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Diamonds Factory Biography
James Butler: Yes, and it can often lead to improved quality in the newly grown CVD [chemical vapor deposited] diamond. Often the quality and defect structure of the CVD grown layer is limited by the defects inherent in the seed crystal. If one gets the growth process right, some of these defects will not propagate or disappear as the new CVD material grows thicker. Similar effects were observed in many other crystal systems, including silicon, where 50 years ago the "best" quality was barely one-inch-diameter, with many impurities and intrinsic defects. Now, nearly perfect, pure 16-inch-diameter silicon wafers are available.
Q: Why do diamonds conduct heat energy so well but not electricity?
Charley Cox, Pensacola, Florida
Butler: In metals, heat is conducted by the electrons, which also conduct charge (electricity). In diamond, heat is conducted by the lattice vibrations (phonons), which have a high velocity and frequency, due to the strong bonding between the carbon atoms and the high symmetry of the lattice. These strong bonds between the carbon atoms also give rise to many other of the extreme properties of diamond, such as hardness, chemical erosion resistance, electrical insulating strength, and optical transparency. As discussed below in the next answer, adding impurity atoms (dopants) can make diamond electrically conductive.
Q: I saw the NOVA scienceNOW special on diamond electronics. I understand that pure diamond is a fantastic electrical insulator, and that it becomes a conductor when boron is added during the manufacturing process. The program suggested it could be used as a switch (like a transistor, I presume). Is diamond only useful as a substrate or insulator like silicon? Can it be made to "switch?" If so, how?
Jack F., Alpharetta, Georgia
Butler: The building blocks of most electronics are resistors, capacitors, inductors, diodes, and switches. Diamond materials can be useful for most of these components. The simplest way is the use of diamond as a heat spreader—to conduct the heat away from a local hot spot, which degrades the performance of a device built from another material, e.g., silicon or gallium arsenide. Pure diamond is an excellent insulator, but when charge carriers (electrons or holes) are injected into diamond, they can move with extremely high velocities. One can incorporate impurity atoms, such as boron or phosphorous, during the growth of diamond, and these atoms can donate an extra electron (in the case of phosphorous), creating an n-type semiconductor, or accept an electron (in the case of boron) from the valance electrons of carbon to create a p-type semiconductor.
There are many ways to design a switch for electricity in a semiconductor, but the most common is a transistor. Transistors are fabricated from combinations of p- and n-type semiconducting and insulating materials, all of which are now possible with diamond. The combinations of the extreme properties of diamond—thermal conductivity, insulating strength, high charge carrier velocities, low dielectric constant, etc.—suggest that diamond should out-perform nearly every other semiconducting material system for electronic applications. IN PRINCIPLE! The reality is that there are many other factors involved in developing and implementing a technology: cost, manufacturing infrastructure, investment, and knowledge base. I think it is fair to say that diamond materials need a lot more research, knowledge, and technology development before they can be considered a mature semiconducting material.
Q: Dr. Butler, Thank you for a peek into this new technology. As an older EE [electrical engineer], I am extremely enthused about the potential impact that diamond technology will have in the electronics industry. How long do you think it will be before the technology is used in practical applications?
Marianne, Portales, New Mexico
Butler: Diamond materials are already used in many practical applications: passive thermal management in advanced microwave and laser diode devices, optical windows for industrial laser machining, cutting tools for automotive and aerospace applications, electrodes for waste water cleanup, etc. How rapidly diamond materials are accepted into new (and old) technologies will depend on many factors, but I think it will mainly depend on the development and growth of the industrial base for CVD diamond. This will depend on both investment and the development of the economic drive for such investment. The insertion of CVD diamond materials into electronics is happening, albeit slowly, because of the availability of competing materials (Si, SiC, GaN), cost (which depends on infrastructure and demand), and knowledge (more research and technology development is necessary). Please see my answer to the previous question for more specific comments about diamond as a semiconductor.
Diamonds Factory Biography
James Butler: Yes, and it can often lead to improved quality in the newly grown CVD [chemical vapor deposited] diamond. Often the quality and defect structure of the CVD grown layer is limited by the defects inherent in the seed crystal. If one gets the growth process right, some of these defects will not propagate or disappear as the new CVD material grows thicker. Similar effects were observed in many other crystal systems, including silicon, where 50 years ago the "best" quality was barely one-inch-diameter, with many impurities and intrinsic defects. Now, nearly perfect, pure 16-inch-diameter silicon wafers are available.
Q: Why do diamonds conduct heat energy so well but not electricity?
Charley Cox, Pensacola, Florida
Butler: In metals, heat is conducted by the electrons, which also conduct charge (electricity). In diamond, heat is conducted by the lattice vibrations (phonons), which have a high velocity and frequency, due to the strong bonding between the carbon atoms and the high symmetry of the lattice. These strong bonds between the carbon atoms also give rise to many other of the extreme properties of diamond, such as hardness, chemical erosion resistance, electrical insulating strength, and optical transparency. As discussed below in the next answer, adding impurity atoms (dopants) can make diamond electrically conductive.
Q: I saw the NOVA scienceNOW special on diamond electronics. I understand that pure diamond is a fantastic electrical insulator, and that it becomes a conductor when boron is added during the manufacturing process. The program suggested it could be used as a switch (like a transistor, I presume). Is diamond only useful as a substrate or insulator like silicon? Can it be made to "switch?" If so, how?
Jack F., Alpharetta, Georgia
Butler: The building blocks of most electronics are resistors, capacitors, inductors, diodes, and switches. Diamond materials can be useful for most of these components. The simplest way is the use of diamond as a heat spreader—to conduct the heat away from a local hot spot, which degrades the performance of a device built from another material, e.g., silicon or gallium arsenide. Pure diamond is an excellent insulator, but when charge carriers (electrons or holes) are injected into diamond, they can move with extremely high velocities. One can incorporate impurity atoms, such as boron or phosphorous, during the growth of diamond, and these atoms can donate an extra electron (in the case of phosphorous), creating an n-type semiconductor, or accept an electron (in the case of boron) from the valance electrons of carbon to create a p-type semiconductor.
There are many ways to design a switch for electricity in a semiconductor, but the most common is a transistor. Transistors are fabricated from combinations of p- and n-type semiconducting and insulating materials, all of which are now possible with diamond. The combinations of the extreme properties of diamond—thermal conductivity, insulating strength, high charge carrier velocities, low dielectric constant, etc.—suggest that diamond should out-perform nearly every other semiconducting material system for electronic applications. IN PRINCIPLE! The reality is that there are many other factors involved in developing and implementing a technology: cost, manufacturing infrastructure, investment, and knowledge base. I think it is fair to say that diamond materials need a lot more research, knowledge, and technology development before they can be considered a mature semiconducting material.
Q: Dr. Butler, Thank you for a peek into this new technology. As an older EE [electrical engineer], I am extremely enthused about the potential impact that diamond technology will have in the electronics industry. How long do you think it will be before the technology is used in practical applications?
Marianne, Portales, New Mexico
Butler: Diamond materials are already used in many practical applications: passive thermal management in advanced microwave and laser diode devices, optical windows for industrial laser machining, cutting tools for automotive and aerospace applications, electrodes for waste water cleanup, etc. How rapidly diamond materials are accepted into new (and old) technologies will depend on many factors, but I think it will mainly depend on the development and growth of the industrial base for CVD diamond. This will depend on both investment and the development of the economic drive for such investment. The insertion of CVD diamond materials into electronics is happening, albeit slowly, because of the availability of competing materials (Si, SiC, GaN), cost (which depends on infrastructure and demand), and knowledge (more research and technology development is necessary). Please see my answer to the previous question for more specific comments about diamond as a semiconductor.
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