Nitrogen doping concentration as determined by photoluminescence in 4H- and 6H-SiC

Low-temperature photoluminescence (PL) spectroscopy is used for determination of the nitrogen doping concentration in noncompensated 4H- and 6H-SIC by comparing the intensity of nitrogen-bound exciton (BE) lines to that of the free exciton (FE), the latter being used as an internal reference. The results are compared with a previous work performed for the case of 6H-SiC only. A line-fitting procedure with the proper line shapes is used to determine the contribution of the BE and FE Lines in the PL spectrum. The ratio of the BE zero-phonon lines (R(0) and S-0 in 6H, Q(0) in 4H) to the FE most intensive phonon replica around 77 meV exhibits very well a direct proportional dependence on the doping as determined by capacitance-voltage (C-V) measurements for both polytypes. The use of fitting procedure which takes into account the real line shapes the influence of the spectrometer transfer function, and the structure: of the PL spectrum in the vicinity of the FE replica allows us determination of the N-doping concentration by PL for doping levels in the region 10(14) cm(-3)-3x10(16) cm(-3) for 4H- and 10(14) cm(-3)-10(17) cm(-3) for 6H-SiC. Above these levels the free-exciton related emission is not observable. (C) 1995 American Institute of Physics.