Uniaxial stress has been used to study the isotropic Cr-related EPR center in $p$-type GaAs: Cr. Stress linearly splits the EPR line into two components, showing that the center is due to substitutional ${\mathrm{Cr}}^{4+}$ $3d^2$ rather than interstitial ${\mathrm{Cr}}^{1+}$ $3d^5$. The stress coefficients are $C_{11}=-8\mathrm{}$ and $C_{44}=168\mathrm{}$ [in units of ${10}^{-13\mathrm{}}$ ${\mathrm{cm}}^{-1\mathrm{}}$/(dyn/${\mathrm{cm}}^2$)], with only relative signs known.

• Received 17 May 1982

DOI:https://doi.org/10.1103/PhysRevB.26.2296