This results in significantly smaller charge carrier mobilities ( µ n ≈ 0.1–2 cm 2/Vs of electrons and µ p ≈ 10 −4 cm 2/Vs of holes ) in a-Si:H TFTs compared to CMOS-transistors ( µ n ≈ 10 3 cm 2/Vs and µ p = 10 2 cm 2/Vs ). For example, a-Si:H lacks of band conduction and conductivity is driven by hopping between localized tail-states. Despite the similarity to the SBMOS, TFTs target different applications due to the significantly lower charge carrier mobility in amorphous semiconductors. Since ion-implantation is not required for SBMOS fabrication, atomically abrupt junctions can be fabricated offering a high scalability and suppressed drain-induced barrier lowering. In TFTs these Schottky junctions are made of metal/semiconductor contacts, whereas for SBMOS these junctions are typically made of metal-silicides such as NiSi. TFTs are similar to Schottky–Barrier transistors (SBMOS), since in both devices Schottky junctions are formed between source and channel, and drain and channel, respectively. Since many thin-film semiconductor materials are transparent, even optically transparent transistors can be fabricated. TFTs can be fabricated on conventional silicon wafers, silicon on insulator, and flexible substrates. A number of fabrication techniques (including pulsed laser deposition and sputtering ) have been used to deposit amorphous TFT-semiconductor materials including hydrogenated silicon (a-Si:H), and indium–gallium–zinc–oxide (IGZO). Thin-film transistors based on metal source- and drain-regions are easy and cheap to fabricate, and are used in many applications including display technology and bio-sensing.
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