JP3213377B2 - Semiconductor laser - 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 capable of high-power operation.

[0002]

2. Description of the Related Art Conventionally, in order to realize a high output operation, a laser element having a current non-injection layer in the vicinity of an end face of a resonator has been developed for an AlGaInP-based visible light semiconductor laser (Japanese Patent Laid-Open No. -153090 [H01S3 / 18]).

As shown in FIG. 7, such a semiconductor laser has an n-GaAs substrate (1), an n-GaInP buffer layer (2), an n-AlGaInP cladding layer (3), a GaInP active layer (4), and a p-type substrate. AlGaInP cladding layer (50)
And a p-GaInP contact layer (6), and an n-type layer is formed on the upper surface of the contact layer (6) near the resonance end face.
A GaAs current blocking layer (7) is formed, and these layers (6)
(7) is covered with a p-GaAs cap layer (8).
On the n-GaAs substrate (1) side, a Cr-Sn / Au electrode (9), p-GaAs
On the cap layer (8) side, a Cr / Au electrode (10) is arranged.

Incidentally, the carrier concentration of the p-AlGaInP cladding layer (50) is constant (for example, 2-3 × 10 ¹⁷ cm ^-3 ) over the entire region in the cavity length direction (the horizontal direction in FIG. 7).

When current is applied to both electrodes (9) and (10) of the semiconductor laser, a current flows around the n-GaAs current blocking layer (7) as shown by a broken line in FIG. The current density in the vicinity of the end face to be reduced is reduced, and the instantaneous optical damage (CO
D; Catastrophic Optical Damage) is suppressed, and high-output operation is enabled.

[0006]

However, in the semiconductor laser shown in FIGS. 7 and 8, both current blocking layers (7) are used.
There is a problem that the current density locally increases in the current injection region inside (7), and the life in high-power operation is shortened due to the deterioration of the current injection region.

An object of the present invention is to provide a semiconductor laser which can alleviate a local increase in current density in a current injection region and can achieve a long life at a high output operation.

A semiconductor laser according to the present invention comprises an n-GaAs substrate (1)
An n-AlGaInP cladding layer (3), a GaInP active layer (4) and
A p-AlGaInP cladding layer (5) is formed. The carrier concentration of the p-AlGaInP cladding layer (5) changes in the longitudinal direction of the resonator. The n-GaAs current blocking layers (7) are formed on the p-AlGaInP cladding layer (5) and in the vicinity of the cavity end faces, respectively.
(7) is formed, and the p-AlGaInP clad layer (5) has a high carrier concentration in a region sandwiched between the current blocking layers (7) and (7).

[0009]

The p-AlGaInP cladding layer (5) can be formed to have a lower carrier concentration than the center of the resonator by containing hydrogen in the vicinity of the resonator end face.

[0011]

The p-AlGaInP cladding layer (5) has a low carrier concentration in the vicinity of the end face of the resonator and has a large electric resistance, and the central part of the resonator has a high carrier concentration and a small electric resistance. . Therefore, when current is applied between both electrodes, the current density is gradually distributed according to the resistance change, and no local increase in the current density occurs.

Further, since the n-GaAs current blocking layers (7) are formed in the vicinity of the end faces of the resonator, current flows through the resistance regions further inside the current blocking layers (7) and (7). As a result, the concentration of the current density inside the current blocking layers 7 is alleviated.

In addition, by incorporating hydrogen into the p-AlGaInP cladding layer (5) in the vicinity of the cavity end face, the hydrogen is combined with the p-type dopant in the cladding layer to lower the carrier concentration. Let it.

[0014]

According to the semiconductor laser of the present invention, a local increase in current density at the current injection portion is mitigated, and a long life at high output operation is realized.

[0015]

DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment in which the present invention is applied to an AlGaInP-based visible light semiconductor laser will be described in detail with reference to the drawings.

The semiconductor laser shown in FIG. 1 is an n-GaAs substrate
On (1), an n-GaInP buffer layer (2), an n-AlGaInP cladding layer (3), a GaInP active layer (4), a p-AlGaInP cladding layer (5) and a p-GaInP contact layer (6) are formed. On top of the contact layer (6), n-GaAs is
Forming current blocking layers (7) and (7), and further forming these layers (6) and (7)
A p-GaAs cap layer (8) is formed to cover (7).

The thickness of the n-GaAs substrate (1) is 100 μm, n-GaInP
The thickness of the buffer layer (2) is 0.3 μm, the thickness of the n-AlGaInP cladding layer (3) is 1.0 μm, and the thickness of the GaInP active layer (4) is 0.3 μm.
07 μm. The p-AlGaInP clad layer (5) is formed to have a thickness of 0.8 μm at the center and 0.2 μm at both ends,
The thickness of the n-GaAs current blocking layer 7 is 0.8 μm, and the thickness of the p-GaAs cap layer 8 is 2 μm. In addition, both clad layers (3)
The aluminum composition ratio of (5) is 0.65.

Here, in the p-AlGaInP cladding layer (5), a current injection region (51) sandwiched between both current blocking layers (7) and (7) is formed with a high carrier concentration. Resistance has been reduced. The carrier concentration in the current injection region of the p-AlGaInP cladding layer (5) is 5 to 7 × 10 ¹⁸ cm ⁻³ , and the carrier concentration in the vicinity of the end face (current non-injection region) is 2 to 7 × 10 ¹⁸ cm ⁻³ .
It is 3 × 10 ¹⁷ cm ⁻³ .

Therefore, when a current flows between both electrodes, the current becomes
As shown by the broken line in FIG. 2, the current flows through the low resistance portion in the high carrier concentration region, and the concentration of the current density inside the current blocking layers 7 is reduced.

The semiconductor laser shown in FIG. 3 has an n-GaAs current blocking layer (7) formed on both sides of the resonator length direction, and has a lateral mode control type high output structure.

The semiconductor laser has a current non-injection region B near the cavity facet and a current injection region A at the center of the cavity, similarly to the semiconductor laser of FIG. 1, and has a p-AlGaInP cladding layer.
The carrier concentration in the current injection region A of (5) is formed to be higher (5 to 7 × 10 ¹⁸ cm ⁻³ ) than the carrier concentration in the current non-injection region (2 to 3 × 10 ¹⁷ cm ⁻³ ). I have.

The semiconductor laser shown in FIG. 3 is manufactured through the steps shown in FIGS. First, as shown in FIG.
On a GaAs substrate (1), n-GaInP was grown by the first crystal growth using reduced pressure MOCVD (metal organic chemical vapor deposition).
A buffer layer (2), an n-AlGaInP cladding layer (3), a GaInP active layer (4), a p-AlGaInP cladding layer (5), a p-GaInP contact layer (6) and a p-GaAs layer (80) are formed. Then, a wafer having a double hetero structure is obtained.

Next, as shown in FIG. 4B, a stripe-shaped SiO ₂ mask (12) having a width of about 4 μm is formed on the wafer, and etching is performed using hydrobromic acid to form a ridge portion.
Form (11). After that, only the both ends of the SiO ₂ mask (12) are removed as shown.

Subsequently, an n-GaAs current blocking layer (7) is formed by the second crystal growth as shown in FIG. 4 (c). At this time, the n-GaAs current blocking layer (7) is selectively grown only on the surface area not covered by the SiO ₂ mask (12). Thereafter, the SiO ₂ mask (12) is removed with hydrofluoric acid.

Next, as shown in FIG.
4) housed in an atmosphere of N ₂ : H ₂ = 9: 1
Heat to ° C. Then, the laser beam from the CO ₂ laser disposed outside the thermostatic layer (14) is reflected by the reflection mirror (15) and the Si mirror.
The light is condensed to a spot diameter of 100 μm via the lens (16), and the laser light is irradiated to the opening (13) of the n-GaAs current blocking layer (7).

As a result, only the wafer region exposed from the opening (13) is heated to 500 to 600 ° C. for 5 to 10 seconds. As a result, H ₂ contained in the crystal is discharged, and p
Zinc, which is the p-type dopant of the -AlGaInP cladding layer (5), is activated, and the carrier concentration increases.

Further, as shown in FIG. 6, a p-GaAs cap layer (8) having a thickness of about 2 is formed on the wafer surface by the third crystal growth.
Form to μm. Finally, the n-type and p-type ohmic electrodes (9) and (10) are formed by a vacuum deposition method to complete the semiconductor laser according to the present invention.

FIG. 9 compares the results of reliability tests of the semiconductor laser of the present invention shown in FIG. 3 and a conventional semiconductor laser. The reliability test was performed at an ambient temperature of 40 ° C.
The APC operation was performed to maintain the laser output at a constant value of 20 mW. In the conventional semiconductor laser, COD is generated in about 300 hours, whereas in the semiconductor laser of the present invention, the drive current is only slightly increased over 1000 hours, and high reliability is obtained. You can see that it has been done.

The semiconductor laser of the present invention shown in FIGS. 10 and 11 utilizes the phenomenon that the carrier concentration decreases due to the increase in the hydrogen content of the p-type crystal layer, and the carrier concentration of the p-AlGaInP cladding layer (5) is increased. In the region near the cavity facet (52) (5
It is formed low in 2).

On an n-GaAs substrate (1), an n-GaInP buffer layer (2), an n-AlGaInP cladding layer (3), a GaInP active layer (4),
And a p-AlGaInP cladding layer (5) having a ridge portion (11), a p-GaInP contact layer (6) on the ridge portion (11), and n-type layers on both sides of the ridge portion (11). GaAs current blocking layer
(7) and (7) are formed, and these layers (6), (7) and (7)
It is covered by a GaAs cap layer (8). And n-
Cr-Sn-Au electrode (9), Cr-Au electrode (10) on GaAs substrate (1) side
Is arranged. The aluminum composition ratio of the cladding layers (3) and (5) is set to 0.4 or more.

Here, the p-AlGaInP cladding layer (5) reduces the carrier concentration in the region (52) near the cavity end face as described above, so that the electric resistance of the region (52) is higher than that of other regions. It is formed to a high value (0.5 Ω · cm or more).

The above-described semiconductor laser is manufactured through the steps shown in FIGS. First, as shown in FIG.
On a GaAs substrate (1), an n-GaInP buffer layer (2), an n-AlGaInP
A cladding layer (3), a GaInP active layer (4), a p-AlGaInP cladding layer (5), a p-GaInP contact layer (6) and a p-GaAs layer (80) are formed to obtain a double heterostructure wafer.

Here, the thickness of the n-GaInP buffer layer (2) is 0.3 μm, the thickness of the n-AlGaInP cladding layer (3) is 1 μm,
The thickness of the AlGaInP cladding layer (5) is 0.8 μm, the thickness of the p-GaInP contact layer (6) is 0.1 μm, and the thickness of the p-GaAs layer (80) is 0.3 μm.

Next, as shown in FIG.
After forming a stripe-shaped SiO ₂ mask (12) having a thickness of 0.6 μm, the p-GaAs layer (80) is
P-GaInP contact layer by HBr etchant (6)
Then, the ridge portion (11) is formed by etching the p-AlGaInP cladding layer (5). At this time, the p-AlGaInP cladding layer
In (5), both ends are left at a thickness of 0.2 μm. or,
The entire width of the ridge portion (11) is formed to be about 4 μm.

Subsequently, by the second crystal growth, the n-GaAs current blocking layers (7) and (7) are formed to a thickness of 0.8 μm as shown in FIG. At this time, the n-GaAs current blocking layer (7)
Selectively grows only on the surface area not covered by the SiO ₂ mask (12). Then, the SiO ₂
The mask (12) is removed with hydrofluoric acid.

Further, by the third crystal growth, FIG.
A p-GaAs cap layer (8) is formed on the wafer surface as shown in FIG.
Form to μm. Then, a Cr-SnAu layer and a Cr-Au layer are formed by a vacuum evaporation method to form n-type and p-type ohmic electrodes (9) and (10), respectively.

As described above, the semi-finished semiconductor laser (17) obtained by the same process as the conventional one is arranged in the high resistance layer forming apparatus shown in FIG. The apparatus converts a hydrogen gas in a chamber (18) into a plasma by turning on a high frequency power supply (19). As a result, the semiconductor laser (17) in the chamber (18) has its cavity end face in the hydrogen plasma (20).
, And impregnated with hydrogen in the vicinity of the end face, thereby forming a high resistance layer.

FIG. 15 shows the time change of the film thickness of the high resistance layer formed on the p-AlGaInP clad layer (5).
It can be seen that a high resistance layer of about 1 μm is formed in 0 minutes. The electric resistance value of the high resistance layer is approximately 0.5 Ω · cm.

Thus, the carrier concentration of the p-AlGaInP cladding layer (5) is low in the regions (52) and (52) near the resonator end face, and
A high semiconductor laser of the present invention is completed at the center of the resonator.

FIG. 16 shows a comparison of the driving current-light output characteristics of the semiconductor laser of the present invention and the conventional semiconductor laser. While any semiconductor laser is also 50mW or more light output can be obtained, a semiconductor laser of the present invention, the threshold current has lowered nearly 20 m A than conventional semiconductor lasers, enables low-power operation I know there is.

This is because, in the conventional semiconductor laser, light absorption in the region near the end face increases due to the temperature rise in the region.

As a result, according to the semiconductor lasers shown in FIGS. 10 and 11, a long life with a high output operation is realized.

According to the steps shown in FIGS. 12 to 14, the semiconductor laser of the present invention can be manufactured very easily, and the yield can be improved as compared with the steps shown in FIGS.

The description of the above embodiments is for the purpose of illustrating the present invention and should not be construed as limiting the invention described in the claims or reducing the scope thereof. Further, the configuration of each part of the present invention is not limited to the above-described embodiment, and it is needless to say that various modifications can be made within the technical scope described in the claims.

For example, without irradiating the wafer obtained through the process shown in FIG. 4 with a laser, a p-GaAs cap layer (8) and electrodes (9) and (10) are formed as shown in FIG. By forming a high-resistance layer in the current non-injection region near the end face using the apparatus shown in FIG. 14, it is also possible to obtain the semiconductor laser of the present invention.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view of a semiconductor laser according to the present invention along a cavity length direction.

FIG. 2 is a diagram showing a current distribution in the semiconductor laser of FIG.

FIG. 3 is a partially broken perspective view showing an example in which the present invention is applied to a lateral mode control type semiconductor laser.

FIG. 4 is a series of perspective views showing the first half of a manufacturing process of the semiconductor laser of FIG. 3;

FIG. 5 is a perspective view showing a step of forming a high carrier concentration region in a p-AlGaInP cladding layer after the step of FIG. 4;

FIG. 6 is a perspective view of a semiconductor laser obtained through the above steps.

FIG. 7 is a cross-sectional view of a conventional semiconductor laser along a cavity length direction.

FIG. 8 is a diagram showing a current distribution in the semiconductor laser of FIG. 7;

FIG. 9 is a graph showing a change in drive current with respect to an operation time.

FIG. 10 is a cross-sectional view along a resonator length direction of a semiconductor laser according to the present invention having a high resistance layer in a region near a resonator end face.

FIG. 11 is a front view of the semiconductor laser of FIG. 10;

FIG. 12 is a series of front views showing the first half of the manufacturing process of the semiconductor laser of FIG. 10;

FIG. 13 is a front view of the semiconductor laser obtained through the step of FIG.

14 is a partially cutaway side view showing a schematic configuration of an apparatus for forming a high-resistance layer on the semiconductor laser of FIG.

FIG. 15 is a graph showing a change in thickness of a high-resistance layer formed by the device of FIG.

FIG. 16 is a graph showing drive current-light output characteristics.

[Explanation of symbols]

 (1) n-GaAs substrate (3) n-AlGaInP cladding layer (4) GaInP active layer (5) p-AlGaInP cladding layer (51) current injection region (6) p-GaInP contact layer (7) n-GaAs current Blocking layer (8) p-GaAs cap layer

Claims (2)

(57) [Claims] 1. A semiconductor laser having a first conductivity type cladding layer (3), an active layer (4) and a second conductivity type cladding layer (5) formed on a first conductivity type semiconductor substrate (1). In the crystal layer including the second conductivity type cladding layer (5), the carrier concentration changes in the resonator length direction, and is formed at a low concentration near the resonator end face and a high concentration at the resonator center. In addition, the first conductivity type current blocking layers (7) and (7) are formed on the second conductivity type clad layer (5) in the vicinity of the cavity end face, respectively, and the second conductivity type clad layer (5) is formed. Is a semiconductor laser in which a region between the current blocking layers (7) and (7) is formed with a high carrier concentration. 2. The semiconductor laser according to claim 1, wherein the crystal layer including at least the cladding layer of the second conductivity type has a low carrier concentration containing hydrogen in the vicinity of the cavity end face.