Raised Source/Drain Germanium Junctionless MOSFET for Subthermal OFF-to-ON Transition

This paper reports the significance of device architecture to enhance impact ionization (I.I.) resulting in steep increase in the current from OFFto ON-state. Recognizing that the area over which I.I. occurs is a key factor governing impact generated power per unit volume in the semiconductor film, we use raised source/drain (RSD) architecture to achieve sub-60-mV/decade subthreshold swing (S-swing) in germanium (Ge) junction less (JL) devices at drain bias (V
_ds
) of 0.9 V. The performance of RSD Ge JL device is compared with double-gate Ge JL transistor to highlight the occurrence of sub thermal S-swing <;5 mV/decade in RSD topology. The impact of band-to-band tunneling (BTBT) on the switching characteristics shows that RSD JL device with relatively thicker side oxide can effectively suppress BTBT while enhancing I.I. The influence of parasitic capacitance due to RSD regions and vertical doping gradient is also analyzed. Results highlight new viewpoints for the design of RSD Ge JL MOSFETs with channel doping (N
_ch
) ≥ 5 × 10
¹⁸
cm
^-3
to facilitate sharp current transition.