Strain-Dependent Electron Paramagnetic Resonance and Spin-Valley Coupling of Shallow Triplet Sn Donors in GaP

We describe electron-paramagnetic-resonance studies of shallow tin donors in GaP under applied uniaxial stress. Because of the $X_3$ symmetry of the conduction-band minima relative to a Ga site, the Sn donor states are "orbital" triplets whose components correspond to the three valleys, with the sixfold degeneracy (including spin) split by a weak spin-valley coupling. The valleys are mixed also by the angular momentum operator of the Zeeman Hamiltonian with a small effective intervalley $g$ factor $g_L$. From the stress dependence of the resonance we have determined directly the one-valley $g$ factors $g_{\perp }=1.997\mathrm{}\pm 0.001$ and $g_{\parallel }=1.991\mathrm{}\pm 0.003$ and the intervalley $g$ factor $g_L=0.010\mathrm{}\pm 0.002$. This is the first time that these parameters are determined for GaP. In addition, we deduce the value (4.8 ± 0.7) × ${10}^{-4\mathrm{}}$ for the rms value of random strain and 5.2 ± 0.4 eV for the deformation potential ${\Xi }_u^{*}$ of the bound state.