JP6347573B2 - Semiconductor laser element - Google Patents

Description

  The present invention relates to a semiconductor laser device.

  Semiconductor laser devices are widely used for recording / reproducing applications of CD (Compact Disc) and DVD (Digital Versatile Disc). In recent years, semiconductor laser elements are expected to be applied to solid-state laser devices, remote sensing applications, gas laser alternative applications, green laser light sources using SHG (Second Harmonic Generation), and the like. These applications require laser oscillation in the infrared region and a high output exceeding 200 mW.

  As a factor that limits the increase in the output of a semiconductor laser element, COD (catalytic optical damage) is known. COD is caused by non-radiative recombination due to the deep interface state between the end face coating film formed on the laser emission end face of the resonator and the end face active layer, thereby generating heat near the end face, With this heat generation, the band gap is further reduced, and as a result, positive feedback occurs in which non-radiative recombination is further promoted. Eventually, the semiconductor crystal is eluted by high heat, and laser oscillation becomes impossible. It is a phenomenon. Hereinafter, an output voltage at which the semiconductor laser element reaches the COD is also referred to as a COD level.

  As means for increasing the COD level, for example, as disclosed in Japanese Patent Application Laid-Open No. 2009-27012 (Patent Document 1), impurities are diffused near the end face of the laser emitting portion of the resonator, and the band gap near the end face is widened. Thus, an end window structure that reduces light absorption has been proposed. Further, for example, Japanese Patent Laid-Open No. 05-218593 (Patent Document 2) proposes a method of forming a window structure in which only a window layer in which Zn is diffused as an impurity is increased in energy. These techniques are applied to, for example, a 650 nm band semiconductor laser for DVD.

  Japanese Patent Laid-Open No. 2001-345514 (Patent Document 3) relates to a semiconductor laser in an infrared region having a window structure, by using a compound semiconductor having a quaternary composition of AlGaInP as a cladding layer of a laser part, There is disclosed a technique for improving the diffusion coefficient, promoting the mixed crystallization of AlGaAs / GaAs, which is a multiple quantum well layer (hereinafter also referred to as MQW (Multiple Quantum Well) layer), and forming a window structure. This technique is used for, for example, a semiconductor laser for CD.

JP 2009-27012 A JP 05-218593 A JP 2001-345514 A

  However, with any of the above technologies, in a semiconductor laser having an oscillation wavelength of 800 nm or more, which is expected as a light source for solid-state laser devices and remote sensing applications, a window structure that can withstand a high-power laser exceeding 200 mW can be formed. It was difficult.

  This is because an increase in threshold current due to carrier overflow cannot be sufficiently suppressed. Carrier overflow is a phenomenon in which, when a large current is applied, carriers in the optical waveguide of the resonator leak from the active layer to the cladding layer due to heat generated during laser oscillation and cause gain saturation. In general, in order to increase the output of a semiconductor laser, it is necessary to reduce the light density by reducing the active layer to improve the light output. However, with the thinning of the active layer, it becomes difficult to confine carriers injected into the active layer in the active layer. Thereby, it becomes easy to leak a carrier and it leads to a carrier overflow.

  Since the threshold current increases due to the carrier overflow, the low threshold operation and the light emission efficiency cannot be improved due to the quantum effect. Further, when the threshold current increases, useless power consumption increases and the temperature of the resonator rises to induce COD.

Here, in general, the threshold current (J _th ) is represented by the following formula (1).

In equation (1), η _i indicates the internal quantum efficiency, Γ indicates the optical confinement factor, Rf indicates the exit-side end surface reflectivity, Rr indicates the reflect-side end surface reflectivity, and L indicates the length of the resonator. , D represents the thickness of the active layer, α _i represents the internal absorption coefficient, and β represents the gain coefficient.

  From equation (1), it is considered effective to reduce the thickness d of the active layer to reduce the threshold current. However, for example, in a semiconductor laser using a GaAs quantum well as in Patent Document 2, considering that the bulk wavelength of GaAs is about 873 nm, the thickness of the well layer is required for low threshold operation due to the quantum effect. The thickness cannot be 8 nm or less, and the emission wavelength is limited to about 840 nm.

  Further, when the well layer is thick as described above, there is a problem in that when the AlGaAs as the barrier layer and the guide layer is mixed and crystallized in the formation of the window structure, the window portion is difficult to become transparent. .

  In addition, conventionally, it is known that introducing a compressive strain in a quantum well, solving the degeneration of heavy holes and light holes, and reducing the effective mass of heavy holes is effective for lowering the threshold current. However, it is not sufficient as means for solving the above problems.

  The present invention has been made in view of the current situation as described above. The object of the present invention is to oscillate at a wavelength of 800 nm to 960 nm and maintain a low threshold current and high efficiency while maintaining a high COD level. Another object is to provide a semiconductor laser device.

  The present inventor has intensively studied to solve the above-mentioned problems. As a result, in a resonator having a region (hereinafter also referred to as a window region) in which a window structure in which impurities are diffused is formed in the vicinity of the end face of the laser emitting portion. In the case where the MQW layer is composed of a thin well layer using InGaAs, and a barrier layer and a guide layer using AlGaAs, it is found that In and Al are interdiffused in each layer. If this phenomenon is utilized, In can be diffused into the active layer to further widen the band gap of the active layer belonging to the window region, and it is not possible to form a high-quality window structure that can withstand high-power lasers. I came up with the idea. Based on this idea, the present inventor has further studied to construct a semiconductor laser device that can be operated with a low threshold current by compressive strain and that can achieve a high output of an emission wavelength of about 900 nm. The title and the present invention have been completed.

That is, the semiconductor laser device of the present invention includes a first conductivity type GaAs substrate, a first conductivity type first cladding layer formed on the substrate, and an In _y Ga _{( 1-y)} an active layer including a well layer made of As (0.08 <y <0.25), a second conductivity type second cladding layer formed on the active layer, and the second cladding layer A ridge stripe-shaped laminated body in which a second conductivity type third cladding layer, a first intermediate layer, a second intermediate layer, and a contact layer are laminated in this order. The laminated body constitutes an optical waveguide, and the band gap of the active layer is maximum on the end face perpendicular to the longitudinal direction of the optical waveguide.

  Here, the first conductivity type means a p-type or n-type conductivity type, and the second conductivity type means a p-type or n-type conductivity type different from the first conductivity type.

  Moreover, it is preferable that the well layer in the end face perpendicular to the longitudinal direction of the optical waveguide is mixed.

  The active layer on the end face perpendicular to the longitudinal direction of the optical waveguide is a window region in which impurities are diffused, and it is preferable that Zn is diffused in the window region. Furthermore, it is preferable that In of the well layer is diffused in the window region.

The active layer preferably has a multiple quantum well structure in which the well layers and barrier layers made of Al _x Ga _(1-x) As (0 ≦ X ≦ 0.5) are alternately stacked. .

The thickness of the active layer is preferably 3 nm or more and 8 nm or less.
Further, the relative lattice constant difference Δa between AlGaAs as the guide layer and the barrier layer and InGaAs as the well layer and the lattice constant a of the barrier layer are expressed by the following formula:
0.01 ≦ Δa / a ≦ 0.02
It is preferable to satisfy.

The active layer preferably includes at least two well layers.
When the difference between the peak wavelength of the photoluminescence spectrum of the active layer not belonging to the window region and the peak wavelength of the photoluminescence spectrum of the active layer belonging to the window region is Δλ, Δλ is preferably 50 nm or more. Hereinafter, photoluminescence is also referred to as PL (Photoluminescence), and the peak wavelength of the PL spectrum is also referred to as PL peak wavelength.

  Moreover, it is preferable that the energy difference of the relative valence band between the third cladding layer, the first intermediate layer, the second intermediate layer, and the contact layer is 0.15 eV or less.

  The third cladding layer preferably contains AlGaInP.

  The semiconductor laser device of the present invention oscillates at a wavelength of 800 nm to 960 nm, and exhibits an excellent effect that the COD level is high while maintaining a low threshold current and high efficiency.

It is a typical perspective view of the semiconductor laser element of an embodiment. It is a typical top view of the semiconductor laser element of an embodiment. It is sectional drawing in the resonator longitudinal direction seen from the cut surface line III-III shown by FIG. It is typical sectional drawing which shows an example of the active layer of the semiconductor laser element of embodiment. It is typical sectional drawing which shows an example of the intermediate | middle layer of the semiconductor laser element of embodiment. It is a figure which shows the relationship between the difference ((DELTA) (lambda)) of PL peak wavelength of the active layer except a window area | region, and PL peak wavelength of the active layer which belongs to the window area | region where the impurity diffused, and impurity diffusion time. It is a figure which shows the relationship between (DELTA) (lambda) and a COD level. It is a figure which shows the relationship between (DELTA) a / a and a critical film thickness. It is a figure which shows the relationship between (DELTA) a / a and a threshold current. It is a figure which shows the relationship between critical film thickness and In composition ratio of a well layer. It is a figure which shows the relationship between critical film thickness at the time of setting a well thickness fixed, and In composition ratio of a well layer. It is a figure which shows the relationship between In composition ratio of a well layer, and PL peak wavelength. It is a figure which shows the relationship between the structure of an intermediate | middle layer, and IV characteristic. It is a figure which shows the relationship between element resistance and the relative energy difference between each layer.

  A semiconductor laser device according to an embodiment of the present invention will be described below with reference to FIGS. In the drawings of the present invention, the same reference numerals represent the same or corresponding parts. In addition, dimensional relationships such as length, width, thickness, and depth are changed as appropriate for clarity and simplification of the drawings, and do not represent actual dimensional relationships.

<Semiconductor laser element>
≪Element configuration≫
Hereinafter, the configuration of the semiconductor laser device 1 of the embodiment will be described. FIG. 1 is an example of a schematic perspective view of the semiconductor laser element 1, and FIG. 2 is an example of a schematic top view of the semiconductor laser element 1. 3 is a cross-sectional view taken along the line III-III of the semiconductor laser device 1 shown in FIG.

As shown in FIG. 3, the semiconductor laser device 1 includes an n-type GaAs buffer layer (not shown) and an n-type GaInPAs first cladding layer on an n-type GaAs substrate 2. 3, a lower guide layer 4 made of n-type AlGaAs, and an active layer 5 including a well layer 51 made of In _y Ga _(1-y) As. As shown in FIG. 4, the active layer 5 is an MQW layer in which well layers 51 made of In _y Ga _(1-y) As and barrier layers 52 made of Al _x Ga _(1-x) As are alternately stacked. It is.

  On the active layer 5, an upper guide layer 6 made of p-type AlGaAs and a second cladding layer 7 made of p-type AlGaAs are stacked.

  Further, on the second cladding layer 7, a third cladding layer 8 made of p-type GaInP, an intermediate layer 9 made of p-type AlGaAs, and a contact layer 10 made of p-type GaAs are arranged in this order. A ridge stripe-shaped laminated body 30 including a structure laminated in the above is provided. The ridge stripe-shaped laminate 30 constitutes an optical waveguide. The intermediate layer 9 has a two-layer structure including a first intermediate layer 91 and a second intermediate layer 92 as shown in FIG.

  In addition, as shown in FIGS. 1 and 2, the semiconductor laser device 1 has a window region 20 having a depth t in the longitudinal direction of the resonator and Zn (zinc) diffused as an impurity at the cavity end face. ing. A current non-injection region (not shown) is formed so as to cover the window region 20 shown in FIG.

  The semiconductor laser device 1 is characterized in that the band gap of the active layer 5 in the optical waveguide is maximum at the end face of the optical waveguide. Here, the phrase “maximum at the end face” means that it is maximum at at least one of the two end faces of the optical waveguide, and preferably maximum at both end faces.

  The semiconductor laser device 1 of the embodiment having the above configuration has high output and high reliability in the infrared wavelength band (that is, wavelength of 800 nm or more and 960 nm or less), and has a low threshold current. It is an excellent semiconductor laser device having both characteristics.

Hereinafter, each part which comprises the semiconductor laser element 1 of embodiment is demonstrated.
≪GaAs substrate≫
The GaAs substrate 2 is preferably composed of GaAs (gallium arsenide) doped with n-type impurities. For example, Si (silicon) can be used as the n-type impurity. The thickness of the substrate 2 is not particularly limited, and can be about 450 μm, for example.

≪Buffer layer≫
A buffer layer (not shown) is stacked on the GaAs substrate 2. The buffer layer is preferably made of GaAs doped with n-type impurities. For example, Si can be used as the n-type impurity. The thickness of the buffer layer is not particularly limited, and can be about 200 nm, for example.

≪First cladding layer≫
The first cladding layer 3 is laminated on the buffer layer and has a function of efficiently confining light generated from the carriers and the active layer 5. The first cladding layer 3 is preferably composed of GaInPAs (gallium indium phosphide arsenide) doped with n-type impurities. For example, Si can be used as the n-type impurity. The thickness of the first cladding layer 3 is not particularly limited, and can be, for example, about 3000 nm. The chemical composition of GaInPAs is preferably Ga _0.5 In _0.5 PAs.

≪Lower guide layer≫
The lower guide layer 4 is stacked on the first cladding layer 3 and has a function of confining light in cooperation with the first cladding layer 3. Here, the lower guide layer 4 is formed so as to have a higher refractive index than the first cladding layer 3, whereby light can be confined to the lower guide layer 4 side. The lower guide layer 4 is preferably made of AlGaAs (aluminum gallium arsenide) doped with n-type impurities. Here, for example, Si can be used as the n-type impurity. The thickness of the lower guide layer 4 is not particularly limited, and can be about 80 nm, for example. In addition, AlGaAs preferably has a chemical composition of Al _0.3 Ga _0.7 As.

≪Active layer≫
The active layer 5 is a layer that generates light by radiative recombination of electrons and holes, and as shown in FIG. 4, non-doped In _y Ga _(1-y) As (0.08 <y <0.25). Well layers 51 and barrier layers 52 made of Al _x Ga _(1-x) As (0 ≦ x ≦ 0.5) doped with p-type impurities are stacked in multiple quantum wells It has a structure. The thickness of the active layer 5 is preferably 65 nm or more and 100 nm or less.

  The thickness of the well layer 51 is preferably 3 nm or more and 8 nm or less. If the thickness of the well layer 51 is less than 3 nm, it is difficult to control the thickness, which is not preferable from the viewpoint of productivity. If the thickness exceeds 8 nm, Zn as an impurity becomes difficult to diffuse when forming the window region. There is a problem that. Here, a more preferable thickness of the well layer 51 is 5 nm.

The active layer 5 preferably includes at least two well layers 51 made of In _y Ga _(1-y) As (0.08 <y <0.25). Thereby, good laser oscillation characteristics can be obtained. Furthermore, the well layer 51 belonging to the window region 20 is preferably mixed. The window region 20 can be made to have a higher quality window structure by the mixed crystallization.

  In the semiconductor laser device of the embodiment, the band gap of the active layer in the optical waveguide has a feature that it is the largest on at least one of the end faces perpendicular to the longitudinal direction of the optical waveguide. That is, by making the band gap of the end face active layer relatively large compared to the inside of the device, it is possible to reduce laser light absorption, prevent end face destruction, and increase the COD level. The active layer having such characteristics is realized by diffusing In contained in the well layer into the window region near the laser emission end face as follows.

Here, in the case where a well layer made of GaAs conventionally known is used for the MQW layer, and in the case where the well layer made of In _0.15 Ga _0.85 As (ie, y = 0.15) is used for the MQW layer, FIG. 6 shows the relationship between Δλ and the impurity diffusion time, where Δλ is the difference between the PL peak wavelength of the active layer not belonging to the active layer and the PL peak wavelength of the active layer belonging to the window region where impurities are diffused. Here, Δλ indicates the degree of completion of the window region 20. In measuring the data of FIG. 6, the impurity diffusion temperature is 537.degree.

  As is apparent from FIG. 6, in the case where a well layer made of GaAs is used for the MQW layer, Δλ shows a maximum value around a diffusion time of 120 minutes and then decreases. This is considered to be because In in AlGaInP used for the cladding layer diffuses into the window region, the PL peak wavelength in the window region becomes longer, and as a result, Δλ is reduced.

On the other hand, when the well layer made of InGaAs is used for the MQW layer, Δλ increases according to the impurity diffusion time, and is approximately 2 as compared with the maximum value of the well layer made of GaAs around the impurity diffusion time of 180 minutes. It is about 90 nm which is twice or more. This is because when the well layer made of InGaAs is used for the MQW layer, the PL peak wavelength in the window region is shortened by the diffusion of In in the well layer, and Al is mixed in from the AlGaAs used in the barrier layer. Therefore, it is considered that the wavelength shift of the window region becomes large. Therefore, since the active layer 5 includes the well layer 51 made of In _y Ga _(1-y) As, it is possible to configure Δλ to be 50 nm or more.

  FIG. 7 shows the relationship between Δλ and the COD level (the output at which the semiconductor laser element reaches COD). There is a strong correlation between Δλ and the COD level, and the COD level increases as Δλ increases. That is, as Δλ increases, the window structure becomes of higher quality and the output of the semiconductor laser device can be increased. If Δλ is 50 nm or more, a high-power semiconductor laser device of 200 mW or more can be realized.

In addition, as described below, the semiconductor laser device of the embodiment has a guide layer and a barrier formed by limiting the In composition ratio y of the well layer made of In _y Ga _(1-y) As to a specific range. It is possible to operate with a low threshold current while controlling the lattice strain between the layer and the well layer and ensuring the crystal quality of the guide layer, the barrier layer, and the well layer.

  Here, when the lattice constant of the barrier layer and the guide layer made of AlGaAs is a, and when the relative difference between the lattice constant of the barrier layer and the guide layer and the lattice constant of the well layer made of InGaAs is Δa, Δa is a The value divided by, that is, Δa / a can be used as an index of lattice distortion. Hereinafter, Δa / a is also referred to as a strain amount.

  FIG. 8 shows the relationship between Δa / a and the critical film thickness. In FIG. 8, the critical film thickness decreases as Δa / a increases. Here, the critical film thickness means a limit film thickness that allows normal crystal growth with respect to the strain amount (Δa / a). When the critical film thickness is exceeded, lattice distortion increases and the morphology of the crystal surface cannot be controlled, so that high-quality crystals cannot be formed.

The semiconductor laser device 1 of the present embodiment includes a well layer 51 made of at least two In _y Ga _(1-y) As, and the thickness of the well layer 51 is opaque in the mixed crystal window region. In order to prevent the problem which becomes, it is preferable that it is 3 nm or more and 8 nm or less. Therefore, when a double quantum well layer (hereinafter also referred to as a DQW (Double Quantum Well) layer) in which the thickness of the well layer 51 is about 5 nm is assumed, the critical film thickness needs to be at least about 10 nm. Therefore, from FIG. 8, Δa / a is preferably 0.02 or less.

  FIG. 9 shows the relationship between Δa / a and the threshold current. From FIG. 9, in order to realize a low threshold current (40 mA or less) by compressive strain, Δa / a is preferably 0.01 or more. Therefore, Δa / a preferably satisfies the relational expression of 0.01 ≦ Δa / a ≦ 0.02.

  Further, from FIG. 8, in order to make Δa / a 0.01 or more, it is preferable that the upper limit of the critical film thickness is about 30 nm.

Further, FIG. 10 shows the relationship between the critical film thickness and y when y is changed in the well layer made of In _y Ga _(1-y) As. From FIG. 10, as described above, in order to ensure a critical film thickness of about 10 nm, y needs to be smaller than 0.25.

FIG. 11 shows the relationship between the critical film thickness and y when y of the well layer made of In _y Ga _(1-y) As is changed when the well thickness is fixed. From FIG. 11, as described above, in order to limit the upper limit of the critical film thickness to about 30 nm, y needs to be larger than 0.08.

Therefore, in the well layer made of In _y Ga _(1-y) As, y needs to satisfy 0.08 <y <0.25.

FIG. 12 shows the calculation result of the PL peak wavelength when the thickness of the well layer is constant below the critical film thickness. If the well layer is made of In _y Ga _(1-y) As (0.08 <y <0.25) and the thickness thereof is 8 nm or less, laser oscillation is possible at a wavelength of 800 nm to 960 nm. I can confirm.

≪Upper guide layer≫
The upper guide layer 6 is laminated on the active layer 5 and plays the same role as the lower guide layer 4 and is used to confine light. The upper guide layer 6 is preferably made of AlGaAs (aluminum gallium arsenide) doped with p-type impurities. Here, as the p-type impurity, for example, Zn can be used. The thickness of the upper guide layer 6 is not particularly limited, and can be about 80 nm, for example. The chemical composition of AlGaAs is preferably Al _0.3 Ga _0.7 As.

≪Second cladding layer≫
The second cladding layer 7 is stacked on the upper guide layer and has a function of confining light in cooperation with the upper guide layer. The second cladding layer 7 is preferably composed of AlGaAs doped with p-type impurities. Here, as the p-type impurity, for example, Zn can be used. The thickness of the second cladding layer 7 is not particularly limited, and can be, for example, about 150 nm. The chemical composition of AlGaAs is preferably Al _0.5 Ga _0.5 As.

≪Third cladding layer, intermediate layer and contact layer≫
The third cladding layer 8, the intermediate layer 9, and the contact layer 10 are stacked on the second cladding layer 7 in this order to form a ridge stripe-shaped stacked body 30. The ridge stripe-shaped laminate 30 constitutes an optical waveguide.

(Third cladding layer)
The third cladding layer 8 is stacked on the second cladding layer 7. The third cladding layer 8 has a function similar to that of the second cladding layer 7 and is preferably composed of GaInP doped with p-type impurities. Here, as the p-type impurity, for example, Zn can be used. The thickness of the third cladding layer 8 is not particularly limited, and can be about 1000 nm, for example. The chemical composition of AlGaInP is preferably Al _0.7 Ga _0.3 InP. AlGaInP is preferable because of its high carrier overflow suppression effect.

(Contact layer)
The contact layer 10 is provided to make an ohmic contact with the electrode. The contact layer 10 is preferably GaAs doped with p-type impurities. Here, as the p-type impurity, for example, Zn can be used. The thickness of the contact layer 10 is preferably 400 nm or less, more preferably 300 nm or less. If the thickness exceeds 400 nm, it is difficult to obtain an ohmic junction, which is not preferable.

(Middle layer)
The intermediate layer 9 is formed so as to be sandwiched between the third cladding layer 8 and the contact layer 10, and has a function of reducing a band energy difference between the third cladding layer 8 and the contact layer 10. Unlike the conventional intermediate layer, the intermediate layer of the present embodiment has a two-layer structure including a first intermediate layer 91 and a second intermediate layer 92 as shown in FIG. The thickness of the intermediate layer 9 is not particularly limited, and can be, for example, about 50 nm. The chemical composition of GaInP constituting the first intermediate layer 91 is preferably Ga _0.5 In _0.5 P, and the chemical composition of AlGaAs constituting the second intermediate layer 92 is preferably Al _0.25 Ga _0.75 As. .

  In the configuration using the conventional intermediate layer, the configuration of the contact layer / intermediate layer / cladding layer is GaAs contact layer / p-type GaInP intermediate layer / p-type AlGaInP cladding layer. At this time, the relative valence band energies of the respective layers based on GaAs are GaAs = 0 eV, GaInP = −0.23 eV, and AlGaInP = −0.46 eV. Therefore, the relative valence band energy difference Ev between the layers is 0.23 eV.

On the other hand, in the semiconductor laser device 1 of the embodiment, the intermediate layer 9 includes the first intermediate layer 91 and the second intermediate layer 92. That is, the configuration of the contact layer / intermediate layer / cladding layer is GaAs contact layer / p-type Al _0.25 Ga _0.75 As second intermediate layer / p-type GaInP first intermediate layer / p-type AlGaInP clad layer. At this time, the relative valence band energies of the respective layers based on GaAs are GaAs = 0 eV, Al _0.25 Ga _0.75 As = −0.11 eV, GaInP = −0.23 eV, and AlGaInP = −0.46 eV. Therefore, the relative valence band energy difference Ev between the layers is 0.15 eV or less.

FIG. 13 shows the case where the intermediate layer is a p-type Al _0.25 Ga _0.75 As second intermediate layer / p-type GaInP first intermediate layer and the intermediate layer is only a p-type GaInP layer. This is a comparison of IV characteristics between a GaAs contact layer and a p-type AlGaInP cladding layer.

  As is apparent from FIG. 13, when the intermediate layer has the configuration of the present invention, a lower voltage is maintained in any current band as compared with the conventional configuration. That is, by setting the energy difference Ev to 0.15 eV or less, it is possible to save power in the semiconductor laser element.

  FIG. 14 shows the relationship between the element resistance Rd and the relative energy difference Ev between valence bands. FIG. 14 shows that the element resistance can be reduced as Ev becomes smaller. That is, the smaller the Ev, the lower the power consumption of the semiconductor laser element. Therefore, from the viewpoint of power saving of the semiconductor laser device, the relative valence band energy difference Ev between the third cladding layer, the first intermediate layer, the second intermediate layer, and the contact layer is 0.15 eV or less. Is more preferably 0.10 eV or less, and particularly preferably 0.05 eV or less. Here, as a method of making Ev smaller than 0.15 eV, for example, a method of further adding an intermediate layer, a method of adjusting carrier concentration, and the like can be considered.

≪Window area≫
The window region 20 is a region in which impurities are diffused. As shown in FIG. 1, the window region 20 penetrates from the upper surface of the semiconductor laser element 1 in the thickness direction of the GaAs substrate 2 and penetrates the active layer 5 to form the first cladding. Layer 3 has been reached. Further, the window region 20 penetrates from both end faces of the resonator in the longitudinal direction of the resonator. Here, the range of the depth t that the window region 20 penetrates in the longitudinal direction of the resonator is preferably about 40 nm. Here, for example, Zn can be used as the impurity.

≪Current injection region and current non-injection region≫
A current non-injection region (not shown) is a portion of the optical waveguide covered with an insulating layer, and a portion of the optical waveguide that is not covered with an insulating layer is a current injection region. Here, the current non-injection region is formed so as to cover at least the window region. As the insulating layer for forming the current non-injection region, for example, SiO ₂ (silicon oxide), SiN (silicon nitride), or the like can be used.

≪Current block layer≫
The current blocking layer (not shown) is an insulating layer made of SiO ₂ or the like, and is formed so as to cover the side surface portion of the ridge stripe-shaped stacked body 30 and the exposed surface of the second cladding layer 7. Thereby, a current can be efficiently passed through the contact layer 10.

  Such a semiconductor laser device of the present invention is manufactured by the following manufacturing method. In other words, the semiconductor laser device manufactured by the following manufacturing method exhibits the above characteristics. Therefore, the semiconductor laser device of the present invention has an excellent effect of lasing at a wavelength of 800 nm to 960 nm and having a high COD level while maintaining a low threshold current and high efficiency.

<Method for Manufacturing Semiconductor Laser Element>
Hereinafter, the manufacturing method of the semiconductor laser device 1 of the embodiment will be described in detail.

  First, a buffer layer made of n-type GaAs and a first cladding layer made of n-type GaInP are formed on an n-type GaAs substrate 2 using an MOCVD (Metal Organic Chemical Vapor Deposition) apparatus. 3 is formed at a growth temperature of 760 ° C.

Next, the temperature is lowered while supplying a group V raw material, and an active layer 5 having a DQW structure in which barrier layers 52 made of Al _0.3 Ga _0.7 As and well layers 51 made of InGaAs having a thickness of 5 nm are alternately stacked is set. It is formed at a temperature of 680 ° C. Here, the MQW structure is not limited to the DQW structure (double quantum well structure), and the number of stacked layers can be appropriately changed as long as the critical film thickness is not exceeded. Therefore, for example, a triple quantum well structure may be used.

Next, the temperature is raised again to 760 ° C. while supplying the group V raw material, the p-type second cladding layer 7 made of Al _0.5 Ga _0.5 As using Zn as the p-type dopant, and the etching stop made of GaAs. A third clad layer 8 made of Ga _0.5 In _0.5 P using Zn as a p-type dopant, a first intermediate layer 91 made of Ga _0.5 In _0.5 P, and Al _0.25 Ga _0.75 As The second intermediate layer 92 made of and the contact layer 10 made of GaAs are sequentially stacked. As described above, a wafer having a semiconductor laser structure is obtained.

  Next, a step of opening a portion where the window region 20 is to be formed is performed from the front surface side of the wafer (that is, from above the contact layer 10) by using a photolithography technique.

  First, a photosensitive resist is applied on the contact layer 10 to form a stripe pattern having a width of 60 μm and a pitch of 1100 μm.

Next, a mixed film composed of ZnO (zinc oxide) and SiO ₂ (hereinafter also referred to as a ZnO / SiO ₂ mixed film) is formed on the contact layer 10 using the photosensitive resist as a mask. Here, the ZnO / SiO ₂ mixed film can be formed using, for example, an RF (Radio Frequency) sputtering apparatus.

Next, the photosensitive resist is removed by immersion in an organic solvent such as acetone and ultrasonic cleaning, and a ZnO / SiO ₂ mixed film patterned in a stripe shape is formed on the contact layer 10.

Next, a ZnO / SiO ₂ mixed film is formed by sputtering so as to cover the entire surface of the wafer, and then an SiO ₂ film is deposited on the entire surface of the wafer as a cover on the ZnO / SiO ₂ mixed film.

  Next, by annealing the wafer, Zn is diffused to penetrate the MQW layer (that is, the active layer 5). Thereby, the window region 20 is formed. Here, the annealing conditions can be, for example, about 532 ° C. for about 2 hours.

After the annealing, the wafer is subjected to wet etching using HF (hydrogen fluoride) to remove the ZnO / SiO ₂ mixed film formed on the wafer surface. Here, the time for performing the wet etching can be, for example, about 30 seconds.

Next, a SiO ₂ film is deposited again on the entire wafer surface. Then, a resist stripe is formed on the SiO ₂ film by using a photolithography technique so as to be parallel to the emission end face. A stepper can be used to form the resist stripe. The stripe width is preferably 1 μm to 2 μm. Using the resist stripe as a mask, reactive ion etching is performed to form a stripe mask layer made of SiO ₂ along the resist stripe, and the resist is removed by organic cleaning and ashing.

Next, a step of forming the ridge stripe-shaped laminate 30 is executed. Using the striped mask layer made of SiO ₂ as a mask, dry etching is performed using an inductively coupled plasma etching apparatus. At this time, etching is performed up to the etching stop layer made of GaAs. Thereby, the ridge stripe-shaped laminate 30 can be formed. Thereafter, the striped mask layer is removed by wet etching using BHF (buffered hydrofluoric acid).

Next, SiO ₂ is deposited again on the entire surface of the wafer in the thickness direction to form a SiO ₂ film. The SiO ₂ film is formed so as to cover the etching stop layer made of GaInP and the ridge stripe-shaped laminate 30.

Next, of the portion of the SiO ₂ film laminated on one surface in the thickness direction of the ridge stripe-shaped laminate 30, the portion laminated in the region where the MQW layer is disordered by diffusing Zn (Zn diffusion region) The remaining portion except for is removed, and a current non-injection region made of the remaining SiO ₂ film is formed.

Here, the current non-injection region is formed so as to cover at least the window region 20, that is, provided so as to cover the Zn diffusion region. Here, as a method of forming the current non-injection region, a method of removing the SiO ₂ film by performing wet etching or reactive ion etching using BHF or the like is preferable.

  Next, after the surface opposite to the one surface in the thickness direction of the wafer (that is, the back surface of the wafer) is thinned to adjust the thickness of the wafer, Au (gold), Ge (germanium), Ni (nickel), Mo (molybdenum) ), Au are formed in this order, and an N-type back electrode is formed. Here, as a film forming method, for example, a sputtering method, an EB (Electron Beam) vapor deposition method, or the like can be used. Further, in order to form an ohmic junction between the formed N-type back electrode and the GaAs substrate 2, it is preferable to perform annealing after the electrode is formed. Here, the annealing conditions can be, for example, about 440 ° C. for about 15 minutes.

  Next, a P-type surface electrode is formed on one surface in the wafer thickness direction. First, Ti (titanium) and Au are formed in this order using a sputtering apparatus. Next, electroplating is formed on the portion excluding the window region 20 using the previously formed Ti and Au films as a base. Thus, by not forming the electroplating in the window region 20, when the wafer is divided into the resonator lengths, the division becomes easy.

  Next, a ruled line is entered between the window regions 20 for each resonator length, and then the wafer is divided to obtain bars. Here, in the semiconductor laser device 1 of the embodiment, the resonator length is 1100 μm.

Next, an end face coating film is applied to the emission end face and the reflection end face of the resonator of the divided bar using an ECR (Electron Cyclotron Resonance) sputtering apparatus or an EB deposition apparatus so that the reflectance at these end faces becomes asymmetric. Form. In the semiconductor laser device 1 according to the embodiment, an Al ₂ O ₃ film of about 140 nm is formed on the emission end face so that the reflectance of the emission end face is 2%, and the SiO ₂ film and Ta are formed on the reflection end face. A multi-coat film in which a ₂ O ₅ film (tantalum pentoxide film) is laminated is formed to have a reflectance of 96%.

  Next, the end-coated bar as described above is divided into semiconductor laser elements (chips). In the semiconductor laser device 1 of the embodiment, the chip width is 100 μm.

  Finally, the divided semiconductor laser chip is joined to a submount made of AlN (aluminum nitride) with a P-type surface electrode at the bottom, and the submount with the semiconductor laser chip is joined to a terminal called a stem. Then, the cap is put on for the purpose of protecting the semiconductor laser chip. In this way, the semiconductor laser device 1 can be manufactured.

  The configuration and effects of the semiconductor laser device of the present invention described above are summarized as follows.

The semiconductor laser device of the present invention includes a first conductivity type GaAs substrate 2, a first conductivity type first cladding layer 3 formed on the substrate 2, and In _y Ga formed on the first cladding layer 3. _(1-y) an active layer 5 including a well layer 51 made of As (0.08 <y <0.25); a second conductivity type second cladding layer 7 formed on the active layer 5; A ridge stripe-shaped laminate 30 in which a second conductivity type third clad layer 8, a first intermediate layer 91, a second intermediate layer 92, and a contact layer 10 are laminated in this order provided on the second clad layer 7. The ridge stripe-shaped laminate 30 constitutes an optical waveguide, and in the optical waveguide, the band gap of the active layer 5 is maximum at the end face perpendicular to the longitudinal direction of the optical waveguide. It is.

  With the configuration as described above, the semiconductor laser device of the present invention oscillates at a wavelength of 800 nm to 960 nm, and exhibits an excellent effect that the COD level is high while maintaining a low threshold current and high efficiency.

  Moreover, it is preferable that the well layer 51 in the end face perpendicular to the longitudinal direction of the optical waveguide is mixed. Thereby, the window area | region 20 can be made into a higher quality window structure.

  The active layer 5 on the end face perpendicular to the longitudinal direction of the optical waveguide is a window region 20 in which impurities are diffused, and it is preferable that Zn is diffused in the window region 20. Furthermore, it is preferable that In of the well layer 51 is diffused in the window region 20. Thereby, it is possible to increase the COD level and increase the output of the semiconductor laser element.

The active layer 5 has a multiple quantum well structure in which well layers 51 and barrier layers 52 made of Al _x Ga _(1-x) As (0 ≦ x ≦ 0.5) are alternately stacked. preferable. Thereby, good laser oscillation characteristics can be obtained.

  The thickness of the well layer 51 is preferably 3 nm or more and 8 nm or less. As a result, it is possible to prevent a problem that the mixed crystal window region becomes opaque.

The relative difference Δa between the lattice constant of the barrier layer 52 and the lattice constant of the well layer 51 and the lattice constant a of the barrier layer 52 are expressed by the following formula:
0.01 ≦ Δa / a ≦ 0.02
It is preferable to satisfy. Thereby, distortion due to lattice mismatch between the well layer 51 and the barrier layer 52 can be reduced, and a high-quality crystal can be grown.

  In addition, the active layer 5 includes at least two well layers 51, so that it is possible to obtain a laser whose output efficiency is not easily lowered even at high output.

  Further, when the difference between the peak wavelength of the photoluminescence spectrum of the active layer 5 not belonging to the window region 20 and the peak wavelength of the photoluminescence spectrum of the active layer 5 belonging to the window region 20 is Δλ, Δλ is 50 nm or more. It is preferable. Thereby, it is possible to increase the COD level and increase the output of the semiconductor laser element.

  In addition, the relative energy difference between the valence band between the third cladding layer 8, the first intermediate layer 91, the second intermediate layer 92, and the contact layer 10 is preferably 0.15 eV or less. As a result, the operating voltage can be reduced and the power consumption of the semiconductor laser element can be reduced.

  The third cladding layer 8 preferably contains AlGaInP. As a result, a high energy barrier can be secured, and high temperature operation is possible by reducing carrier overflow.

  The embodiment disclosed this time should be considered as illustrative in all points and not restrictive. The scope of the present invention is defined by the terms of the claims, rather than the description above, and is intended to include any modifications within the scope and meaning equivalent to the terms of the claims.

  DESCRIPTION OF SYMBOLS 1 Semiconductor laser element, 2 GaAs substrate, 3rd cladding layer, 4 Lower guide layer, 5 Active layer, 51 Well layer, 52 Barrier layer, 6 Upper guide layer, 7 2nd cladding layer, 8 3rd cladding layer, 9 Intermediate layer, 91 1st intermediate layer, 92 2nd intermediate layer, 10 contact layer, 20 window region, 30 Ridge stripe-shaped laminate.

Claims (3)

A first conductivity type GaAs substrate;
A first conductivity type first cladding layer formed on the substrate;
It is formed on the first cladding _{layer, In y Ga (1-y} ) As and the well layer made of (0.08 <y <0.25), Al x Ga (1-x) As (0 An active layer in which barrier layers made of ≦ x ≦ 0.5 are alternately laminated ,
A second conductivity type second cladding layer formed on the active layer;
A ridge stripe-shaped laminate in which a second conductivity type third cladding layer, a first intermediate layer, a second intermediate layer, and a contact layer are stacked in this order, provided on the second cladding layer; ,
The ridge stripe-shaped laminate constitutes an optical waveguide,
In the optical waveguide, the band gap of the active layer is maximum at an end surface perpendicular to the longitudinal direction of the optical waveguide,
The active layer on the end face perpendicular to the longitudinal direction of the optical waveguide is a window region in which impurities are diffused,
Zn and In of the well layer are diffused in the window region,
The peak wavelength of the photoluminescence spectrum of the active layer that does not belong to the window region, when the difference between the peak wavelength of the photoluminescence spectrum of the active layer belonging to the window region was [Delta] [lambda], Ri der [Delta] [lambda] is 50nm or more,
The semiconductor laser device , wherein the well layer has a thickness of 6 nm or less . The semiconductor laser device according to claim 1, wherein a thickness of the well layer is 3 nm or more and 6 nm or less.   3. The semiconductor according to claim 1, wherein a relative valence band energy difference among the third cladding layer, the first intermediate layer, the second intermediate layer, and the contact layer is 0.15 eV or less. Laser element.

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