Special Issue Paper 235 INTRODUCTIONSilicon carbide is a very promising semiconductor for high-power, high frequency and high temperature applications. 1-3 One of the interesting features that distinguishes SiC from traditional narrow bandgap semiconductors, such as for example silicon, is that common doping impurities in SiC have activation energies which are larger than k B T at room temperature. This results in a nonzero occupation number for such impurities, and leads to various effects related to impurity ionization and neutralization when the impurity quasi-Fermi level position changes, for example due to a change in an applied bias. The situation is also complicated by the existence of inequivalent lattice sites with different parameters for the same impurity species in many, e.g., 4H and 6H, SiC polytypes. (Because the crystalline lattice of these polytypes is not a Bravais lattice and does not possess full hexagonal symmetry.) Additionally, for such imIncomplete impurity ionization is investigated in the case of nitrogen donors and aluminum and boron acceptors in 4H and 6H SiC. We calculate the degree of ionization for these impurities residing on different lattice sites in a broad temperature range and for different impurity concentrations. It is shown that the degree of carrier freeze-out is significant in heavily N-doped 6H SiC and in Al-and B-doped SiC. Using the general Schottky junction admittance model we calculate the temperature and frequency dependencies of the junction admittance in the case when impurity ionization by the applied ac bias is present. It is shown that admittance frequency dispersion may be significant at room temperature in the case of N-and B-doped SiC. Finally, we calculate the Schottky junction capacitance as a function of the applied dc bias and simulate the doping profile, using the capacitance-voltage data. The calculated profile is shown to deviate from the actual impurity concentration profile if the impurity ionization time constant is comparable with the ac bias period, which is so for Nand B-doped SiC with certain values of the impurity activation energy and capture cross-section.
Room-temperature Fourier transform infrared reflection (FTIR) spectroscopy was carried out on heavily and lightly doped 4H-SiC films grown by chemical vapor deposition on conducting, n-type (nitrogen) doped substrates. A modelbased curve fit of the experimentally observed reflectance spectra from these samples is performed using a dielectric function that accounts for the phononphoton coupling and plasmon-photon coupling. The value of the longitudinaloptical (LO) phonon frequency estimated from the reflectance spectrum in the range 600-1,200 cm Ϫ1 is observed to increase in direct correlation with the electron free-carrier concentration (FCC). This shift reflects phonon-plasmon coupled modes. The shift from the undisturbed ω LO observed, for example, in semi-insulating SiC is exploited to improve the model-based estimation of epi parameters such as thickness and doping in cases where the free-carrier concentration is less than about 2 ϫ 10 18 cm Ϫ3 .
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.