JP4549111B2 - GaAs polycrystal production furnace - Google Patents

Description

The present invention relates to a furnace for producing a GaAs polycrystal used as a raw material for growing a GaAs single crystal.

  GaAs is a substance that does not exist in nature. In order to obtain a single crystal of GaAs, it is necessary to synthesize GaAs from raw materials Ga and As and to grow a single crystal from a GaAs melt. is there. And the method of manufacturing a single crystal through these two steps is roughly divided into the following two.

  One is a method in which a GaAs synthesis process and a single crystal growth process are performed separately. In this method, GaAs is synthesized from Ga and As by a synthesis apparatus, and first, GaAs polycrystal is obtained. Thereafter, the GaAs polycrystal is filled into a crucible for single crystal growth, and a single crystal is grown from a GaAs melt by a single crystal growth apparatus. Since the GaAs synthesis process and the single crystal growth process are independent, it is also called a two-step method. The other is a method in which the synthesis of GaAs and the growth of a single crystal are performed as a series of steps in a single apparatus. This method is also called a direct synthesis method.

  However, during GaAs synthesis, the crucible must be sealed or high pressure around 6 MPa to prevent As sublimation, and temperature control conditions and volume changes differ between GaAs synthesis and single crystal growth. Therefore, the direct synthesis method in which the GaAs synthesis and the single crystal growth are continuously performed is often difficult, and the two-step method is often adopted in the GaAs single crystal growth. Among various GaAs single crystal growth methods, the LEC method and the HB method are relatively easy to realize a direct synthesis method and have been put to practical use. A single crystal is grown by placing a seed crystal at the bottom of the crucible. In the VB method and VGF method, in the direct synthesis method, it is cumbersome to prevent the dissolution of the seed crystal during GaAs synthesis, and the shape of the crucible itself provided with the seed crystal holding portion is also complicated, so that the direct synthesis is performed. When the method is carried out, the average density of Ga melt and As solid is larger than the density of GaAs solid, which causes a problem of crucible breakage. Therefore, especially when single crystal growth is performed by the VB method or the VGF method, the two-step method is the mainstream.

  Here, regarding a method for producing GaAs polycrystal, Japanese Patent Application Laid-Open No. 59-111923 discloses a method of synthesizing GaAs by blowing gas As into molten liquid Ga. Japanese Patent Laid-Open No. 3-275517 discloses a method for obtaining a GaAs polycrystal by dropping Ga droplets in an As atmosphere.

JP 59-111923 A JP-A-3-275517

  When manufacturing a GaAs polycrystal, the synthesized GaAs can be solidified using the HB method, the LEC method, the VB method, the VGF method, or the like. However, the HB method cannot produce a cylindrical GaAs polycrystal. In the two-step method, when a GaAs polycrystal prepared in advance is used as a raw material and single crystal growth is performed by the VB method or the VGF method, the GaAs polycrystal put in the crucible enters the cylindrical crucible without any gaps. Such a cylindrical shape is desirable. By placing the cylindrical GaAs polycrystal in the crucible without any gap, the raw material filling rate can be increased and a longer single crystal can be manufactured, so that the manufacturing efficiency is improved.

  However, since the cylindrical GaAs polycrystal cannot be obtained by the HB method, when a single crystal growth is performed by the VB method or the VGF method, a large sized GaAs polycrystal is shaved to fit into a crucible. Work to shape is required. For this reason, when a GaAs polycrystal is manufactured by the HB method, the entire synthesized GaAs polycrystal cannot be used as a raw material for single crystal growth, resulting in a raw material loss. In addition, extra work such as cutting GaAs polycrystals is required. Furthermore, when the GaAs polycrystal is crushed to charge the granular GaAs polycrystal in the crucible in order to reduce the raw material loss, the filling rate is deteriorated.

  On the other hand, the LEC method can obtain a generally cylindrical GaAs polycrystal, but it is still difficult to produce a clean columnar GaAs polycrystal that can be put in a crucible without any gaps. When manufacturing GaAs polycrystals by the LEC method, it is necessary to cut the large GaAs polycrystals into a cylindrical shape that fits into the crucible. Extra work such as shaving is also required. In addition, since the LEC method requires a crystal pulling drive mechanism, the manufacturing furnace itself tends to be expensive, which is disadvantageous in terms of cost.

  On the other hand, according to the VB method and the VGF method, by selecting the shape and size of the crucible, a cylindrical GaAs polycrystal that can be put into a crucible for growing a single crystal without any gap is manufactured. This reduces the material loss and eliminates the need for cutting GaAs polycrystals. In this case, it is conceivable to produce a GaAs polycrystal by using a crucible for single crystal growth by the VB method or the VGF method as it is. However, as described above, this causes a problem such as crucible breakage. In addition, it is considerably difficult to solidify GaAs synthesized in a crucible without using a seed crystal. For example, if GaAs synthesized in the crucible is solidified from the upper part of the crucible, the solidified GaAs will block the upper part of the crucible. Then, since the GaAs melt expands in volume when solidified, the solidification of GaAs in the crucible progresses toward the bottom with the top closed, so that the pressure of GaAs in the crucible accompanying volume expansion There is a concern that the crucible will be damaged. In addition, when trying to solidify the GaAs synthesized in the crucible from the bottom of the crucible, the temperature at the bottom of the crucible is usually non-uniform. GaAs polycrystal grows. Thus, the volume-expanded GaAs polycrystal has a specific gravity smaller than that of the GaAs melt, so that the difference in specific gravity causes the GaAs polycrystal to float up and eventually the solidified GaAs closes the top of the crucible. It will cause problems.

Accordingly, an object of the present invention, the synthesized GaAs in a crucible from the bottom of the crucible, without to float, to provide a synthesis furnace of GaAs polycrystal can go solidified toward the top.

  In order to achieve this goal, according to the present invention, there is provided a method for producing a GaAs polycrystal, in which Ga, As and a sealing material are placed in a substantially cylindrical crucible, and the upper part is sealed in the crucible. It is characterized in that after melting Ga and As and synthesizing GaAs in a state sealed with a material, the melted GaAs is solidified upward from below the crucible while maintaining the soaking of the bottom of the crucible. A method for producing GaAs polycrystals is provided. The term “soaking of the bottom of the crucible” in the present invention is a temperature distribution in which GaAs that has been crystallized from the entire bottom surface of the crucible and solidified adheres to the bottom of the crucible.

B ₂ O ₃ is preferably used as the sealing material. Further, when solidifying GaAs upward from below the crucible, a temperature gradient is formed at the solid-liquid interface of GaAs at a temperature gradient of 7 ° C./cm or higher, and at the solid-liquid interface of GaAs. The rising speed is preferably 5 mm / hr or more.

  The present invention also provides a GaAs polycrystal produced by such a production method. In addition, a GaAs polycrystal having a shape that fits into a crucible provided in a growth furnace for a GaAs single crystal without a gap is provided.

According to the present invention, there is also provided a furnace for producing GaAs polycrystal, which has a substantially cylindrical crucible, a carbon susceptor holding the crucible, and a desired temperature gradient disposed around the susceptor. There is provided a GaAs polycrystal manufacturing furnace, characterized in that the bottom surface of the susceptor is 0.4 times or more the inner diameter of the crucible. An auxiliary heater for soaking the bottom surface of the susceptor may be provided, and the auxiliary heater may be disposed below the bottom surface of the susceptor .

  The crucible is preferably made of pBN. The inner diameter of the crucible is preferably equal to or slightly smaller than the inner diameter of the crucible provided in the GaAs single crystal growth furnace. Moreover, it is preferable to have a raising / lowering mechanism which raises / lowers the crucible and the heater relatively.

According to the present invention, the thickness of the bottom surface of the carbon susceptor holding the crucible is set to 0.4 times or more the inner diameter of the crucible, so that the molten GaAs is kept in the crucible while maintaining the soaking of the crucible bottom. It can be solidified from below to above. Then, by solidifying GaAs while maintaining the soaking of the bottom of the crucible in this way, local lump solidification on the bottom of the crucible is suppressed, and the solidified GaAs is started by crystallization from the entire bottom. It comes in close contact with the bottom. For this reason, a GaAs solid having a specific gravity smaller than that of the GaAs melt does not float but grows upward from the lower part of the crucible.

Further, according to the present invention, in a two-step method in which a GaAs synthesis step and a single crystal growth step are separately performed, a GaAs single crystal growth furnace that is optimal for performing a single crystal growth by a VB method or a VGF method thereafter. A cylindrical GaAs polycrystal that can enter the cylindrical crucible provided without any gaps can be obtained. According to the present invention, it is possible to increase the raw material filling rate when single crystal growth is performed by the VB method or the VGF method, and it becomes possible to grow a longer single crystal, thereby improving the manufacturing efficiency. Further, since the GaAs polycrystal produced according to the present invention is solidified gradually from the bottom to the top of the crucible, impurities are reduced by the segregation effect. Further, by using B ₂ O ₃ as a liquid sealing material at the time of synthesis, impurities can be reduced by the gettering effect.

  Hereinafter, preferred embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a longitudinal sectional view showing a schematic configuration of a GaAs polycrystal production furnace 1 (hereinafter referred to as “polycrystal production furnace 1”) according to an embodiment of the present invention. This polycrystal production furnace 1 is for producing GaAs polycrystals by the VB method.

  As shown in FIG. 1, a polycrystalline production furnace 1 includes a polycrystalline crucible 11 for producing GaAs polycrystal (hereinafter referred to as “polycrystalline production crucible 11” in the center of an airtight container 10 that can withstand a pressure of 6 MPa or more. ”) Is arranged. The polycrystalline crucible 11 is made of pBN. The polycrystalline manufacturing crucible 11 includes a cylindrical portion 12 having an open top and a bottom surface 13 that closes the lower portion of the cylindrical portion 12. The inner diameter d of the polycrystalline manufacturing crucible 11 is a growth furnace 2 for a GaAs single crystal described later. It is set to be equal to or slightly smaller than the inner diameter of the single crystal growth crucible 31 provided in FIG. Further, the bottom surface 13 of the polycrystalline crucible 11 is substantially horizontal, and the bottom surface 13 is not provided with a portion into which a seed crystal is placed.

  The polycrystalline crucible 11 is held by a cylindrical carbon susceptor 15 whose bottom is closed. The susceptor 15 is supported on the upper end of the rod 16. The susceptor 15 has a cylindrical shape whose upper end is open and whose bottom is closed, and a single crystal growth crucible 31 is accommodated therein. The thickness t of the bottom surface of the susceptor 15 is set to 0.4 times or more (t> 0.4d) of the inner diameter d of the polycrystalline crucible 11. The lower end of the rod 16 protrudes below the hermetic container 10 via a seal ring 17 mounted on the lower surface of the hermetic container 10, and a rotary lifting mechanism 18 is connected to the lower end of the rod 16. The operation of the rotary lift mechanism 18 allows the susceptor 15 and the polycrystalline crucible 11 to be integrally rotated and lifted via the rod 16. The inside of the airtight container 10 is kept airtight by the seal ring 17.

  In the airtight container 10, a plurality of stages of heaters 20 are arranged at each height so as to surround the periphery of the susceptor 15. The heaters 20 at the respective heights can be controlled independently, and a desired temperature gradient or temperature distribution can be formed in the airtight container 10 in the vertical direction. The outside of the heater 20 is surrounded by a heat insulating material 21 so that the heat of the heater 20 is effectively transferred into the inside of the polycrystalline crucible 11.

In the polycrystal production furnace 1 configured as described above, as shown in FIG. 2, Ga and As are put in a polycrystal production crucible 11, and a sealing material a is put on these Ga and As. At this time, the polycrystalline crystal crucible 11 does not contain a seed crystal used for crystal growth such as a single crystal. Even if polycrystalline manufacturing crucible 11 is once removed from susceptor 15, Ga, As and sealing material a are placed in polycrystalline manufacturing crucible 11, and after polycrystalline charging, polycrystalline manufacturing crucible 11 is held in susceptor 15. good. The charge form of Ga may be liquid or solid. The melting point of the sealing material a must be lower than the melting point (sublimation point) of As. For example, B ₂ O ₃ is used as the sealing material a.

  Then, after raising the inside of the hermetic container 10 to a predetermined pressure and heating it with the heater 20, the temperature of Ga and As and the sealing material a charged in the polycrystalline crucible 11 is raised. The temperature is raised to a temperature at which a melts, and Ga and As in the polycrystalline crucible 11 are covered with a sealing material a that is a melt to prevent As from volatilizing.

  Thereafter, GaAs is synthesized in a state where the melting point of As is further increased and the upper part of the polycrystalline crucible 11 is sealed with the sealing material a. At this time, the heater 20 may be controlled so as to preferentially heat from the lower side of the polycrystalline crucible 11 so that the synthesis of GaAs starts from the bottom of the polycrystalline crucible 11. Such adjustment of the heating position (height) can be easily performed by lowering the polycrystalline crucible 11 by operating the rotary lifting mechanism 18. When the synthesis is completed, the temperature is further raised to the melting point of GaAs or more, and as shown in FIG. 3, GaAs in the polycrystalline crucible 11 is completely melted.

  Next, as shown in FIG. 4, the GaAs in the polycrystalline crucible 11 is gradually cooled from the bottom of the polycrystalline crucible 11 to solidify the GaAs gradually from the bottom upward. A GaAs polycrystal b is grown from the bottom of the crucible 11. In this case, as described above, the thickness t of the bottom surface of the carbon susceptor 15 holding the polycrystalline manufacturing crucible 11 is 0.4 times or more the inner diameter d of the polycrystalline manufacturing crucible 11. The bottom of the crystal production crucible 11 is kept warm by the bottom surface of the susceptor 15 having a sufficient thickness. As a result, the bottom of the polycrystalline crucible 11 is soaked and the temperature of the entire bottom becomes substantially equal.

  When the entire bottom of the polycrystalline crucible 11 in the soaked state becomes a temperature lower than the melting point of GaAs (1238 ° C.), as shown in FIG. 4, the entire bottom of the polycrystalline crucible 11 is removed. Crystallization is started, and the solidified GaAs polycrystal b is formed in close contact with the entire bottom surface of the polycrystal production crucible 11.

  When solidifying GaAs in this way, by controlling the heating temperature of the heater 20, the upper temperature is higher than the melting point of GaAs (1238 ° C.), and the lower temperature is lower than the melting point of GaAs (1238 ° C.). , A region is formed in which a temperature gradient is formed in which the temperature is increased at a rate of 7 ° C./cm or more upward. Then, the operation of the rotary elevating mechanism 18 lowers the polycrystalline production crucible 11 and allows the polycrystalline production crucible 11 to pass through this temperature gradient region from top to bottom. Thus, if errors due to heat transfer characteristics are ignored, the polycrystalline crucible is produced when the heating temperature by the heater 20 passes through the position (height) at which the melting point of GaAs (1238 ° C.) is in the temperature gradient region. 11 is solidified, and the GaAs is solidified sequentially from the bottom to the top in the polycrystalline crucible 11. And above the position (height) where the heating temperature by the heater 20 is the melting point (1238 ° C.) of GaAs (above the position where the heating temperature by the heater 20 is the melting point of GaAs (1238 ° C.)). Then, GaAs in the polycrystalline crucible 11 is a melt, and below it (below the position where the heating temperature by the heater 20 is the melting point of GaAs (1238 ° C.)), GaAs becomes a solid (GaAs polycrystal b). Thus, as shown in FIG. 5, the position where the heating temperature by the heater 20 is the melting point of GaAs (1238 ° C.) in the temperature gradient region Δ gradually moves upward from the bottom surface in the polycrystalline crucible 11. This coincides with the position (height) of the solid-liquid interface L of GaAs to be solidified. In other words, across the solid-liquid interface L, the upper side is higher than the melting point of GaAs (1238 ° C.) and the lower side is lower than the melting point of GaAs (1238 ° C.). A temperature gradient region Δ that rises in temperature at / cm or more is formed.

  On the other hand, at the position (solid-liquid interface L) where the melting point (1238 ° C.) of GaAs in the temperature gradient region Δ is reached while passing through the polycrystalline crucible 11 from above to the temperature gradient region Δ. In the process of continuously solidifying GaAs and growing GaAs polycrystal b from the bottom to the top inside the polycrystalline crucible 11, the descending speed V of the polycrystalline crucible 11 by the operation of the rotary elevating mechanism 18 is set. Control to 5 mm / hr or more. As a result, in the polycrystalline crucible 11, the rising speed of the solid-liquid interface L of GaAs is controlled to 5 mm / hr or more, and the growth rate upward of the GaAs polycrystal b is set to 5 mm / hr or more. Be controlled.

  Thus, by lowering the polycrystalline production crucible 11 and raising the solid-liquid interface L of GaAs in the polycrystalline production crucible 11, all the GaAs in the polycrystalline production crucible 11 is solidified. Note that, while the polycrystalline production crucible 11 is being lowered, the GaAs polycrystal b may be grown while the polycrystalline production crucible 11 is rotated by operating the rotary elevating mechanism 18 as necessary.

  Thus, after all the GaAs in the polycrystalline synthetic crucible 11 is solidified and the growth of the GaAs polycrystalline b is completed, the GaAs polycrystalline b is cooled, and the GaAs polycrystalline b is taken out from the polycrystalline manufacturing crucible 11.

  By producing the GaAs polycrystal b as described above, the GaAs polycrystal b is not peeled off from the bottom of the polycrystal production crucible 11 and is always in close contact with the bottom of the polycrystal production crucible 11. On the other hand, the GaAs polycrystal b can be grown. The thickness t of the bottom surface of the carbon susceptor 15 holding the polycrystalline production crucible 11 is 0.4 times or more the inner diameter d of the polycrystalline production crucible 11, and the temperature is raised at 7 ° C./cm or more at the start of solidification. By allowing the bottom of the polycrystalline crucible 11 to pass through the temperature gradient region Δ, solidified GaAs can be brought into close contact with the entire bottom of the polycrystalline crucible 11 in a soaked state, and the solidified GaAs polycrystal at the bottom of the crucible can be obtained. The crystal b is in close contact with the entire bottom of the polycrystalline crucible 11 formed of pBN, and there is no fear of peeling off during growth. Further, it is possible to grow the GaAs polycrystal b from the bottom to the top in the polycrystal production crucible 11 without using a seed crystal. Further, the bottom surface 13 of the polycrystalline crucible 11 is not provided with a portion for putting a seed crystal, and the polycrystalline crucible 11 has a simple columnar shape, so that it is provided in the GaAs single crystal growth furnace 2. Compared with the single crystal growing crucible 31, the resistance to volume change during GaAs synthesis and solidification is excellent.

Further, by growing the GaAs polycrystal b from the bottom to the top by the VB method, it is possible to reduce impurities using segregation in the manufactured GaAs polycrystal b. Further, by using B ₂ O ₃ as the sealing material a, impurities can be reduced by the gettering effect. Note that the rising speed of the solid-liquid interface L of GaAs (in the embodiment, the lowering speed V of the polycrystalline crucible 11 due to the operation of the rotary lifting mechanism 18) is as follows at the end of the growth of the GaAs polycrystal b and immediately before it. In order to prevent solidification failure due to rapid crystal growth, it is desirable that the rate be 3 to 5 mm / hr.

  The GaAs polycrystal b manufactured in this way has a cylindrical shape having a diameter equal to or slightly smaller than the inner diameter of a single crystal synthesis crucible 31 provided in a growth furnace 2 for a GaAs single crystal described later. In addition, since the sealing material a is also introduced into the polycrystalline synthetic crucible 11, the sealing material a is disposed in a solidified state on the upper surface of the cylindrical GaAs polycrystal b thus manufactured. Become.

  FIG. 6 shows a schematic configuration of a growth furnace 2 (hereinafter referred to as “single crystal growth furnace 2”) for growing a GaAs single crystal using the GaAs polycrystal b manufactured as described above. It is a longitudinal cross-sectional view. This single crystal growth furnace 2 is for growing a GaAs single crystal by the VB method.

  A single crystal manufacturing crucible 31 for manufacturing a GaAs single crystal (hereinafter referred to as “single crystal manufacturing crucible 31”) is disposed in the center of the hermetic container 30. The crucible 31 for producing a single crystal includes a cylindrical portion 32 having an open upper end and a conical portion 33 connected so as to close the lower portion of the cylindrical portion 32, and the apex portion of the conical portion 33 (the lowermost portion of the crucible 31). , A seed crystal mounting portion 34 for inserting a seed crystal is formed. The inner diameter of the single crystal production crucible 31 is set equal to or slightly larger than the inner diameter of the polycrystalline production crucible 11 of the polycrystalline production furnace 1 described above.

  The single crystal manufacturing crucible 31 is held by a cylindrical susceptor 40 whose bottom is closed. The susceptor 40 is supported on the upper end of the rod 41. The lower end of the rod 41 protrudes below the hermetic container 30 through a seal ring 42 mounted on the lower surface of the hermetic container 30, and a rotary lifting mechanism 43 is connected to the lower end of the rod 41. Then, by operating the rotary lift mechanism 43, the susceptor 40 and the single crystal production crucible 31 can be integrally rotated and lifted via the rod 41. The inside of the airtight container 30 is kept airtight by the seal ring 42.

  In the airtight container 30, a plurality of heaters 45 are arranged at each height so as to surround the periphery of the susceptor 40. The heaters 45 at the respective heights can be controlled independently, and a desired temperature gradient or temperature distribution can be formed in the airtight container 30 in the vertical direction. The outside of the heater 45 is surrounded by a heat insulating material 46 so that the heat of the heater 45 is effectively transmitted to the single crystal manufacturing crucible 31.

  In the single crystal growth furnace 2 configured as described above, the seed crystal c is inserted into the seed crystal mounting portion 34 of the single crystal production crucible 31, and the GaAs polycrystal produced in advance by the procedure described above. b, the sealing material a, and if necessary, a dopant is introduced into the crucible 31 for producing a single crystal. As the sealing material a, the sealing material a remaining on the upper surface when the GaAs polycrystal b is manufactured may be used as it is. Alternatively, the upper portion of the GaAs polycrystal b (Tail end of the GaAs polycrystal b) may be removed, and the concentrated portion of impurities segregated upward when the GaAs polycrystal b is manufactured may be removed.

  As described above, the GaAs polycrystal b thus placed in the single crystal production crucible 31 has a cylindrical shape having a diameter equal to or slightly smaller than the inner diameter of the single crystal synthesis crucible 31 provided in the single crystal growth furnace 2. Therefore, the GaAs polycrystal b can be put in the single crystal production crucible 31 without any gaps, and the raw material filling rate can be increased.

  Then, the raw material charged single crystal production crucible 31 is set in the susceptor 40, the inside of the hermetic vessel 30 is increased to a predetermined pressure, and then heated by the heater 45 to heat and melt the entire GaAs polycrystal b, The sealing material a is arranged on the top. Next, by controlling the temperature of each heater 45, a temperature gradient is formed in the GaAs melted in the single crystal production crucible 31, and the single crystal production crucible 31 is lowered by the operation of the rotary elevating mechanism 43. The GaAs is cooled according to the method, and the GaAs is gradually cooled and solidified from the lowermost part in contact with the seed crystal c to grow a GaAs single crystal. In this case, the single crystal production crucible 31 may be rotated by operating the rotary lifting mechanism 43 as necessary. Thus, the grown GaAs single crystal is cooled, and the GaAs single crystal is taken out from the crucible 31 for producing the single crystal.

  Thus, the GaAs polycrystal b produced according to the present invention can be put in the single crystal synthesis crucible 31 provided in the single crystal growth furnace 2 without any gaps, and the raw material filling rate can be increased. As a result, a longer GaAs single crystal can be manufactured, and the manufacturing efficiency is improved. In addition, no special processing is required to enter the single crystal synthesis crucible 31, and there is no material loss. By using the GaAs polycrystal b in which impurities are reduced by the segregation effect and the gettering effect, a GaAs single crystal with higher quality can be manufactured.

  As mentioned above, although preferable embodiment of this invention was described, this invention is not limited to the form illustrated here. For example, as indicated by the alternate long and short dash line in FIG. 1, an auxiliary heater 49 is disposed below the bottom surface of the susceptor 15, and the entire bottom surface 13 of the polycrystalline crucible 11 is heated almost equally by the auxiliary heater 49. The temperature of the entire bottom surface 13 of the crucible 11 may be kept uniform (soaking). Thus, by arranging the auxiliary heater 49 below the bottom surface of the susceptor 15 and soaking the entire bottom surface 13 of the polycrystalline manufacturing crucible 11, the polycrystalline manufacturing crucible is similar to the case described above with reference to FIG. Crystallization is started from the entire bottom surface of the substrate 11, and the solidified GaAs polycrystal b can be formed so as to be in close contact with the entire bottom surface of the polycrystalline crucible 11, and the GaAs polycrystal b is peeled off during growth. There is no worry of going up. When the auxiliary heater 49 is arranged below the bottom surface of the susceptor as described above, the heat retaining effect by the bottom surface of the susceptor 15 can be omitted. It is not necessary to set 0.4 times or more (t> 0.4d).

  In addition, although FIG. 1 etc. demonstrated the example which lowers the polycrystal production crucible 11 at the time of the growth of GaAs polycrystal b, the heater 20 may be raised. Further, the present invention is not limited to the VB method, and can be similarly applied to the case where a GaAs polycrystal is manufactured by the VGF method. If a GaAs polycrystal is manufactured by the VGF method, a lifting mechanism that moves the crucible and the heater relatively up and down can be omitted.

  A high-temperature high-pressure furnace heated by a carbon heater was used as a GaAs polycrystal production furnace. A cylindrical heater having an inner diameter of 240 mm is configured as a multistage heater having four stages. In addition, two stages of donut-shaped auxiliary heaters are installed below the susceptor. Using this polycrystalline furnace, GaAs was synthesized and polycrystalline was grown by the VGF method. As a polycrystalline crucible, a pBN crucible having a lower φ145, an upper φ150, and a length (height) of 300 mm was used. The raw material was charged with 8000 g of Ga (6N) and 8800 g of As (6N). As a sealing material, 2000 g of B2O3 was used. The polycrystalline production crucible charged with the raw material was set on a susceptor and heated to 40 ° C./hr to the set value of each heater 500 ° C. to melt B 2 O 3. Thereafter, the temperature of the lowermost heater was raised to a set value of 800 ° C., and the temperature was further raised at 30 ° C./hr, and GaAs synthesis was started from the bottom of the polycrystalline crucible. Once GaAs synthesis starts, the reaction proceeds from the bottom of the polycrystalline crucible to the top due to the heat of reaction of GaAs. When all Ga and As reacted to become GaAs, the temperature was further raised to completely melt GaAs.

  Thereafter, the lower part of the polycrystalline crucible is adjusted to a temperature higher than the melting point of GaAs (1238 ° C.) and upward with a temperature gradient of 7 ° C./cm. Thereafter, the solid-liquid interface (temperature) in the polycrystalline crucible is adjusted. The position of the temperature gradient is changed so that the rising speed of the temperature during the gradient is 1238 ° C. is 7 to 10 mm / hr, crystallization starts from the bottom of the crucible, and the crystal grows upward. Grew. Each temperature condition was previously determined by melt temperature measurement using the same crucible.

After cooling, the polycrystalline production crucible was taken out in a state where B ₂ O ₃ and GaAs polycrystalline were contained, and after dissolving and removing B ₂ O ₃ with methanol, the polycrystalline GaAs was taken out from the polycrystalline production crucible.

  As a result, the obtained GaAs polycrystal was in a good solid state and a clean columnar crystal was obtained (FIG. 7). In the Hall measurement result, it was a semi-insulating n-type semiconductor, and all the metal impurities were below the detection limit in the impurity analysis by SIMS in the region excluding the tail end of 15 mm.

(Comparative example)
Using a general LEC furnace, 13000 g of Ga (6N) and 14300 g of As (6N) were charged as raw materials, and 1800 g of B ₂ O ₃ was used as a sealing material. After the temperature rise and GaAs synthesis, crystal growth was performed with a target of φ150 by a normal LEC method. Although the obtained crystals were in a solidified state, the shape was somewhat unstable and not a clean cylindrical shape (Fig. 8). For this reason, in order to obtain a cylindrical polycrystalline raw material, it is necessary to grind the outer periphery, resulting in a large raw material loss.

  The present invention can be applied to the production of GaAs polycrystals that are optimal as raw materials for single crystal growth by the VB method or the VGF method.

1 is a longitudinal sectional view showing a schematic configuration of a GaAs polycrystal production furnace according to an embodiment of the present invention. It is a longitudinal cross-sectional view of the polycrystal manufacturing crucible which shows the state which put Ga, As, and a sealing material. It is a longitudinal cross-sectional view of a polycrystalline crucible showing a state in which GaAs is completely melted. It is a longitudinal cross-sectional view of a polycrystalline crucible showing a state in which a GaAs polycrystal is grown from the bottom. It is explanatory drawing which shows the relationship between a temperature gradient and the position (height) of the solid-liquid interface of GaAs. It is a longitudinal cross-sectional view which shows the schematic structure of the growth furnace which grows a GaAs single crystal using a GaAs polycrystal. It is a photograph of the GaAs polycrystal manufactured in the Example. It is a photograph of the GaAs polycrystal manufactured by the comparative example.

Explanation of symbols

a sealing material b GaAs polycrystal 1 polycrystal production furnace 10 hermetic vessel 11 polycrystal production crucible 15 susceptor 18 rotary elevating mechanism 20 heater 49 auxiliary heater

Claims (5)

A GaAs polycrystal production furnace,
A substantially cylindrical crucible, a carbon susceptor holding the crucible, and a heater arranged around the susceptor and capable of forming a desired temperature gradient;
A GaAs polycrystal production furnace, wherein the thickness of the bottom surface of the susceptor is at least 0.4 times the inner diameter of the crucible. 2. The GaAs polycrystal manufacturing furnace according to claim 1 , further comprising an auxiliary heater that soaks the bottom surface of the susceptor, wherein the auxiliary heater is disposed below the bottom surface of the susceptor. 3.   The GaAs polycrystal manufacturing furnace according to claim 1 or 2, wherein the crucible is made of pBN.   The GaAs polycrystal manufacturing furnace according to claim 1, wherein an inner diameter of the crucible is equal to or slightly smaller than an inner diameter of a crucible provided in a GaAs single crystal manufacturing furnace.   The GaAs polycrystal production furnace according to any one of claims 1 to 4, further comprising an elevating mechanism for elevating and lowering the crucible and the heater relatively.