Abstract
Solid phase epitaxially grown GeSn was employed as the platform to assess the eligibility of direct O 2 plasma treatment on GeSn surface for passivation of GeSn N-MOSFETs. It has been confirmed that O 2 plasma treatment forms a GeSnO x film on the surface and the GeSnO x topped by in situ Al 2 O 3 constitutes the gate stack of GeSn MOS devices. The capability of the surface passivation was evidenced by the low interface trap density (D it ) of 1.62 × 10 11 cm -2 eV -1 , which is primarily due to the formation of Ge-O and Sn-O bonds at the surface by high density/reactivity oxygen radicals that effectively suppress dangling bonds and decrease gap states. The good D it not only makes tiny frequency dispersion in the characterization of GeSn MOS capacitors, but results in GeSn N-MOSFETs with outstanding peak electron mobility as high as 518 cm 2 /(V s) which outperforms other devices reported in the literature due to reduced undesirable carrier scattering. In addition, the GeSn N-MOSFETs also exhibit promising characteristics in terms of acceptable subthreshold swing of 156 mV/dec and relatively large I ON /I OFF ratio more than 4 orders. Moreover, the robust reliability in terms small V t variation against high field stress attests the feasibility of using the O 2 plasma-treated passivation to advanced GeSn technology.