JPH03120887A - Semiconductor laser - Google Patents

Abstract

PURPOSE:To acquire high light output by specifying light reflectance of a projecting edge face and light reflectance of a monitor side edge face. CONSTITUTION:After a current constriction region 108 is formed, electrodes 109, 110 are formed. Then, cleavage is made and a laser oscillator edge face and edge face protecting films 111, 112 are formed. At this time, three layers of SiO2/a-Si pair whose film thickness is controlled are laminated on a monitor side projecting edge face. A single layer of SiO2 having a controlled film thickness is laminated on an output side projecting edge face. Light reflectance at the monitor side projecting edge face is made 32 to 100% and light reflectance at the output side projecting edge face is made 2 to 32%.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a semiconductor laser used in optical discs and the like.

[Prior Art] Conventionally, a refractive index waveguide structure is constructed in which the refractive index waveguide width and the current injection width are approximately the same in the vicinity of at least one end face, and the refractive index waveguide width is made sufficiently wider than the current injection width in other regions. By using a structure in which a rib-shaped optical waveguide made of m-v group compound semiconductor stripes with a gain waveguide structure is embedded with a [-VI group compound semiconductor layer, the coherence of the emitted light is reduced, and the return light noise characteristics are improved. Excellent semiconductor lasers were known.

[Problems to be Solved by the Invention] However, the maximum optical output of such conventionally used semiconductor lasers is at the edge destruction level (COD level).
At 40 mW HR Thea 3, Detailed Description of the Invention Also, at the level where reliability can be guaranteed, at most 30 mW
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.

In a semiconductor laser which has a structure in which a shaped leading waveguide is buried in an N-VR group compound semiconductor layer and has end face protection films with different light reflectances on both end faces, the light reflectance of the output end face is between 2% and 32%. It is characterized in that the value is between 32% and 100%, and the light reflectance of the monitor side end face is between 32% and 100%.

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

[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. (Example 1) First example of the present invention As a result, the light reflectance of the output end surface is reduced to 10%, and the light reflectance of the monitor side end surface is reduced to 95%.
%, the maximum optical output and differential quantum efficiency are increased, and the threshold current value remains unchanged.

Figure 1 shows S+0 on the output side emission end face of a multimode oscillation laser.
2 is a perspective view of a semiconductor laser in which an aSt/5IO2 multilayer thin film is formed on the output end face on the monitor side.

First, the manufacturing process will be explained.

n-GaAs buffer layer 1 on n-GaAs substrate 101
02,n-A l 11. aG a a, sA s cladding layer 103, A I [1, [15G a e, 9
sA s active layer 104, p-A I B, aG a
a, eAs cladding layer 105 and p-GaAs:+ contact layer 106 are formed by metal organic chemical vapor deposition (MOCVD).
growth by law).

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

As the material gases, trimethyl gallium (TMG) and trimethyl aluminum (TMA) were used for group (1), and Arunn (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.

Growth conditions are II-VIII0. Growth temperature 700°
C growth was performed at a pressure of 10 Torr.

The reaction tube is a cold wall horizontal furnace.

In addition, as a material gas, dimethyl zinc (D
MZn), dimethyl selenium (DMSe) was used for group ①.

Next, after removing the 5i02 thin film, a SiO2 thin film is again formed by electron beam evaporation, 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, edge protection films 111 and 112 made of 5iQ2 are formed by electron beam evaporation, and the film thickness is controlled at this time.
Si○2/ with a - S j controlled to a film thickness of 66 nm
Three layers of a-3i bare are laminated, and the output end surface has a 190
A single layer of 5i02 with a controlled thickness of nm is laminated.

At this film thickness of the end face protection film, the light reflectance at the output end face on the monitor side is 95%, 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 end face destruction optical output (COD) level is 180m'vV, and 9 of the samples are simply coated with a protective film on both end faces.
Compared to 0mW, it increased approximately twice to 90mW.

In addition, the oscillation threshold is 44 mA, and the reflectance of both end faces without an end face protection film is 32% in this case)
It was almost the same as 43mA.

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 approximately the same) changes with respect to the light intensity, the longitudinal mode characteristics remain unchanged even at high optical output. Performs multi-mode oscillation with low sensitivity.

Therefore, the optical output for multi-mode oscillation can be obtained up to 160 mW, which is 40 mW compared to the sample with only a protective film attached to the end face.
Multimode oscillation was achieved up to an optical output approximately four 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.

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

In this embodiment, a light reflectance of 10% on the exit side and a light reflectance of 95% on the monitor side has been described, but it is of course possible to use a combination of light reflectances different from this. However, if the light reflectance of the output end face is set to 4% or less, the threshold current increases significantly, and if it is set to 2% or less, laser oscillation becomes difficult at room temperature, so the light reflectance of the output end face is reduced to 2%.
As mentioned above, it is preferable to use a value of 4% or more for normal purposes.

Furthermore, if the light reflectance on the monitor side is made too high, the monitor output will become small and signal detection will be hindered, so it is desirable to keep it to a value of 98% or less.

Of course, when using a method of obtaining a feedback signal using a part of the emitted light, there is no problem even if the light reflectance is set to 100%, and it is actually preferable from the point of view of the threshold value and efficiency.

Above, we have described an example in which an AlGaAs double heterojunction substrate is used and Zn5e is used to fill the stripe side surface, but of course it is also possible to use a double heterojunction sliding substrate belonging to other series such as an InP type. .

In addition, the filling material is not limited to Zn5e, but can also be ZnS or 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 inside the semiconductor laser is destroyed, selectivity of the oscillation wavelength does not occur even at a wavelength of 1 to 1 during high output 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 through 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 chip, it is possible to perform a design with an extremely high degree of freedom.

For example, the LPE method (Liquid Phase Ep
Semiconductor laser chips fabricated using ITAXLCY have difficult to stabilize characteristics due to non-uniformity that occurs during crystal growth.
It has been difficult to stably produce a device that maintains low coherence even during high-power operation, but by aligning the characteristics of the device by modulating the reflectance of the end face protection film, the failure rate in the initial characteristics has been reduced by more than half. I was able to do it.

In addition, sufficient reliability can be ensured even in devices where normal protective films have a gain waveguide with insufficient current confinement function, resulting in a considerably large drive current and insufficient reliability. In the life test, we were able to confirm that the estimated lifespan was more than three times as long.

(3) Quantum efficiency is improved and the threshold current value is lowered, so power consumption is reduced and heat generation is suppressed, so reliability is improved. Furthermore, when powered by batteries, the system using this semiconductor laser can be operated for a long time.

[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. oQ 01 02 03 Do layer 04 105 ・ Do layer 06 107 ・ 09 110 ・ 11 12

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 - In 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 and having end face protection films with different light reflectances on both end faces, the light of the output end face is 1. A semiconductor laser having a reflectance between 2% and 32% and a monitor side end face having a light reflectance between 32% and 100%.