Remarkably High-Performance Nanosheet GeSn Thin-Film Transistor

High-performance p-type thin-film transistors (pTFTs) are crucial for realizing low-power display-on-panel and monolithic three-dimensional integrated circuits. Unfortunately, it is difficult to achieve a high hole mobility of greater than 10 cm(2)/V·s, even for SnO TFTs with a unique single-hole band and a small hole effective mass. In this paper, we demonstrate a high-performance GeSn pTFT with a high field-effect hole mobility (μ(FE)), of 41.8 cm(2)/V·s; a sharp turn-on subthreshold slope (SS), of 311 mV/dec, for low-voltage operation; and a large on-current/off-current (I(ON)/I(OFF)) value, of 8.9 × 10(6). This remarkably high I(ON)/I(OFF) is achieved using an ultra-thin nanosheet GeSn, with a thickness of only 7 nm. Although an even higher hole mobility (103.8 cm(2)/V·s) was obtained with a thicker GeSn channel, the I(OFF) increased rapidly and the poor I(ON)/I(OFF) (75) was unsuitable for transistor applications. The high mobility is due to the small hole effective mass of GeSn, which is supported by first-principles electronic structure calculations.