Spin-coated Ge–In–Se thin films: characterization and changes induced by visible and electron radiation in relation to indium content

Abstract

Solution-processed Ge_25−xIn_xSe₇₅ (x = 0, 2.5, 5, 7.5 and 10) thin films were prepared via spin-coating for the first time. The glass transition temperature of source bulk glasses decreased with increasing indium content and subsequently guided the hard-baking temperatures of deposited thin films (60–240 °C). Energy-dispersive X-ray spectroscopy revealed thermally induced selenium loss at elevated temperatures, particularly in indium-rich compositions, and a greater resistance to organic residue removal with higher indium content. Increasing the hard-baking temperature led to structural changes resulting in decreased film thickness and optical bandgap, with a simultaneous increase in refractive index. At 240 °C, the optical parameters converged across indium-containing compositions, likely due to the content of low-index organics. Atomic force microscopy showed low surface roughness with minor porosity in Ge_17.5In_7.5Se₇₅, and Ge₁₅In₁₀Se₇₅ thin films. Raman spectroscopy confirmed thermal structural polymerization, with indium-based units showing difficult reintegration into the glass network. Photo- and electron-sensitivity studies using 532 nm laser exposure and electron beam lithography showed that 2.5 at% of indium significantly enhanced sensitivity, while further increases in indium content resulted in a gradual decline. Notably, Ge_22.5In_2.5Se₇₅ thin films exhibited an etching selectivity of 6.4, among the highest ever reported for solution-processed chalcogenide thin films.