Excitation properties of hydrogen-related photoluminescence in6H−SiC

Abstract

We have studied the excitation properties of a well-known hydrogen-related bound exciton (H-BE) photoluminescence (PL) in $6H\ensuremath{-}\mathrm{SiC}.$ In the case of the so-called primary H-BE's, photoluminescence excitation (PLE) spectroscopy reveals several excited states that have not been reported previously. In order to explain these states we propose a pseudodonor model. The primary H-BE's are thus regarded as donors where strongly localized holes serve as the positive cores. From a comparison between the PLE spectra of the three different primary H-BE's corresponding to the three inequivalent substitutional lattice sites in $6H\ensuremath{-}\mathrm{SiC},$ we attempt to distinguish between the hexagonal and cubic lattice sites. We have also investigated the dependence of the optically 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 exciting light has energy above the threshold for phonon-assisted free-exciton (FE) formation or when its energy coincides with the energy needed for resonant absorption into the H-BE states. When creating FE's, we observe different types of behavior depending on the initial conditions. We argue that our 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 PL), and a metastable one: B (not revealed in the PL spectrum). The recombination of excitons bound at these two configurations can give rise to the transformations $\stackrel{\ensuremath{\rightarrow}}{A}B$ and $\stackrel{\ensuremath{\rightarrow}}{B}A.$ The existence of the B configuration is revealed through the effect of the $\stackrel{\ensuremath{\rightarrow}}{B}A$ process on the temporal changes of the H-BE PL.