Scanning probe microscopy (SPM) techniques have been employed to image and characterise polycrystalline thin films of both pure silicon and Si/Si 1−x Ge x . The layers were grown on oxidised silicon substrates using a rapid thermal chemical vapour deposition (RTCVD) reactor. Microstructural characteristics (roughness and grain size) were measured and their dependence on germane content to the gas flow during deposition elucidated using a range of analysis techniques, including fractal methods. By tracking the evolution of cross-over points in the fractal spectrum, an estimate for the grain size range can be obtained, which tallies extremely well with actual topographical measurements.Thin film transistors (TFTs) are employed in a number of advanced technological environments such as high-density static random access memory (SRAM) for load pull-up devices [1, 2] and also as large-area active matrix liquid crystal displays (AMLCDs) for both switching elements and peripheral driver circuitry [3,4]. Although polycrystalline Si (polySi) is widely used as the active layer in TFT applications, the performance of the device is degraded if the processing temperature is decreased [5]. This means that fabrication of high-performance poly-Si TFTs typically requires high temperatures (T ≥ 600 • C) and also long anneal times. The use and maintenance of elevated temperatures is undesirable, not only from an economic point of view, but also because the integrity of underlying dopant profiles can be degraded by higher-temperature processing.