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

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Abstract
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 (R0 and S0 in 6H, Q0 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 1014 cm−3–3×1016 cm−3 for 4H– and 1014 cm−3–1017 cm−3 for 6H–SiC. Above these levels the free-exciton related emission is not observable.