We present a comprehensive review of the properties of the epitaxial 4H silicon carbide polytype (4H–SiC). Particular emphasis is placed on those aspects of this material related to room, high-temperature and harsh environment ionizing radiation detector operation. A review of the characterization methods and electrical contacting issues and how these are related to detector performance is presented. The most recent data on charge transport parameters across the Schottky barrier and how these are related to radiation spectrometer performance are presented. Experimental results on pixel detectors having equivalent noise energies of 144 eV FWHM (7.8 electrons rms) and 196 eV FWHM at +27 °C and +100 °C, respectively, are reported. Results of studying the radiation resistance of 4H–SiC are analysed. The data on the ionization energies, capture cross section, deep-level centre concentrations and their plausible structures formed in SiC as a result of irradiation with various particles are reviewed. The emphasis is placed on the study of the 1 MeV neutron irradiation, since these thermal particles seem to play the main role in the detector degradation. An accurate electrical characterization of the induced deep-level centres by means of PICTS technique has allowed one to identify which play the main role in the detector degradation.

https://iopscience.iop.org/article/10.1088/0957-0233/19/10/102001/pdf

Silicon carbide and its use as a radiation detector material

We present results of ab initio calculations for the electronic and atomic structures of monovacancies and antisite defects in 4H-SiC in all possible charge states. The calculations make use of a plane-wave pseudopotential method based on density-functional theory and the local spin-density approximation. Formation energies, ionization levels, and local geometries of the relaxed structures are reported for defects at all possible cubic and hexagonal lattice sites. To correct for the electrostatic interaction between charged supercells, we use a Madelung-type correction for the formation energies, leading to good agreement with experimentally observed ionization levels. Our calculations indicate no negative-U behaviour for carbon vacancies. Hence, the singly positive charge state of the carbon vacancy VC+ is stable, as recently found in experiments. The silicon antisite SiC+ is found to be stable at low values of electron chemical potential—again in agreement with experiment.

https://iopscience.iop.org/article/10.1088/0953-8984/13/28/305/pdf

Comprehensive ab initio study of properties of monovacancies and antisites in 4H-SiC

Extreme temperature semiconductor integrated circuits (ICs) are being developed for use in the hot sections of aircraft engines and other harsh-environment applications well above the 300 °C effective limit of silicon-on-insulator IC technology. This paper reviews progress by the NASA Glenn Research Center and Case Western Reserve University (CWRU) in the development of extreme temperature (up to 500 °C) integrated circuit technology based on epitaxial 6H-SiC junction field effect transistors (JFETs). Simple analog amplifier and digital logic gate ICs fabricated and packaged by NASA have now demonstrated thousands of hours of continuous 500 °C operation in oxidizing air atmosphere with minimal changes in relevant electrical parameters. Design, modeling, and characterization of transistors and circuits at temperatures from 24 °C to 500 °C are also described. CWRU designs for improved extreme temperature SiC JFET differential amplifier circuits are demonstrated. Areas for further technology maturation, needed prior to beneficial system insertion, are discussed. Optical micrograph of a 500 °C durable 6H-SiC JFET differential amplifier IC chip fabricated at NASA prior to packaging. Digitized waveforms measured during the 1st (solid black) and 6519th (dashed grey) hour of 500 °C operational testing show no change in output characteristics.

Extreme temperature 6H-SiC JFET integrated circuit technology

Formation of a glue-nanofiller layer between grains, consisting of a middle-temperature spinel-like Lix CoO2 phase, reinforces the strength of the incoherent interfacial binding between anisotropically oriented grains by enhancing the face-to-face adhesion strength. The cathode treated with the glue-layer exhibits steady cycling performance at both room-temperature and 60 °C. These results represent a step forward in advanced lithium-ion batteries via simple cathode coating.

Enhancing Interfacial Bonding between Anisotropically Oriented Grains Using a Glue-Nanofiller for Advanced Li-Ion Battery Cathode.

The authors have investigated deep levels in as-grown and electron-irradiated p-type 4H-SiC epilayers by deep level transient spectroscopy. In as-grown epilayers, the D center and four deep levels are observed. In p-type 4H-SiC, reactive ion etching followed by thermal treatment (at 1150 °C) induces the HK0 (EV+0.79 eV) and HK2 (EV+0.84 eV) centers. By the electron irradiation, two deep levels at 0.98 eV (EP1) and 1.44 eV (EP2) are observed in all the samples irradiated at 116–400 keV, while two additional deep levels (EP3 and EP4) are observed only in the samples irradiated at 400 keV. After annealing at 950 °C, these centers are annealed out, and the HK4 (EV+1.44 eV) concentration is increased. By the electron irradiation at more than 160 keV followed by annealing at 950 °C, three deep levels are always observed at 0.30 eV (UK1), 0.58 eV (UK2), and 1.44 eV (HK4). These centers may be defect complexes including carbondisplacement-related defects. All the centers except for the D center are reduced to bel...

/pdf/deep-level-transient-spectroscopy-on-as-grown-and-electron-fzxxyg5s3e.pdf

Deep level transient spectroscopy on as-grown and electron-irradiated p-type 4H-SiC epilayers

The fluence-dependent properties and the annealing behavior of electron-irradiation-induced deep levels in n-type 6H–SiC have been studied using deep-level transient spectroscopy (DLTS). Sample annealing reveals that the dominant DLTS signal at EC−0.36 eV (labeled as E1 by others) consists of two overlapping deep levels (labeled as ED3L and ED3H). The breakup temperature of the defect ED3L is about 700 °C. The ED3H center together with another deep level located at EC−0.44 eV (so-called E2) can withstand high-temperature annealing up to 1600 °C. It is argued that the involvement of the defect ED3L is the reason that various concentration ratios of E1/E2 were observed in the previous work. The revised value of the capture cross section of the deep-level ED3H has been measured after removing ED3L by annealing. A deep level found at EC−0.50 eV is identified as a vacancy–impurity complex since it was found to have a lower saturated concentration and weak thermal stability. Two other deep levels, EC−0.27 eV an...

/pdf/electron-irradiation-induced-deep-levels-in-n-type-6h-sic-4as3qsg0wp.pdf

Electron-irradiation-induced deep levels in n-type 6H-SiC

Deep level transient spectroscopy has been employed to study the deep level defects introduced in n-type 6H-SiC after neutron irradiation. Deep levels situated at E-C-0.23, E-C-0.36/0.44, E-C-0.50, and E-C-0.62/0.68 eV have been detected in the temperature range of 100-450 K, which have been identified with the previously reported deep levels ED1, E-1/E-2, E-i, and Z(1)/Z(2), respectively. Thermal annealing studies of these deep levels reveal that ED1 and E-i anneal at a temperature below 350degreesC, the Z(1)/Z(2) levels anneal out at 900degreesC, while the intensity of the E-1/E-2 peaks is increased with annealing temperature, reaching a maximum at about 500-750degreesC, and finally annealing out at 1400degreesC. The possible nature of the deep levels ED1, E-1/E-2, E-i, and Z(1)/Z(2) are discussed in the context of their annealing behavior. Upon further annealing at 1600degreesC, four deep levels labeled NE1 at E-C-0.44 eV, NE2 E-C-0.53 eV, NE3 E-C-0.64 eV, and NE4 E-C-0.68 eV are produced. Evidence is given that these levels are different in their origin to E-1/E-2 and Z(1)/Z(2). (C) 2003 American Institute of Physics.

/pdf/deep-level-transient-spectroscopic-study-of-neutron-354ii7re2r.pdf

Deep level transient spectroscopic study of neutron-irradiated n-type 6H-SiC

Deep traps in the boron extended tail region of ion implanted 6H–SiC pn junctions formed during annealing have been studied using deep level transient spectroscopy. Dramatically high concentrations of ∼1016 cm−3 of the D center have been observed through the unusual appearance of minority peaks in the majority carrier spectra. No evidence is found for any shallow boron acceptor in this region, but an induced hole trap Ih at EV+0.46 eV is found under cold implantation conditions. These results support the picture of the extended tail, rich in boron-vacancy complexes such as the D center, which forms as a result of vacancy enhanced indiffusion. The dominance of the electrically active D center in the depletion layer of the technologically important SiC pn junction diode suggests the need for further research in this area.

/pdf/deep-level-traps-in-the-extended-tail-region-of-boron-37x1ajdeyq.pdf

Deep level traps in the extended tail region of boron-implanted n-type 6H–SiC

N-type 6H-SiC samples irradiated with electrons having energies of E(e)=0.2, 0.3, 0.5, and 1.7 were studied by deep level transient technique. No deep level was detected at below 0.2 MeV irradiation energy while for E(e)>/=0.3 MeV, deep levels ED1, E(1)/E(2), and E(i) appeared. By considering the minimum energy required to displace the C atom or the Si atom in the SiC lattice, it is concluded that generation of the deep levels E(1)/E(2), as well as ED1 and E(i), involves the displacement of the C atom in the SiC lattice.

/pdf/low-energy-electron-irradiation-induced-deep-level-defects-42e9b9rphl.pdf

Low energy electron irradiation induced deep level defects in 6H-SiC: the implication for the microstructure of the deep levels E1/E2.

1.7 MeV electron irradiation-induced deep levels in p-type 6H–SiC have been studied using deep level transient spectroscopy. Two deep hole traps are observed, which are located at EV+0.55 eV and EV+0.78 eV. They have been identified as two different defects because they have different thermal behaviors. These defects at EV+0.55 eV and EV+0.78 eV are annealed out at 500–200 °C, respectively, and are different from the main defects E1/E2, Z1/Z2 observed in electron irradiated n-type 6H–SiC. This indicates that new defects have been formed in p-type 6H–SiC during electron irradiation.

/pdf/a-deep-level-transient-spectroscopy-study-of-electron-4st1g1llh1.pdf

M. Gong

Papers

Electron-irradiation-induced deep levels in n-type 6H-SiC

Deep level transient spectroscopic study of neutron-irradiated n-type 6H-SiC

Deep level traps in the extended tail region of boron-implanted n-type 6H–SiC

Low energy electron irradiation induced deep level defects in 6H-SiC: the implication for the microstructure of the deep levels E1/E2.

A deep level transient spectroscopy study of electron irradiation induced deep levels in p-type 6H–SiC