The D1 Exciton in 4H-SiC

Abstract

We report on the properties of the D1 photoluminescence (PL) observed in electron irradiated 4H-SiC. We have investigated the temperature dependence of the PL and its excitation properties. At 2 K the D1 PL spectrum in 4H-SiC consists of one no-phonon line, L1 (2.9010 eV), and its phonon replicas. As the temperature is raised, two higher energy no-phonon lines, M1 (2.9087 eV) and H1 (2.9118 eV), appear while the L1 intensity rapidly decreases. At temperatures between 100 and 200 K the D1 PL is quenched. The associated activation energy is found to be approximately 57 meV. The PL excitation (PLE) spectrum of the L1 no-phonon line at 2 K contains two strong peaks corresponding to the M1 and H1 lines. Furthermore, there is a series of sharp PLE peaks at higher energies. The energy positions of these lines can be fitted by a hydrogenic series of excited states with an associated binding energy of 53 meV. Our results can be explained by exciton recombination at an isoelectronic centre. One of the particles of the exciton is weakly bound, whereas the other is more tightly bound.