JP5437109B2 - Semiconductor laser device - Google Patents

Description

  The present invention relates to a semiconductor laser device, and more particularly to a technique effective when applied to a multi-beam semiconductor laser device.

  With the demand for higher printing speed for PPC (Plain Paper Copier) and laser printers, the demand for multi-beam semiconductor laser devices is rapidly increasing. Since such a multi-beam semiconductor laser device has a plurality of light emitting units arranged one-dimensionally or two-dimensionally, the number of scanning beams can be increased even with a single device, thereby enabling high-speed printing. There is an advantage of becoming.

  Here, a general structure of the multi-beam semiconductor laser device will be described with reference to FIG. FIG. 8 shows an example of a semiconductor laser device having a 4-beam structure as an example of the multi-beam semiconductor laser device described above.

  As shown in the figure, a semiconductor substrate (hereinafter simply referred to as “substrate”) 9, a semiconductor layer 2 having an array of light emitting portions 7, an n-type electrode 1, and a p-type separated in stripes A semiconductor laser element array (laser chip) 8 composed of the electrodes 3 is joined to the stripe-shaped submount electrodes 5 formed on the submount 6 by solder 4. Further, a heat radiating metal layer 10 made of Au plating or the like is formed on the surface of the p-type electrode 3.

  On the other hand, the submount 6 is joined to a heat sink (not shown) made of, for example, Cu via solder or the like. The submount 6 has a role of relieving thermal stress due to a difference in linear expansion coefficient between the heat sink and the semiconductor laser element array 8 and improving heat dissipation of the apparatus. Therefore, in general, as the material of the submount 6, a material having good thermal conductivity and a thermal expansion coefficient close to that of the substrate 9, for example, SiC, Si, CuW, AlN, or the like is used.

  The above-described method of mounting the light emitting portion 7 of the substrate 9 toward the submount 6 side is generally called a junction down method, and heat generated in the light emitting portion 7 can be efficiently released to the submount 6. It has the advantage that. However, in this junction down method, since stress is easily applied to the joint portion between the substrate 9 and the submount 6, the light emitting portion 7 is distorted by the thermal stress at the time of mounting. It is known that non-uniformity (so-called variation) occurs. In particular, in a multi-beam semiconductor laser device, a laser element having uniform light characteristics can be realized by suppressing the difference between beams in the characteristics for each beam such as the wavelength, polarization angle, light emission efficiency, and light output of each light emitting section. Is required. For this reason, in such a junction-down multi-beam semiconductor laser device, it is important to reduce the thermal stress during mounting and to reduce the difference between the distortion beams applied to each light emitting portion.

  Conventionally, as a method for solving the above-described problem, for example, in Patent Document 1 below, a space is formed between a semiconductor laser element and a submount, and a groove is formed at a position corresponding to a mesa-shaped semiconductor layer. A structure has been proposed.

  Patent Document 2 below proposes a method of reducing the influence of strain by providing a gap between the active layer and the substrate and providing notches on both sides of the active layer.

  In addition, it is already known from Patent Document 3 and Non-Patent Document 1 that the semiconductor laser has various effects on the light emission characteristics such as the wavelength and the polarization angle when distortion occurs in the light emitting portion. Yes.

JP 2003-163402 A JP 2002-314184 A JP 2009-144094 A

Kenichi Iga Applied Physics Series Semiconductor Laser Ohmsha Oct. 1994 p.113-131

  By the way, in the semiconductor laser device having a structure as shown in the above-mentioned Patent Document 2, that is, having a space around the ridge portion, the heat dissipation is deteriorated because the ridge portion is not directly joined to the submount. There is a problem. On the other hand, in order to improve heat dissipation in such a structure, it is necessary to secure a heat dissipation path by the metal plating layer as shown in Patent Document 1 above. In addition, this metal plating layer is formed on a semiconductor layer by vapor deposition etc., for example. However, in this metal plating layer, due to the stress caused by the lattice constant difference with the underlying material (hereinafter referred to as “film stress”) and the linear expansion coefficient difference with the adjacent material, Thermal stress is generated. That is, due to the stress generated by such a metal plating layer, a strain distribution exists in the light emitting portion.

  As described above, in particular, as is known from Patent Document 1, in the structure in which the metal plating layer is present beside the light emitting portion, the film stress or thermal stress of the metal plating layer greatly affects the strain of the light emitting portion. Become. For this reason, the light emission characteristics of the semiconductor laser change due to the stress of the metal plating layer.

  On the other hand, in particular, in a multi-beam semiconductor laser, since laser elements are arranged in parallel over a wide range, the film thickness and film stress of the metal plating layer to be deposited are nonuniform (variable) for each laser. There is. Such non-uniformity (variation) in film quality may cause non-uniformity (variation) in the emission characteristics of each semiconductor laser. As described above, since a multi-beam semiconductor laser requires uniform light emission characteristics in each light emitting section, it is necessary to suppress such non-uniformity (variation) of light emission characteristics due to such non-uniformity (variation) of film quality. It becomes.

  Therefore, in the present invention, in view of the above-described problems in the prior art, that is, the nonuniformity (variation) of the light emission characteristics caused by the nonuniformity (variation) of the film stress due to the film thickness of the formed metal plating layer or the like is reduced. It is an object of the present invention to provide a semiconductor laser device having a structure that can be used.

  To achieve the above object, according to the present invention, a semiconductor substrate, a first electrode formed on a first surface of the semiconductor substrate, and a semiconductor layer formed on a second surface of the semiconductor substrate. An insulating layer formed on the surface of the semiconductor layer, a second electrode formed on the surface of the insulating layer, a metal layer formed on the surface of the insulating layer, and formed inside the semiconductor layer. A semiconductor laser device having an active layer forming a light emitting portion, wherein the semiconductor layer has a groove formed on at least one side of both sides of the center position of the light emitting portion, and The groove is formed so that the surface of the second electrode formed at the bottom of the groove is deep enough to be located closer to the first electrode than the interface between the semiconductor substrate and the semiconductor layer. An apparatus is provided.

  According to the present invention, in the semiconductor laser device described above, the groove further includes a surface of the metal layer formed on a surface of the second electrode formed on a bottom portion of the groove. Preferably, it is formed to a depth located on the first electrode side with respect to the interface between the semiconductor layer, and further has a submount, and the light emitting portion of the semiconductor laser element and the submount It is preferable to have a space between them. Furthermore, it is preferable to have a terrace structure portion that mechanically supports the semiconductor substrate and the submount on the side where the groove is formed with respect to the center position of the light emitting portion.

  According to the present invention, in the semiconductor laser device described above, it is preferable that a plurality of light emitting portions are formed in the semiconductor layer, and further, the plurality of light emitting portions are arranged along a plurality of rows. It is preferable that the groove is formed and the groove is formed along the row.

  According to the present invention described above, the influence of the stress is small, that is, the non-uniformity (variation) of the light emission characteristics caused by the nonuniformity (variation) of the film stress due to the film thickness of the formed metal plating layer or the like is reduced. It is possible to provide a semiconductor laser device capable of providing a practically excellent effect.

It is a figure explaining the mechanism of the nonuniformity (variation) in the light emission characteristic which arises by the nonuniformity (variation) of the film thickness of metal plating which becomes the foundation of this invention. It is sectional drawing which shows the structure of the multi-beam semiconductor laser apparatus used as the 1st Example (Example 1) of this invention. It is a figure which shows the manufacturing method of the semiconductor laser element of the said Example 1, and is a typical sectional drawing of the semiconductor substrate in each process from multilayer growth to groove | channel formation especially. It is a figure which shows the manufacturing method of the semiconductor laser element of the said Example 1, and is a typical sectional drawing of the semiconductor substrate in each process especially from insulating film formation to metal electrode formation. It is a figure which shows generation | occurrence | production of the dispersion | variation in the shear strain by the film thickness dispersion | variation in the metal layer in the semiconductor laser device which becomes this invention compared with that of the conventional structure. It is a figure showing the relative temperature ratio of the structure of the semiconductor laser device which becomes Example 1 of this invention, and the conventional structure. It is sectional drawing which shows the structure of the multi-beam semiconductor laser apparatus used as the other Example (Example 2) of this invention. It is sectional drawing which shows the structure of the multi-beam semiconductor laser apparatus used as a prior art.

  Hereinafter, before showing an embodiment of the present invention, first, referring to FIGS. 1 (a) and 1 (b), non-uniformity (variation) in the film thickness of metal plating causes non-uniformity in light emission characteristics (see FIG. The mechanism of occurrence of variation will be described.

  FIG. 1 (a) illustrates the tension region due to metal plating when the metal plating is thin, and FIG. 1 (b) illustrates the tension region due to metal plating when the metal plating is thick. . As shown in FIGS. 1 (a) and 1 (b), when the thickness of the metal plating varies (varies) due to the groove dug beside the light emitting portion, the semiconductor layer is pulled by the metal plating layer. The region (see “Tensile region” in the figure) changes. Thereby, the shear strain in the light emitting portion changes. That is, it is already known that when a shear strain is applied to the light emitting portion, the polarization direction of the beam rotates in proportion to the shear strain (see Patent Document 3 above). , Non-uniformity (variation) occurs.

  The present invention has been achieved on the basis of the mechanism of occurrence of non-uniformity in light emission characteristics due to non-uniformity of the metal plating film thickness, which has been studied by the inventors and the like. explain.

  That is, in order to eliminate the influence of the stress on the light emitting portion due to the tensile stress of the metal layer, it is necessary that at least the metal layer is not located directly beside the light emitting portion. In addition, in order to suppress variation in shear stress due to the film thickness of the metal layer, the surface portion of the metal layer deposited in the groove formed between the ridge portion and the terrace structure portion is further disposed at the interface between the semiconductor substrate and the semiconductor layer. On the other hand, it is formed so as to be located on the semiconductor substrate side having a larger linear expansion coefficient than the semiconductor layer. According to this, since the difference in linear expansion coefficient between the metal layer and the metal layer peripheral member can be reduced, it is possible to suppress the occurrence of variations in shear strain due to variations in film thickness.

  FIG. 2 shows an outline of the configuration of the semiconductor laser device according to the first embodiment (Embodiment 1) of the present invention. In particular, the configuration of the semiconductor laser device equipped with a two-beam multi-beam laser is shown. Is. The semiconductor laser device of the first embodiment is a semiconductor laser device having a configuration in which the linear expansion coefficient of the semiconductor substrate is larger than the linear expansion coefficient of the submount. For example, the semiconductor substrate has GaAs (linear expansion coefficient = 6). .4 × 10 −6 / K) is selected, and SiC (linear expansion coefficient = 4.0 × 10 −6 / K) or AlN (linear expansion coefficient = 4.8 × 10 −6 /) is used for the submount. K) is selected. Further, for example, AlGaInP (linear expansion coefficient = 4.7 × 10 −6 / K) having a smaller linear expansion coefficient than that of the semiconductor substrate is selected for the cladding layer.

  The semiconductor laser device of Example 1 has a structure in which a semiconductor layer 2 having two convex ridges 13 is stacked on a substrate 9 on which an n-type electrode (cathode electrode) 1 that is a common electrode is formed. In addition, the semiconductor layer 2 has a light emitting portion 7. These two ridge portions 13 are arranged so as to be symmetrical with respect to the center position of the substrate 9. These ridge portions 13 are formed so as to extend in the direction of the resonator of the semiconductor laser element, thereby constituting a power feeding portion to which a current is constricted and supplied.

  An insulating layer 12 is formed on both side surfaces of the ridge portion 13 and on the semiconductor layer 2 in the vicinity thereof. A p-type electrode (anode electrode) 3 which is an independent electrode is formed on the insulating layer 12. Is formed in contact with the upper surface of the ridge portion 13. Further, a heat-dissipating Au plating layer (metal layer) 14 is formed on the surface of the p-type electrode 3.

  Next, two submount electrodes 5 are formed on the lower surface of the submount 6 so as to face the p-type electrode 3. The Au plating and the submount electrode 5 are not joined immediately below the ridge portion 13. On the other hand, on the terrace structure portion 11 formed on the outer side with respect to the center position, the solder 4 such as Au—Sn is used. It is joined. Although illustration is omitted here, a heat sink made of Cu is joined to the upper surface of the submount 6 by, for example, solder.

  As shown in FIG. 2, a groove 17 is formed between each ridge portion 13 and the terrace structure portion 11. The heat-dissipating Au plating layer 14 formed in the groove 17 has a surface parallel to the active layer, and the Au plating layer 14 has the surfaces thereof that are the semiconductor layer 2 and the substrate 9. It is formed so as to be located on the cathode electrode 1 side with respect to the interface.

  Next, an example of a manufacturing method of the semiconductor laser device 1 according to the first embodiment will be described with reference to FIGS.

  First, as shown in FIG. 3A, after preparing a semiconductor substrate (n-GaAs substrate) 9 having a thickness of several hundreds μm, the n-GaAs substrate 9 has n − An AlGaInP cladding layer 2a, an active layer 2b having a multiple quantum well structure, a p-AlGaInP first cladding layer 2c, an etching stop layer 2d, a p-AlGaInP second cladding layer 2e, and a p-GaAs contact layer 2f in this order, It is formed by MOCVD (metal organic chemical vapor deposition) multilayer growth. A part of the active layer 2b having the multiple quantum well structure forms a so-called light emitting portion 7.

  Subsequently, as shown in FIG. 3B, a mask 15 made of a silicon oxide film (SiO 2 film) having a width of about 2 μm and a width of about 40 μm is formed on the p-GaAs contact layer 2f. Thereafter, the p-GaAs contact layer 2f and the p-AlGaInP second cladding layer 2e are etched by dry etching to form the ridge stripe portion 13 and the terrace structure portion 11.

  Further, as shown in FIG. 3C, after forming an etching mask material over the entire second surface 9b of the n-GaAs substrate 9, this etching mask material is selectively removed by etching, so-called mask. 16 is formed. The etching removal portion is provided between the ridge stripe portion 13 and the terrace structure portion 11. Subsequently, the multilayer growth layer is etched using the mask 16 as an etching mask, and the bottom surface thereof reaches at least the surface layer (interface) of the n-GaAs substrate 9 as shown in the figure. The groove 17 is formed until reaching the inside. The distance from the side surface of the ridge stripe portion 13 to the edge of the groove 17 is 3.5 μm.

  Next, the mask 16 is removed. Thereafter, as shown in FIG. 4A, the insulating layer 12 is formed on the entire second surface 9b of the n-GaAs substrate 9, and then the upper surface of the ridge stripe portion 13 (p-GaAs contact layer 2f). A portion of the insulating layer 12 is removed by etching. The insulating layer 12 is formed of, for example, a silicon oxide film (SiO 2 film) formed by thermal CVD (vapor chemical deposition). The upper surface of the ridge stripe portion 13 is a current injection region, and when a voltage is applied to the electrodes, the current flows through the p-GaAs contact layer 2f and the p-AlGaInP second cladding layer 2e. It will be.

  Next, as shown in FIG. 4B, an electrode material is formed over the entire area of the second surface 9b of the n-GaAs substrate 9, and then a part thereof is removed by etching. A so-called metal multilayer film made of, for example, titanium, platinum, or gold is deposited on the second surface 9b. The second electrode 3 thus formed is connected to the p-GaAs contact layer 2f and covers the groove 17 formed between the ridge stripe portion 13 and the terrace structure portion 11 (FIG. 2). See). At this time, the groove 17 described above is in this state, that is, in a state before performing the plating process described below, the bottom surface of the n-GaAs substrate 9 with respect to the interface between the semiconductor layer 2 and the substrate 9. It is formed so as to be located on the first surface 9a side. According to this, it becomes possible to reduce non-uniformity (variation) of distortion due to the displacement of the plating layer in the plating process described below.

  Subsequently, as shown in FIG. 4C, a metal having a higher thermal conductivity than the n-GaAs substrate 9, for example, gold (Au) is vapor-deposited on the second electrode 3, so that the metal plating layer 14. Form. At that time, the bottom 18 of the groove 17 formed as described above is positioned on the first surface 9 a side of the substrate 9 with respect to the interface 19 between the n-AlGaInP cladding layer 2 a and the n-GaAs substrate 9. Form. That is, according to this, it is possible to reduce non-uniformity (variation) of distortion with respect to non-uniformity (variation) in the thickness of the plating layer in the plating process.

  Finally, as shown in FIG. 4C, a metal multilayer film made of, for example, titanium, platinum, gold or the like is formed on the first surface 9a of the n-GaAs substrate 9 by vapor deposition. One electrode 1 is formed.

  Subsequently, with reference to FIG. 5 attached, the semiconductor laser device of the present invention whose detailed structure has been described above has a non-uniformity (variation) in light emission characteristics due to a deviation or nonuniformity (variation) in the thickness of the metal plating layer. ) Can be reduced.

  In FIG. 5, the horizontal axis indicates the thickness of the plating layer (plating thickness), and the vertical axis indicates the shear strain generated in the light emitting portion. That is, as is apparent from the characteristic curve shown in the graph of this figure, in the conventional structure, when the plating layer is displaced, there is a large difference in the shear strain generated in the light emitting portion depending on the presence or absence. On the other hand, according to the structure of the present invention, it can be seen that there is almost no difference in the shear strain generated in the light emitting portion regardless of whether or not the plating layer is displaced. In addition, it can be seen that the shear strain generated in the light emitting portion is substantially constant even when the thickness of the metal plating layer is changed.

  Next, using FIG. 6 attached, it will be shown that the structure of the present invention can maintain substantially the same heat dissipation as compared with the conventional structure. In FIG. 6, the maximum temperature in the above-described light emitting portion of the present invention is the structure described in Patent Document 1 in which the deepest portion of the surface of the metal layer formed in the groove 17 is located between the active layer and the submount. The relative temperature ratio is shown assuming that the conventional structure has a maximum temperature of 1 in the light emitting part of the conventional structure. From this result, it can be seen that the structure of the present invention has almost the same heat dissipation as the conventional structure.

FIG. 7 attached herewith is a cross-sectional view showing the structure of a semiconductor laser device according to another embodiment (embodiment 2) of the present invention. In the structure of embodiment 2 in this figure, the metal layer inside the groove 17 is shown. In particular, the metal plating layer 14 is selectively thickened to improve heat dissipation. In the structure of the second embodiment, since the rate of change in strain when the thickness of the metal layer is increased is small, the film thickness can be increased compared to the conventional structure. As described above, when the thickness of the metal layer is increased, the cross-sectional area of the heat dissipation path is increased, and thus the heat dissipation performance is improved. That is, by applying the above-described structure of the present invention to a semiconductor laser device, particularly a multi-beam semiconductor laser device, it is possible to obtain a device having better heat dissipation than the conventional structure.

  In the above-described embodiments, the case of a two-beam laser is described as an example of a multi-beam laser. However, the present invention is not limited to this, and includes, for example, three or more beams. In this case, the occurrence of non-uniformity (variation) in shear strain due to non-uniformity (variation) in the film thickness can be suppressed, and as a result, the optical characteristics between the beams can be reduced. It is possible to suppress the occurrence of non-uniformity (variation).

  In the embodiment described above, the thickness of the substrate 9 is about several hundreds μm, whereas the assumed depth of the groove 17 is about several μm to several tens of μm. For this reason, there is no problem of adverse effects on the mechanical strength of the substrate due to the digging of the grooves 17.

  The present invention has been specifically described above based on the embodiment. However, the present invention is not limited to the above-described embodiment, and various modifications can be made without departing from the scope of the invention. Needless to say.

DESCRIPTION OF SYMBOLS 1 ... 2nd electrode, 2 ... Semiconductor layer, 2a ... 1st conductivity type cladding layer, 2b ... Active layer, 2c ... 2nd conductivity type 1st cladding layer (p-AlGaInP 1st cladding layer), 2d ... Etching stop Layers, 2e ... second conductivity type second cladding layer (p-AlGaInP second cladding layer), 2f ... contact layer (p-GaAs contact layer), 3 ... first electrode, 4 ... solder, 5 ... submount electrode , 6 ... Submount, 7 ... Light emitting part, 8 ... Semiconductor laser element array (laser chip), 9 ... Semiconductor substrate (n-GaAs substrate), 9a ... First surface of semiconductor substrate, 10 ... Metal layer, 11 ... terrace structure, 12 ... insulating layer, 13 ... ridge stripe (ridge), 14 ... Au plated layer (metal layer), 15 ... SiO ₂ mask, 16 ... mask, 17 ... groove, 18 ... bottom, 19 ... interface.

Claims (5)

A semiconductor substrate;
A first electrode formed on a first surface of the semiconductor substrate;
A semiconductor layer formed on the second surface of the semiconductor substrate;
An insulating layer formed on the surface of the semiconductor layer;
A second electrode formed on the surface of the insulating layer;
A metal layer formed on the surface of the second electrode ;
An active layer formed inside the semiconductor layer and forming a light emitting portion;
In a semiconductor laser device having
In the semiconductor layer, a groove is formed on at least one side of both sides with respect to the center position of the light emitting unit, and the groove has a surface of the metal layer formed on the bottom thereof. A semiconductor laser device, wherein the semiconductor laser device is formed to a depth located closer to the first electrode than an interface between a semiconductor substrate and the semiconductor layer. In the semiconductor laser device according to claim 1, further comprising a submount, the semiconductor laser device characterized by having an air gap between the front Symbol emitting portion and the submount. 3. The semiconductor laser device according to claim 2 , further comprising a terrace structure portion that mechanically supports the semiconductor substrate and the submount on a side where the groove is formed with respect to a center position of the light emitting portion. A semiconductor laser device. The claims in the semiconductor laser device according to any one of claim 1 to 3, a semiconductor laser device wherein a plurality of light emitting portions on the semiconductor layer is formed. 5. The semiconductor laser device according to claim 4 , wherein the plurality of light emitting portions are formed along a plurality of rows, and the grooves are formed along the rows. apparatus.

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