Effect of Different Doping Concentrations on the Properties of Fe²⁺:ZnSe and Fe²⁺, Cr²⁺:ZnSe Crystals Grown by the Chemical Vapor Transport Method

The Fe²⁺:ZnSe crystal is an important material for 3-5 μm mid-infrared lasers. In this work, we have grown different doping concentrations of Fe²⁺:ZnSe and Fe²⁺, Cr²⁺:ZnSe by the chemical vapor transport method. The doped crystals have the same structure. The lattice constant increases slightly with a higher Fe²⁺ concentration, while the doped Cr²⁺ has a great influence on the lattice constant. Besides, with a higher Fe²⁺ concentration, the TO mode has no change and the LO mode presents a small blue shift. The doped ZnSe crystals all have a wide absorption peak in the range of 2.3-4.5 μm, and these absorption peaks widen with the increase of the Fe²⁺ doping concentration. Besides, in the range of 5-20 μm, the crystals have good transparency. The concentrations of 3, 2, and 1% Fe²⁺ samples are calculated to be 4.15 × 10¹⁹, 3.27 × 10¹⁹, and 3.02 × 10¹⁹ cm^-3, respectively, and the Fe²⁺ concentration of the Fe²⁺, Cr²⁺:ZnSe sample is 3.71 × 10¹⁹ cm^-3. The band gap decreases from 2.52 to 2.27 eV with a higher Fe²⁺ doping concentration. Therefore, we can modulate the absorption bandwidth and band gap by doping the ion concentration, which is more suitable for developing mid-infrared gain medium applications.