JPS6140077A - Buried type surface plane laser oscillator - Google Patents

Abstract

PURPOSE:To operate a GaAs/GaAlAs laser with a low oscillation threshold current, by making the area of an active layer smaller than that of a clad layer, and forming a p-n junction current constriction layer between the active and clad layers. CONSTITUTION:An n type GaAlAs clad layer 13, a p tyep GaAs active layer 16, a p type GaAlAs split layer 17, a p type GaAlAs clas layer 18 and p type GaAlAs cap layer 19 are epitaxially grown on an n type GaAs substrate 12, and the layers 17-19 are etched in the shape of a column. The active layer 16 is selectively melted back, and the space around the active layer 16 is filled with a p type GaAlAs current block layer 14. The split layer 17 is selectively melted back, and an n type GaAlAs layer 15 is deposited so as to bury the layer 17 and the like. The substrate 12 is etched to expose the epitaxial surface which serves as a reflecting mirror, and electrodes 20, 21 are formed. In this way, the current constricting function is increased, and it is therefore possible to operate a plane emission laser with a low oscillation threshold current.

Description

Detailed Description of the Invention [Field of Industrial Application] The present invention relates to a GaAs/GaAQAs surface-emitting laser oscillation device, and particularly relates to a structure in which the area of an active layer is smaller than that of a cladding layer, and a p-n junction. By reliably forming a current confinement layer using the reverse bias of G a
The present invention relates to a surface emitting laser oscillator.

[Conventional technology]

FIG. 2 shows an example of a conventional surface emitting laser. In the figure, 1 is an n-type GaAs substrate, 2 is an n-type GaA
QAs cladding collapse, 3 is GaAs active layer, 4 is p-type Ga
AQAs cladding layer, 5 is a reflective surface, 6 is an electrode, 7 is a mirror electrode, 8 is a current, 9 is an active area, IO is an optical resonance path,
11 represents a laser beam. □ The illustrated device generates an active region 9 in the GaAs active layer 3 by passing a current 8 of a predetermined level or higher between the electrode 6 and the specular electrode 7, and creates an active region 9 between the reflective surface 5 and the specular electrode 7. A Fabry Bellows resonator is formed. As a result, optical resonance occurs along the optical resonance path 10, and laser light 11 is emitted.

(Problems to be solved by the invention) □ In the conventional surface emitting laser exemplified above, the gain region is only as long as the thickness of the active layer, so the oscillation threshold current density is high, and the p-type The threshold current becomes high because there is a large amount of leakage current that does not contribute to oscillation due to the current flow in the redundant layer and the diffusion of fractional carriers and rears in the active layer.
There was a problem in that continuous operation at room temperature was difficult due to the generation of heat.

In order to reduce the threshold current due to oscillation, the threshold current density must be lowered or the area of the active region must be reduced. There are two ways to lower the threshold current density: forming a reflector with a high reflectance, or increasing the gain region by thickening the active layer, but the former has the problem of significantly decreasing laser light output. However, even in the latter method, the thickness of the active layer is limited to less than the carrier diffusion length.

[Means for solving problems]

This invention solves the above-mentioned problems and enables surface-emitting lasers to operate with a lower oscillation threshold current than conventional systems by reducing the area of the active layer relative to the area of the cladding layer. The purpose is to introduce a buried structure that can form a current confinement layer reliably with good reproducibility.

〔Example〕

FIG. 1 is a cross-sectional view of one embodiment of a surface emitting laser based on the present invention, in which 12 is an n-type GaAs substrate, 13 is an n-type GaAs substrate, and 13 is an n-type GaAs substrate.
14 is a p-type Ga A fl A s (X At=0.4) cladding layer,
At ='0.4) Current blocking layer, 15 is n-type Ga
A Q A s (XAL=0.4) layer 1.16 is p-type GaAs active layer, 17 is p-type Ga A Q A
s (XAL = 0.3) split layer, 18 is p-type G
a A , Q A s (X at =0.45) cladding layer, 19 is P''-G, aAUAs camp layer, 2
0 is a p-side electrode such as Au/Zn/Au, 21
22 is an Au reflective film, 23 is an optical resonance path, 24 is a current, and 25 is a laser beam.

The manufacturing process of the structure shown in FIG. 1 is as follows i) to vi). Note that this step is performed in steps i) to vi) in Figure 3.
are shown correspondingly.

i) 13.16. which forms a DH structure in the first crystal growth.
After the layers 17, 18, and 19 are epitaxially grown, the layers 17, 18, and 19 are etched into a cylindrical shape by chemical etching or the like. (Fig. 3i)) Then, a second liquid phase growth is performed. (Fig. 3 ii) to v)) ii) First, the p-type GaAs active layer shown with diagonal lines was 16 is selectively melted back. (Fig. 3 1i) ) , iii , ) and p-type G a A Q A s
(XAL=0.4) The area around the active layer 16 is filled with the current blocking layer 14. (Fig. 3 1ii)) ” iv) Furthermore, a selection node is applied to the p-type GaAD.
A s (X at =0.3) The split layer 17 is melted back. (Fig. 3 1v)) ■) Then n-type G a A II A 5 (Xa
t = 0.4) Fill in the surrounding area with 15. (Figure 3 V)
vi) Finally, the GaAs substrate 12 is etched to expose the shrimp surface that will serve as a reflecting mirror, and the electrodes 20, 21, etc. are formed, and the processing process is completed. (FIG. 3 vi)) This laser is a buried laser in which a constriction-shaped mesa structure is formed by the selective meltback method to strengthen the current confinement function, as shown in FIG. 3 V).

Therefore, heat dissipation is excellent. In addition, a new p-type Ga
By providing the A II A s (Xat=0.3) split layer 17 between the p-type rad layer 1B and the active layer 16, the current confinement structure
Since it is formed by the reverse direction characteristic of the n-junction, it is further strengthened.

Furthermore, conventionally, when forming a current confinement structure with a pnpn structure, it was necessary to finely control the film thickness during the second crystal growth, but with this laser, the p-type Ga A Q A around each mesa is s (XAL=0.4)
Even if the thickness of the current blocking layer 14 is slightly different, by selectively melting back the split layer 17, a current confinement structure can be reliably formed.

[Comparison with conventional method]

FIG. 4 shows a structural diagram of a mesa-waisted buried structure (BGM) GaAffiAs laser reported by NEC. The features of this laser are as follows.

i) This is a mesa stripe laser in which the GaAQAS active layer is selectively etched by chemical etching to make the width of the active layer narrower than the width of the cladding layer.

ii) The current confinement structure forms a pnpn structure by utilizing the properties specific to the liquid composition and length that the growth of the p-type GaAQAs current blocking layer is completely stopped in the recessed portion. Incidentally, in a surface emitting laser that resonates light in the film thickness direction, the thickness of the active layer needs to be several tens of times thicker than that of a normal striped laser. Therefore, crystal growth occurs on both sides of the active layer, and as in the above-mentioned BCM laser, p
The growth of the GaAIJAs current blocking layer cannot be stopped, making it impossible to form a pnpn current confinement structure. In such a case, it is effective to form a pnpn structure by providing a split layer and selectively melting back this layer as described above.

〔Effect of the invention〕

As described in detail above, according to the present invention, the oscillation threshold current can be significantly lowered compared to conventional surface emitting lasers, and a surface emitting laser with high reliability can be realized. In addition to the excellent features of conventional surface emitting lasers, such as monolithic resonator fabrication, single-longitudinal mode operation due to short resonator structure, Sayama radiation angle, and two-dimensional array formation, the surface emitting laser according to the present invention has the following advantages: It also has high reliability due to low threshold operation, and is expected to be widely used in the construction of future optical integrated circuits, making it extremely important.

[Brief explanation of the drawing]

FIG. 1 is a sectional view of an embodiment of a surface emitting laser according to the present invention, FIG. 2 is a sectional view of a conventional surface emitting laser, and FIG. 3 is an explanation showing the manufacturing process of the embodiment shown in FIG. 1. 4 are sectional views of a conventional example for explaining the present invention in detail. In the figure, 12 is an n-type GaAs substrate, 13 is an n-type GaA
Q A s (XAL=0.4) cladding layer, 14 is p-type Ga A Q A s (XAL=0.4) current blocking layer, 15 is n-type Ga A Q A s (
X At =0.4) layer, 16 is a p-type GaAs active layer,
17 is p-type GaAQAS (XAL-0,3) layer, 18
is p-type G a AA A s (Xat=0.45)
A cladding layer, 19 a P''-GaAQAs chip layer, 20 a p-side electrode such as Au/Zn/Au, 21 an n-side electrode such as Au/Ge, 22 an Au reflective film, Reference numeral 23 represents an optical resonance path, 24 represents an electric current, and 25 represents a laser beam.Patent applicant: Patent attorney, New Technology Development Corporation, Fumihiro Hase, Figure 2, Figure 3, Figure 4.

Claims (1)

[Claims] In GaAs/GaAlAs lasers, the selective meltback method is used to form the active layer area smaller than the cladding layer area, and a current confinement layer is created between the active layer and the cladding layer using the reverse bias characteristics of the pn junction. What is claimed is: 1. A buried surface emitting laser oscillation device characterized by forming: