Patents by Inventor Toshiaki Asahi

Toshiaki Asahi has filed for patents to protect the following inventions. This listing includes patent applications that are pending as well as patents that have already been granted by the United States Patent and Trademark Office (USPTO).

  • Patent number: 7229494
    Abstract: A method for producing a compound semiconductor single crystal by a liquid encapsulated Czochralski method, including containing a semiconductor raw material and an encapsulating material in a raw material melt-containing portion having a first crucible having a bottom and a cylindrical shape and a second crucible disposed within the first crucible and having a communication hole communicating with the first crucible in a bottom portion thereof; melting the raw material by heating the raw material melt-containing portion; and growing a crystal by making a seed crystal contact with a surface of the raw material melt in a state covered with the encapsulating material and by pulling up the seed crystal. A heater temperature is controlled so that a diameter of a growing crystal becomes approximately equal to an inner diameter of the second crucible, and the crystal is grown by maintaining a surface of the growing crystal in a state covered with the encapsulating material until termination of crystal growth.
    Type: Grant
    Filed: December 17, 2002
    Date of Patent: June 12, 2007
    Assignee: Nippon Mining & Metals Co., Ltd.
    Inventors: Toshiaki Asahi, Kenji Sato, Atsutoshi Arakawa
  • Patent number: 7175705
    Abstract: A process for producing compound semiconductor single crystal, comprises the steps of: putting a compound semiconductor raw material into a crucible, setting the crucible in a vertical type of heating furnace to heat and melt the raw material by a heater, promoting a nucleation on a surface of a raw material melt by leaving a solid raw material in a part of the raw material melt, solidifying the raw material melt gradually from the surface of the raw material melt without a seed crystal, and growing a crystal by using a nucleus generated by the nucleation.
    Type: Grant
    Filed: January 4, 2001
    Date of Patent: February 13, 2007
    Assignee: Nippon Mining & Metals Co., Ltd.
    Inventors: Shigeto Fujimura, Toshiaki Asahi, Kenji Sato
  • Patent number: 6989059
    Abstract: In a production method for producing a compound semiconductor single crystal by LEC method using a crystal growth apparatus with a double crucible structure, it was made to grow up a crystal by covering the second crucible with a plate-like member having a pass-through slot for being capable of introducing a crystal pulling-up shaft having a seed crystal holding part at a tip into the second crucible and creating a state where an atmosphere within the second crucible scarcely changes (a semi-sealed structure).
    Type: Grant
    Filed: October 3, 2003
    Date of Patent: January 24, 2006
    Assignee: Nikko Materials Co., Ltd.
    Inventors: Toshiaki Asahi, Kenji Sato, Takayuki Yabe, Atsutoshi Arakawa
  • Publication number: 20050118739
    Abstract: A method for producing a compound semiconductor single crystal by a liquid encapsulated Czochralski method, including containing a semiconductor raw material and an encapsulating material in a raw material melt-containing portion having a first crucible having a bottom and a cylindrical shape and a second crucible disposed within the first crucible and having a communication hole communicating with the first crucible in a bottom portion thereof; melting the raw material by heating the raw material melt-containing portion; and growing a crystal by making a seed crystal contact with a surface of the raw material melt in a state covered with the encapsulating material and by pulling up the seed crystal. A heater temperature is controlled so that a diameter of a growing crystal becomes approximately equal to an inner diameter of the second crucible, and the crystal is grown by maintaining a surface of the growing crystal in a state covered with the encapsulating material until termination of crystal growth.
    Type: Application
    Filed: December 17, 2002
    Publication date: June 2, 2005
    Applicant: Nikko Materials Co., Ltd.
    Inventors: Toshiaki Asahi, Kenji Sato, Atsutoshi Arakawa
  • Publication number: 20050000403
    Abstract: In a production method for producing a compound semiconductor single crystal by LEC method using a crystal growth apparatus with a double crucible structure, it was made to grow up a crystal by covering the second crucible with a plate-like member having a pass-through slot for being capable of introducing a crystal pulling-up shaft having a seed crystal holding part at a tip into the second crucible and creating a state where an atmosphere within the second crucible scarcely changes (a semi-sealed structure).
    Type: Application
    Filed: October 3, 2003
    Publication date: January 6, 2005
    Inventors: Toshiaki Asahi, Kenji Sato, Takayuki Yabe, Atsutoshi Arakawa
  • Publication number: 20040155255
    Abstract: The present invention relates to a method for producing an n-type ZnTe system compound semiconductor single crystal having high carrier concentration and low resistivity, the ZnTe system compound semiconductor single crystal, and a semiconductor device produced by using the ZnTe system compound semiconductor as a base member. Concretely, a first dopant and a second dopant are co-doped into the ZnTe system compound semiconductor single crystal so that the number of atoms of the second dopant becomes smaller than the number of atoms of the first dopant, the first dopant being for controlling a conductivity type of the ZnTe system compound semiconductor to a first conductivity type, and the second dopant being for controlling the conductivity type to a second conductivity type different from the first conductivity type. By the present invention, a desired carrier concentration can be achieved with a doping amount smaller than in earlier technology, and crystallinity of the obtained crystal can be improved.
    Type: Application
    Filed: March 31, 2004
    Publication date: August 12, 2004
    Inventors: Tetsuya Yamamoto, Atsutoshi Arakawa, Kenji Sato, Toshiaki Asahi
  • Patent number: 6334897
    Abstract: A method for producing a compound semiconductor single crystal, comprises the steps of: using a crucible having a bottom, a cylindrical shape, a diameter increasing portion having a reversed conical shape in a lower end side of the crucible, and a set portion for a seed crystal in a center of the bottom of the diameter increasing portion; setting a seed crystal in the seed crystal set portion of the crucible; putting a raw material of the compound semiconductor and an encapsulating material into the crucible; enclosing the crucible in an inner container; thereafter setting the inner container in a vertical type furnace; heating the raw material and the encapsulating material by a heating means to melt; and solidifying the obtained raw material melt from the seed crystal toward an upper side with annealing the raw material melt from a lower side to grow a single crystal of the compound semiconductor; wherein a rate of crystal growth at the diameter increasing portion of the crucible is made not less than 20 mm
    Type: Grant
    Filed: November 30, 1999
    Date of Patent: January 1, 2002
    Assignee: Japan Energy Corporation
    Inventors: Toshiaki Asahi, Keiji Kainosho, Tatsuya Nozaki, Kenji Sato
  • Publication number: 20010007239
    Abstract: A process for producing compound semiconductor single crystal, comprises the steps of: putting a compound semiconductor raw material into a crucible, setting the crucible in a vertical type of heating furnace to heat and melt the raw material by a heater, promoting a nucleation on a surface of a raw material melt by leaving a solid raw material in a part of the raw material melt, solidifying the raw material melt gradually from the surface of the raw material melt without a seed crystal, and growing a crystal by using a nucleus generated by the nucleation.
    Type: Application
    Filed: January 4, 2001
    Publication date: July 12, 2001
    Inventors: Shigeto Fujimura, Toshiaki Asahi, Kenji Sato
  • Patent number: 5871580
    Abstract: Using a thin plate seed crystal 10 having a different material from a bulk crystal to be grown and having a great diameter, before crystal growth is started, a temperature in the lower portion of a solution 12s in which material is solved into a solvent (or a melt 12m) is set to a higher temperature than the upper portion to cause convection so that the surface of seed crystal 10 is rinsed by the convection by keeping in the state for a predetermined period. Then, the crystal growth is started by the Bridgman method or gradient freezing method.
    Type: Grant
    Filed: July 11, 1996
    Date of Patent: February 16, 1999
    Assignee: Japan Energy Corporation
    Inventors: Toshiaki Asahi, Osamu Oda, Kenji Sato
  • Patent number: 5603763
    Abstract: A single crystal growing method for producing a high-quality and large-diameter single crystal of a compound semiconductor with a good yield, is disclosed.A volatile element 2 is first put into a reservoir portion 1A of a quartz ampule 1. Further, a crucible 4 made of pBN, which contains a raw material 3A of a compound semiconductor, is placed in the quartz ampule 1, the vacuum sealing of which is then performed. While a vapor pressure controlling operation is performed, a furnace temperature distribution is controlled in such a manner that a vertical first temperature gradient .alpha. .degree. C./cm) in the vicinity of an outside wall of the quartz ampule corresponding to a raw melt 3B is smaller than a vertical second temperature gradient (.beta. .degree. C./cm) in a range above the top end of the crucible 4 and simultaneously, the temperature is gradually lowered. Furthermore, .alpha. ranges from 51/D.sup.2 to 102/D.sup.2 .degree. C./cm, and preferably ranges from 58/D.sup.2 to 83/D.sup.2 .degree. C.
    Type: Grant
    Filed: October 18, 1995
    Date of Patent: February 18, 1997
    Assignee: Japan Energy Corporation
    Inventors: Yoshiteru Taniguchi, Toshiaki Asahi