JP2008311472A - Semiconductor laser element - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a semiconductor laser element wherein laser output causing no COD is increased and a proportional limit on a low output side of an input electric power and the laser output is made small. <P>SOLUTION: The semiconductor laser element A includes a substrate 1 and a semiconductor layer 2 wherein an outgoing end surface 2a is formed on the semiconductor layer 2, and a p-type second cladding layer 5d acting as a ridge stripe extending in an axis direction x is formed. The semiconductor laser element A further includes an insulating layer 7 which covers a part connected to the outgoing end surface 2a out of the p-type second cladding layer 5d acting as the ridge stripe, has a thickness of 100-500 Å, and exposes a middle part in the axis direction x out of the p-type second cladding layer 5d. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a semiconductor laser device used, for example, in an optical pickup for recording and reproducing CDs and DVDs.

  Laser light is widely used for recording and reproduction of CDs and DVDs. Normally, a relatively large output laser beam is used when performing a recording process, and a relatively small output laser beam is used when performing a reproduction process. For this reason, an optical pickup that performs both recording and reproduction processing is required to have a semiconductor laser element having a wide output range of light that can be emitted.

  FIG. 9 shows an example of a semiconductor laser element used for such an application (see, for example, Patent Document 1). The semiconductor laser device X shown in the figure includes a substrate 91, a semiconductor layer 92, a current confinement layer 96a, a p-type contact layer 96b, an n-side electrode 98a, and a p-side electrode 98b. The substrate 91 is made of n-type GaAs, for example, and supports the semiconductor layer 92. The semiconductor layer 92 includes an n-type cladding layer 93a, an n-type guide layer 93b, an active layer 94, a p-type guide layer 95a, a p-type first cladding layer 95b, an etching stop layer 95c, and a p-type second cladding layer 95d in the vertical direction. For example, it is composed of an InGaAlP-based compound semiconductor. The current confinement layer 96a is formed so as to sandwich the p-type second cladding layer 95d in the lateral direction y, and is made of, for example, an n-type semiconductor. The p-type contact layer 96b is made of a p-type semiconductor, and is provided to make an ohmic contact with the p-side electrode 98b. The n-side electrode 98 a and the p-side electrode 98 b are electrodes for applying a voltage to the semiconductor layer 92.

  The p-type second cladding layer 95d has a trapezoidal cross section extending in the axial direction x, and is a so-called ridge stripe. Of the semiconductor layer 92, only the p-type second cladding layer 95d in the ridge stripe contacts the p-type contact layer 96b. Thereby, the light emitted from the active layer 94 is guided along the p-type second cladding layer 95d. The guided light is emitted as laser light by repeating reflection between the emission end faces 92a arranged in parallel in the axial direction x. Laser light guided by a structure having a ridge stripe is suitable for high output.

  When performing a recording process on a CD or DVD, it is aimed to increase the laser output for the purpose of improving the recording speed. However, when a high-power laser beam is emitted, optical damage (hereinafter referred to as COD: Catastrophic Optical Damage) in which the vicinity of the emission end surface 92a of the semiconductor layer 92 is damaged by heat generation is likely to occur. For this reason, when the semiconductor laser element X is used, it is necessary to suppress the output to such an extent that no COD occurs.

  On the other hand, when performing reproduction processing on a CD or DVD, it is aimed to make the laser output as small as possible. However, in order to properly control the semiconductor laser element X, it is necessary to use it in a range where the input power and the laser output are in a proportional relationship. When the input power is too small, the proportional limit between the input power and the laser output falls below, and appropriate control cannot be performed.

Thus, in order to use the semiconductor laser element X for recording and reproduction of CDs and DVDs, the laser output that does not cause COD is further increased, and the proportional limit on the low output side between the input power and the laser output is further reduced. Is required.
JP 2004-214289 A

  The present invention has been conceived under the circumstances described above, and it is possible to increase the laser output that does not cause COD and to reduce the proportional limit on the low output side between the input power and the laser output. It is an object of the present invention to provide a semiconductor laser element.

  A semiconductor laser device provided by a first aspect of the present invention includes a substrate and a semiconductor layer including a first conductivity type semiconductor layer, an active layer, and a second conductivity type semiconductor layer stacked on the substrate. The semiconductor layer has an emission end face perpendicular to the in-plane direction of the substrate, and the second conductive semiconductor layer has a ridge stripe extending in a direction perpendicular to the emission end face. The semiconductor laser device is configured to cover a portion of the ridge stripe connected to the emission end face and to expose a portion near the center in the extending direction of the ridge stripe and have a thickness of 100 to 500 mm. It is further characterized by further comprising an insulating layer.

  According to such a configuration, it is possible to appropriately limit the magnitude of the current flowing in the vicinity of the emission end face of the second semiconductor layer. Thereby, the laser output that does not cause COD can be increased to 550 mW or more, and the proportional limit on the low output side between the input power and the laser output can be made smaller than 2 mW.

  In a preferred embodiment of the present invention, the semiconductor device further includes a current confinement layer made of a first conductivity type semiconductor sandwiching the ridge stripe, and the insulating layer is formed to straddle the ridge stripe and the current confinement layer. Has been. According to such a configuration, it is possible to prevent the portion other than the ridge stripe in the second conductivity type semiconductor layer from being unnecessarily conducted with, for example, a contact layer.

  The method of manufacturing a semiconductor laser device provided by the second aspect of the present invention includes a step of forming a semiconductor layer including a first conductivity type semiconductor layer, an active layer, and a second conductivity type semiconductor layer laminated on a substrate. And forming a strip-shaped mask layer covering the second conductive semiconductor layer, and removing a portion of the second conductive semiconductor layer exposed from the mask layer, thereby forming the second conductive semiconductor layer. A step of forming a ridge stripe, a step of forming a current confinement layer made of a first conductivity type semiconductor so as to sandwich the ridge stripe, a step of removing the mask layer, and the ridge stripe and the current confinement layer. A step of forming an insulating layer straddling the semiconductor layer, and dividing the semiconductor layer so as to form an emission end face that is perpendicular to a direction in which the ridge stripe extends and intersects the insulating layer It is characterized by having a step.

  According to such a configuration, the semiconductor laser device provided by the first aspect of the present invention can be appropriately manufactured.

  Other features and advantages of the present invention will become more apparent from the detailed description given below with reference to the accompanying drawings.

  Hereinafter, preferred embodiments of the present invention will be specifically described with reference to the drawings.

FIG. 1 shows an example of a semiconductor laser device according to the present invention. The semiconductor laser device A of this embodiment includes a substrate 1, a semiconductor layer 2, a current confinement layer 6a, a p-type contact layer 6b, an insulating layer 7, an n-side electrode 8a, and a p-side electrode 8b. The semiconductor laser element A includes a semiconductor layer 2
For example, infrared light having a wavelength of 780 nm and red light having a wavelength of 650 nm can be emitted from the emission end face 2a.

  The substrate 1 is a base of the semiconductor laser element A, and is a GaAs substrate, for example. The GaAs substrate is suitable for lattice matching with the semiconductor layer 2. In the present embodiment, the substrate 1 is an n-type semiconductor.

  The semiconductor layer 2 is formed by laminating a layer made of an n-type semiconductor that is a first conductivity type semiconductor, a layer made of a p-type semiconductor that is a second conductivity type semiconductor, and an active layer sandwiched therebetween. . In the present embodiment, the semiconductor layer 2 includes an n-type cladding layer 3a, an n-type guide layer 3b, an active layer 4, a p-type guide layer 5a, a p-type first cladding layer 5b, an etching stop layer 5c, and a p-type first layer. The two clad layers 5d are stacked. The semiconductor layer 2 is formed with a pair of emission end faces 2a extending along the vertical direction x and the horizontal direction y perpendicular to the axial direction x. The semiconductor layer 2 described below is an example made of an InGaAlP-based semiconductor, but is not limited to this. For example, the semiconductor layer 2 may be made of an AlGaAs-based semiconductor.

The n-type cladding layer 3a is a layer for confining light emitted from the active layer 4 in the active layer 4, the n-type guide layer 3b and the p-type guide layer 5a sandwiching the active layer 4. The n-type cladding layer 3a has, for example, n-type In _0.5 (Ga _{1 -p} Al _p ) _0.5 P (0.3 ≦ p ≦ 0.9, for example, p = 0.7) and a carrier concentration of 8 × 10 ¹⁷ cm ^−. The thickness is about ³ , and the thickness is about 1 to ³ μm.

The n-type guide layer 3 b is a layer for confining electrons and holes injected into the active layer 4. The n-type guide layer 3b is made of, for example, undoped In _0.5 (Ga _{1 -q} Al _q ) _0.5 P (0.4 ≦ q ≦ 0.6, for example, q = 0.5), and has a thickness of 2 to 10 nm. It is said that.

The active layer 4 is a layer that emits light by recombination of electrons and holes. The active layer 4 has a well layer made of In _0.5 (Ga _{1 -r} Al _r ) _0.5 P (0 ≦ r ≦ 0.1, for example, r = 0) having a thickness of 3 to 9 nm and a thickness of 3 to 9 nm, for example. A multi-quantum well structure (for example, 3 well layers) with a barrier layer of undoped In _0.5 (Ga _{1 -s} Al _s ) _0.5 P (0.1 ≦ s ≦ 0.5, preferably s = 0.5) Layer and barrier layer).

The p-type guide layer 5 a is a layer for confining electrons and holes injected into the active layer 4. The p-type guide layer 5a is made of, for example, undoped In _0.5 (Ga _{1 -q} Al _q ) _0.5 P (0.4 ≦ q ≦ 0.6, for example, q = 0.5), and has a thickness of 5 to 15 nm. It is said that.

The p-type first cladding layer 5b is a layer for confining light emitted from the active layer 4 in the active layer 4, the n-type guide layer 3b and the p-type guide layer 5a sandwiching the active layer 4. The p-type first cladding layer 5b is formed of p-type In _0.5 (Ga _{1 -t} Al _t ) _0.5 P (0.3 ≦ t ≦ 0.9, for example, t = for example, having a carrier concentration of about 1 × 10 ¹⁸ cm ^−3. 0.7), and its thickness is 0.1 to 0.4 μm.

The etching stop layer 5c is a layer for preventing the etching process for forming the p-type second cladding layer 5d from reaching the p-type first cladding layer 5b. The etching stop layer 5c is, for example, p-type In _0.5 (Ga ₁ -u Al _u ) _0.5 P (0 ≦ u ≦ 0.5, having a thickness of 1 to 5 nm and a carrier concentration of about 1 × 10 ¹⁸ cm ⁻³ . For example, p-type In _0.5 (Ga _{1 -v} Al _v ) _0.5 P (0 ≦ v ≦ 0) having a layer of u = 0.1) and a carrier concentration of ³ to 10 nm and a carrier concentration of about 1 × 10 ¹⁸ cm ^−3. 0.5, for example, v = 0.4) is formed by laminating three and two layers, respectively.

The p-type second cladding layer 5d is finished in a trapezoidal cross section extending in the axial direction x, and is a ridge stripe that is one of the characteristic portions of a general semiconductor laser element. The p-type second cladding layer 5d is, for example, p-type In _0.5 (Ga _{1 -t} Al _t ) _0.5 P (0.3 ≦ t ≦ 0.9, preferably about 1 × 10 ¹⁸ cm ⁻³ , preferably t = 0.7), the thickness is 1 to 1.7 μm, and the width is 1 to 3 μm.

The current confinement layer 6a is a layer for limiting the portion of the semiconductor layer 2 that is directly connected to the p-type contact layer 6b to the p-type second cladding layer 5d. The current confinement layer 6a is formed on the etching stop layer 5c so as to sandwich the p-type second cladding layer 5d. The current confinement layer 6a is made of, for example, n-type In _0.5 (Ga _{1 -a} Al _a ) _0.5 P (0.3 ≦ a ≦ 0.9, eg, a = 0.8), and has a thickness of 0.15. ˜0.5 μm.

  The p-type contact layer 6b is a layer for avoiding the occurrence of a Schottky barrier between the semiconductor layer 2 and the p-side electrode 8b and realizing an ohmic contact state. The p-type contact layer 6b is made of, for example, p-type GaAs and has a thickness of about 1 to 3 μm.

  The insulating layer 7 has a strip shape extending in the lateral direction y, and covers a portion of the p-type second cladding layer 5d and the current confinement layer 6a that are connected to the emission end face 2a. In the present embodiment, the insulating layer 7 is formed over the entire width y of the semiconductor laser element A in the lateral direction. The insulating layer 7 is made of, for example, SiNx, and has a thickness of 100 to 500 mm and a width of about 10 to 40 μm.

  The n-side electrode 8a covers the back surface of the substrate 1, and has a structure in which, for example, Au / Ge / Ni / Ti / Au is laminated. The p-side electrode 8b covers the p-type contact layer 6b and has a structure in which, for example, Ti / Au or the like is laminated.

  Next, an example of a method for manufacturing the semiconductor laser element A will be described below with reference to FIGS. In this manufacturing method, a plurality of semiconductor laser elements A are manufactured in a lump. In these drawings, an area slightly larger than an area where one semiconductor laser element A is obtained is shown.

First, as shown in FIG. 2, a semiconductor layer 2 ′ is formed on a substrate 1 ′. The substrate 1 ′ is sized so that a plurality of substrates 1 shown in FIG. 1 can be obtained, and is an n-type GaAs substrate. The substrate 1 ′ is placed in, for example, a MOCVD (metal organic chemical vapor deposition) apparatus, and reactive gases such as triethylgallium (TEG), trimethylaluminum (TMA), trimethylindium (TMIn), phosphine (PH ₃ ), arsine (AsH). ₃ ) Depending on the conductivity type of the semiconductor layer, SiH ₄ as an n-type dopant gas or dimethyl zinc (DMZn) as a p-type dopant is introduced together with hydrogen (H ₂ ) as a carrier gas, and a semiconductor is formed at about 500 to 700 ° C. Is epitaxially grown. Thus, the n-type cladding layer 3a ′, the n-side guide layer 3b ′, the active layer 4 ′, the p-side guide layer 5a ′, the p-type first cladding layer 5b ′, the etching stop layer 5c ′, and the p-type second cladding. Layer 5d 'is formed. n-type cladding layer 3a ′, n-side guide layer 3b ′, active layer 4 ′, p-type guide layer 5a ′, p-type first cladding layer 5b ′, etching stop layer 5c ′, and p-type second cladding layer 5d ′ The n-type cladding layer 3a, the n-side guide layer 3b, the active layer 4, the p-type guide layer 5a, the p-type first cladding layer 5b, the etching stop layer 5c, and the p-type second cladding are described above. Same as layer 5d. Then, a mask layer 52 is formed on the second p-type cladding layer 5d ′. The mask layer 52 is formed by, for example, a CVD method using SiO ₂ or SiNx, and has a strip shape with a width of 1 to 3 μm extending in the axial direction x.

  Next, as shown in FIG. 3, the p-type second cladding layer 5d 'is etched, for example. In this etching, the mask layer 52 performs a mask function, so that a portion of the p-type second cladding layer 5d 'exposed from the mask layer 52 is removed. Thereby, the p-type second cladding layer 5d 'is finished in a trapezoidal strip shape extending in the axial direction x. The etching stop layer 5c 'is configured not to be eroded by this etching. Therefore, the etching does not reach the p-type first cladding layer 5b '.

  Next, as shown in FIG. 4, a current confinement layer 6a 'is formed. In order to create the current confinement layer 6a ′, for example, by appropriately setting the growth conditions in MOCVD, the semiconductor is applied to the portions of the etching stop layer 5c ′ and the p-type second cladding layer 5d ′ that are exposed from the mask layer 52. The process of selectively growing is performed. Thus, the current confinement layer 6a 'is formed so as to sandwich the p-type second cladding layer 5d' in a region avoiding the mask layer 52.

  Next, as shown in FIG. 5, the mask layer 52 is removed by etching, for example. As a result, the p-type second cladding layer 5d 'and the current confinement layer 6a' are exposed. Next, as shown in FIG. 6, an insulating layer 7 'is formed. The insulating layer 7 'is formed, for example, by patterning a film made of SiNx formed by a CVD method by etching. In the present embodiment, a plurality of strip-like insulating layers 7 ′ extending in the lateral direction y are arranged at equal intervals in the direction x. Next, the p-type contact layer 6b 'is formed by, for example, the MOCVD method so as to cover the plurality of insulating layers 7', the p-type second cladding layer 5d ', and the current confinement layer 6a'. Then, a p-side electrode 8b 'is formed so as to cover the p-type contact layer 6b'. Further, after the substrate 1 ′ is appropriately thinned by grinding or the like, the n-side electrode 8 a ′ is formed on the back surface of the substrate 1 ′. Thereafter, the substrate 1 'is broken along the cutting line Cy. By this cleavage step, the emission end face 2a is formed. Immediately after this cleavage step, a coating process for protecting the emission end face 2a may be appropriately performed. Next, the substrate 1 ′ is divided along the cutting line Cx. Through the above steps, the semiconductor laser device A shown in FIG. 1 is obtained.

  Next, the operation of the semiconductor laser element A and its manufacturing method will be described.

  In the present embodiment, the insulating layer 7 serves to limit the current flowing through both end portions in the axial direction x of the second p-type cladding layer 5d. Thereby, the effect which suppresses the heat_generation | fever in the emission end surface 2a vicinity part of the semiconductor layer 2 is acquired. If heat generation in the vicinity of the exit end face 2a is suppressed, light absorption in this portion is reduced, and heat generation due to light absorption is also suppressed. Therefore, it is possible to avoid COD caused by a so-called positive feedback loop of heat generation due to current and heat generation due to light absorption.

  On the other hand, a portion of the active layer 4 that is made a current non-injection region by the insulating layer 7 is a region that absorbs light because an inversion portion is not formed even when current is applied. Only when the light emission phenomenon (gain) from the current injection region of the active layer 4 exceeds the light absorption (loss) by the current non-injection region, laser oscillation becomes possible. Therefore, when the current flowing through the semiconductor laser element A exceeds a certain value, the output of the laser beam rises sharply.

  As a means for suppressing light absorption in the vicinity of the emission end face 2a, a so-called window structure is formed. The window structure is formed, for example, by diffusing Zn in the vicinity of the emission end face 2a. However, for example, an AlGaAs semiconductor has a small Zn diffusion coefficient, and it is difficult to form a window structure.

  As described above, in a semiconductor laser element having a current non-injection region but cannot be applied with a window structure, the specific specification of the insulating layer 7 that causes the current injection region is important. As a result of repeated studies on this point, the inventors have found that the above-described problem can be solved by setting the thickness of the insulating layer 7 to 100 to 500 mm.

  FIG. 7 shows the relationship between the lower limit level Lk at which the input power to the semiconductor laser element A and the luminance of the emitted laser light can maintain a proportional relationship, and the thickness t of the insulating layer 7. As shown in the figure, if the thickness t is smaller than 500 mm, the lower limit level Lk can be set to a value lower than 2 mW. Thereby, for example, when reproducing a CD or DVD, it is possible to use a laser beam with a very low output of 2 mW or less.

  On the other hand, FIG. 8 shows the relationship between the level Lc at which COD occurs at the emission end face 2 a and the thickness t of the insulating layer 7. As shown in the figure, when the thickness t is 100 mm or more, the level Lc can be set to 550 mW or more. Therefore, it is possible to use a relatively high-power laser beam when performing, for example, a CD or DVD recording process.

Setting the level Lk to a small value and the level Lc to a large value is achieved by appropriately limiting the magnitude of the current flowing through the second p-type cladding layer 5d by the insulating layer 7. In order to provide such a function to the insulating layer 7, it is preferable to use SiNx as the material of the insulating layer 7. SiNx is a material having a slightly better electrical conductivity than, for example, SiO _2, and it is easy to control the magnitude of the flowing current by its thickness.

  Further, if the insulating layer 7 is provided over the entire width y of the semiconductor laser element A, there is no possibility that the p-type second cladding layer 5d and the p-type contact layer 6b are unfairly contacted in the vicinity of the emission end face 2a. . In the manufacturing process of the semiconductor laser element A, the mask layer 52 shown in FIG. 4 is used to finish the p-type second cladding layer 5d ′ as a ridge stripe, the mask layer 52 is removed, and the p-type second cladding layer 5d ′ If the insulating layer 7 ′ is formed with the current confinement layer 6a ′ exposed, the insulating layer 7 ′ can be easily formed so as to straddle the p-type second cladding layer 5d ′ and the current confinement layer 6a ′ sandwiching the p-type second cladding layer 5d ′. Can be formed.

  The semiconductor laser device and the manufacturing method thereof according to the present invention are not limited to the above-described embodiments. The specific configuration of the semiconductor laser device and the manufacturing method according to the present invention can be varied in design in various ways.

It is a perspective view which shows an example of the semiconductor laser element concerning this invention. It is a principal part perspective view which shows the process of forming a semiconductor layer in an example of the manufacturing method of the semiconductor laser element concerning this invention. It is a principal part perspective view which shows the process of forming a ridge stripe in an example of the manufacturing method of the semiconductor laser element concerning this invention. It is a principal part perspective view which shows the process of forming a current confinement layer in an example of the manufacturing method of the semiconductor laser element concerning this invention. It is a principal part perspective view which shows the process of removing a mask layer in an example of the manufacturing method of the semiconductor laser element concerning this invention. It is a principal part perspective view which shows the process of forming an insulating layer in an example of the manufacturing method of the semiconductor laser element concerning this invention. It is a graph which shows the relationship between the thickness of an insulating layer, and a proportional limit level. It is a graph which shows the relationship between the thickness of an insulating layer, and the level which produces COD. It is a perspective view which shows an example of the conventional semiconductor laser element.

Explanation of symbols

A Semiconductor laser element x Axial direction y Horizontal direction z Longitudinal direction 1, 1 ′ Substrate 2, 2 ′ Semiconductor layer 2a, 2a ′ Emission end face 3a, 3a ′ n-type cladding layer 3b, 3b ′ n-type guide layer 4, 4 ′ Active layers 5a, 5a ′ p-type guide layers 5b, 5b ′ p-type first cladding layers 5c, 5c ′ etching stop layers 5d, 5d ′ p-type second cladding layers 6a, 6a ′ current confinement layers 6b, 6b ′ p-type Contact layer 7, 7 'Insulating layer 8a, 8a' n-side electrode 8b, 8b 'p-side electrode 52 Mask layer

Claims (3)

A semiconductor layer including a substrate and a first conductive semiconductor layer, an active layer, and a second conductive semiconductor layer stacked on the substrate;
The semiconductor layer has an emission end face that is perpendicular to the in-plane direction of the substrate,
A semiconductor laser element in which a ridge stripe extending in a direction perpendicular to the emission end face is formed on the second conductivity type semiconductor layer,
Covering the portion of the ridge stripe connected to the emission end face, exposing the portion of the ridge stripe closer to the center in the extending direction, and further comprising an insulating layer having a thickness of 100 to 500 mm. A semiconductor laser device characterized by the above. A current confinement layer made of a first conductivity type semiconductor sandwiching the ridge stripe;
2. The semiconductor laser device according to claim 1, wherein the insulating layer is formed so as to straddle the ridge stripe and the current confinement layer. Forming a semiconductor layer including a first conductivity type semiconductor layer, an active layer, and a second conductivity type semiconductor layer stacked on each other on a substrate;
Forming a strip-shaped mask layer covering the second conductive semiconductor layer;
Removing a portion of the second conductive semiconductor layer exposed from the mask layer to form a ridge stripe made of the second conductive semiconductor;
Forming a current confinement layer made of a first conductivity type semiconductor so as to sandwich the ridge stripe;
Removing the mask layer;
Forming an insulating layer straddling the ridge stripe and the current confinement layer;
Dividing the semiconductor layer so as to form an emission end face that is perpendicular to a direction in which the ridge stripe extends and intersects the insulating layer;
A method for manufacturing a semiconductor laser device, comprising:

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