JPH0438888A - Semiconductor laser - Google Patents

Abstract

PURPOSE:To get high light output by forming end face protective films different in reflectance at both end faces of a semiconductor laser. CONSTITUTION:An SiO2 film is formed by electron beam deposition method, and then a current confricting region 108 is formed by photoetching process, and next electrodes 109 and 110 are formed, and then cleavage is performed to form a laser resonator end face. Next, by electron beam deposition method, end face protective films 111 and 112 consisting of SiO2 are formed. At this time, thickness control is performed for the films such that the thickness is 286nm at the emitting end face on the monitor side and 190nm at the emitting end face on the output side. At the time of this end face protective film, the light reflectance at the emitting end face on the monitor side is 32%, and the light reflectance is 10% at the emitting end face on the output side. Lastly, an electrode metal is formed by vacuum deposition method, and then it is mounted on a package.

Description

[Detailed Description of the Invention] [Industrial Field of Application] The present invention relates to semiconductors used in optical disks, etc. [Prior Art] Conventionally, near at least one end face, the refractive index waveguide width and the current injection width are set to be approximately the same and refraction is performed. The refractive index waveguide width is made sufficiently wider than the current injection width in other regions to form a gain waveguide structure.■-A rib-shaped optical waveguide made of a V group compound semiconductor layer is made of an n-VI group compound semiconductor layer. Semiconductor lasers have been known that use a layered structure to reduce the coherence of emitted light and have excellent return optical noise characteristics.

[Problem B to be solved by the invention] However, in conventionally used semiconductor lasers, the maximum optical output is at the edge destruction level (COD level).
It is about 40mW.

Also, at a level where reliability can be guaranteed, it is 30mW at most.
is the maximum rating.

However, since a commonly used magneto-optical disk requires a maximum optical output of about 50 mW, this optical output is insufficient.

Further, the threshold current value also becomes a considerably large value, resulting in increased power consumption.

SUMMARY OF THE INVENTION Therefore, the present invention aims to solve these conventional problems and provide a semiconductor laser that can provide high optical output.

[Means for Solving the Problems] In order to solve these conventional problems, the semiconductor laser of the present invention uses a refractive index waveguide with the refractive index waveguide width and the current injection width being approximately the same in the vicinity of at least one end face. In other regions, the refractive index waveguide width is made sufficiently wider than the current injection width, and a rib-shaped optical waveguide made of an m-v group compound semiconductor layer is embedded with an n-Vl group compound semiconductor layer to form a gain waveguide structure. The present invention is characterized by having end face protection films having different light reflectances on both end faces of a semiconductor laser having a structure.

[Example of implementation] Embodiments of the present invention will be described below with reference to the drawings.

(Example 1) As a first example of the present invention, a semiconductor laser in which the light reflectance of the output side emission end face is reduced to 10% and the maximum optical output is increased will be described.

FIG. 1 is a perspective view of a semiconductor laser in which a SiO2 thin film is formed on the output side emission end face and the monitor side emission end face of a multimode oscillation laser.

First, the manufacturing process will be explained.

n-GaAs buffer layer 1 on n-GaAs substrate 101
02, n-A I g, 4G ae sA s cladding layer 103, A l s, ssG a s, ssA
s active layer 104, p-A l 11. aG a 11
．． The eAS cladding layer 105 and the p-GaAs:+ contact layer 1-06 are formed by metal organic chemical vapor deposition (MOCVD).
growth by law).

The growth conditions were a v-m ratio of 75, a growth temperature of 670° C., and a pressure cuff of 0 Torr during growth. The reaction tube is a cold wall horizontal furnace.

As material gases, trimethylgallium (TMG) and trimethylaluminum (TMA) were used for group (1), and arsine (AsH3) was used for group V.

Next, a SiO2 thin film is formed by electron beam evaporation, and then patterned into the shape shown in FIG. 2 by an ordinary photoetching process.

Next, rib-shaped regions are formed using a sulfuric acid-based etching solution.

Subsequently, ZnS e107 is embedded into the side surfaces of the rib by selective MOCVD.

The growth conditions were an n-VI ratio of 10, a growth temperature of 700° C., and a growth pressure of 10 Torr.

The reaction tube is a cold wall horizontal furnace.

In addition, as a material gas, dimethyl sink (D
Dimethyl selenium (DMSe) was used for the MZn) and Vl groups.

Next, after removing the 5102 thin film, a 5102 thin film is formed again by electron beam evaporation, and then a current confinement region 108 is formed by a normal photoetching process, and then the electrode 1
After forming 09.110, cleavage is performed to form a laser resonator end face.

Next, end face protection films 111 and 112 made of SiO2 are formed by electron beam evaporation, and at this time, the film thickness is controlled to 286 nm on the monitor side emission end face and 190 nm on the output side emission facet. do.

At this film thickness of the end face protection film, the light reflectance at the output end face on the monitor side is 32%, and the light reflectance at the output end face is 1.
It is 0%.

Finally, electrode metal was formed by vacuum evaporation and mounted on a package to complete the manufacturing process.

Next, the characteristics of this semiconductor laser were evaluated.

The edge destruction optical output (COD) level is 150mW,
90mW of a sample with just a protective film on both end faces
Compared to the above, an increase rate of about 60 mW, nearly 70%, was obtained.

In addition, since the optical intensity distribution and optical gain distribution inside the semiconductor laser change greatly by changing the reflectance of the end face protection film, it is important to note that the gain waveguide (the part where the refractive index waveguide width is sufficiently wider than the current injection width) and the end face Since the gain distribution between the nearby refractive index waveguide section (the section where the refractive index waveguide width and the current injection width are similar) changes with the light intensity, the longitudinal mode characteristics are coherent even at high optical output. It performs multimode oscillation with small oscillation.

Therefore, the optical output for multimode oscillation can be obtained up to 110 mW, which is 40 mW compared to the sample with only a protective film attached to the end face.
Multi-mode oscillation was achieved up to an optical output approximately 2.5 times that of mW.

In addition, the far-field pattern (FFP) remained unimodal up to the edge destruction light output level, regardless of the reflectance of the edge protection film.

The oscillation threshold is 52 mA, and the 43 mm without end face protection film (reflectance of both end faces is 32% in this case)
The increase was limited to about 9 mA compared to mA.

These data are average values of the measured values of 500 samples excluding initial defects.

(Example 2) As a second example of the present invention, a semiconductor laser will be described in which the light reflectance of the output facet on the monitor side is increased to 99%, the oscillation threshold current value is decreased, and the differential quantum efficiency is improved.

FIG. 2 is a perspective view of a semiconductor laser in which a SiO2 thin film is formed on the emission end face of a multimode oscillation laser, and a multilayer reflective film of 5io2/a-si (amorphous silicon) is formed on the monitor side emission end face.

The manufacturing process of the semiconductor laser is the same as that described in Example-1. The edge protection film was formed using an electron beam evaporation method with a switching source. The material of the end face protection film on the output end face on the output side is 5i02, and the film thickness is 286 nm.

The material of the end face protection film 301 on the output end face on the monitor side [c Si
It is a multilayer reflective film of O2/a-3i (amorphous silicon).

The film thickness is 143 nm for 5i02 and 31 nm for a-Sl.
It is.

Further, the number of stacked layers is 10.

When this end face protection film is used, the light reflectance at the output end face on the monitor side is 99%, and the light reflectance at the output end face is 32%.

Next, the characteristics of this semiconductor laser were evaluated in the same manner as in Example-1.

The oscillation threshold is 28 mA, and the 43 mm without end face protection film (reflectance of both end faces is 32% in this case)
It decreased by about 15 mA compared to mA.

Further, the driving current value of the semiconductor laser was 120 mA at an optical output of 50 mW, which was about 40 mA lower than that of a device in which protective films were simply formed on both end faces.

Therefore, an increase in temperature of the semiconductor laser chip can be avoided.

As a result, the edge destruction optical output (COD) level increases and 11
A COD level of 0 mW was obtained, and the maximum optical output was also increased by about 20 mW compared to 90 mW for a sample with just a protective film on both end faces.

In addition, since the optical intensity distribution and optical gain distribution inside the semiconductor laser change greatly by changing the reflectance of the end face protection film, it is important to note that the gain waveguide (the part where the refractive index waveguide width is sufficiently wider than the current injection width) and the end face Since the gain distribution between the nearby refractive index waveguide section (the section where the refractive index waveguide width and the current injection width are similar) changes with the light intensity, the longitudinal mode characteristics are coherent even at high optical output. It performs multimode oscillation with small oscillation.

Therefore, the state of multimode oscillation is 1, which is the COD level.
Multi-mode oscillation was achieved with an optical output of up to 10 mW, approximately 2.5 times as much as the 40 mW of a sample with a simple protective film attached to the end face.

In addition, the far-field pattern (F F P) remained unimodal up to the end face destruction optical output level, regardless of the reflectance of the end face protective film.

These data are average values of the measured values of 500 samples excluding initial defects.

Furthermore, especially for applications requiring low noise characteristics, it is effective to increase the reflectance of the output end face to about 70%.

An example has been described above in which an AlGaAs-based double heterojunction substrate is used and Zn5e is used to fill the stripe side surface, but it is of course possible to use a double-heterojunction gantry substrate belonging to another series such as an InP-based substrate.

In addition, the filling material is not limited to Zn5e (ZnS, Z
It may be a material such as nTe or a mixed crystal thereof.

In particular, when using an AlGaAs-based double heterojunction substrate, it is particularly promising to use a mixed crystal of ZnSe and ZnS because lattice matching with the substrate can be achieved.

Further, the basic structure of the semiconductor laser can also be made low in threshold by using a method such as a buried type.

[Effects of the Invention The semiconductor laser of the present invention has the following effects.

(1) By changing the reflectance of the end face protection film, the light intensity distribution and optical gain distribution inside the semiconductor laser, as well as the carrier density distribution accompanying this phenomenon, are significantly modulated.

Moreover, this phenomenon strongly depends on the light intensity inside the semiconductor laser.

Therefore, it has a gain waveguide section (a section where the refractive index waveguide width is sufficiently wider than the current injection width) and a refractive index waveguide section near the end face (a section where the refractive index waveguide width and current injection width are approximately the same). Since the electromagnetic symmetry within the semiconductor laser is disrupted, selectivity of the oscillation wavelength does not occur even during high-power operation.

Therefore, return light noise due to reflected return light from the irradiated medium is not generated.

This characteristic is essential for high-speed optical discs that must simultaneously have high output and low return optical noise.

In addition, since the emitted light has no coherence, unnecessary interference fringes are not generated when the light is focused using an optical system, so high quality can be achieved when used in a laser beam printer or the like.

(2) Since the coherence can be controlled in the state of the semiconductor laser beam, a design with an extremely high degree of freedom can be performed.

For example, the LPE method (LIquld Phase Ep
Semiconductor laser chips made using LTAXICY have difficult to stabilize characteristics due to non-uniformity that occurs during crystal growth.
It has been difficult to stably create a device that maintains low coherence even during high-8 force operation, but by aligning the device characteristics by modulating the reflectance of the end face protection film, the failure rate in the initial characteristics can be reduced by half or less. I was able to do it.

In addition, since a normal protective film has a gain waveguide with insufficient current confinement function, the drive current is quite large (which makes it difficult to ensure sufficient reliability even in devices that cannot achieve sufficient reliability. In the life test, we were able to confirm that the estimated lifespan was more than three times longer.

[Brief explanation of drawings]

FIG. 1 is a perspective view of a semiconductor laser for explaining Example 1 of the present invention. FIG. 2 is a perspective view in the middle of a semiconductor laser manufacturing process for explaining Example 1 of the present invention. n-GaAs substrate n-GaAs buffer layer n -A 1 s, aGa a, eAs cladding layer 105 / do layer 107 / 112 / -A 1 a, 1lsGa s, ssAs active layer p
-A l 11. JG a 11.6A S Crapple - GaAs contact layer nSe Electrode end face protective film End face protective film Applicant Seiko Epson Corporation Agent Patent attorney Kizobe Suzuki and 1 other person

Claims (1)

[Claims] In the vicinity of at least one end face, the refractive index waveguide width and the current injection width are approximately the same, creating a refractive index waveguide structure, and in the other regions, the refractive index waveguide width is sufficiently wider than the current injection width to create a gain waveguide structure.III - A semiconductor laser having a structure in which a rib-shaped optical waveguide made of a group V compound semiconductor layer is embedded with a group II-VI compound semiconductor layer, characterized by having end face protection films having different light reflectances on both end faces. semiconductor laser.