Electron Mobility Enhancement of (111)-Oriented Extremely Thin Body Ge-on-Insulator nMOSFETs by Flipped Smart-Cut Substrates

The effectiveness of (111)-oriented substrates with a flipped method, in which layer transfer is performed again after the Smart-Cut process, has been proven to significantly enhance the performance of extremely thin body Ge-on-insulator (GOI) nMOSFETs. This superior performance is attributed to the markedly improved quality of the GOI film and the interface with a buried oxide layer achieved through the flip process. A record-thin (111) GOI nMOSFET of 2.1 nm is achieved, exhibiting low SSmin of 70 mV/dec and a high on-off ratio of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$1.1\times 10^{{7}}$ </tex-math></inline-formula> at <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${V}_{g} =2$ </tex-math></inline-formula> V. Additionally, the electron mobility of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$168~\pm ~34$ </tex-math></inline-formula> cm2/V<inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\cdot $ </tex-math></inline-formula>s and <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$60~\pm ~12$ </tex-math></inline-formula> cm2/V<inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\cdot $ </tex-math></inline-formula>s are obtained for (111) GOI nMOSFETs with the channel thickness of 6.1 and 2.7 nm, respectively. Similar performance improvement is also observed in (100)-oriented flipped Smart-Cut GOI, while (111)-oriented substrates exhibit significantly higher electron mobility and ON-OFF ratio over all the channel thicknesses. This work demonstrates the potential of ETB (111) Ge nMOSFETs as a substitute channel material for future 3-D sequential complementary FETs (CFETs).