JP2005340576A - Semiconductor laser element and its manufacturing method, optical disk device as well as light transmission system - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a semiconductor laser element having long period reliability in addition to the capability of low threshold current and high output operation, further, abundant in the degree of freedom of optical characteristic designing and capable of coping with both of stabilized optical characteristics and cost reduction by simplification of manufacturing processes. <P>SOLUTION: At least an active layer 106, a p-type first semiconductor layer 109, and p-type second semiconductor layers 110, 111 are provided sequentially on an n-type semiconductor substrate 101. Further, p-type third semiconductor layers 112, 113, 114, which form a stripe-like ridge 130, are provided on the second semiconductor layer 111. The p-type doping density of the first semiconductor layer 109 is substantially uniform with respect to the direction of the layer. The p-type doping density of the immediately lower part 110a, 111a of the ridge of second semiconductor layers 110, 111 is higher than that of the side parts 110c, 111c of the ridge. An electrode layer 115 is provided with ohmic bonding between the summit of the ridge 130 while forming schottky junction between the ridge side 111c of the second semiconductor layer 111. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a semiconductor laser device and a manufacturing method thereof, and typically relates to a semiconductor laser device with high output and low power consumption used for an optical disk device, an optical transmission system, and the like and a manufacturing method thereof.

  The present invention also relates to an optical disc apparatus and an optical transmission system provided with such a semiconductor laser element.

  Among various semiconductor laser elements, the ridge-embedded semiconductor laser element can reduce the reactive current that does not contribute to laser oscillation because of its structure, and can separate the crystal regrowth interface during the element manufacturing process from the active layer. It is known as a structure capable of realizing high temperature operation and transverse mode stability while achieving both high reliability and low power consumption (low threshold current).

  In the ridge embedded structure, the portion exposed to the atmosphere during the manufacturing process is away from the active region during laser oscillation, so that excess light absorption is suppressed and reliability can be ensured.

  Further, by providing a current blocking layer having a small refractive index outside the ridge portion, it is possible to confine light in the horizontal direction only by the current confinement and the real refractive index. Since light absorption is not used for light confinement in the direction, waveguide loss during laser oscillation is small, and power consumption can be kept low.

  In manufacturing such a ridge-embedded semiconductor laser device, generally, crystal (re) growth is further performed twice on a semiconductor substrate on which an active layer or the like is previously laminated.

  However, performing crystal regrowth twice is a significant cost increase factor in producing a semiconductor laser device. Therefore, there is an idea of simplifying the manufacturing process by laminating an electrode layer that is Schottky-bonded to the cladding layer and ohmic-bonded to the contact layer (for example, Patent Document 1 (Japanese Patent Laid-Open No. 4-111375, particularly page 3). See FIG. 1).

  FIG. 10 shows a cross-sectional structure of the semiconductor laser element described in Patent Document 1. This semiconductor laser device is manufactured as follows. First, an n-InGaP cladding layer 402, an InGaAs / GaAs strained quantum well active layer 403, a p-InGaP cladding layer 404, and a p-InGaAs contact layer 405 are formed on an n-GaAs substrate 401 by metal organic chemical vapor deposition (MOCVD). Are sequentially stacked, and a part of the p-InGaP cladding layer 404 (parts on both sides in FIG. 10) is etched from the surface side to the middle by a technique such as photolithography to form a forward mesa-shaped ridge portion 408. Ti / Pt / Au is sequentially deposited as the p-side electrode 406, and Au—Ge—Ni / Au is sequentially deposited as the n-side electrode 407. As a result, a Schottky junction is formed between the p-side electrode 406 and the p-InGaP cladding layer 404, and an ohmic junction is formed between the p-side electrode 406 and the p-InGaAs contact layer 405. . When a current is passed between the p-side electrode 406 and the n-side electrode 407 of the device manufactured in this way, a current flows only through the ohmic junction, and current confinement is performed.

  With such a structure, a total of three crystal growth steps in a general ridge embedding structure can be performed once, and as a result, the number of manufacturing steps can be greatly reduced.

  However, in the semiconductor laser device that performs current confinement using the Schottky junction disclosed in Patent Document 1, it has a low threshold current (for example, 30 mA or less and exceeds 150 mW as realized in a semiconductor laser device having a general ridge buried structure). Like)), could not perform high power operation. Moreover, it has been difficult to design an element that meets the optical characteristic specifications required for various applications. Furthermore, the reliability of the Schottky junction is poor and long-term reliability has not been realized.

  The reason why the low threshold current and the high output operation could not be realized is that the current confinement property of the Schottky junction part is insufficient, and particularly the leakage current when the fine stripe structure is used cannot be sufficiently reduced. Can be mentioned.

  In addition, a configuration that can achieve both low element resistance and current confinement is not disclosed, and as a result, the element resistance increases, which is one factor that hinders high output operation.

Further, in order to ensure the current confinement properties (such as lattice-matched to GaAs) large energy discontinuity (barrier) Delta] E _V of the valence band using AlGaAs material system of InGaP or high mixed crystal cladding layer Inevitably, there was little room to change the refractive index of the cladding layer. For this reason, the degree of freedom in designing optical characteristics has been limited. Furthermore, the structure of the Schottky junction that is resistant to breakdown is not disclosed, and only a long-term reliability is lacking.

More specifically, in the above-described semiconductor laser device and the manufacturing method thereof in Patent Document 1, the layer thicknesses of both sides of the p-InGaP cladding layer 404 (portions left after being etched halfway) vary. Therefore, there is a problem that the optical characteristics of the laser element are greatly affected, and the far-field pattern (FFP) in the horizontal direction varies and the stability of the transverse mode is deteriorated. Furthermore, when the thickness of the InGaP layer varies, the characteristics of the Schottky junction formed thereon also vary, and current confinement may not be sufficiently performed. Further, since the refractive index of the InGaP layer under the lattice matching condition is uniquely determined, the optical design can be adjusted only by changing the thickness of the InGaP film, and the degree of freedom is small. Furthermore, by using InGaP on the p-cladding side, there is a problem that ΔEv increases and the efficiency of hole injection into the active layer is limited.
JP-A-4-111375

  Therefore, the object of the present invention is to enable low threshold current and high output operation, and to have long-term reliability, and to have a high degree of freedom in designing optical characteristics, and stable optical characteristics and a simplified manufacturing process. An object of the present invention is to provide a semiconductor laser device that achieves both cost reduction by making it easier.

In order to solve the above problems, a semiconductor laser device of the present invention is
An active layer laminated on a semiconductor substrate of the first conductivity type;
A first semiconductor layer stacked on the active layer and having a second conductivity type and a substantially uniform doping concentration;
The second conductivity type doping concentration of the portion immediately below the ridge, which is laminated on the first semiconductor layer, is of the second conductivity type, and is directly below the stripe-shaped ridge formed above, corresponds to the side of the ridge. A second semiconductor layer having a higher doping concentration of the second conductivity type in the side portion of the ridge
A third semiconductor layer of a second conductivity type formed on the second semiconductor layer and forming the stripe-shaped ridge;
An electrode layer is provided that forms an ohmic junction with the top of the ridge, and forms a Schottky junction with the ridge side portion of the second semiconductor layer.

  Here, “first conductivity type” refers to one conductivity type of n-type and p-type, and “second conductivity type” refers to the other conductivity type of n-type and p-type.

  The “active layer” refers to a layer that performs laser oscillation.

  The “substantially uniform” doping concentration of the second conductivity type of the first semiconductor layer in the layer direction means that it is uniform within the range of manufacturing variation.

  In addition, the second semiconductor layer having a high doping concentration in the second semiconductor layer may include not only the strict “directly under the ridge” but also the vicinity thereof. Here, the “vicinity” refers to a region where the second conductivity type dopant diffuses into the “ridge side portion” beyond the “directly under the ridge” by the heat treatment in the element forming process.

  In the semiconductor laser device of the present invention, like the semiconductor laser device of Patent Document 1, the crystal growth process can be completed once at the manufacturing stage. Therefore, as compared with a semiconductor laser device having a general ridge embedded structure, the manufacturing process is greatly reduced, and the semiconductor laser device is manufactured at a low cost.

  When a current is passed between the electrode layer and the substrate of the semiconductor laser device of the present invention, the current is cut off at the interface between the ridge side portion of the second semiconductor layer and the electrode layer, and the top of the ridge and the electrode layer Current flows only through the interface. Thereby, current confinement is performed.

  Here, in the semiconductor laser device according to the present invention, the doping concentration of the second conductivity type in the portion immediately below the ridge corresponding to the portion immediately below the ridge in the second semiconductor layer is equal to the side of the ridge in the second semiconductor layer. Is higher than the doping concentration of the second conductivity type in the side portion of the ridge corresponding to. That is, since the second conductivity type doping concentration in the ridge side portion of the second semiconductor layer is relatively low, it is favorable at the interface between the ridge side portion of the second semiconductor layer and the electrode layer. A Schottky junction is formed and the current is cut off. On the other hand, since the doping concentration of the second conductivity type in the portion immediately below the ridge of the second semiconductor layer is high, the series resistance immediately below the ridge serving as the current injection path is low. Therefore, it is possible to provide a highly reliable semiconductor laser device that achieves both a low threshold current and a high output operation. Furthermore, since it has the first semiconductor layer of the second conductivity type, it is possible to realize a stable optical characteristic with a high degree of design freedom for matching the optical characteristic.

  In addition, it is desirable that another electrode layer that forms an ohmic junction with this surface is provided on the surface of the semiconductor substrate opposite to the surface on which the layers are stacked. As a result, energization is easily performed between the two electrode layers through the active layer, and laser oscillation is realized.

In one embodiment, the second semiconductor layer has a second conductivity type doping concentration of 1 × 10 ¹⁷ cm ⁻³ or more in the portion immediately below the ridge of the second semiconductor layer, and the ridge side of the second semiconductor layer. It is preferable that the doping concentration of the second conductivity type in this part is 1 × 10 ¹⁷ cm ⁻³ or less.

According to the semiconductor laser device of the above embodiment, the second conductivity type doping concentration in the side portion of the ridge of the second semiconductor layer is 1 × 10 ¹⁷ cm ⁻³ or less. Since good current confinement can be exhibited with high reliability, low threshold current oscillation is possible. Further, since the second conductivity type doping concentration in the portion immediately below the ridge of the second semiconductor layer is 1 × 10 ¹⁷ cm ⁻³ or more, the series resistance of the current injection path is kept low, and the low power consumption operation can be realized.

  In one embodiment, it is preferable that the second conductivity type dopant in the portion immediately below the ridge of the second semiconductor layer is zinc (Zn).

  Since zinc (Zn) has the property of relatively easily diffusing, according to the semiconductor laser device of the above embodiment, only the portion immediately below the ridge of the second semiconductor layer is selectively made to have a second conductivity type with a higher concentration. It becomes possible to do. This makes it possible to achieve both current confinement on the side of the ridge and low series resistance directly below the ridge.

  In one embodiment, the second conductivity type dopant of the first semiconductor layer is preferably carbon (C).

  According to the semiconductor laser device of the above embodiment, the diffusion of the second conductivity type dopant from the first semiconductor layer to the second semiconductor layer can be prevented by using carbon (C), which is difficult to diffuse, as a dopant. The second conductivity type doping concentration of the second semiconductor layer can be kept low. As a result, it is possible to provide a semiconductor laser element exhibiting good current confinement with good controllability without adding a separate crystal regrowth step. Furthermore, by freely changing the first semiconductor layer, optical design that meets various required specifications becomes easy.

  In the semiconductor laser device of one embodiment, the second conductivity type doping concentration of the first semiconductor layer is preferably equal to or higher than the second conductivity type doping concentration of the second semiconductor layer immediately below the ridge. .

  According to the semiconductor laser device of the above embodiment, when the concentration of the impurity serving as the second conductivity type dopant has the above magnitude relationship, the second conductivity type dopant contained in the second semiconductor layer is It does not diffuse to the first semiconductor layer side. As a result, it is possible to provide a semiconductor laser device having good characteristics and reliability without degradation in efficiency and reliability due to dopant diffusion into the active layer.

  In one embodiment, the second semiconductor layer includes an Al-containing semiconductor layer disposed on the first semiconductor layer side and an InGaAsP semiconductor layer disposed on the third semiconductor layer side. It is preferable to be a laminate of

  According to the semiconductor laser device of the above embodiment, since the surface of the second semiconductor layer does not contain easily oxidized aluminum (Al), generation of deep levels due to oxidation is eliminated, and light absorption due to the deep levels is eliminated. Therefore, the internal loss is reduced and the current confinement is not deteriorated even during long-term device operation. Furthermore, InGaAsP has a smaller ΔEv than InGaP, and does not lower the hole injection efficiency. As a result, it is possible to provide a semiconductor laser element having good reliability and capable of high efficiency operation.

  In one embodiment, the second semiconductor layer preferably has a thickness of 0.1 μm or more and 0.4 μm or less.

  According to the semiconductor laser device of the above embodiment, since the thickness of the second semiconductor layer is not less than 0.1 μm and not more than 0.4 μm, good Schottky junction is exhibited on the side of the ridge.

In one embodiment, the second conductivity type doping concentration at the top of the ridge is 1 × 10 ¹⁸ cm ⁻³ or more, and the electrode is formed at the interface between the electrode layer and the top of the ridge. A high-concentration compound layer comprising the constituent elements of the layer and the constituent elements of the top of the ridge is formed, and the doping concentration of the side portion of the second ridge of the second semiconductor layer is 1 × 10 ¹⁷ cm ⁻³ or less, Preferably, a low-concentration compound layer composed of the constituent elements of the electrode layer and the constituent elements of the second semiconductor layer is formed at the interface between the electrode layer and the ridge side portion of the second semiconductor layer. .

According to the semiconductor laser device of the above embodiment, in the ohmic junction between the ridge top having a doping concentration of 1 × 10 ¹⁸ cm ⁻³ or more and the electrode layer, a lower contact resistance is obtained by the high concentration compound layer. In the Schottky junction between the ridge side portion having a doping concentration of 1 × 10 ¹⁷ cm ⁻³ or less and the electrode layer in the second semiconductor layer, sufficient current confinement is obtained by the low concentration compound layer. Since the ohmic junction and the Schottky junction are enhanced in this way, the crystal regrowth process of the buried layer (current blocking layer) for current confinement and the crystal of the contact layer for obtaining low contact resistance. Sufficient current constriction and low contact resistance can be realized without performing a separate regrowth process, and thermal and electrical reliability is improved. Therefore, low threshold current and high output operation are possible, long-term reliability can be obtained, cost can be reduced by simplifying the manufacturing process, and reliability and high output characteristics equivalent to or better than conventional semiconductor laser elements Can be realized with low power consumption.

In addition, the method for manufacturing the semiconductor laser device of the present invention includes:
On the first conductivity type substrate, an active layer, a second conductivity type first semiconductor layer, a second conductivity type doping concentration of 1 × 10 ¹⁷ cm ⁻³ or less, and a second conductivity type substrate Sequentially forming a third semiconductor layer having a doping concentration of 1 × 10 ¹⁷ cm ⁻³ or more;
Removing a part of the third semiconductor layer to form a striped ridge made of the material of the third semiconductor layer;
Heat treatment is performed to diffuse the second conductivity type dopant of the third semiconductor layer into a portion of the second semiconductor layer immediately below the ridge corresponding to the region immediately below the ridge, so that the second conductivity type of the portion immediately below the ridge is diffused. A step of increasing the doping concentration to 1 × 10 ¹⁷ cm ⁻³ or more;
Forming an electrode layer covering a ridge side portion corresponding to a side of the ridge among the surface of the ridge and the second semiconductor layer.

  According to the method of manufacturing a semiconductor laser device of the above embodiment, a Schottky junction is formed at the interface between the ridge side portion of the second semiconductor layer and the electrode layer, current is cut off, and the top of the ridge and the electrode layer At the interface, it is finished in an ohmic contact state. Since the doping concentration of the portion immediately below the ridge in the second semiconductor layer can be selectively increased, the ridge side portion of the second semiconductor layer, the electrode layer, and the like can be obtained without deteriorating the series resistance of the semiconductor laser element immediately below the ridge. It becomes possible to sufficiently increase the current confinement property. As a result, a method of manufacturing a semiconductor laser device that can be manufactured at low cost and that can operate with low threshold current oscillation and high output is provided.

  In one embodiment of the method for manufacturing a semiconductor laser device, the step of forming the ridge includes a step of forming a striped etching mask made of an inorganic insulating film on the third semiconductor layer, and the inorganic insulating film. Preferably, the method includes a step of removing portions corresponding to both sides of the mask of the third semiconductor layer using the mask as a mask.

  According to the method for manufacturing a semiconductor laser device of the above embodiment, the inorganic insulating film becomes a surface protective film that is favorable to heat treatment, and therefore, the top of the ridge that forms an ohmic junction in current injection may be exposed during the heat treatment. Accordingly, it is possible to suppress the problem of increasing the resistance of the element due to the decrease in crystallinity of the semiconductor layer at the top of the ridge and the re-evaporation of the second conductivity type dopant.

  Also, in one embodiment of the method for manufacturing a semiconductor laser device, after forming the ridge and before performing the heat treatment, an inorganic insulating film that covers the surface of the ridge and the side portion of the second ridge of the second semiconductor layer is formed. It is preferable to include the process of forming.

  According to the method for manufacturing a semiconductor laser device of the above embodiment, when the heat treatment step is performed, all the surface of the semiconductor layer on the ridge side is covered with the inorganic insulating film. In addition, it is possible to suppress the crystallinity degradation of other semiconductor surfaces and the re-evaporation of the dopant.

  In one embodiment, when the third semiconductor layer is formed, at least the lowest layer of the third semiconductor layer is doped with zinc (Zn) as the second conductivity type dopant. It is preferable.

  According to the method of manufacturing a semiconductor laser device of the above embodiment, when forming the third semiconductor layer immediately above the second semiconductor layer, at least the lowest layer of the third semiconductor layer as the second conductivity type dopant. Doping with zinc (Zn). Therefore, after forming the ridge by patterning the third semiconductor layer, the heat treatment is performed to diffuse zinc only in the region immediately below the ridge of the second semiconductor layer, thereby reducing the resistance of the current injection path. Is possible.

  In one embodiment, when forming the first semiconductor layer, the first semiconductor layer is preferably doped with carbon (C) as a dopant of the second conductivity type.

  According to the method for manufacturing a semiconductor laser device of the above embodiment, carbon (C) is extremely difficult to diffuse, and thus the diffusion of the second conductivity type dopant from the first semiconductor layer side to the second semiconductor layer can be prevented. Therefore, even after the above-described heat treatment, the doping concentration of the second conductivity type in the ridge side portion of the second semiconductor layer is not increased, and a good Schottky is formed on the surface of the ridge side portion of the second semiconductor layer. A bond can be formed.

  Also, in one embodiment of the method for manufacturing a semiconductor laser device, the doping concentration of the second conductivity type using the carbon (C) of the first semiconductor layer as a dopant is changed to the ridge of the second semiconductor layer by the heat treatment. It is preferable to set the doping concentration of the second conductivity type reached by the portion immediately below.

  According to the method of manufacturing a semiconductor laser device of the above embodiment, the second conductivity type doping concentration reached by the portion immediately below the ridge of the second semiconductor layer is lower than the second conductivity type doping concentration of the first semiconductor layer. Therefore, the zinc (Zn) dopant diffused from the lowermost semiconductor layer of the third semiconductor layer does not diffuse to the first semiconductor layer side. Therefore, impurity (zinc) diffusion into the active layer can be prevented. When zinc diffuses into the active layer, non-radiative recombination centers increase and the reliability and oscillation efficiency decrease, but it has good reliability as a result of preventing such impurity diffusion phenomenon into the active layer. Thus, it becomes possible to manufacture a semiconductor laser device capable of high-efficiency oscillation.

  In one embodiment of the semiconductor laser device manufacturing method, the heat treatment is preferably performed at a temperature of 600 ° C. to 800 ° C.

  According to the method of manufacturing a semiconductor laser device of the above embodiment, zinc can be diffused from a semiconductor layer doped with zinc formed in the lowermost layer of the third semiconductor layer into a region immediately below the ridge, It becomes possible to reduce the element resistance in the implantation region.

In addition, a method for manufacturing a semiconductor laser device according to one embodiment includes:
Forming a semiconductor layer having a second conductivity type doping concentration of 1 × 10 ¹⁸ cm ⁻³ or more as the uppermost layer of the third semiconductor layer;
Heat treatment is performed after the formation of the electrode layer to form a high-concentration compound layer composed of the constituent elements of the electrode layer and the constituent elements of the ridge top at the interface between the electrode layer and the top of the ridge. It is preferable to form a low-concentration compound layer comprising the constituent elements of the electrode layer and the constituent elements of the second semiconductor layer at the interface between the electrode layer and the ridge side portion of the second semiconductor layer.

According to the method for manufacturing a semiconductor laser device of the above embodiment, the low concentration compound is used in the Schottky junction between the electrode layer and the ridge side portion of the second semiconductor layer having a doping concentration of 1 × 10 ¹⁷ cm ⁻³ or less. A sufficient current confinement can be obtained by the layer, and a lower contact resistance can be obtained by the high-concentration compound layer in the ohmic junction between the top of the ridge having a doping concentration of 1 × 10 ¹⁸ cm ⁻³ or more and the electrode layer. Since the Schottky junction and the ohmic junction are further strengthened in this way, a low threshold current and a high output operation can be performed without performing a current block layer burying regrowth process and an electrode contact layer crystal regrowth process. It is possible and long-term reliability can be obtained, and the cost can be reduced by simplifying the manufacturing process. Therefore, it is possible to manufacture a semiconductor laser device that can obtain a sufficient current confinement property and excellent device reliability, and that can operate at high power with low power consumption.

  An optical disk apparatus according to the present invention includes the semiconductor laser element according to the present invention.

  As described above, since the semiconductor laser device of the present invention can operate with a low threshold current and a high output, according to the optical disk apparatus of the present invention, data writing can be performed at high speed with low power consumption compared with the conventional optical disk apparatus. Is possible. Further, the optical disk apparatus of the present invention is configured at a lower cost.

  An optical transmission system according to the present invention includes the semiconductor laser device according to the present invention.

  As described above, since the semiconductor laser device of the present invention can operate with a low threshold current and a high output, according to the optical transmission system of the present invention, compared with the conventional optical transmission system, low power consumption and high speed. Data transmission is possible. Further, the optical transmission system of the present invention is configured at a lower cost.

  As is clear from the above, the semiconductor laser device of the present invention is capable of low threshold current and high output operation, has long-term reliability, and has a high degree of freedom in designing optical characteristics and is stable. Both optical characteristics and cost reduction due to simplification of the manufacturing process can be achieved.

  The method of manufacturing a semiconductor laser device of the present invention has sufficient current confinement, excellent device reliability, without performing a current block layer burying regrowth step and a crystal regrowth step of an electrode contact layer, and It becomes possible to manufacture a semiconductor laser device capable of high power operation with low power consumption.

  According to the optical disk apparatus of the present invention, by using the semiconductor laser element of the present invention, it is possible to write data at low power consumption and at a high speed as compared with the conventional optical disk apparatus, and to be configured at a lower cost.

  Further, according to the optical transmission system of the present invention, by using the semiconductor laser element of the present invention for the optical transmission module, it is possible to provide an optical transmission module that is overwhelmingly cheaper and more reliable than the conventional one. Therefore, the price of the optical transmission system can be reduced.

  Hereinafter, the present invention will be described in detail with reference to the illustrated embodiments.

  In the following description, “n−” represents the n-type as the first conductivity type, and “p−” represents the p-type as the second conductivity type.

[First Embodiment]
FIG. 1 shows the structure of the semiconductor laser device according to the first embodiment of the present invention. This semiconductor laser element oscillates at a wavelength of 890 nm and is used for infrared communication.

This semiconductor laser device includes an n-GaAs substrate 101, an n-GaAs buffer layer 102, an n-Al _0.5 Ga _0.5 As first lower cladding layer 103, an n-Al _0.422 Ga _0.578 As second lower cladding layer 104, an Al _0.25 Ga _0.75 As lower guide layer 105, multiple strained quantum well active layer 106, Al _0.25 Ga _0.75 As first upper guide layer 107, Al _0.4 Ga _0.6 As second upper guide layer 108, p as an example of the first semiconductor layer The -Al _0.456 Ga _0.544 As first upper cladding layer 109, the p-Al _0.456 Ga _0.544 As second upper cladding layer 110, and the p-In _0.1568 Ga _0.8432 As _0.4 P _0.6 semiconductor layer 111 are sequentially stacked.

The p-Al _0.456 Ga _0.544 As second upper cladding layer 110 and the p-In _0.1568 Ga _0.8432 As _0.4 P _0.6 semiconductor layer 111 constitute a second semiconductor layer group. As will be described in detail later, portions of the second semiconductor layer groups 110 and 111 corresponding to the portion 119a immediately below the ridge 130 (hereinafter referred to as “portions immediately below the ridge”) 110a and 111a and the vicinity thereof are only the second semiconductor layer group 110. , 111 have a higher p-type doping concentration than portions corresponding to the side 119b of the ridge 130 (hereinafter referred to as “ridge side portion”) 110c and 111c. Each semiconductor layer has a uniform doping concentration in the layer direction unless otherwise specified.

On this semiconductor layer 111, a p-Al _0.5 Ga _0.5 As third upper cladding layer 112 having a forward mesa-shaped cross section and forming a ridge 130 extending in a stripe shape perpendicular to the paper surface of FIG. , A p-GaAs contact layer 113 and a p ⁺ -GaAs contact layer 114 are provided.

The p-Al _0.5 Ga _0.5 As third upper cladding layer 112, the p-GaAs contact layer 113 and the p ⁺ -GaAs contact layer 114 constitute a third semiconductor layer group.

  Further, the p-side electrode made of a multilayer metal thin film formed by laminating Ti / Pt / Au in this order as an electrode layer in such a manner that the top portion, the side surface portion of the ridge 130 and the upper surface of the second upper cladding layer 109 are continuously covered. 115 is provided. Reference numerals 115a, 115b, and 115c denote portions covering the top and side portions of the ridge 130 and the upper surface of the ridge side portion 111c of the semiconductor layer 111 (this is appropriately referred to as an “electrode portion”). The electrode portion 115a and the top of the ridge 130 (contact layer 114) form an ohmic junction, while the electrode portion 115c and the upper surface of the semiconductor layer 111 form a Schottky junction. As will be described in detail later, 120 (including 120a, 120b, and 120c) represents a compound layer in which the p-side electrode 115 and the semiconductor layer in contact with the p-side electrode 115 are alloyed. An n-side electrode 116 made of a multilayer metal thin film of AuGe / Ni / Au is formed on the back surface of the substrate 101 as another electrode layer. Further, an Au wire (not shown) for electrical connection with an external circuit is bonded to the portion 115 c formed on the ridge side portion 111 c of the semiconductor layer 111 in the p-side electrode 115. .

  Next, a method for manufacturing the semiconductor laser device will be described with reference to FIGS.

First, as shown in FIG. 2, an n-GaAs buffer layer 102 (layer thickness: 0.5 μm, Si doping concentration: 7.2 × 10 ¹⁷ cm ⁻³ ) is formed on the (100) plane of the n-GaAs substrate 101. n-Al _0.5 Ga _0.5 As first lower cladding layer 103 (layer thickness: 2.0 μm, Si doping concentration: 5.4 × 10 ¹⁷ cm ⁻³ ), n-Al _0.422 Ga _0.578 As second lower cladding layer 104 ( Layer thickness: 0.1 μm, Si doping concentration: 5.4 × 10 ¹⁷ cm ⁻³ ), Al _0.25 Ga _0.75 As lower guide layer 105 (layer thickness: 3.0 nm), multiple strain quantum well active layer 106, Al _0.25 Ga _0.75 As first upper guide layer 107 (layer thickness: 3.0 nm), Al _0.4 Ga _0.6 As second upper guide layer 108 (layer thickness: 0.1 μm), p-Al _0.456 Ga as an example of the first semiconductor layer _0.544 As first upper cladding layer 109 (thickness: 0 2 [mu] m, C doping ^{concentration: 1 × 10 18 cm -3)} , Al 0.456 Ga 0.544 As second upper cladding layer 110 (thickness: 0.1 [mu] m, p-type carrier concentration: 2 × 10 ¹⁶ cm ^-3 or less), an In _0.1568 Ga _0.8432 As _0.4 P _0.6 semiconductor layer 111 (layer thickness: 15 nm, p-type carrier concentration: 5 × 10 ¹⁵ cm ⁻³ or less), p-Al _0.5 Ga _0.5 As third upper cladding layer 112 (layer thickness: 1. 28 μm, Zn doping concentration 4 × 10 ¹⁸ cm ⁻³ ), p-GaAs contact layer 113 (layer thickness: 0.2 μm, Zn doping concentration: 3 × 10 ¹⁸ cm ⁻³ ), p ⁺ -GaAs contact layer 114 (layer) Thickness: 0.3 μm, Zn doping concentration: 1 × 10 ²⁰ cm ⁻³ ) are successively grown by MOCVD (metal organic chemical vapor deposition). The multiple strained quantum well active layer 106, In _0.1001 Ga _0.8999 As compressive strained quantum well layer (strain 0.7%, layer thickness: 46 Å, 2-layer) and In _0.238 Ga _0.762 As _0.5463 P _0.4537 tensile strain barrier layer (strained 0.1%, band gap Eg≈1.60 eV, layer thickness from substrate side: 215Å, 79Å, 215Å, the closest layer to the substrate 101 is the n-side barrier layer, the farthest one is the p-side barrier Layer) are alternately arranged.

Subsequently, a 300 nm silicon nitride (SiNx) film 118 is formed on the p ⁺ -GaAs contact layer 114 by plasma-CVD (chemical vapor deposition).

  Next, on the region 119a (see FIG. 1) where the ridge 130 is to be formed, as shown in FIG. 2, a resist mask 119 (mask width 3.5 μm) is formed by a photolithography process. The resist mask 119 is formed so as to extend in a stripe shape in the <0-11> direction corresponding to the direction in which the ridge 130 to be formed extends.

  Using this resist mask 119 as a mask, the silicon nitride film 118 is etched into a stripe shape using buffered hydrofluoric acid. After the silicon nitride film 118 is processed into a stripe shape, the resist mask 119 is removed.

  Next, as shown in FIG. 3, portions of the semiconductor layers 114, 113, and 112 corresponding to both sides of the silicon nitride film 118 are removed by etching, and a forward mesa stripe ridge is formed immediately below the silicon nitride film 118. 130 is formed. This etching is performed using a mixed aqueous solution of sulfuric acid and hydrogen peroxide until the ridge side portion 111c of the semiconductor layer 111 is exposed. Subsequently, an overhang portion of the GaAs contact layers 113 and 114 is taken with a mixed aqueous solution of ammonia and hydrogen peroxide. The depth of etching is 1.78 μm, and the width of the lowermost portion of the ridge 130 is about 3.2 μm.

Thereafter, using a sealed bake furnace that can be heated to a high temperature (in this embodiment, the chamber of the MOCVD apparatus used for crystal growth was used), AsH ₃ was allowed to flow to recycle arsenic from the semiconductor layer surface. Heating was performed at 750 ° C. for 30 minutes while preventing evaporation. After removal from the bake furnace, the buffered hydrofluoric acid was used again to remove the striped silicon nitride film 118.

The Zn doping concentration of the p-Al _0.5 Ga _0.5 As third upper cladding layer 112 constituting the lowermost layer of the ridge 130 by the heat treatment at 750 ° C. is 4 × 10 ¹⁸ cm ⁻³ before the heat treatment on the semiconductor layer 111 side. To 1.5 × 10 ¹⁸ cm ⁻³ . At the same time, the doping concentration of the portion 110a immediately below the ridge of the Al _0.456 Ga _0.544 As second upper cladding layer 110 was 2 × 10 ¹⁶ cm ⁻³ or less before the heat treatment. The layer 109 side is 1.0 × 10 ¹⁸ cm ⁻³ , and the doping concentration increases almost linearly therefrom, while the In _0.1568 Ga _0.8432 As _0.4 P _0.6 semiconductor layer 111 side is 1.5 × 10 ¹⁸ cm ^−3. It became. Further, the doping concentration of the portion 111a immediately below the ridge of the In _0.1568 Ga _0.8432 As _0.4 P _0.6 semiconductor layer 111 is increased from a state of 5 × 10 ¹⁵ cm ⁻³ or less before heat treatment to 1.5 × 10 ¹⁸ cm ^−3. I was able to.

  FIG. 5 is a diagram for explaining a change in doping concentration around the ridge 130 due to the heat treatment step. FIG. 5A shows the periphery of the ridge 130 in an enlarged manner. Further, in FIG. 5A, a schematic profile of the second conductivity type concentration in each of the cross sections AA ′ and BB ′ is shown in FIG. 5B, and in FIG. FIG. 5C shows a schematic profile of the second conductivity type concentration in the section CC ′.

  In FIG.5 (b), a thick continuous line shows the 2nd conductivity type density | concentration profile in the cross section AA 'after a heat processing process, and the continuous line from BB' to a BB 'is the cross section A- before a heat processing process. The second conductivity type concentration profile in A ′ is shown. In addition, the second conductivity type concentration profile of the cross section B-B ′ does not change before and after the heat treatment.

  In FIG. 5C, as can be seen from the second conductivity type concentration profile of the cross section C-C ', the second conductivity type concentration of the portion 111a immediately below the ridge of the semiconductor layer 111 is higher corresponding to the region 111a. In the semiconductor layer 111, the strict "not only the portion 111a directly under the ridge 111a but also a portion 111b in the vicinity thereof has a high doping concentration of the second conductivity type. By the heat treatment, the dopant of the second conductivity type is immediately below the ridge 111a. In this embodiment, the neighboring portion 111b corresponds to a region having a width of about 0.15 μm from the ridge end toward the outside.

  Subsequently, as shown in FIG. 4, a metal thin film is formed in the order of Ti (layer thickness: 50 nm) / Pt (layer thickness: 50 nm) / Au (layer thickness: 400 nm) as the p-side electrode 115 by using an electron beam evaporation method. Laminate.

  Thereafter, as shown in FIG. 1, the substrate 101 is ground from the back surface side to a desired thickness (here, about 100 μm) by a lapping method. Then, by using resistance heating vapor deposition from the back side, as the n-side electrode 116, AuGe alloy (alloy of Au 88% and Ge 12%, layer thickness: 100 nm), Ni (layer thickness: 15 nm), Au (layer thickness: 300 nm) ).

Thereafter, an alloy process is performed by heating at 400 ° C. for 1 minute in an N ₂ atmosphere. As a result, a compound layer 120 in which Ti and each semiconductor layer material are alloyed is formed at the interface between the p-side electrode 115 and each semiconductor layer in contact with the p-side electrode 115. Reference numerals 120 a, 120 b, and 120 c denote portions corresponding to the ridge top portion, the ridge side surface, and the ridge side portion 111 c of the semiconductor layer 111 in the compound layer 120, respectively.

  After dividing the substrate 101 into a plurality of bars having a desired resonator length (here, 500 μm), end coating is performed on the bars, and the bars are further divided into chips (500 μm × 250 μm). The chip after the division is fixed on a stem (not shown) using In glue. Then, an Au wire (not shown) for electrical connection with an external circuit is bonded onto the portion 120c corresponding to the ridge side portion 111c of the semiconductor layer 111 in the p-side electrode 115. Thus, the semiconductor laser element is completed.

  When a current is passed between the p-side electrode 115 and the n-side electrode 116 of the semiconductor laser device manufactured in this way, the current is cut off at the Schottky junction on the side of the ridge 130 and passed through the ohmic junction at the top of the ridge 130. Only current flows. Thereby, current confinement is performed. Then, a portion of the active layer 106 corresponding to the portion immediately below the ridge 130 is energized to perform laser oscillation.

In the semiconductor laser device of the present embodiment, the p-type doping concentration of the portions 110a and 111a immediately below the ridges of the second semiconductor layer group 110, 111 provided on the active layer 106 is 1 × 10 ¹⁸ cm ⁻³ or more. The ridge side portions 110c and 111c of the two semiconductor layer groups 110 and 111 have a p-type doping concentration of 1 × 10 ¹⁷ cm ⁻³ or less (in this example, the p-type doping concentrations of the ridge side portions 110c and 111c are 2 × 10 ¹⁶ cm ⁻³ , 1 × 10 ¹⁵ cm ⁻³ ), so that the electrical resistance of the portions 110a and 111a immediately below the ridges of the second semiconductor layer groups 110 and 111 is kept low, and provided outside the ridges. The current confinement property due to the Schottky junction between the formed electrode portion 120c and the ridge side portion 111c of the semiconductor layer 111 can be greatly increased. It became so. Therefore, it was possible to achieve both an oscillation operation at a low threshold current due to a small leakage current, a low power consumption and a high output operation due to a low series resistance.

  In order to realize the above-described configuration, in the method of manufacturing a semiconductor laser device of the present invention, after the ridge 130 is formed by etching, a heat treatment is once applied so that only a low-doping semiconductor layer directly below the ridge 130 is selectively used. Highly doped. In the ridge etching process described above, a silicon nitride (SiNx) film that reliably covers and protects the contact layer at the top of the ridge and can withstand high temperatures was used as an etching mask.

Zinc (Zn) is diffused into the second semiconductor layer groups 111 and 110 by heating from the lowermost layer 112 (layer in contact with the semiconductor layer 111) of the semiconductor layers constituting the ridge 130, and the second semiconductor layer group Since the p-type doping concentration in the portion immediately below the ridge is selectively increased, the p-type doping concentration in the region exposed by the ridge formation process, that is, the ridge side portion of the second semiconductor layer group remains low. In this step, it is particularly preferable that the zinc dopant has a concentration gradient because it can be easily diffused by heating. In addition, the heat treatment step was performed at 750 ° C. in the present embodiment. At this time, it tends to diffuse deeper as the temperature is higher, but about 600 to 800 ° C. is preferable for the present diffusion step. When the temperature is lower than 600 ° C., sufficient diffusion does not occur. When the temperature is higher than 800 ° C., the diffusion proceeds, but the roughness due to re-evaporation of As from the surface of the semiconductor layer becomes severe. In order to prevent the re-evaporation of As described above, in this embodiment, the heat treatment was performed in an AsH ₃ atmosphere.

In the manufacturing method of the semiconductor laser device of this embodiment, the heat treatment is performed in a state where the silicon nitride film used as an etching mask when forming the ridge 130 is left on the top of the ridge. As a result, it was possible to suppress a decrease in crystallinity due to re-evaporation of As in the semiconductor layer 114 at the top of the ridge serving as the contact layer and re-evaporation of zinc as the second conductivity type dopant. In order to suppress a decrease in crystallinity due to re-evaporation of As on the side surface of the ridge 130 and the surface of the second semiconductor layer group as well as the top of the ridge 130 and the re-evaporation of the dopant, before performing the heat treatment step, For example, a process of forming an inorganic insulating film such as a silicon nitride film again may be added. However, in this embodiment, adding such a process leads to an increase in cost, and heat treatment is performed in an AsH ₃ atmosphere, so that As can be prevented from re-evaporation. In the current confinement region due to the Schottky junction, since the dopant may be re-evaporated and the carrier concentration may be lowered, a process of covering only the top of the ridge 130 with a silicon nitride film is adopted. Yes.

In the semiconductor laser device of this embodiment, as described above, the p-type doping concentration in the ridge side portions 110c and 111c of the second semiconductor layer groups 110 and 111 is 1 × 10 ¹⁷ cm ⁻³ or less (in this example, Since the p-type doping concentrations of the ridge side portions 110c and 111c are 2 × 10 ¹⁶ cm ⁻³ and 1 × 10 ¹⁵ cm ⁻³ , respectively, when the Schottky junction is formed in the region outside the ridge The current constriction is very large. The current confinement property of this portion increases rapidly when the doping concentration is 1 × 10 ¹⁷ cm ⁻³ or less, and becomes better as the doping concentration is lower. It was also found that the stability during energization was improved. On the other hand, the portion immediately below the ridge of the second upper cladding layer 110 is doped with a p-type doping concentration of 1 × 10 ¹⁸ cm ⁻³ , but this region is doped with at least 1 × 10 ¹⁷ cm ⁻³ or more. It is desirable. The higher the doping concentration, the lower the series resistance of the device. However, when the cladding layer is doped at 1 × 10 ¹⁹ cm ⁻³ or more, various characteristics of the device may be deteriorated due to a decrease in crystallinity.

  In the conventional semiconductor laser device, since the doping concentration distribution in the direction parallel to the active layer 106 is uniform in the semiconductor layers corresponding to the second semiconductor layer groups 111 and 110, the low series resistance and the high current as described above are obtained. It was difficult to achieve both stenosis.

  In addition, like the semiconductor laser device of this embodiment, the outermost surface of the second semiconductor layer group (semiconductor layer 111 exposed in the ridge forming step) is preferably InGaAsP containing no Al. By using InGaAsP on the surface of the second semiconductor layer group in this way, a significant oxidation reaction does not occur even in the thermal diffusion process of Zn, and the device reliability is improved, compared with the case where a semiconductor layer containing Al is used. There is an effect to make. In addition, since there is no generation of deep non-light emitting levels due to oxidation, there is an effect that the oscillation efficiency does not deteriorate. Similarly, InGaP that does not contain Al has a large ΔEv, so that the hole injection efficiency decreases, and depending on the growth conditions, it tends to be a natural superlattice, and the refractive index changes greatly at that time. This is not preferable compared to InGaAsP in terms of surface and optical stability.

InGaAsP that does not contain Al has a lower level of p-type spontaneously when compared to a semiconductor layer containing Al during crystal growth using the MOCVD method, and easily realizes a non-doped state of 5 × 10 ¹⁵ cm ⁻³ or less. can do. It is preferable to use InGaAsP from the viewpoint that a low carrier concentration state can be easily obtained. On the other hand, AlGaAs is formed to about 2 × 10 ¹⁶ cm ⁻³ or less in the non-doped state, although it depends on the Al mixed crystal ratio and growth conditions. That is, in the manufacturing process of the semiconductor laser device described above, the second semiconductor layer groups 110 and 111 were crystal-grown in a non-doped state (without adding a dopant) by MOCVD. As described above, the smaller the p-type carrier concentration during the crystal growth of the second semiconductor layer group 110, 111, the more preferable the current confinement property after the device is completed. Therefore, it is desirable to set the growth conditions in the MOCVD method so that crystal growth with such a low carrier concentration can be realized.

  In the semiconductor laser device of this embodiment, the thickness of the second semiconductor layer group 110, 111 is 0.115 μm. In order to obtain sufficient current confinement, the thickness of the second semiconductor layer group 110, 111 having a low doping concentration needs to be at least 0.1 μm or more. The maximum value has no upper limit from the viewpoint of increasing the resistance directly under the ridge, but it has been found that even if it is thicker than 0.4 μm, the current confinement property is not further improved.

Further, like the semiconductor laser device of the present embodiment, the first semiconductor layer 109 is preferably doped with carbon (C). Since carbon is not easily diffused by the heating process, there is no dopant diffusion from the lower side with respect to the second semiconductor layer groups 110 and 111 in the above heating process, and the p-type doping concentration is increased just below the ridge. This structure can be easily obtained. Further, by setting the carbon doping concentration of the first semiconductor layer 109 to be higher than the doping concentration after Zn diffusion just below the ridge, the second semiconductor layer groups 110 and 111 are transferred from the relationship of the dopant concentration gradient. It becomes possible to prevent the diffused Zn from further diffusing into the first semiconductor layer 109. When crystal growth is performed by MOCVD as in the present embodiment, carbon is an MO (organic metal) that becomes a crystal raw material without newly adding a dopant gas supply line by appropriately setting the growth conditions. It is possible to dope from the material. Therefore, the apparatus manufacturing cost and the raw material cost can be further reduced, which is particularly preferable. Of course, a new dopant gas supply line may be added and carbon may be doped using a material such as bromine carbide (CBr ₄ ). Moreover, when adding a gas supply line, magnesium (Mg) which is hard to thermally diffuse like carbon can also be used as a dopant.

  Further, in the semiconductor laser device of this embodiment, when current confinement is performed using a Schottky junction as described above, an electrode layer 115 is formed by performing heat treatment after forming an electrode, as shown in FIG. Since the compound layer 120 is formed at the interface between the lowermost electrode material constituting the semiconductor layer and the semiconductor layer in contact with the electrode material, the Schottky junction property in the current confinement region on the side of the ridge 130 and the ohmic junction in the contact layer 114 are formed. Thus, the current can be injected only into the ridge 130 with lower resistance.

  As a result, the semiconductor laser device and the manufacturing method thereof according to the present embodiment can provide a semiconductor laser device having a low oscillation threshold current and capable of high output operation at a very low cost.

  Although the laser oscillation wavelength is 890 nm, it is naturally not limited to this. The present invention is, for example, an AlGaAs / GaAs semiconductor laser device having a wavelength of 780 nm used for CD, an InGaAlP / GaAs semiconductor laser device having a wavelength of 650 nm used for DVD, and an InGaN / GaN system which is a material of 405 nm band. The present invention can also be applied to a semiconductor laser element using a material. Further, an interface protective layer made of, for example, GaAs may be provided at the interface between semiconductor layers having different material systems, that is, between the upper guide layer and the barrier layer, and between the lower guide layer and the barrier layer.

[Second Embodiment]
FIG. 6 shows an example of the structure of the optical disc apparatus 200 according to the present invention. This is for writing data on the optical disc 201 or reproducing the written data. As a light emitting element used at that time, a wavelength of 780 nm using the configuration of the first embodiment described above is used. A semiconductor laser element 202 that oscillates is provided.

  The optical disk device 200 will be described in more detail. At the time of writing, the signal light emitted from the semiconductor laser element 202 is converted into parallel light by the collimator lens 203, passes through the beam splitter 204, and the polarization state is adjusted by the λ / 4 polarizing plate 205. The light is condensed and irradiated onto the optical disc 201. At the time of reading, the optical disc 201 is irradiated with a laser beam not carrying a data signal along the same path as at the time of writing. This laser beam is reflected on the surface of the optical disc 201 on which data is recorded, passes through the laser beam irradiation objective lens 206, the λ / 4 polarizing plate 205, and then is reflected by the beam splitter 204 to change the angle by 90 °. The light is condensed by the light receiving element objective lens 207 and is incident on the signal detecting light receiving element 208. The recorded data signal is converted into an electric signal by the intensity of the laser beam incident in the signal detection light-receiving element 208, and is reproduced by the signal light reproducing circuit 209 to the original signal.

  Since the optical disk device 200 of the second embodiment uses the semiconductor laser element 202 that operates at a higher light output than before, it is possible to read and write data even when the disk rotation speed is increased. Accordingly, the access time to the disk 201, which is a problem particularly during writing, is much shorter than that of a conventional apparatus using a semiconductor laser element. In addition, since the semiconductor laser element 202 can be manufactured at a lower cost than before, an optical disc apparatus that can be operated more comfortably can be provided at a low cost.

  Here, an example in which the semiconductor laser element 202 using the configuration of the first embodiment is applied to a recording / reproducing optical disc apparatus has been described. However, an optical disc recording apparatus, an optical disc reproducing apparatus, and other devices using the same wavelength 780 nm band. Needless to say, the present invention can also be applied to an optical disc device in a wavelength band (for example, 650 nm band).

[Third Embodiment]
FIG. 7 is a cross-sectional view showing an optical transmission module 300 used in the optical transmission system according to the third embodiment of the present invention. FIG. 8 is a perspective view showing a light source portion of the light transmission module 300. In the third embodiment, the InGaAs semiconductor laser element (laser chip) 301 having the oscillation wavelength of 890 nm described in the first embodiment is used as the light source, and the silicon (Si) pin photodiode is used as the light receiving element 302. As will be described in detail later, by providing the same optical transmission module 300 on both sides (for example, a terminal and a server) that perform communication, an optical transmission system that transmits and receives optical signals between the two optical transmission modules 300 is configured. The

  In FIG. 7, a pattern of both positive and negative electrodes for driving a semiconductor laser is formed on a circuit board 306. As shown in the drawing, a recess 306a having a depth of 300 μm is provided in a portion where a laser chip is mounted. A laser mount (mounting material) 310 on which the laser chip 301 is mounted is fixed to the recess 306a with solder. The flat portion 313 of the positive electrode 312 of the laser mount 310 is electrically connected to a laser driving positive electrode portion (not shown) on the circuit board 306 by a wire 307a. The recess 306a has a depth that does not hinder the emission of laser light, and the roughness of the surface does not affect the emission angle.

  The light receiving element 302 is also mounted on the circuit board 306, and an electric signal is taken out by the wire 307b. In addition, an IC circuit 308 for laser driving / reception signal processing is mounted on the circuit board 306.

  Next, an appropriate amount of a liquid silicon resin 309 is dropped on a portion where the laser mount 310 fixed to the concave portion with solder is mounted. In the silicon resin 309, a filler that diffuses light is mixed. The silicon resin 309 stays in the recess due to surface tension, covers the laser mount 310, and is fixed to the recess 306a. In the third embodiment, the recess 306a is provided on the circuit board 306 and the laser mount 310 is mounted. However, as described above, the silicon resin 309 remains on the laser chip surface and its vicinity due to surface tension. 306a is not necessarily provided.

  Thereafter, it is heated at 80 ° C. for about 5 minutes to be cured until it forms a jelly. Next, it is covered with a transparent epoxy resin mold 303. Above the laser chip 301, a lens part 304 for controlling the radiation angle is formed, and above the light receiving element 302, a lens part 305 for condensing the signal light is integrally formed as a molded lens. .

  Next, the laser mount 310 will be described with reference to FIG. As shown in FIG. 8, a laser element 301 is die-bonded to an L-shaped heat sink 311 using In glue. The laser chip 301 is the InGaAs-based semiconductor laser element described in the first embodiment, and the chip lower surface 301b is coated with a high reflection film, while the laser chip upper surface 301a is coated with a low reflection film. ing. These reflective films also serve as protection for the end face of the laser chip.

  A positive electrode 312 is fixed to the base 311 b of the heat sink 311 with an insulator so as not to be electrically connected to the heat sink 311. The positive electrode 312 and the electrode region 301c provided on the Schottky junction on the surface of the laser chip 301 are connected by a gold wire 307c. As described above, the laser mount 310 is soldered to the negative electrode (not shown) of the circuit board 306 in FIG. 7, and the flat portion 313 on the upper side of the positive electrode 312 and the positive electrode portion (see FIG. (Not shown) with a wire 307a. By forming such wiring, the optical transmission module 300 that can obtain the laser beam 314 by oscillation is completed.

  Since the optical transmission module 300 of the third embodiment uses the single growth type semiconductor laser device that can be manufactured at a low cost as described above, the unit price of the module can be significantly reduced as compared with the conventional one.

  As described above, by providing the same optical transmission module 300 on both sides that perform communication, an optical transmission system that transmits and receives optical signals between both optical transmission modules 300 is configured. FIG. 9 shows a configuration example of an optical transmission system using the optical transmission module 300. In this optical transmission system, the base station 316 installed on the ceiling of the room includes the optical transmission module 300, and the personal computer 315 includes the same optical transmission module as described above (denoted by reference numeral 300 ′ for distinction). ing. The optical signal emitted from the light source of the optical transmission module 300 ′ on the personal computer 315 side is received by the light receiving element of the optical transmission module 300 on the base station 316 side. The optical signal emitted from the light source of the optical transmission module 300 on the base station 316 side is received by the light receiving element of the optical transmission module 300 ′ on the personal computer 315 side. In this way, data communication using light (infrared rays) can be realized.

  Note that the semiconductor laser device, the optical disk device, and the optical transmission system of the present invention are not limited to the above illustrated examples. For example, various changes can be made without departing from the gist of the present invention, such as the layer thickness and the number of layers of the well layers and barrier layers.

It is a figure which shows the cross section of the surface perpendicular | vertical with respect to stripe-shaped ridge of the semiconductor laser element concerning 1st Embodiment of this invention. It is a figure which shows the cross section of the surface perpendicular | vertical with respect to the stripe direction after completion | finish of the mask process for stripe formation of the semiconductor laser element concerning 1st Embodiment of this invention. It is a figure which shows the cross section of a surface perpendicular | vertical with respect to a stripe direction after completion | finish of a mesa stripe formation etching process of the semiconductor laser element concerning 1st Embodiment of this invention. It is a figure which shows the cross section of the surface perpendicular | vertical with respect to the stripe direction after the completion | finish of the p side electrode formation process of the semiconductor laser element concerning 1st Embodiment of this invention. (A)-(c) is a figure for demonstrating p-type doping concentration distribution of the semiconductor laser element concerning 1st Embodiment of this invention. It is the schematic of the optical disk apparatus of 2nd Embodiment of this invention. It is the schematic of the optical transmission module used for the optical transmission system of 3rd Embodiment of this invention. It is a perspective view of the light source concerning the optical transmission system of a 3rd embodiment of the present invention. It is a perspective view which shows the structural example of the optical transmission system of 3rd Embodiment of this invention. It is a figure which shows the cross section of the semiconductor laser element concerning a prior art example.

Explanation of symbols

101 n-GaAs substrate 102 n-GaAs buffer layer 103 n-AlGaAs first lower cladding layer 104 n-AlGaAs second lower cladding layer 105 AlGaAs lower guide layer 106 multiple strain quantum well active layer 107 AlGaAs first upper guide layer 108 p -AlGaAs second upper guide layer 109 p-AlGaAs first upper cladding layer 110 p-AlGaAs second upper cladding layer 111 p-InGaAsP semiconductor layer 112 p-AlGaAs third upper cladding layer 113 p-GaAs contact layer 114 p ⁺ - GaAs contact layer 115 p-side electrode 116 n-side electrode 118 silicon nitride film 119 resist mask 119a mesa stripe 119b area outside mesa stripe 120 compound layer 110a, 111a 110 ridge portion 110c, 111c The side portion 130 Ridge 200 Optical disk device 201 Optical disk 202 Semiconductor laser element 203 Collimator lens 204 Beam splitter 205 λ / 4 polarizing plate 206 Objective lens 207 Objective lens for light receiving element 208 Light receiving element for signal detection 209 Signal light reproducing circuit 300, 300 '' Optical transmission module 301 Semiconductor laser element (laser chip)
301a Low reflection film 301b High reflection film 301c Schottky bonded electrode region 302 Light receiving element 303 Epoxy resin mold 304, 305 Lens part 306 Circuit board 306a Recessed part 307a, 307b, 307c Wire 308 IC circuit 309 Silicon resin 310 Laser mount 311 Heat sink 311b Base 312 Positive electrode 313 Flat part 314 Laser beam 315 Personal computer 316 Base station

Claims (18)

An active layer laminated on a semiconductor substrate of the first conductivity type;
A first semiconductor layer stacked on the active layer and having a second conductivity type and a substantially uniform doping concentration;
The second conductivity type doping concentration of the portion immediately below the ridge, which is laminated on the first semiconductor layer, is of the second conductivity type, and is directly below the stripe-shaped ridge formed above, corresponds to the side of the ridge. A second semiconductor layer having a higher doping concentration of the second conductivity type in the side portion of the ridge
A third semiconductor layer of a second conductivity type formed on the second semiconductor layer and forming the stripe-shaped ridge;
A semiconductor laser device comprising: an electrode layer that forms an ohmic junction with the top of the ridge, and forms a Schottky junction with the ridge side portion of the second semiconductor layer. The semiconductor laser device according to claim 1,
The second conductivity type doping concentration in the portion immediately below the ridge of the second semiconductor layer is 1 × 10 ¹⁷ cm ⁻³ or more, and the second conductivity type doping concentration in the side portion of the ridge of the second semiconductor layer is 1. A semiconductor laser device having a size of 1 × 10 ¹⁷ cm ⁻³ or less. The semiconductor laser device according to claim 1,
A semiconductor laser element, wherein the second conductivity type dopant immediately below the ridge of the second semiconductor layer is zinc (Zn). The semiconductor laser device according to claim 1,
A semiconductor laser element, wherein the second conductivity type dopant of the first semiconductor layer is carbon (C). The semiconductor laser device according to claim 1,
2. A semiconductor laser device according to claim 1, wherein a doping concentration of the second conductivity type of the first semiconductor layer is equal to or higher than a doping concentration of the second conductivity type in a portion immediately below the ridge of the second semiconductor layer. The semiconductor laser device according to claim 1,
The semiconductor laser, wherein the second semiconductor layer is a stack of a semiconductor layer containing Al disposed on the first semiconductor layer side and a semiconductor layer made of InGaAsP disposed on the third semiconductor layer side. element. The semiconductor laser device according to claim 1,
A semiconductor laser element having a thickness of the second semiconductor layer of 0.1 μm or more and 0.4 μm or less. The semiconductor laser device according to claim 1,
The doping concentration of the second conductivity type at the top of the ridge is 1 × 10 ¹⁸ cm ⁻³ or more, and the constituent element of the electrode layer and the constituent element of the top of the ridge are formed at the interface between the electrode layer and the top of the ridge. A high-concentration compound layer consisting of
The doping concentration of the second ridge side portion of the second semiconductor layer is 1 × 10 ¹⁷ cm ⁻³ or less, and the electrode layer has an interface between the electrode layer and the second ridge side portion of the second semiconductor layer. A semiconductor laser device, characterized in that a low concentration compound layer comprising a constituent element and a constituent element of the second semiconductor layer is formed. On the first conductivity type substrate, an active layer, a second conductivity type first semiconductor layer, a second conductivity type doping concentration of 1 × 10 ¹⁷ cm ⁻³ or less, and a second conductivity type substrate Sequentially forming a third semiconductor layer having a doping concentration of 1 × 10 ¹⁷ cm ⁻³ or more;
Removing a part of the third semiconductor layer to form a striped ridge made of the material of the third semiconductor layer;
Heat treatment is performed to diffuse the second conductivity type dopant of the third semiconductor layer into a portion of the second semiconductor layer immediately below the ridge corresponding to the region immediately below the ridge, so that the second conductivity type of the portion immediately below the ridge is diffused. A step of increasing the doping concentration to 1 × 10 ¹⁷ cm ⁻³ or more;
Forming a surface of the ridge and an electrode layer covering a side portion of the ridge corresponding to the side of the ridge among the second semiconductor layer. In the manufacturing method of the semiconductor laser device according to claim 9,
The step of forming the ridge includes a step of forming a striped etching mask made of an inorganic insulating film on the third semiconductor layer, and a step of forming the mask of the third semiconductor layer using the inorganic insulating film as a mask. A method of manufacturing a semiconductor laser device, comprising a step of removing portions corresponding to both sides. In the manufacturing method of the semiconductor laser device according to claim 9,
A step of forming an inorganic insulating film covering the surface of the ridge and the side portion of the ridge of the second semiconductor layer after the ridge is formed and before the heat treatment is performed. Production method. In the manufacturing method of the semiconductor laser device according to claim 9,
A method of manufacturing a semiconductor laser device, wherein when forming the third semiconductor layer, at least a lowermost layer of the third semiconductor layer is doped with zinc (Zn) as the dopant of the second conductivity type. In the manufacturing method of the semiconductor laser device according to claim 9,
A method of manufacturing a semiconductor laser device, wherein when forming the first semiconductor layer, the first semiconductor layer is doped with carbon (C) as a dopant of the second conductivity type. In the manufacturing method of the semiconductor laser device according to claim 13,
The doping concentration of the second conductivity type using the carbon (C) as a dopant in the first semiconductor layer is set to be equal to or higher than the doping concentration of the second conductivity type reached by the heat treatment and the portion immediately below the ridge of the second semiconductor layer. A method of manufacturing a semiconductor laser device. In the manufacturing method of the semiconductor laser device according to claim 9,
A method of manufacturing a semiconductor laser device, wherein the heat treatment is performed at a temperature of 600 to 800 ° C. In the manufacturing method of the semiconductor laser device according to claim 9,
Forming a semiconductor layer having a second conductivity type doping concentration of 1 × 10 ¹⁸ cm ⁻³ or more as the uppermost layer of the third semiconductor layer;
Heat treatment is performed after the formation of the electrode layer to form a high-concentration compound layer composed of the constituent elements of the electrode layer and the constituent elements of the ridge top at the interface between the electrode layer and the top of the ridge. A low-concentration compound layer comprising a constituent element of the electrode layer and a constituent element of the second semiconductor layer is formed at an interface between the electrode layer and the ridge side portion of the second semiconductor layer. Manufacturing method of semiconductor laser device.   An optical disc apparatus comprising the semiconductor laser element according to claim 1.   An optical transmission system comprising the semiconductor laser device according to claim 1.

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