JP2011114167A - Semiconductor laser device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a semiconductor laser that acquires high output power without raising an operating current. <P>SOLUTION: The semiconductor laser device includes: a laser element 20; and a laser element 30 which is laminated on the laser element 20 and emits the light of the same wavelength band as that of the light emitted from the laser element 20. Furthermore, a current constriction structure is disposed in the laser element 30, and thicknesses of an n-type optical guide layer 22 and a p-type optical guide layer 24 in the laser element 20 are larger than those of an n-type optical guide layer 32 and a p-type optical guide layer 34 in the laser element 30. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a semiconductor laser device, and more particularly to a semiconductor laser device having a plurality of laser element portions.

  2. Description of the Related Art In recent years, semiconductor laser devices have been mounted on various devices. However, since the performance of these various devices has been increasingly increased, there is a demand for improving the characteristics of semiconductor laser devices. For example, in a vehicle-mounted radar system, a high-power semiconductor laser device is necessary.

  Therefore, in order to realize a high output of the semiconductor laser device, there has been conventionally proposed a structure in which a plurality of laser element portions (light emitting portions) are formed on a single substrate so that a high output can be obtained. (For example, refer to Patent Document 1). An example of the structure of a conventional semiconductor laser device having a plurality of laser element portions will be briefly described below.

  As a structure of a conventional semiconductor laser device, an n-type semiconductor layer, an active layer, and a p-type semiconductor layer are formed in this order on an n-type semiconductor substrate. The n-type semiconductor layer is a layer including an n-type cladding layer and an n-type light guide layer. On the other hand, the p-type semiconductor layer is a layer including a p-type cladding layer and a p-type light guide layer. Then, one laser element part is constituted by a laminate composed of an n-type semiconductor layer, an active layer, and a p-type semiconductor layer, and emits light together with another laser element part described later.

  On the laser element portion, another laser element portion is formed via a tunnel layer. As a result, a plurality of laser element portions are vertically stacked on the n-type semiconductor substrate.

  The upper laser element portion has substantially the same structure as the lower laser element portion. That is, the upper laser element portion sandwiches the active layer together with the n-type semiconductor layer formed on the lower laser element portion, the active layer formed on the n-type semiconductor layer, and the n-type semiconductor layer. It is comprised by the laminated body which consists of the p-type semiconductor layer formed in this. The thickness and composition of each layer constituting the upper laser element portion are the same as the thickness and composition of each layer constituting the lower laser element portion. However, unlike the p-type semiconductor layer of the lower laser element portion, the p-type semiconductor layer of the upper laser element portion further includes a p-type contact layer.

  Further, in order to supply current to the laser element portion, a p-side electrode is formed on the upper laser element portion, and the back surface of the n-type semiconductor substrate (the surface opposite to the side where the laser element portion is stacked) An n-side electrode is formed on the top.

  Conventionally, in order to increase the density of current supplied to the laser element portion, a current confinement structure is provided in the p-type semiconductor layer of the upper laser element portion, thereby narrowing the current supplied to the laser element portion. Like to do. In order to obtain such a current confinement structure, for example, a ridge portion (convex portion) protruding from other portions may be formed in the p-type semiconductor layer of the upper laser element portion.

JP-A-5-41561

  However, in the conventional semiconductor laser device described above, the current density is increased by providing the current confinement structure, but the supply current spreads as the separation distance from the current confinement structure increases. That is, the lower laser element part has a disadvantage that it is difficult to obtain the effect of providing the current confinement structure as compared with the upper laser element part. In other words, the current density is not so high in the lower laser element portion, and the threshold current increases.

  Therefore, the conventional semiconductor laser device has a problem that the operating current increases.

  The present invention has been made to solve the above problems, and an object of the present invention is to provide a semiconductor laser device capable of obtaining a high output without causing an increase in operating current.

  In order to achieve the above object, a semiconductor laser device according to an aspect of the present invention includes a first active layer and a pair of first light guide layers sandwiching the first active layer, and light in a predetermined wavelength band. A first laser element unit that emits light, a second active layer, and a pair of second light guide layers that sandwich the second active layer. The first laser element unit is stacked on the first laser element unit. And a second laser element unit that emits light in the same wavelength band as the light emitted from the element unit. A current confinement structure is provided on the opposite side of the second laser element portion from the first laser element portion side, and current is supplied to the second active layer and the first active layer through the current confinement structure. The thickness of at least one of the pair of first light guide layers is larger than the thickness of the pair of second light guide layers.

  In the semiconductor laser device according to this aspect, as described above, the thickness of at least one of the pair of first light guide layers (light guide layers sandwiching the first active layer) is set to the pair of second light guides. By making it larger than the thickness of the layer (the light guide layer sandwiching the second active layer), the following effects can be obtained.

  That is, in the semiconductor laser device according to one aspect, since the light density in the first active layer is increased, the first laser element portion (the laser element portion including the first active layer sandwiched between the pair of first light guide layers). ) Threshold current decreases. For this reason, even if the current density of the first laser element portion, which is the laser element portion having the larger separation distance from the current confinement structure, is lowered, the threshold current of the first laser element portion is lowered, so that the first It can suppress that the current-output characteristic of a laser element part deteriorates. As a result, high output can be obtained without causing an increase in operating current.

  The reason why the current density of the first laser element portion is low is that when current is supplied through the current confinement structure, the spread of the supply current increases as the distance from the current confinement structure increases. .

  In the semiconductor laser device according to the aforementioned aspect, it is more preferable that the thickness of both the pair of first light guide layers is larger than the thickness of the pair of second light guide layers. If comprised in this way, the light density in a 1st active layer can be raised more easily. In this case, the thicknesses of the pair of first light guide layers may be the same or different from each other as long as they are larger than the thickness of the pair of second light guide layers. May be.

  In the semiconductor laser device according to the aforementioned aspect, the plurality of first laser element units are sequentially stacked, and the second laser element is disposed on the first laser element unit positioned at the top of the plurality of first laser element units. The parts may be stacked. If comprised in this way, a 1st laser element part is provided with two or more, and a higher output semiconductor laser apparatus can be obtained.

  In this case, the thickness of at least one of the pair of first light guide layers included in the first laser element portion having the larger separation distance from the current confinement structure is the first laser having the smaller separation distance from the current confinement structure. The thickness is preferably larger than the thickness of the pair of first light guide layers included in the element portion. If comprised in this way, a several 1st laser element part is laminated | stacked one by one, and a 2nd element part is laminated | stacked on the 1st laser element part located in the top among the several 1st laser element parts Thus, in the semiconductor laser device designed to increase the output, a high output can be easily obtained without causing an increase in operating current. The number of stacked first laser element portions can be changed according to the application.

  In the semiconductor laser device according to the aforementioned aspect, the first active layer and the second active layer preferably have the same structure. If comprised in this way, the light of the mutually same wavelength band can be easily light-emitted from each of a 1st laser element part and a 2nd laser element part. Note that the same structure means that the thickness and composition are the same.

  In the semiconductor laser device according to the aforementioned aspect, it is preferable that both light emitted from each of the first laser element unit and the second laser element unit is infrared light. With this configuration, infrared light can be emitted with high output, which is effective when mounted on equipment that requires high output infrared light.

  As described above, according to the present invention, it is possible to obtain a high output without causing an increase in operating current.

It is sectional drawing of the semiconductor laser apparatus by one Embodiment of this invention. It is the figure which represented typically the breadth of the electric current supplied to the semiconductor laser apparatus by one Embodiment of this invention. It is sectional drawing which showed the modification of the semiconductor laser apparatus by one Embodiment of this invention.

  The semiconductor laser device according to the present embodiment will be explained below with reference to FIGS.

  The semiconductor laser device according to the present embodiment emits infrared light, and is mounted on an in-vehicle radar system and used as a light source.

  In addition, the semiconductor laser device according to the present embodiment has a plurality of edge-emitting laser element portions 10, 20 and 30 that each generate infrared light to emit light, thereby enabling light emission at a high output. It has become. The plurality of laser element portions 10, 20, and 30 are stacked by being stacked vertically in this order, and emit light in the same wavelength band (that is, infrared light). ing. The laser element units 10 and 20 are examples of the “first laser element unit” of the present invention, and the laser element unit 30 is an example of the “second laser element unit” of the present invention.

  First, as a structure of the laser element unit 10, an n-type cladding layer 11 and an n-type light guide layer 12 are formed in this order on an n-type substrate 1 made of n-type GaAs. The n-type cladding layer 11 is made of n-type AlGaAs (Al composition ratio: 0.40) and has a thickness of about 1.2 μm. The n-type light guide layer 12 is made of n-type AlGaAs (Al composition ratio: 0.30).

  An active layer 13 is formed on the n-type light guide layer 12. The active layer 13 includes a well layer made of InGaAs and a barrier layer made of AlGaAs. The active layer 13 is an example of the “first active layer” in the present invention.

  A p-type light guide layer 14 and a p-type cladding layer 15 are formed in this order on the active layer 13. The p-type light guide layer 14 is made of p-type AlGaAs (Al composition ratio: 0.30). The p-type cladding layer 15 is made of p-type AlGaAs (Al composition ratio: 0.40) and has a thickness of about 1.2 μm.

  The laser element unit 10 is composed of these semiconductor layers (11 to 15) on the n-type substrate 1, and generates current and emits infrared light when current is supplied to the active layer 13. Yes. The light density in the active layer 13 is adjusted by the n-type light guide layer 12 and the p-type light guide layer 14 sandwiching the active layer 13. The pair of n-type light guide layer 12 and p-type light guide layer 14 sandwiching the active layer 13 is an example of the “first light guide layer” in the present invention.

  On the laser element portion 10 (p-type cladding layer 15), a tunnel layer 2 made of GaAs is formed with a thickness of about 0.2 μm. The laser element portion 20 is in a state of being laminated on the laser element portion 10 (p-type cladding layer 15) via the tunnel layer 2. The tunnel layer 2 enables current supply between the laser element unit 20 and the laser element unit 10.

  As a structure of the laser element section 20, an n-type cladding layer 21 and an n-type light guide layer 22 are formed in this order on the tunnel layer 2. The n-type cladding layer 21 is made of n-type AlGaAs (Al composition ratio: 0.40) and has a thickness of about 1.2 μm. The n-type light guide layer 22 is made of n-type AlGaAs (Al composition ratio: 0.30).

  On the n-type light guide layer 22, an active layer 23 having the same structure as the active layer 13 of the laser element unit 10 is formed. That is, the active layer 23 includes a well layer made of InGaAs and a barrier layer made of AlGaAs, and is formed so that the thickness and composition are the same as the thickness and composition of the active layer 13 of the laser element section 10. ing. The active layer 23 is an example of the “first active layer” in the present invention.

  On the active layer 23, a p-type light guide layer 24 and a p-type cladding layer 25 are formed in this order. The p-type light guide layer 24 is made of p-type AlGaAs (Al composition ratio: 0.30). The p-type cladding layer 25 is made of p-type AlGaAs (Al composition ratio: 0.40) and has a thickness of about 1.2 μm.

  The laser element portion 20 is constituted by these semiconductor layers (21 to 25) on the tunnel layer 2, and has almost the same structure as the structure of the laser element portion 10. Similarly to the laser element unit 10, the current is supplied to the active layer 23 to generate infrared light to emit light, and the n-type light guide layer 22 and the p-type light sandwiching the active layer 23. The light density in the active layer 23 is adjusted by the guide layer 24. The pair of n-type light guide layer 22 and p-type light guide layer 24 sandwiching the active layer 23 is an example of the “first light guide layer” in the present invention.

  A tunnel layer 3 made of GaAs is formed on the laser element portion 20 (p-type cladding layer 25) to a thickness of about 0.2 μm, and the laser element portion 30 is connected to the laser element portion via the tunnel layer 3. 20 (p-type cladding layer 25). The current supply between the laser element unit 30 and the laser element unit 20 is made possible by the tunnel layer 3 formed between them.

  As a structure of the laser element section 30, an n-type cladding layer 31 and an n-type light guide layer 32 are formed in this order on the tunnel layer 3. The n-type cladding layer 31 is made of n-type AlGaAs (Al composition ratio: 0.40) and has a thickness of about 1.2 μm. The n-type light guide layer 32 is made of n-type AlGaAs (Al composition ratio: 0.30) and has a thickness of about 1.0 μm.

  On the n-type light guide layer 32, an active layer 33 having the same structure as the active layer 13 (23) of the laser element section 10 (20) is formed. That is, the active layer 33 includes a well layer made of InGaAs and a barrier layer made of AlGaAs, and the thickness and composition of the active layer 33 are the thickness and composition of the active layer 13 (23) of the laser element portion 10 (20). It is formed to be the same. The active layer 33 is an example of the “second active layer” in the present invention.

  On the active layer 33, a p-type light guide layer 34 and a p-type cladding layer 35 are formed in this order. The p-type light guide layer 34 is made of p-type AlGaAs (Al composition ratio: 0.30) and has a thickness of about 1.0 μm. The p-type cladding layer 35 is made of p-type AlGaAs (Al composition ratio: 0.40) and has a thickness of about 1.2 μm. A p-type contact layer 36 made of p-type GaAs is formed on the p-type cladding layer 35 with a thickness of about 0.7 μm.

  The laser element part 30 is constituted by these semiconductor layers (31 to 36) on the tunnel layer 3, and has almost the same structure as the structure of the laser element part 10 (20). Similarly to the laser element section 10 (20), the current is supplied to the active layer 33 to generate and emit infrared light, and the n-type light guide layer 32 sandwiching the active layer 33 and The light density in the active layer 33 is adjusted by the p-type light guide layer 34. The pair of n-type light guide layer 32 and p-type light guide layer 34 sandwiching the active layer 33 is an example of the “second light guide layer” in the present invention.

Further, a current confinement structure is provided on the upper surface side of the laser element portion 30 (the side opposite to the laser element portion 20 side). Specifically, the current confinement layer 4 made of Si ₃ N ₄ is formed with a thickness of about 0.1 μm on the laser element portion 30 (p-type contact layer 36). The current confinement layer 4 has a striped (elongated) opening 4a, and a predetermined portion on the upper surface of the laser element portion 30 (p-type contact layer 36) extends from the opening 4a of the current confinement layer 4. Exposed in stripes.

  A p-side electrode 5 is formed on the current confinement layer 4, and a part of the p-side electrode 5 is embedded in the opening 4 a of the current confinement layer 4. Thus, a part of the p-side electrode 5 is in contact (electrically connected) only with a predetermined portion of the upper surface of the laser element portion 30 (p-type contact layer 36). That is, the current from the p-side electrode 5 is narrowed by the current confinement layer 4 and then supplied to the laser element portion 30 (p-type contact layer 36). An n-side electrode 6 that contacts (electrically connects) the entire back surface of the n-type substrate 1 is formed on the back surface of the n-type substrate 1 (surface opposite to the laser element portion 10 side). Yes.

  By the way, the reason for providing such a current confinement structure is to suppress the spread of the supply current and thereby increase the current density. However, since the current confinement structure is provided on the upper surface side of the laser element unit 30 (the side opposite to the laser element unit 20 side), in the laser element unit 30, the spread of the supply current can be satisfactorily reduced. As the distance from the laser element unit 30 increases, the spread of the supply current gradually increases. That is, the current density of the laser element unit 20 is lower than the current density of the laser element unit 30, and the current density of the laser element unit 10 is lower than the current density of the laser element unit 20. The spread of the supply current is schematically shown as a dotted line in FIG.

  Here, in this embodiment, the thicknesses of both the n-type light guide layer 22 and the p-type light guide layer 24 of the laser element unit 20 are set to be the same as the n-type light guide layer 32 and the p-type light guide layer 34 of the laser element unit 30. It is larger than the thickness (about 1.0 μm).

  Furthermore, in the present embodiment, the thicknesses of both the n-type light guide layer 12 and the p-type light guide layer 14 of the laser element unit 10 are set to be the same as those of the n-type light guide layer 22 and the p-type light guide layer 24 of the laser element unit 20. It is larger than the thickness. That is, the thicknesses of both the n-type light guide layer 12 and the p-type light guide layer 14 of the laser element unit 10 are larger than the thicknesses of the n-type light guide layer 32 and the p-type light guide layer 34 of the laser element unit 30. ing.

  In other words, in the present embodiment, the thicknesses of the n-type light guide layer 12 and the p-type light guide layer 14 of the laser element unit 10 located at the lowest stage among the laser element units 10, 20 and 30 sequentially stacked are the largest. The n-type light guide layer 32 and the p-type light guide layer 34 of the laser element portion 30 (laser element portion provided with a current confinement structure) 30 located at the uppermost stage are the smallest. The thicknesses of the n-type light guide layer 22 and the p-type light guide layer 24 of the laser element unit 20 located in the middle stage are the same as those of the n-type light guide layer 12 and the p-type light guide layer of the laser element part 10 located in the lowermost stage. 14 and smaller than the thickness of the n-type light guide layer 32 and the p-type light guide layer 34 of the laser element portion 30 located at the uppermost stage.

  As a result, the light density in the active layer 23 of the laser element unit 20 located in the middle stage is increased, and the light density in the active layer 13 of the laser element part 10 located in the lowermost stage is further increased.

  In the present embodiment, by laminating the plurality of laser element portions 10, 20, and 30 having the above-described structure in this order, the following effects can be obtained.

  That is, the thickness of both the n-type light guide layer 22 and the p-type light guide layer 24 of the laser element unit 20 located in the middle stage is set to the laser element part (laser element part provided with a current confinement structure) located in the uppermost stage. By making the thickness larger than the thickness of the n-type light guide layer 32 and the p-type light guide layer 34, the light density in the active layer 23 of the laser element unit 20 is increased, so that the threshold current of the laser element unit 20 decreases. . As a result, even if the current density of the laser element unit 20 is lowered, the threshold current of the laser element unit 20 is lowered, so that deterioration of the current-output characteristics of the laser element unit 20 can be suppressed. .

  Further, regarding the thicknesses of both the n-type light guide layer 12 and the p-type light guide layer 14 of the laser element unit 10 located at the lowermost stage, the n-type light guide layer 22 and the p-type of the laser element part 20 located at the middle stage are used. Since the thickness is made larger than the thickness of the light guide layer 24, it is possible to suppress the deterioration of the current-output characteristics of the laser element portion 10.

  As a result, infrared light can be emitted at a high output without causing an increase in operating current.

  In the present embodiment, a semiconductor device capable of emitting light with high output while suppressing an increase in operating current is obtained. By mounting the semiconductor laser device in an in-vehicle radar system, the in-vehicle radar system High performance can be achieved.

  In the present embodiment, the n-type light guide layer 22 and the p-type light guide layer 24 of the middle laser element unit 20 (the n-type light guide layer 12 and the p-type light guide layer 14 of the lowermost laser element unit 10). Since it is only necessary to change the thickness, the manufacture is easy.

  As a method for manufacturing the semiconductor laser device of this embodiment, MOCVD (metal organic chemical vapor deposition) is used to form each semiconductor layer constituting each of the laser element portions 10, 20 and 30 on the n-type substrate 1. What is necessary is just to grow sequentially. That is, it can be manufactured using a known manufacturing method.

  It should be thought that embodiment disclosed this time is an illustration and restrictive at no points. The scope of the present invention is shown not by the above description of the embodiments but by the scope of claims for patent, and includes all modifications within the meaning and scope equivalent to the scope of claims for patent.

  For example, in the above-described embodiment, an example in which the present invention is applied to a semiconductor laser device mounted on an in-vehicle radar system has been described. However, the present invention is not limited thereto, and is mounted in equipment other than the in-vehicle radar system. The present invention may be applied to a semiconductor laser device.

  In the above embodiment, the three laser element units are stacked on the substrate. However, the present invention is not limited to this, and the number of laser element units can be changed according to the application. Specifically, the number of laser element units stacked on the substrate may be two (one “first laser element unit” of the present invention), or the number of laser element units stacked on the substrate may be The number may be four or more (three or more “first laser element portions” of the present invention). 3 shows a semiconductor laser device in which two laser element portions 10 and 30 are stacked on an n-type substrate 1, that is, a semiconductor laser device in which the middle laser element portion 20 is omitted from the above embodiment. ing.

  Further, in the above embodiment, the thickness of both the n-type light guide layer and the p-type light guide layer of the laser element part in the middle stage or lower is set to the thickness of the uppermost laser element part (laser element part provided with the current confinement structure). The thickness is larger than the thickness of the n-type light guide layer and the p-type light guide layer. However, the present invention is not limited to this, and one of the n-type light guide layer and the p-type light guide layer of the laser element portion below the middle stage is not limited thereto. Only the thickness may be larger than the thicknesses of the n-type light guide layer and the p-type light guide layer of the uppermost laser element portion.

  In the above embodiment, the thicknesses of the n-type light guide layer and the p-type light guide layer are the same in each of the three laser element units. However, the present invention is not limited to this, and the p-type light guide layer and The thicknesses of the n-type light guide layers may be different from each other.

  In the above embodiment, the compositions of the n-type light guide layers (p-type light guide layers) of the three laser element units are the same. However, the present invention is not limited to this, and the three laser element units have the same composition. The composition of each n-type light guide layer (p-type light guide layer) may be different from each other depending on the operating temperature. Also in this case, the thickness of the n-type light guide layer (p-type light guide layer) of the laser element part in the middle stage or less is larger than the thickness of the uppermost laser element part (laser element part provided with the current confinement structure). By doing so, the same effect as the above-described embodiment can be obtained. Furthermore, the compositions of the n-type cladding layers (p-type cladding layers) of the three laser element portions may be different from each other according to the operating temperature.

  In the above embodiment, the current confinement structure is obtained by forming the current confinement layer on the flat upper surface of the uppermost p-type semiconductor layer. However, the present invention is not limited to this, and the uppermost p-type semiconductor layer is not limited thereto. A current confinement structure may be obtained by forming a convex portion (ridge portion) on the upper surface side of the type semiconductor layer. Further, the current confinement structure may be obtained by a method other than the method described here.

10, 20 Laser element part (first laser element part)
12, 22 n-type light guide layer (first light guide layer)
13, 23 Active layer (first active layer)
14, 24 p-type light guide layer (first light guide layer)
30 Laser element part (second laser element part)
32 n-type light guide layer (second light guide layer)
33 Active layer (second active layer)
34 p-type light guide layer (second light guide layer)

Claims (6)

A first laser element section that includes a first active layer and a pair of first light guide layers sandwiching the first active layer, and emits light of a predetermined wavelength band;
It includes a second active layer and a pair of second light guide layers sandwiching the second active layer, and is laminated on the first laser element unit, and is the same as the light emitted from the first laser element unit A second laser element unit that emits light in a wavelength band,
A current confinement structure is provided on the opposite side of the second laser element portion from the first laser element portion side, and current is supplied to the second active layer and the first active layer through the current confinement structure. Is supposed to be
A semiconductor laser device, wherein a thickness of at least one of the pair of first light guide layers is larger than a thickness of the pair of second light guide layers.   2. The semiconductor laser device according to claim 1, wherein the thickness of both of the pair of first light guide layers is larger than the thickness of the pair of second light guide layers.   A plurality of the first laser element units are sequentially stacked, and the second laser element unit is stacked on the first laser element unit located at the top of the plurality of first laser element units. The semiconductor laser device according to claim 1, wherein the semiconductor laser device is a semiconductor laser device.   The thickness of at least one of the pair of first light guide layers included in the first laser element portion having the larger separation distance with respect to the current confinement structure has the smaller separation distance with respect to the current confinement structure. 4. The semiconductor laser device according to claim 3, wherein the thickness of the pair of first light guide layers included in one laser element portion is larger than the thickness of the pair.   5. The semiconductor laser device according to claim 1, wherein the first active layer and the second active layer have the same structure.   6. The semiconductor laser device according to claim 1, wherein light emitted from each of the first laser element unit and the second laser element unit is infrared light.

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