JP3238974B2 - 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 semiconductor laser device in which noise due to return light of output laser light is reduced.

[0002]

2. Description of the Related Art In a conventional semiconductor laser device, when return light of output laser light is re-incident on the semiconductor laser device, noise caused by the return light (hereinafter referred to as return light noise) is included in the output laser light. There was a problem that occurred. Such return light noise is generated, for example, when a semiconductor laser device is used as a light source of an optical disk device, and return light of output laser light due to reflection from a disk surface or the like re-enters the semiconductor laser device.

[0003] In order to reduce the return light noise of this semiconductor laser device, a method utilizing a self-excited oscillation phenomenon is known. For example, Japanese Patent Application Laid-Open No. 63-202083 (H01S3)
/ 18) It is disclosed in the gazette.

In such a semiconductor laser device, AlGaAs is used.
Among the cladding layers sandwiching the active layer, one of the cladding layers has energy (oscillation wavelength energy: h
It is described that self-excited oscillation is performed by using a refractive index layer having a band gap energy considerably larger than ν) or a light absorbing layer having a band gap energy considerably smaller than the oscillation wavelength energy.

[0005]

However, according to the experimental results of the applicant of the present invention, in the case of a refractive index layer having a band gap energy considerably larger than the above-mentioned oscillation wavelength energy, the astigmatic difference becomes large, while the oscillation wavelength energy becomes large. It has been found that in the case of the light absorbing layer having a much smaller band gap energy, the operating current value becomes larger.

The present invention has been made in view of the above problems, and has as its object to provide a semiconductor laser device that performs self-sustained pulsation with a small astigmatic difference and a small operating current value.

[0007]

According to the present invention, there is provided a semiconductor laser device comprising: a semiconductor substrate of a first conductivity type; a first cladding layer of a first conductivity type provided on the semiconductor substrate; And a second conductive type second cladding layer provided on the active layer, wherein the first and second cladding layers have a smaller refractive index and a larger band gap than the active layer. A semiconductor laser device having a saturable light absorbing layer (saturable light absorbing layer) having a band gap of energy substantially equal to oscillation wavelength energy in at least one of the first and second cladding layers ; First
The cladding layer comprises a first AlGaAs cladding layer and a second Al
A first GaAs cladding layer.
A first conductive layer between the lad layer and the second AlGaAs cladding layer.
Al _u Ga _1-u As (0 ≦ u <1) first supersaturated light absorption
An active layer, and the second cladding layer is formed on the active layer.
The formed third AlGaAs cladding layer and the third AlG
Stripe-shaped ridge formed on aAs clad layer
And a fourth AlGaAs cladding layer,
The second conductivity type Al _u Ga is formed on the 3AlGaAs cladding layer.
_{A 1-u} As (0 ≦ u <1) second saturable light absorbing layer is formed .

[0008]

[0009]

According to the present invention, a supersaturated light absorbing layer having a band gap energy substantially equal to the oscillation wavelength energy is provided in at least one of the first and second cladding layers sandwiching the active layer. Oscillation occurs in low astigmatism, low operating current, and single transverse mode.

In particular, the first cladding layer is formed of a first AlG
an aAs cladding layer and a second AlGaAs cladding layer, a first conductivity type Al _u Ga _1-u As first supersaturated light absorbing layer between the first and second AlGaAs cladding layers, and the second cladding layer is A third layer formed on the active layer;
AlGaAs cladding layer and fourth Al forming a stripe-shaped ridge formed on the third AlGaAs cladding layer
Consists of a GaAs cladding layer, due to the configuration of forming the second conductivity type Al _u Ga _1-u As second saturable light absorbing layer on the 3AlGaAs cladding layer, the Al _u Ga _1-u As second supersaturation light Fourth A in which the absorption layer forms a stripe-shaped ridge portion
Since it also functions as an etching stop layer when forming the lGaAs cladding layer, the third layer formed on the active layer
The thickness of the AlGaAs cladding layer can be formed with high precision and ease.

[0011]

DESCRIPTION OF THE PREFERRED EMBODIMENTS One embodiment according to the present invention will be described in detail with reference to the drawings. FIG. 1 is a sectional view showing an AlGaAs-based semiconductor laser device according to the present embodiment.

Referring to FIG. 1, reference numeral 1 denotes an n-type GaAs substrate;
N-type first n-type GaAs substrate 1 having a layer thickness of 1 to 2 μm
Al _xa Ga _1-xa As (AlGaAs) clad layer (typically composition ratio xa = 0.51) 2a, n-type A with layer thickness S ₁
l _u Ga _1-u As first saturable light absorbing layer (composition ratio u of 0.1
2 ≦ u ≦ 0.14, carrier concentration 2 × 10 ^{17 to} 5 × 10
¹⁷ cm ⁻³ ) 3 and an n-type second layer having a layer thickness t ₁ of 0.3 μm.
An Al _xb Ga _1-xb As (AlGaAs) cladding layer (typically, composition xb = 0.51) 2b is formed in this order, and the first cladding layer 2 is constituted by the cladding layers 2a and 2b. I have. That is, the first cladding layer 2
A saturable light absorbing layer 3 is formed.

On the first cladding layer 2, a layer thickness of 0.08
μm undoped Al _q Ga _{1 -q} As (composition ratio q = 0.
13) The active layer 4 is formed.

On the active layer 4, the layer thickness t ₂ is 0.3 μm.
p-type third Al _ya Ga _1-ya As (AlGaAs
s) Cladding layer (typically composition ratio ya = 0.51) 5
a, p-type layer thickness _{S 2 Al u Ga 1-u} As second saturable light absorbing layer (composition ratio u is 0.12 ≦ u ≦ 0.14, the carrier concentration of ^{4 × 10 17 ~2 × 10 18} cm - ³ ) 6 and height 0.5
P-type fourth Al _yb Ga _1-yb As (AlG) forming a stripe-shaped ridge portion having a stripe lower surface width W of 4 μm with a width of 1 μm to ₁ μm
aAs) Cladding layer (typically composition ratio yb = 0.5
1) 5b is formed in this order, and the cladding layer 5
The second clad layer 5 having the stripe-shaped ridge portion is constituted by a and 5b.

On the upper surface of the ridge portion of the fourth AlGaAs cladding layer 5b, a p-type GaAs cap layer 7 having a thickness of 0.3 μm is formed, and a side surface of the p-type GaAs cap layer 7 and the fourth AlGaAs cladding layer are formed. On the side surface 5b and on the second saturable light absorbing layer 6, n-type GaAs current blocking layers 8 having a thickness of 0.8 μm are formed. A 4 μm-thick p-type GaAs contact layer 9 is formed on the n-type GaAs current blocking layers 8 and 8 and the p-type GaAs cap layer 7.
Are formed.

Although not shown, a p-type ohmic electrode made of Au-Cr is formed on the p-type GaAs contact layer 9, and Au-Sn-Cr is formed on the lower surface of the n-type GaAs substrate 1.
Is formed.

In the semiconductor laser device, the n-type Al _u Ga _1-u As first supersaturated light absorbing layer 3 and the p-type Al _u
The composition ratio u (here, both have the same composition ratio) and the layer thickness (here, both have the same layer thickness: S ₁ = S ₂ ) of the Ga _1-u As second supersaturated light absorption layer 6 are changed to obtain a γ value ( (Visibility), astigmatism, and operating current value at an optical output of 3 mW were examined. Here, as an example, an example in which an element having a laser resonator length of 250 μm is applied without end face coating is shown.

Here, the γ value indicates the degree of self-excited oscillation (interference between longitudinal modes). When γ = 1, self-excited oscillation is not performed. Strengthen.
According to the experimental results of the inventor of the present application, when a semiconductor laser element is mounted on an optical disk device, a good C / N value is obtained when the γ value is 0.7 or less, and a particularly good C / N value is obtained when the γ value is 0.6 or less. Has been found to be obtained, and the astigmatic difference is 17% in an optical system used in a general disk drive.
A good value of C / N can be obtained by concentrating a sufficient laser beam with a small value of less than μm, and a better C / N value can be obtained by concentrating a good laser beam with a small value of 15 μm or less. I found that I could do it.

First, FIG. 2 shows that the composition ratio u of the Al _u Ga _1-u As first and second supersaturated light absorbing layers 3 and 6 is 0.12 to 0.12.
The relationship between the thickness of the first and second supersaturated light absorbing layers 3 and 6 and the γ value in the range of 0.14 is shown.

FIG. 2 shows that the γ value is 0.7 or less when the thickness of the supersaturated light absorbing layers 3 and 6 is 0.01 μm or more, and 0.6 or less when the thickness is 0.02 μm or more. I understand.

Next, FIG. 3 shows the first and second supersaturated light absorbing layers 3 and 6 in which the composition ratio u of the first and second supersaturated light absorbing layers 3 and 6 is in the range of 0.12 to 0.14. Shows the relationship between the layer thickness and the astigmatic difference.

FIG. 3 shows that if the thickness of the first and second supersaturated light absorbing layers 3 and 6 is 0.01 μm or more and the composition ratio u is 0.13 or less, the astigmatic difference of 17 μm or less is obtained. It can be seen that an astigmatic difference of 17 μm or less can be obtained when the composition ratio u is in the range of 0.14 or less at 0.02 μm or more.

Subsequently, FIG. 4 shows the first and second supersaturated light absorbing layers 3 and 6 in which the composition ratio u of the first and second supersaturated light absorbing layers 3 and 6 is in the range of 0.12 to 0.14. The relationship between the layer thickness and the operating current at a light output of 3 mW is shown.

FIG. 4 shows that when the composition ratio is 0.12 or more, the thickness of the first and second supersaturated light absorbing layers 3 and 6 is 0.0
32 μm or less, when the composition ratio is 0.13 or more, the layer thickness is 0.041 μm or less, and when the composition ratio is 0.14 or more, the layer thickness is 0.043 μm or less, and the operating current is 80 mA or less, which is practically no problem. It can be seen that the value is small.

As can be seen from FIGS. 2 to 4, the n-type Al _u Ga _1-u As first supersaturated light absorbing layer 3 and the p-type Al _u
Ga _1-u As second saturable light absorbing layer 6 is the Al _q Ga _1-q
The difference of the Al composition ratio with the As active layer 4 is -0.01 to 0.0
1 (ie, q-0.01 ≦ u ≦ q + 0.01; 0 ≦ u <
In the range of 1), it is a single transverse mode and γ
The value, astigmatism, and operating current value can all be in good ranges. The reason for such a good effect is that
The first and second supersaturated light-absorbing layers 3 and 6 have a bandgap energy of 0.04 in absolute value difference from the bandgap energy of the active layer 3, that is, the oscillation wavelength energy.
This is because the supersaturation state is good because the supersaturation state is equal to or less than 125 eV.

More specifically, the composition ratio q of the Al _q Ga _1-q As active layer 4 is not limited to 0.13, and even when the composition ratio q is selected from the range of 0 ≦ q <1, Al _u Ga _1-u. As the respective composition ratios u (0 ≦ u <) of the first and second supersaturated light absorbing layers 3 and 6
1) and the values S ₁ and S ₂ of each layer thickness can be selected from the range indicated by the hatched portion in FIG.
Both the astigmatic difference and the operating current value are better values than in the past.

In the above description, the thickness t ₁ of the second AlGaAs cladding layer 2 b and the third AlGaAs cladding layer 5 a
The thickness t ₂ but are both 0.3 [mu] m, the thickness t _1, t
_By changing both ₂ to the layer thickness t, the γ value (visibility),
The operating current value at the time of astigmatism and light output of 3 mW was examined. still,
Here, the composition ratio u and the layer thickness of the Al _u Ga _1-u As first and second supersaturated light absorbing layers 3 and 6 are both u = 0.13 and 0.0.
The composition ratio q of the Al _q Ga _{1 -q} As active layer 4 was 0.13.

FIG. 6 shows the layer thickness t and the γ value (visibility).
Shows the relationship. From this figure, the layer thickness t is 0.27 μm or more, the γ value is 0.7 or less, and the layer thickness is 0.28 μm
From the above, it can be seen that the γ value becomes 0.6 or less.

FIG. 7 shows the relationship between the layer thickness t and the astigmatic difference. From this figure, it can be seen that the astigmatism is 17 μm or less when the layer thickness t is 0.33 μm or less, and the astigmatism is 15 μm or less when the layer thickness t is 0.32 μm or less.

FIG. 8 shows the relationship between the layer thickness t and the operating current. From this figure, it can be seen that a particularly good value is obtained when the layer thickness t is 0.33 μm or less, and a remarkably good value is obtained when the layer thickness t is 0.32 μm or less.

Accordingly, the thickness t of the second AlGaAs cladding layer 2b and the third AlGaAs cladding layer 5a can be selected within the range of 0.27 μm or more and 0.33 μm or less, preferably within the range of 0.28 μm or more and 0.32 μm or less. Can be selected with. The second AlGaAs cladding layer 2b and the third AlGaAs cladding layer 5a have a thickness t.
Although the (0.27μm ≦ t ≦ 0.33μm), the layer thickness t _1, t ₂ is likewise effect can be obtained even if selected in 0.33 .mu.m or less the range of 0.27 [mu] m, in particular 0.28μ
A more desirable effect can be obtained when the selection is made in the range of m to 0.32 μm.

It is to be noted that the second AlGaAs cladding layer 2b and the second AlGaAs cladding layer 2b also have different composition ratios and thicknesses of the Al _u Ga _1-u As first and second supersaturated light absorbing layers 3 and 6 and the active layer 4. A favorable effect can be obtained by optimizing the thickness of the 3AlGaAs cladding layer 5a.

A method for manufacturing such a semiconductor laser device will be described with reference to FIG.

First, as shown in FIG. 9A, an n-type first AlGaAs cladding is formed on an n-type GaAs substrate 1 by metal organic chemical vapor deposition (MOCVD) or molecular beam epitaxy (MBE). Layer 2a, n-type Al _u G
a _1-u As first supersaturated light absorbing layer 3, n-type second AlGa
As cladding layer 2b, undoped Al _q Ga _1-q As active layer 4, p-type third AlGaAs cladding layer 5a, p-type Al _u Ga _1-u As second supersaturated light absorbing layer 6, p-type fourth A
The lGaAs cladding layer 5b and the p-type GaAs cap layer 7 are continuously grown in this order.

Next, as shown in FIG. 9B, a stripe-shaped SiO 2 layer having a thickness of 0.2 μm is formed on the p-type GaAs cap layer 7 by using a usual photolithography technique or the like.
_{2 A} mask layer 10 is formed. Using the SiO ₂ mask layer 10 as a mask, the p-type GaAs cap layer 7 and the p-type fourth AlGaAs such that the p-type fourth AlGaAs cladding layer 5b is left with a thickness of 0.1 to 0.3 μm using a phosphoric acid-based etchant. After etching the cladding layer 5b, the remaining cladding layer 5b is etched with a hydrochloric acid etching solution.
Is removed by etching to form a stripe-shaped ridge shape. Here, in the hydrochloric acid etching solution, Al _t Ga _1-t As having a small Al composition ratio is replaced with Al _s Ga having a large Al composition ratio.
_Since the etching rate is lower than that of _1-s As (t <s), the p-type Al _u Ga _1-u As second supersaturated light absorbing layer 6 is formed.
Has also a function as a so-called etching stop layer. Therefore, the etching can be stopped by the second supersaturated light absorbing layer 6 with good controllability.

Thereafter, as shown in FIG.
With the iO ₂ mask layer 10 interposed therebetween, the second supersaturated light absorption layer 6 and the side surfaces of the p-type GaAs cap layer 7 and the p-type fourth AlGaAs cladding layer 5 b forming the ridge portion are formed by MOCVD or MBE. The n-type GaAs current blocking layers 8 are formed.

[0037] Subsequently, as shown in FIG. 1, the SiO ₂
The mask layer 10 is removed with a hydrofluoric acid-based etching solution to remove the p layer.
After exposing the p-type GaAs cap layer 7, a p-type GaAs contact layer 9 is formed on the exposed p-type GaAs cap layer 7 and the n-type GaAs current blocking layers 8, 8 by MOCVD or MBE. Thereafter, the upper surface of the p-type GaAs contact layer 9 and the n-type GaAs substrate 1
A p-type ohmic electrode made of Au—Cr and an n-type ohmic electrode made of Au—Sn—Cr are respectively formed on the lower surface of the substrate.

As described above, the p-type Al _u Ga _1-u As
Since the second supersaturated light absorbing layer 6 has a band gap energy substantially equal to the oscillation wavelength energy, the (Al _t G
a _1-t As has a larger band gap and a smaller refractive index as its composition ratio t increases), and the fourth Al _yb Ga
_Since the Al composition ratio is smaller (u <yb) than the _1-yb As cladding layer 5b, the etching rate is slower than the cladding layer 5b, and a sufficient layer thickness is selected because excessive light absorption is not performed. it can. As a result, the second supersaturated light absorbing layer 6 sufficiently functions as an etching stop layer at the time of the mesa etching.
The layer thickness of the aAs cladding layer 5a can be made highly accurate.

In the above embodiment, the active layer 4 is made of Al _q G
Although the a _1-q As (0 ≦ q <1) layer was used, a quantum well structure may of course be used. Also in this case, if each composition ratio u is selected so that the bandgap energy of the first and second supersaturated light absorbing layers 3 and 6 becomes substantially equal to the oscillation wavelength energy, similarly, a low astigmatic difference at a low operating current, Good self-sustained pulsation occurs in the single transverse mode, and the second supersaturated light absorbing layer 6 has a higher Al thickness than the fourth AlGaAs cladding layer 5b.
The composition ratio is considerably small, and functions as an etching stop layer. The first and second AlGaAs cladding layers 2a,
2b, third and fourth AlGaAs cladding layers 5a, 5b
When (0 <xa, xb, ya, yb <1), the refractive index is smaller and the band gap is larger than that of the active layer 4 as in the above embodiment, that is, light and carriers having an oscillation wavelength can be sufficiently confined. To the extent possible, each layer thickness or each composition ratio is optimized.

The second supersaturated light absorbing layer 6 is not limited to the above-mentioned position, and the third and fourth AlGaAs cladding layers 5a, 5b
May be provided at an appropriate position in the layer 5a or the layer 5b by appropriately changing the layer thickness, and further, the absolute value difference from the oscillation wavelength energy is 0.0125 eV or less, and the band gap energy is substantially equal. The saturable light-absorbing layer has the same effect as provided on one of the cladding layers sandwiching the active layer and separated from the active layer by an appropriate distance. For example, the present invention is not limited to the ridge-type semiconductor laser device of the present embodiment. The present invention is also effective when used in a semiconductor laser device having another structure such as a self-aligned type. However, it is preferable to provide a saturable light absorbing layer on both sides of the active layer because the spot shape of the output laser light is more symmetric than providing a saturable light absorbing layer on only one of the active layers.

Further, the AlGaAs semiconductor laser device has been described above. However, other materials such as an AlGaInP-based semiconductor laser device may be provided with a supersaturated light absorbing layer having a band gap energy substantially equal to the oscillation wavelength energy in at least one cladding layer. A similar effect is obtained such as low astigmatism at low operating current and good self-sustained pulsation in single transverse mode.

The term "having a supersaturated light absorbing layer in the clad layer" as used in the present invention includes those provided on the upper or lower surface of the clad layer.

[0043]

According to the present invention, a saturable light absorbing layer having a band gap energy substantially equal to the oscillation wavelength energy is provided in at least one of the first and second cladding layers. At a sufficiently small operating current, good self-sustained pulsation occurs in the astigmatic difference and single transverse mode, which are much smaller than in the past. As a result, a return laser noise can be reduced, an optical system is easy, and a highly reliable semiconductor laser device can be obtained.

In particular, the first cladding layer comprises a first AlG
an aAs cladding layer and a second AlGaAs cladding layer, a first conductivity type Al _u Ga _1-u As first supersaturated light absorbing layer between the first and second AlGaAs cladding layers, and the second cladding layer is A third layer formed on the active layer;
An AlGaAs cladding layer and a fourth A layer forming a stripe-shaped ridge formed on the third AlGaAs cladding layer.
consists of a lGaAs cladding layer, since the formation of the second conductivity type Al _u Ga _1-u As second saturable light absorbing layer on the 3AlGaAs cladding layer, the Al _u Ga _1-u As second saturable light absorbing layer Is the fourth AlG in the form of a stripe ridge.
Since it also functions as an etching stop layer when forming an aAs cladding layer, there is an effect that the thickness of the third AlGaAs cladding layer on the active layer can be made with high precision.
As a result, a semiconductor laser device that is resistant to return light noise, has a simple optical system, and has high reliability can be easily formed with high yield.

[Brief description of the drawings]

FIG. 1 is a sectional view of a semiconductor laser device according to one embodiment of the present invention.

FIG. 2 is a diagram showing a relationship between a composition ratio u and a layer thickness of a saturable light absorbing layer of the above embodiment and a γ value.

FIG. 3 is a diagram showing a relationship between a composition ratio u and a layer thickness of the saturable light absorbing layer of the above embodiment and an astigmatic difference.

FIG. 4 is a diagram showing a relationship between a composition ratio u and a layer thickness of the saturable light absorbing layer and an operating current in the example.

FIG. 5 is a diagram showing a relationship between a composition ratio u and a layer thickness of a saturable light absorbing layer of the above example and good characteristics.

FIG. 6 is a diagram showing the relationship between the thickness t of the second and third AlGaAs cladding layers and the γ value in the above embodiment.

FIG. 7 is a diagram showing the relationship between the thickness t of the second and third AlGaAs cladding layers and the astigmatic difference in the above embodiment.

FIG. 8 is a diagram showing the relationship between the thickness t of the second and third AlGaAs cladding layers and the operating current in the above embodiment.

FIG. 9 is a view showing a manufacturing process of the semiconductor laser device of the embodiment.

[Explanation of symbols]

1 n-type GaAs substrate (semiconductor substrate) 2 first cladding layer 2a n-type first 1AlGaAs cladding layer 2b n-type first 2AlGaAs cladding layer 3 n-type Al _u Ga _1-u As first saturable light absorbing layer 4 active layer 5 second cladding layer 5a n-type first 1AlGaAs cladding layer 5b n-type first 2AlGaAs clad layer (ridge portion) 6 p-type Al _u Ga _1-u As second saturable light absorbing layer

Continued on the front page (72) Inventor Kotaro Furusawa 2-18-18 Keihanhondori, Moriguchi-shi, Osaka Sanyo Electric Co., Ltd. (72) Inventor Atsushi Tajiri 2--18 Keihanhondori, Moriguchi-shi, Osaka Sanyo Electric Co., Ltd. Within the company (72) Inventor Tohru Ishikawa 2--18 Keihanhondori, Moriguchi-shi, Osaka Sanyo Electric Co., Ltd. (72) Inventor Kenichi Matsukawa 2--18 Keihanhondori, Moriguchi-shi, Osaka Sanyo Electric Co., Ltd. (72) Inventor Teruaki Miyake 2-18-18 Keihanhondori, Moriguchi-shi, Osaka Sanyo Electric Co., Ltd. (72) Inventor Soken 2-18-18 Keihanhondori, Moriguchi-shi, Osaka Sanyo Electric Co., Ltd. 56) References JP-A-61-84891 (JP, A) JP-A-2-148784 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) H01S 5/00-5/50

Claims (2)

(57) [Claims] 1. A semiconductor substrate of a first conductivity type, a first cladding layer of a first conductivity type provided on the semiconductor substrate, an active layer provided on the first cladding layer, and The second provided
A second cladding layer of a conductive type, wherein the first and second cladding layers have a smaller refractive index and a larger bandgap than the active layer, and include at least one of the first and second cladding layers. A semiconductor laser device having a saturable light absorbing layer having a band gap of energy substantially equal to oscillation wavelength energy , wherein the first cladding layer
Is a first AlGaAs cladding layer and a second AlGaAs cladding layer.
And a first AlGaAs cladding layer.
A first conductivity type Al between the second AlGaAs cladding layer and the second AlGaAs cladding layer;
_u Ga _1-u As (0 ≦ u <1) having a first saturable light absorbing layer
And the second cladding layer is formed on the active layer.
The third AlGaAs cladding layer and the third AlGaAs cladding layer.
The stripe-shaped ridge formed on the lad layer
4AlGaAs cladding layer, the third AlG
Al _u Ga _1-u As the second conductivity type aAs cladding layer
(0 ≦ u <1) The second supersaturated light absorbing layer is formed.
Semiconductor laser element according to symptoms. 2. The method according to claim 1, wherein the active layer is formed of Al _q Ga _{1 -q} As (0 ≦ q
<1) Each of the first and second supersaturated light absorbing layers
The composition ratio u is in the range of q−0.01 ≦ u ≦ q + 0.01.
2. The semiconductor laser device according to claim 1, wherein said semiconductor laser device is selected.