JP2009253188A - Optical semiconductor device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an optical semiconductor device equipped with an embedding structure wherein a current constriction function is never rapidly lost even when an injection current is increased. <P>SOLUTION: This optical semiconductor device is provided with: an n-type semiconductor substrate; a mesa structure where a cross-sectionally projecting semiconductor laminate structure is extended on the semiconductor substrate; a pn embedding structure having an embedding layer formed of a p-type first semiconductor material, and laminated on the semiconductor substrate, and a current constriction layer formed of an n-type first semiconductor material, and laminated on the embedding layer, and covering both side faces of the mesa structure; a first electronic barrier layer formed of a p-type second semiconductor material having energy at the lower end of a conduction band higher than that of the first semiconductor material, and laminated on the mesa structure and the pn-type embedding structure; and a clad layer formed of a p-type semiconductor material, and laminated on the first electronic barrier layer. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to an optical semiconductor device in which a side surface of a mesa structure is covered with a buried layer formed of a p-type semiconductor and a current confinement layer formed of an n-type semiconductor.

  An optical semiconductor device that operates by current injection such as a semiconductor optical amplifier or a semiconductor laser (hereinafter referred to as a current injection type optical semiconductor device) is an important component of a light handling system such as an optical communication system. .

  For example, semiconductor optical amplifiers are used as inline amplifiers, booster amplifiers, preamplifiers and the like in optical communication systems. Furthermore, the semiconductor optical amplifier is mounted on a semiconductor optical integrated circuit and used as a functional element such as an optical gate switch.

  In most of such current injection type optical semiconductor devices, a mesa structure including an active layer is embedded by an n-p-n-p thyristor structure (Patent Document 1).

  FIG. 1 is a sectional view of such a semiconductor optical amplifier 2.

  As shown in FIG. 1, the semiconductor optical amplifier 2 includes an n-type semiconductor substrate 4 (for example, an n-InP substrate) and a mesa structure 6 extending on the semiconductor substrate 4. The mesa structure 6 includes, for example, an n-type lower clad layer 8, an active layer 10, and a p-type upper clad layer 12.

  The semiconductor optical amplifier 2 includes a buried layer 14 formed of a p-type semiconductor material (for example, p-InP) and stacked on the semiconductor substrate 4, and an n-type semiconductor material (for example, n-InP). And a pn buried structure 18 having a current confinement layer 16 stacked directly on the buried layer 14. Here, the pn buried structure 18 is formed so as to cover both side surfaces of the mesa structure 6.

  Further, the semiconductor optical amplifier 2 includes a clad layer 20 formed of a p-type semiconductor material (for example, p-InP) and directly stacked on the mesa structure 6 and the pn buried structure 18, and the clad layer 20. The contact layer 22 is directly laminated on the substrate.

  The pn buried structure 18 covering both side surfaces of the mesa structure 6 is formed of a semiconductor material (for example, InP) having a smaller refractive index and a larger band gap than that of the active layer 10 (for example, InGaAsP multiple quantum well structure). .

In the optical semiconductor device having the cross-sectional structure as shown in FIG. 1, the semiconductor layer surrounding the mesa structure 6, that is, the n-type semiconductor substrate 4, the pn buried structure 18, and the cladding layer 20, the npnp thyristor structure 24. Formed on both sides of structure 6.
Japanese Patent Laid-Open No. 2003-60309

  Here, consider a case where the semiconductor substrate 4 is grounded, a positive voltage is applied to the contact layer 22, and a current is injected into the semiconductor optical amplifier 2. In this case, a current flows through the mesa structure 6, but no current flows through the np-n-p thyristor structure 24.

  This is because the pn junction formed in the pn buried structure 18 is reverse-biased by the positive voltage applied to the contact layer 22 (because current flows through the reverse-biased pn junction). Absent.).

  For this reason, the current injected into the semiconductor optical amplifier 2 is intensively injected into the active layer 10 disposed inside the mesa structure 6. That is, the pn buried structure 18 has a current confinement function. Therefore, the efficiency of current injection into the active layer 10 is increased.

  However, as the current injected into the semiconductor optical amplifier 2 increases, the applied voltage also increases. As a result, finally, an electron avalanche breakdown occurs at the reverse-biased pn junction, and the thyristor structure 24 is turned on. Then, as shown in FIG. 2, the leakage current 26 flowing through the pn buried structure 18 increases rapidly, and the current confinement function of the pn buried structure 18 is lost.

  As a result, the current injected into the active layer 10 is rapidly reduced, and the output of the semiconductor optical amplifier 2 is significantly reduced. This phenomenon becomes more prominent as the operating temperature increases. A similar phenomenon can be seen in other optical semiconductor devices having the np-n-p thyristor structure 24.

  Accordingly, an object of the present invention is to provide an optical semiconductor device having a buried structure in which the current confinement function does not rapidly disappear even when the injection current increases.

  FIG. 2 is a conceptual diagram for explaining current leakage in the current injection type optical semiconductor device.

  In order to achieve the above object, an optical semiconductor device according to the present invention includes an n-type semiconductor substrate, a mesa structure in which a semiconductor laminated structure having a convex cross section extends on the semiconductor substrate, and a p-type first semiconductor substrate. A buried layer formed of one semiconductor material and stacked on the semiconductor substrate, and a current confinement layer formed of the first semiconductor material of n type and stacked on the buried layer; A pn buried structure covering both side surfaces of the mesa structure, and a p-type second semiconductor material having a lower energy of a conduction band higher than that of the first semiconductor material, and above the mesa structure and the pn buried structure. And a cladding layer formed of a p-type semiconductor material and stacked on the first electron barrier layer.

  In the present optical semiconductor device, even if an electron avalanche breakdown occurs in the reverse-biased pn buried structure, the first electron barrier layer prevents the electron flow that is the main component of the leakage current in the pn buried structure. Therefore, according to the optical semiconductor device, even if the injection current is increased, the current confinement function of the pn buried structure does not rapidly disappear.

  According to the optical semiconductor device of the present invention, even if the injection current increases and the electron avalanche breakdown occurs in the pn buried structure, the electron barrier layer blocks the electron current that is the main component of the leakage current. The current confinement function is not suddenly lost.

  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.

(Embodiment 1)
This embodiment includes an electron barrier layer formed of a second semiconductor material (for example, InGaP) whose energy at the lower end of the conduction band is higher than that of the first semiconductor material (for example, InP) that forms the pn buried structure. The present invention relates to a semiconductor optical amplifier.

(1) Device Configuration FIG. 3 is a cross-sectional view of a main part of a semiconductor optical amplifier according to the present embodiment. FIG. 4 is a main part plan view of the semiconductor optical amplifier according to the present embodiment.

  The semiconductor optical amplifier 28 according to the present embodiment has a semiconductor substrate 4 formed of n-type InP and a so-called mesa structure 6 in which a semiconductor laminated structure having a convex cross section extends on the semiconductor substrate 4. ing. FIG. 3 shows a cross section of the mesa structure 6 extending in a direction perpendicular to the paper surface.

The semiconductor optical amplifier 28 includes a buried layer 14 formed of p-type InP and stacked on the semiconductor substrate 4, and a current confinement layer formed of n-type InP and stacked on the buried layer 14. 16 and a pn buried structure 18 that covers both side surfaces of the mesa structure 6. In the example shown in FIG. 3, the buried layer 14 is formed on the semiconductor substrate 4 not directly but via a part of the lower cladding layer 8 described later.
The semiconductor optical amplifier 28 according to the present embodiment is formed of a p-type semiconductor material (InGaP in the present embodiment) whose energy at the lower end of the conduction band is higher than that of InP, and the mesa structure 6 and the pn buried structure 18. The electron barrier layer 30 is stacked thereon.

  The semiconductor optical amplifier 28 includes a clad layer 20 formed of p-type InP and stacked on the electron barrier layer 30, and a contact formed of p-type InGaAsP and stacked on the clad layer 20. It has a layer 22.

  Further, the semiconductor optical amplifier 28 has a p-side contact electrode (not shown) formed on the contact layer 22 and an n-side contact electrode (not shown) formed on the back surface of the semiconductor substrate 4. Yes.

  The mesa structure 6 includes a lower cladding layer 8 formed of n-type InP, an active layer 10 formed of, for example, an InGaAsP multiple quantum well structure, and an upper cladding layer 12 formed of p-type InP. ing.

  Such a structure is cleaved in a (a pair of) sections perpendicular to the extending direction of the mesa structure 6, and light is reflected on both sections obtained by cleavage at the operating wavelength of the semiconductor optical amplifier 28. An antireflective film 32 is formed to prevent this (see FIG. 4).

(2) Operation Next, the operation of the semiconductor optical amplifier 28 according to the present embodiment will be described with reference to FIGS.

  FIG. 3 is a cross-sectional view of the main part of the semiconductor optical amplifier 28 according to the present embodiment, as already described. FIG. 4 is a plan view of the main part of the semiconductor optical amplifier 28. FIG. FIG. 5 is a band diagram along the line XY in FIG. On the other hand, FIG. 6 is a band diagram along the line X′-Y ′ of FIG.

  For the operation of the semiconductor optical amplifier 28, first, the negative electrode of the drive power source (not shown) is connected to the n-side contact electrode (not shown) formed on the back surface of the semiconductor substrate 4. On the other hand, a positive electrode of a driving power source is connected to a p-side contact electrode (not shown) formed on the contact layer 22.

  Next, a current necessary for generating a desired gain is supplied from the driving power source to the semiconductor optical amplifier 28. For example, a large current (for example, 500 mA) that causes an electron avalanche breakdown in the pn buried structure 18 is supplied to the semiconductor optical amplifier 28.

  Even if such a large current is supplied, in the semiconductor optical amplifier 28 according to the present embodiment, as described below, the electron barrier layer 30 blocks the flow of electrons, so that a rapid increase in leakage current is suppressed. The

  Therefore, in the semiconductor optical amplifier 28 according to the present embodiment, a larger current can be injected into the active layer 10 than in the conventional semiconductor optical amplifier 2. Therefore, the gain of semiconductor optical amplifier 28 according to the present embodiment is larger than that of conventional semiconductor optical amplifier 2.

  As shown in the band diagram of FIG. 5, a pn junction 31 is formed between the buried layer 14 formed of p-type InP and the current confinement layer 16 formed of n-type InP. While the drive current is being injected into the semiconductor optical amplifier 28, a positive voltage is applied to the p-side contact electrode (relative to the n-side contact electrode). Accordingly, during this time, the pn junction 31 is reverse-biased.

  As the drive current of the semiconductor optical amplifier 28 increases and the applied voltage increases, the internal electric field of the pn junction 31 also increases. Further, when the drive current increases, an electron avalanche breakdown finally occurs at the pn junction 31.

  However, even if an electron avalanche breakdown occurs, in the semiconductor optical amplifier 28 according to the present embodiment, the flow of electrons 37 generated by the electron avalanche breakdown is blocked by the electron barrier 30 formed of InGaP. As shown in FIG. 5, the energy of the semiconductor material forming the electron barrier layer 30, that is, the conduction band lower end 33 of InGaP, is higher than the energy of the semiconductor layer forming the p-cladding layer 20, ie, the conduction band lower end 33 'of InP. This is because it is expensive.

In order to stop the flow of electrons with certainty, the height ΔE of the barrier (with respect to electrons) formed by the electron barrier layer 30 needs to be sufficiently high. For this purpose, the composition of InGaP forming the electron barrier layer 30 may be, for example, In _0.8 Ga _0.2 P. In this case, the barrier height ΔE is 70 meV.

  On the other hand, as shown in FIG. 5, there is no barrier that blocks the flow of the holes 39 generated by the avalanche breakdown (the p-type cladding layer 20 and the p-type electron barrier 30 and the n-type current confinement layer 16). Since the pn junction 41 between them and the pn junction 43 between the p-type buried layer 14 and the n-type semiconductor substrate 4 are forward-biased, they do not serve as a barrier against both electrons and holes.

However, InP to in hole mobility of (200cm ² / v · s) since only one of dozens of electron mobility ^{(5400cm 2 / v · s)} , the leakage current flowing through the pn buried structure 18 The main component of 26 (see FIG. 2) is the flow of electrons, and the contribution of the hole flow is negligible (this tendency is common to other semiconductor materials). Accordingly, if the electron flow is blocked by the electron barrier 30, the leakage current 26 flowing through the pn buried structure 18 can be suppressed.

Therefore, even if the driving current increases and the electron avalanche breakdown occurs in the pn buried layer 18, the leakage current 26 (see FIG. 2) does not increase rapidly. Therefore, a large current can be injected into the active layer 10, and the gain of the semiconductor optical amplifier 28 according to the present embodiment is larger than that of the conventional semiconductor optical amplifier 2. Such a leakage current suppressing effect is remarkable at high temperatures.
Therefore, as shown in FIG. 4, the signal light 36 incident on the light incident surface 34 of the semiconductor optical amplifier 28 is amplified to a greater degree than the conventional semiconductor optical amplifier 2 to become amplified light 40 and is emitted from the light emitting surface 38. .

  The above is the operation of the semiconductor optical amplifier 28 according to the present embodiment. By the way, as is apparent from the upper end 35 of the valence band along the X′-Y ′ line shown in FIG. 6, the electron barrier 30 formed of InGaP forms a barrier against holes. do not do. Therefore, the holes 39 easily flow through the electron barrier layer 30 from the clad layer 20 made of p-type InP into the upper clad layer 12 also made of p-type InP. That is, the electron barrier layer 30 does not hinder hole injection into the active layer 10. However, even if the electron barrier layer 30 is made of a material that forms a barrier against holes, the electron flow is not interrupted because the electron barrier layer 30 is made of a p-type semiconductor material. .

  That is, in the semiconductor optical amplifier according to the present embodiment in which the electron barrier layer 30 is formed of a p-type semiconductor material, hole injection into the active layer 10 is hindered by the electron barrier layer 30, thereby hindering optical amplification. It does not occur.

  By the way, when a large current is injected into the semiconductor optical amplifier 28, electrons having a small effective mass overflow from the active layer (so-called overflow) and flow into the upper cladding layer 12 and further into the cladding layer 20. This electron flow becomes a carrier flow that does not contribute to light amplification, that is, a leakage current. Therefore, when an electron overflow occurs, the efficiency of electron injection into the active layer 10 is lowered, and the gain of the semiconductor optical amplifier is lowered.

  However, in the semiconductor optical amplifier 28 according to the present embodiment, since the electron barrier layer 30 is also provided on the mesa structure 6 including the active layer 10, such an electron flow (leakage current) is blocked ( (See FIG. 7). For this reason, the overflow 27 of electrons from the active layer 10 is suppressed, and the efficiency of injection of electrons into the active layer 10 is improved.

  Therefore, in the semiconductor optical amplifier 28 according to the present embodiment, even when a large current that causes an overflow of electrons from the active layer 10 is injected, deterioration of the injection efficiency of electrons into the active layer 10 is suppressed. . For this reason, gain saturation is unlikely to occur.

(3) Manufacturing Method Finally, a manufacturing method of the semiconductor optical amplifier 28 illustrated in FIG. 3 will be described.

  First, an n-type InP lower cladding layer 8 and an InGaAsP multiple quantum well were formed on an n-type (100) InP substrate 4 by metal organic chemical vapor deposition (MOCVD). An active layer 10 and a p-type InP upper cladding layer 12 are formed (first growth).

At this time, as the source gas, one or both of trimethylindium (TMI) and triethylgallium (TEG) is used for the group III element. On the other hand, for group V elements, one or both of phosphine (PH ₃ ) and arsine (arsine; AsH ₃ ) is used as a source gas.

As the dopant gas, diethylzinc (DEZn) is used as the p-type dopant. On the other hand, monosilane (silane; SiH ₄ ) is used as the n-type dopant.

Next, an insulating film made of SiO ₂ is deposited on the p-type InP cladding layer 12 by chemical vapor deposition (CVD).

Next, the insulating film is patterned by a photolithography technique and etching to form a stripe-like SiO ₂ mask having a width of about 2 μm extending in the [011] direction, for example.

Next, from the p-type upper InP cladding layer 12 exposed on both sides of the stripe-like SiO ₂ mask to the inside of the n-type lower InP cladding layer 8 (or the n-type semiconductor substrate 4). The semiconductor layer obtained by the first growth is dry etched. The mesa structure 6 is formed by this dry etching.

Next, the p-type InP is formed on both side surfaces of the mesa structure 6 and the n-type lower InP cladding 8 (or the n-type semiconductor substrate 4) by the MOCVD method with the SiO ₂ mask remaining. The buried layer 14 and the current confinement layer 16 made of n-type InP are selectively formed sequentially (second growth). By this growth, both side surfaces of the mesa structure 6 are covered with the pn buried structure 18 having the buried layer 14 and the current confinement layer 16.

Next, the SiO ₂ mask covering the top of the mesa structure 6 is removed.

  Next, an electron barrier layer 30 formed of a p-type InGaP layer, a cladding layer 20 formed of p-type InP, and a contact layer 22 formed of p-type InGaAs are sequentially formed by MOCVD. .

  Next, a p-side contact electrode (not shown) and an n-side contact electrode (not shown) are respectively formed on the front surface of the contact layer 22 and the back surface of the semiconductor substrate 4.

  Thereafter, the semiconductor layers formed by the first and second growths are cleaved together with the semiconductor substrate 4 to form the light incident surface 34 and the light emitting surface 38 (see FIG. 4).

Finally, an antireflection film 32 made of SiO ₂ or the like is formed on the surfaces of the light incident surface 34 and the light emitting surface 38.

  By the way, InGaP and InP do not have the same lattice constant. Therefore, it is impossible to grow without crystal defects on the current confinement layer 16 and the upper cladding layer 12 made of InP unless the thickness is less than the critical thickness.

FIG. 8 is a graph showing the relationship between the critical thickness of InGaP and the In composition ( _{x when} InGaP is expressed as In _x Ga _1-x P). For example, the critical film thickness of In _0.8 Ga _0.2 P is about 45 nm.

Therefore, when the electron barrier layer 30 is formed of In _0.8 Ga _0.2 P as described above, the thickness of InGaP is preferably 45 nm or less, for example, 10 nm.

(Embodiment 2)
The present embodiment relates to a semiconductor optical amplifier in which another electron barrier layer is further added between the pn buried layer 18 and the electron barrier layer 30 in the semiconductor optical amplifier according to the first embodiment.

(1) Device Configuration FIG. 9 is a cross-sectional view of a main part of a semiconductor optical amplifier according to the present embodiment. On the other hand, the planar structure of semiconductor optical amplifier 42 according to the present embodiment is the same as the planar structure of semiconductor optical amplifier 28 according to the first embodiment described with reference to FIG.

  As shown in FIG. 9, in the optical semiconductor device 42 according to the present embodiment, in the semiconductor optical amplifier 28 according to the first embodiment, the energy at the lower end of the conduction band between the pn buried structure 18 and the electron barrier layer 30 is InP. A second electron barrier layer 44 made of a higher p-type semiconductor material is disposed. The electron barrier layer 30 provided in the semiconductor optical amplifier 28 according to the first embodiment is hereinafter referred to as a first electron barrier layer.

  Here, the semiconductor material forming the second electron barrier layer 44 may be the same as or different from the semiconductor material forming the first electron barrier layer 30. That is, the second electron barrier layer 44 may be formed of InGaP or may be formed of a different material such as InAlAs or AlGaInAs. Further, when the second electron barrier layer 44 is formed of InGaP as in the case of the first electron barrier layer 30, the composition of InGaP forming the second electron barrier layer 44 forms the first electron barrier layer 30. The composition may be the same as or different from the composition of InGaP.

In the present embodiment, the first and second electron barrier layers 30 and 44 are formed such that the sum of the thicknesses does not exceed the critical film thickness. For example, when both the first and second electron barrier layers 30 and 44 are formed of In _0.8 Ga _0.2 P, the sum of the film thicknesses of the first and second electron barrier layers 30 and 44. However, the critical film thickness of In _0.8 Ga _0.2 P on InP is not exceeded 45 nm.

  For example, the first electron barrier layer 30 is formed with a thickness of 10 nm, and the second electron barrier layer 30 is formed with a thickness of 5 nm.

(2) Operation The operation of the semiconductor optical amplifier 42 according to the present embodiment is substantially the same as the operation of the semiconductor optical amplifier 28 according to the first embodiment.

  However, since the two electron barrier layers 30 and 44 are integrated to form a thick electron barrier (for example, 15 nm) on the pn buried structure 18, the (pn buried) is more effective than the case of the first electron barrier layer alone. Electron flow (ie, leakage current) generated by electron avalanche breakdown (in structure 18) is more effectively prevented.

  On the other hand, since only one thin first electron barrier layer 30 (for example, 5 nm) exists on the mesa structure 6, holes smoothly flow from the cladding layer 20 to the upper cladding layer 18. Therefore, holes are easily injected into the active layer 10 even with a low applied voltage. In particular, this tendency is significant when the electron barrier layer 30 is formed of a semiconductor material that also serves as a barrier against holes.

  That is, according to the semiconductor optical amplifier 42 according to the present embodiment, the leakage current of the pn buried structure 18 is more effectively suppressed as compared with the semiconductor optical amplifier 28 according to the first embodiment, and at the same time, to the active layer 10. Hole injection is smoother and the operating voltage is lower.

(3) Manufacturing Method The manufacturing method of the semiconductor optical amplifier 42 according to the present embodiment is substantially the same as the manufacturing method of the semiconductor optical amplifier 28 according to the first embodiment.

  First, the steps until the current confinement layer 16 is formed are performed in the same manner as the method for manufacturing the semiconductor optical amplifier 28 described in the first embodiment.

  However, in the present embodiment, even after the current confinement layer 16 is selectively formed, the growth by the MOCVD method is continued, and the second electron barrier layer 44 is selectively formed on the current confinement layer 16. The

  Thereafter, substantially the same steps as those in the method for manufacturing the semiconductor optical amplifier 28 described in the first embodiment are performed.

(Embodiment 3)
This embodiment relates to a semiconductor optical amplifier in which a third electron barrier layer is arranged inside the upper cladding layer 12 forming the mesa structure 6 in the semiconductor optical amplifier 28 according to the first embodiment.

(1) Device Configuration FIG. 10 is a cross-sectional view of a principal part of a semiconductor optical amplifier 46 according to the present embodiment. On the other hand, the planar structure of semiconductor optical amplifier 46 according to the present embodiment is the same as the planar structure of semiconductor optical amplifier 28 according to the first embodiment described with reference to FIG.

  As shown in FIG. 10, the optical semiconductor device 46 according to the present embodiment includes a lower end of a conduction band in the semiconductor optical amplifier 28 according to the first embodiment, inside the upper cladding layer 12 (which forms the mesa structure 6). A second electron barrier layer 48 made of a p-type semiconductor material whose energy is higher than that of InP is arranged in parallel to the semiconductor substrate 4.

  Here, the semiconductor material forming the third electron barrier layer 48 may be the same as or different from the semiconductor material forming the first or second electron barrier layer 30, 44. That is, the third electron barrier layer 48 may be formed of InGaP or may be formed of a different material such as InAlAs or AlGaInAs.

  When the third electron barrier layer 48 is formed of InGaP as in the case of the first electron barrier layer 30, the composition of InGaP forming the third electron barrier layer 48 forms the first electron barrier layer 30. The composition may be the same as or different from the composition of InGaP.

(2) Operation The operation of the semiconductor optical amplifier 46 according to the present embodiment is substantially the same as the operation of the semiconductor optical amplifier 28 according to the first embodiment. FIG. 11 is a band diagram along the line X′-Y ′ in FIG.

  However, as shown in FIGS. 10 and 11, since the third electron barrier layer 48 is disposed inside the upper cladding layer 12, the position closer to the active layer 10 than the semiconductor optical amplifier 28 according to the first embodiment. Thus, the electrons overflowing from the active layer 10 can be blocked.

  For this reason, the frequency of the electrons overflowing the active layer 10 recombining with the holes of the p-type upper cladding layer 12 is reduced.

  Therefore, the semiconductor optical amplifier 46 according to the present embodiment can more effectively suppress the overflow of electrons than the semiconductor optical amplifier 28 according to the first embodiment.

  Therefore, in the semiconductor optical amplifier 46 according to the present embodiment, the efficiency of electron injection into the active layer 10 is further improved as compared with the semiconductor optical amplifier 28 according to the first embodiment. Therefore, gain saturation is unlikely to occur.

(3) Manufacturing Method The manufacturing method of the semiconductor optical amplifier 46 according to the present embodiment is substantially the same as the manufacturing method of the semiconductor optical amplifier 28 according to the first embodiment.

  However, in the first crystal growth step (first growth) by the MOCVD method, an n-type InP lower cladding layer 8 and an active layer 10 that is an InGaAsP multiple quantum well are formed on an n-type (100) InP substrate 4. A part of the p-type InP upper clad layer 12, a third electron barrier layer 48 made of, for example, InGaP, and the remaining InP upper clad layer 12 are sequentially formed.

  In other respects, the method for manufacturing the semiconductor optical amplifier 46 according to the present embodiment is substantially the same as the method for manufacturing the semiconductor optical amplifier 28 according to the first embodiment.

(Example of use)
FIG. 12 is a conceptual diagram of a semiconductor optical amplifier module 50 in which the semiconductor optical amplifiers 28, 42, and 46 according to the first to third embodiments are combined with other optical components.

  The semiconductor optical amplifier module 50 according to this use example collects the input-side optical fiber 52 to which the signal light 60 is input and the signal light 60 emitted from the input-side optical fiber 52 to collect the semiconductor optical amplifiers 28, 42, and 46. The input side lens system 54 that irradiates the light incident surface 34, any one of the semiconductor optical amplifiers 28, 42, and 46 (according to the first to third embodiments), and the semiconductor optical amplifiers 28, 42, and 46 amplify the light. An output side lens system 56 that condenses the signal light (amplified light 62) emitted from the output surface 38 and irradiates the light incident end face of the output side optical fiber 58; an output side optical fiber 58 that outputs the amplified light 62; A housing 64 to which these members are mounted is provided.

  The semiconductor optical amplifier module 50 electrically connects a pair of positive and negative terminals (not shown) to which an external power source is connected, and the p-side and n-side electrodes of the pair of terminals and the semiconductor optical amplifiers 28, 42, and 46. It has wiring to connect.

  Next, in order to operate the semiconductor optical amplifier module 50, the user drives the external power supply to supply the semiconductor optical amplifiers 28, 42, and 46 with an excitation current corresponding to a desired optical gain. At this time, a large current that could not be used because the leakage current suddenly increased due to the electron avalanche breakdown (in the pn buried structure 18) may be supplied to the semiconductor optical amplifiers 28, 42, and 46. .

  Next, the user inputs the signal light 60 into the input side optical fiber 52.

  Then, the amplified light 62 is output to the output side optical fiber 58. At this time, if the output-side optical fiber 58 is connected to a desired device, the user can use the amplified light 62.

  The above example is an example in which the semiconductor optical amplifiers 28, 42, and 46 are used as individual devices. However, the usage form of the semiconductor optical amplifiers 28, 42, and 46 is not limited to the use example as such an individual apparatus. For example, the semiconductor optical amplifiers 28, 42, and 46 may be used as components of an integrated optical semiconductor device, such as an optical gate switch.

(Modification)
The present invention has been described above using the semiconductor optical amplifier as an example. However, the optical semiconductor device to which the present invention is applicable is not limited to a semiconductor optical amplifier. For example, the present invention can be applied to other optical semiconductor devices such as a semiconductor laser device.

  In addition, although InGaP is exemplified as the main semiconductor material for forming the electron barrier layer, other semiconductor materials such as InAlAs and AlGaInAs can also be used.

For example, in the semiconductor optical amplifier 28 according to the first embodiment, the electron barrier layer 30 formed of In _0.8 Ga _0.2 P is _replaced with In _0.52 Al _0.48 As or In _0.53 Al _{0. 35} Ga _0.12 As may be substituted. However, In _0.52 Al _0.48 As is preferable because the barrier layer against electrons is higher than In _0.53 Al _0.35 Ga _0.12 As. Note that the height of the barrier layer for electrons of In _0.53 Al _0.35 Ga _0.12 As is substantially the same as that of In _0.8 Ga _0.2 P. Further, since In _0.52 Al _0.48 As and In _0.53 Al _0.35 Ga _0.12 As are lattice-matched to InP, the film thickness is not limited.

  In the first to third embodiments, examples in which each semiconductor layer forming the semiconductor optical amplifier is formed of a semiconductor material containing InP as a main component (so-called InP-based optical semiconductor device) have been described.

  However, the optical semiconductor device to which the present invention can be applied is not limited to such an InP-based optical semiconductor device. For example, an optical semiconductor device formed by a semiconductor layer containing GaAs as a main component (so-called GaAs-based optical semiconductor device). The present invention can also be applied to an optical semiconductor device formed of a semiconductor layer mainly composed of another semiconductor material, such as an optical semiconductor device).

  For example, if the electron barrier layer is formed of AlGaAs, the present invention can be applied to a GaAs optical semiconductor device. In this case, the electron barrier layer also functions as a barrier layer for holes.

It is a figure explaining the cross section of the conventional semiconductor optical amplifier. It is a conceptual diagram explaining the current leak in a current injection type optical semiconductor device. 1 is a cross-sectional view of a main part of a semiconductor optical amplifier according to a first embodiment. 1 is a plan view of a main part of a semiconductor optical amplifier according to a first embodiment. 3 is a band diagram along the XY line of the semiconductor optical amplifier according to the first embodiment. 3 is a band diagram along the X′-Y ′ line of the semiconductor optical amplifier according to the first embodiment. It is a conceptual diagram explaining suppression of the overflow in the semiconductor optical amplifier according to the first embodiment. It is the figure which showed the relationship between the critical film thickness of InGaP, and In composition. FIG. 6 is a main part sectional view of a semiconductor optical amplifier according to a second embodiment. It is principal part sectional drawing of the semiconductor optical amplifier according to this Embodiment 3. 10 is a band diagram along the X′-Y ′ line of the semiconductor optical amplifier according to the third embodiment. It is a conceptual diagram of the semiconductor optical amplifier module which combined the semiconductor optical amplifier according to Embodiment 1 thru | or 3, and another optical component.

Explanation of symbols

DESCRIPTION OF SYMBOLS 2 ... Semiconductor optical amplifier 4 ... Semiconductor substrate 6 ... Mesa structure 8 ... Lower clad layer 10 ... Active layer 12 ... Upper clad layer 14 ... Embedded layer 16 ... Current Narrowing layer 18 ... pn buried structure 20 ... cladding layer 22 ... contact layer 24 ... npnp thyristor structure 26 ... leakage current 27 ... overflow of electrons from the active layer (overflow)
28: Semiconductor optical amplifier 30 according to the first embodiment 30 ... (first) electron barrier layer
32 ... Antireflection film 31,41,43 ... pn junction
33, 33 '... lower end of conduction band 34 ... light incident surface
35 ... upper end of valence band 36 ... signal light
37 ... electron 38 ... light exit surface 39 ... hole 40 ... amplified light
42... Semiconductor optical amplifier 44 according to the second embodiment... (Second) electron barrier layer 46... Semiconductor optical amplifier 48 according to the third embodiment... (Third) electron barrier layer 50. ..Semiconductor optical amplifier module 52: input side optical fiber 54 ... input side lens system 56 ... output side lens system 58 ... output side optical fiber 60 ... signal light 62 ... amplified light 64 ... Case

Claims (5)

an n-type semiconductor substrate;
A mesa structure in which a semiconductor laminated structure having a convex cross section extends on the semiconductor substrate;
A buried layer formed of a p-type first semiconductor material and stacked on the semiconductor substrate, and a current confinement layer formed of the n-type first semiconductor material and stacked on the buried layer And a pn buried structure that covers both side surfaces of the mesa structure;
A first electron barrier layer formed of a p-type second semiconductor material having a lower energy of a conduction band higher than that of the first semiconductor material and stacked on the mesa structure and the pn buried structure;
a clad layer formed of a p-type semiconductor material and laminated on the first electron barrier layer;
An optical semiconductor device provided. The optical semiconductor device according to claim 1,
Between the pn buried structure and the first electron barrier layer,
A second electron barrier layer formed of a p-type third semiconductor material having a lower energy of a conduction band higher than that of the first semiconductor material is disposed;
An optical semiconductor device. In the optical semiconductor device according to claim 1 and 2,
The semiconductor multilayer structure has an n-type lower cladding layer, an active layer, and a p-type upper cladding layer,
Furthermore, inside the upper cladding layer,
A third electron barrier layer formed of a p-type fourth semiconductor material having a lower energy of a conduction band higher than that of the first semiconductor material is disposed;
An optical semiconductor device. The optical semiconductor device according to any one of claims 1 to 3,
The first semiconductor material is InP.
An optical semiconductor device. The optical semiconductor device according to claim 4,
The optical semiconductor device, wherein the second semiconductor material is any one semiconductor material selected from the group consisting of InGaP, InAlAs, and AlGaInAs.

Images