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Two distinct boron-related centers are known in silicon carbide polytypes, one shallow (ionization energy ∼300 meV) and the other deep (∼650 meV). In this work, 4H SiC homoepitaxial films are intentionally doped with the shallow boron center by controlling the silicon to carbon source gas ratio during chemical vapor deposition, based on site competition epitaxy. The dominance of the shallow boron center for samples grown with a low Si/C ratio, favoring the incorporation of boron onto the silicon sublattice, is verified by the temperature dependent Hall effect, admittance spectroscopy and deep level transient spectroscopy. In these samples a peak near 3838 Å appears in the low temperature photoluminescence spectrum. Further experiments support the identification of this peak with the recombination of a four particle (bound exciton) complex associated with the neutral shallow boron acceptor as follows: (1) The intensity of the 3838 Å peak grows with added boron. (2) Momentum conserving phonon replicas are observed, with energies consistent with other four particle complexes in SiC. (3) With increasing temperature excited states are observed, as for the neutral aluminum and gallium acceptor four particle complexes. However, the intensity of the shallow boron spectrum is quenched at lower temperatures than the corresponding spectra for Al and Ga, and the lineshapes are strongly sample dependent. These results may be related to the unusual configurational and electronic structure of this center inferred from recent spin resonance experiments by other groups. When the Si/C ratio is high, the optical signatures of the deep boron center, nitrogen-boron donor-acceptor pairs and conduction band to neutral acceptor free-to-bound transitions, are observed in the photoluminescence. At T=2 K well resolved, detailed nitrogen-boron pair line spectra are observed in addition to the peak due to distant pairs. As the temperature is raised, the donor-acceptor pair spectrum decreases in intensity while the free-to-bound no-phonon peak appears. Extrapolation of the temperature dependence of the free-to-bound peak to T=0 K, after correction for the temperature dependence of the exciton energy gap, leads to the value EA(B)−EX=628±1 meV, where EA(B) is the ionization energy of the deep boron center and EX is the binding energy of the free exciton which, for 4H SiC, can only be estimated at this time.

4H-SiC epilayers grown by chemical vapor deposition were characterized by Hall effect, admittance spectroscopy, low-temperature photoluminescence, and deep level transient spectroscopy (DLTS). The nitrogen (N) donor activation energies were estimated as 45–65 meV at hexagonal and 105–125 meV at cubic sites from Hall effect investigations in agreement with the data taken by admittance spectroscopy. In low-temperature photoluminescence, the N bound exciton peaks were dominant, however, free exciton peaks were also observed. DLTS measurements revealed a low concentration of electron traps (∼1013cm−3) for both samples grown on Si and C faces, indicating high-quality epilayers independent of the substrate polarity.

Both 3C-SiC and 6H-SiC single-crystal films can be grown on vicinal (0001) 6H-SiC wafers. We have found that oxidation can be a powerful diagnostic process for (1) ‘‘color mapping’’ the 3C and 6H regions of these films, (2) decorating stacking faults in the films, (3) enhancing the decoration of double positioning boundaries, and (4) decorating polishing damage. Contrary to previously published oxidation results, proper oxidation conditions can yield interference colors that provide a definitive map of the polytype distribution for both the Si face and C face of SiC films. Defects were more effectively decorated by oxidation on the Si face than on the C face.

We have found that, with proper pregrowth surface treatment, 6H-SiC single-crystal films can be grown by chemical vapor deposition (CVD) at 1450 °C on vicinal (0001) 6H-SiC with tilt angles as small as 0.1°. Previously, tilt angles of greater than 1.5° were required to achieve 6H on 6H at this growth temperature. In addition, 3C-SiC could be induced to grow within selected regions on the 6H substrate. The 3C regions contained few (or zero) double-positioning boundaries and a low density of stacking faults. A new growth model is proposed to explain the control of SiC polytype in this epitaxial film growth process.

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We have observed intense line spectra in the neighborhood of 1.54 μm from erbium-implanted samples of 4H, 6H, 15R, and 3C SiC. Samples were implanted to a fluence of about 1013 erbium ions/cm2 using four implant energies. An anneal at 1700 °C in a SiC cavity was used. The temperature dependence of the integrated luminescence intensity from 1.49 to 1.64 μm varies very little from 2 to 400 K. No major differences are found for the spectra of the hexagonal and rhombohedral polytypes but there is a difference for cubic SiC (3C SiC).

New lines in the low temperature luminescence spectra of lightly aluminum doped p-type films of 3C, 6H, and 4H SiC are identified and associated with the recombination of a neutral aluminum acceptor four particle bound exciton complex.