GeSn Quantum Well P-Channel Tunneling FETs Fabricated on Si(001) and (111) With Improved Subthreshold Swing

Ultrathin GeSn channels were epitaxially grown on Si(111) and (001) substrates using solid source molecular beam epitaxy. Well-behaved GeSn quantum well (QW) pTFETs and pMOSFETs were fabricated on Si. GeSn QW pMOSFETs on Si(111) demonstrate a high effective hole mobility of 505 cm
²
/Vs, indicating the high crystallinity of the GeSn material. GeSn QW pTFETs on Si(111) outperform the devices on Si(001) on subthreshold swing (SS) and ON-state current I
_ON
. (111)-oriented GeSn pTFET with a 4-nm-thick channel achieves a steep SS of ~60 mV/decade and a high ON-state/OFF-state current ratio of 10
⁷
, which are superior to those of the other reported non-Si pTFETs with a small bandgap.