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.

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A previously unreported photoluminescence spectrum observed in certain 4H SiC bipolar diodes after extended forward voltage operation is reported. We assign this emission to exciton recombination at local potential fluctuations caused by stacking faults, which are created during operation of the diodes. Possible recombination mechanisms responsible for the spectrum are discussed.

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.

We use the recent findings about the pseudodonor character of the DI defect to establish an energy-level scheme in the band gap for the defect, predicting the existence of a hole trap at about 0.35 eV above the valence band. Using minority carrier transient spectroscopy, we prove that the DI defect indeed is correlated to such a hole trap. In addition, we show that the DI defect is not correlated to the Z1/2 electron trap, in contrast to what was previously reported.