JP2003238287A - Method of manufacturing solid solution single crystal - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To manufacture a solid solution (mixed crystal) single crystal having a long size and a uniform composition with good reproducibility. <P>SOLUTION: The figure of the cross section of a crystal growth vessel 11 in the stage before crystal growth is completed is shown. The melting zone 22 moves toward the direction of a residual raw material 23, that is, upward, with proceeding of transport of InAs to the solid raw material 23 side. The vessel 11 is moved downward (direction of 21) at a speed equal to the moving speed of the melting zone 22 so that the relative position of a crystal growth interface and a heater is always kept at a constant position. The temperature at the crystal growth interface, that is, the InAs concentration is kept constant by keeping the position of the interface by this movement, and an In<SB>0.3</SB>Ga<SB>0.7</SB>As single crystal having a uniform composition is grown. The optimum moving speed for growing the In<SB>0.3</SB>Ga<SB>0.7</SB>As single crystal in an In-Ga-As system is 0.4 to 0.5 mm/h when the temperature gradient is 20°C/cm. <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a method for producing a solid solution (mixed crystal) single crystal having a long and uniform composition with good reproducibility.

[0002]

2. Description of the Related Art When a single crystal of a solid solution (mixed crystal) in which two or more components are mixed at an arbitrary ratio is to be grown, crystal growth is performed while maintaining a uniform composition due to its segregation. It is difficult to realize. As one of the leading methods for producing such a solid solution (mixed crystal) single crystal, only a part of the raw material having a concentration gradient in advance in the direction of crystal growth is melted to form a melting zone to grow the crystal. Accordingly, a method for producing a single crystal by sequentially moving the melting zone has been proposed (JP-A-8-301686, JP-A-2001-72487). The method of forming a melting zone as disclosed in this patent document is called a temperature gradient zone melting method, and in principle, a uniform composition can be obtained.
Actually, there is a problem that in order to obtain a solid solution single crystal having a uniform composition, its control is extremely difficult, and a homogeneous composition solid solution single crystal cannot be stably obtained as a product.

That is, taking the case of In _x Ga _1-x As (0 ≦ X <1) crystal growth as an example, crystals obtained by the temperature gradient zone melting method without movement of raw materials or temperature change of the furnace. In
In the InAs concentration distribution, the equilibrium InAs concentration decreases because the crystal growth interface moves to the high temperature side, and the InAs concentration decreases with crystal growth. Therefore, in order to grow crystals with a uniform composition, the sample must be moved so that the growth interface always has a constant temperature. In this way, when a single crystal is produced by moving the mixed crystal polycrystal to move the mixed crystal polycrystal in order to grow the crystal with a uniform composition, the direction of the movement of the melting zone is set to the direction of the mixed crystal polycrystal production. JP-A-2001-72487 discloses that the direction is from the solidification end side to the solidification start side. However, since the method of setting the exact conditions is not clarified in this known document, it is practically difficult to grow a single crystal of uniform composition with good reproducibility. In particular, there is no specific method for controlling the transition from the first crystal formation portion of a polycrystalline body having a concentration gradient to a single crystal having a uniform composition, and it is possible to obtain a stable single crystal composition with a uniform composition. There was a problem that crystals could not be produced.

Another problem of the prior art is that polycrystallization occurs due to the occurrence of compositional supercooling, which has been an obstacle to smooth single crystallization. When crystal growth occurs, a component having a segregation coefficient smaller than 1 from the growth interface is discharged into the melt zone, and therefore the melt concentration distribution in the melt zone is as follows when convection does not exist in the melt. It is expressed by a formula such as.

Here, the crystallization side interface is represented by A, the interface with the unmelted solid raw material is represented by B, and the axial distance from the interface A to the interface B is represented by Z. C _LA is InA in the melting zone at interface A.
s concentration, C _SA is the InAs concentration in the crystal at the interface A, V is the crystal growth rate, and D is the interdiffusion coefficient between InAs and GaAs. Ideally, a linear solute concentration distribution is formed, but (1)
The formula means that the solute concentration distribution deviates from the linear one in the actual crystal growth. Linear solute concentration distribution
Letting Δ be the difference from the actual solute concentration distribution expressed by equation (1), Δ is expressed by equation (2).

From this equation, it is found that the InAs concentration accompanied by crystal growth shifts to the lower side than the saturation concentration, that is, to the supersaturation. It can be seen that a compositional supercooling region is formed at the center of the melting zone. Further, it is understood that the larger the melting zone width, the larger the depth of supercooling. In such a supercooled region, nucleation may occur due to impurities inevitably contained or the action with the crucible wall, which may cause polycrystallization, and the probability of occurrence is that the degree of supercooling is large. The bigger it gets. In order to obtain a single crystal with good reproducibility, it is necessary to eliminate or minimize the occurrence of this compositional supercooling region.

[0007]

The present invention has been made in view of the above circumstances, and does not provide a method for producing a single crystal capable of stably producing a mixed crystal single crystal having a long and uniform composition with good stability. It is what

[0008]

According to one feature of the present invention, in a method for producing a solid solution single crystal composed of a plurality of components that cause segregation, a solid solution raw material is prepared and the solid solution raw material is charged into a heating furnace. Then, the inside of the heating furnace is adjusted to have a predetermined temperature gradient along the direction from one end of the raw material to the other end, and the region on the one end side having a low melting point is melted to a predetermined temperature gradient direction. The step of forming a melt zone having a width of, and growing the crystal while moving the solid solution raw material to one end side at a predetermined speed specified from the temperature gradient and the physical property value in the heating furnace, wherein the solid solution raw material is The method for producing a solid solution single crystal is characterized in that it has a component ratio such that it exists below a solidus line in a phase diagram of the plurality of components in a region near the other end side of the melting zone. Provided. According to another feature of the present invention, in the method for producing a solid solution single crystal composed of a plurality of components that cause segregation, the component ratio is set so that the melting point increases from one end, which is the starting point of crystal growth, to the other end. Prepare a solid solution raw material adjusted to change, put the solid solution raw material into the heating furnace, so that a predetermined temperature gradient along the direction from one end of the raw material to the other end in the heating furnace Adjust to form a melting zone having a predetermined width in the direction of the temperature gradient by melting the region on the one end side having a low melting point, and the solid solution raw material is heated in a heating furnace at a predetermined temperature specified by a physical property value and a temperature gradient. There is provided a method for producing a solid solution single crystal, which comprises a step of growing a crystal while moving it to one end side at a speed.

Preferably, the moving speed (R) of the solid solution raw material is expressed by the following equation: (Where V is the moving speed of the crystal growth interface, C _S is the concentration of solute in the crystal, C _L is the solute concentration of the liquid phase composition in equilibrium with C _S, and D is the solute and solvent in the liquid phase. The interdiffusion coefficient between them, G is the temperature gradient at the crystal growth interface, and m is the gradient of the liquidus. That is, since the melting zone moves to the high temperature side at a speed proportional to the mutual diffusion coefficient between the solute and the solvent in the liquid phase and the temperature gradient, the solid solution raw material moves at the same speed as the moving speed V in the opposite direction. By doing so, the temperature of the growth interface is always kept constant,
Therefore, a crystal with a constant composition grows.
In the conventional method, the relationship between the moving speed of the interface and the temperature gradient cannot be accurately evaluated in this way, and the control becomes unstable,
The problem is that the stability of the composition of the resulting crystals and the quality of the crystals cannot be guaranteed.

In another preferred embodiment, the composition of the raw material is a component having a lower melting point temperature on the liquidus line than the composition of the liquid phase in equilibrium with the target crystal composition in the raw material region which initially forms the melting zone. And the melting point temperature on the solidus line is higher than the target crystal composition in the unmelted solid phase portion at the boundary portion on the other end side of the melting zone.

Preferably, the width d of the melting zone is not more than the value expressed by the following equation. Where m is the slope of the liquidus line obtained from the equilibrium diagram, C
_S is the concentration in the crystal of the component whose segregation coefficient is less than 1, and C _L is C
_The liquidus concentration is in equilibrium with _S, and G is the temperature gradient at the crystal growth interface. In this case, the composition of the solid solution single crystal is In _x Ga
_{In the case of 1-x} As (0 ≦ X <1), it is desirable that the width d of the melting zone is 25 mm or less.

In the present invention, the temperature distribution in the melting zone is calculated by the following equation, which is obtained from the solute concentration distribution under the diffusion controlled steady state crystal growth. (Here, the crystallization interface is A, the interface with the solid raw material is B, and the interface is
The axial distance from A to interface B is represented by Z. Also, C
_LA is the solute concentration in the melt zone at interface A, C _SA is the solute concentration in the crystal at interface A, V is the migration velocity at the crystal growth interface, and D is the interdiffusion coefficient between the solute and solvent in the liquid phase. . It is preferable to adjust so that the concentration distribution shown by the above) agrees with the saturation concentration (liquidus) to obtain a temperature distribution obtained by back-calculating from the equilibrium diagram.

In this case, the composition of the solid solution single crystal is
In the case of being represented by In _x Ga _1-x As (0 ≦ X <1), the temperature gradient of the melting zone having the temperature distribution of the melting zone is 40 ° C. in the direction from the one end to the other end. /cm
The following is preferable.

As described above, in the present invention, the raw material is moved to the low temperature side at the same speed as the moving speed of the melting zone to the high temperature side so that the temperature at the growth interface is always kept constant to form a single crystal having a uniform composition. In order to obtain a uniform composition growth while preserving high stability by shortening the time until the start of steady growth and limiting the width of the melting zone, by defining the concentration distribution and temperature gradient of the raw material prepared in advance. Giving the conditions for realization. According to the present invention, the solid solution raw material to be prepared may have a component ratio so as to be located below the solidus line in the phase diagram relating to the raw material component. The reason therefor is that the other end side of the melting zone, that is, the melt progressing end side opposite to the seed crystal, has a component composition such that the non-melted state is appropriately maintained. Theoretically, if the component ratios are adjusted so that the melting point increases continuously from one end, which is the starting point of crystal growth, to the other end, which is the end point of crystal formation, the melting zone changes from one end side. It is thought that continuous movement toward the other end will occur smoothly, but in reality,
Rather, it has been found desirable to have a composition that ensures that the solid state is maintained so that the melt edge does not progress too fast. Therefore, as long as this condition can be maintained, even if the component ratio of the solid solution raw material from the one end to the other end is constant, conversely, by adjusting to a component ratio that changes so that the melting point decreases from one end to the other end. Is also good. Also provided is a crystal growth method capable of obtaining a single crystal with good reproducibility by suppressing compositional supercooling by controlling the melting zone width and controlling the temperature distribution of the melting zone.

In the present specification, as a method of keeping the temperature at the growth interface constant, a method of moving the sample while keeping the setting of the furnace constant was described. However, a method of fixing the sample and moving the furnace, Alternatively, it can be applied to a method of moving both the sample and the furnace, and a method of lowering the temperature of the furnace at a constant speed.

[0016]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described in detail below based on embodiments. Here, In _0.3 Ga _0.7 As which is a mixed crystal of InAs and GaAs
The crystal growth will be described as an example. This system has a total solid-solution equilibrium relationship as shown in the phase diagram of FIG. Referring to FIG. 2, there is shown a contact concentration between the seed crystal and the raw material, that is, an axial concentration distribution when a raw material in which the concentration of InAs decreases from one end to the other end with a predetermined tendency is used. . In the case of FIG. 2, a melting zone is formed at the contact point between the seed crystal and the raw material. The temperature at the junction surface between the seed crystal and the raw material is adjusted to a predetermined temperature so that the concentration of InAs in the single crystal becomes the concentration of InAs in the seed crystal. This relationship can be known from the phase diagram of FIG. As described in the above-mentioned known document JP-A-2001-72487, when crystals are grown by a melt crystal growth method using a raw material of a uniform composition composed of a plurality of components accompanied by segregation, many crystals having a predetermined concentration gradient are obtained. Crystals are formed. When a crystal is grown using this polycrystal as a raw material and similarly by the melt crystal growth method starting from the crystal formation termination side of the polycrystal, the crystal having the initial uniform composition is theoretically produced. The present invention basically produces a single crystal having a uniform composition according to this method. That is, as shown in FIG. 2, crystal growth is performed using a raw material and a seed crystal having an InAs concentration gradient line 1 in the axial direction of the raw material, that is, the crystal growth direction.

For this purpose, in the example shown, the temperature in the direction from one end of the raw material (which first melts and comes into contact with the seed crystal and is the starting point for crystal growth) to the other end, that is, in the axial direction. The raw material is heated so that the distribution has a temperature gradient line 2 (about 20 ° C./cm at the crystal growth interface) indicated by the broken line in FIG. The contact area with the seed crystal is heated to 1020 ° C. The saturation concentration of solute (InAs) corresponding to this temperature distribution can be represented by a liquidus line 3 (liquidus) and a solidus line 4 (solidus). The liquidus and solidus lines in FIG. 2 can be obtained from the equilibrium diagram of FIG. In the portion close to the seed crystal in the axial direction of the raw material in FIG. 2, the InAs concentration in the region 5 is higher than the saturation concentration of the melting temperature, so that the region is melted and a molten zone is formed. At this time, the melt tries to reach an equilibrium state in contact with the solid at the two interfaces where the melting zone contacts the solid, that is, the interface between the seed crystal side and the unmelted raw material side. Equilibrium is reached at the interface in a short time, but in order to reach the equilibrium state in the entire melting zone, excess InAs in the melting zone must be transported to the interface by diffusion. InAs-GaAs interdiffusion rate is about 1 × 10 ^-8 m ² / s (K. Kinoshita et al., J. Jpn. Soc. Microgravity A
ppl. vol. 17 (2000) pp.57-63), so depending on the melting zone width, it takes 2-3 hours for the entire melting zone to reach an equilibrium state.

When the equilibrium is reached, the InAs concentration distribution in the melting zone is, as shown in FIG. 3, a concentration gradient approximated by a straight line connecting the compositions of two solid-liquid interfaces (strictly described by equation (1)). Concentration gradient) is formed. It can also be said that InAs at each point in the melting zone is approximately equal to the saturation concentration corresponding to the temperature at that location. Therefore, even after reaching such an equilibrium state, InAs is transported to the unmelted raw material side having a low concentration by diffusion, and sequentially shifts to the equilibrium state near the interface region. In this case, on the seed crystal side, the InAs concentration decreases to below the equilibrium concentration and solidification begins. During solidification, segregation occurs where only a portion of InAs is taken in, so InAs is discharged into the melting zone as crystallization progresses. The discharged InAs is transported to the raw material side by diffusion. In the example shown, In _0.3 G
a _0.7 As crystal is grown, and the InAs concentration is
It is 0.3. When the temperature gradient line 2 as shown in Fig. 2 is given, the InAs concentration decreases by diffusion on the seed crystal side → crystallization → InAs is discharged into the melt in front of the interface due to segregation → the InAs concentration decreases by diffusion. Crystal growth spontaneously proceeds toward the high temperature side (FIG. 3). This crystal growth method is called a temperature gradient zone melting method.

As described above, when the crystal is grown by the temperature gradient zone melting method without the movement of the raw material and the temperature change of the furnace, the InAs concentration distribution in the crystal becomes as shown in FIG. That is, since the crystal growth interface moves to the high temperature side, the equilibrium In
The As concentration decreases and the InAs concentration decreases with crystal growth. Japanese Patent Laid-Open No. 2001-72487 does not teach a specific method for forming a single crystal by the temperature gradient zone melting method using the polycrystalline raw material thus produced.

The first feature of the method of the present invention is the introduction of a moving mechanism for relatively changing the axial position between the raw material position and the heater as the raw material heating source. The sample is moved to the low temperature side in accordance with the moving speed to the temperature, and the temperature of the growth interface, that is, the InAs concentration at the growth interface is kept constant to grow a crystal of uniform composition. This point will be described in more detail below. When diffusion-controlled steady-state crystal growth is established at the growth interface, the melt mass discharged into the melt during crystallization due to segregation is equal to the amount transported to the interface front melt by diffusion. Let V be the moving speed of, then the following relationship holds. Here, C _S is the concentration of solute in the crystal, C _L is the concentration of solute having a liquid phase composition in equilibrium with C _S, and D is the mutual diffusion coefficient between the solute and the solvent in the liquid phase. If we set temperature gradient ∂T / ∂Z = G and gradient of liquidus ∂T / ∂C = m and solve for V, Is obtained. This speed is the moving speed of the growth interface when the diffusion-controlled steady-state crystal growth is established.

The solute concentration C _{S of the} crystal to be grown is 0.3 (InAs is
In the case of 0.3 mol), the solute concentration C _L in the liquid phase in equilibrium with this is determined to be 0.83 from the equilibrium diagram of FIG.
Therefore, the gradient m of the liquidus line is determined to be about 330 ° C / mol. Since D has been found from measurement to be about 1 × 10 ⁻⁸ m ² / s, V is calculated to be 0.4 mm / h when the temperature gradient G = 20 ° C./cm. FIG. 5 shows the analysis result of the solute concentration distribution in the crystal when the sample was moved to the low temperature side according to this speed. Figure 5
In comparison with FIG. 4, which shows the concentration distribution of InAs in the generated single crystal and the concentration distribution of InAs in the single crystal grown without moving the raw material, the concentration distribution in FIG. 5 is almost constant in the crystal growth direction. It can be seen that the composition is uniform. On the other hand, as is clear from FIG. 4, when the crystal is grown without moving the raw material, the crystal growth interface shifts to the high temperature side, so that a concentration distribution occurs in the crystal.
That is, the concentration of InAs is high at the initial stage of crystal growth, and the concentration of InAs tends to decrease toward the end. That is, according to the present invention, by the method of the present invention to control the raw material melting interface temperature to be kept constant while moving the raw material at a predetermined speed that does not prevent the InAs concentration in the melting zone from reaching equilibrium. It can be seen that a single crystal with a long uniform composition is generated and grows. The effect of introducing the raw material moving mechanism of the present invention is remarkable.

The result of FIG. 5 is the composition distribution in the grown crystal in the case where a linear liquidus concentration gradient is formed in the melting zone. In the actual case, the solute concentration in the melting zone is (1) It deviates from linear as shown in the equation. The difference is calculated below. In Equation (1), when Z is small, it is approximated by Tailor expansion. Assuming linear approximation up to a linear expression, in equation (5) terms below quadratic become an error, and error is approximated by a quadratic term.

From the experiment, when the error from the linearity expressed by the equation (6) is within 1%, a single crystal having a uniform composition as shown in FIG. 5 grows. That is, the equation (7) holds for the melting zone width d that gives an error of 1% from the linear shape, and the constraint condition (8) regarding the melting zone width is obtained from the relationship between this and equation (4). That is, this relationship is the relational expression described in claim 3. When the composition of the solid solution single crystal is represented by In _x Ga _1-x As (0 ≦ X <1), the melting zone width d is limited to about 25 mm from the crystal growth experiment results.

Next, another feature of the present invention, that is, formation of a single crystal with good stability will be described. In order to stably grow a single crystal, compositional supercooling should not occur in the melt. For that purpose, it is more advantageous when the temperature distribution is slightly deviated from linear. The reason is that the solute concentration distribution in the melting zone is expressed by an exponential function as in the above equation (1) and deviates from linearity when there is no convection in the melt. As is clear from the phase diagram of FIG.
Solute concentration change is about 0.2 (for example, InAs concentration is 0.8 ~
(Between 0.6), the saturated solute concentration X can be approximated in a form linearly proportional to the temperature T as X = αT + C (α and C are constants). In this case, with respect to the solute concentration distribution represented by the exponential function of the distance Z, the temperature distribution must also be the distribution represented by the same exponential function in order to prevent compositional supercooling.

In the following, the compositional supercooling that occurs when the temperature distribution is linear will be discussed in more detail. Let Δ be the difference between the actual solute concentration distribution expressed by equation (1) and the saturated solute concentration distribution formed under the linear temperature distribution.
It is expressed as in equation (2). FIG. 6 shows the result of calculating this difference as a function of Z using the melting zone width x as a parameter. As shown in FIG. 6, under the linear temperature distribution, the actual InAs concentration deviates to the lower side than the saturation concentration, that is, to the supersaturation, and a compositional supercooling region is formed in the center of the melting zone. You can see that Furthermore, it can be seen from FIG. 6 that the depth of supercooling increases as the melting zone width increases. In such a supercooled region, impurities that are unavoidably contained,
Occurrence of nucleation may occur due to the action with the crucible wall, causing polycrystallization, and the probability of occurrence increases as the degree of supercooling increases. In order to obtain a single crystal with good reproducibility, it is necessary to eliminate or minimize the compositional supercooling region. As discussed above, if the saturation concentration (liquidus composition) depends linearly on the temperature, the saturation concentration distribution corresponding to Eq. (1) is given, and the temperature distribution that does not cause compositional supercooling in the melt is , Similar to solute concentration distribution Must be represented by. Where C ₁ and
C ₂ is a constant. In the equation (9), since the diffusion coefficient D is a value peculiar to the substance, the target temperature distribution can be specifically determined by selecting a certain value with the crystal growth rate V as a parameter.

Crystal production apparatus A case of growing a crystal of In _0.3 Ga _0.7 As will be described.
FIG. 7 shows a schematic configuration of a single crystal manufacturing apparatus 6 to which the manufacturing method of the present invention can be applied.

Referring to FIG. 7, the apparatus 6 for producing a single crystal according to the embodiment of the present invention is a heating apparatus 7 for melting raw materials.
Is equipped with. The heating device 7 has a donut shape,
A raw material container 11 as shown in FIG. 8 in which the raw material is loaded is arranged in the hollow portion along the direction of the center line, that is, the axial direction. The raw material container has a cylindrical shape.
In _x Ga _1-x As is loaded. The raw material container 11 is attached to the tip of a support rod 8 extending in the axial direction, and the base end side of the support rod 8 has a drive mechanism 9 using a step motor as a power source and is formed on the support rod. It receives power from a rack and pinion that meshes with the groove. As a result, the raw material container 11 attached to the tip of the support rod 8 can move in the donut-shaped space of the heating device 7 relative to the heating device 7 at a speed controlled in the axial direction. The moving speed of the raw material container 11 in the heating device space is controlled to a predetermined speed by the control mechanism 10. The control mechanism 10 can set the speed of the raw material container with respect to the heating device 7 by inputting the speed. However, the speed is controlled according to a program by incorporating a microprocessor so that the speed becomes a predetermined speed. You can also do it. As shown in the figure, the heating device 7 of the crystal production apparatus shown in FIG.
It is divided into a, 7b, and 7c, and the temperature can be controlled independently of each other. In this example, the temperature of each heater is controlled so that the temperature increases from the inlet side of the raw material container toward the advancing direction of the raw material container.

FIG. 8 shows a cross-sectional view of a raw material container, that is, a crystal growth container in the subsequent process step.

Crystal growth container, ie, raw material container 11
Is composed of a crucible 12 made of boron nitride, a heat sink 13 that promotes single crystallization, and a quartz container 14 that serves as a vacuum enclosure outside these. In the crucible 12 made of boron nitride, the seed crystal 15, InAs 16 and the raw material 17 prepared by unidirectional solidification in advance are inserted. In this device, the constants C ₁ and C _{2 in the} equation (9) are
A specific example of the determination of is shown below.

When a temperature gradient of 20 ° C./cm is applied at the crystal growth interface and the crystal is grown at a crystal growth rate of 0.4 mm / h, a crystal of In _0.3 Ga _0.7 As of uniform composition can be obtained.
Since the solidus temperature for the In _{0. 3} Ga _0.7 As composition is at 1020 ° C., from the crystal growth interface (Z = 0) (9) wherein Is obtained. Assuming that the temperature gradient of 20 ° C / cm remains unchanged up to about 20 mm from the growth interface, 1070
Since the diffusion coefficient at ℃ is required to be about 1 × 10 ^-8 m ² / s (K. Kinoshita et al., J. Jpn. Soc. Microgravity A
ppl. vol. 17 (2000) pp. 57-63.), Z = 20 m in equation (9)
Substituting m, V = 0.4 mm / h, D = 1 × 10 ^-8 m ² / s,

From equations (10) and (11), C ₁ = 1220, C ₂ = 200
Is required. By substituting this into Eq. (9) again, the temperature distribution to be set can be obtained. When the distribution is illustrated, it becomes a curve as shown in FIG.

Crystal Growth Crystal growth was performed as follows. Purity of 99.999 each
After using 9% of In, Ga, and As to make a composition of In _0.3 Ga _0.7 As, it was vacuum-sealed in a quartz tube. The quartz tube was heated to about 1200 ° C in an electric furnace and heated to In _0.3 Ga _0.7 As.
After the melt having the composition was prepared, the quartz tube was taken out of the electric furnace, immersed in water and rapidly cooled to synthesize a polycrystal of In _0.3 Ga _0.7 As composition. Then, the polycrystalline body was vacuum-sealed in another quartz tube again, and a temperature gradient of about 40 ° C./cm was formed by heating the high temperature portion to about 1200 ° C. and the low temperature portion to about 800 ° C. in a temperature gradient furnace. Utilized to unidirectionally solidify at a solidification rate of about 1 mm / h. The InAs concentration distribution in the obtained crystal is approximately
At 0.06 mol, the distribution was such that the InAs concentration increased toward the other end of the crystal.

Next, the crystal raw material having the above-mentioned concentration gradient produced as described above was used as a part of the raw material in the subsequent step, and it was vacuum sealed in a crystal growth container together with separately prepared InAs and seed crystals. A repaired crystal was grown. In this case, the raw material 17 is obtained by cutting out a part of the crystal raw material produced by directional solidification, and the InAs concentration in the raw material 17 decreases from the end face 18 on one end side to the other end face 19. The end face 18 with the higher InAs concentration is the seed crystal 15 or the InAs in the melting zone.
It is arranged so as to contact with 16.

That is, InAs of the crystal raw material generated above
The side where the concentration is high, that is, the terminal side of crystal growth is located at one end side, that is, the side that contacts the seed crystal, and is arranged in the raw material container 11. FIG. 10 shows the InAs concentration distribution in the axial direction of the seed crystal and the raw material placed in the crystal container.

The temperature distribution inside the electric furnace (heating device) is adjusted and heated so that the temperature distribution shown by the curve in FIG. 9 is produced in the region of the melting zone, and after forming the melting zone, the equilibrium state is reached. After holding for a certain period of time, AsAs and GaAs
Due to the mutual diffusion of InAs, InAs on the solid material side at the rear end of the melting zone
Since it is transported to the low concentration part,
The InAs concentration gradually decreases, and as shown in FIG. 11, the single crystal 20 of In _0.3 Ga _0.7 As composition, which inherits the orientation of the seed crystal 15, grows. FIG. 11 shows a cross-sectional view of the crystal growth container 11 in the middle stage of crystal growth. InAs solid raw material 2
As the transportation to the 3 side progresses, the melting zone 22 becomes the remaining raw material 2
Since it moves in the direction 3 (upward in FIG. 11), the container is moved downward (direction 21) at the same speed to keep the relative position of the crystal growth interface and the heater at a constant position. By keeping the interface position by this movement, the temperature at the crystal growth interface, that is, the InAs concentration is kept constant, and an In _0.3 Ga _0.7 As single crystal with a uniform composition grows. In the case of producing In _0.3 Ga _0.7 As single crystals in the In, Ga, As systems, the optimum moving speed was 0.4 to 0.5 mm / h with respect to the temperature gradient of 20 ° C./cm as described above.

The crystal obtained by the above method is a single crystal over the entire region, and its axial InAs concentration distribution is shown in FIG.
It was as shown in 2. From this figure, it can be seen that the InAs mole fraction is close to the target composition of 0.3 from the early stage of crystal growth, and the constant composition is maintained over almost the entire area of the grown crystal.

The optimum temperature distribution during the crystal growth of the raw material including the melting zone when the temperature gradient at the crystal growth interface is set to 40 ° C./cm is shown in the curve of FIG.
In this case, the asymptotic temperature is 1236 ° C, which is the melting point temperature of GaAs 12
It is almost equal to 38 ℃. If the asymptotic temperature higher than this is set, even if a concentration gradient is given to the raw material, even the GaAs portion having the highest melting point is melted and it is impossible to form a melting zone. Therefore, when growing a crystal of In _0.3 Ga _0.7 As, the temperature gradient is limited to about 40 ° C./cm.

In the description of the above-mentioned embodiments, the solid solution (mixed crystal) of InAs and GaAs of the IIIV group compound semiconductor is taken as an example, but the method of the present invention is not limited to the above substances, but Si and Ge may be used. Solid solution single crystals of various elements or Cd of IIVI group compound semiconductors
It is obvious to those skilled in the art that the present invention can be applied to the production of a solid solution single crystal of Te-HgTe or a PbTe-SnTe solid solution single crystal of a group IVVI compound semiconductor.

[0039]

As described above, according to the method of the present invention, the sample is moved to the low temperature side at a speed substantially the same as the moving speed of the melting zone to the high temperature side due to diffusion, and the temperature at the growth interface is increased. The crystal length having a uniform composition can be greatly increased because the value is always kept constant. Further, according to the method of the present invention, the solute concentration in the melting zone is controlled so as to match the saturation concentration in the equilibrium diagram at any point, so that a supersaturated portion is substantially generated in the melting zone. Crystal growth proceeds in the absence of the crystal. Therefore, in the melting zone, it is possible to effectively prevent nucleation that occurs due to supersaturation, and to produce a single crystal with good reproducibility. Therefore, the present invention can effectively solve the conventional problems, can effectively increase the length of a single crystal having a uniform composition, and can reproducibly produce such a solid solution (mixed crystal) having a uniform composition of a long single crystal. It is possible.

The method of the present invention is not limited to a specific material and can be widely applied to the production of single crystals of general solid solutions. In particular, solid solutions of compound semiconductors such as InAs-GaAs and PbTe-SnTe are laser-processed. This is a promising application field of the present invention because high quality and uniform composition are required as a substrate for producing a diode.

[Brief description of drawings]

Fig. 1 InAs-GaAs pseudo binary system phase diagram,

FIG. 2 is a conceptual diagram showing the composition distribution and the like in the heating stage in the initial stage of crystal growth

FIG. 3 is a conceptual diagram showing a state in which the InAs concentration in the melting zone becomes a saturation concentration, the melting zone moves, and crystal growth proceeds.

FIG. 4 is a graph showing the InAs concentration distribution in the growth axis direction of an In _1-x Ga _x As mixed crystal produced by the temperature gradient zone melting method,

FIG. 5: InAs concentration distribution in the growth axis direction of the In _1-x Ga _x As mixed crystal produced by the method of the present invention,

FIG. 6 is a graph showing the degree of deviation of the InAs concentration in the melting zone from the saturation concentration,

FIG. 7 is a schematic configuration diagram of a crystal manufacturing apparatus according to one embodiment of the present invention,

FIG. 8 is a cross-sectional view of the crystal growth container used in the first embodiment of the method for producing a solid solution single crystal of the present invention,

FIG. 9 is a graph showing the distribution of the applied temperature to the sample during crystal growth in the method for producing a single crystal according to the first embodiment of the present invention,

FIG. 10 is a graph showing an axial InAs concentration distribution before the growth of a crystal growth sample,

FIG. 11 is a cross-sectional view of a container for crystal growth at an intermediate stage of crystal growth in the method for producing a solid solution single crystal of the present invention,

FIG. 12 is a graph showing the InAs concentration distribution along the growth axis direction of the single crystal grown according to the first embodiment of the present invention,

FIG. 13 is a graph showing a distribution of applied temperature to a sample during crystal growth in the single crystal manufacturing method according to the second embodiment of the present invention.

[Explanation of symbols]

1 Unmelted solid solution InAs concentration curve 2 temperature gradient line 3 liquidus 4 Solidus 5 melting zone 6 Crystal production equipment 7 heating device 8 support rods 9 Drive mechanism 10 Control mechanism 11 crystal growth container, 12 crucibles, 13 heat sink 14 Quartz container 15 seed crystals 16 InAs 17 Raw material 18 End face with high InAs concentration of raw material 19 End face with low InAs concentration of raw material 20 grown single crystal 21 Container movement direction 22 Melting zone 23 Remaining solid ingredients

   ─────────────────────────────────────────────────── ─── Continued front page    (72) Inventor Shinichi Yoda             2-1-1 Sengen Space, Tsukuba City, Ibaraki Prefecture             Development Agency Space Environment Utilization System Division             Space environment utilization research system (72) Inventor Yasuhiro Hanagami             2-1-1 Sengen Space, Tsukuba City, Ibaraki Prefecture             Development Agency Space Environment Utilization System Division             Space Environment Utilization Research Center (72) Inventor Hirohiko Nakamura             2-1-1 Sengen Space, Tsukuba City, Ibaraki Prefecture             Development Agency Space Environment Utilization System Division             Space Environment Utilization Research Center (72) Inventor Yasuyuki Ogata             2-1-1 Sengen Space, Tsukuba City, Ibaraki Prefecture             Development Agency Space Environment Utilization System Division             Space Environment Utilization Research Center F-term (reference) 4G077 AA02 BE47 CE03 EA02 EH10                       HA12 NA05 NF11

Claims (8)

[Claims] 1. A method for producing a solid solution single crystal composed of a plurality of components which causes segregation, wherein a solid solution raw material is prepared, the solid solution raw material is charged into a heating furnace, and the inside of the heating furnace is changed from one end to the other end of the raw material. The temperature is adjusted so as to have a predetermined temperature gradient along the direction, the region on the one end side having a low melting point is melted to form a melting zone having a predetermined width in the direction of the temperature gradient, and the solid solution raw material is heated in a furnace. It comprises a step of growing a crystal while moving to one end side at a predetermined speed specified from a temperature gradient and a physical property value in the solid solution raw material, in the vicinity of the other end side of the melting zone. A method for producing a solid solution single crystal, which has a component ratio such that it exists below the solidus in the phase diagram of the components. 2. A method for producing a solid solution single crystal composed of a plurality of components causing segregation, wherein the component ratio is adjusted so that the melting point increases from one end, which is the starting point of crystal growth, to the other end. Prepared solid solution raw material, charging the solid solution raw material into a heating furnace, adjusting the inside of the heating furnace so as to have a predetermined temperature gradient along a direction from one end of the raw material to the other end, A region on one end side is melted to form a molten zone having a predetermined width in the direction of the temperature gradient, and the solid solution raw material is moved to the one end side in the heating furnace at a predetermined speed specified from the temperature gradient and the physical property value. A method for producing a solid solution single crystal, which comprises the step of growing a crystal. 3. The moving speed (R) of the solid solution raw material is expressed by the following equation: (Where V is the moving speed of the crystal growth interface, C _S is the concentration of solute in the crystal, C _L is the solute concentration of the liquid phase composition in equilibrium with C _S, and D is the solute and solvent in the liquid phase. Inter-diffusion coefficient between them, G is a temperature gradient at the crystal growth interface, and m is a gradient of a liquidus line.) The solid solution single substance according to claim 1 or 2, characterized in that: Crystal manufacturing method. 4. The composition of the raw material contains a component whose melting point temperature on the liquidus line is lower than the composition of the liquid phase in equilibrium with the target crystal composition in the raw material region which initially forms the melting zone, 4. The melting point temperature on the solidus line is higher than the target crystal composition in the unmelted solid phase portion at the boundary portion on the other end side of the melting zone. The method for producing a solid solution single crystal according to 1. 5. The width d of the melting zone is expressed by the following formula: (Where m is the gradient of the liquidus line obtained from the equilibrium diagram, C _S is the concentration of solute in the crystal, C _L is the solute concentration of the liquid phase composition in equilibrium with C _S, and G is the crystal growth interface. The temperature is less than or equal to the value represented by the temperature gradient in 1.), The method for producing a solid solution single crystal according to any one of claims 1 to 4, wherein. 6. The composition of the solid solution single crystal is In _x Ga _1-x As (0 ≦
X <1) and the width d of the melting zone is 2
It is 5 mm or less, The manufacturing method of the solid solution single crystal as described in any one of Claim 1 thru | or 5 characterized by the above-mentioned. 7. The temperature distribution in the melting zone is calculated from the solute concentration distribution under the diffusion-controlled steady-state crystal growth. (Here, the crystallization interface is A, the interface with the solid raw material is B, and the interface is
The axial distance from A to interface B is represented by Z. Also, C
_LA is the solute concentration in the melt zone at interface A, C _SA is the solute concentration in the crystal at interface A, V is the migration velocity at the crystal growth interface, and D is the interdiffusion coefficient between the solute and solvent in the liquid phase. . 7. The temperature distribution obtained by performing back calculation from the equilibrium diagram on the assumption that the concentration distribution indicated by () matches the saturation concentration (Liquidus), is adjusted. Method for producing solid solution single crystal. 8. The composition of the solid solution single crystal is In _x Ga _1-x As (0 ≦
When represented by X <1), the temperature gradient of the melting zone having the temperature distribution of the melting zone is 40 ° C./cm or less in the direction from the one end to the other end. The method for producing a solid solution single crystal according to any one of claims 1 to 7.