Excitation properties of hydrogen-related photoluminescence in 6H-SiC

We have studied the excitation properties of a well-known hydrogen-related bound exciton (H-BE) photoluminescence IPL) in 6H-SiC. In the case of the s o-called primary H-BE's, photoluminescence excitation (PLE) spectroscopy re veals several excited states that have not been reported previously. In ord er to explain these states we propose a pseudodonor model. The primary H-BE ' are thus regarded as donors were strongly localized holes serve as the po sitive cores. From a comparison between the PLE spectra of the three differ ent primary H-BE's corresponding to the three inequivalent substitutional l attice sites in 6H-SiC, we attempt to distinguish between the hexagonal and cubic lattice sites. We have also investigated the dependence of the optic ally induced quenching of the H-BE PL on the energy of the exciting light. We observe that the quenching of the H-BE PL is only efficient when the exc iting light has energy above the threshold for phonon-assisted free-exciton (FE) formation or when its energy coincides with the energy needed for res onant absorption into the H-BE states. When creating FE's, we observe diffe rent types of behavior depending on the initial conditions. Wt argue that o ur results are best explained by the existence of two configurations of the same charge state of the H defect, namely a stable one: A (giving rise to the H-BE FL), and a metastable one: B (not revealed in the PL spectrum). Th e recombination of excitons bound at these two configurations can give rise to the transformations A-->B and B-->A. The existence of the B configurati on is revealed through the effect of the B-->A process on the temporal chan ges of the H-BE PL.