Zeeman Effect of Shallow Bound Exciton Lines in CuGaS2

The behavior of two shallow bound exciton absorption lines in a magnetic field was investigated for a CuGaS2 single bulk crystal. Upon application of a magnetic field perpendicular to the c-axis, both partially allowed absorption lines split into two components with an apparent g-value of 4. When the temperature was reduced under the applied magnetic field, the lower energy line of each pair decreased in intensity. Such behavior of bound exciton lines, in energy splitting and intensity ratio of split lines under different magnetic fields and at different temperatures, is shown to be consistent with the calculated absorption spectra for excitons bound to neutral centers using known band parameters of CuGaS2. The observed nearly isotropic apparent g-value of around 4, which is the sum of electron and hole g-values, is interpreted in terms of nondegeneracy of the valence band top and larger crystal field splitting compared to spin-orbit splitting for CuGaS2. The good agreement between the calculated and observed features clearly indicates that the binding centers are neutral.