Ge-Si-Sn-O alloys for uncooled infrared detections

Abstract

We report the investigations of Ge-Si-Sn-O alloys for using them as the sensing layer of microbolometers. The investigated properties include atomic composition, resistivity, temperature coefficient of resistance (TCR), activation energy, transmittance, absorptance and reflectance, optical bandgap and thermal conductivity. We have prepared thin films of GeSi-Sn-O alloys using a combination of direct current (DC) and radio frequency (RF) magnetron sputtering. We bonded pieces of Si substrate on a Ge target by silver paste to obtain a compound Si-Ge target. Si-Ge and Sn were sputtered simultaneously in a Kurt J. Leskar Pro Line PVD-75 sputtering system in Ar+O₂ environment to prepare Ge-Si-Sn-O films. The sputtering power and process gases’ concentrations were varied to obtain appropriate film compositions. Samples were fabricated in a single batch for different tests so that uniform composition and film properties were ensured throughout the samples being analyzed. A room temperature TCR of -3.66%/K and resistivity of 1.885×10⁵ Ω-cm was obtained from the thin film with an atomic composition of Ge₃₉Si₀₅Sn₁₄O₃₆. We also obtained the thermal conductivity of 0.403 Wm^-1 K^-1 for 1339 nm-thick Ge₃₉Si₀₅Sn₁₄O₃₆ film. During our investigation, we found that as the Sn concentration in Ge-Si-Sn-O increased, the absorption also increased. This increased absorption led to decrease the optical bandgap of Ge-Si-Sn-O. Higher Sn concentrations in Ge-Si-Sn-O tend to decrease the resistivity as well TCR. Higher O₂ concentration in Ge-Si-Sn-O, increased the optical bandgap, resistivity and TCR. We also obtained the thermal conductivity of 0.403 Wm^-1 K^-1 for 1339 nm-thick Ge₃₉Si₀₅Sn₁₄O₃₆ film at 300K.