Uniform 4-Stacked Ge0.9Sn0.1 Nanosheets Using Double Ge0.95Sn0.05 Caps by Highly Selective Isotropic Dry Etch.

The undoped 4-stacked Ge_0.9Sn_0.1 nanosheets sandwiched by double Ge_0.95Sn_0.05 caps without parasitic Ge channels underneath are realized by a radical-based highly selective isotropic dry etching. Highly inter-channel uniformity of the stacked GeSn nanosheets is realized by thin Ge_0.9Sn_0.1 (5 nm) channels and thick Ge_0.95Sn_0.05 caps to achieve high I_ON. The caps are the barriers to separate the holes from the dielectrics/cap interface to reduce the surface roughness scattering. The double caps with small strain also stabilize the channels to prevent the channel buckling. The undoped GeSn nanosheets with [B] below the detection limit (< 1 × 10¹⁷ cm⁻³) and heavily doped (~ 2 × 10²¹ cm⁻³) Ge at S/D can suppress the impurity scattering to increase the channel mobility and can reduce the S/D resistance, respectively. The high I_ON = 73 μA per stack (86 μA/μm , normalized by the total perimeter of nanosheets) at V_OV = V_DS = −0.5 V is achieved for the device with the sheet width of 80 nm and the Lg of 80 nm. The quantum mechanical simulation shows that there is heavy hole population at the two ends of nanosheets. [ABSTRACT FROM AUTHOR]