Investigation about elliptical region observed on CdZnTe wafers after etching treatment

Abstract

An elliptical region was observed on the wafer cut from the ingot along (1 1 1) face after etching and the ingot was grown by the Vertical Bridgman method. The wafers with the elliptical region were characterized with zinc concentration distribution scanner and infrared transmission microscope. Infrared transmission images revealed the morphology evolution of Te inclusions from irregular droplets to regular tetrahedrons and different stages from the Te-rich threads to the pearl-string Te inclusions inside the elliptical region. Te atoms preferentially diffused and aggregated in the dislocation direction, which resulted in the formation of Te-rich droplets and Te-rich threads. The Zn component map indicated that Zn concentration varied significantly at the elliptical boundary, the Zn concentration inside the ellipse was lower than other normal region. Based on the above experiments, it was considered that such an elliptical region created because of the occurrence of constitutional supercooling, in other words, it is caused by a drastic change of the Zn concentration gradient in the liquid phase at the front of the solid-liquid interface. The segregation of the Zn concentration in the liquid phase at the front of the interface was related to the growth rate. During crystal growth, when approaching the region where the Zn concentration changed drastically, the growth rate should be appropriately lowered to meet the normal Zn concentration gradient to avoid the generation of elliptical region.