JP6510803B2 - Distributed feedback semiconductor laser device - Google Patents

Description

  The present invention relates to a distributed feedback (DFB) semiconductor laser device.

  Conventional DFB semiconductor laser devices are described, for example, in the following Patent Document 1 and Patent Document 2. The DFB semiconductor laser device includes a lower cladding layer, an active layer formed on the lower cladding layer, an upper cladding layer formed on the active layer, and a diffraction grating layer provided on the lower cladding layer or the upper cladding layer. The laser beam of the wavelength defined by the diffraction grating layer is emitted from the active layer.

Patent 3204474 Patent 3707846 gazette

  However, the conventional DFB semiconductor laser device has a problem that the lifetime is short, and further extension of the lifetime has been expected. An object of the present invention is to provide a DFB semiconductor laser device capable of achieving long life.

  Initially, the cause of the life was unknown, but as a result of intensive investigations by the present inventors, the (111) B surface orientation of the side surface of the diffraction grating layer extending perpendicularly to the resonator length is So, I discovered a phenomenon that the life span increased dramatically. The plane orientation of the top and bottom surfaces of the concavo-convex structure in the diffraction grating layer in this case was the (100) plane.

The present invention is based on such findings and comprises a lower cladding layer, an active layer formed on the lower cladding layer, an upper cladding layer formed on the active layer, the lower cladding layer or the upper layer. And a diffraction grating layer provided in the cladding layer, in a distributed feedback semiconductor laser device having a cavity length of 2000 μm to 6000 μm , a direction perpendicular to both the cavity length direction and thickness direction of the active layer In the width direction, the diffraction grating layer is made of AlGaAs which is a group III-V compound semiconductor having a zinc-blende structure, the composition of Al is more than 0% and 10% or less, The top and bottom surfaces of the concavo-convex structure are (100) planes, and the side surface along the width direction of the concavo-convex structure is (1 1) a B side, the said recess, so that the refractive index is different, said diffraction grating layer and wherein the lower clad layer or the upper clad layer Al composition of different AlGaAs is embedded Do.

  According to the DFB semiconductor laser device of the present invention, since the plane orientation of the side surface of the diffraction grating layer is (111) B plane, the life is dramatically improved compared to the case where this is the (111) A plane. It could be increased.

  The stress in the (111) B plane in the wafer state was measured to examine the cause of the long life, and it was found that this was smaller than the stress in the (111) A plane. This difference in stress is considered to be affecting.

  It is believed that the present invention can be applied to compound semiconductor materials having such a difference in stress because there is a crystal structure having a similar stress relationship. That is, the group III-V compound semiconductor is characterized in having a crystal structure containing As or P. In the case of these crystal structures, the stress stored in the crystal is different between the case of using the (111) B plane and the case of using the (111) A plane. Can be achieved.

  The group III-V compound semiconductor is made of AlGaAs, InGaP, InGaAsP, or InAlGaAs. These semiconductors are well known and can likewise achieve a long life.

  According to the DFB semiconductor laser device of the present invention, the lifetime can be increased.

It is a perspective view of a semiconductor laser device. It is a perspective view of a DFB semiconductor laser element. It is a longitudinal cross-sectional view of a DFB semiconductor laser element. It is a perspective view of a wafer. It is a longitudinal cross-sectional view of a diffraction grating layer. It is a figure (A) for demonstrating a surface orientation, and a perspective view (B) of a diffraction grating layer. It is a perspective view (A) of the diffraction grating layer which makes a side surface (111) A surface, a perspective view (B) of a diffraction grating layer which makes a side surface a (111) B surface, and a perspective view (C) of a wafer. It is a graph which shows the relationship between the electric current (A) supplied to a DFB semiconductor laser element, the output (W) of a laser beam, and electricity-light conversion efficiency (%). It is a graph which shows the relationship between the drive time (hour) of a DFB semiconductor laser element, and the normalized output of a laser beam. Graph (A) showing the intensity distribution in the width direction of the near-field image according to the embodiment and the comparative example, graph (B) showing the intensity distribution in the width direction (horizontal direction) of the far-field image according to the embodiment It is a graph (C) which shows intensity distribution of the width direction (horizontal direction) of the far-field pattern which concerns. It is a graph which shows the polarization ratio to the radiation angle of the width direction concerning an example and a comparative example.

  Hereinafter, a distributed feedback (DFB) semiconductor laser device according to the embodiment will be described. In addition, suppose that the same code | symbol is used for the same element, and the overlapping description is abbreviate | omitted.

  FIG. 1 is a perspective view of a semiconductor laser device.

  The semiconductor laser device 100 includes a base 30 having a step on the upper surface, a submount 20 fixed on the lower surface of the base 30, and a DFB semiconductor laser device whose lower surface is fixed on the submount 20 with conductive paste or the like. (Hereinafter, the semiconductor laser device 10). A plurality of wires W are connected between the upper end surface of the base 30 and the upper electrode E1 of the semiconductor laser device 10. The base 30 is composed of an upper surface conductor 31 and a lower surface conductor 32, and a ceramic insulator is provided between the upper surface conductive member 31 and the lower surface conductive member 32.

  The direction of the resonator length is [011], the length of the upper electrode E1 defining the resonator length is 4 mm, and the width (emission width) of the upper electrode E1 is 100 μm. The thickness direction of the semiconductor laser device 10 is [100], and the direction perpendicular to both [011] and [100] is [01-1].

  FIG. 2 is a perspective view of the semiconductor laser device.

  The semiconductor laser device 10 includes a substrate 1, a lower cladding layer 2 formed on the substrate 1, an active layer 3 formed on the lower cladding layer 2, and an upper cladding layer 4 formed on the active layer 3 ( 4a, 4b), a diffraction grating layer GR provided in the upper cladding layer 4, a contact layer 5 formed on the upper cladding layer 4, and an upper electrode E1 formed on the contact layer 5 . A lower electrode is formed on the lower surface of the substrate 1 with a conductive paste such as silver.

  The upper cladding layer 4 is composed of a first upper cladding layer 4a and a second upper cladding layer 4b, and the diffraction grating layer GR is sandwiched between them. The diffraction grating layer GR has a stripe-shaped concavo-convex structure, and the second upper cladding layer 4b is embedded in the concave part of the concavo-convex structure. The upper cladding layer 4 and the diffraction grating layer GR have different refractive indexes, and regions with different refractive indexes are alternately present along the cavity length direction.

  The diffraction grating layer GR may be provided in the lower cladding layer 2 in the same manner as in the upper cladding layer 4. These cladding layers are equivalent if they are turned upside down. The conductivity type differs between the upper cladding layer and the lower cladding layer. When the lower cladding layer 2 is provided with the diffraction grating layer, the lower cladding layer 2 can be divided into two in the same manner as the upper cladding layer 4. Note that, in the same drawing, XYZ three-dimensional orthogonal coordinate rights are also shown. The YZ plane exists in the plane consisting of [011] and [01-1], the Y axis is at a position rotated 45 degrees from [011] to [01-1], and the Z axis is It is orthogonal to the Y axis. Also, the X-axis is perpendicular to both the Y-axis and the Z-axis and coincides with [100].

  FIG. 3 is a longitudinal sectional view of a semiconductor laser device.

  This figure shows a more detailed structure, and the semiconductor laser device 10 is provided with a first light guide layer 3G1 between the active layer 3 and the lower cladding layer 2, and the active layer 3 and the first upper cladding A second light guide layer 3G2 is provided between it and the layer 4a. In the same drawing, the lower electrode E2 is shown on the back surface side of the substrate 1.

The material, conductivity type and thickness of each layer are as follows.

  The preferred range of the impurity concentration is 1/10 to 10 times the above concentration, and the thickness of each layer operates as an example even when an error of about ± 50% is included, in this case. Also, the laser light is sufficiently emitted. Further, the composition of Al in the diffraction grating layer is preferably more than 0% and 10% or less. This is because the surface is exposed to the air once in the diffraction grating manufacturing process, and if the active Al is contained in an amount of more than 10%, significant deterioration of the device characteristics due to natural oxidation is induced. When Al is contained, there is an advantage that the shape change of the diffraction grating is suppressed in the heating process of regrowth.

  In addition, another light guide layer can be inserted between the second light guide layer 3G2 and the active layer 3. Another light guide layer can be inserted between the first light guide layer 3G1 and the active layer 3. The energy band gap of all the light guide layers is set larger than that of the active layer, but the energy band gap of the light guide layer closer to the active layer is set smaller than that of the far side (ie, the Al composition ratio Is small).

  In addition, if the Al composition in each layer is described in detail, the Al composition of the cladding layer is different from the Al composition of the diffraction grating layer, and the refractive index is different. In AlGaAs, the higher the composition ratio of Al, the larger the energy band gap and the smaller the refractive index. The Al composition in the cladding layer is set to, for example, 45% on the P side and 35% on the N side, and the Al composition in the light guide layer closer to the active layer is set to, for example, 15%. The Al composition of the light guide layers 3G1 and 3G2 is set, for example, to 25%. The Al composition ratio of each layer other than the diffraction grating layer can operate even with an error of ± 5%.

  Note that as a formation method, an MOCVD (metal organic chemical vapor deposition) method can be used. When Al is contained, TMA (trimethylaluminum) can be used, when it contains Ga, TMG (trimethylgallium) can be used as a raw material when containing As. The growth temperature of AlGaAs is around 700 ° C., and the growth method of these materials is well known.

  FIG. 4 is a perspective view of the wafer.

  Comparing the above-described semiconductor laser structure with the semiconductor wafer WF, the surface of the wafer is the (100) plane, with the [100] direction perpendicular to it and the [011] in the direction perpendicular to the plane of the orientation flat OF. [01-1] extends in a width direction perpendicular to both [100] and [011]. The diffraction grating is processed in a stripe shape, but the longitudinal direction of the convex portion of each stripe coincides with the [01-1] direction.

  FIG. 5 is a longitudinal sectional view of the diffraction grating layer GR. This is a cross section obtained by cutting the diffraction grating layer GR in a plane including the resonator length and the thickness direction.

  The diffraction grating layer GR has a concavo-convex structure including a plurality of protrusions and recesses, and both the top surface of the protrusions and the bottom of the recess are (100) planes. Further, the side surface of the convex portion is a slope and is formed of a (111) B surface.

  As described above, the diffraction grating layer GR is formed of a zinc-zinc-type III-V compound semiconductor, and has a concavo-convex structure including a plurality of convex portions and concave portions extending along the width direction [01-1]. The top and bottom surfaces of the uneven structure are (100) planes, and the side surfaces along the width direction [01-1] of the uneven structure are (111) B planes. Note that the uneven structures are formed by etching. However, etching does not allow the recess to reach the bottom of the AlGaAs layer constituting the diffraction grating layer.

  FIG. 6 is a diagram (A) for explaining plane orientation and a perspective view (B) of a diffraction grating layer.

  The (111) B plane passes through the positive position of + Y axis, the positive position of + Z axis, and the positive position of + X axis when drawing a quadrangular pyramid having an apex on the axis in the XYZ orthogonal coordinate system. It is a surface, and the (1-1-1) B surface faces this. The remaining opposite side faces of the quadrangular pyramid become the (111) A plane and the (11-1) A plane. Therefore, as shown in FIG. 6B, the side of the diffraction grating layer GR includes the (111) B plane.

  FIG. 7 is a perspective view (A) of the diffraction grating layer with the side surface of (111) A, a perspective view of the diffraction grating layer with side surface of (111) B (B), and a perspective view of the wafer (C). is there.

  As described above, the side surface of the diffraction grating layer according to the example is the (111) B plane (FIG. 7 (B)). On the other hand, FIG. 7A shows the case where the side surface is a (111) A surface as a comparative example. In the case of the comparative example, the warpage of the light emitting surface is larger than that of the example (warping in the Y direction <warping in the Z direction). In this case, a large stress is generated in the light emitting surface parallel to the stripes in the comparative example. It is considered that the stress causes the lifetime of the semiconductor laser device to be shortened. The A plane is an exposed surface of only the group III atoms, and the B surface is defined as an exposed surface of only the V group atoms.

  FIG. 8 is a graph showing the relationship between the current (A) supplied to the semiconductor laser element, the output (W) of the laser light, and the electro-optical conversion efficiency (%).

  As shown in the figure, the light output for the same current was higher in the example than in the comparative example. In addition, the electricity-light conversion efficiency was also higher in the example than in the comparative example.

  FIG. 9 is a graph showing the relationship between the driving time (hour) of the semiconductor laser device and the normalized output of the laser light, (A) shows data in the case of the comparative example, and (B) shows an example Shows the data for.

  The number of laser elements used in the experiment is four in the comparative example and four in the example, and the temperature at the time of measurement is fixed at the temperature T = 25 ° C. of the laser element by the Peltier element. In the measurement, the drive current supplied to each element is adjusted so that the light output is 5 W at the initial value (time t = 0). The drive current at this time is CW (direct current), which is 4.5A ± 0.2A. When the drive current of each laser element is continuously driven with the initial value state, the light output decreases with time in the comparative example (A). However, as shown in the figure, in the case of the example (B), a large drop (a sharp drop) in light output is not recognized. Thus, in the case of the example, the life is dramatically increased compared to the comparative example.

  FIG. 10 is a graph (A) showing the intensity distribution of the near-field images in the width direction according to the example and the comparative example (A), and a graph showing the intensity distribution in the width direction (horizontal direction) of the far-field image according to the example It is a graph (C) which shows intensity distribution of the cross direction (horizontal direction) of the far-field pattern which concerns on a comparative example. In the graphs (B) and (C), the drive current I was changed to 1A to 6A.

  The measurement temperature is 25 ° C., and as in the above, it is data in the case of continuous light emission. The drive current I = 6A. As compared with the example, it is understood that the variation of the intensity is larger in both the near-field image and the far-field image in the comparative example. From the far-field patterns, it can be seen that the light-gathering characteristics of the example are improved as compared with the comparative example at any drive current.

  FIG. 11 is a graph showing the polarization ratio with respect to the outgoing angle in the width direction according to the example and the comparative example. The measurement temperature is 25 ° C., and the light output is 100 mW. The polarization ratio in the case of the example was 18 times in the vicinity of the angle of 0 degrees, but in the case of the comparative example, the polarization ratio was 9 times. Therefore, it is understood that the embodiment is also superior in terms of the polarization ratio.

  As described above, in the DFB semiconductor laser device according to the above-described embodiment, the lower cladding layer 2, the active layer 3 formed on the lower cladding layer 2, and the upper cladding layer formed on the active layer 3 In a distributed Bragg reflector semiconductor laser device including the fourth embodiment 4 and the diffraction grating layer GR provided in the lower cladding layer 2 or the upper cladding layer 4, a direction perpendicular to both the cavity length direction and the thickness direction of the active layer 3 And the grating layer GR is made of a Group III-V compound semiconductor having a zinc blende structure, and has a plurality of convex portions extending along the width direction [00-1], The top and bottom surfaces of the concavo-convex structure are (100) planes, and the side surfaces along the width direction of the concavo-convex structure are (111) B planes.

  According to the above-described DFB semiconductor laser device, since the plane orientation of the side surface of the diffraction grating layer GR is set to the (111) B plane, the life is dramatically increased as compared to the case where this is set to the (111) A plane. I was able to

  Also, in order to consider the cause of the long life, the stress in the wafer state when using the (111) B plane as a diffraction grating was measured, which is smaller than that when using the (111) A plane. found. This difference in stress is considered to be affecting. The present invention is considered to be applicable to compound semiconductor materials having such a difference in stress. That is, the group III-V compound semiconductor has a DFB crystal structure containing As or P, and in the case of these DFB crystal structures, there is a stress difference between (111) B plane utilization and (111) A plane utilization. Therefore, the long life can be achieved with a certain degree of certainty.

  In addition, AlGaAs, InGaP, InGaAsP, or InAlGaAs can be used as the III-V group compound semiconductor forming the diffraction grating layer. These semiconductors are well known and can likewise achieve a long life. The above-described structure is particularly effective because a broad area type laser having a large resonator length is easily influenced by stress because the emission width is wide. The range of effective resonator length is 2000 μm or more and 6000 μm or less.

  DESCRIPTION OF SYMBOLS 1 ... board | substrate, 2 ... lower clad layer, 3 ... active layer, 4 ... upper clad layer, 5 ... contact layer.

Claims (1)

Lower cladding layer,
An active layer formed on the lower cladding layer;
An upper cladding layer formed on the active layer;
A diffraction grating layer provided on the lower cladding layer or the upper cladding layer;
In a distributed feedback semiconductor laser device having a resonator length of 2000 μm to 6000 μm ,
When the direction perpendicular to both the direction of the resonator length of the active layer and the thickness direction is the width direction,
The grating layer is
It is made of AlGaAs which is a group III-V compound semiconductor of zinc blende structure,
The composition of Al is more than 0% and 10% or less,
It has a concavo-convex structure consisting of a plurality of projections and recesses extending along the width direction,
The top and bottom surfaces of the uneven structure are (100) faces,
The side surface along the width direction of the concavo-convex structure is a (111) B surface,
The lower cladding layer or the upper cladding layer made of AlGaAs having a different Al composition from the diffraction grating layer is embedded in the recess so that the refractive index is different.
A distributed feedback semiconductor laser device characterized in that

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