A crystal grower furnace assembly having a gastight housing, a crystal pulling rod extending into the housing coaxially with the vertical axis of the housing and the heating elements. The housing is divided into a first chamber adapted for growing a crystal by the Czochralski technique, from a melt of the crystalline material, a second chamber above the first chamber having a port for evacuation and admission of gases, and a narrow neck connecting the chambers in coaxial alignment. The rod extends through the neck and is adapted for rotational and vertical movement therein. One heater element, situated near the juncture of the neck portion and the second chamber, is employed to heat boron oxide to a liquid which is used to seal the space between the rod and the inner wall of the neck portion to seal off the first chamber from the second chamber during the crystal growth operation. The second heater is situated near the top of the first chamber and is employed to prevent the condensation of arsenic during crystal growth.
An apparatus for producing a single crystal according to the CZ method, which comprises a closed container consisting of upper and lower halves and having a shaft for pulling up the single crystal, at least a part of which contacting with said vapor of the elements is made of a material containing an element of the same group of the periodic table as that of component elements of the single crystal, a gap between said shaft and the container and an opening between said upper and lower halves of the container being sealed with a sealing material, at least one reservoir positioned in the container for supplying vapor of a volatile component element of the single crystal, and a heating means provided around the container; wherein a hot zone of the apparatus including the container is made of a material which has an X-ray absorption coefficient not larger than 5 cm.sup.2 /g, and said material of the hot zone has such thickness that X-ray transmittance through the whole hot zone is 10.sup.-6 or more so as to monitor the single crystal being pulled up by X-ray fluoroscopy.
The process involves producing a monocrystal from the ferroelectric compound, annealing the monocrystal and cooling the latter in a zero longitudinal temperature gradient. The apparatus comprises means for producing the monocrystal, and heating means for annealing the monocrystal in a zero temperature gradient, as well as for cooling the monocrystal in a zero longitudinal temperature gradient after annealing. The strain-free monocrystals may be used in the production of surface wave filters, modulators and optical amplifiers.
Crystals of wide band gap materials are produced by positioning a holder (106, 274) receiving a seed crystal (106) at the interface (36, 270) between a body (26, 206) of molten wide band gap material and an overlying layer (28 or 288) of temperature-controlled, encapsulating liquid. The temperature of the layer decreases from the crystallization temperature of the crystal at the interface with the melt to a substantially lower temperature at which formation of crystal defects does not occur, suitably a temperature of 200.degree. C. to 600.degree. C. After initiation of crystal growth, the leading edge of the crystal (212) is pulled through the layer until the leading edge of the crystal enters the ambient gas headspace (30, 265) which may also be temperature controlled. The length of the column of liquid encapsulant may exceed the length of the crystal such that the leading edge and trailing edge of the crystal are both simultaneously with the column of the crystal. The crystal can be pulled vertically by means of a pulling-rotation assembly (20) or horizontally by means of a low-angle withdrawal mechanism (210). The temperature of the encapsulating layer is controlled by heating and/or cooling elements (35, 230) submerged with the layers and connected in closed loop with power supplies (50, 52, 240) by means of temperature sensing elements (52, 239). These elements control and provide nucleation and growth of a more perfect crystal in the elongated, heat exchange, encapsulating fluid medium.
An improved method of growing ribbon-shaped crystalline bodies is disclosed. The method comprises the step of pulling the body from a melt pool through a very narrow gap as the body cools through a range of temperatures at which significant plastic deformation can occur so as to reduce the amount of buckling the body otherwise experienced due to transverse residual stress. The method in its preferred form utilizes an improved guidance mechanism for use with apparatus for growing ribbon-shaped bodies. The mechanism comprises a pair of heat-conductive plates rigidly positioned with respect to the melt pool. The plates are disposed in opposing relation so that their opposing surfaces define the gap therebetween and so that the plates are positioned (1) respectively on opposite sides of and close to the side surfaces of the body as the body is being pulled from the melt pool through the gap; and (2) in a region between the melt pool and the body pulling mechanism where the body cools through the range of temperatures at which significant plastic deformation occurs. The plates defining the gap are spaced apart by an amount (1) greater than the expected thickness of the ribbon-shaped bodies being grown, and (2) sufficiently small so that when flatness variations produced in the ribbon shaped body as it is pulled from the melt pool exceed a predetermined maximum as determined by the spacing provided by the gap, the ribbon will interact with the plates and the flatness variations will be reduced so as not to exceed the predetermined maximum.
A single crystal pulling apparatus using Czochralski method includes a first screen in the shape of a hollow round cylinder. One side of the first screen facing a quartz crucible is made of a heat absorbent material and another side of the first screen is made of a heat insulator material. The upper and lower ends of the first screen have an outwardly extending flange and an inwardly extending flange, respectively. The first screen surrounds a single crystal pulling zone such that its lower flange is positioned near a melt charged zone in the crucible. The apparatus also includes a second screen positioned inside the first screen. The vertical section of the second screen has the shape of a substantially parabola and the center of the bottom of the second screen is open and surrounds the single crystal pulling zone. The upper end of the second screen has an outwardly extending flange. The apparatus increases the pulling speed of a grown single crystal and improves preventing degree of dislocation in the grown single crystal due to contamination of the grown single crystal with impurities.
