JP3028641B2 - Semiconductor laser and manufacturing method thereof - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a semiconductor laser used in the field of optical information processing such as an optical disk memory device and a method of manufacturing the same.

[0002]

2. Description of the Related Art Conventionally, as a semiconductor laser used in the optical information processing field, a laser having a low threshold current, a stable transverse mode characteristic, and a high output has been strongly demanded. One of the ways to fulfill these requirements
Finally, disordering by impurity diffusion (IILD; Impu)
right Induced Layer Disorder
ering) technology. As a semiconductor laser capable of achieving high efficiency and high output by confining current and light by using this disordering technique by impurity diffusion, for example, Applied Physics Letters, Vol. 4
9, 133 (1986).

As shown in FIG. 14, the semiconductor laser 100 has an n-type substrate 101, an n-type AlGaAs cladding layer 102 laminated on the n-type substrate 101, and a lamination on the AlGaAs cladding layer 102. Active layer 1
03 and a p-type AlG laminated on the active layer 103.
An aAs cladding layer 104 and a GaAs cap layer 105 laminated on the AlGaAs cladding layer 104 are provided.

In the semiconductor laser 100, n-type Si is diffused into both sides except for the central portion, and as shown by a broken line in FIG.
06 is formed.

As a result, on both sides of the active layer 103,
The disordered region 106 of a predetermined conductivity type having a large refractive index in which the impurity is diffused and determined by the type of the impurity is present. Therefore, only the central portion of the active layer 103 acts as a waveguide, and the active layer 10
3 have pn junctions with the disordered region 106 having a conductivity type determined by the type of the impurity,
Blocking the flow of current allows light and current to be confined laterally. As described above, the leakage current is suppressed, and a semiconductor laser with a low threshold value is realized.

By the way, in order to drive such a semiconductor laser at a high output, the light output is increased by increasing the injection current to the semiconductor laser. So-called spatial hole burning occurs in which recombination is fast and the distribution intensity of carriers is partially reduced. If the density of the injected carriers near the emission end face becomes significantly low due to the spatial hole burning, the population inversion will not be achieved. Therefore, net absorption of light occurs near the end face, and the optical damage (COD) is caused by the heat generated by the light absorption. ; Catast
However, there arises a problem that a ropicoptic damage occurs.

Therefore, in order to prevent optical damage (COD) occurring at the time of high-power oscillation, a semiconductor laser provided with a light transmitting layer near the end face of a resonator using the disordering technique also by impurity diffusion has been proposed. Applied Physics Letters, Vol. 49, 1572 (1986).

As shown in FIG. 15, an n-type GaAs substrate 111 and an n-type AlGa
As clad layer 112, active layer 113, p-type Al
GaAs cladding layer 114 and p-type AlGaAs
In a layer in which the s contact layer 115 and the GaAs cap layer 116 are sequentially stacked, Si is diffused in the vicinity of the emission end face of the semiconductor laser 100 to form the disordered region 117, and the light transmission layer 117 is provided in the vicinity of the end face. Is configured. Then, the light transmission layer 117 provided near the emission end face reduces light absorption near the emission end face of the semiconductor laser 100 and prevents optical damage (COD).

However, in the above semiconductor laser,
For the following two reasons, it is necessary to perform Zn diffusion (IILD) and then diffuse Zn throughout the entire region including the diffusion region. The first reason is that if only Si is diffused, the p-type contact layer 115 is diffused due to abnormal surface diffusion of Si.
This is because Si is also mixed into the semiconductor laser and the series resistance of the semiconductor laser is increased. Second, since the Si diffusion region reaches the n-type cladding layer 112, when current is injected, a leakage current occurs in the region reaching the n-type cladding layer 112, thereby increasing the threshold current. This is because

Therefore, as shown in FIG. 16, there is a semiconductor laser in which Zn is diffused in the entire region including the Si diffusion region. In the figure, 121 is an n-type GaAs substrate, 122
Is an n-type GaAs buffer layer, and 123 is an n-type AlGa
As clad layer, 124 is an n-type AlGaAs light guide layer, 125 is an undoped GaAs active layer, 126 is a p-type AlGaAs light guide layer, and 127 is a p-type AlGaAs
s cladding layer, 128 is a p-type GaAs cap layer, 1
29 is a current injection region, 130 is a SiO ₂ current block layer, 131 is a p-type electrode, 132 is an n-type electrode, and 133 is S
An i-diffusion region 134 indicates a Zn-diffusion region.

As described above, by performing the Zn diffusion 134 over the entire region including the Si diffusion region 133, the carrier concentration of the p-type contact layer 115 is increased to reduce the series resistance, and the Si diffusion region 117 is formed. By forming a pn junction, it is possible to prevent the flow of carriers and prevent an increase in threshold current.

[0012]

However, the above-mentioned prior art has the following problems. That is, in the above-described conventional semiconductor laser, the diffusion of Zn in the entire region including the diffusion region of Si is performed by the diffusion of Si (IIL).
Since it is performed at a relatively low temperature (about 600 ° C.) and in a short time (about 30 minutes) as compared with D), it is difficult to control the diffusion region and the like, and the controllability is poor. A Zn diffusion step has to be performed later, which requires a laborious operation, which causes a problem that the reliability of the semiconductor laser is reduced and mass production is difficult.

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned problems of the prior art. It is an object of the present invention to solve the above-mentioned problems caused by optical damage (C) caused by light absorption near the exit end face.
OD) can be prevented, and a semiconductor laser which can realize a high-output and low-threshold semiconductor laser with high reliability and excellent mass production, and a method of manufacturing the same can be provided. It is in.

[0014]

That is, a semiconductor laser according to the present invention comprises a first cladding layer, an active layer laminated on the first cladding layer, and a second cladding layer laminated on the active layer. And a ridge strut protruding in the direction of light emission on the second clad layer.
The ridge and stripe
The end on the emission end face side of the portion is more than the end face of the second cladding layer.
Cut the ridge stripe so that it is located inside.
Provide a notched notch, other than the ridge stripe
Is formed to provide an impurity diffusion region reaching the active layer from the surface of the substrate.

Further, the method of manufacturing a semiconductor laser according to the present invention includes the steps of: forming a first clad layer, an active layer laminated on the first clad layer, and a second clad layer laminated on the active layer; After the layers are sequentially laminated, the second clad layer is etched to form an optical signal on the second clad layer.
Ridge stripe protruding along the exit direction of light
The ridge stripe is formed
The end on the firing end side is located inside the end surface of the second cladding layer.
Cut out the ridge stripe so that it is
The cut-out portion is formed, the table other than the ridge stripe portion
An impurity is diffused from a surface to provide an impurity diffusion region reaching the active layer.

As an impurity for forming the impurity diffusion region, for example, Si is used. However, the present invention is not limited to this, and Ge or S may be used.

Further, as the active layer, for example, the active layer has a multilayer structure including a light guide layer, but is not limited to this, and may have a single layer structure or a multiple quantum well structure.

Further, as a material constituting the semiconductor laser, for example, a GaAs / AlGaAs-based material is used. However, the material is not limited to this, and is not limited to GaAs / AlGaAs.
Needless to say, an lGaInP-based material or an InP / AlGaInAs-based material may be used.

The semiconductor laser is applied to a single beam and a dual beam laser which can be driven independently, but it is also possible to extract three or more independently driven beams.

[0020]

According to such technical means, a ridge stripe portion is formed above the second cladding layer,
At the end of the ridge stripe portion on the emission end surface side, a cutout portion having the surface thereof flush with the side surface of the ridge stripe portion is provided, and a cutout portion is formed from the side surface and the cutout surface of the ridge stripe portion. Since it is configured to provide the impurity diffusion region reaching the active layer, by providing the impurity diffusion region on the side of the ridge stripe portion, light and current can be confined in the horizontal direction, and high efficiency and high efficiency can be achieved. An output semiconductor laser can be provided. In addition, by providing an impurity diffusion region at the end of the ridge stripe portion on the emission end surface side, a non-light emitting region can be provided at the emission end surface portion to suppress light absorption, thereby limiting the light output due to end surface destruction. Can be enhanced. Further, the impurity diffusion region on the side of the ridge stripe portion and the end portion on the emission end face side,
Since it can be formed by a single impurity diffusion step, the conventional diffusion step of unstable Zn or the like is not required, the time for performing the impurity diffusion step can be shortened, and high reliability and excellent mass production can be achieved. It is possible to manufacture a semiconductor laser in the state in which the semiconductor laser is in a closed state.

[0021]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below based on the illustrated embodiment.

FIGS. 1 to 3 show a semiconductor laser having a window stripe type buried heterostructure as one embodiment of the semiconductor laser according to the present invention.

In the figure, reference numeral 1 denotes an n-type GaAs substrate;
Are carrier concentrations n to n stacked on the GaAs substrate 1.
An n-type GaAs buffer layer 4 × 10 ¹⁸ cm ⁻³ and a thickness of about 0.2 μm 3 has a carrier concentration n of 1 × 10 ¹⁸ cm ⁻³ stacked on the GaAs buffer layer 2 and a thickness of about 1. 0μ
m n-type AlGaAs cladding layer, 4
Carrier concentration n-1 × 1 laminated on s clad layer 3
An n-type AlGaAs optical guide layer of 0 ¹⁸ cm ^-3 and a thickness of 0.1 μm, 5 is an undoped GaAs active layer of a thickness of 100 ° laminated on the AlGaAs optical guide layer 4, and 6 is an undoped GaAs active layer. A p-type AlGaAs light guide layer having a carrier concentration of p.about.1 × 10 ¹⁸ cm ⁻³ and a thickness of about 0.1 μm laminated on 5, and a mesa-type layer 7 is formed at the center on the AlGaAs light guide layer 6. P-type AlG having a carrier concentration of p〜5 × 10 ¹⁷ cm ^-3 and a thickness of １．０1.0 μm
The aAs cladding layer 8 has a carrier concentration of p１1 × 10 5 laminated on the upper surface of the mesa-type AlGaAs cladding layer 7.
A p-type GaAs cap layer having a thickness of ¹⁹ cm ^-3 and a thickness of 0.2 μm, a mesa stripe portion 9 having a width of 3 to 10 μm and a length of 270 μm, and 10 a p-type AlG formed in the above-mentioned mesa shape.
a SiO ₂ layer having a thickness of about 0.2 μm laminated over the upper surface of the aAs cladding layer 7 and the side surface of the mesa stripe portion 9
A current blocking layer 11, a p-type electrode laminated on the GaAs cap layer 8 and the SiO ₂ current blocking layer 10;
Reference numeral 12 denotes an n-type electrode laminated on the back surface of the GaAs substrate 1, and reference numeral 23 denotes a Si diffusion region.

As described above, the semiconductor laser according to this embodiment includes the n-type AlGaAs cladding layer 3 and the AlGa
An n-type AlGaAs optical guide layer 4 laminated on the As clad layer 3; an undoped GaAs active layer 5 laminated on the AlGaAs optical guide layer 4;
A p-type AlGaAs optical guide layer 6 laminated on the aGaAs active layer 5, and a mesa-type p-type AlGaAs clad layer 7 is formed on the center of the AlGaAs optical guide layer 6.
On the p-type AlGaAs cladding layer 7, a mesa stripe protruding in a convex shape along the light emission direction.
And the mesa stripe portion 9 is formed.
The end 9a on the emission end face side is a p-type AlGaAs cladding layer.
7 so as to be located inside the end face 7a of the
A notch 13 in which the trip portion 9 is cut is provided, and the undoped Ga is removed from the surface other than the ridge stripe portion 9.
It is configured to provide a Si diffusion region 23 reaching the As active layer 5.

Next, a method of manufacturing the semiconductor laser according to this embodiment will be described.

In order to manufacture the semiconductor laser, first,
As shown in FIG. 4, on an n-type GaAs substrate 1, an n-type GaAs buffer layer 2, an n-type AlGaAs cladding layer 3, an n-type AlGaAs light guide layer 4, an undoped Ga
An As active layer 5, a p-type AlGaAs light guide layer 6, a p-type AlGaAs cladding layer 7, and a p-type GaAs cap layer 8 are sequentially laminated to a predetermined thickness.

Thereafter, an etching mask 24 is formed by using the photolithography technique as shown in FIGS. 5 and 6, and the portion of the etching mask 24 is left over the undoped GaAs active layer 5 to 0.3 μm. p-type G
aAs cap layer 8, p-type AlGaAs cladding layer 7
Are sequentially removed by anisotropic etching as shown in FIGS. At this time, as an etchant, for example, a H ₂ SO ₄ —H ₂ O ₂ —H ₂ O-based mixed solution is used. As described above, the p-type GaAs cap layer 8 and the p-type AlGaAs cladding layer 7 are sequentially removed by etching while leaving the etching mask 24, so that the upper portion of the p-type AlGaAs cladding layer 7 has a mesa stripe shape. It is formed. The side of the mesa stripe portion 9 of the p-type AlGaAs cladding layer 7 is formed to have a small thickness by etching, and the mesa stripe portion 9 is formed.
The notch 13 whose surface is flush with the side surface of the ridge stripe portion 9 is simultaneously formed at the end portion on the emission end surface side.

Next, using the etching mask 24 as it is as a protective film, as shown in FIG.
After depositing Si21 as a diffusion source on the As cladding layer 7 and the etching mask 24, as shown in FIG. 10, by removing the etching mask 24, the Si21 deposited on the mesa stripe portion 9 becomes It is removed by lift-off together with the etching mask 24. As a result, as shown in FIG. 10, the Si 21 is stacked only on the upper surface of the p-type AlGaAs cladding layer 7 due to over-etching of the substrate.

Thereafter, a SiO ₂ diffusion protective film 22 is deposited from the surface of the substrate so as to cover the diffusion source Si 21 (FIG. 11), and then the diffusion depth is set at 850 ° C. for 1 hour in an electric furnace. A Si diffusion region 23 is formed by performing Si thermal diffusion of about 0.5 μm. The Si diffusion region 23 is formed from the upper surface of the p-type AlGaAs cladding layer 7 to the p-type AlGa
It is formed so as to reach the As light guide layer 6, the undoped GaAs active layer 5, the n-type AlGaAs light guide layer 4, and the n-type AlGaAs clad layer 3. At this time,
The sample is sealed together with arsenic particles in a quartz ampoule having an inner diameter of 15 mm, and is heat-treated in an arsenic atmosphere of 1.7 atm.

Then, Si 21 and SiO ₂ 22 are converted to CF
₄ is removed by plasma etching, SiO ₂ on the entire surface
After depositing the current block layer 10, the SiO ₂ current block layer 10 on the mesa stripe portion 9 is removed again by using the photolithography technique.

Thereafter, similarly to the ordinary semiconductor laser fabrication process, the n-type GaAs substrate 1 is polished to a thickness of about 100 μm, the p-type electrode 11 and the n-type electrode 12 are deposited, and then cleaved to a length of 300 μm. To form a Fabry-Perot resonator. At the time of chip formation, as shown in FIG. 1 and FIG. This semiconductor chip is completed by mounting it on a heat sink and attaching lead wires.

With the above configuration, the semiconductor laser according to this embodiment has a high efficiency, a low threshold current, and can suppress optical damage as follows.
It can be manufactured with high reliability and excellent in mass production.

That is, in the semiconductor laser according to this embodiment, as shown in FIG. 12, the undoped GaAs active layer 5 below the mesa stripe portion 9 becomes a main light emitting region. Further, since the SiO ₂ current block layer 10 is formed so as to surround the mesa stripe portion 9, the injected current I
Flows intensively in the mesa stripe portion 9. At this time, p-type AlGaAs thinned by etching is used.
The current that attempts to spread to the s-clad layer 7 cannot pass through the Si diffusion region 23, and the leakage current is suppressed, so that a low threshold laser is realized. In addition, the output end face of the semiconductor laser is mixed and crystallized by the impurity diffusion 23 of Si, so that the energy band gap is slightly widened and becomes transparent to light emitted from the active layer 5. No absorption occurs. For this reason, end face destruction due to heat generation due to light absorption can be suppressed. Further, as described above, since the current does not flow into the vicinity of the emission end face, the heat generation is greatly reduced, and the end face is hardly destroyed. Therefore, the limit of the optical output can be increased and the output can be increased.

As described above, the semiconductor laser according to the present embodiment employs the disordering technique based on the diffusion of Si impurities with respect to the ridge stripe type laser to obtain a Zn laser.
Even if the diffusion step is omitted, it is possible to prevent an increase in series resistance due to abnormal surface diffusion of Si and a leakage of current in a lateral direction due to connection of the n-type Si diffusion region with the n-type cladding layer. Therefore, a semiconductor laser having a low threshold, a high output, and a stable transverse mode can be obtained.

Since the confinement of light and current and the formation of the window structure at the emission end face can be simultaneously performed by disordering (IILD) by diffusion of Si impurities, the fabrication process can be simplified. .

Furthermore, in the disordering technique by impurity diffusion, since the laser chip is held for a long time in a high-temperature path exceeding 800 ° C., thermal damage to the device cannot be avoided. However, according to this method, since the p-type AlGaAs cladding layer 7 for diffusing impurities is thinned by etching, the impurity can be removed in a shorter time than a conventional laser using the disordering technique using the same impurities. Diffusion can be performed and thermal damage to the device can be reduced.

[0037]

The present invention has the above-described structure and operation. It is possible to prevent optical damage (COD) due to light absorption in the vicinity of the light-emitting end face as well as to achieve high output and low power. It is possible to provide a semiconductor laser capable of realizing a semiconductor laser having a threshold value with high reliability and excellent mass production, and a method of manufacturing the same.

[Brief description of the drawings]

FIG. 1 is a partially broken perspective view showing one embodiment of a semiconductor laser according to the present invention.

FIG. 2 is a sectional view of the same.

FIG. 3 is a sectional view of the same.

FIG. 4 is a cross-sectional view illustrating a manufacturing process of the semiconductor laser according to the present embodiment.

FIG. 5 is a sectional view showing a manufacturing process of the semiconductor laser according to the present embodiment.

FIG. 6 is a sectional view illustrating a manufacturing process of the semiconductor laser according to the present embodiment.

FIG. 7 is a sectional view illustrating a manufacturing process of the semiconductor laser according to the present embodiment.

FIG. 8 is a cross-sectional view illustrating a manufacturing process of the semiconductor laser according to the present embodiment.

FIG. 9 is a cross-sectional view illustrating a manufacturing process of the semiconductor laser according to the present embodiment.

FIG. 10 is a sectional view illustrating a manufacturing process of the semiconductor laser according to the present embodiment.

FIG. 11 is a cross-sectional view illustrating a manufacturing process of the semiconductor laser according to the present embodiment.

FIG. 12 is a sectional view illustrating a manufacturing process of the semiconductor laser according to the present embodiment.

FIG. 13 is a sectional view showing a manufacturing process of the semiconductor laser according to the present embodiment.

FIG. 14 is a sectional view showing a conventional semiconductor laser.

FIG. 15 is a perspective view showing another conventional semiconductor laser.

FIG. 16 is a perspective view showing still another conventional semiconductor laser.

[Explanation of symbols]

1 n-type GaAs substrate, 2 n-type GaAs buffer layer, 3 n-type AlGaAs cladding layer, 4 n-type A
1GaAs light guide layer, 5 p-type undoped GaAs
Active layer, 6p-type AlGaAs light guide layer, 7p-type AlGaAs cladding layer, 8p-type As cap layer, 9 mesa stripe section, 10 current block layer, 1
1 P-side electrode, 12 n-type electrode, 23 Si diffusion region

────────────────────────────────────────────────── ─── Continuation of the front page (56) References JP-A-3-89584 (JP, A) JP-A-4-61391 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) H01S 5/00-5/50 JICST file (JOIS)

Claims (2)

(57) [Claims] A first cladding layer; an active layer laminated on the first cladding layer; and a second cladding layer laminated on the active layer .
Ridge streaks protruding in the direction of light emission
And the ridge stripe
The end on the emission end face side is inside the end face of the second cladding layer.
Cut out the ridge stripe so that
The stomach was cut-out portion is provided, the table other than the ridge stripe portion
A semiconductor laser comprising an impurity diffusion region extending from a surface to the active layer. 2. A method according to claim 1, wherein a first cladding layer, an active layer laminated on the first cladding layer, and a second cladding layer laminated on the active layer are sequentially laminated. By etching, the ridge strikes protruding in the upper part of the second cladding layer along the light emission direction.
The ridge and stripe
The end on the emission end face side of the portion is more than the end face of the second cladding layer.
Cut the ridge stripe so that it is located inside.
Ri-away cutout portion is formed, the ridge-stripe portion or more
A method of manufacturing a semiconductor laser, wherein an impurity is diffused from an outer surface to provide an impurity diffusion region reaching the active layer.