ABSTRACT
Optical absorption measurements were made in the energy range of ~0.41 — 3.5 eV at temperatures from 14 to 300 K for 6H—SiC bulk crystals unintentionally or intentionally doped with boron. The presence of boron is evidenced by two features: (i) the broad photoionization band in the range of 0.5—3.0 eV and (ii) the multiple exciton lines associated with neutral boron in the range of 2.7—3.0 eV. The photoionization band was analyzed for the electronic transition from the valence band to the boron level by taking into account the temperature—dependent phonon broadening effect. The analysis yields the optical activation energy E0= 1.408 eV and the thermal activation energy Eth = 0.394 eV, which indicates a large lattice relaxation. The exciton absorption consists of 18 lines with the stronger lines being at 2.791, 2.826, 2.840, 2.862 and 2.889 eV at 14 K. Excellent correlation between the integrated absorption of the two transitions make it possible to obtain the neutral boron concentration of 2x1018 — 1.2x1019 cm-3 for the present experiment.
