Properties of the D-1 bound exciton in 4H-SiC

In this paper we report an extensive study of the properties of the D-1 pho toluminescence (PL) observed in electron irradiated 4H-SiC. We have investi gated the temperature dependence of the FL, its time decay and excitation p roperties. At low temperatures (T<5 K) the D-1 PL spectrum in 4H-SiC consis ts of one no-phonon line, L-1 (4272.6 Angstrom), and its phonon replicas. A s the temperature is raised, two higher energy no-phonon lines, M-1 (4261.3 Angstrom) and H-1 (4257.0 Angstrom), appear while the L-1 intensity rapidl y decreases. At sufficiently high temperatures (T>100 K) the D-1 PL is quen ched. The associated activation energy is found to be approximately 57 meV. The lifetime of the D-1 PL is around 450 mu s at 1.3 K, but decreases to 2 mu s 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 excit ation (PLE) spectra of phonon replicas of the L-1 line at low temperature r eveal a weak peak corresponding to the L-1 no-phonon line and two strong pe aks 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 associ ated binding energy of 53 meV. Our results can be explained by exciton reco mbination at an isoelectronic center. One of the particles of the exciton i s weakly bound, whereas the other is more tightly bound. [S0163-1829(99)008 03-6].