Electrical and Structural Characteristics of Excimer Laser-Crystallized Polycrystalline SiGe Thin-Film Transistors.

We investigated the characteristics of excimer laser-annealed polycrystalline silicon-germanium (poly-SiGe) thin film and thin-film transistor (TFT). The Ge concentration was increased from 0% to 12.3% using a SiH and GeH gas mixture, and a SiGe thin film was crystallized using different excimer laser densities. We found that the optimum energy density to obtain maximum grain size depends on the Ge content in the poly-SiGe thin film; we also confirmed that the grain size of the poly-SiGe thin film is more sensitive to energy density than the poly-Si thin film. The maximum grain size of the poly-SiGe film was 387.3 nm for a Ge content of 5.1% at the energy density of 420 mJ/cm. Poly-SiGe TFT with different Ge concentrations was fabricated, and their structural characteristics were analyzed using Raman spectroscopy and atomic force microscopy. The results showed that, as the Ge concentration increased, the electrical characteristics, such as on current and sub-threshold swing, were deteriorated. The electrical characteristics were simulated by varying the density of states in the poly-SiGe. From this density of states (DOS), the defect state distribution connected with Ge concentration could be identified and used as the basic starting point for further analyses of the poly-SiGe TFTs.