Comparison of Tin and Indium Thin Film’s Structural, Morphological, Adhesion, and Electrical Properties for Ohmic Contact in HgCdTe-Based Infrared Detectors

As the requirement for high-performance, low weight, and efficient Infrared devices continues to rise, the formation of good ohmic is a critical step in fabrication of IR detector arrays. Structural and adhesion properties of tin (Sn) and indium (In) films and their contact formation n-HgCdTe substrate are studied using the thermal evaporation technique. The x-ray diffractogram indicated polycrystalline bcc phases with (200) orientation plane and (101) of β-Sn and indium films, respectively. The microstrain and dislocation densities were 4.10 and 9.10 × 10¹⁰ lines/cm² and 3.83 and 9.03 × 10¹⁰ lines/cm² of Sn and In, respectively. SEM examination indicated lumpy deposition of particle sizes from a few nanometers to microns in Sn film and uniform continuous films over the entire HgCdTe substrate with very small numbers of randomly oriented particles of 1-2 µm sizes in In film. EDS compositional analysis confirmed the presence of pure Sn and In films, respectively. Using AFM force microscopy in contact mode, adhesion force and thermodynamic adhesion work were 26.95 nN, 0.42 J/m²(DMT), and 0.57 J/m²(JKR) and 50.73 nN, 0.80 J/m²(DMT), and 1.07 J/m² of In and Sn, respectively. Based on the transfer length method (TLM), the Sn/n-HgCdTe interface showed a higher specific contact resistance with nearly ohmic behavior, but the In/n-HgCdTe specific contact resistance of ρ_c = 3 × 10^-4 Ωcm² indicated that the In/n-HgCdTe interface exhibited ohmic features. Based on the experimental results, it was concluded that indium was the most suitable material to use for forming the ohmic n-contact in HgCdTe-based infrared detectors.