17:30 〜 17:45
▲ [13p-B8-9] DLTS and Photoluminescence Analysis of Intentionally B-doped 4H-SiC Epilayers
キーワード：deep levels
The D center and other deep levels in B-doped 4H-SiC epilayers were investigated by deep level transient spectroscopy (DLTS), minority carrier transient spectroscopy (MCTS) and photoluminescence (PL) measurements. The samples were intentionally B-doped (using tri-ethyl-boron (TEB) as the B source) p-type and N+B doped n-type 4H–SiC (0001) epilayers grown by CVD. Three hole traps, namely D center (EV+0.58~0.68 eV), HK2 (EV+0.84 eV) and HK3 (EV+1.23 eV) were detected in the p-type samples through DLTS. The D center concentration was found to increase almost linearly with B doping concentration from 3.9×1015 to 6.4×1016 cm-3 (measured by SIMS) as shown in Fig. 1. The MCTS results for the low N+B doped n-type samples indicated that the D center concentration reduced from 9.0×1012 cm-3 to the detection limit after thermal oxidation. These results are consistent with the D center being a complex consisting of a B atom with an adjacent C vacancy (VC) [1]. The D center concentration reached the 1015 cm-3 level, which is more than two orders higher than typical VC concentrations for the epilayers grown without intentional B doping. This implies that the VC defects consisting of the D center have been formed by the introduction of B. Figure 2 shows the PL spectra of an N (8.6×1018 cm-3) + B (2.8×1017 cm-3) doped 4H-SiC epilayer at 10 K and at room temperature (RT). At 10 K, the many small peaks with regular energy separations observed on a broad luminescence signal (1.9-2.6 eV) indicate phonon assisted donor-acceptor pairs (DAP) recombination. At RT, the DAP luminescence reduced and the free-to-bound luminescence grew, showing the smoothing of the spectrum curve and a blue-shift of the center of the PL spectra. No band-edge luminescence was observed in this N+B doped sample, indicating that band to band recombination was effectively prohibited by the B doping.