JP4829277B2 - Semiconductor laser - Google Patents

Description

  The present invention relates to a semiconductor laser, and more particularly to a semiconductor laser having a window region with little laser light absorption on a light emitting end face. Such a semiconductor laser is used for high output applications such as an optical disk drive.

  In a high-power semiconductor laser used in an optical disk drive or the like, the light emitting end face may be deteriorated due to a strong light density, and may cause damage called COD (Catastrophic Optical Damage). As a countermeasure, it has been proposed to provide a window region that absorbs less laser light in the light emitting end face than in the active layer.

As a high-power conventional semiconductor laser having a window region on the light emitting end face, one as shown in FIG. 23 is known (for example, refer to Japanese Patent Application Laid-Open No. 9-506478). This semiconductor laser includes an n-conductivity type buffer layer 11, an n-conductivity-type first cladding layer 2 ', a first isolation limiting layer 2 ", an active layer 3, a second isolation limiting layer 4", p on an n-type GaAs substrate 1. A conductive second cladding layer 4 ′ and an etching stop layer (thickness 0.01 μm) 5 are provided. A p-conductivity-type second cladding layer 4 ⁰ , a p-conductivity-type intermediate layer 9 and a p-conductivity-type first contact layer are formed on the etching stop layer 5 so as to form a mesa 12 extending in a stripe shape in the II-II line direction. 10 is provided. Regions corresponding to both sides of the mesa 12 are buried with the n-type current blocking layer 13. A second contact layer 6 and an electrode 7 are provided on the mesa 12 and the n-type current blocking layer 13. On the other hand, an electrode 8 is formed on the back surface of the n-type GaAs substrate 1.

  As shown in FIG. 24 (corresponding to the section taken along the line II-II in FIG. 23), the active layer 3 is formed by stacking a quantum well layer 3 ′ and a barrier layer 3 ″. The portions in the vicinity of the end faces 50 and 51 form a window region 3B that absorbs less laser light than the active layer interior 3A.

This semiconductor laser is manufactured as follows. As shown in FIG. 25, first, an n-conductivity type buffer layer 11 to a contact layer 10 are grown on an n-type GaAs substrate 1 by an OMVPE method (metal organic vapor phase epitaxy). Next, a mask layer 30 made of silicon oxide is formed so as to have openings 31 and 32 along the light emission end faces 50 and 51. The wafer in this state is inserted into a sealed capsule together with zinc arsenide and heated at 600 ° C., and Zn atoms 59 are diffused from the surface side of the contact layer 10 so as to exceed the active layer 3. As a result, a portion of the active layer 3 in the vicinity of the light emitting end faces 50 and 51 is mixed to form a window region 3B having a larger energy band gap than the inside of the active layer 3A, and thus less absorbing laser light. After removing the mask 30, as shown in FIG. 26, a striped mask 40 extending perpendicularly to the light emitting end faces 50 and 51 is formed. Then, by etching a portion corresponding to both sides of the mask 40 of the semiconductor layer 10,9,4 ⁰ until the etching stop layer 5, to form a mesa 12 directly below the mask 40. Thereafter, as shown in FIG. 23, the block layers 13 are arranged on both sides of the mesa 12 by the OMVPE method, the surface side is flattened and the mask 40 is removed, and then the second contact layer 6 is again formed by the OMVPE method. Form. Then, electrodes 7 and 8 are formed on the surface of the contact layer 6 and the back surface of the substrate 1, respectively (production completion).
JP-T 9-506478

  By the way, in the manufacturing method, the etching stop layer 5 is also mixed in the step of forming the window region 3B by mixing the active layer 3 by impurity diffusion. For this reason, the etching stop layer 5 and the second cladding layer (lower part) 4 ′ are etched in the etching process for forming the mesa 12, and the processing accuracy of the mesa 12 is lowered. Further, when etching proceeds extremely, there is a problem that the current blocking layer 13 and the n-type cladding layer 11 are electrically short-circuited. If the annealing temperature and time are reduced in order to avoid these problems in the manufacturing process, the window region 3B is not sufficiently mixed crystal and the effect of suppressing the light absorption is hardly obtained. Will occur.

  Accordingly, an object of the present invention is to provide a semiconductor laser having a window region on a light emitting end face, which can be easily manufactured with high accuracy.

In order to solve the above problems, the semiconductor laser of the present invention is
A semiconductor laser that emits laser light through a light emitting end face,
On the substrate, a lower cladding layer, an active layer for generating laser light, and a first upper cladding layer are laminated in this order,
A second upper cladding layer is formed as a ridge above the first upper cladding layer;
A portion of the active layer corresponding to both sides of the ridge in the region along the light emitting end face, and a portion of the active layer corresponding to immediately below the ridge in the region along the light emitting end surface. The energy band gap of the active layer is larger than the internal energy band gap of the active layer other than the region along the light emitting end face.

In the semiconductor laser according to one embodiment, in the region along the light emitting end face, the shift of the portion corresponding to the portion immediately below the ridge of the active layer to the short wavelength side of the photoluminescence wavelength is 18 nm or more, and the active laser The portion of the layer corresponding to both sides of the ridge is shifted to the short wavelength side of the photoluminescence wavelength by 15 nm or less.

In one embodiment, the impurity diffused in a portion along the light emitting end face of the active layer is Zn.

In one embodiment, the impurity contained in the first upper cladding layer and the second upper cladding layer is Be or C.

In the semiconductor laser of one embodiment,
The active layer is formed by alternately stacking quantum well layers and barrier layers,
  The quantum well layer is made of (Al _x Ga _1-x ) _y In _1-y P (where 0 ≦ x ≦ 1, 0 ≦ y ≦ 1),
  The barrier layer has a higher Al content (x) than the quantum well layer (Al _x Ga _1-x ) _y In _1-y It is characterized by comprising P (where 0 ≦ x ≦ 1, 0 ≦ y ≦ 1).

In the semiconductor laser of one embodiment,
The active layer is formed by alternately stacking quantum well layers and barrier layers,
The quantum well layer is In _z Ga _1-z As (however, 0 ≦ z ≦ 1) or Al _x Ga _1-x As (where 0 ≦ x ≦ 1),
The barrier layer has an Al content (x) greater than that of the quantum well layer. _x Ga _1-x It is characterized by comprising As (where 0 ≦ x ≦ 1).

In another aspect, the semiconductor laser of the present invention is a semiconductor laser that emits laser light through a light emitting end face, and has a lower cladding layer, an active layer that generates laser light, a first upper cladding layer, an etching layer on a substrate. Stop layers are stacked in this order, a second upper cladding layer is formed as a ridge on the etching stop layer, and at least in a portion along the light emitting end surface from the etching stop layer to the active layer, which is below the ridge. The impurity is diffused to mix the active layer, and in the region along the light emitting end face, the energy band gap of the active layer corresponding to both sides of the ridge is formed in the light emitting end face. In the region along the active layer, the active layer is smaller than the energy band gap corresponding to the portion immediately below the ridge, and is mixed into the active layer. Greater than the energy band gap of the portion inside which not be characterized.

  In the semiconductor laser of one embodiment, in the region along the light emitting end face, the shift of the photoluminescence wavelength to the short wavelength side due to the mixed crystallization of the portion corresponding to the portion immediately below the ridge in the active layer is 18 nm or more. The shift of the photoluminescence wavelength to the short wavelength side due to the mixed crystallization of the portion corresponding to both sides of the ridge in the active layer is 15 nm or less.

  In one embodiment, the impurity diffused in a portion along the light emitting end surface from the etching stop layer to the active layer is Zn.

  In one embodiment, the impurity contained in the first upper cladding layer and the second upper cladding layer is Be or C.

In the semiconductor laser according to one embodiment, the active layer is formed by alternately stacking quantum well layers and barrier layers, and the quantum well layer is (Al _x Ga _1-x ) _y In _1-y P (where (0 ≦ x ≦ 1, 0 ≦ y ≦ 1), and the barrier layer has a higher Al content (x) than the quantum well layer (Al _x Ga _1-x ) _y In _1-y P (However, 0 ≦ x ≦ 1, 0 ≦ y ≦ 1).

In one embodiment, the etching stop layer is made of Ga _y In _1-y P (where 0 ≦ y ≦ 1), and the first and second upper cladding layers are made of (Al _x Ga _{1). -x) y in 1-y P} ( where, characterized in that it consists of a 0 ≦ x ≦ 1,0 ≦ y ≦ 1.).

In one embodiment, the active layer is formed by alternately stacking quantum well layers and barrier layers, and the quantum well layer is In _z Ga _1-z As (where 0 ≦ z ≦ 1). .) or _Al x _{Ga 1-x} as (however, 0 ≦ x is ≦ 1.) made, large _Al x _{Ga 1-x} as of said barrier layer is Al content than the quantum well layer (x) (Where 0 ≦ x ≦ 1).

In one embodiment, the etching stop layer is made of Al _x Ga _1-x As (where 0 ≦ x ≦ 0.3), and the first and second upper cladding layers are made of Al _y Ga. It is characterized by comprising _1-y As (where x <y ≦ 1).

  In still another aspect, the semiconductor laser of the present invention is a semiconductor laser that emits laser light through a light emitting end face, and on the substrate, a lower cladding layer, an active layer that generates laser light, a first upper cladding layer, Etching stop layers are stacked in this order, a second upper cladding layer is formed on the etching stop layer as a ridge extending perpendicular to the light emitting end face, and current is applied to regions corresponding to both sides of the second upper cladding layer. A blocking layer is embedded, and at least a portion along the light emission end face from the etching stop layer to the active layer below the ridge is diffused and mixed crystal is formed to suppress laser light absorption. In the region along the light emitting end face, the energy band gap of the portion corresponding to both sides of the ridge in the etching stop layer is And wherein the smaller than the energy band gap of the portion directly below the ridge of Tsu quenching stop layer.

  In the semiconductor laser of the present invention, in the region along the light emitting end face, the energy band gap of the etching stop layer corresponding to both sides of the ridge corresponds to the portion immediately below the ridge in the etching stop layer. It is smaller than the energy band gap of the part. Accordingly, in the region along the light emitting end face, portions of the etching stop layer corresponding to both sides of the ridge are etched when the second upper cladding layer is formed in a ridge shape on the etching stop layer. The function to stop can be effectively performed. Therefore, this semiconductor laser is easily manufactured with high accuracy.

  In one embodiment, in the region along the light emitting end face, the energy band gap of the active layer corresponding to the portion immediately below the ridge has a portion corresponding to both sides of the ridge in the active layer. It is characterized by being larger than the energy band gap.

  In the semiconductor laser of this embodiment, in the region along the light emitting end face, the energy band gap of the active layer corresponding to the portion immediately below the ridge corresponds to both sides of the ridge in the active layer. The energy band gap of the active layer that is larger than the energy band gap of the portion is along the light emitting end face, and the portion of the active layer that is directly below the ridge is along the light emitting end face of the active layer, and the ridge. It is larger than the energy band gap of the part corresponding to both sides of Therefore, a portion of the active layer along the light emitting end surface and corresponding to the portion immediately below the ridge can effectively suppress COD as a window region. Further, since the inside of the active layer is not mixed, manufacturing is facilitated. In addition, since COD does not become a problem inside the active layer, mixed crystal inside the active layer is unnecessary.

  In one embodiment of the semiconductor laser, in the region along the light emitting end face, the shift of the photoluminescence wavelength to the short wavelength side due to the mixed crystallization of the portion corresponding to the portion immediately below the ridge in the active layer is 18 nm or more. The shift of the photoluminescence wavelength to the short wavelength side due to the mixed crystallization of the portion corresponding to both sides of the ridge in the active layer is 15 nm or less.

  In the semiconductor laser of this embodiment, in the region along the light emitting end face, the shift of the photoluminescence wavelength to the short wavelength side due to the mixed crystallization of the portion corresponding to the portion immediately below the ridge in the active layer is 18 nm. As described above, the maximum light output is increased by 1.41 times or more as compared with the conventional semiconductor laser. Further, in the region along the light emitting end face, the shift of the photoluminescence wavelength to the short wavelength side due to the mixed crystallization of the portion corresponding to both sides of the ridge in the active layer is 15 nm or less, so that the manufacturing is possible. It becomes extremely easy.

  In one embodiment, the impurity contained in the first upper cladding layer is Be or C, and the impurity diffused in a portion along the light emitting end surface from the etching stop layer to the active layer is Zn. It is characterized by being.

  Zn easily diffuses, and the diffusion easily causes mixed crystals of the active layer. Further, since Be or C has a smaller diffusion constant than Zn, Zn is easily diffused into the active layer while avoiding the phenomenon that impurities (Be or C) contained in the first upper cladding layer are diffused into the active layer. be able to. Therefore, manufacture becomes very easy.

  In one embodiment, the impurity contained in the second upper cladding layer is Be or C.

  Since Be or C has a smaller diffusion constant than Zn, Zn can be easily diffused into the active layer while avoiding the phenomenon that impurities (Be or C) contained in the second upper cladding layer are diffused into the active layer. it can. Therefore, manufacture becomes very easy.

In one embodiment of the semiconductor laser, the active layer is formed by alternately stacking quantum well layers and barrier layers, and the quantum well layer is (Al _x Ga _1-x ) _y In _1-y P (where (0 ≦ x ≦ 1, 0 ≦ y ≦ 1), and the barrier layer has a higher Al content (x) than the quantum well layer (Al _x Ga _1-x ) _y In _1-y P (However, 0 ≦ x ≦ 1, 0 ≦ y ≦ 1).

(Al _x Ga _1-x ) _y In _1-y P forming the quantum well layer and the barrier layer is easily mixed with a relatively low amount such as a diffused Zn concentration of 10 ¹⁸ cm ⁻³ . To do. Therefore, manufacture becomes very easy.

  In this specification, x, y, and z are used to express the composition of the compound semiconductor. However, these x, y, and z can take different values among the respective compound semiconductors.

Furthermore, in one embodiment, the etching stop layer is made of Ga _y In _1-y P (where 0 ≦ y ≦ 1), and the first and second upper cladding layers are made of (Al _x Ga _1-x ) _y In _1-y P (where 0 ≦ x ≦ 1, 0 ≦ y ≦ 1).

Ga _y In _1-y P (where 0 ≦ y ≦ 1) forming the etching stop layer (Al _x Ga _1-x ) _y In ₁₋ forming the first and second upper cladding layers. _{When y} P (where 0 ≦ x ≦ 1, 0 ≦ y ≦ 1) is removed by wet etching, it can be left selectively. Therefore, the step of forming the second upper cladding layer in a ridge shape on the etching stop layer is facilitated.

In one embodiment, the active layer is formed by alternately stacking quantum well layers and barrier layers, and the quantum well layer is In _z Ga _1-z As (where 0 ≦ z ≦ 1). .) or _Al x _{Ga 1-x} as (however, 0 ≦ x is ≦ 1.) made, large _Al x _{Ga 1-x} as of said barrier layer is Al content than the quantum well layer (x) (Where 0 ≦ x ≦ 1).

In _z Ga _1-z As (where 0 ≦ z ≦ 1) or Al _x Ga _1-x As (where 0 ≦ x ≦ 1) and the barrier layer forming the quantum well layer are formed. Al _x Ga _1-x As formed (where 0 ≦ x ≦ 1) is easily mixed by Zn diffusion. Therefore, manufacture becomes very easy.

Further, in one embodiment, the etching stop layer is made of Al _x Ga _1-x As (where 0 ≦ x ≦ 0.3), and the first and second upper cladding layers are made of Al. _It consists of yGa1 _- yAs (however, it is x <y <= 1), It is characterized by the above-mentioned.

The Al _x Ga _1-x As forming the etching stop layer (where 0 ≦ x ≦ 0.3) is the Al _y Ga _1-y As forming the first and second upper cladding layers (provided that x <y ≦ 1)) can be selectively left when removed by wet etching. Therefore, the step of forming the second upper cladding layer in a ridge shape on the etching stop layer is facilitated.

  The semiconductor laser manufacturing method of the present invention is a semiconductor laser manufacturing method for manufacturing a semiconductor laser that emits laser light through a light emitting end face, and includes at least a lower cladding layer, an active layer that generates laser light on a substrate, A laser is provided under the condition that the first upper cladding layer, the etching stop layer, and the second upper cladding layer are stacked in this order, and the etching stop layer maintains the function of stopping the etching for the second upper cladding layer. A first annealing step of diffusing impurities for suppressing light absorption into the second upper cladding layer along a region where the light emitting end face is to be formed; and the second upper cladding layer with respect to the light emitting end face An etching step of etching until reaching the etching stop layer so as to leave a vertically extending ridge, and the ridge-shaped second upper cladding The impurity diffused in the region where the light emitting end face is to be formed in the active layer is re-diffused through the etching stop layer to the active layer, along the light emitting end face to be formed in the active layer, and It has the 2nd annealing process which mix-crystallizes the part corresponded directly under the said ridge.

  In the semiconductor laser manufacturing method of the present invention, as illustrated in FIG. 21A, at least a lower cladding layer 71, an active layer 72 that generates laser light, a first upper cladding layer 73, and an etching stop layer 74 are formed on the substrate. The second upper cladding layer 76 is laminated in this order. The first annealing step is performed under the condition that the etching stop layer maintains the function of stopping the etching for the second upper cladding layer, for example, under the condition of a low temperature or a short time. As illustrated in FIG. 21B, for example, the impurity 89 is diffused from the solid diffusion source 81 to the second upper cladding layer 76, but is not substantially diffused to the etching stop layer 74. Therefore, in the etching process for processing the second upper cladding layer 76 into a ridge shape, the etching stop layer 74 can effectively stop the etching as illustrated in FIG. As a result, the processing accuracy of the ridge is increased and an electrical short circuit between layers is prevented. Further, in the second annealing step, as illustrated in FIGS. 22D1 and 22D2, a portion 72B corresponding to the light emitting end surface to be formed in the active layer and directly below the ridge 76 is sufficiently mixed. Crystallized. This mixed crystal portion 72B functions as a window region with less laser light absorption on the light emitting end face after completion of the semiconductor laser, and can suppress COD. As described above, according to the semiconductor laser manufacturing method of the present invention, a semiconductor laser having a window region on the light emitting end face can be easily manufactured with high accuracy.

  In one embodiment of the semiconductor laser manufacturing method, the shift of the photoluminescence wavelength to the short wavelength side by the first annealing step in the portion along the region where the light emitting end face is to be formed in the active layer is 15 nm or less. The shift of the photoluminescence wavelength to the short wavelength side by the second annealing step in the portion corresponding to the region where the light emitting end face is to be formed in the active layer and corresponding to the region immediately below the ridge is 18 nm or more. It is characterized by.

  If the shift of the portion of the active layer along the region where the light emitting end face is to be formed to the short wavelength side of the photoluminescence wavelength by the first annealing step is 15 nm or less, the etching by the first annealing step is performed. Less stop layer crystallization. Accordingly, it is possible to maintain the function of the etching stop layer stopping the etching for the second upper cladding layer after the first annealing step. Further, the shift of the photoluminescence wavelength to the short wavelength side by the second annealing step in a portion corresponding to the region where the light emitting end face of the active layer is to be formed and immediately below the ridge should be 18 nm or more. For example, the portion is sufficiently mixed with the second annealing step. This mixed crystal portion functions as a window region with less laser light absorption at the light emitting end face after completion of the semiconductor laser, and can suppress COD.

  According to one embodiment of the present invention, there is provided a semiconductor laser manufacturing method comprising: an impurity evaporation prevention layer that prevents evaporation of the impurities from the second upper cladding layer to the outside after the etching step and before the second annealing step. It has the process of providing, It is characterized by the above-mentioned.

  In the state where nothing is provided on the second upper cladding layer as illustrated in FIG. 22D1, a part of the impurity 89 is transferred from the second upper cladding layer 76 to the outside in the second annealing step. Evaporate. On the other hand, as illustrated in FIG. 22D2, in the semiconductor laser manufacturing method of this embodiment, the second annealing step is performed on the substrate from the second upper cladding layer 76 to the outside. This is performed in a state where an impurity evaporation preventing layer 85 for preventing the evaporation of the impurity 89 is provided. Thereby, evaporation of the impurity 89 from the second upper cladding layer 76 to the outside can be prevented. Therefore, mixed crystallization by the second annealing step of the portion 72B along the region where the light emitting end face is to be formed in the active layer and just below the ridge can be further promoted.

  The semiconductor laser manufacturing method according to one embodiment is characterized in that the impurity evaporation prevention layer is made of silicon oxide, silicon nitride, or alumina.

  Since silicon oxide, silicon nitride, or alumina is dense, it is suitable for preventing evaporation of the impurities. In addition, silicon oxide, silicon nitride, or alumina can be selectively removed with an etchant that does not attack the underlying semiconductor layer. Therefore, the semiconductor laser can be easily manufactured with high accuracy.

  The semiconductor laser manufacturing method of one embodiment is characterized in that the impurity evaporation prevention layer is formed of a compound semiconductor layer.

  In general, in a semiconductor laser, a compound semiconductor layer such as a current blocking layer is formed on the etching stop layer. In the semiconductor laser manufacturing method of this embodiment, such a compound semiconductor layer is used as the impurity evaporation prevention layer. Therefore, the manufacturing process can be simplified.

  The semiconductor laser manufacturing method of one embodiment is characterized in that the compound semiconductor layer forming the impurity evaporation prevention layer has a conductivity type different from that of the second upper cladding layer.

  In the semiconductor laser manufacturing method of this embodiment, the compound semiconductor layer forming the impurity evaporation prevention layer has a conductivity type different from that of the second upper cladding layer. Therefore, by using the compound semiconductor layer, a current blocking layer for suppressing a reactive current can be formed in a region corresponding to both sides of the ridge and a portion along the light emitting end face.

  In one embodiment of the semiconductor laser manufacturing method, the impurity evaporation prevention layer is formed at a temperature lower than a temperature at which the impurities are re-diffused in the second annealing step.

  According to the semiconductor laser manufacturing method of this embodiment, the impurities are prevented from evaporating due to the temperature for forming the impurity evaporation prevention layer until the impurity evaporation prevention layer is completely formed. The

  In one embodiment of the semiconductor laser manufacturing method, the impurity contained in the first upper cladding layer is Be or C, and corresponds to the active layer along the region where the light emitting end face is to be formed and immediately below the ridge. The impurity diffused in the portion to be formed is Zn.

  Zn easily diffuses, and the diffusion easily causes mixed crystals of the active layer. Further, since Be or C has a smaller diffusion constant than Zn, Zn is easily diffused into the active layer while avoiding the phenomenon that impurities (Be or C) contained in the first upper cladding layer are diffused into the active layer. be able to. Therefore, manufacture becomes very easy.

  The semiconductor laser manufacturing method of one embodiment is characterized in that the impurity contained in the second upper cladding layer is Be or C.

  Since Be or C has a smaller diffusion constant than Zn, Zn can be easily diffused into the active layer while avoiding the phenomenon that impurities (Be or C) contained in the second upper cladding layer are diffused into the active layer. it can. Therefore, manufacture becomes very easy.

In one embodiment of the semiconductor laser manufacturing method, the active layer is formed by alternately stacking quantum well layers and barrier layers, and the quantum well layer is (Al _x Ga _1-x ) _y In _1-y P ( However, 0 ≦ x ≦ 1, 0 ≦ y ≦ 1, and the barrier layer has an Al content (x) larger than the quantum well layer (Al _x Ga _1-x ) _y In _{1− y} P (where a 0 ≦ x ≦ 1,0 ≦ y ≦ 1.) , characterized in that it consists of.

(Al _x Ga _1-x ) _y In _1-y P forming the quantum well layer and the barrier layer is easily mixed with a relatively low amount such as a diffused Zn concentration of 10 ¹⁸ cm ⁻³ . To do. Therefore, manufacture becomes very easy.

In one embodiment, the etching stop layer is made of Ga _y In _1-y P (where 0 ≦ y ≦ 1), and the first and second upper cladding layers are made of (Al _x Ga _1-x ) _y In _1-y P (where 0 ≦ x ≦ 1, 0 ≦ y ≦ 1).

Ga _y In _1-y P (where 0 ≦ y ≦ 1) forming the etching stop layer (Al _x Ga _1-x ) _y In ₁₋ forming the first and second upper cladding layers. _{When y} P (where 0 ≦ x ≦ 1, 0 ≦ y ≦ 1) is removed by wet etching, it can be left selectively. Therefore, the step of forming the second upper cladding layer in a ridge shape on the etching stop layer is facilitated.

  In one embodiment of the semiconductor laser manufacturing method, the second upper cladding layer is etched with sulfuric acid, hydrochloric acid, or phosphoric acid.

  Sulfuric acid, hydrochloric acid or phosphoric acid is an etchant that etches the second upper cladding layer but does not substantially etch the etching stop layer. Therefore, the ridge can be formed with high accuracy in the etching process in which the second upper cladding layer is left in the shape of a ridge until etching reaches the etching stop layer.

  In one embodiment, the first annealing step is performed at 450 ° C. to 570 ° C. for 10 minutes or more or 550 ° C. to 650 ° C. for 10 minutes or less, and the second annealing step is performed at 570 ° C. to 750 ° C. It is characterized by being carried out under conditions of 10 minutes or more at ℃ or 10 minutes or less at 650 to 850 ° C.

As long as the conditions for the first annealing step are satisfied, when the etching stop layer is made of Ga _y In _1-y P (where 0 ≦ y ≦ 1), the etching stop layer is not mixed. Also, the active layer is activated well under the conditions of the second annealing step. However, if the temperature is equal to or higher than the conditions for the second annealing step, impurities (particularly p-type) in the second upper cladding layer may diffuse to the active layer, which may degrade characteristics such as the laser oscillation threshold. .

  In the present invention, a normal annealing furnace is used for the condition of 450 ° C. to 570 ° C. for 10 minutes or longer in the first annealing step, and the condition of 550 ° C. to 650 ° C. for 10 minutes or less is determined by the RTA method (Rapid Thermal Anneal). Can be used.

In one embodiment of the semiconductor laser manufacturing method, the active layer is formed by alternately stacking quantum well layers and barrier layers, and the quantum well layer is formed of In _z Ga _1-z As (where 0 ≦ z ≦ 1 in a.) or _Al x _{Ga 1-x} as (however, 0 ≦ x ≦ 1 and is.) a greater _Al x _Ga an Al content than the barrier layer is the quantum well layer (x) _1- It is characterized by comprising _x As (where 0 ≦ x ≦ 1).

In _z Ga _1-z As (where 0 ≦ z ≦ 1) or Al _x Ga _1-x As (where 0 ≦ x ≦ 1) and the barrier layer forming the quantum well layer are formed. Al _x Ga _1-x As formed (where 0 ≦ x ≦ 1) is easily mixed by Zn diffusion. Therefore, manufacture becomes very easy.

In one embodiment of the semiconductor laser manufacturing method, the etching stop layer is made of Al _x Ga _1-x As (where 0 ≦ x ≦ 0.3), and the first and second upper cladding layers are made of Al. _It consists of yGa1 _- yAs (however, it is x <y <= 1), It is characterized by the above-mentioned.

The Al _x Ga _1-x As forming the etching stop layer (where 0 ≦ x ≦ 0.3) is the Al _y Ga _1-y As forming the first and second upper cladding layers (provided that x <y ≦ 1)) can be selectively left when removed by wet etching. Therefore, the step of forming the second upper cladding layer in a ridge shape on the etching stop layer is facilitated.

  In one embodiment of the semiconductor laser manufacturing method, the second upper cladding layer is etched with hydrofluoric acid or buffered hydrofluoric acid.

  Hydrofluoric acid or buffered hydrofluoric acid is an etchant that etches the second upper cladding layer but does not substantially etch the etching stop layer. Therefore, the ridge can be formed with high accuracy in an etching process in which portions corresponding to both sides of the ridge of the second upper cladding layer are etched until the etching stop layer is reached.

  The semiconductor laser manufacturing method according to one embodiment is characterized in that the second annealing step is performed by raising the substrate temperature when forming the semiconductor layer by molecular beam epitaxy.

  Molecular beam epitaxy is a method for forming a semiconductor in a high vacuum without using hydrogen. Therefore, if the second annealing step is performed by raising the substrate temperature during the formation of the semiconductor layer by molecular beam epitaxy, impurity inactivation due to the mixing of hydrogen can be suppressed.

  The semiconductor laser manufacturing method according to one embodiment is characterized in that the second annealing step is performed in nitrogen.

  According to the semiconductor laser manufacturing method of this embodiment, it is possible to suppress inactivation of impurities due to the mixing of hydrogen.

  As apparent from the above, the semiconductor laser of the present invention is a semiconductor laser having a window region on the light emitting end face, and can be easily manufactured with high accuracy.

Hereinafter, the present invention will be described in detail with reference to the illustrated embodiments.
Hereinafter, (Al _x Ga _1-x ) _y In _1-y P (where 0 ≦ x ≦ 1, 0 ≦ y ≦ 1) is referred to as AlGaInP, and Ga _y In _1-y P (where 0 ≦ y ≦ 1.) may be abbreviated as GaInP, and Al _x Ga _1-x As (where 0 ≦ x ≦ 1) may be abbreviated as AlGaAs.

(First embodiment)
FIG. 1 shows the element structure of the end face window type semiconductor laser of the first embodiment. 2 shows a cross section taken along the line AA 'in FIG. 1, and FIG. 3 shows a cross section taken along the line BB' in FIG.

  As shown in FIG. 1, an n-type AlGaInP lower cladding layer 101, an active layer 102 for generating laser light, a p-type AlGaInP first upper cladding layer 103, and a p-type GaInP etching stop layer 104 are formed on an n-type GaAs substrate 100. They are stacked in this order. The active layer 102 is formed by alternately stacking undoped quantum well layers and barrier layers. The ridge 105 extending in a stripe shape perpendicular to the light emitting end faces 150 and 151 is composed of a p-type AlGaInP second upper cladding layer 106 and a p-type GaAs cap layer 107. In regions corresponding to both sides of the ridge 105, an n-type AlInP current blocking layer 108 is formed. As can be seen from FIG. 2, the current blocking layer 108 extends on the ridge 105 in the vicinity of the light emitting end faces 150 and 151 (the extended portion is indicated by 108B), and the light emission of the active layer 102 is performed. It covers the end face 150, 151 vicinity 102B. This prevents injection of reactive current into the light emitting end faces 150 and 151 of the active layer 102 in the vicinity of the portion 102B. 2 and 3, the p-type GaAs cap layer 107 and the p-type GaAs contact layer 110 are in contact with each other in the inner region other than the region near the light emitting end faces 150 and 151 in the AA ′ direction. Connected.

  In this semiconductor laser, in the region along the light emitting end faces 150 and 151, the energy band gap of the portion 102 </ b> B corresponding to the portion immediately below the ridge 105 in the active layer 102 is the portion corresponding to both sides of the ridge 105 in the active layer 102. It is larger than the energy band gap. Thereby, the portion 102B is a window region with less laser light absorption.

  This semiconductor laser is manufactured as follows.

First, as shown in FIG. 4A, an n-type (Al _0.7 Ga _0.3 ) _0.5 In _0.5 P layer is formed on an n-type GaAs substrate 100 by MBE (molecular beam epitaxy). The cladding layer 101 (carrier concentration 1 × 10 ¹⁸ cm ⁻³ ), three undoped GaInP layers (thickness 6 nm), four undoped (Al _0.5 Ga _0.5 ) _0.5 In _0.5 P layers (thickness) Active layer 102 having a structure sandwiched by 8 nm), p-type (Al _0.7 Ga _0.3 ) _0.5 In _0.5 P first upper cladding layer 103 (carrier concentration 1.5 × 10 ¹⁸ cm ^{− 3} ), p-type Ga _0.6 In _0.4 P etching stop layer 104 (thickness 6 nm, carrier concentration 1.5 × 10 ¹⁸ cm ⁻³ ), p-type (Al _0.7 Ga _0.3 ) _{0. 5} an In _0.5 P second upper cladding layer 106 (thickness 0. [mu] m, carrier concentration ^{2 × 10 18 cm -3),} p -type GaAs cap layer 107 (carrier concentration 3 × ¹⁰ 18 ^{cm -3)} are formed in this order. Here, the n-type dopant is Si, and the p-type dopant is Be.

Next, as shown in FIG. 4B, on the cap layer 107, a ZnO (zinc oxide) layer as an impurity diffusion source having a thickness of 50 nm is formed in a stripe shape along the region where the light emitting end faces 150 and 151 are to be formed. 131 is formed. Furthermore, a SiO ₂ (silicon oxide) layer 132 having a thickness of 200 nm is formed over the entire area of the substrate 100.

  Next, annealing is performed at 510 ° C. for 2 hours (first annealing), and along the region where the light emitting end faces 150 and 151 are to be formed, from the ZnO (zinc oxide) layer 131 to the cap layer 107 and the second upper cladding. Zn is diffused into the layer 106. Under this annealing condition, Be used as a p-type dopant hardly diffuses into a region other than the region near the light emitting end faces 150 and 151.

  What is important here is that in the first annealing step, neither the etching stop layer 104 nor the active layer 102 is mixed. For example, FIG. 6 shows a shift amount (indicated by ● in FIG. 6) of the photoluminescence wavelength of the active layer when the temperature in the first annealing step is variously changed. It was confirmed that the photoluminescence wavelength of the active layer at the end of the first annealing showed only a shift of 2 nm toward the short wavelength side compared to the photoluminescence wavelength before the first annealing. Further, the function of the etching stop layer 104 to stop the etching in the etching process described below was maintained normally if the wavelength shift amount of the active layer 102 by the first annealing process was 15 nm or less. It was lost when the wavelength shift amount of the active layer 102 due to the process exceeded 15 nm.

After removing the SiO ₂ layer 132 and the ZnO layer 131 with buffered hydrofluoric acid, as shown in FIG. 4 (c), the cap layer 107 is made of a mixed solution of sulfuric acid, hydrogen peroxide solution and water, and p-type upper cladding. Each of the layers 103 is selectively etched with sulfuric acid to form a part of the cap layer 107 and the p-type upper cladding layer 103. The bottom surface has a width of 4 μm and is perpendicular to the light emitting end surfaces 150 and 151. An extending ridge 105 is formed. In this etching process, since the p-type etching stop layer 104 is not substantially etched by sulfuric acid, the p-type first upper cladding layer 103 existing thereunder is not etched.

As shown in FIG. 5D, the n-type Al _0.5 In _0.5 P current blocking layer 108 is formed over the entire area of the substrate 100 by the MBE method.

Thereafter, in order to prevent Zn diffused in the ridge 105 from being released to the outside in the second annealing step to be described below, an SiO layer having a thickness of 500 nm as an impurity evaporation preventing layer is formed on the current blocking layer 108. _{2 A} (silicon oxide) layer 130 is formed.

  Subsequently, annealing at 680 ° C. for 1 hour (second annealing) is performed in nitrogen. As a result, Zn atoms diffused in the region of the ridge 105 where the light emitting end faces 150 and 151 are to be formed are re-diffused through the etching stop layer 104 to the active layer 102, and the etching stop layer 104 and the active layer 102. The portions 104B and 102B corresponding to the light emitting end faces 150 and 151 to be formed and immediately below the ridge 105 are mixed. As shown in FIG. 6, it was confirmed that the photoluminescence wavelength of the mixed portion 102B of the active layer 102 was shifted to the short wavelength side by 70 nm with respect to the non-mixed interior 102A. The mixed crystal portion 102B functions as a window region with less laser light absorption at the light emitting end face after completion of the semiconductor laser, and can suppress COD. Under this annealing condition, Be used as a p-type dopant hardly diffuses into a region other than the region near the light emitting end faces 150 and 151.

As shown in FIG. 5E, the SiO ₂ layer 130 is removed with buffered hydrofluoric acid. Then, a portion of the n-type Al _0.5 In _0.5 P current blocking layer 108 on the ridge 105 and in a region other than the region near the light emitting end faces 150 and 151 is removed. That is, in the n-type Al _0.5 In _0.5 P current blocking layer 108 formed on the substrate 100, the portion 108 B existing in the region near the light emitting end faces 150 and 151, and the portion existing in the regions corresponding to both sides of the ridge 105 (Denoted by 108).

  Thereafter, as shown in FIG. 1, a p-type GaAs contact layer 110 (thickness: 4 μm) is formed on the entire surface of the substrate 100, and electrodes 115 and 116 are formed on the back and front surfaces of the substrate 100, respectively (wafer fabrication is completed). Thereafter, the wafer is cleaved along the region where the light emitting end faces 150 and 151 are to be formed, that is, so that the mixed crystal portion 102B of the active layer 102 becomes the resonator end face. Then, coating is performed so that one end face 150 has a reflectance of 8% as a light emitting end face, and the opposite end face 151 has a reflectance of 91% (completion of laser chip fabrication). The resonator length was 800 μm, and the length of the mixed portion 102B of the active layer 102 was 25 μm for both the light emitting end face 150 and the opposite end face 151.

  Each laser chip was mounted on a stem, and a current was applied to examine the characteristics. A maximum light output of 265 mW was obtained at a wavelength of 654 nm, and it was confirmed that no COD was generated. Further, no leakage current was observed when the etching stop layer was destroyed during etching.

In order to support this effect, the Zn concentration profile in the depth direction in the region where the ridge 105 exists was measured by SIMS (secondary ion mass spectrometry). However, the width of the ridge 105 is set to 500 μm for convenience of SIMS analysis. FIG. 9 shows the Zn concentration profile after the first annealing at 510 ° C. for 2 hours and after the second annealing. From FIG. 9, the Zn during the first annealing termination does not reach to a concentration level that is mixed into the etching stop layer 104, the concentration after completion of the second anneal Zn is intermixed beyond the active layer 102 It can be seen that it has spread to the level .

6 to 7 show the results of the photoluminescence wavelength shift of the active layer under the annealing conditions and the like in the present embodiment. Here, it is easier to measure the photoluminescence of the active layer than the photoluminescence of the etching stop layer, and the active layer and the etching stop layer are separated by only the first upper cladding layer thickness of 0.2 μm, which is about the same Since the mixed crystal is formed, the function of the etching stop layer is evaluated by the photoluminescence of the active layer. A line is drawn at the photoluminescence wavelength shift of 15 nm of the active layer. If the wavelength shift is 15 nm or less, the etching stop layer 104 has a function of stopping the etching, and if the wavelength shift exceeds 15 nm, the etching stop layer. 104 does not have a function of stopping etching. As shown in FIG. 6, when the SiO ₂ layer 130 as the impurity evaporation preventing layer is provided, the wavelength shift is significantly increased after the second annealing compared to after the first annealing. For example, it can be seen that if the first annealing temperature is 450 ° C. or more, the wavelength shift becomes 18 nm or more after the second annealing.

On the other hand, as shown in FIG. 7, when the SiO ₂ layer 130 as the impurity evaporation preventing layer is not provided, the wavelength shift only slightly increases after the first annealing even after the second annealing. For example, if the first annealing temperature is 520 ° C., it can be seen that the wavelength shift amount of the active layer is 18 nm while maintaining the function of the etching stop layer. From this, the first annealing condition was set at 520 ° C. for 2 hours, and a device of a comparative example in which the SiO ₂ layer 130 as the impurity evaporation preventing layer was omitted was fabricated. In this case, the photoluminescence wavelength of the active layer was 18 nm after the second annealing, and COD occurred at a maximum light output of 174 mW. However, it was confirmed that the maximum light output was improved as compared with the case where no window layer was provided (maximum light output 120 mW). FIG. 10 shows the relationship between the wavelength shift amount of the active layer and the maximum light output. The semiconductor laser of this embodiment is mainly intended to improve the writing speed of the next generation DVD-R and DVD-RW, but it is necessary to double the writing speed for each generation, and the optical output of the corresponding semiconductor laser is It is necessary to improve the conventional element by 1.41 times. FIG. 10 shows that this requirement is satisfied if the wavelength shift amount is 18 nm or more.

In the present embodiment, the SiO ₂ layer 130 is employed as the impurity evaporation prevention layer, but the present invention is not limited to this. Silicon nitride or alumina can also be employed as the impurity evaporation preventing layer. These materials can be suitably used as a dense mask material that prevents the evaporation of Zn to the outside, like SiO ₂ . When a semiconductor laser was actually fabricated using silicon nitride and alumina as the impurity evaporation preventing layer, the wavelength shift after the second annealing was 75 nm for silicon nitride and 73 nm for alumina. Silicon nitride and alumina can be removed without etching the underlying compound semiconductor layer with hydrofluoric acid or the like, like SiO ₂ .

  In this embodiment, the p-type dopant is Be. However, by using another dopant having a small diffusion coefficient, particularly C, the diffusion of the p-type dopant into the active layer is suppressed, and excellent device characteristics (laser oscillation) Threshold) and the like.

  In this embodiment, sulfuric acid is used as an etchant for the second upper cladding layer. However, even if phosphoric acid or hydrochloric acid is used, the second upper cladding layer is etched and the etching stop layer is hardly etched (etching rate ratio is 10). Therefore, it can be preferably used.

  In this embodiment, a normal annealing furnace is used for the annealing process, but an RTA furnace can also be used. RTA refers to extremely rapid annealing at a temperature rising rate of 10 ° C./second to 100 ° C./second. In this case, a temperature holding time of about 20 seconds to 10 minutes is appropriate. Since the holding time is short, it is necessary to raise the temperature more than normal annealing.

  FIG. 8 shows the result of the photoluminescence wavelength shift of the active layer when the first annealing time is changed to 10 minutes and when it is changed to 20 seconds. It can be seen that when the first annealing time is changed to 10 minutes, the first annealing temperature is 570 ° C. or less and the wavelength shift is 15 nm or less. When the temperature holding time is 20 seconds, 550 ° C. to 650 ° C. is appropriate for the first annealing, and 650 ° C. to 850 ° C. is appropriate for the second annealing. RTA has an advantage of a short working time, and can be suitably used if attention is paid to temperature uniformity.

(Second Embodiment)
FIG. 11 shows the element structure of the end face window type semiconductor laser of the second embodiment. 12 shows a cross section taken along the line AA 'in FIG. 11, and FIG. 13 shows a cross section taken along the line BB' in FIG.

  As shown in FIG. 11, a lower cladding layer 201, an active layer 202 that generates laser light, a first upper cladding layer 203, and an etching stop layer 204 are stacked in this order on an n-type GaAs substrate 200. The active layer 202 is formed by alternately stacking undoped quantum well layers and barrier layers. A ridge 205 extending in a stripe shape perpendicular to the light emitting end faces 250 and 251 is composed of a second upper cladding layer 206 and a p-type GaAs cap layer 207. In regions corresponding to both sides of the ridge 205, an n-type AlInP current blocking layer 208 and an n-type GaAs current blocking layer 209 are formed. As can be seen from FIG. 12, these current blocking layers 208 and 209 also extend on the ridge 205 in the vicinity of the light emitting end faces 250 and 251 (the extended portions are indicated by 208B and 209B) and are active. The light emitting end faces 250 and 251 near the portion 202B of the layer 202 are covered. As a result, injection of reactive current into the light emitting end faces 250 and 251 in the vicinity of the active layer 202 is prevented. In addition, as can be seen from FIGS. 12 and 13, the p-type GaAs cap layer 207 and the p-type GaAs contact layer 210 are in contact with each other in the inner region other than the region near the light emitting end faces 250 and 251 in the AA ′ direction. Connected.

  In this semiconductor laser, in the region along the light emitting end faces 250 and 251, the energy band gap of the portion 202 </ b> B corresponding to the portion immediately below the ridge 205 in the active layer 202 is the portion corresponding to both sides of the ridge 205 in the active layer 202. It is larger than the energy band gap. As a result, this portion 202B is a window region with less laser light absorption. This portion 202B is formed by the diffusion of impurities contained in the second upper cladding layer 206 of the ridge 205 as will be described later. Accordingly, in the active layer 202, the band gap gradually decreases as the distance from the ridge 205 increases. The light density distribution of the laser light gradually decreases as the distance from the ridge 205 increases, but this is advantageous because light absorption is suppressed.

  This semiconductor laser is manufactured as follows.

First, as shown in FIG. 14A, an n-type (Al _0.7 Ga _0.3 ) _0.5 In _{0.5 is formed} on an n-type GaAs substrate 200 by MOCVD (metal organic chemical vapor deposition). P lower cladding layer 201 (carrier concentration 1 × 10 ¹⁸ cm ⁻³ ), three undoped GaInP layers (thickness 6 nm), four undoped (Al _0.5 Ga _0.5 ) _0.5 In _0.5 P layers Active layer 202 having a structure sandwiched between (thickness 8 nm), p-type (Al _0.7 Ga _0.3 ) _0.5 In _0.5 P first upper cladding layer 203 (carrier concentration 0.7 × 10 ¹⁸ cm ⁻³ ), p-type Ga _0.6 In _0.4 P etching stop layer 204 (carrier concentration 1.5 × 10 ¹⁸ cm ⁻³ ), p-type (Al _0.7 Ga _0.3 ) _0.5 In _0.5 P second upper cladding layer 206 (carrier concentration: 2 10 ¹⁸ cm ^-3), p-type GaAs cap layer 207 (carrier concentration 3 × ¹⁰ 18 ^{cm -3)} are formed in this order. Here, the n-type dopant is Si, the p-type dopant is C for the first upper cladding layer, and Zn for the other p-type layers.

Next, as shown in FIG. 14B, a ZnO (zinc oxide) layer as an impurity diffusion source having a thickness of 50 nm is formed in a stripe shape on the cap layer 207 along the region where the light emitting end faces 250 and 251 are to be formed. 231 is formed. Furthermore, a SiO ₂ (silicon oxide) layer 232 having a thickness of 200 nm is formed over the entire area of the substrate 200.

  Next, annealing is performed at 510 ° C. for 2 hours (first annealing), and from the ZnO (zinc oxide) layer 231 to the cap layer 207 and the second upper cladding along the region where the light emitting end faces 250 and 251 are to be formed. Zn is diffused into the layer 206. What is important here is that, in the first annealing step, neither GaInP etching stop layer 204 nor active layer 202 is mixed.

After removing the SiO ₂ layer 232 and the ZnO layer 231 with buffered hydrofluoric acid, as shown in FIG. 14C, the cap layer 207 is mixed with a mixed solution of sulfuric acid / hydrogen peroxide water / water, and the p-type upper cladding. Each of the layers 203 is selectively etched with sulfuric acid to form a part of the cap layer 207 and the p-type upper cladding layer 203. The bottom surface has a width of 3 μm and is vertically striped with respect to the light emitting end surfaces 250 and 251. An extending ridge 205 is formed. In this etching process, since the p-type etching stop layer 204 is not substantially etched by sulfuric acid, the p-type first upper cladding layer 203 existing thereunder is not etched.

As shown in FIG. 15D, an n-type Al _0.5 In _0.5 P current blocking layer 208 (0.6 μm) and an n-type GaAs current blocking layer 209 (2.0 μm) are formed over the entire area of the substrate 200. Are formed in this order by the MBE method.

Here, the n-type Al _0.5 In _0.5 P current blocking layer 208 grows at a substrate temperature of 490 ° C., and also functions as an impurity evaporation preventing layer that blocks diffusion of impurities to the outside. Further, at the stage of growing the n-type GaAs current blocking layer 209, the substrate temperature is set to 490 ° C. at the start of growth, and the substrate temperature is raised to 630 ° C. after the n-type GaAs has grown to about 0.2 μm. Thus, by setting the substrate temperature to 630 ° C., Zn atoms diffused in the region where the light emitting end faces 250 and 251 of the ridge 205 should be formed are re-diffused to the active layer 202 through the etching stop layer 204, Of the etching stop layer 204 and the active layer 202, the portions 204B and 202B corresponding to the light emission end faces 250 and 251 to be formed and immediately below the ridge 205 are mixed. Actually, it was confirmed that the photoluminescence wavelength of the mixed crystal portion 202B of the active layer 202 was shifted to the short wavelength side by 45 nm with respect to the non-mixed internal 202A. This mixed crystal portion 202B functions as a window region with less laser light absorption at the light emitting end face after completion of the semiconductor laser, and can suppress COD.

As shown in FIG. 15E, the n-type GaAs current blocking layer 209 and the n-type Al _0.5 In _0.5 P current blocking layer on the ridge 205 and other than the regions near the light emitting end faces 250 and 251 Remove any part of the region. That is, of the n-type GaAs current blocking layer 209 and the n-type Al _0.5 In _0.5 P current blocking layer formed on the substrate 200, the portions 209B and 208B in the region near the light emitting end faces 250 and 251 and the ridge 205 The portions (indicated by 209 and 208) existing in the regions corresponding to both sides of the left side are left as they are.

  Thereafter, as shown in FIG. 11, a p-type GaAs contact layer 210 (thickness 4 μm) is formed on the entire surface of the substrate 200, and electrodes 215 and 216 are formed on the front and back surfaces of the substrate 200, respectively (wafer fabrication is completed). Thereafter, the wafer is cleaved along the region where the light emitting end faces 250 and 251 are to be formed, that is, so that the mixed crystal portion 202B of the active layer 202 becomes the resonator end face. Then, coating is performed so that one end face 250 has a reflectance of 8% as a light emitting end face and the opposite end face 251 has a reflectance of 91% (laser chip fabrication is completed). The length of the mixed crystal portion 202B of the active layer 202 was set to 20 μm for both the light emitting end face 250 and the opposite end face 251.

  Each laser chip was mounted on a stem, and a current was applied to examine the characteristics. A maximum light output of 225 mW was obtained at a wavelength of 656 nm, and it was confirmed that no COD occurred. Further, no leakage current was observed when the etching stop layer was destroyed during etching.

In this embodiment, first, the n-type Al _0.5 In _0.5 P current blocking layer 208 is formed at a relatively low temperature, and the n-type GaAs current blocking layer 209 is formed at the substrate temperature for the second annealing. However, the substrate temperature for the second annealing may be set in the middle of the step of forming the n-type Al _0.5 In _0.5 P current blocking layer 208. Thus, by performing the second annealing using the substrate temperature at the time of forming the current blocking layer, the manufacturing process can be simplified as compared with the first embodiment. As a method for forming the current blocking layer, an MOCVD method (metal organic vapor phase epitaxy) may be used in addition to the MBE method.

(Third embodiment)
FIG. 16 shows the element structure of the end face window type semiconductor laser of the third embodiment. 17 shows a cross section taken along the line AA ′ of FIG. 16, and FIG. 18 shows a cross section taken along the line BB ′ of FIG.

  As shown in FIG. 16, on an n-type GaAs substrate 300, an n-type AlGaAs lower cladding layer 301, an active layer 302 for generating laser light, a p-type AlGaAs first upper cladding layer 303, a p-type GaAs etching stop layer 304 ( Are stacked in this order. The active layer 302 is formed by alternately stacking undoped quantum well layers and barrier layers. A ridge 305 extending in a stripe shape perpendicular to the light emitting end faces 350 and 351 is composed of a p-type AlGaAs second upper cladding layer 306 and a p-type GaAs cap layer 307. In regions corresponding to both sides of the ridge 305, an n-type AlGaAs current blocking layer 308 is formed. As can be seen from FIG. 17, this current blocking layer 308 is also present on the ridge 305 in the vicinity of the light emitting end faces 350 and 351 together with the p-type GaAs layer 309 (these portions are indicated by 308B and 308B). The light emitting end faces 350 and 351 in the vicinity of the active layer 302 are covered. As a result, injection of reactive current into the light emitting end faces 350 and 351 in the vicinity of the active layer 302 is prevented. 17 and 18, the p-type GaAs cap layer 307 and the p-type GaAs contact layer 310 are in contact with each other in the inner region other than the region near the light emitting end surfaces 350 and 351 in the AA ′ direction. Connected.

  In this semiconductor laser, in the region along the light emitting end faces 350 and 351, the energy band gap of the portion 302B corresponding to the portion immediately below the ridge 305 in the active layer 302 is the portion corresponding to both sides of the ridge 305 in the active layer 302. It is larger than the energy band gap. As a result, this portion 302B is a window region with little laser light absorption.

  This semiconductor laser is manufactured as follows.

First, as shown in FIG. 19A, an n-type Al _0.5 Ga _0.5 As lower clad layer 301 (carrier concentration 1 × 10 ¹⁸ cm ⁻³ ) is formed on an n-type GaAs substrate 300 by MBE. An active layer 302 having a structure in which two undoped GaAs layers (thickness 10 nm) are sandwiched by three undoped Al _0.3 Ga _0.7 As layers (thickness 8 nm), p-type Al _0.5 Ga _0.5 As First upper cladding layer 303 (carrier concentration 1.0 × 10 ¹⁸ cm ⁻³ ), p-type GaAs etching stop layer 304 (carrier concentration 2.0 × 10 ¹⁸ cm ⁻³ ), p-type Al _0.5 Ga _{0. A 5} As second upper cladding layer 306 (carrier concentration 2.5 × 10 ¹⁸ cm ⁻³ ) and a p-type GaAs cap layer 307 (carrier concentration 3 × 10 ¹⁸ cm ⁻³ ) are formed in this order. Here, the n-type dopant is Si, and the p-type dopant is Be.

Next, as shown in FIG. 19B, on the cap layer 307, a ZnO (zinc oxide) layer as an impurity diffusion source having a thickness of 50 nm is formed in a stripe shape along the region where the light emitting end faces 350 and 351 are to be formed. 331 is formed. Further, an SiO ₂ (silicon oxide) layer 332 having a thickness of 200 nm is formed over the entire area of the substrate 300.

  Next, annealing at 680 ° C. for 2 hours (first annealing) is performed, and along the region where the light emitting end faces 350 and 351 are to be formed, the ZnO (zinc oxide) layer 331 to the cap layer 307 and the second upper cladding are formed. Zn is diffused into the layer 306. Under this annealing condition, Be used as a p-type dopant hardly diffuses into a region other than the region near the light emitting end faces 350 and 351.

After removing the SiO ₂ layer 332 and the ZnO layer 331 with buffered hydrofluoric acid, as shown in FIG. 19 (c), the cap layer 307 is made of a mixed solution of sulfuric acid, hydrogen peroxide solution and water, and p-type upper cladding. Each of the layers 303 is selectively etched with sulfuric acid, and consists of a part of the cap layer 307 and the p-type upper cladding layer 303. The width of the bottom surface is 4 μm, and the stripes are perpendicular to the light emitting end surfaces 350 and 351. An extending ridge 305 is formed. In this etching process, since the p-type etching stop layer 304 is not substantially etched by sulfuric acid, the p-type first upper cladding layer 303 existing thereunder is not etched.

As shown in FIG. 20D, an n-type Al _0.7 Ga _0.3 As current blocking layer 308 and a p-type GaAs layer 309 are formed on the substrate 300 in regions corresponding to both sides of the ridge 305 by MOCVD. Form by law. This layer also covers the top of the ridge 305.

Thereafter, in order to prevent Zn diffused in the ridge 305 from being released to the outside in the second annealing step described below, a 500 nm-thickness as an impurity evaporation preventing layer is formed on the p-type GaAs layer 309. A SiO ₂ (silicon oxide) layer 330 is formed.

  Subsequently, RTA (second annealing) is performed in nitrogen at 950 ° C. for 1 minute. As a result, Zn atoms diffused in the region of the ridge 305 where the light emitting end surfaces 350 and 351 are to be formed are re-diffused through the etching stop layer 304 to the active layer 302, and the etching stop layer 304 and the active layer 302. The portions 304B and 302B corresponding to the light emitting end surfaces 350 and 351 to be formed and immediately below the ridge 305 are mixed. This mixed crystal portion 302B functions as a window region with less laser light absorption at the light emitting end face after completion of the semiconductor laser, and can suppress COD. Under this annealing condition, Be used as a p-type dopant hardly diffuses into a region other than the region near the light emitting end faces 350 and 351. Therefore, Be does not reach the active layer 302 and raise the laser oscillation threshold.

As shown in FIG. 20E, the SiO ₂ layer 330 is removed with buffered hydrofluoric acid. Then, portions of the n-type Al _0.7 Ga _0.3 As current blocking layer 308 and the p-type GaAs layer 309 on the ridge 305 and in regions other than the regions near the light emitting end surfaces 350 and 351 are removed. That is, the n-type Al _0.7 Ga _0.3 As current blocking layer 308 and the p-type GaAs layer 309 formed on the substrate 200, portions 309 B and 308 B in the region near the light emitting end faces 350 and 351, and the ridge 305 The portions (indicated by 309 and 308) existing in the regions corresponding to both sides are left as they are.

  Thereafter, as shown in FIG. 16, a p-type GaAs contact layer 310 (thickness: 4 μm) is formed on the entire surface of the substrate 300, and electrodes 315 and 316 are formed on the back and front of the substrate 300, respectively (wafer fabrication is completed). Thereafter, the wafer is cleaved along the region where the light emitting end faces 350 and 351 are to be formed, that is, so that the mixed crystal portion 302B of the active layer 302 becomes the resonator end face. Then, coating is performed so that one end face 350 has a reflectance of 12% as a light emitting end face, and the opposite end face 351 has a reflectance of 95% (laser chip fabrication is completed). The resonator length was 800 μm, and the length of the mixed portion 302B of the active layer 302 was 25 μm for both the light emitting end face 350 and the opposite end face 351.

  Each laser chip was mounted on a stem, and a current was applied to examine the characteristics. A maximum light output of 325 mW was obtained at a wavelength of 786 nm, and it was confirmed that no COD was generated. Further, no leakage current was observed when the etching stop layer was destroyed during etching.

  In the present embodiment, the p-type dopant is Be, but by using other dopants having a small diffusion coefficient, particularly C, the diffusion of the p-type dopant into the active layer is suppressed and good device characteristics ( Laser oscillation threshold, etc.) can be obtained.

In the present embodiment, the p-type etching stop layer 304 is made of GaAs. However, when hydrofluoric acid or buffered hydrofluoric acid is used as the etchant, the Al _x Ga ₁₋ having a mixed crystal ratio x of 0.3 or less. _x As is not attacked. When Al _x Ga _1-x As (x ≦ 0.3) is adopted as the material of the etching stop layer, the band gap of the etching stop layer increases as x increases, so that light emitted from the active layer is reabsorbed. The rate of performing is reduced.

  In the present embodiment, a normal annealing furnace is used for the first annealing and RTA is used for the second annealing, but this combination is arbitrary.

  In the present embodiment, the active layer 302 is made of AlGaAs, but is not limited to this. The oscillation wavelength may be 980 nm, for example, by enclosing the InGaAs quantum well layer to which In is added with a GaAs or AlGaAs barrier layer.

  Even when a material system other than the material system described in each of the above-described embodiments is used, the present invention can be applied to all window type semiconductor lasers having an etching stop layer. It is also possible to combine an Al-free system that is unlikely to cause COD, for example, a GaInAsP-based cladding and an InGaAs-based active layer.

1 is a perspective view of a semiconductor laser according to a first embodiment of the present invention. It is sectional drawing along the ridge of the semiconductor laser shown in FIG. FIG. 2 is a cross-sectional view in a direction perpendicular to the ridge of the semiconductor laser shown in FIG. 1. It is a figure explaining the manufacturing process of the semiconductor laser of 1st Embodiment of this invention. It is a figure explaining the manufacturing process of the semiconductor laser of 1st Embodiment of this invention. It is a figure which shows the result of the active layer photoluminescence wavelength shift at the time of changing the conditions of 1st annealing. It is a figure which shows the result of the active layer photoluminescence wavelength shift at the time of changing the conditions of 1st annealing. It is a figure which shows the result of the active layer photoluminescence wavelength shift at the time of changing the conditions of 1st annealing. It is a figure which shows Zn concentration distribution of the depth direction of the ridge part in 1st Embodiment. It is explanatory drawing which shows the relationship between the wavelength shift amount of an active layer, and the maximum optical output of the semiconductor laser of 1st Embodiment. It is a perspective view of the semiconductor laser of 2nd Embodiment of this invention. It is sectional drawing along the ridge of the semiconductor laser of 2nd Embodiment of this invention. It is sectional drawing of the direction perpendicular | vertical to the ridge of the semiconductor laser of 2nd Embodiment of this invention. It is a figure which shows the manufacturing process of the semiconductor laser of 2nd Embodiment of this invention. It is a figure which shows the manufacturing process of the semiconductor laser of 2nd Embodiment of this invention. It is a perspective view of the semiconductor laser of 3rd Embodiment of this invention. It is sectional drawing along the ridge of the semiconductor laser of 3rd Embodiment of this invention. It is sectional drawing of the direction perpendicular | vertical to the ridge of the semiconductor laser of 3rd Embodiment of this invention. It is a figure which shows the manufacturing process of the semiconductor laser of 3rd Embodiment of this invention. It is a figure which shows the manufacturing process of the semiconductor laser of 3rd Embodiment of this invention. It is a figure which shows typically the mode of impurity diffusion in the semiconductor laser manufacturing method of this invention. It is a figure which shows typically the mode of impurity diffusion in the semiconductor laser manufacturing method of this invention. It is a perspective view of the semiconductor laser of a prior art example. FIG. 24 is a cross-sectional view along the ridge of the semiconductor laser shown in FIG. 23. It is a figure explaining the manufacturing process of the semiconductor laser of a prior art example. It is a figure explaining the manufacturing process of the semiconductor laser of a prior art example.

Explanation of symbols

100, 200, 300 Substrate 102, 202, 302 Active layer 104, 204, 304 Etching stop layer 105, 205, 305 Ridge 106, 206, 306 Second upper cladding layer

Claims (2)

A semiconductor laser that emits laser light through a light emitting end face,
On the substrate, a lower cladding layer, an active layer for generating laser light, and a first upper cladding layer are laminated in this order,
A second upper cladding layer is formed as a ridge above the first upper cladding layer ;
A portion of the active layer corresponding to both sides of the ridge in the region along the light emitting end face, and a portion of the active layer corresponding to immediately below the ridge in the region along the light emitting end surface. A semiconductor laser characterized in that it is smaller than the energy band gap of the active layer and larger than the internal energy band gap of the active layer other than the region along the light emitting end face . The semiconductor laser according to claim 1, wherein
In region along the light-emitting end face, the shift to the short wavelength side of the photoluminescence wavelength of the portion directly below the ridge of the active layer is not less than 18 nm, on both sides of the ridge of the active layer The semiconductor laser, wherein the shift of the corresponding portion of the photoluminescence wavelength to the short wavelength side is 15 nm or less.

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