JP5163355B2 - Semiconductor laser device - Google Patents

Description

  The present invention relates to a semiconductor laser device having a wide modulation band by shortening a resonator length.

  Optical communication is a technology suitable for large-capacity information transmission. In optical communication, an optical signal is generated using a semiconductor laser, and this optical signal is transmitted by an optical fiber. In recent years, the increase in capacity of optical communication has been increasing, and the bit rate of optical signals has also increased.

  As a method of generating an optical signal, there are a method of directly modulating the current injected into the semiconductor laser and a method of modulating DC light generated by the semiconductor laser with an external modulator. In addition, as a new method for generating an optical signal, a modulator integrated light source in which a semiconductor laser and an optical modulator are integrated is prepared, and DC light generated by the semiconductor laser is integrated on the same substrate. There is a method of modulating with an optical modulator.

  Among these, the method of directly modulating a semiconductor laser, that is, the direct modulation method does not require an optical modulator for generating an optical signal, so the structure of the optical signal generating device (transmitting device) is simple, and the optical signal generation is performed. The drive circuit forming the device is also simple. Therefore, the direct modulation method is superior in cost compared to other methods that require an optical modulator.

  In order to cope with the bit rate that continues to increase by the direct modulation method, it is necessary to make the modulation band of the semiconductor laser wider than the current semiconductor laser.

  As is well known, the upper limit of the modulation band of a semiconductor laser is limited by the relaxation frequency of the semiconductor laser. It is also well known that shortening the cavity length of a semiconductor laser is effective in increasing the relaxation frequency of a semiconductor laser (note that the cavity length is an optical resonator) This is the length of the area where both ends are sandwiched between the reflecting mirrors.)

  As a semiconductor laser for optical communication, a distributed feedback laser (DFB laser) that oscillates at a single wavelength (single longitudinal mode) is widely used.

  In the DFB laser, a diffraction grating is provided along the active layer, and an optical resonator is formed by the diffraction grating. Therefore, in the DFB laser, the resonator length matches the element length. Therefore, in order to make the DFB laser a short resonator, it is necessary to shorten the element itself.

  By the way, generally, both ends of the semiconductor laser are formed by cleavage. Therefore, the lower limit of the element length of the semiconductor laser is the minimum length of the semiconductor substrate that can be cleaved. On the other hand, when the element length is shortened, another problem that handling of the element after cleavage becomes difficult occurs.

  Specifically, when the element length of the semiconductor laser is 150 μm or less, the cleavage and subsequent handling become rapidly difficult.

  Therefore, 150 μm is the limit for shortening the cavity length of the DFB laser. For this reason, the relaxation oscillation that can be achieved by shortening the resonator length of the DFB laser is at most several GHz.

  Therefore, a short cavity semiconductor laser device based on a distributed Bragg reflector type semiconductor laser (DBR laser) whose resonator length is not limited by the element length has been proposed (Non-patent Document 1).

  FIG. 1 is a perspective view illustrating the configuration of a short cavity semiconductor laser device (hereinafter referred to as a short cavity DBR laser) based on a DBR laser. In FIG. 1, the short resonator DBR laser 2 is depicted as being largely cut along the light guiding direction.

  In the short cavity DBR laser 2 shown in FIG. 1, a distributed Bragg reflector 6 (hereinafter referred to as DBR) made of InGaAsP is optically connected to an active layer 4 formed of an InGaAs multiple quantum well. An antireflection film 8 is provided on the front end face of the short resonator DBR laser 2, and a high reflection film 10 is provided on the rear end face.

  That is, an active region 12 is formed in a region sandwiched between the distributed Bragg reflector 6 and the highly reflective film 10, and the active layer 4 is disposed therein.

  In the example disclosed in Non-Patent Document 1, the element length of the short cavity DBR laser 2 itself is not as short as 200 to 300 μm, but the length of the active region 12 is 10 to 100 μm and is a short cavity laser based on a DFB laser. It is much shorter.

  Thus, based on the DBR laser, the shortening of the cavity of the semiconductor laser can be easily realized.

As another short cavity semiconductor laser device, a DR laser (distributed reflector laser) in which a diffraction grating is provided along an active layer in a short cavity DBR laser has also been proposed (Non-patent Document 2). The DR laser is a semiconductor laser that can be easily shortened, similarly to the short cavity DBR laser.
IEEE Photon. Technol. Lett. 18, 22, pp. 2383-2385 (2006). IEEE Photon. Technol. Lett. 2, 6, pp. 385-387 (1990).

  Incidentally, in the short cavity DBR laser, the upper electrode 14 is also shortened as the active region is shortened (see FIG. 1).

  This is because when the upper electrode 14 protrudes above the active layer 4 and extends above the DBR 6, current is injected not only into the active layer 4 but also into the region 18 where the DBR 6 is formed. This is because the current injected into the DBR region 18 instead of the active layer 4 is referred to as a reactive current.

  When the upper electrode 14 is shortened, the contact area between the semiconductor layer (contact layer) with which the upper electrode 14 is in contact and the upper electrode 14 is reduced. As a result, contact resistance (resistance between the upper electrode 14 and the upper cladding layer 20) and the like increase, and the element resistance increases.

  For this reason, in the short cavity DBR laser, the Joule heat increases and the element temperature rises. An increase in element temperature causes a decrease in photon density and suppresses an increase in relaxation oscillation frequency.

  Therefore, if the shortening of the active region is promoted with the short cavity DBR laser, the relaxation oscillation frequency is gradually increased and the relaxation oscillation frequency is saturated. Therefore, the modulation band is also saturated.

  This phenomenon is common to DR lasers as well as short cavity DBR lasers.

  Accordingly, an object of the present invention is to provide a semiconductor laser that uses a distributed Bragg reflector to shorten the active region, and suppresses an increase in element temperature due to the shortening of the active region. This is to widen the modulation band.

  In order to achieve the above object, the present semiconductor laser device includes a semiconductor substrate having a first conductivity type on which a first electrode is formed, an active layer formed above the semiconductor substrate, and the semiconductor substrate. And a passive optical waveguide layer that is optically connected to the active layer and includes a diffraction grating that reflects light generated by the active layer, and is formed above the passive optical waveguide layer. A current confinement layer for blocking current injection into the passive optical waveguide layer; an upper cladding layer having a second conductivity type and formed to extend above the active layer and the current confinement layer; A contact layer having the second conductivity type, formed above the upper clad layer, covering the active layer and extending above the passive optical waveguide layer; and formed above the contact layer Covering the active layer and in front And a second electrode which extends above the passive optical waveguide layer.

  According to the present semiconductor laser device, in a semiconductor laser that uses a distributed Bragg reflector to shorten the optical resonator length, an increase in element temperature due to the shortening of the optical resonator is suppressed, and The modulation band of the semiconductor laser can be widened.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. However, the technical scope of the present invention is not limited to these embodiments, but extends to the matters described in the claims and equivalents thereof.

  First, the reason why the expansion of the modulation band is saturated in a short resonator DBR laser or the like will be described based on a theoretical formula.

As is well known, the relaxation oscillation frequency f _r of the semiconductor laser is expressed by the following equation.

Here, v _g is the light group velocity of the optical resonator. G and n are the gain of the semiconductor laser and the carrier concentration of the active layer, respectively. Dg / dn is the differential gain of the semiconductor laser. S ₀ is the photon density, and τ _p is the photon lifetime.

As is apparent from this equation, the relaxation frequency f _r is proportional to the square root of the photon density S ₀ . Therefore, when the photon density S ₀ is decreased, the relaxation frequency _fr is decreased.

Here, the photon density S ₀ is expressed by the following equation.

Here, I is a current injected into the semiconductor laser, I _th is the threshold current. q is an elementary charge. L, w, and d are the length, width, and thickness of the active layer, respectively. G _th is a threshold gain.

As is clear from Equation (2), the photon density is inversely proportional to the resonator length L. Therefore, when the resonator length is shortened, the photon density is increased and the relaxation oscillation frequency _fr is increased (see equations (1) and (2)).

  On the other hand, when the active region length is shortened, the device resistance increases, the Joule heat increases, and the device temperature rises. An increase in element temperature leads to an increase in leakage current.

  Here, the leakage current includes a current that is not injected into the active layer 4 and a current that overflows from the active layer 4. The current that is not injected into the active layer 4 includes a current that bypasses the active layer 4 and is injected into the DBR region 18 and a current that flows through the buried layer of the semiconductor laser.

  In Formula (2), such a leakage current is not considered. Therefore, as the current value I to be substituted into the equation (2), a current value obtained by subtracting the leakage current from the current injected into the semiconductor laser must be used.

Thus, the current value I decreases with increasing leakage current when the device temperature rises, the photon density S ₀ is reduced.

What reason, when gradually shortened resonator length the injection current is constant initially, increased photon density S ₀ in inverse proportion to the resonator length, the relaxation oscillation frequency increases. However, when the shortening of the active region length in the resonator proceeds, the element resistance increases and the element temperature starts to rise. As a result, the leakage current is increased and the effect of shortening the resonator length is offset. As a result, the photon density S ₀ is saturated and also the saturation increases the relaxation oscillation frequency.

  In this way, when the cavity length is shortened in a semiconductor laser (for example, a short cavity DBR laser or a DR laser) that shortens the optical cavity length by using a distributed Bragg reflector, the modulation band is first Will improve, but will eventually saturate.

  In order to eliminate such a saturation phenomenon of the modulation band, it is considered effective to avoid an increase in element resistance due to the shortening of the resonator. However, as described above, in the conventional short cavity semiconductor laser, an increase in element resistance due to the shortening of the cavity is inevitable.

  Accordingly, a short resonator semiconductor laser device capable of suppressing an increase in element resistance even if the optical resonator is shortened and thus further expanding the modulation band will be described in accordance with each embodiment.

  In addition, if the equation (2) is substituted into the equation (1), the relaxation oscillation frequency fr is expressed as follows.

  Referring to equation (3), it can be seen that when the photon lifetime is constant, the relaxation oscillation frequency increases in inverse proportion to the square root of the resonator length.

(Embodiment 1)
The present embodiment relates to a short resonator DBR laser that suppresses the saturation phenomenon of the modulation band by suppressing an increase in element resistance caused by shortening the element length.

(1) Configuration FIG. 2 is a plan view of short resonator DBR laser 24 (semiconductor laser device according to the present embodiment) according to the present embodiment. FIG. 3 is a view for explaining a cross section taken along line AA of FIG. 2 from the direction of the arrow. In FIG. 2, an active layer 4, a passive optical waveguide layer 28, and a diffraction grating 26, which will be described later, are shown in a transparent state.

  FIGS. 4A and 4B are diagrams for explaining the cross sections taken along the lines BB and CC in FIG. 2 from the direction of the arrows, respectively. It should be noted that even if the drawings are different, corresponding parts are denoted by the same reference numerals, and description thereof will be omitted (the same applies to other embodiments and modifications).

  The short cavity DBR laser 24 according to the present embodiment has a first conductivity type (for example, n-type) in which a first electrode (lower electrode 16) is formed, as shown in FIGS. A semiconductor substrate 20 is provided.

  The short resonator DBR laser 24 includes an active layer 4 formed on the semiconductor substrate 20.

  The short resonator DBR laser 24 is formed on the semiconductor substrate 20 and is optically connected to the active layer 4 and further includes a diffraction grating 26 that reflects light generated by the active layer 4. A passive optical waveguide layer 28 is provided. Here, the period of the diffraction grating 26 is formed so as to satisfy the Bragg condition with respect to the planned oscillation wavelength of the short resonator DBR laser 24. That is, the “passive optical waveguide layer having a diffraction grating” is a distributed Bragg reflector (DBR).

  Here, the “passive optical waveguide layer having a diffraction grating” means a passive optical waveguide layer having a diffraction grating that periodically changes the refractive index (or dielectric constant) of light propagating through the passive optical waveguide layer. I mean. For example, like the passive optical waveguide layer 28 illustrated in FIG. 3, a diffraction grating is provided along the passive optical waveguide layer, and the passive optical waveguide layer is an example of the “passive optical waveguide layer including the diffraction grating”. .

  The short resonator DBR laser 24 includes a current confinement layer 30 that is formed on the passive optical waveguide layer 28 and prevents injection of current into the passive optical waveguide layer 28.

  The short resonator DBR laser 24 has a second conductivity type (for example, p-type), and is formed so as to extend on the active layer 4 and the current confinement layer 30. It has.

  Further, the short cavity DBR laser 24 is formed on the upper cladding layer 32, covers the active layer 4 and extends above the passive optical waveguide layer 28. For example, a contact layer 34 having p-type) and a second electrode (upper electrode 36) formed on the contact layer 34 are provided.

  In the short resonator DBR laser 24, an optical resonator is formed by a passive optical waveguide layer (DBR) including a diffraction grating 26, and the active layer 4 is disposed therein.

  In the short resonator DBR laser 24, the contact layer 34 covers the active layer 4 and extends above the passive optical waveguide layer 28 (DBR). Therefore, even if the length of the active layer 4, that is, the resonator length is shortened, the contact resistance (resistance between the upper electrode 36 and the upper cladding layer 32) or the like does not increase and the element resistance does not increase. In other words, in the short resonator DBR laser 24, the length of the upper electrode 36 is constant even if the resonator length (the length of the active layer 4) is shortened. The increase can be suppressed (provided that the element length is constant).

  Therefore, in the short resonator DBR laser 24, an increase in element temperature due to the short resonator can be suppressed.

  Moreover, in the short resonator DBR laser 24, current injection into the passive optical waveguide layer 28 is blocked by the current confinement layer 30. For this reason, most of the current injected from the upper electrode 36 is not supplied to the passive optical waveguide layer 28 and is injected into the active layer 4. That is, the current injected from the upper electrode 36 is constricted by the current confinement layer 30 and is intensively injected into the active layer 4.

  Therefore, in the short resonator DBR laser 24, most of the injected current is supplied to the active layer 4, so that the reactive current is not generated even if the upper electrode 36 is extended above the passive optical waveguide layer 28 (DBR). Does not occur.

  Therefore, in this short resonator DBR laser 24, there is no reactive current injected into the passive optical waveguide layer 28 instead of the active layer 4, and the element temperature does not rise even if the resonator length is shortened. Therefore, according to the short resonator DBR laser 24, the saturation phenomenon of the modulation band is eliminated and the modulation band is widened.

  Here, the active region length (the length of the active layer 4 in the traveling direction of the laser beam) is preferably shorter than an element length of 150 μm that can be formed by cleavage, and more preferably 100 μm or less. In such a case, the short resonator DBR laser 24 has a wider modulation band than the conventional short resonator semiconductor laser.

  On the other hand, if the resonator length becomes too short, the mirror loss increases and laser oscillation becomes difficult. Therefore, the resonator length is preferably 5 μm or more, more preferably 10 μm or more.

(2) Manufacturing Method Next, the configuration of the short resonator DBR laser 24 according to the present embodiment will be described in detail according to the manufacturing procedure.

  FIG. 5 is a flowchart illustrating a manufacturing procedure of short resonator DBR laser 24 according to the present embodiment. 6 and 7 are process plan views for explaining the manufacturing procedure of the short resonator DBR laser 24. FIG. FIG. 8 and FIG. 9 are process diagrams for explaining the manufacturing procedure of the short resonator DBR laser 24 when the cross section taken along the line AA in FIG. 6 or FIG. FIG. 10A is a process diagram illustrating the manufacturing procedure of the short resonator DBR laser 24 according to the present embodiment when the cross section taken along line BB in FIG. 7 is viewed from the direction of the arrow. FIG. 10B is a process diagram illustrating the manufacturing procedure of the short resonator DBR laser according to the first embodiment when the cross section taken along the line CC in FIG. 7 is viewed from the direction of the arrow. Unless otherwise specified, the following semiconductor layers are formed by metal organic vapor phase epitaxy.

(I) Formation of diffraction grating or the like (step S1)
First, a diffraction grating 26 is formed by electron beam exposure and reactive ion etching on an n-type InP substrate 38 on which a distributed Bragg reflector (DBR) is to be formed (FIG. 6A and FIG. 6). (See FIG. 8 (a)). 6 and 7 show the diffraction grating 26 in a state where the inside of the growth film is seen through.

  Next, an n-type InGaAsP layer 40 having a composition wavelength of 1.15 μm and a thickness of 70 nm and an n-type InP layer 42 having a thickness of 30 nm are sequentially formed on the n-type InP substrate 38 on which the diffraction grating 26 is formed. (See FIG. 8A).

  Next, a strain quantum well 44 having a compressive stress and a first p-type InP layer 46 having a thickness of 100 nm are sequentially formed on the n-type InP layer 42 (FIGS. 6A and 8A). reference).

  Here, the strained quantum well 44 is formed of a quantum well made of AlGaInAs and a barrier layer. The composition and film thickness of each semiconductor layer (quantum well layer and barrier layer) forming the strain quantum well 44 are set such that the emission wavelength of the strain quantum well 44 is 1300 nm.

  In the present embodiment, the n-type InP substrate 38 (composition wavelength is 0.92 μm) is transparent to the light generated in the active layer 4 and has a refractive index higher than those of the passive optical waveguide layer 28 and the active layer 4 described later. Low. Therefore, the n-type InP substrate 38 functions as a lower cladding layer. However, a lower cladding layer made of n-type InP may be provided below the diffraction grating 26.

  However, when a semiconductor laser is manufactured by providing an active layer made of GaAs (or AlGaAs) on a GaAs substrate, a lower cladding layer is provided between the semiconductor substrate and the active layer (and the passive optical waveguide layer). Need to form.

(Ii) Formation of active layer and passive optical waveguide layer (step S2)
Next, a 300 nm thick SiO ₂ film 48 is formed on the region where the active layer 4 is to be formed by using chemical vapor deposition and photolithography.

Next, the first p-type InP layer 46 and the strained quantum well 44 are wet-etched using the SiO ₂ film 48 as an etching mask (see FIGS. 6B and 8B).

Next, an AlGaInAs layer 50 having the same thickness as the strained quantum well 44 is grown using the SiO ₂ film 48 as a selective growth film (see FIGS. 6B and 8B). Here, the composition wavelength of the AlGaInAs layer 50 is 1.15 μm.

  The strained quantum well 44 left without being wet-etched by this step becomes the active layer 4. On the other hand, the AlGaInAs layer 50 regrown after the wet-etched strained quantum well 44 becomes the passive optical waveguide layer 28.

  Here, the active layer 4 and the passive optical waveguide layer 28 are butt-joined by the regrowth and optically connected.

(Iii) Formation of current confinement layer (step S3)
After the formation of the AlGaInAs layer 50, an InP layer 52 doped with Fe and an n-type InP layer 54 are grown without interrupting crystal growth (see FIGS. 6C and 8C).

  The InP layer 52 doped with Fe becomes semiconductor insulating and prevents current from being injected into the passive optical waveguide layer 28.

  On the other hand, in the n-type InP layer 54, impurities (such as Zn) in the second p-type InP layer 56 described later and Fe in the Fe-doped InP layer 52 are interdiffused to prevent the InP layer 52 from disappearing semi-insulating. Is for.

  The current confinement layer 30 is formed by the InP layer 52 and the n-type InP layer 54 doped with Fe. The current confinement layer 30 is formed so as to have a thickness of 100 nm as a whole.

(Iv) Formation of upper clad layer and contact layer (step S4)
Next, the SiO ₂ film 48 is removed by an etchant mainly composed of HF.

Next, a _second p-type InP layer 56 having a thickness of 1500 nm is formed on the semiconductor layer from which the SiO ₂ film 48 has been removed. Thereafter, a p-type InGaAs layer 58 having a thickness of 200 nm is formed without interrupting crystal growth (see FIGS. 7A and 9A).

  The second p-type InP layer 56 formed in this step is integrated with the first p-type InP layer 46 formed in step S1 to form the upper cladding layer 32.

  On the other hand, the p-type InGaAs layer 58 becomes the contact layer 34.

(V) Formation of buried layer (step S5)
Next, a striped (linear) SiO ₂ film 60 (thickness) is formed at a position where a main portion (portion other than the buried layer) of the short cavity DBR laser 24 is to be formed by chemical vapor deposition and photolithography. 500 nm) is formed (see FIG. 7B).

Next, etching reaching the n-type InP substrate 38 is performed by reactive ion etching using the SiO ₂ film 60 as an etching mask. By this etching, a mesa 62 having a height of 3000 nm is formed (see FIGS. 10A and 10B). FIG. 10A is a cross-sectional view across the passive optical waveguide layer 28. On the other hand, FIG. 10B is a cross-sectional view across the active layer 4.

Next, an InP layer 64 doped with Fe is formed using the SiO ₂ film 60 as a selective growth film (see FIGS. 7B, 10A, and 10B). This semi-insulating InP layer 64 fills the mesa 62 to become a buried layer 66.

  Here, the buried layer 66 confines light propagating through the active layer 4 and the passive optical waveguide layer 28 in the lateral direction (of the mesa 62). At the same time, the buried layer 66 confines the current injected into the short cavity DBR laser 24 in the lateral direction (of the mesa 62).

  That is, in this step, both sides of the active layer 4, the passive optical waveguide layer 28, and the upper cladding layer 32 are embedded with the semiconductor insulating semiconductor layer 64.

(Vi) Formation of electrodes (step 6)
Next, an AuGe / Au electrode 68 (lower electrode 16) is formed on the back surface of the n-type InP substrate 38 (see FIG. 9B).

  Next, an AuZn / Au electrode 70 (upper electrode 36) is formed on the contact layer 34 (see FIG. 9B).

(Vii) Individual elementization (step S7)
Next, the structure formed by the above steps is cleaved and divided into individual elements.

  Finally, an antireflective coating film 72 is formed on the cleaved surface to complete the short resonator DBR laser 24 (FIGS. 7C and 9B).

(3) Operation Next, the laser oscillation operation of the short resonator DBR laser 24 will be described.

  First, an operation in which the short resonator DBR laser 24 generates laser light will be described.

  In order to operate the short resonator DBR laser 24, a positive electrode and a negative electrode of a power source (not shown) are connected to the upper electrode 36 and the lower electrode 16, respectively.

  Next, a current is injected from the power source into the upper electrode 36.

  The current injected from the upper electrode 36 is intensively injected into the active layer 4 by the current confinement layer 30. The current injected into the active layer 4 increases the optical gain of the active layer 4 and generates laser light between a pair of DBRs formed by the diffraction grating 26 and the passive optical waveguide layer 28.

  In the short resonator DBR laser 24, the length of the active region is shorter than 150 μm. In addition, since the upper electrode 36 extends above the passive optical waveguide layer 28, the contact resistance of the upper electrode 36 is low. For this reason, the generation | occurrence | production of the Joule heat resulting from element resistance is suppressed.

  Therefore, a high relaxation oscillation frequency can be easily obtained.

  The laser light generated in this way is emitted from both end surfaces where the antireflective coating film 72 is formed, and becomes emitted light 74 (see FIG. 3).

  When the optical signal is generated by directly modulating the short resonator DBR laser 24, the current injected from the power source into the short resonator DBR laser 24 is modulated. While the injection current exceeds the threshold, the short resonator DBR laser 24 generates laser light according to the above operation.

  Here, in the short resonator DBR laser 24, if the resonator length is shortened, the relaxation oscillation frequency increases without saturation. Therefore, according to the present short resonator DBR laser 24, a wide modulation band is realized which surpasses the conventional short resonator semiconductor laser.

(Embodiment 2)
The present embodiment relates to a semiconductor laser device (DR laser) in which an active layer includes a diffraction grating in addition to a passive optical waveguide layer.

(1) Configuration FIG. 11 is a cross-sectional view of the semiconductor laser device (DR laser) 76 according to the present embodiment along the laser beam traveling direction.

  The configuration of the semiconductor laser device 76 is the same as that of the short resonator DBR laser according to the first embodiment except that the active layer 4 also includes the diffraction grating 78. Therefore, description of components other than the diffraction grating 78 is omitted.

  As shown in FIG. 11, in the short resonator semiconductor laser device 76, the diffraction grating 78 is formed not only near (on the lower side) of the passive optical waveguide layer 28 but also near (on the lower side) of the active layer 4. Has been.

  Here, the Bragg wavelength of the diffraction grating 78 is formed so that the short cavity semiconductor laser device 76 also emits light at a predetermined oscillation wavelength below the active layer 4. The diffraction grating 78 is preferably shifted by a so-called 1 / 4λ on the lower center side of the active layer 4.

(2) Manufacturing Method The manufacturing method of the short cavity semiconductor laser device 76 according to the present embodiment has a diffraction grating 78 on the surface of the n-type InP substrate 38 over the region where the passive optical waveguide layer 28 and the active layer 4 are to be formed. Is substantially the same as the manufacturing method according to the first embodiment.

(3) Operation The short resonator semiconductor laser device 76 according to the present embodiment operates in accordance with the short resonator DBR laser according to the first embodiment. Therefore, detailed description is omitted.

(Embodiment 3)
The present embodiment relates to a short resonator semiconductor laser device in which a diffraction grating is formed in a passive optical waveguide layer in the short resonator semiconductor laser device according to the first embodiment.

(1) Configuration FIG. 12 is a cross-sectional view of short resonator semiconductor laser device 80 according to the present embodiment along the direction of travel of laser light. FIG. 13 is a cross-sectional view perpendicular to the light traveling direction of short cavity semiconductor laser device 80 according to the present embodiment. Here, FIG. 13A is a cross-sectional view perpendicularly crossing the passive optical waveguide layer 28. On the other hand, FIG. 13B is a cross-sectional view perpendicularly crossing the active layer 4.

  As shown in FIGS. 12 and 13, the short cavity semiconductor laser device 80 includes not the n-type InGaAsP layer 40 (see FIG. 3) provided near the lower side of the passive optical waveguide layer 28 but the passive optical waveguide layer. A diffraction grating 26 is directly formed on the substrate 28. In other respects, the configuration of the short resonator semiconductor laser device 80 is substantially the same as that of the short resonator semiconductor laser device 24 of the first embodiment (therefore, the short resonator semiconductor laser device 80 includes an n-type). InGaAsP layer 40 is not provided.)

(2) Manufacturing Method and Operation The short resonator semiconductor laser device 80 is manufactured according to the manufacturing method of the first embodiment. The short resonator semiconductor laser device 80 operates in accordance with the operation of the short resonator semiconductor laser device 24 of the first embodiment.

  Therefore, the description regarding the manufacturing method and operation of the short cavity semiconductor laser device 80 is omitted.

(Modification 1)
In the example described above, the current confinement layer 30 is formed by laminating the InP layer 52 doped with Fe and the n-type InP layer 54.

  However, the current confinement layer may be formed by semiconductor layers having different structures.

  FIGS. 14 to 16 show the pn in which the current confinement layer 30 and the n-type semiconductor layer 86 are stacked on the p-type semiconductor layer 84 in the short cavity semiconductor laser devices according to the first to third embodiments, respectively. 6 is a cross-sectional view when formed by a current blocking layer 88. FIG.

  Also in the short cavity semiconductor laser device according to this modification, the current injected from the upper electrode 36 is concentrated on the active layer 4. Therefore, even if the upper electrode 36 is formed to extend above the passive optical waveguide layer 28, no current is injected into the passive optical waveguide layer 28.

(Modification 2)
FIG. 17 is a cross-sectional view of the short cavity semiconductor laser device 82 according to the present modification along the direction of travel of the laser beam.

  In DR laser 76 according to the second embodiment, diffraction grating 78 is formed in n-type InGaAsP layer 40 provided in the vicinity of the lower side of passive optical waveguide layer 28 and active layer 4.

  However, in the short resonator semiconductor laser device 82, the diffraction grating 90 is formed directly on the passive optical waveguide layer 28 and the active layer 4.

  In other respects, the configuration of the short cavity semiconductor laser device 82 is substantially the same as that of the DR laser 76 of the second embodiment.

  The manufacturing method and operation of the short cavity semiconductor laser device 82 are in accordance with the manufacturing method and operation of the DR laser 76 of the second embodiment. Therefore, the description of the manufacturing method and operation is omitted.

(Modification 3)
FIG. 18 is a cross-sectional view of the short cavity semiconductor laser device 92 according to this modification along the direction of travel of the laser beam.

  In the short resonator semiconductor laser device 92 according to the second modification, the current confinement layer 30 is formed by laminating the Fe-doped InP layer 52 and the n-type InP layer 54.

  On the other hand, in the short cavity semiconductor laser device 92 according to this modification, the current confinement layer 30 is formed by a pn current blocking layer 88 in which an n-type semiconductor layer 86 is stacked on a p-type semiconductor layer 84.

  Also in the short cavity semiconductor laser device according to this modification, the current injected from the upper electrode 36 is concentrated on the active layer 4. Therefore, even if the upper electrode 36 is formed to extend above the passive optical waveguide layer 28, no current is injected into the passive optical waveguide layer 28.

  The example described above relates to a short resonator semiconductor laser device in which n-type InP is used as a substrate and an AlGaInAs strained quantum well layer is formed as an active layer thereon. However, the material for forming the short cavity semiconductor laser device according to each of the above examples is not limited to these materials.

  The operating wavelength of the above-described short cavity semiconductor laser device is 1.3 μm. However, the operating wavelength of the short cavity semiconductor laser device according to each of the above examples need not be limited to 1.3 μm.

It is a perspective view explaining the structure of the short resonator semiconductor laser apparatus based on a DBR laser. 2 is a plan view of a short resonator DBR laser according to the first embodiment. FIG. It is a figure explaining the cross section in the AA line of FIG. 2 seeing from the direction of an arrow. It is a figure explaining the cross section in the BB line of FIG. 2, and CC line seeing from the direction of an arrow. FIG. 5 is a flowchart illustrating a manufacturing procedure of a short resonator DBR laser according to the first embodiment. FIG. 6 is a process plan view for explaining the manufacturing procedure of the short resonator DBR laser according to the first embodiment (part 1); FIG. 6 is a process plan view for explaining the manufacturing procedure of the short resonator DBR laser according to the first embodiment (No. 2). FIG. 8 is a process diagram for explaining the manufacturing procedure of the short cavity DBR laser according to the first embodiment when the cross section along the line AA in FIG. 6 or FIG. 7 is viewed from the direction of the arrows (part 1); FIG. 8 is a process diagram for explaining the manufacturing procedure of the short resonator DBR laser according to the first embodiment when the cross section along the line AA in FIG. 6 or FIG. 7 is viewed from the direction of the arrows (part 2). FIG. 6 is a process diagram illustrating a manufacturing procedure of the short resonator DBR laser according to the first embodiment when the cross sections along the BB line and the CC line are viewed from the direction of the arrows. It is sectional drawing in alignment with the advancing direction of a laser beam of the short resonator semiconductor laser apparatus (DR laser) according to Embodiment 2. It is sectional drawing in alignment with the advancing direction of the laser beam of the short resonator semiconductor laser apparatus according to Embodiment 3. FIG. 10 is a cross-sectional view of the short resonator semiconductor laser device according to the third embodiment, perpendicular to the traveling direction of laser light. It is sectional drawing along the advancing direction of the laser beam of the short resonator semiconductor laser apparatus according to the modification 1 (the 1). It is sectional drawing along the advancing direction of the laser beam of the short resonator semiconductor laser apparatus according to the modification 1 (the 2). It is sectional drawing along the advancing direction of the laser beam of the short resonator semiconductor laser apparatus according to the modification 1 (the 3). FIG. 10 is a cross-sectional view of a short resonator semiconductor laser device according to Modification 2 along the traveling direction of laser light. FIG. 11 is a cross-sectional view of a short resonator semiconductor laser device according to Modification 3 along the traveling direction of laser light.

Explanation of symbols

2 ... Short cavity DBR laser (related technology) 4 ... Active layer 6 ... Distributed Bragg reflector (DBR) 8 ... Antireflection film 10 ... High reflection film 12 ... Optical resonance 14 ... Upper electrode 16 ... Lower electrode 18 ... Region where DBR is formed 20 ... Semiconductor substrate 22 ... Upper cladding layer 24 ... Short cavity DBR laser (embodiment) 1st etc.)
26 ... Diffraction grating 28 ... Passive optical waveguide layer 30 ... Current confinement layer 32 ... Upper cladding layer 34 ... Contact layer 36 ... Upper electrode 38 ... n-type InP substrate 40. · · n-type InGaAsP layer 42 ... n-type InP layer 44 ... strained quantum well 46 ... first p-type InP layer 48 ... SiO ₂ film 50 ... AlGaInAs layer 52 ... Fe Doped InP layer (current confinement layer)
54 ... n-type InP layer 56 ... second p-type InP layer 58 ... p-type InGaAs layer 60 ... SiO ₂ film 62 ... mesa 64 ... InP layer doped with Fe (Embedded layer)
66 ... Embedded layer 68 ... AuGe / Au electrode 70 ... AuZn / Au electrode 72 ... Non-reflective coating film 74 ... Outgoing light
76 (according to the second embodiment) Short resonator semiconductor laser device 78 (according to the second embodiment) Diffraction grating 80 (according to the third embodiment) Short resonator semiconductor laser device 82 Short resonator semiconductor laser device 84 ... p-type semiconductor layer 86 ... n-type semiconductor layer 88 ... pn current blocking layer 90 ... (according to variant 2) diffraction grating 92 (according to variant 2) ... Short-cavity semiconductor laser device (according to modification 2)

Claims (5)

A semiconductor substrate having a first conductivity type on which a first electrode is formed;
And the active layer above the length formed of the semiconductor substrate is 5μm or more 150μm or less,
Said formed above the semiconductor substrate, and wherein the active layer optical histological connected by butt coupling, the further passive optical waveguide layer in which the active layer is provided with a diffraction grating that reflects light to produce,
Wherein is the passive optical made form in contact with the passive optical waveguide layer over the waveguide layer, and the current confinement layer for blocking the injection of current into the passive optical waveguide layer,
An upper clad layer having a second conductivity type and formed to extend above the active layer and the current confinement layer;
A contact layer having the second conductivity type, formed above the upper cladding layer, covering the active layer and extending above the passive optical waveguide layer;
A second electrode formed above the contact layer and covering the active layer and extending above the passive optical waveguide layer ;
The current injected into the active layer is modulated
Semiconductors laser devices. That the active layer comprises a diffraction grating;
The semiconductor laser device according to claim 1. The first and second conductivity types are n-type and p-type, respectively.
The current confinement layer is formed by stacking an n-type semiconductor layer on a semiconductor insulating semiconductor layer.
3. The semiconductor laser device according to claim 1, wherein the semiconductor laser device is characterized in that: The current confinement layer is formed by laminating a semiconductor layer of the first conductivity type on a semiconductor layer having the second conductivity type.
3. The semiconductor laser device according to claim 1, wherein the semiconductor laser device is characterized in that: Both sides of the active layer, the passive optical waveguide layer, and the upper cladding layer are buried with a semiconductor insulating semiconductor layer,
The semiconductor laser device according to claim 1, wherein the semiconductor laser device is characterized in that:

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