Synthesis of Polycrystalline CdSiP2 with Two-Temperature Zone Method

Abstract The synthesis of large amount of high-purity CdSiP2 (CSP) polycrystalline material is a key issue for the single crystal growth. In this paper, the transportation and reaction properties of Cd, Si, and P in the two-temperature synthesis of CSP polycrystalline materials was investigated. The major reaction intermediates and the transport phenomena in two-temperature synthesis of CSP were studied by interrupting the synthesis process using quenching technique. The powder X-ray diffraction (XRD) analysis showed that the major reaction intermediates are CdP2, Cd2P3. The phosphorus vapor transported from cold-temperature region to hot-temperature region and then reacted with cadmium to form Cd2P3 at lower temperature of about 550 °C. With increasing the temperature, the pressure of phosphorus increase, Cd2P3 start to react with extra phosphorus vapor, forming CdP2 at the temperature higher than 650 °C. Then, cadmium phosphides transported in the form of vapor and reacted with silicon powder to form CSP when the temperature of the hot region raised to 1050 °C. With increasing the hot region up to 1150 °C, a pyknotic CSP ingot was obtained in the PBN boat. Based on the above reaction mechanism, a modified temperature profile was proposed for the large amount of CSP synthesis, which could synthesize more than 140 g CSP in one synthesis run. The XRD and EDS results demonstrate that the synthesized CSP compound is a pure tetragonal phase. Using the polycrystalline CSP synthesized by two-temperature zone method, a large crack-free single crystal CSP with the dimension of 12mm in diameter and 40 mm in length was grown by vertical Bridgman method, and the transmittance of the as-grown crystal is as high as 57% in 1-6 µm range, which is close to the transmission limit of CSP.