Material synthesis and infrared optical properties of transition metal doped binary and ternary II-VI semiconductors
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0891-EE03-08.1
Material synthesis and infrared optical properties of transition metal doped binary and ternary II-VI semiconductors U. Hömmerich*,+, Ei Ei Nyein*, S.B. Trivedi**, and A.G. Bluiett*** *Hampton University, Department of Physics, Hampton, VA 23668 **Brimrose Corporation of America, 19 Loveton Circle, Baltimore, MD 21152 *** Elizabeth City State University, Dept. of Chemistry and Physics, Elizabeth City, N.C. 27909 +
e-mail: [email protected]
ABSTRACT We report on the material preparation and optical characterization of transition metal (Cr, Co) doped ternary cadmium chalcogenides for possible applications in mid-infrared (MIR) light source development. Cr2+ doped II-VI’s (e.g. ZnSe, ZnS) have received significant attention for MIR solid-state laser development in the 2-3 µm region. Transition metal (TM) doped II-VI thin films are also currently being studied for the development of broadly tunable MIR sources pumped through electrical carrier-injection. In this paper, we present results of the material synthesis and IR spectroscopy of several Cr and Co doped cadmium chalcogenides including CdTe, CdMnTe, CdZnTe, CdMgTe, CdCaTe, and CdSrTe. Following the synthesis and purification of undoped IIVI materials, TM doping was achieved during in-situ Bridgman growth or through a thermal diffusion process. The Cr2+ doped II-VI materials were characterized by broad IR absorption bands centered at ~1800-1900 nm and MIR emission extending from ~2000-3500 nm. The emission lifetimes varied between 1-5 µs, depending on the Cr concentration and host composition. Co2+ doped cadmium chalcogenides exhibited several absorption bands in the infrared region and broad emission extending from ~3-5 µm. Compared to Cr2+ doped II-VI’s, the emission from Co2+ doped cadmium chalcogenides was significantly quenched at roomtemperature due to the onset of non-radiative relaxations. INTRODUCTION
The development of infrared light sources (lasers, LED’s) is of great technological interest for many applications including optical sensing of bio-chemical agents, remotes sensing of atmospheric gases, pollution monitoring, thermal scene illumination, and bio-photonics. Transition metal (TM) doped II-VI semiconductors have recently emerged as a new class of IR luminescent materials with broad bands extending from ~2-5 µm [1-5]. Room temperature lasing in the 2-3.5 µm region has been reported from several Cr2+ doped II-VI’s (e.g. Cr: ZnSe, Cr: ZnS, Cr: CdSe, Cr: CdMnTe) in pulsed and continuous-wave mode [1-5]. Cr2+ is easily incorporated into bulk single crystals and polycrystalline windows using a thermal diffusion process or through in-situ growth. The optical properties of Cr2+ are favorable for solid-state laser applications due to the large absorption and emission cross-sections and negligible excited state absorption [1-5]. Besides Cr2+, laser activity at longer wavelengths around ~4 µm was reported from Fe2+: ZnSe at low temperature [6]. At elevated temperature, the MIR emission from Fe2+ doped ZnSe was strongly quenched due
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