Defects and the Formation of Impurity ‘Hot Spots’ in HgCdTe/CdZnTe
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The formation of impurity ‘hot spot’ macro-defects—localized high impurity level contaminates—is examined. The evolution of macro-defects through their critical stages: as-received CdZnTe substrate, molecular beam epitaxy (MBE) prep etch, Te/oxide desorption and stabilization at deposition temp in MBE chamber, thin (200 nm) HgCdTe deposition, and thick (> 4 μm) MBE HgCdTe deposition, is analyzed. As-received CdZnTe wafers have small and large agglomerations of residual SiO2 and Al2O3 polishing grit. Additionally, macro-defects composed of organic residue, Cd(Zn)Te particulates, and additional impurities are also observed. The MBE preparation etch does not significantly alter the types of defects found on the wafer. The Te/oxide desorption process adds a small number of defects due to colloidal graphite particles. HgCdTe deposition introduces MBE spit defects and Hg droplet residue. There is significant movement of polishing grit and organic macro-defects during the various processing steps. Energy dispersive X-ray spectroscopy (EDS) analysis of MBE spit defects shows they are Cd rich with some of the spit defects containing high concentrations of impurities. The vertical gradient in Te concentration associated with the overgrowth on a metal rich MBE spit defect acts as an impurity pipe for Cu to travel toward the surface to become a ‘hot spot’ defect.
KeywordsCdZnTe substrate HgCdTe molecular beam epitaxy macro-defects impurity contamination
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