Properties of theD1bound exciton in4H−SiC

Abstract

In this paper we report an extensive study of the properties of the $D_1$ photoluminescence (PL) observed in electron irradiated $4H-\mathrm{SiC}.$ We have investigated the temperature dependence of the PL, its time decay and excitation properties. At low temperatures $(T<\mathrm{}5\mathrm{}\mathrm{K})$ the $D_1$ PL spectrum in $4H-\mathrm{SiC}$ consists of one no-phonon line, $L_1$ (4272.6 Å), and its phonon replicas. As the temperature is raised, two higher energy no-phonon lines, $M_1$ (4261.3 Å) and $H_1$ (4257.0 Å), appear while the $L_1$ intensity rapidly decreases. At sufficiently high temperatures $(T>\mathrm{}100\mathrm{}\mathrm{K})$ the $D_1$ PL is quenched. The associated activation energy is found to be approximately 57 meV. The lifetime of the $D_1$ PL is around 450 μs at 1.3 K, but decreases to 2 μs at 70 K. At high temperatures the time decay of the three lines, $L_1,$ $M_1,$ and $H_1,$ is identical, showing that they are thermalized. PL excitation (PLE) spectra of phonon replicas of the $L_1$ line at low temperature reveal a weak peak corresponding to the $L_1$ no-phonon line and two strong peaks corresponding to the $M_1$ and $H_1$ lines. We also notice a weak peak, $N_1,$ about 0.5 meV above the $M_1$ line. Furthermore, there is a series of sharp lines at higher energies in the PLE spectra. 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 center. One of the particles of the exciton is weakly bound, whereas the other is more tightly bound.