Hopping conduction in GeSiSn alloys: Impact of structural disorder on electrical transport

Temperature-dependent charge transport in epitaxial GeSiSn films with varying thicknesses and Si and Sn content, grown on Ge/Si(001) substrates, was investigated using admittance spectroscopy. The conductance exhibits a crossover from Mott variable-range hopping at low temperatures to thermally activated conduction at higher temperatures. Below 150 K, carriers move via localized states in the band tails, with hopping parameters governed by the density and spatial distribution of disorder-induced states. Increasing nominal Sn concentration and thickness enhances structural disorder and Sn segregation, leading to a higher density of states and reduced hopping length. Scanning capacitance microscopy reveals variations in charge-carrier concentration in high-Sn films, indicating the presence of coexisting p-type and n-type regions at the microscale, consistent with compositional fluctuations, Sn segregation, and microstrain. These results demonstrate that transport in GeSiSn alloys is primarily dominated by disorder-assisted hopping at low temperatures, establishing a quantitative link between microscopic disorder and macroscopic electrical response in metastable group-IV semiconductors.