JP4842668B2 - Semiconductor laser device and manufacturing method thereof, optical wireless communication transmitter, and optical disk device - Google Patents

Description

  The present invention relates to a semiconductor laser element that requires high output and low driving power, a method for manufacturing the same, and a transmitter and an optical disc apparatus for optical wireless communication including such a semiconductor laser element.

  In recent years, with the development of IT technology and the spread of broadband, opportunities to handle large volumes of data such as voice and video are increasing. In particular, opportunities for large-capacity data communication between a fixed terminal connected to a high-speed wired infrastructure and a mobile portable terminal via a space are expected to expand rapidly in the future. There are two types of carriers used for such wireless communication: radio waves and light. However, there are many occasions where light is used because of data confidentiality and directivity. Currently, light-emitting diodes (LEDs) are generally used as signal sources for optical carriers because of their low cost and ease of handling. Expectations for the optical wireless communication technology used are high. In light of this situation, development of a new semiconductor laser for high-speed optical wireless communication and standardization work for the standard are currently underway.

  The wavelength of light used in this new optical wireless communication standard is a near infrared wavelength band of 1.0 μm or less centering on 850 to 950 nm. This value is determined by the safety of the human body, particularly the eyes, and the wavelength dependency of the light receiving element, and it is necessary to develop a new semiconductor laser element that operates stably in this wavelength band as a light source for wireless communication.

  However, the near-infrared wavelength band of 1.0 μm or less is just in the middle of the wavelength band used in the existing short-wavelength optical disk apparatus and long-wavelength optical fiber communication, so that these conventional wavelength bands were not a problem. Laser layer structure parameters can greatly affect the characteristics of the laser.

  Among such structural parameters, a parameter that greatly affects the efficiency of the semiconductor laser element is free electron absorption αfc in the semiconductor layer doped with impurities.

This is a phenomenon in which free electrons absorb light in the same valley in the energy band of the valence band or conduction band and transition to a higher energy side, and the wavelength and free electron absorption αfc are used with the doping concentration as a parameter. As the lines (a) to (c) in FIG. 10 showing the relationship, the value of free electron absorption αfc increases as the wavelength of light is longer and the doping concentration is higher. The relationship is sought theoretically,
αfc ∝ {N × (aλ ^1.5 + bλ ^2.5 + cλ ^3.5 )} / τ ∝ (N × λ ^x ) / τ (1)
It is expressed. In this formula (1), N is the doping concentration, λ is the wavelength of light, a to c are coefficients of the wavelength λ having different indices, and τ is the carrier relaxation time. The index x of λ on the rightmost side varies depending on the degree of various scattering by acoustic / optical phonons and ionized impurities. Generally, in the case of III-V group compound semiconductors, a value of about 3.0 to 3.5. It becomes.

  As described above, since absorption by free electrons is proportional to the third power of the wavelength, long wavelength band semiconductor laser devices having a wavelength of 1.3 μm or more that have been used in optical fiber communication have been regarded as very problematic for some time. . In particular, free electron absorption in the p-type conductivity layer was particularly problematic. This is because the value of free electron absorption per carrier concentration in the doped semiconductor layer is determined by the relaxation time of the doping carrier, so that a difference occurs due to the difference in conductivity type even at the same carrier concentration. In fact, according to Non-Patent Document 1 (Heterostructure Laser, 1973), the ratio of the free electron absorption value per carrier concentration in the p-type conductivity type and the n-type conductivity type layer at a wavelength of 780 nm is about 7: 3. Has been. As described above, it has been said that free electron absorption by the p-type dopant is about 7/3 times larger than that by the n-type dopant, so that free electron absorption particularly in the p-type conductivity layer has been a problem.

One solution to this problem is disclosed in Patent Document 1 (Japanese Patent No. 2699848). In this example, by setting the doping concentration of the entire p-type conductivity type layer excluding the cap layer in the InP-based laser to a relatively low value of about 3 × 10 ¹⁷ cm ^{−3 to} 7 × 10 ¹⁷ cm ⁻³ , Free electron absorption in the p-type conductivity layer is suppressed, and the efficiency of the semiconductor laser is improved.

On the other hand, the short wavelength semiconductor laser element used in the optical disk device has a very small influence of free electron absorption unlike the long wavelength semiconductor laser element, so that the doping concentration of the p-type conductivity type layer is 5 × 10 ^18. If it is about cm ⁻³ to 1 × 10 ¹⁹ cm ⁻³ or less, free electron absorption has not been a problem.

A report was also made on the effect of free electron absorption in the p-type conductivity layer for semiconductor laser elements in the near-infrared wavelength band of 1.0 μm or less, which is between the short wavelength band and the long wavelength band. Exists. For example, Non-Patent Document 2 (Appl. Phys. Lett. Vol. 69 No. 20, 1996) includes an n-InGaP cladding layer, an n-InGaAsP lower light guide layer, an undoped quantum well active layer on an n-GaAs substrate, A p-InGaAsP upper optical guide layer, a p-InGaP cladding layer, and a p-GaAs cap layer are laminated in this order from the substrate side, and the active layer has a wavelength of 808 nm (InGaAsP / InGaAsP quantum well active layer) or 980 nm (InGaAs / GaAs quantum well). There are descriptions regarding several types of semiconductor laser elements set to oscillate in the active layer). Although the value of the internal absorption αi of these semiconductor laser elements is about 4 to 5 cm ⁻¹ , in this report, among the factors determining the internal absorption value of about 4 to 5 cm ⁻¹ We conclude that there is almost no influence of free electron absorption αfc.

  In these examples, the layer structure of each layer of the p-type conductivity type layer and each layer of the n-type conductivity type is an etching stop layer present in the p-type conductivity type layer, following the layer structure of a general semiconductor laser element. Except for this, it has a symmetrical layer structure with the active layer in between. The parameters that determine the symmetrical layer structure here are the material constituting each layer, the layer thickness, and the doping concentration. Due to the symmetry of this layer structure, the ratio of the free electron absorption amount of each layer of the p-type conductivity type and each layer of the n-type conductivity type in these semiconductor laser elements is determined only by the difference in relaxation time of both carriers. According to the above, it is considered that the former free electron absorption value is about 7/3 times larger than the latter value. Therefore, in order to improve the efficiency of the semiconductor laser, only the doping concentration of the p-type conductivity type has been regarded as a problem.

By the way, in this example of the near-infrared wavelength band semiconductor laser device, both the p-type and n-type doping concentrations other than the substrate, buffer layer, and cap layer are set to a relatively low value of about 5 × 10 ¹⁷ cm ^−3. Yes. This value is as low as the p-type doping concentration of the long-wavelength semiconductor laser device in which the above-described p-type conductivity type layer is subjected to the free electron absorption suppression measure. Therefore, taking the semiconductor laser in this near-infrared wavelength band as an example, when considering the effect of free electron absorption in that wavelength band, there is no fundamental effect as described in the literature, or at this doping concentration p-type It cannot be determined whether the influence of free electron absorption in the conductive type layer has become apparent.

  There are also many uncertain points regarding the value of free electron absorption per carrier concentration of the n-type conductivity layer, which has not been noticed so far. Certainly, in the previous literature, the value of free electron absorption per carrier concentration of each of the p-type and n-type conductivity type layers is 7: 3 at a wavelength of 780 nm, but this value is theoretically calculated from the carrier relaxation time. It is an estimated value, and it is not certain about the degree of influence on the internal absorption of an actual semiconductor laser element. In particular, since there is no data in the near-infrared wavelength band of 800 nm or more, the degree of contribution of the n-type dopant to the contribution of the p-type dopant is completely unknown. For this reason, depending on the conditions, even for n-type dopants, the value of free electron absorption becomes so high as to be a problem, and the possibility of a decrease in efficiency cannot be denied.

Further, as in the example of the near-infrared wavelength band semiconductor laser element and the long wavelength band semiconductor laser element described above, the doping concentration of the p-type conductivity layer is set to a relatively low value of about 5 × 10 ¹⁷ cm ^−3. When set, free electron absorption is suppressed and the laser efficiency is improved. On the other hand, other laser characteristics such as temperature characteristics and element resistance are deteriorated, and the power consumption of the laser element is particularly increased. For example, in a semiconductor laser device in which the p-type doping concentration of the light guide layer or the cladding layer is set to about 4 × 10 ¹⁷ cm ^{−3 to} 6 × 10 ¹⁷ cm ⁻³ , the device is doped to about 1 × 10 ¹⁸ cm ^−3. Since the conduction band energy level of the corresponding layer is lower than that of, the energy barrier level viewed from the carriers in the well layer, particularly electrons, is lowered. For this reason, carriers easily leak out of the well layer, and the temperature characteristics of the semiconductor laser element deteriorate. This leads to an increase in power consumption particularly at high temperatures. In particular, in the case of a near-infrared wavelength semiconductor laser element, the energy gap of the well layer is larger than that of the long wavelength band. Therefore, when the same material is used for the layer outside the well layer, the gap between the well layer and the outer layer is used. The difference in energy gap is smaller than that in a long wavelength semiconductor laser, and carrier leakage is more likely to occur. For this reason, the power consumption increases even at a doping concentration that was not a problem in the long wavelength semiconductor laser device.

In addition, as for the device resistance, in a semiconductor laser device having a p-type doping concentration as low as about 4 × 10 ¹⁷ cm ^{−3 to} 5 × 10 ¹⁷ cm ^−3, a semiconductor laser device doped with about 1 × 10 ¹⁸ cm ^−3. The resistance value becomes higher than this, which also leads to an increase in power consumption. When such a semiconductor laser element is used as an emission source in an optical wireless communication apparatus, other components in the apparatus may be loaded, or the range of selection of other parts may be reduced.

Incidentally, one of the important characteristics of the semiconductor laser device is reliability. There are a number of laser parameters that affect the reliability, but the most significant effect is the light density of the light emitting layer in the active layer. This is determined by the layer structure of the semiconductor laser element. For example, when the material of both the p-type and n-type cladding layers is changed in the direction in which the material refractive index increases, the light density of the well layer, which is the light emitting layer in the active layer, is increased. Increases and decreases reliability level. In addition, when light is strongly confined in the light emitting layer, the value of the vertical radiation angle increases. However, when this value is 40 degrees or more, the light that does not contribute to communication increases when used as a light emitting source for wireless communication, and driving. It will also lead to an increase in current. In particular, when the layer structure is changed while maintaining the symmetrical structure of the p-type and n-type conductive layers with the active layer interposed therebetween as in the above-described example, this effect becomes more prominent.
Japanese Patent No. 2699848 Heterostructure Laser, 1973 Appl. Phys. Lett. Vol. 69 No. 20, 1996

  In view of the above, the object of the present invention is to provide a semiconductor laser device that satisfies all three types of characteristics that have not been achieved in the past, such as high efficiency, low power consumption, and high reliability in the near-infrared wavelength band of 1.0 μm or less. Is to provide.

  Furthermore, by installing a semiconductor laser element having such advantages as a light source, a transmitter for high-speed optical wireless communication with a new standard that could not be realized in the past has been realized, and in the field of optical disks where competition for higher speed continues. An object of the present invention is to provide an optical disk device that enables higher-speed reading and writing.

であり、
上記ｐ型導電型層ｍの光閉じ込め係数Γ(ｍ)と上記ｐ型導電型層ｍのドーピング濃度Ｐ(ｍ)（単位：ｃｍ^−３）の積の総和

が８．０×１０^１７ｃｍ^−３ 以下であり、
上記複数のｐ型導電型層のうちドーピング濃度が１．０×１０^１８ｃｍ^−３以上であるｐ型導電型層の層厚の合計が上記複数のｐ型導電型層全体の層厚の合計の８０％以上を占めており、
上記ｐ型クラッド層の平均ドーピング濃度が２．０×１０ ^１８ ｃｍ ^−３ 以上であり、
上記ｎ型導電型層ｌの光閉じ込め係数Γ(ｌ)と上記ｎ型導電型層ｌのドーピング濃度Ｎ(ｌ)（単位：ｃｍ ^−３ ）の積の総和

が４．０×１０ ^１８ ｃｍ ^−３ 以下であることを特徴としている。 The semiconductor laser device according to the first aspect of the present invention is provided on a substrate,
A plurality of n-type conductivity layers l (where l = 1, 2,... K, where k is a natural number);
a plurality of p-type conductivity layers m including a p-type cladding layer (where m = 1, 2,..., k ′, where k ′ is a natural number);
An active layer located between the n-type conductivity type layer l and the p-type conductivity type layer m,
The oscillation wavelength is 700 nm or more and 1.0 μm or less,
The ratio of the amount of light present in the n-type conductivity type layer 1 to the total amount of light present in all the layers in the substrate and on the substrate is the optical confinement factor Γ (l), and in all layers in the substrate and on the substrate. Assuming that the ratio of the amount of light existing in the p-type conductivity type layer m to the total amount of existing light is the optical confinement coefficient Γ (m), the relationship between the sum of Γ (l) and the sum of Γ (m) is

And
Sum of products of optical confinement coefficient Γ (m) of p-type conductivity layer m and doping concentration P (m) (unit: cm ⁻³ ) of p-type conductivity layer m

Is 8.0 × 10 ¹⁷ cm ⁻³ or less,
Of the plurality of p-type conductivity layers, the total thickness of the p-type conductivity layers having a doping concentration of 1.0 × 10 ¹⁸ cm ⁻³ or more is the total thickness of the plurality of p-type conductivity layers. and it accounts for 80% or more of,
The p-type cladding layer has an average doping concentration of 2.0 × 10 ¹⁸ cm ⁻³ or more,
Sum of products of optical confinement coefficient Γ (l) of n-type conductivity type layer 1 and doping concentration N (l) (unit: cm ⁻³ ) of n-type conductivity type layer 1

Is 4.0 × 10 ¹⁸ cm ⁻³ or less .

  The sum of Γ (l), the sum of Γ (m), and the sum of products of Γ (m) and P (m) are simply referred to as Σ {Γ (l)} and Σ {Γ (m), respectively. }, Σ {Γ (m) × P (m)}.

In order to determine the “upper limit value” of the p-type doping structure that can avoid free electron absorption in the near-infrared wavelength band having a wavelength of 1.0 μm or less, the present inventors first set the p in a semiconductor laser device that oscillates at a wavelength of about 900 nm. Actually fabricated several types of devices with different combinations of the p-type doping concentration P (m) of the p-type conductivity layer m and the optical confinement coefficient Γ (m) of the same layer, and directly affects the efficiency value and efficiency. The value of the internal absorption αi to be given was calculated. Regarding the symmetry of the layer structure, the layer thickness and the material constituting the layer are the same in both the p-type and n-type conductivity layers except for the p-type etching stop layer as in the past examples. The doping concentration is low as a general semiconductor laser device having an average of 1.0 × 10 ¹⁷ cm ⁻³ or less on the n-type conductivity type side so that only the influence of free electron absorption in the p-type conductivity type layer can be confirmed. Set to value.

As a result, the optical confinement coefficient Γ (m) of each layer m (m = 1, 2,..., K ′, where k is a natural number) and the doping concentration P (m) (cm ⁻³ , hereinafter omitted) of the p-type doping. It was found that there is a relationship as shown in FIG. 7 between the sum Σ {Γ (m) × P (m)} of the product and the internal absorption αi that determines the efficiency value of the semiconductor laser element. According to FIG. 7, the sum Σ {Γ (m) × P (m)} of products of the optical confinement coefficient Γ (m) of the p-type conductivity type layer m and the doping concentration P (m) of the p-type layer. When the value exceeds 8.0 × 10 ¹⁷ cm ⁻³ , it can be seen that the value of the internal absorption αi increases rapidly. The internal absorption αi of the semiconductor laser element is composed of free electron absorption αfc and other absorption αo. In general, the value of other absorption αo that does not depend on the doping concentration is as small as less than 4 to 5 cm ^−1, and the influence on the semiconductor laser element is as follows. not much. Further, as described above, since the n-type doping concentration is set to a very small value in the semiconductor laser device manufactured in this experiment, it is considered that the change in free electron absorption αfc in FIG. 7 is almost due to the contribution of the p-type dopant. Good. That is, from FIG. 7, the absorption αo independent of the p-type doping concentration is about 3 cm ^−1, and free electron absorption αfc derived from the p-type dopant is added to the internal absorption αi of the semiconductor laser element. I understand. From the above, the sum Σ {Γ (m) × P (m)} of the products of the optical confinement coefficient Γ (m) of the p-type conductivity type layer m and the p-type layer doping concentration P (m) is 8 It can be seen that if the range is set to 0.0 × 10 ¹⁷ cm ⁻³ or less, the rapid increase in free electron absorption αfc derived from the p-type dopant in the internal absorption αi can be suppressed. It can also be said that high efficiency can be obtained as long as free electron absorption αfc is suppressed.

Furthermore, in FIG. 7, when the value of the sum Σ {Γ (m) × P (m)} is 6.0 × 10 ¹⁷ cm ⁻³ or less, the value of the internal absorption αi hardly changes. Therefore, it can also be seen that if the p-type doping layer structure is set so that the total value is 6.0 × 10 ¹⁷ cm ⁻³ or less, the influence of the free electron absorption αfc on the internal absorption αi can be almost eliminated.

  These facts are different from the conventional recognition that there is no influence of free electron absorption in the near-infrared wavelength band of 1.0 μm or less, and the influence of free electron absorption by the p-type dopant also depends on the structure even in the above wavelength band. As a result, it has been found that the efficiency of the semiconductor laser element deteriorates. At the same time, by considering not only the p-type doping concentration but also the optical confinement factor of the p-type conductivity type layer, good efficiency can be maintained even at a relatively high p-type doping concentration that may lead to an increase in free electron absorption. I found out that

  By the way, when setting the value of the sum Σ {Γ (m) × P (m)} of the product of the optical confinement coefficient and the p-type doping concentration in the p-type conductivity layer to be within the above range, If the light confinement factor is reduced while maintaining a symmetric structure centering on the active layer including the layer, the light density of the light emitting layer increases as described above, leading to a decrease in reliability. Actually, when the optical confinement coefficient of both the p-type and n-type conductive layers is kept the same and the value is decreased, as the value of the optical confinement coefficient of both decreases as shown by curve A in FIG. The light density of the layer increases exponentially.

In the semiconductor material used for the light emitting layer of the near infrared wavelength band intended in the present invention, when the light density of the light emitting layer exceeds 3.0 × 10 ⁴ cm ⁻¹ , the reliability of the semiconductor laser element is significantly reduced. I know that Accordingly, if this value is the upper limit of the light density of the light emitting layer for ensuring reliability in the semiconductor laser device, the reliability can be ensured in the semiconductor laser device in which the p-type and n-type conductive layers have a symmetrical structure. The required optical confinement coefficient values of the p-type and n-type conductivity type layers are A1 or more from FIG. While satisfying this condition, the total of the optical confinement coefficient of the p-type conductivity layer and the p-type doping concentration Σ {Γ (m) × P (m)} is p-type so as to be 8.0 × 10 ¹⁷ cm ⁻³ or less. When the doping concentration is set, as shown in FIG. 10, the average value of the p-type doping concentration is less than 1.0 × 10 ¹⁸ cm ⁻³ . In order to improve temperature characteristics and device resistance, it is necessary to set the p-type doping concentration so that the average value is 1.0 × 10 ¹⁸ cm ⁻³ or more. Power consumption and high reliability cannot be satisfied. The “average value of the p-type doping concentration” referred to here is a high concentration of all the p-type conductivity layers included in the semiconductor laser element, but the light confinement coefficient is small, so that free electrons and This is an average of the layers excluding the outermost layer which can be ignored in considering the element resistance.

Considering this point, in the present invention, the sum Σ {Γ (l)} of the optical confinement coefficient Γ (l) of the n-type conductivity type layer l and the optical confinement coefficient Γ (m) of the p-type conductivity type layer m are determined. The relationship of the sum Σ {Γ (m)} is set so that Σ {Γ (l)} ÷ Σ {Γ (m)}> 1.0, that is, the optical confinement coefficient Γ (l) of the n-type conductivity type layer l Is set to be larger than the sum of the optical confinement coefficients Γ (m) of the p-type conductivity layer m, and the sum of the optical confinement coefficient and the p-type doping concentration of the p-type conductivity layer Σ { Γ (m) × P (m)} is 8.0 × 10 ¹⁷ cm ⁻³ or less, and the p-type doping concentration is 1 × 10 ¹⁸ in a layer having a thickness of 80% or more of the entire p-type conductivity type layer. The p-type doping concentration was set to be cm ⁻³ or higher.

  At this time, the curve A in FIG. 11 descends downward to become, for example, the curve A ′. Therefore, the sum of the light confinement coefficients of the p-type conductivity type Σ {Γ ( m)} can be set smaller than in the case of the symmetric structure. As a result, temperature characteristics and resistance values are improved to reduce power consumption while simultaneously avoiding a decrease in reliability due to an increase in light density of the light emitting layer and a decrease in efficiency due to an increase in free electron absorption in the p-type conductivity layer. It was possible to realize a semiconductor laser device for near infrared high-speed optical wireless communication of 1.0 μm or less that satisfies all the three types of characteristics that were not compatible with each other.

  Note that “efficiency” in this specification is one of the static characteristics of a semiconductor laser element, and is necessary for obtaining an oscillation threshold current Ith (A) and a certain optical output Pop (W). When the drive current value is Iop (A), this is one of the basic static characteristics of the semiconductor laser element defined by Pop / (Iop-Ith).

In addition, the smaller the value of the internal absorption αi of the semiconductor laser element, the better. However, in general, if it exceeds 10 cm ⁻¹ , the efficiency value is significantly affected, and is necessary for high-speed optical wireless communication of 0.95 W / A or more. The high efficiency value that is achieved cannot be obtained. For this reason, when the semiconductor laser element is mounted on such a transmitter for optical wireless communication, the value of internal absorption is desirably 10 cm ⁻¹ or less, more preferably 5 cm ⁻¹ or less.

  Further, unless otherwise specified, the p-type and n-type conductivity type layers defined in this specification are the p-types present in the ridge and the portion connected to the top and bottom of the ridge when the semiconductor laser element is a ridge buried type. It is a type or n-type conductivity type layer, and does not include a p-type or n-type conductivity type layer that exists only in the buried portion.

が４．０×１０^１８ｃｍ^−３以下であることを特徴としている。 Furthermore, the present invention provides a sum of products of the optical confinement coefficient Γ (l) of the n-type conductivity type layer l and the doping concentration N (l) (unit: cm ⁻³ ) of the n-type conductivity type layer l.

Is 4.0 × 10 ¹⁸ cm ⁻³ or less.

  As described above, the contribution of n-type dopants to free electron absorption in conventional semiconductor laser devices has been considered to be smaller than the contribution of p-type dopants, and this has hardly been a problem. However, as described above, in the semiconductor laser device of the present invention, the optical confinement coefficient of the p-type conductivity layer m is suppressed in order to simultaneously suppress the increase in free electron absorption and the increase in light emission layer light density in the p-type conductivity type layer. Compared to the value of Γ (m), the value of the optical confinement coefficient Γ (l) of the n-type conductivity layer 1 is set to be increased. For this reason, free electron absorption in the n-type conductivity type layer determined by the value of Σ {Γ (l) × N (l)} may also be a problem in the semiconductor laser device of the present invention.

Accordingly, the inventors set the p-type conductivity type layer structure so that there is no influence of free electron absorption by the p-type dopant, contrary to the previous experiment on the p-type conductivity type layer, and then the n-type conductivity type layer. Several devices with different combinations of the n-type doping concentration N (l) of l and the optical confinement coefficient Γ (l) of the same layer are manufactured, and the efficiency value and the value of the internal absorption αi that directly affects the efficiency And calculated. As a result, when the value of Σ {Γ (l) × N (l)} exceeds 4.0 × 10 ¹⁸ cm ⁻³ , the value of the internal absorption αi of the semiconductor laser element increases rapidly. all right.

Accordingly, in the present invention , the value of Σ {Γ (l) × N (l)}, which is the sum of the product of the optical confinement coefficient of the n-type conductivity type layer and its doping concentration, is set to 4.0 × 10 ¹⁸ cm. ^The layer structure is defined to be ⁻³ or less. As a result, it has become possible to define a structure that reliably avoids the effects of free electron absorption by n-type dopants whose contribution to free electron absorption has been unknown.

  In this range, the value of the sum Σ {Γ (l)} of the optical confinement coefficients of the n-type conductivity layer can be set large, so that the p-type is within a range in which the light density of the light emitting layer is not increased accordingly. It becomes possible to set the light confinement coefficient of the conductive layer smaller.

  In other words, when the p-type doping concentration is set to a higher value for the purpose of improving efficiency by suppressing free electron absorption in the p-type conductivity type layer and improving temperature characteristics and resistance values which are in a trade-off relationship therewith. The p-type doping concentration can be set to a higher value without causing a decrease in reliability and an excessive increase in the radiation angle and avoiding the influence of free electron absorption in the n-type conductivity type layer.

であることを特徴としている。 In one embodiment, the sum of the products of the optical confinement coefficient Γ (l) of the n-type conductivity type layer l and the doping concentration N (l) (unit: cm ⁻³ ) of the n-type conductivity type layer l, and the p The relationship between the optical confinement coefficient Γ (m) of the p-type conductivity layer m and the sum of the products of the doping concentration P (m) of the p-type conductivity layer m is

It is characterized by being.

Conventionally, it has been considered that the contribution of n-type dopants to free electron absorption is about 3/7 times that of p-type dopants. However, according to the two types of experiments described above, the contribution of the n-type dopant to free electron absorption is the sum of the product of the optical confinement coefficient and the doping concentration, and the upper limit of 8.0 × in the p-type conductivity type layer. It was found that the upper limit of 4.0 × 10 ¹⁸ cm ⁻³ was about 1/5 with respect to 10 ¹⁷ cm ⁻³ . In other words, the value of the sum of the product of the optical confinement coefficient and the doping concentration can be increased up to about 5 times in the n-type conductivity type layer structure with respect to the p-type conductivity type layer. Similarly, the p-type doping concentration can be set to a higher value while avoiding an increase in free electron absorption, a decrease in reliability, and an increase in the emission angle in both the p-type and n-type conductivity layers.

であることを特徴としている。 In one embodiment, the sum of the products of the optical confinement coefficient Γ (l) of the n-type conductivity type layer l and the doping concentration N (l) (unit: cm ⁻³ ) of the n-type conductivity type layer l, and the p The relationship between the optical confinement coefficient Γ (m) of the p-type conductivity layer m and the sum of the products of the doping concentration P (m) of the p-type conductivity layer m is

It is characterized by being.

  As described above, the contribution of n-type dopants to free electron absorption has been considered to be about 3/7 times that of p-type dopants. It was found that even if the sum of the product of the doping concentration and the concentration exceeds 7/3, there is no significant effect up to about 5 times.

By changing the layer structure of the p-type and n-type conductivity layers while maintaining Σ {Γ (l)} = {(3/7) × Σ {Γ (m)}, the light density and p-type conductivity of the light-emitting layer are changed. The relationship with the optical confinement coefficient of the mold layer is as shown by a straight line B in FIG. At this time, from the viewpoint of suppressing the light density of the light emitting layer, the lower limit value of the sum of the light confinement coefficients of the p-type conductivity type layer for maintaining reliability is B1 in the figure. At this time, using FIG. 10, the sum of the products of the optical confinement coefficient and the doping concentration of the p-type conductivity layer and the value of Σ {Γ (m) × P (m)} is kept below 8.0 × 10 ¹⁷ cm ^−3. When the upper limit value of the obtained p-type doping concentration is calculated, the value B2 is 2.2 × 10 ¹⁸ cm ⁻³ . Of the p-type conductivity type layers, a layer excluding the outermost layer having a low optical confinement factor / high p-type doping concentration and the thinnest layer having a high optical confinement factor / low p-type doping concentration closest to the light emitting layer, a so-called cladding layer In particular, it is desirable to set the p-type doping concentration to an average of about 2.0 to 3.0 × 10 ¹⁸ cm ⁻³ or more in general, especially considering the reduction in device resistance. In this embodiment, since the value of Σ {Γ (l)} is set to be 7/3 or more of Σ {Γ (m)}, the suppression and reliability of free electron absorption by both p-type and n-type conductivity layers are achieved. In addition to ensuring high conductivity, the average doping concentration of the p-type conductivity layer excluding the outermost layer, which is negligible when considering free electrons and device resistance, because it is highly doped but has a small optical confinement factor It becomes possible to raise the value to a value in a more effective range by reducing the element resistance, ie, about 2.0 to 3.0 × 10 ¹⁸ cm ⁻³ , and the power consumption of the near-infrared wavelength semiconductor laser element is effective. Can be reduced.

であることを特徴としている。 In one embodiment, the relationship between the sum of the optical confinement coefficients Γ (l) of the n-type conductivity type layer l and the sum of the light confinement factors Γ (m) of the p-type conductivity type layer m is:

It is characterized by being.

When the resistance of the n-type conductivity type layer and the p-type conductivity type layer are compared at the same doping concentration, since the former is smaller than the latter, the n-type doping concentration of the semiconductor laser device is generally from the viewpoint of device resistance. It is set to a relatively low value of about 4 × 10 ¹⁷ cm ⁻³ to 1 × 10 ¹⁸ cm ⁻³ . The value of the n-type conductive layer Σ {Γ (l) × N (l)} is the sum of the products of the optical confinement coefficient and the doping concentration shown above, and the value of the p-type conductive layer Σ {Γ (m) × Considering together the result of 5 times or less of the value of P (m)}, the sum of the optical confinement coefficients of the n-type conductive layer Σ {Γ (l)} is the sum of the values of the p-type conductive layer. It is possible to set up to 12.5 times. For this reason, the optical confinement coefficient in the p-type conductivity type layer can be set smaller, that is, the doping concentration of the same layer can be set higher.

  In one embodiment, the thickness of the thickest layer among the n-type conductivity type layers is d1, the refractive index of the material constituting the layer is n1, and the thickness of the thickest layer among the p-type conductivity layers is d2, where the refractive index of the material constituting the layer is n2, (d1 × n1)> (d2 × n2).

  Of the p-type and n-type conductivity type layers, the sum of the optical confinement factors of the n-type conductivity layer is actually determined by defining the layer thicknesses of these layers that contribute most to the asymmetry of the optical confinement factor. The sum of the optical confinement coefficients of the p-type conductivity layer can be made larger.

In one embodiment, the active layer includes one or more light emitting layers that emit light, and the ratio of the amount of light present in all the light emitting layers to the total amount of light present in all the layers in the substrate and on the substrate is calculated. When the optical confinement factor is Γ (act) and the total thickness of all the light emitting layers is d (act) (unit: cm), Γ (act) / d (act) ≦ 3.0 × 10 ⁴ cm ^-1 .

The layer structure of this embodiment is intended to suppress the light density of the light emitting layer to 3.0 × 10 ⁴ cm ⁻¹ or less. As described above, in the semiconductor material used for the light emitting layer in the near infrared wavelength band, when the light density of the light emitting layer exceeds 3.0 × 10 ⁴ cm ⁻¹ , the reliability of the semiconductor laser element is significantly lowered. It is because it is known that By setting the layer structure so that Γ (act) / d (act) ≦ 3.0 × 10 ⁴ cm ⁻¹ , it is possible to satisfactorily prevent a decrease in the reliability of the semiconductor laser element.

In one embodiment, when the optical confinement coefficients Γ (m) and Γ (l) of the p-type and n-type conductivity layers m and l are 1.0 × 10 ⁻⁴ or more, the p-type and n-type, respectively. The conductivity type layers m and l have a doping concentration P (m) and N (l) of 8.0 × 10 ¹⁸ cm ⁻³ or less.

When doping of about 10 ¹⁷ to 10 ¹⁸ cm ⁻³ is performed in the semiconductor, generally, the refractive index of the semiconductor layer increases as the doping concentration increases. This tendency becomes significant when the AlGaAs-based semiconductor material exceeds 8.0 × 10 ¹⁸ cm ⁻³ , and as a result, the value of the optical confinement coefficient Γ of the corresponding layer becomes larger than the set value. In this case, the sum Σ {Γ (l) × N (l)}, Σ {Γ (m) × P (m)} of the product of the optical confinement coefficient and the doping concentration of each of the p-type and n-type conductivity type layers Even if it is set below the upper limit according to the present invention, the optical confinement coefficient in both layers increases due to an increase in the refractive index, and there is a possibility that this set upper limit will be exceeded. In this embodiment, such inconvenience is avoided, and a near-infrared wavelength band semiconductor laser device of 1.0 μm or less having the above-described effects can be manufactured with a high yield as designed.

In the present invention, as described above, the oscillation wavelength is Ru der than 700 nm.

In the short wavelength band, the influence of absorption due to valley transition in the energy band of free electron absorption is considered to be large. This is a phenomenon including a component that is inversely proportional to the wavelength, but the inventor has found that the value of the free electron absorption αfc of the p-type conductivity layer exceeds 10 cm ⁻¹ particularly in a wavelength region of less than 700 nm. In the present invention , since the oscillation wavelength is set to be 700 nm or more, a highly efficient semiconductor laser device can be realized without being affected by the free electron absorption component inversely proportional to the wavelength.

  In one embodiment, the light confinement structure confines light in a direction parallel to the active layer, and the plurality of p-type conductivity layers are provided on the side where the light confinement structure exists with the active layer interposed therebetween. The plurality of n-type conductivity layers are provided on the side where the optical confinement structure does not exist. In other words, the sum of the light confinement coefficients of the layer having the light confinement structure with the active layer in between is smaller than the sum of the light confinement coefficients of the layer having no light confinement structure.

  As described above, in the semiconductor laser device of the present invention, the sum of the light confinement coefficients of the p-type conductivity type layer is set to be smaller than that of the n-type conductivity type layer. Therefore, by making the side where the optical confinement structure exists as a p-type conductivity type layer as in this embodiment, the amount of light existing on the optical confinement structure side becomes smaller than the opposite side across the active layer, The difference in refractive index in the direction parallel to the active layer where light is felt is reduced. As a result, the direction parallel to the active layer, that is, the transverse mode can be stabilized, and the deterioration of the relative noise intensity of the semiconductor laser element due to the instability of the transverse mode can be prevented. A semiconductor laser element whose value satisfies the specification range can be realized.

  In the light confinement structure, the region where light is confined can be formed from at least one of the p-type conductivity layers.

In one embodiment, the current injection region includes a current injection region and a non-current injection region, and has a current confinement structure that confines current in a direction parallel to the active layer, and the current injection region is at least one of the p-type conductivity layers. The p-type conductivity layer in the current injection region has a doping concentration of 1.0 × 10 ¹⁸ cm ⁻³ or more.

In order to stabilize the oscillation transverse mode, the current injection region of the current confinement structure is generally set to a narrow value of about several μm, and the layer thickness in the layer stacking direction of the structure is almost the same as that of the p-type conductivity type layer. Occupy. Therefore, among the p-type conductivity type layers, the contribution to the element resistance of the p-type conductivity type layers forming these current injection regions is particularly large. For this reason, in this embodiment, by setting the doping concentration of these layers to be 1.0 × 10 ¹⁸ cm ⁻³ or more, the deterioration of efficiency due to free electron absorption can be avoided more effectively and It was possible to obtain a semiconductor laser device that realized power consumption.

  The semiconductor laser device of the present invention may include the optical confinement structure and the current confinement structure at the same time. In this case, the current injection region of the current confinement structure is generally formed to match the region where the light of the light confinement structure is confined.

In one embodiment, the n-type conductivity type layer includes an n-type cladding layer and an n-type buffer layer positioned between the substrate and the n-type cladding layer, and all the layers in and on the substrate. The ratio of the amount of light existing in the n-type buffer layer to the total amount of light present in the layer is defined as a light confinement coefficient Γ (buf), and in the substrate relative to the total amount of light present in all layers on the substrate and the substrate. When the ratio of the existing light quantity is the optical confinement coefficient Γ (sub), Γ (buf) + Γ (sub) ≦ 5.0 × 10 ⁻⁵ is characterized.

Since the oscillation wavelength of the semiconductor laser device of the present invention is in the near-infrared wavelength band of 1.0 μm or less, in general, when light exceeding a certain value is present on a substrate in which GaAs is used or a buffer layer immediately above it, Either absorption by the band edge or GaAs acts as an optical waveguide, which adversely affects the efficiency and oscillation spectrum of the semiconductor laser device. This influence is particularly remarkable when the sum of the optical confinement coefficients of the n-type buffer layer and the substrate {Γ (buf) + Γ (sub)} is 1.0 × 10 ⁻⁴ or more. In this embodiment, since it is set to 5.0 × 10 ⁻⁵ or less, it is possible to avoid the deterioration of the characteristics of the semiconductor laser element derived from GaAs of the buffer layer and the substrate, and to realize a semiconductor laser having high reliability. it can.

  A high-speed optical wireless communication transmitter according to a second aspect of the present invention is characterized in that a semiconductor laser element having any one of the above-described configurations of the present invention is mounted.

  As described above, the semiconductor laser element used in the present invention realizes high efficiency, low power consumption, and high reliability in consideration of the influence of free electron absorption in the near infrared wavelength of 1.0 μm or less. It is a semiconductor laser element. By using a semiconductor laser element having such characteristics, light having a wavelength of 1.0 μm or less, which will be required in future high-speed optical wireless communication, can be realized with lower power consumption. The transmitter has a high degree of freedom in designing the laser driver and has high reliability.

  An optical disc apparatus according to the third aspect of the present invention is characterized by mounting a semiconductor laser element having any one of the above-described configurations of the present invention.

  According to the present invention, since the mounted semiconductor laser device realizes high efficiency, high temperature characteristics, and low power consumption, the competition for higher output continues in the near infrared wavelength band of 1.0 μm or less. In the optical disk apparatus, the disk rotation speed can be increased more than before. In the optical disk apparatus of the present invention, the access time to the disk, which has been a problem particularly when writing to a CD-R / RW, is much shorter than that of a conventional apparatus using a semiconductor laser element, so that the operation is more comfortable. Can be realized.

  According to the first aspect of the present invention, the deterioration of static characteristics due to the influence of free electron absorption in the p-type and n-type conductivity layers is avoided in the near-infrared wavelength band of wavelength of 1.0 μm or less, and light emission By defining the layer structure within a range where p-type doping can be performed at as high a concentration as possible while suppressing an increase in the light density of the layer, high efficiency and low power consumption that are in a trade-off relationship with the doping concentration It is possible to provide a semiconductor laser device for near-infrared wireless communication having a wavelength of 1.0 μm or less, which is compatible and can be improved in reliability.

  In addition, according to the second aspect of the present invention, high-speed optical wireless communication driven at a wavelength in the near-infrared wavelength band of 1.0 μm or less with high reliability and high degree of freedom in designing a laser driver circuit in the apparatus. A transmission device can be provided.

  In addition, according to the third aspect of the present invention, it is possible to provide an optical disc apparatus in which the data read / write speed is increased as compared with the prior art.

<First Embodiment>
A first embodiment of the present invention will be described with reference to FIGS. 1 and 2 are schematic cross-sectional views showing the structure and manufacturing method of this embodiment, respectively. First, the structure of this embodiment will be described with reference to FIG. In all the subsequent embodiments, the n-type conductivity type layer is represented by “n−”, and the p-type conductivity type layer is represented by “p−”. In addition, “lower” and “upper” in the names of layers mean that they are located on the “substrate side” and “the opposite side of the substrate”, respectively, across the active layer.

  The layer structure consists of a buffer layer 102, a lower cladding layer 103, a lower light guide layer 104, a multiple quantum well active layer 105 composed of a quantum well layer and a barrier layer, an upper light guide layer 106, and an upper first cladding layer on a substrate 101. 107, an etching stop layer 108, an upper second cladding layer 109, and a first cap layer 110 are laminated in this order from the substrate side, and the lowermost portion of the ridge is the etching stop layer between the upper second cladding layer 109 and the first cap layer 110. A ridge stripe structure (ridge stripe portion R) directly above is formed. Further, on both sides of the ridge stripe portion R, a first buried layer 111, a second buried layer 112, and a third buried layer 113 (collectively referred to as a buried portion F) are stacked so as to bury their side surfaces. The buried portion F and the ridge stripe portion R form a current confinement structure in which a current flows mainly directly below the ridge stripe portion R. Further, a second cap layer 114 and a third cap layer 115 are laminated on the entire upper surface of the ridge stripe portion R and the buried portion F. Electrodes 116 and 117 are provided on the third cap layer 115 and on the back surface of the substrate 101, respectively.

In a specific example of the first embodiment, an n-GaAs buffer layer 102 (0.5 μm thickness), an n-Al _0.452 Ga _0.548 As lower cladding layer 103 (1.8 μm) are formed on an n-GaAs substrate 101. N-Al _0.4 Ga _0.6 As lower light guide layer 104 (95 nm thickness), two 0.08% compressive strain In _0.06 Ga _0.94 As quantum well layer (4.5 nm thickness), n-Al _0.4 Ga _0.6 As ) And three layers of unstrained Al _0.15 Ga _0.85 As barrier layers (the thickness of the first and third barrier layers from the substrate side is 21.5 nm, the second is 8 nm thick from the three layers) Alternately stacked undoped multiple quantum well active layers 105 (oscillation wavelength 0.87 μm), p-Al _0.4 Ga _0.6 As upper light guide layer 106 (90 nm thickness), p-Al _0.5 Ga _0.5 As upper first cladding layer 107 (0.15 μm thick), p-GaAs etching stop layer 108 (4 m thick) P-Al _0.53 Ga _0.48 As second upper cladding layer 109 (1.28 thick), p-GaAs first cap layer 110 (0.75 .mu.m thick) are laminated from the substrate side in this order, The upper second cladding layer 109 and the first cap layer 110 form a ridge stripe portion R in which the lowermost portion of the ridge is directly above the etching stop layer.

  The ridge stripe portion R has a height of about 2 μm, and a width (that is, a distance between two boundary surfaces defining the ridge stripe portion R) is about 3.1 μm at the widest point immediately above the etching stop layer 108. Here, the height of the ridge stripe portion R means the sum of the layer thicknesses of the upper second cladding layer 109 and the first cap layer 110, which are removed by using an etching method described later.

Further, the n-Al _0.7 Ga _0.3 As first buried layer 111 (0.6 μm thickness) and the n-GaAs second buried layer 112 (0. 7 μm thick) and a p-GaAs third buried layer 113 (0.7 μm thick) are stacked, and the buried portion F and the ridge stripe portion R form a current confinement structure in which current flows mainly directly under the ridge stripe portion R. There is no. Further, a p-GaAs second cap layer 114 (0.95 μm thickness) and a p-GaAs third cap layer 115 (0.3 μm thickness) are laminated on the entire upper surface of the ridge stripe portion R and the buried portion F.

  A p-side electrode 116 made of a metal thin film is formed on the p-GaAs third cap layer 115, and an n-side electrode 117 also made of a metal thin film is formed on the back surface of the n-GaAs substrate 101. .

  Next, the manufacturing method of this embodiment is demonstrated using FIG. 2A-2C. The constituent materials and layer thickness of the layers are shown above and are omitted here.

  First, as shown in FIG. 2A, a quantum consisting of an n-buffer layer 102, an n-lower cladding layer 103, an n-lower light guide layer 104, two well layers, and three barrier layers on an n-substrate 101. The well active layer 105, the p-upper light guide layer 106, the p-upper first cladding layer 107, the p-etching stop layer 108, the p-upper second cladding layer 109, and the p-first cap layer 110 are treated with an organic metal chemistry. The layers are stacked in this order using a phase growth method (MOCVD method). The growth temperature is set to 690 ° C. for the quantum well active layer and 713 ° C. for the other layers, and the growth starts after the actual substrate temperature reaches the set temperature.

Thereafter, as shown in FIG. 2B, by using an etching method using the insulating film 121 made of SiO ₂ as a mask as an example, the ridge stripe portion R has a height of about 2 μm and a width of about 3.1 μm at the bottom. Is made. Etching is performed up to just above the p-GaAs etching stop layer 108 using a mixed aqueous solution of sulfuric acid and hydrogen peroxide and hydrofluoric acid.

  Next, as shown in FIG. 2C, by using the MOCVD method again, the n-first buried layer 111, the n-second buried layer 112, and the p-third are buried in the side surfaces on both sides of the ridge stripe portion R. The buried layer 113 is sequentially stacked. At this time, since the insulating film 121 is present on the upper surface of the ridge stripe portion R, the buried layers do not grow on the ridge stripe portion R, and the buried layers 111 to 113 are stacked only on both sides of the ridge stripe portion R. can do. Thereafter, the insulating film 121 is removed, and the p-second cap layer 114 and the p-third cap layer 115 are stacked again using the MOCVD method.

  Thereafter, after vapor-depositing p-side and n-side ohmic electrodes 116 and 117 (see FIG. 1) made of Ti / Pt / Au and AuGe / Ni, respectively, on both the p-side and n-side surfaces, The buried ridge type semiconductor laser element having a resonator length of 500 μm that emits light in the stripe direction is obtained through the wafer process (wafer bar division by cleavage, reflection film formation by end face coating, chip division). In this embodiment, silicon Si is used for the n-type and zinc Zn is used for the p-type as the dopant impurity material.

  In this embodiment, a current flows from the upper side of FIG. 1 on the third cap layer side to the lower side of FIG. 1 on the substrate side. At this time, the conductivity type of each layer has a structure as described above. Therefore, the first, second, and third buried layers 111, 112, and 113 serve as non-current injection regions, and current flows from the third cap layer 115 through the ridge stripe portion R that is the current injection region to the active layer 105. A current confinement structure is formed that flows to a layer below the etching stop layer 108 including.

  In addition, the light confinement structure for confining light in the direction parallel to the active layer in the present embodiment includes the upper second cladding layer 109 which is one of the layers constituting the ridge stripe portion R and the non-current injection region. It is formed by the difference in refractive index from the first buried layer 111 which is one of the layers to be formed. That is, the optical confinement structure shares these layers 109 and 111 with the current confinement structure.

The doping concentration N and the optical confinement coefficient Γ of the n-type conductivity type layer of the semiconductor laser device of this embodiment are 8.0 × 10 ¹⁷ cm ⁻³ and less than 1.0 × 10 ^{−5 in} the buffer layer 102, respectively. The lower cladding layer 103 is 5.0 × 10 ¹⁷ cm ⁻³ , 0.200, the lower light guide layer 104 is 5.0 × 10 ¹⁷ cm ⁻³ , 0.308, and the optical confinement factor of the GaAs substrate 101 is Like the buffer layer, it is less than 1.0 × 10 ⁻⁵ , and the n-type conductivity type layers 1 (l = 1, 2, 3 in this embodiment) from the buffer layer 102 to the lower light guide layer 104 on the GaAs substrate 101 are used. The sum Σ {Γ (l) × N (l)} of the product of the optical confinement coefficient Γ (l) and the doping concentration N (l) is 2.54 × 10 ¹⁷ cm ^−3, and n Of the optical confinement coefficient Γ (l) of the p-type conductivity type layer l Σ {Γ The value of l)} is set to be 0.509.

In addition, the doping concentration P and the optical confinement coefficient Γ of the p-type conductivity layer of the semiconductor laser device of this embodiment are 1.35 × 10 ¹⁸ cm ⁻³ and 0.167, respectively, in the upper light guide layer 106. 1.35 × 10 ¹⁸ cm ⁻³ , 0.118 for the first cladding layer 107, 2.4 × 10 ¹⁸ cm ⁻³ , 0.049 for the upper second cladding layer 109, and the first cap for the GaAs cap layer layer 110 at ^{3.0 × 10 18 cm -3, 1.0} × 10 -6, a second cap layer ^{114 3.0 × 10 18 cm -3,} 1.0 × 10 than ^-7, third cap layer 115 is less than 1.0 × 10 ²⁰ cm ⁻³ and less than 1.0 × 10 ^−7, and the p-type from the upper light guide layer 106 adjacent to the active layer 105 to the third cap layer 115 through the ridge stripe portion R Conductive layer m (this implementation The state, m = 1,2 ... 7 optical confinement factor gamma (m) the product sum Σ {Γ (m) × P (m)} value 5.02 × 10 of the doping concentration P (m)) of The sum Σ {Γ (m)} of the optical confinement coefficient Γ (m) of the p-type conductivity type layer m is ¹⁷ cm ⁻³ so that the value of Σ {Γ (l) of the n-type conductivity type layer l is } Is set to be 0.334 smaller than the value of}.

  The ratio Σ {Γ (l)} / Σ of the sum of the optical confinement coefficients of the p-type and n-type conductivity type layers by setting the doping concentration and the optical confinement coefficient of the n-type conductivity type layer and the p-type conductivity type layer. The value of {Γ (m)} is 1.52, and the ratio {Σ {Γ (l) × N () of the product of the optical confinement coefficient of each of the p-type and n-type conductivity type layers and the doping concentration of the same layer. l)}} / {Σ {Γ (m) × P (m)}} has a value of 0.51.

Further, the optical confinement coefficient Γ (act) of the two quantum well layers (hereinafter also simply referred to as “well layers”) is set to the total layer thickness d (act) of these two well layers (in this embodiment, about The so-called light-emitting layer light density {Γ (act)} / {d (act)} divided by 9 nm is set to 1.36 × 10 ⁻⁴ cm ⁻¹ .

  Here, for example, the optical confinement coefficient Γ (l) of the n-type conductivity type layer 1 is, as described above, the amount of light present in the layer l relative to the total amount of light present in all layers on the substrate and on the substrate. It means the ratio.

  It should be noted that the p-etching stop layer 108 has an extremely small thickness compared to other p-type conductivity layers, and therefore the amount of light, more specifically, the light confinement factor, affects the total value. Since it is not negligible, it is excluded from consideration. In the embodiments described later, the p-etching stop layer is similarly handled.

In addition, the doping concentration of the buried layer serving as the non-current injection portion in the current confinement structure is 2.0 × 10 ¹⁸ cm ^{−3 for} the n−first buried layer 111 and 3.0 × for the n−second buried layer 112. 10 ¹⁸ cm ⁻³ , and the p-third buried layer 113 was 2.0 × 10 ¹⁸ cm ⁻³ .

As the characteristics of the semiconductor laser device of this embodiment, an efficiency value of 0.99 W / A and an internal absorption αi value of 4.0 cm ⁻¹ were obtained. Further, the temperature characteristics were as good as 120 K or more, and the resistance value did not increase due to the decrease in the p-type doping concentration. A linear current-light output characteristic was obtained without the occurrence of kinks due to instability of the transverse mode. As for the reliability test, neither end face deterioration nor slow deterioration of the laser characteristics due to the long-term life test occurred. The vertical radiation angle was 34 degrees, which was less than 40 degrees.

In the present embodiment, in a semiconductor laser device that oscillates in the near infrared wavelength band of wavelength 870 nm or less and a wavelength of 1.0 μm or less, the optical confinement coefficient Γ (m) and the doping concentration P (m) of the p-type conductivity type layer m are particularly high. The sum of products Σ {Γ (m) × P (m)} is set to 5.02 × 10 ¹⁷ cm ^{−3 of} 8.0 × 10 ¹⁷ cm ⁻³ or less, and the n-type conductivity layer The value of the total optical confinement coefficient Σ {Γ (l)} is set to 0.509, which is larger than the value 0.334 of the total optical confinement coefficient Σ {Γ (m)} of the p-type conductivity layer. Of all the p-type conductivity type layers, the doping concentration is set to 1.0 × 10 ¹⁸ cm ^{−3 in a} layer corresponding to 80% or more of these p-type conductivity type layers. Specifically, the layer thickness and the doping concentration are respectively 90 nm and 1.35 × 10 ¹⁸ cm ^{−3 for} the upper light guide layer 106, and 0.15 μm and 1.35 × 10 ¹⁸ cm ^{− for the} upper first cladding layer 107. ³ , 4 nm for the etching stop layer 108, 8.2 × 10 ¹⁷ cm ⁻³ , 1.28 μm for the upper second cladding layer 109, 2.4 × 10 ¹⁸ cm ⁻³ , 0.75 μm for the first cap layer 110, 3.0 × 10 ¹⁸ cm ⁻³ , 0.95 μm for the second cap layer 114, 3.0 × 10 ¹⁸ cm ⁻³ , 0.3 μm for the third cap layer 115, 1.0 × 10 ²⁰ cm ⁻³ Of these p-type conductivity type layers, a layer having a thickness substantially equivalent to 100% is set to have a doping concentration of 1.0 × 10 ¹⁸ cm ⁻³ . As a result, consumption is reduced by setting the doping concentration of the p-type conductivity layer high while avoiding a decrease in efficiency due to an increase in free electron absorption in the p-type conductivity layer and a decrease in reliability due to an increase in light density of the light emitting layer. Since the power can be reduced, a near-infrared semiconductor laser device that simultaneously satisfies the three characteristics of high efficiency, low power consumption, and high reliability, which was impossible in the past, could be realized.

Furthermore, in this embodiment, the sum Σ {Γ (l) × N (l) of the product of the optical confinement coefficient Γ (l) of the n-type conductivity type layer l and the doping concentration N (l) of the n-type conductivity type layer l. } Is set to 2.54 × 10 ¹⁷ cm ⁻³ and 4.0 × 10 ¹⁸ cm ⁻³ or less. As a result, the sum of the optical confinement coefficients of the n-type conductivity type layer Σ {Γ (l) while reliably avoiding the influence of free electron absorption by the n-type dopant, whose degree of contribution to free electron absorption has been unknown so far } Can be made larger than the total optical confinement coefficient Σ {Γ (m)} of the p-type conductivity layer, so that high efficiency of 0.99 W / A can be achieved while maintaining high reliability and low power consumption. A semiconductor laser element could be obtained.

In this embodiment, the product value of 5.93 × 10 ^{−4 is} the product of the thickness n of the n-type lower cladding layer 103 of the n-type cladding layer of 1.8 μm and the refractive index of the material constituting the layer 3.293. cm is the product of 4.28 × 10 ⁻⁴ cm, which is the product of the layer thickness of 1.28 μm of the thickest p-upper second cladding layer 109 of the p-type cladding layer and the refractive index of 3.245 of the material constituting the layer. The layer structure is set to be larger.

Of the n-type and p-type conductivity layers, the two layers 103 and 109 contribute most to the magnitude of the sum Σ {Γ (l)} and Σ {Γ (m)} of the light confinement coefficients of each conductivity type layer. However, since the magnitude relationship between the optical confinement coefficients of both can be actually set to a desired relationship, the p-type doping concentration is set to 1 while avoiding an increase in free electron absorption, a decrease in reliability, and an increase in radiation angle. To obtain a semiconductor laser element with low power consumption that can be set to a high value that is effective for maintaining temperature characteristics and reducing resistance, such as .35 × 10 ¹⁸ cm ^{−3 to} 3.0 × 10 ¹⁸ cm ^−3. I was able to.

Further, in the present embodiment, the ratio of the amount of light present in the light emitting layer in the active layer to the total amount of light present in all layers in the substrate and on the substrate is the light confinement coefficient Γ (act), and the layer of the light emitting layer When the total thickness is d (act) (unit: cm), the ratio Γ (act) / d (act) of the former to the latter is 1.36 × 10 ⁴ cm ⁻¹ and 3.0 × 10 ⁴ cm ^{−. The} layer structure is determined to be ¹ or less. This avoids deterioration of characteristics due to free electron absorption and increase in device resistance, and avoids deterioration of reliability due to deterioration of the light emitting layer, and maintains high efficiency and low power consumption in the corresponding wavelength band. However, a highly reliable semiconductor laser could be obtained.

Furthermore, in the present embodiment, the doping concentrations of the upper second cladding layer 109 and the first to third cap layers 110, 114, and 115 are 2.4 × 10 ¹⁸ cm ⁻³ , 3.0 × 10 ¹⁸ cm ⁻³ , respectively. 3.0 × 10 ¹⁸ cm ⁻³ and 1.0 × 10 ²⁰ cm ⁻³ are all set to be 1.0 × 10 ¹⁸ cm ⁻³ or more. These layers constitute a current injection region whose width is determined by a narrow ridge width of several μm in the current confinement structure, and the total thickness of the layers is 3.28 μm, which is about the entire p-type conductivity type layer. Since it accounts for 80% or more of 90%, the contribution of these layers to the device resistance is extremely large. For this reason, by setting the doping concentration of these layers to be 1.0 × 10 ¹⁸ cm ⁻³ or more, it is possible to avoid deterioration of characteristics due to free electron absorption and to reduce the resistance of the element. did it.

In this embodiment, the sum of the optical confinement coefficients Γ (sub) and Γ (buf) of the substrate 101 and the buffer layer 102 is set to a very small value of about 2.0 × 10 ⁻⁶ or less.

In general, in the near-infrared wavelength band of 0.7 to 1.0 μm, a GaAs substrate is used as the substrate, and the same material is mainly used as the buffer layer. Therefore, the substrate and the buffer layer have a higher refractive index than other layers and are transparent to the oscillation wavelength. For this reason, when light having an optical confinement factor exceeding 5.0 × 10 ⁻⁵ exists in the substrate and the buffer layer, these layers become waveguide layers and cause interference with the original guided light passing through the active layer. Since this interference causes a plurality of kinks in the current-light output characteristics, communication quality such as a code error rate is deteriorated. In this embodiment, the sum of the optical confinement coefficients Γ (sub) and Γ (buf) of the substrate and the buffer layer is set to be about 2.0 × 10 ⁻⁶ or less and 5.0 × 10 ⁻⁵ or less. A semiconductor laser element capable of performing a highly efficient and stable communication operation without being affected by these effects was obtained.

  For the definition of the strain of the well / barrier layer constituting the quantum well active layer 105, the lattice constant of the GaAs substrate is a (GaAs) and the lattice constant of the well layer or barrier layer is a. )} / A (GaAs), where the sign is positive is compression strain, and the sign is negative is tensile strain. The magnitude of strain is expressed as an absolute value for both compression / tensile strain.

Second Embodiment
The structure of the semiconductor laser device according to the second embodiment of the present invention will be described with reference to FIG.

  The layer structure consists of a buffer layer 202, a lower first cladding layer 203a, a lower second cladding layer 203b, a lower light guide layer 204, a multiple quantum well active layer 205 composed of a quantum well layer and a barrier layer, an upper light, on a substrate 201. The guide layer 206, the upper first cladding layer 207, the etching stop layer 208, the upper second cladding layer 209, and the first cap layer 210 are laminated in this order from the substrate side, and the upper second cladding layer 209, the first cap layer 210, Thus, a ridge stripe structure (ridge stripe portion R) is formed in which the lowermost portion of the ridge is directly above the etching stop layer. On both sides of the ridge stripe portion R, a first buried layer 211, a second buried layer 212, and a third buried layer 213 (collectively buried portions F) are stacked so as to bury their side surfaces. The stripe portion R forms a current confinement structure in which current flows mainly directly under the ridge stripe portion R. Further, a second cap layer 214 and a third cap layer 215 are laminated on the entire upper surface of the ridge stripe portion R and the buried portion F.

In a specific example of the second embodiment, an n-GaAs buffer layer 202 (0.5 μm thick), an n-Al _0.45 Ga _0.55 As lower first cladding layer 203a (3 0.04 μm thick), n-Al _0.47 Ga _0.53 As lower second cladding layer 203b (0.24 μm thick), n-Al _0.43 Ga _0.57 As lower light guide layer 204 (103 nm thick), Two layers of 0.4% compressive strain In _0.21 Ga _0.79 As _0.62 P _0.38 quantum well layer (7.5 nm thickness) and three layers 0.8% tensile strain In _0.09 Ga _{0 .91} As _0.4 P _0.6 Barrier Layer (Undoped Multiple Quantum Well with Alternating Layers of Layers 10th and 5th Thickness of First and Third Barrier Layers from the Substrate Side of the Three Layers) Active layer 205 (oscillation wavelength 0.75 μm), p-Al _0.43 Ga _0.57 As upper light guide layer 206 (53 nm thickness), p-Al _0.49 Ga _0.51 As upper first cladding layer 207 (0.177 μm thickness), p-GaAs etching stop layer 208 (3 nm thickness), p-Al _0.49 Ga 0.5 _{. A 51} As upper second cladding layer 209 (1.28 μm thickness) and a p-GaAs first cap layer 210 (0.75 μm thickness) are laminated in this order from the substrate side, and the upper second cladding layer 209 and the first cap layer 210 are laminated. Thus, a ridge stripe portion R is formed in which the lowermost portion of the ridge is directly above the etching stop layer. The ridge stripe portion R has a height of about 2 μm and a width of about 2.1 μm at the widest portion immediately above the etching stop layer 208.

The n-Al _0.7 Ga _0.3 As first buried layer 211 (0.6 μm thickness) and the n-GaAs second buried layer 212 (0.7 μm thickness) are embedded on both sides of the ridge stripe portion R. ), A p-GaAs third buried layer 213 (0.7 μm thick) is stacked, and the buried portion F and the ridge stripe portion R form a current confinement structure in which current flows mainly directly below the ridge stripe portion R. . Further, a p-GaAs second cap layer 214 (0.95 μm thickness) and a p-GaAs third cap layer 215 (0.3 μm thickness) are laminated on the entire upper surface of the ridge stripe portion R and the buried portion F.

  A p-side electrode 216 made of a metal thin film is formed on the p-GaAs third cap layer 215, and an n-side electrode 117 made of a metal thin film is also formed on the back surface of the n-GaAs substrate 201. .

  The growth profile such as the growth temperature and interruption when the semiconductor laser device of this embodiment is manufactured using the metal organic chemical vapor deposition method is the same as that of the first embodiment. The process up to the edge emitting semiconductor laser element is also the same as in the first embodiment.

The doping concentration N and the optical confinement coefficient Γ of the n-type conductivity type layer of the semiconductor laser device of this embodiment are 7.0 × 10 ¹⁷ cm ⁻³ and less than 1.0 × 10 ^{−5 in} the buffer layer 202, respectively. 3.0 × 10 ¹⁸ cm ⁻³ and 0.337 for the lower first cladding layer 203 a, 3.0 × 10 ¹⁸ cm ⁻³ and 0.240 for the lower second cladding layer 203 b, and 1 for the lower light guide layer 204. 0 × 10 ¹⁸ cm ⁻³ , 0.176, and the optical confinement coefficient of the GaAs substrate 201 is less than 1.0 × 10 ^−5, similar to the buffer layer 202, and the lower light guide layer is formed from the buffer layer 202 on the GaAs substrate 201. The sum Σ {Γ (l) × N of the product of the optical confinement coefficient Γ (l) and the doping concentration N (l) of the n-type conductivity type layer l up to 204 (in this embodiment, l = 1, 2,... 4). The value of (l)} is 1.83 × 10 ¹ The total sum Σ {Γ (l)} of the optical confinement coefficient Γ (l) of the n-type conductivity type layer 1 is set to be 0.728 so as to be ⁸ cm ⁻⁸ .

Further, the doping concentration P and the optical confinement coefficient Γ of the p-type conductivity layer of the semiconductor laser device of this embodiment are 1.0 × 10 ¹⁸ cm ⁻³ and 0.086 for the upper light guide layer 206, respectively. 1.35 × 10 ¹⁸ cm ⁻³ , 0.133 for one cladding layer 207, 4.0 × 10 ¹⁸ cm ⁻³ , 0.062 for the upper second cladding layer 209, and the first cap layer for the GaAs cap layer 210 × 4.0 × 10 ¹⁸ cm ⁻³ , 5.0 × 10 ⁻⁶ , second cap layer 214 = 3.0 × 10 ¹⁸ cm ⁻³ , less than 1.0 × 10 ⁻⁷ , third cap layer 215 P-type conductivity from the upper light guide layer 206 adjacent to the active layer 205 to the third cap layer 215 through the ridge stripe portion R, and less than 1.0 × 10 ²⁰ cm ⁻³ and 1.0 × 10 ^−7. Mold layer m (this embodiment It is, m = 1,2 ... 7) optical confinement factor gamma (m) and the doping concentration P product sum Σ {Γ (m) × P (m)} value substantially 5.16 × 10 of the (m) of Further, the value of the sum Σ {Γ (m)} of the optical confinement coefficient Γ (m) is set to be 0.282 so as to be ¹⁷ cm ⁻³ .

  The ratio Σ {Γ (l)} / Σ of the sum of the optical confinement coefficients of the p-type and n-type conductivity type layers by setting the doping concentration and the optical confinement coefficient of the n-type conductivity type layer and the p-type conductivity type layer. The value of {Γ (m)} is 2.58, and the ratio {Σ {Γ (l) × N () of the product of the optical confinement coefficient of each of the p-type and n-type conductivity type layers and the doping concentration of this layer l)}} / {Σ {Γ (m) × P (m)}} is 3.56.

Further, the light confinement coefficient Γ (act) of the two well layers is divided by the total layer thickness d (act) of these well layers (in this embodiment, about 15 nm), so-called light emitting layer light density {Γ (act ) The layer structure is set so that the value of} / {d (act)} is 2.45 × 10 ⁴ cm ⁻¹ .

In addition, the doping concentration of the buried layer serving as the non-current injection portion in the current confinement structure is 3.0 × 10 ¹⁸ cm ^{−3 for} the n−first buried layer 211 and 3.0 × 10 for the n−second buried layer 212. 10 ¹⁸ cm ⁻³ and the p-third buried layer 213 were 5.0 × 10 ¹⁸ cm ⁻³ .

As the characteristics of the semiconductor laser device of this embodiment, an efficiency value of 0.97 W / A and an internal absorption αi value of 5 cm ⁻¹ were obtained. Further, the temperature characteristics were as good as 120 K or more, and the resistance value did not increase due to the decrease in the P-type doping concentration. A linear current-light output characteristic was obtained without the occurrence of kinks due to instability of the transverse mode. In terms of reliability, neither end face deterioration nor slow deterioration of laser characteristics due to long-term life test occurred. As for the vertical radiation angle, a value smaller than the first embodiment of 17 degrees could be obtained.

  As described above, in the second embodiment, as in the first embodiment, while maintaining reliability, the second embodiment is not affected by free electron absorption in both the p-type and n-type conductive layers. It was possible to obtain a semiconductor laser element that oscillates in the near-infrared wavelength band of 1.0 μm or less with both high efficiency and high temperature characteristics / low power consumption.

Furthermore, in the present embodiment, the sum Σ {Γ (l) × N (l) of the product of the optical confinement coefficient Γ (l) of the n-type conductivity type layer l and the doping concentration N (l) of the n-type conductivity type layer l. } Is 1.83 × 10 ¹⁸ cm ⁻³ , the sum of products of the optical confinement coefficient Γ (m) of the p-type conductivity layer m and the doping concentration P (m) of the p-type conductivity layer m Σ {Γ (m) × P (m)} is set to 5.16 × 10 ¹⁷ cm ⁻³ , and the layer structure is set so that the former value is 3.56 times the latter value, which is 7/3 or more. ing.

  As explained in the above-mentioned section “Means for Solving the Problems”, the contribution of n-type dopants to free electron absorption has hitherto been about 3/7 times that of p-type dopants. According to the experiments by the inventors, even if the n-type conductive layer exceeds 7/3 times the p-type conductive layer by the sum of the product of the optical confinement coefficient and the doping concentration, it is up to about 5 times. Found no significant impact.

In this embodiment, based on the above experimental results, in addition to the configuration of the first embodiment, the value of Σ {Γ (l)} can be freely set to be 7/3 or more of Σ {Γ (m)}. By setting the light confinement coefficient of the p-type conductivity type layers except for the outermost layer, which can be ignored in consideration of electrons and device resistance, the doping concentration of these p-type conductivity layers is set to 2.0 to It was possible to set a high value of about 4.0 × 10 ¹⁸ cm ⁻³ particularly effective for reducing the element resistance. Therefore, in this embodiment, in addition to suppressing free electron absorption and ensuring reliability by the p-type and n-type conductivity layers, it is possible to reduce the power consumption of the semiconductor laser device compared to the first embodiment.

  Furthermore, in this embodiment, the sum Σ {Γ (l)} of the optical confinement coefficient Γ (l) of the n-type conductivity type layer l is 0.728, and the optical confinement factor Γ (m ) Is set so that the value of the former is 2.582 times the value of the latter and a maximum of 12.5 times. For this reason, the optical confinement coefficient in the p-type conductivity type layer can be made smaller than that in the first embodiment without being affected by free electron absorption in both the p-type and n-type conductivity types, and the doping concentration of the same layer can be reduced. As a result, the power consumption of the semiconductor laser element could be reduced.

Further, in the present embodiment, the present invention is applied to a semiconductor laser element that oscillates at a wavelength shorter than that of the first embodiment, in particular, having an oscillation wavelength of 750 nm. As described above, in the short wavelength band, it is said that the influence of absorption due to transition between valleys in the energy band in the free electron absorption becomes large. This has a component inversely proportional to the wavelength, but the present inventors have found that the value of free electron absorption αfc exceeds 10 cm ⁻¹ particularly at a wavelength of 700 nm or less. Based on this, since the laser oscillation wavelength is set to 750 nm in the present embodiment, a highly efficient semiconductor laser element of 0.97 W / A is obtained without being affected by absorption by the free electron absorption component inversely proportional to the above wavelength. I was able to.

By the way, in the semiconductor laser device of this embodiment, the oscillation wavelength (750 nm) is set to a wavelength band that can be absorbed at the band edge of the GaAs material used for the substrate or the like. However, in this embodiment, since the sum of the optical confinement coefficients of the substrate 201 and the buffer layer 202 is set to a very small value of about 2.0 × 10 ^−6, it is affected by band edge absorption in the substrate and the buffer layer. Thus, a highly efficient semiconductor laser device could be obtained.

<Third Embodiment>
The structure of the semiconductor laser device according to the third embodiment of the present invention will be described with reference to FIG.

  The layer structure of this semiconductor laser device is such that a buffer layer 302, a lower first cladding layer 303a, a lower second cladding layer 303b, a lower light guide layer 304, a multi-quantum well activity comprising a quantum well layer and a barrier layer on a substrate 301. A layer 305, an upper first light guide layer 306a, and an upper second light guide layer 306b (in the drawing, these light guide layers 306a and 306b are represented as one layer for the sake of simplicity). The upper first cladding layer 307, the etching stop layer 308, the upper second cladding layer 309, the first cap layer 310, and the second cap layer 311 are laminated in this order from the substrate side. The two cap layers 310 and 311 form a ridge stripe structure (ridge stripe portion R) in which the bottom of the ridge is directly above the etching stop layer 308. ing. An insulating film 322 is laminated on the side surface and both sides of the ridge stripe portion R, and the insulating film 322 and the ridge stripe portion R form a current confinement structure in which current flows only directly under the ridge stripe portion.

In a specific example of the third embodiment, an n-GaAs buffer layer 302 (0.5 μm thick), an n-Al _0.56 Ga _0.44 As lower first cladding layer 303a (2 0.5 μm thickness), n-Al _0.3 Ga _0.7 As lower second cladding layer 303b (0.05 μm thickness), n-Al _0.41 Ga _0.59 As lower light guide layer 304 (100 nm thickness), Two layers of 0.14% compressive strain In _0.12 Ga _0.88 As quantum well layer (4.8 nm thickness) and three layers of unstrained Al _0.15 Ga _0.85 As barrier layer (substrate out of three) Undoped multiple quantum well active layers 305 (oscillation wavelength 0.895 μm), p-Al _0.4 Ga, in which the first and third barrier layers from the side have a thickness of 22 nm and the second thickness is 8 nm. _0.6 As first optical guide layer 306a (50 nm thick) top, p-Al _0.4 Ga _0.6 As upper Two light guide layer 306 b (50 nm _{thick), p-Al 0.47 Ga 0.53} As first upper cladding layer 307 (0.4 .mu.m thick), p-InGaAsP etch stop layer 308 (15 nm thick), p-Al _{0 .5} Ga _0.5 As upper second cladding layer 309 (1.28 thick), p-GaAs first cap layer 310 (1.7 [mu] m thickness), p-GaAs second cap layer 311 (0.3 [mu] m thick) Stacked in this order from the substrate side, the upper second cladding layer 309 and the first and second cap layers 310 and 311 form a ridge stripe structure (ridge stripe portion R) in which the bottom of the ridge is directly above the etching stop layer 308. is doing.

The ridge stripe portion R has a height of about 3 μm and a width of about 2.7 μm at the widest portion immediately above the etching stop layer 308. A SiO ₂ film is laminated as an insulating film 322 on the side surface and both sides of the ridge stripe portion R to form a current confinement structure in which current flows only directly under the ridge stripe portion.

  A p-side electrode 316 made of a metal thin film is formed on the insulating film 322 and the second cap layer 311, and an n-side electrode 317 made of a metal thin film is also formed on the back surface of the substrate 301.

  Whereas the semiconductor laser elements of the first and second embodiments are ridge buried semiconductor laser elements, the semiconductor laser element of the present embodiment is a ridge waveguide semiconductor laser element.

  In the manufacturing process of the semiconductor laser device of this embodiment, after forming the ridge stripe portion R, the insulating film 322 is formed on the entire surface of the wafer, and then the insulating film portion on the second cap layer 322 is formed by using a photolithography technique. The current path is formed by removing. Except for this point, the manufacturing process of the semiconductor laser device of this embodiment is substantially the same as the manufacturing process of the previous two embodiments, and the growth when growing a crystal using the metal organic chemical vapor deposition method. Growth profiles such as temperature and interruption are the same as those in the first and second embodiments. Further, the process up to the end-emitting semiconductor laser element after electrode formation is the same as in the previous embodiment.

In the semiconductor laser device of the present embodiment, the doping concentration N of the n-type conductivity layer and the value of the optical confinement coefficient Γ are less than 7.0 × 10 ¹⁷ cm ⁻³ and 1.0 × 10 ^{−5 in} the buffer layer 202, respectively. 2.4 × 10 ¹⁸ cm ⁻³ , 0.251 for the lower first cladding layer 303 a, 5.0 × 10 ¹⁷ cm ⁻³ , 0.072 for the lower second cladding layer 203 b, 5 for the lower light guide layer 304. 0.0 × 10 ¹⁷ cm ⁻³ , 0.219, and the optical confinement coefficient of the GaAs substrate 301 is less than 1.0 × 10 ^−5, similar to the buffer layer 302, and the lower light guide from the buffer layer 302 on the GaAs substrate 301. Sum of products of optical confinement coefficient Γ (l) and doping concentration N (l) of n-type conductivity type layer l (in this embodiment, l = 1, 2,... 4) up to layer 304 Σ {Γ (l) × The value of N (l)} is 7.48 × 10 The total sum Σ {Γ (l)} of the optical confinement coefficient Γ (l) of the n-type conductivity type layer 1 is set to 0.542 so as to be ¹⁷ cm ⁻⁸ .

Further, the doping concentration P and the optical confinement coefficient Γ of the p-type conductivity layer of the semiconductor laser device of the present embodiment are 3.0 × 10 ¹⁷ cm ⁻³ , 0.135, and 0.135, respectively, in the upper first light guide layer 306a. 8 × 10 ¹⁷ cm ⁻³ , 0.06 for the upper second light guide layer 306 b, 1.35 × 10 ¹⁸ cm ⁻³ , 0.119 for the upper first cladding layer 307, and 3.10 for the upper second cladding layer 309. For 0 × 10 ¹⁸ cm ⁻³ , 0.011, GaAs cap layer, p-first cap layer 310 is 5.0 × 10 ¹⁸ cm ⁻³ , 1.0 × 10 ⁻⁶ , p-second cap layer. 311 is set to 1.0 × 10 ²⁰ cm ⁻³ and less than 1.0 × 10 ⁻⁷ , from the upper first light guide layer 306 a adjacent to the active layer 305 to the second cap layer 311 through the ridge stripe portion R. p-type conductivity layer m (book In the embodiment, the sum Σ {Γ (m) × P (m)} of products of the optical confinement coefficient Γ (m) and the doping concentration P (m) for m = 1, 2,... 7) is 2.81 ×. Further, the value of the sum Σ {Γ (m)} of the optical confinement coefficient Γ (m) of the p-type conductivity type layer m is set to be 0.325 so as to be 10 ¹⁷ cm ⁻³ .

  The ratio Σ {Γ (l)} / Σ of the sum of the optical confinement coefficients of the p-type and n-type conductivity type layers by setting the doping concentration and the optical confinement coefficient of the n-type conductivity type layer and the p-type conductivity type layer. The value of {Γ (m)} is 1.67, and the ratio {Σ {Γ (l) × N () of the product of the optical confinement coefficient of each of the p-type and n-type conductivity type layers and the doping concentration of the corresponding layer l)}} / {Σ {Γ (m) × P (m)}} has a value of 2.66.

Further, a so-called light emitting layer light density {Γ that is obtained by dividing the optical confinement coefficient Γ (act) of the two well layers by the total layer thickness d (act) of these well layers (in this embodiment, about 9.6 nm). The layer structure is set so that the value of (act)} / {d (act)} is 1.28 × 10 ⁴ cm ⁻¹ .

As the characteristics of the semiconductor laser device of this embodiment, an efficiency value of 0.97 W / A and an internal absorption αi value of 5 cm ⁻¹ were obtained. Further, the temperature characteristics were as good as 120 K or more, and the resistance value did not increase due to the decrease in the p-type doping concentration. A linear current-light output characteristic was obtained without the occurrence of kinks due to instability of the transverse mode. In terms of reliability, neither end face deterioration nor slow deterioration of laser characteristics due to long-term life test occurred. As for the vertical radiation angle, a value of less than 40 degrees could be obtained as in the first and second embodiments of 36 degrees.

  As described above, in this embodiment, as in the first and second embodiments, while maintaining reliability, high efficiency without being affected by free electron absorption in both the p-type and n-type conductive layers. As a result, a semiconductor laser element that oscillates in the near-infrared wavelength band of 1.0 μm or less, which satisfies both high temperature characteristics and low power consumption, can be obtained.

Further, as in the second embodiment, in this embodiment, the sum Σ {Γ of the product of the optical confinement coefficient Γ (l) of the n-type conductivity type layer l and the doping concentration N (l) of the n-type conductivity type layer 1 (L) × N (l)} (7.48 × 10 ¹⁷ cm ⁻³ ), the optical confinement coefficient Γ (m) of the p-type conductivity layer l and the doping concentration P ( The sum of the products of m) becomes 7/3 or more in a range not exceeding 5 times the maximum, compared to the value of Σ {Γ (m) × P (m)} (2.81 × 10 ¹⁷ cm ⁻³ ) It is set as follows.

  Therefore, under the layer structure set to suppress free electron absorption in the p-type conductivity type layer, the contribution of free electron absorption in the n-type conductivity type layer to the contribution of free electron absorption in the p-type conductivity type layer And a high efficiency value of 1.0 W / A could be obtained.

  In particular, in the semiconductor laser device of this embodiment, the oscillation wavelength is set so that the wavelength is 890 nm and does not exceed 900 nm. When the oscillation wavelength is 900 nm or less, the value of the index x of the wavelength λ is small in the above-described equation (1) for obtaining free electron absorption, so that deterioration of efficiency due to free electron absorption can be suppressed as shown in FIG. it can. And it can prevent that the relative noise intensity of a semiconductor laser element rises and the code error rate at the time of communication deteriorates.

  Furthermore, in this embodiment, since the conductivity type of the ridge stripe portion R (the upper second cladding layer 309 and the first cap layer 310) forming the optical confinement structure is p-type, it is free compared with the case where it is n-type. A semiconductor laser element capable of suppressing electron absorption and oscillating with higher efficiency could be obtained. As described above, in the semiconductor laser device of this embodiment, the sum of the optical confinement coefficients of the p-type conductivity type layer is set to be smaller than that of the n-type conductivity type layer. Therefore, if the side where the optical confinement structure exists, that is, the side where the layer forming the ridge exists is a p-type conductivity type layer as in this embodiment, the amount of light existing on the side where the optical confinement structure is present is As a result, the difference in refractive index in the direction parallel to the active layer is reduced. As a result, it is possible to stabilize the transverse mode, which is a mode of light parallel to the active layer, and to prevent the relative noise intensity of the semiconductor laser element from increasing and deteriorating the code error rate during communication. did it. This is a particularly effective means for the structure in which the difference in refractive index tends to be larger in the direction parallel to the active layer because the outside of the ridge is air as in the present embodiment.

In particular, in this embodiment, the sum Σ {Γ (m) × P (m)} of the product of the optical confinement coefficient and the doping concentration of each p-type conductivity type layer is set to be smaller than in the first and second embodiments. FIG. 7 shows a graph showing the relationship between Σ {Γ (m) × P (m)} and the internal absorption αi. From this graph, it can be seen that, in particular, the total Σ {Γ (m) × P (m) } Is set to 6.0 × 10 ¹⁷ cm ⁻³ or less, it can be seen that deterioration of characteristics due to free electron absorption in the p-type conductivity layer can be almost completely prevented.

  In the above three embodiments, a semiconductor laser device having a wavelength of about 750 nm to 900 nm has been described. However, the gist of the present invention is that in the near-infrared wavelength band of 1.0 μm or less where free electron absorption has not been a problem in the past. By grasping the extent of the effect of free electron absorption and defining the sum of the product of the doping concentration of the p-type conductivity layer in the current injection region and the optical confinement factor, the effect of free electron absorption in the target wavelength band can be avoided. And the improvement of the temperature characteristic and the element resistance value while avoiding the decrease in reliability due to the deterioration of the light emitting layer, and the near red that oscillates at a wavelength of 1.0 μm or less, and preferably 700 nm or more The present invention can be applied to all external wavelength band semiconductor laser devices.

  In all the above embodiments, the p-type cladding layer is divided into two parts by the etching stop layer. However, according to the essence of the present invention described above, it is defined by the mixed crystal ratio of the material constituting the layer. The classification of the cladding layer is not directly related to the essence of the present invention. For example, for a BH (buried hetero) structure type semiconductor laser element having no etching stop layer and one clad layer, or for other purposes, a semiconductor laser element having a clad layer composed of three or more layers for other purposes. However, the contents of this patent can be applied.

Further, in all the above embodiments, a GaAs substrate is used and the layer material of the doped layer is all AlGaAs-based material. However, in the case of a III-V group compound semiconductor, p-type, n-type doping concentration and light are used. The contribution to the free electron absorption αfc of the sum of the products of the confinement factors is almost the same, and the dependency of the light emitting layer light density on the reliability tolerance of each active layer material realizing the near-infrared wavelength is also the light emitting layer itself. However, all the semiconductor laser elements composed of other III-V group compound semiconductor materials such as InGaP and InGaAlP can be used as long as the requirements of the present invention are satisfied. It can be applied. In addition, since the light-emitting layer containing Al in the light-emitting layer itself has a stricter reliability resistance to the light density than that of the active layer not containing Al, the sum of the products of the optical confinement coefficient Γ (m) and the doping concentration P (m). In order to maintain high reliability while maintaining the value of Σ {Γ (m) × P (m)} below 8.0 × 10 ¹⁷ cm ⁻³ , the asymmetry of the layer structure of this patent is more important Become an element.

  As for the conductivity type, in both embodiments, the side closer to the substrate than the active layer is n-type and the far side is p-type, but the opposite conductivity type to the above embodiment, that is, the side closer to the substrate than the active layer is p-type and far away. The present invention can also be applied to an n-type configuration.

<Fourth embodiment>
An optical wireless communication transmission apparatus according to the fourth embodiment of the present invention will be described with reference to FIG. This is an apparatus for transmitting signal light to a receiving apparatus located in a spatially separated place using the semiconductor laser element 401 of the first embodiment.

  Specifically, a signal generation source 402, a transmission circuit 403, a laser driver 404, and a semiconductor laser element 401 that converts an electric signal into light and emits it into the space are provided. The electric signal is input to the laser driver 404 through the circuit 403, and this electric signal is E / O (electrical / optical) converted by using the semiconductor laser element 401 to be emitted light 405 to the external space. At this time, a resin mold for diffusing light so as to satisfy the safety standard for the human body, particularly the eyes, is provided outside the semiconductor laser element, and the light emitted from the semiconductor laser element 401 is made incoherent to the extent that the safety standard is satisfied. The external radiation light 405 is used.

Thus, by using the semiconductor laser element of the first embodiment with high efficiency, low power consumption, and extremely low possibility of deterioration of the light emitting layer in terms of light density, it will be required for future high-speed optical wireless communication 1 Light in the near-infrared wavelength band of 0.0 μm or less can be generated with low driving power / voltage.
The power consumption of the laser driver and other circuit components can be increased by this decrease in drive power / voltage, and the degree of design freedom in circuit design can be increased. Further, since the drive current of the semiconductor laser element can be reduced due to the characteristics of the semiconductor laser element used such as high efficiency, high temperature characteristics, and a small radiation angle, the life of the semiconductor laser element is extended and the reliability of the apparatus is improved. In addition, since the light density of the active layer of the semiconductor laser element is set to a value at which deterioration is suppressed, the long-term reliability of the device is also ensured.

<Fifth Embodiment>
An optical disc recording / reproducing apparatus according to the fifth embodiment of the present invention will be described with reference to FIG. This is a device for writing data on the optical disc 501 and reproducing the written data. The light emitting element 502, collimating lens 503, beam splitter 504, λ / 4 polarizing plate 504, The light irradiation objective lens 506, the reproduction light objective lens 507, the signal light detection light receiving element 508, and the signal reproduction circuit 509 are provided. As the light emitting element 502, the semiconductor laser element according to the second embodiment of the present invention described above is used. The operation of this optical disk recording / reproducing apparatus will be described below.

  First, at the time of writing, the signal light emitted from the semiconductor laser element 502 is converted into parallel light by the collimate lens 503, passes through the beam splitter 504, and the polarization state is adjusted by the λ / 4 polarizing plate 505. The light is condensed by the objective lens 506 and irradiated onto the optical disc 501. On the other hand, at the time of reading, laser light without a data signal is irradiated onto the optical disc 501 along the same path as at the time of writing. The laser light is reflected by the surface of the optical disk 501 on which the data is recorded, passes through the laser light irradiation objective lens 506 and the λ / 4 wavelength plate 505, and then is reflected by the beam splitter 504. After changing the angle by 90 degrees, the light is condensed by the reproduction light objective lens 507 and incident on the signal detection light receiving element 508. In the signal detecting light receiving element 508, the recorded data signal is converted into an electric signal by the intensity of the incident laser beam, and the signal light reproducing circuit 509 reproduces the original signal.

  Since the optical disk apparatus of the present embodiment uses a semiconductor laser element that operates at a higher optical output than before, the data can be read and written even if the rotational speed of the disk is made higher than before. Accordingly, an optical disc apparatus that realizes a more comfortable operation because the access time to the disc, which has been a problem particularly when writing to a CD-R / RW, is much shorter than a conventional device using a semiconductor laser element. Could be provided.

1 is a schematic cross-sectional view showing a structure of a semiconductor laser device according to a first embodiment of the present invention. FIG. 6 is a schematic cross-sectional view showing a state where a substrate to a first cap layer are stacked in the manufacturing process of the semiconductor laser device according to the first embodiment of the present invention. It is typical sectional drawing showing the state which the etching process was complete | finished in the manufacture process of the semiconductor laser element of 1st Embodiment of this invention. FIG. 5 is a schematic cross-sectional view showing a state where a third cap layer is stacked in the manufacturing process of the semiconductor laser device according to the first embodiment of the present invention. It is typical sectional drawing which shows the structure of the semiconductor laser element of 2nd Embodiment of this invention. It is typical sectional drawing which shows the structure of the semiconductor laser element of 3rd Embodiment of this invention. It is a block diagram which shows the structure of the transmitter for high-speed optical wireless communication of 4th Embodiment of this invention. It is a typical block diagram which shows the optical disk recording / reproducing apparatus of 5th Embodiment of this invention. It is the graph showing the relationship between the value of internal absorption (alpha) i of the semiconductor laser element obtained by experiment, and the sum total of the product of the doping concentration of a p-type semiconductor layer, and a light density. It is the graph showing the relationship between the value of internal absorption (alpha) i of the semiconductor laser element obtained by experiment, and the sum total of the product of the doping density | concentration of an n-type semiconductor layer, and an optical density. It is the schematic diagram which represented the relationship between free electron absorption and a wavelength by using doping concentration as a parameter. It is a schematic diagram which shows the range of the combination of optical confinement coefficient (GAMMA) (m) and doping concentration P (m) which is not influenced by the free electron absorption by a p-type conductivity type layer. It is a figure of the calculation result which shows the relationship between the sum total of the optical confinement coefficient of both conductivity type layers, and the optical density (light confinement coefficient) of a light emitting layer (well layer).

101, 201, 301 Substrate 102, 202, 302 Buffer layer 103, 203a, 203b, 303a, 303b Lower cladding layer 104a, 104b, 204, 304a, 304b Lower light guide layer 105, 205, 305 Active layer 106, 206, 306a , 306b Upper light guide layer 107, 207, 307 Upper first cladding layer 108, 208, 308 Etching stop layer 109, 209, 309 Upper second cladding layer 110, 210, 310 First cap layer
114, 214, 311 Second cap layer 115, 215 Third cap layer 111, 211 First buried layer 112, 212 Second buried layer 113, 213 Third buried layer 116, 216, 316 P-type electrode 117, 217, 317 n-type electrode 121 insulating film for selective etching 322 insulating film for current confinement 401 semiconductor laser element of first embodiment 402 signal generation source 403 transmission circuit 404 laser driver 405 emitted light to external space 501 optical disc 502 of second embodiment Semiconductor laser element 503 Collimate lens 504 Beam splitter 505 λ / 4 polarizing plate 506 Laser light irradiation objective lens 507 Reproduction light objective lens 508 Signal light detection light receiving element 509 Signal reproduction circuit R Ridge stripe part F Embedding Part

Claims (13)

On the board
A plurality of n-type conductivity layers l (where l = 1, 2,... K, where k is a natural number);
a plurality of p-type conductivity layers m including a p-type cladding layer (where m = 1, 2,..., k ′, where k ′ is a natural number);
An active layer located between the n-type conductivity type layer l and the p-type conductivity type layer m,
The oscillation wavelength is 700 nm or more and 1.0 μm or less,
The ratio of the amount of light present in the n-type conductivity type layer 1 to the total amount of light present in all the layers in the substrate and on the substrate is the optical confinement factor Γ (l), and in all layers in the substrate and on the substrate. Assuming that the ratio of the amount of light existing in the p-type conductivity type layer m to the total amount of existing light is the optical confinement coefficient Γ (m), the relationship between the sum of Γ (l) and the sum of Γ (m) is

And
Sum of products of optical confinement coefficient Γ (m) of p-type conductivity layer m and doping concentration P (m) (unit: cm ⁻³ ) of p-type conductivity layer m

Is 8.0 × 10 ¹⁷ cm ⁻³ or less,
Of the plurality of p-type conductivity layers, the total thickness of the p-type conductivity layers having a doping concentration of 1.0 × 10 ¹⁸ cm ⁻³ or more is the total thickness of the plurality of p-type conductivity layers. and it accounts for 80% or more of,
The p-type cladding layer has an average doping concentration of 2.0 × 10 ¹⁸ cm ⁻³ or more,
Sum of products of optical confinement coefficient Γ (l) of n-type conductivity type layer 1 and doping concentration N (l) (unit: cm ⁻³ ) of n-type conductivity type layer 1

Is 4.0 × 10 ¹⁸ cm ⁻³ or less . The sum of the products of the optical confinement coefficient Γ (l) of the n-type conductivity type layer l and the doping concentration N (l) (unit: cm ⁻³ ) of the n-type conductivity type layer l and the p-type conductivity type layer m The relationship between the optical confinement coefficient Γ (m) and the sum of the products of the doping concentration P (m) of the p-type conductivity layer m is

The semiconductor laser device according to claim 1, wherein: The sum of the products of the optical confinement coefficient Γ (l) of the n-type conductivity type layer l and the doping concentration N (l) (unit: cm ⁻³ ) of the n-type conductivity type layer l and the p-type conductivity type layer m The relationship between the optical confinement coefficient Γ (m) and the sum of the products of the doping concentration P (m) of the p-type conductivity layer m is

The semiconductor laser device according to claim 1, wherein: The relationship between the sum of the optical confinement coefficients Γ (l) of the n-type conductivity type layer l and the sum of the light confinement coefficients Γ (m) of the p-type conductivity type layer m is

The semiconductor laser device according to claim 2 , wherein: Of the n-type conductivity type layers, the thickness of the thickest layer is d1, and the refractive index of the material constituting the layer is n1,
When the thickness of the thickest layer among the p-type conductivity layers is d2, and the refractive index of the material constituting the layer is n2,
(D1 × n1)> (d2 × n2)
The semiconductor laser device according to claim 1, wherein: The active layer includes one or more light emitting layers that emit light,
The ratio of the amount of light present in all the light emitting layers to the total amount of light present in all layers in the substrate and on the substrate is defined as a light confinement factor Γ (act), and the total thickness of all the light emitting layers is d (act) (unit: cm)
Γ (act) / d (act) ≦ 3.0 × 10 ⁴ cm ⁻¹
The semiconductor laser device according to claim 1, wherein: When the optical confinement coefficients Γ (m) and Γ (l) of the p-type and n-type conductivity layers m and l are 1.0 × 10 ⁻⁴ or more, the p-type and n-type conductivity layers m and l 2. The semiconductor laser device according to claim 1, wherein the doping concentrations P (m) and N (l) of the semiconductor are 8.0 × 10 ¹⁸ cm ⁻³ or less. 2. The semiconductor laser device according to claim 1, wherein the oscillation wavelength is 900 nm or less. Having a light confinement structure for confining light in a direction parallel to the active layer,
The plurality of p-type conductivity type layers are provided on the side where the light confinement structure exists, and the plurality of n-type conductivity type layers are provided on the side where the light confinement structure does not exist, with the active layer interposed therebetween. The semiconductor laser device according to claim 1, wherein: A current confinement structure comprising a current injection region and a non-current injection region, and confining current in a direction parallel to the active layer,
The current injection region is composed of at least one of the p-type conductivity layers,
The semiconductor laser device according to claim 1 or 9 doping concentration of p-type conductivity type layer of the current injection region is characterized by at 1.0 × 10 ¹⁸ cm ^-3 or more. The n-type conductivity type layer includes an n-type cladding layer, and an n-type buffer layer positioned between the substrate and the n-type cladding layer,
The ratio of the amount of light present in the n-type buffer layer to the total amount of light present in all layers in the substrate and on the substrate is the light confinement factor Γ (buf), and is present in all layers in the substrate and on the substrate. When the ratio of the amount of light existing in the substrate to the total amount of light to be calculated is the optical confinement factor Γ (sub),
Γ (buf) + Γ (sub) ≦ 5.0 × 10 ⁻⁵
The semiconductor laser device according to claim 1, wherein: A transmitter for optical wireless communication equipped with the semiconductor laser device according to any one of claims 1 to 11 . An optical disc apparatus on which the semiconductor laser element according to any one of claims 1 to 11 is mounted.

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