EPR ofCr(3d3)in GaAs—evidence for strong Jahn-Teller effects

Abstract

The $X$-band EPR spectrum of ${\mathrm{Cr}}^{3+}\left(3\mathrm{}{d}^3\right)$ has been observed in semi-insulating Cr-doped GaAs at 5 K. The Cr is assumed to be substitutional for Ga. The $S=\frac{3}{2}$ center has an orthorhombic ($C_{2\nu }$) symmetry spin Hamiltonian $\mathcal{H}={\mu }_B\Sigma i^{}{g}_i{H}_i{S}_i+D[S_z^2-\frac{S(S+1\mathrm{})\mathrm{}}{3}]+E(S_x^2-S_y^2)$ with $x$, $y$, $z$ being [110], [001], [$1\overline{1}0$] respectively. The zero-field splitting $2{(D^2+3\mathrm{}{E}^2)}^{\frac{1}{2}}=7\mathrm{}\pm 2$ ${\mathrm{cm}}^{-1\mathrm{}}$ while $\frac{E}{D}=0.26\mathrm{}$. Most of the lines observed arise from the ground doublet which can be characterized by a simple $S^{\prime }=\frac{1}{2}$ spin Hamiltonian with $g_x^{\prime }=2.367\mathrm{}$, $g_y^{\prime }=5.154\mathrm{}$, and $g_z^{\prime }=1.636\mathrm{}$. The relative and absolute intensities of the six crystallographically equivalent centers are sensitive to applied stress and upon warming the lines broaden and disappear above 10 K. The spectrum is thought to arise from a strongly Jahn-Teller—distorted Cr center which reorients rapidly above 5 K. The effect of illumination with $h\nu$ less than the band gap has also been measured.