JPH0138389B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a semiconductor laser device that oscillates a single laser beam in both longitudinal mode and transverse mode.

(Prior Art) Conventionally, a semiconductor laser device that oscillates a single laser beam in a longitudinal mode and a transverse mode is a buried semiconductor laser device in which an active layer 1 is surrounded by a semiconductor 4 having a wide forbidden band width, as shown in FIG. It is a distributed feedback type heterostructure in which an optical waveguide 2 having a diffraction grating 3 is provided above or below an active layer 1.

(Problems to be Solved by the Invention) This distributed feedback embedded heterostructure is very complex and requires advanced technology to manufacture, so the following situations often occur, resulting in poor product yield.

(i) Diffraction gratings cannot be formed well on the substrate crystal.

(ii) The diffraction grating formed on the substrate is destroyed during liquid phase growth.

(iii) It is difficult to control the stripe width by chemical etching.

(iv) The semiconductor for embedding the active layer does not grow with good reproducibility.

(v) Since the refractive index changes periodically, it will have two oscillation wavelengths that are slightly different from the Bragg condition, but it is not possible to predict which oscillation wavelength it will oscillate at.

The purpose of this invention is to provide easy manufacturing, excellent reproducibility,
It is an object of the present invention to provide a semiconductor laser device that has substantially the same performance as a conventional distributed feedback buried heterostructure and whose oscillation wavelength can be predicted.

(Means for Solving the Problems) In order to achieve the above object, the present invention uses a multi-quantum well structure as an active layer, which is constructed by alternately stacking three or more layers of two types of compound semiconductor ultrathin films having different compositions. In a semiconductor laser device, both the left and right regions of the active layer, excluding the central striped region, are composed of semiconductors with an average composition of two types of compound semiconductors, and a conductor is placed above or below the striped region, which becomes the light emitting region of the active layer. Provided is a semiconductor laser device characterized in that a semi-insulating layer is provided above or below both left and right regions having an average composition. The central stripe-shaped region of the active layer, which serves as a light-emitting region, is configured, if necessary, so that the quantum well structure and the average composition structure of the two constituent compound semiconductors are distributed at a predetermined period.

(Function) As mentioned above, both the left and right regions of the active layer, excluding the central stripe-shaped region, are composed of semiconductors with an average composition of two types of compound semiconductors forming a quantum well structure. The refractive index is smaller than that of the shaped region, an optical waveguide is formed, and the transverse mode of light is controlled. In addition, by providing a semi-insulating layer on the top or bottom of both the left and right regions made of semiconductors with the above average composition, the current flowing is concentrated in the light emitting region in the same way as in a buried structure, resulting in a small threshold current. Become. Furthermore, by periodically implanting impurity ions into the central striped active layer so that the quantum well structure and the average composition structure of two types of compound semiconductors are alternately distributed, the average composition structure has no gain. , a gain will occur periodically. This period is λo/2n _r (λo: oscillation wavelength,
When the wavelength becomes an integer multiple of nr (refractive index ₎ , only the wavelength λo oscillates due to the Bragg condition, and the longitudinal mode becomes single. By making the active layer of the distributed feedback type in this way, the longitudinal mode becomes single not only during DC operation but also during high-speed modulation, resulting in a semiconductor laser device suitable for optical communication.

(Embodiment) The present invention will be described based on an embodiment shown in the drawings. Reference numeral 11 is a substrate crystal, and an active layer is provided on the substrate crystal 11 with an n-type lower cladding layer 15 interposed therebetween. The central striped region 12, which serves as the light emitting region of the active layer, has a multi-quantum well structure in which three or more ultrathin films of two types of compound semiconductors having different compositions, such as binary, ternary, or quaternary systems, are stacked alternately. Both the left and right regions 13 excluding the light emitting region are semiconductors having an average composition of two types of compound semiconductors constituting a quantum well type. In addition, the central striped area 1
2, the semiconductors 14 having an average composition of two types of compound semiconductors are distributed in the vertical direction at predetermined intervals as necessary.

An example of a method for forming a semiconductor with an average composition of two types of compound semiconductors in the above-mentioned active layer is that after forming a multi-quantum well structure, as shown in Figure 2, Si ions are formed using a focused ion beam. When selectively implanted at a predetermined position and heat-treated, the quantum well structure is disturbed and becomes a semiconductor with an average composition of the two types of compound semiconductors, with a refractive index smaller than that of the multi-quantum well structure. In FIG. 2, impurity ions are also implanted at one end 14' of the central striped region 12 to obtain an average composition.
This is to prevent Fabry-Perot mode.

Gain occurs in the quantum well structure region of the central striped region 12 of the active layer, and no gain occurs in the region 14 into which impurity ions are implanted. Therefore, if this period is an integral multiple of λo/2n _r , the wavelength of λo only will oscillate. This period is about 2000 to 3000 Å when the oscillation wavelength is about 8000 Å, but it can be easily and accurately formed by implanting impurity ions using the above-mentioned focused ion beam.

There is a conductive p-type semiconductor layer 16 on the upper surface of the active layer, and the semiconductor region 1 on both the left and right regions 13 of the active layer
7 is semi-insulating and concentrates the flowing current to the central striped region 12. Although this semiconductor layer 16 is provided on the upper surface of the active layer in the illustrated embodiment, the same effect can be obtained even if it is provided on the lower surface of the active layer.

A p-type upper cladding layer 18 and a p-type semiconductor layer 19 are present on the p-type semiconductor layer 16, and the substrate crystal 11
Electrodes 20 and 21 are provided on the bottom surface of the p-type semiconductor layer 19 and on the top surface of the p-type semiconductor layer 19, respectively, to constitute a semiconductor laser device.

When a current is supplied from the electrodes 20 and 21 of the semiconductor laser device described above, since the semi-insulating layer 17 is present on both the left and right regions 13 of the active layer, the current flows concentratedly in the central striped region 12, causing light emission. Start. Since both sides of the central striped region 12 are made of a semiconductor 13 with a small refractive index, the transverse mode of light is controlled. In addition, since regions with gain and regions without gain are periodically distributed in the central striped region 12, in the case of a conventional distributed feedback semiconductor laser device in which the refractive index changes periodically, Bragg diffraction is similar. Although it is possible to oscillate at two wavelengths, the semiconductor laser device of the present invention oscillates only at the Bragg diffraction wavelength.

Next, an example of a method for manufacturing the semiconductor laser device of the present invention will be described.
An n-type Ga _0.6 Al _0.4 As layer (Si doped, carrier concentration: 1×10 ¹⁸ cm ^-3 ) is epitaxially grown to 3 μm using molecular beam crystal growth method on top of the doped, carrier concentration: 2×10 ¹⁸ cm ^-3 ). . Then undoped 100μm
5 thick GaAs layers and undoped 60μm thick Ga _0.8
Four Al _0.2 As layers are grown alternately to form a quantum well structure.

At this point, the crystal growth is stopped, and the crystal is moved to a focused ion beam implantation device connected to the molecular beam crystal growth device in an ultra-high vacuum, and Si ions are implanted into the quantum well structure layer. The implanted dose of Si ions is 2
×10 ¹⁴ cm ^-2 , acceleration voltage is 200 keV, and focused ion beam diameter is 0.1 μm. The width of the central stripe region is 3 μm, the length of the part with the periodic structure is 300 μm, the length of the part without the periodic structure is 100 μm,
The period of implanting Si ions is 2400 Å. The above Si
By implanting ions, a crystal having the structure shown in FIG. 2 is formed.

This crystal was returned to the molecular beam crystal growth apparatus, a p-type Ga _0.6 Al _0.4 As layer (Be-doped, carrier concentration: 1×10 ¹⁸ cm ^-3 ) was grown to a thickness of 0.2 μm on the active layer, and focused ion beam implantation was performed again. The device is moved to a device, and B ions are implanted into the entire area corresponding to the part without periodic structure in the central stripe area of the above-mentioned p-type GaAlAs layer. B
The ion implantation dose was 2×10 ¹⁴ cm ⁻² , the acceleration voltage was 200 keV, and the focused ion beam diameter was 0.1 μm.

This crystal was returned to the molecular beam crystal growth apparatus again, and a p-type Ga _0.6 Al _0.4 As layer (Be-doped, carrier concentration: 1×10 ¹⁸ cm ^-3 ) of 1 μm was added on top of it, and then a p-type
GaAs layer Be doped, carrier concentration: 1×10 ¹⁸ cm ^-3 )
1 μm epitaxially grown.

The crystals formed in this way are under As pressure (1 atm)
Heat treated at 675℃ for 4 hours using the closed tube method. This heat treatment allows Si to form a multi-quantum well structure in the active layer.
The area where the ions were implanted becomes eroded, and the average composition changes.
This becomes a GaAlAs layer. Furthermore, defects caused by ion implantation in the region of the p-type GaAlAs layer into which B ions were implanted disappear, and the layer becomes a semi-insulating layer. Finally, electrodes are attached to both sides and the semiconductor laser device shown in FIG. 1 is obtained by cutting it to a predetermined length.

This semiconductor laser device had a single mode in both the vertical and horizontal directions, had a threshold current value of 8 mA, and an oscillation wavelength of 8400 Å.

(Effects of the Invention) In this invention, since the central stripe region of the active layer is sandwiched between semiconductor regions with a low refractive index, light is sufficiently confined in the lateral direction, and the manufacturing process is simplified, resulting in improved manufacturing yield. The yield is approximately 80%, which is significantly improved compared to the approximately 10% yield of a semiconductor laser device with a conventional structure.

[Brief explanation of drawings]

FIG. 1 shows an example of a semiconductor laser device of the present invention, and is a partially cutaway perspective view, and FIG. 2 is a perspective view showing an active layer of the semiconductor laser device of FIG.
FIG. 3 is a partially cutaway perspective view of a conventional distributed feedback buried structure semiconductor laser device. 11... Substrate crystal, 12... Central stripe region of active layer, 13, 14... Average composition semiconductor layer,
16...Conductor layer, 17...Semi-insulator layer.

Claims (1)

[Scope of Claims] 1. In a semiconductor laser device whose active layer is a multi-quantum well structure formed by alternately stacking three or more layers of two types of compound semiconductor ultrathin films with different compositions, the central stripe-shaped region of the active layer is Both the left and right regions excluding the left and right regions are composed of semiconductors having an average composition of two types of compound semiconductors, a conductor layer is provided above or below the striped region of the active layer, and a conductor layer is provided above or below both the left and right regions having the average composition. A semiconductor laser device characterized by providing a semi-insulating layer. 2. The semiconductor according to claim 1, wherein the central stripe-shaped region of the active layer is constituted by a periodic distribution of a quantum well structure and an average composition structure of two types of compound semiconductors. laser equipment.