Germanium nMOSFETs With Recessed Channel and S/D: Contact, Scalability, Interface, and Drain Current Exceeding 1 A/mm

A novel recessed channel and source/drain (S/D) technique is employed in Ge nMOSFETs, which greatly improves metal contacts to n-type Ge with contact resistance of down to 0.23
$\Omega \cdot {\rm mm}$
and enhances gate electrostatic control with
$I_{\rm ON} / I_{\rm OFF}$
of
$> 10^{5}$
. The recessed S/D contacts are thoroughly investigated, showing strong dependence on the doping profile. For the first time, the drain current of Ge nMOSFETs has exceeded 1 A/mm with an
$I_{d}$
of 1043 mA/mm on a 40-nm
$L_{\rm ch}$
device. Scalability study is carried out in deep sub-100-nm region on Ge nMOSFETs with
$L_{\rm ch}$
down to 25 nm. Interface study is also conducted with a new postoxidation method introduced, which significantly reduces the interface trap density. Device behaviors corresponding to interface traps are also investigated through a Technology Computer Aided Design simulation.