First Demonstration of Uniform 4-Stacked Ge0.9Sn0.1 Nanosheets with Record ION =73μA at VOV=VDS= -0.5V and Low Noise Using Double Ge0.95Sn0.05 Caps, Dry Etch, Low Channel Doping, and High S/D Doping

The undoped 4-stacked Ge
_0.9
Sn
_0.1
nanosheets sandwiched by double Ge
_0.95
Sn
_0.05
caps without parasitic Ge channels are realized by a radical-based highly selective isotropic dry etching. High inter-channel uniformity of the stacked GeSn nanosheets is achieved to enhance ION by thin Ge
_0.9
Sn
_0.1
(5nm) channels. The carriers are separated from dielectrics by the caps to reduce the impurity and 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 (<; 1E17 cm
^-3
) and heavily doped (~2E21 cm
^-3
) Ge at S/D can increase the channel mobility and reduce the S/D resistance, respectively. The record I
_ON
=73μA per stack (910μA/μm per channel footprint) at V
_OV
=V
_DS
=-0.5V is achieved among GeSn 3D FETs for the sheet width/Lg of 80nm/80nm. The I
_ON
per channel footprint can be improved to 1070μA/μm with the sheet width scaled to 57nm due to the large carrier population at the two ends of nanosheets. The double caps as barriers for the holes in the Ge
_0.9
Sn
_0.1
nanosheets decrease the low frequency noise by reducing trapping/detrapping between the GeSn nanosheets and the gate dielectrics.