JPH0446477B2 - - Google Patents

Description

[Detailed Description of the Invention] <Technical Field> The present invention relates to a distributed feedback type or distributed black reflection type semiconductor laser device with an oscillation wavelength of 660 to 890 nm, which oscillates in a single longitudinal mode and has a diffraction grating formed thereon. .

<Prior art and its problems> When a semiconductor laser device is used as a light source in an optical information system or an optical measurement system using an optical fiber, the semiconductor laser device may have an operating characteristic of oscillating in a single longitudinal mode. desirable. The laser element structure for obtaining single longitudinal mode laser oscillation characteristics is a distributed feedback type or distributed Bragg reflection type laser element in which a periodic uneven diffraction grating is formed in or near the active region. known (Nikkei Electronics 1981, 12, 21, p66-p70).

Conventionally, InGaPAs/InP constructed on an InP substrate
Semiconductor lasers with diffraction gratings with oscillation wavelengths of 1.3 μm to 1.55 μm have been developed using system materials. On the other hand, the wavelength
In semiconductor lasers that have a GaAlAs active layer formed on a GaAs substrate that can emit oscillation light of 890 nm or less, an oxide film is instantaneously formed on the GaAlAs light guide layer that forms the diffraction grating, so regeneration on top of it is difficult. There is a production drawback that it is difficult to grow,
It has not yet been put into practical use. Regarding this point, InGaPA, which is difficult to oxidize, is used as a material for the light guide layer.
A semiconductor laser device that effectively solves the problem by using the above method is disclosed in Japanese Patent Application No. 59-223576 by the present applicant. FIG. 5 shows the structure of this distributed feedback semiconductor laser. n-type on n-type GaAs substrate 1
A GaAlAs cladding layer 2, a non-doped GaAs active layer 3, a p-type InGaPAs optical guide layer 4, a p-type GaAlAs cladding layer 5, and a p-type GaAs cap layer 6 are laminated in this order.
P-side ohmic electrodes 7 and 8 are formed.
A diffraction grating for laser oscillation is formed on the light guide layer 4. With this structure, there is no problem of oxidation of the light guide layer 4, and there is no problem with the second growth on the light guide layer 4. However, some of the electrons injected into the active layer 3 flow into the optical guide layer 4,
Since it becomes a reactive current, it causes an increase in the oscillation threshold and becomes a factor, especially in deterioration of temperature characteristics.

<Summary of the Invention> The present invention provides an active layer for laser oscillation consisting of Ga _1-x Al _x As (0≦x≦0.4) and an active layer for laser oscillation consisting of Ga _1-y Ga _y P _1-z As _z (0.51).
≦y≦1, z≒2.04y−1.04), and a light guide layer is provided between the diffraction grating surface of the diffraction grating forming layer and the active layer. In the semiconductor laser device, the bandgap width is larger than that of the active layer and the optical guide layer.
A barrier layer consisting of Ga _1-x Al _x As (0.2≦x≦1),
A novel distributed feedback type or distributed bragg reflection type semiconductor laser device that is inserted between the active layer and the optical guide layer to reduce reactive current flowing into the optical guide layer and establish good device characteristics. The purpose is to provide

<Example 1> An example of the present invention will be described with reference to FIG. On an n-type GaAs substrate 1, an n-type GaAlAs cladding layer 2, a non-doped GaAs active layer 3, a p-type
GaAlAs barrier layer 9, p-type InGaPAs light guide layer 4
are grown continuously using liquid phase epitaxial growth. Next, a photoresist film is applied on the light guide layer 4, and a photoresist diffraction grating with a period of 2500 Å is formed by interference exposure using an ultraviolet laser. Using this as a mask, a groove is carved on the light guide layer 4 by chemical etching, and the photoresist film is removed. As a result of the above, a periodic pattern is formed on the light guide layer 4.
A 2500 Å uneven diffraction grating is formed. A p-type GaAlAs cladding layer 5 and a p-type GaAs cap layer 6 are sequentially grown on the optical guide layer 4 having a diffraction grating on its surface by the same liquid phase epitaxial growth method, and then the p-type GaAlAs clad layer 5 and the p-type GaAs cap layer 6 are grown on the substrate 1 and the cap layer 6. each on top
N-side and p-side ohmic electrodes 7 and 8 made of Au/Ge/Ni and Au/Zn are formed to form a double heterojunction laser oscillation multilayer crystal structure. The thickness of the active layer 3 is 0.1 μm, and the thickness of the barrier layer 9 is
The thickness of the optical guide layer 4 is approximately 0.3 μm.

In the above embodiment, since the active layer 3 is made of GaAs, the liquid crystal ratio of the Ga _1-x Al _x As cladding layers 2 and 5 is set within the range of x≧0.2, and the oscillation wavelength is approximately 880 nm. . In addition, the light guide layer 4
Consists of In _1-y Ga _y P _1-z As _z mixed crystal, 0.68≦y≦1,
The band gap and refractive index are selected within the range of 0.34≦Z≦1z=2.04y−1.04, and the band gap and refractive index are the same as that of the active layer 3 and the cladding layers 2 and 5.
The value is set to be an intermediate value. Barrier layer 9
is composed of a Ga _1-x Al _x As layer, which has a wider forbidden band width and a smaller refractive index than the active layer 3 and the optical guide layer 4, and the mixed crystal ratio x is the same as that of the cladding layers 2 and 5. It is about the same level. Furthermore, since the barrier layer 9 is very thin at 0.05 μm, it is sufficient as a barrier for carriers, but is insufficient as a barrier for light. The provided diffraction grating acts as a reflector for the laser beam.

FIG. 2 shows the forbidden band width and refractive index distribution of the multilayer crystal structure for laser oscillation. Next, in order to change the oscillation wavelength from infrared to visible light range, the active layer 3 is made of Ga _1-x Al _x As and the mixed crystal ratio is changed within the range of 0≦x≦0.4, or the active layer 3 is Zn,
890 ~ by doping with impurities such as Si
Laser oscillation can be obtained in the 660nm range. In this case, the cladding layers 2 and 5 are set so that their respective forbidden band widths and refractive indices have distributions as shown in FIG. 2, and the materials are Ga _1-x Al _x As, In _1-y Ga _y
Either P _1-z As _z is fine. However, the light guide layer 4
is limited to In _1-y Ga _y P _1-z As _z .

In this embodiment, a barrier layer 9 is inserted between the active layer 3 and the light guide layer 4, and the electrons injected into the active layer 3 are blocked by the barrier layer 9 and cannot reach the light guide layer 4. Therefore, the increase in the oscillation threshold can be suppressed.

When current is injected through the n-side and p-side electrodes 7 and 8, laser oscillation is started in the active layer 3. The resonance direction of laser oscillation corresponds to the horizontal direction in the figure, and the injected current is focused into a band-shaped current path by a well-known internal stripe structure, and the laser beam is emitted from the left and right end surfaces of the active layer 3 corresponding to this current path. radiated. The oscillation wavelength is determined by the period of the diffraction grating,
By appropriately controlling the period of the diffraction grating in accordance with the wavelength of the laser beam, stable laser oscillation in a single longitudinal mode can be obtained. Therefore, when used as a light source for long-distance optical communication or measurement control, high accuracy is maintained, making it an extremely excellent laser light source.

Although the above embodiment has been described with respect to a distributed feedback type semiconductor laser device, the present invention is not limited thereto, and can be applied to other devices such as a distributed Bragg reflection type semiconductor laser device.

<Example 2> FIG. 3 is a configuration diagram of a semiconductor laser device showing another example of the present invention. An n-type InGaP cladding layer 12 is grown on an n-type GaAs substrate 11, and this
After forming a diffraction grating on the InGaP cladding layer 1 by the same means as in Example 1, an n-type InGaPAs optical guide layer 13, an n-type GaAlAs barrier layer 14, a non-doped GaAs active layer 15, and a p-type InGaP cladding layer 1 are formed.
6. Sequentially epitaxially grow p-type GaAs cap layer 17 to form a multilayer crystal with double heterojunction structure for laser oscillation. In this example, n-type
This example differs from Example 1 in that a diffraction grating is formed in the InGaP cladding layer 12. Between the n-type InGaPAs optical guide layer 13 and the GaAs active layer 15, an n-type
Since the GaAlAs barrier layer 14 is inserted, holes injected into the active layer 15 do not reach the optical guide layer 13, and the reactive current is small. The forbidden band width and refractive index distribution of the multilayer crystal structure for laser oscillation of this example are as shown in FIG. Cap layer 17
and an ohmic electrode 18 on the substrate 11, respectively.
By forming 19, the semiconductor laser device of this example is manufactured.

Note that the compositions of the cladding layer 16 and _the optical guide layer ₁₃ are not limited to the above, but may vary depending on the oscillation wavelength (active layer composition) as in Example _1.
An appropriate composition may be selected from Ga _y P _1-z As _z . However, the n-type cladding layer 12 is In _1-y Ga _y
Since it is limited to P _1-z As _z (z=2.04y−1.04, 0.51≦y≦0.8), the obtained oscillation wavelength is 890 nm ~
It is within the range of 770nm. Further, the barrier layer 14 may be selected from Ga _1-x Al _x As (0.2≦x≦1) as in the first embodiment.

Also in this embodiment, the ohmic electrodes 18, 19
oscillation wavelength by injecting a carrier through
Single longitudinal mode laser oscillation of 880nm can be obtained. Laser light is emitted from the end faces in the left and right directions in the figure.
It is of course possible to apply the structure of this embodiment to a distributed Bragg reflection type laser oscillation device.

<Effects of the Invention> As detailed above, in a single longitudinal mode laser element with an oscillation wavelength of 890 nm or less using In _1-y Ga _y P _1-z As _z as a diffraction grating forming layer, the active layer and optical guide layer are By inserting a semiconductor layer with a wider forbidden band width between the two as a barrier layer, invalid carriers flowing from the active layer to the optical guide layer are reduced, resulting in a distributed feedback type or distributed plug reflection type with excellent device characteristics, especially temperature characteristics. It is possible to obtain a semiconductor laser device of.

[Brief explanation of the drawing]

FIGS. 1 and 3 are cross-sectional views taken in a direction parallel to the resonance direction of a distributed feedback semiconductor laser device illustrating an embodiment of the present invention. FIGS. 2 and 4 are explanatory views showing the forbidden band width and refractive index distribution of the multilayer crystal structure in the semiconductor laser devices shown in FIGS. 1 and 3, respectively. FIG. 5 is a cross-sectional view of a conventional distributed feedback semiconductor laser. 1,11...n-type substrate, 2,12...n-type cladding layer, 3,15...non-doped active layer, 4...p-type optical guide layer, 5,16...p-type cladding layer, 6,17...
p-type cap layer, 7, 18... n-side ohmic electrode, 8, 19... p-side ohmic electrode, 9... p-type barrier layer, 13... n-type light guide layer, 14... n-type barrier layer.

Claims (1)

[Claims] An active layer for laser oscillation consisting of 1 Ga _1-x Al _x As (0≦x≦0.4) and In _1-y Ga _y P _1-z As _z (0.51≦y≦
1, z≒2.04y−1.04), and an optical guide layer provided between the diffraction grating surface of the diffraction grating formation layer and the active layer. A barrier layer made of Ga _1-x Al _x As (0.2≦x≦1) having a larger forbidden band width than the active layer and the optical guide layer is inserted between the active layer and the optical guide layer. A semiconductor laser device characterized by: