JPH07120837B2 - Multi-beam semiconductor laser device and manufacturing method thereof - Google Patents

Description

The present invention relates to a so-called multi-beam semiconductor laser device in which a plurality of semiconductor laser devices are integrated in one element and each can be driven independently. The present invention relates to a structure and a manufacturing method for independently controlling the divergence angle of a beam in the vertical direction.

[Prior art]

As a semiconductor laser device for an optical disk, higher output of laser light is desired. As one of the methods for achieving high output, there is known a method in which the active layer is thinned to reduce the light density at the end surface and prevent the end surface from being destroyed during high output operation. Therefore, when the active layer is made thin, light leaks into the cladding layer, so that the light density becomes small and the light emission spot size becomes large, so that the end face breakdown level is improved. However, since the divergence angle (θ⊥) of the laser beam in the vertical direction is small and the coupling with the optical system is good, the laser beam is easily affected by the returning light, and the returning light noise increases. On the other hand, if the active layer is thickened, the light density in the active layer becomes large, and the end face is liable to be destroyed, which makes high output operation difficult.
Since the divergence angle (θ⊥) of the laser beam in the vertical direction becomes large and the coupling with the optical system becomes poor, there is an advantage that it is less affected by the returning light and the returning light noise is reduced.

Therefore, in order to solve the above problems, multi-beam laser can be considered. A laser with a large divergence angle (θ⊥) in the vertical direction of the laser beam is used for reproduction with severe noise requirements, and a laser with a small (θ⊥) is used for recording lasers that require high-power operation. This is because it is possible to use them properly, and by doing so, it is possible to read immediately after writing.

Thus, changing the divergence angle (θ⊥) in the vertical direction of the laser beam for reading and writing is an effective element for the multi-beam semiconductor laser device.

As described above, it is possible to change the divergence angle (θ⊥) in the beam vertical direction by changing the active layer thickness. Therefore, next, the manufacturing method for changing the thickness of the active layer will be described.

The semiconductor laser device utilizes the fact that the double heterojunction is formed by liquid phase growth, but the crystal growth rate on the ledge is slower than the crystal growth rate under the ledge. In other words, if this characteristic of crystal growth is used, the light emission spot of the laser formed on the ridge becomes large due to the light seeping effect due to the thinning of the active layer, and the divergence angle (vertical direction) of the laser beam is increased. θ⊥) is smaller than (θ⊥) in the flat part under the ridge.

Next, a conventional example using this principle will be shown. Fig. 7 shows, for example, the divergence angle (θ⊥) in the vertical direction of two beams by controlling the active layer thickness shown in the proceedings of the Joint Lecture on Applied Physics, Spring 1988, 30p-ZQ-2. It is a cross-sectional view of a conventional multi-beam semiconductor laser that can be adjusted,
(1) is a GaAs substrate, (2) is a ridge formed on the GaAs substrate (1), (3a) is an optical waveguide V groove formed on the ridge (2), and (3b) is a GaAs substrate (1) flat An optical waveguide V-groove formed on the upper part, (4) a first cladding layer made of GaAlAs,
(5) is an active layer made of GaAlAs, (5a) is a thin active layer having a ridge, (5b) is a thick active layer having a flat portion, (6) is a second cladding layer made of GaAlAs, ( 7a)
Is a cap layer on the side having a ridge, (7b) is a cap layer on the side having a flat portion, and (10) is a separation groove for operating the laser independently.

Next, the operation of this laser will be described.

FIG. 8 is a diagram for explaining the operation of this laser. (8a) is an ohmic electrode formed on the cap layer (7a), and (8b) is an ohmic electrode formed on the cap layer (7b). The electrode (9) is a common ohmic electrode formed on the GaAs substrate (1).

Here, for example, a GaAs substrate (1), a first made of GaAlAs
Assuming that the cladding layer (4), the active layer (5) are P-type, the second cladding layer (6) made of GaAlAs, and the cap layers (7a), (7b) are n-type, the anode of the driving power source is common. When the cathode is connected to the ohmic electrode (8a) to the electrode (9) and the signal current 1 is injected into the element having the ridge (2), the current passes through the GaAs substrate (1) and the cap layer. It begins to flow in the (7a) direction and is injected into the active layer (5a). Therefore, recombination of electrons and holes is efficiently performed,
Light of a wavelength corresponding to the band gap of the active layer (5a)
Light is emitted from the active layer (5a) directly above the V groove (3a) formed in the ridge, and finally laser oscillation is reached. Here, even when the anode of the driving power source is connected to the common ohmic electrode (9) and the cathode is connected to the ohmic electrode (8b), and a signal current 2 is passed, the same process as above is performed and the flat part is formed. Light is emitted from the active layer (5b) immediately above the formed V groove (3b), and laser oscillation occurs.

In this way, these two lasers are electrically separated and integrated by the separation groove (10) in one element, and therefore each electric signal is sent to each electrode (8a), (8b). When given, the corresponding separate laser responses are independently obtained.

The divergence angle (θ
Describe the characteristics of ⊥). Since the active layer (5a) directly above the V groove (3a) formed in the ridge is thin as described above, the light seepage effect (θ⊥) is small and high output operation is possible.

In addition, the active layer (5) directly above the V groove (3b) formed in the flat portion.
(θ⊥) from b) is large.

Thus, the laser having the ledge (2) is independently driven as a high-power writing laser having a narrow beam and the other laser being a low-noise reading laser having a wide beam.

[Problems to be Solved by the Invention]

Since the conventional multi-beam semiconductor laser device is configured as described above, a thin active layer thickness difference can be obtained by the liquid phase growth method,
It is relatively difficult to control with the shape of the ridge, and there are problems that the obtained divergence angle (θ⊥) in the vertical direction of the beam varies.

The present invention has been made in order to solve the above-mentioned problems, and it is easy and has good reproducibility and controllability.
The objective is to obtain a multi-beam semiconductor laser device that can set ⊥).

[Means for Solving the Problems]

A multi-beam semiconductor laser device according to the present invention includes a semiconductor substrate having first and second main surfaces and a bottomed groove in a central portion for separating the first main surface into at least two parts, One of the first main surface portions of the semiconductor substrate has a first
Of a clad layer, an active layer, a second clad layer, and a cap layer made of a material that becomes an absorber for the oscillation wavelength from the active layer or a material having a lower refractive index than the second clad layer. The laser diode and the other one of the first main surface portions are provided with an active material having the same material as the first cladding layer and having the same thickness as the first cladding layer and having the same material as the active layer and having the same thickness. A layer, a second clad layer of the same material as the second clad layer and thinner than the second clad layer and having a predetermined thickness, and a cap layer of the same material as the cap layer, independently of the laser diode. And at least one other laser diode sequentially laminated.

A method of manufacturing a multi-beam semiconductor laser device according to the present invention comprises a step of sequentially laminating a first clad layer, an active layer and a second clad layer on a substrate by crystal growth, and a plurality of laser diodes in the multi-beam semiconductor laser device. Part of the second cladding layer is thinned to a predetermined thickness by etching, and a material serving as an absorber for the oscillation wavelength from the active layer or a material having a lower refractive index than the second cladding layer is laminated. And a process.

[Operation] In the multi-beam semiconductor laser device configured as described above, a plurality of laser diodes in one element share a substrate, the first cladding layer on the substrate side and the active layer have the same thickness, By varying the thickness of the second cladding layer between the layer and the cap layer, different divergence angles in the beam vertical direction can be obtained.

In the method of manufacturing a multi-beam semiconductor laser device configured as described above, the first clad layer, the active layer, and the second clad layer are sequentially laminated on the substrate by crystal growth, and each of the plurality of laser diode parts is first laminated. (2) The clad layer is thinned to a predetermined thickness by etching, and the cap layer is further laminated to easily and reproducibly without changing the active layer thickness of a plurality of laser diodes in one device. The divergence angle in the beam vertical direction can be set with good controllability.

[Embodiment] FIG. 1 is a cross-sectional view showing an embodiment of the present invention, in which (5C) is a p-type Ga having a uniform thickness of about 0.05 μm.
_0.85 Al _0.15 As active layer, (6a) is thick n-type Ga of 1 μm or more
_{The 0.52} Al _0.48 As second cladding layer, (6b) is a thin n-type Ga _0.52 Al _0.48 As second cladding layer having a thickness of about 0.5 μm, and other numbers are the same as or equivalent to those in the conventional example. As shown in FIG. 7 of the conventional example, by injecting a current into the active layer (5C) below the thin second cladding layer (6b), the thin second layer is formed.
The light emission spot in the active layer (5C) directly above the V-groove (3) of the laser having the cladding layer (6b) is greatly attenuated by the GaAs cap layer (7) which acts as an absorber for the oscillation wavelength, The vertical spot diameter becomes smaller, and the vertical divergence angle (θ⊥) of the beam becomes larger than (θ⊥) of a laser having a thick cladding layer. In this way, by controlling the thickness of the cladding layer, (θ⊥) can be easily changed. Therefore, the narrow beam laser on the thick second cladding layer (6a) side is used as a high power laser for writing, and the wide beam laser on the thin second cladding layer (6b) side is used as a low noise laser for reading. You can

FIG. 2 is a diagram showing a method of manufacturing the multi-beam semiconductor laser device shown in FIG. The steps a) to d) are shown in sequence.

As shown in FIG. 2 (a), an optical waveguide V groove (3) is formed on the p-type GaAs substrate (1) by the lithography technique and etching.

As shown in FIG. 2 (b), a p-type Ga _0.52 Al _0.48 As first cladding layer (4) having a uniform thickness of about 0.05 μm was formed on the GaAs substrate (1) having a V-groove by the crystal growth technique. P-type Ga
_0.85 Al _0.15 As Active layer (5C), 1 μm thick Ga _0.52 n
A second Al _0.48 As cladding layer (6) is formed.

As shown in FIG. 2 (c), a part of the upper cladding layer (6) is then removed by a lithographic technique and chemical etching so as to form a thin cladding layer (6b) of about 0.5 μm.

As shown in FIG. 2 (d), again by the crystal growth technique,
An n-type GaAs cap layer (7) is formed, and then an isolation groove (10) for independently operating each laser is formed by a lithographic technique and etching.

Through the above steps, the structure of the multi-beam semiconductor laser device shown in FIG. 1 is completed.

FIG. 3 shows the structure of the embodiment of the present invention shown in FIG. 1 with a current blocking layer for current concentration near the optical waveguide V groove (3). In the figure, (12) is a current blocking layer made of n-type GaAs. Other numbers are the same as or equivalent to those in the conventional example. The operating principle is as shown in FIG. 1 and FIG. 8, but the current is blocked by the current blocking layer, and this blocking layer has a width of about 4 μm and is not present.
It is characterized in that the laser light intensively flows only in the so-called V groove (3) and the laser oscillation is performed more efficiently.

FIG. 4 is a sectional view showing another embodiment of the present invention. In the figure, (11) is a terrace formed on the GaAs substrate (1) by etching, and (4a) is a terrace (11) laterally below. Thick
Ga _0.52 Al _0.48 As first cladding layer, (4b) is a thin Ga _0.52 Al _0.48 As first cladding layer on the terrace, and other numbers are the same as in the conventional example or the corresponding portions. As shown in Fig. 7 of the conventional example, the first cladding layer (4b) with a thin electric current is used.
By injecting into the upper active layer (5C), the light emission spots in the active layer (5C) are greatly attenuated on the terrace (11) of the GaAs substrate (1) that acts as an absorber for the oscillation wavelength, The spot diameter in the vertical direction becomes smaller, and the divergence angle (θ⊥) in the vertical direction of the beam becomes larger than (θ⊥) of the laser having the thick first cladding layer (4a). By controlling the thickness of the cladding layer in this way, (θ⊥) can be easily changed, so that a laser having a large divergence angle (θ⊥) in the vertical direction of the laser beam, Laser with small θ ⊥) can be integrated in one device.

FIG. 5 is a diagram showing a method of manufacturing the multi-beam semiconductor laser device shown in FIG. The steps a) to c) are shown in sequence.

As shown in FIG. 5 (a), a terrace having a height of 1 μm is provided on the GaAs substrate (1) by the lithographic technique and etching.

As shown in FIG. 5 (b), an n-type
On the GaAs substrate (1), the n-type first Ga was formed by the liquid phase epitaxy method.
_0.52 Al _0.48 As The cladding layers (4a) and (4b) are grown so as to flatten the convex portion of the terrace. Here, the thick cladding layer (4a) is about 1.5 μm, and the thin cladding layer (4b) is about 0.5 μm.
to be μm. Next, p-type Ga _0.85 Al _0.15 As
An active layer (5C), a p-type second Ga _0.52 Al _0.48 As cladding layer (6) and a p-type cap layer (7) are sequentially grown.

Finally, as shown in FIG. 5 (c), the separation groove (10) is formed by the lithographic technique and etching.

Through the above steps, the structure of the multi-beam semiconductor laser device of FIG. 4 is completed.

FIG. 6 shows the structure of the embodiment of the present invention shown in FIG. 4 in which an optical waveguide for stabilizing the transverse mode and a current blocking layer for current concentration under the groove of the optical waveguide are added. In the figure,
(3c) and (3d) are optical waveguide grooves, and (12) is a current blocking layer made of n-type GaAs. (13) is an optical waveguide groove (3c), (3d)
The upper third p-type Ga _0.52 Al _0.48 As cladding layer and other numbers are the same as or equivalent to those in the conventional example. The principle of operation is as shown in FIGS. 4 and 7, but the current is blocked by the current blocking layer, and this blocking layer has a width of about 4 μm and is not present in the groove regions (3b), (3C ), And laser oscillation and optical waveguide are more efficiently performed.

In the above embodiment shown in FIG. 1.3, Ga having a large absorption with respect to the oscillation wavelength is formed on the second cladding layers (6a) and (6b).
Although the As cap layer (7) is shown, the GaAs cap layer (7) may be provided with a refractive index much lower than those of the second cladding layers (6a) and (6b).

In the above embodiments shown in FIGS. 4 and 6, the GaAs substrate (1a) having a large absorption for the oscillation wavelength is provided on the substrate, but the first cladding layers (4a) and (4b) Also, a material having a very low refractive index may be provided.

Further, in the above-described embodiment shown in FIG. 1, the optical waveguide V groove is provided, but the optical waveguide V groove may be omitted.

Further, in the above-described embodiments, the AlGaAs-based material is shown, but other materials such as AlGaInP-based and InGaAsP-based materials also have the same effect.

Further, in the above-mentioned embodiment, the multi-beam semiconductor laser device with two beams is shown, but the one with three beams or more may be used.

〔The invention's effect〕

Since the present invention is configured as described above,
The following effects are achieved.

In the multi-beam semiconductor laser device of the present invention, a plurality of laser diodes share a substrate, the first clad layer on the substrate side and the active layer have the same thickness, and the second clad layer between the active layer and the cap layer is formed. Since different divergence angles in the beam vertical direction can be provided by changing the thicknesses of a plurality of laser diodes, a plurality of laser diodes having different divergence angles in the beam vertical direction can be easily integrated on the same substrate, for example, wide A low-noise information reading semiconductor laser device having a beam and a high-output writing semiconductor laser device having a narrow beam can be easily integrated on the same substrate.

According to the method of manufacturing a multi-beam semiconductor laser device of the present invention, a first clad layer, an active layer, and a second clad layer are sequentially laminated on a substrate by crystal growth, and the second clad layer of each of the plurality of laser diode portions is etched. The thickness of the laser beam is reduced to a predetermined value by the above method, and the cap layer is further laminated, so that the beam thickness can be easily and reproducibly and easily controlled without changing the active layer thickness of multiple laser diodes in one device. Since the divergence angle in the vertical direction can be set, it becomes possible to easily integrate laser diodes having different divergence angles in the beam vertical direction on the same substrate, and it is possible to fabricate with a high yield.

[Brief description of drawings]

FIG. 1 is a sectional view showing a semiconductor laser device according to an embodiment of the present invention, FIG. 2 is a view showing a method for manufacturing a semiconductor laser device of the present invention, and FIGS. 3 and 4 are other embodiments of the present invention. FIG. 5 is a sectional view showing a semiconductor laser device, FIG. 5 is a diagram showing a method for manufacturing the semiconductor laser device of the invention of FIG. 4, and FIG. 6 is a sectional view showing a semiconductor laser device according to another embodiment of the present invention. FIG. 8 is a sectional view showing a conventional semiconductor laser device, and FIG. 8 is a sectional view showing an operation of the conventional semiconductor laser device. In the figure, (1) is the substrate, (2) is the ledge, (3) is the groove, (4) is the first cladding layer, (5) is the active layer, and (6).
Is the second cladding layer, (7) is the cap layer, (8),
(9) is an electrode, (10) is a separation groove, (11) is a terrace, (1
2) is the current blocking layer, and (13) is the third cladding layer. The same reference numerals in the drawings indicate the same or corresponding parts.

Claims (2)

[Claims] 1. A semiconductor substrate having first and second main surfaces, and a bottomed groove for separating the first main surface into at least two parts in a central portion, and a first semiconductor substrate of the semiconductor substrate. On one of said parts of the main surface of
A clad layer, an active layer, a second clad layer, and a cap layer made of a material serving as an absorber for the oscillation wavelength from the active layer or a material having a refractive index lower than that of the second clad layer are sequentially laminated. One laser diode, the other one of the portions of the first main surface, the first cladding layer of the same material and the same thickness as the first cladding layer, the same material of the active layer and the same. An active layer having a thickness, a second cladding layer having the same material as the second cladding layer and thinner than the second cladding layer, and a cap layer having the same material as the cap layer, A multi-beam semiconductor laser device comprising: at least one other laser diode that is sequentially stacked independently of the diode. 2. A step of sequentially laminating a first clad layer, an active layer, and a second clad layer on a substrate by crystal growth, and a step of forming the second clad layer for each of a plurality of laser diode parts in a multi-beam semiconductor laser device. A step of thinning the layer to a predetermined thickness by etching, and a step of laminating a material to be an absorber for the oscillation wavelength from the active layer or a material having a refractive index lower than that of the second cladding layer. Method of manufacturing multi-beam semiconductor laser device.