Device for growing crystals in the form of rods and tubes from the melt

 

(57) Abstract:

The invention relates to techniques for growing shaped crystal pulling from the melt with rotation using formers and can be used to produce monocrystalline tubes and rods with periodically varying impurity content along the length of the crystal. The inventive device includes a crucible 1 with a dividing partition 2 dividing the melt 3 and 4 with different content of impurities, additional shaper 5, secured in one of the tanks crucible with the melt 3), the screen 6 with an opening 7 and is fixed on the screen shaper 8. The device allows you to receive periodic patterns with the changing ratio of the heights of layers of different composition in the process of growing the crystal by means of vertical and horizontal movement in the plane of the screen for more shaper by raising, lowering or rotating the crucible. In the grown crystal can be obtained variables periodic structure, the ratio of the height of the layers of different composition andi/biin which changes in the range (-a)/(a+a) ai/bi(+a)/(-a). 2 Il.

Izobreteniyem of formers and can be used to produce monocrystalline tubes and rods with periodically varying impurity content along the length of the crystal.

The closest technical solution is a device for receiving a tubular crystals with periodically varying along the length of the structure [1] . The device contains two or more crucibles for melts of different compositions, the shaper mounted on the screen above the crucible. The working surface of the shaper made in the form of isolated from other areas located around the circumference, each of the sections has a capillary channel to the corresponding melt composition and the seed crystal mounted in structurally connected with the mechanism of rotation and displacement. Using this device were obtained pipe with a layered structure LiF-LiF: MgF2[2] .

However, this device does not allow to obtain crystals with various and variable duty cycle regular patterns with a given frequency, i.e. with a constant and/or variable thickness ratio of layers of different compositions.

The technical result achieved by the present invention is to obtain crystals with a periodic distribution of impurity concentration, determined according to a given program with constant or variable ratio of the thickness of the various layers is monocrystalline rods and tubes from the melt with a layered distribution of impurities, including structurally connected with the mechanism of its movement and rotation, a crucible mounted for movement, and the shaper mounted on the screen, the crucible is made with a dividing partition for melts with different content of impurities and is mounted for rotation in one of the tanks of the crucible is rigidly fixed additional shaper, and the screen is made the hole for the free movement of additional shaper. In the crucible, separated by a partition, are the melts with different content of impurities. On the screen is the former, power is provided from one of the tanks, and also made a special hole that allows you to perform manipulations on the vertical and horizontal movement in the plane of the screen, shaper, rigidly fixed to the other tank of the crucible. All moving additional shaper is done using the vertical movement and rotation of the crucible, while fixed on the screen shaper remains stationary. The crystal growth is carried out layer by layer by simultaneously rotating and pulling ZAT is ovately in a specific mode. The device allows to achieve the same periodic structure as by means of vertical movement of the crucible, and the rotation of the crucible within 90o. Vertical movement of the crucible h, limited by the range of allowable values in the range 0 h hmwhere hmthe meniscus height, allows you to change the height of the working edges additional shaper relative to the working surface level shaper associated with the screen, allowing the meniscus height on the secondary shaper will vary in the same proportion, which in turn determines the width of the corresponding layer in a periodic structure. The variation of the position of the crucible lifting and lowering allows you to control the width of the layer of one of the compositions of the periodic structure. A similar result in periodic structures and changes in the ratio of layers of these structures directly in the process of growing crystal can be achieved by rotating the crucible about its axis within 90o. When the rotation of the crucible additional shaper moves freely in the hole. The height of the crystallized layer of the melt for one revolution of structurally is the sum of savannaha a layer of rolling shaper is determined by the ratio a = ()/2, where v is the velocity of extrusion, mm/min, the rotation frequency, Rev/main, the angle at which offset additional shaper. In this case, if the additional rotation of the former coincides with the direction of rotation of structurally, the values lie in the range of 0 90in the case of rotation of the additional shaper against the direction of rotation of structurally changes in the range -900. Accordingly, the height of the layer b is determined by the same ratio, but the sign in front of each case is reversed.

In Fig. 1 presents a General view of the apparatus for growing crystals, this shows the operation of the device at the time of lowering of the crucible, resulting in a change in the thickness of one of the components of the periodic structure. In Fig. 2 presents a view of the device at the moment of changing the ratio of components of the periodic structure in the rotation of the crucible.

The device includes a crucible 1 with a dividing partition 2 dividing the melt 3 and 4 with different content of impurities, additional shaper 5, secured in one of the tanks crucible with the melt 3), the screen 6 with an opening 7 and is fixed on the screen vormoor the melt 3, 4 with different dopant content. The persecution of the crystal is carried out on the working surfaces of the formers 5 and 8 are at the same level and in diametrically opposite positions, through which enter the melt 3 and 4, respectively (Fig. 1). During subsequent rotation of the seed crystal and its simultaneous pulling is carried out layer-by-layer growth of a crystal, and this position of the formers allows to obtain monocrystalline pipe with a periodic structure in which the thickness of layers of different composition (assuming equality of the areas of the working surfaces of the formers) are equal.

Getting regular structures with the changing ratio of layers of different compositions in the crystal growth process may be done in two ways. The first method is the vertical movement of the additional shaper 5 using the raising and lowering of the crucible (Fig. 1). The level of working shaper edges 8 remains constant, while the level of working shaper edges 5 depends on the height of the raising or lowering of the crucible. The width of the periodically repeating regions with the composition of the melt 3 is increased in the case of SDA is th same dependencies. Raising the crucible leads to the opposite effect.

The second use case allows the device to achieve the same periodic structure. Hole 7 provides a free horizontal movement of the shaper 5 around the circumference in the plane of the screen when you rotate the crucible (Fig. 2). The rotation of the crucible 1 at an angle in the direction of rotation of structurally leads the shaper 5 in the movement of the hole 7, the smaller the angle between the formers 5 and 8 are changed to values. When the rotation of the crucible against the direction of rotation of structurally the reverse effect. Thus in the growing crystal can be obtained variables periodic structure, the ratio of the height of the layers of ai/bithat can vary (-)/(+) ai/bi(+)/(-). Doped and undoped layers in these crystals represent the helix angle of the lifting screw line = arctan(/2R) [3], where R is the distance from the axis of rotation of structurally to the centers of the formers (in case of equal distance of the location of the formers from the axis of rotation of structurally).

Example 1. Grown tubes sapphire diameter of 25 mm, wall thickness which was rawnie impurities did not exceed 10-4weight. %), another molten sapphire with the addition of titanium (0,5 weight. %). The thickness of the partition walls of the crucible was 3 mm, the diameters used in these experiments, the formers were equal to 4 mm, and the distance between them is ~ 21 mm Persecution was carried out on a rotating seed. The growing crystal was carried out with the speed of extrusion of 0.4 mm/min and rotational speed of structurally 2 rpm Additional shaper is fixed in the tank with alloyed molten. At diametrically opposite placement of the formers, the thickness of the layers of the periodic structure was equal to 100 μm (Fig. 2, a). Then the crucible was started to rotate at the rotation speed of structurally, i.e., ~ 2 rpm During the rotation of the crucible in the direction of rotation of structurally the ratio of doped and undoped layers were changed depending on the angle of movement of the crucible (Fig. 2, b). So, when you rotate the crucible at 45othe relationship between the layers was 75 μm/125 μm, and in the end position of the formers, i.e., when the rotation of the crucible 90othe ratio of the layers was equal to 50 μm/150 μm. Rotating the crucible from this position in the opposite direction, i.e. against the direction of rotation of the La>othe ratio of the layers was changed to the value of 150 μm/50 μm. Thus, we have obtained single-crystal tube with periodic structures in which the change in the ratio between layers with different concentration was controlled during crystal pulling.

Example 2. Grown sapphire tube outer diameter of 23 mm and an inner diameter of 9 mm, length 150 mm, wall thickness which was equal to 6 mm In one part of the molybdenum crucible was unalloyed melt sapphire (impurity content of not more than 10-4weight. %), and another was placed melt sapphire with the addition of titanium up to 0.5 weight. %. The thickness of the partition walls of the crucible ~ 3 mm, the diameters of the formers were equal to 6 mm, the distance between them is 15 mm. Conditions and modes of persecution and pulling of the crystal similar to that shown in example 1. Additional shaper was enshrined in the tank with alloyed molten. Managing change in the ratio of the layers was carried out by the lifting and lowering of the crucible in the range of 50 microns. In the initial position of the formers (Fig. 2, and in modes pulling speed of 0.4 mm/min and rotation speed of 2 rpm thickness of the doped and undoped periodic structures were changed to the values respectively of 75 μm/125 μm and 50 μm/150 μm. The height of the lifting and lowering of the crucible was changed with a speed of 0.4 mm/min After lifting 50 μm crucible with this speed was down to 100 microns, i.e., to a value of -50 μm initial position of the crucible. The result has also been obtained monocrystalline tube with periodic structures in which the change in the thickness of layers with different concentration during crystal pulling ranged from 1/3 to 3/1.

Compared with the prototype of the proposed solution allows to obtain crystals with controlled periodic structures, the ratio of the layer thicknesses which may vary in the process of growing the crystal.

LITERATURE

1. Yu, noses, P. I. Antonov, and S. P. Nikanorov. The method of obtaining single-crystal tubes, and a device for its implementation. USSR author's certificate N 1306173, C 30 15/34,1985.

2. Antonov P. I. , noses, Y. G. , Nikanorov S. P. Formation of crystals of form element melt. - Izv. An SSSR, ser. physical , 1985, I. 49, S. 2295-2297.

3. C. N. Kurlov, S. C. Belenko. Receive periodic structures in shaped sapphire crystals, activated ions Ti3+, Cr3+. - Neorg. materials, such as 34, 1998, No. 6, S. 697-699.


 

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