Material preparation and infrared spectroscopy of diffusion doped Cr: ZnSe and Cr: CdTe

The preparation and infrared spectroscopy of diffusion doped Cr:ZnSe and Cr:CdTe windows will be reported. Cr$^{2+}$ doped II-VI semiconductors are of significant current interest as gain media in mid-infrared (2-3 $\mu $m) solid-state lasers. Compared to Cr:ZnSe, Cr:CdTe exhibits an extended infrared emission, which is of interest for laser applications beyond 3$\mu $m. Cr doping in ZnSe and CdTe was achieved through a thermal diffusion process controlled by temperature and time. Commercial CrSe powder was used as the dopant source in the diffusion experiments. Various samples of Cr:ZnSe and Cr:CdTe were prepared with Cr$^{2+}$ peak absorption coefficients ranging from $\sim $0.8 cm$^{-1}$ to 28.7 cm$^{-1}$. The corresponding Cr$^{2+}$ concentrations ranged from $\sim $1x10$^{17}$cm$^{-3}$ to $\sim $3x10$^{19}$cm$^{-3}$ assuming absorption-cross sections of 1.1x10$^{-18}$cm$^{2}$ for Cr:ZnSe and 2.2x10$^{-18}$cm$^{2}$ for Cr:CdTe. For low Cr$^{2+}$ concentrations ($\sim $1x10$^{18}$cm$^{-3})$ the room-temperature decay time varied between 5-6 $\mu $s for Cr:ZnSe and 2-3$\mu $s for Cr:CdTe. The effect of Cr concentration quenching on the mid-infrared emission was observed for doping concentrations above $\sim $1x10$^{19}$cm$^{3}$.