Process for preparing semiconducting silicon carbide sintered body

Claim 1

A method of producing an N-type semiconductor having an electrical resistivity at 20° C. ranging from 10 ohm centimeters to 10 -2 ohm centimeter and an electrical resistance that shows a positive temperature coefficient at temperatures ranging from about 800° C. to about 2000° C. and which retains N-type semiconducting properties at temperatures ranging from about -100° C. to 2000° C. which comprises providing a substantially homogeneous mixture of a submicron powder consisting essentially of β-silicon carbide, an amount of boron additive selected from the group consisting of boron and boron carbide equivalent to about 0.3 part to 3.0 parts by weight of boron based on 100 parts by weight of said β-silicon carbide, and an amount of a carbonaceous additive selected from the group consisting of free carbon and a carbonaceous organic material equivalent to 0.1 part to 1.0 part by weight of free carbon based on 100 parts by weight of said β-silicon carbide, said carbonaceous organic material completely decomposing at a temperature ranging from about 50° C. to 1000° C. to said free carbon and gaseous product of decomposition, shaping the mixture into a green body, and sintering the green body at a temperature ranging from about 1280° C. to 2300° C. in a sintering atmosphere which ranges from atmospheric pressure to superatmospheric pressure of 5 atmospheres and which contains nitrogen from a partial pressure of 10 -1 atmosphere to a pressure of 5 atmospheres producing a sintered body having a density of at least 90% of the theoretical density for silicon carbide and having pores which are substantially non-interconnecting.

Claim 2

A method of producing an N-type semiconductor having an electrical resistivity at 20° C. ranging from 10 ohm centimeters to 10 -2 ohm centimeter and an electrical resistance that shows a positive temperature coefficient at temperatures ranging from about 800° C. to about 2000° C. and which retains N-type semiconducting properties at temperatures ranging from about -100° C. to 2000° C. which comprises providing a substantially homogeneous mixture of a submicron powder consisting essentially of β-silicon carbide, an amount of boron additive selected from the group consisting of boron and boron carbide equivalent to about 0.3 part to 3.0 parts by weight of boron based on 100 parts by weight of said β-silicon carbide, and an amount of a carbonaceous additive selected from the group consisting of free carbon and a carbonaceous organic material equivalent to 0.1 part to 1.0 part by weight of free carbon based on 100 parts by weight of said β-silicon carbide, said carbonaceous organic material completely decomposing at a temperature ranging from about 50° C. to 1000° C. to said free carbon and gaseous product of decomposition, shaping the mixture into a green body, and sintering the green body at a temperature ranging from about 1280° C. to 2300° C. in a sintering atmosphere which ranges from atmospheric pressure to superatmospheric pressure of 5 atmospheres and which contains nitrogen from a partial pressure of 10 -1 atmosphere to a pressure of 5 atmospheres producing a sintered body having a density of at least 90% of the theoretical density for silicon carbide and having pores which are substantially non-interconnecting.