JP2806533B2 - Semiconductor laser device - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a semiconductor laser device having a diffraction grating,
In particular, a distributed feedback (DFB) type semiconductor laser device capable of lasing at a short wavelength of 660 to 890 nm in a single longitudinal mode, or a distributed Bragg reflection (Distributed Br)
agg reflector) type semiconductor laser device.

(Prior art) When a semiconductor laser is used as a light source of an optical information transmission system or an optical measurement system using an optical fiber,
It is desirable that the semiconductor laser has an operating characteristic of oscillating in a single longitudinal mode because noise due to reflected light from the optical fiber can be reduced when coupling with the optical fiber. In a semiconductor laser, a single longitudinal mode oscillation can be obtained if the reflection mirror of the resonator is constituted by a diffraction grating having the same principle as that of the spectroscope. As such semiconductor lasers, there are known a distributed feedback (DFB) type semiconductor laser in which an active region or a periodic uneven diffraction grating is formed near the active region, and a distributed black reflection (DBR) type semiconductor laser. ing.

In particular, DFB type semiconductor lasers that oscillate laser light with a short wavelength of 660 to 890 nm have been used in MBEs, mainly for AlGaAs-based materials.
It is manufactured by the method (molecular beam epitaxy), MOCVD (metal organic chemical vapor deposition), LPE (liquid phase epitaxy), or a combination of LPE and MDCVD.

FIG. 4 shows an example of a DFB semiconductor laser device that oscillates short-wavelength laser light of 780 mm or less using an AlGaAs / GaAs material. The DFB type semiconductor laser has an n-type GaAs substrate on a p-type GaAs substrate 41.
After stacking the s current blocking phase 42, a V-groove is formed so that its bottom reaches the p-type GaAs substrate 41 for transverse mode control and current confinement. Next, a p-type AlGaAs cladding layer 43 is grown in the V-groove and on the n-type GaAs cladding layer 42 so that the surface becomes flat, and then a p-type AlGaAs active layer 44 is formed on the p-type AlGaAs cladding layer 43. , n-type AlGaAs carrier barrier layer 45,
And an n-type AlGaAs optical guide layer 46 are sequentially laminated, and the n-type AlGaAs
An uneven diffraction grating is formed on the surface of the GaAs light guide layer 46 by a two-beam interference exposure method or the like. Then, an n-type AlGaAs cladding layer 47 and an n-type GaAs cap layer 48 are sequentially laminated on the diffraction grating of the n-type AlGaAs optical guide layer 46. After that, n-type GaAs
By arranging the n-side automic electrode 51 on the cap layer 48 and arranging the p-side ohmic electrode 52 on the p-type GaAs substrate 41, a DFB semiconductor laser device can be obtained.

In the DFB semiconductor laser device having such a structure, a diffraction grating is formed on the AlGaAs light guide layer 46, and the Al grating is formed on the diffraction grating.
A GaAs cladding layer 47 is laminated. However, a crystal containing Al as a component, such as the AlGaAs light guide layer 46, has the property of being easily oxidized in air and instantaneously forming an oxide film. Therefore, when a diffraction grating is formed on the AlGaAs light guide layer 46, an oxide film is formed on the diffraction grating, and it is not easy to grow the AlGaAs cladding layer 47 on the AlGaAs light guide layer 46. Therefore, a semiconductor laser device with a diffraction grating using an AlGaAs / GaAs material and having an oscillation wavelength of 780 mm or less is required.
Not easy to manufacture.

InGaAsP is used instead of AlGaAs crystal as the diffraction grating formation layer.
DFB semiconductor laser devices using crystals have also been developed. The DFB semiconductor laser device is, as shown in FIG.
Instead of the n-type AlGaAs carrier barrier layer 45 and the n-type AlGaAs optical guide layer 46 of the DFB semiconductor laser shown in FIG.
nGaAsP diffraction grating forming layer 53 and n-type AlGaAs cladding layer 54
Are sequentially laminated between the p-type AlGaAs active layer 44 and the n-type AlGaAs cladding layer 47. An uneven diffraction grating is formed on the surface of the InGaAsP diffraction grating forming layer 53. Other configurations are the same as those of the DFB semiconductor laser device shown in FIG. 4, and therefore, the same components are denoted by the same reference numerals as in FIG. 4 and description thereof is omitted.

In the DFB semiconductor laser device having such a configuration, since the diffraction grating is formed on the InGaAsP diffraction grating forming layer 53, the n-type AlG
The aAs cladding layer 54 can be easily grown on the InGaAsP diffraction grating forming layer 53.

(Problems to be Solved by the Invention) In a DFB semiconductor laser device having such an InGaAsP diffraction grating forming layer 53, the InGaAsP diffraction grating-formed InGaAsP
When an n-type AlGaAs cladding layer 54 is laminated on the diffraction grating forming layer 53, the InGaAsP diffraction grating forming layer 5 is melt-backed.
The diffraction grating 3 may be eroded. For example, the InG
If the diffraction grating formed on the aP diffraction grating formation layer 53 has a rectangular waveform, the corners of the rectangular waveform are eroded by meltback and rounded, and when the waveform is eroded by the melt back, a triangular waveform is formed. It becomes a shape. For this reason, in the obtained DFB semiconductor laser, it is difficult to obtain single longitudinal mode oscillation, and the coupling efficiency with the optical fiber is significantly reduced.

In the DFB semiconductor laser, the InGaAsP diffraction grating forming layer 53 is used.
When a diffraction grating having a pitch of 2500 mm and a height of 800 mm is actually formed and an AlGaAs cladding layer 54 is grown on the InGaAsP diffraction grating forming layer 53, the height of the diffraction grating is reduced to about 600 mm. It has been found that the volume of the lattice is also reduced by 30 to 40% as compared to before the AlGaAs cladding layer 54 is laminated.

The present invention has been made to solve the above-mentioned conventional problems, and an object of the present invention is to excel in the preservation of the shape of a diffraction grating when laminating semiconductors. An object of the present invention is to provide a semiconductor laser device having excellent coupling efficiency with an optical system.

(Means for Solving the Problems) A semiconductor laser device according to the present invention has a diffraction grating forming layer formed of a semiconductor compound which does not contain Al as a composition and is laminated with an active layer in which a laser is oscillated. A channel forming layer formed on the diffraction grating forming layer so as to form a stripe region corresponding to an active region of the active layer, the channel forming layer including a semiconductor compound containing Al as a composition; It comprises a diffraction grating provided in a stripe region on the diffraction grating forming layer, and a semiconductor compound layer laminated on the diffraction grating, thereby achieving the above object.

(Example) Hereinafter, the present invention will be described with reference to examples.

As shown in FIG. 1, the semiconductor laser device of the present invention
On an n-type GaAs substrate 11, an n-type AlGaAs current blocking layer 12 is laminated. At the center of the n-type GaAs current blocking layer 12, a V-shaped groove for lateral mode control and current confinement is provided in a stripe shape, and the bottom of the V-shaped groove reaches the p-type GaAs substrate 11. In the V-groove and on the n-type GaAs current blocking layer 12, p
AlGaAs cladding layer 13 is laminated, and the p-type AlGaAs
The upper surface of the cladding layer 13 is flat. The p-type AlGaAs
On the cladding layer 13, a p-type AlGaAs active layer 14, undoped In
_1-x Ga _x As _y P _1-y diffraction grating forming layers 15 are sequentially laminated. In the In _1-x G a _x As _y P _1-y diffraction grating forming layer 15, a diffraction grating 15 a in which irregularities are periodically formed is formed in a central stripe region above the V groove. The diffraction grating 1
The width of 5a is wider than the opening width of the V-groove formed in the n-type GaAs current blocking layer 12.

On each side of the In _1-x Ga _x As _y P _1-y diffraction grating forming layer 15 except for the central portion where the diffraction grating 15a is formed, an n-type Al _z Ga _1-z As
A channel forming layer 16 is laminated, and the n-type Al _z Ga _1-z As
The channel formation layer 16 is also provided with a diffraction grating 16a in which irregularities are periodically formed. On the diffraction grating 16a on the n-type Al _z Ga _1-z As channel forming layer 16 and on the diffraction grating 15a of the In _1-x Ga _x As _y P _1-y diffraction grating forming layer 15, n-type Al _w Ga _{The 1-w} As clad layer 17 is laminated. The n-type Al _w Ga _1-w As cladding layer
The upper surface of 17 is flat, and an n-type GaAs cap layer 18 is laminated on the n-type Al _w Ga _1-w As clad layer 17.

An n-side ohmic metal electrode 21 is provided on the n-type GaAs cap layer 18, and a p-side ohmic metal electrode 22 is provided on the p-type GaAs substrate 11.

The semiconductor laser device of the present invention having such a configuration is manufactured as follows.

After laminating an n-type GaAs current blocking layer 12 on a p-type GaAs substrate 11, the n-type GaAs current blocking layer 12 is used for lateral mode control and current confinement.
A V-groove is formed in the center of the
A stripe is formed so as to reach the As substrate 11.

Next, the p-type is formed in the V-groove and on the n-type GaAs current blocking layer 12.
A type AlGaAs cladding layer 13 is grown. The upper surface of the p-type AlGaAs cladding layer 13 is made flat. Then, on the p-type AlGaAs cladding layer 13, a p-type AlGaAs active layer 14, a non _- doped In _1-x Ga
sequentially stacked _x As _y P _1-y diffraction grating layer 15, n-type Al _z Ga _1-z As channel forming layer 16.

Thereafter, the region above the V-groove of the GaAs current blocking layer 12 in the n-type Al _z Ga _{1 -z} As channel forming layer 16, that is, the p-type AlGa
A photoresist film is applied to form a stripe pattern in a region above the active region of the As active layer 14 so that a stripe having a width wider than the opening width of the V groove is formed. Then, the photoresist film as a mask, by chemical etching, the central portion of the n-type Al _z Ga _1-z As channel forming layer 16, the undoped _{In 1-x Ga x As y} P 1-y diffraction grating layer 15 Remove to form a channel.

Then, n-type Al _z Ga _1-z As after removing the photoresist film on the channel forming layer 16, the n-type Al _z Ga _1-z As channel forming layer 16 top surface and exposed undoped In _1-x Ga _x As _y P _1-y
A photoresist film is applied on the upper surface of the diffraction grating forming layer 15, and a two-beam interference exposure using an ultraviolet laser is performed, and a period of 2000 to 30 is applied.
A photoresist diffraction grating is formed at 00 °, and periodic etching is performed on the n-type Al _z Ga _1-z As channel formation layer 16 and the non _- doped In _1-x Ga _x As _y P _1-x diffraction grating formation layer 15 by chemical etching. The diffraction gratings 16a and 15a are respectively formed by forming irregularities on the substrate. Then, after removing the photoresist film, an n-type Al _w Ga _1-w As clad layer 17 is grown on each of the diffraction gratings 15a and 16a to flatten its upper surface, and the n-type Al _w Ga _1-w As An n-type GaAs cap layer 18 is laminated on the cladding layer 17. And
An n-side ohmic metal electrode is formed on the n-type GaAs cap layer 18.
By arranging the p-side ohmic metal electrode 22 on the p-type GaAs substrate 11, the DFB semiconductor laser device shown in FIG. 1 is obtained.

The DFB type semiconductor laser device has a quaternary layer of In _1-x Ga _x A
The mixed crystal ratio of the s _y P _1-x diffraction grating forming layer 15 is 0.68 ≦ x ≦ 1,0.34
It is set so as to satisfy ≦ y ≦ 1, y = 2.04x−1.04.
Further, the mixed crystal ratio of the _{In 1-x Ga x As y} P 1-y n -type are stacked on each side of the diffraction grating layer 15 Al _z Ga _1-z As channel forming layer 16, 0 It is set in the range of ≦ z ≦ 0.5. Thus, In
_1-x Ga _x As _y P _1-y diffraction grating forming layer 15 and n-type Al _z Ga _1-z As
If the mixed crystal ratio of the channel forming layer 16 is set, the In _1-x Ga _x As
by laminating the n-type Al _z Ga _1-z As channel forming layer 16 on the _y P _1-y diffraction grating layer 15, the n-type Al _z Ga _1-z As channel forming layer 16
The striped channel in the central portion of the _{In 1-x Ga x As y} P
When formed to reach the _1-y diffraction grating forming layer 15, the Al _z
Since the upper surface of the Ga _1-z As channel forming layer 16 contains Al, an oxide film is formed on the surface. Therefore, the n-type Al _w G is formed in the channel and on the Al _z Ga _{1 -z} As channel forming layer 16.
When the a _1-w As clad layer 17 is grown by liquid phase epitaxy, the crystal grown on the Al _z Ga _1-z As channel forming layer 16 is grown at the start of growth due to the influence of the surface oxide film. Speed slows down. As a result, a solution of growth is the crystal on the _{In 1-x Ga x As y} P 1-y diffraction grating layer 15 in the channel in the liquid phase epitaxy method, tends supersaturated, the growth rate of the crystal is _{faster, in 1-x Ga x as} y P 1-y diffraction grating layer 15 uneven diffraction grating formed in is not eroded by the melt-back, the shape is reliably maintained.

N-type Al _w Ga _1-w laminated on each of the diffraction gratings 15a and 16a
The mixed crystal ratio of the As clad layer 17 depends on the Al _w Ga _1-w As clad layer 17.
There is set to be higher refractive index than the _{In 1-x Ga x As y} P 1-y diffraction grating layer 15. Therefore, the mixed crystal ratio may be the same as that of the n-type Al _z Ga _{1 -z} As channel forming layer 16 on which the diffraction grating 16a is formed.

In the above embodiment, the n-type Al _z Ga _1-z As channel forming layer
A diffraction grating is formed on both the upper surface of the In _1-x Ga _x As _y P _1-y diffraction grating forming layer 15 and the outer surface of the n-type Al _z Ga _1-z As channel forming layer 16 in the 16 channels. it is configured to form, in a configuration in which only a diffraction grating is formed on the _{in 1-x Ga x as y} P 1-y diffraction grating layer 15 in the channel corresponding to the active region of the p-type AlGaAs active layer 14 Is also good.

In addition, as the diffraction grating forming layer 15, the diffraction grating forming layer
It is only necessary that the solution of the crystal stacked in the channel formed on the substrate 15 be in a supersaturated state during growth.
As may be used.

A diffraction grating 15a in the form of a rectangular wave with a pitch of 2500 mm and a height of 800 mm
Was formed to manufacture the semiconductor laser device of this embodiment, the diffraction grating 15a was not melted back,
Its height was also kept at 800 cm.

FIG. 2 shows another embodiment of the semiconductor laser device of the present invention. In this embodiment, between the p-type AlGaAs active layer 14 and the _{In 1-x Ga x As y} P 1-y diffraction grating layer 15 of the DFB semiconductor laser device shown in FIG. 1, n-type AlGaAs carrier barrier Layer 31 is interposed. Other configurations are the same as those of the semiconductor laser device shown in FIG. 1, and the same components are denoted by the same reference numerals and description thereof will be omitted.

In this embodiment, the carrier barrier layer 31 is a p-type AlGaAs active layer.
A1 of the p-type AlGaAs active layer 14
The mixed crystal ratio can be increased, and laser oscillation in a shorter wavelength band becomes possible. Also, in this case, the coupling efficiency of the diffraction grating can be improved because the InGaAsP diffraction grating forming layer 15 becomes the light guide layer.

In this embodiment, the n-type Al _w Ga _1-w
It is preferable that the As cladding layer 17 be set to have a lower refractive index than the InGaAsP diffraction grating forming layer 15.

FIG. 3 shows still another embodiment of the semiconductor laser device of the present invention. In this embodiment, the n-type AlGaAs cladding layer 17 is grown only in the channel on the InGaAsP diffraction grating forming layer 15, and the n-type AlGaAs channel forming layer outside the channel is grown.
The n-type AlGaAs cladding layer 17 is not laminated on 16.
Then, an n-type AlGaAs cladding layer 17 is laminated in the channel so as to extend from the channel, and an n-side ohmic metal electrode 21 is disposed on the n-type AlGaAs cladding layer 17. Other configurations are the same as those of the semiconductor laser device shown in FIG. 1, and the same components are denoted by the same reference numerals and description thereof will be omitted.

Also in this embodiment, the diffraction element 15a formed on the InGaAsP diffraction grating forming layer 15 is an n-type AlGa layer stacked on the diffraction grating 15a.
The predetermined shape is maintained without being melted back by the As cladding layer 17. In addition, since current is injected only into the n-type AlGaAs cladding layer 17, lateral current confinement in the p-type AlGaAs active layer 14 is good.

(Effect of the Invention) In the semiconductor laser device of the present invention, since the semiconductor compound is grown on the diffraction grating at a high speed in a solution in a supersaturated state, there is no possibility that the diffraction grating is eroded by meltback. A single longitudinal mode is reliably obtained, and the coupling efficiency with an optical system such as an optical fiber is excellent.

[Brief description of the drawings]

1 to 3 are perspective views each showing an example of a semiconductor laser device of the present invention, and FIGS. 4 and 5 are perspective views each showing an example of a conventional semiconductor laser device. 11 ... p-type GaAs substrate, 12 ... n-type GaAs current blocking layer, 13 ...
p-type AlGaAs cladding layer, 14 ... p-type AlGaAs active layer, 15 ...
In _1-x Ga _x As _y P _1-y diffraction grating forming layer, 16 ... _Alz Ga _1-z As channel forming layer, 17 ... Al _w Ga _1-w As cladding layer, 18 ... n-type Ga
As cap layer, 31 ... n-type AlGaAs carrier barrier layer.

──────────────────────────────────────────────────続 き Continuation of front page (72) Inventor Satoshi Sugawara 22-22 Nagaikecho, Abeno-ku, Osaka-shi, Osaka Inside Sharp Corporation (56) References JP-A-63-136586 (JP, A) (58) Investigated Field (Int.Cl. ⁶ , DB name) H01S 3/18

Claims (1)

(57) [Claims] 1. A diffraction grating forming layer formed of a semiconductor compound containing no Al as a composition and having an active layer in which a laser is oscillated, and the active layer is formed on the diffraction grating forming layer. Are stacked so that a stripe region corresponding to the active region of the layer is formed.
a semiconductor comprising: a channel forming layer formed of a semiconductor compound containing l as a composition; a diffraction grating provided in a stripe region on the diffraction grating forming layer; and a semiconductor compound layer stacked on the diffraction grating. Laser element.