JPS5841676B2 - Manufacturing method of semiconductor laser device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for manufacturing a double heterostructure crystal necessary for forming a semiconductor laser device.

In general, multicomponent semiconductors containing lead have a narrow energy gap and are widely used as materials for infrared laser elements and 61 infrared photoelectric conversion elements.

When forming such an infrared laser element, as shown in FIG. 1, a first crystal layer 2, a second crystal layer 3, and a third crystal layer 4 having different crystal compositions are formed on a multi-component semiconductor substrate 1 containing lead. The formed heterostructure is taken, and these crystal layers are called a buffer layer, an active layer, and a top layer, respectively.

To explain the operation of a laser device having such a structure, when electrons are injected into the P-N junction plane 5 formed in the second crystal layer 3, that is, the active layer in FIG. and recombine to generate photons.

This photon and the injected carriers are described above as the heterointerface 6 between the first crystal layer 2, that is, the buffer layer and the active layer 3, and the active layer 3.
The third crystal layer 4, ie, the top layer, is confined by the hetero interface 7 between them, increasing the efficiency of converting electrical energy into light, resulting in the effect of lowering the threshold current density for starting laser oscillation.

As a method for forming such a heterojunction interface, a heterogeneous multicomponent semiconductor to be grown on a multicomponent semiconductor substrate, for example, a lead-tellurium (PbTe) substrate, such as a lead-tin-tellurium (PbTe) substrate, is used.
A liquid phase epitaxial growth method is generally used in which the temperature of a crystalline melt of Pb, -xSnxTe is lowered and the melt is solidified to form a crystal growth layer on the substrate.

In order to make the oscillation wavelength of the laser element formed here longer than 10 μm, it is necessary to
A crystal layer with an X value of 0.05 to 0.18 expressed as a component ratio of bl-xsnxTe is formed as a buffer layer, and a Pb1 layer with an X value of 0.20 to 0.30 is formed thereon.
- It has been found that xSnxTe crystals must be formed as the active layer.

Using conventional liquid phase epitaxial growth method, X is 0.05~
When forming as an active layer a crystal layer of Pb, -xsnxTe, in which the value of After forming the above-mentioned buffer layer on top, a semiconductor melt having the above-mentioned composition, which will become an active layer, is brought into contact with the buffer layer at a temperature of about 600°C, and then the temperature of the heating furnace is increased to about 600°C. It was formed by lowering the temperature from C at a rate of 1° C./min for 2 to 3 minutes.

However, in order to make the oscillation wavelength of the laser element a long wavelength of 10 μm or more, P bl- where X is 0.05 to 018
A crystal layer having a composition of xSnxTe is used as a buffer layer, and Pb1 with an X value of 0.20 to 0.30 is formed on the buffer layer.
- When forming a crystal layer having a composition of xSnxTe as an active layer, it was found that under the above-mentioned conventional formation conditions, unevenness occurred at the interface between the buffer layer 11 and the active layer 12, as shown in FIG. did.

If a crystalline material with such unevenness at the interface between the buffer layer and the active layer is used in a laser device, the threshold current at which the laser device starts oscillating increases, which impairs the reliability of the device. will occur.

The reason why the above-mentioned unevenness occurs at the interface between the buffer layer and the active layer will be explained with reference to FIG.

Figure 3 shows lead (Pb), tin (Sn), and tellurium (Te).
This is a phase diagram of a crystalline material represented by the composition Pb, -xsnxTe, where the vertices A, B, and C of the equilateral triangle are Te.

Pb;Sn indicates a state of 100%.

Here, the side 21 connecting A and B indicates the case where the crystal material of Pb1-X5nXTe is formed from pb and Te, and B.

A side 22 connecting C and A is formed of Pb and Sn, and a side 23 connecting C and A is formed of Sn and Te.

A line segment 24 connecting D and E is P bl-x generated from the melt.
It represents the composition of snxTe crystal, and regardless of the value of
The value of e is constant (50% in atomic ratio), and kf46 of all solidified Pb1-xSnxTe crystals lies on this line.

Curves 25 and 26 are the solidus lines of crystals with compositions of Pb and -xSnxTe with X values of 0.15 and 0.20, respectively, and when the above crystals are solidified from the melt, the temperature of the liquid phase changes. The locus of the point at which the same silk precipitate crystals are precipitated depending on the case is shown.

Here, a Pb, -xsnxTe crystal having a composition with an X value of 0.15 is formed as a buffer layer on a PbTe substrate using a conventional liquid phase epitaxial method. and becomes the active layer P b, -
- Based on the above phase diagram, when the active layer is formed by contacting the melt of the xsnxTe crystal material overnight at 600°C and then lowering the temperature of the heating furnace at a rate of 1°C/1 minute. explain.

In this case, at a temperature of 600'C (1), a material with a composition in which solid and liquid phases are in equilibrium and X is 0.20 has a solidus line of 26 at x = 0.20 and a liquidus line at 27 is a melt or molten metal having an introduction F & at the intersection with
A material having a composition where X is 0.15 is a melt having a composition G at the intersection of the solidus line 25 where X is 0.15 and the liquidus line 27 at 600'C.

The melt having the composition at point G is cooled and follows the locus of the solidus line 25, and the melt having the composition at point F is cooled onto the solid phase buffer layer, which has the composition at point 41, following the solidus line 25. Following the locus of 26, an active layer of the same phase with the composition of point 2 is precipitated.

When the active layer is formed by bringing the melt of the active layer material into contact with the solidified buffer layer, a part of the solid phase buffer layer also melts to some extent, and the buffer layer and the melt of the active layer forming material melt. Some amount of atomic movement occurs between the two.

The greater the movement of atoms, the more uneven the interface between the buffer layer and the active layer formed thereon.

As in this example, the solidus line 26 of the Pb1-xSnxTe active layer forming material with x=0.20 is largely curved to the right, and the active layer forming material at the liquidus line 27 of 600'C The distance between the composition F of the melt and the composition G of the buffer layer is large, and therefore the difference in composition between the two materials is large.

Therefore, the movement of atoms between the two increases,
Irregularities occur at the interface between the formed buffer layer and active layer.

Although not illustrated in this figure, P b where x>0.20
Since the solidus lines of l-xSnxTe are all curved to the right, the result is the same as when x = 2.0.

Therefore, in order to eliminate the unevenness at the interface between the buffer layer and the active layer crystals formed in this way, when crystals are precipitated from the melt of the active layer material, the melt is supercooled to grow the crystals as quickly as possible. Therefore, it is necessary to reduce the time in which the solid-liquid interface is in a non-equilibrium state.

The present invention has been made in view of the above-mentioned points, and the present invention has been made in view of the above-mentioned points.
When a plurality of multicomponent semiconductor crystal layers made of lead, tin, and tellurium having a component ratio of
．． 0.05 to 0.18 is formed.

Thereafter, when forming a second crystal layer having an X value of 0.20 to 0.30 on the first crystal layer,
The temperature of the liquid phase of the crystal material for forming the crystal layer is once lowered from the temperature at the time of forming the first crystal layer to a supercooled state within a range where the liquid phase does not solidify.

It is an object of the present invention to provide a novel method for manufacturing a semiconductor laser device, characterized in that a second crystal layer is formed by subsequent crystal growth.

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

As shown in FIG. 4, a melt 3 of PbO0g5Sn□, 15Te is used to form the first crystal layer that will become a buffer layer.
1, P bo,'ys Sno, 2□T for forming the second crystal layer which becomes the active layer.
a carbon slider 37 having a second reservoir 34 for storing a melt 33 of e, and a third reservoir 36 for storing a melt 35 of P bo, s S no, 2 Te for forming the top layer; , a recess 3 having a dummy substrate 38 to be described later.
A liquid phase epitaxial growth jig consisting of a carbon boat 42 having a recess 41 for accommodating a laser element substrate 40 made of PbTe and PbTe is placed in a quartz tube 43 in a hydrogen gas atmosphere, and heated to approximately 600°C in a heating furnace 44. Heat to temperature.

After this process, the apparatus diagram shown in FIG. 4 and the temperature history during liquid phase epitaxial growth will be explained using FIG. 5.

Here, FIG. 5 is a diagram showing the relationship between the furnace temperature in the epitaxial growth process according to the present invention and the time during which the carbon jig is left at that furnace temperature, where the vertical axis represents the furnace temperature and the horizontal axis represents the furnace temperature. Indicates the amount of time left unattended.

As mentioned above, when the temperature inside the furnace rises to 612 DEG C. as shown at point a, the temperature inside the furnace is kept constant for about 30 to 40 minutes from that point on.

After that, move the slider in FIG. 4 in the direction of the arrow to move the first liquid reservoir 31 onto the dummy substrate 38 to slightly increase the temperature as shown at point b in FIG. Keep the temperature constant for about 35 minutes from point C to point C.

In this way, when the carbon jig is slid, a crystal layer with an unstable composition that is first deposited from the melt is deposited on the dummy substrate.

Thereafter, as shown in FIG. 4, the carbon slider is moved to bring the first liquid reservoir 31 onto the laser element substrate 40.

At this time, the second liquid reservoir 34 is on the dummy substrate 38.

At the end of this movement, as shown in Figure 5, the temperature inside the furnace was raised from 614°C at point C to 622°C at point d, and then kept at a constant temperature for about 20 minutes until point e. The melt of the crystal material forming the buffer layer and the laser element substrate are blended together.

Next, the substrate and melt are slowly cooled at a rate of 0.2° C./min to lower the temperature in the furnace from 622° C. at point e to 607° C. at point f.

The slow cooling time during this period is about 1 hour and 10 minutes.

Furthermore, the temperature inside the furnace was increased from 607°C at point f to 600°C at point g.
The melt forming the laser element substrate and the crystal layer is rapidly cooled at a cooling rate of about 3° C./min.

At this stage of rapid cooling, a crystal layer that will become a buffer layer is deposited and formed on the laser element substrate, and at this time the dummy substrate 38
The overlying melt 33 forming the active layer is maintained in a supercooled state on the verge of solidification.

At point g of 600° C., the slider is moved to move the supercooled melt forming the active layer on the verge of solidification onto the laser element substrate on which the crystal layer of the buffer layer is formed.

At the end of this movement, an active layer is formed on the buffer layer, and for the reason mentioned above, no unevenness occurs at the interface between the two crystal layers.

Next, the temperature inside the furnace is lowered from point g of 600°C to point h of 595°C in Figure 5 at a rate of 1°C/min so that the active layer grows on the buffer layer at an optimal rate. .

This growth time is very short, about 2 to 3 minutes.

Next, as shown in Fig. 4, move the slider to move the melt 35 of the crystal material for forming the top layer on the substrate from point h of 595°C to point 2 of 590°C in Fig. 5. 1
The temperature of the heating furnace is lowered at a temperature gradient of 8C/1 minute to form a top crystal layer on the laser element substrate on which the buffer layer and active layer have been formed.

When a heterojunction of laser element materials is formed by the method according to the present invention as described above, the crystals of the active layer formed on the buffer layer are formed by rapid cooling from the liquid phase, so crystal growth from the liquid phase is possible. The time period in which the solid-liquid interface is in a non-equilibrium state during this process is shortened, and therefore the unevenness phenomenon of the crystal interface is eliminated, and a smooth crystal interface is obtained.

Note that the method of the present invention can also be applied to the case of forming a top layer crystal layer other than the active layer.

If such a crystal material is used as a laser element, the threshold current value for starting oscillation is reduced, and there is an advantage that a laser element with high power efficiency and high reliability can be obtained.

[Brief explanation of the drawing]

Figure 1 is a diagram explaining the structure of a laser element, Figure 2 is a diagram showing the crystal interface of a conventional laser element, Figure 3 is a diagram of the state of materials during the formation of the laser element, and Figure 4 is a diagram of the book. FIG. 5 is a cross-sectional view showing the structure of an example of an apparatus for carrying out liquid phase epitaxial growth using the method of the invention, and FIG. 5 is a diagram showing the relationship between temperature and heating time of a heating furnace for carrying out the method of the invention. be. 1: Multidimensional semiconductor substrate, 2: Buffer layer, 3: Active layer, 4
Nidotsubu layer, 5: P-N junction surface, 6: hetero interface, 7:
Hetero interface, 11: buffer layer, 12: active layer, 21:
Line segment composed of two components pb and Te, 22: pb and S
A line segment composed of two components of n, 'l 3: Te and S
A line segment composed of two components of n, 24:PbTe(!:
Line segment composed of 5nTe, 25: Liquid phase of x-=0.15, line, 26: Liquidus line of X20.20, 31: Melt of buffer layer forming material, 32: Liquid reservoir, 33 : Melt of active layer forming material, 34: Liquid reservoir, 35 Melt of Nidotsubu layer forming material, 36: Liquid reservoir, 37: Carbon slider, 38: Dummy substrate, 39: Recess, 4Q: PbTe substrate, 41:
Recess, 42: carbon port, 43: quartz tube, 44: heating furnace, A: 100% Te state, B: 100% Pb state, C: 80100% state, D: 50% Pb and Te5
0% state, E:5n50% and Te50% state, F:
Intersection of solidus and liquidus at x=0.20, G: x=0.1
Intersection of the solidus line and liquidus line in 5, H: composition when the melt with the composition at point 0 solidifies and 6-, ■: composition when the melt with the composition at point F solidifies, a, b, c z cle, f ,
g, h, ni: Furnace temperature.

Claims (1)

[Claims] 1. When a multi-component semiconductor crystal layer having a composition represented by Pb1-xsnxTe is formed on a multi-component semiconductor substrate containing lead as a semiconductor laser element material by liquid phase epitaxial growth, a layer of 0.05 to 0.0.
Form a first crystalline layer with an X value of up to 18, while 0.
Temperature of a liquid phase containing a crystal material for forming a second crystal layer having an 1. A method of manufacturing a semiconductor laser device, which comprises bringing the liquid phase into a supercooled state and then bringing the liquid phase into contact with a first crystal layer to form a second crystal layer.