invention, comprising a first conductivity type buffer layer (2) and an active layer (3) on a first conductivity type semiconductor substrate (1). ) And the second conductivity type cladding layer (4) are stacked in this order, and the width of the region of the active layer into which the current is injected has a large width .
The light emitting region changes linearly along the longitudinal direction of the resonator so that the ratio of the width to the width of the narrow portion becomes about 2: 1.
A semiconductor laser has been made to load, high-reflection film on the end face of the wide side of the active layer current is injected (10)
Are formed, and high-order mode oscillation light is emitted from the end face on which the high reflection film is not formed. In order to achieve the above object, a composite semiconductor laser according to the present invention provides a semiconductor laser (1
The semiconductor laser is stacked in multiple stages, including the method 5).

[0014]

DESCRIPTION OF THE PREFERRED EMBODIMENTS A semiconductor laser according to the present invention has a structure shown in FIG.
The configuration is as shown in FIG. That is, the light emitting region 9
Are formed in a flare structure, and a high-reflection end face film 10 having a wider light-emitting area and a low-reflection film 11 are formed on an end face on a narrower side of the light-emitting area. The light emitting region 9 corresponds to a region of the active layer where current is injected. In order to compare the characteristics of the flare structure semiconductor laser according to the present invention with those of the conventional example, the active region width on the light emission side is 1 here.
The width of the active region on the rear end side is 200 μm, and the length of the active region is 1000 μm. In the laser according to the present invention, since the active region width is set to be large as described above, the emitted light includes light of a higher-order mode.

FIGS. 9 (b) to 9 (d) show that the light emitting region width is 1
The top view of each conventional semiconductor laser having a thickness of 00 μm is shown. FIG. 9B shows a broad area laser diode described as a first conventional example. Active area width is 10
0 μm, and the active region length is 1000 μm. FIG. 9 (c)
Is a semiconductor laser having a flare structure described as a second conventional example, wherein the active region width on the light emitting side is 100 μm, the active region width on the rear end side is 4 μm, and the active region length is 1000 μm.
It is. FIG. 9D shows an amplifier integrated laser described as a third conventional example, in which the active region width on the light emitting side is 1.
The width of the active region on the rear end side is 4 μm, and the length of the active region of the amplifier portion is 1000 μm. That is, in this conventional example, the laser light formed in the DFB laser region 16 is amplified by the amplifier region 17 and then emitted through the non-reflection film 18.

FIG. 10 collectively shows the current-light output characteristics of each element of FIG. The semiconductor lasers shown in FIGS. 9A, 9B and 9C are considered to have substantially the same efficiency because the reflection mirrors have the same reflectance and the internal losses are almost the same. . Also, the light output increases with the injection of current, but the light output is more saturated than a certain current density, so that the light output is limited. Experimentally, this current density was estimated to be about 66 kA / cm ² (indicated by a triangle in the figure, the current density was 66 kA / c 2).
shows a point m ^2). If the current density and the efficiency are the same, a high output can be obtained with the laser of the present invention having a wide light emitting region. Actually, the current density at which the optical output starts to be saturated is 66 kA / c.
m ² , an optical output of 50 W can be obtained with the semiconductor laser of the present invention, whereas in the first and second conventional examples, 3 W
It is about 2W and 27W.

In the amplifier integrated laser shown in FIG. 9D, the optical output is limited by the saturation output of the amplifier. Here, the reflectivity of the end face was set to 0.001%, and the maximum injection current was set to 4A. With a semiconductor laser having this structure, it is difficult to obtain an output of 10 watts or more. From the above, it can be seen that the flared semiconductor laser of the present invention can provide a larger output in a narrow light emission region than in each conventional example.

[0018]

Next, embodiments of the present invention will be described with reference to the drawings. (Embodiment 1) FIG. 1 is a schematic plan view of a flared semiconductor laser according to the present invention, and FIG. 2 is a sectional view taken along line AA 'in FIG. A semiconductor laser having this structure can be manufactured as follows. First, the n-InP substrate 1
An n-InP buffer layer 2 (thickness 0.2 μm), an active layer 3 and a p-InP cladding layer 4 (thickness 0.3 μm) are sequentially grown thereon. Here, the active layer 3 has a multiple quantum well structure whose energy band structure is shown in FIG.
InGaAsP well layer 3 with a compressive strain of 0.8% introduced
a (8 nm thick) 5 layers, In composition of 1.2 μm emission wavelength
GaAsP barrier layer 3b (thickness 6 nm), emission wavelength 1.
InGaAsP-SCH (Separate Confi.
nement Hetero-structure) 3c (50 nm in thickness). The emission wavelength of the active layer 3 is 1.5 μm.

After forming an SiO ₂ insulating film on such a semiconductor wafer, an opening whose width changes in the length direction is formed, and the p-InP ridge cladding layer 4a (thickness) is selectively formed in this opening. 2.5 μm), p- with an emission wavelength of 1.64 μm
An InGaAs contact layer 5 (0.5 μm thick) is grown. The ridge waveguide structure has a width of 100 μm and a width of 200 μm in a narrow region and a wide region, respectively, and a length of 900 μm.
The width was linearly changed over m. Thereafter, an insulating film 6 was formed on the epitaxial growth layer, a window was opened on the contact layer 5, a p-side electrode 7 was formed on the contact layer 5, and an n-side electrode 8 was formed on the back surface of the substrate.

Finally, a laser chip is cut out, and a high-reflection film 10 (reflectance 90%) is provided on the end face on the side with the widest emission width, and a low-reflection film 11 (reflectance 10%) is provided on the end face on the side with a small total emission width. Each is formed to obtain a desired semiconductor laser having a flare structure. A linear waveguide having a length of 50 μm is formed on both sides of a tapered region having a length of 900 μm.
μm.

By applying a pulse current of 20 ns width and repetition of 10 kHz to the semiconductor laser fabricated in this manner, the light emission in the horizontal direction without ripple and having a full width at half maximum of 20 ° without ripples up to a peak light output of 50 W. Far-field images were obtained. The oscillation threshold current and the slope efficiency were 3 A and 0.25 W / A, respectively, and the total light emitting region width in the light emitting region was 100 μm.

In a conventional broad area laser having a light emitting region width of 100 μm, an element having a cavity length of 1000 μm
The maximum optical output was 33 W at a slope efficiency of 0.25 W / A, and the maximum optical output was improved by 1.5 times in this embodiment. In the first conventional example in which the resonator length is 1500 μm,
A maximum light output of 50 W is obtained. In this case, the slope efficiency is 0.18 W / A, and the efficiency of the laser according to the present embodiment is improved by 1.4 times in comparison with this.

(Embodiment 2) FIG. 4 is a schematic plan view showing a flare-structure semiconductor laser according to a second embodiment of the present invention.
FIG. 5 is a sectional view taken along line BB ′ in FIG. An element having this structure can be manufactured as follows. First, an n-InP buffer layer 2 (0.2 μm in thickness), an active layer 3 and a p-InP clad layer 4 are formed on an n-InP substrate 1.
(Thickness: 0.3 μm). Here, the active layer 3 has an SCH multiple quantum well structure similar to that of the first embodiment, whose energy band structure is shown in FIG.

After an SiO ₂ insulating film is formed on such a semiconductor wafer, an opening whose width changes in the longitudinal direction of the resonator is formed, and the p-InP ridge cladding layer 4a is selectively formed in this opening. (Thickness 2.5 μm), emission wavelength 1.64 μm
P-InGaAs contact layer 5 (0.5 μm thick)
Are sequentially grown. The ridge waveguide structure has widths of 100 μm and 200 μm in a narrow region and a wide region, respectively.
The width was linearly changed over 900 μm in length. Thereafter, the area outside the ridge cladding layer 4a is reduced to 10 μm.
The p-InP cladding layer 4 and the active layer 3 are removed by etching while leaving m each.

Thereafter, an insulating film 6 is formed on the epitaxial growth layer, a window is opened on the contact layer 5, a p-side electrode 7 is formed on the contact layer 5, and an n-side electrode 8 is formed on the back surface of the substrate. Form. Finally, cut into laser chips,
The high reflection film 10 (reflectance 90
%), And a low-reflection film 11 (reflectance 10%) is formed on the end face on the narrow side of the total light emission width to obtain a desired flare structure semiconductor laser. 50 μm on both sides of a 900 μm long tapered region
The configuration was such that m linear waveguides were formed, and the total element length was 1000 μm.

By applying a pulse current having a width of 20 ns and a repetition of 10 kHz to the semiconductor laser manufactured in this manner, the light emission in the horizontal direction without ripple and having a full width at half maximum of 20 ° and a ripple-free width up to a peak optical output of 50 W is obtained. Far-field images were obtained. The oscillation threshold current and the slope efficiency were 3 A and 0.25 W / A, respectively, and the total light emitting region width in the light emitting region was 100 μm.

(Embodiment 3) FIG. 6 is a schematic plan view showing a flare structure semiconductor laser according to a third embodiment of the present invention.
FIG. 7 is a sectional view taken along line CC ′ in FIG. An element having this structure can be manufactured as follows. First, an n-InP buffer layer 2 (0.2 μm in thickness), an active layer 3 and a p-InP clad layer 4 are formed on an n-InP substrate 1.
(Thickness 2 μm), p-InGa having an emission wavelength of 1.64 μm
An As contact layer 5 (thickness 0.5 μm) is sequentially grown. Here, the active layer 3 has an SCH multiple quantum well structure similar to that of the first embodiment, whose energy band structure is shown in FIG.

After an SiO ₂ insulating film is formed on such a semiconductor wafer, it is processed into a taper pattern whose width changes in the length direction of the resonator to form an SiO ₂ etching mask. The structure of the tapered waveguide has a width of 100 μm and a width of 200 μm in a narrow region and a wide region, respectively, and a length of 900 μm.
The shape was such that the width changed linearly over μm.

Thereafter, the outer region of the tapered mask is removed by etching up to the active layer 3, and the p-InP buried layer 12 and the n-InP buried layer 13 are grown in the etched region. Next, the SiO ₂ etching mask is removed, and an insulating film 6 is formed on the epitaxial growth layer.
After opening a window on the contact layer 5, a p-side electrode 7 is formed on the contact layer 5, and an n-side electrode 8 is formed on the back surface of the substrate. Finally, a laser chip is cut out, and a high-reflection film 10 (reflectance 90%) is formed on the end face on the side with a wide total emission width, and a low-reflection film 11 (reflectance 10%) is formed on the end face on the narrow side with a total emission width. As a result, a desired semiconductor laser having a flare structure is obtained. The total length of the element was 1000 μm, and a linear waveguide of 50 μm was formed on both sides of a tapered region of 900 μm length.

By applying a pulse current having a width of 20 ns and a repetition rate of 10 kHz to the semiconductor laser manufactured in this manner, the light emission in the horizontal direction without ripple and having a full width at half maximum of 20 ° and a ripple-free width up to a peak optical output of 50 W is obtained. Far-field images were obtained. The oscillation threshold current and the slope efficiency were 3 A and 0.25 W / A, respectively, and the total light emitting region width in the light emitting region was 100 μm.

(Embodiment 4) FIG. 8 is a schematic perspective view of a composite semiconductor laser showing a fourth embodiment of the present invention. In this embodiment, the four flared semiconductor lasers 14 according to the first to third embodiments are stacked so as to be electrically connected in series. The flared semiconductor laser 14 is electrically a pn diode. Therefore, the individual flared semiconductor lasers 14 are arranged such that the p-side electrode 7 side (or the n-side electrode 8 side) is on the upper side, and the light emitting region 9 and the light emitting region 15 of the individual flared structure semiconductor laser 14 are stacked in the stacking direction. Are arranged so as to substantially overlap each other, and then are bonded to each other using a conductive melting material to perform electrical series connection. The thickness of each of the flared semiconductor lasers 14 is about 50
Since the thickness is about μm, a semiconductor laser having a small total light emission area can be formed according to this embodiment.

In such a semiconductor laser, the width is 20n.
s, a pulsed current of 10 kHz was repeatedly applied to obtain a peak-to-peak output power of 200 W, a single-peak full-width at half-maximum width of 20 °, and a ripple-free horizontal far-field image with no ripple.
The oscillation threshold current and slope efficiency are 3A and 1W, respectively.
/ A, the light emitting area 15 was 100 μm × 150 μm.

(Modifications of Embodiments) Although the preferred embodiments have been described above, the present invention is not limited to these embodiments, and appropriate modifications can be made within the scope described in the claims. For example, in the embodiment, InP
Although an element having an oscillation wavelength of about 1.5 μm using a substrate has been described, oscillation can be performed at an appropriate wavelength by using another material such as a GaAs-based or InGaAlAs-based material. Further, current constriction may be performed by forming a current block layer in the semiconductor layer.

[0034]

As described above, according to the semiconductor laser of the present invention, it is possible to provide a semiconductor laser having a high power-light output conversion efficiency and a large output in a narrow light emission region.

[Brief description of the drawings]

FIG. 1 is a schematic plan view of a first embodiment of the present invention.

FIG. 2 is a sectional view of the first embodiment of the present invention.

FIG. 3 is a band energy diagram of the first embodiment of the present invention.

FIG. 4 is a schematic plan view of a second embodiment of the present invention.

FIG. 5 is a sectional view of a second embodiment of the present invention.

FIG. 6 is a schematic plan view of a third embodiment of the present invention.

FIG. 7 is a sectional view of a third embodiment of the present invention.

FIG. 8 is a schematic perspective view of a fourth embodiment of the present invention.

FIG. 9 is a schematic plan view showing a conventional example and an embodiment of the present invention.

FIG. 10 is an operation explanatory diagram of a conventional example and an embodiment of the present invention.

FIG. 11 is a perspective view of a conventional example.

FIG. 12 is a schematic plan view of a conventional example.

[Explanation of symbols]

 Reference Signs List 1 n-InP substrate 2 n-InP buffer layer 3 active layer 3a InGaAsP well layer 3b InGaAsP barrier layer 3c InGaAsP-SCH layer 4 p-InP clad layer 4a p-InP ridge clad layer 5 p-InGaAs contact layer 6 insulating film 7 p-side electrode 8 n-side electrode 9 light-emitting region 10 high-reflection film 11 low-reflection film 12 p-InP buried layer 13 n-InP buried layer 14 flare structure semiconductor laser 15 light emission region 16 DFB laser region 17 amplifier region 18 non-reflection film DESCRIPTION OF SYMBOLS 21 Substrate 22 Buffer layer 23 Current block layer 24 Lower clad layer 25 Active layer 26 Upper clad layer 27 Contact layer 28, 29 Electrode

Continuation of the front page (56) References JP-A-6-283807 (JP, A) JP-A-7-58400 (JP, A) 1994 (Heisei 6) Proceedings of the Spring Society of Materials Science 28P-K-11 p. 991 1995 (Heisei 7) Spring Proceedings of the Society of Applied Chemistry 29P-ZG-4 p. 1086

Claims (5)

(57) [Claims] A first conductive type buffer layer, an active layer, and a second conductive type clad layer are stacked in this order on a first conductive type semiconductor substrate, and the width of a region of the active layer into which a current is injected has a width.
The ratio of the width of the narrow portion of the wide portion is 2: has changed linearly along the <br/> cavity longitudinally so that about 1, emission territory
A semiconductor laser pass is made broad, the current has a high reflection film is formed on the end face of the wide side of the active layer to be injected, the high from the end face of the side where the high-reflection film is not formed A semiconductor laser that emits next-mode oscillation light. 2. The semiconductor laser according to claim 1, wherein the second conductivity type cladding layer has a planar ridge structure substantially following a pattern of a current injection region of the active layer. 3. The cladding layer of the second conductivity type has a planar ridge structure substantially following a pattern of a current injection region of the active layer, and the remaining portion of the cladding layer of the active layer and the cladding layer of the second conductivity type is provided. Is processed so as to have the same planar shape as the ridge structure or slightly wider than that, and the side surfaces of the active layer and the second conductivity type cladding layer are covered with an insulating film or a semiconductor layer. The semiconductor laser according to claim 1, wherein: 4. The multi-quantum well structure or a multi-quantum well structure and an SCH sandwiching the multi-quantum well structure from both sides.
The semiconductor laser according to claim 1, further comprising a layer. 5. A composite semiconductor laser comprising a plurality of semiconductor lasers including the semiconductor laser according to claim 1.