JPH0936493A - Semiconductor laser and compound semiconductor laser - Google Patents

Abstract

(57) [Summary] [Object] To provide a semiconductor laser with high power-to-light output conversion efficiency and high output in a narrow light emitting region. A buffer layer, an active layer, a cladding layer, and a contact layer are formed on a semiconductor substrate so that a current injection region into the active layer changes linearly along the length direction of the resonator. As a result, the light emitting region 9 that changes in a tapered shape is obtained. The high reflection film 10 is formed on the end face of the light emitting region 9 on the wide side, and the low reflection film 11 is formed on the end face of the light emitting region on the narrow side.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a semiconductor laser used as a light source for optical measurement or for exciting a solid-state laser and capable of high-power operation of several tens of watts class, and particularly high power can be obtained in a narrow light emitting region. 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 distance measuring device for measuring a distance to a certain point has been developed, and a high-power laser diode capable of generating a light output of a watt class to several tens of watts is required as a light source. Is becoming available.

As the 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). (See (b)), Yamanaka et al. Obtained an optical output of 6 W in a light emitting region width of 600 μm (Yamanaka et al., Laser Research, Vol. 18, No. 55).
P. 5, 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 in a total light emitting region width of 7200 μm by Harnagei et al. (Applied Physics Letter). Vol. 49, page 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 in which the width of the active layer is widened in the cavity direction is used to perform a stable large output operation in the transverse fundamental mode up to the watt class. is there. Such semiconductor lasers are expected to have various applications such as optical measurement systems. Reported by Shigihara et al. In FIG. 11 (Electronic Letters, Vol. 24, No. 18, No. 1, 1988).
182 to 1183) A perspective view of a flare structure semiconductor laser is shown.

In this example, the buffer layer 2 is formed on the substrate 21.
2. After growing the current blocking layer 23, a part of the current blocking layer 23 is removed by etching so as to change the width in the cavity direction, and the lower cladding layer 24 and the active layer are formed on the entire surface. 25, an upper clad layer 26, and a contact layer 27 are sequentially laminated, and an electrode 28 is formed on the epi growth layer side and the substrate side.
29 is formed, and the high reflection film 10 is formed on the end surface of the current block layer 23 on the side where the narrow width is removed, to obtain a desired flare structure semiconductor laser. Since the current is injected only into the removed portion of the current blocking layer 23, the width of the light emitting region 9 changes in the light resonance direction in the element plan view shown in FIG. 12 (toward the light emission direction). (Spread) shape.

Using such an element, a light output of 4 W is obtained in a light emitting region having a width of 200 μm (1
Issue 993, IEE Photonics Technology Letters, Volume 5, Item 605, 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, the document AIE 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 is obtained in a light emitting region of 200 μm width. Has been.

[0008]

When a semiconductor laser is applied to an optical measuring device or the like, it is necessary to make the output from the laser a parallel beam with a lens, but the optical system is kept within a certain size. Since it is necessary, the width of the light emitting region of the semiconductor laser is limited. Therefore, a semiconductor laser capable of obtaining a large output in a narrow light emitting region is needed.

In the method of increasing the light output by widening the width of 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 drawback that the optical system becomes large when configuring the device for optical measurement.

In the flare structure semiconductor laser of the second conventional example, the light output is increased by extracting light from a portion having a narrow active region width and expanding the light emitting region width of the portion having a wide active region width. Although a large output is obtained, since the divergence angle of the light emitting region is limited due to mode control, it is necessary to lengthen the resonator in order to increase the output. -The conversion efficiency of the light output is reduced. Therefore, this conventional example has a drawback that the capacity of the current source for driving the laser increases when the device for optical measurement is configured.

In the third conventional example, it is not possible to increase the current density in order to suppress oscillation in the amplifier region, and in order to increase the output, the amplifier region is lengthened or the light emission region width of the amplifier is widened. It will correspond by doing. In the former case, the loss in the amplifier area increases,
As in the second conventional example, the capacity of the current source for driving the laser becomes large. Further, in the latter case, since the light emitting area becomes large, there is a drawback that the optical system becomes large when constructing a device for optical measurement.

The present invention has been made in view of the above problems of the conventional example, and an object thereof is to have a high conversion efficiency of power-light output and a light emitting far field in a narrow light emitting region. An object of the present invention is to provide a semiconductor laser capable of obtaining a large output with a single peak image.

[0013]

A semiconductor laser according to the present invention for achieving the above object comprises 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 clad layer (4) are stacked in this order, and in the semiconductor laser in which the width of the region of the active layer into which the current is injected changes linearly along the longitudinal direction of the cavity, A high-reflection film (10) is formed on the end face on the wide side of the active layer to be emitted, and high-order mode oscillation light is emitted from the end face on the side on which the high-reflection film is not formed. There is. The composite semiconductor laser according to the present invention for achieving the above object is a multi-layered semiconductor laser including the semiconductor laser (15) having the above configuration.

[0014]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The semiconductor laser of the present invention is shown in FIG.
It is configured as shown in (a). That is, the light emitting region 9
Is formed in a flare structure, and the end face high reflection film 10 where the light emitting region is widened and the low reflection film 11 is formed on the end face where the light emitting region is narrowed. The light emitting region 9 corresponds to a region of the active layer into which current is injected. In order to compare the characteristics of the flare structure semiconductor laser according to the present invention and the conventional example, here, the width of the active region on the light emitting side is 1
00 μm, the active region width on the rear end side is 200 μm, and the active region length is 1000 μm. In the laser according to the present invention, the active region width is thus set large, so that the emitted light includes light of a higher order mode.

In FIGS. 9B to 9D, the width of the light emitting region is set to 1
The top view of the semiconductor laser of each prior art example set to 00 micrometers is shown. FIG. 9B shows the broad area laser diode described as the first conventional example. The width of the active area is 10
0 μm, active region length is 1000 μm. FIG. 9 (c)
Is a flare structure semiconductor laser described as a second conventional example, in which the width of the active region on the light emitting side is 100 μm, the width of the active region 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 explained as a third conventional example, in which the active region width on the light emitting side is 1
00 μm, the active region width on the rear end side is 4 μm, and the active region length 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 in the amplifier region 17 and then emitted through the antireflection film 18.

FIG. 10 shows a summary of the current-light output characteristics of each element shown in FIG. In the semiconductor lasers of FIGS. 9A, 9B and 9C, the reflectances of the reflecting mirrors are similar to each other, and the internal losses are also similar to each other, so that the efficiencies are considered to be almost the same. . Further, the light output increases with the injection of current, but the saturation of the light output becomes remarkable at a certain current density, and therefore the light output is limited. Experimentally, this current density was estimated to be about 66 kA / cm ² (current density 66 kA / c indicated by ∇ in the figure).
m ² points are shown). If the current density and efficiency are the same, a high output can be obtained with the laser of the present invention having a wide emission region. Actually, the current density at which the optical output starts to be saturated is 66 kA / c
At m ² , the semiconductor laser of the present invention can obtain an optical output of 50 W, while in the first and second conventional examples, the optical output is 3 W, respectively.
It is about 2W and 27W.

In the amplifier integrated laser of FIG. 9D, the optical output is limited by the saturated output of the amplifier. Here, the reflectance of the end face was 0.001% and the maximum injection current was 4A. With a semiconductor laser having this structure, it is difficult to obtain an output of 10 watts or more. From the above, it is understood that the flare structure semiconductor laser of the present invention can provide a large output in a narrow light emitting region as compared with 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 flare structure semiconductor laser according to the present invention, and FIG. 2 is a sectional view taken along the line AA ′ in FIG. The 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 clad 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 0.8% compressive strain introduced
a (thickness 8 nm) 5 layers, emission wavelength 1.2 μm In
GaAsP barrier layer 3b (thickness 6 nm), emission wavelength 1.
InGaAsP-SCH (Separate Confi
nement Hetero-structure) 3c (thickness 50 nm). The emission wavelength of the active layer 3 is 1.5 μm.

After depositing a SiO ₂ insulating film on such a semiconductor wafer, an opening whose width changes in the lengthwise 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 (thickness 0.5 μm) is grown. The ridge waveguide structure has a width of 100 μm and a width of 100 μm in a wide region and a length of 900 μm.
The width was changed linearly over m. After that, 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 was cut out, and a high reflection film 10 (reflectance 90%) was provided on the end face with a wide total emission width, and a low reflection film 11 (reflectance 10%) was provided on the end face with a narrow total emission width. Each is formed to obtain a desired flare structure semiconductor laser. A linear waveguide of 50 μm is formed on each side of a 900 μm-long tapered region, and the total length of the device is 1000.
μm.

In the semiconductor laser thus manufactured, a pulse current having a width of 20 ns and a repetition rate of 10 kHz is applied, so that the peak light output is 50 W and the full width at half maximum is 20 °. A far field image was obtained. The oscillation threshold current and slope efficiency were 3 A and 0.25 W / A, respectively, and the total emission region width in the light emission region was 100 μm.

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

(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 the line BB 'in FIG. The element having this structure can be manufactured as follows. First, the n-InP buffer layer 2 (thickness: 0.2 μm), the active layer 3, and the p-InP clad layer 4 are formed on the n-InP substrate 1.
(Thickness 0.3 μm) is sequentially grown. Here, the active layer 3 has the same SCH multiple quantum well structure as that of the first embodiment, the energy band structure of which is shown in FIG.

After forming a SiO ₂ insulating film on such a semiconductor wafer, an opening whose width changes in the cavity length direction 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 (thickness 0.5 μm)
Are sequentially grown. The ridge waveguide structure has a width of 100 μm and a width of 200 μm in a wide region,
The width was changed linearly over a length of 900 μm. After this, the outer region of the ridge cladding layer 4a is set to 10 μm.
The p-InP clad layer 4 and the active layer 3 are removed by etching, leaving m each.

After that, 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
%), A low reflection film 11 (reflectance 10%) is formed on the end face on the side where the total emission width is narrow, to obtain a desired flare structure semiconductor laser. 50μ on both sides of 900μm long tapered region
The configuration was such that linear waveguides of m each were formed, and the total length of the device was 1000 μm.

In the semiconductor laser thus manufactured, a pulse current having a width of 20 ns and a repetition rate of 10 kHz is applied, so that the peak light output is 50 W and the full width at half maximum is 20 °. A far field image was obtained. The oscillation threshold current and slope efficiency were 3 A and 0.25 W / A, respectively, and the total emission region width in the light emission 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 the line CC ′ of FIG. The element having this structure can be manufactured as follows. First, the n-InP buffer layer 2 (thickness: 0.2 μm), the active layer 3, and the p-InP clad layer 4 are formed on the n-InP substrate 1.
(Thickness 2 μm), emission wavelength 1.64 μm p-InGa
An As contact layer 5 (thickness 0.5 μm) is sequentially grown. Here, the active layer 3 has the same SCH multiple quantum well structure as that of the first embodiment, the energy band structure of which is shown in FIG.

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

After that, the outer region of the tapered mask is removed up to the active layer 3 by etching, and the p-InP buried layer 12 and the n-InP buried layer 13 are grown in this etched region. Next, the SiO ₂ etching mask is removed, the 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, it is cut into a laser chip, and a high reflection film 10 (reflectance 90%) is formed on the end face with a wide total emission width, and a low reflection film 11 (reflectance 10%) is formed on the end face with a narrow total emission width. Thus, a desired flare structure semiconductor laser is obtained. The total length of the device was 1000 μm, and linear waveguides of 50 μm each were formed on both sides of a 900 μm long tapered region.

In the semiconductor laser thus manufactured, a pulse current having a width of 20 ns and a repetition rate of 10 kHz is applied, so that the peak light output is 50 W and the full width at half maximum is 20 °. A far field image was obtained. The oscillation threshold current and slope efficiency were 3 A and 0.25 W / A, respectively, and the total emission region width in the light emission region was 100 μm.

(Fourth Embodiment) FIG. 8 is a schematic perspective view of a composite semiconductor laser according to a fourth embodiment of the present invention. In this embodiment, four flare structure semiconductor lasers 14 of the first to third embodiments are stacked in an arrangement such that they are electrically connected in series. The flare structure semiconductor laser 14 is electrically a pn diode. Therefore, the individual flare structure semiconductor lasers 14 are arranged so that the p-side electrode 7 side (or the n-side electrode 8 side) faces upward, and the light emitting regions 9 and the light emitting regions 15 of the individual flare structure semiconductor lasers 14 are stacked in the stacking direction. Are arranged so as to be substantially overlapped with each other, and then they are bonded to each other by using a conductive fusing material to perform electrical series connection. The thickness of each flare structure semiconductor laser 14 is about 50.
Since this is about μm, a semiconductor laser having a small total light emitting region area can be constructed by this embodiment.

In such a semiconductor laser, the width is 20n
By repeatedly applying a pulse current of 10 kHz for 10 seconds, a luminescence far-field image in a horizontal direction with a full width at half maximum of 20 ° and a single peak and no ripple was obtained up to a peak light output of 200 W.
Oscillation threshold current and slope efficiency are 3A and 1W respectively
/ A, the light emitting region 15 had a size of 100 μm × 150 μm.

(Modifications of Embodiments) The preferred embodiments have been described above, but the present invention is not limited to these embodiments, and appropriate modifications can be made within the scope of the claims. For example, in the embodiment, InP
Although the element using the substrate and having the oscillation wavelength of around 1.5 μm has been described, other materials such as GaAs and InGaAlAs can be used to oscillate at an appropriate wavelength. Further, the current confinement may be performed by forming a current blocking 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 emitting region.

[Brief description of 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 the second embodiment of the present invention.

FIG. 5 is a sectional view of the 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]

 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 burying layer 13 n-InP burying layer 14 flare structure semiconductor laser 15 light emitting region 16 DFB laser region 17 amplifier region 18 non-reflection film 21 substrate 22 buffer layer 23 current blocking layer 24 lower clad layer 25 active layer 26 upper clad layer 27 contact layer 28, 29 electrode

Claims (5)

[Claims] 1. A first-conductivity-type semiconductor layer, a first-conductivity-type buffer layer, an active layer, and a second-conductivity-type cladding layer are stacked in this order on a first-conductivity-type semiconductor substrate, and a width of a region of the active layer into which a current is injected is a resonator. In a semiconductor laser that changes linearly along the longitudinal direction, a high reflection film is formed on the end face of the active layer on which the current is injected on the wide side, and the high reflection film on the side where the high reflection film is not formed is formed. A semiconductor laser characterized in that high-order mode oscillation light is emitted from an end face. 2. The semiconductor laser according to claim 1, wherein the second conductivity type cladding layer has a planar ridge structure that substantially follows the pattern of the current injection region of the active layer. 3. The second conductivity type clad layer has a planar ridge structure that substantially follows the pattern of the current injection region of the active layer, and the rest of the active layer and the second conductivity type clad layer. Is processed so as to have the same planar shape as the ridge structure or to be slightly wider than the ridge structure, 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 active layer has a multiple quantum well structure, or a multiple quantum well structure and SCHs sandwiching the multiple quantum well structure from both sides.
The semiconductor laser according to claim 1, wherein the semiconductor laser has a layer. 5. A composite semiconductor laser including the semiconductor lasers according to claim 1, wherein the semiconductor lasers are stacked in multiple stages.