Provided is a method for producing a lithium tantalate single crystal substrate capable of suppressing increase in volume resistivity of the lithium tantalate single crystal substrate owing to reduction failure even when a lithium carbonate power is repeatedly used in heat treatment for the lithium tantalate single crystal substrate. The invention is a method for producing a lithium tantalate single crystal substrate having a volume resistivity of 1×10.sup.10 Ω.Math.cm or more and less than 1×10.sup.12 Ω.Math.cm, including a step of heat-treating a lithium tantalate single crystal substrate having a volume resistivity of 1×10.sup.12 Ω.Math.cm or more and having a single-domain structure, under normal pressure and at a temperature of 350° C. or higher but not higher than the Curie temperature thereof while burying it in a lithium carbonate powder having a BET specific surface area of 0.13 m.sup.2/g or more, wherein the lithium carbonate powder is a used lithium carbonate powder that has been used in burying a lithium tantalate single crystal substrate in heat treatment for the lithium tantalate single crystal structure under normal pressure and at a temperature of 350° C. or higher but not higher than the Curie temperature thereof, and in the heat treatment step, the heat treatment is carried out in a mixed gas atmosphere of an inert gas and a reducing gas at the start of the heat treatment, and after the heat treatment in the mixed gas atmosphere, the heat treatment is carried out in a single gas atmosphere of an inert gas.

Provided is a method for producing a lithium tantalate single crystal substrate capable of suppressing increase in volume resistivity of the lithium tantalate single crystal substrate owing to reduction failure even when a lithium carbonate power is repeatedly used in heat treatment for the lithium tantalate single crystal substrate. The invention is a method for producing a lithium tantalate single crystal substrate having a volume resistivity of 1×10.sup.10 Ω.Math.cm or more and less than 1×10.sup.12 Ω.Math.cm, including a step of heat-treating a lithium tantalate single crystal substrate having a volume resistivity of 1×10.sup.12 Ω.Math.cm or more and having a single-domain structure, under normal pressure and at a temperature of 350° C. or higher but not higher than the Curie temperature thereof while burying it in a lithium carbonate powder having a BET specific surface area of 0.13 m.sup.2/g or more, wherein the lithium carbonate powder is a used lithium carbonate powder that has been used in burying a lithium tantalate single crystal substrate in heat treatment for the lithium tantalate single crystal structure under normal pressure and at a temperature of 350° C. or higher but not higher than the Curie temperature thereof, and in the heat treatment step, the heat treatment is carried out in a mixed gas atmosphere of an inert gas and a reducing gas at the start of the heat treatment, and after the heat treatment in the mixed gas atmosphere, the heat treatment is carried out in a single gas atmosphere of an inert gas.

Provided is an apparatus and a method for continuous crystal pulling. The apparatus includes: a crucible including a first sub-crucible and a second sub-crucible located at inner side of the first sub-crucible; a draft tube located above the crucible; and a delivery duct supplying materials to the crucible. A ratio of inner diameter of the second sub-crucible to outer diameter of the draft tube is ≥1.05. In a first state, a distance between bottom surface of the draft tube and bottom surface of the crucible is a first distance, in a second state, a distance between bottom surface of the draft tube and bottom surface of the crucible is a second distance. The first distance is greater than the second distance. In the first and second states, a distance between a crystal-liquid interface in the crucible and the bottom surface of the draft tube remains substantially unchanged.

The present disclosure discloses a method for growing a crystal with a short decay time. According to the method, a new single crystal furnace and a temperature field device are adapted and a process, a ration of reactants, and growth parameters are adjusted and/or optimized, accordingly, a crystal with a short decay time, a high luminous intensity, and a high luminous efficiency can be grown without a co-doping operation.

A mono-crystalline silicon growth apparatus is provided. The mono-crystalline silicon growth apparatus includes a furnace, a support base disposed in the furnace, a crucible disposed on the support base, and a heating module. The support base and the crucible do not rotate relative to the heating module, and an axial direction is defined to be along a central axis of the crucible. The heating module is disposed at an outer periphery of the support base and includes a first heating unit, a second heating unit, and a third heating unit. The first heating unit, the second heating unit, and the third heating unit are respectively disposed at positions with different heights corresponding to the axial direction.

A method for preparing a single crystal silicon ingot and a wafer sliced therefrom are provided. The ingots and wafers comprise nitrogen at a concentration of at least about 1×1014 atoms/cm3 and/or germanium at a concentration of at least about 1×1019 atoms/cm3, interstitial oxygen at a concentration of less than about 6 ppma, and a resistivity of at least about 1000 ohm cm.

Disclosed are a yttrium-doped barium fluoride crystal and a preparation method and the use thereof, wherein the yttrium-doped barium fluoride crystal has a chemical composition of Ba.sub.(1−x)Y.sub.xF.sub.2+x, in which 0.01≤x≤0.50. The yttrium-doped BaF.sub.2 crystal of the present invention has improved scintillation performance. The yttrium doping may greatly suppress the slow luminescence component of the BaF.sub.2 crystal and has an excellent fast/slow scintillation component ratio. The doped crystal is coupled to an optical detector to obtain a scintillation probe which is applicable to the fields of high time resolved measurement radiation such as high-energy physics, nuclear physics, ultrafast imaging and nuclear medicine imaging.

A silicon wafer having a BMD density of 5×10.sup.8/cm.sup.3 or more and 2.5×10.sup.10/cm.sup.3 or less in a region of 80 μm to 285 μm from the wafer surface when the silicon wafer is heat-treated at a temperature X (° C., 700° C.≤X≤1000° C.) for a time Y (min) and then subjected to an infrared tomography method in which the laser power is set to 50 mW and the exposure time of a detector is set to 50 msec. The time Y and the temperature X satisfy Y=7.88×10.sup.67×X.sup.−22.5.

Methods for producing single crystal silicon ingots in which the dopant concentration in the silicon melt is controlled are disclosed. The control of the dopant concentration enhances ingot quality by the reduction or elimination of dislocations in the neck, crown, and main body portions of the single crystal silicon ingot.

A method for growing a single crystal according to a Czochralski method (CZ method) or a magnetic field applied CZ method (MCZ method), the method including: a first step of obtaining a melt by melting a silicon raw material loaded in a crucible; a second step of forming a solidified layer by solidifying a part of the melt; a third step of removing at least a part of the melt in a state where the solidified layer and the melt coexist; a fourth step of obtaining a melt by melting the solidified layer; and a fifth step of growing a silicon single crystal from the melt. Consequently, a method for purifying a silicon raw material and growing a single crystal on one CZ pulling apparatus and growing a single crystal with a reduced impurity concentration is provided.