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.

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The Zeeman effect on two absorption lines in CuGaS2 has been investigated for the first time for I-III-VI2 chalcopyrite semiconductors. Both of these absorption lines split into two components in a magnetic field where the magnetic field was perpendicular to the crystal c-axis. These splittings exhibited the same linear dependence on magnetic field, reaching about 1.1 meV at 5 T. These splittings can be described with apparent g value of about 4. Additional lines whose peak energies were close to those in zero-magnetic filed appeared in a magnetic field where the angle between magnetic field and crystal c-axis was 35°. The intensities of the lowest energy lines of these split lines decreased with a decrease of temperature in both configurations. The observed behavior is shown to be well explained with the model of excitons bound to neutral centers.