Abstract
We investigated the characteristics of excimer laser-annealed polycrystalline silicon–germanium (poly-Si1−xGex) thin film and thin-film transistor (TFT). The Ge concentration was increased from 0% to 12.3% using a SiH4 and GeH4 gas mixture, and a Si1−xGex 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-Si1−xGex thin film; we also confirmed that the grain size of the poly-Si1−xGex thin film is more sensitive to energy density than the poly-Si thin film. The maximum grain size of the poly-Si1−xGex film was 387.3 nm for a Ge content of 5.1% at the energy density of 420 mJ/cm2. Poly-Si1−xGex 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-Si1−xGex. 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-Si1−xGex TFTs.
Highlights
Polycrystalline silicon thin-film transistors (TFTs) are widely used for the backplane of display devices, such as active matrix liquid crystal displays (AMLCD) or active matrix organic light-emitting diodes (AMOLEDs), because their field-effect mobility and electrical stability are superior to those of hydrogenated amorphous silicon (a-Si:H) TFTs [1,2]
Poly-Si1−xGex thin films crystallized via pulsed excimer laser annealing (ELA) are rarely reported in previous literature
We investigated crystallized via pulsed ELA are rarely reported in previous literature
Summary
Polycrystalline silicon (poly-Si) thin-film transistors (TFTs) are widely used for the backplane of display devices, such as active matrix liquid crystal displays (AMLCD) or active matrix organic light-emitting diodes (AMOLEDs), because their field-effect mobility (μFE ) and electrical stability are superior to those of hydrogenated amorphous silicon (a-Si:H) TFTs [1,2]. There is no reported optimization of excimer laser density conditions and Ge concentrations to achieve the fabrication of high-performance poly-Si1−x Gex TFTs with desirable characteristics. We investigated the characteristics of poly-Si1−x Gex thin films with different Ge concentrations and analyzed their electrical characteristics. To optimize the performance of the TFT, the excimer laser energy density was varied, and the resulting structural characteristics, such as grain size, roughness, and crystallinity, as well as the electrical characteristics, of the poly-Si1−x Gex thin film were analyzed. Samples of the poly-Si1−x Gex TFTs with different Ge concentrations were fabricated, and their electrical performance was evaluated. This study is expected to elucidate the poly-Si1−x Gex TFT fabrication process and optimize the electrical characteristics of the TFTs
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