JPS63153884A - Distributed feedback type semiconductor laser - Google Patents

Abstract

PURPOSE:To produce an MQW-DFB laser high in coupling factor and excellent in active layer quality and in performance characteristics by a method wherein a superlattice guide layer is first grown on a diffraction grating and the guide layer surface is ensured to be flat even in a very thin design. CONSTITUTION:On an Inp substrate 1, a diffraction grating 2 is formed by laser interference exposure, whereon a superlattice guide layer 6, consisting of ten 80Angstrom thick InP barrier layers 7 and ten 30Angstrom -thick In0.53Ga0.47As well layers 8; an MQW active layer 4, consisting of eight 100Angstrom -thick InP barrier layers 9 and eight 100Angstrom -thick In0.53Ga0.47As well layers 10; and an Inp clad layer 5, are grown in that order. The effective emission wavelength composition of the superlattice guide layer 6 is equivalent to approximately 1.3mum, and that of the MQW active layer 4 is equivalent to approximately 1.55mum. In this example, the superlattice guide layer 6 is only 1100Angstrom thick, as measured from the ridge of the approximately 500Angstrom -thick diffraction grading 2. The surface involving the growth, however, is virtually flat.

Description

[Detailed description of the invention] (Industrial application field) The present invention relates to a distributed feedback semiconductor laser.

(Prior Art) Distributed feedback semiconductor lasers (DFB-LDs), which have a diffraction grating adjacent to an active layer that recombines light, are being actively researched and developed as a light source for long-distance, large-capacity optical fiber communications. ing. Its characteristics.

Reliability is also reaching a level comparable to that of conventional Fabry-Bello type semiconductor lasers. In order to further improve the characteristics, it is considered effective to employ a multiple quantum well structure in the active layer. Multiple quantum well (Mul
triple Quantum %4ell, abbreviated as MQ
W) Flu structure is made by growing different semiconductor thin films alternately in multiple layers. A semiconductor laser employing this MQW topography is expected to reflect the MQW step-like state density function, lowering the threshold, improving temperature characteristics, and reducing the spectral width during pulse modulation.

Dutta et al. of AT&T Be1l Laboratory, Applied Physics Letters (^pot.

Phys, Lett, Vol. 46.01036
-1038.1985) and an InGaAsP well layer with an emission wavelength of 1.34.

have reported an MQW laser in which several layers of InGaAsP barriers m (all about 300 layers thick) with a composition of 1.031 Jm are laminated. This laser has excellent characteristics such as low threshold current and high efficiency, and Dutta et al.
It was demonstrated that the temperature characteristics of MQW lasers are superior to lasers.

From the above, it is expected that a DFB laser in which an MQW top layer is introduced in the active layer will exhibit excellent characteristics.

(Problems to be Solved by the Invention) However, when attempting to manufacture a DFB laser by introducing an MQW structure only into the active layer using a conventional method, the following problems occur. That is, as shown in FIG. 2, a diffraction grating 2 is formed on a substrate 1, and I n O, 73G a corresponding to a wavelength of 1.34 is formed on the diffraction grating 2 using, for example, the MOVPE method.
0.27 A So, bo Po, ao guide layer 31I no, 53Gao, nyAs/I nP
When the MQW active layer 4 is grown, the thickness of the guide layer 3 is 0.1
4 or less, the surface of the guide layer 3 is not completely flat, and the active layer 4 is grown on the uneven surface.
The quality of the product may deteriorate. Of course, the surface can be flattened by growing the guide layer 3 thicker, but in that case, the coupling coefficient becomes smaller as the guide layer 3 becomes thicker.
The same problem occurs even if crystal growth is performed using the E method.
In the LPE method, guide Jw3 is 0. The surface of the guide JW3 tends to be flat even at IIJm, but in the case of the LPE method, multilayer thin r! :! It is difficult to form an ellipsoid.

An object of the present invention is to provide an MQW-DFB laser with a large coupling coefficient and excellent characteristics.

(Means for Solving the Problems) The present invention provides a distributed feedback type semiconductor in which a diffraction grating is formed in the vicinity of an active layer, and the active layer and the diffraction grating are optically coupled by a guide layer. The above-mentioned problems are solved by a distributed feedback semiconductor laser characterized in that the active layer and the guide layer have a superlattice structure formed by growing multiple layers of different semiconductor thin films.

(Function) The inventor of the present invention achieved the following by growing a semiconductor multilayer thin film similar to the active layer on the diffraction grating in the MOVPE method.
We found that flattening progresses with a relatively small thickness.
For example, when growing a crystal on an InP diffraction grating with a depth of 500 people, 100 people InP, 100 people I n 6.53
It was found that by laminating 5 layers each of Gao and 47A S with a total thickness of 0.1, the growth surface was almost flattened.

(Example) The present invention will be explained in more detail below with reference to drawings showing examples.An example of the present invention is shown in FIG. A diffraction grating 2 (period: 2400) was formed by interference exposure method, and an 80-layer InP barrier layer 7.30
, s3G a 0.47A S well layer 8 each 107
Super lattice guide layer formed by laminating one layer at a time 6゜100 In
Pn brim 9f G a 6, 47 A S well layer 10 8 each! fl
MQW active layer 4 consisting of a t-layer, InP cladding! f! J
5 in sequence. The effective emission wavelength composition of the superlattice guide layer 6 corresponds to about 1.34, and the effective emission wavelength composition of the MQW activity corresponds to about 1.55. In this example, the thickness of the superlattice guide layer 6 is only 1100 mm measured from the peak of the diffraction grating 2 which is about 500 mm deep, but as a result of growth, the growth surface has become almost flat. confirmed.

The MQW-DFB laser fabricated in this way was made into a normal buried structure and its characteristics were evaluated.
Elements of about 5% were obtained with good reproducibility.

When we evaluated the temperature characteristics of the laser, we found that its characteristic temperature ′!
゛. was 90 to 100, a significant improvement compared to the normal DH beam laser. The temperature dependence of the carrier lifetime at the threshold value also has a smaller rate of change compared to the DH tank structure, and furthermore, M Q W ! Reflecting the step-like density of states function created by the IL structure, the oscillation spectrum spread during pulse modulation is also 172 to 1/
It was found that the number was reduced to 3.

(Effects of the Invention) As described above, in the present invention, by first growing the superlattice guide layer 6 on the diffraction grating 2, it is possible to flatten the growth surface even if the total thickness is about 0.1 μm. It was possible to provide an MQW-DFB laser with a large coupling coefficient, a good quality active layer, and excellent characteristics.

In the example, the superlattice guide layer 6 is made of 80 InP, 30 InO,! 130 a 0.47
A: Although a superlattice structure consisting of 8 layers was used, it is also possible to use an MQW'WI structure with the same structure as that used for the active layer 4 as a guide layer.Of course, the material system used can also be I
nP-, -I n□! The present invention is not limited to the 13Gao4yAs type material, and the present invention can also be realized using GaAρAs to GaAs type materials.

[Brief explanation of the drawing]

FIG. 1(a) is a sectional view showing one embodiment of the present invention, FIG. 1(b) is an enlarged sectional view showing the vicinity of the active layer, and FIG. 2(a) is a conventional MQw-DFB. A cross-sectional view showing a laser,
FIG. 2(b) is an enlarged cross-sectional view showing the vicinity of the active layer. In the figure, 1 is a substrate, 2 is a diffraction grating, 3 is an InGaAsP guide layer, 4 is an MQW guide layer, 5 is a 1nP cladding layer,
6 is a superlattice guide layer, and 7 and 9 are InPn and As wafer layers, respectively.

Claims (1)

[Claims] In a distributed feedback semiconductor laser in which a diffraction grating is formed in the vicinity of an active layer, and the active layer and the diffraction grating are optically coupled by a guide layer, the active layer and the guide layer are made of different semiconductor thin films. A distributed feedback semiconductor laser characterized by having a superlattice structure grown in multiple layers.