Effect of aqueous sulfide treatments on HgCdTe surface after KI-based polishing for MWIR FPA fabrication

Abstract

In this work, aqueous sulfide passivation of Hg1−xCdxTe (x = 0.29) surfaces was systematically investigated using a combination of spectroscopic and electrical techniques. Time-dependent treatments in ammonium sulfide [(NH4)2Sx], sodium sulfide (Na2S), and thioacetamide (CH3CSNH2) were examined by ellipsometry and x-ray photoelectron spectroscopy (XPS) on the epilayers. Ellipsometry measurements confirmed the formation of a uniform sulfide film upon (NH4)2Sx treatment, with an average thickness of ∼6.5 nm and a refractive index of 2.6 after 30 min of exposure. XPS spectra revealed the progressive replacement of surface oxides (TeO2, CdTeO3, and HgTeO3) by stable sulfide compounds (HgS and CdS), indicating stabilization of the HgCdTe interface. Overall, the results demonstrate that 30 min of (NH4)2Sx treatment produces an optimally passivated HgCdTe surface, characterized by minimal oxides, uniform sulfide coverage, and superior electrical stability. These findings highlight the potential of sulfur passivation for improving the performance and reliability of HgCdTe-based infrared detectors. Metal–insulator–semiconductor (MIS) capacitors in the form CdS/CdTe/ZnS/Cr–Au MIS were subsequently fabricated, and high-frequency C–V measurements at 80 K were performed to evaluate the electrical stability of the passivated interfaces. The results identify a 30 min (NH4)2Sx treatment leading to an electrolytic growth of CdS, followed by CdTe/ZnS deposition as an effective route for reducing oxide content at the interface, supporting its use in achieving a stable HgCdTe interface suitable for high-performance infrared device applications.