P2p peaks of phosphorus in samples doped with P and Zn 3 P 2 always fall in the range from 133.2 to 134.3 eV (Fig. ) that corresponds to compounds containing P +5 oxidation state. While it is hard to predict the exact coordination of phosphorus in the samples, small shifts in peak position suggest that different forms of initial dopants might produce different types of P-based centers. In addition, there is a difference in phosphorus content determined by EDX between P-and Zn 3 P 2 -doped samples, similar to doping with Sb and Zn 3 Sb 2 , with a much lower phosphorus concentration in the latter (about 2.0 % for P-doped and 0.8 % for Zn 3 P 2 -doped samples) found by EDX.