JP2956623B2 - Self-excited oscillation type semiconductor laser device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a self-pulsation type semiconductor laser device.

[0002]

2. Description of the Related Art A self-pulsation type semiconductor laser diode (LD) has been studied in order to reduce return light noise of a semiconductor laser used as a light source for pickup of an optical disk device. A self-excited laser has already been realized by introducing a saturable absorption layer inside the p-cladding layer of the laser.

In order to obtain a stable self-pulsation type laser having a small threshold, the absorption wavelength of the saturable absorption layer should be substantially equal to the oscillation wavelength of the laser, the lifetime of carriers generated in the saturable absorption layer should be short, It is important that the absorption wavelength of the saturable absorption layer is stable.

[0004] Regarding the control of the absorption wavelength of the saturable absorption layer, for example, see 26a-C-10 on page 1024 of the proceedings of the Conference on Related Physics in the Spring of 1996.
There is a report entitled "Self-excited oscillation characteristics of saturable absorption layer structure in red semiconductor laser". It shows that it is necessary to optimize the absorption wavelength of the saturable absorption layer with respect to the oscillation wavelength in consideration of the band gap reduction effect at the time of laser oscillation.

[0005] Regarding the control of the carrier lifetime, the carrier lifetime is shortened by increasing the p-dopant concentration of the saturable absorbing layer to increase the probability of radiative recombination. For example, there is a report entitled "Design of self-pulsation type red semiconductor laser using a saturable absorption layer" in 26p-ZA-5 on page 1058 of the proceedings of the Joint Lecture Meeting on Applied Physics, Spring 1995. . There, in order to maintain self-sustained pulsation, the p-dopant concentration of the saturable absorption layer is set to 2 × 10 ¹⁸ cm.
It is indicated that it needs to be ^-3 or more.

[0006] When the dopant concentration of the saturable absorbing layer is increased as described above, diffusion of the dopant tends to occur. In particular, in a semiconductor LD using an AlGaInP-based material, p
In many cases, Zn is used as a dopant, and when the dopant concentration of Zn in the GaInP saturable absorption layer is increased, AlGaIn in or around the GaInP saturable absorption layer during crystal growth is used.
It is known that Zn diffuses into the P layer.

The GaInP layer and the AlGaInP layer are spontaneously formed with an ordered structure of a group III atom arrangement, which is a natural superlattice, and the band gap energy of these materials may be smaller than that of the disordered structure. Are known. When Zn diffuses into these ordered structure layers, the ordered structure is disordered, so that the GaInP layer or AlGa
The energy band gap of the InP layer increases, and the absorption wavelength of the saturable absorption layer changes. GaInP for saturable absorption layer
/ AlGaInP quantum well structure, Zn
The quantum well structure itself is disordered by diffusion, and the change in absorption wavelength becomes larger.

With respect to stabilization of the absorption wavelength of the saturable absorption layer, for example, there is an invention of a self-pulsation type semiconductor laser device in Japanese Patent Application Laid-Open No. Hei 7-263794. There, the Zn dopant concentration of the saturable absorption layer is set to 3 × 10 ¹⁸ cm ⁻³ to 1 × 1.
It has been proposed that the saturable absorbing layer be disordered by setting it to 0 ¹⁹ cm ^-3 .

Particularly useful AlGa having a wavelength of 650 nm or less
In an InP-based semiconductor laser, the effect of confining carriers is weak due to material limitations, and electrons easily overflow from the active layer to the p-cladding layer. In particular, when the operating temperature increases, the overflow of electrons increases, and the threshold current value increases. The saturable absorption layer of the conventional self-pulsation type semiconductor laser is p
Since the saturable absorbing layer is provided in the cladding layer, the overflow of electrons is easily promoted by the saturable absorbing layer. Further, since the overflowed electrons are captured by the saturable absorption layer, the absorption wavelength of the saturable absorption layer changes, the amount of absorption decreases, and a stable self-sustained pulsation operation cannot be obtained.

When the overflow occurs, the carrier density of the active layer increases to maintain the light output. In general,
The carrier lifetime due to radiative recombination depends on the carrier density, and as the carrier density increases, the carrier lifetime decreases. In particular, when laser oscillation occurs, the carrier density of the active layer is very high, so that the carrier life of the active layer is very short, approaching the carrier life of the saturable absorption layer. Eventually, the carrier density of the active layer increases due to the overflow of electrons, the carrier lifetime of the active layer becomes shorter than that of the saturable absorption layer, and self-sustained pulsation stops.

As a conventional technique for reducing the overflow of electrons, a multiple quantum barrier (MQB) has been proposed.
It has been practiced to provide the structure in a p-cladding layer between the active layer and the saturable absorbing layer. This is an attempt to increase the effective hetero barrier for electrons due to the interference effect of multiple reflection of electron waves.

[0012]

However, the self-pulsation type semiconductor laser of the prior art has problems such as a high threshold value, a low temperature characteristic, and a short operating life. In the prior art, high concentration p doping is performed on the saturable absorption layer. This causes the controllability and stability of the absorption wavelength to be impaired.

In the above conventional invention, the saturable absorbing layer is also provided.
Of 3 × 10¹⁸cm ^-3Above and very high
The dopant concentration of the adjacent p-cladding layer.
Since the difference from the temperature is large, Zn diffuses. Thereby
If the dopant concentration of the saturable absorption layer changes,
The quantum well structure consisting of the converging layer and p-cladding layer changes
I do. In particular, when the saturable absorption layer has a multiple quantum well structure
Means that the multiple quantum well structure itself is disordered by Zn diffusion
There is a risk of doing this. Such a phenomenon is not only during growth
What happens during operation as an LD element
It has been reported. For example, the threshold of the device may increase,
Oscillation disappears. This is the absorption wave of the saturable absorption layer.
It is believed that the length changes. Also satiable
Since the dopant concentration of the sum absorption layer is high, the active
Diffusion of the dopant occurs in the conductive layer, and the crystal quality of the light emitting layer
And the above-mentioned problem may occur.
You.

On the other hand, in order to reduce the overflow of electrons, the MQB structure has a p-type structure between the active layer and the saturable absorbing layer.
Although it is provided in the cladding layer, the coherence length of the electrons is only a few cycles of the MQB quantum well, and the effect is unlikely to appear. There is also a problem that the overflowed electrons are accumulated in the well layer having the MQB structure, and the band structure of the MQB is changed. As a result, the saturable absorber layer provided between the p-cladding layers promotes the overflow of electrons, thereby reducing the absorption wavelength and the absorption amount of the saturable absorber layer, and making it impossible to obtain a stable self-excited oscillation operation. cause. In addition, the saturable absorption layer is often provided only between the p-cladding layers.
Since the light intensity distribution confined in the vicinity of the active layer is not symmetrical with respect to the center of the active layer, there is a problem that the light spot is distorted.

An object of the present invention is to solve the above-mentioned problems and to provide a self-sustained pulsation type semiconductor laser device having a long operating life, a small threshold value and stable and excellent characteristics. Another object of the present invention is to provide a self-sustained pulsation type semiconductor laser device that reduces laser return light noise when used as a light source for pickup of an optical disk device and enables a high-performance optical disk device to be realized at low cost.

[0016]

Means for Solving the Problems The present inventors have conducted various studies to achieve the above object, and as a result, completed the present invention.

According to a first aspect of the present invention, there is provided a self-pulsation type semiconductor laser device having a saturable absorption layer, wherein at least one saturable absorption layer has a minimum forbidden band in a semiconductor layer constituting the saturable absorption layer. The lattice defect density of at least one semiconductor layer 1 having a width is at least one semiconductor layer 2 having a minimum forbidden band width among the semiconductor layers forming the active layer.
A self-sustained pulsation type semiconductor laser device having a lattice defect density of 5 times or more.

The second invention relates to a lattice defect having a deep energy level whose energy level difference from a conduction band or a valence band is 0.5 eV or more, wherein the lattice defect density of the semiconductor layer 1 is lower than that of the semiconductor layer 2. The present invention relates to a self-pulsation type semiconductor laser device according to a first invention, which has a lattice defect density of 10 times or more.

According to a third aspect of the present invention, the semiconductor layer 1 has a first or second dopant concentration of 1 × 10 ¹⁷ to 1 × 10 ¹⁸ cm ^-3 .
The invention relates to a self-pulsation type semiconductor laser device of the invention.

According to a fourth aspect of the present invention, the forbidden band width Eg1 of the semiconductor layer 1 is disordered to the extent that Eg ≧ Eg1> Eg−10 meV with respect to the forbidden band width Eg when the semiconductor layer 1 is completely disordered. The present invention relates to a self-pulsation type semiconductor laser device according to the first, second or third invention.

According to a fifth aspect of the present invention, there is provided a self-excited oscillation according to any one of the first to fourth aspects, wherein the dopant concentration of the semiconductor layer 1 is equal to the dopant concentration of the cladding layer provided in contact with the saturable absorbing layer. Semiconductor laser device.

The sixth invention relates to the self-pulsation type semiconductor laser device according to any one of the first to fifth inventions, wherein the semiconductor layer 1 uses a material containing Al.

The seventh invention relates to the self-pulsation type semiconductor laser device according to any one of the first to sixth inventions, wherein the saturable absorption layer has a single quantum well structure or a multiple quantum well structure.

An eighth invention is directed to any one of the first to sixth inventions, wherein the saturable absorption layer has a strain-compensated multiple quantum well structure in which the well layer and the barrier layer have lattice-matching strains of opposite signs. The present invention relates to a self-pulsation type semiconductor laser device.

According to a ninth aspect, the structure of the saturable absorbing layer is such that the difference between the lowest transition energy of the saturable absorbing layer and the lowest transition energy of the active layer when not doped is controlled within 10 meV. The present invention relates to a self-pulsation type semiconductor laser device according to any one of the first to eighth inventions.

The tenth invention relates to the self-pulsation type semiconductor laser device according to any one of the first to ninth inventions, wherein a saturable absorption layer is provided only between the n-type cladding layers.

According to an eleventh aspect, there is provided a self-pulsation type semiconductor laser device in which a saturable absorption layer is provided only between one conductive type clad layer and the other conductive type semiconductor laser device having no saturable absorption layer. A new semiconductor layer is provided between the cladding layers of the mold, and the layer thickness and band gap of the semiconductor layer are such that the light distribution near the active layer in a direction perpendicular to the layer (layer thickness direction) is substantially line-symmetric with respect to the center of the active layer. A self-oscillation type semiconductor laser device characterized in that the semiconductor layer is set so as not to absorb laser light.

According to a twelfth aspect of the present invention, a substrate having a plane orientation of G
An aAs substrate, a cladding layer, an active layer, and a saturable absorbing layer, (Al _x Ga _{1 -x} ) _y In _{1 -y} P (0 ≦ x ≦ 1, 0 ≦
The present invention relates to a self-pulsation type semiconductor laser device according to any one of the first to eleventh inventions using a material satisfying y ≦ 1).

According to a thirteenth aspect, the substrate is a sapphire substrate having an arbitrary plane orientation, and (Al _x Ga _{1 -x} ) _y In _{1 -y} N (0 ≦ x) as a cladding layer, an active layer, and a saturable absorbing layer. ≤ 1, 0
The present invention relates to a self-pulsation type semiconductor laser device according to any one of the first to eleventh inventions using a material satisfying ≦ y ≦ 1).

[0030]

DESCRIPTION OF THE PREFERRED EMBODIMENTS In order to realize a self-sustained pulsation operation, it is necessary to control physical properties such as an absorption coefficient, a differential gain and a carrier life of an active layer and a saturable absorption layer. FIG. 20 shows an example of a condition diagram for satisfying the differential gain ratio and the carrier life ratio of the active layer and the saturable absorption layer for realizing the self-pulsation operation. τ _act and τ _sa represent the carrier lifetimes of the active layer and the saturable absorption layer, respectively, and g _act and g _sa are
Each represents the differential gain of the active layer and the saturable absorption layer. This is a typical case where the relative unsaturated absorption constant (β) is −3 and the volume ratio (h) of the absorption region is 0.1.

As shown in FIG. 20, in a semiconductor laser device having a saturable absorption layer, the oscillation of the bistable region, the stable oscillation region, and the self-excited oscillation region depends on the values of the differential gain ratio and the carrier life ratio. There are three areas of different operation. The self-sustained pulsation operation is realized when the differential gain of the active layer and the saturable absorption layer and the carrier lifetime belong to the self-sustained pulsation region of FIG. The arrows in FIG. 20 indicate that when the carrier lifetime of the saturable absorption layer is reduced, the region changes from a stable oscillation region to a self-excited oscillation region.

The above description shown in FIG. 20 is qualitatively stated. To realize the self-sustained pulsation operation, the differential gain of the saturable absorbing layer is larger than the differential gain of the active layer. It can be said that the carrier life is preferably shorter than the carrier life of the active layer.

In the self-pulsation type semiconductor laser device of the present invention, the former condition is satisfied by optimally adjusting the transition energy of the saturable absorption layer with respect to the transition energy of the active layer. The latter condition is that, in addition to the reduction of carrier lifetime by light emission recombination of carriers by shallow doping in the saturable absorption layer, the introduction of deep energy impurities and lattice defects into the saturable absorption layer or its interface causes carrier This is achieved by increasing the probability of trapping due to non-radiative recombination and reducing the carrier lifetime.

In the self-pulsation type semiconductor laser of the present invention, the transition energy of the saturable absorption layer can be finely adjusted by controlling the dopant concentration. By introducing the compound, the carrier lifetime of the saturable absorbing layer can be reduced.

FIG. 21 shows (Al _X Ga _{1 -x} ) _0.5 In _0.5 P
Bulk carrier lifetime τ and photoluminescence (PL)
It is a graph which shows Al composition X dependence of intensity | strength. FIG. 21 shows that the carrier lifetime and the PL intensity decrease as the Al composition increases. This is because, as the Al composition increases, the concentration of impurities that form a deep energy level, such as oxygen, increases, and the probability of non-radiative recombination increases.
In particular, when the Al composition is small, impurities such as oxygen are taken in direct proportion to the Al composition, forming a deep energy order. From FIG. 21, the Al composition is small (0.2 or less).
In AlGaInP bulk, carrier lifetime and PL
It can be seen that the strength decreases at the same rate as the Al composition increases. That is, when the PL intensity decreases by one digit, the carrier lifetime also decreases by one digit. As described above, when forming a deep energy order, there is a strong correlation between the PL intensity and the carrier lifetime.

FIG. 22 shows (Al _0.7 Ga _0.3 ) _0.5 In _0.5
5 is a graph showing the growth temperature dependence of the defect density of PL deep energy levels (D1, D2, D3) and PL intensity.
Defect levels are 0.45 eV (D1) and 0.50 eV
(D2), a 1.3 eV (D3), respectively the capture cross section of the carrier ^{6 × 10 -13 cm 2 (D1} ), 1 × 10 - 15
cm ² (D2) and 2 × 10 ⁻¹⁰ cm ² (D3). FIG.
From 2, the defect density of the deep levels D2 and D3 increases as the growth temperature decreases, but the defect density of D1 does not change much. D1 has the highest defect density, while D3 has a very large carrier cross section. Therefore, it can be interpreted that when the defect density of D3 increases, most of the carriers are captured by the defect levels of D3 and recombine non-radiatively, so that the PL intensity decreases. In FIG. 22, the growth temperature is from 700 ° C. to 660 °.
When the temperature was lowered to ° C., the defect density of D3 increased by one digit and the PL intensity decreased by one digit. Therefore, as described above, PL
Assuming that the carrier life is reduced by one digit when the strength is reduced by one digit, it can be seen that the carrier life is reduced by one digit when the defect density of D3 increases by one digit. Therefore, it is understood that effective in reducing the carrier lifetime is to increase the density of lattice defects having a deep energy level whose energy level difference from the conduction band (or valence band) is 0.5 eV or more. . In addition, such an increase in the lattice defect density can be evaluated by a decrease in the PL intensity.

The self-pulsation type semiconductor laser of the present invention has a feature that the lattice defect density of the saturable absorbing layer is five times or more the lattice defect density of the active layer. Can be expected to have a carrier life of 1/5 or less of the active layer, and a more stable self-pulsation type semiconductor laser can be realized.

Alternatively, in the self-pulsation type semiconductor laser of the present invention, the saturable absorption layer is used especially for lattice defects having a deep energy level whose energy level difference from the conduction band or the valence band is 0.5 eV or more. Has a feature that the lattice defect density of the active layer is 10 times or more of the lattice defect density of the active layer. Therefore, it can be expected that the carrier life due to non-radiative recombination of the saturable absorption layer becomes 1/10 or less of the active layer. Further, a stable self-pulsation type semiconductor laser can be realized.

Alternatively, the self-sustained pulsation type semiconductor laser device of the present invention is formed under growth conditions that increase the number of defects in the saturable absorption layer.
Even in the case of × 10 ¹⁷ to 1 × 10 ¹⁸ cm ⁻³ , the carrier trapping amount due to the defect compensates for the carrier trapping amount due to the doped impurity, so that the lifetime of the carrier in the saturable absorbing layer is reduced, and self-pulsation is possible. It is.

Alternatively, in the self-pulsation type semiconductor laser device of the present invention, the saturable absorption layer has a dopant concentration of 1 × 10
^Since it has a characteristic of ¹⁷ to 1 × 10 ¹⁸ cm ⁻³ , the dopant diffuses into the active layer and deteriorates the crystal quality of the cladding layer or the active layer, or the pn junction position is separated from the active layer to stop laser oscillation. No such problems occur.

Alternatively, in the present invention, since the saturable absorbing layer has a feature in which the saturable absorbing layer is disordered in addition to the above-described features, the absorption wavelength of the saturable absorbing layer does not change due to disordering due to diffusion of the dopant.

In the present invention, in addition to the above characteristics, the dopant concentration of the saturable absorbing layer is equal to the dopant concentration of the cladding layer provided in contact with the saturable absorbing layer. It is possible to prevent the quality of the clad layer from deteriorating due to the diffusion and the accompanying excessive concentration doping. The quality of the cladding layer can be kept good by using the growth conditions for increasing the number of defects used in the present invention only when growing the saturable absorbing layer.

Alternatively, in the present invention, in addition to the above-described features, since a material containing Al is used for the saturable absorbing layer, the carrier is formed at a deep energy level formed by oxygen impurities mixed with Al during crystal growth. Recombination is promoted, and the carrier lifetime is further reduced.

Alternatively, in the present invention, since the saturable absorbing layer has a single or multiple quantum well structure in addition to the above-described characteristics, the carrier energy of the deep interface energy level formed at a plurality of quantum well interfaces is increased. Recombination is promoted and carrier lifetime is further reduced. The quantum well structure is advantageous because the absorption wavelength of the saturable absorption layer can be controlled with a precision of several meV by precisely controlling the width of the quantum well.

Alternatively, in the present invention, in addition to the above-described features, a feature of using a strain-compensated multiple quantum well structure in the saturable absorbing layer is provided, so that the carrier lifetime is further reduced due to interface defects.

Alternatively, in the present invention, in addition to the above characteristics, in the saturable absorption layer having the quantum well structure, the dopant concentration of the saturable absorption layer is suppressed to 1 × 10 ¹⁷ to 1 × 10 ¹⁸ cm ^−3. Alternatively, since the saturable absorption layer and the p-cladding layer have the same dopant concentration, diffusion of the dopant hardly occurs. Therefore, the quantum well structure is not easily lost or deformed due to the diffusion of the dopant, and thus has an effect of stabilizing the absorption wavelength of the saturable absorption layer. Also,
The saturable absorption layer can be designed easily and with high accuracy so that the absorption wavelength of the saturable absorption layer becomes substantially equal to the oscillation wavelength of the laser.

Alternatively, according to the present invention, in addition to the above features, in the structure of the saturable absorbing layer, the difference between the transition energy of the saturable absorbing layer when not doped and the transition energy of the active layer is controlled within 10 meV. It has features that are structural.
That is, for example, when the active layer has a multiple quantum well structure, a saturable absorbing layer having the same structure as the active layer and a different number of wells is grown, and the dopant concentration of the saturable absorbing layer is adjusted.
The absorption wavelength is set to an optimum value for self-sustained pulsation, and independently of this, the carrier density is controlled to increase the defect density of the saturable absorption layer. Since the quantum well structure of the undoped saturable absorption layer is the same as that of the active layer, there is an advantage that the saturable absorption layer can be manufactured with good reproducibility.

An oscillation wavelength of 650 nm, which has been attracting attention in practical use
In the following AlGaInP-based LDs, since the effect of confining carriers by the potential barrier is small, electrons injected into the active layer easily overflow into the p-cladding layer.

FIG. 23 is a schematic diagram of a band structure near an active layer of a conventional self-pulsation type semiconductor laser device having a saturable absorption layer between p-cladding layers. In this case, the electron (2305)
Is pulled by the saturable absorbing layer (2304) and the p-cladding layer (230
It easily overflows (2306) to 2). When the overflow occurs, the carrier density of the active layer increases to maintain the light output. Generally, the carrier life depends on the carrier density, and as the carrier density increases, the carrier life decreases. In particular, when laser oscillation occurs, the carrier density of the active layer is very high, so that the carrier life of the active layer becomes very short and approaches the carrier life of the saturable absorption layer. Eventually, when the electron overflow increases, the carrier lifetime of the active layer becomes shorter,
Self-excited oscillation stops.

Further, when there is a saturable absorbing layer between the p-cladding layers, the overflowed electrons are injected into the saturable absorbing layer. When the carrier density of the saturable absorption layer increases, the absorption wavelength changes, the absorption amount also decreases, and a stable self-pulsation operation cannot be obtained.

FIG. 24 is a schematic view of the band structure near the active layer of the self-pulsation type semiconductor laser device of the present invention. The present invention has a feature that a saturable absorption layer is provided only between n clad layers, in addition to the feature of introducing a defect into the saturable absorption layer to control the carrier lifetime. The minority carriers in the saturable absorption layer provided between the n cladding layers are holes. Since holes have a mass several tens of times larger than electrons, they do not easily overflow from the active layer. Therefore, the saturable absorbing layer provided between the n-cladding layers is less likely to promote the overflow of carriers and is less likely to accumulate carriers in the saturable absorbing layer than the saturable absorbing layer provided between the p-cladding layers. Thereby, the absorption wavelength of the saturable absorption layer is stabilized, and a self-sustained pulsation operation with good temperature characteristics (for example, a self-sustained pulsation operation at a relatively high temperature of 60 ° C. or higher) can be obtained.

The self-pulsation type semiconductor laser of the present invention has a feature that a saturable absorbing layer is provided between the n-cladding layers and a semiconductor layer is newly provided between the p-cladding layers having no saturable absorbing layer. (Light distribution adjusting layer), the layer thickness and band gap of the light distribution adjusting layer are such that the light distribution near the active layer in a direction perpendicular to the layer becomes substantially line-symmetric with respect to the center of the active layer, and the light distribution The adjustment layer is characterized in that it is set so as not to absorb the laser beam. FIG. 15 is a diagram showing conduction band energy and light intensity distribution near the active layer of the self-pulsation type semiconductor laser of the present invention provided with a light distribution adjusting layer. For this reason, the light intensity distribution inside the semiconductor laser device of the present invention has less distortion than the light intensity distribution inside the conventional semiconductor laser device in which the saturable absorption layer is provided only on one of the conductive type cladding layers. Not good. Since the shape of the focused beam reflects the light intensity distribution inside the laser, a focused beam shape with less distortion can be obtained. Therefore, the self-sustained pulsation type semiconductor laser device of the present invention can achieve both a self-sustained pulsation operation with good temperature characteristics and a focused beam shape with little distortion.

[0053]

EXAMPLES The present invention will be further described below with reference to examples, but the present invention is not limited to these examples.

Embodiment 1 FIG. 1 is a sectional view showing the configuration of an AlGaInP-based self-pulsation type semiconductor laser device according to a first embodiment of the present invention. This device is a red laser device in the 630 nm band, and has an n-electrode (101), an n-GaAs substrate (102), and a 300 nm-thick n-layer.
-GaAs buffer layer (103), n-G having a thickness of 100 nm
aInP buffer layer (1O4), 800 nm thick (Al _0.7
N-AlGa with Ga _{0.3) 0.5} In _0.5 P having a composition
InP clad layer (105), 50 nm thick (Al _0.5 Ga
An AlGaInP optical confinement layer (106) having a composition of _0.5 ) _0.5 In _0.5 P, a multiple quantum well active layer (107) having a quantum well structure having four well layers, and a 50 nm thick (Al
AlGaI with _0.5 Ga _{O.5) 0.5} In _O.5 P a composition
nP light confinement layer (108), 100 nm thick (Al _0.7 G
p-AlGaI having a _{0.3) O.5} In _0.5 P having a composition
nP cladding layer (109), saturable absorption layer (110), layer thickness 100
0 nm (mesa side cladding layer thickness 300 nm) of (Al _0.7
P-AlGa with Ga _{0.3) 0.5} In _0.5 P having a composition
InP clad layer (111) (mesa width about 5 μm), layer thickness 70
0 nm n-GaAs block layer (112), layer thickness 100 n
It is composed of a p-GaInP contact layer (113) having a composition of m Ga _0.5 In _0.5 P, a p-GaAs contact layer (114) having a thickness of 200 nm, and a p-electrode (115).

The dopant of each layer of the device of the present embodiment will be described below.
The concentration will be described. n-GaAs buffer layer (103),
n-GaInP buffer layer (104), n-AlGaInP
Doping of the cladding layer (105) and the n-GaAs blocking layer (112)
-Punt concentration is 5 × 10¹⁷cm ^-3And p-AlGa
The dopant concentration of the InP cladding layers (109, 111) is 8 ×
10¹⁷cm^-3And p-GaInP contact layer (11
3) The dopant concentration is 2 × 10¹⁸cm^-3, P-GaAs
The dopant concentration of the contact layer (114) is 5 × 10^{1 8}cm
^-3And AlGaInP light confinement layers (106, 108) and
The multiple quantum well active layer (107) was an undoped layer.

FIG. 2 shows a cross-sectional view of the multiple quantum well active layer (107). The multiple quantum well active layer is composed of a Ga _0.58 In _0.42 P well layer (202) having a thickness of 10 nm and an (A) layer having a thickness of 4 nm.
consists _{l 0.5 Ga 0.5) O.48 In 0.52} P barrier layer (201), GaInP / AlGaI having four well layers
It has an nP quantum well structure. The multiple quantum well active layer has a 0.5% tensile strain in the GaInP well layer (202) and a 0.3% compressive strain in the AlGaInP barrier layer (201). It has a multiple quantum well structure.

FIG. 3 is a sectional view showing the structure of the saturable absorbing layer (110). The saturable absorption layer (110) is a p-G layer having a thickness of 11 nm.
a _0.58 In _0.42 P well layer (302) and p-layer of 4 nm thick
(Al _0.7 Ga _0.3 ) _0.48 In _0.52 p-GaInP / A composed of a P barrier layer (301) and having two well layers
It has an lGaInP quantum well structure. This saturable absorbing layer has a 0.5% tensile strain in the p-GaInP well layer (302) and a 0.3% tensile strain in the p-AlGaInP barrier layer (301).
And has a strain-compensated multiple quantum well structure having a compression strain of
The saturable absorber layer has a dopant concentration of 2 × 10 ¹⁸
cm ^-3 .

In the device of this embodiment, the lattice defect density of the p-GaInP well layer (302) of the saturable absorption layer (110) is smaller than that of the GaInP well layer (202) of the multiple quantum well active layer (107). The density is 5 times or more, the saturable absorption layer (110) has a double quantum well structure, and the well layer and the barrier layer have a strain-compensated multiple quantum well structure with opposite lattice-matching strain. The transition energy of the multiple quantum well active layer (107) and the transition energy of the undoped saturable absorbing layer (110) are set equal. Also, p-
The thickness of the AlGaInP cladding layer (111) is set so that the light confinement coefficient of the saturable absorption layer satisfies the value required for self-pulsation.

In order to make the lattice defect density of the GaInP well layer of the saturable absorption layer (110) five times or more the lattice defect density of the GaInP well layer of the active layer (107), the gas source M
When the BE method is used, the GaInP well layer of the active layer is used.
V-group / III same as V-group / III ratio when (202) was grown
The n-GaInP well layer (302) of the saturable absorption layer may be grown at a temperature lower by 40 ° C. or more than the growth temperature of the active layer in the group ratio. The self-pulsation type semiconductor laser device of the present invention can be implemented not only by the gas source MBE method but also by another growth method such as the MOVPE method.

Hereinafter, a case where a gas source MBE method is used will be described as an example of a method of growing the self-pulsation type semiconductor laser device of this embodiment. Group III raw materials use solid metals, and Group V raw materials use AsH ₃ and PH ₃ gases. The p dopant is Be,
As the n dopant, Si is used. In the gas source MBE method, Be with low diffusion can be easily used as the p dopant.

FIG. 4 is a diagram showing a band structure of a conduction band near an active layer of the AlGaInP-based self-pulsation type semiconductor laser device of this embodiment, and a profile of a relative defect density and a growth temperature. GaInP and AlGaInP were grown at a growth rate of 1 μm / h and a PH ₃ flow rate of 4 sccm during growth.
Was performed under the following conditions. The GaInP / AlGaInP multiple quantum well active layer (107) was grown at a growth temperature of 540 ° C. at which the maximum PL peak intensity was obtained.

The p-GaInP well layer (302) of the saturable absorption layer (110) is grown at a growth temperature of 500 ° C.
The GaInP barrier layer (301) was grown at a growth temperature of 540 ° C. Immediately before growing the first p-GaInP well layer (302), the state where only P was supplied to the substrate surface and the supply of Ga and In was suspended for 3 minutes, during which the substrate temperature was lowered by 40 ° C. . GaInP / A of saturable absorption layer
All the interfaces of the 1GaInP multiple quantum well were similarly waited for 3 minutes. The last p- of the saturable absorption layer
Immediately after the growth of the GaInP well layer (302), the substrate temperature is increased by 40 ° C. during the interface standby for 3 minutes, and the p-A
An lGaInP cladding layer (111) was grown. When the interface waits for 3 minutes, impurities such as carbon and oxygen are adsorbed to the interface, so that a deep energy level is formed at the interface, which is effective in reducing the carrier lifetime.

In observation of the growth surface using a reflection high-energy electron diffraction (RHEED) apparatus, a (2 × 1) RHEED pattern was obtained when the GaInP well layer (202) of the active layer was grown, and a saturable absorption layer was obtained. p-GaInP well layer
At the time of growth of (302), a (2 × 2) RHEED pattern was obtained, and the surface reconstruction structures at the time of growth were different from each other.

Embodiment 2 In the self-pulsation type semiconductor laser device of the second embodiment, the energy level difference between the conduction band and the valence band in the p-GaInP well layer (302) of the saturable absorption layer (110) is described. Is 0.5 eV
Regarding the lattice defect having a deep energy level as described above, the lattice defect density of the p-GaInP well layer (302) of the saturable absorption layer is changed to the GaInP well layer (202) of the active layer (107).
The structure was the same as that of the self-pulsation type semiconductor laser device of Example 1 except that the lattice defect density was 10 times or more.

In this embodiment, at the same growth rate and group V flow rate as in the first embodiment, the GaInP / AlGaInP multiple quantum well active layer (107) is grown at a growth temperature of 540 ° C. at which the maximum PL peak intensity can be obtained. And saturable absorbing layer (1
The p-GaInP well layer of 10) was grown at a low growth temperature of 480 ° C. The GaInP well layer (20) of the active layer (107)
The RHEED pattern during the growth of (2) is (2 × 1), and the RHEED pattern during the growth of the p-GaInP well layer (302) of the saturable absorption layer (110) is close to (1 × 1) ( It was possible to grow with good reproducibility with reference to 2 × 2).

Embodiment 3 A self-pulsation type semiconductor laser device according to a third embodiment comprises a p-GaInP well layer of a saturable absorption layer (110) and a p-AlGa
Regarding lattice defects having a deep energy level in which the energy level difference from the conduction band or the valence band in the InP barrier layer is 0.5 eV or more, the p-GaI
The lattice defect density of the nP well layer and the p-AlGaInP barrier layer is respectively 10 times or more the lattice defect density of the GaInP well layer and the AlGaInP barrier layer of the active layer (107). The structure was the same as that of the oscillation type semiconductor laser device.

Since the wave function of the carrier is seeping into the AlGaInP barrier layer of the saturable absorbing layer (110), the carrier is non-radiatively recombined via the defect level of the AlGaInP barrier layer, which is effective in reducing the carrier lifetime. There is.

FIG. 5 is a view showing the band structure of the conduction band near the active layer of the AlGaInP-based self-pulsation type semiconductor laser device of this embodiment, and the profile of the relative defect density and the growth temperature. In this embodiment, the multiple quantum well active layer (107) was grown at the same growth rate and group V flow rate as in the first embodiment at a growth temperature of 540 ° C. at which the maximum PL peak intensity was obtained.

The entire saturable absorbing layer is grown at a low growth temperature of 480 ° C. with an interface waiting time of 3 minutes at the quantum well interface, and then the p-cladding layer (111) is
Grow at 40 ° C.

The GaInP well layer of the active layer and the AlGaI
The RHEED pattern during the growth of the nP barrier layer is (2 ×
1) GaInP well layer of saturable absorption layer and AlGaI
The RHEED pattern during the growth of the nP barrier layer is (1 ×
It was possible to grow with good reproducibility on the basis of (2 × 2) close to 1).

Embodiment 4 The self-pulsation type semiconductor laser device of the fourth embodiment has a saturable
Dopant concentration of p-GaInP well layer of absorption layer (110)
Degree 9 × 10¹⁷cm^-3And 1 × 10¹⁸cm ^-3less than
Except for being suppressed, the self-excited oscillation type semiconductor of Example 3
The structure was the same as that of the laser element. P-G of saturable absorption layer
The aInP well layer has a dopant concentration of 9 × 10¹⁷cm
^-3However, due to lattice defects introduced into the same layer,
A self-pulsating semiconductor laser device with a short life
You.

Embodiment 5 The self-pulsation type semiconductor laser device of the fifth embodiment has a saturable absorption layer (110) and a p-AlGaInP cladding layer (109, 11).
The structure was the same as that of the self-pulsation type semiconductor laser device of Example 4 except that the dopant concentration in 1) was 8 × 10 ¹⁷ cm ⁻³ . In the present embodiment, in addition to the configuration of the fourth embodiment, the p-dopant concentration of the saturable absorption layer is suppressed to 1 × 10 ¹⁸ cm ⁻³ or less, and the cladding provided in contact with the saturable absorption layer P-AlGaInP cladding layers (109, 11
It is characterized in that the dopant concentration of 1) is equal to that of 1).

In this embodiment, the dopant concentration in the quantum well structure in the saturable absorption layer (110) is constant, and the dopant concentration between the cladding layer (109) and the cladding layer (111) sandwiching the saturable absorption layer is different. Since there is no difference, diffusion of the p dopant is unlikely to occur.

Embodiment 6 A self-pulsation type semiconductor laser device according to a sixth embodiment has a GaI
The p-GaInP well layer of the saturable absorption layer (110) is provided for the band gap Eg when the nP well layer is completely disordered.
The forbidden band width Eg1 of the undoped (302) is Eg ≧ Eg1
The structure was the same as that of the self-excited oscillation type semiconductor laser device of Example 5, except that it was disordered to the extent of> Eg-10 meV.

In the gas source MBE method, the growth temperature is MO
Since the temperature is lower by about 100 ° C. than the VPE method, an ordered structure tends to be hardly formed. Forbidden band width Eg of GaInP layer grown on (001) GaAs substrate by gas source MBE method
2 is disordered to the extent that Eg2 ≒ Eg-20 meV. Further, the growth temperature is set to 570 ° C. or more or 480 ° C.
° C or lower, Eg ≧ Eg1> Eg−10meV
Disordered to some extent.

By disordering the saturable absorbing layer, an effect of stabilizing the absorption wavelength of the saturable absorbing layer can be obtained. In addition,
Even when the MOVPE method is used, the defect density of the saturable absorbing layer can be increased and disordered by controlling the growth temperature and the group V / III ratio.

Embodiment 7 FIG. 6 is a sectional view showing the configuration of an AlGaInP-based self-pulsation type semiconductor laser device according to a seventh embodiment of the present invention. The self-pulsation type semiconductor laser device of this embodiment has the same structure as that of the sixth embodiment except that AlGaInP is used for the well layer of the saturable absorption layer.

FIG. 7 shows the structure of the saturable absorbing layer (600) of this embodiment. This saturable absorption layer has a thickness of 12 nm.
(Al _0.1 Ga _0.9 ) _0.58 In _0.42 P well layer (602) and 4 nm thick (Al _0.7 Ga _0.3 ) _0.48 In _0.52 P barrier layer
(601). The saturable absorption layer has a defect density 10% lower than that of the active layer.
The dopant concentration of the saturable absorption layer and the p-AlGaInP cladding layer (109, 111) is 8 × 10 ¹⁷ cm.
^-3 . The thickness of the well layer was strictly fine-tuned to efficiently absorb the oscillation wavelength.

In this embodiment, the well layer (6
In 02), oxygen is taken in with Al and a deep energy order is formed in the crystal as in the case of the defect, so that it is effective in reducing the carrier lifetime.

Embodiment 8 FIG. 8 shows an AlGaInP-based alloy according to an eighth embodiment of the present invention.
FIG. 2 is a cross-sectional configuration diagram of the self-pulsation type semiconductor laser device of FIG. This
The device has an n electrode (801), an n-GaAs substrate (802), and a layer thickness.
300 nm n-GaAs buffer layer (803), layer thickness 10
0 nm n-GaInP buffer layer (804), layer thickness 800
nm (Al_0.7Ga_0.3)_0.5In_0.5Has the composition P
N-AlGaInP cladding layer (805), quantum well structure
Saturable absorber layer (806) having a thickness of 100 nm (Al
_0.7Ga_0.3)_0.5In_0.5N-AlG having composition P
aInP clad layer (807), 50 nm thick (Al_0.5G
a _0.5)_0.5In_0.5AlGaInP having composition P
Optical confinement layer (808), multiple quantum well with quantum well structure
Door active layer (809), 50 nm thick (Al_0.5Ga_0.5)_{0 .Five}
In_0.5AlGaInP light confinement with composition P
Layer (810), layer thickness 1000 nm (mesa side cladding layer thickness 30
0 nm) of (Al_0.7Ga_0.3)_0.5In_0.5The composition of P
P-AlGaInP cladding layer (811) having a mesa width of about
5 μm) and an 800 nm thick n-GaAs block layer (8
12), Ga having a thickness of 100 nm_0.5In_0.5Has composition P
P-GaInP contact layer (813), layer thickness 200 n
m-p-GaAs contact layer (814) and p-electrode (815)
Be composed.

The device of this embodiment has a saturable absorbing layer (806) provided only between the n cladding layers, an n-GaInP well layer (1002) of the saturable absorbing layer and an n-AlGaIn
The lattice defect density of the P barrier layer (1001) is different from that of the GaInP well layer (902) of the multiple quantum well active layer (809) and that of AlGa.
It must be at least 10 times the lattice defect density of the InP barrier layer (901), the saturable absorber layer has a double quantum well structure, and the well layer and barrier layer have lattice-matching strains of opposite signs. It has a multiple quantum well structure.

The dopant of each layer of the device of this embodiment is described below.
The concentration will be described. n-GaAs buffer layer (803),
n-GaInP buffer layer (804), n-AlGaInP
The cladding layer (805) and the n-GaAs blocking layer (812)
-Punt concentration is 5 × 10¹⁷cm ^-3And p-AlGa
The dopant concentration of the InP cladding layer (811) is 8 × 10¹⁷
cm^-3And Doping of p-GaInP contact layer (813)
-Punt concentration is 1 × 10^{1 8}cm^-3, P-GaAs contour
814) has a dopant concentration of 5 × 10¹⁸cm^-3age
Was. Multiple quantum well active layer (809) and AlGaInP optical closure
The confinement layers (808, 810) were undoped layers.

FIG. 9 is a sectional view showing the structure of a multiple quantum well active layer (809). The multiple quantum well active layer includes a Ga _0.58 In _0.42 P well layer (902) having a thickness of 10 nm and a (A) layer having a thickness of 4 nm.
consists _{l 0.5 Ga 0.5) 0.48 In 0.52} P barrier layer (901), GaInP / AlGaI having four well layers
It has an nP quantum well structure.

FIG. 10 shows a sectional view of the structure of the saturable absorbing layer (806). The saturable absorption layer is n-Ga having a thickness of 10 nm.
_0.58 In _0.42 P well layer (1002) and 4 nm thick n- (A
n _0.7 Ga _0.3 ) _0.48 In _0.52 n-GaInP / AlG comprising a P barrier layer (1001) and having two well layers
It has an aInP quantum well structure. The dopant concentration of this saturable absorption layer was 2 × 10 ¹⁸ cm ⁻³ .

In the device of this embodiment, since the saturable absorbing layer (806) is provided only between the n cladding layers, overflowed electrons are not injected into the saturable absorbing layer. Also, M
In the case of growing using the OVPE method, Si having a smaller diffusion than that of Zn can be used as a dopant of the saturable absorbing layer, which is more advantageous than the case where the saturable absorbing layer is provided between the p clad layers. is there.

The device of this embodiment was grown at the same growth rate and group V flow rate as in the first embodiment. The n-cladding layers (805, 807) are grown at
The growth was carried out at 0 ° C., and the GaInP / AlGaInP multiple quantum well active layer (809) was grown at a growth temperature of 540 ° C. at which the maximum PL peak intensity was obtained.

The GaInP well layer of the saturable absorption layer and Al
The RHEED pattern when growing the GaInP barrier layer is close to (1 × 1) (2 × 2), and the RHEED pattern when growing the GaInP well layer and the AlGaInP barrier layer of the active layer is (2 × 1). It grew with good reproducibility.

Embodiment 9 In the self-pulsation type semiconductor laser device according to a ninth embodiment of the present invention, the structure of the saturable absorbing layer is such that the minimum transition energy of the saturable absorbing layer when not doped and the minimum The structure was the same as that of Example 8 except that the difference from the transition energy was controlled within 10 meV.

When the lowest transition energies of the active layer and the saturable absorbing layer are completely equal, the differential gain of the saturable absorbing layer does not become positive at the lowest transition energy value of the active layer, so that no self-excited oscillation occurs. It is preferable that the lowest transition energy of the saturable absorption layer be smaller than the lowest transition energy value of the active layer by about 10 meV.
For that purpose, it is desirable that the minimum transition energy of the saturable absorption layer when not doped and the minimum transition energy of the active layer coincide within 10 meV.

The minimum transition energy of the saturable absorbing layer can be adjusted by changing the thickness of the well layer. In this embodiment, when the well width changes from 9 nm to 10 nm, the minimum transition energy decreases by about 20 meV. Therefore, in order to control the minimum transition energy difference between the saturable absorbing layer and the active layer within 10 meV, it is necessary to control both well layers within one molecular layer. The gas source MBE method can control the atomic layer order and can form a steeper interface than the MOVPE method, which is advantageous for the growth of a self-pulsation type semiconductor laser.

Since the energy region where the differential gain of the saturable absorbing layer is large is as narrow as about 10 meV, it is desirable that the absorbed energy of the saturable absorbing layer can be finely adjusted on the order of 1 meV. Even in the MOVPE method, the absorption energy of the saturable absorption layer can be finely adjusted on the order of 1 meV by adjusting the dopant concentration of the saturable absorption layer. Since the carrier lifetime of the saturable absorbing layer of this embodiment is already short due to defects introduced into the saturable absorbing layer, the dopant concentration of the saturable absorbing layer can be independently adjusted while maintaining self-sustained pulsation. Therefore, in this embodiment, the absorption energy of the saturable absorption layer can be finely adjusted on the order of 1 meV.

Embodiment 10 FIG. 11 shows an AlGaIn according to a tenth embodiment of the present invention.
FIG. 2 is a cross-sectional configuration diagram of a P-based self-pulsation type semiconductor laser device.
This device has an n-electrode (1101), an n-GaAs substrate (1102),
300 nm thick n-GaAs buffer layer (1103), 100 nm thick n-GaInP buffer layer (1104), 1 layer thickness
N-AlGaInP cladding layer (1105) having a composition of (Al _0.7 Ga _0.3 ) _0.5 In _0.5 P of 000 nm, saturable absorption layer (1106) having a quantum well structure, and (Al _0.7 Ga _0.3 ) _0.5 In having a thickness of 100 nm. _N- having a composition of _0.5 P
AlGaInP cladding layer (1107), 50 nm thick (A
AlGa having a composition of l _0.5 Ga _0.5 ) _0.5 In _0.5 P
InP optical confinement layer (1108), a multiple quantum well active layer having a quantum well structure (1109), the thickness 50 nm (Al _{0. 5} Ga
An AlGaInP optical confinement layer (1110) having a composition of _0.5 ) _0.5 In _0.5 P, (Al _0.7 G
p-AlGaI having a _{0.3) 0.5} In _0.5 P having a composition
nP cladding layer (1111), light distribution adjusting layer (1112), layer thickness 10
(Al of mesa side cladding layer thickness 300 nm)
P-AlG having a composition of _0.7 Ga _0.3 ) _0.5 In _0.5 P
aInP cladding layer (1113) (mesa width about 5 μm), n-G
aAs block layer (1114), Ga _0.5 I having a thickness of 100 nm
p-GaInP contact layer of n _0.5 P having a composition (111
5), a 200 nm thick p-GaAs contact layer (111
6) and a p-electrode (1117).

Hereinafter, the dopant concentration of each layer of the device of this embodiment will be described. n-GaAs buffer layer (1103),
n-GaInP buffer layer (1104), n-AlGaInP
The dopant concentration of the cladding layers (1105, 1107) is 8 × 10
¹⁷ cm ^-3 . The dopant concentration of the n-GaAs block layer (1114) was set to 5 × 10 ¹⁷ cm ⁻³ . p-AlGaI
The dopant concentration of the nP cladding layer (1111, 1113) is 8 ×
It was set to 10 ¹⁷ cm ^-3 . p-GaInP contact layer (111
5) The dopant concentration is 1 × 10 ¹⁸ cm ⁻³ , p-GaAs
The dopant concentration of the contact layer (1116) is 5 × 10 ¹⁸ cm.
^-3 . Multiple quantum well active layer (1109) and AlGaIn
The P light confinement layers (1108, 1110) were undoped layers.

FIG. 12 shows a cross section of the multiple quantum well active layer (1109).
FIG. The multiple quantum well active layer has a thickness of 10 nm.
Ga_0.58In_0.42P well layer (1202) and 4 nm thick
(Al _0.5Ga_0.5)_0.48In_0.52From P barrier layer (1201)
GaInP / AlG having four well layers
It has an aInP quantum well structure.

FIG. 13 is a sectional view showing the structure of the saturable absorbing layer (1106). The saturable absorption layer is n-Ga having a thickness of 10 nm.
_0.58 In _0.42 P well layer (1302) and 4 nm thick n- (A
l _0.7 Ga _0.3 ) _0.48 In _0.52 n-GaInP / AlG composed of a P barrier layer (1301) and having two well layers
It has an aInP quantum well structure. The dopant concentration of the saturable absorption layer was set to 8 × 10 ¹⁷ cm ⁻³ .

FIG. 14 is a sectional view of the light distribution adjusting layer (1112). The light distribution adjusting layer is made of p- (Al
_0.2 Ga _0.8 ) _0.5 In _0.5 P well layer (1402) and layer thickness 4 nm
N- (Al _0.7 Ga _0.3 ) _0.5 In _0.5 P barrier layer (1401)
P-GaInP having two well layers
/ AlGaInP quantum well structure. The dopant concentration of the light distribution adjusting layer was set to 8 × 10 ¹⁷ cm ⁻³ .

The self-pulsation type semiconductor laser device of this embodiment has the same structure as that of the ninth embodiment except that a light distribution adjusting layer (1112) is newly provided between the P cladding layers.

FIG. 15 is a diagram showing the conduction band energy near the active layer of the self-pulsation type semiconductor laser device of the present embodiment and the light intensity distribution during laser oscillation. The distance, layer thickness, and band gap of the light distribution adjusting layer from the active layer are such that the light distribution near the active layer in a direction perpendicular to the layer is almost line-symmetric with respect to the center of the active layer.
(1500) and the light distribution adjusting layer was set so as not to absorb the laser light.

Thus, distortion of the shape of the focused beam spot can be reduced. Further, even if electrons overflowing from the active layer accumulate in the light distribution adjustment layer during the oscillation operation, the light distribution adjustment layer does not absorb laser light and does not become a loss layer. Further, since the saturable absorbing layer is provided between the n-cladding layers, electrons overflowing from the active layer do not accumulate in the saturable absorbing layer, and the absorption wavelength of the saturable absorbing layer does not change.

Embodiment 11 A self-pulsation type semiconductor laser device according to an eleventh embodiment of the present invention is an AlGaInN-based self-pulsation type semiconductor laser device having the features of the AlGaInP-based self-pulsation type semiconductor laser device of Embodiment 10. It is a laser element.

FIG. 16 is a sectional view showing the configuration of an AlGaInN-based self-pulsation type semiconductor laser device according to this embodiment. The device according to the present embodiment is an A-plane sapphire substrate (1
601), a GaN buffer layer (1602) having a thickness of 30 nm, and a layer thickness of 3
μm n-GaN cladding layer (1603), 100 nm thick n-In _0.1 Ga _0.9 N crack prevention layer (1604), layer thickness 40
0 nm n-Al _0.12 Ga _0.88 N cladding layer (1605), n
Type saturable absorption layer (1606), n-Al _0.12 G with a thickness of 50 nm
a _0.88 N cladding layer (1607), 100 nm thick n-Ga
N light confinement layer (1608), multiple quantum well active layer (1609), p-GaN light confinement layer (1610) having a thickness of 100 nm, layer thickness of 5
0 nm p-Al _0.15 Ga _0.85 N cladding layer (1611), p
-Type InGaN light distribution adjusting layer (1612), 400 nm thick p
-Al _{0. 15} Ga _0.85 N cladding layer (1613), the layer thickness 500n
m-p-GaN cladding layer (1614), 15 nm thick p-GaN
GaAs _0.04 N _0.96 contact layer (1615), p electrode (1616)
And an n-electrode (1617).

FIG. 17 is a sectional view showing the structure of the p-type light distribution adjusting layer (1612). The p-type light distribution adjusting layer has a layer thickness of 15 nm.
-GaN barrier layer (1701) and 3.4 nm thick p-In
_0.1 Ga _0.9 N well layer (1702) and 5 nm p-GaN
It is composed of a barrier layer (1703) and has a structure having two well layers.

FIG. 18 is a sectional view showing the structure of a multiple quantum well active layer (1609). The multiple quantum well active layer is composed of a p-In _0.05 Ga _0.95 N barrier layer (1801) having a thickness of 5 nm and a thickness of 2.5 n.
m-p-In _0.2 Ga _0.8 N well layer (1802) and has a structure having eight well layers.

FIG. 19 is a sectional view showing the structure of the n-type saturable absorbing layer (1606). The n-type saturable absorption layer has a thickness of 10 nm.
-GaN barrier layer (1901) and 5 nm thick n-In _0.05 G
a _{0. 95} N barrier layer (1902) having a thickness of 2.6 nm n-an In
It is composed of a _0.2 Ga _0.8 N well layer (1903) and has a structure having two well layers.

In the present embodiment, an n-type saturable absorption layer (1606) and a p-type light distribution adjusting layer (1
612), and by changing the growth temperature, the n-type saturable absorber layer (1606) has a defect density ten times or more that of the multiple quantum well active layer (1609). With these characteristic configurations, a blue semiconductor laser device having an oscillation wavelength of 420 nm and having stable and excellent self-excited oscillation characteristics was obtained.

The above-mentioned element is manufactured by MOVPE method or gas source M
It can be manufactured using the BE method. Hereinafter, an example of a method for manufacturing the LD element by the MOVPE method will be described.

Group V raw materials include NH ₃ and AsH ₃ , and Group III raw materials include trimethyl indium (TMIn), trimethyl gallium (TMGa), and trimethyl aluminum (TMA).
1) is used. CP ₂ Mg is used as the p dopant material, and SiH ₄ is used as the n dopant material.

First, the A-plane sapphire substrate (1601) is introduced into a reaction tube, which is a growth chamber, and an H ₂ carrier gas is caused to flow through the reaction tube. In this state, the substrate was heated to 1150 ° C., heated for 10 minutes, and then cooled to 550 ° C., and NH ₃ and TMGa were introduced to grow a GaN buffer layer (1602) having a thickness of 30 nm. Although the sapphire substrate and GaN have a lattice mismatch of 10% or more, a GaN layer with good crystallinity can be obtained by growing a low-temperature grown GaN buffer layer (1602) first and controlling its thickness. Was.

Thereafter, the substrate temperature was raised to 1000 ° C. while the H ₂ carrier gas was flowing through the reaction tube, and NH ₃ and TMGa were added.
Then, an n-GaN cladding layer (1603) having a thickness of 3 μm was grown by introducing SiH ₄ and SiH ₄ . This n-GaN cladding layer
The growth was performed at a growth temperature of 1000 ° C. and a group V / group ratio of 750.

Then, TMIn is introduced to a thickness of 100 nm.
The n-In _0.1 Ga _0.9 N crack preventing layer (1604) was grown. At the same Group V / III ratio, the subsequent 400 nm thick n
-Al _0.15 Ga _0.85 N cladding layer (1605, 1607) is 107
The n-type saturable absorber layer (1606) was grown at 0 ° C.
The multi-quantum well active layer (1609) was grown at 1000C. Thereby, the n-type saturable absorbing layer (1
606) can have a defect density ten times or more that of the multiple quantum well active layer (1609). The n dopant concentration of each layer was set to 8 × 10 ¹⁷ cm ⁻³ .

In this way, a p-type layer was also sequentially grown. The p-GaAs _0.04 N _0.96 contact layer (1615)
H _3, AsH _3, and by introducing TMGa and CP ₂ Mg were grown. By setting the thickness of the p-GaAs _0.04 N _0.96 contact layer to 15 nm, a crystal of good quality within the critical thickness was obtained.

After the growth, thermal annealing was performed at 600 ° C. for 1 hour to expel H atoms taken into the crystal, activate Mg, and improve the hole concentration. The p dopant concentration of the p cladding layer is 8 × 10 ¹⁷ cm ⁻³ , and p-GaAs _0.04 N
The p dopant concentration of the _0.96 contact layer (1615) is 5 × 10
¹⁸ cm ^-3 .

After the growth was completed, the temperature was lowered slowly so that the sapphire substrate was not broken. After removing the wafer, n
-Etching to the GaN cladding layer (1603) surface,
An n-electrode (1617) is attached to this n-GaN cladding layer,
p-electrode on p-GaAs _0.04 N _0.96 contact layer (1615)
(1615) was attached to obtain an LD element.

[0114]

As is apparent from the above description, according to the present invention, the absorption wavelength of the saturable absorption layer is substantially equal to the oscillation wavelength of the laser, the lifetime of carriers generated in the saturable absorption layer is short, Since the absorption wavelength of the absorption layer is stable, a self-sustained pulsation laser element having a long operating life, a small threshold value, and stable and excellent characteristics can be obtained.

Since the self-pulsation type semiconductor laser device of the present invention has the light distribution adjusting layer, the distortion of the light spot shape is small.

By using the semiconductor laser device of the present invention as a light source for pickup of an optical disk device, a high-performance optical disk device with reduced laser return light noise can be realized at low cost.

[Brief description of the drawings]

FIG. 1 is a sectional configuration diagram of an AlGaInP-based self-pulsation type semiconductor laser device according to a first embodiment of the present invention.

FIG. 2 is a cross-sectional configuration diagram of a multiple quantum well active layer of the self-pulsation type semiconductor laser device according to the first embodiment of the present invention.

FIG. 3 is a sectional configuration diagram of a saturable absorption layer of the self-pulsation type semiconductor laser device according to the first embodiment of the present invention.

FIG. 4 is a view showing a band structure of a conduction band near an active layer of the AlGaInP-based self-pulsation type semiconductor laser device of Example 1, and a profile of a relative defect density and a growth temperature.

FIG. 5 is a diagram showing a band structure of a conduction band near an active layer of an AlGaInP-based self-pulsation type semiconductor laser device of Example 3, and a profile of a relative defect density and a growth temperature.

FIG. 6 is a sectional configuration diagram of an AlGaInP-based self-pulsation type semiconductor laser device of Example 7.

FIG. 7 is a sectional structural view of a saturable absorption layer of the device of Example 7.

FIG. 8 is a cross-sectional configuration diagram of an AlGaInP-based self-pulsation type semiconductor laser device of Example 8.

FIG. 9 is a sectional configuration diagram of a multiple quantum well active layer of the device of Example 8.

FIG. 10 is a sectional configuration diagram of a saturable absorption layer of the device of Example 8.

FIG. 11 is a sectional configuration diagram of an AlGaInP-based self-pulsation type semiconductor laser device of Example 10.

FIG. 12 is a sectional configuration diagram of a multiple quantum well active layer of the device of Example 10;

FIG. 13 is a sectional configuration diagram of a saturable absorption layer of the device of Example 10.

FIG. 14 is a cross-sectional configuration diagram of a light distribution adjusting layer of Example 10.

FIG. 15 is a diagram showing the conduction band energy near the active layer of the self-pulsation type semiconductor laser device of Example 10 and the light intensity distribution during laser oscillation.

FIG. 16 is a sectional configuration diagram of an AlGaInN-based self-pulsation type semiconductor laser device of Example 11;

FIG. 17 is a cross-sectional configuration diagram of a p-type light distribution adjustment layer of the device of Example 11;

FIG. 18 is a sectional view showing the structure of a multiple quantum well active layer of the device according to Example 11;

FIG. 19 is a sectional configuration diagram of an n-type saturable absorption layer of the device of Example 11;

FIG. 20 is a diagram showing conditions to be satisfied for a differential gain ratio and a carrier life ratio of an active layer and a saturable absorption layer to realize a self-sustained pulsation operation of a semiconductor laser device.

FIG. 21 is a graph showing the carrier life and photoluminescence (PL) intensity of the (Al _x Ga _{1 -x} ) _0.5 In _0.5 P bulk as a function of Al composition.

FIG. 22 is a graph showing the growth temperature dependence of the defect density and PL intensity of the deep energy levels (D1, D2, D3) of (Al _0.7 Ga _0.3 ) _0.5 In _0.5 P bulk.

FIG. 23 is a schematic view of a band structure near an active layer of a conventional self-pulsation type semiconductor laser device.

FIG. 24 is a schematic diagram of a band structure near an active layer of the self-pulsation type semiconductor laser device of the present invention.

[Explanation of symbols]

101, 801, 1101, 1617 n-electrode 102, 802, 1102 n-GaAs substrate 103, 803, 1103 n-GaAs buffer layer 104, 804, 1104 n-GaInP buffer layer 105, 805, 807, 1105, 1107 n-
AlGaInP cladding layers 106, 108, 808, 810, 1108, 1110
AlGaInP light confinement layer 107, 809, 1109, 1609 Multiple quantum well active layer 109, 811, 1111, 1113 p-AlGa
InP cladding layer 110, 600, 806, 1106 Saturable absorption layer 111 p-AlGaInP cladding layer 112, 812, 1114 n-GaAs block layer 113, 813, 1115 p-GaInP contact layer 114, 814, 1116 p-GaAs contact layer 115, 815, 1117, 1616 p electrode 201, 901, 1201 AlGaInP barrier layer 202, 902, 1202 GaInP well layer 301, 601, 1401 p-AlGaInP barrier layer 302 p-GaInP well layer 602, 1402 p-AlGaInP well layer 1001 , 1301 n-AlGaInP barrier layer 1002, 1302 n-GaInP well layer 1112 light distribution adjusting layer 1601 A-plane sapphire substrate 1602 GaN buffer layer 16 3 n-GaN cladding layer 1604 n-InGaN crack prevention layer 1605 n-AlGaN cladding layer 1606 n-type saturable absorption layer 1607 n-AlGaN cladding layer 1608 n-GaN light confinement layer 1610 p-GaN light confinement layer 1611, 1613 p -AlGaN cladding layer 1612 p-type light distribution adjusting layer 1614 p-GaN cladding layer 1615 p-GaAsN contact layer 1701 p-GaN barrier layer 1702 p-InGaN well layer 1703 p-GaN barrier layer 1801 InGaN barrier layer 1802 InGaN well layer 1901 n-GaN barrier layer 1902 n-InGaN barrier layer 1903 n-InGaN well layer 2301, 2401 n clad layer 2302 p clad layer 2303, 2403 Multiple quantum well active Layer 2304 p-type saturable absorbing layer 2305 electron 2306 Overflow 2402 n-type saturable absorbing layer 2405 holes (positive holes)

──────────────────────────────────────────────────の Continued on the front page (58) Field surveyed (Int.Cl. ⁶ , DB name) H01S 3/18 JICST file (JOIS)

Claims (13)

(57) [Claims] 1. A self-pulsation type semiconductor laser device having a saturable absorption layer, wherein at least one of the semiconductor layers constituting the saturable absorption layer has at least one forbidden band width among at least one saturable absorption layer. Self-excitation characterized in that the lattice defect density of one semiconductor layer 1 is at least five times the lattice defect density of at least one semiconductor layer 2 having the minimum forbidden band width among the semiconductor layers constituting the active layer. Oscillation type semiconductor laser device. 2. Regarding lattice defects having a deep energy level whose energy level difference from a conduction band or a valence band is 0.5 eV or more, the lattice defect density of the semiconductor layer 1 is lower than the lattice defect density of the semiconductor layer 2. 2. The self-pulsation type semiconductor laser device according to claim 1, wherein the value is 10 times or more. 3. The semiconductor layer 1 having a dopant concentration of 1 × 10
¹⁷~ 1 × 10¹⁸cm ^-3Self-excitation according to claim 1 or 2,
Oscillation type semiconductor laser device. 4. The forbidden band width Eg1 of the semiconductor layer 1 with respect to the forbidden band width Eg when the semiconductor layer 1 is completely disordered.
4. The self-sustained pulsation type semiconductor laser device according to claim 1, wherein the semiconductor is disordered to the extent that Eg ≧ Eg1> Eg−10 meV. 5. The self-pulsation type semiconductor according to claim 1, wherein the dopant concentration of the semiconductor layer 1 is equal to the dopant concentration of the cladding layer provided in contact with the saturable absorption layer. Laser element. 6. The self-pulsation type semiconductor laser device according to claim 1, wherein a material containing Al is used for the semiconductor layer 1. 7. The self-pulsation type semiconductor laser device according to claim 1, wherein the saturable absorption layer has a single quantum well structure or a multiple quantum well structure. 8. The self-excited pump according to claim 1, wherein the saturable absorption layer has a strain-compensated multi-quantum well structure in which the well layer and the barrier layer have lattice-matching strains of opposite signs. Oscillation type semiconductor laser device. 9. The structure of the saturable absorption layer wherein the difference between the lowest transition energy of the saturable absorption layer and the lowest transition energy of the active layer when not doped is controlled within 10 meV. 9. The self-pulsation type semiconductor laser device according to any one of 8. 10. The self-pulsation type semiconductor laser device according to claim 1, wherein a saturable absorption layer is provided only between the n-type cladding layers. 11. A self-sustained pulsation type semiconductor laser device in which a saturable absorption layer is provided only between one conductive type clad layer and another conductive type clad layer not provided with a saturable absorption layer. A new semiconductor layer, the thickness and band gap of the semiconductor layer are such that the light distribution near the active layer in a direction perpendicular to the layer becomes substantially line-symmetric with respect to the center of the active layer, and the semiconductor layer emits laser light. A self-sustained pulsation type semiconductor laser device which is set so as not to absorb light. 12. A GaAs substrate having an arbitrary plane orientation, and a cladding layer, an active layer, and a saturable absorption layer formed of (Al
The self-excited oscillation type semiconductor laser device according to claim 1, wherein a material of _x Ga _1−x ) _y In _1−y P (0 ≦ x ≦ 1, 0 ≦ y ≦ 1) is used. 13. A sapphire substrate having an arbitrary plane orientation, and a cladding layer, an active layer, and a saturable absorbing layer (A
12. The self-pulsation type semiconductor laser device according to claim 1, wherein a material of l _x Ga _1-x ) _y In _1-y N (0 ≦ x ≦ 1, 0 ≦ y ≦ 1) is used. .