JP2011181974A - Semiconductor laser element - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a semiconductor laser element which stably maintains multimode oscillation characteristics and temperature characteristics in a longitudinal mode in a wide temperature range and has good temperature characteristics. <P>SOLUTION: The semiconductor laser element is equipped with a light emitter comprising: a first clad layer 103 on a substrate 101; an active layer 104 formed on the first clad layer 103; a second clad layer 105 which is formed on the active layer 104 and has a ridge stripe 111 for injecting a current into the active layer 104; and a current constriction layer 109 which is formed on both sides of the ridge stripe 111 so that a current may be constricted by the ridge stripe 111. Here, a distance d1 from a lower surface of the current constriction layer 109 to an upper surface of the active layer 104 is a value in a prescribed range. The current expands wider than the width of the ridge stripe 111 after passing the ridge stripe 111 before reaching the active layer 104. <P>COPYRIGHT: (C)2011,JPO&amp;INPIT

Description

  The present invention relates to a semiconductor laser device, and more particularly to a semiconductor laser device including a self-pulsation type whose longitudinal mode is a multimode.

  2. Description of the Related Art In recent years, semiconductor laser elements are frequently used as optical pickup light sources used in optical recording devices and reading devices for recording media such as optical disks and magneto-optical recording disks. The optical disc market continues to expand for a wide variety of uses such as recorders, PCs, and in-vehicle use. In particular, the demand for in-vehicle use represented by car navigation is high, and the demand for optical pickup devices capable of reproducing all CD and DVD discs is increasing.

  There are strong demands for in-vehicle optical pickup devices: (1) miniaturization of optical pickup devices, (2) wide operating temperature guarantees capable of operating from low to high temperatures, and (3) suppression of signal degradation (low noise). Can be mentioned.

  First, (1) In order to reduce the size of the optical pickup device, it is effective to simplify the device by reducing the number of optical components. As one method, a 650 nm band red semiconductor laser for DVD and a CD are used. And a monolithic semiconductor laser in which an infrared semiconductor laser of 780 nm band is integrated on the same semiconductor substrate. As a result, not only the semiconductor laser itself can be integrated into one component, but also optical components such as a collimator lens and a beam splitter can be shared by the red semiconductor laser and the infrared semiconductor laser, which is effective for downsizing of the apparatus.

  In addition, (2) as a wide operating temperature guarantee, it is necessary to improve the temperature characteristics of the semiconductor laser element itself. As one method for that purpose, Patent Document 1 is known. In Patent Document 1, the taper stripe structure in which the width of the ridge changes in the optical path direction results in a lower current density than the normal straight stripe structure, and the decrease in differential resistance due to the wide ridge width. It is described that heat generation of the element can be suppressed and temperature characteristics can be improved.

  Next, regarding (3) signal deterioration suppression (low noise reduction), first, the cause of noise is considered.

  There is a slight amount of return light from the optical disk, the optical recording medium, the optical system, and the like for the semiconductor laser element. For this reason, it is known that when the coherence of the laser beam is high, the light in the resonator and the return beam interact with each other, resulting in noise in the output of the semiconductor laser element. .

  As a method for solving such noise caused by the return light, a method such as high-speed modulation of the semiconductor laser element, multi-mode oscillation of the semiconductor laser element, or a pulse oscillation state of the semiconductor laser element itself is used. Has been taken.

  However, the method for high-speed modulation of the semiconductor laser element uses a high-frequency superposition module, which increases the number of components, and is disadvantageous in terms of downsizing or cost of the optical pickup. Further, in recent cars, in addition to a high-frequency superposition module that modulates a semiconductor laser element at high speed, many equipment (for example, ETC equipment: Electronic Toll Collection system) using high frequency is installed. For this reason, the frequencies of the devices may resonate and problems such as device malfunction may occur. Therefore, it is difficult to say that the method of modulating the semiconductor laser element at high speed is the best method.

  On the other hand, as a method of making the oscillation mode multi-mode, it is well known that the optical waveguide mechanism has a gain guide structure, but on the other hand, this gain guide structure has a higher oscillation threshold value, which increases the operating power. , Disadvantageous to temperature characteristics.

  Further, as a method of causing pulse oscillation, there is a method in which a current spread is made narrower than a light spread and a saturable absorber is formed in an active layer. As one of the means, Patent Document 2 is known. In Patent Document 2, the resistance of the semiconductor layer between the current confinement layer and the active layer is made higher than that of the active layer, so that the current spread reaches the active layer with the same extent as the width of the ridge stripe. On the other hand, since there is no current outside the stripe width, there is no supply of light, and laser light is absorbed in that portion to form a saturable absorber, and self-oscillation is possible.

  In such a semiconductor laser element, the film thickness of the semiconductor layer between the current confinement layer and the active layer is about 0.45 μm to 0.65 μm for the infrared laser element, and 0.25 μm to about 0.25 μm for the red laser element. 0.4 μm.

JP 2000-174385 A Japanese Patent No. 31836992

  According to the above structure, since the current spread is equal to the stripe width, stable self-oscillation is possible at room temperature. However, at a high temperature, since current spreading is suppressed, the current injected into the active layer is concentrated in the portion immediately below the stripe, and the operating current density increases. As a result, the leakage current increases, the amount of heat generated by the element increases, and the light emission efficiency decreases. For this reason, at high temperatures, there is a problem that the light output is thermally saturated due to heat generation of the element in the current-light output characteristics (IL characteristics), which is great for in-vehicle lasers that require a wide operating temperature guarantee. Will have an impact. Therefore, this solution is a problem.

  In view of the above problems, an object of the present invention is to provide a semiconductor laser device in which a longitudinal mode can stably maintain multimode oscillation (including self-excited oscillation) characteristics and temperature characteristics in a wide temperature range from low temperature to high temperature. Is to provide.

  In order to achieve the above object, a first semiconductor laser device according to the present invention includes a first clad layer, an active layer formed on the first clad layer, and an active layer. A second clad layer formed and having a ridge stripe for injecting current into the active layer; and a current confinement layer formed on both sides of the ridge stripe and configured to confine the current to the ridge stripe A light emitting portion is provided, and the distance from the lower surface of the current confinement layer to the upper surface of the active layer is a value within a predetermined range, and the current exceeds the width of the ridge stripe after passing through the ridge stripe and reaching the active layer. It has spread.

  Here, the full width at half maximum of the current distribution is considered as the current spread. In other words, in the first semiconductor laser element, the full width at half maximum of the current distribution on the upper surface of the active layer of the current that has passed through the ridge stripe extends beyond the width of the ridge stripe. Also, the expressions width and lateral spread refer to distances in the parallel direction.

  According to the first semiconductor laser element, since the distance (remaining thickness) from the lower surface of the current confinement layer to the upper surface of the active layer is a predetermined value or more, the current that has passed through the ridge stripe reaches the upper surface of the active layer. In the horizontal direction (parallel direction), the full width at half maximum of the current distribution extends beyond the width of the ridge stripe. However, since the light distribution spreads laterally beyond such current spread, a sufficient saturable absorber is formed as a result, and multimode oscillation is stably generated. In addition, by setting an upper limit on the remaining thickness, oscillation in the high-order transverse mode is suppressed and oscillation is performed only in the fundamental transverse mode.

  The predetermined range has a lower limit at a point at which an increase in the lateral spread of the current with respect to an increase in the distance (distance from the lower surface of the current confinement layer to the upper surface of the active layer, that is, the remaining thickness) becomes gentle, It is preferable that the upper limit is the distance at the point where the increase in the full width at half maximum of NFP is moderate with respect to the increase in distance.

  By defining the predetermined range in this way, it is possible to reliably obtain the effects of stable multimode oscillation and oscillation in the fundamental transverse mode. It can be experimentally obtained that the increase in the remaining thickness is moderate for the lateral spread of the current and the full width at half maximum of NFP.

  Specifically, the predetermined range is preferably 0.65 μm or more and 1.2 μm or less. By setting the remaining thickness within this range, it is possible to realize oscillation in the basic transverse mode and the multi-longitudinal mode.

  Further, according to the first semiconductor laser element, the current that has passed through the current confinement layer spreads in the lateral direction, so that it is avoided that the current is concentrated in the active layer and the current density is increased. For this reason, generation of leakage current and heat generation in the semiconductor laser device are suppressed, and the semiconductor laser device operates stably even at high temperatures.

  As described above, according to the first semiconductor laser element, it is possible to achieve both a wide operating temperature guarantee and oscillation in the basic transverse mode and the multi-longitudinal mode.

The active layer is made of Al _x Ga _1-x As (0 ≦ x ≦ 1), and the first cladding layer and the second cladding layer are made of an AlGaInP-based material. It is desirable.

  With the semiconductor laser device having such a configuration, it is possible to ensure both a wide operating temperature guarantee and oscillation in the basic transverse mode and the multi-longitudinal mode.

Note that the material of AlGaInP system, means _{(Al w Ga 1-w)} z In 1-z P (0 <w <1,0 <z <1) and the material of the composition represented.

  The width of the ridge stripe is preferably 1 μm or more and 4 μm or less.

  By doing so, it is possible to prevent the horizontal far field pattern (FFP) from being bimodal due to being 4 μm or less. On the other hand, if the width of the ridge stripe is too small, the resistance becomes high and heat is generated, resulting in deterioration of temperature characteristics. In order to avoid this, the width of the ridge stripe is preferably 1 μm or more. Further, being 1 μm or more also shows an example of the narrowest width that can be realized in the process for forming the ridge stripe.

The predetermined range is preferably 0.4 μm or more and 0.7 μm or less. The active layer is made of Ga _y In _1-y P (0 <y <1), and the first cladding layer and the second cladding layer are made of an AlGaInP-based material. Is also preferable. Furthermore, it is also preferable that the width of the ridge stripe is 2.5 μm or more and 5.5 μm or less.

  In these cases as well, the effect of the semiconductor laser device of the present invention can be reliably obtained.

  Further, it is preferable that the side surfaces of the ridge stripe are all perpendicular to the main surface of the substrate.

  When the vertical ridge is thus formed, the differential resistance Rs can be reduced as compared with the ridge stripe in which the width of the upper surface of the ridge stripe is smaller than the width of the lower surface, so that the heat generation of the element is suppressed. As a result, a wider operating temperature guarantee of the semiconductor laser element can be realized.

  In order to achieve the above object, a second semiconductor laser device of the present invention comprises at least a first light emitting part and a second light emitting part on a substrate, and the first light emitting part and the second light emitting part are A first cladding layer, an active layer formed on the first cladding layer, and a second cladding layer formed on the active layer and having a ridge stripe for injecting current into the active layer, And a current confinement layer that is formed on both sides of the ridge stripe so that the current is confined to the ridge stripe, and the lower surface of the current confinement layer in both the first light-emitting portion and the second light-emitting portion. The distance from the active layer to the upper surface of the active layer is a value in a predetermined range, and the current spreads beyond the width of the ridge stripe after passing through the ridge stripe and reaching the active layer.

  Here, as in the case of the first semiconductor laser element, the full width at half maximum is considered as the current spread.

  According to the second semiconductor laser device, in the first and second light-emitting portions, the distance (remaining thickness) from the lower surface of the current confinement layer to the upper surface of the active layer is defined, so that both the basic transverse mode and the multi-vertical mode are achieved. Mode oscillation can be generated stably. At the same time, since the current spreads in the active layer, an increase in current density is avoided, and the monolithic two-wavelength laser element that operates stably even at high temperatures is obtained.

  Specifically, the predetermined distance in the first light emitting unit is 0.65 μm or more and 1.2 μm or less, and the predetermined distance in the second light emitting unit is 0.4 μm or more and 0.7 μm or less. Preferably there is.

  By setting the remaining thickness to a value in such a range, it is possible to realize a wide operating temperature guarantee and oscillation mode stability in each of the light emitting units that emit different types of lasers.

  Note that the ridge stripes included in each of the first light-emitting portion and the second light-emitting portion are preferably formed at the same time.

  In this way, the light emitting point interval between the first light emitting unit and the second light emitting unit (the interval between the ridge stripes that each has) is more accurate than when each ridge stripe is formed separately. This is very advantageous when a laser element and an optical component are mounted in an optical pickup device or the like. In other words, if there is a variation in the light emitting point interval, it is necessary to mount an optical component corresponding to the variation, resulting in characteristic deterioration such as an increase in the difficulty of the assembly process and a reduction in the efficiency of capturing the laser beam. However, such a problem is avoided by forming a plurality of ridge stripes at the same time. In addition, there exists an effect that the man-hour in a manufacturing process is reduced compared with the case where it forms separately.

  Moreover, it is preferable that the side surface of the ridge stripe in at least one of the first light emitting unit and the second light emitting unit is perpendicular to the main surface of the substrate.

  In this way, the differential resistance Rs can be reduced as compared with the ridge stripe in which the width of the upper surface of the ridge stripe is smaller than the width of the lower surface, so that the heat generation of the element is suppressed. As a result, a wider operating temperature guarantee of the semiconductor laser element can be realized.

The active layer included in the first light-emitting portion is formed of Al _x Ga _1-x As (0 ≦ x ≦ 1), and the active layer included in the second light-emitting portion is Ga _y In _1-y P ( Preferably, the first cladding layer and the second cladding layer are both formed of an AlGaInP-based material.

  In this way, it is possible to reliably achieve a wide operating temperature guarantee and oscillation mode stability in each light emitting section.

  The width of the ridge stripe included in the first light-emitting portion is 1.0 μm or more and 4.0 μm or less, and the width of the ridge stripe included in the second light-emitting portion is 2.5 μm or more and 5.5 μm or less. It is preferable that

  In this case, the width of the ridge stripe is 4 μm or less in the first light emitting part and 5.5 μm or less in the second light emitting part, so that the horizontal FFP becomes bimodal. Can be prevented. In addition, the lower limit (1 μm) of the width in the first light emitting part is an example of the narrowest width in the process, and the lower limit (2.5 μm) of the width in the second light emitting part is an IL characteristic. It is obtained as a value that can avoid the occurrence of nonlinearity in the external differential efficiency Se.

  In addition, it is preferable that at least one of the ridge stripes included in each of the first light emitting portion and the second light emitting portion has a taper stripe structure having a change in width.

  With such a taper stripe structure, since the stripe width can be made wider than that of the straight stripe, the differential resistance Rs can be reduced to suppress the heat generation of the element, and the temperature characteristics can be improved.

  Furthermore, the taper stripe structure is preferably a structure in which the width gradually increases from the light emitting end face side from which light is emitted toward the rear end face side facing the light emitting end face.

  Further, the taper stripe structure may be a structure in which the width gradually decreases from the central portion toward the light emitting end face side from which light is emitted and toward the rear end face side facing the light emitting end face. preferable.

  A specific structure of the taper stripe structure may be as described above. In the case of such a taper stripe structure, the width of the ridge stripe is an average width obtained by converting the taper stripe structure as a straight line.

  According to the semiconductor laser device of the present invention, the current spread in the lateral direction in the active layer is controlled by defining the distance from the lower surface of the current confinement layer to the upper surface of the active layer within a predetermined range. As a result, oscillation in the basic transverse mode and multi-longitudinal mode is realized, and since the increase in current density in the active layer is suppressed, generation of leakage current and generation of heat are suppressed, and stable operation is performed even at high temperatures. It has become.

FIGS. 1A to 1C are diagrams showing a configuration of a semiconductor laser device according to the first embodiment of the present invention, in which FIG. 1A is a cross section, and FIG. 1B is a detailed active layer. The structure, FIG. 1 (c) shows the planar shape of the stripe portion. FIG. 2A shows the relationship between the distance (remaining thickness) d1 from the lower surface of the current confinement layer to the upper surface of the active layer and the full width at half maximum of the oscillation spectrum in the first embodiment. (D) shows the spectrum for each d1. FIG. 3A is an NFP image in the oscillation threshold state in the semiconductor laser device of the first embodiment, and FIG. 3B shows the lateral expansion current and the full width at half maximum of NFP with respect to the remaining thickness d1. FIG. 4A shows an NFP image when a current of 10 mA is passed through the semiconductor laser device of the first embodiment, and FIG. 4B is a diagram showing the relationship between the stripe width and the full width at half maximum of NFP. is there. FIG. 5A is a diagram showing the relationship between the stripe width and the full width at half maximum of the oscillation spectrum in the semiconductor laser device of the first embodiment. FIGS. It is a figure which shows an oscillation spectrum. FIG. 6A is a diagram showing IL characteristics for the first embodiment and the related art, and FIG. 6B shows an oscillation spectrum at 25 ° C. and 85 ° C. in the first embodiment. FIG. 6 (c) is a diagram showing oscillation spectra at 25 ° C. and 85 ° C. of the prior art. FIGS. 7A to 7C are views showing a structure when a vertical ridge is formed in the semiconductor laser device of the first embodiment. FIGS. 8A to 8C are diagrams showing the configuration of the semiconductor laser device according to the second embodiment of the present invention. FIG. 8A is a cross section, and FIG. 8B is a red laser portion. The detailed structure of the active layer, FIG. 8C, shows the planar shape of the stripe portion. FIG. 9A shows the relationship between the distance (remaining thickness) d2 from the lower surface of the current confinement layer to the upper surface of the active layer and the full width at half maximum of the oscillation spectrum in the red laser portion of the second embodiment. (B)-(d) show the spectrum with respect to each d2. FIG. 10A is an NFP image of the oscillation threshold state of the red laser part in the semiconductor laser device of the second embodiment, and FIG. 10B is a lateral expansion current and a full width at half maximum of NFP with respect to the remaining thickness d2. Indicates. FIG. 11A shows an NFP image when a current of 10 mA is passed through the red laser part in the semiconductor laser device of the second embodiment, and FIG. 11B shows the relationship between the stripe width and the full width at half maximum of NFP. FIG. FIG. 12A is a diagram showing the relationship between the stripe width of the red laser portion and the full width at half maximum of the oscillation spectrum in the semiconductor laser device of the second embodiment, and FIGS. It is a figure which shows the oscillation spectrum with respect to the stripe width | variety. FIG. 13A is a diagram showing the IL characteristics of the red laser unit and the conventional technology in the second embodiment, and FIG. 13B is a diagram showing 25 ° C. in the red laser unit of the second embodiment. And FIG. 13 (c) is a diagram showing the oscillation spectra at 25 ° C. and 85 ° C. of the prior art. FIGS. 14A to 14C are views showing the structure when a vertical ridge is formed in the semiconductor laser device of the second embodiment. 15A and 15B are diagrams showing the configuration of a semiconductor laser device according to the third embodiment of the present invention. FIG. 15A is a cross-sectional view, FIG. 15B is a detailed structure of an active layer, and FIG. Indicates the planar shape of the stripe portion.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings.

(First embodiment)
A semiconductor laser device according to the first embodiment of the present invention will be described. FIGS. 1A, 1B and 1C are views showing an example of the semiconductor laser device of the present invention. First, FIG. 1A shows a cross-sectional view.

  The semiconductor laser device includes an n-type GaAs buffer layer 102, an n-type (AlGa) InP cladding layer 103, an active layer 104, a p-type (AlGa) InP first cladding layer 105, a p-type GaInP etching on an n-type GaAs substrate 101. The stop layer 106, the p-type (AlGa) InP second cladding layer 107, the p-type GaInP intermediate layer 108, and the p-type GaAs contact layer 110 are stacked in this order from the bottom. As a result, the semiconductor laser device has a double hetero structure in which the active layer 104 is sandwiched between two clad layers of the n-type (AlGa) InP clad layer 103 and the p-type (AlGa) InP first clad layer 105. .

  Here, as shown in FIG. 1B, the active layer 104 is a quantum well active layer having three wells. That is, three GaAs well layers 1045w, 1043w, and 1041w are formed in order from the bottom, with two (AlGa) InP barrier layers 1044b and 1042b sandwiched between them, and a laminated structure of these five layers has two (AlGa) layers. The structure is sandwiched between InP guide layers 1040g and 1046g. As a result, 1046g, 1045w, 1044b, 1043w, 1042b, 1041w, and 1040g are stacked in this order from the lower side (n-type (AlGa) InP cladding layer 103 side). Note that the p-type (AlGa) InP first cladding layer 105 is positioned on the uppermost (AlGa) InP guide layer 1040g.

  Further, as shown in FIG. 1A, the p-type (AlGa) InP second cladding layer 107, the p-type GaInP intermediate layer 108, and the p-type GaAs contact layer 110 are processed into a mesa-type stripe shape as a ridge stripe. The stripe portion 111 has a shape in which the width on the lower surface is wider than the width on the upper surface. Further, an n-type GaAs current confinement layer 109 is embedded on both sides of the stripe portion 111. As described above, the stripe portion 111 and the n-type GaAs current confinement layer 109 formed on the p-type (AlGa) InP first clad layer 105 constitute a current confinement structure for confining the region of current injected into the active layer 104. Has been.

  Here, in FIG. 1A, the distance (remaining thickness) from the lower surface of the n-type current confinement layer 109 (in other words, the lower surface of the ridge stripe) to the upper surface of the active layer 104 is shown as d1.

  A planar configuration of such a current confinement structure is schematically shown in FIG. Here, the shape 111a of the lower surface of the stripe portion 111 is shown, and the width is the same from the light emitting end surface A to the rear end surface B. The width on the lower surface of the stripe portion 111 is defined as a stripe width Ws. The remaining portion of the planar shape is the shape 109 a of the lower surface of the n-type current confinement layer 109.

  Further, although not shown in the drawings, a p-type electrode is formed on the p-type GaAs contact layer 110 and the n-type current confinement layer 109, and an n-type is formed on the back surface of the n-type GaAs substrate 101. An electrode is formed. As described above, a semiconductor laser element is configured, which is a laser element that emits an infrared laser.

Here, as an example of the composition ratio of the material constituting each layer, an n-type (AlGa) InP cladding layer 103, a p-type (AlGa) InP first cladding layer 105, and a p-type (AlGa) InP second cladding layer 107 are shown. Is (Al _0.7 Ga _0.3 ) _0.51 In _0.49 P. Further, (AlGa) and InP guide layer 1040g and 1046 g, with respect to the (AlGa) InP barrier layer 1042b and 1044b are set to _{(Al 0.4 Ga 0.6) 0.51 In} 0.49 P.

  FIG. 2A shows the behavior of the multimode property (full width at half maximum of the oscillation spectrum) with respect to the change in the remaining thickness d1 of the semiconductor laser device having the above configuration. Here, the stripe width Ws is constant at 1.5 μm, and the measurement conditions are room temperature and 4 mW.

  As shown in FIG. 2A, when the remaining thickness d1 is increased, the full width at half maximum of the oscillation spectrum is increased accordingly, and when the remaining thickness d1 is 1 μm or more, the full width at half maximum of the oscillation spectrum is substantially constant. . FIGS. 2B, 2C, and 2D show actual spectrum waveforms when the thickness d1 remains in order is 0.6 μm, 0.95 μm, and 1.45 μm. The oscillation spectrum is close to a single peak when the remaining thickness shown in FIG. 2B is 0.6 μm, and is a multimode with a wide full width at half maximum when it is 0.95 μm shown in FIG. In the case of 1.45 μm shown in 2 (d), bimodality has begun to be exhibited.

  This can be explained by the effective refractive index difference (Δn) between the portion corresponding to the stripe portion 111 and the portions corresponding to both sides thereof.

When the remaining thickness d1 is 0.6 μm, Δn = 1 × 10 ⁻³ or so, and because of this relatively large Δn, light cannot bleed out to the side of the ridge, and a saturable absorber is formed. A difficult situation. As a result, the full width at half maximum of the oscillation spectrum is reduced.

On the other hand, when the remaining thickness is 1.45 μm, Δn = 1 × 10 ^{−5 is} so small that light can ooze out to the side of the ridge, but at the same time the remaining thickness is too thick to spread the current. Pass. As a result, there is gain over a wide wavelength range, multimode oscillation is likely to occur, and higher order transverse mode oscillation is also possible. Since the propagation constants are different between the high-order transverse mode and the fundamental transverse mode, two oscillation spectra corresponding to the higher-order transverse mode and those corresponding to the fundamental transverse mode are generated as oscillation spectra. This is considered to be a cause of a bimodal spectrum as shown in FIG.

  As described above, the range of the remaining thickness d1 that maintains the stable fundamental transverse mode as shown in FIG. 2C and enables multimode oscillation is about 0.65 μm to 1.2 μm. It was confirmed.

Here, a remaining thickness d1 for self-excited oscillation of an infrared laser by a semiconductor laser element generally used in the past is 0.45 μm to 0.65 μm (Δn: 3 × 10 ⁻³ to 1 × 10 ^−3. ). On the other hand, in the present embodiment, the remaining thickness d1 is as thick as 0.65 μm to 1.2 μm (Δn: 1 × 10 ^{−3 to} 5 × 10 ⁻⁵ ) as described above. Multimode oscillation (including self-excited oscillation) is possible. The reason for this will be described below.

  FIG. 3A shows a near field pattern (NFP) image in an oscillation threshold state in a sample in which the stripe width Ws is constant at 1.5 μm and the remaining thickness d1 is 0.9 μm. The NFP image shows a light distribution (light intensity distribution), and the extent of light spread can be shown using the full width at half maximum obtained from this light distribution.

  FIG. 3B shows the full width at half maximum (denoted by a dotted line) of the NFP in the oscillation threshold state when normalized with the remaining thickness d1 = 0.6 μm as a reference, and when normalized with the remaining thickness d1 = 0 μm as the reference. The lateral spreading current (calculated value: indicated by a solid line) is shown. That is, each is shown as a ratio to the reference value. The full width at half maximum of NFP initially increases as the remaining thickness d1 increases, and when the remaining thickness d1 exceeds approximately 1.2 μm, the increase becomes moderate and becomes a substantially constant value. On the other hand, the lateral spreading current increases until the remaining thickness d1 is about 0.65 μm, and thereafter tends to be saturated (that is, the increase becomes moderate).

  Thus, in the range where the remaining thickness d1 is 0.65 to 1.2 μm, the current spread in the lateral direction is generally saturated and the light distribution (spread) is increased, so this range is a saturable absorber. It can be said that this is an area where the increase is made. On the other hand, when the remaining thickness d1 is 1.2 μm or more, the light distribution (spreading) and the lateral current are both substantially constant, so that the saturable absorber is not increased. As a result, the full width at half maximum of the oscillation spectrum is obtained. Is considered to be almost constant. Therefore, the region where the saturable absorber is easily formed is a region where the remaining thickness d1 is 0.65 μm or more. Since the region where the oscillation spectrum is not bimodal is the region where the remaining thickness d1 is 1.2 μm or less, the desirable range of the remaining thickness d1 capable of stable multimode oscillation is 0.65 μm to 1. 2 μm.

  As described above, in the semiconductor laser device of the present embodiment, the remaining thickness is larger than in the case of the prior art, so that the current spread in the lateral direction is increased, but the light emission range is further expanded. As a result, saturable absorbers are sufficiently formed, and a stable fundamental transverse mode is maintained and multimode oscillation is possible.

  Next, the extent of current spreading with respect to the stripe width Ws is shown using an NFP image before laser oscillation. Since the NFP image before oscillation has a strong correlation with the current density distribution injected into the active layer, it is possible to verify the spread of current.

  FIG. 4A is an NFP image when a current of 10 mA is passed when the stripe width Ws is 1.7 μm and the remaining thickness d1 is 0.9 μm, and may be considered as a current distribution due to the strong correlation. it can. As shown in FIG. 4 (a), since the remaining thickness d1 is relatively large at 0.9 μm, the current spreads widely in the lateral direction, which is 5.8 μm in terms of the full width at half maximum. Since the stripe width Ws is 1.7 μm, the stripe width Ws is greatly expanded by more than three times.

  Similarly to this, FIG. 4B shows the behavior of the current spreading width when the stripe width Ws is changed by the full width at half maximum. According to FIG. 4B, the full width at half maximum is 5.7 μm when the stripe width Ws is 1 μm, the current spread increases as the stripe width Ws increases, and the full width at half maximum is 8 μm or more when the stripe width Ws is 5 μm. ing.

  As described above, in the case of the conventional semiconductor laser element, the lateral spread of the current is equal to the stripe width, whereas in the case of the semiconductor laser element of the present embodiment, the remaining thickness d1 is large and the current spread is striped. It was confirmed that it would be more than the width.

  Further, FIG. 5A shows the behavior of the multimode property (full width at half maximum of the oscillation spectrum) when the remaining thickness d1 is constant at 0.85 μm and the stripe width is changed. Here, the oscillation spectra when the stripe width Ws is 1.3 μm, 2.3 μm, and 4.2 μm, respectively, are shown in FIG. 5B, FIG. 5C, and FIG. As shown in FIGS. 5B to 5D, it can be confirmed that the full width at half maximum of the oscillation spectrum decreases as the stripe width Ws increases.

  This is considered to be due to the following reasons. First, the wider the stripe width Ws, the greater the lateral diffusion distance under the ridge stripe portion of the current. For this reason, the volume of the active layer into which current is injected is increased below the ridge stripe portion. As a result, the volume of the saturable absorber formed in the active layer below the current confinement layer is relatively small with respect to the volume of the active layer into which the current is injected. From this, it is considered that self-excited oscillation is less likely to occur.

  In addition, when the stripe width Ws is 4.2 μm, a phenomenon that a horizontal far field pattern (Far field pattern: FFP) becomes bimodal and a kink occurs near 9 mW is confirmed. From this, it is considered that the upper limit of the stripe width Ws is about 4 μm due to characteristics. Further, since the stripe width of 1 μm is a process limit when forming a stripe, the lower limit is set to 1 μm. When the stripe width is further narrower than the lower limit, the differential resistance becomes high, so that heat is generated and the temperature characteristics are adversely affected.

Based on the above results, the temperature characteristics of the structure of the semiconductor laser device according to this embodiment and the structure of the prior art were compared. As a result, FIG. 6A shows the temperature dependence of the IL characteristic, and FIGS. 6B and 6C show the temperature dependence of the oscillation spectrum in this embodiment and the prior art in order. Here, the remaining thickness d1 is 0.83 μm in the structure of the present embodiment, and the remaining thickness is 0.5 μm in the structure of the prior art. When this remaining thickness d1 is converted to Δn, Δn = 4 × 10 ⁻⁴ in the structure of the present embodiment and Δn = 2.5 × 10 ⁻³ in the structure of the prior art. The stripe width Ws is 2.7 μm for both structures, and the composition ratio is as described above.

  As shown in FIG. 6A, the IL structure at 25 ° C. has a lower oscillation threshold in the prior art structure. However, at 85 ° C., the oscillation threshold is lower in the structure of the present embodiment. This is because, in the case of 25 ° C., the structure of the prior art has a smaller thickness than the present embodiment, so that the lateral spread of the current is reduced, and the reactive current that does not contribute to oscillation is reduced, which is efficient. It is thought that it is converted into light. In addition, since Δn is relatively large, the waveguide loss in the active layer is also considered to be a cause of good IL characteristics. On the other hand, in the case of 85 ° C., according to the prior art structure, the current injected into the active layer is concentrated in the portion immediately under the stripe and the current density is increased. It is thought that it will deteriorate. Thus, the semiconductor laser device of this embodiment has a wider operating temperature guarantee than the conventional one.

  As shown in FIGS. 6B and 6C, the full width at half maximum of the oscillation spectrum is larger in the case of the structure of the present embodiment than in the structure of the prior art at both 25 ° C. and 85 ° C. It is thought that it has produced.

  As described above, by defining the range of the remaining thickness d1, it is possible to realize a semiconductor laser device with good temperature characteristics while stably maintaining multimode characteristics with a wide full width at half maximum of the oscillation spectrum. That is, the remaining thickness d1 is set to a range in which the current spread is substantially constant with respect to the increase in the remaining thickness d1, and the lateral light spread in the active layer is significantly increased as the remaining thickness d1 is increased. .

  For this purpose, in the region where the light distribution (full width at half maximum of NFP) is about three times or less than the stripe width with reference to the remaining thickness at which the current spread starts to become substantially constant regardless of the increase in the remaining thickness d1. You only have to set it.

Specifically, as described above, the distance (remaining thickness) d1 from the lower surface of the n-type current confinement layer 109 to the upper surface of the active layer 104 is set to 0.65 to 1.2 μm (Δn = 1 × 10 ^{−). 3 to} 5 × 10 ⁻⁵ ) and the stripe width Ws may be set to 1.0 to 4.0 μm.

  The material of each clad layer preferably has a resistance of 0.1 Ωcm or more, and as a specific example, AlGaInP is preferably used. If the resistance of the cladding layer is too small (for example, less than 0.1 Ωcm using AlGaAs), the current spreads in the lateral direction and no saturable absorber is formed. Therefore, in order to reliably form the saturable absorber, the resistance value as described above is desirable.

  In this embodiment, as the ridge stripe, an inclined ridge, that is, a stripe portion 111 having a shape in which the width on the lower surface is wider than the width on the upper surface as shown in FIG. However, instead of this, a vertical ridge whose width on the lower surface is equal to the width on the upper surface may be used. Such a case is shown in FIGS. These correspond to FIGS. 1A to 1C, respectively, and as shown in FIG. 7A, the p-type (AlGa) InP second cladding layer 107, the p-type GaInP intermediate layer 108, and the p-type layer. The GaAs contact layer 110 forms a stripe portion 211 whose width on the lower surface is equal to the width on the upper surface. Also in this case, the current confinement layer 209 is formed so as to cover the side surface of the stripe portion 211.

  The other points are the same as those of the semiconductor laser element shown in FIGS. For example, the configuration of the active layer 104 shown in FIG. 7B is the same as that shown in FIG. FIG. 7C schematically shows the planar configuration of the stripe portion 211, and specifically shows the shape 211a of the lower surface of the stripe portion 211 and the shape 209a of the lower surface of the n-type current confinement layer 209. Has been. In addition, the same code | symbol is attached | subjected to the same component and detailed description is abbreviate | omitted.

  When the vertical ridge is used in this way, the differential resistance Rs can be reduced because the width of the upper surface of the stripe portion 211 is wider than that of the inclined ridge shown in FIG. As a result, heat generation of the element is suppressed and temperature characteristics are improved.

(Second Embodiment)
Hereinafter, a semiconductor laser device according to the second embodiment will be described.

  FIGS. 8A, 8B and 8C are diagrams showing an example of the semiconductor laser device of the present invention. First, FIG. 8A shows a cross-sectional view. The semiconductor laser element is a monolithic two-wavelength laser element in which an infrared laser part 700 and a red laser part 730 are mounted on the same n-type GaAs substrate 701.

  First, the infrared laser unit 700 has a structure similar to that of the semiconductor laser device of the first embodiment. That is, the n-type GaAs buffer layer 702, the n-type (AlGa) InP cladding layer 703, the active layer 704, and the p-type are formed on the n-type GaAs substrate 701 common to the red laser unit 730, independently of the red laser unit 730. A (AlGa) InP first cladding layer 705, a p-type GaInP etching stop layer 706, a p-type (AlGa) InP second cladding layer 707, a p-type GaInP intermediate layer 708, and a p-type GaAs contact layer 710 are stacked in this order from the bottom. Has been. As a result, a double heterostructure is formed in which the active layer is sandwiched between two clad layers.

  Further, the active layer 704 is a quantum well active layer having three wells, like the active layer 104 in the semiconductor laser device of the first embodiment shown in FIG.

  Further, as shown in FIG. 8A, the p-type (AlGa) InP second cladding layer 707, the p-type GaInP intermediate layer 708, and the p-type GaAs contact layer 710 are processed into a mesa-type stripe shape as a ridge stripe. The stripe portion 711 is configured such that the width on the lower surface is wider than the width on the upper surface. An n-type GaAs current confinement layer 709 is formed on both sides of the stripe portion 711, thereby forming a current confinement structure for constricting a region of current injected into the active layer 704. Such a structure is also the same as that shown in FIG.

  Further, the distance (remaining thickness) from the lower surface of the current confinement layer 709 to the active layer 704 is indicated as d1.

Here, regarding the composition ratio of the materials constituting each layer of the infrared laser part 700, the n-type (AlGa) InP cladding layer 703, the p-type (AlGa) InP first cladding layer 705, and the p-type (AlGa) InP second cladding. The layer 707 is (Al _0.7 Ga _0.3 ) _0.51 In _0.49 P. The (AlGa) InP barrier layers 1042b and 1044b constituting the active layer 704 are (Al _0.4 Ga _0.6 ) _0.51 In _0.49 P (see FIG. 1B).

  Next, the basic configuration of the red laser unit 730 is the same as that of the infrared laser unit 700. That is, an n-type GaAs buffer layer 732, an n-type (AlGa) InP cladding layer 733, an active layer 734, and an n-type GaAs substrate 701 common to the infrared laser unit 700 are provided independently of the infrared laser unit 700. A p-type (AlGa) InP first cladding layer 735, a p-type GaInP etching stop layer 736, a p-type (AlGa) InP second cladding layer 737, a p-type GaInP intermediate layer 738, and a p-type GaAs contact layer 740 in this order from the bottom. Are stacked. As a result, a double heterostructure is formed in which the active layer is sandwiched between two clad layers.

  However, the active layer 734 is a quantum well active layer having five wells, as shown in FIG. 8B. That is, five GaInP well layers 7349w, 7347w, 7345w, 7343w, and 7341w are formed in order from the bottom, with four (AlGa) InP barrier layers 7348b, 7346b, 7344b, and 7342b being interposed between these nine layers. The laminated structure is a structure sandwiched from below and above by two (AlGa) InP guide layers 7350g and 7340g. As a result, 7350g, 7349w, 7348b, 7347w, 7346b, 7345w, 7344b, 7343w, 7342b, 7341w and 7340g are laminated in this order from the lower side (n-type (AlGa) InP cladding layer 733 side).

  Further, as shown in FIG. 8A, similar to the infrared laser unit 700, the p-type (AlGa) InP second cladding layer 737, the p-type GaInP intermediate layer 738, and the p-type GaAs contact layer 740 make a mesa type. A stripe shape (stripe portion 741) is formed, and an n-type GaAs current confinement layer 709 is embedded on both sides thereof, thereby forming a current confinement structure.

  Furthermore, the distance (remaining thickness) from the lower surface of the current confinement layer 709 (in other words, the lower surface of the ridge stripe) to the active layer 734 is indicated as d2.

Further, regarding the composition ratio of the materials constituting each layer of the red laser portion 730, the n-type (AlGa) InP cladding layer 733, the p-type (AlGa) InP first cladding layer 735, and the p-type (AlGa) InP second cladding layer 737 are used. Is (Al _0.7 Ga _0.3 ) _0.51 In _0.49 P. Further, (AlGa) and InP guide layer 7340g and 7350g, (AlGa) InP barrier layer 7342b, 7344b, terms and 7346b and 7348b are set to _{(Al 0.5 Ga 0.5) 0.51 In} 0.49 P. Further, the GaInP well layers 7349w, 7347w, 7345w, 7343w and 7341w are Ga _0.43 In _0.57 P.

  Next, FIG. 8C shows the planar shapes of the stripe portion 711 in the infrared laser portion 700 and the stripe portion 741 in the red laser portion 730. Here, the shape of the lower surface of the stripe portion 711 is a shape 711a having the same width from the light emitting end surface A to the rear end surface B, as in FIG. On the other hand, the planar shape of the stripe portion 741 in the red laser portion 730 is a tapered stripe structure shape 741a that gradually increases in width from the light emitting end surface A toward the rear end surface B. Here, in the red laser part 730, the stripe width on the light emitting end face A side is expressed as Ws.

  The stripe portion 711 in the infrared laser portion 700 and the stripe portion 741 in the red laser portion 730 are formed simultaneously. The current confinement layer 709 is also formed simultaneously in the infrared laser portion 700 and the red laser portion 730. Further, although not shown in the drawings, a p-type electrode is formed on the p-type GaAs contact layers 710 and 740 and the n-type current confinement layer 709, and the back surface of the n-type GaAs substrate 701. Is formed with an n-type electrode. These p-type electrode and n-type electrode are also formed simultaneously in the infrared laser part 700 and the red laser part 730.

  As described above, the semiconductor laser device of this embodiment is a monolithic two-wavelength laser device including the infrared laser unit 700 and the red laser unit 730. FIG. 9A shows the behavior of the multimode property (full width at half maximum of the oscillation spectrum) when the remaining thickness of the semiconductor laser element is changed as in the first embodiment. However, since the infrared laser unit 700 is the same as the semiconductor laser device of the first embodiment, it is omitted and only the red laser unit 730 is shown.

  Here, the stripe width is 3 μm at the light emitting end face A and 5 μm at the rear end face B, and the measurement conditions are room temperature and 3.5 mW.

  As shown in FIG. 9A, when the remaining thickness d2 is increased, the full width at half maximum of the oscillation spectrum is initially increased accordingly, and when the remaining thickness d2 is 0.45 μm or more, the full width at half maximum of the oscillation spectrum is substantially constant. It becomes. 9B, 9C, and 9D show actual spectrum waveforms in the case where the remaining thickness d2 is 0.39 μm, 0.47 μm, and 0.72 μm in order. The oscillation spectrum is close to a single peak when the remaining thickness shown in FIG. 9B is 0.39 μm, and is 0.47 μm shown in FIG. 9B and 0.72 μm shown in FIG. 9D. In some cases, a multimode spectrum with a wide full width at half maximum is obtained.

  This can be explained by the effective refractive index difference (Δn) between the portion corresponding to the stripe portion 741 and the portions corresponding to both sides thereof.

In the case where the remaining thickness d2 is 0.39 μm, Δn = 1.2 × 10 ⁻³ or so, and this relatively large Δn prevents light from leaking out to the side of the ridge. It becomes difficult to form. As a result, the full width at half maximum of the oscillation spectrum is reduced.

On the other hand, when the remaining thickness d2 is 0.47 μm and 0.72 μm, Δn is as small as about Δn = 3.8 × 10 ⁻⁴ and 3.6 × 10 ⁻⁵ , respectively. It is considered that the saturable absorber is sufficiently formed and multimode oscillation occurs. However, when the remaining thickness d2 is 0.72 μm, although not shown in the figure, a phenomenon occurs in which the FFP in the horizontal direction becomes bimodal. For this reason, it was confirmed that the remaining thickness d2 capable of realizing both stable multi-mode properties and fundamental transverse mode oscillation was 0.4 to 0.7 μm.

Here, generally, the remaining thickness d2 for self-excited oscillation of the red laser by the conventional semiconductor laser element is 0.25 μm to 0.4 μm (Δn: 3 × 10 ⁻³ to 1 × 10 ⁻³ ). On the other hand, in the present embodiment, the remaining thickness d2 is as thick as 0.4 μm to 0.7 μm (Δn: 1 × 10 ^{−3 to} 5 × 10 ⁻⁵ ) as described above. Multimode oscillation (including self-excited oscillation) is possible. The reason for this will be described below.

  FIG. 10A shows an NFP image in the oscillation threshold state when the stripe width is 3 μm at the light emitting end face A, 5 μm at the rear end face, and the remaining thickness d2 is 0.47 μm. As in the case of the first embodiment, the full width at half maximum obtained from the light distribution indicated by the NFP image can be used to indicate the degree of light spread.

  FIG. 10B shows the full width at half maximum (denoted by a dotted line) of NFP in the oscillation threshold state when normalized with reference to the remaining thickness d2 = 0.39 μm, and when normalized with reference to the remaining thickness d2 = 0 μm. The lateral spreading current (calculated value: indicated by a solid line) is shown. The full width at half maximum of NFP initially increases as the remaining thickness d2 increases, and becomes substantially constant when the remaining thickness d2 exceeds approximately 0.7 μm. On the other hand, the lateral spreading current increases until the remaining thickness d2 is about 0.4 μm, and thereafter tends to be saturated.

  Thus, in the range where the remaining thickness d2 is 0.4 μm to 0.7 μm, the current spread in the lateral direction is generally saturated and the light distribution (spread) is increased, so this range is a saturable absorber. It can be said that this is an area where the increase is made. On the other hand, when the remaining thickness d2 is 0.7 μm or more, the light distribution (spreading) and the lateral current are both substantially constant, so that there is no significant increase in the saturable absorber. It is thought that the full width at half maximum was also almost constant. Therefore, the region where the saturable absorber is easily formed is a region where the remaining thickness d2 is 0.4 μm or more. Since the region where the FFP is not bimodal is the region where the remaining thickness d1 is 0.7 μm or less, the range of the remaining thickness d1 capable of stable multimode oscillation is 0.4 μm to 0.7 μm. Become.

  Next, the extent of current spreading with respect to the stripe width is shown using an NFP image before laser oscillation. FIG. 11A shows an NFP image when the stripe width is 3.3 μm at the light emitting end face A and 6 μm at the rear end face B, the remaining thickness d2 is 0.43 μm, and the current is supplied at 10 mA. This has a strong correlation with the current density distribution injected into the active layer and can be viewed as a current distribution. As shown in FIG. 11A, since the remaining thickness d2 is relatively large at 0.43 μm, the current spreads widely in the lateral direction and is 5.9 μm in terms of the full width at half maximum. This value has a considerably large spread that is nearly twice as large as the stripe width Ws of 3.3 μm at the light exit end face A.

  Similarly to this, the behavior of the full width at half maximum of the current distribution by NFP when the stripe width on the rear end face B side is constant at 6 μm and the stripe width Ws on the light emitting end A side is changed is shown in FIG. (B). According to FIG. 11B, the current spread (full width at half maximum) is 5.3 μm when the stripe width Ws on the light emitting end A side is 2.9 μm, and the current spread increases as the stripe width increases. At 5 μm, the full width at half maximum is 8 μm or more. As described above, it was confirmed that when the remaining thickness d2 is increased as compared with the conventional case, the current spread becomes larger than the stripe width.

  Next, the multimode property (full width at half maximum of oscillation spectrum) when the remaining thickness d2 is constant at 0.45 μm, the stripe width of the rear end face B is constant at 6 μm, and the stripe width Ws of the light exit end face A is changed. The behavior is shown in FIG. Here, the oscillation spectra when the stripe width Ws of the light emitting end face A is 2.2 μm, 4.2 μm, and 5.8 μm are shown in FIGS. 12B, 12C, and 12D in order. As shown in FIGS. 12B to 12D, it can be confirmed that the full width at half maximum of the oscillation spectrum decreases as the stripe width Ws of the light emitting end face A becomes wider. This is considered to be due to the same reason as in the first embodiment. That is, as the stripe width Ws of the light emitting end face A increases, the volume of the active layer into which current is injected is increased below the ridge stripe portion, so that the saturable absorber formed in the active layer below the current confinement layer. Since the volume is relatively small, it is considered that self-excited oscillation is less likely to occur.

  In addition, when the stripe width is 5.8 μm, it has been confirmed that the FFP in the horizontal direction causes bimodal high-order transverse mode oscillation and kinks are generated around 7 mW. From this, the upper limit of the stripe width is considered to be about 5.5 μm due to characteristics.

  Further, when the stripe width was 2.2 μm, nonlinearity occurred in the external differential efficiency Se in the IL characteristic. This is because the waveguide loss rapidly decreases when the volume of the saturable absorber increases and the saturable absorber becomes transparent. Such an IL characteristic is not preferable because it is difficult to make an APC (Auto Power Control) operation practically. Therefore, the lower limit of the stripe width is about 2.5 μm.

Based on the above results, the temperature characteristics of the structure of the semiconductor laser device according to the present embodiment and the structure of the prior art were actually compared. As a result, FIG. 13A shows the temperature dependence of the IL characteristic, and FIGS. 13B and C show the temperature dependence of the oscillation spectrum in this embodiment and the prior art in order. Here, the remaining thickness d2 is 0.42 μm in the structure of the present embodiment, and the remaining thickness is 0.33 μm in the prior art structure. When this remaining thickness d2 is converted to Δn, Δn = 5 × 10 ^{−4 in} the structure of the present invention and Δn = 1.4 × 10 ⁻³ in the conventional structure. In both structures, the stripe width is 3.2 μm on the light emitting end face A side and 5.2 μm on the rear end face B side, and the composition ratio is the value described above.

  As shown in FIG. 13A, the IL structure at 25 ° C. has a lower oscillation threshold value in the prior art structure. However, at 85 ° C., the oscillation threshold is lower in the structure of the present embodiment. This reason is also considered to be the same as in the case of the first embodiment. That is, first, at 25 ° C., the current structure does not spread greatly in the lateral direction due to the remaining thickness of the structure of the prior art, so that the reactive current that does not contribute to oscillation is reduced and converted to light efficiently. This is probably because of this. In addition, since Δn is relatively large, the waveguide loss in the active layer is also considered to be a cause of good IL characteristics. On the other hand, in the case of 85 ° C., according to the structure of the prior art, the current injected into the active layer is concentrated in the portion immediately under the stripe and the current density increases, so that a leakage current is generated in the element, leading to heat generation. It is considered that the temperature characteristics deteriorate. In the case of the semiconductor laser device of the present embodiment, the current spread is larger than that of the conventional technique, so the current density is also lower than that of the conventional technique, and the generation of leakage current is suppressed. Have.

  Further, as shown in FIGS. 13B and 13C, the full width at half maximum of the oscillation spectrum is larger in the case of the structure of the present embodiment than in the structure of the prior art at 25 ° C. and 85 ° C., and good multimode characteristics are obtained. Is obtained.

  As described above, as in the case of the first embodiment, according to the present embodiment, by defining the range of the remaining thickness d2, it is possible to stably maintain the multimode characteristics with a wide full width at half maximum of the oscillation spectrum. However, a semiconductor laser device with good temperature characteristics can be realized. That is, the remaining thickness d2 is set to a range in which the current spread is substantially constant with the increase in the remaining thickness d2 and the lateral light spread in the active layer increases with the increase in the remaining thickness d2. For this purpose, in the region where the light distribution (full width at half maximum of NFP) is less than twice the stripe width with reference to the remaining thickness at which the current spread begins to become substantially constant regardless of the increase in the remaining thickness d2. You only have to set it.

As specific dimensions, as already indicated, the distance from the lower surface of the n-type current blocking layer 709 to the upper face of the active layer 734 (remaining thickness) d2 of 0.4~0.7μm (Δn = 1 × 10 ^{- 3 to} 5 × 10 ⁻⁵ ) and the average stripe width (average width when the taper stripe structure is converted as a straight stripe) may be 2.5 to 5.5 μm. In addition to the above, when the infrared laser unit 700 is configured in the same manner as the semiconductor laser element of the first embodiment, stable characteristics can be obtained as a monolithic two-wavelength laser.

  The material of each clad layer preferably has a resistance of 0.1 Ωcm or more, and as a specific example, AlGaInP is preferably used.

  In this embodiment, as the ridge stripe, an inclined ridge, that is, a stripe portion 711 having a shape in which the width on the lower surface is wider than the width on the upper surface as shown in FIG. However, as in the case of the first embodiment, instead of this, a vertical ridge whose width on the lower surface is equal to the width on the upper surface may be used. An example of a specific structure is shown in FIGS. This corresponds to the order of FIGS. 8A to 8C. As shown in FIG. 14A, the p-type (AlGa) InP second cladding layer 707, the p-type GaInP intermediate layer 708, and the p-type GaAs contact. The layer 710 forms a stripe portion 811 whose width on the lower surface is equal to the width on the upper surface. The p-type (AlGa) InP second cladding layer 737, the p-type GaInP intermediate layer 738, and the p-type GaAs contact layer 740 constitute a stripe portion 841 having a width on the lower surface equal to that on the upper surface. A current confinement layer 809 is formed so as to cover the side surfaces of the stripe portions 811 and 841.

  Since the other points are the same as those of the semiconductor laser element shown in FIGS. 8A to 8C, detailed description will be omitted by giving the same reference numerals.

  As described above, when the vertical ridge is used, the differential resistance Rs can be reduced because the width of the upper surface of the stripe portions 811 and 841 is wider than that of the inclined ridge shown in FIG. As a result, heat generation of the element is suppressed and temperature characteristics are improved.

  In the present embodiment, the monolithic two-wavelength laser element in which the same infrared laser unit 700 and red laser unit 730 as those in the first embodiment are formed on the common n-type GaAs substrate 701 has been described. However, as a matter of course, it is possible to form a laser element on which only the red laser part 730 is mounted as the light emitting part for oscillating the laser. Also in this case, needless to say, by using the red laser portion having the remaining thickness as described in the present embodiment, a laser element that operates stably in a wider temperature range than before can be obtained.

(Third embodiment)
Hereinafter, a semiconductor laser device according to the third embodiment will be described.

  FIGS. 15A, 15B and 15C are views showing an example of the semiconductor laser device of the present invention. Here, the semiconductor laser element has the same structure as the semiconductor laser element of the second embodiment except for a part thereof. For this reason, only the differences in structure will be described in detail. The same constituent elements as those of the semiconductor laser element are denoted by the same reference numerals in FIGS. 13A to 13C as in FIGS.

  The semiconductor laser device of this embodiment includes a p-type (AlGa) InP second cladding layer 707, a stripe portion 911 composed of a p-type GaInP intermediate layer 708 and a p-type GaAs contact layer 710, and a p-type (AlGa) InP second cladding. The stripe portion 941 including the layer 737, the p-type GaInP intermediate layer 738, and the p-type GaAs contact layer 740 has a planar shape different from that of the semiconductor laser device of the second embodiment.

  Specifically, for both the stripe portions 911 and 941, as shown in FIG. 15C, the stripe width gradually increases inward from the light emitting end face A, and the central portion is a straight having a uniform width. It becomes a stripe and then has a shape that gradually decreases in width toward the rear end face B. In other words, a portion having a constant stripe width exists on the inner side, and a portion that tapers from both ends toward the light emitting end surface A and the rear end surface B is continuously formed.

  In such a taper stripe structure, since the stripe width can be made wider than that of the straight stripe, the differential resistance Rs can be reduced, the heat generation of the element can be suppressed, and the temperature characteristics can be improved.

  However, the average width of the stripe portions 911 in the infrared laser portion 700 (average width converted as a straight stripe structure) is 1 to 4 μm, and the average width of the stripe portions 730 in the red laser portion 730 is 2.5 to 5. Must be 5 μm. This is the same size range as described in the first and second embodiments. Outside this range, problems such as kinks occur, the oscillation spectrum and FFP exhibit bimodality, and the manufacturing yield of the laser device decreases.

In the first, second and third embodiments described above, an n-type GaAs layer is used as the current confinement layer. However, there is no problem in using a metal such as Ti / Au, a semiconductor such as AlGaAs, AlInP or α-Si, or an insulating film such as SiN _x or SiO _x instead. Further, the composition ratio of (Al _0.5 Ga _0.5 ) _0.51 In _0.49 P or the like is not particularly limited to this.

  Moreover, although the number of wells in the active layer is 3 layers on the infrared side and 5 layers on the red side, good characteristics can be obtained in the range of 3 to 5 layers on the infrared side and 4 to 7 layers on the red side.

  Furthermore, the stripe structure has been described in three ways: a straight stripe structure, a tapered stripe structure in which the light exit end face A side is narrow and the rear end face B side is wide, and a structure in which the central part is wide and narrows according to both end faces. Not limited to this, a structure in which the rear end surface B side is narrow and the light emission end surface A side is wide, a structure in which the central portion is narrow and widens toward both end surface sides, and the like may be used. However, it is required that the average stripe width (average width in which the taper stripe structure is converted as a straight) is 1 to 4 μm in the infrared laser portion and 2.5 to 5.5 μm in the red laser portion.

  Furthermore, it goes without saying that the present invention can be applied to various lasers such as AlGaAs / GaAs, AlGaN / InGaN, and ZnMgSSe / ZnS.

  The semiconductor laser device of the present invention is stable as a fundamental transverse mode and multi-longitudinal mode oscillation even at high temperature operation, and has good temperature characteristics. In particular, it is useful as a laser light source or the like in the field of optical disk systems.

101 n-type GaAs substrate 102 n-type GaAs buffer layer 103 n-type (AlGa) InP first cladding layer 104 active layer 1040 g (AlGa) InP first guide layer 1041 w GaAs first well layer 1042 b (AlGa) InP first barrier layer 1043 w GaAs second well layer 1044b (AlGa) InP second barrier layer 1045w GaAs third well layer 1046g (AlGa) InP second guide layer 105 p-type (AlGa) InP first cladding layer 106 p-type etching stop layer 107 p-type ( AlGa) InP second cladding layer 108 p-type GaInP intermediate layer 109 n-type GaAs current confinement layer 109a n-type GaAs current confinement layer bottom surface shape 110 p-type GaAs contact layer 111 stripe portion 111a stripe-side bottom surface Jo d1 remaining thickness 211 stripe part

700 Infrared laser part 701 n-type GaAs substrate 702 n-type GaAs buffer layer 703 n-type (AlGa) InP first cladding layer 704 active layer 705 p-type (AlGa) InP first cladding layer 706 p-type etching stop layer 707 p-type (AlGa) InP second cladding layer 708 p-type GaInP intermediate layer 709 n-type GaAs current confinement layer 709a shape of n-type GaAs current confinement layer lower surface 710 p-type GaAs contact layer 711 stripe portion 711a shape of stripe portion lower surface d1 remaining thickness

730 Red laser part 732 n-type GaAs buffer layer 733 n-type (AlGa) InP first cladding layer 734 active layer 7340 g (AlGa) InP first guide layer 7341 w GaAs first well layer 7342 b (AlGa) InP first barrier layer 7342 w GaAs Second well layer 7343b (AlGa) InP second barrier layer 7345w GaAs third well layer 7346b (AlGa) InP third barrier layer 7347w GaAs fourth well layer 7348b (AlGa) InP fourth barrier layer 7349w GaAs fifth well layer 7350g (AlGa) InP second guide layer 735 p-type (AlGa) InP first cladding layer 736 p-type etching stop layer 737 p-type (AlGa) InP second cladding layer 738 p-type GaInP intermediate layer 740 p-type Remaining thickness aAs contact layer 741 stripe portion 741a stripe partial bottom of the shape d2

811, 841, 911, 941 Striped portion

Claims (3)

On the substrate, at least a first light emitting unit and a second light emitting unit are provided,
The first light emitting unit and the second light emitting unit are formed on the active layer, the active layer formed on the first clad layer, the active layer formed on the first clad layer, respectively. A second clad layer having a ridge stripe for injecting a current into the ridge stripe, and a current confinement layer formed on both sides of the ridge stripe so that the current is confined to the ridge stripe,
The ridge stripe of the first light emitting unit and the ridge stripe of the second light emitting unit are formed simultaneously,
The cross-sectional shape of the ridge stripe is a vertical ridge,
Each of the ridge stripes included in each of the first light emitting unit and the second light emitting unit has a taper stripe structure having a change in width.
In both the first light emitting unit and the second light emitting unit, the distance from the lower surface of the current confinement layer to the upper surface of the active layer is a value within a predetermined range, and the current is the ridge stripe. After passing through the width of the ridge stripe to reach the active layer,
The predetermined distance in the first light emitting unit is 0.65 μm or more and 1.2 μm or less,
The predetermined distance in the second light emitting unit is 0.4 μm or more and 0.7 μm or less;
The width of the ridge stripe included in the first light emitting unit is 1.0 μm or more and 4.0 μm or less,
The width of the ridge stripe of the second light emitting part is 2.5 μm or more and 5.5 μm or less;
The predetermined distance in the first light emitting unit is larger than the predetermined distance in the second light emitting unit,
The width of the ridge stripe included in the first light emitting unit is smaller than the width of the ridge stripe included in the second light emitting unit.
The active layer of the first light emitting unit is formed of Al _x Ga _1-x As (0 ≦ x ≦ 1),
The active layer of the second light emitting unit is formed of Ga _y In _1-y P (0 <y <1),
The first cladding layer and the second cladding layer are both made of an AlGaInP-based material and the same composition,
A semiconductor laser element characterized by being a self-excited oscillation type. In claim 1,
The taper stripe structure is a structure in which the width gradually decreases from a central portion toward a light emitting end face side from which light is emitted and a rear end face side facing the light emitting end face. A semiconductor laser. In claim 1,
2. The semiconductor laser device according to claim 1, wherein the taper stripe structure has a structure in which a width gradually increases from a light emitting end face side from which light is emitted toward a rear end face side facing the light emitting end face.

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