The D-1 exciton in 4H-SiC

We report on the properties of the D-1 photoluminescence (PL) observed in e lectron irradiated 4H-SiC. We have investigated the temperature dependence of the PL and its excitation properties. At 2 K the D-1 PL spectrum in 4H-S iC consists of one no-phonon line, L-1 (2.9010 eV), and its phonon replicas . As the temperature is raised, two higher energy no-phonon lines, M-1 (2.9 087 eV) and H-1 (2.9118 eV), appear while the L-1 intensity rapidly decreas es. At temperatures between 100 and 200 K the D-1 PL is quenched. The assoc iated activation energy is found to be approximately 57 meV. The PL excitat ion (PLE) spectrum of the L-1 no-phonon line at 2 K contains two strong pea ks corresponding to the M-1 and H-1 lines. Furthermore, there is a series o f sharp PLE peaks at higher energies. The energy positions of these lines c an be fitted by a hydrogenic series of excited states with an associated bi nding energy of 53 meV. Our results can be explained by exciton recombinati on at an isoelectronic centre. One of the particles of the exciton is weakl y bound, whereas the other is more tightly bound.