Production of detector grade CdZnTe crystal with VGF furnace by analyzing segregation of Zn and In

Production of CdZnTe crystals for radiation detector applications through Bridgman and Vertical Gradient Freeze (VGF) techniques is challenging in many aspects. Due to the structural characteristics of CdZnTe, it is not possible to obtain a large single crystalline ingots from the melt growth technique. In addition, the segregation of dopants and Zn decrease the yield significantly. In order to achieve detector-grade CdZnTe crystals, zinc segregation behavior should be fully understood, and optimum dopant concentration (In) should be determined. In this work, indium-doped Cd0.9Zn0.1Te single crystals grown via the Vertical Gradient Freeze (VGF) technique were compared in terms of dopant segregation, defect concentration, electron mobility, and electrical resistivity. It is observed that Zn segregates towards the tip of the ingot while In segregates towards the heel. Zn segregation coefficient is calculated as 1.35 while In segregation coefficient is found to be 0.4 for the VGF method. The variation of Zn throughout the ingot and excessive In dopant concentration degraded the detector performance. CdZnTe crystals having In doping concentrations of more than 5 ppm were unresponsive to gamma radiation. (mu tau)e of VGF-grown crystals in METU Crystal Growth Laboratory is calculated as 4-5 x 10-4 cm2/V.

Automated summary

Production of CdZnTe crystals for radiation detector applications is challenging due to its structural characteristics and segregation behavior of dopants and Zn. In this study, indium-doped Cd0.9Zn0.1Te single crystals grown via the Vertical Gradient Freeze (VGF) technique were compared in terms of dopant segregation and electrical properties. Zn segregation coefficient was found to be 1.35 while In segregation coefficient was 0.4 for the VGF method. Excessive In doping and variation of Zn throughout the ingot degraded the detector performance.