JP3410481B2 - Semiconductor laser device - 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 device.

[0002]

2. Description of the Related Art One of the factors that determines the reliability of a semiconductor laser device is crystal breakdown at the cavity facet of the semiconductor laser device (laser light emitting facet of the chip body).
This crystal destruction occurs by the following mechanism. First,
At the cavity facet of the semiconductor laser device, oxygen in the atmosphere adheres to and bonds with the crystal surface to increase the surface level, and the band gap is narrower than that inside the chip. The laser oscillation wavelength of the semiconductor laser device is substantially determined according to the bandgap of the active layer that constitutes the chip body, but since the bandgap at the end face of the resonator is narrower than the bandgap inside the chip, the oscillated laser Light is absorbed at the end faces of the resonator. Therefore, heat is generated due to absorption of laser light at the cavity end face, and this heat generation further narrows the band gap of the active layer at the cavity end face. As a result, the absorption amount of laser light is further increased, and a positive feedback loop is generated. For this reason, finally, for example, the resonator end face is melted and crystal breakdown occurs. Even if the crystal is not destroyed, the temperature rises due to heat generation, and defects or dislocations in the crystal grow or grow. Such a phenomenon is particularly remarkable when the semiconductor laser is composed of a III-V group semiconductor mixed crystal containing Al. As is known, such crystal breakdown, defects, and dislocations deteriorate the semiconductor laser device and reduce the reliability.

In order to suppress deterioration due to the above mechanism and improve reliability, semiconductor laser devices as shown in FIGS. 6 and 7 have been proposed. In the semiconductor laser device shown in FIG. 6, the thickness of the active layer 605 near the cavity end face is made thinner than the thickness inside the chip, and the cavity end faces 602a, 602 are formed.
This is an attempt to suppress the absorption of laser light in b. 6 (b) and 6 (c) respectively show a BB ′ cross section and a CC ′ cross section in FIG. 6 (a). As shown in FIG. 3A, this semiconductor laser device has a mesa-shaped ridge 601 on a semiconductor substrate 600 in which portions 601a and 601b near the cavity end face have narrow widths and portions 601c inside the chip have wide widths. Is provided. An active layer 605 is grown on this. At this time, the thickness of the active layer 605 depends on the width of the ridge 601, and is thinly grown in the vicinity of the cavity end face where the width of the ridge 601 is narrow, while it is grown thick inside the chip where the width of the ridge 601 is wide. Therefore, during operation, more carriers are accumulated in the portion 605a of the active layer 605 near the resonator end face than in the portion 605c inside the chip, and the portion 605a near the resonator end face due to the effect of band filling.
Has a relatively high Fermi level. This makes it possible to reduce the amount of laser light absorbed in the cavity end face 602a and suppress the occurrence of crystal defects.
However, this semiconductor laser device has an active layer 605.
During growth, it is difficult to control the thickness of each part 605a, 605b, 605c with high precision. In addition, the width of the ridge 601 affects not only the thickness of the active layer 605 but also the thickness of other layers, so that the oscillation characteristic, for example, the far-field pattern becomes unstable. On the other hand, in the semiconductor laser device shown in FIG. 7, a portion of the active layer 705 near the cavity end face is removed by mesa etching, and a guide layer 720 is embedded around the active layer 705 (around the mesa). Note that FIG. 7 (b) shows the broken line portion in FIG. 7 (a) shifted to the right, and FIG. 7 (c) shows the CC ′ line cross section in FIG. 7 (a). This semiconductor laser device
Since the portion of the active layer 705 near the cavity end face is removed, the absorption of the laser light in the cavity end faces 702a and 702b can be eliminated. However, this semiconductor laser device is difficult to manufacture because the precision of mesa etching is poor and the embedded guide layer 720 has poor crystallinity, and furthermore, the end face (mesa slope) 711 of the active layer 705 and the guide layer 711. There is a problem that the interface with 720 deteriorates. Thus, each of the above semiconductor laser devices has a manufacturing surface,
None of them were satisfactory in terms of reliability.

On the other hand, recently, as shown in FIG.
A semiconductor laser device has been proposed in which window layers 803a and 803b are provided on the cavity end faces 802a and 802b (Matsumoto et al., 1990.
Proceedings of the 51st Annual Meeting of the Applied Physics Conference, Fall: 28p
-R-5-6). In this semiconductor laser device, each layer constituting the chip body 800 is made of a GaAlAs-based mixed crystal, and window layers 803a, 8 made of a semiconductor material having a bandgap larger than that of the active layer 805 are formed on the cavity end faces 802a, 802b.
03b is provided. Specifically, the laser oscillation wavelength is 7
In the case of 80 nm, Al of the active layer 805 corresponding to this wavelength
Since the mixed crystal ratio x is 0.14, the material for the window layers 803a and 803b is Ga _1-x Al _x As having an Al mixed crystal ratio x of 0.14 or more.
To use. As a result, the window layer 803 rather than the active layer 805
The band gaps of a and 803b are increased to reduce the absorption amount of laser light at the resonator end faces 802a and 802b and prevent deterioration of the device. In fact, the absorption amount of laser light can be significantly reduced as compared with the case where the window layer is not provided. Moreover, this semiconductor laser device is different from the semiconductor laser devices shown in FIGS. 6 and 7 in that there is no difficulty in manufacturing and the characteristics with good reproducibility can be obtained.

[0005]

By the way, in the semiconductor laser device shown in FIG. 8, the Al mixed crystal ratio x of the window layers 803a and 803b is set sufficiently larger than the Al mixed crystal ratio of the active layer 805. This is because the light absorption edge of Ga _1-x Al _x As is very broad, and the band gap difference must be increased in order to effectively reduce the amount of laser light absorption. However, when it contains a large amount of Al, the window layer 80
3a, 803b outside the stability of the surface state is impaired, Al
Is combined with oxygen in the atmosphere to form many surface states.
As a result, the outer portions of the window layers 803a and 803b still serve as heat sources. Further, the instability of the surface state causes the generation of crystal defects. Therefore, when energized for a long time,
There is a problem that the crystal defects multiply and grow to impair the reliability.

Therefore, an object of the present invention is to reduce the generation of crystal defects by reducing the surface level of the outer portion of the window layer in a semiconductor laser device having a window layer provided on the cavity end face. An object of the present invention is to provide a semiconductor laser device that can improve reliability.

[0007]

To achieve the above object, the present invention has a chip body including an active layer and a band gap larger than that of the chip body, and covers a laser light emitting end face of the chip body. In the semiconductor laser device comprising a window layer, the active layer and the window layer are made of a III-V group compound semiconductor containing Al, outside the window layer, III-V
Made of Group III compound semiconductors, having a smaller bandgap than the active layer and suppressing heat generation due to absorption
Is characterized in that a sufficiently thin surface protective layer is provided.
In the semiconductor laser element of one embodiment, wherein the thickness of the surface protective layer is not more than 3 n m. In the semiconductor laser device of one embodiment, the Al of the surface protection layer is
The mixed crystal ratio is zero. Furthermore, in the semiconductor laser device of one embodiment, the surface protective layer is made of GaA.
It is characterized by comprising s.

[0008]

According to the present invention, Al is provided outside the window layer rather than the active layer.
Since the surface protective layer having a small mixed crystal ratio is provided, the window layer is not exposed to the atmosphere, and the surface level is reduced. Therefore, the surface condition is improved and the reliability is improved in the long term. Since the bandgap of the surface protective layer is smaller than the bandgap of the active layer, the surface protective layer absorbs more oscillation laser light than the window layer. However, by forming the surface protective layer to be sufficiently thin, heat generation due to absorption can be easily suppressed to a level that does not cause a problem. Further, since the surface protective layer is made of a III-V group compound semiconductor containing only the same element as the window layer, it can be continuously formed by the same growth method as that for forming the window layer. In the semiconductor laser device of one embodiment, since the Al mixed crystal ratio of the surface protective layer is 0, the surface state of the window layer is further stabilized. Further, since it is not necessary to supply the Al element, it is not necessary to control the Al mixed crystal ratio, which facilitates the growth. In particular, when the surface protective layer is made of GaAs, a semiconductor laser device that can withstand practical use can be obtained (details will be described later).

[0009]

The semiconductor laser device of the present invention will be described in detail below with reference to the embodiments shown in the drawings.

As shown in FIG. 1, this semiconductor laser device comprises a chip body 1 having a VSIS (V-channeled substrate inner stripe) structure, and cavity end faces 2a of the chip body 1 facing each other. The window layers 3a, 3b covering 2b and the surface protective layers 4a, 4b provided outside the window layers 3a, 3b. The chip body 1 has a p-type GaAs substrate 201 and a stripe-shaped groove 203.
Type GaAs current confinement layer 202, p type Ga _0.55 Al _0.45 As clad layer 204, p type Ga _0.86 Al _0.14 As active layer 205
And n-type Ga _0.55 Al _0.45 As clad layer 206 and n-type Ga
It has an As contact layer 207. The active layer 20
The Al mixed crystal ratio of 0.14 of 5 corresponds to the oscillation wavelength of 780 nm.
The window layers 3a and 3b are made of Ga _1-x Al _x As (x> 0.14),
It has a band gap larger than that of the active layer 205. On the other hand, the surface protective layers 4a and 4b are formed of Ga _1-y Al _y As (y <
0.14), which is smaller than the active layer 205.
It has a mixed crystal ratio. The surface protection layers 4a and 4b are provided on the end surface 2a of the chip body 1 at a location 22 for emitting laser light.
It is provided separately on both sides of 0.

This semiconductor laser device is manufactured as follows. First, as shown in FIG. 3 (a), an LPE (Liquid Phase Epitaxial Growth) method was used to form a p-type GaAs substrate 201.
The n-type GaAs current confinement layer 202 is grown to a thickness of 0.8 μm. The width of the current confinement layer 202 reaching the substrate 201 is 3 μm.
A stripe-shaped groove 203 having m and a depth of 1.0 μm is formed by chemical etching. After that, the second LPE growth is performed, and the p-type Ga _0.55 Al _0.14 As clad layer 204 is flattened.
0.2 μm (the part where the groove 203 does not exist), p-type Ga _0.86 A
_0.14 As active layer 205 to 0.06 μm, n-type Ga _0.55 Al
_{A 0.45} As cladding layer 206 and an n-type GaAs contact layer 207 are continuously grown to a thickness of 1 μm and 2 μm, respectively. The wafer on which the growth is completed is cleaved or etched to be processed into a bar (strip) shape 200 as shown in the lower side of FIG. 3A (the upper side of FIG. 3A shows one chip). .). Next, as shown in FIG. 2B, Ga having a larger Al mixed crystal ratio than the active layer 204 is formed on the end surfaces 2a, 2b and the upper surface 2c of the bar 200 by MOCVD (metal organic chemical vapor deposition). _1-x Al _x As window layer 210 to 0.1 μm, window layer 21
Ga _1-y Al _y As surface protective layer 211 having a lower Al mixed crystal ratio than 0
The laminated grown to a thickness of 3 n m. For example, the mixed crystal ratio of the window layer 210 is set to x = 0.6 so that the active layer 205 has a sufficiently large bandgap so that the light absorption amount is reduced. On the other hand, the mixed crystal ratio of the surface protective layer 211 is y =
It is set to 0, that is, Al is not contained in the crystal as GaAs to stabilize the surface state and reduce the surface level. Next, as shown in FIG. 2C, etching is performed to remove portions of the window layer 210 and the surface protective layer 211 on the upper surface of the bar 200. Thereby, the end faces 2a, 2b
Window layers 3a and 3b that cover the window layers 3a and 3b and surface protection layers 4a and 4b that cover the outside of the window layers 3a and 3b. Finally, electrodes 212 and 213 are formed on the top and bottom of the chip body 1.

This semiconductor laser device includes window layers 3a and 3b.
Since the surface protective layers 4a, 4b having a smaller Al mixed crystal ratio than the active layer 205 are provided on the outside of the window, the window layers 3a, 3b are prevented from being exposed to the atmosphere to reduce the surface level. ing. Therefore, the surface condition of the window layers 3a and 3b can be improved,
Reliability can be improved in the long term. Further, the surface protective layer functions as an absorption layer for the oscillated laser light, but by forming the surface protective layer to be sufficiently thin, heat generation due to absorption can be easily suppressed to a level that does not cause a problem. Actually, as shown in FIG. 2, it was possible to improve the light output characteristics and to endure long-term energization at 150 mW for 5000 hours or more.

The chip body may have a structure in which the current confinement layer 416 is sandwiched between the cladding layers 415a and 415b as shown in FIG. In this case, first, the clad layer 413, the active layer 414, and the clad layer 415a are sequentially laminated by the LPE method. Next, after growing the current confinement layer 416, a stripe-shaped groove 417 is formed. Next, a clad layer 415b having the same composition as the clad layer 415a is grown by the LPE method.

Further, the chip body may have a structure having a mesa portion 516 as shown in FIG. In this case, first, the clad layer 513, the active layer 514, and the clad layer 515 are sequentially laminated by the LPE method using an InGaAlP-based material. Next, the clad layer 515 is etched on both sides while leaving the central portion in a stripe shape, and a mesa portion 516 is formed. Then, the current confinement layer 517 is grown by the LPE method. At this time, crystals do not grow on the upper surface of the mesa portion 516, and a stripe-shaped current path can be formed along the mesa portion 516. The composition of the window layers 503a and 5603b is, for example, (Al _0.65 Ga _0.35 ) _0.5 In _0.5 P, and the composition of the surface protective layers 504a and 504b is Ga _0.5 In _0.5 P to Ga.
Let As.

[0015]

As is apparent from the above, in the semiconductor laser device of the present invention, the stable surface protective layer having a smaller Al mixed crystal ratio than the active layer is provided on the outside of the window layer. It can be prevented from being exposed to the inside and the surface level can be suppressed, and the reliability can be improved in the long term. Further, the surface protection layer contains III-V containing only the same element as the window layer.
Since it is made of a group compound semiconductor, it can be continuously formed by the same growth method as that for forming the window layer. In the semiconductor laser device of one embodiment, since the Al mixed crystal ratio of the surface protective layer is 0, the surface state of the window layer can be further stabilized. Further, since it is not necessary to supply the Al element, it is not necessary to control the Al mixed crystal ratio, which facilitates the growth. In particular, when the surface protective layer is made of GaAs, a semiconductor laser device that can be used practically can be obtained.

[Brief description of drawings]

FIG. 1 is a perspective view showing the structure of a semiconductor laser device according to an embodiment of the present invention.

FIG. 2 is a diagram showing current-light output characteristics of the semiconductor laser device.

FIG. 3 is a diagram showing a manufacturing process of the semiconductor laser device.

FIG. 4 is a perspective view showing the structure of a semiconductor laser device according to another embodiment of the present invention.

FIG. 5 is a perspective view showing the structure of a semiconductor laser device according to another embodiment of the present invention.

FIG. 6 is a perspective view showing the structure of a conventional semiconductor laser device.

FIG. 7 is a perspective view showing a structure of a conventional semiconductor laser device.

FIG. 8 is a perspective view showing a structure of a conventional semiconductor laser device.

[Explanation of symbols]

1,400,500 Chip body 2a, 2b, 402a, 402b, 502a, 502b End face 3a, 3b, 403a, 403b, 503a, 503b Window layer 4a, 4b, 404a, 404b, 504a, 504b Surface protective layer 201 p-type GaAs Substrate 202 n-type GaAs current confinement layer 203 stripe-shaped groove 204 p-type Ga _0.55 Al _0.45 As clad layer 205 p-type Ga _0.86 Al _0.14 As active layer 206 n-type Ga _0.55 Al _0.45 As clad layer 207 n-type GaAs contact layer 220 , 420, 520 Laser light emitting point

   ─────────────────────────────────────────────────── ─── Continued front page       (56) References JP-A-1-227485 (JP, A)                 JP 63-227090 (JP, A)

Claims (4)

(57) [Claims] 1. A chip body including an active layer, and a window layer having a bandgap larger than that of the chip body and covering a laser light emitting end face of the chip body, wherein the active layer and the window layer contain Al. In a semiconductor laser device made of a III-V compound semiconductor containing, outside the window layer, made of a III-V compound semiconductor, having a smaller bandgap than the active layer, and absorption.
A semiconductor laser device having a surface protective layer thin enough to suppress heat generation . 2. A semiconductor laser device according to claim 1, the semiconductor laser element, wherein a thickness of the surface protective layer is not more than 3 n m. 3. The semiconductor laser device according to claim 2, wherein the surface protective layer has an Al mixed crystal ratio of 0. 4. The semiconductor laser device according to claim 3, wherein the surface protection layer is made of GaAs.