Optical Absorption ofFe2+in CdTe in the Near and Far Infrared

Abstract

The optical-absorption spectrum of ${\mathrm{Fe}}^{2+}$ $3d^6$ impurities in CdTe crystals has been measured over the wave-number range from 10 to 120 ${\mathrm{cm}}^{-1\mathrm{}}$ in the far infrared at 4.2 and 20°K, and from 2000 to 13 000 ${\mathrm{cm}}^{-1\mathrm{}}$ in the near infrared at 2, 14, and 300°K. Transitions between the five spin-orbit levels of the ${}_{}{}^5{}_{}{}^{}E$ ground state have been seen in the far infrared, while transitions from ${}_{}{}^5{}_{}{}^{}E$ to the ${}_{}{}^5{}_{}{}^{}T_2^{}{}_{}{}^{}$ and possibly higher states have been seen in the near infrared. The far-infrared results give the energies for two of the ${}_{}{}^5{}_{}{}^{}E$ levels as ${\Gamma }_1=0\mathrm{}$ and ${\Gamma }_4=18.6\mathrm{}$ ${\mathrm{cm}}^{-1\mathrm{}}$, and two unspecified lines at $\overline{\nu }=66.7\mathrm{} \mathrm{and} 73.2$ ${\mathrm{cm}}^{-1\mathrm{}}$. These results also give phonon energies at several critical points in the Brillouin zone as $\mathrm{TA}\mathrm{}\left(L\right)=36\mathrm{}$ ${\mathrm{cm}}^{-1\mathrm{}}$, $\mathrm{TA}\mathrm{}\left(X\right)=46\mathrm{}$ ${\mathrm{cm}}^{-1\mathrm{}}$, $\mathrm{LA}\mathrm{}\left(L\right)=104.5\mathrm{}$ ${\mathrm{cm}}^{-1\mathrm{}}$. The ${\Gamma }_4$ level of ${}_{}{}^5{}_{}{}^{}E$ has been found to split in a magnetic field with $g=1.02\mathrm{}$. The magnetic susceptibility of ${\mathrm{Fe}}^{2+}$-doped CdTe has been measured from 4 to 300°K, and the results agree with predictions based on the calculated level positions of the ${}_{}{}^5{}_{}{}^{}E$ state in an applied magnetic field. An appendix is presented in which the theory of the splitting of the ${}_{}{}^5{}_{}{}^{}D$ free-ion state in the tetrahedral crystal field is given, and the resultant energies and wave functions of the...