Multiquanta transitions in Cd-In-S crystals

The dependence of the photoconductivity signal on the light intensity of the Q-switched ruby and Nd lasers, working under multimode conditions, was studied. Optically homogeneous In2S3 and CdIn2S4 single crystals were examined as polished plates, less than or equal to 0.2 mm thick. The characteristic relaxation times of excess carriers were > 10-6 sec at 3000K; the light pulse and temporal registration resolution were 3.5 x 10-8 and not poorer than 10-7 sec, respectively. One-photon reflection and photoconductivity spectra (1-6 eV) were measured. At 3000K, the impurity, 2-, and 3-photon Nd-laser light absorptions were observed, whereas at 77.30K, only the impurity and 3-photon absorptions were observed. With the ruby laser, the impurity and 2-photon absorptions were observed at 77.30K, whereas only the impurity absorption appeared at 3000K. For In2S3, the existence of allowed and forbidden (direct) transitions at 2.3 and 3.8 eV, respectively, was assumed in a dipole approximation with absorption of 1 photon. For such transitions, the absorptions of 2 (this transition was forbidden in the dipole approximation) and 4 Nd-laser photons (hω/2π=1.17 eV) are possible. For ruby laser photons of 1.78 eV, only the 3-photon transition to the 2nd band was possible, when its magnitude was greater than or equal to 1.6 eV. The suggested method is especially convenient for studying transitions forbidden in the dipole approximation and those having a high 1-photon absorption coefficient