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Expectations of the Semiconductor Industry for High-Quality Diamonds (Part Two)
Release Time:
2022-10-18
Source:
Wen/Pengcheng Semiconductor
2. The Conductivity Mechanism of Diamond Semiconductor Materials
The conductivity mechanism of semiconductor materials is achieved through two types of charge carriers: electrons and holes, which can be classified into N-type and P-type. Diamond, as a group IV element, has a crystal structure that can be viewed as two face-centered cubic structures translated along the body diagonal by 1/4 of the lattice constant. Carbon atoms bond with four neighboring carbon atoms through covalent bonds using sp3 hybrid orbitals, forming a tetrahedral structure. By doping diamond with appropriate elements, its electrical properties can be altered, allowing it to be widely used as a semiconductor material in electrical devices.
Doping of diamond includes p-type doping and n-type doping. Natural diamonds containing impurities exhibit p-type conductivity. In industrial production, boron can be doped into diamond through ion implantation and CVD methods. However, there are no naturally occurring n-type conductive diamonds in nature, and lattice defects can compensate for charge carriers, preventing the effective activation of doped impurity elements, making n-type doping of diamond a persistent challenge for scientists. Currently, boron is recognized as an effective p-type dopant, while phosphorus is used for n-type doping. The quality semiconductor doping technology is microwave plasma CVD.
(1) P-type Doping
P-type boron-doped semiconductor diamond single crystals are the preferred materials for the preparation of high-temperature, high-power semiconductor devices, with broad application prospects in fields such as electronics, nuclear energy, and aerospace. Further research should be conducted on boron doping in diamond, enhancing the carrier mobility of boron-doped diamond by selecting suitable boron sources and adjusting the doping concentration, and applying it in the fabrication of diodes, field-effect transistors, and detectors to improve device performance.
(2) N-type Doping
The realization of n-type conductive homoepitaxial diamond is crucial for electronic applications based on pn junctions and is key to the development of bipolar devices. Scientists have attempted to dope diamond with elements such as nitrogen, sulfur, lithium, and phosphorus to achieve n-type conductivity. Due to the deep impurity energy level of nitrogen in diamond (at a depth of 1.7-2eV from the conduction band edge), nitrogen-doped diamond is a good insulator at room temperature and cannot achieve n-type conductivity. Sulfur atoms, being much larger than carbon atoms, cause significant lattice distortion when doped into diamond, resulting in numerous lattice defects, rendering most sulfur inactive electrically. For example, the electrical properties of sulfur-doped diamond are primarily temperature-dependent, exhibiting n-type conductivity at high temperatures and p-type conductivity at low temperatures. Therefore, although sulfur-doped diamond films can achieve n-type conductivity, there are still significant challenges for practical applications in electronics. Lithium-doped diamond can exist at grain boundaries, defects, interstitial sites, and substitutional sites. When lithium atoms exist as interstitial atoms, they can form donor impurities; as substitutional atoms, they can form deep acceptor impurities; and when present at grain boundaries or lattice defects, they do not exhibit semiconductor properties. Phosphorus, with a covalent bond radius 1.4 times that of carbon, has an energy level located 0.58eV below the conduction band edge, forming shallow energy levels in diamond films, making it an ideal element for achieving n-type doping in diamond.
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Expectations of the Semiconductor Industry for High-Quality Diamonds (Part 1)
Band gap: determined by the electronic states and atomic configurations of semiconductors, it reflects the energy required for the valence electrons of the atoms that make up this material to be excited from a bound state to a free state; the band gap is an important characteristic parameter of semiconductors. A band gap of zero indicates a metal, a large band gap (generally greater than 4.5 eV) indicates an insulator, and a medium band gap indicates a semiconductor.
Expectations of the Semiconductor Industry for High-Quality Diamonds (Part Two)
The conduction mechanism of semiconductor materials is achieved through two types of charge carriers: electrons and holes, which are classified as N-type and P-type. Diamond, as a group IV element, can be viewed as having a crystal structure formed by two face-centered cubic structures translated along the body diagonal by 1/4 of the lattice constant. Carbon atoms bond with four neighboring carbon atoms through covalent bonds using sp3 hybrid orbitals, forming a tetrahedral structure. By doping diamond with appropriate elements, its electrical properties can be altered, allowing it to be widely used as a semiconductor material in electrical devices.
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