Growth of Cr- and Co-doped CdSe crystals from high-temperature selenium solutions

Transition metals in the group II-VI semiconductors have attracted considerable attention for their application as tunable mid-infrared (IR) lasers at room temperature. Very recently, Co-doped II-VI hosts have been considered as saturable absorber materials.(1) In the present study, we have grown both Cr-doped and Co-doped CdSe by a high-temperature solution growth technique using Se as solvent. The Cr-doped CdSe was grown in 4,000-ppm concentration. The Co-doped CdSe crystals were grown in concentrations of 2,000 ppm and 4,000 ppm. The crystals were characterized by optical-absorption spectroscopy. The absorption-peak position for Cr was 1.92 mum, and for Co, the peak position was 1.8 mum. The doping concentrations for Cr-doped samples were estimated from optical-absorption spectra using the Beer-Lambert law. Good-quality, crack-free single crystals were grown; however, our near-IR transmission microscopy showed Se inclusions, which were also confirmed by differential scanning calorimetry (DSC). The electrical-resistivity dependence on doping concentrations is presented and discussed. Glow discharge mass spectrometric (GDMS) measurements for the Co-doped sample are reported. The absorption cross section for Co was calculated for the first time using the Beer-Lambert law.