JP2008047641A - Semiconductor laser element and its fabrication process, optical disc drive, and optical transmission module - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a semiconductor laser element which can perform low power consumption operation with high oscillation efficiency. <P>SOLUTION: A ridge waveguide-type semiconductor laser element comprises a first conductive lower clad layer, an active layer, a second conductive first upper clad layer containing Al, a second conductive second upper clad layer of stripe ridge shape, and a second conductive contact layer. When the first upper clad layer has electron affinity of χ1 and forbidden band width of Eg1, and the contact layer has electron affinity of χ2 and forbidden band width of Eg2; a relation of (χ1+Eg1)>(χ2+Eg2) is satisfied if the first conductivity type is n-type and the second conductivity type is p-type, a relation of χ1<χ2 is satisfied if the first conductivity type is p-type and the second conductivity type is n-type, an oxide layer is formed by surface oxidation of the first upper clad layer in a region excepting directly under the ridge, and a metal electrode layer is provided to directly cover the contact layer on top of the ridge, the side face of the ridge and the oxide layer continuously. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a semiconductor laser device and a manufacturing method thereof, and more particularly to a semiconductor laser device and a manufacturing method thereof that can be suitably used for an optical transmission module portion of an optical disk device or an optical transmission system. The present invention also relates to an optical disc apparatus and an optical transmission module provided with such a semiconductor laser element.

  Semiconductor laser elements are widely used in optical disk devices and optical transmission systems. In particular, a semiconductor laser element called a ridge embedded type is known as a laser element having high reliability and capable of operating with low power consumption. However, the ridge buried type semiconductor laser device has a second time for forming a current confinement layer in addition to the first crystal growth step performed for forming a semiconductor stack including an active layer and a cladding layer in the manufacturing process. The crystal growth step and the third crystal growth step for forming the contact layer are required, and the manufacturing process must be performed through a complicated process. Therefore, the ridge buried type semiconductor laser device has a problem that its yield is low and its manufacturing cost is high.

  Therefore, as a semiconductor laser device that can be manufactured more simply and at low cost, a ridge waveguide semiconductor laser device that has a ridge portion on an active layer and can be manufactured by a single crystal growth process is taught in the prior art. (For example, refer to Japanese Patent Laid-Open No. 4-111375 of Patent Document 1).

  FIG. 16 is a schematic cross-sectional view showing a laminated structure of a ridge waveguide semiconductor laser element according to Patent Document 1. The ridge waveguide semiconductor laser device 600 is manufactured as follows.

  First, an n-InGaP lower cladding layer 602, an InGaAs / GaAs strained quantum well active layer 603, a p-InGaP upper cladding layer 604, and a p- layer are formed on an n-GaAs substrate 601 by MOCVD (metal organic chemical vapor deposition). InGaAs contact layers 605 are sequentially stacked. Then, etching is performed from the upper surface of the p-InGaAs contact layer 605 to a depth in the middle of the p-InGaP upper cladding layer 604 by a technique such as photolithography to form a mesa serving as a ridge portion. Thereafter, Ti / Pt / Au is sequentially deposited as the p-type metal electrode layer 606, and Au—Ge—Ni / Au is sequentially deposited as the n-type metal electrode layer 607.

  In the ridge waveguide laser element manufactured as described above, a Schottky junction 608 is formed between the upper cladding layer 604 and the p-type metal electrode layer 606. Therefore, current can flow only between the p-type electrode layer 606 and the contact layer 605, and current confinement can be performed.

As described above, the conventional and conventional ridge-embedded semiconductor laser device requires a total of three crystal growth steps and a complicated manufacturing process. However, the conventional ridge-waveguide semiconductor laser device according to Patent Document 1 is required. There is only one crystal growth step. Further, since the ridge waveguide semiconductor laser element of Patent Document 1 uses a Schottky junction without using an inorganic insulating film for current confinement, its element structure is simple and manufactured at a very low cost. can do.
Japanese Patent Laid-Open No. 4-111375 (FIG. 1)

  However, the ridge waveguide semiconductor laser element of Patent Document 1 cannot realize a low threshold current and a high output operation. The biggest reason for this is that the Schottky junction has poor reliability and current confinement is insufficient, and the leakage current cannot be sufficiently reduced particularly when the ridge is formed into a fine stripe. That is, if the semiconductor layer and the metal layer are simply bonded, the Schottky barrier formed at the bonded portion does not always have a sufficient withstand voltage with respect to the voltage required for driving the semiconductor laser element. Because there is no. Since the semiconductor laser device according to Patent Document 1 has no margin in withstand voltage, the current confinement property becomes unstable for each manufactured laser device, and the production yield is lowered. If the laser element is operated for a long period of time, current leakage easily occurs and the element characteristics are deteriorated.

  In view of the problems in the prior art as described above, the present invention provides a semiconductor laser device capable of obtaining a high oscillation efficiency and having a low power consumption operation with a sufficient current confinement capability by a low-cost manufacturing method. The purpose is that. Another object of the present invention is to provide an optical disk device and an optical transmission module using such a semiconductor laser element.

  According to one aspect of the present invention, a first conductivity type lower cladding layer, an active layer, a second conductivity type first upper cladding layer containing Al, and a striped ridge are formed on a first conductivity type semiconductor substrate. A ridge waveguide semiconductor laser element in which a second conductivity type second upper cladding layer and a second conductivity type contact layer are sequentially provided, wherein the electron affinity of the first upper cladding layer is χ1 and the forbidden band width Where Eg1 is the electron affinity of the contact layer and χ2 and the forbidden band width is Eg2, when the first conductivity type is n-type and the second conductivity type is p-type, the relationship of (χ1 + Eg1)> (χ2 + Eg2) When the first conductivity type is p-type and the second conductivity type is n-type, the relationship of χ1 <χ2 is satisfied, and the upper surface of the first upper cladding layer is oxidized in a region other than immediately below the ridge. A formed oxide layer is provided and Contact layer on top of di, is characterized in that it comprises at least one side of the ridge, and a metal electrode layer covering directly continuous over the oxide layer.

Note that the second conductivity type doping concentration in the contact layer is 1 × 10 ¹⁸ cm ⁻³ or more, and the region of the first upper clad layer that is in contact directly under the oxide layer has the second conductivity type doping concentration. A lightly doped region of 1 × 10 ¹⁷ cm ⁻³ or less is preferable. In the first upper cladding layer, a doped region of the second conductivity type having a doping concentration greater than 1 × 10 ¹⁷ cm ⁻³ is formed between the lightly doped region and the active layer. preferable.

  The upper surface layer of the contact layer preferably does not contain Al. The Al composition ratio in the group III element on the upper surface of the first upper cladding layer is preferably larger than 0.45. The thickness of the oxide layer is preferably 2 nm or more and 20 nm or less.

  The second upper cladding layer is preferably made of a material that can be selectively etched with respect to the first upper cladding layer.

  In the first upper cladding layer, an oxidation stop layer made of a semiconductor having an Al composition ratio lower than that of the first upper cladding layer or not containing Al is inserted, and the oxide layer is oxidized in the first upper cladding layer. It is preferably formed by oxidizing the upper part of the stop layer. The Al composition ratio in the group III element on the upper surface of the first upper cladding layer is preferably 0.9 or more.

According to another aspect of the present invention, there is provided a method for manufacturing a semiconductor laser device, comprising: a first conductivity type lower clad layer; an active layer; and a second conductivity type first layer including Al on a first conductivity type semiconductor substrate. A step of sequentially forming an upper cladding layer, a second conductivity type second upper cladding layer, and a second conductivity type contact layer not containing Al; and removing the second upper cladding layer and a part of the contact layer Forming a stripe-shaped ridge, partially exposing the upper surface of the first upper cladding layer in a region excluding the ridge, and oxidizing the exposed upper surface of the first upper cladding layer in a region excluding the region immediately below the ridge; Forming an oxide layer, and forming a contact layer on the top of the ridge, at least one ridge side surface of the ridge, and an electrode layer that directly covers the metal layer on the oxide layer. Including first The first conductivity type is n-type and the second conductivity type is p-type when the electron affinity of the lad layer is χ1 and the forbidden band width is Eg1, the electron affinity of the contact layer is χ2 and the forbidden band width is Eg2. Satisfies the condition of (χ1 + Eg1)> (χ2 + Eg2), and satisfies the condition of χ1 <χ2 when the first conductivity type is p-type and the second conductivity type is n-type.

  In the step of forming the first cladding layer, an oxidation stop layer made of a III-V group semiconductor having an Al composition ratio lower than that of the first upper cladding layer or not containing Al is included in the first upper cladding layer. In the step of providing and forming the oxide layer, it is preferable to form the oxide layer by oxidizing the layer above the oxidation stop layer in the first upper cladding layer.

  In the step of partially exposing the upper surface of the first upper cladding layer by forming a ridge, when the upper surface of the first upper cladding layer is exposed, the exposed surface is brought into contact with a liquid or gas having oxidizing properties. It is preferable to form an oxide layer. For this purpose, the Al composition ratio in the group III element in the uppermost portion of the first upper cladding layer is preferably 0.9 or more.

  In the step of partially exposing the upper surface of the first upper cladding layer by forming a ridge, a stripe-shaped etching mask is formed on the contact layer, and regions other than the mask are sequentially removed from the upper layer by etching. In the final etching, the upper surface of the first upper cladding layer is exposed using a liquid etching solution containing hydrogen peroxide, and then the exposed surface is directly contacted with the etching solution to form an oxide layer. It is preferable.

  By using the semiconductor laser element according to the present invention as a light source as described above, it is possible to provide an optical disc apparatus and an optical transmission module with few failures even in a long-term operation at a low cost.

  In the ridge waveguide semiconductor laser device of the present invention, the current blocking ability in the region other than the ridge is improved and the current can be stably confined in the ridge by a new and simple structural modification compared to the conventional ridge waveguide semiconductor laser device. . Therefore, the ridge waveguide semiconductor laser device of the present invention can oscillate with a low threshold current and has a high oscillation efficiency, so that it can operate at a high output with a low power consumption, and is high by a low cost manufacturing method with a small number of steps. Can be provided in yield. In addition, the optical disk apparatus using the semiconductor laser element of the present invention is configured at a lower cost than the conventional optical disk apparatus and has fewer failures in long-term operation. Furthermore, the optical transmission module using the semiconductor laser element of the present invention is also configured at a lower cost than the conventional optical transmission module and has fewer failures in long-term operation.

(Embodiment 1)
FIG. 1 is a schematic cross-sectional view showing a stacked structure of a ridge waveguide semiconductor laser element according to Embodiment 1 of the present invention. In the drawings of the present application, the same reference numerals represent the same or corresponding parts. In addition, dimensional relationships such as thickness, length, and width in the drawings are appropriately changed for clarity and simplification of the drawings, and do not represent actual dimensional relationships.

In the semiconductor laser device 100 of FIG. 1, on an n-GaAs substrate 101, an n-GaAs buffer layer 102, an n-Al _0.45 Ga _0.55 As lower cladding layer 103, an n-Al _0.4 Ga _0.6 As lower guide layer 104, multiple layers The strained quantum well active layer 105, the p-Al _0.4 Ga _0.6 As upper guide layer 106, the p-Al _0.5 Ga _0.5 As first upper cladding layer 107, and the lightly doped p-Al _0.5 Ga _0.5 As upper cladding layer 108 are sequentially stacked. Has been.

A p-In _0.1568 Ga _0.8432 As _0.4 P _0.6 etching stop layer 111 and a p-Al _0.5 Ga _0.5 As second upper cladding are formed on the lightly doped upper cladding layer 108 so as to form a ridge 120 having a forward mesa stripe shape. A layer 112, a p-GaAs contact layer 113, and a p ⁺ -GaAs contact layer 114 are provided.

  Here, the upper surface layer of the lightly doped upper cladding layer 108 is converted to the oxide layer 108b in the region 121b other than the ridge formation region 121a. The ridge side surface portion of the second upper cladding layer 112 is also converted into the oxide layer 112b. A p-type electrode layer 115 made of a multilayer metal thin film of Ti / Pt / Au is provided on the top and side surfaces of the ridge 120 and the oxide layer 108b.

  In the schematic cross-sectional views of FIGS. 2 to 4, the manufacturing method of the ridge waveguide semiconductor laser device of FIG. 1 is illustrated.

First, as shown in FIG. 2, an n-GaAs buffer layer 102 (thickness 0.5 μm, Si doping concentration 7.2 × 10 ¹⁷ cm ⁻³ ), n is formed on the (100) plane of the n-GaAs substrate 101. -Al _0.45 Ga _0.55 As lower cladding layer 103 (thickness 1.88 μm, Si doping concentration 5.4 × 10 ¹⁷ cm ⁻³ ), n-Al _0.4 Ga _0.6 As lower guide layer 104 (thickness 0.09 μm, Si Doping concentration 5.4 × 10 ¹⁷ cm ⁻³ ), multiple strained quantum well active layer 105, p-Al _0.4 Ga _0.6 As upper guide layer 106 (thickness 0.09 μm, Zn doping concentration 1.35 × 10 ¹⁸ cm ^{− 3} ), p-Al _0.5 Ga _0.5 As first upper cladding layer 107 (thickness 0.2 μm, Zn doping concentration 1.35 × 10 ¹⁸ cm ⁻³ ), low-doped p-Al _0.5 Ga _0.5 As upper cladding layer 108 (Thickness 0.2 μm, Zn Doping concentration ^{1 × 10 17 cm -3),} p-In 0.1568 Ga 0.8432 As 0.4 P 0.6 etch stop layer 111 (thickness 4 nm, Zn doping concentration ^{2.4 × 10 18 cm -3),} p-Al 0.5 Ga 0.5 As second upper cladding layer 112 (thickness 1.28 μm, Zn doping concentration 2.4 × 10 ¹⁸ cm ⁻³ ), p-GaAs first contact layer 113 (thickness 0.2 μm, Zn doping concentration 3 × 10 ¹⁸⁾ cm ⁻³ ) and p ⁺ -GaAs second contact layer 114 (thickness 0.3 μm, Zn doping concentration 1 × 10 ¹⁹ cm ⁻³ ) sequentially grown by MOCVD (metal organic chemical vapor deposition) Thus, a semiconductor laminated wafer is formed.

In the multi-strain quantum well active layer 105, an Al _0.15 Ga _0.85 As barrier layer (thicknesses 21.5 nm, 7.9 nm from the substrate 101 side) is formed on an Al _0.25 Ga _0.75 As lower intermediate layer (thickness 3.0 nm). And 3 layers of 21.5 nm) and In _0.072 Ga _0.928 As compressive strain quantum well layers (strain 0.51%, thickness 4.6 nm, 2 layers) are alternately laminated, and Al _0.25 Ga _0.75 As is formed thereon. An upper intermediate layer (thickness 3.0 nm) is further laminated.

  Next, a resist mask 130 (mask width 4.5 μm) is formed by photolithography on the region 121a (see FIG. 1) where the ridge 120 is to be formed, as shown in FIG. The resist mask 130 is formed to extend in a stripe shape along the <0-11> direction of the substrate crystal corresponding to the direction in which the ridge 120 to be formed extends.

  Then, as shown in FIG. 3, ridge formation outside regions on both sides of the resist mask 130 among the second upper cladding layer 112, the first contact layer 113, and the second contact layer 114 by etching using the resist mask 130. The portion 121b is removed by etching, and a forward mesastrip-shaped ridge 120 is formed immediately below the resist mask 130.

In this etching, first, as an etchant that etches the second upper cladding layer 112, the first contact layer 113, and the second contact layer 114, which are AlGaAs-based materials, but does not etch the InGaAsP-based etching stop layer 111, Use a mixed aqueous solution of sulfuric acid and hydrogen peroxide. At this time, since the etching rate of the second upper cladding layer 112 is slightly higher than that of the first contact layer 113 and the second contact layer 114, the overhang of the first contact layer 113 and the second contact layer 114 on the side surface of the ridge 120. Can do. Therefore, the overhang portions of the first contact layer 113 and the second contact layer 114 are removed with a mixed aqueous solution of ammonia and hydrogen peroxide. That is, the mixed aqueous solution of ammonia and hydrogen peroxide etches the first contact layer 113 and the second contact layer 114 made of GaAs, but is the second upper cladding layer 112 made of Al _0.5 Ga _0.5 As or an InGaAsP system. An etchant that does not etch the etching stop layer 111.

  Thereafter, the etching stop layer 111 is removed by etching in the outer ridge formation region 121b to expose the lightly doped upper cladding layer. In this etching, hydrochloric acid is used as an etchant that etches the InGaAsP-based etching stop layer 108 but does not etch the AlGaAs-based second upper cladding layer 112, the first contact layer 113, and the second contact layer 114. . The width of the lowermost portion of the ridge 120 finally formed is about 3 μm. When the etching is completed, the resist mask 130 is removed, and the semiconductor laminated wafer is washed with water and dried by nitrogen blowing or the like.

  Next, this wafer is put into a heating furnace in which water vapor flows, and a heat treatment is performed at 500 ° C. for 2 hours. As a result, as shown in FIG. 4, the oxide layer 108b is formed by oxidizing the surface of the lightly doped upper cladding layer 108, which is a layer containing Al, to a depth of about 3 nm. At the same time, an oxide layer 112b having the same thickness is also formed on the ridge side surface of the second upper cladding layer 112, which is a layer containing Al.

  Then, using an electron beam evaporation method, a metal thin film is laminated in the order of a Ti layer (thickness 50 nm), a Pt layer (thickness 50 nm), and an Au layer (thickness 300 nm), and the p-type electrode layer 115 is formed. Form (see FIG. 1).

Subsequently, the substrate 101 is ground by a lapping method from the lower surface side until a desired thickness (for example, about 100 μm) is reached. Then, using a resistance heating vapor deposition method, an AuGe alloy layer (88% Au-12% Ge, thickness 100 nm), an Ni layer (thickness 15 nm), and an Au layer (thickness 300 nm) are stacked in this order, An n-type electrode layer 116 on the lower surface side is formed (see FIG. 1). Further, the n-type metal electrode layer 116 is alloyed by heat treatment at 390 ° C. for 1 minute in an N ₂ atmosphere.

  Thereafter, the semiconductor laminated wafer including the substrate 101 is divided into a plurality of bars having a desired resonator length (for example, 500 μm) by cleavage. Then, the end face of the resonator is coated on the cleavage plane of each bar, and the bar is further divided into chips (500 μm × 250 μm). The divided chips are fixed on a stem (not shown) using In glue. An Au wire (not shown) for electrical connection with an external circuit is bonded on the p-type metal electrode layer 115, thereby completing a ridge waveguide semiconductor laser element.

If a current is passed between the p-type electrode 115 and the n-type electrode 116 of the ridge waveguide semiconductor laser device manufactured in this way, the lightly doped upper cladding layer 108 and the oxide layer 108b in the both side regions 121b of the ridge 120 are used. Between the p ⁺ -GaAs contact layer 114 and p ⁺ -GaAs contact layer 114, which is a high-concentration doping layer provided on the uppermost portion of the ridge 120. A current flows only through the ohmic junction with the mold metal electrode layer 115. As a result, current confinement is performed, and laser light oscillates just below the ridge 120 and is emitted from the cleavage plane.

  In the semiconductor laser device 100 of the first embodiment shown in FIG. 1, since the oxide layer 108b is formed between the p-type electrode layer 115 and the low-doped upper cladding layer 108, the region other than the ridge 120 is formed. A sufficient current blocking property can be obtained at 121b, and a current confinement structure that is stable against long-term thermal and electrical stress can be obtained. On the other hand, in the laser device structure of Patent Document 1 shown in FIG. 16, Schottky characteristics have instabilities due to interface defect levels that are difficult to avoid in manufacturing at the Schottky junction 608, and leakage current is generated at the junction. Is easy to flow. Therefore, the laser element of Patent Document 1 is likely to break down at a lower voltage due to the influence of long-term thermal and electrical stress. However, by providing the oxide layer 108b between the p-type metal electrode layer 115 and the lightly doped upper cladding layer 108 as in the first embodiment, current leakage at the Schottky junction can be reliably prevented. And stable current confinement ability can be obtained. The operation of such a Schottky junction will be described in more detail below.

First, in FIG. 5A, a schematic band structure diagram at a Schottky junction between a general metal and a p-type semiconductor is shown. In this figure, the horizontal axis represents the position in the direction perpendicular to the interface between the metal and the p-type semiconductor, and the vertical axis represents the electron energy. In addition, φm is the work function of a metal, χs is the electron affinity of the semiconductor, Eg the semiconductor forbidden band width, Ec the bottom of the conduction band of the semiconductor, Ev is the top of the semiconductor of the valence band and E _F is the Fermi level, Represents. Φ _B represents the height of the Schottky barrier, and φ _B = χs + Eg−φm. In such a band structure, when a voltage is applied so that the metal side is positive and the p-type semiconductor side is negative, current does not flow up to a higher voltage as φ _B increases.

In the current confinement structure by Schottky junction in Patent Document 1, the p-type metal electrode layer 606 is formed on the p-type upper cladding layer 604 and the contact layer 605 (see FIG. 16). Therefore, in order to confine the current in the contact layer 605 region at the top of the ridge, at least the Schottky barrier φ _B in the upper cladding layer 604 must be larger than the Schottky barrier φ _B in the contact layer 605. That is, it is necessary to increase (χs + Eg) in the upper cladding layer 604 as compared with (χs + Eg) in the contact layer 605.

  However, when a Schottky barrier is formed between the p-type metal electrode layer 606 and the upper clad layer 604, the upper clad layer is formed after the ridge is formed and before the p-type electrode layer 606 is deposited. The surface of 604 is exposed to the atmosphere or the like, where unstable oxide film formation or impurity adsorption occurs. Therefore, even if the p-type metal electrode layer 606 is deposited on the surface of the upper cladding layer 604, an interface defect level that is difficult to avoid in production is generated in the Schottky junction 608. In this Schottky portion 608, a leak current easily flows, and the laser element is likely to break down at a lower voltage due to long-term thermal and electrical stress.

On the other hand, the semiconductor laser device 100 of the first embodiment shown in FIG. 1 also forms a current confinement structure by a Schottky junction, so that (χs + Eg) in the lightly doped upper cladding layer 108 is (χs + Eg) in the second contact layer 114. ). In addition, in the semiconductor laser element 100, an oxide layer 108b is provided between the p-type electrode layer 115 and the low-doped upper cladding layer 108.

  A schematic band structure diagram at the Schottky junction between the metal and the p-type semiconductor in this case is shown in FIG. Here, the oxide layer 108b is formed by intentionally oxidizing the lightly doped upper cladding layer 108 as described above. Therefore, the oxide layer 108b can be formed as far as the inner side of the lightly doped upper cladding layer 108 as compared to the position of the interface state generated when the lightly doped upper cladding layer 108 is exposed to the atmosphere when the ridge 120 is formed. it can. That is, the oxide layer 108b is a stable insulating film formed by a sufficient oxidation process, and the leakage current due to the interface state is less likely to flow than when only the Schottky barrier exists. Further, the oxide layer 108b formed by oxidation from the surface of the lightly doped upper cladding layer 108 and the lightly doped upper cladding layer 108 are naturally not exposed to the atmosphere, and the interface state at the interface between these two is not affected. The rank is very few. Therefore, the leakage current is also reduced in the Schottky barrier between the oxide layer 108b and the lightly doped upper cladding layer 108.

  That is, it is considered that the current blocking capability is enhanced by a combination of the Schottky barrier having a reduced interface state and the barrier made of an insulating oxide layer that hardly generates a leak current with respect to the interface state. As a result, current leakage at the Schottky junction can be reliably prevented, and stable current confinement capability can be obtained.

In the semiconductor laser device 100 of the first embodiment, the doping amount of the lightly doped upper cladding layer 108 in the outer ridge formation region 121b is set to be low as 1 × 10 ¹⁷ cm ⁻³ . In the Schottky junction, the depletion layer (see FIG. 5) is thickened by reducing the doping amount on the semiconductor side, thereby making it difficult to generate a leak current in the Schottky barrier portion. In particular, by setting the doping amount to 1 × 10 ¹⁷ cm ⁻³ or less, the current blocking capability can be further improved, and a stable junction can be obtained even for long-term thermal and electrical stress. The second contact layer 114 at the top of the ridge has a high doping concentration of 1 × 10 ¹⁹ cm ⁻³ . In the second contact layer 114, by setting the doping concentration to 1 × 10 ¹⁸ cm ⁻³ or more, a good ohmic junction having a lower contact resistance with the p-type metal electrode layer 115 can be realized. it can.

Furthermore, in the semiconductor laser device 100 according to the first embodiment, the upper guide layer 106 and the first upper cladding layer 107 between the active layer 105 and the lightly doped upper cladding layer 108 are doped with a lightly doped upper cladding layer. It is set to 1.35 × 10 ¹⁸ cm ⁻³ , which is higher than that of 108. Here, since the lightly doped upper cladding layer 108 is located in the current path immediately below the ridge, the device resistance can be suppressed lower if the doping amount is set lower. Therefore, the lightly doped upper cladding layer 108 is suppressed to a necessary and sufficient thickness for current blocking characteristics, and the element resistance is increased by setting the doping amount to 1 × 10 ¹⁷ cm ⁻³ or more for the active layer side. It is possible to prevent the device characteristics from deteriorating.

  On the other hand, in the method for manufacturing the semiconductor laser device 100 according to the first embodiment, compared with the method for manufacturing the semiconductor laser device 600 of Patent Document 1, the leakage current is reduced only by adding an oxide layer forming step in the middle. The obtained semiconductor laser can be obtained. This oxide layer forming step is a simple step that is allowed to stand in heated steam for a certain period of time, and this provides a great advantage that the current confinement capability can be stabilized.

In the semiconductor laser device of the first embodiment, GaAs not containing Al is used for the second contact layer 114 at the top of the ridge. The second contact layer 114 is a current injection path and preferably has a low electrical resistance with the p-type metal electrode layer 115. However, in the oxidation process of the first embodiment, the surface of the second contact layer 114 is also exposed to water vapor. Therefore, in order to suppress the generation of oxide as much as possible on the surface of the second contact layer 114, it is desirable to use a group III-V semiconductor material (GaAs in this embodiment 1) that does not contain Al for the second contact layer. . As a result, the electrical resistance between the second contact layer 114 and the p-type electrode layer 115 can be kept low.

  Further, in the semiconductor laser device of the first embodiment, the Al composition ratio in the group III element is set to 0.5 in the Al-containing lightly doped upper cladding layer 108 which is the original material for forming the oxide layer 108b. Has been. If the Al composition ratio of the layer 108 is 0.45 or less, the oxidation of the semiconductor layer 108 is difficult to proceed and it is difficult to form a homogeneous oxide layer 108b. If the oxidation state of the oxide layer 108b is inhomogeneous, a uniform current blocking capability cannot be obtained and a leak current is generated. Therefore, in order to obtain a good current blocking capability, it is effective to set the Al composition ratio in the lightly doped upper cladding layer 108 to 0.45 or more. The upper limit of the Al composition ratio is not particularly limited, and an Al composition ratio of 1 is applicable.

  If the oxide layer 108b is formed uniformly by an oxidation process even with a small layer thickness, the leakage current is reduced as compared with a structure in which current is confined only by the Schottky barrier 608 as in Patent Document 1. It is possible to reduce. However, as a matter of course, the thicker the oxide layer 108b, the more remarkable the barrier effect. If the thickness of the oxide layer 108b is at least 2 nm or more, the barrier effect of the oxide layer is more stable, and current leakage can be reliably reduced.

  On the other hand, the oxide layer 108b is formed by oxidizing the semiconductor layer 108 having a high Al composition. The semiconductor layer can be grown in a lattice-matched manner with respect to the substrate, but if it is oxidized, the lattice constant changes greatly, so that distortion occurs between the semiconductor layer in the vicinity thereof. In the laser element 100 according to the first embodiment, since a part of the semiconductor layer 108 is changed to the oxide 108b, the adhesion between the semiconductor layer 108 and the oxide layer 108b is high and is easily affected by strain. Since the distance from the oxide layer 108b to the active layer 105 is relatively small, the distortion greatly affects the reliability and characteristics of the laser element. Therefore, in order to minimize the influence of the distortion, it is desirable that the oxide layer 108b does not have a thickness more than necessary for current confinement. More specifically, by setting the thickness of the oxide layer 108b to 20 nm or less, the influence of strain on the active layer 105 can be remarkably reduced, and a semiconductor laser element with little deterioration over a long period of time can be obtained.

  In the semiconductor laser device 100 of the first embodiment, an etching stop layer 111 is provided between the low-doped upper cladding layer 108 and the second upper cladding layer 112. The lightly doped upper cladding layer 108 and the second upper cladding layer 112 are AlGaAs having the same composition and have the same etching characteristics, whereas the etching stop layer 111 is InGaAsP and has different etching characteristics. Accordingly, it is possible to easily expose the upper surface of the lightly doped upper cladding layer 108 by forming a layer above the lightly doped upper cladding layer 108 in a ridge shape.

  In the above, the example in which the oxide layer is provided between the p-type semiconductor layer and the metal electrode layer has been described. However, in the laser element in which the p-type and the n-type are reversed, the n-type semiconductor layer and the metal electrode layer Of course, the same effect can be obtained even when an oxide layer is provided between them. In this regard, FIG. 6 similar to FIG. 5 schematically shows a band structure at the junction of the n-type semiconductor layer and the metal electrode layer.

FIG. 6A shows a band structure formed only of an n-type semiconductor layer and a metal electrode layer, and FIG. 6B shows a band when an oxide layer is interposed between the n-type semiconductor layer and the metal electrode layer. Represents the structure. The meaning of each symbol in FIG. 6 is the same as in FIG. Even in the case of an n-type semiconductor layer, an oxide layer can be formed at an effective position with respect to many interface states by oxidizing the surface, so that the same effect as in the case of a p-type semiconductor layer can be obtained. It is done. However, in the case of an n-type semiconductor layer, the Schottky barrier height φ _B has a relationship of φ _B = φm−χs. Therefore, as in the case of the p-type semiconductor layer, in order to increase the Schottky barrier φ _B related to the n-type first upper cladding layer compared to the n-type contact layer, the n-type low-doped upper cladding layer 108 It is necessary to make χs smaller than χs in the n-type second contact layer 114.

  Note that the present invention is not limited to the structure described above in Embodiment 1, and it is obvious that the thickness and material of each layer can be changed as appropriate.

(Embodiment 2)
FIG. 7 is a schematic cross-sectional view showing the laminated structure of the semiconductor laser device according to the second embodiment of the present invention. In the laser device 200 of FIG. 7, the lightly doped upper cladding layer 108 and the oxide layer 108b are lower in the lightly doped upper cladding layer 208, the oxidation stop layer 209, and the lightly doped upper cladding layer, compared with the laser device 100 in FIG. The only difference is that it is replaced by an upper portion 210. As the oxidation stop layer 209, a III-V group compound semiconductor that does not contain Al or has a low content can be used.

That is, in the second embodiment, an Al _0.5 Ga _0.5 As low-doped upper cladding layer lower portion 208 (thickness 0.2 μm, Zn doping concentration 1 × 10 ¹⁷ cm ⁻³ ) on the first upper cladding layer 107, p−. In _0.1568 Ga _0.8432 As _0.4 P _0.6 oxidation stop layer 209 (thickness 3 nm, Zn doping concentration 1 × 10 ¹⁷ cm ⁻³ ), and Al _0.5 Ga _0.5 As low-doped upper cladding layer 210 (thickness 3 nm, Zn doping concentration) 1 × 10 ¹⁷ cm ⁻³ ) is grown.

  Thereafter, when the ridge 120 is formed, the lower doped upper clad layer 210 is exposed in the region 121b other than the ridge forming region 121a. Then, in the ridge formation outer region 121b, the lower doped upper clad layer upper portion 210 is oxidized and converted into an oxide layer 210b (thickness 3 nm). At this time, in the ridge region 121a, the lower doped upper cladding layer upper surface portion 210a is left without being oxidized.

  Thus, the oxide layer 210b having a low refractive index can be reliably controlled to have a predetermined thickness, and the improved light emission characteristics of the laser element can be obtained with higher reproducibility. Further, with respect to the oxide layer 210b which is a strain generation source, the downward progress of oxidation can be reliably stopped at the position of the oxidation stop layer 209, and the influence of the strain can be controlled. This can prevent the progress of oxidation from the oxide layer 210b to the lower active layer 106 not only during the step of forming the oxide layer 210b but also when the semiconductor laser device 200 is operated for a long period of time. This produces an effect of improving the reliability of the laser element.

In the second embodiment, as compared with the first embodiment, the layer in contact with the oxide layer 210b in the region where current blocking is performed is changed from the low-doped lower cladding layer 108 to the oxidation stop layer 209. This oxidation stop layer 209 uses InGaAsP as a material lattice-matched to the GaAs substrate 101 and having a large χs + Eg. Further, in the oxidation stop layer 209, the doping amount is also reduced to 1 × 10 ¹⁷ cm ⁻³ , similarly to the low-doped lower cladding layer 208. This can also act to improve current blocking capability. Thus, in the second embodiment, a sufficient barrier is obtained in the current blocking region.

(Embodiment 3)
FIG. 8 is a schematic cross-sectional view showing a laminated structure of a semiconductor laser device according to Embodiment 3 of the present invention. In the laser device 300 of FIG. 8, compared with the laser device 200 of FIG. 7, the lower doped upper cladding layer 210 is replaced with an AlGaAs layer 310 having a higher Al composition ratio, the etching stop layer 111 is omitted, and ridge formation is performed. The only difference is that the oxide layer 310b is formed by oxidizing the high Al composition layer 310 in the outer region 121b.

  A method for manufacturing the semiconductor laser device 300 according to the third embodiment will be described below with reference to the schematic cross-sectional views of FIGS.

First, as shown in FIG. 9 similar to FIG. 2, also in the third embodiment, similarly to the second embodiment, a plurality of semiconductor layers are sequentially grown on the n-GaAs substrate 101 by MOCVD. However, at this time, in the third embodiment, the lower doped upper cladding layer 210 in the second embodiment is replaced with the p-AlAs layer 310 (thickness 5 nm, Zn doping concentration: 1 × 10 ¹⁷ m ⁻³ ). . Also in FIG. 9, the resist mask 130 is formed as in the case of FIG.

  Next, as shown in FIG. 10 similar to FIG. 3, the second upper cladding layer 112, the first contact layer 113, and the second contact layer 114 are formed on the ridges on both sides of the mask 130 by etching using the resist mask 130. The ridge 120 having a forward mesa stripe shape is formed immediately below the mask 130 by being removed in the non-formation region 121b.

  In this etching, first, the second upper cladding layer 112, the first contact layer 113, and the second contact layer 114, which are AlGaAs-based materials having an Al composition ratio of less than 0.6 in the group III element, are etched. A mixed aqueous solution of tartaric acid and hydrogen peroxide is used as an etchant that does not etch the high Al composition layer 310 that is an AlGaAs-based material having an Al composition ratio of 0.6 or more in the element. The width of the lowermost portion of the ridge 120 to be formed is about 3 μm. After the etching is completed, the resist mask 130 is removed. Then, the wafer including the substrate 110 is washed with water and dried by nitrogen blowing or the like.

  In the etching process as described above, the exposed portion of the high Al composition layer 310 is oxidized between the time when the ridge 120 is formed and the high Al composition layer 310 is exposed in the outer region 121b of the ridge until the time of washing with water. As shown, the oxide layer 310b is formed. This is because the high Al composition layer 310 is a material containing a very large amount of Al and is easily oxidized from the surface by being in contact with an etching solution containing hydrogen peroxide water, moisture, or the like. Since the high Al composition layer 310 is about 5 nm thin, the oxidation proceeds from the surface of the high Al composition layer 310 to the interface with the oxidation stop layer 209 below and stops.

  Thereafter, also in the third embodiment, as in the first embodiment, formation of the p-type metal electrode 115, grinding of the substrate 101, formation of the n-type metal electrode 116 and alloy processing, cleavage from the wafer to the bar. Then, the semiconductor laser 300 is completed by performing chip division, fixing to the stem, and wire bonding.

  If current is passed between the p-type electrode 115 and the n-type electrode 116 of the fabricated semiconductor laser device of the third embodiment (see FIG. 8), the oxidation stop layer 209 and the oxide layer in the outer ridge region 121b Current is cut off at the junction between 310b and the p-type electrode layer 115, and the ohmic contact between the second contact layer 114, which is the uppermost semiconductor layer of the ridge 120, and the p-type metal electrode layer 115 is interrupted. Current flows only through the junction. In this way, current confinement is performed, and laser light oscillates just below the ridge 120 and is emitted from the cleavage plane.

  As described above, the semiconductor laser device of the third embodiment also includes an oxide layer between the metal electrode layer and the semiconductor layer. By having such a configuration, the third embodiment also has a sufficient current blocking property in the region outside the ridge due to the same effects as the first and second embodiments, and can withstand long-term thermal and electrical stress. A stable current confinement structure can be obtained. That is, by providing a thin oxide layer between the metal electrode layer and the semiconductor layer, current leakage can be reliably prevented, and stable current confinement capability can be obtained.

  In the semiconductor laser device of the third embodiment, the semiconductor layer 310 to be oxidized is AlAs and the Al composition ratio is very large as compared with the second embodiment. Therefore, in the third embodiment, the semiconductor layer 310 is oxidized very easily and uniformly, and the current blocking capability can be more stably exhibited. Further, since the oxidation stop layer 209 is provided under the high Al composition layer 310, the oxidation is surely stopped at the interface between them.

  Further, in the third embodiment, the high Al composition layer 310 is also used as an etching stop layer when the ridge 120 is formed. Since the tartaric acid-based etchant has a characteristic of etching a layer having a low Al composition ratio but not etching a layer having a high Al composition ratio, the Al composition ratio of the second upper cladding layer 112 is set lower than that of the high Al composition layer 310. By doing so, the etching during the formation of the ridge 120 can be reliably stopped at the high Al composition layer 310. That is, since the high Al composition layer 310 also has a function of stopping etching when forming the ridge, simultaneously with the completion of the formation of the ridge 120, the region to be oxidized in the high Al composition layer 310 is exposed, and the laser element The manufacturing process can be simplified. In addition, by performing such selective etching, the distance between the active layer that greatly affects the light distribution of the ridge waveguide semiconductor laser element and the surface outside the ridge region can be controlled with good reproducibility. Can stabilize the far-field image characteristics.

  As described above, the oxidation of the high Al composition layer 310 in the third embodiment is performed using contact with an etching solution containing hydrogen peroxide or moisture in the step of forming the ridge 120. That is, the high Al composition layer 310 of AlAs is a layer that is very easy to oxidize, and its thickness is as thin as 5 nm. Therefore, the etching process and the oxidation process using hydrogen peroxide water or water as in the third embodiment are substantially performed. Thus, the oxide layer 310b can be formed simultaneously. Thus, a semiconductor laser device having a high current confinement capability can be obtained with substantially the same number of steps as compared with the case of Patent Document 1.

  Needless to say, the present invention is not limited to the third embodiment, and after the semiconductor layer to be oxidized is exposed in the ridge formation process, the exposed semiconductor layer is a liquid such as an etching solution, an etching gas, water, and air. Contact with gas. Therefore, by selecting a material that is easily oxidized by either of these liquids or gases and forming the exposed semiconductor layer, the ridge formation step and the oxidation step can proceed substantially simultaneously. In addition, the semiconductor laser device can be fabricated with substantially the same number of steps as in Patent Document 1. In particular, by setting the Al composition ratio in the group III element to 0.9 or more as the high Al composition layer 310, oxidation by contact with an oxidizing liquid or gas can be performed more uniformly, and the formed oxidation The material layer can provide a significantly stable and high current blocking capability. In addition, since the hydrogen peroxide solution has a high ability to oxidize a semiconductor layer containing Al, the semiconductor layer to be oxidized is exposed by etching by using an etching solution containing hydrogen peroxide solution for the last etching at the time of ridge formation. At that time, the etching can be performed as it is. That is, the ridge formation step and the oxidation step can be easily performed almost simultaneously.

Of course, in order to oxidize the exposed semiconductor layer more reliably and uniformly, a dedicated process for oxidation can be provided after the ridge formation is completed. For example, the wafer may be put into a 300 ° C. heating furnace in which water vapor is flowed for 5 minutes to perform heat treatment. In the third embodiment, the exposed semiconductor layer is A.
It is lAs and has a very high Al composition ratio compared to Al _0.5 Ga _0.5 As, which is the exposed semiconductor layer of Embodiment 1, and can be easily oxidized. Therefore, for the oxidation of the exposed semiconductor layer in the third embodiment, a heat treatment at a much lower temperature and in a short time is sufficient as compared with the exposed semiconductor layer in the first embodiment. The AlAs semiconductor layer 310 can be more uniformly oxidized up to the interface with the oxidation stop layer 209 immediately below.

  When the high Al composition layer 310 is oxidized by the method described above, the oxidation proceeds not only in the thickness direction approaching the active layer 105 but also in the horizontal direction toward the ridge region 121a. However, since the very thin AlAs semiconductor layer 310 is oxidized in the horizontal direction, the oxidation using the etching solution and moisture does not proceed so deeply as in the case of the third embodiment, and the depth is the end of the ridge 120. To about 10 to 20 nm. Further, even when the wafer is put into a 300 ° C. heating furnace in which water vapor flows as described above and the heat treatment is performed for 5 minutes, the depth of oxidation into the ridge region 121a is about 50 nm. This is 1/50 or less compared with the width of 3 μm of the ridge, which is very small and does not substantially affect the distribution of current flowing into the active layer 105 through the ridge region 121a.

  If the heat treatment described above is performed at a higher temperature for a longer time, the oxidation proceeds in the horizontal direction for a long time, and a narrower current confinement region is formed in the ridge region 121a. In this horizontal oxidation, if the oxidation is performed for a long time at a high temperature, it is difficult to make the oxidation length constant even if the oxidation is performed under the same conditions, and the width of the current confinement region in the ridge region 121a is different for each element. Therefore, stable laser element characteristics cannot be obtained. Therefore, when heat treatment is used for more reliable oxidation in the third embodiment, oxidation by heat treatment is performed at the time when the oxide layer 310b having a sufficient thickness for blocking current in the outside ridge region 121b is formed. And the horizontal oxidation extending into the ridge region 121a is substantially prevented.

(Embodiment 4)
FIG. 12 is a schematic block diagram showing an example of an optical disc apparatus according to Embodiment 4 of the present invention. The optical disk device 400 includes a semiconductor laser element 402 that can write data on the optical disk 401 and reproduce the written data. This semiconductor laser element 402 is similar to the semiconductor laser element of the third embodiment, and differs only in that an AlGaAs-based semiconductor is used for its active layer and guide layer and oscillates in a wavelength of 780 nm band.

  At the time of writing in the optical disk device 400, the signal light emitted from the semiconductor laser element 402 is collimated by the collimator lens 403. The parallel light passes through the beam splitter 404, the polarization state is adjusted by the λ / 4 polarizing plate 405, is collected by the objective lens 406, and is irradiated onto the optical disc 401. At the time of reading, a laser beam not carrying a data signal is irradiated on the optical disc 401 along the same path as that at the time of writing, and is reflected by the surface of the optical disc 401 on which data is recorded. The reflected light passes through the laser light irradiation objective lens 406 and the λ / 4 polarizing plate 405 and is then reflected by the beam splitter 404 to change the angle by 90 °. The light enters the light receiving element 408 for detection. The read data signal is converted into an electric signal in the signal detecting light receiving element 408 corresponding to the intensity of the incident laser beam, and is reproduced by the signal light reproducing circuit 409 to the original signal.

  In the optical disk apparatus according to the fourth embodiment, since the semiconductor laser element 402 that can be manufactured at a low cost and has a stable current confinement capability is used, an optical disk apparatus that has fewer failures even in the long-term operation than the conventional optical disk apparatus is inexpensive. Can be provided.

Here, the example in which the semiconductor laser element 402 having the same configuration as that of the third embodiment except for the active layer and the guide layer is applied to the recording / reproducing optical disc device has been described. However, an optical disc recording device using the same wavelength 780 nm band and Needless to say, the present invention is also applicable to an optical disk reproducing apparatus and an optical disk apparatus using another wavelength band (for example, 650 nm band).

(Embodiment 5)
FIG. 13 is a schematic cross-sectional view of an optical transmission module 500 used in an optical transmission system according to Embodiment 5 of the present invention. FIG. 14 is an enlarged view showing the vicinity of the light source of the optical transmission module 500, and FIG. 15 is a schematic perspective view showing an optical transmission system using the optical transmission module 500.

  In the fifth embodiment, the InGaAs semiconductor laser element (laser chip) 300 having an oscillation wavelength of 890 nm according to the third embodiment is used as a light source, and a silicon (Si) pin photodiode element is used as the light receiving element 521. By providing the same optical transmission module 500 on both sides (for example, a terminal and a server) that perform communication, an optical transmission system that transmits and receives optical signals between both optical transmission modules 500 can be configured.

  As shown in FIG. 13, the optical transmission module 500 includes a light emitting unit 510 for data transmission and a light receiving unit 520 for data reception. The light emitting unit 510 includes a semiconductor laser element 300 and a transmission lens 512 that shapes the transmitted light above the semiconductor laser element 300. The light receiving unit 520 includes a photodiode element 521 and a receiving lens 522 that collects received light from the outside. The semiconductor laser element 300 and the photodiode element 521 are mounted on a circuit board 501 and connected to a wiring pattern (not shown) on the circuit board 501 by wires 517 and 526, respectively. An integrated circuit element 530 for operating the light transmission module 500 is incorporated at a position between the light emitting unit 510 and the light receiving unit 520.

  The upper surface of the circuit board 501 is covered with an epoxy resin mold 502 that is transparent to light having a wavelength of 850 to 900 nm so as to cover the semiconductor laser element 300, the photodiode element 521, and the integrated circuit element 530. Here, the epoxy resin mold 502 itself includes a transmission lens 512 and a reception lens 522 based on its shape. That is, the epoxy resin mold 502 is integrally molded so that the transmission lens 511 is disposed above the semiconductor laser element 300 and the reception lens 522 is disposed above the photodiode 521.

  Referring to FIG. 14 in which the light emitting portion 510 is enlarged, a concave portion 513 having a depth of about 300 μm is formed on the circuit board 501, and a mounting surface 514 which is a metal film is formed on the surface thereof. Next to the recess 513, a wire bond pad 515 is formed as a part of the wiring pattern on the circuit board 501. At the bottom of the recess 513, the semiconductor laser element 300 is mounted so that the n-type electrode on the lower surface thereof is in contact with the mounting surface 514. The p-type electrode on the upper surface of the semiconductor laser element 300 is electrically connected to the wire bond pad 515 by a wire 517.

  In the recess 513, the liquid silicone resin 516 is filled and cured as a light diffusion portion. In the silicone resin 516, a filler that diffuses light (for example, polystyrene particles, average particle diameter of 1 μm (not shown)) is mixed. That is, an appropriate amount of liquid silicone resin 516 is dropped into the recess 513 and remains in the recess 513 due to the surface tension to cover the semiconductor laser element 300. The liquid silicone resin 516 after the dripping is heated at 80 ° C. for about 5 minutes, and is cured until it becomes a jelly. A transmission lens 512 is formed by covering the cured silicone resin 516 with an epoxy resin mold 502.

  When the semiconductor laser element 300 is driven in the light emitting portion 510, light is emitted in the horizontal direction from the end face of the laser element 300 as indicated by an arrow in FIG. 15, and the emitted light enters the silicone resin 516. The process proceeds while being diffused by the filler in the resin. And it reflects on the mounting surface 514 of the metal film in the side part of the recessed part 513, and goes upwards. Thereafter, the light enters the transparent epoxy resin mold 502 from the upper surface of the silicone resin 516, is further shaped by the transmission lens 512, and is emitted to the outside.

  Here, since the emission point of the semiconductor laser element 300 is very small, having a diameter of several μm and the emission intensity is high, there is a safety problem for eyes if the laser light is emitted to the outside as it is. Since the laser beam is diffused and the emission point seen from the outside appears to spread on the upper surface of the silicone resin 516, there is no safety problem. By adopting such a configuration of the light emitting unit 510, it is possible to use the semiconductor laser element 300 in place of the conventional light emitting diode element.

  That is, the optical transmission module of Embodiment 5 can be manufactured at low cost by using the semiconductor laser device of the present invention, and the failure is small even in long-term operation. Further, by providing a pair of the same optical transmission modules 500 on both sides performing communication, an optical transmission system that transmits and receives an optical signal between both optical transmission modules 500 can be configured.

  FIG. 15 is a schematic perspective view showing an example of an optical transmission system using a pair of optical transmission modules 500a and 500b. In this optical transmission system, a base station 541 installed on the ceiling of a room includes an optical transmission module 500a, and a personal computer 542 includes the same type of optical transmission module 500b. An optical signal emitted with information from the light source of the optical transmission module 500b on the personal computer 542 side is received by the light receiving element of the optical transmission module 500a on the base station 541 side. The optical signal emitted from the light source of the optical transmission module 500a on the base station 541 side is received by the light receiving element of the optical transmission module 500b on the personal computer 542 side. In this way, data communication using light (infrared rays) can be realized.

  As described above, according to the present invention, it is possible to provide a semiconductor laser device capable of producing a high oscillation efficiency and having a low power consumption operation by having a sufficient current confinement capability by a low-cost manufacturing method. In addition, according to the present invention, an optical disk device and an optical transmission module using such a semiconductor laser element can also be provided.

1 is a schematic cross-sectional view showing a laminated structure of a semiconductor laser element according to Embodiment 1 of the present invention. FIG. 2 is a schematic cross-sectional view for explaining a manufacturing process of the semiconductor laser element of FIG. 1. FIG. 3 is a schematic cross-sectional view for explaining a manufacturing step subsequent to FIG. 2. FIG. 4 is a schematic cross-sectional view for explaining a manufacturing process subsequent to FIG. 3. It is a typical energy band structure figure in the Schottky junction part of a metal and a p-type semiconductor. It is a typical energy band structure figure in the Schottky junction part of a metal and an n-type semiconductor. It is typical sectional drawing which shows the laminated structure of the semiconductor laser element by Embodiment 2 of this invention. It is typical sectional drawing which shows the laminated structure of the semiconductor laser element by Embodiment 3 of this invention. FIG. 9 is a schematic cross-sectional view for explaining a manufacturing step for the semiconductor laser element of FIG. 8. FIG. 10 is a schematic cross-sectional view for explaining a manufacturing step subsequent to FIG. 9. It is typical sectional drawing for demonstrating the manufacturing process following FIG. It is a typical block diagram which shows the optical disk apparatus by Embodiment 4 of this invention. It is typical sectional drawing which shows the optical transmission module used for the optical transmission system by Embodiment 5 of this invention. FIG. 14 is a schematic cross-sectional view that enlarges and displays the vicinity of a semiconductor laser element in the optical transmission module of FIG. It is a typical perspective view which shows an example of the optical transmission system by Embodiment 5 of this invention. FIG. 10 is a schematic cross-sectional view for explaining a laminated structure of a semiconductor laser element and a manufacturing method thereof according to Patent Document 1.

Explanation of symbols

101 n-GaAs substrate, 102 n-GaAs buffer layer, 103 n-AlGaAs lower cladding layer, 104 n-AlGaAs lower guide layer, 105 multiple strain quantum well active layer, 106 p-AlGaAs upper guide layer, 107 p-AlGaAs second 1 upper cladding layer, 108 p-AlGaAs lightly doped upper cladding layer, 108 b oxide layer, 111 p-InGaAsP etching stop layer, 112 p-AlGaAs second upper cladding layer, 112 b oxide layer, 113 p-GaAs contact layer, 114 p + -GaAs contact layer, 115 p-type metal electrode layer, 116 n-type metal electrode layer, 120 ridge, 121a ridge formation region, 121b ridge formation outside region, 130 resist mask, 208
p-AlGaAs lightly doped upper cladding layer lower part, 209 oxidation stop layer, 210, 210a
p-AlGaAs lightly doped upper cladding layer surface, 210b oxide layer, 310, 310a AlAs high Al composition layer, 310b oxide layer, 400 optical disk device, 401 optical disk, 402 semiconductor laser element, 403 collimator lens, 404 beam splitter, 405 λ / 4 polarizing plate, 406 objective lens, 407 objective lens for light receiving element, 408 light receiving element for signal detection, 409 signal light reproduction circuit, 500, 500a, 500b optical transmission module, 501 circuit board, 510 light emitting unit, 512 sending Trust lens, 513
Recessed portion, 516 silicone resin, 517 wire, 520 light receiving portion, 521 photodiode, 522 receiving lens, 526 wire, 530 integrated circuit element, 514 mounting surface, 515 wire bond pad, 541 base station, 542 personal computer, 601 n− GaAs substrate, 602 n-InGaP lower cladding layer, 603 InGaAs / GaAs strained quantum well active layer, 604 p-InGaP upper cladding layer, 605 p-InGaAs contact layer, 606 p-type metal electrode layer, 607 n-type metal electrode Layer, 608 Schottky junction.

Claims (16)

A second conductivity type second upper layer on which a first conductivity type lower cladding layer, an active layer, a second conductivity type first upper cladding layer containing Al, and a striped ridge are formed on a first conductivity type semiconductor substrate. A ridge waveguide semiconductor laser element in which a cladding layer and a second conductivity type contact layer are sequentially provided,
When the electron affinity of the first upper cladding layer is χ1 and the forbidden band is Eg1, the electron affinity of the contact layer is χ2 and the forbidden band is Eg2, the first conductivity type is n-type and the second When the conductivity type is p-type, the relationship of (χ1 + Eg1)> (χ2 + Eg2) is satisfied, and when the first conductivity type is p-type and the second conductivity type is n-type, the relationship of χ1 <χ2 is satisfied,
An oxide layer formed by oxidizing the upper surface of the first upper cladding layer is provided in a region except directly below the ridge,
A semiconductor laser device comprising: the contact layer at the top of the ridge; at least one side surface of the ridge; and a metal electrode layer that is directly coated on the oxide layer. The contact layer has a second conductivity type doping concentration of 1 × 10 ¹⁸ cm ⁻³ or more, and a region of the first upper cladding layer that is in contact with the oxide layer immediately below the oxide layer has a second conductivity type doping concentration. 2. The semiconductor laser device according to claim 1, wherein the semiconductor laser device is a lightly doped region of 1 × 10 ¹⁷ cm ⁻³ or less. In the first upper cladding layer, a doped region of a second conductivity type having a doping concentration greater than 1 × 10 ¹⁷ cm ⁻³ is formed between the lightly doped region and the active layer. 3. The semiconductor laser device according to claim 2, wherein   4. The semiconductor laser device according to claim 1, wherein the uppermost surface layer of the contact layer does not contain Al.   5. The semiconductor laser device according to claim 1, wherein an Al composition ratio in a group III element on the upper surface of the first upper cladding layer is larger than 0.45.   6. The semiconductor laser device according to claim 1, wherein a thickness of the oxide layer is 2 nm or more and 20 nm or less.   7. The semiconductor laser device according to claim 1, wherein the second upper cladding layer is made of a material that can be selectively etched with respect to the first cladding layer.   In the first upper cladding layer, an oxidation stop layer made of a semiconductor having a lower Al composition ratio than Al or not containing Al is inserted compared to the first upper cladding layer, and the oxide layer is formed on the first upper cladding layer. 8. The semiconductor laser device according to claim 1, wherein the semiconductor laser device is formed by oxidizing a portion of the cladding layer above the oxidation stop layer.   9. The semiconductor laser device according to claim 8, wherein an Al composition ratio in the group III element on the upper surface of the first upper cladding layer is 0.9 or more. A first conductivity type lower cladding layer, an active layer, a second conductivity type first upper cladding layer containing Al, a second conductivity type second upper cladding layer, and Al are formed on a first conductivity type semiconductor substrate. Sequentially forming a contact layer of a second conductivity type that does not include;
Removing the second upper cladding layer and a part of the contact layer to form a striped ridge, and partially exposing the upper surface of the first upper cladding layer in a region excluding the ridge;
Forming an oxide layer by oxidizing from the exposed upper surface of the first upper cladding layer in a region except directly under the ridge;
Forming a contact layer on top of the ridge, at least one side surface of the ridge, and an electrode layer that directly covers the metal layer on the oxide layer;
When the electron affinity of the first upper cladding layer is χ1 and the forbidden band width is Eg1, and the electron affinity of the contact layer is χ2 and the forbidden band width is Eg2, the first conductivity type is n-type and the second conductivity type. When p is p-type, the condition of (χ1 + Eg1)> (χ2 + Eg2) is satisfied, and when the first conductivity type is p-type and the second conductivity type is n-type, the condition of χ1 <χ2 is satisfied Manufacturing method of semiconductor laser device. In the step of forming the first cladding layer, an oxidation stop layer made of a III-V group semiconductor having an Al composition ratio lower than that of the first upper cladding layer or not containing Al is included in the first upper cladding layer. Provided,
11. The semiconductor according to claim 10, wherein in the step of forming the oxide layer, the oxide layer is formed by oxidizing a layer above the oxidation stop layer in the first upper cladding layer. A method for manufacturing a laser element.   In the step of forming the ridge and partially exposing the upper surface of the first upper cladding layer, when the upper surface of the first upper cladding layer is exposed, a liquid having an oxidizing property with respect to the exposed surface or 12. The method of manufacturing a semiconductor laser device according to claim 10, wherein the oxide layer is formed by contacting with a gas.   13. The method of manufacturing a semiconductor laser device according to claim 12, wherein an Al composition ratio in the group III element in the uppermost portion of the first upper cladding layer is 0.9 or more.   In the step of forming the ridge and partially exposing the upper surface of the first upper cladding layer, a striped etching mask is formed on the contact layer, and regions other than the mask are sequentially removed from the upper layer by etching. In the final etching, the upper surface of the first upper cladding layer is exposed using a liquid etching solution containing hydrogen peroxide, and then the exposed surface is directly brought into contact with the etching solution. 14. The method of manufacturing a semiconductor laser device according to claim 12, wherein an oxide layer is formed.   10. An optical disk apparatus using the semiconductor laser element according to claim 1.   An optical transmission module using the semiconductor laser device according to claim 1.

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