<title>Novel lasing materials based on CdSe crystals doped with Cr</title>

Abstract

Recently efficient room temperature lasing material for this IR range has been demonstrated in II-VI semiconductors doped with transition metals. These dopants incorporated into CdSe substitute metallic atoms and create deep levels in the band gap. The room temperature mid-infrared absorption in CdSe:Cr is observed due to the intracenter transtion ⁵T₂→⁵E of Cr²⁺ ions. These tetrahedrally-coordinated ions are especially attractive as laser centers on account of high luminescence quantum yields for emission in the 2-3 μm range. Electrical and optical measurements are obtained with CdSe single crystals doped with chromium from a gas soruce CrSe over a wide temperature range (500-1050°C). These processes are intended to control the concentrations of the impurity and intrinsic defects. The low temperature annealing of CdSe crystals in CrSe atmosphere allows obtaining high electron mobility up to 9000 cm²/Vs at 80 K and dmeonstrates the low native defect concentration. A high temperature annealing gives a rise of electron concentration with decreased mobility. Optical absorption measurements show that at the high annealing temperature effective doping with Cr takes place. The impurity absorption beyond the absorption edge is interpreted by the excitation of Cr²⁺ and Cr¹⁺ deep levels. Mid-infrared absorptin spectrum in 1.2-3.8 μm was measured. A discovered absorption peak at 1.9 μm corresponds to the intracenter transition ⁵T₂→⁵E of Cr²⁺ ions. The intensity of this peak increases with increasing annealing temperature due to the growth of the impurity concentration. The maximal absorption coefficient in peak has a value of 4 cm^-1 Cr²⁺ concentration in samples was calculated by using the peak absorption coefficient and it was varied from 10¹⁷ to 2×10¹⁸ cm^-3.