JPS58196084A - Distributed feedback type semiconductor laser element - Google Patents

Abstract

PURPOSE:To reduce the threshold value by a method wherein a region provided with grating is lengthened enough to obtain sufficient amount of feedback, then an active layer is restricted to a part thereof in the optical direction and made transparent to laser oscillated light at regions other than that part. CONSTITUTION:In the section of the surface parallel with the direction of advancement of laser light of DFB type semiconductor laser, an N-Ga1-xAlxAs clad layer 2, Ga1-yAlyAs active layer 3, and a P-Ga1-zAlzAs clad layer 4 are grown on an N-GaAs substrate 1, and the periodic grating 10 is formed by a chemical etching. Thereafter, a P-Ga1-xAlxAs clad layer 5 and a P-GaAs cap layer 6 are grown, and next Zn is selectively diffused into a region 9 by leaving regions 11 and 11. Afterwards, an N-side electrode 8 and a P-side electrode 7 are formed. The band gap becomes small at the Zn diffused region, and the active layer 3 becomes transparent to laser light at the regions 11 and 11.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a distributed feedback semiconductor laser with a small threshold.

In a distributed feedback type semiconductor laser, in order to obtain sufficient feedback density, reduce reflection loss, and reduce current density, it is necessary to lengthen the portion where periodic unevenness (grating) is provided.

For this reason, a grating is provided over the entire area of the active layer in the optical axis direction, and current flows throughout the entire area.
The so-called D F B (1) distributedl;
The 'eedback) type had the disadvantage that the threshold current was large. On the other hand, in the so-called DBR type, in which the grating is provided only in a part of the active layer and current flows into the other region, the active layer in the grating part is not excited, so absorption loss increases and the threshold The drawback was that the current was large.

An object of the present invention is to provide a controlled longitudinal mode semiconductor laser with a small threshold value.

In order to eliminate the above-mentioned drawbacks and reduce the threshold tm value, for the DFB type, the length of the area where the grating is provided is set to such a length that a -tf) feedback can be obtained, and its length is set in the optical axis direction. By limiting the active layer to a portion and making the other region transparent to laser oscillation light, it is possible to reduce the current value of coalescence.

For the DBR type as well, the current value can be reduced if the portion where the grating is provided is illuminated with laser oscillation light to make it transparent.

The present invention will be explained below using an example shown in FIG.

FIG. 1 is a cross-sectional view of a DFB type semiconductor laser in a plane parallel to the direction in which laser light travels. n-GJ-xA4AI cladding layer 2, Gap-yAt on n-GIAI substrate 1
, an As active layer 3 (K>7), and a p-GJ-sA4AI cladding layer 4 (K, M>)'), and a periodic grating 10 is formed by chemical etching. At this time,
The period A of the grating, the laser oscillation wavelength of the active layer is λ, and the effective refractive index of the laser mode is n sff,
Do as follows.

17', '1, i wz m *λ/ 2 n met However,
m3 integer % P-Ga, -xAlxAs layer 5, p-Q&A-cap layer 6 are then grown, and then Zn is selectively diffused into region 9, leaving regions 11 and 11'.

After this, the n-side electrode 8 and pit electrode 7 are formed. In the region where Zn is diffused, the band e gap becomes small due to the band till, and the active layer 3 becomes transparent to the laser oscillation light in the regions 1'l and 11', and does not undergo absorption loss. For this reason, feedback by the grating occurs over the entire area of the device including 11.11', and current is injected only into region 9. As an example of threshold characteristics, for a device with a stripe width of 5 μm, the threshold current value is ~40 mA. there were. Note that the arrows in each of the F1 figures below indicate laser light.

FIG. 2 shows a DBR type row made through a similar process. Area 11 in which grating 10 is provided. j
At l', since the active layer 3 is transparent, the laser light does not suffer any loss and the threshold value can be reduced.

FIG. 3 shows another embodiment, in which a l
iS50 A (D GaAs layer, 100'4 (DA
IAtsM is alternately formed to a total thickness of α1 μm. This thin film multilayer portion 12 is used as an active region layer. Only area 11.11'7. When selective diffusion of n is performed, the multilayer structure disappears in the diffusion part, and the average composition of GaAtAs
It becomes a layer. For this reason, area 11. ! 1' becomes transparent to the laser beam, and can achieve the same purpose as in FIG.

FIG. 4 shows another embodiment, in which a grating 10 is provided between the n-type cladding layer 2 and the n-type light guide layer 13, and on the n-type light guide layer, an active layer 3, a p-type cladding layer 5, a p-type Grow the cap layer 6. Thereafter, the regions 11.11' are selectively removed by chemical etching up to the surface of the n-type optical guide layer, and then the n-type GaB-b At bAs layer 14 (b
:L is selectively grown. In this case too, the area 11.11'
becomes transparent when sealed with laser oscillation light, and the current flows through the active layer 3.
Since it is limited to a certain area, the same effect as in FIG. 1 can be expected.

Note that the light guide layer is composed of a semiconductor layer that has a lower refractive index than the active layer and a higher refractive index than the cladding layer. G'A
In the S GaAjAs system, the cladding layer Ga, -.

From the AlAl mixed crystal ratio (y) of the Ata A1 layer, that (X) of the light guide layer G as-x Al z A' layer is made smaller (x
<y).

The effective light output can be increased by the light guide layer.

In the above example, explanation was given regarding a GILAI-QaAtAl semiconductor laser device, but other material systems, such as 1n
-v Compound semiconductor, GaA II Ga (
A I P ) pIn Qa P@In G
jl A1. In RAM, Qa-At-As
-P, Ga-As-8b, Al-Ga-8b.

It is also applicable to semiconductor lasers using etc. The current value can be reduced.

Note that the gt table shows specific examples of each layer when the ()aAs-GaAtAI system is used.

For example, if you imagine a semiconductor with the structure shown in Figures 1 and 2,
The semiconductor laser device of the present invention was also realized using the 9-day configuration shown in Table 2.

Further, in the above description, only one-dimensional DFB and DBR were explained, but the same effect can be achieved even when two-dimensional DFB and DBR are used.

Furthermore, it goes without saying that the present invention is equally applicable to semiconductor lasers in which the conductivity types of the substrates and semiconductor layers in the above-mentioned rows are opposite conductivity types.

[Brief explanation of the drawing]

Figure 1 is a longitudinal cross-sectional view of the DFB type relay system, Figure 2 is the DB
43 and 4 are vertical cross-sectional views of the R-cedar laser element, and FIG. 4 is a vertical cross-sectional view of the DFB type laser beam.

Claims (1)

[Claims] 1. A semiconductor laser element having a structure in which periodic unevenness is provided in or around an active layer that emits recombinant light, and light is reflected by the unevenness to generate laser oscillation, With respect to the optical axis direction in which laser oscillation occurs, the active layer is limited to a part of the device, and the unevenness is also provided in areas other than the area where the active layer exists, and the areas where there is no active layer and where the unevenness is provided are not suitable for laser oscillation. A distributed feedback semiconductor laser device characterized in that it is made of a material that is transparent to light. 2 Claim 1 characterized in that periodic unevenness is not provided in the part where the active layer is present.
Distributed feedback semiconductor laser device as described in .