Silicon carbide (SiC), a material long known with potential for high-temperature, high-power, high-frequency, and radiation hardened applications, has emerged as the most mature of the wide-bandgap (2.0 eV ≲ Eg ≲ 7.0 eV) semiconductors since the release of commercial 6HSiC bulk substrates in 1991 and 4HSiC substrates in 1994. Following a brief introduction to SiC material properties, the status of SiC in terms of bulk crystal growth, unit device fabrication processes, device performance, circuits and sensors is discussed. Emphasis is placed upon demonstrated high-temperature applications, such as power transistors and rectifiers, turbine engine combustion monitoring, temperature sensors, analog and digital circuitry, flame detectors, and accelerometers. While individual device performances have been impressive (e.g. 4HSiC MESFETs with fmax of 42 GHz and over 2.8 W mm−1 power density; 4HSiC static induction transistors with 225 W power output at 600 MHz, 47% power added efficiency (PAE), and 200 V forward blocking voltage), material defects in SiC, in particular micropipe defects, remain the primary impediment to wide-spread application in commercial markets. Micropipe defect densities have been reduced from near the 1000 cm−2 order of magnitude in 1992 to 3.5 cm−2 at the research level in 1995.

Status of silicon carbide (SiC) as a wide-bandgap semiconductor for high-temperature applications: A review

The formation of the Schottky barrier height (SBH) is a complex problem because of the dependence of the SBH on the atomic structure of the metal-semiconductor (MS) interface. Existing models of the SBH are too simple to realistically treat the chemistry exhibited at MS interfaces. This article points out, through examination of available experimental and theoretical results, that a comprehensive, quantum-mechanics-based picture of SBH formation can already be constructed, although no simple equations can emerge, which are applicable for all MS interfaces. Important concepts and principles in physics and chemistry that govern the formation of the SBH are described in detail, from which the experimental and theoretical results for individual MS interfaces can be understood. Strategies used and results obtained from recent investigations to systematically modify the SBH are also examined from the perspective of the physical and chemical principles of the MS interface.

The physics and chemistry of the Schottky barrier height

For more than three decades, SiC has been investigated as a wide band gap semiconductor. This paper reviews ohmic and rectifying metal contacts on n- and p-type α- and β-SiC reported throughout that time period. Electrical characteristics, Schottky barrier heights (SBHs), thermal stability, and chemical reactions are discussed. Most metals formed very good rectifying contacts in the as-deposited condition on both n- and p-type 6H-SiC with Schottky barrier heights ⪖ 1 eV. Low ideality factors (n 1100 V) have been displayed in this material. The electrical properties of contacts on 3C-SiC have been more dependent on the quality of the 3C-SiC films, which have been plagued by higher defect densities than 6H-SiC. In general, a partial pinning of the Fermi level has been evidenced by positive correlations, which are less than 1 (≈ 0.2–0.6), between the SBHs and the metal work functions. Ohmic contacts with low contact resistivities (⪕ 10−5 Ω cm2), especially important for high power applications, on any of the SiC polytypes have been exceptionally difficult to achieve. Most of the ohmic contacts have relied on high doping concentrations in combination with annealing at temperatures between 800 and 1300 °C. Annealed Ni and Al have primarily been used in ohmic contact metallizations for n- and p-type SiC, respectively. The tendency of SiC to react with metals to form carbides and/or silicides at potential device operating temperatures ( ∼ 600 °C) can be a problem for potential long term applications at high temperature. These critical issues are discussed along with future perspectives for research approaches.

A critical review of ohmic and rectifying contacts for silicon carbide

The deposition of silicon carbide thin films and the associated technologies of impurity incorporation, etching, surface chemistry, and electrical contacts for fabrication of solid-state devices capable of operation at temperatures to 925 K are addressed. The results of several research programs in the United States, Japan and the Soviet Union, and the remaining challenges related to the development of silicon carbide for microelectronics are presented and discussed. It is concluded that the combination of alpha -SiC on alpha -SiC appears especially viable for device fabrication. In addition, considerable progress in the understanding of the surface science, ohmic and Schottky contacts, and dry etching have recently been made. The combination of these advances has allowed continual improvement in Schottky diode p-n junction, MESFET, MOSFET, HBT, and LED devices. >

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Thin film deposition and microelectronic and optoelectronic device fabrication and characterization in monocrystalline alpha and beta silicon carbide

A silicon carbide metal-insulator semiconductor field effect transistor having a u-shaped gate trench and an n-type silicon carbide drift layer. A p-type region is formed in the silicon carbide drift layer and extends below the bottom of the u-shaped gate trench so as to prevent field crowding at the corner of the gate trench. A unit cell of a metal-insulator semiconductor transistor having a bulk single crystal silicon carbide substrate of n-type conductivity silicon carbide. A first epitaxial layer of n-type conductivity silicon carbide and a second epitaxial layer of p-type conductivity silicon carbide formed on the first epitaxial layer. A first trench is formed which extends downward through the second epitaxial layer and into the first epitaxial layer. A second trench, adjacent the first trench, is also formed extending downward through the second epitaxial layer and into the first epitaxial layer. A region of n-type conductivity silicon carbide is formed between the first and second trenches and having an upper surface opposite the second epitaxial layer. An insulator layer is formed in the first trench where the upper surface of the gate insulator layer formed on the bottom of the first trench is below the lower surface of the second epitaxial layer. A region of p-type conductivity silicon carbide is formed in the first epitaxial layer below the second trench. Gate and source contacts are formed in the first and second trenches respectively and a drain contact is formed on the substrate. Preferably the gate insulator layer is an oxide such that the transistor formed is a metal-oxide field effect transistor.

Silicon carbide metal-insulator semiconductor field effect transistor

Formation of Schottky barrier contacts to n‐type β‐SiC(100) was systematically investigated for several metals with various physical and chemical properties. The metals (Pd, Au, Co, Ti, Ag, Tb, and Al) were deposited onto oxygen terminated (∼1 monolayer) surfaces. Metal/β‐SiC interface chemistry and Schottky barrier height φB during contact formation were obtained by x‐ray photoemission spectroscopy; the corresponding electrical properties of thick contacts were characterized by capacitance‐voltage and current‐voltage methods. The metal/β‐SiC interface is unreactive at room temperature. X‐ray photoemission spectroscopy and electrical measurements demonstrate that these metal contacts exhibit a wide range of φB , 0.95–0.16 eV; within this range an individual contact φB value depends strongly on the metal work function in general accord with the Schottky–Mott limit.

R. W. Grant

Papers

Formation and Schottky barrier height of metal contacts to β‐SiC