JP2010021342A - Semiconductor laser device - Google Patents

Abstract

A semiconductor laser device made of a group III nitride having stable self-excited oscillation characteristics that can be sufficiently used as a light source of a reproducing optical disk system is realized.
A semiconductor laser device is formed on the substrate _11, the n-type cladding layer 13 made of Al x _{Ga 1-x} N, the MQW active layer 15 formed on the n-type cladding layer 13, A p-type cladding layer 19 formed on the MQW active layer 15 and made of Al _y Ga _1-y N, a p-type contact layer 20 formed on the p-type cladding layer 19, a substrate 11, and an n-type cladding The n-type antireflection layer 12 made of Al _z Ga _1-z N is formed between the layers 13. The Al composition x in the n-type cladding layer 13, the Al composition y in the p-type cladding layer 19, and the Al composition z in the n-type antireflection layer 12 satisfy the relationship x <z and y <z.
[Selection] Figure 9

Description

  The present invention relates to a semiconductor laser device, and more particularly to a self-excited oscillation type semiconductor laser device.

  2. Description of the Related Art In recent years, semiconductor laser devices are frequently used as optical pickup light sources used in optical recording devices and optical reading devices for recording media such as optical disks and magneto-optical recording disks. The optical disk market continues to expand, with a wide range of applications such as recorders, PCs, and in-vehicle use. Recently, among the next generation DVD (Digital Versatile Disc) using a group III nitride semiconductor having a blue-violet emission wavelength, that is, a so-called gallium nitride semiconductor (AlGaInN) laser device, the Blu-ray market has started up rapidly. ing. Among them, the proportion of the next-generation DVD dedicated to reproduction is high, and research and development of a blue-violet semiconductor laser device for in-vehicle use is underway.

  By the way, a low noise characteristic is mentioned as a characteristic calculated | required by the semiconductor laser apparatus used as the light source of an optical pick-up apparatus.

  Hereinafter, noise generation factors in the semiconductor laser device will be described.

  When a semiconductor laser device is used as an optical pickup light source, reflected light from an optical disk or an optical recording medium and an optical system member is fed back to the semiconductor laser device. In this case, when the coherence of the laser light is high, the light in the resonator and the reflected light in the semiconductor laser device interfere with each other, resulting in noise in the output of the semiconductor laser device. I know that. In order to reduce the coherence of this laser beam, it is effective to oscillate the oscillation spectrum in the semiconductor laser device in a multimode.

For example, as a solution for noise caused by incident light, (1) a semiconductor laser device is modulated using a high-frequency superposition circuit, and the oscillation spectrum is converted into a multimode. (2) A method of making the oscillation spectrum into a multimode is known by using a semiconductor laser device as a self-excited oscillation (pulse oscillation) type laser device.
(1) The method of modulating a semiconductor laser device with a high-frequency superposition circuit is disadvantageous in terms of downsizing and cost of the optical pickup device because the number of components increases because a high-frequency superposition module is used. Moreover, there is a possibility that malfunction of other electronic devices may occur due to unnecessary radiation from the high frequency superimposing circuit.
(2) As a method for converting the oscillation spectrum into a multimode without using a high frequency superposition circuit, there is a method in which a saturable absorber is formed in a waveguide of a semiconductor laser device to cause self-excited oscillation. As a result, the oscillation intensity due to laser oscillation periodically changes in a pulsed manner over time. As a result, the oscillation spectrum becomes multimode, so that the coherence of the laser beam is reduced. In such a semiconductor laser device with reduced coherence, even if the reflected light from the optical disk returns to the semiconductor laser device, the emitted light from the laser device and the return light from the reflection do not cause interference, and noise is generated. Therefore, data read errors can be prevented. In addition, since the semiconductor laser device itself is in a pulse oscillation state, there is no need to provide additional components such as a high-frequency superposition circuit, so that it is possible to reduce the size, weight, and cost, and to prevent unnecessary radiation. Have

Patent document 1 is known as such a self-excited oscillation type semiconductor laser device. Here, the number of well layers in the active layer is 2 to 4, the thickness is 10 nm or less, and the Al composition in the cladding layer made of Al _x Ga _1-x N is 0 ≦ x ≦ 0.3. Thus, it is described that a blue-violet laser device that realizes stable self-excited oscillation can be obtained.
JP-A-11-214788

  However, the conventional self-pulsation type semiconductor laser device using the group III nitride semiconductor has the following problems.

  First, Group III nitride semiconductors have a higher differential modal gain than AlGaAs and AlGaInP materials that make up the active layer of infrared laser devices and red laser devices. The information on the optical disk may be rewritten even during the light output operation during reproduction. Here, the differential modal gain is the product of the differential gain of the active layer (change in gain relative to the operating carrier density) and the optical confinement coefficient in the active layer. The larger this value, the easier the laser to oscillate at a lower injected carrier density. It can be said that it is a device. However, when the differential modal gain is large, when the saturable absorber becomes transparent with respect to the laser beam due to the saturable absorption effect, the light output increases rapidly with time, and the pulse of light due to self-excited oscillation is increased. Since the peak power intensity is high, the information on the optical disc is rewritten even by the operating light output during reproduction.

  FIG. 13 shows differential modal gains of a self-excited oscillation type infrared laser device, a red laser device, and a blue-violet laser device that have been conventionally reported. As can be seen from FIG. 13, the differential modal gain increases in the order of the infrared laser device, the red laser device, and the blue-violet laser device, and the blue-violet laser device tends to have high peak power intensity during self-excited oscillation. .

  FIG. 14A and FIG. 14B show the time response characteristics of the light output during the self-oscillation of the conventional blue-violet laser device and the red laser device. In the red laser device shown in FIG. 14B, the value of the ratio between the peak power intensity and the average output is 5.3 times, whereas in the blue-violet laser device shown in FIG. The peak power intensity of the optical pulse is higher than the average output, and the value of the ratio between the peak power intensity and the average output is 8.1 times. Here, it has been found that when the peak power intensity is 7 times or more of the average output, the information on the optical disk may be rewritten. Therefore, the value of the ratio between the peak intensity and the average output needs to be set to 7 times or less.

  A self-pulsation type laser device using a group III nitride semiconductor has a high differential modal gain, so that an optical disk can be rewritten with a high peak power intensity even during reproduction, while the effective mass of holes is large. Due to the above, there is a problem that the oscillation threshold value becomes large. An increase in the oscillation threshold causes a deterioration in temperature characteristics, leading to a decrease in reliability.

  Therefore, if the differential modal gain is increased, the peak intensity of the self-excited oscillation light increases, and the information on the optical disk may be rewritten during the reproducing operation. On the other hand, if the differential modal gain is reduced in order to suppress the peak power intensity of light, the oscillation threshold increases, leading to a decrease in reliability. For this reason, an optimum differential modal gain is required that suppresses the peak power intensity and does not increase the oscillation threshold.

  Furthermore, in addition to noise characteristic deterioration due to reflected light, gallium nitride (GaN), which is a substrate for crystal growth of a blue-violet laser device (laser chip), is transparent to the oscillation wavelength, and thus absorbs laser light. Compared with an infrared laser device or a red laser device using a substrate, there is more reflected light from the substrate. In addition, spontaneous emission light or scattered laser light is often generated at the interface between the GaN substrate and the cladding layer, so-called stray light inside the chip.

  As can be seen from the current (Iop) -light output (Po) characteristics in the conventional blue-violet laser device, infrared laser device, and red laser device shown in FIG. The violet laser device has more stray light than the infrared laser device and the red laser device. When stray light is absorbed by the active layer, the light output fluctuates, resulting in a high noise level and an increase in relative intensity noise (RIN: Relativistic Intensity Noise). In order to avoid this, in the blue-violet laser device, a measure is taken to make the light output during reproduction higher than that of the red laser device and the infrared laser device, and relatively reduce the contribution of spontaneous emission light. Yes. In general, the light output of the red laser device and the infrared laser device is 5 mW, whereas the blue-violet laser device requires 10 mW or more. When the light output exceeds 10 mW, the self-excited oscillation stops and the oscillation spectrum is single. It becomes a mode.

  Thus, in the blue-violet self-oscillation laser device, it is necessary to suppress the amount of stray light to realize low noise characteristics and to maintain self-oscillation even under a high output of 10 mW or more.

  As described above, when the well layer generally used has a thickness of 10 nm or less and the number of layers is 2 to 4, due to the high differential modal gain, the optical disc with high peak power intensity during self-excited oscillation is used. Rewriting occurs. In addition, since the gain necessary for laser oscillation is insufficient, there arises a problem that the oscillation threshold is increased.

  Furthermore, even if self-excited oscillation occurs, there is a problem that the amount of stray light is large and noise characteristics are deteriorated.

In addition, when the Al composition of the cladding layer made of Al _x Ga _1-x N is relatively high (0.1 <x ≦ 0.3), cracks are generated in the cladding layer, reducing reliability. At the same time, it causes problems.

  An object of the present invention is to solve the above-mentioned conventional problems, and to realize a semiconductor laser device made of a group III nitride having stable self-excited oscillation characteristics that can be sufficiently used as a light source for a reproducing optical disk system. Objective.

  In order to achieve the above object, the present invention provides a semiconductor laser device in which a reflection is made of aluminum gallium nitride (AlGaN) having a higher aluminum composition than a first cladding layer close to the substrate and a second cladding layer far from the substrate. The suppression layer is configured to be formed between at least one of the substrate and the first cladding layer and between the second cladding layer and the contact layer.

Specifically, the semiconductor laser device according to the present invention is formed on a substrate and formed on a first clad layer of the first conductivity type made of Al _x Ga _1-x N and the first clad layer. Active layer formed on the active layer, a second conductivity type second clad layer made of Al _y Ga _1-y N, and a second conductivity type formed on the second clad layer And a reflection suppression layer made of Al _z Ga _1-z N and formed between at least one of the substrate and the first cladding layer and between the second cladding layer and the contact layer, The Al composition x in the first cladding layer, the Al composition y in the second cladding layer, and the Al composition z in the reflection suppression layer satisfy the relationship x <z and y <z.

According to the semiconductor laser device of the present invention, the reflection suppression layer formed of Al _z Ga _1-z N is formed between at least one of the substrate and the first cladding layer and between the second cladding layer and the contact layer. The Al composition x in the first cladding layer, the Al composition y in the second cladding layer, and the Al composition z in the antireflection layer satisfy the relationship of x <z and y <z. Alternatively, the spread of light distribution to the contact layer can be suppressed. Thereby, it is possible to prevent stray light reflected from the substrate or the contact layer from being reabsorbed by the active layer and increasing noise. Further, since the reflection suppression layer made of Al _z Ga _1-z N having a higher Al composition than each cladding layer is lower than the refractive index of each cladding layer, the reflection suppression layer having a low refractive index is at least one of the cladding layers. Therefore, the optical confinement factor to the active layer that can realize the self-excited characteristic can be improved.

  In the semiconductor laser device of the present invention, the Al composition x in the first cladding layer is 0.03 ≦ x ≦ 0.1, and the Al composition y in the second cladding layer is 0.03 ≦ y ≦ 0. 1, the Al composition z in the reflection suppression layer is 0.1 <z ≦ 0.3, and the thickness of the reflection suppression layer is preferably 5 nm or more and 15 nm or less.

In this way, it is possible to sufficiently secure light confinement in the active layer necessary for self-oscillation, and to suppress cracks generated in the semiconductor layer, so that a highly reliable semiconductor laser device can be obtained. Further, by setting the Al composition in the reflection suppression layer to 0.1 <z ≦ 0.3 and the film thickness to be 5 nm or more and 15 nm or less, the spread of the light distribution to the substrate or the contact layer can be sufficiently attenuated. Therefore, generation of stray light can be suppressed and increase in noise can be prevented. Furthermore, the light confinement efficiency in the active layer that can realize the self-excited oscillation characteristic can be improved. As a result, a self-excited oscillation type semiconductor laser device having low noise characteristics can be obtained. In addition, by making the Al composition and the film thickness in the reflection suppression layer within a predetermined range, it is possible to suppress the occurrence of cracks due to the stress caused by lattice mismatch, without reducing the reliability, In the semiconductor laser device of the present invention capable of realizing a desired operating characteristic, the second cladding layer has a stripe portion formed thereon and into which current is selectively injected. A current blocking layer is preferably formed on the side of the stripe portion.

  In this case, the current blocking layer is preferably made of a dielectric material or a semiconductor material.

  In this case, when the current blocking layer is formed of a dielectric material, the process of epitaxially growing the nitride semiconductor layer can be simplified, and the manufacturing cost can be reduced. On the other hand, when the current blocking layer is formed of a semiconductor material, since the In composition or Al composition of the nitride semiconductor can be adjusted, a desired refractive index can be set, so that the degree of design freedom is improved. The material constituting the current blocking layer may be a material that is substantially transparent to light having an oscillation wavelength or a material that absorbs the light. When a transparent material is used for the current blocking layer, light loss in the current blocking layer is reduced, so that slope efficiency is improved and temperature characteristics are improved. When an absorbing material is used for the current blocking layer, light absorption occurs in the current blocking layer, thereby suppressing stray light inside the chip and stabilizing the shape of the light divergence angle.

  In the semiconductor laser device of the present invention, the active layer is a quantum well active layer formed by alternately stacking quantum well layers and barrier layers, the number of well layers is 5, and the thickness of the well layer is 2 nm. The thickness is preferably 4 nm or less.

  In this way, it is possible to obtain a peak power intensity that does not rewrite information on the optical disk and to form a sufficient saturable absorber inside the active layer. Therefore, during a light output operation of 10 mW or more In addition, stable self-excited oscillation can be obtained, and an optimum differential modal gain with a sufficiently small oscillation threshold can be obtained.

  In the semiconductor laser device of the present invention, the active layer is formed of a quantum well active layer in which quantum well layers and barrier layers are alternately stacked, the number of well layers is 6, and the thickness of the well layer is 0. It is preferably 8 nm or more and 2.5 nm or less.

  In this way, the peak power intensity is suppressed, and a saturable absorption layer necessary for self-oscillation can be sufficiently formed inside the active layer. Therefore, self-excited oscillation is possible even during a high output operation of 10 mW or more, and a low oscillation threshold can be realized.

  In the semiconductor laser device of the present invention, the active layer is formed of a quantum well active layer in which quantum well layers and barrier layers are alternately stacked, the number of well layers is 7, and the thickness of the well layer is 0. It is preferably 4 nm or more and 1.5 nm or less.

  In this way, the amount of indium (In) added to the well layer becomes relatively large, and In segregation occurs spatially. When the In composition is high, the band gap energy is locally reduced, and therefore, absorption occurs at the oscillation wavelength, so that In segregation easily forms a saturable absorber. In addition, since the number of well layers is as large as seven, a saturable absorber formed in the active layer can be secured.

  With the above configuration, a stable self-oscillation can be obtained even during a high output operation of 10 mW or more. In addition, according to the present invention, since the value of the ratio between the peak power intensity and the average output is 7 times or less, the optical disk is not rewritten, and the oscillation threshold is lowered because the well layer is thin. it can.

  According to the semiconductor laser device of the present invention, since the differential modal gain and the generation of stray light can be controlled, the self-excited oscillation characteristic with an optical output of 10 mW or more can be obtained, and the intensity of the self-excited peak power can be suppressed. Furthermore, a semiconductor laser device having excellent noise characteristics can be realized.

  In the invention of the present application, the inventors of the present invention conducted a detailed study as follows to solve the above-described problems in the prior art.

  As shown in FIG. 1, a group III nitride semiconductor laser device according to a prototype of the present invention includes an n-type cladding layer 102 made of AlGaN and a p-type cladding formed on a substrate 101 made of n-type GaN, for example. A multi-quantum well active layer 103 made of InGaN sandwiched between layers 104 is provided.

  A ridge stripe portion 150 is formed on the p-type cladding layer 104, and a p-type contact layer 105 is formed on the ridge stripe portion 150. In addition, current blocking layers 106 are formed on both sides of the ridge stripe 150 and on both sides. Note that a current passing through the ridge stripe 150 is injected into the multiple quantum well active layer 103 to emit light.

  In this prototype, the clad layers 102 and 104 have three Al compositions of 0.02, 0.07, and 0.12, respectively, and the number of well layers in the multiple quantum well active layer 103 is 1 w, A total of nine laser devices were fabricated with 3 wells, 3w, 5w, 7w, and 9w, and three well layers with thicknesses of 1 nm, 3 nm, and 5 nm, and their characteristics were confirmed. The result is shown in FIG.

  As can be seen from FIG. 2, the thickness of the well layer 1w and the like and the Al compositions of the cladding layers 102 and 104 cause laser oscillation without self-excited oscillation and laser oscillation with self-excited oscillation, respectively. As a result, a laser device and a laser device having a high oscillation threshold and not causing laser oscillation were obtained. It has been confirmed that the self-excited laser device generates self-excited oscillation even when the optical output exceeds 10 mW. Further, when the intensity of the oscillation peak power was measured, the laser device in which the Al composition of the cladding layer was 0.07 and the thickness of the well layer was 5 nm had a ratio value of the oscillation peak intensity to the average output value of 8. As a result, the laser device in which the Al composition of the cladding layer is 0.07 and the film thickness of the well layer is 3 nm is 6.3 times the value of the ratio between the oscillation peak intensity and the average output value. Have gained.

  In order to elucidate this phenomenon, the present inventor calculated the differential modal gain by paying attention to the gain and loss of the multiple quantum well active layer and the optical confinement coefficient in the multiple quantum well active layer. The result is shown in FIG. The following can be confirmed from the prototype result (symbol 結果) and the calculation result.

  First, as can be seen from FIG. 3, the laser device having a well layer thickness of 1 nm did not cause laser oscillation because the well layer has a small thickness, so that the differential modal gain necessary for laser oscillation is low. This is thought to be because there was not enough. The reason for laser oscillation without reaching self-excited oscillation is that although a differential modal gain necessary for oscillation is obtained, a differential modal gain sufficient to cause self-excited oscillation cannot be obtained. Even if the thickness of the well layer is 1 nm, it is possible to increase the optical confinement factor in the active layer if the Al composition of the cladding layer is 0.12. For this reason, although a differential modal gain that causes self-excited oscillation is obtained, when the Al composition exceeds 0.1, the lattice mismatch with the substrate 101 increases, and the clad layers 102 and 104 are caused by the stress generated by the lattice mismatch. Since cracks occur, the reliability decreases.

  Next, in the laser device in which the Al composition of the cladding layer was 0.02 and the thickness of the well layer was 3 nm or 5 nm, although the self-excited oscillation occurred, the temperature characteristics deteriorated. This is presumably because when the Al composition is 0.02, the band gap difference between the active layer and the cladding layer is small, and carriers are not effectively confined in the active layer, so that the temperature characteristics are deteriorated.

  Next, a laser device in which the Al composition of the cladding layer is 0.07 and the thickness of the well layer is 3 nm or 5 nm will be described. Although these laser devices can obtain self-oscillation, the laser device having a well layer thickness of 5 nm has a self-oscillation peak intensity enough to rewrite information on the optical disk with the reproduction power (10 mW). . This is because the differential modal gain is too large, and it is necessary to optimize the differential modal gain in order to achieve an appropriate self-excited oscillation peak intensity.

From the above experiments and calculation results, in order to realize self-oscillation and suppress the self-oscillation peak intensity, the Al composition of the cladding layer and the thickness and number of layers of the active layer are optimized, and the active layer It has been found that it is necessary to design a waveguide structure that can control the gain and loss of light and the optical confinement factor in the active layer to obtain a desired differential modal gain. The desirable range is that the differential modal gain is 1.5 × 10 ⁻¹⁷ cm ² or more and 2.4 × 10 ⁻¹⁷ cm ² or less, and in order to realize this, in the case where there are five well layers, The film thickness is 2 nm or more and 4 nm or less, and the Al composition of the cladding layer is 0.03 or more and 0.1 or less.

  Similarly, the calculation results of the differential modal gain when the Al composition of the cladding layer made of AlGaN is 0, 0.05 and 0.1, respectively, and the number of well layers in the active layer is 6 or 7 are shown in FIG. And shown in FIG.

  The reason why the differential modal gain increases by increasing the thickness of the well layer is that the gain of the active layer increases as the thickness of the well layer increases. However, as can be seen from FIG. 4 and FIG. 5, the self-excited peak power intensity is large, the laser oscillation that does not lead to self-excited oscillation and the oscillation threshold value are large, so that laser oscillation does not occur, and the temperature characteristics deteriorate. In consideration of such problems, the range in which the optimum self-excited oscillation can be realized is that when the number of well layers is 6, the thickness of the well layers is 0.8 nm or more and 2.5 nm or less. It was found that when the number of well layers was 7, the thickness of the well layers was 0.4 nm or more and 1.5 nm or less.

Next, the semiconductor laser device for trial with the configuration of FIG. 1, the Al composition than the n-type cladding layer 102 is high _Al z _{Ga 1-z} N layer between the substrate 101 and the n-type cladding layer 102 The contribution to noise characteristics was studied. Here, the Al _z Ga _1-z N layer has an Al composition of 0.3 and a thickness of 10 nm.

FIG. 6 shows the results of noise characteristics (RIN characteristics) with and without the Al _z Ga _1-z N layer. As can be seen from FIG. 6, by providing the Al _z Ga _1-z N layer, an improvement of about 3 dB / Hz can be seen at a light output of 10 mW.

In considering this, it was confirmed by the near field pattern (NFP) how the light distribution changed depending on the presence or absence of the Al _z Ga _1-z N layer. The result is shown in FIG. As can be seen from FIG. 7, when the Al _z Ga _1-z N layer is not provided, the bottom of the light distribution on the substrate side vibrates. This vibration is caused by the stray light reflected from the substrate 101, and the presence of this stray light causes the noise characteristics to deteriorate. On the other hand, when the Al _z Ga _1-z N layer is provided, the light distribution on the substrate side is rapidly attenuated. Thus, Al z _Ga 1-z _N layer having a higher Al composition than that of the clad layer, it is confirmed that the effect as the antireflection layer.

From the above results, the reflection suppressing layer made of Al _z Ga _1-z N was formed between the substrate 101 and the n-type cladding layer 102 to suppress the spread of the light distribution to the substrate 101, whereby the substrate 101 It is considered that the stray light reflected from the light is not reabsorbed by the active layer 103, and as a result, the RIN characteristics are improved. Further, it has been newly found that there is an effect of improving the optical confinement coefficient in the active layer 103 that can realize the self-excited oscillation characteristic.

_Moreover, when provided with the antireflection layer made of Al z _{Ga 1-z} N only between the p-type cladding layer 104 and the p-type contact layer 105, and further in between the substrate 101 and the n-type cladding layer 102 The improvement of the RIN characteristic is also confirmed in the case where it is provided.

Note that when the Al composition of the Al _z Ga _1-z N layer is 0.1 or less, the RIN characteristics are deteriorated. This is because when the Al composition of the Al _z Ga _1-z N layer is smaller than 0.1, the refractive index of the Al _z Ga _1-z N layer is larger than that of the cladding layer, and the reflection from the cladding layer This is because light is reflected at the interface with the suppression layer and the amount of stray light increases.

Thus, for example, by providing a reflection suppressing layer made of Al _z Ga _1-z N having an Al composition higher than that of the n-type cladding layer 102 between the substrate 101 and the n-type cladding layer 102, reflection from the substrate 101 is performed. The generation of stray light is suppressed, the RIN characteristic is improved and the self-excited oscillation characteristic is improved. However, like the Al composition of the n-type cladding layer 102, if the Al composition of the reflection suppression layer becomes too high or too thick, cracks will occur in the reflection suppression layer. Therefore, studies were made to obtain preferable values of the Al composition and thickness of the Al _z Ga _1-z N layer that does not cause cracks in the antireflection layer. The result is shown in FIG. As can be seen from FIG. 8, cracks tend to occur when the Al composition of the Al _z Ga _1-z N layer increases or becomes thicker.

More specifically, if the thickness of the reflection suppressing layer made of Al _z Ga _1-z N is smaller than 5 nm or the Al composition is smaller than 0.1, the spread of light distribution cannot be suppressed, and stray light is generated. As a result, the RIN characteristic is deteriorated. On the other hand, if the thickness of the reflection suppression layer is greater than 15 nm or the Al composition is greater than 0.3, cracks may occur in the reflection suppression layer, so that the Al composition is 0.1 <z ≦ 0.3. The thickness is preferably 5 nm or more and 15 nm or less.

  When a semiconductor laser device was fabricated and evaluated using a reflection suppressing layer in this range, good results were obtained with self-excited oscillation characteristics and RIN characteristics, and it was confirmed that the semiconductor laser apparatus was practical.

  Hereinafter, embodiments will be described as specific examples.

(First embodiment)
A semiconductor laser device according to a first embodiment of the present invention will be described with reference to the drawings.

  FIG. 9 shows a cross-sectional configuration of the semiconductor laser device according to the first embodiment of the present invention.

9, the semiconductor laser device according to the first embodiment, for example, n-type successively epitaxially grown on a substrate 11 of gallium nitride (GaN) and becomes to a thickness of 10nm of the n-type Al _{0 .15} Ga _0.85 N n-type antireflection layer 12, 2.5 μm thick n-type Al _0.05 Ga _0.95 N clad layer 13, and 90 nm thick Al _A guide layer 14 made of _0.003 Ga _0.997 N, a multiple quantum well (MQW) active layer 15 made of InGaN, and a first intermediate layer 16 made of In _0.02 Ga _0.98 N having a thickness of 35 nm. A second intermediate layer 17 made of In slightly doped GaN with a thickness of 65 nm, an overflow suppression (OFS) layer 18 made of Al _0.2 Ga _0.8 N with a thickness of 20 nm, and a thickness of 480 nm p A p-type cladding layer 19 made of p-type Al _0.05 Ga _0.95 N and a p-type contact layer 20 made of p-type GaN having a thickness of 50 nm are provided.

Here, the MQW active layer 15 has five barrier layers 0b, 2b,..., 8b made of In _0.02 Ga _0.98 N each having a thickness of 7.5 nm, and each having a thickness of 2.5 nm. an in _0.05 Ga _0.95 consisting N 5 well layer 1w, 3w, ..., and 9w are formed by stacking alternately.

A ridge stripe portion 50 including the p-type contact layer 20 is formed on the p-type cladding layer 19. The areas of both sides and on both sides of the ridge stripe portion 50, for example, the current blocking layer 21 thickness is from 400nm silicon oxide (SiO ₂₎ is formed. Here, the stripe width W of the ridge stripe portion 50 is 1.4 μm. The distance (remaining thickness) dp from the lower surface of the current blocking layer 21, that is, the lower surface of the ridge stripe portion 50 to the upper surface of the MQW active layer 15 is 160 nm. Although not shown, a p-side electrode is formed from above the p-type contact layer 20 to the current blocking layer 21, and an n-side electrode is formed on the surface of the substrate 11 opposite to the n-type antireflection layer 12. Is formed.

In the present invention, the main surface of the substrate 11 made of n-type GaN may be an a-plane, r-plane, or m-plane, and may have another plane orientation. The substrate 11 is not limited to GaN, and sapphire (single crystal Al ₂ O ₃ ), silicon carbide (SiC), or silicon (Si) can be used.

Further, the n-type antireflection layer 12 according to the first embodiment, the thickness was used n-type _Al 0.15 _{Ga 0.85} N of 10 nm, Al composition and thickness are an example. As described above, the Al composition in Al _z Ga _1-z N is set to 0.1 <z ≦ 0.3, and the thickness is set to 5 nm or more and 15 nm or less, so that cracks in the n-type antireflection layer 12 are reduced. Generation | occurrence | production can be prevented and the spread of the light distribution to the board | substrate 11 can also be suppressed. As a result, stray light reflected from the substrate 11 can be prevented from being reabsorbed by the MQW active layer 15 and the RIN characteristics can be improved.

Further, the n-type antireflection layer 12 made of n-type Al _0.15 Ga _0.85 N is formed between the substrate 11 and the n-type cladding layer 13, so that the generated light is transferred to the MQW active layer 15. There is also an effect of effectively confining, and self-excited oscillation characteristics can be realized even during a high output operation of 10 mW.

In the n-type cladding layer 13 made of n-type Al _0.05 Ga _0.95 N having a thickness of 2.5 μm and the p-type cladding layer 19 made of p-type Al _0.05 Ga _0.95 N having a thickness of 480 nm. However, the Al composition and its thickness are not limited to this. For example, by setting the Al composition in Al _x Ga _1-x N and Al _y Ga _1-y N to 0.03 ≦ x ≦ 0.1 and 0.03 ≦ y ≦ 0.1, respectively, the MQW active layer 15 can sufficiently secure the light confinement effect necessary for the self-excited oscillation. In addition, it is possible to suppress a crack generated in each of the cladding layers 13 and 19 and manufacture a highly reliable laser device.

  The thicknesses of the clad layers 13 and 19 may be appropriately changed in consideration of a desired light confinement effect and light distribution (expansion angle). Further, the Al compositions of the n-type cladding layer 13 and the p-type cladding layer 19 are not symmetrical (x = y), and may be different such that x> y or x <y. For example, in the case of x> y, since the light distribution is closer to the substrate side, absorption by the p-side electrode is eliminated, so that a light loss is reduced and a laser device having excellent temperature characteristics can be obtained. Conversely, when x <y, the light distribution is on the p-side electrode side, so that the light confinement effect in the horizontal direction (direction parallel to the substrate surface) can be further enhanced.

  Thereby, there is an effect that the light output level of bending (kink), which is a phenomenon in which nonlinearity in the current-light output characteristics occurs, is improved, and the divergence angle is stabilized.

  Each of the cladding layers 13 and 19 may have a superlattice structure in which, for example, AlGaN / AlGaN or AlGaN / GaN having different compositions are stacked in multiple layers. In this case, the average Al composition may be within the ranges of 0.03 ≦ x ≦ 0.1 and 0.03 ≦ y ≦ 0.1. Thus, the operating voltage can be reduced by making each of the cladding layers 13 and 19 have a superlattice structure.

The energy gap of the guide layer 14 made of Al _0.003 Ga _0.997 N, the first intermediate layer 16 made of In _0.02 Ga _0.98 N, and the second intermediate layer 17 made of In slightly-doped GaN is MQW. As long as the material has a value between the energy gap of the well layer 1w constituting the active layer 15 and the energy gap of the clad layers 13 and 19, the material may not be AlGaN and InGaN. The guide layer 14, the first intermediate layer 16, and the second intermediate layer 17 are appropriately selected in consideration of not only the Al composition or In composition but also the film thickness of the desired light confinement effect and light distribution (expansion angle). It may be changed. Furthermore, the guide layer 14 and the intermediate layers 16 and 17 may be doped with donors or acceptors in all or part thereof. As a result, the carrier concentration increases, and the oscillation threshold and the operating voltage can be reduced.

Each InW of the barrier layer made of In _0.02 Ga _0.98 N with a thickness of 7.5 nm and the well layer made of In _0.05 Ga _0.95 N with a thickness of 2.5 nm in the MQW active layer 15. What is necessary is just to set the composition and each thickness according to a desired laser oscillation wavelength. For example, when the number of the well layers 1w and the like is 5, the thickness of the well layers 1w and the like needs to be set to 2 nm or more and 4 nm or less, respectively. In this way, the peak power intensity can be set so as not to rewrite the information on the optical disc, and self-oscillation is possible even during an optical output operation of 10 mW or more. Furthermore, an optimum differential modal gain with a sufficiently small oscillation threshold can be obtained. Note that GaN may be used in place of InGaN for the barrier layer in the MQW active layer 15.

The overflow suppression (OFS) layer 18 made of Al _0.2 Ga _0.8 N having a thickness of 20 nm may not have this Al composition and thickness. When the Al composition of the OFS layer 18 is low or the thickness is small, the mobility of carriers increases, so that the resistance of the laser device can be reduced. On the other hand, when the Al composition is high or the thickness is large, the probability of electrons jumping over the OFS layer 18 is reduced, and the electrons effectively contribute to light emission, so that the internal quantum efficiency is improved. Also, the OFS layer 18 may be doped with Mg, which is a p-type dopant, so that holes are easily injected from the p-type cladding layer 19.

  Although the stripe width in the ridge stripe portion 50 is 1.4 μm, there is no problem if it is 0.7 μm or more and 2.5 μm or less. For example, if the stripe width is 0.7 μm or less, the operating voltage increases. Further, the value of 2.5 μm of the stripe width is a limit for maintaining various characteristics such as a kink level and a unimodal divergent shape.

  Further, the ridge stripe portion 50 may have a tapered stripe shape in which the upper width is smaller than the lower width. By adopting the taper stripe shape, injected carriers can be used efficiently, so that various characteristics such as improvement of temperature characteristics and kink level, reduction of operating voltage, and promotion of self-excited oscillation can be achieved. Further, the remaining thickness dp of the p-type cladding layer 19 is not limited to 160 nm, and may be set to a value that can realize desired characteristics such as a kink level and a divergence angle.

The thickness of the current blocking layer 21 is not limited to 400 nm. Also, the material can be a dielectric material such as silicon nitride (SiN) or amorphous silicon (α-Si), or a semiconductor material such as InGaN or AlGaN, instead of SiO ₂ .

  When the current blocking layer 21 is formed of a dielectric material, the number of times of epitaxial growth when growing an epitaxial layer made of a nitride semiconductor can be reduced, so that the manufacturing cost is reduced. Further, when the current blocking layer 21 is formed of a nitride semiconductor material, a desired refractive index can be set by changing the In composition and the Al composition at the time of forming the current blocking layer 21, so that the degree of freedom in design is improved.

  The current blocking layer 21 may be made of a material that is substantially transparent to light having an oscillation wavelength, and may be a material that absorbs light having an oscillation wavelength. When a transparent material is used for the current blocking layer 21, since the loss in the current blocking layer 21 is reduced, the slope efficiency is improved and the temperature characteristics are improved. On the other hand, when an absorbing material is used for the current blocking layer 21, stray light in the semiconductor laser device (chip) can be suppressed by absorbing light in the current blocking layer 21, and the light spreading angle shape can be reduced. Stabilize.

  Furthermore, the current blocking layer 21 may be a laminated structure in which two or more layers are laminated instead of a single layer. When laminating two or more layers, it is possible to improve various characteristics of the operation of the semiconductor laser device by combining a material that is transparent to light having an oscillation wavelength and a material that can be absorbed to take advantage of both features. In addition, the degree of freedom in design can be improved.

  Hereinafter, various characteristics of the operation of the semiconductor laser device according to the first embodiment will be described.

  10A shows the wavelength characteristics when the output is 10 mW, FIG. 10B shows the oscillation response characteristics (oscillation peak power intensity), and FIG. 10C shows the RIN characteristics.

  From FIG. 10A, it can be seen that the oscillation spectrum is multi-moded and self-oscillated because the wavelength width is widening around the oscillation wavelength of 401.5 nm. FIG. 10B shows that the oscillation peak power intensity is 5.8 times the average output value, and is suppressed to 7 times or less. Furthermore, FIG. 10C shows that the RIN characteristic when the output is 10 mW is about −130 dB / Hz, and a good RIN characteristic can be obtained.

  As described above, according to the first embodiment, the number and thickness of the MQW active layers 15 and the respective Al compositions in the n-type cladding layer 13, the p-type cladding layer 19 and the reflection suppression layer are set within a predetermined range. Thus, by controlling the differential modal gain and the generation of stray light, the self-excited oscillation characteristic can be maintained and the self-excited peak power intensity can be suppressed even during a high output operation with an output of 10 mW or more. Furthermore, a semiconductor laser device having excellent noise characteristics can be obtained.

(Second Embodiment)
Hereinafter, a semiconductor laser device according to a second embodiment of the present invention will be described with reference to the drawings.

  FIG. 11 shows a cross-sectional structure of a semiconductor laser device according to the second embodiment of the present invention. In FIG. 11, the same components as those shown in FIG.

As shown in FIG. 11, in the second embodiment, instead of providing the n-type antireflection layer 12 made of n-type Al _0.15 Ga _0.85 N between the substrate 11 and the n-type cladding layer 23. It is provided with a p-type antireflection layer 22 made of p-type _Al z _{Ga 1-z} N between the p-type cladding layer 29 and the p-type contact layer 20.

Here, the n-type cladding layer 23 is made of n-type Al _0.07 Ga _0.93 N having a thickness of 2.8 μm, and the p-type cladding layer 29 is p-type Al _0.07 Ga having a thickness of 500 nm. _It consists of _0.93 N.

Further, MQW active layer 25 are each thickness 7.5nm of _In 0.02 _{Ga 0.98} consisting N 6 layers of the barrier layer 0b, 2b, ..., 10b and a thickness of 1.5nm, respectively In Six well layers 1w, 3w,..., 11w made of _0.07 Ga _0.93 N are alternately stacked.

In order to realize a differential modal gain value of 1.5 × 10 ⁻¹⁷ cm ² or more and 2.4 × 10 ⁻¹⁷ cm ² or less that can provide good characteristics, the Al _x Ga of each of the cladding layers 23 and 29 can be realized. _{When the} Al composition in _1-x N and Al _y Ga _1-y N is 0.03 ≦ x, y ≦ 0.1, and the number of layers such as the well layer 1w is 6, as described above, It is necessary to set the thickness of the well layer 1w and the like to 0.8 nm or more and 2.5 nm or less, respectively. As a result, the peak power intensity that does not rewrite information on the optical disk can be obtained, and stable self-oscillation can be maintained even at a high light output of 10 mW or more, and an optimum differential modal gain with a sufficiently small oscillation threshold can be obtained. Can do.

The p-type antireflection layer 22 made of p _- type Al _z Ga _1-z N formed between the p-type cladding layer 29 and the p-type contact layer 20, which is a feature of the second embodiment, has an Al composition. Is set to 0.1 <z ≦ 0.3 and the thickness is set to 5 nm or more and 15 nm or less, cracks generated in the p-type antireflection layer 22 can be prevented.

  Moreover, since the p-type reflection suppressing layer 22 according to the second embodiment suppresses the spread of light from the MQW active layer 25 to the p-type contact layer 20, it prevents stray light reflected from the p-type contact layer 25. , RIN characteristics are improved. Further, since the p-type antireflection layer 22 has an effect of increasing the confinement factor of light in the MQW active layer 25, self-excited oscillation characteristics can be realized even during high output operation.

  In the second embodiment, the ridge type laser structure is described. However, the ridge type laser structure is not limited to the ridge type laser structure. In the buried laser structure, an intermediate layer, a p-type OFS layer, a p-type first cladding layer, and an n-type current blocking layer are formed on an active layer, and then a current is injected into a part of the n-type current blocking layer. And a p-type second cladding layer, a p-type antireflection layer, and a p-type contact layer are formed by regrowth. The layers between the active layer and the n-type current blocking layer are not limited to the intermediate layer, the p-type OFS layer, and the p-type first cladding layer, and a desired semiconductor layer may be selected as appropriate.

  In the ridge type laser structure according to the second embodiment, since the p-type cladding layer 29, the p-type antireflection layer 22 and part of the p-type contact layer 20 have a stripe shape, the plane area of the p-type contact layer 20 is reduced. Is small. On the other hand, in the case of the buried laser structure, the p-type contact layer is provided on the entire surface above the active layer, so that the area of the p-type contact layer is extremely large compared to the ridge laser structure. As described above, the large area of the p-type contact layer causes a large amount of reflected stray light, leading to deterioration of noise characteristics. However, in such a buried laser structure, the p-type reflection is entirely present above the active layer. Since the suppression layer is formed, the spread of light distribution to the p-type contact layer can be suppressed and the amount of reflected stray light can be greatly reduced, so that deterioration of noise characteristics can be reliably suppressed.

  Thus, when the p-type antireflection layer is formed between the p-type cladding layer and the p-type contact layer, the buried laser structure has a greater effect on noise suppression than the ridge laser structure. be able to.

  In the semiconductor laser device according to the second embodiment, it has been confirmed that the oscillation spectrum is in multimode due to self-excited oscillation even when the optical output is 10 mW. Also in the time response characteristics of the optical output, the value of the ratio between the oscillation peak power intensity and the average output is 7 times or less, and the oscillation peak power intensity that does not cause rewriting of information to the optical disc is realized. Also, the RIN characteristic is about -130 dB / Hz.

  As described above, a nitride-based semiconductor laser device practical as an optical pickup light source can be realized.

(Third embodiment)
Hereinafter, a semiconductor laser device according to a third embodiment of the present invention will be described with reference to the drawings.

  FIG. 12 shows a cross-sectional structure of a semiconductor laser device according to the third embodiment of the present invention. In FIG. 12, the same components as those shown in FIG.

As shown in FIG. 12, in the third embodiment, an n-type antireflection layer 12 made of n-type n-type Al _z Ga _1-z N is provided between the substrate 11 and the n-type cladding layer 33, and The p-type antireflection layer 22 made of p _- type Al _z Ga _1-z N is also provided between the p-type cladding layer 39 and the p-type contact layer 20.

Here, the n-type cladding layer 33 is made of n-type Al _0.1 Ga _0.9 N having a thickness of 2.4 μm, and the p-type cladding layer 39 is p-type Al _0.1 Ga having a thickness of 460 nm. _0.9 N.

The MQW active layer 35 includes seven barrier layers 0b, 2b,..., 12b made of In _0.02 Ga _0.98 N each having a thickness of 7.5 nm, and In layers having a thickness of 0.7 nm. Seven well layers 1w, 3w,..., 13w made of _0.1 Ga _0.9 N are alternately stacked.

In order to realize a differential modal gain value of 1.5 × 10 ⁻¹⁷ cm ² or more and 2.4 × 10 ⁻¹⁷ cm ² or less for obtaining good characteristics, Al _{x of} each cladding layer 33, 39 is used. When the Al composition in Ga _1-x N and Al _y Ga _1-y N is 0.03 ≦ x, y ≦ 0.1, and the number of layers such as the well layers 1w is 7, as described above The thicknesses of the well layers 1w and the like need to be set to 0.4 nm or more and 1.5 nm or less, respectively. When the thickness of the well layer 1w or the like is set to this level, the amount of In added to the well layer 1w or the like becomes relatively large. As the amount of indium (In) added increases, In segregation occurs spatially. In addition, when the In composition is high, the band gap energy is locally reduced, so that absorption occurs with respect to the oscillation wavelength. Therefore, segregation of In has an advantage that a saturable absorber is easily formed. Moreover, since the number of layers such as the well layer 1w is as large as 7, a saturable absorber formed in the MQW active layer 35 can be secured.

  As a result, a peak power intensity that does not cause writing to the disk can be obtained, stable self-oscillation is maintained even at a high light output of 10 mW or more, and an optimal differential modal gain with a sufficiently small oscillation threshold value can be obtained. be able to.

The n-type antireflection layer 12 made of n-type Al _z Ga _1-z N and the p-type cladding layer 39 and p, which are the features of the third embodiment, are formed between the substrate 11 and the n-type cladding layer 33. The p-type antireflection layer 22 made of p _- type Al _z Ga _1-z N formed between the p-type contact layer 20 has an Al composition of 0.1 <z ≦ 0.3 and a thickness of 5 nm. By setting the thickness to 15 nm or less, cracks generated in the reflection suppression layers 12 and 22 can be prevented.

  Further, each of the reflection suppression layers 12 and 22 according to the third embodiment suppresses the spread of light from the MQW active layer 35 to the substrate 11 side and the spread of light to the p-type contact layer 20 side, Since stray light reflected from the substrate 11 and the p-type contact layer 20 is prevented, the RIN characteristics are improved. Furthermore, since each of the reflection suppression layers 12 and 22 has an effect of increasing the confinement factor of light in the MQW active layer 35, self-excited oscillation characteristics can be realized even during high output operation.

  The semiconductor laser device according to the third embodiment has confirmed that the oscillation spectrum becomes multimode and self-oscillates even when the optical output is 10 mW. Also in the time response characteristics of the optical output, the value of the ratio between the oscillation peak power intensity and the average output is 7 times or less, and the oscillation peak power intensity that does not cause rewriting of information to the optical disc is realized. Furthermore, by providing each of the reflection suppression layers 12 and 22, the RIN characteristics can be obtained as good as about -130 dB / Hz.

  As described above, a nitride-based semiconductor laser device practical as an optical pickup light source can be realized.

  In each embodiment of the present invention, the conductivity type of the substrate 11 is n-type. However, the present invention is not limited to this, and a p-type substrate may be used. In this case, a p-type antireflection layer is provided between the p-type substrate and the MQW active layer, and n-type antireflection is provided between the n-type cladding layer and the n-type contact layer formed on the MQW active layer. A layer may be provided.

  The semiconductor laser device according to the present invention maintains a self-excited oscillation operation at the time of a high output operation, suppresses the oscillation peak intensity and has excellent noise characteristics, and is useful as a laser light source in the field of optical disc systems. .

1 is a schematic cross-sectional view showing a semiconductor laser device according to a prototype of the present invention. It is a graph which shows the trial manufacture result of the semiconductor laser apparatus which concerns on nine kinds of trial manufacture examples of this invention. 6 is a graph showing the relationship between the differential modal gain and the Al composition of a cladding layer in a semiconductor laser device according to a prototype having five well layers according to the present invention, with the thickness of the well layer as a parameter. 6 is a graph showing the relationship between the differential modal gain and the Al composition of a cladding layer in a semiconductor laser device according to a prototype having six well layers of the present invention, with the thickness of the well layer as a parameter. 6 is a graph showing the relationship between the differential modal gain and the Al composition of a cladding layer in a semiconductor laser device according to a prototype having seven well layers according to the present invention, with the thickness of the well layer as a parameter. It is a graph showing with prototype example having no antireflection layer RIN characteristic in the semiconductor laser device according to the prototype example having a reflection suppressing layer made of Al z _Ga 1-z _N of the present invention. It is a graph showing with prototype example having no antireflection layer near-field image (NFP) in the semiconductor laser device according to the prototype example having a reflection suppressing layer made of Al z _Ga 1-z _N of the present invention. It is a graph showing the relationship between the occurrence of the Al composition and thickness and cracks in the antireflection layer of the semiconductor laser device according to the prototype example having a reflection suppressing layer made of Al z _Ga 1-z _N of the present invention. 1 is a schematic cross-sectional view showing a semiconductor laser device according to a first embodiment of the present invention. (A)-(c) shows the operating characteristic of the semiconductor laser apparatus based on the 1st Embodiment of this invention, (a) is a graph which shows a wavelength characteristic, (b) is a self-excited oscillation time response characteristic. (C) is a graph which shows a relative noise intensity (RIN) characteristic. It is a typical structure sectional view showing the semiconductor laser device concerning a 2nd embodiment of the present invention. It is a typical structure sectional view showing a semiconductor laser device concerning a 3rd embodiment of the present invention. It is a graph which shows the operating carrier density dependence of the differential modal gain in the conventional red, infrared, and blue-violet laser apparatus. (A) And (b) shows the self-excited oscillation time response characteristic in the conventional semiconductor laser device, (a) is a blue-violet laser device, (b) is a red laser device. It is a graph which shows the electric current (Iop) -light output (Po) characteristic in the conventional red, infrared, and blue-violet laser apparatus.

Explanation of symbols

Reference Signs List 101 substrate 102 n-type cladding layer 103 multiple quantum well active layer 104 p-type cladding layer 105 p-type contact layer 106 current blocking layer 150 ridge stripe portion 11 substrate 12 n-type antireflection layer 13 n-type cladding layer 14 guide layer 15 multiple quantum Well (MQW) active layer 16 first intermediate layer 17 second intermediate layer 18 overflow suppression (OFS) layer 19 p-type cladding layer 20 p-type contact layer 21 current blocking layer 22 p-type antireflection layer 23 n-type cladding layer 25 multiple Quantum well (MQW) active layer 29 p-type cladding layer 33 n-type cladding layer 39 p-type cladding layers 0b, 2b, 4b, 6b, 8b, 10b, 12b Barrier layers 1w, 3w, 5w, 7w, 9w, 11w, 13w Well layer 50 Ridge stripe

Claims (7)

A first conductivity type first clad layer formed on the substrate and made of Al _x Ga _1-x N;
An active layer formed on the first cladding layer;
A second clad layer of the second conductivity type formed on the active layer and made of Al _y Ga _1-y N;
A second conductivity type contact layer formed on the second cladding layer;
A reflection suppressing layer formed between at least one of the substrate and the first cladding layer and between the second cladding layer and the contact layer, and comprising Al _z Ga _1-z N;
The Al composition x in the first clad layer, the Al composition y in the second clad layer, and the Al composition z in the antireflection layer satisfy the relationship x <z and y <z. Laser device. The Al composition x in the first cladding layer is 0.03 ≦ x ≦ 0.1,
The Al composition y in the second cladding layer is 0.03 ≦ y ≦ 0.1,
2. The semiconductor according to claim 1, wherein an Al composition z in the reflection suppression layer is 0.1 <z ≦ 0.3, and a thickness of the reflection suppression layer is 5 nm or more and 15 nm or less. Laser device. The second cladding layer has a stripe portion formed on the top thereof, into which current is selectively injected,
3. The semiconductor laser device according to claim 1, wherein a current blocking layer is formed on a side of the stripe portion in the second cladding layer.   The semiconductor laser device according to claim 1, wherein the current blocking layer is made of a dielectric material or a semiconductor material. The active layer comprises a quantum well active layer formed by alternately stacking quantum well layers and barrier layers,
The number of well layers is 5,
5. The semiconductor laser device according to claim 1, wherein the thickness of the well layer is 2 nm or more and 4 nm or less. The active layer comprises a quantum well active layer formed by alternately stacking quantum well layers and barrier layers,
The number of the well layers is 6,
5. The semiconductor laser device according to claim 1, wherein the thickness of the well layer is not less than 0.8 nm and not more than 2.5 nm. The active layer comprises a quantum well active layer formed by alternately stacking quantum well layers and barrier layers,
The number of well layers is 7,
5. The semiconductor laser device according to claim 1, wherein the thickness of the well layer is not less than 0.4 nm and not more than 1.5 nm.

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