JP3762669B2 - Self-oscillation type semiconductor laser device - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a self-excited oscillation type semiconductor laser element in which return light noise caused by return light of output laser light is reduced.
[0002]
[Prior art]
The conventional semiconductor laser device has a problem that when the return light of the output laser light reenters the semiconductor laser device, noise (hereinafter referred to as return light noise) due to the return light is generated in the output laser light. It was. Such return light noise is generated when, for example, a semiconductor laser element is used as a light source of an optical disk device, the return light of the output laser light due to reflection from the disk surface or the like re-enters the semiconductor laser element.
[0003]
In order to reduce the return light noise of this semiconductor laser element, a method using a self-excited oscillation phenomenon is known, and is disclosed in, for example, Japanese Patent Laid-Open No. 63-202083 (H01S 3/18).
[0004]
In such a semiconductor laser element, one of the clad layers sandwiching the AlGaAs active layer has a refractive index layer having a band gap energy much larger than the energy of oscillation light (oscillation wavelength energy: hν) or the energy of the oscillation light. It is described that self-oscillation is caused by using a light absorption layer having a considerably smaller band gap energy.
[0005]
However, according to the experiment results of the applicant of the present application, in the case of a refractive index layer having a band gap energy that is considerably larger than the energy of the oscillation light, the astigmatic difference becomes large, and on the other hand, a band gap energy that is considerably smaller than the energy of the oscillation light is obtained. In the case of the light absorption layer, it has been found that the operating current value increases.
[0006]
As a solution to this problem, Japanese Patent Application Laid-Open No. 61-84891 (H01S 3/18) has a saturable absorption characteristic for laser light (oscillation light) having substantially the same composition as the active layer. A semiconductor laser device is disclosed that includes a layer (saturable light absorption layer) and is close enough to the active layer and the saturable light absorption layer to function as a coupled optical waveguide.
[0007]
[Problems to be solved by the invention]
However, according to experiments by the applicant of the present application, in the case of an AlGaInP semiconductor laser element having a saturable light absorption layer, self-excited oscillation occurs immediately after operation, but single mode oscillation occurs after a short operation time. It turns out that there is.
[0008]
This AlGaInP semiconductor laser element is formed by an epitaxial growth method such as a metal organic chemical vapor deposition method (MOCVD method) or a molecular beam epitaxy growth method (MBE method). Under normal growth conditions in such a method, an (Al _z1 Ga ₁ -z1) _z2 In _{1 -z2} P crystal (0 ≦ z1 ≦ 1: hereinafter referred to as an AlGaInP-based crystal) is disordered as a natural superlattice structure or a natural superlattice structure. It is known to take a gap between the structures.
[0009]
The applicant of the present application has found the cause of single mode oscillation after a short operating time.
[0010]
That is, immediately after a current is applied to this element, the band gap of the saturable light absorption layer and the energy of the oscillation light are set to be approximately equal, so that self-oscillation occurs. However, since the saturable light absorption layer is set to have a small thickness in order to reduce the oscillation threshold current, impurities are diffused from the adjacent layer to the saturable light absorption layer by continuing to apply the current. As a result, the saturable light absorption layer changes to a more disordered structure.
[0011]
As the disordered structure becomes more completely disordered, the band gap becomes larger, so that the saturable light absorbing layer transmits the oscillation light, and as a result, single mode oscillation occurs.
[0012]
In addition, the problem that self-excited oscillation does not occur in this way also exists in a semiconductor laser device including a saturable light absorption layer made of a semiconductor material that can take a natural superlattice structure other than an AlGaInP semiconductor.
[0013]
The present invention has been made in view of such a problem, and provides a self-pulsation type semiconductor laser device including a saturable light absorption layer made of a semiconductor material capable of taking a natural superlattice structure that stably oscillates. The purpose is to provide.
[0014]
[Means for Solving the Problems]
A self-oscillation type semiconductor laser device of the present invention includes a first conductivity type semiconductor substrate, a first conductivity type cladding layer formed on the substrate, an active layer formed on the cladding layer, A second conductivity type cladding layer formed on the active layer,
A saturable light absorption layer made of a semiconductor material capable of forming a natural superlattice structure is provided in which at least one of the two cladding layers is sandwiched between undoped impurity diffusion prevention layers. .
[0015]
The self-excited oscillation type semiconductor laser device of the present invention includes a first conductivity type GaAs substrate and a first conductivity type (Al _x Ga _1-x ) _0.5 In _0.5 P (0 < x ≦ 1) a clad layer, an active layer formed on the clad layer, and a second conductivity type (Al _y Ga _1-y ) _0.5 In _0.5 P (0 <y ≦) formed on the active layer 1) a cladding layer,
A saturable light absorption layer made of a semiconductor material capable of forming a natural superlattice structure is provided in which at least one of the two cladding layers is sandwiched between undoped impurity diffusion prevention layers. .
[0016]
The self-oscillation type semiconductor laser device of the present invention includes a first conductivity type semiconductor substrate, a first conductivity type cladding layer formed on the substrate, an active layer formed on the cladding layer, And a second conductivity type cladding layer formed on the active layer, an undoped first impurity diffusion prevention layer formed on the cladding layer, and the first impurity diffusion prevention layer. A saturable light absorption layer of a second conductivity type made of a semiconductor material capable of taking a natural superlattice structure, an undoped second impurity diffusion prevention layer formed on the saturable light absorption layer, and the second impurity And a second conductivity type cladding layer having a striped ridge shape formed on the diffusion prevention layer.
[0017]
In particular, the second impurity diffusion preventing layer is an etching stop layer.
[0018]
In particular, a saturable light absorption layer of the first conductivity type having both surfaces sandwiched between impurity diffusion prevention layers is provided in the first conductivity type cladding layer.
[0021]
In particular, the saturable light absorbing layer is characterized by a _{(Al t Ga 1-t)} u In 1-u P (0 ≦ t <1) layer.
[0022]
In particular, the saturable light absorbing layer has a band gap with energy substantially equal to that of oscillation light.
[0023]
In particular, the impurity diffusion preventing layer is an undoped layer.
[0024]
In particular, the impurity diffusion preventing layer does not absorb oscillation light.
[0025]
In particular, an energy barrier is formed between the impurity diffusion preventing layer and the adjacent cladding layer.
[0026]
Further, the impurity diffusion preventing layer is provided on both surfaces of the saturable light absorbing layer at least in a substantial light confinement region.
[0027]
According to the present invention, since both surfaces (both sides) of the saturable light absorption layer are sandwiched between impurity diffusion prevention layers such as undoped layers, impurity diffusion into the saturable light absorption layer is prevented. As a result, the saturable light absorption layer does not fluctuate in the band gap due to further disordering or the like, and is always constant, so that it oscillates stably for a long time. Further, if the impurity diffusion preventing layer is provided on both surfaces of the saturable light absorption layer at least in the substantial light confinement region, the same effect can be obtained.
[0028]
In particular, when the saturable light absorption layer has a band gap with substantially the same energy as the oscillation light, the self-excited oscillation can be stably performed for a longer time, and the astigmatic difference and the operating current value can be reduced.
[0029]
Furthermore, when the active layer has undoped layers on both sides thereof, the wavelength of the oscillation light is more stable, so that self-excited oscillation can be performed stably for a longer time.
[0030]
A first impurity diffusion prevention layer; a saturable light absorption layer formed on the first impurity diffusion prevention layer; a second impurity diffusion prevention layer formed on the saturable light absorption layer; A second conductivity type cladding layer having a striped ridge shape formed in a part on the second impurity diffusion preventing layer, the saturable light absorbing layer is a cladding layer. Since it has material components that differ greatly, it becomes an etching stop layer when the clad layer having the stripe ridge shape is formed. In particular, when the second impurity diffusion preventing layer is an etching stop layer, the saturable light absorption layer is not etched, and there is no possibility that the saturable light absorption characteristic of the layer for each element changes.
[0031]
Further, when the impurity diffusion preventing layer absorbs oscillation light, the impurity is diffused into the layer, so that the amount of light absorption may change and the self-excited oscillation state may be changed. It is desirable that the diffusion preventing layer does not always absorb oscillation light.
[0032]
Further, when an energy barrier is formed between the impurity diffusion prevention layer and the adjacent cladding layer, the material or composition of the impurity diffusion prevention layer and the adjacent cladding layer is different. It is prevented from spreading. Therefore, it becomes difficult for impurities to diffuse by the saturable light absorption layer. As a result, since the layer thickness of the impurity diffusion preventing layer can be reduced, the resistance of the element can be reduced when this layer is an undoped layer.
[0033]
DETAILED DESCRIPTION OF THE INVENTION
An embodiment according to the present invention will be described in detail with reference to the drawings. FIG. 1 is a sectional view showing a self-excited oscillation type AlGaInP semiconductor laser element according to this embodiment, and FIG. 2 is a band structure diagram in the vicinity of an active layer of this semiconductor laser element.
[0034]
In FIG. 1, 1 is an n-type GaAs semiconductor substrate, and one principal surface thereof is a surface inclined by 5 ° in the [011] crystal axis direction from the (100) plane. An n-type Ga _0.5 In _0.5 P buffer layer 2 having a layer thickness of 0.3 μm and an n-type (Al _0.7 Ga _0.3 ) _0.5 In _0.5 P first cladding layer 3 having a layer thickness of 0.6 μm are formed on the inclined surface. Formed in order.
[0035]
On the n-type first cladding layer 3, the layer thickness 200Å undoped _{(Al 0.7 Ga 0.3) 0.5 In} 0.5 P impurity diffusion preventing layer 4 is formed.
[0036]
As shown in FIG. 2, an n-type Ga _0.58 In _0.42 P tensile strain well layer (strain amount: −0.5%, all three layers) 5a having a layer thickness of 100 mm is formed on the impurity diffusion prevention layer 4 and the layer thickness. It consists of a tensile strained multiple quantum well structure layer (tensile strain MQW layer) in which 40 n-type (Al _0.7 Ga _0.3 ) _0.5 In _0.5 P barrier layers (all 2 layers) 5b are alternately stacked, and the energy of oscillation light A saturable light absorption layer 5 having a band gap substantially equal to is formed.
[0037]
On the saturable light absorbing layer 5, the layer thickness 200Å undoped _{(Al 0.7 Ga 0.3) 0.5 In} 0.5 P impurity diffusion preventing layer 6 is formed.
[0038]
On this impurity diffusion preventing layer 6, an n-type (Al _0.7 Ga _0.3 ) _0.5 In _0.5 P second cladding layer 7 having a layer thickness of 0.25 μm and an undoped (Al _0.5 Ga _0.5 ) _0.5 In _0.5 P layer having a layer thickness of 500 mm. The light guide layer 8 is formed in this order.
[0039]
On this optical guide layer 8, a Ga _0.58 In _0.42 P tensile strain well layer (strain: −0.5%, total of 6 layers) 9 a having a layer thickness of 75 mm and (Al _0.5 Ga _0.5 ) _0.5 In having a layer thickness of 40 mm. _An undoped active layer 9 composed of a tensile strained multiple quantum well structure layer (tensile strain MQW layer) in which _0.5 P barrier layers (5 layers in total) 9b are alternately stacked is formed.
[0040]
An undoped (Al _0.5 Ga _0.5 ) _0.5 In _0.5 P light guide layer 10 having a thickness of 500 mm is formed on the active layer 9.
[0041]
The light guide layers 8 and 10 have a band gap (the lower end of the conduction band) that is greater than or equal to the band gap value of the barrier layer 9b (the energy position where the lower end of the conduction band is greater than or equal to the lower end of the conduction band of the barrier layer 9b). Is set at an energy position smaller than the lower end of the conduction band of the cladding layer), light and electrons can be confined, and the oscillation threshold current and the like can be reduced. Further, since the light guide layers 8 and 10 are undoped, it is possible to prevent impurities from diffusing into the active layer 9.
[0042]
A p-type (Al _0.7 Ga _0.3 ) _0.5 In _0.5 P first cladding layer 11 having a layer thickness of 250 mm is formed on the optical guide layer 10. On this p-type first cladding layer 11, a p-type Ga _0.5 In _0.5 P well layer (a total of 10 layers) 12a having a layer thickness of 11 mm and a p-type (Al _0.7 Ga _0.3 ) _0.5 In _0.5 P barrier layer having a layer thickness of 17 mm ( A multiple quantum barrier layer (MQB layer) 12 is formed by alternately laminating a total of nine layers) 12b. In this MQB layer, since the thickness and period of the well layer 12a and the barrier layer 12b are set so that electrons are reflected, it is possible to prevent electrons from overflowing from the active layer 9 and to reduce the oscillation threshold current and the like. Can be planned.
[0043]
A p-type (Al _0.7 Ga _0.3 ) _0.5 In _0.5 P second cladding layer 13 having a layer thickness of 0.25 μm is formed on the MQB layer 12.
[0044]
On this first cladding layer 13, the layer thickness 200Å undoped _{(Al 0.7 Ga 0.3) 0.5 In} 0.5 P impurity diffusion preventing layer 14 is formed.
[0045]
Hereinafter, as shown in detail in FIG. 2, a p-type Ga _0.58 In _0.42 P tensile strain well layer (strain amount: −0.5%, all three layers) having a layer thickness of 100 mm is formed on the impurity diffusion preventing layer 14. 15a and p-type layer thickness _{40Å (Al 0.7 Ga 0.3) 0.5} in 0.5 P barrier layers oscillation composed of (total 2-layer) 15b and are alternately laminated tensile strain multiple quantum well structure layer (tensile strain MQW layer) A saturable light absorption layer 15 having a band gap substantially equal to the energy of light is formed.
[0046]
This is approximately the center of the saturable light absorbing layer 15, the resonator length direction (direction perpendicular to the paper surface) in a stripe shape extending in the thickness 200Å undoped _{(Al 0.7 Ga 0.3) 0.5 In} 0.5 P impurity diffusion preventing layer 16 is formed.
[0047]
On this impurity diffusion preventing layer 16, a p-type (Al _0.7 Ga _0.3 ) _0.5 In having a striped ridge shape with a height of 0.8 μm and a width of 5 μm extending in the resonator length direction (perpendicular to the paper surface). _{A 0.5} P third cladding layer 17 is formed.
[0048]
On the saturable light absorption layer 15, an n-type GaAs current blocking layer 18 having a thickness of 1 μm is formed so as to cover the side surface of the impurity diffusion preventing layer 16 and the side surface of the ridge portion.
[0049]
A p-type Ga _0.5 In _0.5 P contact layer 19 having a layer thickness of 0.1 μm is formed on the upper surface of the ridge portion of the third cladding layer 17. A p-type GaAs cap layer 20 having a thickness of 2 μm on the contact layer 19 is formed on the current blocking layer 18 and the contact layer 19.
[0050]
A p-type ohmic electrode 21 is formed on the upper surface of the cap layer 20, and an n-type ohmic electrode 22 is formed on the lower surface of the n-type GaAs substrate 1.
[0051]
When the saturable light absorption layers 5 and 15 have a quantum well structure as described above, the energy of the oscillation light and the band gap energy of the saturable light absorption layer are substantially equal to each other in the well layer of the saturable light absorption layer. It is defined that the energy difference between the quantum levels of the conduction band and the valence band is approximately equal to the energy of the oscillation light.
[0052]
In addition, since the layer thickness of the well layer 12a of the MQB layer 12 is small and the energy width between the quantum levels of the conduction band and the valence band is large, the oscillation light is not absorbed. Further, the impurity diffusion preventing layers 4, 6, 8, 10, 14, and 16 do not absorb oscillation light.
[0053]
Next, a method for manufacturing such a semiconductor laser device will be briefly described.
[0054]
First, on an n-type GaAs substrate 1, an n-type buffer layer 2, an n-type first cladding layer 3, an undoped impurity diffusion prevention layer 4, an n-type saturable light absorption layer 5, an undoped impurity diffusion prevention layer 6, n-type second cladding layer 7, undoped light guide layer 8, undoped active layer 9, undoped light guide layer 10, p-type first cladding layer 11, p-type MQB layer 12, p-type second cladding layer 13, The undoped impurity diffusion preventing layer 14, the p-type saturable light absorbing layer 15, the undoped impurity diffusion preventing layer 16, the p-type third cladding layer 17 and the p-type contact layer 19 are formed by MOCVD (metal organic chemical vapor deposition). Due to continuous growth.
[0055]
Next, a mask made of striped SiO ₂ or the like is formed on the p-type contact layer 19, and the p-type contact layer 19, the p-type third cladding layer 17, and the impurity diffusion preventing layer 16 are interposed through the mask. Then, the n-type current blocking layer 18 is formed by MOCVD.
[0056]
Subsequently, after removing the mask and exposing the contact layer 19, a p-type cap layer 20 is formed on the n-type current blocking layer 18 and the contact layer 19 by MOCVD.
[0057]
Next, a p-type ohmic electrode 21 is formed on the upper surface of the cap layer 20, and an n-type ohmic electrode 22 is formed on the lower surface of the n-type GaAs substrate 1 by vapor deposition.
[0058]
Since the clad layer needs to confine the oscillation light as is well known in the art, it has a band gap of energy larger than that of the oscillation light. Therefore, since the saturable light absorbing layer contains a material having a smaller band gap than the cladding layer, for example, in the case of a semiconductor material containing Al as described above, the saturable light absorbing layer is made of Al compared to the cladding layer. Since the composition ratio is small, the cladding layer 17 and the impurity diffusion layer 16 having the same composition as the cladding layer can be selectively etched as compared with the saturable light absorption layer 15. That is, when the ridge portion is formed by etching, the saturable light absorption layer 15 becomes an etching stop layer.
[0059]
As a result of conducting an operation experiment of such a semiconductor laser device, it was confirmed that the semiconductor laser device stably oscillates for a long time.
[0060]
The reason for such stable self-excited oscillation for a long time is as follows.
[0061]
In the device of this embodiment, the undoped impurity diffusion preventing layer is provided on both surfaces of the saturable light absorbing layer, so that impurities that diffuse and move during operation can be taken into the undoped impurity diffusion preventing layer. Impurities do not reach the saturated light absorption layer. Therefore, the saturable light absorption layer does not become more disordered, and the size of the band gap of the saturable light absorption layer does not vary.
[0062]
The impurity diffusion preventing layer 16 is provided only under the third cladding layer 16 because the portion of the saturable light absorption layer 15 that is not under the third cladding layer 16 is not a substantial light confinement region. is there.
[0063]
In this example, the energy of oscillation light and the energy of the band gap of the saturable light absorption layer are set to be approximately equal, so that the astigmatic difference and the operating current value are also small.
[0064]
The undoped impurity diffusion layer has the same composition (same band gap size) as the cladding layer, but a different composition may be selected as long as it does not absorb oscillation light. An example is shown below.
[0065]
Next, a second embodiment will be described with reference to the drawings. 3 is a cross-sectional structure diagram of the self-excited oscillation type semiconductor laser device of the present embodiment, and FIG. 4 is a band structure diagram in the vicinity of the active layer. The explanation is omitted.
[0066]
This embodiment is different from the first embodiment in that the band gap of the cladding layer adjacent to the impurity diffusion preventing layer is different, an energy barrier is formed at the interface between the layers, and the entire surface of the saturable light absorbing layer 15. Is provided with an impurity diffusion preventing layer.
[0067]
In FIG. 3, 24, 26, and 34 are undoped (Al _0.3 Ga _0.7 ) _0.5 In _0.5 P impurity diffusion preventing layers having a layer thickness of 100 mm.
[0068]
Reference numeral 36 denotes an undoped (Al _0.3 Ga _0.7 ) _0.5 In _0.5 P impurity diffusion preventing layer having a layer thickness of 100 mm provided on the entire surface of the saturable light absorption layer 15.
[0069]
As shown in FIG. 4, when an energy barrier is formed at the interface between the saturable light absorbing layer and the adjacent clad layer, this barrier has an effect of preventing impurity diffusion, and therefore, compared with the first embodiment. Thus, the thickness of the impurity diffusion preventing layer may be reduced. In this case, the thickness of the undoped layer is reduced, so that the element resistance can be reduced.
[0070]
The impurity diffusion preventing layer 36 also functions as an etching stop layer when the ridge portion is formed by chemical etching because the Al composition ratio is greatly different from that of the third cladding layer 17. However, when the impurity diffusion preventing layer 36 is thin as in this embodiment, it may be etched in the same manner as in the first embodiment.
[0071]
Further, as the impurity diffusion preventing layers 24, 26, 34, and 36, by introducing tensile strain, for example, as an undoped (Al _0.7 Ga _0.3 ) _0.58 In _0.42 P impurity diffusion preventing layer having a larger band gap than the cladding layer. The same effect can be obtained.
[0072]
In the above description, an active layer having a tensile strain quantum well structure is used as the active layer. However, the active layer according to the present invention may be an active layer having a compressive strain quantum well structure or an active layer having an unstrained quantum well structure. Or a bulk active layer. Since the active layer may also be diffused and disordered to change the wavelength, an undoped layer for preventing the diffusion of impurities such as an undoped light guide layer is provided on both sides of the active layer as described above. Is desirable.
[0073]
The saturable light absorbing layer according to the present invention is appropriately selected from a tensile strained quantum well structure, a compressive strained quantum well structure, an unstrained quantum well structure, and a bulky saturable light absorbing layer depending on the oscillation light. Is done.
[0074]
The saturable light absorbing layer according to the present invention may be in at least one of the n-type and p-type cladding layers.
[0075]
Furthermore, the self-pulsation type semiconductor laser device of the present invention may of course have various structures other than the structure having the ridge portion.
[0076]
The term “having a saturable light absorbing layer in the clad layer” in the present invention includes the case where it is provided adjacent to the clad layer.
[0077]
In addition, as described above, other layers such as an MQB layer may be included in the cladding layer according to the present invention, and there may be no MQB layer. Furthermore, the composition of the cladding layer may be different in the layer.
[0078]
In addition, the present invention is not limited to an AlGaInP semiconductor laser element having a saturable light absorption layer made of GaInP or AlGaInP, and of course is applicable to a semiconductor laser element having a saturable light absorption layer capable of taking another natural superlattice structure. it can. That is, in the self-pulsation type semiconductor laser device provided with the saturable light absorption layer, an impurity diffusion preventing layer may be provided on both surfaces of the saturable light absorption layer.
[0079]
Further, the crystal growth surface of the GaAs semiconductor substrate is a surface inclined in the <011> crystal axis direction from the {100} plane which is equivalent to a surface inclined in the [011] crystal axis direction from the (100) plane. In addition, a tilt angle of 17 ° or less or a {100} plane may be used.
[0080]
Even if the saturable light absorption layer does not have a band gap with substantially the same energy as the oscillation light, the saturable light absorption layer becomes transparent to the oscillation light, or the self-excited state changes due to the change in the amount of light absorption. Therefore, it is desirable to provide an impurity diffusion prevention layer on both surfaces of the saturable light absorption layer. However, when there is no band gap having substantially the same energy as described above, the astigmatic difference and the operating current value increase as described above.
[0081]
Further, as described above, it is effective if the impurity diffusion preventing layer is on at least a portion of the saturable light absorbing layer that is substantially in the light confinement region, that is, on both sides of the portion where the saturable light absorbing layer substantially works. .
[0082]
【The invention's effect】
According to the present invention, since both surfaces of the saturable light absorbing layer are sandwiched between impurity diffusion preventing layers such as a blocking layer or an undoped layer, impurity diffusion into the saturable light absorbing layer is prevented. As a result, the saturable light absorption layer is always constant without fluctuation of the band gap due to disordering or the like, and therefore, the saturable light absorbing layer oscillates stably for a long time. Further, if the impurity diffusion preventing layer is provided on both surfaces of the saturable light absorption layer at least in the substantial light confinement region, the same effect can be obtained.
[0083]
In particular, when the saturable light absorption layer has a band gap with substantially the same energy as the oscillation light, the self-excited oscillation can be stably performed for a longer time, and the astigmatic difference and the operating current value can be reduced.
[0084]
Furthermore, when the active layer has undoped layers on both sides thereof, the wavelength of the oscillation light is more stable, so that self-excited oscillation can be performed stably for a longer time.
[0085]
A first impurity diffusion prevention layer; a saturable light absorption layer formed on the first impurity diffusion prevention layer; a second impurity diffusion prevention layer formed on the saturable light absorption layer; A second conductivity type cladding layer having a striped ridge shape formed in a part on the second impurity diffusion preventing layer, the saturable light absorbing layer is a cladding layer. Since it has material components that differ greatly, it becomes an etching stop layer when the clad layer having the stripe ridge shape is formed. In particular, when the second impurity diffusion preventing layer is an etching stop layer, the saturable light absorption layer is not etched, and there is no possibility that the saturable light absorption characteristic of the layer for each element changes.
[0086]
Furthermore, when the impurity diffusion preventing layer does not absorb oscillation light, there is no possibility of changing the self-excited oscillation state.
[0087]
Further, when an energy barrier is formed between the impurity diffusion prevention layer and the adjacent cladding layer, the material or composition of the impurity diffusion prevention layer and the adjacent cladding layer is different. It is prevented from spreading. Therefore, it becomes difficult for impurities to diffuse by the saturable light absorption layer. As a result, since the layer thickness of the impurity diffusion preventing layer can be reduced, the resistance of the element can be reduced when this layer is an undoped layer.
[Brief description of the drawings]
FIG. 1 is a schematic sectional view of a semiconductor laser device according to a first embodiment of the present invention.
FIG. 2 is a schematic band structure diagram in the vicinity of an active layer of the above example.
FIG. 3 is a schematic sectional view of a semiconductor laser device according to a second embodiment of the present invention.
FIG. 4 is a schematic band structure diagram in the vicinity of an active layer of the above example.
[Explanation of symbols]
1 n-type GaAs substrate (semiconductor substrate)
3 n-type first cladding layer 4 impurity diffusion preventing layer 5 n-type saturable light absorbing layer 6 impurity diffusion preventing layer 7 n-type second cladding layer 8 light guide layer 9 active layer 10 light guide layer 11 p-type first cladding layer 13 p-type second cladding layer 14 impurity diffusion preventing layer 15 p-type saturable light absorbing layer 16 impurity diffusion preventing layer 17 p-type second cladding layer 18 n-type current blocking layer

Claims (11)

A first conductivity type semiconductor substrate; a first conductivity type clad layer formed on the substrate; an active layer formed on the clad layer; and a second conductivity type clad layer formed on the active layer. A cladding layer,
A saturable light absorption layer made of a semiconductor material capable of forming a natural superlattice structure is provided in which at least one of the two cladding layers is sandwiched between undoped impurity diffusion prevention layers. Self-excited semiconductor laser device. A first conductivity type GaAs substrate, a first conductivity type (Al _x Ga _1-x ) _0.5 In _0.5 P (0 <x ≦ 1) clad layer formed on the substrate, and formed on the clad layer And a second conductivity type (Al _y Ga _1-y ) _0.5 In _0.5 P (0 <y ≦ 1) cladding layer formed on the active layer,
A saturable light absorption layer made of a semiconductor material capable of forming a natural superlattice structure is provided in which at least one of the two cladding layers is sandwiched between undoped impurity diffusion prevention layers. Self-excited semiconductor laser device. A first conductivity type semiconductor substrate; a first conductivity type clad layer formed on the substrate; an active layer formed on the clad layer; and a second conductivity type clad layer formed on the active layer. A second conductive layer comprising a cladding layer, an undoped first impurity diffusion preventing layer formed on the cladding layer, and a semiconductor material capable of forming a natural superlattice structure formed on the first impurity diffusion preventing layer; Type saturable light absorption layer, an undoped second impurity diffusion prevention layer formed on the saturable light absorption layer, and a striped ridge shape formed on the second impurity diffusion prevention layer A self-pulsation type semiconductor laser device comprising: a second conductivity type cladding layer.   4. The self-pulsation type semiconductor laser device according to claim 3, wherein the second impurity diffusion preventing layer is an etching stop layer.   5. The self-oscillation type semiconductor according to claim 3, wherein a first conductivity type saturable light absorption layer having both surfaces sandwiched between impurity diffusion prevention layers is provided in the first conductivity type cladding layer. Laser element. 6. The self-pulsation type semiconductor laser device according to claim 1, wherein both sides of the active layer are sandwiched between undoped layers . The saturable light absorbing _{layer, (Al t Ga 1-t} ) u In 1-u claim 2, 3, 4, 5 or 6, characterized in that P is a (0 ≦ t <1) layer The self-pulsation type semiconductor laser device described. 8. The self-pulsation type semiconductor laser device according to claim 1, wherein the saturable light absorption layer has a band gap with energy substantially equal to that of oscillation light . 9. The self-pulsation type semiconductor laser device according to claim 1, wherein the impurity diffusion preventing layer does not absorb oscillation light . 10. The self barrier according to claim 1, wherein an energy barrier is formed between the impurity diffusion preventing layer and the adjacent cladding layer. Excited oscillation type semiconductor laser device. The said impurity diffusion prevention layer is provided in both surfaces of the part which exists in an at least substantial light confinement area | region among the said saturable light absorption layers, The 1, 2, 3, 4, 5, 6 characterized by the above-mentioned. , 7, 8, 9 or 10 A self-pulsation type semiconductor laser device.

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