JPS60137086A - Semiconductor laser device and manufacture thereof - Google Patents

Abstract

PURPOSE:To obtain a high output semiconductor laser having a narrow window region by bending a hetero epitaxial crystal layer which contains an active layer near a light producing end. CONSTITUTION:A groove 22 is formed at the position corresponding to the end of a laser resonator to match the interval of the length of the resonator on an N type GaAs substrate 21. A buffer layer 23, a clad layer 24, a Ga0.9Al0.1As active layer 25, and a P type Ga0.65Al0.35As clad layer 26, and a current blocking layer 27 are sequentially grown thereon. Subsequently, the layer 27 is selectively etched to form a striped groove 28. Then, a coating layer 29 and a contacting layer 30 are sequentially formed. Then, an electrode layer 31 is formed on the layer 30 under the substrate 21.

Description

[Detailed Description of the Invention] [Technical Field of the Invention] The present invention relates to a semiconductor laser device and a method for manufacturing the same, and particularly to a semiconductor laser device that suppresses optical destruction at the light extraction end face and enables high output operation, and the manufacturing thereof. Regarding the method.

[Technical background of the invention and its problems] In recent years, semiconductor lasers, particularly Ga AJlAs lasers, have come to be used as laser light sources for optical disc players such as digital audio discs and video discs. In the case of these applications, the required laser light output is simply for detecting the intensity of the reflected light from the optical disk surface, so it does not need to be so large, and it is not necessary to use a commonly available semiconductor laser for practical use. can be written.

On the other hand, in the case of so-called white-writable optical disk devices, which are capable of recording signals on an optical disk on which no signals have been recorded and reproducing them again, a large laser beam is used for writing. Output is requested. The writing process for this optical disc is a type of laser processing, that is, a process in which the material is evaporated and processed by the heat absorbed by the material, so even in the case of optical discs that are said to be highly sensitive, the beam focused by the optical system is applied to the surface of the optical disc. Approximately 5 when expressed as a light output of
A light output of ~10 [mW'] is required. The laser light output that satisfies this required light output becomes even greater at the semiconductor laser emission end face. This value varies greatly depending on values such as the radiation beam pattern of the laser light emitted from the semiconductor laser or the astigmatism of the beam, but roughly speaking, this value is 20 to 3.0[rrLW].

By the way, in the case of a semiconductor laser, the opening of the resonator from which the laser beam is emitted is as small as the wavelength of the laser beam.
Its size is almost the same as the size of the laser beam (spora) that is focused onto the optical disk to be used. As can be easily understood from this, when using a normal semiconductor laser, the semiconductor laser itself has a large optical output, A situation occurs in which the material is processed one by one. Despite these capabilities, optical disk devices capable of writing using semiconductor lasers that can obtain relatively high output power have come into practical use as document files. Although there are semiconductor lasers that can be put to practical use, they are barely put into practical use, and there are problems such as the inability to write on low-sensitivity optical discs, or in other words, optical discs that are superior in terms of reliability. Even higher output is required when considering applications such as video recording and high-speed optical disc memory.

In order to achieve a reasonably high output of a semiconductor laser, it is necessary to solve the above-mentioned problem that the semiconductor laser itself is laser-processed by its own laser light. This is observed as a phenomenon in which when the optical output of a semiconductor laser is gradually increased, it suddenly breaks down at a certain optical output value and the optical output value decreases. (Catast
ropl+1cQpNcal Damaoe: CO
D, sudden optical damage). By the way, this C
In most cases, the site where OD occurs is the cavity end face of the semiconductor laser.

This is closely related to the mechanism that generates COD; firstly, when looking at the axial direction of the resonator, there are circumstances in which the optical density is maximum at the end facets;
This is because there are many defects on the resonator end face, which makes it easy for photogeneration to occur, and these defects become a trigger to absorb laser light and cause thermal destruction.

A good way to suppress COD at the laser resonator end face is to protect the laser resonator end face with a material that is transparent to laser light. Particularly effective is a method in which the laser resonator end face is made of a semiconductor layer that is transparent to laser light, and this is called a window structure. If the end face is made of a material that is inherently difficult to absorb laser light, even if a defect happens to occur on the end face, absorption of light by the defect is extremely unlikely, and COD will hardly occur.

A typical semiconductor laser incorporating a window structure is shown in FIG. The laser shown in Figure 1 is a type of so-called buried laser, in which a double heterostructure including an active layer is left in the form of a mesa and then buried with a semiconductor layer with a wide bandgap. It has a structure in which not only the side surfaces but also both ends in the axial direction of the laser resonator are buried with a wide bandgap semiconductor layer. In the figure, 11 is an n-GaAs substrate, 12 is an n-GaAJlAs cladding layer, and 13 is a GaA-1! ,
A'S active layer, 14 is a p-GaAJlAs cladding layer,
15 is D-GaAs: ] contact layer, 16 is 1l-
A GaAs substrate buried layer, 17 a resonator end face, and 18 a window region. COD is extremely effective with this laser.
It has been reported that the problem has been resolved and a high output of more than I C) O [mW] can now be achieved. By the way, the semiconductor laser having this structure is manufactured based on liquid phase epitaxial growth technology. In the liquid phase growth method, the crystal growth rate is highly dependent on the plane of the crystal, which is an extremely large plane anisotropy. Therefore, if the (100) plane, which is a slow-growing plane, is used as the main plane of the substrate crystal, the mesa etching process will not be possible. In the second crystal growth process that covers the formation of the second buried layer, crystal growth is selectively performed on the side surfaces of the mena, and the substrate surface has unevenness -C also has a flat crystal growth surface. C takes advantage of the feature that a surface is formed.

By the way, as shown in FIG. 1 (in the case of an end-face buried laser, the optical waveguide does not extend beyond the cavity end face 17. Therefore, the light that has been guided by the mesa stripe-shaped leading wave part is located near the end face. Although it spreads greatly in the buried layer part, it is reflected by the end face 17 and is guided again to the mesa stripe part, but because of this spread, only a small portion of the light is guided. If the coupling efficiency is expressed as how much the amount of light is reduced compared to when it is assumed that the light does not spread due to the diffraction effect in the embedded part, that is, the window region [18], then this coupling efficiency is calculated by the length of the window region 18. It strongly depends on is 1 [μm], x2 [μm]
The calculation results are shown for the case of [m], and it has been confirmed experimentally that it also holds true. As is clear from FIG. 2, it can be said that if the length of the window region 18 is set to 5 [μTrL] or less, the decrease in coupling efficiency will not be much of a problem.

However, it is actually very difficult to make the length of the window region 5 [μrn] or less. Semiconductor lasers are normally manufactured by growing a substrate crystal and cutting it into a predetermined shape using the cleavage properties of the crystal, but the controllability of the process of forming cleavage planes is currently insufficient. For this reason, even if it is possible to control and cut out the length of the above-mentioned window region to 5 [μm] or less, the current situation is that the process has no choice but to have an extremely low yield.

[Object of the present invention] An object of the present invention is to provide a high-output semiconductor laser device having a narrow window region, and another object of the present invention is to provide a semiconductor laser device that can realize the narrow window region with high yield. Another object of the present invention is to provide a method for manufacturing a semiconductor laser device that facilitates manufacturing and reduces O-loss.

[Summary of light intensity] The gist of the present invention is that instead of forming a buried layer on the end face of a laser resonator, a heteroepitaxial crystal layer containing an active layer is bent near the light extraction end face in the direction of the cavity axis (R The objective is to make the cladding layer near the end face have the same effect as the buried layer.

That is, the present invention provides a semiconductor comprising a heteroepitaxial crystal layer including at least an active layer grown on a semiconductor substrate, and a light extraction end face in the laser resonator axis direction formed by cleaving the substrate and the crystal layer. In the laser device, the target crystal layer is bent near the end face, and the cladding layer, contact layer 1, etc. near the end face are used in place of the conventional buried layer.

Further, in the present invention, when manufacturing a semiconductor laser device having the above structure, after forming a cleavage groove on a semiconductor substrate,
A heteroepitaxial crystal layer including at least an active layer is grown on the substrate so that grooves corresponding to the grooves remain, and then the substrate and the crystal layer are separated along the grooves so that the crystal layer is aligned in the axial direction of the laser resonator. This is a method in which a light extraction end face is formed.

[Effect of light amount] In the present invention, crystal growth is performed on a substrate having grooves as a substrate crystal, and in this case, it is appropriate to use a crystal growth method that tends to leave grooves on the surface of the growth layer. .

For example, the MOCVD (organic metal vapor phase epitaxial growth) method and the MBE (molecular beam epitaxial growth) method are good, but the liquid phase growth method, which tends to flatten the surface of the growing crystal, is not necessarily a good method.

While a sliver electrode is built or formed in the direction perpendicular to the direction in which the groove extends in the grown crystal, the crystal is cleaved along the groove to form a laser beam extraction surface. When formed in this manner, the laser resonator axis is formed perpendicular to the groove, and the active layers at both ends of the laser resonator are bent toward the substrate crystal side.

The laser light is guided to the active layer inside the resonator, and is directed against the groove.
The light is amplified and travels in the vertical direction, but since the active layer is bent at the resonator end face, it goes straight, passes through the cladding layer, reaches the crystal end face, is reflected, and returns. Since the cladding layer is transparent to the emission wavelength of the active layer, as a result, the cavity end face of this laser is covered with a transparent crystal, creating a so-called window? 11ji! I'm yelling. Therefore, even if a high current is injected into this laser and the laser is operated at a high optical output, the end face will not be destroyed, and the transverse mode will be well controlled and the laser beam will be 100 [rrLW].
I was able to confirm that a high output of 1q can be produced.

By the way, a major feature of this laser is that the central part of the window region to be cleaved can be clearly recognized as the presence of a cavity when the substrate is in the same state as before cleavage. By using this groove, cleavage can be performed with extremely high positional accuracy. For example, when bending stress is applied to both sides of the groove, the stress concentrates on the groove part. Alternatively, the groove can be recognized as a position mark and the cleavage position can be determined by applying a cleavage blade to the groove position. You may also decide.

As described above, since the position of the window region to be separated can be accurately determined, the length of the window region in the axial direction of the laser resonator can be made extremely small. Therefore, a high output laser can be easily created. That is,
Conventional lasers with this type of window structure have a window region width of 5 μr.
rL] This is an extremely effective effect compared to setting it below. Although it has been possible to obtain a laser of 5 [μTrL] or less in the past, the yield would be extremely poor, and it was not possible to make the width of the window region a desirable chain.

[Embodiment of the Invention] FIG. 3 is a partially cutaway perspective view showing a schematic structure of a semiconductor laser according to an embodiment of the present invention, and FIG. 4(a)
-(d) are perspective views showing the manufacturing process of the above laser. First, as shown in FIG. 4(a), a laser beam is placed on the n-GaAs substrate 21 to a depth of 1 [μm] at a position corresponding to the end face of the laser resonator.
] grooves 22 are formed to match the length intervals of the resonators. In this case, the plane orientation of the substrate was the (001) plane, and the grooves 22 were formed in the so-called normal meridian direction. As shown in FIG. 4(b), a thickness of 0.3 [μrn
II-QaAS ・Barafu' layer '2-4' (S
e To-72X 10”8cm-3) 0.06 [μ#
L] G an, 9 A − (lo, + A S active layer 25, thickness 1 [μm] l + −, G a,), 65
A 11.55A s Clarado layer 2G (l l+doped 2x 10 cm"), thickness 0.8 [μm]
n-GaAs current blocking layer 27 (Se 75x1
0"CM-') was successively grown. MO-CVD method was used for this first crystal growth, and the growth conditions were: substrate temperature 150V, V/'m-20, Kij+ +)
7 Gas (+2) flow rate ~ 10 increments/1n], Hara F
31 is l-limethyl gallium (TMG: (CH)3
Ga), hlymethylaluminum (T~IA: (C
I~13)3 Af) Arsine (Ast 13), p-
Dorvant: Diejiru Wa (DEZ: (C21
-15) 2 Zll > , +1-t < nt: Hydrogen selenide (+2 Se ), the growth rate is 0.25 [μ
m/a+in]. Although it is not necessarily necessary to use the MO-CVD method for the first crystal growth, MO-CVD allows for crystal growth with good uniformity over a large area.
Using the method is more advantageous than the LPE method when considering mass production.

Next, a resist I (not shown) is applied on the current blocking layer 1!27, a striped window with a width of 2 [μm] is formed in the resist, and the current blocking layer 27 is selectively etched using this as a mask. Then, striped grooves 28 were formed as shown in FIG. 4(C). Thereafter, the resist was removed and surface cleaning treatment was performed.

Next, a second crystal growth is performed by the MO-CVD method, and as shown in FIG. 4(d), the entire surface is grown to a thickness of 1.5 [
II m]'s ll-G ao, 6s A fo, 3s
As coating layer 29 (Zl) doped 3X10"Cm"3
) and p-GaAs : ] contact@30 (Zn-doped lXl0"Cm-') were formed in sequence. From this point on, normal electrode attachment was performed by depositing Cr-A on the contact layer 30.
The ulil layer 31 is applied to the bottom surface of the substrate 21.
l! 32 was deposited to obtain the structure shown in FIG. 4(d).

A V-shaped groove is left on the surface of the p-electrode of the wafer thus removed, and the wafer is cleaved at a predetermined position using this V-groove as a mark, and the active layer 25 is bent at the end surface as shown in FIG. It was possible to obtain a semiconductor laser having a desired structure. The obtained laser has a power of 100[1rL] in CW operation.
It was confirmed that there was no edge acid IR up to the optical output of [W], and that the maximum value of the optical output was limited by the optical output saturation phenomenon due to temperature rise. In addition, the optical vibration threshold current is also 50
[The optical oscillation threshold current of a laser with the same structure except that it does not have a normal window structure is around 1 mA and 45 [mA]
The price was only slightly higher than that of the previous year.

As described above, according to this embodiment, it is now possible to fabricate a window structure laser with a short window region length of 5 [μm] or less, which has traditionally been difficult to obtain with good reproducibility, at an extremely high yield. Ta. As a result, it has become possible to obtain high-performance, high-output lasers with a low threshold, no disturbance in transverse mode characteristics, and high output with a good yield. In this G) point, the industrial value of the present invention is extremely high.

Note that the present invention is not limited to the present embodiment described above, and can be implemented with various modifications without departing from the gist thereof. For example, the transverse mode control structure can be applied not only to the present invention, but also to gain guide structures and other fixed guide structures. Furthermore, it is clear that the semiconductor laser can be applied not only to Ga AfAs but also to lasers made of other materials such as AfGa In P and In Ga As P.

[Brief explanation of drawings]

Fig. 1 is a partially cutaway perspective view showing the schematic structure of a conventional window structure semiconductor laser, Fig. 2 is a characteristic diagram for explaining the problems of the above laser, and Fig. 3 is an embodiment of the present invention. FIGS. 4(a) to 4(d) are perspective views showing a schematic structure of the semiconductor laser according to the embodiment, with a portion cut away, and FIGS. 21...n -Qa As substrate, 22... Cleavage groove, 23.n -Ga As buff 77' layer, 24.n
-G ao, 65A-eo, 55AS cladding layer, 2
5-GaO, 9A-Co, IAs active layer, 2
6 ・-1) -G ao, 65 A, 1. (325
As cladding layer, 27-n-GaAs current confinement layer, 28... current confinement groove, 29-p-Ga, 65A-1to, 4 As
Attracted L30・p-Ga As ml unit 1 layer, 3
1.32...electrode. Applicant's agent Patent attorney Takehiko Suzue/TS x LO+rs -su r- representative -I -ノ/++11-

Claims (2)

[Claims] (1) Comprising a teloepitaxy crystal layer including at least an active layer grown on a semiconductor substrate, and a light extraction end face in the laser resonator axis direction formed by cleaving the substrate and crystal layer. A semiconductor laser device characterized in that the crystal layer is bent near the end face. (2) forming a cleavage groove on the semiconductor substrate;
Next, a step of growing a heteroepitaxial crystal layer including at least an active layer on the substrate so that a groove corresponding to the shape of the groove remains, and then cleaving the substrate and crystal layer along the groove to form a laser resonator. 1. A method of manufacturing a semiconductor laser device, comprising the step of forming an axial light extraction end face.