The theory of line broadening given by Lax is found not to apply to shallow impurities in Ge and Si. Observed broadening may be instrumental at low temperatures and may be due to lifetime broadening through phonon interaction at nitrogen temperature. Calculations suggest that $p$-type spin resonance in germanium and silicon may be observable.

• Received 27 January 1960

DOI:https://doi.org/10.1103/PhysRev.119.40