JPS6237910B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to improvements in infrared laser elements.

Compound semiconductors containing lead, such as lead telluride (PbTe), tin lead telluride (Pb _1-x Sn _x Te, and lead selenium telluride (PbTe _1-y Se _y )) have narrow energy gaps and are suitable for infrared laser devices. It is used as a material.

The structure of an infrared laser device formed using such a compound semiconductor containing lead is shown in Figures 1 and 2.
As shown in the figure.

First, as shown in Figure 1, the structure of a conventional infrared laser element is a Pb _1-x Sn _x Te substrate 1 on a P-type PbTe substrate 1.
A crystal layer of Pb 1-x Sn x Te with varying X values is formed as the first cladding layer 2, and a crystal layer of Pb _1-x Sn _x Te with varying X values forms the active layer 3, which is the laser emission region. The Pb _1-x Sn _x Te crystal layer is formed as the second cladding layer 4 by a liquid phase epitaxial growth method.

The reason why the active layer 3 is sandwiched between the upper and lower parts of the crystal layers 2 and 4 having a composition different from that of the active layer is that the band gap and refractive index of each crystal layer are determined at the interface between the active layer 3 and the crystal layers 2 and 4. This is because the injected carriers and the generated light are confined within the active layer by changing the wavelength, thereby increasing the luminous efficiency. A laser element with such a structure is called a double hetero type laser element.

By the way, the laser element with the structure described above is
The Pb _1-x Sn _x Te crystal layer forming the active layer and the Pb _1-x Sn _x Te crystal layer forming the first and second cladding layers have different lattice constants, and therefore the active layer When forming layer 3 and cladding layers 2 and 4 by liquid phase epitaxial growth, active layer 3 and cladding layers 2 and 4 are formed by liquid phase epitaxial growth.
A state of lattice mismatch occurs in which the lattices between the respective crystals do not match at the interfaces 5 and 6 with the crystals. Such a state of lattice mismatch tends to cause lattice defects in that part, causing injected carriers to be trapped in that part, resulting in an increase in the threshold current density of the device for starting laser emission. .

FIG. 2 shows the structure of a laser device that has improved this drawback.

As shown in the figure, a P-type lead tellurium selenide (Pb _1-y Sey) crystal layer is formed as a first cladding layer 12 on a P-type PbTe substrate 11, and a P-type tellurium crystal layer is formed on the first clad layer 12. A crystal layer of lead tin oxide (Pb _1-x Sn _x Te) is formed as the active layer 13, and an N-type lead tellurium selenide (PbTe _1-y Se _y ) crystal layer is formed thereon as a second cladding layer. 14.

Here, although the active layer 13 and the cladding layers 12 and 14 have different compositions, their lattice constants match, so as mentioned above, the active layer 13 and the cladding layers 12 and 14
Since lattice defects due to lattice matching are not formed at the interface with the material, the threshold current density of the device that starts emitting light can now be reduced to about 1/5 of that of the conventional device.

However, the PbTe _1-y Se _y crystal layer forming the above-mentioned cladding layers 12 and 14 contains selenium (Se) in the crystal layer, so the crystal itself is brittle and easily cracks. When a chip for forming a laser element is taken out by cleavage after forming a crystal layer, the crystal layer may not be cleaved to a mirror surface, or cracks may occur in the grown crystal layer. Especially the board 11
Cracks are likely to occur due to the cladding layer sandwiched between the active layer 13 and the active layer 13. This is because the cladding layer 12 is sandwiched between crystals with different compositions, so when force is applied to the crystals to cleave them, strain occurs. It is thought that this is because it occurs in the cladding layer 12 portion.

An object of the present invention is to provide an infrared laser device that eliminates the above-mentioned drawbacks.

According to the present invention, this purpose is to provide a first cladding layer made of Pb _1-x Sn _x Te on a substrate made of Pb _x Te, and a first cladding layer made of Pb _1-x of the same conductivity type with a different composition coefficient x from the first cladding layer. The active layer consists of an active layer made of Sn _x Te, and a second clad layer made of PbTe _1-x Se _y , which is of the opposite conductivity type to the active layer, and the lattice constant between the active layer and the second clad layer is This is achieved by an infrared laser element characterized by matching.

An embodiment of the present invention will be described in detail below with reference to the drawings.

FIG. 3 is a sectional view showing the structure of the infrared laser device of the present invention, and FIG. 4 is a sectional view of the apparatus used to form the laser device.

As shown in FIG. 3, the laser device of the present invention has a P-type Pb _{1-x Sn x Te crystal layer as a first clad layer 22 on a P-type PbTe substrate 21, and a P-type Pb 1-x} Sn _x Te crystal layer as a first cladding layer 22. A P-type Pb _1-x Sn _x Te crystal layer is used as an active layer 23, and an N-type PbTe _1-y Se _y crystal layer is formed as a second cladding layer 24 on top of the active layer 23 by liquid phase epitaxial method. It is formed by twisting. By performing lattice matching of the PN junction that emits laser light in this way, the light confinement effect by this second cladding layer is effectively achieved, and only this second cladding layer is made of PbTe _1-y Se _y. This solves the problem of cracks occurring during cleavage.

In order to form such a laser element, a liquid phase epitaxial growth apparatus comprising a slide member 31 made of carbon and a support stand 32 as shown in FIG. 4 is used. That is, the support table includes a P-type PbTe substrate 33 doped with thallium (Tl).
and a dummy PbTe thin plate 34, and a P-type liquid reservoir 35 provided on the slide member.
Pb _1-x Sn _x Te material is used for the liquid reservoir 36, P-type Pb _1-x Sn _x Te material with different X value is used for the liquid reservoir 37, and N-type PbTe _1-y Se _y material is used for the liquid reservoir 37. The apparatus is introduced into a reaction tube in a hydrogen (Hz) gas atmosphere, and the reaction tube is heated at a temperature of about 500°C.

After that, the slide member 31 is moved in the direction of arrow A while lowering the temperature, and the liquid reservoir 35 is left still on the dummy thin plate 34, so that the components of the dummy thin plate are saturated with the liquid phase of Pb _1-x Sn _x Te in the liquid reservoir. . After that, the slide member is further moved in the direction of arrow A, the liquid reservoir 35 is placed on the substrate 33, and a P-type is placed on the substrate.
A crystal layer of Pb _1-x Sn _x Te is formed as the first cladding layer. Thereafter, the slide member is further moved in the direction of arrow A, and the liquid reservoir 36 is placed on the substrate 33 to form a P-type Pb _1-x Sn _x Te crystal layer as an active layer on the substrate. Next, move the slide member further by arrow A
The liquid reservoir 37 is placed on the substrate, and an N-type PbTe _1-y Se _y crystal layer is formed on the substrate as a second cladding layer.

In this way, an active layer will be formed.
Since only the upper part of the Pb _1-x Sn _x Te crystal layer is formed of the PbTe _1-y Se _y crystal layer, there are almost no cracks that occur when the crystal is cleaved as in the conventional method, and the epitaxial Yield is improved when the grown crystal is cleaved and chips are taken out.

In addition, since the region in the active layer region that emits laser light is near the P-N junction interface with the second clad layer above it, if only the second clad layer is lattice matched with the active layer, the lattice near the interface will be Since no defects are formed, there is no reduction in laser emission efficiency.

As described above, the structure of the infrared laser device of the present invention has the advantage that the yield of manufacturing chips for device formation is improved and a low-cost infrared laser device can be obtained.

[Brief explanation of the drawing]

1 and 2 are diagrams showing the structure of a conventional infrared laser device, FIG. 3 is a diagram showing the structure of an infrared laser device according to the present invention, and FIG. 4 is a diagram showing the structure of an infrared laser device according to the present invention. It is a figure showing an apparatus. In the figure, 1, 11, 21, 33 are PbTe substrates, 2, 12, 22 are first clad layers, 3, 1
3, 23 are active layers 4, 14, 24 are second cladding layers, 5, 6 are crystal interfaces, 31 is a slide member,
32 is a support stand, 34 is a dummy thin plate, 35, 3
6 and 37 are liquid reservoirs, and A is an arrow indicating the sliding direction.

Claims (1)

[Claims] 1 A first clad layer made of Pb _1-x Sn _x Te on a substrate made of PbTe, an active layer made of Pb _1-x Sn _x Te of the same conductivity type with a different composition coefficient x from the first clad layer, and It is characterized by comprising a second clad layer on top of the active layer made of PbTe _1-y Se _y of a conductivity type opposite to that of the active layer, and the lattice constants of the active layer and the second clad layer are made to match. Infrared laser element.